JP2000109771A - Adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare an adhesive sheet that can alleviate stress concentration occurring in the shrinkage of a base material or the like, inhibits liquid crystal cells from whitening or occurring uneven coloring, and shows excellent reworking properties. SOLUTION: This adhesive sheet 1A comprises a base material 2 and an adhesive layer 3 that is formed by using an adhesive composition containing a polymer of high molecular weight having a weight-average molecular weight of 600,000-2,000,000 and a polymer of low molecular weight having a weight- average molecular weight of <=500,000. In a preferred embodiment, at least one of monomers constituting the low molecular weight polymer is a monomer that constitutes the high molecular weight polymer. The low molecular weight polymer is added to the high molecular weight polymer in an amount of 0.1-50 pts.wt. per 100 pts.wt. of the high molecular weight polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive adhesive sheet, and more particularly to a pressure-sensitive adhesive sheet constituting a polarizing plate having a pressure-sensitive adhesive layer, which is adhered to a liquid crystal cell or the like of a liquid crystal display device.

[0002]

2. Description of the Related Art A polarizing plate is attached to an optical component such as a liquid crystal cell of a liquid crystal display device.

A polarizing plate generally has a three-layer structure in which a TAC (triacetylcellulose) -based protective film is sandwiched on both sides of a PVA (polyvinyl alcohol) -based polarizer. Has a pressure-sensitive adhesive layer formed thereon, and the pressure-sensitive adhesive layer is covered with a release sheet.

When such a polarizing plate is mounted on a liquid crystal display device or the like, the release sheet is peeled off and adhered to a liquid crystal cell or the like via an adhesive layer. However, the polarizing plate as described above has poor dimensional stability due to its material properties, and particularly under heat or wet heat conditions, the dimensional change due to expansion and contraction is large, so that curling or the like is liable to occur. Floating, peeling, etc. of the pressure-sensitive adhesive layer were likely to occur.

[0005] In order to solve such a problem, a two-liquid crosslinking type having a high adhesive strength and a high shearing force has been used as the adhesive constituting the adhesive layer. By using such a pressure-sensitive adhesive composition, the adhesiveness and adhesion of the pressure-sensitive adhesive layer to an adherend can be improved, and problems such as floating and peeling of the pressure-sensitive adhesive layer due to shrinkage of a polarizing plate and the like can be improved. can do. However, it is not possible to sufficiently absorb and relax the stress caused by the dimensional change of the polarizing plate generated under heat or wet heat conditions, and therefore, the distribution of the residual stress acting on the polarizing plate becomes non-uniform, and in particular, the outer peripheral portion As a result of stress concentration on
The liquid crystal cell (TFT) has a problem that white dropout occurs and the STN liquid crystal cell easily causes color unevenness.

To solve such a problem, Japanese Patent Application Laid-Open No.
No. 7593 proposes a method of improving the flexibility of the pressure-sensitive adhesive layer by adding a plasticizer to the pressure-sensitive adhesive composition. This eliminates the problem of white dropout and color unevenness of the liquid crystal cell.However, when re-attaching the polarizing plate attached to the liquid crystal cell, when the polarizing plate is peeled off, the surface of the liquid crystal cell becomes cloudy or adhesive. There has been a case where a new problem such as reduction in reworkability occurs, which causes a residue or the like.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pressure-sensitive adhesive sheet which relieves stress concentration caused by shrinkage of a base material, suppresses white spots and color unevenness of a liquid crystal cell and has excellent reworkability. The purpose is to:

[0008]

This and other objects are achieved by the present invention which is defined below as (1) to (6).

(1) A pressure-sensitive adhesive sheet having a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises a high-molecular-weight polymer having a weight-average molecular weight of 600,000 to 2,000,000 and a weight-average molecular weight of 50
A pressure-sensitive adhesive sheet formed using a pressure-sensitive adhesive composition containing 10,000 or less low molecular weight polymers.

(2) The pressure-sensitive adhesive sheet according to (1), wherein the low molecular weight polymer is contained in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the high molecular weight polymer.

(3) The pressure-sensitive adhesive sheet according to the above (1) or (2), wherein at least one of the monomers constituting the low molecular weight polymer is a monomer constituting the high molecular weight polymer.

(4) The pressure-sensitive adhesive sheet according to any one of the above (1) to (3), wherein the pressure-sensitive adhesive composition contains 5 parts by weight or less of a crosslinking agent with respect to 100 parts by weight of the pressure-sensitive adhesive composition.

(5) The adhesive according to any one of the above (1) to (4), wherein the high molecular weight polymer and the low molecular weight polymer are each copolymerized with a monomer having a functional group capable of reacting with the crosslinking agent. Sheet.

(6) The pressure-sensitive adhesive sheet according to any one of (1) to (5), wherein the substrate is a polarizing plate.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the pressure-sensitive adhesive sheet for a polarizing plate of the present invention will be described in detail.

FIG. 1 is a sectional view showing a first embodiment of the pressure-sensitive adhesive sheet of the present invention.

As shown in the figure, the pressure-sensitive adhesive sheet 1A of the present invention
Is mainly used by being adhered to a TN liquid crystal cell (TFT). An adhesive layer 3 is provided on one surface of a base material 2, and the adhesive layer 3 is laminated on the base material 2. The release sheet 4 is adhered to the surface opposite to the surface.

In the present embodiment, the substrate 2 is a polarizing plate, for example, a three-layer structure in which a TAC (triacetyl cellulose) -based protective film is laminated on both sides of a PVA (polyvinyl alcohol) -based polarizer. be able to. Such a polarizing plate itself has poor stability against changes in environmental conditions due to the characteristics of its constituent materials, and tends to show a remarkable dimensional change particularly in a high-temperature or high-temperature and high-humidity environment.

The pressure-sensitive adhesive layer 3 has a weight average molecular weight of 600,000 to 2
It is formed using a pressure-sensitive adhesive composition containing a high-molecular-weight polymer of 100,000 and a low-molecular-weight polymer having a weight-average molecular weight of 500,000 or less.

The weight average molecular weight of the high molecular weight polymer is 60
10,000 to 2,000,000, and more preferably 800,000 to 1.8,000,000. The weight average molecular weight of the high molecular weight polymer is 60
If it is less than 10,000, the cohesive force becomes insufficient and sufficient adhesion to the substrate 2 cannot be obtained. Also, the difference between the molecular weight of the low-molecular-weight polymer described below is small, and the plasticizing action of the low-molecular-weight polymer is not sufficiently exhibited,
The flexibility of the pressure-sensitive adhesive layer 3 cannot be improved, and
Adhesion, durability, etc. are reduced. On the other hand, if the weight average molecular weight exceeds 2,000,000, the elasticity and flexibility of the pressure-sensitive adhesive layer 3 decrease, and it becomes impossible to sufficiently absorb and reduce the shrinkage stress of the base material 2 and prevent white spots and color unevenness. No effect.
On the other hand, if it exceeds 2,000,000, the viscosity at the time of use is large, and the workability may be impaired.

The high molecular weight polymer may be any of a rubber type, an acrylic type and a silicone type, but is preferably made of an acrylic type polymer. By using an acrylic polymer, a pressure-sensitive adhesive layer having good weather resistance and good cohesion can be formed. Further, a colorless and transparent pressure-sensitive adhesive layer can be easily formed.

For example, in the case of a high molecular weight polymer composed of an acrylic polymer, a main monomer component for providing tackiness,
It can be composed of a polymer or copolymer mainly comprising a comonomer component for providing adhesiveness or cohesive strength, and a functional group-containing monomer component for improving crosslinking points and adhesiveness.

Examples of the main monomer component include alkyl acrylates such as ethyl acrylate, butyl acrylate, amyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, cyclohexyl acrylate, benzyl acrylate, and methoxyethyl acrylate. Esters and alkyl methacrylates such as butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate.

Examples of the comonomer component include methyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, styrene, acrylonitrile and the like.

Examples of the functional group-containing monomer component include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid, 2-hydroxyethyl (meth) acrylate, and 2-hydroxypropyl (meth). Examples include hydroxyl group-containing monomers such as acrylate and N-methylolacrylamide, acrylamide, methacrylamide, and glycidyl methacrylate.

The use of each of these components improves the adhesive strength and cohesive strength of the pressure-sensitive adhesive composition. In addition, such an acrylic polymer does not have an unsaturated bond in the molecule, so that stability against light and oxygen can be improved. Furthermore, by selecting the type and molecular weight of the monomer,
It is possible to obtain a pressure-sensitive adhesive composition having quality and characteristics according to the use.

Examples of the rubber-based high molecular weight polymer include natural rubber, isoprene rubber, styrene-butadiene, recycled rubber, polyisobutylene, styrene-isoprene-styrene, styrene-butadiene-styrene and the like. And those mainly comprising a block copolymer containing a rubber.

Examples of the silicone-based high molecular weight polymer include dimethylsiloxane-based and diphenylsiloxane-based polymers.

The pressure-sensitive adhesive composition of the present invention contains a low molecular weight polymer having a weight average molecular weight of 500,000 or less. The low molecular weight polymer penetrates between the three-dimensional structures formed by the high molecular weight polymer, and acts to reduce the cohesive force and provide plasticity.
Thereby, the elasticity and flexibility of the pressure-sensitive adhesive layer 3 can be improved. Further, the wettability of the pressure-sensitive adhesive layer 3 is improved, and the contraction stress of the substrate 2 can be sufficiently absorbed and reduced while maintaining the adhesion to the substrate 2. Therefore, the adhesive sheet 1
Even if A is exposed to moist heat and contraction stress acts, the polarizing plate as a base material does not shift, so that white dropout and color unevenness are prevented.

As the low molecular weight polymer, the same polymers as those mentioned for the high molecular weight polymer can be used. The low molecular weight polymer has a weight average molecular weight of 500,000 or less, but preferably 10,000 to 500,000,
10,000 to 400,000 is more preferable. When the weight average molecular weight of the low molecular weight polymer exceeds 500,000, 3
It becomes difficult to penetrate between the dimensional structures, the plasticizing action is not sufficiently exhibited, and the above-mentioned white spotting and color unevenness cannot be prevented.

If the amount of the low molecular weight polymer is relatively large, bleed-out may occur and cohesive failure may occur.

The low molecular weight polymer is preferably one in which at least one of the monomers constituting the low molecular weight polymer is a monomer constituting a high molecular weight polymer. That is, when the high molecular weight polymer is a copolymer composed of the monomers A and B, the low molecular weight polymer preferably contains at least one of the monomers A and B as a copolymer component. Thereby, the compatibility between the low molecular weight polymer and the high molecular weight polymer can be improved. As long as at least one of the monomers constituting the low molecular weight polymer is a monomer constituting the high molecular weight polymer, it may be a homopolymer or a copolymer containing other monomer components.

Further, the proportion of the same monomer as the monomer constituting the high molecular weight polymer in the low molecular weight polymer is preferably at least 20 parts by weight, more preferably at least 50 parts by weight, based on 100 parts by weight of all the monomers constituting the low molecular weight polymer. The above is more preferable. By setting the ratio of such a monomer, the compatibility between the low molecular weight polymer and the high molecular weight polymer is improved, and the cohesive force of the pressure-sensitive adhesive layer can be maintained.

The low molecular weight polymer is used in an amount of 0.1 to 100 parts by weight in the pressure-sensitive adhesive composition.
It is preferably contained in an amount of 50 parts by weight, more preferably 3 to 30 parts by weight. 0.1 low molecular weight polymer
If the amount is less than parts by weight, the plasticization of the pressure-sensitive adhesive layer 3 may not be sufficiently achieved. Therefore, the shrinkage stress of the base material 2 cannot be sufficiently absorbed and relieved, and there is a case where white dropout and color unevenness cannot be reliably prevented. On the other hand, if the low-molecular weight polymer exceeds 50 parts by weight, it causes cohesive failure,
There is a possibility that the adhesiveness and adhesiveness of the pressure-sensitive adhesive layer 3 to the substrate 2 may be reduced.

As the pressure-sensitive adhesive composition used in the present invention, any of a cross-linking type subjected to a cross-linking treatment and a non-cross-linking type not subjected to a cross-linking treatment can be used, but a cross-linking type is more preferable. When a crosslinked type is used, a pressure-sensitive adhesive layer having more excellent cohesive strength can be formed.

In the case of a cross-linkable pressure-sensitive adhesive composition, the method of cross-linking treatment (curing) includes, for example, an epoxy compound, an isocyanate compound, a metal chelate compound, a metal alkoxide, a metal salt, an amine compound, a hydrazine compound,
Examples thereof include a method of adding a crosslinking agent such as an aldehyde compound and a method of irradiating radiation.

When a crosslinking agent is added to the pressure-sensitive adhesive composition, the crosslinking agent is preferably contained in an amount of 5 parts by weight or less based on 100 parts by weight of the pressure-sensitive adhesive composition. When the pressure-sensitive adhesive composition contains the crosslinking agent in such an amount, the cohesive force of the pressure-sensitive adhesive layer 3 can be more favorably improved.

In this case, the high molecular weight polymer is preferably obtained by copolymerizing a monomer having a functional group capable of reacting with the crosslinking agent, and the high molecular weight polymer and the low molecular weight polymer are each capable of reacting with the crosslinking agent. More preferably, the monomer is obtained by copolymerizing a monomer having a functional group. Thereby, the reworkability of the pressure-sensitive adhesive layer is improved.

Further, the low molecular weight polymer is more preferably formed by copolymerizing a monomer having a functional group capable of reacting with a crosslinking agent in an amount of 10 parts by weight or less, and further preferably contains 0.1 to 5 parts by weight.

When the amount of the monomer having a functional group capable of reacting with the crosslinking agent in the low molecular weight polymer exceeds 10 parts by weight, the monomer actively participates in the bonding with the crosslinking agent, and the pressure-sensitive adhesive layer may be excessively cured. There is.

Examples of the monomer having a functional group capable of reacting with the crosslinking agent include those similar to the functional group-containing monomer component of the high molecular weight polymer.

In the case of irradiation, the curing speed is high,
Crosslinking and curing can be quickly completed even under mild conditions such as normal temperature and normal pressure, and a pressure-sensitive adhesive layer can be formed. Therefore, after applying the pressure-sensitive adhesive composition to the substrate 2, it is not necessary to leave the substrate as seasoning for many days, and the process can be immediately shifted to the next step, and the manufacturing process can be sped up.

When the pressure-sensitive adhesive composition is irradiated with radiation and cured to form a pressure-sensitive adhesive layer, it preferably contains a radiation-curable compound. Thereby, the pressure-sensitive adhesive layer can be easily and quickly formed. The radiation curable compound is preferably added in an amount of about 0.05 to 50 parts by weight based on 100 parts by weight of the pressure-sensitive adhesive component.

In the pressure-sensitive adhesive composition used in the present invention, various additives such as a tackifier and a stabilizer can be used as needed as long as the tackiness, cohesiveness and the like are not impaired. When curing is performed using ultraviolet rays as radiation, it is preferable to add a photopolymerization initiator.

As a method of forming the pressure-sensitive adhesive layer 3, for example,
A method in which the above-mentioned pressure-sensitive adhesive composition is applied to the base material 2 and, if necessary, is coated with a release sheet 4 to form the pressure-sensitive adhesive layer 3 to form the pressure-sensitive adhesive sheet 1A. A method of applying a pressure-sensitive adhesive composition to the coated surface to form a pressure-sensitive adhesive layer 3 and then transferring the pressure-sensitive adhesive layer 3 to the base material 2 to form a pressure-sensitive adhesive sheet 1A.

The method of applying the pressure-sensitive adhesive composition to the base material 2 or the release sheet 4 is not particularly limited, and examples of the application method include a roll knife coater,
Examples of the method include a die coater, a roll coater, a bar coater, a gravure roll coater, a reverse roll coater, and dipping.

Although the thickness (dry film thickness) of the pressure-sensitive adhesive layer 3 is not particularly limited, it is preferably about 3 to 400 μm, and preferably about 5 to 400 μm, when used for applications such as the present embodiment.
About 150 μm is more preferable, and about 10 to 90 μm is further preferable.

The release sheet 4 attached to the pressure-sensitive adhesive layer 3 is
Any material may be used. For example, a film made of various resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, and polyarylate is used as a base material, and a bonding surface of the base material with the adhesive layer 3 is
Those subjected to release treatment (silicone treatment or the like) can be used.

Although not shown, a surface protection sheet (protective film) is adhered to the surface of the base material 2 (the surface opposite to the surface on which the pressure-sensitive adhesive layer 3 is laminated) on the pressure-sensitive adhesive sheet 1A. May be.

FIG. 2 is a sectional view showing a second embodiment of the pressure-sensitive adhesive sheet of the present invention. Adhesive sheet 1 shown in this figure
B is mainly used by sticking to an STN liquid crystal cell, and a retardation plate 5 and an adhesive layer (second adhesive layer) 6 between the adhesive layer 3 and the release sheet 4. It is the same as the above-mentioned pressure-sensitive adhesive sheet 1A, except that is provided. In the figure, the same items as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The pressure-sensitive adhesive sheet 1B constitutes a polarizing plate that can obtain elliptically polarized light as a whole by providing the retardation plate 5.

The retardation film 5 is laminated on the surface of the pressure-sensitive adhesive layer 3 opposite to the surface on which the substrate 2 is laminated. This phase difference plate 5
Is an optical compensator for improving the display contrast of the liquid crystal cell and the viewing angle characteristics of the display color.
Wave plate and half-wave plate. As a constituent material of the retardation plate 5, for example, a single layer product or a multilayer product of a uniaxially stretched polymer film such as polycarbonate, polyarylate, polystyrene, and polysulfone is preferably used.

A pressure-sensitive adhesive layer 6 is bonded to the surface of the retardation plate 5 opposite to the surface on which the pressure-sensitive adhesive layer 3 is laminated. As the pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer 6, the same one as the pressure-sensitive adhesive layer 3 can be used.

The above-mentioned release sheet 4 is adhered to the surface of the pressure-sensitive adhesive layer 6 opposite to the surface on which the retardation film 5 is laminated.

In the pressure-sensitive adhesive sheet 1B having such a structure, when the base material 2 shrinks, the pressure-sensitive adhesive layer 3 maintains the adhesive strength with the base material 2 and prevents the adhesive layer 3 from floating and peeling off. Relieves stress caused by shrinkage (absorption, dispersion)
And prevents local concentration of residual stress. Therefore, when the pressure-sensitive adhesive sheet 1B of the present invention is used by attaching it to an STN liquid crystal cell or the like, color unevenness can be prevented.

In each of the above embodiments, a polarizing plate is used as the substrate 2. However, the pressure-sensitive adhesive sheet of the present invention is not limited to this, and the substrate may be, for example, an analyzer, a retarder (a quarter-wave plate). , A half-wave plate, etc.), an optical rotator (Faraday element, a natural optical rotator), and other plate-shaped optical components such as various optical filters.

The pressure-sensitive adhesive sheet of the present invention is not limited to a sheet used by sticking to a liquid crystal cell or a sheet applied to an optical component used for other purposes. The present invention can be applied to a case in which the material is easily deformed such as expansion, contraction, and warpage in response to a change in conditions.

[0058]

Next, specific examples of the present invention will be described.

1. Production of pressure-sensitive adhesive sheet A pressure-sensitive adhesive layer was formed by using a polarizing plate as a substrate and a pressure-sensitive adhesive composition having the following composition to prepare a pressure-sensitive adhesive sheet.

(Example 1) Adhesive composition High molecular weight polymer: 100 parts by weight (Mw (weight average molecular weight) = 1.5 million) (butyl acrylate / acrylic acid = 9)
5/5)

Low molecular weight polymer: 10 parts by weight (Mw = 1
(Butyl acrylate / hydroxyethyl acrylate = 99.5 / 0.5) Acrylic acid is a functional group (COO) capable of reacting with a crosslinking agent.
H)), and hydroxyethyl acrylate is a monomer having a functional group (OH group) capable of reacting with a crosslinking agent.

Crosslinking agent: 0.1 parts by weight (trimethylolpropane tolylene diisocyanate)

Substrate A polarizing plate (thickness: 180 μm) of a three-layer laminate of a triacetyl cellulose film / polyvinyl alcohol film / triacetyl cellulose film

Release sheet Polyester film (one side subjected to silicone treatment) (SP PET3 manufactured by Lintec Co., Ltd.)
8), thickness: 38 μm

The above-mentioned pressure-sensitive adhesive composition was prepared, this preparation was applied on a release sheet 4 and dried, and
Is transferred to one side of the adhesive layer 3 (thickness: 25 μm).
m) was formed. This was seasoned at room temperature for 7 days to produce an adhesive sheet 1A as shown in FIG.

Further, on the surface of the pressure-sensitive adhesive sheet 1A opposite to the surface on which the base material 2 of the pressure-sensitive adhesive layer 3 is laminated, the above-mentioned pressure-sensitive adhesive composition is coated with a retardation plate 5 (1/4 wavelength plate, polycarbonate film). , A thickness: 60 μm), and a second pressure-sensitive adhesive layer 6 formed by applying and drying on one side is laminated.
Release sheet 4 on the surface opposite to the surface to be laminated with retardation plate 5
To prepare an adhesive sheet 1B.

Example 2 As a low molecular weight polymer, a butyl acrylate homopolymer (Mw = 300,000) was used.
Except for the addition of parts by weight, pressure-sensitive adhesive sheets 1A and 1B were produced in the same manner as in Example 1.

Example 3 As the high molecular weight polymer, butyl acrylate / 2-hydroxyethyl methacrylate = 95/5 (Mw = 1.3 million) was used, and the amount of the low molecular weight polymer was changed to 100 parts by weight of the high molecular weight polymer. The adhesive sheets 1A and 1B were produced in the same manner as in Example 2 except that the amount was 10 parts by weight and the amount of the crosslinking agent was 0.15 part by weight.

The 2-hydroxyethyl methacrylate is a monomer having a functional group (OH group) capable of reacting with a crosslinking agent.

(Example 4) Except that 4 parts by weight of dipentaerythritol hexaacrylate as a radiation-curable compound and 0.5 part by weight of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator were added, and no crosslinking agent was added. Prepared an adhesive composition having the same composition as in Example 1.

This is applied to a release sheet and dried in the same manner as in Example 1. After irradiating the adhesive composition with ultraviolet light,
The pressure-sensitive adhesive layer (thickness: 25) is transferred to one side of the substrate.
μm). This was seasoned at normal temperature for one day to produce pressure-sensitive adhesive sheets 1A and 1B as shown in FIG.

Comparative Example 1 Adhesive sheets 1A and 1A were prepared in the same manner as in Example 1 except that the low molecular weight polymer was not added and the weight average molecular weight of the high molecular weight polymer was 2.1 million.
An adhesive sheet of the same type as B was produced.

Comparative Example 2 A low molecular weight polymer was not added, the weight average molecular weight of the high molecular weight polymer was set to 400,000,
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1 except that the amount of the crosslinking agent was changed to 1.0 part by weight.

Comparative Example 3 An adhesive sheet was prepared in the same manner as in Example 1 except that 7 parts by weight of trioctyl trimellitate was added as a plasticizer without adding a low molecular weight polymer.

2. Evaluation of Adhesive Properties of Adhesive Sheet The following adhesive properties were evaluated for the adhesive sheets prepared in Examples 1 to 4 and Comparative Examples 1 to 3 above.

First, the pressure-sensitive adhesive sheet prepared in each of the examples and comparative examples was applied to a glass plate for a liquid crystal cell (Nippon Sheet Glass Co., Ltd.).
("H-coated glass") made on both sides so as to form orthogonal Nicols.

Next, this was dried at 90 ° C. under dry conditions for 100 hours.
0 hours, 60 ° C., 90% RH for 1000 hours after each application, and then the appearance of white spots and color unevenness caused by the residual stress due to the durability of the adhesive layer and the dimensional change of the substrate. Was visually observed. In addition, the adhesive sheet 1A
Of the adhesive sheet 1B was evaluated for the state of color unevenness.

The durability of the pressure-sensitive adhesive layer was evaluated in the following four stages. A: No change in appearance such as floating, peeling, foaming, etc. was observed. : Little change in appearance such as floating, peeling, foaming, etc. was observed. Δ: Appearance changes such as floating, peeling and foaming are slightly noticeable. X: Appearance changes such as floating, peeling and foaming are remarkably observed.

Evaluation of the appearance of white spots or color unevenness is as follows.
The following four steps were performed. ◎: No white drop and color unevenness were observed at all. : White dropout and uneven color are hardly noticeable. Δ: White dropout and color unevenness are somewhat noticeable. X: White dropout and color unevenness are remarkably observed.

The reworkability was evaluated as follows. First, a 25 mm × 150 mm test piece was prepared from each pressure-sensitive adhesive sheet.

Next, this test piece was stuck on a glass plate for a liquid crystal cell (“H-coated glass” manufactured by Nippon Sheet Glass Co., Ltd.) using a sticking device (“Rami Packer” manufactured by Fuji Plastics Machinery Co., Ltd.). Autoclave treatment was performed at 5 kg / cm ² for 20 minutes. Subsequently, after performing a heat treatment at 70 ° C. for 2 hours, the adhesive test piece was peeled in a 180 ° direction at a speed of 300 mm / min in an atmosphere of 23 ° C. and 65% RH, and then the surface of the glass plate was removed. The condition was visually observed.

The reworkability was evaluated according to the following four stages based on the state of the glass plate surface. : No fogging or adhesive residue is observed on the glass plate surface. ：: Almost no fogging is observed on the glass plate surface. Δ: Clouding or the like is observed on the surface of the glass plate. ×: Adhesive residue is observed on the surface of the glass plate. Table 1 shows the above results.

[0083]

[Table 1]

As is clear from these results, according to the pressure-sensitive adhesive sheets (polarizing plates with pressure-sensitive adhesive layers) of Examples 1 to 4,
It was confirmed that when used by sticking to a liquid crystal cell, it has excellent durability and can prevent white spots and color unevenness. Furthermore, it turned out that it is excellent in reworkability and does not cause adhesive residue or surface fogging even when the adhesive sheet is peeled off.

Further, in Example 4 using a pressure-sensitive adhesive composition to which an ultraviolet-curable polymer was added, the pressure-sensitive adhesive composition had excellent curability, and a good pressure-sensitive adhesive layer was formed in one day in seasoning. I understood.

On the other hand, in the pressure-sensitive adhesive sheet of Comparative Example 1,
Since the weight average molecular weight of the high molecular weight polymer was too large, the flexibility of the pressure-sensitive adhesive layer was poor, and the durability and reworkability were excellent, but the white spots and color unevenness were remarkable. In the pressure-sensitive adhesive sheet of Comparative Example 2, the weight-average molecular weight of the high-molecular-weight polymer was too small, the cohesive force of the pressure-sensitive adhesive layer was insufficient, the durability and reworkability were poor, and white spots and the like were remarkable. Furthermore, in Comparative Example 3, since the plasticizer was added, it was durable, had no white spots and no color unevenness, but was poor in reworkability.

[0087]

As described above, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention is excellent in flexibility and adhesion to a substrate, and can be used for a long time in a severe environment of high temperature and high humidity. However, there is no possibility that the pressure-sensitive adhesive layer floats and peels off. Further, since the pressure-sensitive adhesive layer absorbs and relaxes the stress caused by the dimensional change of the base material under wet heat conditions, it is possible to reduce local stress concentration at the edge of the pressure-sensitive adhesive sheet and the like.

For this reason, for example, a TN liquid crystal cell (TFT)
Optical defects caused by non-uniform stress distribution in a polarizing plate or the like as a base material, such as white spots, color unevenness of an STN liquid crystal cell, or the like.

Further, the reworkability is excellent, and no adhesive residue or clouding occurs on the surface of the adherend even when the adhesive sheet once adhered is peeled off.

Further, the pressure-sensitive adhesive sheet of the present invention can achieve the above-mentioned effects with a relatively simple structure, and is easy to manufacture.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the pressure-sensitive adhesive sheet of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the pressure-sensitive adhesive sheet of the present invention.

[Explanation of symbols]

 1A, 1B Adhesive sheet 2 Base material 3 Adhesive layer 4 Release sheet 5 Retardation plate 6 Adhesive layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J004 AA05 AA10 AA11 AA17 AB01 AB07 CA06 CC02 CE01 DA03 DA04 DB02 DB03 FA04 FA10 4J040 JA09 JB09 KA16 LA01 LA06 LA10 MB05 NA17

Claims (6)

[Claims] 1. A pressure-sensitive adhesive sheet having a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a weight-average molecular weight of 600,000 to 2,000,000 and a low-molecular weight polymer having a weight-average molecular weight of 500,000 or less. A pressure-sensitive adhesive sheet formed using a pressure-sensitive adhesive composition comprising: 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the low molecular weight polymer is contained in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the high molecular weight polymer. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein at least one of the monomers constituting the low molecular weight polymer is a monomer constituting the high molecular weight polymer. 4. The pressure-sensitive adhesive composition comprises the pressure-sensitive adhesive composition 10
The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive sheet contains 5 parts by weight or less of a crosslinking agent with respect to 0 parts by weight. 5. The pressure-sensitive adhesive sheet according to claim 1, wherein the high-molecular-weight polymer and the low-molecular-weight polymer are each formed by copolymerizing a monomer having a functional group capable of reacting with the crosslinking agent. 6. The pressure-sensitive adhesive sheet according to claim 1, wherein the substrate is a polarizing plate.