JPH08152517A - Double-face tacky adhesive sheet for optical film and its production - Google Patents

Abstract

PURPOSE: To prevent intrusion of water vapor from a polarizing plate and to maintain a high display performance without peeling of a polarizing plate or a phase difference plate even under high temp. and high humidity conditions by applying different or the same kinds of tacky adhesive layer on both surfaces of an intermediate layer and constituting the intermediate layer of one or more kinds of water-inpermeable resin layers. CONSTITUTION: Different or the same kinds of tacky adhesive layers are applied on both surfaces of an intermediate layer and the intermediate layer consists of one or more kinds of water-impermeable resins. And, the intermediate layer consists of a resin essentially comprising a polymer prepared by copolymn. of one or more kinds of long-chain alkyl (meth) acrylates having 8-20C in alkyl groups and vinyl monomers which can copolymerize with the above acrylates. By using this polymer, firm interlayer adhesion strength is obtd. between the intermediate layer and adhesive layers. Further, the obtd. sheet has high water-proofing property and transparency and hardly causes optical defects such as double refraction. The carbon number of alkyl groups is preferably 8 to 20. If the number is smaller than 8, enough water intermeability is not obtd., while if the number exceeds 20, the resin becomes hard and has inferior bending property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided pressure-sensitive adhesive sheet for an optical film and a method for producing the same, and particularly for laminating optical films such as polarizing plates and retardation plates used in liquid crystal display devices with each other or with a glass substrate. The present invention relates to a double-sided PSA sheet and a manufacturing method.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have come to be used as display devices for small TVs, laptop personal computers, word processors, etc., in addition to simple display devices for watches and electric appliances, and have higher and higher resolutions. Is required. A liquid crystal display device uses various optical films such as a polarizing plate and a retardation plate, and an adhesive is widely used for laminating these optical films because of their simplicity. The pressure-sensitive adhesive used for laminating the optical films is required to have high durability so as not to peel even in a harsh environment.

Of the optical films, especially the polarizing plate and the retardation plate are used together in the STN type liquid crystal display device, the polarizing plate polarizes the light, and the retardation plate plays the role of preventing the appearance color shift. Usually, the retardation plate is attached to a liquid crystal cell made of glass mainly by using an acrylic adhesive, and the polarizing plate is also attached to the retardation plate in the same manner. Therefore, normally, a polarizing plate is arranged on the outermost surface, and a retardation plate and a glass plate are sequentially attached thereto to form a liquid crystal cell.

Acrylic adhesives are used as the adhesives for sticking these because they are more durable against heat, ultraviolet rays, etc. than rubber adhesives. However, the glass surface is very hydrophilic compared to ordinary acrylic adhesives, and especially under high temperature and high humidity conditions, the water vapor that has permeated the polarizing plate, which is the outermost surface, eventually causes the glass plate and the retardation plate to become defective. A thin film is formed at the adhesive interface with. For this reason, the adhesive layer peels off from the glass due to wetness, which may result in incomplete display in the liquid crystal display device or lack of display to make it impossible to display.

In order to improve this, Japanese Unexamined Patent Publication No. 4-268.
Japanese Patent No. 504 proposes to mix water-repellent liquid paraffin into an adhesive to prevent water from entering.
Further, JP-A-3-148603 proposes to coat the surface of the polarizing plate with a water impermeable layer to prevent migration of water vapor.

[0006]

However, when a hydrophobic component such as liquid paraffin is added to the pressure-sensitive adhesive to make it water-repellent, the adhesiveness between the pressure-sensitive adhesive and the glass plate is generally weakened, and the polarizing plate There is a problem in that the film is easily peeled off due to the heat shrinkage of. Therefore, the high temperature durability of the polarizing plate is impaired.

Further, when the water impermeable layer is coated on the surface of the polarizing plate, the number of steps of coating the water impermeable layer in the production of the polarizing plate is increased, resulting in an increase in cost. The object of the present invention is to prevent the invasion of water vapor from the polarizing plate without causing the above-mentioned problems, and even under high temperature and high humidity, the polarizing plate, the optical film such as the retardation plate is sufficiently adhered to the glass plate. It is intended to provide a double-sided pressure-sensitive adhesive sheet for an optical film and a method for producing a double-sided pressure-sensitive adhesive sheet for an optical film, which can maintain the required bonding strength and perform the bonding with high durability.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that, with respect to wet peeling, water vapor that has permeated through a polarizing plate causes adhesion between an adhesive layer and a retardation plate or a glass plate. It was found that due to the difference in the water vapor transmission rate of the above, they were concentrated and accumulated at a specific site, resulting in the loss of adhesiveness of the adhesive layer.

That is, in the configuration of the polarizing plate portion of the liquid crystal cell, after the water vapor passes through the polarizing plate, it easily passes through the adhesive layer having a higher water vapor transmission rate than the polarizing plate and reaches the retardation plate or the glass surface. Since these have a lower water vapor transmission rate than the adhesive layer, water vapor is accumulated at this interface, and as a result, when peeling stress is applied, peeling easily occurs.

Therefore, if a water impermeable layer is provided somewhere in the adhesive layer from the polarizing plate to these interfaces to prevent the invasion of water vapor, the above problems can be solved and the present invention has been accomplished. . That is, the invention according to claim 1 is a double-sided pressure-sensitive adhesive sheet for an optical film, wherein different kinds or the same kind of pressure-sensitive adhesive layers are provided on both surfaces of the intermediate layer, and the intermediate layer is at least one kind of water-impermeable resin. It is characterized by being composed of layers.

For the intermediate layer, a water-impermeable resin is used, and polyamide, polyimide, poly (meth) acrylate, polymethyl (meth) acrylate, polyethylene terephthalate, polystyrene, polysulfone, polyether sulfone, polyether ether ketone, poly Acrylate, polyester, polyvinyl chloride, polyvinylidene chloride and modified products and copolymers thereof can be used.

The intermediate layer preferably has high light transmittance and low birefringence. The double-sided pressure-sensitive adhesive sheet for an optical film according to claim 2, wherein the intermediate layer has at least one kind of long-chain alkyl (meth) acrylate having an alkyl group having 8 to 20 carbon atoms and a vinyl monomer copolymerizable therewith. It is characterized by being composed of a resin whose main component is a polymer obtained by copolymerizing

By using the above polymer, a strong interlayer adhesion strength between the intermediate layer and the adhesive layer can be obtained. Further, it has high waterproofness and transparency, and is unlikely to cause optical defects such as birefringence. The number of carbon atoms of the alkyl group is preferably 8 to 20, and if it is less than 8, the water impermeability is insufficient, and if it exceeds 20, the resin is hard and
Inferior in flexibility. The content of the alkyl (meth) acrylate monomer is preferably 1 to 99.8% by weight, more preferably 20 to 95% by weight, and if it is less than this, water impermeability is insufficient, and if it is more than this, cohesive force is insufficient. And inferior in heat resistance.

Examples of monomers corresponding to this include 2-ethylhexyl (meth) acrylate, octyl acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate. These long-chain alkyl groups suppress the permeation of water vapor and act as a water impermeable layer, so that wet peeling can be prevented and the resin is flexible and has high conformability. As a result, even if stress such as bending is applied, the peeling of the adhesive layer due to strain is unlikely to occur.

The double-sided pressure-sensitive adhesive sheet for optical films according to the present invention requires a copolymerization component for improving cohesive force in addition to the above components. This is a long chain alkyl (meth)
It is selected from vinyl monomers compatible with and copolymerizable with acrylates. For example, (meth) acrylic acid, maleic acid (anhydride), itaconic acid, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, glycidyl (meth) acrylate, 2-
Hydroxyethyl (meth) acrylate, styrene, styrene oligomer (macromonomer), N-vinylpyrrolidone, N-vinyloxazoline, acrylamide, acrylonitrile, vinyl acetate, vinyl chloride, vinylidene chloride, 1,6-hexanediol acrylate, silicone macromonomer Etc. can be illustrated. By copolymerizing these, the cohesive force of the polymer can be increased and the heat resistance can be improved. For the copolymerization, general polymerization methods such as solution polymerization, emulsion polymerization, suspension polymerization and photocoating polymerization can be selected.

Further, by introducing a functional group, it is possible to improve cohesive force by crosslinking. As a cross-linking agent, an oligomer or metal reactive with a functional group is used. Examples of the cross-linking agent include isocyanate type, aziridine type, epoxy type, silane type, chelate type and organic metal type. Alternatively, a polyvinyl compound may be used for copolymerization and crosslinking. At this time, a photo-coating polymerization method is useful as a polymerization method. That is, a photoreactive radical generator is dissolved in a monomer mixture and sufficiently stirred, the dissolved oxygen is replaced with an inert gas such as nitrogen, and after coating on a support, irradiation with ultraviolet rays, γ rays, electron beams, etc. Thus, a polymerization reaction and a crosslinking reaction occur simultaneously. When a support is used as an adhesive layer by this method and the water-impermeable layer is formed by directly coating on the adhesive layer, high interlayer strength can be obtained.

The method for producing a double-sided pressure-sensitive adhesive sheet for an optical film according to claim 3, wherein at least one kind of long-chain alkyl (meth) acrylate having an alkyl group having 8 to 20 carbon atoms and vinyl copolymerizable therewith. The composition is characterized in that a composition obtained by mixing a monomer with a photopolymerization initiator is cast on an adhesive layer and cured by light irradiation to form an intermediate layer.

By photopolymerizing the above-mentioned composition forming the intermediate layer on the pressure-sensitive adhesive layer, the adhesiveness between the intermediate layer and the pressure-sensitive adhesive layer is improved, and re-peeling and heat shrinkage stress of the polarizing plate are prevented. It is possible to prepare a double-sided pressure-sensitive adhesive sheet that is resistant to delamination. The photopolymerization uses light other than visible light, such as ultraviolet rays, electron beams, γ rays, or electromagnetic waves, and uses a photopolymerization initiator that reacts with them to generate radicals, thereby copolymerizing the monomer composition. The monomer composition before photopolymerization may be an oligomer composition in which copolymerization is partially advanced in advance and polymerized to increase the viscosity.

By casting these reactive compositions on the pressure-sensitive adhesive layer, they polymerize following minute irregularities on the pressure-sensitive adhesive layer to enhance the anchor effect and improve the adhesion. As the photopolymerization initiator, 4- (hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, α-hydroxy-α, α'-dimethyl-
Examples thereof include acetophenone, methoxyacetophenone, acetophenone such as 2,2-dimethoxy-2-phenylacetophenone, ketal such as benzyl ketal, halogenated ketone, acylphosphinoxide, acylphosphonate and the like.

The amount of these photoreactive radical generators added is appropriately adjusted in consideration of the reactivity of the monomer components used, but generally 0.01-1. It is often added in the range of 0% by weight. This means that if the added amount is less than 0.01% by weight,
If the amount of unreacted substances increases due to insufficient copolymerization and the amount added exceeds 1.0% by weight, the amount of radicals generated is too large and the radical polymerization causes rapid heat generation, causing the monomer to reach a high temperature. Because there is a risk of explosion.

The amount of the photoreactive radical generator added depends on the kind and intensity of light for irradiating the radical generation amount, time,
It also varies with the amount of dissolved oxygen in the monomer and solvent mixture. When the amount of dissolved oxygen is large, the amount of radicals generated is suppressed, the polymerization does not proceed sufficiently, and unreacted substances increase.Before irradiation with light, an inert gas such as nitrogen is blown into the composition to generate oxygen. Is preferably substituted.

In photopolymerization, the type of light, the irradiation intensity, and the irradiation time affect the molecular weight and molecular weight distribution of the polymer. As the type of light, electromagnetic waves of short wavelength or electron beams are often used because they have high energy and must excite photoreactive radical generator molecules. The electromagnetic waves of short wavelength include ultraviolet rays (UV) and gamma rays, but in general, they are easy to generate and can make the device compact, and ultraviolet rays that do not cause cross-linking due to molecular cleavage or polymer hydrogen abstraction. Is often used. Irradiation with ultraviolet rays is preferably performed by a lamp having an emission distribution at a wavelength of 400 nm or less. This is because the wavelength distribution is sufficient to decompose the radical generator, the device is simple, and the running cost is low. Examples of such lamps include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, and metal halide lamps.

The ultra-high pressure mercury lamp is particularly preferable because it absorbs light in the active wavelength region of the photoreactive radical generator well and does not reduce the tackiness of the resulting polymer. It has a sharp wavelength distribution and does not contain short wavelength light. The reason is that the cross-linking reaction between molecules that does not depend on the cross-linking agent does not occur and it is easy to control the molecular weight and cross-linking amount of the polymer. Further, since it does not have long wavelength light, the reaction composition is not heated and evaporated.

The light irradiation intensity of these lamps is determined by the molecular weight and molecular weight distribution of the polymer obtained as described above. Generally, when a cleavage type photoreactive radical generator having an acetophonone group is used. Is preferably in the range of 0.1 to 100 mW / cm ² . This is because if it is lower than 0.1 mW / cm ² , the reaction does not sufficiently occur and the amount of unreacted substances increases, and if it exceeds 100 mW / cm ² , polymerization rapidly occurs and there is a risk of explosion due to heat generation or runaway. Because there is.

At the time of photopolymerization, dissolved oxygen in the polymerization composition acts as a polymerization inhibitor and affects the polymerization rate, molecular weight and molecular weight distribution of the resulting polymer, so it is preferable to remove it beforehand. Polymerization inhibition by dissolved oxygen is due to oxygen trapping generated radicals. At this time, if more radicals than are trapped in dissolved oxygen are generated,
Polymerization is possible, but the efficiency of the radical generator is poor, and it becomes difficult to control the polymerization. Therefore, generally, nitrogen is blown into the polymerization composition to replace the dissolved oxygen. Further, oxygen in the atmosphere in the light irradiation zone also becomes a polymerization inhibiting factor, and therefore it is also preferable to substitute it with nitrogen. Although this is referred to as "inert atmosphere", the oxygen concentration in the inert atmosphere is preferably 5000 ppm or less, more preferably 1000 ppm or less.

In the present invention, the molecular weight of the resin is not particularly limited, but a higher molecular weight is preferable in order to improve water impermeability. Particularly preferably, the molecular weight is 1,000,000 or more. In addition, the introduction of the crosslinked structure further improves the waterproof property. Alternatively, the composition obtained by blending the above-mentioned monomer mixture with a photopolymerization initiator may be disposed between the adhesive layers and copolymerized by irradiation with light to form the intermediate layer.

Also in this case, the anchor effect is enhanced by the resin composition forming the intermediate layer following the minute irregularities on the adhesive layer, and the adhesiveness between the adhesive layers on both sides and the intermediate layer formed of the water impermeable resin is improved. It is possible to prevent delamination between the pressure-sensitive adhesive layer and the intermediate layer against a stress such as increased peeling or contraction of the polarizing plate. Further, in the photoirradiation polymerization method, after replacing the dissolved oxygen in the monomer composition, it was necessary to cover it with a plastic film such as PET or to purge the irradiation atmosphere with nitrogen so that oxygen in the atmosphere would not be redissolved. But PE
Although T cover and nitrogen purging may increase the cost and decrease the productivity, in the present invention, by covering the resin composition coated and coated on another adhesive layer with an adhesive layer, oxygen recovery The pressure-sensitive adhesive sheet can be efficiently produced by omitting the polymerization inhibition due to dissolution and the step of transferring the pressure-sensitive adhesive layer. At this time, two types of adhesive layers are used, one for applying and coating the resin composition and the other for the adhesive layer provided on the coated resin composition, but these may be the same or different.

Water impermeable in the present invention means water vapor transmission
Rate is about 100g / m²・ Being about 24 hours or less
The water vapor permeability of the resin layer that constitutes the intermediate layer is
It is preferably used in such a thickness that it falls within this range.
Water vapor transmission rate is 100g / m ²・ Larger than 24 hours
In some cases, it may not be able to function as a waterproof layer. . This
If the thickness of the intermediate layer is thick, the liquid crystal cell becomes thicker,
It is disadvantageous in making the cell thinner and smaller.
Poor appearance due to wrinkles and creases, resulting in low coatability.
In addition, it is the same when laminating the retardation plate and the glass plate.
Workability is poor, which is not preferable. Suitable thickness is 1
It is about 80 μ, and more preferably about 6 to 60 μ.
It However, this is a constant considering the light transmittance and isotropic property of the substrate.
Should be set.

In addition, the intermediate layer is required to have optical characteristics higher than mechanical strength. In particular, an anisotropic material causes optical defects such as interference fringes of transmitted light and bleeding due to birefringence. Therefore, it is preferably an isotropic material. Further, since the stretched film is liable to suffer from optical distortion, it is necessary to take care so that optical defects such as interference fringes do not occur during use. Further, the transparency is necessary to avoid obscuring the display and is not particularly limited to this, but 60 to 70% or more of transparency is often required.

In consideration of isotropy, it is desirable that the resin layer used is not stretched. This is because the stretching may cause polarized light. Therefore, the resin layer is preferably formed by the casting method. The casting method is metal,
A thin film is formed on a plastic film or belt-shaped support by applying it in the form of a solution or a monomer and heating or irradiating with light. By transferring this to the adhesive layer, a double-sided adhesive sheet can be formed. Alternatively, the resin layer may be directly formed on the adhesive layer. Instead of the support, an adhesive layer formed on the support is used, and it is directly cast on the adhesive layer and dried in the same manner.
When it is solidified, the adhesion between the adhesive layer and the resin layer becomes good, and it becomes difficult to separate the layers.

Also, an adhesive layer can be formed on the resin layer formed in reverse, and the same effect can be expected. further,
Even by the transfer method, the interlayer strength can be improved by thermal lamination. Since the peeling between layers results in the peeling of the polarizing plate and the retardation plate, the interlayer adhesion must be greater than the adhesive strength of the polarizing plate, the retardation plate, or the glass plate.

Further, the water impermeable intermediate layer may not be a single resin layer. That is, it is possible to improve the water impermeability by forming the resin layer into a multilayer. For example, in the above manufacturing process, if a water-impermeable plastic film is used as the support to which the resin layer is applied and both are used as the water-impermeable layer, wet peeling can be greatly reduced.
At this time, if a surface oxidation treatment such as corona treatment is applied to the adhesive layer side of the film (the side on which the water-impermeable resin is not cast), delamination between the adhesive layer and the film on this surface can be prevented. Similarly, in the case of a single layer, the interlayer strength can be improved by the surface oxidation treatment.

Examples of the adhesive layer used in the present invention include acrylic, rubber and silicone adhesives. Acrylic pressure-sensitive adhesives are particularly preferable because they are superior in weather resistance to rubber-type pressure-sensitive adhesives and can add various properties depending on the selection of the copolymerization monomer. An example of the acrylic adhesive is a copolymer of alkyl acrylate and acrylic acid. Examples of the alkyl group of the acrylic acid alkyl ester include butyl, ethyl, methyl, 2-ethylhexyl, isooctyl, octyl and the like. It is known that the copolymer obtained by these copolymers has a high adhesiveness and adheres very well to a glass plate or a retardation plate. Especially when the number of parts of acrylic acid is set to about 2 to 10 parts by weight, the pressure-sensitive adhesive has high glass adhesion and is difficult to peel off under thermal conditions.

The molecular weight of the adhesive is preferably as high as possible for the purpose of obtaining a retardation plate adhesive processed product having excellent durability.
It is more preferably at least 0,000. Further, when the pressure-sensitive adhesive is cross-linked to some extent, the heat resistance durability can be improved. Crosslinking is carried out with a crosslinking agent, and a thermal crosslinking type such as isocyanate type, epoxy type, aziridine type, organometallic type, chelate type, amine type, or a copolymerizable crosslinking agent such as diacrylate, triacrylate or divinyl type is used. However, the cross-linking structure and the cross-linking method are not particularly limited.

If desired, additives such as tackifiers, plasticizers, fillers, stabilizers, and ultraviolet absorbers can be used. In particular, the tackifier is used to improve the adhesive physical properties such as peel adhesive strength and shear adhesive strength of the adhesive,
It is preferable to mix them in a range that does not impair optical characteristics such as light transmittance and hue. The rubber-based pressure-sensitive adhesive is preferably a synthetic rubber-based pressure-sensitive adhesive in order to improve weather resistance and heat resistance. Examples of the base polymer include resins such as SEBS, SBS and SIS. Adhesiveness can be imparted by adding a tackifier or a plasticizer thereto. As the tackifier, a petroleum-based resin, a terpene-based resin, a rosin-based resin, a phenol-based resin, or the like is used, and these are preferably hydrogenated. This is because the deterioration of the resin can be suppressed by eliminating the double bond. Examples of the plasticizer include dioctyl phthalate and dibutyl phthalate. In addition to the above, a stabilizer, a cross-linking agent, an ultraviolet absorber, a filler and the like may be added.

The silicone adhesive is a mixed composition of silicone rubber and silicone resin, which is excellent in water resistance and moisture resistance, and exhibits extremely high durability when used as an adhesive for fixing a polarizing plate or a retardation plate. The thickness of the above-mentioned pressure-sensitive adhesive layer should be determined by the adhesiveness, but generally it is preferably about 5 to 30 μ in order to reduce the thickness of the cell. More preferably, it is 10 to 20 μ. Moreover, in order to reduce the influence of water vapor on the pressure-sensitive adhesive, it is preferable that the thickness of the pressure-sensitive adhesive on both sides of the water-impermeable layer be thin on the side close to the polarizing plate when it is attached to the cell.

Different adhesives can be used on both sides of the double-sided adhesive tape. Therefore, use an adhesive suitable for the polarizing plate, an adhesive suitable for the material of the retardation plate on the retardation plate surface, and an adhesive suitable for the glass plate on the glass surface. You can Therefore, in terms of durability, higher durability can be easily realized as compared with the single-layer pressure-sensitive adhesive layer. In particular, it is preferable to use a silicone-based pressure-sensitive adhesive on the surface to which the glass is attached, because peeling due to poor adhesion due to adsorbed water on the glass plate can be prevented. Therefore, the combination of optical films to be attached can be freely selected.

[0038]

[Operation] When a water-impermeable resin layer is formed as an intermediate layer,
It is possible to obtain a liquid crystal display device in which water vapor is prevented from entering the polarizing plate and the polarizing plate or the retardation plate is not peeled off even under high temperature and high humidity conditions, and high display performance can be maintained.

[0039]

EXAMPLES Examples of the present invention will be described below and described in detail. [Examples 1 and 2] As the adhesive, 1428F and 1831 were selected from the "SKDyne" series manufactured by Soken Kagaku. This pressure sensitive adhesive is an acrylic type, and the composition of other components is as shown in Table 1. In addition, in Table 1, Epicoat 82
8 is an epoxy-based crosslinking agent, which is a trade name manufactured by Yuka Shell Co., Ltd.

[0040]

[Table 1]

The pressure-sensitive adhesives shown in Table 1 were applied to the water-impermeable intermediate layer in the combinations shown in Table 2 to prepare double-sided pressure-sensitive adhesive tapes. The creation method is all transfer method. The release agent of a commercially available release polyester film 380-S (manufactured by Lintec Co., Ltd.) was coated with the above adhesive with a comma coater and dried, and then the water-impermeable resin PET or PVD shown in Table 2 was used.
The intermediate layer of C and PEEK (impermeable thin film) was laminated at room temperature. The pressure-sensitive adhesive shown in Table 1 was applied to both surfaces of this intermediate layer to prepare a double-sided pressure-sensitive adhesive sheet. 3 kg / cm ^{2 of} this on a polarizing plate and a retarder with a rubber roller
Samples of type 1 and type 3 were prepared by sticking under the pressure of.

After the polarizing plate or retardation plate was attached to the sample as shown in Table 2, finally, as shown in FIGS. 1 (a) and 1 (c).
As shown in FIG. 5, the sheet was cut into a size of 200 × 100 mm and attached to a glass plate. The stretching direction was the long side direction of the sample. Further, in Table 2, the thickness of the adhesive layer is 10 μm on the A side and 15 μm on the B side. FIG.
(A) shows a sample of type 1, which is a laminate of the polarizing plate 1 and the glass plate 7, and the laminating layer a is present between the polarizing plate 1 and the glass plate 7.

FIG. 1 (c) shows a sample of type 3, which is a laminate of the polarizing plate 1, two retardation plates 3 and 5, and the glass plate 7, and is placed in parallel with the polarizing plate 1. The laminating layer a is between the retardation plate 3 and the laminating layer b is between the retardation plates 3 and 5.
However, the bonding layer c exists between the retardation plate 5 and the glass plate 7.

[Comparative Examples 1 and 2] In Comparative Examples 1 and 2, the adherends were joined with one having no water-impermeable thin film, that is, one adhesive layer. As a method for preparing a sample, a mixture prepared by mixing a pressure-sensitive adhesive solution with a predetermined additive was coated on a release PET and dried as in the example. This was similarly pressure-bonded to a polarizing plate and a retardation plate to prepare a sample. The thickness of the adhesive is 25
was set to μ. As the polarizing plate, an iodine / popal type polarizing film sandwiched with triacetyl cellulose (TAC) and having a thickness of 200 μm was used. The retardation plate used was a polycarbonate resin having a thickness of 60 μm. As the glass plate, # 7250 manufactured by Asahi Glass Co., Ltd. was used.

[Evaluation] The samples represented in Table 2 below and FIG. 1 were placed in a constant temperature and humidity chamber of 65 ° C. × 95% RH.
The sample was peeled off for 0 hour. Example 1,
In No. 2, no wet peeling occurred in any of the bonded parts. On the other hand, in Comparative Examples 1 and 2, wet peeling occurred.

[0046]

[Table 2]

[Examples 3 to 12] An acrylic pressure-sensitive adhesive obtained by copolymerizing butyl acrylate as a main component was used as the pressure-sensitive adhesive layer. The copolymer composition and various physical properties are shown in Table 3. This polymer solution is referred to as solution A.

[0048]

[Table 3]

In Table 3, BA is butyl acrylate, AAc is acrylic acid, 2HEA is 2-hydroxyethyl acrylate, AIBN is azobisisobutyronitrile, and DDM is dodecanethiol. The mixture in Table 4 was blended with the solution A, and the mixture was thoroughly mixed and stirred as a pressure-sensitive adhesive and stirred and deaerated, and then the thickness after drying was applied to the release surface of the release polyester "Coat film 3811" (38μ) manufactured by Lintec Co., Ltd. Of 12 μm was applied and dried with a comma coater to form an adhesive layer.

[0050]

[Table 4]

As the intermediate layer, those shown in Table 5 were used.

[0052]

[Table 5]

The composition of the resin in Table 5 is as shown in Table 6.

[0054]

[Table 6]

Polymerization methods 1 and 2 in Table 6 will be described. -Method 1 A monomer solution composed of the above resin composition, in which dissolved oxygen has been replaced by a nitrogen purge, is directly applied onto a pressure-sensitive adhesive layer prepared by applying and drying the solution A using a gravure coater, and is irradiated with ultraviolet rays under a nitrogen atmosphere. In the zone, irradiation was performed with a high-pressure mercury lamp so that the intensity of the irradiation surface was adjusted to 15 mW / cm ² at maximum. In addition, the light intensity is UVR made by Tokyo Optical Machinery Co., Ltd.
It was measured at -1. Light irradiation was continuously performed for 1.5 minutes.
In addition, the inert atmosphere has an oxygen concentration of 1000 pp.
m. The degree of crosslinking of the obtained resin was 98%.

Method 2 A monomer solution consisting of the above resin composition, in which dissolved oxygen was replaced by a nitrogen purge, was directly applied onto a pressure-sensitive adhesive layer prepared by applying and drying Solution A by means of a gravure coater, and then applied thereon. The adhesive layer was laminated so that the adhesive surface was in contact with the monomer liquid. This was irradiated with ultraviolet rays in the usual atmosphere in the same manner as in Method 1 to copolymerize the monomers to form a resin layer. The degree of crosslinking of the obtained resin was 94%.

The resin is a commercially available film, and the pressure sensitive adhesive is directly laminated on both sides to obtain a double-sided pressure-sensitive adhesive sheet. Before laminating, both sides of the film were subjected to corona treatment with a corona treatment machine. Resin, release PET
“3811” was coated with a comma coater so that the final resin thickness would be 8 μ, and the solvent component was heat dried. Epoxy cross-linking agent "EA
Crosslinking was performed by blending 0.05 part by weight of "X" manufactured by Soken Chemical Industry Co., Ltd. This was transferred to a pressure sensitive adhesive, and after releasing the release PET, the pressure sensitive adhesive was further transferred to obtain a double-sided pressure sensitive adhesive sheet. The following items were implemented as evaluation items.

[Humidity Resistance Acceleration Evaluation] 10 was obtained by adhering a polarizing plate and a retardation plate under a high temperature and high humidity environment of 60 ° C. × 95% RH.
After leaving for 0 hours, peeling was observed. It can be said that those that do not peel off have high moisture resistance. [Delamination test] A sample similar to the one used in the moisture resistance accelerated evaluation was subjected to gear opening at 70 ° C and 95 ° C.
After standing for 0 hour, delamination of each layer was observed. Since heat is applied to the polarizing plate, it is thermally shrunk and a peeling stress is applied between the layers. Therefore, it can be said that the interlayer strength is high unless peeling occurs at a high temperature. The results of these evaluations are summarized in the table.

[0059]

[Table 7]

Next, how to read Table 7 will be described. Example 3-
7 and 11 are polarizing plate-glass plate cells (type 1; FIG.
Example of (a)). The upper surface of the adhesive layer is the polarizing plate side, and the lower surface is the glass plate side. Examples 8, 9 and 12 are examples of a polarizing plate-retarder-glass plate cell (type 2; see FIG. 1B). In Example 8, the glue B having no intermediate layer was used for the c layer between the retardation plate and the glass plate. In this case as well, it is considered that the reason why the wet peeling does not occur is that the permeation of water vapor is prevented by the intermediate layer (resin B) in the b layer.

Example 10 is an example of a polarizing plate-retarder-retarder-glass plate cell (type 3; see FIG. 1C). Comparative Examples 3 to 5 are examples of type 1 without an intermediate layer. It cannot be prevented from permeating water vapor and peels off. Comparative Example 6 is a case where the intermediate layer has a lower alkyl chain (butyl = C4). In this case, a paste was used to form the intermediate layer. Peeling due to insufficient carbon number and insufficient penetration of water vapor. In addition, the comparative example of the higher alkyl chain has not been carried out because the monomer exceeding stearyl is not commercially available. However, Tg is stearyl at 35 ° C,
It is presumed that it will be higher than this, so in the text it is said that the resin becomes hard.

[0062]

By using the double-sided pressure-sensitive adhesive sheet for an optical film according to the present invention, a liquid crystal display device having high durability in which the polarizing plate and the retardation film are not peeled off even under high temperature and high humidity conditions and display is not lost. It is possible to easily obtain a polarizing plate or a retardation plate adhesive processed product that does not require any special treatment on the polarizing plate, the retardation plate or the glass plate and can be used in any combination.

Further, according to the method for producing a double-sided pressure-sensitive adhesive sheet for an optical film according to the present invention, the resin composition forming the intermediate layer follows the minute irregularities on the pressure-sensitive adhesive layer to enhance the anchor effect, and thus the pressure-sensitive adhesive layers on both sides. A double-sided pressure-sensitive adhesive sheet for optical films, which has improved adhesion between the water-impermeable resin and the intermediate layer and is excellent in delamination resistance between the pressure-sensitive adhesive layer and the intermediate layer against stress such as re-peeling or contraction of the polarizing plate. To be

[Brief description of drawings]

FIG. 1A is an explanatory diagram schematically showing a sample.

[Explanation of symbols]

 1 ... Polarizing plate 3, 5 ... Retardation plate 7 ... Glass plate a, b, c ... Laminating layer

Claims (3)

[Claims] 1. A double-sided pressure-sensitive adhesive sheet for an optical film, wherein different kinds or the same kind of pressure-sensitive adhesive layers are provided on both surfaces of the intermediate layer, and the intermediate layer is composed of at least one kind of water-impermeable resin layer. . 2. The intermediate layer has an alkyl group having 8 carbon atoms.
20 to 20 at least one kind of long-chain alkyl (meth) acrylate and a polymer obtained by copolymerizing a vinyl monomer copolymerizable therewith with a resin as a main component. Item 2. The double-sided pressure-sensitive adhesive sheet for an optical film according to Item 1. 3. The method for producing a double-sided pressure-sensitive adhesive sheet according to claim 2, wherein at least one kind of long-chain alkyl (meth) acrylate having an alkyl group having 8 to 20 carbon atoms and copolymerizable therewith. A method for producing a double-sided pressure-sensitive adhesive sheet for an optical film, which comprises forming a composition by mixing a vinyl monomer mixture with a photopolymerization initiator on an adhesive layer and curing the composition by light irradiation to form an intermediate layer.