TW201936819A - Adhesive sheet, manufacturing method thereof, and method for manufacturing image display device made of an adhesive composition including a base polymer and a photocurable compound - Google Patents

Abstract

The invention relates to a photocurable adhesive sheet; the adhesive sheet (5) is formed in a layer form from an adhesive composition including a base polymer and a photocurable compound. The haze value of the adhesive sheet (5) is 1% or less, the adhesion force to a glass is 1.5 N/10 mm or less, and the storage shear elastic modulus at a temperature of 25 DEG C is 0.15 MPa or less. The glass transition temperature of the adhesive sheet (5) is made to be -3 DEG C or less when the polymerization rate is 99% by curing, and the storage shear elastic modulus at a temperature of 25 DEG C is 0.16 MPa or more.

Description

Adhesive sheet, manufacturing method thereof, and manufacturing method of image display device

The present invention relates to a light-curing adhesive sheet and a method for manufacturing the same. Furthermore, the present invention relates to a method for manufacturing an image display device using the adhesive sheet.

As various image display devices such as mobile phones, smart phones, car navigation devices, personal computer monitors, and televisions, liquid crystal display devices or organic EL display devices are widely used. In order to prevent damage to the image display panel caused by impact from the outer surface, a transparent resin plate or a front transparent plate such as a glass plate (also referred to as a "cover window") may be provided on the visible side of the image display panel. "Wait). In addition, in recent years, devices equipped with a touch panel on the visual recognition side of the image display panel are spreading.

As a method of arranging a front transparent member such as a front transparent plate or a touch panel in front of the image display panel, an "interlayer filling structure" is proposed in which the image display panel and the front transparent member are bonded via an adhesive sheet. Sometimes an adhesive sheet is also provided between the touch panel and the front transparent plate. In the interlayer filling structure, the gaps between the components are filled with an adhesive, so that the refractive index difference at the interface is reduced, and it is possible to suppress a decrease in visibility due to reflection or scattering. In addition, in the interlayer filling structure, the members are bonded and fixed by using an adhesive sheet. Therefore, compared with the case where the front transparent member is fixed only to the case, the front transparent member is less likely to be caused by impact such as dropping. The advantages of peeling.

A colored layer (decorative printing layer) is sometimes formed on the edge of the front transparent member for the purpose of decoration or shading. When an adhesive is bonded to a transparent member having a decorative printing layer, bubbles are easily generated around the printing step. By using an adhesive sheet having a large thickness, it has step-absorptivity, which can suppress defects such as air bubbles from being mixed. In addition, by using a thick adhesive sheet, the impact resistance tends to be improved.

Since a large thickness adhesive sheet can be formed with a uniform thickness, a solventless photocuring adhesive is widely used for the adhesive sheet for interlayer filling (for example, refer to Patent Documents 1 and 2). In the case of using a photo-curable adhesive, a part of the adhesive composition in an uncured state (semi-cured) may be adhered to the adherend, and then light-cured. In this method, the fluidity of the semi-hardened adhesive sheet is high, and therefore, the step absorptivity at the time of bonding is high, and the subsequent holding force can be improved by light curing thereafter.
[Prior technical literature]
[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2014-125524
[Patent Document 2] International Publication No. 2013/161666

[Problems to be solved by the invention]

Previously, the size of the front transparent member covering the window and the like was larger than that of the display panel, and the front transparent member and the casing were bonded together using an adhesive tape or the like in an area further outside than the outer periphery of the display panel. That is, the front transparent member is fixed by combining the bonding to the case and the bonding to the surface of the display panel using an interlayer filling adhesive sheet.

In recent years, centering on mobile devices such as smart mobile phones, narrower or borderless display devices are being promoted. With the narrow frame or borderless, the size of the display panel 10 is the same as or larger than the size of the front transparent member 7. In such a configuration, the casing 9 and the front transparent member 7 cannot be fixed by an adhesive tape or the like, and the front transparent member 7 must be fixed only by the interlayer filling adhesive sheet 5 (see FIG. 2). As a result, a higher adhesive force is required for the interlayer filling adhesive sheet, and peeling due to impact such as dropping is not required in a wide temperature range.

In addition, when the size of the display panel is equal to or larger than that of the front transparent member 7, in order to fill the gap 90 between the case 9 and the front transparent member 7, a resin material may be used for sealing. For example, a resin material in a molten state flows into the gap 90 and is then cooled to room temperature to solidify the resin, thereby sealing with the resin material. When a high-temperature resin flows into the gap 90, the front transparent member 7, the housing 9, and the adhesive sheet 5 reach high temperatures near the gap 90, and are cooled when the resin is cured. The adhesive sheet 5 is required to have durability against deformation stress so that even with such a temperature change, dimensional deformation in the front transparent member and the case does not cause peeling between the adherends.

The conventional glass-adhesive sheet for interlayer filling disclosed in Patent Document 1 and the like has a high glass transition temperature, and therefore has low adhesiveness or impact resistance at low temperatures. On the other hand, the adhesive sheet of low glass temperature disclosed in Patent Document 2 has low adhesion resistance to deformation stress, and it is difficult to have both impact resistance at low temperature and durability against deformation stress during heating and cooling of a resin seal, etc. Sex.

In view of the above circumstances, an object of the present invention is to provide an adhesive sheet having step absorptivity, excellent impact resistance over a wide temperature range, and excellent adhesion to deformation stress.
[Technical means to solve the problem]

The present invention relates to an adhesive sheet in which a base polymer-containing adhesive is formed in a sheet shape. The haze of the adhesive sheet is below 1%.

In one embodiment, the pressure-sensitive adhesive sheet is a light-curable pressure-sensitive adhesive sheet formed by laminating an adhesive composition containing a base polymer and a light-curable compound. The adhesion of the photocurable adhesive sheet to the glass is 1.5 N / 10 mm or more, and the shear storage elastic modulus at a temperature of 25 ° C is 0.15 MPa or less.

The photocurable adhesive composition is preferably in a so-called semi-hardened state, and has a polymerization rate of 90% to 98%. The glass transition temperature of the semi-hardened adhesive sheet is preferably -5 ° C or lower. The peak top value of the loss tangent of the semi-hardened adhesive sheet is preferably 1.6 or more.

One embodiment of the adhesive sheet of the present invention is that the polymerization rate of the adhesive composition is about 99% or more. Such a completely hardened adhesive sheet can be obtained, for example, by light curing of the above-mentioned semi-hardened adhesive sheet. It is also possible to obtain a fully cured adhesive sheet by light curing of a photocurable adhesive sheet having a polymerization rate of less than 90%.

The glass transition temperature of the fully hardened adhesive sheet is preferably -3 ° C or lower. The shear storage elastic modulus G 'at _{25 °} C of the fully hardened adhesive sheet is preferably 0.16 MPa or more. The peak tangent of the loss tangent of the fully hardened adhesive sheet is preferably 1.5 or more. The semi-hardened adhesive sheet preferably has a glass transition temperature at which the polymerization rate is increased to 99% by hardening and G _{'25 ° C} within the above-mentioned range, and more preferably the peak top value of the loss tangent is within the above-mentioned range.

As the base polymer contained in the adhesive sheet, for example, a polymer obtained by crosslinking an acrylic polymer chain with a urethane-based segment is used. In order to satisfy the aforementioned various characteristics, the content of the urethane-based segment is preferably 3 to 30 parts by weight based on 100 parts by weight of the acrylic polymer chain. The weight average molecular weight of the urethane-based segment is preferably 4,000 to 50,000.

The base polymer obtained by cross-linking an acrylic polymer chain with a urethane-based segment is, for example, a monomer component constituting an acrylic polymer chain and having (meth) at least two ends. Obtained by copolymerization of urethane (meth) acrylate of acrylfluorenyl. The polyfunctional urethane (meth) acrylate is preferably a diurethane (meth) acrylate having a (meth) acrylfluorenyl group at both ends.

The weight average molecular weight of the urethane (meth) acrylate is preferably 4,000 to 50,000. The glass transition temperature of the urethane (meth) acrylate is preferably 0 ° C or lower.

An adhesive sheet containing a base polymer obtained by cross-linking an acrylic polymer chain with a urethane-based segment is obtained, for example, by containing an acrylic monomer and / or a partial polymer thereof, The urethane (meth) acrylate composition is applied to the substrate in a layer form, and then the composition is irradiated with active light to be light-cured. The content of the urethane (meth) acrylate in the adhesive composition is preferably 3 to 30 parts by weight based on 100 parts by weight of the total of the acrylic monomer and its partial polymer.

The adhesive sheet of the present invention is used, for example, for bonding a transparent member in an image display device in which a transparent member is disposed on a visual side surface. When a semi-hardened adhesive sheet is used, an image display device can be formed by bonding the adhesive sheet to the above-mentioned transparent member, and then irradiating the adhesive sheet with active light to light-cure the adhesive sheet.
[Effect of the invention]

The adhesive sheet of the present invention has lower glass transition temperature and larger shear storage elastic modulus after being completely hardened, and therefore, it can have both impact resistance such as drop in a wide temperature range and subsequent durability to deformation stress. Sex. In addition, in the semi-hardened state, the shear storage elastic modulus is small, and therefore, the step absorbency is excellent. An image display device in which an adhesive sheet of the present invention is bonded to a visible side surface with a cover window or the like has excellent bonding reliability, and can also respond to narrow frame or frameless.

FIG. 1 shows an adhesive sheet with a release film 1 and 2 temporarily attached to both sides of the adhesive sheet 5. FIG. 2 is a cross-sectional view showing a configuration example of an image display device in which a front transparent plate 7 is fixed using an adhesive sheet.

[Physical properties of adhesive sheet]
The adhesive sheet of the present invention is an adhesive sheet in which the adhesive is formed in a sheet shape. The adhesive sheet is a transparent adhesive sheet having a haze of less than 1.0%.

In one embodiment, the adhesive constituting the adhesive sheet is a photocurable adhesive containing a monomer or oligomer (photopolymerizable compound) having a photopolymerizable functional group. The polymerization rate of the photocurable adhesive sheet is preferably 90 to 98%. In other words, the photocurable adhesive sheet is preferably in a semi-cured state and contains 2 to 10% by weight of a photopolymerizable compound. The polymerization rate of the adhesive sheet is calculated from the weight before and after heating the adhesive sheet at 130 ° C. for 3 hours, and is calculated according to the following formula. The polymerization rate of the prepolymer described later was also calculated by the same method.
Polymerization rate (%) = weight after drying / weight before drying × 100

Causes the adhesive sheet having the step absorbability, prevent air bubbles from mixing in the vicinity of the printing step difference viewpoint, the temperature of the semi-cured adhesive sheet of 25 deg.] C under the shear storage elastic modulus G _{'25 ℃} preferably 0.15 MPa or less . On the other hand, from the viewpoint of the moldability or operability of the adhesive sheet, the G _{'25 ° C of the} semi-hardened adhesive sheet is preferably 0.03 MPa or more, more preferably 0.05 MPa or more, and even more preferably 0.07 MPa or more.

When the semi-hardened adhesive sheet is adhered to the adherend and then subjected to photohardening (post-hardening), the polymerization rate increases by the polymerization reaction of the photopolymerizable compound, and the shear storage elastic modulus of the adhesive sheet increases. The shear storage elastic modulus G 'at _{25 ° C} of the adhesive sheet after complete hardening (when the polymerization rate is set to 99% or more) obtained by post-hardening is preferably 0.16 MPa or more. The G _{'25 ℃} of the fully cured adhesive sheet is 0.16 MPa or more, and then the reliability is improved. From the viewpoint of improving the adhesion reliability at high temperature, the shear storage elastic modulus G 'at _{80 °} C of the fully cured adhesive sheet is preferably 0.11 MPa or more.

On the other hand, from the viewpoint of making the adhesive sheet moderately tacky and ensuring wettability, the G _{'25 ℃ of the} cured sheet is preferably 1 MPa or less, more preferably 0.5 MPa or less, and more preferably It is preferably below 0.4 MPa. From the same viewpoint, the G _{'80 ° C of the} fully cured adhesive sheet is preferably 0.6 MPa or less, more preferably 0.4 MPa or less, and further preferably 0.3 MPa or less.

The glass transition temperature of the semi-hardened adhesive sheet is preferably -5 ° C or lower. The glass transition temperature of the semi-hardened adhesive sheet is preferably -25 ° C or higher, more preferably -20 ° C or higher, and even more preferably -18 ° C or higher. The glass transition temperature of the fully cured adhesive sheet is preferably -3 ° C or lower. The glass transition temperature of the fully cured adhesive sheet is preferably -20 ° C or higher, more preferably -15 ° C or higher, and even more preferably -13 ° C or higher. When the glass transition temperature is within the above range, the adhesive sheet has appropriate viscosity even in a low temperature range, and therefore, it tends to have excellent impact resistance.

The peak top value of the loss tangent tan δ of the semi-hardened adhesive sheet (that is, tan δ at the glass transition temperature) is preferably 1.6 or more, more preferably 1.7 or more, and even more preferably 1.8 or more. The peak top value of tan δ of the fully cured adhesive sheet is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. The adhesive sheet with a larger peak value of tan δ tends to have larger adhesive behavior and excellent impact resistance.

The shear storage elastic modulus G 'of the adhesive sheet, the glass transition temperature, and the peak top value of tanδ were determined by viscoelasticity measurement at a frequency of 1 Hz. The glass transition temperature is the temperature at which tan δ reaches its maximum (peak temperature). tanδ is the ratio G '' / G 'of the loss elastic modulus G' 'to the storage elastic modulus G'. The storage elastic modulus G 'corresponds to a portion stored as elastic energy when a material deforms, and is an index indicating the degree of hardness. The larger the storage elastic modulus of the adhesive sheet, the higher the subsequent holding force, which tends to suppress peeling due to deformation. The loss elastic modulus G '' corresponds to a portion of the energy lost due to internal friction and the like when the material is deformed, and indicates the degree of viscosity. The larger the tanδ, the stronger the tendency of viscosity, the deformation behavior becomes a liquid behavior, and there is a tendency that the resilience energy decreases.

For any one of the semi-hardened adhesive sheet and the completely cured adhesive sheet, the upper limit of the peak top value of tan δ is not particularly limited, and is usually 3.0 or less. From the viewpoint of subsequent holding force, the peak top value of tan δ is preferably 2.7 or less, and more preferably 2.5 or less.

The adhesive force of the semi-hardened adhesive sheet is preferably 3 N / 10 mm or more, more preferably 4 N / 10 mm or more, and even more preferably 5 N / 10 mm or more. When the adhesive force of the semi-hardened adhesive sheet is within the above range, the release film 2 (light release film) temporarily attached to one side of the adhesive sheet 5 is peeled off and adhered to the adherend, and then temporarily adhered to another When the release film 1 (heavy release film) on one surface is peeled off, peeling of the interface between the adherend and the adhesive sheet 5 can be suppressed.

The adhesive force of the fully cured adhesive sheet is preferably 2 N / 10 mm or more, more preferably 2.5 N / 10 mm or more, and even more preferably 3 N / 10 mm or more. When the adhesive force of the fully cured adhesive sheet is within the above range, it is possible to prevent the adhesive sheet from peeling off from the adherend when a stress caused by deformation or an impact caused by dropping or the like is generated.

The subsequent force was determined by a peel test using a glass plate as the adherend and a tensile speed of 60 mm / min and a peel angle of 180 °. Unless otherwise specified, the adhesive force is a measured value at 25 ° C.

The adhesive force of the semi-hardened adhesive sheet at 65 ° C. is preferably 1 N / 10 mm or more, more preferably 1.5 N / 10 mm or more, and even more preferably 2 N / 10 mm or more. The adhesive force at 65 ° C. of the fully cured adhesive sheet is preferably 1 N / 10 mm or more, more preferably 1.5 N / 10 mm or more, and even more preferably 2 N / 10 mm or more.

The thickness of the adhesive sheet is not particularly limited, and may be set according to the type, shape, or the like of the adherend. When a member having a printing step such as a front transparent plate is used as an adherend, the thickness of the adhesive sheet is preferably greater than the thickness of the printing step. The thickness of the adhesive sheet for bonding the front transparent plate (covering the window) is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 50 μm or more. By increasing the thickness of the adhesive sheet, there is a tendency that the level absorption and impact resistance are increased. The upper limit of the thickness of the adhesive sheet is not particularly limited. From the viewpoint of productivity of the adhesive sheet and the like, it is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 250 μm or less.

[Composition of adhesive]
As long as the adhesive sheet of the present invention satisfies the above characteristics, the composition of the adhesive is not particularly limited, and acrylic polymers, polysiloxane polymers, polyesters, polyurethanes, and polyfluorenes can be appropriately selected and used. Polymers such as amines, polyvinyl ethers, vinyl acetate / vinyl chloride copolymers, modified polyolefins, epoxy-based, fluorine-based, natural rubber, synthetic rubber and other rubber-based polymers are used as adhesives for basic polymers.

In particular, it is preferable to use an acrylic polymer as a base polymerization in terms of excellent optical transparency, showing moderate wettability, cohesiveness, and adhesion properties such as adhesion and excellent weather resistance or heat resistance. Acrylic adhesive. Among them, an acrylic base polymer having a structure in which an acrylic polymer chain is crosslinked by a urethane-based segment is preferred.

[Base polymer]
The acrylic polymer chain is crosslinked by the urethane-based segment, thereby achieving a high adhesion force at a low glass transition temperature. The content of the urethane segment in the base polymer is preferably 3 parts by weight or more based on 100 parts by weight of the acrylic polymer chain.

When the amount of the urethane-based segment is excessively increased, the viscosity of the adhesive may decrease with an increase in the cross-linking density, and the level absorption or impact resistance may decrease. In addition, if the amount of the urethane-based segment is excessively increased, the transparency of the adhesive sheet may decrease and the haze may increase. Therefore, the amount of the urethane-based segment in the base polymer is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less with respect to 100 parts by weight of the acrylic polymer chain.

＜ Acrylic polymer chain ＞
The acrylic polymer chain contains an alkyl (meth) acrylate as a main constituent monomer component. In addition, in this specification, "(meth) acrylic acid" means acrylic acid and / or methacrylic acid.

As the (meth) acrylic acid alkyl ester, an (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms is preferably used. The alkyl (meth) acrylate may have a branched chain or a cyclic alkyl group.

Specific examples of the alkyl (meth) acrylate having a chain alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and (meth) Isobutyl acrylate, second butyl (meth) acrylate, third butyl (meth) acrylate, amyl (meth) acrylate, isoamyl (meth) acrylate, neopentyl (meth) acrylate , Hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, (meth) Nonyl acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, twelve (meth) acrylate Alkyl ester, isotridecyl (meth) acrylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, Hexadecyl (meth) acrylate, Hexadecyl (meth) acrylate, Stearyl (meth) acrylate, Isooctadecyl (meth) acrylate, (meth) acrylic acid Undecyl esters and the like.

Specific examples of the alkyl (meth) acrylate having an alicyclic alkyl group include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, Cycloalkyl (meth) acrylates such as cyclooctyl (meth) acrylate; (meth) acrylates having bicyclic aliphatic hydrocarbon rings, such as isopropyl (meth) acrylate; and (meth) acrylic acid di Cyclopentyl, dicyclopentyloxyethyl (meth) acrylate, tricyclopentyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl- (meth) acrylate- (Meth) acrylic acid esters having tricyclic or more aliphatic hydrocarbon rings such as 2-adamantyl ester and 2-ethyl-2-adamantyl (meth) acrylate.

The amount of the alkyl (meth) acrylate is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more with respect to the total amount of the monomer components constituting the acrylic polymer chain. From the viewpoint that the glass transition temperature (Tg) of the polymer chain is within an appropriate range, the (meth) acrylic alkyl group having a chain alkyl group having 4 to 10 carbon atoms in the acrylic polymer chain The amount of the ester is preferably 30% by weight or more, more preferably 40% by weight or more, and still more preferably 45% by weight or more with respect to the total amount of the constituent monomer components. The monomer component constituting the acrylic polymer chain means a monomer component other than a urethane (meth) acrylate or the like as a constituent component of the urethane-based segment.

The acrylic polymer chain may contain a hydroxyl-containing monomer or a carboxyl-containing monomer as a constituent monomer component. The acrylic polymer chain has a hydroxyl group-containing monomer as a constituent monomer component, which can improve the transparency of the adhesive sheet and suppress the white turbidity in a high temperature and high humidity environment.

Examples of the hydroxyl-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and (meth) 6-hydroxyhexyl acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, or (meth) acrylic acid (4 -(Meth) acrylates such as methylolcyclohexyl) methyl ester. Among these, from the viewpoint of high compatibility with the urethane-based segments and improving the transparency of the adhesive sheet, the acrylic polymer chain is preferably one containing a hydroxyalkyl group having 4 to 8 carbon atoms. A (meth) acrylate is a constituent monomer component.

The amount of the hydroxyl-containing monomer is preferably 1 to 35% by weight, more preferably 3 to 30% by weight, and still more preferably 5 to 25% by weight based on the total amount of the monomer components constituting the acrylic polymer chain.

Examples of the carboxyl group-containing monomer include acrylic monomers such as (meth) acrylic acid, carboxyethyl (meth) acrylate, and carboxypentyl (meth) acrylate, or itaconic acid, maleic acid, and Maleic acid, crotonic acid, etc.

The acrylic polymer chain may contain a nitrogen-containing monomer as a constituent monomer component. Examples of the nitrogen-containing monomer include: N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, Vinyl imidazole, vinyl oxazole, vinyl morpholine, (meth) acrylic oxomorph, vinyl monomers such as N-vinylcarboxamide, N-vinyl caprolactam, or acrylonitrile, Cyano-containing acrylic monomers, such as methacrylonitrile.

The acrylic polymer chain contains a highly polar monomer such as a hydroxyl group-containing monomer and a carboxyl group-containing monomer as a constituent monomer component, which can improve the cohesive force of the adhesive and tends to improve adhesion at high temperatures. On the other hand, when the content of the high-polarity monomer is too large, the glass transition temperature increases, and the adhesion at low temperatures or impact resistance may decrease. Therefore, the amount of highly polar monomers (total of hydroxyl-containing monomers, carboxyl-containing monomers, and nitrogen-containing monomers) is preferably 3 to 40% by weight relative to the total amount of monomer components constituting the acrylic polymer chain. , More preferably 5 to 35% by weight, and still more preferably 10 to 30% by weight. In addition, the amount of the nitrogen-containing monomer is preferably 1 to 25% by weight, more preferably 2 to 20% by weight, and still more preferably 3 to 15% by weight with respect to the total amount of monomer components constituting the acrylic polymer chain. .

Acrylic polymer chains may contain monomers containing anhydride groups, caprolactone adducts of (meth) acrylic acid, monomers containing sulfonic acid groups, monomers containing phosphate groups, vinyl acetate, vinyl propionate Vinyl monomers such as styrene, α-methylstyrene; cyano-containing acrylic monomers such as acrylonitrile and methacrylonitrile; epoxy-containing monomers such as glycidyl (meth) acrylate; Glycol acrylates such as polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, and methoxypolypropylene glycol (meth) acrylate Monomers; acrylate monomers such as tetrahydrofurfuryl (meth) acrylate, fluoro (meth) acrylate, polysiloxane (meth) acrylate, 2-methoxyethyl (meth) acrylate, etc. As a monomer component other than the above.

The acrylic polymer chain may contain a polyfunctional monomer or oligomer. The polyfunctional compound contains two or more (meth) acrylfluorene groups or vinyl polymerizable functional groups having an unsaturated double bond in one molecule. Examples of the polyfunctional compound include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polybutylene glycol di (meth) acrylate, and bisphenol A ethylene oxide. Di (meth) acrylate, bisphenol A propylene oxide modified di (meth) acrylate, alkanediol di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, Ethoxylated isocyanurate triacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, di-trimethylolpropane Tetra (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol poly (meth) acrylate, dipentaerythritol hexa (meth) acrylate, neopentyl Glycol di (meth) acrylate, glycerol di (meth) acrylate, epoxy (meth) acrylate, butadiene (meth) acrylate, isoprene (meth) acrylate, and the like.

The acrylic polymer chain contains a polyfunctional monomer as a constituent monomer component, thereby introducing a branched structure (crosslinked structure) into the polymer chain. As described later, in the adhesive of the present invention, a crosslinked structure is introduced into the acrylic polymer chain through the urethane-based segment. When the introduction amount of the cross-linked structure caused by a polyfunctional monomer component other than the urethane-based segment increases, the low-temperature adhesive force of the adhesive may decrease. Therefore, the amount of the polyfunctional compound (other than the acrylic urethane) is preferably 3% by weight or less, more preferably 1% by weight or less, and more preferably relative to the total amount of the monomer components constituting the acrylic polymer chain. It is 0.5% by weight or less, and particularly preferably 0.3% by weight or less.

In the acrylic polymer chain, it is preferable that the content of the alkyl (meth) acrylate is the largest among the monomer components. It is easy to control the characteristics of the adhesive sheet according to the type of the monomer (main monomer) having the most content in the constituent monomers of the acrylic polymer chain. For example, when the main monomer of an acrylic polymer chain is a (meth) acrylic acid alkyl ester having a chain alkyl group having a carbon number of 6 or less, the peak value of tan δ increases and the impact resistance improves. tendency. In particular, when a C ₄ alkyl acrylate such as butyl acrylate is a main monomer, the peak top value of tan δ tends to increase. The amount of the (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbons relative to the total amount of monomer components constituting the acrylic polymer chain is preferably 30% to 80% by weight, and more preferably It is 35 to 75% by weight, and more preferably 40 to 70% by weight. In particular, the content of butyl acrylate as a constituent monomer component is preferably within the above range.

The theoretical Tg of the acrylic polymer chain is preferably -50 ° C or higher. The theoretical Tg of the acrylic polymer chain is preferably -10 ° C or lower, more preferably -20 ° C or lower, and even more preferably -25 ° C or lower. The theoretical Tg is calculated from the glass transition temperature Tg _i of the homopolymer of the monomer component constituting the acrylic polymer chain and the weight fraction W _i of each monomer component using the following Fox equation.
1 / Tg = Σ (W _i / Tg _i )

Tg is the glass transition temperature of the polymer chain (unit: K), W _i is the weight fraction of the monomer component i constituting the segment (copolymerization ratio on a weight basis), and Tg _i is the homopolymer of the monomer component i Glass transition temperature (unit: K). As the glass transition temperature of the homopolymer, a value described in Polymer Handbook 3rd Edition (John Wiley & Sons, Inc., 1989) can be used. The Tg of the homopolymer of a monomer not described in the above-mentioned document may be a peak top temperature of a loss tangent (tan δ) obtained by dynamic viscoelasticity measurement.

<Carbamate-based Segments>
The urethane-based segment is a molecular chain having a urethane bond. The two ends of the urethane-based segment are covalently bonded to the acrylic polymer chain. The chain introduces a cross-linked structure.

(Structure of Urethane Segment)
The urethane-based segment typically contains a polyurethane chain capable of reacting a diol with a diisocyanate. From the viewpoint of obtaining an adhesive capable of having both low-temperature adhesiveness and high-temperature retention, the molecular weight of the polyurethane chain in the urethane-based segment is preferably 4,000 to 50,000, and more preferably 4500. ∼40,000, more preferably 5,000∼30,000.

The larger the molecular weight of the polyurethane chain in the urethane-based segment, the longer the distance between the crosslinking points of the acrylic polymer chain. In the case where the molecular weight of the polyurethane chain is too small and the distance between the cross-linking points is short, as the cohesive force increases, the storage elastic modulus increases. As a result, the adhesiveness of the adhesive sheet decreases, and tan δ decreases. Therefore, there is a tendency that the level absorption or impact resistance decreases. In the case where the molecular weight of the polyurethane chain is too large and the distance between the crosslinking points is long, the storage elastic modulus may be small, and then the holding force may be insufficient. When the molecular weight of the polyurethane chain is within the above range, the adhesive has moderate agglutination, and therefore can have both impact resistance and adhesion.

Examples of the diol used to form a polyurethane chain include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, and hexanediol; polyester polyols and polyether polyols High molecular weight polyols such as alcohols, polycarbonate polyols, acrylic polyols, epoxy polyols, and caprolactone polyols.

Polyether polyols are obtained by ring-opening addition polymerization of alkylene oxides in polyols. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran. Examples of the polyhydric alcohol include the above-mentioned diols, glycerin, and trimethylolpropane.

The polyester polyol is a polyester having a hydroxyl group at its terminal, and is obtained by reacting a polybasic acid with a polyhydric alcohol in such a manner that the alcohol equivalent is excessive relative to the carboxylic acid equivalent. The polybasic acid component and the polyhydric alcohol component constituting the polyester polyol are preferably a combination of a dibasic acid and a diol.

Examples of the dibasic acid component include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; hexahydrophthalic acid, tetrahydrophthalic acid, and 1,3-cyclohexane Alicyclic dicarboxylic acids such as alkane dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid; oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, Aliphatic dicarboxylic acids such as decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, eicosanedicarboxylic acid; anhydrides of these dicarboxylic acids, lower alcohol esters, and the like.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexane Alkylenedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and the like.

Examples of the polycarbonate polyol include a polycarbonate polyol obtained by subjecting a diol component to a polycondensation reaction with phosgene; a diol component and dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dicarbonate. Polycarbonate obtained by transesterification of carbonic acid diesters such as isopropyl ester, dibutyl carbonate, ethylbutyl carbonate, ethylene carbonate, propylene carbonate, diphenyl carbonate, dibenzyl carbonate, etc. Polyols; copolymerized polycarbonate polyols obtained by using two or more polyol components together; polycarbonate polyols obtained by esterifying the various polycarbonate polyols described above with carboxyl-containing compounds; A polycarbonate polyol obtained by subjecting a carbonate polyol to a hydroxyl group-containing compound by an etherification reaction; a polycarbonate polyol obtained by subjecting the above-mentioned various polycarbonate polyols to an ester interchange reaction with an ester compound; Polycarbonate polyol obtained by transesterifying a carbonate polyol with a hydroxyl-containing compound; obtained by polycondensation of various polycarbonate polyols and dicarboxylic acid compounds described above The polyester polycarbonate polyols; polyether by copolymerization to make the above polycarbonate polyol with an alkylene oxide obtained by copolymerizing the polycarbonate polyol.

The polyacrylic polyol is obtained by copolymerizing a (meth) acrylate with a monomer component having a hydroxyl group. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2- (meth) acrylate Hydroxyalkyl esters of (meth) acrylic acid such as hydroxybutyl ester, 4-hydroxybutyl (meth) acrylate, 2-hydroxypentyl (meth) acrylate, etc .; (A) of polyols such as glycerol, trimethylolpropane, etc. Group) acrylic acid monoester; N-hydroxymethyl (meth) acrylamide and the like. Examples of the (meth) acrylate include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like.

The polyacrylic polyol may contain a monomer component other than the above as a copolymerization component. Examples of the comonomer components other than the above include unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid and their anhydrides; and mono- or diesters; (meth) Unsaturated nitriles such as acrylonitrile; unsaturated methylamines such as (meth) acrylamide, N-hydroxymethyl (meth) acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; methyl Vinyl ethers such as vinyl ether; α-olefins such as ethylene and propylene; halogenated α, β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; α, β such as styrene and α-methylstyrene -Unsaturated aromatic monomers and the like.

The diisocyanate for forming the polyurethane chain may be any of an aromatic diisocyanate and an aliphatic diisocyanate. Examples of the aromatic diisocyanate include 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diphenyldimethylmethane diisocyanate, and tetramethyl Diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2-chloro-1,4-phenyl diisocyanate, 2,4-toluene diisocyanate, 2, 6-toluene diisocyanate, xylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenylfluorene diisocyanate, 4,4'-diphenylfluorene diisocyanate, 4,4'-biphenyl diisocyanate and the like. Examples of the aliphatic diisocyanate include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethyl ether. Hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis (isocyanatomethyl Group) cyclohexane, methylcyclohexane diisocyanate, and the like.

Derivatives of isocyanate compounds can also be used as diisocyanates. Examples of the derivative of the isocyanate compound include a dimer of polyisocyanate, a trimer of isocyanate (isocyanurate), a polymerized MDI, an addition product with trimethylolpropane, and a modified biuret , Urea-formate modified body, urea modified body and the like. As the diisocyanate component, a urethane prepolymer having an isocyanate group at the terminal can be used.

(Using urethane-based segments to introduce a cross-linked structure into an acrylic polymer chain)
By using a compound having a functional group capable of copolymerizing with a monomer component constituting the acrylic polymer chain at the end of the polyurethane chain, or having a polymerizable acrylic acid at the end of the polyurethane chain A compound having functional groups such as a carboxyl group and a hydroxyl group contained in the material chain can introduce a crosslinked structure formed from a urethane-based segment into the acrylic polymer chain. Since it is easy to introduce the acrylic polymer chain into the crosslinking point uniformly, and the acrylic polymer chain has excellent compatibility with the urethane chain segment, it is preferably used for the polyurethane chain. A diurethane (meth) acrylate having a (meth) acrylfluorenyl group at both ends is introduced into a crosslinked structure formed from a urethane-based segment. For example, by copolymerizing a monomer component constituting an acrylic polymer chain with a diurethane (meth) acrylate, it is possible to introduce a urethane-based segment into the acrylic polymer chain. Crosslinked structure.

A dicarbamate (meth) acrylate having a (meth) acrylfluorenyl group at both ends is, for example, a (meth) group having a hydroxyl group in addition to a diol component in the polymerization of polyurethane. ) Obtained from an acrylic compound. From the viewpoint of controlling the chain length (molecular weight) of the urethane-based segment, it is preferred to synthesize an isocyanate-terminated polyurethane by reacting a diol with a diisocyanate in such a manner that an isocyanate is excessive, and then adding a hydroxyl group The (meth) acrylic compound reacts the terminal isocyanate group of the polyurethane with the hydroxyl group of the (meth) acrylic compound.

By reacting a polyol with a polyisocyanate compound in such a way that the polyisocyanate compound is excessive, a polyurethane chain having an isocyanate group at the terminal is obtained. In order to obtain an isocyanate-terminated polyurethane, the diol component and the diisocyanate component may be used so that the NCO / OH (equivalent ratio) is preferably 1.1 to 2.0, and more preferably 1.15 to 1.5. The diol component and the diisocyanate component can be mixed in approximately equal amounts and reacted, and then the diisocyanate component can be added.

Examples of the (meth) acrylic compound having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and (hydroxy) (meth) acrylate Hexyl ester, hydroxymethacrylamide, hydroxyethylacrylamide and the like.

As the urethane (meth) acrylate, various companies such as Arakawa Chemical Industry, Shin Nakamura Chemical Industry, Toa Synthesis, Kyoeisha Chemical, Nippon Kayaku, Nippon Synthetic Chemical Industry, Negami Industries, Daicel allnex, etc. Commercial items sold. The weight average molecular weight of the urethane (meth) acrylate is preferably 4,000 to 50,000, more preferably 4500 to 40,000, and even more preferably 5,000 to 30,000.

The glass transition temperature of the urethane (meth) acrylate is preferably 0 ° C or lower, more preferably -10 ° C or lower, and even more preferably -20 ° C or lower. By using a low Tg aminomethyl (meth) acrylate, low-temperature adhesion can be obtained even when the cohesive force of the base polymer is improved by introducing a crosslinked structure using a urethane-based segment. Excellent adhesive. The lower limit of the glass transition temperature of the urethane (meth) acrylate is not particularly limited. From the viewpoint of obtaining an adhesive with excellent high-temperature retention, it is preferably -100 ° C or higher, and more preferably -90 ° C. The above is more preferably -80 ° C or more.

When a urethane (meth) acrylate is used to introduce a crosslinked structure formed from a urethane-based segment onto an acrylic polymer chain, the urethane-based chain of the base polymer The glass transition temperature of the segment is approximately equal to the glass transition temperature of the urethane (meth) acrylate.

＜ Preparation of base polymer ＞
The polymer which introduce | transduced the crosslinked structure which consists of a urethane type segment into an acrylic polymer chain can be polymerized by various well-known methods. When a urethane (meth) acrylate is used as the constituent component of the urethane-based segment, the monomer component for constituting the acrylic polymer chain and the urethane ( Copolymerization of meth) acrylate is sufficient.

The use amount of the urethane (meth) acrylate is preferably 3 to 30 parts by weight, and more preferably 4 to 25 parts by weight based on 100 parts by weight of the monomer component constituting the acrylic polymer chain. . By adjusting the use amount of the urethane (meth) acrylate, a base polymer having a content of the urethane-based segment within the above range can be prepared. When the content of the urethane-based segment is too small, the adhesive strength of the adhesive sheet tends to decrease due to the decrease in the cohesiveness of the base polymer. When the content of the urethane-based segment is too large, the adhesiveness of the adhesive sheet decreases with the increase of the cohesiveness of the base polymer, and the impact resistance tends to decrease.

The polymerization method of the base polymer is preferably photopolymerization. In photopolymerization, a polymer can be prepared without the use of a solvent, so that drying and removal of the solvent are not required when forming an adhesive sheet, and an adhesive sheet having a large thickness can be uniformly formed. In addition, in photopolymerization, it is relatively easy to adjust the degree of polymerization, and polymerization can be restarted by re-light irradiation, so it is suitable for forming a semi-hardened adhesive sheet.

In the preparation of the base polymer, the entire amount of the monomer components constituting the acrylic polymer chain and the urethane (meth) acrylate used to introduce the crosslinked structure can be reacted at one time. Polymerization is performed in multiple stages. As a method for polymerizing in multiple stages, the following method is preferred: a monofunctional monomer constituting an acrylic polymer chain is polymerized to form a prepolymer composition (prepolymerization), and the prepolymer composition is slurried; A polyfunctional compound such as a diurethane (meth) acrylate is added to polymerize (formally polymerize) the prepolymer composition and the polyfunctional monomer. The prepolymer composition is a partial polymer containing a low-polymerization degree polymer and an unreacted monomer.

By pre-polymerizing the constituents of the acrylic polymer, branch points (crosslinking points) obtained by using polyfunctional compounds such as diurethane (meth) acrylate can be uniformly introduced into the acrylic polymer chain. ). In addition, an adhesive sheet can also be formed by applying a mixture (adhesive composition) of a low-molecular-weight polymer or a part of the polymer and an unpolymerized monomer component to a substrate, followed by formal polymerization on the substrate.

Low-polymerization compositions such as prepolymer compositions are low-viscosity and excellent in applicability. Therefore, according to the application of the adhesive composition as a mixture of the prepolymer composition and the polyfunctional compound, the polymer is polymerized on the substrate. This method can improve the productivity of the adhesive sheet, and can make the thickness of the adhesive sheet uniform. In addition, by adjusting the polymerization rate of the main polymerization, a semi-hardened adhesive sheet having excellent step absorbency can be formed.

[Adhesive sheet]
As described above, a low-polymerization prepolymer composition is prepared by prepolymerization. An adhesive composition such as a polyfunctional compound is added to the prepolymer composition, and the substrate is coated in a layered manner. By polymerizing (formally polymerizing) the above adhesive composition, a semi-hardened adhesive sheet can be obtained.

＜ Pre-polymerization ＞
The prepolymer composition can be prepared, for example, by polymerizing a composition obtained by mixing a monomer component constituting an acrylic polymer chain with a polymerization initiator. The composition for forming a prepolymer may contain a polyfunctional compound (polyfunctional monomer or polyfunctional oligomer). For example, the composition for forming a prepolymer may include a part of a polyfunctional compound as a raw material of a polymer, and the remaining part of the polyfunctional compound may be added after polymerization of the prepolymer to perform formal polymerization.

The composition for forming a prepolymer preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include benzoin ether-based photopolymerization initiator, acetophenone-based photopolymerization initiator, α-keto alcohol-based photopolymerization initiator, and aromatic sulfonyl chloride-based photopolymerization initiator. Agent, photoactive oxime-based photopolymerization initiator, benzoin-based photopolymerization initiator, benzophenone-based photopolymerization initiator, benzophenone-based photopolymerization initiator, ketal-based photopolymerization initiator, A thioxanthone-based photopolymerization initiator, a fluorenylphosphine oxide-based photopolymerization initiator, and the like.

During the polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retarder), or the like can be used for the purpose of adjusting the molecular weight and the like. Examples of the chain transfer agent include α-thioglycerol, laurylthiol, glycidylthiol, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2 , Mercaptans such as 3-dimercapto-1-propanol, or α-methylstyrene dimer.

The composition for forming a prepolymer may contain a chain transfer agent and the like in addition to the monomer and the polymerization initiator. The polymerization initiator or chain transfer agent used in the prepolymerization is not particularly limited, and for example, the above-mentioned photopolymerization initiator or chain transfer agent can be used.

The polymerization rate of the prepolymer is not particularly limited. From the viewpoint of setting the viscosity suitable for coating on a substrate, it is preferably 3 to 50% by weight, and more preferably 5 to 40% by weight. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type or amount of the photopolymerization initiator, the irradiation intensity and irradiation time of active light such as UV light, and the like.

＜ Preparation of adhesive composition ＞
In the above-mentioned prepolymer composition, a urethane (meth) acrylate and, if necessary, the remainder of a monomer component constituting an acrylic polymer chain, a polymerization initiator, a chain transfer agent, and others Additives and the like are mixed to prepare an adhesive composition. The adhesive composition preferably has a viscosity (for example, about 0.5 to 20 Pa · s) suitable for coating on a substrate. The viscosity of the adhesive composition can be adjusted by adjusting the polymerization rate of the prepolymer, the addition amount of the urethane (meth) acrylate, the composition of other components (such as oligomers), the molecular weight, and the addition amount. Adjust to the appropriate range. For the purpose of adjusting viscosity, etc., a viscosity-increasing additive can be used.

The polymerization initiator or chain transfer agent used in the main polymerization is not particularly limited, and for example, the above-mentioned photopolymerization initiator or chain transfer agent can be used. In the case where the polymerization initiator at the time of prepolymerization is not deactivated and remains in the prepolymer composition, the addition of a polymerization initiator for formal polymerization may be omitted.

(Oligomer)
The adhesive composition may contain various oligomers for the purpose of adjusting the adhesive force of the adhesive sheet or adjusting the viscosity. As the oligomer, for example, an oligomer having a weight average molecular weight of about 1,000 to 30,000 can be used. The oligomer is preferably an acrylic oligomer in terms of excellent compatibility with the acrylic base polymer.

The acrylic oligomer contains an alkyl (meth) acrylate as a main constituent monomer component. Among them, it is preferable to include an alkyl (meth) acrylate (chain (meth) acrylate) having a chain alkyl group and an alkyl (meth) acrylate ((meth) acrylate having an alicyclic alkyl group (( Acrylic oligomers of monomers of alicyclic alkyl (meth) acrylate) as monomer components. Specific examples of the (meth) acrylic acid chain alkyl ester and the (meth) acrylic acid alicyclic alkyl ester are exemplified as the constituent monomers of the acrylic polymer chain.

The glass transition temperature of the acrylic oligomer is preferably 20 ° C or higher, more preferably 30 ° C or higher, and even more preferably 40 ° C or higher. When a low-Tg base polymer and a high-Tg acrylic oligomer are used in combination to introduce a cross-linked structure formed from a urethane-based segment, the adhesion strength of the adhesive sheet tends to increase. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, and is generally 200 ° C or lower, preferably 180 ° C or lower, and more preferably 160 ° C or lower. The glass transition temperature of the acrylic oligomer was calculated using the above-mentioned Fox formula.

Among the (meth) acrylic acid alkyl esters exemplified, as the (meth) acrylic acid chain alkyl ester, methacrylic acid is preferred in terms of higher glass transition temperature and excellent compatibility with the base polymer. Methyl ester. The alicyclic alkyl (meth) acrylate is preferably dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. That is, the acrylic oligomer preferably contains one or more members selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methacrylic acid. Methyl esters are used as constituent monomer components.

The amount of the (meth) acrylic alicyclic alkyl ester is preferably from 10 to 90% by weight, more preferably from 20 to 80% by weight, and more preferably from the total amount of monomer components constituting the acrylic oligomer. 30 to 70% by weight. The amount of the (meth) acrylic chain alkyl ester is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and still more preferably 30 to the total amount of monomer components constituting the acrylic oligomer. ~ 70% by weight.

The weight average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1500 to 10,000, and even more preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight in this range, there is a tendency that the adhesive force or the adhesive force of the adhesive is increased.

An acrylic oligomer can be obtained by superposing | polymerizing the said monomer component by various polymerization methods. When polymerizing an acrylic oligomer, various polymerization initiators can be used. A chain transfer agent may be used for the purpose of adjusting the molecular weight.

When the adhesive composition contains an oligomer component such as an acrylic oligomer, the content is preferably 0.5 to 20 parts by weight, and more preferably 1 to 15 parts by weight based on 100 parts by weight of the base polymer. And more preferably 2 to 10 parts by weight. When the content of the oligomer in the adhesive composition is within the above range, there is a tendency that the adhesion at high temperature and the high-temperature holding force tend to be improved.

(Silane coupling agent)
For the purpose of adjusting the adhesive force, a silane coupling agent may be added to the adhesive composition. When a silane coupling agent is added to an adhesive composition, the addition amount is about 0.01-5.0 weight part with respect to 100 weight part of base polymers, Preferably it is about 0.03-2.0 weight part.

(Crosslinking agent)
The base polymer may have a crosslinked structure other than the above-mentioned polyfunctional compound, if necessary. Since the crosslinking agent is contained in the adhesive composition, a crosslinked structure can be introduced into the base polymer. Examples of the crosslinking agent include compounds that react with a functional group such as a hydroxyl group or a carboxyl group contained in the polymer. Specific examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and fluorene. An oxazoline-based crosslinking agent, an aziridine-based crosslinking agent, a carbodiimide-based crosslinking agent, a metal chelate-based crosslinking agent, and the like.

When the introduction amount of the crosslinked structure formed of a substance other than the urethane-based segment is increased, the viscosity may be lowered and the impact resistance may be lowered. Therefore, the use amount of the crosslinking agent is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and still more preferably 1 part by weight or less based on 100 parts by weight of the base polymer.

(Other additives)
In addition to the components exemplified above, the adhesive composition may contain a tackifier, a plasticizer, a softener, a deterioration inhibitor, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, an antistatic agent, and the like. additive.

<Coating and Formal Polymerization of Adhesive Compositions>
The substrate is coated with the adhesive composition in a layered form and then irradiated with active light to perform photo-hardening. When light curing is performed, it is preferable to provide a cover sheet on the surface of the coating layer, and irradiate the active light with the adhesive composition sandwiched between the two sheets to prevent polymerization inhibition by oxygen.

As a base material for forming an adhesive sheet and a cover sheet, any appropriate base material can be used. The base material and the cover sheet may be a release film having a release layer on a contact surface with the adhesive sheet.

As a film base material of a release film, the film containing various resin materials can be used. Examples of the resin material include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyether fluorene resins, polycarbonate resins, and polyamides. Resin, polyimide resin, polyolefin resin, (meth) acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, polymer Aromatic ester resins, polyphenylene sulfide resins, and the like. Among these, a polyester resin such as polyethylene terephthalate is particularly preferred. The thickness of the film substrate is preferably 10 to 200 μm, and more preferably 25 to 150 μm. Examples of the material of the release layer include a silicone release agent, a fluorine release agent, a long-chain alkyl release agent, and a fatty ammonium release agent. The thickness of the release layer is generally about 10 to 2000 nm.

As a method for applying the adhesive composition to a substrate, a roll coating method, a contact roll coating method, a gravure coating method, a reverse coating method, a roll brush method, a spray method, a dip roll coating method, Various methods such as a doctor blade coating method, a doctor blade coating method, an air knife coating method, a curtain coating method, a lip mold coating method, and a die coater.

Forming the main composition by irradiating the adhesive composition in a layered manner on the substrate with active light. In the formal polymerization, the unreacted monomer component in the prepolymer composition reacts with the urethane (meth) acrylate to obtain the introduction of the urethane-based segment from the acrylic polymer chain. The base polymer of the formed crosslinked structure. By adjusting the polymerization rate in the main polymerization, a part of the polymerizable compound is left unreacted to obtain a semi-hardened adhesive sheet.

The active light may be selected according to the type of a polymerizable component such as a monomer or a urethane (meth) acrylate, or the type of a photopolymerization initiator. Generally, ultraviolet light or short-wavelength visible light is used. The accumulated light amount of the irradiation light is preferably about 100 to 5000 mJ / cm ² . As a light source for light irradiation, there is no particular limitation as long as it can irradiate light in a wavelength range with sensitivity of the photopolymerization initiator contained in the adhesive composition. It is preferable to use an LED light source, a high-pressure mercury lamp, and an ultra-high voltage. Mercury lamps, metal halide lamps, xenon lamps, etc. After reaching a specific polymerization rate, the light irradiation is stopped, whereby the polymerization rate can be adjusted to a specific range. As described above, the polymerization rate of the semi-hardened adhesive sheet is preferably 90% to 98%.

Since the release films 1 and 2 are adhered to the surface of the semi-hardened adhesive sheet 5, an adhesive film having a release film temporarily attached to both sides as shown in FIG. 1 can be obtained. The release film used as a base material or a cover sheet when forming an adhesive sheet can be directly used as the release film 1, 2.

When the release films 1 and 2 are provided on both sides of the adhesive sheet 5, the thickness of one release film 1 and the thickness of the other release film 2 may be the same or different. The peeling force when the self-adhesive sheet 5 peels the release film temporarily attached to one side and the peeling force when the self-adhesive sheet 5 peels the release film temporarily attached to the other side may be the same or different. When the peeling force of the two is different, the release film 2 (light peeling film) having a relatively small peeling force is peeled off from the adhesive sheet 5 first, and then is bonded to the first adherend, and then the peeling force is opposed. The larger release film 1 (heavy release film) is peeled off and adhered to the second adherend. In this case, the workability is excellent.

[Image display device]
The adhesive sheet of the present invention can be used for bonding various transparent members or opaque members. The type of the adherend is not particularly limited, and examples thereof include various resin materials, glass, and metals. Since the adhesive sheet of the present invention has high transparency, it is suitable for bonding optical members such as image display devices. In particular, the adhesive sheet of the present invention is preferably used for bonding a transparent member such as a front transparent plate or a touch panel to a visible side surface of an image display device because of excellent level absorption or impact resistance.

FIG. 2 is a cross-sectional view showing an example of a laminated constitution of an image display device in which the front transparent plate 7 is bonded to the front side surface of the image display panel 10 through an adhesive sheet 5. The image display panel 10 includes a polarizing plate 3 bonded to an image-side display surface of an image display unit 6 such as a liquid crystal cell or an organic EL unit via an adhesive sheet 4. The front transparent plate 7 is provided with a printing layer 76 on the periphery of one surface of the transparent flat plate 71. The transparent plate 71 is, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate. The transparent plate 71 may have a touch panel function. As the touch panel, a touch panel of any method such as a resistive film method, an electrostatic capacitance method, an optical method, and an ultrasonic method is used.

The polarizing plate 3 provided on the surface of the image display panel 10 and the printing layer 76 forming surface of the front transparent plate 7 are bonded together via an adhesive sheet 5. The order of bonding is not particularly limited. The bonding of the adhesive sheet 5 to the image display panel 10 may be performed first, or the bonding of the adhesive sheet 5 to the front transparent plate 7 may be performed first. Alternatively, the two may be bonded together. From the standpoint of workability of lamination, it is preferable to peel off one release film (light release film) 2 and then adhere the surface of the exposed adhesive sheet 5 to the image display panel 10, and then release the other The release film 1 (heavy release film) is peeled off, and the surface of the exposed adhesive sheet is bonded to the front transparent plate 7.

After the adhesive sheet 5 is bonded to the front transparent plate 7, it is preferable to perform defoaming to remove the interface between the adhesive sheet 5 and the flat plate 71 portion of the front transparent plate 7 or the non-flat parts such as the printing layer 76. . As the defoaming method, a suitable method such as heating, pressure, and pressure reduction can be used. For example, it is preferable to adhere while suppressing the mixing of bubbles under reduced pressure and heating, and then pressurizing while treating with an autoclave is equivalent to heating for the purpose of suppressing delayed foaming. When defoaming is performed by heating, the heating temperature is generally about 40 to 150 ° C. When pressurizing, the pressure is usually about 0.05 MPa to 2 MPa.

The shear storage elastic modulus of the adhesive sheet of the present invention in a semi-hardened state is 0.15 MPa or less. Therefore, it is easy to follow the step shape of the printed layer 76 and the like, and therefore, generation of voids can be suppressed.

The semi-hardened adhesive sheet is adhered to an adherend such as a front transparent plate, and then the adhesive sheet is light-cured (post-cured). The polymerization rate rises by post-hardening, and as a result, the storage elastic modulus of the adhesive sheet increases, and the adhesion between the adhesive sheet 5 and the front transparent member 70 improves. The polymerization rate of the post-hardened adhesive sheet is preferably 99% or more.

When there is a gap 90 between the case 9 and the front transparent plate 7, it is preferable to fill the gap 90 with a resin material or the like and seal it. As described above, the shear storage elastic modulus of the adhesive sheet after hardening is large, and therefore, the bonding reliability is excellent in a wide temperature range. Therefore, even when stress deformation occurs at the bonding interface of the adhesive sheet due to a temperature change during sealing with a resin material or the like, peeling at the bonding interface can be suppressed. In addition, since the post-hardened adhesive sheet has a low glass transition temperature and a large peak top value of tan δ, it has excellent impact resistance over a wide temperature range, and peeling due to impact such as dropping is unlikely to occur.

As described above, when the adhesive sheet is in a semi-hardened state containing an unreacted photopolymerizable compound, the shear storage elastic modulus is small and the step absorbency is excellent. Therefore, it is preferably used for bonding to the surface of an image display panel such as a transparent plate or a touch panel with a printing step.

The method will be described focusing on the method of using a semi-hardened adhesive sheet to adhere to a transparent plate with a printing step caused by a printing layer and then performing post-curing. However, when step absorption is not required, it can be completely cured. The subsequent adhesive sheet is attached to the adherend. For example, the adhesive composition is applied in a layer form on a substrate, and then the polymer is polymerized so that the polymerization rate becomes 99% or more, thereby obtaining an adhesive sheet after the adhesive is completely hardened. When a fully cured adhesive sheet is used, as in the case of using a semi-hardened adhesive sheet for bonding and post-curing, peeling due to stress deformation or impact such as dropping is unlikely to occur, and excellent reliability can be achieved. Then.

[Optical film with adhesive sheet]
As for the adhesive sheet of the present invention, in addition to a form in which a release film is temporarily attached to both sides as shown in FIG. 1, it can also be used as a film with an adhesive for fixing the adhesive sheet to an optical film or the like. For example, in the form shown in FIG. 3, a release film 1 is temporarily attached to one surface of the adhesive sheet 5, and a polarizing plate 3 is fixed to the other surface of the adhesive sheet 5. In the form shown in FIG. 4, an adhesive sheet 4 is further provided on the polarizing plate 3, and a release film 2 is temporarily attached thereto.

In this way, in a form where an optical film such as a polarizing plate is pasted on the adhesive sheet in advance, the release film 1 temporarily attached to the surface of the adhesive sheet 5 can be peeled off, pasted with a transparent member in front, and then the adhesive sheet can be applied as necessary. 5 After hardening.
Examples

The present invention will be described in more detail with examples and comparative examples below, but the present invention is not limited to these examples.

[Production of acrylic oligomer]
60 parts by weight of dicyclopentyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent were mixed Under nitrogen atmosphere, the mixture was stirred at 70 ° C for 1 hour. Next, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN), which is a thermal polymerization initiator, was added, and the mixture was reacted at 70 ° C for 2 hours, and then heated to 80 ° C for 2 hours. Then, the reaction solution was heated to 130 ° C., and toluene, a chain transfer agent, and unreacted monomers were removed by drying to obtain a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer was 5,100.

[Example 1]
(Prepolymer polymerization)
52.8 parts by weight of butyl acrylate (BA), 10.9 parts by weight of cyclohexyl acrylate (CHA), 9.7 parts by weight of N-vinyl-2-pyrrolidone (NVP), 14.8 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 11.8 parts by weight of isostearyl acrylate (ISTA) and a photopolymerization initiator ("Irgacure184" manufactured by BASF: 0.035 parts by weight and "Irgacure651" manufactured by BASF: 0.035 parts by weight as monomer components for forming a prepolymer, Then, it was irradiated with ultraviolet rays to perform polymerization so that the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30 ° C.) reached about 20 Pa · s, thereby obtaining a prepolymer composition (polymerization rate: about 9%).

(Preparation of photocurable adhesive composition)
To the above prepolymer composition, a terminal acrylic modified polyether urethane ("UV-3300B" manufactured by Nippon Synthetic Chemical Industry) is added as a urethane (meth) acrylate: 7 weight Parts and terminal acrylic modified polyester urethane ("UV-3010B" manufactured by Nippon Synthetic Chemical Industry): 3 parts by weight, the aforementioned acrylic oligomer: 5 parts by weight, Irgacure184 as a photopolymerization initiator : 0.05 parts by weight and Irgacure651: 0.57 parts by weight, α-methylstyrene dimer as a chain transfer agent ("Nofmer MSD" manufactured by Nippon Oil): 0.1 parts by weight, and manufactured by Shin-Etsu Chemical Co., Ltd. as a silane coupling agent "KBM403"): 0.3 parts by weight, and then these were uniformly mixed to prepare an adhesive composition.

(Production of adhesive sheet)
A 75 μm-thick polyethylene terephthalate (PET) film ("Diafoil MRF75" manufactured by Mitsubishi Chemical Corporation) with a polysilicone-based release layer on the surface was used as a base material (also a release film). The said photocurable adhesive composition was apply | coated so that thickness might be 150 micrometers on a material, and the coating layer was formed. A 75 μm-thick PET film (“Diafoil MRE75” manufactured by Mitsubishi Chemical Corporation) was attached to the coating layer as a cover sheet (also a light release film) and subjected to a polysiloxane peeling treatment on one side. A black light lamp was used to adjust the position of the irradiation surface directly below the lamp at 5 mW / cm ^2. The laminated body was irradiated with ultraviolet light for 130 seconds from the cover sheet side to perform light curing to obtain a thickness of 150 μm and a polymerization rate. 94% adhesive sheet.

[Examples 2 to 7, Comparative Examples 1 to 10]
The monomer composition used in the polymerization of the prepolymer, and the polyfunctional compound (acrylic urethane and / or polyfunctional acrylate), acrylic oligomer, and photopolymerization initiator added to the adhesive composition And the types and addition amounts of the chain transfer agents are changed as shown in Tables 1-1 and 1-2. A photocurable adhesive composition was prepared in the same manner as in Example 1 except that the photocurable adhesive composition was applied to the substrate and photocured to obtain an adhesive sheet. In Example 4, Comparative Example 4, and Comparative Example 5, the same adhesive composition as in Example 3 was used, and the irradiation time of ultraviolet rays was changed to obtain an adhesive sheet having a polymerization rate shown in Table 1-1.

[Evaluation]
＜ Weight average molecular weight ＞
The weight average molecular weight (Mw) of the acrylic oligomer and the urethane (meth) acrylate was measured using a GPC (gel permeation chromatography) device (product name "HLC-8120GPC") manufactured by Tosoh. For the measurement sample, a filtrate obtained by dissolving a base polymer in tetrahydrofuran to make a 0.1% by weight solution using a 0.45 μm membrane filter was used. The measurement conditions of GPC are as follows.
(Measurement conditions)
Column: made by Tosoh Corporation, G7000HXL + GMHXL + GMHXL
Column size: 7.8 mm each × 30 cm (total column length: 90 cm)
Column temperature: 40 ° C, flow rate: 0.8 mL / min
Injection volume: 100 μL
Eluent: Tetrahydrofuran Detector: Differential Refractometer (RI)
Standard sample: polystyrene

<Storage elastic modulus, glass transition temperature, and tanδ peak of the adhesive sheet>
A laminate of 10 adhesive sheets was made into a material having a thickness of about 1.5 mm as a sample for measurement. "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific was used for dynamic viscoelasticity measurement under the following conditions.
(Measurement conditions)
Deformation mode: Torsion measurement frequency: 1 Hz
Heating rate: 5 ° C / min Shape: Parallel plate 7.9 mm

The shear storage elastic modulus is determined by reading the storage elastic modulus G 'at each temperature based on the measurement results. The temperature (peak top temperature) when the loss tangent (tan δ) reached a maximum was taken as the glass transition temperature of the adhesive sheet. In addition, the value of tan δ (peak top value) at the glass transition temperature was read.

＜ Adhesive force ＞
The light release film was peeled from the adhesive sheet, a PET film having a thickness of 50 μm was bonded, cut into a width of 10 mm × length of 100 mm, and then the heavy release film was peeled off, and then pressed onto a glass plate with a 5 kg roller to produce an adhesive force. Measurement sample. After holding the sample for adhesion measurement in an environment of 25 ° C or 65 ° C for 30 minutes, a tensile tester was used to peel the glass plate at a tensile speed of 300 mm / min and a peeling angle of 180 °. Sheet, and the peeling force was measured.

<Haze>
A test piece obtained by bonding an adhesive sheet to a 800 μm-thick alkali-free glass (total light transmittance 92%, haze 0.4%), and a haze meter ("HM-150" manufactured by Murakami Color Technology Research Institute) ) Determine the haze. The value obtained by subtracting the haze (0.4%) of the alkali-free glass from the measured value was used as the haze of the adhesive sheet.

＜ Step difference absorption ＞
The adhesive sheet was cut to a size of 75 mm × 45 mm, and the light release film was peeled from the adhesive sheet. The roll laminator (pressure between rolls: 0.2 MPa, transportation speed: 100 mm / min) was bonded to the cut sheet to 100 The center of a PET film with a thickness of 50 mm and a thickness of 125 μm. Then, the heavy release film was peeled off, and it was bonded to a thickness of 500 μm with black ink having a thickness of 20 μm printed on the periphery by a frame using a roll laminator (pressure between rolls: 0.2 MPa, conveying speed: 100 mm / min). μm glass plate (100 mm × 50 mm). The ink printing area of the glass plate is 5 mm from both ends in the short side direction and 15 mm from both ends in the long side direction. The black ink layer is connected to the area of 5 mm from the ends of the four sides of the adhesive sheet. This sample was processed in an autoclave (50 ° C, 0.5 MPa) for 30 minutes, and then observed with a digital microscope at a magnification of 20 times to confirm the presence or absence of air bubbles near the boundary of the printing area of the black ink.

＜ Peelability of self-releasing film ＞
The adhesive sheet was cut into a size of 75 mm × 45 mm, and the light release film was peeled from the adhesive sheet. A roll laminator (pressure between rolls: 0.2 MPa, transport speed: 100 mm / min) and glass with a thickness of 500 μm were used. The boards (100 mm x 50 mm) are fitted. Pick up the pick-up tape at the end of the heavy release film temporarily attached to the adhesive sheet, and peel it at a peeling angle of 90 °. Samples that are peeled off at the interface between the adhesive sheet and the heavy release film will be recorded as OK, and will be placed on the glass plate. A sample that was peeled from the interface of the heavy release film was referred to as NG.

<Layer indirect contact>
(Manufacture of test samples)
The adhesive sheet was cut into a size of 75 mm × 45 mm, the light release film was peeled from the adhesive sheet, and the thickness was 500 μm using a roll laminator (pressure between rolls: 0.2 MPa, conveying speed: 100 mm / min). The center of the glass plate (100 mm × 50 mm). The self-adhesive sheet was peeled from the heavy release film, and a 500 μm-thick glass plate (50 mm × 50 μm thick) printed with a black ink having a thickness of 30 μm was formed on the periphery by vacuum pressure bonding (surface pressure 0.3 MPa, pressure 100 Pa). 100 mm, ink printing area is the same as that used in the step absorbency test). The sample was processed in an autoclave (50 ° C, 0.5 MPa) for 30 minutes, and then cured by irradiating ultraviolet rays from the glass plate side of the printing layer with black ink using a metal halide lamp (300 mW / cm ² ), Increase the polymerization rate to 99%.

The sample was kept at 60 ° C for 30 minutes. Then, as shown in FIG. 5A, a 200 μm thick polystyrene sheet was inserted between the two glass plates from the end of the adhesive sheet to a distance of 1 mm. Hold for 10 seconds. The end of the adhesive sheet was observed using a digital microscope with a magnification of 20 times. A sample in which streaked bubbles (see FIG. 5B) occurred or peeling of the adhesive sheet from the glass plate was recorded as NG, and a sample in which neither air bubbles nor peeling occurred was recorded as OK.

＜ Impact resistance ＞
Except changing the size of the glass plate without the black ink printing layer to 100 mm × 70 mm, the glass plate was bonded to both sides of the adhesive sheet in the same manner as in the production of the sample for the indirect adhesion test of the above layer. Autoclave treatment and hardening of the adhesive to produce test samples. As shown in FIG. 6, both ends of the short-side direction of the test sample 95 are placed on a table 93 arranged at a distance of 60 mm so that the glass plate 7 on which the print layer 76 is provided is on the lower side. The upper surface of the end portion of the glass plate 5 on which the printing layer is not provided is fixed on the stage 80 by an adhesive tape (not shown). The test sample 95 fixed on the table 93 with an adhesive tape is held at -5 ° C for 24 hours, and then taken out at room temperature within 40 seconds, so that a metal ball 97 having a mass of 11 g is dropped from a height of 300 mm to The glass plate 7 was subjected to an impact resistance test.

In the impact resistance test, in order to fix the falling position of the metal ball, a cylindrical guide 99 was used, and the inner edge of the frame of the printing area of the printing layer 76 was spaced from the corner by 10 mm in the short direction and the long direction. Position so that the metal ball 97 falls. Two tests were performed, and a sample in which peeling of the glass plate did not occur in any of the tests was recorded as OK, and a sample in which peeling of the glass plate occurred in one or two of the two cases was recorded as NG.

<Physical properties of adhesive sheet after hardening>
In the production of the adhesive sheets of each example and comparative example, the ultraviolet irradiation time was changed to produce an adhesive sheet having a polymerization rate of 99%. The viscoelasticity (storage elastic modulus, glass transition temperature, and tan δ peak), haze, and adhesion. Regarding Example 4, Comparative Example 4, and Comparative Example 5, since the composition of the adhesive was the same as that of Example 6, the measurement of the physical properties of the adhesive sheet after curing was not performed.

[Evaluation results]
The formulation of the adhesive composition used in the production of each adhesive sheet is shown in Table 1-1 and Table 1-2, and the evaluation results are shown in Table 2-1 and Table 2-2. In addition, in Table 1-1 and Table 1-2, each component is described by the following abbreviation.
<Acrylic monomer>
BA: butyl acrylate
2HEA: 2-ethylhexyl acrylate
CHA: cyclohexyl acrylate
NVP: N-vinyl-2-pyrrolidone
4HBA: 4-hydroxybutyl acrylate
2HEA: 2-hydroxyethyl acrylate
ISTA: Isostearyl Acrylate

<Acrylic Carbamate>
UV-3300B: "UV-3300B" manufactured by Nippon Synthetic Chemical Industry (weight average molecular weight of about 12000, glass transition temperature of -30 ° C, diacrylate polyether urethane)
3400: Diacrylate polyether urethane having a weight average molecular weight of about 3400
UA-4200: "UA-4200" manufactured by Shin Nakamura Chemical Industries (weight-average molecular weight of about 1,000 diacrylic polyether urethanes)
UN-350: "Art Resin UN-350" manufactured by Genjo Industrial (a diacrylic polyester urethane having a weight average molecular weight of about 12,500 and a glass transition temperature of -57 ° C)
UV-3000B: "UV-3000B" manufactured by Nippon Synthetic Chemical Industry (weight-average molecular weight of about 18000, glass transition temperature of -39 ° C, diacrylic polyester urethane)
UV-3010B: "UV-3010B" manufactured by Japan Synthetic Chemical Industry (diacrylate acrylic urethane having a weight average molecular weight of about 11,000)
Monoacrylate urethane: a polyacrylate urethane monoacrylate having a weight average molecular weight of about 1300)
＜ Multifunctional acrylates ＞
HDDA: Hexanediol diacrylate <Photopolymerization initiator>
Irg651: Irgacure651 (2,2-dimethoxy-1,2-diphenylethane-1-one)
Irg184: Irgacure184 (1-hydroxycyclohexyl-phenyl-one)

[Table 1-1]

[Table 1-2]

[table 2-1]

[Table 2-2]

In Examples 1 and 2 in which an adhesive composition such as diacrylate urethane was added to a prepolymer composition obtained by prepolymerization of an acrylic monomer using butyl acrylate as a main monomer, The semi-hardened adhesive sheet has excellent level absorption and no paste residue. In the evaluation using a fully cured adhesive sheet, both the layer indirect adhesion and the drop impact durability are good.

In Comparative Example 1 using a low molecular weight urethane diacrylate, in any of the cases before and after light hardening, the adhesive force of the adhesive sheet to the adherend was small, and the layer indirect adhesion and drop impact durability were both Worse. In Comparative Example 2 in which the amount of the diacrylate urethane was increased, the haze of the adhesive sheet was high and the transparency was decreased. In addition, the G _{'25 ℃} of the adhesive sheet before hardening is large, so the step absorbency is poor. In Comparative Example 3 in which a monoacrylate urethane was used, the adhesive storage sheet after light hardening had a low modulus of elasticity in shear storage, followed by poor durability.

In Examples 3 and 5, and Examples 6 and 7 in which the composition of the acrylic monomer in the composition for forming a prepolymer was changed, good adhesion was also shown in Examples 1 and 2. characteristic.

In Example 4 in which the same adhesive composition as in Example 3 was used and the polymerization rate was reduced to 92%, the glass transition temperature of the adhesive sheet in the semi-hardened state was lower than that in Example 3, and G ′ _{25 ℃} and G _{'80 ℃} decreased. In Comparative Example 4 in which the polymerization rate was further decreased, the glass transition temperature, G _{'25 ° C,} and G' _{80 ° C} of the adhesive sheet in the semi-hardened state were further decreased, and the adhesive force was insufficient. On the other hand, in Comparative Example 5 in which the polymerization rate was set to 99%, the step absorption was insufficient due to a rise in G _{'25 ° C.}

In Comparative Example 6 in which the glass transition temperature was reduced by adjusting the composition of the acrylic monomer without using a urethane-based material, the G _{'25 ℃} and G' _{80 ℃} of the adhesive sheet after light curing were smaller. , Then the reliability is poor. In Comparative Example 7 where the cohesiveness was improved by increasing the ratio of the polar monomers (NVB and 4HBA) in the acrylic monomer component, the adhesion was good, but the impact resistance was reduced because the glass transition temperature was high. The same tendency was also found in Comparative Example 10.

In Comparative Example 8 in which the ratio of the polyfunctional acrylate in the adhesive composition was increased, the peak top value of tan δ was small and the viscosity was low. Therefore, the adhesion force was insufficient and the impact resistance was also poor. The same tendency was also found in Comparative Example 9 where a crosslinked structure was introduced by a low molecular weight urethane diacrylate. In these comparative examples, the main monomer of the acrylic polymer chain is considered to be C ₈ alkyl acrylate (2-ethylhexyl acrylate) and the main monomer is C ₄ alkyl acrylate (butyl acrylate ) Is one of the factors that are smaller than tan δ in Examples 1 to 7.

From these results, it is known that an adhesive sheet containing a base polymer using a diacrylate urethane having a specific molecular weight to introduce a cross-linked structure into an acrylic polymer chain also shows a higher value at a low glass transition temperature. Since the shear storage modulus is large and tan δ is large, it can have both adhesion durability and impact resistance.

1, 2‧‧‧ release film

3‧‧‧ polarizing plate

4‧‧‧ Adhesive sheet

5‧‧‧ Adhesive sheet

6‧‧‧Image display unit

7‧‧‧ front transparent plate

9‧‧‧shell

10‧‧‧Image display panel

100‧‧‧Image display device

FIG. 1 is a cross-sectional view showing a configuration example of an adhesive sheet with a release film.

FIG. 2 is a cross-sectional view showing a configuration example of an image display device.

3 and 4 are cross-sectional views showing an example of a laminated structure of an optical film with an adhesive sheet.

FIG. 5A is a photograph showing a situation of a layer indirect adhesion test, and FIG. 5B is an observation picture of a sample in which stripe bubbles are generated in the layer indirect adhesion test.

Fig. 6 is a schematic diagram showing the arrangement of samples in an impact resistance test.

Claims (13)

An adhesive sheet is a light-curable adhesive sheet formed by laminating an adhesive composition containing a base polymer and a photo-curable compound, wherein Haze is below 1%, For glass adhesion is 1.5 N / 10 mm or more, The modulus of shear storage elasticity at a temperature of 25 ° C is below 0.15 MPa, When the above-mentioned adhesive composition is hardened and the polymerization rate is set to 99%, the glass transition temperature is -3 ° C or lower, and the shear storage elastic modulus at a temperature of 25 ° C is 0.16 MPa or higher. For example, the adhesive sheet of claim 1, wherein the polymerization rate of the above-mentioned adhesive composition is 90 to 98%. For the adhesive sheet of item 1 or 2, the glass transition temperature is below -5 ° C. If the adhesive sheet of item 1 or 2 is requested, the peak value of the loss tangent is 1.6 or more. For example, the adhesive sheet of claim 1 or 2, wherein when the above-mentioned adhesive composition is hardened and the polymerization rate is set to 99%, the peak top value of the loss tangent is 1.5 or more. The adhesive sheet according to claim 1, wherein in the above-mentioned base polymer, the acrylic polymer chain is crosslinked by the urethane-based segment, and the content of the urethane-based segment is relative to that of the acrylic acid 100 parts by weight of the polymer chain is 3 to 30 parts by weight. The adhesive sheet according to claim 6, wherein the weight average molecular weight of the urethane-based segment is 4,000 to 50,000. The adhesive sheet according to claim 6 or 7, wherein, in the above-mentioned base polymer, a monomer component constituting the above-mentioned acrylic polymer chain and a urethane (methyl) Copolymerization of acrylate), and a cross-linked structure formed of the urethane-based segment is introduced into the acrylic polymer chain. A method of manufacturing an image display device, which is a method of manufacturing an image display device in which a transparent member having a stepped portion is arranged on a visually-identified side surface, and The adhesive sheet according to any one of claims 1 to 8 is bonded to the transparent member, and then the adhesive sheet is irradiated with active light to thereby perform light curing of the adhesive sheet. A method for manufacturing an adhesive sheet, which is the method for manufacturing an adhesive sheet according to any one of claims 1 to 8, and A composition containing an acrylic monomer and / or a partial polymer thereof and a urethane (meth) acrylate is applied in a layer form to a substrate, and then the composition is irradiated with active light to perform light irradiation. hardening. For example, the method for producing an adhesive sheet according to claim 10, wherein in the composition, the content of the urethane (meth) acrylate is 100 parts by weight with respect to the total of the acrylic monomer and a part of the polymer thereof, It is 3 to 30 parts by weight. The method for manufacturing an adhesive sheet according to claim 10 or 11, wherein the weight average molecular weight of the urethane (meth) acrylate is 4,000 to 50,000. The method for producing an adhesive sheet according to claim 10 or 11, wherein the glass transition temperature of the urethane (meth) acrylate is 0 ° C or lower.