EP0953025A1

EP0953025A1 - Hot melt adhesive based on an ethylene copolymer and an alkyl (meth)acrylate

Info

Publication number: EP0953025A1
Application number: EP98955642A
Authority: EP
Inventors: Eric Radigon; Jean Lebez; Jean-Michel Pierrot
Original assignee: Elf Atochem SA
Current assignee: Arkema SA
Priority date: 1997-11-14
Filing date: 1998-11-12
Publication date: 1999-11-03
Also published as: WO1999025785A1; AU1241299A; CA2277787A1

Abstract

The invention concerns a hot melt adhesive comprising: an ethylene-alkyl (meth)acrylate copolymer (A), the alkyl group containing at least 5 carbon atoms; at least a tackifier resin, optionally a plasticizer and optionally a wax. Said adhesive is hot-deposited on a substrate. Said products are used for making self-adhesive tapes and labels.

Description

HEAT-MELT ADHESIVE BASED ON ETHYLENE COPOLYMER AND

OF AN ALKYL (METH) ACRYLATE

The present invention relates to a hot-melt adhesive based on a copolymer of ethylene and an alkyl (meth) acrylate.

Hotmelt (adhesives) are thermoplastic materials which are solid at room temperature and which, when heated, become viscous liquids. These viscous liquids are applied to a first substrate and then covered with a second surface. By cooling, an adhesion is obtained between the substrate and the second surface. The open time is the period during which the adhesive which has been applied to a substrate which is at room temperature remains tacky, that is to say the time interval during which the second surface can be applied and by cooling to obtain adhesion between the substrate and the second surface.

After this open time period, it is no longer possible to obtain sufficient adhesion between the substrate and the second surface.

These adhesives are designated by the abbreviation HMA (hot melt adhesives). Adhesives with infinite open time are required for self-adhesive labels or adhesive tapes used at room temperature. Depending on the nature of the adhesive, more or less strong adhesions can be obtained, for example peeling off and re-sticking the label. Bonding is carried out by pressure at room temperature. The adhesive is deposited on the substrate (for example label or tape) when hot. These adhesives are designated by HMPSA (hot melt pressure sensitive adhesives), they are also sometimes designated as self-adhesive hot-melt compositions. The present invention relates to these two types of hot-melt adhesives, that is to say HMA and HMPSA.

According to the prior art, see for example ULLMANN'S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY, 5th edition (1 995) Vol A 26 p. 659-660, the HMPSAs are preferably based on block copolymers SIS (styrene-isoprene-styrene) but also SBS (styrene-butadiene-styrene).

In patent US 5373041 concerning HMPSA, the disadvantages of SBS and SIS have been cited as their instability under hot conditions and to UV rays as well as their poor resistance to oils. It was therefore proposed in this patent to replace the SBS and SIS with copolymers consisting of 60 to 70% (by weight) of ethylene, 30 to 40% of n-butyl acrylate and 0 to 5% of (meth) acrylic acid which can be neutralized by metal ions. Application WO 97/12007 describes HMPSAs, based on ethylene - alkyl acrylate copolymer. The examples relate only to butyl acrylate.

It has now been discovered that ethylene- (meth) acrylate copolymers, the alkyl group having at least 5 carbon atoms and advantageously 6 to 24 carbon atoms, make it possible to prepare HMPSA adhesives with properties essentially similar to those based on SIS or SBS while having better loop tack, better finger tack, better peel level than ethylene butyl acrylate copolymers.

As for the HMA type adhesives, the heavy (meth) acrylates of the 2-ethylhexyl acrylate type provide better resistance at low temperature by comparison with butyl or ethyl acrylate. In addition, they are applicable at low temperature (COOL MELT), for example between 130 and 1 50.

The present invention is therefore a hot-melt adhesive comprising:

^• a copolymer (A) ethylene- (meth) acrylate, the alkyl group having at least 5 carbon atoms, ^• a tackifying resin, optionally a plasticizer and optionally a wax.

The adhesives of the HMPSA type are deposited hot (in fusion) on a substrate such as for example a paper tape, in polyamide, or polyolefinic or polyester substrate; by cooling, an adhesive face is obtained at room temperature. This adhesive side can be protected before use by a silicone paper or the other side of the substrate (winding of an adhesive tape on itself).

In the rest of the text, reference is made to different tests or measurement methods making it possible to determine the properties of HMPSA and HMA.

FTM9: The loop tack test is the FINAT FTM 9 test described in the FINAT technical manual, Laan Copes Van Cattenbubch 79, NL 2585 EW LA HAYE (1 995) (HMPSA).

This test characterizes instant adhesion or "tack". The tack is defined as being the force required to take off a loop of PET (Polyethylene terephthalate) coated with HMPSA, of which a determined surface has been previously brought into contact with a stainless steel plate. The HMPSA is coated between 140 ° C and 180 ° C on a PET strip of (25 * 400) mm ² . The thickness being constant, the grammage is between 18 g / m ² and 22 g / m ² . The test strips must be conditioned at least four hours before the test in an air-conditioned room at (23 ± 2) ° C, (50 ± 5)% RH (relative humidity). The self-adhesive tape is applied using a standard 2 kg standard roller.

The test is carried out using a dynamometer, at a traction speed of 300 mm / min in an air-conditioned room at (23 ± 2) ° C, (50 ± 5)% RH.

The loop-tack is quantified by the value of the maximum force. The result of the loop tack measurement test is given in N / cm. The type of rupture must also be mentioned.

The different types of failure are defined as follows:

Adhesive failure

HMPSA does not adhere to one of the two substrates. Cohesive rupture

There is a break in the adhesive joint. In this case the two glued substrates entrain a part of the joint during traction.

Mixed break

The rupture is undecided and one can observe on the same test tube the two types of ruptures described above.

FTM8: The creep resistance is determined by the FTM8 test (FINAT Manual already cited) (HMPSA).

The creep test measures the capacity of an HMPSA to resist a static force of 1 kgf at a given temperature (at room temperature in the examples of the present invention).

The static shear resistance is defined by the time necessary to separate by parallel vertical sliding an area of (25 x 25) mm ² coated with HMPSA, of a flat stainless steel plate.

The HMPSA is coated between 140 ° C and 180 ° C on a PET strip of (25 x 400) mm ² . The thickness being constant, the grammage is between 18 g / m ² and 22 g / m ² . The test strips must be conditioned at least four hours before the test in an air-conditioned room at (23 ± 2) ° C, (50 ± 5)% RH. The self-adhesive tape is applied using a standard 2 kg standard roller. The result of the creep test is given in minutes. The type of rupture must also be mentioned.

FTM1: The adhesion to steel is determined by the FTM1 test (FINAT Manual already mentioned) (HMPSA). This test quantifies the adhesive power. The latter is defined as the force required to remove a PET strip coated with HMPSA from a stainless steel plate.

The HMPSA is coated between 140 ° C and 180 ° C on a PET strip of (25 * 400) mm ² . The thickness being constant, the grammage is between 18 g / m ² and 22 g / m ² . The test strips must be conditioned at least four hours before the test in an air-conditioned room at (23 ± 2) ° C, (50 ± 5)% RH. The self-adhesive tape is applied using a standard 2 kg standard roller. The adhesion strength is measured 20 minutes after application.

The test is carried out using a dynamometer, under a 180 ° peeling angle, at a speed of 300 mm / min in an air-conditioned room at (23 ± 2) ° C, (50 ± 5)% RH.

The result of the peel test is given in N / cm. The type of rupture must be mentioned.

Cloud point (HMA and HMPSA):

The cloud point is determined as follows: the glue is heated to 175 ° C., then a drop is placed on the bulb of a thermometer

ASTM then the temperature at which the haze appears during cooling is noted. A value below 50 ° C or 60 ° C indicates good compatibility between the constituents of the hot melt.

Brookfield viscosity (HMA and HMPSA):

Measured at 170 ° C, needle 27 at 10 rpm according to ASTM D 3236. SAFT (shear adhesion failure temperature) (HMA and HMPSA)

The SAFT test (ASTM D 4498) measures the capacity of a hot-melt adhesive to resist a static force of 0.5 kg (or 0.25 kg), under the effect of a regular rise in temperature of 0.4 ° C / min .

The SAFT is defined by the temperature at which one can observe a separation, by parallel vertical sliding of an area of (25 x 25) mm ² coated with HMPSA, of a flat stainless steel plate.

The hot-melt adhesive is coated between 140 ° C and 180 ° C on a PET strip of (25 x 400) mm ² . The thickness being constant, the grammage is between 1 8 g / m ² and 22 g / m ² . The test strips must be conditioned at least four hours before the test in an air-conditioned room at (23 ± 2) ° C, (50 ± 5)% RH. The self-adhesive tape is applied using a standard 2 kg standard roller. The SAFT result is given in ° C. The type of rupture must be mentioned.

Finger Tack (internal method) (HMPSA)

This test gives an idea of the immediate adhesion of an HMPSA coated on a PET support. The finger tack value is between 0 and 3.

0: zero tack,

1: insufficient tack,

2: good tack, 3: excellent tack.

Rolling bail tack ASTM D 31 21 of 1,989 (HMPSA)

When determining the tack of an adhesive according to the Rolling Bail Tack method, a steel ball is dropped at the top of an inclined plane. This accelerates and rolls along a horizontal surface covered by the product to be tested. The tack is determined by measuring the distance traveled by the ball before it is stopped. Equipment

- Equipment fitted with an inclined plane of (20.0 ± 0.2) ° - Steel ball with a mass of (5.60 ± 0.05) g

- Polyethylene terephthalate (PET) strips coated with products to be tested.

The copolymer (A) ethylene- (meth) acrylate is such that the alkyl group contains at least 5 carbon atoms. The Applicant has indeed discovered that alkyls having at least 5 carbon atoms give tack to HMPSA and good properties at low temperature to HMA.

The alkyl can be linear, branched or cyclic. Advantageously, it comprises 6 to 24 carbon atoms. By way of example of these alkyl (meth) acrylates, mention may be made of 2-ethylhexyl (meth) acrylate and octyl acrylate.

The (meth) acrylate content is advantageously at most

50% and preferably between 20 and 40% by weight. The melt index (or MFI) can be between 0, 1 and 1000 and is preferably at least 200 (in g / 10 min according to ASTMD 1 238-73 conditions E at 190 ° C under a load of 2, 1 6 kg).

It would not be departing from the scope of the invention to use a mixture of at least two ethylene- (meth) acrylate copolymers. According to another form of the invention (A) can be a mixture of two copolymers (A-]) and (A2) of different MFIs.

Advantageously (A- |) has an MFI less than 10 and (A2) has an MFI greater than 10. For example the MFI of (A- |) is between 1 and 3 and the MFI of (A2) is between 50 and 400 .

As regards HMAs, the adhesives of the invention contain one or more tackifying resins, at least one wax, optionally fillers and / or stabilizers.

With regard to HMPSA, the adhesives of the invention contain one or more tackifying resins, one or more plasticizers and optionally stabilizers.

Suitable tackifying resins are, for example, rosin, rosin esters, hydrogenated rosin, polyterpenes and derivatives, aromatic or aliphatic petroleum resins, hydrogenated cyclic resins. These resins typically have a ring ball softening temperature between 25 ° C and 180 ° C and preferably between 50 ° C and 135 ° C.

The amount of tackifying resin can be from 50 to 180 parts per 100 parts of (A) and preferably 100 to 150 parts. Other examples of rosin derivatives are described in

ULLMAN'S (cited above) Vol A 23 p. 79 - 86, the content being incorporated into the present application.

Mention may be made, as rosin derivatives, of those obtained by hydrogenation, dehydrogenation, polymerization, esterification. These derivatives can be used as such or in the form of polyol esters such as pentaerythritol, polyethylene glycol and glycerol esters.

Mention may also be made, as tackifying resin, of dicyclopentadienes.

The adhesives of the invention may contain waxes. They make it possible to adjust the fluidity, the open time and the setting time.

The waxes can be recovered during the refining of petroleum fractions. These are, for example, waxes consisting essentially of paraffinic hydrocarbons and containing sufficient amounts of branched, cyclic and aromatic hydrocarbons to be much less crystalline than paraffins. Synthetic waxes can also be used, such as FISCHER TROPSCH waxes. Advantageously, the paraffin waxes used in the adhesives of the invention have a melting temperature above 50 ° C and preferably between 60 ° C and 70 ° C.

The amount of wax can be between 30 and 80 parts per 100 parts of copolymer (A).

The plasticizers which can be used in the adhesives of the invention are, for example, aromatic or naphthenic paraffinic mineral oils. They are essentially used to lower the viscosity and to provide tack. The amount of plasticizer can be between 10 and 30 parts per 100 parts of (A).

Mention may also be made, as plasticizer, of phthalates, azelates, adipates, tricresyl phosphate and polyesters.

As regards HMA, the adhesives of the invention may contain fillers. Mention may be made, as examples of fillers, of silica, alumina, glass, glass beads, calcium carbonates, fibers and metal hydroxides. These fillers must not reduce the tack or the mechanical properties of the glue after its application. The quantity of charges can represent up to 100 parts per 100 parts of (A).

It is recommended to add stabilizers such as antioxidants, we can use the usual antioxidants of thermoplastics.

The hot-melt adhesives of the invention are prepared by mixing in the molten state at temperatures between 130 ° C. and 200 ° C. until a homogeneous mixture is obtained. The mixing time can be of the order of 30 minutes to 3 hours. The usual devices for thermoplastics can be used such as extruders, cylinders, Banbury or Brabender mixers, or propeller mixers.

Examples

The following products were used:

SIS: styrene-isoprene-styrene block copolymer containing 15% by weight of polystyrene sold by SHELL CHIMIE under the reference KRATON-D- 1,161 N.

E-2 EHA / 3 to 8: ethylene-2-ethylhexyl acrylate (2 EHA) copolymers with characteristics:

PERMALYN 5095: solid rosin glycerol ester (produced by HERCULES)

CATENEX N 956 aliphatic paraffinic oil (produced by SHELL) IRGANOX 1010 phenolic antioxidant (produced by CIBA

SPECIALITY CHEMICALS).

The following tables show the properties of the HMPSAs produced with SIS (not in accordance with the invention) and according to the invention with E-2 EHA copolymers. The composition of the HMPSA is listed at the top of each table.

For example, the column E-2 EHA / 7 means that it is an HMPSA based on the copolymer E-2 EHA / 7.

35 BA 40 denotes an ethylene butyl acrylate copolymer at 35% by weight of acrylate and MFI: 40 (in g / 10 min at 190 ° C. under a load of 2.16 kg according to ASTM D 1 238), Tg 67 ° C.

28 BA 175 denotes a copolymer of ethylene butyl acrylate at 28% by weight of acrylate and of MFI: 1,75 (in g / 10 min at 1 90 ° C under a load of 2, 1 6 kg according to ASTM D 1 238) , Tg 80 ° C.

30 BA 02 denotes an ethylene butyl acrylate copolymer at 30% by weight of acrylate and of MFI: 2 (in g / 10 min at 190 ° C. under a load of 2.16 kg according to ASTM D 1 238), Tg 78 ° C.

35 BA 320 denotes an ethylene butyl acrylate copolymer at 35% by weight of acrylate and of MFI: 320 (in g / 10 min at 190 ° C. under a load of 2.16 kg according to ASTM D 1 238), Tg 66 ° C. Table 1

35% (Copolymer (A) or SIS) - 40% Permalyn 5095 - 25% Catenex N956 0.2% Irganox 1010

RA: Adhesive failure - RC: Cohesive failure - RM: Adhesive mixed failure (RA): Adhesive failure with slight deposit of material on the plate Table 2 35% (Copolymer (A) or SIS) - 40% Permalyn 5095 - 25% Catenex N956

RA: Adhesive failure - RC: Cohesive failure - RM: Adhesive mixed failure (RA): Adhesive failure with slight deposit of material on the plate * 3: Strong tack - 2: Medium tack - 1: Weak tack - 0: Zero tack

Table 3 30% (Copolymer (A) or SIS) - 40% Permalyn 5095 - 30% Catenex N956 - 0.2% Irganox 1010

RA: Adhesive failure - RC: Cohesive failure - RM: Adhesive mixed failure (RA): Adhesive failure with slight deposit of material on the plate * 3: Strong tack - 2: Medium tack - 1: Weak tack - 0: Zero tack Table 4

30% (Copolymer (A) or SIS) - 40% Permalyn 5095 - 30% Catenex N956 0.2% Irganox 1010

Table 5

(15% Copolymer (A- |) + 15% Copolymer (A2) or 30% SIS) - 40% Permalyn 5095 - 30% Catenex N956 0.2% Irganox 1010

RA: Adhesive failure - RC: Cohesive failure

RM: Mixed adhesive rupture

(RA): Adhesive failure with slight deposit of material on the plate

Table 6

(15% Copolymer (A- |) + 15% Copolymer (A) or 30% SIS) - 40% Permalyn 5095 - 30% Catenex N956 0.2% Irganox 1010

RA: Adhesive failure - RC: Cohesive failure - RM: Adhesive mixed failure (RA): Adhesive failure with slight deposit of material on the plate

Table 7

(15% Copolymer (A <|) + 15% Copolymer (A2) or 30% SIS) - 40% Permalyn 5095 - 30% Catenex N956 - 0.2% Irganox 1010

Claims

1 - hot-melt adhesive comprising: - an ethylene- (meth) acrylate copolymer (A), the alkyl group having at least 5 carbon atoms.

- at least one tackifying resin, optionally a plasticizer and optionally a wax.

This adhesive being hot deposited on a substrate.

2 - Adhesive according to claim 1 wherein the alkyl group of the alkyl (meth) acrylate has from 6 to 24 carbon atoms.

3 - Adhesive according to claim 1 wherein (A) is a copolymer of ethylene and 2-ethylhexyl acrylate.

4 - Adhesive according to any one of the preceding claims in which the amount of tackifying resin is from 50 to 180 parts (by weight), preferably 100 to 150 for 100 parts of (A).

5. Pressure-sensitive hot-melt adhesive (HMPSA) according to any one of the preceding claims and comprising

- the copolymer (A)

- at least one tackifying resin - at least one plasticizer

- possibly stabilizers.

6. Hot-melt adhesive (HMA) according to any one of claims 1 to 4 and comprising: - the copolymer (A)

- at least one tackifying resin

- at least one wax

- possibly stabilizers.