Adhesive tape

Abstract

To provide an adhesive tape that has high adhesive strength to rough surfaces and excellent shear strength at high temperatures.SOLUTION: An adhesive tape has a base material and an adhesive layer. The adhesive layer includes a (meth)acrylic copolymer and a cross-linking agent. When a sol component of the adhesive layer is subjected to measurement by GPC based on differential refractometer RI detection, the proportion of molecular weights of 100,000 or less is 5-75% and the proportion of molecular weights of 600,000 or more is 0.5-16% within the region of molecular weights of 5,000 or more. The content of the (meth)acrylic monomer in the adhesive layer is 2.5 wt.% or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In a process for polishing semiconductor wafers, glass substrates for liquid crystal displays, etc. to a predetermined thickness (for example, a Chemical-Mechanical-Polishing (CMP) process), polishing is performed using a polishing pad (polishing cloth) fixed to the platen of a polishing machine. In order to fix the polishing pad to the platen of the polishing machine, a double-sided adhesive tape is usually used. This double-sided adhesive tape for fixing the polishing pad is required to have sufficient adhesive strength to prevent the polishing pad from peeling off during polishing, and to be able to be peeled off from the platen without leaving any adhesive residue when replacing the used polishing pad.

[0003] As an example of a double-sided adhesive tape for fixing an abrasive pad, Patent Documents 1 and 2 describe a double-sided adhesive tape for fixing an abrasive, in which a specific heat-activated adhesive is provided on one side of a plastic film support and a re-peelable adhesive layer is provided on the other side of the plastic film support, with the heat-activated adhesive layer being the bonding surface with the abrasive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-145611 [Patent Document 2] Japanese Patent Application Publication No. 6-172721 Summary of the Invention [Problem to be solved by the invention]

[0005] The performance required for the double-sided adhesive tape for fixing polishing pad is becoming more and more advanced year by year.For example, in order to increase the polishing speed in order to improve the polishing efficiency, it is necessary to increase the amount of strongly acidic or strongly alkaline slurry liquid used during polishing and to use a soft polishing pad.For example, polyurethane foam and the like are considered as such soft polishing pads.However, the soft polishing pad has many cavities on its surface and has a rough surface, so that the adhesion of the double-sided adhesive tape for fixing polishing pad is poor, and the adhesive force is insufficient. In addition, when the polishing speed is increased to improve the polishing efficiency, the adhesive layer is likely to slip or peel off due to the temperature rise caused by frictional heat or the application of strong shear force, which is also a problem. A double-sided adhesive tape for fixing a polishing pad is required to have excellent resistance (creep resistance) against slippage or peeling when a strong shear force is applied at such high temperatures.

[0006] The present invention aims to provide an adhesive tape having high adhesion to a rough surface and excellent shear strength at high temperatures. In particular, the present invention aims to provide an adhesive tape having high adhesion to a polishing pad having a rough surface and excellent shear strength at high temperatures. [Means for solving the problem]

[0007] Disclosure 1 is an adhesive tape having a substrate and an adhesive layer, the adhesive layer containing a (meth)acrylic copolymer and a crosslinking agent, and when a sol component of the adhesive layer is subjected to GPC measurement by RI detection with a differential refractometer, in a region of molecular weight of 5,000 or more, the proportion of molecular weights of 100,000 or less is 5% or more and 75% or less, and the proportion of molecular weights of 600,000 or more is 0.5% or more and 16% or less, and the content of (meth)acrylic monomer in the adhesive layer is 2.5% by weight or less. Disclosure 2 is the pressure-sensitive adhesive tape of Disclosure 1, in which, when the GPC measurement is carried out, the proportion of molecular weights of 150,000 or less in the region of molecular weights of 5,000 or more is 5% or more and 65% or less. The present disclosure 3 is the pressure-sensitive adhesive tape of the present disclosure 1 or 2, in which, when the GPC measurement is carried out, the proportion of molecular weights of 500,000 or more is 1% or more and 20% or less in the region of molecular weights of 5,000 or more. The present disclosure 4 is the pressure-sensitive adhesive tape according to the present disclosure 1, 2, or 3, wherein the content of the (meth)acrylic monomer in the pressure-sensitive adhesive layer is 0.1% by weight or more. The present disclosure 5 is an adhesive tape according to the present disclosure 1, 2, 3 or 4, in which the difference Mp(UV-RI) between the peak of molecular weight distribution (Mp(UV)) when the sol component of the adhesive layer is subjected to GPC measurement by ultraviolet (UV) detection at an absorption wavelength of 254 nm and the peak of molecular weight distribution (Mp(RI)) when the sol component of the adhesive layer is subjected to GPC measurement by RI detection with a differential refractometer is 5000 or more. The present disclosure 6 is a pressure-sensitive adhesive tape according to the present disclosure 1, 2, 3, 4 or 5, in which, when the sol component of the pressure-sensitive adhesive layer is subjected to GPC measurement using RI detection with a differential refractometer, the molecular weight distribution peak (Mp(RI)) is 100,000 or more and 400,000 or less in the molecular weight region of 5,000 or more. A seventh aspect of the present disclosure is the pressure-sensitive adhesive tape of the first, second, third, fourth, fifth or sixth disclosure, wherein the pressure-sensitive adhesive layer has a gel fraction of 15% by weight or more and 70% by weight or less. In the present disclosure 8, the pressure-sensitive adhesive layer has a storage modulus G'(100°C) of 3.5×10 4 The pressure-sensitive adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, or 7, wherein the compressive strength is 100 Pa or more. The present disclosure 9 is the pressure-sensitive adhesive tape of the present disclosure 1, 2, 3, 4, 5, 6, 7, or 8, wherein the pressure-sensitive adhesive layer further contains a tackifier resin, the softening temperature of the tackifier resin is 100° C. or more and 180° C. or less, and the content of the tackifier resin is 10 parts by weight or more and 60 parts by weight or less relative to 100 parts by weight of the (meth)acrylic copolymer. A tenth aspect of the present disclosure is the pressure-sensitive adhesive tape of the first, second, third, fourth, fifth, sixth, seventh, eighth, or nineth aspect of the present disclosure, wherein the (meth)acrylic copolymer contains 8% by weight or more of a constituent unit derived from a carboxy group-containing monomer. Present Disclosure 11 is a pressure-sensitive adhesive tape according to Present Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the (meth)acrylic copolymer has a content of structural units derived from an alkyl (meth)acrylate having an alkyl group with 4 or less carbon atoms of 25% by weight or more and 70% by weight or less, and a content of structural units derived from an alkyl (meth)acrylate having an alkyl group with 6 or more carbon atoms of 22% by weight or more and 67% by weight or less. A twelfth aspect of the present disclosure is the pressure-sensitive adhesive tape of the first, second, third, fourth, fifth, sixth, seventh, eighth, nineth, tenth, or eleventh aspect of the present disclosure, wherein the pressure-sensitive adhesive layer has a thickness of 10 μm or more and 150 μm or less. The present disclosure 13 is the pressure-sensitive adhesive tape of the present disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, having the pressure-sensitive adhesive layers on both sides of the substrate. Disclosure 14 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, used for fixing a polishing pad to a platen of a polishing machine. The present invention will be described in detail below.

[0008] The present inventors have studied the optimization of the molecular weight distribution of the sol component of the adhesive layer by using an adhesive layer containing a (meth)acrylic copolymer and a crosslinking agent as an adhesive layer for fixing a polishing pad to the platen of a polishing machine, particularly an adhesive layer that can be used on the surface to be bonded to the polishing pad. Specifically, when the sol component of the adhesive layer was subjected to GPC measurement by RI detection with a differential refractometer, the inventors studied the adjustment of the ratio of low molecular weight components having a molecular weight of 100,000 or less and the ratio of high molecular weight components having a molecular weight of 600,000 or more to a specific range in the molecular weight region of 5000 or more. Furthermore, the present inventors have studied the suppression of the content of (meth)acrylic monomer in the adhesive layer to a certain value or less. The present inventors have found that an adhesive tape having such an adhesive layer has high adhesion to a rough surface and excellent shear strength at high temperatures, and have completed the present invention.

[0009] The pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive tape having a substrate and a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer contains a (meth)acrylic copolymer and a crosslinking agent. When the sol component of the above adhesive layer is subjected to GPC measurement by RI detection using a differential refractometer, in the region of molecular weight of 5,000 or more, the proportion of molecular weights of 100,000 or less is 5% or more and 75% or less, and the proportion of molecular weights of 600,000 or more is 0.5% or more and 16% or less. In this specification, (meth)acrylic means acrylic or methacrylic.

[0010] Here, the "sol component" refers to the component excluding the "gel component" from the pressure-sensitive adhesive layer. That is, the relationship "sol fraction (wt%) = 100 (wt%) - gel fraction (wt%)" holds. The "gel component" is a low-fluidity component in which the (meth)acrylic copolymer, the tackifier resin blended as necessary, and the like build a crosslinked structure via the crosslinking agent, and the "sol component" is a high-fluidity component that is not involved in such a crosslinked structure.

[0011] The sol component of the pressure-sensitive adhesive layer can be obtained, for example, by immersing the pressure-sensitive adhesive layer in tetrahydrofuran (THF) at 23° C. for 24 hours and removing the insoluble matter by filtration through a 200-mesh wire screen. When the sol component of the pressure-sensitive adhesive layer is subjected to GPC measurement by RI detection using a differential refractometer, for example, the following method can be adopted: That is, using a column LF-804 manufactured by SHOKO Co., Ltd., the sol component of the pressure-sensitive adhesive layer is analyzed by gel permeation chromatography (GPC) (manufactured by Waters, 2690 Separations Model) to measure the molecular weight distribution in terms of polystyrene. Eluent: tetrahydrofuran (THF) Flow rate: 0.4mL / min Detector: RI differential refractometer Column temperature (measurement temperature): 40℃ Injection volume: 20μL In addition, the GPC measurement by differential refractometer RI detection can mainly determine the molecular weight distribution of the (meth)acrylic copolymer contained in the sol component of the pressure-sensitive adhesive layer. Meanwhile, the GPC measurement by ultraviolet (UV) detection described later can detect components that particularly exhibit ultraviolet (UV) absorption (for example, components having aromatic rings in the molecule, more specifically, for example, crosslinkers, tackifier resins, and molecules having structures derived therefrom, etc., contained in the sol component of the pressure-sensitive adhesive layer).

[0012] If the proportion of molecular weights of 100,000 or less (proportion of low molecular weight components) is 5% or more, the bulk fluidity of the pressure-sensitive adhesive layer is increased, and the pressure-sensitive adhesive layer can have high adhesive strength to rough surfaces. If the proportion of molecular weights of 100,000 or less is 75% or less, the bulk cohesive strength of the pressure-sensitive adhesive layer is not reduced more than necessary, and the shear strength of the pressure-sensitive adhesive layer at high temperatures is improved. The preferred lower limit of the proportion of molecular weights of 100,000 or less is 10%, the preferred upper limit is 70%, the more preferred lower limit is 20%, and the more preferred upper limit is 65%.

[0013] If the proportion of the molecular weight of 600,000 or more (proportion of high molecular weight components) is 0.5% or more, the bulk cohesive strength of the pressure-sensitive adhesive layer increases, and the shear strength at high temperatures improves. If the proportion of the molecular weight of 600,000 or more is 16% or less, the bulk fluidity of the pressure-sensitive adhesive layer does not decrease more than necessary, and the pressure-sensitive adhesive layer can have high adhesive strength to a rough surface. The preferred lower limit of the proportion of the molecular weight of 600,000 or more is 2%, the preferred upper limit is 15%, the more preferred lower limit is 3%, and the more preferred upper limit is 10%.

[0014] The proportion of the molecular weight of 150,000 or less is not particularly limited, but is preferably 5% or more and 65% or less. If the proportion of the molecular weight of 150,000 or less is 5%, the bulk fluidity of the pressure-sensitive adhesive layer is further increased, and the pressure-sensitive adhesive layer can have a higher adhesive strength to a rough surface. If the proportion of the molecular weight of 150,000 or less is 65% or less, the bulk cohesive strength of the pressure-sensitive adhesive layer is not reduced more than necessary, and the shear strength of the pressure-sensitive adhesive layer at high temperatures is further improved. The more preferable lower limit of the proportion of the molecular weight of 150,000 or less is 15%, the more preferable upper limit is 60%, the even more preferable lower limit is 25%, and the even more preferable upper limit is 55%.

[0015] The proportion of molecular weights of 500,000 or more is not particularly limited, but is preferably 1% or more and 20% or less. If the proportion of molecular weights of 500,000 or more is 1% or more, the bulk cohesive force of the pressure-sensitive adhesive layer is further increased, and the shear strength at high temperatures is further improved. If the proportion of molecular weights of 500,000 or more is 20% or less, the bulk fluidity of the pressure-sensitive adhesive layer is not reduced more than necessary, and the pressure-sensitive adhesive layer can have even higher adhesive strength to rough surfaces. A more preferred lower limit of the proportion of molecular weights of 500,000 or more is 2.5%, a more preferred upper limit is 15%, an even more preferred lower limit is 4%, and an even more preferred upper limit is 10%.

[0016] The proportion of the molecular weight of 100,000 to 600,000 is not particularly limited, but is preferably 9% or more and 94.5% or less. If the proportion of the molecular weight of 100,000 to 600,000 is 9% or more and 94.5% or less, the bulk fluidity and bulk cohesive strength of the pressure-sensitive adhesive layer are not lowered more than necessary, so that the pressure-sensitive adhesive layer has high adhesive strength to a rough surface and has improved shear strength at high temperatures. The more preferred lower limit of the proportion of the molecular weight of 100,000 to 600,000 is 15%, the more preferred upper limit is 88%, the even more preferred lower limit is 25%, and the even more preferred upper limit is 77%.

[0017] The proportion of the molecular weight of 150,000 to 500,000 is not particularly limited, but is preferably 15% or more and 94% or less. If the proportion of the molecular weight of 150,000 to 500,000 is 15% or more and 94% or less, the adhesive layer has a higher adhesive strength to a rough surface and has a higher shear strength at high temperatures. The more preferred lower limit of the proportion of the molecular weight of 150,000 to 500,000 is 17.5%, the more preferred upper limit is 75%, the even more preferred lower limit is 35%, and the even more preferred upper limit is 71%.

[0018] The pressure-sensitive adhesive layer preferably has a molecular weight distribution peak (Mp(RI)) of 100,000 or more and 400,000 or less in a molecular weight range of 5,000 or more when the sol component of the pressure-sensitive adhesive layer is subjected to GPC measurement with RI detection using a differential refractometer. If the peak of the molecular weight distribution (Mp(RI)) is 100,000 or more, the proportion of high molecular weight components increases while the proportion of low molecular weight components decreases, so that the cohesive force of the bulk of the pressure-sensitive adhesive layer increases and the shear strength at high temperatures is improved. If the peak of the molecular weight distribution (Mp(RI)) is 400,000 or less, the proportion of high molecular weight components decreases while the proportion of low molecular weight components increases, so that the fluidity of the bulk of the pressure-sensitive adhesive layer increases and the pressure-sensitive adhesive layer can have a higher adhesive strength to a rough surface. The lower limit of the peak of the molecular weight distribution (Mp(RI)) is more preferably 120,000, the upper limit is more preferably 350,000, the even more preferably 150,000, and the even more preferably 300,000. The peak of the molecular weight distribution (Mp(RI)) means the molecular weight at the highest peak in the molecular weight distribution curve. Even if a shoulder or two or more peaks are present in the molecular weight distribution curve, the peak of the molecular weight distribution (Mp(RI)) means the molecular weight at the highest peak in the molecular weight distribution curve.

[0019] It is preferable that the above-mentioned pressure-sensitive adhesive layer has a difference Mp(UV-RI) of 5000 or more between the peak of molecular weight distribution (Mp(UV)) when the sol component of the pressure-sensitive adhesive layer is subjected to GPC measurement by ultraviolet (UV) detection at an absorption wavelength of 254 nm and the peak of molecular weight distribution (Mp(RI)) when the sol component of the pressure-sensitive adhesive layer is subjected to GPC measurement by RI detection with a differential refractometer. Here, the GPC measurement using differential refractometer RI detection detects the entire (meth)acrylic copolymer, whereas the GPC measurement using ultraviolet (UV) detection detects only components that absorb ultraviolet (UV) light (e.g., components having aromatic rings in the molecule, more specifically, for example, crosslinking agents, tackifier resins, and molecules having structures derived therefrom, contained in the sol components of the pressure-sensitive adhesive layer). The sol component of the pressure-sensitive adhesive layer may contain a large amount of molecular chains of the (meth)acrylic copolymer having a relatively small molecular weight. This is believed to be because the molecular chains having a relatively small molecular weight are difficult to bind to the gel component and difficult to be incorporated into the crosslinked structure due to the non-uniformity of the polymerization reaction, as the content of the constituent units derived from the crosslinkable functional group-containing monomer is relatively small. It is preferable that the low molecular chains contained in such a sol component have a functional group introduced at the end, and the low molecular chains having the functional group form a bond (e.g., a dimer, etc.) via the crosslinking agent, or via a bond between the crosslinking agent and a tackifier resin blended as necessary. The low molecular weight chain bond in the sol component of the pressure-sensitive adhesive layer contains a component that absorbs ultraviolet (UV). If the amount of the low molecular weight chain bond increases, the peak of the molecular weight distribution detected by GPC measurement using ultraviolet (UV) detection (Mp(UV)) shifts to the higher molecular weight side than the peak of the molecular weight distribution detected by GPC measurement using differential refractometer RI detection (Mp(RI)).

[0020] If the difference Mp(UV-RI) is 5000 or more, it can be determined that the sol component of the pressure-sensitive adhesive layer contains a sufficient amount of the low molecular weight chain bond. That is, it can be said that the (meth)acrylic copolymer contained in the sol component of the pressure-sensitive adhesive layer has a high molecular weight as a whole. Therefore, the proportion of the molecular weight of 150,000 or less is more likely to be within the above range, the bulk cohesive force of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is further improved. In addition, when the (meth)acrylic copolymer has a high molecular weight in this way, even if the molecular weight of the (meth)acrylic copolymer as a raw material is adjusted to a relatively low range, the shear strength at high temperatures is improved, so the molecular weight of the (meth)acrylic copolymer as a raw material can be adjusted to a relatively low range. Therefore, the pressure-sensitive adhesive layer can also have a higher adhesive strength to a rough surface. A more preferable lower limit of the difference Mp(UV-RI) is 10,000, and an even more preferable lower limit is 30,000.

[0021] When the sol component of the pressure-sensitive adhesive layer is subjected to GPC measurement by ultraviolet (UV) detection with an absorption wavelength of 254 nm, for example, the following method can be adopted: That is, using a SHOKO column LF-804 as a column, the sol component of the pressure-sensitive adhesive layer is analyzed by gel permeation chromatography (GPC) (Waters, 2690 Separations Model) to measure the molecular weight distribution in terms of polystyrene. Eluent: tetrahydrofuran (THF) Flow rate: 0.4mL / min Detector: UV detector (absorption wavelength 254 nm) Column temperature (measurement temperature): 40℃ Injection volume: 20μL

[0022] In the pressure-sensitive adhesive tape of the present invention, the upper limit of the content of the (meth)acrylic monomer in the pressure-sensitive adhesive layer is 2.5% by weight. If the content of the monomer is 2.5% by weight or less, the glass transition temperature (Tg) of the pressure-sensitive adhesive layer increases, so that the bulk cohesive force increases and the shear strength at high temperatures improves. In addition, since the content of the monomer is 2.5% by weight or less, the shear strength at high temperatures improves even if the molecular weight of the (meth)acrylic copolymer as a raw material is adjusted to a relatively low range, so that the molecular weight of the (meth)acrylic copolymer as a raw material can be adjusted to a relatively low range. Therefore, the pressure-sensitive adhesive layer can also have a higher adhesive strength to a rough surface. The preferred upper limit of the content of the monomer in the pressure-sensitive adhesive layer is 1.5% by weight, and more preferably 1% by weight. There is no particular limitation on the lower limit of the content of the monomer in the pressure-sensitive adhesive layer, but from the viewpoint of ensuring the bulk fluidity of the pressure-sensitive adhesive layer and improving the adhesive strength to a rough surface, a preferred lower limit is 0.1% by weight. The monomer may be an unreacted monomer that remains without being incorporated into the polymerization during the production of the (meth)acrylic copolymer. The monomer can be adjusted to a predetermined range by increasing the polymerization efficiency during the production of the (meth)acrylic copolymer.

[0023] The content of the monomer in the pressure-sensitive adhesive layer can be determined, for example, by performing GC-MS (gas chromatograph mass spectrometer) measurement on the pressure-sensitive adhesive layer. For example, the pressure-sensitive adhesive is weighed out from the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape, and the pressure-sensitive adhesive is immersed in a solvent such as chloroform. The dissolved components are subjected to GC-MS measurement under the following conditions, and the peak area value of each monomer in the total ion chromatogram is determined, thereby determining the monomer concentration contained in the sample. From this monomer concentration, the content of the monomer contained in the weighed pressure-sensitive adhesive can be calculated. It is preferable to perform the measurement and calculation using a calibration curve of the concentration and peak area value of each monomer. (Measurement conditions) GC-MS equipment GC:78906B (manufactured by Agilent technology), MS: JMS-Q1500 (manufactured by JEOL Ltd.) Column: SLBTM-5ms (low polarity) 0.25mmφ×30m×0.25μm Inlet temperature: 250℃ He flow rate: 1.0 mL / min (split ratio 1:50) Column temperature: After holding at 40°C for 3 minutes, increase the temperature at 10°C / min, then hold at 300°C for 10 minutes. MS measurement range: 35-800 amu Ionization voltage: 70 eV, ionization method: EI method, measurement mode: scan Ion source temperature: 230℃, interface temperature: 250℃

[0024] Regarding the sol component of the pressure-sensitive adhesive layer, the proportion of the molecular weight of 100,000 or less, the proportion of the molecular weight of 150,000 or less, the proportion of the molecular weight of 500,000 or more, the proportion of the molecular weight of 600,000 or more, the proportion of the molecular weight of 100,000 to 600,000, the proportion of the molecular weight of 150,000 to 500,000, the peak of the molecular weight distribution (Mp(RI)), and the difference Mp(UV-RI) are adjusted to the above ranges, and the content of the monomer in the pressure-sensitive adhesive layer is adjusted to the above ranges, but is not particularly limited. Specific examples include a method using a (meth)acrylic copolymer obtained by living radical polymerization, free radical polymerization, or the like. Among them, from the viewpoint of shortening the reaction time and suppressing costs, a method using a (meth)acrylic copolymer obtained by free radical polymerization is preferred.

[0025] Among the above free radical polymerizations, a method using a (meth)acrylic copolymer obtained under relatively mild polymerization conditions such as keeping the polymerization temperature and the concentration of the monomer mixture constant is preferred. This makes it possible to make the composition of the (meth)acrylic copolymer more uniform, or to reduce the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the (meth)acrylic copolymer, and makes it easier to adjust the molecular weight distribution of the sol component of the pressure-sensitive adhesive layer to the above range. Examples of polymerization methods that provide such relatively mild polymerization conditions include a method of performing free radical constant temperature polymerization, and a method of free radical boiling point polymerization in which half of the monomer mixture and a polymerization initiator are added to a reaction vessel to initiate polymerization, and then the remaining half of the monomer mixture is added dropwise or all at once.

[0026] The polymerization reaction time of the free radical polymerization is not particularly limited, but is preferably relatively short, with a preferred lower limit of 2 hours and a preferred upper limit of 10 hours. If the polymerization reaction time of the free radical polymerization is within the above range, the content of the monomer in the pressure-sensitive adhesive layer can be easily adjusted to the above range. The more preferred lower limit of the polymerization reaction time of the free radical polymerization is 3 hours, and the more preferred upper limit is 8 hours.

[0027] Examples of the polymerization initiator used in the free radical polymerization include organic peroxides and azo compounds. The azo compound is not particularly limited as long as it is one that is generally used in radical polymerization. Examples of the azo compound include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1-azobis(cyclohexane-1-carbonitrile), 1-[(1-cyano-1- methylethyl)azo]formamide, 4,4'-azobis(4-cyanovaleric acid), dimethyl-2,2'-azobis(2-methylpropionate), dimethyl-1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis{2-methyl-N-[1,1'-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl )propionamide], 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline-2- 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2'-azobis(2,4,4-trimethylpentane), etc. These azo compounds may be used alone or in combination of two or more. 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, t-butylperoxylaurate, etc. These organic peroxides may be used alone or in combination of two or more.

[0028] Among these, it is preferable to use a polymerization initiator having a functional group. By using a polymerization initiator having the above functional group, it becomes easier to adjust the molecular weight distribution of the sol component of the above pressure-sensitive adhesive layer within the above range. That is, by using the polymerization initiator having the functional group, a functional group can be introduced to the end of the (meth)acrylic copolymer, and in particular, a functional group can be introduced to the end of a molecular chain (non-crosslinkable low molecular chain) that does not have a constituent unit derived from a crosslinkable functional group-containing monomer and has a relatively small molecular weight among the (meth)acrylic copolymers. Since such low molecular chains have a functional group at the end and are incorporated into a crosslinked structure via the crosslinking agent, the cohesive force of the bulk of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is further improved. Even if the low molecular chains are not involved in the crosslinked structure, the low molecular chains can form a bond (e.g., a dimer, etc.) between themselves via the crosslinking agent or via a bond between the crosslinking agent and a tackifier resin, etc., which is blended as necessary, by having a functional group at the end. In such a case, it can be said that the (meth)acrylic copolymer contained in the sol component of the pressure-sensitive adhesive layer has a high molecular weight as a whole. Therefore, the proportion of the molecular weight of 150,000 or less is more likely to be within the above range, and the cohesive force of the bulk of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is further improved. The functional group is not particularly limited, and examples thereof include hydroxyl, carboxyl, silyl, glycidyl, amino, amide, nitrile, alkoxy, and acetoacetyl groups. Among these, hydroxyl and carboxyl groups are preferred. As the polymerization initiator having the functional group, among the above-mentioned polymerization initiators, for example, 2,2'-azobis{2-methyl-N-[1,1'-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 4,4'-azobis(4-cyanovaleric acid (valeric acid)), and the like can be mentioned. These polymerization initiators having functional groups may be used alone or in combination of two or more kinds.

[0029] The amount of the polymerization initiator to be added is not particularly limited, but the preferred lower limit is 0.01 parts by weight and the preferred upper limit is 0.5 parts by weight relative to 100 parts by weight of the monomer mixture. By setting the amount of the polymerization initiator to be added within the above range, it becomes easier to adjust the proportion of the molecular weight of 150,000 or less, the proportion of the molecular weight of 500,000 or more, and the peak (Mp) of the molecular weight distribution in the sol component of the pressure-sensitive adhesive layer to the above range. The more preferred lower limit of the amount of the polymerization initiator to be added is 0.02 parts by weight, and the more preferred upper limit is 0.3 parts by weight.

[0030] In the above free radical polymerization, a chain transfer agent may be used. The chain transfer agent is not particularly limited, and examples thereof include thiol compounds such as lauryl mercaptan, mercaptopropionic acid, mercaptosuccinic acid, 3-mercapto-1,2-propanediol, 1-butanethiol, cyclohexyl 3-mercaptopropionate, 2-ethylhexyl mercaptoacetate, 1-hexadecanethiol, 2-mercaptoethanol, mercaptoacetic acid, ethyl mercaptoacetate, 1-octanethiol, tridecyl 3-mercaptopropionate, and thiophenol. In addition, 2,4-diphenyl-4-methyl-1-pentene and the like can be mentioned. These chain transfer agents may be used alone or in combination of two or more kinds.

[0031] Among these, it is preferable to use a chain transfer agent having a functional group. Use of a chain transfer agent having the above functional group also makes it easier to adjust the molecular weight distribution of the sol component of the above pressure-sensitive adhesive layer within the above range. In other words, by using a chain transfer agent having the above-mentioned functional group, a functional group can be introduced to the end of the low molecular weight chain, just as in the case of using a polymerization initiator having the above-mentioned functional group, and as a result, the cohesive strength of the bulk of the pressure-sensitive adhesive layer is increased and the shear strength at high temperatures is improved. The functional group is not particularly limited, and examples thereof include hydroxyl, carboxyl, silyl, glycidyl, amino, amide, nitrile, alkoxy, and acetoacetyl groups. Among these, hydroxyl and carboxyl groups are preferred, and hydroxyl is more preferred. The number of functional groups in the chain transfer agent having the functional group is not particularly limited, but it is preferable that the functional group is polyvalent, since the crosslinked structure is easily made highly dimensional and easily networked, and the bulk cohesive force of the pressure-sensitive adhesive layer is further increased. Examples of the chain transfer agent having the functional group include mercaptopropionic acid, mercaptosuccinic acid, and 3-mercapto-1,2-propanediol, among the chain transfer agents described above. These chain transfer agents having functional groups may be used alone, or two or more of them may be used in combination.

[0032] The amount of the chain transfer agent is not particularly limited, but the preferred lower limit is 0.01 parts by weight and the preferred upper limit is 0.5 parts by weight relative to 100 parts by weight of the monomer mixture. By setting the amount of the chain transfer agent within the above range, it becomes easier to adjust the proportion of the molecular weight of 150,000 or less, the proportion of the molecular weight of 500,000 or more, and the peak (Mp) of the molecular weight distribution in the sol component of the pressure-sensitive adhesive layer to the above range. The more preferred lower limit of the amount of the chain transfer agent is 0.02 parts by weight and the more preferred upper limit is 0.3 parts by weight.

[0033] In the free radical polymerization, a dispersion stabilizer may be used. Examples of the dispersion stabilizer include polyvinylpyrrolidone, polyvinyl alcohol, methyl cellulose, ethyl cellulose, poly(meth)acrylic acid, poly(meth)acrylic acid ester, and polyethylene glycol. When a polymerization solvent is used in the above free radical polymerization, the polymerization solvent is not particularly limited, and examples of the polymerization solvent that can be used include non-polar solvents such as hexane, cyclohexane, octane, toluene, xylene, etc., and highly polar solvents such as water, methanol, ethanol, propanol, butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, N,N-dimethylformamide, etc. These polymerization solvents may be used alone or in combination of two or more kinds. The polymerization temperature is preferably 0 to 110° C. from the viewpoint of the polymerization rate.

[0034] The (meth)acrylic copolymer is not particularly limited, but it preferably contains a structural unit derived from an alkyl (meth)acrylate having an alkyl group having 4 or less carbon atoms. The alkyl (meth)acrylate having an alkyl group having 4 or less carbon atoms is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, and butyl (meth)acrylate. These alkyl (meth)acrylates having an alkyl group having 4 or less carbon atoms may be used alone or in combination of two or more. Among them, butyl (meth)acrylate is preferred.

[0035] The content of the constituent unit derived from the alkyl (meth)acrylate having an alkyl group having 4 or less carbon atoms is not particularly limited, but the preferred lower limit is 25% by weight, and the preferred upper limit is 70% by weight. If the content is 25% by weight or more, the glass transition temperature (Tg) of the (meth)acrylic copolymer is sufficiently high, so that the bulk cohesive force of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is further improved. If the content is 70% by weight or less, the glass transition temperature (Tg) of the (meth)acrylic copolymer is not too high, so that the bulk fluidity of the pressure-sensitive adhesive layer is increased, and the pressure-sensitive adhesive layer can have a higher adhesive strength to a rough surface. The more preferred lower limit of the content is 30% by weight, the more preferred upper limit is 65% by weight, the even more preferred lower limit is 35% by weight, and the even more preferred upper limit is 60% by weight.

[0036] The (meth)acrylic copolymer preferably contains a structural unit derived from an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms. The alkyl (meth)acrylate having an alkyl group with 6 or more carbon atoms is not particularly limited, and the alkyl group preferably has 6 to 16 carbon atoms, and more preferably has 6 to 12 carbon atoms. The alkyl group of the alkyl (meth)acrylate having 6 or more carbon atoms may be branched or unbranched, but is preferably unbranched. Since the alkyl group of the alkyl (meth)acrylate having 6 or more carbon atoms has a linear structure, the pressure-sensitive adhesive layer has a low storage modulus from low temperature to room temperature, but a high storage modulus at high temperatures, and therefore the shear strength at high temperatures is improved and the adhesive strength to a rough surface can be higher. Specific examples of the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms include n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, isostearyl acrylate, and arachidyl (meth)acrylate. These alkyl (meth)acrylates having an alkyl group having 6 or more carbon atoms may be used alone or in combination of two or more. Among them, n-heptyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred. In this specification, (meth)acrylate means acrylate or methacrylate.

[0037] The content of the constituent unit derived from the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms is not particularly limited, but the preferred lower limit is 22% by weight, and the preferred upper limit is 67% by weight. If the content is 22% by weight or more, the glass transition temperature (Tg) of the (meth)acrylic copolymer is sufficiently low, so that the bulk fluidity of the pressure-sensitive adhesive layer is increased, and the pressure-sensitive adhesive layer can have a higher adhesive strength to a rough surface. If the content is 67% by weight or less, the glass transition temperature (Tg) of the (meth)acrylic copolymer is not too low, so that the cohesive strength of the bulk of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is further improved. The more preferred lower limit of the content is 27% by weight, the more preferred upper limit is 62% by weight, the even more preferred lower limit is 32% by weight, and the even more preferred upper limit is 57% by weight.

[0038] The (meth)acrylic copolymer preferably has a structural unit derived from a crosslinkable functional group-containing monomer. The (meth)acrylic copolymer has a constituent unit derived from the crosslinkable functional group-containing monomer, and the (meth)acrylic copolymer and the tackifier resin, which is blended as necessary, etc., construct a crosslinked structure via the crosslinking agent, thereby increasing the bulk cohesive force of the pressure-sensitive adhesive layer and improving the shear strength at high temperatures. Examples of the crosslinkable functional group include a hydroxyl group, a carboxyl group, a silyl group, a glycidyl group, an amino group, an amide group, a nitrile group, an alkoxy group, and an acetoacetyl group. Among them, a hydroxyl group and a carboxyl group are preferred because they are easy to adjust the bulk cohesive force of the pressure-sensitive adhesive layer.

[0039] Examples of the hydroxyl group-containing monomer include (meth)acrylic acid esters having a hydroxyl group, such as 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate. Examples of the carboxy group-containing monomer include (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, etc. Of these, acrylic acid is preferred. An example of the glycidyl group-containing monomer is glycidyl (meth)acrylate. Examples of the amide group-containing monomer include hydroxyethylacrylamide, isopropylacrylamide, and dimethylaminopropylacrylamide. The nitrile group-containing monomer may, for example, be acrylonitrile.

[0040] The content of the constituent unit derived from the crosslinkable functional group-containing monomer is not particularly limited, but the preferred lower limit is 0.05% by weight, and the preferred upper limit is 20% by weight. If the content is 0.05% by weight or more, the bulk cohesive force of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is improved. If the content is 20% by weight or less, the bulk fluidity of the pressure-sensitive adhesive layer is increased, and the pressure-sensitive adhesive layer can have a higher adhesive strength to a rough surface. The more preferred lower limit of the content is 0.1% by weight, and the more preferred upper limit is 15% by weight. In particular, when the (meth)acrylic copolymer contains a constituent unit derived from the carboxyl group-containing monomer, the preferred lower limit of the content of the constituent unit is 8% by weight. If the content is 8% by weight or more, the glass transition temperature (Tg) of the (meth)acrylic copolymer is sufficiently high, so that the bulk cohesive force of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is further improved. If the content is 8% by weight or more, the polarity of the (meth)acrylic copolymer is also increased, so that the pressure-sensitive adhesive layer can have a higher adhesive strength to an adherend having a high polarity. The more preferred lower limit of the content of the constituent unit derived from the carboxyl group-containing monomer is 9% by weight, and the even more preferred lower limit is 10% by weight.

[0041] In addition, when the (meth)acrylic copolymer contains a structural unit derived from the hydroxyl group-containing monomer, the preferred upper limit of the content of the structural unit is 0.5% by weight. If the content is 0.5% by weight or less, the reaction between the (meth)acrylic copolymer and the crosslinking agent proceeds mildly, so that it is easier to adjust the proportion of the molecular weight of 150,000 or less, the proportion of the molecular weight of 500,000 or more, and the difference Mp(UV-RI) in the sol component of the pressure-sensitive adhesive layer to the above ranges. A more preferred upper limit of the content of the structural unit derived from the hydroxyl group-containing monomer is 0.1% by weight. The lower limit of the content of the structural unit derived from the hydroxyl group-containing monomer is not particularly limited, and the closer to 0% by weight, the more preferable, and it may be 0% by weight.

[0042] The (meth)acrylic copolymer may contain, as necessary, a structural unit derived from another copolymerizable polymerizable monomer other than the alkyl (meth)acrylate having an alkyl group with 4 or less carbon atoms, the alkyl (meth)acrylate having an alkyl group with 6 or more carbon atoms, and the structural unit derived from the crosslinkable functional group-containing monomer.

[0043] The weight average molecular weight (Mw) of the (meth)acrylic copolymer is not particularly limited, but from the viewpoint of adjusting the molecular weight distribution of the sol component of the pressure-sensitive adhesive layer within the above range, a preferred lower limit is 150,000, a preferred upper limit is 450,000, a more preferred lower limit is 170,000, and a more preferred upper limit is 400,000. In addition, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the (meth)acrylic copolymer is not particularly limited, but from the viewpoint of adjusting the molecular weight distribution of the sol component of the pressure-sensitive adhesive layer within the above range, a preferred upper limit is 10, and a more preferred upper limit is 5. The weight average molecular weight (Mw) of the (meth)acrylic copolymer and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) can be measured in the same manner as in the case of performing GPC measurement by RI detection with a differential refractometer on the sol component of the pressure-sensitive adhesive layer.

[0044] The crosslinking agent is not particularly limited, and is selected from, for example, isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-type crosslinking agents, etc., depending on the type of crosslinkable functional group of the (meth)acrylic copolymer. Among them, isocyanate-based crosslinking agents are preferred because they can selectively crosslink hydroxyl groups and carboxyl groups and are easy to control the crosslinked structure. Examples of the isocyanate-based crosslinking agents include Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.), Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Mytech NY260A (manufactured by Mitsubishi Chemical Corporation). By appropriately adjusting the type or amount of the crosslinking agent, the bulk cohesive strength of the pressure-sensitive adhesive layer can be easily adjusted. The number of functional groups in the crosslinking agent is not particularly limited, but it is preferably polyvalent because this makes it easier for the crosslinked structure to have a higher dimension and to form a network, and further increases the bulk cohesive strength of the pressure-sensitive adhesive layer.

[0045] The content of the crosslinking agent is not particularly limited, but is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, based on 100 parts by weight of the (meth)acrylic copolymer.

[0046] The pressure-sensitive adhesive layer preferably further contains a tackifier resin. By including a tackifier resin in the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer can have higher adhesive strength to an adherend.

[0047] The softening temperature of the tackifier resin is not particularly limited, but the preferred lower limit is 100°C, and the preferred upper limit is 180°C. If the softening temperature is 100°C or higher, the heat resistance of the adhesive layer is increased, and the shear strength at high temperatures is further improved. If the softening temperature is 180°C or lower, the adhesive layer is likely to become flexible, and can have higher adhesive strength to a rough surface. The more preferred lower limit of the softening temperature is 110°C, the more preferred upper limit is 170°C, the even more preferred lower limit is 120°C, and the even more preferred upper limit is 165°C. The softening temperature is a softening temperature measured by the ring and ball method according to JIS K2207.

[0048] The hydroxyl value of the tackifier resin is not particularly limited, but a preferred lower limit is 25 mgKOH / g, a preferred upper limit is 150 mgKOH / g, a more preferred lower limit is 30 mgKOH / g, and a more preferred upper limit is 100 mgKOH / g. The hydroxyl value can be measured according to JIS K1557 (phthalic anhydride method).

[0049] The tackifier resin is not particularly limited, and examples thereof include rosin-based resins such as rosin ester-based resins, terpene-based resins such as terpene phenol resins, petroleum-based resins, etc. Among these, rosin ester-based resins, terpene phenol resins, and combinations thereof are preferred, and terpene phenol resins are more preferred. The terpene phenol resin has good compatibility with the (meth)acrylic copolymer, and is easily grafted with the (meth)acrylic copolymer, and is easily incorporated into the pressure-sensitive adhesive layer. Therefore, the surface of the pressure-sensitive adhesive layer becomes polymer-rich and flexible, and can have higher adhesive strength to rough surfaces. Meanwhile, the grafting of the terpene phenol resin with the (meth)acrylic copolymer increases the bulk cohesive strength of the pressure-sensitive adhesive layer, and therefore the pressure-sensitive adhesive layer also has improved shear strength at high temperatures.

[0050] The rosin ester resin is a resin obtained by esterifying, with an alcohol, a rosin resin mainly composed of abietic acid, a disproportionated rosin resin, a hydrogenated rosin resin, a dimer of a resin acid such as abietic acid (polymerized rosin resin), etc. The hydroxyl value is adjusted to the above range by containing, without being used in the esterification, a part of the hydroxyl group of the alcohol used in the esterification in the resin. Examples of the alcohol include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol. In addition, a resin obtained by esterifying a rosin resin is a rosin ester resin, a resin obtained by esterifying a disproportionated rosin resin is a disproportionated rosin ester resin, a resin obtained by esterifying a hydrogenated rosin resin is a hydrogenated rosin ester resin, and a resin obtained by esterifying a polymerized rosin resin is a polymerized rosin ester resin. The terpene phenol resin is a resin obtained by polymerizing terpene in the presence of phenol.

[0051] Examples of the disproportionated rosin ester resin include Super Ester A75 (hydroxyl value 23 mg KOH / g, softening temperature 75° C.), Super Ester A100 (hydroxyl value 16, softening temperature 100° C.), Super Ester A115 (hydroxyl value 19 mg KOH / g, softening temperature 115° C.), and Super Ester A125 (hydroxyl value 15 mg KOH / g, softening temperature 125° C.), all manufactured by Arakawa Chemical Industries Co., Ltd. Examples of the hydrogenated rosin ester resin include Pine Crystal KE-359 (hydroxyl value 42 mg KOH / g, softening temperature 100° C.), and Ester Gum H (hydroxyl value 29 mg KOH / g, softening temperature 70° C.), all manufactured by Arakawa Chemical Industries Co., Ltd. Examples of the polymerized rosin ester resin include Arakawa Chemical Industries' Pencel D135 (hydroxyl value 45 mg KOH / g, softening temperature 135°C), Arakawa Chemical Industries' Pencel D125 (hydroxyl value 34 mg KOH / g, softening temperature 125°C), and Arakawa Chemical Industries' Pencel D160 (hydroxyl value 42 mg KOH / g, softening temperature 160°C). Examples of the terpene resins include Yasuhara Chemical's YS Polystar G150 (hydroxyl value 140 mg KOH / g, softening temperature 150°C), Yasuhara Chemical's YS Polystar T100 (hydroxyl value 60 mg KOH / g, softening temperature 100°C), Yasuhara Chemical's YS Polystar G125 (hydroxyl value 140 mg KOH / g, softening temperature 125°C), Yasuhara Chemical's YS Polystar T115 (hydroxyl value 60 mg KOH / g, softening temperature 115°C), Yasuhara Chemical's YS Polystar T130 (hydroxyl value 60 mg KOH / g, softening temperature 130°C), and Yasuhara Chemical's YS Polystar T160 (hydroxyl value 60 mg KOH / g, softening temperature 160°C). These tackifier resins may be used alone or in combination of two or more kinds.

[0052] The content of the tackifier resin is not particularly limited, but the preferred lower limit is 10 parts by weight and the preferred upper limit is 60 parts by weight relative to 100 parts by weight of the (meth)acrylic copolymer. If the content is 10 parts by weight or more, the glass transition temperature (Tg) of the pressure-sensitive adhesive layer increases, so that the bulk cohesive force increases and the shear strength at high temperatures is improved. If the content is 60 parts by weight or less, the pressure-sensitive adhesive layer is prevented from becoming too hard due to an increase in the glass transition temperature (Tg), and the pressure-sensitive adhesive layer can have sufficient adhesive strength. The more preferred lower limit of the content is 15 parts by weight, the more preferred upper limit is 50 parts by weight, the even more preferred lower limit is 20 parts by weight, and the even more preferred upper limit is 45 parts by weight.

[0053] The pressure-sensitive adhesive layer may contain other resins and the like, such as additives including a plasticizer, an emulsifier, a softener, a filler, a pigment, a dye, a silane coupling agent, and an antioxidant, as necessary.

[0054] The gel fraction of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit is 15% by weight, and the preferred upper limit is 70% by weight. If the gel fraction is 15% by weight or more, the bulk cohesive force of the pressure-sensitive adhesive layer is increased, and the shear strength at high temperatures is improved. If the gel fraction is 70% by weight or less, the pressure-sensitive adhesive layer has sufficient flexibility and can have a higher adhesive strength to a rough surface. The more preferred lower limit of the gel fraction is 20% by weight, and the more preferred upper limit is 65% by weight, and the even more preferred lower limit is 25% by weight, and the even more preferred upper limit is 60% by weight.

[0055] The gel fraction of the pressure-sensitive adhesive layer can be measured, for example, by the following method. That is, first, W1 (g) of the pressure-sensitive adhesive layer is sampled, the sampled pressure-sensitive adhesive layer is immersed in ethyl acetate at 23°C for 24 hours, and the insoluble matter is filtered through a 200-mesh wire net. The residue on the wire net is dried by heating at 110°C, and the weight W2 (g) of the resulting dried residue is measured. The gel fraction (degree of cross-linking) is calculated according to the following formula (1). Gel fraction (wt%) = 100 × W2 / W1 (1)

[0056] The storage modulus of the pressure-sensitive adhesive layer is not particularly limited, but it is preferable that the storage modulus G'(100°C) at 100°C is 3.5×10 4 The storage modulus G'(100°C) at 100°C is preferably 3.5×10 Pa or more. 4 If the storage modulus G'(100°C) is 4×10 Pa or more, the pressure-sensitive adhesive layer has a higher bulk cohesive force at high temperatures and has a higher shear strength at high temperatures. 4 Pa, and a more preferable lower limit is 4.5×10 4 It is Pa. The upper limit of the storage modulus G'(100°C) at 100°C is not particularly limited. However, if it is too high, the storage modulus at room temperature also increases, and the adhesive strength to a rough surface decreases. Therefore, the preferred upper limit is 2.0×10 5 It is Pa.

[0057] The storage modulus G'(100°C) of the pressure-sensitive adhesive layer at 100°C can be measured, for example, by the following method. That is, first, samples of the pressure-sensitive adhesive layer are stacked to prepare a laminate having a thickness of about 1 mm, and then cut into a 6 mm x 10 mm specimen. Measurement is performed on the specimen in a shear mode under a nitrogen atmosphere at a measurement temperature of -40 to 140°C, a heating rate of 5°C / min, a frequency of 10 Hz, and a strain of 0.08% using a dynamic viscoelasticity measuring device (IT Measurement and Control Co., Ltd., DVA-200).

[0058] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit is 10 μm, and the preferred upper limit is 150 μm. If the thickness is 10 μm or more, the pressure-sensitive adhesive layer is more likely to bite into the adherend, and the peel resistance is increased, so that the pressure-sensitive adhesive layer can have high adhesive strength to a rough surface. If the thickness is 150 μm or less, the amount of displacement when a shear force is applied to the pressure-sensitive adhesive layer is reduced, so that the shear strength of the pressure-sensitive adhesive layer at high temperatures is further improved. The more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 20 μm, the more preferred upper limit is 120 μm, the even more preferred lower limit is 40 μm, and the even more preferred upper limit is 100 μm.

[0059] The substrate is not particularly limited, but is preferably a resin film. The resin film is not particularly limited, and examples thereof include polyester resin film, polypropylene resin film, etc. Among them, polyester resin film is preferred because it is flat, has small thickness variation, and has high strength, and among polyester resin films, polyethylene terephthalate film is more preferred. The above-mentioned base material may contain additives such as a filler, an ultraviolet absorber, a light stabilizer, and an antistatic agent, within the range that does not impair the physical properties of the base material. The thickness of the substrate is not particularly limited, but a preferred lower limit is 10 μm, a preferred upper limit is 200 μm, a more preferred lower limit is 15 μm, and a more preferred upper limit is 150 μm.

[0060] The pressure-sensitive adhesive tape of the present invention is not particularly limited as long as it has the substrate and the pressure-sensitive adhesive layer, and may have the pressure-sensitive adhesive layer on only one side of the substrate, or may have the pressure-sensitive adhesive layer on both sides of the substrate. In particular, it is preferable that the pressure-sensitive adhesive layer is on both sides of the substrate.

[0061] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited. For example, when the pressure-sensitive adhesive layer has the same composition and thickness on both sides of the substrate, the following method can be mentioned. First, a pressure-sensitive adhesive solution containing a (meth)acrylic copolymer, a crosslinking agent, and, if necessary, other components such as a tackifier resin is prepared. Next, the pressure-sensitive adhesive solution obtained above is applied to the release-treated surface of a release film, one side of which has been release-treated, and then dried to prepare a laminated sheet having a pressure-sensitive adhesive layer on the release-treated surface of the release film. A total of two laminated sheets are prepared in the same manner. Next, the pressure-sensitive adhesive layers of the two laminated sheets are transferred to a substrate and laminated together to obtain a pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers on both sides of the substrate.

[0062] The use of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but since it has high adhesive strength to a rough surface, particularly to a polishing pad having a rough surface, and has excellent shear strength at high temperatures, it is preferably used to fix a polishing pad to the platen of a polishing machine in a process of polishing a semiconductor wafer, a glass substrate for liquid crystal display, etc. to a predetermined thickness. Examples of such a polishing process include a chemical-mechanical-polishing (CMP) process. The pressure-sensitive adhesive tape of the present invention is more preferably used on the surface that will be bonded to a polishing pad than on the surface that will be bonded to the platen of a polishing machine. The polishing pad is not particularly limited, and may be any polishing pad that is fixed to the platen of a polishing machine and is made of an absorbent material, a nonwoven fabric, a polyurethane foam, etc. The pressure-sensitive adhesive tape of the present invention can have high adhesive strength even to a soft polishing pad made of polyurethane foam, etc., that is, a polishing pad having many cavities on the surface and a rough surface. Effect of the Invention

[0063] According to the present invention, it is possible to provide an adhesive tape that has high adhesive strength to rough surfaces and excellent shear strength at high temperatures. [Brief description of the drawings]

[0064] [Figure 1] FIG. 2 is a schematic diagram showing a method for measuring the shear strength (creep resistance test) of the double-sided pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0066] (Preparation of (meth)acrylic copolymer A (free radical boiling point polymerization)) A reactor equipped with a thermometer, a stirrer, and a cooling tube was prepared, and a total of 50 parts by weight of the monomer mixture and 90 parts by weight of ethyl acetate were added to the reactor. As the monomer mixture, 22 parts by weight of butyl acrylate (BA), 22 parts by weight of 2-ethylhexyl acrylate (2EHA), and 6 parts by weight of acrylic acid (AAc) were used. After nitrogen replacement, the reactor was heated to start reflux. 30 minutes after the ethyl acetate boiled, 0.03 parts by weight of the chain transfer agent 3-mercapto-1,2-propanediol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and 0.04 parts by weight of V-60 (2,2'-azobisisobutyronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as the polymerization initiator 1, and polymerization was started under reflux. After 30 minutes, a total of 50 parts by weight of the monomer mixture was dropped into the reactor using a dropping funnel over 1 hour. As the monomer mixture, 22 parts by weight of butyl acrylate (BA), 22 parts by weight of 2-ethylhexyl acrylate (2EHA), and 6 parts by weight of acrylic acid (AAc) were used. Then, 0.15 parts by weight of V-60 (2,2'-azobisisobutyronitrile, Fujifilm Wako Pure Chemical Industries, Ltd.) was further added as a polymerization initiator 2, and the polymerization reaction was carried out for a total of 6 hours from the start of polymerization, to obtain a (meth)acrylic copolymer A-containing solution.

[0067] (Preparation of (meth)acrylic copolymers B-J and a-d (free radical boiling point polymerization)) (Meth)acrylic copolymers B to J and a to d were prepared in the same manner as (meth)acrylic copolymer A, except that the monomer composition, the amount of initiator, the type and amount of chain transfer agent, and the amount of solvent were changed as shown in Table 1.

[0068] [Table 1]

[0069] (Preparation of (meth)acrylic copolymer K (free radical constant temperature polymerization)) A reactor equipped with a thermometer, a stirrer, and a cooling tube was prepared, and a total of 100 parts by weight of the monomer mixture, 30 parts by weight of ethyl acetate, and 90 parts by weight of toluene were added to the reactor. As the monomer mixture, 44 parts by weight of butyl acrylate (BA), 44 parts by weight of 2-ethylhexyl acrylate (2EHA), and 12 parts by weight of acrylic acid (AAc) were used. Argon gas was introduced into the reactor to remove dissolved oxygen, and the solution temperature was heated to 60°C. Subsequently, 0.03 parts by weight of 3-mercapto-1,2-propanediol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a chain transfer agent was added to the reactor, and 0.05 parts by weight of V-60 (2,2'-azobisisobutyronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a polymerization initiator, and polymerization was started under reflux. The polymerization reaction was carried out for 6 hours from the start of polymerization, and a (meth)acrylic copolymer K-containing solution was obtained.

[0070] (Preparation of (meth)acrylic copolymers L-Q and e (free radical constant temperature polymerization)) (Meth)acrylic copolymers L to Q and e were prepared in the same manner as for (meth)acrylic copolymer K, except that the monomer composition, the type and amount of chain transfer agent, the amount of initiator, and the amount of solvent were changed as shown in Table 2.

[0071] [Table 2]

[0072] Example 1 (1) Manufacture of adhesive tapes Ethyl acetate was added to 100 parts by weight of the non-volatile content of the obtained (meth)acrylic copolymer-containing solution and stirred, and 40 parts by weight of a tackifier resin, a terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd., product name "T160"), and 6 parts by weight of an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L45") were added and stirred to obtain an adhesive solution.

[0073] A polyethylene terephthalate film with one side treated for release was prepared. The adhesive solution obtained above was applied to the release-treated surface of this polyethylene terephthalate film so that the thickness after drying was 80 μm, and dried at 110 ° C for 5 minutes to promote crosslinking of the (meth)acrylic copolymer in the (meth)acrylic copolymer-containing solution, and a laminate sheet having an adhesive layer on the release-treated surface of the polyethylene terephthalate film was produced. Another laminate sheet was produced in the same manner, and a total of two of the above laminate sheets were obtained. Next, a polyethylene terephthalate film (thickness 50 μm) was prepared as a substrate. One of the laminated sheets was laminated on one surface of this substrate from the adhesive layer side, and the adhesive layer was transferred to the substrate and laminated together. The other laminated sheet was laminated on the other surface of the substrate from the adhesive layer side, and the adhesive layer was transferred to the substrate and laminated together. As a result, a double-sided adhesive tape was obtained in which an adhesive layer having a thickness of 80 μm was provided on both sides of the substrate.

[0074] (2) GPC measurement of sol components (RI and UV) The adhesive layer of the double-sided adhesive tape was immersed in tetrahydrofuran (THF) at 23° C. for 24 hours, and the insoluble matter was removed by filtration through a 200-mesh wire screen to obtain a sol component of the adhesive layer. The sol component of the obtained pressure-sensitive adhesive layer was subjected to GPC measurement by RI detection using a differential refractometer by the following method: That is, using a SHOKO column LF-804 as the column, the sol component of the obtained pressure-sensitive adhesive layer was analyzed by gel permeation chromatography (GPC) (Waters, 2690 Separations Model) to measure the molecular weight distribution in terms of polystyrene. Eluent: tetrahydrofuran (THF) Flow rate: 0.4mL / min Detector: RI differential refractometer Column temperature (measurement temperature): 40℃ Injection volume: 20μL

[0075] Table 3 shows the percentage of molecular weights of 100,000 or less, the percentage of molecular weights of 150,000 or less, the percentage of molecular weights of 500,000 or more, the percentage of molecular weights of 600,000 or more, the percentage of molecular weights between 100,000 and 600,000, the percentage of molecular weights between 150,000 and 500,000, and the peak of the molecular weight distribution (Mp(RI)).

[0076] The sol component of the obtained pressure-sensitive adhesive layer was subjected to GPC measurement by ultraviolet (UV) detection at an absorption wavelength of 254 nm by the following method: That is, using a SHOKO column LF-804 as the column, the sol component of the obtained pressure-sensitive adhesive layer was analyzed by gel permeation chromatography (GPC) (Waters, 2690 Separations Model) to measure the molecular weight distribution in terms of polystyrene. Eluent: tetrahydrofuran (THF) Flow rate: 0.4mL / min Detector: UV detector (absorption wavelength 254 nm) Column temperature (measurement temperature): 40℃ Injection volume: 20μL

[0077] From the obtained molecular weight distribution, the peak difference in the molecular weight distribution (Mp(UV-RI)) was determined and is shown in Table 3.

[0078] (3) Measurement of storage modulus The storage modulus G'(100°C) of the adhesive layer of the double-sided adhesive tape at 100°C was measured by the following method. That is, first, samples of the adhesive layer were stacked to prepare a laminate with a thickness of about 1 mm, and then cut into 6 mm x 10 mm to obtain a test piece. Using a dynamic viscoelasticity measuring device (IT Measurement and Control Co., Ltd., DVA-200), the test piece was measured in shear mode in a nitrogen atmosphere at a measurement temperature of -40 to 140°C, a heating rate of 5°C / min, a frequency of 10 Hz, and a strain of 0.08%.

[0079] (4) Measurement of gel fraction The gel fraction of the adhesive layer of the double-sided adhesive tape was measured by the following method. That is, first, W1 (g) of the adhesive layer was sampled, and the sampled adhesive layer was immersed in ethyl acetate at 23°C for 24 hours, and the insoluble matter was filtered through a 200-mesh wire net. The residue on the wire net was heated and dried at 110°C, and the weight W2 (g) of the obtained dried residue was measured. The gel fraction (degree of crosslinking) was calculated by the following formula (1). Gel fraction (wt%) = 100 × W2 / W1 (1)

[0080] (5) Measurement of monomer content The adhesive layer of the double-sided adhesive tape was subjected to GC-MS (gas chromatograph mass spectrometer) measurement under the conditions below to determine the monomer content in the adhesive layer. (Measurement conditions) GC-MS equipment GC:78906B (manufactured by Agilent technology), MS: JMS-Q1500 (manufactured by JEOL Ltd.) Column: SLBTM-5ms (low polarity) 0.25mmφ×30m×0.25μm Inlet temperature: 250℃ He flow rate: 1.0 mL / min (split ratio 1:50) Column temperature: After holding at 40°C for 3 minutes, increase the temperature at 10°C / min, then hold at 300°C for 10 minutes. MS measurement range: 35-800 amu Ionization voltage: 70 eV, ionization method: EI method, measurement mode: scan Ion source temperature: 230℃, interface temperature: 250℃

[0081] (Examples 2 to 20, Comparative Examples 1 to 5) Double-sided pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the types or amounts of the (meth)acrylic copolymer, tackifier resin, and crosslinking agent were changed as shown in Tables 3 and 4. In Tables 3 and 4, "T130" is a terpene phenol resin that is a tackifier resin (manufactured by Yasuhara Chemical Co., Ltd., product name "T130"), "D135" is a polymerized rosin ester resin that is a tackifier resin (manufactured by Arakawa Chemical Co., Ltd., Pencel D135), "KE388" is a hydrogenated rosin ester resin that is a tackifier resin (manufactured by Arakawa Chemical Co., Ltd., Pine Crystal KE-388), "KE359" is a hydrogenated rosin ester resin that is a tackifier resin (manufactured by Arakawa Chemical Co., Ltd., Pine Crystal KE-359), and "G150" is a terpene resin that is a tackifier resin (manufactured by Yasuhara Chemical Co., Ltd., YS Polystar G150).

[0082] <Evaluation> The double-sided pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 3 and 4.

[0083] (1) Adhesion to polishing pad The polishing pad was a polyurethane foam sliced ​​to a thickness of 3 mm (mainly made of PPG as polyether polyol, TDI as isocyanate, and MOCA as a curing agent). When this polyurethane foam was observed with a laser microscope, the surface roughness Sa was 3.99 μm and the contact area ratio was 77%.

[0084] The double-sided adhesive tape was cut into strips of 25 mm width to prepare test pieces. One of the release PET films of the test piece was peeled off to expose the adhesive layer. After washing with ethanol, the test piece was placed on the above-mentioned polishing pad that had been wiped dry so that the adhesive layer faced each other. A 2 kg rubber roller was moved back and forth on the test piece at a speed of 300 mm / min to bond the test piece and the polishing pad. This laminate was passed once through a laminator (manufactured by Aco Brands Japan, Multi Laminator GDRH355 A3) under conditions of a roll temperature of 85°C, a roll gap of 2 mm, and a speed of 7.5 rpm, and pressed at a pressure of 1.2 MPa. After that, it was left to stand for 24 hours at a temperature of 23°C and a relative humidity of 50% to obtain a test sample. Using a tensile tester, a 180° peel test was performed on the test sample at a peel speed of 300 mm / min and a peel angle of 180° in accordance with JIS Z0237.

[0085] (2) Shear strength measurement (creep resistance test) FIG. 1 is a schematic diagram showing a method for measuring the shear strength (creep resistance test) of the double-sided pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples. The double-sided adhesive tape was cut to a width of 10 mm and a length of 120 mm, and backed with a PET film having a thickness of 25 μm to prepare a test piece 1. As shown in FIG. 1, the test piece 1 was attached to the stainless steel measuring terminal part 2 of the tester with an adhesive area of ​​10×10 mm. The temperature of the stainless steel measuring terminal part 2 was set to 60° C. A mirror-finished quartz block 3 (quartz glass with chrome deposition) was placed on the attached surface of the test piece 1, and a 50 gf weight 5 was attached to the test piece 1. The displacement (deviation) (μm) in the direction of the arrow in the figure 3 minutes after the load of the weight 5 was applied was measured from the movement of the mirror-finished quartz block 3 on the test piece 1 by a laser interferometer 4 (Keyence Corporation, SI-F10), and was taken as the cohesive force displacement value.

[0086] (3) Overall evaluation A rating of ◯ was given when the adhesive strength to the polishing pad measured in (1) above was 50 N / 25 mm or more and the cohesive force displacement value measured in (2) above was 50 μm or less; a rating of △ was given when the adhesive strength was 45 N / 25 mm or more, less than 50 N / 25 mm, and the cohesive force displacement value was 50 μm or less; and a rating of × was given when the adhesive strength was less than 45 N / 25 mm or the cohesive force displacement value was less than 50 μm.

[0087] [Table 3]

[0088] [Table 4] [Industrial Applicability]

[0089] According to the present invention, it is possible to provide an adhesive tape that has high adhesive strength to rough surfaces and excellent shear strength at high temperatures. [Explanation of symbols]

[0090] 1 Test piece 2 Stainless steel measuring terminal 3. Mirror-finished quartz block 4. Laser interferometer 5 weights (50gf)

Claims

1. An adhesive tape having a base material and an adhesive layer, wherein: the adhesive layer contains a (meth)acrylic copolymer and a crosslinking agent; when GPC measurement by differential refractometer RI detection is performed on the sol component of the adhesive layer, in the region where the molecular weight is 5000 or more, the proportion of the molecular weight of 100,000 or less is 5% or more and 75% or less, and the proportion of the molecular weight of 600,000 or more is 0.5% or more and 16% or less; in the adhesive layer, the content of the (meth)acrylic monomer is 2.5% by weight or less. An adhesive tape characterized by the above.

2. The adhesive tape according to claim 1, wherein when the GPC measurement is performed, in the region where the molecular weight is 5000 or more, the proportion of the molecular weight of 150,000 or less is 5% or more and 65% or less.

3. The adhesive tape according to claim 1 or 2, wherein when the GPC measurement is performed, in the region where the molecular weight is 5000 or more, the proportion of the molecular weight of 500,000 or more is 1% or more and 20% or less.

4. The adhesive tape according to claim 1 or 2, wherein in the adhesive layer, the content of the (meth)acrylic monomer is 0.1% by weight or more.

5. The adhesive tape according to claim 1 or 2, wherein the difference Mp(UV - RI) between the peak (Mp(UV)) of the molecular weight distribution when GPC measurement by UV detection at an absorption wavelength of 254 nm is performed on the sol component of the adhesive layer and the peak (Mp(RI)) of the molecular weight distribution when GPC measurement by differential refractometer RI detection is performed on the sol component of the adhesive layer is 5000 or more.

6. The adhesive tape according to claim 1 or 2, wherein when GPC measurement by differential refractometer RI detection is performed on the sol component of the adhesive layer, in the region where the molecular weight is 5000 or more, the peak (Mp(RI)) of the molecular weight distribution is 100,000 or more and 400,000 or less.

7. The adhesive tape according to claim 1 or 2, wherein the adhesive layer has a gel fraction of 15% by weight or more and 70% by weight or less.

8. The adhesive layer has a storage elastic modulus G'(100°C) at 100°C of 3.5×10 ４ Pa or more. The adhesive tape according to claim 1 or 2.

9. The adhesive tape according to claim 1 or 2, wherein the adhesive layer further contains a tackifier resin, the softening temperature of the tackifier resin is 100°C or more and 180°C or less, and the content of the tackifier resin is 10 parts by weight or more and 60 parts by weight or less with respect to 100 parts by weight of the (meth)acrylic copolymer.

10. The adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer contains 8% by weight or more of structural units derived from carboxy group-containing monomers.

11. The (meth)acrylic copolymer has a content of a structural unit derived from an alkyl (meth)acrylate having an alkyl group with 4 or less carbon atoms of 25% by weight or more and 70% by weight or less, and a content of a structural unit derived from an alkyl (meth)acrylate having an alkyl group with 6 or more carbon atoms of 22% by weight or more and 67% by weight or less. The pressure-sensitive adhesive tape according to claim 1 or 2.

12. The pressure-sensitive adhesive layer has a thickness of 10 μm or more and 150 μm or less. The pressure-sensitive adhesive tape according to claim 1 or 2.

13. The pressure-sensitive adhesive tape according to claim 1 or 2, having the pressure-sensitive adhesive layer on both sides of the base material.

14. The pressure-sensitive adhesive tape according to claim 1 or 2, which is used for fixing a polishing pad to a surface plate of a polishing machine.

Images