JP7808082B2 - Release paper base paper and release paper - Google Patents

Description

The present invention relates to a base paper for release paper used in release papers for adhesive labels, etc., and to a release paper in which a release agent layer is provided on this base paper for release paper.

Release paper is attached to the adhesive surface of adhesive labels, adhesive stickers, adhesive tapes, etc. to protect the adhesive surface and prevent the adhesive surface from becoming dirty, the adhesive strength from decreasing, etc. The release paper has a release agent layer on the surface that comes into contact with the adhesive surface so that it can be easily peeled off from the adhesive surface.
Silicone resin is generally used as the release agent, but since silicone resin is very expensive, polyethylene laminated paper, which has excellent sealing properties and is difficult for silicone resin coating liquid to penetrate, is used as the base paper for the release paper so that a release agent layer can be formed with a small amount of silicone resin.
However, polyethylene-laminated paper has a tough polyethylene coating formed on the surface of the paper, which makes it difficult to disintegrate after use, making it unsuitable for recycling.

In Patent Document 1, the applicant has proposed a base paper for release paper that has a pigment coating layer to suppress the penetration of a release agent coating liquid such as a silicone resin, and that is recyclable because it uses a base paper mainly made of wood pulp.Furthermore, in Patent Document 2, the applicant has proposed a base paper for release paper that is recyclable and has a filling layer containing a pigment component, allowing the release agent coating liquid to be applied uniformly.
These base papers for release paper have been developed to suppress the penetration of release agents while maintaining releasability, but further improvements in performance are required.

Japanese Patent Application Laid-Open No. 2000-282397 Japanese Patent Application Laid-Open No. 2016-223036

The objective of the present invention is to provide a base paper for release paper that has excellent sealing properties, can form a uniform release agent layer, and is recyclable, as well as a release paper that has a uniform release agent layer and is excellent in releasability, adhesion, and durability.

The means for solving the problems of the present invention are as follows.
1. A base paper and a sealing layer on at least one surface of the base paper,
the sealing layer contains a pigment and an adhesive in a mass ratio of 75/25 to 25/75 (pigment/adhesive: dry mass),
the adhesive contains a starch-based compound and a synthetic resin latex in an amount of 80% by mass or more relative to the total amount of the adhesive and in a mass ratio of 90/10 to 50/50 (starch-based compound/synthetic resin latex: dry mass);
A release paper base paper having an air resistance (Oken type testing machine method) in accordance with JIS P 8117:2009 of 3,000 seconds or more and 20,000 seconds or less.
2. The release paper base paper according to 1., wherein the coating amount of the filling layer is 2 g/ ^m2 or more and 6 g/ ^m2 or less in dry mass per side.
3. The release paper base paper according to 1. or 2., wherein the smoothness of the sealing layer measured in accordance with JIS P8155:2010 (Oken type testing machine method) is 50 seconds or more and 300 seconds or less.
4. The release paper base paper according to any one of 1. to 3., wherein the basis weight of the base paper is 30 g/ ^m2 or more and 80 g/ ^m2 or less.
5. A release paper characterized by having a release agent layer on the sealing layer of the release paper base paper described in any one of 1. to 4.
6. On at least one side of the base paper,
A method for producing base paper for release paper, characterized in that a coating solution for a sealing layer containing at least a pigment and an adhesive in a mass ratio of 75/25 to 25/75 (pigment/adhesive, dry mass), and containing a starch-based compound and a synthetic resin latex as the adhesive in an amount of 80 mass% or more based on the total amount of the adhesive and in a mass ratio of 90/10 to 50/50 (starch-based compound/synthetic resin latex, dry mass), is applied by an on-machine coater.

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 with excellent adhesion, releasability, and durability. 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 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.

The release paper base paper of the present invention comprises a base paper and a sealing layer on at least one surface of the base paper,
the sealing layer contains a pigment and an adhesive in a mass ratio of 75/25 to 25/75 (pigment/adhesive: dry mass),
The adhesive contains a starch-based compound and a synthetic resin latex in an amount of 80% by mass or more relative to the total amount of the adhesive and in a mass ratio of 90/10 to 50/50 (starch-based compound/synthetic resin latex: dry mass),
The air resistance (Oken type testing machine method) according to JIS P 8117:2009 is 3000 seconds or more and 20000 seconds or less.
In this specification, the expression "A to B (A and B are numbers)" means a numerical range including the values of A and B, that is, A or more and B or less.

"Base paper"
In the present invention, the base paper is a sheet composed of papermaking fibers, fillers, various auxiliaries, etc. Wood pulp is preferably used as the papermaking fiber. 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. These wood pulps can be used alone or in combination of two or more. Furthermore, 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 as needed.
It is preferable to use softwood kraft pulp because the coating liquid for the filler layer is less likely to penetrate into the resulting base paper, allowing for the formation of a dense filler layer. It is also preferable to reduce the freeness of the papermaking fiber. Specifically, the freeness (Canadian Standard Freeness: CSF) of the papermaking fiber is preferably 500 ml or less, and more preferably 450 ml or less.

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 fillers. In the present invention, fillers are optional components, and the paper may be free of fillers. The inclusion of a filler improves the smoothness, opacity, whiteness, etc. of the base paper, but also makes it easier for the coating liquid for the filling layer to penetrate into the resulting base paper. Therefore, the amount of filler to be incorporated should be determined taking these properties into consideration. The filler content 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.

Auxiliaries 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, and other papermaking aids. Furthermore, dyes, fluorescent brighteners, pH adjusters, defoamers, pitch control agents, slime control agents, and other additives can also be added as needed.

The method for manufacturing the base paper (papermaking) is not particularly limited, and the base paper can be manufactured using known Fourdrinier formers, on-top hybrid formers, gap formers, etc., by acidic, neutral, or alkaline papermaking methods. The base paper may be composed of a single layer, or two or more layers.

Furthermore, the surface of the base paper can be treated with various chemicals, such as polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retaining agents, thickeners, and lubricants, 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.
The basis weight of the base paper is not particularly limited, but is preferably 30 g/m ² or more and 80 g/m ² or less, and more preferably 40 g/m ² or more and 70 g/m ² or less.

"Sealing layer"
The filling layer is provided on at least one surface of the base paper, and may be provided on both surfaces.
The filling layer contains a pigment and an adhesive in a mass ratio of 75/25 to 25/75 (pigment/adhesive, dry mass), and contains a starch-based compound and a synthetic resin latex in an amount of 80 mass% or more relative to the total amount of adhesive, and in a mass ratio of 90/10 to 50/50 (starch-based compound/synthetic resin latex, dry mass). The base paper for release paper of the present invention has good filling properties because the filling layer satisfies this composition, and by providing a release agent layer on this filling layer, it is possible to obtain a release paper with excellent releasability, adhesion, and durability.
The filling layer may also contain various auxiliaries such as CNF, MFC, dispersants, water-resistant agents, lubricants, antifoaming agents, thickeners, water-retaining agents, crosslinking agents, surfactants, preservatives, dyes, and fluorescent dyes, within a range that does not impair the effects of the present invention.

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, and organic pigments such as solid, hollow, and core-shell pigments can be used alone or in combination of two or more.

The pigment preferably has a 50% volume average particle size (D50, median diameter) measured by a laser diffraction/scattering method of 2.0 μm or more and 7.0 μm or less, more preferably 3.0 μm or more, and even more preferably 5.0 μm or less.
If the D50 of the pigment is less than 2.0 μm, the effect of filling the gaps between the fibers on the surface of the base paper can be obtained, but the resin latex cannot sufficiently bond the pigments, and the number of fine gaps increases, which may result in a decrease in the filling ability and a decrease in the uniformity of the release agent layer. Also, if the D50 of the pigment exceeds 7.0 μm, the unevenness of the surface of the filling layer may increase, which may also result in a decrease in the uniformity of the release agent layer.
Examples of measuring devices that use 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.

Adhesive The adhesive contains at least a starch-based compound and a synthetic resin latex.
The adhesive may contain other adhesives within the scope of the present invention, such as polyvinyl alcohols (fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymer polyvinyl alcohol, etc.), proteins (casein, soy protein, synthetic protein, etc.), cellulose derivatives (carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, etc.), polyvinylpyrrolidone, sodium alginate, etc., and water-soluble resins.

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.

The synthetic resin latex is not particularly limited, and can be a variety of 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. One or more types can be used in combination. Among these, styrene-butadiene copolymer latexes are preferred, as they offer excellent sealing properties for silicone resins. Furthermore, synthetic resin latexes with an average particle size of 100 μm or greater, and 150 μm or greater, as measured by dynamic light scattering (photon correlation spectroscopy) are preferred. An example of a measuring device using dynamic light scattering (photon correlation spectroscopy) is the "FPAR-1000" manufactured by Otsuka Electronics Co., Ltd.

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 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.
The Tg of the synthetic resin latex is determined by pretreating the synthetic resin latex at 130°C for 30 minutes, and then measuring the change in specific heat accompanying the second-order transition with a differential scanning calorimeter (heating a 10 mg sample at 20°C/min in a nitrogen atmosphere in accordance with JIS K-7122), and then calculating it from the following formula:
Tg=Tg1×α1+Tg2×α2+...+Tgn×αn
Tg1, Tg2...Tgn: Measured glass transition temperature (K) of each composition alone
α1, α2...αn: mass fraction (%) of each component with respect to the total resin mass

In the filling layer, the mass ratio of the pigment to the adhesive (pigment/adhesive, dry mass) is preferably 70/30 to 30/70, and more preferably 60/40 to 40/60.
The total proportion of the starch-based compound and synthetic resin latex to the total amount of the adhesive is preferably 85% by mass or more, more preferably 90% by mass or more, and the mass ratio of the starch-based compound to the synthetic resin latex (starch-based compound/synthetic resin latex, dry mass) is preferably 80/20 to 55/45.

The coating method for the sealing layer is not particularly limited, and the coating can be performed using a known coating device and coating system. Examples of the coating device 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, an aqueous coating system using water as a medium is preferred.
In the present invention, it is preferable to carry out coating using an on-machine coater in which a paper machine and a coating device are integrated. When coating is carried out using an off-machine coater in which the paper machine and the coating device are separate, the base paper is made on the paper machine, then wound up onto a reel, and the reel is then subjected to coating in the off-machine coater. However, coating using an on-machine coater can omit the steps of winding up the base paper and subjecting it to the coater, thereby improving production efficiency.
On the other hand, in coating by an on-machine coater, the coating speed needs to be synchronized with the papermaking speed of the papermaking machine, and therefore adjustment of the coating amount is more difficult than in coating by 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 particularly small, and therefore it is easy to satisfy the desired performance even when coating by an on-machine coater.
The method for drying the filling layer may 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.

The coating amount of the sealing layer is preferably 2 g/ ^m2 or more and 6 g/ ^m2 or less in dry mass per side. If this coating amount is less than 2 g/ ^m2 , it may be difficult for the resulting sealing layer to prevent penetration of the coating liquid for the release agent layer. On the other hand, even if this coating amount exceeds 6 g/ ^m2 , there is almost no improvement in sealing property and the cost becomes high. The coating amount of the sealing layer is more preferably 3 g/ ^m2 or more in dry mass per side, and even more preferably 4 g/ ^m2 or more. Furthermore, the coating amount of the sealing layer is more preferably 5 g/ ^m2 or less in dry mass per side.

In the release paper base paper of the present invention, the air resistance (Oken Tester Method) of the surface having the sealing layer, as specified in JIS P 8117:2009, is 3,000 seconds or more and 20,000 seconds or less. When the air resistance (Oken Tester Method) is within this range, the release agent can be applied uniformly, and the release paper obtained has excellent adhesion and releasability, as well as excellent disintegration properties. It is more preferable that the air resistance (Oken Tester Method) be 5,000 seconds or more and 15,000 seconds or less.

In the release paper base paper of the present invention, the smoothness (Oken testing machine method) of the surface having the sealing layer, measured in accordance with JIS P8155:2010, is preferably 50 seconds or more and 300 seconds or less, and more preferably 70 seconds or more and 280 seconds or less.

"Release paper"
Release paper can be produced by coating a release agent on the sealing layer of the base paper for release paper of the present invention to form a release agent layer. As the release agent, any material with low surface energy and weak adhesive strength to the adhesive, such as silicone resin, fluorine compound, aminoalkyd compound, polyester compound, etc., can be used without any particular limitation, but 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.

The method for applying the release agent is not particularly limited, and the release agent can be applied using a known coating device and coating system, such as 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, or a gate roll coater.
The release agent layer can be dried by any conventional method, such as using a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, or cylinder dryer.

The coating amount of the release agent layer is preferably 0.2 g/ ^m2 or more and 3.0 g/ ^m2 or less in dry mass per side. If the coating amount is less than 0.2 g/ ^m2 , it becomes difficult to obtain a uniform release agent layer. On the other hand, even if the coating amount exceeds 3.0 g/ ^m2 , there is almost no improvement in releasability, and the effect becomes saturated. The coating amount of the release agent layer is more preferably 0.3 g/ ^m2 or more and 2.0 g/ ^m2 or less in dry mass per side. It is even more preferable that the coating amount of the release agent layer is 0.4 g/ ^m2 or more in dry mass per side. It is even more preferable that the coating amount of the release agent layer is 1.2 g/ ^m2 or less in dry mass per side.

As described above, the release paper base paper of the present invention has a highly uniform filling layer and good filling properties, and a uniform release agent layer can be formed on this filling layer.

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 weight in the examples refer to parts by weight on an bone-dry basis unless otherwise specified.

The volume 50% average particle size (D50) of the pigments used in the examples, measured by a laser diffraction/scattering method, as well as the quality of the base paper for release paper and the quality of the release paper, were measured and evaluated by the following methods.
<50% Volume Average Particle Diameter (D50) of Pigment Measured by Laser Diffraction/Scattering Method>
Measurement was carried out using a laser diffraction/scattering particle size distribution analyzer (manufactured by Malvern Instruments, device name: Mastersizer S).

<Quality evaluation of release paper base paper>
(1) Air resistance (Oken tester method)
Measurement was carried out by a method conforming to JIS P 8117:2009 (Oken type testing machine method).
(2) Smoothness (Oken type testing machine method)
Based on JIS P8155:2010, the surface of the filling layer was measured using an Oken type smoothness meter (manufactured by Asahi Seiko Co., Ltd.: KY-5).
(3) Disintegrability A 40 g bone dry mass of base paper for release paper was immersed in 2 L of water and disintegrated for 60 minutes using a pulp disintegration tester (manufactured by Kumagai Riki Kogyo Co., Ltd., in accordance with JIS P 8220). The degree of disintegration into the aqueous solution was visually observed and evaluated according to the following three levels:
○: Pulp fibers are dispersed and disintegration is good.
△: A small amount of pulp fiber remains bound together, but the defibration properties are generally good.
×: Clumps of pulp fibers or bundles of pulp fibers remain, and disintegration is poor.

<Quality evaluation of release paper>
(1) Peel strength An acrylic emulsion adhesive (AT-27, manufactured by Saiden Chemical Co., Ltd.) was applied onto the release agent layer of the release paper so that the coating amount was 50 g/ ^m2 in dry mass, and then dried at 110°C for 3 minutes to form an adhesive layer. Next, wood-free paper (basis weight 64 g/ ^m2 ) was attached onto the adhesive layer to prepare adhesive paper.
This pressure-sensitive 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 where the fine paper was peeled off in a 180° direction at a rate of 300 mm/min, in accordance with JIS Z0237: 2009. A peel strength of 40 to 150 mN/30 mm is acceptable for practical use.
(2) Adhesion The surface of the release agent layer of the release paper was rubbed with a finger (loaded with approximately 3 kg) back and forth over an area of about 5 cm five times, and the surface condition was visually observed and evaluated according to the following three levels.
○: No marks are left on the rubbed area.
Δ: Marks were left at the rubbed areas, but the release agent layer was not peeled off.
×: The release agent layer peeled off at the rubbed area.
(3) Durability After treatment for 3 days in an environment of 70°C and 90% RH, the surface of the release agent layer of the release paper was rubbed with a finger (with a load of approximately 3 kg) back and forth over an area of approximately 5 cm five times, and the surface condition was visually observed and evaluated according to the following three levels.
○: No marks are left on the rubbed area.
Δ: Marks were left at the rubbed areas, but the release agent layer was not peeled off.
×: The release agent layer peeled off at the rubbed area.

[Example 1]
(Preparation of coating liquid for sealing layer)
A coating solution for a sealing layer was prepared by blending 50 parts by mass of kaolin (KCS, D50: 4.6 μm, manufactured by Imerys Co., Ltd.) as a pigment, 30 parts by mass of oxidized starch (MS#3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) as a starch-based compound, 20 parts by mass of styrene-butadiene copolymer latex (SN-307R, Tg: 8° C., manufactured by Nippon A&L Inc.) as a synthetic resin latex, and 0.1 parts by mass of a lubricant (Nopcoat C-104, manufactured by San Nopco Ltd.).

(Preparation of base paper)
100 parts by mass of hardwood kraft pulp (LBKP) with a Canadian Standard Freeness (CSF) of 300 ml was used as the raw pulp. 0.3 parts by mass of cationic starch was added as a paper strength agent to 100 parts by mass of the raw pulp, and then 1.5 parts by mass of aluminum sulfate was added. Papermaking was then carried out using a fourdrinier multi-cylinder papermaking machine to obtain a base paper with a basis weight of 56 g/ ^m2 .

(Preparation of base paper for release paper)
The coating liquid for the filling layer was applied to one side of the obtained base paper using an on-machine blade coater so that the coating amount was 4.0 g/ ^m2 in dry mass, and then dried to obtain a base paper for release paper.

[Example 2]
A base paper for release paper was obtained in the same manner as in Example 1, except that the amount of kaolin in the coating liquid for the filling layer was 70 parts by mass, the amount of the starch-based compound was 20 parts by mass, and the amount of the synthetic resin latex was 10 parts by mass.
[Example 3]
A base paper for release paper was obtained in the same manner as in Example 1, except that the amount of kaolin in the coating liquid for the filling layer was 30 parts by mass and the amount of the starch-based compound was 50 parts by mass.
[Example 4]
A base paper for release paper was obtained in the same manner as in Example 1, except that the starch-based compound in the coating liquid for the filling layer was 45 parts by mass and the synthetic resin latex was 5 parts by mass.
[Example 5]
A base paper for release paper was obtained in the same manner as in Example 1, except that the starch-based compound and the synthetic resin latex in the coating liquid for the filling layer were 25 parts by mass and 25 parts by mass, respectively.

[Comparative Example 1]
A base paper for release paper was obtained in the same manner as in Example 1, except that the amount of kaolin in the coating liquid for the filling layer was 20 parts by mass and the amount of the starch-based compound was 60 parts by mass.
[Comparative Example 2]
A base paper for release paper was obtained in the same manner as in Example 1, except that the amount of kaolin in the coating liquid for the filling layer was 80 parts by mass, the amount of the starch-based compound was 10 parts by mass, and the amount of the synthetic resin latex was 10 parts by mass.
[Comparative Example 3]
A base paper for release paper was obtained in the same manner as in Example 1, except that the starch-based compound in the coating liquid for the filling layer was 46 parts by mass and the synthetic resin latex was 4 parts by mass.
[Comparative Example 4]
A base paper for release paper was obtained in the same manner as in Example 1, except that the starch-based compound in the coating liquid for the filling layer was 20 parts by mass and the synthetic resin latex was 30 parts by mass.

[Comparative Example 5]
A base paper for release paper was obtained in the same manner as in Example 1, except that 20 parts by mass of the synthetic resin latex in the coating liquid for the filling layer was changed to 20 parts by mass of fully saponified polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.).
[Comparative Example 6]
A release paper base paper was obtained in the same manner as in Example 1, except that 50 parts by mass of kaolin in the coating liquid for the sealing layer was changed to 50 parts by mass of silica (Mizukasil P-50, D50: 10.0 μm, manufactured by Mizusawa Industrial Chemicals Co., Ltd.).
[Comparative Example 7]
A base paper for release paper was obtained in the same manner as in Example 1, except that the coating liquid for the filling layer was applied so that the coating amount was 8 g/m ² in terms of dry mass, and then dried.

(Preparation of Coating Solution for Release Agent Layer)
Two parts of a catalyst were added to a solventless silicone resin (manufactured by Toray Dow Corning Silicone Co., Ltd.: LTC-1053L) to prepare a coating liquid for the release agent layer.

(Preparation of release paper)
The coating solution for the release agent layer was applied onto the sealing layer of the base paper for release paper using an RI printing machine so that the coating amount was 1.0 g/ ^m2 in terms of dry mass, and then the coating solution was cured in a dryer (130°C, 30 seconds) to obtain a release paper.

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

Claims (6)

A base paper and a sealing layer on at least one surface of the base paper,
the sealing layer contains a pigment and an adhesive in a mass ratio of 75/25 to 25/75 (pigment/adhesive: dry mass),
The adhesive contains a starch-based compound and a synthetic resin latex in an amount of 80% by mass or more based on the total amount of the adhesive, and in a mass ratio (starch-based compound/synthetic resin latex: dry mass) of 80/20 to 55/45 ,
A release paper base paper having an air resistance (Oken type testing machine method) in accordance with JIS P 8117:2009 of 3,000 seconds or more and 20,000 seconds or less. 2. The release paper base paper according to claim 1, wherein the coating amount of the filling layer is 2 g/m ^{<2 >} or more and 6 g/m ^{<2 >} or less in dry mass per side. The release paper base paper according to claim 1 or 2, characterized in that the smoothness of the sealing layer, measured in accordance with JIS P8155:2010 (Oken type testing machine method), is 50 seconds or more and 300 seconds or less. 4. The release paper base paper according to claim 1, wherein the basis weight of the base paper is 30 g/m ² or more and 80 g/m ² or less. A release paper characterized by having a release agent layer on the sealing layer of the release paper base paper described in any one of claims 1 to 4. On at least one side of the base paper,
A method for producing base paper for release paper, characterized in that a coating solution for a sealing layer containing at least a pigment and an adhesive in a mass ratio of 75/25 to 25/75 (pigment/adhesive, dry mass), and containing a starch-based compound and a synthetic resin latex as the adhesive in an amount of 80 mass% or more based on the total amount of the adhesive and in a mass ratio of 80/20 to 55/45 (starch-based compound/synthetic resin latex, dry mass), is applied by an on-machine coater.