Base paper for release paper

Abstract

To provide base paper for release paper that is easy to recycle.SOLUTION: Base paper for release paper 10 includes a paper substrate 11 and a coat layer 12 provided on one face 11a of the paper substrate 11. A beating degree of a pulp used in the paper substrate 11 is 30° SR or over, the coat layer 12 does not include a water-insoluble resin, but includes an inorganic pigment and a water-soluble resin. The water-soluble resin is contained at a rate of 10 pts.mass or over and 400 pts.mass or under to 100 pts.mass of the inorganic pigment, and a content mass rate of a hardwood pulp in the pulp used in the paper substrate is 90 mass% or over.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a release paper base paper. [Background technology]

[0002] As a label to be affixed to various objects, there is an adhesive label composed of a release paper and an adhesive layer formed thereon. Usually, the release paper is coated on one or both sides of the release paper base paper with a release agent made of silicone resin or the like to facilitate peeling of the adhesive layer, and this release agent is called a coating layer, release agent layer, or the like.

[0003] For example, Patent Document 1 discloses a release paper base paper in which a water-soluble resin sealing layer, a water-soluble resin intermediate layer, and a release layer are sequentially provided on at least one surface of a base paper made from pulp with a beating degree of 20 to 44°SR.

[0004] Patent Document 2 discloses a release paper base material in which a substrate, coating layer 1, and coating layer 2 are arranged in this order, the mass percentage of hardwood pulp in the pulp used in the substrate is 50 mass% or more, the beating degree of the pulp used in the substrate is 30°SR or more, coating layer 1 contains a resin, and coating layer 2 contains clay and a binder resin.

[0005] Furthermore, Patent Document 3 describes a release paper for adhesive labels, which is made by sequentially laminating at least a transparent layer and a release layer on the surface of plain paper, the plain paper being made of wood pulp having a freeness of 350 to 500 ml CSF, the release paper having a light transmittance of 10 to 20% at 940 to 960 nm, and a tightness of 0.90 to 1.15 g / cm 3 A release paper for adhesive labels is disclosed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-166504 A [Patent Document 2] JP 2023-23121 A [Patent Document 3] JP 2003-253600 A Summary of the Invention [Problem to be solved by the invention]

[0007] The release paper of an adhesive label is discarded after the adhesive layer is peeled off. In recent years, from the viewpoint of environmental conservation, it is desired to reuse the release paper. When a silicone resin serving as a release agent is applied to the surface of the release paper base paper, highly beaten pulp is used as the base material of the release paper base paper in order to favorably support the silicone resin and maintain the barrier properties. On the other hand, a beating process is required to recover release paper and produce waste paper pulp, but in release paper base paper using highly beaten pulp, the pulp fibers may become too thin and short in the beating process. Therefore, when recycled release paper produced using waste paper pulp is recovered again to produce waste paper pulp, there is a problem that it is difficult to produce recycled paper. Furthermore, the latex used as a binder resin in the filling treatment is water-insoluble, which becomes a factor that inhibits disintegration during the regeneration treatment.

[0008] In the inventions described in the above patent documents, the barrier properties and disintegration properties of the release paper base paper are satisfactory, but there is room for improvement in terms of ease of reuse of the recycled release paper produced using waste paper pulp. The present invention has been made in view of the above circumstances, and has an object to provide a release paper base paper that is easily recycled. [Means for solving the problem]

[0009] The present inventors have found that it is possible to obtain a release paper base paper which can favorably support the resin of the coating layer and is easy to reuse even when a paper base material with a low degree of beating is used, and have arrived at the present invention. That is, the present invention provides a release paper base paper comprising a paper base material and a coating layer provided on one side of the paper base material, wherein the beating degree of the pulp used in the paper base material is 30°SR or more, the coating layer does not contain a water-insoluble resin but contains an inorganic pigment and a water-soluble resin, and contains 10 to 400 parts by mass of the water-soluble resin per 100 parts by mass of the inorganic pigment, and the mass proportion of hardwood pulp in the pulp used in the paper base material is 90 mass% or more.

[0010] The inorganic pigment is preferably kaolin.

[0011] The water-soluble resin is preferably at least one selected from polyvinyl alcohol, casein, dextrin, starch, oxidized starch, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and polyvinylpyrrolidone.

[0012] The hardwood pulp is preferably bleached hardwood kraft pulp (LBKP). Effect of the Invention

[0013] According to the present invention, it is possible to obtain a release paper base paper that is easily recyclable. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view of a release paper base paper according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Release paper base paper] A release paper base paper 10 according to one embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, a release paper base paper 10 of this embodiment comprises a paper substrate 11 and a coating layer 12 provided on one surface 11a of the paper substrate 11.

[0016] <Paper base material> As the paper base material 11, for example, fine paper, glassine paper, kraft paper, etc. are preferable. The hardwood pulp content in the pulp used in the paper base material 11 is 90% by mass or more. A hardwood pulp content of 90% by mass or more improves the smoothness of the release paper base paper surface. The hardwood pulp content is preferably more than 90% by mass, more preferably 95% by mass or more, even more preferably 98% by mass or more, and most preferably 100% by mass.

[0017] The hardwood pulp used in the paper base material 11 is not particularly limited, and virgin pulp and recycled paper pulp can be used. As the virgin pulp, it is preferable to use wood pulp. As the virgin pulp of hardwood pulp, various known pulps can be used, such as chemical pulps such as bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite hardwood pulp, and mechanical pulps such as stone ground pulp (SGP), pressed stone ground pulp (TGP), chemi-ground pulp (CGP), groundwood 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 hardwood sulfite pulp are preferred, and bleached hardwood kraft pulp (LBKP) is more preferred.

[0018] Examples of softwood pulp that can be used for the paper base material 11 include various known pulps, such as chemical pulps such as bleached softwood kraft pulp (NBKP), unbleached softwood kraft pulp (NUKP), semi-bleached softwood kraft pulp (NSBKP), and softwood sulfite pulp, and mechanical pulps such as stone ground pulp (SGP), pressed stone ground pulp (TGP), chemi-ground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP).

[0019] The pulp content of the paper base material 11 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.

[0020] The paper base material 11 may be manufactured by a known method. For example, softwood pulp and hardwood pulp are dispersed in water in a predetermined mass ratio, and the pulp is beaten to a predetermined degree by a beater to obtain a pulp slurry. Then, additives and the like are added to the obtained pulp slurry as desired. The prepared slurry is made into paper using a known papermaking machine such as a Fourdrinier papermaking machine, a cylinder papermaking machine, or a twin-wire papermaking machine to obtain a paper base material. The papermaking method is not particularly limited, and either acidic papermaking or neutral papermaking can be selected.

[0021] - Beating degree - In the present invention, the beating degree of the pulp used in the paper base material 11 is 30° SR or more. The beating degree of the pulp used in the paper base material 11 is preferably 60° SR or less. By having the degree of beating of the pulp beating of 30°SR or more and 60°SR or less, when the release paper base paper 10 is recovered after use and recycled paper is produced, the pulp fibers are thin and do not become too short even if the beating process is repeated, so that the recycled paper can be produced satisfactorily.

[0022] -Thickness- The thickness of the paper substrate 11 is preferably 40 μm or more and 300 μm or less. By making the thickness 40 μm or more, the occurrence of wrinkles during the production of the release paper base paper 10 can be suppressed, and the suitability for the punching process in the label processing during the production of the adhesive label can be improved. Furthermore, by making the thickness 300 μm or less, the rigidity does not become too high, and the handling property does not decrease. Note that this thickness can be measured in accordance with JIS P 8118:2014.

[0023] -Basic weight- The basis weight of the paper base material 11 is 35 g / m2 More than 120g / m 2 It is preferable that the thickness is less than 50 g / m 2 More than 100g / m 2 It is more preferable that the basis weight is within this range. By controlling the basis weight within this range, suitability for papermaking is further improved. The basis weight of the paper base material 11 is a value measured based on the basis weight testing method of JIS P 8124:2011.

[0024] <Coat layer> The coating layer 12 contains an inorganic pigment and a water-soluble resin, and is formed on the paper base material 11 to improve adhesion with the release agent layer.

[0025] -Inorganic pigments- Examples of inorganic pigments contained in the coating layer 12 include kaolin, talc, bentonite, smectite, vermiculite, mica, chlorite, wood clay, gairome clay, halloysite, and mica. These may be used alone or in combination of two or more. Among these, kaolin is more preferable.

[0026] -Water-soluble resin- Examples of the water-soluble resin include polyvinyl alcohol, casein, dextrin, starch, oxidized starch, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, etc. These resins may be used alone or in combination of two or more. Among these, in terms of adhesion to the release agent, the resin preferably contains polyvinyl alcohol, and particularly preferably contains only polyvinyl alcohol.

[0027] Polyvinyl alcohol includes not only normal polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate, but also modified polyvinyl alcohol. Examples of modified polyvinyl alcohol include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, and nonion-modified polyvinyl alcohol. Among them, the polyvinyl alcohol is preferably normal polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate.

[0028] The degree of saponification of polyvinyl alcohol is preferably 80% or more and 100% or less by mole, and more preferably 85% or more and 100% or less by mole. The molecular weight of polyvinyl alcohol is usually about 5,000 to 150,000, and preferably about 10,000 to 100,000.

[0029] - Mass ratio of inorganic pigment to water-soluble resin - The coating layer 12 contains 10 to 400 parts by mass of water-soluble resin per 100 parts by mass of inorganic pigment. When the amount of water-soluble resin is within the above range, the release paper base paper 10 has good disaggregation properties, allowing for good production of recycled paper. More preferably, the coating layer 12 contains 80 to 200 parts by mass of water-soluble resin per 100 parts by mass of inorganic pigment.

[0030] -Water insoluble resin- The coating layer 12 of the present invention does not contain a water-insoluble resin. Conventional coating layers contain a water-insoluble resin as a binder between the inorganic pigment and the water-soluble resin. This causes a problem of inhibiting disintegration of the release paper base paper. The coating layer 12 of the present invention does not contain a water-insoluble resin, so disintegration proceeds smoothly during the recycled paper manufacturing process. Here, the term "water-insoluble resin" refers to a substance that does not re-dissolve in water after drying and forming a film. Examples of water-insoluble resins include copolymers such as styrene-butadiene copolymers, styrene-acrylic copolymers, ethylene-vinyl chloride copolymers, methyl methacrylate-butadiene copolymers, ethylene-vinyl acetate copolymers, and (meth)acrylic acid ester copolymers.

[0031] The coating layer 12 can be formed by applying and drying a coating layer-forming composition on a substrate. The application method is not particularly limited, but can be a method of applying the composition by appropriately selecting 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, a multi-stage roll coater, a roll coater, a reverse roll coater, a curtain coater, a spray coater, a gate roll coater, a size press coater, or a shim sizer. The composition for forming the coating layer is prepared by mixing a resin, an additive, and a solvent as necessary. Examples of the additive include fillers such as silica, calcium carbonate, titanium oxide, and zinc oxide, dispersants, thickeners, defoamers, foam inhibitors, viscosity adjusters, lubricants, water-resistant agents, water retention agents, and coloring materials. The solvent is appropriately selected depending on the form of the resin. When the resin is polyvinyl alcohol, the solvent is, for example, water.

[0032] The surface coated with the coating layer 12 may be smoothed by a supercalender treatment. By performing the supercalender treatment, the effects of sealing and stiffening are improved.

[0033] In a preferred embodiment, the surface roughness of the coating layer 12 of the release paper base paper 10 can be preferably 0.70 μm or less, more preferably less than 0.50 μm, in terms of arithmetic mean roughness (Ra) in accordance with JIS B 0601: 2013. The lower limit of the arithmetic mean roughness (Ra) of the coating layer 12 is preferably as small as possible, but is usually 0.10 μm or more.

[0034] (Tension) The density of the release paper base paper 10 of the present invention is 1.0 g / m 3 That's all. The tightness in the present invention is measured over the entire release paper base paper 10, which is a paper substrate 11 on which a coating layer 12 is provided. The tightness of the paper substrate is a value determined by measuring the basis weight and thickness at eight points in the width direction over a total width of 2000 mm to 2500 mm, and standardizing the measured value in accordance with JIS P 8118:1998. When the tightness of the release paper base paper 10 is 1.0 g / m2 Due to the above, when a resin is applied onto the paper substrate 11 of the release paper base paper 10 as the coating layer 12, the resin is prevented from penetrating into the paper substrate 11, and the coating layer 12 can be formed satisfactorily. The density of the release paper base paper 10 is 1.0 g / m 3 More than 1.30g / m 3 It is preferable that:

[0035] (Yonetsubo) The basis weight of the release paper base paper 10 is 100g / m 2 Preferably, it is 85 g / m or less. 2 It is more preferable that the basis weight is 100 g / m or less. 2 By satisfying the following, the amount of waste can be reduced, making it an environmentally friendly product. The basis weight of the release paper base paper 10 in the present invention is measured for the entire release paper base paper 10 having the coating layer 12 provided on the paper substrate 11. The basis weight of the release paper base paper 10 is a value measured based on the basis weight testing method of JIS P 8124:2011.

[0036] (Other configurations) The release paper is formed by forming a release agent layer on the coating layer 12. Examples of the release agent forming the release agent layer include silicone-based release agents, rubber-based elastomers such as olefin-based resins, isoprene-based resins, and butadiene-based resins, long-chain alkyl-based resins, long-chain alkyl acrylate-based resins, alkyd-based 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 μm or more and 5 μm or less.

[0037] In a preferred embodiment, the surface roughness of the release paper on the release agent layer side can be 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 arithmetic mean roughness (Ra) in accordance with 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 is usually 0.10 μm or more.

[0038] <Adhesive sheet> The pressure-sensitive adhesive sheet has, in this order from the release agent layer side of the release paper, a pressure-sensitive adhesive layer, and a substrate.

[0039] The release paper base paper of the present invention has the advantages of being able to support the resin of the coating layer well while using low-beaten pulp, thus providing good barrier properties and being easy to reuse. EXAMPLES

[0040] The present invention will be described below with reference to examples and comparative examples. Unless otherwise specified, all operations are carried out at room temperature (25° C.).

[0041] [Release paper base paper] The release paper base paper used in the examples and comparative examples will be described below.

[0042] [Example 1] The release paper base paper of Example 1 was prepared as follows. (Paper base material) Softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP) were mixed in the ratios shown in Table 1, beaten in water using the Shopper-Rigler method to the degree of beating shown in Table 1, and dispersed in water to obtain a pulp slurry with a concentration of approximately 1% by mass. The pulp slurry was then made into paper using a fourdrinier multi-cylinder paper machine, with a basis weight of 55 g / m 2 The thickness of the paper substrate was 62 μm.

[0043] (Coat layer) Next, a coating liquid was prepared containing flat plate-like kaolin (average particle size 4.3 μm), oxidized starch, and polyvinyl alcohol (saponification degree 98 mol%, molecular weight 75,000) in the proportions (solid content) shown in Table 1, and water as a solvent in a predetermined proportion. 2 The resulting coating was applied to a paper substrate so that the coating was in the range of 100 μm to 200 μm, and then dried and passed through a supercalender roll to form a coating layer, thereby obtaining a release paper base paper. The coating layer thus formed had a thickness of 3 μm.

[0044] [Examples 2 to 8, Comparative Example 1] Using the blending ratios shown in Table 1, release paper base paper was prepared in the same manner as in Example 1.

[0045] [evaluation] The following evaluations were carried out for the above-mentioned Examples and Comparative Examples. The evaluation results are shown in Table 1.

[0046] (Tension) The tightness was determined in accordance with JIS P 8118:1998 by measuring the basis weight and thickness at eight points across the width of 2000mm to 2500mm and standardizing the results.

[0047] (Disintegration) 50 g of the obtained release paper base paper was cut into a 5 cm x 5 cm square, added to 1200 ml of water (20°C), and stirred for 2 minutes using a standard disintegrator according to JISP8209. Next, the disintegrated slurry (solid content = 6.25 g) was used to make a square handmade sheet (25 cm x 25 cm) using a handmade sheet machine, which was then sandwiched between dehydrating filter paper and rolled twice with a 20 kg press roll, and pressed at 3.5 kg / cm by a press machine. 2 The handmade sheet was pressed with a pressure of 1000 psi. The handmade sheet was then dried in a blower dryer for 2 hours while still sandwiched between the filter papers, and then peeled off from the filter papers. The undisintegrated matter contained in the peeled handmade sheet was observed, and the disintegration property of the release paper base paper was evaluated using the following three-point scale. Note that undisintegrated matter refers to small portions of the release paper that have not been disintegrated and remain. These can be observed as black spots when the handmade sheet is placed on a light diffusing board (for example, frosted glass with a light emitter on the inside). <Evaluation criteria> ◎ No undisintegrated matter is observed △ Undissociated material was observed

[0048] [Table 1]

[0049] As shown in Table 1, the release paper base papers of Examples 1 to 8 of the present invention were able to achieve good results in terms of releasability. [Explanation of symbols]

[0050] 10 Release paper base paper 11 Paper base material 11a (one side of paper substrate) 12 Coating Layer

Claims

1. The present invention comprises a paper substrate and a coating layer provided on one surface of the paper substrate, The degree of beating of the pulp used in the paper base material is 30° SR or more; the coating layer does not contain a water-insoluble resin, but contains an inorganic pigment and a water-soluble resin, and contains the water-soluble resin in an amount of 10 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the inorganic pigment; The release paper base paper, wherein the mass ratio of hardwood pulp in the pulp used in the paper base material is 90 mass % or more.

2. 2. The release paper base paper according to claim 1, wherein the inorganic pigment is kaolin.

3. 2. The release paper base paper according to claim 1, wherein the water-soluble resin is at least one selected from the group consisting of polyvinyl alcohol, casein, dextrin, starch, oxidized starch, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and polyvinylpyrrolidone.

4. 2. The release paper base paper according to claim 1, wherein the hardwood pulp is bleached hardwood kraft pulp (LBKP).

Images