Adhesive tape

Abstract

The present invention is an adhesive tape which is provided with an adhesive agent layer containing natural rubber and a rubber component other than natural rubber, and in which the molecular weight of the natural rubber is at least 450,000, the rubber component other than natural rubber is a block copolymer, and the adhesive agent layer is crosslinked with an isocyanate-based crosslinking agent. The present invention makes it possible to provide an adhesive tape that is provided with an adhesive agent layer containing natural rubber, has excellent instantaneous workability, and has high holding power.

Description

adhesive tape

[0001] The present invention relates to an adhesive tape having an adhesive layer containing natural rubber.

[0002] Since their appearance, pressure-sensitive adhesives containing natural rubber have dominated the market, and are used in a wide variety of applications, including packaging tape, electrical insulating tape, electronic component transport tape, masking tape, surface protection tape, double-sided tape, and medical tape. This is because they exhibit excellent adhesion to a variety of adherends and can be supplied inexpensively. Demand for them has also been increasing in recent years from the perspective of reducing environmental impact. Pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive containing natural rubber are known as prior art, for example, from Patent Documents 1 to 3.

[0003] In the pressure-sensitive adhesive sheet described in Patent Document 1, the pressure-sensitive adhesive in the pressure-sensitive adhesive layer contains natural rubber, an isocyanate-based crosslinking agent, and a crosslinking regulator, which allows the pressure-sensitive adhesive sheet described in Patent Document 1 to have excellent adhesive strength, high-temperature retention, and releasability to a variety of adherends.

[0004] In the pressure-sensitive adhesive sheet described in Patent Document 2, the pressure-sensitive adhesive layer contains a rubbery polymer and a medium-molecular-weight natural rubber having a weight molecular weight of 100,000 to 400,000, which results in the pressure-sensitive adhesive sheet described in Patent Document 2 having excellent low-temperature rough surface adhesion and high-temperature adhesion.

[0005] In the pressure-sensitive adhesive sheet described in Patent Document 3, the pressure-sensitive adhesive of the pressure-sensitive adhesive layer is produced without solvent by heating and kneading raw materials containing natural rubber, a tackifier, and an isocyanate-based crosslinking agent.

[0006] Patent No. 7072735 Patent No. 4557305 Patent No. 4651767

[0007] However, in the pressure-sensitive adhesive sheets described in Patent Documents 1 and 3, crosslinking of the pressure-sensitive adhesive in the pressure-sensitive adhesive layer takes time, and therefore, if the cutting process is carried out shortly after the application of the pressure-sensitive adhesive, the pressure-sensitive adhesive may protrude from the side of the cut pressure-sensitive adhesive sheet. In other words, the pressure-sensitive adhesive sheets described in Patent Documents 1 and 3 have poor immediate processability. Furthermore, the pressure-sensitive adhesive sheet described in Patent Document 2 may have insufficient holding power for use in packaging and office applications. Therefore, an object of the present invention is to provide a pressure-sensitive adhesive tape that has an adhesive layer containing natural rubber, is excellent in immediate processability, and has high holding power.

[0008] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using a high-molecular-weight natural rubber in combination with a block copolymer and crosslinking the pressure-sensitive adhesive layer with an isocyanate-based crosslinking agent, and have thus completed the present invention. The gist of the present invention is as follows: [1] A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing natural rubber and a rubber component other than natural rubber, wherein the natural rubber has a molecular weight of 450,000 or more, the rubber component other than natural rubber is a block copolymer, and the pressure-sensitive adhesive layer is crosslinked with an isocyanate-based crosslinking agent. [2] The pressure-sensitive adhesive tape according to [1] above, wherein the block copolymer contains a styrene-isoprene-styrene block copolymer. [3] The pressure-sensitive adhesive tape according to [1] or [2] above, wherein the content of the block copolymer in the pressure-sensitive adhesive layer is 5 parts by mass or more and 1,000 parts by mass or less per 100 parts by mass of natural rubber. [4] The pressure-sensitive adhesive tape according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive layer has a gel fraction of 10% or more. [5] The pressure-sensitive adhesive tape according to any one of [1] to [4] above, wherein the amount of residual solvent in the pressure-sensitive adhesive layer is 10 ppm by mass or less. [6] The pressure-sensitive adhesive tape according to any one of [1] to [5] above, further comprising a substrate provided on one surface of the pressure-sensitive adhesive layer, wherein the substrate is a paper substrate or an oriented polypropylene substrate. [7] The pressure-sensitive adhesive tape according to any one of [1] to [6] above, wherein the SP adhesive strength is 4 N / 24 mm or more. [8] The pressure-sensitive adhesive tape according to any one of [1] to [7] above, wherein the ball tack value is 8 or more. [9] The pressure-sensitive adhesive tape according to any one of [1] to [8] above, wherein the pressure-sensitive adhesive layer further comprises a tackifier resin, wherein the tackifier resin is a petroleum resin-based tackifier resin.

[0009] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has a pressure-sensitive adhesive layer containing natural rubber, has excellent immediate processability, and has high holding power.

[0010] [Adhesive Tape] The adhesive tape of the present invention is an adhesive tape having an adhesive layer containing natural rubber and a rubber component other than natural rubber, wherein the natural rubber has a molecular weight of 450,000 or more, the rubber component other than natural rubber is a block copolymer, and the adhesive layer is crosslinked with an isocyanate-based crosslinking agent. This improves the immediate processability of the adhesive tape and increases the holding power of the adhesive tape.

[0011] (Adhesive Layer) The adhesive layer in the adhesive tape of the present invention contains natural rubber and a rubber component other than natural rubber. As will be described later, the adhesive layer is preferably formed from an adhesive containing natural rubber, a rubber component other than natural rubber, and other components that are appropriately blended as necessary.

[0012] By including natural rubber in the adhesive layer, the adhesive tape can exhibit excellent adhesiveness to various adherends. Furthermore, the adhesive tape can be produced inexpensively. Furthermore, the environmental impact of the adhesive tape can be reduced. The natural rubber contained in the adhesive layer of the adhesive tape of the present invention is obtained by coagulating latex extracted from Hevea Brasiliensis (Hevea genus, Hevea family, Hevea family), which is cultivated mainly in Southeast Asia, the west coast of equatorial Africa, the Amazon basin in Brazil, and other regions. Examples of natural rubber include smoked sheet (RSS), pale crepe, blanket crepe, and hevea crumb. Among these, smoked sheet (RSS) is preferred.

[0013] From the viewpoints of improving holding power, improving paper peelability, and reducing the environmental load, the content of natural rubber in the PSA layer is preferably 5 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the total rubber components. Furthermore, from the viewpoint of ensuring a predetermined content of rubber components other than natural rubber, as described below, the content of natural rubber in the PSA layer is preferably 95 parts by mass or less, preferably 85 parts by mass or less, and even more preferably 75 parts by mass or less, per 100 parts by mass of the total rubber components.

[0014] The molecular weight of the natural rubber in the pressure-sensitive adhesive layer is 450,000 or more. If the molecular weight of the natural rubber in the pressure-sensitive adhesive layer is less than 450,000, the holding power of the pressure-sensitive adhesive tape may decrease. From this perspective, the molecular weight of the natural rubber in the pressure-sensitive adhesive layer is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more. The upper limit of the range of the molecular weight of the natural rubber in the pressure-sensitive adhesive layer is not particularly limited, but is usually 1,400,000. The molecular weight of the natural rubber in the pressure-sensitive adhesive layer can be measured by the method described in the Examples below.

[0015] The natural rubber preferably contains a crosslinkable functional group. Natural rubber is obtained by coagulating and drying natural rubber latex, which is the sap of rubber trees, and is a substance primarily composed of cis-1,4-polyisoprene. The molecular structure of natural rubber is said to be such that one end of each cis-1,4-isoprene unit is a protein terminal, the other end is bound to a phospholipid, and a long-chain fatty acid is further bound to this phospholipid terminal. Natural rubber also contains 3 to 4% by mass of non-rubber components such as proteins and lipids. Therefore, natural rubber can be easily crosslinked and cured using a crosslinking agent, as described below. Since the pressure-sensitive adhesive composition according to the present invention is cured by crosslinking, the crosslinked product is also referred to as a cured product. From the perspective of improving holding power, the natural rubber is preferably crosslinked with an isocyanate-based crosslinking agent.

[0016] The pressure-sensitive adhesive layer contains a block copolymer as a rubber component other than natural rubber. By containing a block copolymer as a rubber component other than natural rubber, pseudo-crosslinking occurs in the pressure-sensitive adhesive layer, thereby improving the immediate processability of the pressure-sensitive adhesive tape. By improving the immediate processability of the pressure-sensitive adhesive tape, it is possible to prevent the pressure-sensitive adhesive from spilling out even if cutting is performed before or during crosslinking of the pressure-sensitive adhesive layer.

[0017] The block copolymer is preferably a hydrogenated product of a block copolymer having at least a block derived from an aromatic vinyl monomer and a block derived from a conjugated diene monomer. Examples of the aromatic vinyl monomer include styrene, alpha-methylstyrene, para-methylstyrene, and chlorostyrene. These aromatic vinyl monomers may be used alone or in combination of two or more. Among these, styrene is preferred due to its excellent immediate processability and holding power. The aromatic vinyl monomer may further have a structure derived from, for example, a compound having a cyclic structure or a compound with a short side chain substituent, as long as the effects of the present invention are not impaired. The content of the block derived from the aromatic vinyl monomer in the block copolymer is not particularly limited, but a preferred upper limit is 45% by mass. Having a content of the block derived from the aromatic vinyl monomer of 40% by mass or less further improves paper peelability. A more preferred upper limit of the aromatic vinyl monomer is 35% by mass, and even more preferred is 30% by mass. The preferred lower limit of the content of the block derived from the aromatic vinyl monomer is 5% by mass. When the content of the block derived from the aromatic vinyl monomer is 5% by mass or more, immediate processability and holding power are further improved. A more preferred lower limit of the content of the block derived from the aromatic vinyl monomer is 8% by mass, and an even more preferred lower limit is 10% by mass. Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-octadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, myrcene, and chloroprene. These conjugated diene monomers may be used alone or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred due to their high polymerization reactivity and ease of industrial availability.The content of the block derived from the conjugated diene monomer in the block copolymer is not particularly limited as long as the effects of the present invention are exhibited; however, a preferred lower limit is 55% by mass, a more preferred lower limit is 60% by mass, and a preferred upper limit is 65% by mass, a more preferred upper limit is 70% by mass. The block copolymer may contain a crosslinkable functional group within a range that does not impair the effects of the present invention. Examples of block copolymers include styrene-based block copolymers such as styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), and styrene-ethylene-butylene-styrene block copolymer (SEBS). These block copolymers can be used alone or in combination of two or more. Among these block copolymers, styrene-isoprene-styrene block copolymer (SIS) is preferred from the viewpoint of immediate processability of the pressure-sensitive adhesive tape.

[0018] From the viewpoint of immediate processability of the pressure-sensitive adhesive tape, the content of the block copolymer in the pressure-sensitive adhesive layer is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 25 parts by mass or more, per 100 parts by mass of the total rubber components. Also, from the viewpoint of ensuring a predetermined content of natural rubber, the content of the block copolymer in the pressure-sensitive adhesive layer is preferably 95 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of the total rubber components.

[0019] From the viewpoint of immediate processability of the pressure-sensitive adhesive tape, the content of the block copolymer in the pressure-sensitive adhesive layer is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of natural rubber. Also, from the viewpoint of ensuring a predetermined content of natural rubber, the content of the block copolymer in the pressure-sensitive adhesive layer is preferably 1,000 parts by mass or less, more preferably 950 parts by mass or less, and even more preferably 900 parts by mass or less, per 100 parts by mass of natural rubber.

[0020] The rubber component may further contain a rubber component other than natural rubber and block copolymer, as long as the effects of the present invention are not impaired. Examples of rubber components other than natural rubber and block copolymer include styrene-butadiene rubber (SBR), polyisobutylene rubber, and liquid rubber. The content of the rubber component other than natural rubber and block copolymer, relative to 100 parts by mass of the total rubber component, is preferably 0 parts by mass or more and 10 parts by mass or less, more preferably 0 parts by mass or more and 5 parts by mass or less, even more preferably 0 parts by mass or more and 2 parts by mass or less, and even more preferably 0 parts by mass.

[0021] (Isocyanate-Based Crosslinking Agent) The adhesive layer in the pressure-sensitive adhesive tape of the present invention is crosslinked with an isocyanate-based crosslinking agent. This can further improve the immediate processability of the pressure-sensitive adhesive tape and further increase the holding power of the pressure-sensitive adhesive tape. The isocyanate-based crosslinking agent is not particularly limited as long as it is a compound having two or more isocyanate groups per molecule, and examples thereof include aromatic isocyanates such as tolylene diisocyanate (TDI), naphthalene diisocyanate, diphenylmethane diisocyanate (MDI), and polymeric MDI, and aliphatic isocyanates such as hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), and isophorone diisocyanate. Further examples of the isocyanate-based crosslinking agent include trimethylolpropane adducts of the above isocyanate compounds, such as the tolylene diisocyanate adduct of trimethylolpropane. Specific isocyanate-based crosslinking agents are preferably hexamethylene diisocyanate (HDI) and diphenylmethane diisocyanate (MDI). Among the above, aliphatic isocyanates are preferred, with hexamethylene diisocyanate (HDI) being more preferred. The use of an aliphatic isocyanate such as HDI can promote gelation and make the crosslinked structure flexible, thereby increasing the holding power and improving the paper peelability at low temperatures. The isocyanate-based crosslinking agents may be used alone or in combination of two or more.

[0022] From the viewpoint of the holding power of the adhesive tape and the viewpoint of improving paper peelability, the amount of crosslinking agent added in the adhesive layer is preferably 0.1 parts by mass or more and 8.0 parts by mass or less, more preferably 0.5 parts by mass or more and 6.0 parts by mass or less, and even more preferably 1.0 parts by mass or more and 4.0 parts by mass or less, relative to 100 parts by mass of the total rubber components.

[0023] (Tackifying Resin) The pressure-sensitive adhesive layer may contain a tackifying resin from the viewpoint of improving adhesive strength. Examples of tackifying resins include rosin-based tackifying resins, terpene-based tackifying resins, and petroleum resin-based tackifying resins. Examples of rosin-based tackifying resins include rosin, hydrogenated rosin, heterogenized rosin, polymerized rosin, and esterified products thereof. Examples of terpene-based tackifying resins include terpene resins (α,β-pinene), terpene phenol resins, aromatic-modified terpene resins, and hydrogenated terpene resins. Examples of petroleum resin-based tackifying resins include aliphatic petroleum resins, aromatic petroleum resins, copolymerized petroleum resins, and hydrogenated petroleum resins. These tackifying resins may be used alone or in combination of two or more. Among these, petroleum resin-based tackifying resins are preferred, and aliphatic petroleum resins are more preferred. From the viewpoint of improving the cohesive strength and adhesive strength of the PSA, the softening point of the tackifier resin may be about 95°C or higher, but preferably includes one of 120°C or higher. For example, one of 95°C or higher but lower than 120°C and one of 120°C or higher but 150°C or higher may be used in combination. The softening point may be measured by the ring and ball method specified in JIS K 2207. The content of the tackifier resin in the PSA layer is preferably 10 parts by mass or higher but 200 parts by mass or lower, more preferably 20 parts by mass or higher but 150 parts by mass or lower, and even more preferably 40 parts by mass or higher but 130 parts by mass or lower, per 100 parts by mass of the total rubber components.

[0024] (Softener) The pressure-sensitive adhesive layer may contain a softener. By containing a softener, the processability of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer can be improved. Examples of softeners include polybutene, polyisobutylene, process oil, and naphthenic oil. The content of the softener in the pressure-sensitive adhesive layer is preferably 5 parts by mass or more and 100 parts by mass or less, more preferably 10 parts by mass or more and 50 parts by mass or less, and even more preferably 15 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the total rubber component.

[0025] (Microparticles) The pressure-sensitive adhesive layer may contain microparticles. Examples of the microparticles include inorganic hollow particles such as glass balloons, shirasu balloons, and fly ash balloons; organic hollow particles made of polymethyl methacrylate, acrylonitrile-vinylidene chloride copolymer, polystyrene, and phenolic resin; inorganic microparticles such as glass beads, silica beads, calcium carbonate, clay, carbon, titanium oxide, zinc oxide, and synthetic mica; and organic microparticles such as polyethyl acrylate, polyurethane, polyethylene, and polypropylene. The content of the microparticles in the pressure-sensitive adhesive layer is preferably 10 parts by mass or more and 100 parts by mass or less, more preferably 20 parts by mass or more and 70 parts by mass or less, and even more preferably 30 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the total rubber component.

[0026] (Antiaging Agent) The pressure-sensitive adhesive layer may contain an antioxidant. By containing an antioxidant, deterioration of the pressure-sensitive adhesive layer due to oxidation can be suppressed. Examples of antioxidants include phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, and waxes. The content of the antioxidant in the pressure-sensitive adhesive layer is preferably 0.01 parts by mass or more and 50 parts by mass or less, more preferably 0.1 parts by mass or more and 20 parts by mass or less, and even more preferably 0.5 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the total rubber component.

[0027] (Other Components) In addition to the components described above, the pressure-sensitive adhesive layer may contain various additives conventionally used in pressure-sensitive adhesives, such as pigments, dyes, polymerization initiators, flame retardants, and thickeners.

[0028] Since the pressure-sensitive adhesive layer in the pressure-sensitive adhesive tape of the present invention contains natural rubber and a block copolymer, the pressure-sensitive adhesive used to form the pressure-sensitive adhesive layer is easily plasticized and fluidized by heat. Therefore, the pressure-sensitive adhesive layer can be formed substantially without using a solvent. This further reduces the environmental impact. Forming the pressure-sensitive adhesive layer substantially without using a solvent can reduce the amount of residual solvent in the pressure-sensitive adhesive layer. The amount of residual solvent in the pressure-sensitive adhesive layer is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, and even more preferably 1 ppm by mass or less. The lower limit of the range of the amount of residual solvent in the pressure-sensitive adhesive layer is not particularly limited, but is, for example, 0 ppm by mass.

[0029] <Gel Fraction> The gel fraction of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive tape of the present invention is preferably 10% or more. When the gel fraction of the pressure-sensitive adhesive layer is 10% or more, the holding power of the pressure-sensitive adhesive tape can be further improved. From this perspective, the gel fraction of the pressure-sensitive adhesive layer is more preferably 15% or more, and even more preferably 20% or more. The upper limit of the range of the gel fraction of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 50% or less, more preferably 40% or less. The gel fraction of the pressure-sensitive adhesive layer can be measured by the method described in the Examples below. The gel fraction of the pressure-sensitive adhesive layer can be adjusted by the type and content of rubber in the rubber component of the pressure-sensitive adhesive layer, and the type and amount of crosslinking agent added.

[0030] <Thickness> The thickness of the pressure-sensitive adhesive layer is not particularly limited, but may be, for example, from about 5 μm to 200 μm, and preferably from 10 μm to 100 μm. When the thickness of the pressure-sensitive adhesive layer is within this range, the resulting pressure-sensitive adhesive tape can exhibit sufficient adhesive strength.

[0031] (Substrate) The adhesive tape of the present invention may further comprise a substrate, and an adhesive layer may be provided on one side of the substrate. Examples of substrate materials include paper such as kraft paper, Japanese paper, crepe paper, fine paper, coated paper, and synthetic paper; cloth such as cotton cloth, staple fiber cloth, acetate cloth, glass cloth, and polyester cloth; nonwoven fabric such as polyester nonwoven fabric and rayon nonwoven fabric; cellophane film, polyvinyl chloride film, oriented polypropylene film, unoriented polypropylene film, polyethylene film, polyester film, and acetate film; metal foil such as aluminum foil and copper foil; and foams such as polyurethane foam, polyethylene foam, vinyl chloride foam, chloroprene foam, natural rubber foam, and butyl rubber foam. Among these, a paper substrate or oriented polypropylene film is preferred. Kraft paper is preferred as the paper.

[0032] The thickness of the substrate is not particularly limited, but is preferably 30 μm or more and 400 μm or less, more preferably 35 μm or more and 300 μm or less, and even more preferably 40 μm or more and 200 μm or less.

[0033] When a paper substrate such as kraft paper is used as the substrate material, a sealing layer may be formed on at least one surface of the paper substrate. The sealing layer may be provided on the surface of the substrate on which the adhesive layer is provided, but is preferably provided on the surface opposite to the surface on which the adhesive layer is provided. A release layer, as described below, may then be formed on the sealing layer provided on the opposite surface. The sealing layer may be formed of a polyolefin layer or the like. Examples of polyolefin resins constituting the sealing layer include polyethylene-based resins and polypropylene-based resins, with polyethylene-based resins being more preferred. The sealing layer may be formed by laminating a resin such as a polyolefin resin onto the surface of the substrate by lamination or the like. The thickness of the sealing layer is not particularly limited, but is preferably 1 μm or more and 20 μm or less, and more preferably 2 μm or more and 15 μm or less.

[0034] The pressure-sensitive adhesive tape may have a release agent layer provided on the surface of the substrate opposite to the surface on which the pressure-sensitive adhesive layer is provided. The release agent layer may be laminated directly on the substrate, but is preferably laminated on the substrate via the above-mentioned sealing layer. By providing the release agent layer, when the pressure-sensitive adhesive tape is wound into a roll to form a roll, the pressure-sensitive adhesive layer comes into contact with the release agent layer, making it possible to easily unwind the pressure-sensitive adhesive tape from the roll. The release agent layer may be formed from a known release agent such as a silicone-based release agent or a long-chain alkyl-based release agent.

[0035] (Biobased content) The biobased content (content of biologically derived carbon) of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of the present invention is preferably 5% or more. When the biobased content of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of the present invention is 5% or more, petroleum resources can be saved in the production of the pressure-sensitive adhesive tape, and carbon dioxide emissions associated with the production of the pressure-sensitive adhesive tape can be suppressed, thereby reducing the environmental burden. From this perspective, the biobased content of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of the present invention is more preferably 15% or more, even more preferably 20% or more, and even more preferably 25% or more. The upper limit of the range of the biobased content of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but is preferably 100%. The biobased content of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape can be measured by the method described in the Examples below. The biobased content of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape can be adjusted by, for example, the proportion of natural rubber in the pressure-sensitive adhesive layer.

[0036] (SP adhesive strength) The SP adhesive strength of the pressure-sensitive adhesive tape of the present invention is preferably 4 N / 24 mm or more. When the SP adhesive strength of the pressure-sensitive adhesive tape is 4 N / 24 mm or more, the holding power of the pressure-sensitive adhesive tape can be further improved. From this viewpoint, the SP adhesive strength of the pressure-sensitive adhesive tape of the present invention is more preferably 5 N / 24 mm or more, and even more preferably 6 N / 24 mm or more. The upper limit of the range of the SP adhesive strength of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but is usually 30 N / 24 mm. The SP adhesive strength of the pressure-sensitive adhesive tape can be measured by the method described in the Examples below. The SP adhesive strength of the pressure-sensitive adhesive tape can be adjusted, for example, by the type and amount of isocyanate-based crosslinking agent, the type and content of rubber, the type and content of tackifying oil and fat, etc.

[0037] (Ball Tack Value) The ball tack value of the pressure-sensitive adhesive tape of the present invention is preferably 8 or more. When the ball tack value of the pressure-sensitive adhesive tape is 8 or more, the pressure-sensitive adhesive tape can immediately exhibit practically usable adhesive strength when applied to an adherend. From this viewpoint, the ball tack value of the pressure-sensitive adhesive tape of the present invention is more preferably 9 or more, and even more preferably 10 or more. The upper limit of the range of the ball tack value of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but is usually 30. The ball tack value of the pressure-sensitive adhesive tape can be measured by the method described in the Examples below. The ball tack value of the pressure-sensitive adhesive tape can be adjusted, for example, by the type and amount of isocyanate-based crosslinking agent, the type and content of rubber, the type and content of tackifying oil and fat, etc.

[0038] (Method for Producing an Adhesive Tape) The adhesive tape of the present invention can be produced by melt-mixing adhesive components, such as natural rubber, a rubber component other than natural rubber, an isocyanate-based crosslinking agent, and optionally a tackifying resin, fine particles, a softener, and an antioxidant, at high temperatures to obtain an adhesive, and then coating the resulting root adhesive on the surface of a support to form an adhesive layer. This method has the advantages of not requiring a drying step because it does not involve solvents, allowing for fast coating speeds and eliminating the risk of explosions and fires. The kneading temperature during melt-mixing is not particularly limited, but may be, for example, 130 to 180°C, preferably 150 to 170°C. The kneading time during melt-mixing is not particularly limited, but may be, for example, 100 to 1,000 seconds, preferably 100 to 700 seconds. For melt-mixing of the adhesive components, for example, a high-speed pressurized kneader, an extruder-type mixer, or a plastomill may be used. For coating, for example, a slit die coater or a roll coater may be used, but is not particularly limited.

[0039] The pressure-sensitive adhesive layer is crosslinked by an isocyanate-based crosslinking agent, and the crosslinking of the pressure-sensitive adhesive layer can be carried out by a known method. The crosslinking rate varies depending on the storage temperature; the higher the temperature, the faster the crosslinking rate, and the lower the temperature, the slower the crosslinking rate. For example, crosslinking can be achieved by leaving the tape at 60°C for about one day, or at 25°C for about seven days. The obtained pressure-sensitive adhesive tape may be wound appropriately to form a roll. The pressure-sensitive adhesive tape may also be cut appropriately to a desired size; for example, when a roll is to be formed, the tape may be wound and then cut. The pressure-sensitive adhesive tape of the present invention has good immediate processability, so that even if the tape is cut before crosslinking, protrusion of the pressure-sensitive adhesive during or after cutting can be prevented.

[0040] (Uses of the adhesive tape) The uses of the adhesive tape of the present invention are not particularly limited, but since the adhesive tape of the present invention uses natural rubber and has excellent immediate processability, the production costs of the adhesive tape of the present invention are low and the holding power is also high, making it suitable for packaging and office use, and it is particularly suitable as a packaging tape. Furthermore, as the packaging tape, kraft tape having a kraft paper substrate and OPP tape having an OPP substrate are preferred, with kraft tape being particularly preferred.

[0041] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0042] [Evaluation method]

[0043] In the examples and comparative examples, the pressure-sensitive adhesive tapes were evaluated by the following evaluation methods.

[0044] (Molecular Weight of Natural Rubber) The molecular weight of natural rubber was measured by Gel Permeation Chromatography (GPC), and the peak top molecular weight was taken as the molecular weight of natural rubber. Specifically, the GPC analysis was performed using an ACQUITY APC (manufactured by Waters) as the apparatus and an ACQUITY APCXT125-XT45-XT45 (manufactured by Waters, 3 μm, 4.6 × 150 mm) as the column, and polystyrene was used as the GPC reference material when calculating the molecular weight, and tetrahydrofuran was used as the GPC measurement solvent. The molecular weight of natural rubber was specifically measured as follows. A sample was collected from the pressure-sensitive adhesive layer of the obtained pressure-sensitive adhesive tape and dissolved in toluene to prepare a GPC measurement sample, and GPC measurement of the GPC measurement sample was performed. The peaks in the measurement results obtained by GPC measurement of the GPC measurement sample were identified by isolating each component by preparative GPC and analyzing the isolated components. The isolated components were identified by GC / MS analysis or IR spectrum analysis. The molecular weight of natural rubber was then determined from the peak corresponding to natural rubber. (Measurement conditions) Mobile phase: tetrahydrofuran 1.0 mL / min Sample concentration: 0.2 mass% Detector: differential refractive index (RI) detector, photodiode array (PDA) detector GPC reference material: polystyrene (manufactured by Waters, molecular weight: 266-1,800,000) Column temperature: 40°C

[0045] (Gel Fraction of Pressure-Sensitive Adhesive Layer) A test piece of the pressure-sensitive adhesive layer was collected, and the mass A (mg) of the test piece was precisely weighed. Next, toluene was added to the test piece so that the pressure-sensitive adhesive solids concentration became 6% by mass. The test piece was immersed in toluene and shaken for 24 hours, and then filtered through a 200-mesh wire net to collect the insoluble matter on the wire net. This was then vacuum-dried, and the mass B (mg) of the insoluble matter was precisely weighed. From the obtained value, the gel fraction (% by mass) was calculated using the following formula: Gel fraction (% by mass) = 100 × (B / A)

[0046] (Amount of Residual Solvent in Pressure-Sensitive Adhesive Layer) The amount of residual solvent in the pressure-sensitive adhesive layer was measured by gas chromatography (GC-2014, manufactured by Shimadzu Corporation) under the following conditions: Vial warming temperature: 100°C Vial warming time: 8 minutes Injection volume: 1.0 mL Column: RTX-1 (inner diameter 0.32 mm x length 30 m film thickness 0.5 μm) Column temperature: 50°C Injection port temperature: 150°C Column inlet pressure: 100 kPa Column flow rate: 3.4 mL / min Detector: FID Sample volume: 10 cm x 10 cm

[0047] (Bio-based Degree of Adhesive Tape) The bio-based degree of the adhesive tape was measured in accordance with ASTM 6866.

[0048] (SP adhesive strength of adhesive tape) At room temperature (23°C) and a relative humidity of 50%, the adhesive layer side of the adhesive tape was pressed against a SUS 304 steel plate by rolling it back and forth twice with a 2 kg roller. After leaving it in this environment for 30 minutes, the 180° peel strength at a width of 24 mm was measured using a tensile tester at a pulling rate of 300 mm / min in accordance with the method of JIS Z0237, and this was taken as the SP adhesive strength.

[0049] (Ball Tack Value of Adhesive Tape) The ball tack value of the adhesive tape was measured and calculated using a ball tack tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS Z 0237 under conditions of a temperature of 23°C and a relative humidity of 50%.

[0050] (Low-temperature paper peeling of adhesive tape) A peeling test to evaluate tack at low temperatures was conducted as follows. The test adhesive tape was cut into 50 mm x 70 mm pieces and placed in a constant temperature bath at 0°C together with a corrugated cardboard plate as an adherend and a 2 kg roller 12 hours before the start of the test. The corrugated cardboard plate was placed in the constant temperature bath at 0°C, and the test adhesive tape was attached to it without applying force under certain conditions. A 2 kg roller was moved back and forth over the tape to press it, and the tape was immediately peeled off at a 90-degree angle at a peeling speed of 100 mm / sec, and the destruction area rate (%) of the cardboard at the adhesive part was measured. <Evaluation criteria> A: The cardboard was peeled off considerably (55% or more of the surface layer of the cardboard was peeled off) B: The cardboard was peeled off a little (45% or more but less than 55% of the surface layer of the cardboard was peeled off) C: The cardboard was not peeled off much (less than 45% of the surface layer of the cardboard was peeled off)

[0051] (SP holding strength of adhesive tape) The adhesive layer side was attached to a polished SUS plate so that the adhesion area was 24 mm x 24 mm, and the tape was left to stand for 30 minutes under conditions of 23°C x 50% RH. Thereafter, a load of 2 kg was applied under conditions of 23°C, and the slippage 24 hours after the application of the 2 kg load was measured in accordance with the holding strength measurement method of JIS Z 0237. In Table 1, "dropped" indicates that the slippage was too large and the adhesive tape fell off the polished SUS plate.

[0052] (Liner paper holding strength of adhesive tape (50°C)) The adhesive layer side was attached to liner paper (K ​​liner) so that the adhesion area was 10 mm x 10 mm, and the tape was left to stand for 30 minutes under conditions of 23°C x 50% RH. After storing the tape for 30 minutes under conditions of 50°C, a 500 g load was applied and the time until the tape fell off the liner paper was recorded. The presence or absence of the tape falling off was checked every 60 minutes up to a maximum of 180 minutes.

[0053] (Immediate Processability of Adhesive Tape) The adhesive tape wound by the method described in each Example and Comparative Example was cut within 3 hours of winding to obtain a 50 mm x 50 m roll sample. Five of the obtained samples were aligned and stacked in an oven at 40°C, and a 10 kg load was applied and left for one week. After one week, the load was removed, and the resistance felt when trying to remove each roll of adhesive tape was evaluated sensorily according to the following rating scale. <Evaluation Criteria> A: Can be removed without applying force. B: Can be removed with slight force, feels sticky when peeled off. C: Peels off with strong force. Feels a strong side sticking sensation.

[0054] [Examples 1 to 11, Comparative Examples 1 to 5] Pressure-sensitive adhesive components blended according to the blending amounts shown in Table 1 were placed in a kneading-extrusion tester (manufactured by Toyo Seiki Seisaku-sho, Ltd., product name "Labo Plastomill (registered trademark)"). The pressure-sensitive adhesive components were then melt-kneaded under the conditions shown in Table 1, extrusion-molded, and coated on paper (kraft paper) or OPP (oriented polypropylene film) to produce pressure-sensitive adhesive tapes of the Examples and Comparative Examples. The obtained pressure-sensitive adhesive tapes were left to stand for one week in an environment of 23°C and a relative humidity of 50%, and then evaluated. The evaluation results are shown in Table 1.

[0055]

[0056] The components in Table 1 are as follows. Natural rubber: smoked sheet (RSS grade 1), product after mastication and pelletization; Mooney viscosity was adjusted by mastication time. Block copolymer: styrene-isoprene-styrene block copolymer (SIS), manufactured by JSR Corporation, product name "SIS5506". Isocyanate crosslinking agent (HDI): hexamethylene diisocyanate (HDI), manufactured by Asahi Kasei Corporation, product name "Duranate TPA-100". Isocyanate crosslinking agent (MDI): diphenylmethane diisocyanate, manufactured by MCC Trading Co., Ltd., product name "diphenylmethane diisocyanate". Aziridine crosslinking agent (HDU): manufactured by Sogo Pharmaceutical Co., Ltd., product name "N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide)". Epoxy crosslinking agent: manufactured by Mitsubishi Gas Chemical Trading Co., Ltd., product name "TETRAD-X". Tackifier resin: Aliphatic petroleum resin produced primarily from 1,3-pentadiene extracted from C5 fraction, manufactured by Zeon Corporation, product name "Quinton A-100" Softener: Process oil, manufactured by JXTG Nippon Oil & Energy Corporation, product name "Crisef Oil F220" Fine particles: Calcium carbonate, manufactured by Nitto Funka Kogyo Co., Ltd., product name "NS#100" Antiaging agent: Phenol-based antiaging agent (2,2'-methylenebis-(4-ethyl-6-t-butylphenol)), manufactured by Yoshitomi Pharmaceutical Co., Ltd., product name "Yoshinox 425"

[0057] The pressure-sensitive adhesive tapes of Examples 1 to 11 had a pressure-sensitive adhesive layer containing natural rubber and a rubber component other than natural rubber, the molecular weight of the natural rubber being 450,000 or more, the rubber component other than natural rubber being a block copolymer, and the pressure-sensitive adhesive layer being crosslinked with an isocyanate-based crosslinking agent, so they had high holding power and good immediate processability. The pressure-sensitive adhesive tape of Comparative Example 1 had poor immediate processability because the pressure-sensitive adhesive layer did not contain a block copolymer. The pressure-sensitive adhesive tape of Comparative Example 2 had low holding power because the pressure-sensitive adhesive layer did not contain natural rubber. The pressure-sensitive adhesive tapes of Comparative Examples 3 and 4 had poor holding power because they were not crosslinked with an isocyanate-based crosslinking agent. The pressure-sensitive adhesive tape of Comparative Example 5 had low holding power and poor immediate processability because the molecular weight of the natural rubber was less than 450,000.

Claims

1. An adhesive tape having an adhesive layer containing natural rubber and a rubber component other than natural rubber, wherein the molecular weight of the natural rubber is 450,000 or more, the rubber component other than natural rubber is a block copolymer, and the adhesive layer is crosslinked with an isocyanate-based crosslinking agent.

2. The adhesive tape of claim 1, wherein said block copolymer comprises a styrene-isoprene-styrene block copolymer.

3. The adhesive tape according to claim 1, wherein the content of said block copolymer in said adhesive layer is 5 parts by mass or more and 1,000 parts by mass or less per 100 parts by mass of natural rubber.

4. The adhesive tape according to claim 1, wherein the gel fraction of the adhesive layer is 10% or more.

5. The adhesive tape according to claim 1, wherein the amount of residual solvent in the adhesive layer is 10 ppm by mass or less.

6. The adhesive tape according to claim 1, further comprising a substrate provided on one surface of said adhesive layer, said substrate being a paper substrate or a stretched polypropylene film.

7. The adhesive tape according to claim 1, having an SP adhesive strength of 4 N / 24 mm or more.

8. The adhesive tape according to claim 1, which has a ball tack value of 8 or more.

9. The adhesive tape according to claim 1, wherein the adhesive layer further comprises a tackifier resin, and the tackifier resin is a petroleum resin-based tackifier resin.