JP2011214158A - Base paper for release paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide base paper for release paper that has excellent paper stiffness, a disintegration property, slightly causes paper powder and has optical transparency with no problem of position detection performance by a photoelectric tube.SOLUTION: The base paper for release coated paper having a spectral transmittance at 960 nm of ≥30% is obtained by providing at least one side of base sheet with a filling property-imparting layer comprising a polyvinyl alcohol and/or starch as a main component. The base sheet is composed of a delignified cellulose-based fiber as a main component, contains 1-20 mass% of a core/shell type acrylic copolymer. In the core/shell type acrylic copolymer, the glass transition temperature of a resin constituting the core part is 0-40°C, the glass transition temperature of a resin constituting the shell part is ≥100°C, the ratio of the core part is 50-80 mass% and the ratio of the shell part is 20-50 mass%.

Description

  The present invention relates to a base paper for release paper used for release paper for adhesive labels and the like.

  Adhesive labels are widely used for labels and stickers such as glass containers, plastic containers, and paper containers, stickers, and emblems. This adhesive label usually has a release paper bonded to the opposite surface, and the release paper is discarded when the label is applied to a product container or the like.

When used in supermarkets, adhesive labels are printed, die-cut and wound into rolls one by one, and automatically weighed products are printed with quantities and barcodes using a printer, peeled off from release paper, and placed in product containers. Affixed. When used in this way, glassine paper with excellent light transmission is used for the release paper in order to use the difference in light transmission between the adhesive paper and the release paper in order to attach the surface label to the container accurately. It is common.
Glassine paper is made by pulverizing pulp and applying a water-soluble polymer resin such as polyvinyl alcohol or starch on the surface to which the release agent such as silicone resin is applied to increase the sealing effect of the release agent. In general, the sheet is compressed by a calendar or a super calendar.

For example, Patent Document 1 defines a glassine paper that uses a pulp having a Canadian standard freeness of 130 to 240 ml and defines a Cobb method sizing degree at a contact time of 30 seconds.
In Patent Document 2, paper made using chemical pulp with a Canadian freeness of 130 to 210 ml as a main raw material, and further subjected to on-machine coating with a coating solution containing a polyvinyl alcohol resin is subjected to compression treatment. The glassine paper to be finished is specified.
Further, Patent Document 3 stipulates a release paper for pressure-sensitive adhesive labels that is calendered after laminating a transparent layer on plain paper made from wood pulp with a Canadian standard freeness of 350 to 500 ml. .

Japanese Patent No. 3250340 JP-A-9-41286 JP 2003-253600 A

However, in the glassine paper of Patent Literature 1 and Patent Literature 2, in order to achieve transparency by increasing the bonding area between fibers by using high beaten pulp, and further densifying the paper layer by compression treatment, The paper becomes thinner and the paper becomes lower. Due to the reduction in paper stiffness, wrinkles and misalignments are likely to occur during die cutting and printing, resulting in poor work efficiency.
In addition, basically, the entire paper layer excluding the paper layer surface is mainly composed of pulp fibers, so that paper dust is likely to occur when cutting paper. If a lot of paper dust is generated, printing failure, barcode reading failure, mixing into foods, etc. will be a problem.
Also, in view of the recent increase in prevention of environmental pollution, the release paper is sometimes discarded after the adhesive paper label is affixed to a product container or the like, and is required to be able to be treated as paper waste or recycled as waste paper. Yes. However, glassine paper has the disadvantage that it does not disperse in water even when trying to disaggregate, because the fiber-to-fiber bond is strengthened by calendering, etc., in addition to using the pulp of the raw material extremely beaten. Yes. Furthermore, even if the mechanical treatment is strengthened, the fiber is remarkably damaged due to the strengthening of the beating treatment, and further the fiber damage proceeds by the disaggregation treatment. Therefore, it is difficult to reuse it as a raw material for general paper. is there.

  Moreover, in the release paper for pressure-sensitive adhesive labels of Patent Document 3, a clearing agent is laminated instead of using high beaten pulp to achieve transparency, but if the clearing agent is too sticky, the release paper There is a problem that even if it is attempted to disaggregate and recycle, there is a problem that it does not disperse in water. On the other hand, if the tackifier of the clearing agent is low, paper dust is generated when the release paper is cut.

  In view of the circumstances as described above, the present invention provides a base paper for release paper that has good paper stiffness and disaggregation, little generation of paper dust, and light transmittance that does not have a problem with position detection performance in a phototube. The purpose is to provide.

  As a result of intensive studies by the present inventors, by including a specific core / shell type acrylic copolymer, which is the purpose of imparting transparency, in the base paper, it has high light transmittance and disaggregation, And it discovered that the generation amount of paper powder decreased.

  Accordingly, the base paper for release paper of the present invention is a release paper having a spectral transmittance at 960 nm of 30% or more, wherein a sealing property-imparting layer mainly composed of polyvinyl alcohol and / or starch is provided on at least one side of the base paper. A base paper for paper, wherein the base paper is mainly composed of delignified cellulosic fibers and contains a core / shell type acrylic copolymer in an amount of 1 to 20% by mass, and the core / shell Type acrylic copolymer has a glass transition temperature of the resin constituting the core part of 0 ° C. to 40 ° C., a glass transition temperature of the resin constituting the shell part of 100 ° C. or more, and the ratio of the core part of 50 to 50 ° C. A base paper for release paper, characterized in that 80% by mass and the ratio of the shell part is 20 to 50% by mass.

The cellulosic fibers constituting the base paper preferably have a Canadian standard freeness of 150 to 350 ml. Further, the basis weight of the release paper base paper is preferably ³⁰ to 80 g / m ² and the density is 0.85 to 1.25 g / cm ³ .

  According to the present invention, high optical transparency can be obtained by adding a core / shell type acrylic copolymer to the base paper. In addition, by making the glass transition temperature of the core part 0 to 40 ° C, it is possible to reduce the amount of paper dust generated, and by making the glass transition temperature of the shell part 100 ° C or more, high disintegration can get. From the above, a release paper base paper having a contradictory performance of a small amount of paper dust generation and a high disaggregation property while having high light transmittance can be obtained.

  As cellulosic fibers constituting the base paper of the present invention, it is essential to use delignified wood-based chemical pulp fibers (bleached kraft pulp, bleached sulfite pulp). Either softwood or hardwood can be used as the material. If non delignified pulp such as crushed wood pulp or thermomechanical pulp is used, the intended light transmission cannot be obtained and it is unsuitable. In the base paper of the present invention, it is preferable that 90% by mass or more of the pulp fiber used as a raw material is delignified wood-based chemical pulp fiber.

  The pulp beating degree is preferably from 100 ml to 350 ml in Canadian standard freeness. If the Canadian standard freeness is less than 100 ml, the dewaterability of the wire part at the time of papermaking is significantly reduced, so it is not preferable because the papermaking speed needs to be greatly reduced. Further, if the Canadian standard freeness exceeds 350 ml, the bonding area between the fibers decreases, so even if pressure densification is carried out, the improvement in light transmittance is low, and the desired light transmittance cannot be obtained.

  Regarding the paper making of the above-mentioned base paper, paper additives such as paper strength enhancers, fixing agents, yield improvers, dyes, and carbonic acid as long as they do not affect the quality of light transmission, release agent sealing properties, etc. Internal fillers such as calcium, kaolin, talc and aluminum hydroxide can be added. However, it is preferable not to add a filler from the viewpoint of light transmittance and a paper dust suppressing effect.

  In the present invention, in order to impart light transmittance, disaggregation, and paper dust suppressing effect, the base paper needs to contain a core / shell type acrylic copolymer. The above-mentioned core / shell type acrylic copolymer is an aqueous emulsion of an acrylic copolymer having a core / shell structure, and at least two stages so that the polymer emulsion particles have a core / shell structure. The monomer mixture emulsified by changing the composition ratio of the monomer is prepared, and the first stage monomer mixture is dropped, and after the polymerization is almost completed, the second stage is dropped. It can be produced by a core / shell polymerization method in which emulsion polymerization is performed by a multistage monomer emulsion dropping method.

  The glass transition temperature of the core / shell type acrylic copolymer of the present invention is such that the core part is 0 ° C. to 40 ° C. and the shell part is 100 ° C. or higher, preferably the core part is 5 ° C. to 35 ° C. Part is 110 ° C. or higher. When the glass transition temperature of the core portion is less than 0 ° C., the acrylic copolymer becomes soft and the paper stiffness is lowered, and the adhesiveness becomes high, and it becomes difficult to disaggregate. If it exceeds 40 ° C., the acrylic copolymer becomes difficult to form a film, so the effect of suppressing paper dust is reduced, and at the same time, there are many interfaces between the copolymer particles, and the light transmittance is also reduced. On the other hand, when the glass transition temperature of the shell portion is less than 100 ° C., the acrylic copolymer becomes soft, so that the paper stiffness is lowered and the adhesiveness becomes high, so that it is difficult to disaggregate.

  Furthermore, the ratio of the core part of the core / shell type acrylic copolymer of the present invention is 50 to 80% by mass, and the mass ratio of the shell part is 20 to 50% by mass, more preferably the ratio of the core part. Is 60-75 mass%, and the ratio of a shell part is 25-40 mass%. When the ratio of the core part is less than 50% by mass and the ratio of the shell part exceeds 50% by mass, the acrylic copolymer becomes difficult to form a film, so the paper dust suppressing effect is reduced. Since there are many interfaces, the light transmittance is also lowered. In addition, the paper becomes too hard. For example, when the paper passes through a roll or bar having a small diameter, it is not preferable because the paper is broken or easily cracked. On the other hand, when the ratio of the core part exceeds 80% by mass and the ratio of the shell part is less than 20% by mass, the acrylic copolymer becomes soft and lowers the paper stiffness, and the adhesiveness becomes high, so it is difficult to disaggregate. Become.

  Here, the glass transition temperature of the copolymer refers to the weight fraction of each monomer in which the copolymer is formed, and the glass transition temperature of a single polymer derived from each monomer (K: Kelvin). Calculated as the reciprocal of the sum of each quotient obtained by dividing by the value.

  The content of the acrylic copolymer needs to be 1 to 20% by mass with respect to the base paper. If it is less than 1% by mass, the effect of imparting transparency and the effect of suppressing the generation of paper dust is insufficient, and if it exceeds 20% by mass, the imparting of transparency is sufficient, but the amount of resin becomes excessive, so the disaggregation property is impaired. In addition, the cost is increased and the practicality is poor. The transparency-imparting layer may contain various commonly used auxiliaries such as a dispersant, a release agent, a thickener, a water retention agent, an antifoaming agent, a preservative, and a water-resistant agent.

  Moreover, in order to obtain light transmittance, disaggregation, and paper dust suppression effect, it is preferable that the acrylic copolymer described above is not only penetrated into the surface layer but also penetrated into the paper layer to some extent. For this reason, it is preferable that the sizing degree of the base paper is 1 second or less, more preferably non-size paper.

  In the present invention, it is necessary to provide a sealing property-imparting layer mainly composed of polyvinyl alcohol and / or starch on at least one side of the base paper in order to impart the sealing property of the release agent. As the polyvinyl alcohol, it is possible to use fully saponified or partially saponified polyvinyl alcohol. As starch, unmodified starch can be used, but enzyme-modified starch, oxidized modified starch, and modified starch such as phosphate esterified starch, hydroxyethylated starch, cationized starch, and dialdehyde starch can be used.

Laydown of the sealing-imparting layer is preferably 1.0 g / ^{m 2} or more 10.0 g / ^{m 2} or less, and more preferred range is 2.0~8.0g / ^{m 2.} When the coating amount is less than 1.0 g / m ² , the release agent has insufficient sealability, and when it exceeds 10 g / m ² , the release agent has sufficient sealability, but the drying load increases. Rolls and canvas stains occur in the drying process and calendar process. For the sealing property-imparting layer, in addition to polyvinyl alcohol and starch, casein, acrylic resin, styrene-acrylic resin, vinyl acetate resin, and the like can be appropriately selected and used. Good. Moreover, you may contain various auxiliary agents normally used, such as a dispersing agent, a mold release agent, a thickener, a water retention agent, an antifoamer, antiseptic | preservative, and a water-resistant agent.

  As a method of incorporating the acrylic copolymer into the base paper, any known method may be used as long as the aqueous emulsion of the acrylic copolymer can be impregnated into the base paper. For the impregnation treatment, for example, an impregnation machine such as a 2-roll size press, a gate roll coater, an air knife coater, a blade coater, a comma coater, or a bar coater installed in the middle of the paper making process can be used. In addition, after papermaking, it is possible to impregnate using the above-mentioned impregnation machine or coating machine in an off-machine.

  Moreover, as a method of providing the sealing property-imparting layer, it is possible to apply by various impregnation machines or coating machines installed in the middle of the paper making process. Further, after the paper is formed, it can be applied by the above-described coating machine in post-processing.

The basis weight of the base paper for release paper of the present invention is preferably 30 g / m ² or more and 80 g / m ² or less. If the basis weight is less than 30 g / m ² , the paper becomes insufficient, and wrinkles and misalignments are likely to occur during die cutting and printing. When it exceeds 80 g / m ² , the film becomes too thick and the light transmittance is lowered. In addition, it is essential that the light transmittance has a spectral transmittance of 960 nm of 30% or more. If it is less than 30%, the difference in light transmittance between the label and the release paper is so small that it cannot be detected by the phototube and the position cannot be detected. Preferably it is 32% or more.

The base paper is further subjected to a compression treatment in order to enhance the sealing property and light transmittance of the release agent. The compression device can be achieved by using a known calendar, a super calendar, a soft calendar, or the like. The density after the compression treatment is preferably in the range of 0.85 g / cm ³ or more and 1.25 g / cm ³ . When the density is less than 0.85 g / cm ^3, it is not possible to obtain sufficient release agent light transmittance. On the other hand, if it exceeds 1.25 g / cm ³ , the paper becomes too thin and the paper becomes lower, which is not preferable. Accordingly, the density is preferably 0.85 g / cm ³ or more and 1.25 g / cm ³ or less in order to satisfy the release agent sealing property and light transmittance while maintaining a good paper level. In the present invention, the basis weight of the base paper for release paper is measured according to JIS P 8124 “Paper and board—Method of measuring basis weight”, and the density is measured according to JIS P 8118 “Paper and board—Testing method of thickness and density”. To do.

When producing release paper using the release paper base paper thus obtained, a release agent is applied to the surface of the release paper base paper on which the sealing property-imparting layer is provided to provide a release layer. As the release agent, silicone resin, polyethylene resin, alkyd resin and the like can be used. The coating amount is not particularly limited, but is suitably adjusted in the range of about 0.1 g / m ^{2 to} 3.0 g / m ² , preferably about 0.5 g / m ^{2 to} 2.0 g / m ^2. . When the coating amount is less than 0.1 g / m ² , the peelability is insufficient and heavy peeling occurs, and when it is more than 3.0 g / m ² , the practicality is poor from the economical viewpoint.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by these examples. In addition, the part in an example and% show a mass part and the mass%, respectively. Further, the coating amount, the number of parts, the mixing ratio, etc. were all expressed in solid content.
The light transmittance, the amount of paper dust, and the disaggregation property were measured and evaluated by the following methods for the base papers for release paper produced in Examples and Comparative Examples.

<Quality evaluation method>
-Light transmittance: An integrating sphere was attached to a self-recording spectrophotometer UV-3100PC manufactured by Shimadzu Corporation, and the light transmittance of release paper base paper having a wavelength of 960 nm was measured.
Evaluation criteria ○: 30% or more ×: Less than 30%

-Paper dust generation amount: SEMI standard Doc. No. A rubbing test was carried out in accordance with 2363, and the number per 0.01 ft ^{3 of} paper powder having a diameter of 0.3 μm or more was measured.
Evaluation criteria ○: 500 pieces / 0.01ft ^{3 or} less △: 500 pieces / 0.01ft ³ or more 1000 pieces / less than 0.01ft ³ ×: 1000 pieces / 0.01ft ³ or more

-Disaggregation property: The sample was cut into a 1 cm square, subjected to 20 separation and disintegration treatment with a Tappi standard disaggregator at 2% sample concentration and 2 L capacity, and the degree of disaggregation was visually observed.
Evaluation criteria ○: Good disaggregation △: Some undissolved material remains ×: Undissolved

-Paper stiffness (Clark stiffness): Measured in the longitudinal direction of the paper according to JIS P 8143.
○: 45cm ^3/100 over 60cm ^3/100 or less ×: other than the above

<Example 1>
As a monomer mixture, 32.1 parts of styrene, 20.4 parts of 2-ethylhexyl acrylate, 20.7 parts of methyl methacrylate, 1.8 parts of methacrylic acid, sodium alkylallylsulfosuccinate as a reactive emulsifier (trade name: Eleminol JS-2, Sanyo Chemical Industries) 3.6 parts), sodium polyoxyethylene nonylphenyl ether sulfate (trade name: Lebenol WZ, manufactured by Kao) 5.6 parts and 31.2 parts deionized water are stirred and emulsified. In a reactor equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet tube and dropping funnel, 57 parts of deionized water, 0.26 parts of the above-mentioned reactive emulsifier sodium alkylallylsulfosuccinate, and sodium polyoxyethylene nonylphenyl ether sulfate Charge 0.4 parts, inject nitrogen, raise the internal temperature to 80 ° C, and add 2 parts of ammonium persulfate dissolved in 10% with deionized water. Subsequently, a monomer mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 part of methacrylic acid is dropped over 1 hour, and emulsion polymerization is performed at an internal temperature of 80 to 85 ° C. Here, the monomer mixture emulsified in advance in a beaker is dropped over 3 hours, and in parallel, 2 parts of ammonium persulfate dissolved in 10% with deionized water is dropped. After completion of dropping, the mixture is aged at the same temperature for 3 hours and then cooled to room temperature. Acrylic copolymer A was obtained by adjusting with 1.6 parts of 25% aqueous ammonia and water.

Use raw pulp (adjusted to Canadian standard freeness of 304 ml) consisting of 70% by weight hardwood bleached kraft pulp (Canadian standard freeness 220 ml) and softwood bleached kraft pulp (Canadian standard freeness 500 ml) A wet paper strength agent (trade name: WS547, manufactured by Japan PMC) was added in an amount of 0.1% by mass, and a papermaking pH was adjusted to 4.5 with a sulfuric acid band, and papermaking was performed with a long mesh multi-cylinder papermaking machine. Subsequently, the acrylic copolymer A obtained above was impregnated with a size press installed in the middle of the paper making process so as to be 5% per paper mass. Subsequently, in a post-process using a blade coater, 70 parts of partially saponified polyvinyl alcohol (trade name: PVA217, manufactured by Kuraray) as a sealant-imparting solution on one side, phosphate esterified starch (trade name: MS-4400, Japanese food) (Manufactured) 30 parts of the mixture was coated at 2.0 g / m ² . Then, it was pressed and compressed by a super calender so that the density was 1.00 g / cm ^3, and a release paper base paper having a basis weight of 65 g / m ² was produced. The release paper base paper was evaluated for light transmittance, amount of paper dust, and disaggregation.

<Example 2>
Instead of a monomer mixture of 32.1 parts of styrene, 20.4 parts of 2-ethylhexyl acrylate, 20.7 parts of methyl methacrylate and 1.8 parts of methacrylic acid, 26.5 parts of styrene, 31.6 parts of 2-ethylhexyl acrylate, 15.4 parts of methyl methacrylate, 1.5 parts of methacrylic acid A base paper for release paper was produced in the same manner as in Example 1 except that the acrylic copolymer B obtained as a monomer mixture was used in place of the acrylic copolymer A.

<Example 3>
Acrylic copolymer C obtained as a monomer mixture of 2.9 parts of styrene, 11.7 parts of methyl methacrylate and 10.4 parts of methacrylic acid instead of a monomer mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 part of methacrylic acid Was used in the same manner as in Example 1 except that it was used in place of the acrylic copolymer A to produce a release paper base paper.

<Example 4>
Monomer mixture of 31.4 parts of styrene, 19.1 parts of 2-ethylhexyl acrylate, 22 parts of methyl methacrylate, 1.8 parts of methacrylic acid, 21.4 parts of styrene, 12.7 parts of 2-ethylhexyl acrylate, 14.6 parts of methyl methacrylate, 1.2 parts of methacrylic acid Acrylic copolymer D obtained as a mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 parts of methacrylic acid as a monomer mixture of 8.3 parts of styrene, 40.7 parts of methyl methacrylate and 1.0 part of methacrylic acid Was used in the same manner as in Example 1 except that it was used in place of the acrylic copolymer A to produce a release paper base paper.

<Example 5>
A base paper for release paper was produced in the same manner as in Example 1 except that the papermaking conditions were adjusted and the basis weight was 34 g / m ² .

<Example 6>
A base paper for release paper was produced in the same manner as in Example 1 except that the papermaking conditions were adjusted and the basis weight was 73 g / m ² .

<Example 7>
A base paper for release paper was produced in the same manner as in Example 1 except that the pressure was compressed so that the density was 0.88 g / cm ³ .

<Example 8>
A release paper base paper was produced in the same manner as in Example 1 except that the pressure was compressed so that the density was 1.21 g / cm ³ .

<Comparative Example 1>
Instead of a monomer mixture of 32.1 parts of styrene, 20.4 parts of 2-ethylhexyl acrylate, 20.7 parts of methyl methacrylate and 1.8 parts of methacrylic acid, 26.8 parts of styrene, 15.2 parts of 2-ethylhexyl acrylate, 30.9 parts of methyl methacrylate, 2.1 parts of methacrylic acid A base paper for release paper was produced in the same manner as in Example 1 except that the acrylic copolymer E obtained as a monomer mixture was used in place of the acrylic copolymer A.

<Comparative example 2>
In place of the monomer mixture of 32.1 parts of styrene, 20.4 parts of 2-ethylhexyl acrylate, 20.7 parts of methyl methacrylate, and 1.8 parts of methacrylic acid, 38.4 parts of styrene, 38.4 parts of 2-ethylhexyl acrylate, 3 parts of methyl methacrylate, 2.1 parts of methacrylic acid A base paper for release paper was produced in the same manner as in Example 1 except that the acrylic copolymer F obtained as a monomer mixture was used instead of the acrylic copolymer A.

<Comparative Example 3>
Instead of a monomer mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 part of methacrylic acid, a monomer mixture of 3.1 parts of styrene, 1 part of 2-ethylhexyl acrylate, 20.4 parts of methyl methacrylate and 0.5 part of methacrylic acid was obtained. A base paper for release paper was produced in the same manner as in Example 1 except that the acrylic copolymer G was used instead of the acrylic copolymer A.

<Comparative example 4>
Monomer mixture of 32.1 parts of styrene, 20.4 parts of 2-ethylhexyl acrylate, 20.7 parts of methyl methacrylate, 1.8 parts of methacrylic acid, 17.1 parts of styrene, 10.9 parts of 2-ethylhexyl acrylate, 11 parts of methyl methacrylate, 1 part of methacrylic acid Acrylic copolymer H obtained as a mixture of a monomer mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 part of methacrylic acid as a monomer mixture of 10 parts of styrene, 48.8 parts of methyl methacrylate and 1.2 parts of methacrylic acid Was used in the same manner as in Example 1 except that it was used in place of the acrylic copolymer A to produce a release paper base paper.

<Comparative Example 5>
A monomer mixture of 32.1 parts of styrene, 20.4 parts of 2-ethylhexyl acrylate, 20.7 parts of methyl methacrylate, 1.8 parts of methacrylic acid, and 38.6 parts of styrene, 24.4 parts of 2-ethylhexyl acrylate, 24.8 parts of methyl methacrylate, 2.2 parts of methacrylic acid Acrylic copolymer I obtained as a mixture of a monomer mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 parts of methacrylic acid as a monomer mixture of 1.7 parts of styrene, 8.1 parts of methyl methacrylate and 0.2 parts of methacrylic acid Was used in the same manner as in Example 1 except that it was used in place of the acrylic copolymer A to produce a release paper base paper.

<Comparative Example 6>
Example 1 except that acrylic copolymer J obtained without dripping a monomer mixture of 4.2 parts of styrene, 20.3 parts of methyl methacrylate and 0.5 part of methacrylic acid was used in place of acrylic copolymer A In the same manner as described above, a base paper for release paper was produced.

<Comparative Example 7>
Exfoliation was carried out in the same manner as in Example 1 except that the acrylic copolymer K obtained without dripping the monomer mixture emulsified in advance in a beaker was used instead of the acrylic copolymer A. Paper base paper was produced.

  As is clear from these results, the release paper bases of Examples 1 to 8 had good light transmittance, disaggregation and paper stiffness, and produced less paper dust. On the other hand, the base paper for release paper of Comparative Example 1 in which the glass transition temperature of the core portion of the acrylic copolymer exceeds 40 ° C. is inferior in light transmittance, and the glass transition temperature of the core portion of the acrylic copolymer is 0 ° C. Comparative Example 2 in which the glass transition temperature of the acrylic copolymer shell part is less than 100 ° C., Comparative Example 5 in which the ratio of the core part of the acrylic copolymer exceeds 80% by mass, Shell The base paper for release paper of Comparative Example 6 using an acrylic copolymer having no part was inferior in disintegration property. In addition, the base paper for release paper of Comparative Example 4 in which the ratio of the shell part of the acrylic copolymer exceeds 50% by mass has a large amount of paper dust, and Comparative Example 7 using an acrylic copolymer without a core part. The base paper for release paper was inferior in light transmittance and generated a large amount of paper dust.

Claims (3)

  A base paper for release paper having a spectral transmittance at 960 nm of 30% or more, in which a sealing property-imparting layer mainly composed of polyvinyl alcohol and / or starch is provided on at least one side of the base paper, Consists mainly of delignified cellulosic fibers, contains a core / shell type acrylic copolymer in a proportion of 1 to 20% by mass, and the core / shell type acrylic copolymer comprises a core part The glass transition temperature of the resin constituting the resin is 0 ° C. to 40 ° C., the glass transition temperature of the resin constituting the shell part is 100 ° C. or higher, the ratio of the core part is 50 to 80% by mass, and the ratio of the shell part is 20 to 20%. A base paper for release paper, which is 50% by mass.   The base paper for release paper according to claim 1, wherein the cellulosic fibers constituting the base paper have a Canadian standard freeness of 150 ml to 350 ml. The base paper for release paper according to claim 1 or 2, wherein the basis weight is 30 to 80 g / m ² and the density is 0.85 to 1.25 g / cm ³ .