Release paper base sheet and release paper

Abstract

The present invention addresses the problem of providing: a release paper base sheet which has excellent sealing capability, which can be recycled, and on which a uniform release agent layer can be formed; and release paper having a release agent layer formed on said release paper base sheet. Provided as a solution to the problem are: a release paper base sheet which comprises base sheet and a sealing layer on at least one surface of the base paper, and in which the sealing layer contains a pigment and an adhesive agent at a mass ratio of 70 / 30 to 80 / 20 (pigment / adhesive agent: dry mass), the pigment contains at least 90 mass% of a flat pigment, the adhesive agent contains at least a starch-based compound and a synthetic resin latex, the blended amount of the synthetic resin latex with respect to 100 parts by mass of the pigment is 22-30 parts by mass, and the Cobb absorbency (30 seconds) of the surface of the sealing layer is 5-25 g / m2 as measured on the basis of ISO535:1991; and a release paper having a release agent layer on the sealing layer of the release paper base sheet.

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 used by being attached to the adhesive surface of adhesive labels, adhesive stickers, adhesive tapes, double-sided tapes, etc., to protect the adhesive surface and prevent a decrease in adhesive strength. It is also used as a process paper during the production of so-called prepregs, where resin materials are cured on the release paper (process paper). The release paper has a release agent layer on the surface that contacts the adherend so that it can be easily released from the adherend. Silicone resins are generally used as release agents, but silicone resins are very expensive. Therefore, polyethylene-laminated paper, which has excellent sealing properties and is resistant to penetration of silicone resin coating liquid, is used as the base paper for the release paper so that a release agent layer can be formed with a small amount. However, polyethylene-laminated paper has a problem in that it is not suitable for recycling because a tough polyethylene coating is formed on the paper surface and is difficult to disintegrate after use.

[0003] In Patent Document 1, the applicant proposes a recyclable release paper base paper having a pigment coating layer composed of a flat pigment having a particle size and aspect ratio within a specific range and a synthetic resin latex, which does not require a polyethylene laminate. In Patent Document 2, the applicant proposes a release paper that is recyclable and suppresses the penetration of release agents such as silicone resins into the sealing layer, by blending 8 to 20 parts by weight of synthetic resin latex with 100 parts by weight of a pigment having a particle size within a specific range. In Patent Document 3, the applicant proposes a recyclable release paper base paper containing a pigment and an adhesive in a mass ratio of 75 / 25 to 25 / 75, in which the adhesive contains a starch-based compound and a synthetic resin latex in an amount of 80% by weight or more relative to the total amount of adhesive and in a mass ratio of 90 / 10 to 50 / 50, and which has an air resistance (Oken type testing machine method) of 3,000 seconds to 20,000 seconds.

[0004] JP 2000-282397 A JP 2016-223036 A International Publication No. 2022 / 190860

[0005] In the release papers proposed in Patent Documents 1 to 3, if the coating amount is reduced to make the coating layer (sealing layer) thinner in order to improve recyclability, there is a concern that the air resistance will be lowered, the sealing performance will be reduced, and the penetration of the coating liquid for forming the release agent layer will be insufficiently suppressed. An object of the present invention is to provide a base paper for release paper that has excellent sealing performance, is capable of forming a uniform release agent layer, and is recyclable, and a release paper having a release agent layer formed on this base paper for release paper.

[0006] The means for solving the problems of the present invention are as follows: 1. A paper sheet comprising a base paper and a filling layer on at least one surface of the base paper, wherein the filling layer contains a pigment and an adhesive in a mass ratio of 70 / 30 to 80 / 20 (pigment / adhesive: dry mass), wherein the pigment contains 90 mass % or more of a flat pigment, wherein the adhesive contains at least a starch-based compound and a synthetic resin latex, wherein the blending amount of the synthetic resin latex per 100 mass parts of the pigment is 22 mass parts to 30 mass parts, and wherein the Cobb water absorbency (30 seconds) of the surface of the filling layer measured in accordance with ISO 535:1991 is 5 g / m ２ 25g / m or more ２ 2. A release paper base paper characterized in that the basis weight of the release paper base paper is 40 g / m or less. ２ 90g / m or more ２ the coating amount of the sealing layer is 5 g / m or less in terms of dry mass per one side ２ 10g / m or more ２1. The release paper base paper according to 1., characterized in that: 3. The release paper base paper according to 1. or 2., characterized in that the 50% volume average particle size of the flat pigment is 1.0 μm or more and 7.0 μm or less. 4. The release paper base paper according to any one of 1. to 3., characterized in that the shrinkage rate in the lateral direction after immersion in water for 1 hour is 2.5% or less. 5. The release paper base paper according to any one of 1. to 4., characterized in that the release paper base paper has an Oken air resistance in accordance with JIS P 8117:2009 of 20,000 seconds or more. 6. The release paper base paper according to any one of 1. to 5., characterized in that the Oken smoothness of the surface of the sealing layer in accordance with JIS P 8155:2010 is 500 seconds or more and 2,000 seconds or less. 7. 10. The release paper base paper according to any one of 1. to 6., characterized in that the ash content of the release paper base paper according to JIS P 8251:2003 is 8% or more and 30% or less. 8. The release paper base paper according to any one of 1. to 7., characterized in that there is no primer layer between the base paper and the filling layer. 9. The release paper base paper according to any one of 1. to 8., characterized in that the base paper contains a total of 90% by mass or more of hardwood pulp and softwood pulp based on the total papermaking fibers, the solids mass ratio of the hardwood pulp to the softwood pulp (hardwood pulp:softwood pulp) is 80:20 to 50:50, the freeness of the hardwood pulp is 300 ml CSF or more and 400 ml CSF or less, and the freeness of the softwood pulp is 300 ml CSF or more and 450 ml CSF or less. 10.1. 11. 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 items 1 to 9. 11. The release paper according to item 10, characterized in that the ΔE (after test - before test) of the release paper before and after a silicone holdout test is 10 or less.12. A method for producing a base paper for release paper, comprising the steps of: applying, on at least one surface of the base paper, a coating liquid for a filling layer, the coating liquid comprising a pigment and an adhesive in a mass ratio of 70 / 30 to 80 / 20 (pigment / adhesive: dry mass), the pigment comprising 90 mass% or more of a flat pigment, the adhesive comprising at least a starch-based compound and a synthetic resin latex, the amount of the synthetic resin latex blended being 22 to 30 parts by mass per 100 parts by mass of the pigment, using an on-machine coater; and wherein the Cobb water absorbency (30 seconds) of the filling layer surface of the resulting base paper for release paper, measured in accordance with ISO 535:1991, is 5 g / m. ２ 25g / m or more ２ A method for producing a base paper for release paper, characterized in that:

[0007] The release paper base paper of the present invention can prevent the penetration of the release agent, and by providing a release agent layer on the sealing layer, it is possible to obtain a release paper that is excellent in hardening, adhesion, releasability, and durability. The release paper base paper of the present invention has excellent workability when processed into adhesive labels, etc., and also has excellent disintegration properties, allowing it to be recycled as waste paper material. The release paper base paper of the present invention can be reused as release paper base paper without disintegration, and can be used as so-called casting paper. The release paper base paper of the present invention has sufficient sealing properties even when the coating weight of the sealing layer is at least. In particular, when a 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 filler layer on at least one surface of the base paper, the filler layer containing a pigment and an adhesive in a mass ratio (pigment / adhesive: dry mass) of 70 / 30 to 80 / 20, the pigment containing 90 mass % or more of a flat pigment, the adhesive containing at least a starch-based compound and a synthetic resin latex, the blending amount of the synthetic resin latex per 100 mass parts of the pigment being 22 mass parts or more and 30 mass parts or less, and the Cobb water absorbency (30 seconds) of the surface of the filler layer measured in accordance with ISO 535:1991 is 5 g / m or less. ２ 25g / m or more ２In 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 newsprint, 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 pulps such as kenaf, hemp, and bamboo, glass fibers, and polyethylene fibers, can be blended.

[0010] The use of softwood pulp is preferred because it makes it difficult for the coating liquid for the sealing layer to penetrate into the resulting base paper, facilitating the formation of a dense sealing layer, and it also makes it easier to ensure the strength required for label processing, etc. However, if the amount of softwood pulp is too high, uneven formation becomes more noticeable, resulting in a poor appearance. Therefore, it is preferable that the total papermaking fiber contains at least 90 mass% of hardwood pulp and softwood pulp, the solids mass ratio of hardwood pulp to softwood pulp (hardwood pulp:softwood pulp) is 80:20 to 50:50, the freeness of the hardwood pulp is 300 ml CSF or more and 400 ml CSF or less, and the freeness of the softwood pulp is 300 ml CSF or more and 450 ml CSF or less. By blending specific amounts of softwood pulp and hardwood pulp with these freenesses, a good balance of sealing properties, formation, dimensional stability, etc. can be achieved.

[0011] The total ratio of hardwood pulp and softwood pulp to the total papermaking fibers is more preferably 93% by mass or more, even more preferably 96% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass. The solids mass ratio of hardwood pulp to softwood pulp is more preferably 75:25 to 60:40. The freeness of the hardwood pulp is more preferably 320 ml CSF or more, even more preferably 340 ml CSF or more, and more preferably 390 ml CSF or less. The freeness of the softwood pulp is more preferably 320 ml CSF or more, even more preferably 340 ml CSF or more, and more preferably 430 ml CSF or less, and even more preferably 410 ml CSF or less.

[0012] The base paper of the present invention can contain a filler. Known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers can be used as the filler. In the present invention, the filler is an optional component, and the base paper may not contain a filler. The incorporation of a filler improves the smoothness, opacity, whiteness, etc. of the base paper, but tends to reduce the strength of the resulting base paper and facilitate penetration of the coating liquid for the filling layer. Therefore, the amount of filler to be incorporated is determined taking these properties into consideration. The content of the filler in the base paper is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0013] Examples of auxiliary agents that can be used as needed include aluminum sulfate and various anionic, cationic, nonionic, or amphoteric retention aids, drainage aids, paper strength agents, internal sizing agents, etc. Furthermore, dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents, etc. can also be added as needed.

[0014] The basis weight of the base paper is not particularly limited, but is preferably 30 g / m ２ 75g / m or more ２ A low basis weight is desirable for the release paper from the viewpoint of reducing waste and improving transportation costs. ２More preferably, 60 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 it difficult to handle. Therefore, the basis weight of the base paper is set to 35 g / m ２ More preferably, 40 g / m or more ２ The above is even more preferable.

[0015] 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.

[0016] 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, lubricants, etc., and these can be used alone or in combination of two or more. The method for surface treatment of the base paper is not particularly limited, but 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. Furthermore, it is preferable to perform a calendar treatment in order to apply the filling layer uniformly.

[0017] The base paper for release paper of the present invention preferably does not have an undercoat layer between the base paper and the filling layer. The absence of an undercoat layer means that the filling layer is directly coated on the base paper without any other layer in between. The absence of an undercoat layer allows the coating liquid for forming the filling layer to easily penetrate into the base paper, improving anchoring properties and interlayer strength between the base paper and the filling layer.

[0018] "Sealing Layer" The sealing layer is provided on at least one side of the base paper. By providing sealing layers on both sides of the base paper, it can be made into a base paper for release paper for double-sided tape. The sealing layer contains a pigment and an adhesive in a mass ratio of 70 / 30 to 80 / 20 (pigment / adhesive: dry mass, total 100), the pigment contains 90 mass% or more of a flat pigment, the adhesive contains at least a starch-based compound and a synthetic resin latex, and the blending amount of the synthetic resin latex per 100 mass parts of pigment is 22 mass parts to 30 mass parts. The release paper base paper of the present invention has good sealing properties because the sealing layer satisfies this composition, and by providing a release agent layer on this sealing layer, it can be made into a release paper with excellent curing properties, releasability, adhesion, and durability. 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.

[0019] The pigment contains 90% or more by mass of flat pigment. When coated, flat pigments are oriented in the plane direction of the base paper, which effectively prevents the penetration of release agents and provides excellent filling properties. Pigments also contribute to preventing roll contamination and blocking. In this specification, flat pigment refers to a pigment with an aspect ratio of 5 or more. The aspect ratio of flat pigments is more preferably 8 or more, and even more preferably 10 or more. There is no particular upper limit to the aspect ratio of flat pigments, but it is, for example, approximately 120 or less. 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 the Journal of the Japan Paper and Pulp Technology Association, Vol. 65, No. 12.

[0020] As the flat pigment, for example, inorganic pigments such as kaolin, engineered kaolin, clay, delaminated clay, talc, aluminum hydroxide, and mica can be used alone or in combination. Furthermore, the present invention requires that the flat pigment be contained in an amount of 90% by mass or more, and non-flat pigments such as heavy calcium carbonate and light calcium carbonate can also be contained. However, the proportion of the flat pigment relative to the total pigment content is preferably 93% by mass or more, more preferably 96% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0021] The flat pigment preferably has a volume 50% average particle size (D50, median diameter, hereinafter also referred to as "average particle size") of 1.0 μm or more and 7.0 μm or less, measured by laser diffraction / scattering. If the average particle size of the flat pigment is less than 1.0 μm, the gaps between the fibers on the base paper surface can be filled, but the specific surface area of ​​the flat pigment is large, preventing the adhesive from sufficiently filling the gaps between the flat pigments, resulting in many fine gaps and a deterioration in the sealing ability to prevent the release agent from seeping in. On the other hand, if the average particle size of the flat pigment exceeds 7.0 μm, the unevenness of the sealing layer surface increases, increasing the amount of release agent required to cover the sealing layer surface, and since release agents are expensive, the cost increases. The average particle size of the flat 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 types of flat pigments are used, it is preferable that the average particle size of at least one of the types is within the above-mentioned range, and the proportion of flat pigments satisfying this average particle size relative to the total flat pigments is preferably 50% by mass or more, and more preferably 70% by mass or more. Examples of measuring devices using the laser diffraction / scattering method include the particle size distribution measuring device "Partica" from Horiba, Ltd. and the particle size distribution measuring device "MASTER SIZER S" from Malvern Instruments.

[0022] The adhesive contains at least a starch-based compound and a synthetic resin latex. The adhesive may contain other adhesives as long as the effects of the present invention are not impaired. Examples of other adhesives include 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] In the sealing layer, the mass ratio of pigment to adhesive (pigment / adhesive, dry mass, total 100) is 70 / 30 to 80 / 20. If the pigment ratio in this mass ratio exceeds 80 (adhesive less than 20), the pigment ratio becomes too high, and the adhesive does not sufficiently fill the gaps between the pigments, resulting in the formation of many fine voids. As a result, it becomes impossible to prevent the coating liquid for the release agent layer from penetrating into the sealing layer, and sealing performance deteriorates. On the other hand, if the pigment ratio is less than 70 (adhesive more than 30), the water dissociation property of the release paper base paper deteriorates, making it difficult to use it as recycled paper.

[0027] In the filling layer, the amount of synthetic resin latex per 100 parts by mass of pigment is 22 to 30 parts by mass. If the amount of synthetic resin latex is less than 22 parts by mass, it becomes difficult for the coating liquid for the release agent layer to uniformly coat the surface of the filling layer, and the performance required for release paper, particularly release performance with aqueous pressure-sensitive adhesives, cannot be obtained. On the other hand, if the amount of synthetic resin latex exceeds 30 parts by mass, the water dissociation property of the base paper for release paper deteriorates, making it difficult to use it as recycled paper.

[0028] The coating method for the filling 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 main medium is preferred. In the present invention, the dehydration amount of the coating solution 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 the value of this dehydration amount, the less the coating liquid is absorbed into the base 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 interlayer strength will decrease, the disaggregation property will also decrease, and the stiffness of the base paper itself will increase, making it more likely to produce creases during processing. This dehydration amount is 20 g / m ２ 60g / m or more ２ By satisfying the following conditions, it becomes easy to form a base paper for release paper that has an excellent balance of sealing properties, interlayer strength, releasability, stiffness, etc.

[0029] 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 wound up onto a reel after papermaking on the papermaking machine, and then the reel is applied to the off-machine coater for coating. However, coating using an on-machine coater eliminates the need to wind up the base paper and apply it to the coater, thereby improving production efficiency. 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 weight 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 weight is small, so that the desired performance can easily be achieved even when coated using an on-machine coater. Conventional methods, such as a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, or cylinder dryer, can be used to dry the sealing layer.

[0030] The coating amount of the sealing layer is 5 g / m2 in dry mass per side. ２ 10g / m or more ２ The coating amount is preferably 5 g / m or less. ２ If the coating amount is less than 10 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 weight exceeds 1000 ppm, the paper may have poor releasability and may lack strength. From the viewpoint of the sealing performance, the coating weight of the sealing layer is 5.5 g / m2 in terms of dry mass per side. ２ More preferably, it is 6 g / m or more. ２ More preferably, it is 6.5 g / m or more. ２ It is even more preferable that the content is 7 g / m or more. ２ On the other hand, from the viewpoint of disintegration property, it is more preferable that the dry mass per side is 9.5 g / m or more. ２ More preferably, it is 9 g / m or less. ２ It is more preferable that the coating amount of the filling layer on each surface is the same or different.

[0031] "Base Paper for Release Paper" The base paper for release paper of the present invention has a Cobb water absorbency (30 seconds) of 5 g / m2 measured in accordance with ISO 535:1991. ２ 25g / m or more ２ This Cobb water absorbency is 5 g / m or less. ２ If the thickness is less than 25 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, and the releasability is also reduced. ２ If the coating amount exceeds this, the required coating amount of release agent increases, resulting in high costs.

[0032] The basis weight of the base paper for release paper of the present invention is not particularly limited, but is preferably 40 g / m ２ 90g / m or more ２ A low basis weight is desirable for release paper from the viewpoint of reducing waste and improving transportation costs. Therefore, the basis weight of the base paper for release paper is preferably 85 g / m or less. ２ More preferably, 80 g / m or less ２ More preferably, 75 g / m or less ２ Even more preferably, 70 g / m 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 release paper base paper is set to 44 g / m ２ More preferably, 48 g / m or more ２ The above is even more preferable.

[0033] The release paper base paper of the present invention preferably has a shrinkage rate in the transverse direction of 2.5% or less after immersion in water for 1 hour. If this shrinkage rate exceeds 2.5%, wrinkles are likely to occur during humidification treatment for curl correction or heat treatment for drying. This shrinkage rate is more preferably 2.3% or less, even more preferably 2.1% or less, and even more preferably 2.0% or less.

[0034] In the release paper base paper of the present invention, the air resistance (Oken Tester Method) of the surface having the sealing layer is preferably 20,000 seconds or more as specified in JIS P 8117:2009. When the air resistance (Oken Tester Method) is within the above range, the release agent can be uniformly coated, and the resulting release paper has excellent adhesion and releasability. Here, the upper limit of the measurement of air resistance (Oken Tester Method) is 100,000 seconds. In release paper base paper, the higher the air resistance (Oken Tester Method) value, the better the sealing ability. However, since the release paper base paper of the present invention has high sealing ability due to the flat pigment, the air resistance (Oken Tester Method) does not need to exceed 100,000 seconds, and the upper limit of air resistance (Oken Tester Method) can be, for example, 90,000 seconds or less, or 80,000 seconds or less.

[0035] The release paper base paper of the present invention preferably has an Oken smoothness of 500 seconds or more and 2,000 seconds or less on the surface having the sealing layer, as specified in JIS P 8155:2010. If the Oken smoothness is less than 500 seconds, the amount of expensive release agent required to be applied increases, which is uneconomical. On the other hand, if it exceeds 2,000 seconds, the anchoring ability of the release agent decreases, and there is a concern that the release agent layer may collapse during processing into an adhesive label.

[0036] The release paper base paper of the present invention preferably has an ash content of 8% or more and 30% or less according to JIS P 8251:2003. If the ash content is less than 8%, the paper shrinkage during processing into an adhesive label, etc., will easily cause wrinkles to form in the top paper (the paper substrate of the adhesive label, etc., to be attached to the release paper). On the other hand, if the ash content exceeds 30%, the strength of the paper will decrease, making it more likely to tear during processing into an adhesive label, etc. The ash content is more preferably 9% or more, even more preferably 10% or more, and more preferably 25% or less, even more preferably 20% or less.

[0037] "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. When the release paper base paper has sealing layers on both sides, a release agent layer can be formed on at least one of the sealing layers. Furthermore, by using a release paper base paper with sealing layers on both sides and forming a release agent layer on both sides of this release paper base paper, it can be made into a release paper for double-sided tape. 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. As the release agent, any material with low surface energy and weak adhesive strength to the adhesive, such as a silicone resin, a fluorine compound, an aminoalkyd compound, or a polyester compound, can be used without any particular limitation. However, in the present invention, it is preferable to use a silicone resin. 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 a release agent layer is formed on both sides, the composition of the coating liquid for forming the release agent layer on each side may be the same or different.

[0038] 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.

[0039] 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. ２Even 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.

[0040] 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.

[0041] 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.

[0042] <Physical Properties of Inorganic Pigments> (1) 50% Volume Average Particle Diameter (D50) This was measured using a laser diffraction / scattering particle size distribution analyzer (MASTER SIZER S, manufactured by Malvern Instruments).

[0043] <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.

[0044] <Quality evaluation of release paper base 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) 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. (4) Oken air resistance: Measured using a method (Oken testing machine method) in accordance with JIS P 8117:2009. (5) Ash content: Measured in accordance with JIS P 8251:2003.

[0045] (6) 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 removing them from the water, excess water was wiped off. The length in the transverse direction was measured, and the shrinkage before and after immersion was calculated.

[0046] (7) Cobb water absorbency: Measured according to ISO 535:1991 with a contact time of 30 seconds. (8) Cellopic strength: Measurement environment: The coating layer strength was measured using a cellopic measuring device at 23°C and 50% humidity. For the measurement, a transparent adhesive tape (CT24, 24 mm wide, manufactured by Nichiban) was applied to the surface of the sealing layer and pressed back and forth with a rubber roller (2 kg) 20 times, and the force required to peel it off was measured using a digital force gauge (FGX-2, manufactured by SHIMPO) (peel speed: 20 m / min, peel angle: 180°).

[0047] (9) 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 for paper according to the following criteria. If the evaluation was ○ or △, there was no problem in practical use. [Evaluation criteria] ○: Pulp fibers were dispersed, disintegration was good, and the paper could be reused for paper. △: There were slight bundles of pulp fibers. ×: Clumps of pulp fibers or bundles of pulp fibers remained, the paper could not be disintegrated, and the paper could not be reused for paper.

[0048] <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 five times back and forth over an area of ​​approximately 5 cm with a finger (load of approximately 500 g), and the surface condition was visually observed and evaluated according to the following three levels. 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.

[0049] (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 three levels. 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.

[0050] (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 sheet 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. 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.

[0051] (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. ２The 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 Industries) 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 one shown in Figure 1), 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.

[0052] (5) A release paper suitable for scrap removal is coated with an adhesive (Saibinol AT-27, manufactured by Saiden Chemical) at a rate of 30 g / m ２ The top paper (cast coated paper for labels, 60 g / m ２ ) was adhered to an adhesive label paper, which was die-cut into a label of a predetermined shape, and the non-label portion was peeled off at a speed of 300 m / min. The surface of the release paper was evaluated according to the following criteria. If the evaluation was ○ or △, there was no problem in practical use. [Evaluation criteria] ○: A clean surface with no scratches or paper tears. △: Some areas where the surface of the coating layer had been slightly removed were visible. ×: Some areas where the paper had been torn or the coating layer had been removed were visible on the surface of the release paper.

[0053] (6) Silicone Holdout (Sealing Ability of Silicone) 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. Then, the L value of UVIn was measured using a spectrophotometer (Murakami Color Research Laboratory Co., Ltd., CMS-35SPXM) in accordance with JIS P 8148:2018. ＊ a ＊ b ＊ Before and after the application of malachite green, L ＊ a ＊ b ＊ The ΔE (color difference) was calculated from the above.

[0054] [Example 1] (Preparation of base paper) 70 parts by mass of hardwood kraft pulp (LBKP, 360 ml CSF) and 30 parts by mass of softwood kraft pulp (NBKP, 400 ml CSF) were mixed to prepare a raw pulp. 3 parts by mass of light calcium carbonate was added as a filler to 100 parts by mass of the raw pulp. Then, 0.5 parts by mass of cationized starch, 1.0 part by mass of an internal sizing agent, and 1.5 parts by mass of aluminum sulfate were added as paper strength agents. The paper was then made using a fourdrinier multi-cylinder paper machine and calendered to a basis weight of approximately 49 g / m. ２ The base paper was obtained.

[0055] (Preparation of coating liquid for filling layer) A coating liquid for filling layer was prepared by blending 100 parts by mass of solid content kaolin (KCS manufactured by Imerys, D50: 4.6 μm, aspect ratio: 13) as an inorganic pigment, 25 parts by mass (on bone dry basis) of synthetic resin latex (manufactured by Nippon A&L Co., Ltd., trade name: PA0330, styrene-butadiene copolymer latex, Tg -10°C) as an adhesive, 5 parts by mass of starch-based compound (MS#3800 manufactured by Nippon Shokuhin Kako Co., Ltd.), and 1 part by mass of lubricant (Nopcoat C-104 manufactured by San Nopco Ltd.). (Coating) Immediately after the preparation of the base paper, the coating liquid for filling layer was applied to the surface (release agent-coated surface) of the base paper using a blade coater so that the target coating amount on one side was 8 g / m2 in terms of dry mass. ２ On the back side, to correct curling, a blade coater was used to apply the same coating solution for the filler layer to a target dry mass of 3 g / m. ２ The resulting coating was dried and calendered to obtain a base paper for release paper.

[0056] (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.

[0057] (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. ２ After 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.

[0058] [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 22 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 starch-based compound in the coating liquid for the filling layer was 10 parts by mass and the amount of synthetic resin latex was 30 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 sizing agent in the base paper was 2 parts by mass relative to the pulp.

[0059] Example 5 A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the amount of sizing agent in the base paper was changed to 0.5 parts by mass based on the pulp.

[0060] [Example 6] The coating amount of the sealing layer was 4.5 g / m in terms of dry mass. ２ A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the sealing layer was coated so that the coating amount was 12.0 g / m2 in terms of dry mass. ２ A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the LBKP had a freeness of 200 ml CSF and the NBKP had a freeness of 220 ml CSF.

[0061] [Example 9] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that the filler in the base paper was 18 parts by mass relative to the pulp. [Example 10] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that 90 parts by mass of LBKP and 10 parts by mass of NBKP were used. [Example 11] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that 40 parts by mass of LBKP and 60 parts by mass of NBKP were used.

[0062] [Example 12] The coating liquid for the filling layer was also applied to the back side of the base paper in a single-side coating amount of 8 g / m2 in terms of dry mass. ２ A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the coating liquid for the filler layer was also applied to the back side of the base paper in a single-side coating amount of 8 g / m2 in terms of dry mass, and then dried to form a filler layer, and release layers were formed on the filler layers on both sides in the order of the front side and the back side. ２The base paper for release paper and the release paper were obtained in the same manner as in Example 2, except that the coating liquid for the filler layer was also applied to the back side of the base paper in a single-side coating amount of 8 g / m2 in terms of dry mass, and then dried to form a filler layer, and release layers were formed on the filler layers on both sides in the order of the front side and the back side. ２ A base paper for release paper and a release paper were obtained in the same manner as in Example 3, except that the coating liquid for the filler layer was also applied to the back side of the base paper in a single-side coating amount of 8 g / m2 in terms of dry mass, and then dried to form a filler layer, and release layers were formed on the filler layers on both sides in the order of the front side and the back side. ２ A base paper for release paper and a release paper were obtained in the same manner as in Example 4, except that a filler layer was formed by coating and drying the filler layer so that the filler layer was formed on both sides, and release layers were formed on the front and back surfaces in that order.

[0063] [Comparative Example 1] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that the pigment in the filling layer was heavy calcium carbonate (TP-SO-10, manufactured by Okutama Kogyo Co., Ltd., D50: 8.0 μm, aspect ratio 1). [Comparative Example 2] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that the amount of synthetic resin latex in the filling layer coating liquid was 20 parts by mass. [Comparative Example 3] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that the amount of starch-based compound in the filling layer coating liquid was 15 parts by mass and the amount of synthetic resin latex was 30 parts by mass. [Comparative Example 4] A release paper base paper and release paper were obtained in the same manner as in Example 1, except that the amount of synthetic resin latex in the filling layer coating liquid was 35 parts by mass.

[0064] [Comparative Example 5] A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the LBKP had a freeness of 200 ml CSF, the NBKP had a freeness of 220 ml CSF, and the amount of sizing agent in the base paper was 2 parts by mass relative to the pulp. [Comparative Example 6] A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the amount of sizing agent in the base paper was 0.2 parts by mass relative to the pulp. [Comparative Example 7] A sealing layer was formed with a coating amount of 15.0 g / m2 in terms of dry mass. ２ A base paper for release paper and a release paper were obtained in the same manner as in Comparative Example 2, except that the coating was carried out so that the thickness of the base paper was 100 μm or more.

[0065] [Comparative Example 8] A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the coating liquid for the filling layer did not contain a pigment. [Comparative Example 9] A base paper for release paper and a release paper were obtained in the same manner as in Example 1, except that the synthetic resin latex in the coating liquid for the filling layer was completely saponified polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.).

[0066] Tables 1 to 3 show the evaluation results of the base paper for release paper and the release paper obtained in each example and comparative example.

[0067]

[0068]

[0069] In Examples 1 to 15 and Comparative Examples 1 and 8, when a base paper for release paper containing a pigment in the filling layer, and the pigment was a flat pigment, was provided with a release agent layer thereon, release paper with excellent silicone suitability could be obtained. In Examples 1 to 15 and Comparative Examples 2, 4, and 7, when a base paper for release paper in which the blending amount of synthetic resin latex in the coating liquid for the filling layer was 22 parts by mass or more and 30 parts by mass or less was provided with a release agent layer thereon, release paper with excellent silicone suitability could be obtained. In Examples 1 to 15 and Comparative Examples 3 and 8, when a base paper for release paper in which the mass ratio of pigment to adhesive in the filling layer was 70 / 30 to 80 / 20 was provided with a release agent layer thereon, release paper with excellent silicone suitability could be obtained.

[0070] From Examples 1 to 15 and Comparative Examples 5 and 6, the Cobb water absorption (30 seconds) of the surface of the filling layer measured according to ISO 535:1991 was 5 g / m ２ 25g / m or more ２By providing a release agent layer on the release paper described below, it was possible to obtain release paper with excellent silicone suitability. Examples 1 to 15 and Comparative Example 9 demonstrate that by providing a release agent layer on the release paper using a synthetic resin latex in the coating liquid for the filling layer, it was possible to obtain release paper with excellent silicone suitability. It was confirmed that the release paper base paper obtained in the Examples of the present invention was disintegrable and could be recycled as waste paper material. Furthermore, the release paper base paper obtained in the Examples of the present invention was excellent in silicone curing property, silicone adhesion, releasability, appearance after moisture absorption and desorption, and sludge removal suitability, and maintained its original physical properties and shape almost unchanged even after the adherend was removed, making it possible to reuse the release paper base paper as it was without disintegration.

Claims

1. A paper substrate comprising a base paper and a filler layer on at least one surface of the base paper, the filler layer containing a pigment and an adhesive in a mass ratio of 70 / 30 to 80 / 20 (pigment / adhesive: dry mass), the pigment containing 90 mass% or more of a flat pigment, the adhesive containing at least a starch-based compound and a synthetic resin latex, the blending amount of the synthetic resin latex per 100 mass parts of the pigment being 22 mass parts to 30 mass parts, and the Cobb water absorbency (30 seconds) of the surface of the filler layer measured in accordance with ISO 535:1991 is 5 g / m ２ 25g / m or more ２ A release paper base paper characterized by the following:

2. The basis weight of the release paper base paper is 40 g / m ２ 90g / m or more ２ the coating amount of the sealing layer is 5 g / m or less in terms of dry mass per one side ２ 10g / m or more ２ 2. The release paper base paper according to claim 1, wherein the release paper base paper is:

3. The base paper for release paper according to claim 1, characterized in that the average particle size of the flat pigment at 50% by volume is 1.0 μm or more and 7.0 μm or less.

4. 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 2.5% or less.

5. The release paper base paper according to claim 1, characterized in that the Oken air resistance of the release paper base paper in accordance with JIS P 8117:2009 is 20,000 seconds or more.

6. 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 500 seconds or more and 2,000 seconds or less.

7. 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 8% or more and 30% or less.

8. The release paper base paper according to claim 1, characterized in that there is no undercoat layer between the base paper and the filling layer.

9. The release paper base paper according to claim 1, characterized in that the base paper contains a total of 90% by mass or more of hardwood pulp and softwood pulp relative to the total papermaking fibers, the solid mass ratio of the hardwood pulp to the softwood pulp (hardwood pulp:softwood pulp) is 80:20 to 50:50, the freeness of the hardwood pulp is 300 ml CSF or more and 400 ml CSF or less, and the freeness of the softwood pulp is 300 ml CSF or more and 450 ml CSF or less.

10. 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 9.

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

12. A method for producing a base paper for release paper, comprising the steps of: applying, on at least one surface of the base paper, a coating solution for a filling layer, the coating solution containing a pigment and an adhesive in a mass ratio of 70 / 30 to 80 / 20 (pigment / adhesive: dry mass), the pigment containing 90 mass% or more of a flat pigment, the adhesive containing at least a starch-based compound and a synthetic resin latex, the amount of the synthetic resin latex blended relative to 100 mass parts of the pigment being 22 mass parts to 30 mass parts, by on-machine coater; and ２ 25g / m or more ２ A method for producing a base paper for release paper, characterized in that:

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