Adhesive composition

Abstract

To provide an adhesive composition that has a high elastic modulus while retaining adhesion even if a substrate or an adhesive layer is a thin film, also has excellent thermostability, and suppresses zipping during peeling.SOLUTION: An adhesive composition comprises an acryl copolymer comprising a polymerized monomer composition, which comprises a methacrylic monomer having a substituent with 12 or more carbon atoms (a) of 5-30 wt.%, a vinyl acetate (b) of 5-30 wt.%, a monomer having adjacent carbonyl groups (c) of 5-15 wt.% and a substituted maleimide compound (d) of 0.1-10 wt.%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive composition, and more particularly to an adhesive composition having a high elastic modulus while maintaining adhesiveness.

Background Art

[0002] Adhesives used in the production of light-transmissive members such as touch panels are required to have durability that can maintain transparency and adhesiveness even under high temperature and high humidity. In addition, when used in portable electronic devices, elasticity is also required so that the cover glass on the surface does not scatter due to the impact of dropping. Furthermore, touch panels and portable electronic devices are becoming thinner, and the base material and adhesive layer are also required to be thinner.

Prior Art Documents

Patent Documents

[0003] Patent Document 1 discloses an adhesive for the purpose of preventing glass breakage, but it is a type that can be attached and peeled off multiple times for alignment, and there is room for improvement in that the adhesive strength cannot be obtained unless the film thickness is increased. In addition, when the elastic modulus is increased, a phenomenon called dipping occurs, in which peeling does not occur continuously during peeling, but after a certain stress is applied, peeling occurs partially at once, making it difficult to perform the peeling workability.

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide an adhesive composition that has a high elastic modulus while maintaining adhesiveness even when the base material and the adhesive layer are thin films, has excellent heat resistance, and suppresses dipping during peeling.

Means for Solving the Problems

[0005] A (meth)acrylic monomer (a) having a substituent with 12 or more carbon atoms, vinyl acetate (b), and a monomer (c) having adjacent carbonyl groups 、 A substituted maleimide compound (d) and containing a (meth)acrylic monomer (e) in which the glass transition temperature of the homopolymer is -30°C or lower, wherein (a) contains isostearyl acrylate and (d) is cyclohexyl maleimide An acrylic copolymer obtained by polymerizing a monomer composition containing and a thermosetting agent The pressure-sensitive adhesive composition contains

Advantages of the Invention

[0006] The pressure-sensitive adhesive composition of the present invention has a high elastic modulus while maintaining the adhesive force even when it is a thin film, and is also excellent in heat resistance. Therefore, when used for the touch panel of a portable electronic device, even if the cover glass on the surface is cracked by the impact of dropping, it is difficult to scatter. In addition, since dipping hardly occurs during peeling, there is no catching feeling and it can be peeled off smoothly.

Embodiments for Carrying Out the Invention

[0007] The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer. The acrylic copolymer is obtained by polymerizing a monomer composition containing a (meth)acrylic monomer and monomers copolymerizable therewith. In the present invention, (meth)acrylic includes acrylic and methacrylic, and the (meth)acrylic monomer refers to a monomer having a (meth)acrylic acid ester structure. The monomer composition includes a (meth)acrylic monomer (a) having a substituent with 12 or more carbon atoms, vinyl acetate (b), a monomer (c) having adjacent carbonyl groups, and a substituted maleimide compound (d).

[0008] By using a (meth)acrylic monomer (a) having a substituent with 12 or more carbon atoms, dipping can be suppressed. Specifically, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, isododecyl (meth)acrylate, isotridecyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, isoheptadecyl (meth)acrylate, etc. can be mentioned. The proportion in the monomer composition is preferably 5 to 30% by weight. By setting it at 5% by weight or more, dipping can be significantly suppressed, and by setting it at 30% by weight or less, there is no risk of a decrease in elastic modulus or durability.

[0009] By using vinyl acetate (b) and a monomer (c) having an adjacent carbonyl group in combination, the elastic modulus, final adhesive strength, and durability can be improved. When only one of them is used, even if the blending amount is increased, one of the performances will decrease, so it is presumed that both act in a composite manner. Examples of the monomer having an adjacent carbonyl group include maleic anhydride. The proportion in the monomer composition is preferably 5 to 30% by weight of vinyl acetate and 5 to 15% by weight of maleic anhydride. When the blending amount is excessive, the initial adhesive strength decreases and dipping is likely to occur, which is not preferable.

[0010] By using a substituted maleimide compound (d), the elastic modulus can be further increased, and furthermore, high adhesive strength can be imparted even when the film thicknesses of the adhesive layer and the base material are thin. Specifically, cyclohexyl maleimide, phenyl maleimide, etc. can be mentioned. The proportion in the monomer composition is preferably 0.1 to 10% by weight.

[0011] Furthermore, by using a (meth)acrylic monomer (e) in which the glass transition temperature of the homopolymer is -30°C or lower, basic adhesive performance can be obtained, and in particular, the initial adhesiveness is improved. Specifically, n-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, etc. can be mentioned. The proportion in the monomer composition is preferably 30 to 70% by weight.

[0012] Within a range that does not impair the effects of the present invention, various monomers other than the above can be used. Hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-chloropropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, amide group-containing monomers such as (meth)acrylamide, dimethyl (meth)acrylamide, diethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, (meth)acryloylmorpholine, N-vinylpyrrolidone, diacetone (meth)acrylamide, carboxyl group-containing monomers such as (meth)acrylic acid, itaconic acid, maleic acid, and styrene, acrylonitrile can be mentioned.

[0013] An acrylic copolymer can be prepared by polymerizing these monomers by known methods such as solution polymerization, emulsion polymerization, bulk polymerization, etc., but solution polymerization is preferred.

[0014] Examples of solvents used in solution polymerization include organic solvents such as methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane, isopropyl alcohol, n-butanol, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monomethyl ether acetate, and propylene carbonate. However, there is no problem in using solvents other than these, and two or more solvents may be used in combination.

[0015] It is preferable to use a thermal decomposition type polymerization initiator as the polymerization initiator. Azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis[N-(2-propenyl)-2-methoxypropionamide], 1-[(1-cyano-1-methylethyl)azo]formamide, 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), [1,1'-azobis(1-acetoxy-1-phenylethane)], etc., lauroyl peroxide, octanoyl peroxide, benzoyl peroxide, ethyl methyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, cumyl peroxineodecanoate, t-hexyl peroxineodecanoate, t-butyl peroxy-2-ethylhexanoate, dicumyl peroxide, isobutyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(2-ethylhexyl) peroxydicarbonate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 3,3,5-trimethylcyclohexanoyl peroxide and other organic peroxide compounds can be used. In addition, it is also possible to carry out redox polymerization by using a reducing agent such as N,N-dimethyltoluidine and N,N-diethyltoluidine in combination with the peroxide compound.

[0016] The polymerization initiator is used in an amount of 0.05 to 3 parts by weight based on 100 parts by weight of the monomer composition. If the amount of the polymerization initiator used is increased, the molecular weight of the obtained copolymer tends to decrease, and if the amount of the polymerization initiator used is decreased, the molecular weight of the obtained copolymer tends to increase.

[0017] It is preferable to blend a curing agent with the acrylic copolymer in the pressure-sensitive adhesive composition of the present invention. By reacting the curing agent with the functional groups in the acrylic copolymer, various physical properties can be improved. Specifically, polyvalent epoxy compounds, polyvalent isocyanate compounds, metal chelate compounds, etc. can be mentioned.

[0018] The storage elastic modulus of the pressure-sensitive adhesive composition of the present invention at a measurement temperature of 25°C and a frequency of 1 Hz is preferably 5×10 5 ~1×10 7 Pa. When it is within this range, when bonding the adherend, the pressure-sensitive adhesive composition does not flow excessively and protrude from the edge of the adherend, and the adherend can be firmly fixed, achieving both the prevention of scattering due to damage to the adherend.

[0019] The pressure-sensitive adhesive composition of the present invention may further contain various additives such as ultraviolet absorbers, near-infrared absorbers, antioxidants, preservatives, fungicides, tackifying resins, plasticizers, defoaming agents, and wettability modifiers.

[0020] When the peeling strength when bonding the pressure-sensitive adhesive film obtained by coating the pressure-sensitive adhesive composition of the present invention on a 23-μm-thick PET film with a film thickness of 13 μm to glass is 15 N / 25 mm or more, it is considered particularly useful for preventing the glass of the touch panel of a portable electronic device from scattering.

[0021] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but these are specific examples and are not particularly limited thereto. All parts are by weight.

Examples

[0022] Example 1 As monomers, 58 parts of butyl acrylate (BA), 15 parts of lauryl acrylate (LA), 1 part of acrylic acid (AA), 15 parts of vinyl acetate, 8 parts of maleic anhydride, 3 parts of cyclohexyl maleimide (CHMI), 0.17 part of azobisdimethylvaleronitrile as a polymerization initiator, and 27 parts of ethyl acetate as a solvent were added to prepare a monomer mixture. 50 parts of ethyl acetate as a solvent was added to a separable flask equipped with a stirrer and a reflux condenser, and the temperature was raised to 65°C. Nitrogen gas was introduced for 30 minutes or more to remove oxygen in the polymerization system. Then, the monomer mixture was dropped over 3 hours while maintaining the temperature at 65 ± 1°C, and the reaction was carried out for 2 hours while maintaining the temperature at 65 ± 1°C. Thereafter, the reaction temperature was raised to 70°C and maintained at 70 ± 1°C for 1 hour, and further the reaction temperature was raised to 78°C and maintained at 78 ± 1°C for 1 hour to complete the polymerization reaction. After completion of the reaction, 67 parts of ethyl acetate was added for dilution to obtain an acrylic copolymer solution which was a pale yellow transparent viscous liquid. The viscosity was 5,000 mPa·s, the solid content was 45%, and the weight average molecular weight was 420,000. Further, 0.05 part by weight of TETRAD-X (manufactured by Mitsubishi Gas Chemical Company, trade name), which is a tetrafunctional epoxy compound, was added based on 100 parts by weight of the acrylic copolymer to obtain the adhesive composition of Example 1.

[0023] Examples 2 to 4, Comparative Examples 1 to 5 Except for the materials used in Example 1, a monomer mixture having the formulation described in Table 1 was prepared using 2-ethylhexyl acrylate (2EHA), butyl methacrylate (BMA), phenyl maleimide (PMI), and isostearyl acrylate (ISTA) as monomers, and an acrylic copolymer was prepared in the same manner as in Example 1. Further, TETRAD-X or Narsem Aluminum (manufactured by Nippon Chemical Industry Co., Ltd., trade name) was added in the formulation described in Table 1 to prepare the adhesive compositions of Examples 2 to 4 and Comparative Examples 1 to 5 having a solid content of 45%.

[0024]

Table 1

[0025] Production of the pressure-sensitive adhesive sheet The adhesive composition was applied onto a release film (PET film treated with silicone) so that the thickness after drying was 13 μm. After heating and drying at 100 °C for 2 minutes, a PET film with a film thickness of 23 μm was laminated, and this sheet was left standing in an atmosphere of 40 °C and 50% RH for 3 days to obtain an adhesive sheet.

[0026] Storage elastic modulus The films on both sides of the adhesive sheet were peeled off to prepare an adhesive film. Using a DMA (DMS6100 type) manufactured by Hitachi High-Technologies Corporation, the storage elastic modulus of each was measured under the conditions of a frequency of 1 Hz, a temperature of 23 °C, and a sample thickness of 400 μm.

[0027] Adhesive strength The adhesive sheet was cut into strips with a width of 25 mm, the release film was peeled off, and it was laminated onto glass with a hand roller for 2 round trips to prepare test pieces. They were left standing in an atmosphere of 23 °C and 50% RH for 24 hours, pulled in the 180° direction at a pulling speed of 300 mm / min, and the central value was taken as the adhesive strength.

[0028] Dipping When measuring the above-mentioned adhesive strength, the presence or absence of dipping was confirmed. The evaluation criteria are as follows. ○: Without dipping ×: With dipping

[0029] Damp heat test The adhesive sheet was cut into strips with a width of 25 mm, the release film was peeled off, and it was laminated onto glass with a hand roller for 2 round trips to prepare test pieces. After leaving them standing in an atmosphere of 23 °C and 50% RH for 24 hours, they were left standing in an atmosphere of 85 °C × 85% RH for 72 hours, and after cooling for 1 hour in an atmosphere of 23 °C and 50% RH, the presence or absence of foaming and whitening was confirmed. The haze was measured using a HAZE-GARDII manufactured by Toyo Seiki Seisakusho Co., Ltd. The evaluation criteria are as follows. ○: Haze is less than 1.5 ×: Haze is 1.5 or more ○: Without foaming ×: With foaming

[0030] Each of the adhesive compositions of the examples exhibited a high storage elastic modulus, was able to impart a high adhesive force even in the form of a thin film, and furthermore was excellent in resistance to wet heat without dipping during peeling.

Claims

1. An acrylic copolymer obtained by polymerizing a monomer composition containing a (meth)acrylic monomer (a) having a substituent with 12 or more carbon atoms, vinyl acetate (b), a monomer (c) having adjacent carbonyl groups, a substituted maleimide compound (d), and a (meth)acrylic monomer (e) whose homopolymer has a glass transition temperature of -30°C or lower, wherein the (a) contains isostearyl acrylate and the (d) contains cyclohexyl maleimide, and an adhesive composition containing a thermosetting agent.

2. In the blending ratio in the monomer composition, the (meth)acrylic monomer (a) having a substituent with 12 or more carbon atoms is 5 to 30% by weight, vinyl acetate (b) is 5 to 30% by weight, the monomer (c) having adjacent carbonyl groups is 5 to 15% by weight, the substituted maleimide compound (d) is 0.1 to 10% by weight, and the (meth)acrylic monomer (e) whose homopolymer has a glass transition temperature of -30°C or lower is 30 to 70% by weight. The adhesive composition according to Claim 1.

3. The storage elastic modulus at a measurement temperature of 25°C and a frequency of 1 Hz is 5 × 10 ５ to 5 × 10 ７ Pa, and the pressure-sensitive adhesive composition according to claim 1 or 2, characterized in that.

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