Adhesive composition, adhesive sheet, and reinforcing film

Abstract

A pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet (2) contains an acrylic base polymer, a crosslinking agent, an acrylic oligomer having a weight-average molecular weight of 1000-30,000 and a glass transition temperature of 40 DEG C or higher, an antistatic agent, and a polyol having a number-average molecular weight of 600-30,000. In the adhesive composition, the content of the acrylic oligomer is preferably 1-50 parts by weight and the content of the polyol is preferably 3-70 parts by weight with respect to 100 parts by weight of the acrylic base polymer, and the content of the antistatic agent is preferably 0.01-2% by weight with respect to the total amount of non-volatile components of the adhesive composition.

Description

Technical Field

[0001] The present invention relates to an adhesive composition and an adhesive sheet. Furthermore, the present invention relates to a reinforcing film in which an adhesive sheet is laminated and bonded to a film substrate. Background Art

[0002] Before the device is used, such as during assembly, processing, and transportation, the adhesive film is temporarily bonded to the surface of the device or the device component, thereby suppressing damage and breakage of the adherend. This adhesive film is a step material and is peeled off and removed from the adherend before the device is used. For example, Patent Document 1 discloses a surface protective film having an adhesive layer with weak adhesion on a plastic substrate, and records that the adhesive has antistatic properties, which can suppress the adherend from being charged due to static electricity when the surface protective film is peeled off.

[0003] Patent document 2 records that by attaching a protective film (reinforcement film) having an adhesive layer on a film substrate to the back of a substrate of a display, in addition to suppressing the occurrence of adverse conditions during the manufacturing process of the device, it is also possible to suppress the occurrence of adverse conditions in the use environment of the device. Such a reinforcement film does not need to be peeled off from the device even in the use environment of the device, but is used while maintaining the reinforcement film and the device in contact. Therefore, as an adhesive for the reinforcement film, a strong adhesive for the purpose of permanently bonding the adherend can be used.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-111856

[0007] Patent Document 2: Japanese Patent Application Publication No. 2017-219843 Summary of the invention

[0008] Problems to be solved by the invention

[0009] Insulating materials such as glass and resin films are used in the substrates of display devices, so the devices are easily charged. In particular, the substrates of devices using resin film substrates such as foldable devices are easily charged, which may cause electrostatic damage to the devices due to static electricity.

[0010] As a method of suppressing the charging of insulating substrates, it is considered to reduce the resistance by making the adhesive of the reinforcing film attached to the substrate contain an antistatic agent, thereby removing the static electricity of the substrate. However, even if an antistatic agent is added to a common adhesive such as an acrylic adhesive, the resistance will not be sufficiently reduced. If the amount of antistatic agent added is increased, the antistatic agent will seep out and cause corrosion of the metal wiring provided on the substrate.

[0011] In view of the above circumstances, an object of the present invention is to provide an adhesive and an adhesive sheet having high adhesive strength to glass and resin films and excellent antistatic properties.

[0012] Solutions for solving problems

[0013] The present invention relates to an adhesive composition and an adhesive sheet formed into a layer of the adhesive composition. The adhesive composition comprises an acrylic base polymer, a crosslinking agent, an acrylic oligomer, an antistatic agent and a polyol. The content of the antistatic agent is preferably 0.01 to 2 weight % relative to the total amount of non-volatile components of the adhesive composition.

[0014] The acrylic base polymer contains an alkyl (meth)acrylate as a monomer unit. The acrylic base polymer may also contain butyl acrylate as a monomer unit. The amount of butyl acrylate may be 70% by weight or more relative to the total amount of monomer components constituting the acrylic base polymer.

[0015] The acrylic base polymer contains one or more monomer units selected from the group consisting of a hydroxyl-containing monomer and a carboxyl-containing monomer. The total amount of the carboxyl-containing monomer and the hydroxyl-containing monomer is preferably 0.1 to 15% by weight relative to the total amount of the monomer components constituting the acrylic base polymer. In the acrylic base polymer, the amount of the carboxyl-containing monomer can be 0.1 to 15% by weight relative to the total amount of the monomer components constituting the acrylic base polymer.

[0016] The crosslinking agent can bond with the carboxyl group and / or hydroxyl group of the acrylic base polymer, and a crosslinking structure is introduced by bonding the crosslinking agent with the carboxyl group and / or hydroxyl group of the acrylic base polymer. When the acrylic base polymer contains a carboxyl group, the crosslinking agent is preferably an epoxy crosslinking agent. The content of the crosslinking agent in the adhesive composition is preferably 0.03 to 2 parts by weight relative to 100 parts by weight of the acrylic base polymer.

[0017] The weight average molecular weight of the acrylic oligomer is 1,000 to 30,000, and the glass transition temperature is 40° C. or higher. The content of the acrylic oligomer in the pressure-sensitive adhesive composition is preferably 1 to 50 parts by weight based on 100 parts by weight of the acrylic base polymer.

[0018] The number average molecular weight of the polyol is 1000 to 30000. The polyol may not contain an ethylene oxide chain. The polyol may be polypropylene glycol or polytetramethylene glycol. The polyol may be a diol type or a triol type. The content of the polyol in the adhesive composition is preferably 3 to 70 parts by weight relative to 100 parts by weight of the acrylic base polymer.

[0019] By forming the adhesive composition into a layer, an adhesive sheet can be obtained. In the adhesive sheet, the acrylic base polymer is preferably crosslinked by a crosslinking agent. The reinforcing film includes the adhesive sheet on one main surface of a film substrate.

[0020] The content of the antistatic agent in the adhesive sheet is preferably 0.01 to 2 wt%. The surface resistance of the adhesive sheet is preferably 9.0×10 11 The adhesive strength of the adhesive sheet to the glass is preferably 5N / 25mm or more.

[0021] Effects of the Invention

[0022] The adhesive composition and the adhesive sheet have high adhesive force to the adherend and can be used as a strong adhesive sheet for the purpose of permanently bonding the adherend. Since the adhesive composition contains a polyol in addition to the antistatic agent, the adhesive sheet can be made low-resistance even when the amount of the antistatic agent is small, which helps to prevent static electricity on the adherend and prevent metal corrosion of the adherend. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a cross-sectional view showing the laminated structure of the reinforcing film.

[0024] Figure 2 It is a cross-sectional view showing the laminated structure of the reinforcing film. DETAILED DESCRIPTION

[0025] Figure 1 1 is a cross-sectional view showing an embodiment of a reinforcement film. The reinforcement film 10 includes an adhesive sheet 2 on one main surface of a film substrate 1. The adhesive sheet 2 is laminated on one main surface of the film substrate 1. Figure 2 As shown, a release liner 5 may be temporarily bonded to the adhesive sheet 2 of the reinforcement film 10 .

[0026] The PSA sheet 2 has strong adhesive properties and is intended to permanently bond an adherend. The PSA sheet 2 is formed by forming a PSA composition into a layer and crosslinking a base polymer of the PSA composition.

[0027] [Adhesive composition]

[0028] The adhesive composition used for forming the adhesive sheet 2 contains an acrylic base polymer, a crosslinking agent, an acrylic oligomer, an antistatic agent, and a polyol. Preferred embodiments of the components constituting the adhesive composition will be described below in order.

[0029] <Base polymer>

[0030] The base polymer is the main constituent of the PSA composition. From the viewpoint of excellent adhesion to an adherend, an acrylic polymer is used as the base polymer of the PSA composition.

[0031] As the acrylic polymer, it is preferable to use a polymer containing an alkyl (meth)acrylate as a main monomer component. In addition, in this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0032] As the alkyl (meth)acrylate, it is preferred to use an alkyl (meth)acrylate having an alkyl group with 1 to 20 carbon atoms. The alkyl group of the alkyl (meth)acrylate may be a straight chain or a branched chain. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, propylene (meth)acrylate, and tert-butyl (meth)acrylate. isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

[0033] Among the alkyl (meth)acrylates exemplified, (meth)acrylate C is preferred because the homopolymer has a low glass transition temperature and can exert adhesive strength to an adherend in a wide temperature range. 1－9 The alkyl ester is preferably a (meth)acrylic acid alkyl ester whose homopolymer has a glass transition temperature of -50°C or lower. 1－9 Specific examples of the alkyl esters include 2-ethylhexyl acrylate (Tg: -70°C), n-hexyl acrylate (Tg: -65°C), n-octyl acrylate (Tg: -65°C), isononyl acrylate (Tg: -60°C), n-nonyl acrylate (Tg: -58°C), isooctyl acrylate (Tg: -58°C), butyl acrylate (Tg: -55°C), etc.

[0034] Among them, butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) are preferred, and butyl acrylate is particularly preferred from the viewpoint of adhesion to the adherend. In addition, acrylic polymers with butyl acrylate as the main constituent monomer have high compatibility with polyols (details will be described below) and can reduce the haze of the adhesive, so butyl acrylate is also particularly preferred as the (meth)acrylic acid alkyl ester from the viewpoint of transparency.

[0035] The content of the alkyl (meth)acrylate is preferably 70% by weight or more, more preferably 80% by weight or more, and further preferably 85% by weight or more, and may be 90% by weight or more, 93% by weight or more, or 95% by weight or more, relative to the total amount of the monomer components constituting the acrylic base polymer. 1－9 The amount of the alkyl ester is within the above range, and more preferably the total amount of 2-ethylhexyl acrylate and butyl acrylate is within the above range. The amount of butyl acrylate may also be within the above range.

[0036] The acrylic base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymer component. Examples of the monomer having a crosslinkable functional group include a hydroxyl-containing monomer and a carboxyl-containing monomer. The acrylic base polymer may contain both a hydroxyl-containing monomer and a carboxyl-containing monomer as copolymer components, or may contain only one of them as a copolymer component. By introducing a crosslinking structure into the acrylic base polymer, the cohesive force is improved, and the adhesive force to the adherend is improved.

[0037] Examples of hydroxyl-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate. Among them, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute greatly to improving the adhesive strength of the adhesive.

[0038] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Among them, acrylic acid is particularly preferred because it contributes greatly to improving adhesive strength.

[0039] In the acrylic base polymer, the total amount of the hydroxyl-containing monomer and the carboxyl-containing monomer is preferably 0.1 to 15% by weight, more preferably 0.5 to 12% by weight, further preferably 1 to 10% by weight, and may be 2 to 8% by weight or 3 to 7% by weight relative to the total amount of the monomer components. In the case where the acrylic base polymer contains a carboxyl group, the acrylic base polymer and the polyol show high compatibility and can reduce the haze of the adhesive. Therefore, in the use form requiring transparency (for example, an adhesive sheet configured on the display surface of a display), the acrylic base polymer preferably contains a carboxyl-containing monomer such as (meth) acrylic acid as a constituent monomer component, and the content of the carboxyl-containing monomer is preferably within the above range.

[0040] The acrylic base polymer may contain nitrogen-containing monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxamides, and N-vinylcaprolactam as constituent monomer components.

[0041] The acrylic base polymer may contain monomer components other than those mentioned above. For example, the acrylic base polymer may contain vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfonic group-containing monomers, phosphoric acid group-containing monomers, acid anhydride group-containing monomers, etc. as monomer components.

[0042] The glass transition temperature of the acrylic base polymer is preferably below -30°C, and may be below -40°C or below -45°C. By making the glass transition temperature of the acrylic base polymer sufficiently lower than the ambient temperature of use, high adhesiveness can be exhibited within the ambient temperature range of use. The lower limit of the glass transition temperature of the acrylic base polymer is not particularly limited, but is usually above -80°C, and may be above -70°C, above -65°C, above -60°C, or above -55°C.

[0043] The glass transition temperature is the temperature (peak temperature) at which the loss tangent tanδ reaches a maximum value in the viscoelasticity measurement. The theoretical Tg calculated according to the Fox equation can be used instead of the glass transition temperature obtained by the viscoelasticity measurement. The theoretical Tg is calculated according to the following Fox equation, and is the glass transition temperature Tg of the homopolymer of the monomer component of the acrylic base polymer. i and the weight fraction W of each monomer component i to calculate.

[0044] 1 / Tg=Σ(W i / Tg i )

[0045] Tg is the glass transition temperature of the polymer chain (unit: K), W i is the weight fraction of monomer component i constituting the chain segment (copolymerization ratio based on weight), Tg i is the glass transition temperature of the homopolymer of monomer component i (unit: K). As the glass transition temperature of the homopolymer, the value described in the third edition of Polymer Handbook (John Wiley & Sons, Inc., 1989) can be used. The Tg of the homopolymer of the monomer not described in the above literature can be the peak temperature of tan δ obtained by dynamic viscoelasticity measurement.

[0046] The above-mentioned monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic polymer as a base polymer. From the perspective of the balance of characteristics such as the adhesion and holding power of the adhesive, and the cost, solution polymerization is preferred. As a solvent for solution polymerization, ethyl acetate, toluene, etc. can be used. The solution concentration is usually about 20 to 80% by weight. As a polymerization initiator, various known polymerization initiators such as azo and peroxide can be used. In order to adjust the molecular weight, a chain transfer agent can be used. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0047] The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. When a crosslinking structure is introduced into the acrylic base polymer, the molecular weight of the acrylic base polymer refers to the molecular weight before the crosslinking structure is introduced.

[0048] <Cross-linking agent>

[0049] The adhesive composition contains a crosslinking agent that can crosslink with the acrylic base polymer by bonding with the carboxyl group and / or hydroxyl group of the acrylic base polymer. For example, the adhesive composition is applied in a layer and then heated as needed to introduce a crosslinking structure into the acrylic base polymer.

[0050] As the crosslinking agent, there can be cited isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, metal chelate crosslinking agents, etc. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the acrylic base polymer to form a crosslinked structure. From the perspective of high reactivity with hydroxyl groups and carboxyl groups of the acrylic base polymer and easy introduction of a crosslinked structure, isocyanate crosslinking agents and epoxy crosslinking agents are preferred.

[0051] As described above, from the viewpoint of compatibility with polyols, the acrylic base polymer preferably has a carboxyl group derived from a carboxyl group-containing monomer such as acrylic acid. It is preferred to introduce a crosslinking structure into the acrylic base polymer having a carboxyl group using an epoxy crosslinking agent.

[0052] As the epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy crosslinking agent may be an epoxy crosslinking agent having three or more or four or more epoxy groups in one molecule. The epoxy group of the epoxy crosslinking agent may be a glycidyl group. Examples of the epoxy crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As the epoxy crosslinking agent, commercially available products such as "DENACOL" manufactured by Nagase ChemteX, and "TETRAD X" and "TETRAD C" manufactured by Mitsubishi Gas Chemical can also be used.

[0053] As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the isocyanate crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trimethylolpropane / toluene diisocyanate trimer adduct (e.g., "TAKENATE D101E" manufactured by Mitsui Chemicals), trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh), trimethylolpropane adduct of xylylene diisocyanate (e.g., "TAKENATE D110N" manufactured by Mitsui Chemicals), isocyanurate of hexamethylene diisocyanate (e.g., "Coronate 100N" manufactured by Tosoh), and isocyanurate of toluene diisocyanate (e.g., "Coronate 100N" manufactured by Mitsui Chemicals). HX") and other isocyanate adducts.

[0054] The amount of the crosslinking agent used may be appropriately adjusted according to the composition and molecular weight of the acrylic base polymer. The amount of the crosslinking agent used is about 0.03 to 2 parts by weight, preferably 0.05 to 1 part by weight, more preferably 0.08 to 0.8 part by weight, and may also be 0.1 to 0.5 part by weight, relative to 100 parts by weight of the acrylic base polymer.

[0055] In order to promote the formation of a crosslinked structure, a crosslinking catalyst may be used. The amount of the crosslinking catalyst used is usually 0.5 parts by weight or less based on 100 parts by weight of the acrylic base polymer.

[0056] <Oligomer>

[0057] The adhesive composition contains an acrylic oligomer having a molecular weight lower than that of the acrylic base polymer. When the adhesive contains an oligomer in addition to the base polymer, the adhesive strength to adherends such as glass and resin films is increased.

[0058] The weight average molecular weight of the acrylic oligomer is about 1000 to 30000. There is a tendency that the greater the molecular weight of the oligomer, the higher the adhesive force. On the other hand, when the molecular weight of the oligomer is too large, its compatibility with the acrylic base polymer tends to decrease. The weight average molecular weight of the acrylic oligomer is preferably 1500 to 10000, more preferably 2000 to 8000, and may also be 2500 to 6000 or 3000 to 5000.

[0059] The glass transition temperature of the acrylic oligomer is preferably above 40°C, more preferably above 50°C, further preferably above 60°C, and may also be above 65°C or above 70°C. By including an acrylic oligomer with a high glass transition temperature in the adhesive composition, the adhesive strength of the adhesive tends to be improved. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, and is usually below 200°C. From the viewpoint of improving the adhesive retention of the adhesive in the low temperature region, the glass transition temperature of the acrylic oligomer is preferably below 190°C, more preferably below 180°C, and may also be below 170°C or below 160°C. The glass transition temperature of the acrylic oligomer can be calculated using the above-mentioned Fox formula.

[0060] The acrylic oligomer contains an alkyl (meth)acrylate as a main monomer component. The content of the alkyl (meth)acrylate in the monomer components of the acrylic oligomer is more preferably 50% by weight or more, further preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, or 90% by weight or more relative to the total amount of the monomer components of the acrylic oligomer.

[0061] Examples of the alkyl (meth)acrylate include alkyl (meth)acrylates having a chain alkyl group (chain alkyl (meth)acrylates) and alkyl (meth)acrylates having an alicyclic alkyl group (alicyclic alkyl (meth)acrylates). Examples of the alkyl (meth)acrylates having a chain alkyl group include those listed above as constituent monomers of the acrylic base polymer.

[0062] Specific examples of the alkyl (meth)acrylate having an alicyclic alkyl group include: cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate and the like; (meth)acrylate having a dicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; (meth)acrylate having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentyl (meth)acrylate, dicyclopentyloxyethyl (meth)acrylate, tricyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate. The alkyl (meth)acrylate having an alicyclic alkyl group may be a compound having a substituent on the ring such as 3,3,5-trimethylcyclohexyl (meth)acrylate. Furthermore, the (meth)acrylate alkyl ester having an alicyclic alkyl group may be a (meth)acrylate having a condensed ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

[0063] From the viewpoint of increasing the glass transition temperature, the acrylic oligomer preferably contains an alkyl (meth)acrylate whose homopolymer glass transition temperature is 40° C. or higher. Among the alkyl (meth)acrylates whose homopolymer glass transition temperature is 40° C. or higher, alicyclic alkyl (meth)acrylates are particularly preferred.

[0064] The acrylic oligomer preferably uses alicyclic alkyl (meth)acrylate as the main constituent monomer. In the acrylic oligomer using alicyclic alkyl (meth)acrylate as the main constituent monomer component, the amount of alicyclic alkyl (meth)acrylate is preferably 50% by weight or more, and may also be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more relative to the total amount of the constituent monomer components. The amount of alicyclic alkyl (meth)acrylate may also be 99% by weight or less, 97% by weight or less, or 95% by weight or less relative to the total amount of the constituent monomer components of the acrylic oligomer.

[0065] The acrylic oligomer having alicyclic alkyl (meth)acrylate as a main constituent monomer may also contain monomer components other than alicyclic alkyl (meth)acrylate. Examples of monomers other than alicyclic alkyl (meth)acrylate include linear alkyl (meth)acrylate, hydroxyl-containing monomers, carboxyl-containing monomers, nitrogen-containing monomers, and the like.

[0066] The acrylic oligomer may contain a functional group capable of bonding with a crosslinking agent, similar to the acrylic base polymer. For example, when an epoxy crosslinking agent is used, if the acrylic oligomer has a carboxyl group, a crosslinking structure may be introduced by the reaction between the carboxyl group of the acrylic oligomer and the epoxy group of the crosslinking agent.

[0067] As an example of an acrylic oligomer having alicyclic alkyl (meth)acrylate as a main constituent monomer, there can be cited an acrylic oligomer having alicyclic alkyl (meth)acrylate with two or fewer rings as a main component and containing 1 to 10% by weight of a carboxyl group-containing monomer such as acrylic acid as a comonomer. As another example of an acrylic oligomer having alicyclic alkyl (meth)acrylate as a main constituent monomer, there can be cited an acrylic oligomer having alicyclic alkyl (meth)acrylate with three or more rings as a main component and containing 10 to 50 parts by weight of a chain alkyl (meth)acrylate having a homopolymer glass transition temperature of 40° C. or higher such as methyl methacrylate as a comonomer.

[0068] The acrylic oligomer can be obtained by polymerizing the above-mentioned monomer components using various polymerization methods. Various polymerization initiators can be used when polymerizing the acrylic oligomer. In addition, a chain transfer agent can also be used for the purpose of adjusting the molecular weight.

[0069] The content of the acrylic oligomer in the adhesive composition is preferably 1 to 50 parts by weight, more preferably 5 to 45 parts by weight, further preferably 10 to 40 parts by weight, and may be 15 to 35 parts by weight or 20 to 30 parts by weight relative to 100 parts by weight of the acrylic base polymer. When the content of the oligomer in the adhesive composition is within the above range, the adhesiveness at high temperature and the high temperature retention tend to be improved.

[0070] <Antistatic Agent>

[0071] Examples of the antistatic agent include ionic compounds containing organic cations, alkali metal salts, ion-conductive polymers, ion-conductive fillers, conductive polymers, etc. Among them, ionic compounds containing organic cations and alkali metal salts are preferred because of their excellent compatibility with the acrylic base polymer.

[0072] The ionic compound containing an organic cation may be an ionic liquid which is liquid at room temperature, or may be an ionic solid which is solid at room temperature. The ionic compound containing an organic cation preferably consists of a fluorine organic anion or a fluorine inorganic anion and an onium cation.

[0073] Examples of the onium cation include nitrogen-containing onium cations, sulfur-containing onium cations (eg, trialkylsulfonium cations), phosphorus-containing onium cations (eg, tetraalkylphosphonium cations), etc. Among them, nitrogen-containing onium cations are preferred.

[0074] Examples of the nitrogen-containing onium cation include pyridinium cation, pyrrolidinium cation, piperidinium cation, cations having a pyrroline skeleton, cations having a pyrrole skeleton, imidazolium cations, tetrahydropyrimidinium cations, dihydropyrimidinium cations, pyrazolium cations, pyrazolinium cations, and tetraalkylammonium cations.

[0075] The fluorinated organic anions constituting the ionic compound containing the organic cation may be completely fluorinated (perfluorinated) or partially fluorinated. As the fluorinated organic anions, perfluoroalkyl sulfonates, bis(fluorosulfonyl)imides, bis(perfluorinated alkanesulfonyl)imides, more specifically, for example, trifluoromethanesulfonates, pentafluoroethanesulfonates, heptafluoropropanesulfonates, nonafluorobutanesulfonates, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, etc. may be cited. As the fluorinated inorganic anions, hexafluorophosphoric acid, tetrafluoroboric acid, etc. may be cited.

[0076] The alkali metal salt is preferably composed of the above-mentioned fluorine organic anion or fluorine inorganic anion and an alkali metal cation. The alkali metal cation is Li + 、Na + or K + , among which Li + .

[0077] The content of the antistatic agent in the adhesive composition is about 0.01 to 3 parts by weight, preferably 0.03 to 2 parts by weight, more preferably 0.05 to 1 part by weight, and further preferably 0.1 to 0.7 parts by weight relative to 100 parts by weight of the acrylic base polymer. The content of the antistatic agent is about 0.01 to 2% by weight, preferably 0.03 to 1% by weight, more preferably 0.05 to 0.7% by weight, further preferably 0.1 to 0.5% by weight, and may also be 0.15 to 0.4% by weight relative to the total amount of non-volatile components in the adhesive composition.

[0078] The content of the antistatic agent is equal to the content of the antistatic agent in the adhesive sheet 2 prepared by removing volatile components such as solvents from the adhesive composition relative to the total amount of non-volatile components of the adhesive composition. If the amount of the antistatic agent is small, the adhesive may not be sufficiently low in resistance. If the amount of the antistatic agent is too much, it may cause corrosion of metal wiring, etc. caused by the antistatic agent, and contamination of the adherend caused by the seeping antistatic agent.

[0079] <Polyol>

[0080] The adhesive composition contains a polyol. Since the adhesive contains a polyol in addition to the antistatic agent, the adhesive has a further lower resistance, so the amount of the antistatic agent used can be reduced, and corrosion of metal wiring and contamination of adherends caused by the antistatic agent can be suppressed.

[0081] Examples of the polyol include a polyol having two hydroxyl groups in one molecule (diol), a polyol having three hydroxyl groups in one molecule (triol), a polyol having four hydroxyl groups in one molecule (tetraol), a polyol having five hydroxyl groups in one molecule (pentaol), and a polyol having six hydroxyl groups in one molecule (hexaol).

[0082] As the polyol, a high molecular weight polyol is preferably used, and the number average molecular weight of the polyol is preferably 600 or more. When the molecular weight of the polyol is less than 600, the polyol is easy to ooze out on the surface of the adhesive sheet, forming an adhesion barrier layer (weak boundary layer: Weak Boundary Layer; WBL) at the bonding interface with the adherend, and there is a tendency for the adhesion to the adherend to decrease. When the molecular weight of the polyol is too large, the compatibility with the acrylic base polymer is low, and the transparency of the adhesive is sometimes reduced (causing white turbidity).

[0083] From the viewpoint of adhesive properties of the adhesive, the number average molecular weight of the polyol is preferably 1000 or more, more preferably 2000 or more, and may be 3000 or more, 4000 or more, or 5000 or more. The larger the molecular weight of the polyol, the greater the adhesive strength of the adhesive tends to be.

[0084] On the other hand, when the molecular weight of the polyol is too large, there is a tendency that the compatibility with the acrylic base polymer is low and the transparency of the adhesive is reduced. Therefore, the number average molecular weight of the polyol is preferably 30,000 or less, more preferably 25,000 or less, further preferably 20,000 or less, and may be 15,000 or less or 12,000 or less.

[0085] Examples of the high molecular weight polyol include polyether polyol, polyester polyol, polycarbonate polyol, caprolactone polyol, etc. Among them, polyether polyol is preferred because it has a high effect of reducing the resistance of the adhesive in the presence of an antistatic agent.

[0086] Polyether polyols can be obtained by ring-opening addition polymerization of alkylene oxides and low molecular weight polyols. Examples of low molecular weight diols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, pentylene glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, etc. Examples of low molecular weight triols include glycerol and trimethylolpropane.

[0087] Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran (tetramethylene oxide).

[0088] By subjecting alkylene oxide to ring-opening addition polymerization of a low molecular weight diol, a diol type polyether polyol can be obtained. By subjecting ethylene oxide to ring-opening addition polymerization of a low molecular weight triol, a triol type polyether polyol can be obtained.

[0089] The polyol is preferably liquid at room temperature because of its high compatibility with the acrylic base polymer and its high resistance-lowering effect on the adhesive in the presence of an antistatic agent such as an ionic liquid. Since high molecular weight polyols having ethylene oxide chains such as polyethylene glycol are solid at room temperature, the polyol preferably does not contain ethylene oxide chains.

[0090] As the polyol, polypropylene glycol or polytetramethylene glycol is preferred, and diol type or triol type is preferred, because it is liquid at room temperature even when the molecular weight is 10,000 or more, and has excellent compatibility with the acrylic base polymer. The freezing point of the polyol is preferably 0°C or less, and may be -5°C or less, -10°C or less, -15°C or less, -20°C or less, or -25°C or less.

[0091] The content of the polyol in the adhesive composition is preferably 3 to 70 parts by weight relative to 100 parts by weight of the acrylic base polymer. If the amount of the polyol is too small, the adhesive may not be sufficiently low in resistance. If the amount of the polyol is too much, the adhesive strength may sometimes be insufficient. The content of the polyol in the adhesive composition is more preferably 5 to 60 parts by weight, more preferably 10 to 50 parts by weight, and may also be 15 to 45 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight relative to 100 parts by weight of the acrylic base polymer.

[0092] <Other ingredients>

[0093] As described above, the adhesive composition contains an antistatic agent and a polyol in addition to the acrylic base polymer, a crosslinking agent and an acrylic oligomer. In addition to the above components, the adhesive composition may contain additives such as a silane coupling agent, a tackifier, a plasticizer, a softener, an anti-degradation agent, a filler, a colorant, an ultraviolet absorber, an antioxidant, and a surfactant within the range that does not impair the characteristics of the present invention.

[0094] [Adhesive sheet and reinforcement film]

[0095] The adhesive composition is applied in a layered form, and the solvent is removed by drying, thereby obtaining an adhesive sheet 2 in which the adhesive is formed in a layered form. By laminating the adhesive sheet 2 on the film substrate 1, a reinforcing film in which the adhesive sheet 2 is laminated on the film substrate 1 can be obtained. When making the reinforcing film, the adhesive composition can be applied on the film substrate 1 to form the adhesive sheet 2 on the film substrate 1, or the adhesive sheet 2 formed on another substrate can be transferred to the film substrate 1.

[0096] By using roller coating, roller lick coating, gravure coating, reverse coating, roller brush, spray coating, dip roller coating, rod coating, blade coating, air knife coating, curtain coating, die lip coating, die coating, etc., the above-mentioned adhesive composition is applied to the substrate, and the solvent is dried and removed as needed to form an adhesive sheet 2. As a drying method, an appropriate method can be appropriately adopted. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and more preferably 10 seconds to 10 minutes.

[0097] While or after the solvent is dried, a crosslinking reaction is carried out by heating or aging, and a crosslinking structure is introduced into the acrylic base polymer by the crosslinking agent. The heating temperature and heating time are appropriately set according to the type of crosslinking agent used, and crosslinking is usually carried out by heating at a range of 20°C to 160°C for about 1 minute to 7 days. The heating for drying and removing the solvent can also serve as the heating for crosslinking.

[0098] When the PSA sheet 2 is formed by applying the PSA composition onto the film substrate 1, a release liner 5 is preferably provided on the PSA sheet 2 for the purpose of protecting the PSA sheet 2. The PSA sheet 2 may be crosslinked after the release liner 5 is provided.

[0099] When an adhesive composition is applied to a release liner 5 to form an adhesive sheet 2, by attaching a film substrate 1 to the adhesive sheet 2, a reinforcing film can be obtained in which the film substrate 1 is bonded to one main surface of the adhesive sheet 2 and the release liner is bonded to the other main surface of the adhesive sheet 2.

[0100] As the film substrate 1 of the reinforcement film, a flexible plastic film can be used. The thickness of the film substrate 1 is, for example, about 4 to 300 μm. From the viewpoint of strengthening adherends such as devices by imparting rigidity and mitigating impact, the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, further preferably 20 μm or more, and particularly preferably 25 μm or more. From the viewpoint of making the film substrate 1 flexible, the thickness of the film substrate is preferably 200 μm or less, more preferably 150 μm or less, and may also be 125 μm or less or 100 μm or less.

[0101] Examples of the plastic material constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyetheretherketone, polyethersulfone, polyarylate resins, and aromatic polyamide resins. In a use form where transparency is required, such as when the film substrate 1 is disposed on a display surface of a display, the film substrate 1 is preferably a transparent film, and as the resin material of the film substrate 1, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; transparent polyimide, and transparent aromatic polyamide are preferably used.

[0102] Functional coatings such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coating layer, and an antireflection layer may also be provided on the surface of the film substrate 1. It should be noted that, in order to make the film substrate 1 and the adhesive sheet 2 adhere to each other, it is preferred that no release layer is provided on the surface of the film substrate 1 on which the adhesive sheet 2 is attached. In the case where an antistatic layer is provided on the surface of the film substrate, it is preferred that an antistatic layer be provided on the surface of the film substrate 1 on which the adhesive layer 2 is attached from the viewpoint of reducing the surface resistance of the adhesive layer.

[0103] As the release liner 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, polyester film, etc. is preferably used. The thickness of the release liner is usually 3 to 200 μm, preferably about 10 to 100 μm. It is preferred that the contact surface of the release liner 5 with the adhesive sheet 2 is subjected to a release treatment using a release agent such as a silicone, fluorine, long-chain alkyl or fatty acid amide, or silica powder. By subjecting the surface of the release liner 5 to a release treatment, when the film substrate 1 and the release liner 5 are peeled off, peeling occurs at the interface between the adhesive sheet 2 and the release liner 5, and the state in which the adhesive sheet 2 is adhered to the film substrate 1 is maintained. As for the release liner 5, an antistatic treatment can be applied to either or both of the release-treated surface and the non-treated surface.

[0104] The thickness of the adhesive sheet 2 is, for example, about 1 to 300 μm. There is a tendency that the greater the thickness of the adhesive sheet 2, the higher the adhesion to the adherend. On the other hand, when the thickness of the adhesive sheet is too large, it is sometimes difficult to handle. Therefore, the thickness of the adhesive sheet 2 is preferably 5 to 100 μm, more preferably 10 to 50 μm. From the viewpoint of thinning, the thickness of the adhesive sheet 2 may also be less than 25 μm, less than 20 μm, or less than 18 μm.

[0105] The surface resistance of the adhesive sheet 2 is preferably 9.0×10 11 Ω or less, more preferably 7.0×10 11 Ω or less, and can also be 5.0×10 11 Ω or less, 4.0×10 11 Ω or less or 3.0×10 11 As described above, the PSA composition constituting the PSA sheet 2 contains an antistatic agent and a polyol, so that the resistance of the PSA sheet 2 can be reduced.

[0106] Since the adhesive sheet 2 has such a surface resistance, static electricity of the adherend to which the adhesive sheet 2 is bonded is removed by the adhesive sheet 2, thereby suppressing the adherend from being charged. Therefore, electrostatic damage and other problems caused by static electricity in the device to which the reinforcing film is bonded can be suppressed.

[0107] The adhesive strength of the adhesive sheet 2 to the glass is preferably 5N / 25mm or more, more preferably 8N / 25mm or more, further preferably 10N / 25mm or more, and can also be 12N / 25mm or more. The adhesive strength of the adhesive sheet 2 to the polyimide film is preferably 3N / 25mm or more, more preferably 5N / 25mm or more, further preferably 8N / 25mm or more, and can also be 10N / 25mm or more. The adhesive strength is obtained by a peel test with a tensile speed of 300mm / min and a peeling angle of 180°. Unless otherwise specified, the adhesive strength is the measured value at 25°C.

[0108] In the use form where transparency is required, such as when the adhesive sheet 2 is arranged on the display surface of a display, the total light transmittance of the adhesive sheet 2 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. In the case where transparency is required for the adhesive sheet 2, the haze of the adhesive sheet 2 is preferably 2% or less, more preferably 1% or less, further preferably 0.7% or less, particularly preferably 0.5% or less, and may also be 0.3% or less. As described above, when the acrylic base polymer contains a carboxyl group, the acrylic base polymer and the polyol show high compatibility, so a low haze adhesive sheet can be obtained.

[0109] The adhesive sheet 2 of the present invention can be used as a double-sided adhesive sheet for bonding various components, and as described above, can also be used as a reinforcing film in which the adhesive sheet 2 is laminated on a film substrate 1. The type of adherend of the reinforcing film is not particularly limited, and examples thereof include various resin materials, glass, metal, and the like.

[0110] The reinforcement film can also be used as a back protective film of the display. By attaching the adhesive sheet 2 of the reinforcement film as a surface protective film to the back of the display substrate, appropriate rigidity is given, and stress is relaxed and dispersed, thereby suppressing various adverse conditions that may occur in the manufacturing steps, improving production efficiency, and improving yield rate.

[0111] When the device is used after completion, even if an external force is accidentally applied due to the device being dropped, a heavy object being placed on the device, or a flying object colliding with the device, the device can be prevented from being damaged by the bonding reinforcement film. In addition, the adhesive sheet 2 has a high adhesive force, so the reinforcement film is firmly bonded to the adherend, and even if it is used for a long time, the reinforcement film is not easy to peel off, and the reliability is excellent.

[0112] Moreover, the adhesive sheet 2 has a low resistance, so the static electricity of the adherend can be removed by the adhesive sheet 2, and the electrostatic damage of the device caused by charging (static electricity) can be suppressed. In addition, the adhesive sheet 2 has low corrosion to metals, so when it is attached to an insulating substrate provided with metal wiring, the degradation caused by corrosion of the metal wiring can be prevented.

[0113] Example

[0114] The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0115] [Polymerization of acrylic acid-based polymer]

[0116] <Polymer A>

[0117] In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet pipe, 95 parts by weight of butyl acrylate (BA) and 4 parts by weight of acrylic acid (AA) as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent were added, and nitrogen was introduced and nitrogen replacement was performed for about 1 hour while stirring. Then, the mixture was heated to 60° C. and reacted for 7 hours to obtain a solution of an acrylic polymer A having a weight average molecular weight (Mw) of 600,000.

[0118] <Polymer B, C>

[0119] The amount of monomer added was changed as shown in Table 1. Solutions of polymers B and C were obtained in the same manner as in the polymerization of polymer A except for the above.

[0120] The ratio of added monomers of acrylic polymers A to C is shown in Table 1. The numerical values ​​in parentheses of the composition ratios in Table 1 are weight ratios (%) of monomers, and the monomers are described by the following abbreviations.

[0121] BA: Butyl acrylate.

[0122] 2EHA: 2-ethylhexyl acrylate.

[0123] AA: Acrylic acid.

[0124] 2HEA: 2-Hydroxyethyl acrylate.

[0125] [Polymerization of acrylic oligomer]

[0126] In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet tube, 95 parts by weight of cyclohexyl methacrylate and 5 parts by weight of acrylic acid as monomers, 0.2 parts by weight of AIBN as a polymerization initiator, and 103.2 parts by weight of toluene as a solvent were added, and nitrogen was introduced and nitrogen substitution was performed for about 1 hour while stirring. Then, the reaction was heated to 70° C. for 3 hours and then at 75° C. for 2 hours to obtain a solution of an acrylic oligomer having a weight average molecular weight (Mw) of 4000.

[0127] [Preparation of adhesive sheet]

[0128] <Example 1>

[0129] (Preparation of Adhesive Composition)

[0130] To a solution of acrylic polymer A (based on 100 weight of the solid content of the polymer), 0.8 weight parts of a tetrafunctional epoxy crosslinking agent ("TETRAD C" manufactured by Mitsubishi Gas Chemical) as a crosslinking agent, 25 weight parts of the above-mentioned acrylic oligomer based on the solid content, 0.31 weight parts of 1-butyl-3-methylpyridinium bistrifluoromethanesulfonyl imide salt ("CIL-312" manufactured by Japan Carlit) as an antistatic agent, and 5 weight parts of polypropylene glycol ("PREMINOLS3011" manufactured by AGC) as a polyol were added and uniformly mixed to prepare an adhesive composition having the composition shown in Table 1.

[0131] <Application and cross-linking of adhesive solution>

[0132] The adhesive composition was applied to a polyethylene terephthalate film of 70 μm thickness without surface treatment using an applicator in such a manner that the thickness after drying became 15 μm. After drying at 130° C. for 1 minute to remove the solvent, the release-treated surface of a release liner (polyethylene terephthalate film of 25 μm thickness with one side subjected to silicone release treatment) was attached to the applied surface of the adhesive. Then, an aging treatment was performed for 4 days in an atmosphere of 25° C., and cross-linking was performed to obtain an adhesive film (reinforcement film) in which an adhesive sheet was laminated on a polyethylene terephthalate film substrate and a release liner was temporarily bonded thereon.

[0133] <Examples 2 to 17, Comparative Examples 1 to 11>

[0134] The type of acrylic polymer, the type and amount of crosslinking agent, the amount of acrylic oligomer, the type and amount of antistatic agent, and the type and amount of polyol were changed as shown in Table 1 to prepare an adhesive composition, and the coating and crosslinking were carried out in the same manner as in Example 1 to produce an adhesive film. In Table 1, the amount of crosslinking agent, oligomer, antistatic agent and polyol is the amount of addition relative to 100 parts by weight of the solid content of acrylic polymer, and the ratio of antistatic agent is the content (weight %) of antistatic agent relative to the total amount of non-volatile components (solid content) of the adhesive composition. The details of the crosslinking agent, antistatic agent and polyol are as follows.

[0135] (Crosslinking agent)

[0136] TC: N,N,N',N'-tetraglycidyl meta-xylylenediamine (tetrafunctional epoxy compound, "TETRAD C" manufactured by Mitsubishi Gas Chemical).

[0137] C-HX: isocyanurate of hexamethylene diisocyanate ("Coronate HX" manufactured by Tosoh).

[0138] (Antistatic Agent)

[0139] CIL312: 1-Butyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide salt ("CIL-312" manufactured by Japan Carlit).

[0140] AS110: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ("ELEXCEL AS-110" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0141] LiTFSI: lithium bis(trifluoromethanesulfonyl imide) ("LBG-43511" manufactured by KISHIDA CHEMICAL).

[0142] (Polyol)

[0143] S3011: polypropylene glycol, triol type ("PREMINOL S3011" manufactured by AGC, Mn=10000).

[0144] GP3000: polypropylene glycol, triol type ("SANNIX GP-3000" manufactured by Sanyo Chemical Industries, Ltd., Mn=3000).

[0145] GP1000: polypropylene glycol, triol type ("SANNIX GP-1000" manufactured by Sanyo Chemical Industries, Ltd., Mn=1000).

[0146] GP400: polypropylene glycol, triol type ("SANNIX GP-400" manufactured by Sanyo Chemical Industries, Ltd., Mn=400).

[0147] GP250: polypropylene glycol, triol type ("SANNIX GP-250" manufactured by Sanyo Chemical Industries, Ltd., Mn=250).

[0148] PP3000: polypropylene glycol, diol type ("SANNIX PP-3000" manufactured by Sanyo Chemical Industries, Ltd., Mn=3000).

[0149] PTGL3000: polytetramethylene glycol, triol type (“PTGL3000” manufactured by Hodogaya Chemical Industries, Ltd., Mn=3000).

[0150] PEG200: polyethylene glycol ("PEG-250" manufactured by Sanyo Chemical Industries, Ltd., Mn=200).

[0151] [evaluate]

[0152] <Haze>

[0153] The test piece obtained by peeling off the release liner from the surface of the reinforcing film cut into 50 mm × 50 mm was used as a sample, and the haze was measured using a haze meter ("HM-150" manufactured by Murakami Color Technology Research Institute) in accordance with JIS-K-7136. The value obtained by subtracting the haze (3.0%) of the polyethylene terephthalate film with a thickness of 70 μm used as the film substrate from the measured value is the haze of the adhesive sheet. Comparative Example 11, in which the haze of the adhesive sheet exceeded 10%, was not evaluated except for corrosion resistance.

[0154] <Surface resistance of adhesive sheet>

[0155] The release liner was peeled off from the adhesive film to expose the adhesive sheet, and a probe ("Model 152P-2P" manufactured by TREK) was brought into contact with the surface of the adhesive sheet under an environment of a temperature of 25°C and a relative humidity of 50%, and the surface resistance was measured using a resistivity meter ("Model 152-1" manufactured by TREK) under the conditions of an applied voltage of 100 V and a voltage application time of 10 seconds.

[0156] <Adhesion to glass>

[0157] A test piece was peeled off from the surface of an adhesive film cut into a size of 25 mm wide x 100 mm long using a hand roller and then bonded to a glass plate to prepare a test sample. The test piece was held with a chuck and the adhesive film was peeled off at 180° at a tensile speed of 300 mm / min to measure the peel strength.

[0158] <Adhesion to polyimide>

[0159] A polyimide film (Ube Industries, Ltd., "Upilex 25S") with a thickness of 25 μm was attached to a glass plate using a double-sided tape (Nitto Denko, Ltd., "No. 531") to obtain a polyimide film substrate for measurement. The release liner was peeled off from the surface of the adhesive film cut into a width of 25 mm × a length of 100 mm, and it was attached to the polyimide film substrate for measurement using a hand roller to prepare a test sample. Using this test sample, the test piece was held with a chuck, and the adhesive film was peeled 180° at a tensile speed of 300 mm / min, and the peel strength was measured.

[0160] <Corrosion resistance>

[0161] The adhesive film was cut into a size of 30 mm × 80 mm and pressed onto a 50 mm × 100 mm aluminum foil using a hand roller to prepare an evaluation sample. After the evaluation sample was placed in an environment of 60°C and 90% relative humidity for 24 hours, the adhesive film was peeled off from the aluminum foil and the surface of the aluminum foil was visually observed. The sample was evaluated as NG if discoloration due to corrosion was observed, and as OK if no discoloration was observed.

[0162] Table 1 shows the composition and evaluation results of the adhesives of each example and comparative example.

[0163] [Table 1]

[0164]

[0165] For Examples 1 to 17 in which the adhesive composition contains an antistatic agent and a high molecular weight polyol in addition to the base polymer, the crosslinking agent and the oligomer, the surface resistance of the adhesive is in the range of 8×10 11Ω or less, and the corrosion resistance to metals is also good. In addition, it shows high adhesion to glass and polyimide films.

[0166] In Comparative Example 10, in which the adhesive composition does not contain an oligomer, the adhesive strength to glass and polyimide film is small, and the adhesive strength is insufficient as an adhesive sheet for the purpose of permanent bonding to an adherend. In Comparative Example 11, in which a polymer C not containing a carboxyl group is used, the adhesive sheet has a high haze and poor transparency. It is believed that the reason for the reduced transparency is the low compatibility of the base polymer with the polyol.

[0167] Comparative Examples 7 to 9 using low molecular weight polyols contained oligomers but had insufficient adhesive strength. In Comparative Example 9 using low molecular weight polyethylene glycol, the adhesive strength was significantly reduced. In addition, in Comparative Examples 8 and 9, the haze of the adhesive sheet was large and the transparency was insufficient. By comparing Examples 4, 7, and 8 with Comparative Examples 7 and 8, the following tendency can be observed: the larger the molecular weight of the polyol, the greater the adhesive strength of the adhesive sheet.

[0168] In Comparative Example 1 in which the adhesive composition does not contain a polyol, the surface resistance of the adhesive sheet exceeds 1×10 12 Ω. In Comparative Example 2, in which the content of the antistatic agent is twice that of Comparative Example 1, the surface resistance of the adhesive sheet is lower than that of Comparative Example 1, but the surface resistance is larger than that of the example, and the antistatic property is poor. In Comparative Example 3, in which the content of the antistatic agent is 10 times that of Comparative Example 1, although the adhesive sheet has a low resistance, metal corrosion is observed in the corrosion resistance test.

[0169] In Comparative Example 4, in which the content of the antistatic agent was the same as that in Comparative Example 3 and the composition contained a polyol, metal corrosion was observed similarly to Comparative Example 3. In Comparative Examples 3 and 4, it is considered that the antistatic agent precipitated on the surface of the PSA sheet caused the metal corrosion.

[0170] In Comparative Example 5, in which the amount of the polyol was 1 part by weight relative to 100 parts by weight of the base polymer, the surface resistance of the PSA sheet exceeded 1×10 12 Ω. In Comparative Example 6, in which the amount of polyol is 80 parts by weight relative to 100 parts by weight of the base polymer, although the adhesive sheet has low resistance, the adhesion to glass and polyimide film is insufficient. By comparing Examples 1 to 6 with Comparative Examples 5 and 6, it can be seen that the greater the amount of polyol added, the lower the resistance of the adhesive sheet and the lower the adhesion to the adherend.

[0171] Comparison of Examples 4, 15, and 16 with Comparative Example 4 shows that, although the surface resistance of the PSA sheet tends to decrease as the amount of the antistatic agent increases, an excessive amount of the antistatic agent may cause metal corrosion.

[0172] From the above results, it can be seen that even if the amount of the antistatic agent is less than 1% by weight, the high molecular weight polyol can be used to maintain high adhesion to the adherend, achieve a sufficiently low resistance, and inhibit metal corrosion. By comparing Examples 4, 12, and 13, it can be seen that regardless of the type of the antistatic agent, the presence of a polyol can achieve a low resistance.

[0173] Example 9 using triol type polytetramethylene glycol as the polyol showed low haze, low electrical resistance, and high adhesive strength similarly to Example 8. The same was true for Example 14 using polytetramethylene glycol as the polyol.

[0174] Comparing Example 11 using polymer A with butyl acrylate as a main constituent monomer and Example 17 using polymer B with 2-ethylhexyl acrylate as a main constituent monomer, it can be seen that Example 11 has lower resistance, higher adhesion, and lower haze, and has more excellent characteristics.

[0175] Description of Reference Numerals

[0176] 2: adhesive sheet; 1: film substrate; 10: reinforcing film; 5: release liner.

Claims

1. An adhesive composition comprising: an acrylic base polymer, a crosslinking agent capable of crosslinking with the acrylic base polymer, an acrylic oligomer, an antistatic agent and a polyol, The acrylic base polymer contains one or more monomer units selected from the group consisting of hydroxyl-containing monomers and carboxyl-containing monomers, and the total amount of the carboxyl-containing monomers and the hydroxyl-containing monomers is 0.1 to 15% by weight relative to the total amount of the constituent monomer components. The acrylic oligomer has a weight average molecular weight of 1,000 to 30,000 and a glass transition temperature of 40° C. or higher. The number average molecular weight of the polyol is 600 to 30,000. The adhesive composition comprises 1 to 50 parts by weight of the acrylic oligomer and 3 to 70 parts by weight of the polyol relative to 100 parts by weight of the acrylic base polymer. The content of the antistatic agent is 0.01 to 2 weight % relative to the total amount of non-volatile components in the composition.

2. The adhesive composition according to claim 1, wherein The acrylic base polymer contains a carboxyl group-containing monomer as a monomer unit, and the amount of the carboxyl group-containing monomer is 0.1 to 15% by weight based on the total amount of the constituent monomer components.

3. The adhesive composition according to claim 2, wherein The crosslinking agent is an epoxy crosslinking agent.

4. The adhesive composition according to any one of claims 1 to 3, wherein The pressure-sensitive adhesive composition includes 0.03 to 2 parts by weight of the cross-linking agent based on 100 parts by weight of the acrylic base polymer.

5. The adhesive composition according to any one of claims 1 to 3, wherein The polyols described do not contain ethylene oxide chains.

6. The adhesive composition according to claim 5, wherein The polyol is polypropylene glycol or polytetramethylene glycol.

7. The adhesive composition according to claim 5, wherein The polyol is of diol type or triol type.

8. The adhesive composition according to any one of claims 1 to 3, wherein The acrylic base polymer contains butyl acrylate as a monomer unit, and the amount of butyl acrylate is 70% by weight or more based on the total amount of the constituent monomer components.

9. An adhesive sheet, wherein: The adhesive composition according to claim 1 is formed into a layer, and the acrylic base polymer is cross-linked by the cross-linking agent.

10. The adhesive sheet according to claim 9, wherein The surface resistance is 9.0×10 11 Ω or less.

11. The adhesive sheet according to claim 9, wherein The adhesion to glass is 5N / 25mm or more. 12 . A reinforcing film comprising the pressure-sensitive adhesive sheet according to claim 9 laminated and bonded to one main surface of a film substrate.

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