Release paper base, release paper, and adhesive tape

Abstract

To provide a base sheet for release paper that is less likely to cause a decrease in the transparent clarity of an adhesive tape and achieves a reduction in environmental load, and to provide release paper and an adhesive tape.SOLUTION: A base sheet for release paper 10 includes a substrate 11 and a sealing layer 12 on at least part of a surface of the substrate 11. The substrate 11 includes pulp with a hardwood pulp content of more than 50 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to release paper base paper, release paper, and adhesive tape. [Background technology]

[0002] Adhesive tape is used for labels attached to transparent containers made of glass, plastic, and other materials. In these applications, transparency of the label is desirable so that the substrate or contents of the container beneath the label can be seen even after the label has been applied.

[0003] Release paper is a component that protects the adhesive layer of adhesive tape and prevents a decrease in adhesiveness. Because the release paper is positioned adjacent to the adhesive layer until it is attached to the substrate, the adhesive layer is prone to picking up irregularities on the surface of the release paper. Therefore, if there are irregularities on the release surface of the release paper, it can cause a decrease in the transparency of the adhesive tape.

[0004] Therefore, in applications where transparency of adhesive tape is required, it is important that the release surface of the release paper is smooth. For example, Patent Document 1 discloses a release sheet having an adhesive layer made of a silicone-based adhesive laminated on it, which peels off from the adhesive layer when peeled off, comprising a paper substrate, a pigment coating layer formed on one side of the paper substrate, a first polyolefin layer formed on the side of the pigment coating layer opposite to the paper substrate side, and a second polyolefin layer formed on the other side of the paper substrate, wherein the surface of the first polyolefin layer opposite to the pigment coating layer side is highly smoothed, and the adhesive layer is directly laminated to this surface. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-230611 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, it has been found that the release sheet described in Patent Document 1 has a problem in that it makes it difficult to clearly see text, scenery, etc., through the adhesive tape, and the clarity of the adhesive tape's transparency tends to decrease.

[0007] Furthermore, in recent years, there has been a growing demand for release paper that does not use a polyolefin layer, as it reduces plastic waste (so-called "plastic-free") and is recyclable, from the perspective of reducing environmental impact.

[0008] The present invention has been made in view of the above circumstances, and its main objective is to provide a release paper base, release paper, and adhesive tape that do not easily reduce the transparency clarity of the adhesive tape and reduce the environmental impact. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above-mentioned objectives, the inventors have found that a release paper base comprises a base material and a sealing layer laminated on at least a portion of the surface of the base material, wherein the hardwood pulp content in the pulp of the base material exceeds 50% by mass, and have thus completed the present invention.

[0010] In other words, the present invention is as follows.

[0011] (1) The release paper base comprises a base material and a sealing layer laminated on at least a portion of the surface of the base material, wherein the hardwood pulp content in the pulp of the base material exceeds 50% by mass. (2) The release paper base paper described in (1) is wherein the pulp used in the base material has a beaten degree of 30°SR or higher. (3) The sealing layer is a release paper base according to (1) or (2), containing a binder resin and an inorganic pigment. (4) The stop layer includes a first stop layer containing a polyvinyl alcohol-based resin and a second stop layer containing a binder resin and an inorganic pigment, and is the release paper base material according to (1) or (2). (5) The binder resin contains a styrene-based resin, and is the release paper base material according to (3) or (4). (6) The release paper includes the release paper base material according to any one of (1) to (5) and a release agent layer laminated on at least a part of the surface of the stop layer of the release paper base material. (7) The adhesive tape includes a transparent resin substrate, an adhesive layer laminated on at least a part of the surface of the transparent resin substrate, and the release paper according to (6) laminated on the surface of the adhesive layer on the side opposite to the transparent resin substrate. [Effect of the Invention]

[0012] According to the present invention, it is possible to provide a release paper base material, a release paper, and an adhesive tape that are less likely to reduce the transmission clarity of the adhesive tape and reduce the environmental load. [Brief Description of the Drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of the release paper base material according to the present embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of the release paper according to the present embodiment.[[ID=3I]] [Figure 3] FIG. 3 is a schematic cross-sectional view of the adhesive tape according to the present embodiment. [Embodiments for Carrying Out the Invention]

[0014] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an exemplification for explaining the present invention and is not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of its gist.

[0015] Furthermore, identical elements in the drawings will be given the same reference numeral, and redundant explanations will be omitted. Unless otherwise specified, positional relationships such as top, bottom, left, and right will be based on those shown in the drawings. Moreover, the dimensional ratios in the drawings are not limited to those shown.

[0016] Furthermore, unless otherwise specified in this specification, "(meth)acrylic" includes methacrylic and acrylic. For example, (meth)acrylic means methacrylic, acrylic, or both.

[0017] <Release paper base>

[0018] The release paper base 10 according to this embodiment comprises a base material 11 and a sealing layer 12 laminated on at least a portion of the surface of the base material 11, wherein the hardwood pulp content in the pulp of the base material 11 exceeds 50% by mass.

[0019] (base material)

[0020] The hardwood pulp content in the pulp of the base material 11 exceeds 50% by mass. A hardwood pulp content exceeding 50% by mass makes it difficult for the coating liquid for the sealing layer (described later) to penetrate, allowing for the formation of a dense sealing layer 12. Furthermore, an increase in hardwood pulp content improves the form of the base material 11, thereby improving the surface smoothness of the release paper base 10. The hardwood pulp content is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably exceeding 80% by mass, and most preferably 100% by mass. From the viewpoint of reducing environmental impact, it is preferable that the base material 11 does not contain polyolefins. If the base material 11 is a polyolefin-free base material that does not contain polyolefins, it can adequately meet the requirements for "plastic-free" and recyclability mentioned above.

[0021] The hardwood pulp used in the base material 11 is not particularly limited, and virgin pulp and recycled paper pulp can be used. As virgin pulp, wood pulp is preferred. Examples of hardwood pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite pulp, as well as mechanical pulps such as stone ground pulp (SGP), pressurized stone ground pulp (TGP), chemigland pulp (CGP), crushed wood pulp (GP), and thermomechanical pulp (TMP). Among these, from the viewpoint of surface smoothness, chemical pulps such as bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite pulp are preferred, and bleached hardwood kraft pulp (LBKP) is more preferred.

[0022] Hardwood pulp is preferable to be southern hardwood pulp because it has a good form and yields a smoother release paper base 10. Southern hardwood pulp refers to pulp manufactured from wood containing southern hardwoods such as eucalyptus, lauan, and mangrove. Pulp is classified into chemical pulp such as sulfite pulp (SP) and kraft pulp (KP) depending on the manufacturing method, and mechanical pulp such as thermomechanical pulp and ground pulp, but in this embodiment, hardwood pulp manufactured by any of these methods may be used.

[0023] The pulp used in the base material 11 may also include pulps other than hardwood pulp. For example, various known pulps can be used, such as chemical pulps like bleached softwood kraft pulp (NBKP), unbleached softwood kraft pulp (NUKP), semi-bleached softwood kraft pulp (NSBKP), and softwood sulfite pulp, or mechanical pulps like stone ground pulp (SGP), pressurized stone ground pulp (TGP), chemigland pulp (CGP), crushed wood pulp (GP), and thermomechanical pulp (TMP). In addition, non-wood pulps such as cotton pulp, hemp, bagasse, kenaf, esparto, paper mulberry, mitsumata, and ganpi can be used as appropriate.

[0024] Furthermore, the content ratio of coniferous pulp to hardwood pulp (pulp N / L ratio, mass ratio) is preferably 50 / 50 to 0 / 100 (i.e., 1 or less), more preferably 40 / 60 to 0 / 100, even more preferably 30 / 70 to 0 / 100, and even more preferably 20 / 80 to 0 / 100.

[0025] The pulp content of the base material 11 is not particularly limited, but is preferably 60 to 100% by mass. This pulp content is the proportion (mass ratio) of the total amount of pulp in the base material 11. The lower limit of this content is more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The upper limit of this content is more preferably 98% by mass or less, and even more preferably 97% by mass or less.

[0026] The base material 11 may further contain various additives. Examples of additives include known fillers, oxidized starch, sizing agents such as rosin-based sizing agents and AKD (alkyl ketene dimer)-based sizing agents, wetting enhancers, resin materials such as urethane resin, acrylic resin, styrene-acrylic resin, and polyvinyl alcohol, colorants such as dyes and pigments, fixing agents such as aluminum sulfate, cationized starch, and cationic polymer electrolytes, papermaking aids, and flocculants. These may be used individually or in combination of two or more.

[0027] The thickness of the base material 11 is not particularly limited, but is preferably 40 μm or more and 300 μm or less. The upper limit of this thickness is more preferably 100 μm or less, even more preferably 60 μm or less, and even more preferably 50 μm or less. The lower limit of this thickness is more preferably 45 μm or more. By setting the thickness of the base material 11 to be above the lower limit, the occurrence of wrinkles during the manufacture of the release paper 20 can be further suppressed, and the suitability for die-cutting label processing during the manufacture of adhesive labels can be further improved. Furthermore, by setting the thickness of the base material 11 to be below the upper limit, excessive rigidity can be further suppressed, and a decrease in handling ease can be further suppressed. This thickness can be measured in accordance with JIS P 8118:2014.

[0028] The basis weight of the base material 11 is not particularly limited, but is between 35 and 120 g / m². 2 Preferably, it is 40-100 g / m² 2 It is more preferable that the amount be 50-70 g / m². 2 It is even more preferable that this be the case.

[0029] Hardwood pulp may be beaten beforehand and then mixed with other beaten pulps (for example, other hardwood pulps). Alternatively, hardwood pulp may be mixed with other pulps before beating, and then these mixtures may be beaten.

[0030] The degree of beatenness of the base paper of the substrate 11 is not particularly limited, but is preferably 30°SR or higher, and more preferably 40°SR or higher. Furthermore, the upper limit of the degree of beatenness is not particularly limited, but is generally preferably 90°SR or lower, more preferably 70°SR or lower, and even more preferably 65°SR or lower. This degree of beatenness can be measured using a Schöpper-Rigler type beatenness tester in accordance with JIS P 8121.

[0031] The manufacturing method of the base material 11, the papermaking method, and the type of paper machine are not particularly limited. For example, known manufacturing (papermaking) methods and paper machines such as long-wire paper machines, cylinder paper machines, short-wire paper machines, gap formers, hybrid formers (on-top formers), and twin-wire paper machines can be selected. Furthermore, the pH during papermaking is not particularly limited and may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking). After papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper layer. In addition, the base material 11 may be a single layer or may consist of two or more layers.

[0032] (Sealing layer)

[0033] The sealing layer 12 effectively suppresses the penetration of the release agent into the substrate 11 and ensures a smooth surface on the release agent layer 21. The sealing layer 12 preferably contains a binder resin. Furthermore, from the viewpoint of reducing environmental impact, the sealing layer 12 preferably does not contain polyolefins. If the sealing layer 12 is a polyolefin-free sealing layer, it can adequately meet the aforementioned requirements for "plastic-free" and recyclability.

[0034] The binder resin is not particularly limited, and any resin usable in the coated paper field, etc., can be used as appropriate. Specific examples of binder resins include polyvinyl alcohol-based resins such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymerized polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, and other modified polyvinyl alcohols; methyl methacrylate-butadiene copolymer, (meth)acrylic acid, and monomer components copolymerizable with (meth)acrylic acid (excluding olefins). Examples include acrylic resins; cellulose derivatives such as hydroxyethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, and acetylcellulose; starches such as oxidized starch, etherified starch, and esterified starch; styrene resins such as styrene-maleic anhydride copolymer, styrene-butadiene copolymer, and styrene-acrylic copolymer; casein, gum arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrene and their copolymers, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, coumarone resins, dextrin, ethylene-vinyl chloride copolymer, and ethylene-vinyl acetate copolymer. Among these, it is preferable that at least one is selected from the group consisting of polyvinyl alcohol resins, starches, and styrene resins. More preferably, it is at least one selected from the group consisting of polyvinyl alcohol (fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol), oxidized starch, and styrene copolymers (styrene-maleic anhydride copolymer, styrene-butadiene copolymer, styrene-acrylic copolymer, etc.). These may be used individually or in combination of two or more types.

[0035] The sealing layer 12 preferably contains an inorganic pigment, and more preferably contains the binder resin and the inorganic pigment described above. Examples of inorganic pigments include light calcium carbonate, heavy calcium carbonate, kaolin, calcined kaolin, engineered kaolin, clay, delaminated clay, talc, silica, colloidal silica, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, aluminum hydroxide, alumina, magnesium carbonate, magnesium hydroxide, kaolinite, antigorite, smectite, vermiculite, mica, and the like. Among these, it is preferable that at least one is selected from the group consisting of kaolin, calcined kaolin, and engineered kaolin, with kaolin being more preferable. These may be used individually or in combination of two or more.

[0036] The inorganic pigment content is not particularly limited, but from the viewpoint of smoothness and binding properties, it is preferably 1 to 1400 parts by mass, more preferably 200 to 600 parts by mass, even more preferably 250 to 500 parts by mass, and even more preferably 300 to 400 parts by mass per 125 parts by mass of binder resin by dry weight.

[0037] The sealing layer 12 may contain various commonly used auxiliary agents as needed, such as sizing agents, water-resistant agents, water-repellent agents, dyes, surfactants, dispersants, thickeners, water-retaining agents, defoaming agents, water-resistant agents, dyes, fluorescent dyes, and crosslinking agents.

[0038] The amount of sealing layer 12 applied is 0.2 to 20 g / m² by dry weight. 2 It is preferable to do so. The lower limit of this coating amount is 0.5 g / m². 2 It is more preferable that the value be greater than or equal to 0.7 g / m 2 It is even more preferable that the amount is greater than or equal to 10 g / m². Furthermore, the upper limit of this application amount is 10 g / m². 2 More preferably, the following is true: 8 g / m 2It is even more preferable that the following conditions are met: By setting the amount of sealing layer 12 applied to be above the lower limit, the penetration of the release agent into the substrate 11 can be suppressed more effectively, and the smoothness of the surface of the release agent layer 21 can be further improved. On the other hand, by setting the amount of sealing layer 12 applied to be below the upper limit, the drying load during coating can be further reduced, which is more preferable in terms of operation and cost. When the sealing layer 12 consists of two or more layers, it is preferable that the application amount of at least one layer of each sealing layer is within the above range, and it is more preferable that the application amount of all layers of the sealing layer 12 is within the above range.

[0039] The sealing layer 12 may be a single layer or a multi-layered layer of two or more. If the sealing layer 12 consists of multiple layers, these layers may be identical or different, and there are no particular limitations on the combination of these layers. Among these, it is preferable that the sealing layer 12 consists of two or more layers. Having multiple layers in the sealing layer 12 makes it easier to achieve both the effect of effectively suppressing the penetration of the release agent into the substrate 11 and the effect of obtaining a smooth surface for the release agent layer 21.

[0040] Although not shown in the figures, a preferred example of a sealing layer 12 consisting of two or more layers is one that includes a first sealing layer containing a polyvinyl alcohol-based resin and a second sealing layer containing a binder resin and an inorganic pigment. The first and second sealing layers have different compositions. Preferably, the first sealing layer does not contain an inorganic pigment. Preferably, the first sealing layer is positioned on the substrate 11 side and the second sealing layer is positioned on the release agent layer 21 side. Therefore, when the sealing layer 12 consists only of the first and second sealing layers, it is preferable that the first sealing layer is in contact with the substrate 11 and the second sealing layer is in contact with the release agent layer 21. In this case, it is preferable that neither the first nor the second sealing layer contains polyolefin.

[0041] Examples of polyvinyl alcohol-based resins for the first sealing layer include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymer polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, and other modified polyvinyl alcohols. Among these, polyvinyl alcohol (fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol) is preferred.

[0042] The binder resin and inorganic pigment of the second sealing layer can be those described above, and among them, the binder resin is preferably at least one selected from the group consisting of polyvinyl alcohol-based resins, starches, and styrene-based resins, and more preferably at least one selected from the group consisting of polyvinyl alcohol (fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol), oxidized starch, and styrene-butadiene copolymer. Furthermore, in the case of the second sealing layer, it is even more preferable that the binder resin contains two or more of these. In particular, it is even more preferable that it contains polyvinyl alcohol and styrene-based resin.

[0043] The release paper base paper 10 can be manufactured by coating a coating liquid for forming a sealing layer 12 onto a substrate 11 and then drying it. The method for coating the sealing layer 12 is not particularly limited and can be done using known coating equipment and coating systems. For example, coating equipment can include blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters, gate roll coaters, size press coaters, shim sizers, etc. Coating systems can include water-based coating using solvents such as water, and solvent-based coating using solvents such as organic solvents.

[0044] The method for drying the sealing layer 12 is not particularly limited, and conventional methods such as steam heaters, gas heaters, infrared heaters, electric heaters, hot air heaters, microwaves, and cylinder dryers can be used.

[0045] <Release paper>

[0046] The release paper 20 according to this embodiment includes the release paper base paper 10 described above and a release agent layer 21 laminated on at least a portion of the surface of the sealing layer 12 of the release paper base paper 10. From an environmental standpoint, it is preferable that the release paper 20 does not have a layer containing polyolefin (polyolefin layer). This polyolefin layer is a layer that contains a total of 50% by mass or more of polyolefin in the layer. This makes it possible to meet the requirements for "plastic reduction" and recyclability described above.

[0047] Although not shown in the figures, the release paper 20 may be a double-sided release paper by providing a sealing layer 12 and a release agent layer 21 on both sides of the base material 11. Furthermore, the release paper 20 may have a curl suppression layer or the like on the side of the base material 11 opposite to the side where the sealing layer 12 and the release agent layer 21 are provided. The curl suppression layer is not particularly limited and any known layer can be used.

[0048] (Release agent layer)

[0049] The release agent contained in the release agent layer 21 is not particularly limited, and examples include silicone resins, fluororesins, alkyd resins, long-chain alkyl resins, and various waxes. Among these, a silicone resin is preferred as the release agent from the viewpoint of excellent release properties.

[0050] Examples of silicone resins include homopolymers or copolymers such as trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, diphenyldichlorosilane, phenyltrichlorosilane, methylvinyldichlorosilane, etc. These may be used alone or in combination of two or more.

[0051] The silicone resin can be used in any form of solvent type, solventless type, or emulsion type, but emulsion type and solventless type are preferred.

[0052] The thickness of the release agent layer 21 is preferably 0.01 to 10 μm. The lower limit of this thickness is more preferably 0.1 μm or more. Also, the upper limit of this thickness is more preferably 5 μm or less.

[0053] The release agent layer 21 can be formed by applying and heating a coating liquid containing the above-mentioned release agent on a part of the surface of the sizing layer 12 of the release paper base paper 10 to cure it. The coating method is not particularly limited, and for example, a method of appropriately selecting various coating apparatuses such as a blade coater, an air knife coater, a rod blade coater, a bar blade coater, a gravure coater, a bar coater, a multi-stage roll coater, etc. and applying can be adopted.

[0054] And the coating amount of the release agent is preferably 0.4 to 3.0 g / m 2 in terms of dry weight. The lower limit of this coating amount is more preferably 0.6 g / m 2 or more, and even more preferably 0.8 g / m 2 or more. Also, the upper limit of this coating amount is more preferably 2.0 g / m 2 or less, and even more preferably 1.8 g / m 2 or less. By controlling the coating amount within such a range, a more suitable release force for the release paper 20 can be obtained.

[0055] The surface roughness of the release liner 20 on the release agent layer 21 side is preferably 0.70 μm or less, more preferably 0.65 μm or less, even more preferably 0.5 μm or less, and even more preferably less than 0.5 μm, in accordance with JIS B 0601:2013. The lower limit of the arithmetic mean roughness (Ra) of the release agent layer 21 is preferable as small as possible, but is usually 0.10 μm or more.

[0056] <Adhesive tape>

[0057] The adhesive tape 30 according to this embodiment includes a transparent resin substrate 31, an adhesive layer 32 laminated on the surface of the transparent resin substrate 31, and the release paper 20 described above laminated on the surface of the adhesive layer 32 opposite to the transparent resin substrate 31. Note that the adhesive layer 32 only needs to be formed on at least a part of the surface of the transparent resin substrate 31. That is, the adhesive tape 30 is laminated in the following order: substrate 11, sealing layer 12, release layer 21, adhesive layer 32, and transparent resin substrate 31.

[0058] (Transparent resin base material)

[0059] The transparent resin substrate 31 has a transmittance of 80% or more in the visible light region, preferably 90% or more (upper limit 100%). Here, the transmittance of the transparent resin substrate 31 can be measured according to JIS K 7361-1:1997 (Plastics - Test method for total light transmittance of transparent materials). The material constituting the transparent resin substrate 31 is not particularly limited and can include, for example, polyester films such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate; polyolefin films such as polyethylene (PE) and polypropylene (PP); cellophane, diacetylcellulose film, triacetylcellulose film, acetylcellulose butyrate film, polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film, polystyrene film, polycarbonate film, polymethylpentene film, polysulfone film, fluororesin film, acrylic resin film, norbornene-based resin film, cyclic olefin film, etc. Among these, in terms of transparency, the transparent resin substrate 31 is preferably polyester or polyolefin, more preferably polyethylene terephthalate (PET), polyethylene (PE), or polypropylene (PP), and even more preferably polyethylene terephthalate (PET).

[0060] The transparent resin substrate 31 may optionally contain stabilizers, lubricants, softeners, UV absorbers, antioxidants, antistatic agents, twist-resistant agents, etc. Furthermore, the transparent resin substrate 31 may have an easy-adhesion layer to improve adhesion with other functional layers such as printed layers.

[0061] The thickness of the transparent resin substrate 31 is not particularly limited, but is preferably 5 to 250 μm. The lower limit of this thickness is more preferably 20 μm or more, even more preferably 30 μm or more, and even more preferably 40 μm or more. The upper limit of this thickness is more preferably 200 μm or less, even more preferably 150 μm or less, and even more preferably 70 μm or less.

[0062] (Adhesive layer)

[0063] The adhesive contained in the adhesive layer 32 is not particularly limited, and examples include rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, epoxy-based adhesives, polyester-based adhesives, urethane-based adhesives, polyolefin-based adhesives, vinyl ether-based adhesives, etc. Among these, acrylic-based adhesives and urethane-based adhesives are preferred from the viewpoint of excellent transparency and good durability, and acrylic-based adhesives are more preferred.

[0064] As an example of an adhesive, while not particularly limited, an acrylic adhesive is formed by using an acrylic polymer constituting an acrylic adhesive, with an adhesive (meth)acrylate alkyl ester as the main monomer component, and optionally using a monomer copolymerizable to an agglomerating (meth)acrylate alkyl ester (copolymerizable monomer) and a copolymerizable monomer having a crosslinking functional group.

[0065] Examples of tacky alkyl (meth)acrylates include butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. These may be used individually or in combination of two or more. Examples of cohesive copolymerizable monomers include methyl (meth)acrylate, vinyl acetate, styrene, and acrylonitrile. These may be used individually or in combination of two or more.

[0066] The adhesive preferably contains a crosslinking agent in addition to an acrylic polymer. Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents. The amount of crosslinking agent added is preferably 0.001 to 10 parts by mass, and more preferably 0.005 to 2.0 parts by mass, per 100 parts by mass of the acrylic polymer.

[0067] Furthermore, solvent-free adhesives such as solvent-type adhesives, emulsion-type adhesives, and hot-melt-type adhesives, as well as energy-ray-curing adhesives that harden and become re-peelable upon irradiation with energy rays, may also be used. In addition, crosslinking agents, tackifiers, softeners, antioxidants, fillers, colorants such as dyes or pigments, diluents, etc., may be added to the adhesive as needed.

[0068] In this embodiment, the adhesive tape 30 can also be expected to have the effect of suppressing the transparency clarity of the adhesive tape 30 when an adhesive containing a tackifier is used as the adhesive layer 32. Therefore, it is preferable that the adhesive layer 32 is formed from an adhesive composition containing an adhesive and a tackifier. For example, in conventional adhesive tapes, if a tackifier is incorporated into the adhesive layer, the transparency clarity may decrease significantly. However, according to this embodiment, even when a tackifier is incorporated, the decrease in transparency clarity can be effectively suppressed. Specifically, it is preferable that the adhesive layer 32 is formed from an adhesive composition containing an acrylic adhesive and a tackifier. When the adhesive layer 32 contains a tackifier, the blending ratio is usually 5 to 100 parts by mass, preferably 10 to 70 parts by mass, per 100 parts by mass of adhesive.

[0069] In this embodiment, the adhesive tape 30 preferably has a storage modulus at 23°C of the adhesive constituting the adhesive layer 32 of 0.01 MPa or more, more preferably 0.03 MPa or more, and even more preferably 0.05 MPa or more. Furthermore, the storage modulus at 23°C is preferably 1.00 MPa or less, more preferably 0.50 MPa or less, even more preferably 0.20 MPa or less, and even more preferably 0.10 MPa or less. This storage modulus can be measured by the torsional shear method at a measurement frequency of 1 Hz in accordance with JIS K 7244-6.

[0070] The adhesive layer 32 can be formed by applying and heating a coating solution containing the adhesive described above. The coating method is not particularly limited, and various coating devices such as blade coaters, air knife coaters, rod blade coaters, bar blade coaters, gravure coaters, bar coaters, and multi-stage roll coaters can be appropriately selected and used for coating.

[0071] The solid content concentration of the coating liquid (adhesive composition) containing the adhesive is typically 10 to 60% by mass. Generally, when the solid content concentration of the coating liquid is high, the surface condition of the adhesive layer 32 after coating deteriorates, and the transparency clarity of the adhesive layer 32 itself tends to decrease. However, since the adhesive tape 30 according to this embodiment uses the release paper 20 described above, even if the solid content concentration of the adhesive composition is high, the effect of suppressing the transparency clarity of the adhesive tape 30 can be expected. Specifically, the solid content concentration of the coating liquid for the adhesive layer 32 may be 40% by mass or higher.

[0072] The thickness of the adhesive layer 32 is not particularly limited, but is preferably 5 to 200 μm. The lower limit of this thickness is more preferably 10 μm or more. The upper limit of this thickness is more preferably 100 μm or less, even more preferably 50 μm or less, and even more preferably 30 μm or less.

[0073] Furthermore, a print-receiving layer, a printable layer, or the like may be provided on the surface of the adhesive tape 30 opposite to the adhesive layer 32 (the outermost surface).

[0074] Furthermore, to protect toner, ink, etc., the adhesive tape 30 may have a coating layer applied to the surface of the adhesive tape 30 or the print receiving layer (the outermost surface). A conventionally known laminate film may also be provided.

[0075] <Transparency and clarity of adhesive sheets>

[0076] The transmission clarity of the adhesive sheet is preferably 40% or higher, more preferably 45% or higher, and even more preferably 48% or higher, or 50% or higher. The higher the transmission clarity, the clearer the adherend can be seen through the adhesive sheet. Furthermore, even when the adhesive sheet is attached to a transparent adherend such as glass or a PET bottle, visibility through the adhesive sheet and the adherend is further enhanced. There is no particular upper limit to the transmission clarity of the adhesive sheet, but it is usually 100% or less, more preferably 80% or less, and even more preferably 60% or less. The transmission clarity of the adhesive sheet refers to the value obtained when an evaluation value of the image clarity is acquired for the adhesive sheet by forming a slit that transmits irradiated light using an optical comb with a width of 0.25 mm (slit width 0.25 mm) in accordance with JIS K 7374:2007, as described later in the examples.

[0077] As described above, the release paper base 10 according to this embodiment does not easily reduce the transparency clarity of the adhesive tape 30, and can reduce the environmental burden. For this reason, the release paper base 10 can be suitably used as an environmentally friendly release paper 20, and the adhesive tape 30 using the release paper 20 can be suitably used as various labels for overlamination, as well as for management purposes (e.g., labels for inventory management, process management, logistics management, etc.), stationery and office supplies (concealing labels, fancy labels, etc.), sales promotion and advertising purposes (e.g., labels for POP displays), and various other applications such as toy equipment. [Examples]

[0078] The present invention will be described in more detail by the following examples and comparative examples, but the present invention is not limited in any way by the following examples.

[0079] <Example 1>

[0080] 1. Preparation of the base material

[0081] Bleached kraft pulp from southern hardwoods of the eucalyptus genus (labeled "LBKP2" in Table 1) was beaten in water using the Schöpper-Rigler method to achieve a beat degree of 42°SR. This was then dispersed in water to obtain a pulp dispersion with a concentration of approximately 1.0% by mass. To 100 parts by mass of pulp in this dispersion, 0.4 parts by mass of rosin sizing agent and 0.2 parts by mass of aluminum sulfate as a fixative were added to obtain a pulp slurry. Next, this pulp slurry was used to make paper using a multi-cylinder paper machine with a long screen, resulting in a basis weight of 59 g / m². 2 A base material 11 was obtained. The thickness of the base material 11 was 49 μm. This base material 11 does not contain polyolefin.

[0082] 2. Preparation of release paper base

[0083] (Preparation of coating liquid for sealing layer) Coating solution 1 for sealing layer and coating solution 2 for sealing layer were prepared by stirring and dispersing a mixture consisting of the following components.

[0084] <Sealing coating liquid 1> • 100 parts by mass of polyvinyl alcohol (saponification degree 98 mol%, molecular weight 75,000) ·550 parts by mass of water

[0085] <Sealing coating liquid 2> ·80 parts by mass of oxidized starch • Polyvinyl alcohol (saponification degree 98 mol%, molecular weight 75,000) 5 parts by mass • 40 parts by mass of styrene-based resin (styrene-butadiene resin, glass transition temperature -3°C) (Total amount of binder resin: 125 parts by mass) 350 parts by mass of flattened kaolin (average particle size 4.3 μm) ·1800 parts by mass of water

[0086] On one side of the substrate 11 obtained in "1. Preparation of Substrate," apply the sealing layer coating liquid 1 by dry weight at a rate of 1.0 g / m². 2The material was applied in this manner and dried to form a first sealing layer (not shown). The thickness of the formed first sealing layer was 1 μm.

[0087] Next, apply coating liquid 2 for the sealing layer at a dry weight of 5.2 g / m². 2 The material was then applied to the first sealing layer, dried, and passed through a supercalender roll to form a second sealing layer (not shown), thereby obtaining a release paper base 10 (substrate 11 / sealing layer 12 (=first sealing layer / second sealing layer), see Figure 1). The thickness of the formed second sealing layer was 5 μm (i.e., the total thickness of the sealing layer 12 was 6 μm). This release paper base 10 does not contain a polyolefin layer.

[0088] 3. Preparation of release paper

[0089] On the second sealing layer of the release paper base paper 10 obtained in "2. Preparation of release paper base paper," a silicone-based release agent (Shin-Etsu Chemical Co., Ltd., "KNS-3051") is applied at a dry weight of 1.7 g / m². 2 The material was applied in this manner and cured at 150°C for 30 seconds to form a release agent layer 21, thereby obtaining release paper 20 (substrate 11 / first sealing layer / second sealing layer / release agent layer 21, see Figure 2).

[0090] 4. Making adhesive tape

[0091] An acrylic adhesive composition was obtained by mixing 100 parts by mass of an acrylic resin (n-butyl acrylate / acrylic acid = 98 / 2, monomer ratio), 30 parts by mass of a rosin ester tackifier (softening point: 100°C), 1.5 parts by mass of an isocyanate crosslinking agent (Tosoh Corporation, "Coronate L"), and a solvent. The storage modulus of this acrylic adhesive composition at 23°C was 0.07 MPa. The storage modulus (MPa) was measured in accordance with JIS K 7244-6, using a viscoelasticity measuring device (Physica Corporation, product name "MCR300") by the torsional shear method at a measurement frequency of 1 Hz.

[0092] The above adhesive composition is applied at a dry weight of 20 g / m². 2 The adhesive was applied to the release paper 20 obtained in "3. Preparation of release paper" and the resulting coating was dried to form an adhesive layer 32 (thickness 20 μm). Next, the surface of the adhesive layer 32 was bonded to a transparent resin substrate 31, which is a PET substrate (thickness 50 μm), to produce an adhesive tape 30 (substrate 11 / first sealing layer / second sealing layer / release layer 21 / adhesive layer 32 / transparent resin substrate 31, see Figure 3).

[0093] <Examples 2-3>

[0094] Except for the changes shown in Table 1, the release paper base paper 10, release paper 20, and adhesive tape 30 were prepared in the same manner as in Example 1.

[0095] <Example 4>

[0096] The pulp type was changed to a ratio of 30 parts by mass of bleached softwood kraft pulp (NBKP in Table 1) and 70 parts by mass of bleached hardwood kraft pulp (LBKP2), and the amount of the second sealing layer applied was changed to 4.4 g / m². 2 Except for the change made, the release paper base paper 10, release paper 20, and adhesive tape 30 were prepared in the same manner as in Example 1.

[0097] <Example 5>

[0098] Release paper base paper 10, release paper 20, and adhesive tape 30 were prepared in the same manner as in Example 1, except that the type of pulp was changed to 100 parts by mass of bleached kraft pulp made from northern hardwoods of the Aspen genus (labeled "LBKP1" in Table 1).

[0099] <Comparative Examples 1-2>

[0100] Except for the changes shown in Table 1, the release paper base, release paper, and adhesive tape were prepared in the same manner as in Example 1. Note that Comparative Example 2 does not have a second sealing layer.

[0101] <Comparative Example 3>

[0102] On one side of the substrate, a sealing layer is applied using low-density polyethylene (melt mass flow rate (MFR) measured according to ISO 1872-1:1993: 4.5 g / 10 min, density: 923 kg / m³). 3 After melt-extrude lamination of the material to a thickness of 17 μm, a polyolefin layer was formed by supercalendering, passing the material continuously between a cooling roll (mirror-finished roll) with a mirror-finished surface and a pressing roll, with the first polyolefin layer in contact with the mirror-finished roll. Release paper base paper, release paper, and adhesive tape were prepared in the same manner as in Example 1, except for the changes shown in Table 1.

[0103] <Evaluation Method>

[0104] (Market conditions) The texture of the release paper was evaluated on a 3-point scale based on the following criteria, by visually observing B4-sized release paper under sunlight and fluorescent light. "3" is the best. 3: There is almost no difference in the intensity contrast of transmitted light within the plane, and the intensity of transmitted light is uniform. 2: There is a slight difference in the intensity contrast of transmitted light within the plane. 1: The difference in intensity contrast of transmitted light within the plane can be clearly observed.

[0105] (Transparency and clarity) Measurements were taken using the "ICM-10P" image clarity measuring instrument manufactured by Suga Test Instruments Co., Ltd., in accordance with JIS K 7374-2007. The measurement angle was 0°, and the value of the optical comb slit (slit width: 0.25 mm) was expressed as "transmission clarity". The transmission clarity was measured for two layers of "transparent resin substrate 31 / adhesive layer 32" obtained by peeling the release paper 20 off the adhesive tape 30. Specifically, these two layers were laminated onto a 2 mm thick soda-lime glass plate using a laminator to prevent any gaps, and this was used as the measurement sample.

[0106] Table 1 shows the conditions and results for each example and comparative example.

[0107] [Table 1]

[0108] Based on the above, it has been confirmed that, according to this embodiment, a release paper base, release paper, and adhesive tape can be obtained that do not easily reduce the transparency clarity of the adhesive tape and reduce the environmental impact. [Explanation of symbols]

[0109] 10: Release paper base, 11: Base material, 12: Sealing layer, 20: Release paper, 21: Release agent layer, 30: Adhesive tape, 31: Transparent resin base material, 32: Adhesive layer

Claims

1. Substrate and The substrate includes a sealing layer laminated on at least a portion of its surface, The content of hardwood pulp in the pulp of the aforementioned substrate exceeds 50% by mass. The aforementioned sealing layer is A first sealing layer containing a polyvinyl alcohol-based resin, A second sealing layer containing a binder resin and an inorganic pigment, including, Release paper base.

2. The degree of beating of the pulp used in the aforementioned substrate is 30°SR or higher. The release paper base according to claim 1.

3. The binder resin contains a styrene-based resin. The release paper base according to claim 1.

4. A release paper base according to any one of claims 1 to 3, A release agent layer laminated on at least a portion of the surface of the sealing layer of the release paper base paper, Release paper, including the release liner.

5. A transparent resin substrate and An adhesive layer laminated on at least a portion of the surface of the transparent resin substrate, The release paper according to claim 4 is laminated on the surface of the adhesive layer opposite to the transparent resin substrate, Adhesive tape, including

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