Release paper base sheet and release paper

Abstract

The present invention addresses the problem of providing: a release paper base sheet that has light transmissivity; and a release paper having said release paper base sheet. The present invention provides, as a means for solving said problem: a release paper base sheet which comprises a base sheet and a sealing layer on at least one surface of the base sheet, and which has a density of 0.85-1.05 g / cm3, and an opacity of 45-65% in accordance with JIS P 8149:2000; and a release paper base sheet production method which comprises a step for coating at least one surface of the base sheet with a coating liquid for a sealing layer by using an on-machine coater, and with which a release paper base sheet having a density of 0.85-1.05 g / cm3 and an opacity of 45-65% in accordance with JIS P 8149:2000 is obtained.<sp / > <sp / >

Description

Release paper base paper and release paper

[0001] The present invention relates to a base paper for release paper used in release papers for adhesive labels and the like, and to a release paper obtained by providing a release agent layer on this base paper for release paper.

[0002] Release paper is attached to the adhesive surface of adhesive labels, adhesive stickers, adhesive tapes, double-sided tapes, etc. to protect the adhesive surface, prevent a decrease in adhesive strength, etc. The release paper has a release agent layer on the surface that contacts the adhesive surface so that it can be easily peeled off from the adhesive surface. The release paper may be required to have a certain degree of light transparency, for example, when it is attached using a labeler equipped with a transmission position detector that transmits light after attachment to inspect the number of contents and the presence or absence of foreign matter. As such light-transmitting release paper, it has been proposed to use light-transmitting paper such as glassine paper or semi-glassine paper as the base paper (Patent Documents 1 and 2, etc.).

[0003] Glassine paper and semi-glassine paper have poor disintegration properties because the pulp is highly beaten and the fibers are firmly bonded together through resin coating, supercalendering, and other processes. Even if the paper is disintegrated through intensified mechanical processing, the pulp is highly beaten and damaged, and the strong mechanical processing during disintegration further accelerates the damage to the pulp, making it difficult to reuse the paper as a papermaking material. Furthermore, release paper is sometimes subjected to a humidification treatment to correct curling during adhesive label processing, and may also be heated and dried after being coated with a release agent. Glassine paper and semi-glassine paper have a problem in that they are prone to wrinkling when subjected to humidification or heat treatment, because many thin, branched fibers are bonded together through hydrogen bonds.

[0004] Japanese Patent Laid-Open No. 9-272847 Japanese Patent Laid-Open No. 2005-314844

[0005] An object of the present invention is to provide a base paper for release paper having optical transparency, and a release paper having this base paper for release paper.

[0006] The means for solving the problems of the present invention are as follows: 1. A paper sheet having a base paper and a filling layer on at least one surface of the base paper, and a density of 0.85 g / cm ３ 1.05g / cm or more ３or less, and characterized in that the opacity in accordance with JIS P 8149:2000 is 45% to 65%. 2. The release paper base paper according to 1., characterized in that the filling layer contains a pigment and an adhesive in a mass ratio (pigment / adhesive: dry mass) of 60 / 40 to 40 / 60. 3. The release paper base paper according to 2., characterized in that the pigment has a volume 50% average particle size of 1.0 μm to 7.0 μm. 4. The release paper base paper according to 2. or 3., characterized in that the adhesive contains at least a starch-based compound and a synthetic resin latex, and the ratio of the synthetic resin latex to 100 parts by mass of the pigment is 70 parts by mass to 130 parts by mass. 5. The release paper base paper according to 4., characterized in that the synthetic resin latex is a styrene-butadiene copolymer latex. 6. 7. The release paper base paper according to any one of 1. to 5., characterized in that the shrinkage rate in the transverse direction after immersion in water for 1 hour is 3.0% or less. 8. The release paper base paper has a Cobb water absorbency (30 seconds) of 10 g / m or less, measured in accordance with ISO 535:1991. ２ 30g / m or more ２ 8. The release paper base paper according to any one of 1. to 6., characterized in that the Oken smoothness of the surface of the sealing layer in accordance with JIS P 8155:2010 is 300 seconds or more and 1500 seconds or less. 9. The coating amount of the sealing layer is 1 g / m2 in terms of dry mass per side. ２ 5g / m or more ２ 10. The release paper base paper according to any one of 1. to 8., characterized in that the basis weight of the release paper base paper is 30 g / m or less. ２ 60g / m or more ２11. The release paper base paper according to any one of 1. to 10., characterized in that the ash content of the release paper base paper according to JIS P 8251:2003 is 1% or more and 8% or less. 12. A release paper characterized in that the release paper base paper according to any one of 1. to 11. has a release agent layer on the filling layer. 13. The release paper according to 12., characterized in that the ΔE (after test - before test) of the release paper before and after a silicone holdout test is 10 or less. 14. A method for producing a release paper base paper comprising the steps of: applying a coating liquid for a filling layer to at least one surface of a base paper by an on-machine coater; and ３ 1.05g / cm or more ３ and an opacity in accordance with JIS P 8149:2000 of 45% to 65%.

[0007] The release paper base paper of the present invention has optical transparency and can be suitably used in applications requiring optical transparency. By providing a release agent layer on the sealing layer, the release paper base paper of the present invention can obtain a release paper with practically usable adhesion, releasability, and durability. Since the pulp constituting the base paper of the present invention is not highly beaten, it can be disintegrated and recycled as a papermaking material, and wrinkles are less likely to occur even when subjected to humidification or heat treatment. The release paper base paper of the present invention can exhibit sufficient sealing properties even when the coating weight of the sealing layer is small. In particular, when the coating liquid for the sealing layer is applied using an on-machine coater, a uniform release agent layer with excellent sealing properties can be formed even when the coating weight of the sealing layer is small.

[0008] The base paper for release paper of the present invention comprises a base paper and a sealing layer on at least one surface of the base paper, and has a density of 0.85 g / cm ３ 1.05g / cm or more ３ and the opacity according to JIS P 8149:2000 is 45% or more and 65% or less. In this specification, the expression "A to B (A and B are numerical values ​​or ratios)" means a numerical range including the values ​​of A and B.

[0009] "Base Paper" In the present invention, the base paper is a sheet comprising papermaking fibers, fillers, various auxiliaries, and the like. It is preferable to use wood pulp as the papermaking fibers. Examples of wood pulp include chemical pulps such as softwood kraft pulp, hardwood kraft pulp, and sulfite pulp; mechanical pulps such as thermomechanical pulp, stone-grind pulp, and refiner-grind pulp; and recycled pulp obtained from newspaper, coated paper, and fine paper. One or more of these wood pulps can be used in combination. If necessary, one or more fibrous materials other than cellulose fibers, such as non-wood pulp from kenaf, hemp, or bamboo, glass fiber, or polyethylene fiber, can be blended. It is preferable to include softwood kraft pulp, as this makes it difficult for the coating liquid for the filling layer to penetrate into the resulting base paper, facilitating the formation of a dense filling layer. Furthermore, when the freeness of the papermaking fiber is reduced, the transparency of the obtained base paper increases and the coating solution for the filling layer becomes less likely to penetrate, making it easier to form a dense filling layer; however, since the disintegration property decreases, the freeness of the papermaking fiber (Canadian Standard Freeness: CSF) is preferably 220 ml or more and 500 ml or less, and more preferably 240 ml or more and 450 ml or less.

[0010] The base paper of the present invention can contain a filler. Examples of fillers that can be used include known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, zeolite, and synthetic resin fillers. In the present invention, the filler is an optional component, and the base paper may be free of fillers. The incorporation of a filler improves the smoothness of the base paper, but reduces transparency. Since the release paper base paper of the present invention has transparency, the filler content in the base paper is preferably low, preferably 10% by mass or less, more preferably 6% by mass or less, even more preferably 3% by mass or less, even more preferably 2% by mass or less, even more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less, even more preferably 0.1% by mass or less, and most preferably 0% by mass (none).

[0011] As the auxiliary, aluminum sulfate and various anionic, cationic, nonionic, or amphoteric retention aids, drainage aids, paper strength enhancers, internal sizing agents, and other internal papermaking aids can be used as needed. When using an internal sizing agent, it is preferable to use a rosin-based sizing agent, which exhibits a relatively slow sizing effect, because this allows the paint to penetrate into the base paper when the filling layer is applied, making it easier to achieve high transparency. Furthermore, dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents, and the like can also be added as needed.

[0012] The basis weight of the base paper is not particularly limited, but is preferably 25 g / m ２ More than 59g / m ２ A low basis weight is desirable for the release paper from the viewpoint of reducing waste and improving transportation costs. Therefore, the basis weight of the base paper is preferably 55 g / m or less. ２ More preferably, 50 g / m or less ２ On the other hand, if the basis weight is too low, wrinkles and paper breaks tend to occur during processing, and the stiffness weakens, making the paper less easy to handle. Therefore, the basis weight of the base paper is set to 30 g / m ２ More preferably, 35 g / m or more ２ The above is even more preferable.

[0013] The method for producing the base paper (papermaking) is not particularly limited, and the base paper can be produced by acidic papermaking, neutral papermaking, or alkaline papermaking using a known Fourdrinier former, on-top hybrid former, gap former machine, etc. The base paper may be composed of one layer or two or more layers.

[0014] Furthermore, the surface of the base paper can be treated with various chemicals. Examples of chemicals that can be used include polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water retention agents, thickeners, and lubricants, and these can be used alone or in combination of two or more. However, from the viewpoint of transparency, it is preferable not to coat the surface of the base paper with chemicals. The method for treating the surface of the base paper is not particularly limited, and known coating devices such as a rod metering size press, a pond-type size press, a gate roll coater, a spray coater, a blade coater, and a curtain coater can be used. Calendering is preferred to uniformly apply the sealing layer.

[0015] "Sealing Layer" The sealing layer is provided on at least one side of the base paper. While sealing layers can be provided on both sides of the base paper, providing one on only one side is preferred from the viewpoint of transparency. However, when using the base paper as a release paper base for double-sided tape, sealing layers are provided on both sides of the base paper. There are no particular restrictions on the sealing layer as long as it can prevent the penetration of the release agent. However, from the viewpoint of preventing the penetration of the release agent, it preferably contains a pigment and an adhesive, and the mass ratio of the pigment to the adhesive (pigment / adhesive, dry mass, total 100) is more preferably 60 / 40 to 40 / 60. If the pigment exceeds 60% in this mass ratio, light transmittance may decrease, while if the pigment is less than 40%, roll contamination and winding blocking are likely to occur. This mass ratio of the pigment to the adhesive is more preferably 58 / 42 to 42 / 58, and even more preferably 56 / 44 to 44 / 56. The filling layer may also contain various auxiliaries such as CNF, MFC, dispersant, water-resistant agent, lubricant, antifoaming agent, thickener, water retention agent, crosslinking agent, surfactant, preservative, dye, fluorescent dye, etc., within a range that does not impair the effects of the present invention. When filling layers are provided on both sides, the compositions of the coating liquids for forming the respective filling layers may be the same or different.

[0016] The pigment is not particularly limited, and pigments commonly used in papermaking can be used. For example, inorganic pigments such as kaolin, engineered kaolin, clay, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, aluminum hydroxide, mica, illite, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as solid, hollow, or core-shell organic pigments can be used alone or in combination of two or more.

[0017] The pigment preferably has a volume 50% average particle size (D50, median size, hereinafter also referred to as "average particle size") of 1.0 μm or more and 7.0 μm or less, measured by a laser diffraction / scattering method. If the average particle size of the pigment is less than 1.0 μm, the gaps between the fibers on the surface of the base paper can be filled, but the specific surface area of ​​the pigment is large, making it impossible for the adhesive to sufficiently fill the gaps between the pigments, resulting in an increase in fine gaps and possibly a deterioration in the sealing ability to prevent the penetration of the release agent. On the other hand, if the average particle size of the pigment exceeds 7.0 μm, the unevenness of the surface of the sealing layer increases, increasing the amount of release agent required to cover the surface of the sealing layer, and since the release agent is expensive, the cost increases. The average particle size of the pigment is more preferably 2.0 μm or more, even more preferably 3.0 μm or more, and more preferably 6.0 μm or less, even more preferably 5.0 μm or less. When two or more inorganic pigments are contained, it is preferable that the average particle size of at least one of the inorganic pigments is within the above-mentioned range, and the proportion of the inorganic pigments satisfying this average particle size relative to the total inorganic pigments is preferably 50% by mass or more, and more preferably 70% by mass or more. Examples of measuring devices for the laser diffraction / scattering method include the particle size distribution measuring device "Partica" manufactured by Horiba, Ltd. and the particle size distribution measuring device "MASTER SIZER S" manufactured by Malvern Instruments, Ltd.

[0018] From the viewpoint of improving filling performance, it is preferable that the inorganic pigment has an aspect ratio of 5 or more. The aspect ratio of the inorganic pigment is more preferably 8 or more, and even more preferably 10 or more. The upper limit of the aspect ratio of the inorganic pigment is not particularly limited, but is, for example, about 120 or less. When two or more inorganic pigments are contained, it is preferable that the aspect ratio of at least one of them is within the above-mentioned numerical range, and the proportion of inorganic pigments satisfying this aspect ratio relative to the total inorganic pigments is preferably 50% by mass or more, more preferably 70% by mass or more. The aspect ratio can be calculated using measurements obtained with a particle size analyzer using the calculation method described in "Basic Research on the Relationship between Coating Pigment Properties and Coated Paper Quality" in Paper and Pulp Technology Journal, Vol. 65, No. 12.

[0019] The adhesive can be any adhesive capable of adhering pigments, base paper, etc., and can be one or more of the following: starch-based compounds, synthetic resin latex, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and ethylene copolymer polyvinyl alcohol, proteins such as casein, soy protein, and synthetic protein, cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose, and water-soluble resins such as polyvinylpyrrolidone and sodium alginate. Of these, it is preferable to use a starch-based compound in combination with a synthetic resin latex in terms of sealing properties, coating film strength, etc.

[0020] Starch-based compounds are mainly blended to increase the water retention capacity of the paint and improve the sealing properties. Examples of starch-based compounds that can be used include starches such as starch, oxidized starch, hydroxyesterified starch (HES), phosphate ester starch, esterified starch, cationized starch, and urea phosphate esterified starch, as well as dextrin obtained by hydrolyzing starch.

[0021] The synthetic resin latex is not particularly limited, and various copolymer latexes such as styrene-butadiene copolymers, styrene-acrylic copolymers, ethylene-vinyl acetate copolymers, butadiene-methyl methacrylate copolymers, vinyl acetate-butyl acrylate copolymers, maleic anhydride copolymers, and acrylic acid-methyl methacrylate copolymers can be used, and one or more can be used in combination. Among these, it is preferable to use a styrene-butadiene copolymer latex, which has excellent sealing properties and surface strength for silicone resins. Furthermore, the synthetic resin latex preferably has an average particle size of 100 μm or more, and more preferably 150 μm or more, as measured by dynamic light scattering (photon correlation spectroscopy). An example of a measuring device using dynamic light scattering (photon correlation spectroscopy) is the "FPAR-1000" manufactured by Otsuka Electronics Co., Ltd.

[0022] The glass transition temperature (Tg) of the synthetic resin latex is preferably -20°C or higher and 30°C or lower. If the Tg of the synthetic resin latex is lower than -20°C, the filling layer becomes too soft and is easily scratched, and the uniformity of the release agent layer provided on the filling layer may decrease. If the Tg exceeds 30°C, the uniformity of the filling layer may decrease, and the uniformity of the release agent layer provided on the filling layer may also decrease. In this specification, the glass transition temperature means the midpoint glass transition temperature measured in accordance with JIS K 7121-1987.

[0023] In the filling layer, the ratio of the synthetic resin latex to 100 parts by mass of the pigment is preferably 70 parts by mass or more and 130 parts by mass or less. If the ratio is less than 70 parts by mass, the components required to fill the interfiber voids may be insufficient, resulting in reduced transparency and insufficient filling ability. On the other hand, if the ratio of this synthetic resin latex exceeds 130 parts by mass, the pulp's disintegration properties may be reduced, making recycling difficult. Furthermore, many synthetic resin latexes contain curing inhibitors for addition-curing release agents, which may cause a decrease in adhesion (durability) with the release agent over time or increase the amount of heat required to cure the release agent. The ratio of this synthetic resin latex is more preferably 72 parts by mass or more, even more preferably 75 parts by mass or more, even more preferably 77 parts by mass or more, even more preferably 80 parts by mass or more, and more preferably 125 parts by mass or less, even more preferably 120 parts by mass or less, even more preferably 115 parts by mass or less, and even more preferably 110 parts by mass or less.

[0024] The coating method for the sealing layer is not particularly limited, and the coating can be carried out using a known coating device and coating system. Examples of coating devices include a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a gravure coater, a spray coater, a size press coater, and a gate roll coater. As the coating system, a water-based coating using water as a medium is preferred. In the present invention, the dehydration amount of the coating solution for the sealing layer relative to the base paper used is 20 g / m. ２ 60g / m or more ２ It is preferable that the dehydration amount is 20 g / m or less. The smaller this value of the dehydration amount, the less the coating liquid is absorbed into the paper. The smaller the value of the dehydration amount and the less the penetration of the coating liquid into the base paper, the more effective the sealing layer will be. However, if the penetration into the base paper is too little, the transparency will not increase, the disintegration property will also decrease, and the stiffness of the base paper itself will increase, making it more likely to develop creases during processing. ２ 60g / m or more ２ By satisfying the above conditions, it becomes easy to form a base paper for release paper that has an excellent balance of sealing properties, transparency, releasability, stiffness, etc.

[0025] In the present invention, coating is preferably performed using an on-machine coater in which a papermaking machine and a coating device are integrated. When coating is performed using an off-machine coater in which the papermaking machine and the coating device are separate, the base paper is first made on the papermaking machine, then wound up onto a reel, and then the reel is again subjected to coating by the off-machine coater. However, coating using an on-machine coater eliminates the need to wind up the base paper and then subject it to coating, improving production efficiency. Furthermore, on-machine coaters contain approximately 5% by mass of moisture even after drying (before coating). Because internal sizing agents exhibit sizing properties after drying, on-machine coaters can coat the base paper before the effects of the internal sizing agents contained in the base paper are exerted. This allows the coating material for forming the filling layer to easily penetrate into the base paper, improving transparency. On the other hand, coating using an on-machine coater requires that the coating speed be synchronized with the papermaking speed of the papermaking machine, making it more difficult to adjust the coating amount than coating using an off-machine coater, which does not require synchronization. The sealing layer of the present invention has high uniformity and good sealing properties, even when the coating amount is small, and therefore, it is easy to satisfy the desired performance even when coated by an on-machine coater. As a method for drying the sealing layer, for example, a conventional method such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, or a cylinder dryer is used.

[0026] The coating amount of the sealing layer is 1 g / m2 in dry mass per side. ２ 5g / m or more ２ It is preferable that the coating amount is 1 g / m or less. ２ If the coating amount is less than 5 g / m, it may be difficult for the resulting sealing layer to prevent the penetration of the coating liquid for the release agent layer. ２ If the coating amount of the sealing layer exceeds 2 g / m2 in terms of dry mass per side, the transparency may decrease and the disintegration property also decreases. ２ More preferably, it is 2.5 g / m or more. ２ The coating amount of the filling layer is more preferably 4.5 g / m2 in terms of dry mass per side. ２When the filling layer is formed on both sides, the coating amount of the filling layer on each side may be the same or different.

[0027] "Release Paper Base Paper" The release paper base paper of the present invention comprises a base paper and a sealing layer on at least one side of the base paper, and has a density of 0.85 g / cm ３ 1.05g / cm or more ３ The base paper for release paper is required to be lightweight (low basis weight) and stiff (easy to handle and wrinkle resistant). The density is 0.85 g / cm ３ If the density is less than 1.05 g / cm, it becomes difficult to ensure the necessary sealing properties. ３ If it exceeds 1.00 g / cm, the stiffness will be weakened when the basis weight is reduced, wrinkles will easily occur, and handling will also decrease. ３ It is more preferable that the opacity of the release paper base paper is 45% or more and 65% or less. If the opacity is less than 45%, unevenness in the formation becomes noticeable, deteriorating the appearance, while if the opacity is more than 65%, it becomes difficult to apply the release paper base paper to applications requiring light transmittance. By satisfying the above-mentioned density and opacity, the release paper base paper of the present invention can be suitably used as a substitute for release paper base paper using glassine paper or semi-glassine paper.

[0028] The basis weight of the base paper for release paper of the present invention is not particularly limited, but is preferably 30 g / m ２ 60g / m or more ２ It is preferable that the release paper has a low basis weight in order to reduce waste and improve transportation costs. Therefore, the basis weight of the base paper for release paper is 55 g / m or less. ２ More preferably, 50 g / m or less ２ On the other hand, if the basis weight is too low, wrinkles and paper breaks are likely to occur during processing, and the stiffness is weakened, making the paper less easy to handle. Therefore, the basis weight of the release paper base paper is set to 35 g / m ２ More preferably, 40 g / m or more ２ The above is even more preferable.

[0029] The release paper base paper of the present invention preferably has an ash content of 1% or more and 8% or less in accordance with JIS P 8251:2003. If the ash content is less than 1%, the paper is more likely to shrink and wrinkle during processing. On the other hand, if the ash content exceeds 8%, transparency may be insufficient, and the paper strength may decrease, making the paper more likely to tear during adhesive processing. From the viewpoint of transparency, the ash content is preferably low, more preferably 7% or less, even more preferably 6% or less, even more preferably 5% or less, even more preferably 4% or less, even more preferably 3% or less, and even more preferably 2% or less.

[0030] The release paper base paper of the present invention preferably has a shrinkage rate in the transverse direction of 3.0% or less after immersion in water for 1 hour. If this shrinkage rate exceeds 3.0%, wrinkles are likely to occur during humidification treatment for curl correction or heat treatment for drying. This shrinkage rate is more preferably 2.8% or less, even more preferably 2.6% or less, even more preferably 2.4% or less, even more preferably 2.2% or less, and even more preferably 2.0% or less.

[0031] The base paper for release paper of the present invention has a Cobb water absorbency (30 seconds) of 10 g / m2 measured in accordance with ISO 535:1991. ２ 30g / m or more ２ It is preferable that the Cobb water absorbency is 10 g / m or less. ２ If the thickness is less than 30 g / m, the anchoring property of the release agent layer is low, and the adhesion between the release agent layer and the base paper is insufficient, which may cause the release agent layer to collapse during the adhesive label processing. Also, the releasability is reduced. ２ If the coating amount exceeds this, the required coating amount of release agent increases, resulting in high costs.

[0032] The release paper base paper of the present invention preferably has an Oken smoothness of 300 seconds or more and 1,500 seconds or less on the surface of the sealing layer, as specified in JIS P 8155:2010. An Oken smoothness of less than 300 seconds increases the required coating amount of expensive release agent, which is uneconomical. On the other hand, an Oken smoothness of more than 1,500 seconds reduces the anchoring ability of the release agent, raising concerns that the release agent layer may collapse during adhesive label processing. The release paper base paper of the present invention preferably has a 75° gloss of 20% or more and 60% or less on the surface of the sealing layer, as measured in accordance with JIS P 8142:2005. A gloss within this range can be expected to provide excellent smoothness and sealing properties for the sealing layer. It is preferable that the release paper base paper of the present invention has an ISO brightness (UVIn) of 70% or more and 85% or less on the surface of the sealing layer, as measured in accordance with JIS P 8148:2018, in order to achieve excellent appearance.

[0033] "Release Paper" Release paper can be produced by coating a release agent on the sealing layer of the release paper base paper of the present invention to form a release agent layer. Release paper for double-sided tape can be produced by using a release paper base paper with sealing layers on both sides and forming release agent layers on both sides. The release paper base paper of the present invention has a highly uniform sealing layer and good sealing properties, so a uniform release agent layer can be formed on this sealing layer. Materials with low surface energy and weak adhesive strength to adhesives, such as silicone resins, fluorine compounds, aminoalkyd compounds, and polyester compounds, can be used as release agents without any particular restrictions. However, in the present invention, it is preferable to use silicone resins. Examples of silicone resins used as release agents include solventless silicone resins, solvent-based silicone resins, aqueous emulsion silicone resins, and solventless UV-curable silicone resins. When release agent layers are formed on both sides, the release agents on each side may be the same or different.

[0034] The method for applying the release agent is not particularly limited, and the application can be performed using a known coating device and coating system. Examples of coating devices include a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a gravure coater, a spray coater, a size press coater, and a gate roll coater. The method for drying the release agent layer can be a conventional method such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, or a cylinder dryer.

[0035] The coating amount of the release agent layer is 0.2 g / m2 in dry mass per side. ２ 3.0g / m or more ２ The coating amount is preferably 0.2 g / m or less. ２ If the coating amount is less than 3.0 g / m, it becomes difficult to obtain a uniform release agent layer. ２ Even if the coating amount of the release agent layer exceeds 0.3 g / m2 in terms of dry mass per side, the releasability is hardly improved and the effect becomes saturated. ２ 2.0g / m or more ２ The coating amount of the release agent layer is more preferably 0.4 g / m2 or less in terms of dry mass per side. ２ The coating amount of the release agent layer is more preferably 1.2 g / m2 or more in terms of dry mass per side. ２ It is more preferable that the following is satisfied: When a release agent layer is formed on both sides, the coating amount of the release agent layer on each side may be the same or different.

[0036] The release paper of the present invention preferably has a ΔE (after test - before test) of 10 or less before and after the silicone hold-out test. The silicone hold-out test is a test to measure the ease of penetration into the surface of the release agent layer, i.e., the sealing ability, with a lower value indicating better sealing ability. If this ΔE exceeds 10, the release agent layer may not be able to fully prevent the penetration of the adhesive applied, and the peel force required to peel the label may become heavy. The ΔE before and after this test is more preferably 8 or less, even more preferably 6 or less, even more preferably 4 or less, and even more preferably 2 or less.

[0037] The present invention will be specifically illustrated by the following examples, but the present invention is not limited to the descriptions in the examples. Furthermore, parts by mass in the examples refer to parts by mass on an bone-dry basis unless otherwise specified.

[0038] <Paint Properties> (1) Amount of Water Removed from Coating Liquid (Water Retention) Using an AA-GWR Water Retention Meter Model 250 manufactured by Kaltec, 10 sheets of base paper were stacked on top of each other, and a 5 μm thick filter (AA-GWR Test Filters) was placed on top of them, and measurements were carried out with 20 ml of coating liquid, a cell pressure of 50 kPa, and a pressure time of 40 seconds. The amount of water removed was calculated from the difference in mass of the base paper before and after the measurement. The smaller this value, the higher the dynamic water retention.

[0039] <Quality evaluation of base paper for release paper> (1) Basis weight: Measured in accordance with JIS P 8124: 2011. (2) Paper thickness and density: Measured in accordance with JIS P 8118: 2014. (3) Gloss: Measured on the surface coated with the sealing layer in accordance with JIS P 8142: 2005.

[0040] (4) Oken smoothness: The surface of the sealing layer was measured using an Oken smoothness meter (KY-5 manufactured by Asahi Seiko Co., Ltd.) based on JIS P 8155:2010. (5) Oken air resistance: Measured by a method (Oken tester method) in accordance with JIS P 8117:2009. (6) ISO whiteness: The coating surface of the sealing layer was measured in accordance with JIS P 8148:2018.

[0041] (7) Opacity: Measured in accordance with JIS P 8149: 2000. (8) Ash content: Measured in accordance with JIS P 8251: 2003. (9) Cobb water absorbency: Measured in accordance with ISO 535: 1991 with a contact time of 30 seconds.

[0042] (10) Shrinkage (Transverse Direction) Ten samples measuring 15 mm in the machine direction (MD) and 150 mm in the cross direction (CD) were taken from the obtained release paper base paper. The samples were immersed in water for 1 hour, and after being taken out of the water, excess water was wiped off. The length in the transverse direction was measured, and the average shrinkage before and after immersion was calculated.

[0043] (11) Disintegrability The release paper base paper was immersed in water to a concentration of 2.0% by mass and disintegrated for 60 minutes using a Tappi standard disintegrator. The degree of disintegration in water was evaluated according to the following criteria. If the evaluation was ○ or △, there was no problem in practical use. [Evaluation criteria] ○: Pulp fibers were dispersed and disintegration was good. △: There were slight bundles of pulp fibers. ×: Clumps of pulp fibers or bundles of pulp fibers remained and disintegration was not possible.

[0044] <Quality evaluation of release paper> (1) Immediately after coating with the coating liquid for the silicone curable release agent layer, the surface of the release agent layer of the release paper was rubbed back and forth five times over an area of ​​approximately 5 cm with a finger (loaded at approximately 500 g), and the surface condition was visually observed and evaluated according to the following criteria. Regarding the use of a silicone-based release agent, if the evaluation is ○ or △, there is no problem in practical use. [Evaluation criteria] ○: No marks are left at the rubbed area, and the silicone resin is cured. △: Some marks are left at the rubbed area, but the silicone resin is mostly cured. ×: Marks are left at the rubbed area, and the silicone resin is not sufficiently cured.

[0045] (2) Silicone Adhesion (Anchor Properties, Durability) After treating the release paper for 3 days in an environment of 70°C and 95% RH, the surface of the release agent layer of the release paper was rubbed five times back and forth over an area of ​​about 5 cm with a finger (loaded with approximately 3 kg), and the surface condition was visually observed and evaluated according to the following criteria. If the evaluation was ○ or △, there was no problem in practical use. [Evaluation Criteria] ○: No mark was left at the rubbed area. △: Mark was left at the rubbed area, but the release agent layer did not peel off. ×: The release agent layer peeled off at the rubbed area.

[0046] (3) An acrylic emulsion adhesive (AT-27, manufactured by Saiden Chemical Co., Ltd.) was applied to the release agent layer of the release paper in a coating amount of 50 g / m2 in terms of dry mass. ２ After coating the adhesive layer so that the adhesive layer was coated, the adhesive layer was dried at 110°C for 3 minutes to form an adhesive layer. Next, a sheet of wood-free paper (basis weight 64 g / m) was placed on the adhesive layer. ２) was attached to the adhesive paper to prepare an adhesive paper. This adhesive paper was left to stand for one week in an environment of 23°C and 50% RH, and then the peel strength between the fine paper and the release agent layer was measured using a tensile tester under conditions in which the fine paper was peeled off in a 180-degree direction at a speed of 300 mm / min in accordance with JIS Z 0237:2009, and evaluated according to the following criteria. If the evaluation was ○ or △, there was no problem in practical use. [Evaluation criteria] ○: 30 mN / 50 mm or more and 100 mN / 50 mm or less. △: More than 100 mN / 50 mm and 200 mN / 50 mm or less. ×: Other than the above.

[0047] (4) Appearance after moisture absorption and desorption (effect of moisture absorption and desorption on surface properties) A: 10 g / m of water was applied to the backside of the release paper. ２ The surface was visually inspected before and after treatment and evaluated according to the following criteria: B: 30 g / m of adhesive (Saibinol AT-27, manufactured by Saiden Chemical Co., Ltd.) was applied to the release paper after drying in the above A. ２ The top paper (60 g / m ２ The paper was laminated with a cast coated label paper (such as the above), dried (120°C x 1 minute), and conditioned for 1 day (23°C, 50% RH). The surface properties of the top paper before and after treatment were visually inspected and evaluated according to the following criteria. If the evaluation was ○ or △, there was no problem in practical use. [Evaluation criteria] ○: For both A and B, the surface properties were unchanged before and after treatment. △: For only one of A and B, unevenness or wrinkles were observed on the surface after treatment. ×: For both A and B, surface defects such as unevenness or wrinkles were observed on the surface after treatment.

[0048] (5) Labeler suitability (phototube suitability) The paper after adhesive processing was placed in a paper feed detector using an automatic labeler, and the light of a phototube was passed through to check whether it was detectable. The evaluation criteria are as follows. If the evaluation is ○, there is no problem in practical use. [Evaluation criteria] ○: Detection is possible with a phototube. ×: Detection is impossible with a phototube. (6) Silicone holdout (silicone pore-filling ability) The surface of the release agent layer was immersed in a 2% aqueous solution of malachite green for 30 seconds, then wiped off with gauze, and the UVIn L ＊ a＊ b ＊ Before and after the application of malachite green, L ＊ a ＊ b ＊ The ΔE (color difference) was calculated from the above.

[0049] [Example 1] (Preparation of base paper) 55 parts by mass of hardwood kraft pulp (LBKP, 350 ml CSF) and 45 parts by mass of softwood kraft pulp (NBKP, 350 ml CSF) were mixed to prepare a raw pulp. 0.5 parts by mass of cationic starch was added as a paper strength agent to 100 parts by mass of the raw pulp. 1.0 part by mass of an internal sizing agent and 1.5 parts by mass of aluminum sulfate were then added. The paper was then made using a fourdrinier multi-cylinder paper machine and calendered to a basis weight of approximately 40 g / m. ２ The base paper was obtained.

[0050] (Preparation of coating liquid for filling layer) 100 parts by mass of kaolin (KCS manufactured by Imerys, D50: 4.6 μm, aspect ratio 13) as a pigment, 10 parts by mass of oxidized starch (MS#3800 manufactured by Nippon Shokuhin Kako Co., Ltd.) as a starch-based compound, 100 parts by mass of styrene-butadiene copolymer latex (PA0330 manufactured by Nippon A&L Co., Ltd., Tg-10°C) as a synthetic resin latex, and 1 part by mass of lubricant (Nopcoat C-104 manufactured by San Nopco Ltd.) were blended to prepare a coating liquid for filling layer. (Coating) Immediately after the preparation of the base paper, the coating liquid for filling layer was applied to one side (the side coated with the release agent) of the base paper using a blade coater so that the coating amount on one side was 3 g / m in terms of dry mass. ２ The back side was coated with a thin layer of starch to correct curling, dried, and calendered (linear pressure 100 kgf / cm x 2 passes) to obtain a base paper for release paper.

[0051] (Preparation of Coating Liquid for Release Layer) Two parts of a catalyst were added to a solvent-free silicone resin (manufactured by Toray Dow Corning Silicone Co., Ltd.: LTC-1053L) to prepare a coating liquid for release layer.

[0052] (Preparation of Release Paper) A coating solution for a release agent layer was applied to the sealing layer of the base paper for release paper using an RI printing machine in a coating amount of 1.0 g / m2 in terms of dry mass. ２After coating so that the composition was in the range of 150° C. to 60 seconds, the composition was cured in a dryer to obtain a release paper.

[0053] [Example 2] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the amount of synthetic resin latex in the coating liquid for the filling layer was 130 parts by mass. [Example 3] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the amount of synthetic resin latex in the coating liquid for the filling layer was 70 parts by mass. [Example 4] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the amount of starch-based compound in the coating liquid for the filling layer was 50 parts by mass.

[0054] [Example 5] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the sizing material in the base paper was 0.5% relative to the pulp, and the starch-based compound and synthetic resin latex in the coating solution for the filling layer were 20 parts by mass and 60 parts by mass, respectively. [Example 6] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the LBKP had a freeness of 400 ml CSF and the NBKP had a freeness of 360 ml CSF. [Example 7] A release paper base paper and a release paper were obtained in the same manner as in Example 6, except that the synthetic resin latex in the coating solution for the filling layer was 50 parts by mass. [Example 8] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the pigments were 85 parts by mass of kaolin and 15 parts by mass of heavy calcium carbonate (TP-SO-10, manufactured by Okutama Kogyo Co., Ltd., D50: 8.0 μm, aspect ratio 1).

[0055] [Comparative Example 1] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the LBKP had a freeness of 220 ml CSF and the NBKP had a freeness of 200 ml CSF. [Comparative Example 2] A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the LBKP had a freeness of 500 ml CSF and the NBKP had a freeness of 450 ml CSF, and the amount of sizing material in the paper was 0.5% relative to the pulp. [Comparative Example 3] The basis weight of the base paper was 34 g / m ２ A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that:

[0056] [Comparative Example 4] A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that precipitated calcium carbonate was added as a filler to the base paper in an amount of 8% by mass relative to the pulp. [Comparative Example 5] A coating amount of 9.9 g / m2 on a dry mass basis was obtained. ２ A release paper base paper and a release paper were obtained in the same manner as in Example 1, except that the coating amount was 9.0 g / m2 on a dry basis. ２ A base paper for release paper and a release paper were obtained in the same manner as in Comparative Example 3. [Comparative Example 7] A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the base paper was used as is without coating with a filling layer.

[0057] Table 1 shows the evaluation results of the base paper for release paper and the release paper obtained in each example and comparative example.

[0058] The release paper base papers obtained in Examples 1 to 8 of the present invention had an excellent balance of transparency and density, and were confirmed to be usable as replacements for glassine paper and semi-glassine paper in release papers based on glassine paper or semi-glassine paper. Furthermore, the release paper base papers obtained in Examples 1 to 8 of the present invention are recyclable and can be disintegrated into papermaking materials. The release paper base papers obtained in Comparative Examples 1 to 6 had at least one of transparency and density outside the appropriate range. The release paper base papers obtained in Comparative Examples 1 to 6 had insufficient performance as release paper coated with a release agent, and were of a level that could not be used as replacements for glassine paper or semi-glassine paper in release papers based on glassine paper or semi-glassine paper. Comparative Example 7 was not coated with a sealing layer, so it lacked sealing properties and could not be used as a release paper base paper.

Claims

1. A base paper and a sealing layer on at least one side of the base paper, having a density of 0.85 g / cm ３ 1.05g / cm or more ３ and an opacity in accordance with JIS P 8149:2000 of 45% or more and 65% or less.

2. The release paper base paper according to claim 1, characterized in that the filling layer contains a pigment and an adhesive in a mass ratio of 60 / 40 to 40 / 60 (pigment / adhesive: dry mass).

3. The base paper for release paper according to claim 2, characterized in that the pigment has a 50% volume average particle size of 1.0 μm or more and 7.0 μm or less.

4. The release paper base paper according to claim 2, characterized in that the adhesive contains at least a starch-based compound and a synthetic resin latex, and the ratio of the synthetic resin latex to 100 parts by mass of the pigment is 70 parts by mass or more and 130 parts by mass or less.

5. The release paper base paper according to claim 4, wherein the synthetic resin latex is a styrene-butadiene copolymer latex.

6. The release paper base paper according to claim 1, characterized in that the shrinkage rate in the transverse direction after immersion in water for 1 hour is 3.0% or less.

7. The Cobb water absorbency (30 seconds) of the release paper base paper measured in accordance with ISO 535:1991 is 10 g / m ２ 30g / m or more ２ 2. The release paper base paper according to claim 1, wherein the release paper base paper is:

8. The base paper for release paper according to claim 1, characterized in that the Oken smoothness of the surface of the filling layer in accordance with JIS P 8155:2010 is 300 seconds or more and 1500 seconds or less.

9. The coating amount of the sealing layer is 1 g / m2 in terms of dry mass per side. ２ 5g / m or more ２ 2. The release paper base paper according to claim 1, wherein the release paper base paper is:

10. The basis weight of the release paper base paper is 30 g / m ２ 60g / m or more ２ 2. The release paper base paper according to claim 1, wherein the release paper base paper is:

11. The release paper base paper according to claim 1, characterized in that the ash content of the release paper base paper in accordance with JIS P 8251:2003 is 1% or more and 8% or less.

12. A release paper characterized by having a release agent layer on the sealing layer of the release paper base paper according to any one of claims 1 to 11.

13. The release paper according to claim 12, wherein the ΔE (after test - before test) of the release paper before and after the silicone holdout test is 10 or less.

14. A method for producing a base paper for release paper, comprising the step of applying a coating liquid for a filling layer to at least one surface of the base paper by an on-machine coater, wherein the resulting base paper for release paper has a density of 0.85 g / cm ３ 1.05g / cm or more ３ and an opacity in accordance with JIS P 8149:2000 of 45% to 65%.

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