JP5576034B2 - Double-sided adhesive tape for touch panel - Google Patents

Description

  The present invention relates to a double-sided pressure-sensitive adhesive tape used for a touch panel, and more specifically, a double-sided pressure-sensitive adhesive for a touch panel that hardly peels off from a touch panel constituent member and does not easily foam at a joint interface when used for joining touch panel constituent members. Regarding tape.

  Conventionally, a double-sided pressure-sensitive adhesive tape has been used to join a touch panel constituent member to a liquid crystal module or to join an optical film such as a polarizing plate or an AR film as a touch panel constituent member to another touch panel constituent member.

  In the double-sided pressure-sensitive adhesive tape used for such applications, the double-sided pressure-sensitive adhesive tape is difficult to peel off from the touch panel constituent member even when the joined body in which the touch panel constituent member is joined by the double-sided adhesive tape is exposed to a high temperature, and the joining interface There is a strong demand for foaming to be difficult.

Patent Document 1 below discloses a pressure-sensitive adhesive composition used for bonding optical films. This pressure-sensitive adhesive composition contains a (meth) acrylic polymer and a crosslinking agent. Here, the weight average molecular weight of the (meth) acrylic polymer is 800,000 or more, and the content of components having a molecular weight of 300,000 or less is 25% by mass or more based on the entire (meth) acrylic polymer. Therefore, this (meth) acrylic polymer includes a component having a weight average molecular weight of 800,000 or more and a component having a molecular weight of 300,000 or less.
International Publication No. 2005/111167 Pamphlet

  In Patent Document 1, since a (meth) acrylic polymer having a molecular weight of 800,000 or more is contained, bleeding out of the (meth) acrylic polymer having a molecular weight of 300,000 or less can be suppressed under high temperature and high humidity, and It is described that lifting and peeling at the joint interface can be suppressed.

  However, a relatively low molecular weight (meth) acrylic material when a joined body in which a touch panel constituent member is joined by an adhesive layer made of an adhesive composition described in Patent Document 1 is exposed to a high temperature for a long time. The bleed out of the polymer could not be sufficiently suppressed. For this reason, the pressure-sensitive adhesive layer may float or peel off from the touch panel constituent member. Furthermore, foaming may occur at the bonding interface between the touch panel constituent member and the pressure-sensitive adhesive layer. In this case, since foaming is visually recognized in the touch panel operation part, the display quality of the touch panel may be deteriorated, or the operability of the touch panel may be deteriorated.

  In Patent Document 1, it is described that the pressure-sensitive adhesive composition is used for joining optical films and the like. However, it is not specifically described here that the pressure-sensitive adhesive composition is used for joining touch panel components.

  An object of the present invention is to provide a double-sided pressure-sensitive adhesive tape for a touch panel that, when used for bonding touch panel constituent members, hardly peels from the touch panel constituent members and hardly causes foaming at the joint interface.

  According to the present invention, the rate of increase in adhesive force determined by the following formula (1) is within the range of 110 to 220%, including the (meth) acrylic acid ester copolymer and the crosslinking agent. The swelling rate calculated | required by (2) exists in the range of 2000-6000 weight%, The double-sided adhesive tape for touchscreens characterized by the above-mentioned is provided.

Increase rate of adhesive force (%) = (P2−P1) / P1 × 100 (1)
P1: Adhesive strength of double-sided pressure-sensitive adhesive tape to a polycarbonate plate measured in accordance with JIS Z0237 after bonding the double-sided pressure-sensitive adhesive tape to a polycarbonate plate and leaving it for 20 minutes at 23 ° C. and 50% relative humidity P2: Double-sided Adhesive strength of the double-sided adhesive tape to the polycarbonate plate measured according to JIS Z0237 after adhering the adhesive tape to the polycarbonate plate and leaving it for 48 hours at 23 ° C. and 50% relative humidity

Swelling ratio (% by weight) = W4 / W3 × 100 (2)
W3: Initial weight of double-sided pressure-sensitive adhesive tape before immersion in ethyl acetate W4: After the double-sided pressure-sensitive adhesive tape was immersed in ethyl acetate at 23 ° C. for 24 hours, ethyl acetate present on the surface of the double-sided pressure-sensitive adhesive tape taken out from ethyl acetate Weight of double-sided adhesive tape when drops are removed

  The double-sided pressure-sensitive adhesive tape according to the present invention has an increase rate of the adhesive force in the range of 110 to 220% and the swelling rate in the range of 2000 to 6000% by weight. In such a case, even if the joined body of the double-sided pressure-sensitive adhesive tape and the touch panel is exposed to a high temperature, the double-sided pressure-sensitive adhesive tape hardly peels from the touch panel constituent member. Furthermore, foaming hardly occurs at the joint interface between the double-sided pressure-sensitive adhesive tape and the touch panel constituent member. For this reason, the visibility of a touch panel operation part can be improved.

  As a result of intensive studies to solve the above problems, the present inventors have adopted a composition containing a (meth) acrylate copolymer and a crosslinking agent in a double-sided pressure-sensitive adhesive tape for a touch panel, and the pressure-sensitive adhesive. Even when the joined body is exposed to a high temperature, the double-sided pressure-sensitive adhesive tape has a touch panel configuration by setting the rate of increase in force within the range of 110 to 220% and the swelling rate within the range of 2000 to 6000% by weight. It was difficult to peel from the member, and it was found that foaming was less likely to occur at the joint interface between the double-sided pressure-sensitive adhesive tape and the touch panel constituent member, and the present invention was made.

  Details of the present invention will be described below.

  The double-sided pressure-sensitive adhesive tape for a touch panel according to the present invention includes a (meth) acrylic acid ester copolymer and a crosslinking agent.

  As for the double-sided adhesive tape of this invention, the increase rate of the adhesive force calculated | required by following formula (1) exists in the range of 110-220%. The adhesive strength is measured by a 180 ° direction tensile test in accordance with JIS Z0237.

Increase rate of adhesive force (%) = (P2−P1) / P1 × 100 (1)
P1: A double-sided pressure-sensitive adhesive tape was bonded to a polycarbonate plate and allowed to stand at 23 ° C. and a relative humidity of 50% for 20 minutes, and then the double-sided pressure-sensitive adhesive tape measured in accordance with JIS Z0237 with respect to the polycarbonate plate (hereinafter, Also called initial adhesive strength P1)
P2: A double-sided pressure-sensitive adhesive tape was bonded to a polycarbonate plate, and left for 48 hours at 23 ° C. and a relative humidity of 50%. Then, the adhesive strength of the double-sided pressure-sensitive adhesive tape measured in accordance with JIS Z0237 to the polycarbonate plate (hereinafter, Also called adhesive strength P2 over time)

  Since the increase rate of the adhesive strength is within the above range, the temporal adhesive strength P2 is higher than the initial adhesive strength P1. Moreover, since the said initial adhesive force P1 of a double-sided adhesive tape is comparatively low, in the initial state, a double-sided adhesive tape has a softness | flexibility. For this reason, it is excellent in the workability | operativity at the time of bonding, and when sticking a double-sided adhesive tape on a touch-panel structural member, the foam bite in a joining interface can be suppressed. Moreover, since the adhesive force of a double-sided adhesive tape becomes high with progress of time, a double-sided adhesive tape can be firmly joined to a touch-panel structural member after time. For this reason, peeling from the touch-panel structural member of a double-sided adhesive tape does not arise easily. Further, even when bubbles are generated at the bonding interface due to heat, for example, the bubbles are pressed down by the double-sided pressure-sensitive adhesive tape, so that generation of bubbles at the bonding interface can be suppressed.

  The initial adhesive strength P1 is preferably in the range of 5.0 to 7.0 N / 25 mm. When the initial adhesive force P1 is within the above range, the initial reworkability of the double-sided pressure-sensitive adhesive tape can be enhanced, and foaming at the time of bonding can be effectively prevented. When the initial adhesive force P1 is too small, the double-sided adhesive tape is easily peeled off from the touch panel constituent member. If the initial adhesive force P1 is too large, it may not be possible to sufficiently suppress foaming at the time of bonding. The initial adhesive force P1 is preferably in the range of 5.5 to 6.5 N / 25 mm.

  The temporal adhesive force P2 is preferably in the range of 12 to 20 N / 25 mm. When the time-dependent adhesive force P2 is within the above range, for example, even if bubbles are generated at the bonding interface due to heat, the bubbles are pressed down by the adhesive force of the double-sided adhesive tape, thereby suppressing the generation of bubbles at the bonding interface. Can do.

  The swelling ratio calculated | required by following formula (2) of the double-sided adhesive tape which concerns on this invention exists in the range of 2000-6000 weight%. When the swelling ratio is within this range, even if small bubbles are generated at the bonding interface, the bubbles are easily dispersed. For this reason, bubble growth can be suppressed.

  The swelling ratio can be measured as follows.

  A double-sided pressure-sensitive adhesive tape cut to have a planar shape of 20 mm × 40 mm is produced. After this double-sided pressure-sensitive adhesive tape is immersed in ethyl acetate at 23 ° C. for 24 hours, the double-sided pressure-sensitive adhesive tape is taken out from ethyl acetate. Next, the ethyl acetate drop which exists on the surface of the double-sided adhesive tape taken out from ethyl acetate is excluded. Thereafter, the weight of the double-sided pressure-sensitive adhesive tape is measured, and the swelling ratio can be calculated by the following formula (2).

Swelling ratio (% by weight) = W4 / W3 × 100 (2)
W3: Weight of double-sided pressure-sensitive adhesive tape before immersion in ethyl acetate W4: Weight of double-sided pressure-sensitive adhesive tape after removal of ethyl acetate drops

  That is, the above W4 is obtained by immersing the double-sided pressure-sensitive adhesive tape in ethyl acetate at 23 ° C. for 24 hours, and then removing the ethyl acetate drops present on the surface of the double-sided pressure-sensitive adhesive tape taken out from ethyl acetate. It is weight.

((Meth) acrylic acid ester copolymer)
The (meth) acrylic acid ester copolymer is not particularly limited as long as it is a copolymer obtained by copolymerizing at least two kinds of (meth) acrylic acid ester monomers.

  In the present specification, “(meth) acryl” means acryl or methacryl.

  The (meth) acrylic acid ester monomer is not particularly limited. Examples of the (meth) acrylic acid ester monomer include (meth) acrylic acid alkyl ester having a C 1-15 alkyl group, benzyl (meth) acrylate, and the like.

  The (meth) acrylic acid ester-based copolymer is obtained by copolymerizing a monomer mixture containing (meth) acrylic acid alkyl ester represented by the following formula (1) and benzyl (meth) acrylate. A (meth) acrylic acid ester copolymer is preferable. In this case, when the double-sided pressure-sensitive adhesive tape is used for joining the touch panel components, the double-sided pressure-sensitive adhesive tape is further peeled from the touch panel components even when the joined body of the double-sided pressure-sensitive adhesive tape and the touch panel is exposed to high temperature and high humidity. It is hard to do. Furthermore, foaming is less likely to occur at the joint interface of the joined body.

上記式（１）中、Ｒ１は、水素原子又はメチル基を表し、Ｒ２は、炭素数３〜５の直鎖状のアルキル基を表す。

In said formula (1), R1 represents a hydrogen atom or a methyl group, R2 represents a C3-C5 linear alkyl group.

  When R1 in the formula (1) is a hydrogen atom, the (meth) acrylic acid alkyl ester is an acrylic acid alkyl ester. When R1 in the formula (1) is a methyl group, the (meth) acrylic acid alkyl ester is a methacrylic acid alkyl ester.

  Examples of R2 in the above formula (1) include an n-propyl group, an n-butyl group, and an n-pentyl group.

  Especially, it is preferable that the (meth) acrylic-acid alkylester represented by the said Formula (1) is (meth) acrylic acid n-butyl.

  The monomer mixture is a weight ratio ((meth) acrylic acid alkyl ester: (meth) acrylic acid benzyl) to (meth) acrylic acid alkyl ester represented by the above formula (1) and benzyl (meth) acrylate, It is preferable to contain in the ratio of 50: 50-95: 5.

  The (meth) acrylic acid ester-based copolymer is composed of n-butyl (meth) acrylate and benzyl (meth) acrylate in a weight ratio ((meth) acrylate n-butyl: (meth) acrylate benzyl). The (meth) acrylic acid ester copolymer obtained by copolymerizing a monomer mixture containing 50:50 to 95: 5 is particularly preferable. When such a (meth) acrylic ester copolymer is used, foaming can be effectively prevented even under high temperature and high humidity. This is because the (meth) acrylic acid ester-based copolymer is less likely to absorb moisture by using the above monomer, and as a result, the adhesive force is less likely to decrease even under high humidity, and the effect of crushing the generated bubbles is obtained. This is probably because of this.

  When the monomer mixture contains the (meth) acrylic acid alkyl ester represented by the above formula (1) in the above ratio together with benzyl (meth) acrylate, the heat resistance and cohesive strength of the double-sided pressure-sensitive adhesive tape are increased. be able to. For this reason, when a double-sided adhesive tape is used for joining a touch panel constituent member, it is difficult for the double-sided adhesive tape to peel from the touch panel constituent member, and foaming hardly occurs at the joint interface between the double-sided adhesive tape and the touch panel constituent member. This is because the double-sided pressure-sensitive adhesive tape is firmly bonded to the touch panel constituent member, so that even if bubbles are generated, the bubbles are pressed by the double-sided pressure-sensitive adhesive tape. This effect becomes remarkable when n-butyl (meth) acrylate is used as the (meth) acrylic acid alkyl ester represented by the above formula (1). When the amount of the (meth) acrylic acid alkyl ester represented by the above formula (1) is too small, the heat resistance may be lowered, and when it is too much, the adhesive force may be lowered.

  When the monomer mixture contains (meth) acrylic acid alkyl ester represented by the above formula (1) and benzyl (meth) acrylate in the above ratio, a double-sided adhesive tape and other touch panel components such as an optical film. When the joined body in which is bonded is exposed to a high temperature, the double-sided adhesive tape follows the thermal contraction of the touch panel constituent member. For this reason, it is difficult for the double-sided pressure-sensitive adhesive tape to peel off from the touch panel constituent member, and foaming hardly occurs at the joint interface. When the amount of benzyl (meth) acrylate is too small, the stress relaxation property may be lowered, and when it is too much, the double-sided pressure-sensitive adhesive tape may be yellowed.

  In 100% by weight of the monomer mixture, the (meth) acrylic acid alkyl ester represented by the above formula (1) and the benzyl (meth) acrylate are contained in the range of 50 to 99% by weight in total. It is preferable. If the total amount of the (meth) acrylic acid alkyl ester represented by the above formula (1) and the (meth) acrylic acid benzyl is too small, the double-sided pressure-sensitive adhesive tape is easily peeled off from the touch panel constituent member and foamed at the bonding interface. Is likely to occur.

  When obtaining the (meth) acrylic acid ester-based copolymer, other monomers than the (meth) acrylic acid alkyl ester and the (meth) acrylic acid benzyl represented by the above formula (1) may be used. . The other monomers may be used alone or in combination of two or more.

  Examples of the other monomer include 2-methylbutyl acrylate and 3-methylbutyl acrylate.

  Moreover, as said other monomer, the (meth) acrylic-type monomer which has functional groups, such as a carboxyl group, a hydroxyl group, an epoxy group, an isocyanate group, or an amino group, is mentioned, for example. Specific examples of the (meth) acrylic monomer having the functional group include (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, glycidyl (meth) acrylate, Examples include (meth) acrylic acid isocyanate ethyl or (meth) acrylic acid aminoethyl.

  Furthermore, examples of the other monomer include conjugated dienes, diallyl phthalate, triallyl isocyanurate, divinylbenzene, styrene, styrene derivatives, vinyl chloride, vinyl esters, and unsaturated nitriles.

  Examples of the conjugated dienes include butadiene and isoprene. Examples of the styrene derivative include α-methylstyrene, p-methylstyrene, p-chlorostyrene, chloromethylstyrene, and the like. Examples of the vinyl esters include vinyl acetate and vinyl propionate. Examples of the unsaturated nitriles include acrylonitrile.

  As said other monomer, at least 1 sort (s) of (meth) acrylic acid, 2-methylbutyl acrylate, and 3-methylbutyl acrylate is used suitably.

  When the other monomer is used, the other monomer is included in the range of 1 to 30% by weight in 100% by weight of the monomer mixture.

  When the monomer mixture is copolymerized, various polymerization initiators are used. Specific examples of the polymerization initiator include persulfates, organic peroxides, and azo compounds. A polymerization initiator may be used independently and 2 or more types may be used together.

  Examples of the persulfate include potassium persulfate, sodium persulfate, and ammonium persulfate. Examples of the organic peroxide include cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, o-chlorobenzoyl peroxide, acetyl peroxide, t-butyl hydroperoxide, and t-butyl peroxide. Examples thereof include oxyacetate, t-butylperoxyisobutyrate, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2-ethylhexanoate, and di-t-butyl peroxide. Examples of the azo compound include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 4,4′-azobis (4-cyanopentanoic acid), Examples include 2,2′-azobis (2-methylbutyronitrile) or azobiscyclohexanecarbonitrile.

  The weight average molecular weight of the (meth) acrylic acid ester copolymer is preferably 500,000 or more. When the weight average molecular weight is less than 500,000, the flexibility of the double-sided pressure-sensitive adhesive tape can be increased, but the cohesive force of the double-sided pressure-sensitive adhesive tape may be lowered. For this reason, the adhesive force to the touch-panel structural member of a double-sided adhesive tape may fall. Moreover, when the weight average molecular weight is less than 500,000, the flexibility of the double-sided pressure-sensitive adhesive tape is too high, and the effect of suppressing the generation of bubbles at the joint interface may not be sufficiently obtained.

  The (meth) acrylic acid ester copolymer preferably has a weight average molecular weight of 500,000 or more and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 0.3 or less. When the molecular weight distribution exceeds 0.3, the amount of the component having a relatively small molecular weight is relatively increased, and the cohesive force of the double-sided pressure-sensitive adhesive tape may not be sufficiently increased.

  The weight average molecular weight of the (meth) acrylic acid ester copolymer is more preferably in the range of 500,000 to 1,500,000. If the weight average molecular weight is too large, the adhesion to the adherend may be reduced, and floating or peeling may occur at the adherend interface.

  The molecular weight distribution of the (meth) acrylic acid ester copolymer is more preferably in the range of 0.15 to 0.30. If the molecular weight distribution is too large, bleeding of low molecular weight components is unavoidable when left standing for a long time under high temperature and high humidity, and there is a problem of causing floating or peeling from the adherend.

  The double-sided pressure-sensitive adhesive tape preferably does not contain a (meth) acrylic acid ester copolymer having a weight average molecular weight of less than 100,000. When a (meth) acrylic acid ester copolymer having a weight average molecular weight of less than 100,000 is contained, the (meth) acrylic acid ester copolymer having a weight average molecular weight of less than 100,000 is a weight average molecular weight. It is contained at a ratio of 10 parts by weight or less with respect to 100 parts by weight of the (meth) acrylic acid ester copolymer of 500,000 or more.

(Crosslinking agent)
The crosslinking agent contained in the double-sided pressure-sensitive adhesive tape for touch panel of the present invention is not particularly limited as long as the (meth) acrylic acid ester copolymer can be crosslinked.

  As said crosslinking agent, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy-type crosslinking agent, or a metal chelate type crosslinking agent etc. are mentioned, for example. Of these, an epoxy-based crosslinking agent is preferable. When an epoxy-based crosslinking agent is used, the double-sided pressure-sensitive adhesive tape is difficult to peel from the touch panel constituent member even if the joined body is exposed to a high temperature. Furthermore, foaming hardly occurs at the joint interface between the double-sided pressure-sensitive adhesive tape and the touch panel constituent member.

  Moreover, the (meth) acrylic acid ester copolymer obtained by copolymerizing a monomer mixture containing n-butyl (meth) acrylate and benzyl (meth) acrylate as the (meth) acrylic acid ester copolymer. When using a copolymer, it is particularly preferable to use an epoxy crosslinking agent. In this case, even when the joined body is exposed to a high temperature, the double-sided pressure-sensitive adhesive tape is more difficult to peel from the touch panel constituent member, and foaming is less likely to occur at the joint interface between the double-sided pressure-sensitive adhesive tape and the touch panel constituent member.

  The crosslinking agent is preferably contained within a range of 0.35 to 0.55 parts by weight with respect to 100 parts by weight of the (meth) acrylic acid ester copolymer.

  By containing the crosslinking agent within the above range, the flexibility of the double-sided pressure-sensitive adhesive tape can be enhanced without the initial adhesive strength of the double-sided pressure-sensitive adhesive tape becoming too high. For this reason, while being able to improve the initial rework property of a double-sided adhesive tape, the bubble bite at the time of bonding can be prevented. Moreover, the adhesive force of a double-sided adhesive tape becomes high with progress of time after pasting a touch panel constituent member with a double-sided adhesive tape by containing the above-mentioned crosslinking agent in the above-mentioned range. The member is firmly joined. For this reason, peeling of a double-sided adhesive tape and generation | occurrence | production of the bubble in a joining interface can be suppressed.

  When there is too little quantity of the said crosslinking agent, there exists a possibility that the adhesive force and adhesive force of a double-sided adhesive tape may become low. If the amount of the crosslinking agent is too large, the crosslinking density becomes too high, and bubbles may not be dispersed when bubbles are generated at the bonding interface. For this reason, peeling of the double-sided pressure-sensitive adhesive tape may easily occur.

  The more preferable minimum of the quantity of the said crosslinking agent is 0.40 weight part with respect to 100 weight part of said (meth) acrylic acid ester-type copolymers, and a more preferable upper limit is 0.50 weight part.

  The epoxy crosslinking agent is not particularly limited as long as it has an epoxy group and can crosslink the (meth) acrylic acid ester copolymer. Examples of the epoxy-based crosslinking agent include ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, and 1,6-hexanediol glycidyl ether.

  As a commercial item of the said epoxy-type crosslinking agent, E-AX (made by Soken Chemical Co., Ltd.) etc. are mentioned, for example.

(Other ingredients)
An additive may be added to the double-sided pressure-sensitive adhesive tape of the present invention, if necessary, in addition to the (meth) acrylic acid ester copolymer and the crosslinking agent.

  Specific examples of the additive include a plasticizer, an emulsifier, a softener, a filler, a pigment, or a dye.

(Double-sided adhesive tape)
The double-sided pressure-sensitive adhesive tape of the present invention can be used as a single-layer double-sided pressure-sensitive adhesive tape. Moreover, a double-sided adhesive tape may be laminated | stacked on both surfaces of a base material, and a double-sided adhesive tape, a base material, and a double-sided adhesive tape may be used as a lamination | stacking double-sided adhesive tape laminated | stacked in this order. However, the double-sided pressure-sensitive adhesive tape is preferably used as a single-layer double-sided pressure-sensitive adhesive tape without being laminated on the substrate.

  When a single-layer double-sided pressure-sensitive adhesive tape is used, there is no influence such as a difference in refractive index between the substrate and the double-sided pressure-sensitive adhesive tape. Furthermore, when a single-layer double-sided pressure-sensitive adhesive tape is used for joining touch panel constituent members, the base material does not adversely affect the operability and visibility of the touch panel.

  In the present specification, the “tape” includes a sheet or a film.

  The manufacturing method of a double-sided adhesive tape is not specifically limited. A double-sided adhesive tape can be manufactured as follows, for example.

  On the release polyethylene terephthalate film, a double-sided pressure-sensitive adhesive tape-forming composition containing the (meth) acrylic acid ester copolymer, the cross-linking agent, and a solvent is applied, and the double-sided pressure-sensitive adhesive tape-forming composition is applied. Form a layer. Next, the solvent layer is distilled off by drying the double-sided pressure-sensitive adhesive tape-forming composition layer, and a double-sided pressure-sensitive adhesive tape is formed on the release polyethylene terephthalate film. Thereafter, the release polyethylene terephthalate film and the double-sided pressure-sensitive adhesive tape are turned over in a bonded state, and laminated on the release polyethylene terephthalate film prepared separately from the double-sided pressure-sensitive adhesive tape side. In this manner, a laminate in which the release polyethylene terephthalate film, the double-sided pressure-sensitive adhesive tape, and the release polyethylene terephthalate film are laminated in this order can be obtained. When this laminate is used, the release polyethylene terephthalate film is peeled from both sides of the double-sided pressure-sensitive adhesive tape.

  The thickness of the double-sided pressure-sensitive adhesive tape of the present invention is preferably in the range of 5 to 100 μm, and more preferably in the range of 25 to 100 μm.

  The gel fraction of the double-sided pressure-sensitive adhesive tape of the present invention is preferably in the range of 40 to 60% by weight. If the gel fraction is too low, the cohesive force of the double-sided pressure-sensitive adhesive tape becomes low, and the durability may deteriorate when the double-sided pressure-sensitive adhesive tape is exposed to high temperatures. When the said gel fraction is too high, the adhesive force of a double-sided adhesive tape may fall. The gel fraction is preferably in the range of 45 to 55% by weight.

  The gel fraction can be measured as follows.

  A double-sided pressure-sensitive adhesive tape cut to have a planar shape of 20 mm × 40 mm is prepared. After this double-sided pressure-sensitive adhesive tape is immersed in ethyl acetate at 23 ° C. for 24 hours, the double-sided pressure-sensitive adhesive tape is taken out from ethyl acetate. The double-sided adhesive tape taken out from the ethyl acetate is dried at 110 ° C. for 1 hour. Next, the weight of the double-sided pressure-sensitive adhesive tape after drying can be measured, and the gel fraction can be calculated by the following formula (3).

Gel fraction (% by weight) = W2 / W1 × 100 (3)
W1: Weight of double-sided adhesive tape before immersion in ethyl acetate W2: Weight of double-sided adhesive tape after drying

  A bonded body obtained by bonding a glass plate or a polycarbonate plate and an optical film such as a polarizing film or a transparent conductive film through the double-sided pressure-sensitive adhesive tape of the present invention is allowed to stand for 500 hours at 60 ° C. and a relative humidity of 90%. In plan view, the area of the bubbles generated at the bonding interface is preferably less than 0.5% of the bonding area. When bubbles are present at the bonding interface, the diameter of the bubbles is preferably less than 0.01 mm.

(Touch panel)
1A and 1B schematically show a touch panel using a double-sided pressure-sensitive adhesive tape according to an embodiment of the present invention in a perspective view and a front sectional view. FIG. 2 schematically shows the touch panel shown in FIGS. 1A and 1B in an exploded perspective view.

  In the touch panel 1 shown in FIGS. 1A and 1B, a film 4 in which an ITO film 5 is formed on the upper surface 2a of the support member 2 via the double-sided adhesive tape 3 according to an embodiment of the present invention. Are laminated from the film 4 side. A glass plate or a polycarbonate plate is preferably used as the support member 2. Of these, a polycarbonate plate is preferable.

  A plurality of spacers 6 are provided on the upper surface 5 a of the ITO film 5. On the upper surface 5 a of the ITO film 5, a film 9 having an ITO film 8 formed on the lower surface is laminated from the ITO film 8 side through a frame-shaped seal member 7. As the films 4 and 9, for example, a PET film or an optical film can be used.

  A seal member 7 is bonded to the outer peripheral edge of the upper surface 5 a of the ITO film 5 and the outer peripheral edge of the lower surface 8 a of the ITO film 8. An internal space A is formed by the upper surface 5 a of the ITO film 5, the inner peripheral surface 7 a of the frame-shaped sealing member 7, and the lower surface 8 a of the ITO film 8.

  A hard coat layer 11 is laminated on the upper surface of the film 9 via a double-sided pressure-sensitive adhesive tape 10 according to an embodiment of the present invention. The hard coat layer 11 is provided to prevent the film 9 from being damaged. The hard coat layer 11 may not be provided.

  A pair of electrodes (not shown) is provided in the vicinity of the opposing ends of the ITO film 5. A pair of electrodes (not shown) is provided in the vicinity of the opposing ends of the ITO film 8. The electrode provided on the ITO film 5 and the electrode provided on the ITO film 8 are provided so as to be orthogonal to each other.

  In a state where the upper surface of the hard coat layer 11 is not pressed, the upper surface 5a of the ITO film 5 and the lower surface 8a of the ITO film 8 are separated from each other. A spacer 6 is provided to prevent the upper surface 5a of the ITO film 5 and the lower surface 8a of the ITO film 8 from coming into contact with each other when the upper surface of the hard coat layer 11 is not pressed.

  Further, by pressing the upper surface of the hard coat layer 11, the upper surface 5 a of the ITO film 5 and the lower surface 8 a of the ITO film 8 can be brought into contact with each other. At this time, by applying voltages to the pair of electrodes provided on the ITO film 5 and the pair of electrodes provided on the ITO film 8, the positions where the ITO films 5 and 8 are in contact with each other can be detected. .

  The touch panel 1 is used, for example, to configure the liquid crystal display device 21 shown in FIG. In the liquid crystal display device 21, a liquid crystal module (not shown) is built in a recess 21 a provided on the upper surface. A touch panel 1 is laminated on the liquid crystal module. The liquid crystal module and the touch panel 1 can be joined by a double-sided adhesive tape or the like according to an embodiment of the present invention. The liquid crystal display device 21 is configured to be operated by the touch panel 1 and the operation unit 22.

  Note that the touch panel 1 may not include the support member 2. In this case, the lower surface of the film 3 is bonded onto the liquid crystal module via a double-sided adhesive tape or the like.

  Since the liquid crystal display device 21 includes the touch panel in which the touch panel constituent members are joined by the double-sided adhesive tape according to the embodiment of the present invention, the double-sided adhesive tape is difficult to peel off from the touch panel constituent members, and the double-sided adhesive tape and the touch panel. Air bubbles are unlikely to be generated at the joint interface with the constituent members. For this reason, the visibility of a touch panel operation part can be improved.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited only to the following examples.

Example 1
(1) Preparation of (meth) acrylic ester copolymer In a reaction vessel, 2 parts by weight of acrylic acid, 80 parts by weight of n-butyl acrylate, 10 parts by weight of benzyl methacrylate, and n-butyl methacrylate 8 parts by weight, ethyl acetate, and a polymerization initiator were added, and after copolymerization, ethyl acetate was further added to obtain an ethyl acetate solution containing 25% by weight of a (meth) acrylic ester copolymer. Obtained.

(2) Molecular weight of (meth) acrylic acid ester copolymer The obtained (meth) acrylic acid ester copolymer was diluted 50 times with tetrahydrofuran (THF) to obtain a diluted solution. The obtained diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample.

  The obtained measurement sample was supplied to a gel permeation chromatograph (trade name “2690 Separations Model” manufactured by Water), and GPC measurement was performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40 ° C. The molecular weight in terms of polystyrene of the (meth) acrylate ester copolymer was measured, and this value was taken as the weight average molecular weight and number average molecular weight of the (meth) acrylate ester copolymer. In the GPC measurement, a trade name “GPC LF-804” manufactured by Showa Denko KK was used as the column, and a differential refractometer was used as the detector.

  As a result, the (meth) acrylic acid ester copolymer had a weight average molecular weight of 250,000 and a number average molecular weight of 700,000. The molecular weight distribution (weight average molecular weight / number average molecular weight) was 2.8.

(3) Preparation of pressure-sensitive adhesive To 100 parts by weight of a solid content of an ethyl acetate solution containing 25% by weight of the obtained (meth) acrylic acid ester-based copolymer, an epoxy-based curing agent (trade name “E -AX ") 0.5 part by weight was added to prepare a pressure-sensitive adhesive as a composition for forming a double-sided pressure-sensitive adhesive tape.

(Production of double-sided adhesive tape)
The obtained pressure-sensitive adhesive was coated on a release polyethylene terephthalate film to form a pressure-sensitive adhesive layer. Thereafter, the pressure-sensitive adhesive layer was heated to 80 to 110 ° C. and dried to distill off the solvent, thereby forming a double-sided pressure-sensitive adhesive tape having a thickness of 25 μm on the release polyethylene terephthalate film. Thereafter, the release polyethylene terephthalate film and the double-sided pressure-sensitive adhesive tape were turned over in a bonded state, and laminated on the release polyethylene terephthalate film prepared separately from the double-sided pressure-sensitive adhesive tape side. Thus, the laminated body by which the release polyethylene terephthalate film, the double-sided adhesive tape, and the release polyethylene terephthalate film were laminated | stacked in this order was obtained.

(Example 2)
A laminate was produced in the same manner as in Example 1 except that the amount of the epoxy curing agent was changed to 0.40 parts by weight.

(Example 3)
A laminate was produced in the same manner as in Example 1 except that the amount of the epoxy curing agent was changed to 0.45 parts by weight.

(Comparative Example 1)
A laminate was prepared in the same manner as in Example 1 except that the amount of the epoxy curing agent was changed to 0.10 parts by weight.

(Comparative Example 2)
A laminate was prepared in the same manner as in Example 1 except that the amount of the epoxy curing agent was changed to 0.30 part by weight.

(Comparative Example 3)
A laminate was produced in the same manner as in Example 1 except that the amount of the epoxy curing agent was changed to 0.60 parts by weight.

(Evaluation)
(1) Gel fraction The double-sided pressure-sensitive adhesive tape was cut so as to have a planar shape of 20 mm × 40 mm to prepare a test piece. After this test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate. Thereafter, the test piece was dried at 110 ° C. for 1 hour. Next, the weight of the test piece after drying was measured, and the gel fraction was calculated by the above-described formula (3).

(2) Swelling rate The double-sided pressure-sensitive adhesive tape was cut so as to have a planar shape of 20 mm × 40 mm to prepare a test piece. After this test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate. Thereafter, the drop of ethyl acetate present on the surface of the test piece was eliminated. Thereafter, the weight of the test piece was measured, and the swelling rate was calculated by the above-described formula (2).

(3) Initial adhesive strength The obtained laminate was cut so as to have a planar shape of 25 mm × 100 mm. One release polyethylene terephthalate film of the cut laminate was peeled to expose the double-sided adhesive tape. Next, the exposed surface of the double-sided adhesive tape was bonded onto the polyethylene terephthalate film. Further, the other release polyethylene terephthalate film was peeled off to expose the double-sided adhesive tape, and the exposed surface of the double-sided adhesive tape was bonded onto the glass plate. Thus, the lamination sample by which the double-sided adhesive tape and the polyethylene terephthalate film were laminated | stacked in this order on the glass plate was obtained. Thereafter, a 2.0 kg rubber roller is placed on the polyethylene terephthalate film of the laminated sample, and the rubber roller is reciprocated once at a speed of 300 mm / min, whereby the glass plate and the double-sided adhesive tape are bonded together at 23 ° C. for 20 minutes. A test sample was prepared.

  A test sample using a polycarbonate plate (PC plate) instead of the crow plate was prepared.

  The obtained test sample is subjected to a tensile test in the 180 ° direction at a peeling speed of 300 mm / min according to JIS Z0237, the adhesive strength of the double-sided adhesive tape to the glass plate (N / 25 mm), and the polycarbonate plate of the double-sided adhesive tape The adhesive force (N / 25 mm) to was measured. The obtained measured value was defined as initial adhesive strength.

(4) Adhesive strength with time The test sample prepared for the measurement of the initial adhesive strength was 1 hour at 23 ° C, 6 hours at 23 ° C, 12 hours at 23 ° C, 24 hours at 23 ° C, and 48 at 23 ° C. A test sample was prepared after standing for a period of time. About the obtained test sample after the lapse of time, in the same manner as the evaluation of the initial adhesive strength, the adhesive strength of the double-sided adhesive tape to the glass plate (N / 25 mm) and the adhesive strength of the double-sided adhesive tape to the polycarbonate plate (N / 25 mm) ) Was measured. The obtained measured value was defined as the adhesive strength with time.

(5) Existence of peeling and state of bubble generation The obtained double-sided adhesive tape was cut so as to have a flat shape of 46 mm × 61 mm, and a test piece was produced. Through the obtained test piece, a polycarbonate plate having a thickness of 2.0 mm and a planar shape of 50 mm × 125 mm, and a polyethylene terephthalate plate having a thickness of 0.125 mm and a planar shape of 46 mm × 61 mm Were then allowed to stand for 500 hours at 60 ° C. and a relative humidity of 90% to obtain a test sample. The presence or absence of peeling of the double-sided pressure-sensitive adhesive tape in the obtained test sample and the state of bubble generation at the joint interface were visually observed. The state of bubble generation was evaluated according to the following evaluation criteria.

[Evaluation criteria for bubble generation]
◯: No bubbles having a size of 0.01 mm or more Δ: 1 to 5 bubbles having a size of 0.01 mm or more per test sample ×: One test having a size of 0.01 mm or more 6 or more results per sample The results are shown in Table 1 below.

1A and 1B are a perspective view and a front sectional view schematically showing a touch panel using a double-sided pressure-sensitive adhesive tape according to an embodiment of the present invention. FIG. 2 is an exploded perspective view schematically showing a touch panel using a double-sided pressure-sensitive adhesive tape according to an embodiment of the present invention. FIG. 3 is a perspective view schematically showing a liquid crystal display device including a touch panel using a double-sided pressure-sensitive adhesive tape according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Touch panel 2 ... Support member 2a ... Upper surface 2b ... Lower surface 3 ... Double-sided adhesive tape 4 ... Film 5 ... ITO film 5a ... Upper surface 6 ... Spacer 7 ... Sealing member 7a ... Inner peripheral surface 8 ... ITO film 8a ... Lower surface 9 ... Film DESCRIPTION OF SYMBOLS 10 ... Double-sided adhesive tape 11 ... Hard-coat layer 21 ... Liquid crystal display device 21a ... Recessed part 22 ... Operation part

Claims (1)

Including 100 parts by weight of a (meth) acrylic ester copolymer and 0.40 to 0.50 parts by weight of an epoxy crosslinking agent,
The increase rate of the adhesive force calculated | required by following formula (1) exists in the range of 110-220%,
The swelling ratio obtained by the following formula (2) is in the range of 2000 to 6000% by weight,
A double-sided pressure-sensitive adhesive tape for a touch panel, wherein a gel fraction obtained by the following formula (3) is within a range of 40 to 60% by weight.
Increase rate of adhesive force (%) = (P2−P1) / P1 × 100 (1)
P1: Adhesive strength of double-sided pressure-sensitive adhesive tape to a polycarbonate plate measured in accordance with JIS Z0237 after bonding the double-sided pressure-sensitive adhesive tape to a polycarbonate plate and leaving it for 20 minutes at 23 ° C. and 50% relative humidity P2: Double-sided Adhesive tape is bonded to a polycarbonate plate and left for 48 hours at 23 ° C. and 50% relative humidity, and then the adhesive strength of the double-sided adhesive tape measured on the basis of JIS Z0237 against the polycarbonate plate. = W4 / W3 × 100 (2)
W3: Initial weight of double-sided pressure-sensitive adhesive tape before immersion in ethyl acetate W4: After the double-sided pressure-sensitive adhesive tape was immersed in ethyl acetate at 23 ° C. for 24 hours, ethyl acetate present on the surface of the double-sided pressure-sensitive adhesive tape taken out from ethyl acetate Weight of double-sided pressure-sensitive adhesive tape after removing droplets Gel fraction (% by weight) = W2 / W1 × 100 Formula (3)
W1: Weight of double-sided pressure-sensitive adhesive tape cut to have a planar shape of 20 mm × 40 mm before immersion in ethyl acetate W2: Double-sided pressure-sensitive adhesive tape cut to have a planar shape of 20 mm × 40 mm in ethyl acetate at 23 ° C. After being soaked for 24 hours, the double-sided pressure-sensitive adhesive tape is taken out of ethyl acetate, and the weight of the double-sided pressure-sensitive adhesive tape after drying the double-sided pressure-sensitive adhesive tape taken out from ethyl acetate at 110 ° C. for 1 hour

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