JP5582327B2 - Oil-resistant double-sided adhesive tape - Google Patents

Description

  The present invention relates to a double-sided pressure-sensitive adhesive tape excellent in oil resistance against oily components such as human sebum, which is used for fixing parts of portable electronic devices.

  In portable electronic devices such as mobile phones, PHS, digital cameras, electronic notebooks, portable music players, portable game machines, smartphones, etc., a surface panel provided on the surface of an image display module is joined to a casing, a key sheet (sheet Double-sided adhesive tape is used for fixing various members and modules.

  As an adhesive tape used for fixing parts of portable electronic devices, the adhesive has a maximum value of loss tangent tan δ in a frequency band equal to or higher than the maximum natural frequency generated when the electronic device is dropped, and A double-sided pressure-sensitive adhesive sheet in which the maximum value of the loss tangent tan δ is 1 or more is disclosed (see Patent Document 1).

  Furthermore, in the double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of the substrate, at least one pressure-sensitive adhesive layer is a silicone-based pressure-sensitive adhesive layer containing polydiorganosiloxane and is dynamic in a measurement temperature range of −60 to 100 ° C. There is disclosed a double-sided pressure-sensitive adhesive tape characterized in that the temperature at which the tangent loss (tan δ) value of viscoelasticity measurement shows a maximum value is −5 ° C. or more and 70 ° C. or less (see Patent Document 2).

Furthermore, a pressure-sensitive adhesive layer having a maximum value of loss tangent (tan δ) in a temperature range of −40 to −15 ° C. and having a surface adhesive strength of 19 N / cm ² or more with respect to a specific adherend is provided on both surfaces of the support. A double-sided PSA sheet is disclosed (see Patent Document 3). The double-sided pressure-sensitive adhesive sheet has a specific pressure-sensitive adhesive layer, has a good adhesive force, and has excellent impact resistance such that parts are not easily dropped due to an impact when the object falls.

  By the way, mobile phones, PHS, digital cameras, and the like among portable electronic devices have many opportunities to come into contact with human faces (skins), hairs, and the like. Since there are oily components such as sebum and cosmetics in addition to sweat on the surface of the skin and hair, while these devices are used for a long time, for example, gradually from the end of the joint between the protective panel and the housing May penetrate into the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape. Since the oily component has the effect of softening and swelling the pressure-sensitive adhesive, depending on the design, the double-sided pressure-sensitive adhesive tape or the pressure-sensitive adhesive protrudes to the joint display end portion or the information display portion of the protective panel, which may impair the appearance.

However, no technical studies have been made on the resistance to oily components such as sebum (hereinafter referred to as oil resistance), and further studies have been necessary for such problems.
JP 2002-188061 A JP 2003-313515 A JP 2005-187513 A

  Therefore, the problem to be solved by the present invention is that the adhesive is not easily softened / swelled even when oily components such as sebum permeate, and the double-sided adhesive is used when fixing parts of portable electronic devices. The present invention provides a double-sided pressure-sensitive adhesive tape excellent in oil resistance that does not protrude from the tape or pressure-sensitive adhesive.

  As a result of intensive studies to solve the above problems, the present inventors have found a double-sided pressure-sensitive adhesive tape excellent in oil resistance against oily components such as sebum, and have completed the present invention.

  That is, the present invention is a double-sided pressure-sensitive adhesive tape for fixing parts of a portable electronic device, wherein the double-sided pressure-sensitive adhesive tape having a width of 3 mm, a length of 4 cm and a thickness of 160 μm is attached to an ABS plate, and the double-sided pressure-sensitive adhesive tape is attached to oleic acid. And then left to stand at 50 ° C. for 3 days, and then the acrylic sheet was pasted together, applied with 1 kg of load at 80 ° C. for 4 days, the load was removed, and the double-sided adhesive tape was left to stand at 23 ° C. for 3 hours. An oil-resistant double-sided pressure-sensitive adhesive tape is provided in which the rate of change in the width is 15% or less.

  The double-sided pressure-sensitive adhesive tape of the present invention has good adhesion and excellent oil resistance. For this reason, for example, even when there is permeation of oily components such as sebum from the end of the joint between the surface panel provided on the surface of the image display module of the mobile phone and the housing, the double-sided adhesive tape or adhesive Appearance defects due to protrusion can be prevented.

  The oil-resistant double-sided pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape having a width of 3 mm, a length of 4 cm, and a thickness of 160 μm attached to an ABS (acrylonitrile-butadiene-styrene) plate, and the double-sided pressure-sensitive adhesive tape covered with oleic acid Change the width of the double-sided pressure-sensitive adhesive tape when the acrylic plate was bonded together and a 1 kg load was applied at 80 ° C. for 4 days, and then the load was removed and left at 23 ° C. for 3 hours. The oil-resistant double-sided pressure-sensitive adhesive tape is characterized in that the rate is 15% or less.

  The rate of change of the length in the width direction before and after the oil resistance test with oleic acid of the oil-resistant double-sided pressure-sensitive adhesive tape of the present invention is 15% or less, preferably 10% or less, more preferably 5% or less. If the rate of change is 15% or less, even if oily components such as sebum permeate from the joint between the portable electronic device and the component by the oil-resistant double-sided adhesive tape of the present invention, the adhesive does not protrude and the appearance is poor. Such troubles are unlikely to occur.

  As the pressure-sensitive adhesive layer used in the oil-resistant double-sided pressure-sensitive adhesive tape of the present invention, a layer made of a conventionally known pressure-sensitive adhesive can be used as long as it satisfies the change rate before and after the oil resistance test. It consists of an acrylic pressure-sensitive adhesive composition containing an acrylic copolymer that uses an acrylate and a polar group-containing monomer, and the amount of n-butyl acrylate used is 70% by mass or more of the monomer component in the acrylic copolymer. A layer is preferred.

  The content of n-butyl acrylate in the acrylic copolymer is preferably 70 to 99.9% by mass, more preferably 80 to 99% by mass, and still more preferably 87 to 98.5% by mass. By setting the content of n-butyl acrylate in this range, excellent oil resistance can be realized.

  Further, if the content of the n-butyl acrylate is within the range, (meth) acrylate having an alkyl side chain having 1 to 14 carbon atoms other than n-butyl acrylate, styrene, cyclohexyl (meth) acrylate, tetrahydro (Meth) acrylic acid alkyl esters having an alicyclic skeleton such as furfuryl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, etc. You may add the vinyl monomer which can be copolymerized.

  The acrylic copolymer used in the present invention preferably uses a vinyl monomer having a polar group as the polar group-containing monomer. Examples of the vinyl monomer having a polar group include a vinyl monomer having a hydroxyl group, a vinyl monomer having a carboxyl group, and a vinyl monomer having an amide group.

  Examples of the vinyl monomer containing a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, hydroxypropyl (meth) acrylate, and caprolactone-modified (meth) acrylate. Hydroxyl group-containing (meth) acrylates such as polyethylene glycol mono (meth) acrylate and polypropylene glycol (meth) acrylate can be used, among which 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxy It is preferred to use hexyl (meth) acrylate as a copolymerization component.

  As vinyl monomers containing a carboxyl group, acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, (meth) acrylic acid dimer, ethylene oxide modified succinic acid acrylate, etc. can be used. It is preferable to use it as a copolymerization component.

  Examples of vinyl monomers having an amide group include amides such as N-vinyl-2-pyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, N, N-dimethylacrylamide, and 2- (perhydrophthalimido-N-yl) ethyl acrylate. A group-containing vinyl monomer can be used, and among them, N-vinyl-2-pyrrolidone, N-vinylcaprolactam, and acryloylmorpholine are preferably used as a copolymerization component.

  Examples of vinyl monomers having other polar groups include vinyl acetate, acrylonitrile, maleic anhydride, itaconic anhydride and the like.

  The content of the vinyl monomer having a polar group is preferably 0.1 to 20% by mass of the monomer component constituting the acrylic copolymer, more preferably 1 to 13% by mass, More preferably, it is -8 mass%. By containing in the said range, it is easy to adjust the cohesive force, holding force, and adhesiveness of an adhesive to a suitable range.

  In addition, when using an isocyanate type crosslinking agent as a crosslinking agent, the vinyl monomer which has a hydroxyl group is preferable as a vinyl monomer which has the polar group which reacts with this, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) Acrylate and 6-hydroxyhexyl (meth) acrylate are particularly preferred. The content of the vinyl monomer having a hydroxyl group that reacts with the isocyanate-based crosslinking agent is preferably 0.01 to 1% by mass of the monomer component constituting the acrylic copolymer, and is 0.03 to 0.3% by mass. Is particularly preferred.

  The acrylic copolymer can be obtained by copolymerization by a known polymerization method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, supercritical polymerization or the like. Polymerization can be initiated by peroxides such as benzoyl peroxide and lauroyl peroxide, thermal initiation using azo initiators such as azobisisobutyronitrile, acetophenone, benzoin, benzyl ketal. The starting method using ultraviolet rays, such as a system, acylphosphine oxide system, benzophenone system, and maleimide system, and the starting method using an electron beam can be arbitrarily selected. Preferably, there are a heat initiation method using an azo initiator and a light initiation method using an acyl phosphine oxide initiator.

  The molecular weight of the acrylic copolymer is 400,000 to 2,000,000, preferably 600,000 to 1,300,000 in terms of polystyrene as measured by gel permeation chromatography (GPC).

  In the acrylic pressure-sensitive adhesive composition used in the present invention, it is preferable to use a tackifying resin in order to improve the adhesion to the adherend. Tackifying resins include rosin, polymerized rosin, polymerized rosin ester, rosin phenol, stabilized rosin ester, disproportionated rosin ester, hydrogenated rosin ester, terpene, terpene phenol, hydrogenated Examples include terpene phenol-based, petroleum resin-based, and (meth) acrylate-based resins. When used in an emulsion-type pressure-sensitive adhesive composition, it is preferable to use an emulsion-type tackifying resin.

  Among these, a polymerized rosin ester tackifier resin, a disproportionated rosin ester tackifier resin, a rosin phenol tackifier resin, a hydrogenated rosin ester tackifier resin, and a (meth) acrylate tackifier resin are preferable.

  The softening point of the tackifying resin is not particularly defined, but is 30 to 180 ° C, preferably 70 to 140 ° C. Moreover, 1 type (s) or 2 or more types may be used for tackifying resin.

  The blending ratio when using the acrylic copolymer and the tackifying resin is such that the content of the tackifying resin with respect to 100 parts by mass of the acrylic copolymer is preferably 5 to 40 parts by mass, and 10 to 30. More preferably, it is part by mass. By setting the ratio between the two in this range, it becomes easy to ensure the adhesiveness.

  In the acrylic pressure-sensitive adhesive composition, it is preferable to crosslink the pressure-sensitive adhesive in order to increase the cohesive strength of the pressure-sensitive adhesive layer. Examples of such a crosslinking agent include an isocyanate crosslinking agent, an epoxy crosslinking agent, a metal chelate crosslinking agent, and an aziridine crosslinking agent. Preferably, an isocyanate type crosslinking agent and an epoxy type crosslinking agent are preferable.

  As an index of the degree of crosslinking, the value of the gel fraction for measuring the insoluble content when the pressure-sensitive adhesive layer is immersed in toluene for 24 hours is used. If the gel fraction is preferably 25 to 70% by mass, more preferably 30 to 60% by mass, and still more preferably 35 to 55% by mass, both cohesion and adhesiveness are good.

The gel fraction is measured as follows. First, the mass (G1) of the double-sided pressure-sensitive adhesive tape 20 cm ^{2 from} which the release sheet has been peeled off is measured. Next, after immersing in a toluene solution at 23 ° C. for 24 hours, the toluene insoluble matter is separated by filtration through a 300-mesh wire mesh, and the mass (G2) of the residue after drying at 110 ° C. for 1 hour is measured. And a gel fraction is calculated | required according to the following formula | equation. In addition, when there exists a support body in a double-sided adhesive tape, the mass (K) of 20 cm < ² > is calculated | required and correct | amended.
Gel fraction (mass%) = (G2-K) / (G1-K) × 100

  Additives include plasticizers, antioxidants, UV absorbers, glass and plastic fibers, balloons and beads, metal powders, colorants such as pigments and dyes, and leveling materials as long as they do not impair performance as required. It can be optionally added to a pressure-sensitive adhesive composition such as a thickener and an antifoaming agent.

  In the pressure-sensitive adhesive layer used in the oil-resistant double-sided pressure-sensitive adhesive tape of the present invention, the peak value of loss tangent (tan δ) at a frequency of 1 Hz is not particularly defined, but is preferably −40 ° C. to −5 ° C., more preferably −35. ° C to -10 ° C. By setting the peak value of the loss tangent of the pressure-sensitive adhesive layer in this range, it is difficult for components to fall off due to an impact when the portable electronic device is dropped.

  The loss tangent (tan δ) is obtained from the equation of tan δ = G ″ / G ′ from the storage elastic modulus (G ′) and loss elastic modulus (G ″) obtained by dynamic viscoelasticity measurement by temperature dispersion. A peak value of loss tangent (tan δ) at a certain frequency is obtained from dynamic viscoelasticity measurement by temperature dispersion.

  Dynamic viscoelastic properties are the types and ratios of monomers used in the copolymer constituting the pressure-sensitive adhesive, types and amounts of polymerization initiators, types and amounts of crosslinking agents and tackifying resins, polymerization methods, etc. It can adjust by selecting suitably.

  The dynamic viscoelastic properties of the pressure-sensitive adhesive layer are defined by the loss tangent of the dynamic viscoelastic spectrum or the loss tangent and the storage elastic modulus at a specific frequency and a specific temperature. It is defined by the temperature showing the peak of loss tangent in the viscoelastic spectrum or the peak value of loss tangent. In the measurement of dynamic viscoelasticity, using a viscoelasticity tester (manufactured by Rheometrics, trade name: Ares 2KSTD), a test piece is sandwiched between parallel disks having a diameter of 8 mm, which is a measurement part of the tester, The storage elastic modulus (G ′) and loss elastic modulus (G ″) from −50 ° C. to 150 ° C. are measured at a frequency of 1 Hz. The test piece is formed into a circular shape having a diameter of 8 mm after forming an adhesive layer having a thickness of about 2 mm. After punching, it is measured by sandwiching it between parallel disks with a diameter of 8 mm.

  The thickness of the pressure-sensitive adhesive layer used in the present invention is preferably 1 to 150 μm, more preferably 10 to 100 μm in terms of the thickness on one side, because it is easy to ensure adhesion with the adherend.

  The oil-resistant double-sided pressure-sensitive adhesive tape of the present invention may be a double-sided pressure-sensitive adhesive tape comprising the above-mentioned pressure-sensitive adhesive layer, or a double-sided pressure-sensitive adhesive tape provided with the above-mentioned pressure-sensitive adhesive layer on both sides of the support. Therefore, it is preferable to use a double-sided pressure-sensitive adhesive tape having a support.

  Conventionally known and commonly used supports can be used as the support used in the present invention. Specifically, for example, porous support such as nonwoven fabric, cloth, paper, etc., synthetic resin film such as polyester film, polyethylene film, polypropylene film, polyvinyl chloride film, foaming of polyolefin foam, acrylic resin foam, etc. Body, aluminum foil, copper foil, nickel foil and other metal foil, and a support obtained by laminating these. For films and foams, surface corona treatment and anchor coat treatment to improve anchoring properties with the adhesive layer, light-shielding layer to improve light-shielding properties, and reflection to improve the reflectivity of visible light, etc. It may have a layer. In the case of a nonwoven fabric, it is preferable to add or impregnate a strength improver for the purpose of improving strength. Examples of the strength improver include viscose, and examples of the cationic polymer include polyamide, amine, epichlorohydrin resin, and starch.

  In the case of a porous support, a synthetic resin film, and a metal foil, the thickness of the support is preferably 2 to 200 μm, and 10 to 100 μm is preferable in terms of workability and followability of the double-sided pressure-sensitive adhesive tape. On the other hand, in the case of a foam, 50-1200 micrometers is preferable. In the case of fixing electronic device parts, particularly small and thin portable electronic devices, since a double-sided adhesive tape with a small thickness is required, the thickness is preferably 50 to 300 μm, more preferably 75 to 200 μm.

  The thickness of the double-sided pressure-sensitive adhesive tape may be appropriately adjusted according to the required performance. However, when the support is a porous support, a synthetic resin film, or a metal foil, the thickness is preferably 8 to 300 μm, and 10 to 220 μm is preferably the double-sided pressure-sensitive adhesive tape. It is preferable in terms of workability and followability. On the other hand, in the case of a foam, 60-1400 micrometers is preferable. In the case of fixing electronic device parts, particularly small and thin portable electronic devices, since a thin double-sided adhesive tape is required, the thickness is preferably 60 to 400 μm, more preferably 80 to 300 μm.

  The pressure-sensitive adhesive layer can be formed by forming a pressure-sensitive adhesive solution on a release sheet with a roll coater or die coater, and then transferring it to the support. If there is a support, apply it directly on the support. A conventionally known method such as a method for performing the method can be appropriately used.

  Examples of the release sheet include synthetic resin films such as polyethylene, polypropylene, and polyethylene terephthalate (PET), paper, nonwoven fabric, cloth, foam and metal foil, and a support laminated with these. The surface of the release sheet is preferably subjected to release treatment such as silicone treatment, long-chain alkyl treatment, and fluorine treatment in order to enhance the peelability from the pressure-sensitive adhesive. The release sheet used for the double-sided pressure-sensitive adhesive tape of the present invention is preferably treated with silicone.

  The oil-resistant double-sided pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape for enhancing the light shielding property of the concealing portion by the double-sided pressure-sensitive adhesive tape when the display panel of an electronic device, for example, the LCD panel of a mobile phone is fixed to the edge or the body. The total light transmittance of the tape is preferably 20% or less, and more preferably 5% or less. Examples of means for reducing the total light transmittance to 20% or less include a method of adding a pigment or dye having high concealment property such as black to the pressure-sensitive adhesive, and a support having a total light transmittance of 20% or less. However, the present invention is not limited to this.

  As an example of a suitable usage mode of the oil-resistant double-sided pressure-sensitive adhesive tape of the present invention, fixing of a surface panel and fixing of a key in an image display module of a portable electronic device such as a mobile phone or a PDA (Personal Digital Assistant) can be cited.

  As a configuration example of an image display module using the oil-resistant adhesive tape of the present invention, a housing to which an image display device is fixed and a square surface panel are fixed with a double-sided adhesive tape punched into a frame shape. An image display module can be exemplified (FIG. 1).

  As the image display device, an LCD panel or an organic EL panel used for character display or image display in a general image display module can be used, and the LCD panel can be suitably used because it is easily available.

  The surface panel varies depending on the type and application of the portable electronic device, but a surface protection panel made of a transparent plate such as an acrylic plate, a polycarbonate plate, a tempered glass plate, or a touch panel type surface panel is generally used for an image display module. Can be used. A panel made of a transparent plate may be a transparent plate that has been subjected to decoration processing or processing by printing or vapor deposition.

  In the image display module having the above configuration, since a minute gap is formed between the housing and the front panel, sebum from the human body enters through this gap, and the sebum easily comes into direct contact with the adhesive tape. When the oil-resistant double-sided pressure-sensitive adhesive tape of the present invention is used for the image display module having such a configuration, the protrusion of the tape can be suppressed in the image display area due to the swelling of the pressure-sensitive adhesive tape, the appearance is impaired, or the image display area cannot be visually recognized. Can be prevented.

  Therefore, the double-sided pressure-sensitive adhesive tape of the present invention is suitably applied to an image display module, in particular, an image display module used in portable electronic devices such as mobile phones and touch panel type PDAs that frequently contact with the cortex from the human body. it can.

(Adjustment of adhesive solution A)
In a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel and a nitrogen gas inlet, 96.4 parts by mass of n-butyl acrylate, 3.5 parts by mass of acrylic acid, 0.1 mass of 2-hydroxyethyl acrylate Part, 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator was dissolved in a solvent consisting of 100 parts by mass of ethyl acetate, polymerized at 70 ° C. for 12 hours, and the weight average molecular weight was An 800,000 (polystyrene equivalent) acrylic copolymer was obtained. Next, 10 parts by mass of Pencel D135 (polymerized rosin pentaerythritol ester) manufactured by Arakawa Chemical Co., Ltd. and Superester A100 (glycerin ester of disproportionated rosin) manufactured by Arakawa Chemical Co., Ltd. 10 parts per 100 parts by mass of the acrylic copolymer Mass parts were added, and ethyl acetate was added and mixed uniformly to obtain a pressure-sensitive adhesive solution A having a nonvolatile content of 40%.

(Adjustment of adhesive solution B)
In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 71 parts by mass of n-butyl acrylate, 24.9 parts by mass of 2-ethylhexyl acrylate, 4 parts by mass of acrylic acid, 4-hydroxy 0.1 part by mass of butyl acrylate and 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator are dissolved in a solvent consisting of 100 parts by mass of ethyl acetate and polymerized at 70 ° C. for 12 hours. Thus, an acrylic copolymer having a weight average molecular weight of 700,000 (polystyrene conversion) was obtained. Next, 10 parts by mass of Pencel D135 (polymeric rosin pentaerythritol ester) manufactured by Arakawa Chemical Co., Ltd. was added to 100 parts by mass of the acrylic copolymer, and ethyl acetate was added and mixed uniformly. Agent solution B was obtained.

(Adjustment of adhesive solution C)
In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 44.9 parts by mass of n-butyl acrylate, 50 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of acrylic acid, 3 vinyl acetate 70 parts by mass, 0.1 part by mass of 4-hydroxybutyl acrylate, 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator were dissolved in a solvent consisting of 100 parts by mass of ethyl acetate, Polymerization was carried out at 12 ° C. for 12 hours to obtain an acrylic copolymer having a weight average molecular weight of 700,000 (polystyrene conversion). Next, 10 parts by mass of Pencel D135 (polymeric rosin pentaerythritol ester) manufactured by Arakawa Chemical Co., Ltd. was added to 100 parts by mass of the acrylic copolymer, and ethyl acetate was added and mixed uniformly. Agent solution B was obtained.

(Adjustment of adhesive solution D)
In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 93.9 parts by mass of 2-ethylhexyl acrylate, 3 parts by mass of acrylic acid, 3 parts by mass of vinyl acetate, 4-hydroxybutyl acrylate 0.1 part by mass and 0.1 part by mass of 2,2′-azobisisobutyronitrile as a polymerization initiator are dissolved in a solvent consisting of 100 parts by mass of ethyl acetate and polymerized at 70 ° C. for 12 hours, An acrylic copolymer having a weight average molecular weight of 700,000 (polystyrene conversion) was obtained. Next, 10 parts by mass of Pencel D135 (polymeric rosin pentaerythritol ester) manufactured by Arakawa Chemical Co., Ltd. was added to 100 parts by mass of the acrylic copolymer, and ethyl acetate was added and mixed uniformly. Agent solution C was obtained.

<Example 1>
(Adjustment of double-sided adhesive tape)
To 100 parts by mass of the pressure-sensitive adhesive solution A, 1.3 parts by mass of “Coronate L-45” (isocyanate-based crosslinking agent, solid content 45%) manufactured by Nippon Polyurethane Co., Ltd. was stirred for 15 minutes, and then peeled to a thickness of 75 μm. The film was coated on the PET film so that the thickness after drying was 68 μm, and dried at 80 ° C. for 3 minutes to obtain an adhesive tape.
Next, after sticking the adhesive tape one by one on both sides of a polyester film (thickness: 25 μm, transparent, surface with a wetting index of 60 mN / m), roll with a linear pressure of 5 kgf / cm. Laminated. Thereafter, aging was performed at 40 ° C. for 48 hours to obtain a double-sided pressure-sensitive adhesive tape having a thickness of 160 μm. The gel fraction of the aged adhesive was 48%.

<Example 2>
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except that B was used instead of the pressure-sensitive adhesive solution A. The gel fraction was 40%.

<Comparative Example 1>
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except that C was used instead of the pressure-sensitive adhesive solution A. The gel fraction was 52%.

<Comparative example 2>
Example 1 except that D was used in place of the adhesive solution A, and the addition amount of “Coronate L-45” (isocyanate-based crosslinking agent, solid content 45%) manufactured by Nippon Polyurethane was 2.0 parts by mass. A double-sided pressure-sensitive adhesive tape was obtained by the same method. The gel fraction was 65%.

<Comparative Example 3>
In a stainless steel reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet, 90 parts by mass of isooctyl acrylate, 10 parts by mass of acrylic acid, and 0.2 parts by mass of “Irgacure 651” manufactured by Ciba Specialty Chemicals Co., Ltd. After mixing, ultraviolet rays were irradiated with a fluorescent chemical lamp to obtain an acrylic syrup having a polymerization rate of 5% by mass. For 100 parts by mass of this acrylic syrup, 0.3 part by mass of 1,6-hexanediol diacrylate, 0.1 part by mass of “Irgacure 651” manufactured by Ciba Specialty Chemicals, glass microballoon (“H-40 manufactured by Fuji Silysia Co., Ltd.) ”, Density 0.4 g / cm 3, average particle size 50 μm) 8.55 parts by mass, fluorine surfactant (“ TG-656 ”manufactured by Daikin Industries, Ltd.) Defoam. This mixture was supplied to a vibratory stirring mixer, and nitrogen was mixed and dispersed at about 15% by volume to obtain a coating liquid containing fine bubbles having an average diameter of 50 μm or less.
This coating solution was applied to a peeled PET film having a thickness of 75 μm so that the thickness after UV curing was 160 μm, and after the peeled PET film having a thickness of 75 μm was bonded, Using a lamp (wavelength 300 to 400 nm, 350 nm center), UV irradiation was performed for 6 minutes from both sides with an irradiation intensity of 0.32 mW / cm 2 on one side to obtain a double-sided adhesive tape having a thickness of 160 μm. The gel fraction was 85%.

The following evaluation was performed about the double-sided adhesive tape obtained in the said Example and comparative example. The results obtained are shown in the table.
[Double-sided adhesive tape thickness]
After peeling off the release film from the double-sided adhesive tape, the thickness was measured with a thickness meter.

[Surface bond strength]
1) Two double-sided pressure-sensitive adhesive tapes 5 mm wide and 4 cm long on a square acrylic plate (Mitsubishi Rayon Co., Ltd. Acrylite MR200 “trade name”, hue: transparent) with a thickness of 2 mm at 23 ° C. Affix in parallel with an interval of 4 cm.
2) Next, a 2 mm thick, 10 x 15 cm rectangular ABS plate (made by Takiron, hue: natural, no wrinkles) with a 1 cm diameter hole in the center is attached with double-sided adhesive tape made in 1) Adhere the acrylic plate so that the center of the acrylic plate coincides with the center of the ABS plate, and the sides of the acrylic plate and the ABS plate are parallel. Let stand for 1 hour to make a test piece.
3) Place the test piece on a square measuring table (outside 8 cm square, inner size 8 cm, height 6 cm, made of aluminum) so that the center of the test piece and the center of the measuring table coincide with each other. Through the hole, the acrylic plate was pushed at 10 mm / min with a tensile tester equipped with a stainless steel probe having a diameter of 8 mm, and the strength with which the acrylic plate was peeled was measured.

[Oil resistance test]
1) At 23 ° C, two double-sided adhesive tapes with a width of 3 mm and a length of 4 cm are parallel to a 2 mm-thick ABS plate (made by Takiron, hue: natural, no wrinkles) with a tape spacing of 3 cm. Affix to
2) Next, after peeling off the release paper of the double-sided adhesive tape, it is hung on the double-sided tape so as to cover 2 cm ³ of oleic acid.
3) After standing at 50 ° C. for 3 days, the ABS plate was left standing for 1 hour to remove excess oleic acid, and then a 2 mm thick, 4 cm × 5 cm square acrylic plate (Mitsubishi Rayon Acrylite) MR200 “trade name”, hue: transparent) was affixed so that the outer periphery of the acrylic plate and the outer periphery of the ABS plate were parallel.
4) After placing 1 kg of weight on the acrylic plate of the test piece in an 80 ° C. atmosphere, leave it horizontally for 4 days.
5) After leaving still at 23 degreeC for 3 hours or more, the width | variety of the double-sided adhesive tape was measured with the flaw, and the change rate from before a test was evaluated.
(Change rate of double-sided adhesive tape width) = (double-sided adhesive tape width mm-3 mm after test) / 3 mm × 100 [%]

[Extrusion test]
1) A double-sided adhesive tape was processed into a frame-shaped sample having an outer diameter of 64 mm × 45 mm and a width of 2 mm, and an acrylic plate having a thickness of 2 mm and an outer diameter of 67 mm × 47 mm (Mitsubishi Rayon Co., Ltd. Acrylite MR200 “trade name”, hue: transparent ), Affixed to an ABS plate having a thickness of 2 mm and an outer shape of 100 mm × 50 mm, pressed once with a 2 kg roller, and allowed to stand at 23 ° C. for 24 hours to obtain a test piece.
2) After applying 1 cm ³ of artificial sebum liquid (oleic acid 20% by mass, triolein 60%, squalene mass% 20) to two joints on the long side of the test piece, horizontally at 80 ° C. for 7 days Leave still.
3) The deviation between the double-sided pressure-sensitive adhesive tape and the acrylic plate or ABS plate when the double-sided tape portion on the long side of the test piece that was left still was pressed several times with a finger was evaluated.
○: No deviation △: Less than 1 mm deviation ×: More than 1 mm deviation

  As apparent from the above examples, the oil-resistant double-sided pressure-sensitive adhesive tape of the present invention can suppress swelling due to sebum and does not easily deteriorate visibility and appearance even when used in an image display module such as a liquid crystal display. It was.

It is a section schematic diagram of an image display module using a double-sided adhesive tape of the present invention.

Explanation of symbols

1: Double-sided adhesive tape 2: Front panel 3: Housing 4: Image display device

Claims (6)

A double-sided pressure-sensitive adhesive tape used for fixing a housing and a front panel, which constitutes a portable electronic device , to which an image display device is fixed ,
It is a double-sided pressure-sensitive adhesive tape provided with a pressure-sensitive adhesive layer on both sides of the support,
The support is made of a synthetic resin film,
The pressure-sensitive adhesive layer contains an acrylic copolymer, a tackifier resin, and a crosslinking agent,
The acrylic copolymer has n-butyl acrylate and a vinyl monomer having a polar group as monomer components, and the content of n-butyl acrylate in the monomer component forming the acrylic copolymer is 70% by mass. The content of the vinyl monomer having a polar group is 0.1 to 20% by mass,
The tackifier resin is a polymerized rosin ester tackifier resin, a disproportionated rosin ester tackifier resin, a rosin phenol tackifier resin, a hydrogenated rosin ester tackifier resin,
It is at least one selected from (meth) acrylate tackifying resins,
The gel fraction of the pressure-sensitive adhesive layer is 25 to 70% by mass,
The maximum value of the loss tangent in the dynamic viscoelastic spectrum at a frequency of 1 Hz of the pressure-sensitive adhesive layer is −40 ° C. to −5 ° C.,
A double-sided pressure-sensitive adhesive tape having a width of 3 mm, a length of 4 cm and a thickness of 160 μm was applied to an ABS plate, the double-sided adhesive tape was covered with oleic acid and allowed to stand at 50 ° C. for 3 days. The oil-resistant double-sided pressure-sensitive adhesive is characterized in that the rate of change of the width of the double-sided pressure-sensitive adhesive tape is 15% or less when a load of 1 kg is applied for 4 days and the load is removed and left to stand at 23 ° C. for 3 hours. tape. The oil-resistant double-sided pressure-sensitive adhesive tape according to claim 1, wherein the synthetic resin film is a polyester film, a polyethylene film, a polypropylene film, or a polyvinyl chloride film. The oil-resistant double-sided pressure-sensitive adhesive tape according to claim 1 or 2, wherein the vinyl monomer having a polar group is at least one selected from a vinyl monomer having a hydroxyl group, a vinyl monomer having a carboxyl group, and a vinyl monomer having an amide group. The oil-resistant double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 3, wherein the crosslinking agent is at least one selected from an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. 5. The oil-resistant double-sided pressure-sensitive adhesive tape according to claim 1, wherein the content of the tackifying resin is 5 to 40 parts by mass with respect to 100 parts by mass of the acrylic copolymer. A housing an image display device is fixed, and the surface panel, fixed image display module double-sided pressure-sensitive adhesive tape according to any one of claims 1-5.

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