Adhesive tape

Abstract

To provide an adhesive tape that is excellent in yellowing resistance.SOLUTION: Provided is an adhesive tape, which is an adhesive tape having a (meth)acrylic copolymer-containing adhesive layer and in which the (meth)acrylic copolymer contains a constitutional unit derived from alkoxy group-containing (meth)acrylate by 60 mass% or more.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, when fixing components in electronic devices, adhesive tapes have been widely used. Specifically, for example, an adhesive tape is used to adhere a cover panel for protecting the surface of a portable electronic device to a touch panel module or a display panel module, or to adhere a touch panel module and a display panel module. The adhesive tape used for fixing such electronic device components is required to have functions such as heat resistance, thermal conductivity, and impact resistance in addition to high adhesiveness according to the environment of the used site (for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, due to the miniaturization, weight reduction, and cost reduction of electronic devices, types of electronic devices that are always worn or placed at hand, such as mobile phones, smartphones, and wearable terminals, have become widely popular. In these electronic devices, miniaturization and large screen sizes have advanced in recent years. Along with this, there has been a problem that yellowing of the display screen becomes prominent. In view of the above situation, an object of the present invention is to provide an adhesive tape having excellent yellowing resistance.

Means for Solving the Problems

[0005] The present invention relates to an adhesive tape having an adhesive layer containing a (meth)acrylic copolymer, wherein the (meth)acrylic copolymer contains 60% by weight or more of a structural unit derived from an alkoxy group-containing (meth)acrylate, and is an adhesive tape. The present invention will be described in detail below.

[0006] The inventors of the present invention examined the cause of yellowing when manufacturing electronic devices using adhesive tapes. As a result, it was found that the adhesive tape for bonding the cover panel and the touch sensor panel swells due to sebum, and the width and thickness increase, causing the internal liquid crystal to be compressed and distorted, resulting in yellowing. As a result of further intensive studies, the inventors of the present invention found that yellowing can be prevented by using a (meth)acrylic copolymer containing a structural unit derived from an alkoxy group-containing (meth)acrylate in an adhesive tape having an adhesive layer containing a (meth)acrylic copolymer, and completed the present invention.

[0007] The adhesive tape of the present invention has an adhesive layer containing a (meth)acrylic copolymer. The above (meth)acrylic copolymer contains a structural unit derived from an alkoxy group-containing (meth)acrylate. The alkoxy group-containing (meth)acrylate has the property of having a relatively high SP value while having a relatively low glass transition temperature. The adhesive layer containing a (meth)acrylic copolymer containing a structural unit derived from an alkoxy group-containing (meth)acrylate is not easily swollen by sebum, and in addition, even if it swells, it exhibits stress relaxation properties that do not impose a load on the liquid crystal, and can exhibit excellent yellowing resistance. Further, the above adhesive layer can exhibit excellent followability to unevenness.

[0008] Examples of the alkoxy group-containing (meth)acrylate include compounds represented by the following general formula (1).

[0009] [Chemical formula]

[0010] In general formula (1), R1 represents a hydrogen atom or a methyl group, R2 represents an alkylene group having 2 to 4 carbon atoms, R3 represents an alkyl group or an aryl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 10.

[0011] Specific examples of the alkoxy group-containing (meth)acrylate include, for example, 2-methoxyethyl acrylate (MOEA), ethyl carbitol acrylate (CBA), phenoxyethyl acrylate (PHEA), methoxy triethylene glycol acrylate (MTG), and the like. Among them, 2-methoxyethyl acrylate (MOEA) is preferred because particularly high yellowing resistance can be obtained.

[0012] The lower limit of the content of the structural unit derived from the alkoxy group-containing (meth)acrylate in the (meth)acrylic copolymer is 60% by weight. By using a (meth)acrylic copolymer containing 60% by weight or more of the structural unit derived from the alkoxy group-containing (meth)acrylate, the pressure-sensitive adhesive tape of the present invention can exhibit high yellowing resistance. The content of the structural unit derived from the alkoxy group-containing (meth)acrylate is preferably 70% by weight or more, and more preferably 75% by weight or more. The upper limit of the content of the structural unit derived from the alkoxy group-containing (meth)acrylate is not particularly limited, but is preferably 97% by weight, and more preferably 85% by weight.

[0013] The (meth)acrylic copolymer preferably further contains a structural unit derived from a (meth)acrylate having a glass transition temperature of 60°C or higher and not containing a carboxyl group. The pressure-sensitive adhesive layer containing a (meth)acrylic copolymer containing a structural unit derived from the above alkoxy group-containing (meth)acrylate is difficult to swell by sebum, and in addition, even if it swells, it exhibits stress relaxation properties that do not impose a load on the liquid crystal, and excellent yellowing resistance can be exhibited. However, since the pressure-sensitive adhesive layer having such excellent stress relaxation properties is highly flexible, there is a risk of foaming due to the gas remaining when the cover panel and the touch sensor panel are bonded together. By using a (meth)acrylate having a glass transition temperature of 60°C or higher in combination, the storage elastic modulus of the pressure-sensitive adhesive layer at room temperature (23°C) and high temperature (140°C) can be made relatively high, and foaming can be suppressed. Here, the reason for specifying "not containing a carboxyl group" is that if a (meth)acrylic copolymer containing many structural units derived from a (meth)acrylate containing a carboxyl group is used, the resulting pressure-sensitive adhesive layer may easily swell with sebum and the yellowing resistance may decrease.

[0014] Specific examples of the (meth)acrylate having a glass transition temperature of 60°C or higher and not containing a carboxyl group include methyl methacrylate (MMA), isobornyl acrylate (IBOA), cyclohexyl methacrylate (CHMA), and the like. Among them, methyl methacrylate (MMA) is preferred because a pressure-sensitive adhesive layer having particularly excellent anti-foaming properties can be obtained. In addition, the (meth)acrylate having a glass transition temperature of 60°C or higher and not containing a carboxyl group preferably does not contain nitrogen. By not containing nitrogen, swelling by sebum and a decrease in yellowing resistance can be suppressed.

[0015] The glass transition temperature in the above (meth)acrylic copolymer is 60°C or higher, and the preferable lower limit of the content of the structural unit derived from the (meth)acrylate not containing a carboxyl group is 3% by weight, and the preferable upper limit is 15% by weight. The pressure-sensitive adhesive layer containing the structural unit derived from the (meth)acrylate not containing a carboxyl group within this range when the glass transition temperature is 60°C or higher can exhibit excellent yellowing resistance and foam resistance. The more preferable lower limit of the content of the structural unit derived from the (meth)acrylate not containing a carboxyl group is 5% by weight, and the more preferable upper limit is 10% by weight.

[0016] The above (meth)acrylic copolymer preferably further contains a structural unit derived from a monomer having a crosslinkable functional group. When containing the structural unit derived from the monomer having a crosslinkable functional group, the (meth)acrylic copolymer chains are crosslinked when a crosslinking agent is used in combination. At that time, the gel fraction can be adjusted by adjusting the degree of crosslinking.

[0017] Examples of the above crosslinkable functional group include a hydroxyl group, a carboxyl group, a glycidyl group, etc. Among them, since it is easy to adjust the gel fraction of the pressure-sensitive adhesive layer, a hydroxyl group or a carboxyl group is preferable. Although an amino group, an amide group, a nitrile group, etc. are also crosslinkable functional groups, when using a monomer having these crosslinkable functional groups, the pressure-sensitive adhesive layer is likely to swell in sebum, and there is a risk of deterioration in yellowing resistance. Therefore, it is preferably not used in the present invention.

[0018] Examples of the monomer having the above hydroxyl group include (meth)acrylic acid esters having a hydroxyl group such as 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Examples of the monomer having the above carboxyl group include (meth)acrylic acid, etc. Examples of the monomer having the above glycidyl group include glycidyl (meth)acrylate, etc.

[0019] The content of the structural unit derived from the monomer having the crosslinkable functional group in the above (meth)acrylic copolymer is not particularly limited, but the preferable lower limit is 0.01% by weight and the preferable upper limit is 5% by weight. Particularly when the crosslinkable functional group is a carboxyl group, the content of the structural unit derived from the monomer having the carboxyl group is preferably 5% by weight or less. When the content of the structural unit derived from the monomer having a carboxyl group exceeds 5% by weight, the adhesive layer is likely to swell in sebum, and the yellowing resistance may decrease.

[0020] The above (meth)acrylic copolymer may further contain structural units derived from other alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, and n-hexyl (meth)acrylate, as long as the effects of the present invention are not inhibited. Further, it may contain structural units derived from (meth)acrylates having an aromatic group such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate. However, when using (meth)acrylates with a long chain length (specifically, 6 or more carbon atoms), the SP of the resulting (meth)acrylic copolymer tends to be low, and the adhesive layer may easily swell in sebum. Therefore, as described later, it is preferable to select the type and blending amount of other alkyl (meth)acrylates within the range where the SP value of the (meth)acrylic copolymer is 10.2 or more.

[0021] The above (meth)acrylic copolymer preferably does not contain a structural unit derived from a nitrogen-containing (meth)acrylate. When the above (meth)acrylic copolymer contains a structural unit derived from a nitrogen-containing (meth)acrylate, the adhesive layer is likely to swell in sebum, and the yellowing resistance may decrease.

[0022] The above (meth)acrylic copolymer preferably has an SP value calculated by the Fedors method of 10.2 or more. When the SP value is 10.2 or more, it becomes difficult to swell in sebum and excellent yellowing resistance can be exhibited. The SP value is more preferably 10.25 or more, and still more preferably 10.3 or more. The upper limit of the SP value is not particularly limited, but is about 10.6 as the upper limit because synthesis is difficult. Incidentally, the SP value is called the solubility parameter and is an index that can represent the ease of dissolution. In this specification, the Fedors method (R.F. Fedors, Polym. Eng. Sci., 14(2), 147-154(1974)) is used for calculating the SP value. Further, the SP value of the (meth)acrylic copolymer can be calculated using its blending ratio (molar ratio) based on the SP value of each repeating unit alone in the copolymer. The SP value of the above (meth)acrylic copolymer can be adjusted by the selection of the monomers used in the polymerization of the (meth)acrylic copolymer and the blending ratio of the monomers.

[0023] The above (meth)acrylic copolymer preferably has a weight average molecular weight of 250,000 or more. When the weight average molecular weight of the above (meth)acrylic copolymer is 250,000 or more, the resulting adhesive tape can be made to have more excellent adhesive strength, and an adhesive tape that is even more excellent in resistance to sebum and yellowing resistance can be obtained. A more preferable lower limit of the weight average molecular weight of the above (meth)acrylic copolymer is 300,000, a still more preferable lower limit is 400,000, and a particularly preferable lower limit is 500,000. The upper limit of the weight average molecular weight of the above (meth)acrylic copolymer is not particularly limited, but a preferable upper limit is 2,000,000, and a more preferable upper limit is 1,800,000. Incidentally, the weight average molecular weight can be adjusted by polymerization conditions (for example, the type or amount of polymerization initiator, polymerization temperature, monomer concentration, etc.).

[0024] The method for preparing the above (meth)acrylic copolymer is not particularly limited, and examples thereof include a method of subjecting a (meth)acrylic monomer that is a source of the above structural unit to a radical reaction in the presence of a polymerization initiator. The polymerization method is not particularly limited, and conventionally known methods can be used. For example, solution polymerization (boiling point polymerization or isothermal polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc. are included. Among them, solution polymerization is preferred because the synthesis is simple.

[0025] When solution polymerization is used as the polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether, etc. These reaction solvents may be used alone or in combination of two or more.

[0026] The above polymerization initiator is not particularly limited, and examples thereof include organic peroxides, azo compounds, etc. Examples of the above organic peroxides include 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexyl peroxypivalate, t-butyl peroxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexyl peroxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxyisobutyrate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate, etc. Examples of the above azo compounds include azobisisobutyronitrile, azobiscyclohexanecarbonitrile, etc. These polymerization initiators may be used alone or in combination of two or more.

[0027] The above pressure-sensitive adhesive layer preferably contains a crosslinking agent. When the above (meth)acrylic copolymer contains a structural unit derived from a monomer having the above crosslinkable functional group, a crosslinked structure can be constructed by the crosslinking agent. The crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, metal chelate type crosslinking agents, and the like. Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred. When the pressure-sensitive adhesive tape of the present invention is used as an optical transparent pressure-sensitive adhesive tape, from the viewpoint of weather resistance, it is preferable to use a crosslinking agent that does not contain an aromatic ring.

[0028] The blending amount of the crosslinking agent preferably has a lower limit of 0.01 part by weight and an upper limit of 10 parts by weight, more preferably a lower limit of 0.1 part by weight and an upper limit of 5 parts by weight, based on 100 parts by weight of the (meth)acrylic copolymer.

[0029] The pressure-sensitive adhesive layer may contain a silane coupling agent. By containing a silane coupling agent, the adhesion to the adherend can be improved, so that the resistance of the pressure-sensitive adhesive tape to sebum and alkaline cleaning agents can be further enhanced.

[0030] The silane coupling agent is not particularly limited, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethylmethoxysilane, N-(2-aminoethyl)3-aminopropyltriethoxysilane, N-(2-aminoethyl)3-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptobutyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and the like. Among them, γ-glycidoxypropyltriethoxysilane and γ-mercaptopropyltrimethoxysilane are preferred.

[0031] The content of the above silane coupling agent is not particularly limited, but the preferable lower limit with respect to 100 parts by weight of the above (meth)acrylic copolymer is 0.1 part by weight, and the preferable upper limit is 5 parts by weight. When the content of the above silane coupling agent is 0.1 part by weight or more, the resistance to sebum and alkaline cleaning agents can be further enhanced. When the content is 5 parts by weight or less, the remaining glue during re-peeling can be suppressed. The more preferable lower limit of the content of the above silane coupling agent is 1 part by weight, and the more preferable upper limit is 3 parts by weight.

[0032] The above pressure-sensitive adhesive layer may contain, if necessary, additives such as plasticizers, emulsifiers, softeners, fillers, pigments, dyes, etc., tackifiers such as rosin-based resins and terpene-based resins, and other resins.

[0033] The above pressure-sensitive adhesive layer preferably has a gel fraction of 70% or more and 99% or less. When the gel fraction is within this range, the resistance to sebum can be further enhanced, and more excellent yellowing resistance can be exhibited. The more preferable lower limit of the gel fraction is 72%, and the further preferable lower limit is 75%. The more preferable upper limit of the gel fraction is 90%, and the further preferable upper limit is 80%. In addition, the "gel fraction" in this specification is a value expressed as a percentage of the weight of the pressure-sensitive adhesive layer after immersion in ethyl acetate and drying with respect to the weight of the pressure-sensitive adhesive layer before immersion in ethyl acetate as shown in the following formula. Gel fraction (wt%) = 100×(W2 - W0) / (W1 - W0) (W0: weight of the base material, W1: weight of the pressure-sensitive adhesive tape test piece before immersion in ethyl acetate, W2: weight of the pressure-sensitive adhesive tape test piece after immersion in ethyl acetate and drying)

[0034] The thickness of the above adhesive layer is not particularly limited, but the preferable lower limit is 5 μm and the preferable upper limit is 500 μm. When the thickness of the adhesive layer is 5 μm or more, the resulting adhesive tape can be made to have better adhesiveness. When the thickness of the adhesive layer is 500 μm or less, the resulting adhesive tape can be made to have better processability.

[0035] The above adhesive layer is not particularly limited, and examples thereof include an adhesive layer formed from a solvent-based adhesive composition, a hot-melt adhesive composition, an aqueous dispersion adhesive composition, and an active energy ray-curable adhesive composition. That is, examples of the above adhesive layer include a solvent-based adhesive layer, a hot-melt adhesive layer, an aqueous dispersion adhesive layer, and an active energy ray-curable adhesive layer. Here, the solvent-based adhesive composition means an adhesive composition in a form in which an adhesive (adhesive layer-forming component) is contained in an organic solvent. Also, the aqueous dispersion adhesive composition means an adhesive composition in a form in which an adhesive is contained in a solvent (aqueous solvent) mainly composed of water. From the viewpoint of suitably realizing adhesive characteristics, the above adhesive layer is preferably a non-active energy ray-curable adhesive layer. Among them, a solvent-based adhesive layer is preferable.

[0036] The adhesive tape of the present invention may be of a support type having a substrate or a non-support type having no substrate. In the case of the support type, the above adhesive layer may be formed on one side of the substrate or on both sides of the substrate.

[0037] The above-mentioned base material is not particularly limited. For example, polyolefin resin films such as polyethylene films and polypropylene films, polyester resin films such as PET films, ethylene-vinyl acetate copolymer films, polyvinyl chloride resin films, polyurethane resin films, etc. can be mentioned. In addition, polyolefin foam sheets such as polyethylene foam sheets and polypropylene foam sheets, polyurethane foam sheets, etc. can be mentioned. Among these base materials, a PET film is preferred. Also, from the viewpoint of impact resistance, a polyolefin foam sheet is preferred. In addition, as the above-mentioned base material, a base material printed black for preventing light transmission, a base material printed white for improving light reflectivity, a base material vapor-deposited with a metal, etc. can also be used.

[0038] The manufacturing method of the pressure-sensitive adhesive tape of the present invention is not particularly limited. For example, when the pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape having a base material, the following methods can be mentioned. First, a solvent is added to a (meth)acrylic copolymer and, if necessary, a crosslinking agent, etc. to prepare a solution of acrylic pressure-sensitive adhesive a. The obtained solution of acrylic pressure-sensitive adhesive a is applied to the surface of the base material, and the solvent in the solution is completely dried and removed to form an adhesive layer a. Next, a release film is superposed on the formed adhesive layer a in a state where its release-treated surface faces the adhesive layer a. Then, a release film different from the above release film is prepared, and a solution of acrylic pressure-sensitive adhesive b is applied to the release-treated surface of this release film, and the solvent in the solution is completely dried and removed, whereby a laminated film having an adhesive layer b formed on the surface of the release film is prepared. The obtained laminated film is superposed on the back surface of the base material on which the adhesive layer a is formed in a state where the adhesive layer b faces the back surface of the base material to prepare a laminate. Then, by pressing the above laminate with a rubber roller or the like, a pressure-sensitive adhesive tape having adhesive layers on both surfaces of the base material and the surfaces of the adhesive layers covered with release films can be obtained.

[0039] Further, two sets of laminated films are produced in the same manner, and these laminated films are overlapped on each of the two sides of the base material with the adhesive layer of the laminated film facing the base material to produce a laminate. By pressing this laminate with a rubber roller or the like, an adhesive tape having adhesive layers on both sides of the base material and the surface of the adhesive layer covered with a release film may be obtained.

[0040] The use of the adhesive tape of the present invention is not particularly limited, but since it has excellent yellowing resistance, it can be particularly preferably used for fixing parts of electronic devices that are frequently touched by human hands. Specifically, it can be preferably used for fixing members constituting display devices such as cover panels, touch panels, and touch sensors used in display devices such as liquid crystal display elements and organic EL elements.

[0041] The shape of the adhesive tape of the present invention is not particularly limited and may be square, rectangular, etc. However, when used for fixing members constituting a display device, a frame shape is preferable. Since the adhesive tape of the present invention can maintain a high adhesive force even at a site that is frequently touched by human hands, it can be preferably used even if the width of the frame-shaped adhesive tape is narrow.

Effects of the Invention

[0042] According to the present invention, an adhesive tape excellent in yellowing resistance can be provided.

Modes for Carrying Out the Invention

[0043] Examples will be given below to explain the aspects of the present invention in more detail, but the present invention is not limited only to these examples.

[0044] (Example 1) (1) Production of (meth)acrylic copolymer Ethyl acetate was added as a polymerization solvent into the reaction vessel and bubbled with nitrogen. Then, while nitrogen was flowing in, the reaction vessel was heated to start reflux. Subsequently, a polymerization initiator solution prepared by diluting 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator 10-fold with ethyl acetate was introduced into the reaction vessel. Further, 62.9 parts by weight of 2-methoxyethyl acrylate (MOEA), 14.5 parts by weight of methyl methacrylate (MMA), 0.3 part by weight of acrylic acid (Aac), 2.9 parts by weight of hydroxyethyl acrylate (HEA), and 19.4 parts by weight of ethyl acrylate (EA) were added dropwise over 2 hours. After completion of the dropwise addition, a polymerization initiator solution prepared by diluting 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator 10-fold with ethyl acetate was introduced into the reaction vessel again, and a polymerization reaction was carried out for 4 hours to obtain a solution containing a (meth)acrylic copolymer. The SP value of the (meth)acrylic copolymer calculated by the Fedors method is 10.27. Regarding the obtained (meth)acrylic copolymer, using GPC LF-804 (manufactured by Showa Denko KK) as a column, the weight average molecular weight was determined by gel permeation chromatography (Waters Corporation, 2690 Separations Model) and found to be 480,000.

[0045] (2) Manufacture of the pressure-sensitive adhesive tape Coronate L-45 (manufactured by Tosoh Corporation) as an isocyanate-based crosslinking agent was added to the obtained solution containing the (meth)acrylic copolymer so as to be 0.72 part by weight in terms of solid content ratio with respect to the (meth)acrylic copolymer. The obtained solution was coated on a PET film having a thickness of 75 μm and subjected to a release treatment so that the thickness of the pressure-sensitive adhesive layer after drying was 15 μm, and then dried at 110°C for 5 minutes. This pressure-sensitive adhesive layer was transferred onto a corona-treated PET film having a thickness of 50 μm as a base material and cured at 40°C for 48 hours to obtain a pressure-sensitive adhesive tape.

[0046] (3) Measurement of the gel fraction of the pressure-sensitive adhesive layer The obtained adhesive tape was cut into a flat rectangular shape of 20 mm × 40 mm to prepare test pieces, and the weights were measured. After immersing the test pieces in ethyl acetate at 23°C for 24 hours, the test pieces were taken out from ethyl acetate and dried at 110°C for 1 hour. The weights of the dried test pieces were measured, and the gel fraction was calculated using the following formula. Gel fraction (wt%) = 100×(W2 - W0) / (W1 - W0) (W0: weight of the base material, W1: weight of the adhesive tape test piece before immersion in ethyl acetate, W2: weight of the adhesive tape test piece after immersion in ethyl acetate and drying)

[0047] (Examples 2 to 11, Comparative Examples 1 to 3) An adhesive tape was obtained in the same manner as in Example 1 except that the types and blending amounts of the monomers used and the amount of the crosslinking agent were as shown in Table 1. In the table, CBA represents ethyl carbitol acrylate, PHEA represents phenoxy acrylate. MA represents methyl acrylate, nOA represents n-octyl acrylate, DMAA represents dimethylacrylamide, IBOA represents isobornyl acrylate, CHMA represents cyclohexyl methacrylate, and MTG represents methoxy triethylene glycol acrylate.

[0048] (Evaluation) The following evaluations were performed on the adhesive tapes obtained in the examples and comparative examples. The results are shown in Table 1.

[0049] (1) Yellowing resistance test A 50 mm × 100 mm, 100 μm thick PET film provided with a black printing layer having a width of 2 mm and a height of 15 μm on four sides was prepared. The obtained adhesive tape was cut into a rectangular shape of 50 mm × 100 mm, one surface was bonded to the prepared PET film, and the other surface was bonded to a 89 mm × 156 mm liquid crystal panel (manufactured by Innolux Corporation) to prepare a test piece. 10 mL of sebum fluid was dropped at the end of the test piece, and it was allowed to stand at room temperature, and the presence or absence of yellowing at the end of the screen was visually confirmed. Those in which the end of the screen did not turn yellow for 5 days or more were evaluated as "○", and those in which the end of the screen turned yellow in less than 5 days were evaluated as "×".

[0050] (2) Foam resistance test The obtained adhesive tape was cut into a rectangular shape of 50 mm × 125 mm. One side was bonded to a PET film (50 mm × 125 mm, thickness 50 μm), and the other side was bonded to an acrylic plate (50 mm × 125 mm, thickness 2 mm) to prepare a test piece. The test piece was left standing in an environment of 40°C / 0.3 MPa for 30 minutes, and the presence or absence of foaming of the test piece was visually confirmed. Those with no foaming observed at the end of the test piece were evaluated as "◎", those with only foaming less than 0.3 mm in diameter observed were evaluated as "○", and those with foaming of 0.3 mm or more in diameter observed were evaluated as "×".

[0051]

Table 1

Industrial applicability

[0052] According to the present invention, an adhesive tape excellent in yellowing resistance can be provided.

Claims

1. An adhesive tape having an adhesive layer containing a (meth)acrylic copolymer, the (meth)acrylic copolymer containing 60% by weight or more of structural units derived from an alkoxy group-containing (meth)acrylate.

2. 2. The adhesive tape according to claim 1, wherein the alkoxy group-containing (meth)acrylate is a compound represented by the following general formula (1): 【Chemistry 1】 In general formula (1), R １ represents a hydrogen atom or a methyl group, R ２ represents an alkylene group having 2 to 4 carbon atoms, R ３ represents an alkyl group or an aryl group having 1 or more and 10 or less carbon atoms, and n represents an integer of 1 or more and 10 or less.

3. 3. The adhesive tape according to claim 1, wherein the alkoxy group-containing (meth)acrylate is 2-methoxyethyl acrylate.

4. 4. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer further contains a structural unit derived from a (meth)acrylate having a glass transition temperature of 60° C. or higher and containing no carboxyl group.

5. 5. The adhesive tape according to claim 4, wherein the (meth)acrylate having a glass transition temperature of 60[deg.] C. or higher and containing no carboxyl group is methyl methacrylate.

6. 6. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer further comprises a structural unit derived from a monomer having a crosslinkable functional group.

7. 7. The pressure-sensitive adhesive tape according to claim 1, 2, 3, 4, 5 or 6, wherein the (meth)acrylic copolymer does not contain any structural unit derived from a nitrogen-containing (meth)acrylate.

8. 8. The adhesive tape according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the (meth)acrylic copolymer has an SP value of 10.2 or more as calculated by the Fedors method.

9. 9. The adhesive tape according to claim 1, which is used for fixing components of electronic devices.

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