JP4682296B2 - Adhesive sheet - Google Patents

Description

  The present invention relates to an adhesive sheet. More specifically, the present invention relates to a pressure-sensitive adhesive sheet excellent in adhesive strength, antistatic performance, transparency, and durability.

  In the process of sticking the polarizing plate having the pressure-sensitive adhesive layer to the liquid crystal panel, there is a problem that the liquid crystal operates after sticking due to charging of the sticking polarizing plate. Such charging of the polarizing plate mainly occurs when the peeling substrate is peeled from the pressure-sensitive adhesive layer provided on the polarizing plate. In contrast, measures such as kneading an antistatic agent into the release substrate have been taken, but such measures alone do not provide a sufficient effect, and the adhesive layer also has antistatic performance. It is required to be granted.

  As an adhesive composition having antistatic performance, an adhesive composition containing an antistatic agent such as a surfactant is known. Thus, when an antistatic agent such as a surfactant is added to the adhesive composition, the antistatic performance is imparted, but the compatibility between the surfactant and the adhesive polymer is poor. When the layer is formed, the surfactant bleeds over time or under heat or wet heat conditions, and there are problems such as contamination of the adherend and decrease in adhesive strength.

  On the other hand, Patent Document 1 discloses a chargeable pressure-sensitive adhesive containing an organic salt having a polyoxyalkylene structure as an antistatic agent for the purpose of improving the compatibility between the antistatic agent and the adhesive polymer. Has been.

  However, the organic salt having the polyoxyalkylene structure is still not sufficient with respect to the compatibility with the acrylic polymer mainly used for sticking a polarizing plate, etc. There was a risk that the organic salt would bleed and cause peeling. In addition, when organic salts are used, there is a problem that odor may remain.

  Also, by using a polymer having a polyoxyalkylene structure and bonding it to the main polymer in the pressure-sensitive adhesive by crosslinking or grafting, the anti-static agent bleed is suppressed, and the anti-static property is good for the pressure-sensitive adhesive layer. Some attempts have been made to grant this.

  For example, Patent Document 2 discloses that a (meth) acrylic polymer, a radiation polymerizable compound, a radiation polymerization initiator, a polyisocyanate crosslinking agent, and an antistatic agent (a composite of polyalkylene glycol and lithium perchlorate). The adhesive sheet for semiconductor processing obtained from the body is disclosed.

  However, since the adhesive sheet for semiconductor processing is intended for temporary adhesion and re-peeling for the convenience of the semiconductor processing process, it is not expected to be used for a long period of time such as for polarizing plates. For use in applications, the durability during heat and wet heat is poor and the adhesive strength is not sufficient.

Furthermore, it is desirable that the pressure-sensitive adhesive layer provided on the polarizing plate has excellent transparency even during wet heat so as not to impair the optical properties of the polarizing plate. According to the above-mentioned patent document 2, the combination of a specific (meth) acrylic polymer, a polyisocyanate crosslinking agent, and an antistatic agent (a complex of polyalkylene glycol and lithium perchlorate). In the pressure-sensitive adhesive layer obtained from the above, dullness was generated at the time of wet heat, and the optical characteristics of the polarizing plate might be hindered (see Comparative Example 12).

  Patent Document 3 discloses a conductive structure obtained by adding an ionic compound and a solvent to a graft copolymer obtained from a mixture containing a monomer having a dissociative functional group and a polyalkylene oxide compound to form a crosslinked structure. An adhesive is disclosed.

  However, the conductive pressure-sensitive adhesive is used for an electrode pad used as a contact medium with the surface of a living body, and has a short adhesion period and is immediately peeled off after use. Is not envisaged, and for use in such applications, the durability during heat and wet heat is poor and the adhesive strength is not sufficient.

Therefore, it goes without saying that it has antistatic performance, and further has a pressure-sensitive adhesive layer having durability and adhesive strength suitable for long-term use such as a polarizing plate, and preferably also has transparency during wet heat. The advent of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer and a polarizing plate has been strongly desired.
Special Table 2004-536940 JP 2002-285134 A JP-A-8155040

  The present invention provides an adhesive layer having antistatic performance and durability and adhesive strength suitable for long-term use such as for polarizing plates, and more preferably also having transparency during wet heat It aims at providing the adhesive sheet which has a layer.

  Furthermore, this invention also makes it the subject to provide the polarizing plate which has this adhesive layer.

The pressure-sensitive adhesive sheet according to the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one surface of a support, and the pressure-sensitive adhesive layer contains the following (A), (B), and (C). And (A) (a1) 0.3 to 5% by weight of a hydroxyl group-containing monomer and (a2) a carboxyl group, wherein the adhesive sheet has an adhesive strength of 400 g / 25 mm or more. 0 to 0.01% by weight of a monomer containing at least one of an amino group and an amide group, and (a3) substituted and / or unsubstituted alkyl (meth) acrylates other than (a1) and (a2) 95 to
The number average molecular weight having (B) a polyoxyalkylene structure and a hydroxyl group with respect to 100 parts by weight of a (meth) acrylic polymer having a weight average molecular weight of 1,000,000 or more obtained by copolymerization with 99.7% by weight 0.1 to 2 parts by weight of an antistatic agent obtained by blending an ionic substance with 300 to 1500 polymers, and 0.03 to 1 part by weight of (C) an isocyanate crosslinking agent.

  The ionic substance is at least one selected from the group consisting of alkali metal salts of perchloric acid, alkaline earth metal salts of perchloric acid, alkali metal salts of organic boron complexes, and alkaline earth metal salts of organic boron complexes. Preferably it is a seed.

The surface resistance value of the pressure-sensitive adhesive sheet is preferably 10 ¹² Ω / □ or less.
Furthermore, the haze value of the pressure-sensitive adhesive sheet is preferably 2% or less.
Moreover, in the adhesive sheet of this invention, it is desirable that the said support body is a polarizing plate.

According to the pressure-sensitive adhesive sheet of the present invention, durability and pressure-sensitive adhesiveness suitable for long-term use such as antistatic performance, polarizing plate applications, and transparency during wet heat can also be realized. Therefore, when the pressure-sensitive adhesive sheet of the present invention is used for a polarizing plate, it does not cause problems such as operating the liquid crystal even if it is attached to a liquid crystal panel, and the optical properties of the polarizing plate itself may be hindered. And suitable for long-term use.

Hereinafter, the present invention will be specifically described.
The pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer obtained from a specific pressure-sensitive adhesive composition on at least one surface of a support.

First, the pressure-sensitive adhesive composition will be described, and then the pressure-sensitive adhesive sheet will be described.
<Adhesive composition>
First, (A) a (meth) acrylic polymer having a weight average molecular weight of 1 million or more and (B) a polymer having a number average molecular weight of 300 to 1500 having a polyoxyalkylene structure and a hydroxyl group contained in the pressure-sensitive adhesive composition are ionic. The antistatic agent, (C) isocyanate-based crosslinking agent, etc. formed by blending substances will be described.

≪ (A) (Meth) acrylic polymer≫
As the (meth) acrylic polymer that can be used in the present invention, the following monomers (a1) and (a3) are essential, and if necessary, the monomers (a2) and (a4) can be used in specific amounts. Examples thereof include polymers obtained by copolymerization.

  From the point of improving the durability at the time of heat and wet heat of the pressure-sensitive adhesive layer obtained by preparing a pressure-sensitive adhesive composition containing the polymer and removing the solvent from the pressure-sensitive adhesive composition, The weight average molecular weight is preferably 1,000,000 or more, and more preferably in the range of 1.3 million to 1.8 million. When the weight average molecular weight is 1,000,000 or more, preferably within the above range, the cohesive force of the pressure-sensitive adhesive layer is improved, and durability during heat and wet heat, specifically, foaming and adhesion of the pressure-sensitive adhesive layer. The streaky float at the end of the pressure-sensitive adhesive layer when adhered to the body, peeling, etc. can be improved.

  In the present specification, the weight average molecular weight is determined in terms of polystyrene by gel permeation chromatography (GPC), and the number average molecular weight is calculated from the hydroxyl value obtained by end group quantification, specifically by titration. Is done.

  The (meth) acrylic polymer can be produced by copolymerization by a known method. Although it is not particularly limited, for example, after introducing a monomer described later into a reaction solvent and replacing the air in the reaction system with an inert gas such as nitrogen gas, polymerization is performed by heating and stirring in the presence of a reaction initiator if necessary. It can be produced by reacting.

  As the reaction solvent used here, an organic solvent is used. Specifically, aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as n-hexane, and esters such as ethyl acetate and butyl acetate. And aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol, and ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone.

  Further, when a reaction initiator is used, for example, azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, and the like can be used as the reaction initiator.

The reaction temperature of the above polymerization reaction is usually 50 to 90 ° C., and the reaction time is usually 2 to 20 hours, preferably 4 to 12 hours. The reaction solvent is used in an amount of 50 to 300 parts by weight with respect to 100 parts by weight of the total amount of monomers, and the reaction initiator is usually used in an amount of 0.01 to 10 parts by weight.

  In the above reaction, each monomer can be blended corresponding to the amount of each repeating unit in the (meth) acrylic polymer to be obtained, and specifically, it can be used in a specific amount described later. desirable.

(a1) Hydroxyl-containing monomer Specific examples of the hydroxyl-containing monomer that can be used in the synthesis of the (meth) acrylic polymer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4- Hydroxyalkyl (meth) acrylates such as hydroxybutyl (meth) acrylate; halogenated hydroxyalkyl (meth) acrylates such as chloro-2-hydroxypropyl (meth) acrylate; diethylene glycol mono (meth) acrylate, and allyl alcohol . These may be used alone or in combination of two or more. Among these, hydroxyalkyl (meth) acrylates are described below in view of copolymerization with (a3) substituted and / or unsubstituted alkyl (meth) acrylates and reactivity with (C) isocyanate-based crosslinking agents. Is preferred, and 4-hydroxybutyl (meth) acrylate is more preferred.

  These hydroxyl group-containing monomers are usually 0.3 to 5% by weight, preferably 1 to 3% by weight when the total amount of monomers used for copolymerization is 100% by weight. It is subjected to copolymerization to obtain a polymer. When a hydroxyl group-containing monomer is used in an amount within the above range, the obtained (meth) acrylic polymer reacts with the (C) isocyanate crosslinking agent described later to form a three-dimensional crosslinked structure. By expressing the cohesive force, foaming at the time of heat and wet heat, streaky floating at the end, peeling and the like can be suppressed. If the cohesive force is insufficient, foaming or streaky floating at the end occurs during heat and wet heat, and excessive cohesion may cause peeling during heat and wet heat.

In the present specification, compounds having a hydroxyl group, a carboxyl group, an amino group, and an amide group are classified not as the component (a1) but as the component (a2) described later.
(a2) A monomer containing at least one of a carboxyl group, an amino group, and an amide group As a monomer containing at least one of a carboxyl group, an amino group, and an amide group that can be used for the synthesis of the (meth) acrylic polymer. ,In particular,
Unsaturated monocarboxylic acids such as (meth) acrylic acid, β-carboxyethyl acrylate, crotonic acid, α-methyl crotonic acid, α-ethyl crotonic acid, isocrotonic acid, tiglic acid and ungeric acid; fumaric acid, itaconic acid, malee Carboxyl group-containing monomers represented by unsaturated carboxylic acids such as acids, citraconic acid, mesaconic acid, glutaconic acid and hydromuconic acid;
Amino group-containing monomers such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate,
Amide group-containing monomers such as (meth) acrylamide, dimethyl (meth) acrylamide, diethyl (meth) acrylamide,
Examples thereof include monomers containing a combination of a carboxyl group, amino group, and amide group such as dimethylaminopropyl (meth) acrylamide.

These monomers can be used alone or in combination of two or more.
These monomers containing at least one of a carboxyl group, an amino group, and an amide group are combined with the components (a1) and (a3) as well as the component (a4) used as necessary, as described above (meta ) It may be subjected to copolymerization to obtain an acrylic polymer. Specifically, when the total amount of monomers used for copolymerization is 100% by weight, it may be usually used in an amount of 0 to 0.01% by weight, but it is preferably not used. If it exceeds the upper limit, the surface resistance value may increase.

(a3) Substituted and / or unsubstituted alkyl (meth) acrylate Substituted and / or unsubstituted alkyl (meth) acrylates other than the above (a1) and (a2) that can be used for the synthesis of the above (meth) acrylic polymers As (a3), the above (a1) and (a2)
Substituted and / or unsubstituted alkyl (meth) acrylates. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meta ) Acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, etc .; methoxyethyl (meth) acrylate and ethoxy Alkoxy (meth) acrylates such as ethyl (meth) acrylate, butoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate; It can gel.

  These monomers may be used alone or in combination of two or more so that the glass transition point (Tg) of the resulting (meth) acrylic polymer is 0 ° C. or lower, preferably −20 ° C. or lower. Among these, it is preferable to use a combination of alkyl acrylate and alkoxyalkyl (meth) acrylate from the viewpoint of reducing the surface resistance value and improving the adhesive strength, and n-butyl acrylate and methoxyethyl A combination with (meth) acrylate is more preferred.

These substituted and / or unsubstituted alkyl (meth) acrylates can be subjected to copolymerization to obtain the (meth) acrylic polymer as a main monomer component. Specifically, when the total amount of monomers used for copolymerization is 100% by weight, the amount is usually 95 to 99.7% by weight, preferably 97 to 99% by weight.

(a4) Other monomer In addition, when manufacturing the said (A) (meth) acrylic-type polymer, you may use other monomers other than said (a1)-(a3) as needed. Such other monomers include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene and octyl styrene, fluorostyrene, chlorostyrene, Examples thereof include styrene monomers such as bromostyrene, dibromostyrene and iodostyrene nitrostyrene, acetylstyrene and methoxystyrene; vinyl monomers such as vinylpyrrolidone, vinylcarbazole, divinylbenzene, vinyl acetate and acrylonitrile. These monomers can be used alone or in combination of two or more.

The other monomer (a4) can be used in an amount within a range not impairing the effects of the present invention.
≪ (B) Antistatic agent≫
Examples of the antistatic agent that can be used in the present invention include an antistatic agent obtained by blending an ionic substance with a polymer having a polyoxyalkylene structure and a hydroxyl group and having a number average molecular weight of 300 to 1,500.

Examples of the polymer constituting the antistatic agent include polymers having a polyoxyalkylene structure and having a hydroxyl group at the end of the polymer chain. Specific examples include polyethylene glycol, polypropylene oxide, poly (ethylene glycol / propylene oxide) copolymer, and the like. Of these, poly (ethylene glycol / propylene oxide) copolymers are preferred.

  The ionic substance to be blended in the polymer comprises an alkali metal salt of perchloric acid, an alkaline earth metal salt of perchloric acid, an alkali metal salt of an organic boron complex, and an alkaline earth metal salt of an organic boron complex. There may be mentioned at least one selected from the group.

Examples of the alkali metal include lithium, sodium, and potassium, and examples of the alkaline earth metal include magnesium.
Among these, lithium salts are preferable and lithium perchlorate is more preferable because of low energy at the time of ion dissociation and high ion mobility.

  When these ionic substances are blended in the polymer, they are stabilized in a state of solvation and ionic dissociation by ether oxygen in the polyoxyalkylene chain. The dissociated cations and anions are easily moved by the molecular vibration of the polyoxyalkylene chain. Therefore, when an electric field is applied from the outside, the cations and anions move toward the electrodes having opposite charges. In this way, the cation and the anion move to express ionic conductivity and can function as an antistatic agent.

It is desirable that the ionic substance is blended in the total amount of the antistatic agent in an amount of usually 5 to 50% by weight, preferably 10 to 30% by weight.
Since the polymer has a hydroxyl group at the polymer chain end, it is bonded to the (A) (meth) acrylic polymer via a crosslinked structure by using the (C) isocyanate-based crosslinking agent described later. Can be made. Therefore, the antistatic agent does not bleed.

In this case as well, as described above, it is considered that the polymer holds cations and anions in a dissociated state.
The number average molecular weight of the polymer constituting the antistatic agent is usually 300 to 1500, and preferably 800 to 1300. When the number average molecular weight is within the above range, the compatibility with the above-mentioned (A) (meth) acrylic polymer is good. Therefore, the (A) (meth) acrylic polymer and (C) isocyanate-based crosslinking agent. At the same time, when the pressure-sensitive adhesive composition is prepared and the pressure-sensitive adhesive layer is formed by removing the solvent from the pressure-sensitive adhesive composition, the haze value is reduced even during wet heat, and the transparency is excellent. Such excellent transparency is suitable for optical applications such as polarizing plates. On the other hand, when the number average molecular weight of the polymer constituting the antistatic agent is smaller than the above range, the crosslinking is inhibited, the cohesive force is lowered, and the durability during heat and wet heat may be inferior.

Specifically, for example, PEL-20A (manufactured by Nippon Carlit Co., Ltd.) that is commercially available as an ion conductive polymer can be used as the antistatic agent.
The antistatic agent is usually 0.1 to 2 parts by weight, preferably 0.15 to 1 part by weight, based on 100 parts by weight of the (A) (meth) acrylic polymer. Used for things.

When the antistatic agent is used in an amount within the above range, the surface resistance value of the pressure-sensitive adhesive layer can be lowered to a suitable value when the pressure-sensitive adhesive layer is formed from the obtained pressure-sensitive adhesive composition. In addition, when (C) an isocyanate-based crosslinking agent is used, crosslinking is not inhibited, so that the polymer in the antistatic agent is not present in a free state and is in a state of being bonded to (A) (meth) acrylic polymer. Since it exists, the cohesive force and adhesive force of an adhesive layer are not reduced.

≪ (C) Isocyanate-based crosslinking agent≫
Specific examples of the isocyanate-based crosslinking agent that can be used in the present invention include toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, hydrogenated xylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, and tetramethyl. Examples thereof include xylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, and adducts of these with polyols such as trimethylolpropane (for example, trimethylolpropane-added xylene diisocyanate).

  The isocyanate-based crosslinking agent is usually contained in an amount of 0.03 to 1 part by weight, preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the (A) (meth) acrylic polymer. Used in pressure-sensitive adhesive compositions.

  When the isocyanate-based crosslinking agent is used in an amount within the above range, when the pressure-sensitive adhesive layer is formed from the obtained pressure-sensitive adhesive composition, the cohesive force can be improved by crosslinking and the durability can be improved.

≪ (D) Others≫
In the pressure-sensitive adhesive composition, as other components other than the above components (A) to (C), various conventionally known additives such as tackifiers, plasticizers, and the like in amounts within the range not impairing the effects of the present invention. You may mix | blend a softener, dye, a pigment, a silane coupling agent, an inorganic filler, etc. As said other component, a well-known component can be mix | blended individually by 1 type or in combination of 2 or more types.

≪Manufacture of adhesive composition≫
The pressure-sensitive adhesive composition contains at least (A) a (meth) acrylic polymer having a weight average molecular weight of 1 million or more, (B) an antistatic polymer, and (C) an isocyanate-based crosslinking agent in specific amounts. However, the (A) (meth) acrylic polymer is usually obtained as a solution or dispersion containing 15 to 70% by weight in the reaction solvent by the reaction described above.

  Therefore, after removing the solvent from the dispersion, the obtained (A) (meth) acrylic polymer can be mixed with other components. However, the reaction solvent can be dispersed in the reaction solvent without removing the reaction solvent. It is preferable to mix the (A) (meth) acrylic polymer and the other components in a state where they are in a dry state. In general, the (A) (meth) acrylic polymer obtained as described above is stably dispersed in a reaction solvent, and by using such a dispersion as it is, the respective components are uniformly mixed. Because it can.

(A) The mixing method of the (meth) acrylic polymer and other components is not particularly limited, and a known method can be employed. In addition, since (C) isocyanate type crosslinking agent has reactivity with (A) (meth) acrylic-type polymer and (B) antistatic agent, it is preferable to mix just before coating.
<Adhesive sheet, polarizing plate>
A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one side of the support can be obtained by applying the pressure-sensitive adhesive composition obtained as described above onto at least one side of the support and removing the solvent. .

  Specific examples of the support include a polyester film, a polyester film coated with a release agent such as silicone resin and provided with a release agent layer, and a known polarizing plate. The support usually has a thickness of 4 to 200 μm.

  The method for forming the pressure-sensitive adhesive layer on the support is not particularly limited, and the above-mentioned pressure-sensitive adhesive composition is applied to the support with a doctor blade, knife coater, comma coater, reverse roll coater or gravure coater, and the solvent is added. By removing, the pressure-sensitive adhesive layer may be provided on one side or both sides of the support, and the pressure-sensitive adhesive layer is coated on the support by previously applying the pressure-sensitive adhesive composition to another support by the above-mentioned means. Then, the pressure-sensitive adhesive layer may be transferred onto an original support using a laminator roll or the like.

In this way, a pressure-sensitive adhesive sheet can be obtained by forming a pressure-sensitive adhesive layer having a thickness of usually 5 to 100 μm, preferably 10 to 50 μm on the support.
The obtained adhesive sheet has suitable adhesive force, surface resistance value, haze, and durability.

Specifically, the adhesive strength measured in accordance with the procedures of the following examples is usually 400 g / 25 mm or more, preferably 400 to 700 g / 25 mm.
Further, the surface resistance value of the pressure-sensitive adhesive layer measured in accordance with the procedure of the following examples is usually 10 ¹² Ω / □ or less, preferably 10 ⁹ to 10 ¹¹ Ω / □.

Furthermore, it is desirable that the haze value obtained according to the procedure of the following examples is usually 2% or less, preferably 1 to 1.8%.
Furthermore, even when the pressure-sensitive adhesive sheet is used for a long time in a thermal environment or a moist heat environment, the pressure-sensitive adhesive layer does not cause foaming, floating from the adherend or peeling, and has excellent durability.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.
In the following examples, the weight average molecular weight (Mw) was measured using GPC (HLC-8120; manufactured by Tosoh Corporation) under the following conditions using polystyrene as a standard substance (column used: G7000HXL × 1) , GMHXL × 2, G2000HXL × 1, solvent: THF, flow rate: 1.0 ml / min, measurement temperature: 40 ° C.).

The number average molecular weight (Mn) was calculated as follows (1) and (2) based on the terminal group quantification method.
(1) Calculation of hydroxyl value Acetic anhydride was added to the polymer for which Mn was to be obtained, and after acetylating the hydroxyl group of the polymer, excess acetic acid was neutralized and titrated with potassium hydroxide to determine the hydroxyl value of the polymer (KOHmg / g
) Was calculated.

(2) Calculation of Mn Since the molecular weight of KOH (about 56) and both ends of the polymer are hydroxyl groups, the Mn was calculated by the following formula. Mn = (56 × 2 × 1000) / hydroxyl value [Synthesis Example 1] Production of acrylic polymer 79 parts by weight of n-butyl acrylate (BA), 20 parts by weight of methoxyethyl acrylate (MEA), 4-hydroxybutyl acrylate (4HBA ) 1 part by weight, 100 parts by weight of ethyl acetate and 0.2 part by weight of azobisisobutyronitrile (AIBN) were placed in a reaction vessel, and the air in the reaction vessel was replaced with nitrogen gas. Thereafter, while stirring in a nitrogen atmosphere, the reaction vessel was heated to 60 ° C. and reacted for 6 hours. After completion of the reaction, it was diluted with ethyl acetate to obtain an acrylic polymer solution. The weight average molecular weight of the acrylic polymer contained in the solution was 1,600,000.

[Synthesis Example 2] Production of acrylic polymer An acrylic polymer was synthesized in the same manner as in Synthesis Example 1 except that 100 parts by weight of ethyl acetate was changed to 140 parts by weight of ethyl acetate and 10 parts by weight of toluene. The weight average molecular weight of the acrylic polymer contained in the obtained acrylic polymer solution was 700,000.

Synthesis Example 3 Production of Acrylic Polymer An acrylic polymer was synthesized in the same manner as in Synthesis Example 1 except that 79.9 parts by weight of BA, 20 parts by weight of MEA and 0.1 part by weight of 4HBA were used. The weight average molecular weight of the acrylic polymer contained in the obtained acrylic polymer solution was 1,600,000.

Synthesis Example 4 Production of Acrylic Polymer An acrylic polymer was synthesized in the same manner as in Synthesis Example 1 except that 73 parts by weight of BA, 20 parts by weight of MEA, and 7 parts by weight of 4HBA were used. The weight average molecular weight of the acrylic polymer contained in the obtained acrylic polymer solution was 1,600,000.

[Synthesis Example 5] Production of acrylic polymer Same as Synthesis Example 1, except that 78.8 parts by weight of BA, 20 parts by weight of MEA, 1 part by weight of 4HBA and 0.2 part by weight of acrylic acid (AA) were used. Acrylic polymer was synthesized. The weight average molecular weight of the acrylic polymer contained in the obtained acrylic polymer solution was 1,600,000.

[Synthesis Example 6] Production of acrylic polymer 50 parts by weight of 2-ethylhexyl acrylate (2EHA), 10 parts by weight of BA, 37 parts by weight of vinyl acetate (VAc), 3 parts by weight of 2-hydroxyethyl methacrylate (2HEMA), An acrylic polymer was synthesized in the same manner as in Synthesis Example 1 except that 150 parts by weight of ethyl acetate was used. The weight average molecular weight of the acrylic polymer contained in the obtained acrylic polymer solution was 500,000.

[Example 1]
An antistatic agent (PEL) in which lithium perchlorate is combined with a poly (ethylene glycol / propylene oxide) copolymer having a number average molecular weight of 1300 with respect to 100 parts by weight of the solid content of the acrylic polymer solution obtained in Synthesis Example 1. -20A; manufactured by Nippon Carlit Co., Ltd. 0.2 parts by weight and 0.15 parts by weight of an isocyanate-based crosslinking agent (trimethylolpropane-added xylene diisocyanate) were mixed to obtain an adhesive composition.

The obtained pressure-sensitive adhesive composition was applied on a release layer of a release-treated polyester film (PET3811; manufactured by Lintec Corporation), and then dried at 90 ° C. for 3 minutes to form a pressure-sensitive adhesive layer having a thickness of 25 μm. The provided adhesive sheet I was obtained.

The obtained pressure-sensitive adhesive sheet I was affixed to one side of a polarizing plate and aged for 7 days under conditions of a temperature of 23 ° C. and a relative humidity of 65% to obtain a pressure-sensitive adhesive sheet II provided with a pressure-sensitive adhesive layer.
The pressure-sensitive adhesive sheet I and pressure-sensitive adhesive sheet II were used to measure or evaluate adhesive strength, surface resistance value, haze value, and durability by the following test methods. The results are shown in Table 1.

((Adhesive force))
The pressure-sensitive adhesive sheet II is cut into 2.5 cm × 15 cm, the polyester film is peeled off, and the pressure-sensitive adhesive sheet II is placed on a non-alkali glass plate (trade name: 1737, manufactured by Corning) so that the pressure-sensitive adhesive layer comes into contact therewith. 20 minutes after application, one end of the adhesive sheet II is pulled in a 180 ° direction at a peeling speed of 300 mm / min, and the force to start peeling is used as the adhesive force.
It was measured with 1 (manufactured by Toyo Seiki Co., Ltd.).

((Surface resistance))
The surface resistance value of the pressure-sensitive adhesive layer that appeared after peeling the polyester film from the pressure-sensitive adhesive sheet II was measured with TERA OHMMETER P-601 (manufactured by Kawaguchi Electric Co., Ltd.) under the condition of 23 ° C. and 65% RH.

((Haze value))
A pressure-sensitive adhesive sheet I was attached to one side of a 0.7 mm-thick non-alkali glass plate (trade name: 1737, manufactured by Corning) using a laminator roll so that the pressure-sensitive adhesive layer contacted to obtain a laminate. Next, the obtained laminate was allowed to stand for 48 hours under conditions of 60 ° C. and 95% RH, and then the total light transmittance and diffuse transmittance of the laminate were measured using HM-150 (Murakami Color Research Laboratory Co., Ltd.). And the haze value was calculated by the following formula: “haze value (%) = 100 × diffuse transmittance / total light transmittance”.

((durability))
After the adhesive sheet II was cut into 240 mm × 140 mm, the polyester film was peeled off, and a 0.7 mm-thick alkali-free glass plate (trade name; 1737, manufactured by Corning) was used so that the appeared adhesive layer contacted A laminated body was obtained by sticking on one side using a laminator roll. Next, the laminate was placed in an autoclave at 50 ° C. and 5 atm for 20 minutes to be bonded to obtain a sample.

  The obtained sample was allowed to stand for 500 hours under conditions of 85 ° C./dry and 60 ° C./95% RH, and the presence or absence of foaming of the pressure-sensitive adhesive layer, peeling from the adherend or floating was visually observed according to the following evaluation criteria. evaluated.

Evaluation criteria ○: No appearance defects such as foaming, peeling or floating are observed.
X: At least one of foaming, peeling, and floating is observed.
[Examples 2 and 3]
According to Table 1, adhesive compositions and adhesive sheets I and II were obtained in the same manner as in Example 1 except that the blending amount of the antistatic agent (PEL-20A; manufactured by Nippon Carlit Co., Ltd.) was changed.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Examples 1 and 2]
According to Table 1, adhesive compositions and adhesive sheets I and II were obtained in the same manner as in Example 1 except that the blending amount of the antistatic agent (PEL-20A; manufactured by Nippon Carlit Co., Ltd.) was changed.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 3]
According to Table 1, the same procedure as in Example 1 was used except that an antistatic agent (PEL-100; manufactured by Nippon Carlit Co., Ltd.) in which lithium perchlorate was combined with polypropylene oxide having a number average molecular weight of 2000 was used as the antistatic agent. Thus, pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets I and II were obtained.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 4]
In accordance with Table 1, as an antistatic agent, an antistatic agent obtained by combining lithium perchlorate with polypropylene oxide having a number average molecular weight of 2000 (PEL-100; manufactured by Nippon Carlit)
A pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets I and II were obtained in the same manner as in Example 1, except that the amount was changed.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 5]
Example 1 except that an antistatic agent obtained by combining lithium perchlorate with polyoxypropylene glycol having a number average molecular weight of 200 (Sanix PP-200; manufactured by Sanyo Kasei) was used as an antistatic agent according to Table 1. In the same manner, pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets I and II were obtained.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 6]
According to Table 1, an adhesive composition and adhesive sheets I and II were obtained in the same manner as in Example 1 except that the acrylic polymer obtained in Synthesis Example 2 was used.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 7]
According to Table 1, an adhesive composition and adhesive sheets I and II were obtained in the same manner as in Example 1 except that the acrylic polymer obtained in Synthesis Example 3 was used.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 8]
According to Table 1, an adhesive composition and adhesive sheets I and II were obtained in the same manner as in Example 1 except that the acrylic polymer obtained in Synthesis Example 4 was used.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 9]
According to Table 1, an adhesive composition and adhesive sheets I and II were obtained in the same manner as in Example 1 except that the acrylic polymer obtained in Synthesis Example 5 was used.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Examples 10 and 11]
A pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets I and II were obtained in the same manner as in Example 1 except that the amount of the isocyanate-based crosslinking agent was changed according to Table 1.

Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.
[Comparative Example 12]
According to Table 1, an antistatic agent obtained by combining lithium perchlorate with polypropylene oxide having a number average molecular weight of 2000 as an antistatic agent using the acrylic polymer obtained in Synthesis Example 6 (PEL-100; manufactured by Nippon Carlit) A pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets I and II were obtained in the same manner as in Example 1 except that the amount of the isocyanate-based crosslinking agent was changed.

  Using these, the adhesive strength, surface resistance value, haze value, and durability were measured and evaluated in the same manner as in Example 1. The results are also shown in Table 1.

From Table 1, the following tendencies are understood.
In Examples 1-3, it turns out that the adhesive sheet which has an adhesive layer suitable for being used for a polarizing plate use was obtained by all the points of surface resistance value, adhesive force, durability, and haze.

  Further, in Comparative Example 1 in which the addition amount of the antistatic agent is less than a specific range, the surface resistance value becomes large and the antistatic performance becomes poor, while in Comparative Example 2 in which the addition amount of the antistatic agent is large, the adhesive strength is reduced. It turns out that a haze value becomes large with doing. When the results of Examples 1 to 3 and Comparative Examples 1 and 2 are represented by graphs of the addition amount of the antistatic agent, the surface resistance value, and the adhesive strength, the tendency as shown in FIG. 1 is observed.

  Further, in Comparative Example 3 and Comparative Example 4 in which the number average molecular weight of the polymer constituting the antistatic agent is larger than a specific range, the adhesive strength is slightly lowered, and the haze value is remarkably increased as the blending amount is increased. Yes. On the other hand, it can be seen that there is a problem in durability in Comparative Example 5 in which the number average molecular weight of the polymer is smaller than a specific range. In addition, when these results are represented by a graph of the number average molecular weight (Mn) and haze (%) of the polymer constituting the antistatic agent, a tendency as shown in FIG. 2 is obtained.

  Further, in Comparative Example 6 in which the weight average molecular weight of the acrylic polymer is less than 1 million, Comparative Example 7 and Comparative Example 8 in which the copolymer composition ratio of the acrylic polymer is changed and (a1) the amount of the hydroxyl group-containing monomer is out of a specific range It can be seen that although the adhesive force is improved, the durability is inferior.

  In Comparative Example 9 in which the copolymer composition ratio of the acrylic polymer is changed and the amount of the monomer containing (a2) at least one of a carboxyl group, an amino group, and an amide group is out of a specific range, the surface resistance value increases. It can be seen that the antistatic performance is poor.

  Further, in Comparative Example 10 in which the amount of the isocyanate-based crosslinking agent is smaller than a specific range, the adhesive strength is increased but the durability is poor. On the other hand, in Comparative Example 11 in which the amount is larger than the specific range, the adhesive strength is slightly lowered and durability is increased. It turns out that the nature is not enough.

  In addition, the combination of the acrylic polymer, the antistatic agent and the isocyanate-based crosslinking agent disclosed as examples of Comparative Example 12 to Patent Document 2 has extremely low adhesive strength, increased haze, and insufficient durability. I understand that there is.

FIG. 1 is a graph showing the relationship between the antistatic agent addition amount, the surface resistance value, and the adhesive strength. FIG. 2 is a graph showing the relationship between the number average molecular weight of the polymer constituting the antistatic agent and haze.

Claims (4)

An adhesive sheet having an adhesive layer on at least one side of a support,
The pressure-sensitive adhesive layer is obtained from a pressure-sensitive adhesive composition containing the following components (A), (B), and (C), and the pressure-sensitive adhesive sheet has an adhesive strength of 400 g / 25 mm or more. Pressure-sensitive adhesive sheet;
(A) (a1) 0.3 to 5% by weight of a hydroxyl group-containing monomer, (a2) 0 to 0.01% by weight of a monomer containing at least one of a carboxyl group, an amino group and an amide group, and (a3) the above (Meth) acrylic resins having a weight average molecular weight of 1 million or more, obtained by copolymerizing 95 to 99.7% by weight of substituted and / or unsubstituted alkyl (meth) acrylates other than (a1) and (a2) For 100 parts by weight of polymer,
(B) a polymer having a polyoxyalkylene structure and a hydroxyl group and having a number average molecular weight of 300 to 1500 , an alkali metal salt of perchloric acid, an alkaline earth metal salt of perchloric acid, an alkali metal salt of an organic boron complex, and organic 0.1 to 2 parts by weight of an antistatic agent comprising at least one ionic substance selected from the group consisting of alkaline earth metal salts of boron complexes ;
(C) 0.03 to 1 part by weight of an isocyanate-based crosslinking agent. The pressure-sensitive adhesive sheet according to claim 1 , wherein the surface resistance value is 10 ¹² Ω / □ or less. The pressure-sensitive adhesive sheet according to claim 1 or 2 , wherein the haze value is 2% or less. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3 , wherein the support is a polarizing plate.

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