JP4543140B2 - Circuit board protecting adhesive sheet and method for producing the same - Google Patents

Description

  The present invention relates to a sheet for temporarily adhering onto a circuit formed on a surface of a substrate such as a silicon wafer to protect the circuit board and a method for manufacturing the sheet. More specifically, the present invention has good followability to the unevenness formed by the circuit so that the circuit can be protected by adhering to the substrate surface on which the circuit is formed. The present invention relates to a protective pressure-sensitive adhesive sheet having an adhesive strength that does not damage a circuit and free from contamination of the circuit by an adhesive component, and a method for producing the same.

Conventionally, acrylic adhesives have been widely used as adhesives or adhesives. Examples of such acrylic adhesives include alkyl (meth) acrylates and other vinyl monomers copolymerizable therewith as described in Patent Document 1 (Japanese Patent Laid-Open No. 10-306267). The photopolymerization composition containing a photopolymerization initiator, a polyfunctional vinyl compound and a radical chain transfer agent is applied to a base film so that the gel fraction of the partially crosslinked polymer is 5 to 60% by weight, The weight average molecular weight is 50,000 to 700,000, and the glass transition temperature is −10 ° C. to +30.
A self-adhesive sheet set at ℃ is known. By photopolymerizing the photopolymerizable composition as described above, an acrylic polymer main chain composed of an alkyl (meth) acrylate and another vinyl monomer is formed, and this acrylic polymer main chain is converted into a polyfunctional vinyl compound. An acrylic adhesive having a cross-linked structure is formed. When producing an acrylic adhesive having such a crosslinked structure, the alkyl (meth) acrylate as the monomer component, other vinyl monomers, and the polyfunctional vinyl compound as the crosslinking agent are all united. In order to perform photopolymerization using the polymerizable composition, the crosslinked structure is uniformly formed in the acrylic polymer main chain. As the number of such cross-linked structures increases, the adhesive becomes harder and the adhesive strength decreases. Therefore, the formation density of the cross-linked structure in the adhesive is expressed in gel fraction, and the upper limit (gel fraction) is 80. It was said that the basic characteristics as an adhesive would not be manifested when formed at a high density so as to be higher than wt%.

  Therefore, also in the above-mentioned Patent Document 1, the upper limit of the gel fraction of the partially crosslinked polymer is 60%, and an acrylic polymer having a crosslinked structure formed at a high density so that the gel fraction is 80% by weight or more is bonded. It was thought that it could not be used as an agent.

Apart from these general acrylic adhesives, in the field of electronic equipment industry, a photopolymerizable component is blended into an acrylic adhesive and a cross-linked structure is formed in the acrylic adhesive by photopolymerization. It is used to adjust the adhesive strength of acrylic adhesives. For example, as shown in Patent Document 2 (Japanese Patent Application Laid-Open No. 61-64773), a light-curing type sensation that converts adhesiveness to adhesiveness by irradiating light to an adhesive layer having normal-time adhesiveness. A pressure-sensitive adhesive is used, and this photo-curable pressure-sensitive adhesive forms a pressure-sensitive adhesive layer in which a photopolymerizable component is blended with a pre-manufactured pressure-sensitive adhesive, and uses the pressure-sensitive adhesive force of this pressure-sensitive adhesive layer After attaching electronic parts, etc., the adhesive layer where no electronic parts are attached is irradiated with light to form a crosslinked structure in the adhesive layer to reduce the tack of the adhesive layer The photocurable pressure sensitive adhesive.

However, in Patent Document 2, specifically, for example, as shown in the Examples, an acrylic monomer such as butyl acrylate, methyl acrylate, and acrylic acid is dispersed in water and subjected to emulsion polymerization. Discloses a photo-curing pressure-sensitive adhesive in which dimethylbenzyl ketal, benzophenone and bisdiethylaminobenzophenone are added to pentaerythritol triacrylate and 2-hydroxy-3-phenoxypropyl acrylate and dispersed by rapid stirring. In this way, after preparing an acrylic polymer in advance, a new acrylic monomer and polyfunctional monomer, and further a photopolymerization initiator are added, and the components involved in photopolymerization after the acrylic polymer is thus manufactured in advance Is added to the acrylic polymer and photopolymerization. There is a risk that the components are not uniformly mixed. Moreover, the emulsifier used for emulsion polymerization may bleed at the time of sticking and may contaminate an electronic component. Furthermore, the photocurable pressure-sensitive adhesive described in Patent Document 2 is a portion where a stainless steel plate that is attached in the form of an electronic component is attached and irradiated with ultraviolet rays, and the stainless steel plate is not attached. At this time, the peel adhesive strength of the stainless steel plate is increased to around 2000 g / 20 mm. By forming a cured body by irradiation with ultraviolet rays, the adhesion to the adherend is increased. Is rising. Therefore, in adhesives that contain a photopolymerization component in an adhesive, the adhesive strength with the adherend is more than doubled due to the curing reaction of the photopolymerization component at the part where the adherend is already bonded. By forming a photopolymer, a strong adhesive force is newly developed between the adherend and the photopolymer, and the polymer in the syrup is also crosslinked due to the use of a hydrogen abstraction initiator. Due to the involvement, the photopolymer thus formed is hard.

By the way, in paragraph [0004] of Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-180013), “In addition to adding a photoinitiator to the monomer syrup, a photocured adhesive composition includes an ultraviolet cured product thereof. A polyfunctional monomer is added so as to form a crosslinked structure, etc. In the ultraviolet curing reaction of such a photopolymerizable adhesive composition, the crosslinked structure is composed of a polyfunctional monomer and a monomer component (monofunctional monomer) in the monomer syrup. The high molecular weight material such as a thickening polymer in the monomer syrup is not involved in crosslinking, and is present in the resulting cured product so that the cured product has an initial tack, adhesive strength, It is possible to form an adhesive layer with a good balance of cohesive strength adhesive properties. " Further, in paragraph [0005], “in general, an adhesive layer having a balanced adhesive property has a gel fraction of the cured product of 20 to 60% by weight, in other words, a high molecular weight such as the thickening polymer. It is desired to include an uncrosslinkable component in a proportion of about 80 to 40% by weight. "

  However, since the adhesive used for the circuit board protecting adhesive sheet to be attached to protect the circuit formed on the silicon wafer peels off the protecting adhesive sheet in a later step, the above-mentioned patent document No high adhesive strength as described in 3 is required. Rather, it is desirable that the adhesive strength is low so as not to damage the circuit formed when the protective adhesive sheet is peeled off. Thus, the adhesive sheet for protecting a circuit board has a low adhesive strength so as not to damage the circuit when it is peeled off, and follows the unevenness formed by the circuit formed in a convex shape on the substrate. It is necessary to protect the substrate and not to contaminate the circuit during peeling.

Thus, in order to ensure the form followability of the pressure-sensitive adhesive sheet for circuit board protection, it is necessary that the pressure-sensitive adhesive layer is flexible. By making the pressure-sensitive adhesive layer soft, this pressure-sensitive adhesive for circuit board protection is used. When the sheet is peeled off, a new problem arises that the adhesive layer is often transferred to the surface of the circuit board and contaminates the surface of the circuit board.
Japanese Patent Laid-Open No. 10-306267 JP 61-64773 A JP 2002-180013 A

An object of this invention is to provide the adhesive sheet for protecting a circuit board, and the method of manufacturing this adhesive sheet.
Furthermore, the present invention has good shape following so as to protect the circuit and the substrate formed in a convex shape on the circuit board substrate, and damages the circuit formed when the protective adhesive sheet is peeled off. It is an object of the present invention to provide a pressure-sensitive adhesive sheet for protecting a circuit board and a method for producing the pressure-sensitive adhesive sheet that does not give the substrate and does not contaminate the board with the pressure-sensitive adhesive.

  The pressure-sensitive adhesive sheet for protecting a circuit board according to the present invention comprises a (meth) acrylic polymer having a weight average molecular weight of 50,000 to 800,000; a monomer containing 20 to 75% by weight and a (meth) acrylic monomer; Syrup (however, the total of (meth) acrylic polymer and (meth) acrylic monomer is 100% by weight) and 100 parts by weight of (meth) acrylic monomer contained in the monomer syrup, A polyfunctional monomer having two or more ethylenic double bonds; 5 to 30 parts by weight and a photopolymerization composition containing a photopolymerization initiator are irradiated with light and contained in the monomer syrup. A (meth) acrylic monomer and the polyfunctional monomer are contained in a photopolymer obtained by photopolymerization so that the gel fraction is 90% by weight or more and the monomer syrup. (A) having a pressure-sensitive adhesive layer in which a (meth) acrylic polymer coexists, the average thickness of the pressure-sensitive adhesive layer being in the range of 250 to 2000 μm, and the pressure-sensitive adhesive strength of the pressure-sensitive adhesive layer being 500 g / 20 mm or less. It is characterized by.

  Moreover, the manufacturing method of the adhesive sheet for circuit board protection of this invention melt | dissolves 20-75 weight% and (meth) acrylic-type polymer of the (meth) acrylic-type polymer whose weight average molecular weight is 50,000-800,000 ( The monomer syrup (total 100% by weight) containing 25 to 80% by weight of the (meth) acrylic monomer is 5 to 30 parts by weight with respect to 100 parts by weight of the (meth) acrylic monomer in the monomer syrup. A photopolymerizable composition obtained by blending a polyfunctional monomer having two or more ethylenic double bonds in the molecule and a photopolymerization initiator on a base film having a thickness after curing of 250 to After coating to 2000 μm, the photopolymerizable composition layer is irradiated with light so that the gel fraction of the (meth) acrylic monomer and the polyfunctional monomer in the monomer syrup is 90% by weight or more. Na By photopolymerization as, adhesive strength is characterized by, and forming a pressure-sensitive adhesive layer was adjusted to below 500 g / 20 mm.

  In the pressure-sensitive adhesive sheet for circuit board protection of the present invention, a photopolymer (crosslinked polymer) formed by photopolymerization of a (meth) acrylic monomer and a polyfunctional monomer contained in the monomer syrup, and a monomer syrup The pressure-sensitive adhesive layer is formed in a state where the (meth) acrylic polymer contained therein is mixed at the molecular level, and the crosslinked polymer and the (meth) acrylic polymer exist independently. . Therefore, the pressure-sensitive adhesive layer is soft and has excellent followability with respect to the unevenness formed by the substrate and the circuit. However, the coexistence of the photopolymer and the (meth) acrylic polymer does not increase the adhesive strength while being soft, and damages the circuit formed when the protective adhesive sheet is peeled off. And does not contaminate the circuit. Furthermore, since the pressure-sensitive adhesive layer of the protective pressure-sensitive adhesive sheet of the present invention does not contain low molecular weight substances such as emulsifiers and plasticizers, the surface of the circuit board is not contaminated by bleed components such as emulsifiers.

In the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention, a crosslinked structure is formed with a high crosslinking density on a photopolymerized product formed by photopolymerization of a (meth) acrylic monomer and a specific polyfunctional monomer in a monomer syrup. The cross-linked polymer structure thus formed and the (meth) acrylic polymer having a weight average molecular weight of 50,000 to 800,000 contained in the monomer syrup coexist to form an adhesive layer. Yes. This (meth) acrylic polymer having a weight average molecular weight of 50,000 to 800,000 has adhesiveness, but is contained in a crosslinked polymer structure in the adhesive layer and has this adhesiveness (meth). Contact with the adherend of the acrylic polymer is regulated by the crosslinked polymer structure, and the adhesive strength of the adhesive layer is suppressed to 500 g / 20 mm or less. On the other hand, the cohesive (meth) acrylic polymer coexists so that the entire pressure-sensitive adhesive layer made of a crosslinked polymer encapsulating the (meth) acrylic polymer does not become hard, and the average of the pressure-sensitive adhesive layer By setting the thickness to 250 to 2000 μm, the pressure-sensitive adhesive layer is deformed corresponding to the unevenness caused by the circuit formed on the substrate.

  Therefore, when the pressure-sensitive adhesive sheet of the present invention is stuck on a substrate on which a circuit is formed, the pressure-sensitive adhesive layer is deformed following the unevenness of the circuit, and this pressure-sensitive adhesive sheet is uniformly stuck on the entire surface of the circuit board. Can be reliably protected. Moreover, the adhesive strength of this adhesive sheet is sufficient to hold the adhesive sheet on the substrate surface, but it is not so high as to damage the circuit formed on the substrate when it is peeled off, and has adhesiveness ( Since the (meth) acrylic polymer is held in a structure made of a crosslinked polymer, the (meth) acrylic polymer having adhesiveness does not transfer to the substrate and contaminate the substrate surface. Furthermore, since the adhesive layer does not contain any easily bleeding component such as an emulsifier, the surface of the circuit board is not contaminated with such an emulsifier.

  Therefore, by using the pressure-sensitive adhesive sheet of the present invention as a protective pressure-sensitive adhesive sheet for a circuit board, it is possible to protect the circuit board by adhering to the entire attachment surface of the circuit board regardless of the form of the formed circuit. In addition, when the adhesive sheet is peeled off, the circuit board is not damaged, and the adhesive component does not move (transfer) onto the circuit board, so that the circuit board is contaminated. Nor. Furthermore, since the pressure-sensitive adhesive layer does not contain an emulsifier that is easily separated, contamination by such bleed components does not occur.

Next, the pressure-sensitive adhesive sheet for protecting a circuit board of the present invention and the production method thereof will be specifically described.
The pressure-sensitive adhesive sheet of the present invention usually has a base film and a pressure-sensitive adhesive layer formed on the surface of the base film. In this pressure-sensitive adhesive layer, a photopolymerizable composition in which a specific polyfunctional monomer and a photopolymerization initiator are blended in a monomer syrup in which a specific (meth) acrylic polymer is dissolved in a (meth) acrylic monomer. In the monomer syrup, a photopolymer obtained by photopolymerizing a (meth) acrylic monomer and a polyfunctional monomer contained in the monomer syrup so as to have a gel fraction of 90% by weight or more. And a specific (meth) acrylic polymer contained in the coexisting.

The monomer syrup used in the present invention comprises a specific (meth) acrylic polymer and a (meth) acrylic monomer that dissolves the (meth) acrylic polymer.
The weight average molecular weight of the (meth) acrylic polymer contained in the monomer syrup is in the range of 50,000 to 800,000, and preferably in the range of 100,000 to 400,000. This (meth) acrylic polymer imparts tackiness to the pressure-sensitive adhesive sheet of the present invention, and usually has tackiness. Therefore, the glass transition temperature (Tg) of this acrylic polymer is usually within the range of −100 ° C. to 0 ° C., preferably −70 to −30 ° C. In the present invention, the glass transition temperature of the polymer is a value measured by gel permeation chromatography (GPC).

This (meth) acrylic polymer is usually a copolymer of a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 18 carbon atoms and another monomer copolymerizable therewith.
The (meth) acrylic acid alkyl ester used in the present invention is a compound in which the number of carbon atoms of the alkyl group forming the ester is usually 1 to 18, preferably 3 to 12, and this alkyl group may be linear. You may have a branch. Examples of such (meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, and hexyl (meth) acrylate. , (Meth) acrylic acid alkyl esters having alkyl groups such as octyl (meth) acrylate and nonyl (meth) acrylate; branches such as 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate and t-butyl (meth) acrylate And (meth) acrylic acid alkyl esters having a cyclic alkyl group, such as (meth) acrylic acid alkyl esters having a linear alkyl group, isobornyl (meth) acrylate, and cyclohexyl (meth) acrylate. . These (meth) acrylic acid alkyl esters can be used alone or in combination.

  Moreover, as other monomers which react with the above (meth) acrylic acid alkyl ester to form an acrylic polymer, other than (meth) acrylic acid, a hydroxyl group-containing (meth) acrylic compound and (meth) acrylic acid It is preferable to use any of the carboxyl group-containing compounds.

Examples of (meth) acrylic acid include acrylic acid, methacrylic acid, acid anhydrides thereof, and salts thereof.
Hydroxyl group-containing (meth) acrylic compounds include (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid-2-hydroxypropyl, monoesters and lactones of (meth) acrylic acid and polypropylene glycol or polyethylene glycol And a hydroxyl group-containing vinyl compound such as an adduct of (meth) acrylic acid-2-hydroxyethyl.

  Examples of the carboxyl group-containing compound excluding (meth) acrylic acid include unsaturated carboxylic acids such as itaconic acid, crotonic acid, maleic acid and fumaric acid.

  In the (meth) acrylic polymer in the present invention, another monofunctional monomer copolymerizable with the (meth) acrylic monomer may be further copolymerized. Examples of other functional group monomers include (meth) acrylic acid alkoxy esters, (meth) acrylic acid allyl esters, and other (meth) acrylic monomers other than the above, and vinyl monomers such as vinyl acetate and styrene.

In the present invention, the (meth) acrylic polymer contained in the monomer syrup, when the total amount of forming monomers is 100 parts by weight, the (meth) acrylic acid alkyl ester is
It is usually copolymerized in an amount in the range of 85 to 100 parts by weight, preferably 90 to 99 parts by weight, and (meth) acrylic acid is usually 0 to 15 parts by weight, preferably 1 to 10 parts by weight. The hydroxyl group-containing (meth) acrylic compound is usually copolymerized in an amount in the range of 0 to 10 parts by weight, preferably 0 to 10 parts by weight, and is carboxyl group-containing. The compound is usually copolymerized in an amount in the range of 0 to 15 parts by weight, preferably 0 to 10 parts by weight, and the other monomers are usually 0 to 10 parts by weight, preferably 0 to 5 parts by weight. Is copolymerized in an amount in the range of However, in order to express the adhesive force required by the (meth) acrylic polymer contained in the monomer syrup, in addition to the (meth) acrylic acid alkyl ester, 100 parts by weight of the (meth) acrylic acid alkyl ester On the other hand, it is desirable that the monomer containing a polar group is usually 1 to 10 parts by weight, preferably about 1 to 5 parts by weight.

  In the (meth) acrylic polymer contained in the monomer syrup as described above, a crosslinked structure is usually not formed. Therefore, even when the gel fraction of this (meth) acrylic polymer is measured, It is 0 to 1% by weight, preferably substantially 0% by weight.

  The monomer syrup used in the present invention contains the (meth) acrylic polymer as described above and a (meth) acrylic monomer that dissolves the (meth) acrylic polymer.

As the acrylic monomer that forms the monomer syrup, an acrylic monomer that makes the monomer syrup flowable when the acrylic polymer is dissolved or uniformly dispersed is used. In the present invention, a monomer syrup having a viscosity at 25 ° C. of usually 3 to 50 Pa · s, preferably 5 to 30 Pa · s can be used as the monomer syrup.

The monomer syrup as described above is selected from the group consisting of (meth) acrylic acid alkyl esters having 1 to 18 carbon atoms in the alkyl group, (meth) acrylic acid, hydroxyl group-containing (meth) acrylic compounds and carboxyl group-containing compounds. And at least one kind of monomer. The (meth) acrylic acid alkyl ester contained in the monomer syrup is a compound in which the alkyl group forming the ester usually has 1 to 18 carbon atoms, preferably 3 to 12 carbon atoms, and the alkyl group is linear. Or you may have a branch. Examples of such (meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, and hexyl (meth) acrylate. , (Meth) acrylic acid alkyl esters having alkyl groups such as octyl (meth) acrylate and nonyl (meth) acrylate; branches such as 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate and t-butyl (meth) acrylate Mention may be made of (meth) acrylic acid alkyl esters having an alkyl group. These (meth) acrylic acid alkyl esters can be used alone or in combination.

  Moreover, as other monomers which react with the above (meth) acrylic acid alkyl ester to form an acrylic polymer, other than (meth) acrylic acid, a hydroxyl group-containing (meth) acrylic compound, (meth) acrylic acid It is preferable to use any of the carboxyl group-containing compounds.

Here, examples of (meth) acrylic acid include acrylic acid, methacrylic acid, acid anhydrides thereof, and salts thereof.
Hydroxyl group-containing (meth) acrylic compounds include (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid-2-hydroxypropyl, monoesters and lactones of (meth) acrylic acid and polypropylene glycol or polyethylene glycol And a hydroxyl group-containing vinyl compound such as an adduct of (meth) acrylic acid-2-hydroxyethyl.

  Examples of the carboxyl group-containing compound excluding (meth) acrylic acid include unsaturated carboxylic acids such as itaconic acid, crotonic acid, maleic acid and fumaric acid.

The (meth) acrylic polymer contained in the monomer syrup may further be copolymerized with another monofunctional monomer that can be copolymerized with the (meth) acrylic monomer.
In the present invention, in 100 parts by weight of the (meth) acrylic monomer contained in the monomer syrup, the above (meth) acrylic acid alkyl ester is usually in the range of 85 to 100 parts by weight, preferably 90 to 99 parts by weight. The (meth) acrylic acid is usually contained in an amount in the range of 0 to 15 parts by weight, preferably 1 to 10 parts by weight, and the hydroxyl group-containing (meth) acrylic compound is In general, it is contained in an amount in the range of 0 to 15 parts by weight, preferably 0 to 10 parts by weight, and the carboxyl group-containing compound is usually in the range of 0 to 15 parts by weight, preferably in the range of 0 to 10 parts by weight. The other monomer is usually contained in an amount in the range of 0 to 10 parts by weight, preferably 0 to 5 parts by weight.

  The monomer composition of the (meth) acrylic polymer contained in the monomer syrup may or may not coincide with the composition of the monomer contained in the monomer syrup. That is, when a (meth) acrylic polymer is formed by partial polymerization of a (meth) acrylic monomer, the composition of the monomer syrup and the monomer composition of the (meth) acrylic polymer are the same. In addition, when a (meth) acrylic polymer is separately prepared and uniformly dissolved or dispersed in the monomer, the monomer composition of the (meth) acrylic polymer and the composition of the monomer contained in the monomer syrup Can not match.

  The (meth) acrylic polymer contained in the monomer syrup of the present invention preferably has the same composition as that of the monomer forming the monomer syrup. In order to align the composition of the (meth) acrylic monomer forming the monomer syrup in this way with the monomer composition constituting the (meth) acrylic polymer dissolved in this to form the monomer syrup, Adopting a method of polymerizing a part of the (meth) acrylic monomer using a composition in which a small amount of polymerization initiator as described later and a chain transfer agent such as n-dodecyl mercaptan are blended in the mixture of the monomer based Is preferred.

In the monomer syrup (100% by weight) used in the present invention, the content of the (meth) acrylic polymer is in the range of 20 to 75% by weight, preferably 25 to 65% by weight.
The content of the (meth) acrylic monomer is 25 to 80% by weight, preferably 35 to 75% by weight.
It is in the range.

  In the present invention, a photopolymerizable composition is prepared by blending a monomer syrup having the above composition with a polyfunctional monomer having two or more ethylenic double bonds in the molecule and a photopolymerization initiator. .

The polyfunctional monomer having two or more ethylenic double bonds in the molecule used here has two or more ethylenic double bonds such as a (meth) acryloyl group in the molecule, and is a monomer syrup. It is a compound copolymerizable with an acrylic monomer contained therein. Examples of such multifunctional monomers having two or more ethylenic double bonds in the molecule include trimethylolpropane di (meth) acrylate, trimethylolpropane triacrylate, tetramethylolpropane tri (meta ) Polyvalent acrylic esters such as acrylate, hexanediol di (meth) acrylate, 1,4-butylene glycol diacrylate and neopentyl glycol di (meth) acrylate;
Di (meth) acrylic acid ester of ethylene glycol, di (meth) acrylic acid ester of diethylene glycol, di (meth) acrylic acid ester of triethylene glycol, di (meth) acrylic acid ester of polyethylene glycol, di (meta) of propylene glycol And (poly) alkylene glycol di (meth) acrylates such as acrylate acrylate, dipropylene glycol di (meth) acrylate and tripropylene glycol di (meth) acrylate. These can be used alone or in combination.

In the present invention, the polyfunctional monomer as described above is in the range of 5 to 30 parts by weight, preferably 8 to 25 parts by weight with respect to 100 parts by weight of the (meth) acrylic monomer contained in the monomer syrup. Used in quantity. In particular, this polyfunctional monomer is photopolymerized with a (meth) acrylic monomer contained in the monomer syrup to form a photopolymer so that the gel fraction is 90% by weight or more, preferably 98 to 100% by weight. Is. By using the polyfunctional monomer in such an amount, when all of the (meth) acrylic monomer contained in the monomer syrup is photopolymerized with the polyfunctional monomer to form a photopolymer, the photopolymer The gel fraction is surely 90% by weight or more, preferably 98% by weight or more, particularly preferably 99 to 100%.
% By weight.

  This polyfunctional monomer is copolymerized with an acrylic monomer contained in the monomer syrup to form a crosslinked structure in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention. By using a large amount of polyfunctional monomer as described above in the present invention, a crosslinked structure can be formed with a very high crosslinking density. When used as a general adhesive, when the polyfunctional monomer is used in the above amount as in the present invention, the adhesive strength, initial tack, cohesive force, etc. are used as a general adhesive. It cannot be within the allowable range. However, the pressure-sensitive adhesive sheet of the present invention protects a circuit formed by adhering to a circuit board on which a circuit is formed on the substrate, and the pressure-sensitive adhesive sheet of the present invention is peeled off after use. It is necessary to be attached with a slight adhesive strength so as not to damage the circuit protected at the time of peeling. In order to develop a slight adhesive force that does not damage the circuit when peeled in this way, and to prevent contamination of the circuit due to oozing out of the adhesive component, the polyfunctional monomer is added as described above. It is necessary to use in such an amount.

  Therefore, if the amount of the polyfunctional monomer is less than the above-mentioned amount, the adhesive strength becomes too high and the circuit may be damaged at the time of peeling, and the adhesive layer having high adhesive strength Some may be transferred to the circuit board side and may contaminate the board. In addition, if an amount of the polyfunctional monomer exceeding the above amount is used, the adhesive force sufficient to adhere the adhesive sheet of the present invention to the circuit board surface cannot be expressed, and the adhesive layer is hard. Therefore, the form followability in which the pressure-sensitive adhesive layer deforms following the unevenness of the surface of the circuit board that is the surface to be adhered is significantly reduced.

The photopolymerization initiator contained in the polymerizable composition used in the present invention is formed by irradiating energy rays such as visible light, ultraviolet rays, α rays and X rays, preferably ultraviolet rays having a wavelength of 200 to 400 nm. The monomer component in the adhesive composition can be radically polymerized. Examples of such photopolymerization initiators include benzoin ethers such as benzoin methyl ether, benzoin isopropyl ether and 2,2-dimethoxy-1,2-diphenylethane-1-one; substituted benzoin ethers such as anisole methyl ether; Substituted acetophenones such as 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone and 1-hydroxy-cyclohexyl-phenyl-ketone; substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone; 2 -Aromatic sulfonyl chlorides such as naphthalenesulfonyl chloride; Photoactive oximes such as 1-phenyl-1,1-propanedione-2- (o-ethoxycarbonyl) -oxime; and acylphosphine oxide . These photopolymerization initiators can be used alone or in combination. In the present invention, the use of a hydrogen abstraction initiator such as a benzophenone-based polymer draws hydrogen from the polymer in the monomer syrup and participates in the crosslinking reaction, so that the flexibility of the formed pressure-sensitive adhesive layer is lost, resulting in unevenness. This is not preferable because the followability with respect to is deteriorated.

  Such a photopolymerization initiator is usually used in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 2 parts by weight, based on 100 parts by weight of the monomer syrup. By using the photopolymerization initiator in the amount as described above, the crosslinked polymer can be formed by reacting the total amount of the (meth) acrylic monomer and the polyfunctional monomer contained in the monomer syrup. Furthermore, the photopolymerization reaction can proceed smoothly.

In producing the pressure-sensitive adhesive sheet for protecting a circuit board of the present invention, the photopolymerizable composition as described above is applied so that the thickness after curing is 250 to 2000 μm, preferably 300 to 1000 μm. The photopolymerizable composition used in the present invention is a liquid having a viscosity that can be applied using a (meth) acrylic monomer as a solvent, does not contain a non-reactive organic solvent, and the like by photopolymerization. Since the thickness is not significantly reduced, the coating thickness of the photopolymerizable composition and the thickness of the pressure-sensitive adhesive layer are almost the same. Therefore, the coating thickness of the photopolymerizable composition may be the same as the thickness of the set pressure-sensitive adhesive layer.

Said photopolymerizable composition is normally apply | coated on a base material sheet. Examples of the base sheet used here include polyester films such as polyethylene terephthalate film (PET film), synthetic resin films such as polyamide film and polyolefin film, and fiber sheets such as paper, nonwoven fabric and woven fabric. Can do. Among these, it is preferable to use a synthetic resin film having transparency such as a PET film. Such a substrate sheet preferably has a hardness such that the unevenness of the circuit board does not appear on the surface of the substrate, and is usually 50 μm or more, preferably 100 μm or more.

For example, when photopolymerizing a photopolymerizable composition layer coated on a base sheet as described above, it is desirable to dispose a protective film on the surface of the photopolymerizable composition layer. That is, since the activity of the surface of the photopolymerizable composition layer increases during photopolymerization, it is preferable to photopolymerize the photopolymerizable composition layer in a non-contact state with air (particularly oxygen). For this purpose, for example, a film having a peelable property is arranged on the surface of the photopolymerizable composition layer formed as described above to block the contact between the photopolymerizable composition layer and air, and then photopolymerize. It is preferable. Examples of the film imparted with releasability used herein include PET films and polyolefin films imparted with releasability.

Since the photopolymerizable composition layer formed as described above is irradiated with light to carry out a copolymerization reaction, at least one of the base sheet and / or the protective film, preferably both are light transmissive. In the present invention, a PET film imparted with peelability can be suitably used as the protective film.

An acrylic monomer and a polyfunctional monomer constituting the monomer syrup in the photopolymerizable composition by irradiating the photopolymerizable resin layer formed as described above with energy rays, preferably ultraviolet rays having a wavelength of 200 to 400 nm. Are photopolymerized to form a three-dimensional crosslinked structure. For example, when irradiating with ultraviolet rays, the irradiation conditions of the ultraviolet rays can be selected as appropriate, but the illuminance is usually set in the range of 0.1 to 400 mW / cm ² , and the light intensity is usually 100 to 5000 mJ / cm ^2. Is set within the range.

  The crosslinked structure formed in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention is formed by copolymerization of a polyfunctional monomer having two or more ethylenic double bonds with an acrylic monomer. The ethylenic double bond of the monomer usually forms the main chain of the acrylic resin together with the acrylic monomer. Therefore, in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention, a cross-linked structure that connects the functional groups in the side chain of the acrylic copolymer using a polyisocyanate compound, an epoxy compound, or the like is not formed.

  When the pressure-sensitive adhesive layer is formed by light irradiation as described above, the (meth) acrylic polymer contained in the monomer syrup and the crosslinked polymer produced by photopolymerization are molecules in this pressure-sensitive adhesive layer. Coexist in a mixed state. The cross-linked polymer has a predetermined form-retaining property, but is plasticized by a (meth) acrylic polymer mixed at a molecular level, and this pressure-sensitive adhesive layer has good unevenness followability. On the other hand, the adhesive strength of this pressure-sensitive adhesive layer is mainly due to the (meth) acrylic polymer contained in the monomer syrup, but the shape retention power of the cross-linked polymer mixed at the molecular level is (meth) By acting to counteract the adhesive strength of acrylic polymers, the adhesive strength of this adhesive layer as a whole is 500 g / 20 mm or less, preferably 50 to 500 g / 20 mm, particularly preferably 50 to 300 g / 20 mm. It is suppressed within the range.

Generally, the wiring formed on the substrate and the substrate are in close contact with each other with a certain degree of adhesion strength. Therefore, even if the protective adhesive sheet of the present invention is stuck on the substrate on which the circuit is formed, this protective adhesive Since the force (corresponding to the adhesive force) applied to the circuit when the sheet is peeled does not exceed the adhesion between the circuit and the substrate, the circuit is not damaged. On the other hand, the adhesive strength of this adhesive layer is 50 g
As long as the thickness is 20 mm or more, the protective adhesive sheet does not spontaneously peel off when the substrate with the protective adhesive sheet attached is handled, and the substrate and circuit that are to be protected can be sufficiently protected.

  After preparing the photopolymerizable composition which mix | blended the specific polyfunctional monomer with the monomer syrup as mentioned above, and forming the coating layer which consists of this photopolymerizable composition, this coating layer (photopolymerizable composition layer) In addition, a photopolymerization reaction is performed by irradiating light to react a (meth) acrylic monomer contained in the monomer syrup with a polyfunctional monomer to form a cross-linked polymer. A cross-linked structure is not formed in the (meth) acrylic polymer that is concentrated in the coalescence and contained in the monomer syrup.

The gel fraction (3) of the crosslinked polymer formed by photopolymerization in the protective pressure-sensitive adhesive sheet of the present invention is determined from the amount of the gel component in the pressure-sensitive adhesive layer determined from the gel fraction (2) of the pressure-sensitive adhesive layer. The difference from the amount of the gel component in the monomer syrup obtained from the gel fraction (1) of the monomer syrup was obtained, and the ratio of the obtained gel component amount to the total amount of the crosslinked heavy rod formed by light irradiation was as follows. It can be calculated by the formula.
{[(Amount of gel component in pressure-sensitive adhesive layer determined from gel fraction (2) of pressure-sensitive adhesive layer-Amount of gel component in monomer syrup determined from gel fraction (1) of monomer syrup) / photopolymerization Total amount of polymer produced by x]}.

  The protective pressure-sensitive adhesive sheet of the present invention is used by peeling off a protective film imparted with peelability and attaching it to a substrate surface on which a circuit is formed. The protective pressure-sensitive adhesive sheet of the present invention has pressure-sensitive adhesiveness and is usually stuck under pressure. In addition, it can also heat in addition to a pressure if needed.

As described above, in the pressure-sensitive adhesive sheet for protecting a circuit board of the present invention, a light having a specific polyfunctional monomer blended with a monomer syrup in which a specific (meth) acrylic polymer is dissolved, using a (meth) acrylic monomer as a solvent. Using the polymerizable composition, the (meth) acrylic monomer forming the monomer syrup and the specific polyfunctional monomer are photopolymerized to have a gel fraction of 80% by weight or more, preferably 98% by weight or more, particularly Preferably, 99 to 100% by weight of a photopolymer is formed, and the pressure-sensitive adhesive layer is present in a state where the crosslinked polymer and the (meth) acrylic polymer contained in the monomer syrup are mixed at the molecular level. Is forming. Thus, although a crosslinked structure is formed by photopolymerization, the photopolymerization reaction that forms this crosslinked structure does not affect the (meth) acrylic polymer contained in the monomer syrup. However, by using a monomer syrup, form-retaining property is formed by forming a pressure-sensitive adhesive layer in which a (meth) acrylic polymer having adhesive force and a crosslinked polymer having form-retaining property are mixed at the molecular level. The (meth) acrylic polymer acts as a plasticizer for photopolymers having a surface to give unevenness to the pressure-sensitive adhesive layer, and the photopolymer for other (meth) acrylic polymers. It acts as an adhesive force inhibitor, and imparts removability (suppressed adhesiveness) to the adhesive layer. Therefore, the pressure-sensitive adhesive layer in the protective pressure-sensitive adhesive sheet of the present invention has a cross-linked structure concentrated on the photopolymer. For example, a small amount of a polyfunctional monomer is blended with the monomer to partially form a cross-linked structure. The composition of the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive is different, and a (meth) acrylic polymer obtained by polymerizing a (meth) acrylic monomer, and a (meth) acrylic monomer and a polyfunctional monomer were polymerized. It is also different from the structure of the pressure-sensitive adhesive layer made of a mixture prepared by separately producing a crosslinked polymer. That is, for example, in a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive in which a small amount of a multifunctional monomer is blended with a monomer to form a partially crosslinked structure, the crosslinked structure is uniformly formed throughout the pressure-sensitive adhesive, and the same gel content is obtained. Even if it has a rate, uneven | corrugated followability and removability are not expressed. Further, for example, a (meth) acrylic monomer was polymerized (
In the pressure-sensitive adhesive layer consisting of a mixture of a (meth) acrylic polymer and a cross-linked polymer obtained by polymerizing a (meth) acrylic monomer and a polyfunctional monomer, the (meth) acrylic polymer and the cross-linked polymer Since the polymer cannot be mixed uniformly at the molecular level, similarly, even if it has the same gel fraction, unevenness followability and re-peelability do not appear.

  In this way, a specific polyfunctional monomer is blended with the monomer syrup in which the (meth) acrylic polymer of the present invention is uniformly dissolved in the (meth) acrylic monomer, and contained in the monomer syrup by photopolymerization (meta ) An acrylic monomer and a polyfunctional monomer were photopolymerized so that the gel fraction was 90% by weight or more, preferably 98% by weight or more, and particularly preferably 99 to 100% by weight, thus forming a crosslinked structure. By causing the polymer and the (meth) acrylic polymer contained in the monomer syrup to coexist, the pressure-sensitive adhesive force of the pressure-sensitive adhesive layer becomes a slight pressure-sensitive adhesive force of 500 g / 20 mm or less. The form of the pressure-sensitive adhesive layer changes following the unevenness of the substrate surface, which becomes soft and has unevenness due to the formation of the circuit. Therefore, the pressure-sensitive adhesive sheet of the present invention can be securely adhered to the surface of the circuit board on which the unevenness is formed to protect the circuit board. Further, when the pressure-sensitive adhesive sheet is peeled off, no adhesive residue is left on the surface of the circuit board, and the circuit is not damaged by the peeling of the pressure-sensitive adhesive sheet.

  By photopolymerizing as described above, the polyfunctional monomer and the acrylic monomer in the monomer syrup are photopolymerized to form a crosslinked structure, but the (meth) acrylic polymer contained in the monomer syrup is It does not participate in this cross-linked structure formation reaction. The gel fraction of all components forming the pressure-sensitive adhesive layer obtained by crosslinking polymerization in this manner is usually in the range of 25 to 80% by weight, preferably in the range of 35 to 75% by weight.

  The pressure-sensitive adhesive sheet for protecting a circuit board of the present invention has the above-described configuration, but other components may be blended unless it is contrary to the object of the present invention. For example, a coloring agent, a filler, etc. can be mix | blended.

〔Example〕
Hereinafter, although an Example is shown and demonstrated about the adhesive sheet for circuit board protection of this invention, and its manufacturing method, this invention is not limited by these.

Preparation of monomer syrup [1] In a 2 liter four-necked flask equipped with a stirrer, a nitrogen gas inlet tube and a condenser tube, 980 g of 2-ethylhexyl acrylate (hereinafter referred to as “2EHA”) and acrylic acid (hereinafter referred to as “2EHA”) 20 g, described as “AA”, 0.1 g of n-dodecyl mercaptan and 0.05 g of 2,2-dimethoxy-2-phenylacetophenone as a photopolymerization initiator, and irradiated with ultraviolet rays in a nitrogen gas atmosphere to give a monomer concentration A monomer syrup of 50% by weight and a polymer concentration of 50% by weight was prepared. The weight average molecular weight of the polymer contained in this monomer syrup was 300,000. The gel fraction of the acrylic polymer in the monomer syrup (1) was 0% by weight. The monomer syrup [1] had a viscosity of 20 Pa · s at 25 ° C. The monomer syrup composition, polymer molecular weight, polymer gel fraction and viscosity are shown in Table 1.
Preparation of photopolymerizable composition [1] Three ethylenic double bonds in the molecule were prepared in 100 parts by weight of monomer syrup [1] having a polymer concentration of 50% by weight and a monomer concentration of 50% by weight prepared as described above. 10 parts by weight of trimethylolpropane triacrylate (TMP-A) (20 parts by weight based on 100 parts by weight of monomer) and 2-hydroxy-2-ethyl-1-phenylpropane-1 which is a photopolymerization initiator
-On (trade name: Dycure 1173, manufactured by Ciba Geigy) 0.4 part by weight was added to prepare a photopolymerizable composition [1].
Preparation of protective pressure-sensitive adhesive sheet << 1 >> The photopolymerizable composition [1] obtained as described above is formed on a polyethylene terephthalate film (PET film) having an average thickness of 100 μm, and the average thickness of the pressure-sensitive adhesive layer. After coating to 300 μm, the coated surface was coated with a peelable PET film, and then irradiated with a high pressure mercury lamp with a wavelength of 200 to 400 nm for 75 seconds to (meth) acrylic in the coating layer made of the photopolymerizable composition A protective pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which a (meth) acrylic polymer and a cross-linked polymer are mixed at a molecular level by photopolymerizing a monomer and TMP-A to form a cross-linked polymer << 1 Was prepared.

  The pressure-sensitive adhesive sheet <1> having the pressure-sensitive adhesive layer thus formed had a pressure-sensitive adhesive strength of 150 g / 20 mm. Moreover, the gel fraction measured about resin which forms this adhesive layer was 50 weight%.

Therefore, the gel fraction (3) of the polymer produced by photopolymerization is 100% by weight.
The obtained pressure-sensitive adhesive sheet << 1 >> was adhered to a circuit board, and the protection state of the circuit was evaluated. The results are shown in Table 2-1 and Table 2-2.
Measurement of gel fraction In the present invention, the gel fraction (1) of the monomer syrup is obtained by using toluene as the solvent for the (meth) acrylic polymer obtained by removing the (meth) acrylic monomer from the monomer syrup. The weight of the insoluble component was determined, and the weight ratio of the insoluble component in the monomer syrup was calculated. The gel fraction (2) of the pressure-sensitive adhesive layer is obtained by collecting the resin components forming the pressure-sensitive adhesive layer, using toluene as the solvent, and determining the weight of the component insoluble in this solvent. The weight ratio of insoluble components was calculated and determined. The gel fraction (3) of the polymer produced by photopolymerization is calculated from the amount of the gel component in the pressure-sensitive adhesive layer obtained from the gel fraction (2) of the pressure-sensitive adhesive layer obtained as described above, from the monomer syrup. The difference from the amount of the gel component in the monomer syrup obtained from the gel fraction (1) is obtained, and the ratio of the obtained gel component amount to the total amount of cross-linked heavy rods formed by light irradiation {[(adhesive The amount of gel component in the pressure-sensitive adhesive layer determined from the gel fraction (2) of the layer—the amount of gel component in the monomer syrup determined from the gel fraction (1) of the monomer syrup) / polymer produced by photopolymerization Total amount] × 100}.
Concavity and convexity follow-up test The pressure-sensitive adhesive sheet produced as described above was cut out in a size of 150 × 150 mm to obtain a test piece. The peelable PET film is peeled off from the test piece, placed on a metal plate having a large number of wart-like protrusions with a height of 50 μm on the surface, and pressure-bonded using a 2 kg roller, and the wart-like shape of the test piece is obtained. The adhesion to the metal surface on which the protrusions were formed was visually observed.
Re-peeling test A pressure-sensitive adhesive sheet was pressure-bonded to the metal plate used in the unevenness follow-up test and left for 24 hours. Then, the adhesive sheet was peeled off from the metal plate, and it was confirmed whether the adhesive layer was transcribe | transferred on the metal plate surface.
Measurement of weight average molecular weight In the present invention, the weight average molecular weight is determined by gel permeation chromatography (GPC).
It is the value measured by.

The composition and characteristics of the obtained pressure-sensitive adhesive sheet are shown in Table 2-1 and Table 2-2.
For comparison, a polymer equivalent to the (meth) acrylic polymer contained in the monomer syrup used in Example 1 was produced by the solution polymerization method as follows.

A 2-liter four-necked flask equipped with a stirrer, a nitrogen gas introduction tube and a cooling tube was charged with 980 g of 2EHA, 20 g of AA, and 1000 g of ethyl acetate, and dimethyl-2, A polymer was produced by adding 0.3 g of 2′-azobis (2-methylpropionate) and setting the reaction temperature to 75 ° C. and the reaction time to 6 hours so that the weight average molecular weight was 300,000. The gel fraction of this polymer is 0% by weight, and no crosslinked structure is formed. The pressure-sensitive adhesive strength of a pressure-sensitive adhesive sheet having a thickness of 300 μm formed using this polymer was measured to be 640 g / 20 mm. When this pressure-sensitive adhesive sheet was attached to a substrate on which a circuit was formed and peeled off, A part of the circuit was transferred from the base material to the adhesive sheet side to damage the circuit.

Separately from the above polymer, 2EHA 980 g, AA 20 g, TMP-A 20 g and 2,2-dimethoxy-2-phenylacetophenone 8 g as a photopolymerization initiator were mixed and adhered onto a 100 μm polyethylene terephthalate film (PET film). The average thickness of the agent layer is 30
After coating to 0 μm and covering the coated surface with a peelable PET film, the wavelength is 200
A pressure-sensitive adhesive sheet having a gel fraction of 100% was formed by photopolymerization of 2EHA, AA and TMP-A by irradiation with a high pressure mercury lamp of ˜400 nm for 75 seconds to produce a pressure-sensitive adhesive sheet. Although the adhesive strength of this adhesive sheet was 50 g / mm, when an unevenness follow-up test was conducted in the same manner as described above, the adhesive layer was in contact with the top of the protrusion formed on the metal plate. The pressure-sensitive adhesive layer was hardly in contact with the recess.

  Also, a pressure-sensitive adhesive composition obtained by mixing a polymer having a molecular weight of 300,000 produced by solution polymerization as described above and a photopolymerization product (gel fraction: 100% by weight) of 2EHA, AA and TMP-A separately prepared. The pressure-sensitive adhesive composition was applied to produce a pressure-sensitive adhesive sheet. However, in the absence of a solvent, the two could not be mixed uniformly, so the production of the pressure-sensitive adhesive sheet was abandoned.

  In the preparation of the photopolymerizable composition of Example 1, the amount of trimethylolpropane triacrylate (TMP-A) added to 100 parts by weight of the monomer syrup [1] having a polymer concentration of 50% by weight and a monomer concentration of 50% by weight was determined. A photopolymerizable composition [9] was prepared in the same manner except that the amount was 2.5 parts by weight (5 parts by weight with respect to 100 parts by weight of the monomer in the monomer syrup).

  An adhesive sheet << 12 >> was produced in the same manner as in Example 1 except that this photopolymerizable composition [9] was used. (Gel fraction of resin forming the pressure-sensitive adhesive layer; 48% by weight). Therefore, the gel fraction of the resin formed by photopolymerization is 95% by weight.

  The obtained adhesive sheet << 12 >> was stuck on a circuit board, and the protection state of the circuit was evaluated. The results are shown in Table 2-1 and Table 2-2. The pressure-sensitive adhesive sheet did not contaminate or damage the circuit board, and also had good shape followability, and was able to protect the circuit board satisfactorily. The workability at the time of peeling tended to be somewhat inferior because it was somewhat high.

Monomer syrup [4] in the same manner as in the preparation of the monomer syrup of Example 1, except that the monomer used (2EHA = 980 g, AA = 20 g) was changed to 2-EHA = 1000 g.
Manufactured. Properties of this monomer syrup are shown in Table 1.

  In the production of the photopolymerizable composition of Example 1, an adhesive sheet << 13 >> was prepared in the same manner except that the monomer syrup [4] was used. The adhesive strength of this adhesive sheet << 13 >> was 70 g / 20 mm.

The obtained adhesive sheet << 13 >> was stuck on a circuit board and evaluated for the protection state of the circuit.
The results are shown in Table 2-1 and Table 2-2. The pressure-sensitive adhesive sheet did not contaminate or damage the circuit board, and also had good shape followability, and was able to protect the circuit board satisfactorily. The tendency was somewhat low and somewhat inferior in adhesion to the circuit board.
[Comparative Example 1]
Preparation of photopolymerizable composition [2] In Example 1, monomer syrup [1] [monomer concentration 50 wt%, polymer concentration 50 wt%, polymer weight average molecular weight 300,000, gel fraction (1) 0 wt% ] For 100 parts by weight, 0.1 part by weight of TMP-A (0.2 part by weight for 100 parts by weight of monomer in the monomer syrup), and 2-hydroxy-2- A photopolymerizable composition [2] was prepared by adding 0.4 parts by weight of ethyl-1-phenylpropan-1-one. The monomer syrup composition, polymer molecular weight, polymer gel fraction and viscosity are shown in Table 1.
Preparation of protective adhesive sheet << 2 >> In Preparation Example 1, the same procedure was used except that the photopolymerizable composition [2] obtained as described above was used instead of the photopolymerizable composition [1]. A protective pressure-sensitive adhesive sheet << 2 >> having a pressure-sensitive adhesive layer was prepared.

The pressure-sensitive adhesive sheet << 2 >> having the pressure-sensitive adhesive layer thus formed had an adhesive strength of 1500 g / 20 mm. In addition, the gel fraction (2) measured for the resin forming this adhesive layer is
It was 32% by weight.

Therefore, the gel fraction (3) of the polymer produced by photopolymerization is 64% by weight.
Using the pressure-sensitive adhesive sheet << 2 >> produced as described above, an unevenness follow-up test and a re-peeling test were performed.

Since this pressure-sensitive adhesive sheet << 2 >> had high adhesive strength, adhesive residue was generated on the surface of the circuit board at the time of peeling, and part of the circuit was damaged.
The composition and properties of the obtained pressure-sensitive adhesive sheet << 2 >> are shown in Tables 2-1 and 2-2.
[Comparative Example 2]
Preparation of photopolymerizable composition [3] In Example 1, monomer syrup [1] [monomer concentration 50 wt%, polymer concentration 50 wt%, polymer weight average molecular weight 300,000, gel fraction (1) 0 wt% ] With respect to 100 parts by weight, without using TMP-A, 10 parts by weight of 1,3-bis (diglycidylaminomethyl) cyclohexane and 2-hydroxy-2-ethyl- 1-Phenylpropane-1-
Photopolymerizable composition [3] was prepared by adding 0.3 part by weight of ON. The monomer syrup composition, polymer molecular weight, polymer gel fraction and viscosity are shown in Table 1.
Preparation of protective adhesive sheet << 3 >> In Preparation Example 1, the same procedure was used except that instead of the photopolymerizable composition [1], the photopolymerizable composition [3] obtained as described above was used. A protective pressure-sensitive adhesive sheet << 3 >> having a pressure-sensitive adhesive layer was prepared. Since this pressure-sensitive adhesive sheet << 3 >> has a crosslinked structure formed of 1,3-bis (diglycidylaminomethyl) cyclohexane, the gel fraction of the polymer produced by photopolymerization cannot be measured.

The adhesive strength of the protective adhesive sheet << 3 >> having the adhesive layer thus formed is 50 g / 20 mm.
Met. Moreover, the gel fraction (2) measured about resin which forms this adhesive layer was 85 weight%.

Using the pressure-sensitive adhesive sheet << 3 >> produced as described above, an unevenness follow-up test and a re-peeling test were performed.
The composition and properties of the obtained pressure-sensitive adhesive sheet << 3 >> are shown in Tables 2-1 and 2-2. In this pressure-sensitive adhesive sheet << 3 >>, the entire pressure-sensitive adhesive layer was cross-linked, so that the unevenness followability was not expressed. [Comparative Example 3]
Preparation of monomer syrup [2] In a 2-liter four-necked flask equipped with a stirrer, nitrogen gas inlet tube and condenser tube, 980 g of 2EHA, 20 g of AA, 0.1 g of n-dodecyl mercaptan and 2,2- Dimethoxy-2-phenylacetophenone (0.05 g) was added, and ultraviolet rays were irradiated in a nitrogen gas atmosphere to prepare a monomer syrup having a monomer concentration of 88% by weight and a polymer concentration of 12% by weight. The weight average molecular weight of the polymer contained in this monomer syrup was 300,000. The gel fraction of the acrylic polymer in the monomer syrup [2] was 0% by weight. The monomer syrup [2] had a viscosity at 25 ° C. of 3 Pa · s. The monomer syrup composition, polymer molecular weight, polymer gel fraction and viscosity are shown in Table 1.
Preparation of photopolymerizable composition [4] In Example 1, instead of monomer syrup [1] [monomer concentration 50 wt%, polymer concentration 50 wt%], monomer syrup [2] [2] [ Monomer concentration 88% by weight, polymer concentration 15% by weight, polymer weight average molecular weight 1.5 million, gel fraction 0% by weight], and 10 parts by weight of TMP-A (based on 100 parts by weight of monomer in the monomer syrup) 11.4 parts by weight) A photopolymerizable composition [4] was prepared in the same manner except that it was added.
Preparation of protective adhesive sheet << 4 >> In Preparation Example 1, the same procedure was used except that the photopolymerizable composition [4] obtained as described above was used instead of the photopolymerizable composition [1]. A protective pressure-sensitive adhesive sheet << 4 >> having a pressure-sensitive adhesive layer was prepared.

The adhesive strength of the protective adhesive sheet “4” having the adhesive layer thus formed is 20 g / 20 mm.
Met. Moreover, the gel fraction (2) measured about resin which forms this adhesive layer was 88 weight%.

Therefore, the gel fraction (3) of the polymer produced by photopolymerization is 100% by weight.
Using the pressure-sensitive adhesive sheet << 4 >> produced as described above, an unevenness follow-up test and a re-peeling test were performed.

The composition and properties of the resulting pressure-sensitive adhesive sheet << 4 >> are shown in Tables 2-1 and 2-2. Since this pressure-sensitive adhesive sheet has a large amount of gel, it has poor conformity to the circuit board.
[Comparative Example 4]
Preparation of monomer syrup [3] In a 2-liter four-necked flask equipped with a stirrer, a nitrogen gas inlet tube and a cooling tube, 980 g of 2EHA, 20 g of AA, 0.1 g of n-dodecyl mercaptan and 2,2- Dimethoxy-2-phenylacetophenone (0.05 g) was added, and ultraviolet rays were irradiated in a nitrogen gas atmosphere to prepare a monomer syrup having a monomer concentration of 15% by weight and a polymer concentration of 85% by weight. The weight average molecular weight of the polymer contained in this monomer syrup was 300,000. The gel fraction of this monomer syrup [3] was 0% by weight. The monomer syrup [3] had a viscosity at 25 ° C. of 50 Pa · s.
Preparation of photopolymerizable composition [5] In Example 1, instead of monomer syrup [1] [monomer concentration 50 wt%, polymer concentration 50 wt%, polymer weight average molecular weight 300,000, gel fraction 0 wt%] The monomer syrup [3] prepared as described above [monomer concentration 15% by weight, polymer concentration 8
5 wt%, polymer weight average molecular weight 100,000, gel fraction 0 wt%], and 10 parts by weight of TMP-A (66.7 parts by weight with respect to 100 parts by weight of monomer in monomer syrup) A photopolymerizable composition [5] was prepared in the same manner as described above.
Preparation of protective adhesive sheet << 5 >> In Preparation Example 1, the same procedure was used except that the photopolymerizable composition [5] obtained as described above was used instead of the photopolymerizable composition [1]. A protective pressure-sensitive adhesive sheet << 5 >> having a pressure-sensitive adhesive layer was prepared.

  The pressure-sensitive adhesive sheet << 5 >> having the pressure-sensitive adhesive layer thus formed had an adhesive strength of 1700 g / 20 mm. Moreover, the gel fraction (2) measured about resin which forms this adhesive layer was 15 weight%.

Therefore, the gel fraction (3) of the polymer produced by photopolymerization is 100% by weight.
Using the pressure-sensitive adhesive sheet << 5 >> produced as described above, an unevenness follow-up test and a re-peeling test were performed.

The composition and properties of the obtained pressure-sensitive adhesive sheet << 5 >> are shown in Tables 2-1 and 2-2. Since the obtained pressure-sensitive adhesive sheet had a small gel content, adhesive residue was generated and the surface of the circuit board was contaminated. [Comparative Example 5]
A photopolymerizable composition [6] was prepared in the same manner except that 10 parts by weight of TMP-A (20 parts by weight with respect to 100 parts by weight of monomer in the monomer syrup) was added to the monomer syrup used in Example 1. .

  In Example 1, instead of the photopolymerizable composition [1], the above-mentioned photopolymerizable composition [6] was used, and the pressure-sensitive adhesive sheet << 6 >> (the gel fraction of the pressure-sensitive adhesive sheet; 50% by weight). Therefore, the gel fraction of the photopolymerization component is 100 parts by weight.

The resulting adhesive sheet << 6 >> had an adhesive strength of 130 g / 20 mm. This pressure-sensitive adhesive sheet << 6 >> was stuck on a substrate on which a circuit was formed in the same manner as in Example 1 to investigate the unevenness followability.
Irregularities due to circuit irregularities were observed on the film surface.

The composition and properties of the obtained pressure-sensitive adhesive sheet << 6 >> are shown in Tables 2-1 and 2-2.
[Comparative Example 6]
1 part by weight of TMP-A (2 parts by weight with respect to 100 parts by weight of monomer in the monomer syrup) using a polymer syrup containing 2EHA in Example 1; 980 g and AA; 20 g
A photopolymerizable composition [7] was prepared by mixing 15 g of 2-hydroxy-2-ethyl-1-phenylpropan-1-one as a photopolymerization initiator.

In Example 1, an adhesive sheet << 7 >> was produced in the same manner except that the above photopolymerizable composition [7] was used instead of the photopolymerizable composition [1] (gel fraction; 72 weights) %).
The pressure-sensitive adhesive sheet << 7 >> obtained had an adhesive strength of 500 g / 20 mm, and clouding occurred when the formed pressure-sensitive adhesive layer was peeled off.

The composition and properties of the obtained pressure-sensitive adhesive sheet << 7 >> are shown in Tables 2-1 and 2-2.
[Comparative Example 7]
In Example 1, 17.5 parts by weight of TMP-A (35 parts by weight with respect to 100 parts by weight of monomer in the monomer syrup) and 2-hydroxy-2-ethyl-1-phenylpropane- which is a photopolymerization initiator 1-one; 15 g was mixed to prepare a photopolymerizable composition [8]. The pressure-sensitive adhesive strength of the pressure-sensitive adhesive sheet << 8 >> having a 300 [mu] m pressure-sensitive adhesive layer formed using this photopolymerizable composition [8] was measured and found to be 20 g / 20 mm. When the substrate was stuck and peeled, it was highly cross-linked and the function of the pressure-sensitive adhesive layer was suppressed, voids were formed, and circuit board protection was incomplete.

The composition and properties of the resulting pressure-sensitive adhesive sheet << 8 >> are shown in Tables 2-1 and 2-2.
[Comparative Example 8]
Preparation of monomer syrup [5] To a 2-liter four-necked flask equipped with a stirrer, nitrogen gas inlet tube and condenser tube, 980 g of 2EHA, 20 g of AA, 0.8 g of n-dodecyl mercaptan and 2,2- Dimethoxy-2-phenylacetophenone (0.05 g) was added and irradiated with ultraviolet rays in a nitrogen gas atmosphere to prepare a monomer syrup [5] having a monomer concentration of 50% by weight and a polymer concentration of 50% by weight. The weight average molecular weight of the polymer contained in this monomer syrup [5] is 40,000, the gel fraction of this polymer is 0% by weight, and no crosslinked structure is formed.

  Except that this monomer syrup [5] was used, the pressure-sensitive adhesive strength of the pressure-sensitive adhesive sheet << 9 >> formed with a pressure-sensitive adhesive layer having a thickness of 300 μm was measured in the same manner as in Example 1 and found to be 300 g / 20 mm. When the adhesive sheet << 9 >> was adhered to the substrate on which the circuit was formed and peeled off, the circuit was contaminated by the adhesive layer of the adhesive sheet << 9 >> because the polymer had a low molecular weight.

The composition and properties of the obtained pressure-sensitive adhesive sheet << 9 >> are shown in Tables 2-1 and 2-2.
[Comparative Example 9]
Preparation of monomer syrup [6] In a 2-liter four-necked flask equipped with a stirrer, nitrogen gas inlet tube and condenser tube, 980 g of 2EHA, 20 g of AA, 0.003 g of n-dodecyl mercaptan and 2,2- Dimethoxy-2-phenylacetophenone 0.05 g was added and irradiated with ultraviolet rays in a nitrogen gas atmosphere to prepare a monomer syrup [6] having a monomer concentration of 50% by weight and a polymer concentration of 50% by weight. The weight average molecular weight of the polymer contained in the monomer syrup [6] is 1 million, the gel fraction of this polymer is 0% by weight, and no crosslinked structure is formed.

  The pressure-sensitive adhesive strength of the pressure-sensitive adhesive sheet << 11 >> having a 300-μm-thick pressure-sensitive adhesive layer was measured in the same manner as in Example 1 except that this monomer syrup was used, and it was 170 g / 20 mm. 11 >> and the circuit had a slight gap, and the circuit was not completely protected.

  The composition and properties of the obtained pressure-sensitive adhesive sheet << 11 >> are shown in Tables 2-1 and 2-2.

  The pressure-sensitive adhesive sheet for protecting a circuit board according to the present invention provides light to a photopolymerizable composition in which a polyfunctional monomer having a plurality of ethylenic double bonds is blended with a monomer syrup containing a specific (meth) acrylic polymer. Irradiated to photopolymerize the (meth) acrylic monomer contained in the monomer syrup and the polyfunctional monomer. Therefore, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for circuit board protection of the present invention contains a photopolymer having a gel fraction of 80% by weight or more formed by the photopolymerization reaction as described above and a monomer syrup. The (meth) acrylic polymer that has been used coexists in a mixed state at the molecular level. The pressure-sensitive adhesive sheet for protecting a circuit board according to the present invention having such a pressure-sensitive adhesive layer having a thickness of 250 to 2000 μm is such that a photopolymer (crosslinked polymer) and a (meth) acrylic polymer interact with each other. The adhesive strength of the sheet is such that the sheet does not damage the circuit, the adhesive is not transferred to the surface of the circuit board when it is peeled off, and the sheet does not spontaneously peel off. Further, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for circuit board protection of the present invention follows the unevenness on the board caused by the photopolymer being a crosslinked polymer and the (meth) acrylic polymer jointly forming a circuit. Soft enough to do. Therefore, when the protective adhesive sheet of the present invention is attached to the substrate surface on which the circuit is formed, the adhesive layer is deformed corresponding to the irregularities on the substrate and attached to the entire substrate surface. Although the pressure-sensitive adhesive layer is soft so as to have such good unevenness followability, when this protective pressure-sensitive adhesive sheet is peeled off, an adhesive residue is generated in which the pressure-sensitive adhesive layer separates and moves to the substrate surface. Hateful.

  Therefore, by sticking the protective adhesive sheet of the present invention to the surface of the circuit board, the circuit board can be well protected, and the circuit board is damaged by sticking the protective adhesive sheet. Or it does not occur that the circuit board is contaminated and is extremely useful as a sheet for protecting the circuit board.

Claims (18)

  (Meth) acrylic polymer having a weight average molecular weight of 50,000 to 800,000; monomer syrup containing 20 to 75% by weight and (meth) acrylic monomer; 25 to 80% by weight (provided that (meth) acrylic polymer and ( And a total of 100 wt% of the (meth) acrylic monomer) and 100 parts by weight of the (meth) acrylic monomer contained in the monomer syrup. (Meth) acrylic monomer and polyfunctional monomer contained in the monomer syrup by irradiating a photopolymerizable composition containing 5 to 30 parts by weight of a functional monomer and a photopolymerization initiator with light And a (meth) acrylic polymer contained in the monomer syrup coexisting with a photopolymer obtained by photopolymerization so that the gel fraction is 90% by weight or more A pressure-sensitive adhesive layer for protecting a circuit board, wherein the pressure-sensitive adhesive layer has an average thickness of 250 to 2000 μm, and the pressure-sensitive adhesive strength of the pressure-sensitive adhesive layer is 500 g / 20 mm or less Sheet.   2. The adhesive sheet for protecting a circuit board according to claim 1, wherein a gel fraction of the crosslinked polymer forming the adhesive layer is 98% by weight or more.   2. The adhesive sheet for protecting a circuit board according to claim 1, wherein the (meth) acrylic polymer contained in the monomer syrup has a gel fraction of 0 to 1% by weight.   2. The pressure-sensitive adhesive sheet for protecting a circuit board according to claim 1, wherein a gel fraction of the whole pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is in a range of 25 to 85% by weight.   The adhesive for protecting a circuit board according to claim 1, wherein the (meth) acrylic monomer and the polyfunctional monomer are cross-linked and polymerized so that the adhesive strength of the adhesive layer is 50 to 500 g / 20 mm. Sheet.   The composition of the (meth) acrylic monomer that forms the monomer syrup is substantially the same as the monomer composition of the (meth) acrylic polymer that forms the monomer syrup together with the (meth) acrylic monomer. 6. The adhesive sheet for protecting a circuit board according to any one of claims 1 to 5, wherein: 20 to 75% by weight of a (meth) acrylic polymer having a weight average molecular weight of 50,000 to 800,000 and a (meth) acrylic monomer that dissolves the (meth) acrylic polymer in an amount of 25 to 80% by weight Monomer syrup (100% by weight in total)
Photopolymerizability obtained by blending a polyfunctional monomer having two or more ethylenic double bonds in a molecule of 5 to 30 parts by weight and a photopolymerization initiator with respect to 100 parts by weight of a (meth) acrylic monomer. The composition was applied on a substrate film so that the thickness after curing was 250 to 2000 μm, and then the photopolymerizable composition layer was irradiated with light to (meth) acrylic in the monomer syrup. A circuit board characterized in that an adhesive layer having an adhesive strength adjusted to 500 g / 20 mm or less is formed by photopolymerization of a system monomer and the polyfunctional monomer so that the gel fraction is 90% by weight or more. A method for producing a protective adhesive sheet.   8. The method for producing a pressure-sensitive adhesive sheet for protecting a circuit board according to claim 7, wherein the cross-linked polymer forming the pressure-sensitive adhesive layer has a gel fraction of 98% by weight or more.   The method for producing an adhesive sheet for protecting a circuit board according to claim 7, wherein the (meth) acrylic polymer contained in the monomer syrup has a gel fraction of 0 to 1% by weight.   The method for producing a pressure-sensitive adhesive sheet for protecting a circuit board according to claim 7, wherein the gel fraction of the whole pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is in the range of 25 to 80% by weight. The (meth) acrylic polymer having a weight average molecular weight of 50,000 to 800,000 contained in the monomer syrup is a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 18 carbon atoms, and (meth) acrylic acid. 8. The adhesive for protecting a circuit board according to claim 7, wherein the adhesive is a copolymer with at least one monomer selected from the group consisting of a hydroxyl group-containing (meth) acrylic compound and a carboxyl group-containing compound. Sheet manufacturing method. The (meth) acrylic monomer forming the monomer syrup is a (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl group, (meth) acrylic acid, a hydroxyl group-containing (meth) acryl compound and a carboxyl group The method for producing an adhesive sheet for protecting a circuit board according to claim 7, comprising at least one monomer selected from the group consisting of compounds.   8. The photopolymerizable composition is applied to a substrate film surface, the surface of the applied photopolymerizable composition is coated with a peelable film, and then irradiated with light. Of manufacturing a pressure-sensitive adhesive sheet for circuit board protection.   The method for producing an adhesive sheet for protecting a circuit board according to claim 7, wherein the (meth) acrylic polymer contained in the monomer syrup has a gel fraction of 0 to 1% by weight.   8. The circuit board protecting adhesive according to claim 7, wherein the (meth) acrylic monomer and the polyfunctional monomer are cross-linked and polymerized so that the adhesive strength of the adhesive layer is 50 to 500 g / 20 mm. Sheet manufacturing method.   The method for producing a pressure-sensitive adhesive sheet for protecting a circuit board according to claim 7 or 13, wherein at least one of the base film and the peelable covering film has light permeability.   The composition of the (meth) acrylic monomer that forms the monomer syrup is substantially the same as the monomer composition of the (meth) acrylic polymer that forms the monomer syrup together with the (meth) acrylic monomer. The manufacturing method of the adhesive sheet for circuit board protection of any one of Claim 7 thru | or 16 to do.   18. The method for producing an adhesive sheet for protecting a circuit board according to claim 17, wherein the monomer syrup is formed by partially polymerizing a mixture of (meth) acrylic monomers.