Adhesive tape

Abstract

The present invention addresses the problem of providing an adhesive tape that is reduced in adhesion to a backing and has excellent recyclability.　The present invention is an adhesive tape comprising a paper base material, an adhesive layer provided on one surface side of the base material, and a release layer provided on the other surface side of the base material, wherein the release layer contains an aqueous polymer, and the sizing degree of the paper base material as measured in accordance with JIS P 8122:2004 is 15 seconds or more.

Description

adhesive tape

[0001] The present invention relates to an adhesive tape having a paper substrate.

[0002] In recent years, recycling of packaging materials such as cardboard has been recommended from the perspective of environmental conservation. Adhesive tape is widely used in packaging materials to seal the inside, and adhesive tape often remains attached to used packaging materials. Some adhesive tapes used in packaging materials, such as kraft tape, which has a paper base, can be recycled along with the packaging material, allowing the process of removing the adhesive tape to be omitted when recycling the packaging material.

[0003] For example, Patent Document 1 discloses a kraft adhesive tape that can be recycled without leaving any residue while remaining attached to cardboard, the kraft adhesive tape having a kraft paper substrate, a release layer made of a mixture of a water-soluble resin and a silicone emulsion on one side thereof, and a water-soluble adhesive layer on the other side thereof. Patent Document 2 also discloses an adhesive tape that has excellent recyclability when recycled together with paper materials such as packaging materials, the adhesive tape having a paper substrate, an adhesive layer on one side of the substrate, and a release agent layer on the other side of the substrate, the adhesive tape leaving no more than 50% residue in a disintegration test.

[0004] Japanese Patent Application Laid-Open No. 08-081661 Japanese Patent Application Laid-Open No. 2021-107512

[0005] In the above-mentioned pressure-sensitive adhesive tape, from the viewpoint of eliminating the use of plastics, it is required not to use plastics, particularly polyethylene, in the sealing layer. Patent Documents 1 and 2 disclose examples in which polyvinyl alcohol is used in the sealing layer.

[0006] However, if the sizing degree of the substrate is low and the sealant permeates into the substrate, the pulp will not be sufficiently loosened when the adhesive tape is recycled, which reduces the recyclability of the adhesive tape. In addition, if the sealant permeates into the substrate, the sealing effect will be weakened and the release agent will also be taken into the substrate, increasing the adhesive strength of the back surface, which can lead to problems such as paper peeling and layer cracking when unfolding an adhesive tape that has been stored in a roll.

[0007] Therefore, an object of the present invention is to provide a pressure-sensitive adhesive tape that has low adhesive strength on its back surface and is highly recyclable.

[0008] As a result of extensive investigation, the present inventors have found that the above-mentioned problems can be solved by using a paper base having a sizing degree of at least a certain level and by containing a specific type of sealer in an adhesive tape comprising a paper base, an adhesive layer provided on one side of the paper base, and a release layer provided on the other side of the paper base. That is, the present invention provides the following [1] to

[10] .

[0009] [1] A pressure-sensitive adhesive tape comprising a paper base material, a pressure-sensitive adhesive layer provided on one side of the paper base material, and a release layer provided on the other side of the paper base material, wherein the release layer contains a water-based polymer, and the paper base material has a sizing degree of 15 seconds or more in accordance with JIS P 8122:2004. [2] The pressure-sensitive adhesive tape according to [1], wherein the release layer is composed of a release agent layer containing a release agent and a filler layer containing a filler, or is composed of a release layer containing both a filler and a release agent, and the filler is a water-based polymer. [3] The pressure-sensitive adhesive tape according to [1], wherein the basis weight of the filler layer is 20 g / m ２The pressure-sensitive adhesive tape according to [2], wherein the release agent is a silicone-based release agent or a long-chain alkyl-based release agent. [4] The pressure-sensitive adhesive tape according to [2] or [3], wherein the release agent is a silicone-based release agent or a long-chain alkyl-based release agent. [5] The pressure-sensitive adhesive tape according to any one of [1] to [4], wherein the aqueous polymer is starch or a PVA resin. [6] The pressure-sensitive adhesive tape according to any one of [1] to [5], wherein the pressure-sensitive adhesive layer comprises a rubber-based pressure-sensitive adhesive. [7] The pressure-sensitive adhesive tape according to [6], wherein the rubber-based pressure-sensitive adhesive is natural rubber. [8] The pressure-sensitive adhesive tape according to any one of [1] to [7], wherein the laminate of the paper substrate and the release layer has a bio-based content of 85% or more. [9] A structure comprising the pressure-sensitive adhesive tape according to any one of [1] to [8], and a packaging material.

[10] A method for recycling the pressure-sensitive adhesive tape according to any one of [1] to [8], while it is attached to the packaging material.

[0010] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has low adhesive strength on its back surface and is excellent in recyclability.

[0011] 1 is a schematic diagram showing an embodiment of a pressure-sensitive adhesive tape of the present invention. 2 is a schematic diagram showing an embodiment of a pressure-sensitive adhesive tape of the present invention. 3 is an image showing the result of iodine dyeing of a paper substrate in Example 1. 4 is an image showing the result of iodine dyeing of a paper substrate in Comparative Example 1.

[0012] [Adhesive Tape] The adhesive tape of the present invention comprises a paper base material, an adhesive layer provided on one surface of the paper base material, and a release layer provided on the other surface of the base material, wherein the release layer contains a water-based polymer, and the paper base material has a sizing degree of 15 seconds or more in accordance with JIS P 8122:2004.

[0013] (Paper Substrate) The pressure-sensitive adhesive tape of the present invention includes a paper substrate as a substrate, and the paper substrate has a sizing degree (hereinafter simply referred to as "sizing degree") according to JIS P 8122:2004 of 15 seconds or more. The release layer is formed by applying a coating liquid containing a sealer, followed by heating and drying. In typical manufacturing equipment, the release layer is formed by heating and drying within 15 seconds after application is completed. If the sizing degree is less than 15 seconds, the sealer contained in the release layer is likely to penetrate into the paper substrate, making it difficult to loosen the pulp during recycling of the pressure-sensitive adhesive tape, which may reduce recyclability. Furthermore, if the sealing effect is weakened, the release agent may also penetrate into the paper substrate, increasing the adhesive strength to the back surface. The present inventors have discovered that by setting the sizing degree of the paper substrate to 15 seconds or more, an adhesive tape with excellent recyclability and low adhesive strength to the back surface can be obtained. From this perspective, the sizing degree is preferably 18 seconds or more, and more preferably 20 seconds or more. Furthermore, in view of the properties of the paper substrate, the sizing degree is practically, for example, 45 seconds or less, preferably 40 seconds or less, and more preferably 37 seconds or less.

[0014] The sizing degree is measured in accordance with JIS P 8122:2004. The sizing degree can also be estimated from the degree of penetration of the filler into the paper substrate by methods such as dyeing the filler or analyzing the paper substrate while scraping it in the thickness direction. When the sizing degree of the paper substrate is less than 15 seconds, penetration of the filler into the paper substrate is observed. When the sizing degree of the paper substrate is 15 seconds or more, the filler does not penetrate into the paper substrate, or the filler is only slightly unevenly distributed on the release layer side of the paper substrate.

[0015] Examples of methods for adjusting the sizing degree include adjusting the type and content of sizing agents. Examples of sizing agents include acidic papermaking sizing agents, alkaline papermaking sizing agents, and neutral papermaking sizing agents. These agents may be used separately or in combination depending on their compatibility with other additives. Examples of acidic papermaking sizing agents include reinforced rosin sizing agents, rosin emulsion sizing agents, and synthetic sizing agents. Examples of alkaline papermaking sizing agents include alkyl ketene dimers, alkenyl succinic anhydrides, and cationic polymer sizing agents. Examples of neutral papermaking sizing agents include rosin-based neutral sizing agents. The content of the sizing agent is, for example, 0.1 to 10 parts by mass, preferably 0.3 to 3 parts by mass, per 100 parts by mass of the paper substrate.

[0016] Examples of the paper substrate include paper sheets such as kraft paper, glassine paper, and fine paper, with kraft paper being preferred. Examples of kraft paper include unbleached kraft paper, semi-bleached kraft paper, bleached kraft paper, those that have been subjected to Clupak processing to impart extensibility, and those that have been subjected to wet strength processing to impart wet strength.

[0017] The basis weight of the paper substrate is not particularly limited, but is preferably 10 to 150 g / m ２ and more preferably 30 to 130 g / m ２ When the basis weight of the paper substrate is equal to or greater than these lower limit values, the strength of the adhesive tape increases, and when it is equal to or less than these upper limit values, the thickness of the adhesive tape can be reduced, improving workability and the like.

[0018] (Release Layer) The pressure-sensitive adhesive tape of the present invention has a release layer provided on the surface of the substrate opposite to the surface on which the pressure-sensitive adhesive layer described below is provided. The release layer contains a water-based polymer. By containing a water-based polymer, the components of the release layer are more likely to remain on the surface of the paper substrate, improving the recyclability of the pressure-sensitive adhesive tape and reducing the adhesive strength on the back side. As described below, the water-based polymer is preferably used as a sealant.

[0019] Specific examples of aqueous polymers include water-soluble polymers such as starch, polyvinyl alcohol resin (PVA resin), acrylic resin, and carboxymethyl cellulose, and water-dispersible polymers such as aqueous latex and aqueous urethane. Among these, it is preferable to use a water-soluble polymer, more preferably starch or PVA resin, and even more preferably α-starch or PVA resin. The release layer may have a multilayer structure consisting of a release agent layer containing a release agent and a filler layer containing a filler, or it may have a single-layer structure consisting of a release layer containing both a filler and a release agent. That is, the release layer may be composed of a release agent layer containing a release agent and a layer containing an aqueous polymer (aqueous polymer layer), or may be composed of a release layer containing both an aqueous polymer and a release agent.

[0020] When the release layer has a single-layer structure containing both a sealer and a release agent, it is preferable that the adhesive tape 10 includes a release layer 11, a paper substrate 12, and an adhesive layer 13 in this order, as shown in Fig. 1. When the release layer has a multilayer structure consisting of a release agent layer and a sealer layer, it is preferable that the sealer layer is provided on the paper substrate side. That is, it is preferable that the adhesive tape 10 includes a release agent layer 11A, a sealer layer (aqueous polymer layer) 11B, a paper substrate 12, and an adhesive layer 13 in this order, as shown in Fig. 2. It should be noted that in this specification, the "release agent layer" is a layer that constitutes the release layer together with the sealer layer (aqueous polymer layer), and is a different concept from the release layer.

[0021] <Sealing Agent (Water-Based Polymer)> The sealing agent serves to retain the release agent on the surface of the paper substrate, and by using a sealing agent, the adhesive strength of the adhesive tape itself can be reduced. The above-mentioned water-based polymers can be used as the sealing agent. Among the above-mentioned water-based polymers, examples of α-starch include starch or modified starch that is heated in the presence of water, gelatinized, and then dried so that the starch dissolves or swells in water at room temperature. The α-starch may be unprocessed or may be further processed before use. Examples of types of processing include conventionally known etherification, phosphate cross-linking, acetylation, etherification, oxidation, and combinations thereof.

[0022] When α-starch is used as the filler (aqueous polymer), as described above, the α-starch obtained by heating starch or modified starch in the presence of water and gelatinizing it can be used as the filler (aqueous polymer). In this case, the heated aqueous solution containing α-starch is applied to the paper substrate to form a filler layer (aqueous polymer layer), and a release agent layer is further formed thereon, or the aqueous solution and the release agent are mixed to form a single-layer release layer on the paper substrate.

[0023] Furthermore, when α-starch is used as the filler (water-based polymer), commercially available α-starch may be used. In this case, the commercially available α-starch may be dissolved in water, and the aqueous solution may be applied to the paper substrate to form a filler layer (water-based polymer layer), and a release agent layer may be further formed thereon, or the aqueous solution may be mixed with the release agent to form a single-layer release layer on the paper substrate. Commercially available α-starch products include Amycol HF, Amycol C, Amycol KF, Amycol HG-N, Amycol BJ-2, ​​Amycol W, Starch MH-A, Amycol A, Amycol FW (all manufactured by Nippon Starch Chemical Co., Ltd.), Nisshoku Alstar, Nisshoku Alstar H, Nisshoku Waxy α (all manufactured by Nippon Shokuhin Kako Co., Ltd.), Corn αY, Corn αS-1, Industrial Tapioca α, Industrial Tapioca αTP-2, Wheat Starch αWA-105 (manufactured by Sanwa Starch Industry Co., Ltd.), Amilox No. 1, and Amilox No. 1A (manufactured by Nippon Corn Starch Co., Ltd.).

[0024] PVA resins are obtained by polymerizing vinyl esters to obtain polymers according to conventionally known methods, and then saponifying, i.e., hydrolyzing, the polymers. Saponification generally uses an alkali or an acid, but alkali is preferred. As PVA resins, one type may be used alone, or two or more types may be used in combination. Furthermore, derivatives in which other monomers are added to the hydroxyl groups of saponified polyvinyl alcohol may also be used.

[0025] Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, and vinyl benzoate. The method for polymerizing vinyl esters is not particularly limited, but examples include solution polymerization, bulk polymerization, and suspension polymerization.

[0026] The PVA resin may be unmodified PVA or modified PVA. Examples of unmodified PVA include saponified polyvinyl esters. Examples of modified PVA include saponified polymers of vinyl esters and other unsaturated monomers. Examples of other unsaturated monomers include monomers other than vinyl esters that have a carbon-carbon double bond, such as a vinyl group. Examples of such monomers include olefins, (meth)acrylic acid and salts thereof, (meth)acrylic acid esters, unsaturated acids other than (meth)acrylic acid, salts and esters thereof, (meth)acrylamides, N-vinylamides, vinyl ethers, nitriles, vinyl halides, allyl compounds, vinylsilyl compounds, isopropenyl acetate, sulfonic acid group-containing compounds, and amino group-containing compounds.

[0027] The saponification degree of the PVA resin is preferably 50 to 99.5 mol%, more preferably 60 to 90 mol%, from the viewpoint of ensuring water solubility and facilitating good recyclability of the pressure-sensitive adhesive tape. The saponification degree is measured in accordance with JIS K6726. The saponification degree indicates the proportion of units that are actually saponified to vinyl alcohol units among units converted to vinyl alcohol units by saponification. The method for adjusting the saponification degree is not particularly limited. The saponification degree can be adjusted appropriately by the saponification conditions, i.e., the hydrolysis conditions.

[0028] The degree of polymerization of the PVA resin is not particularly limited, but is, for example, 700 to 3000, preferably 1000 to 2500, and more preferably 1500 to 2000. When the degree of polymerization is equal to or greater than the above-mentioned lower limit, the adhesive strength of the back surface of the pressure-sensitive adhesive tape is likely to be kept low. Furthermore, when the degree of polymerization is equal to or greater than the above-mentioned lower limit, the sealing agent serves to reinforce the paper substrate, preventing the pressure-sensitive adhesive tape from breaking due to its adhesive strength when peeling it off and leaving part of the pressure-sensitive adhesive tape on the adherend. This makes it less likely that problems such as paper peeling and layer cracking will occur when, for example, a roll of pressure-sensitive adhesive tape is unrolled. On the other hand, when the degree of polymerization is equal to or less than the above-mentioned upper limit, the recyclability of the pressure-sensitive adhesive tape is likely to be improved.

[0029] Examples of aqueous latexes include alkyd resins, acrylic resins, vinyl resins, cellulose resins, urethane resins, polyester resins, etc. When using these aqueous latexes, by using one with a relatively high molecular weight, the filler reinforces the paper substrate, and defects such as paper peeling and layer cracking are less likely to occur when, for example, a roll-shaped adhesive tape is unfolded.

[0030] The basis weight of the filler layer (water-based polymer layer) is 20 g / m ２ Preferably, the weight is 15 g / m or less. ２ Preferably, it is 10 g / m or less. ２ Preferably, the amount is 6 g / m or less. ２ Preferably, the amount is 4 g / m or less. ２ More preferably, it is 3 g / m or less. ２ When the basis weight of the filler layer (aqueous polymer layer) is equal to or less than the above upper limit, the environmental load is likely to be reduced. Furthermore, the basis weight of the filler layer (aqueous polymer layer) is not particularly limited, but from the viewpoint of allowing the release agent to remain on the surface of the paper substrate and making it easy to keep the adhesive strength to the backside low, it is preferably 0.3 g / m ２ More preferably, it is 0.5 g / m or more. ２ More preferably, it is 0.8 g / m or more. ２ That's all.

[0031] <Release Agent> Examples of the release agent include silicone-based release agents, long-chain alkyl-based release agents, and fluorine-based release agents. Among these, silicone-based release agents or long-chain alkyl-based release agents are preferred. That is, the release agent layer preferably contains a silicone compound or a long-chain alkyl group-containing compound as the release agent. By using a silicone-based release agent, the adhesive strength of the back surface can be easily reduced. Furthermore, by using a long-chain alkyl-based release agent, the environmental load can be easily reduced. Note that the long-chain alkyl-based release agent is preferably an aqueous release agent that is an aqueous dispersion of a long-chain alkyl group-containing compound.

[0032] In the long-chain alkyl group-containing compound, the long-chain alkyl group is preferably an alkyl group having 8 or more carbon atoms. The number of carbon atoms may be 10 or more, or 12 or more. The long-chain alkyl group is preferably an alkyl group having 30 or less carbon atoms. The number of carbon atoms may be 28 or less, or 26 or less. The long-chain alkyl group-containing compound preferably has a long-chain alkyl group on its side chain.

[0033] Examples of long-chain alkyl group-containing compounds include long-chain alkyl group-containing polyvinyl resins, long-chain alkyl group-containing alkyd resins, long-chain alkyl group-containing acrylic resins, long-chain alkyl group-containing polyester resins, etc. Among these, long-chain alkyl group-containing polyvinyl resins are preferred.

[0034] When a release agent layer is formed, the basis weight of the release agent layer is not particularly limited, but is, for example, 0.1 g / m ２ 10g / m or more ２ or less, preferably 0.2 g / m ２ 5g / m or more ２ or less, more preferably 0.3 g / m ２ 2g / m or more ２ The following is the result.

[0035] The sealing layer (aqueous polymer layer) may be formed from a sealing agent (aqueous polymer), and may contain appropriate additives as needed. The sealing agent layer may be formed by applying a sealing agent diluted with a solvent or the like to the surface of the substrate opposite to the surface on which the pressure-sensitive adhesive layer is provided, and then heating, drying, or the like as needed. The release agent layer may also contain appropriate additives other than the above-mentioned release agents, such as a photopolymerization initiator, inactive particles, and antioxidants. The release agent layer may be formed by forming a sealing agent layer on the surface of the substrate, and then applying a release agent diluted with a solvent or the like to the surface of the sealing agent layer, and then heating, drying, or the like as needed.

[0036] When the release layer is a single layer containing both a filler (aqueous polymer) and a release agent, the release layer may be formed from a mixture of the filler (aqueous polymer) and the release agent, and the mixture may contain the above-mentioned additives as appropriate. A single-layer release layer may be formed by applying a coating liquid containing the release agent and the filler, diluted appropriately with a solvent, to the surface of the paper substrate opposite to the surface on which the pressure-sensitive adhesive layer is formed, and then heating and drying as necessary. When the release layer contains both a filler (aqueous polymer) and a release agent, the amount of the release agent used is, for example, 1 to 200 parts by weight, preferably 5 to 100 parts by weight, and more preferably 10 to 60 parts by weight per 100 parts by weight of the filler (aqueous polymer). The basis weight of the release layer is not particularly limited, but is preferably 0.3 g / m ２ 30g / m or more ２ or less, preferably 0.4 g / m ２ 25g / m or more ２ or less, preferably 0.5 g / m ２ 15g / m or more ２ or less, preferably 0.6 g / m ２ 8g / m or more ２ Less than 1 g / m, more preferably ２ 4.5g / m or more ２ When the release layer is composed of a filling layer (aqueous polymer layer) and a release agent layer, the basis weight of the release layer is the sum of the basis weight of the filling layer and the basis weight of the release agent layer.

[0037] (Adhesive Layer) The adhesive tape of the present invention has an adhesive layer provided on one side of the substrate. The adhesive layer is a layer formed of an adhesive. The type of adhesive is not particularly limited, but examples include acrylic adhesives, rubber adhesives, urethane adhesives, and silicone adhesives. These may be used alone or in combination. Of these, rubber adhesives are preferred.

[0038] Examples of acrylic adhesives that can be used include acrylic polymers obtained by copolymerizing various (meth)acrylic acid alkyl esters with monomers other than (meth)acrylic acid alkyl esters, such as monomers such as vinyl acetate and acrylonitrile, or monomers containing functional groups such as carboxyl groups and hydroxyl groups, such as (meth)acrylic acid and hydroxyacrylate. In addition to the acrylic polymer, the acrylic adhesive used in the adhesive layer may contain various additives conventionally used in adhesives, such as tackifying resins, fine particles, crosslinking agents, plasticizers, softeners, pigments, dyes, dispersants, photopolymerization initiators, flame retardants, antioxidants, and antioxidants.

[0039] The rubber-based adhesive preferably uses a rubber component as the main component. Examples of the rubber component include synthetic rubbers such as styrene-isoprene block copolymer (SIS), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), isoprene rubber, butyl rubber (IIR), butadiene rubber (BR), and chlorosulfonated polyethylene, as well as natural rubber. Among these, natural rubber is preferred. The use of natural rubber facilitates reducing environmental impact. It is also preferred to use natural rubber in combination with synthetic rubber such as SIS.

[0040] The rubber-based pressure-sensitive adhesive may contain a tackifier in addition to the rubber component. The tackifier imparts tackiness to the rubber-based pressure-sensitive adhesive to improve the adhesive performance of the pressure-sensitive adhesive layer. Examples of tackifiers include rosin-based resins, terpene-based resins, coumarone-indene resins, petroleum-based resins, and terpene-phenol resins, with petroleum-based resins being preferred. The content of the tackifier in the pressure-sensitive adhesive is, for example, 20 to 200 parts by mass, preferably 50 to 150 parts by mass, per 100 parts by mass of the rubber component.

[0041] The rubber-based adhesive may contain a softener in addition to the tackifier. By containing a softener, the rubber-based adhesive softens, making it easier to improve its application properties and adhesive performance. Examples of softeners include mineral oils (also called process oils) such as paraffin oil and naphthenic oil, liquid polybutene, liquid lanolin, liquid polyisoprene, and liquid polyacrylate. The content of the softener in the adhesive is, for example, 5 to 80 parts by mass, preferably 10 to 50 parts by mass, per 100 parts by mass of the rubber component.

[0042] In addition to the above, the rubber-based adhesive constituting the adhesive layer may appropriately contain known additives used in adhesives, such as fillers, antioxidants, anti-aging agents, ultraviolet inhibitors, and pigments.

[0043] Examples of the filler include calcium carbonate, zinc oxide (zinc oxide), silica, aluminum silicate, talc, diatomaceous earth, silica sand, pumice powder, slate powder, mica powder, asbestos, aluminum sol, alumina white, aluminum sulfate, barium sulfate, lithopone, calcium sulfate, molybdenum disulfide, graphite, glass fiber, glass spheres, single-crystal potassium titanate, carbon fiber, activated zinc oxide, zinc carbonate, magnesium oxide, basic magnesium carbonate, litharge, red lead, white lead, calcium hydroxide, activated calcium hydroxide, and titanium oxide.

[0044] Among these fillers, calcium carbonate, zinc oxide, silica, titanium oxide, etc. are preferred. Blending these fillers can impart appropriate cohesiveness to the adhesive. The content of the filler in the adhesive is, for example, 0.1 to 150 parts by mass, preferably 1 to 100 parts by mass, and more preferably 3 to 80 parts by mass, per 100 parts by mass of the rubber component. By adjusting the content to 0.1 parts by mass or more, the effect of adding the filler can be exerted. Furthermore, by adjusting the content to 150 parts by mass or less, the filler can be appropriately added to the adhesive, and various physical properties of the adhesive tape can be more easily improved.

[0045] Examples of the antioxidant include naphthylamine compounds, diphenylamine compounds, p-phenylenediamine compounds, other amine compounds, amine compound mixtures, quinoline compounds, hydroquinone derivatives, monophenol compounds, bisphenol compounds, trisphenol compounds, polyphenol compounds, thiobisphenol compounds, etc. The blending ratio of the antioxidant is not particularly limited, but for example, in a rubber-based pressure-sensitive adhesive, it is usually 0.1 to 5 parts by mass, and preferably 0.5 to 2 parts by mass, per 100 parts by mass of the rubber component.

[0046] The basis weight of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 3 to 50 g / m ２ and more preferably 10 to 40 g / m ２ By setting the basis weight of the pressure-sensitive adhesive layer to the above lower limit or more, the adhesive strength is likely to be increased. On the other hand, by setting the basis weight of the pressure-sensitive adhesive layer to the above upper limit or less, the adhesive strength according to the thickness can be obtained.

[0047] The thickness of the adhesive layer is not particularly limited, but is preferably 10 to 150 μm, more preferably 15 to 50 μm. By making the thickness of the adhesive layer equal to or greater than the above lower limit, the adhesive strength tends to be increased.

[0048] (Adhesive Strength on the Back Side) The adhesive tape of the present invention preferably has an adhesive strength on the back side of 4 N / 24 mm or less, more preferably 3 N / 24 mm or less, even more preferably 2 N / 24 mm or less, and even more preferably 1.5 N / 24 mm or less. When the adhesive strength on the back side is equal to or less than the above upper limit, problems such as paper peeling and layer cracking can be easily prevented, for example, when unrolling a roll of adhesive tape. The adhesive strength on the back side is not particularly limited, but in practice it is, for example, 0.1 N / 24 mm or more, preferably 0.3 N / 24 mm or more, and more preferably 0.5 N / 24 mm or more. The adhesive strength on the back side can be measured by attaching the adhesive tape to the surface of the paper substrate on which the release layer is provided, leaving it to stand for a certain period of time, and then peeling the adhesive tape at a peeling speed of 30 m / min. The detailed procedure is as described in the Examples.

[0049] (Product Recycle Rate, Pulp Recovery Rate) The pressure-sensitive adhesive tape of the present invention preferably has a product recycle rate of 40% or more, more preferably 45% or more, and even more preferably 50% or more. The pulp recovery rate is preferably 65% ​​or more, more preferably 67% or more, and even more preferably 70% or more. When the product recycle rate and pulp recovery rate are equal to or greater than the above-mentioned lower limits, the recyclability of the pressure-sensitive adhesive tape can be said to be excellent. The higher the product recycle rate, the better, provided that it is 100% or less. In practical terms, it is, for example, 80% or less, preferably 70% or less, and more preferably 65% ​​or less. The pulp recovery rate, too, is preferably 100% or less, and in practical terms, it is, for example, 90% or less, preferably 85% or less, and more preferably 80% or less. Both the product recycle rate and the pulp recovery rate can be calculated by a disintegration test, the detailed procedure of which is as described in the Examples.

[0050] (Biobased content) In the pressure-sensitive adhesive tape of the present invention, the biobased content of the laminate of the paper substrate and the release layer is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. When the biobased content is equal to or greater than the above-mentioned lower limit, the recyclability of the pressure-sensitive adhesive tape is likely to be improved. The biobased content is a value measured in accordance with ASTM D6866 and can be estimated from the content of the carbon isotope with mass number 14. The biobased content of the laminate of the paper substrate and the release layer can usually be determined by measuring the biobased content of the laminate consisting of the paper substrate and the release layer. However, if there is another layer between them, the biobased content of the laminate including that layer can also be measured.

[0051] (Uses) The pressure-sensitive adhesive tape of the present invention is not particularly limited, but is preferably used for sealing the inside of packaging materials, more preferably for sealing the inside of cardboard. As described above, the pressure-sensitive adhesive tape of the present invention does not cause any problems when unfolded from a roll that has been stored, for example, and therefore has excellent handleability when used for sealing the inside of packaging materials, and can improve the efficiency of the sealing work. Furthermore, the pressure-sensitive adhesive tape of the present invention has excellent recyclability, so that the packaging materials can be recycled with the pressure-sensitive adhesive tape attached to them, and the step of peeling off the pressure-sensitive adhesive tape can be omitted when recycling the packaging materials.

[0052] [Structure, Recycling Method] The present invention also provides a structure comprising the above-described pressure-sensitive adhesive tape and packaging material, and a recycling method thereof. The structure of the present invention preferably comprises the above-described pressure-sensitive adhesive tape and paper packaging material, and more preferably comprises the above-described pressure-sensitive adhesive tape and cardboard. Furthermore, since the above-described pressure-sensitive adhesive tape has excellent recyclability, the structure of the present invention can be recycled without separating the pressure-sensitive adhesive tape and the packaging material. That is, in the present invention, both the pressure-sensitive adhesive tape and the packaging material can be recycled with the adhesive tape attached to the packaging material, without peeling the adhesive tape from the packaging material. Recycling can be carried out in the same manner as conventional waste paper recycling, and can be carried out by, for example, macerating the packaging material in a pulper or other such disintegrator. In this case, in the present invention, the packaging material and the adhesive tape are not separated, and the packaging material with the adhesive tape attached can be fed into the disintegrator.

[0053] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0054] [Various Physical Properties] Various physical properties were measured and evaluated by the following methods.

[0055] (Paper Sizing Degree) Measured in accordance with JIS P 8122:2004.

[0056] (Back Adhesion Strength) An adhesive tape (Adhesive Tape A) obtained in each Example and Comparative Example and adjusted to a dimension of 25 mm x 200 mm was prepared. Adhesive Tape A was fixed to a SUS plate via an adhesive layer, and another adhesive tape B was bonded to the release layer-covered side of the fixed adhesive tape A via an adhesive layer. The adhesive tape B was bonded by similarly preparing a test piece with a width of 25 mm and a length of 300 mm, folding one end 12 mm to form a tab so that the adhesive was in contact with the adhesive, and then attaching the other end to one end of the tape to be tested. The back side was then pressed against the other end by two longitudinal strokes using an automatic or manual roller. The tape was then left to stand for two days at 40°C and 50% RH. After this standing, the adhesive tape B was peeled at a peel angle of 180° and a peel speed of 30 m / min at 23°C and 50% RH, and the peel force measured was measured as the back adhesive strength. For adhesive tape B, "Kraft Tape No. 500" manufactured by Sekisui Chemical Co., Ltd. was used.

[0057] (Layer cracking) When the adhesive strength of the adhesive tape itself was measured, the adhesive tape B was peeled from the adhesive tape A, and the occurrence of layer cracking was evaluated based on the following evaluation criteria. A: The adhesive tape A did not break during the period from the start of peeling the adhesive tape B to the completion of the peeling. B: The adhesive tape A broke during the period from the start of peeling the adhesive tape B to the completion of the peeling.

[0058] (Biobased Degree) The biobased degrees of the substrate and release layer of the pressure-sensitive adhesive tape were measured in accordance with ASTM D 6866. The biobased degree of the release layer is the biobased degree of the laminate of the release agent layer and the filler layer.

[0059] (Residue Rate, Product Recycle Rate, Pulp Recovery Rate) The residue rate, product recycle rate, and pulp recovery rate were measured and calculated by conducting a disintegration test. The disintegration test was carried out as follows. 30 g of the adhesive tape was placed in 2000 mL of water and disintegrated at 25°C and a cumulative propeller rotation speed of 3000 rpm using a standard disintegrator conforming to JIS P8220-1 to form a pulp slurry. The pulp slurry was then subjected to a flat screen treatment.

[0060] The percentage of undisintegrated material in the disintegration test was calculated as [100 × (mass of undisintegrated material) / (mass of pulp slurry treated in disintegration test) (%)], and this was defined as the residue percentage. The flat screen treatment was carried out in accordance with TAPPI T275 using a flat screen equipped with a 0.3 mm wide screen plate, with a water flow rate of 8.6 liters / minute and a treatment time of 20 minutes.

[0061] The product recycling rate was calculated using the following formula: Product recycling rate (%) = 100 - residue rate (%) However, in Examples 9 and 10, since the basis weight of the sealing layer was large, the pulp slurry after the flat screen treatment was filtered with filter paper to take the sealing layer into consideration, and the percentage of the recovered pulp weight [100 × (mass of recovered pulp) / (mass of pulp slurry treated in the disintegration test) (%)] was calculated and used as the product recycling rate.

[0062] The pulp recovery rate was calculated using the following formula: Pulp recovery rate (%) = product recycling rate (%) / pulp content (wt%) × 100

[0063] (Pulp content) The pulp content was calculated by the following formula: Pulp content (wt%) = Basis weight of paper (g / m ２ ) / Basis weight of the entire tape (g / m ２ )

[0064] [Components Used] The components used in each example and comparative example are as follows: (Paper base material) Kraft paper: Clupak-processed and wet strength-processed, basis weight 73 g / m ２ Unbleached kraft paper. The sizing degree was adjusted appropriately by adding a sizing agent.

[0065] (Release agent) Silicone-based release agent ("KNS-3051" manufactured by Shin-Etsu Chemical Co., Ltd.) Long-chain alkyl-based release agent ("Rezem K-256" manufactured by Chukyo Yushi Co., Ltd.)

[0066] (Sealing agents) PVA resin 1: PVA (average degree of polymerization 1700, degree of saponification 99 mol%) was added to water at room temperature with stirring to give a solids concentration of 15%, and the mixture was dispersed for 5 to 10 minutes, then heated and kept at 90 to 95°C for 30 minutes to obtain a sealant. α-starch: Starch ("Coating Starch PN-500" manufactured by Sanwa Starch Industrial Co., Ltd.) was added to water at 90°C to give a solids concentration of 20%, and the mixture was kept warm for 30 minutes to gelatinize it. Polyethylene resin ("Suntec LD" manufactured by Asahi Kasei Corporation) Urethane ("Hydran HW-350" manufactured by DIC Corporation) Latex ("Nipol LX110" manufactured by Nippon Zeon Co., Ltd.) Of the sealants, for PVA resin 1, a diluted solution was prepared according to the formulation shown in Table 1, and the prepared solution was used to form the sealant layer.

[0067]

[0068] (Adhesive Layer) The adhesive composition for forming the adhesive layer contained the following components. The components below were mixed in the formulations shown in Table 2 to prepare adhesive composition 1 for synthetic rubber-based adhesives and adhesive composition 2 for natural rubber-based adhesives. The blended adhesive components were placed in a kneading-extrudability tester (manufactured by Toyo Seiki Seisaku-sho, Ltd., trade name "Labo Plastomill (registered trademark)"), melt-kneaded, extrusion-molded, and coated on kraft paper to produce adhesive tapes of Examples and Comparative Examples.

[0069]

[0070] [Example 1] Basis weight 70 g / m ２ On one side of the paper base material made of kraft paper with a basis weight of 2 g / m ２ A long-chain alkyl-based release agent was applied onto the filler layer so that the basis weight after drying was 0.5 g / m. ２ Next, PSA composition 2 was applied to the surface of the substrate opposite to the surface on which the release agent layer and the filler layer were formed, and dried to form a release agent layer having a basis weight of 26 g / m. ２ The structure of the adhesive tape and the measurement results are shown in Table 3.

[0071] [Examples 2 to 7, 9, 10, Comparative Examples 1 to 6, Reference Example] Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the types of paper substrate, filler layer, release agent layer, and pressure-sensitive adhesive layer, as well as their basis weights, were changed as shown in Tables 3 and 4. The configurations of the pressure-sensitive adhesive tapes and the measurement results are shown in Tables 3 and 4.

[0072] [Example 8] Basis weight 70 g / m ２ A mixed solution of α-starch aqueous solution and a long-chain alkyl-based release agent was applied to one side of a paper substrate made of kraft paper of 2.5 g / m2 ２ The mixture was obtained by mixing an aqueous α-starch solution and a long-chain alkyl-based release agent in a ratio of α-starch to long-chain alkyl-based release agent of 100:25. Next, PSA composition 1 was applied to the surface of the substrate opposite to the surface on which the release layer was formed, and a release layer having a basis weight of 26 g / m was formed. ２ The structure of the adhesive tape and the measurement results are shown in Table 3.

[0073]

[0074]

[0075] As is clear from the above examples, the pressure-sensitive adhesive tapes satisfying the requirements of the present invention exhibited excellent recyclability and low adhesive backing strength, at least compared to the pressure-sensitive adhesive tapes produced in the Reference Examples, which used polyethylene resin as a sealant. In contrast, the pressure-sensitive adhesive tape produced in Comparative Example 1 had a paper substrate sizing degree of 0, which allowed the sealant to penetrate into the paper substrate, resulting in the release agent also penetrating into the paper substrate and increasing the adhesive backing strength. This resulted in layer cracking. Furthermore, the pressure-sensitive adhesive tapes produced in Comparative Examples 2 to 6 had a paper substrate sizing degree of 0, which allowed the sealant to penetrate into the paper substrate, resulting in insufficient pulp separation in the disintegration test, resulting in reduced recyclability. When the paper substrates of Example 1 and Comparative Example 1 were dyed with iodine, the paper substrate of Example 1 was only slightly stained on the release layer side, as shown in the image in Figure 3. On the other hand, the paper substrate of Comparative Example 1 was dyed over its entire surface, as shown in the image in Figure 4, and it was observed that the starch sealant had penetrated into the paper substrate.

Claims

1. An adhesive tape comprising a paper base material, an adhesive layer provided on one side of the paper base material, and a release layer provided on the other side of the paper base material, wherein the release layer contains a water-based polymer, and the sizing degree of the paper base material according to JIS P 8122:2004 is 15 seconds or more.

2. The pressure-sensitive adhesive tape according to claim 1, wherein the release layer comprises a release agent layer containing a release agent and a filler layer containing a filler, or comprises a release layer containing both a filler and a release agent, and the filler is a water-based polymer.

3. The basis weight of the filler layer is 20 g / m ２ The adhesive tape according to claim 2, wherein:

4. The adhesive tape according to claim 2, wherein the release agent is a silicone-based release agent or a long-chain alkyl-based release agent.

5. The adhesive tape according to claim 1 or 2, wherein the water-based polymer is starch or PVA resin.

6. The adhesive tape according to claim 1 or 2, wherein the adhesive layer comprises a rubber-based adhesive.

7. The adhesive tape according to claim 6, wherein the rubber-based adhesive is natural rubber.

8. The adhesive tape according to claim 1 or 2, wherein the laminate of the paper substrate and the release layer has a bio-based content of 85% or more.

9. A structure comprising the adhesive tape according to claim 1 or 2 and a packaging material.

10. A method for recycling the adhesive tape according to claim 1 or 2 while it is attached to the packaging material.

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