Adhesive tape

Abstract

An objective of the present invention is to provide a pressure-sensitive adhesive tape that has excellent adhesiveness to a non-smooth surface such as paper and can be easily peeled off without damaging the adherend. The present invention provides a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer having a shear storage elastic modulus of 1 × 104 Pa to 5 × 104 Pa at 23°C and 1 Hz, a 180° adhesive strength of 0.3-0.7 N / 25 mm, and a thickness of 30 μm or more.

Description

[Technical Field]

[0001] This invention relates to adhesive tape. [Background technology]

[0002] Adhesive tapes have been widely used to fix components in electronic components, vehicles, housing, and building materials. In addition, low-tack tapes that are intended to be peeled off (re-peeled) after use are used, for example, in packaging applications. Patent Document 1 describes a re-peelable packaging adhesive tape having an adhesive layer made of a specific adhesive containing a plasticizer on at least one side of a substrate. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-046118 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Such adhesive tapes are desirable to be easily removed without damaging the adherend, but if the adhesive strength is too low, they will peel off during use. In particular, when the surface of the adherend is not smooth (rough), the adhesive tape may not adhere sufficiently to the adherend. While increasing the thickness of the adhesive layer can improve adhesion to uneven surfaces, generally speaking, in adhesive tapes, thicker adhesive layers result in higher adhesive strength. Therefore, it has been difficult to obtain an adhesive layer that has a certain thickness, adheres sufficiently to the substrate, and can be easily peeled off. Furthermore, if one attempts to lower the adhesive strength while maintaining the thickness of the adhesive layer, one might consider increasing the cohesive force of the adhesive layer. However, increasing the molecular weight of the base polymer or increasing the degree of crosslinking of the adhesive layer can sometimes worsen adhesion to substrates with low surface smoothness, such as paper.

[0005] An object of the present invention is to provide an adhesive tape that has excellent adhesion to a non-smooth surface such as paper and can be easily peeled off without damaging the adherent.

Means for Solving the Problems

[0006] The present invention is an adhesive tape having an adhesive layer, wherein the adhesive layer has a shear storage modulus at 23°C and 1 Hz of 1×10 4 , 4 , 4 , 4 , 4 , Pa or more and 5×10 4 Pa or less, and an adhesion of 180° is 0.3 N / 25 mm or more and 0.7 N / 25 mm or less, and the thickness is 30 μm or more. The present invention will be described in detail below.

[0007] The inventor has studied adjusting the shear storage modulus of the adhesive layer at 23°C and 1 Hz to a specific relatively low range and adjusting the 180° adhesion of the adhesive layer to a specific relatively low range in an adhesive tape having an adhesive layer with a thickness of 30 μm or more. The inventor has found that such an adhesive tape has excellent adhesion to a non-smooth surface such as paper while having an adhesive layer with a certain thickness or more, and can be easily peeled off without damaging the adherent, and has thus completed the present invention.

[0008] The adhesive tape of the present invention is an adhesive tape having an adhesive layer. The adhesive layer has a lower limit of the shear storage modulus at 23°C and 1 Hz of 1×10[[ID=​​​​​​​​​​​​​​Pa, a more preferable upper limit is 3 × 10 4 Pa, and a more preferable lower limit is 2 × 10⁻⁶ 4 It is Pa. The shear storage modulus of the adhesive layer at 23°C and 1 Hz can be obtained, for example, by measuring the dynamic viscoelastic spectrum from -40 to 140°C using a viscoelastic spectrometer (DVA-200, manufactured by IT Measurement Control Co., Ltd.) under the conditions of a simple heating mode with a heating rate of 5°C / min and 1 Hz, and then obtaining the storage modulus at 23°C. The shape of the sample used for measurement is not particularly limited, but for example, the adhesive layer can be measured as a rectangle with a thickness of 1 mm, a length of 10 mm, and a width of 6 mm.

[0009] The adhesive layer described above has a 180° adhesion strength of 0.3 N / 25 mm at the lower limit and 0.7 N / 25 mm at the upper limit. If the 180° adhesive strength is 0.3 N / 25 mm or higher, the adhesive layer has adequate adhesive strength, improving adhesion to non-smooth surfaces such as paper. If the 180° adhesive strength is 0.7 N / 25 mm or lower, the adhesive strength of the adhesive layer is sufficiently low, allowing for easy removal (re-removal) without damaging the adherend. The preferred lower limit of the 180° adhesive strength is 0.35 N / 25 mm, the preferred upper limit is 0.65 N / 25 mm, the more preferred lower limit is 0.4 N / 25 mm, and the more preferred upper limit is 0.6 N / 25 mm. The 180° adhesion strength of the adhesive layer can be measured by the following method. A sample for measurement is obtained by first cutting adhesive tape to a width of 25 mm and a length of 10 cm, attaching it to a polyethylene terephthalate board measuring 50 mm in width, 12.5 cm in length, and 2 mm in thickness (for example, PET-6010, manufactured by Takiron CI Co., Ltd., or an equivalent product), and running a 2 kg roller back and forth once. A peel test is then performed on the obtained sample using, for example, an Autograph (manufactured by Shimadzu Corporation), in accordance with JIS Z0237:2009, at a temperature of 23°C and a relative humidity of 50%, at a tensile speed of 300 mm / min, peeling the adhesive tape off the polyethylene terephthalate board in a 180° direction, and measuring the 180° adhesive strength (N / 25 mm).

[0010] Methods for adjusting the shear storage modulus and 180° adhesion of the adhesive layer at 23°C and 1Hz to the above range include, for example, adjusting the composition and molecular weight (weight-average molecular weight (Mw)) of the base polymer contained in the adhesive layer, and adjusting the degree of crosslinking (gel fraction) of the adhesive layer.

[0011] The adhesive layer described above is not particularly limited and includes, for example, an acrylic adhesive layer, a rubber-based adhesive layer, a urethane adhesive layer, a silicone-based adhesive layer, and the like. Among these, an acrylic adhesive layer containing a (meth)acrylic polymer is preferred because it is easy to adjust the molecular weight and degree of crosslinking, and it is excellent in terms of heat resistance, weather resistance, and cost.

[0012] The above-mentioned (meth)acrylic polymer is a polymer that contains constituent units derived from (meth)acrylic monomers. The above (meth)acrylic monomers are not particularly limited, and examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, isomiristyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc. These (meth)acrylic monomers may be used alone or in combination of two or more. Note that "(meth)acrylic" means acrylic or methacrylic, and "(meth)acrylate" means acrylate or methacrylate.

[0013] In particular, (meth)acrylic acid esters having an alkyl group with 12 or more carbon atoms and having a glass transition temperature (Tg) of 0°C or less when homopolymerized (hereinafter also referred to as "(meth)acrylic acid ester (a)") are preferred. That is, it is preferable that the above (meth)acrylic polymer contains constituent units derived from the above (meth)acrylic acid ester (a). Furthermore, it is also preferable to use in combination a (meth)acrylic acid ester (hereinafter also referred to as "(meth)acrylic acid ester (b)") having an alkyl group with 8 or more carbon atoms and less than 12 carbon atoms, and having a glass transition temperature (Tg) of 0°C or less when formed as a homopolymer. That is, it is more preferable that the (meth)acrylic polymer contains, in addition to the constituent units derived from the (meth)acrylic acid ester (a), constituent units derived from the (meth)acrylic acid ester (b). The inclusion of these relatively long-carbon alkyl groups in the (meth)acrylic polymer makes it easier to adjust the shear storage modulus and 180° adhesive strength of the adhesive layer at 23°C and 1 Hz to within the specified range. As a result, the adhesive layer exhibits improved adhesion to non-smooth surfaces such as paper, and can be peeled off more easily without damaging the adherend during peeling (re-peeling).

[0014] The glass transition temperature (Tg) of the above (meth)acrylic acid ester (a) and the above (meth)acrylic acid ester (b) is not particularly limited as long as it is 0°C or lower. However, from the viewpoint of adjusting the shear storage modulus and 180° adhesion of the adhesive layer at 23°C and 1 Hz to a more preferable range, the preferred lower limit is -80°C and the preferred upper limit is -5°C. A more preferred lower limit for the above glass transition temperature (Tg) is -70°C and a more preferred upper limit is -10°C. The glass transition temperature (Tg) of the homopolymer can be measured, for example, using differential scanning calorimetry (manufactured by TA Instruments) or the like for homopolymers with a weight average molecular weight (Mw) of about 5000 to 1,000,000 or a degree of polymerization of about 50 to 10,000. More specifically, the value obtained in the 2nd run can be used when measurement is performed under a nitrogen atmosphere at a heating rate of 10 °C / min.

[0015] The above (meth)acrylate (a) is not particularly limited. Among the above-mentioned (meth)acrylic monomers, for example, lauryl acrylate (Tg of the homopolymer is -23 °C), lauryl methacrylate (Tg of the homopolymer is -65 °C), etc. can be mentioned. Further, isomyristyl acrylate (Tg of the homopolymer is -56 °C), isostearyl acrylate (Tg of the homopolymer is -18 °C), etc. can be mentioned. Among them, at least one selected from the group consisting of lauryl acrylate, lauryl methacrylate, and isostearyl acrylate is preferable because it is easier to adjust the shear storage modulus and 180° adhesive strength of the above adhesive layer at 23 °C and 1 Hz to a more preferable range. Further, lauryl acrylate is more preferable.

[0016] In the above (meth)acrylic polymer, the content of the structural unit derived from the above (meth)acrylate (a) is not particularly limited, but the preferable lower limit is 40% by weight. If the content of the above structural unit is 40% by weight or more, it becomes easier to adjust the shear storage modulus and 180° adhesive strength of the above adhesive layer at 23 °C and 1 Hz to the above range. Thereby, the above adhesive layer has better adhesion to non-smooth surfaces such as paper and can be peeled off more easily without damaging the adherend during peeling (re-peeling). The more preferable lower limit of the content of the above structural unit is 45% by weight. The upper limit of the content of the above structural unit is not particularly limited, but the preferable upper limit is 90% by weight, and the more preferable upper limit is 80% by weight.

[0017] The above (meth)acrylic acid ester (b) is not particularly limited. Among the above-mentioned (meth)acrylic monomers, for example, 2-ethylhexyl acrylate (Tg of the homopolymer is -70°C), octyl acrylate (Tg of the homopolymer is -65°C), etc. can be mentioned. Furthermore, isononyl acrylate (Tg of the homopolymer is -58°C), isodecyl acrylate (Tg of the homopolymer is -62°C), etc. can be mentioned. Among them, 2-ethylhexyl acrylate is preferred because the shear storage modulus of the above adhesive layer at 23°C and 1 Hz is more easily adjusted to a more preferable range.

[0018] In the above (meth)acrylic polymer, the content of the structural unit derived from the above (meth)acrylic acid ester (b) is not particularly limited. From the viewpoint of adjusting the shear storage modulus and 180° adhesive strength of the above adhesive layer to a more preferable range, the preferable lower limit of the content of the above structural unit is 20% by weight, the preferable upper limit is 60% by weight, the more preferable lower limit is 30% by weight, and the more preferable upper limit is 50% by weight.

[0019] The above (meth)acrylic polymer preferably further contains a structure derived from a crosslinkable functional group-containing monomer. Since the above (meth)acrylic polymer contains a structure derived from the above crosslinkable functional group-containing monomer, the cohesive force of the above adhesive layer can be adjusted by crosslinking of the crosslinkable functional group. Therefore, it becomes easier to adjust the adhesive strength of the above adhesive layer to the above range, and it also becomes easier to adjust the shear storage modulus at 23°C and 1 Hz to the above range. As a result, the adhesion of the above adhesive layer to a non-smooth surface such as paper is further improved, and it can be peeled off more easily without damaging the adherend during peeling (re-peeling). The above crosslinkable functional group may or may not be crosslinked, but it is more preferable that it is crosslinked. However, even if it remains in a non-crosslinked structure, the cohesive force of the above adhesive layer is increased by the interaction between the functional groups.

[0020] Examples of the above-mentioned crosslinkable functional group-containing monomers include monomers containing carboxyl groups, hydroxyl groups, epoxy groups, double bonds, triple bonds, amino groups, amide groups, nitrile groups, and the like. These crosslinkable functional group-containing monomers may be used individually or in combination of two or more. Among these, at least one selected from the group consisting of carboxyl group-containing monomers and hydroxyl group-containing monomers is preferred. Hydroxyl group-containing monomers are more preferred because crosslinking with an isocyanate-based crosslinking agent makes it easier to adjust the shear storage modulus of the adhesive layer at 23°C and 1 Hz to the above range. Furthermore, the above-mentioned monomer containing a crosslinkable functional group may also contain alkyl groups, ether groups, carbonyl groups, ester groups, carbonate groups, amide groups, urethane groups, and the like.

[0021] Examples of carboxyl group-containing monomers include (meth)acrylic acid-based monomers such as (meth)acrylic acid. Examples of hydroxyl group-containing monomers include 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Examples of epoxy group-containing monomers include glycidyl (meth)acrylate. Examples of double bond-containing monomers include allyl (meth)acrylate and hexanediol di(meth)acrylate. Examples of triple bond-containing monomers include propargyl (meth)acrylate. Examples of amide group-containing monomers include (meth)acrylamide.

[0022] The content of the structure derived from the monomer having the crosslinkable functional group in the above (meth)acrylic polymer is not particularly limited, but from the viewpoint of adjusting the shear storage modulus of the adhesive layer at 23°C and 1 Hz to a more preferable range, the preferred lower limit of the content of the above constituent units is 0.1% by weight and the preferred upper limit is 30% by weight. The more preferred lower limit of the content of the above constituent units is 0.5% by weight and the more preferred upper limit is 25% by weight. Furthermore, while the content of the structure derived from the hydroxyl group-containing monomer in the (meth)acrylic polymer is not particularly limited, from the viewpoint of adjusting the shear storage modulus of the adhesive layer at 23°C and 1 Hz to a more preferable range, the preferred lower limit of the content of the constituent unit is 1% by weight, and the preferred upper limit is 20% by weight. A more preferred lower limit of the content of the constituent unit is 3% by weight, and a more preferred upper limit is 10% by weight.

[0023] To obtain the above (meth)acrylic polymer, a monomer mixture containing the above (meth)acrylic monomer and the above crosslinkable functional group-containing monomer can be copolymerized by radical reaction in the presence of a polymerization initiator. Conventional known methods can be used for radical reaction of the above monomer mixture, i.e., polymerization methods, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, and bulk polymerization.

[0024] The weight-average molecular weight (Mw) of the above (meth)acrylic polymer is not particularly limited, but a preferred upper limit is 1 million. If the weight-average molecular weight (Mw) is 1 million or less, the shear storage modulus of the adhesive layer at 23°C and 1 Hz can be easily adjusted to the above range, and the adhesion of the adhesive layer to non-smooth surfaces such as paper is further improved. A more preferred upper limit for the weight-average molecular weight (Mw) is 950,000, and an even more preferred upper limit is 900,000. The lower limit of the weight-average molecular weight (Mw) is not particularly limited, but from the viewpoint of the adhesive strength and shape retention of the adhesive layer, a preferred lower limit is 400,000, and a more preferred lower limit is 500,000. The weight-average molecular weight of (meth)acrylic polymers can be determined, for example, by GPC (Gel Permeation Chromatography) on a standard polystyrene basis. More specifically, for example, it can be measured using a Waters 2690 Separations Module as the measuring instrument, a Showa Denko GPC KF-806L column, and ethyl acetate as the solvent, with a sample flow rate of 1 mL / min and a column temperature of 40°C.

[0025] The above adhesive layer may contain a tackifying resin. Examples of the tackifying resins mentioned above include rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, coumarone indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, and C5-C9 copolymer petroleum resins. These tackifying resins may be used individually or in combination of two or more types.

[0026] The content of the tackifying resin is not particularly limited, but it is preferable not to include the tackifying resin from the viewpoint that the adherend can be peeled off more easily without damaging it during peeling (re-peeling). If the tackifying resin is included, the preferred upper limit is 10 parts by weight per 100 parts by weight of the resin that is the main component of the adhesive layer (for example, a (meth)acrylic polymer). If the content of the tackifying resin is 10 parts by weight or less, the adherend can be peeled off more easily without damaging it during peeling (re-peeling).

[0027] Preferably, the adhesive layer contains a crosslinking agent so that a crosslinked structure is formed between the main chains of the resin constituting the adhesive layer (for example, the (meth)acrylic polymer, the tackifying resin, etc.). The above crosslinking agent is not particularly limited and examples include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. In particular, when the (meth)acrylic polymer contains structural units derived from the hydroxyl group-containing monomer, isocyanate-based crosslinking agents are preferred because crosslinking with the hydroxyl group makes it easier to adjust the shear storage modulus of the adhesive layer at 23°C and 1 Hz to the above range. The amount of the crosslinking agent is preferably 0.01 to 10 parts by weight, and more preferably 0.1 to 7 parts by weight, per 100 parts by weight of the resin (for example, the (meth)acrylic polymer) that forms the main component of the adhesive layer.

[0028] The above adhesive layer may further contain an inorganic filler such as fumed silica. By incorporating the above inorganic filler, the cohesive force of the adhesive layer can be increased.

[0029] The adhesive layer described above may further contain known additives such as plasticizers, resins, surfactants, waxes, and particulate fillers. These additives may be used individually or in combination of two or more.

[0030] The gel fraction of the adhesive layer described above is not particularly limited, but a preferred lower limit is 85% by weight and a preferred upper limit is 95% by weight. If the gel fraction is 85% by weight or more, the 180° adhesive strength of the adhesive layer is more easily adjusted to the above range, and peeling (re-peeling) can be done more easily without damaging the adherend. If the gel fraction is 95% by weight or less, the shear storage modulus of the adhesive layer at 23°C and 1 Hz is more easily adjusted to the above range, and the adhesion of the adhesive layer to non-smooth surfaces such as paper is further improved. A more preferred lower limit for the gel fraction is 86% by weight, a more preferred upper limit is 94% by weight, an even more preferred lower limit is 87% by weight, and an even more preferred upper limit is 93% by weight. The gel fraction of the adhesive layer can be measured by the following method. 0.1 g of only the adhesive layer (adhesive composition) is taken from the adhesive tape and immersed in 50 mL of ethyl acetate. The mixture is shaken in a shaker at 23°C and 200 rpm for 24 hours. After shaking, the ethyl acetate and the adhesive composition that has absorbed and swollen with ethyl acetate are separated using a metal mesh (mesh size #200). The separated adhesive composition is dried at 110°C for 1 hour. The weight of the adhesive composition including the metal mesh after drying is measured, and the gel fraction of the adhesive layer is calculated using the following formula. Gel fraction (weight %) = 100 × (W1 - W2) / W0 (W0: initial weight of adhesive composition, W1: weight of adhesive composition including metal mesh after drying, W2: initial weight of metal mesh)

[0031] The minimum thickness of the adhesive layer is 30 μm. The adhesive tape of the present invention has an adhesive layer with a certain thickness, yet exhibits excellent adhesion to non-smooth surfaces such as paper, and can be easily peeled off without damaging the adherend, because the shear storage modulus and 180° adhesive strength of the adhesive layer at 23°C and 1 Hz are adjusted to the above range. However, if the thickness of the adhesive layer is reduced, the conformability decreases, which may reduce the adhesion of the adhesive layer to the adherend. The preferred lower limit for the thickness of the adhesive layer is 40 μm, and the more preferred lower limit is 50 μm. The upper limit of the thickness of the adhesive layer is not particularly limited, but from the viewpoint of adhesive strength, shape retention, etc., a preferred upper limit is 200 μm, and a more preferred upper limit is 150 μm.

[0032] The adhesive tape of the present invention may be a non-support type without a base material, but it is preferable to be a support type having a base material. In the case of a support type, the adhesive tape of the present invention may be a single-sided adhesive tape having an adhesive layer on only one side of the base material, or a double-sided adhesive tape having adhesive layers on both sides of the base material, but it is preferable to be a single-sided adhesive tape having an adhesive layer on only one side of the base material.

[0033] The above-mentioned substrate is not particularly limited, and examples of materials for the substrate include polyethylene terephthalate, polyethylene naphthalate, polyacetal, polyamide, polycarbonate, polyphenylene ether, polybutylene terephthalate, ultra-high molecular weight polyethylene, syndiotactic polystyrene, polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, liquid crystal polymer, etc. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred due to their excellent heat resistance.

[0034] The thickness of the above-mentioned substrate is not particularly limited, but a preferred lower limit is 5 μm and a preferred upper limit is 188 μm. By having the thickness of the above-mentioned substrate within the above range, an adhesive tape with appropriate stiffness and excellent handling properties can be obtained. A more preferred lower limit for the thickness of the above-mentioned substrate is 12 μm and a more preferred upper limit is 125 μm.

[0035] The adhesive tape of the present invention has an adhesive layer with a certain thickness or greater, yet exhibits excellent adhesion to non-smooth surfaces such as paper, and can be easily peeled off without damaging the adherend, because the shear storage modulus and 180° adhesive strength of the adhesive layer at 23°C and 1 Hz are adjusted to the above range. Methods for adjusting the shear storage modulus and 180° adhesive strength of the adhesive layer at 23°C and 1 Hz to the above range include, as described above, adjusting the composition and molecular weight (weight-average molecular weight (Mw)) of the base polymer contained in the adhesive layer, and adjusting the degree of crosslinking (gel fraction) of the adhesive layer. In particular, it is especially preferable that the adhesive layer contains a (meth)acrylic polymer, that the (meth)acrylic polymer contains 40% by weight or more of the constituent units derived from the (meth)acrylic acid ester (a) described above, has a weight-average molecular weight of 1 million or less, has a gel fraction of 85% by weight or more and 95% by weight or less of the adhesive layer, and has a thickness of 30 μm or more. An adhesive tape having such an adhesive layer is also one of the present inventions. In such an adhesive tape of the present invention, it is preferable that the adhesive layer, the (meth)acrylic polymer, etc. are the same as described above, and in particular, it is preferable that the shear storage modulus of the adhesive layer at 23°C and 1 Hz is adjusted to the above range. In other words, the above adhesive layer has a shear storage modulus of 1 × 10 at 23°C and 1 Hz. 4 Pa or higher, 5×10 4 It is preferable that the value is Pa or less.

[0036] The applications of the adhesive tape of the present invention are not particularly limited, but it is preferably used as a low-tack tape intended to be peeled off (re-peeled off) after use, for example, in packaging applications. [Effects of the Invention]

[0037] According to the present invention, it is possible to provide an adhesive tape that has excellent adhesion to non-smooth surfaces such as paper and can be easily peeled off without damaging the adherend. [Modes for carrying out the invention]

[0038] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0039] (Example 1) (1) Preparation of (meth)acrylic polymers 52 parts by weight of ethyl acetate was placed in a reactor equipped with a thermometer, stirrer, and condenser, and after purging with nitrogen, the reactor was heated and reflux was started. Thirty minutes after the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. 47.2 parts by weight of 2-ethylhexyl acrylate, 47.5 parts by weight of lauryl acrylate, 5 parts by weight of 4-hydroxybutyl acrylate, and 0.3 parts by weight of acrylic acid were added dropwise over 1 hour and 30 minutes, uniformly and gradually, and the reaction was allowed to proceed. Thirty minutes after the end of the dropwise addition, 0.1 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction was continued for a further 5 hours. A solution of (meth)acrylic polymer was obtained by cooling while diluting the reactor with ethyl acetate. The weight-average molecular weight of the obtained (meth)acrylic polymer was measured using a Waters 2690 Separations Module as the measuring instrument, a Showa Denko GPC KF-806L as the column, and ethyl acetate as the solvent, under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C.

[0040] (2) Manufacturing of adhesive tape To the obtained (meth)acrylic polymer solution, Coronate L-45 (manufactured by Tosoh Corporation) was added as an isocyanate crosslinking agent to 100 parts by weight of (meth)acrylic polymer, so that the solid content was 0.8 parts by weight, and the mixture was thoroughly stirred to obtain an adhesive solution. The obtained adhesive solution was coated onto a 100 μm thick polyethylene terephthalate (PET) film as a substrate using an applicator so that the dry film thickness would be 30 μm, and the tape was dried at 110°C for 3 minutes to obtain an adhesive tape.

[0041] (3) Measurement of gel fraction 0.1 g of only the adhesive layer (adhesive composition) was taken from the adhesive tape and immersed in 50 mL of ethyl acetate. The mixture was shaken in a shaker at 23°C and 200 rpm for 24 hours. After shaking, the ethyl acetate and the adhesive composition that had absorbed and swollen with ethyl acetate were separated using a metal mesh (mesh size #200). The separated adhesive composition was dried at 110°C for 1 hour. The weight of the adhesive composition including the metal mesh after drying was measured, and the gel fraction of the adhesive layer was calculated using the following formula. Gel fraction (weight %) = 100 × (W1 - W2) / W0 (W0: initial weight of adhesive composition, W1: weight of adhesive composition including metal mesh after drying, W2: initial weight of metal mesh)

[0042] (4) Measurement of 180° adhesion Adhesive tape, pre-cut to a width of 25 mm and a length of 10 cm, was attached to a polyethylene terephthalate board (manufactured by Takiron CI Co., Ltd., product name PET-6010) measuring 50 mm wide, 12.5 cm long, and 2 mm thick. A 2 kg roller was then passed back and forth once to obtain a sample for measurement. Using an Autograph (manufactured by Shimadzu Corporation), a peel test was performed on the obtained sample in accordance with JIS Z0237:2009, at a temperature of 23°C and a relative humidity of 50%, at a tensile speed of 300 mm / min, peeling the adhesive tape off the polyethylene terephthalate board in a 180° direction. The 180° adhesive strength (N / 25 mm) was then measured.

[0043] (5) Measurement of shear storage modulus For the adhesive tape, the dynamic viscoelastic spectrum was measured from -40 to 140°C using a viscoelastic spectrometer (IT Measurement Control Co., Ltd., DVA-200) under the conditions of a simple heating mode with a heating rate of 5°C / min and 1 Hz. The storage modulus at 23°C was defined as the shear storage modulus of the adhesive layer at 23°C and 1 Hz.

[0044] (Examples 2-12, Comparative Examples 1-11) Adhesive tapes were obtained in the same manner as in Example 1, except that the composition and weight-average molecular weight of the (meth)acrylic polymer and the amount of crosslinking agent were changed as shown in Tables 1 and 2. As crosslinking agents, Coronate HX (manufactured by Tosoh Corporation), an isocyanate-based crosslinking agent, and Tetrad C (manufactured by Mitsubishi Gas Chemical Company), an epoxy-based crosslinking agent, were also used.

[0045] <Rating> The adhesive tapes obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 1 and 2.

[0046] (1) Damage assessment of the adherend Adhesive tape was applied to the paper of a Campus notebook (manufactured by Kokuyo Co., Ltd.) and left to stand for 20 minutes. After standing, a peel test was performed using a high-speed peel tester (manufactured by Tester Sangyo Co., Ltd.) to peel off the adhesive tape in a 180° direction at a tensile speed of 50 M / min. A circle (○) indicated that the surface of the notebook paper did not tear, while a cross (×) indicated that it did. In Comparative Example 11, however, the adhesive layer underwent cohesive failure, leaving adhesive residue on the notebook paper and preventing peeling.

[0047] (2) Evaluation of adhesion to non-smooth surfaces Adhesive tape was applied to the paper of a Campus notebook (Kokuyo Co., Ltd.) and to washi paper (Kokuyo Co., Ltd., flowing cloud pattern), respectively, and then pressed down by passing a 2kg roller back and forth once. When the adhesive tape portion was grasped and lifted, it was marked as ◎ if both the notebook paper and washi paper lifted together with the adhesive tape, ○ if the notebook paper lifted together with the adhesive tape but the washi paper did not lift and the adhesive tape peeled off, and × if neither the notebook paper nor the washi paper lifted and the adhesive tape peeled off.

[0048] [Table 1]

[0049] [Table 2]

[0050] BA: Butyl acrylate 2-EHA:2-Ethylhexylacrylate LA: Lauryl acrylate LMA: Lauryl methacrylate ISTA: Isostearyl acrylate 4-HBA:4-hydroxybutyl acrylate AAc: Acrylic acid [Industrial applicability]

[0051] According to the present invention, it is possible to provide an adhesive tape that has excellent adhesion to non-smooth surfaces such as paper and can be easily peeled off without damaging the adherend.

Claims

1. An adhesive tape having an adhesive layer, The adhesive layer has a shear storage modulus of 1 × 10 at 23°C and 1 Hz. ４ Pa or more, 5×10 ４ The pressure is less than or equal to Pa, the 180° adhesive strength is 0.3 N / 25 mm or more and 0.7 N / 25 mm or less, and the thickness is 30 μm or more. The adhesive layer contains a (meth)acrylic polymer, The (meth)acrylic polymer contains a constituent unit derived from a (meth)acrylic acid ester having an alkyl group with 12 or more carbon atoms and having a glass transition temperature of 0°C or less when homopolymerized, and the content of the constituent unit is 90% by weight or less. The (meth)acrylic polymer further contains a structure derived from a crosslinkable functional group-containing monomer, and the crosslinkable functional group-containing monomer includes at least one selected from the group consisting of carboxyl group-containing monomers and hydroxyl group-containing monomers. The adhesive layer further comprises at least one selected from the group consisting of isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. An adhesive tape characterized by the following features.

2. The (meth)acrylic polymer contains 40% by weight or more of constituent units derived from (meth)acrylic acid esters having an alkyl group with 12 or more carbon atoms and having a glass transition temperature of 0°C or less when homopolymerized, and has a weight-average molecular weight of 1 million or less. The adhesive layer has a gel fraction of 85% by weight or more and 95% by weight or less. The adhesive tape according to feature 1.

3. The adhesive tape according to claim 1 or 2, characterized in that the (meth)acrylic acid ester having an alkyl group with 12 or more carbon atoms and having a glass transition temperature of 0°C or less when homopolymerized contains at least one selected from the group consisting of lauryl acrylate, lauryl methacrylate, and isostearyl acrylate.

4. The adhesive tape according to claim 3, characterized in that the (meth)acrylic acid ester having an alkyl group with 12 or more carbon atoms and having a glass transition temperature of 0°C or less when formed as a homopolymer contains lauryl acrylate.

5. The adhesive tape according to claim 1, 2, 3, or 4, characterized in that the (meth)acrylic polymer further contains constituent units derived from a (meth)acrylic acid ester having an alkyl group having 8 or more carbon atoms and less than 12 carbon atoms, and having a glass transition temperature of 0°C or less when homopolymerized.

6. The adhesive tape according to claim 1, 2, 3, 4, or 5, characterized in that the (meth)acrylic polymer contains 1% by weight or more of structural units derived from hydroxyl group-containing monomers.

7. The adhesive tape according to claim 1, 2, 3, 4, 5, or 6, characterized in that the adhesive layer contains an isocyanate crosslinking agent.

8. An adhesive tape having an adhesive layer, The adhesive layer contains a (meth)acrylic polymer, The (meth)acrylic polymer contains 40% to 90% by weight of constituent units derived from (meth)acrylic acid esters having an alkyl group with 12 or more carbon atoms and having a glass transition temperature of 0°C or less when homopolymerized, and has a weight-average molecular weight of 1,000,000 or less. The (meth)acrylic polymer further contains a structure derived from a crosslinkable functional group-containing monomer, and the crosslinkable functional group-containing monomer includes at least one selected from the group consisting of carboxyl group-containing monomers and hydroxyl group-containing monomers. The adhesive layer further comprises at least one selected from the group consisting of isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents, wherein the adhesive layer has a gel fraction of 85% by weight or more and 95% by weight or less, and a thickness of 30 μm or more. An adhesive tape characterized by the following features.

9. The adhesive layer has a shear storage modulus of 1 × 10 at 23°C and 1 Hz. ４ Pa or more, 5×10 ４ The adhesive tape according to claim 8, characterized in that it is Pa or less.

Images