Adhesive tape

Abstract

The present application is an adhesive tape having an adhesive layer containing natural rubber and a rubber component other than natural rubber, and 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 by an isocyanate crosslinking agent. According to the present application, an adhesive tape having an adhesive layer containing natural rubber, and excellent in immediate processability and high in holding force can be provided.

Description

Technical Field

[0001] This invention relates to adhesive tape having an adhesive layer comprising natural rubber. Background Technology

[0002] Adhesives containing natural rubber have been the mainstream adhesives since their inception and are used in almost all applications, including packaging tapes, electrical insulation tapes, electronic component conveying tapes, masking tapes, surface protection tapes, double-sided tapes, and medical tapes. This is due to their excellent adhesion to various substrates and their inexpensive availability. Furthermore, demand has been steadily increasing in recent years due to concerns about reducing environmental impact. Adhesive sheets comprising an adhesive layer containing natural rubber are known as prior art, for example, those described in Patent Documents 1-3.

[0003] In the adhesive sheet described in Patent Document 1, the adhesive layer contains natural rubber, isocyanate crosslinking agents, and crosslinking modifiers. Therefore, the adhesive sheet described in Patent Document 1 exhibits excellent adhesion, high-temperature retention, and peelability to a variety of adhered materials.

[0004] In the adhesive sheet described in Patent Document 2, the adhesive layer comprises a rubbery polymer and a medium molecular weight natural rubber with a molecular weight of 100,000 to 400,000. Therefore, the adhesive sheet described in Patent Document 2 exhibits excellent low-temperature rough surface adhesion and high-temperature adhesion.

[0005] In the adhesive sheet described in Patent Document 3, the adhesive layer is manufactured by heating and mixing raw materials including natural rubber, tackifier and isocyanate crosslinking agent under solvent-free conditions.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 7072735

[0009] Patent Document 2: Japanese Patent No. 4557305

[0010] Patent Document 3: Japanese Patent No. 4651767 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, for the adhesive sheets described in Patent Documents 1 and 3, because the cross-linking of the adhesive layer takes time, if the cutting process is carried out shortly after the adhesive is applied, the adhesive may sometimes overflow from the side of the cut adhesive sheet. In other words, the adhesive sheets described in Patent Documents 1 and 3 have poor immediate processability. Furthermore, for the adhesive sheet described in Patent Document 2, the holding power sometimes becomes insufficient when used for packaging and office applications.

[0013] Therefore, the object of the present invention is to provide an adhesive tape having an adhesive layer comprising natural rubber and having excellent immediate processability and high holding power.

[0014] Problem-solving methods

[0015] The inventors conducted in-depth research and discovered that the above-mentioned problems can be solved by using high molecular weight natural rubber and block copolymers together, and by using isocyanate crosslinking agents to crosslink the adhesive layer, thus completing the present invention. The main points of the present invention are as follows.

[0016] [1] An adhesive tape having an adhesive layer comprising natural rubber and rubber components other than natural rubber, The molecular weight of the natural rubber is above 450,000. The rubber components other than natural rubber are block copolymers. The adhesive layer is cross-linked using an isocyanate cross-linking agent.

[0017] [2] According to the adhesive tape described in [1] above, the block copolymer comprises a styrene-isoprene-styrene block copolymer.

[0018] [3] According to the adhesive tape described in [1] or [2] above, the content of the block copolymer in the adhesive layer is more than 5 parts by mass and less than 1,000 parts by mass relative to 100 parts by mass of natural rubber.

[0019] [4] The adhesive tape according to any one of [1] to [3] above, wherein the gel content of the adhesive layer is 10% or more.

[0020] [5] The adhesive tape according to any one of [1] to [4] above, wherein the amount of residual solvent in the adhesive layer is less than 10 ppm by mass.

[0021] [6] The adhesive tape according to any one of [1] to [5] above further comprises a substrate disposed on one side of the adhesive layer, the substrate being a paper substrate or a stretched polypropylene substrate.

[0022] [7] The adhesive tape according to any one of [1] to [6] above has an SP adhesive force of 4N / 24mm or more.

[0023] [8] The adhesive tape according to any one of [1] to [7] above has a ball adhesion value of 8 or more.

[0024] [9] The adhesive tape according to any one of [1] to [8] above, the adhesive layer further comprises a tackifying resin, the tackifying resin being a petroleum resin-based tackifying resin.

[0025] Invention Effects

[0026] According to the present invention, an adhesive tape having an adhesive layer comprising natural rubber and having excellent immediate processability and high holding power can be provided. Detailed Implementation

[0027] Adhesive tape

[0028] The adhesive tape of the present invention comprises an adhesive layer containing natural rubber and rubber components other than natural rubber. The natural rubber has a molecular weight of 450,000 or more, and the rubber components other than natural rubber are block copolymers. The adhesive layer is cross-linked using an isocyanate cross-linking agent. This results in good immediate processability of the adhesive tape and improves its holding power.

[0029] (Adhesive layer)

[0030] The adhesive layer in the adhesive tape of the present invention comprises natural rubber and rubber components other than natural rubber. As described below, the adhesive layer may be formed from an adhesive containing natural rubber, rubber components other than natural rubber, and other components as appropriate as needed.

[0031] By incorporating natural rubber into the adhesive layer, the adhesive tape exhibits excellent adhesion to a wide variety of substrates. Furthermore, it can be manufactured inexpensively. Moreover, its environmental impact can be reduced.

[0032] The adhesive layer of the adhesive tape of the present invention contains natural rubber primarily obtained by coagulating latex collected from Brazilian rubber trees (Hevea Brasiliensis, Euphorbiaceae family, Rubber genus) cultivated in Southeast Asia, the west coast of equatorial Africa, and the Amazon basin of Brazil. Examples of natural rubber include smoked sheet rubber (RSS), crepe rubber, felted rubber, and rubber scraps. Smoked sheet rubber (RSS) is preferred.

[0033] From the perspectives of improving holding power, improving paper peelability, and reducing environmental impact, the content of natural rubber in the adhesive 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, relative to 100 parts by mass of all rubber components. Furthermore, from the perspective of ensuring the specified content of rubber components other than natural rubber as described later, the content of natural rubber in the adhesive layer is preferably 95 parts by mass or less, more preferably 85 parts by mass or less, and even more preferably 75 parts by mass or less, relative to 100 parts by mass of all rubber components.

[0034] The molecular weight of the natural rubber in the adhesive layer is 450,000 or higher. When the molecular weight of the natural rubber in the adhesive layer is lower than 450,000, the holding power of the adhesive tape may sometimes decrease. From this perspective, the molecular weight of the natural rubber in the adhesive layer is preferably 600,000 or higher, more preferably 700,000 or higher, and even more preferably 800,000 or higher. There is no particular upper limit to the range of the molecular weight of the natural rubber in the adhesive layer, and it is usually 1.4 million. It should be noted that the molecular weight of the natural rubber in the adhesive layer can be determined by the method described in the examples below.

[0035] The aforementioned natural rubber preferably contains cross-linking functional groups. Natural rubber is a substance obtained by coagulating and drying natural rubber latex, which is the sap of rubber trees, and is mainly composed of cis-1,4-polyisoprene. The structure of the natural rubber molecule can be described as follows: one end of the cis-1,4-isoprene unit is composed of a protein terminus, the other end is bonded to a phosphate lipid, and this phosphate lipid terminus is further bonded to a long-chain fatty acid. In addition, natural rubber contains 3-4% by mass of non-rubber components such as proteins and lipids.

[0036] Therefore, natural rubber can be easily crosslinked and cured using the crosslinking agent described later. It should be noted that since the adhesive composition of the present invention is crosslinked and cured, the crosslinked body is also referred to as the cured product. From the perspective of improving holding power, the above-mentioned natural rubber is preferably crosslinked using an isocyanate-based crosslinking agent.

[0037] The adhesive layer contains block copolymers as a rubber component other than natural rubber. By including block copolymers as a rubber component other than natural rubber, pseudo-crosslinking occurs in the adhesive layer, resulting in good immediate processability of the adhesive tape. For the adhesive tape, due to the improved immediate processability, adhesive overflow can be prevented even if cutting is performed before or during the crosslinking process of the adhesive layer.

[0038] The block copolymers described above are preferably hydrides of block copolymers having at least blocks derived from aromatic vinyl monomers and blocks derived from conjugated diene monomers.

[0039] Examples of the aforementioned aromatic vinyl monomers include styrene, α-methylstyrene, p-methylstyrene, and chlorostyrene. These aromatic vinyl monomers can be used alone or in combination of two or more. Among them, styrene is preferred considering its excellent immediate processability and holding power.

[0040] The aforementioned aromatic vinyl monomers may further have structures, for example, derived from compounds with cyclic structures or compounds with short side-chain substituents, without impairing the effects of the present invention.

[0041] The content of blocks derived from the aromatic vinyl monomers in the above-mentioned block copolymers is not particularly limited, but preferably has an upper limit of 45% by mass. By keeping the content of the blocks derived from the aromatic vinyl monomers below 40% by mass, the paper release properties are further improved. A more preferred upper limit for the aromatic vinyl monomers is 35% by mass, and a more preferably upper limit is 30% by mass.

[0042] Furthermore, the preferred lower limit for the content of the aforementioned blocks derived from aromatic vinyl monomers is 5% by mass. By making the content of the aforementioned blocks derived from aromatic vinyl monomers 5% by mass or more, the immediate processability and holding power are further improved. The more preferred lower limit for the content of the aforementioned blocks derived from aromatic vinyl monomers is 8% by mass, and the even more preferred lower limit is 10% by mass.

[0043] Examples of the aforementioned conjugated diene monomers include, for instance, 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 can 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.

[0044] In the above-mentioned block copolymer, the content of blocks derived from the above-mentioned conjugated diene monomer is not particularly limited, as long as the effect of the present invention is achieved. The preferred lower limit is 55% by mass, the more preferred lower limit is 60% by mass, the preferred upper limit is 65% by mass, and the more preferred upper limit is 70% by mass.

[0045] The block copolymers described above may contain crosslinking functional groups within a range that does not impair the effects of the present invention.

[0046] Examples of block copolymers include styrene-isoprene-styrene block copolymers such as styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), and styrene-ethylene-butene-styrene block copolymer (SEBS). These block copolymers can be used alone or in combination of two or more. Considering the immediate processability of the adhesive tape, styrene-isoprene-styrene block copolymer (SIS) is preferred among these block copolymers.

[0047] From the perspective of the immediate processability of the adhesive tape, the content of block copolymers in the 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, relative to 100 parts by mass of the total rubber component. Furthermore, from the perspective of ensuring the specified content of natural rubber, the content of block copolymers in the 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, relative to 100 parts by mass of the total rubber component.

[0048] From the perspective of the immediate processability of the adhesive tape, the content of block copolymers in the 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, relative to 100 parts by mass of natural rubber. Furthermore, from the perspective of ensuring the specified content of natural rubber, the content of block copolymers in the adhesive layer is preferably 1000 parts by mass or less, more preferably 950 parts by mass or less, and even more preferably 900 parts by mass or less, relative to 100 parts by mass of natural rubber.

[0049] Without impairing the effects of the present invention, the rubber component may further include rubber components other than natural rubber and block copolymers. Examples of rubber components other than natural rubber and block copolymers include styrene-butadiene rubber (SBR), polyisobutylene rubber, and liquid rubber. The content of rubber components other than natural rubber and block copolymers is preferably 0 parts by weight or more and 10 parts by weight or less, more preferably 0 parts by weight or more and 5 parts by weight or less, further preferably 0 parts by weight or more and 2 parts by weight or less, and even more preferably 0 parts by weight or less.

[0050] (Isocyanate crosslinking agents)

[0051] The adhesive layer in the adhesive tape of the present invention is cross-linked using an isocyanate cross-linking agent. This improves the immediate processability of the adhesive tape and further enhances its holding power.

[0052] Isocyanate crosslinking agents are not particularly limited to compounds having two or more isocyanate groups per molecule. Examples include aromatic isocyanates such as toluene diisocyanate (TDI), naphthalene diisocyanate, diphenylmethane diisocyanate (MDI), and polymeric MDI, as well as aliphatic isocyanates such as hexamethylene diisocyanate (HDI), phenylenediamine diisocyanate (XDI), and isophorone diisocyanate. Additionally, trimethylolpropane adducts of the aforementioned isocyanate compounds, such as toluene diisocyanate adducts of trimethylolpropane, can also be used as isocyanate crosslinking agents.

[0053] As specific isocyanate crosslinking agents, hexamethylene diisocyanate (HDI) and diphenylmethane diisocyanate (MDI) are preferred. Furthermore, aliphatic isocyanates are preferred among the above-mentioned varieties, and hexamethylene diisocyanate (HDI) is more preferred. By using aliphatic isocyanates such as HDI, gelation can proceed well, the crosslinked structure can be made soft, holding power can be improved, or paper peelability at low temperatures can be improved.

[0054] Isocyanate crosslinking agents can be used alone or in combination with two or more.

[0055] Considering the retention force of the adhesive tape and the improvement of paper peelability, the amount of crosslinking agent added to the adhesive layer is preferably 0.1 parts by mass or more and 8.0 parts by mass or less relative to 100 parts by mass of the total rubber component, 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.

[0056] (Tackifying resin)

[0057] To improve adhesion, the adhesive layer may contain a tackifying resin. 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, heterogeneous rosin, polymerized rosin, and esters formed by esterification of these. Examples of terpene-based tackifying resins include terpene resins (α,β-pinene), terpene phenolic resins, aromatic modified terpene resins, and hydrogenated terpene resins. Examples of petroleum resin-based tackifying resins include aliphatic petroleum resins, aromatic petroleum resins, copolymer petroleum resins, and hydrogenated petroleum resins. These tackifying resins can be used alone or in combination of two or more. Petroleum resin-based tackifying resins are preferred, and aliphatic petroleum resins are more preferred.

[0058] To improve the cohesiveness and adhesion of the adhesive, the softening point of the tackifying resin should be around 95°C or higher, preferably including tackifying resins with a softening point above 120°C. For example, a combination of tackifying resins with a softening point above 95°C and below 120°C and tackifying resins with a softening point above 120°C and below 150°C can be used. It should be noted that the softening point can be determined using the ring and ball method specified in JIS K 2207.

[0059] The content of tackifying resin in the adhesive layer is preferably 10 parts by weight or more and 200 parts by weight or less relative to 100 parts by weight of all rubber components, more preferably 20 parts by weight or more and 150 parts by weight or less, and even more preferably 40 parts by weight or more and 130 parts by weight or less.

[0060] (Softener)

[0061] The adhesive layer may contain a plasticizer. By including a plasticizer, the processability of the adhesive that makes up the adhesive layer can be improved.

[0062] Examples of plasticizers include polybutene, polyisobutylene, processing oils, and naphthenic oils.

[0063] The content of the softener in the adhesive layer is preferably 5 parts by mass and less than 100 parts by mass relative to 100 parts by mass of all rubber components, more preferably 10 parts by mass and less than 50 parts by mass, and even more preferably 15 parts by mass and less than 30 parts by mass.

[0064] (particle)

[0065] The adhesive layer may contain microparticles. Examples of microparticles include inorganic hollow particles such as glass hollow spheres, volcanic ash hollow spheres, and fly ash hollow spheres; organic hollow particles including polymethyl methacrylate, acrylonitrile-vinylidene chloride copolymer, polystyrene, and phenolic resin; inorganic microparticles such as glass beads, silica beads, calcium carbonate, clay, carbon, titanium dioxide, zinc oxide, and synthetic mica; and organic microparticles such as ethyl acrylate, polyurethane, polyethylene, and polypropylene.

[0066] The content of microparticles in the adhesive layer is preferably 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of all rubber components, 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.

[0067] (Anti-aging agent)

[0068] The adhesive layer may contain anti-aging agents. By including anti-aging agents, the degradation caused by oxidation of the adhesive layer can be inhibited.

[0069] As anti-aging agents, examples include phenolic anti-aging agents, amine anti-aging agents, phosphorus anti-aging agents, and waxes.

[0070] The content of the anti-aging agent in the adhesive layer is preferably 0.01 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of all rubber components, 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.

[0071] (Other ingredients)

[0072] In addition to the above-mentioned components, the adhesive layer may also contain pigments, dyes, polymerization initiators, flame retardants, thickeners, and other additives that have been used in adhesives in the past.

[0073] The adhesive layer in the adhesive tape of the present invention comprises natural rubber and block copolymers; therefore, the adhesive used to form the adhesive layer can be easily plasticized and flowed by heat. Thus, the adhesive layer can be formed substantially without the use of solvents. This further reduces the environmental impact.

[0074] If the adhesive layer is formed without the use of solvents, the amount of residual solvent in the adhesive layer can be reduced. The amount of residual solvent in the 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. There is no particular limitation on the lower limit of the range of residual solvent in the adhesive layer; for example, it can be 0 ppm by mass.

[0075] <Gel fraction>

[0076] The gel content of the adhesive layer in the adhesive tape of the present invention is preferably 10% or more. If the gel content of the adhesive layer is 10% or more, the holding power of the adhesive tape can be further improved. From this perspective, the gel content of the adhesive layer is more preferably 15% or more, and even more preferably 20% or more. There is no particular upper limit to the range of the gel content of the adhesive layer, but it is preferably 50% or less, and more preferably 40% or less. It should be noted that the gel content of the adhesive layer can be determined by the method described in the examples below. The gel content of the adhesive layer can be adjusted by the type and content of rubber in the rubber component of the adhesive layer, as well as the type and amount of crosslinking agent added.

[0077] <Thickness>

[0078] There are no particular limitations on the thickness of the adhesive layer; for example, it can be about 5 μm or more and 200 μm or less, preferably 10 μm or more and 100 μm or less. When the thickness of the adhesive layer is within this range, the resulting adhesive tape can exert sufficient adhesive force.

[0079] (Substrate)

[0080] The adhesive tape of the present invention may further include a substrate, on which an adhesive layer is disposed. Examples of substrate materials include, for instance, kraft paper, washi paper, crepe paper, coated paper, synthetic paper, etc.; cotton cloth, synthetic short fiber cloth, acetate cloth, glass cloth, polyester cloth, etc.; nonwoven fabrics such as polyester nonwoven fabric and rayon nonwoven fabric; films such as glassine film, polyvinyl chloride film, stretched polypropylene film, unstretched polypropylene film, polyethylene film, polyester film, acetate film, etc.; metal foils such as aluminum foil and copper foil; foams such as polyurethane foam, polyethylene foam, vinyl chloride foam, chloroprene foam, natural rubber foam, butyl rubber foam, etc. Preferably, the substrate material is a paper substrate or a stretched polypropylene film. Kraft paper is preferred.

[0081] 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.

[0082] When a paper substrate such as kraft paper is used as the substrate material, a barrier layer can be formed on at least one surface of the paper substrate. The barrier layer can be provided on the surface of the substrate where the adhesive layer is provided, but it is preferably provided on the surface opposite to the surface where the adhesive layer is provided. Then, a release layer (described later) can be formed on the barrier layer provided on the opposite surface. The barrier layer can be formed of a polyolefin layer or the like. Examples of polyolefin resins constituting the barrier layer include polyethylene resins and polypropylene resins, but polyethylene resins are more preferred. The barrier layer can be formed by laminating a resin such as a polyolefin resin onto the surface of the substrate.

[0083] There is no particular limitation on the thickness of the barrier layer, but it is preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less.

[0084] The adhesive tape may have a release agent layer applied to the surface of the substrate opposite to the surface where the adhesive layer is applied. The release agent layer can be directly laminated to the substrate, but it is preferable to laminate it through the aforementioned barrier layer. By providing the release agent layer, when the adhesive tape is wound into a roll to form a coil, the adhesive layer and the release agent layer come into contact, thus allowing the adhesive tape to be easily released from the coil. The release agent layer can be formed from known release agents such as silicone-based release agents or long-chain alkyl-based release agents.

[0085] (Bio-based content)

[0086] The bio-based content (content of carbon derived from organisms) of the adhesive layer of the adhesive tape of the present invention is preferably 5% or more. If the bio-based content of the adhesive layer of the adhesive tape of the present invention is 5% or more, petroleum resources can be saved in the manufacture of the adhesive tape, and carbon dioxide emissions associated with the manufacture of the adhesive tape can be suppressed, thereby reducing the environmental impact. From this perspective, the bio-based content of the adhesive layer of the adhesive tape of the present invention is more preferably 15% or more, further preferably 20% or more, and even more preferably 25% or more. There is no particular upper limit to the range of the bio-based content of the adhesive layer of the adhesive tape of the present invention, but it is preferably 100%. It should be noted that the bio-based content of the adhesive layer of the adhesive tape can be measured by the method described in the examples described later. The bio-based content of the adhesive layer of the adhesive tape can be adjusted by the proportion of natural rubber in the adhesive layer, etc.

[0087] (SP Adhesion)

[0088] The SP adhesive strength of the adhesive tape of the present invention is preferably 4 N / 24 mm or more. If the SP adhesive strength of the adhesive tape is 4 N / 24 mm or more, the holding power of the adhesive tape can be further improved. From this perspective, the SP adhesive strength of the 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. There is no particular upper limit to the range of the SP adhesive strength of the adhesive tape of the present invention, which is typically 30 N / 24 mm. It should be noted that the SP adhesive strength of the adhesive tape can be measured using the method described in the examples below. The SP adhesive strength of the adhesive tape can be adjusted, for example, by the type and amount of isocyanate crosslinking agent, the type and content of rubber, and the type and content of tackifying oil.

[0089] (Ball viscosity value)

[0090] The rolling ball tack value of the adhesive tape of the present invention is preferably 8 or higher. When the rolling ball tack value of the adhesive tape is 8 or higher, the adhesive tape can immediately exert a durable and practical adhesive force when bonded to the substrate. From this perspective, the rolling ball tack value of the adhesive tape of the present invention is more preferably 9 or higher, and even more preferably 10 or higher. The upper limit of the range of rolling ball tack values ​​of the adhesive tape of the present invention is not particularly limited, and is generally 30. It should be noted that the rolling ball tack value of the adhesive tape can be measured by the method described in the embodiments described later. The rolling ball tack value of the adhesive tape can be adjusted, for example, by the type and amount of isocyanate crosslinking agent, the type and content of rubber, the type and content of tackifying oil, etc.

[0091] (Method for manufacturing adhesive tape)

[0092] The adhesive tape of the present invention can be manufactured, for example, by melting and mixing natural rubber, rubber components other than natural rubber, isocyanate crosslinking agents, tackifying resins as needed, microparticles, softeners, anti-aging agents, and other adhesive components at high temperature to obtain an adhesive, and then forming an adhesive layer by applying the obtained adhesive to the surface of a support. This method, because it is solvent-free, has the advantages of not requiring a drying process, having a fast coating speed, and posing no risk of explosion or fire.

[0093] Here, the mixing temperature during melt mixing is not particularly limited, for example, it can be 130~180℃, preferably 150~170℃. In addition, the mixing time during melt mixing is not particularly limited, for example, it can be 100~1000 seconds, preferably 100~700 seconds.

[0094] The adhesive components can be melt-mixed using methods such as pressurized high-speed kneaders, extrusion mixers, and plastic compounders. Coating can be applied using methods such as die coaters and roller coaters, without particular limitations.

[0095] The adhesive layer is cross-linked using an isocyanate-based cross-linking agent, and this cross-linking can be achieved using known methods. The cross-linking rate varies with storage temperature; the higher the temperature, the faster the cross-linking, and the lower the temperature, the slower the cross-linking. For example, cross-linking can occur in about one day at 60°C, and in about seven days at 25°C.

[0096] The resulting adhesive tape can be appropriately wound to form a wound body. Furthermore, the adhesive tape can be appropriately cut to the desired size; for example, in the case of forming a wound body, cutting can be performed after the wound body is formed. The adhesive tape of the present invention has good immediate processability; therefore, even if cutting is performed before crosslinking, it is possible to prevent adhesive overflow during or after cutting.

[0097] (Uses of adhesive tape)

[0098] The adhesive tape of the present invention has no particular limitation on its application. Because it uses natural rubber and has excellent immediate processability, the adhesive tape of the present invention has low manufacturing cost and high holding power, making it suitable for packaging and office applications, and particularly suitable for bundling straps. Furthermore, for bundling straps, kraft paper straps with kraft paper as the base material and OPP straps with OPP as the base material are preferred, with kraft paper straps being particularly preferred.

[0099] Example

[0100] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0101] [Evaluation Method]

[0102] In the examples and comparative examples, the adhesive tape was evaluated using the following evaluation methods.

[0103] (Molecular weight of natural rubber)

[0104] The molecular weight of natural rubber was determined by GPC (Gel Permeation Chromatography) analysis, and the peak molecular weight was taken as the molecular weight of natural rubber. Specifically, the GPC analysis used an ACQUITY APC (Waters Corporation) as the instrument, and an ACQUITY APCXT125-XT45-XT45 (Waters Corporation, 3μm, 4.6×150mm) column as the column. Polystyrene was used as the GPC standard when calculating the molecular weight, and tetrahydrofuran was used as the solvent for GPC determination. It should be noted that the molecular weight of natural rubber was determined as follows: A sample was collected from the adhesive layer of the obtained adhesive tape, dissolved in toluene, and a GPC determination sample was prepared. The peaks obtained from the GPC determination sample were identified by separating the components using a fractional GPC and analyzing the separated components. The identification of the separated components was performed by GC / MS analysis or IR spectroscopy analysis. Then, the molecular weight of natural rubber was determined from the peaks corresponding to natural rubber.

[0105] (Measurement conditions)

[0106] Mobile phase: Tetrahydrofuran 1.0 mL / min

[0107] Sample concentration: 0.2% by mass

[0108] Detectors: Differential refractive index (RI) detector, photodiode array (PDA) detector

[0109] GPC standard material: polystyrene (manufactured by Waters Corporation, molecular weight: 266~1,800,000)

[0110] Column temperature: 40℃

[0111] (Gel fraction of the adhesive layer)

[0112] Collect adhesive layer test pieces and accurately weigh the mass A (mg) of the test pieces. Next, add toluene to the test pieces to achieve an adhesive solids concentration of 6% by mass. Immerse the test pieces in toluene and shake for 24 hours. Filter through a 200-mesh metal mesh, collect the insoluble components on the mesh, vacuum dry, and accurately weigh the mass B (mg) of the insoluble components. Calculate the gel fraction (mass %) from the obtained value using the following formula.

[0113] Gelation rate (mass%) = 100 × (B / A)

[0114] (Residual solvent content in the adhesive layer)

[0115] The residual solvent content of the adhesive layer was determined by gas chromatography (Shimadzu Corporation, GC-2014) under the following conditions.

[0116] Bottle insulation temperature: 100℃

[0117] Small bottle insulation time: 8 minutes

[0118] Injection volume: 1.0 mL

[0119] Column: RTX-1 (inner diameter 0.32mm × length 30m, film thickness 0.5μm)

[0120] Column temperature: 50℃

[0121] Inlet temperature: 150℃

[0122] Column inlet pressure: 100 kPa

[0123] Column flow rate: 3.4 mL / min

[0124] Detector: FID

[0125] Sample size: 10cm × 10cm

[0126] (Bio-based content of adhesive tape)

[0127] The bio-based content of the adhesive tape was determined in accordance with ASTM 6866.

[0128] (SP adhesive force of adhesive tape)

[0129] At room temperature (23℃) and relative humidity of 50%, the adhesive layer of the adhesive tape was pressed onto a SUS 304 steel plate by repeatedly pressing it against one side with a 2kg roller. After being left in this environment for 30 minutes, the 180° peel strength at a width of 24mm was measured using a tensile testing machine at a tensile speed of 300mm / min, according to JIS Z0237. This strength was taken as the SP adhesive force.

[0130] (Ball adhesion value of adhesive tape)

[0131] The ball tack value of the adhesive tape was measured and calculated using a ball tack tester (manufactured by Yasuda Seiki Co., Ltd.) in accordance with JISZ 0237 at an environment of 23°C and 50% relative humidity.

[0132] (Low-temperature paper peeling of adhesive tape)

[0133] The peel test for evaluating low-temperature adhesion was conducted as follows. The test adhesive tape was cut into 50mm × 70mm pieces and, together with the corrugated cardboard (the substrate) and a 2kg roller, was placed in a 0°C constant temperature bath 12 hours before the test. The corrugated cardboard was placed in the 0°C bath, and the test adhesive tape was adhered to it without applying force under certain conditions. The 2kg roller was then pressed back and forth once, and immediately peeled at a peel speed of 100mm / s to a 90-degree angle. The percentage of damaged area (%) of the bonded corrugated cardboard was measured.

[0134] <Evaluation Criteria>

[0135] A: Severe removal of corrugated paper (more than 55% of the surface layer of corrugated paper has been removed).

[0136] B: Slightly peel off the corrugated paper (the surface layer of the corrugated paper should be peeled off by more than 45% but less than 55%).

[0137] C: Corrugated paper not largely removed (less than 45% of the surface layer of corrugated paper removed)

[0138] (SP holding power of adhesive tape)

[0139] The adhesive layer was applied to the SUS abrasive plate with an adhesion area of ​​24mm × 24mm, and left to stand for 30 minutes at 23°C and 50% RH. Then, a 2kg load was applied at 23°C, and the offset was measured 24 hours after the application of the 2kg load, according to the holding force test method of JIS Z 0237. It should be noted that in Table 1, "fallen" indicates that the adhesive tape fell off the SUS abrasive plate due to excessive offset.

[0140] (Adhesive tape backing paper holding power (50℃))

[0141] The adhesive layer is applied to the backing paper (K ​​backing) with an application area of ​​10mm × 10mm, and left to stand at 23°C and 50%RH for 30 minutes. Then, after being kept at 50°C for 30 minutes, a load of 500g is applied, and the time from when the backing paper falls off is recorded. Check for falling off every 60 minutes, up to a maximum of 180 minutes.

[0142] (Instant processability of adhesive tape)

[0143] The adhesive tape wound using the methods described in the various embodiments and comparative examples was cut within 3 hours of being wound to obtain 50mm × 50m samples. Five rolls of the obtained samples were arranged and stacked in an oven at 40°C, and then a 10kg load was applied for one week. After one week, the load was removed, and a sensory evaluation was performed according to the rating system to assess the resistance felt when attempting to take one roll of adhesive tape at a time, as described below.

[0144] <Evaluation Criteria>

[0145] A: It can be obtained without applying force.

[0146] B: It can be obtained with a little force, and it feels sticky when peeled off.

[0147] C: Peeled off with strong force. Has a strong sense of adhesion on the sides.

[0148] [Examples 1-11, Comparative Examples 1-5]

[0149] The adhesive components, prepared according to the proportions listed in Table 1, were placed in a mixing-extrusion testing apparatus (manufactured by Toyo Seiki Co., Ltd., product name "Labo Plastomil" (registered trademark)). The adhesive components were then melt-mixed under the conditions shown in Table 1, extruded, and coated onto paper (kraft paper) or OPP (extruded polypropylene film) to produce adhesive tapes for the examples and comparative examples. The resulting adhesive tapes were then placed at 23°C and 50% relative humidity for one week before various evaluations were conducted. The evaluation results are shown in Table 1.

[0150]

[0151] The components in Table 1 are described below.

[0152] Natural rubber: Smoked sheet (RSS1 grade), a product after mastication and granulation, with Mooney viscosity adjusted by mastication time.

[0153] Block copolymer: Styrene-isoprene-styrene block copolymer (SIS), manufactured by JSR Corporation, product name "SIS5506"

[0154] Isocyanate crosslinking agent (HDI): Hexamethylene diisocyanate (HDI), manufactured by Asahi Kasei Corporation, product name "Deylanet TPA-100".

[0155] Isocyanate crosslinking agent (MDI): Diphenylmethane diisocyanate, manufactured by MCC Trending Co., Ltd., product name "Diphenylmethane Diisocyanate".

[0156] Aziridine crosslinking agent (HDU): Manufactured by Mutual Pharmaceutical Co., Ltd., product name "N,N′-hexamethylene-1,6-bis(1-aziridinecarboxamide)"

[0157] Epoxy crosslinking agent: Manufactured by Mitsubishi Gas Chemical Transforming Co., Ltd., product name "TETRAD-X".

[0158] Tackifying resin: An aliphatic petroleum resin manufactured primarily from 1,3-pentadiene extracted from C5 fractions, produced by Zeon Corporation of Japan, under the product name "Quinton A-100".

[0159] Softener: Processing oil, manufactured by JXTG Energy Co., Ltd., product name "Crystal Oil F220"

[0160] Particulate matter: Calcium carbonate, manufactured by Nitto Powdered Chemicals Co., Ltd., product name "NS#100".

[0161] Anti-aging agent: Phenolic anti-aging agent (2,2'-methylenebis-(4-ethyl-6-tert-butylphenol)), manufactured by Yoshitomi Pharmaceutical Co., Ltd., product name "Yosinox 425"

[0162] The adhesive tapes of Examples 1-11 have an adhesive layer comprising natural rubber and rubber components other than natural rubber. The natural rubber has a molecular weight of 450,000 or more, and the rubber components other than natural rubber are block copolymers. The adhesive layer is cross-linked by an isocyanate cross-linking agent, thus resulting in high holding power and good immediate processability.

[0163] The adhesive tape of Comparative Example 1 has poor immediate processability because the adhesive layer does not contain block copolymers.

[0164] The adhesive tape of Comparative Example 2 has low holding power because the adhesive layer does not contain natural rubber.

[0165] The adhesive tapes in Comparative Examples 3 and 4 were not cross-linked by isocyanate cross-linking agents, and therefore had poor holding power.

[0166] The adhesive tape of Comparative Example 5 has low holding power and poor immediate processability because the molecular weight of natural rubber is less than 450,000.

Claims

1. An adhesive tape comprising an adhesive layer containing natural rubber and rubber components other than natural rubber, The molecular weight of the natural rubber is above 450,000. The rubber components other than natural rubber are block copolymers. The adhesive layer is cross-linked using an isocyanate cross-linking agent.

2. The adhesive tape according to claim 1, wherein the block copolymer comprises a styrene-isoprene-styrene block copolymer.

3. The adhesive tape according to claim 1, wherein the content of the block copolymer in the adhesive layer is 5 parts by weight or more and 1000 parts by weight or less relative to 100 parts by weight of natural rubber.

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

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

6. The adhesive tape according to claim 1 further comprises a substrate disposed on one side of the adhesive layer, wherein the substrate is a paper substrate or a stretched polypropylene film.

7. The adhesive tape according to claim 1, wherein the SP adhesive force is 4N / 24mm or more.

8. The adhesive tape according to claim 1, wherein the rolling ball adhesion value is 8 or higher.

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

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