JP2012214545A - Pressure-sensitive adhesive and pressure-sensitive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet excellent in both light leakage resistance and durability when applied to an optical element of a polarizing plate or the like.SOLUTION: The pressure-sensitive adhesive includes: a first (meth)acrylic acid ester polymer (A) having 500,000-3,000,000 of a weight average molecular weight; and a component formed by crosslinking a second (meth)acrylic acid ester polymer (B) having 8,000-300,000 of a weight average molecular weight, wherein the percentage of stress relaxation after extended by 900% by a tensile test, and maintained for 300 seconds is at least 60%, and the gel fraction is 30-90%.

Description

  The present invention relates to a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet, and particularly relates to a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet suitable for optical members such as polarizing plates.

  In general, in a liquid crystal panel, a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition is often used to bond a polarizing plate or a retardation plate to a glass substrate or the like. However, since optical members such as polarizing plates and retardation plates are easily shrunk by heat, etc., shrinkage occurs due to thermal history, and as a result, the adhesive layer laminated on the optical member cannot follow the shrinkage. Problems have been pointed out, such as peeling at the interface (so-called floating or peeling), or light leakage (so-called white spots) due to displacement of the optical axis of the optical member due to stress during contraction of the optical member. .

  As a method for preventing this, (1) a method of suppressing the contraction of the optical member itself by bonding a pressure-sensitive adhesive layer having high adhesive strength and excellent shape stability to an optical member such as a polarizing plate. Or (2) a method using a pressure-sensitive adhesive layer having a small stress when the optical member is contracted. As the method (1), it is effective to use a pressure-sensitive adhesive layer having a high storage elastic modulus as disclosed in Patent Document 1. On the other hand, as the method (2), it is effective to use a pressure-sensitive adhesive layer having excellent stress relaxation properties that can flexibly cope with deformation of the optical member. However, conventionally, when it was attempted to form such an adhesive layer having excellent stress relaxation properties, it was necessary to design a low crosslinking density in the adhesive layer. If it does so, there existed a problem that the intensity | strength of adhesive layer itself fell and durability deteriorated.

  Therefore, in Patent Documents 2 to 4, by adding a plasticizer, liquid paraffin, urethane elastomer or the like to the acrylic pressure-sensitive adhesive instead of lowering the cross-linking density of the pressure-sensitive adhesive layer, the resulting pressure-sensitive adhesive composition becomes moderately soft. Thus, stress relaxation is imparted to the pressure-sensitive adhesive layer, thereby obtaining light leakage resistance and durability.

JP 2006-235568 A Japanese Patent Laid-Open No. 5-45517 Japanese Patent Laid-Open No. 9-137143 JP 2005-194366 A

  However, the pressure-sensitive adhesive composition to which a plasticizer or liquid paraffin is added has a drawback that the formed pressure-sensitive adhesive layer bleeds out the plasticizer and liquid paraffin over time. As a result, various problems such as a decrease in adhesion durability and contamination of the liquid crystal cell as an adherend have been a concern. Moreover, since the upper limit of the addition amount of the urethane elastomer was limited when it was going to maintain compatibility, the adhesive composition which added the urethane elastomer showed the tendency for the improvement of stress relaxation property to become inadequate. Furthermore, when the addition amount of the urethane elastomer is increased in order to improve the stress relaxation property, the compatibility with the acrylic pressure-sensitive adhesive is lowered, and problems such as cloudiness have occurred. As described above, it has been difficult for the conventional technology to fundamentally improve the light leakage resistance and durability of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for optical members.

  The present invention has been made in view of such a situation, and provides a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that are excellent in both light leakage resistance and durability when applied to an optical member such as a polarizing plate. Objective.

  In order to achieve the above object, first, the present invention includes a first (meth) acrylic acid ester polymer (A) having a weight average molecular weight of 500,000 to 3,000,000, and a weight average molecular weight of 8,000 to 300,000. And a component formed by crosslinking the second (meth) acrylic acid ester polymer (B), the stress relaxation rate after being stretched by 900% in a tensile test and held for 300 seconds is 60% or more, A pressure-sensitive adhesive having a gel fraction of 30 to 90% is provided (Invention 1).

  The pressure-sensitive adhesive according to the invention (Invention 1) is presumed to have a structure in which a plurality of high molecular weight polymers (A) are inserted into a three-dimensional network structure formed by crosslinking of a low molecular weight polymer (B). In addition to having a large stress relaxation rate, it has a predetermined gel fraction. Thereby, the said adhesive exhibits the suitable cohesion force and the outstanding stress relaxation property. By using this pressure-sensitive adhesive having excellent stress relaxation properties, a pressure-sensitive adhesive sheet excellent in both light leakage resistance and durability can be obtained when applied to an optical member such as a polarizing plate.

  In the said invention (invention 1), the ratio of the said 2nd (meth) acrylic acid ester polymer (B) with respect to 100 mass parts of said 1st (meth) acrylic acid ester polymers (A) is 5-50 mass. Part (Invention 2).

  In the said invention (invention 1 and 2), the said 2nd (meth) acrylic acid ester polymer (B) before bridge | crosslinking has a reactive functional group containing monomer more than 1 mass% as a structural component, and 50 mass%. It is preferable to contain less than (Invention 3).

  In the said invention (invention 3), said 2nd (meth) acrylic ester polymer (B) is bridge | crosslinked by reaction with the crosslinking agent (C) which has a crosslinkable group which can react with the said reactive functional group. (Invention 4)

  Secondly, the present invention provides a pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive (inventions 1 to 4). (Invention 5)

  In the said invention (invention 5), it is preferable that the said base material is an optical member (invention 6).

  Thirdly, the present invention is an adhesive sheet comprising two release sheets and an adhesive layer sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets. A layer provides the adhesive sheet characterized by consisting of the said adhesive (invention 1-4) (invention 7).

  In the pressure-sensitive adhesive according to the present invention, a low molecular weight polymer forms a three-dimensional network structure by chemical crosslinking, and a plurality of high molecular weight polymers are inserted into the three-dimensional network structure. It is presumed that the molecular weight polymers are constrained and a pseudo-crosslinked structure is formed between the high molecular weight polymers. Therefore, the pressure-sensitive adhesive has a large stress relaxation rate and a predetermined gel fraction. Thereby, the said adhesive exhibits the suitable cohesion force and the outstanding stress relaxation property. By using this pressure-sensitive adhesive having excellent stress relaxation properties, a pressure-sensitive adhesive sheet excellent in both light leakage resistance and durability can be obtained when applied to an optical member such as a polarizing plate.

It is sectional drawing of the adhesive sheet which concerns on the 1st Embodiment of this invention. It is sectional drawing of the adhesive sheet which concerns on the 2nd Embodiment of this invention. It is a figure which shows the measurement area | region of the light leak test in a polarizing plate with an adhesive layer. It is a figure (color) which shows the evaluation criteria of the light-leakage test (visual observation) in a polarizing plate with an adhesive layer.

Hereinafter, embodiments of the present invention will be described.
[Adhesive]
The pressure-sensitive adhesive according to this embodiment includes a first (meth) acrylic acid ester polymer (A) having a weight average molecular weight (Mw) of 500,000 to 3,000,000, and a second one having a weight average molecular weight of 8,000 to 300,000. And a component formed by crosslinking the (meth) acrylic acid ester polymer (B). In this specification, (meth) acrylic acid ester means both acrylic acid ester and methacrylic acid ester. The same applies to other similar terms. Further, the “polymer” includes the concept of “copolymer”.

  The pressure-sensitive adhesive preferably has a first (meth) acrylic acid ester polymer (A) having a weight average molecular weight of 500,000 to 3,000,000 and a second (meth) having a weight average molecular weight of 8,000 to 300,000. Obtained by crosslinking a pressure-sensitive adhesive composition containing an acrylic ester polymer (B) and a crosslinking agent (C), particularly preferably a pressure-sensitive adhesive composition further containing a silane coupling agent (D). Can do. In such an adhesive, a low molecular weight polymer conventionally used as a plasticizer is used to form a three-dimensional network structure by chemical crosslinking, and a plurality of high molecular weight polymers are added to the three-dimensional network structure. By inserting, it is presumed that the high molecular weight polymers are constrained to form a pseudo cross-linked structure between the high molecular weight polymers. Thereby, the obtained adhesive can exhibit appropriate cohesive force and excellent stress relaxation properties. Hereinafter, the said adhesive composition is demonstrated.

The second (meth) acrylic acid ester polymer (B) is
(1) A monomer having a functional group (b1) that reacts with the crosslinking agent (C) is a constituent component, and the functional group that reacts with the crosslinking agent (C) contained in the polymer (B) is substantially functional. Or only the group (b1)
(2) A functional group in which the reactivity with the crosslinking agent (C) satisfies the following formula (I) and the reactivity of the monomer having the functional group (b1) with the crosslinking agent (C) satisfies the following formula (I) ( The monomer having b2) is preferably used as a constituent component.
Reactivity with crosslinking agent (C): functional group (b2) <functional group (b1) (I)
That is, in the polymer (B) of (2), the reactivity of the functional group (b1) with the crosslinking agent (C) is higher than the reactivity of the functional group (b2) with the crosslinking agent (C). preferable.

  The (meth) acrylic acid ester polymer (A) or (B) is a monomer having a functional group that reacts with the alkyl group (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms and the crosslinking agent (C). A copolymer of (reactive functional group-containing monomer) and another monomer used as desired is preferable. In addition, what does not contain the said reactive functional group containing monomer as a structural unit is also preferable for a 1st (meth) acrylic acid ester polymer (A).

  Examples of the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and (meth) acrylic acid n-. Butyl, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n- (meth) acrylate Examples include decyl, n-dodecyl (meth) acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, and the like. These may be used alone or in combination of two or more.

  On the other hand, the reactive functional group-containing monomer includes a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxyl group-containing monomer), and a monomer having an amino group in the molecule (amino group). Preferred monomer).

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, (meth And (meth) acrylic acid hydroxyalkyl esters such as 3-hydroxybutyl acrylate and 4-hydroxybutyl (meth) acrylate. These may be used alone or in combination of two or more.

  Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. These may be used alone or in combination of two or more.

  Examples of the amino group-containing monomer include aminoethyl (meth) acrylate, n-butylaminoethyl (meth) acrylate, and the like. These may be used alone or in combination of two or more.

  Furthermore, as said other monomer, (meth) acrylic acid ester which has aromatic rings, such as (meth) acrylic acid ester which has aliphatic rings, such as (meth) acrylic acid cyclohexyl, and (meth) acrylic acid phenyl, for example Non-crosslinkable acrylamide such as acrylamide, methacrylamide, etc., and non-crosslinkable tertiary amino groups such as N, N-dimethylaminoethyl (meth) acrylate and N, N-dimethylaminopropyl (meth) acrylate (Meth) acrylic acid ester, vinyl acetate, styrene and the like can be mentioned. These may be used alone or in combination of two or more.

  The reactive functional group (a1) -containing monomer used in the first (meth) acrylic acid ester polymer (A) and the reactivity used in the second (meth) acrylic acid ester polymer (B). The selection of the functional group (b1) -containing monomer and the reactive functional group (b2) -containing monomer is determined by the reactivity relationship with the crosslinking agent (C) used. Details will be described later.

  Here, the second (meth) acrylic acid ester polymer (B) contains the reactive functional group (b1) -containing monomer in excess of 1% by mass, and the upper limit thereof is less than 50% by mass. Is preferred. Preferably, the reactive functional group (b1) -containing monomer is contained in an amount of 5 to 30% by mass, particularly preferably 10 to 20% by mass, and further preferably 12 to 18% by mass. By containing the reactive functional group (b1) -containing monomer in the above range, the degree of crosslinking of the second (meth) acrylic acid ester polymer (B) becomes preferable, and the first (meth) acrylic acid ester weight In the combination with the coalescence (A), the stress relaxation rate of the obtained pressure-sensitive adhesive can be a predetermined value or more, and the gel fraction can be within a predetermined range. As a result, the pressure-sensitive adhesive has both durability and light leakage resistance. In addition, when the content of the reactive functional group (b1) -containing monomer is 1% by mass or less, the second (meth) acrylic acid ester polymer (B) is not sufficiently crosslinked, and the gel fraction is more than a predetermined range. The durability may be lowered. On the other hand, when the content of the reactive functional group (b1) -containing monomer is 50% by mass or more, the second (meth) acrylic acid ester polymer (B) is excessively crosslinked, and the resulting pressure-sensitive adhesive gel While the fraction becomes higher than the predetermined range, the stress relaxation rate may be lower than the predetermined value. In addition, the light leak resistance of the adhesive sheet obtained becomes more excellent by making the upper limit of content of a reactive functional group (b1) containing monomer into 30 mass%.

  The “substantially only functional group (b1)” in the polymer (B) of (1) means that other functional groups that react with the crosslinking agent (C) are the functional group (b1) and the crosslinking agent (C). (In this case, the polymer (B) in (1) and the polymer (B) in (2) are duplicated). That is, the second (meth) acrylic acid ester polymer (B) is a monomer (reactive functional group) having a functional group (b2) that is less reactive with the crosslinking agent (C) than the functional group (b1). It is particularly preferable not to contain (b2) containing monomer) as a constituent component. However, when the reactive functional group (b2) -containing monomer is contained as a constituent component, the mass ratio is 1/5 or less of the content of the reactive functional group (b1) -containing monomer, particularly 1/10 or less. It is preferable to contain by quantity.

  The second (meth) acrylic acid ester polymer (B) has a reactive functional group (b2) -containing monomer in an amount exceeding 1/5 of the content of the reactive functional group (b1) -containing monomer as a mass ratio. When it contains, there exists a possibility that durability of the adhesive layer obtained may fall. If there are too many reactive functional groups (b2) in the second (meth) acrylic acid ester polymer (B), many reactive functional groups (b2) remain in the three-dimensional network structure formed thereby. Therefore, it is estimated that the compatibility between the three-dimensional network structure and the first (meth) acrylic acid ester polymer (A) is changed. As a result, the haze value may increase. In addition, the three-dimensional network structure in which a large amount of the reactive functional group (b2) remains has excessive mobility of the first (meth) acrylate polymer (A) inserted in the three-dimensional network structure. It is also estimated that it is limited to. As a result, the stress relaxation rate of the obtained pressure-sensitive adhesive is less than a predetermined value, and the durability may deteriorate.

  Furthermore, when the adhesive composition which concerns on this embodiment contains a silane coupling agent (D), a silane coupling agent (D) is the reactivity of a 1st (meth) acrylic acid ester polymer (A). A glass substrate or the like that is an adherend in the resulting pressure-sensitive adhesive when it reacts with the functional group (a1) (particularly a carboxyl group) and binds to the high molecular weight first (meth) acrylate polymer (A). The second (meth) acrylic acid ester polymer (B) contains an excessive amount of the reactive functional group (b2) -containing monomer, which is presumed to be excellent in adhesion with the silane coupling agent ( The alkoxysilyl group of D) reacts with the reactive functional group (b2) (especially carboxyl group) of the second (meth) acrylic acid ester polymer (B) to give a second low molecular weight (meth). Acrylic ester polymerization It is presumed to bind (B). As a result, the obtained pressure-sensitive adhesive is inferior in adhesiveness with a glass substrate or the like as an adherend, thereby possibly reducing the durability of the pressure-sensitive adhesive layer.

  Here, the 2nd (meth) acrylic acid obtained by superposing | polymerizing the (meth) acrylic-acid alkylester whose carbon number of an alkyl group is 1-20, and the monomer which has a functional group which reacts with a crosslinking agent (C). The polymerization mode of the ester polymer (B) may be a random copolymer or a block copolymer.

  In this embodiment, said 2nd (meth) acrylic-ester type polymer (B) may be used individually by 1 type, and may be used in combination of 2 or more type.

  The weight average molecular weight of the second (meth) acrylic acid ester polymer (B) is 8000 to 300,000, preferably 10,000 to 200,000, particularly preferably 50,000 to 100,000. That is, the second (meth) acrylic acid ester polymer (B) is a low molecular weight polymer component. In addition, the weight average molecular weight in this specification is the value of polystyrene conversion measured by the gel permeation chromatography (GPC) method.

  When the weight average molecular weight of the second (meth) acrylic acid ester polymer (B) is within the above range, a three-dimensional network structure peculiar to the pressure-sensitive adhesive composition according to this embodiment is formed, and excellent stress is obtained. This will contribute to relaxation. That is, when the weight average molecular weight of the second (meth) acrylic acid ester polymer (B) is less than 8000, a good three-dimensional network structure cannot be obtained. On the other hand, when the weight average molecular weight of the second (meth) acrylic acid ester polymer (B) exceeds 300,000, the compatibility with the first (meth) acrylic acid ester polymer (A) and the like decreases, Insertion of the polymer (A) into the three-dimensional network structure formed by the polymer (B) becomes insufficient, and the gel fraction may fall below a predetermined range. As a result, the resulting adhesive may be inferior in durability and reworkability.

  The first (meth) acrylic acid ester polymer (A) preferably does not contain a monomer having a functional group that reacts with the crosslinking agent (C) as a constituent component or the second (meth) acrylic acid ester polymer. It contains a monomer having a functional group (a1) that is less reactive with the crosslinking agent (C) than the functional group (b1) of the union (B) as a constituent component, and particularly preferably the functional group (b1). The monomer which has a functional group with high reactivity with a crosslinking agent (C) than is not contained as a structural component.

  The first (meth) acrylic acid ester polymer (A) may not contain a monomer having a functional group that reacts with the crosslinking agent (C). However, the monomer (reactive functional group (a1) -containing monomer having a reactive functional group (a1) that is less reactive than the reactive functional group (b1) of the second (meth) acrylic ester polymer (B) ) May be further preferred. When the reactive functional group (a1) is contained in the polymer (A), the reaction between the second (meth) acrylic acid ester polymer (B) and the crosslinking agent (C) is promoted, or silane When the coupling agent (D) is used, the reactive functional group (a1) of the first (meth) acrylic acid ester polymer (A) reacts with the silane coupling agent (D) and is obtained. The durability of adhesion of the agent to the glass surface of a liquid crystal cell or the like can be further improved, and may be preferable.

  When the first (meth) acrylic acid ester polymer (A) contains the reactive functional group (a1) -containing monomer, the content is usually 20% by mass or less and 15% by mass or less. It is preferable that it is 10 mass% or less especially. When the content of the reactive functional group (a1) -containing monomer exceeds 20% by mass, the glass transition temperature (Tg) of the first (meth) acrylic acid ester polymer (A) becomes too high, and the resulting adhesive is obtained. There is a possibility that the stress relaxation rate of the agent is lower than a predetermined value. In addition, from the viewpoint of imparting reworkability to the pressure-sensitive adhesive, the content of the reactive functional group (a1) -containing monomer is preferably 15% by mass or less.

  Moreover, in comparison with the reactive functional group (b1) -containing monomer contained in the second (meth) acrylic acid ester polymer (B), the first (meth) acrylic acid ester polymer (A) is contained. The proportion of the reactive functional group (a1) -containing monomer in the first (meth) acrylate polymer (A) is the reactivity contained in the second (meth) acrylate polymer (B). It is preferably smaller than the proportion of the functional group (b1) -containing monomer in the second (meth) acrylic acid ester polymer (B). Thereby, reaction with the reactive functional group (a1) and the crosslinking agent (C) contained in the first (meth) acrylic acid ester polymer (A) is suppressed, and the second (meth) acrylic acid ester weight is reduced. The reactive functional group (b1) contained in the coalescence (B) and the crosslinking agent (C) can be reacted reliably. Thereby, the stress relaxation rate and gel fraction of the obtained adhesive can be set within predetermined values.

  The first (meth) acrylic acid ester polymer (A) has the same reactivity with the crosslinking agent (C) as the reactive functional group (b1) of the second (meth) acrylic acid ester polymer (B). It is preferable not to contain a monomer having the above functional group in the molecule. However, if contained, the content of the monomer having the functional group in the molecule is preferably 1% by mass or less, particularly 0.5% by mass or less, in the polymer (A). It is preferable. When the content of the monomer exceeds 1% by mass, the reaction between the second (meth) acrylic acid ester polymer (B) to be preferentially reacted and the crosslinking agent (C) may be inhibited. As a result, a predetermined stress relaxation rate may not be obtained.

  Here, the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group and the reactive functional group-containing monomer are polymerized with the first (meth) acrylic acid ester polymer (A). A random copolymer may be sufficient as a superposition | polymerization aspect, and a block copolymer may be sufficient as it.

  In this embodiment, said 1st (meth) acrylic acid ester polymer (A) may be used individually by 1 type, and may be used in combination of 2 or more type.

  The weight average molecular weight of the first (meth) acrylic acid ester polymer (A) is 500,000 to 3,000,000, preferably 700,000 to 2,500,000, particularly preferably 1,000,000 to 2,000,000. That is, the first (meth) acrylic acid ester polymer (A) is a high molecular weight polymer component.

  When the weight average molecular weight of the first (meth) acrylate polymer (A) is within the above range, the three-dimensional network structure formed by the second (meth) acrylate polymer (B) When the first (meth) acrylic acid ester polymer (A) is satisfactorily inserted and two or more molecules of the polymer (A) are via a pseudo-crosslinked structure, the polymer (A) has a certain degree of freedom. It is estimated that it is restrained in a state having a degree. In addition, the polymer (A) has a relatively large molecular weight as described above, and thus maintains a pseudo-crosslinked state via the three-dimensional network structure formed by the polymer (B), It also has a high degree of freedom as a chain. Thereby, the pressure-sensitive adhesive formed has a predetermined stress relaxation rate and gel fraction, and has both an appropriate cohesive force and excellent stress relaxation properties. As a result, the pressure-sensitive adhesive is excellent in light leakage resistance, has sufficient adhesion durability under high-temperature conditions, and can prevent floating and peeling.

  Here, when the weight average molecular weight of the first (meth) acrylic acid ester polymer (A) is less than 500,000, the gel fraction of the resulting pressure-sensitive adhesive is lowered, and the durability and reworkability are inferior. There is a risk. Moreover, when the weight average molecular weight of the first (meth) acrylic acid ester polymer (A) exceeds 3 million, the compatibility with the second (meth) acrylic acid ester polymer (B) and the like deteriorates. There exists a possibility that the stress relaxation rate of the obtained adhesive may be less than a predetermined value.

  The ratio of the second (meth) acrylic acid ester polymer (B) to 100 parts by mass of the first (meth) acrylic acid ester polymer (A) is preferably 5 to 50 parts by mass, and 5 to 40 parts. It is more preferable that it is a mass part, and it is especially preferable that it is 10-30 mass parts.

  In the pressure-sensitive adhesive obtained from the pressure-sensitive adhesive composition containing the first (meth) acrylic acid ester polymer (A) and the second (meth) acrylic acid ester polymer (B) at the above-mentioned ratio, The (meth) acrylic acid ester polymer (B) (low molecular weight polymer) forms a three-dimensional network structure via the cross-linking agent (C), and the first (meth) acrylic acid ester weight is added to the three-dimensional network structure. It is presumed that the polymer (A) (high molecular weight polymer) has a pseudo-crosslinked structure in which two or more molecules are inserted and the polymer (A) is constrained with a certain degree of freedom. Is done. Thereby, the obtained adhesive has both a predetermined stress relaxation rate and a gel fraction. Therefore, the obtained adhesive is excellent in durability and light leakage resistance.

  Preferred examples of the crosslinking agent (C) include an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, and a metal chelate crosslinking agent.

  The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate. , And their biuret bodies, isocyanurate bodies, and adduct bodies that are a reaction product with low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, castor oil, and the like.

  Examples of the epoxy crosslinking agent include 1,3-bis (N, N′-diglycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl. Examples include ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, diglycidylamine and the like.

  Examples of the aziridine-based crosslinking agent include diphenylmethane-4,4′-bis (1-aziridinecarboxamide), trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethanetri-β-aziridinyl. Propionate, toluene-2,4-bis (1-aziridinecarboxamide), triethylenemelamine, bisisophthaloyl-1- (2-methylaziridine), tris-1- (2-methylaziridine) phosphine, And trimethylolpropane tri-β- (2-methylaziridine) propionate.

  Metal chelate crosslinking agents include chelate compounds whose metal atoms are aluminum, zirconium, titanium, zinc, iron, tin, etc., but aluminum chelate compounds are preferred from the viewpoint of performance. Examples of the aluminum chelate compound include diisopropoxy aluminum monooleyl acetoacetate, monoisopropoxy aluminum bis oleyl acetoacetate, monoisopropoxy aluminum monooleate monoethyl acetoacetate, diisopropoxy aluminum monolauryl acetoacetate, diisopropoxy Examples thereof include aluminum monostearyl acetoacetate and diisopropoxy aluminum monoisostearyl acetoacetate.

  The content of the crosslinking agent (C) is such that the crosslinking group (for example, isocyanate group) of the crosslinking agent (C) is the reactive functional group (b1) of the second (meth) acrylate polymer (B) ( For example, the amount is usually 0.05 to 5 equivalents, preferably 0.1 to 3.5 equivalents, particularly preferably 0.3 to 1.0 equivalents relative to the amount of hydroxyl groups). This is the amount. When the amount of the crosslinkable group is less than 0.05 equivalent, the gel fraction of the obtained pressure-sensitive adhesive is less than 30%, and there is a possibility that sufficient cohesive force cannot be exhibited. Further, when the amount of the crosslinkable group is 0.1 equivalent or more, particularly 0.3 equivalent or more, the obtained pressure-sensitive adhesive can be made more excellent in durability. On the other hand, if the amount of the crosslinkable group is 3.5 equivalents or less, the resulting pressure-sensitive adhesive can be made excellent in reworkability. Furthermore, if the amount of the crosslinkable group is 1.0 equivalent or less, the crosslinking agent (C) contributes only to the formation of the three-dimensional network structure of the polymer (B), and the crosslinking of the polymer (A) is effective. It is estimated that this can be prevented. As a result, the obtained pressure-sensitive adhesive has excellent stress relaxation properties.

  In the present embodiment, as the crosslinking agent (C), a plurality of types of crosslinking agents may be used as long as the types of crosslinking agents have the same reactivity relationship with both the reactive functional group (b1) and the reactive functional group (a1). May be used in combination. From the viewpoint of facilitating control of the three-dimensional network structure formed by the second (meth) acrylic acid ester polymer (B), for example, only one isocyanate-based crosslinking agent is used. It is preferable to use only a crosslinking agent, and it is particularly preferable to use only one crosslinking agent as the compound.

  Here, as a combination of the crosslinking agent (C) and the reactive functional group-containing monomers of the (meth) acrylic acid ester polymers (A) and (B), the crosslinking agent (C) is an isocyanate crosslinking agent. In this case, the reactive functional group (a1) -containing monomer of the polymer (A) is a carboxyl group-containing monomer, and the reactive functional group (b1) -containing monomer of the polymer (B) is a hydroxyl group-containing monomer or an amino group-containing monomer. Preferably selected.

  On the other hand, when the crosslinking agent (C) is an epoxy crosslinking agent, an aziridine crosslinking agent or a metal chelate crosslinking agent, the reactive functional group (a1) -containing monomer of the polymer (A) is a hydroxyl group-containing monomer or polymer. As the reactive functional group (b1) -containing monomer (B), a carboxyl group-containing monomer is preferably selected.

  The flexibility of the bond formed between the cross-linking agent (C) and the polymer (B), and the mildness of the cross-linking reaction. Furthermore, the reactive group of the polymer (A) is combined with the silane coupling agent (D). Since it reacts appropriately and contributes to improving the adhesive durability of the resulting pressure-sensitive adhesive, the crosslinking agent (C) contains an isocyanate-based crosslinking agent, and the polymer (A) contains a reactive functional group (a1) -containing monomer that contains a carboxyl group. It is particularly preferable that the monomer or the reactive functional group (b1) -containing monomer of the polymer (B) is a hydroxyl group-containing monomer and the reactive functional group (b2) -containing monomer is not used.

  The adhesive composition according to this embodiment preferably further contains a silane coupling agent (D). When this silane coupling agent (D) is contained, when the first (meth) acrylic acid ester polymer (A) has a carboxyl group, the organic reactive group and the like of the silane coupling agent (D) and the first The carboxyl group of the (meth) acrylic acid ester polymer (A) reacts, and on the other hand, the alkoxysilyl group of the silane coupling agent (D) acts on the adherend surface such as a glass substrate. For this reason, when bonding a polarizing plate to a liquid crystal glass cell etc., the adhesiveness between an adhesive and a liquid crystal glass cell becomes more favorable, for example.

  The silane coupling agent (D) is an organosilicon compound having at least one alkoxysilyl group in the molecule, having good compatibility with the pressure-sensitive adhesive component, and having light transmittance, for example, substantially A transparent one is preferred. The amount of the silane coupling agent (D) added is preferably 0.01 to 0.5 parts by mass with respect to 100 parts by mass of the first (meth) acrylic acid ester polymer (A). In particular, it is preferably 0.05 to 0.3 parts by mass.

  Specific examples of the silane coupling agent (D) include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, Silicon compounds having an epoxy structure such as 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- Examples include amino group-containing silicon compounds such as (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, and 3-isocyanatopropyltriethoxysilane. These may be used individually by 1 type and may be used in combination of 2 or more type.

  In the above-mentioned adhesive composition, various additives usually used for acrylic adhesives, for example, tackifiers, antioxidants, ultraviolet absorbers, light stabilizers, softeners, fillers, antistatic agents, are optionally used. An agent, a refractive index adjusting agent, etc. can be added.

  While the said adhesive composition mixes a 1st (meth) acrylic acid ester polymer (A) and a 2nd (meth) acrylic acid ester polymer (B), it is a crosslinking agent ( C) and, if desired, can be produced by adding a silane coupling agent (D).

  As a preferred specific example, the (meth) acrylic acid ester polymers (A) and (B) are separately prepared by a normal radical polymerization method. The polymerization of the (meth) acrylic acid ester polymers (A) and (B) can be carried out by a solution polymerization method or the like using a polymerization initiator as desired. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like. Two or more kinds may be used in combination.

  Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more kinds may be used in combination. Examples of the azo compound include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane 1-carbonitrile), 2 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2′-azobis (2-methylpropionate) 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis (2-hydroxymethylpropionitrile), 2,2′-azobis [2- (2-imidazolin-2-yl) Propane] and the like.

  Examples of the organic peroxide include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, and di (2-ethoxyethyl) peroxy. Examples include dicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

  Next, the solutions of the obtained polymers (A) and (B) are mixed, and a diluting solvent is added. Thereafter, the cross-linking agent (C) and, if desired, the silane coupling agent (D) are added and mixed thoroughly to obtain an adhesive composition (coating solution) diluted with a solvent.

  Examples of the dilution solvent for diluting the adhesive composition to form a coating solution include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, methylene chloride, and ethylene chloride. Halogenated hydrocarbons, alcohols such as methanol, ethanol, propanol, butanol and 1-methoxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethyl cellosolve A cellosolve solvent such as is used.

  The concentration / viscosity of the coating solution thus prepared is not particularly limited as long as it can be coated, and can be appropriately selected depending on the situation. For example, it dilutes so that the density | concentration of an adhesive composition may be 10-40 mass%. In addition, when obtaining an application | coating solution, addition of a dilution solvent etc. is not a necessary condition, and if a viscosity etc. which can be coated with an adhesive composition, it is not necessary to add a dilution solvent. In this case, the adhesive composition becomes the coating solution as it is.

  The above-mentioned pressure-sensitive adhesive is obtained by crosslinking the above pressure-sensitive adhesive composition. Crosslinking of the pressure-sensitive adhesive composition can be performed by heat treatment. In addition, this heat processing can also serve as the drying process at the time of volatilizing the dilution solvent etc. of an adhesive composition.

  When performing heat processing, it is preferable that heating temperature is 50-150 degreeC, and it is especially preferable that it is 70-120 degreeC. The heating time is preferably 30 seconds to 3 minutes, particularly preferably 50 seconds to 2 minutes. Furthermore, it is particularly preferable to provide a curing period of about 1 to 2 weeks at room temperature (for example, 23 ° C., 50% RH) after the heat treatment.

  By the heat treatment (and curing), it is presumed that the second (meth) acrylic acid ester polymer (B) is crosslinked by the crosslinking agent (C) to form a three-dimensional network structure. And, by inserting two or more molecules of the first (meth) acrylate polymer (A) into the three-dimensional network structure without direct chemical bonds or with very few chemical bonds. The polymer (A) is constrained and presumed to form a pseudo cross-linked structure. When the first (meth) acrylic acid ester polymer (A) has a carboxyl group, the first (meth) acrylic acid ester polymer (A) reacts with the silane coupling agent (D). Thus, durability of adhesion of the obtained pressure-sensitive adhesive to a glass surface such as a liquid crystal cell can be further improved.

  The stress relaxation rate after the adhesive according to this embodiment is stretched 900% in a tensile test and held for 300 seconds is 60% or more, and preferably 62% or more. This tensile test is performed as a single pressure-sensitive adhesive layer without a substrate or the like. When the pressure-sensitive adhesive made of the above-described material has such a large stress relaxation rate, the pressure-sensitive adhesive exhibits excellent stress relaxation properties and can be excellent in both light leakage resistance and durability.

  Further, the stress relaxation rate after the adhesive according to the present embodiment is stretched by 900% in a tensile test and held for 100 seconds is preferably 50% or more, and particularly preferably 52% or more.

Specifically, the tensile test was carried out using an adhesive molded to a thickness of 500 μm, a width of 10 mm, and a length of 75 mm (of which the measurement range was 20 mm) at 200 ° C./min in an environment of 23 ° C. and 50% RH. It is assumed that the stretching is performed at a speed of 900%. The stress relaxation rate is calculated by the following formula.
Stress relaxation rate (%) = {(stress immediately after stretching 900% −stress after holding for 300 seconds) / stress immediately after stretching 900%} × 100

  Moreover, when the adhesive according to the present embodiment is stretched under the same conditions as in the tensile test, it is preferably stretchable by 1500% or more before breaking, particularly preferably by 3000% or more.

  Furthermore, the stress immediately after 900% elongation by the tensile test is preferably 10 N or less, and particularly preferably 1.5 N or less. The smaller the stress immediately after stretching by 900%, the smaller the stress generated when the adherend (for example, a polarizing plate) is deformed. Therefore, it is preferable for improving the light leakage resistance. On the other hand, the lower limit of the stress immediately after 900% elongation is preferably 0.2 N or more, and particularly preferably 0.5 N or more. This is because if the maximum stress is too low, the durability may deteriorate.

  The gel fraction of the pressure-sensitive adhesive according to this embodiment is 30 to 90%, preferably 40 to 80%, and particularly preferably 45 to 75%. When the gel fraction, that is, the degree of crosslinking is within this range, a three-dimensional network structure is well formed by crosslinking of the second (meth) acrylic acid ester polymer (B), and the pressure-sensitive adhesive has light leakage resistance and It can be excellent in both durability. In addition, the gel fraction of an adhesive is a value at the time of sticking (after progress of an aging period). Specifically, it refers to the gel fraction after the adhesive composition is applied to a release sheet and heat-treated, and then stored for 7 days in an environment of 23 ° C. and 50% RH. This is because the gel fraction of the pressure-sensitive adhesive fluctuates before the aging period. From this point of view, if it is unclear whether the aging period has elapsed or not, it is only necessary that the gel fraction be within the above range after being stored again for 23 days in an environment of 23 ° C. and 50% RH. .

  The above-described pressure-sensitive adhesive can be preferably used for an optical member. For example, adhesion between a polarizing plate and a retardation plate, or a polarizing plate (polarizing film) or a retardation plate (retardation film) and a glass substrate. Suitable for bonding. The pressure-sensitive adhesive layer formed by the above-mentioned pressure-sensitive adhesive has excellent stress relaxation properties, so even if the dimensional change of the adherend is large, the pressure-sensitive adhesive layer absorbs / relaxes stress that can be generated by the dimensional change. Therefore, it becomes difficult to peel off from the adherend over a long period of time, and light leakage can be effectively prevented when used in the optical member as described above. That is, the pressure-sensitive adhesive according to this embodiment achieves both light leakage resistance and durability when used in an optical member.

[Adhesive sheet]
As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 </ b> A according to the first embodiment is laminated on the pressure-sensitive adhesive layer 11, the pressure-sensitive adhesive layer 11 stacked on the release surface of the release sheet 12, and the pressure-sensitive adhesive layer 11. And the formed base material 13.

  In addition, as shown in FIG. 2, the adhesive sheet 1B according to the second embodiment includes the two release sheets 12a and 12b and the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. And the pressure-sensitive adhesive layer 11 sandwiched between the release sheets 12a and 12b. In addition, the release surface of the release sheet in this specification refers to a surface having peelability in the release sheet, and includes both a surface that has been subjected to a release treatment and a surface that exhibits peelability without being subjected to a release treatment. .

  In any of the pressure-sensitive adhesive sheets 1A and 1B, the pressure-sensitive adhesive layer 11 is made of a pressure-sensitive adhesive formed by crosslinking the above-described pressure-sensitive adhesive composition.

  The thickness of the pressure-sensitive adhesive layer 11 is appropriately determined according to the purpose of use of the pressure-sensitive adhesive sheets 1A and 1B, but is usually in the range of 5 to 100 μm, preferably 10 to 60 μm, for example, for optical members, particularly for polarizing plates. When used as a PSA layer, it is preferably 10 to 50 μm, particularly preferably 10 to 30 μm.

  There is no restriction | limiting in particular as the base material 13, What was used as a base material sheet of a normal adhesive sheet can be used. For example, in addition to desired optical members, woven or non-woven fabrics using fibers such as rayon, acrylic, polyester, etc .; papers such as fine paper, glassine paper, impregnated paper, coated paper; metal foils such as aluminum and copper; urethane Foams, foams such as polyethylene foams; polyester films such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, cellulose films such as triacetyl cellulose, polyurethane films, polyethylene films, polypropylene films, polyvinyl chloride films, polychlorinated Vinylidene film, polyvinyl alcohol film, ethylene-vinyl acetate copolymer film, polystyrene film, polycarbonate film, acrylic resin film, norbornene resin film, cycloolefin resin Plastic films such as Irumu; and the like of two or more kinds of those laminates. The plastic film may be uniaxially stretched or biaxially stretched.

  Examples of the optical member include a polarizing plate (polarizing film), a polarizer, a retardation plate (retarding film), a viewing angle compensation film, a brightness enhancement film, a contrast enhancement film, and a liquid crystal polymer film. Among these, since the polarizing plate (polarizing film) easily shrinks and has a large dimensional change, it is suitable as a target for forming the pressure-sensitive adhesive of the present embodiment (the pressure-sensitive adhesive layer 11) from the viewpoint of light leakage resistance.

  Although the thickness of the base material 13 changes with kinds, for example in the case of an optical member, they are 10 micrometers-500 micrometers normally, Preferably they are 50 micrometers-300 micrometers.

  As the release sheets 12, 12a, 12b, for example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, Polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene / (meth) acrylic acid copolymer film, ethylene / (meth) acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film A fluororesin film or the like is used. These crosslinked films are also used. Furthermore, these laminated films may be sufficient.

  The release surface of the release sheet (particularly the surface in contact with the pressure-sensitive adhesive layer 11) is preferably subjected to a release treatment. Examples of the release agent used for the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax release agents.

  Although there is no restriction | limiting in particular about the thickness of the peeling sheets 12, 12a, 12b, Usually, it is about 20-150 micrometers.

In order to manufacture the pressure-sensitive adhesive sheet 1A, a solution (coating solution) containing the pressure-sensitive adhesive composition is applied to the release surface of the release sheet 12, and heat treatment is performed to form the pressure-sensitive adhesive layer 11. A base material 13 is laminated on the agent layer 11. Then, it is preferable to provide a curing period.
In addition, about the conditions of heat processing and curing, it is as having mentioned above.

  Moreover, in order to manufacture the said adhesive sheet 1B, the coating solution containing the said adhesive composition is apply | coated to the peeling surface of one peeling sheet 12a (or 12b), heat processing is performed, and the adhesive layer 11 is formed. After that, the release surface of the other release sheet 12b (or 12a) is overlaid on the adhesive layer 11.

  As a method for applying the coating solution, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, or the like can be used.

  Here, for example, to manufacture a liquid crystal display device composed of a liquid crystal cell and a polarizing plate, a polarizing plate is used as the base material 13 of the pressure-sensitive adhesive sheet 1A, and the release sheet 12 of the pressure-sensitive adhesive sheet 1A is peeled off. What is necessary is just to bond the exposed adhesive layer 11 and a liquid crystal cell.

  For example, in order to manufacture a liquid crystal display device in which a retardation plate is disposed between a liquid crystal cell and a polarizing plate, as an example, first, one release sheet 12a (or 12b) of the adhesive sheet 1B is released. Then, the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet 1B and the phase difference plate are bonded together. Next, the release sheet 12 of the pressure-sensitive adhesive sheet 1A using a polarizing plate as the base material 13 is peeled off, and the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet 1A and the retardation plate are bonded. Furthermore, the other release sheet 12b (or 12a) is peeled from the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet B, and the pressure-sensitive adhesive layer 11 exposed from the pressure-sensitive adhesive sheet B is bonded to the liquid crystal cell.

  According to the above pressure-sensitive adhesive sheets 1A and 1B, since the pressure-sensitive adhesive layer 11 is very excellent in stress relaxation properties, even when applied to adhesion of a polarizing plate, for example, the stress that can be generated by deformation of the polarizing plate is applied to the pressure-sensitive adhesive layer 11. It can be assumed that excellent light leakage resistance and high durability can be exhibited.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, the release sheet 12 of the adhesive sheet 1A may be omitted, or one of the release sheets 12a and 12b in the adhesive sheet 1B may be omitted.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further more concretely, the scope of the present invention is not limited to these Examples etc.

[Example 1]
1. Preparation of polymer (A) In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device and a nitrogen introducing tube, 97.0 parts by mass of n-butyl acrylate, 3.0 parts by mass of acrylic acid, ethyl acetate 200 parts by mass and 0.02 parts by mass of 2,2′-azobisisobutyronitrile were charged, and the air in the reaction vessel was replaced with nitrogen gas. While stirring in this nitrogen atmosphere, the reaction solution was heated to 60 ° C., reacted for 16 hours, and then cooled to room temperature. Here, a part of the obtained solution was subjected to GPC measurement by a method described later, and production of a polymer (A) having a weight average molecular weight of 1,500,000 was confirmed.

2. Preparation of polymer (B) In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device and a nitrogen introduction tube, 85.0 parts by mass of n-butyl acrylate, 15.0 masses of 2-hydroxyethyl acrylate Part, 200 parts by mass of ethyl acetate, 0.16 parts by mass of 2,2′-azobisisobutyronitrile, and 0.3 parts by mass of 2-mercaptoethanol were charged, and the air in the reaction vessel was replaced with nitrogen gas. . While stirring in this nitrogen atmosphere, the reaction solution was heated to 70 ° C., reacted for 6 hours, and then cooled to room temperature. Here, GPC measurement was performed on a part of the obtained solution by a method described later, and the production of a polymer (B) having a weight average molecular weight of 60,000 was confirmed.

3. Preparation of Adhesive Composition 100 parts by mass (solid value converted value) of the polymer (A) obtained in the step (1) and 15 parts by mass (solid) of the polymer (B) obtained in the step (2). And a tolylene diisocyanate (TDI-based) adduct of trimethylolpropane in an amount corresponding to 0.6 equivalent of the hydroxyl group of the polymer (B) as a cross-linking agent (C). (Product name, “Coronate L”) 2.21 parts by mass. Finally, as a silane coupling agent (D), 0.2 part by mass of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KBM403”) is added, and the mixture is sufficiently stirred, thereby allowing adhesion. A diluted solution of the sex composition was obtained.

Here, Table 1 shows the composition of the adhesive composition. Details of the abbreviations and the like described in Table 1 are as follows.
[Polymers (A) and (B)]
BA: n-butyl acrylate AA: acrylic acid HEA: 2-hydroxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate
[Plasticizer]
Adeka Sizer C-8: Trimellitic acid ester plasticizer (Tris (2-ethylhexyl) trimellitate) (trade name “Adeka Sizer C-8” manufactured by Asahi Denka Kogyo Co., Ltd.)
[Crosslinking agent (C)]
・ Isocyanate-based cross-linking agent Coronate L: Tolylene diisocyanate adduct of trimethylolpropane (trade name “Coronate L” manufactured by Nippon Polyurethane Co., Ltd.)
Takenate D-110N: xylene diisocyanate adduct of trimethylolpropane (trade name “Takenate D-110N” manufactured by Mitsui Chemicals Polyurethanes)
Epoxy-based crosslinking agent TETRAD-X: N, N, N ′, N′-tetraglycidyl-m-xylylenediamine (trade name “TETRAD-X” manufactured by Mitsubishi Gas Chemical Company, Inc.)
[Silane coupling agent (D)]
KBM403: 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KBM403”)
KBE9007: 3-isocyanatopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KBE9007”)

  After drying the diluted solution of the obtained adhesive composition on the release-treated surface of a release sheet (SP-PET3811, thickness: 38 μm, manufactured by Lintec Co., Ltd.) obtained by releasing one side of a polyethylene terephthalate film with a silicone-based release agent After coating with a knife coater so that the thickness of the adhesive layer became 25 μm, a pressure-sensitive adhesive layer was formed by heat treatment at 90 ° C. for 1 minute.

  Next, a polarizing plate made of a polarizing film with a discotic liquid crystal layer and integrated with a polarizing film and a viewing angle widening film is bonded so that the pressure-sensitive adhesive layer and the discotic liquid crystal layer are in contact with each other at 23 ° C., 50%. A polarizing plate with an adhesive layer was obtained by curing with RH for 7 days.

[Examples 2 to 13, Comparative Examples 1 to 5]
Table 1 shows the types and ratios of the respective monomers constituting the adhesive composition, the types and addition amounts of the plasticizer, the crosslinking agent and the silane coupling agent, and the blending ratio of the polymer (A) and the polymer (B). A polarizing plate with a pressure-sensitive adhesive layer was produced in the same manner as in Example 1 except that the above was changed.

Here, the above-mentioned weight average molecular weight (Mw) is a polystyrene-reduced weight average molecular weight measured under the following conditions (GPC measurement) using gel permeation chromatography (GPC).
<Measurement conditions>
GPC measurement device: manufactured by Tosoh Corporation, HLC-8020
GPC column (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (× 2)
TSK gel G2000HXL
・ Measurement solvent: Tetrahydrofuran ・ Measurement temperature: 40 ° C.

[Test Example 1] (Measurement of gel fraction)
Instead of the polarizing plate used for the production of the polarizing plate with the pressure-sensitive adhesive layer in the examples or comparative examples, a release sheet obtained by peeling one side of the polyethylene terephthalate film with a silicone release agent (manufactured by Lintec Corporation, SP-PET 3801, thickness) S: 38 μm) was used to prepare an adhesive sheet. Specifically, the release sheet is subjected to a release treatment on the exposed adhesive layer of the release sheet / adhesive layer (thickness: 25 μm) obtained in the production process of the example or the comparative example. The layers were laminated so that the surface side was in contact. Thereby, the adhesive sheet which consists of a structure of a peeling sheet / adhesive layer / release sheet was produced.

  The obtained pressure-sensitive adhesive sheet was cured for 7 days under the conditions of 23 ° C. and 50% RH. Thereafter, the pressure-sensitive adhesive sheet was sampled to a size of 80 mm × 80 mm, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200), and the mass of the pressure-sensitive adhesive alone was weighed with a precision balance. The mass at this time is M1.

  Next, the pressure-sensitive adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23 ° C.) for 24 hours. Thereafter, the pressure-sensitive adhesive was taken out, air-dried for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 50%, and further dried in an oven at 80 ° C. for 12 hours. The mass of only the pressure-sensitive adhesive after drying was weighed with a precision balance. The mass at this time is M2. The gel fraction (%) is represented by (M2 / M1) × 100. The results are shown in Table 2.

[Test Example 2] (Measurement of optical performance)
As a measurement sample, an adhesive sheet (cured for 7 days) similar to the adhesive sheet used for measuring the gel fraction was prepared. About the adhesive layer of the said adhesive sheet, the haze value (%) (it may abbreviate to Hz (%)) was measured according to JISK7105 using the haze meter (Nippon Denshoku Industries Co., Ltd. make, NDH2000). . The results are shown in Table 2. In addition, the range of a preferable haze value is 0 to 5%.

[Test Example 3] (Durability evaluation)
The pressure-sensitive adhesive layer-attached polarizing plate obtained in Examples or Comparative Examples was adjusted to a size of 233 mm × 309 mm using a cutting device (Super cutter manufactured by Hadano Seisakusho, PN1-600). The release sheet was peeled off and attached to alkali-free glass (Corning Corp., Eagle XG) through the exposed adhesive layer, and then pressurized at 0.5 MPa and 50 ° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho.

Then, it put into the environment of 80 degreeC dry durability conditions, and observed using the 10 time magnifier 500 hours later. Appearance change was based on the following. The results are shown in Table 2.
A: No defects on 4 sides. O: No defects on the sides of 0.6 mm or more from the outer peripheral edge on 4 sides. X: 0.6 mm or more from the outer edge on at least one side of the four sides. There are abnormal appearance defects of adhesives of 0.1 mm or more such as floating, peeling, foaming, streaks

[Test Example 4] (Light leakage test)
The pressure-sensitive adhesive layer-attached polarizing plate obtained in Examples or Comparative Examples was adjusted to a size of 233 mm × 309 mm using a cutting device (Super cutter manufactured by Hadano Seisakusho, PN1-600). The release sheet was peeled off and attached to alkali-free glass (Corning Corp., Eagle XG) through the exposed adhesive layer, and then pressurized at 0.5 MPa and 50 ° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho. In addition, the said bonding was performed on the front and back of non-alkali glass so that the polarizing axis may be in a crossed nicols state (polarizing axis: ∠45 °, ∠135 °). In this state, it was allowed to stand for 250 hours in an 80 ° C. dry environment, and then left for 2 hours in an environment of 23 ° C. and 50% RH. Using this as a sample, light leakage was evaluated by the following method. The results are shown in Table 2.

<Evaluation of light leakage: ΔL ^* >
Using the MCPD-2000 manufactured by Otsuka Electronics Co., Ltd., the lightness L ^{* of} each region shown in FIG. 3 in the above sample was measured, and the lightness difference ΔL ^* was expressed by the formula ΔL ^* = [(b + c + d + e) / 4] −a
(Where a, b, c, d, and e are the lightness values at predetermined measurement points (one central portion of each region) in the A region, B region, C region, D region, and E region, respectively. ) To obtain light leakage. A smaller value of ΔL ^* indicates less light leakage. Note that L ^* max indicates the maximum brightness in all the above regions.

<Evaluation of light leakage: visual inspection>
The sample was placed on a flat illuminator (Dentsu Sangyo Co., Ltd., HF-SL-A312LC, illuminance: 26,000 Lux, luminance: 10,000 cd), and a two-dimensional color luminance meter (Konica Minolta, CA-2000). ) And converted into a luminance distribution image by analysis software (Konica Minolta, CA-S20w). The luminance distribution image of the obtained sample was evaluated based on the evaluation criteria shown in FIG.

[Test Example 5] (Tensile test)
The adhesive composition prepared in Examples and Comparative Examples has a coating thickness after drying on the release treatment surface of a release sheet (SP-PET3811, manufactured by Lintec Co., Ltd.) obtained by releasing one side of a polyethylene terephthalate film with a silicone release agent. It apply | coated so that it might become 25 micrometers, and it heated at 100 degreeC for 1 minute, and formed the adhesive layer. The pressure-sensitive adhesive layer was bonded to a release surface of another release sheet (SP-PET 3801, manufactured by Lintec Co., Ltd.) obtained by releasing one side of the polyethylene terephthalate film with a silicone-based release agent to obtain an adhesive sheet.

  A plurality of the pressure-sensitive adhesive layers are laminated so that the total thickness of the pressure-sensitive adhesive layers in the pressure-sensitive adhesive sheet is 500 μm, and only the outermost release sheet of the laminate remains, and an atmosphere of 23 ° C. and 50% RH Left under for 2 weeks. Thereafter, a 10 mm wide × 75 mm long sample is cut out from the pressure sensitive adhesive sheet in which a plurality of the pressure sensitive adhesive layers are laminated, and the release sheet laminated on the outermost layer of the laminate is peeled off so that the sample measurement range becomes 10 mm wide × 20 mm long. A sample is set in the sample and stretched in the length direction at a tensile rate of 200 mm / min using a tensile tester (Orientec, Tensilon) in an environment of 23 ° C. and 50% RH, and 100 seconds at 900% elongation. The stress (N) after holding for 300 seconds or 1200 seconds and the stress (N) immediately after 900% elongation were measured. From these measurement results, the stress relaxation rate (%) after holding the adhesive for 100 seconds and the stress relaxation rate (%) after holding for 300 seconds were calculated. The results are shown in Table 2.

  As is clear from Table 2, in the polarizing plate with the pressure-sensitive adhesive layer obtained in Examples, the stress relaxation rate after holding for 300 seconds when the pressure-sensitive adhesive is 900% elongated is 60% or more, and durability and light resistance Both leaks were excellent. On the other hand, in the polarizing plate with the pressure-sensitive adhesive layer obtained in the comparative example, the stress relaxation rate after holding for 300 seconds at 900% elongation of the pressure-sensitive adhesive is less than 60%, and both durability and light leakage resistance are both or any. Either was inferior.

  The pressure-sensitive adhesive of the present invention is suitable for adhesion of optical members such as polarizing plates and retardation plates, and the pressure-sensitive adhesive sheet of the present invention is suitable as a pressure-sensitive adhesive sheet for optical members such as polarizing plates and retardation plates. is there.

1A, 1B ... Adhesive sheet 11 ... Adhesive layer 12, 12a, 12b ... Release sheet 13 ... Base material

Claims (7)

A first (meth) acrylic acid ester polymer (A) having a weight average molecular weight of 500,000 to 3,000,000,
A component obtained by crosslinking the second (meth) acrylic acid ester polymer (B) having a weight average molecular weight of 8000 to 300,000,
The stress relaxation rate after stretching by 900% in the tensile test and holding for 300 seconds is 60% or more,
A pressure-sensitive adhesive having a gel fraction of 30 to 90%.   The ratio of the second (meth) acrylic acid ester polymer (B) to 100 parts by mass of the first (meth) acrylic acid ester polymer (A) is 5 to 50 parts by mass. The pressure-sensitive adhesive according to claim 1.   The second (meth) acrylic acid ester polymer (B) before crosslinking contains a reactive functional group-containing monomer in an amount of more than 1% by mass and less than 50% by mass as a constituent component. The pressure-sensitive adhesive according to 1 or 2.   The second (meth) acrylic acid ester polymer (B) is crosslinked by a reaction with a crosslinking agent (C) having a crosslinking group capable of reacting with the reactive functional group. Item 4. The pressure-sensitive adhesive according to item 3. A pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer,
The said adhesive layer consists of an adhesive as described in any one of Claims 1-4, The adhesive sheet characterized by the above-mentioned.   The pressure-sensitive adhesive sheet according to claim 5, wherein the base material is an optical member. Two release sheets,
An adhesive sheet comprising an adhesive layer sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets,
The said adhesive layer consists of an adhesive as described in any one of Claims 1-4, The adhesive sheet characterized by the above-mentioned.

Images