JP4682299B2 - Pressure sensitive adhesive for protective sheet - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive for protective sheets excellent in high-speed peelability. More specifically, the pressure-sensitive adhesive for protective sheets has a small force required for peeling even during high-speed peeling and a small change in peeling force depending on the peeling speed. The present invention relates to an agent and a surface protective sheet for an optical film using the same.

  In recent years, with the development of the display field, special optical members are increasing. Among them, there are a great many optical films such as polarizing plates, retardation plates, brightness enhancement films used for liquid crystal displays, AR films, electromagnetic wave shielding films, IR cut films used for plasma displays. These are known and are often laminated and used.

  And until the display is assembled, these optical films usually go through processes such as punching, transportation, inspection, etc., but the surface is usually free from scratches, dirt, etc. A surface protection sheet is attached.

  These surface protective sheets are peeled off and discarded when they are no longer needed after each process. However, since such peeling work is mainly manual work, the peeling speed is relatively high and the speed is also high. It was difficult to maintain a constant from the start to the end of peeling.

  In general, the faster the peeling speed, the greater the force required for peeling (hereinafter abbreviated as “peeling force”), and therefore the work efficiency of surface protection sheet peeling deteriorates, and the optical film is damaged or contaminated during peeling. There was a problem such as. In addition, there is a problem that a phenomenon called so-called zipping, which produces a crisp sound without peeling off smoothly, occurs. Furthermore, if the peeling force is made sufficiently small, problems such as floating and peeling may occur during the work process. For this reason, there is an increasing demand for a surface protection sheet that has a small peeling force and does not cause problems such as floating and peeling even in high-speed peeling or low-speed peeling.

  In general, as a pressure-sensitive adhesive for a sheet for protecting the surface of a plastic plate, a metal plate such as stainless steel, a glass plate, etc., a (meth) acrylic acid ester and a monomer having a functional group in the side chain are used. A polymer obtained by adding a crosslinking agent to a polymer obtained by copolymerization is known. However, these protective sheets are used while being adhered to the substrate without being peeled off, and of course they were not intended to improve the peelability.

  As such an example, for example, Patent Document 1 describes a pressure-sensitive adhesive using two types of (meth) acrylic polymers having different glass transition temperatures, but in this prior art, the glass transition temperature is high. Since the polymer is simply added to increase the adhesiveness, the obtained pressure-sensitive adhesive film requires an extremely large peeling force at the time of high-speed peeling, and cannot be applied at all in a field having a peeling process.

  As a technology for improving the peelability of a protective sheet used in a field having a peeling process, a technique in which a small amount of a plasticizer such as polyester is added to an adhesive made of an acrylic polymer and a crosslinking agent is known. (See Patent Document 2). However, even in this case, when the composition is such that the peeling force in high-speed peeling is generally large and the peeling force in high-speed peeling is small, only a surface protective sheet that causes floating or peeling can be obtained.

JP-A-10-310754 JP 2000-328016 A

  Therefore, there is a need to provide a pressure-sensitive adhesive for surface protection sheets that has good high-speed peelability, does not cause zipping, has little change in peel force due to the peel speed, and does not cause floating or peeling when heated. Therefore, the present invention aims to provide such an adhesive.

  As a result of intensive studies in order to solve the above problems, the present inventors have found that a (meth) acrylic polymer having a glass transition temperature of a certain value or less and a (meth) acrylic polymer having a glass transition temperature of a certain value or more. The pressure-sensitive adhesive for a protective sheet, which is used in combination and is subjected to a crosslinking reaction so that the gel fraction becomes a certain value or more, has found that the above problems can be solved, and has led to the present invention.

That is, the present invention includes the following components (A), (B) and (C),
(A) A (meth) acrylic polymer having a glass transition temperature of −40 ° C. or lower formed by copolymerization of at least a (meth) acrylic acid alkyl ester and a functional group-containing monomer. (Meth) acrylic polymer having a glass transition temperature of 80 ° C. or higher as a component (C) Crosslinking containing a crosslinking agent and blending component (B) at 5 to 20 parts by weight with respect to 100 parts by weight of component (A) The pressure-sensitive adhesive for protective sheets is obtained by crosslinking the adhesive composition so that the gel fraction becomes 80% or more.

  Moreover, this invention provides the surface protection sheet formed by coating the said pressure sensitive adhesive for protective sheets on a support body.

  The present invention obtained by using two types of (meth) acrylic polymers having different glass transition temperatures in a limited blending ratio and adjusting the degree of crosslinking with a crosslinking agent to bring the gel fraction to a certain value or more. When the pressure-sensitive adhesive for protective sheet is used as a pressure-sensitive adhesive for surface protective sheet, it has good high-speed peelability, does not cause zipping, does not contaminate the adherend after peeling, and depends on the peeling speed. It is possible to provide a surface protective sheet with little change in peeling force. Furthermore, it is possible to provide a durable surface protective sheet that does not float or peel off even if it is heated after being attached.

  In addition, by limiting the molecular weight ranges of the two types of (meth) acrylic polymers having different glass transition temperatures, it is possible to provide a surface protective sheet in which the change in peeling force due to the peeling speed is further reduced.

  In particular, by reducing the peeling force in high-speed peeling, it is possible to provide a surface protective sheet that can improve the efficiency of various production processes related to the optical film.

  Component (A), which is an essential component of the pressure-sensitive adhesive for protective sheets of the present invention, has a glass transition temperature of at least −40 ° C. formed by copolymerization of at least a (meth) acrylic acid alkyl ester and a functional group-containing monomer. It is a (meth) acrylic polymer.

  The (meth) acrylic acid alkyl ester used as the copolymerization component of component (A) is not particularly limited as long as the glass transition temperature of the (meth) acrylic polymer after copolymerization can be made -40 ° C. or lower. Not. Furthermore, the alkyl group of the alkyl ester may have an organic substituent such as a phenyl group. Specific examples include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, (meth ) Cyclohexyl acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, (meth) Examples include benzyl acrylate, phenylethyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol ester (meth) acrylate, and the like. These are used alone or in combination.

  Since the component (A) needs to have a glass transition temperature of −40 ° C. or lower, it is preferable to use an alkyl acrylate ester, and particularly preferably an alkyl acrylate having 4 to 12 carbon atoms in the alkyl group. Among them, 2-ethylhexyl acrylate is most preferable.

  In addition, the functional group-containing monomer which is another essential copolymerization component of the component (A) is a functional group that chemically reacts or interacts with a crosslinking agent described later, such as an epoxy group, a carboxyl group, an acid anhydride residue, an isocyanate. Although it will not specifically limit if it is a (co) polymerizable monomer which has group, a hydroxyl group, etc. in a molecule | numerator, Especially, what has a carboxyl group or a hydroxyl group as a functional group is mentioned.

  Specific examples of the functional group-containing monomer as described above include epoxy group-containing monomers such as glycidyl (meth) acrylate; carboxyl group-containing monomers such as (meth) acrylic acid, itaconic acid, crotonic acid, and fumaric acid; Acid anhydride residue-containing monomers such as maleic anhydride; hydroxyl-containing monomers such as 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate; ) Amino group-containing monomers such as dimethylaminoethyl acrylate.

  Among these, particularly preferred are (meth) acrylic acid having a carboxyl group as a functional group and 2-hydroxyethyl (meth) acrylate having a hydroxyl group as a functional group.

  Component (A) may be a copolymer obtained by copolymerizing only the above essential copolymerization component, but in addition to that vinyl acetate is copolymerized, it floats on the protective sheet and is less likely to cause peeling. Particularly preferred.

  Furthermore, in the production of the component (A), polymerizable monomers other than those described above can also be used. Examples of such polymerizable monomers include vinyl group-containing compounds such as styrene, vinyl toluene, α-methyl styrene, and allyl acetate.

  The copolymerization ratio of each monomer in producing the component (A) is not particularly limited, but preferably 50 to 99% by mass of (meth) acrylic acid alkyl ester (hereinafter, “% by mass” is simply “%”). And a copolymerization ratio of 1 to 10% of a functional group-containing monomer and 0 to 40% of vinyl acetate. Particularly preferable ranges of the copolymerization ratio are as follows.

(1) When vinyl acetate is not included as a copolymerization component
Particularly preferred range More particularly preferred range (Meth) acrylic acid alkyl ester 90-99% 93-97%
Functional group-containing monomer 1-10% 3-7%

(2) When vinyl acetate is included as a copolymerization component
Particularly preferred range More particularly preferred range (meth) acrylic acid alkyl ester 50-80% 60-75%
Functional group-containing monomer 1-10% 3-7% Vinyl acetate 10-40% 20-35%

  The production method of the component (A) using each of the above components is not particularly limited, and a known method can be used, but a radical polymerization method is preferable, a solution polymerization method is easy to adjust the molecular weight, and there are few impurities. It is preferable because it is possible.

It is necessary for the glass transition temperature (Tg) of the component (A) obtained as described above to be −40 ° C. or less in order to provide a good surface protective sheet having a small high-speed peeling force. A more preferable range is -70 ° C to -50 ° C. As the glass transition temperature in the present invention, an actual polymer measurement value may be used. However, when the glass transition temperature of the homopolymer is known, it can also be calculated by the following FOX equation.
1 / Tg = Wa / Tga + Wb / Tgb
Tg: Glass transition temperature of copolymer Tga, Tgb,...: Glass transition temperature Wa, Wb of homopolymer of monomer a, monomer b...: Monomer a, single amount Weight fraction of body b ...

  The molecular weight of component (A) is not particularly limited, but is preferably 100,000 or more and particularly preferably 200,000 or more in terms of weight average molecular weight. If the molecular weight is too small, it is necessary to add a large amount of a crosslinking agent in order to adjust the gel fraction, which may make it difficult to balance the performance. A more preferable range of weight average molecular weight is 300,000 to 1,000,000.

  On the other hand, the component (B) which is an essential component of the pressure-sensitive adhesive for protective sheets of the present invention is a (meth) acrylic polymer having a glass transition temperature of 80 ° C. or higher. The (meth) acrylic polymer refers to a homopolymer or copolymer of at least a (meth) acrylic acid alkyl ester.

  The (meth) acrylic acid alkyl ester that is the raw material of the component (B) is not particularly limited as long as the glass transition temperature of the component (B) can be 80 ° C. or higher, and examples thereof include (meth) acrylic acid. Methyl, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, octyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate Examples thereof include ethyl and phenoxyethyl (meth) acrylate, and these are used alone or in combination.

  As said (meth) acrylic-acid alkylester, in order to make the glass transition temperature of a component (B) 80 degreeC or more, a methacrylic acid alkylester is preferable, More preferably, the C1-C4 methacrylic acid of an alkyl group is preferable. Alkyl esters, particularly methyl methacrylate is most preferred.

  Moreover, although it is not an essential copolymerization component of a component (B), since the compatibility of a component (A) and a component (B) is made favorable, it is preferable that the functional group containing monomer is copolymerized. The thing preferable as a functional group containing monomer in a component (B) and its specific example can mention the functional group containing monomer quoted by the component (A).

  In the production of component (B), polymerizable monomers other than those described above can also be used. Examples of the polymerizable monomer that can be copolymerized include vinyl group-containing compounds such as vinyl acetate, styrene, vinyl toluene, α-methylstyrene, and allyl acetate.

  The production method of the component (B) using each of the components described above is not particularly limited, and a known method can be used, but a radical polymerization method is preferable, and among them, a solution polymerization method is particularly preferable.

  The glass transition temperature of the component (B) thus obtained is 80 ° C. or higher, which is necessary for suppressing high-speed peeling force and for preventing floating and peeling. Preferably, it is 90 ° C. or higher.

  The molecular weight of the component (B) is not particularly limited, but is preferably 1000 to 50,000, and particularly preferably 3000 to 30,000 in terms of weight average molecular weight. If the molecular weight is too large, the compatibility with the component (A) may deteriorate.

  The component (C) cross-linking agent that is an essential component of the pressure-sensitive adhesive for protective sheets of the present invention is a substance that cross-links the component (A) through chemical reaction or interaction with at least the functional group of the component (A). It is. The component (C) is not particularly limited as long as such conditions are satisfied, but a compound having an epoxy group, a compound having an isocyanate group, an aziridine derivative, a metal chelate compound, and the like are preferable.

  Among them, the compound having an epoxy group is not particularly limited, and specifically, bisphenol A epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether. 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, 1,3-bis ( N, N′-diamine glycidylaminomethyl) cyclohexane and the like include compounds having two or more epoxy groups in the molecule.

  Further, the compound having an isocyanate group is not particularly limited, and specifically, tolylene diisocyanate, chlorophenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, etc. A compound having two isocyanate groups in the molecule; a compound obtained by subjecting them to addition reaction with a polyhydric alcohol such as trimethylolpropane or pentaerythritol, an isocyanate compound, an isocyanurate compound, a burette type compound, or a known poly Addition reaction with ether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, polyisoprene polyol, etc. The urethane prepolymer type in the molecule can be exemplified compounds having two or more isocyanate groups. These are used alone or in combination of two or more.

  Among these, preferred are polyhydric alcohol adducts such as tolylene diisocyanate, xylylene diisocyanate or hexamethylene diisocyanate or trimethylolpropane thereof.

  Furthermore, as the aziridine derivative, 1,1 ′-(methylene-di-p-phenylene) bis-3,3-aziridylurea, 1,1 ′-(hexamethylene) bis-3,3-aziridylurea, 2,4 , 6-triaziridinyl-1,3,5-triazine, trimethylolpropane-tris- (2-aziridinylpropionate), and the like.

  Furthermore, examples of the metal chelate compound include compounds in which acetylacetone, ethyl acetoacetate, and the like are coordinated to a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium. It is done.

  The crosslinkable composition used in the present invention contains the component (A), the component (B), and the component (C). Among these, the amount of the component (B) is 100% by weight of the component (A). 5 to 20 parts by weight with respect to parts. When the blending amount of the component (B) is less than 5 parts by weight, the peeling speed is greatly dependent on the peeling speed, and the adhesive force at the time of high-speed peeling may be too large. Zipping may occur. Preferably, it is 8-15 weight part. On the other hand, the amount of the component (C) is not particularly limited, but is preferably about 0.5 to 10 parts by weight, particularly preferably 1 to 5 parts by weight with respect to 100 parts by weight of the component (A).

  The crosslinkable composition containing the component (A) to the component (C) as an essential component is coated on a support according to a conventional method, the solvent is distilled off, aging is performed, and crosslinking is performed to form a protective sheet feeling. Although it becomes a pressure adhesive, it is essential that the pressure sensitive adhesive for protective sheets of the present invention has a gel fraction of 80% or more. Here, the gel fraction in this invention is defined as what was calculated | required with the measuring method described in the Example. When the gel fraction is less than 80%, the adhesive strength may become too large.

  The pressure sensitive adhesive for protective sheet of the present invention obtained as described above preferably has a high speed peeling force of 100 gf / 24 mm (1 inch) or less. Here, “the high-speed peeling force of the pressure-sensitive adhesive for protective sheet” in the present invention has the pressure-sensitive adhesive for protective sheet produced by the same method as the production method described in Example 1 on the support. It is defined that the surface protective film was measured according to the high speed peel force measuring method described in the examples.

  Moreover, it is preferable that the low pressure peeling force is 20 gf / 24 mm or less as for the pressure sensitive adhesive for protective sheets of this invention. Here, “the low-speed peeling force of the pressure-sensitive adhesive for protective sheet” in the present invention has the pressure-sensitive adhesive for protective sheet produced by the same method as the production method described in Example 1 on the support. The surface protective film is defined as measured according to the low speed peel force measuring method described in the examples.

  By coating the crosslinkable composition containing at least component (A), component (B) and component (C) on a support, and performing coating solvent distillation, aging, etc., the protective sheet of the present invention A surface protective sheet in which a pressure sensitive adhesive is coated on a support can be obtained. Although it does not specifically limit as a support body used here, Plastic films, such as polyester, such as a polyethylene terephthalate (PET), polyethylene, a polypropylene, and an ethylene vinyl acetate copolymer, can be used conveniently.

  In the coating, a solvent may be used, and the solvent to be used is not particularly limited, and examples thereof include ethyl acetate, toluene, methyl ethyl ketone and the like.

  Furthermore, as a coating method, a conventionally known method can be used, and a release sheet may be bonded to the adhesive surface of the obtained surface protective sheet.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by these Examples.

Example 1
As component (A), the copolymer composition shown in Table 1, the glass transition temperature and 100 parts by weight of (meth) acrylic polymer (A-1) having a weight average molecular weight, and as component (B) are shown in Table 2. Using 10 parts by weight of (meth) acrylic polymer (B-1) having a copolymer composition, glass transition temperature and weight average molecular weight, and 3 parts by weight of tetrad C as a crosslinking agent, these are dissolved in ethyl acetate to form a crosslinkable composition. A product solution was obtained. The obtained solution was applied onto a polyethylene terephthalate (hereinafter abbreviated as “PET”) film having a thickness of 38 μm so that the thickness after drying was 20 μm, and the solvent was removed at 80 ° C. Next, a 38 μm-thick silicone-coated PET film for cover was bonded to the dry surface and aged for 7 days in an atmosphere of 23 ° C. and 65% humidity to obtain a surface protective film.

Examples 2 to 7 and Comparative Examples 1 to 11
Except that the (meth) acrylic polymer shown in Tables 1 and 2 and the crosslinking agent of the component (C) shown in Table 3 were used in the amounts shown in Table 3, respectively, in the same manner as in Example 1. A surface protective film was obtained.

Here, the symbols in the table are as follows.
2EHA: 2-ethylhexyl acrylate AA: acrylic acid 2HEA: 2-hydroxyethyl acrylate VAc: vinyl acetate BA: butyl acrylate MA: methyl acrylate MMA: methyl methacrylate DM: dimethylaminoethyl acrylate 2HEMA: methacrylic acid 2 -Hydroxyethyl IBMA: Isobutyl methacrylate
Tetrad C: Epoxy-based crosslinking agent Coronate L manufactured by Mitsubishi Gas Chemical Co., Ltd .: Isocyanate-based crosslinking agent Chemitite PZ-33 manufactured by Nippon Polyurethane Industry Co., Ltd. Tg represents the glass transition temperature

Test Example The following methods were used to test the gel fraction, the low speed peel force, the high speed peel force, and the heat peeling when the surface protective films of Examples 1 to 7 and Comparative Examples 1 to 11 were used. Table 4 shows the test results.

(Gel fraction)
Each said surface protection film was cut | judged to 50 mm x 50 mm, the adhesive was peeled off from the cut surface protection film, and the initial weight of the adhesive was weighed. The adhesive was immersed in 100 g of ethyl acetate and allowed to stand at room temperature for 24 hours. Thereafter, the mixture was filtered through a 200 mesh wire mesh, and the residue remaining on the mesh was dried at 80 ° C. for 2 hours and weighed. From the initial weight and the remaining weight, the gel fraction was calculated by the following formula.
Gel fraction (%) = 100 × (weight of residual) / (initial weight)

(Low speed peeling force)
Each of the above surface protective films was cut into 25 mm × 150 mm, the cover PET film was peeled off, and then attached to a polarizing plate (triacetyl cellulose surface) and left at room temperature for 24 hours. Then, it pulled in 180 degree direction (reverse method) at a peeling speed of 300 mm / min, and the force which starts peeling was made into the low speed peeling force.

(High speed peeling force)
Each of the above surface protective films was cut into 25 mm × 150 mm, the cover PET film was peeled off, and then attached to a polarizing plate (triacetyl cellulose surface) and left at room temperature for 24 hours. Thereafter, the pulling speed was 10,000 mm / min, and the film was pulled in the 180 ° direction (reverse method), and the force for starting peeling was defined as the high-speed peeling force.

(Hagare in the heat)
Each of the above surface protective films is cut into 60 mm × 120 mm, the cover PET film is peeled off, and then attached to a glass substrate, and left at 85 ° C., dry for 500 hours, and at 60 ° C., 95% RH for 500 hours. The state of float and peeling generated on the protective film was visually observed. Evaluation was made according to the following criteria.
○: Peeling did not occur on the pressure-sensitive adhesive sheet Δ: Slight peeling occurred on the pressure-sensitive adhesive sheet ×: Peeling occurred on the pressure-sensitive adhesive sheet

  As shown in Table 4, the surface protective films using the pressure-sensitive adhesives for protective sheets of Examples 1 to 7 all have a low-speed peel force of 20 g / 24 mm or less and a high-speed peel force of 100 g / 24 mm or less. In addition to excellent peelability, there was little variation in peel force due to changes in peel speed. Furthermore, no zipping occurred at the time of high-speed peeling, and no heat float or peeling occurred, and the durability was excellent.

The pressure-sensitive adhesive for protective sheets of the present invention can provide a surface protective sheet that has good high-speed peelability, does not cause zipping, and has little change in peel force depending on the peel speed. Therefore, the surface protective sheet using the pressure-sensitive adhesive for protective sheet of the present invention is durable and does not cause floating or peeling even if heated after being applied, and is used in the display field. It can be advantageously used for surface protection of films, various plastic plates, metal plates such as stainless steel, and glass plates.
more than

Claims (7)

Next component (A), component (B) and component (C),
(A) A (meth) acrylic polymer having a weight average molecular weight of 100,000 to 1,000,000 and a glass transition temperature of −40 ° C. or less (B) , which is obtained by copolymerizing at least 2-ethylhexyl acrylate and a functional group-containing monomer. The weight average molecular weight mainly composed of (meth) acrylic acid alkyl ester is 1000.
(Meth) acrylic polymer having a glass transition temperature of 80 ° C. or higher (C) containing a crosslinking agent, and the component (B) is 5 to 20 parts by weight with respect to 100 parts by weight of the component (A). The crosslinkable composition to be blended is subjected to a crosslinking reaction so that the gel fraction is 80% or more, and a solution in which this is dissolved in ethyl acetate is dried on a polyethylene terephthalate (PET) film having a thickness of 38 μm. The film was applied to a thickness of 20 μm, the solvent was removed at 80 ° C., and then a 38 μm-thick silicone-coated cover PET film was bonded to the dry surface, and the atmosphere was 23 ° C. and humidity 65%. The surface protective film obtained by aging for 7 days was cut to 25 mm × 150 mm, the cover PET film was peeled off, and then attached to the polarizing plate (triacetyl cellulose surface). After standing times, when Tsu pulling the peeling speed of 10000 mm / min at 180 ° direction (reverse process), the force to initiate peeling (fast peel strength) of not more than 100 gf / 24 mm (1inch), peeling speed 300mm / when Tsu pulling direction of 180 ° (reverse process) in minutes, the force to initiate peeling (slow peel force) pressure sensitive adhesive protective sheet is not more than 20 gf / 24 mm.   The pressure-sensitive adhesive for protective sheets according to claim 1, wherein the component (A) is a (meth) acrylic polymer obtained by further copolymerizing vinyl acetate.   The pressure sensitive adhesive for protective sheets according to claim 1 or 2, wherein the functional group-containing monomer is copolymerized in the component (A) in an amount of 1 to 10% by mass.   The pressure-sensitive adhesive for a protective sheet according to any one of claims 1 to 3, wherein the functional group of the functional group-containing monomer copolymerized with the component (A) is a carboxyl group or a hydroxyl group.   The pressure-sensitive adhesive for a protective sheet according to any one of claims 1 to 4, wherein the component (B) is a (meth) acrylic polymer obtained by further copolymerizing a functional group-containing monomer.   The pressure-sensitive adhesive for protective sheets according to any one of claims 1 to 5, wherein component (C) is a compound having an epoxy group, a compound having an isocyanate group, an aziridine derivative or a metal chelate compound. A surface protective sheet obtained by coating the pressure sensitive adhesive for protective sheet according to any one of claims 1 to 6 on a support.