JP2010065095A - Self-adhesive, double-sided pressure-sensitive adhesive sheet, and display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double-sided pressure-sensitive adhesive sheet forming a self-adhesive layer which is hardly peeled off even when the adherend deforms, and exhibiting satisfactory adhesion even when the adhesive layer is thinned to the thickness of about 10 μm. <P>SOLUTION: This self-adhesive comprises an acrylic ester-based resin having a weight-average molecular weight of 500,000-1,500,000 calculated in terms of polystyrene according to GPC, a tackifying resin having an alcoholic hydroxy group and a softening point of 140-170°C, and a terpene phenol resin, and has a gel fraction of 5-40 wt.%. The self-adhesive forms a self-adhesive layer which is hardly peeled off by peeling stress due to the deformation of the adherend even when the layer is thin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pressure-sensitive adhesive capable of forming a pressure-sensitive adhesive layer that is difficult to peel off even if the adherend is deformed, a double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive, and the double-sided pressure-sensitive adhesive sheet The present invention relates to a display device in which a display panel and a backlight are attached via a panel.

  In recent years, liquid crystal display devices (LCD modules) have been used in many electrical devices such as televisions, personal computers, and mobile phones. The liquid crystal display device includes a liquid crystal panel, a drive circuit (driver IC) disposed around the liquid crystal panel, and a backlight attached to the back side of the liquid crystal panel.

  The backlight is a member serving as a light source of a liquid crystal display device, and an optical sheet such as a cold cathode tube, a reflection plate, a light guide plate, a diffusion plate, and a prism sheet is arranged in this order in a backlight casing. The surface of the backlight is in a state where the optical sheet is exposed from the opening of the backlight housing.

  And the double-sided adhesive sheet is used for sticking a liquid crystal panel and a backlight at the time of manufacture of the liquid crystal display device because the thickness and width can be easily controlled and can be easily attached. As a method of attaching the liquid crystal panel and the backlight with the double-sided pressure-sensitive adhesive sheet, the back surface of the double-sided pressure-sensitive adhesive sheet punched into a frame shape so that the width is 0.5 to 1.0 mm is used as the surface of the backlight. It sticks so that both a body and an optical sheet may touch. Furthermore, the surface of the double-sided pressure-sensitive adhesive sheet is adhered to the back surface of the liquid crystal panel. Thus, the method of sticking a liquid crystal panel and a backlight via a double-sided adhesive sheet is used. Here, the double-sided pressure-sensitive adhesive sheet has not only a role of attaching the liquid crystal panel and the backlight, but also a role of fixing the position of the optical sheet exposed from the opening of the backlight housing. .

  In recent years, along with the downsizing and thinning of devices equipped with liquid crystal display devices such as mobile phones, small and thin liquid crystal display devices have been demanded, and the double-sided adhesive sheets that make up liquid crystal display devices have also been downsized. There is also a need for thinning.

  Since the members constituting the liquid crystal display device are easily deformed such as warping due to its thinning, the double-sided pressure-sensitive adhesive sheet corresponding to the miniaturization and thinning of the liquid crystal display device is a liquid crystal panel or back. It must be able to withstand the peeling stress generated with the deformation of the light. Further, since the size of the liquid crystal display device and the backlight are required to be highly accurate due to the miniaturization of the liquid crystal display device, a double-sided pressure-sensitive adhesive sheet that is not easily deformed by a shearing force during punching is required. ing.

  As a double-sided pressure-sensitive adhesive sheet that can cope with the downsizing and thinning of such a liquid crystal display device, Patent Document 1 discloses that an acrylic copolymer having a weight average molecular weight of 800 to 1,500,000, A double-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing at least one tackifying resin selected from a leveled rosin ester, a polymerized rosin ester, and a petroleum resin has been proposed.

  However, when the thickness of the pressure-sensitive adhesive layer is reduced to about 10 μm, the double-sided pressure-sensitive adhesive tape is easily peeled off due to peeling stress caused by deformation of the liquid crystal panel or the backlight. Furthermore, the problem that it deform | transforms with the shear force applied in the case of a punching process also arises. Therefore, it has not been able to cope with the recent reduction in size and thickness of liquid crystal display devices.

JP 2005-97393 A

  The present invention is a pressure-sensitive adhesive that can form a pressure-sensitive adhesive layer that is difficult to peel off even when the adherend is deformed, and exhibits sufficient adhesive force even when the thickness of the pressure-sensitive adhesive layer is reduced to about 10 μm, Provided are a double-sided pressure-sensitive adhesive sheet containing a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive, and a liquid crystal display device excellent in reliability in which a display panel and a backlight are bonded via the double-sided pressure-sensitive adhesive sheet.

  The pressure-sensitive adhesive of the present invention has an acrylate ester resin having a weight average molecular weight of 500,000 to 1,500,000 measured as a polystyrene-converted molecular weight by GPC (gel permeation chromatography) method, an alcoholic hydroxyl group, and a softening point of 140. It includes a tackifier resin and a terpene phenol resin that are ˜170 ° C., and has a gel fraction of 5 to 40% by weight.

  As the acrylic ester resin constituting the pressure-sensitive adhesive, an acrylic acid alkyl ester resin obtained by homopolymerizing an acrylic acid alkyl ester monomer, a methacrylic acid alkyl ester resin obtained by homopolymerizing a methacrylic acid alkyl ester monomer, two types Acrylic acid alkyl ester resin obtained by copolymerization of the above acrylic acid alkyl ester monomers, a methacrylic acid alkyl ester resin obtained by copolymerization of two or more methacrylic acid alkyl ester monomers, an acrylic acid alkyl ester monomer and a methacrylic acid alkyl ester A copolymer with a monomer, a copolymer of one or both of an acrylic acid alkyl ester monomer and a methacrylic acid alkyl ester monomer with another vinyl monomer copolymerizable therewith, and the like. One or with both either acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer, a copolymer of this and other copolymerizable vinyl monomer.

  The acrylic acid alkyl ester monomer is not particularly limited, but is preferably one obtained by esterification reaction of a primary or secondary alkyl alcohol having 1 to 12 carbon atoms of an alkyl group with acrylic acid. Examples thereof include ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, and preferably contain ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. In addition, the said acrylic acid alkylester monomer may be used independently, or 2 or more types may be used together.

  If the content of the ethyl acrylate component in the acrylate ester-based resin is small, the formed pressure-sensitive adhesive layer may be easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend. If the amount is too large, the viscosity of the pressure-sensitive adhesive becomes too high and the coating property is lowered, or the pressure-sensitive adhesive layer to be formed may become too hard, so 5 to 30% by weight is preferable, and 8 to 25% by weight. % Is more preferable.

  The other vinyl monomer copolymerizable with the alkyl acrylate monomer or the alkyl methacrylate monomer may be either or both of the alkyl acrylate monomer and the alkyl acrylate monomer, It is added for the purpose of improving the cohesive strength of the resulting pressure-sensitive adhesive by modifying a copolymer with a vinyl monomer, for example, increasing the glass transition temperature (Tg) of an acrylic ester resin. Those that contribute to the formation of a crosslinked structure between the main chains of the acrylic ester resin are used.

  The vinyl monomer that raises the glass transition temperature (Tg) of the acrylate resin is not particularly limited, and examples thereof include carboxy group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid. A hydroxyl group-containing monomer such as n-methylolacrylamide; maleic anhydride, vinyl acetate, styrene and the like. As the vinyl monomer, acrylic acid is preferred because it hardly affects the control of the molecular weight of the acrylic ester resin and is excellent in the adhesiveness of the resulting adhesive.

  If the total content of the vinyl monomer component that raises the glass transition temperature is small, the glass transition temperature of the resulting pressure-sensitive adhesive may become too low and the cohesive force of the pressure-sensitive adhesive may decrease. In the acrylic ester resin, 0.01 to 10% by weight is preferable, and 0.05 to 5% by weight is more preferable.

  Although it does not specifically limit as a vinyl monomer which contributes to forming a crosslinked structure between the principal chains of acrylic ester resin, A hydroxyl-containing acrylic acid ester and a hydroxyl-containing methacrylate ester are preferable.

  By using either one or both of a hydroxyl group-containing acrylate monomer or a hydroxyl group-containing methacrylate ester and an isocyanate crosslinking agent described later, the gel fraction of the pressure-sensitive adhesive can be easily adjusted to 5 to 40% by weight, and repulsion resistance An adhesive having excellent performance and anti-peeling performance can be obtained.

  Examples of the hydroxyl group-containing acrylate monomer include, for example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, and 4-hydroxybutyl acrylate. And those obtained by adding caprolactone to 2-hydroxypropyl acrylate.

  Examples of the hydroxyl group-containing methacrylic acid ester monomer include, for example, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, and 4-hydroxybutyl methacrylate. And those obtained by adding caprolactone to 2-hydroxypropyl methacrylate.

  The total content of the hydroxyl group-containing acrylic acid ester monomer component and the hydroxyl group-containing methacrylate monomer component is preferably 0.01 to 0.5% by weight, and 0.05 to 0.3% by weight in the acrylic ester resin. More preferred.

  If the total content of the hydroxyl group-containing acrylate monomer component and the hydroxyl group-containing methacrylate ester monomer component is small, the gel fraction of the pressure-sensitive adhesive is difficult to increase, and the gel fraction of the pressure-sensitive adhesive is adjusted to an appropriate gel fraction. A large amount of a cross-linking agent is required, and the cross-linking of the pressure-sensitive adhesive proceeds as time passes, so that the rebound resistance of the pressure-sensitive adhesive becomes unstable.

  If the total content of the hydroxyl group-containing acrylate monomer component and the hydroxyl group-containing methacrylate ester monomer component is large, the gel fraction of the pressure-sensitive adhesive is easily increased, and the gel fraction of the pressure-sensitive adhesive is adjusted to an appropriate gel fraction. This is because it is necessary to carry out with a small amount of a crosslinking agent, and the variation of the gel fraction due to the variation in the amount of the crosslinking agent in the pressure-sensitive adhesive increases, so that a uniform crosslinked structure may not be obtained.

  Furthermore, when the weight average molecular weight measured as a polystyrene-converted molecular weight by the GPC (Gel Permeation Chromatography) method of the acrylate resin is small, the pressure-sensitive adhesive layer formed is deformed of the adherend. While it is easy to peel off from the adherend due to the peeling stress that accompanies, the adhesive strength of the pressure-sensitive adhesive is reduced when it is large, and the pressure-sensitive adhesive layer that is formed also has a peeling stress that accompanies deformation of the adherend Is easy to peel from the adherend, it is limited to 500,000 to 1,500,000, preferably 500,000 to 1,000,000, more preferably 550,000 to 900,000.

  In addition, the weight average molecular weight measured as a polystyrene conversion molecular weight by GPC method of the said acrylate ester-type resin filtered the dilution liquid obtained by diluting acrylic ester-type resin with tetrahydrofuran (THF) 50 times with a filter. Based on the obtained filtrate, it can be obtained by measuring the polystyrene equivalent molecular weight of the acrylic ester resin by gel permeation chromatography. As the gel permeation chromatograph, for example, a product commercially available from Water under the trade name “2690 Separations Model” can be used.

  And in order to obtain the said acrylic ester resin, either one or both of the acrylic acid alkyl ester monomer or the methacrylic acid alkyl ester monomer, if necessary, either the acrylic acid alkyl ester monomer or the methacrylic acid alkyl ester monomer What is necessary is just to make it radical-react in presence of a polymerization initiator with the other vinyl monomer copolymerizable with one or both. In addition, as a polymerization method, a conventionally well-known method is used, for example, solution polymerization, emulsion polymerization, suspension polymerization, block polymerization, etc. are mentioned.

  The polymerization initiator is not particularly limited. For example, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylper Oxypivalate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate And t-butyl peroxyisobutyrate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate and the like. 1,1-bis (t-hexylper Oxy) -3,3,5-trimethylcyclohexane and t-hexylperoxypivalate are preferred. In addition, the said polymerization initiator may be used independently, or 2 or more types may be used together.

  The pressure-sensitive adhesive of the present invention has an alcoholic hydroxyl group and a softening point of 140 to 170 ° C. so that the pressure-sensitive adhesive can form a pressure-sensitive adhesive layer that is difficult to peel off even when the adherend is deformed. A tackifying resin is contained.

  The tackifying resin having an alcoholic hydroxyl group is not particularly limited, and examples thereof include rosin ester resins and hydrogenated terpene phenol resins, rosin ester resins are preferable, and polymerized rosin ester resins are more preferable.

  The rosin ester-based resin includes a rosin resin mainly composed of abietic acid, a disproportionated rosin resin, a hydrogenated rosin resin, a dimer of a resin acid such as abietic acid (polymerized rosin resin), and the like. A resin obtained by esterification with an alcohol, wherein a part of the hydroxyl group of the alcohol used for esterification is contained in the resin without being used for esterification. Esterified rosin resin is rosin ester resin, disproportionated rosin resin is esterified disproportionated rosin ester resin, hydrogenated rosin resin is esterified hydrogenated rosin ester resin, polymerized rosin resin The esterified product is a polymerized rosin ester resin.

  Examples of alcohols used for the esterification include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol.

  Furthermore, examples of the hydrogenated terpene phenol resin include a resin obtained by hydrogenating a terpene phenol resin obtained by polymerizing a terpene in the presence of phenol.

  The softening point of the tackifying resin is limited to 140 to 170 ° C, and preferably 145 to 165 ° C. When the thickness of the pressure-sensitive adhesive layer using the pressure-sensitive adhesive of the present invention is thin when the softening point of the tackifying resin is 140 to 170 ° C., the pressure-sensitive adhesive layer has excellent adhesive strength, resilience resistance, And, the deformation followability to the adherend is exhibited. If the softening point of the tackifier is low, the fluidity of the adhesive increases when heat is applied to the adhesive or the adhesive is used for a long time, and it becomes easy to peel off from the adherend. If it is high, the pressure-sensitive adhesive becomes hard, and when the adherend is deformed, the pressure-sensitive adhesive layer using the pressure-sensitive adhesive of the present invention is easily peeled off from the adherend. In addition, the softening point of tackifying resin means what was measured based on JISK2207.

  The hydroxyl value of the tackifying resin is preferably 35 or more, more preferably 35 to 60, and particularly preferably 40 to 58. This is because when the hydroxyl value of the tackifying resin is small, the pressure-sensitive adhesive layer to be formed is easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend, and when it is too large, Thus, when an isocyanate type crosslinking agent is added to crosslink the pressure sensitive adhesive, poor crosslinking may occur. The hydroxyl value of the tackifying resin is a value measured according to JIS K0070.

  And, if the content of the tackifying resin in the pressure-sensitive adhesive is small, the formed pressure-sensitive adhesive layer may be easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend. If the amount is too large, the pressure-sensitive adhesive becomes hard and the adhesive strength and tack may be lowered. Therefore, the amount is preferably 5 to 40 parts by weight, more preferably 8 to 35 parts by weight, relative to 100 parts by weight of the acrylate resin.

  Furthermore, the pressure-sensitive adhesive of the present invention contains a terpene phenol resin for the purpose of improving the pressure-sensitive adhesive strength, particularly the pressure-sensitive adhesive strength to the polycarbonate resin. The terpene phenol resin is a resin obtained by polymerizing terpene in the presence of phenol, and a hydrogenated terpene phenol resin obtained by subjecting a terpene phenol resin to hydrogenation is excluded. This is because it is presumed that the aromatic ring in the terpene phenol resin contributes to the improvement of the adhesive strength, particularly the interaction with the polycarbonate resin.

  In addition, as mentioned above, it is estimated that the ring which has aromaticity in terpene phenol contributes to the improvement of adhesive force, especially the interaction with polycarbonate resin. Therefore, the possibility that another compound containing a ring having aromaticity can be used in place of the terpene phenol resin is also suggested.

  When the softening point of the terpene phenol resin is low, the heat resistance of the pressure-sensitive adhesive may be lowered. Therefore, 140 ° C. or higher is preferable, and when it is too high, the pressure-sensitive adhesive becomes hard and the pressure-sensitive adhesiveness and tack are reduced. Furthermore, since the pressure-sensitive adhesive layer to be formed may be easily peeled off from the adherend due to peeling stress caused by deformation of the adherend, 145 to 170 ° C. is more preferable. In addition, the softening point of the said terpene phenol resin means what was measured based on JISK2207.

  And if there is little content of the terpene phenol resin in the said adhesive, while the heat resistance and adhesive force of an adhesive may fall, on the other hand, an adhesive will become hard and adhesive strength and tack will fall. Furthermore, since the pressure-sensitive adhesive layer to be formed may be easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend, 3 to 3 parts by weight with respect to 100 parts by weight of the acrylate resin. 20 parts by weight is preferable, and 5 to 15 parts by weight is more preferable.

  Moreover, in the said adhesive, it is preferable to add a crosslinking agent and to form a crosslinked structure between the principal chains of resin which comprises an adhesive. By appropriately adjusting the type and amount of the crosslinking agent, it becomes easy to adjust the gel fraction of the pressure-sensitive adhesive to a desired range. The crosslinking agent is not particularly limited, and examples thereof include an isocyanate crosslinking agent, an aziridine crosslinking agent, an epoxy crosslinking agent, and a metal chelate crosslinking agent, and an isocyanate crosslinking agent is preferable. This is because the isocyanate group in the isocyanate-based crosslinking agent reacts with the alcoholic hydroxyl group in the above-mentioned tackifying resin to form a urethane bond. Therefore, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive can be made difficult to be peeled off from the adherend due to the peeling stress caused by the deformation of the adherend. Further, when a double-sided PSA sheet is prepared using the PSA as described later, a PSA using an isocyanate-based cross-linking agent as the cross-linking agent is preferable because it has excellent adhesion to the substrate.

  If the blending amount of the crosslinking agent is small, the crosslinking of the pressure-sensitive adhesive may be insufficient, and if it is large, the adhesive strength and tack of the pressure-sensitive adhesive may be reduced. On the other hand, 0.5 to 1.7 parts by weight is preferable, and 0.7 to 1.5 parts by weight is more preferable.

  That is, even if the gel fraction of the pressure-sensitive adhesive is high or low, the formed pressure-sensitive adhesive layer is easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend. It is limited to 10% by weight, preferably 10 to 40% by weight, and more preferably 15 to 35% by weight.

Here, as a method for measuring the gel fraction of the pressure-sensitive adhesive, a double-sided pressure-sensitive adhesive sheet obtained as described below was cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece, and this test piece was ethyl acetate. After being immersed in it at 23 ° C. for 24 hours, the test piece is taken out from ethyl acetate and dried at 110 ° C. for 1 hour. And the weight of the test piece after drying is measured, and a gel fraction is computed using a following formula. Note that a release film as described below is not laminated on the test piece.
Gel fraction (% by weight) = 100 × (W ₂ −W ₀ ) / (W ₁ −W ₀ )
(W ₀ : weight of base material, W ₁ : weight of test piece before immersion, W ₂ : weight of test piece after immersion and drying)

  Moreover, you may add additives, such as a plasticizer, an emulsifier, a softener, a filler, a pigment, and dye, to the adhesive of this invention as needed.

  Next, the double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive is laminated and integrated on both surfaces of the base material will be described. The substrate is not particularly limited. For example, a polyolefin resin film such as a polyethylene film or a polypropylene film, a polyester resin film such as a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, or a polyvinyl chloride resin film. And polyurethane resin films, and polyester resin films are preferred. In addition, as said base material, the thing printed in black for light transmission prevention, the thing printed in white for the light reflectivity improvement, the thing vapor-deposited by metal, etc. can be used.

  And, if the thickness of the base material is thin, the mechanical strength of the double-sided PSA sheet may be reduced or the handleability may be reduced. Since it may be difficult to adhere and adhere along the shape of the body, 3 to 30 μm is preferable, and 5 to 25 μm is more preferable.

  Further, when the thickness of the pressure-sensitive adhesive layer on both sides laminated and integrated on both surfaces of the base material is large, when a shear stress is applied to the pressure-sensitive adhesive layer in the surface direction of the pressure-sensitive adhesive layer, Since the layer may be deformed and a displacement may occur at the bonding site using the double-sided pressure-sensitive adhesive sheet, it is preferable that both the pressure-sensitive adhesive layers have a thickness of 30 μm or less. Since it may become easy to peel from a to-be-adhered body by the peeling stress which arises with a deformation | transformation of a to-be-adhered body, it is more preferable that both the adhesive layers of both surfaces are 10-25 micrometers.

  The double-sided pressure-sensitive adhesive sheet usually has a pressure-sensitive adhesive layer in order to prevent the pressure-sensitive adhesive layer from adhering to another member before use or to prevent dust from adhering to the pressure-sensitive adhesive layer. A release film is detachably laminated on the surface. As the release film, a film similar to the above-described base material can be used, and a release treatment is performed on the surface in contact with the pressure-sensitive adhesive layer.

  Next, the manufacturing method of a double-sided adhesive sheet is demonstrated. As a method for producing a double-sided pressure-sensitive adhesive sheet, for example, a solvent is added to the pressure-sensitive adhesive to prepare a pressure-sensitive adhesive solution, and this pressure-sensitive adhesive solution is applied to the surface of the substrate, and the solvent in the pressure-sensitive adhesive solution is completely removed by drying. To form an adhesive layer. Next, a release film is overlaid on the formed pressure-sensitive adhesive layer so that the release treatment surface faces the pressure-sensitive adhesive layer. Subsequently, by preparing a release film different from the release film, applying the pressure-sensitive adhesive solution to the release-treated surface of the release film, and completely drying and removing the solvent in the pressure-sensitive adhesive solution A laminated film having a pressure-sensitive adhesive layer formed on the surface of the release film is produced. This laminated film is laminated on the back surface of the base material in a state where the pressure-sensitive adhesive layer faces the back surface of the base material to produce a laminate. Then, by pressing the laminate with a rubber roller or the like, a double-sided pressure-sensitive adhesive sheet is obtained in which the pressure-sensitive adhesive layer is laminated and integrated on both surfaces of the base material, and the release film is detachably laminated on the surface of the pressure-sensitive adhesive layer. A method is mentioned.

  In addition, two sets of laminated films are produced in the same manner as described above, and these laminated films are superposed on both sides of the base material with the pressure-sensitive adhesive layer of the laminated film facing the base material. A double-sided pressure-sensitive adhesive sheet is produced by pressing the laminated body with a rubber roller or the like so that the pressure-sensitive adhesive layer is laminated and integrated on both surfaces of the substrate and the release film is peeled and laminated on the surface of the pressure-sensitive adhesive layer. It may be manufactured.

  In addition, after applying the above-mentioned pressure-sensitive adhesive solution to the surface of the substrate and completely removing the solvent in the pressure-sensitive adhesive solution to form a pressure-sensitive adhesive layer, a release film is formed on the pressure-sensitive adhesive layer. The treatment surface is overlapped with the pressure-sensitive adhesive layer, and then the pressure-sensitive adhesive layer is formed on the back surface of the base material in the same manner, and the release film is placed on the pressure-sensitive adhesive layer. By superimposing in a state facing the pressure-sensitive adhesive layer, a laminate in which the pressure-sensitive adhesive layer and the release film are laminated on each of both surfaces of the base material is manufactured, and the laminate is pressed by a rubber roller or the like. You may manufacture the double-sided adhesive sheet by which an adhesive layer is laminated | stacked and integrated on both surfaces of a material, and a release film is laminated | stacked on the surface of an adhesive layer so that peeling is possible.

  In the above description, the double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layers are laminated and integrated on both surfaces of the base material formed in the sheet shape has been described. By cutting the double-sided pressure-sensitive adhesive sheet into strips, a double-sided pressure-sensitive adhesive tape It can also be used as

  The double-sided pressure-sensitive adhesive sheet of the present invention can be used as a double-sided pressure-sensitive adhesive sheet for producing a display device. Specifically, the double-sided pressure-sensitive adhesive sheet is used for adhering a display panel of a display device and a backlight. Next, a method for manufacturing a display device by integrating a display panel and a backlight using the double-sided pressure-sensitive adhesive sheet of the present invention will be described. First, a backlight is manufactured by arranging a reflector, a cold cathode tube, a light guide plate, a diffusion plate, and a prism sheet in this order in a backlight housing. The prism sheet is exposed from the opening of the backlight casing of the backlight. An example of the display panel is a liquid crystal display panel.

  Then, a double-sided pressure-sensitive adhesive sheet punched into a frame shape is prepared, and the back surface of the double-sided pressure-sensitive adhesive sheet is adhered so as to be in contact with at least one of the backlight housing and the prism sheet on the surface of the backlight, preferably both. And the display panel provided with the drive circuit was prepared, and the display panel and the backlight were stuck via the double-sided pressure-sensitive adhesive sheet by sticking the surface of the double-sided pressure-sensitive adhesive sheet to the back surface of the display panel. A display device can be manufactured.

  The pressure-sensitive adhesive of the present invention has an acrylic ester resin having a weight average molecular weight of 500,000 to 1,500,000 measured as a polystyrene-equivalent molecular weight by the GPC method, has an alcoholic hydroxyl group, and has a softening point of 140 to 170 ° C. It contains a tackifier resin and a terpene phenol resin, and has a gel fraction of 5 to 40% by weight. Therefore, the pressure-sensitive adhesive can form a pressure-sensitive adhesive layer that is not easily peeled off due to peeling stress generated by deformation of the adherend even if it is thin.

  And since the double-sided pressure-sensitive adhesive sheet of the present invention can make the pressure-sensitive adhesive layer thin, stringing occurs in the punched portion during the punching process of the sheet, and the workability is hardly deteriorated. For example, the sheet can be suitably used for manufacturing a display device that is used by punching it into a frame shape.

  And the double-sided pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer that is excellent in adhesive force and can thin the pressure-sensitive adhesive layer, and the thickness of the entire double-sided pressure-sensitive adhesive sheet is also thin. It can be suitably used for the purpose of manufacturing a thin display device.

  Furthermore, in the display device of the present invention, the double-sided pressure-sensitive adhesive sheet used for adhering the display panel and the backlight strengthens both in spite of the peeling stress caused by the deformation of the display panel and the backlight. Integrated and maintains excellent quality over a long period of time.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

[Examples 1-3, 6-22, Comparative Examples 1-6, 8-14]
(Preparation of acrylic ester resin)
A reactor equipped with a thermometer, a stirrer, and a cooling pipe was prepared. In this reactor, predetermined amounts of ethyl acrylate, acrylic acid-n-butyl, acrylic acid-2-ethylhexyl, and acrylic shown in Tables 1 and 2 were prepared. After adding acid-2-hydroxyethyl and acrylic acid and a predetermined amount of ethyl acetate shown in Tables 1 and 2, the reactor was heated to start refluxing. Subsequently, 0.01 parts by weight of 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane was added as a polymerization initiator in the reactor, and polymerization was started under reflux. It was. Next, after 1 hour and 2 hours from the start of polymerization, 0.01 parts by weight of 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane was added, and the polymerization was started. 4 hours later, 0.05 part by weight of t-hexylperoxypivalate was added to continue the polymerization reaction. Then, 8 hours after the start of polymerization, ethyl acetate was added to the reactor and cooled while diluting to obtain an acrylic ester resin solution having a solid content of 30% by weight.

[Examples 4 and 5, Comparative Example 7]
A reactor equipped with a thermometer, a stirrer, and a cooling pipe was prepared. In this reactor, predetermined amounts of ethyl acrylate, acrylic acid-n-butyl, acrylic acid-2-ethylhexyl, and acrylic shown in Tables 1 and 2 were prepared. After adding acid-2-hydroxyethyl and acrylic acid and a predetermined amount of ethyl acetate as shown in Tables 1 and 2, nitrogen was blown into the reactor for 30 minutes to replace the air in the reactor with nitrogen did.

  Next, 0.01 parts by weight of 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane was added as a polymerization initiator in the reactor, and polymerization was started at 70 ° C. . Next, after 1 hour and 2 hours from the start of polymerization, 0.01 parts by weight of 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane was added, and the polymerization was started. 4 hours later, 0.05 part by weight of t-hexylperoxypivalate was added to continue the polymerization reaction. When the viscosity of the reaction solution became too high during the polymerization reaction, a small amount of ethyl acetate was added into the reactor as necessary to dilute the reaction solution. Then, 8 hours after the start of polymerization, ethyl acetate was added to the reactor and cooled while diluting to obtain an acrylic ester resin solution having a solid content of 30% by weight.

(Manufacture of double-sided PSA sheet)
A predetermined amount of polymerized rosin ester resin A (hydroxyl value: 46) shown in Tables 1 and 2 is added to 100 parts by weight of the acrylic ester resin solid content in the acrylic ester resin solution obtained as described above. , Softening point: 152 ° C., hydrogenated rosin ester resin B (trade name “Pine Crystal KE359” manufactured by Arakawa Chemical Co., Ltd., hydroxyl value: 40, softening point: 100 ° C.), disproportionated rosin ester resin C (Arakawa Chemical Co., Ltd.) Product name “Superester A125”, hydroxyl value: 15, softening point: 125 ° C., polymerized rosin ester resin D (trade name “Pencel D125” manufactured by Arakawa Chemical Co., Ltd., hydroxyl value: 32, softening point: 125 ° C.), Polymerized rosin ester resin E (trade name “Pencel D135”, manufactured by Arakawa Chemical Co., Ltd., hydroxyl value: 40, softening point: 135 ° C.), polymerized rosin ester resin F (produced by Arakawa Chemical Co., Ltd.) Name “Pencel D160”, hydroxyl value: 41, softening point: 160 ° C., terpene phenol resin G (trade name “Mighty Ace G150”, softening point: 150 ° C.), terpene phenol resin H (product made by Yashara Chemical Co., Ltd.) Name “YS Polystar T130”, softening point: 130 ° C.) and petroleum resin (trade name “FTR6100” manufactured by Mitsui Petrochemical Co., Ltd., softening point: 100 ° C.), ethyl acetate was added and stirred, By adding a predetermined amount of an isocyanate-based crosslinking agent (trade name “Coronate L45” manufactured by Nippon Polyurethane Co., Ltd.) shown in Tables 1 and 2 and stirring, an adhesive solution having a solid content of 20% by weight was obtained. In addition, the quantity of the isocyanate type crosslinking agent in Table 1, 2 shows the weight part of solid content of an isocyanate type crosslinking agent.

  Next, the pressure-sensitive adhesive solution was applied to the surface of a polyethylene terephthalate film having a thickness of 23 μm as a base material and dried at 100 ° C. for 5 minutes to remove ethyl acetate in the pressure-sensitive adhesive solution. After forming a thick adhesive layer A, a 50 μm thick polyethylene terephthalate film to be a release film is layered on this adhesive layer A so that the release treatment surface faces the adhesive layer A. Combined.

  Subsequently, a polyethylene terephthalate film having a thickness of 50 μm to be a release film is prepared separately from the polyethylene terephthalate film laminated on the pressure-sensitive adhesive layer A, and the pressure-sensitive adhesive solution is applied to the release-treated surface of the film. Then, after drying at 100 ° C. for 5 minutes to remove ethyl acetate in the adhesive solution, the adhesive layer B having the thickness shown in Tables 1 and 2 is formed on the release treatment surface of the polyethylene terephthalate film having a thickness of 50 μm. A laminated film was prepared.

  Then, the pressure-sensitive adhesive layer of the laminated film is superposed on the back surface of the polyethylene terephthalate film serving as the base material to produce a laminated body, and a 2 kg rubber roller is formed on the laminated body at a speed of 300 mm / min. The sheet was cured at 23 ° C. for 7 days to produce a double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layers A and B having the thicknesses shown in Tables 1 and 2 were laminated and integrated on both surfaces of the base material. . In addition, the 50-micrometer-thick release film was laminated | stacked on the adhesive layers A and B of a double-sided adhesive sheet so that peeling was possible.

  Next, the gel fraction of the pressure-sensitive adhesive obtained as described above is measured as described above, and the weight-average molecular weight of the acrylate-based resin, as well as the adhesive strength, peel stress resistance, and resistance of the double-sided pressure-sensitive adhesive sheet. The repulsive force, punchability and shear resistance were measured in the following manner, and the results are shown in Tables 1 and 2.

(Weight average molecular weight of acrylic ester resin)
The obtained acrylate resin was diluted 50-fold with tetrahydrofuran (THF), and the diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to obtain a measurement sample. Prepared. Next, this measurement sample is supplied to a gel permeation chromatograph (trade name “2690 Separations Model” manufactured by Water), and GPC measurement is performed under the conditions of a sample flow rate of 1 ml / min and a column temperature of 40 ° C. The molecular weight in terms of polystyrene of the ester resin was measured, and this value was taken as the weight average molecular weight of the acrylate resin. In the GPC measurement, a column commercially available from Showa Denko KK under the trade name “GPC LF-804” was used as the column, and a differential refractometer was used as the detector.

(Adhesive force)
The obtained double-sided pressure-sensitive adhesive sheet was cut into a strip having a width of 25 mm to prepare a test piece, and the release film on the pressure-sensitive adhesive layer A of the test piece was peeled off to expose the pressure-sensitive adhesive layer. Subsequently, the test piece was placed on a polycarbonate resin plate so that the adhesive layer faced the polycarbonate resin plate, and then a 2 kg rubber roller was reciprocated once at a speed of 300 mm / min on the test piece. Then, a test piece and a polycarbonate resin plate were adhered, and then allowed to stand at 23 ° C. for 30 minutes to prepare a test sample. And about this test sample, according to JISZ0237, the tensile test of the 180 degree direction was done by peeling speed 300mm / min, and adhesive force (N / 25mm) was measured.

(Peeling stress resistance)
As shown in FIG. 1, the obtained double-sided pressure-sensitive adhesive sheet was cut into a strip having a width of 20 mm to produce a test piece 1, and the release film was peeled off from the surface of the test piece 1 to remove the pressure-sensitive adhesive layer. It was exposed and placed on the polycarbonate resin plate 2 so that the pressure-sensitive adhesive layer faced.

  Subsequently, the release film was peeled off from the back surface of the test piece 1, and a polyethylene terephthalate film having a thickness of 23 μm was laminated on the exposed pressure-sensitive adhesive layer, and then the speed was 300 mm / min on the back surface of the test piece 1. Then, the test piece 1 and the polycarbonate resin plate 2 were adhered by reciprocating a 2 kg rubber roller once, and the test sample 3 was prepared by leaving still for 24 hours under conditions of 23 ° C. and 50% relative humidity.

  Next, the test sample 3 is put in an oven at 85 ° C., and as shown in FIG. 1, a load is applied to one end of the test piece 1 of the test sample 3 in a direction perpendicular to the sticking surface. Thus, after attaching 50 g weight 4 and leaving still for 24 hours, the maximum length L (mm) of the part which the test piece 1 peeled from the polycarbonate resin board 2 was measured.

(Repulsion resistance)
As shown in FIG. 2, the obtained double-sided pressure-sensitive adhesive sheet was cut into a plane rectangular shape of 25 mm wide × 150 mm long to produce a test piece 5, and a release film provided on both sides of the test piece 5 was peeled off The pressure-sensitive adhesive layer was exposed by removing.

  Thereafter, an aluminum plate 6 having a width of 25 mm × a length of 150 mm × a thickness of 0.3 mm was superimposed on the surface of the test piece 5, and a polycarbonate resin plate 7 having a width of 25 mm × length of 200 mm × thickness of 1 mm was superimposed on the back surface of the test piece 5. In addition, it adjusted so that the test piece 5 might be located in the center part of the length direction of the polycarbonate resin board 7. FIG.

  Next, a 2 kg rubber roller is reciprocated once on the polycarbonate resin plate 7 at a speed of 300 mm / min so that the polycarbonate resin plate 7 and the aluminum plate 6 are integrated through the test piece 5 at 23 ° C. for 24 hours. By leaving still, the test sample 8 in which the aluminum plate 6 was stuck and integrated with the central part of the vertical direction of the polycarbonate resin plate 7 through the test piece 5 was produced.

  Subsequently, as shown in FIG. 2, the test sample 8 is set on a jig 9, and bending stress is applied in the longitudinal direction of the test sample 8, so that the test sample 8 is subjected to both ends in the length direction of the polycarbonate resin plate 7. The test sample 8 was placed in an oven at 85 ° C. and allowed to stand for 24 hours in this state.

  After that, the test sample 8 is taken out from the oven while being curved in an arc shape, and the height H (mm) of the floating between the aluminum plate 6 and the polycarbonate resin plate 7 is measured with a caliper, and this value is repulsion-resistant. The value of force evaluation was used.

  Here, the height H (mm) of the float between the aluminum plate 6 and the polycarbonate resin plate 7 of the test sample 8 is the aluminum plate 6 and the polycarbonate resin plate 7 in the direction perpendicular to the upper surface of the jig 9. The position where the distance between the opposing surfaces of the aluminum plate 6 takes the maximum value is specified, and at this position, in the direction perpendicular to the upper surface of the jig 9, the test piece is determined from the distance between the opposing surfaces of the aluminum plate 6 and the polycarbonate resin plate 7. The value obtained by reducing the thickness of 5.

(Punchability)
The obtained double-sided PSA sheet was cut with a cutter knife and allowed to stand at 23 ° C. for 3 hours while the cut surfaces were butted together, and then the cut surfaces were pulled apart by hand. When the cut surfaces are separated from each other, the state of the stringing that occurs between the cut surfaces is visually observed. If the stringing is not observed, ○, if the stringing is slightly observed, Δ, if the stringing is severe. The case was evaluated as x.

(Shear resistance)
The obtained double-sided pressure-sensitive adhesive sheet was cut into a flat square shape with a side of 20 mm to produce a test piece. The release film was peeled off from the surface of the test piece to expose the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer was placed on top so as to face each other.

  Subsequently, the release film was peeled and removed from the back surface of the test piece, and a polyethylene terephthalate film having a thickness of 23 μm was laminated on the exposed adhesive layer, and then 2 kg on the back surface of the test piece at a rate of 300 mm / min. A test sample was prepared by reciprocating the rubber roller once to attach the test piece and the polycarbonate resin plate and allowing to stand at 23 ° C. for 24 hours.

  Next, a weight was attached to the test piece of the test sample, and the test piece was left to stand at 23 ° C. for 3 hours so that a load of 200 g was applied in a direction along the bonding surface of the test piece. Thereafter, before and after attaching the weight to the test piece, the displacement length of the test piece on the polycarbonate resin plate was measured using a loupe.

  In Examples 1 to 5, the composition of the monomer component of the acrylic ester resin is the same, but the weight average molecular weight of the acrylic ester resin is different. In Example 1, since the weight average molecular weight of the acrylic ester resin is below the lower limit of the more preferable range, the value of the peel resistance is larger than those in Examples 2-4. Since Examples 3-5 exceed the upper limit of a more preferable range, compared with Examples 1 and 2, adhesive force is inferior and the value of repulsion resistance is large.

  In Examples 6 and 7, the amount of 2-hydroxyethyl acrylate is different from each other. In Example 6, the amount of 2-hydroxyethyl acrylate is the lower limit of the more preferable range. Therefore, in spite of blending more crosslinking agent than Example 7, the gel fraction of the pressure-sensitive adhesive is small, which is below the lower limit of the preferred range.

  Examples 11-15 differ in the amount of ethyl acrylate. In Example 11, since the amount of ethyl acrylate is below the preferred range, the peel resistance is a large value. In Examples 14 and 15, since the amount of ethyl acrylate exceeds the upper limit of the more preferable range, the repulsion resistance is a large value. This is presumably because the pressure-sensitive adhesive layer is hard.

  In Examples 16-18, the compounding quantity of rosin ester differs. In Examples 16 and 18, since the amount of the rosin ester-based resin is out of the more preferable range, the value of the resilience resistance is large.

  In Comparative Examples 1 and 12, the gel fraction of the pressure-sensitive adhesive is too high, and the repulsion resistance value is large. In Comparative Examples 2 and 6, the weight average molecular weight of the acrylic ester resin is too small, and the peel resistance is a large value.

  In Comparative Examples 3, 4, 8, 9, 13, and 14, since the tackifier resin having a softening point of 140 to 170 ° C. is not blended, the peel resistance is a large value. In Comparative Example 7, the weight average molecular weight of the acrylic ester resin is too large, the adhesive strength of the adhesive is reduced, and the peel resistance is a large value. In Comparative Example 11, the gel fraction is too small and the peel resistance is a large value. Although the comparative example 10 is not compounded with a tackifying resin having a softening point of 140 to 170 ° C., the pressure-sensitive adhesive layers A and B are as thick as 35 μm. The anti-peeling stress is improved as compared with Comparative Examples 3, 4, 8, 9, 13, and 14.

It is the figure which showed the test method of peeling stress resistance. It is the figure which showed the test method of the resilience force.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polycarbonate resin board 2 Test piece 3 Test sample 4 50g weight 5 Test piece 6 Aluminum plate 7 Polycarbonate resin board 8 Test sample 9 Jig L The maximum length (mm) of the part which peeled
H Height of float between aluminum plate and polycarbonate resin plate (mm)

  The pressure-sensitive adhesive of the present invention can form a pressure-sensitive adhesive layer that is not easily peeled off due to peeling stress generated by deformation of the adherend even if it is thin. Therefore, the pressure-sensitive adhesive of the present invention can be suitably used for the production of display devices, particularly small display devices and thin display devices.

Claims (9)

An acrylic ester resin having a weight average molecular weight of 500,000 to 1,500,000 measured as a polystyrene equivalent molecular weight by the GPC method, a tackifying resin having an alcoholic hydroxyl group and a softening point of 140 to 170 ° C., and a terpene A pressure-sensitive adhesive comprising a phenol resin and having a gel fraction of 5 to 40% by weight. The pressure-sensitive adhesive according to claim 1, wherein the tackifying resin is a rosin ester-based resin. The weight average molecular weight measured as a polystyrene-equivalent molecular weight by GPC method of an acrylic ester resin is 500,000 to 1,000,000, and the gel fraction is 10 to 40% by weight. The adhesive as described. The pressure-sensitive adhesive according to claim 1, wherein the acrylic ester resin contains 5 to 30% by weight of an ethyl acrylate component. The pressure-sensitive adhesive according to claim 1, comprising 5 to 40 parts by weight of a rosin ester resin and 3 to 20 parts by weight of a terpene phenol resin with respect to 100 parts by weight of the acrylic ester resin. A double-sided pressure-sensitive adhesive sheet, wherein a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to claim 1 is laminated and integrated on both surfaces of a base material. The double-sided pressure-sensitive adhesive sheet according to claim 6, wherein the thickness of the pressure-sensitive adhesive layer laminated and integrated on both surfaces of the substrate is 30 µm or less. The double-sided pressure-sensitive adhesive sheet according to claim 6 or 7, which is used for production of a display device. A display device, wherein a display panel and a backlight are attached via the double-sided pressure-sensitive adhesive sheet according to claim 8.

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