Backup board and its manufacturing method

Abstract

To provide a backup board in which peeling adhesive tape hardly causes paper to be peeled off no matter which direction the adhesive tape is peeled off.SOLUTION: A backup board includes: two or more paper base materials; one or more adhesive layers made of a water-soluble adhesive that adheres the paper base materials; and one or more pigment coating layers on at least one surface. The pigment coating layer contains 0.1 pt.wt. to 30 pts.wt. of a water-soluble or water-dispersible binder per 100 pts.wt. of flat pigment with a ratio of 5 or more, and has a hardness of 75 or more as measured with a type D durometer according to JIS K6253.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a backup board that is placed under a workpiece during machining such as drilling, milling, grinding, etc., and a method for manufacturing the same. [Background technology]

[0002] During machining processes such as drilling, milling, and grinding, a backup board may be placed under the workpiece to prevent damage to the stage caused by a tool penetrating the workpiece and to improve machining accuracy. For example, drilling, one of the manufacturing processes for printed wiring boards, is generally performed with the entry board, multiple substrates that will become the printed wiring boards, and a backup board stacked in this order from the drill entry side. The backup board placed under the substrate prevents damage to the stage caused by a drill bit penetrating the substrate and reduces the occurrence of burrs in the drilled portion of the substrate. In this case, the entry board, workpiece (e.g., substrate), and backup board are integrated and bonded with adhesive tape to prevent misalignment during machining, and then machined. Furthermore, the backup board is first bonded to the workpiece on one side, and then flipped over and bonded to the other side.

[0003] The present inventors have proposed a recyclable, inexpensive backup board that is primarily made of paper (Patent Document 1). With the backup board described in Patent Document 1, the paper is less likely to peel off when the adhesive tape attached to it is peeled off from the main surface of the backup board. However, peeling the paper sometimes occurs when the adhesive tape is peeled off from the edge (side) surface of the backup board. If the peeling occurs deep in the paper, a large step will be created on the surface of the backup board. If the adhesive tape is peeled off after using one side of the backup board, resulting in a large step, and the backup board is then turned over for use, the other side with the step will be attached to the workpiece. This creates a gap between the workpiece and the backup board due to the step in the backup board, which can result in burrs and other defects during machining. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6961322 Summary of the Invention [Problem to be solved by the invention]

[0005] To provide a backup board on which paper is less likely to peel off even when an adhesive tape is peeled from any direction. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. A paper sheet having two or more sheets of paper substrate, an adhesive layer made of a water-soluble adhesive that adheres the paper substrates, and a pigment coating layer on at least one surface, the pigment coating layer contains 0.1 parts by weight or more and 30 parts by weight or less of a water-soluble or water-dispersible binder per 100 parts by weight of a flat pigment having an aspect ratio of 5 or more; A backup board characterized by having a hardness of 75 or more as measured with a type D durometer in accordance with JIS K6253. 2. The coating amount of the pigment coating layer is 4 g / m 2 The backup board according to 1. above is characterized by the above. 3. A backup board according to 1. or 2., characterized in that the Mohs hardness of the flat pigment is 5 or less. 4. The backup board according to 1. or 2., wherein the water-soluble or water-dispersible binder is a polyvinyl alcohol or a starch. [Effects of the Invention]

[0007] The backup board of the present invention has a pigment coating layer on at least one surface. This pigment coating layer is the weakest point in the thickness direction of the backup board, and when the adhesive tape is peeled off, the pigment coating layer breaks. Because the backup board of the present invention peels off at the pigment coating layer rather than the paper, the depth of the step that occurs when the adhesive tape is peeled off is very shallow, within the thickness of the pigment coating layer, and even when the surface with this step is bonded to a workpiece and machined, defects such as burrs are unlikely to occur. The backup board of the present invention has sufficient hardness and can be used as a substitute for conventionally used bakelite boards, fiberboards, aluminum metal plates, etc. The backup board of the present invention is less expensive than conventional bakelite boards, etc. The backup board of the present invention can be disintegrated, so it can be recycled as waste paper, reducing disposal costs and the burden on the environment. The backup board of the present invention, in which the flat pigment contained in the pigment coating layer has a Mohs hardness of 5 or less, can reduce tool wear. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below. The backup board of the present invention comprises two or more paper substrates, an adhesive layer made of a water-soluble adhesive that bonds the paper substrates, and a pigment coating layer on at least one surface, wherein the pigment coating layer contains 0.1 to 30 parts by weight of a water-soluble or water-dispersible binder per 100 parts by weight of flat pigment with an aspect ratio of 5 or more, and has a hardness of 75 or more as measured with a Type D durometer in accordance with JIS K6253. The backup board of the present invention is suitable for machining processes such as drilling, milling, and grinding, but is particularly suitable for drilling.

[0009] <Paper base material> In the present invention, the paper substrate is a sheet made of pulp, fillers, various auxiliaries, and the like. Pulp may be any of a variety of known pulps, including bleached softwood kraft pulp (NBKP), unbleached softwood kraft pulp (NUKP), bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), and sulfite pulp (SP) and other wood-based chemical pulps; ground pulp (GP), refiner ground pulp (RGP), stone ground pulp (SGP), chemi-ground pulp (CGP), semi-chemical pulp (SCP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP); non-wood pulp obtained from kenaf, bagasse, bamboo, hemp, straw, and the like; and recycled paper pulp obtained by removing the ink contained in recycled paper through a deinking process.

[0010] If foreign matter gets mixed into the paper base material, it can cause damage and wear to tools such as drills, so it is preferable to use chemical pulp such as LBKP or NBKP, which is less likely to get mixed in. Furthermore, because there is a risk of foreign matter getting mixed in, of the two or more paper base materials that make up the backup board of the present invention, at least the two outermost paper base materials preferably contain 1.0% by weight or less of recycled paper pulp relative to the total pulp, more preferably 0.5% by weight or less, and most preferably no recycled paper pulp is contained (blended).

[0011] The freeness (Canadian Standard Freeness (hereinafter also referred to as CSF)) of the pulp used is preferably 600 ml or less, more preferably 540 ml or less, and even more preferably 480 ml or less. Furthermore, as will be described in detail below in <Backup board manufacturing method>, particularly when no pressing process is performed during backup board manufacturing, the freeness of the pulp used is preferably 480 ml or less, more preferably 440 ml or less, and even more preferably 400 ml or less. When the paper base material uses multiple types of pulp, the multiple types of pulp may be beaten separately or mixed together. When beating separately, the freeness of each pulp is not particularly limited, but is adjusted so that the freeness of the pulp slurry after mixing the pulps satisfies the above conditions.

[0012] Examples of fillers that can be used include known fillers such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate; and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and hollow microparticles. In the backup board of the present invention, the paper base material does not need to contain filler, and in order to prevent wear of tools such as drills, it is preferable that the filler content of at least the two outermost paper base materials of the two or more paper base materials that make up the backup board of the present invention is 1.0% by weight or less, more preferably 0.5% by weight or less, and it is most preferable that no filler is contained (blended).

[0013] Examples of various auxiliaries include various internal sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA); various nonionic, cationic, and amphoteric retention aids, freeness improvers, paper strength improvers, various starches, polyacrylamide, urea resin, melamine resin, epoxy resin, polyamide resin, polyamine resin, polyethyleneimine, vegetable gum, polyvinyl alcohol, latex, polyethylene oxide, hydrophilic crosslinked polymer particle dispersions and derivatives or modified products thereof; basic aluminum compounds such as aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum chloride, and basic polyaluminum hydroxide; water-soluble aluminum compounds such as alumina sol that is easily decomposed in water; polyvalent metal compounds such as ferrous sulfate and ferric sulfate; silica sol, antifoaming agents, coloring dyes, fluorescent brighteners, pH adjusters, pitch control agents, and slime control agents, and these can be appropriately selected and used as needed.

[0014] The backup board of the present invention has two or more paper substrates, and the raw material, basis weight, density, thickness, etc. of each paper substrate may be the same or different. In the backup board of the present invention, at least one of the paper substrates used preferably has a pulp freeness (Canadian Standard Freeness) of 480 ml or less, more preferably 440 ml or less, and even more preferably 400 ml or less. A paper substrate with a low pulp freeness forms strong hydrogen bonds and is hard, which results in improved hardness of the backup board. The freeness is the Canadian Standard Freeness measured in accordance with JIS P8121 after disintegrating the paper substrate according to the method specified in JIS P8220-1. In the backup board of the present invention, it is more preferable that at least half of the paper substrates used satisfy the above freeness, and it is even more preferable that all of the paper substrates satisfy the above freeness.

[0015] If the pulp freeness at disintegration is not 480 ml or less for all paper base materials, the mixed pulp freeness at disintegration expressed by the following formula (1) is preferably 480 ml or less, more preferably 440 ml or less, and even more preferably 400 ml or less. Formula (1) Mixed deflocculation freeness = f1 × (g1 / G) + f2 × (g2 / G) + ... +fn×(gn / G) (where n represents the number of sheets of paper substrate, f1, f2, fn are the freeness of paper base materials 1 to n, respectively. g1, g2, gn are the basis weights of paper base materials 1 to n, respectively. G represents the sum of the basis weights of paper base materials 1 to n (G = g1 + g2 + + gn).

[0016] If the pulp freeness at disaggregation is not 480 ml or less for all paper base materials, the pulp freeness at disaggregation is preferably 600 ml or less for paper base materials having a pulp freeness at disaggregation exceeding 480 ml, more preferably 560 ml or less, and even more preferably 520 ml or less.

[0017] If the pulp freeness of all paper base materials is not 480 ml or less, the number of paper base materials with a pulp freeness exceeding 480 ml is preferably 2 or less, and more preferably 1. In particular, when three or more paper base materials are laminated together, it is preferable that half or more of the paper base materials have a pulp freeness of 480 ml or less, more preferably 65% ​​or more, and even more preferably 80% or more.

[0018] The paper substrate must have a basis weight of at least 150 g / m 2 It is preferable that the weight is 200 g / m or more. 2 More preferably, it is 250 g / m or more. 2 It is more preferable that the basis weight of all paper substrates is 150 g / m or more. 2If the basis weight is less than 650 g / m, the number of sheets of paper substrate necessary to form the backup board of the present invention will increase. 2 Preferably, it is 600 g / m or less. 2 More preferably, it is 550 g / m or less. 2 In the present invention, it is more preferable that at least half of the paper base materials used satisfy the above basis weight, and it is even more preferable that all of the paper base materials satisfy the above basis weight. Furthermore, when three or more paper substrates are laminated together, the ratio of the total basis weight of the paper substrates having a disaggregation freeness of 480 ml or less to the total basis weight of the paper substrates used is preferably 50% by weight or more, more preferably 65% ​​by weight or more, and even more preferably 80% by weight or more.

[0019] The paper substrate has a density of at least 0.7 g / cm 3 It is preferable that the concentration is 0.75 g / cm or more. 3 More preferably, it is 0.8 g / cm or more. 3 It is more preferable that the density is 1.2 g / cm or more. 3 Preferably, it is 1.15 g / cm or less. 3 More preferably, it is 1.1 g / cm or less. 3 It is even more preferable that: When the density of at least one of the paper substrates is within the above range, a backup board that satisfies the predetermined hardness is easily obtained. Furthermore, in the present invention, it is more preferable that at least half of the two or more paper substrates used satisfy the above density, and even more preferable that all of the paper substrates satisfy the above density.

[0020] The papermaking method and type of papermaking machine for the paper substrate are not particularly limited, and known manufacturing (papermaking) methods and papermaking machines can be selected, such as a Fourdrinier papermaking machine, a twin-wire papermaking machine, a cylinder papermaking machine, a gap former, a hybrid former (on-top former), etc., and a multilayer papermaking machine that combines these. Among these, it is preferable to use a single-layer papermaking machine. A multilayer paper substrate made using a multilayer papermaking machine may have weak interlayer strength. In addition, backup boards are sometimes used by attaching them to machine tool stages, workpieces, entry boards, etc. with adhesive tape, but multilayer paper substrates may peel from the joined parts when the adhesive tape is removed. The pH during papermaking may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking), and after papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper base. Furthermore, water squeezing, drying, size pressing, calendering, etc. after wire parting can be performed by methods known in the papermaking field.

[0021] The paper substrate is preferably subjected to a calendering or supercalendering process, which strongly crushes the paper substrate and improves its hardness, making it easier to make the backup board even harder.

[0022] <Water-soluble adhesive> The water-soluble adhesive used to bond the paper substrate is not particularly limited, and examples thereof include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and terminally alkyl-modified polyvinyl alcohol; starches such as starch, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, etherified starch (e.g., hydroxyethylated starch), and cationized starch; and cellulose ethers and their derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and acetyl cellulose. Also usable are hot-melt water-soluble adhesives that can be subjected to heat treatments such as heat sealing. Because the backup board of the present invention uses a water-soluble adhesive to bond the paper substrate, it is easily disintegrated and can be recycled as waste paper.

[0023] <Pigment coating layer> The backup board of the present invention has, on at least one side, a pigment coating layer containing 0.1 to 30 parts by weight of a water-soluble or water-dispersible binder (hereinafter also referred to as binder) per 100 parts by weight of a flat pigment having an aspect ratio of 5 or more. The pigment coating layer can also be provided on both sides of the backup board. The pigment coating layer contains flat pigments and has a low binder content relative to the flat pigments. Therefore, in the pigment coating layer, the flat pigments are laid out so that their flat surfaces are approximately parallel to the main surface of the backup board, but the bonding between the flat pigments is weak due to the small amount of binder. As a result, the pigment coating layer of the present invention has weak bonding between the flat pigments stacked in the thickness direction, which makes it the area with the weakest strength in the thickness direction of the backup board, and therefore the area that will break when the adhesive tape is peeled off.

[0024] Flat pigments The aspect ratio (long diameter / thickness) of the flat pigment is 5 or more. When the aspect ratio of the flat pigment is 5 or more, the flat faces of the flat pigment are arranged approximately parallel to the main faces, and the flat pigment is likely to exist in a layered manner in the thickness direction. The aspect ratio of the flat pigment is preferably 8 or more, and more preferably 10 or more. There is no particular upper limit to this aspect ratio, but it is about 200 or less. The 50% volume average particle size (D50) of the flat pigment (hereinafter also referred to as "average particle size") is not particularly limited, but is preferably 5 μm or more. From the viewpoint of preventing tool wear, the Mohs hardness of the flat pigment is preferably 5 or less. The Mohs hardness of the flat pigment is more preferably 4 or less, and even more preferably 3 or less.

[0025] Any flat pigment with an aspect ratio (long diameter / thickness) of 5 or greater can be used without particular limitation, and examples thereof include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as solid, hollow, and core-shell organic pigments. One or more flat pigments can be used, or two or more can be mixed together. When two or more flat pigments are used, the aspect ratios, average particle sizes, and Mohs hardnesses of the individual flat pigments can be the same or different.

[0026] Water-soluble or water-dispersible binder The water-soluble or water-dispersible binder binds the flat pigment particles together. As the water-soluble binder, one or a mixture of two or more of the polyvinyl alcohols, starches, cellulose ethers and derivatives thereof listed above as the water-soluble adhesives can be used. As the water-dispersible binder, styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, acrylic emulsion, vinyl acetate emulsion, etc. can be used alone or in combination of two or more. Among these, water-soluble binders are preferred, and polyvinyl alcohols or starches are more preferred, since they are easy to disintegrate and can be easily recycled as waste paper.

[0027] In the present invention, the pigment coating layer contains 0.1 to 30 parts by weight of binder per 100 parts by weight of flat pigment. The pigment coating layer of the present invention has a lower binder content than typical pigment coating layers. As a result, the pigment coating layer of the present invention has weaker bonds between the flat pigments, resulting in fractures in the thickness direction. A lower amount of binder per 100 parts by weight of flat pigment is preferable because it weakens the bonds between the flat pigments. It is preferably 25 parts by weight or less, and more preferably 20 parts by weight or less. However, the strength of the binding force between the flat pigments varies depending on the type of binder used. For example, in the case of polyvinyl alcohols, it is preferable to use approximately 0.1 to 10 parts by weight of polyvinyl alcohol per 100 parts by weight of flat pigment, more preferably 0.5 parts by weight or more, even more preferably 1 part by weight or more, and more preferably 7 parts by weight or less, and even more preferably 4 parts by weight or less. In the case of starches, it is preferable to use about 1 to 20 parts by weight of starch per 100 parts by weight of flat pigment, more preferably 2.5 parts by weight or more, even more preferably 5 parts by weight or more, and more preferably 16 parts by weight or less, even more preferably 12 parts by weight or less.

[0028] In addition to the flat pigment and binder, the pigment coating layer may contain additives such as surfactants, preservatives, antifoaming agents, and dyes. The pigment coating layer may also contain non-flat pigments with an aspect ratio of less than 5. In this case, if the amount of non-flat pigments added is large, the alignment of the flat pigments will be disrupted. Therefore, the proportion of the flat pigments to the total pigments is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass (excluding the non-flat pigments). Furthermore, the Mohs hardness of the non-flat pigments is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.

[0029] The coating weight of the pigment coating layer is 4 g / m2 in solids. 2 A coating amount of 5 g / m or more is preferable because it has a sufficient thickness as a pigment coating layer and can adhere to the adhesive tape at its edge (side) and become the starting point of destruction. 2 The upper limit of the coating amount is not particularly limited, but is preferably 20 g / m 2 The effect will be almost the same even if the amount is increased further, but the cost of raw materials, drying costs, etc. will increase.

[0030] <Backup board> The backup board of the present invention has a hardness of 75 or more as measured with a Type D durometer in accordance with JIS K6253. The backup board of the present invention has sufficient hardness and is less prone to bending and denting during processing, allowing high processing accuracy to be maintained, and for example, the generation of burrs during drilling can be reduced. The hardness of the backup board of the present invention is preferably 77 or more, and more preferably 79 or more.

[0031] The thickness of the backup board can be set depending on the type of machine tool, processing dimensions, etc., but for example, when used for drilling printed wiring boards, the thickness of the backup board is preferably 1.0 mm or more, more preferably 1.2 mm or more, and even more preferably 1.4 mm or more. The thickness and number of sheets of paper base material that make up the backup board can be selected depending on the desired thickness of the backup board.

[0032] The density of the backup board is 0.9g / cm 3 It is preferable that the concentration is 0.92 g / cm or more. 3 More preferably, it is 0.94 g / cm or more. 3 It is more preferable that the density of the backup board is 0.9 g / cm or more. 3 As a result, deformation of the backup board during processing is reduced, and high processing accuracy can be maintained.

[0033] The backup board of the present invention has a paper base material, an adhesive layer made of a water-soluble adhesive, and a pigment coating layer using a water-soluble or water-dispersible resin as a binder, and therefore can be easily disintegrated in water to form a slurry. As a result, the backup board of the present invention can be recycled as waste paper, which reduces the burden on the environment and reduces processing costs.

[0034] <Backup board manufacturing method> In the backup board of the present invention, the method for bonding paper substrates with a water-soluble adhesive is not particularly limited, and can be carried out by bonding paper substrates together with a water-soluble adhesive according to a conventional method. Pressing can be carried out before or after the adhesive has hardened. In this specification, pressing means a pressure of 15 kg / cm. 2 For example, a pressure of 15 kg / cm is applied to bond a paper substrate to a water-soluble adhesive. 2 Pressing processes that apply less pressure than this are not included in the press process.

[0035] When no pressing treatment is performed, the freeness of the pulp constituting the paper base material is preferably low. Specifically, it is preferred that the freeness (Canadian standard freeness) of the pulp of all of the paper base materials is 600 ml or less, and that the freeness of the pulp of at least one sheet of paper base material is 480 ml or less. For paper substrates with a pulp freeness of 480 ml or less, the freeness is preferably 440 ml or less, and even more preferably 400 ml or less. Furthermore, for paper substrates with a pulp freeness of more than 480 ml, the freeness is preferably 560 ml or less, and even more preferably 520 ml or less. Pulp with a low freeness forms stronger hydrogen bonds, resulting in a harder paper substrate, making it easier to obtain a hard backup board without pressing. In the backup board of the present invention, it is more preferable that at least half of the two or more paper base materials used have a pulp freeness of 480 ml or less, and it is even more preferable that all of the paper base materials have a pulp freeness of 480 ml or less.

[0036] When not all of the paper base materials have a pulp freeness of 480 ml or less, the number of paper base materials having a pulp freeness of more than 480 ml is preferably two or less, and more preferably one. In particular, when three or more paper substrates are laminated together, it is preferable that half or more of the paper substrates have a pulp freeness of 480 ml or less, more preferably 65% ​​or more, and even more preferably 80% or more. Furthermore, when three or more paper substrates are laminated together, the ratio of the total basis weight of the paper substrates having a pulp freeness of 480 ml or less to the total basis weight of the paper substrates used is preferably 50% by weight or more, more preferably 65% ​​by weight or more, and even more preferably 80% by weight or more.

[0037] When performing press processing, the press pressure is 15 kg / cm as mentioned above. 2 The pressing pressure is 40 kg / cm 2 It is preferable that the resistance is 60 kg / cm or more. 2The above is more preferable. By performing the pressing process, it becomes easier to make the backup board higher in density and hardness. This is presumably because the pulp is crushed and the water-soluble adhesive penetrates into the gaps between the pulp particles. When press processing is performed, sufficient hardness can be imparted to the backup board regardless of the hardness of the paper base material itself, so the freeness of the pulp of the paper base material may be about 600 ml or less, more preferably 560 ml or less, and even more preferably 520 ml or less. When press processing is performed, the density of the backup board is 0.9 g / cm 3 It is preferable that the concentration is 1.0 g / cm or more. 3 More preferably, it is 1.05 g / cm or more. 3 More preferably, it is equal to or greater than this. The pressing treatment is preferably carried out under heating. Heating during the pressing treatment can dry the water-soluble adhesive, and in the case of a hot-melt water-soluble adhesive, melt the adhesive to firmly bond the materials.

[0038] The method for providing a pigment coating layer on at least one surface of the backup board is not particularly limited, and any conventional coating method known in the art, such as a blade coater, bar coater, air knife coater, curtain coater, spray coater, roll coater, reverse roll coater, size press coater, or gate roll coater, can be used. From the viewpoint of coatability, it is preferable to provide the pigment coating layer on the paper substrate in advance, and then to bond the paper substrate with the pigment coating layer on the outermost surface using a water-soluble adhesive. [Example]

[0039] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0040] ·Create a backup board Using raw material with a pulp freeness of 397 ml, the paper has a basis weight of 298.2 g / m 2The base paper used was a 299 μm thick base paper. This base paper did not contain recycled paper pulp or fillers. "Example 1" Five sheets of paper substrate were prepared, and two of them were coated with a water-based coating solution (solid content 30%) containing 10.0 parts of a water-soluble starch binder (product name: MS-4600, manufactured by Nippon Shokuhin Kako Co., Ltd.) to 100 parts of a flat pigment (kaolin, manufactured by Imerys Co., Ltd., product name: Capim DG, aspect ratio 11-12, Mohs hardness 1.5-2), with the target coating weight being 10.0 g / m2 in solid content. 2 The coating was then air-dried to obtain a pigment coating layer consisting of the water-soluble resin and the pigment. Next, five paper substrates were stacked together with the two paper substrates with pigment coating layers positioned on the outermost surface, and a water-soluble adhesive (manufactured by Kuraray Co., Ltd., product name: Kuraray Poval 28-98, target solid weight per adhesive layer: 2.5 g / m) was applied. 2 ) and then air-dried without pressing to obtain a backup board.

[0041] "Example 2" The target coating weight of the pigment coating layer is 7g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 1, except that: "Example 3" A backup board was obtained in the same manner as in Example 1, except that an aqueous coating liquid (solid content 30%) containing 7.5 parts of water-soluble binder added to 100 parts of flat pigment was applied. Example 4 The target coating weight of the pigment coating layer is 7g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 3, except that: "Example 5" A backup board was obtained in the same manner as in Example 1, except that an aqueous coating liquid (solid content 30%) containing 2.5 parts of water-soluble binder added to 100 parts of flat pigment was applied. "Example 6" The target coating weight of the pigment coating layer is 7g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 5, except that:

[0042] "Example 7" A backup board was obtained in the same manner as in Example 1, except that polyvinyl alcohols (manufactured by Kuraray Co., Ltd., product name: Kuraray Poval 28-98) were used as the water-soluble binder, and an aqueous coating liquid (solid content 30%) containing 2.0 parts of water-soluble binder was applied to 100 parts of flat pigment. "Example 8" The target coating weight of the pigment coating layer is 7g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 7, except that: "Example 9" The target coating weight of the pigment coating layer is 5g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 7, except that: "Example 10" A backup board was obtained in the same manner as in Example 7, except that an aqueous coating liquid (solid content 30%) containing 0.5 parts of water-soluble binder added to 100 parts of flat pigment was applied. "Example 11" The target coating weight of the pigment coating layer is 7g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 10, except that:

[0043] "Comparative Example 1" A backup board was obtained in the same manner as in Example 1, except that no pigment coating layer was provided. "Comparative Example 2" A water-based coating solution (30% solids) containing only a water-soluble starch binder (manufactured by Sanwa Starch Industries Co., Ltd., product name: PLV-500) without any flat pigments was used, with the target coating weight of 10.0 g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 1, except that the coating was carried out so that the thickness of the backing board was 1 / 4 of the thickness of the backing board. "Comparative Example 3" The water-based coating solution (10% solids) does not contain any flat pigments and contains only a water-soluble binder, which is a polyvinyl alcohol (Kuraray Co., Ltd., product name: Kuraray Poval 28-98), with a target coating weight of 10.0 g / m2 in solids. 2 A backup board was obtained in the same manner as in Example 1, except that the coating was performed as follows.

[0044] The obtained backup boards were evaluated by the following evaluation methods, and the results are shown in Table 1. <Evaluation method> ·Basic weight Measurement was carried out in accordance with JIS P8124. ·Paper thickness Measurement was carried out in accordance with JIS P8118. ·density It was calculated from the basis weight and paper thickness in accordance with JIS P8124 and JIS P8118.

[0045] ·hardness The prepared backup board was conditioned for at least 24 hours in an environment of 23°C and 50% RH, and then measurements were taken at 10 random locations using a Type D durometer (manufactured by Nishitokyo Seimitsu Co., Ltd., product number: WR-105D) in accordance with JIS K6253, and the average value was calculated.

[0046] Paper peeling Adhesive tape (Nichiban Co., Ltd., industrial cellophane tape No. 430 colored tape, 15 mm wide) was cut into 3 cm lengths. A total of eight pieces of tape were attached, four in the MD direction and four in the CD direction, so that the adhesive tape wrapped around the sides of the backup board. The adhesive strength of the adhesive tape increases over time and reaches saturation in about two weeks, so the tape was left in an environment of 23°C and 50% humidity for two weeks. After leaving it for two weeks, each adhesive tape was vigorously peeled off from the main surface (two in the MD and two in the CD), and the remaining four from the edge, and the number of tapes that did not peel off was evaluated. In other words, if no peeling occurred, the rating was 4, which is the best, and if peeling occurred on all four tapes, the rating was 0, which is the worst.

[0047] [Table 1]

[0048] None of the backup boards having a pigment coating layer according to the present invention obtained in the examples showed peeling. After peeling, the backup boards had a step in the pigment coating layer because part of the pigment coating layer had adhered to the adhesive tape and peeled off, but the depth of the step was very shallow, within the thickness of the pigment coating layer. In contrast, the backup board without a coating layer obtained in Comparative Example 1 showed peeling whether peeled from the main surface or the edge surface. Furthermore, the backup boards with a coating layer containing only a water-soluble binder obtained in Comparative Examples 2 and 3 did not show peeling when the adhesive tape was peeled from the main surface, but did show peeling when peeled from the edge surface. After peeling, the backup boards had large steps at the locations where the peeling occurred.

Claims

1. The paper sheet has two or more paper substrates, an adhesive layer made of a water-soluble adhesive that bonds the paper substrates, and a pigment coating layer on at least one surface, the pigment coating layer contains 0.1 parts by weight or more and 30 parts by weight or less of a water-soluble or water-dispersible binder per 100 parts by weight of a flat pigment having an aspect ratio of 5 or more; A backup board having a hardness of 75 or more as measured with a type D durometer in accordance with JIS K6253.

2. The coating amount of the pigment coating layer is 4 g / m ２ 2. The backup board according to claim 1, wherein:

3. 3. The backup board according to claim 1, wherein the flat pigment has a Mohs hardness of 5 or less.

4. 3. The backup board according to claim 1, wherein the water-soluble or water-dispersible binder is a polyvinyl alcohol or a starch.

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