Pressure-sensitive adhesive agent composition and pressure-sensitive adhesive tape

Abstract

This pressure-sensitive adhesive agent composition contains an acrylic copolymer having a structural unit derived from a (meth)acrylic acid alkyl ester and a structural unit derived from an olefin-based polymer having a polymerizable unsaturated double bond at a terminal, and satisfies the following first compositional make-up and / or second compositional make-up.　First compositional make-up: Contained is at least one tackifying resin T1 selected from the group consisting of terpene phenol resins, hydrogenated terpene phenol resins, and xylene resins. The contained amount of T1 is 5-50 parts by mass. A tackifying resin T2 different from T1 is not contained, or when T2 is contained, the amount thereof is 10 parts by mass or less with respect to 100 parts by mass of the acrylic copolymer.　Second compositional make-up: The acrylic copolymer has a structural unit derived from a polar functional group-containing monomer, has, in an amount of 30-90 mass%, a structural unit derived from a (meth)acrylic acid alkyl ester in which an alkyl group bound to an oxygen atom of an ester bond has 1-4 carbon atoms, and does not contain a tackifying resin, or contains the tackifying resin at an amount of 5 parts by mass or less with respect to 100 parts by mass of the acrylic copolymer.

Description

Adhesive composition and adhesive tape

[0001] The present invention relates to a pressure-sensitive adhesive composition. The present invention also relates to a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition.

[0002] Adhesive tapes are used for assembly of portable electronic devices such as mobile phones and personal digital assistants (PDAs) (see, for example, Patent Documents 1 and 2), and also for bonding optical members (see, for example, Patent Document 3).

[0003] JP 2009-242541 A JP 2009-258274 A JP 2012-214544 A

[0004] Pressure-sensitive adhesive compositions and pressure-sensitive adhesive tapes used for fixing optical components are required to have both adhesive strength and optical transparency, and in particular, in recent years, with the miniaturization and thinning of electronic devices and devices, there has been a demand for thinner coating thicknesses of pressure-sensitive adhesive compositions and thinner pressure-sensitive adhesive tapes. However, when the coating thicknesses of conventional pressure-sensitive adhesive compositions and thinner thicknesses of pressure-sensitive adhesive tapes are reduced, sufficient adhesive strength cannot be exerted.

[0005] Furthermore, conventionally, adhesive strength has been improved by incorporating a tackifier resin into a pressure-sensitive adhesive composition or pressure-sensitive adhesive tape. However, when a pressure-sensitive adhesive composition or pressure-sensitive adhesive tape contains a tackifier resin, turbidity or yellowing occurs, and optical transparency may not be achieved.

[0006] An object of the present invention is to provide a pressure-sensitive adhesive composition that can achieve both excellent adhesive strength and excellent optical transparency even when applied to a thin thickness, and to provide a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition.

[0007] Disclosure 1 relates to a pressure-sensitive adhesive composition that contains an acrylic copolymer having a structural unit derived from a (meth)acrylic acid alkyl ester and a structural unit derived from an olefin-based polymer having a terminal polymerizable unsaturated double bond, and that satisfies at least one structural element selected from the group consisting of the following first structural element and the following second structural element: First structural element: The pressure-sensitive adhesive composition contains at least one tackifier resin T1 selected from the group consisting of a terpene phenolic resin, a hydrogenated terpene phenolic resin, and a xylene resin, and the content of the tackifier resin T1 is 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the acrylic copolymer, and does not contain a tackifier resin T2 that is different from the terpene phenolic resin, the hydrogenated terpene phenolic resin, and the xylene resin, or contains the tackifier resin T2, and if the tackifier resin T2 is contained, the content of the tackifier resin T2 is 10 parts by mass or less per 100 parts by mass of the acrylic copolymer.

[0014] Second configuration: the acrylic copolymer has structural units derived from polar functional group-containing monomers, the acrylic copolymer has structural units derived from (meth)acrylic acid alkyl esters in which the alkyl group bonded to the oxygen atom of the ester bond in the (meth)acrylic acid alkyl ester has 1 to 4 carbon atoms, the content of structural units derived from (meth)acrylic acid alkyl esters in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms in the acrylic copolymer is 30 to 90 mass%; the acrylic copolymer does not contain a tackifier resin, or contains a tackifier resin, and if a tackifier resin is contained, the content of the tackifier resin is 5 parts by mass or less per 100 parts by mass of the acrylic copolymer.

[0015] Disclosure 2 is the pressure-sensitive adhesive composition of Disclosure 1 in the first configuration, wherein the acrylic copolymer has structural units derived from polar functional group-containing monomers.

[0016] Disclosure 3 is the pressure-sensitive adhesive composition of Disclosure 1 or 2, wherein the structural units derived from the polar functional group-containing monomers include at least one structural unit selected from the group consisting of structural units derived from carboxy group-containing monomers and structural units derived from hydroxy group-containing monomers.

[0014] Disclosure 4 is the PSA composition of Disclosure 3, wherein the structural units derived from the polar functional group-containing monomer include structural units derived from the carboxy group-containing monomer. Disclosure 5 is the PSA composition of Disclosure 4, wherein, in the second configuration, the content of structural units derived from the carboxy group-containing monomer in the acrylic copolymer is 10% by mass or less. Disclosure 6 is the PSA composition of Disclosure 4 or 5, wherein the content of structural units derived from the carboxy group-containing monomer in the acrylic copolymer is 1% by mass or less. Disclosure 7 is the PSA composition of Disclosure 3, 4, 5, or 6, wherein the structural units derived from the polar functional group-containing monomer include structural units derived from the hydroxyl group-containing monomer. Disclosure 8 is the PSA composition of Disclosure 1, 2, 3, 4, 5, 6, or 7, wherein, in the first configuration, the tackifier resin T1 includes the hydrogenated terpene phenol resin. Disclosure 9 relates to the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, or 8, wherein, in the second configuration, the acrylic copolymer has structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 1 to 2, and the content of structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 10% by mass or more and 60% by mass or less. Disclosure 10 relates to the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein, in the second configuration, the acrylic copolymer has structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 3 to 4, and the content of structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 60% by mass or more. Disclosure 11 is a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. Disclosure 12 is the pressure-sensitive adhesive tape of Disclosure 11, wherein the pressure-sensitive adhesive layer has a gel fraction of 10% by mass or more and 80% by mass or less. Disclosure 13 is the pressure-sensitive adhesive tape of Disclosures 11 or 12, wherein the pressure-sensitive adhesive layer has a thickness of 15 μm or less.Disclosure 14 is the pressure-sensitive adhesive tape of Disclosure 13, which has a 180° peel strength from glass at 23°C of 9 N / inch or more after being left to stand at 23°C for 24 hours after application. Disclosure 15 is the pressure-sensitive adhesive tape of Disclosure 11, 12, 13, or 14, which has a haze of 1.0% or less at 23°C. Disclosure 16 is the pressure-sensitive adhesive tape of Disclosure 11, 12, 13, 14, or 15, which does not have a substrate. The present invention will be described in detail below. Note that matters common to the first and second configurations will be described as not being particularly specified.

[0008] The present inventors have studied the composition of a pressure-sensitive adhesive composition, and have included an acrylic copolymer having a specific structure. They have also studied the content and type of tackifier resin to be included in the pressure-sensitive adhesive composition. As a result, they have found that a pressure-sensitive adhesive composition can be obtained that can achieve both excellent adhesive strength and excellent optical transparency even when the applied thickness is thin, and have thus completed the present invention.

[0009] The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer having structural units derived from a (meth)acrylic acid alkyl ester and structural units derived from an olefin polymer having a terminal polymerizable unsaturated double bond. In this specification, "(meth)acrylic" refers to acrylic or methacrylic. The acrylic copolymer has a structure in which structural units derived from an olefin polymer having a terminal polymerizable unsaturated double bond aggregate through interaction to form pseudo-crosslinked points. When the acrylic copolymer has such a structure, the pressure-sensitive adhesive composition exhibits hard properties like a crosslinked pressure-sensitive adhesive composition when strain is small, improving holding power. On the other hand, when peel stress is applied and strain increases, the pseudo-crosslinks are broken and the molecules of the acrylic copolymer stretch, so the pressure-sensitive adhesive composition exhibits high flexibility and improving adhesive power. In other words, when the pressure-sensitive adhesive composition contains the acrylic copolymer, the adhesive power and holding power of the pressure-sensitive adhesive composition are improved.

[0010] Examples of the (meth)acrylic acid alkyl ester include (meth)acrylic acid alkyl esters obtained by dehydration condensation of (meth)acrylic acid with an alcohol having a linear or branched alkyl group having from 1 to 24 carbon atoms. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, n-heptyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n- Examples of the alkyl (meth)acrylate include octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate. These alkyl (meth)acrylates may be used alone or in combination of two or more.

[0011] In the acrylic copolymer, the content of the structural units derived from the (meth)acrylic acid alkyl ester is preferably 50% by mass at the lower limit and 95% by mass at the upper limit. By having the content of the structural units derived from the (meth)acrylic acid alkyl ester within the above range, the adhesive strength and holding power of the pressure-sensitive adhesive composition are further improved. The content of the structural units derived from the (meth)acrylic acid alkyl ester is more preferably 60% by mass at the lower limit, even more preferably 70% by mass at the lower limit, and more preferably 90% by mass at the upper limit, even more preferably 85% by mass at the upper limit.

[0012] The olefin polymer having a terminal polymerizable unsaturated double bond may have a polymerizable unsaturated double bond at one terminal or at both terminals. Among them, an olefin polymer having a terminal polymerizable unsaturated double bond is preferred from the viewpoint of facilitating the formation of an appropriate number of pseudo-crosslinks.

[0013] Examples of the olefin polymer having a polymerizable unsaturated double bond at its terminal include ethylene-butylene copolymers, ethylene-propylene copolymers, ethylene polymers, propylene polymers, butylene polymers, etc., which have a group having a polymerizable unsaturated double bond at one or both terminals. These olefin polymers having a polymerizable unsaturated double bond at their terminals may be used alone or in combination of two or more.

[0014] Examples of the group having a polymerizable unsaturated double bond include a (meth)acryloyl group, a vinyl ether group, a styryl group, etc. Among these, a (meth)acryloyl group is preferred because of its excellent copolymerizability with the (meth)acrylic acid alkyl ester.

[0015] Examples of olefin polymers having a (meth)acryloyl group at their termini include an ethylene macromonomer having a (meth)acryloyl group at one terminus, a propylene macromonomer having a (meth)acryloyl group at one terminus, an ethylene-butylene macromonomer having a (meth)acryloyl group at one terminus, and an ethylene-propylene macromonomer having a (meth)acryloyl group at one terminus. Of these, from the viewpoints of making it easier to adjust the glass transition temperature (described below) within an appropriate range and further improving the adhesive strength of the pressure-sensitive adhesive composition, an ethylene-butylene macromonomer having a (meth)acryloyl group at one terminus and an ethylene-propylene macromonomer having a (meth)acryloyl group at one terminus are preferred. In this specification, the term "macromonomer" refers to a monomer having a polymerizable functional group and a weight-average molecular weight of approximately 1,000 to 100,000.

[0016] In the acrylic copolymer, the content of the structural units derived from the olefin polymer having a terminal polymerizable unsaturated double bond is preferably 5% by mass at the lower limit, and preferably 30% by mass at the upper limit. When the content of the structural units derived from the olefin polymer having a terminal polymerizable unsaturated double bond is 5% by mass or more, an appropriate number of pseudo-crosslinks are formed in the acrylic copolymer, thereby further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. When the content of the structural units derived from the olefin polymer having a terminal polymerizable unsaturated double bond is 30% by mass or less, cohesive failure of the pressure-sensitive adhesive composition can be further suppressed. The content of the structural units derived from the olefin polymer having a terminal polymerizable unsaturated double bond is more preferably 8% by mass at the lower limit, even more preferably 10% by mass at the lower limit, and more preferably 27% by mass at the upper limit, even more preferably 25% by mass at the upper limit.

[0017] The pressure-sensitive adhesive composition of the present invention satisfies at least one constitution selected from the group consisting of the following first constitution and the following second constitution: First constitution: The pressure-sensitive adhesive composition contains at least one tackifier resin T1 selected from the group consisting of a terpene phenol resin, a hydrogenated terpene phenol resin, and a xylene resin, and the content of the tackifier resin T1 is 5 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the acrylic copolymer, and does not contain a tackifier resin T2 different from the terpene phenol resin, the hydrogenated terpene phenol resin, and the xylene resin, or contains the tackifier resin T2, and if it contains the tackifier resin T2, the content of the tackifier resin T2 is 10 parts by mass or less relative to 100 parts by mass of the acrylic copolymer. Second configuration: the acrylic copolymer has a structural unit derived from a polar functional group-containing monomer, the acrylic copolymer has a structural unit in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms, the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms in the acrylic copolymer is 30 to 90 mass% by mass, and the acrylic copolymer does not contain a tackifier resin, or contains a tackifier resin, and if it contains a tackifier resin, the content of the tackifier resin is 5 parts by mass or less per 100 parts by mass of the acrylic copolymer. When the pressure-sensitive adhesive composition of the present invention satisfies at least one configuration selected from the group consisting of the following first configuration and the following second configuration, it becomes possible to achieve both excellent adhesive strength and excellent optical transparency even when the thickness is thin.

[0018] In the first configuration, the acrylic copolymer preferably has a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 8 carbon atoms. When the acrylic copolymer has a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms, the polarity of the acrylic copolymer increases, and the interaction with the adherend is enhanced, thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. When the acrylic copolymer has a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 4 to 8 carbon atoms, the glass transition temperature (described below) can be easily adjusted within an appropriate range, and the adhesive strength of the pressure-sensitive adhesive composition is further improved. The structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 8 carbon atoms may be used alone or in combination of two or more types.

[0019] In the second configuration, the acrylic copolymer has a structural unit derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is from 1 to 4. When the acrylic copolymer has a structural unit derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is from 1 to 4, the polarity of the acrylic copolymer increases, and the interaction with the adherend increases, thereby improving the adhesive strength of the pressure-sensitive adhesive composition.

[0020] In the second configuration, the lower limit of the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms in the acrylic copolymer is 30% by mass, and the upper limit is 90% by mass. When the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms is 30% by mass or more, the polarity of the acrylic copolymer increases, enhancing the interaction with the adherend, thereby improving the adhesive strength of the pressure-sensitive adhesive composition. When the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms in the acrylic copolymer is 90% by mass or less, structural units derived from an olefin polymer having a terminal polymerizable unsaturated double bond can form pseudo-crosslinking points that provide high cohesive strength in the acrylic copolymer. As a result, the adhesive strength and holding power of the pressure-sensitive adhesive composition are improved. The lower limit of the content of structural units derived from a (meth)acrylic acid alkyl ester in which the number of carbon atoms in the alkyl group bonded to the oxygen atom of the ester bond is 1 or more and 4 or less is preferably 40 mass%, more preferably 50 mass%, and the upper limit is preferably 85 mass%, more preferably 80 mass%.

[0021] Examples of the alkyl (meth)acrylate ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms include alkyl (meth)acrylate esters obtained by dehydration condensation of (meth)acrylic acid with an alcohol having a linear or branched alkyl group having 1 to 4 carbon atoms. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, and isobutyl (meth)acrylate.

[0022] In the second configuration, from the viewpoint of adhesive strength of the pressure-sensitive adhesive composition, the acrylic copolymer preferably has structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 1 to 2. The preferred lower limit of the content of structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 10% by mass, and the preferred upper limit is 60% by mass. When the content of structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 10% by mass or more, the polarity of the acrylic copolymer is increased, and the interaction with the adherend is further enhanced, thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. When the content of structural units derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 60% by mass or less, the glass transition temperature (described later) of the acrylic copolymer can be easily adjusted to an appropriate range, thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. The lower limit of the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 2 carbon atoms is more preferably 15% by mass, and even more preferably 30% by mass.

[0023] In the second configuration, from the viewpoint of the optical transparency of the pressure-sensitive adhesive composition, the acrylic copolymer preferably contains structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 3 to 4 carbon atoms. In the acrylic copolymer, the preferred lower limit of the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 3 to 4 carbon atoms is 60% by mass. By having the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 3 to 4 carbon atoms being 60% by mass or more, pseudo-crosslinking points formed by aggregation of structural units derived from an olefin polymer having a terminal polymerizable unsaturated double bond become smaller, thereby further improving the optical transparency of the pressure-sensitive adhesive composition. A more preferred lower limit of the content of structural units derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 3 to 4 carbon atoms is 70% by mass, and an even more preferred lower limit is 75% by mass. Furthermore, the preferred upper limit of the content of structural units derived from (meth)acrylic acid alkyl esters in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 3 to 4 is 90% by mass. When the content of structural units derived from (meth)acrylic acid alkyl esters in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 90% by mass or less, the adhesive strength is further improved. A more preferred upper limit of the content of structural units derived from (meth)acrylic acid alkyl esters in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 85% by mass, and an even more preferred upper limit is 80% by mass.

[0024] In the second configuration, the structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 4 carbon atoms may be used alone, or two or more types may be used in combination. Among these, it is preferable to use a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 3 to 4 carbon atoms in combination with a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 2 carbon atoms. By using a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 3 to 4 carbon atoms, it becomes easier to adjust the glass transition temperature of the acrylic copolymer to within the range described below, and the adhesive strength of the pressure-sensitive adhesive composition is further improved. Furthermore, by using a structural unit derived from a (meth)acrylic acid alkyl ester in which the alkyl group bonded to the oxygen atom of the ester bond has 1 to 2 carbon atoms, the polarity of the acrylic copolymer is increased, and the interaction with the adherend is further enhanced, thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. In other words, by using in combination a structural unit derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 3 or more and 4 or less, and a structural unit derived from a (meth)acrylic acid alkyl ester in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 1 or more and 2 or less, the adhesive strength of the pressure-sensitive adhesive composition is further improved.

[0025] In the second configuration, the acrylic copolymer has a structural unit derived from a polar functional group-containing monomer. The acrylic copolymer has a structural unit derived from the polar functional group-containing monomer, which enhances interaction with the adherend, thereby improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. Furthermore, when the pressure-sensitive adhesive composition contains a crosslinking agent described below, the acrylic copolymer is crosslinked via the crosslinking agent, thereby improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. By adjusting the degree of crosslinking, the gel fraction of the pressure-sensitive adhesive layer described below can be adjusted within an appropriate range. Furthermore, in the first configuration, the acrylic copolymer preferably has a structural unit derived from a polar functional group-containing monomer. The acrylic copolymer has a structural unit derived from the polar functional group-containing monomer, which enhances interaction with the adherend, thereby further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. Furthermore, when the pressure-sensitive adhesive composition contains a crosslinking agent described below, the acrylic copolymer is crosslinked via the crosslinking agent, thereby further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. By adjusting the degree of crosslinking at this time, the gel fraction of the pressure-sensitive adhesive layer, which will be described later, can be adjusted to an appropriate range.

[0026] Examples of the polar functional group-containing monomer include carboxy group-containing monomers, hydroxy group-containing monomers, amide group-containing monomers, and amino group-containing monomers. In particular, from the viewpoint of further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition, it is preferable that the polar functional group-containing monomer contains at least one selected from the group consisting of carboxy group-containing monomers and hydroxy group-containing monomers. That is, it is preferable that the structural unit derived from the polar functional group-containing monomer contains at least one structural unit selected from the group consisting of structural units derived from carboxy group-containing monomers and structural units derived from hydroxy group-containing monomers. These polar functional group-containing monomers may be used alone, or two or more may be used in combination.

[0027] The acrylic copolymer has a structural unit derived from the carboxyl group-containing monomer, which enhances the interaction with the adherend, thereby further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. Examples of the carboxyl group-containing monomer include unsaturated carboxylic acids such as (meth)acrylic acid, (meth)acryloylacetic acid, (meth)acryloylpropionic acid, (meth)acryloylbutyric acid, (meth)acryloylpentanoic acid, crotonic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid.

[0028] In the first configuration, the preferred upper limit of the content of the structural units derived from the carboxyl group-containing monomer in the acrylic copolymer is 1% by mass. When the content of the structural units derived from the carboxyl group-containing monomer is 1% by mass or less, the metal corrosiveness of the pressure-sensitive adhesive composition is further reduced. A more preferred upper limit of the content of the structural units derived from the carboxyl group-containing monomer is 0.5% by mass. From the viewpoint of metal corrosiveness, it is preferable that the acrylic copolymer does not have structural units derived from the carboxyl group-containing monomer.

[0029] In the second configuration, the preferred upper limit of the content of the structural units derived from the carboxyl group-containing monomer in the acrylic copolymer is 10% by mass. When the content of the structural units derived from the carboxyl group-containing monomer is 10% by mass or less, the metal corrosiveness of the pressure-sensitive adhesive composition is further reduced. A more preferred upper limit of the content of the structural units derived from the carboxyl group-containing monomer is 1% by mass. From the viewpoint of metal corrosiveness, it is preferable that the acrylic copolymer does not have structural units derived from the carboxyl group-containing monomer.

[0030] The acrylic copolymer having a structural unit derived from the hydroxyl group-containing monomer facilitates crosslinking between the acrylic copolymer and the molecules of the adherend via the crosslinking agent, thereby improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. Examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate.

[0031] In the acrylic copolymer, the preferred lower limit of the content of the structural units derived from the hydroxyl group-containing monomer is 0.01% by mass, and the preferred upper limit is 2% by mass. When the content of the structural units derived from the hydroxyl group-containing monomer is 0.01% by mass or more, crosslinking of the acrylic copolymer via the crosslinking agent occurs more easily, and the adhesive strength and holding power of the pressure-sensitive adhesive composition are further improved. When the content of the structural units derived from the hydroxyl group-containing monomer is 2% by mass or less, the acrylic copolymer does not become too hard, and the adhesive strength of the pressure-sensitive adhesive composition is further improved. A more preferred lower limit of the content of the structural units derived from the hydroxyl group-containing monomer is 0.05% by mass, and a more preferred upper limit is 1% by mass.

[0032] Examples of the amide group-containing monomer include N-vinyl-2-pyrrolidone, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, and N-isopropyl(meth)acrylamide.

[0033] Examples of the amino group-containing monomer include (meth)acryloylmorpholine, 2-dimethylaminoethyl (meth)acrylate, and 2-diethylaminoethyl (meth)acrylate.

[0034] In the acrylic copolymer, the preferred lower limit of the total content of the structural units derived from the polar functional group-containing monomer is 0.1% by mass, and the preferred upper limit is 10% by mass. When the total content of the structural units derived from the polar functional group-containing monomer is 0.1% by mass or more, the interaction between the acrylic copolymer and the adherend is further enhanced, thereby further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. Furthermore, when the pressure-sensitive adhesive composition contains a crosslinking agent described below, crosslinking of the acrylic copolymer via the crosslinking agent occurs more easily, thereby further improving the adhesive strength and holding power of the pressure-sensitive adhesive composition. When the total content of the structural units derived from the polar functional group-containing monomer is 10% by mass or less, the acrylic copolymer does not become too hard, and the adhesive strength of the pressure-sensitive adhesive composition is further improved. A more preferred lower limit of the total content of the structural units derived from the polar functional group-containing monomer is 1% by mass, and even more preferred is 3% by mass, and a more preferred upper limit is 8% by mass, and even more preferred is 6% by mass.

[0035] The glass transition temperature (Tg) of the acrylic copolymer is preferably in the range of -100°C or higher and 200°C or lower, with a more preferred upper limit being -20°C. When the glass transition temperature of the acrylic copolymer is -20°C or lower, the molecules of the acrylic copolymer are more likely to stretch, thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. A more preferred upper limit of the glass transition temperature of the acrylic copolymer is -30°C, and an especially preferred upper limit is -35°C. Furthermore, when the pressure-sensitive adhesive composition contains a plurality of acrylic copolymers, it is preferred that the glass transition temperatures of all of the acrylic copolymers contained in the pressure-sensitive adhesive composition are -20°C or lower. The glass transition temperature of the acrylic copolymer can be measured by differential scanning calorimetry. More specifically, the glass transition temperature of the acrylic copolymer can be measured in a nitrogen atmosphere (nitrogen flow, flow rate 50 mL / min) using a differential scanning calorimeter (manufactured by Seiko Instruments Inc., "220C" or the like) according to a method in accordance with JIS K6240:2011 under conditions of a measurement temperature of -100°C to 200°C and a temperature rise rate of 10°C / min.

[0036] The glass transition temperature of the acrylic copolymer can be adjusted by the type and amount of the monomers that are the raw materials for the acrylic copolymer.

[0037] The weight-average molecular weight (Mw) of the acrylic copolymer preferably has a lower limit of 500,000 and a higher limit of 2,000,000. When the weight-average molecular weight of the acrylic copolymer is 500,000 or more, the bulk cohesive strength of the pressure-sensitive adhesive composition is increased, and the adhesive strength and heat resistance of the pressure-sensitive adhesive composition are further improved. When the weight-average molecular weight of the acrylic copolymer is 2,000,000 or less, the pressure-sensitive adhesive composition does not become too hard, and the adhesive strength is further improved. The weight-average molecular weight of the acrylic copolymer more preferably has a lower limit of 650,000 and a higher limit of 1,500,000.

[0038] The polydispersity of the acrylic copolymer preferably has a lower limit of 1.0 and a higher limit of 6.0. When the polydispersity of the acrylic copolymer is within the above range, the adhesive strength and holding power of the pressure-sensitive adhesive composition are further improved. The polydispersity of the acrylic copolymer more preferably has a lower limit of 1.5 and a higher limit of 4.5. The polydispersity refers to the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn).

[0039] In this specification, the weight average molecular weight, the number average molecular weight, and the polydispersity can be determined from the polystyrene-equivalent molecular weight distribution measured using gel permeation chromatography (GPC). Specifically, for example, they can be determined by measuring under the following conditions using gel permeation chromatography (Waters Corporation's "2690 Separations Module," etc.). Solvent: tetrahydrofuran Sample flow rate: 1 mL / min Detector: differential refractometer RI Column: GPC KF-806L (Showa Denko KK) Column temperature (measurement temperature): 40°C Injection volume: 20 μL

[0040] The content of the acrylic copolymer in the pressure-sensitive adhesive composition is not particularly limited, but is preferably greater than 50% by mass in the pressure-sensitive adhesive composition (i.e., the acrylic copolymer is the main component in the pressure-sensitive adhesive composition). When the content of the acrylic copolymer is greater than 50% by mass, the pressure-sensitive adhesive composition becomes more transparent, and the optical transparency of the pressure-sensitive adhesive composition is further improved.

[0041] In the first aspect, the pressure-sensitive adhesive composition of the present invention contains a tackifier resin T1. The tackifier resin T1 is at least one tackifier resin selected from the group consisting of terpene phenol resins, hydrogenated terpene phenol resins, and xylene resins. The tackifier resin T1 has relatively high polarity and good compatibility with the acrylic copolymer, and is therefore easily incorporated into the acrylic copolymer. As a result, the tackifier resin is prevented from inhibiting the formation of pseudo-crosslinking points due to interactions between structural units derived from the olefin polymer having a terminal polymerizable unsaturated double bond, which has low polarity. This improves the adhesive strength of the pressure-sensitive adhesive composition while maintaining the excellent adhesive strength of the acrylic copolymer. Furthermore, as described above, because the tackifier resin T1 is easily incorporated into the acrylic copolymer, the pressure-sensitive adhesive composition can be prevented from becoming cloudy and exhibit excellent optical transparency. Furthermore, because the tackifier resin T1 does not have a polymerizable unsaturated double bond in its molecular structure and is resistant to oxidation, the pressure-sensitive adhesive composition can be prevented from yellowing and is less likely to lose its optical transparency even after long-term use. The tackifier resin T1 may be used alone or in combination of two or more kinds.

[0042] The tackifier resin T1 preferably contains at least one selected from the group consisting of the terpene phenol resin and the hydrogenated terpene phenol resin. When the tackifier resin T1 contains at least one selected from the group consisting of the terpene phenol resin and the hydrogenated terpene phenol resin, the tackifier resin T1 has a hydroxyl group, which enhances the interaction with the adherend, thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. Among these, the hydrogenated terpene phenol resin is more preferred from the viewpoint of the resin having a light color and excellent optical transparency.

[0043] The terpene phenolic resin is a resin obtained by polymerizing a terpene compound in the presence of a phenolic compound. Examples of the phenolic compound include phenol, cresol, xylenol, propylphenol, norylphenol, methoxyphenol, bromophenol, bisphenol A, bisphenol F, bisphenol S, dihydroxynaphthalene, resorcinol, pyrocatechol, hydroquinone, pyrogallol, 1,2,4-trihydroxybenzene, and phloroglucinol. Examples of the terpene compound include α-pinene, β-pinene, limonene, dipentene, δ-3-carene, dimethyloctatriene, alloocimene, myrcene, ocimene, linalool, and cosmene. Furthermore, other compounds may be polymerized within the terpene phenolic resin. The phenolic compound, terpene compound, and other compounds may be used alone or in combination of two or more.

[0044] The terpene phenol resin may be a commercially available product, and examples of the commercially available product include YS Polystar G150 (manufactured by Yasuhara Chemical Co., Ltd.).

[0045] The hydrogenated terpene phenolic resin is a resin in which unsaturated bonds in the terpene phenolic resin are reduced to saturated bonds by hydrogenation. For example, the benzene rings in the terpene phenolic resin are converted to cyclohexane rings by hydrogenation. Examples of methods for hydrogenating the terpene phenolic resin include the following methods. Specifically, the terpene phenolic resin is dissolved in purified and dried cyclohexane to a polymer concentration of 5% by mass, and then the hydrogenation reaction is initiated with stirring at a hydrogen gas supply pressure of 0.7 MPa-Gauge and a reaction temperature of 80°C. Once hydrogen absorption is complete, the reaction solution is returned to room temperature and pressure, and the solution is withdrawn from the reactor, thereby obtaining the hydrogenated terpene phenolic resin.

[0046] The hydrogenated terpene phenol resin may be a commercially available product, and examples of the commercially available product include YS Polystar UH115 (manufactured by Yasuhara Chemical Co., Ltd.).

[0047] The xylene resin is a resin obtained by reacting and polymerizing m-xylene and formaldehyde in the presence of an acid catalyst. Furthermore, other compounds may be polymerized into the xylene resin, and among these, it is preferable to polymerize a phenolic compound. Polymerization of a phenolic compound into the xylene resin increases the polarity of the tackifier resin T1, improving its compatibility with the acrylic copolymer and thereby further improving the adhesive strength of the pressure-sensitive adhesive composition. The phenolic compound polymerized into the xylene resin may be the same as the phenolic compound polymerized into the terpene phenolic resin. The other compounds may be used alone or in combination of two or more.

[0048] The xylene resin may be a commercially available product, such as GHP-150 (manufactured by Fudow Co., Ltd.).

[0049] The lower limit of the content of the tackifier resin T1 is 5 parts by mass and the upper limit is 50 parts by mass relative to 100 parts by mass of the acrylic copolymer. When the content of the tackifier resin T1 is 5 parts by mass or more, the adhesive strength of the PSA composition is improved. When the content of the tackifier resin T1 is 50 parts by mass or less, the PSA composition does not become too hard, and the adhesive strength of the PSA composition is improved. The lower limit of the content of the tackifier resin T1 is preferably 10 parts by mass, more preferably 15 parts by mass, and the upper limit is preferably 45 parts by mass, more preferably 40 parts by mass.

[0050] In the first aspect, the pressure-sensitive adhesive composition of the present invention does not contain a tackifier resin T2 different from a terpene phenol resin, a hydrogenated terpene phenol resin, and a xylene resin, or contains the tackifier resin T2. ​​If the pressure-sensitive adhesive composition of the present invention contains the tackifier resin T2, the upper limit of the content of the tackifier resin T2 is 10 parts by mass per 100 parts by mass of the acrylic copolymer. If the pressure-sensitive adhesive composition of the present invention does not contain the tackifier resin T2, or contains the tackifier resin T2 and contains the tackifier resin T2, by keeping the content of the tackifier resin T2 at 10 parts by mass or less, the pressure-sensitive adhesive composition can be prevented from becoming cloudy or yellowing, and have excellent optical transparency. If the pressure-sensitive adhesive composition contains the tackifier resin T2, the upper limit of the content of the tackifier resin T2 is preferably 5 parts by mass.

[0051] In the pressure-sensitive adhesive composition, the content of the tackifier resin T1 is preferably greater than the content of the tackifier resin T2. ​​When the content of the tackifier resin T1 is greater than the content of the tackifier resin T2, the pressure-sensitive adhesive composition has better optical transparency.

[0052] In the second aspect, the pressure-sensitive adhesive composition of the present invention does not contain a tackifier resin, or contains a tackifier resin. If a tackifier resin is contained, the upper limit of the tackifier resin content is 5 parts by mass per 100 parts by mass of the acrylic copolymer. If the pressure-sensitive adhesive composition of the present invention does not contain a tackifier resin, or contains a tackifier resin, and contains a tackifier resin, by keeping the tackifier resin content at 5 parts by mass or less, the pressure-sensitive adhesive composition can be further prevented from becoming cloudy or yellowing, and the pressure-sensitive adhesive composition has excellent optical transparency. If the pressure-sensitive adhesive composition contains a tackifier resin, the upper limit of the tackifier resin content is preferably 4 parts by mass.

[0053] In the second configuration, when the pressure-sensitive adhesive composition contains a tackifier resin, examples of the tackifier resin include terpene phenol resin, hydrogenated terpene phenol resin, xylene resin, etc. Among these, hydrogenated terpene phenol resin is preferred from the viewpoint of light color of the resin and excellent optical transparency.

[0054] The pressure-sensitive adhesive composition preferably contains a crosslinking agent. When the pressure-sensitive adhesive layer contains a crosslinking agent, the acrylic copolymer is crosslinked via the crosslinking agent. By adjusting the degree of crosslinking at this time, the gel fraction of the pressure-sensitive adhesive layer, which will be described later, can be adjusted within an appropriate range. In order for the acrylic copolymer to be crosslinked via the crosslinking agent, the acrylic copolymer preferably has a constituent unit derived from the polar functional group-containing monomer.

[0055] Examples of the crosslinking agent include epoxy-based crosslinking agents, isocyanate-based crosslinking agents, etc. Among these, isocyanate-based crosslinking agents are preferred because they make it easier to adjust the gel fraction of the pressure-sensitive adhesive layer (described below) within an appropriate range, and further improve the adhesive strength and holding power of a pressure-sensitive adhesive tape having the pressure-sensitive adhesive layer.

[0056] The preferred lower limit of the content of the crosslinking agent relative to 100 parts by mass of the acrylic copolymer is 0.05 parts by mass, and the preferred upper limit is 5 parts by mass. By having the content of the crosslinking agent within this range, it becomes easier to adjust the gel fraction of the pressure-sensitive adhesive layer (described later) within an appropriate range, and the adhesive strength and holding power of the pressure-sensitive adhesive tape having the pressure-sensitive adhesive layer are further improved. The more preferred lower limit of the content of the crosslinking agent is 0.1 parts by mass, and the more preferred upper limit is 3 parts by mass.

[0057] The pressure-sensitive adhesive composition 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.

[0058] The present invention also relates to a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition of the present invention. By having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition, the pressure-sensitive adhesive tape of the present invention can achieve both excellent adhesive strength and excellent optical transparency even when the tape is thin.

[0059] The preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 10% by mass, and the preferred upper limit is 80% by mass. When the gel fraction of the pressure-sensitive adhesive layer is 10% by mass or more, the pressure-sensitive adhesive layer becomes hard, and the holding power of the pressure-sensitive adhesive tape is further improved. In addition, the bulk cohesive force of the pressure-sensitive adhesive layer becomes greater, and the heat resistance of the pressure-sensitive adhesive tape is further improved. When the gel fraction of the pressure-sensitive adhesive layer is 80% by mass or less, the pressure-sensitive adhesive layer becomes more easily stretched, and the adhesive strength of the pressure-sensitive adhesive tape is further improved. The more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 15% by mass, and the more preferred upper limit is 75% by mass. The gel fraction of the pressure-sensitive adhesive layer can be measured by the following method. That is, when the pressure-sensitive adhesive layer W ０ (g) is sampled, and the sampled pressure-sensitive adhesive layer is immersed in 50 mL of tetrahydrofuran and shaken in a shaker at a temperature of 23°C and 200 rpm for 24 hours. After shaking, the sample is passed through a metal mesh (opening #200 mesh, mass: W １ The pressure-sensitive adhesive layer that has absorbed tetrahydrofuran and swollen is filtered using a filter (g). The separated pressure-sensitive adhesive layer is dried at 110°C for 1 hour, and then the mass W of the pressure-sensitive adhesive layer including the metal mesh is measured. ２(g) is measured. ０ , W １ , and W ２ The gel fraction can be measured by a method of calculating the gel fraction from the following formula (1) using the above formula: Gel fraction (mass%) = 100 × (W ２ -W １ ) / W ０ (1) (W ０ : initial pressure-sensitive adhesive layer mass, W １ : initial mass of the metal mesh, W ２ : mass of adhesive layer including metal mesh after drying)

[0060] The preferred upper limit of the thickness of the pressure-sensitive adhesive layer is 15 μm. When the thickness of the pressure-sensitive adhesive layer is 15 μm or less, the pressure-sensitive adhesive tape can be suitably used for fixing small or thin electronic devices, etc. The more preferred upper limit of the thickness of the pressure-sensitive adhesive layer is 10 μm, and the even more preferred upper limit is 5 μm. There is no particular preferred lower limit of the thickness of the pressure-sensitive adhesive layer, but from the viewpoint of handleability of the pressure-sensitive adhesive tape, the lower limit is about 2 μm.

[0061] The pressure-sensitive adhesive tape may be a non-support type having no substrate, or a supported type having the pressure-sensitive adhesive layer formed on a substrate. Among these, the pressure-sensitive adhesive tape is preferably a non-support type having no substrate. Since the pressure-sensitive adhesive tape does not have a substrate, the thickness of the pressure-sensitive adhesive tape becomes thinner and the optical transparency of the pressure-sensitive adhesive tape becomes more excellent, so the pressure-sensitive adhesive tape can be suitably used for fixing small and thin electronic devices, devices, etc.

[0062] When the pressure-sensitive adhesive tape has a substrate, it may be a single-sided pressure-sensitive adhesive tape having the pressure-sensitive adhesive layer on one side of the substrate, or a double-sided pressure-sensitive adhesive tape having the pressure-sensitive adhesive layers on both sides.

[0063] Examples of the substrate include sheets made of resins such as acrylic, olefin, polycarbonate, vinyl chloride, ABS, polyethylene terephthalate (PET), nylon, urethane, and polyimide, sheets having a mesh structure, and sheets with holes.

[0064] The preferred lower limit of the thickness of the substrate is 5 μm, and the preferred upper limit is 10 μm. When the thickness of the substrate is 5 μm or more, the pressure-sensitive adhesive tape has appropriate stiffness and excellent handleability. When the thickness of the substrate is 10 μm or less, the pressure-sensitive adhesive tape can be suitably used for fixing small or thin electronic devices, devices, etc.

[0065] The preferred upper limit of the haze of the substrate at 23°C is 0.5%. When the haze of the substrate at 23°C is 0.5% or less, the optical transparency of the pressure-sensitive adhesive tape becomes even more excellent. The more preferred upper limit of the haze of the substrate at 23°C is 0.3%. There is no particular preferred lower limit of the haze of the substrate at 23°C, but from the viewpoint of the optical transparency of the pressure-sensitive adhesive tape, the closer to 0%, the more preferable. The haze of the substrate can be measured, for example, using a haze meter (such as "NDH4000" manufactured by Nippon Denshoku Industries Co., Ltd.).

[0066] The pressure-sensitive adhesive tape may further have other layers within the range that does not impair the effects of the present invention.

[0067] The method for producing the pressure-sensitive adhesive tape is not particularly limited, and conventionally known methods can be used. For example, first, the (meth)acrylic acid alkyl ester, the olefin polymer having a terminal polymerizable unsaturated double bond, and, if necessary, a polar functional group monomer or the like are copolymerized by a conventional method to obtain the acrylic copolymer. Next, a solution containing a pressure-sensitive adhesive composition containing the obtained acrylic copolymer, and, if necessary, a tackifier resin such as the tackifier resin T1 or the tackifier resin T2, and other additives, is applied to a film that has been subjected to a release treatment, followed by drying to produce the pressure-sensitive adhesive tape. The pressure-sensitive adhesive tape produced by the above-mentioned method can also be laminated to a substrate as a pressure-sensitive adhesive layer to produce a support-type pressure-sensitive adhesive tape.

[0068] When the thickness of the pressure-sensitive adhesive layer is 15 μm or less, the preferred lower limit of the 180° peel strength from glass at 23° C. after the pressure-sensitive adhesive tape has been left to stand at 23° C. for 24 hours is 9 N / inch. When the pressure-sensitive adhesive layer has a 180° peel strength from glass at 23° C. after the pressure-sensitive adhesive tape has been left to stand at 23° C. for 24 hours, the pressure-sensitive adhesive tape can be more suitably used for fixing small or thin electronic devices, etc. A more preferred lower limit of the 180° peel strength from glass at 23° C. after the pressure-sensitive adhesive tape has been left to stand at 23° C. for 24 hours is 10 N / inch. There is no particular preferred upper limit of the 180° peel strength from glass at 23° C. after the pressure-sensitive adhesive tape has been left to stand at 23° C. for 24 hours. The 180° peel strength from glass at 23° C. after the pressure-sensitive adhesive tape has been left to stand at 23° C. for 24 hours can be measured by the following method, etc. That is, the pressure-sensitive adhesive tape having the pressure-sensitive adhesive layer is cut into a flat rectangular shape of 25 mm wide x 60 mm long to prepare a test piece, and the obtained test piece is then attached to a glass plate ("Large Slide Glass White Edge Polished No. 2" manufactured by Matsunami Glass Industrial Co., Ltd.) using a 2 kg hand roller. After leaving it to stand at 23 ° C. for 24 hours, the obtained measurement sample is subjected to a 180 ° peel test using a tensile tester ("RTI-1310" manufactured by A&D Co., Ltd., etc.) in accordance with JIS Z0237:2009 under conditions of 23 ° C. and a pulling speed of 300 mm / min, and the 180 ° peel strength against glass at 23 ° C. after leaving it to stand at 23 ° C. for 24 hours can be measured.

[0069] The preferred upper limit of the haze of the pressure-sensitive adhesive tape at 23°C is 1.0%. If the haze of the pressure-sensitive adhesive tape at 23°C is 1.0% or less, the optical transparency of the pressure-sensitive adhesive tape will be superior. The more preferred upper limit of the haze of the pressure-sensitive adhesive tape at 23°C is 0.5%, and even more preferred upper limit is 0.3%. There is no particular preferred lower limit of the haze of the pressure-sensitive adhesive tape at 23°C, but from the viewpoint of the optical transparency of the pressure-sensitive adhesive tape, the closer to 0%, the more preferable. The haze of the pressure-sensitive adhesive tape at 23°C can be measured by the following method, etc. That is, the pressure-sensitive adhesive tape (adhesive layer thickness: 5 μm) is cut into a 40 mm x 40 mm flat rectangular shape, and then the polyethylene terephthalate film on one side of the cut pressure-sensitive adhesive tape is peeled off and the cut pressure-sensitive adhesive tape is laminated to a soda glass (0.7 mm x 56 mm x 86.6 mm) using a 2 kg hand roller. Thereafter, the other polyethylene terephthalate film of the bonded adhesive tape is peeled off, and the color can be measured at room temperature (23°C) using a spectrophotometer (e.g., "CM-3700" manufactured by Konica Minolta, Inc.) by a method of evaluating light transmitted from the single-layer sheet surface to the soda glass surface using the SCI method.

[0070] Yellowing degree b of the above adhesive tape at 23°C ＊ The preferred upper limit of the yellowing index b of the pressure-sensitive adhesive layer at 23°C is 0.4. ＊ When the yellowing index b of the pressure-sensitive adhesive tape at 23°C is 0.4 or less, the pressure-sensitive adhesive tape has better optical transparency. ＊ The more preferable upper limit of the yellowing index b of the pressure-sensitive adhesive tape at 23°C is 0.2. ＊can be measured by the following method. That is, the above-mentioned pressure-sensitive adhesive tape (adhesive layer thickness: 15 μm) is cut into a 40 mm × 40 mm flat rectangular shape, and then the polyethylene terephthalate film on one side of the cut pressure-sensitive adhesive tape is peeled off and the tape is laminated to a soda glass (0.7 mm × 56 mm × 86.6 mm) using a 2 kg hand roller. Thereafter, the polyethylene terephthalate film on the other side of the laminated pressure-sensitive adhesive tape is peeled off, and the colorimetric value can be measured at room temperature (23°C) using a spectrophotometer (e.g., "CM-3700" manufactured by Konica Minolta, Inc.) by evaluating light transmitted from the single-layer sheet surface to the soda glass surface using the SCI method.

[0071] Yellowing degree b of the above adhesive tape after heating at 85°C for 500 hours ＊ The preferred upper limit of the yellowing index b of the pressure-sensitive adhesive tape after heating at 85°C for 500 hours is 0.4. ＊ When the yellowing index b of the pressure-sensitive adhesive tape is 0.4 or less, the pressure-sensitive adhesive tape has excellent optical transparency. In addition, the pressure-sensitive adhesive tape is less likely to lose its optical transparency even after long-term use. ＊ The more preferable upper limit of the yellowing index b of the pressure-sensitive adhesive tape after heating at 85° C. for 500 hours is 0.2. ＊ can be measured by the following method. That is, the above-mentioned pressure-sensitive adhesive tape (adhesive layer thickness: 15 μm) is cut into a 40 mm × 40 mm flat rectangular shape, and the cut pressure-sensitive adhesive tape is then heated in an oven at 85°C for 500 hours. Thereafter, the heated pressure-sensitive adhesive tape is allowed to cool naturally to room temperature (23°C), and the polyethylene terephthalate film on one side is peeled off and the tape is bonded to soda glass (0.7 mm × 56 mm × 86.6 mm) with a hand roller. The polyethylene terephthalate film on the other side of the bonded pressure-sensitive adhesive tape is then peeled off, and the colorimetric value can be measured at room temperature (23°C) using a spectrophotometer (e.g., "CM-3700" manufactured by Konica Minolta, Inc.) by evaluating light transmitted from the single-layer sheet surface to the soda glass surface using the SCI method.

[0072] The applications of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but because it has excellent adhesive strength and excellent optical transparency, it is preferably used for bonding optical members of electronic devices, devices, etc. In particular, the pressure-sensitive adhesive tape of the present invention can exhibit excellent adhesive strength and excellent optical transparency even when the thickness of the pressure-sensitive adhesive layer is thin, and therefore can be preferably used for fixing small or thin electronic devices, devices, etc.

[0073] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition that can achieve both excellent adhesive strength and excellent optical transparency even when applied to a thin thickness, and also to provide a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition.

[0074] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

[0075] (Synthesis of Acrylic Copolymers A to S) 300 mL of ethyl acetate and the structural unit monomers shown in Tables 1 and 2 were added to a reactor equipped with a thermometer, a stirrer, and a condenser, and the reactor was then heated to initiate reflux. Subsequently, 0.01 parts by mass of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane was added as a polymerization initiator to the reactor, and polymerization was initiated under reflux. Thereafter, 0.01 parts by mass of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane were added one hour and two hours after the start of polymerization, and 0.05 parts by mass of t-hexylperoxypivalate was added four hours after the start of polymerization to continue the polymerization reaction. The polymerization reaction was then carried out for a total of eight hours from the start of polymerization to obtain ethyl acetate solutions containing acrylic copolymers A to S. The ethylene-butylene macromonomer shown in Tables 1 and 2 was L-1253 (manufactured by Kuraray Co., Ltd.). Furthermore, the molecular weight distribution of the obtained acrylic copolymer was measured in terms of polystyrene using gel permeation chromatography (GPC) (Waters, "2690 Separations Module") under the following conditions. The weight average molecular weight (Mw), number average molecular weight (Mn), and polydispersity (Mw / Mn) of the acrylic copolymer were determined from the obtained molecular weight distribution curve. <GPC measurement conditions> Solvent: tetrahydrofuran Sample flow rate: 1 mL / min Detector: differential refractometer RI Column: GPC KF-806L (Showa Denko KK) Column temperature (measurement temperature): 40°C Injection volume: 20 μL

[0076]

[0077]

[0078] (Examples 1-1 to 1-28, 2-1 to 2-19, Comparative Examples 1 to 9) (1) Preparation of Pressure-Sensitive Adhesive Compositions To the obtained ethyl acetate solutions containing acrylic copolymers A to S, the materials were added in the compositions shown in Tables 3 to 8, and the mixture was stirred to obtain pressure-sensitive adhesive compositions.

[0079] (2) Preparation of Adhesive Tape A polyethylene terephthalate film with one release-treated surface was prepared. The adhesive composition obtained in "(1) Preparation of Adhesive Composition" above was applied to the release-treated surface of this polyethylene terephthalate film so that the dry film had the desired thickness, and dried at 110°C for 5 minutes to prepare a laminate sheet having an adhesive layer of the desired thickness on the release-treated surface of the polyethylene terephthalate film. Next, a polyethylene terephthalate film with one release-treated surface was superimposed on the adhesive layer surface of the obtained laminate sheet to obtain an adhesive tape having an adhesive layer of the desired thickness.

[0080] (3) Gel fraction of adhesive layer The gel fraction of the adhesive layer W from the obtained adhesive tape ０ (g) was sampled, and the sampled pressure-sensitive adhesive layer was immersed in 50 mL of tetrahydrofuran and shaken in a shaker at a temperature of 23°C and 200 rpm for 24 hours. After shaking, the sample was passed through a metal mesh (opening #200 mesh, mass: W １ The pressure-sensitive adhesive layer that had absorbed tetrahydrofuran and swelled was filtered using a filter (g). The separated pressure-sensitive adhesive layer was dried at 110°C for 1 hour, and then the mass W of the pressure-sensitive adhesive layer including the metal mesh was measured. ２ The measured W (g) was ０ , W １ , and W ２ The gel fraction of the pressure-sensitive adhesive layer was calculated from the following formula (1) using the above formula. The results are shown in Tables 3 to 8. Gel fraction (mass%) = 100 × (W ２ -W １ ) / W ０ (1) (W ０ : initial pressure-sensitive adhesive layer mass, W １ : initial mass of the metal mesh, W ２ : mass of adhesive layer including metal mesh after drying)

[0081] <Evaluation> The pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 3 to 8.

[0082] (Adhesive strength) After preparing an adhesive tape having a thickness of 15 μm according to the method of "(2) Preparation of adhesive tape", the obtained adhesive tape was cut into a flat rectangular shape of 25 mm wide x 60 mm long to prepare a test piece. Next, the obtained test piece was attached to a glass plate ("Large slide glass white edge polished No. 2" manufactured by Matsunami Glass Industrial Co., Ltd.) by moving a 2 kg hand roller back and forth at a speed of 300 mm / min. Then, after leaving it at 23 ° C. for 24 hours, the obtained measurement sample was subjected to a 180 ° peel test using a tensile tester (manufactured by A & D Co., Ltd., "RTI-1310") in accordance with JIS Z0237:2009 under conditions of 23 ° C. and a pulling speed of 300 mm / min. After the adhesive tape was attached, the 180 ° peel force against the glass at 23 ° C. was measured after leaving it at 23 ° C. for 24 hours. The adhesive strength of the pressure-sensitive adhesive tape was evaluated as follows: if the 180° peel strength from glass at 23°C after application and then leaving it to stand at 23°C for 24 hours was 10 N / inch or more, then it was marked "◎", if it was 9 N / inch or more and less than 10 N / inch, then it was marked "◯", if it was 8 N / inch or more and less than 9 N / inch, then it was marked "△", and if it was less than 8 N / inch, then it was marked "X". Furthermore, for pressure-sensitive adhesive tapes having a pressure-sensitive adhesive layer thickness of 5 μm, the 180° peel strength from glass at 23°C after application and then leaving it to stand at 23°C for 24 hours was measured in the same manner, and the adhesive strength of the pressure-sensitive adhesive tape was evaluated.

[0083] (Optical Transparency) (1) Haze at 23°C After preparing an adhesive tape having a pressure-sensitive adhesive layer thickness of 5 μm using the method described above in "(2) Preparation of Pressure-Sensitive Adhesive Tape," the resulting adhesive tape was cut into a 40 mm x 40 mm flat rectangular shape. The polyethylene terephthalate film on one side of the cut adhesive tape was peeled off, and the tape was bonded to a soda glass (0.7 x 56 x 86.6 mm) by reciprocating at a speed of 300 mm / min using a 2 kg hand roller. The polyethylene terephthalate film on the other side of the bonded adhesive tape was then peeled off, and the haze of the adhesive tape at 23°C was measured at room temperature (23°C) using a spectrophotometer (Konica Minolta, Inc., "CM-3700") by evaluating light transmitted from the single-layer sheet surface to the soda glass surface using the SCI method. The optical transparency of the pressure-sensitive adhesive tape was evaluated as follows: if the haze at 23°C obtained was 0.5% or less, it was marked "◎"; if it was more than 0.5% and 1.0% or less, it was marked "○"; if it was more than 1.0% and 1.5% or less, it was marked "△"; and if it was more than 1.5%, it was marked "×".

[0084] (2) Yellowing at 23°C b ＊ An adhesive tape having an adhesive layer thickness of 15 μm was prepared by the method described in "(2) Preparation of adhesive tape" above, and the resulting adhesive tape was cut into a 40 mm × 40 mm flat rectangular shape. The polyethylene terephthalate film on one side of the cut adhesive tape was peeled off, and the tape was bonded to a soda glass (0.7 × 56 × 86.6 mm) by rolling it back and forth at a speed of 300 mm / min using a 2 kg hand roller. The polyethylene terephthalate film on the other side of the bonded adhesive tape was then peeled off, and the yellowing index b of the adhesive layer at 23°C was measured by evaluating light transmitted from the single-layer sheet surface to the soda glass surface using a spectrophotometer (Konica Minolta, Inc., "CM-3700") at room temperature (23°C) using the SCI method. ＊ The yellowing index b at 23°C was measured. ＊ The optical transparency of the pressure-sensitive adhesive tape was evaluated as follows: when the value was 0.2 or less, it was marked as "◎"; when it was more than 0.2 and 0.4 or less, it was marked as "◯"; when it was more than 0.4 and 0.5 or less, it was marked as "△"; and when it was more than 0.5, it was marked as "×".

[0085] (3) Yellowing after heating at 85°C for 500 hours b ＊ After preparing an adhesive tape having an adhesive layer thickness of 15 μm using the method described in "(2) Preparation of Adhesive Tape" above, the obtained adhesive tape was cut into a 40 mm × 40 mm flat rectangular shape, and the cut adhesive tape was heated in an oven at 85 ° C for 500 hours. Thereafter, the heated adhesive tape was allowed to cool to room temperature (23 ° C) by natural cooling, and then the polyethylene terephthalate film on one side was peeled off and the tape was bonded to a soda glass (0.7 × 56 × 86.6 mm) by rolling it back and forth at a speed of 300 mm / min using a 2 kg hand roller. The other polyethylene terephthalate film of the bonded adhesive tape was peeled off, and the yellowing index b after heating at 85 ° C for 500 hours was measured at room temperature (23 ° C) by using a spectrophotometer (Konica Minolta, Inc., "CM-3700") to evaluate light transmitted from the single-layer sheet surface to the soda glass surface using the SCI method. ＊ The yellowing degree b after heating at 85°C for 500 hours was measured. ＊ The optical transparency of the pressure-sensitive adhesive tape was evaluated as follows: when the value was 0.2 or less, it was marked as "◎"; when it was more than 0.2 and 0.4 or less, it was marked as "◯"; when it was more than 0.4 and 0.5 or less, it was marked as "△"; and when it was more than 0.5, it was marked as "×".

[0086] (Metal Corrosion) After the 180° peel test of a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer thickness of 15 μm conducted in the evaluation of "(Adhesion)" above, the surface of the SUS plate from which the pressure-sensitive adhesive tape was peeled was visually observed. The metal corrosivity of the pressure-sensitive adhesive composition was evaluated by rating it as "○" when no corrosion was observed on the surface of the SUS plate, and rating it as "×" when corrosion was observed on the surface of the SUS plate. Even when the rating is "×", the pressure-sensitive adhesive composition of the present invention can achieve both excellent adhesion and excellent optical transparency even when the thickness is thin, and therefore can be used without problems depending on the intended use.

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition that can achieve both excellent adhesive strength and excellent optical transparency even when applied to a thin thickness, and also to provide a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition.

Claims

Claim 1 containing an acrylic copolymer having a structural unit derived from an alkyl (meth)acrylate and a structural unit derived from an olefin polymer having a polymerizable unsaturated double bond at the terminal, satisfying at least one configuration selected from the group consisting of the following first configuration and the following second configuration The pressure-sensitive adhesive composition is characterized by the above. First configuration: containing at least one tackifier resin T1 selected from the group consisting of terpene phenol resin, hydrogenated terpene phenol resin, and xylene resin, with respect to 100 parts by mass of the acrylic copolymer, the content of the tackifier resin T1 is 5 parts by mass or more and 50 parts by mass or less, not containing a tackifier resin T2 different from terpene phenol resin, hydrogenated terpene phenol resin, and xylene resin, or containing the tackifier resin T2, and when containing the tackifier resin T2, with respect to 100 parts by mass of the acrylic copolymer, the content of the tackifier resin T2 is 10 parts by mass or less Second configuration: the acrylic copolymer has a structural unit derived from a polar functional group-containing monomer, the acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 1 or more and 4 or less, in the acrylic copolymer, the content of the structural unit derived from an alkyl (meth)acrylate in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 1 or more and 4 or less is 30% by mass or more and 90% by mass or less, not containing a tackifier resin, or containing a tackifier resin, and when containing a tackifier resin, with respect to 100 parts by mass of the acrylic copolymer, the content of the tackifier resin is 5 parts by mass or less Claim 2 The pressure-sensitive adhesive composition according to claim 1, wherein in the first configuration, the acrylic copolymer has a structural unit derived from a polar functional group-containing monomer. Claim 3 The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the structural unit derived from the polar functional group-containing monomer includes at least one structural unit selected from the group consisting of a structural unit derived from a carboxy group-containing monomer and a structural unit derived from a hydroxy group-containing monomer. Claim 4 The pressure-sensitive adhesive composition according to claim 3, wherein the structural unit derived from the polar functional group-containing monomer includes a structural unit derived from the carboxy group-containing monomer. Claim 5 In the second configuration, the pressure-sensitive adhesive composition according to claim 4, wherein the content of the structural unit derived from the carboxyl group-containing monomer in the acrylic copolymer is 10% by mass or less.

6. The pressure-sensitive adhesive composition according to claim 4, wherein the content of the structural unit derived from the carboxyl group-containing monomer in the acrylic copolymer is 1% by mass or less.

7. The pressure-sensitive adhesive composition according to claim 3, wherein the structural unit derived from the polar functional group-containing monomer includes the structural unit derived from the hydroxyl group-containing monomer.

8. In the first configuration, the pressure-sensitive adhesive composition according to claim 1 or 2, wherein the tackifier resin T1 includes the hydrogenated terpene phenol resin.

9. In the second configuration, the acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 1 or more and 2 or less, The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the structural unit derived from an alkyl (meth)acrylate in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond in the acrylic copolymer is 1 or more and 2 or less is 10% by mass or more and 60% by mass or less.

10. In the second configuration, the acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond is 3 or more and 4 or less, The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the structural unit derived from an alkyl (meth)acrylate in which the carbon number of the alkyl group bonded to the oxygen atom of the ester bond in the acrylic copolymer is 3 or more and 4 or less is 60% by mass or more.

11. A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition according to claim 1 or 2.

12. The pressure-sensitive adhesive tape according to claim 11, wherein the gel fraction of the pressure-sensitive adhesive layer is 10% by mass or more and 80% by mass or less.

13. The pressure-sensitive adhesive tape according to claim 11, wherein the thickness of the pressure-sensitive adhesive layer is 15 μm or less.

14. The pressure-sensitive adhesive tape according to claim 13, wherein the 180° peel strength with respect to glass at 23°C after standing at 23°C for 24 hours after sticking is 9 N / inch or more.

15. The pressure-sensitive adhesive tape according to claim 11, wherein the haze at 23°C is 1.0% or less.

16. The pressure-sensitive adhesive tape according to claim 11, which does not have a base material.