JPS6254778A - Pressure-sensitive adhesion composition and pressure-sensitive adhesive sheet - Google Patents

Abstract

PURPOSE:To obtain a pressure-sensitive adhesion composition having excellent adhesive power which can be reduced by irradiation with ultraviolet rays, made of an elastic polymer, an ultraviolet-crosslinking acrylate, a polymerization initiator, and a polyisocyanate as principal components. CONSTITUTION:An elastic polymer (A) such as a saturated copolyester resin or a polyacrylate is mixed with an ultraviolet-crosslinking acrylate (B) (e.g., trimethylolpropane triacrylate), a polymerization initiator (C) (e.g., benzoin methyl ether), and a polyisocyanate (D) (e.g., 2,4-toluene diisocyanate), as principal components, to give an objective pressure-sensitive adhesion composition. A pressure-sensitive adhesive sheet obtained by forming a layer of this composition on an ultraviolet-transmitting resin sheet has high initial adhesive power which decreases by irradiation with ultraviolet rays; hence it is suitable for use as a film for silicon wafer dicing.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet, and more particularly, to a pressure-sensitive adhesive composition whose adhesive strength can be reduced by ultraviolet irradiation. and pressure-sensitive adhesive sheets.

(Prior Art) Generally, pressure-sensitive adhesive sheets or pressure-sensitive adhesive sheets, which are made by coating a pressure-sensitive adhesive on a base sheet, are used for various purposes in general households and industry, but in recent years, pressure-sensitive The characteristics required for adhesive sheets are diverse and wide-ranging, and various functionalities are now required depending on the application.

For example, in the production of integrated circuits, in order to cut a silicon wafer into predetermined dimensions, that is, to obtain dice by dicing, the silicon wafer is placed on a pressure-sensitive adhesive sheet called a dicing film. After being pressure-sensitive adhesively fixed onto a dicing film and cut, it is picked up, that is, peeled off, from the dicing film. Therefore, in order to accurately dice silicon wafers, the dicing film must have strong adhesion to the silicon wafer during dicing.
On the other hand, when picking up the obtained dice from the dicing film, the dicing film needs to have weak adhesive strength. For example, when dicing silicon wafers, the dicing film has a weight of 1 (10) to 8 (10) g, although it is not limited in any way.
/ 25 mm, while the dicing film has an adhesive strength of about 20 to 5 mm when picking up the dice.
It is said that it is desirable to have an adhesive strength of about 0g/25n or less.

However, like this 5. Pressure-sensitive adhesive compositions and pressure-sensitive adhesive seeds with such properties that can optionally reduce their adhesion after application to an adhered surface are not yet known.

On the other hand, for example, in general, in the field of adhesives, ultraviolet crosslinkable adhesives consisting of a photopolymerizable oligomer, a photopolymerizable oligomer 1 photopolymerization initiator, and other additives are already known; - It is a wave-shaped adhesive, has fast curing properties, and is excellent in that it does not require heating.
In this adhesive, ultraviolet irradiation is originally performed in order to cause the adhesive to develop the required adhesive strength.

(Purpose of the Invention) As a result of intensive research to obtain a pressure-sensitive adhesive that originally had strong adhesive strength and could reduce the adhesive strength as needed, the inventors unexpectedly found that It has been found that when a pressure-sensitive adhesive composition consisting of a mixture containing a polymer and an ultraviolet crosslinkable acrylic ester as main components is irradiated with ultraviolet light, its adhesive strength is significantly reduced.

As a result of further research, the present inventors found that a pressure-sensitive adhesive composition further containing polyisocyanate as a component exhibits more remarkable adhesive strength when irradiated with ultraviolet rays. The present invention has been developed based on the discovery that this can be reduced.

Therefore, the present invention provides a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that have strong adhesive strength when not irradiated with ultraviolet rays, and whose adhesive strength can be significantly reduced by irradiating them with ultraviolet rays. The purpose is to

(Structure of the Invention) The pressure-sensitive adhesive of the present invention whose adhesive strength can be reduced by ultraviolet irradiation is characterized by containing an elastic polymer, an ultraviolet crosslinkable acrylic ester, a polymerization initiator, and a polyisocyanate as main components. Moreover, the pressure-sensitive adhesive sheet according to the present invention has a base resin sheet that can transmit ultraviolet rays, and
It is characterized by being formed with a pressure-sensitive adhesive layer containing as main components an elastic polymer, an ultraviolet crosslinkable acrylic ester, a polymerization initiator, and a polyisocyanate.

Conventionally, various pressure-sensitive adhesive compositions have been known, for example, as described in "Adhesion Handbook (2nd Edition)" (edited by Japan Adhesive Association, published by Nikkan Kogyo Shimbun, 1980), pages 398-414. However, typical pressure-sensitive adhesive compositions have an elastomeric polymer as the main component, and a tackifier and plasticizer with good compatibility with this, as well as a filler and an anti-aging agent, if necessary. It is a mixture made by uniformly mixing , coloring agent, etc. In the present invention, particularly preferred examples of such elastic polymers include saturated copolymerized polyester resins, polyacrylic esters, and copolymers of acrylic esters.

First, saturated copolymerized polyester resins are usually made by combining two or more different saturated divalent carboxylic acids and saturated divalent carboxylic acids, as described in, for example, "Industrial Materials" Vol. 25, No. 11, No. 101-106. A saturated copolymer resin with a relatively low glass transition point obtained by polycondensation with alcohol.
As the saturated dihydric carboxylic acid, an aromatic dihydric carboxylic acid and an aliphatic dihydric carboxylic acid are used in combination, and as the saturated dihydric alcohol, an aliphatic or alicyclic dihydric alcohol, that is, a glycol is used. In particular, in the present invention, aromatic 2
valent carboxylic acid/aliphatic divalent carboxylic acid molar ratio is 80/2
0 to 20/80, preferably 70/30 to 5015
A saturated copolymerized polyester resin obtained by polycondensing a saturated dicarboxylic acid mixture of 0 and glycol in equimolar amounts is preferably used. In the present invention, the aromatic divalent carboxylic acid is terephthalic acid, the aliphatic polycarboxylic acid is sebacic acid, adipic acid, and the glycol is ethylene glycol, 4-butanediol, propylene glycol, etc. Polymerized polyester resins are preferably used. If necessary, in the production of the saturated copolymerized polyester resin, a saturated polyhydric carboxylic acid having a valence of 3 or more or a polyhydric alcohol having a valence of 3 or more may be used in combination as the carboxylic acid component.

Further, the polyacrylic acid ester or acrylic acid copolymer includes any one that is used as an elastic polymer as a main component in adhesives conventionally known as acrylic adhesives. Polymers used as elastic polymers in acrylic adhesives are usually
It is essentially an acrylic ester copolymer. This copolymer usually uses an alkyl acrylate ester such as ethyl acrylate, butyl acrylate, or 2-ethylhexyl acrylate, which forms a polymer with a low glass transition temperature to provide adhesive properties. , comonomers that form hard polymers with a high glass transition temperature to provide cohesive properties, such as vinyl acetate, acrylonitrile, styrene, methyl acrylate, methyl methacrylate, etc., and to improve crosslinking and adhesion properties. Monomers having functional groups such as carboxylic acid groups, hydroxyl groups, amide groups, glycidyl groups, and hydroxylmethyl groups, such as acrylic acid, methacrylic acid, itaconic acid, hydroxylethyl methacrylate, hydroxylpropyl methacrylate,
It is a copolymer made by copolymerizing monomers such as acrylamide and glycidyl methacrylate.

The ultraviolet crosslinkable acrylic ester according to the present invention refers to an acrylic ester or methacrylic ester as an oligomer or monomer that is crosslinked by ultraviolet irradiation, and has at least two acryloyl or methacryloyl groups in the molecule. Specifically, such oligomers include, for example, oligoester acrylate, and monomers include, for example, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, tetramethylolmethanetetraacrylate, and dipentaerythritol. Ester of polyhydric alcohol and acrylic acid such as hexaacrylate, or ester of polyhydric alcohol and methacrylic acid such as 1,6-hexanediol diacrylate, trimethylolpropane trimethacrylate, tetramethylolmethanetetramethacrylate, dipentaerythritol pentamethacrylate etc. can be mentioned.

The pressure-sensitive adhesive composition according to the present invention comprises the elastic polymer 1 (
10) 15 to 2 (10) parts by weight, preferably 50 to 1 parts by weight of the above ultraviolet crosslinkable acrylic ester
It is contained in a range of 50 parts by weight. Elastic polymer 1 (10)
When the amount of the ultraviolet crosslinkable acrylic ester is less than 15 parts by weight, even when the resulting adhesive composition is irradiated with ultraviolet rays, its adhesive strength does not substantially change; 10) When exceeding the weight part, the adhesive force can be reduced by UV irradiation, but
For example, when picking up dice after dicing a silicon wafer, adhesive may remain on the dice, which is undesirable.

The pressure-sensitive adhesive composition according to the invention preferably further contains a tackifier. In particular, when the elastic polymer used is a saturated copolymerized polyester resin, it is preferable to use this tackifier in combination. The tackifier that can be used is not particularly limited, and those conventionally used in the production of adhesives can be used as appropriate. Examples of such tackifiers include xylene resins, modified rosin resins such as rosin, polymerized rosin, hydrogenated rosin, and rosin esters;
Terpene resins, terpene phenol resins, terpene resins such as rosin phenol resins, aliphatic, aromatic and alicyclic petroleum resins, coumaron resins, styrene resins,
Examples include alkylphenol resins. The tackifier is generally used in an amount of 10 to 2 (10) parts by weight per 1 (10) parts by weight of the saturated copolyester resin.

When the amount of the tackifier is too small, the adhesive strength or adhesion is insufficient, and on the other hand, when it is too large, the amount of decrease in adhesive strength after irradiating the resulting adhesive composition with ultraviolet rays is small. In addition, when such an adhesive composition is applied to a dicing film, the tackifier may remain on the dice when the dice are picked up after dicing the silicon wafer, which is undesirable.

The pressure-sensitive adhesive composition according to the present invention further contains a polymerization initiator or a photosensitizer, and if necessary, a polymerization inhibitor. The polymerization initiator is used to promote crosslinking of the ultraviolet crosslinkable acrylic ester by ultraviolet irradiation.

Such polymerization initiators are generally well known in the technical field of ultraviolet crosslinking polymerization, and in the present invention,
Conventionally known polymerization initiators can be used. Specific examples of such polymerization initiators include benzoin alkyl ethers such as benzoin methyl ether and benzoin isopropyl ether, and aromatic oxyketones and aromatic ketones such as benzoin, benzyl, and benzophenone. It is not limited to.

The thermal polymerization inhibitor is added as necessary to prevent the above-mentioned ultraviolet crosslinkable acrylic and sulfuric acid esters from polymerizing due to heat, for example, regardless of ultraviolet irradiation, and as such a polymerization inhibitor. Also, conventionally known polymerization inhibitors can be used. As such a polymerization inhibitor, for example, picric acid, phenol, hydroquinone, hydroquinone monomethyl ether, etc. can be used.

The blending amounts of the polymerization initiator and polymerization inhibitor may be in accordance with those generally used in the technical field of ultraviolet crosslinking polymerization. About the part 1-20
The polymerization inhibitor is used in an amount of 0.1 to 1 part by weight, if necessary.

The pressure sensitive adhesive composition according to the invention further comprises an elastic polymer 1
(10) Regarding parts by weight, polyisocyanate 1 to 1 (
10) Contains parts by weight. Due to the presence of the polyisocyanate, the pressure-sensitive adhesive composition exhibits a greater decrease in adhesive strength after irradiation with ultraviolet rays than a pressure-sensitive adhesive composition having the same composition but not including the polyisocyanate. The exact reason is not yet clear, and the present invention is not limited by the reason; , a ruboxyl group, or a hydroxyl group, which appears to contribute to a significant decrease in the adhesive strength of the pressure-sensitive adhesive composition after irradiation with ultraviolet rays. However, when the amount of polyisocyanate is less than 1 part by weight per 1 (10) parts by weight of the elastic polymer, the effect of reducing the adhesive strength after UV irradiation is not sufficient; When the amount is more than 1, the adhesive strength of the resulting pressure-sensitive adhesive composition before irradiation with ultraviolet rays decreases over time. Particularly preferable blending amount ranges are: 1 (10) parts by weight of the elastic polymer;
It is 3 to 40 parts by weight.

The polyisocyanate is not particularly limited, but diisocyanates and triisocyanates are preferred in the present invention.

Examples of the diisocyanate include 2,4-toluene diisocyanate, m-phenylene diisocyanate,
m-xylylene diisocyanate, 4,4°-diphenyl diisocyanate, 4.4°-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate,
Examples include isophorone diisocyanate, dianisidine diisocyanate, and hexamethylene diisocyanate. Furthermore, various triisocyanates are commercially available. For example, trimethylolpropane toluene diisocyanate, which is commercially available from Sumitomo Chemical Casting Co. as "Sumidur L", can be suitably used as the polyisocyanate in the present invention. This is an example of a triisocyanate that can be produced.

Furthermore, a so-called urethane prepolymer of terminal isocyanate obtained by reacting a diisocyanate and a polyol in the presence of an excess amount of the diisocyanate can also be used as the polyisocyanate.

The pressure-sensitive adhesive composition according to the present invention contains an elastic polymer, an ultraviolet crosslinkable acrylic ester, a polymerization initiator, and a polyisocyanate in the above-mentioned amounts, and optionally a tackifier, a polymerization inhibitor, and a filler. , an anti-aging agent, a coloring agent, etc., in an appropriate organic solvent that dissolves them, such as aromatic hydrocarbons, ketones, or a mixture thereof, to obtain a uniform solution composition.

As the solvent, for example, specifically, a mixed solvent of toluene and methyl ethyl ketone is preferably used, but the solvent is not limited thereto.

Further, the content of the elastic polymer in the adhesive composition is appropriately selected depending on the application and the like, but is usually in the range of 10 to 50% by weight. However, it is not limited to this.

The method for preparing the pressure-sensitive adhesive composition as described above is not limited in any way, but the elastic polymer and tackifier are usually commercially available in the form of a solution, and these can be used. As it is convenient, for example, these solutions may be mixed and UV-crosslinkable acrylic ester, polymerization initiator and polyisocyanate, and if necessary, a polymerization inhibitor, filler, anti-aging agent, colorant, etc. may be added. Just add, mix, and dissolve.

Furthermore, the pressure-sensitive adhesive composition according to the present invention may contain a plasticizer such as liquid polyacrylate, liquid polybutene, mineral oil, lanolin, filler, anti-aging agent, etc. as necessary. You can leave it there.

In the pressure-sensitive adhesive sheet according to the present invention, a layer of the above-mentioned pressure-sensitive adhesive composition is formed on a base sheet that can transmit ultraviolet rays. Therefore, for example, it can be obtained by applying a pressure-sensitive adhesive composition as a solution composition as described above onto a base sheet and drying it.

As the base sheet, as long as it can transmit ultraviolet rays,
Although various sheets can be used without particular limitation, transparent or translucent synthetic resin sheets are usually used. For example, resin sheets made of vinyl chloride resin, vinyl chloride-vinylidene chloride copolymer resin, vinyl chloride-vinyl acetate copolymer resin, vinylidene chloride resin, polyolefin, acetyl cellulose, polyvinyl alcohol, polyamide, polyester, polycarbonate, etc. are suitable. used for.

Among the various base resin sheets described above, a resin sheet made of polyvinyl chloride or a copolymer of vinyl chloride containing a plasticizer is particularly preferred in the present invention because it is flexible and inexpensive. Can be used. In addition to vinyl chloride resin sheets, there are also materials that can be suitably used as base sheets containing plasticizers. for example,
Examples include vinyl chloride-vinylidene chloride copolymer resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-acrylic acid ester copolymer resin, polyvinylidene chloride, acetyl cellulose, and the like.

Examples of the plasticizer include, but are not limited to, phthalic acid diesters such as dibutyl phthalate, dioctyl phthalate, didecyl phthalate, ditridecyl phthalate, and butylbenzyl phthalate, tricresyl phosphate, and trioctyl phosphate. , phosphoric acid esters such as triphenyl phosphate, 2-ethylhexyldiphenyl phosphate, talesyl diphenyl phosphate, fatty acid diesters such as dioctyl adipate, dioctyl sebacate, dioctyl azelate, tri-2-ethylhexyl acetyl citrate, polypropylene adipate, polypropylene sebacate Examples include polyester plasticizers such as, epoxy plasticizers such as epoxidized soybean oil, and chlorine plasticizers such as chlorinated paraffin and chlorinated fatty acid ester.

However, when a resin sheet containing a plasticizer is used as the base resin sheet of the pressure-sensitive adhesive sheet, the plasticizer migrates from this resin sheet into the pressure-sensitive adhesive composition, and Usually, since the plasticizer and the UV-crosslinkable acrylic ester have good compatibility, the UV-crosslinkable acrylic ester contained in the pressure-sensitive adhesive composition migrates into the resin sheet, and due to such mutual migration, The effect of reducing the adhesive strength of the pressure-sensitive adhesive sheet after UV irradiation is significantly reduced.

Therefore, in the present invention, when a resin sheet containing a plasticizer is used as the base sheet of the pressure-sensitive adhesive sheet, the plasticizer and ultraviolet cross-linkable It is preferable to interpose a barrier layer made of a resin layer that does not allow acrylic ester to pass through.

However, this barrier layer must not impede the transmission of ultraviolet light.

That is, this barrier layer does not prevent the transmission of ultraviolet rays in any way, but it prevents the plasticizer contained in the base resin sheet from migrating into the pressure-sensitive adhesive composition. In this way, the plasticizer contained in the base resin sheet is retained in this base material, and the acrylic acid ester contained in The ultraviolet crosslinkable acrylic ester contained in the pressure adhesive composition is retained in the adhesive composition to prevent the adhesive strength of the pressure sensitive adhesive sheet from decreasing over time due to ultraviolet irradiation.

As the barrier layer, a film of poly-α-olefin such as polyethylene or polypropylene, or polyalkylene terephthalate such as polyethylene terephthalate,
A resin coating layer, such as a resin coating layer made of modified polyacrylic resin, is preferably used. Therefore, the barrier layer can be formed by pressing a film made of the above-mentioned resin onto a base resin sheet, or by applying a melt of this resin and cooling it, or by applying a solution of the above-mentioned resin and drying it. can be formed. Further, the barrier layer can also be obtained, for example, by applying a modified polyacrylic resin solution and, if necessary, heating and drying it to form a coating film.

Various types of modified polyacrylic resins have been known in the past, but in the present invention, they generally have excellent solvent resistance, and are therefore suitable for UV-crosslinkable acrylic esters and plasticizers contained in the base resin sheet. Alkyd-modified polyacrylic resins and thermosetting polyacrylic resins that do not dissolve or swell in agents are suitable. As the thermosetting polyacrylic resin, for example, acid type, hydroxyl type, epoxy type, amide type, etc. are preferably used.

However, in the present invention, as described above, as long as the barrier layer does not substantially transmit the ultraviolet crosslinkable acrylic ester contained in the pressure-sensitive adhesive composition and the plasticizer contained in the base resin sheet, In particular, it is easily understood that the material is not limited, and is selected depending on the specific ultraviolet crosslinkable acrylic ester and plasticizer used in the present invention.

The means and method for irradiating the pressure-sensitive adhesive composition or pressure-sensitive adhesive sheet with ultraviolet rays according to the present invention are not particularly limited, and are commonly used in the technical fields of ultraviolet-curable resin coatings and ultraviolet-curable adhesives. It can be done by the means and methods used in For example, an ultraviolet light source such as a xenon lamp, low pressure, medium pressure, high pressure, or ultra-high pressure mercury lamp may be used as the irradiation means, and the irradiation may be performed for several seconds to several minutes.

(Effects of the Invention) As described above, the pressure-sensitive adhesive sheet of the present invention has an elastic polymer, an ultraviolet crosslinkable acrylic ester, a polymerization initiator, and a polyisocyanate on a base resin sheet that can transmit ultraviolet rays. A layer of the pressure-sensitive adhesive contained as the main component is formed, and although the reason for this is not necessarily clear, the adhesive strength of the pressure-sensitive adhesive composition is significantly reduced by irradiation with ultraviolet rays. After applying such a pressure-sensitive adhesive sheet to an adherend surface, the pressure-sensitive adhesive sheet can be easily peeled off from the adherend surface by irradiating ultraviolet rays from the side of the base resin sheet.

Therefore, the pressure-sensitive adhesive sheet according to the present invention can be suitably used, for example, as a film for dicing silicon wafers, as described above.

(Example) Examples are shown below, but the present invention is not limited to these examples. Furthermore, in the examples, parts indicate parts by weight.

Example 1 A pressure-sensitive adhesive having the composition shown in Table 1 was applied onto release paper, and 1
It was dried at 20° C. for 1 minute to form a pressure-sensitive adhesive layer with a solid content of 10 μm thick.

Here, as the saturated copolymerized polyester resin, a glass transition polyester resin obtained by polycondensing a saturated divalent carboxylic acid mixture with a terephthalic acid/sebacic acid molar ratio of 70/30 and ethylene glycol in equimolar amounts at 10°C is used. Using resin.

Next, polyvinyl chloride 1 (1
A modified acrylic resin solution is applied onto a sheet with a thickness of 0.1 m formed from a vinyl chloride resin composition consisting of 35 parts of dioctyl phthalate or polyester plasticizer as a plasticizer and an appropriate amount of a stabilizer. It was dried to form a barrier layer. Thereafter, the pressure-sensitive adhesive layer was laminated and laminated on the surface of the barrier layer of this base resin sheet to obtain a pressure-sensitive adhesive sheet according to the present invention.

For comparison, pressure-sensitive adhesive compositions containing no polyisocyanate were also prepared (Comparative Examples 1 and 2).

After leaving each of the pressure-sensitive adhesive sheets obtained in this way at a predetermined temperature for a predetermined time, the release paper was peeled off and the adhesive strength was measured as it was, and separately from the vinyl chloride resin sheet side. After irradiating with ultraviolet rays at a main wavelength of 365 mμ and 120 W/cm for 7 seconds, the adhesive strength was measured. The results are shown in Table 1.

According to the pressure-sensitive adhesive sheet of the present invention, the adhesive strength decreases significantly even after long-term irradiation with ultraviolet rays, and by appropriate formulation design, it can initially have an adhesive strength of several hundred g/25 tm, and even after irradiation with ultraviolet rays, After that, the adhesive force can be reduced to about several tens of g/25 shavings, so as mentioned above, it can be suitably used for dicing silicon wafers.

However, according to the pressure-sensitive adhesive sheets of Comparative Examples 1 and 2,
Compared to the adhesive strength before UV irradiation, the reduction in adhesive strength after UV irradiation is smaller.

The method for measuring adhesive strength is as follows. That is, a pressure-sensitive adhesive sheet was cut into a test piece with a width of 25 mm and a length of 1 (10 mm), which was stacked on a stainless steel plate as an adherend and then reciprocated 5 times using a 3 kg roller. After pressing, a 1.80° peel test was conducted using a Schopper at a tensile rate of 3 (10) H/min.

Example 2 Acrylic adhesive solution containing polyacrylic ester or acrylic ester copolymer as an elastic polymer (Polysic 6103A manufactured by Sanyo Chemical Industries, Ltd., polyacrylic ester or acrylic ester copolymer content heavy) Dipentaerythritol hexaacrylate and benzoin isopropyl ether in the amounts shown in Table 2 were dissolved in 1 (10) parts by weight, and the same polyisocyanate shown in Table 2 as used in Example 1 was added. A pressure sensitive adhesive composition was prepared by mixing.

This pressure-sensitive adhesive composition was applied onto release paper and dried at 120°C for 1 minute to form a pressure-sensitive adhesive layer with a solid content of 10 μm.
It was formed thickly.

Next, the same modified acrylic resin solution as in Example 1 was applied onto a sheet having the same thickness of 0.1 as in Example 1, and after drying to form a barrier layer, this base resin sheet The above pressure-sensitive adhesive layer was laminated and laminated on the surface of the barrier layer to obtain a pressure-sensitive adhesive sheet according to the present invention.

Regarding the pressure-sensitive adhesive sheet thus obtained, the adhesive strength after irradiation with ultraviolet rays was measured in the same manner as in Example 1. The results are shown in Table 2.

Claims (10)

[Claims] (1) A pressure-sensitive adhesive composition whose adhesive strength can be reduced by ultraviolet irradiation, characterized by containing an elastic polymer, an ultraviolet crosslinkable acrylic ester, a polymerization initiator, and a polyisocyanate as main components. (2) The pressure-sensitive adhesive composition according to claim 1, wherein the elastic polymer is a saturated copolymerized polyester resin. (3) The pressure-sensitive adhesive composition according to claim 1, wherein the elastic polymer is a polyacrylic ester or a copolymer of an acrylic ester. (4) The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive contains a tackifier. (5) A pressure-sensitive adhesive layer containing as main components an elastic polymer, an ultraviolet crosslinkable acrylic ester, a polymerization initiator, and a polyisocyanate is formed on a base resin sheet that can transmit ultraviolet rays. A pressure-sensitive adhesive sheet whose adhesive strength can be reduced by irradiation with ultraviolet rays. (6) The pressure-sensitive adhesive sheet according to claim 5, wherein the elastic polymer is a saturated copolymerized polyester resin. (7) The pressure-sensitive adhesive sheet according to claim 5, wherein the elastic polymer is a polyacrylic ester or an acrylic ester copolymer. (8) The pressure-sensitive adhesive sheet according to claim 5, wherein the pressure-sensitive adhesive contains a tackifier. (9) The base resin sheet contains a plasticizer, and the plasticizer and the ultraviolet crosslinkable acrylic ester are not transmitted between the base resin sheet and the pressure-sensitive adhesive composition layer, but the ultraviolet rays are transmitted. 6. The pressure-sensitive adhesive sheet according to claim 5, further comprising a barrier layer made of a resin that can be used as a material. (10) The pressure-sensitive adhesive sheet according to claim 5, wherein the base resin sheet is a sheet made of polyvinyl chloride or a vinyl chloride copolymer containing a plasticizer.