JP2005036379A - Coated paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide coated paper having excellent air permeability, without causing blisters when printed by an off-set rotary printing process, nor by an electrophotographic process, scarcely forming wrinkles caused by off-set rotary printing, and having excellent adaptability to folding and breaking. <P>SOLUTION: This coated paper has a paper-like base material and at least two coated layers formed on at least one of surfaces of the base material, wherein a pigment having a crystal structure based on any one kind of a needlelike crystal, a fusiform crystal, a columnar crystal, and a rice grain-shaped crystal is contained in an inner coated layer adjacent to the paper-like base material, and thermoplastic organic fine particles having a glass transition temperature of 20-150°C are contained in an outermost coated layer formed on the inner coated layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coated paper, and particularly to a coated paper that has excellent air permeability, can effectively suppress the generation of blisters during printing, and has a good print finish.

  Offset rotary printing (hereinafter also referred to as “off-wheel printing”), which is one form used for commercial printing, is performed by a dryer after printing paper is fed by winding and ink is transferred onto the paper. The ink is dried and taken up again. Further, it is folded by a folding machine. In either case, if the ink on the surface of the paper that has left the dryer is not completely dry, the coated paper surface and the printing machine may become dirty. Although used, there is a case where a defect called a blister occurs in the paper.

  Blisters (called paper blisters) in this off-wheel printing are phenomena in which the vapor pressure rises due to the rapid vaporization of moisture in the paper, which causes a force in the thickness direction on the paper and creates voids due to delamination in the paper layer. Therefore, it is said that the cause is that moisture in the paper does not dissipate smoothly. For this reason, the generation of blisters is likely to occur particularly in printing paper having a coating layer with poor air permeability on the front and back sides. With the recent increase in printing speed, the drying temperature tends to be higher, and it is becoming difficult to suppress blistering. Among them, the high gloss printing paper obtained through the gloss imparting process using a super calender has a more dense coating layer, so that it becomes a coating layer with poorer air permeability and blisters are particularly likely to occur.

  Many proposals have been made for suppressing the occurrence of blisters in off-wheel printing. It can be broadly classified into two methods. The first is to increase the interlayer strength of the paper-like substrate of coated paper (hereinafter sometimes referred to as “base paper”), and to expand due to water vapor pressure. The second is a method that does not cause delamination against resistance, and the second is a method in which the air permeability of the coating layer is improved and the generated water vapor is released to lower the vapor pressure.

  Various proposals have been made for improving the interlayer strength of the base paper. For example, a method of setting the interlayer strength of the base paper to a specific value or more (see, for example, JP-A-11-160906 (page 2) (Patent Document 1)), a method of containing a specific amount of cationized starch and polyacrylamide in the base paper ( For example, Japanese Patent Laid-Open No. 6-25996 (see page 2) (see Patent Document 2) has been proposed and put to practical use. However, the above-described method for improving the interlayer strength of the base paper is that when the air permeability of the coating layer formed on the base paper is high, the dissipation of water vapor is greatly hindered by the coating layer, so only the interlayer strength of the base paper is improved. Then, blister generation cannot be suppressed completely.

  Many proposals have also been made regarding methods for improving the air permeability of the coating layer. For example, among the undercoat layer and the overcoat layer, a method using a latex having a specific gel content in the undercoat layer (see, for example, JP-A-9-324395 (page 2) (Patent Document 3)), a specific pigment And a method of surface treatment with a surface-roughening roll using a binder (see, for example, JP-A-5-247891 (page 2) (Patent Document 4)), a glass transition point (hereinafter referred to as “Tg”). ) Different latexes on a paper-like substrate or undercoat layer (see, for example, JP-A-59-22683 (page 2) (Patent Document 5)), kaolin having a specific aspect ratio. A method to be used (for example, see JP-A-2000-226791 (page 2) (Patent Document 6)), a method to use superheated steam or the like for drying a coating layer containing a high Tg latex (for example, JP-A-8- 1 8297 JP (page 2) (Patent Document 7) reference), or the like. However, when there are a plurality of coating layers, the thickness of the coating layer increases, and it is difficult to achieve the desired air permeability. In addition, the production cost is high due to the multiple coating steps. In addition, when the surface-roughening process is performed, coated paper with high gloss cannot be obtained. In addition, when applying latex with a different Tg on a paper-like substrate or undercoat layer, it is necessary to control the drying conditions within a specific range, so that stable production is difficult, and only latex is applied. In addition, the coated paper has a problem that water absorption and inking during printing are inferior. Furthermore, the use of kaolin having a specific aspect ratio has a limit to high glossiness, and a method using superheated steam or the like for drying a coating layer containing a high Tg latex is one form of the main printing method of commercial printing. Ink printing, which is called an ink set in flat printing, is extremely slow, and when there is no drying process during the printing process, the printing workability is greatly reduced, and stains caused by undried ink occur on the printed matter. There is a risk of reducing the print finish. As described above, although the effect can be seen in any case, the printing finish is good, and it is not always a sufficient level to cope with the recent increase in printing speed, and further improvement is desired. It was rare.

  In addition, the occurrence of blistering may also be a problem even in a printing method using a toner transfer method (so-called electrophotographic method), which is one of the forms of on-demand printing that has been attracting attention in recent years. There are two types of toner transfer type blisters, and one is a paper blister in which the paper is delaminated due to the vapor pressure generated by the evaporation of moisture in the paper, similar to the blister in off-wheel printing. The other is that when the solid toner transferred onto the paper is melted and solidified in the heat fixing unit, the air that exists between the toners cannot be passed through the coating layer and is smoothed. This is a toner blister that is generated by detaching from the surface of the layer. The toner blister peculiar to this toner transfer system is difficult to solve by the method of suppressing the occurrence of blistering in off-ring printing, and an effective solution has not yet been found.

  The voids present on the surface of the coating layer of general coated paper include fine voids (hereinafter referred to as “pore A”) that are not filled with other components between the pigment particles, and the drying process of the coating layer. Vapor permeation holes (hereinafter referred to as “pores B”) generated by the rupture of the coating layer resulting from the brittleness of the coating layer to the tensile stress due to film shrinkage during drying (hereinafter referred to as “crack”). In order to fix the ink to the paper during printing (so-called ink set), absorption of the ink solvent due to the capillary phenomenon of the pores plays an extremely important role. Plays. The pore diameter of the pore A varies depending on the size of the pigment used, but is usually about 0.02 to 0.2 μm and greatly contributes to the ink set. Incidentally, there are reports that the pores most effective for the ink set are those having a pore diameter of about 0.12 to 0.15 μm (for example, Tomoyuki Terao et al. “Effect of coating layer structure of coated paper on ink set”, Papa Gikyokyo, Vol. 51, No. 9, pp. 79-85 (September 1997) (see Non-Patent Document 1)). It is very difficult to control the occurrence of the pore B, and in some cases, a circular hole with a size that can be visually discerned on a white paper or printed matter may be generated. Suppression of the occurrence is desired. The crack is usually produced so as to suppress the generation as much as possible in order to reduce the surface strength of the coating layer. Although it is known that cracks are generated on the surface of the coating layer by a method using latexes having different glass transition points (see, for example, Patent Document 5), it is difficult to produce stably as described above. The crack size on the surface of the coating layer is estimated to be a size that can improve the ink set as described in Patent Document 5, that is, about 0.02 to 0.20 μm. Until now, it has not been proposed to effectively and stably generate a void having a size of 0.2 μm or more as defined in the present invention.

  As described above, in the prior art, since it is difficult to control the voids existing on the surface of the coating layer, generation of blisters in off-wheel printing, and generation of paper blisters and toner blisters in the electrophotographic method are suppressed. A satisfactory coated paper was not obtained, and further improvement was desired.

JP 11-160906 A (2 pages) JP-A-6-25996 (page 2) JP-A-9-324395 (2 pages) JP-A-5-247891 (page 2) JP 59-22683 A (2 pages) JP 2000-226791 A (page 2) JP-A-8-158297 (page 2)

Tomoyuki Terao et al. “Effects of Coating Layer Structure of Coated Paper on Ink Set”, Papa Gikyo Paper, Vol. 51, No. 9, pp. 79-85 (September 1997)

  An object of the present invention is to provide a coated paper that is excellent in air permeability and does not generate blisters during off-wheel printing and electrophotographic printing. In addition, an object of the present invention is to provide a coated paper that is less likely to generate off-wheel wrinkles and has excellent breakability.

  As a result of diligent study in view of the present situation, the present inventors have provided at least two coating layers, and the inner coating layer adjacent to the paper-like substrate has a specific crystal structure. It is particularly effective that the outermost coating layer formed on the inner coating layer contains a thermoplastic organic fine particle having a specific glass transition temperature. I found it.

Accordingly, the present invention includes the following aspects.
(1) In a coated paper in which a paper-like substrate and at least two coating layers are provided on at least one surface thereof, the inner coating layer adjacent to the paper-like substrate has a needle-like shape. A glass transition temperature of 20 is contained in the outermost coating layer containing a pigment having any one crystal structure of crystals, spindle-shaped crystals, columnar crystals, and rice granular crystals, and formed on the inner coating layer. A coated paper comprising thermoplastic organic fine particles of ˜150 ° C.
(2) The coated paper according to (1), wherein the inner coating layer adjacent to the paper-like substrate contains starch.
(3) The coated paper according to (1), wherein the thermoplastic organic fine particles are a styrene-butadiene copolymer.
(4) The thermoplastic organic fine particles contain a non-film-forming hollow organic pigment, and 1 to 10 parts by weight of the non-film-forming hollow organic pigment is contained in 100 parts by weight of all pigments in the outermost coating layer. The coated paper according to (2).
(5) The coated paper according to (1), which contains crack formation promoting particles in the outermost coated layer.
(6) The crack formation promoting particles have an average particle diameter of 3.0 to 30.0 μm, and 0.1 to 10 parts by mass in 100 parts by mass of the outermost coating layer. The coated paper described.
(7) In any one of (1) to (6), 40 to 90 parts by mass of an inorganic pigment and 5 to 60 parts by mass of thermoplastic organic fine particles are contained in 100 parts by mass of the outermost coating layer. Coated paper.
(8) The outermost coating layer surface, width 0.2 to 3.0 [mu] m, cracks in length 3～1000Myuemu, either 1 mm ² per 1 to 1000 present (1) to (7) Coated paper as described in 1.
(9) The surface of the outermost coating layer has a white paper glossiness of 45 to 85% based on JIS Z 8741 and an incident / light receiving angle of 75 degrees, and the JAPAN TAPPI paper pulp test method no. The coated paper according to any one of (1) to (8), wherein the Oken air permeability based on 5-2: 2000 is 8000 seconds or less.

  The coated paper according to the present invention does not generate blisters in off-wheel printing and electrophotographic printing, has a good print finish, does not generate off-ring wrinkles, does not crack, and is extremely practical. Useful.

  The present inventors have conducted extensive research on the suppression of blisters at the time of offset printing, and further on the suppression of blisters in the electrophotographic method. As a result, the coated paper is provided with at least two coating layers, and is a paper-like sheet. The inner coating layer adjacent to the substrate contains a pigment having a specific crystal structure, and the outermost coating layer formed on the inner coating layer has a specific glass transition temperature. It has been found that the inclusion of the thermoplastic organic fine particles can improve without impairing other aptitudes.

  The reason why the coated paper obtained in the present invention is extremely effective in suppressing the generation of blisters is considered as follows. That is, there is a crack on the outermost coating layer surface, and this crack is different from a crack generated in general coated paper production, and the thermoplastic organic fine particles having a specific glass transition temperature in the outermost coating layer. Because of its large size and large number, it is considered that water vapor and air are efficiently dissipated, and blistering during off-wheel printing and electrophotographic printing can be greatly suppressed. .

On the other hand, the inner coating layer is provided with a pigment having a crystal structure of any one of acicular crystals, spindle-shaped crystals, columnar crystals, and rice granular crystals, giving the coated paper anti-cracking properties and air permeability. It is easy to obtain a coating layer having, and is preferably used.
Means a fine pigment having a crystal structure of any one of acicular crystals, spindle-shaped crystals, columnar crystals and rice granular crystals constituting the inner coating layer, for example, at least one of phosphoric acid and water-soluble salts thereof In which a calcium hydroxide suspension having a specific concentration is reacted with a carbon dioxide-containing gas (Japanese Examined Patent Publication No. 57-30815), and in the presence of at least one of a specific carboxylic acid and a water-soluble salt thereof. Method (Japanese Examined Patent Publication No. 57-31530), carbon dioxide reaction gas is introduced into a water suspension containing a specific needle columnar crystal nucleus calcium carbonate and calcium hydroxide at a specific temperature to perform a carbonation reaction. It is produced by a method for obtaining a calcium bundle (Japanese Patent Laid-Open No. 59-232916) or the like.
These pigments have an acicular shape in which the average dimension observed by observation with an electron microscope is a minor axis dimension (W) of 0.005 to 0.5 μm, a major axis dimension (L) of 0.1 to 10 μm, and an aspect ratio (L / W) of 2 to 1000. It is a fine particle pigment having a crystal structure of any one of a crystal, spindle-shaped crystal, columnar crystal, and rice granular crystal, and is appropriately selected and used.

In order to suppress blister generation, 1 to 1000 cracks having a width of 0.2 to 3.0 μm and a length of 3 to 1000 μm are required per 1 mm ² . Incidentally, if the number of cracks is less than 1 per 1 mm ² , the width of the crack is less than 0.2 μm, or the length of the crack is less than 3 μm, the effect of improving the air permeability is lowered, Generation may not be effectively suppressed. Conversely, if the number exceeds 1000 per 1 mm ² , the width of the crack exceeds 3.0 μm, or the length of the crack exceeds 1000 μm, the printing strength may be reduced. When the number of cracks is 50 to 500 per mm ² , the crack width is 0.5 to 2.0 μm, and the crack length is in the range of 10 to 500 μm, the improvement in the air permeability of the coating layer and other qualities The balance is good and the most preferable.
When printing on coated paper having a crack defined in the present invention, it is very difficult to visually confirm the crack on the printed matter, and a good print finish is obtained.
In addition, it is better that a crack exists independently without being connected. If cracks are connected, the printing strength may be inferior, which is not preferable.

In the present invention, the number of cracks per 1 mm ² is a linear, curved, semicircular shape that is present on the surface of the coating layer and is independently present without branching as shown in FIGS. crack Jo like, and reticulated combinations shape as shown in FIG. 2D～g, lattice-like, triangular, cracks such as arrow-shaped, in which the total number per 1 mm ^2. In addition, the crack of the said combined shape is counted as one crack.

  The components of the coating layer of the present invention are not particularly limited as long as desired cracks can be obtained, but preferable materials include thermoplastic organic fine particles. Among these, thermoplastic organic fine particles whose surface or the whole is softened under the coating and drying conditions are preferable. Further, Tg (glass), which has a higher film forming temperature than latex generally used as an adhesive for coated paper, is preferable. Transition point) Thermoplastic organic fine particles made of a resin having a temperature in the range of 20 to 150 ° C. are excellent in terms of generation of cracks, and are more preferable. Especially, the thing of the range whose Tg is 20-80 degreeC is preferable on the balance of a desired crack generation effect and printing strength, and the thing of the range which is 30-80 degreeC is especially preferable. When Tg is less than 20 ° C., the occurrence of cracks is small and the gas permeability is poor as viewed from the intended level, and the effect of suppressing blistering is poor. When Tg exceeds 150 ° C., the printing strength may be lowered under normal drying conditions, which is not preferable.

  In the present invention, a resin having a Tg in the temperature range of 20 to 150 ° C. is used rather than a single thermoplastic organic fine particle composed of a resin having a Tg in the temperature range of 20 to 150 ° C. in the outermost coating layer. A system comprising two or more kinds of thermoplastic organic fine particles having different film forming conditions is more preferable. For example, a combination of thermoplastic organic fine particles having different Tg, or a combined system of thermoplastic organic fine particles having a single Tg and thermoplastic organic fine particles having a non-single Tg (two peaks or broader). In a system in which one kind of thermoplastic organic fine particles composed of a resin having a Tg of 20 to 150 ° C. is used alone, when the inside of the drier of the coating machine is manufactured under the condition that the amount of water vapor increases at a high temperature, the film formation proceeds at a stretch. The voids are reduced, the coated paper has a slow ink setting, and printing stains are likely to occur due to undried ink after printing. However, the above combined system suppresses the rapid film formation at the time of drying and forms good voids, so that the air permeability is good and the paper has good ink setting properties. As thermoplastic organic fine particles having a non-single Tg (2 peaks or more or broad), a major Tg peak in a range of 20 to 150 ° C. or a broad peak is observed among a plurality of peaks in a Tg measuring instrument. In such a case, it is preferable that 80% or more of the peak is in the range of 20 to 150 ° C, or that the Tg calculated from the contained monomer composition is in the range of 20 to 150 ° C. The blending ratio of the plurality of thermoplastic organic fine particles can be arbitrarily set according to the quality design of the coated paper. Examples of the thermoplastic organic fine particles used in the present invention include non-homogeneous structured fine particles such as core / shell fine particles, in addition to normal fine particles which are homogeneous as a whole. In the case of core / shell type fine particles, the Tg of the resin on the shell side is important and is preferably in the range of 20 to 150 ° C. However, although the performance of the obtained sheet is inferior, a sheet having a Tg of 20 ° C. or lower can be used. Specifically, what is called a binder pigment is mentioned.

  Examples of the thermoplastic organic fine particles include polydienes such as polyisoprene, polyneoprene, and polybutadiene, polyalkenes such as polybutene, polyisobutylene, polypropylene, and polyethylene, vinyl halide, vinyl acetate, styrene, (meth) acrylic acid, (meta ) Vinyl polymers and copolymers such as acrylic ester, (meth) acrylamide, methyl vinyl ether, synthetic rubber latex such as styrene-butadiene and methyl methacrylate-butadiene, polyurethane resin, polyester resin, polyamide Examples thereof include resins, olefin-maleic anhydride resins, vinylidene chloride resins, and the like. One or more of these are appropriately selected and used.

  As a compounding quantity to the coating liquid of the said thermoplastic organic fine particle, the range of 5-60 mass parts is preferable with respect to 100 mass parts (dry) of a coating layer. When the blending amount is less than 5 parts by mass, the generation of cracks cannot be promoted, the air permeability is high, and the effect of suppressing the generation of blisters is considerably inferior to the target. On the other hand, when the blending amount exceeds 60 parts by mass, the resin component in the coating layer increases and the ink vehicle absorbability is inferior, so that ink transfer failure is likely to occur, and the texture as coated paper is further reduced. Therefore, it is not preferable.

  In addition to the above-mentioned thermoplastic organic fine particles, a pigment can be blended in the coating liquid of the present invention as necessary. Examples of the pigment include known inorganic pigments and organic pigments other than the thermoplastic organic fine particles. Examples of inorganic pigments include heavy calcium carbonate, light calcium carbonate, kaolin, calcined kaolin, structural kaolin, delaminated kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, and silica. , Magnesium aluminosilicate, calcium silicate, white carbon, bentonite, zeolite, sericite, smectite and the like. Examples of organic pigments include polystyrene resins, styrene-butadiene copolymer resins, styrene-acryl copolymer resins, styrene-methacryl copolymer resins, acrylic resins, vinylidene chloride resins, urea resins, and melamine resins. Examples thereof include resins and benzoguanamine resins. Examples of the organic pigment include a solid type, a hollow type, a through-hole type, and a core / shell type. One or more of these are appropriately selected and used. Among these, hollow organic pigments are easily deformed by pressure, and when applying gloss in a smoothing process such as supercalender, the desired gloss can be obtained at a lower processing pressure. A material that suppresses the decrease and exhibits good air permeability is preferably used. In addition, as a compounding quantity to the coating liquid of a hollow organic pigment, 20 mass parts or less are preferable with respect to 100 mass parts (dry) of a coating layer, and 1-10 mass parts is more preferable. When the amount exceeds 20 parts by mass, an opacity lowering phenomenon called calendar burn or blacking may occur in a smoothing process such as a super calendar.

As a compounding quantity to the coating liquid of the said inorganic pigment, the range of 40-90 mass parts is preferable with respect to 100 mass parts (dry) of a coating layer. When the blending amount is less than 40 parts by mass, the generation of cracks cannot be promoted, the air permeability is high, and the blister generation suppressing effect is considerably inferior. Further, when the blending amount exceeds 90 parts by mass, the surface strength is inferior and stable printing cannot be performed.
Among these, when a coating liquid composed of an inorganic pigment in the range of 40 to 90 parts by mass and a thermoplastic organic fine particle in the range of 5 to 60 parts by mass is used, particularly good cracks are obtained, which is preferable.

  If necessary, an adhesive and crack formation promoting particles are further added to the coating liquid used in the present invention. The adhesive is used for increasing the surface strength of the coating layer and imparting good printability. The crack formation promoting particles are blended when the formation of cracks does not reach the desired level.

  As the adhesive, a water-soluble or water-dispersible polymer compound can be used, for example, cationic starch, amphoteric starch, oxidized starch, enzyme-modified starch, thermochemically-modified starch, esterified starch, etherified starch, etc. Starches, cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, natural or semi-synthetic polymer compounds such as gelatin, casein, soy protein, natural rubber, polydienes such as polyvinyl alcohol, polyisoprene, polyneoprene, polybutadiene, polybutene, poly Polyalkenes such as isobutylene, polypropylene, and polyethylene, vinyl halides, vinyl acetate, styrene, (meth) acrylic acid, (meth) acrylic acid esters, (meth) acrylamide, methyl vinyl ether and other vinyl polymers and copolymers, Styling -Synthetic polymer latex such as butadiene-based, methyl methacrylate-butadiene-based synthetic rubber latex, polyurethane-based resin, polyester-based resin, polyamide-based resin, olefin-maleic anhydride-based resin, melamine-based resin, etc. . One type or two or more types of adhesives are appropriately selected as necessary. Among the adhesives, an adhesive having a Tg of 20 ° C. or less is preferable, and particularly preferably 0 ° C. or less. As a compounding quantity to the coating liquid of an adhesive agent, 15 mass parts or less are preferable with respect to 100 mass parts (dry) of a coating layer. When the amount exceeds 15 parts by mass, the generation of cracks is hindered, making it difficult to obtain the desired effect of the present invention. As the adhesive, latex having a core / shell structure can also be used. In this case, it is preferable that the Tg of the shell portion contributing to film formation is 20 ° C. or less. When using a water-soluble polymer compound such as starch as an adhesive, if the amount used is increased, the desired air permeability cannot be obtained, so the blending amount in the coating liquid is 5 parts by mass or less, It is preferable that it is 2 mass parts or less.

  The crack formation accelerating particles are particles having an average particle diameter in the range of 3.0 to 30.0 μm having a promoting effect on crack formation, and particles in the range of 5.0 to 15.0 μm are particularly preferable. When the average particle size is less than 3.0 μm, the effect of adding particles is hardly exhibited. If it exceeds 30.0 μm, problems such as ink transfer failure may occur during printing. The particle size distribution of the crack formation promoting particles is preferably in the range of 1.0 to 50.0 μm. As the crack formation promoting particles, spherical particles having a spherical shape are preferable, and spherical calcium carbonate particles are particularly preferably used. The size of the crack formation promoting particles is particularly important, and the material is not particularly selected. For example, the same materials as those exemplified for the thermoplastic organic fine particles or the pigment can be used. As a compounding quantity to the coating liquid of a crack formation promotion particle, the range of 0.1-10 mass parts is preferable with respect to 100 mass parts (dry) of a coating layer. If the blending amount is less than 0.1 parts by mass, the effect of adding particles is difficult to appear, whereas if it exceeds 10 parts by mass, the printing strength may be reduced.

  In the coating liquid used in the present invention, various auxiliary agents such as a surfactant, a pH adjuster, a viscosity adjuster, a water retention agent, a softening agent, a gloss imparting agent, a wax, a dispersant, Flow modifier, antistatic agent, stabilizer, antistatic agent, crosslinking agent, sizing agent, fluorescent brightener, colorant, ultraviolet absorber, antifoaming agent, water-resistant agent, plasticizer, preservative, fragrance, etc. Is appropriately blended.

  As the water retention agent, it is preferable to use a cellulose derivative such as carboxymethyl cellulose or hydroxyethyl cellulose, or a synthetic water retention agent such as an alkali swelling acrylic thickener.

  About the pulp which forms the paper-like base material used for this invention, it does not specifically limit about a manufacturing method, a kind, etc., a chemical pulp like KP and SP, mechanical pulps, such as SGP, RGP, BCTMP, and CTMP, Organic synthesis such as chlorine-free pulp such as ECF pulp and TCF pulp, waste paper pulp such as deinked pulp, non-wood pulp such as kenaf, bagasse, bamboo, straw, hemp etc., polyamide fiber, polyester fiber, polynosic fiber, etc. Examples thereof include inorganic fibers such as fibers, glass fibers, ceramic fibers, and carbon fibers.

  In the paper-like substrate, a filler, a yield improver, a freeness improver, a paper strength enhancer, a fixing agent, an internal sizing agent, a dye, a fluorescent brightening agent, a pH adjuster, and an antifoaming agent, as necessary An internal additive for papermaking such as an agent, a pitch control agent and a slime control agent can be appropriately blended. The filler is not particularly limited, but various pigments generally used for fine paper, such as kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, zinc oxide, alumina, carbonate Organic pigments such as mineral pigments such as magnesium, magnesium oxide, silica, white carbon, bentonite, zeolite, sericite, smectite, polystyrene resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins Solid, micro hollow, and through-hole type particles.

The paper-making method of the paper-like substrate is not particularly limited, and includes, for example, an acidic paper-making method in which the paper-making pH is around 4.5, and a neutral sizing agent and / or an alkaline filler such as calcium carbonate as a main component, It can be applied to all papermaking methods, from weakly acidic papermaking pH of 6 to weak alkaline neutral papermaking of papermaking pH of about 9, and the paper machine can be a long net paper machine, twin wire paper machine, round net paper machine Known paper machines such as Yankee paper machines and inclined wire paper machines can be used as appropriate.
The basis weight of the paper-like substrate used in the present invention is not particularly limited, but usually a basis weight in the range of 40 to 200 g / m ² is preferably used.

  The paper-making method for the paper-like substrate is not particularly limited, but even if the air permeability of the coating layer is good, the effect of suppressing the generation of blisters is obtained if the paper-like substrate has extremely poor gas permeability. It may not be possible. Therefore, the JAPAN TAPPI paper pulp test method no. The air permeability based on 5-2: 2000 is preferably 30 seconds or less, and more preferably 20 seconds or less.

Although the total coating amount of the coating layer of this invention is not specifically limited, It is 2-25 g / m < ² > by dry mass with respect to the single side | surface of a paper-like base material, Preferably it is 5-20 g / m < ² >. . When the coating amount is less than ² g / m ^2, it is difficult to form a coating layer uniformly on the base paper. On the other hand, when the coating amount exceeds 25 g / m ² , cracks due to shrinkage of the coating layer occur. It becomes difficult.

  The inner coating layer of the present invention is formed by applying a water-based coating liquid containing an inorganic pigment and a water-soluble adhesive as components to a paper-like substrate. Calcium, light calcium carbonate, kaolin, calcined kaolin, structural kaolin, deramikaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, magnesium aluminosilicate, calcium silicate, white Examples thereof include carbon, bentonite, zeolite, sericite, smectite, etc., which are appropriately selected from these and used in combination of one or more.

  You may mix | blend an organic pigment as another pigment with the coating liquid for inner side coating layers. Examples of the organic pigment include polystyrene resin, styrene-butadiene copolymer resin, styrene-acryl copolymer resin, styrene-methacryl copolymer resin, acrylic resin, vinylidene chloride resin, urea resin, and melamine. Resin, benzoguanamine resin, and the like, which are appropriately selected from these and used in combination of one or more.

  As a compounding quantity to the coating liquid for inner side coating layers of an inorganic pigment, the range of 40-90 mass parts is preferable with respect to 100 mass parts (dry) of the coating layer. When the blending amount is less than 40 parts by mass, it tends to be inferior in terms of air permeability. Moreover, when a compounding quantity exceeds 90 mass parts, it will become inferior in terms of interlayer strength. Moreover, as a compounding quantity to the coating liquid for inner side coating layers of an organic pigment, 30 mass parts or less are preferable with respect to 100 mass parts (dry) of a coating layer. It is not preferable to exceed 30 parts by mass in terms of coating solution cost.

  Examples of the adhesive in the inner coating layer include starches such as starch, oxidized starch, esterified starch, etherified starch, cationized starch, amphoteric starch, enzyme-modified starch, and thermochemically modified starch, methylcellulose, carboxymethylcellulose, Examples include cellulose derivatives such as hydroxyethyl cellulose, proteins such as casein and soy protein, water-soluble adhesives such as polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, polyacrylamide, and olefin-maleic anhydride resin. These are appropriately selected from these and used alone or in combination of two or more. Among water-soluble adhesives, starches are particularly preferable because they are easy to impart rigidity and are inexpensive.

  As an adhesive in the inner coating layer, a water dispersible adhesive may be blended. Examples of such water-dispersible adhesives include conjugated diene copolymer latexes such as styrene-butadiene latex, acrylonitrile-butadiene latex, and methyl methacrylate-butadiene latex, and polymers such as (meth) acrylate polymers or copolymers. Emulsion, vinyl acetate emulsion such as ethylene-vinyl acetate emulsion, styrene-acrylic emulsion, vinylidene chloride emulsion, polyester emulsion, polyurethane emulsion, polyamide emulsion, etc. One type or two or more types are used in combination.

  As a compounding quantity to the coating liquid for inner side coating layers of a water-soluble adhesive, the range of 2-25 mass parts is preferable with respect to 100 mass parts (dry) of coating layers. When the blending amount is less than 2 parts by mass, the interlayer strength tends to be inferior, and the rigidity is likely to be small. Moreover, when a compounding quantity exceeds 25 mass parts, it becomes easy to become a thing with high air permeability. As a compounding quantity to the coating liquid for inner side coating layers of a water dispersible adhesive agent, 20 mass parts or less are preferable with respect to 100 mass parts (dry) of coating layers. When it exceeds 20 parts by mass, it tends to have a high air permeability.

  In the coating liquid for the inner coating layer, various auxiliary agents such as surfactants, pH regulators, viscosity modifiers, water retention agents, softeners, gloss imparting agents, waxes, dispersants, if necessary Flow modifier, antistatic agent, stabilizer, antistatic agent, crosslinking agent, sizing agent, fluorescent brightener, colorant, ultraviolet absorber, antifoaming agent, water-resistant agent, plasticizer, preservative, fragrance, etc. Is appropriately blended.

The coating amount of the inner coating layer and the outermost coating layer is not particularly limited, but in the case of the inner coating layer, the dry weight per side is usually 0.1 to 10 g / m ² , preferably 0. 0.5 to 5 g / m ² . When the amount is less than 0.1 g / m ² , the effect of the two layers becomes extremely small. On the other hand, when the amount exceeds 10 g / m ² , the gas permeability tends to be inferior. In the present invention, the inner coating layer is provided on one side or both sides of the paper-like substrate. Further, the number of inner coating layers per one side is usually one layer, but it may be a laminate of two or more layers. In this case, the coating liquids forming the inner coating layer are not necessarily the same, and may be different.

  As a coating method of the coating liquid, generally known coating devices such as blade coaters, air knife coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, slot die coaters, gravure coaters, Champlex coaters, brush coaters, A slide bead coater, a two-roll or metering blade type size press coater, a bill blade coater, a short dwell coater, a gate roll coater or the like is used. In view of the crack generation mechanism, a flat coating method in which unevenness due to fibers on the surface of the base paper is covered and flattened is preferable to a contour coating method in which a uniform thickness is applied on the base paper. Drying when the thermoplastic organic fine particles are blended in the coating liquid is preferably performed under conditions where the paper surface temperature is higher than the Tg of the thermoplastic organic fine particles.

  The coated paper of the present invention is usually subjected to a smoothing treatment. The smoothing process is performed on-machine or off-machine using a known apparatus such as a super calendar, a gloss calendar, or a soft calendar. The processing conditions such as the pressure of the pressure device, the heating temperature, and the number of nips are appropriately adjusted. In the present invention, since the generated cracks are considerably large and many in comparison with the size of the cracks usually observed in general printing coated paper, the cracks are blocked by the gloss treatment such as super calendar. And good air permeability can be provided.

  Paper blisters and toner blisters in the electrophotographic system are coated with JAPAN TAPPI paper pulp test method No. By setting the Oken air permeability based on 5-2: 2000 to 8000 seconds or less, the desired level can be achieved. Especially, 5000 seconds or less are preferable, More preferably, it is 3000 seconds or less, More preferably, it is 2000 seconds or less.

  In the present invention, in terms of the texture of the coated paper, the white paper glossiness at an incident / light receiving angle of 75 degrees based on JIS Z 8741 is preferably in the range of 45 to 85%, more preferably 55 to 85%. .

  In order to obtain a coated paper with a high incidence of white paper with an incident / light-receiving angle of 75 degrees according to JIS Z 8741, smoothing processing under high pressure conditions is required. Although the pores are blocked and only those with poor air permeability can be obtained, the coated paper according to the present invention contributes to cracks and can ensure air permeability even if smoothing treatment is performed under high pressure conditions, blistering Can be suppressed.

  When the coating layer is provided on one side of the paper-like substrate, a coating layer can be provided on the back side for preventing curling, imparting printability, imparting paper supply / discharge, providing antistatic properties, and the like. The back surface can be post-processed to impart properties such as adhesion, heat-sensitive recording, magnetic recording, flame retardancy, heat resistance, water resistance, oil resistance, and slip resistance. In addition, post-processing such as a thermal transfer receiving layer and an ink jet recording layer can be performed.

  The water content of the coated paper of the present invention is usually adjusted to a range of 3 to 10%. More preferably, it is 4 to 8% of range. When the water content is less than 3%, curling occurs on the paper and stable printing cannot be performed. If the water content exceeds 10%, blisters are extremely likely to occur.

  The coated paper obtained in the present invention has extremely good performance as an offset printing or electrophotographic paper, but can also be used as an image recording paper such as a thermal transfer system or an ink jet system.

In particular, in an electrophotographic system in which an image is formed with toner particles of about 5 to 7 μm, an extremely high quality image can be obtained by using the above-mentioned coating sheet.
For example, when an image is formed and evaluated using an electrophotographic printer based on a method in conformity with ISO-13660 draft standard QEA (Quality Engineering Associates, Inc.), a mottle at a tile size of 40 μm is 10 GSV (Gray Scale). (Value) or less, the line ragedness (jaggedness) is 10 μm or less, and the brilliance (blurring degree) is 11 μm or less, and an extremely good image can be obtained.

  It has been found that the coated paper of the present invention has a great effect on off-wheel wrinkles and folding suitability. Off-wheel wrinkles are wrinkles on the paper that occur during off-wheel printing, and cracking suitability is the crack resistance of the ink layer at the fold or trough in the folding machine processing after off-wheel printing. It is. The reason why off-wheel wrinkles have a great effect is that the paper has low air permeability, so that moisture contained in the drying process of the off-wheel printing occurs uniformly, so that there is no variation in paper moisture. It is considered that no wrinkles are generated and no wrinkles are generated. In addition, the reason why there is a great effect on the foldability is that the surface strength of the coating layer is strong even though the paper has low air permeability, and even if force is applied by folding, the coating layer does not collapse, and as a result It is conceivable that the upper ink layer is hardly cracked. In addition, with regard to off-wheel wrinkles and folding suitability, a system in which a binder and a binder pigment are further blended shows particularly good results.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these ranges. In the examples, “parts” and “%” indicate “parts by mass (solid component)” and “mass%” unless otherwise specified. In addition, when the measured Tg is not a single peak, the main peak temperature or Tg calculated from the monomer composition is indicated as “Tg representative value”, and when the measured Tg is a single peak, the measurement is performed. The value or Tg calculated from the monomer composition is shown as “Tg value”.

Example 1
[Creation of paper-like substrate]
90 parts of LBKP (freeness (CSF) = 450 ml), 10 parts of NBKP (freeness (CSF) = 450 ml), 5 parts of light calcium carbonate (PC: manufactured by Shiroishi Calcium Co.), 1.5 parts of starch, alkenyl anhydride A stock was prepared by adding 0.1 part of succinic acid and 0.6 part of sulfuric acid band. Subsequently, the paper stock is used to make a paper by a long paper machine, and in the paper making process, starch is applied using a size press machine so that the dry weight becomes 1 g / m ^2. Smoothing was performed so that the smoothness was 30 seconds, and a paper-like substrate having a basis weight of 65 g / m ² was obtained.

[Preparation of coating solution for inner coating layer]
To 100 parts of acicular light calcium carbonate (trade name: TPX121, manufactured by Okutama Kogyo Co., Ltd.), add 10 parts of oxidized starch (trade name; Ace A, manufactured by Oji Constarch Co., Ltd.), which is a water-soluble adhesive, and add water. A coating solution having a solid concentration of 45% was prepared.
[Formation of inner coating layer]
Apply the coating liquid on both sides of the paper-like substrate at a coating speed of 500 m / min using a gate roll coater so that the dry coating amount per side is 1.0 g / m ^2. An inner coating layer-formed paper was obtained.
[Preparation of coating solution for outermost coating layer]
To water, 5 parts of kaolin (trade name: Milagros 91, manufactured by Engelhard) and 0.01 part of a dispersant (trade name: Aron A-9, manufactured by Toagosei Co., Ltd.) are added and dispersed with a Coreless disperser. A kaolin dispersion having a solid content of 72% was obtained. To this dispersion, 65 parts by weight of heavy calcium carbonate having a solid content concentration of 75% (trade name; FMT-97, manufactured by Pimatech) was added to prepare a pigment slurry. To this pigment slurry, thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; trade name; trade name; AG gum HE No. 2, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0.3 parts, styrene-butadiene copolymer. POT-7092, manufactured by Nippon Zeon Co., Ltd.) was added and stirred, and water was further added to prepare a coating solution having a solid content concentration of 55%.

[Create laminated coated paper]
The innermost coating layer-forming paper is coated at a coating speed of 500 m / min using a blade coater so that the outermost coating layer coating solution has a dry coating amount of 8.5 g / m ² per side. Then, the coated paper having a white paper gloss of 70% and a basis weight of 84 g / m ² was obtained by processing in a pressure nip composed of a metal roll and an elastic roll.

Example 2
In preparing the coating solution for the outermost coating layer, instead of 30 parts of thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; POT-7092, manufactured by Nippon Zeon Co., Ltd.), thermoplastic organic fine particles having a Tg of 55 ° C. (trade name; Coated paper having a white paper gloss of 70% and a basis weight of 84 g / m ^{2 in} the same manner as in Example 1, except that 30 parts (0640, manufactured by JSR) were used and the pressure nip treatment conditions were changed. Got.

Example 3
In the preparation of the coating solution for the outermost coating layer, thermoplastic organic fine particles having a Tg representative value of 46 ° C. (instead of 30 parts of thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; POT-7092, manufactured by Nippon Zeon Co., Ltd.)) (Trade name: L-8804, manufactured by Asahi Kasei Kogyo Co., Ltd.) Except for using 30 parts and changing the pressure nip treatment conditions, the gloss of white paper is 70% and the basis weight is 84 g / gram as in Example 1. A coated paper of m ² was obtained.

Example 4
In the preparation of the coating solution for the outermost coating layer, instead of 30 parts of thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; POT-7092, manufactured by Nippon Zeon Co., Ltd.), thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; P0T-7092, manufactured by Nippon Zeon Co., Ltd.) 10 parts, and Tg 55 ° C. thermoplastic organic fine particles (trade name; 0640, manufactured by JSR Corporation) 20 parts, and the point that the pressure nip treatment conditions were changed, In the same manner as in Example 1, a coated paper having a white paper gloss of 70% and a basis weight of 84 g / m ² was obtained.

Example 5
In the preparation of the coating solution for the outermost coating layer, instead of 30 parts of thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; POT-7092, manufactured by Nippon Zeon Co., Ltd.), thermoplastic organic fine particles having a Tg of 75 ° C. (trade name; S2577 (A), manufactured by JSR Co., Ltd.), except that 30 parts were used and the pressure nip treatment conditions were changed, and the white paper gloss was 70% and the basis weight was 84 g / m ² as in Example 1. Coated paper was obtained.

Comparative Example 1
In the preparation of the coating solution for the outermost coating layer, a water-dispersible adhesive having a Tg of 0 ° C. or lower is used instead of 10 parts of oxidized starch (trade name; Ace A, manufactured by Oji Constarch) which is a water-soluble adhesive. Except for using 10 parts of latex (trade name: T2531E, manufactured by JSR) and changing the pressure nip treatment conditions, the gloss of white paper is 70% and the basis weight is 84 g / m as in Example 1. ² coated papers were obtained.

Comparative Example 2
It is a water-dispersible adhesive having a Tg of 0 ° C. or lower in place of 30 parts of thermoplastic organic fine particles having a Tg of 35 ° C. (trade name; POT-7092, manufactured by Nippon Zeon Co., Ltd.) in the preparation of the coating solution for the outermost coating layer. Except for using 30 parts of latex (trade name: T2531E, manufactured by JSR Corporation) and changing the pressure nip treatment conditions, the gloss of white paper is 70% and the basis weight is 84 g / m as in Example 1. ² coated papers were obtained.

Example 6
In the preparation of the coating solution for the outermost coating layer, heavy calcium carbonate (trade name: FMT-97, manufactured by PMMA Tech) was changed from 65 parts to 62 parts, and crack formation promoting particles (average particle diameter of 10 μm) were changed. (Light calcium carbonate, manufactured by Yonesho Lime Industry Co., Ltd.) 4 parts were added, and the pressure nip treatment conditions were changed, except that the white paper gloss was 70% and the basis weight was 84 g / m ² , as in Example 1. Coated paper was obtained.

Example 7
In the preparation of the coating solution for the outermost coating layer, heavy calcium carbonate (trade name; FMT-97, manufactured by PMMA Tech) was changed from 65 parts to 61 parts, and a hollow organic pigment (trade name; HP-1055). , Manufactured by Rohm and Haas Japan Co., Ltd.) The same as in Example 1 except that 4 parts were added and the pressure nip treatment conditions were changed. The white paper gloss was 70% and the basis weight was 84 g / m ² . Coated paper was obtained.

The coated paper obtained in Examples 1 to 7 and Comparative Examples 1 and 2, as well as the off-wheel printed material and the color copy printed material were evaluated by the following evaluation methods.
[Number of cracks on coating layer surface]
The surface of the coated paper was observed with an electron microscope at a magnification of 100 times or 500 times, the number of cracks existing at 100 mm ² was examined, and the number of cracks per 1 mm ² was calculated.

[Evaluation of glossiness of blank paper]
Based on JIS Z 8741, the glossiness of white paper was measured under the conditions of an incident angle and a light receiving angle of 75 degrees. For the measurement, GLOSS METER MODEL GM-26D manufactured by Murakami Color Research Laboratory was used.

[Evaluation of air permeability]
JAPAN TAPPI Paper Pulp Test Method No. Based on 5-2: 2000, the air permeability of the paper was measured using a fully automatic digital type Oken air permeability and smoothness tester EYO manufactured by Asahi Seiko Co., Ltd. The smaller the air permeability value (seconds), the better the air permeability.

[Printing coated paper]
[Off-wheel printing]
Using an offset rotary printing press (Mitsubishi Lisopia L-BT3-1100 / Mitsubishi Heavy Industries), both sides are 4 color solid design, printing speed is 600 rpm, paper surface temperature at the dryer outlet is 120 ° C, cooling after passing through the dryer The roll was folded continuously with printing through cooling water at 10 ° C.

[Evaluation of off-wheel blister]
The blister generation state of the off-wheel printed material was visually judged and evaluated in 5 stages of 1 to 5.
5: A blister is not observed at all and is a very excellent level.
4: The blister is hardly observed and is an excellent level.
3: A small amount of fine blisters are observed, but there is no practical problem.
2: A level in which a large amount of fine blisters are observed and there is a practical problem.
1: A large amount of large blisters is observed, and there is a problem in practical use.

[Evaluation of color copy blister]
Using a color copying machine IPSiO Color 2100 manufactured by RICOH, 100 continuous color prints were made on A4 size coated paper, and the blister generation status was visually judged and evaluated in 5 stages from 1 to 5.
5: A blister is not observed at all and is a very excellent level.
4: The blister is hardly observed and is an excellent level.
3: A small amount of fine blisters are observed, but there is no practical problem.
2: A level in which a large amount of fine blisters are observed and there is a practical problem.
1: A large amount of large blisters is observed, and there is a problem in practical use.

[Evaluation of print finish]
The printed finished state of the above-mentioned off-wheel printed matter was visually judged and evaluated in 5 stages from 1 to 5.
5: Extremely excellent level.
4: Level that is quite excellent.
3: Slightly inferior, but practically no problem.
2: Level that is considerably inferior and problematic in practical use.
1: Significantly inferior and practically problematic level.

[Evaluation of off-wheel wrinkles]
The off-ring wrinkle generation state of the double-sided, four-color solid printing part was visually judged and evaluated in five stages of 1 to 5.
5: Very good level with no wrinkles observed.
4: The generation | occurrence | production of wrinkles is hardly recognized and it is the level which is excellent.
3: Occurrence of mild wrinkles is recognized, but there is no practical problem.
2: Occurrence of wrinkles was observed and there was a problem in practical use.
1: A level where there is a problem in practical use because of severe wrinkles.

[Crack evaluation]
The printed coated paper is cut into A4 size, folded in half with a paper folding machine (made by Horizon) in an environment of temperature 20 ° C and humidity 30% RH, and the bent part is observed with an enlarged loupe. , 1 to 5 were evaluated.
5: The coating layer at the bent portion has no cracks or tears and is good.
4: The coating layer at the bent portion has almost no cracks or tears and has no practical problem.
3: Some cracks are observed in the coating layer at the bent portion, but there is no practical problem.
2: Cracks and tears are seen in the coating layer at the bent part, which is problematic in practice.
1: Cracks and tears are observed in the coating layer at the bent part, and the pulp fibers of the paper substrate are exposed, which is extremely inferior.

  The above evaluation results are shown in Table 1.

Crack shape 1. Crack shape 2.

Claims (9)

  In a coated paper comprising a paper-like base material and at least two coating layers on at least one surface thereof, in the inner coating layer adjacent to the paper-like base material, there are needle crystals, spindles In the outermost coating layer formed on the inner coating layer, which contains a pigment having a crystal structure of any one of a cylindrical crystal, a columnar crystal and a rice granular crystal, a glass transition temperature of 20 to 150 ° C. Coated paper characterized by containing thermoplastic organic fine particles.   The coated paper of Claim 1 in which the inner side coating layer adjacent to the said paper-like base material contains starch.   The coated paper according to claim 1, wherein the thermoplastic organic fine particles are a styrene-butadiene copolymer.   The thermoplastic organic fine particles contain a non-film-forming hollow organic pigment, and 1 to 10 parts by mass of the non-film-forming hollow organic pigment is contained in 100 parts by mass of all pigments in the outermost coating layer. 2. Coated paper according to 2.   The coated paper according to claim 1, wherein the outermost coating layer contains crack formation promoting particles.   The coating according to claim 5, wherein the crack formation promoting particles have an average particle diameter of 3.0 to 30.0 μm, and 0.1 to 10 parts by mass in 100 parts by mass of the outermost coating layer. Craft paper.   The coating according to any one of claims 1 to 6, comprising 40 to 90 parts by mass of an inorganic pigment and 5 to 60 parts by mass of thermoplastic organic fine particles in 100 parts by mass of the outermost coating layer. paper. 8. The crack according to claim 1, wherein 1 to 1000 cracks having a width of 0.2 to 3.0 μm and a length of 3 to 1000 μm are present on 1 mm ^{2 on} the outermost coating layer surface. Coated paper.   The surface of the outermost coating layer has a white paper glossiness of 45 to 85% at an incident / light receiving angle of 75 degrees according to JIS Z 8741, and the JAPAN TAPPI paper pulp test method no. The coated paper according to any one of claims 1 to 8, wherein the Oken air permeability based on 5-2: 2000 is 8000 seconds or less.

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