JP2001294828A - Pressure sensitive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensitive adhesive sheet capable of decreasing stress concentration by relaxing stress caused by the shrinkage of a substrate layer and the like, and capable of restraining the white voids and unevenness of color of a liquid crystal cell. SOLUTION: This pressure sensitive adhesive sheet 1A is used in a stuck condition on a liquid crystal cell and has a structure that a pressure sensitive adhesive layer 3 is adhered to the one side of the substrate layer 2 composing a polarizing plate; besides, a releasable sheet 4 is stuck on the layer 3 in such a way as to be situated on the other side from the layer 2. The layer 3 is composed of a laminate formed by laminating layers 31 and 32. A pressure sensitive adhesive agent composing the layers 31 and 32 is made mainly of e.g. an acrylic pressure sensitive adhesive. By making the layer 31 differ from the layer 32 in a degree of cross linking, an amount of a plasticizer added, or the like, the shear modulus and the relaxation modulus of the layer 32 are made smaller than those of the layer 31.

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 to be adhered to an adherend, and more particularly to a pressure-sensitive adhesive sheet which is used by being adhered to a liquid crystal cell or the like of a liquid crystal display device and constitutes an optical component such as a polarizing plate.

[0002]

2. Description of the Related Art A polarizing plate is attached to a liquid crystal cell of a liquid crystal display (LCD). On one surface of the polarizing plate, an adhesive layer for sticking to another optical component such as a liquid crystal cell (hereinafter, represented by “liquid crystal cell”) is formed. The mold sheet is stuck. Further, a protective sheet (protective film) composed of a protective sheet base material and an adhesive layer is adhered to a surface of the polarizing plate opposite to the adhesive layer in order to protect the surface.

[0003] In this case, the polarizing plate is used after peeling off the release sheet, affixing it to the liquid crystal cell with the exposed adhesive layer, and then peeling off the protective sheet.

Most of the polarizer base materials used in liquid crystal cells have a three-layer structure in which a PVA polarizer is sandwiched between two TAC (triacetylcellulose) protective films. Due to the characteristics, dimensional stability is poor,
Particularly, in a high temperature or high temperature and high humidity environment, a dimensional change due to shrinkage is large.

Therefore, when such a polarizing plate is adhered to a liquid crystal cell with an adhesive, defects such as foaming in the adhesive layer, floating and peeling of the adhesive layer are likely to occur.

Heretofore, in order to prevent these defects, a two-liquid crosslinking type adhesive having high adhesive strength and high shearing force has been used as the adhesive constituting the adhesive layer. The use of such an adhesive has improved problems such as lifting and peeling due to shrinkage of the polarizing plate base material, but the shrinkage stress of the polarizing plate base material cannot be absorbed and alleviated by the adhesive. The distribution of the residual stress in the plate base material becomes non-uniform, and stress concentration occurs particularly on the outer peripheral portion of the polarizing plate base material. As a result, white spots occur in a TN (TFT) liquid crystal cell, and color unevenness easily occurs in an STN liquid crystal cell. Problem.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pressure-sensitive adhesive sheet which can reduce stress caused by shrinkage of a base material layer and reduce stress concentration. In particular, it is an object of the present invention to provide a pressure-sensitive adhesive sheet capable of suppressing white drop and color unevenness of a liquid crystal cell.

[0008]

This and other objects are achieved by the present invention which is defined below as (1) to (8).

(1) A pressure-sensitive adhesive sheet having a base material layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer includes a plurality of first and second layers closest to the base material layer. The first layer and the second layer each include an acrylic pressure-sensitive adhesive, and the amount of the plasticizer in the constituent material of the second layer is determined by the adhesive composition. For 100 parts by weight of the product
A pressure-sensitive adhesive sheet, wherein the amount is 0.1 to 50 parts by weight, and the amount of a plasticizer added to the constituent material of the second layer is larger than that of the first layer.

(2) The polymer according to (1), wherein the degree of crosslinking of the polymer material constituting the second layer is lower than the degree of crosslinking of the polymer material constituting the first layer. Adhesive sheet.

(3) An adhesive sheet having a substrate layer and an adhesive layer, wherein the adhesive layer includes a plurality of layers including a first layer and a second layer closest to the substrate layer. The first layer and the second layer each include an acrylic pressure-sensitive adhesive, and the degree of crosslinking of the polymer material forming the second layer is the first layer and the second layer. A pressure-sensitive adhesive sheet characterized by having a lower degree of crosslinking than a polymer material constituting a layer.

(4) The base layer and the first layer are in intimate contact with each other, and the first layer is of such an extent that cohesive failure and interfacial failure do not occur due to shear stress accompanying shrinkage of the base layer. The pressure-sensitive adhesive sheet according to any one of the above (1) to (3), which has a shear elastic modulus of:

(5) The first layer and the second layer are in close contact with each other, and the adhesion between them is slightly greater than the adhesive strength of the pressure-sensitive adhesive layer to the adherend. The pressure-sensitive adhesive sheet according to any one of the above (1) to (4).

(6) The thickness of the second layer is equal to the thickness of the first layer.
The pressure-sensitive adhesive sheet according to any one of the above (1) to (5), wherein the thickness of the layer is about 0.5 to 15 times the thickness of the layer.

(7) The above-mentioned (1) to (6), wherein the pressure-sensitive adhesive layer is formed by a transfer lamination method.
The pressure-sensitive adhesive sheet according to any one of the above.

(8) The pressure-sensitive adhesive sheet according to any one of the above (1) to (7), wherein the base material layer is a plate-shaped optical component.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the pressure-sensitive adhesive sheet of the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment in which the pressure-sensitive adhesive sheet of the present invention is applied to a polarizing plate adhered to a liquid crystal cell. As shown in the figure, the pressure-sensitive adhesive sheet 1A of the present invention
Is mainly used by sticking to a TN (TFT) liquid crystal cell. An adhesive layer 3 is bonded to one surface of a base material layer 2, and the other side of the adhesive layer 3 is opposite to the base material layer 2. Has a structure in which the release sheet 4 is adhered to the surface of.

The substrate layer 2 in the present embodiment is a polarizing plate (plate-shaped optical component), for example, having a three-layer structure in which a PVA polarizer is interposed between two triacetyl cellulose films. It is.

The substrate layer 2 itself has low dimensional stability against changes in environmental conditions, and in particular, has the property of shrinking and reducing its dimensions when placed in a high-temperature or high-temperature, high-humidity environment.

The pressure-sensitive adhesive layer 3 includes a plurality of layers 31 and layers 32
Are laminated. First, each layer 31,
32 will be described.

The pressure-sensitive adhesive (adhesive composition) constituting each of the layers 31 and 32 contains an acrylic pressure-sensitive adhesive, and particularly preferably is mainly composed of an acrylic pressure-sensitive adhesive.

The adhesive (adhesive composition) may include a rubber-based adhesive, a silicone-based adhesive, and the like.

The acrylic pressure-sensitive adhesive mainly includes a low Tg main monomer component for providing tackiness, a high Tg comonomer component for providing adhesion and cohesion, and a functional group-containing monomer component for crosslinking and improving adhesion. Consisting of a polymer or a copolymer.

The main monomer components include, for example, alkyl acrylates such as ethyl acrylate, butyl acrylate, amyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, cyclohexyl acrylate and benzyl acrylate, and methacrylic acid. Examples thereof include alkyl methacrylates such as butyl, 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.

Such materials are preferred because they have excellent adhesive and cohesive strength, and have high stability against light and oxygen due to the absence of unsaturated bonds in the polymer. This is because it is possible to obtain arbitrary quality and characteristics according to the conditions.

Examples of the rubber-based pressure-sensitive adhesive include natural rubber-based, isoprene rubber-based, styrene-butadiene-based, reclaimed rubber-based and polyisobutylene-based adhesives, and rubbers such as styrene-isoprene-styrene and styrene-butadiene-styrene. And those mainly comprising a block copolymer containing

Examples of the silicone-based pressure-sensitive adhesive include dimethylsiloxane-based and diphenylsiloxane-based pressure-sensitive adhesives.

As the pressure-sensitive adhesive as described above, any of a crosslinked type and a non-crosslinked type can be used. In the case of a cross-linking type, a method using various cross-linking agents such as an epoxy compound, an isocyanate compound, a metal chelate compound, a metal alkoxide, a metal salt, an amine compound, a hydrazine compound, and an aldehyde compound, or a method of irradiating radiation, etc. And
These are appropriately selected according to the type of the functional group and the like.

It is preferable that such an adhesive has a light transmitting property (particularly, a substantially transparent or translucent one).

A plasticizer is added to such an adhesive as needed. The plasticizer is phthalate,
Esters such as trimellitic acid ester, pyromellitic acid ester, adipic acid ester, sebacic acid ester, phosphoric acid triester, glycol ester and the like, process oil, liquid polyether, liquid polyterpene, other liquid resins, and the like. One or more of these can be used in combination.

It is preferable that such a plasticizer has good compatibility with the pressure-sensitive adhesive and has a light transmitting property (particularly, a substantially transparent or translucent one).

In addition to the plasticizer, various additives such as an ultraviolet absorber and an antioxidant can be added to the pressure-sensitive adhesive, if necessary.

The conditions such as the kind, composition, and amount of the pressure-sensitive adhesives and additives may be the same or different for the layer 31 and the layer 32, respectively.

Next, a layer (first layer) that adheres to the base material layer 2
31 and a layer on the side separated from the base material layer 2 (second layer)
32 will be described. The layer 31 and the layer 32 satisfy at least one of the following conditions [1] and [2].

Further, the layer 31 and the layer 32 correspond to the following [3] to
It is preferable that at least one of the conditions shown in [5] is satisfied.

[1] When the above-described plasticizer is added to the constituent material of the layer 32, the amount of the plasticizer is determined by the amount of the plasticizer added to the constituent material of the layer 31 (including the case of no addition). Many compared. Thus, when the base layer 2 shrinks, the layer 31 maintains the adhesion to the base layer 2 and prevents the base layer 2 from floating and peeling off.
Can alleviate (absorb and disperse) the stress caused by the shrinkage of the base material layer 2 and prevent local concentration of residual stress.

The added amount of the plasticizer in the constituent material of the layer 32 is as follows.
The pressure-sensitive adhesive (adhesive composition) varies depending on conditions such as the type and composition of the pressure-sensitive adhesive (adhesive composition) and is not particularly limited, but is usually 0.1 to 50 parts by weight based on 100 parts by weight of the adhesive (adhesive composition). And more preferably 1.0 to 30 parts by weight. If the amount is less than 0.1 part by weight, the softening of the layer 32 due to the addition of the plasticizer becomes insufficient, so that stress relaxation is difficult. If the amount exceeds 50 parts by weight, depending on the type and composition of the pressure-sensitive adhesive, coagulation may occur. In some cases, physical properties such as destruction may be reduced.

[2] The degree of crosslinking (degree of polymerization) of the polymer material constituting the layer 32 is lower than the degree of crosslinking (degree of polymerization) of the polymer material constituting the layer 31. Accordingly, when the base layer 2 contracts, the layer 31 maintains the adhesion to the base layer 2 to prevent the base layer 2 from floating and peeling off. The stress caused by the shrinkage of the layer 2 can be relaxed (absorbed and dispersed), and local concentration of residual stress can be prevented.

The degree of cross-linking of the polymer material constituting each of the layers 31 and 32 depends on various conditions such as the type and composition of the pressure-sensitive adhesive (adhesive composition) and is not particularly limited. The sol-gel fraction is preferably 10 to 95%, more preferably 15 to 90%, and the degree of crosslinking of the layer 32 is 5 to 90% in sol-gel fraction.
Is preferably, and more preferably 10 to 85%. In such a range, the above effect is more effectively exhibited.

[3] The shear modulus of the layer 32 is lower than the shear modulus of the layer 31. Thereby, when contraction or expansion of the base material layer 2 (hereinafter, represented by “shrinkage”) occurs, the layer 31 maintains the adhesive force with the base material layer 2, prevents floating and peeling, and performs shearing. The layer 32 having a low elastic modulus relaxes (absorbs and disperses) the stress generated due to the shrinkage of the base material layer 2 and can prevent local concentration of residual stress.

In this case, the shear modulus of the layer 31 is preferably such that cohesive failure and interfacial failure do not occur due to shear stress generated by shrinkage of the base material layer 2 and the like.
In the present embodiment, preferably 4.0 × 10 ^{5 to} 9.0 × 1.
0 ⁶ [dyn / cm ^2], more preferably about 5.0 × 10 ⁵
It is set to about 8.0 × 10 ⁶ [dyn / cm ² ].

The ratio of the shear modulus of the layer 32 to the shear modulus of the layer 31 is preferably from 5 to 99%.
More preferably, it is 90%. If this ratio exceeds 99%, the above-mentioned effect due to the difference in shear modulus becomes insufficient, and if it is less than 5%, the shear modulus of the layer 32 becomes insufficient, and cohesive failure may occur. .

[4] The relaxation modulus of the layer 32 is lower than the relaxation modulus of the layer 31. Thereby, when the base material layer 2 contracts, the layer 31 maintains the adhesive force with the base material layer 2, prevents floating and peeling, and has a low relaxation elasticity.
2 relaxes the stress caused by the shrinkage of the base material layer 2 (absorption,
(Dispersion), and local concentration of residual stress can be prevented.

Here, the relaxation modulus is defined as a time elapsed after applying a constant strain γ ₀ in stress relaxation, t,
The stress at that time is σ (t), and σ (t) is proportional to γ _0, and σ (t) = G (t) γ ₀
Say (t). In the present invention, t = 100 seconds.

The ratio of the relaxation modulus of the layer 32 to the relaxation modulus of the layer 31 is preferably from 1 to 99%.
More preferably, it is 90%. When this ratio exceeds 99%, the above-mentioned effect due to the difference in relaxation elastic modulus becomes insufficient, and when it is less than 1%, the relaxation elastic modulus of the layer 32 becomes insufficient, which may cause cohesive failure. .

The relaxation elastic modulus of each of the layers 31 and 32 is
The following values are preferable. That is, the relaxation elastic modulus G (100) of the layer 31 after 100 seconds is 2.0 × 10
^It is preferably ^{5 to} 5.0 × 10 ⁶ [dyn / cm ² ],
More preferably, it is 3.0 × 10 ^{5 to} 4.0 × 10 ⁶ [dyn / cm ² ]. The relaxation elastic modulus G (100) of the layer 32 after 100 seconds is from 7.0 × 10 ^{4 to} 2.0 × 10 ^6.
[Dyn / cm ² ], preferably from 8.0 × 10 ⁴ to
More preferably, it is 1.0 × 10 ⁶ [dyn / cm ² ].
In such a range, the above effect is more effectively exhibited.

[5] The types and compositions of the adhesives constituting the layers 31 and 32 are different, and as a result, at least one of the above conditions [3] and [4] is satisfied. .

When at least one of the above conditions [1] and [2] is satisfied, the stress distribution in the base material layer 2 becomes more uniform due to the stress relaxation effect of the pressure-sensitive adhesive layer 3, so that a TN (TFT) liquid crystal cell or the like can be obtained. When the adhesive sheet 1A is attached and used,
The occurrence of the white spot phenomenon caused by the change in transmittance is prevented or suppressed.

When any of the above conditions [3] to [5] is satisfied, the stress relaxing action of the pressure-sensitive adhesive layer 3 is more effectively exhibited, and the stress distribution in the base material layer 2 becomes more uniform. When the pressure-sensitive adhesive sheet 1A is attached to a TN (TFT) liquid crystal cell or the like and used, the occurrence of a white drop phenomenon due to a change in transmittance is prevented or suppressed.

In this embodiment, the pressure-sensitive adhesive sheet 1
The shrinkage ratio accompanying the stress relaxation of A is preferably 5.0% or less, particularly preferably about 0.1 to 4.5%.

Adhesive layer 3 composed of a laminate of layers 31 and 32
Suitable forming methods include a general coating method, in particular, a lamination method by transfer. When the pressure-sensitive adhesive layer 3 having stress relaxation properties is formed as in the present invention, the adhesion between the layers 31 and 32 does not necessarily need to be strong, and there is an adhesion that slightly exceeds the adhesion to the adherend. Good. Rather, if the adhesive force between the layers 31 and 32 is weak, when the base layer 2 contracts, the interface (layer) between the layers 31 and 32 is likely to shift (move), and the stress relaxation effect due to this is also increased. It is preferable because it is exhibited. For such a reason, the lamination method by transfer becomes possible.

In a coating method typified by a transfer lamination method, the coating liquid used may be either an organic solvent type or an emulsion type, or may be an aqueous solution adhesive.

As another method for forming the pressure-sensitive adhesive layer 3, there is a co-extrusion method (multi-layer extrusion molding) using a die or the like, whereby a laminate of a plurality of layers can be formed at one time.

Although the total thickness (dry film thickness) of the pressure-sensitive adhesive layer 3 is not particularly limited, it is preferably about 3 to 300 μm when it is used for applications such as the present embodiment.
It is more preferably about 00 μm, and 10 to 60 μm
It is more preferable to set the degree.

Although the thickness of each of the layers 31 and 32 is not particularly limited, the thickness of the layer (the second layer) 32 is 0.5 to 15 times the thickness of the layer (the first layer) 31. The ratio is preferably about twice, more preferably about 1 to 10 times. In such a range, the above effect is more effectively exhibited.

The interface between the layer 31 and the layer 32 does not necessarily need to be clear, and the composition and the above conditions [1] to [5] change continuously near the interface. Is also good.

As the release sheet 4 to be attached to the pressure-sensitive adhesive layer 3 as described above, any release sheet may be used.
A base material is a film made of various resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, and polyarylate, and a release coat layer (silicone layer) (not shown) is provided on a bonding surface of the base material with the adhesive layer 3.
Can be used.

Although not shown, a protective sheet (protective film) may be adhered to the surface of the base material layer 2 (the surface opposite to the pressure-sensitive adhesive layer 3).

FIG. 2 is a sectional view showing another embodiment in which the pressure-sensitive adhesive sheet of the present invention is applied to a polarizing plate adhered to a liquid crystal cell. The adhesive sheet 1B shown in FIG.
(TFT) It is used by sticking to a liquid crystal cell, and is the same as the pressure-sensitive adhesive sheet 1A except that the layer structure of the pressure-sensitive adhesive layer 3 is different.

The pressure-sensitive adhesive layer 3 in the pressure-sensitive adhesive sheet 1B is composed of a laminate in which a layer 31, a layer 32 and a layer 33 are laminated. Items common to the layers 31 to 33 are the same as described above.

Further, a layer (first layer) in close contact with the base material layer 2
31 and an intermediate layer (second layer) 32 are the [1],
Whether at least one of the conditions shown in [2] is satisfied, or the layer (first layer) 31 and the layer (second layer) 33 farthest from the base material layer 2 are formed by the aforementioned [ 1],
At least one of the conditions shown in [2] is satisfied.

In the former case, the conditions for the remaining layer 33 are not particularly limited, and the conditions may be the same as those of one of the layers 31 and 32, or may be the same as those of the layers 31 and 32. Good. Also, in the latter case, the conditions for the remaining layer 32 are not particularly limited.
33, even under the same conditions as one of the layers 33,
Any of the conditions different from any of the three conditions may be used.

According to the pressure-sensitive adhesive sheet 1B having the pressure-sensitive adhesive layer 3 having such a structure, when the base material layer 2 contracts,
The layer 31 maintains the adhesive force with the base layer 2 to prevent floating and peeling, and the layer 32 and / or the layer 33 relieves stress (absorption, dispersion) caused by shrinkage of the base layer 2.
However, local concentration of residual stress can be prevented. In addition, as described above, when the adhesion between the layers 31, 32, and 33 is relatively weak, the interface between the adjacent layers is likely to shift (move), and the stress relieving action is also exhibited. You. Therefore, when the pressure-sensitive adhesive sheet 1B is adhered to a TN (TFT) liquid crystal cell or the like and used, the occurrence of a white drop phenomenon due to a change in transmittance is prevented or suppressed.

The pressure-sensitive adhesive layer 3 on the pressure-sensitive adhesive sheet 1B
Is also the same as described above.

FIG. 3 is a sectional view showing another embodiment in which the pressure-sensitive adhesive sheet of the present invention is applied to a polarizing plate adhered to a liquid crystal cell. The adhesive sheet 1C shown in FIG.
It is used by sticking to a liquid crystal cell, except that a retardation plate 5 and an adhesive layer (second adhesive layer) 6 are provided between the adhesive layer 3 and the release sheet 4. This is the same as that of the pressure-sensitive adhesive sheet 1B.

The adhesive sheet 1C constitutes a polarizing plate from which elliptically polarized light can be obtained as a whole by installing the retardation plate 5. The retardation plate 5 is joined to the surface of the pressure-sensitive adhesive layer 3 on the side opposite to the base material layer 2. The retardation 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, and a quarter-wave plate and a half-wave plate are also special examples. As such a retardation plate 5, for example, a monolayer product or a multilayer product of a uniaxially stretched polymer film such as polycarbonate, polyarylate, polystyrene, and polysulfone is used.

The pressure-sensitive adhesive layer 6 is bonded to the surface of the retardation plate 5 opposite to the pressure-sensitive adhesive layer 3. This pressure-sensitive adhesive layer 6
It is composed of a single layer, and its constituent material can be the same as that described in each of the layers 31 to 33 of the pressure-sensitive adhesive layer 3 described above.

The pressure-sensitive adhesive layer 6 may be composed of a laminate of a plurality of layers, and in particular, may have the same configuration as the pressure-sensitive adhesive layer 3 described above.

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

Also in the pressure-sensitive adhesive sheet 1C having such a structure, when the base layer 2 contracts, the layer 31 is not
Layer 32 and / or layer 33 reduce (absorb, disperse) the stress caused by the shrinkage of the base material layer 2 and maintain the residual stress locally. Concentration can be prevented. In addition, as described above, when the adhesion between the layers 31, 32, and 33 is relatively weak, the interface between the adjacent layers is likely to shift (move), and the stress relieving action is also exhibited. You. Therefore, when the pressure-sensitive adhesive sheet 1C is attached to an STN liquid crystal cell or the like and used, the occurrence of color unevenness is prevented or suppressed.

In the present invention, the pressure-sensitive adhesive layer may be composed of a laminate of four or more layers. In this case, the first layer described above is provided on the side closest to the substrate layer (particularly, in close contact with the substrate layer), and at least one of the remaining layers may be the second layer described above. .

In each of the above embodiments, the polarizing plate is used as the base layer 2. However, the present invention is not limited to this. For example, an analyzer, a phaser (a quarter-wave plate, a half-wave plate, etc.), Other plate-like optical components such as an optical rotator (Faraday element, natural optical rotator) and various optical filters may be used.

Further, the pressure-sensitive adhesive sheet of the present invention is not limited to one used by sticking it to a liquid crystal cell or one applied to an optical component used for other purposes.

In particular, the present invention is preferably applied to a material in which the base material layer easily undergoes deformation such as expansion, contraction, and warpage in response to changes in environmental conditions such as temperature and humidity.

[0078]

Next, the present invention will be described in more detail with reference to specific examples.

Example 1 An adhesive layer was formed on one surface of a polarizing plate substrate as a substrate layer by a coating and transfer laminating method, and a release sheet was adhered to the adhesive layer. The pressure-sensitive adhesive sheet of the present invention having the structure shown in FIG.
150 mm wide). The configuration of each layer is as follows.

Polarizer base material Constituent material: Trilayer laminate of triacetyl cellulose film / polyvinyl alcohol film / triacetyl cellulose film Thickness: 180 μm

Adhesive layer Layer structure: two-layer laminate Manufacturing method: transfer method (details are as follows)

[First Layer (Polarizing Plate Substrate Side)] Acrylic acid: 5 parts by weight to butyl acrylate: 95 parts by weight Acrylic ester-based polymer (adhesive): 99.9 parts by weight Was mixed with 0.1 part by weight of trimethylolpropane tolylene diisocyanate (crosslinking agent) to prepare an adhesive solution. This solution was coated on the same film as the release sheet described below and dried, and the obtained film was transferred to one surface of a polarizing plate substrate by a transfer method.

[Second Layer (Releasing Sheet Side)] Di-2-ethylhexyl adipate (plasticizer): 5 parts by weight was mixed with an adhesive solution (solid content: 100 parts by weight) having the same composition as the first layer. Then, an adhesive solution was prepared. This solution was applied on the same film as described above and dried, and the obtained film was transferred to the surface of the first layer by a transfer method.

The obtained two-layer laminate was aged at room temperature for one week. Conditions of each layer: shown in Table 1 below.

Release sheet Constituent material: Polyester film, silicone treatment on one side (manufactured by Lintec, SP PET38) Thickness: 38 μm

(Example 2) An adhesive sheet similar to that of Example 1 except that the plasticizer added to the second layer of the adhesive layer was changed to 6 parts by weight of di-2-ethylhexyl phthalate. Was manufactured. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

Example 3 Example 1 was repeated except that the crosslinking agent (the same composition) added to the second layer of the pressure-sensitive adhesive layer was 0.08 parts by weight, and the plasticizer was 5 parts by weight of liquid polyether. Manufactured the same pressure-sensitive adhesive sheet as in Example 1. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

Example 4 Example 3 was repeated except that a third layer having the same composition as the second layer was formed on the surface of the second layer in the same manner as in Example 1, and the adhesive layer was formed into a three-layer laminate. Example 1
The same pressure-sensitive adhesive sheet (structure shown in FIG. 2) was produced. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

(Example 5) In Example 1, a third layer having the same composition as the second layer in Example 2 was formed on the surface of the second layer by the same method, and a three-layered pressure-sensitive adhesive layer was formed. Pressure-sensitive adhesive sheet (structure shown in FIG. 2) similar to that of Example 1 except that
Was manufactured. Table 1 shows the conditions of each layer constituting the pressure-sensitive adhesive layer.
Shown in

Example 6 In Example 3, a third layer was formed on the surface of the second layer by the same method except that the plasticizer added to the second layer was changed to 10 parts by weight of trioctyl trimellitate. Then, a pressure-sensitive adhesive sheet (structure shown in FIG. 2) similar to that of Example 3 was produced except that the pressure-sensitive adhesive layer was a three-layer laminate. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

(Example 7) In Example 2, a third layer having the same composition as the first layer was formed on the surface of the second layer by the same method, and the adhesive layer was formed into a three-layer laminate. A pressure-sensitive adhesive sheet (structure shown in FIG. 2) similar to that of Example 2 was manufactured. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

Example 8 A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the second layer of the pressure-sensitive adhesive layer was formed as follows.

[Second Layer] 2-ethylhexyl acrylate: 95 parts by weight of acrylic acid: 5 parts by weight of acrylic acid ester-based polymer (adhesive): 99.95 parts by weight of trimethylolpropane Tolylene diisocyanate (crosslinking agent): 0.05 parts by weight was mixed to prepare an adhesive solution. This solution was applied on the same film as described above and dried, and the obtained film was transferred to the surface of the first layer by a transfer method. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

Example 9 An adhesive sheet similar to that of Example 4 (the structure shown in FIG. 2) except that the second and third layers of the adhesive layer were formed as follows. Was manufactured.

[Second layer] 2-ethylhexyl acrylate: 95 parts by weight of acrylic acid: 5 parts by weight of acrylic acid ester-based polymer (adhesive): 99.9 parts by weight of trimethylolpropane Tolylene diisocyanate (crosslinking agent): 0.1 part by weight was mixed to prepare an adhesive solution. This solution was applied on the same film as described above and dried, and the obtained film was transferred to the surface of the first layer by a transfer method.

[Third Layer] An adhesive solution prepared by mixing 5 parts by weight of di-2-ethylhexyl adipate (plasticizer) with an adhesive solution having the same composition as the second layer (100 parts by weight of solid content) Was coated on the same film as described above and dried, and the obtained film was transferred to the surface of the second layer by a transfer method. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

Comparative Example 1 A pressure-sensitive adhesive layer was formed on one side of a polarizing plate substrate as a substrate layer by a coating method, and a release sheet was adhered to the pressure-sensitive adhesive layer. A pressure-sensitive adhesive sheet having the same dimensions as in Example 1 was produced. The configuration of each layer is as follows.

Polarizing Substrate Same as in Example 1.

Adhesive layer Layer constitution: single layer structure Production method: transfer method (details are as follows)

A pressure-sensitive adhesive solution having the same composition as the first layer in Example 1 was prepared, and this solution was applied to one surface of a polarizing plate substrate and dried to form a pressure-sensitive adhesive layer. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

Release Sheet Same as in Example 1.

Comparative Example 2 A pressure-sensitive adhesive sheet similar to that of Comparative Example 1 was produced except that the conditions for the pressure-sensitive adhesive layer were as follows. Layer composition: single layer structure Manufacturing method: transfer method (details are as follows)

To the pressure-sensitive adhesive solution (solid content: 100 parts by weight) having the same composition as that of the first layer in Example 1, 15 parts by weight of di-2-ethylhexyl adipate (plasticizer) was mixed to prepare a pressure-sensitive adhesive solution. . This solution was applied to one side of a polarizing plate substrate and dried to form an adhesive layer. Table 1 below shows the conditions of each layer constituting the pressure-sensitive adhesive layer.

[0104]

[Table 1]

<Experiment 1> The release sheet was removed from each of the pressure-sensitive adhesive sheets of Examples 1 to 9 and Comparative Examples 1 and 2, and the exposed pressure-sensitive adhesive layers became orthogonal Nicols on both sides of the liquid crystal cell glass plate. Respectively. These samples were used for 80
C., Dry, 1000 hours of environmental conditions (first condition) and 60 ° C. × 90% RH, 1000 hours of environmental conditions (second condition) to determine the state of occurrence of the white drop phenomenon (change in transmittance). It was determined visually. The results are shown in Table 2 below.

[0106]

[Table 2]

The criteria in Table 2 are as follows. ◎: No white drop is visually observed. : White spots are hardly noticeable visually. Δ: White spots are somewhat noticeable. ×: White spots are noticeable. XX: White spots are very noticeable.

As is evident from the results shown in Table 2, according to the pressure-sensitive adhesive sheets (adhesive polarizing plates) of Examples 1 to 9 of the present invention, when they are used after being adhered to a liquid crystal cell, the white drop phenomenon is suppressed. It was confirmed that it was possible.

On the other hand, in the pressure-sensitive adhesive sheet of Comparative Example 1,
The whitening phenomenon was remarkable, and in the pressure-sensitive adhesive sheet of Comparative Example 2, the pressure-sensitive adhesive layer was peeled off from the polarizing plate substrate, and was not practically usable.

(Examples 1 'to 9', Comparative Example 1 ')
A phase difference plate (1/4 wavelength plate) having a second pressure-sensitive adhesive layer and a release sheet on one surface side of the pressure-sensitive adhesive layer of each pressure-sensitive adhesive sheet obtained in Examples 1 to 9 and Comparative Example 1 Adhesive sheets that adhere to the other surface and constitute an elliptically polarizing plate as a whole (Examples 1 ′ to 1 corresponding to Examples 1 to 9 and Comparative Example 1, respectively)
9 ′ and Comparative Example 1 ′) were produced. In these cases, the configurations of the retardation plate and the second pressure-sensitive adhesive layer are as follows.

Retardation plate Constituent material: Polycarbonate film (single layer) Thickness: 60 μm

Second pressure-sensitive adhesive layer Layer constitution: single-layer structure Manufacturing method: transfer method (details are as follows) A pressure-sensitive adhesive solution having the same composition as the first layer in Example 1 was prepared, and this solution was subjected to a phase difference. It was applied on one side of the plate and dried to form a second pressure-sensitive adhesive layer (dry film thickness 30 μm).

<Experiment 2> The release sheet was removed from each of the pressure-sensitive adhesive sheets of Examples 1 ′ to 9 ′ and Comparative Example 1 ′, and the exposed second pressure-sensitive adhesive layer was applied to both surfaces of the glass plate for a liquid crystal cell. Each was adhered so as to be orthogonal Nicols. These samples were placed under the first condition and the second condition, and the occurrence of color unevenness was visually determined. The results are shown in Table 3 below.

[0114]

[Table 3]

The criteria in Table 3 are as follows. ◎: No color unevenness is visually observed. : Color unevenness is hardly noticeable visually. Δ: Color unevenness is somewhat noticeable. X: Color unevenness is conspicuous.

As is clear from the results shown in Table 3, according to the pressure-sensitive adhesive sheets (pressure-sensitive adhesive polarizing plates) of the present invention of Examples 1 'to 9', when they were used after being adhered to a liquid crystal cell, color unevenness was observed. It was confirmed that generation can be suppressed. On the other hand, in the pressure-sensitive adhesive sheet of Comparative Example 1 ′, the occurrence of color unevenness was remarkable.

[0117]

As described above, according to the pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive layer does not float and peel off from the substrate layer, and also occurs due to shrinkage of the substrate layer. The stress is alleviated by the pressure-sensitive adhesive layer, and local stress concentration on the edge of the sheet or the like can be reduced.

Therefore, there is an effect of suppressing various phenomena caused by non-uniform stress distribution in the substrate layer and the like, such as white spots in a TN (TFT) liquid crystal cell and color unevenness in an STN liquid crystal cell.

Further, the pressure-sensitive adhesive sheet of the present invention can be manufactured by a method of laminating the pressure-sensitive adhesive layer by transfer, co-extrusion, or the like, and is easy to manufacture.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional view showing another embodiment of the pressure-sensitive adhesive sheet of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1A, 1B, 1C Adhesive sheet 2 Base material layer 3 Adhesive layer 31-33 layers 4 Release sheet 5 Retardation plate 6 Adhesive layer

Claims (8)

[Claims] 1. A pressure-sensitive adhesive sheet having a base material layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a first layer and a second layer closest to the base material layer.
The first layer and the second layer each include an acrylic pressure-sensitive adhesive, and include a plasticizer in a constituent material of the second layer. The addition amount is 0.1 to 50 parts by weight with respect to 100 parts by weight of the adhesive composition, and the addition amount of the plasticizer in the constituent material of the second layer is smaller than that of the first layer. Adhesive sheet characterized by many. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the degree of crosslinking of the polymer material forming the second layer is lower than the degree of crosslinking of the polymer material forming the first layer. . 3. A pressure-sensitive adhesive sheet having a base material layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a first layer and a second layer closest to the base material layer.
The first layer and the second layer each include an acrylic pressure-sensitive adhesive, and the cross-linking of the polymer material forming the second layer is performed. A pressure-sensitive adhesive sheet having a degree lower than the degree of crosslinking of the polymer material constituting the first layer. 4. The substrate layer and the first layer are in close contact with each other, and the first layer has such an extent that cohesive failure and interfacial failure do not occur due to shear stress accompanying shrinkage of the substrate layer. 4. The pressure-sensitive adhesive sheet according to claim 1, which has a shear modulus. 5. The method according to claim 1, wherein the first layer and the second layer are in close contact with each other, and the adhesion between the first layer and the second layer slightly exceeds the adhesive force of the adhesive layer to the adherend. Item 1
5. The pressure-sensitive adhesive sheet according to any one of items 4 to 4. 6. The pressure-sensitive adhesive sheet according to claim 1, wherein the thickness of the second layer is about 0.5 to 15 times the thickness of the first layer. 7. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer is formed by a transfer lamination method. 8. The pressure-sensitive adhesive sheet according to claim 1, wherein the base material layer is a plate-shaped optical component.