Release paper base paper

Abstract

To provide release paper base paper that is easy to reuse.SOLUTION: Release paper base paper 10 according to the present invention has a paper base material 11 and a coating layer 12 provided on one side 11a of the paper base material 11, wherein the degree of beating of the pulp used for the paper base material 11 is 45° SR or less, wherein the coating layer 12 contains clay and a water-soluble resin without a water-insoluble resin, wherein the mass ratio of clay to water-soluble resin is between 3:7 and 7:3, and wherein the bulk density of this release paper base paper is 0.95 g / m3 or less.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 the 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 paper base material and a coating layer provided on one side of the paper base material, in which the beating degree of pulp used in the paper base material is 45°SR or less, the coating layer does not contain a water-insoluble resin but contains clay and a water-soluble resin, the mass ratio of the clay to the water-soluble resin is 3:7 or more and 7:3 or less, and the compactness is 0.95 g / m 3 The release paper base paper is as follows.

[0010] Preferably the clay is kaolin.

[0011] The water-soluble resin is preferably polyvinyl alcohol.

[0012] The release paper base paper has a basis weight of 55 g / m 2 It is preferable that:

[0013] The release paper base paper has a density of 0.89 g / m 3 More than 0.95g / m 3 It is preferable that: Effect of the Invention

[0014] According to the present invention, it is possible to obtain a release paper base paper that is easily recyclable. [Brief description of the drawings]

[0015] [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

[0016] [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.

[0017] (Tension) The density of the release paper base paper 10 of the present invention is 0.95 g / m3 The following is the result. The tightness in the present invention is measured over the entire release paper base paper 10 having the coating layer 12 provided on the paper substrate 11. The tightness of the paper substrate is a value determined by measuring and standardizing the basis weight and thickness at eight points in the width direction over an overall width of 2000 mm to 2500 mm in accordance with JIS P 8118:1998. The density of the release paper base paper 10 is 0.95 g / m 3 By satisfying the above condition, the release paper can be easily disintegrated when it is recovered to produce recycled paper pulp. The density of the release paper base paper 10 is 0.89 g / m 3 More than 0.95g / m 3 The density of the release paper 10 is preferably 0.89 g / m or less. 2 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.

[0018] (Yonetsubo) The basis weight of the release paper base paper 10 is 55 g / m 2 It is preferable that the thickness is less than 45 g / m 2 It is more preferable that the basis weight is 55 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.

[0019] <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 50% by mass or more. A hardwood pulp content of 50% by mass or more improves the smoothness of the release paper base paper surface. The hardwood pulp content 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.

[0020] Furthermore, from the viewpoint of smoothness, the mass ratio of hardwood pulp to the total amount of hardwood pulp and softwood pulp in the paper base material 11 is preferably greater than 50 mass%, more preferably 60 mass% or more, even more preferably 70 mass% or more, particularly preferably greater than 80 mass%, and most preferably 100 mass%.

[0021] 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.

[0022] 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).

[0023] 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.

[0024] 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.

[0025] - Beating degree - In the present invention, the beating degree of the pulp used in the paper base material 11 is 45°SR or less. By having the beating degree of the pulp beating degree of 45°SR or less, when the release paper base paper 10 is recovered after use to produce recycled paper, 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. The beating degree of the pulp used in the paper base material 11 is preferably 38°SR or less.

[0026] -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.

[0027] -Basic weight- The basis weight of the paper base material 11 is 35 g / m 2 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.

[0028] <Coat layer> The coating layer 12 contains clay and a water-soluble resin, and is formed on the paper substrate 11 to improve adhesion with the release agent layer.

[0029] -clay- Examples of clays contained in the coating layer 12 include kaolin, talc, bentonite, smectite, vermiculite, mica, chlorite, wood-bush clay, gairome clay, halloysite, and mica. These may be used alone or in combination of two or more. Among these, kaolin is more preferable.

[0030] -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.

[0031] 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.

[0032] 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.

[0033] -Mass ratio of clay to water-soluble resin- In the coating layer 12, the mass ratio of clay to water-soluble resin is 3:7 or more and 7:3 or less. By having the mass ratio of 3:7 or more and 7:3 or less, the release paper base paper 10 has good disintegration properties, and recycled paper can be produced satisfactorily. The mass ratio of clay to water-soluble resin is preferably 4:6 or more and 6:4 or less.

[0034] -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 clay and the water-soluble resin. This causes a problem of inhibiting the 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.

[0035] 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.

[0036] The surface coated with the coating layer 12 may be smoothed by a supercalender treatment. By performing the supercalender treatment, the effect of sealing and the effect of increasing rigidity are improved.

[0037] 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.

[0038] (Other configurations) A release agent layer may be provided on the coating layer 12. Examples of the release agent that forms 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 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 μm or more and 5 μm or less.

[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. In the examples, the term "parts" or "%" may be used, but unless otherwise specified, it means "parts by mass" or "% by mass". Furthermore, unless otherwise specified, each operation is 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) 25% by mass of softwood bleached kraft pulp (NBKP) and 75% by mass of hardwood bleached kraft pulp (LBKP) were mixed and beaten in water using the Shopper-Rigler method to a degree of beating of 38°SR, and then 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 coating was applied onto the coating layer so that the thickness of the coating was 3 μm, and the coating was dried and passed through a supercalender roll to form a coating layer, thereby obtaining a release paper base paper.

[0044] [Examples 2 and 3, Comparative Examples 1 and 2] 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 △ A small amount of undissociated material was observed ×: A large amount of undisintegrated material was observed.

[0048] (Magic Barrier) A straight line 1 to 3 mm wide and 20 cm long was drawn on the coating layer using a black oil-based marker (product name: ZEBRA Co., Ltd.), and when observed from the back side of the release paper base paper (the surface opposite the coating layer), whether the straight line was visible was evaluated according to the following criteria. <Evaluation criteria> ◎ No traces of magic marker are visible △ Magic marks are slightly visible × The markings on the marker are clearly visible and it is difficult to tell the difference between the front and back

[0049] [Table 1]

[0050] As shown in Table 1, Examples 1 to 3 were able to obtain good results in both disintegration property and magic barrier property. [Explanation of symbols]

[0051] 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 45° SR or less; the coating layer does not contain a water-insoluble resin, but contains clay and a water-soluble resin, the mass ratio of the clay to the water-soluble resin being 3:7 or more and 7:3 or less; Tightness: 0.95 g / m ３ The release paper base paper is as follows.

2. 2. The release paper base paper according to claim 1, wherein said clay is kaolin.

3. 2. The release paper base paper according to claim 1, wherein the water-soluble resin is polyvinyl alcohol.

4. Basis weight: 55g / m ２ The release paper base paper according to claim 1, which is as follows:

5. Tightness: 0.89 g / m ３ 0.95g / m or more ３ The release paper base paper according to claim 1, which is as follows:

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