JP7166762B2 - PSA SHEET, MANUFACTURING METHOD THEREOF, AND IMAGE DISPLAY DEVICE - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive sheet and a method for producing the same. Furthermore, the present invention relates to an image display device using the adhesive sheet.

Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile phones, smart phones, car navigation devices, personal computer monitors, and televisions. For the purpose of preventing damage to the image display panel due to impact from the outer surface, etc., a front transparent plate (also called a "cover window") such as a transparent resin plate or glass plate is provided on the viewing side of the image display panel. Sometimes. In recent years, devices having a touch panel on the viewing side of the image display panel have become popular.

As a method for arranging a front transparent member such as a front transparent plate or a touch panel on the front surface of the image display panel, an "interlayer filling structure" has been proposed in which the image display panel and the front transparent member are bonded together via an adhesive sheet. An adhesive sheet may also be provided between the touch panel and the front transparent plate. In the interlayer filling structure, since the gaps between the members are filled with the adhesive, the refractive index difference at the interface is reduced, and the deterioration of visibility due to reflection and scattering is suppressed. In addition, in the interlayer filling structure, since the members are bonded together by adhesive sheets and fixed, the front transparent member is more likely to peel off due to impact such as dropping compared to the case where the front transparent member is fixed only to the housing. It has the advantage of being difficult. In particular, impact resistance tends to be improved by using a thick pressure-sensitive adhesive sheet. Since it is possible to form a thick adhesive sheet with a uniform thickness, a solvent-free photocurable adhesive is widely used for the adhesive sheet for interlayer filling (for example, Patent Documents 1 and 2 reference).

JP 2014-125524 A WO2013/161666

Conventionally, the front transparent member such as a cover window is larger in size than the display panel, and the front transparent member and the housing are bonded together with an adhesive tape or the like in a region outside the outer peripheral edge of the display panel. That is, the front transparent member is fixed by both bonding to the housing and bonding to the surface of the display panel using the interlayer filling pressure-sensitive adhesive sheet.

2. Description of the Related Art In recent years, mainly in mobile devices such as smartphones, display devices have become narrower in frame and bezelless. The size of the display panel 10 has become equal to the size of the front transparent member 7 or larger than the size of the display panel due to the narrowing of the frame and the elimination of the bezel. In such a configuration, it is not possible to fix the housing 9 and the front transparent member 7 with an adhesive tape or the like, and it is necessary to fix the front transparent member 7 only with the adhesive sheet 5 for interlayer filling (see FIG. 2). ). Along with this, the pressure-sensitive adhesive sheet for interlayer filling is required to have higher adhesive strength and not to cause peeling due to impact such as dropping in a wide temperature range.

Further, when the size of the display panel is equal to or larger than the size of the front transparent member, sealing with a resin material is required to fill the gap 90 between the housing 9 and the front transparent member 7. may be done. For example, sealing with the resin material is performed by pouring a molten resin material into the gap 90 and then cooling it to room temperature to solidify the resin. When high-temperature resin is poured into the gap 90, the front transparent member 7, the housing 9, and the adhesive sheet 5 in the vicinity of the gap 90 become hot and are cooled when the resin solidifies. The pressure-sensitive adhesive sheet 5 has adhesion durability against strain stress so that the adherends do not peel off even when the front transparent member and the housing are dimensionally strained due to such temperature changes. is required.

The conventional pressure-sensitive adhesive sheets for interlayer filling disclosed in Patent Document 1 and the like have a high glass transition temperature, and thus are poor in adhesiveness and impact resistance at low temperatures. On the other hand, the low glass temperature pressure-sensitive adhesive sheet disclosed in Patent Document 2 has low adhesion durability against strain stress, and has low impact resistance at low temperatures and durability against strain stress during heating and cooling such as resin sealing. It is difficult to be compatible with sexuality.

In view of the above, an object of the present invention is to provide a pressure-sensitive adhesive sheet having excellent impact resistance in a wide temperature range and adhesive durability against strain stress.

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive containing a base polymer is formed into a sheet. The adhesive sheet has a haze of 1% or less. The glass transition temperature of the adhesive sheet is preferably −3° C. or lower. The shear storage modulus G' at _25° C of the pressure-sensitive adhesive sheet is preferably 0.16 MPa or more. The peak top value of the loss tangent of the adhesive sheet is preferably 1.5 or more.

As the base polymer contained in the pressure-sensitive adhesive sheet, for example, a polymer obtained by cross-linking an acrylic polymer chain with a urethane-based segment is used. In order to satisfy the above characteristics, the content of the urethane-based segment is preferably 3 to 30 parts by weight per 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.

A base polymer in which an acrylic polymer chain is crosslinked by a urethane-based segment is obtained, for example, by copolymerizing a monomer component constituting the acrylic polymer chain and a urethane (meth)acrylate having (meth)acryloyl groups at at least two ends. obtained by As the polyfunctional urethane (meth)acrylate, urethane di(meth)acrylate having (meth)acryloyl groups at both ends is preferred.

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

A pressure-sensitive adhesive sheet containing a base polymer in which an acrylic polymer chain is crosslinked by a urethane-based segment is obtained by, for example, layering a composition containing an acrylic monomer and/or its partial polymer and urethane di(meth)acrylate on a substrate. After application, the composition is irradiated with actinic rays for photocuring. The pressure-sensitive adhesive composition preferably contains 3 to 30 parts by weight of urethane (meth)acrylate with respect to a total of 100 parts by weight of the acrylic monomer and its partial polymer.

The pressure-sensitive adhesive sheet of the present invention is used, for example, for laminating a transparent member in an image display device in which the transparent member is arranged on the viewing side surface. For example, the image display device is formed by adhering the front transparent member to the viewing side surface of the image display panel via the adhesive sheet.

Since the pressure-sensitive adhesive sheet of the present invention has a low glass transition temperature and a high shear storage modulus, it is possible to achieve both impact resistance such as dropping and adhesion durability against strain stress in a wide temperature range. An image display device in which a cover window or the like is attached to the viewing side surface using the pressure-sensitive adhesive sheet of the present invention has excellent adhesion reliability, and can be adapted to narrow frame and bezel-less.

FIG. 2 is a cross-sectional view showing a configuration example of a pressure-sensitive adhesive sheet with a release film; It is a sectional view showing an example of composition of an image display. FIG. 3 is a cross-sectional view showing an example of a laminated structure of an optical film with a pressure-sensitive adhesive sheet; FIG. 3 is a cross-sectional view showing an example of a laminated structure of an optical film with a pressure-sensitive adhesive sheet; It is a photograph which shows the state of an interlayer adhesion test. It is an observation photograph of a sample in which streak-like air bubbles were generated in an interlayer adhesion test. It is a schematic diagram which shows the arrangement|positioning of the sample in an impact resistance test.

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

[Physical properties of adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention is formed by forming a pressure-sensitive adhesive into a sheet. The adhesive sheet is a transparent adhesive sheet with a haze of 1.0% or less. The pressure-sensitive adhesive sheet preferably has a shear storage modulus G' at _25°C of 0.16 MPa or more. Adhesion reliability is enhanced when the adhesive sheet has a G'25 _°C of 0.16 MPa or more. From the viewpoint of enhancing adhesion reliability at high temperatures, the shear storage modulus G'80 _° C of the pressure-sensitive adhesive sheet at 80°C is preferably 0.11 MPa or more.

On the other hand, from the viewpoint of ensuring wettability by imparting appropriate viscosity to the adhesive sheet, the G'25 _°C of the adhesive sheet is preferably 1 MPa or less, more preferably 0.5 MPa or less, and even more preferably 0.4 MPa or less. From the same point of view, the G'80 _°C of the adhesive sheet is preferably 0.6 MPa or less, more preferably 0.4 MPa or less, and even more preferably 0.3 MPa or less.

The glass transition temperature of the adhesive sheet is preferably −3° C. or lower. The glass transition temperature of the 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 pressure-sensitive adhesive sheet has an appropriate viscosity even in a low-temperature region, and tends to be excellent in impact resistance.

The peak top value of tan δ of the pressure-sensitive adhesive sheet is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. A pressure-sensitive adhesive sheet having a large peak top value of tan δ tends to exhibit large viscous behavior and excellent impact resistance.

The shear storage modulus G', glass transition temperature, and peak top value of tan ? of the PSA sheet are determined by viscoelasticity measurement at a frequency of 1 Hz. The glass transition temperature is the temperature at which tan δ becomes maximum (peak top temperature). tan δ is the ratio G″/G′ of the storage modulus G′ and the loss modulus G″. The storage elastic modulus G' corresponds to the portion stored as elastic energy when the material is deformed, and is an index representing the degree of hardness. The higher the storage modulus of the PSA sheet, the higher the adhesive holding power, and the tendency to suppress peeling due to strain. The loss elastic modulus G″ corresponds to the loss energy portion dissipated by internal friction and the like when the material is deformed, and represents the degree of viscosity. The impact resilience energy tends to be small.

Although the upper limit of the peak top value of tan δ of the adhesive sheet is not particularly limited, it is generally 3.0 or less. From the viewpoint of adhesive holding power, the peak top value of tan δ is preferably 2.7 or less, more preferably 2.5 or less.

The adhesive strength of the 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 adhesive sheet is within the above range, it is possible to prevent the adhesive sheet from peeling off from the adherend when stress due to distortion or impact due to dropping or the like occurs. The adhesive strength is determined by a peel test using a glass plate as an adherend at a tensile speed of 60 mm/min and a peel angle of 180°. Adhesion is measured at 25° C. unless otherwise specified.

The adhesive strength of the 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 thickness of the adhesive sheet is not particularly limited, and may be set according to the type and shape of the adherend. When a member having printed steps is used as an adherend, the thickness of the pressure-sensitive adhesive sheet is preferably larger than the thickness of the printed steps. The thickness of the adhesive sheet used for bonding the front transparent plate (cover window) is preferably 30 µm or more, more preferably 40 µm or more, and even more preferably 50 µm or more. Increasing the thickness of the pressure-sensitive adhesive sheet tends to increase the level difference absorbability and impact resistance. Although the upper limit of the thickness of the adhesive sheet is not particularly limited, it is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less from the viewpoint of productivity of the adhesive sheet.

[Composition of adhesive]
In the pressure-sensitive adhesive sheet of the present invention, the composition of the pressure-sensitive adhesive is not particularly limited as long as it satisfies the above properties. It is possible to appropriately select and use a polymer having a base polymer such as a modified polyolefin, an epoxy-based polymer, a fluorine-based polymer, a natural rubber, or a rubber-based polymer such as a synthetic rubber.

In particular, acrylic adhesives containing acrylic polymers as the base polymer have excellent optical transparency, exhibit adhesive properties such as moderate wettability, cohesiveness and adhesiveness, and are also excellent in weather resistance and heat resistance. agents are preferably used. Among them, an acrylic base polymer having a structure in which acrylic polymer chains are crosslinked by urethane segments is preferable.

[Base polymer]
By cross-linking the acrylic polymer chain with the urethane-based segment, it is possible to exhibit high adhesive holding power at a low glass transition temperature. The base polymer preferably contains 3 parts by weight or more of the urethane-based segment relative to 100 parts by weight of the acrylic polymer chain.

When the amount of the urethane-based segment is excessively large, the viscosity of the pressure-sensitive adhesive decreases as the crosslink density increases, and the impact resistance may decrease. Moreover, when the amount of the urethane-based segment is excessively large, the transparency of the pressure-sensitive 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, more preferably 25 parts by weight or less, relative to 100 parts by weight of the acrylic polymer chain.

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

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

Specific examples of (meth)acrylic acid alkyl esters having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and (meth)acrylate. s-butyl acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate , undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridodecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, (meth)acrylate cetyl acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctacyl (meth)acrylate, nonadecyl (meth)acrylate, aralkyl (meth)acrylate and the like.

Specific examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. (meth) acrylic acid cycloalkyl ester; (meth) acrylic acid ester having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth) acrylate; dicyclopentanyl (meth) acrylate, dicyclopentanyloxy Tricyclics such as ethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate (Meth)acrylic acid esters having the above aliphatic hydrocarbon ring can be mentioned.

The amount of (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more, based on the total amount of the monomer components constituting the acrylic polymer chain. From the viewpoint of setting the glass transition temperature (Tg) of the polymer chain in an appropriate range, the amount of (meth)acrylic acid alkyl ester having a chain alkyl group having 4 to 10 carbon atoms relative to the total amount of the constituent monomer components of the acrylic polymer chain is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 45% by weight or more. Note that the monomer component constituting the acrylic polymer chain does not include urethane (meth)acrylate and the like, which are constituent components of the urethane-based segment.

The acrylic polymer chain may contain a hydroxyl group-containing monomer or a carboxy group-containing monomer as constituent monomer components. By having a hydroxyl group-containing monomer as a constituent monomer component of the acrylic polymer chain, the transparency of the pressure-sensitive adhesive sheet tends to be improved and white turbidity tends to be suppressed in a high-temperature and high-humidity environment.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and (meth)acrylic acid. (Meth)acrylic acid esters such as 8-hydroxyoctyl acid, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate and (4-hydroxymethylcyclohexyl)-methylacrylate. Among these, from the viewpoint of high compatibility with the urethane-based segment and improving the transparency of the adhesive sheet, the acrylic polymer chain has a hydroxyalkyl group having 4 to 8 carbon atoms as a constituent monomer component (meth) It preferably contains an acrylic acid ester.

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

Carboxy group-containing (meth)acrylic acid esters include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and croton. acids and the like.

The acrylic polymer chain may contain a nitrogen-containing monomer as a constituent monomer component. Nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinyl Vinyl monomers such as carboxylic acid amides and N-vinylcaprolactam, and cyanoacrylate monomers such as acrylonitrile and methacrylonitrile can be used.

By containing a highly polar monomer such as a hydroxyl group-containing monomer or a carboxyl group-containing monomer as a constituent monomer component of the acrylic polymer chain, the cohesive force of the adhesive is enhanced, and there is a tendency for the adhesion retention at high temperatures to be improved. be. On the other hand, when the content of the highly polar monomer is excessively high, the glass transition temperature becomes high, and the adhesion at low temperatures and the impact resistance may deteriorate. Therefore, the amount of highly polar monomer (total of hydroxyl group-containing monomer, carboxy group-containing monomer, and nitrogen-containing monomer) relative to the total amount of monomer components constituting the acrylic polymer chain is preferably 3 to 40% by weight, and 5 to 35% by weight. More preferably, 10 to 30% by weight is even more preferable. The amount of the nitrogen-containing monomer is preferably 1 to 25% by weight, more preferably 2 to 20% by weight, even more preferably 3 to 15% by weight, based on the total amount of the monomer components constituting the acrylic polymer chain.

The acrylic polymer chain contains, as monomer components other than the above, an acid anhydride group-containing monomer, a caprolactone adduct of (meth)acrylic acid, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, vinyl acetate, vinyl propionate, styrene, vinyl-based monomers such as α-methylstyrene; cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing monomers such as glycidyl (meth)acrylate; polyethylene glycol (meth)acrylate and polypropylene (meth)acrylate Glycol acrylic ester monomers such as glycol, methoxyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate; tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate and (meth)acrylate ) It may contain an acrylate monomer such as 2-methoxyethyl acrylate.

The acrylic polymer chain may contain polyfunctional monomers or oligomers. The polyfunctional compound contains two or more polymerizable functional groups having unsaturated double bonds such as (meth)acryloyl groups or vinyl groups in one molecule. Examples of polyfunctional compounds include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di( meth)acrylate, alkanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, ethoxylated isocyanuric acid triacrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylol Propane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythrol poly(meth)acrylate, dipentaerythrol hexa(meth)acrylate, neopentylglycol di(meth)acrylate, glycerin di(meth)acrylate, epoxy(meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate and the like.

A branched structure (crosslinked structure) is introduced into the polymer chain by including a polyfunctional monomer as a constituent monomer component in the acrylic polymer chain. As will be described later, in the pressure-sensitive adhesive of the present invention, the urethane-based segment introduces a crosslinked structure into the acrylic polymer chain. When the introduction amount of the crosslinked structure by the polyfunctional monomer component other than the urethane-based segment increases, the low-temperature adhesive strength of the pressure-sensitive adhesive may decrease. Therefore, the amount of the polyfunctional compound (excluding urethane acrylate) is preferably 3% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less, relative to the total amount of the monomer components constituting the acrylic polymer chain. , 0.3% by weight or less is particularly preferred.

The acrylic polymer chain preferably has the highest content of (meth)acrylic acid alkyl ester among the above monomer components. The properties of the pressure-sensitive adhesive sheet are likely to be affected by the type of monomer (main monomer) that has the highest content among the constituent monomers of the acrylic polymer chain. For example, when the main monomer of the acrylic polymer chain is a (meth)acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms, the peak top value of tan δ tends to increase and the impact resistance tends to improve. be. In particular, when a _C4 alkyl acrylate such as butyl acrylate is the 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 carbon atoms is preferably 30 to 80% by weight, more preferably 35 to 75% by weight, based on the total amount of the monomer components constituting the acrylic polymer chain. , 40 to 70% by weight is more preferred. In particular, it is preferable that the content of butyl acrylate as a constituent monomer component is 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 less, more preferably −20° C. or less, and even more preferably −25° C. or less. The theoretical Tg is calculated by the following Fox formula from the glass transition temperature Tg _i of the homopolymer of the constituent monomer components of the acrylic polymer chain and the weight fraction W _i of each monomer component.
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 based on weight), and Tg _i is the glass transition temperature of the homopolymer of the monomer component i. (unit: K). As the glass transition temperature of the homopolymer, the numerical value described in Polymer Handbook 3rd Edition (John Wiley & Sons, Inc., 1989) can be used. For the Tg of homopolymers of monomers not described in the above literature, the peak top temperature of the loss tangent (tan δ) obtained by dynamic viscoelasticity measurement may be adopted.

<Urethane segment>
The urethane-based segment is a molecular chain having a urethane bond, and both ends of the urethane-based segment are covalently bonded to the acrylic polymer chain, thereby introducing a crosslinked structure to the acrylic polymer chain.

(Structure of urethane segment)
A urethane-based segment typically includes a polyurethane chain obtained by reacting a diol and a diisocyanate. The molecular weight of the polyurethane chain in the urethane-based segment is preferably from 4,000 to 50,000, more preferably from 4,500 to 40,000, and even more preferably from 5,000 to 30,000, from the viewpoint of obtaining a pressure-sensitive adhesive capable of achieving both low-temperature adhesiveness and high-temperature holding power.

The larger the molecular weight of the polyurethane chain in the urethane-based segment, the longer the distance between cross-linking points of the acrylic polymer chain. When the molecular weight of the polyurethane chain is too small and the distance between cross-linking points is short, the storage elastic modulus increases as the cohesion increases. Along with this, the viscosity of the pressure-sensitive adhesive sheet is lowered, and tan δ is lowered, so that the impact resistance tends to be lowered. When the molecular weight of the polyurethane chain is excessively large and the distance between cross-linking points is long, the storage elastic modulus may be small and the adhesive holding power may be insufficient. When the molecular weight of the polyurethane chain is within the above range, the pressure-sensitive adhesive has appropriate cohesiveness, and thus both impact resistance and adhesive holding power can be achieved.

Diols used for forming polyurethane chains include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, hexamethylene glycol; polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, epoxy polyols, caprolactone polyols, etc. of high molecular weight polyols.

A polyether polyol is obtained by ring-opening addition polymerization of an alkylene oxide to a polyhydric alcohol. Alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, and the like. Examples of polyhydric alcohols include the aforementioned diols, glycerin, trimethylolpropane, and the like.

A polyester polyol is a polyester having terminal hydroxyl groups, and is obtained by reacting a polybasic acid and a polyhydric alcohol such that the alcohol equivalent is excessive with respect to the carboxylic acid equivalent. A combination of a dibasic acid and a diol is preferable as the polybasic acid component and the polyhydric alcohol component that constitute the polyester polyol.

Dibasic acid components include aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid and terephthalic acid; Formula dicarboxylic acids; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid; and acid anhydrides and lower alcohol esters of dicarboxylic acids.

Diol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F , hydrogenated bisphenol A, hydrogenated bisphenol F and the like.

Examples of polycarbonate polyols include polycarbonate polyols obtained by subjecting a diol component and phosgene to a polycondensation reaction; Polycarbonate polyols obtained by transesterification condensation with carbonic acid diesters such as diphenyl and dibenzyl carbonate; copolymerized polycarbonate polyols obtained by combining two or more polyol components; esterification of the above various polycarbonate polyols and carboxy group-containing compounds Polycarbonate polyols obtained by reacting; Polycarbonate polyols obtained by etherification reaction of various polycarbonate polyols and hydroxyl-containing compounds; Polycarbonate polyols obtained by transesterification of various polycarbonate polyols and ester compounds; Polycarbonate polyol obtained by subjecting a polyol and a hydroxyl group-containing compound to a transesterification reaction; Polyester-based polycarbonate polyol obtained by polycondensation of the various polycarbonate polyols described above and a dicarboxylic acid compound; Copolymerizing the various polycarbonate polyols described above with an alkylene oxide. Copolymerized polyether-based polycarbonate polyols and the like obtained are included.

A polyacrylic polyol is obtained by copolymerizing a (meth)acrylic acid ester and a monomer component having a hydroxyl group. Examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, (meth) ) Hydroxyalkyl esters of (meth)acrylic acid such as 4-hydroxybutyl acrylate and 2-hydroxypentyl (meth)acrylate; (meth)acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; N- Methylol (meth)acrylamide and the like can be mentioned. (Meth)acrylic acid esters include methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

The polyacrylic polyol may contain monomer components other than the above as copolymer components. 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; and unsaturated nitriles such as (meth)acrylonitrile. Unsaturated amides such as (meth)acrylamide and N-methylol (meth)acrylamide; Vinyl esters such as vinyl acetate and vinyl propionate; Vinyl ethers such as methyl vinyl ether; α-olefins such as ethylene and propylene; halogenated α,β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene;

Diisocyanates used to form polyurethane chains may be either aromatic diisocyanates or aliphatic diisocyanates. Examples of aromatic diisocyanates include 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diphenyldimethylmethane diisocyanate, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4- Phenylene diisocyanate, 2-chloro-1,4-phenyl diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl sulfoxide diisocyanate , 4,4′-diphenylsulfone diisocyanate, 4,4′-biphenyl diisocyanate, and the like. Aliphatic diisocyanates include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, and isophorone diisocyanate. , dicyclohexylmethane-4,4′-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate and the like.

Derivatives of isocyanate compounds can also be used as diisocyanates. Derivatives of isocyanate compounds include polyisocyanate dimers, isocyanate trimers (isocyanurate), polymeric MDI, adducts with trimethylolpropane, biuret modified products, allophanate modified products, urea modified products, and the like. . As the diisocyanate component, a urethane prepolymer having terminal isocyanate groups may be used.

(Introduction of crosslinked structure to acrylic polymer chain by urethane segment)
A compound having a functional group at the end of the polyurethane chain that can be copolymerized with the monomer component that constitutes the acrylic polymer chain, or a functional group at the end of the polyurethane chain that can react with the carboxy group, hydroxyl group, etc. contained in the acrylic polymer chain. By using a compound having a group, it is possible to introduce a crosslinked structure by a urethane-based segment into an acrylic polymer chain. A urethane di(meth) urethane having (meth)acryloyl groups at both ends of the urethane chain because it is easy to uniformly introduce cross-linking points into the acrylic polymer chain and has excellent compatibility between the acrylic polymer chain and the urethane segment. It is preferable to use an acrylate to introduce a crosslinked structure by a urethane-based segment. For example, by copolymerizing a monomer component constituting an acrylic polymer chain and urethane di(meth)acrylate, a crosslinked structure by urethane-based segments can be introduced into the acrylic polymer chain.

A urethane di(meth)acrylate having (meth)acryloyl groups at both ends can be obtained, for example, by using a (meth)acrylic compound having a hydroxyl group in addition to a diol component in polyurethane polymerization. From the viewpoint of controlling the chain length (molecular weight) of the urethane-based segment, after synthesizing an isocyanate-terminated polyurethane by reacting a diol and a diisocyanate so that the isocyanate is excessive, a (meth)acrylic compound having a hydroxyl group is added. Therefore, it is preferable to react the terminal isocyanate groups of the polyurethane with the hydroxyl groups of the (meth)acrylic compound.

By reacting the polyhydric alcohol and the polyisocyanate compound so that the polyisocyanate compound is excessive, a urethane chain having an isocyanate group at the end can be obtained. To obtain isocyanate-terminated polyurethanes, diol and diisocyanate components are used such that the NCO/OH (equivalence ratio) is preferably between 1.1 and 2.0, more preferably between 1.15 and 1.5. do it. The diisocyanate component may be added after approximately equal amounts of the diol component and the diisocyanate component are mixed and reacted.

Examples of (meth)acrylic compounds having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethylacrylamide, and hydroxyethyl. acrylamide and the like.

As urethane (meth)acrylate, using commercial products sold by companies such as Arakawa Chemical Industry, Shin-Nakamura Chemical Industry, Toagosei, Kyoeisha Chemical, Nippon Kayaku, Nippon Synthetic Chemical Industry, Negami Kogyo, Daicel Ornex, etc. good too. The weight average molecular weight of the urethane (meth)acrylate is preferably 4,000 to 50,000, more preferably 4,500 to 40,000, 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 urethane acrylate with a low Tg, it is possible to obtain a pressure-sensitive adhesive with excellent low-temperature adhesive strength even when a crosslinked structure is introduced by a urethane-based segment to increase the cohesive strength of the base polymer. The lower limit of the glass transition temperature of the urethane (meth)acrylate is not particularly limited, but from the viewpoint of obtaining a pressure-sensitive adhesive with excellent high temperature holding power, it is preferably -100 ° C. or higher, more preferably -90 ° C. or higher, and -80 ° C. or higher. More preferred.

When urethane (meth)acrylate is used to introduce a crosslinked structure with urethane segments into the acrylic polymer chain, the glass transition temperature of the urethane segments of the base polymer is approximately equal to the glass transition temperature of urethane (meth)acrylate. .

<Preparation of base polymer>
A polymer in which a crosslinked structure by a urethane-based segment is introduced into an acrylic polymer chain can be polymerized by various known methods. When urethane (meth)acrylate is used as a constituent component of the urethane-based segment, the urethane (meth)acrylate may be copolymerized with the monomer component for constituting the acrylic polymer chain.

The amount of urethane (meth)acrylate used is preferably 3 to 30 parts by weight, more preferably 4 to 25 parts by weight, based on 100 parts by weight of the monomer component for forming the acrylic polymer chain. By adjusting the amount of urethane (meth)acrylate used, a base polymer having a urethane-based segment content within the range described above can be prepared. When the content of the urethane-based segment is excessively small, the cohesiveness of the base polymer is lowered, which tends to lower the adhesive holding power of the PSA sheet. When the content of the urethane-based segment is excessively high, the cohesiveness of the base polymer increases and the viscosity of the pressure-sensitive adhesive sheet tends to decrease, resulting in a decrease in impact resistance.

Photopolymerization is preferred as the method of polymerizing the base polymer. Since the polymer can be prepared by photopolymerization without using a solvent, it is not necessary to remove the solvent by drying when forming the adhesive sheet, and a thick adhesive sheet can be uniformly formed.

In the preparation of the base polymer, the total amount of the monomer component constituting the acrylic polymer chain and the urethane (meth)acrylate for introducing the crosslinked structure may be reacted at once, or the polymerization may be carried out in multiple stages. As a method of performing polymerization in multiple stages, monofunctional monomers constituting acrylic polymer chains are polymerized to form a prepolymer composition (prepolymerization), and urethane di(meth)acrylate is added to the syrup of the prepolymer composition. A method of polymerizing (main polymerization) the prepolymer composition and the polyfunctional monomer by adding a polyfunctional compound such as the above is preferred. The prepolymer composition is a partially polymerized product containing a polymer with a low degree of polymerization and unreacted monomers.

By prepolymerizing the constituent components of the acrylic polymer, branching points (crosslinking points) due to a polyfunctional compound such as urethane di(meth)acrylate can be uniformly introduced into the acrylic polymer chain. Alternatively, a mixture (adhesive composition) of a low-molecular-weight polymer or a partially polymerized product and an unpolymerized monomer component may be applied onto a substrate and then subjected to main polymerization on the substrate to form an adhesive sheet. can also

Since a low polymer composition such as a prepolymer composition has a low viscosity and is excellent in coatability, a method of applying a pressure-sensitive adhesive composition, which is a mixture of a prepolymer composition and a polyfunctional compound, and then performing main polymerization on a substrate. According to this, the productivity of the adhesive sheet can be improved, and the thickness of the adhesive sheet can be made uniform.

[Adhesive sheet]
As described above, a prepolymer composition with a low degree of polymerization is prepared by prepolymerization, and a pressure-sensitive adhesive composition obtained by adding a polyfunctional compound or the like to the prepolymer composition is applied in layers on a substrate, and A pressure-sensitive adhesive sheet is obtained by polymerizing the pressure-sensitive adhesive composition (main polymerization).

<Preliminary polymerization>
A prepolymer composition can be prepared, for example, by polymerizing a composition obtained by mixing a monomer component constituting an acrylic polymer chain and a polymerization initiator. The prepolymer-forming composition may contain a polyfunctional compound (polyfunctional monomer or polyfunctional oligomer). For example, a part of the polyfunctional compound as a raw material of the polymer may be contained in the prepolymer-forming composition, and after the prepolymer is polymerized, the rest of the polyfunctional compound may be added and subjected to the main polymerization.

The prepolymer-forming composition preferably contains a photopolymerization initiator. Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, Examples include benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

In the polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retarder), or the like may be used for the purpose of molecular weight adjustment or the like. Chain transfer agents include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, Examples include α-methylstyrene dimer and the like.

The prepolymer-forming composition may contain a chain transfer agent and the like, if necessary, in addition to the monomers and the polymerization initiator. The polymerization initiator and chain transfer agent used for prepolymerization are not particularly limited, and for example, the photopolymerization initiator and chain transfer agent described above can be used.

Although the polymerization rate of the prepolymer is not particularly limited, it is preferably 3 to 50% by weight, more preferably 5 to 40% by weight, from the viewpoint of obtaining a viscosity suitable for coating on a substrate. The polymerization rate of the prepolymer can be adjusted within a desired range by adjusting the type and amount of the photopolymerization initiator used, and the irradiation intensity and irradiation time of actinic rays such as UV light. The polymerization rate of the prepolymer is calculated by the following formula from the weights before and after heating at 130° C. for 3 hours. The polymerization rate of the adhesive sheet is also calculated by the same method.
Polymerization rate (%) = weight after drying / weight before drying x 100

<Preparation of adhesive composition>
The above prepolymer composition is mixed with urethane (meth)acrylate and, if necessary, the remainder of the monomer components constituting the acrylic polymer chain, a polymerization initiator, a chain transfer agent, other additives, etc. to form an adhesive. A composition is prepared. The pressure-sensitive adhesive composition preferably has a viscosity (for example, about 0.5 to 20 Pa·s) suitable for application onto a substrate. By adjusting the polymerization rate of the prepolymer, the amount of urethane (meth)acrylate added, and the composition, molecular weight, amount, etc. of other components (for example, oligomers), the viscosity of the pressure-sensitive adhesive composition can be adjusted to an appropriate range. can. A thickening additive or the like may be used for the purpose of viscosity adjustment or the like.

The polymerization initiator and chain transfer agent used in this polymerization are not particularly limited, and for example, the photopolymerization initiator and chain transfer agent described above can be used. When the polymerization initiator used in the prepolymerization remains uninactivated in the prepolymer composition, the addition of the polymerization initiator for the main polymerization can be omitted.

(oligomer)
The pressure-sensitive adhesive composition may contain various oligomers for the purpose of adjusting the adhesive force of the pressure-sensitive adhesive sheet, adjusting the viscosity, and the like. As the oligomer, for example, one having a weight average molecular weight of about 1,000 to 30,000 is used. As the oligomer, an acrylic oligomer is preferable because of its excellent compatibility with the acrylic base polymer.

The acrylic oligomer contains a (meth)acrylic acid alkyl ester as a main constituent monomer component. Among them, as constituent monomer components, a (meth)acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth)acrylate) and a (meth)acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl (Meth)acrylate) is preferred. Specific examples of chain alkyl (meth)acrylates and alicyclic alkyl (meth)acrylates are as exemplified above as monomers constituting acrylic polymer chains.

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. The combined use of a low-Tg base polymer into which a cross-linked structure with urethane-based segments has been introduced and a high-Tg acrylic oligomer tends to improve the adhesive holding power of the pressure-sensitive adhesive sheet. Although the upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, it 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 is calculated by the aforementioned Fox formula.

Among the exemplified (meth)acrylic acid alkyl esters, methyl methacrylate is preferable as the chain alkyl (meth)acrylate because of its high glass transition temperature and excellent compatibility with the base polymer. Preferred alicyclic alkyl (meth)acrylates are dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate. That is, the acrylic oligomer contains, as constituent monomer components, one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate. Those containing are preferred.

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

The weight average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, even more preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight within this range, there is a tendency for the adhesive strength and adhesive holding power of the pressure-sensitive adhesive to improve.

Acrylic oligomers are obtained by polymerizing the above monomer components by various polymerization methods. Various polymerization initiators may be used in the polymerization of the acrylic oligomer. A chain transfer agent may also be used for the purpose of adjusting the molecular weight.

When the pressure-sensitive adhesive composition contains an oligomer component such as an acrylic oligomer, the content thereof is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, relative to 100 parts by weight of the base polymer. , 2 to 10 parts by weight are more preferable. When the content of the oligomer in the pressure-sensitive adhesive composition is within the above range, the adhesiveness at high temperatures and the high-temperature holding power tend to be improved.

(Silane coupling agent)
A silane coupling agent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting adhesive strength. When a silane coupling agent is added to the adhesive composition, the amount added is usually about 0.01 to 5.0 parts by weight, and 0.03 to 2.0 parts by weight, relative to 100 parts by weight of the base polymer. It is preferable that it is a degree.

(crosslinking agent)
The base polymer may have a crosslinked structure other than the above polyfunctional compound, if necessary. By including a cross-linking agent in the pressure-sensitive adhesive composition, a cross-linked structure can be introduced into the base polymer. Examples of the cross-linking agent include compounds that react with functional groups such as hydroxyl groups and carboxy groups contained in the polymer. Specific examples of cross-linking agents include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, carbodiimide-based cross-linking agents, and metal chelate-based cross-linking agents.

When the introduction amount of the crosslinked structure other than the urethane-based segment increases, the viscosity may decrease and the impact resistance may decrease. Therefore, the amount of the cross-linking agent used is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and even more preferably 1 part by weight or less with respect to 100 parts by weight of the base polymer.

(other additives)
In addition to the components exemplified above, the adhesive composition includes tackifiers, plasticizers, softeners, antidegradants, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, antistatic agents, and the like. may contain additives.

<Application and main polymerization of adhesive composition>
After applying the pressure-sensitive adhesive composition in layers on a substrate, photocuring is performed by irradiating actinic rays. When performing photocuring, it is possible to prevent polymerization inhibition by oxygen by attaching a cover sheet to the surface of the coating layer and irradiating actinic rays while the pressure-sensitive adhesive composition is sandwiched between two sheets. preferable.

Any appropriate base material can be used as the base material and the cover sheet used to form the pressure-sensitive adhesive sheet. The base material and the cover sheet may be a release film having a release layer on the contact surface with the pressure-sensitive adhesive sheet.

Films made of various resin materials are used as the film substrate of the release film. Examples of resin materials include polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate, acetate-based resins, polyethersulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, (meth)acrylic-based resins, Polyvinyl chloride-based resins, polyvinylidene chloride-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, polyarylate-based resins, polyphenylene sulfide-based resins, and the like are included. Among these, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the film substrate is preferably 10-200 μm, more preferably 25-150 μm. Materials for the release layer include silicone-based release agents, fluorine-based release agents, long-chain alkyl-based release agents, fatty acid amide-based release agents, and the like. The thickness of the release layer is generally about 10 to 2000 nm.

Methods for applying the adhesive composition onto the substrate include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, and curtain coating. , lip coat, die coater and the like are used.

Main polymerization is carried out by irradiating actinic rays to the pressure-sensitive adhesive composition applied in layers on the substrate. In this polymerization, the unreacted monomer component in the prepolymer composition reacts with urethane (meth)acrylate to obtain a base polymer in which a cross-linked structure by urethane-based segments is introduced into the acrylic polymer chain.

Actinic rays may be selected according to the type of polymerizable components such as monomers and urethane (meth)acrylates, the type of photopolymerization initiator, etc. Generally, ultraviolet rays and/or short wavelength visible light are used. . The integrated light quantity of the irradiation light is preferably about 100 to 5000 mJ/cm ² . The light source for light irradiation is not particularly limited as long as it can irradiate light in the wavelength range to which the photopolymerization initiator contained in the pressure-sensitive adhesive composition is sensitive. Lamps, metal halide lamps, xenon lamps and the like are preferably used. The polymerization rate of the pressure-sensitive adhesive sheet after main polymerization is preferably 97% or more, more preferably 98% or more, and even more preferably 99% or more. In order to increase the rate of polymerization, the adhesive sheet after photocuring may be heated to volatilize residual monomers, unreacted polymerization initiators, and the like.

By pasting the release films 1 and 2 on the surface of the adhesive sheet 5, the adhesive sheet with the release films temporarily adhered to both sides is obtained as shown in FIG. A release film used as a base material or a cover sheet when forming an adhesive sheet may be used as the release films 1 and 2 as they are.

When the release films 1 and 2 are provided on both sides of the pressure-sensitive 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. Even if the peeling force when peeling the release film temporarily attached to one surface from the adhesive sheet 5 and the peeling force when peeling the release film temporarily attached to the other surface from the adhesive sheet 5 are the same. can be different. When the peel strengths of the two are different, the release film 2 (light release film) having a relatively small peel strength is first peeled from the adhesive sheet 5 and then bonded to the first adherend. It is excellent in workability when the release film 1 (heavy release film) with a large release force is peeled off and the second adherend is laminated.

[Image display device]
The pressure-sensitive adhesive sheet of the present invention can be used for laminating various transparent members and opaque members. The type of the adherend is not particularly limited, and examples include various resin materials, glass, metals, and the like. Since the pressure-sensitive adhesive sheet of the present invention has high transparency, it is suitable for bonding optical members such as image display devices. In particular, the pressure-sensitive adhesive sheet of the present invention is excellent in adhesion durability and impact resistance, and thus is suitably used for bonding a transparent member such as a front transparent plate or a touch panel to the viewing side surface of an image display device.

FIG. 2 is a cross-sectional view showing an example of the lamination structure of the image display device in which the front transparent plate 7 is attached to the viewer side surface of the image display panel 10 with the adhesive sheet 5 interposed therebetween. The image display panel 10 includes a polarizing plate 3 attached to the viewing side surface of an image display cell 6 such as a liquid crystal cell or an organic EL cell with an adhesive sheet 4 interposed therebetween. The front transparent plate 7 may be a transparent flat plate 71 provided with a step formed by a printed layer 76 or the like on the peripheral edge of one surface thereof. As the transparent plate 71, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate is used. The transparent plate 71 may have a touch panel function. As the touch panel, any type of touch panel such as a resistive type, capacitive type, optical type, ultrasonic type, or the like is used.

The polarizing plate 3 provided on the surface of the image display panel 10 and the front transparent plate 7 are bonded together with the adhesive sheet 5 interposed therebetween. The order of bonding is not particularly limited, and the adhesive sheet 5 may be bonded to the image display panel 10 first, or the adhesive sheet 5 may be bonded to the front transparent plate 7 first. good. Moreover, both bonding can be performed at the same time. From the viewpoint of bonding workability, after peeling one release film (light release film) 2, the exposed surface of the adhesive sheet 5 is bonded to the image display panel 10, and then the other release film 1 is attached. It is preferable to peel off the (heavy release film) and attach the exposed surface of the adhesive sheet to the front transparent plate 7 .

After bonding the adhesive sheet 5 and the front transparent plate 7, defoaming is performed to remove air bubbles at the interface between the adhesive sheet 5 and the flat plate 71 portion of the front transparent plate 7 and near the non-flat portions such as the printed layer 76. may be performed. Appropriate methods such as heating, pressurization, and decompression can be employed as defoaming methods. For example, lamination may be performed under reduced pressure and heating while suppressing inclusion of air bubbles, and thereafter, for the purpose of suppressing delay bubbles, etc., pressure may be applied simultaneously with heating by autoclave treatment or the like. When defoaming is performed by heating, the heating temperature is generally about 40 to 150.degree. When pressurization is performed, the pressure is generally about 0.05 MPa to 2 MPa.

If a gap 90 exists between the housing 9 and the front transparent plate 7, it is preferable to seal the gap 90 by filling the gap 90 with a resin material or the like. As described above, the pressure-sensitive adhesive sheet 5 has a high shear storage modulus, and therefore has excellent adhesion reliability over a wide temperature range. Therefore, even if stress strain occurs at the bonding interface of the adhesive sheet due to temperature change during sealing with a resin material or the like, peeling at the bonding interface can be suppressed. Moreover, since the adhesive sheet 5 has a low glass transition temperature and a large peak top value of tan δ, it has excellent impact resistance in a wide temperature range and is less likely to peel off due to impact such as dropping.

[Optical film with adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention can be used as a film with a pressure-sensitive adhesive, in which the pressure-sensitive adhesive sheet is fixed to an optical film or the like, in addition to the form in which release films are temporarily attached on both sides as shown in FIG. For example, in the form shown in FIG. 3 , the release film 1 is temporarily attached to one surface of the adhesive sheet 5 and the 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 the release film 2 is temporarily attached thereon.

In this way, in the form in which an optical film such as a polarizing plate is attached to the adhesive sheet in advance, the release film 1 temporarily attached to the surface of the adhesive sheet 5 is peeled off, and the adhesive sheet 5 is attached to the front transparent member. You can do it.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Preparation of acrylic oligomer]
60 parts by weight of dicyclopentanyl 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, and nitrogen The mixture was stirred at 70° C. for 1 hour under atmosphere. Next, 0.2 parts by weight of 2,2′-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator, reacted at 70° C. for 2 hours, and then heated to 80° C. for 2 hours. reacted. After that, the reaction solution was heated to 130° C., and the toluene, chain transfer agent and unreacted monomer were removed by drying to obtain a solid acrylic oligomer. The acrylic oligomer had a weight average molecular weight of 5,100.

[Example 1]
(Polymerization of prepolymer)
As monomer components for forming the prepolymer, butyl acrylate (BA) 52.8 parts by weight, cyclohexyl acrylate (CHA) 10.9 parts by weight, N-vinyl-2-pyrrolidone (NVP) 9.7 parts by weight, acrylic acid 4-Hydroxybutyl (4HBA) 14.8 parts by weight, and isostearyl acrylate (ISTA) 11.8 parts by weight, and a photopolymerization initiator (BASF "Irgacure 184": 0.035 parts by weight, and BASF " Irgacure 651": After blending 0.035 parts by weight, the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30 ° C.) is irradiated with ultraviolet rays until the viscosity reaches about 20 Pa s to polymerize. A composition (polymerization rate: about 9%) was obtained.

(Preparation of photocurable pressure-sensitive adhesive composition)
In the above prepolymer composition, as urethane (meth) acrylate, terminal acrylic-modified polyether urethane (manufactured by Nippon Synthetic Chemical Industry "UV-3300B"): 7 parts by weight, and terminal acrylic-modified polyester urethane (manufactured by Nippon Synthetic Chemical Industry "UV-3010B"): 3 parts by weight, the above acrylic oligomer: 5 parts by weight, Irgacure 184: 0.05 parts by weight and Irgacure 651: 0.57 parts by weight as a photopolymerization initiator, As a chain transfer agent, α-Methylstyrene dimer (Nofuma MSD manufactured by NOF Corporation): 0.1 parts by weight, and Shin-Etsu Chemical Co., Ltd. "KBM403" as a silane coupling agent): After adding 0.3 parts by weight, these are uniformly to prepare a pressure-sensitive adhesive composition.

(Preparation of adhesive sheet)
A 75 μm-thick polyethylene terephthalate (PET) film (Mitsubishi Chemical “Diafoil MRF75”) having a silicone-based release layer on the surface is used as a substrate (double release film), and the above photocurable adhesive is applied on the substrate. A coating layer was formed by coating the agent composition so as to have a thickness of 150 μm. A 75 μm-thick PET film (“Diafoil MRE75” manufactured by Mitsubishi Chemical Co., Ltd.) having one side subjected to silicone release treatment was laminated as a cover sheet (which also serves as a light release film) onto this coating layer. This laminate was irradiated with ultraviolet rays from the cover sheet side by a black light whose position was adjusted so that the irradiation intensity on the irradiation surface directly below the lamp was 5 mW/cm ² , and photocuring was performed, resulting in a thickness of 150 μm and a polymerization rate of 99. % adhesive sheet was obtained.

[Examples 2 to 5, Comparative Examples 1 to 8]
The composition of the monomers charged in the polymerization of the prepolymer, and the types and amounts of polyfunctional compounds (urethane acrylate and/or polyfunctional acrylate), acrylic oligomers, photopolymerization initiators, and chain transfer agents added to the adhesive composition are shown. 1 has been modified. Otherwise, a photocurable adhesive composition was prepared in the same manner as in Example 1, applied onto a substrate, and photocured to obtain an adhesive sheet.

[evaluation]
<Weight average molecular weight>
The weight average molecular weights (Mw) of acrylic oligomers and urethane (meth)acrylates were measured using a Tosoh GPC (gel permeation chromatography) device (product name “HLC-8120GPC”). As a measurement sample, a 0.1% by weight solution obtained by dissolving the base polymer in tetrahydrofuran was filtered through a 0.45 μm membrane filter, and the filtrate was used. The measurement conditions of GPC are as follows.
(Measurement condition)
Column: manufactured by Tosoh Corporation, G7000HXL + GMHXL + GMHXL
Column size: each 7.8 mmφ x 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 tan δ peak value of pressure-sensitive adhesive sheet>
A sample for measurement was prepared by laminating 10 pressure-sensitive adhesive sheets to a thickness of about 1.5 mm. Dynamic viscoelasticity was measured under the following conditions using "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific.
(Measurement condition)
Deformation mode: Torsion Measurement frequency: 1Hz
Heating rate: 5°C/min Shape: Parallel plate 7.9mmφ

The shear storage modulus was determined by reading the storage modulus G' at each temperature from the measurement results. The temperature (peak top temperature) at which the loss tangent (tan δ) becomes maximum was defined as the glass transition temperature of the adhesive sheet. Also, the tan δ value (peak top value) at the glass transition temperature was read.

<Adhesive strength>
Peel off the light release film from the adhesive sheet, attach a 50 μm thick PET film, cut into 10 mm width × 100 mm length, peel off the heavy release film, and press and adhere to the glass plate with a 5 kg roller. A sample for force measurement was prepared. After holding the adhesive force measurement sample in an environment of 25° C. or 65° C. for 30 minutes, using a tensile tester, the test piece was peeled from the glass plate under the conditions of a tensile speed of 300 mm/min and a peeling angle of 180°. to measure the peel force.

<Haze>
Using a test piece in which an adhesive sheet is attached to an 800 μm thick non-alkali glass (total light transmittance 92%, haze 0.4%), using a haze meter (“HM-150” manufactured by Murakami Color Research Laboratory), Haze was measured. The value obtained by subtracting the haze (0.4%) of alkali-free glass from the measured value was taken as the haze of the adhesive sheet.

<Interlayer adhesion>
(Preparation of test sample)
Cut out the adhesive sheet to a size of 75 mm × 45 mm, peel off the light release film from the adhesive sheet, put a roll laminator in the center of a glass plate (100 mm × 50 mm) with a thickness of 500 μm (pressure between rolls: 0.2 MPa, feed speed: 100 mm / min). After that, the heavy release film was peeled off, and a glass plate (50 mm × 100 mm) with a thickness of 500 µm on which black ink with a thickness of 30 µm was printed in a frame shape on the peripheral edge was vacuum pressed (surface pressure: 0.3 MPa, pressure: 100 Pa). pasted together. The ink-printed area of the glass plate was 5 mm from both ends in the short side direction and 15 mm from both ends in the long side direction, and the black ink layer was in contact with the area of 5 mm from the ends of the four sides of the adhesive sheet. This sample was treated in an autoclave (50° C., 0.5 MPa) for 30 minutes.

After holding the above sample in an environment of 60 ° C. for 30 minutes, as shown in FIG. Hold for 10 seconds. The edge of the adhesive sheet was observed with a digital microscope with a magnification of 20 times. When streak-like air bubbles (see FIG. 5B) or peeling of the adhesive sheet from the glass plate occurred, it was evaluated as NG, and when neither air bubbles nor peeling occurred, it was evaluated as OK.

<Impact resistance>
Glass plates were laminated on both sides of the adhesive sheet in the same manner as in the preparation of the sample for the interlayer adhesion test, except that the size of the glass plate without the black ink printed layer was changed to 100 mm × 70 mm. , and autoclave to prepare a test sample. As shown in FIG. 6, both ends of the test sample 95 in the short side direction were placed on a table 93 with an interval of 60 mm so that the glass plate 7 provided with the printed layer 76 was on the lower side. , and the upper surface of the end portion of the glass plate 5 not provided with the printed layer was fixed on the table 80 with an adhesive tape (not shown). After holding the test sample 95 fixed on the table 93 with adhesive tape for 24 hours in an environment of −5° C., the metal ball 97 having a mass of 11 g was placed on the glass plate 7 within 40 seconds after it was taken out to room temperature. was dropped from a height of 300 mm to conduct an impact resistance test.

In the impact resistance test, a cylindrical guide 99 was used to keep the falling position of the metal balls constant, and the guides 99 were placed at intervals of 10 mm in each of the short side and long side directions from the corners of the inner edge of the frame of the printed area of the printed layer 76 . A metal ball 97 was dropped on the position. Two tests were performed, and in both tests, the case where the glass plate was not peeled off was evaluated as OK, and the case where the glass plate was peeled off in either or both of the two tests was evaluated as NG.

[Evaluation results]
Table 1 shows the formulation of the adhesive composition used to prepare each adhesive sheet and the evaluation results of the adhesive sheet. In addition, in Table 1, each component is described by the following abbreviations.
<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

<Urethane acrylate>
UV-3300B: "UV-3300B" manufactured by Nippon Synthetic Chemical Industry (polyether urethane diacrylate with a weight average molecular weight of about 12000 and a glass transition temperature of -30 ° C.)
3400: polyether urethane diacrylate with a weight average molecular weight of about 3400)
UA-4200: Shin-Nakamura Chemical Co., Ltd. “UA-4200” (polyether urethane diacrylate with a weight average molecular weight of about 1000)
UN-350: "Art Resin UN-350" manufactured by Negami Kogyo (polyester urethane diacrylate with a weight average molecular weight of about 12,500 and a glass transition temperature of -57 ° C.)
UV-3010B: Nippon Synthetic Chemical Industry "UV-3010B" (polyester urethane diacrylate with a weight average molecular weight of about 18000)
Urethane monoacrylate: polyether urethane monoacrylate with a weight average molecular weight of about 1300)
<Polyfunctional acrylate>
HDDA: hexanediol diacrylate <photoinitiator>
Irg651: Irgacure 651 (2,2-dimethoxy-1,2-diphenylethan-1-one)
Irg184: Irgacure 184 (1-hydroxy-cyclohexyl-phenyl-ketone)

In Examples 1 and 2 using a pressure-sensitive adhesive composition obtained by adding urethane diacrylate or the like to a prepolymer composition obtained by prepolymerizing acrylic monomers having butyl acrylate as the main monomer, interlayer adhesion and fall All impact durability was good.

In Comparative Example 1 using a low-molecular-weight urethane diacrylate, the pressure-sensitive adhesive sheet had a low adhesive strength to an adherend, and was inferior in interlayer adhesion and drop impact durability. In Comparative Example 2 in which the amount of urethane diacrylate added was increased, the haze of the pressure-sensitive adhesive sheet was high and the transparency was lowered. In Comparative Example 3 using urethane monoacrylate, the pressure-sensitive adhesive sheet had a low shear storage modulus and poor adhesion durability.

Also in Example 3, Example 4 and Example 5 in which the composition of the acrylic monomer in the prepolymer-forming composition was changed, good adhesive properties were exhibited as in Examples 1 and 2.

In Comparative Example 4, in which the glass transition temperature was lowered by adjusting the composition of the acrylic monomer without using a urethane-based material, the G'25 _°C and G'80 _° C of the pressure-sensitive adhesive sheet were small, and the adhesion reliability was poor. . In Comparative Example 5, in which cohesiveness was increased by increasing the ratio of polar monomers (NVB and 4HBA) in the acrylic monomer component, adhesion was good, but impact resistance was low due to the high glass transition temperature. Was. A similar tendency was observed in Comparative Example 8 as well.

In Comparative Example 6, in which the ratio of the polyfunctional acrylate in the pressure-sensitive adhesive composition was increased, the peak top value of tan δ was small and the viscosity was low, resulting in insufficient adhesion and poor impact resistance. A similar tendency was observed in Comparative Example 7 in which a cross-linked structure was introduced with a low-molecular-weight urethane diacrylate. In these comparative examples, the main monomer of the acrylic polymer chain is either C8 alkyl acrylate ( ₂ -hydroxyethyl acrylate) or _C4 alkyl acrylate (butyl acrylate). This is considered to be one of the reasons why tan δ is smaller than in Examples 1 to 5 and the like.

From these results, the pressure-sensitive adhesive sheet containing a base polymer in which a crosslinked structure is introduced into the acrylic polymer chain using urethane diacrylate having a predetermined molecular weight exhibits a high shear storage modulus even at a low glass transition temperature, and a tan δ of Since it is large, it can be seen that both adhesion durability and impact resistance can be achieved.

5 adhesive sheet 1, 2 release film 3 polarizing plate 4 adhesive sheet 6 image display cell 10 image display panel 7 front transparent plate 9 housing 100 image display device

Claims (4)

A pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive containing an acrylic base polymer in which a crosslinked structure is introduced into an acrylic polymer chain is formed in a sheet form,
haze is 1% or less,
Adhesive force to glass is 2.0 N / 10 mm or more,
The glass transition temperature is -3 ° C. or less,
The shear storage modulus at a temperature of 25 ° C. is 0.16 MPa or more,
The peak top value of the loss tangent is 1.5 or more ,
The acrylic base polymer is formed by copolymerizing a monomer component constituting the acrylic polymer chain and a urethane di(meth)acrylate having (meth)acryloyl groups at both ends to form the urethane di(meth)acrylic polymer chain on the acrylic polymer chain. ) is introduced with a crosslinked structure by acrylate,
In the acrylic polymer chain, the amount of (meth)acrylic acid alkyl ester having a chain alkyl group of 6 or less carbon atoms with respect to the total amount of constituent monomer components is 30 to 80% by weight,
The urethane di(meth)acrylate has a weight average molecular weight of 4000 to 50000 and a glass transition temperature of 0° C. or less,
The amount of the urethane di(meth)acrylate is 3 to 30 parts by weight with respect to 100 parts by weight of the monomer component constituting the acrylic polymer chain.
adhesive sheet. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive contains an acrylic oligomer having a weight average molecular weight of 1,000 to 30,000. A method for producing the pressure-sensitive adhesive sheet according to claim 1 or 2 ,
After applying a composition containing an acrylic monomer and/or its partial polymer and urethane di(meth)acrylate in a layer on a substrate, the composition is irradiated with actinic rays for photocuring ,
In the acrylic monomer and/or its partial polymer, the amount of (meth)acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms is 30 to 80% by weight with respect to the total amount of the monomer component,
The urethane di(meth)acrylate has a weight average molecular weight of 4000 to 50000 and a glass transition temperature of 0° C. or less,
In the composition, the content of the urethane (meth)acrylate is 3 to 30 parts by weight with respect to a total of 100 parts by weight of the acrylic monomer and the partially polymerized product thereof.
A method for manufacturing an adhesive sheet. 3. An image display device, wherein a front transparent member is fixed to the viewing side surface of an image display panel with the pressure-sensitive adhesive sheet according to claim 1 or 2 .

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