JP2011168658A - Adhesive composition and adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive composition which is filled between a surface protection plate and an image display module, and an adhesive sheet including the adhesive composition as an adhesive layer. <P>SOLUTION: The adhesive composition 7 contains a polymer, prepared by copolymerizing at least an alkyl acrylate, a hydroxyl group-containing monomer, vinyl acetate and a carboxyl group-containing monomer, wherein the weight proportion of the carboxyl group-containing monomer to the polymer is 0.01-1.0 pt.wt., and a crosslinking agent. The ball tack of the adhesive composition 7 is confined to 12-30. When the adhesive composition 7 is stuck to a surface protection plate having a printed portion, it exhibits high initial adhesion (tack force) and excellent embedding conformability to the printing unevenness. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. More specifically, a pressure-sensitive adhesive composition used to fill a gap between the surface protection plate of the image display device and the image display module, a gap between the surface protection plate and the touch panel, a gap between the image display module and the touch panel, and The present invention relates to an adhesive sheet having the adhesive composition as an adhesive layer.

  2. Description of the Related Art Conventionally, an image display device used for a mobile phone, a mobile terminal, a touch panel, and the like includes an image display module such as a liquid crystal module or electroluminescence, a touch panel, and a surface protection plate that protects the image display module and the touch panel. . An air layer having a constant thickness is provided between the constituent members. The air layer is provided for the purpose of preventing the impact from being directly transmitted to the image display module when the image display device receives some impact from the outside. For example, an air layer of about 0.5 mm is usually provided between the image display module and the surface protection plate, between the image display module and the touch panel, and between the touch panel and the surface protection plate. Moreover, the printing etc. which border a surface protection board may be provided in the side facing a touch panel among surface protection boards.

  When an air layer is provided between the surface protection plate and the touch panel and the image display module, light scattering occurs due to a difference in refractive index between the surface protection plate or the touch panel and the air layer, and the visibility of the image display device Decreases. On the other hand, a resin, structure and apparatus have been proposed that have an impact absorbing function and a refractive index equivalent to that of the surface protection plate, and can improve optical characteristics by filling instead of an air layer. Yes. For example, there has been proposed an optical confusion prevention structure that fills a gap between a liquid crystal cell and a protective panel with a silicone gel that is cured by ultraviolet rays (see Patent Document 1). A display device in which a gap between the liquid crystal display panel and the touch panel on the surface layer is filled with a polymerizable resin composition has been proposed (see Patent Document 2). In addition, an image display device and a light-transmitting pressure-sensitive adhesive sheet in which a gel-like light-transmitting pressure-sensitive adhesive sheet such as silicone gel is disposed between a liquid crystal display panel and a transparent protective plate have been proposed (see Patent Document 3). In addition, a transparent double-sided PSA sheet containing an acrylic polymer and a carboxyl group-containing oligomer has been proposed (see Patent Document 4).

JP-A-6-337411 Japanese Patent Laid-Open No. 2004-77887 JP 2006-290960 A JP 2005-255877 A

  However, in the structures and apparatuses described in Patent Document 1 and Patent Document 2, for example, a polymerizable resin composition in a liquid state is filled between the liquid crystal display panel and the surface protection plate, and then irradiated with light such as ultraviolet rays. The resin must be cured with Therefore, there is a problem that bubbles are mixed in the process of filling the polymerizable resin in a liquid state. In addition, there is a problem in that a difference in the degree of curing due to variations in light irradiation intensity occurs in the step of curing the polymerizable resin with light irradiation equipment. Further, there is a problem in that defective products are likely to be generated due to volume shrinkage during resin curing.

  For example, although the light-transmitting pressure-sensitive adhesive sheet described in Patent Document 3 fulfills the function as an impact absorbing material, it is easy for air bubbles to be mixed during bonding, and even if it is subjected to heat and pressure autoclave treatment, There is a problem that remains. In particular, when the surface protection plate has border printing, bubbles are likely to remain at the step (printing step portion) between the printing portion and the non-printing portion. For this reason, the light-transmitting pressure-sensitive adhesive sheet described in Patent Document 3 has a problem that the appearance deteriorates due to remaining bubbles. In addition, the pressure-sensitive adhesive sheet described in Patent Document 3 has a problem that durability is low as compared with the polymerizable resin, and floating, peeling, color change and the like are likely to occur.

  Further, for example, the transparent double-sided pressure-sensitive adhesive sheet described in Patent Document 4 can be prevented from being lifted off from the adherend, particularly under high temperature and high temperature and high humidity conditions. Since an acid component derived from an acid corrodes particularly a metal part of an electronic component, there is a problem that an electronic device as an adherend malfunctions or fails. However, if the acid component derived from the carboxylic acid is reduced from the pressure-sensitive adhesive sheet, sufficient adhesive properties (particularly holding power) cannot be obtained, and floating and peeling under high temperature and high temperature and high humidity conditions cannot be prevented. It is not possible to balance sex. In addition, the polymer obtained from the carboxyl group-containing monomer generally has a high glass transition point (Tg) (for example, Tg of polyacrylic acid is 106 ° C.), so that the pressure-sensitive adhesive sheet containing a large amount of the carboxyl group-containing monomer also becomes hard. Bubbles are likely to remain at the step between the printed portion and the non-printed portion (printed step portion). For this reason, the light-transmitting pressure-sensitive adhesive sheet described in Patent Document 4 has a problem that the appearance deteriorates due to remaining bubbles.

  In addition, border printing or the like may be applied to the surface protection plate of an image display device used for recent cellular phones, portable terminals, touch panels, etc. for the purpose of decorativeness. In such a surface protection plate, the printing thickness tends to be increased from about 10 μm to about 20 μm from the conventional thickness in order to suppress the light transmittance of the border printing portion. Therefore, it is required that air bubbles do not remain in a printing step of about 20 μm at the time of bonding even to the adhesive sheet that fills the air layer between the surface protection plate and the touch panel and the image display module.

  An object of the present invention is to provide an adhesive composition filled between a surface protection plate and an image display module or a touch panel, and an adhesive sheet provided with the adhesive composition as an adhesive layer. Specifically, the image display device has excellent visibility, is easy to process, and has high initial adhesion (tack force) when attached to a printed surface protection plate such as a mobile phone, and is embedded in a printing step. Adhesive composition having excellent durability and stability with good followability, no bubbles remaining, no appearance or color tone change under high temperature and high temperature and humidity environment, and the pressure sensitive adhesive composition as an adhesive layer It is in providing the provided adhesive sheet.

  In order to solve the above-mentioned problems, the pressure-sensitive adhesive composition of the invention according to claim 1 is a polymer in which at least an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer are copolymerized. The pressure-sensitive adhesive composition is characterized in that a weight ratio of the carboxyl group-containing monomer in the polymer is 0.01 to 1.0 part by weight, contains a crosslinking agent, and has a ball tack of 12 to 30. It is characterized by being.

  Further, in the pressure-sensitive adhesive composition of the invention according to claim 2, in addition to the constitution of the invention according to claim 1, the crosslinking agent is a xylylene diisocyanate crosslinking agent or a hexamethylene diisocyanate crosslinking agent. Features.

  In the pressure-sensitive adhesive composition of the invention according to claim 3, the alkyl acrylate is butyl acrylate and 2-ethylhexyl acrylate, and the polymer has a weight average molecular weight of 200,000 to 1,000,000. And

  Moreover, the adhesive sheet of the invention which concerns on Claim 4 has the said adhesive composition in any one of Claim 1 to 3 as an adhesion layer.

  The pressure-sensitive adhesive composition is a polymer in which at least an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer are copolymerized, and the weight ratio of the carboxyl group-containing monomer in the polymer is 0.00. It is 01 to 1.0 part by weight, contains a crosslinking agent, and has a ball tack of 12 to 30. Such a pressure-sensitive adhesive composition has high initial adhesion (tack force) when bonded to a surface protective plate having a printed portion, and is excellent in followability to be embedded in a printing step. Therefore, when the adhesive composition is used for the purpose of filling a gap provided between the surface protection plate in the image display device and the touch panel and the image display module, bubbles near the step of the printed portion of the surface protection plate The gap between the surface protection plate and the touch panel and the image display module can be satisfactorily filled. By using the pressure-sensitive adhesive sheet in which such a pressure-sensitive adhesive composition is used, it is possible to easily realize pressure-sensitive adhesive processing between the surface protection plate, the touch panel, and the image display module. In addition, it is possible to manufacture an image display device that has good visibility and hardly changes in appearance and color tone in a high temperature and high temperature and high humidity environment. Furthermore, an image display device excellent in durability and stability can be produced.

2 is a cross-sectional view showing a physical configuration of the pressure-sensitive adhesive sheet 10. FIG. 3 is a cross-sectional view showing a physical configuration of the image display device 11. FIG.

  Hereinafter, the pressure-sensitive adhesive composition 7 and the pressure-sensitive adhesive sheet 10 in the embodiment of the present invention will be described with reference to the drawings. These drawings are used to explain the technical features that can be adopted by the present invention, and the configuration of the apparatus described is limited to that unless otherwise specified. It is not an intent but merely an illustrative example.

  With reference to FIG. 1, the physical structure of the adhesive sheet 10 in which the adhesive composition 7 was used is demonstrated. As shown in FIG. 1, the pressure-sensitive adhesive sheet 10 includes a pressure-sensitive adhesive layer 3, and a release sheet 5 and a release sheet 6 that are attached to the pressure-sensitive adhesive layer 3 so as to sandwich the pressure-sensitive adhesive layer 3. The pressure-sensitive adhesive layer 3 is a polymer obtained by copolymerizing at least an alkyl acrylate, vinyl acetate, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer, and the weight ratio of the carboxyl group-containing monomer in the polymer is 0.01 to 1. 0.0 part by weight, and is constituted by the pressure-sensitive adhesive composition 7 containing a crosslinking agent.

  The polymer will be described. The polymer is a polymer obtained by copolymerizing at least an alkyl acrylate, vinyl acetate, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer, and the weight ratio of the carboxyl group-containing monomer in the polymer is 0.01 to 1.0. Parts by weight.

As the acrylic acid alkyl ester, an alkyl ester having an alkyl group having 1 to 10 carbon atoms can be used. For example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate and n-pentyl group structural isomer, n-hexyl acrylate and n-hexyl group structural isomer, 2-ethylhexyl acrylate, etc. Can be mentioned. Furthermore, it is preferable to use an alkyl acrylate ester having 4 to 8 carbon atoms in the alkyl group. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more type. Among these, it is preferable to use n-butyl acrylate and 2-ethylhexyl acrylate. Furthermore, when n-butyl acrylate and 2-ethylhexyl acrylate are used in combination, they have excellent flexibility at room temperature and high initial adhesion (tack force) when bonded to an adherend. It is further preferable from the viewpoint that the followability of embedding in the level difference generated by the printed portion is good.

  The alkyl acrylate is preferably contained in the range of 79.5 to 97.5 parts by weight in 100 parts by weight of the monomer in terms of solid content. If the amount is less than 79.5 parts by weight, the characteristics of the monomer used in combination are remarkably exhibited, and the adhesive composition has sufficient adhesive performance and good follow-up ability to the level difference generated by the printed part of the surface protection plate such as a mobile phone. Product 7 is difficult to obtain. Exceeding 97.5 parts by weight is not preferable because the cohesiveness of the pressure-sensitive adhesive layer 3 is remarkably lowered, and it becomes difficult to obtain durability under a high temperature and high temperature and high humidity environment required for an image display device.

  Among the alkyl acrylates, the weight ratio of n-butyl acrylate and 2-ethylhexyl acrylate is preferably 88.5: 5 to 53.5: 40 for butyl acrylate: 2-ethylhexyl acrylate, and 83.5: More preferably, it is 10 to 63.5: 30. When the weight ratio of 2-ethylhexyl acrylate is less than 5 parts, it is difficult to obtain a pressure-sensitive adhesive sheet having good embeddable followability to a step generated by a printed part of a surface protection plate such as a mobile phone. When the proportion of 2-ethylhexyl acrylate exceeds 40 parts, the cohesiveness of the pressure-sensitive adhesive composition 7 is remarkably lowered, and the pressure-sensitive adhesive sheet 10 having durability in a high temperature and high temperature and high humidity environment required for an image display device is obtained. Since it becomes difficult to obtain, it is not preferable. The remaining 6.5 parts can contain other monomer components such as a hydroxyl group-containing monomer, vinyl acetate or a carboxyl group-containing monomer.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and hydroxyalkyl acrylates such as 4-hydroxybutyl acrylate, and 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, which are hydroxyalkyl esters of methacrylic acid, It is preferable to use 4-hydroxybutyl methacrylate and the like. Of these hydroxyl group-containing monomers, 2-hydroxyethyl acrylate is most preferably used in combination with the alkyl acrylate described above. By using 2-hydroxyethyl acrylate in combination with alkyl acrylate, the pressure-sensitive adhesive sheet 10 has excellent cohesiveness with the above-mentioned alkyl acrylate and reactivity with the crosslinking agent, and has excellent adhesive performance. Since it can be used as the pressure-sensitive adhesive composition 7, it is preferable.

  The hydroxyl group-containing monomer is preferably blended in the range of 0.5 to 15 parts by weight, more preferably in the range of 1.0 to 10 parts by weight, out of 100 parts by weight of the monomer in terms of solid content. . When the amount is less than 0.5 parts by weight, peeling tends to occur in a high-temperature or high-humidity environment due to insufficient cohesive force. In addition, since the pressure-sensitive adhesive composition 7 becomes soft, the pressure-sensitive adhesive composition 7 tends to adhere to the blade during slitting, or protrudes from the fracture surface and easily contaminates the surroundings. This is not preferable because the workability may be greatly reduced. Exceeding 15 parts by weight is not preferable because the follow-up performance to the step generated by the printed portion of the surface protection plate such as a mobile phone is deteriorated.

  A pressure-sensitive adhesive composition 7 having excellent durability can be obtained by including, in the pressure-sensitive adhesive composition 7, a polymer obtained by further copolymerizing vinyl acetate as a monomer in addition to the above-described alkyl acrylate ester and hydroxyl group-containing monomer. Can do. In order to fill the step generated by the printed portion of the surface protection plate, particularly the step having a high printing thickness (about 20 μm), a polymer having excellent flexibility in which an alkyl acrylate ester and a hydroxyl group-containing monomer are copolymerized is used. . However, when vinyl acetate is not used in combination as a monomer, the pressure-sensitive adhesive composition 7 is easily peeled off from the surface protective plate or the printed portion after being bonded. It peels off especially in a high temperature or high temperature and high humidity environment. On the other hand, the cohesiveness of the pressure-sensitive adhesive composition 7 is improved by using vinyl acetate as a monomer, and peeling in a high temperature or high temperature and high humidity environment can be prevented.

  Vinyl acetate is preferably blended in a proportion of 0.5 to 15 parts by weight, more preferably 1.0 to 10 parts by weight, based on 100 parts by weight of the monomer in terms of solid content. If the amount is less than 0.5 parts by weight, the effect of imparting cohesiveness becomes insufficient, and peeling may occur in a high temperature or high temperature and high humidity environment, which is not preferable. If the amount exceeds 15 parts by weight, the initial adhesion (tack force) when the adhesive sheet 10 is bonded to the adherend is reduced, and the follow-up ability to the step generated by the printed part of the surface protection plate of a mobile phone or the like is reduced. descend. For this reason, since there exists a tendency for a surface protection board to peel from an adhesive sheet and an image display module after bonding an adhesive sheet to a surface protection board, it is unpreferable.

  By using a polymer in which an alkyl acrylate ester and a hydroxyl group-containing monomer are copolymerized, it has excellent flexibility and increased initial adhesion (tacking force) when bonded to an adherend, thereby protecting the surface of mobile phones and the like. The follow-up property to the level difference generated by the printed portion of the plate is good. In addition, the cohesive force can be improved by making a copolymer obtained by adding vinyl acetate as a monomer to an acrylic acid alkyl ester and a hydroxyl group-containing monomer, so that it can float and peel off under high temperature and high temperature and high humidity conditions. It is possible to obtain a pressure-sensitive adhesive composition 7 that is less prone to occurrence and excellent in durability.

  By using a carboxyl group-containing monomer in combination with an acrylic acid alkyl ester, vinyl acetate, and a hydroxyl group-containing monomer as the monomer component, the pressure-sensitive adhesive sheet 10 that is more difficult to peel can be obtained and processability can be improved. When a polymer in which an alkyl acrylate ester, a hydroxyl group-containing monomer, and vinyl acetate are copolymerized is used, the flexibility of the pressure-sensitive adhesive composition 7 and the embedding and durability of printing steps are improved. May cause peeling in a high temperature or high temperature and high humidity environment. Moreover, the adhesive composition 7 adheres to the cutting blade in a processing step such as slitting or punching. Furthermore, the pressure-sensitive adhesive composition 7 protrudes from the fracture surface of the pressure-sensitive adhesive sheet 10 and is contaminated. For this reason, in addition to the above-mentioned monomer, a carboxyl group-containing monomer is contained in an amount of 0.01 to 1.0 part by weight, preferably 0.02 to 0.8 part by weight in terms of solid content, to form a polymer. By adding the carboxyl group-containing monomer, the reactivity between the hydroxyl group-containing monomer used in the present invention and the crosslinking agent is increased catalytically. In particular, it is preferable to use an isocyanate compound and / or an epoxy compound as a cross-linking agent because a particularly high cross-linking structure can be formed because of high reactivity. Therefore, durability of the pressure-sensitive adhesive composition 7, in particular, lifting and peeling under high temperature and high temperature and high humidity environment can be suppressed, and workability of the pressure-sensitive adhesive sheet 10 can be improved. In general, the pressure-sensitive adhesive sheet is provided with an aging period until the crosslinking reaction reaches an equilibrium. However, when a monomer having a carboxyl group is contained, the aging temperature can be carried out at room temperature because the crosslinking reaction is fast. If the carboxyl group-containing monomer is not contained, aging needs to be performed under heating conditions, for example, it is necessary to raise the temperature to about 40 ° C., and the profitability deteriorates.

  In general, a polymer obtained from a carboxyl group-containing monomer has a high glass transition point (Tg) (for example, Tg of polyacrylic acid is 106 ° C.). Therefore, the pressure-sensitive adhesive composition 7 containing a carboxyl group-containing monomer becomes hard and the step embedding property tends to decrease. However, as in the present invention, in addition to a flexible adhesive containing an alkyl acrylate, vinyl acetate, and a hydroxyl group-containing monomer as a monomer constituting the polymer, 0.01 to 1.0 part by weight of a carboxyl group-containing monomer is contained. This prevents durability from being lifted off under high temperature and high temperature and high humidity conditions without hindering the effects of the present invention, such as the ability to follow the embedding in the level difference caused by the printed part of the surface protection plate of a mobile phone or the like. It can be aged at room temperature, is soft, and has a high ball tack and adhesive strength, while being able to obtain a high holding power. Such a pressure-sensitive adhesive sheet is preferable because sufficiently high embedding property and holding power can be obtained even for a printing step of about 20 μm, for example. In addition, the carboxyl group is an acid, and particularly easily corrodes the metal part of the electronic component at a high temperature. However, if the content is 0.01 to 1.0 part by weight as in the present invention, the metal part of the electronic component is particularly Corrosion can be prevented.

  When the carboxyl group-containing monomer exceeds 1.0 part by weight out of 100 parts by weight of the monomer in terms of solid content, the adhesive composition 7 adheres to the cutting blade in a processing step such as slitting or punching, or an adhesive sheet The trouble that the pressure-sensitive adhesive composition 7 protrudes from the broken surface of 10 and is contaminated is reduced. However, on the other hand, the resulting pressure-sensitive adhesive composition 7 becomes hard and the step embedding property tends to be lowered, and the durability under high temperature and high temperature and high humidity conditions deteriorates, and the effects of the present invention cannot be obtained. In addition, it corrodes particularly metal parts of electronic components under high temperature environment. When the monomer having a carboxyl group is less than 0.01 parts by weight, especially when it is not blended, a pressure-sensitive adhesive having a high ball tack and adhesive strength can be obtained. Become. On the other hand, it is inferior in holding power and durability. In addition, the effect of catalytically enhancing the chemical reaction between the hydroxyl group-containing monomer and the crosslinking agent used in the present invention is difficult to obtain, and the aging period until the crosslinking reaction reaches equilibrium and stabilizes the adhesive properties becomes long. It is necessary to warm and accelerate the crosslinking reaction. For example, from the viewpoint of productivity, the aging period is desirably within 7 days at 23 ° C., but if less than 0.01 parts by weight, the crosslinking reaction does not reach equilibrium even after 7 days at 23 ° C. For this reason, when peeling a peeling sheet, the malfunction which the adhesive layer 3 fracture | ruptures may generate | occur | produce and it is necessary to extend an aging period or to heat.

  As the monomer having a carboxyl group, known aliphatic carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid can be used. Acrylic acid having good copolymerizability with a hydroxyl group-containing monomer and vinyl acetate is preferred.

  In addition to the alkyl ester, hydroxyl group-containing monomer, vinyl acetate, and carboxyl group-containing monomer described above, a monomer component that can be radically copolymerized in an organic solvent and generally used as an adhesive can be used in combination. Examples of such a monomer component include monomers having an aromatic ring such as methacrylic acid alkyl ester, acrylic amide, acrylonitrile, and styrene.

  As described above, at least an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer are used in combination as the polymer group monomer, and 0.01 to 1.0 part by weight of the carboxyl group-containing monomer is contained. If this is done, the adhesive is excellent in flexibility and has improved initial adhesion (tacking force) when bonded to an adherend, and has good embedment and followability to the level difference generated by the printed part of the surface protection plate of a mobile phone or the like. Composition 7 and pressure-sensitive adhesive sheet 10 are obtained. In addition, the reactivity between the isocyanate-based crosslinking agent and / or the epoxy-based crosslinking agent and the hydroxyl group-containing monomer is increased catalytically, thereby forming a denser crosslinked structure. For this reason, it is preferable because the durability of the pressure-sensitive adhesive composition 7 under high-temperature and high-humidity conditions and the processability of the pressure-sensitive adhesive sheet 10 are easily improved. Furthermore, after the preparation of the pressure-sensitive adhesive sheet 10, the aging period until the crosslinking reaction reaches an equilibrium can be shortened, or aging can be performed at room temperature without heating. The content ratio of these components is 79.5 to 97.5 parts by weight in terms of solid content with respect to 100 parts by weight of the pressure-sensitive adhesive, and 100% by weight of hydroxyl group-containing monomer in 100 parts by weight of monomer in terms of solid content. It is preferable to obtain a copolymer with 5 to 15 parts by weight, 0.5 to 15 parts by weight of vinyl acetate, and 0.01 to 1.0 parts by weight of the carboxyl group-containing monomer.

  A method for producing the polymer used in the present invention will be described. The polymer can be produced by various known methods. For example, a radical polymerization method such as a bulk polymerization method, a solution polymerization method, or a suspension polymerization method can be appropriately selected. As the polymerization initiator, azo polymerization initiators such as azobisisobutyronitrile (AIBN), peroxide compounds such as lauroyl peroxide and benzoyl peroxide (BPO), benzophenone initiators such as benzophenone, 2-methyl Thioxanthone initiators such as thioxanthone, benzoin ether initiators such as benzoin ethyl ether, and the like can be used. Of these, an azo polymerization initiator such as azobisisobutyronitrile is particularly preferred from the viewpoint of polymerizability. And the polymer solution is prepared by dissolving the polymer manufactured by the said method in solvents, such as toluene, ethyl acetate, and methyl ethyl ketone.

  The weight average molecular weight (Mw) of the polymer is not particularly limited, but is preferably 200,000 to 1,000,000, more preferably 350,000 to 600,000. When the molecular weight is less than 200,000, foaming, floating, and peeling occur in the adhesive layer 3 when used as an image display device such as a mobile phone, a portable terminal, a touch panel, etc., which is assumed to be used in a severe environment such as high temperature and high humidity. Since it becomes easy, it is not preferable. Also, the holding force tends to decrease. Furthermore, after sticking to a structural member, a protrusion, a shift | offset | difference, etc. occur easily. When the molecular weight exceeds 1,000,000, the initial adhesion to the surface protective plate is lowered, and bubbles tend to remain, which is not preferable. In the present specification, the weight average molecular weight (Mw) is a value in terms of polystyrene measured by gel permeation chromatography (GPC method). In addition, the storage elastic modulus mentioned later can be adjusted also with the weight average molecular weight of a polymer.

  In the above polymer solution, in addition to the above components, a tackifier, a silane coupling agent, a colorant, a plasticizer, a filler, an antistatic agent, an antioxidant, an ultraviolet absorber, etc. These additives may be appropriately added within a range that does not impair the effects of the present invention.

  The crosslinking agent added to the above polymer solution will be described. The solution of the pressure-sensitive adhesive composition 7 (hereinafter referred to as “pressure-sensitive adhesive solution”) is prepared by adding a crosslinking agent to the above polymer solution. Examples of the crosslinking agent used in the present invention include an isocyanate crosslinking agent that is a compound having two or more isocyanate groups in one molecule, or an epoxy crosslinking agent that is a compound having two or more epoxy groups in one molecule. Can be mentioned.

  Examples of the isocyanate-based crosslinking agent include HDI-based isocyanate crosslinking agents such as hexamethylene diisocyanate (hereinafter referred to as “HDI”) and trimethylolpropane hexamethylene diisocyanate (hereinafter referred to as “HDI-TMP”), and tolylene diisocyanate. (Hereinafter referred to as “TDI”), TDI-based isocyanate crosslinking agents such as trimethylolpropane tolylene diisocyanate (hereinafter referred to as “TDI-TMP”), xylylene diisocyanate (hereinafter referred to as “XDI”) XDI-based isocyanate crosslinking agents such as trimethylolpropane xylylene diisocyanate (hereinafter referred to as “XDI-TMP”), o-toluidine isocyanate, isophorone diisocyanate, 4-4′-diphenylmethane diisocyanate Over DOO, naphthylene-1,5-diisocyanate, and triphenylmethane triisocyanate, products of isocyanates and polyalcohols can be used and polyisocyanates produced by condensation of isocyanates. Among these, when XDI-TMP and HDI-TMP are used, even if the resulting pressure-sensitive adhesive composition 7 is left in a high-temperature, high-humidity environment, the pressure-sensitive adhesive composition 7 changes in color tone such as yellowing. Hateful. Therefore, the pressure-sensitive adhesive sheet 10 suitable for an application for filling a gap between the constituent members of the mobile phone having excellent durability can be manufactured.

  As the cross-linking agent, an epoxy-based cross-linking agent can be used in addition to the isocyanic cross-linking agent, and can be used in combination as required. Epoxy hydrin type epoxy resin, ethylene glycol glycidyl ether, polyethylene diglycidyl ether, trimethylolpropane diglycidyl ether, glycerin diglycidyl ether, 1,3-bis (N, N-diglycidylaminomethyl) Examples include epoxy compounds such as cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, N, N, N ′, N′-tetraglycidylaminophenylmethane, and the like. Among these, when N, N, N ′, N′-tetraglycidylaminophenylmethane is used, even if the obtained pressure-sensitive adhesive composition 7 is left in a high-temperature or high-temperature and high-humidity environment, It is difficult for color changes such as yellowing to occur. Therefore, the pressure-sensitive adhesive sheet 10 that is excellent in durability and suitable for filling a gap between the constituent members of the mobile phone can be produced.

  In the present invention, at least a polymer obtained by copolymerizing an alkyl acrylate, ethyl acetate, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer, and a system crosslinking agent are contained. When an epoxy-based crosslinking agent is used alone as a crosslinking agent, the reactivity is generally lower than when an isocyanate-based crosslinking agent is used alone or when an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent are used in combination. For this reason, the crosslinking density of the obtained pressure-sensitive adhesive composition 7 tends to be low, that is, the cohesive force tends to decrease. Accordingly, the adhesive composition 7 is likely to protrude or shift after being bonded to the constituent member, and is likely to be peeled off in a high temperature or high temperature and high humidity environment, so that it tends to be difficult to use in the application of the present invention. However, since the epoxy-based crosslinking agent hardly changes color tone such as yellowing in a high temperature or high temperature and high humidity environment, there is an advantage that it can be suitably used for the pressure-sensitive adhesive sheet 10 of the present invention. Therefore, in the present invention, it is preferable to use an epoxy-based cross-linking agent and use an XDI-based and / or HDI-isocyanate-based cross-linking agent which is more difficult to peel off. As a result, it is possible to obtain a pressure-sensitive adhesive sheet 10 that is particularly free from occurrence of bubbles, floats, and peeling in a high-temperature or high-humidity environment, can suppress a change in color tone of the pressure-sensitive adhesive composition 7, and is particularly excellent in pressure-sensitive physical properties and holding power. it can. Even if an epoxy-based crosslinking agent and a TDI-based isocyanate crosslinking agent are used in combination, they are not preferable because they easily peel off in a high-temperature and high-humidity environment.

  The blending ratio of the polymer and the crosslinking agent is not particularly limited, but the adhesion performance, storage elastic modulus, embedding property, and durability can be adjusted by adjusting the intermolecular crosslinking of the polymer. . From the viewpoint of ensuring excellent properties in terms of embedding in printing steps of the surface protective plate, storage elastic modulus, adhesive physical properties, and durability, the amount of the crosslinking agent added is calculated in terms of solid content with respect to 100 parts by weight of the polymer. It is preferable to contain 0.05-5.0 weight part, Furthermore, 0.1-3.0 weight part is contained. If the amount is less than 0.05 parts by weight, the cohesive force is insufficient, so that it becomes soft and the holding force and durability tend to be lowered. In addition, the pressure-sensitive adhesive composition 7 is likely to protrude from the end face during sheet processing, and the pressure-sensitive adhesive composition 7 is likely to protrude due to heat generated by an image display module such as an LCD or an organic EL. When the amount exceeds 5.0 parts by weight, not only the adhesive strength is greatly reduced and the step embedding property is likely to be lowered, but also a color change such as appearance or yellowing in a high temperature or high temperature and high humidity environment may occur.

  In addition, since it is easy to yellow when using a TDI type | system | group crosslinking agent, 0.1 weight part or more and 3.0 weight part or less with respect to 100 weight part of adhesives, Furthermore, 0.15 weight part or more and 2.0 weight part The following is preferable. If the amount is less than 0.1 parts by weight, the cohesive force is insufficient and the durability tends to deteriorate, which is not preferable. If the amount exceeds 3.0 parts by weight, yellowing tends to occur, which is not preferable. Moreover, when using a TDI type | system | group crosslinking agent, when a carboxyl group-containing monomer shall be 0.5 mass part or less, since the adhesive sheet which does not easily change yellow is obtained, it is preferable.

  In the present invention, if necessary, as a crosslinking agent, a crosslinking agent other than an isocyanate crosslinking agent and an epoxy crosslinking agent, such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, vanadium, chromium, zirconium, etc. A metal chelate compound in which acetylacetone, ethyl acetoacetate, etc. are coordinated to a polyvalent metal element, metal salt, metal alkoxide, aldehyde-based, non-amino resin-based amino compound, urea-based, melamine-based, aziridine-based, etc. it can.

  The cross-linking reaction can be controlled by the temperature and time when the adhesive solution is applied to the release sheet and then dried. The crosslinking temperature is appropriately adjusted according to the type of the pressure-sensitive adhesive composition 7, but generally 70 to 150 ° C. is preferable. Moreover, it is preferable that the crosslinking time is generally terminated in about 1 to 5 minutes.

  When producing the pressure-sensitive adhesive composition 7, a silane coupling agent can be contained in the above-described polymer. By containing a silane coupling agent, the adhesion between the substrate containing a silica component such as a glass substrate and the pressure-sensitive adhesive composition 7 is increased, and the pressure-sensitive adhesive strength and durability in a high-temperature environment are easily improved. Examples of the silane coupling agent include methacryloxy compounds such as methacryloxypropyltrimethoxysilane and 3-methacryloxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- ( 3,4-epoxycyclohexyl) epoxy systems such as ethyltrimethoxysilane, mercapto systems such as 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane, vinyl systems such as vinyltrimethoxysilane and vinyltriethoxysilane, There are amino systems such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) 3-aminopropyltrimethoxysilane, and N- (2-aminoethyl) -3aminopropylmethyldimethoxylane. Among these, when 3-glycidoxypropyltrimethoxysilane is used, in particular, when a polarizing plate is used as a surface protective plate or a substrate containing a silica component such as glass as a substrate for a touch panel, or a surface layer of a liquid crystal module. The pressure-sensitive adhesive composition 7 and the pressure-sensitive adhesive sheet 10 have not only excellent adhesive properties and durability under a high-temperature environment but also have an embedding property capable of following the step even if the printing is as thick as 20 μm and the printing step is large. Therefore, it is preferable.

  The blending ratio of the polymer and the silane coupling agent is not particularly limited, but increases the adhesive force between the base material containing a silica component such as glass and the polarizing plate on the surface layer of the liquid crystal module, under a high temperature environment. In order to improve adhesive strength and durability, 0.05 to 2.0 parts by weight, and further 0.1 to 1.0 parts by weight in terms of solid content with respect to 100 parts by weight of the polymer. Part or less is preferred. If the amount is less than 0.05 parts by weight, the durability tends to decrease, and if it exceeds 2.0 parts by weight, problems such as a decrease in durability and an increase in peeling force tend to occur.

  In the pressure-sensitive adhesive solution prepared as described above, a colorant such as a dye or a pigment is added as necessary when there is a demand for fine adjustment of color tone as an image display device. As the dye, one or more selected from basic dyes, acid dyes, direct dyes, acid mordant dyes, or mordant dyes can be used. There are various types of dyes, and the chemical structure includes azo dyes, anthraquinone dyes, triphenylmethane dyes, pyrazolone dyes, stilbene dyes, diphenylmethane dyes, azomethine dyes, xanthene dyes, alizarin dyes, acridine dyes, quinoneimine dyes. (Azine dye, oxazine dye, thiazine dye), cyanine dye, quinoline dye, thiazole dye, methine dye, nitro dye and the like. Examples of the pigment include azo pigment, anthraquinone pigment, indigo pigment, thioindigo pigment, perylene / perinone pigment, quinacridone pigment, dioxazine pigment, quinophthalone pigment, isoindolinone pigment, pyrrole pigment, phthalocyanine pigment, aniline black pigment. , Organic pigments such as carbon black pigments, metal oxide pigments such as titanium oxide pigments and iron oxide pigments, chromate pigments, sulfide pigments, silicate pigments, carbonate pigments, ferrocyanians Examples thereof include inorganic pigments such as compounds. It is preferable to use a pigment having an average particle diameter of 0.03 to 0.30 μm. This is because a desired storage elastic modulus can be obtained and can be uniformly dispersed in the pressure-sensitive adhesive layer 3. Any one or two or more colorants such as dyes and pigments can be used in appropriate combination. The color tone can be adjusted by the blending ratio of the colorant to be combined.

  Although coloring agents, such as dye and a pigment, are not specifically limited, For example, a coloring agent is added about 0.1-10 weight part in conversion of solid content with respect to 100 weight part of polymers. This reduces adhesion to the surface protection plate, touch panel, and image display module, suitability for embedding the surface protection plate in printing steps, visibility after exposure to high temperature environments, and durability under high temperature and high humidity environments The color tone required for the image display apparatus can be appropriately corrected while maintaining the light transmission performance without impairing the excellent characteristics such as the property.

  The storage elastic modulus obtained by the viscoelasticity test depends on the above-mentioned polymer as the main component. In order to ensure excellent characteristics in terms of embedding of printing steps on the surface protection plate, adhesion performance, durability under high temperature and high humidity environment, and transparency and color change such as yellowing, a monomer having an alkyl ester and a hydroxyl group is used. In addition to the polymer to be included, the storage modulus can be set by appropriately adjusting the crosslinking agent within a predetermined range.

  As explained above, as a monomer to be a polymer group, an acrylic acid alkyl ester and a hydroxyl group-containing monomer, 0.01 to 1.0 part by weight of vinyl acetate and a carboxyl group-containing monomer are used in combination, and a crosslinking agent is contained. . Preferably, an XDI-based or TDI-based isocyanate crosslinking agent is used as the crosslinking agent, more preferably butyl acrylate and 2-ethylhexyl acrylate are used as the alkyl acrylate, and the weight average molecular weight of the polymer is 200,000 to 1,000,000. For example, it has excellent embedding properties, tacky physical properties (tackiness, adhesive strength and holding power), durability, processability, and transparency to a glass substrate, and less color change such as yellowing. The composition 7 and the adhesive sheet 10 can be obtained.

  Particularly, among 100 parts by weight of monomer in terms of solid content, 79.5 to 97.5 parts by weight of acrylic acid alkyl ester, 0.5 to 15 parts by weight of hydroxyl group-containing monomer, and 0.5 to 15 parts by weight of vinyl acetate The polymer is formed from 0.01 to 1.0 part by weight of the carboxyl group-containing monomer. The crosslinking agent is contained in an amount of 0.05 to 5.0 parts by weight, more preferably 0.1 to 3.0 parts by weight in terms of solid content with respect to 100 parts by weight of the polymer. More preferably, an XDI-based and / or HDI-based isocyanate-based crosslinking agent is used as the crosslinking agent. As a result, it has excellent embedding properties, adhesive physical properties (adhesive strength and holding power), durability, processability and transparency with respect to the surface protective plate including the printed portion, and has excellent color composition such as yellowing and little color change. 7 and the pressure-sensitive adhesive sheet 10 are preferable because they are easily obtained.

  The pressure-sensitive adhesive sheet 10 thus obtained has a sufficiently high embedding even in a surface protection plate made of a substrate containing a silica component such as a glass substrate, particularly having a printing step (printing thickness: about 20 μm). Sex can be obtained. Further, it is preferable because it has high adhesive physical properties (tackiness, adhesive strength and holding power), durability, processability and transparency, and has little change in color tone such as yellowing.

  The release sheet 5 and the release sheet 6 will be described. As release sheet 5 and release sheet 6, synthetic resin films such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyethylene terephthalate, rubber sheet, foam sheet, metal foil, paper, non-woven fabric Alternatively, an appropriate thin leaf made of a laminate or the like can be used. The surfaces of the release sheet 5 and the release sheet 6 may be subjected to a release treatment such as silicone treatment, long-chain alkyl treatment, fluorine treatment, etc. as necessary in order to enhance the peelability from the pressure-sensitive adhesive layer 3. The peelability of the release sheet 5 and the release sheet 6 can be controlled by adjusting the type of chemical used for the release treatment and the parameter of the coating amount.

  A method for forming the pressure-sensitive adhesive layer 3 will be described. The method for forming the pressure-sensitive adhesive layer 3 is not particularly limited. For example, the pressure-sensitive adhesive solution prepared as described above may be a known method such as a gravure printing method, a spray method, a dipping method, a roll coater method, or a die coater method. The release sheet 5 is coated by the method. After drying, it is bonded to a release sheet 6 having a different peeling force. Thereby, the adhesive sheet 10 which is a double-sided adhesive sheet without a core material can be created.

  The thickness of the pressure-sensitive adhesive layer 3 is preferably 50 μm or more and 500 μm or less, and more preferably 100 μm or more and 500 μm or less. If it is less than 50 μm, the embedding property is lowered when the printing part 2 (see FIG. 2, see below) having a step of 10 μm or more, particularly 20 μm or more is printed and formed on the surface protection plate 1 (see FIG. 2, see below). Or unintentional peeling or peeling easily occurs due to insufficient adhesive strength or holding power. When it exceeds 500 μm, the light transmittance of the pressure-sensitive adhesive layer 3 is reduced, and the pressure-sensitive adhesive composition 7 is likely to protrude during processing.

  The pressure-sensitive adhesive sheet 10 is preferably produced in a roll shape from the viewpoint of work efficiency in continuous production. Thereafter, it can be formed into a predetermined shape for incorporation into an image display device used in a mobile phone, a portable terminal, a touch panel, or the like by a technique such as punching or laser cutting.

  The usage pattern of the adhesive sheet 10 will be described. FIG. 2 shows a cross-sectional configuration when the adhesive sheet 10 is applied to the image display device 11. As shown in FIG. 2, the image display device 11 includes an image display module 4 and a surface protection plate 1 disposed on a side (upper side in FIG. 2) on which an image is displayed in the image display module 4. . The pressure-sensitive adhesive composition 7 is filled in a portion sandwiched between the image display module 4 and the surface protection plate 1. Note that the printing unit 2 is printed on the surface of the surface protection plate 1 that is close to the image display module 4 (the surface that is in contact with the adhesive composition 7). The printing unit 2 is printed on the surface protection plate 1 when, for example, a frame-shaped outer peripheral frame is formed on the display unit of the image display device 11. The printing unit 2 has a predetermined thickness (about 10 μm to about 20 μm). Although not shown in FIG. 2, the touch panel may be incorporated between the surface protection plate 1 and the image display module 4. In this case, the pressure-sensitive adhesive sheet 10 of the present invention can also be applied to the gap between the surface protection plate 1 and the touch panel and the gap between the touch panel and the image display module 4.

  The surface protection plate 1 will be described. The material and shape of the surface protection plate 1 are not particularly limited as long as they are a light-transmitting sheet or plate-shaped body. Specifically, polyethylene terephthalate (PET) resin, polymethyl methacrylate (PMMA) resin, polycarbonate (PC) resin, triacetyl cellulose (TAC) resin, polyvinyl alcohol (PVA) resin, norbornene resin, cycloolefin (grease Ring) transparent resin such as resin, synthetic resin mainly composed of at least one of the group consisting of translucent resin such as polyethylene resin, polypropylene resin and silicone resin, or soda lime glass, alkali-free glass, tempered glass, Inorganic materials such as heat-resistant glass can be used. From the viewpoint of weight reduction and thickness reduction, a resin material such as a transparent resin or a translucent resin is preferable. PMMA resin, PC resin, soda lime glass, non-alkali glass, and tempered glass are particularly preferable from the viewpoint of molding processability and durability.

  As the surface protection plate 1, a glass plate having a thickness of 0.5 to 2.0 mm, a sheet-like molded body having a thickness of 12 to 300 μm, a plate-like molded body having a thickness of 0.3 to 10.0 mm, and the like. It is possible to use. In particular, a sheet-like molded body having a thickness of 38 to 300 μm is preferable. Alternatively, a plate-like formed body having a thickness of 0.3 to 3.0 mm, particularly 0.8 mm to 1.2 mm is preferable.

  In addition, as long as the present invention is not hindered, functional layers such as an antiglare layer, an antireflection layer, an antistatic treatment layer, a hard coat layer, an antifouling layer, and an antibacterial layer are formed on the surface layer of the surface protective plate 1 or an optical function. The film coated with the layer can be bonded via the pressure-sensitive adhesive composition 7. In this case, surface treatment such as corona treatment, alkali treatment, plasma treatment, and easy-adhesion resin layer coating treatment may be performed in order to improve the adhesion between the functional layer, the optical functional layer, and the like and the other layers.

  A surface protection plate 1 of an image display device used for a recent mobile phone, mobile terminal, touch panel, or the like may be provided with a printing unit 2 for the purpose of decoration. In order to suppress the light transmittance as compared with the conventional case, the printing thickness of the printing unit 2 tends to increase from about 10 μm to about 20 μm. Therefore, when the pressure-sensitive adhesive sheet 10 is applied to a printing step of about 20 μm, no bubbles remain, and an adhesive force that does not peel from the printing step of 20 μm can be maintained under high temperature and high temperature and humidity. is needed.

  The image display module 4 will be described. As the image display module 4, various types of image display modules such as a liquid crystal method and an organic EL method can be used.

  Of the image display module 4, the surface in contact with the pressure-sensitive adhesive composition 7 has a polyethylene terephthalate (PET) resin, a polymethyl methacrylate (PMMA) resin, a polycarbonate (PC) resin, a triacetyl cellulose (TAC) resin, and polyvinyl alcohol. (PVA) resin, norbornene resin, functional film resin layer made of transparent resin such as cycloolefin (alicyclic) resin, special adhesive coating layer made of acrylic resin, polyurethane resin, etc., conductive coating layer, etc. A coat layer is disposed.

  A production method when the image display device 11 is produced using the adhesive sheet 10 will be described. The release sheet 6 of the pressure-sensitive adhesive sheet 10 is peeled off. Next, the surface of the pressure-sensitive adhesive layer 3 that is exposed when the release sheet 6 is peeled off is attached to the image display module 4. Next, the release sheet 5 is peeled off from the pressure-sensitive adhesive layer 3. Next, the surface protection plate 1 is attached to the surface of the pressure-sensitive adhesive layer 3 that is exposed when the release sheet 5 is peeled off. As described above, the image display module 4 and the surface protection plate 1 are bonded together to create the image display device 11.

  It is preferable that the above-mentioned production process is performed in a vacuum environment, and this can suppress the occurrence of foaming, peeling, and floating of the pressure-sensitive adhesive composition 7. Moreover, when the image display module 4 and the surface protection board 1 are bonded together by the adhesive composition 7, a heat-pressing process is performed after bonding. Thereby, generation | occurrence | production of foaming, peeling, etc. of the adhesive composition 7 by bonding can be suppressed. Further, durability in a high temperature and high humidity state (for example, 60 ° C. 95% RH, left for 168 hours) can be improved.

As described above, the pressure-sensitive adhesive sheet 10 is used for the purpose of filling the space between the image display module 4 and the surface protection plate 1 (or between these and the touch panel). Excellent durability in wet environments. As a result, the surface protection plate 1 and the image display module 4 can be adhered well. In addition, since the pressure-sensitive adhesive composition 7 absorbs the impact applied to the surface protection plate 1 satisfactorily, it is possible to prevent the impact from being transmitted to the image display module 4. Moreover, since the surface protection board 1 and the image display module 4 can be bonded using the adhesive sheet 10, the image display apparatus 11 can be created easily and air bubbles are mixed into the adhesive composition 7. Can be prevented. Furthermore, since the adhesive composition 7 exhibits high transparency, it becomes possible to improve the visibility of the image displayed on the image display module 4.
Example 1

The present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited by these. Hereinafter, 1. Details of evaluation sample, 2. 2. Evaluation method, It demonstrates in order of an evaluation result.
1. Evaluation sample details

  First, the adjustment method of an adhesive solution is demonstrated. The monomer used as the base of the polymer was blended based on the types and parts by weight shown in Tables 1 and 2. To the blended monomer, 0.6 part by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator was added and copolymerized. Next, 30 parts by weight of the polymer produced by copolymerization was dissolved in 70 parts by weight of solvent (a solvent obtained by mixing 20 parts by weight of toluene and 50 parts by weight of ethyl acetate). As a result, a polymer solution having a solid content of 45% by weight was obtained. The respective weight average molecular weights (Mw) are as shown in Tables 1 and 2. Next, a crosslinking agent and a silane coupling agent of the types and amounts shown in Table 3 and Table 4 were added to the obtained polymer solution to obtain an adhesive solution.

  As the acrylic acid alkyl ester, methyl acrylate (MA), n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and methyl methacrylate (MMA) were used. 2-hydroxyethyl acrylate (2HEA) was used as the hydroxyl group-containing monomer. Vinyl acetate (VAc) was used. Acrylic acid (AA) was used as a carboxylic acid group-containing monomer.

  As an isocyanate-based crosslinking agent, trimethylolpropane xylylene diisocyanate (XDI-TMP) (Takenate D110N, manufactured by Mitsui Takeda Chemical Co., Ltd.) (indicated in the table as “XDI”), trimethylolpropane tolylene diisocyanate (TDI-TMP) (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) (indicated as “TDI” in the table), Trimethylolpropane hexamethylene diisocyanate (HDI-TMP) (Coronate HL, manufactured by Nippon Polyurethane Industry Co., Ltd.) ”). As the epoxy crosslinking agent, N, N, N ′, N′-tetraglycidylaminophenylmethane (Tetrad X, manufactured by Mitsubishi Gas Chemical Company) was used. As a silane coupling agent, 3-glycidoxypropyltrimethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) was used.

  The manufacturing method of the adhesive sheet 10 is demonstrated. A release sheet 5 made of a PET film having a thickness of 75 μm and having a silicone resin coated on one side was prepared. Next, the pressure-sensitive adhesive solution prepared above was applied to the silicone resin-coated surface of the release sheet 5 and dried at 100 ° C. for 3 minutes. Thereby, the pressure-sensitive adhesive layer 3 having a thickness of 100 μm after drying was formed.

  Next, a release sheet 6 made of a PET film having a thickness of 38 μm is bonded to the surface of the pressure-sensitive adhesive layer 3 opposite to the side on which the release sheet 5 is applied, and is 23 ± 2 ° C. and 50 ± 5%. Aged for over a week. In addition, the kind of release agent was selected so that the relationship between the release forces of the release sheets 5 and 6 could be “release sheet 5> release sheet 6”. In this way, an adhesive sheet 10 for evaluation was obtained. However, in Comparative Example 4 which does not contain a carboxyl group-containing monomer, the crosslinking reaction is difficult to proceed. Therefore, the mixture was heated to 40 ± 2 ° C. and aged for 3 days or more. The aging period does not need to be exactly one week (three days), and the period is not particularly limited as long as it is one week (three days) or longer.

２．評価方法および評価結果

2. Evaluation method and result

About the adhesive sheet 10 (Examples 1-29, Comparative Examples 1-5) created as mentioned above and the adhesive composition 7 which comprises these, (1) Adhesive physical property (ball tack, adhesive force, holding power) (2) Storage elastic modulus (3) Embeddability (4) Durability (appearance, color tone change) was evaluated. Details of the measurement and evaluation methods are shown below.
(1) Physical properties of adhesive (1-a) Ball tack

  JIS Z 0237 (established in 1980 (revised 2000)) conformed to the inclined ball tack test. A test piece was attached to a 30-degree inclined plate, and a ball was rolled on the surface of the test piece. The maximum ball number that stops in the measuring section was the ball tack value. The results are shown in Tables 5 and 6.

When the ball tack is 12 or more, when the surface protection plate with a printed step and the image display module are bonded together, the adhesiveness of the printed step portion is good and the entrapment of bubbles is reduced. In particular, when the ball tack is 18 or more, good adhesion is achieved even when the height of the printed step is 20 μm. However, if the ball tack exceeds 30, the adhesive composition 7 tends to protrude from the end when processing into a sheet shape. In addition, the adhesive composition 7 tends to protrude due to heat inside the image display device. When the ball tack is less than 12, the tackiness is low in the first place, so that the floating is likely to occur.
(1-b) Adhesive strength

  JIS Z 0237 (established in 1980 (revised 2000)) conformed to 180-degree peeling adhesion test. The release sheets 5 and 6 were peeled off, bonded to a 100 μm-thick PET film on one side, and cut into a width of 25 mm was used as a test piece. The side where the pressure-sensitive adhesive composition 7 was exposed was pressure-bonded to a soda lime glass plate (hereinafter simply referred to as “glass plate”), and the adhesive strength after 24 hours was measured. The results are shown in Tables 5 and 6.

When the adhesive strength is 7 N / 25 mm or less, peeling off from the printed step portion of the surface protection plate is likely to occur at high temperature and high temperature and humidity.
(1-c) Holding power

  JIS Z 0237 (established in 1980 (revised 2000)) conforming to the holding power test. A test piece was prepared by peeling the release sheet 6 and bonding it to a 100 μm thick PET film on one side. The release sheet 5 of the test piece consisting of the PET film, the pressure-sensitive adhesive layer 3 and the release sheet 5 was peeled off and pressure-bonded so that the pressure-sensitive adhesive layer 3 was in contact with the SUS304 plate with an area of 25 mm × 25 mm. Whether the SUS304 plate and the test piece hang vertically under a temperature of 40 ° C and a humidity of 65%, a load of 1 kg is applied to the end of the test piece, and the distance after 17 hours or whether the test piece falls from the test piece Was measured. The results are shown in Tables 5 and 6. When dropped from the test piece, it was indicated as “x”.

When the deviation after 17 hours is 3 mm or more or falls within 17 hours, the holding power is lowered under the high temperature and high humidity required for the image display device.
(2) Storage modulus

  The storage elastic modulus of the pressure-sensitive adhesive composition 7 was measured for the purpose of evaluating the properties of the pressure-sensitive adhesive composition 7 as a viscoelastic body. Using a viscoelasticity measuring device (manufactured by Nippon Sebel Hegner, product number: MCR301), the storage elastic modulus (G ′) at 25 ° C. and 1 Hz of the pressure-sensitive adhesive composition 7 used for each sample was measured. The results are shown in Tables 5 and 6.

When the storage elastic modulus is 9.0 × 10 ⁴ or less, when the surface protective plate with a printed step and the image display module are bonded together, the adhesiveness of the printed step portion is good and the entrapment of bubbles is reduced. Furthermore, when the storage elastic modulus is 5.0 × 10 ⁴ or less, even if the printing step is 20 μm, the entrapment of bubbles is reduced. On the other hand, when the storage elastic modulus exceeds 9.0 × 10 ⁴ , the followability to the printing step portion is inferior, so that bubbles are easily caught.
(3) Embeddability

  The pressure-sensitive adhesive composition 7 which was dewed by peeling the release sheet 5 was bonded to the surface protection plate 1 (material: soda lime glass, dimensions: 52 mm × 74 mm) on which the frame-shaped printing unit 2 was printed. . The release sheet 6 was peeled off, and a glass plate that was not printed was bonded. The state immediately after pasting and the state after the heat and pressure treatment (50 ° C., 5 atm, 30 minutes) were observed with a magnifying microscope (VH-6300, manufactured by Keyence Corporation) at a magnification of 100 times. It was judged whether or not bubbles were mixed, floated and peeled. The results are shown in Tables 5 and 6. Two types of surface protection plates 1 (thickness of 10 μm and 20 μm (common to a width of 5 mm)) having different thicknesses of the printing unit 2 were used.

In Tables 5 and 6, “◯” indicates that bubbles are not mixed, floated, or peeled off immediately after application and after pressing. “Δ” indicates that air bubbles are mixed, floated, and peeled immediately after sticking, and that air bubbles are not mixed, floated, and peeled after the heat and pressure treatment. “X” indicates that bubbles were mixed, floated, and peeled in both the state immediately after the application and the state after the heat and pressure treatment.
(4) Durability (appearance, color change)

The durability of the prepared sample was confirmed. A surface protective plate 1 (material: glass plate) on which printing was not performed was bonded to both surfaces of the pressure-sensitive adhesive composition 7. This sample was placed in a constant temperature and humidity chamber maintained at (A) temperature 85 ° C., humidity 0%, (B) temperature 60 ° C. and humidity 95%, and left for 1,000 hours. Thereafter, changes in appearance and color tone were evaluated.
(4-a) Appearance

Appearance evaluation evaluated whether the bubble, the float, and peeling had generate | occur | produced visually about the sample left to stand at predetermined temperature and humidity for 1,000 hours. The results are shown in Tables 5 and 6. In Tables 5 and 6, “◯” indicates that bubbles are not generated, floated, or peeled off. “Δ” indicates that bubbles were generated, but they were not floated and peeled off, and could be used. "X" indicates that bubbles are generated, floated, and peeled off and cannot be used.
(4-b) Color tone change

The prepared sample was allowed to stand for 1,000 hours, and then the transmittance in the visible light region (measurement wavelength: 380 to 780 nm) was measured with an ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation, model number: UV-3150). (A) Temperature was 85 ° C., humidity was 0%, and (B) temperature was 60 ° C., humidity was 95%. According to JIS-Z-8729-1994, color tones L ^* , a ^* , b ^* were calculated, respectively. The color tone change ΔE ^* was determined by the following equation.
ΔE ^* = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^1/2
Here, L ^* represents lightness, a ^* value, and b ^* value represents color coordinates. The results are shown in Tables 5 and 6.

  When the color tone change is 0.5 or less, the color tone change is small and the transparency is excellent. When the color tone change exceeds 0.5, a color tone change such as yellowing is observed and the transparency is inferior, but it is in a practically usable range. If it exceeds 1.0, the degree of color tone change such as yellowing becomes large, and it becomes a level that can be visually confirmed, which is not preferable in actual use.

３．評価結果

3. Evaluation results

  The pressure-sensitive adhesive sheets of Examples 1 to 29 and Comparative Examples 1 to 5 each have a total light transmittance of 85% or more measured in the wavelength range of 380 nm to 780 nm with an ultraviolet-visible spectrophotometer (UV-3150: manufactured by Shimadzu Corporation). It was an adhesive sheet excellent in transparency that can be used by being bonded to a surface protection plate, an image display module, a touch panel or the like of an image display device.

  As shown in the table, Examples are at least a polymer in which an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer are copolymerized, and the weight ratio of the carboxyl group-containing monomer in the polymer is 0. 0.01 to 1.0 parts by weight and contains a cross-linking agent, so the image display device is excellent in visibility (total light transmittance), easy to process, and attached to a surface protection plate with print such as a mobile phone. High initial adhesion (tacking force) when combined, good followability of embedding in printing steps, no bubbles remaining, no change in appearance and color tone under high temperature and high temperature and humidity environment, durability and stability A pressure-sensitive adhesive composition having excellent surface properties and a pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive composition as a pressure-sensitive adhesive layer.

  On the other hand, the comparative example is not a polymer in which an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer are copolymerized, or the weight ratio of the carboxyl group-containing monomer in the polymer exceeds 1.0 part by weight. Therefore, an adhesive composition inferior in visibility (total light transmittance), ease of processing, initial adhesion (tack force), embedding followability, durability and stability of an image display device and the adhesive composition It is an adhesive sheet provided as a layer.

DESCRIPTION OF SYMBOLS 1 Surface protection board 2 Printing part 3 Adhesive layer 4 Image display modules 5 and 6 Release sheet 7 Adhesive composition 10 Adhesive sheet 11 Image display apparatus

Claims (4)

At least a polymer obtained by copolymerization of an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer,
The weight ratio of the carboxyl group-containing monomer in the polymer is 0.01 to 1.0 part by weight,
Contains a crosslinking agent,
A pressure-sensitive adhesive composition having a ball tack of 12 to 30.   The pressure-sensitive adhesive composition according to claim 1, wherein the crosslinking agent is a xylylene diisocyanate crosslinking agent or a hexamethylene diisocyanate crosslinking agent. The acrylic acid alkyl ester is butyl acrylate and 2-ethylhexyl acrylate,
The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the polymer has a weight average molecular weight of 200,000 to 1,000,000. The adhesive sheet which has the said adhesive composition in any one of Claim 1 to 3 as an adhesion layer.

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