Adhesive tape

Abstract

The purpose of the present invention is to provide an adhesive tape which exhibits high adhesive strength to a fluororesin and excellent retention performance and which can reduce contamination of an adherend. The present invention is an adhesive tape having an adhesive agent layer. The adhesive agent layer contains a (meth)acrylic copolymer and an tackifying resin (T1) having at least one type of constituent unit (A) selected from the group consisting of a constituent unit (A-1), a constituent unit (A-1'), a constituent unit (A-2), a constituent unit (A-2'), a constituent unit (A-3), a constituent unit (A-3'), a constituent unit (A-4) and a constituent unit (A-4'), which are represented by formulae shown below. The loss tangent (tanδ) of the adhesive agent layer, as measured at a frequency of 10 Hz, has a peak within the temperature range of not lower than -40ºC and lower than -20ºC.

Description

adhesive tape

[0001] The present invention relates to an adhesive tape.

[0002] Conventionally, adhesive tapes have been widely used to fix components in electronic devices. Specifically, adhesive tapes are used, for example, to adhere a cover panel for protecting the surface of a portable electronic device to a touch panel module or a display panel module, or to adhere a touch panel module to a display panel module. Adhesive tapes used to fix such electronic device components are required to have not only high adhesiveness but also functions such as heat resistance, thermal conductivity, and impact resistance depending on the environment of the location where they are used (e.g., Patent Documents 1 to 3).

[0003] JP 2015-052050 A JP 2015-021067 A JP 2015-120876 A

[0004] In recent years, the demand for fluororesins has been increasing in various fields due to their excellent heat resistance, chemical resistance, low dielectric properties, and water repellency.

[0005] Fluoropolymers are generally used to bond dissimilar materials, but they do not readily exhibit adhesive properties with adhesive tape, making bonding difficult with standard adhesive tape. Among fluoropolymers, ethylene-tetrafluoroethylene copolymer (ETFE) is used in a wide range of applications, including wire coatings, building materials, and solar cells, due to its high mechanical strength, excellent processability, and transparency. However, it is particularly difficult to achieve adhesive properties with adhesive tape. Therefore, bonding fluoropolymers to dissimilar materials typically involves applying a liquid adhesive to a fluoropolymer surface that has been treated for easy adhesion, or attaching the material via adhesive tape using a silicone-based adhesive. However, using liquid adhesives poses challenges, such as the complicated process involved, and the contamination of components caused by the volatilization and penetration of low-molecular-weight components with silicone-based adhesives.

[0006] The present invention provides a pressure-sensitive adhesive tape that has high adhesive strength to fluororesins, excellent holding performance, and is capable of reducing contamination of adherends.

[0007] Disclosure 1 is a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer contains a (meth)acrylic copolymer and a tackifier resin (T1) having at least one structural unit (A) selected from the group consisting of structural units (A-1), (A-1'), (A-2), (A-2'), (A-3), (A-3'), (A-4), and (A-4') represented by the following formula, wherein the loss tangent (tan δ) measured at a frequency of 10 Hz has a peak in a temperature range of −40° C. or higher and lower than −20° C. Disclosure 2 is a pressure-sensitive adhesive tape according to Disclosure 1, wherein the pressure-sensitive adhesive layer does not contain an organosilicon compound, or the content of the organosilicon compound in the pressure-sensitive adhesive layer is 3.0 mass% or less. Disclosure 3 is the pressure-sensitive adhesive tape of Disclosure 1 or 2, wherein the (meth)acrylic copolymer has structural units derived from an alkyl(meth)acrylate, and the alkyl(meth)acrylate comprises an alkyl(meth)acrylate having an alkyl group having from 6 to 8 carbon atoms at an ester terminal. Disclosure 4 is the pressure-sensitive adhesive tape of Disclosure 3, wherein the alkyl(meth)acrylate having an alkyl group having from 6 to 8 carbon atoms at an ester terminal comprises n-heptyl(meth)acrylate. Disclosure 5 is the pressure-sensitive adhesive tape of Disclosure 3 or 4, wherein the (meth)acrylic copolymer contains structural units derived from an alkyl(meth)acrylate having an alkyl group having from 6 to 8 carbon atoms at an ester terminal of the (meth)acrylic copolymer at a content of 50% by mass or more and 99.99% by mass or less.

[0013] Disclosure 6 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, or 5, wherein the (meth)acrylic copolymer has structural units derived from a carboxy group-containing monomer, and the content of the structural units derived from the carboxy group-containing monomer in the (meth)acrylic copolymer is from 0.01% by mass to 3.0% by mass. Disclosure 7 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, or 6, wherein the (meth)acrylic copolymer has structural units derived from a hydroxyl group-containing monomer, and the content of the structural units derived from the hydroxyl group-containing monomer in the (meth)acrylic copolymer is from 0.01% by mass to 3.0% by mass.Disclosure 8 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, or 7, wherein the (meth)acrylic copolymer has a weight-average molecular weight of 500,000 or more and 1,600,000 or less. Disclosure 9 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, or 8, wherein the tackifier resin (T1) has a structural unit (B) derived from at least one monomer (b) selected from the group consisting of a terpene monomer, a vinyl monomer, and a conjugated diene monomer. Disclosure 10 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein the content of the tackifier resin (T1) is 5 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the (meth)acrylic copolymer.

[0023] Disclosure 11 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the pressure-sensitive adhesive layer further contains at least one tackifier resin (T2) selected from the group consisting of rosin ester resins, terpene resins, terpene phenolic resins, and petroleum-based resins. Disclosure 12 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the pressure-sensitive adhesive layer further contains a curing agent. Disclosure 13 is the pressure-sensitive adhesive tape of Disclosure 12, wherein the curing agent comprises an isocyanate-based curing agent. Disclosure 14 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, wherein the pressure-sensitive adhesive layer further contains at least one selected from the group consisting of a light stabilizer and an ultraviolet absorber. Disclosure 15 is a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer containing a (meth)acrylic copolymer, a tackifier resin (T1) having at least one structural unit (A) selected from the group consisting of structural units (A-1), (A-1'), (A-2), (A-2'), (A-3), (A-3'), (A-4), and (A-4') represented by the following formulas, and at least one selected from the group consisting of a light stabilizer and an ultraviolet absorber. Disclosure 16 is a pressure-sensitive adhesive tape having a shear storage modulus of 1.0 x 10 measured at 25°C and a frequency of 10 Hz. ４ Pa or more 5.0×10 ５

[0033] Disclosure 17 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the pressure-sensitive adhesive layer has a gel fraction of 5% by mass or more and 50% by mass or less. Disclosure 18 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17, which has a substrate. Disclosure 19 is the pressure-sensitive adhesive tape of Disclosure 18, wherein the substrate includes a resin film containing a fluororesin. Disclosure 20 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19, wherein the pressure-sensitive adhesive tape has a light transmittance of 85% or more at a wavelength of 550 nm. Disclosure 21 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, wherein the pressure-sensitive adhesive tape has a haze value of 3% or less. Disclosure 22 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, which is used for fixing solar cells or solar cell components. Disclosure 23 is the pressure-sensitive adhesive tape of Disclosure 22 used for fixing a front sheet or a back sheet of a film-type solar cell.

[0008]

[0009]

[0010]

[0011]

[0012] In formulas (A-1) to (A-4) and formulas (A-1′) to (A-4′), R １ ~R ７each represents a hydrogen atom, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a polar functional group, an aliphatic hydrocarbon group having a polar functional group, or an aromatic hydrocarbon group having a polar functional group. n and l each represent an integer of 2 or more and 4 or less, and n' and l' each represent an integer of 2 or more and 5 or less. m and k each represent an integer of 1 or more and 4 or less, and m' and k' each represent an integer of 1 or more and 5 or less. * represents a linking portion.

[0013] The present invention will be described in detail below. The pressure-sensitive adhesive tape of Disclosure 1 will also be referred to as the "pressure-sensitive adhesive tape of Invention 1," and the pressure-sensitive adhesive tape of Disclosure 15 will also be referred to as the "pressure-sensitive adhesive tape of Invention 2." Furthermore, matters common to the pressure-sensitive adhesive tape of Invention 1 and the pressure-sensitive adhesive tape of Invention 2 will not be specified in particular, or will be described as the "pressure-sensitive adhesive tape of the present invention."

[0014] The present inventors investigated the incorporation of a tackifier resin (T1) having a specific structural unit into a pressure-sensitive adhesive layer containing a (meth)acrylic copolymer, and further investigated adjusting the temperature range in which the loss tangent (tan δ) peaks at a specific frequency. As a result, they found that a pressure-sensitive adhesive tape can be obtained that has high adhesive strength to fluororesins, excellent holding performance, and can reduce contamination of the adherend, and thus completed the present invention. In this specification, "(meth)acrylic" means acrylic or methacrylic.

[0015] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer contains a (meth)acrylic copolymer. By containing the (meth)acrylic copolymer in the pressure-sensitive adhesive layer, the resulting pressure-sensitive adhesive tape becomes relatively stable against light, heat, moisture, etc.

[0016] The (meth)acrylic copolymer preferably has a structural unit derived from an alkyl (meth)acrylate. The alkyl (meth)acrylate preferably contains an alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal. That is, the (meth)acrylic copolymer preferably has a structural unit derived from an alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal. When the (meth)acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal, the glass transition temperature (Tg) of the (meth)acrylic copolymer is further reduced. As a result, the shear storage modulus (G') of the pressure-sensitive adhesive layer measured at 25°C and a frequency of 10 Hz, as described below, is appropriately reduced, and the flexibility of the pressure-sensitive adhesive layer is further improved, thereby further improving the adhesive strength of the resulting pressure-sensitive adhesive tape to fluororesin. In this specification, "(meth)acrylate" means acrylate or methacrylate. In this specification, "an alkyl (meth)acrylate having an alkyl group at the ester terminal" means a (meth)acrylate in which an alkyl group is bonded to the oxygen atom of the ester bond.

[0017] Examples of the alkyl(meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal include 2-ethylhexyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, 1-methylheptyl(meth)acrylate, etc. These alkyl(meth)acrylates having an alkyl group having 6 to 8 carbon atoms at the ester terminal may be used alone or in combination of two or more.

[0018] The alkyl(meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester end preferably includes n-heptyl(meth)acrylate, since this further improves the adhesive strength of the pressure-sensitive adhesive tape. Generally, alkyl(meth)acrylates having an alkyl group with an odd number of carbon atoms at the ester end are less likely to pack with each other, and the glass transition temperature (Tg) of the alkyl(meth)acrylate tends to be lowered. Therefore, by including a structural unit derived from n-heptyl(meth)acrylate in the (meth)acrylic copolymer, packing between the alkyl groups at the ester end in the (meth)acrylic copolymer can be further suppressed, thereby further lowering the glass transition temperature (Tg) of the (meth)acrylic copolymer. As a result, the shear storage modulus (G') of the pressure-sensitive adhesive layer, as described below, measured at 25°C and a frequency of 10 Hz is appropriately reduced, and the flexibility and cohesion of the pressure-sensitive adhesive layer are further improved. This not only further improves the adhesive strength of the resulting pressure-sensitive adhesive tape to fluororesins, but also exhibits high retention performance.

[0019] The content of the structural units derived from alkyl (meth)acrylate having an alkyl group with 6 to 8 carbon atoms at the ester terminal in the (meth)acrylic copolymer is preferably 50% by mass or more. When the content of the structural units derived from alkyl (meth)acrylate having an alkyl group with 6 to 8 carbon atoms at the ester terminal is 50% by mass or more, the glass transition temperature (Tg) of the (meth)acrylic copolymer is further reduced, resulting in an appropriate reduction in the shear storage modulus (G') at 23°C of the pressure-sensitive adhesive layer described below, further improving the flexibility of the pressure-sensitive adhesive layer and further improving the adhesive strength of the resulting pressure-sensitive adhesive tape to fluororesin. A more preferred lower limit of the content of the structural units derived from alkyl (meth)acrylate having an alkyl group with 6 to 8 carbon atoms at the ester terminal is 90% by mass, and an even more preferred lower limit is 95% by mass. Furthermore, the upper limit of the constituent units derived from alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal may be 99.99% by mass, but from the viewpoint of the cohesive strength of the bulk of the pressure-sensitive adhesive layer, a preferred upper limit is 99% by mass.

[0020] The alkyl(meth)acrylate may include alkyl(meth)acrylates other than the alkyl(meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal. Examples of the other alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, esters of 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)octanol-1 and (meth)acrylic acid, esters of alcohols having a total of 18 carbon atoms and one or two methyl groups in the linear main chain and (meth)acrylic acid, behenyl (meth)acrylate, arachidyl (meth)acrylate, etc. These other alkyl (meth)acrylates may be used alone or in combination of two or more.

[0021] The (meth)acrylic copolymer preferably further contains a structural unit derived from a polar functional group-containing monomer. By containing a structural unit derived from a polar functional group-containing monomer in the (meth)acrylic copolymer, the cohesive strength of the bulk of the pressure-sensitive adhesive layer is increased, and the adhesive strength and holding performance of the obtained pressure-sensitive adhesive tape are further improved.

[0022] The polar functional group is reactive for crosslinking reactions and the like, and is preferably at least one selected from the group consisting of a carboxy group, a hydroxyl group, an amino group, and an epoxy group. Of these, a carboxy group or a hydroxyl group is more preferred, as it can contribute to improving the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape. Examples of the carboxy group-containing monomer include (meth)acrylic acid. Examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Examples of the epoxy group-containing monomer include glycidyl (meth)acrylate. These polar functional group-containing monomers may be used alone, or two or more may be used in combination.

[0023] The content of the structural unit derived from the carboxyl group-containing monomer in the (meth)acrylic copolymer is preferably 0.01% by mass at the lower limit and 3.0% by mass at the upper limit. By having the content of the structural unit derived from the carboxyl group-containing monomer in this range, the cohesive strength of the bulk of the pressure-sensitive adhesive layer can be appropriately adjusted, so that the resulting pressure-sensitive adhesive tape has better adhesive strength and holding performance. The content of the structural unit derived from the carboxyl group-containing monomer is more preferably 0.05% by mass at the lower limit and 2.0% by mass at the upper limit.

[0024] The content of the structural units derived from the hydroxyl group-containing monomer in the (meth)acrylic copolymer is preferably 0.01% by mass at the lower limit and 3.0% by mass at the upper limit. By ensuring that the content of the structural units derived from the hydroxyl group-containing monomer is within this range, the cohesive strength of the bulk of the pressure-sensitive adhesive layer can be appropriately adjusted, resulting in a pressure-sensitive adhesive tape with superior adhesive strength and holding performance. The content of the structural units derived from the hydroxyl group-containing monomer is more preferably 0.05% by mass at the lower limit and 2.0% by mass at the upper limit.

[0025] The total content of the structural units derived from the polar functional group-containing monomer in the (meth)acrylic copolymer is preferably 0.01% by mass at the lower limit and 6.0% by mass at the upper limit. By ensuring that the total content of the structural units derived from the polar functional group-containing monomer falls within this range, the bulk cohesive strength of the pressure-sensitive adhesive layer can be appropriately adjusted, resulting in a pressure-sensitive adhesive tape with superior adhesive strength and holding performance. The more preferred lower limit of the content of the structural units derived from the polar functional group-containing monomer is 0.1% by mass, and the more preferred upper limit is 3.0% by mass.

[0026] The (meth)acrylic copolymer may optionally contain structural units derived from other copolymerizable polymerizable monomers other than the structural units derived from the alkyl (meth)acrylates and the structural units derived from the polar functional group-containing monomers described above. Examples of such other monomers include benzyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and polypropylene glycol mono(meth)acrylate. Furthermore, examples of such other monomers include various monomers commonly used in acrylic polymers, such as vinyl carboxylates such as vinyl acetate and styrene. These other monomers may be used alone or in combination of two or more.

[0027] The weight-average molecular weight (Mw) of the (meth)acrylic copolymer preferably has a lower limit of 500,000 and an upper limit of 1,600,000. When the weight-average molecular weight (Mw) of the (meth)acrylic copolymer is 500,000 or more, the bulk cohesive strength of the pressure-sensitive adhesive layer is improved, and the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape are further improved. When the weight-average molecular weight (Mw) of the (meth)acrylic copolymer is 1,600,000 or less, the interfacial wettability of the pressure-sensitive adhesive layer is further improved, and interfacial peeling can be suppressed. The weight-average molecular weight (Mw) of the (meth)acrylic copolymer more preferably has a lower limit of 700,000 and an upper limit of 1,200,000.

[0028] The ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the (meth)acrylic copolymer (polydispersity, Mw / Mn) preferably has a lower limit of 1.05 and an upper limit of 5.0. When the polydispersity (Mw / Mn) of the (meth)acrylic copolymer is 1.05 or more, the flexibility of the pressure-sensitive adhesive layer is improved, and the adhesive strength of the resulting pressure-sensitive adhesive tape to fluororesin is further improved. When the polydispersity (Mw / Mn) of the (meth)acrylic copolymer is 5.0 or less, the proportion of low-molecular-weight components is reduced, the cohesive strength of the bulk of the pressure-sensitive adhesive layer is improved, and the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape are further improved. The upper limit of the polydispersity (Mw / Mn) of the (meth)acrylic copolymer is more preferably 4.5, even more preferably 4.0, and even more preferably 3.5.

[0029] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) refer to the weight average molecular weight measured in gel permeation chromatography (GPC) in terms of standard polystyrene. Specifically, the (meth)acrylic copolymer is diluted 50 times with tetrahydrofuran (THF), and the diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The obtained filtrate is supplied to a gel permeation chromatograph (Waters, "2690 Separations Module", etc.), and GPC measurement is performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40 ° C., and the weight average molecular weight (Mw) and number average molecular weight (Mn) of the (meth)acrylic copolymer are measured in terms of polystyrene. As the column, for example, a GPC KF-802.5L (Showa Denko KK) or the like is used, and as the detector, for example, a differential refractometer or the like can be used. Furthermore, the polydispersity (Mw / Mn) can be calculated using the weight average molecular weight (Mw) and number average molecular weight (Mn) thus obtained.

[0030] The weight average molecular weight (Mw) and polydispersity (Mw / Mn) of the (meth)acrylic copolymer can be adjusted to fall within the above ranges by, for example, adjusting the composition, polymerization method, polymerization conditions, etc. of the (meth)acrylic copolymer.

[0031] The glass transition temperature (Tg) of the (meth)acrylic copolymer preferably has a lower limit of −70°C and an upper limit of −30°C. When the glass transition temperature of the (meth)acrylic copolymer is within the above range, the shear storage modulus (G') of the pressure-sensitive adhesive layer, as described below, measured at 25°C and a frequency of 10 Hz, can be easily adjusted to an appropriate range, thereby resulting in an adhesive tape having superior adhesive strength and retention performance to fluororesins. The glass transition temperature (Tg) of the (meth)acrylic copolymer is more preferably −60°C in lower limit and more preferably −40°C in upper limit. In this specification, the glass transition temperature can be measured using a differential scanning calorimeter (e.g., SII Exstar 6000 / DSC 6220, manufactured by Hitachi High-Tech Science Corporation) in a nitrogen atmosphere at a heating rate of 10°C / min, and the value obtained in one run can be used.

[0032] The polymerization method for synthesizing the (meth)acrylic copolymer can be a conventionally known method of radically reacting monomers from which the structural units are derived in the presence of a polymerization initiator, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, and bulk polymerization. Among these, solution polymerization is preferred because of its ease of synthesis. Furthermore, emulsion polymerization is preferred, particularly when the content of structural units derived from acrylonitrile is to be increased.

[0033] When solution polymerization is used as the polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether, etc. These reaction solvents may be used alone or in combination of two or more.

[0034] Examples of the polymerization initiator include organic peroxides and azo compounds. Examples of the organic peroxides include 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of the azo compounds include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination of two or more.

[0035] The pressure-sensitive adhesive layer contains a tackifier resin (T1) having at least one structural unit (A) selected from the group consisting of the structural unit (A-1), the structural unit (A-1'), the structural unit (A-2), the structural unit (A-2'), the structural unit (A-3), the structural unit (A-3'), the structural unit (A-4), and the structural unit (A-4') represented by the above formula. By containing the tackifier resin (T1), the pressure-sensitive adhesive layer can exhibit high adhesive strength, and in particular, can exhibit adhesive strength even to adherends with low polarity, such as fluororesins. In particular, since the interaction with the adherend can be greatly improved and therefore the adhesive strength to the adherend can also be increased, the structural unit (A) is preferably at least one selected from the group consisting of the structural unit (A-1), the structural unit (A-1'), the structural unit (A-2), the structural unit (A-2'), the structural unit (A-3), and the structural unit (A-3'), and more preferably at least one selected from the group consisting of the structural unit (A-1) and the structural unit (A-1'). When the structural unit (A) is at least one selected from the group consisting of the structural unit (A-1) and the structural unit (A-1'), not only can the interaction with the adherend be further greatly improved, but the tackifier resin (T1) has a moderate polarity, and therefore compatibility with the (meth)acrylic copolymer also becomes more excellent. Furthermore, since it is easy to use monomers containing biologically derived materials, which will be described later, as monomers that form the structural unit (A-1) and the structural unit (A-1'), this is preferable from the perspective of saving petroleum resources.

[0036] The tackifier resin (T1) may have the structural unit (A) in a side chain, or in the main chain skeleton or at an end of the main chain skeleton. In particular, the tackifier resin (T1) preferably has the structural unit (A) in the main chain skeleton or at an end of the main chain skeleton, since this allows the tackifier resin to have suitable physical properties required as a tackifier resin.

[0037] In the structural unit (A), R １ ~R ７respectively represent a hydrogen atom, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a polar functional group, an aliphatic hydrocarbon group having a polar functional group, or an aromatic hydrocarbon group having a polar functional group. The aliphatic hydrocarbon group is not particularly limited, and examples thereof include linear, branched, or cyclic alkyl groups having 1 to 20 carbon atoms. The aromatic hydrocarbon group is not particularly limited, and examples thereof include substituted or unsubstituted aryl groups having 1 to 20 carbon atoms. The polar functional group is not particularly limited, and R １ As the polar functional group other than the hydroxyl group, R ２ is a polar functional group other than a carboxy group, ３ As for OR ４ A polar functional group other than the group represented by R ５ As for NR ６ R ７ Polar functional groups other than those represented by the formula (I) can be used. Specific examples of the polar functional group include an amino group, a carboxy group, a carbonyl group, an alkoxy group, a hydroxyl group, a nitrile group, and a nitro group. The aliphatic hydrocarbon group having the polar functional group is not particularly limited, and for example, a group in which one or more hydrogen atoms in the aliphatic hydrocarbon group described above have been substituted with the polar functional group described above can be used. The aromatic hydrocarbon group having the polar functional group is also not particularly limited, and for example, a group in which one or more hydrogen atoms in the aromatic hydrocarbon group described above have been substituted with the polar functional group described above can be used.

[0038] In the tackifier resin (T1), multiple R １ may be the same or different. １ Similarly, the multiple R １ may be the same or different. １ may be the same or different.

[0039] Similarly, multiple R ２may be the same or different. ２ Similarly, the multiple R ２ may be the same or different. ２ may be the same or different.

[0040] Similarly, multiple R ３ may be the same or different. ３ Similarly, the multiple R ３ may be the same or different. ３ may be the same or different.

[0041] Similarly, multiple R ４ may be the same or different. ４ Similarly, the multiple R ４ may be the same or different. ４ may be the same or different.

[0042] Similarly, multiple R ５ may be the same or different. ５ Similarly, the multiple R ５may be the same or different. ５ may be the same or different.

[0043] Similarly, multiple R ６ and R ７ may be the same or different. ６ and R ７ Similarly, the multiple R ６ and R ７ may be the same or different. ６ and R ７ may be the same or different.

[0044] In the structural unit (A), n and l are each an integer of 2 or more and 4 or less, and n' and l' are each an integer of 2 or more and 5 or less, but from the viewpoint of ease of availability of raw materials, n, l, n', and l' are preferably 2 or 3. It is more preferable that n, l, n', and l' are 3, as this can further increase the adhesive strength of the pressure-sensitive adhesive layer.

[0045] In the structural unit (A), m and k are each an integer of 1 or more and 4 or less, and m' and k' are each an integer of 1 or more and 5 or less, but from the viewpoint of ease of availability of raw materials, m, k, m', and k' are preferably 1, 2, or 3. It is more preferable that m, k, m', and k' are 1, since this will further increase the adhesive strength of the pressure-sensitive adhesive layer.

[0046] More specific examples of the structural unit (A-1) and the structural unit (A-1') include a structural unit derived from dihydroxybenzene or a derivative thereof (when n and n' are 2), and a structural unit derived from trihydroxybenzene or a derivative thereof (when n and n' are 3). These structural units may be used alone, or two or more types may be used in combination. The dihydroxybenzene or derivative thereof is not particularly limited, and examples include resorcinol, pyrocatechol, hydroquinone, dihydroxytoluene, dihydroxyxylene, dihydroxyphenylethylamine hydrochloride, dihydroxybenzoic acid, dihydroxyphenylacetic acid, dihydroxyhydrocinnamic acid, dihydroxyphenylpropionic acid, dihydroxyphenylalanine, dihydroxybenzaldehyde, dihydroxyacetophenone, diacetyldihydroxybenzene, dihydroxyphenyl-2-butanone, dihydroxyphenylmethyl acetate, benzyl dihydroxyphenyl ketone, dihydroxybenzamide, dihydroxymethoxybenzene, dihydroxybenzyl alcohol, dihydroxyphenylethanol, dihydroxyphenyl glycol, dihydroxyphenylacetonitrile, and dihydroxynitrobenzene. Among these, pyrocatechol is preferred because it has little steric hindrance and easily interacts with the adherend. These dihydroxybenzenes or derivatives thereof may be used alone, or two or more may be used in combination. The trihydroxybenzenes or derivatives thereof are not particularly limited, and examples thereof include pyrogallol, 1,2,4-trihydroxybenzene, phloroglucinol, trihydroxytoluene, trihydroxydiphenylmethane, 6-hydroxy-L-dopa, gallic acid, methyl gallate, butyl gallate, isobutyl gallate, isoamyl gallate, hexadecyl gallate, stearyl gallate, trihydroxyacetophenone, trihydroxyphenylethanone, trihydroxyphenylbutanone, trihydroxybenzaldehyde, trihydroxybenzamide, and trihydroxynitrobenzene. Among these, pyrogallol is preferred because it has little steric hindrance and easily interacts with the adherend. These trihydroxybenzenes or derivatives thereof may be used alone, or two or more may be used in combination.

[0047] More specific examples of the structural unit (A-2) and the structural unit (A-2') include structural units derived from benzoic acid, salicylic acid, dihydroxybenzoic acid, gallic acid, 2-methylbenzoic acid, 3-methylbenzoic acid, 4-methylbenzoic acid, 2-ethylbenzoic acid, 3-ethylbenzoic acid, 4-ethylbenzoic acid, 4-tert-butylbenzoic acid, 2-vinylbenzoic acid, 3-vinylbenzoic acid, 4-vinylbenzoic acid, 4,4'-stilbene dicarboxylic acid, and derivatives thereof. Of these, 4-vinylbenzoic acid is preferred because it has little steric hindrance and easily interacts with the adherend. These structural units may be used alone, or two or more types may be used in combination.

[0048] More specific examples of the structural unit (A-3) and the structural unit (A-3') include a structural unit derived from a dialkoxybenzene or a derivative thereof (when l and l' are 2), and a structural unit derived from a trialkoxybenzene or a derivative thereof (when l and l' are 3). The dialkoxybenzene or derivative thereof is not particularly limited, and examples include 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, and 1,4-dimethoxybenzene. The trialkoxybenzene or derivative thereof is not particularly limited, and examples include 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, and 1,3,5-trimethoxybenzene. Of these, 1,2,3-trimethoxybenzene is preferred due to its low steric hindrance and ease of interaction with the adherend. These trialkoxybenzenes or derivatives thereof may be used alone, or two or more types may be used in combination.

[0049] More specific examples of the structural unit (A-4) and the structural unit (A-4') include structural units derived from aminobenzene or derivatives thereof (when k and k' are 1). The aminobenzene or derivatives thereof are not particularly limited, and examples include aniline, methylaniline, ethylaniline, dimethylaniline, diethylaniline, etc. These aminobenzenes or derivatives thereof may be used alone, or two or more types may be used in combination.

[0050] The structural unit (A) may consist solely of petroleum-derived materials, but preferably contains a biologically-derived material. The depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products are becoming problems. Therefore, attempts have been made to conserve petroleum resources by using biologically-derived materials instead of petroleum-derived materials. It is preferable for the structural unit (A) to contain a biologically-derived material from the perspective of conserving petroleum resources. Furthermore, if the structural unit (A) contains a biologically-derived material, since biologically-derived materials are originally produced by absorbing carbon dioxide from the atmosphere, it is thought that burning it will not increase the total amount of carbon dioxide in the atmosphere, which is also preferable from the perspective of reducing carbon dioxide emissions. Examples of monomers that constitute the structural unit (A) containing a biological material include resorcinol, dihydroxyphenylethylamine hydrochloride, dihydroxyhydrocinnamic acid, dihydroxyphenylalanine, dihydroxybenzaldehyde, dihydroxybenzyl alcohol, pyrogallol, 1,2,4-trihydroxybenzene, phloroglucinol, 6-hydroxy-L-dopa, gallic acid, methyl gallate, butyl gallate, isobutyl gallate, isoamyl gallate, hexadecyl gallate, stearyl gallate, trihydroxyacetophenone, trihydroxybenzaldehyde, trihydroxybenzamide, and trihydroxynitrobenzene.

[0051] The content (by mole) of the structural unit (A) in the tackifier resin (T1) is not particularly limited, but a preferred lower limit is 1 mol% and a preferred upper limit is 60 mol%. A structural unit (A) content of 1 mol% or more can further increase the adhesive strength of the pressure-sensitive adhesive layer. A structural unit (A) content of 60 mol% or less can allow the tackifier resin (T1) to have suitable physical properties required as a tackifier resin. A more preferred lower limit of the structural unit (A) content is 5 mol%, a more preferred upper limit is 50 mol%, an even more preferred lower limit is 10 mol%, and an even more preferred upper limit is 30 mol%. The content (by mass) of the structural unit (A) in the tackifier resin (T1) is not particularly limited, but a preferred lower limit is 0.9 mass% and a preferred upper limit is 60 mass%. A structural unit (A) content of 0.9 mass% or more can further increase the adhesive strength of the pressure-sensitive adhesive layer. When the content of the structural unit (A) is 60% by mass or less, the tackifier resin (T1) can have suitable physical properties required as a tackifier resin. The lower limit of the content of the structural unit (A) is more preferably 5% by mass, the upper limit is more preferably 50% by mass, the even more preferably 10% by mass, and the even more preferably 30% by mass.

[0052] The tackifier resin (T1) preferably contains a structural unit (B) derived from at least one monomer (b) selected from the group consisting of a terpene monomer, a vinyl monomer, and a conjugated diene monomer. By containing the structural unit (B), the tackifier resin (T1) can have the suitable physical properties required for a tackifier resin. Among these, a structural unit derived from a terpene monomer or a structural unit derived from a vinyl monomer is preferred because it can further enhance the adhesive strength of the PSA layer. It is also preferred to use a structural unit derived from a terpene monomer in combination with a structural unit derived from a vinyl monomer. Furthermore, from the viewpoint of improving the compatibility between the tackifier resin (T1) and the (meth)acrylic copolymer, a structural unit derived from a terpene monomer or a structural unit derived from a conjugated diene monomer is preferred. Because these structural units contain an aliphatic hydrocarbon group having an unsaturated double bond, the inclusion of these structural units in the tackifier resin (T1) further improves the compatibility between the tackifier resin (T1) and the (meth)acrylic copolymer, thereby suppressing a decrease in the adhesive strength of the PSA layer due to poor compatibility.

[0053] The terpene monomer is not particularly limited, and examples thereof include α-pinene, β-pinene, limonene, dipentene, δ-3-carene, dimethyloctatriene, alloocimene, myrcene, ocimene, linalool, and cosmene. Among these, α-pinene, β-pinene, or limonene is preferred because it can further enhance the adhesive strength of the pressure-sensitive adhesive layer. The vinyl monomer is not particularly limited, but from the viewpoint of improving the compatibility between the tackifier resin (T1) and the (meth)acrylic copolymer, a vinyl monomer that does not have a structure containing two or more aromatic rings in one molecule (e.g., a naphthalene structure, an anthracene structure, a biphenyl structure, an anthraquinone structure, a benzophenone structure, etc.) is preferred. Examples of the vinyl monomer not having a structure containing two or more aromatic rings per molecule include ethylene, propylene, butylene, hexene, vinyl acetate, vinyl chloride, styrene, α-methylstyrene, coumarone, indene, vinyltoluene, divinylbenzene, divinyltoluene, and 2-phenyl-2-butene. Of these, styrene is preferred because it can further enhance the adhesive strength of the pressure-sensitive adhesive layer. Examples of the conjugated diene monomer include butadiene, isoprene, piperylene, and cyclopentadiene. Of these, isoprene is preferred because it can further enhance the adhesive strength of the pressure-sensitive adhesive layer. These monomers (b) may be used alone, or two or more of them may be used in combination.

[0054] The structural unit (B) may consist solely of petroleum-derived materials, but preferably contains a biologically-derived material. The depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products are becoming increasingly problematic. Therefore, attempts have been made to conserve petroleum resources by replacing petroleum-derived materials with biologically-derived materials. It is preferable for the structural unit (B) to contain a biologically-derived material from the perspective of conserving petroleum resources. Furthermore, since the biologically-derived material is originally produced by absorbing carbon dioxide from the atmosphere, its combustion is thought to not increase the total amount of carbon dioxide in the atmosphere, which is also preferable from the perspective of reducing carbon dioxide emissions. Examples of the monomer (b) constituting the structural unit (B) containing a biologically-derived material include terpene monomers, ethylene, propylene, hexene, butadiene, and isoprene.

[0055] The content of the structural unit (B) in the tackifier resin (T1) is preferably 40 mol% at the lower limit and 99 mol% at the upper limit. When the content of the structural unit (B) is 40 mol% or more, the tackifier resin (T1) can have the suitable physical properties required for a tackifier resin. When the content of the structural unit (B) is 99 mol% or less, the content of the structural unit (A) can be sufficiently ensured, thereby further increasing the adhesive strength of the pressure-sensitive adhesive layer, and particularly, the adhesive strength can be further increased even for adherends with low polarity such as fluororesins. The more preferred lower limit of the content of the structural unit (B) is 50 mol%, and the more preferred upper limit is 90 mol%.

[0056] The tackifier resin (T1) is not particularly limited as long as it is a compound having the structural unit (A), but is preferably a copolymer having a structure represented by the following formula: When the structural unit (A) is contained in the main chain skeleton or at the end of the main chain skeleton, it is preferably a copolymer having a structure represented by the following formula: A copolymer having such a structure is a copolymer obtained by a method using cationic polymerization as described below, and can further increase the adhesive strength of the pressure-sensitive adhesive layer, and can particularly further increase the adhesive strength even to adherends with low polarity.

[0057]

[0058] In the formula, A represents the structural unit (A), B represents the structural unit (B), and s and t each represent an integer of 1 or greater. * represents a linking moiety.

[0059] The tackifier resin (T1) is not particularly limited as long as it is a compound having the structural unit (A), but is preferably a copolymer having the structural unit (A) and the structural unit (B), and may further contain other structural units. When it is a copolymer, the structural unit (A) and the structural unit (B) may be copolymerized randomly, or may be copolymerized with regularity or periodicity, for example, in such a manner that each of them forms a block segment and then the block segments are bonded to each other.

[0060] The tackifier resin (T1) preferably has an aliphatic hydrocarbon group having an unsaturated double bond. The tackifier resin (T1) may have the aliphatic hydrocarbon group having an unsaturated double bond in the structural unit (A) or the structural unit (B), or in another structural unit. In particular, from the viewpoint of ease of synthesis and improving compatibility between the tackifier resin (T1) and the (meth)acrylic copolymer, it is preferable that the aliphatic hydrocarbon group having an unsaturated double bond be contained in the structural unit (B) or another structural unit. The structural unit (B) or other structural unit having such an aliphatic hydrocarbon group having an unsaturated double bond is not particularly limited, but a structural unit (B) derived from at least one monomer (b) selected from the group consisting of terpene monomers and conjugated diene monomers is preferred. That is, the tackifier resin (T1) preferably has the aliphatic hydrocarbon group having an unsaturated double bond in a structural unit (B) derived from at least one monomer (b) selected from the group consisting of a terpene monomer and a conjugated diene monomer, and more preferably in a structural unit derived from a terpene monomer, since this can further enhance the adhesive strength of the PSA layer.

[0061] Furthermore, examples of the other structural units include structural units derived from other phenolic monomers not included in the structural unit (A), structural units derived from maleic anhydride, etc. Examples of the other phenolic monomers include phenol, cresol, xylenol, propylphenol, norylphenol, methoxyphenol, bromophenol, bisphenol A, bisphenol F, bisphenol S, dihydroxynaphthalene, etc. These other phenolic monomers may be used alone, or two or more types may be used in combination.

[0062] The molecular weight of the tackifier resin (T1) is not particularly limited, but the preferred lower limit of the weight average molecular weight (Mw) is 400, and the preferred upper limit is 10,000. When the weight average molecular weight (Mw) of the tackifier resin (T1) is within the above range, the tackifier resin (T1) can have suitable physical properties required as a tackifier resin. The more preferred lower limit of the weight average molecular weight (Mw) of the tackifier resin (T1) is 500, the more preferred upper limit is 5,000, the even more preferred lower limit is 700, and the even more preferred upper limit is 3,000. The weight average molecular weight (Mw) of the tackifier resin (T1) can be adjusted to fall within the above range by, for example, adjusting the composition, polymerization method, polymerization conditions, etc. of the tackifier resin (T1).

[0063] The preferred lower limit of the Young's modulus of the tackifier resin (T1) at 25°C is 10 MPa. When the Young's modulus of the tackifier resin (T1) at 25°C is 10 MPa or more, the tackifier resin (T1) has appropriate hardness and can have suitable physical properties required as a tackifier resin. The more preferred lower limit of the Young's modulus of the tackifier resin (T1) at 25°C is 50 MPa, and the even more preferred lower limit is 70 MPa. There are no particular restrictions on the upper limit of the Young's modulus of the tackifier resin (T1) at 25°C, but from the viewpoint of preventing the pressure-sensitive adhesive layer from becoming too hard and losing its adhesive strength, the preferred upper limit is 10,000 MPa, and more preferably 5,000 MPa. The Young's modulus of the tackifier resin (T1) at 25° C. can be measured by conducting a tensile test using a tensile tester (for example, "Tensilon" manufactured by ORIENTEC Corporation) under conditions of a tensile speed of 200 mm / min, a gripper distance of 15 mm, and 25° C. The measurement sample can be prepared, for example, by filling a mold having a size of 10 × 50 mm with the compound and melting it at a temperature 100° C. higher than the glass transition temperature to produce a test piece having a thickness of 1 mm.

[0064] The Young's modulus at 25°C of the tackifier resin (T1) can be adjusted to fall within the above range by, for example, adjusting the molecular weight or weight average molecular weight of the tackifier resin (T1), the composition and content of the structural unit (A) and the structural unit (B) in the tackifier resin (T1), and the like.

[0065] The glass transition temperature of the tackifier resin (T1) preferably has a lower limit of 0°C and an upper limit of 200°C. When the glass transition temperature of the tackifier resin (T1) is within the above range, the Young's modulus at 25°C of the tackifier resin (T1) can be easily adjusted to be within the above range, and the tackifier resin (T1) can have suitable physical properties required as a tackifier resin. The lower limit of the glass transition temperature of the tackifier resin (T1) is more preferably 10°C, and the upper limit is more preferably 150°C.

[0066] The iodine value of the tackifier resin (T1) is preferably 2 g / 100 g at its lower limit and 180 g / 100 g at its upper limit. When the iodine value of the tackifier resin (T1) is 2 g / 100 g or more, a decrease in the adhesive strength of the pressure-sensitive adhesive layer due to poor compatibility between the tackifier resin (T1) and the (meth)acrylic copolymer can be suppressed. When the iodine value of the tackifier resin (T1) is 180 g / 100 g or less, the adhesive strength of the pressure-sensitive adhesive layer can be further increased, particularly to adherends with low polarity such as fluororesins. The iodine value of the tackifier resin (T1) is more preferably 70 g / 100 g at its lower limit and 170 g / 100 g at its upper limit. The iodine value is an index indicating the amount of unsaturated double bonds (C═C bond amount) and is measured in accordance with the method described in "JIS K 0070:1992."

[0067] The preferred lower limit of the content of biologically-derived carbon (carbon atoms) in the total carbon (carbon atoms) in the tackifier resin (T1) is 10%. A biologically-derived carbon content of 10% or more is an indicator of a "bio-based product." A biologically-derived carbon content of 10% or more in the tackifier resin (T1) is preferred from the perspective of saving petroleum resources and reducing carbon dioxide emissions. A more preferred lower limit of the biologically-derived carbon content in the tackifier resin (T1) is 30%, an even more preferred lower limit is 60%, an even more preferred lower limit is 70%, and an especially preferred lower limit is 90%. The upper limit of the biologically-derived carbon content in the tackifier resin (T1) is not particularly limited and may be 100%. Note that biologically-derived carbon contains a certain percentage of the radioactive isotope (C-14), whereas petroleum-derived carbon contains almost no C-14. Therefore, the biologically-derived carbon content in the tackifier resin (T1) can be calculated by measuring the concentration of C-14 contained in the compound. Specifically, it can be measured in accordance with ASTM D6866-22, a standard used in many bioplastic industries.

[0068] The tackifier resin (T1) also includes a hydrogenated product of the tackifier resin (T1) described above. The hydrogenated product is a compound in which the carbon-carbon double bonds present in the tackifier resin (T1) described above are at least partially saturated by hydrogenation. That is, the PSA layer may contain a hydrogenated product in which some of the carbon-carbon double bonds in the tackifier resin (T1) are hydrogenated, or a hydrogenated product in which all of the carbon-carbon double bonds in the tackifier resin (T1) are hydrogenated. Even such a hydrogenated product is suitable for use as a tackifier resin to be incorporated into the PSA layer, and can increase the adhesive strength of the PSA layer, particularly to adherends with low polarity such as fluororesins.

[0069] Although there are no particular limitations on the method for producing the tackifier resin (T1), when the structural unit (A) is contained in the main chain skeleton or at the end of the main chain skeleton, the following method is preferred, for example: That is, a method of copolymerizing a monomer (a) constituting the structural unit (A) with at least one monomer (b) selected from the group consisting of a terpene monomer, a vinyl monomer, and a conjugated diene monomer constituting the structural unit (B) (hereinafter, also referred to as production method [I]).

[0070] The monomer (a) is preferably at least one selected from the group consisting of monomer (a-1), monomer (a-2), monomer (a-3), and monomer (a-4) represented by the following formulas:

[0071]

[0072]

[0073]

[0074]

[0075] In formulas (a-1) to (a-4), R １ ~R ７respectively represent a hydrogen atom, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a polar functional group, an aliphatic hydrocarbon group having a polar functional group, or an aromatic hydrocarbon group having a polar functional group. n'' represents an integer of 2 or more and 5 or less, preferably 2 or 3, and more preferably 3. m'' represents an integer of 1 or more and 5 or less. l'' represents an integer of 2 or more and 5 or less. k'' represents an integer of 1 or more and 5 or less.

[0076] In the method [I] for producing the tackifier resin (T1), it is preferable to copolymerize the monomer (a) and the monomer (b) by cationic polymerization. By using cationic polymerization, the monomer (a) and the monomer (b) can be copolymerized without first protecting the functional groups of the monomer (a), such as the phenolic hydroxyl group, carboxy group, alkoxy group, and amino group, by chemical modification, and subsequent deprotection is also unnecessary. Therefore, the monomer (a) and the monomer (b) can be copolymerized by a simpler one-step reaction process, which also leads to a reduction in impurities and an improvement in yield.

[0077] As a method for copolymerizing the monomer (a) and the monomer (b) by cationic polymerization, a method in which the monomer (a) and the monomer (b) are reacted in the presence of a Lewis acid is preferred. According to such a method, it is believed that a cation of the monomer (b) is generated, and the cationic polymerization of the monomers (b) proceeds, while the Friedel-Crafts alkylation reaction between the monomers (a) and (b) proceeds. By repeating such a reaction, a copolymer having a structural unit (A) derived from the monomer (a) and a structural unit (B) derived from the monomer (b) can be obtained. The Lewis acid is not particularly limited, and a conventionally known Lewis acid can be used, for example, aluminum chloride (AlCl ３ ), diethylaluminum chloride (Et ２ AlCl ２ ), tin(IV) chloride (SnCl ４ ), titanium(IV) chloride (TiCl ４ ), boron trichloride (BCl ３ ), boron trifluoride ether complex (BF３ Among them, aluminum chloride (AlCl ) is preferred because it can produce a copolymer in a higher yield. ３ ) is preferred.

[0078] More specifically, for example, pyrogallol is used as the monomer (a) and α-pinene is used as the monomer (b), and these are reacted with aluminum chloride (AlCl), which is a Lewis acid, to form a copolymer. ３ When the reaction is carried out in the presence of a monomer (b), the reaction shown in the following scheme is believed to proceed. That is, a cation of α-pinene, the monomer (b), is generated, and cationic polymerization of α-pinenes proceeds (upper part of the scheme below), while a Friedel-Crafts alkylation reaction between pyrogallol, the monomer (a), and α-pinene, the monomer (b), proceeds (middle part of the scheme below). By repeating this reaction, a copolymer having structural units derived from pyrogallol and structural units derived from α-pinene can be obtained (lower part of the scheme below). Note that such a copolymer has structural units derived from pyrogallol in the main chain skeleton or at the terminal of the main chain skeleton.

[0079]

[0080] In the formula, s and t each represent an integer of 1 or more, and * represents a linking moiety.

[0081] When the structural unit (A) is contained in a side chain, the following method is preferred as a method for producing the tackifier resin (T1): That is, a method of copolymerizing a monomer (a') obtained by further introducing an unsaturated double bond into the monomer (a) constituting the structural unit (A) with at least one monomer (b) selected from the group consisting of a terpene monomer, a vinyl monomer, and a conjugated diene monomer constituting the structural unit (B) (hereinafter also referred to as production method [II]).

[0082] Examples of the monomer (a') include 2-vinylbenzoic acid, 3-vinylbenzoic acid, 4-vinylbenzoic acid, and 4,4'-stilbene dicarboxylic acid. Among these, 4-vinylbenzoic acid is preferred because it has little steric hindrance and easily interacts with the adherend. These monomers (a') may be used alone or in combination of two or more.

[0083] In the method [II] for producing the tackifier resin (T1), it is preferable to copolymerize the monomer (a') and the monomer (b) by cationic polymerization, as in the method [I] for producing the tackifier resin (T1). A preferred method for copolymerizing the monomer (a') and the monomer (b) by cationic polymerization is to react the monomer (a') and the monomer (b) in the presence of a Lewis acid as described above. According to this method, cationic polymerization of the unsaturated double bond in the monomer (a') and the unsaturated double bond in the monomer (b) proceeds, thereby producing a copolymer having the structural unit (A) derived from the monomer (a') and the structural unit (B) derived from the monomer (b).

[0084] The tackifier resin (T1) can enhance the adhesive strength of the pressure-sensitive adhesive layer even in a small amount compared to conventional tackifier resins. The content of the tackifier resin (T1) is preferably 5 parts by mass or less and 30 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic copolymer. When the content of the tackifier resin (T1) is 5 parts by mass or more, the adhesive strength of the pressure-sensitive adhesive layer can be further enhanced, particularly when applied to adherends with low polarity, such as fluororesins. When the content of the tackifier resin (T1) is 30 parts by mass or less, the pressure-sensitive adhesive layer can be prevented from becoming too hard and losing its adhesive strength. The lower limit of the content of the tackifier resin (T1) is more preferably 10 parts by mass, and the upper limit is more preferably 20 parts by mass.

[0085] When the tackifier resin (T1) has a structural unit derived from a terpene monomer as the structural unit (B), the content of the tackifier resin (T1) relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass at its lower limit and more preferably 20 parts by mass at its upper limit.

[0086] When the tackifier resin (T1) has a structural unit derived from the vinyl-based monomer as the structural unit (B), the content of the tackifier resin (T1) relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass at its lower limit and more preferably 20 parts by mass at its upper limit.

[0087] When the tackifier resin (T1) has a structural unit derived from the conjugated diene monomer as the structural unit (B), the content of the tackifier resin (T1) relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass at its lower limit and more preferably 20 parts by mass at its upper limit.

[0088] When the tackifier resin (T1) has, as the structural unit (B), a structural unit derived from the terpene monomer and the vinyl monomer, the content of the tackifier resin (T1) is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass at its lower limit and more preferably 20 parts by mass at its upper limit, relative to 100 parts by mass of the (meth)acrylic copolymer.

[0089] When the tackifier resin (T1) has, as the structural unit (B), structural units derived from the terpene monomer and the conjugated diene monomer, the content of the tackifier resin (T1) relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass at its lower limit and more preferably 20 parts by mass at its upper limit.

[0090] When the tackifier resin (T1) has, as the structural unit (B), a structural unit derived from the vinyl monomer and a structural unit derived from the conjugated diene monomer, the content of the tackifier resin (T1) is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass at its lower limit and more preferably 20 parts by mass at its upper limit, relative to 100 parts by mass of the (meth)acrylic copolymer.

[0091] When the tackifier resin (T1) has, as the structural unit (B), a structural unit derived from the terpene monomer, a structural unit derived from the vinyl monomer, and a structural unit derived from the conjugated diene monomer, the content of the tackifier resin (T1) is preferably 5 parts by mass at its lower limit and 30 parts by mass at its upper limit, more preferably 10 parts by mass and 20 parts by mass at its upper limit, relative to 100 parts by mass of the (meth)acrylic copolymer.

[0092] The pressure-sensitive adhesive layer preferably further contains at least one tackifier resin (T2) selected from the group consisting of rosin ester resins, terpene resins, terpene phenol resins, and petroleum-based resins. By containing the tackifier resin (T2) in the pressure-sensitive adhesive layer, the adhesive strength of the resulting pressure-sensitive adhesive tape can be further increased. In particular, the pressure-sensitive adhesive layer preferably contains at least one tackifier resin selected from the group consisting of rosin ester resins and terpene phenol resins, since this further increases the adhesive strength of the resulting pressure-sensitive adhesive tape.

[0093] The rosin ester resin is a resin obtained by esterifying, with an alcohol, a rosin resin primarily composed of abietic acid, a disproportionated rosin resin, a hydrogenated rosin resin, a dimer (polymerized rosin resin) of a resin acid such as abietic acid, or the like. The hydroxyl value is adjusted to the above-mentioned range by retaining some of the hydroxyl groups of the alcohol used in the esterification without being used in the esterification and remaining in the resin. Examples of the alcohol include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol. A specific example of the rosin ester resin is Pine Crystal KE-359 (manufactured by Arakawa Chemical Industries, Ltd.).

[0094] The terpene resin is a resin having a structural unit derived from a monoterpene compound and not having a structural unit derived from an aromatic compound. Examples of the terpene resin include YS Resin PX1250 (manufactured by Yasuhara Chemical Co., Ltd.).

[0095] The terpene phenolic resin is a resin having structural units derived from a monoterpene compound and structural units derived from a phenolic compound. In this specification, the term "phenolic compound" in the terpene phenolic resin refers to a compound that contains an aromatic ring structure having only one phenolic hydroxyl group and does not contain an aromatic ring structure having two or more phenolic hydroxyl groups. The structural units derived from the phenolic compound in the terpene phenolic resin do not include the structural units (A-1) and (A-1'). Examples of the terpene phenolic resin include YS Polystar G150 (manufactured by Yasuhara Chemical Co., Ltd.).

[0096] Examples of the petroleum-based resin include Alcon P-140 (manufactured by Arakawa Chemical Industries, Ltd.).

[0097] The softening temperature of the tackifier resin (T2) preferably has a lower limit of 70°C and an upper limit of 170°C. A softening temperature of 70°C or higher can prevent the pressure-sensitive adhesive layer from becoming too soft and losing its adhesive strength. A softening temperature of the tackifier resin (T2) of 170°C or lower can further improve the wettability of the interface of the pressure-sensitive adhesive layer, preventing interfacial peeling. A more preferred lower limit of the softening temperature of the tackifier resin (T2) is 100°C and a more preferred upper limit is 150°C. The softening temperature is the softening temperature measured according to JIS K2207 (ring and ball method).

[0098] The tackifier resin (T2) preferably has a hydroxyl value of 25 mg KOH / g (lower limit) and 150 mg KOH / g (upper limit). The hydroxyl value of the tackifier resin (T2) within this range improves the wettability of the interface of the pressure-sensitive adhesive layer, thereby preventing interfacial peeling. The hydroxyl value of the tackifier resin (T2) is more preferably 30 mg KOH / g (lower limit) and 130 mg KOH / g (upper limit). The hydroxyl value can be measured according to JIS K1557 (phthalic anhydride method).

[0099] The content of the tackifier resin (T2) relative to 100 parts by mass of the (meth)acrylic copolymer preferably has a lower limit of 10 parts by mass and an upper limit of 100 parts by mass. When the content of the tackifier resin (T2) is 10 parts by mass or more, the adhesive strength of the PSA layer can be further increased. When the content of the tackifier resin (T2) is 100 parts by mass or less, the PSA layer can be prevented from becoming too hard and losing its adhesive strength. The lower limit of the content of the tackifier resin (T2) is more preferably 15 parts by mass, and a more preferably upper limit is 60 parts by mass, an even more preferably upper limit is 50 parts by mass, and an even more preferably upper limit is 40 parts by mass.

[0100] From the viewpoint of further reducing contamination of the adherend by the pressure-sensitive adhesive tape, the pressure-sensitive adhesive layer preferably does not contain an organosilicon compound, or the content of the organosilicon compound in the pressure-sensitive adhesive layer is preferably 3.0 mass% or less. When the pressure-sensitive adhesive layer contains the organosilicon compound, the upper limit of the content is more preferably 1.0 mass%. It is particularly preferred that the pressure-sensitive adhesive layer does not contain the organosilicon compound.

[0101] The organosilicon compound is not particularly limited as long as it is an organic compound containing a silicon atom, and examples thereof include commercially available silicone-based adhesives, silane coupling agents, silicone oils, and the like.

[0102] The pressure-sensitive adhesive layer preferably further contains a curing agent. By containing a curing agent in the pressure-sensitive adhesive, the (meth)acrylic copolymer can form a structure crosslinked by chemical crosslinking, thereby further improving the cohesive strength of the bulk of the pressure-sensitive adhesive layer and increasing the gel fraction of the pressure-sensitive adhesive layer, which will be described later, thereby further improving the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape.

[0103] Examples of the curing agent include an isocyanate-based curing agent, an aziridine-based curing agent, an epoxy-based curing agent, a metal chelate-based curing agent, etc. Among these, it is preferable that the pressure-sensitive adhesive layer contains an isocyanate-based curing agent, from the viewpoint of enabling appropriate chemical crosslinking of the (meth)acrylic copolymer and further improving the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape.

[0104] Examples of the isocyanate curing agent include Coronate L-45 (manufactured by Tosoh Corporation), Takenate 500 (manufactured by Mitsui Chemicals, Inc.), and Desmodur L-75 (manufactured by Covestro).

[0105] The content of the curing agent relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 0.01 parts by mass at the lower limit and 10 parts by mass at the upper limit. By having the content of the curing agent within the above range, appropriate chemical crosslinking of the (meth)acrylic copolymer is possible, and the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape are further improved. The lower limit of the content of the curing agent is more preferably 0.1 parts by mass, more preferably 5 parts by mass at the upper limit, even more preferably 0.5 parts by mass at the lower limit, and even more preferably 2.0 parts by mass at the upper limit.

[0106] In the pressure-sensitive adhesive tape of the first invention, the pressure-sensitive adhesive layer preferably contains at least one selected from the group consisting of a light stabilizer and an ultraviolet absorber (hereinafter, sometimes simply referred to as a "light stabilizer or ultraviolet absorber"). When the pressure-sensitive adhesive layer contains a light stabilizer or an ultraviolet absorber, the pressure-sensitive adhesive tape of the first invention has excellent light resistance (particularly ultraviolet resistance) and can suppress deterioration due to light irradiation. This makes the pressure-sensitive adhesive tape of the first invention more suitable for use in, for example, fixing displays, optical components, outdoor members, etc., and particularly for fixing solar cells or solar cell components. Furthermore, in the pressure-sensitive adhesive tape of the second invention, the pressure-sensitive adhesive layer contains at least one selected from the group consisting of a light stabilizer and an ultraviolet absorber. Since the pressure-sensitive adhesive layer contains a light stabilizer and an ultraviolet absorber, the pressure-sensitive adhesive tape of present invention 2 has excellent light resistance (particularly ultraviolet resistance) and can further suppress deterioration due to light irradiation. Therefore, the pressure-sensitive adhesive tape of present invention 2 can be suitably used for fixing, for example, displays, optical components, outdoor members, etc., and can be particularly suitably used for fixing solar cells or solar cell components.

[0107] The light stabilizer traps radicals generated by light irradiation, and thus can trap radicals derived from components in the pressure-sensitive adhesive layer generated by light irradiation, thereby suppressing deterioration of the pressure-sensitive adhesive tape. The light stabilizer is not particularly limited as long as it traps radicals generated in the pressure-sensitive adhesive layer by light irradiation or the like, and examples thereof include hindered amine light stabilizers, hindered phenol light stabilizers, etc. Among these, hindered amine light stabilizers are preferred from the viewpoint of long-term reliability.

[0108] Specific examples of the hindered amine light stabilizer include Tinuvin 123, Tinuvin 144, Tinuvin 152, Tinuvin 249, and Tinuvin 292 (all manufactured by BASF).

[0109] The ultraviolet absorber absorbs the irradiated ultraviolet light, thereby suppressing the generation of radicals derived from the components in the pressure-sensitive adhesive layer that are generated by the irradiation of ultraviolet light, and therefore can suppress the deterioration of the pressure-sensitive adhesive tape. Examples of the ultraviolet absorber include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. Among these, benzotriazole-based ultraviolet absorbers are preferred from the viewpoint of compatibility with the (meth)acrylic copolymer.

[0110] Specific examples of the benzotriazole-based ultraviolet absorbers include Tinuvin 384-2, Tinuvin 900, and Tinuvin 928 (all manufactured by BASF).

[0111] The content of the light stabilizer or UV absorber relative to 100 parts by mass of the (meth)acrylic copolymer preferably has a lower limit of 0.1 parts by mass and an upper limit of 10 parts by mass. When the content of the light stabilizer or UV absorber is 0.1 parts by mass or more, the pressure-sensitive adhesive tape of the present invention has superior light resistance and can further suppress deterioration due to light irradiation. When the content of the light stabilizer or UV absorber is 10 parts by mass or less, the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape are further improved. The lower limit of the content of the light stabilizer or UV absorber is more preferably 0.5 parts by mass, more preferably 7 parts by mass, even more preferably 1 part by mass, and even more preferably 5 parts by mass.

[0112] The pressure-sensitive adhesive layer may further contain a colorant for the purpose of imparting light-blocking properties. Examples of the colorant include carbon black, aniline black, titanium oxide, etc. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable.

[0113] The pressure-sensitive adhesive layer may contain conventionally known fine particles and additives, such as inorganic fine particles, conductive fine particles, antioxidants, foaming agents, organic fillers, and inorganic fillers, as needed.

[0114] In the pressure-sensitive adhesive tape of present invention 1, the loss tangent (tan δ) of the pressure-sensitive adhesive layer measured at a frequency of 10 Hz has a peak in a temperature range of -40°C or higher and lower than -20°C. When the loss tangent (tan δ) of the pressure-sensitive adhesive layer measured at a frequency of 10 Hz has a peak in a temperature range of -40°C or higher, the resulting pressure-sensitive adhesive tape of present invention 1 has excellent adhesive strength. Furthermore, when the loss tangent (tan δ) of the pressure-sensitive adhesive layer measured at a frequency of 10 Hz has a peak in a temperature range of less than -20°C, the zipping phenomenon that occurs when peeling off the film protecting the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of present invention 1 can be suppressed, and the pressure-sensitive adhesive tape of present invention 1 can be used without losing adhesive strength. Furthermore, when the loss tangent (tan δ) of the pressure-sensitive adhesive layer measured at a frequency of 10 Hz has a peak in a temperature range of less than -20°C, the pressure-sensitive adhesive tape of present invention 1 has excellent adhesive strength even to adherends with low polarity, such as fluororesins. The pressure-sensitive adhesive layer preferably has a peak temperature at which the loss tangent measured at a frequency of 10 Hz reaches a peak (hereinafter sometimes simply referred to as "peak temperature of loss tangent") of -35°C as its lower limit, and a preferred upper limit of -22°C as its upper limit, more preferably -30°C as its lower limit, and more preferably -24°C as its upper limit. In the pressure-sensitive adhesive tape of present invention 2, the pressure-sensitive adhesive layer preferably has a peak loss tangent (tan δ) measured at a frequency of 10 Hz in a temperature range of -40°C or higher and lower than -20°C. When the pressure-sensitive adhesive layer has a peak loss tangent (tan δ) measured at a frequency of 10 Hz in a temperature range of -40°C or higher, the resulting pressure-sensitive adhesive tape of present invention 2 has superior adhesive strength. When the pressure-sensitive adhesive layer has a peak loss tangent (tan δ) measured at a frequency of 10 Hz in a temperature range of lower than -20°C, the pressure-sensitive adhesive tape of present invention 2 can be prevented from experiencing a zipping phenomenon that occurs when peeling off a film that protects the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of present invention 2. Furthermore, since the loss tangent (tan δ) of the pressure-sensitive adhesive layer measured at a frequency of 10 Hz has a peak in a temperature region of less than −20° C., the pressure-sensitive adhesive tape of invention 2 has excellent adhesive strength even to adherends with low polarity, such as fluororesins.The pressure-sensitive adhesive layer has a peak temperature at which the loss tangent measured at a frequency of 10 Hz reaches a peak. A more preferred lower limit is -35°C, a more preferred upper limit is -22°C, an even more preferred lower limit is -30°C, and an even more preferred upper limit is -24°C.

[0115] The pressure-sensitive adhesive layer has a shear storage modulus (G') measured at 25°C and a frequency of 10 Hz (hereinafter, sometimes simply referred to as "shear storage modulus") of preferably 1.0 x 10 ４ Pa, and the preferred upper limit is 5.0 × 10 ５ When the shear storage modulus of the pressure-sensitive adhesive layer is within the above range, the resulting pressure-sensitive adhesive tape has superior adhesive strength and holding performance. A more preferable lower limit of the shear storage modulus of the pressure-sensitive adhesive layer is 3.0 × 10 ４ Pa, and a more preferable upper limit is 4.0 × 10 ５ Pa, and a more preferable lower limit is 5.0 × 10 ４ Pa, and a more preferable upper limit is 3.5×10 ５ It is Pa.

[0116] The peak temperature of the loss tangent and the shear storage modulus of the pressure-sensitive adhesive layer can be measured by dynamic viscoelasticity measurement. Specifically, a measurement sample consisting of only the pressure-sensitive adhesive layer is prepared by laminating a pressure-sensitive adhesive layer to a thickness of 1 mm, and the shear storage modulus of the pressure-sensitive adhesive layer can be measured by measuring the dynamic viscoelasticity spectrum of the obtained measurement sample from -50°C to 200°C using a dynamic viscoelasticity measurement device such as a viscoelasticity spectrometer (manufactured by IT Measurement & Control Co., Ltd., "DVA-200", etc.) under conditions of shear mode, a heating rate of 5°C / min, and a measurement frequency of 10 Hz. Furthermore, the peak temperature of the loss tangent of the pressure-sensitive adhesive layer can be obtained from the dynamic viscoelasticity spectrum obtained at this time.

[0117] The loss tangent (tan δ) measured at a frequency of 10 Hz and the shear storage modulus measured at a frequency of 10 Hz at 25°C of the pressure-sensitive adhesive layer can be adjusted by changing the type of alkyl (meth)acrylate monomer constituting the (meth)acrylic copolymer, increasing or decreasing the content ratio of the polar functional group-containing monomer constituting the (meth)acrylic copolymer, increasing or decreasing the weight average molecular weight of the (meth)acrylic copolymer, increasing or decreasing the weight average molecular weight of the (meth)acrylic copolymer, the presence or absence of the tackifier resin (T2), changing the types of the tackifier resin (T1) and the tackifier resin (T2) to those with different softening points or hydroxyl values, increasing or decreasing the contents of the tackifier resin (T1) and the tackifier resin (T2), increasing or decreasing the gel fraction of the pressure-sensitive adhesive layer described below, and the like.

[0118] The preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 5% by mass, and the preferred upper limit is 50% by mass. A gel fraction of the pressure-sensitive adhesive layer of 5% by mass or more increases the bulk strength of the pressure-sensitive adhesive layer, further improving the adhesive strength and holding performance of the resulting pressure-sensitive adhesive tape. A gel fraction of the pressure-sensitive adhesive layer of 50% by mass or less improves the interfacial wettability of the pressure-sensitive adhesive layer, thereby preventing interfacial peeling. A more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 10% by mass, a more preferred upper limit is 45% by mass, an even more preferred lower limit is 20% by mass, and an even more preferred upper limit is 40% by mass. The gel fraction of the pressure-sensitive adhesive layer can be measured by the following method. A pressure-sensitive adhesive tape is cut into a 50 mm x 100 mm flat rectangular shape to prepare a test specimen. The test specimen is immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate, and dried at 110°C for 1 hour. The mass of the dried test specimen is measured, and the gel fraction is calculated using the following formula (1): The test piece is not laminated with a release film to protect the adhesive layer. ０ = 0. Gel fraction (mass%) = 100 × (W ２ -W ０ ) / (W １ -W ０ ) (1) (W ０ : Mass of the substrate, W １: mass of test piece before immersion, W ２ : Mass of test piece after immersion and drying)

[0119] The gel fraction of the pressure-sensitive adhesive layer can be adjusted to within the above range by, for example, adjusting the type and content ratio of the monomers constituting the (meth)acrylic copolymer, the weight average molecular weight of the (meth)acrylic copolymer, the type and content of the curing agent, etc.

[0120] The thickness of the pressure-sensitive adhesive layer preferably has a lower limit of 20 μm and an upper limit of 100 μm. If the thickness of the pressure-sensitive adhesive layer is within this range, the pressure-sensitive adhesive layer can have sufficient adhesive strength. A more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 25 μm and a more preferred upper limit is 80 μm. The thickness of the pressure-sensitive adhesive layer can be measured using a dial thickness meter (such as the "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation).

[0121] The pressure-sensitive adhesive tape of the present invention may be a non-support type having no substrate, or a supported type having a substrate, but it is preferable that the pressure-sensitive adhesive tape of the present invention has a substrate. When the pressure-sensitive adhesive tape of the present invention has a substrate, the pressure-sensitive adhesive tape has excellent handleability. When the pressure-sensitive adhesive tape of the present invention has a substrate, the pressure-sensitive adhesive layer may be laminated on one side of the substrate, or on both sides of the substrate.

[0122] Examples of the substrate include resin films. The resin film is not particularly limited, and examples include polyolefin resin films such as polyethylene film and polypropylene film, polyester resin films such as polyethylene terephthalate (PET) film, ethylene-vinyl acetate copolymer films, polyvinyl chloride resin films, polyurethane resin films, and resin films containing fluororesins. Other examples of the substrate include polyolefin foam sheets such as polyethylene foam sheets and polypropylene foam sheets, and polyurethane foam sheets. Of these, resin films containing fluororesins are preferred. By including a resin film containing fluororesin in the substrate, bonding of the fluororesin to dissimilar materials using an adhesive tape becomes easier. Examples of the resin film containing fluororesin include resin films containing a copolymer having structural units derived from tetrafluoroethylene.

[0123] The thickness of the substrate is preferably 5 μm at the lower limit and 30 μm at the upper limit. When the thickness of the substrate is within the above range, the pressure-sensitive adhesive tape of the present invention has excellent handleability and sufficient adhesive strength. The thickness of the substrate is more preferably 8 μm at the lower limit and 20 μm at the upper limit.

[0124] The pressure-sensitive adhesive tape of the present invention may have layers other than the pressure-sensitive adhesive layer and the substrate, if necessary.

[0125] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited. For example, when the pressure-sensitive adhesive layers are laminated on both sides of the substrate, the following method can be used. First, a solution of pressure-sensitive adhesive A is prepared by adding a solvent to a (meth)acrylic copolymer, a tackifier resin (T1), a tackifier resin (T2), a curing agent, etc., and the solution of pressure-sensitive adhesive A is applied to the surface of the substrate. The solvent in the solution is completely dried and removed to form pressure-sensitive adhesive layer A. Next, a release film is superimposed on the formed pressure-sensitive adhesive layer A with its release-treated surface facing pressure-sensitive adhesive layer A. Next, a release film separate from the release film is prepared, and a solution of pressure-sensitive adhesive B is applied to the release-treated surface of this release film. The solvent in the solution is completely dried and removed to produce a laminate film in which pressure-sensitive adhesive layer B is formed on the surface of the release film. The obtained laminate film is superimposed on the back surface of the substrate on which pressure-sensitive adhesive layer A has been formed, with the pressure-sensitive adhesive layer B facing the back surface of the substrate, to produce a laminate. The laminate is then pressed with a rubber roller or the like. This makes it possible to obtain a double-sided adhesive tape having adhesive layers on both sides of the substrate, with the surfaces of the adhesive layers covered with release films.

[0126] Alternatively, two sets of laminate films may be prepared in a similar manner, and these laminate films may be superimposed on both sides of a substrate with the pressure-sensitive adhesive layers of the laminate films facing the substrate to prepare a laminate, which may then be pressed with a rubber roller, etc. This makes it possible to obtain a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of the substrate, the surfaces of which are covered with release films.

[0127] The pressure-sensitive adhesive tape of the present invention has a preferred lower limit of light transmittance at a wavelength of 550 nm of 85%. A light transmittance of 85% or more at a wavelength of 550 nm makes it possible to fix components without impairing the color development of displays or the performance of optical components. Furthermore, since sunlight is efficiently absorbed by the battery cell, the tape is more suitable for fixing solar cells or components such as solar cells. A more preferred lower limit of the light transmittance at a wavelength of 550 nm is 90%, and an even more preferred lower limit is 95%. There is no particular preferred upper limit for the light transmittance at a wavelength of 550 nm, and a higher value is preferable. The light transmittance at a wavelength of 550 nm of the pressure-sensitive adhesive tape of the present invention can be measured for the pressure-sensitive adhesive tape in accordance with JIS K 7136:2000 using a haze meter (e.g., "NDH 400" manufactured by Nippon Denshoku Industries Co., Ltd.). Furthermore, when the pressure-sensitive adhesive tape has a substrate, the light transmittance of the entire pressure-sensitive adhesive tape, including the substrate, is measured.

[0128] Methods for adjusting the light transmittance of the pressure-sensitive adhesive tape of the present invention at a wavelength of 550 nm within the above range include adding the above ultraviolet absorbents and using a substrate with good ultraviolet absorption properties.

[0129] The pressure-sensitive adhesive tape of the present invention preferably has an upper limit of the haze value of 3%. When the pressure-sensitive adhesive tape of the present invention has a haze value of 3% or less, it is possible to fix components without impairing the color development of displays or the performance of optical components. Furthermore, since sunlight is efficiently absorbed by the battery cell, it is more suitable for use in fixing solar cells and other components. A more preferred upper limit of the haze value is 2%, and an even more preferred upper limit is 1%. There is no particular preferred lower limit for the haze value, and the lower the haze value, the better. The haze value of the pressure-sensitive adhesive tape of the present invention can be measured for the pressure-sensitive adhesive tape in accordance with JIS K 7136:0000 using a haze meter (such as "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.). Furthermore, when the pressure-sensitive adhesive tape has a substrate, the haze value of the entire pressure-sensitive adhesive tape, including the substrate, is measured.

[0130] As a method for adjusting the haze value of the pressure-sensitive adhesive tape of the present invention to fall within the above range, a method using a tackifier resin that has good compatibility with the (meth)acrylic copolymer may be mentioned.

[0131] The uses of the pressure-sensitive adhesive tape of the present invention are not particularly limited. However, since the tape has high adhesive strength even to adherends with low polarity (e.g., poorly adhesive adherends such as adherends made of polyolefin resins or fluororesins), it is suitable for use, for example, in fixing electronic device components or vehicle-mounted components. More specifically, it is suitable for use, for example, in fixing components in televisions, monitors, portable electronic devices, vehicle-mounted electronic devices, etc. In particular, since the pressure-sensitive adhesive tape of the present invention has high adhesive strength to fluororesins, it is suitable for use in bonding fluororesins to electronic device components or vehicle-mounted components, or for fixing fluororesins-containing components such as solar cells or solar cell components. Furthermore, when a substrate containing fluororesins is used, it can also be suitable for use as a covering material for electronic device components or a building material. Furthermore, when the pressure-sensitive adhesive tape of the present invention has excellent light resistance, it can be more suitable for use, for example, in fixing displays, optical components, outdoor components, etc., and particularly for fixing solar cells or solar cell components, and even more suitable for fixing the front sheet or back sheet of a film-type solar cell.

[0132] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has high adhesive strength to fluororesin, excellent holding performance, and is capable of reducing contamination of an adherend.

[0133] FIG. 1 is a schematic diagram showing a method for a retention test.

[0134] The following examples will explain the present invention in more detail, but the present invention is not limited to these examples.

[0135] (Preparation of Acrylic Copolymer) (Synthesis Example 1) 100 parts by mass of ethyl acetate was placed in a reactor equipped with a thermometer, a stirrer, and a condenser. The atmosphere was replaced with nitrogen, and the reactor was heated to initiate reflux. 30 minutes after the ethyl acetate boiled, 0.08 parts by mass of azobisisobutyronitrile was added as a polymerization initiator. The monomer mixture shown in Table 1 was added dropwise evenly and gradually over 1 hour and 30 minutes to allow the reaction to proceed. 30 minutes after the dropwise addition was completed, 0.1 parts by mass of azobisisobutyronitrile was added, and the polymerization reaction was continued for another 5 hours. Ethyl acetate was added to the reactor to dilute the mixture while cooling, yielding an acrylic copolymer solution with a solids content of 25% by mass. The resulting acrylic copolymer solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The obtained filtrate was supplied to a gel permeation chromatograph (Waters, 2690 Separations Module), and GPC measurement was performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the acrylic copolymer was measured, and the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined. A GPC KF-806L (Showa Denko KK) was used as the column, and a differential refractometer was used as the detector. The results are shown in Table 1.

[0136] (Synthesis Examples 2 to 13) Acrylic copolymers were obtained in the same manner as in Synthesis Example 1, except that the monomer mixture was changed as shown in Table 1. The results are shown in Table 1.

[0137] The structural unit monomers shown in Table 1 are as follows: BA: n-butyl acrylate, 2EHA: 2-ethylhexyl acrylate, nHA: n-heptyl acrylate, HEA: 2-hydroxyethyl acrylate, Aac: acrylic acid.

[0138]

[0139] (Preparation of Tackifier Resin (T1)) (Synthesis Example A) 50 parts by mass of toluene was placed in a reactor equipped with a thermometer, a stirrer, and a condenser, and the atmosphere was replaced with nitrogen. The reactor was then heated to initiate reflux. After 30 minutes, aluminum chloride (AlCl) was added to the toluene while maintaining the temperature at 75°C. ３2 parts by mass of catechol (pyrocatechol) (n=2) and α-pinene (50 parts by mass in total, the molar ratio is as shown in Table 2) dissolved in 50 parts by mass of toluene was gradually added dropwise to the reactor over 1 hour and 30 minutes to allow the reaction to proceed. After the polymerization reaction had continued for 4 hours, the reactor was cooled while 0.1 parts by mass of pyridine was added to the reactor, and aluminum chloride (AlCl ３ The hydrochloric acid generated from the reaction mixture was neutralized. The precipitate formed by the neutralization was filtered, and the obtained filtrate was subjected to a liquid separation operation. Then, the toluene was evaporated to obtain a solid tackifier resin (T1). Regarding the obtained tackifier resin (T1), １ H-NMR measurement was performed to confirm that the tackifier resin (T1) was a copolymer having a structural unit (A) derived from catechol (pyrocatechol) and a structural unit (B) derived from α-pinene (a copolymer having the structural unit (A) in the main chain skeleton or at the end of the main chain skeleton). A solution of the obtained tackifier resin (T1) dissolved in tetrahydrofuran was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The obtained filtrate was supplied to a gel permeation chromatograph (Waters, 2690 Separations Module), and GPC measurement was performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40 °C. The polystyrene-equivalent molecular weight of the tackifier resin (T1) was measured, and the weight average molecular weight (Mw) was determined. A GPC KF-802.5L (Showa Denko KK) was used as the column, and a differential refractometer was used as the detector. The results are shown in Table 2.

[0140] (Measurement of Bio-derived Carbon Content of Tackifier Resin (T1)) The bio-derived carbon content of the obtained tackifier resin (T1) was measured in accordance with ASTM D6866-22. The results are shown in Table 2.

[0141] (Synthesis Examples B to D and F to I) Tackifier resins (T1) were obtained and measurements were carried out in the same manner as in Synthesis Example A above, except that in "(Preparation of tackifier resin (T1))", the monomers were changed as shown in Table 2. The results are shown in Table 2.

[0142] Synthesis Example E Preparation of Tackifier Resin (T1) 50 parts by mass of toluene was placed in a reactor equipped with a thermometer, a stirrer, and a condenser, and the atmosphere was replaced with nitrogen. The reactor was then heated to initiate reflux. After 30 minutes, aluminum chloride (AlCl) was added to the toluene while maintaining the temperature at 75°C. ３ 2 parts by mass of 4-vinylbenzoic acid (m=1) and α-pinene (70 parts by mass in total, the molar ratio is as shown in Table 2) dissolved in 50 parts by mass of toluene was gradually added dropwise to the reactor over 1 hour and 30 minutes to allow the reaction to proceed. After the polymerization reaction had been carried out for 4 hours, the reactor was cooled while 0.1 parts by mass of pyridine was added to the reactor, and aluminum chloride (AlCl ３ The hydrochloric acid generated from the reaction mixture was neutralized. The precipitate formed by the neutralization was filtered, and the obtained filtrate was subjected to a liquid separation operation. Then, the toluene was evaporated to obtain a solid tackifier resin (T1). Regarding the obtained tackifier resin (T1), ｌ H-NMR measurement was performed to confirm that the tackifier resin (T1) was a copolymer having a structural unit (A) derived from 4-vinylbenzoic acid and a structural unit (B) derived from α-pinene (a copolymer having the structural unit (A) in its side chain). A solution of the obtained tackifier resin (T1) dissolved in tetrahydrofuran was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The obtained filtrate was supplied to a gel permeation chromatograph (Waters, 2690 Separations Module), and GPC measurement was performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the tackifier resin (T1) was measured, and the weight average molecular weight (Mw) was determined. A GPC KF-802.5L (Showa Denko KK) was used as the column, and a differential refractometer was used as the detector. The results are shown in Table 2.

[0143] (Measurement of Bio-derived Carbon Content of Tackifier Resin (T1)) The bio-derived carbon content of the obtained tackifier resin (T1) was measured in accordance with ASTM D6866-22. The results are shown in Table 2.

[0144]

[0145] Example 1 (1) Preparation of Adhesive Tape 10 parts by mass of tackifier resin (T1) (Synthesis Example A) was added to 100 parts by mass of the solid content of the acrylic copolymer (Synthesis Example 1). Furthermore, 30 parts by mass of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.) and 0.5 parts by mass of an isocyanate-based curing agent (manufactured by Tosoh Corporation, "Coronate L45") were added and stirred to obtain an adhesive solution. A 150 μm-thick release film was prepared, and the solution of the adhesive composition was applied to the release-treated surface of this release film. This was dried at 100°C for 5 minutes to form a 50 μm-thick adhesive layer. A 150 μm-thick release PET film was then prepared and placed on the adhesive layer with the release-treated surface. The film was then heated at 40°C for 48 hours to cure. This resulted in an adhesive tape in which the surface of the adhesive layer was covered with the release PET film.

[0146] (2) Measurement of the peak temperature of the loss tangent (tan δ) measured at a frequency of 10 Hz on the pressure-sensitive adhesive layer A measurement sample consisting of only the pressure-sensitive adhesive layer was prepared by laminating a pressure-sensitive adhesive layer to a thickness of 1 mm. The dynamic viscoelasticity spectrum of the obtained measurement sample was measured from -100°C to 200°C using a viscoelasticity spectrometer (manufactured by IT Measurement & Control Co., Ltd., "DVA-200") under conditions of shear mode, a heating rate of 5°C / min, and a measurement frequency of 10 Hz, and the peak temperature (°C) of the loss tangent (tan δ) was obtained from the obtained dynamic viscoelasticity spectrum. The results are shown in Table 3.

[0147] (3) Measurement of shear storage modulus of pressure-sensitive adhesive layer measured at 25°C and a frequency of 10 Hz A measurement sample consisting of only the pressure-sensitive adhesive layer was prepared by laminating a pressure-sensitive adhesive layer to a thickness of 1 mm. The dynamic viscoelastic spectrum of the obtained measurement sample was measured from -50°C to 200°C using a viscoelasticity spectrometer (manufactured by IT Measurement & Control Co., Ltd., "DVA-200") under conditions of shear mode, heating rate of 5°C / min, and measurement frequency of 10 Hz, and the storage modulus at 25°C was measured. The results are shown in Table 3.

[0148] (4) Measurement of gel fraction of pressure-sensitive adhesive layer A test piece was prepared by cutting the pressure-sensitive adhesive tape into a flat rectangular shape of 50 mm x 100 mm. The test piece was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The mass of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1). Note that no release film for protecting the pressure-sensitive adhesive layer was laminated on the test piece. The results are shown in Table 3. Gel fraction (mass%) = 100 x (W ２ -W ０ ) / (W １ -W ０ ) (1) (W ０ : Mass of the substrate, W １ : mass of test piece before immersion, W ２ : Mass of test piece after immersion and drying)

[0149] (5) Measurement of Light Transmittance of Pressure-Sensitive Adhesive Tape at a Wavelength of 550 nm The light transmittance (%) of the pressure-sensitive adhesive tape at a wavelength of 550 nm was measured using a spectroscopic haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., "SH 7000") in accordance with JIS K 7375: 2008. The results are shown in Tables 3 to 5.

[0150] (6) Measurement of Haze Value of Pressure-Sensitive Adhesive Tape The haze value (%) of the obtained pressure-sensitive adhesive tape was measured using a haze meter ("SH 7000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7136: 2000. The results are shown in Tables 3 to 5.

[0151] (Examples 2 to 40, Comparative Examples 1 to 6) Pressure-sensitive adhesive tapes were prepared and measurements were carried out in the same manner as in Example 1, except that in the above-mentioned "(1) Preparation of Pressure-sensitive Adhesive Tapes", the compositions of the pressure-sensitive adhesive layers were changed as shown in Tables 3 to 5. The results are shown in Tables 3 to 5.

[0152] <Evaluation> The pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples were evaluated by the following methods. The results are shown in Tables 3 to 5.

[0153] (1) Adhesion to Fluorocarbon Resin The release PET film on one side (the side not measured) of the obtained pressure-sensitive adhesive tape was peeled off, and the surface of the exposed pressure-sensitive adhesive layer was backed with a 50 μm thick polyethylene terephthalate film (manufactured by Futamura Chemical Co., Ltd., "FE2002"), and then cut into a width of 25 mm and a length of 75 mm to prepare a test specimen. The release PET film of the obtained test specimen was peeled off, and the specimen was placed on an ethylene-tetrafluoroethylene (ETFE) plate (manufactured by Nippon Test Panel Co., Ltd.). Next, a 2 kg rubber roller was reciprocated once on the test specimen at a speed of 300 mm / min to press the test specimen and the ETFE plate together, and then the test specimen was left to stand at 23 ° C. for 1 hour to prepare a test sample. The obtained test samples were subjected to a 180° peel test in accordance with JIS Z0237 using a universal tensile tester (manufactured by A&D Co., Ltd., "Tensilon RTI-1310") under conditions of 23°C, 50% RH, and a peel rate of 300 mm / min. The adhesive tape was peeled from the ETFE plate, and the 180° peel strength (N / 25 mm) of the adhesive tape to the ETFE plate was measured. Using the obtained 180° peel strength (N / 25 mm), the adhesive strength of the adhesive tape to the fluororesin was evaluated according to the following criteria. ⊚: The 180° peel strength was 4.0 N / 25 mm or more. ○: The 180° peel strength was 3.0 N / 25 mm or more and less than 4.0 N / 25 mm. △: The 180° peel strength was 1.0 N / 25 mm or more and less than 3.0 N / 25 mm. ×: The 180° peel force was less than 1.0 N / 25 mm.

[0154] (2) Contamination of Adherend After the 180° peel test of the adhesive tape in the above-mentioned "(1) Adhesion to Fluoroplastics," the surface of the ETFE plate from which the adhesive tape had been peeled was measured using a scanning X-ray photoelectron spectrometer (manufactured by ULVAC-PHI, Inc., "PHI 5000 VersaProbe II") to measure the silicon atom concentration (at%) of the surface of the ETFE plate from which the adhesive tape had been peeled. XPS measurement was performed under the following conditions. <Measurement Conditions> X-ray source: Monochromated AlKα (1486.6 eV) Spectrometer: Electrostatic concentric hemispherical analyzer Photoelectron take-off angle: 45 degrees Charge neutralization: Yes X-ray beam diameter: 200 μm Pass energy: 117 eV Using the obtained silicon atom concentration (at%), contamination of the adherend by the adhesive tape was evaluated according to the following criteria. ○: The silicon atom concentration was 0.1 at% or less. Δ: The silicon atom concentration was greater than 0.1 at % and equal to or less than 1.0 at %. ×: The silicon atom concentration was greater than 1.0 at %.

[0155] (3) Holding Performance The obtained adhesive tape was cut into 25 mm wide strips and then bonded to a SUS plate (SUS304 plate washed with ethanol and then wiped dry) by rolling a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Next, an incision was made in the adhesive tape so that the adhesive area was 25 mm x 25 mm. The tape was then left to stand at 23°C for 20 minutes, placed in an oven at 80°C, and heated for another 20 minutes. A 1 kg weight was then hung from the tape and a load was applied in the shear direction under conditions of 80°C and 50% RH, as shown in Figure 1. One hour after applying the load, the amount of displacement (movement) (mm) from the incision position was measured with a scale magnifier. The obtained displacement (mm) was used to evaluate the holding performance of the adhesive tape according to the following criteria: ⊚: The displacement was 0.5 mm or less. ◯: The displacement was greater than 0.5 mm and 1.0 mm or less. Δ: The amount of deviation was greater than 1.0 mm and not greater than 2.0 mm. ×: The amount of deviation was greater than 2.0 mm.

[0156] (4) Light resistance The obtained pressure-sensitive adhesive tape was cut into a size of 5 cm wide and 10 cm long to prepare a test piece. After peeling off the release PET films on both sides of the prepared test piece, the exposed pressure-sensitive adhesive layer was subjected to light resistance testing using a xenon lamp accelerated weathering tester (manufactured by Iwasaki Electric Co., Ltd., "Xenon Tester XER-W83") with a xenon lamp (irradiation intensity 18.0 mW / cm ２ (wavelength: 300 nm to 400 nm)) for 500 hours. The pressure-sensitive adhesive layer irradiated with light for 500 hours was measured for light transmittance (%) at a wavelength of 550 nm through the pressure-sensitive adhesive tape using a spectroscopic haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., "SH 7000") in accordance with JIS K 7375:2008. Using the obtained light transmittance, the light resistance of the pressure-sensitive adhesive tape was evaluated according to the following criteria: ○: Light transmittance at a wavelength of 550 nm was 85% or more. ×: Light transmittance at a wavelength of 550 nm was less than 85%. Note that even if the evaluation is "×", the pressure-sensitive adhesive tape of the present invention can still be used without any problems depending on the application.

[0157]

[0158]

[0159]

[0160] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has high adhesive strength to fluororesin, excellent holding performance, and is capable of reducing contamination of an adherend.

[0161] 1. Adhesive tape 2. SUS304 plate 3. 1 kg weight

Claims

1. An adhesive tape having an adhesive layer, The pressure-sensitive adhesive layer comprises a (meth)acrylic copolymer, and a tackifier resin (T1) having at least one structural unit (A) selected from the group consisting of structural units (A-1), (A-1'), (A-2), (A-2'), (A-3), (A-3'), (A-4), and (A-4') represented by the following formulas: The pressure-sensitive adhesive layer has a peak in the loss tangent (tan δ) measured at a frequency of 10 Hz in a temperature range of −40° C. or higher and lower than −20° C. An adhesive tape characterized by: 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 In formulas (A-1) to (A-4) and formulas (A-1′) to (A-4′), R １ ~R ７ each represents a hydrogen atom, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a polar functional group, an aliphatic hydrocarbon group having a polar functional group, or an aromatic hydrocarbon group having a polar functional group. n and l each represent an integer of 2 or more and 4 or less, and n' and l' each represent an integer of 2 or more and 5 or less. m and k each represent an integer of 1 or more and 4 or less, and m' and k' each represent an integer of 1 or more and 5 or less. * represents a linking portion.

2. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the pressure-sensitive adhesive layer does not contain an organosilicon compound, or the content of the organosilicon compound in the pressure-sensitive adhesive layer is 3.0 mass % or less.

3. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate, and the alkyl (meth)acrylate includes an alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms at an ester terminal.

4. 4. The pressure-sensitive adhesive tape according to claim 3, wherein the alkyl(meth)acrylate having an alkyl group having 6 to 8 carbon atoms at the ester terminal includes n-heptyl(meth)acrylate.

5. The pressure-sensitive adhesive tape according to claim 3, wherein the (meth)acrylic copolymer contains 50% by mass or more and 99.99% by mass or less of structural units derived from alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms at an ester terminal.

6. 3. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer has a structural unit derived from a carboxy group-containing monomer, and the content of the structural unit derived from the carboxy group-containing monomer in the (meth)acrylic copolymer is 0.01 mass% or more and 3.0 mass% or less.

7. 3. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer has structural units derived from hydroxyl group-containing monomers, and the content of the structural units derived from hydroxyl group-containing monomers in the (meth)acrylic copolymer is 0.01 mass% or more and 3.0 mass% or less.

8. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer has a weight average molecular weight of 500,000 or more and 1,600,000 or less.

9. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the tackifier resin (T1) has a structural unit (B) derived from at least one monomer (b) selected from the group consisting of a terpene-based monomer, a vinyl-based monomer, and a conjugated diene-based monomer.

10. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the content of the tackifier resin (T1) is 5 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the (meth)acrylic copolymer.

11. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the pressure-sensitive adhesive layer further contains at least one tackifying resin (T2) selected from the group consisting of rosin ester resins, terpene resins, terpene phenol resins, and petroleum-based resins.

12. The adhesive tape according to claim 1 or 2, wherein the adhesive layer further contains a curing agent.

13. The adhesive tape according to claim 12, wherein the curing agent includes an isocyanate-based curing agent.

14. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the pressure-sensitive adhesive layer further contains at least one selected from the group consisting of a light stabilizer and an ultraviolet absorber.

15. An adhesive tape having an adhesive layer, The pressure-sensitive adhesive layer comprises a (meth)acrylic copolymer, a tackifier resin (T1) having at least one structural unit (A) selected from the group consisting of structural units (A-1), (A-1'), (A-2), (A-2'), (A-3), (A-3'), (A-4), and (A-4') represented by the following formulas; Contains at least one selected from the group consisting of a light stabilizer and an ultraviolet absorber. An adhesive tape characterized by: 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 In formulas (A-1) to (A-4) and formulas (A-1′) to (A-4′), R １ ~R ７ each represents a hydrogen atom, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a polar functional group, an aliphatic hydrocarbon group having a polar functional group, or an aromatic hydrocarbon group having a polar functional group. n and l each represent an integer of 2 or more and 4 or less, and n' and l' each represent an integer of 2 or more and 5 or less. m and k each represent an integer of 1 or more and 4 or less, and m' and k' each represent an integer of 1 or more and 5 or less. * represents a linking portion.

16. The pressure-sensitive adhesive layer has a shear storage modulus of 1.0×10 measured at 25° C. and a frequency of 10 Hz. ４ Pa or more 5.0×10 ５ The adhesive tape according to claim 1 or 15, wherein the viscosity is 0.05 Pa or less.

17. The pressure-sensitive adhesive tape according to claim 1 or 15, wherein the pressure-sensitive adhesive layer has a gel fraction of 5% by mass or more and 50% by mass or less.

18. The adhesive tape according to claim 1 or 15, which comprises a substrate.

19. The pressure-sensitive adhesive tape according to claim 18 , wherein the substrate comprises a resin film containing a fluororesin.

20. The adhesive tape according to claim 1 or 15, wherein the adhesive tape has a light transmittance of 85% or more at a wavelength of 550 nm.

21. The adhesive tape according to claim 1 or 15, wherein the adhesive tape has a haze value of 3% or less.

22. The pressure-sensitive adhesive tape according to claim 1 or 15, which is used for fixing a solar cell or a solar cell component.

23. The pressure-sensitive adhesive tape according to claim 22, which is used to fix a front sheet or a back sheet of a film-type solar cell.

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