Removable adhesive composition and adhesive sheet

Abstract

To provide a re-releasable adhesive composition that is not too low in initial adhesion, prevents the adhesion from becoming too high after heating, and avoids contaminating a bonding object after heating.SOLUTION: A re-releasable adhesive composition contains following components (A)-(C): (A) a (meth)acrylic resin that is a polymer of a monomer predominantly composed of a (meth)acrylate acid alkyl ester having an alkyl group with 2 or less carbon atoms, (B) a compound having an ethylenically unsaturated bond and (C) a polymerization initiator.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a removable pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. [Background technology]

[0002] Pressure-sensitive adhesive sheets for surface protection are used in the manufacturing processes of electronic devices such as semiconductors, electronic components, and display components. Acrylic pressure-sensitive adhesives are often used as pressure-sensitive adhesive compositions for pressure-sensitive adhesive sheets used in such processes (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 034353 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] The pressure-sensitive adhesive sheet and pressure-sensitive adhesive composition may be heated during processing of components in the manufacturing process of the electronic device, etc. In such cases, the adhesive strength of the pressure-sensitive adhesive sheet may become too high after heating, making it difficult to peel, or the pressure-sensitive adhesive sheet may contaminate the components after peeling.

[0005] On the other hand, if the initial adhesive strength (the adhesive strength immediately after the pressure-sensitive adhesive sheet is adhered to the adherend) is too low, poor adhesion may occur if the member to be protected has fine features or a rough surface.

[0006] Therefore, the adhesive composition and adhesive sheet must have the properties of not having too low an initial adhesive strength, not becoming too high an adhesive strength after heating, and not being likely to contaminate the adherend after heating.

[0007] Therefore, an object of the present invention is to provide a removable pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that have an initial adhesive strength that is not too low, that do not become too high in adhesive strength after heating, and that are less likely to contaminate the adherend after heating. [Means for solving the problem]

[0008] In order to achieve the above object, the removable pressure-sensitive adhesive composition of the present invention is characterized by comprising the following components (A) to (C): (A) A (meth)acrylic resin that is a polymer of a monomer whose main component is a (meth)acrylic acid alkyl ester having an alkyl group having two or less carbon atoms. (B) Compounds having an ethylenically unsaturated bond (C) Polymerization initiator

[0009] The pressure-sensitive adhesive sheet of the present invention is characterized by having a pressure-sensitive adhesive layer on at least one surface of a substrate, and the pressure-sensitive adhesive layer containing the removable pressure-sensitive adhesive composition of the present invention. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a removable pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that have an initial adhesive strength that is not too low, an adhesive strength that does not become too high after heating, and that are less likely to contaminate the adherend after heating. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described below with reference to examples, but the present invention is not limited to the following description.

[0012] In the removable pressure-sensitive adhesive composition of the present invention, the (meth)acrylic resin (A) may be, for example, a copolymer of a monomer mixture containing at least one of a monomer having a hydroxyl group and a monomer having a carboxy group.

[0013] The removable pressure-sensitive adhesive composition of the present invention may further contain, for example, the following component (D). (D) Crosslinking agent

[0014] In the removable pressure-sensitive adhesive composition of the present invention, the (meth)acrylic resin (A) may be, for example, a copolymer of a monomer mixture containing 2.0 to 49.9% by weight of a monomer having a hydroxyl group.

[0015] In the removable pressure-sensitive adhesive composition of the present invention, for example, the content of the compound (B) having an ethylenically unsaturated bond may be 40 to 200 parts by weight per 100 parts by weight of the (meth)acrylic resin (A).

[0016] In the removable pressure-sensitive adhesive composition of the present invention, for example, the compound (B) having an ethylenically unsaturated bond may contain a compound having four or more ethylenically unsaturated bonds in the molecule.

[0017] In the removable pressure-sensitive adhesive composition of the present invention, the polymerization initiator (C) may be, for example, an organic peroxide.

[0018] In the present invention, "initial adhesive strength" refers to the adhesive strength after adhering the PSA sheet to an adherend and before subjecting it to heat treatment. In the present invention, the method for measuring the initial adhesive strength of the removable PSA composition or PSA sheet is not particularly limited, but can be measured, for example, by the measurement method described in the Examples below.

[0019] In the present invention, there is no particular distinction between "adhesion" and "adhesion," and they are synonymous. Furthermore, in the present invention, the term "removable pressure-sensitive adhesive composition" refers to a pressure-sensitive adhesive composition that is removable. That is, the removable pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition that can be removed.

[0020] Generally, a relatively thick material is called a "sheet" and a thin material is called a "film" to distinguish between the two, but in the present invention, there is no particular distinction between "sheet" and "film" and they are considered to be synonymous.

[0021] In the present invention, "(meth)acrylic" means "at least one of acrylic and methacrylic." For example, "(meth)acrylic acid" means at least one of acrylic acid and methacrylic acid. Furthermore, "(meth)acrylic acid alkyl ester" means at least one of acrylic acid alkyl ester and methacrylic acid alkyl ester. Furthermore, "(meth)acrylic resin" means a resin that is a polymer of a monomer containing at least one of an acrylic acid ester and a methacrylic acid ester.

[0022] In the present invention, "alkyl" includes, for example, straight-chain or branched alkyl. In the present invention, the alkyl group is not particularly limited, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an icosyl group.

[0023] In the present invention, "weight" may be read as "mass" unless otherwise specified. For example, "weight ratio" may be read as "mass ratio" unless otherwise specified, and "wt%" may be read as "mass%" unless otherwise specified.

[0024] The following describes the embodiments of the present invention in more detail, but the present invention is not limited to the following embodiments.

[0025] [1. Removable adhesive composition] As described above, the removable pressure-sensitive adhesive composition of the present invention is characterized by comprising the following components (A) to (C): (A) A (meth)acrylic resin that is a polymer of a monomer whose main component is a (meth)acrylic acid alkyl ester having an alkyl group having two or less carbon atoms. (B) Compounds having an ethylenically unsaturated bond (C) Polymerization initiator

[0026] As described above, the removable pressure-sensitive adhesive composition of the present invention has an initial adhesive strength that is not too low, an adhesive strength that is not too high after heating, and is less likely to contaminate the adherend after heating. For example, because the initial adhesive strength is not too low, adhesion defects can be suppressed or prevented. For example, because the adhesive strength after heating is not too high, the composition is easily removable from the adherend even after a heating step.

[0027] For example, in the manufacturing process of electronic devices such as semiconductors, electronic components, and display components, in recent years, due to the thinning of components, there is a need for removable pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets that can be peeled off with a light force even after heating so as not to damage the components.On the other hand, due to the miniaturization of components, a certain degree of adhesive strength is also required.In addition, due to the change of materials and the rationalization of production, heat resistance at higher temperatures is required.The removable pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet of the present invention can, for example, meet all of these requirements.

[0028] Generally, when an attempt is made to reduce the adhesive strength of a removable pressure-sensitive adhesive composition after heating, the initial adhesive strength tends to decrease. On the other hand, increasing the initial adhesive strength can result in excessively high adhesive strength after heating or in contamination of the adherend after heating. However, the removable pressure-sensitive adhesive composition of the present invention, which contains the components (A) to (C), exhibits the effects of not having too low an initial adhesive strength, not having too high an adhesive strength after heating, and not being prone to contaminating the adherend after heating, as described above. In particular, it is believed that component (B) (a compound having an ethylenically unsaturated bond) reacts, hardens, and shrinks at high temperatures, preventing excessively high adhesive strength even after heating, enabling the composition to be peeled off with light force.

[0029] [1-1. (Meth)acrylic resin (A)] In the removable pressure-sensitive adhesive composition of the present invention, the component (A) is a (meth)acrylic resin as described above, and the (meth)acrylic resin is a polymer of a monomer (hereinafter sometimes referred to as a "raw material monomer for component (A)" or simply as a "raw material monomer") whose main component is a (meth)acrylic acid alkyl ester having an alkyl group with two or less carbon atoms. In the present invention, the component (A) may be referred to as a (meth)acrylic resin (A).

[0030] In the present invention, the term "main component" refers to the component in the mixture that accounts for the largest amount by mass (weight) of the total mass (weight) of the mixture. The raw material monomer may consist solely of a (meth)acrylic acid alkyl ester having an alkyl group having 2 or less carbon atoms, or may be a monomer mixture containing other monomer components.

[0031] In the (meth)acrylic resin (A), the content of the (meth)acrylic acid alkyl ester having an alkyl group with two or less carbon atoms in the raw material monomer is not particularly limited, but is, for example, 50 to 98 wt %, or 60 to 90 wt %. When the (meth)acrylic acid alkyl ester having an alkyl group with two or less carbon atoms is 50 to 98 wt %, it is easy to obtain an appropriate initial adhesive strength and to easily suppress contamination after heating.

[0032] In the removable pressure-sensitive adhesive composition of the present invention, the method for producing the (meth)acrylic resin (A) is not particularly limited. That is, the (meth)acrylic resin (A) need only have a structure as a polymer of the raw material monomers, and does not necessarily have to be produced by polymerization of the raw material monomers.

[0033] In the raw material monomers, the (meth)acrylic acid alkyl ester having an alkyl group having 2 or less carbon atoms is specifically methyl (meth)acrylate and ethyl (meth)acrylate, and these may be used alone or in combination.

[0034] Furthermore, the (meth)acrylic resin (A) may be a copolymer of a monomer mixture containing at least one of a monomer having a hydroxyl group and a monomer having a carboxyl group, as described above. That is, the raw material monomer may be a monomer mixture containing, in addition to the (meth)acrylic acid alkyl ester having an alkyl group having 2 or less carbon atoms, at least one of a monomer having a hydroxyl group and a monomer having a carboxyl group.

[0035] In the (meth)acrylic resin (A), the monomer having a hydroxyl group and the monomer having a carboxyl group function as reaction sites with, for example, the crosslinking agent (D) described below. The total content of the monomer having a hydroxyl group and the monomer having a carboxyl group in the monomer mixture (raw material monomer) is not particularly limited, but for example, a content of 2.0 to 49.9 wt% facilitates the prevention of staining after heating. In particular, using 2.0 to 49.9 wt% of the monomer having a hydroxyl group facilitates the prevention of staining after heating and facilitates the attainment of an appropriate initial adhesive strength. Furthermore, for the reaction with the crosslinking agent (D) described below, the content of the monomer having a hydroxyl group is preferably 2.0 wt% or more.

[0036] The monomer having a hydroxyl group is not particularly limited, and examples thereof include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc. These may be used alone or in combination.

[0037] The monomer having a carboxy group is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, citraconic acid, itaconic anhydride, maleic anhydride, etc. These may be used alone or in combination.

[0038] Furthermore, the monomer components in the raw material monomers of the (meth)acrylic resin (A) may or may not contain other monomers as optional components. Examples of the other monomers include (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of more than 2, such as n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; Examples of suitable monomers include non-aromatic ring-containing (meth)acrylic acid esters such as cycloalkyl (meth)acrylates and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylic acid esters such as phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate and methylglycidyl (meth)acrylate; vinyl ester monomers such as vinyl acetate and vinyl propionate; styrene monomers such as styrene and α-methylstyrene; olefin monomers such as ethylene, propylene, isoprene, and butadiene; and vinyl ether monomers such as vinyl ether.

[0039] The weight average molecular weight of the (meth)acrylic resin (A) is not particularly limited, but is, for example, 100,000 to 1,000,000.

[0040] The glass transition temperature of the (meth)acrylic resin (A) is not particularly limited, but is, for example, -30°C to 30°C. When the glass transition temperature of the (meth)acrylic resin (A) is in this range, an appropriate initial adhesive strength is likely to be obtained. In the present invention, the method for measuring the glass transition temperature is not particularly limited, and it can be measured using, for example, a differential scanning calorimeter (DSC). However, if the glass transition temperature of a homopolymer of each monomer is known, it can be calculated using the following Fox equation. For the glass transition temperature of a homopolymer of a monomer, for example, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003) can be used.

[0041]

number

[0042] [1-2. Production method of (meth)acrylic resin (A)] As mentioned above, the method for producing the (meth)acrylic resin (A) is not particularly limited, but can be, for example, produced by polymerizing all of the copolymerization components of the (meth)acrylic resin (A). The polymerization method is also not particularly limited, and may be the same as or similar to a known polymerization method. Examples of the polymerization method include solution polymerization, bulk polymerization, and suspension polymerization. The polymerization initiator used in the polymerization is not particularly limited, and can be appropriately selected from known initiators. More specifically, examples of the polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), and dimethyl-2 Examples of suitable polymerization initiators include azo-based polymerization initiators such as 2'-azobis(2-methylpropionate); and peroxide-based polymerization initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane. In the case of solution polymerization, it is preferable to use an oil-soluble polymerization initiator. One type of polymerization initiator may be used alone, or two or more types may be used in combination. The amount of polymerization initiator used is not particularly limited, and may be, for example, a commonly used amount or a similar amount.

[0043] When the (meth)acrylic resin (A) is produced by solution polymerization, various common solvents can be used. Examples of such solvents include organic solvents such as esters (e.g., ethyl acetate, n-butyl acetate, etc.); aromatic hydrocarbons (e.g., toluene, benzene, etc.); aliphatic hydrocarbons (e.g., n-hexane, n-heptane, etc.); alicyclic hydrocarbons (e.g., cyclohexane, methylcyclohexane, etc.); and ketones (e.g., methyl ethyl ketone, methyl isobutyl ketone, etc.). These solvents may be used alone or in combination. The concentration, reaction time, reaction temperature, etc., of the copolymerization components in the solution polymerization process are not particularly limited and can be appropriately determined, for example, with reference to a general solution polymerization process. The weight-average molecular weight of component (A) can be adjusted by appropriately adjusting the concentration, reaction time, reaction temperature, etc., of the copolymerization components. For example, lowering the concentration of the copolymerization components, shortening the reaction time, or increasing the reaction temperature tends to decrease the weight-average molecular weight of the (meth)acrylic resin (A). Furthermore, for example, if the concentration of the copolymerization component is increased, or the reaction time is extended, or the reaction temperature is lowered, the weight average molecular weight of the (meth)acrylic resin (A) tends to increase.

[0044] The (meth)acrylic resin (A) can be obtained, for example, in the form of a solution of the (meth)acrylic resin (A). Specifically, for example, when the (meth)acrylic resin (A) is produced by the solution polymerization method or the like, the (meth)acrylic resin (A) can be obtained in the form of a solution in the solvent. In such a case, for example, the solution may be used in the production of the removable pressure-sensitive adhesive composition of the present invention without removing the solvent.

[0045] [1-3. Compound (B) having an ethylenically unsaturated bond] In the removable pressure-sensitive adhesive composition of the present invention, the component (B) is a compound having an ethylenically unsaturated bond, as described above. In the present invention, the component (B) may be referred to as the compound (B) having an ethylenically unsaturated bond.

[0046] In the removable pressure-sensitive adhesive composition of the present invention, the content of the compound (B) having an ethylenically unsaturated bond is not particularly limited, but is preferably 40 to 200 parts by weight, more preferably 40 to 150 parts by weight, per 100 parts by weight of the (meth)acrylic resin (A). When the content is within the above-mentioned range, it is easy to suppress an increase in adhesive strength after heating, and it is also easy to obtain an appropriate initial adhesive strength. In particular, to suppress an increase in adhesive strength after heating, it is preferable that the content of the compound (B) having an ethylenically unsaturated bond be 40 parts by weight or more per 100 parts by weight of the (meth)acrylic resin (A).

[0047] Furthermore, as described above, the compound (B) having an ethylenically unsaturated bond may contain a compound having four or more ethylenically unsaturated bonds in the molecule. The compound (B) having an ethylenically unsaturated bond more preferably contains a compound having four to eight ethylenically unsaturated bonds in the molecule. When the number of ethylenically unsaturated bonds in the molecule is within the above-described range, it is easy to suppress an increase in adhesive strength after heating.

[0048] Moreover, from the viewpoint of reactivity, the compound (B) having an ethylenically unsaturated bond is preferably a (meth)acrylate compound.

[0049] The compound (B) having an ethylenically unsaturated bond is not particularly limited, and examples thereof include the same types of monomers as those exemplified as the monomer components in the raw material monomer of the (meth)acrylic resin (A). In addition, examples of the compound (B) having an ethylenically unsaturated bond include compounds having two ethylenically unsaturated bonds in the molecule, such as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate. compounds having three ethylenically unsaturated bonds in the molecule, such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, and ethoxylated isocyanuric acid tri(meth)acrylate; compounds having four ethylenically unsaturated bonds in the molecule, such as ditrimethylolpropane tetra(meth)acrylate and pentaerythritol tetra(meth)acrylate; and compounds having five or more ethylenically unsaturated bonds in the molecule, such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate. The compound (B) having an ethylenically unsaturated bond may be used alone or in combination of two or more types.

[0050] [1-4. Polymerization initiator (C)] As described above, the component (C) in the removable pressure-sensitive adhesive composition of the present invention is a polymerization initiator. In the present invention, the component (C) may be referred to as a polymerization initiator (C).

[0051] In the removable pressure-sensitive adhesive composition of the present invention, the content of the polymerization initiator (C) is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 1 to 8 parts by weight, per 100 parts by weight of the (meth)acrylic resin (A).

[0052] Examples of the polymerization initiator (C) include polymerization initiators used when polymerizing the (meth)acrylic resin (A). The polymerization initiator (C) is not particularly limited, but since azo-based polymerization initiators generate nitrogen when heated, organic peroxides are preferred, as described above. From the viewpoint of storage stability, the polymerization initiator (C) preferably has a high half-life temperature, and more preferably has a 10-hour half-life temperature of 80°C or higher. Examples of organic peroxides having a 10-hour half-life temperature of 80°C or higher include 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-amylperoxy)cyclohexane, t-butylperoxylaurate, t-butylperoxy 2-ethylhexyl monocarbonate, t-amylperoxy 2-ethylhexyl monocarbonate, n-butyl 4,4-di-(t-butylperoxy)valerate, and dicumyl peroxide.

[0053] [1-5. Crosslinking Agent (D)] The removable pressure-sensitive adhesive composition of the present invention may or may not contain optional components other than the components (A) to (C). An example of the optional components is the component (D). As described above, the component (D) is a crosslinking agent. In the present invention, the component (D) may be referred to as the crosslinking agent (D).

[0054] For example, when the (meth)acrylic resin (A) has at least one of a hydroxyl group and a carboxyl group, the crosslinking agent (D) reacts with these groups. The crosslinking agent (D) is not particularly limited, but examples thereof include isocyanate crosslinking agents, epoxy crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, and metal crosslinking agents. Among these, isocyanate crosslinking agents are preferred from the viewpoint of adhesion to substrates.

[0055] When the removable pressure-sensitive adhesive composition of the present invention contains the isocyanate crosslinking agent as the crosslinking agent (D), its content is not particularly limited, but is preferably 1 to 50 parts by weight, more preferably 6 to 45 parts by weight, per 100 parts by weight of the (meth)acrylic resin (A). From the viewpoint of increasing the initial adhesive strength of the removable pressure-sensitive adhesive composition, it is preferable that the content of crosslinking agent (D) is not too high, and from the viewpoints of suppressing an increase in adhesive strength after heating and contamination of the adherend after heating, it is preferable that the content of crosslinking agent (D) is not too low.

[0056] In the crosslinking agent (D), the isocyanate crosslinking agent is not particularly limited, and examples thereof include known polyisocyanates such as aliphatic polyisocyanates such as 1,6-hexamethylene diisocyanate and 1,5-pentamethylene diisocyanate, aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and naphthalene diisocyanate, araliphatic polyisocyanates such as xylene diisocyanate and tetramethylxylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and norbornene diisocyanate. The polyisocyanates may be used alone or in combination.

[0057] In addition, some of the above polyisocyanates may be used in combination with isocyanurates, biurets, allophanates, or adducts obtained by reacting them with trimethylolpropane or the like through cyclotrimerization.

[0058] The polyisocyanate is preferably an aliphatic polyisocyanate, and particularly preferably hexamethylene diisocyanate.

[0059] As the polyisocyanate, an isocyanurate obtained by cyclotrimerizing an aliphatic polyisocyanate is preferred, and an isocyanurate of hexamethylene diisocyanate is particularly preferred.

[0060] In the removable pressure-sensitive adhesive composition of the present invention, the crosslinking agent (D) may be used alone or in combination of two or more types.

[0061] [1-6. Other optional ingredients] The removable pressure-sensitive adhesive composition of the present invention may or may not contain optional components other than the crosslinking agent (D). Examples of the optional components include solvents, antioxidants, plasticizers, crosslinking accelerators, crosslinking inhibitors, fillers, colorants, antifoaming agents, light stabilizers, leveling agents, and tackifying resins. These optional components may be used alone or in combination. In particular, the use of an antioxidant helps to suppress contamination.

[0062] The antioxidant is not particularly limited, and examples thereof include pentaerythritol tetrakis[3-(3,5-di-t-butyl-4 hydroxyphenyl)propionate], octadecyl 3-(3,5-di-t-butyl-4 hydroxyphenyl)propionate, tris(2,4-di-t-butylphenyl)phosphite, triisodecyl phosphite, di(tridecyl) 3,3′-thiodipropionate, etc. Only one type of antioxidant may be used, or multiple types may be used.

[0063] The amount of antioxidant used is not particularly limited, but may be 0.1 to 2.0 parts by weight per 100 parts by weight of the (meth)acrylic resin (A).

[0064] [2. Method for producing removable adhesive composition] The method for producing the removable pressure-sensitive adhesive composition of the present invention is not particularly limited, and may, for example, simply be to mix the components of the removable pressure-sensitive adhesive composition of the present invention. Furthermore, as described above, component (A) can be obtained in the form of a solution of component (A) by solution polymerization or the like. In such a case, for example, as described above, the solution may be used in the production of the removable pressure-sensitive adhesive composition of the present invention without removing the solvent. Furthermore, dilution by further adding a solvent may or may not be necessary.

[0065] [3. Adhesive sheets, their manufacturing methods, uses, etc.] Next, the pressure-sensitive adhesive sheet of the present invention, its manufacturing method, uses, etc. will be described with examples.

[0066] As described above, the pressure-sensitive adhesive sheet of the present invention is characterized by having an adhesive layer on at least one surface of a substrate, the adhesive layer containing the removable pressure-sensitive adhesive composition of the present invention. The manufacturing method is not particularly limited, and the sheet can be manufactured, for example, by the following first manufacturing method or second manufacturing method. In the first manufacturing method, the removable pressure-sensitive adhesive composition of the present invention is applied to a release film, heated to form an adhesive layer, and then laminated to the substrate. In the second manufacturing method, the removable pressure-sensitive adhesive composition of the present invention is applied directly to the substrate, and heated to form an adhesive layer. However, the manufacturing method of the pressure-sensitive adhesive sheet of the present invention is not limited to these two manufacturing methods and is arbitrary, and any method may be used.

[0067] The substrate is not particularly limited and may be, for example, plastic, paper, or metal foil, with plastic being preferred. Examples of the plastic include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyethylene (PE), polypropylene (PP), and polycarbonate (PC).

[0068] The shape of the substrate is not particularly limited, and examples thereof include a sheet, a film, a foam, etc. From the viewpoint of ease of handling and storage of the PSA sheet after production, the substrate is preferably in the form of, for example, a long tape that can be wound up.

[0069] Furthermore, the substrate may be, for example, a substrate in which an adhesion-facilitating treatment has been applied to the surface of the substrate on which the adhesive layer is to be formed, as necessary. The adhesion-facilitating treatment is not particularly limited, but specific examples thereof include a method of treating with corona discharge and a method of applying an anchor coating agent.

[0070] The release film is also not particularly limited, and may be, for example, the same as or similar to a commonly used release film.The release film may, for example, be immediately peeled off from the adhesive layer.The release film may, for example, remain attached to the adhesive layer until just before use of the adhesive sheet, or may be peeled off from the adhesive layer just before use.

[0071] When the removable pressure-sensitive adhesive composition of the present invention does not contain a crosslinking agent (D), it is preferable to mix the crosslinking agent (D) and then coat the composition on a substrate or a release film. When the crosslinking agent (D) contains a polyisocyanate, the polyisocyanate is not particularly limited, but is, for example, as described above, and may be used alone or in combination with multiple types. The amount of crosslinking agent (D) used is, for example, as described above. Furthermore, a solvent may be further mixed prior to coating, for the purpose of facilitating mixing of the removable pressure-sensitive adhesive composition of the present invention with the crosslinking agent (D) or facilitating coating on the substrate or the release film. The type of solvent is not particularly limited, but is, for example, the same as the solvents exemplified in "1-2. Production method of (meth)acrylic resin (A)" above, and may be used alone or in combination with multiple types.

[0072] The coating method is not particularly limited and may be any known method, such as a roll coater method, a comma coater method, a die coater method, a reverse coater method, a silk screen method, or a gravure coater method.

[0073] The amount of the removable adhesive composition to be applied to a substrate or a release film is not particularly limited, but is adjusted so that the thickness of the adhesive layer in the adhesive sheet to be produced is, for example, 1 to 50 μm, 2 to 30, or 5 to 20 μm.

[0074] Furthermore, after coating on a substrate or a release film, the coated removable pressure-sensitive adhesive composition is heated. This heating step, for example, dries the removable pressure-sensitive adhesive composition (volatilizes the solvent), forming an adhesive layer. Hereinafter, this heating step may be referred to as the "first heating step" to distinguish it from the second heating step described below. The heating temperature in the heating step (first heating step) is not particularly limited, but is, for example, 60°C or higher, a temperature exceeding 60°C, 90°C or higher, or a temperature exceeding 90°C. The upper limit of the heating temperature is not particularly limited, but is, for example, 120°C or lower.

[0075] The heating time in the heating step (first heating step) is not particularly limited, but is preferably a time that allows the applied removable pressure-sensitive adhesive composition to be sufficiently dried (solvent removed) and that does not damage the substrate due to heat. Specific heating times vary depending on the types of the solvent and substrate, but are, for example, 30 to 240 seconds or 60 to 180 seconds.

[0076] Furthermore, in the method for producing a pressure-sensitive adhesive sheet according to the present invention, it is preferable to include a second heating step after the heating step (first heating step), in which heating is performed at a temperature lower than that of the first heating step. The second heating step may or may not be performed, but performing it allows stable adhesive properties to be obtained. The phenomenon that occurs in the second heating step is unknown, but it is speculated that, for example, curing (crosslinking) of the adhesive layer progresses further. However, this speculation does not limit the present invention in any way. The heating temperature in the second heating step is not particularly limited, but is, for example, 30 to 50°C or 35 to 45°C. The heating time in the second heating step is also not particularly limited, but is, for example, 24 to 120 hours or 48 to 96 hours.

[0077] The use of the pressure-sensitive adhesive sheet of the present invention is not particularly limited, but, as described above, it is preferably a pressure-sensitive adhesive sheet that is attached to a product and used as a protective sheet for the product. More specifically, it can be used as a protective sheet for electronic devices such as electronic substrates, semiconductors, electronic components, and display components used in electronic calculators (computers), image display devices, etc., to prevent heat, impact, dirt, etc. in the manufacturing process of the electronic calculators, image display devices, etc. It can also be used as a protective sheet for heat, impact, dirt, etc. in the manufacturing process of electronic devices such as electronic substrates, semiconductors, electronic components, and display components.

[0078] When a protective sheet (surface-protecting pressure-sensitive adhesive sheet) is used in the manufacturing process of the aforementioned electronic computers, image display devices, electronic devices, etc., the adhesive strength of the removable pressure-sensitive adhesive composition increases due to heating (under high-temperature conditions), which can cause the removable pressure-sensitive adhesive composition to remain on the adhesive surface of the adherend, preventing it from being re-detached and potentially contaminating the adherend. Furthermore, for example, if the adherend has low strength, the increased adhesive strength of the removable pressure-sensitive adhesive composition may damage the adherend itself. Specifically, for example, if the adherend is a thin substrate, the increased adhesive strength of the removable pressure-sensitive adhesive composition may cause the substrate to bend when the protective sheet is removed. In such cases, for example, a method can be used in which the pressure-sensitive adhesive sheet is peeled off before heating and then re-applied after heating. However, this method requires complicated processes and reduces efficiency. In contrast, the pressure-sensitive adhesive sheet of the present invention, for example, can suppress or prevent an increase in adhesive strength at high temperatures, allowing it to be heat-treated with the pressure-sensitive adhesive sheet attached, and can be easily re-detached even after heating.

[0079] When the pressure-sensitive adhesive sheet of the present invention is used as a protective sheet, the method of use is not particularly limited. For example, as described above, it is possible to heat-treat the pressure-sensitive adhesive sheet while it is attached to the adherend. The heating conditions are not particularly limited. However, as described above, the pressure-sensitive adhesive sheet of the present invention undergoes a curing reaction upon heating, so it is preferable to use it under heating conditions appropriate for the polymerization initiator (C). For example, when using the aforementioned organic peroxide with a 10-hour half-life temperature of 80°C or higher, the heating temperature is preferably 130°C to 260°C, and the heating time is preferably 5 minutes to 6 hours. In other respects, the method of using the pressure-sensitive adhesive sheet of the present invention as a protective sheet is also not particularly limited. For example, it may be the same as or equivalent to the method of using a general pressure-sensitive adhesive sheet or protective sheet.

[0080] When a flexible printed circuit (FPC) is manufactured using the pressure-sensitive adhesive sheet of the present invention as a protective sheet, the following procedure may be used, for example. First, the pressure-sensitive adhesive sheet of the present invention is laminated as a reinforcing backing material to the polyimide surface of a copper-clad laminate (CCL), thereby reinforcing the CCL. At this time, for example, guide holes for automatic transport may be formed. Next, the copper foil surface to which the pressure-sensitive adhesive sheet is not attached is processed. That is, first, a photosensitive material (resist) is applied to the copper foil surface, and the resist is pattern-exposed and developed. After this, the soluble resist that was not exposed and not hardened is removed by development, and the copper foil on the exposed copper foil surface is etched. After etching is completed, the non-soluble resist that was exposed and hardened is removed. This leaves only the copper foil portion exposed to the desired pattern, and the remaining copper foil portions are removed, thereby forming a circuit. After the circuit is formed, a coverlay is laminated on the exposed copper foil surface to form an insulating layer, and a surface treatment such as plating is performed. After this series of manufacturing steps, the pressure-sensitive adhesive sheet of the present invention is peeled off, yielding a CCL with a circuit formed thereon. A flexible wiring board can be manufactured by laminating other auxiliary materials such as a reinforcing material, solder resist, and electromagnetic wave shielding on the CCL with the circuit formed thereon, and then performing a punching process. The pressure-sensitive adhesive sheet of the present invention can also be used as a reinforcing material during the punching process after circuit formation. These manufacturing processes may involve, for example, processing in a sheet form or processing in a roll form.

[0081] The pressure-sensitive adhesive sheet of the present invention can also be used as a protective sheet in, for example, a solder reflow process or an indium tin oxide (ITO) electrode formation process. For example, in the ITO electrode formation process, an ITO electrode layer is formed on a laminate, and then the pressure-sensitive adhesive sheet of the present invention is attached as a protective sheet and heated (annealed) while attached. The ITO electrode can be used as a transparent electrode, for example, as a component of a touch panel used in a mobile information terminal such as a touch panel smartphone.

[0082] Furthermore, the uses of the pressure-sensitive adhesive sheet of the present invention are not limited thereto, and it can be used in a wide range of applications, for example, similar to general pressure-sensitive adhesive sheets, pressure-sensitive adhesive films, pressure-sensitive adhesive tapes, etc. The pressure-sensitive adhesive sheet of the present invention does not contaminate the adherend after peeling, even when exposed to moist heat, and has excellent wettability and excellent adhesion between the removable pressure-sensitive adhesive composition and the substrate, and therefore can be used in a wide range of applications, as described above. Furthermore, the uses of the removable pressure-sensitive adhesive composition of the present invention are not particularly limited to the pressure-sensitive adhesive sheet of the present invention, and it can be used in a wide range of applications, for example, similar to general removable pressure-sensitive adhesive compositions. [Example]

[0083] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0084] First, acrylic resins A1, A2, and A3 were produced according to the following Production Examples A1, A2, and A3, respectively. Acrylic resins A1 and A2 are copolymers of raw material monomers (monomer mixtures) primarily composed of methyl acrylate or ethyl acrylate, respectively, and correspond to component (A) in the removable adhesive composition of the present invention, i.e., "a (meth)acrylic resin that is a polymer of a monomer primarily composed of a (meth)acrylic acid alkyl ester having an alkyl group having two or fewer carbon atoms." In contrast, acrylic resin A3 is a copolymer of raw material monomers (monomer mixtures) primarily composed of butyl acrylate, and does not correspond to component (A) in the removable adhesive composition of the present invention.

[0085] [Manufacturing Example A1] A reactor equipped with a stirrer, thermometer, dropping funnel, and reflux condenser was charged with 125 parts by weight of ethyl acetate as the polymerization solvent (solvent). The temperature was raised to 78°C under a nitrogen atmosphere while stirring, resulting in a reflux state. Next, a monomer mixture consisting of 79.8 parts by weight of methyl acrylate (a (meth)acrylic acid alkyl ester having an alkyl group containing 2 or less carbon atoms), 19.95 parts by weight of 4-hydroxybutyl acrylate (a monomer having a hydroxyl group), 0.25 parts by weight of acrylic acid (a monomer having a carboxyl group), and 0.32 parts by weight of 2,2'-azoisobutyronitrile as a polymerization initiator was prepared and added dropwise over 2 hours to the reactor in which the polymerization solvent was refluxing. After the addition was completed, the reaction was continued for 3 hours while maintaining the reflux state. After the reaction, the mixture was diluted with ethyl acetate to a solids concentration of 35% by weight, yielding a solution of acrylic resin A1 with a viscosity of 2600 mP·s. This solution was used directly in the production of the removable pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets of the examples, as described below.

[0086] [Manufacturing example A2] A polymerization reaction (solution polymerization) was carried out in the same manner as in Production Example A1, except that the monomer components were changed to 79.8 parts by weight of ethyl acrylate, 19.95 parts by weight of 4-hydroxybutyl acrylate, 0.25 parts by weight of acrylic acid, and 0.08 parts by weight of 2,2'-azoisobutyronitrile. After the reaction, the mixture was diluted with ethyl acetate to a solids concentration of 21% by weight, yielding a solution of acrylic resin A2 with a viscosity of 1200 mP·s. This solution was used directly in the production of removable pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets of the examples, as described below.

[0087] [Manufacturing example A3] A polymerization reaction (solution polymerization) was carried out in the same manner as in Production Example A1, except that the monomer components were changed to 79.8 parts by weight of butyl acrylate, 19.95 parts by weight of 4-hydroxybutyl acrylate, 0.25 parts by weight of acrylic acid, and 0.02 parts by weight of 2,2'-azoisobutyronitrile. After the reaction, the mixture was diluted with ethyl acetate to a solids concentration of 27% by weight, yielding a solution of acrylic resin A3 with a viscosity of 2200 mP·s. This solution was used directly in the production of the removable pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet of the comparative example, as described below.

[0088] The compositions of the raw material monomers for acrylic resins A1 to A3 produced in Production Examples A1 to A3, as well as the weight-average molecular weights and glass transition temperatures of the produced acrylic resins A1 to A3, are summarized in Table 1 below. In Table 1 below, the weight-average molecular weights of acrylic resins A1 to A3 were measured by gel permeation chromatography (GPC) under the following conditions. The glass transition temperatures of acrylic resins A1 to A3 were calculated using the Fox equation described above. (Method for measuring weight average molecular weight by GPC method) Equipment: Waters Alliance e2695 Column configuration: Waters HSPgel RT MB-H (applicable molecular weight 5,000-10,000,000) x 2, RT2.0 (applicable molecular weight 500-10,000) x 1 Column temperature: 40℃ Mobile phase: tetrahydrofuran Sample concentration: 0.3 wt% Standard material: Standard polystyrene

[0089] [Table 1]

[0090] Furthermore, removable pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets of Examples and Comparative Examples were produced using the acrylic resins A1 to A3 produced in Production Examples A1 to A3 as follows: As described above, the acrylic resins A1 to A3 were used as the solutions produced in Production Examples A1 to A3.

[0091] [Example 1] To 286 parts by weight of the acrylic resin A1 ((meth)acrylic resin (A)) solution (corresponding to 100 parts by weight of the acrylic resin A1), 100 parts by weight of dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester A-DPH") as the compound (B) having an ethylenically unsaturated bond, 3 parts by weight of t-butyl peroxylaurate (manufactured by NOF Corporation, product name "Perbutyl L") as the polymerization initiator (C), 11 parts by weight of an isocyanate-based crosslinking agent (manufactured by Asahi Kasei Chemicals Corporation, product name "Duranate TKA-100") as the crosslinking agent (D), and 0.6 parts by weight of an antioxidant (manufactured by ADEKA Corporation, product name "ADK STAB AO-60") were blended to prepare a removable adhesive composition. Next, a polyethylene terephthalate (PET) film (manufactured by PANAC Corporation, product name "NP-50B", thickness: 50 μm) with a release-treated surface was prepared as the substrate. The removable adhesive composition was applied to the release-treated surface to a dry thickness of approximately 10 μm and dried at 100°C for 1 minute (first heating step). Thereafter, a polyimide film (trade name "Kapton 100H" manufactured by DuPont-Toray Co., Ltd., thickness: 25 μm) was laminated onto the coated surface, and aging was carried out at 40°C for 2 days (second heating step) to obtain an adhesive tape (adhesive sheet).

[0092] [Examples 2 to 4, Comparative Examples 1 to 4] Removable pressure-sensitive adhesive compositions and pressure-sensitive adhesive tapes (pressure-sensitive adhesive sheets) were produced in the same manner as in Example 1, except that the composition of the removable pressure-sensitive adhesive composition (type and amount of each component) was changed as shown in Table 2 below. In Comparative Examples 1 to 3, the (meth)acrylic resin (A) in the removable pressure-sensitive adhesive composition of the present invention was not used, and instead a copolymer not primarily composed of a (meth)acrylic acid alkyl ester having an alkyl group containing two or fewer carbon atoms (acrylic resin A3 produced in Production Example A3) was used. In Comparative Example 3, the compound (B) having an ethylenically unsaturated bond and the polymerization initiator (C) were not used. In Comparative Example 4, the (meth)acrylic resin (A) in the removable pressure-sensitive adhesive composition of the present invention was used, but the compound (B) having an ethylenically unsaturated bond and the polymerization initiator (C) were not used.

[0093] Furthermore, the pressure-sensitive adhesive sheets (pressure-sensitive adhesive tapes) of each of the above-mentioned Examples and Comparative Examples were evaluated for initial adhesive strength, adhesive strength after heating (adhesive strength after heat resistance), and contamination of the adherend after heating (adherend contamination after heat resistance) using the following evaluation methods.

[0094] (Initial adhesive strength) Under an environment of 23°C and 50% RH humidity, the pressure-sensitive adhesive tapes of the above-mentioned Examples and Comparative Examples were cut into 25 mm widths to prepare test pieces. glass plate ) with a 2 kg roller rolling load three times. After curing for 1 hour, one end of the test piece was peeled off in a 180° direction at a rate of 300 mm / min using an autograph, and the peel force (N / 25 mm) was recorded as the initial adhesive strength. Note that the initial adhesive strength is preferably 0.1 N / 25 mm or more from the viewpoint of holding the member (adherend).

[0095] (Adhesion strength after heat resistance) The pressure-sensitive adhesive tapes of the Examples and Comparative Examples were cut to 25 mm widths in an environment of 23°C and 50% RH, and these were used as test pieces. The test pieces were then attached to an adherend (glass plate) with a 2 kg roller, rolling back and forth three times. After curing for 1 hour, the test pieces were left in a hot air dryer at 260°C for 5 minutes, and then left to stand for 1 hour in an environment of 23°C and 50% RH. The peel force (N / 25 mm) measured when one end of the test piece was peeled off in a 180° direction using an autograph at a rate of 300 mm / min was used as the post-heat-resistant adhesive strength. The post-heat-resistant adhesive strength value is preferably 0.5 N / 25 mm or less to prevent damage to the member (adherend).

[0096] (Contamination of adherend after heat resistance) After the above-mentioned post-heat resistance adhesive strength test was conducted, the test specimens were peeled off, and then the contamination of the adherend was visually confirmed and evaluated as follows: Test specimens rated as ◯ were judged to be good products that were unlikely to contaminate the adherend. No contamination or adhesive residue on the adherend: 〇 Contamination or adhesive residue on the adherend: ×

[0097] The compositions of the removable pressure-sensitive adhesive compositions of the respective Examples and Comparative Examples, and the evaluation results of the initial adhesive strength, adhesive strength after heating (adhesive strength after heat resistance), and contamination of the adherend after heating (adherend contamination after heat resistance), evaluated by the above-mentioned methods, are summarized in Table 2 below.

[0098] [Table 2]

[0099] As shown in Table 2 above, the removable adhesive compositions of the Examples and the adhesive tapes (adhesive sheets) of the Examples produced using the same were all good in initial adhesive strength, adhesive strength after heating (adhesive strength after heat resistance), and contamination of the adherend after heating (adherend contamination after heat resistance). In contrast, the initial adhesive strength of Comparative Example 1 was too low. Furthermore, the contamination of the adherend after heating (adherend contamination after heat resistance) of Comparative Example 2 was poor, resulting in contamination of the adherend. The adhesive strength of Comparative Examples 3 and 4 after heating (adherend contamination after heat resistance) was too high, making it difficult to re-release the compositions from the adherend after heating.

Claims

1. Contains the following components (A) to (C): (A) A (meth)acrylic resin that is a copolymer of a monomer mixture containing 60 to 90% by weight of a (meth)acrylic acid alkyl ester having an alkyl group having 2 or less carbon atoms (provided that the monomer mixture does not contain a halogen-containing monomer). (B) Compounds having 4 to 8 ethylenically unsaturated bonds in the molecule (C) Polymerization initiator a removable pressure-sensitive adhesive composition, wherein the (meth)acrylic resin (A) is a copolymer of a monomer mixture containing 2.0% by weight or more and less than 40% by weight of a monomer having a hydroxyl group, and the polymerization initiator (C) is an organic peroxide.

2. 2. The removable pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic resin (A) is a copolymer of a monomer mixture further containing a monomer having a carboxy group.

3. The removable pressure-sensitive adhesive composition according to claim 1 or 2, further comprising the following component (D): (D) Crosslinking agent

4. 4. The removable pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic resin (A) is a (meth)acrylic resin that is a copolymer of a monomer mixture containing 60 to 90% by weight of a (meth)acrylic acid alkyl ester having an alkyl group having 2 or less carbon atoms (provided that the monomer mixture does not contain a halogen-containing monomer or an ethylene oxide monomer).

5. 5. The removable pressure-sensitive adhesive composition according to claim 1, wherein the content of the compound (B) having an ethylenically unsaturated bond is 40 to 200 parts by weight per 100 parts by weight of the (meth)acrylic resin (A).

6. The removable pressure-sensitive adhesive composition according to claim 1 , wherein the compound (B) having an ethylenically unsaturated bond is a (meth)acrylate compound.

7. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer on at least one surface thereof, the pressure-sensitive adhesive layer comprising the removable pressure-sensitive adhesive composition according to claim 1 .

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