Adhesive and adhesive tape

Abstract

Provided are an adhesive and an adhesive tape that have high flame retardance even when there is little flame retardant in the adhesive layer.　Specifically provided is an adhesive containing a resin component and a flame retardant, wherein the flame retardant includes a pentaerythritol diphosphonate compound.

Description

Adhesives and adhesive tapes

[0001] The present invention relates to an adhesive and an adhesive tape, and more particularly to an adhesive and an adhesive tape having excellent flame retardancy.

[0002] Conventionally, pressure-sensitive adhesive tapes have come to be used for a variety of purposes, and in particular, pressure-sensitive adhesive tapes used for aircraft, automobiles, and construction are required to have improved flame retardancy due to the recent trend toward greater emphasis on safety. In particular, pressure-sensitive adhesive tapes used to fix aircraft components are required to have an excellent balance of hand tearability, flame retardancy, peelability, etc., and are particularly required to have high flame retardancy.

[0003] Methods for imparting flame retardancy to adhesive tapes include incorporating a flame retardant into the adhesive tape substrate or into the adhesive layer. However, to maintain the strength of the substrate, the flame retardant is added to the adhesive layer rather than the substrate. However, when incorporating a flame retardant into the adhesive layer, in order to ensure sufficient flame retardancy in the adhesive tape, the ratio of flame retardant to adhesive in the adhesive layer must be increased. Increasing the ratio of flame retardant tends to reduce the adhesive properties of the adhesive layer. Therefore, there has been a demand for flame-retardant tapes containing flame retardants that can impart high flame retardancy even with small amounts of flame retardant. Halogen-based flame retardants generally have high flame retardancy, but they suffer from the problem of generating halogen gas during combustion. Therefore, phosphorus-based flame retardants have been mainly used in recent years, but adhesive tapes containing phosphorus-based flame retardants have insufficient flame retardancy.

[0004] JP 2009-114374 A JP 2017-179329 A

[0005] The pressure-sensitive adhesive tape of Patent Document 1 discloses a pressure-sensitive adhesive tape in which the flame retardant is contained in a relatively small amount in the pressure-sensitive adhesive layer, with 10 to 20 parts by mass of the flame retardant per 100 parts by mass of the resin component of the pressure-sensitive adhesive layer, but the examples describe a pressure-sensitive adhesive tape in which the flame retardant is also contained in the substrate, and it is shown that flame retardancy is insufficient when the substrate does not contain a flame retardant.Patent Document 2 discloses a pressure-sensitive adhesive composition in which a small amount of a phosphate ester-based flame retardant is contained in the pressure-sensitive adhesive layer, but the flame retardancy is not sufficient, and even higher flame retardancy is required.

[0006] In view of this background, the present invention provides a pressure-sensitive adhesive and a pressure-sensitive adhesive tape that have high flame retardancy even when the pressure-sensitive adhesive layer contains a small amount of flame retardant.

[0007] However, in view of these circumstances, the present inventors have conducted extensive research and have found that an adhesive tape having a flame retardant in the adhesive layer, which is a pentaerythritol diphosphonate compound, can be an adhesive tape with high flame retardancy.

[0008] That is, the present invention has the following aspects: [1] A pressure-sensitive adhesive containing a resin component and a flame retardant, wherein the flame retardant comprises a pentaerythritol diphosphonate compound. [2] The pressure-sensitive adhesive according to [1], wherein the pentaerythritol diphosphonate compound is a compound of the following formula (1): In the above formula (1), R 1 ~R 6 each represent hydrogen, an alkyl group, or a phenyl group, and may be the same or different. [3] The pressure-sensitive adhesive according to [1] or [2], wherein the resin component contains an acrylic resin. [4] The pressure-sensitive adhesive according to any one of [1] to [3], wherein the resin component contains a crosslinking agent. [5] A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive according to any one of [1] to [4] on at least one surface of a substrate. [6] The pressure-sensitive adhesive tape according to [5], wherein the substrate is a substrate comprising flat yarn cloth.

[0009] The pressure-sensitive adhesive of the present invention is a pressure-sensitive adhesive containing a resin component and a flame retardant, and since the flame retardant is a pressure-sensitive adhesive containing a pentaerythritol diphosphonate compound, it has high flame retardancy, and the resulting pressure-sensitive adhesive tape also has high flame retardancy. Therefore, it can be suitably used as a pressure-sensitive adhesive for pressure-sensitive adhesive tapes for fixing aircraft components, which require particularly high flame retardancy.

[0010] In the present invention, when the pentaerythritol diphosphonate compound is a compound of the following formula (1), an adhesive that can be used for an adhesive tape having higher flame retardancy can be obtained. In the above formula (1), R 1 ~R6 and each represent a hydrogen atom, an alkyl group, or a phenyl group, and may be the same or different.

[0011] In the present invention, when the resin component contains an acrylic resin, the adhesive can be made into an adhesive tape having excellent adhesive properties.

[0012] Furthermore, in the present invention, when the adhesive further contains a crosslinking agent, the adhesive can be made into an adhesive tape having excellent adhesive properties.

[0013] The adhesive tape of the present invention, which has an adhesive layer containing the above-mentioned adhesive on at least one surface of a substrate, can be an adhesive tape having high flame retardancy and excellent adhesive properties.

[0014] In the present invention, the substrate is particularly excellent in hand tearability when it contains a flat yarn cloth.

[0015] The present invention will be described below based on examples of embodiments for carrying out the present invention. However, the present invention is not limited to the embodiments described below. In the present invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate, respectively. Furthermore, an acrylic resin is a resin obtained by polymerizing a copolymerization component containing at least one (meth)acrylate monomer. In the present invention, "tape" also includes "film" and "sheet." In the present invention, the "main component" refers to the component that is most abundant in the target object, and typically accounts for 50% by mass or more of the target object, preferably 60% by mass or more, more preferably 70% by mass or more, particularly preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass.

[0016] Furthermore, in the present invention, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it means "X or more and Y or less", as well as "preferably greater than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number) is expressed, it also means "preferably greater than X" or "preferably less than Y". Furthermore, "X and / or Y (X and Y are any configurations)" means at least one of X and Y, and can mean three possibilities: X only, Y only, or X and Y.

[0017] <<Adhesive>> A pressure-sensitive adhesive according to one embodiment of the present invention (hereinafter sometimes referred to as “the pressure-sensitive adhesive”) is a pressure-sensitive adhesive containing a resin component and a flame retardant, wherein the flame retardant includes a pentaerythritol diphosphonate compound. Each of the constituent components used in the pressure-sensitive adhesive is described in detail below.

[0018] <Resin Component> The resin component used in the present pressure-sensitive adhesive is used as the main component of the present pressure-sensitive adhesive. The resin component is not particularly limited as long as it is a known resin component used in pressure-sensitive adhesives, but examples include acrylic resins (A1), epoxy resins, phenolic resins, polyester resins (A2), etc., which can be used alone or in combination of two or more. Among these, acrylic resins (A1) are preferably used. Furthermore, when using acrylic resins (A1) as the resin component, it is preferable to use acrylic resins (A1) as the main component of the resin component.

[0019] The acrylic resin (A1) used in the present pressure-sensitive adhesive refers to a resin obtained by polymerizing a copolymerization component containing at least one (meth)acrylate monomer, and examples thereof include a homopolymer of alkyl (meth)acrylate and a copolymer obtained by polymerizing a copolymerizable monomer therewith. Each monomer unit that can constitute the acrylic resin (A1) will be described below.

[0020] [Hydroxyl Group-Containing Monomer (a1) Unit] The acrylic resin (A1) preferably has a hydroxyl group-containing monomer (a1) unit. Examples of copolymerizable monomers for forming the hydroxyl group-containing monomer (a1) unit include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; N-methylol (meth)acrylate; Examples of suitable monomers include primary hydroxyl group-containing monomers such as hydroxyl group-containing (meth)acrylamides, such as acrylamide, N-hydroxyethyl(meth)acrylamide, and N-methylolpropane(meth)acrylamide, and 2-acryloyloxyethyl-2-hydroxyethylphthalic acid; secondary hydroxyl group-containing monomers, such as 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, 3-chloro-2-hydroxypropyl(meth)acrylate, and 2-hydroxy-3-phenoxypropyl(meth)acrylate; and tertiary hydroxyl group-containing monomers, such as 2,2-dimethyl-2-hydroxyethyl(meth)acrylate. These monomers can also be referred to as "hydroxyl group-containing (meth)acrylic acid ester monomers."

[0021] Among these, primary hydroxyl group-containing monomers are preferred because of their excellent reactivity with crosslinking agents, and (meth)acrylic acid hydroxyalkyl esters are more preferred, with 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate being particularly preferred.

[0022] The hydroxyl group-containing monomer (a1) units are useful because they form crosslinking points with the crosslinking agent (C) described below, particularly the isocyanate-based crosslinking agent (c1). The content of such hydroxyl group-containing monomer (a1) units is typically 0.01 to 5 mass%, preferably 0.05 to 3 mass%, and more preferably 0.05 to 2 mass%, based on the total acrylic resin (A1). If the content of such monomer (a1) units is too low, flame retardancy tends to decrease, while if it is too high, adhesive strength tends to decrease. The content of the hydroxyl group-containing monomer (a1) units can be adjusted by the blending ratio of the monomers used in producing the acrylic resin (A1), and can be analyzed by NMR or the like.

[0023] [Carboxy Group-Containing Monomer (a2) Unit] The acrylic resin (A1) preferably also contains a carboxy group-containing monomer (a2) unit. Examples of the carboxy group-containing monomer (a2) unit include a (meth)acrylic acid monomer unit, a crotonic acid monomer unit, a maleic acid monomer unit, a maleic anhydride monomer unit, a fumaric acid monomer unit, a citraconic acid monomer unit, a glutaconic acid monomer unit, an itaconic acid monomer unit, an acrylamide N-glycolic acid monomer unit, and a cinnamic acid monomer unit. Among these, a (meth)acrylic acid monomer unit is preferred. It is also preferable that the carboxy group-containing monomer (a2) unit contains a terminal carboxy group-containing monomer unit represented by the following formula:

[0024] Here, R 1 is hydrogen or a methyl group, R 2 represents a divalent saturated aliphatic group, an unsaturated aliphatic group, an aromatic group, a saturated alicyclic group, or an unsaturated alicyclic hydrocarbon group, and n represents a positive number of 1 or more.

[0025] The above R 1 is preferably hydrogen, and R 2The hydrocarbon is usually an alkylene having 1 to 10 carbon atoms, such as a methylene group, more preferably 1 to 5, and particularly preferably 1 or 2 carbon atoms, such as phenyl, phenylene, and especially preferably ethylene, and the above n is preferably 1 to 10, more preferably 1 to 5, particularly preferably 1 to 3, and particularly preferably 1 or 2, and may have a combination thereof.

[0026] The content of the carboxyl group-containing monomer (a2) units is usually 0.1 to 5 mass%, preferably 0.5 to 4.5 mass%, and more preferably 1 to 4 mass%, based on the total mass of the acrylic resin (A1). If the content of the carboxyl group-containing monomer (a2) units is too small, the adhesive strength tends to decrease, whereas if it is too large, the viscosity of the coating liquid tends to increase, resulting in decreased coatability.

[0027] [Alkyl (meth)acrylate ester monomer (a3) ​​units] The acrylic resin (A1) preferably also contains alkyl (meth)acrylate ester monomer (a3) ​​units having an alkyl group containing 4 to 24 carbon atoms. The copolymerizable monomer for forming such alkyl (meth)acrylate ester monomer (a3) ​​units may be any alkyl (meth)acrylate monomer having an alkyl group containing 4 to 24 carbon atoms, and it is particularly preferred to contain both an alkyl (meth)acrylate monomer (a3-1) having an alkyl group containing 4 to 7 carbon atoms and an alkyl (meth)acrylate monomer (a3-2) having an alkyl group containing 8 to 24 carbon atoms. Note that alkyl (meth)acrylate monomers having an alkyl group containing 4 to 24 carbon atoms and also having a hydroxyl group are classified as hydroxyl group-containing monomers (a1).

[0028] Examples of the alkyl(meth)acrylate monomer (a3-1) having an alkyl group having 4 to 7 carbon atoms include n-butyl(meth)acrylate, t-butyl(meth)acrylate, isobutyl(meth)acrylate, n-hexyl(meth)acrylate, etc. Among these, n-butyl(meth)acrylate is preferred because of its easy availability and economical efficiency.

[0029] Examples of the alkyl(meth)acrylate monomer (a3-2) having an alkyl group having 8 to 24 carbon atoms include 2-ethylhexyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, isononyl(meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate, tridecyl(meth)acrylate, isotridecyl(meth)acrylate, myristyl(meth)acrylate, isomyristyl(meth)acrylate, cetyl(meth)acrylate, stearyl(meth)acrylate, isostearyl(meth)acrylate, behenyl(meth)acrylate, etc. Among these, alkyl(meth)acrylates having an alkyl group having 8 to 12 carbon atoms are preferred, and 2-ethylhexyl(meth)acrylate is particularly preferred, due to their low polarity and low glass transition temperature.

[0030] The content of the monomer (a3) ​​units is usually 55 to 97% by mass, preferably 70 to 98% by mass, and more preferably 80 to 95% by mass, based on the total mass of the acrylic resin (A1). If the content of the monomer (a3) ​​units is too small, the adhesive strength tends to decrease, whereas if the content of the monomer (a3) ​​units is too large, the adhesive strength and the holding power tend to decrease.

[0031] Furthermore, when the monomer (a3-1) and the monomer (a3-2) are used in combination, the ratio of the monomer (a3-1) units to the monomer (a3-2) units is preferably (a3-1) / (a3-2)=15 / 85 to 85 / 15 by mass, more preferably 25 / 75 to 75 / 25, even more preferably 30 / 70 to 70 / 30, particularly preferably 40 / 60 to 60 / 40, and especially preferably 45 / 55 to 55 / 45. If the ratio of the monomer (a3-1) units is too small, the holding power tends to decrease, and if it is too large, the flame retardancy tends to decrease.

[0032] [Monomer (a4) Unit] The acrylic resin (A1) may further contain an alkyl (meth)acrylate monomer (a4-1) unit having an alkyl group having 1 to 3 carbon atoms, a cyclic structure-containing monomer (a4-2) unit, and a vinyl ester monomer (a4-3) unit having 3 to 10 carbon atoms. The monomers (a4-1) to (a4-3) are collectively referred to as monomer (a4). Furthermore, monomers that fall under the category of monomer (a4) but also contain a hydroxyl group are classified as hydroxyl group-containing monomers (a1).

[0033] Examples of copolymerizable monomers for forming the alkyl(meth)acrylate monomer (a4-1) units having an alkyl group having 1 to 3 carbon atoms include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, etc. Of these, methyl(meth)acrylate and ethyl(meth)acrylate are preferred.

[0034] The copolymerizable monomer for forming the cyclic structure-containing monomer (a4-2) unit is usually a (meth)acrylic monomer having a substituent containing a cyclic structure, and examples thereof include heterocycle-containing (meth)acrylates having a heterocycle such as a morpholine ring, a piperidine ring, a pyrrolidine ring, or a piperazine ring, such as N-(meth)acryloylmorpholine, N-vinylpyrrolidone, N-vinylcaprolactam, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and further, phenyl(meth)acrylate, phenoxyethyl(meth)acrylate, and the like. Examples of the (meth)acrylate include phenyl diethylene glycol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, nonylphenol polyethylene glycol (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate, isobornyl (meth)acrylate, and biphenyloxyethyl (meth)acrylate. Other examples of the (meth)acrylic monomer that are not (meth)acrylic monomers include styrene and α-methylstyrene. Among these, heterocycle-containing (meth)acrylates having a morpholine ring are preferred because of their good balance of various physical properties, and N-(meth)acryloylmorpholine is particularly preferred from the standpoints of availability and safety.

[0035] Examples of copolymerizable monomers for forming the vinyl ester monomer (a4-3) units having 3 to 10 carbon atoms include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, etc. Among these, vinyl acetate is preferred because of its easy availability.

[0036] The content of the monomer (a4) unit is usually 11% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less, based on the total acrylic resin (A1). If the content of the monomer (a4) unit is too high, the adhesive strength to the adherend tends to decrease. The lower limit of the content of the monomer (a4) unit is usually 0% by mass, but preferably 1% by mass or more.

[0037] [Other Monomer (a5) Unit] The acrylic resin (A1) may contain other monomer (a5) units as needed. Examples of copolymerizable monomers for forming the other monomer (a5) units include functional group-containing monomers such as acetoacetyl group-containing monomers, isocyanate group-containing monomers, glycidyl group-containing monomers, amino group-containing monomers, and amide group-containing monomers, as well as other copolymerizable monomers.

[0038] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0039] Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

[0040] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0041] Examples of the amino group-containing monomer include a monomer having an ethylenically unsaturated double bond and an amino group (unsubstituted or substituted amino group). For example, mono-substituted amino group-containing (meth)acrylic acid esters such as aminoalkyl (meth)acrylates such as aminomethyl (meth)acrylate, aminoethyl (meth)acrylate, aminopropyl (meth)acrylate, and aminoisopropyl (meth)acrylate, and (meth)acrylic acid esters of N-alkylaminoalkyl such as N-(t-butyl)aminoethyl (meth)acrylate; di-substituted amino group-containing (meth)acrylic acid esters such as N,N-dialkylaminoalkyl (meth)acrylic acid esters such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylate. dialkylaminoalkyl(meth)acrylamides such as N,N-dimethylaminopropyl(meth)acrylamide, and quaternized salts of these amino group-containing monomers; amino group-containing styrenes such as p-aminostyrene; styrenes having a dialkylamino group such as 3-(dimethylamino)styrene and dimethylaminomethylstyrene; dialkylaminoalkyl vinyl ethers such as N,N-dimethylaminoethyl vinyl ether and N,N-diethylaminoethyl vinyl ether; allylamine, 4-diisopropylamino-1-butene, trans-2-butene-1,4-diamine, and 2-vinyl-4,6-diamino-1,3,5-triazine.

[0042] The amide group-containing monomer includes a monomer having an ethylenically unsaturated double bond and an amide group (a group having an amide bond). For example, (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide, N-isobutyl(meth)acrylamide, N-s-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, diacetone(meth)acrylamide, N,N'-methylenebis(meth)acrylamide, and N-(1,1-dimethyl-3-oxobutyl)(meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-diisobutyl(meth)acrylamide, and N,N-di(s N,N-dialkyl(meth)acrylamides such as N,N-di(t-butyl)(meth)acrylamide, N,N-dipentyl(meth)acrylamide, N,N-dihexyl(meth)acrylamide, N,N-diheptyl(meth)acrylamide, N,N-dioctyl(meth)acrylamide, N,N-diallyl(meth)acrylamide, and N,N-ethylmethylacrylamide; dialkylaminoalkyl(meth)acrylamides such as N,N-dimethylaminopropyl(meth)acrylamide; substituted amide group-containing monomers such as N-vinylacetamide, N-vinylformamide, (meth)acrylamidoethylethyleneurea, and (meth)acrylamido-t-butylsulfonic acid; alkoxy group-containing (meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide; and quaternized salts of these amide group-containing monomers.

[0043] Examples of the other copolymerizable monomers include monomers containing an alkoxy group or an oxyalkylene group, such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and polypropylene glycol mono(meth)acrylate; acrylonitrile, methacrylonitrile, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, allyl trimethylammonium chloride, and dimethyl allyl vinyl ketone.

[0044] The other monomer (a5) can be used to adjust the physical properties depending on the application, as long as the effects of the present invention are not impaired. For example, the content of the other monomer (a5) units is usually 10% by mass or less, with the lower limit usually being 0% by mass, based on the total mass of the acrylic resin (A1).

[0045] The acrylic resin (A1) can be obtained by appropriately polymerizing one or more monomers selected from the above monomers (a1) to (a5). That is, the acrylic resin (A1) can be obtained having the above monomer units (a1) to (a5) appropriately. For example, the acrylic resin (A1) can be obtained having preferably the above monomer unit (a1), more preferably the monomer unit (a2), even more preferably the monomer unit (a3), particularly preferably the monomer unit (a4), and optionally further the monomer unit (a5). The monomer units (a1) to (a5) can be used alone or in combination of two or more types.

[0046] As the polymerization, it is preferable to employ solution polymerization, since it is possible to safely and stably produce the acrylic resin (A1) with any monomer composition.

[0047] Such solution polymerization can be carried out according to a conventional method. For example, the monomers (a1) to (a5) and a polymerization initiator are mixed or added dropwise to an organic solvent, and polymerization can be carried out under reflux or at 50 to 98°C for 0.1 to 20 hours. The acrylic resin (A1) polymerized in an organic solvent is an organic solvent-based acrylic resin.

[0048] As the polymerization initiator, a conventional radical polymerization initiator can be used. Specific examples include azo-based polymerization initiators such as azobisisobutyronitrile and azobisdimethylvaleronitrile; and peroxide-based polymerization initiators such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide and cumene hydroperoxide. These polymerization initiators may be used alone or in combination of two or more. The amount of polymerization initiator used is usually 0.001 to 5 parts by mass per 100 parts by mass of the copolymerization components.

[0049] [Solubility parameter (SP value)] The resin component used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), usually has a solubility parameter (SP value) of 10 (cal / cm 3 ) 1 / 2 Preferably, 9.9 (cal / cm 3 ) 1 / 2 or less, more preferably 9.8 (cal / cm 3 ) 1 / 2 If the SP value is too large, the flame retardancy and adhesive properties tend to decrease. The lower limit of the SP value is usually 7 (cal / cm 3 ) 1 / 2 It is preferably 8 (cal / cm 3 ) 1 / 2 More preferably, 8.5 (cal / cm 3 ) 1 / 2 More preferably, 9.0 (cal / cm 3 ) 1 / 2 More preferably, 9.5 (cal / cm 3 ) 1 / 2 That's all.

[0050] The SP value can be determined from the evaporation energy (ΔE), molar volume (ΔV) and molar ratio of the resin components used in the present pressure-sensitive adhesive, particularly the (meth)acrylic acid alkyl ester monomer and copolymerizable monomer that constitute the acrylic resin (A1), and specifically, can be determined by the following formula (1).

[0051] [Formula] SP value (cal / cm 3 ) 1 / 2 = (ΔE / ΔV) 1 / 2 (1)

[0052] ΔE=(x×ΔEx / Mx)+(y×ΔEy / My)+...(n×ΔEn / Mn)×(1 / C) ΔV=(x×ΔVx / Mx)+(y×ΔVy / My)+...(n×ΔVn / Mn)×(1 / C) C=(x / Mx)+(y / My)+...(n / Mn) x: content of monomer X relative to the copolymerization component (mass%) ΔEx: evaporation energy of monomer X ΔVx: molar volume of monomer X Mx: molecular weight of monomer X y: content of monomer Y relative to the copolymerization component (mass%) ΔEy: evaporation energy of monomer Y ΔVy: molar volume of monomer Y My: molecular weight of monomer Y n: content of monomer N relative to the copolymerization component (mass%) ΔEn: evaporation energy of monomer N ΔVn: molar volume of monomer N Mn: molecular weight of monomer N C: molar ratio of resin component

[0053] The resin components used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), have an SP value of 10 (cal / cm 3 ) 1 / 2 The following method may be exemplified by a method of adjusting the type and content of the monomers (a1) to (a5), particularly the type and content of the functional group-containing monomer.

[0054] [Average Molecular Weight] The weight average molecular weight of the resin component used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), is usually 100,000 to 5,000,000, preferably 300,000 to 1,500,000, and more preferably 400,000 to 900,000. If the weight average molecular weight is too small, durability tends to decrease, while if it is too large, adhesive strength tends to decrease.

[0055] The resin components used in the pressure-sensitive adhesive, particularly the acrylic resin (A1), preferably have a polydispersity (weight average molecular weight / number average molecular weight) of 20 or less, more preferably 15 or less, even more preferably 10 or less, and particularly preferably 7 or less. If the polydispersity is too high, the durability of the pressure-sensitive adhesive layer tends to decrease and foaming and the like tends to occur easily. From the viewpoint of production limitations, the polydispersity is preferably 1.1 or more, more preferably 3 or more, and even more preferably 4 or more.

[0056] The weight-average molecular weight of the resin components used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), is a weight-average molecular weight calculated in terms of standard polystyrene molecular weight. The weight-average molecular weight was measured using a high-performance liquid chromatograph (manufactured by Waters Japan, "Waters 2695 (main body)" and "Waters 2414 (detector)") equipped with a column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 7 Separation range: 100 to 2 x 10 7 The number average molecular weight can be measured by using three columns in series (each column having a theoretical plate number of 10,000, a filler material of styrene-divinylbenzene copolymer, and a filler particle size of 10 μm). The number average molecular weight can also be measured by the same method.

[0057] [Glass Transition Temperature] The glass transition temperature (Tg) of the resin component used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), is usually −80 to 10° C., preferably −70 to −10° C., and more preferably −65 to −20° C. If the glass transition temperature is too high, tackiness tends to be insufficient, and if it is too low, heat resistance tends to decrease.

[0058] The glass transition temperature (Tg) is a value calculated by applying the glass transition temperature and mass fraction of each of the monomers constituting the acrylic resin (A1) to the following Fox's formula when the monomers are converted into homopolymers.

[0059]

[0060] Tg: glass transition temperature (K) of the resin component (particularly the acrylic resin (A1)); Tga: glass transition temperature (K) of the homopolymer of monomer A; Wa: mass fraction of monomer A; Tgb: glass transition temperature (K) of the homopolymer of monomer B; Wb: mass fraction of monomer B; Tgn: glass transition temperature (K) of the homopolymer of monomer N; Wn: mass fraction of monomer N (Wa + Wb + ... + Wn = 1)

[0061] Here, the glass transition temperature when the monomer constituting the resin component used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), is made into a homopolymer is usually a value measured by a differential scanning calorimeter (DSC) according to a method in accordance with JIS K7121-1987 or JIS K6240, or a value listed in a catalog.

[0062] The resin components used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), are typically adjusted in viscosity with a solvent or the like and applied as a resin solution. From the standpoint of ease of handling, the viscosity of the resin solution is preferably 500 to 20,000 mPa·s / 25°C, more preferably 1,000 to 18,000 mPa·s / 25°C, and even more preferably 2,000 to 15,000 mPa·s / 25°C. If the viscosity is too high, the fluidity tends to decrease, making handling difficult, while if the viscosity is too low, coating of the pressure-sensitive adhesive solution tends to be difficult. The solution concentration in this case is typically 10 to 70% by mass.

[0063] The solvent that can be used to adjust the viscosity is not particularly limited as long as it dissolves the resin components used in the pressure-sensitive adhesive, particularly the acrylic resin (A1), and examples thereof include ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol solvents such as methanol, ethanol, and propyl alcohol. Among these, ethyl acetate and methyl ethyl ketone are preferred, and ethyl acetate is more preferred, in terms of solubility, drying property, cost, etc. Among these solvents, any one of them may be used alone, or two or more may be used in combination.

[0064] The viscosity of the resin components used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1) solution, is measured by a rotational viscometer method using a Brookfield viscometer for a resin solution adjusted to 25°C.

[0065] The resin component used in the present pressure-sensitive adhesive is preferably a polyester resin (A2). The polyester resin (A2) is preferably obtained by copolymerizing (condensation polymerizing) a copolymerization component containing a polycarboxylic acid component (I) and a polyol component (II) as constituent raw materials.

[0066] (Polycarboxylic Acid Component (I)) Examples of the polycarboxylic acid component (I) include dicarboxylic acids such as aromatic dicarboxylic acids (a1), aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids, and trivalent or higher polycarboxylic acids.

[0067] Examples of the aromatic dicarboxylic acid (Ia) include isophthalic acid, terephthalic acid, benzylmalonic acid, diphenic acid, 4,4'-oxydibenzoic acid, and naphthalenedicarboxylic acid.

[0068] Examples of aliphatic dicarboxylic acids include malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, thiodipropionic acid, and diglycolic acid.

[0069] Examples of the alicyclic dicarboxylic acid include 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, and adamantanedicarboxylic acid.

[0070] Examples of trivalent or higher polyvalent carboxylic acids include trimellitic acid, pyromellitic acid, adamantanetricarboxylic acid, trimesic acid, etc. These may be used alone or in combination of two or more.

[0071] In the present pressure-sensitive adhesive, the polycarboxylic acid component (I) preferably contains 50 mol% or more of the aromatic dicarboxylic acid (Ia), more preferably 55 to 100 mol%, even more preferably 55 to 90 mol%, particularly preferably 60 to 85 mol%, and especially preferably 60 to 80 mol%.

[0072] If the content is too low, the cohesive strength of the PSA will decrease, and lifting or peeling will tend to occur easily, whereas if the content is too high, the flexibility of the polyester resin (A2) will be lost, and the initial tackiness of the PSA will tend to decrease.

[0073] Furthermore, the aromatic dicarboxylic acid (Ia) contains isophthalic acid, and the content of isophthalic acid relative to the total aromatic dicarboxylic acid (Ia) is preferably 60 mol % or more, more preferably 62 mol % or more, even more preferably 65 mol % or more, particularly preferably 70 mol %, and most preferably 80 mol % or more.

[0074] If the content is too low, the polyester resin (A2) tends to have high crystallinity and low solvent solubility.

[0075] In the present pressure-sensitive adhesive, the polyvalent carboxylic acid component (I) other than the aromatic dicarboxylic acid (Ia) is preferably an aliphatic dicarboxylic acid having 4 or more carbon atoms (including the carbon atoms in the carboxy group), from the viewpoint of improving the initial adhesiveness of the pressure-sensitive adhesive, and more preferably an aliphatic dicarboxylic acid having 9 to 12 carbon atoms (including the carbon atoms in the carboxy group), such as azelaic acid or sebacic acid.

[0076] In order to impart a tacky feel, it is preferable to contain an aliphatic dicarboxylic acid, particularly preferably an aliphatic dicarboxylic acid having 4 to 12 carbon atoms (including the carbon atoms in the carboxy group), and even more preferably sebacic acid.

[0077] The content of such aliphatic dicarboxylic acid is preferably less than 50 mol %, more preferably 10 to 45 mol %, and even more preferably 20 to 45 mol %, based on the entire polycarboxylic acid component (I).

[0078] If the content ratio is too low, the glass transition temperature of the polyester resin (A2) tends to be high, making it difficult to obtain sufficient adhesive strength. If the content ratio is too high, the adhesive component tends to be reduced, resulting in a decrease in adhesive strength to polar adherends.

[0079] In the present pressure-sensitive adhesive, a trivalent or higher polycarboxylic acid may be used for the purpose of increasing the branching points in the polyester resin (A2). Among these, trimellitic acid is preferably used because it is relatively less likely to cause gelation during production.

[0080] The content of the trivalent or higher polycarboxylic acid is preferably 10 mol % or less, more preferably 0.1 to 5 mol %, based on the total polycarboxylic acid component (I) in terms of the cohesive strength of the adhesive. If the content is too high, the polyester resin (A2) tends to gel easily during production.

[0081] (Polyol Component (II)) In the present pressure-sensitive adhesive, the polyol component (II) preferably contains a diol compound (IIb) having a hydrocarbon group on the side chain.

[0082] Examples of the diol compound (IIb) having a hydrocarbon group in the side chain include dipropylene glycol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-methyl-2-ethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3- Examples of the diol include aliphatic diols having a branched structure such as butanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol, and alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol. These may be used alone or in combination of two or more.

[0083] Among these, from the viewpoint of making crystallization less likely to occur while maintaining mechanical strength and heat resistance, diol compounds having a hydrocarbon group having 1 to 6 carbon atoms, particularly 1 to 4 carbon atoms, are preferred, and neopentyl glycol and 2-methyl-2-ethyl-1,3-propanediol are more preferred.

[0084] The content of the diol compound (IIb) having a hydrocarbon group in a side chain is preferably 5 mol % or more, more preferably 15 to 90 mol %, and even more preferably 30 to 80 mol %, based on the entire polyol component (II).

[0085] If the content is too low, the polyester resin (A2) tends to crystallize, resulting in a decrease in the initial adhesive strength of the adhesive. If the content is too high, the reactivity of the polyester resin (A2) during production tends to decrease.

[0086] In addition to the above, examples of the polyol component (II) other than the diol compound (IIb) having a hydrocarbon group in a side chain used in the present pressure-sensitive adhesive include, for example, a linear aliphatic diol, a dihydric alcohol such as an aromatic diol, and a trihydric or higher polyhydric alcohol.

[0087] Examples of the linear aliphatic diol include linear aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polytetramethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol, as well as ethylene oxide and propylene oxide adducts thereof.

[0088] Examples of aromatic diols include 4,4'-thiodiphenol, 4,4'-methylenediphenol, bisphenol S, bisphenol A, bisphenolfluorene, 4,4'-dihydroxybiphenyl, o-, m- and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and the like, as well as ethylene oxide and propylene oxide adducts thereof.

[0089] Examples of trihydric or higher polyhydric alcohols include pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,3,6-hexanetriol, adamantanetriol, etc. These may be used alone or in combination of two or more.

[0090] Among these, it is preferable to use a linear aliphatic diol because it has excellent adhesive strength, and it is particularly preferable to use diethylene glycol, 1,4-butanediol, 1,5-pentanediol, or 1,6-hexanediol, and it is further preferable to use 1,4-butanediol or 1,6-hexanediol because it reduces the crystallinity of the polyester resin (A2) and provides even more excellent adhesive strength.

[0091] The content of such a linear aliphatic diol is preferably 5 to 95 mol %, more preferably 10 to 85 mol %, and even more preferably 20 to 70 mol %, based on the entire polyol component (II).

[0092] If the content is too high, the polyester resin (A2) tends to crystallize, resulting in a decrease in the initial adhesive strength of the adhesive. If the content is too low, the reactivity of the polyester resin (A2) during production tends to decrease.

[0093] In addition, in this pressure-sensitive adhesive, it is preferable to use a trihydric or higher polyhydric alcohol in order to form reaction sites in the polyester resin (A2) with the crosslinking agent (C) described below and increase the cohesive strength, and among these, it is preferable to use trimethylolpropane in order to prevent gel formation.

[0094] The content of such trihydric or higher polyhydric alcohol is preferably 10 mol % or less, more preferably 0.1 to 5 mol %, based on the total amount of the polyol component (II).

[0095] If the content is too high, the polyester resin (A2) tends to gel during production, making production difficult.

[0096] The polyester resin (A2) used in the present pressure-sensitive adhesive can be produced, for example, by subjecting a polycarboxylic acid component (I) and a polyol component (II) to a polycondensation reaction in the presence of a catalyst by a known method.

[0097] In this case, the blending ratio of the polycarboxylic acid component (I) to the polyol component (II) is preferably 1 to 2 equivalents, particularly preferably 1.1 to 1.7 equivalents, of the polyol component (II) per equivalent of the polycarboxylic acid component (I). If the content ratio of the polyol component (II) is too low, the acid value tends to be high, making it difficult to achieve a high molecular weight, while if the content ratio of the polyol component (II) is too high, the yield tends to be low.

[0098] In the polycondensation reaction, an esterification reaction is first carried out, followed by the polycondensation reaction. Examples of catalysts used in the esterification reaction include titanium-based catalysts such as tetraisopropyl titanate and tetrabutyl titanate, antimony-based catalysts such as antimony trioxide, and germanium-based catalysts such as germanium dioxide, as well as zinc acetate, manganese acetate, and dibutyltin oxide. These catalysts may be used alone or in combination of two or more.

[0099] Among these, it is preferable to use, for example, antimony trioxide, tetrabutyl titanate, germanium dioxide, and zinc acetate in view of the balance between high catalytic activity and color.

[0100] The amount of the catalyst to be added is preferably 1 to 10,000 ppm, more preferably 10 to 5,000 ppm, and even more preferably 10 to 3,000 ppm, relative to the polycarboxylic acid component (I). If the amount is too small, the polymerization reaction tends to proceed insufficiently, whereas if the amount is too large, there is no advantage such as shortening the reaction time, and side reactions tend to occur easily.

[0101] The reaction temperature during the esterification reaction is preferably 160 to 280°C, more preferably 180 to 270°C, and even more preferably 200 to 260°C. If the reaction temperature is too low, the reaction tends not to proceed sufficiently, while if it is too high, side reactions such as decomposition tend to occur easily. In addition, the pressure during the reaction may usually be normal pressure.

[0102] The reaction time for the esterification reaction is preferably 1 to 48 hours, more preferably 1.5 to 24 hours, and even more preferably 2 to 12 hours.

[0103] After the esterification reaction, a polycondensation reaction is carried out. As reaction conditions for the polycondensation reaction, the same catalyst as that used in the esterification reaction is further compounded in the same amount, the reaction temperature is preferably 220 to 280 ° C (more preferably 230 to 270 ° C), and the reaction system is gradually reduced in pressure until the reaction is finally carried out at 5 hPa or less. If the reaction temperature is too low, the reaction tends to proceed poorly, and if it is too high, side reactions such as decomposition tend to occur easily.

[0104] The reaction time for the polycondensation reaction is preferably 1 to 48 hours, more preferably 1.5 to 24 hours, and even more preferably 2 to 12 hours.

[0105] The number average molecular weight of the polyester resin (A2) used in the present pressure-sensitive adhesive is preferably 5,000 or more, more preferably 10,000 to 150,000, and even more preferably 15,000 to 80,000.

[0106] If the number average molecular weight is too low, the adhesive will not have sufficient cohesive strength, and the heat resistance and mechanical strength will tend to decrease, whereas if the number average molecular weight is too high, the adhesive will lose flexibility and the initial adhesive strength will tend to decrease.

[0107] The number average molecular weight in this specification is the number average molecular weight converted into the molecular weight of standard polystyrene, and was measured using a high performance liquid chromatography (manufactured by Tosoh Corporation, "HLC-8320GPC") with a column: TSKgel SuperMultipore HZ-M (exclusion limit molecular weight: 2 × 10 6 The measurement is carried out by using two columns in series (theoretical plate number: 16,000 columns / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 4 μm).

[0108] The polyester resin (A2) used in the present pressure-sensitive adhesive preferably has a glass transition temperature of -80 to +30°C, more preferably -60 to +25°C, and even more preferably -50 to +10°C.

[0109] If the glass transition temperature exceeds the upper limit, the flexibility of the polyester resin (A2) is lost, the initial adhesion of the pressure-sensitive adhesive (adhesion when attached to an adherend) is reduced, and sufficient adhesive strength tends to be difficult to exhibit. On the other hand, if the glass transition temperature is lower than the lower limit, the cohesive strength of the pressure-sensitive adhesive tends to be reduced, and sufficient adhesive strength tends to be difficult to exhibit.

[0110] The glass transition temperature (Tg) of the polyester resin (A2) is a value measured using a differential scanning calorimeter DSC Q20 manufactured by TA Instruments, Inc. The measurement temperature range is from −90° C. to +100° C., and the temperature rise rate is 10° C. / min.

[0111] The acid value of the polyester resin (A2) used in the present pressure-sensitive adhesive is preferably 10 mgKOH / g or less, more preferably 5 mgKOH / g or less, even more preferably 1 mgKOH / g or less, and particularly preferably 0.5 mgKOH / g or less. The lower limit is 0 mgKOH / g.

[0112] If the acid value is too high, the pressure-sensitive adhesive layer made of the polyester-based pressure-sensitive adhesive composition tends to be hydrolyzed, resulting in a decrease in durability.

[0113] The acid value of the polyester resin (A2) is determined by dissolving 10 g of the polyester resin (A2) in a mixed solvent of toluene and methanol at a volume ratio of 7 / 3 (toluene / methanol), and then subjecting the solution to neutralization titration in accordance with JIS K 0070. In this pressure-sensitive adhesive, the acid value of the polyester resin (A2) refers to the content of carboxy groups in the resin.

[0114] <Flame Retardant (B)> The flame retardant (B) used in the present pressure-sensitive adhesive contains a pentaerythritol diphosphonate compound among the phosphate ester flame retardants (b1).

[0115] The pentaerythritol diphosphonate compound is not particularly limited as long as it is a pentaerythritol diphosphonate compound, but among them, a pentaerythritol diphosphonate compound represented by the following formula (1) is preferred.

[0116] In the above formula (1), R 1 ~R 6 and each represent a hydrogen atom, an alkyl group, or a phenyl group, and may be the same or different.

[0117] Among them, R 1 ~R 6 At least one of R is preferably an alkyl group or a phenyl group, and particularly preferably a phenyl group. 1 ~R 3 One of them, R 4 ~R 6 More preferably, one of the groups is a phenyl group and the other is hydrogen. Specifically, it is a compound represented by the following formula (2).

[0118]

[0119] From the viewpoint of flame retardancy, it is preferable that the pentaerythritol diphosphonate compound is the main component of the flame retardant (B), and the content of the pentaerythritol diphosphonate compound is preferably 50% by mass or more of the flame retardant (B), more preferably 70% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass.

[0120] The reason why a flame retardant (B) containing a pentaerythritol diphosphonate compound results in a highly flame-retardant adhesive is unclear. However, the phosphate ester flame retardant (b1) generally used as the flame retardant (B) is prone to volatilization and decomposition at low temperatures, and therefore fails to exhibit sufficient flame retardancy near the high decomposition temperature of the resin in the adhesive during combustion. Methods for increasing the decomposition temperature of the phosphate ester flame retardant (b1) include introducing an aromatic ring into the alkyl group or polymerizing it to increase crystallinity. However, these methods result in a lower phosphorus concentration in the flame retardant, necessitating the addition of a larger amount to achieve sufficient flame retardancy. Because pentaerythritol diphosphonate flame retardants have a high phosphorus concentration and a high decomposition temperature, their addition to an adhesive can impart high flame retardancy. On the other hand, if the decomposition temperature of the flame retardant (B) is higher than the decomposition temperature of the resin component (A), the flame retardant (B) does not decompose during combustion while the resin component (A) is thermally decomposing, and therefore fails to exhibit sufficient flame retardancy. Therefore, it is preferable that the decomposition temperature of the flame retardant (B) is high and lower than the decomposition temperature of the resin component (A).

[0121] The decomposition temperature of the flame retardant (B) is expressed as the 5% mass loss temperature Td5, which is the temperature at which the mass of a sample decreases by 5% due to thermal decomposition caused by heating using a thermogravimetric and differential thermal analyzer (TG-DTA). The 5% mass loss temperature Td5 can be measured using a thermogravimetric and differential thermal analyzer (TG-DTA) at a heating rate of 10°C / min.

[0122] The decomposition temperature of resin component (A) is expressed as the decomposition peak top temperature Tdmax, which refers to the temperature at which the thermal decomposition of a sample peaks due to heating, as measured using a thermogravimetric and differential thermal analyzer (TG-DTA). The decomposition peak top temperature Tdmax can be measured using a thermogravimetric and differential thermal analyzer (TG-DTA) at a heating rate of 10°C / min. In other words, the 5% mass loss temperature Td5 of flame retardant (B) is preferably lower than the decomposition peak temperature Tdmax of resin component (A).

[0123] The phosphorus concentration of the phosphate ester-based flame retardant (b1) is preferably 9% by mass or more, more preferably 11% by mass or more, and even more preferably 13% by mass or more. The upper limit of the phosphorus concentration is usually 30% by mass. The phosphorus concentration can be measured by thermal decomposition with nitric acid / sulfuric acid followed by inductively coupled plasma (ICP) emission spectroscopy or energy dispersive X-ray analysis (EDX), for example.

[0124] The phosphate ester-based flame retardant (b1) other than the pentaerythritol diphosphonate-based compound is preferably a non-halogen-based flame retardant, and examples thereof include aliphatic phosphate esters such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, tris(i-butyl phosphate), trioctyl phosphate, and tris(butoxyethyl) phosphate; triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, trixylenyl phosphate, 2-naphthyl diphenyl phosphate, and cresyl phosphate; aromatic phosphate esters such as triaryl di-2,6-xylenyl phosphate, tris(t-butylated phenyl)phosphate, tris(isopropylated phenyl)phosphate, and triaryl isopropyl phosphate; aromatic condensed phosphate esters such as (1,3-phenylenedioxy)bis(diphenyl phosphonate), bisphenol A bis(diphenyl phosphate), and 1,3-phenylene bis(di-2,6-xylenyl phosphate); and phosphonate esters such as dimethyl methyl phosphonate and diethyl methyl phosphonate. Among these, condensed phosphate ester-based flame retardants and / or phosphonate ester-based flame retardants are preferred, and aromatic condensed phosphate esters are more preferred, in terms of providing good dispersibility in resin components, particularly the acrylic resin (A1).

[0125] Specific examples of aromatic condensed phosphate ester products include "CR-733S," "CR-741," and "PX-200" (all manufactured by Daihachi Chemical Industry Co., Ltd.), with "PX-200" being particularly preferred due to its excellent dispersibility in the resin components used in the PSA, particularly the acrylic resin (A1). Note that "CR-733S" contains (1,3-phenylenedioxy)bis(diphenyl phosphonate), "CR-741" contains bisphenol A bis(diphenyl phosphate), and "PX-200" contains 1,3-phenylenebis(di-2,6-xylenyl phosphate).

[0126] Flame retardants other than the phosphate ester-based flame retardant (b1) are not soluble or compatible with the resin components, particularly the acrylic resin (A1), used in this adhesive, making it difficult to uniformly disperse them in the resin components, particularly the acrylic resin (A1). Therefore, the amount of flame retardant must be increased to achieve sufficient flame retardancy, resulting in a decrease in the adhesive strength of the resin components, particularly the acrylic resin (A1). In contrast, in adhesives containing the phosphate ester-based flame retardant (b1) and a resin component, particularly the acrylic resin (A1), the phosphate ester-based flame retardant (b1) is thought to soften the resin components, particularly the acrylic resin (A1), thereby improving the adhesive strength. However, the adhesive may contain a flame retardant other than the phosphate ester-based flame retardant (b1) as the flame retardant (B) within a range that does not interfere with the achievement of the object of the present invention.

[0127] The content of the flame retardant (B) is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the resin component, particularly the acrylic resin (A1), used in the present pressure-sensitive adhesive, and is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less. If the content of the flame retardant (B) is too high, it is thought that some of the flame retardant (B) will remain undissolved in the resin component, particularly the acrylic resin (A1), and the adhesive properties of the pressure-sensitive adhesive tape will tend to deteriorate, whereas if the content is too low, the flame retardancy will tend to be insufficient.

[0128] The content of the phosphate ester flame retardant (b1), particularly the content of the pentaerythritol diphosphonate compound, is also preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the resin component used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1), and is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less.

[0129] <Crosslinking Agent (C)> In addition to the above components, the present pressure-sensitive adhesive contains a crosslinking agent (C). Examples of the crosslinking agent (C) include an isocyanate-based crosslinking agent (c1), an epoxy-based crosslinking agent (c2), an aziridine-based crosslinking agent, a melamine-based crosslinking agent, an aldehyde-based crosslinking agent, an amine-based crosslinking agent, and a metal chelate-based crosslinking agent. These may be used alone or in combination of two or more.

[0130] The isocyanate-based crosslinking agent (c1) contains at least two isocyanate groups, and examples thereof include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. Examples of such crosslinking agents include biurets and isocyanurates of these crosslinking agents, as well as adducts formed by reaction with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Particularly preferred is an adduct of tolylene diisocyanate and trimethylolpropane. These crosslinking agents can be used alone or in combination of two or more.

[0131] Examples of the epoxy crosslinking agent (c2) include aliphatic epoxy crosslinking agents such as ethylene glycol diglycidyl ether, trimethylolpropane diglycidyl ether, and diglycidylamine; alicyclic epoxy crosslinking agents such as 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, and N,N,N',N'-tetraglycidyl-m-xylylenediamine; aromatic epoxy crosslinking agents such as diglycidylaniline; and heterocyclic epoxy crosslinking agents such as 1,3,5-tris-(2,3-epoxybutyl)isocyanurate, 1,3,5-tris-(3,4-epoxybutyl)isocyanurate, and 1,3,5-tris-(4,5-epoxypentyl)isocyanurate, with alicyclic epoxy crosslinking agents being preferred. These may be used alone or in combination of two or more.

[0132] Examples of the aziridine crosslinking agent include diphenylmethane-4,4'-bis(1-aziridinecarboxamide), trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethane tri-β-aziridinylpropionate, toluene-2,4-bis(1-aziridinecarboxamide), triethylenemelamine, bisisophthaloyl-1-(2-methylaziridine), tris-1-(2-methylaziridine)phosphine, and trimethylolpropane tri-β-(2-methylaziridine)propionate.

[0133] Examples of the melamine-based crosslinking agent include melamine; methylolmelamine derivatives such as amino group-containing methylolmelamine obtained by condensing melamine with formaldehyde, imino group-containing methylolmelamine, and hexamethylolmelamine; and alkylated methylolmelamines such as partially or completely alkylated methylolmelamine and imino group-containing partially or completely alkylated methylolmelamine obtained by reacting a methylolmelamine derivative with a lower alcohol such as methyl alcohol or butyl alcohol to partially or completely etherify it.

[0134] Examples of the aldehyde crosslinking agent include aldehyde compounds that liberate aldehyde in an aqueous solution, such as formaldehyde, acetaldehyde, propionaldehyde, butylaldehyde, glyoxal, glutaraldehyde, dialdehyde starch, hexamethylenetetramine, 1,4-dioxane-2,3-diol, 1,3-bis(hydroxymethyl)-2-imidazolidine, dimethylol urea, N-methylol acrylamide, urea formalin resin, and melamine formalin resin; and aromatic aldehyde compounds, such as benzaldehyde, 2-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, and m-hydroxybenzaldehyde.

[0135] Examples of the amine-based crosslinking agent include 4,4'-methylene-bis(2-chloroaniline) (hereinafter abbreviated as "MOCA"), modified MOCA, and diethyltoluenediamine.

[0136] Examples of the metal chelate crosslinking agent include chelate compounds whose metal atom is aluminum, zirconium, titanium, zinc, iron, tin, etc., and aluminum chelate compounds are preferred from the viewpoint of performance. Examples of the aluminum chelate compounds include diisopropoxyaluminum monooleyl acetoacetate, monoisopropoxyaluminum bisoleyl acetoacetate, monoisopropoxyaluminum monooleate monoethyl acetoacetate, diisopropoxyaluminum monolauryl acetoacetate, diisopropoxyaluminum monostearyl acetoacetate, diisopropoxyaluminum monoisostearyl acetoacetate, etc.

[0137] The crosslinking agent (C) may be one or more selected from the above crosslinking agents, but preferably contains at least an isocyanate-based crosslinking agent (c1). A crosslinking agent (C) containing only the isocyanate-based crosslinking agent (c1) or a crosslinking agent (C) containing the isocyanate-based crosslinking agent (c1) and one or more other crosslinking agents may be used. The content of the isocyanate-based crosslinking agent (c1) in the crosslinking agent (C) is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95 to 100% by mass, based on 100% by mass of the crosslinking agent (C).

[0138] The crosslinking agent (C) reacts with functional groups in the resin components used in this adhesive, particularly the acrylic resin (A1), to form a crosslinked structure, and the use of an isocyanate-based crosslinking agent (c1) as the crosslinking agent (C) further enhances the flame retardancy improvement effect when the flame retardant (B) is contained. The reason for this further enhancement in flame retardancy is not clear, but it is thought that the reaction of the isocyanate-based crosslinking agent (c1) with the functional groups, particularly the hydroxyl groups, in the resin components, particularly the acrylic resin (A1), allows the formation of an adhesive layer with a high crosslink density, and therefore the addition of a small amount of flame retardant (B) can improve flame retardancy.

[0139] The content of the crosslinking agent (C) is preferably 0.01 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, even more preferably 0.3 to 3 parts by mass, and particularly preferably 0.4 to 1 part by mass, relative to 100 parts by mass of the resin component, particularly the acrylic resin (A1). If the content is too low, the holding power tends to decrease, whereas if the content is too high, the adhesive power tends to decrease.

[0140] The crosslinking agent (C) is usually used after being diluted with a solvent or the like, and the above content indicates the substantial (solid content) content of the crosslinking agent excluding the solvent or the like.

[0141] Furthermore, the crosslinking agent (C) contained in the present adhesive may have the same structure as the unreacted crosslinking agent when mixed with the resin component, particularly the acrylic resin (A1), or may have a structure that has reacted with a functional group in the resin component, particularly the acrylic resin (A1). Therefore, the content of the crosslinking agent (C) contained in the present adhesive refers to the content of both the unreacted and reacted crosslinking agent structures, and is equivalent to the content of the crosslinking agent (C) when mixed with the resin component, particularly the acrylic resin (A1), during the preparation of the present adhesive.

[0142] <Tackifier (D)> The present PSA may further contain a tackifier (D), although it is not an essential component, to further enhance the favorable physical properties of the resin components used in the PSA, particularly the acrylic resin (A1). As the tackifier (D), a resin compatible with the resin components used in the PSA, particularly the acrylic resin (A1), is used, such as rosin-based resins, terpene-based resins, xylene-based resins, phenol-based resins, coumarone-based resins, and petroleum-based resins. These tackifiers (D) may be used alone or in combination of two or more. Among these, rosin-based resins, terpene-based resins, and petroleum-based resins are preferred, as described in detail below.

[0143] Examples of the rosin-based resin include rosin ester resins obtained by hydrogenating, disproportionating, dimerizing, or adding an acid to raw rosin, followed by esterification with glycerin or pentaerythritol, and rosin phenol resins obtained by adding phenol to raw rosin. The use of any of these rosin-based resins allows the resin components used in the present PSA, particularly the acrylic resin (A1), to exhibit their excellent physical properties. Among these, preferred are disproportionated rosin esters obtained by disproportionating raw rosin and esterifying it with glycerin or pentaerythritol to adjust the softening point to a range of 70 to 130°C, polymerized rosin esters obtained by dimerizing raw rosin and esterifying it with pentaerythritol to adjust the softening point to a range of 110 to 170°C, and rosin phenols obtained by adding phenol to raw rosin to adjust the softening point to a range of 120 to 160°C.

[0144] The terpene resin is a general term for compounds based on the isoprene principle and represented by the molecular formula (CH). Examples of the tackifier (D) used in this embodiment include resins obtained by homopolymerizing or copolymerizing monoterpenes (e.g., α-pinene, β-pinene, limonene, etc.) using a Friedel-Crafts catalyst. Specific examples of resins obtained by homopolymerizing or copolymerizing monoterpenes include α-pinene resins, β-pinene resins, dipentene resins, terpene phenol resins, aromatic-modified terpene resins, and hydrogenated terpene resins obtained by hydrogenating these resins. Among these, terpene phenol resins are preferred because of their good compatibility with the resin components used in the present PSA, particularly the acrylic resin (A1). Any of the terpene phenol resins can further exhibit the good physical properties of the resin component, particularly the acrylic resin (A1). In particular, those having a softening point of 90 to 170°C and a hydroxyl value of 20 to 250 (mgKOH / g) are preferred, and those having a softening point of 100 to 150°C and a hydroxyl value of 50 to 150 (mgKOH / g) are more preferred.

[0145] The petroleum-based resins are obtained, for example, by polymerization and further hydrogenation of C4-C5 and C9-C11 fraction monomers produced by thermal decomposition of naphtha or the like. Depending on the type of raw material fraction, examples include pure monomer-based resins, aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, and hydrogenated petroleum-based resins. The use of any of these petroleum-based resins allows the resin components, particularly the acrylic resin (A1), to exhibit their excellent physical properties. Among these, those with a softening point in the range of 90 to 130°C are preferred, and copolymers of styrene-based monomers and aliphatic monomers are also preferred.

[0146] The softening point of the tackifier (D) can be measured by the ring and ball method of JIS K 2531, and the hydroxyl value can be measured by potentiometric titration in accordance with JIS K 0070.

[0147] When the present PSA contains a tackifier (D), the content of the tackifier (D) is usually 50 parts by mass or less, preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, per 100 parts by mass of the resin components used in the PSA, particularly the acrylic resin (A1). The lower limit is 0 parts by mass, but is preferably 1 part by mass or more, more preferably 5 parts by mass or more. However, the tackifier (D) may be blended in an appropriate amount depending on the physical properties required of the PSA, and the content of the tackifier (D) is not limited to the above range.

[0148] <Other Components> The present adhesive may contain other components, such as acrylic monomers, polymerization inhibitors, antioxidants, corrosion inhibitors, crosslinking accelerators, radical generators, peroxides, UV absorbers, plasticizers, pigments, stabilizers, fillers, radical scavengers, and other additives, as well as metal and resin particles, within the scope of not impairing the effects of the present invention. These may be used alone or in combination of two or more. In addition to the above, the adhesive may contain small amounts of impurities contained in the manufacturing raw materials of the adhesive's constituent components.

[0149] When the present pressure-sensitive adhesive contains other components, the content of the other components is preferably 5 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less, relative to 100 parts by mass of the resin components used in the present pressure-sensitive adhesive, particularly the acrylic resin (A1). The lower limit is usually 0 parts by mass. If the content is too high, the compatibility with the acrylic resin (A1) tends to decrease, and durability tends to decrease. However, for additives (pigments, fillers, metals, resin particles, etc.) that do not exhibit their effects at the above-mentioned contents, an appropriate amount may be added within a range that does not inhibit the effects of the present invention while exhibiting the effects of the additive.

[0150] The present pressure-sensitive adhesive is a pressure-sensitive adhesive composition containing the above-mentioned resin components, particularly the acrylic resin (A1) and the flame retardant (B), as well as optionally a crosslinking agent (C), a tackifier (D), and other components, in which at least a portion of the composition is crosslinked. That is, the present pressure-sensitive adhesive composition includes not only cases in which almost the entire pressure-sensitive adhesive composition is crosslinked, but also cases in which a portion of the pressure-sensitive adhesive composition contains an uncrosslinked pressure-sensitive adhesive composition, and cases in which a portion of the pressure-sensitive adhesive composition is crosslinked. The pressure-sensitive adhesive or pressure-sensitive adhesive composition in which the acrylic resin (A1) is an organic solvent-based acrylic resin is an organic solvent-based pressure-sensitive adhesive or organic solvent-based pressure-sensitive adhesive composition. The method for preparing the pressure-sensitive adhesive composition is not particularly limited, and in addition to the commonly known mechanical kneading dispersion method, known methods such as solvent dispersion and ultrasonic dispersion can be used as necessary.

[0151] In order to increase the holding power, the present pressure-sensitive adhesive preferably has a gel fraction of 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. The gel fraction can be adjusted by adjusting the type and content of the crosslinking agent (C). The upper limit of the gel fraction is preferably 70% by mass, more preferably 60% by mass, and even more preferably 50% by mass. If the gel fraction is too low, the holding power tends to decrease, and if the gel fraction is too high, the peel strength tends to decrease. In addition, if the gel fraction is too low, the flame retardancy tends to decrease, and conversely, if the gel fraction is too high, the pressure-sensitive adhesive layer becomes too hard, and therefore the substrate does not shrink, and the flame retardancy tends to decrease.

[0152] The gel fraction is a measure of the degree of crosslinking (degree of hardening) and can be determined by the method described below.

[0153] <<Adhesive Tape>> An adhesive tape according to one embodiment of the present invention (hereinafter may be referred to as "the present adhesive tape") has a substrate and an adhesive layer on at least one surface (one side) of the substrate, and this adhesive layer contains an adhesive obtained by crosslinking the above-mentioned adhesive composition. For example, the above-mentioned adhesive composition is dissolved in a solvent such as ethyl acetate to prepare an adhesive composition solution for coating so that the solids concentration is 10 to 70 mass %, and this solution is applied to a substrate and dried, whereby the adhesive composition crosslinks to form an adhesive layer containing the adhesive, thereby producing an adhesive tape.

[0154] The method for producing the present pressure-sensitive adhesive tape is not particularly limited, and known production methods can be used. For example, the present pressure-sensitive adhesive tape can be produced by a method in which a pressure-sensitive adhesive composition solution is applied to one side of a substrate and dried to form a pressure-sensitive adhesive layer, and then a release liner is superimposed on the surface of the pressure-sensitive adhesive layer, or a method in which a pressure-sensitive adhesive composition solution is applied to one side of a release liner and then dried to form a pressure-sensitive adhesive layer, and then a substrate is superimposed on the surface of the pressure-sensitive adhesive layer. Among these, the method in which a pressure-sensitive adhesive composition solution is applied to one side of a release liner and then dried to form a pressure-sensitive adhesive layer is preferred from the standpoint of handling, etc.

[0155] The substrate is preferably hand-tearable. The surface of the substrate may be appropriately subjected to a known or conventional surface treatment, for example, a physical treatment such as corona discharge treatment or plasma treatment, or a chemical treatment such as a primer treatment.

[0156] The substrate is not particularly limited and may be any known substrate, such as rayon cloth, cotton cloth, polyester cloth, a cloth made of a blend of rayon and polyester, a woven fabric such as flat yarn cloth, a nonwoven fabric, or a laminated film in which a plastic film or the like is laminated on a woven fabric such as flat yarn cloth. Among these, substrates containing woven fabrics are preferred because of their high tensile strength in the longitudinal direction, and substrates having flat yarn cloth are more preferred. The pressure-sensitive adhesive tape using a substrate having flat yarn cloth can further have excellent flame retardancy and ease of hand tearing.

[0157] The term "substrate having flat yarn cloth" conceptually includes not only the flat yarn cloth itself but also a laminated film in which a plastic film or the like is laminated to the flat yarn cloth.

[0158] Flat yarn cloth is a woven fabric made by cutting a film called flat yarn into strips and stretching it to give it strength, and the flat yarns are woven together. Usually, the crossings of the flat yarns that cross the fabric vertically and horizontally are fixed by heat fusion to prevent misalignment. As the material for the flat yarn, an olefin resin such as polyethylene or polypropylene is preferred, polyethylene is more preferred, and high-density polyethylene is even more preferred.

[0159] The use of a base material containing flat yarn cloth as the base material of this adhesive tape makes it possible to produce an adhesive tape with even better flame retardancy. The reason for this is not clear, but it is thought that flat yarn cloth is made by weaving yarns stretched in one direction, and when an ignition source approaches and the temperature rises, it shrinks, making it more difficult for the ignition source to catch fire as it moves away.

[0160] Using a substrate in which a plastic film is laminated to a flat yarn cloth is preferred because it provides stable adhesive properties and releasability. This is thought to be because, in the case of double-sided adhesive tapes, the plastic film prevents the adhesive on one side from penetrating the substrate and mixing with the adhesive on the other side, and inhibits additives contained in the adhesive on one side, such as crosslinking agents, flame retardants, and plasticizers, from migrating to the adhesive on the other side. Furthermore, laminating a plastic film to a flat yarn cloth improves hand-tearability and the linearity of the fracture surface, possibly due to smooth propagation of the fracture point. A polyethylene film is preferred as the plastic film to be laminated to the flat yarn cloth, and a low-density polyethylene film is more preferred.

[0161] Furthermore, the substrate in which a plastic film is laminated to a flat yarn cloth is preferably lightweight, and the plastic film is preferably thin. The thickness of the plastic film is preferably 10 to 80 μm. The plastic film may be laminated to only one side of the flat yarn cloth, or may be laminated to both sides. Regarding the method of laminating the film to the flat yarn cloth, extrusion lamination is preferred because it can reduce weight without using an adhesive.

[0162] The thickness of the substrate containing the flat yarn cloth is preferably 10 to 200 μm, more preferably 50 to 100 μm, and even more preferably 60 to 90 μm. If the thickness is too thin, hand tearability will be improved but defects such as the inclusion of wrinkles during the production of the adhesive tape will tend to increase, while if the thickness is too thick, defects during the production of the adhesive tape will be reduced but a greater force will be required to cut, and hand tearability will tend to be reduced.

[0163] Examples of the release liner include paper obtained by laminating a film such as polyethylene onto glassine paper, kraft paper, or clay-coated paper; paper coated with a resin such as polyvinyl alcohol or an acrylic ester copolymer; and synthetic resin films obtained by coating a synthetic resin film such as polyester or polypropylene with a release agent such as a fluorine-based resin or a silicone-based resin. These may be used alone or in combination of two or more. Among these, paper release liners are preferred because they are easily torn by hand, and base paper with a basis weight of 40 to 120 g / m 2 , preferably 50 to 80 g / m 2 A paper release liner having the following structure is particularly preferred. Furthermore, the thickness of such a release liner is preferably 40 to 180 μm, more preferably 60 to 140 μm, and even more preferably 80 to 120 μm. If the thickness is too thin, wrinkles may occur during winding, making production difficult, while if the thickness is too thick, hand tearability may be reduced.

[0164] The coating device used when coating the PSA composition on one side of the substrate or release liner can be any commonly used coating device, such as a roll knife coater, die coater, roll coater, bar coater, gravure roll coater, reverse roll coater, dipping coater, blade coater, etc.

[0165] The thickness of the pressure-sensitive adhesive layer after drying is preferably 5 to 200 μm, more preferably 10 to 150 μm, and even more preferably 15 to 130 μm. If the thickness is too thick, it tends to be difficult to apply the pressure-sensitive adhesive composition, and if the thickness is too thin, sufficient adhesive strength tends to be difficult to obtain.

[0166] The drying conditions for drying the pressure-sensitive adhesive composition solution may be any conditions that allow the solvent and residual monomers in the pressure-sensitive adhesive composition to be dried and removed, and allow the functional groups of the resin components used in the pressure-sensitive adhesive, particularly the acrylic resin (A1), to react with the crosslinking agent (C) to form a crosslinked structure. Drying conditions are preferably, for example, 60 to 120°C and about 1 to 5 minutes. After drying, the sheet-like substrate laminated with the pressure-sensitive adhesive layer is aged to further promote the crosslinking reaction.

[0167] The present pressure-sensitive adhesive tape may be a single-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on one side of a substrate, or a double-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on each side of a substrate. Furthermore, both pressure-sensitive adhesive layers of the double-sided pressure-sensitive adhesive tape may be pressure-sensitive adhesive layers having the same composition, or pressure-sensitive adhesive layers having different compositions.

[0168] When a release liner is laminated on the adhesive layer of a double-sided adhesive tape, it is preferable to select the release liners laminated on both sides so that they have different peel strengths, in order to improve workability. For example, workability can be improved by selecting a release liner with a lighter peel strength on the side of the double-sided adhesive tape that is applied first than on the side of the double-sided adhesive tape that is applied second.

[0169] The pressure-sensitive adhesive tape may be in the form of a roll or a sheet, or may be processed into various shapes. When the pressure-sensitive adhesive tape is a double-sided pressure-sensitive adhesive tape in the form of a sheet, it is preferable that a release liner be provided on both surfaces of the two pressure-sensitive adhesive layers, and when it is in the form of a roll, it is preferable that a release liner be provided on only the surface of one of the two pressure-sensitive adhesive layers.

[0170] The present adhesive tape is thus obtained, and it is preferable that the adhesive properties of the present adhesive tape do not deteriorate even when applied to adherends or substrates that deteriorate the adhesive properties. It is also preferable that the present adhesive tape has good holding power. Furthermore, when a substrate that can be easily torn by hand is used as the substrate, the tape can be easily torn by hand at any position in the width direction of the tape without using a tape cutter or the like, making it particularly useful as an adhesive tape.

[0171] The adhesive strength of the adhesive layer in this pressure-sensitive adhesive tape is preferably 1 to 100 N / 25 mm in 180° peel strength against the adherend used. In particular, when a test plate made of SUS304 stainless steel, which has a relatively high polarity, is used as the adherend, the 180° peel strength is preferably 10 N / 25 mm or more, more preferably 20 N / 25 mm or more, and even more preferably 30 N / 25 mm or more. The upper limit is usually about 100 N / 25 mm.

[0172] The adhesive strength can be measured in accordance with JIS Z 0237. Specifically, an adhesive tape is cut to a width of 25 mm and a length of 150 mm, and the adhesive layer of the adhesive tape is pressed against a test plate, and the adhesive tape is peeled off from the test plate at a peel angle of 180° and a rate of 300 mm / min, to measure the peel strength.

[0173] The adhesive strength varies depending on the composition (material), surface condition (surface roughness), treatment (cleaning) conditions, etc. of the adherend, and is therefore not limited to the above range of peel strength.

[0174] When the test piece is a double-sided adhesive tape, the adhesive side not being tested can be covered with a polyethylene terephthalate film (Lumirror S10, manufactured by Toray Industries, Inc.) having a nominal thickness of 25 μm as specified in JIS C2318 for measurement.

[0175] Furthermore, when the holding power of the pressure-sensitive adhesive layer in this pressure-sensitive adhesive tape is measured by the method described below, it is particularly preferable that the test piece does not fall off the test plate after 24 hours (1,440 minutes) have elapsed. Even if the test piece falls off within 24 hours, the holding time is preferably 100 minutes or more, more preferably 150 minutes or more, and even more preferably 500 minutes or more.

[0176] The holding power can be measured by cutting an adhesive tape to a width of 25 mm and a length of 75 mm, pressing the adhesive layer of the adhesive tape to a SUS plate so that the contact area between the tape and the SUS plate is 25 mm wide x 25 mm long, attaching a 1000 g weight to the SUS plate so that the adhesive tape hangs down vertically, and then measuring the time it takes for the adhesive tape to fall in an environment of 40°C.

[0177] The gel fraction of the adhesive layer of the present adhesive tape is the same as that of the adhesive, and is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. The upper limit of the gel fraction is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. By setting the gel fraction within the above range, an adhesive tape having flame retardancy tends to be obtained.

[0178] The gel fraction is a measure of the degree of crosslinking (degree of curing) and can be measured, for example, by the following method.

[0179] To measure the gel fraction, a 200-mesh SUS wire mesh large enough to encase the adhesive tape is prepared and its mass is measured (1). The paper release liner is peeled off from the adhesive tape, and the tape is wrapped in the aforementioned SUS wire mesh and the mass of the tape together with the wire mesh is measured (2). The tape is immersed in toluene maintained at 23°C for 48 hours, then thoroughly dried and the mass of the tape together with the wire mesh is measured (3). After immersion, the tape is removed from the wire mesh, the remaining adhesive layer is removed, and the mass of the substrate is measured (4). Subtraction is performed as shown in the following formula, and the mass percentage of the adhesive component after immersion relative to before immersion is determined as the gel fraction.

[0180] [Formula] Gel fraction (%) = (mass of tape after immersion including the mass of SUS wire mesh (3) - mass of substrate (4) - mass of SUS wire mesh (1)) / (mass of tape before immersion including the mass of SUS wire mesh (2) - mass of substrate (4) - mass of SUS wire mesh (1)) x 100

[0181] The gel fraction of the pressure-sensitive adhesive can be adjusted to fall within the above range by adjusting the type and amount of the crosslinking agent (C), for example.

[0182] This adhesive tape passes the flame retardancy test prescribed in 14 CFR Part 25 Appendix F Part I Section (a)(1)(ii), which is the flame retardancy standard for articles used on aircraft.

[0183] The pressure-sensitive adhesive tape produced by the above method not only has high adhesive properties but also high flame retardancy, making it suitable for use as a pressure-sensitive adhesive tape for fixing aircraft components, construction tape, or airtight waterproof tape, which require high flame retardancy. Examples of aircraft components include carpets, vinyl chloride sheets, flooring, and wall materials. Carpets, vinyl chloride sheets, and flooring materials are particularly suitable. Examples of carpets include known carpets used on aircraft, specifically carpets made with nylon or olefin fibers. Examples of vinyl chloride sheets include hard vinyl chloride sheets with a relatively low content of plasticizer (softener) and soft vinyl chloride sheets with a relatively high content of plasticizer (softener). Examples of flooring materials include metal alloys such as aluminum alloys and titanium alloys, composites of glass-reinforced fibers and epoxy resins, and composites of glass-reinforced fibers and phenolic resins. Furthermore, when the pressure-sensitive adhesive tape is in the form of a double-sided pressure-sensitive adhesive tape, it can be used to bond two or more aircraft components. Examples of combinations of aircraft components bonded together using the double-sided pressure-sensitive adhesive tape include flooring and carpet.

[0184] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are based on mass.

[0185] First, an acrylic resin (A1) serving as a resin component was prepared as follows: The weight average molecular weight, polydispersity, glass transition temperature, and viscosity of the resin component, particularly the acrylic resin (A1), were measured according to the methods described above.

[0186] <Acrylic Resin (A1)> Prior to the production of the acrylic resin (A1), the following were prepared as copolymerization components (monomers) to be used in the production: Monomer (a1): 2-hydroxyethyl methacrylate Monomer (a2): acrylic acid Monomer (a3-1): n-butyl acrylate Monomer (a3-2): 2-ethylhexyl acrylate Monomer (a4): vinyl acetate

[0187] [Production of Acrylic Resin (A1-1)] A reactor equipped with a thermometer, a stirrer, and a reflux condenser was charged with the following copolymerization components: 0.1 part of 2-hydroxyethyl methacrylate (a1), 2.9 parts of acrylic acid (a2), 46 parts of n-butyl acrylate (a3-1), 46 parts of 2-ethylhexyl acrylate (a3-2), and 5 parts of vinyl acetate (a4), as well as 40 parts of ethyl acetate as a solvent and 0.1 parts of azobisisobutyronitrile as a polymerization initiator. The mixture was heated with stirring and polymerized for 9 hours at the reflux temperature of the ethyl acetate mixture. The reaction mixture was then diluted with toluene to obtain an acrylic resin (A1-1) solution with a solids content of 45%. The resulting acrylic resin (A1-1) had a weight average molecular weight of 600,000, a polydispersity of 4.8, a glass transition temperature of -57°C, and an SP value of 9.65 (cal / cm 3 ) 1 / 2 The viscosity of the acrylic resin (A1-1) solution was 7500 mPa·s / 25°C, and the decomposition peak temperature Tdmax was 389.5°C.

[0188] [Production of Acrylic Resin (A1-2)] A reactor equipped with a thermometer, a stirrer, and a reflux condenser was charged with copolymerization components: 0.2 parts of 2-hydroxyethyl methacrylate (a1), 3 parts of acrylic acid (a2), 93.8 parts of 2-ethylhexyl acrylate (a3-2), and 3 parts of vinyl acetate (a4), as well as 40 parts of ethyl acetate and 15 parts of acetone as solvents, and 0.12 parts of azobisisobutyronitrile as a polymerization initiator. The mixture was heated with stirring and polymerized for 7 hours at the reflux temperature of the ethyl acetate (mixture). After that, 3 parts of Mighty Ace G-125 (a terpene-based resin, manufactured by Yasuhara Chemical Co., Ltd.) and 2 parts of Nikanol H-80 (a xylene-based resin, manufactured by Mitsubishi Gas Chemical Company, Inc.) were added as tackifiers (D), and the reaction mixture was diluted with toluene and ethyl acetate to obtain an acrylic resin (A1-2) solution with a solids content of 40%. The weight average molecular weight of the obtained acrylic resin (A1-2) was 600,000, the dispersity was 4.7, the glass transition temperature was -65°C, and the viscosity of the acrylic resin (A1-2) solution was 6,000 mPa·s / 25°C.

[0189] A polyester resin (A2) serving as a resin component was prepared as follows: The number average molecular weight and glass transition temperature of the polyester resin (A2) were measured according to the methods described above.

[0190] [Production of Polyester Resin (A2-1)] A reactor equipped with a thermometer, a stirrer, a rectification column, a nitrogen inlet tube, and a vacuum device was charged with 76.9 parts (0.5 mol) of isophthalic acid and 374.3 parts (1.9 mol) of sebacic acid as the polycarboxylic acid component (I), 216.8 parts (2.1 mol) of neopentyl glycol, 104.2 parts (1.2 mol) of 1,4-butanediol, 23.8 parts (0.2 mol) of 1,6-hexanediol, and 4 parts (0.03 mol) of trimethylolpropane as the polyol component (II), and 0.05 parts of tetrabutyl titanate as a catalyst. The internal temperature was gradually raised to 250°C, and an esterification reaction was carried out over 4 hours.

[0191] Thereafter, the internal temperature was raised to 260°C, 0.05 parts of tetrabutyl titanate was charged as a catalyst, the pressure was reduced to 1.33 hPa, and a polymerization reaction was carried out over 3 hours to produce a polyester resin (A2-1). The resulting polyester resin (A2-1) had a number average molecular weight of 25,000 and a glass transition temperature of -48.5°C.

[0192] <Flame Retardant (B)> The following was prepared as the flame retardant (B): Flame retardant (b1-1): pentaerythritol diphosphonate (manufactured by Teijin Limited, trade name "FCX-210", phosphorus concentration: 15% by mass, 5% mass loss temperature Td5: 348.1°C)

[0193] Flame retardant (b1-2): Phosphate ester flame retardant (manufactured by Daihachi Chemical Industry Co., Ltd., product name "SR-3000", phosphorus concentration: 7% by mass, 5% mass loss temperature Td5: 395.7°C)

[0194] <Crosslinking Agent (C)> The following crosslinking agents (C) were prepared: Isocyanate-based crosslinking agent (c1-1): Coronate L-55E (solid content 55%) manufactured by Tosoh Corporation Epoxy-based crosslinking agent (c2-1): Tetrad C (1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane) manufactured by Mitsubishi Gas Chemical Company, Inc.

[0195] Example 1 Preparation of Double-Sided Pressure-Sensitive Adhesive Tape A pressure-sensitive adhesive composition solution was prepared by adding 0.5 parts of an isocyanate-based crosslinking agent (c1-1), 10 parts of a pentaerythritol diphosphonate-based flame retardant (b1-1), and an appropriate amount of methyl ethyl ketone to 100 parts of the solid content of the acrylic resin (A1-1), and mixing until homogeneous. The resulting solution was then coated with a paper release liner (manufactured by Shinomura Chemical Industry Co., Ltd., product name "SSW-53FOAG"; base paper basis weight 93 g / m 2 The solution was applied to the heavy release surface of the adhesive layer (1) using an applicator so that the thickness after application would be 100 μm, and then dried at 80°C for 5 minutes to produce a paper release liner (1) with an adhesive layer (i). Next, 2.75 parts of an isocyanate-based crosslinking agent (c1-1) and an appropriate amount of ethyl acetate were added to 100 parts of the solid content of the acrylic resin (A1-2) and mixed until homogeneous, and another paper release liner (Shinomura Chemical Industry Co., Ltd., trade name "SSW-53FOAG": base paper basis weight 93 g / m) was used. 2 The adhesive layer (ii) was applied to the light-release surface of the release liner (2) using an applicator so that the thickness after application was 35 μm, and then dried at 80° C. for 3 minutes to produce a paper release liner (2) with an adhesive layer (ii). Furthermore, a lightweight substrate (manufactured by Diatex Co., Ltd.: 47 g / m) was prepared by laminating a low-density polyethylene film on one side of a high-density polyethylene flat yarn cloth. 2 The adhesive side of the paper release liner (1) with the adhesive layer (i) was bonded to the side of the base material that was not laminated with the low-density polyethylene film (1, 62 μm thick), and then the adhesive side of the paper release liner (2) with the adhesive layer (ii) was bonded to the opposite side of the base material (the low-density polyethylene film side). This was then subjected to a heat aging treatment in a dryer at 40° C. for 7 days, to obtain a double-sided adhesive tape of Example 1.

[0196] Example 2 A double-sided pressure-sensitive adhesive tape of Example 2 was obtained in the same manner as in Example 1 above, except that 0.014 parts of the epoxy-based crosslinking agent (c2-1) was added as the crosslinking agent (C) of the pressure-sensitive adhesive layer (i).

[0197] Example 3 A double-sided pressure-sensitive adhesive tape of Example 3 was obtained in the same manner as in Example 1 above, except that a polyester resin (A2-1) was used as the resin component (A) instead of the acrylic resin (A1-1), and the amount of the isocyanate crosslinking agent (c1-1) was changed to 1.8 parts.

[0198] Comparative Example 1 A double-sided pressure-sensitive adhesive tape of Comparative Example 1 was obtained in the same manner as in Example 1 above, except that the flame retardant (B) was not contained in the pressure-sensitive adhesive layer (i).

[0199] Comparative Example 2 A double-sided pressure-sensitive adhesive tape of Comparative Example 2 was obtained in the same manner as in Example 2, except that the flame retardant (B) was not contained in the pressure-sensitive adhesive layer (i).

[0200] Comparative Example 3 A double-sided pressure-sensitive adhesive tape of Comparative Example 3 was obtained in the same manner as in Example 1 above, except that the flame retardant (B) in the pressure-sensitive adhesive layer (i) was replaced with a phosphate ester-based flame retardant SR-3000 (manufactured by Daihachi Chemical Industry Co., Ltd.) (b1-2).

[0201] The double-sided adhesive tapes obtained in the above Examples and Comparative Examples were subjected to the following evaluation tests. The results are summarized in Table 1.

[0202] <Flame retardancy test> A test was conducted in accordance with the flame retardancy test specified in 14 CFR Part 25 Appendix F Part I Section (a)(1)(ii), which is the flame retardancy standard for items used on aircraft, and a pass / fail judgment was made.

[0203] <Peel strength> The paper release liner covering the adhesive layer on the side opposite to the adhesive layer on the measurement surface of the double-sided adhesive tape obtained above was peeled off, and the tape was lined with a polyethylene terephthalate film (manufactured by Toray Industries, Inc., trade name "Lumirror S10": thickness 25 μm), which was then cut to a width of 25 mm and a length of 150 mm to prepare a test piece. Next, the corona-treated side of a polyethylene terephthalate film (manufactured by Toray Industries, Inc., trade name "Lumirror S10": thickness 38 μm) cut to a width of 25 mm and a length of 180 mm was bonded to the adhesive layer exposed by peeling off about 3 cm of one edge of the paper release liner covering the adhesive layer on the measurement surface of the test piece, and the bonded parts were fixed with a stapler. The adherend was a SUS-BA (bright annealed stainless steel) test plate that had been heat-dried at 175°C for 1 hour. The paper release liner covering the adhesive layer to be measured was peeled off from the test piece, and the exposed adhesive layer was placed on the test plate. A 2 kg roller was then moved back and forth twice at a compression speed of 10 mm / s to press the adhesive layer against the test plate. After pressing, the test piece was left to stand in an atmosphere of 23°C and 50% RH for 20 minutes. The test piece was then folded back 180° and peeled 30 mm. The test piece was then secured to the lower chuck of a peel strength tester in the same atmosphere, and the end opposite to the polyethylene terephthalate film with one end bonded to the test piece was secured to the upper chuck. The 180° peel strength (N / 25 mm) was measured when the adhesive tape was peeled from the adherend at a peel angle of 180° and a speed of 300 mm / min.

[0204]

[0205] From the results in Table 1 above, the double-sided pressure-sensitive adhesive tapes of Examples 1 to 3, which used the flame retardant (b1-1) of pentaerythritol diphosphonate, passed the flame retardancy test.

[0206] In contrast, the double-sided pressure-sensitive adhesive tapes of Comparative Examples 1 and 2, which did not use the flame retardant (B), and Comparative Example 3, which used the phosphate ester-based flame retardant (b1-2), had low flame retardancy and failed the flame retardancy test.

[0207] Furthermore, when comparing the peel strengths of Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, Examples 1 and 2, which contain a pentaerythritol diphosphonate flame retardant, have improved peel strengths compared to Comparative Examples 1 and 2, demonstrating that adhesives containing pentaerythritol diphosphonate flame retardants have excellent adhesive properties.

[0208] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0209] The pressure-sensitive adhesive and pressure-sensitive adhesive tape of the present invention have excellent flame retardancy, and are particularly excellent as pressure-sensitive adhesive tapes for fixing aircraft components, and are therefore highly anticipated.

Claims

1. An adhesive comprising a resin component and a flame retardant, wherein the flame retardant comprises a pentaerythritol diphosphonate compound.

2. The pressure-sensitive adhesive according to claim 1, wherein the pentaerythritol diphosphonate compound is a compound of the following formula (1): 【Chemical 1】 In the above formula (1), R 1 ~R 6 and each represent a hydrogen atom, an alkyl group, or a phenyl group, and may be the same or different.

3. The pressure-sensitive adhesive according to claim 1 or 2, wherein the resin component contains an acrylic resin.

4. The pressure-sensitive adhesive according to claim 1 or 2, which contains a crosslinking agent.

5. An adhesive tape having an adhesive layer containing the adhesive according to claim 1 or 2 on at least one surface of a substrate.

6. The adhesive tape according to claim 5 , wherein the substrate comprises a flat yarn cloth.

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