JP2017115078A - Adhesive composition, adhesive agent by crosslinking the same, adhesive agent for masking film, adhesive agent for heat resistant adhesive film and heat resistant adhesive film for masking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition containing no organic tin compound, excellent in quick curability while having sufficient pot life, less in increase of adhesive force after using under a high temperature condition, capable of being peeled with small power and further hardly generating contamination when peeled from an adherend and capable of being used for a heat resistant adhesive film for masking.SOLUTION: There is provided an adhesive composition containing an acrylic resin having a hydroxyl group (A), an isocyanate-based crosslinking agent (B) and a zinc compound (C). There is provided an adhesive composition preferably having content of the isocyanate-based crosslinking agent (B) of 0.5 to 40 pts.wt. based on 100 pts.wt. of the acrylic resin (A). There is provided an adhesive composition having content ratio (weight ratio) of the isocyanate-based crosslinking agent (B) and the zinc compound (C) (solid component conversion amount), (C)/(B) of 0.0001 to 0.5.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive obtained by crosslinking this, a pressure-sensitive adhesive for masking film, a pressure-sensitive adhesive for heat-resistant pressure-sensitive adhesive film, and a heat-resistant pressure-sensitive adhesive film for masking. A pressure-sensitive adhesive composition that can be used for a heat-resistant pressure-sensitive adhesive film for masking, etc., having excellent immediate curing properties and excellent heat resistance, and a pressure-sensitive adhesive for heat-resistant pressure-sensitive adhesive films comprising the pressure-sensitive adhesive, the pressure-sensitive adhesive It is related with the heat-resistant adhesive film for masking which has the adhesive layer which consists of these on a film.

  Conventionally, a re-peelable adhesive film has been used to temporarily fix and protect members when processing various members. In recent years, for example, circuit boards such as flexible printed wiring (FPC) boards and ITO It is used as a masking adhesive film for temporarily protecting the surface of a transparent electrode layer, and as a surface protecting adhesive film for flat panel displays, touch panels, and the like. Since the manufacturing process of the FPC board and the ITO transparent electrode layer includes a process exposed to high temperature, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive film is fixed to the laminated plate, and the FPC board and the ITO transparent electrode layer are peeled off when the pressure-sensitive adhesive film is peeled off. Laminate may be damaged or contamination due to adhesive residue may occur. For this reason, even after a high temperature process, it is required that the adhesive can be peeled off with a light force without any adhesive residue.

  As a pressure-sensitive adhesive composition used for such a heat-resistant pressure-sensitive adhesive sheet, for example, in Patent Document 1, even under high temperature conditions, contamination hardly occurs when peeled from an adherend, and the pressure-sensitive adhesive performance is sufficiently high. Furthermore, as a pressure-sensitive adhesive composition suitably used for a heat-resistant pressure-sensitive adhesive sheet with a short aging period during film production, it is obtained by polymerizing a monomer component containing a nitrogen atom-containing monomer, and has a glass transition temperature of −40 ° C. or higher. A pressure-sensitive adhesive composition containing an acrylic resin is disclosed.

  However, in the technique of Patent Document 1, in order to balance the adhesive physical properties of the adhesive, it is necessary to perform an aging treatment for a certain time after producing the adhesive sheet, and until the adhesive composition is crosslinked in the aging process. Moreover, the fine unevenness | corrugation etc. of a base film or a separator may be transcribe | transferred to an adhesive layer, and the adhesive film with a smooth adhesive layer surface may not be obtained. When the pressure-sensitive adhesive sheet is used for protecting the surface of an optical film such as a flat panel display or a touch panel, the fine irregularities of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet are transferred to the optical film as the adherend, and the visibility is reduced. Problems can arise.

  Here, in Patent Document 2, as the pressure-sensitive adhesive composition that satisfies the necessary physical properties of the pressure-sensitive adhesive for surface protective film and can shorten the curing time without shortening the pot life, An acrylic pressure-sensitive adhesive composition comprising an acrylic copolymer having a reactive hydroxyl group, a dialkylacetylacetone tin complex catalyst, and an acrylic pressure-sensitive adhesive composition containing an isocyanate compound is disclosed.

  However, although the technique of Patent Document 2 has a heat resistance of 70 ° C. in terms of heat resistance, the heat resistance under higher temperature conditions is inferior, and adhesive residue may be generated. In recent years, the toxicity problem of organotin compounds has been pointed out, and in particular, tributyltin contained in dibutyltin dilaurate is also concerned as an endocrine disrupting substance.

JP 2013-32504 A JP 2008-13634 A

  Therefore, the present invention, under such a background, does not contain an organotin compound, has a sufficient pot life, is excellent in immediate curing, and has little increase in adhesive strength after use under high temperature conditions. An object of the present invention is to provide a pressure-sensitive adhesive composition that can be used for a masking heat-resistant pressure-sensitive adhesive film that can be peeled off with a small force and is less susceptible to contamination when peeled from an adherend.

  The present invention also provides a pressure-sensitive adhesive obtained by crosslinking this pressure-sensitive adhesive composition, a pressure-sensitive adhesive for masking film comprising the pressure-sensitive adhesive, a pressure-sensitive adhesive for heat-resistant pressure-sensitive adhesive film comprising the pressure-sensitive adhesive, and a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive. Another object of the present invention is to provide a heat-resistant adhesive film for masking having a film on a film.

  However, as a result of intensive studies by the present inventors, the pressure-sensitive adhesive composition containing an acrylic resin having a hydroxyl group and an isocyanate-based crosslinking agent further contains a zinc compound that is rarely used in a pressure-sensitive adhesive composition. As a result, it was found that a pressure-sensitive adhesive composition that solves the above problems was obtained, and the present invention was completed.

  This is because the pressure-sensitive adhesive composition of the present invention has a zinc compound that is not too reactive as compared to commonly used metal compounds such as zirconium and aluminum, which have the effect of accelerating the crosslinking reaction of the isocyanate-based crosslinking agent. Since it has moderate reactivity, it is presumed that immediate curing can be achieved without reducing the pot life.

  That is, the gist of the present invention relates to a pressure-sensitive adhesive composition containing an acrylic resin (A) having a hydroxyl group, an isocyanate-based crosslinking agent (B), and a zinc compound (C).

  The gist of the present invention is that the pressure-sensitive adhesive composition of the present invention is crosslinked, the pressure-sensitive adhesive for masking film characterized by comprising the pressure-sensitive adhesive of the present invention, and the pressure-sensitive adhesive of the present invention. The present invention also relates to a heat-resistant pressure-sensitive adhesive film for masking, characterized in that the film has a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive of the present invention.

  According to the pressure-sensitive adhesive composition of the present invention and a pressure-sensitive adhesive obtained by crosslinking the same, since it has a very excellent quick-curing property while having a sufficient pot life, Can form a smooth pressure-sensitive adhesive layer surface without transferring irregularities. Furthermore, after use under high temperature conditions, it is difficult to cause contamination when peeled off from the adherend, and peels off with a small force. A heat-resistant adhesive film for masking that can be produced can be produced.

The present invention will be described in detail below, but these show examples of desirable embodiments. In the present specification, (meth) acryl means acryl or methacryl, (meth) acryloyl means acryloyl or methacryloyl, and (meth) acrylate means acrylate or methacrylate.
In the present invention, the “adhesive film” conceptually includes an adhesive sheet, an adhesive film, and an adhesive tape.

  The acrylic resin (A) having a hydroxyl group used in the present invention is obtained by polymerizing a polymerization component containing a (meth) acrylic acid ester monomer (a1) and a hydroxyl group-containing monomer (a2) as essential components. Yes, if necessary, a functional group-containing monomer (a3) other than a hydroxyl group and other polymerizable monomer (a4) can be appropriately contained as a polymerization component.

  The (meth) acrylic acid ester monomer (a1) used in the present invention is a (meth) acrylate having an aliphatic or alicyclic alkyl ester. Carbon number of alkyl in the alkyl ester is usually 1-20, preferably 1-12, particularly preferably 1-8. When there are too many carbon numbers, there exists a tendency for the adherend contamination after a heating process to increase.

Specifically, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-propyl (meth) acrylate , N-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, iso-octyl acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, cetyl (meth) acrylate, stearyl ( Aliphatic (meth) acrylic acid alkyl esters such as meth) acrylate and iso-stearyl (meth) acrylate; Alicyclic (meth) acrylic acid alkyl esters such as cyclohexyl (meth) acrylate and isobornyl (meth) acrylate Ester, and the like.
Preferred (meth) acrylic acid ester monomers (a1) include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, and tert-butyl (meth) acrylate. , N-propyl (meth) acrylate, n-hexyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.
These can be used alone or in combination of two or more.

The content of the (meth) acrylic acid ester monomer (a1) in the polymerization component is usually 40 to 99.99% by weight, preferably 45 to 99.9% by weight, particularly preferably 50 to 99% by weight. It is. If the content is too small, the adhesive strength after the heating step tends to be too high, and if it is too large, adherend contamination after the heating step tends to increase.
Further, in the (meth) acrylic acid ester monomer (a1), the content of the (meth) acrylic acid alkyl ester monomer having an alkyl group having 1 to 8 carbon atoms is 80% by weight or more after the heating step. In view of excellent adherence contamination, it is preferably 85% by weight or more, more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

Examples of the hydroxyl group-containing monomer (a2) include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8- Hydroxyalkyl esters of acrylic acid such as hydroxyoctyl (meth) acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth) acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth) acrylate and polyethylene glycol (meth) acrylate; Primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethylphthalic acid; 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyrate Can be mentioned 2,2-dimethyl-2-hydroxyethyl (meth) tertiary hydroxyl group-containing monomers such as acrylate; (meth) acrylate, secondary hydroxyl group-containing monomers such as 3-chloro-2-hydroxypropyl (meth) acrylate.
Among the hydroxyl group-containing monomers, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferably used in terms of excellent reactivity with the isocyanate-based crosslinking agent (B).
In addition, it is preferable to use two or more kinds of hydroxyl group-containing monomers in combination because the cross-linked structure can be made dense and the heat resistance is improved. In particular, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meta) ) It is preferable to use acrylate together.

  The content of the hydroxyl group-containing monomer (a2) in the polymerization component is preferably 0.1 to 30% by weight, more preferably 0.5 to 25% by weight, and particularly preferably 1 to 20% by weight. If the content is too small, the degree of cross-linking tends to decrease and adherend contamination tends to increase. If it is too large, the adhesive strength immediately after application tends to be too high.

  In addition, as a hydroxyl-containing monomer used by this invention, it is also preferable to use a thing with the content rate of di (meth) acrylate which is an impurity 0.5% or less, Furthermore 0.2% or less, especially Is preferably 0.1% or less.

  Examples of the functional group-containing monomer (a3) other than the hydroxyl group-containing monomer include a carboxyl group-containing monomer, an acetoacetyl group-containing monomer, an isocyanate group-containing monomer, a glycidyl group-containing monomer, an amino group-containing monomer, and an amide group-containing monomer. Can be mentioned.

  Examples of the carboxyl group-containing monomer include (meth) acrylic acid, acrylic acid dimer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, acrylamide N-glycolic acid, and cinnamon. Among them, (meth) acrylic acid is preferably used, but when used for a metal substrate, it is preferable not to contain a carboxyl group from the viewpoint of preventing corrosion.

  Examples of the acetoacetyl group-containing monomer include 2- (acetoacetoxy) ethyl (meth) acrylate and allyl acetoacetate.

  Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

  Examples of the glycidyl group-containing monomer include glycidyl (meth) acrylate, allyl glycidyl (meth) acrylate, and the like.

  Examples of the amino group-containing monomer include monomers having an ethylenically unsaturated double bond and an amino group (unsubstituted or substituted amino group), such as aminomethyl (meth) acrylate, aminoethyl (meth) acrylate, N-alkylaminoalkyl (meth) acrylates such as aminopropyl (meth) acrylate, aminoalkyl (meth) acrylate such as aminoisopropyl (meth) acrylate, and N- (t-butyl) aminoethyl (meth) acrylate Mono-substituted amino group-containing (meth) acrylic acid ester such as acrylic acid ester; (meth) acrylic acid N, N-dimethylaminoethyl, (meth) acrylic acid N, N-diethylaminoethyl, (meth) acrylic acid N, N -(Meth) acrylic acid esters of N, N-dialkylaminoalkyl such as dimethylaminopropyl Disubstituted amino group-containing (meth) acrylic acid esters; dialkylaminoalkyl (meth) acrylamides such as N, N-dimethylaminopropyl (meth) acrylamide; quaternized salts of these amino group-containing monomers; p-amino Amino group-containing styrenes such as styrene; styrenes having a dialkylamino group such as 3- (dimethylamino) styrene and dimethylaminomethylstyrene; dialkyls such as N, N-dimethylaminoethyl vinyl ether and N, N-diethylaminoethyl vinyl ether Aminoalkyl vinyl ethers; and allylamine, 4-diisopropylamino-1-butene, trans-2-butene-1,4-diamine, 2-vinyl-4,6-diamino-1,3,5-triazine and the like.

  Examples of the amide group-containing monomer include monomers having an ethylenically unsaturated double bond and an amide group (group having an amide bond), such as (meth) acrylamide; N-methyl (meth) acrylamide, N-ethyl. (Meth) acrylamide, N-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, Nn-butyl (meth) acrylamide, N-isobutyl (meth) acrylamide, Ns-butyl (meth) acrylamide, N -T-butyl (meth) acrylamide, N-hexyl (meth) acrylamide, diacetone (meth) acrylamide, N, N'-methylenebis (meth) acrylamide, N- (1,1-dimethyl-3-oxobutyl) (meta ) N-alkyl (meth) acrylics such as acrylamide N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dipropyl (meth) acrylamide, N, N-diisopropyl (meth) acrylamide, N, N-di (n- Butyl) (meth) acrylamide, N, N-diisobutyl (meth) acrylamide, N, N-di (s-butyl) (meth) acrylamide, N, N-di (t-butyl) (meth) acrylamide, N, N -Dipentyl (meth) acrylamide, N, N-dihexyl (meth) acrylamide, N, N-diheptyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N, N-diallyl (meth) acrylamide, N, N -N, N-dialkyl (meth) acrylamide such as ethylmethylacrylamide; N, N-dimethyla Dialkylaminoalkyl (meth) acrylamides such as nopropyl (meth) acrylamide; N-vinylacetamide, N-vinylformamide, (meth) acrylamide ethylethyleneurea, substituted amide group-containing single amounts such as (meth) acrylamide t-butylsulfonic acid Body; hydroxyl group-containing (meth) acrylamide such as N-methylol (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-methylolpropane (meth) acrylamide; N-methoxymethyl (meth) acrylamide, N- (n -Alkoxy group-containing (meth) acrylamides such as butoxymethyl) (meth) acrylamide; and quaternized salts of these amide group-containing monomers.

These functional group-containing monomers (a2) may be used alone or in combination of two or more.
Among these, in the present invention, it is preferable to contain a functional group-containing monomer containing a nitrogen atom from the viewpoint of crosslinking promotion effect, particularly preferably an amino group-containing monomer, an amide group-containing monomer, and more preferably dimethylamino. Ethyl (meth) acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl (meth) acrylamide, dimethyl (meth) acrylamide, particularly preferably dimethylaminopropyl acrylamide.

  The content of the functional group-containing monomer (a3) other than the hydroxyl group in the polymerization component is usually 0.001 to 30% by weight, preferably 0.01 to 20% by weight, particularly preferably 0.05 to 15% by weight. %. If the content is too small, the degree of cross-linking tends to decrease and adherend contamination tends to increase. If it is too large, the adhesive strength immediately after application tends to be too high.

  When the functional group-containing monomer other than the hydroxyl group (a3) contains an amino group-containing monomer and / or an amide group-containing monomer, the content of the monomer in the polymerization component is preferably 0.001 to 30% by weight, Especially preferably, it is 0.005 to 5 weight%, More preferably, it is 0.01 to 2 weight%. If the content is too high, the molecular weight tends to decrease during polymerization or the pressure-sensitive adhesive tends to be colored. If the content is too low, the crosslinking promoting effect tends to be insufficient.

As other copolymerizable monomer (a4), for example,
One fragrance such as phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, styrene, α-methylstyrene, etc. A monomer containing a ring;
Biphenyloxy structure-containing (meth) acrylic acid ester monomers such as biphenyloxyethyl (meth) acrylate;
Alkoxy such as 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and polypropylene glycol mono (meth) acrylate A monomer containing a group or an oxyalkylene group;
Acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride Methyl vinyl ketone, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, and the like.
These can be used alone or in combination of two or more.

  The content of the other copolymerizable monomer (a4) in the polymerization component is usually 0 to 40% by weight, preferably 0.001 to 30% by weight, and particularly preferably 0.01 to 25% by weight. . When there is too much content, there exists a tendency for an adhesive characteristic to fall easily.

  In the polymerization of the acrylic resin (A) having a hydroxyl group, conventionally known methods such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be employed. For example, in the organic solvent, the (meth) acrylic acid ester monomer (a1), the hydroxyl group-containing monomer (a2), and, if necessary, a functional group-containing monomer other than a hydroxyl group (a3), other copolymerizable monomers ( A polymerization component containing a4) and a polymerization initiator are mixed or dropped, and polymerization is carried out at reflux or at 50 to 90 ° C. for 2 to 20 hours.

  The weight average molecular weight of the acrylic resin (A) having a hydroxyl group of the present invention is usually 100,000 to 2,500,000, preferably 200,000 to 2,200,000, particularly preferably 400,000 to 2,000,000. If the weight average molecular weight is too low, the heat resistance of the pressure-sensitive adhesive layer tends to decrease and the adherend contamination tends to increase. If it is too high, a large amount of dilution solvent is required, which is disadvantageous in terms of coating properties and cost. Tend to be.

  The degree of dispersion (weight average molecular weight / number average molecular weight) of the acrylic resin (A) having a hydroxyl group is, for example, usually 20 or less, preferably 15 or less, particularly preferably 10 or less, and the lower limit is usually 1 .1. If the degree of dispersion is too high, the heat resistance of the pressure-sensitive adhesive layer tends to decrease, and foaming and the like tend to occur.

In addition, said weight average molecular weight is a weight average molecular weight by standard polystyrene molecular weight conversion, and it is a column in a high performance liquid chromatography (The Japan Waters company, "Waters 2695 (main body)" and "Waters 2414 (detector)"). : Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical plate number: 10,000 plates / piece, filler material: styrene-divinylbenzene copolymer, filler The particle diameter is measured by using three series of 10 μm), and the same method can be used for the number average molecular weight. The degree of dispersion is determined from the weight average molecular weight and the number average molecular weight.
In the measurement, the polymer may be derivatized or the type of the eluent may be appropriately changed.

  Furthermore, the glass transition temperature of the acrylic resin (A) having a hydroxyl group is usually −80 to 0 ° C., preferably −75 to −5 ° C., particularly preferably −70 to −10 ° C. If the glass transition temperature is too high, the adhesive strength after the heating step tends to be high, and if the glass transition temperature is too low, the heat resistance tends to decrease and adherend contamination tends to increase.

The glass transition temperature is calculated from the following Fox equation.

  The pressure-sensitive adhesive composition of the present invention preferably contains 30 to 99% by weight, particularly preferably 40 to 97% by weight, more preferably the acrylic resin (A) having a hydroxyl group based on the total amount of the pressure-sensitive adhesive composition. 50 to 95% by weight.

  It is important that the pressure-sensitive adhesive composition of the present invention contains an isocyanate-based crosslinking agent (B) as a crosslinking agent in terms of high reactivity and improved heat resistance.

As said isocyanate type crosslinking agent (B), for example,
Aromatic diisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate;
Cycloaliphatic diisocyanates such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, dimer acid diisocyanate, norbornene diisocyanate, trans-cyclohexane diisocyanate, hydrogenated tolylene diisocyanate;
Aliphatic isocyanates such as hexamethylene diisocyanate;
Etc.
Furthermore, adduct bodies of these polyisocyanate compounds and polyol compounds such as trimethylolpropane, burette bodies and isocyanurate bodies of these polyisocyanate compounds can be mentioned.

  Among them, the isocyanurate form of hexamethylene diisocyanate and 2,4-tolylene diisocyanate and / or 2,6-tolylene diisocyanate and trimethylolpropane are small in the increase in adhesive strength after heating and good in heat resistance. And adduct bodies of 2,4-tolylene diisocyanate and / or 2,6-tolylene diisocyanate isocyanurate, and tetramethylxylylene diisocyanate and trimethylolpropane are preferred.

  Content of the said isocyanate type crosslinking agent (B) is 0.5-40 weight part with respect to 100 weight part of acrylic resin (A) which has a hydroxyl group, More preferably, it is 1-30 weight part, Especially preferably, it is 2- 25 parts by weight. If the content of the isocyanate-based crosslinking agent is too large, the crosslinking of the pressure-sensitive adhesive proceeds excessively, and the adhesive strength is reduced. Therefore, there is a tendency to cause floating between the adherend surface. There is a tendency that the cohesive strength of the agent is lowered and the heat-resistant stain resistance is lowered.

Moreover, in this invention, the other crosslinking agent normally used for an adhesive composition can also be used together in the range which does not impair the objective of this invention.
Examples of such a crosslinking agent include an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, an oxazoline-based crosslinking agent, a melamine-based crosslinking agent, an aldehyde-based crosslinking agent, and an amine-based crosslinking agent.

  It is important that the pressure-sensitive adhesive composition of the present invention contains a zinc compound (C) in that both a pot life and an immediate curing property can be achieved and a smooth pressure-sensitive adhesive layer can be obtained.

As said zinc compound (C), a metal simple substance (zinc simple substance), inorganic zinc, organic zinc etc. are mention | raise | lifted, for example. These can be used alone or in combination of two or more.
Examples of the inorganic zinc include zinc oxide, zinc hydroxide, zinc inorganic salt, and zinc inorganic acid salt.
Examples of the organic zinc include alkoxide zinc compounds in which alcohol is bonded, and zinc chelate compounds in which β-diketone compounds such as acetylacetone and ethyl acetoacetate are coordinated. Examples include zinc propoxide, zinc butoxide, zinc acetyl acetate, zinc ethyl acetoacetate, zinc acetylacetonate, etc. In the present invention, zinc acetylacetonate is used from the viewpoint of achieving both sufficient pot life and quick curing. It is preferable.

In addition, as said zinc compound (C), "X-1301" by a Matsumoto fine chemical company made from a commercial item, Tokyo Chemical Industry Co., Ltd. "Bis (2, 4-pentandionato) zinc (II)"
"King Industries, Inc." “K-KAT 670” or the like manufactured by the manufacturer may be used.

  It is preferable that content of the said zinc compound (C) is 0.001-30 weight part with respect to 100 weight part of acrylic resin (A) which has a hydroxyl group, More preferably, 0.005-20 weight part, Particularly preferred is 0.01 to 15 parts by weight. When there is too little content of a zinc compound (C), there exists a tendency for immediate curability to fall, and when there is too much, there exists a tendency for a metal to precipitate.

Further, the content ratio (weight ratio) (C) / (B) of the isocyanate-based crosslinking agent (B) and the zinc compound (C) (solid content equivalent amount) is preferably 0.0001 to 10, more preferably. 0.001 to 1.0, particularly preferably 0.002 to 0.5.
When there is too much content of a zinc compound (C) with respect to content of an isocyanate type crosslinking agent (B), there exists a tendency for a metal to precipitate.
If the amount is too small, the immediate curing property is insufficient, and the surface of the smooth pressure-sensitive adhesive layer tends not to be obtained.

  Moreover, it is preferable that the adhesive composition of this invention contains a crosslinking retarder (D) at the point which extends pot life and improves applicability | paintability.

Examples of the crosslinking retarder (D) include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, stearyl acetoacetate, acetylacetone, and 2,4-hexanedione. And β-diketones such as benzoylacetone. These are ketoenol tautomeric compounds. By protecting the zinc compound (C), the catalytic activity in the solution state of the zinc compound is reduced, and excessive viscosity increase or gelation of the pressure-sensitive adhesive composition after blending is achieved. And the pot life of the pressure-sensitive adhesive composition can be extended.
Among these, it is preferable to use acetylacetone as the crosslinking retarder (D) from the viewpoint of the balance between pot life and immediate curing.
These crosslinking retarders (D) can be used alone or in combination of two or more.

  As the crosslinking retarder (D), commercially available products such as “acetylacetone” manufactured by Daicel Corporation, “acetylacetone” manufactured by Tokyo Chemical Industry, “acetylacetone” manufactured by Wako Pure Chemical Industries, “acetylacetone” manufactured by Kishida Chemical, etc. may be used. .

Since the crosslinking retarder (D) has the effect of suppressing crosslinking, contrary to the crosslinking promotion effect of the zinc compound (C), the ratio of the crosslinking retarder (D) to the zinc compound (C) is appropriately set. It is preferable to do.
In order to extend the pot life of the pressure-sensitive adhesive composition and not impair the immediate curing, the content ratio (weight ratio) of the crosslinking retarder (D) and the zinc compound (C) (solid content equivalent amount) is zinc. Compound (C): Crosslinking retarder (D) is preferably in the range of 0.01: 1 to 15: 1, more preferably 0.1: 1 to 13: 1, and particularly preferably 0. .5: 1 to 10: 1.
If the content of the crosslinking retarder (D) is too small relative to the content of the zinc compound (C), the pot life tends to be short and the coating property tends to decrease, and if too much, the quick curability tends to decrease. There is.

  The pressure-sensitive adhesive composition of the present invention further includes an antistatic agent, an antioxidant, a plasticizer, a filler, a pigment, a diluent, an anti-aging agent, an ultraviolet absorber, and an ultraviolet stabilizer as long as the effects of the present invention are not impaired. Further, an additive such as a tackifying resin may be further contained, and these additives may be used alone or in combination of two or more. In particular, the antioxidant is effective for maintaining the stability of the pressure-sensitive adhesive layer. The content when the antioxidant is blended is not particularly limited, but is preferably 0.01 to 5% by weight. In addition to the additives, a small amount of impurities contained in the raw materials for producing the constituent components of the pressure-sensitive adhesive composition may be contained.

The gel fraction of the pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition of the present invention with an isocyanate-based crosslinking agent (B) is usually 40 to 100%, preferably 60 to 100%, particularly preferably 80 to 100%. More preferably, it is 85 to 100%, and particularly preferably 90 to 100%.
If the gel fraction is too low, the cohesive force of the pressure-sensitive adhesive is lowered, and adhesive residue is generated, which tends to cause adherend contamination.

  The gel fraction is a measure of the degree of crosslinking, and is calculated, for example, by the following method. That is, a pressure-sensitive adhesive sheet (not provided with a separator) in which a pressure-sensitive adhesive layer is formed on a polymer sheet (for example, polyethylene terephthalate film or the like) as a base material is wrapped with a 200-mesh SUS wire mesh, and 23 in toluene. The weight percentage of the insoluble pressure-sensitive adhesive component immersed in the wire mesh at 24 ° C. for 24 hours is defined as the gel fraction. However, the weight of the substrate is subtracted.

  The pressure-sensitive adhesive composition of the present invention exhibits a pressure-sensitive adhesive strength (about 2 N / 25 mm or less), and temporarily protects the surface of the adherend by crosslinking with a crosslinking agent to form a pressure-sensitive adhesive. Therefore, it is suitably used as a masking film pressure-sensitive adhesive or a heat-resistant pressure-sensitive adhesive film pressure-sensitive adhesive to be bonded to an adherend for a short period (several hours to several days).

  In the present invention, a masking film and a heat-resistant adhesive film are prepared by preparing a pressure-sensitive adhesive for a masking film or a heat-resistant adhesive film from the above-mentioned pressure-sensitive adhesive composition, and forming a pressure-sensitive adhesive layer on the base film. Alternatively, a heat-resistant adhesive film for masking (hereinafter sometimes collectively referred to as an adhesive film) can be obtained. In addition, the adhesive which comprises an adhesive layer is what the said adhesive composition bridge | crosslinked with the isocyanate type crosslinking agent (B).

  Examples of the base material on which the pressure-sensitive adhesive layer is laminated include a single layer or laminated film made of metal, polyester resin, polyfluorinated ethylene resin, polyimide and derivatives thereof, epoxy resin, and the like. In the masking film, the heat-resistant adhesive film or the heat-resistant adhesive film for masking, it is preferable to further provide a release film on the surface of the pressure-sensitive adhesive layer opposite to the base material. When the masking film, the heat-resistant adhesive film or the heat-resistant adhesive film for masking is put to practical use, the release film is peeled off and used. As the release film, a silicon release film, an olefin release film, a fluorine release film, a long-chain alkyl release film, and an alkyd release film can be used.

  The method for producing the above adhesive film is as follows: [1] A method in which a pressure-sensitive adhesive composition is applied on a substrate and dried, and then a release film is bonded and an aging treatment is performed. [2] A release film Examples include a method of applying an adhesive composition on the top, drying the substrate, pasting a base material, and performing an aging treatment. Among these, the method [1] is preferable in terms of improving the adhesion to the substrate, workability and stable production.

  The aging treatment is carried out to balance the physical properties of the adhesive. As the aging conditions, the temperature is usually 0 to 150 ° C., preferably 10 to 100 ° C., particularly preferably 20 to 80 ° C., and the time is Usually, it is 30 days or less, preferably 14 days or less, particularly preferably 7 days or less. Specifically, it can be carried out under conditions such as 3 to 10 days at 23 ° C., 1 to 7 days at 40 ° C. .

  In order to allow the crosslinking reaction to sufficiently proceed, the pressure-sensitive adhesive film imparted with heat resistance usually requires an aging treatment, but in the present invention, by containing the above zinc compound, it has excellent immediate curing properties. Therefore, a smooth pressure-sensitive adhesive layer surface can be formed without transferring fine irregularities to the pressure-sensitive adhesive layer during aging.

  In applying the pressure-sensitive adhesive composition, it is preferable to dilute and apply the pressure-sensitive adhesive composition to a solvent, and the dilution concentration is preferably 5 to 60% by weight, particularly preferably 10 to 50% by weight. The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition. For example, ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; acetone, methyl ethyl ketone, A ketone solvent such as methyl isobutyl ketone; an aromatic solvent such as toluene and xylene; and an alcohol solvent such as methanol, ethanol and propyl alcohol can be used. Among these, ethyl acetate, methyl ethyl ketone, and toluene are preferably used from the viewpoints of solubility, drying property, price, and the like.

  The pressure-sensitive adhesive composition can be applied by a conventional method such as roll coating, die coating, gravure coating, comma coating, or screen printing.

  The thickness of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive film is usually 5 to 300 μm, preferably 5 to 50 μm, and particularly preferably 10 to 30 μm. If this pressure-sensitive adhesive layer is too thin, the physical properties of the adhesive tend to be difficult to stabilize, and if it is too thick, the entire pressure-sensitive adhesive film tends to be too thick and the usability tends to deteriorate.

  As the adherend of the adhesive film, it is preferable to use a base material of a material having heat resistance, such as a metal plate or metal foil of aluminum, copper, iron, stainless steel, magnesium, nickel, titanium, etc .; polyethylene terephthalate, Polyester resins such as polyethylene naphthalate, polybutylene terephthalate, polyethylene terephthalate / isophthalate copolymer, ester acrylate; polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, etc. Polyfluorinated ethylene resin; polyimide and its derivatives; bisphenol type epoxy resin, epoxy resin composite material, alicyclic epoxy resin, epoxy novolac, biphenyl type epoxy resin, epoxy acrylate, etc. And the like.

  The adhesive strength of the adhesive layer of the adhesive film is adjusted as appropriate according to the material of the adherend. For example, when pasting on a SUS-BA plate, a hard-coated PET film, glass, a polyimide film, etc. The adhesive strength immediately after coating (before aging) is preferably 0.01 to 1.0 N / 25 mm, particularly preferably 0.05 to 0.5 N / 25 mm, more preferably 0.1 to 0. .3 N / 25 mm.

  Moreover, it is preferable that the adhesive force of the adhesive layer of the adhesive film after an aging is 0.01-1.0N / 25mm, Especially preferably, it is 0.05-0.5N / 25mm, More preferably, it is 0.1. It is -0.3N / 25mm.

  Further, the adhesive strength of the adhesive layer of the adhesive film after heating is preferably 0.01 to 1.2 N / 25 mm, particularly preferably 0.05 to 0.6 N / 25 mm, and more preferably 0.1 to 1.2 N / 25 mm. 0.3 N / 25 mm.

The masking film, the heat-resistant adhesive film or the heat-resistant adhesive film for masking obtained using the pressure-sensitive adhesive composition of the present invention is hardly contaminated when peeled from the adherend even after being used under high temperature conditions. Because it can be peeled off with a small force, it can be used in masking applications that require heat resistance, such as masking adhesive films for temporarily protecting the surface of circuit boards such as FPC boards and ITO transparent electrode layers, or in the manufacturing process. It can be used for all temporary fixing applications for temporary fixing for holding and reinforcement.
In addition, the pressure-sensitive adhesive composition of the present invention has an immediate curing property, and fine unevenness of the release film is difficult to be transferred to the pressure-sensitive adhesive surface of the pressure-sensitive adhesive layer, so that it is used for protective films for displays such as flat panel displays and touch panels. Even when used as, it is possible to prevent a decrease in visibility due to unevenness.

  As a method for using the heat-resistant adhesive film for masking obtained using the pressure-sensitive adhesive composition of the present invention, the heat-resistant adhesive film for masking is stuck on the surface of the adherend, usually 100 ° C. or higher (preferably 110 ° C. or higher, especially It is preferable that the masking heat-resistant adhesive film is peeled off from the adherend surface after being subjected to a heating step of preferably 120 ° C. or higher, more preferably 130 ° C. or higher.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded. In the examples, “%” and “parts” mean weight basis.

<Manufacture of acrylic resin (A) solution>
[Production Example 1: Acrylic resin (A-1)]
In a reactor equipped with a thermometer, a stirrer, a dropping funnel and a reflux condenser, 74.2 parts of ethyl acetate was charged, the temperature was increased while stirring, and when the temperature reached about 80 ° C., 91.85 parts of butyl acrylate (BA). , Hydroxyethyl acrylate (HEA) 7.0 parts, dimethylaminopropyl acrylamide (DMAPAA) 0.15 parts, azobisisobutyronitrile (AIBN) 0.06 parts, ethyl acetate 6.0 parts mixed and mixed The solution was added dropwise over 2 hours. Further, during the polymerization, a mixed solution obtained by mixing 0.3 part of ethyl acetate with 0.8 part of 4-hydroxybutyl acrylate (4HBA), mixed solution of 0.05 part of AIBN mixed with 0.3 part of ethyl acetate, While continuously adding a mixed solution in which 0.3 part of ethyl acetate was mixed with 0.2 part of 4HBA, and finally a mixed solution in which 0.05 part of AIBN was mixed with 0.3 part of ethyl acetate, 7.5 ° After refluxing for hours, the solution was diluted with ethyl acetate to obtain a 42% solution of acrylic resin (A-1).

<Isocyanate-based crosslinking agent (B)>
(B-1)
Hexamethylene diisocyanate trimer (Nippon Polyurethane Industry Co., Ltd. “Coronate HX”)

<Metal compound>
[Zinc compound (C)]
(C-1)
Zinc acetylacetonate (Matsumoto Fine Chemical Co., Ltd. “X-1301”, solid content 19%)

[Metal compounds other than zinc]
(C′-1: zirconium compound)
Zirconium tetraacetylacetonate (Matsumoto Fine Chemical Co., Ltd. “ZC-700”, solid content 20%)
(C'-2: Aluminum compound)
Tris (2,4-pentanedionato) aluminum (III) (“Narsem Aluminum” manufactured by Nippon Chemical Industry Co., Ltd., solid content concentration 100%)
(C′-3: tin compound)
Dibutyltin dilaurate (Kishida Chemical Co., Ltd.)
(C′-4: tin compound)
Dialkylacetylacetone tin complex solution: 30 parts of acetylacetone was added to 10 parts of a 1% solution of dibutyltin dilaurate (DBTL) dissolved in toluene to prepare a catalyst solution containing 0.25% by weight of dialkylacetylacetone tin complex.

<Crosslinking retarder (D)>
・ (D-1)
Acetylacetone

<Example 1>
(Preparation of pressure-sensitive adhesive composition)
11.8 parts of the isocyanate-based crosslinking agent (B-1) and 0.1 part of the zinc compound (C-1) with respect to 100 parts of the solid content of the acrylic resin (A-1) obtained above ( Solid content equivalent amount) and 20 parts of acetylacetone (D-1) were blended to prepare an adhesive composition.

[Pot life]
About the adhesive composition prepared above, pot life was evaluated by the following method.
After preparing the adhesive composition, it was put in a storage bottle and placed in a constant temperature water bath at 25 ° C., and the viscosity of the adhesive composition after 1 hour was measured with a B-type viscometer at 25 ° C. for 1 minute. Then, it was further continued in a constant temperature water bath at 25 ° C., and the viscosity after 8 hours from the adjustment was measured with a B-type viscometer at 25 ° C. × 1 minute, and evaluated according to the following criteria.
(Evaluation criteria)
○: The viscosity after 8 hours is less than twice the viscosity after 1 hour. Δ ... The viscosity after 8 hours is more than 2 times and less than 3 times the viscosity after 1 hour. ..Viscosity after 8 hours is more than 3 times the viscosity after 1 hour

[Production of adhesive film]
The pressure-sensitive adhesive composition prepared above was applied to a base PET film (thickness: 38 μm) so that the thickness of the spreader layer after drying was about 25 μm, and then dried at 150 ° C. for 2 minutes. Thereafter, a release-treated PET film was attached to the coated surface to protect the pressure-sensitive adhesive layer, and a pressure-sensitive adhesive film was produced.
The following evaluation was performed using the obtained adhesive film. The results are shown in Table 1.

[Immediate curing]
A 25 mm × 100 mm test piece was prepared using the adhesive film after 3 hours from the preparation of the adhesive film, and the release film was peeled off. Then, a 25 μm-thick polyimide film (Toray Industries, Inc.)・ Applied to the polyimide film surface of the adherend to which DuPont's “Kapton 100H”) was attached in an atmosphere of 23 ° C. and a relative humidity of 50% by two reciprocations of 2 kg rubber rollers, and 30 under the same atmosphere. After standing for a minute, 180 degree peel strength (N / 25 mm) was measured at a peel rate of 300 mm / min, and evaluated according to the following criteria.
In addition, it shows that the pressure-sensitive adhesive layer is more cross-linked as the numerical value of the peel strength is smaller, and it can be seen that the cross-linking proceeds in a short time such as 3 hours from the production of the pressure-sensitive adhesive film. Therefore, it can be judged that the surface of the pressure-sensitive adhesive layer is smooth without transferring the fine irregularities of the release-treated PET film.
(Evaluation criteria)
○ ... less than 0.3N / 25mm △ ... 0.3N / 25mm or more, less than 0.5N / 25mm × ... 0.5N / 25mm or more

〔Heat-resistant〕
<Adhesive strength: Before heating>
After the adhesive film obtained above was aged at 40 ° C. for 7 days, a test piece of 25 mm × 100 mm was prepared and the release film was peeled off, and then a polyimide film having a thickness of 25 μm on a stainless steel plate (SUS304BA plate). (Applying “Kapton 100H” manufactured by Toray DuPont Co., Ltd.) Attached to the polyimide film surface of the adherend by two reciprocations of a 2 kg rubber roller in an atmosphere of 23 ° C. and a relative humidity of 50%. After being left for 30 minutes, 180 degree peel strength (N / 25 mm) was measured at a peel rate of 300 mm / min, and evaluated according to the following criteria.
(Evaluation criteria)
○ ... less than 0.3N / 25mm △ ... 0.3N / 25mm or more, less than 0.5N / 25mm × ... 0.5N / 25mm or more

<Adhesive strength: After heating>
After the adhesive film obtained above was aged at 40 ° C. for 7 days, a test piece of 25 mm × 100 mm was prepared and the release film was peeled off, and then a polyimide film having a thickness of 25 μm on a stainless steel plate (SUS304BA plate). (Applying “Kapton 100H” manufactured by Toray DuPont Co., Ltd.) Affixed to the polyimide surface of the adherend with two reciprocations of a 2 kg rubber roller in an atmosphere of 23 ° C. and a relative humidity of 50%. Left for 30 minutes. Then, it exposed to 150 degreeC conditions for 1.5 hours, and returned to 23 degreeC after that. Further, after being left for 2 hours in an atmosphere of 23 ° C. and 50% relative humidity, 180 ° peel strength (N / 25 mm) was measured at a peel rate of 300 mm / min, and evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ less than 0.3N / 25mm △ ・ ・ ・ 0.3N / 25mm or more, less than 0.6N / 25mm × ・ ・ ・ 0.6N / 25mm or more

[Heat resistant contamination]
The adhesive film obtained above was aged at 40 ° C. for 7 days, and then a 25 mm × 100 mm test piece was prepared, and a 25 μm thick polyimide film (“Kapton 100H” manufactured by Toray DuPont Co., Ltd.) was used. ”) Was affixed to the adherend by reciprocating 2 kg rubber roller in an atmosphere of 23 ° C. and a relative humidity of 50%, and left in the same atmosphere for 30 minutes. Then, it exposed to 150 degreeC conditions for 1.5 hours, and returned to 23 degreeC after that. Further, after being left for 2 hours in an atmosphere of 23 ° C. and 50% relative humidity, the state of the adherend surface after 180 ° peeling was observed at a peeling speed of 300 mm / min, and evaluated according to the following criteria.
(Evaluation criteria)
○: Adhesive residue and stick marks were scarcely confirmed ×: Substrate interface peeling was confirmed

[Appearance of adhesive layer surface]
The pressure-sensitive adhesive film obtained above was aged at 40 ° C. for 7 days, and then the release film of the pressure-sensitive adhesive film was peeled off, and platinum was deposited on the pressure-sensitive adhesive layer surface at 30 mA for 40 seconds using a JFC-1600 auto fine coater. I let you. Thereafter, the surface of the pressure-sensitive adhesive layer on which platinum was vapor-deposited was observed with a microscope (VHX-900 (model number) manufactured by Keyence Corporation) and evaluated according to the following criteria.
(Evaluation criteria)
◯: Unevenness on the surface was hardly confirmed.
Δ: Some irregularities on the surface were confirmed.
X: Many irregularities on the surface were confirmed.

<Example 2, Comparative Examples 1-5>
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the components of the pressure-sensitive adhesive composition were blended in the proportions shown in Table 1, and a pressure-sensitive adhesive film was produced. Evaluation similar to Example 1 was performed using the obtained adhesive composition and adhesive film. The results are shown in Table 1.

  In the pressure-sensitive adhesive compositions of Examples 1 and 2 having a pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive composition containing a specific amount of an isocyanate-based cross-linking agent (B) as a cross-linking agent and a zinc-based compound (C) as a cross-linking catalyst, The adhesive strength increase rate after 8 hours after time is low, that is, it has a sufficient pot life, and in the adhesive film, the adhesive strength of the adhesive film after 3 hours is low, the appearance of the coating film is Good, that is, excellent in rapid curing, and does not become excessive even after being exposed to a high temperature condition of 150 ° C. for 1.5 hours, and peels off from the adherend with a small force. It can be seen that contamination is less likely to occur when peeled from the adherend.

On the other hand, Comparative Example 1, which does not contain a zinc compound, was inferior in immediate curability, had irregularities on the surface of the pressure-sensitive adhesive layer, and was inferior in appearance. Furthermore, the adhesive strength after heating was high, and the light peelability was poor.
Moreover, in Comparative Examples 2-5 using metal compounds other than zinc (zirconium compound, aluminum compound, tin compound), the rate of increase in the viscosity of the adhesive composition is high, and it does not have a sufficient pot life, or after production 3 It can be seen that the adhesive force of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive film over time is high and the coating film has irregularities, that is, it is inferior in immediate curing.

  The pressure-sensitive adhesive composition of the present invention includes a heat-resistant adhesive film for masking and a flat panel display for masking and fixing in a heating process included in a manufacturing process of touch panel-related members such as circuit boards such as FPC boards and ITO transparent electrodes. It can be suitably used for a surface protective adhesive film such as a touch panel.

Claims (8)

  A pressure-sensitive adhesive composition comprising an acrylic resin (A) having a hydroxyl group, an isocyanate-based crosslinking agent (B), and a zinc compound (C).   The pressure-sensitive adhesive composition according to claim 1, wherein the content of the isocyanate-based crosslinking agent (B) is 0.5 to 40 parts by weight with respect to 100 parts by weight of the acrylic resin (A) having a hydroxyl group. .   The content ratio (weight ratio) (C) / (B) of the isocyanate-based crosslinking agent (B) and the zinc compound (C) (solid content conversion amount) is 0.0001 to 0.5. 3. The pressure-sensitive adhesive composition according to 1 or 2.   The pressure-sensitive adhesive composition according to any one of claims 1 to 3, further comprising a crosslinking retarder (D).   A pressure-sensitive adhesive, wherein the pressure-sensitive adhesive composition according to any one of claims 1 to 4 is crosslinked with an isocyanate-based crosslinking agent (B).   A pressure-sensitive adhesive for masking film, comprising the pressure-sensitive adhesive according to claim 5.   A pressure-sensitive adhesive for a heat-resistant pressure-sensitive adhesive film, comprising the pressure-sensitive adhesive according to claim 5.   A heat-resistant adhesive film for masking, comprising an adhesive layer comprising the adhesive according to claim 5 on the film.