Release paper base, release paper, adhesive label, and method for manufacturing release paper

Abstract

To provide a release paper base paper that improves transparency of an adhesive label when the adhesive label is obtained without using a polyolefin laminate.SOLUTION: In a release paper base paper 10, a base material 11, a first coat layer 12 and a second coat layer 13 are arranged in this order, a content mass ratio of hardwood pulp in pulp used for the base material is 50 mass% or more, a beating degree of the pulp used for the base material is 30° SR or higher, the first coat layer 12 contains resin, and the second coat layer 13 contains clay and binder resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to release paper base paper, release paper, adhesive labels, and a method for manufacturing release paper. [Background technology]

[0002] Adhesive labels are used for labels applied 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 an adhesive label and prevents a decrease in its 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 label.

[0004] Therefore, in applications where transparency of adhesive labels is required, it is important that the release surface of the release liner is smooth. For example, Patent Document 1 discloses a method for smoothing the release surface of the release liner by forming a pigment coating layer on a paper substrate and then forming a polyolefin layer on top of it. Release liner typically has a structure in which a release agent layer is formed on a release base paper. [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, in the case of laminated release paper with polyolefin layers, as shown in Patent Document 1, it was difficult to recycle the release paper because the polyolefin layers were insoluble in water.

[0007] Therefore, the present invention has been made in view of the above circumstances, and aims to provide a release paper base that improves the transparency of the adhesive label when used as an adhesive label without using polyolefin laminate, a release paper having a release paper base, an adhesive label, and a method for manufacturing a release paper base. [Means for solving the problem]

[0008] The present invention relates to a release paper base in which a base material, a first coat layer, and a second coat layer are arranged in that order, the mass percentage of hardwood pulp in the pulp used for the base material is 50% by mass or more, the degree of beating of the pulp used for the base material is 30°SR or more, the first coat layer contains resin, and the second coat layer contains clay and binder resin.

[0009] The binder resin contained in the second coating layer preferably contains a styrene-butadiene copolymer.

[0010] The resin contained in the first coating layer preferably contains polyvinyl alcohol.

[0011] A beaten degree of 40°SR or higher is preferable.

[0012] The ratio of binder resin to clay in the second coat layer is preferably 25% by mass or more.

[0013] The release paper of the present invention comprises a release paper base paper of the present invention and a release agent layer laminated on at least a portion of the surface of the second coat layer of the release paper base paper.

[0014] Another release paper of the present invention has a base material, a first coat layer, and a second coat layer arranged in this order. The content mass ratio of hardwood pulp in the pulp used for the base material is 50% by mass or more, the beating degree of the pulp used for the base material is 30°SR or more, the first coating layer contains a resin, the second coating layer contains clay and a binder resin, the binder resin contained in the second coating layer includes a styrene-butadiene copolymer, the resin contained in the first coating layer includes polyvinyl alcohol, the ratio of the binder resin to the clay contained in the second coating layer is 25% by mass or more, a release paper base material, and a release agent layer laminated on at least a part of the surface of the second coating layer of the release paper base material.

[0015] The adhesive label of the present invention has the release paper of the present invention.

[0016] Another adhesive label of the present invention may have another release paper of the present invention.

[0017] The method for producing the release paper base material of the present invention is to apply a composition for forming a first coating layer containing a resin on a base material in which the content mass ratio of hardwood pulp is 50% by mass or more and the beating degree of the pulp is 30°SR or more to form a first coating layer, and apply a composition for forming a second coating layer containing clay and a binder resin on the first coating layer to form a second coating layer.

Advantages of the Invention

[0018] According to the release paper base material of the present invention and the release paper including the release paper base material, the transparency of the adhesive label is improved when it is made into an adhesive label without using a polyolefin laminate. According to the method for producing the release paper base material of the present invention, it is possible to provide a release paper base material with improved transparency when made into an adhesive label.

Brief Description of the Drawings

[0019] [Figure 1]This is a schematic cross-sectional view showing one embodiment of release paper base. [Figure 2] This is a schematic cross-sectional view showing another embodiment of the release paper base. [Figure 3] This is a schematic cross-sectional view showing one embodiment of release paper. [Figure 4] This is a schematic cross-sectional view showing one embodiment of an adhesive label. [Modes for carrying out the invention]

[0020] In this specification, the range "X~Y" means "X or greater and Y or less". Unless otherwise specified, operations and measurements of physical properties are performed under room temperature (20~25°C) / relative humidity 45~55%RH. Furthermore, in this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid.

[0021] [Release paper base] A first embodiment of the present invention is a release paper base in which a base material, a first coat layer, and a second coat layer are arranged in that order, the mass percentage of hardwood pulp in the pulp used for the base material is 50% by mass or more, the degree of beating of the pulp used for the base material is 30°SR or more, the first coat layer contains resin, and the second coat layer contains clay and binder resin.

[0022] Figure 1 is a schematic cross-sectional view illustrating the structure of the release paper base 10. The release paper base 10 consists of a base material 11, a first coating layer 12, and a second coating layer 13 arranged in this order. As shown in Figure 2, which is another embodiment of the release paper base 20, the first coating layer 12 may be formed on both sides of the release paper base 10.

[0023] The basis weight of the release paper base is 35-120 g / m². 2 Preferably, it is 50-100 g / m 2 It is preferable that it be so.

[0024] The surface roughness of the second coat layer side of the release paper base can, in a preferred embodiment, be 0.70 μm or less, and more preferably less than 0.50 μm, in terms of arithmetic mean roughness (Ra) according to JIS B 0601:2013. The lower limit of the arithmetic mean roughness (Ra) of the second coat layer is preferable as it is smaller, but is usually 0.10 μm or more. In this embodiment, despite the very high smoothness of the release paper base, adhesion with the release agent layer is ensured by the layer configuration of the present invention.

[0025] (base material) The mass percentage of hardwood pulp in the pulp used as the base material is 50% by mass or more. A hardwood pulp mass percentage of 50% by mass or more improves the smoothness of the release paper base. The hardwood pulp mass percentage is preferably greater than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably greater than 80% by mass, and most preferably 100% by mass.

[0026] Furthermore, from the viewpoint of smoothness, the mass ratio of hardwood pulp to the total amount of softwood pulp in the base material is preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably more than 80% by mass, and most preferably 100% by mass.

[0027] The hardwood pulp used as the base material is not particularly limited, and virgin pulp and recycled paper pulp can be used. Wood pulp is preferred as the virgin pulp. Various known pulps can be used as the virgin hardwood pulp, such as chemical pulps like bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite pulp, or mechanical pulps like stone ground pulp (SGP), pressure-pressurized stone ground pulp (TGP), chemigland pulp (CGP), crushed wood pulp (GP), and thermomechanical pulp (TMP). Among these, in terms of surface smoothness, it is preferable to use chemical pulps such as bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite hardwood pulp, with bleached hardwood kraft pulp (LBKP) being more preferable.

[0028] Various known softwood pulps can be used as base materials, including chemical pulps such as bleached softwood kraft pulp (NBKP), unbleached softwood kraft pulp (NUKP), semi-bleached softwood kraft pulp (NSBKP), and softwood 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).

[0029] In a preferred embodiment, when the content of bleached softwood kraft pulp is XN [mass%] and the content of bleached hardwood kraft pulp is XL [mass%], it is preferable that the relationship 0 ≤ XN / XL ≤ 1 is satisfied, more preferably that 0 ≤ XN / XL < 1 is satisfied, more preferably that 0 ≤ XN / XL ≤ 3 / 7 is satisfied, even more preferably that 0 ≤ XN / XL < 2 / 8 is satisfied, and particularly preferably that XN / XL = 0 / 100.

[0030] The pulp content of the base material is not particularly limited, but is preferably 60% by mass or more and 100% by mass or less. 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.

[0031] The pulp used as the base material has a beaten degree of 30°SR or higher. If the pulp beaten degree is less than 30°SR, the haze when it is made into an adhesive label becomes significantly higher. The detailed mechanism by which the haze is lower when the pulp beaten degree is 30°SR or higher is unknown, but it is thought that in the wet coating process when forming the first coat layer on the base material, a beaten degree of 30°SR or higher makes it less likely for the coating liquid to sink into the base material, thus ensuring surface smoothness after coating. In addition, if the pulp used as the base material has a beaten degree of 30°SR or higher, the transparency of the release paper increases. High transparency has the advantage of making it easier to detect the label when applying it by machine, for example.

[0032] The degree of beating is preferably 40°SR or higher, and more preferably 45°SR or higher. While there is no particular upper limit to the degree of beating, it is preferably 90°SR or lower, and more preferably 70°SR or lower, as this allows for a faster papermaking speed. The degree of pulp beating can be controlled by the gap thickness of the double disc refiner during beating.

[0033] The thickness of the base material is preferably between 40 μm and 300 μm. A thickness of 40 μm or more suppresses wrinkle formation during the manufacturing of the release liner and improves the suitability of the label for die-cutting during label manufacturing. Furthermore, a thickness of 300 μm or less prevents excessive rigidity and maintains good handling. This thickness can be measured in accordance with JIS P 8118:2014. The basis weight of the base material is 35-120 g / m². 2Preferably, it is 50-100 g / m 2 It is more preferable that this be the case. By controlling the basis weight within this range, the papermaking suitability is further improved.

[0034] When used in adhesive labels as described later, the base material may contain colorants such as dyes and pigments, as this makes it easier to distinguish the label base material from the release liner and to make it easier to peel off the release liner. The base material may contain other additives. Other additives include 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; fixing agents such as aluminum sulfate, cationized starch, and cationic polymer electrolytes; papermaking aids; and flocculants. One or more of these may be used in combination. The resin material may also function as a sizing agent.

[0035] (First coat layer) The release paper base of the present invention has a first coating layer. The presence of the first coating layer improves smoothness compared to the case where only the second coating layer is present. This is thought to be because the presence of the first coating layer prevents the resin of the second coating layer from seeping into the paper-based substrate, thereby allowing the second coating layer to perform its role effectively.

[0036] The first coat layer contains a resin. Examples of resins include copolymers such as styrene-butadiene copolymer, ethylene-vinyl chloride copolymer, methyl methacrylate-butadiene copolymer, ethylene-vinyl acetate copolymer, and (meth)acrylic acid ester copolymer; and water-soluble resins such as casein, dextrin, starch, oxidized starch, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, and polyvinyl alcohol. These resins may be used individually or in combination of two or more. Among these, in terms of adhesion to the release agent, the resin preferably contains polyvinyl alcohol, and is particularly preferably polyvinyl alcohol alone.

[0037] Polyvinyl alcohol includes not only ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, but also modified polyvinyl alcohol. Examples of modified polyvinyl alcohol include cationic modified polyvinyl alcohol, anionic modified polyvinyl alcohol, and nonionic modified polyvinyl alcohol. Among these, ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate is preferred.

[0038] The degree of saponification of polyvinyl alcohol is preferably 80 to 100 mol%, and more preferably 85 to 100 mol%. The molecular weight of polyvinyl alcohol is usually 5,000 to 150,000, and preferably 10,000 to 100,000.

[0039] The first coat layer may contain other additives. Examples of other additives include fillers such as clay, silica, calcium carbonate, titanium dioxide, and zinc oxide, as well as dispersants, thickeners, defoamers, anti-foaming agents, viscosity modifiers, lubricants, water-resistant agents, water-retaining agents, and colorants. A form in which the first coat layer does not contain fillers is a preferred embodiment.

[0040] The coated surface to which the first coat layer has been applied may be subjected to supercalendering to smooth the surface. Supercalendering improves the sealing effect and rigidity effect.

[0041] (Second coat layer) The release paper base of the present invention has a second coat layer in addition to a first coat layer.

[0042] The second coat layer contains clay and binder resin. The clay can fill in any depressions that could not be sufficiently smoothed in the first coat layer, improving the surface smoothness.

[0043] Examples of binder resins used in the second coat layer include copolymers such as styrene-butadiene copolymer, styrene-acrylic copolymer, ethylene-vinyl chloride copolymer, methyl methacrylate-butadiene copolymer, ethylene-vinyl acetate copolymer, and (meth)acrylic acid ester copolymer; and water-soluble resins such as casein, dextrin, starch, oxidized starch, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, and polyvinyl alcohol. These binder resins may be used individually or in combination of two or more. Among these, the resin is preferably styrene-butadiene copolymer in terms of film-forming properties. Furthermore, the styrene-butadiene resin (styrene-butadiene copolymer) is preferably latex type (styrene-butadiene rubber latex) due to its high solids content, low viscosity, and excellent productivity. The glass transition temperature of the styrene-butadiene resin is preferably -50°C to 50°C, and more preferably -20°C to 20°C, in terms of ease of smoothing by pressurization in the supercalendering process. The minimum film-forming temperature for the latex type (styrene-butadiene rubber latex) is preferably in the range of 10 to 150°C. The minimum film-forming temperature is the lowest temperature required for a continuous film to be formed when the moisture in the styrene-butadiene rubber latex evaporates and dries, and is obtained by the temperature gradient plate method. Commercially available products may be used as the latex type of styrene-butadiene copolymer, for example, Smartex® SN-309R (styrene-butadiene rubber latex, manufactured by Nippon A&L Co., Ltd., glass transition temperature 4°C), Smartex® SN-307R (styrene-butadiene rubber latex, manufactured by Nippon A&L Co., Ltd., glass transition temperature 10°C), JSR0693 (styrene-butadiene rubber latex, manufactured by JSR, Inc., glass transition temperature 20°C), etc.

[0044] Furthermore, it is preferable to use a combination of starch and polyvinyl alcohol as the binder resin, in addition to the styrene-butadiene copolymer. This combination improves film-forming properties and adhesion to the release agent layer, and also improves processability.

[0045] From the viewpoint of film-forming properties and adhesion to the release agent layer, the amount of starch added is more preferably 40 to 70% by mass, and even more preferably 50 to 60% by mass, relative to the styrene-butadiene copolymer. The starch used can be made from corn, potatoes, tapioca, rice, etc. Modified starches such as oxidized starch, hydroxyethyl etherified starch, and oxygen-modified starch can be used.

[0046] From the viewpoint of film-forming properties and adhesion to the release agent layer, the amount of polyvinyl alcohol added is preferably 5 to 40% by mass, preferably 10 to 25% by mass, and more preferably 13 to 20% by mass, relative to the styrene-butadiene copolymer. As the polyvinyl alcohol, the same type as described in the section on the first coat layer can be used.

[0047] Examples of clays that can be used include kaolin, talc, bentonite, smectite, vermiculite, mica, chlorite, kibushi clay, gailome clay, halloysite, and mica. Among these, it is preferable that the clay contains kaolin. The shape of the clay is not particularly limited, but from the viewpoint of smoothness, it is preferably flattened into a plate shape. The average particle size of the clay is not particularly limited, but for example, it is between 0.1 μm and 10 μm. The average particle size is volume-based and can be measured by a laser diffraction particle size distribution analyzer.

[0048] When the clay is in the form of a flattened plate, the ratio of the average particle size to the average thickness, i.e., the aspect ratio, is preferably 3.0 or higher, more preferably 5.0 or higher, and even more preferably 7.0 or higher. The upper limit of the aspect ratio of the clay may be 10.0 or lower.

[0049] From the viewpoint of smoothness and binding properties, the clay content in the second coat layer is preferably 60-85% by mass, and more preferably 70-80% by mass.

[0050] In the second coat layer, the mass ratio of binder resin to clay is preferably 25% by mass or more, and more preferably 30% by mass or more. When the mass ratio of binder resin to clay is above the lower limit mentioned above, the resin can adequately fill the gaps formed by the clay, suppressing the penetration of the release agent layer applied on top, and further improving the smoothness. Considering the effect of the clay, the upper limit of the mass ratio of binder resin to clay is preferably 50% by mass or less, and more preferably 45% by mass or less.

[0051] The second coating layer may contain other additives. Examples of other additives include pigments, pigment dispersants, defoamers, anti-foaming agents, viscosity modifiers, lubricants, water-resistant agents, water-retaining agents, colorants, and the like.

[0052] Furthermore, it is preferable to perform supercalendering on the coated surface to which the second coat layer has been applied to make the surface smooth. Supercalendering improves the sealing effect and rigidity effect.

[0053] (Opacity of the release liner paper) The opacity of the release paper base 10, measured in accordance with ISO 2471, is preferably 85% or less, and more preferably 83% or less. If the opacity exceeds 85%, the suitability of the adhesive label using the release paper base to the photocell becomes insufficient, which is undesirable. Specifically, if the opacity of the release paper base exceeds 85%, the adhesive label cannot be detected by the photocell when applied by an automatic labeler, which reduces the suitability for labeling and is therefore undesirable. On the other hand, there is no particular lower limit to the opacity, but generally, 50% or more is preferred.

[0054] [Manufacturing method for release paper base] One embodiment of a method for manufacturing release paper base is a method for manufacturing release paper base, comprising applying a composition for forming a first coat layer containing a resin onto a substrate having a hardwood pulp content of 50% by mass or more and a pulp beaten degree of 30°SR or more to form a first coat layer, and then applying a composition for forming a second coat layer containing clay and binder resin onto the first coat layer to form a second coat layer.

[0055] 1. Manufacturing of the base material First, the pulp raw material is beaten in water to produce a pulp slurry. Internal additives are then added to the pulp slurry as needed.

[0056] Next, a paper-based substrate is obtained by papermaking using a slurry containing the pulp and, optionally, additives obtained as described above. Additionally, a sizing agent may be added during papermaking if necessary. Examples of sizing agents include oxidized starch, styrene-acrylic resin, acrylic resin, and polyacrylamide resin. When adding a sizing agent, it is usually applied to both sides of the paper, but it may also be applied to only one side.

[0057] 2. Application of the composition for forming the first coat layer to the substrate. A composition for forming the first coat layer is prepared by mixing the resin, additives as needed, and a solvent. The solvent is appropriately selected depending on the form of the resin; if the resin is polyvinyl alcohol, the solvent is, for example, water.

[0058] Subsequently, the first coat layer is formed by applying the first coat layer formation composition to the paper-based substrate obtained as described above. The application method is not particularly limited, and conventionally known methods can be employed, such as applying the first coat layer formation composition containing a resin component onto the paper-based substrate and drying it to form the first coat layer. The application method is not particularly limited, but various coating devices such as blade coaters, air knife coaters, rod blade coaters, bar blade coaters, gravure coaters, bar coaters, multi-stage roll coaters, roll coaters, reverse roll coaters, curtain coaters, spray coaters, gate roll coaters, size press coaters, and shim sizers can be appropriately selected and used for application. The amount of the first coat layer formation composition applied (solid content) (or the amount applied to one side in the case of double-sided coating of the paper-based substrate) is preferably 0.2 to 4.0 g / m² from the viewpoint of effectiveness. 2 , more preferably 0.5~3.0 g / m 2 That is the case.

[0059] After applying the first coat layer forming composition, a drying process may be performed. The drying conditions are set as appropriate, but for example, 80 to 160°C for 10 to 60 seconds.

[0060] 3. Application of the composition for forming the second coat layer to the substrate. A composition for forming the second coat layer is prepared by mixing the binder resin, clay, additives as needed, and a solvent. The solvent is appropriately selected depending on the form of the binder resin. When the binder resin is a latex-type resin or a water-soluble polymer, the solvent is preferably water or alcohols (e.g., ethanol, isopropanol, etc.), and more preferably water. The solvent may be used alone or in combination of two or more.

[0061] Subsequently, the second coat layer forming composition is applied to the surface of the paper-based substrate on which the first coat layer obtained as described above is formed, thereby forming the second coat layer. An example of the application method is the same as the application method for the first coat layer forming composition described above.

[0062] From the viewpoint of effectiveness, the amount (solid content) of the composition for forming the second coat layer applied is preferably 2 to 30 g / m². 2 , comfortably 3-20g / m 2 The composition for forming the second coat layer may be applied and then subjected to a drying process. The drying conditions are set as appropriate, but for example, 80 to 160°C for 10 to 60 seconds.

[0063] [Release paper] Figure 3 is a schematic cross-sectional view showing the structure of the release paper. In the release paper 30 of Figure 3, a release agent layer 14 is formed on the second coat layer 13 of the release paper base paper 10 of Figure 1.

[0064] Examples of release agents used to form the release agent layer include silicone-based release agents, olefin-based resins, isoprene-based resins, rubber-based elastomers such as butadiene-based resins, long-chain alkyl resins, long-chain alkyl acrylate resins, alkyd resins, and fluorine-based resins. Among these, silicone-based release agents are preferred. The thickness of the release agent layer is usually about 0.01 to 5 μm.

[0065] Examples of resins used in silicone-based release agents include homopolymers or copolymers of trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, diphenyldichlorosilane, phenyltrichlorosilane, and methylvinyldichlorosilane. These can be used individually or in combination of any two or more. Furthermore, silicone-based release agents can be used in solvent-based, solvent-free, or emulsion forms, but from an environmental standpoint, emulsion or solvent-free forms are preferred.

[0066] The release agent layer preferably has a thickness of 0.01 μm to 10 μm, and more preferably 0.1 μm to 5 μm.

[0067] The method for applying the release agent to the second coating layer is not particularly limited. For example, various coating devices such as a blade coater, an air knife coater, a rod blade coater, a bar blade coater, a gravure coater, a bar coater, and a multi-stage roll coater can be appropriately selected and used.

[0068] The coating amount (solid content) of the release agent is preferably 0.1 g / m 2 or more from the viewpoint of smoothness after coating, more preferably exceeding 0.4 g / m 2 and even more preferably exceeding 1.0 g / m 2 On the other hand, from the viewpoint of suppressing the occurrence of blocking during winding, the coating amount of the release agent is preferably 2.5 g / m 2 or less, more preferably 2.0 g / m 2 or less.

[0069] As a preferred embodiment, the surface roughness on the release agent layer side of the release paper is preferably 0.70 μm or less, more preferably 0.65 μm or less, even more preferably 0.5 μm or less, and particularly preferably less than 0.5 μm in terms of the arithmetic mean roughness (Ra) conforming to JIS B 0601:2013. The lower limit of the arithmetic mean roughness (Ra) of the release agent layer is preferably as small as possible, but usually 0.10 μm or more.

[0070] [Adhesive label] Figure 4 is a schematic cross-sectional view showing the configuration of the adhesive label. The adhesive label 40 in Figure 4 has, in order from the release agent layer 14 side of the release paper 30 in Figure 3, an adhesive layer 15 and a label base material 16.

[0071] (Label base material) The label substrate is not particularly limited and may be a resin substrate or a paper substrate. The label substrate is preferably a transparent substrate because the release paper in the above embodiment has high smoothness and can reduce the haze of the adhesive label. Here, transparent means that the transmittance in the visible light region is 80% or more, and preferably 90% or more (upper limit 100%). The transmittance of the transparent substrate can be measured according to JIS K7361-1:1997 (Plastics - Test method for total light transmittance of transparent materials).

[0072] There are no particular restrictions on the materials that constitute the transparent substrate. Examples include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin films such as polyethylene and polypropylene; 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, and cyclic olefin-based film. Among these, in terms of transparency, the resin substrate is preferably polyester or polyolefin, more preferably polyethylene terephthalate, polyethylene, or polypropylene, and even more preferably polyethylene terephthalate.

[0073] The label substrate may contain stabilizers, lubricants, softeners, UV absorbers, antioxidants, antistatic agents, twist-resistant agents, etc., as needed. The resin substrate may also have an easy-adhesion layer to improve the adhesion of the printed layer.

[0074] There are no particular restrictions on the thickness of the label substrate, but it is preferably 5 to 250 μm.

[0075] (Adhesive layer) The adhesive used in the adhesive layer is not particularly limited, and acrylic adhesives, rubber adhesives, silicone adhesives, urethane adhesives, polyester adhesives, vinyl alkyl ether adhesives, etc., can be used. The above adhesives may be used individually or in combination of two or more.

[0076] As an adhesive, acrylic adhesives are particularly suitable from the viewpoint of adhesive reliability. The acrylic polymer constituting the acrylic adhesive is formed by using an adhesive alkyl (meth)acrylate as the main monomer component, and optionally using a monomer copolymerizable to an alkyl (meth)acrylate that has cohesive properties (copolymerizable monomer) and a copolymerizable monomer having a crosslinkable functional group.

[0077] 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.

[0078] Examples of copolymerizable monomers with cohesive properties include methyl (meth)acrylate, vinyl acetate, styrene, and acrylonitrile. These may be used individually or in combination of two or more.

[0079] Examples of copolymerizable monomers having crosslinkable functional groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylic acid. These may be used individually or in combination of two or more types.

[0080] The weight-average molecular weight of the acrylic polymer is not particularly limited, but it is preferably between 100,000 and 1,000,000. The weight-average molecular weight is the polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0081] The adhesive preferably contains a crosslinking agent in addition to the 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.

[0082] The adhesive layer may contain, as needed, fillers, light stabilizers, antioxidants, colorants, antistatic agents, tackifiers, wetting agents, leveling agents, thickeners, defoamers, preservatives, and other additives.

[0083] The thickness of the adhesive layer is not particularly limited, but from the viewpoint of adhesion and thinness, a range of 10 to 100 μm is preferred.

[0084] The method for forming the adhesive layer is not particularly limited, but typically the adhesive is applied to the release layer of the release paper, dried, and then transferred to the label substrate surface. The application method is not particularly limited and can be applied using known application devices such as roll coaters, knife coaters, air knife coaters, bar coaters, blade coaters, slot die coaters, lip coaters, and gravure coaters. The drying conditions are not particularly limited and are usually carried out at 60 to 150°C for 10 to 60 seconds.

[0085] (Printing layer) Adhesive labels may, for example, have a printed layer on a label substrate. The method of forming the printed layer is not particularly limited and may be, for example, by flexographic printing, offset printing, letterpress printing, gravure printing, screen printing, etc.

[0086] The information displayed on the printed layer may be, for example, letters, numbers, illustrations, photographs, graphs, etc., or a combination thereof. [Examples]

[0087] The effects of the present invention will be explained using the following examples and comparative examples. In the examples, the units "parts" or "%" may be used, but unless otherwise specified, they represent "parts by mass" or "mass%". Unless otherwise specified, each operation is performed at room temperature (25°C).

[0088] [Example 1] 1. Preparation of paper-based substrates Bleached hardwood kraft pulp (LBKP) was beaten in water using the Schoper-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 fixing agent were added to obtain a pulp slurry. This pulp slurry was then used to make paper using a multi-cylinder, long-wire paper machine, resulting in a basis weight of 59 g / m². 2 A paper-based substrate was obtained. The thickness of the paper-based substrate was 49 μm.

[0089] 2. Preparation of release paper base On one side of the paper-based substrate obtained in step 1, apply a composition containing polyvinyl alcohol (saponification degree 98 mol%, molecular weight 75,000) and water in predetermined proportions, at a rate of 1.0 g / m². 2 The material was applied in this manner and dried to form the first coat layer. The thickness of the formed first coat layer was 1 μm.

[0090] Next, a coating solution was prepared containing flattened kaolin (average particle size 4.3 μm), oxidized starch, polyvinyl alcohol (saponification degree 98 mol%, molecular weight 75,000), and styrene-butadiene resin (styrene-butadiene rubber latex, glass transition temperature -3°C, minimum film formation temperature 100°C) in the proportions (solid content) shown in Table 1 below, with water as the solvent in a predetermined proportion. Then, the coating solution was applied at a rate of 5.2 g / m². 2 The material was applied to the first coat layer, dried, and then passed through a supercalender roll to form a second coat layer and obtain a release paper base. The thickness of the formed second coat layer was 5 μm.

[0091] 3. Preparation of release paper 2. Apply a silicone-based release agent (KNS-3051, manufactured by Shin-Etsu Chemical Co., Ltd.) to the second coat layer of the release paper base obtained in step 2, at a rate 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 and obtain release paper.

[0092] 4. Making adhesive labels An acrylic adhesive composition was obtained by mixing 100 parts by mass (solids) of an acrylic resin (n-butyl acrylate / acrylic acid = 90 / 10), 30 parts by mass (solids) of a rosin ester-based tackifier (softening point: 100°C), and 1.5 parts by mass (solids) of an isocyanate-based crosslinking agent (Coronate L, manufactured by Tosoh Corporation).

[0093] The above adhesive composition is applied at a rate of 20 g / m². 2 The adhesive was then applied to the release paper obtained in step 3. Next, the adhesive layer was bonded to a transparent resin substrate, a PET substrate (50 μm thick), and left to stand at 23°C for one week to produce an adhesive label.

[0094] [Example 2] Release paper base, release paper, and adhesive labels were obtained in the same manner as in Example 1, except that bleached hardwood kraft pulp (LBKP) was beaten in water using the Schoper-Rigler method to achieve a beat degree of 49°SR.

[0095] [Example 3] The application amount of silicone-based release agent (KNS-3051, manufactured by Shin-Etsu Chemical Co., Ltd.) is 1.0 g / m². 2 Release paper base paper, release paper, and adhesive label were obtained in the same manner as in Example 1, except that the coating was applied in such a manner.

[0096] [Example 4] The application amount of silicone-based release agent (KNS-3051, manufactured by Shin-Etsu Chemical Co., Ltd.) is 0.4 g / m². 2 Release paper base paper, release paper, and adhesive label were obtained in the same manner as in Example 1, except that the coating was applied in such a manner.

[0097] [Example 5] The composition was changed from 100 parts by mass of bleached hardwood kraft pulp (LBKP) to 30 parts by mass of bleached softwood kraft pulp (N-BKP) and 70 parts by mass of bleached hardwood kraft pulp (LBKP), and the amount of the second coat layer applied was further reduced to 4.4 g / m². 2 Except for the change made, a release paper base, release paper, and adhesive label were obtained in the same manner as in Example 1.

[0098] [Example 6] Release paper base, release paper, and adhesive labels were obtained in the same manner as in Example 1, except that the amount of bleached hardwood kraft pulp (LBKP) was changed from 100 parts by mass to 50 parts by mass to bleached softwood kraft pulp (N-BKP) and 50 parts by mass to bleached hardwood kraft pulp (LBKP).

[0099] [Example 7] Bleached hardwood kraft pulp (LBKP) was beaten in water using the Schoper-Rigler method to achieve a beat degree of 42°SR, and this was 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, 0.2 parts by mass of aluminum sulfate as a fixative, and 0.010 parts of copper(II) phthalocyanine (β-type) as a coloring agent were added to obtain a pulp slurry. Next, this pulp slurry was used to make paper using a multi-cylinder long-wire paper machine, resulting in a basis weight of 90 g / m². 2 A paper-based substrate was obtained. Subsequently, release paper base paper, release paper, and adhesive labels were obtained in the same manner as in Example 1.

[0100] [Comparative Example 1] Release paper base, release paper, and adhesive labels were obtained in the same manner as in Example 1, except that bleached hardwood kraft pulp (LBKP) was beaten in water using the Schoper-Rigler method to achieve a beat degree of 23°SR.

[0101] [Comparative Example 2] Release paper base, release paper, and adhesive label were obtained in the same manner as in Example 1, except that a second coating layer was not provided.

[0102] [Comparative Example 3] Release paper base, release paper, and adhesive label were obtained in the same manner as in Example 1, except that the first coating layer was not provided.

[0103] (Evaluation method 1: Arithmetic mean roughness Ra) The arithmetic mean roughness Ra of the release agent layer surface of the release paper was measured using a contact surface roughness meter (Mitutoyo SV-3000) in accordance with JIS B0601:2013. The results are shown in Table 1 below.

[0104] (Evaluation method 2: haze) The haze was measured after the release liner was removed from each adhesive label. The haze was measured using a haze meter (NDH 5000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000. The results are shown in Table 1 below.

[0105] (Evaluation method 3: Opacity) The opacity of the release paper of the examples and comparative examples was measured in accordance with JIS P 8149:2000. The results are shown in Table 1 below. Note that a lower opacity value indicates higher transparency.

[0106] (Measurement method 4: Labeler suitability (photocell suitability)) The adhesive labels obtained in the examples and comparative examples were fed into a paper feed detector on an automatic labeler, and it was confirmed whether the photocell could detect them by passing light through it. The evaluation criteria are as follows. ○...Detection is possible using a photocell. ×...Detection by photocell is impossible.

[0107] [Table 1]

[0108] The release paper base paper and release paper produced in the examples exhibited high smoothness. Furthermore, the adhesive labels of Examples 1 to 7 demonstrated high transparency. On the other hand, the adhesive labels of Comparative Example 1, which had a beaten degree of less than 30°SR, Comparative Example 2, which lacked a second coat layer, and Comparative Example 3, which lacked a first coat layer, exhibited low transparency. [Explanation of Symbols]

[0109] 10, 20 Release paper base 11 Base material 12. First coat layer 13. Second Coat Layer 14. Release agent layer 15 Adhesive layer 16 Label substrate 30 Release paper 40 Adhesive Labels

Claims

1. The substrate, the first coat layer, and the second coat layer are arranged in this order. The pulp used in the aforementioned base material contains 50% by mass or more of hardwood pulp. The degree of beating of the pulp used in the aforementioned substrate is 30°SR or higher. The first coating layer contains a resin containing polyvinyl alcohol, The second coating layer contains clay and binder resin, The binder resin comprises a styrene-butadiene copolymer, polyvinyl alcohol, and starch. Release paper base.

2. The release paper base according to claim 1, wherein the degree of beating is 40°SR or higher.

3. The release paper base according to claim 1, wherein the ratio of the binder resin to the clay contained in the second coating layer is 25% by mass or more.

4. The release paper base according to claim 1, A release agent layer laminated on at least a portion of the surface of the second coating layer of the release paper base, Release paper, including the release liner.

5. The substrate, the first coat layer, and the second coat layer are arranged in this order. The pulp used in the aforementioned base material contains 50% by mass or more of hardwood pulp. The degree of beating of the pulp used in the aforementioned substrate is 30°SR or higher. The first coating layer contains resin, The second coating layer contains clay and binder resin, The binder resin contained in the second coating layer comprises a styrene-butadiene copolymer, polyvinyl alcohol, and starch. The resin contained in the first coating layer contains polyvinyl alcohol, The ratio of the binder resin to the clay contained in the second coating layer is 25% by mass or more, and the release paper base paper, A release agent layer laminated on at least a portion of the surface of the second coating layer of the release paper base, Release paper, including the release liner.

6. An adhesive label having the release paper described in claim 4.

7. An adhesive label having the release paper described in claim 5.

8. A first coat layer is formed by applying a first coat layer-forming composition containing a resin containing polyvinyl alcohol to a substrate having a hardwood pulp content of 50% by mass or more and a pulp beaten degree of 30°SR or more. The method involves applying a composition for forming a second coat layer, which includes clay and a binder resin, onto the first coat layer to form a second coat layer. The binder resin comprises a styrene-butadiene copolymer, polyvinyl alcohol, and starch. A method for manufacturing release paper base.

9. The amount (solid content) of the second coating layer forming composition applied is 2.0 g / m². ２ The method for manufacturing release paper base paper according to claim 8.

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