CN115595073B - Pressure-sensitive adhesive sheet, method for producing the same, and image display device - Google Patents

Abstract

The invention relates to an adhesive sheet, a method for manufacturing the same, and an image display device. The adhesive sheet (5) has a haze of 1% or less, an adhesive strength to glass of 2.0N/10mm or more, a glass transition temperature of-3 ℃ or less, and a shear storage modulus at a temperature of 25 ℃ of 0.16MPa or more. The pressure-sensitive adhesive sheet (5) can be obtained, for example, by: a composition containing an acrylic monomer and/or a partial polymer thereof and a urethane (meth) acrylate is applied in a layer on a substrate, and then the composition is irradiated with an active ray to be photo-cured.

Description

Pressure-sensitive adhesive sheet, method for producing the same, and image display device

The application relates to a divisional application of Chinese patent application with the application date of 2019, 1 month and 22 days and the application number of 201910058367.1.

Technical Field

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

Background

As various image display devices such as mobile phones, smart phones, car navigation devices, personal computer displays, and televisions, liquid crystal display devices and organic electroluminescence (organic EL) display devices are widely used. For the purpose of preventing breakage of the image display panel due to impact from the outer surface, a front transparent plate (also referred to as a "cover window" or the like) such as a transparent resin plate or a glass plate may be provided on the viewing side of the image display panel. In addition, in recent years, devices having a touch panel on the viewing side of an image display panel have been popular.

As a method of disposing a front surface transparent member such as a front surface transparent plate or a touch panel on the front surface of an image display panel, an "interlayer filling structure" is proposed in which the image display panel and the front surface transparent member are bonded to each other via an adhesive sheet. An adhesive sheet is sometimes provided between the touch panel and the front surface transparent plate. In the interlayer filling structure, the gaps between the members are filled with the adhesive, and therefore, the refractive index difference at the interface is reduced, and the deterioration of visibility due to reflection and scattering can be suppressed. In addition, in the interlayer filling structure, since the members are bonded and fixed by the adhesive sheet, there is an advantage that peeling of the front surface transparent member due to an impact such as dropping is less likely to occur than when the front surface transparent member is fixed only to the case. In particular, the use of a pressure-sensitive adhesive sheet having a large thickness tends to improve impact resistance. Since a pressure-sensitive adhesive sheet having a large thickness can be formed with a uniform thickness, solvent-free photocurable adhesives are widely used for pressure-sensitive adhesive sheets for interlayer filling (see, for example, patent document 1 and patent document 2).

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open publication No. 2014-125524

Patent document 2: international publication No. 2013/161666

Disclosure of Invention

Problems to be solved by the invention

Conventionally, a front transparent member such as a cover window has a size larger than that of a display panel, and is bonded to a case by an adhesive tape or the like in a region outside an outer periphery of the display panel. That is, the front surface transparent member is fixed by bonding to the case and bonding to the surface of the display panel by the interlayer filling adhesive sheet.

In recent years, a display device has been narrowed and borderless, mainly in a mobile device such as a smart phone. With the reduction of the frame and the non-frame, the size of the display panel 10 is equal to or larger than the size of the front surface transparent member 7. In such a configuration, the case 9 and the front surface transparent member 7 cannot be fixed by an adhesive tape or the like, and it is necessary to fix the front surface transparent member 7 by the adhesive sheet 5 for interlayer filling only (see fig. 2). Accordingly, the pressure-sensitive adhesive sheet for interlayer filling is required to have a higher adhesive strength and to be free from peeling due to impact such as dropping in a wide temperature range.

In addition, when the size of the display panel is equal to or larger than the size of the front transparent member 7, the display panel may be sealed with a resin material in order to fill the gap 90 between the case 9 and the front transparent member 7. For example, the resin material in a molten state is flowed into the gap 90, and then cooled to room temperature to solidify the resin, thereby sealing with the resin material. When the resin having a high temperature is flowed into the gap 90, the front surface transparent member 7, the case 9, and the adhesive sheet 5 reach a high temperature in the vicinity of the gap 90, and are cooled when the resin is solidified. The pressure-sensitive adhesive sheet 5 is required to have such a resistance to adhesive bonding against deformation stress that peeling between adherends does not occur even when dimensional deformation occurs in the front surface transparent member, the case, and the like with such a temperature change.

The conventional pressure-sensitive adhesive sheet for interlayer filling disclosed in patent document 1 and the like has a high glass transition temperature, and therefore has poor tackiness at low temperature and impact resistance. On the other hand, the adhesive sheet with a low glass temperature disclosed in patent document 2 has low adhesive resistance to deformation stress, and it is difficult to achieve both impact resistance at low temperature and durability to deformation stress upon heating and cooling of resin sealing and the like.

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

Means for solving the problems

The present invention relates to an adhesive sheet obtained by forming an adhesive containing a base polymer into a sheet shape. The haze of the adhesive sheet is 1% or less. The glass transition temperature of the pressure-sensitive adhesive sheet is preferably-3 ℃ or lower. The shear storage modulus G' _25℃ of the pressure-sensitive adhesive sheet at a temperature of 25 ℃ is preferably 0.16MPa or more. The peak top value of the loss tangent of the pressure-sensitive 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 crosslinking an acrylic polymer chain with a urethane segment is used. In order to satisfy the above-mentioned respective characteristics, the content of the urethane 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 segment is preferably 4000 to 50000.

The base polymer obtained by crosslinking an acrylic polymer chain with a urethane segment is obtained, for example, by copolymerizing a monomer component constituting the acrylic polymer chain with a urethane (meth) acrylate having a (meth) acryloyl group at least at both ends. As the polyfunctional urethane (meth) acrylate, urethane di (meth) acrylate having a (meth) acryloyl group at both ends is preferable.

The weight average molecular weight of the urethane (meth) acrylate is preferably 4000 to 50000. The glass transition temperature of the urethane (meth) acrylate is preferably 0 ℃ or lower.

An adhesive sheet containing a base polymer obtained by crosslinking an acrylic polymer chain with a urethane segment is obtained, for example, by applying a composition containing an acrylic monomer and/or a partial polymer thereof and a urethane (meth) acrylate in a layer form on a substrate, and then irradiating the composition with an active light to effect photocuring. 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 the partial polymer thereof.

The pressure-sensitive adhesive sheet of the present invention is used for bonding a transparent member to an image display device having a transparent member disposed on a viewing side surface. For example, an image display device is formed by fixing a front surface transparent member to a viewing side surface of an image display panel via the adhesive sheet.

Effects of the invention

The pressure-sensitive adhesive sheet of the present invention has a low glass transition temperature and a high shear storage modulus, and therefore can achieve both impact resistance against dropping and the like and adhesive durability against deformation stress in a wide temperature range. The adhesive sheet of the present invention is used to attach an image display device such as a cover window to a viewing side surface, and has excellent adhesion reliability, and can also cope with a narrow frame or no frame.

Drawings

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

Fig. 2 is a sectional view showing a configuration example of the image display device.

Fig. 3 is a cross-sectional view showing an example of a laminated structure of an optical film with an adhesive sheet.

Fig. 4 is a cross-sectional view showing an example of a laminated structure of an optical film with an adhesive sheet.

Fig. 5A is a photograph showing the case of the interlayer adhesiveness test.

Fig. 5B is a photograph of a sample in which streaked bubbles were generated in the interlayer adhesiveness test.

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

Reference numerals

5. Pressure-sensitive adhesive sheet

1.2 Release film

3. Polarizing plate

4. Pressure-sensitive adhesive sheet

6. Image display unit

10. Image display panel

7. Front surface transparent plate

9. Shell body

100. Image display device

Detailed Description

Fig. 1 shows a release film-equipped adhesive sheet having release films 1 and 2 temporarily attached to both sides of an adhesive sheet 5. Fig. 2 is a cross-sectional view showing an exemplary configuration of an image display device in 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 a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive is formed into a sheet shape. The adhesive sheet is a transparent adhesive sheet having a haze of 1.0% or less. The shear storage modulus G' _25℃ at 25℃of the pressure-sensitive adhesive sheet is preferably 0.16MPa or more. The G' _25℃ of the pressure-sensitive adhesive sheet is 0.16MPa or more, thereby improving the adhesive reliability. From the viewpoint of improving the adhesive reliability at high temperature, the shear storage modulus G' _80℃ at 80 ℃ of the adhesive sheet is preferably 0.11MPa or more.

On the other hand, from the viewpoint of ensuring wettability by providing an adhesive sheet with a proper tackiness, G' _25℃ of the adhesive sheet is preferably 1MPa or less, more preferably 0.5MPa or less, and still more preferably 0.4MPa or less. From the same viewpoint, G' _80℃ of the pressure-sensitive adhesive sheet is preferably 0.6MPa or less, more preferably 0.4MPa or less, and still more preferably 0.3MPa or less.

The glass transition temperature of the pressure-sensitive adhesive sheet is preferably-3 ℃ or lower. The glass transition temperature of the pressure-sensitive adhesive sheet is preferably-20℃or higher, more preferably-15℃or higher, and still more preferably-13℃or higher. When the glass transition temperature is within the above range, the pressure-sensitive adhesive sheet has an appropriate tackiness even in a low temperature range, and thus tends to be excellent in impact resistance.

The peak top value of the loss tangent tan δ of the pressure-sensitive adhesive sheet is preferably 1.5 or more, more preferably 1.6 or more, and still more preferably 1.7 or more. Adhesive sheets having a large peak top value of tan δ tend to have a large tackiness and excellent impact resistance.

The shear storage modulus G', the glass transition temperature and the peak top value of tan delta of the adhesive sheet were obtained by viscoelasticity measurement at a frequency of 1 Hz. The glass transition temperature is a temperature (peak top temperature) at which tan δ reaches a maximum. tan delta is the ratio G '/G' of the loss modulus G 'to the storage modulus G'. The storage modulus G' corresponds to a portion stored as elastic energy when the material is deformed, and is an index indicating the degree of hardness. The greater the storage modulus of the adhesive sheet, the higher the adhesive holding force, tending to inhibit peeling due to deformation. The loss modulus g″ corresponds to a loss energy portion that is dissipated by internal friction or the like when the material is deformed, and indicates the degree of tackiness. the greater tan δ, the greater the tendency for tackiness, the deformation behavior becomes a liquid behavior, and the rebound resilience energy tends to decrease.

The upper limit of the peak top value of tan δ of the pressure-sensitive adhesive sheet is not particularly limited, and is usually 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 pressure-sensitive adhesive sheet is preferably 2N/10mm or more, more preferably 2.5N/10mm or more, and still more preferably 3N/10mm or more. The adhesive strength of the adhesive sheet is in the above range, whereby peeling of the adhesive sheet from the adherend can be prevented when stress due to deformation, impact due to dropping, or the like is generated. The adhesive strength was determined by a peel test at a tensile speed of 60 mm/min and a peel angle of 180℃using a glass plate as an adherend. Unless otherwise specified, the adhesive strength was measured at 25 ℃.

The adhesive strength of the pressure-sensitive adhesive sheet at 65℃is preferably 1N/10mm or more, more preferably 1.5N/10mm or more, and still more preferably 2N/10mm or more.

The thickness of the pressure-sensitive adhesive sheet is not particularly limited, and may be set according to the type, shape, and the like of the adherend. When a member having a print level difference is used as the adherend, the thickness of the pressure-sensitive adhesive sheet is preferably larger than the thickness of the print level difference. The thickness of the pressure-sensitive adhesive sheet for bonding the front surface transparent plate (covering the window) is preferably 30 μm or more, more preferably 40 μm or more, and still more preferably 50 μm or more. By increasing the thickness of the adhesive sheet, the level difference absorbency tends to be high and the impact resistance tends to be high. The upper limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, and further preferably 250 μm or less from the viewpoint of productivity of the pressure-sensitive adhesive sheet.

[ Composition of adhesive ]

The pressure-sensitive adhesive sheet of the present invention is not particularly limited as long as the above characteristics are satisfied, and a pressure-sensitive adhesive containing a polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyvinyl ether, a vinyl acetate/vinyl chloride copolymer, a modified polyolefin, an epoxy, a fluorine-containing polymer, a natural rubber, or a synthetic rubber as a base polymer can be appropriately selected and used.

In particular, an acrylic adhesive containing an acrylic polymer as a base polymer is preferably used because it is excellent in optical transparency, exhibits suitable adhesive properties such as wettability, cohesiveness and tackiness, and is also excellent in weather resistance, heat resistance and the like. Among them, an acrylic base polymer having a structure in which an acrylic polymer chain is crosslinked by a urethane segment is preferable.

[ Base Polymer ]

The acrylic polymer chains are crosslinked by urethane segments, thereby enabling high adhesive retention at low glass transition temperatures. The content of the urethane segment in the base polymer is preferably 3 parts by weight or more per 100 parts by weight of the acrylic polymer chain.

When the amount of the urethane segment excessively increases, the tackiness of the adhesive sometimes decreases with an increase in the crosslinking density, and the impact resistance decreases. If the amount of the urethane segment is excessively increased, the transparency of the adhesive sheet may be lowered and the haze may be increased. Therefore, the amount of the urethane segment in the base polymer is preferably 30 parts by weight or less, more preferably 25 parts by weight or less, per 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 the present specification, "(meth) acrylic acid" means acrylic acid and/or methacrylic acid.

As the alkyl (meth) acrylate, an alkyl (meth) acrylate having an alkyl group with 1 to 20 carbon atoms is preferably used. In the alkyl (meth) acrylate, the alkyl group 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, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, isotridecyl (meth) acrylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, and nonadecyl (meth) acrylate.

Specific examples of the alkyl (meth) acrylate having an alicyclic alkyl group include cycloalkyl (meth) acrylates such as cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, and cyclooctyl (meth) acrylate; (meth) acrylic esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth) acrylate; (meth) acrylic esters having three or more aliphatic hydrocarbon rings, such as tetrahydrodicyclopentadiene (meth) acrylate, tetrahydrodicyclopentadiene oxyethyl (meth) acrylate, tetrahydrotricyclopentadienyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, 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, relative to the total amount of the monomer components constituting the acrylic polymer chain. From the viewpoint of adjusting the glass transition temperature (Tg) of the polymer chain to be within an appropriate range, the amount of the alkyl (meth) acrylate having a chain alkyl group having 4 to 10 carbon atoms in the acrylic polymer chain is preferably 30% by weight or more, more preferably 40% by weight or more, still more preferably 45% by weight or more, relative to the total amount of the constituent monomer components. The monomer components constituting the acrylic polymer chain refer to monomer components other than urethane (meth) acrylate and the like, which are constituent components of the urethane segment.

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

Examples of the hydroxyl group-containing monomer include (meth) acrylic esters such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, and (4-hydroxymethylcyclohexyl) methyl (meth) acrylate. Among them, from the viewpoint of high compatibility with urethane segments and improvement of transparency of the adhesive sheet, the acrylic polymer chain preferably contains a (meth) acrylate having a hydroxyalkyl group having 4 to 8 carbon atoms as a constituent monomer component.

The amount of the hydroxyl group-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, relative to 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, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

The acrylic polymer chain may contain a nitrogen-containing monomer as a constituent monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methyl vinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyridine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, and vinylpyrazineVinyl monomers such as oxazole, vinyl morpholine, (meth) acryloylmorpholine, N-vinylcarboxylic acid amide, and N-vinylcaprolactam, and cyano-containing acrylic monomers such as acrylonitrile and methacrylonitrile.

The acrylic polymer chain contains a highly polar monomer such as a hydroxyl group-containing monomer or a carboxyl group-containing monomer as a constituent monomer component, thereby improving the cohesive force of the adhesive and tending to improve the adhesive retention at high temperatures. On the other hand, when the content of the high-polarity monomer is too large, the glass transition temperature may be increased, and the tackiness and impact resistance at low temperature may be lowered. Therefore, the amount of the high-polarity monomer (the total of the hydroxyl group-containing monomer, the carboxyl group-containing monomer, and the nitrogen-containing monomer) relative to the total amount of the monomer components constituting the acrylic polymer chain is preferably 3 to 40% by weight, more preferably 5 to 35% by weight, and still more preferably 10 to 30% by weight. 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, based on the total amount of the monomer components constituting the acrylic polymer chain.

The acrylic polymer chain may contain, 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 monomers such as vinyl acetate, vinyl propionate, styrene, and α -methylstyrene; cyanoacrylate-containing monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing monomers such as glycidyl (meth) acrylate; glycol acrylic ester monomers such as polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, and methoxypolypropylene glycol (meth) acrylate; tetrahydrofurfuryl (meth) acrylate, fluorine-containing (meth) acrylate, polysiloxane (meth) acrylate, 2-methoxyethyl (meth) acrylate, and other acrylate monomers.

The acrylic polymer chain may contain multifunctional monomers or oligomers. The polyfunctional compound has two or more polymerizable functional groups having an unsaturated double bond such as a (meth) acryloyl group or a vinyl group in one molecule. Examples of the polyfunctional compound include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polybutylene glycol di (meth) acrylate, bisphenol a ethylene oxide modified di (meth) acrylate, bisphenol a propylene oxide modified di (meth) acrylate, alkanediol di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, ethoxylated isocyanuric acid triacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, ethoxylated 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, whereby a branched structure (crosslinked structure) is introduced into the polymer chain. As described later, in the adhesive of the present invention, a crosslinked structure is introduced on an acrylic polymer chain through a urethane segment. When the amount of the crosslinked structure derived from the polyfunctional monomer component other than the urethane segment is increased, the low-temperature adhesive strength of the adhesive may be reduced. Therefore, the amount of the polyfunctional compound (excluding urethane acrylate) is preferably 3% by weight or less, more preferably 1% by weight or less, further preferably 0.5% by weight or less, particularly preferably 0.3% by weight or less, relative to the total amount of the monomer components constituting the acrylic polymer chain.

Among the above monomer components, the acrylic polymer chain preferably contains the largest amount of alkyl (meth) acrylate. The properties of the adhesive sheet can be easily controlled by the kind of the monomer (main monomer) having the largest 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 be increased, and impact resistance tends to be improved. In particular, when a C ₄ alkyl acrylate such as butyl acrylate is used as a main monomer, the peak top value of tan δ tends to be high. The amount of the alkyl (meth) acrylate 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, and still more preferably 40 to 70% by weight, based on the total amount of monomer components constituting the acrylic polymer chain. 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℃or higher. The theoretical Tg of the acrylic polymer chain is preferably-10℃or lower, more preferably-20℃or lower, and still more preferably-25℃or lower. The theoretical Tg is calculated 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 by the following Fox formula.

1/Tg＝Σ(W_i/Tg_i)

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

< Urethane segment >

The urethane segment is a molecular chain having a urethane bond, and is covalently bonded to the acrylic polymer chain through both ends of the urethane segment, thereby introducing a crosslinked structure in the acrylic polymer chain.

(Structure of urethane segment)

The urethane segments typically comprise polyurethane chains obtained by reacting diols with diisocyanates. The molecular weight of the polyurethane chain in the urethane segment is preferably 4000 to 50000, more preferably 4500 to 40000, and even more preferably 5000 to 30000, from the viewpoint of obtaining an adhesive that can achieve both low-temperature tackiness and high-temperature retention.

The larger the molecular weight of the polyurethane chain in the urethane segment, the longer the inter-crosslink distance between the acrylic polymer chains. When the molecular weight of the polyurethane chain is too small and the distance between crosslinking points is short, the storage modulus increases as the cohesive force increases. With this, the tackiness of the pressure-sensitive adhesive sheet decreases, and tan δ decreases, so that impact resistance tends to decrease. When the molecular weight of the polyurethane chain is too large and the distance between crosslinking points is long, the storage 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 adhesive has moderate cohesiveness, and therefore can achieve both impact resistance and adhesive holding power.

Examples of the diol used for forming the polyurethane chain include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, and hexamethyleneglycol; high molecular weight polyols such as polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, epoxy polyols, caprolactone polyols, and the like.

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, trimethylolpropane, and the like.

The polyester polyol is a polyester having hydroxyl groups at the 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 polyacid component and the polyol 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; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1, 3-cyclohexanedicarboxylic acid, and 1, 4-cyclohexanedicarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and eicosanedioic acid; anhydrides of these dicarboxylic acids, lower alcohol esters, and the like.

The diol component may be: ethylene glycol, 1, 2-propylene glycol, 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.

The polycarbonate polyol may be obtained by polycondensation of a diol component and phosgene; polycarbonate polyols obtained by transesterification condensation of a diol component with a diester carbonate such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethylbutyl carbonate, ethylene carbonate, propylene carbonate, diphenyl carbonate, dibenzyl carbonate, etc.; a copolycarbonate polyol obtained by combining two or more kinds of polyol components; a polycarbonate polyol obtained by subjecting the above-mentioned various polycarbonate polyols to an esterification reaction with a carboxyl group-containing compound; a polycarbonate polyol obtained by subjecting the above-mentioned various polycarbonate polyols to etherification reaction with a hydroxyl group-containing compound; a polycarbonate polyol obtained by transesterification of the various polycarbonate polyols with an ester compound; a polycarbonate polyol obtained by subjecting the above-mentioned various polycarbonate polyols to transesterification with a hydroxyl group-containing compound; polyester-based polycarbonate polyols obtained by polycondensation of the above-mentioned various polycarbonate polyols with a dicarboxylic acid compound; and copolyether-type polycarbonate polyols obtained by copolymerizing the above-mentioned various polycarbonate polyols with an alkylene oxide.

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 hydroxyalkyl esters of (meth) acrylic acid such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 2-hydroxypentanyl (meth) acrylate; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; n-methylol (meth) acrylamides, and the like. Examples of the (meth) acrylic acid ester 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 copolymerized components. Examples of the comonomer component other than the above include unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid, anhydrides thereof, and monoesters or diesters thereof; 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; alpha-olefins such as ethylene and propylene; halogenated alpha, beta-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; and alpha, beta-unsaturated aromatic monomers such as styrene and alpha-methylstyrene.

The diisocyanate used to form the polyurethane chain may be any of aromatic diisocyanate and aliphatic diisocyanate. Examples of the aromatic diisocyanate include 1, 5-naphthalene diisocyanate, 4' -diphenylmethane diisocyanate (MDI), 2-bis (4-isocyanatophenyl) propane, tetramethyldiphenylmethane 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' -diphenyl ether diisocyanate, 4' -diphenyl sulfoxide diisocyanate, 4' -diphenyl sulfone diisocyanate, and 4,4' -biphenyl diisocyanate. Examples of aliphatic diisocyanates include butane-1, 4-diisocyanate, hexamethylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, cyclohexane-1, 4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4, 4' -diisocyanate, 1, 3-bis (isocyanatomethyl) cyclohexane, methylcyclohexane diisocyanate, and the like.

Derivatives of isocyanate compounds may also be used as diisocyanates. Examples of the derivative of the isocyanate compound include dimers of polyisocyanates, trimers (isocyanurates) of isocyanates, polymeric MDI, adducts with trimethylolpropane, biuret modified products, allophanate modified products, and urea modified products. As the diisocyanate component, a urethane prepolymer having an isocyanate group at the end can be used.

(Introduction of crosslinked Structure into acrylic Polymer chain Using urethane segment)

By using a compound having a functional group copolymerizable with a monomer component constituting the acrylic polymer chain at the terminal of the urethane chain or a compound having a functional group reactive with a carboxyl group, a hydroxyl group, or the like contained in the acrylic polymer chain at the terminal of the urethane chain, a crosslinked structure formed of a urethane segment can be introduced into the acrylic polymer chain. It is preferable to use urethane di (meth) acrylate having (meth) acryloyl groups at both ends of the urethane chain to introduce a crosslinked structure formed of urethane segments, because crosslinking points are easily and uniformly introduced on the acrylic polymer chain and compatibility of the acrylic polymer chain with the urethane segments is excellent. For example, a crosslinked structure formed of a urethane segment can be introduced into an acrylic polymer chain by copolymerizing a monomer component constituting the acrylic polymer chain with a urethane di (meth) acrylate.

Urethane di (meth) acrylate having (meth) acryloyl groups at both ends is obtained, for example, by using a (meth) acrylic compound having a hydroxyl group in addition to a diol component in polymerization of polyurethane. From the viewpoint of controlling the chain length (molecular weight) of the urethane segment, it is preferable to synthesize an isocyanate-terminated polyurethane by reacting a diol with a diisocyanate in such a manner that the isocyanate is excessive, and then adding a (meth) acrylic compound having a hydroxyl group to react 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 manner 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, more preferably 1.15 to 1.5. The diisocyanate component may be added in addition to the substantially equal amounts of the diol component and the diisocyanate component after the reaction.

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

As the urethane (meth) acrylate, commercially available products sold by various companies such as the Sichuan chemical industry, the Xinzhou chemical industry, the east Asian synthesis, the Cooperation chemical industry, the Japanese chemical industry, the root industry, daicel allnex, etc. can be used. The weight average molecular weight of the urethane (meth) acrylate is preferably 4000 to 50000, more preferably 4500 to 40000, still more preferably 5000 to 30000.

The glass transition temperature of the urethane (meth) acrylate is preferably 0 ℃ or lower, more preferably-10 ℃ or lower, and further preferably-20 ℃ or lower. By using a urethane (meth) acrylate having a low Tg, an adhesive excellent in low-temperature adhesive strength can be obtained even when the cohesive force of the base polymer is improved by introducing a crosslinked structure with a urethane segment. The lower limit of the glass transition temperature of the urethane (meth) acrylate is not particularly limited, but is preferably-100℃or higher, more preferably-90℃or higher, and still more preferably-80℃or higher, from the viewpoint of obtaining an adhesive excellent in high-temperature retention.

In the case of introducing a crosslinked structure formed of urethane segments on an acrylic polymer chain using urethane (meth) acrylate, the glass transition temperature of the urethane segments of the base polymer is approximately equal to that of the urethane (meth) acrylate.

< Preparation of base Polymer >

Polymers incorporating a crosslinked structure formed from urethane segments on the acrylic polymer chain may be polymerized by various well known methods. In the case of using urethane (meth) acrylate as a constituent component of the urethane segment, the monomer component for constituting the acrylic polymer chain may be copolymerized with urethane (meth) acrylate.

The amount of the urethane (meth) acrylate used is preferably 3 to 30 parts by weight, more preferably 4 to 25 parts by weight, relative to 100 parts by weight of the monomer component for constituting the acrylic polymer chain. By adjusting the amount of urethane (meth) acrylate used, a base polymer having a urethane segment content within the above range can be produced. If the content of the urethane segment is too small, the adhesive holding power of the adhesive sheet tends to be lowered due to the lowered cohesiveness of the base polymer. When the content of the urethane segment is too large, the tackiness of the adhesive sheet tends to decrease with an increase in the cohesiveness of the base polymer, and the impact resistance tends to decrease.

As a polymerization method of the base polymer, photopolymerization is preferable. In photopolymerization, since a polymer can be produced without using a solvent, drying and removal of a solvent are not required in forming an adhesive sheet, and an adhesive sheet having a large thickness can be uniformly formed.

In the preparation of the base polymer, the entire amount of the monomer component constituting the acrylic polymer chain and the entire amount of the urethane (meth) acrylate for introducing the crosslinked structure may be reacted at one time, or may be polymerized in multiple stages. As a method of conducting polymerization in multiple stages, the following method is preferable: the monofunctional monomer constituting the acrylic polymer chain is polymerized to form a prepolymer composition (prepolymerization), and a polyfunctional compound such as urethane di (meth) acrylate is added to a slurry of the prepolymer composition to polymerize (main polymerization) the prepolymer composition with the polyfunctional monomer. The prepolymer composition is a partial polymer containing a polymer of low degree of polymerization and unreacted monomer.

By performing the prepolymerization of the constituent components of the acrylic polymer, branch points (crosslinking points) obtained by a polyfunctional compound such as urethane di (meth) acrylate can be uniformly introduced into the acrylic polymer chain. In addition, an adhesive sheet can be formed by coating a mixture (adhesive composition) of a low molecular weight polymer or a part of the polymer and an unpolymerized monomer component on a substrate and then subjecting the substrate to main polymerization.

Since the low-polymerization-degree composition such as the prepolymer composition is low in viscosity and excellent in coatability, according to the method of performing main polymerization on the substrate after coating the adhesive composition as a mixture of the prepolymer composition and the polyfunctional compound, 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, the adhesive sheet can be obtained by preparing a prepolymer composition having a low degree of polymerization by prepolymerization, applying an adhesive composition containing a polyfunctional compound or the like added to the prepolymer composition in a layer form on a substrate, and polymerizing (main polymerizing) the adhesive composition on the substrate.

< Prepolymerization >

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 prepolymer-forming composition may contain a polyfunctional compound (polyfunctional monomer or polyfunctional oligomer). For example, the prepolymer-forming composition may contain a part of the polyfunctional compound as a raw material of the polymer, and the prepolymer may be polymerized and then the remainder of the polyfunctional compound may be added to carry out the main polymerization.

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

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

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

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

The polymerization rate of the prepolymer was calculated from the weight before and after heating at 130℃for 3 hours by the following formula. The polymerization rate of the adhesive sheet was also calculated by the same method.

Polymerization rate (%) =weight after drying/weight before drying×100

< Preparation of adhesive composition >

In the prepolymer composition, 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, and the like are mixed to prepare an adhesive composition. The adhesive composition preferably has a viscosity suitable for coating on a substrate (e.g., about 0.5 Pa-s to about 20 Pa-s). The viscosity of the adhesive composition can be adjusted to be within an appropriate range by adjusting the polymerization rate of the prepolymer, the addition amount of the urethane (meth) acrylate, the composition of other components (for example, oligomer), the molecular weight, the addition amount, and the like. For the purpose of adjusting viscosity and the like, a thickening additive and the like may 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 the preliminary polymerization remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for the main polymerization may be omitted.

(Oligomer)

The adhesive composition may contain various oligomers for the purpose of adjusting the adhesive force, adjusting the viscosity, and the like of the adhesive sheet. As the oligomer, for example, an oligomer having a weight average molecular weight of about 1000 to about 30000 can be used. As the oligomer, an acrylic oligomer is preferable in view of excellent compatibility with the acrylic base polymer.

The acrylic oligomer contains an alkyl (meth) acrylate as a main constituent monomer component. Among them, an acrylic oligomer containing, as a constituent monomer component, a monomer containing an alkyl (meth) acrylate having a chain alkyl group (a chain alkyl (meth) acrylate), and an alkyl (meth) acrylate having an alicyclic alkyl group (an alicyclic alkyl (meth) acrylate) is preferable. Specific examples of the chain alkyl (meth) acrylate and the alicyclic alkyl (meth) acrylate are as exemplified above as the constituent monomers of the acrylic polymer chain.

The glass transition temperature of the acrylic oligomer is preferably 20℃or higher, more preferably 30℃or higher, and still more preferably 40℃or higher. The adhesive holding power of the adhesive sheet tends to be improved by using a low Tg base polymer and a high Tg acrylic oligomer together, which introduce a crosslinked structure formed of urethane segments. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but is usually 200℃or lower, preferably 180℃or lower, more preferably 160℃or lower. The glass transition temperature of the acrylic oligomer was calculated by the above Fox formula.

Among the exemplified alkyl (meth) acrylates, methyl methacrylate is preferred from the viewpoint of high glass transition temperature and excellent compatibility with the base polymer as the chain alkyl (meth) acrylate. As the alicyclic alkyl (meth) acrylate, tetrahydrodicyclopentadiene methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer preferably contains one or more selected from the group consisting of tetrahydrodicyclopentadiene acrylate, tetrahydrodicyclopentadiene methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate as constituent monomer components.

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

The weight average molecular weight of the acrylic oligomer is preferably 1000 to 30000, more preferably 1500 to 10000, still more preferably 2000 to 8000. By using the acrylic oligomer having a molecular weight in this range, the adhesive strength and adhesive holding power of the adhesive tend to be improved.

The acrylic oligomer can be obtained by polymerizing the above monomer components by various polymerization methods. In the polymerization of the acrylic oligomer, various polymerization initiators may be used. In addition, for the purpose of adjusting the molecular weight, a chain transfer agent may be used.

When the 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, and even more preferably 2 to 10 parts by weight, based on 100 parts by weight of the base polymer. When the content of the oligomer in the adhesive composition is within the above range, tackiness at high temperature and high-temperature retention 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. In the case of adding the silane coupling agent to the adhesive composition, the amount thereof to be added is usually about 0.01 to about 5.0 parts by weight, preferably about 0.03 to about 2.0 parts by weight, relative to 100 parts by weight of the base polymer.

(Crosslinking agent)

The base polymer may have a crosslinked structure other than the above-described polyfunctional compound as needed. By including a crosslinking agent in the adhesive composition, a crosslinked structure can be incorporated in the base polymer. Examples of the crosslinking agent include compounds that react with functional groups such as hydroxyl groups and carboxyl groups contained in the polymer. Specific examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents,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 amount of the crosslinked structure derived from a substance other than the urethane segment is increased, tackiness may be lowered and impact resistance may be lowered. Therefore, the amount of the crosslinking agent to be used 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 above-exemplified components, the adhesive composition may contain additives such as tackifiers, plasticizers, softeners, degradation inhibitors, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, antistatic agents, and the like.

< Coating of adhesive composition and Main polymerization >

The photo-curing is performed by coating the adhesive composition in a layer on the substrate, and then irradiating active light. In the case of photocuring, it is preferable to provide a cover sheet on the surface of the coating layer, and to irradiate the active light with the adhesive composition sandwiched between the two sheets, thereby preventing polymerization inhibition by oxygen.

As the base material and the cover sheet for forming the adhesive sheet, any suitable base material may 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 the film base material of the release film, films containing various resin materials can be used. Examples of the resin material include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, vinyl acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins. Among them, polyester resins such as polyethylene terephthalate are particularly preferable. The thickness of the film base material is preferably 10 μm to 200 μm, more preferably 25 μm to 150 μm. Examples of the material of the release layer include a silicone release agent, a fluorine-containing release agent, a long-chain alkyl release agent, and a fatty acid amide release agent. The thickness of the release layer is typically from about 10nm to about 2000nm.

As a method of applying the adhesive composition to the substrate, various methods such as a roll coating method, a roll lick coating method, a gravure coating method, a reverse coating method, a roll brush method, a spray coating method, a dip roll coating method, a bar coating method, a blade coating method, an air knife coating method, a curtain coating method, a lip die coating method, and a die coater can be used.

The main polymerization is performed by irradiating the adhesive composition coated in a layer on the substrate with an activating ray. In the main polymerization, unreacted monomer components in the prepolymer composition react with urethane (meth) acrylate to give a base polymer having a crosslinked structure formed by urethane segments incorporated in the acrylic polymer chain.

The active light ray may be selected according to the kind of polymerizable component such as monomer or urethane (meth) acrylate, the kind of photopolymerization initiator, etc., and ultraviolet rays and/or visible light having a short wavelength are generally used. The cumulative amount of light irradiated is preferably from about 100mJ/cm ² to about 5000mJ/cm ². The light source used for the light irradiation is not particularly limited as long as it can irradiate light in a wavelength range where the photopolymerization initiator contained in the adhesive composition has sensitivity, and an LED light source, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, or the like is preferably used. The polymerization rate of the adhesive sheet after main polymerization is preferably 97% or more, more preferably 98% or more, and still more preferably 99% or more. In order to increase the polymerization rate, the pressure-sensitive adhesive sheet after photo-curing may be heated to volatilize the residual monomer, unreacted polymerization initiator, and the like.

By attaching the release films 1 and 2 to the surface of the pressure-sensitive adhesive sheet 5, a pressure-sensitive adhesive sheet having release films temporarily attached to both surfaces as shown in fig. 1 can be obtained. The release films used as the base material or cover sheet in forming the adhesive sheet may be used as the release films 1, 2 as they are.

In the case where 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 may be the same as or different from the thickness of the other release film 2. The release force when the release film temporarily attached to one surface is peeled off from the adhesive sheet 5 may be the same or different from the release force when the release film temporarily attached to the other surface is peeled off from the adhesive sheet 5. When the release forces are different from each other, the release film 2 (light release film) having a relatively small release force is peeled off from the adhesive sheet 5 and then bonded to the first adherend, and then the release film 1 (heavy release film) having a relatively large release force is peeled off and bonded to the second adherend, so that the workability is excellent.

[ Image display device ]

The pressure-sensitive adhesive sheet of the present invention can be used for bonding various transparent members and opaque members. The kind of the adherend is not particularly limited, and various resin materials, glass, metal, and the like can be cited. The pressure-sensitive adhesive sheet of the present invention is suitable for bonding optical members such as image display devices, because of its high transparency. In particular, the pressure-sensitive 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 surface on the visual side of an image display device because of excellent durability and impact resistance of adhesion.

Fig. 2 is a cross-sectional view showing an example of a laminated structure of the image display device in which the front transparent plate 7 is bonded to the viewing side surface of the image display panel 10 via the adhesive sheet 5. The image display panel 10 has a polarizing plate 3 bonded to the viewing side surface of an image display unit 6 such as a liquid crystal unit or an organic EL unit via an adhesive sheet 4. The front transparent plate 7 may be a front transparent plate in which a height difference due to a print layer 76 or the like is provided on the periphery of one surface of the transparent flat plate 71. As the transparent plate 71, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, a glass plate, or the like is used. The transparent plate 71 may have a touch panel function. As the touch panel, any touch panel such as a resistive film type, a capacitive type, an optical type, and an ultrasonic type is used.

The polarizing plate 3 provided on the surface of the image display panel 10 and the front transparent plate 7 are bonded via the adhesive sheet 5. The order of the bonding is not particularly limited, and 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 surface transparent plate 7 may be performed first. In addition, the bonding of both may be performed simultaneously. From the viewpoint of workability of bonding, it is preferable to peel off one release film (light release film) 2, then bond the surface of the exposed adhesive sheet 5 to the image display panel 10, and then peel off the other release film 1 (heavy release film), and bond the surface of the exposed adhesive sheet to the front surface transparent plate 7.

After the adhesive sheet 5 is bonded to the front surface transparent plate 7, deaeration for removing bubbles near the interface between the adhesive sheet 5 and the flat plate 71 portion of the front surface transparent plate 7, the printed layer 76, and other non-flat portions can be performed. As the defoaming method, a suitable method such as heating, pressurizing, and depressurizing can be used. For example, bonding may be performed while suppressing the mixing of bubbles under reduced pressure and heating, and then pressurizing may be performed while heating by autoclave treatment or the like for the purpose of suppressing delayed foaming or the like. In the case of deaeration by heating, the heating temperature is usually about 40 to about 150 ℃. In the case of pressurization, the pressure is generally about 0.05MPa to about 2MPa.

When the gap 90 is provided between the case 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 adhesive sheet 5 has a large shear storage modulus, and therefore, has excellent adhesive reliability in a wide temperature range. Therefore, even when stress deformation occurs at the bonding interface of the adhesive sheet due to a temperature change at the time of sealing with a resin material or the like, peeling at the bonding interface can be suppressed. Further, the pressure-sensitive adhesive sheet 5 has a low glass transition temperature and a large peak top value of tan δ, and therefore has excellent impact resistance in a wide temperature range, and is less likely to be peeled off by an impact such as dropping.

[ Optical film with adhesive sheet ]

The pressure-sensitive adhesive sheet of the present invention can be used as a pressure-sensitive adhesive-carrying film for fixing the pressure-sensitive adhesive sheet to an optical film or the like, in addition to a form in which a release film is temporarily attached to both surfaces as shown in fig. 1. For example, in the form shown in fig. 3, the release film 1 is temporarily attached to one surface of the pressure-sensitive adhesive sheet 5, and the polarizing plate 3 is fixed to the other surface of the pressure-sensitive 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 the form in which the optical film such as the polarizing plate is previously bonded to the pressure-sensitive adhesive sheet, the release film 1 temporarily attached to the surface of the pressure-sensitive adhesive sheet 5 can be peeled off and bonded to the front surface transparent member.

Examples

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

[ Production of acrylic acid oligomer ]

Tetrahydrodicyclopentadiene methacrylate (DCPMA) 60 parts by weight, methyl Methacrylate (MMA) 40 parts by weight, alpha-thioglycerol as a chain transfer agent 3.5 parts by weight and toluene 100 parts by weight as a polymerization solvent were mixed and stirred at 70℃for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by weight of 2,2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, reacted at 70℃for 2 hours, and then heated to 80℃for 2 hours. Then, the reaction solution was heated to 130℃and dried to remove toluene, chain transfer agent and unreacted monomers, thereby obtaining a solid acrylic acid oligomer. The weight average molecular weight of the acrylic oligomer was 5100.

Example 1

(Polymerization of prepolymer)

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 (4 HBA) and 11.8 parts by weight of isostearyl acrylate (ISTA), and a photopolymerization initiator (BASF manufactured "Irgacure 184":0.035 parts by weight and BASF manufactured "Irgacure 651":0.035 parts by weight were blended, and then ultraviolet ray was irradiated to polymerize so that the viscosity (BH viscometer No.5 rotor, 10rpm, measurement temperature 30 ℃) became about 20 Pa.s, thereby obtaining a prepolymer composition (polymerization rate: about 9%).

(Preparation of photocurable adhesive composition)

To the prepolymer composition, a terminal acrylic-modified polyether urethane (manufactured by the japanese synthetic chemical industry "UV-3300B"): 7 parts by weight and a terminal acrylic-modified polyester urethane (manufactured by the Japanese synthetic chemical industry, "UV-3010B"): 3 parts by weight of the above acrylic oligomer: 5 parts by weight of Irgacure 184 as photopolymerization initiator: 0.05 part by weight and Irgacure 651:0.57 parts by weight of an alpha-methylstyrene dimer (manufactured by daily oil, "Nofmer MSD"): 0.1 parts by weight, "KBM403" from Xinyue chemical as a silane coupling agent: 0.3 parts by weight, and then they were uniformly mixed, thereby preparing an adhesive composition.

(Production of adhesive sheet)

A coating layer was formed by coating a base material (double release film) of a polyethylene terephthalate (PET) film (Diafoil MRF "manufactured by Mitsubishi chemical corporation) having a thickness of 75 μm and provided with a silicone release layer on the surface thereof, with the photocurable adhesive composition so as to have a thickness of 150 μm. A 75 μm thick PET film (mitsubishi chemical product "Diafoil MRE") having one side subjected to a silicone release treatment was attached to the coating layer as a cover sheet (light release film). The laminate was irradiated with ultraviolet rays from the cover sheet side by a black light lamp whose position was adjusted so that the irradiation intensity of the irradiation surface immediately below the lamp was 5mW/cm ², and was photo-cured, whereby an adhesive sheet having a thickness of 150 μm and a polymerization rate of 99% was obtained.

Examples 2 to 5 and comparative examples 1 to 8

The monomer composition charged in the polymerization of the prepolymer, and the types and amounts of the polyfunctional compound (urethane acrylate and/or polyfunctional acrylate), the acrylic oligomer, the photopolymerization initiator, and the chain transfer agent added to the adhesive composition are shown in table 1. Except that a photocurable adhesive composition was prepared in the same manner as in example 1 and applied and photocured on a substrate, an adhesive sheet was obtained.

[ Evaluation ]

< Weight average molecular weight >

The weight average molecular weight (Mw) of the acrylic acid oligomer and the urethane (meth) acrylate was measured by a GPC (gel permeation chromatography) apparatus (product name "HLC-8120 GPC") manufactured by Tosoh. The measurement sample used a filtrate obtained by filtering a substance obtained by dissolving a base polymer in tetrahydrofuran to prepare a 0.1 wt% solution by using a 0.45 μm membrane filter. GPC measurement conditions were as follows.

(Measurement conditions)

Column: manufactured by Tosoh corporation, G7000HXL+GMHXL+GMHXL

Column dimensions: each of which is provided with(Aggregate column Length: 90 cm)

Column temperature: 40 ℃ flow: 0.8 mL/min

Sample injection amount: 100 mu L

Eluent: tetrahydrofuran (THF)

A detector: differential Refractometer (RI)

Standard sample: polystyrene

< Storage modulus, glass transition temperature, tan delta Peak value of adhesive sheet >

The 10-layered adhesive sheets were prepared into a material having a thickness of about 1.5mm as a sample for measurement. Dynamic viscoelasticity measurements were performed using the "advanced rheology expansion System (Advanced Rheometric Expansion System, ARES)" manufactured by Rheometric Scientific company under the following conditions.

(Measurement conditions)

Deformation mode: torsion

Measuring frequency: 1Hz

Heating rate: 5 ℃/min

Shape: parallel plate

The shear storage modulus was obtained by reading the storage modulus G' at each temperature from the measurement results. The temperature at which the loss tangent (tan δ) reaches a maximum (peak top temperature) is taken as the glass transition temperature of the adhesive sheet. In addition, the value of tan δ at the glass transition temperature (peak top value) was read.

< Adhesive force >

The light release film was peeled from the pressure-sensitive adhesive sheet, and a PET film having a thickness of 50 μm was bonded thereto, and the film was cut into a width of 10 mm. Times.100 mm in length, and then the heavy release film was peeled, and was pressed against a glass plate by a roller of 5kg, whereby a sample for measuring adhesive strength was produced. The sample for measuring adhesive strength was kept at 25℃or 65℃for 30 minutes, and then the test piece was peeled from the glass plate using a tensile tester at a tensile speed of 300 mm/min and a peeling angle of 180℃to measure the peeling force.

< Haze >

The haze was measured using a haze meter (HM-150 manufactured by color technology research, village) using a test piece obtained by bonding an adhesive sheet to an alkali-free glass having a thickness of 800 μm (total light transmittance 92%, haze 0.4%). The haze value (0.4%) of the alkali-free glass was subtracted from the measured value to obtain the haze value of the pressure-sensitive adhesive sheet.

< Interlayer tackiness >

(Preparation of test sample)

The pressure-sensitive adhesive sheet was cut into a size of 75 mm. Times.45 mm, and a light release film was peeled off from the pressure-sensitive adhesive sheet, and the sheet was laminated on the center of a 500 μm thick glass plate (100 mm. Times.50 mm) by a roll laminator (roll-to-roll pressure: 0.2MPa, transport speed: 100 mm/min). Then, the heavy release film was peeled off, and a 500 μm thick glass plate (50 mm. Times.100 mm) having a black ink of 30 μm thickness was laminated in a frame shape on the peripheral edge portion by vacuum press bonding (surface pressure 0.3MPa, pressure 100 Pa). The ink printed area of the glass plate was 5mm from both ends in the short side direction and 15mm from both ends in the long side direction, and was in contact with the black ink layer in an area 5mm from the end portions of the four sides of the adhesive sheet. The sample was subjected to a treatment for 30 minutes in an autoclave (50 ℃ C., 0.5 MPa).

The above sample was kept at 60℃for 30 minutes, and then, as shown in FIG. 5A, a polystyrene sheet having a thickness of 200 μm was inserted between two glass plates at a distance of 1mm from the end of the adhesive sheet and kept for 10 seconds. The end of the adhesive sheet was observed with a digital microscope at 20 times magnification. Samples in which streak-like bubbles were generated (see fig. 5B) or peeling of the adhesive sheet from the glass plate was designated NG, and samples in which neither bubbles nor peeling was generated were designated OK.

< Impact resistance >

A test sample was produced by bonding glass plates to both sides of an adhesive sheet and autoclave-treating the same as the production of the test sample for interlayer adhesiveness test described above except that the size of the glass plate on which the black ink was not provided was changed to 100mm×70 mm. As shown in fig. 6, the test sample 95 was placed on the table 93 disposed at a distance of 60mm so that the glass plate 7 provided with the printed layer 76 was positioned at the lower side, and the upper surface of the end portion of the glass plate 5 not provided with the printed layer was fixed to the table 80 by an adhesive tape (not shown). The test specimen 95 fixed on the stage 93 by an adhesive tape was held at-5℃for 24 hours, and then after being taken out to room temperature, a metal ball 97 having a mass of 11g was dropped from a height of 300mm onto the glass plate 7 within 40 seconds, whereby an impact resistance test was performed.

In the impact resistance test, in order to make the drop position of the metal ball constant, a cylindrical guide 99 was used, and the metal ball 97 was dropped at a position spaced apart from the corner by 10mm in the short side direction and the long side direction of the inner edge of the frame of the printing region of the printing layer 76. The test was performed twice, and the sample in which the glass plate was not peeled off in either test was designated as OK, and the sample in which the glass plate was peeled off in either or both of the two tests was designated as NG.

[ Evaluation results ]

Table 1 shows the results of evaluation of the adhesive compositions used for producing the adhesive sheets. In table 1, each component is described below for short.

< Acrylic monomer >

BA: butyl acrylate

2HEA: 2-ethylhexyl acrylate

CHA: cyclohexyl acrylate

NVP: n-vinyl-2-pyrrolidone

4HBA: acrylic acid 4-hydroxybutyl ester

2HEA: acrylic acid 2-hydroxy ethyl ester

ISTA: isostearyl acrylate

< Urethane acrylate >

UV-3300B: "UV-3300B" (polyether urethane diacrylate having a weight average molecular weight of about 12000 and a glass transition temperature of-30 ℃ C.) manufactured by the Japanese synthetic chemistry industry

3400: Polyether urethane diacrylate having a weight average molecular weight of about 3400

UA-4200: "UA-4200" (polyether urethane diacrylate with weight average molecular weight of about 1000) manufactured by Xinzhongcun chemical industry

UN-350: "Art Resin UN-350" (polyester urethane diacrylate having a weight average molecular weight of about 12500 and a glass transition temperature of-57 ℃ C.) manufactured commercially on-line

UV-3010B: "UV-3010B" (polyester urethane diacrylate having a weight-average molecular weight of about 11000) manufactured by Japanese synthetic chemistry industry

Urethane monoacrylate: polyether urethane monoacrylate having weight average molecular weight of about 1300)

< Multifunctional acrylate >

HDDA: hexanediol diacrylate

< Photopolymerization initiator >

Irg651: irgacure 651 (2, 2-dimethoxy-1, 2-diphenylethane-1-one)

Irg184: irgacure 184 (1-hydroxycyclohexyl phenyl ketone)

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In examples 1 and 2 using an adhesive composition in which urethane diacrylate or the like was added to a prepolymer composition obtained by prepolymerization of an acrylic monomer containing butyl acrylate as a main monomer, both interlayer adhesiveness and drop impact durability were good.

In comparative example 1 using a low molecular weight urethane diacrylate, the adhesive sheet had a small adhesive strength to an adherend, and had poor interlayer adhesiveness and drop impact durability. In comparative example 2 in which the amount of urethane diacrylate added was increased, the adhesive sheet had high haze and reduced transparency. In comparative example 3 using urethane monoacrylate, the adhesive sheet had a low shear storage modulus and poor adhesive durability.

In example 3, and in examples 4 and 5, in which the composition of the acrylic monomer in the prepolymer-forming composition was changed, good adhesive properties were also exhibited in the same manner 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 the urethane material, G '_25℃ and G' _80℃ of the adhesive sheet were small, and the adhesive reliability was poor. In comparative example 5 in which the cohesiveness was improved by increasing the ratio of the polar monomers (NVB and 4 HBA) in the acrylic monomer component, the adhesiveness was good, but since the glass transition temperature was high, the impact resistance was lowered. The same tendency was found in comparative example 8.

In comparative example 6 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 tackiness was low, and therefore, the adhesive strength was insufficient and the impact resistance was also poor. The same tendency was found in comparative example 7 in which a crosslinked structure was introduced by a low molecular weight urethane diacrylate. In these comparative examples, it is considered that the C ₈ alkyl acrylate (2-ethylhexyl acrylate) as the main monomer of the acrylic polymer chain is also one of factors that tan delta is smaller than examples 1 to 5 and the like in which the C ₄ alkyl acrylate (butyl acrylate) as the main monomer.

From these results, it is clear that an adhesive sheet containing a base polymer having a crosslinked structure introduced into an acrylic polymer chain using a urethane diacrylate having a predetermined molecular weight exhibits a high shear storage modulus even at a low glass transition temperature and has a large tan δ, and therefore can achieve both adhesive durability and impact resistance.

Claims (5)

1. An adhesive sheet comprising an acrylic base polymer and an acrylic oligomer each having a crosslinked structure incorporated in an acrylic polymer chain, wherein the adhesive sheet is obtained by forming an adhesive into a sheet,

The adhesive sheet has a haze of 1% or less,

The adhesive strength of the adhesive sheet to glass is 2.0N/10mm or more,

The adhesive sheet has a glass transition temperature of-3 ℃ or lower,

The adhesive sheet has a shear storage modulus at 25 ℃ of 0.16MPa or more,

The peak value of the loss tangent of the adhesive sheet is 1.5 or more,

In the acrylic base polymer, a crosslinked structure formed by urethane di (meth) acrylate having (meth) acryloyl groups at both ends is introduced into the acrylic polymer chain by copolymerization of a monomer component constituting the acrylic polymer chain and the urethane di (meth) acrylate,

The weight average molecular weight of the urethane di (methyl) acrylate is 4000-50000, the glass transition temperature is below 0 ℃,

The amount of the urethane di (meth) acrylate is 3 to 30 parts by weight based on 100 parts by weight of the constituent monomer components of the acrylic polymer chain,

The weight average molecular weight of the acrylic oligomer is 1000-30000, the glass transition temperature is above 20 ℃,

The acrylic oligomer is contained in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the acrylic base polymer.

2. The adhesive sheet according to claim 1, wherein the adhesive has a polymerization rate of 97% or more.

3. An adhesive sheet with a release film, which has the adhesive sheet according to claim 1 or 2 and release films temporarily attached to both sides of the adhesive sheet.

4. A method for producing an adhesive sheet according to claim 1 or 2, wherein,

A composition containing an acrylic monomer and/or a partial polymer thereof, a urethane di (meth) acrylate, and an acrylic oligomer is applied in a layer form to a substrate, and then the composition is irradiated with an active light to be photo-cured,

The weight average molecular weight of the urethane di (methyl) acrylate is 4000-50000, the glass transition temperature is below 0 ℃,

The weight average molecular weight of the acrylic oligomer is 1000-30000, the glass transition temperature is above 20 ℃,

In the composition, the urethane di (meth) acrylate is contained in an amount of 3 to 30 parts by weight and the acrylic oligomer is contained in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the total of the acrylic monomer and the partial polymer thereof.

5. An image display device, wherein the front surface transparent member is fixed to the viewing side surface of the image display panel with the adhesive sheet according to claim 1 or 2.