JP6352196B2 - Adhesive composition and adhesive film - Google Patents

Description

  The present invention relates to an adhesive composition and an adhesive film.

  When an article such as a metal plate, a coated steel plate, or a synthetic resin plate is processed or transported, an adhesive film is attached to protect the article surface from damage or dirt. The adhesive film is peeled off from the adherend when protection of the article is no longer necessary. The adhesive film used here generally has an adhesive layer for adhering to an article (hereinafter also referred to as an adherend) on one side of a sheet-like substrate.

  The pressure-sensitive adhesive layer of the pressure-sensitive adhesive film has such a degree of adhesiveness that it does not cause displacement or fall off from the surface of the adherend while it is necessary to protect the adherend. It is required to be easily peeled from the adherend (hereinafter also referred to as peelability) and to be difficult to contaminate the surface of the adherend (hereinafter also referred to as stainability).

  In addition, the adherend may be heat-treated in a state protected by an adhesive film. In general, the pressure-sensitive adhesive film is not easily peeled off from the adherend due to an increase in the adhesive strength of the pressure-sensitive adhesive layer due to heat treatment, and the surface of the adherend tends to be contaminated. For this reason, the adhesive film is required to have good peelability and contamination even after heat treatment.

  In response to these requirements, Patent Document 1 discloses a pressure-sensitive adhesive in which a reactive oligomer is added to an acrylic polymer as a pressure-sensitive adhesive having little increase in adhesive strength even after heat treatment. Patent Document 2 discloses an acrylic high molecular weight copolymer having a functional group and an acrylic low molecular weight having a functional group as a pressure-sensitive adhesive composition that has little increase in adhesive strength even after heat treatment and has good peelability. An adhesive composition containing a molecular weight copolymer is disclosed. Patent Document 3 discloses that a pressure-sensitive adhesive having good high-speed peelability and good stainability includes an acrylic polymer having a functional group and a low molecular weight acrylic polymer having a functional group. A pressure-sensitive adhesive is disclosed.

  Furthermore, an adhesive film is normally manufactured through a drying process and a curing process, after applying an adhesive composition to a base material. Increasing the coating speed is important from the viewpoint of improving productivity. However, increasing the coating speed may cause streaks in the pressure-sensitive adhesive layer and deteriorate the appearance of the pressure-sensitive adhesive film. Therefore, the pressure-sensitive adhesive composition is required to be less likely to cause streaks in the pressure-sensitive adhesive layer even when the coating speed is increased (hereinafter also referred to as coating property).

JP 2003-277707 A JP 2008-38103 A JP 2005-146151 A

In recent years, there has been a growing demand for improved peelability and contamination after heat treatment. For this reason, it has been found that the conventional pressure-sensitive adhesive composition described in the above-mentioned patent document may not be able to sufficiently meet these requirements for the peelability and contamination after the heat treatment. Moreover, in the said patent document, no examination is made about the applicability | paintability of an adhesive composition.
Therefore, an object of the present invention is to provide a pressure-sensitive adhesive composition that provides a pressure-sensitive adhesive film that is excellent in coatability and excellent in releasability and contamination after heat treatment when used as a pressure-sensitive adhesive film. Moreover, let it be a subject to provide the adhesive film which has an adhesive layer formed from the said adhesive composition.

Specific means for solving the above-described problems are as follows.
(1) a (meth) acrylic polymer having a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group and having a weight average molecular weight of 300,000 to 1500,000;
A (meth) acrylic oligomer having a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, an acid value of 70 mgKOH / g or more, and a weight average molecular weight of 1,000 to 30,000; ,
A crosslinking agent,
The acid value of the (meth) acrylic polymer is C (mgKOH / g), the acid value of the (meth) acrylic oligomer is D (mgKOH / g), and the content of the (meth) acrylic polymer is c (mass). Part), when the content of the (meth) acrylic oligomer is d (parts by mass), the total acid value represented by the following formula is 30 mgKOH / g to 90 mgKOH / g.
Total acid value = C × {c / (c + d)} + D × {d / (c + d)}

<2> The pressure-sensitive adhesive according to <1>, wherein the ratio of the (meth) acrylic oligomer to the total mass of the (meth) acrylic polymer and the (meth) acrylic oligomer is 1% by mass to 40% by mass. Composition.

<3> Functionality that contributes to crosslinking with respect to a total of 1 equivalent of the carboxy group contained in the (meth) acrylic polymer and the carboxy group contained in the (meth) acrylic oligomer, in which the content of the crosslinking agent is <1> or <2> The pressure-sensitive adhesive composition according to <1>, wherein the group is in an amount of 0.4 equivalent to 2.2 equivalent.

<4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein a glass transition temperature (Tg) of the (meth) acrylic polymer is −50 ° C. or lower.

<5> The (meth) acrylic oligomer has 50 structural units derived from a monomer having a glass transition temperature (Tg) of −50 ° C. or less when a homopolymer is used with respect to 100% by mass of all structural units. The pressure-sensitive adhesive composition according to any one of <1> to <4>, containing at least mass%.

<6> The pressure-sensitive adhesive composition according to any one of <1> to <5>, wherein the crosslinking agent is at least one selected from the group consisting of an epoxy compound and an isocyanate compound.

A pressure-sensitive adhesive film comprising a <7> base material and a pressure-sensitive adhesive layer provided on the base material and derived from the pressure-sensitive adhesive composition according to any one of <1> to <6>.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in applicability | paintability, the adhesive composition which is excellent in the peelability after heat processing when it is set as an adhesive film and the contamination | pollution property is provided. Moreover, the adhesive film which has an adhesive layer formed from the said adhesive composition is provided.

In this specification, the term “step” is not limited to an independent step, and is included in the term if the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps.
In the present specification, a numerical range indicated by using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
The amount of each component in the composition means the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition.

In the present specification, the (meth) acrylic polymer or (meth) acrylic oligomer means a polymer or oligomer in which at least a main component of the monomers constituting the monomer is a monomer having a (meth) acryloyl group. . The monomer as the main component means a monomer having the largest content (mass%) among monomers constituting the polymer or oligomer. In an embodiment of the (meth) acrylic polymer or (meth) acrylic oligomer of the present invention, the content of the structural unit derived from the (meth) acrylate monomer as the main component is 50% by mass or more of the total structural unit. .
In the present specification, “(meth) acryl” means both “acryl” and “methacryl”, “(meth) acrylate” means both “acrylate” and “methacrylate”, and “(meth) acryloyl” Means both “acryloyl” and “methacryloyl”.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present invention includes a (meth) acrylic polymer having a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and having a weight average molecular weight of 300,000 to 1500,000. A (meth) acrylic oligomer having a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, an acid value of 70 mgKOH / g or more, and a weight average molecular weight of 1,000 to 30,000; A crosslinking agent,
The acid value of the (meth) acrylic polymer is C (mgKOH / g), the acid value of the (meth) acrylic oligomer is D (mgKOH / g), and the content of the (meth) acrylic polymer is c (mass). Part), when the content of the (meth) acrylic oligomer is d (parts by mass), the total acid value represented by the following formula is 30 mgKOH / g to 90 mgKOH / g.
Total acid value = C × {c / (c + d)} + D × {d / (c + d)}

  By satisfy | filling the said requirements, the adhesive composition of this invention is excellent in the peelability after a heat processing when it is set as an adhesive film, and contamination | contamination property, when it is set as an adhesive film. The present inventors consider the reason as follows.

  In general, a pressure-sensitive adhesive composition containing an oligomer tends to have a lower adhesive force and a higher peelability than a case where no oligomer is contained. On the other hand, the pressure-sensitive adhesive composition containing the oligomer tends to remain on the adherend when it is peeled off, and the contamination tends to decrease.

  By using a (meth) acrylic oligomer having an acid value of 70 mgKOH / g or more as the oligomer contained in the pressure-sensitive adhesive composition, the adhesive force is reduced, the peelability is improved, and the contamination property is increased. It was found that the decrease in the amount was also suppressed. This is because the amount of the carboxy group of the (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention is large, and the (meth) acrylic polymer and the (meth) acrylic oligomer in the pressure-sensitive adhesive composition are sufficient. It is considered that the (meth) acrylic oligomer is less likely to remain on the adherend due to crosslinking.

  In the pressure-sensitive adhesive composition of the present invention, when the total of the acid value of the (meth) acrylic polymer and the acid value of the (meth) acrylic oligomer is 30 mgKOH / g or more, the crosslinking proceeds sufficiently, and heating It is considered that the adhesive strength after the treatment can be lowered. In addition, when the total of the acid value of the (meth) acrylic polymer and the acid value of the (meth) acrylic oligomer is 90 mgKOH / g or less, the necessary adhesive force is maintained without excessive crosslinking. It is considered possible.

Furthermore, the pressure-sensitive adhesive composition of the present invention is less likely to cause streaks during high-speed coating. The reason is considered as follows.
It is known that a pressure-sensitive adhesive composition containing two or more kinds of polymers tends to have strong pseudoplasticity due to entanglement between the polymers. In addition, it is known that a pressure-sensitive adhesive composition having a large amount of carboxy groups contained in a polymer is likely to have strong pseudoplasticity due to hydrogen bonding. In the study by the present inventors, it was found that if the pseudoplasticity is strong, the coating property tends to be poor. In the pressure-sensitive adhesive composition of the present invention, by using an oligomer having a sufficiently low molecular weight in combination with a polymer, physical entanglement between polymers is very small, pseudoplasticity is kept low, and coating properties are excellent. it is conceivable that. In addition, by making the total acid value of the (meth) acrylic polymer and (meth) acrylic oligomer within a specific range, pseudoplasticity due to hydrogen bonding can be kept low, so it is considered excellent in coatability. It is done.

  The acid value of the (meth) acrylic oligomer is preferably 85 mgKOH / g or more, and more preferably 100 mgKOH / g or more, from the viewpoint of sufficient crosslinking with the (meth) acrylic polymer. The acid value of the (meth) acrylic oligomer is preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, and 160 mgKOH / g from the viewpoint of appropriate adhesive strength and haze of the pressure-sensitive adhesive layer. More preferably, it is as follows.

  The total of the acid value of the (meth) acrylic polymer and the acid value of the (meth) acrylic oligomer is preferably 35 mgKOH / g or more, and 45 mgKOH / g or more from the viewpoint of sufficiently proceeding with the crosslinking. More preferably, it is more preferably 50 mgKOH / g or more. The total of the acid value of the (meth) acrylic polymer and the acid value of the (meth) acrylic oligomer is preferably 85 mgKOH / g or less, and 80 mgKOH / g or less from the viewpoint of suppressing excessive crosslinking. It is more preferable that

  The ratio of the acid value of the (meth) acrylic polymer to the acid value of the (meth) acrylic oligomer (acid value of the (meth) acrylic polymer / acid value of the (meth) acrylic oligomer) in the adhesive composition is a contamination. From the viewpoint of property, it is preferably 0.6 or more, and more preferably 1.0 or more. From the viewpoint of adhesive strength, the ratio is preferably 15 or less, and more preferably 10 or less.

  The acid value of the (meth) acrylic polymer or (meth) acrylic oligomer is determined by the following calculation formula.

Acid value (mgKOH / g) = {(A / 100) ÷ B} × 56.1 × 1000
A = Content of monomer having carboxy group (% by mass) in all monomers used in (meth) acrylic polymer or (meth) acrylic oligomer
B = Molecular weight of monomer having carboxy group used for (meth) acrylic polymer or (meth) acrylic oligomer 56.1 is the molecular weight of KOH.

  When the monomer having a carboxy group used in the (meth) acrylic polymer or (meth) acrylic oligomer is two or more kinds, the acid value was obtained according to the above formula for each monomer, and obtained. The acid value is obtained by summing up the values.

  The sum of the acid values of the (meth) acrylic polymer and the (meth) acrylic oligomer is determined by the following calculation formula.

Total acid value (mgKOH / g) = C × {c / (c + d)} + D × {d / (c + d)}
C = acid value of (meth) acrylic polymer D = acid value of (meth) acrylic oligomer c = content of (meth) acrylic polymer (parts by mass)
d = (Meth) acrylic oligomer content (parts by mass)

  The ratio of the acid value of the (meth) acrylic polymer and the acid value of the (meth) acrylic oligomer in the pressure-sensitive adhesive composition is determined by the following calculation formula.

Ratio of acid value = C × {c / (c + d)} / D × {d / (c + d)}
C = acid value of (meth) acrylic polymer D = acid value of (meth) acrylic oligomer c = content of (meth) acrylic polymer (parts by mass)
d = (Meth) acrylic oligomer content (parts by mass)

  In the pressure-sensitive adhesive composition of the present invention, the ratio of the (meth) acrylic oligomer is 1% by mass to 40% by mass with respect to a total of 100% by mass of the (meth) acrylic polymer and the (meth) acrylic oligomer. Is preferred. The effect which added the (meth) acrylic-type oligomer to the adhesive composition as the ratio of a (meth) acrylic-type oligomer is 1 mass% or more is fully acquired. When the proportion of the (meth) acrylic oligomer is 40% by mass or less, contamination of the adherend by the oligomer can be sufficiently suppressed. From the same viewpoint, the proportion of the (meth) acrylic oligomer is more preferably 3% by mass to 30% by mass with respect to the total of 100% by mass of the (meth) acrylic polymer and the (meth) acrylic oligomer, More preferably, it is 3 mass%-20 mass%.

<(Meth) acrylic polymer>
The (meth) acrylic polymer contained in the pressure-sensitive adhesive composition of the present invention includes a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and has a weight average molecular weight of 300,000 to 1500,000. is there.

  Adhesive force can be easily adjusted because a (meth) acrylic-type polymer contains the structural unit derived from an alkyl (meth) acrylate. Moreover, it is bridge | crosslinked by the below-mentioned crosslinking agent because a (meth) acrylic-type polymer contains the structural unit derived from the monomer which has a carboxy group. Furthermore, when the weight average molecular weight of the (meth) acrylic polymer is 300,000 or more, the contamination property is excellent, and when it is 1500,000 or less, the coating property and the conformability are excellent. The (meth) acrylic polymer contained in the pressure-sensitive adhesive composition of the present invention may be only one type or two or more types having different monomer compositions, molecular weights, and the like.

  In the present specification, the “structural unit derived from alkyl (meth) acrylate” means a structural unit formed by addition polymerization of alkyl (meth) acrylate. The “structural unit derived from a monomer having a carboxy group” means a structural unit formed by addition polymerization of a monomer having a carboxy group.

  The alkyl (meth) acrylate constituting the structural unit derived from the alkyl (meth) acrylate is an unsubstituted alkyl (meth) acrylate, and the type thereof is not particularly limited. The alkyl group of the alkyl (meth) acrylate may be linear, branched or cyclic. Moreover, it is preferable that it is the range of 1-18, and, as for carbon number of an alkyl group, it is more preferable that it is the range of 1-12. When the number of carbon atoms of the alkyl group is within the above range, it is advantageous in terms of adhesiveness and adhesiveness to the substrate when used as an adhesive film.

  Specific examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylate, and t-butyl. (Meth) acrylate, n-octyl (meth) acrylate, i-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, i-nonyl (meth) acrylate, n-decyl (meth) ) Acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and the like. Alkyl (meth) acrylate may be used individually by 1 type, or may use 2 or more types together.

  The alkyl (meth) acrylate is selected from the group consisting of 2-ethylhexyl (meth) acrylate, n-butyl (meth) acrylate and lauryl (meth) acrylate from the viewpoint of imparting appropriate adhesive strength and compatibility with the substrate. It is preferable to include at least one selected.

  The proportion of the structural unit derived from the alkyl (meth) acrylate in the total structural unit of the (meth) acrylic polymer is 75% by mass or more with respect to 100% by mass of the total structural unit from the viewpoint of imparting appropriate adhesive strength. It is preferable that it is 78 mass% or more, and it is further more preferable that it is 80 mass% or more. From the viewpoint of contamination, the proportion of structural units derived from alkyl (meth) acrylate in all structural units of the (meth) acrylic polymer is 97% by mass or less with respect to 100% by mass of all structural units. Preferably, it is 96 mass% or less, More preferably, it is 95 mass% or less.

  The kind in particular of the monomer which has a carboxy group which comprises the structural unit derived from the monomer which has a carboxy group is not restrict | limited. For example, (meth) acrylic acid, polyalkylene glycol (meth) acrylate having carboxy group, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, citraconic acid, cinnamic acid, 2- (meth) acryloyloxy Ethyl succinic acid, monohydroxyethyl (meth) acrylate maleate, monohydroxyethyl (meth) acrylate fumarate, monohydroxyethyl (meth) acrylate phthalate, 1,2-dicarboxycyclohexane monohydroxyethyl (meth) acrylate, ( And (meth) acrylic acid dimer, ω-carboxy-polycaprolactone mono (meth) acrylate, and the like.

  Examples of the alkylene glycol constituting the polyalkylene glycol moiety of the polyalkylene glycol (meth) acrylate having a carboxy group include ethylene glycol, propylene glycol, a combination of ethylene glycol and propylene glycol.

  From the viewpoint of obtaining appropriate adhesive strength and good peelability to the adherend, the monomer having a carboxy group is (meth) acrylic acid, 2-methacryloyloxyethyl succinic acid, polyalkylene glycol (meth) having a carboxy group. More preferably, it contains at least one selected from the group consisting of acrylate, ω-carboxy-polycaprolactone mono (meth) acrylate and (meth) acrylic acid dimer, (meth) acrylic acid, 2-methacryloyloxyethyl succinate It is further preferable to include at least one selected from the group consisting of an acid, a polyalkylene glycol (meth) acrylate having a carboxy group, and ω-carboxy-polycaprolactone mono (meth) acrylate.

  The (meth) acrylic polymer preferably contains 50% by mass or more of a structural unit derived from a monomer having an acryloyl group (hereinafter also referred to as an acrylic monomer) with respect to 100% by mass of all the structural units. By containing 50% by mass or more of structural units derived from acrylic monomers with respect to 100% by mass of all structural units, the copolymerizability is improved and the carboxy group can be distributed more uniformly in the (meth) acrylic polymer. Further, unevenness of crosslinking is further suppressed, and contamination is further improved. The (meth) acrylic polymer preferably contains 60% by mass or more of structural units derived from acrylic monomers with respect to 100% by mass of all structural units, and contains 80% by mass or more of structural units derived from acrylic monomers. Further preferred.

  The (meth) acrylic polymer may contain other structural units other than the structural unit derived from the alkyl (meth) acrylate and the structural unit derived from the monomer having a carboxy group within the range in which the effects of the present invention are exhibited. Good. In this case, the total ratio of the structural unit derived from the alkyl (meth) acrylate and the structural unit derived from the monomer having a carboxy group is 70% by mass with respect to 100% by mass of all the structural units of the (meth) acrylic polymer. % Or more, preferably 75% by mass or more, and more preferably 80% by mass or more.

  The type of monomer constituting other structural units is not particularly limited. Specific examples of such monomers include (meth) acrylate monomers having a cyclic group such as benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, alkoxy such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate. Alkyl (meth) acrylate monomers, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, vinyltoluene and other aromatic monovinyl monomers, acrylonitrile, methacrylonitrile and other cyanogenated vinyl monomers, formic acid Examples thereof include vinyl ester monomers such as vinyl, vinyl acetate, vinyl propionate and vinyl versatate, and various derivatives of these monomers. Moreover, the monomer which has functional groups other than a carboxy group, such as a hydroxyl group, a glycidyl group, an amide group or an N-substituted amide group, and a tertiary amino group, is mentioned.

  Specific examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl. (Meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-butyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate, glycerin mono (meth) Accel Relay , Polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, poly (ethylene glycol - propylene glycol) mono (meth) acrylate.

  Specific examples of the monomer having a glycidyl group include glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, glycidyl vinyl ether, 3,4-epoxycyclohexyl vinyl ether, glycidyl (meth) allyl ether, 3,4 -Epoxy cyclohexyl (meth) allyl ether etc. are mentioned.

  Specific examples of the monomer having an amide group or an N-substituted amide group include acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, and N-ethoxy. Examples include methyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-tert-butylacrylamide, N-octylacrylamide, diacetone acrylamide and the like.

  Specific examples of the monomer having a tertiary amino group include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide and the like.

  The weight average molecular weight of the (meth) acrylic polymer is preferably 400,000 or more, and more preferably 500,000 or more from the viewpoint of contamination. The weight average molecular weight of the (meth) acrylic polymer is preferably 1300000 or less, more preferably 1200000 or less, and even more preferably 1000000 or less, from the viewpoint of conformability and coating properties.

  The dispersity (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the (meth) acrylic polymer is not particularly limited. From the viewpoint, it is preferably in the range of 1-30.

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the (meth) acrylic polymer are values measured by the following method. Specifically, the measurement is performed according to the following (1) to (3).
(1) A solution of a (meth) acrylic polymer is applied to a release paper and dried at 100 ° C. for 2 minutes to obtain a film-like (meth) acrylic polymer.
(2) Using the film-like (meth) acrylic polymer obtained in (1) and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained.
(3) The weight average molecular weight (Mw) and number average molecular weight (Mn) of the (meth) acrylic polymer under the following conditions as standard polystyrene conversion values using gel permeation chromatography (GPC) under the following conditions: ).

-Condition-
・ GPC: HLC-8220 GPC [manufactured by Tosoh Corporation]
Column: 4 TSK-GEL GMHXL used Mobile phase solvent: Tetrahydrofuran Flow rate: 0.6 mL / min Column temperature: 40 ° C

  The glass transition temperature (Tg) of the (meth) acrylic polymer is preferably −50 ° C. or lower. When the Tg of the (meth) acrylic polymer is −50 ° C. or lower, the elasticity of the (meth) acrylic polymer is sufficiently low, the adhesive strength after the heat treatment can be suppressed low, and the peelability is further improved.

  The Tg of the (meth) acrylic polymer is -50 ° C by setting the monomer having a Tg of -50 ° C or lower when all or part of the monomer constituting the (meth) acrylic polymer is a homopolymer. The following can be achieved. Specific examples of the monomer having a Tg of −50 ° C. or less as a homopolymer include butyl acrylate (−55 ° C.), 2-ethylhexyl acrylate (−76 ° C.), lauryl methacrylate (−65 ° C.), Examples include octyl acrylate (−65 ° C.), isooctyl acrylate (−58 ° C.), isononyl acrylate (−58 ° C.), and isomyristyl acrylate (−56 ° C.).

Tg of the (meth) acrylic polymer is a value obtained by converting the absolute temperature (K) obtained by calculation from the following formula into Celsius temperature (° C.).
1 / Tg = w1 / Tg1 + w2 / Tg2 +... + W (k-1) / Tg (k-1) + wk / Tgk
In the formula, Tg1, Tg2,..., Tg (k-1), and Tgk each represent a glass transition temperature (K) when a homopolymer of each monomer constituting the (meth) acrylic polymer is used. w1, w2,..., w (k-1), wk each represents a mass fraction of each monomer constituting the (meth) acrylic polymer, and w1 + w2 + ... + w (k-1) + wk = 1. It is.

<(Meth) acrylic oligomer>
The (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention includes a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and has an acid value of 70 mgKOH / g or more. Yes, the weight average molecular weight is 1000-30000.

  When the (meth) acrylic oligomer contains a structural unit derived from an alkyl (meth) acrylate, an appropriate adhesive force and compatibility with a substrate are imparted to the adhesive composition. In addition, the (meth) acrylic oligomer is excellent in contamination by including a structural unit derived from a monomer having a carboxy group. Furthermore, when the weight average molecular weight of the (meth) acrylic oligomer is 1000 or more, the contamination property is excellent, and when it is 30000 or less, the coating property is excellent. Furthermore, when the acid value of the (meth) acrylic oligomer is 70 mgKOH / g or more, the (meth) acrylic polymer is sufficiently cross-linked and excellent in contamination. The pressure-sensitive adhesive composition of the present invention may contain only one (meth) acrylic oligomer, or two or more different monomer compositions, weight average molecular weights, and the like.

  The ratio of the structural unit derived from the alkyl (meth) acrylate in the total structural units of the (meth) acrylic oligomer is based on 100% by mass of all the structural units from the viewpoint of imparting appropriate adhesive strength to the pressure-sensitive adhesive composition. It is preferably 85% by mass or more, more preferably 87% by mass or more, and further preferably 90% by mass or more. From the viewpoint of adhesive strength and contamination, the proportion of structural units derived from alkyl (meth) acrylate in all structural units of the (meth) acrylic oligomer is 96% by mass or less with respect to 100% by mass of all structural units. Preferably, it is 95% by mass or less, and more preferably 94% by mass or less. Examples of the alkyl (meth) acrylate include the alkyl (meth) acrylates described above for the (meth) acrylic polymer, and preferred examples are also the same.

  Preferred examples of the monomer having a carboxy group constituting the structural unit derived from the monomer having a carboxy group of the (meth) acrylic oligomer include the monomers having the carboxy group described above for the (meth) acrylic polymer. Is the same.

  The (meth) acrylic oligomer preferably contains 50% by mass or more of structural units derived from acrylic monomers with respect to 100% by mass of all structural units. By including 50% by mass or more of the acrylic monomer with respect to 100% by mass of all the structural units, the copolymerizability is improved, the carboxy group can be more uniformly distributed in the (meth) acrylic oligomer, and unevenness of crosslinking is caused. It is suppressed more and pollution property improves more. The (meth) acrylic oligomer more preferably contains 60% by mass or more of structural units derived from acrylic monomers with respect to 100% by mass of all structural units, and is derived from acrylic monomers with respect to 100% by mass of all structural units. More preferably, the structural unit is contained in an amount of 70 mass% or more.

  The (meth) acrylic oligomer may contain structural units other than the structural unit derived from the alkyl (meth) acrylate and the structural unit derived from the monomer having a carboxy group within the range in which the effects of the present invention are exhibited. In this case, the total proportion of the structural unit derived from the alkyl (meth) acrylate in the total structural unit of the (meth) acrylic oligomer and the structural unit derived from the monomer having a carboxy group is 100% by mass of the total structural unit. Is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. Examples of the monomer constituting the constituent unit other than the constituent unit derived from the alkyl (meth) acrylate and the constituent unit derived from the monomer having a carboxy group include the monomers described above for the (meth) acrylic polymer.

  The weight average molecular weight of the (meth) acrylic oligomer is preferably 4000 or more, more preferably 7000 or more, from the viewpoint of contamination. The weight average molecular weight of the (meth) acrylic oligomer is preferably 25000 or less, and more preferably 20000 or less, from the viewpoint of coatability.

  The dispersity (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the (meth) acrylic oligomer is not particularly limited. From the viewpoint, it is preferably in the range of 1-30.

  The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the (meth) acrylic oligomer are the same as the method for measuring the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the (meth) acrylic polymer. Measured.

  The glass transition temperature (Tg) of the (meth) acrylic oligomer is preferably −20 ° C. or lower. When the Tg of the (meth) acrylic oligomer is −20 ° C. or lower, the adhesive strength after the heat treatment can be kept low, and the peelability is further improved.

  The glass transition temperature (Tg) of the (meth) acrylic oligomer is calculated in the same manner as the above-described method for calculating the glass transition temperature of the (meth) acrylic polymer.

  The (meth) acrylic oligomer has a structural unit derived from a monomer having a glass transition temperature of −50 ° C. or lower when a homopolymer is used, and is 50% relative to 100% by mass of all structural units of the (meth) acrylic oligomer. It is preferable to contain at least mass%. In this case, the glass transition temperature of the (meth) acrylic oligomer is sufficiently low, and the pressure-sensitive adhesive layer is more easily adapted to the adherend. This makes it easier to prevent the adhesive layer from falling off during processing of the adherend. Examples of the monomer having a Tg of −50 ° C. or less when the homopolymer is used include monomers having a Tg of −50 ° C. or less when the homopolymer described above for the (meth) acrylic polymer is used.

<Crosslinking agent>
The pressure-sensitive adhesive composition of the present invention contains a crosslinking agent. The kind of crosslinking agent will not be restrict | limited especially if the (meth) acrylic-type polymer and (meth) acrylic-type oligomer which are contained in the adhesive composition of this invention can be bridge | crosslinked. For example, an epoxy compound having an epoxy group, an isocyanate compound having an isocyanate group, or the like can be used.

  Examples of the epoxy compound include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, resorcin diglycidyl ether, 2,2-dibromo Neopentyl glycol diglycidyl A , Trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris (glycidyl) isocyanurate, tris (glycidoxyethyl) isocyanurate, 1 , 3-bis (N, N-glycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine and the like. These epoxy compounds can be used individually by 1 type or in mixture of 2 or more types.

  Examples of the isocyanate compound include aromatic polyisocyanate compounds such as xylylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated products of the above-described aromatic polyisocyanate compounds. Linear or cyclic aliphatic polyisocyanate compounds, biuret bodies, dimers, trimers or pentamers of these polyisocyanate compounds, adducts of these polyisocyanate compounds and polyol compounds such as trimethylolpropane Examples include the body. These isocyanate compounds can be used individually by 1 type or in mixture of 2 or more types.

  When the pressure-sensitive adhesive composition is used for applications in which transparency is important, the epoxy compound may be tris (glycidyl) isocyanurate, tris (glycidoxyethyl) isocyanurate and 1,3-bis (N, N-glycidylamino). At least one selected from the group consisting of (methyl) cyclohexane is preferred, and 1,3-bis (N, N-glycidylaminomethyl) cyclohexane is more preferred. The isocyanate compound is at least selected from the group consisting of a chain or cyclic aliphatic polyisocyanate compound and a biuret, dimer, trimer or pentamer of a chain or cyclic aliphatic polyisocyanate compound and an adduct. One is preferable, and at least one selected from the group consisting of an isocyanate compound having an isocyanurate structure which is a trimer of hexamethylene diisocyanate, an adduct of hexamethylene diisocyanate, and a biuret of hexamethylene diisocyanate is more preferable. Since these isocyanate compounds do not have a structure derived from an aromatic ring, the pressure-sensitive adhesive layer after the heat treatment is hardly yellowed, and a pressure-sensitive adhesive film that is superior in transparency can be obtained.

  As a commercial item of the epoxy compound as a crosslinking agent, what is marketed by brand names, such as Tetrad-X and Tetrad-C [above, Mitsubishi Gas Chemical Co., Ltd.], can be used conveniently, for example.

  A commercial item can be used for a crosslinking agent. As a commercial item of the isocyanate compound as a crosslinking agent, for example, "Coronate HX", "Coronate HL-S", "Coronate L", "Coronate 2031", "Coronate 2030", "Coronate 2234", "Coronate 2785" , “Aquanate 200”, “Aquanate 210” (manufactured by Nippon Polyurethane Co., Ltd.), “Sumijoule N3300”, “Desmodur N3400”, “Sumijoule N-75” [manufactured by Sumitomo Bayer Urethane Co., Ltd. ], “Duranate E-405-80T”, “Duranate 24A-100”, “Duranate TSE-100” (manufactured by Asahi Kasei Kogyo Co., Ltd.), “Takenate D-110N”, “Takenate D-120N”, “Takenate” M-631N "" MT-Olestar NP120 "[Or more, manufactured by Mitsui Takeda Chemical Co., Ltd.] can be preferably used those which are commercially available by the trade names such as.

  The content of the crosslinking agent is, for example, when the total of the carboxy group contained in the (meth) acrylic polymer and the carboxy group contained in the (meth) acrylic oligomer is 1 equivalent, with respect to 1 equivalent of this total carboxy group Thus, the amount of the functional group contributing to crosslinking can be 0.4 equivalent to 2.2 equivalent. When the equivalent of functional groups contributing to crosslinking is 0.4 equivalent or more with respect to 1 equivalent of total carboxy groups, the pressure-sensitive adhesive layer after crosslinking becomes sufficiently hard, and the adhesive strength after heat treatment becomes sufficiently low and peeling. Property is improved. Moreover, since the quantity of the (meth) acrylic oligomer which is not bridge | crosslinked decreases, it is excellent in stain resistance. When the equivalent of functional groups contributing to crosslinking is 2.2 equivalents or less with respect to 1 equivalent of total carboxy groups, the amount of the crosslinking agent that has not reacted with the (meth) acrylic polymer can be kept low, and the contamination property is excellent. . The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present invention contributes to crosslinking with respect to a total of 1 equivalent of the carboxy group contained in the (meth) acrylic polymer and the carboxy group contained in the (meth) acrylic oligomer. It is more preferable that the amount of the functional group is 0.6 equivalent to 1.8 equivalent, and it is further preferable that the functional group contributing to the crosslinking is 0.7 equivalent to 1.3 equivalent.

(Other ingredients)
In addition to the (meth) acrylic polymer, the (meth) acrylic oligomer and the crosslinking agent, the pressure-sensitive adhesive composition of the present invention may include a crosslinking catalyst, a chelating agent, a solvent, a weather resistance stabilizer, Examples include tackifiers, plasticizers, softeners, dyes, pigments, inorganic fillers, polymers other than (meth) acrylic polymers, and oligomers other than (meth) acrylic oligomers. Content in case an adhesive composition contains these components can be set in the range with which the effect of this invention is exhibited.

<Polymerization method of (meth) acrylic polymer and (meth) acrylic oligomer>
The polymerization method of the (meth) acrylic polymer and (meth) acrylic oligomer used in the pressure-sensitive adhesive composition of the present invention is not particularly limited. For example, known methods such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization can be applied. Among these, solution polymerization is preferable because the treatment process is relatively simple and can be performed in a short time.

  In solution polymerization, a predetermined organic solvent, a monomer, a polymerization initiator and, if necessary, a chain transfer agent are generally charged in a polymerization tank and heated for several hours with stirring in a nitrogen stream or at the reflux temperature of the organic solvent. Let In this case, at least a part of the organic solvent, the monomer, the polymerization initiator, and / or the chain transfer agent may be sequentially added.

  Examples of the organic solvent used in the polymerization reaction include fragrances such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha. Aliphatic hydrocarbons, n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, terpine oil, and other aliphatic or alicyclic hydrocarbons, ethyl acetate , Esters such as n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, methyl benzoate, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone , Ketones such as methylcyclohexanone, ethylene glycol Glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n -Alcohols, such as butyl alcohol, i-butyl alcohol, s-butyl alcohol, t-butyl alcohol, etc. are mentioned. These organic solvents can be used individually by 1 type or in mixture of 2 or more types.

  Among the organic solvents, when polymerizing the (meth) acrylic polymer and the (meth) acrylic oligomer, it is preferable to use an organic solvent that hardly causes chain transfer during the polymerization reaction of esters, ketones, and the like. In particular, ethyl acetate, methyl ethyl ketone, acetone and the like are preferable from the viewpoints of solubility of the (meth) acrylic polymer and (meth) acrylic oligomer, ease of polymerization reaction, and the like.

As the polymerization initiator, it is possible to use organic peroxides, azo compounds, and the like used in ordinary solution polymerization.
Examples of the organic peroxide include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxide. Carbonato, t-butylperoxybivalate, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,4-di-t-amylperoxycyclohexyl) propane, 2,2-bis (4,4-di-t-octylperoxycyclohexyl) propane, 2,2-bis (4,4-di-α-cumylperoxycyclohexyl) propane, 2,2-bis (4,4 -Di-t-butylperoxycyclohexyl) butane, 2,2-bi (4,4-di -t- octyl peroxy cyclohexyl) butane and the like.
Examples of the azo compound include 2,2′-azobis-i-butylnitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, 2,2′-azobis-4-methoxy-2,4-dimethyl. Examples include valeronitrile, 1,1′-azobis-cyclohexane-1-carbonitrile, 2,2′-azobis (methyl isobutyrate), and the like.

  Among the polymerization initiators, in the polymerization of the (meth) acrylic polymer and the (meth) acrylic oligomer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and an azobis polymerization initiator is particularly preferable. . The amount of the polymerization initiator used in the polymerization of the (meth) acrylic polymer is in the range of 0.01 to 2 parts by mass with respect to 100 parts by mass of the total amount of monomers constituting the (meth) acrylic polymer. It is preferable that it is in the range of 0.1 parts by mass to 1 part by mass. In the polymerization of the (meth) acrylic oligomer, the content is preferably in the range of 0.1 to 20 parts by mass with respect to 100 parts by mass of the total amount of monomers constituting the (meth) acrylic oligomer. More preferably, it is in the range of -10 parts by mass.

In the polymerization of the (meth) acrylic polymer and the (meth) acrylic oligomer, a chain transfer agent can be used as necessary as long as the object and effect of the present invention are not impaired.
Examples of the chain transfer agent include cyanoacetic acid, cyanoacetic acid alkyl esters having 1 to 8 carbon atoms, bromoacetic acid, bromoacetic acid alkyl esters having 1 to 8 carbon atoms, α-methylstyrene, anthracene, phenanthrene, fluorene. , Aromatic compounds such as 9-phenylfluorene, aromatic nitro compounds such as p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol and p-nitrotoluene, benzoquinone, 2,3, Benzoquinone derivatives such as 5,6-tetramethyl-p-benzoquinone, borane derivatives such as tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, Bromotrichloromethane, tribromomethane, 3-chloro -1- Carbonates of halogenated hydrocarbons such as propene, aldehydes such as chloral and furaldehyde, alkyl mercaptans having 1 to 18 carbon atoms, aromatic mercaptans such as thiophenol and toluene mercaptan, mercaptoacetic acid, mercaptoacetic acid Examples thereof include 1-10 alkyl esters, C1-C12 hydroxyalkyl mercaptans, terpenes such as binene and terpinolene.

  The amount of the chain transfer agent used is, for example, in the range of 0.005 parts by mass to 10.0 parts by mass with respect to 100 parts by mass of the total amount of monomers constituting the (meth) acrylic polymer and the (meth) acrylic oligomer. can do.

  The polymerization temperature during the polymerization reaction is preferably in the range of 30 ° C to 180 ° C, more preferably in the range of 50 ° C to 150 ° C. In particular, the polymerization temperature when producing a (meth) acrylic polymer and a (meth) acrylic oligomer is more preferably in the range of 60 ° C to 100 ° C, and preferably in the range of 70 ° C to 90 ° C. Further preferred.

<Adhesive film>
The pressure-sensitive adhesive film of the present invention includes a base material and a pressure-sensitive adhesive layer provided on the base material and derived from the pressure-sensitive adhesive composition of the present invention. The pressure-sensitive adhesive film of the present invention is excellent in appearance by having a pressure-sensitive adhesive layer derived from the pressure-sensitive adhesive composition of the present invention, and is excellent in peelability and contamination even after heat treatment.

  The material of the base material constituting the pressure-sensitive adhesive film of the present invention is not particularly limited. From the viewpoint of inspection and management of optical members by fluoroscopy, for example, polyester resin, acetate resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, acrylic resin, etc. Can be mentioned. Among these, a polyester resin is preferable from the viewpoint of surface protection performance, and a polyethylene terephthalate resin is more preferable from the viewpoint of practicality.

  The thickness of the substrate is not particularly limited. For example, it can be 500 μm or less, preferably in the range of 5 μm to 300 μm, and more preferably in the range of 10 μm to 200 μm.

  The formation method in particular of the adhesive layer provided on a base material is not restrict | limited, It can carry out by the method used normally. For example, the pressure-sensitive adhesive composition of the present invention can be applied directly to a base film substrate and dried to remove the solvent as it is or diluted with a solvent as necessary. it can. As other methods, the pressure-sensitive adhesive composition of the present invention is applied on a release sheet such as paper or polyester film that has been subjected to a release treatment with a silicone resin or the like, and heated and dried to form a pressure-sensitive adhesive layer. Next, the surface of the release sheet on which the pressure-sensitive adhesive layer is formed is brought into contact with the substrate and pressed to transfer the pressure-sensitive adhesive layer to the substrate side. If necessary, a release film may be laminated on the surface of the pressure-sensitive adhesive layer on the substrate thus prepared.

  The pressure-sensitive adhesive layer formed on the substrate is preferably cured for a certain period after drying. The curing conditions can be, for example, 4 to 14 days in an environment of 23 ° C. and 50% RH. By curing the pressure-sensitive adhesive layer, the (meth) acrylic polymer and the (meth) acrylic oligomer can be sufficiently crosslinked by the crosslinking agent contained in the pressure-sensitive adhesive layer.

  The thickness of an adhesive layer can be set according to the adhesive force calculated | required according to the use of an adhesive film, the surface roughness of a to-be-adhered body, etc. Generally, it is in the range of 1 μm to 100 μm, preferably in the range of 5 μm to 50 μm, and more preferably in the range of 15 μm to 30 μm.

  In the pressure-sensitive adhesive film of the present invention, the pressure-sensitive adhesive layer has a sufficient pressure-sensitive adhesive force to the adherend (the pressure-sensitive adhesive force at the time of peeling at low speed is sufficiently large) and can be easily peeled off at the time of peeling at medium speed ( It is preferable that the adhesive force during peeling at medium speed does not increase. Furthermore, the pressure-sensitive adhesive layer is not only applied to an adherend having a sufficiently conformable and smooth surface, but also when used for an adherend having minute irregularities on the surface. It is preferable that the surface of the adherend can be sufficiently wetted and has good conformability (the cut end does not turn up when cut).

That is, the adhesive force of 180 ° peel at 23 ° C. to the adherend of the adhesive layer is such that the adhesive force (peeling force) at a peeling speed of 10 m / min (medium speed peeling) is 0.6 N / 25 mm or less. preferable. It can peel easily because the adhesive force at the time of medium speed peeling is 0.6 N / 25 mm or less. In particular, the peelability at a wide width is improved.
From the same viewpoint, the peeling force in the medium speed peeling is more preferably 0.3 N / 25 mm or less.

  The gel fraction of the pressure-sensitive adhesive layer is preferably 90% by mass to 100% by mass, more preferably 93% by mass to 100% by mass, and still more preferably 95% by mass to 100% by mass from the viewpoint of adhesive strength.

In the present specification, the gel fraction of the pressure-sensitive adhesive layer is a ratio of a solvent-insoluble content measured using ethyl acetate as an extraction solvent. Specifically, the measurement is performed according to the following (1) to (4).
(1) Apply about 0.25 g of the pressure-sensitive adhesive layer to a 250-mesh wire mesh (100 mm × 100 mm) whose mass has been accurately measured with a precision balance, and wrap the gel so that it does not leak. Thereafter, the mass is accurately measured with a precision balance to prepare a sample.
(2) The obtained sample is immersed in 80 ml of ethyl acetate for 3 days.
(3) A sample is taken out, washed with a small amount of ethyl acetate, and dried at 120 ° C. for 24 hours. Thereafter, the mass is accurately measured with a precision balance.
(4) The gel fraction is calculated by the following formula.
Gel fraction (mass%) = (Z−X) / (Y−X) × 100
Where X is the mass (g) of the wire mesh, Y is the mass (g) before immersion of the wire mesh with the adhesive layer attached, and Z is the mass (g) of the wire mesh with the adhesive layer attached after drying. is there.

  As an application of the pressure-sensitive adhesive film of the present invention, an application to be applied to an adherend to be heat-treated can be mentioned. Specifically, for example, a surface protective film of an optical member that is subjected to a heat treatment such as hard coat PET, a surface protective film that is used in a manufacturing process of an electronic member such as a flexible printed board, and a reinforcing film can be used. That is, the pressure-sensitive adhesive film of the present invention can be used as a heat-resistant pressure-sensitive adhesive film that protects or reinforces the surface of the adherend in the heat treatment step and can be easily peeled off without contamination after the heat treatment step. Heat processing can be made into the range of 100 to 250 degreeC, for example.

  In addition, the adhesive film of this invention uses the carboxy group as a crosslinking point at the time of bridge | crosslinking an adhesive layer. Thereby, a crosslinking reaction can be caused to occur without using a crosslinking catalyst containing an organotin compound, which is often used when a polymer having a hydroxyl group as a crosslinking point is crosslinked with an isocyanate compound. Cross-linking catalysts containing organotin compounds tend to be repelled due to their toxicity.

  Among them, since the pressure-sensitive adhesive composition of the present invention has high transparency, the pressure-sensitive adhesive film provided with the pressure-sensitive adhesive layer derived from the pressure-sensitive adhesive composition of the present invention is inspected for appearance inspection and the like in a state of being bonded to an adherend. A process can be performed. For this reason, it is suitable for the surface protection film use of optical members, such as hard coat PET. The surface protective film of the optical member is laminated on the surface of the optical member to protect the surface of the optical member from being contaminated or damaged. The optical member is subjected to heat treatment such as a high-temperature dry printing step and an etching step while the surface protective film is laminated on the optical member. Thereafter, when the surface protection becomes unnecessary, the optical member is peeled off.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” and “%” are based on mass.

-Production of (meth) acrylic polymers-
(Production Example 1)
In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a sequential dropping device, 31.7 parts by mass of ethyl acetate, 23.75 parts by mass of 2-ethylhexyl acrylate (2EHA) as an alkyl acrylate having no acid, 1.25 parts by weight of acrylic acid (AA) and 0.013 parts by weight of 2,2′-azobis-i-butyronitrile (AIBN) are added as monomers having a carboxy group, and the temperature in the reaction vessel is refluxed while stirring. The temperature was raised until it occurred. 20 minutes after the start of refluxing, a solution prepared by dissolving 71.25 parts by mass of 2EHA, 3.75 parts by mass of AA, and 0.038 parts by mass of AIBN in 9.2 parts by mass of ethyl acetate was added dropwise over 120 minutes. The reaction was completed over a period of minutes. After completion of the reaction, the solution was diluted with methyl ethyl ketone so that the solid content was 35% by mass to prepare a solution of a (meth) acrylic polymer.

Table 1 shows the monomer composition (mass%), weight average molecular weight (Mw), acid value, and Tg of the (meth) acrylic polymer obtained. The weight average molecular weight (Mw, unit: 10,000) is measured by the method described above. The acid value and Tg are calculated by the method described above. Specifically, the acid value was calculated as follows. The molecular weight of AA is 72.1.
{(5/100) ÷ 72.1} × 56.1 × 1000 = 38.9 (mgKOH / g)
The “solid content” is an amount of residue obtained by removing a volatile component such as a solvent from a solution of a (meth) acrylic polymer.

(Production Examples 2 to 11)
In Production Example 1, the composition of the monomer was changed as shown in Table 1, and the molecular weight was adjusted as shown in Table 1 below by adjusting the amount of solvent and the amount of initiator, as in Production Example 1. A (meth) acrylic polymer solution was prepared by the method. Table 1 shows the composition (mass%), weight average molecular weight (Mw, unit: 10,000), and Tg of the obtained (meth) acrylic polymer. In the table, “MA” represents methyl acrylate, and “LMA” represents lauryl methacrylate.

-Production of (meth) acrylic oligomers-
(Production Example A)
In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a sequential dropping device, 5.1 parts by mass of 2-ethylhexyl acrylate (2EHA) as alkyl acrylate and acrylic acid (AA) 0 as a monomer having a carboxy group .9 parts by mass, 19 parts by mass of toluene, 19 parts by mass of methyl ethyl ketone, and 0.4 parts by mass of 2,2′-azobis (methyl isobutyrate) (V-601: manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added and stirred. The temperature in the reaction vessel was raised until reflux occurred. 10 minutes after the start of reflux, 4E part of 2EHA, 8.1 parts by weight of AA, 5.4 parts by weight of 2,2′-azobis (isobutyric acid) dimethyl (V-601: Wako Pure Chemical Industries, Ltd.) were added to methyl ethyl ketone 8. A solution dissolved in 8 parts by mass was added dropwise over 90 minutes, and after completion of the addition, the reaction was completed over 230 minutes. After completion of the reaction, toluene was added so that the solid content was 35% to prepare a (meth) acrylic oligomer solution.

Table 2 shows the monomer composition (mass%), weight average molecular weight (Mw), and acid value of the obtained (meth) acrylic oligomer. The weight average molecular weight (Mw, unit: 10,000) is measured by the method described above. The acid value and Tg are calculated by the method described above. Specifically, the acid value was calculated as follows.
{(15/100) ÷ 72.1} × 56.1 × 1000 = 16.7 (mgKOH / g)
In addition, "solid content" is the amount of residue which removed volatile components, such as a solvent, from the solution of a (meth) acrylic-type oligomer.

(Production Examples B to M)
In Production Example A, the composition of the monomer was changed as shown in Table 2, and the molecular weight was adjusted as shown in Table 2 below by adjusting the amount of the solvent and the amount of the initiator, as in Production Example A. A solution of (meth) acrylic oligomer was prepared by the method. Table 2 shows the composition (mass%), weight average molecular weight (Mw, unit: 10,000), and acid value of the obtained (meth) acrylic oligomer. In the table, “MA” represents methyl acrylate, and “LMA” represents lauryl methacrylate.

Example 1
-Production of pressure-sensitive adhesive composition-
90 parts by mass of the (meth) acrylic polymer solution (solid content: 35%) prepared in Production Example 1 and 10 parts by mass of the (meth) acrylic oligomer solution (solid content: 35%) prepared in Production Example A And 2.65 parts by mass of an epoxy compound (Tetrad-C manufactured by Mitsubishi Gas Chemical Co., Ltd.) (total equivalent of carboxy group contained in (meth) acrylic polymer and carboxy group contained in (meth) acrylic oligomer) 1 equivalent The epoxy group contained in the epoxy compound was mixed with 1.00 equivalent), and stirred sufficiently to obtain an adhesive composition. Using the obtained pressure-sensitive adhesive composition, a test pressure-sensitive adhesive film was prepared according to the following method for preparing a test pressure-sensitive adhesive film, and various tests were performed. The total acid value and the ratio of the acid values are shown in Table 3.
The sum of the acid values and the ratio of the acid values were calculated by the method described above, and specifically calculated as follows.
Total acid value 38.9 × {90 / (90 + 10)} + 116.7 × {10 / (90 + 10)} = 46.7 (mgKOH / g)
Ratio of acid value 38.9 × {90 / (90 + 10)} / 116.7 × {10 / (90 + 10)} = 3.0

-Production of adhesive film for test-
Using the pressure-sensitive adhesive composition obtained above, a test pressure-sensitive adhesive film was produced as follows. On the polyethylene terephthalate (PET) film (Lumirror U35, manufactured by Toray Industries, Inc., thickness: 125 μm), the pressure-sensitive adhesive composition was applied so that the coating amount after drying was 20 g / m ^2. The pressure-sensitive adhesive layer was formed by drying at 100 ° C. for 60 seconds with a dryer. Thereafter, a PET film was placed on the release film whose surface was protected with a silicone release agent so that the pressure-sensitive adhesive layer was in contact with the pressure-sensitive adhesive nip roll. Thereafter, curing was conducted for 7 days in an environment of 23 ° C. and 50% RH to prepare an adhesive film for testing.
Table 3 shows the gel fraction of the obtained pressure-sensitive adhesive layer. The gel fraction is measured by the method described above.

-Measurement and evaluation-
[Peelability]
The test adhesive film prepared above was cut to a size of 25 mm × 150 mm, the release film was peeled off from the obtained adhesive film piece, and a hard-coated PET film (KB film G01S, manufactured by Kimoto Co., Ltd.) Affixed to the hard-coated surface, a 2 kg rubber roll was reciprocated once for pressure bonding. This test sample was allowed to stand in an environment of 23 ° C. and 50% RH for 1 hour, then heat-treated in an environment of 150 ° C. for 1 hour, and then left to stand in an environment of 23 ° C. and 50% RH for 1 hour. Then, the adhesive force in 180 degree peeling at the time of peeling an adhesive film to a long side (150 mm) direction was measured on the conditions of peeling speed 10m / min (medium speed peeling), and evaluated according to the following references | standards. The results are shown in Table 3.

A: When it is 0.1 N / 25 mm or more and less than 0.25 N / 25 mm (peelability is very good)
B: When 0.05 N / 25 mm or more and less than 0.1 N / 25 mm, or 0.25 N / 25 mm or more and less than 0.4 N / 25 mm (good peelability)
C: 0.4N / 25mm or more and less than 0.5N / 25mm (Slightly poor peelability but within acceptable range)
D: When it is 0.5 N / 25 mm or more or less than 0.05 N / 25 mm (poor peelability is poor)

[Contamination]
2 μL of pure water was dropped on the hard-coated surface of the hard-coated PET film after peeling off the test protective film used for the measurement of the adhesive strength after the heat treatment, and 30 seconds after the dropping. Later, the contact angle (θ1) of water was measured using a contact angle measuring device (Drop Master DM-701, manufactured by Kyowa Interface Science Co., Ltd.). The absolute value (Δθ = | θ1-θ0 |) of the difference between the obtained value and the contact angle (θ0 = 84 °) of the water on the hard coat treated surface that had been measured in advance and was not attached with the test protective film ) Was evaluated according to the following criteria. The results are shown in Table 3.

A: When Δθ is 2.0 or less (very good contamination)
B: When Δθ exceeds 2.0 and is 4.5 or less (contamination is good)
C: When Δθ exceeds 4.5 and is 7.5 or less (poor contamination, but within the allowable range)
D: When Δθ exceeds 7.5 (poor contamination and poor)

[Coating properties]
The solution of the (meth) acrylic polymer prepared in Production Examples 1 to 11 and the solution of the (meth) acrylic oligomer prepared in Production Examples A to K were blended at a blending ratio shown in Table 3 to obtain a mixed solution. The shear viscosity of the prepared mixture was measured under the following conditions. Measuring equipment is MCR-301 (manufactured by Anton Paar) with a 25 mm diameter cone plate (CP25-2) attached, stage temperature: 25 ° C., shear rate: 0.001 to 3000 (1 / second), measurement time: 60 Second, the temperature of the mixture: 25 ° C. In the obtained graph, a base line is drawn in a portion where the shear rate (1 / second) is 0.01 to 0.1, and the shear rate (1 / second) when the measured value is away from the baseline is read. Evaluation was made according to criteria. The results are shown in Table 3.

A: When the shear rate (1 / second) is 5.0 or more (coating property is very good)
B: When the shear rate (1 / second) is 1.0 or more and less than 5.0 (coating property is good)
C: When the shear rate (1 / second) is 0.5 or more and less than 1.0 (coating property is poor but within an allowable range)
D: When the shear rate (1 / second) is less than 0.5 (coating property is poor and inappropriate)

[Familiarity]
The test pressure-sensitive adhesive film produced above is a 25 mm × 210 mm strip having a portion having a pressure-sensitive adhesive layer with an area of 25 mm × 150 mm and a portion not formed with a 30 mm pressure-sensitive adhesive layer on both sides thereof. Cut into. The release film was peeled off from the obtained adhesive film piece, curved so that the adhesive layer was on the outside, and both ends of the portion where the adhesive layer was not formed were overlapped and pinched with fingers. The part corresponding to the tip of the curved pressure-sensitive adhesive layer is brought into contact with the surface of the hard-coated PET film (KB film G01S, manufactured by Kimoto Co., Ltd.), and the pressure-sensitive adhesive layer is placed on the hard-coated surface of the PET film after releasing the finger. The time until it spreads out and wets all over was measured and evaluated according to the following criteria. The results are shown in Table 3.

A: When it is less than 30 seconds (good compatibility and very good)
B: When it is 30 seconds or more and less than 60 seconds (good conformability is good)
C: 60 seconds or more and less than 120 seconds (Familiarity is slightly bad, but is within an allowable range)
D: 120 seconds or more, or when the pressure-sensitive adhesive layer does not spread all the way to the edge (poor compatibility and out of tolerance)

(Examples 2-22, Comparative Examples 1-9)
The types and ratios of (meth) acrylic polymer and (meth) acrylic oligomer were changed as shown in Table 3, and the amount of epoxy compound was changed to carboxy contained in (meth) acrylic polymer and (meth) acrylic oligomer. A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the epoxy group contained in the epoxy compound was adjusted to the equivalent amount shown in Table 3 with respect to 1 equivalent of the total group. A test adhesive film was prepared in the same manner as in Example 1 using the prepared adhesive composition. The obtained test adhesive film was evaluated in the same manner as in Example 1. The results are shown in Table 3.

As shown in Table 3, the pressure-sensitive adhesive compositions prepared in Examples 1 to 22 were evaluated to be good or within an acceptable range in any of peelability, stainability, coating property, and conformability.
In Examples 1 to 19, 21, and 22, the glass transition temperature (Tg) when the homopolymer is used with respect to 100% by mass of all the structural units of the (meth) acrylic oligomer is −50 ° C. or lower. The structural unit derived from a monomer is 50 mass% or more.
The pressure-sensitive adhesive composition of Comparative Example 1 containing no (meth) acrylic oligomer had a low peelability evaluation.
The pressure-sensitive adhesive compositions of Comparative Example 2 and Comparative Example 3 in which the acid value of the (meth) acrylic oligomer was lower than 70 mgKOH / g had a low evaluation of contamination.
The pressure-sensitive adhesive composition of Comparative Example 4 in which the total acid value of the (meth) acrylic polymer and the (meth) acrylic oligomer was lower than 30 mgKOH / g had a low evaluation of peelability and contamination.
The pressure-sensitive adhesive composition of Comparative Example 5 in which the total acid value of the (meth) acrylic polymer and the (meth) acrylic oligomer was higher than 90 mgKOH / g had low peelability and conformability evaluation.
The pressure-sensitive adhesive composition of Comparative Example 6 in which the weight average molecular weight of the (meth) acrylic polymer was greater than 1500,000 was poor in evaluation of coatability and conformability.
The pressure-sensitive adhesive composition of Comparative Example 7 in which the weight average molecular weight of the (meth) acrylic polymer was less than 300,000 had a low evaluation of the contamination property.
The pressure-sensitive adhesive composition of Comparative Example 8 in which the weight average molecular weight of the (meth) acrylic oligomer was less than 1000 had a low evaluation of contamination.
The pressure-sensitive adhesive composition of Comparative Example 9 in which the weight average molecular weight of the (meth) acrylic oligomer was greater than 30000 had a low applicability evaluation.

Claims (5)

A (meth) acrylic polymer comprising a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and having a weight average molecular weight of 300,000 to 1500,000,
A (meth) acrylic oligomer having a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, an acid value of 70 mgKOH / g or more, and a weight average molecular weight of 1,000 to 30,000; ,
A crosslinking agent,
The ratio of the (meth) acrylic oligomer to the total mass of the (meth) acrylic polymer and the (meth) acrylic oligomer is 1% by mass to 40% by mass,
The said (meth) acrylic-type oligomer is 50 mass% or more of structural units derived from the monomer whose glass transition temperature (Tg) when it is set as a homopolymer is -50 degrees C or less with respect to 100 mass% of all the structural units. Including
The acid value of the (meth) acrylic polymer is C (mgKOH / g), the acid value of the (meth) acrylic oligomer is D (mgKOH / g), and the content of the (meth) acrylic polymer is c (mass). Part), when the content of the (meth) acrylic oligomer is d (parts by mass), the total acid value represented by the following formula is 30 mgKOH / g to 90 mgKOH / g.
Total acid value = C × {c / (c + d)} + D × {d / (c + d)} The content of the cross-linking agent is such that the functional group contributing to cross-linking is 0 with respect to a total of 1 equivalent of the carboxy group contained in the (meth) acrylic polymer and the carboxy group contained in the (meth) acrylic oligomer. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition is in an amount of 4 equivalents to 2.2 equivalents. The pressure-sensitive adhesive composition according to claim 1 or 2 , wherein a glass transition temperature (Tg) of the (meth) acrylic polymer is -50 ° C or lower. The pressure-sensitive adhesive composition according to any one of claims 1 to 3 , wherein the crosslinking agent is at least one selected from the group consisting of an epoxy compound and an isocyanate compound. An adhesive film provided with a base material and the adhesive layer which is provided on the said base material and originates in the adhesive composition of any one of Claims 1-4 .