DE102019208668A1 - Bonding process using a hardening structural adhesive - Google Patents

Abstract

The present invention relates to a method for producing an adhesive bond between a first substrate and a second substrate by activating a heat-activatable adhesive layer, the heat required for activation being generated in a radiation-absorbing layer adjacent to the heat-activatable adhesive layer, which can at least absorb electromagnetic radiation of a certain wavelength is, wherein - the heat-activatable adhesive layer is arranged between the first and the second substrate, - the radiation-absorbing layer is arranged between the heat-activatable adhesive layer and the first substrate and is in contact with the heat-activatable adhesive layer, - the first substrate for radiation absorbable in the radiation-absorbing layer is at least partially transparent, and wherein the radiation-absorbing layer is acted upon by absorbable radiation through the first substrate, the The radiation-absorbing layer is heated up to a maximum temperature at which no damage and no melting of the absorption layer occurs, so that the adhesive layer is heated and activated in the contact area by means of the heat generated in the radiation-absorbing layer, characterized in that the adhesive layer is a reactive, heat-activated adhesive layer and the heat activation initiates a hardening reaction that includes a frontal progression reaction.

Description

The present invention relates to a method for producing an adhesive bond between two substrates by means of a curable adhesive, the curing of the adhesive being heat-activated. The heat is generated by absorbing electromagnetic radiation - and in particular converting the absorbed energy into thermal energy - in an absorption layer and transferring this heat to an adjacent area of the adhesive.

The font JP 6046329 B ( JP 2011156858 A ) discloses the basic method of heating a design layer on a laser-transparent substrate, wherein the design layer is in contact with an adhesive layer and the design layer is heated by means of laser radiation without damaging it. The adhesive layer is heated and can subsequently stick together better or the adhesive is melted and thus converted into an adhesive state. Pressure sensitive adhesives and hot melt adhesives are disclosed as adhesives.

The font JP 2012218316 A by the same applicant discloses the addition of a latent hardener to a reactive adhesive formulation, the latent hardener being activated by non-destructive heating of a design layer on a laser-transparent substrate, as in the above document, the design layer being in contact with the adhesive layer and the adhesive layer with the hardener warmed up. A number of materials are disclosed for the reactive curing adhesive layer, in particular acrylates and epoxies. Some systems are also disclosed for the latent hardener, such as certain imidazoles, polyamines, polyamino-ureido compounds and amine adducts.

The disadvantage of the process, as it is described in the aforementioned documents, is that the latent hardener is distributed in the adhesive layer and the activation temperature must be reached in the entire adhesive layer for activation. In particular if the second substrate is a good heat conductor, e.g. In the case of glass, metal or ceramic, the heat introduced via the design layer is quickly dissipated again through the thin adhesive layer, so that the temperature required to activate the latent hardener has to be reached by means of a very high heating rate. There is a great risk that the design layer will be damaged.

The control of the heating is extremely complex. So the right balance of e.g. Feed speed, number of repeated scans (number of cycles), laser power, pulse rate and beam expansion can be determined. The temperature actually reached in the cross section of the adhesive layer is very difficult to determine, so that direct control by means of a temperature measurement is hardly possible.

In the JP 2014091755 A will that be in the JP 06046329 B disclosed methods are only restricted with regard to the transmission of a specific adhesive tape structure. However, the combination of transmission in the visible wavelength range with absorption in the IR range is fulfilled by almost every non-transparent tape, as there is usually a lack of transparency in visible light (<10% transmission) with a lack of transparency in IR ((absorption> 20% = Transmission <80%), especially with soot-filled tapes. Put simply, almost all tapes with a light transmission <10% meet this requirement.

task

The task was to do this in the JP 6046329 B ( JP 2011156858 A ) to improve disclosed bonding methods. In this case, a radiation-absorbing layer is heated through a radiation-transmitting layer by means of electromagnetic radiation and the heat is passed on to an adhesive layer adjoining the radiation-absorbing layer, comprising a heat-activatable adhesive, so that the heat-activatable adhesive is activated. The radiation-absorbing layer is only heated to such an extent that this layer is not damaged, such as melting, discoloration or decomposition.

The problem is the large amount of heat required for complete activation of the adhesive layer, the transport of this amount of heat to the surface of the second substrate / joining partner opposite the radiation-absorbing layer and the heat dissipation through the second substrate, which means that the activation temperature is reached at the interface of the adhesive layer to the second substrate difficult. The improved solution should therefore, in particular, require a lower amount of heat for complete activation than the solutions known from the prior art.

Solution of the task:

• - die wärmeaktivierbare Klebstoffschicht zwischen dem ersten und dem zweiten Substrat angeordnet ist,
• - die strahlungsabsorbierende Schicht zwischen der wärmeaktivierbaren Klebstoffschicht und dem ersten Substrat angeordnet ist und in - unmittelbarem und/oder mittelbarem - Kontakt zur wärmeaktivierbaren Klebstoffschicht steht,
• - das erste Substrat für in der strahlungsabsorbierenden Schicht absorbierbare Strahlung zumindest teildurchlässig ist,

und wobei die strahlungsabsorbierende Schicht durch das erste Substrat hindurch mit absorbierbarer Strahlung beaufschlagt wird, wobei die strahlungsabsorbierende Schicht bis auf eine maximale Temperatur erwärmt wird, bei der keine Schädigung und kein Aufschmelzen der Absorptionsschicht eintritt,
so dass die Klebstoffschicht mittels der in der strahlungsabsorbierenden Schicht erzeugten Wärme im Kontaktbereich erwärmt und aktiviert wird,
dadurch gekennzeichnet, dass
die Klebstoffschicht eine reaktive hitzeaktiviert verklebende Klebstoffschicht ist und durch die Wärmeaktivierung eine Härtungsreaktion initiiert wird, die eine Frontfortschrittsreaktion umfasst.The object is achieved by a method for producing an adhesive bond of a first substrate to a second substrate by means of activation of a heat-activatable adhesive layer, the heat required for activation in a radiation-absorbing layer adjacent to the heat-activatable adhesive layer, which can at least absorb electromagnetic radiation of a certain wavelength, is generated, where

• - The heat-activatable adhesive layer is arranged between the first and the second substrate,
• the radiation-absorbing layer is arranged between the heat-activatable adhesive layer and the first substrate and is in direct and / or indirect contact with the heat-activatable adhesive layer,
• the first substrate is at least partially transparent to radiation that can be absorbed in the radiation-absorbing layer,

and wherein the radiation-absorbing layer is acted upon by absorbable radiation through the first substrate, the radiation-absorbing layer being heated to a maximum temperature at which no damage and no melting of the absorption layer occurs,
so that the adhesive layer is heated and activated in the contact area by means of the heat generated in the radiation-absorbing layer,
characterized in that
the adhesive layer is a reactive, heat-activated adhesive adhesive layer, and the heat activation initiates a hardening reaction which comprises a frontal progression reaction.

According to the invention, the contact between the absorption layer and the adhesive must enable heat transfer. In a preferred embodiment of the invention, the absorption layer is in direct contact with the adhesive layer, that is to say directly adjoins it - in particular in the full contact area. In this way, a very efficient heat transfer can be guaranteed.

In an alternative but also advantageous embodiment of the invention, the absorption layer is only indirectly in contact with the adhesive layer. For example, a heat-conducting layer (such as vapor-deposited metal) can be provided between the layers mentioned. Such layers can be used, for example, to regulate the heat transfer in a targeted manner.
In an advantageous embodiment variant, a layer provided between the absorption layer and the adhesive has a thermal conductivity of more than 0.5 W / m · K. Of course, embodiments of the invention can also be implemented and advantageously carried out in which one or more partial surfaces of the absorption layer and the adhesive layer directly adjoin one another and one or more other partial surfaces are in indirect contact, for example by arranging a thermally conductive intermediate layer there.

It is not detrimental to the invention if surface areas between the absorption layer and the adhesive layer are not in heat-transferring - direct or indirect - contact, provided that the heat transferring contact of the other surfaces is sufficiently large for the successful implementation of the inventive teaching.

The first substrate is at least partially permeable to the irradiated radiation, that is to say for example transparent or translucent, so that the radiation-absorbing layer can be irradiated through the substrate. In the following, a “radiation-permeable substrate” is used in this regard.
The radiation emanating from the radiation source passes through the radiation-permeable substrate and reaches the radiation-absorbing layer - hereinafter also referred to as "absorption layer" for short - where the radiation is completely or partially absorbed and the absorption layer is heated as a result. The temperature of the absorption layer achieved in this way is in a range that the absorption layer neither melts nor is destroyed; in particular, the temperature achieved does not exceed either a possible melting temperature or a possible decomposition temperature of the material of the absorption layer. Very brief exceedances can be acceptable if this does not result in any destructive melting or decomposition.
The radiation-permeable layer and the absorption layer as well as the absorption layer and the adhesive layer do not each need to be of the same area, so the absorption layer can for example only be provided in partial areas between the radiation-permeable layer and the adhesive layer. Due to the nature of the front progress reaction, the adhesive layer can also cure completely come when this is only activated in parts of its surface, see also the explanations below.

In a preferred procedure, the first substrate is at least partially equipped with the radiation-absorbing layer on the side facing the adhesive layer, so the radiation-absorbing layer can be printed or otherwise coated on the first substrate.

A “front progress reaction” in the sense of the present document is generally a chemical reaction, in particular a polymerization or crosslinking reaction, which is initially only initiated in the area of the surface in contact with the absorption layer and then progresses temporally and spatially through the adhesive layer, in particular until the curing reaction has completely passed through the adhesive layer and the adhesive layer has cured. Advantageous examples of corresponding initiation processes can take place cationically, anionically, radically or coordinatively. In principle, front progression reactions can also be carried out as polycondensation or polyaddition reactions.

The contact area between the absorption layer and the adhesive layer can in principle assume any geometric shapes. The first substrate can be provided with the absorption layer completely on the side facing the adhesive layer or only in one or more partial areas of its surface; wherein the absorption layer can also consist of several layer sections which can be in contact with one another or which can be without contact with one another - quasi island-like. According to the invention, the term “absorption layer” thus encompasses both coherent, uninterrupted and interrupted - for example reticulated - flat structures as well as the entirety of the - partial - flat structures formed from several separate layer sections. The planar appearance of absorption layers that are interrupted or composed of separate partial areas can be regular or irregular.
The polymerization or crosslinking reaction is initiated by a so-called stimulus, for example by externally supplied radiation energy or heat. In the present case, radiation energy is converted into heat in the absorption layer and the reaction is initiated thermally. After the initiation, the stimulus can be removed (but it does not have to be), as the reaction progresses automatically.
The absorption layer can fill the entire interface between the first substrate and the adhesive layer, or it can only partially fill it; for example, the absorption layer - even in the case of a one-piece design - can be smaller overall than the interface that results from the surface of the first substrate to be glued and the adjoining adhesive layer surface.

As a model for the reaction type of a front progression reaction, one can imagine a large number of points arranged on the contact surface at which the activation of the reaction takes place and this is thus initiated and from which the further reaction as a reaction front is radially symmetrical into the adhesive layer - similar to a wave front - propagates, with the respective propagation fronts correspondingly superimposed. The reaction front will run out accordingly at the edge areas of the adhesive layer.
A corresponding overall front propagation can occur essentially over a large area, in particular perpendicular to the respective (partial) surface of the radiation-absorbing layer, for example in the case of essentially (at least partially) parallel, flat substrate surfaces and thus a flat radiation-absorbing layer, or can occur by superimposing the radial fronts Front propagation perpendicular to the substrate-related tangential plane of each point forming an initiation focus - especially in the case of non-planar radiation-absorbing layers - happens. In each case, a temporally and spatially progressing reaction course of the overall front through the adhesive layer is decisive.

As a result, the adhesive layer is advantageously fully cured. If the hardening reaction includes other types of reactions in addition to the frontal progression reaction, the sum of all partial hardening reactions leads to full hardening. The front progression reaction is preferably the only hardening reaction.

Frontal progression reactions include, for example, frontal polymerizations such as those from WO 2017035551 A are known. In the case of frontal polymerization, it can generally be assumed that the reaction itself is so exothermic that it itself generates the activation energy required to advance the front. In addition to such reactions, the term “front progress reaction” also includes reactions in which the ambient temperature (usually room temperature) is sufficient to maintain the reaction, in which only the thermal impulse was required to start it.

The advantage of the method according to the invention is that the curing reaction only has to be heat-activated in the edge area of the adhesive layer adjoining the radiation-absorbing layer and then continues automatically in time and place without any additional external active energy supply, especially at room temperature, until the entire layer is cured. As a result, only a small amount of heat needs to be generated in the radiation-absorbing layer, which is just sufficient to start the reaction in the adjacent edge area of the adhesive layer. The risk of damage to the radiation-absorbing layer is thus significantly lower. The heat transport in the adhesive layer and the heat dissipation through the second substrate can essentially be neglected, since the entire adhesive layer no longer has to be heated.

A substrate is understood to be a body to be bonded which has at least one surface to be bonded. The surface can be aligned along a plane or else curved.

The hardening reaction taking place as a front progression reaction is activated in particular thermally. The procedure according to the invention is that by irradiating electromagnetic radiation, a layer that contacts the adhesive layer to be cured and absorbs the electromagnetic radiation (the absorption layer) is heated by absorbing the radiation. The temperature of the absorption layer rises to a value that enough heat can be transferred to the adhesive layer that at least the activation temperature of the initiation of the curing reaction is reached there, at least in the area of the contact surface with the absorption layer ("indirect heating"). In particular, the adhesive layer is not or only very slightly heated directly by the electromagnetic radiation - in that, for example, its absorption behavior in relation to the electromagnetic radiation is sufficiently low - so that its activation temperature would not be reached by direct heating of the adhesive layer; in particular such that the temperature of the adhesive layer remains in the region of room temperature in the absence of the absorbent layer. The adhesive layer to be cured preferably has a transmission of electromagnetic radiation of more than 70%.

Detailed description of the invention

The adhesive of the adhesive layer advantageously comprises one or more initiators for the polymerization or crosslinking reaction. As used herein, the term initiator (or also hardener) stands for a compound that can initiate (“initiate”) a polymerization reaction or crosslinking reaction of the adhesive. However, the initiator takes part in the reaction process to a very small extent and consequently does not form any polymer fraction that determines the properties of the bond.
Optionally, the adhesive of the adhesive layer can furthermore comprise one or more activators. As used here, the term activator stands for a compound which, even at very low concentrations, enables or in particular accelerates the course of the polymerization. Activators can also be called accelerators or accelerators. Activators can be so beneficial in increasing the speed of frontal progression reactions.

The stimulus is used in particular to provide the initiation energy. According to the invention, this can be done in particular by converting different forms of energy into one another, such as radiant energy into thermal energy, and the initiator is not activated directly by the externally introduced form of energy (such as radiant energy), but by the converted form of energy (such as thermal energy). The energy conversion from other forms of energy in the absorption layer - such as ultraviolet radiation, infrared radiation, radiation in the wavelength range of visible light, electron beams, etc. - allows the direct exposure of heat to the substrate and thus the risk of damage to it to be avoided. The aforementioned forms of energy can each advantageously be used individually or in combination. However, electron beams can have the disadvantage that they directly damage the adhesive or other components.
The energy conversion takes place in particular in the absorption layer. In particular, thermal initiators can be used as they are known in principle to the person skilled in the art for initiating the curing reaction. The process according to the invention can be optimized by choosing special initiators. Activators may also be present, for example those that promote or accelerate the frontal progression reaction.
The advantage of the method according to the invention is the locally limited and precisely controlled introduction of heat into the system, in that a corresponding amount of heat is generated in the absorption layer. It is therefore not necessary to heat the entire adhesive bond in a heating cabinet, with heating plates or the like.

stimulation

The irradiation by means of electromagnetic waves can in principle be selected from the spectrum of electromagnetic waves known to the person skilled in the art. This spectrum includes, for example, UV radiation, visible light or near to far infrared radiation. According to the known state of the art, the selection and intensity must be adjusted so that the radiation-absorbing layer is not damaged.

In a preferred embodiment of the method according to the invention, NIR radiation (near-infrared radiation) is used as the electromagnetic radiation. The radiation-absorbing layer is advantageously heated in a wavelength range from 0.8 to 1.2 μm. The NIR irradiation offers the advantage that the heating takes place almost immediately, usually with heating times of a few seconds (often in the range from 2 to about 10 seconds).

In principle, the radiation sources known to those skilled in the art can be used to generate the electromagnetic radiation. Laser radiation is particularly preferably used.

The person skilled in the art is able to determine the temperature reached in the radiation-absorbing layer by parameters such as e.g. set the wavelength, the speed of movement of the beam (scan speed), the number of irradiation repetitions (scan cycles), the laser power, the beam shape (modes), the pulse rate, the focus position or beam expansion measures.

The irradiation is set in such a way that when the absorption layer is heated, a maximum temperature is reached at which the absorption layer is neither destroyed nor melted. The adhesive layer should also not be destroyed at the temperature reached. In the case of thermoplastic reactive adhesives, it can be advantageous if the adhesive melts (partial melting or melting) in order to improve the adhesion process. In a preferred procedure for the method according to the invention, however, the adhesive layer neither melts nor is it destroyed - for example, decomposed. The final fixation is then effected by the heat-initiated curing.
Melting is a transfer of the physical state from a solid to a fluid (= melt) achieved by increasing the temperature. In particular, a substance with a viscosity of less than 10 ⁸ Pas is referred to as a fluid. The viscosity / flowability is expressed and described below by the dynamic viscosity.
The dynamic viscosity is usually - and for the information in this document - determined according to DIN 53019. The viscosity is measured in a cylinder rotation viscometer with a standard geometry according to DIN 53019-1 at a measuring temperature of 25 ° C. and a shear rate of 1 s ^-1 . Since very high viscosities cannot be determined with this method, the determination of the (complex) viscosity according to ISO 6721-10 at 25 ° C and a frequency of 1 rad / s is also common.
The fluid is not restricted in its flowability; it can be Newtonian, dilatant, pseudoplastic, plastic (according to Bingham or Casson fluids, shear time-dependent, thixotropic or rheopex fluids.

In a preferred procedure, radiation of a single wavelength in the range from 300 to 400 nm, radiation of several isolated wavelengths from this range and / or a contiguous section from this wavelength range - up to the full wavelength range - is radiated, since in this range most of the radiation is visible Wavelength range of translucent materials still transmit sufficient radiation, conventional radiation-absorbing layers almost completely absorb even with very thin layer thicknesses, so that almost all of the radiation power is converted into heat.

For the irradiation of a single or several isolated wavelengths, irrespective of the wavelength range, lasers, LEDs or an excimer radiator are advantageous; a laser is preferably used.

• - Strahlung einer einzigen Wellenlänge im Bereich von 400 bis 2700 nm,
• - oder Strahlung mehrerer isolierter Wellenlängen, wobei die isolierten Wellenlängen zum Teil oder bevorzugt vollständig im Bereich von 400 bis 2700 nm liegen, und/oder
• - ein zusammenhängender Abschnitt in diesem Wellenlängenbereich
• - mehrere zusammenhängender Abschnitte die zum Teil oder bevorzugt vollständig in diesem Wellenlängenbereich liegen,
• - der volle Wellenlängenbereich von 400 bis 2700 nm

eingestrahlt, da in diesem Bereich viele transluzente Substratmaterialien eine hohe Transmission für die Strahlung aufweisen
Besonders bevorzugt wird vorstehend jeweils eine Wellenlänge im Bereich 800 - 1200 nm genutzt, da in diesem Bereich das Aufheizen der strahlungsabsorbierenden Schicht effizient ist und sich gut steuern lässt.In a further preferred procedure,

• - radiation of a single wavelength in the range from 400 to 2700 nm,
• - or radiation of several isolated wavelengths, the isolated wavelengths partially or preferably completely in the range from 400 to 2700 nm, and / or
• - a coherent section in this wavelength range
• - several contiguous sections which are partly or preferably completely in this wavelength range,
• - the full wavelength range from 400 to 2700 nm

irradiated, since in this area many translucent substrate materials have a high transmission for the radiation
A wavelength in the range 800-1200 nm is particularly preferably used above, since in this range the heating of the radiation-absorbing layer is efficient and can be easily controlled.

One (or more) lasers are advantageously used for irradiating one or more isolated wavelengths. In principle, the laser sources known to the person skilled in the art can be used for this, the laser source being selected in particular with regard to the desired irradiated wavelength. The type of laser source can in particular be matched to the nature (material, geometry - such as, in particular, thickness - etc.) of the radiation-permeable first substrate, the second substrate, the absorption layer and / or the adhesive layer in order to optimally adapt the process to the required conditions - such as about preservation of the absorption layer and initiation and course of the front progress reaction - to adapt. For example, gas lasers - such as ion lasers, metal vapor lasers, neutral non-metal lasers - solid-state lasers - such as semiconductor lasers, color center lasers, doped non-conductor lasers, fiber lasers and lasers with a liquid laser medium (dye laser) can be used. Synchrotron radiation sources (so-called "free electron lasers") can also be used as radiation sources.

Radiolucent substrate

The first substrate is at least partially permeable to the radiation used for absorption - that is to say in the wavelength range that is decisive for heating the radiation-absorbing layer - that is to say, for example, transparent or translucent.

According to the invention, a substrate is sufficiently permeable to radiation if the transmission for radiation of the irradiated defined wavelength - at a temperature of 23 ° C and 50% relative humidity - is more than 70% or for radiation of the irradiated wavelength range on average more than 70%.

The transmission is determined by means of a spectrophotometer at 23 ° C. and 50% relative humidity for the radiation of the defined wavelength or in the wavelength range used for the method according to the invention and is related to the thickness of the substrate to be irradiated. Correction for interface reflection losses is not made.
In principle, all materials can be used as the first substrate which, as stated above, are at least partially transparent to radiation of the relevant wavelength or the relevant wavelength range. Examples, without wishing to be limited thereby, are glass, plastics - such as polycarbonate, polymethyl methacrylate (acrylic glass), polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, polystyrene, cyclic olefin copolymers, etc., but also mineral materials and crystals such as quartz, Called ruby, emerald or sapphire.

Radiation absorbing layer

The radiation-absorbing layer can in principle be any layer that is suitable for absorbing the correspondingly irradiated radiation energy, warming up in the process and then dissipating this thermal energy to the adjacent adhesive layer.

The radiation-absorbing layer particularly preferably absorbs near-infrared radiation. Ideally, the radiation-absorbing layer is only slightly transparent to the radiation to be absorbed, nor does it reflect it, so that a maximum of absorption takes place. As a result of the impermeability of the radiation-absorbing layer to the radiated radiation - or the limited permeability - damage to the adhesive layer by the radiation is also avoided or at least greatly reduced. However, radiation-absorbing layers that partially transmit the radiation energy and / or partially reflect it can also be used advantageously according to the invention if the dose of the irradiated energy is regulated in such a way that, on the one hand, sufficient absorption of the radiation takes place in the absorption layer and on the other hand, damage to the absorption layer or the adhesive layer is sufficiently avoided.

Radiation-absorbing substances can advantageously be mixed into the absorption layer in order to improve the absorption capacity.

In an advantageous embodiment of the invention, the absorption layer is formed by a layer which is formed by adhering an ink containing a dye or a pigment to the rear side of the transparent or translucent substrate. Such an ink can for example be printed on, but according to the invention can also be applied by all other layer-forming processes known from the prior art. The matrix of the ink can in particular be realized by a curable polymeric compound, for example based on acrylate, urethane acrylate, epoxy acrylate, carboxyl group-modified epoxy acrylate, polyester acrylate, unsaturated polyester resin, copolymer acrylate, polyacrylic acrylate, alicyclic epoxy resin, glycidyl ether-epoxy resin, a vinyl ether compound, etc., an oxetane compound Examples of a curable ink include those that dry and / or cure without further external influence - for example under the present conditions in the air - and those that dry and / or cure thermally by baking and drying. Further usable as the curable inks are two-component reaction curing types using a curing agent, and radiation curing types which cure by, for example, ultraviolet light and electron beam. Even thermoplastic materials can be used as a matrix as long as the heating of the absorption layer by the radiation leads to a temperature below the melting point.

The dye may be any dye which has laser beam absorption, and it may be a natural dye such as reddish or safflower, a reaction, a sulfurized synthetic dye such as naphthol, a fluorescent dye, or the like. The pigment can be any that are not transparent to laser light, for example, inorganic pigments such as carbon black and composite oxide pigments, phthalocyanine pigments, azo pigments, sea pigments, polycyclo pigments. Organic pigments can also be used. When the design layer is printed, a fine design can be obtained. As the printing method, for example, various printing methods such as letterpress printing, gravure printing, flexographic printing, offset printing, silk printing, gravure printing, laser printing, inkjet printing and the like can be used.

In an advantageous embodiment of the invention, the matrix of the absorption layer is made on the same chemical basis as the adhesive used according to the invention. The radiation-absorbing additives are then accordingly mixed into this matrix layer. On the same chemical basis here means that the matrix has reactive groups, which the reactive resin also has, for example cyclic ethers, hydroxyl groups, carbonyl groups, amines and vinyl or allyl groups before the formation of the absorption layer (i.e. possibly before curing).

Since the absorption layer is irradiated through the transparent or translucent substrate, it can be seen through the substrate in the design variants in which this substrate is also permeable to visible light. It is then possible to optically design the absorption layer accordingly in order to create a corresponding appearance of the component on the irradiated side. For example, the absorption layer can be designed black in order to make the corresponding component surface appear black.
The optical design can, for example, be brought about by the additives that bring about or increase the absorption - as explained above - for example when corresponding inks or carbon black are used as absorbents. On the other hand, the optical design can - alternatively or in addition - be brought about by additional additives to the absorption layer, for example by additional, non-radiation-absorbing additives. In the case of the last-mentioned additional additives, the additives should advantageously be chosen in such a way that the absorption capacity in relation to the irradiated radiation and the heating capacity are not or at least not excessively negatively influenced.

Ceramic layers are advantageously used as absorption layers, especially those whose application processes are digitally controlled (e.g. digital printing, inkjet printing).

It is also advantageous to use absorption layers which are produced by introducing radiation-absorbing substances into the surface of the first substrate facing the adhesive layer, as is the case, for example, with the Cromoglass technology from Veneto Vetro (Italy) with ceramic inks from Ferro Corporation (USA) or ion transfer -Glass marking process by Boraident is implemented. Furthermore, absorption layers are advantageously used which are produced by material conversion of the substrate material or at least parts thereof on the surface of the first substrate facing the adhesive layer. For example, by adding a laser pigment of the Iriostat 8000 series from Merck (Darmstadt), polycarbonate remains transparent, so that it is the first substrate according to the invention is used. By the action of a laser on the surface of this first substrate facing the adhesive layer, a dark, radiation-absorbing layer is produced there, which further acts as an absorption layer.

In an advantageous embodiment, the absorption layer is covered with a further layer in order to protect the absorption layer from chemical interactions with the adhesive layer. This layer advantageously has a thickness below that of the absorption layer, in particular below 1 μm, in order to enable good heat transport from the absorption layer into the adhesive layer. The protective layer also advantageously has a high thermal conductivity of more than 1 W / mK. Suitable are e.g. Metal, semi-metal or oxide layers that are deposited from the gas phase.

Heat-activated activatable adhesives

Heat-activated bonding adhesives can basically be classified into two categories: thermoplastic heat-activated bonding adhesives (hot-melt adhesives) and reactive, heat-activated bonding adhesives (reactive adhesives). This classification also includes those adhesives that can be assigned to both categories, namely reactive thermoplastic heat-activated adhesive adhesives (reactive hot melt adhesives). Heat-activated adhesive compositions can already be pressure-sensitive adhesive at room temperature. The heat activation increases the adhesive strength.

Thermoplastic adhesives are based on polymers which, due to their inherent properties, reversibly soften when heated and solidify again when cooled. Non-reactive hot-melt adhesives stick solely because of this softening and solidification behavior, so such adhesives can flow onto the substrates to be bonded, for example when heat is supplied, wet them and then hold the fixation in a re-solidified state.

In contrast, reactive, heat-activatedly bonding adhesives contain reactive components. The latter constituents are also referred to as “reactive monomers” or “reactive resins” (collectively also referred to as “reactive components”), depending on whether they are monomers, oligomers or polymers. By means of the reactive components, the heating initiates a polymerization and / or crosslinking process which, after completion of the polymerization reaction or crosslinking reaction, ensures a permanent, stable connection, even under pressure. The curing of the adhesive for the final fixation is then based on this crosslinking process. For the linking of the building blocks in the crosslinking reaction, in particular, the same reaction mechanisms can be used as for linking the monomers in the polymerization reactions. Crosslinking reactions are usually used when not monomers but rather longer building blocks are linked to one another via bridges.
To form an adhesive layer, the adhesive advantageously comprises a longer-chain polymer component, particularly in the case of shorter-chain reactive components, in order to give the overall composition a sufficient viscosity (hereinafter also referred to as “matrix polymer” or “film former”). This enables it to be formed into a largely dimensionally stable film and thus the application of reactive adhesive films. The task of this matrix is to form a basic structure for the reactive monomers and / or reactive resins so that they are not in liquid form, but rather are embedded in a film or foil. In this way, easier handling is guaranteed.
In principle, it is possible to include such matrix polymers - through the presence of suitable functional groups on these polymers - in the crosslinking reaction; In particular, however, the matrix polymers can be essentially inert with respect to the polymerization or crosslinking reaction, so that the matrix polymers are not involved in the curing reaction and so, for example, an interpenetrating polymer system or network in the base polymer - such as the polymer matrix - due to the curing reaction of the reactive components. is built. The film former can consist of one polymer or of several polymers (blends).
The polymer (s) for suitable film formers for use in the present invention is / are selected, for example, from the following list: thermoplastic polymers, such as polyesters or copolyesters, polyamides or copolyamides, polyacrylic acid esters, acrylic acid ester copolymers, polymethacrylic acid ester, methacrylic acid ester copolymers, thermoplastic polyurethanes and chemically or physically crosslinked substances of the aforementioned compounds. Furthermore, elastomers and thermoplastic elastomers can also be used alone or in a mixture as polymeric film formers. Thermoplastic polymers, in particular semi-crystalline, are preferred.

In addition to the reactive components, thermoplastic reactive adhesives preferably contain elastic components, for example synthetic nitrile rubbers, which can be present alongside the matrix polymer or are used as such. Such elastic components give the heat-activatedly bonded adhesive, owing to their high flow viscosity, particularly high dimensional stability, even under pressure, or contribute to the impact modification.

An advantageous reactive, heat-activatedly bonded adhesive has in particular a matrix polymer and a modification resin, the modification resin comprising an adhesive resin and / or a reactive resin. As a result of the use of a matrix polymer, it is possible to obtain adhesive layers with excellent dimensional stability.
A reactive, heat-activated bonding adhesive enables bonding with rapid activation, in which the final bond strength is already achieved within a short time, so that overall a well-adhering connection is ensured.

The elastomers customary in the field of adhesives can preferably be used as the matrix polymer, for example in the “Handbook of Pressure Sensitive Adhesive Technology” by Donatas Satas (Satas & Associates, Warwick 1999 ) are described. These are, for example, elastomers based on acrylates and / or methacrylates, polyurethanes, natural rubbers, synthetic rubbers such as butyl, (iso) butyl, nitrile or butadiene rubbers, styrene block copolymers with an elastomer block made of unsaturated or partially or fully hydrogenated polydiene blocks (polybutadiene, Polyisoprene, poly (iso) butylene, copolymers of these and other elastomer blocks familiar to the person skilled in the art), polyolefins, fluoropolymers and / or silicones.
If rubber or synthetic rubber or blends produced from them are used as matrix polymer, then the natural rubber can basically be made of all available qualities such as crepe, RSS, ADS, TSR or CV types, depending on the required purity and viscosity level, and synthetic rubber or synthetic rubbers from the group of randomly copolymerized styrene-butadiene rubbers (SBR), butadiene rubbers (BR), synthetic polyisoprene (IR), butyl rubbers (IIR), halogenated butyl rubbers (XIIR) ), acrylate rubbers (ACM), ethylene vinyl acetate copolymers (EVA), nitrile rubbers (NBR), ethylene-propylene-diene rubbers (EPDM) or polyurethanes and / or their blends.
According to a preferred embodiment of the invention, these elastomers have a molar mass which is greater than their 5-fold, preferably 25-fold, entanglement molar mass. “On the basis of” or “on the basis of” means here that the properties of the polymer mixture are at least largely determined by the basic properties of this polymer (the so-called “base polymer”), although it is of course not excluded that these are due to use are additionally influenced by modifying auxiliaries or additives or by other polymers in the composition. In particular, this can mean that the proportion of the base polymer in the total mass of the matrix polymer phase is more than 50% by weight.

The polymer can have a linear, branched, star-shaped or grafted structure, to give just a few examples, and be constructed as a homopolymer, a random copolymer, an alternating or block copolymer. For the purposes of this invention, the term “statistical copolymer” includes not only those copolymers in which the comonomers used in the polymerization are incorporated purely randomly, but also those in which gradients in the comonomer composition and / or local enrichment of individual comonomer types occur in the polymer chains . Individual polymer blocks can be built up as a copolymer block (random or alternating).

Before curing, the adhesive is preferably a pressure-sensitive adhesive. According to the invention, a “pressure-sensitive adhesive” is understood, as is generally customary, to mean a substance which - in particular at room temperature - is permanently tacky and also tacky. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and remains adhered there, the pressure to be applied and the duration of this pressure being not defined in more detail. In some cases, depending on the exact type of pressure-sensitive adhesive, the temperature and humidity as well as the substrate, the application of a short-term, minimal pressure, which does not go beyond a light touch for a brief moment, is enough to achieve the adhesive effect, in others Long-term exposure to high pressure may also be necessary in some cases.

With the attribute "pressure-sensitive" - also as a component of nouns such as in pressure-sensitive adhesive - or synonymously with the attribute "self-adhesive" - also as a component of nouns - in the context of this document, those compositions are referred to that already under relatively weak pressure - if not otherwise specified, at room temperature, i.e. 23 ° C - a permanent bond with the primer and can be removed from the primer after use, essentially without leaving any residue. Pressure-sensitive adhesives are preferably used in the form of adhesive tapes. For the purposes of the present invention, a pressure-sensitive adhesive tape has a bond strength in the uncured state of at least 0.1 N / cm.

Pressure-sensitive adhesives thus have a permanently tacky effect at room temperature, that is to say they have a sufficiently low viscosity and high tack so that they wet the surface of the respective adhesive base even with a slight pressure. The adhesiveness of the pressure-sensitive adhesives is based on their adhesive properties and the redetachability on their cohesive properties.

Pressure sensitive adhesives have special, characteristic viscoelastic properties that lead to permanent tack and adhesiveness. They are characterized by the fact that when they are mechanically deformed, both viscous flow processes and the build-up of elastic restoring forces occur. Both processes are related to one another in terms of their respective proportions, depending on the exact composition, structure and degree of crosslinking of the pressure-sensitive adhesive as well as on the speed and duration of the deformation and on the temperature.

The proportionate viscous flow is necessary to achieve adhesion. Only the viscous components, caused by macromolecules with relatively high mobility, enable good wetting and good flow onto the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive tack (also referred to as tack or surface tack) and thus often also to high bond strength. Strongly crosslinked systems, crystalline or glass-like solidified polymers are generally not or at least only slightly tacky due to the lack of flowable components.

The proportional elastic restoring forces are necessary to achieve cohesion. They are caused, for example, by very long-chain and tightly entangled macromolecules as well as physically or chemically cross-linked macromolecules and enable the forces acting on an adhesive bond to be transmitted. They mean that an adhesive bond can withstand a permanent load acting on it, for example in the form of permanent shear stress, to a sufficient extent over a longer period of time.

The storage modulus (G ') and loss modulus (G' ') can be used for a more precise description and quantification of the amount of elastic and viscous components as well as the ratio of the components to one another using dynamic mechanical analysis (DMA). G 'is a measure for the elastic part, G' 'a measure for the viscous part of a substance. Both sizes are dependent on the deformation frequency and the temperature.

The sizes can be determined with the aid of a rheometer. The material to be examined is exposed to a sinusoidally oscillating shear stress in a plate-plate arrangement, for example. In the case of devices controlled by shear stress, the deformation is measured as a function of time and the time offset of this deformation with respect to the introduction of the shear stress. This time offset is referred to as the phase angle δ.

The storage modulus G 'is defined as follows: G' = (τ / γ) · cos (δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between shear stress and deformation vector). The definition of the loss modulus G '' is: G '' = (τ / γ) sin (δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between the shear stress and deformation vector).

For pressure-sensitive adhesive substances, it is preferred that at room temperature, here by definition at 23 ° C., in the deformation frequency range from 10 ⁰ to 10 ¹ rad / sec G 'is at least partly in the range from 10 ³ to 10 ⁷ Pa and that G ″ is also at least is partly in this area. “Partly” means that at least a section of the G 'curve lies within the window that is defined by the deformation frequency range from 10 ⁰ to 10 ¹ rad / sec inclusive (abscissa) and the range of G' values from 10 ³ inclusive up to and including 10 ⁷ Pa (ordinate) is spanned. This applies accordingly to G ″.

In principle, it can be advantageous if thermally conductive fillers are added to the adhesive, for example metal oxides - such as aluminum oxides, silicon oxides, magnesium oxides -, inorganic nitrides - such as silicon nitrides, boron nitrides, aluminum nitrides, titanium nitrides, zirconium nitrides, tantalum nitrides, niobium nitrides. Other thermally conductive fillers that can be used include potassium titanate, aluminum borate, magnesium sulfate, calcium carbonate and the like, fibers made from the aforementioned compounds, glass fibers, carbon fibers, metal fibers or powder, aramid fibers, asbestos, silicon carbide, ceramic, barium sulfate, calcium sulfate, kaolin, clay, silica, pyitrophyllite, benton , Sericite, zeolite, montmorillonite, mica, mica, nepheline syenite, Talc, atalvalite, wollastonite, polycarbon monofluoride, ferrite, calcium silicate, magnesium carbonate, dolomite, zinc oxide, titanium oxide, magnesium oxide, iron oxide, molybdenum disulfide, graphite, gypsum, glass beads, glass powder, glass spheres, quartz, quartz glass and the like.
According to the invention, adding thermally conductive fillers to the adhesive - in particular the adhesive layer - can, however, be rather counterproductive, since the heat is then dissipated from the radiation-absorbing layer and the initiation temperature is reached later. According to the invention, therefore, the embodiment of the invention in which the adhesive - in particular the adhesive layer - contains less than 5% by weight of filler, in particular less than 5% by weight of filler with a thermal conductivity of more than 1 W / mK. Particularly advantageously, the adhesive layer itself has a thermal conductivity of less than 0.2 W / mK before curing.

The reactive heat-activated adhesive layer to be bonded is preferably provided in film form, that is to say in particular not applied as a fluid (liquid adhesive) to one of the substrate surfaces to be bonded, but rather provided and applied already in film form.

In particular, a film is a planar arrangement of a system whose dimensions in one spatial direction (thickness or height) are significantly smaller than in the other two spatial directions which define the main extent (length and width). Such a flat structure can be compact or also perforated and consist of a single material or of different materials. A film can have a constant thickness over its entire surface area or it can have different thicknesses. It can also consist of a single layer or of several layers that can be arranged congruently or at least partially not overlapping.

Self-supporting adhesive films are preferably used as single-layer adhesive films. These differ from "films" of liquid adhesives applied to a substrate in particular in that they - if necessary applied to the auxiliary carrier as a manageability support - have sufficient inherent stability, in particular sufficient cohesion, to be handled, assembled, stored, transported as an independent object, to be able to be re-laminated and / or applied. Liquid films, on the other hand, only arise and exist on the substrate that is ultimately to be bonded, since they are applied to it in a liquid - i.e. comparatively low-viscosity - form. The main advantage of self-supporting adhesive films is their simple and extremely adaptable introduction into the adhesive process. Auxiliary carriers are not regarded as part of the - single or multilayer - adhesive film; they are removed for or during the application of the adhesive film and are not part of the final adhesive bond.

If the viscosity of the reactive components is sufficient, the reactive component can readily be suitable for forming the film shape. However, especially with a lower viscosity of the reactive adhesive, it can be advantageous to form a film to mix the reactive component into a matrix polymer or a mixture of matrix polymers ("film former"; see also the explanations above), which is particularly inert with regard to polymerization - or crosslinking reaction of the reactive component. As described above, matrix polymers can advantageously have elastomeric properties.

In a particular embodiment, the adhesive film can have a multilayer structure, the front progression reaction being initiated in particular in the adhesive layer adjoining the absorption layer. In particular, multilayer adhesive films are those that are composed exclusively of - preferably self-supporting - adhesive films.

The adhesive is particularly preferably provided as a pressure-sensitively adhesive film.

A pressure-sensitive adhesive film can be brought into a pre-bond with the second substrate or the radiation-absorbing layer by applying slight pressure, so that the joining process is simplified. After the preliminary bond has been produced, a preliminary adhesive bond can also be produced by applying slight pressure. This is then finally produced by the method according to the invention. The pressure can be maintained during the irradiation, but it can also be omitted due to the pressure-sensitive adhesive properties. There is preferably no pressure.

In an advantageous embodiment, the adhesive consists of at least one layer of a pressure-sensitive adhesive film and at least one layer of a non-pressure-sensitively adhesive film, in particular a hot-melt adhesive film, in which the frontal progression reaction is initiated at least in the pressure-sensitive adhesive film. A front progression reaction is preferably also initiated in the non-pressure-sensitive adhesive layer. is particularly preferred in both Layers initiate the same front progress reaction so that it can progress from one layer to the other. In this embodiment, the adhesive film is advantageously pre-fixed with the pressure-sensitive adhesive side on the second substrate. The connection with the first substrate and initiation of the front progression reaction takes place, preferably under pressure, by heating the non-pressure-sensitively adhesive layer by means of irradiation of the absorption layer. This embodiment has the advantage that the non-adhesive layer makes it easier to adjust the alignment of the joining partners with respect to one another.

If non-pressure-sensitive adhesive films are used, the film is preferably brought into a pre-bond with the second substrate while being heated to a temperature below the activation temperature. After the preliminary bond has been produced, the adhesive bond can finally be produced under pressure by the method according to the invention. The pressure must essentially be maintained during the irradiation in order to ensure adhesion to the radiation-absorbing layer on the first substrate. After the end of the irradiation and while the frontal polymerization is progressing, the pressure can be dispensed with. This is also preferred because it shortens the cycle time.

The adhesive film is preferably in a prefabricated form, for example as a die cut. It can completely cover the area delimited by its outer periphery or leave parts of it free, e.g. with a frame-shaped die cut.

Front progress reaction

In the context of the present document, a front progress reaction is understood to mean a reaction in which the reaction zone migrates through the material in which the reaction takes place (compare the statements above). In particular, the front progress reaction is a variant of polymerization or crosslinking reactions in which the reaction zone migrates through the reacting polymerizable or crosslinkable material. The polymerization or crosslinking is triggered in a partial area of the material volume by a stimulus and then penetrates the entire volume over time, whereby the locally achieved degree of polymerization does not have to be the same everywhere.

In the context of the invention, the stimulus used is the heat generated in the absorption layer by radiated electromagnetic energy - for example UV radiation or NIR radiation - and transferred to the adhesive.

The polymerization or crosslinking reaction can take place at an ambient temperature in the range of room temperature (in particular in the range of 15-25 ° C; the room temperature itself is defined in the context of this document as 23 ° C) after initiation without further maintenance of the stimulus through the entire Advance material volume. The rate of reaction can be increased by increasing the temperature. In some variants of the front progression reactions, such as the frontal polymerizations mentioned, so much heat is generated locally by an exothermic reaction that the temperature reached itself again forms the stimulus for the further progress of the polymerisation front, in other variants the reaction front also proceeds at ambient temperature Material volume continued.

In principle, all reactions known to the person skilled in the art, which can be carried out as heat-activated front progression reaction, can be used according to the invention, provided the radiation-absorbing layer is not damaged by chemical or thermal interaction.

Preferred embodiment (A1) of the adhesive used according to the invention

In a preferred embodiment A1 of the invention, a cationic polymerization is used as the frontal polymerization, particularly preferably one of cyclic ethers, that is to say those compounds which contain one or more groups which represent a bridging of one or more CC bonds by the -O- group (Groups to be designated with the prefix “Epoxy” according to the definition of IUPAC, Rule C-212.2 and R-9.2.1.4; in the following “oxygen bridges”). Cyclic ethers advantageous according to the invention include, for example, epoxides (synonymously “oxiranes” in the context of this document; compounds comprising at least one heterocyclic three-membered ring with two carbon atoms and one oxygen atom; this heterocyclic three-membered ring is hereinafter referred to as or oxirane ring) and / or oxetanes (compounds comprising at least one heterocyclic four-membered ring with three carbon atoms and one oxygen atom) and / or oxolanes (compounds comprising at least one heterocyclic five-membered ring with four carbon atoms and one oxygen atom). In principle, compounds can also be used according to the invention which have at least one heterocyclic ring with more than four carbon atoms and one oxygen atom include. It is also possible to use "mixed compounds" of the aforementioned classes of compounds, that is to say compounds which have oxygen atoms in two or more than two heterocyclic rings with different numbers of carbon atoms. For example, adhesives such as those described in FIG US 2004 225025 A are shown.

The reactive, heat-activated, adhesive layer of adhesive layer of the invention embodiment A1 advantageously comprises at least one epoxide (oxirane) and / or one oxetane and an initiator for a cationic polymerization.

Epoxy-containing materials or epoxy resins which are useful in the compositions of embodiment A1 of the invention are any organic compounds having at least one oxirane ring which can be polymerized by a ring opening reaction. Such materials, commonly referred to as epoxides, include both monomeric and polymeric epoxides and can be aliphatic, cycloaliphatic, or aromatic. These materials generally have an average of at least two epoxy groups per molecule, preferably more than two epoxy groups per molecule. The “average” number of epoxy groups per molecule is defined as the number of epoxy groups in the epoxy-containing material divided by the total number of epoxy molecules present. The polymeric epoxides include linear epoxy terminated polymers (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers with backbone oxirane units (e.g., polybutadiene-polyepoxide), and polymers with pendant epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). The molecular weight of the epoxy-containing material can vary from 58 to about 100,000 g / mol or more. Mixtures of various epoxy-containing materials can also be used in the hot melt compositions of the invention. Useful epoxy-containing materials include those containing cyclohexene oxide groups such as the epoxycyclohexane carboxylates represented by 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane carboxylate, and bis (3 , 4-epoxy-6-methylcyclohexylmethyl) adipate are exemplified. For a more detailed list of useful epoxies of this type see on U.S. Patent No. 3,117,099 referenced.
Other epoxy-containing materials that are particularly useful in practicing Embodiment A1 of the invention include glycidyl ether monomers. Examples are the glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol with an excess of chlorohydrin such as epichlorohydrin (e.g. the diglycidyl ether of 2,2-bis- (2,3-epoxypropoxyphenol) propane). Further examples of epoxides of this type that can be used in invention embodiment A1 are shown in FIG U.S. Patent No. 3,018,262 described. In addition, epoxy-containing materials are included, which are obtained by modifying the abovementioned raw materials with fatty acids, in particular dimeric fatty acids.
There are a variety of commercially available epoxy-containing materials that can be used in invention embodiment A1. In particular, epoxides that are readily available include octadecylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide, glycidol, glycidyl methacrylate, diglycidyl ethers of bisphenol A (e.g., those sold under the trade names EPON 828, EPON 1004, and EPON 1001F by Shell Chemical Co. and DER -332 and DER-334 are available from Dow Chemical Co.), diglycidyl ether of bisphenol F (e.g. ARALDITE GY281 from Ciba-Geigy), vinylcyclohexene dioxide (e.g. ERL 4206 from Union Carbide Corp.), 3,4 -Ep-oxycyclohexylmethyl-3,4-epoxycyclohexenecarboxylate (e.g. ERL-4221 from Union Carbide Corp.), 2- (3,4-Epo-xycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane metadioxane (e.g. ERL-4234 from Union Carbide Corp.), bis (3,4-epoxycyclohexyl) adipate (e.g. ERL-4299 from Union Carbide Corp.), dipentene dioxide (e.g. ERL-4269 from Union Carbide Corp.), epoxidized polybutadiene (e.g. OXIRON 2001 from FMC Corp.), silicone resin-containing epoxy functionality, epoxysilanes (e.g. beta- (3,4-epoxycyclohexyl) ethyltrimethoxysilane and gamma-glycido-xypropyltrimethoxysilane, commercially available from Union Carbide), fire retardant epoxy resins (e.g. DER-542, a brominated bisphenol-type epoxy resin available from Dow Chemical Co.), 1,4-butanediol diglycidyl ether (e.g. ARALDITE RD-2 from Ciba-Geigy), hydrogenated bisphenol A-epichlorohydrin-based epoxy resins (e.g. E.g. EPONEX 1510 from Shell Chemical Co.) and polyglycidyl ethers of phenol-formaldehyde novolak (e.g. DEN-431 and DEN-438 from Dow Chemical Co.).

Examples of cyclic ethers which can advantageously be used according to the invention in embodiment A1 and have more than two carbon atoms in the ring are (meth) acrylates containing oxolane groups and (meth) acrylates containing oxolane groups, 3-ethyl-3-oxetanemethanol and derivatives, bis [1-ethyl (3 -oxetanyl) methyl) ethers and derivatives.

Compounds containing cyclic ether groups, such as epoxy compounds, can be used in their monomeric or also dimeric, trimeric, etc. up to their oligomeric form.

In embodiment A1 of the invention, the cationic frontal polymerization is preferably started by means of thermal initiators (thermally activatable initiators). As already stated, the temperature of the absorption layer rises when exposed to radiation to a value that so much heat on the Adhesive layer can be transferred so that at least the activation temperature of the initiation of the curing reaction is reached there, at least in the area of the contact surface with the absorption layer. The required activation temperature is then that at which the thermal initiator or initiators are converted into the active form in sufficient numbers.

In the sense of embodiment A1 of the present invention, thermally activatable initiators for cationic curing of epoxides which can be used are in particular pyridinium, ammonium (especially anilinium) and sulfonium (especially thiolanium) salts and lanthanide triflates.
N-Benzylpyridinium salts and benzylpyridinium salts are very advantageous, it being possible for aromatics to be substituted, for example, by alkyl, alkoxy, halogen or cyano groups. J. Polym. Sci. A, 1995, 33, 505ff; US 2014/0367670 A ; U.S. 5,242,715 A ; J. Polym. Sci. B, 2001, 39, 2397ff; EP 393 893 A ; Macromolecules, 1990, 23, 431ff; Macromolecules, 1991, 24, 2689; Macromol. Chem. Phys., 2001, 202, 2554ff; WO 2013/156509 A and JP 2014/062057 A give examples of corresponding compounds which according to the invention can advantageously be used as initiators.
Of the commercially available initiator systems, examples of compounds that can be used very advantageously are San-Aid SI 80 L, San-Aid SI 100 L, San-Aid SI 110 L from Sanshin, Opton CP-66 and Opton CP-77 from Adeka and K-Pure TAG 2678, K-Pure CXC 1612 and K-Pure CXC 1614 from King Industries.
Lanthanide triflates (samarium III triflate, ytterbium III triflate, erbium III triflate, dysprosium III triflate) are also available from Sigma Aldrich and Alfa Aesar (lanthanum III triflate).

Suitable anions for the initiators that can be used for embodiment A1 of the invention include hexafluoroantimonate, hexafluorophosphate, hexafluoroarsenate, tetrafluoroborate and tetra (pentafluorophenyl) borate. Anions can also be used JP 2012-056915 A1 and EP 393893 A1 .

Another preferred embodiment of the adhesive used according to the invention

In a further advantageous embodiment A2 According to the invention, an adhesive layer made of a reactive adhesive is used which is curable by means of radical polymerization. In addition to at least one reactive monomer and / or at least one reactive resin, the reactive adhesive here comprises both a blocked radical initiator and an activator. The blocked radical initiator is heated at the interface to the radiation-absorbing layer by the stimulus to a temperature above the deblocking temperature and starts the hardening reaction. The activator enables free radical polymerisation even in those areas of the adhesive where the deblocking temperature has not been exceeded, so that a frontal progression reaction occurs.

Blocked radical initiators are those radical initiators which have a half-life temperature for a half-life of 1 min (hereinafter also referred to as 1-minute half-life temperature T (t _1/2 = 1min)) of more than 80 ° C, preferably more than 120 ° C , particularly preferably of more than 150 ° C. A higher 1 minute half-life temperature improves the shelf life of the adhesive. The determination of the half-life refers to the method specified in the “Test methods” section.
Furthermore, a 1-minute half-life temperature of less than 200 ° C. is preferred, since this reduces the risk of damage to the absorption layer. The rate of disintegration of the radical initiators is a characteristic criterion for their reactivity and is quantified by specifying the half-lives at certain temperatures [t _1/2 (T)], where the half-life represents the time after which half of the peroxide at the specified temperatures Conditions has fallen apart. As a rule, the higher the temperature, the shorter the half-life of the decay. So the higher the rate of disintegration, the shorter the half-life.
The half-life temperature [T (t _1/2 )] is the temperature at which the half-life corresponds to a predetermined value, so the 1-minute half-life temperature [T (t _1/2 = 1min)] is the temperature at which the Half-life of the substance examined is just 1 minute.

Preferred free radical initiators for embodiment A2 of the invention are those peroxides, peroxyesters, persulfates and azo compounds whose half-life temperatures correspond to the above conditions.

Hydroperoxides are less suitable because the storage stability is severely limited in combination with the activator.

Also suitable as blocked radical initiators are those radical initiators whose self-accelerating decomposition temperature (SADT; temperature of self-accelerating decomposition, container: 220 l steel drum) is above 70 ° C.

Preferred initiators are accordingly 2,2'-azodi- (2-methylbutyronitrile), 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) -hexane, 1,1,3,3-tetramethylbutylperoxy-2- ethylhexanoate, tert-amyl peroxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxydiethyl acetate, tert-butyl peroxyisobutyrate, 1,1-di- (tert.- butylperoxy) -3,3,5-trimethylcyclohexane, 1,1 -di (tert-butylperoxy) -cyclohexane, tert-amyl-peroxy-2-ethylhexyl carbonate, rt.-butyl-peroxy-3,5,5- trimethylhexanoate, 2,2-di- (tert-butylperoxy) -butane, tert-butylperoxyisopropyl carbonate, tert-butyl peroxy-2-ethylhexyl carbonate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, di-tert .-amyl peroxide, dicumyl peroxide, di- (2-tert-butyl-peroxyisopropyl) -benzene, 2,5-dimethyl-2,5-di- (tert-butylperoxy) -hexane, tert-butylcumyl-peroxide , 2,5-dimethyl-2,5-di (tert-butylperoxy) hexyn-3, di-tert-butyl-peroxide, 3,6,9-triethyl-3,6,9-trimethyl-1,4 , 7-triperoxonane.

Dilauroyl peroxide and di- (4-tert-butyl-cyclohexyl) peroxydicarbonate are particularly preferred.

The amount of the radical initiator is, for example, in the range from about 0.5 to 20% by weight, preferably about 1-10% by weight, based on the total mixture of the constituents of the reactive adhesive. Most preferably about 5 to 10% by weight of free radical initiator, based on the total mixture of the constituents of the reactive adhesive, is used. The total mixture of the constituents of the reactive adhesive stands for the total amount of the components used, which include the reactive monomers and / or reactive resins, the activators, the radical initiators, the polymeric film-forming matrix and, if appropriate, further - optionally present - components which, as a sum (in wt.%) Is obtained.

As used herein, the reactive component - that is, reactive monomer or reactive resin - is intended to stand for one or more monomers and / or one or more resins that are particularly capable of free-radical chain polymerization. According to the invention, the reactive component or the constituents of the reactive component are selected from the group consisting of acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, diacrylates, dimethacrylates, triacrylates, trimethacrylates, higher functional acrylates, higher functional methacrylates, vinyl compounds and / or oligomeric or polymeric ones Compounds with carbon-carbon double bonds.
In an advantageous procedure of the invention embodiment A2, the reactive component or the constituents of the reactive component are selected from the representatives of the group consisting of: methyl methacrylate (CAS No. 80-62-6), methacrylic acid (CAS No. 79-41- 4), cyclohexyl methacrylate (CAS No. 101-43-9), tetrahydrofurfuryl methacrylate (CAS No. 2455-24-5), 2-phenoxyethyl methacrylate (CAS No. 10595-06-9), hydroxyalkyl methacrylates, especially 2-hydroxyethyl methacrylate (CAS No. 868-77-9), 2-hydroxypropyl methacrylate (CAS No. 923-26-2 and 27813-02-1), 4-hydroxybutyl methacrylate (CAS No. 29008-35-3 and 997-46 -6), di- (ethylene glycol) methyl ether methacrylate (CAS No. 45103-58-0) and / or ethylene glycol dimethacrylate (CAS No. 97-90-5).
In a further advantageous procedure of embodiment A2 of the invention, the reactive adhesive contains a mixture of cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, methacrylic acid and ethylene glycol dimethacrylate as reactive monomers to be polymerized. In a further preferred embodiment according to the invention, the reactive adhesive contains a mixture of 2-phenoxyethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and ethylene glycol dimethacrylate as reactive monomers to be polymerized.
In a further advantageous procedure of embodiment A2 of the invention, the reactive adhesive contains a mixture of 2-phenoxyethyl methacrylate, 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate as reactive monomers to be polymerized. In a further advantageous procedure of embodiment A2 of the invention, the reactive adhesive contains 2-phenoxyethyl methacrylate as the reactive monomer to be polymerized. In a further advantageous procedure of embodiment A2 of the invention, the reactive adhesive contains a mixture of methyl methacrylate, methacrylic acid and ethylene glycol dimethacrylate as reactive monomers to be polymerized.
In a further advantageous procedure of embodiment A2 of the invention, the reactive adhesive contains a mixture of 2-phenoxyethyl methacrylate and ethylene glycol dimethacrylate as reactive monomers to be polymerized.
In a further advantageous procedure of embodiment A2 of the invention, the reactive adhesive contains a mixture of di- (ethylene glycol) methyl ether methacrylate and ethylene glycol dimethacrylate as reactive monomers to be polymerized.

Oligomeric mono-, di-, tri- and more highly functionalized (meth) acrylates can be selected as reactive resin (s). These are very advantageously used in a mixture with at least one reactive monomer.

The free-radically curable adhesive layer advantageously further comprises a film former, as introduced at the beginning. The aforementioned monomers and / or reactive resins can accordingly be mixed with one or more film-forming polymer (s) - e.g. a thermoplastic polyurethane, e.g. Desmomelt 530®, or one or more of the other matrix polymers mentioned at the beginning - can be combined.

The amount of the reactive component (s) is advantageously in the range from about 20 to 100% by weight, preferably from about 40 to 80% by weight, based on the total mixture of the constituents of the reactive adhesive. Most preferably about 40 to 60% by weight of reactive components (i.e. of the reactive monomer or the reactive monomers or the reactive resin or the reactive resins or combinations thereof), based on the total mixture of the constituents of the reactive adhesive, are used. The total mixture of the constituents of the reactive adhesive is - as defined above - the total amount of the components used, which include the reactive monomers and / or reactive resins, the activators, the free radical initiators, the polymeric film-forming matrix and, if applicable, further - optionally present - components, which is obtained as the sum (in% by weight).

A manganese (II) complex, an iron (II) complex or a cobalt (II) complex, each with a compound selected from porphyrin, porphyrazine or phthalocyanine or a derivative of one of these compounds, is advantageously used as an activator for the free-radically curable adhesive , provided as a ligand.

In the present invention, an activator is added to the reactive adhesive - which is preferably present as an adhesive film - which comprises a complex compound with a manganese, iron or cobalt ion as the central atom and a compound containing carbon-nitrogen double bonds as ligand. The compound containing carbon-nitrogen double bonds is present in the complex compound in anionic form. The manganese, iron or cobalt ion is doubly positively charged in the complex compound, while the compound containing carbon-nitrogen double bonds is doubly negatively charged. The manganese, iron or cobalt ion replaces two hydrogen atoms in the complex compound that the ligand carried on the nitrogen atoms before the conversion to the complex compound.

In a preferred embodiment of the invention in terms of embodiment A2, the ligand has a cyclic structure, preferably a porphyrin, porphyrazine or phthalocyanine ring structure. These structures are to be understood as framework structures. The ligands can optionally carry substituents instead of the H atoms bonded to carbon atoms. In this case one speaks of derivatives of these compounds. Suitable substituents are selected from the group consisting of fluorine, chlorine, bromine, iodine, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, -OH, -NH2, -N02. A particularly suitable activator includes iron (II) phthalocyanine (CAS No. 132-16-1).

According to the invention, the amount of activator is in the range from greater than 0 to about 10% by weight, preferably about 0.1-5.0% by weight. Most preferably about 0.2-3.0% by weight, even more preferably 0.5-2.0% by weight, of activator, based on the total mixture of the constituents of the reactive adhesive, are used. The total mixture of the constituents of the reactive adhesive is as defined above.

In preferred variants of embodiment A2, the adhesive film is multilayered, preferably composed of several layers of the adhesive used according to the invention, and in particular such that initiator and / or activator is not contained in all layers of the film. The initiator is particularly preferably arranged in the surface layer of the adhesive film facing the radiation-absorbing layer in the bond.

Second substrate

In principle, there are no special requirements to be placed on the second substrate to be bonded; in particular, it can assume all desired shapes and also be designed in three dimensions. The second substrate can be completely transparent, partially transparent or impermeable to the radiated radiation.
In an advantageous manner, the second substrate is opaque to the radiation used, for example the laser light. Corresponding ceramics, metals and also corresponding plastics may be mentioned as examples of such materials.
The second substrate is particularly preferably selected from aluminum, in particular anodized aluminum, stainless steel, polyamide, polycarbonate, acrylonitrile-butadiene-styrene copolymer and glass fiber reinforced plastic.

Advantageous procedures

The method according to the invention can advantageously be carried out in such a way that the temperature in the radiation-absorbing layer is measured by means of a pyrometer (radiation thermometer). This procedure can be used particularly advantageously in the method according to the invention, since the radiation-absorbing layer is usually thin and has good thermal conductivity, so that the temperature of this layer can be used to infer the temperature at the interface that initiates the frontal polymerization there.

In a further advantageous embodiment of the method according to the invention, the frontal polymerization is accelerated by increasing the temperature. The maximum possible temperature is one at which the substrates, radiation-absorbing layer and adhesive are not damaged. The maximum temperature reached in the method according to the invention is preferably 100 ° C. (so that the temperature control is therefore designed in such a way that this maximum temperature is not exceeded).
The temperature preferably remains below 60 ° C. in order to keep the thermal stresses in the bonded substrates and the adhesive joint, which arise during cooling after the reaction due to different thermal expansion coefficients, low.

Experimental part

Test methods:

Push-out resistance

The push-out test ( 1 ) enables statements to be made about the bond strength of an adhesive product in the direction of the normal to the adhesive layer. To do this, a square substrate ( 1 ) with an edge length of 21 mm with the adhesive layer to be examined on a second substrate ( 2 ) glued. The second substrate has a circular hole with a diameter of 9 mm, the first substrate was applied centered with the adhesive layer over this hole. The adhesive layer also has a square geometry with an edge length of 21 mm, i.e. it covers the entire surface of the substrate ( 1 ). A composite was made from the substrate ( 1 ) Float glass (thickness 5 mm) with radiation-absorbing layer and substrate ( 2 ) Polycarbonate (Macrolon 099, 3 mm thick) without a radiation-absorbing layer examined.
The radiation-absorbing layer was UV cured black ink (Marabu UVG3C) in a layer thickness of about 15 µm using screen printing on the substrate ( 1 ) (Corona pretreatment using Tantec Spot-Tec, UV curing using a medium-pressure mercury lamp in a UV cube from Hönle (dose 300 mJ / cm ² )) The adhesive layer is applied as adhesive transfer tape to the radiation-absorbing layer at 23 ° C on substrate ( 1 ) and the composite (substrate ( 1 ) and tape) then on substrate ( 2 ) laminated. The entire composite is then pressed together under the action of pressure (force 50 N, time, 10 s).
Using a cylindrical punch (diameter 7 mm) clamped in a tensile testing machine, the hole in the substrate ( 2 ) onto the composite (substrate ( 1 ) and adhesive tape) and thus exerted a force on the adhesive joint in the composite. Substrate ( 2 ) is fixed in the tensile testing machine in such a way that a flat support / fixing on all sides is guaranteed, whereby substrate ( 1 ) can be pushed out freely through the stamp. The test speed is 10 mm / s. The force at which the bond fails and the substrate ( 1 ) of substrate ( 2 ) is solved. The force is related to the bond area (377 mm ² ), so that push-out strengths result in units of N / mm ² .
The test climate is 23 ° C. and 50% relative humidity, the test specimens are stored in the test climate for 120 h after the laser irradiation. The results are mean values from three individual tests and are given in N / mm ² (MPa).

Bond strength

The bond strengths were determined analogously to ISO 29862 (method 3) at 23 ° C. and 50% relative humidity at a peel speed of 300 mm / min and a peel angle of 180 °. The thickness of the adhesive layer was 100 μm in each case. An etched PET film with a thickness of 50 μm, such as is available from Coveme (Italy), was used as the reinforcement film. Steel plates according to the standard were used as the substrate. The measuring strip was bonded by means of a Rolling machine made with 4 kg at a temperature of 23 ° C. The adhesive tapes were peeled off immediately after application. The measured value (in N / cm) was the mean value from three individual measurements.

Half-life / half-life temperatures

mit

[I₀]

= Ausgangskonzentration des Initiators (zum Zeitpunkt des Starts des I nitiatorzerfalls)

[I]

= Konzentration des Initiators zur Zeit t

t

= Zeit seit Start des Initiatorzerfalls; in s

The equation for the thermal decomposition of initiators (first order reaction) is: $$\left[\text{l}\right]=\left[{\text{l}}_0\right]\cdot {\text{e}}^{-\text{kt}}$$

With

[I ₀ ]

= Initial concentration of the initiator (at the time of the start of the initiator disintegration)

[I]

= Concentration of the initiator at time t

t

= Time since initiator disintegration started; in s

$$\text{mit k}=\text{Z}\cdot \text{e}{-}^{\text{Ea/RT}}$$

wobei

k

= Geschwindigkeitskonstante der Dissoziation des Initiators; in s^-1

Z

= Arrhenius-Frequenzfaktor; in s^-1

Ea

= Aktivierungsenergie der Initiator-Dissoziation; in J/mol

R

= 8.3142 J/(mol.K)

T

= Temperatur, in K

t_1/2

= Halbwertszeit, in s

The determination of the activation energy Ea of the decay of initiators (initiator dissociation) and the frequency factor Z (pre-exponential factor) is carried out by means of dynamic differential calorimetry / thermal activity monitoring (English-scientific: differential scanning calorimetry - thermal activity monitoring, abbreviation: DSCTAM) according to ASTM E698 - 18 carried out. For a large number of initiators, the corresponding activation energies Ea and frequency factors Z are also listed in the literature or in lists of the providers concerned. Using the activation energy Ea of the initiator dissociation and the Arrhenius frequency factor Z, the half-life is calculated using the Arrhenius equation: $${\text{<figure-callout id="1" label="t" filenames="DE102019208668A1\_0004.png" state="{{state}}">t</figure-callout>}}_{1/2}=\text{<figure-callout id="2" label="ln" filenames="DE102019208668A1\_0004.png" state="{{state}}">ln</figure-callout>}2\text{/ k}$$

$$\text{with K}=\text{Z}\cdot \text{e}{-}^{\text{Ea / RT}}$$

in which

k

= Rate constant of the dissociation of the initiator; in s ^-1

Z

= Arrhenius frequency factor; in s ^-1

Ea

= Activation energy of initiator dissociation; in J / mol

R.

= 8.3142 J / (mol.K)

T

= Temperature, in K

t _1/2

= Half-life, in s

The decay process and, accordingly, its half-life is temperature-dependent. Correspondingly, such temperatures T (t _1/2 ') (so-called half-life temperatures) can be determined for decay processes at which the half-life t _{1/2 of} the corresponding decay just assumes a certain size t _1/2 ' (for example 1 min); so t _1/2 = t _1/2 '. Writing convention for a half-life of 1 min: T (t _1/2 ') = T (t _1/2 = 1 min) for t _1/2 = t _1/2 ' = 1 min.

Examples:

Raw materials used.

Desmomelt 530 Largely linear hydroxyl polyurethane. Desmomelt 530 is a strongly crystallizing, elastic polyurethane with very low thermoplasticity from Bayer MaterialScience. The enthalpy of fusion measured by DSC is 54.7 J / g. Araldite ECN 1299 solid epoxy-cresol-novolak from Huntsman with a weight per epoxy of 206-230 g / eq and a softening temperature (DIN51920) of 85 to 100 ° C Epikote 828 LVEL Distilled difunctional bisphenol-A / epichlorohydrin liquid epoxide with a weight per epoxide of 185 to 192 g / eq from Hexion. Viscosity at 25 ° C from 10 to 12 Pa s. K-PURE CXC 1614 Cationic, thermally activated ammonium triflate initiator from King Industries with an activation temperature of about 123 ° C Epiclon N-673 Solid o-cresol novolak epoxy resin from DIC with a weight per epoxy of 208 to 212 g / eq., Softening temperature (DIN51920) 75 to 79 ° C Voranol P400 Polypropylene glycol homopolymer diol with a weight average molecular weight of about 400 g / mol PKHB solid phenoxy resin (polymer made from epichlorohydrin and bisphenol A with terminal hydroxyl groups that are repeated on the chain) from Inchem; weight average molecular weight of about 32,000 g / mol Ajicure PN-23 Solid amine adduct hardener from Ajinomoto made from bisphenol A epoxy resin (epoxy equivalent 184-194 g / eq), 2-ethyl-4-methylimidazole and phthalic anhydride, with a softening point of 100-105 ° C. Polymer A Homopolymer of 3,4-epoxycyclohexylmethyl methacrylate with a weight average molecular weight of 15,900 g / mol, prepared according to Example A in FIG DE 10 2016 207 548 A1 ; The glass transition temperature of the uncured polymer was 32 ° C (first heating ramp) and 72 ° C (second heating ramp) Dynasilan GLYEO 3-glycidyloxypropyltriethoxysilane from Evonik 2-phenoxyethyl methacrylate Sigma-Aldrich 2-hydroxyethyl methacrylate Sigma-Aldrich 2-hydroxypropyl methacrylate Sigma-Aldrich N-vinyl caprolactam Sigma-Aldrich Ethylene glycol dimethacrylate Sigma-Aldrich Iron (II) phthalocyanine Sigma-Aldrich, purity approx. 90% Pergan LP Dilauroyl peroxide with a half-life temperature (1 min) of 117 ° C UVG3C UV cured black ink from Marabu, specifications according to, Technical Data Sheet Ultra Glass UVG3C, Vers. 4, December 8th, 2015, Marabu GmbH, Tamm '

Adhesives according to the invention (Examples E1 to E3 and A1) and comparative adhesives (Examples V1 to V3) were prepared as follows in accordance with the compositions given in the table below and subjected to the test methods given.

Adhesives:

Epoxy based adhesive:

The PSAs or adhesives (Comparative Example 2 not pressure-sensitive) were produced in the laboratory by dissolving the polyurethane in butanone at 23 ° C. The reactive resin (s) and any further components present (see table) were then added. The hardener was then added by stirring under strong shear.

To produce layers of adhesive, the various adhesives were applied from a solution to a conventional liner (siliconized polyester film) using a laboratory spreader and dried. The thickness of the adhesive layer after drying is 100 ± 10 μm. The drying took place each first at RT for 10 minutes and 30 minutes at 65 ° C. in a laboratory drying cabinet. The dried layers of adhesive were each laminated immediately after drying with a second liner (siliconized polyester film with lower release force) on the open side.

The ejection resistance after curing of the adhesive layer (storage time after irradiation 5 min and 120 h, storage at 23 ° C., 50% relative humidity) was determined.

• • Leistung: 20 W
• • Vorschubgeschwindigkeit 100 mm/s
• • 1 Scan-Zyklus mit einem Strahldurchmesser von 3,2 mm und einer Spurüberlappung von 0,2 mm. Der Laser war in einem Abstand von etwa 90 mm oberhalb der Probe angeordnet.

The curing took place by heating the radiation-absorbing layer with a Contineous Wave diode laser LD-HEATER L10060-4 from Hamamatsu-Photonics Corporation with a wavelength of 940 nm. Unless otherwise described, the following parameters were set

• • Power: 20 W
• • Feed rate 100 mm / s
• • 1 scan cycle with a beam diameter of 3.2 mm and a track overlap of 0.2 mm. The laser was positioned about 90 mm above the sample.

No further pressing took place during the heating. Example: E1 E2 E3 V1 V2 composition Parts by weight Parts by weight Parts by weight Parts by weight Parts by weight Desmomelt 530 20th 20th 15th 20th 50 Polymer A 50 Epon Resin 828 Epikote 828 LVEL 20th 40 32.5 20th Araldite ECN1299 60 40 60 Epiclon N-673 32.5 Voranol P400 10 PKHB 10 K-PURE CXC 1614 2 2 2 1 Ajicure PN-23 15th GLYEO 3 Characteristics: Adhesive strength unhardened (steel) [N / cm] 9 6.1 10.2 8.1 0 Ejection strength unhardened [MPa] 0.6 0.4 0.7 0.6 <0.1 Ejection strength 5 min [MPa] 0.7 0.4 0.7 0.6 <0.1 Ejection strength 120 h [MPa] 4.1 3.4 2.8 0.7 <0.1

It was found that in Examples E1, E2 and E3 the ejection strengths 5 min after curing essentially correspond to that of the uncured adhesive, while structural strengths of several MPa are achieved after passing through the cationic frontal polymerization.

Comparative example C1 realizes an imidazole hardening which requires complete heating of the adhesive layer, since it does not represent a frontal polymerization. Therefore, even after 5 days, the polymerization has not progressed any further and structural strengths are not achieved.

Comparative example V2 realizes a cationic frontal polymerization, but the adhesive is not a pressure-sensitive adhesive. Therefore, prior to curing, no significant bond is established with the substrates, which bond is not noticeably increased during the curing process. According to the invention, a 21 × 21 mm ² section V2 was tested with the substrate ( 2 ) pre-laminated at a temperature of 85 ° C (force 50 N, time, 10 s). A substrate that extends beyond the edge of the tape section ( 1 ) with a radiation-absorbing layer was applied and the edges projecting beyond the adhesive tape section were subjected to pressure without the area above the adhesive tape section being covered by the printing device. The laser was then irradiated while maintaining the pressure (force 50 N). After the irradiation was complete, the pressure was maintained for an additional 30 seconds. The ejection strength 5 minutes after the irradiation was 1.2 MPa, that after 5 days was 4.2 MPa.

Acrylate-based adhesive:

150.0 g of the 20% acetone solution of Desmomelt 530® (PU solution) are mixed with 18.2 g of 2-phenoxyethyl methacrylate, 16.7 g of 2-hydroxyethyl methacrylate, 11.1 g of 2-hydroxypropyl methacrylate, 3.0 g, 7 g of N-vinylcaprolactam, 3 g of ethylene glycol dimethacrylate and 9.0 g of dilauroyl peroxide are mixed for 10 minutes with a commercially available laboratory stirrer, so that a mixture with dissolved components is formed.
For the example, 1 g of iron (II) phthalocyanine is added.
The parts by weight of the composition are shown in the following table: example A1 V3 composition Parts by weight Parts by weight Desmomelt 530 (20% by weight in acetone) 30.0 30.0 2-phenoxyethyl methacrylate 18.2 18.2 2-hydroxyethyl methacrylate 16.7 16.7 2-hydroxypropyl methacrylate 11.1 11.1 N-vinyl caprolactam 12.0 12.0 Ethylene glycol dimethacrylate 3.0 3.0 Iron (II) phthalocyanine 1.0 - Dilauroyl peroxide 9.0 9.0 total 101.0 100.0 Characteristics: Adhesive strength unhardened (steel) [N / cm] 9 6.1 Ejection strength unhardened [MPa] 0.3 0.3 Ejection strength 5 min [MPa] 0.3 0.3 Ejection strength 120 h [MPa] 2.3 0.8

Due to the peroxide which is suitable according to the invention, the formulation is stable and can be used for the process according to the invention. By heating the radiation-absorbing layer by means of radiation, the peroxide is only activated / unblocked at the interface between the adhesive layer and the radiation-absorbing layer, and radicals are formed. Due to the iron complex, the reaction is carried on through the entire layer as frontal polymerization without the peroxide having to be activated in the deeper areas of the adhesive layer. In the comparative example, the formulation constituent that enables frontal polymerization, the iron complex, is omitted so that frontal polymerization does not occur.

To produce layers of adhesive, the adhesives were applied to a conventional liner (siliconized polyester film) using a laboratory spreader and dried. The thickness of the adhesive layer after drying is 100 ± 10 μm. The drying was carried out first at RT for 10 minutes and 60 minutes at 50 ° C. in a laboratory drying cabinet. The dried adhesive layers were each laminated immediately after drying with a second liner (siliconized polyester film with lower release force) on the open side.

The ejection resistance was determined after the adhesive layer had cured (after storage for 5 minutes and 120 hours at 23 ° C., 50% relative humidity).

• • Leistung: 20 W
• • Vorschubgeschwindigkeit 100 mm/s
• • 1 Scan-Zyklus mit einem Strahldurchmesser von 3,2 mm und einer Spurüberlappung von 0,2 mm. Der Laser war in einem Abstand von etwa 90 mm oberhalb der Probe angeordnet.

The curing took place by heating the radiation-absorbing layer with a Contineous Wave diode laser LD-HEATER L10060-4 from Hamamatsu-Photonics Corporation with a wavelength of 940 nm. Unless otherwise described, the following parameters were set

• • Power: 20 W
• • Feed rate 100 mm / s
• • 1 scan cycle with a beam diameter of 3.2 mm and a track overlap of 0.2 mm. The laser was positioned about 90 mm above the sample.

No further pressing took place during the heating.

Achieved ejection strengths see table above.

It was found that in the example the ejection strength after 5 min after curing essentially corresponds to that of the uncured adhesive, while structural strengths of several MPa are achieved after the frontal polymerization.

Comparative example C3 realizes radical curing which requires complete heating of the adhesive layer to unblock the peroxide, since it does not represent frontal polymerization. This complete heating is not achieved by the process according to the invention. Therefore, even after 5 days, the polymerization has not progressed significantly and structural strengths are not achieved.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• JP 6046329 B [0002, 0007]
• JP 2011156858 A [0002, 0007]
• JP 2012218316 A [0003]
• JP 2014091755 A [0006]
• JP 06046329 B [0006]
• WO 2017035551 A [0019]
• US 2004225025 A [0079]
• US 3117099 [0081]
• US 3018262 [0081]
• US 2014/0367670 A [0085]
• US 5242715 A [0085]
• EP 393893 A [0085]
• WO 2013/156509 A [0085]
• JP 2014062057 A [0085]
• JP 2012056915 A1 [0086]
• EP 393893 A1 [0086]
• DE 102016207548 A1 [0111]

Claims (13)

A method for producing an adhesive bond of a first substrate to a second substrate by means of activation of a heat-activatable adhesive layer, the heat required for activation being generated in a radiation-absorbing layer adjacent to the heat-activatable adhesive layer, which can absorb at least electromagnetic radiation of a certain wavelength, wherein - the heat-activatable adhesive layer is arranged between the first and the second substrate, - the radiation-absorbing layer is arranged between the heat-activatable adhesive layer and the first substrate and is in contact with the heat-activatable adhesive layer, - the first substrate is at least partially transparent to radiation that can be absorbed in the radiation-absorbing layer, and wherein the radiation-absorbing layer is exposed to absorbable radiation through the first substrate, the radiation-absorbing layer to is heated to a maximum temperature at which no damage and no melting of the absorption layer occurs, so that the adhesive layer is heated and activated in the contact area by means of the heat generated in the radiation-absorbing layer, characterized in that the adhesive layer is a reactive, heat-activated adhesive layer and the heat activation initiates a hardening reaction which includes a frontal progression reaction. Procedure according to Claim 1 , characterized in that the adhesive layer is also a pressure-sensitive adhesive at room temperature. Method according to one of the preceding claims, characterized in that the adhesive layer is provided in film form and is arranged between the first and the second substrate, in particular as a self-supporting adhesive film. Method according to one of the preceding claims, characterized in that the curing reaction also proceeds through the adhesive layer after the absorbable radiation has been removed. Method according to one of the preceding claims, characterized in that UV radiation, visible light and / or infrared radiation is used entirely or in part as electromagnetic radiation. Method according to one of the preceding claims, characterized in that the electromagnetic radiation used is wholly or partially laser radiation. Method according to one of the preceding claims, characterized in that as absorbable radiation - radiation of an isolated wavelength in the range from 400 to 2700 nm, - radiation of several isolated wavelengths in the range from 400 to 2700 nm, - and / or one or more contiguous sections in the Wavelength range from 400 to 2700 nm - up to the full wavelength range - is used. Method according to one of the preceding claims, characterized in that the radiation-absorbing layer is coated, in particular printed, on the surface of the first substrate facing the adhesive. Method according to one of the preceding claims, characterized in that the reactive, heat-activated adhesive bonding is based on at least one matrix polymer and at least one modification resin. Method according to one of the preceding claims, characterized in that the front progress reaction is a heat-activated cationic polymerization, preferably a free-radically induced cationic polymerization. Method according to one of the preceding claims, characterized in that the front progress reaction is a heat-activated radical polymerization. Method according to one of the preceding claims, characterized in that the front progress reaction proceeds in the region of room temperature. Method according to one of the preceding claims, characterized in that no pressure is applied to the bond during the initiation and during the progress of the front progression reaction.

Images