JP2021046232A - Packaging paper - Google Patents

Abstract

To provide packaging paper that achieves a reduced amount of use of plastic, and is excellent in processing suitability.SOLUTION: This invention relates to packaging paper having at least one heat seal layer on at least one side of a paper substrate, the heat seal layer containing an ionomer, and a total amount of dry coating of the heat seal layer being 2-10 g/m2. The packaging paper has a basis weight of 80 g/m2 to 500 g/m2, and the packaging paper has a degree of Stockigt sizing of 5 seconds or more.SELECTED DRAWING: None

Description

The present invention relates to a wrapping paper having excellent processability and reducing the amount of plastic used. In particular, the present invention relates to wrapping paper that is suitable for bending and gluing and has excellent heat-sealing properties as thick containers such as boxes and cartons.

In recent years, the plastic waste problem has become more serious. The world's plastic production is said to exceed 400 million tons / year, and the packaging sector is the largest producer of plastic, causing plastic waste. Plastic does not decompose semi-permanently, and the waste becomes microplastic in the natural environment, which has a serious adverse effect on the ecosystem. The most commonly used plastics for packaging containers are polyethylene terephthalate (PET) used for beverage bottles and the like, polyethylene (PE) and polypropylene (PP) used for laminating cash register bags and containers. .. Especially, the pollution of the ocean is remarkable, and it is said that the plastic waste cannot be collected. In the future, it is necessary for the global environment to reduce the use of plastics.

On the other hand, as a measure against plastic waste, applications of biodegradable plastics that can be completely decomposed by microorganisms have been proposed all over the world. Biodegradable plastics are decomposed in nature within a certain period of time, but until they are decomposed, they are still garbage, and unless their usage and disposal amount are reduced, it cannot be said to be an immediate measure ( See Patent Documents 1 and 2).

As a quick-acting countermeasure, it has been proposed to replace plastic with paper, but when processing paper into bags and containers, a large amount of polyethylene or polypropylene is laminated and used as a heat sealant. To. Laminates of these plastics, but different depending on the product concept, generally a 20 to 50 g / ^{m 2,} it may be extensive and 300 g / ^{m 2.} Therefore, even in a packaging container in which plastic is replaced with paper, there is still a problem that the amount of plastic used is not sufficiently reduced, and there is an urgent need for a means for directly reducing the use of plastic.

Japanese Unexamined Patent Publication No. 2012-148444 Japanese Unexamined Patent Publication No. 2013-141763

An object of the present invention is to provide a wrapping paper having excellent processability, which can reduce the amount of plastic used. In particular, the present invention relates to wrapping paper that is suitable for bending and gluing and has excellent heat-sealing properties that can be appropriately used as a thick container such as a box or carton.

In the present invention, an ionomer is used in order to reduce the amount of polyethylene or polypropylene used in the conventional plastic laminated paper (hereinafter sometimes abbreviated as polylami paper). That is, the wrapping paper according to the present invention is a wrapping paper having at least one or more heat-sealing layers on at least one surface of a paper base material, the heat-sealing layers containing ionomers, and the amount of coating of the heat-sealing layers. ^{Is 2} to 10 g / m 2. Compared to the amount of polyethylene or polypropylene laminated in the conventional heat seal layer of polylami paper ^{exceeding 20 g / m 2} , the amount of plastic used in the heat seal layer is up to about 10 to 50% of the conventional amount. Can be reduced. Here, the ionomer is a synthetic resin in which a polymer is made into an aggregate by utilizing the cohesive force of metal ions, and is a synthetic resin in which acrylic acid or methacrylic acid is combined with ethylene or the like. For example, it is produced by adding an acrylic polymer and ethylene to an intermolecular bond by adding a metal cation such as sodium or zinc.

Further, in the present invention, it is necessary that the wrapping paper has a nice human size of 5 seconds or more. If the degree of sizing is less than 5 seconds, the glue is absorbed by the paper during the glue pasting process and the adhesiveness is poor. In addition, the ionomer melted by heat during heat sealing is absorbed by the paper substrate, resulting in poor adhesive strength. Further, especially during the bending process, the wrapping paper is cracked because the heat seal layer is thinner than the polyethylene layer.

Further, the basis weight of the packaging material of the present invention is ^{80g / m 2 ~500g / m 2} , there is no tear-cracking in particular bending step during processing into a box-carton, etc. (potato cartons, etc.), also , A wrapping paper having an appearance suitable for boxes, cartons, etc. can be obtained.

According to the present invention, it is possible to produce a wrapping paper in which the amount of plastic used is reduced. With the container product using the wrapping paper of the present invention, even if it is improperly released as dust in the natural world, it is possible to reduce the adverse effect of plastic dust on the natural environment, and plastic. Helps solve the garbage problem. The wrapping paper in the present invention is processed into, for example, bags, food cups such as ice cream, beverage cups such as coffee, food containers such as hot snacks, and packaging containers such as trays, boxes, cases, vessels, and envelopes. It is possible. In particular, the wrapping paper in the present invention is preferably processed as a thick container (tray, box, case, vessel, carton).

Next, the present invention will be described in detail by showing embodiments, but the present invention is not construed as being limited to these descriptions. The embodiments may be modified in various ways as long as the effects of the present invention are exhibited.

In the present embodiment, ionomer is a general term for synthetic resins in which polymers are aggregates by utilizing the cohesive force of metal ions, and is a resin in which acrylic acid or methacrylic acid is combined with ethylene or the like. That is, the metal salts of ethylene / methacrylic acid copolymers, the metal salts of ethylene / acrylic copolymers, the metal salts of ethylene / urethane copolymers, the metal salts of ethylene / fluorine polymer copolymers, etc. All are called ionomers. Examples of the metal forming the salt include alkali metal ions and alkaline earth metal ions, specifically, sodium, potassium, calcium, magnesium, and zinc ions. In the present invention, it is preferable that the ionomer is a self-emulsifying emulsion which is a metal salt of an ethylene / methacrylic acid copolymer. A heat seal layer having a sufficient heat seal strength can be provided with a relatively small amount of the heat seal layer applied.

In the present embodiment, the heat seal layer can be provided by applying a coating liquid for a heat seal layer containing an ionomer emulsion to at least one surface of a paper base material and drying the coating liquid. By using the ionomer emulsion, the coating amount can be controlled to be relatively low, and by using the water-based ionomer emulsion, VOC emissions can be eliminated and the load on the natural environment can be reduced. The coating amount of the heat seal layer is ² to 10 g / m 2 in terms of solid content, preferably 3 to 8 g / m ² per one side of the paper base material. If it is less than 2 g / m ^2, sufficient heat seal strength cannot be satisfied. On the contrary, ^{when it exceeds 10 g / m 2} , the quality is excessive in terms of heat seal strength, and the plastic reduction effect becomes poor. In the wrapping paper of the present invention, the heat seal layer is usually provided not only on a part of the surface of the paper base material but on the entire surface. That is, the heat seal layer is provided not only on the portion necessary for adhesion by the heat seal, such as a net shape, an island shape, or a linear shape, but is provided so as to cover the entire surface of the paper base material. Is good.

In addition to the ionomer emulsion, various auxiliaries may be added to the coating liquid for the heat seal layer. For example, viscosity modifiers, antifoaming agents, leveling agents such as surfactants and alcohols, coloring pigments, coloring dyes and the like. However, since the addition of these auxiliaries tends to cause a decrease in heat seal strength, it is preferable to add them in a small amount. In the present embodiment, it is preferable that the coating liquid for the heat seal layer is composed only of the ionomer emulsion.

The method for applying the coating liquid for the heat seal layer is not particularly limited, and a generally used coating device can be used. For example, air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray. Various known coating devices such as a coater, a gate roll coater, and a lip coater can be used.

Further, in the present invention, it is necessary that the wrapping paper has a nice human size of 5 seconds or more. If the degree of sizing is less than 5 seconds, the glue is absorbed by the paper during the glue pasting process and the adhesiveness is poor. In addition, the ionomer melted by heat during heat sealing is absorbed by the paper substrate, resulting in poor adhesive strength. Further, especially during the bending process, the wrapping paper is cracked because the heat seal layer is thinner than the polyethylene layer. In order to appropriately adjust the degree of stekihito size, in the present invention, it is preferable to add a sizing agent, particularly to add the sizing agent in the substrate. As the sizing agent, any sizing agent may be used as long as the degree of sizing is less than 5 seconds. For example, it is preferable to use a rosin sizing agent, particularly an acidic rosin sizing agent, and in the base material, 0.01 to 1.0 parts, preferably 0.04 to 0.6 parts, based on 100 parts by mass of pulp. It is preferable to use an acidic rosin sizing agent.

The basis weight of the wrapping paper of the present invention is ^{80g / m 2 ~500g / m 2} . As a result, tearing and cracking in the bending process during processing into boxes, cartons, etc. (potato cartons, etc.) are eliminated, and wrapping paper having an appearance suitable for boxes, cartons, etc. can be obtained.

In the present embodiment, the heat seal layer may be formed of two or more layers. By having two or more layers, the air permeability of the wrapping paper can be increased, water repellency and oil repellency can be imparted, and characteristics similar to or close to those of the plastic film laminated paper can be obtained. Because. When the number of heat-sealing layers is two or more, it is preferable that the coating amount of the lowest heat-sealing layer closest to the paper substrate is larger than the total coating amount of the other heat-sealing layers. This is because the air permeability of the wrapping paper can be further improved, and the water repellency and oil repellency are further improved.

In the present embodiment, the Z-axis strength (JPAPAN TAPPI No. 18-1, strength in the thickness direction of the paper) of the wrapping paper ^{is preferably 150 kN / m 2} or more. Eliminates tears and cracks during folding. Preferably, it is 200 kN / m ² or more.

In the present embodiment, it is preferable that the tensile elongation at break in the vertical direction of the wrapping paper is (JIS P-8113) 1% or more. It is possible to reduce tearing and cracking during folding of thick containers (tray, box, case, vessel, carton). Preferably, the tensile elongation at break in the longitudinal direction is 1.5% or more.

In the present embodiment, the longitudinal tensile strength of the wrapping paper is preferably (JIS P-8113) 5 kN / m or more. It is possible to reduce tearing and cracking during folding of thick containers (tray, box, case, vessel, carton). Preferably, the tensile strength in the longitudinal direction is 8 kN / m or more. The vertical direction referred to in the present invention is the vertical direction (MD), and the horizontal direction is the horizontal direction (CD).

In the present embodiment, the air permeability of the wrapping paper preferably exceeds 10,000 seconds. It is more preferably 12000 seconds or more, and further preferably 15000 seconds or more. By setting the air permeability of the wrapping paper to 10,000 seconds or more, the barrier property in the sense of blocking air is further enhanced, and the water repellency and oil repellency are further improved. The method of setting the air permeability of the wrapping paper to 10,000 seconds or more is not particularly limited, but can be achieved by using, for example, a paper base material having a high air permeability. Further, the air permeability of the wrapping paper can be increased by increasing the smoothness of the surface to which the heat seal coating liquid is applied. This is because pinholes and cracks can be further reduced in the heat seal layer formed thereafter. For example, by providing a pigment coating layer and then performing a calender treatment or the like, the smoothness of the surface to which the heat seal coating liquid is applied can be increased. In addition, coating two or more heat seal layers also has the effect of increasing the air permeability. In the two-layer coating of the heat seal layer, fine pinholes and cracks existing in the first coating layer (lower layer) are removed from the second coating layer (upper layer) provided on the first layer. It is thought that the air permeability will be increased by covering with. Further, increasing the coating amount of the heat seal layer is also effective in improving the air permeability. In terms of film formation of the heat seal layer, the air permeability is likely to be improved by setting the drying temperature of the coating liquid for the heat seal layer after coating to a temperature equal to or higher than the melting point of the ionomer.

In the present embodiment, the smoothness of the surface to which the heat seal coating liquid of the paper base material is applied is preferably 10 seconds or more. More preferably, it is 20 seconds or more. The higher the smoothness of the paper base material, the more likely it is that the film thickness of the heat-sealing layer provided by coating will be uniform (fine irregularities are unlikely to occur), and as a result, variations in heat-sealing strength can be less likely to occur. A uniform heat seal strength can be imparted on a flat surface. The method for increasing the smoothness of the paper substrate is not particularly limited, and examples thereof include a calender treatment using a known calender device such as a super calender, a gloss calender, a shoe nip calender, and a soft calender. .. Further, paper on which the mirror surface of a Yankee dryer is transferred, such as single-gloss kraft paper, is also suitable as a paper base material having high smoothness. The heat-sealing layer may have pinholes and cracks that are invisible to the naked eye, but to that extent, the heat-sealing property is not adversely affected. Further, a leveling agent for the purpose of preventing pinholes can be added to the heat seal layer coating liquid as long as the effects of the present invention are not impaired.

The paper base material used in the present embodiment is not particularly limited, and a known paper base material containing pulp as a main component can be used. The pulp that is the main component of the paper base material is chemical pulp such as LBKP (broadwood bleached kraft pulp) and NBKP (coniferous bleached kraft pulp), GP (crushed wood pulp), PGW (pressurized crushed wood pulp), and RMP (refiner mechanical). Pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemimechanical pulp), mechanical pulp such as CGP (chemigrand pulp), wood pulp such as DIP (deinked pulp), and Kenaf, Bagus , Bamboo, cotton and other non-wood pulp can be used. These can be used alone or in admixture in any proportion. In addition, synthetic fibers can be further blended as long as the desired effect of the present invention is not impaired. From the viewpoint of environmental protection, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, recycled paper pulp, and pulp obtained from planted trees are preferable. The appropriate pulp beating degree is 200 to 700 ml CSF, for example, 450 to 620 ml CSF in Canadian standard freeness (JIS P 8121: 1995 "Pulp freshness test method"). Usually, it is preferable to use 90 to 100 parts by mass of hardwood pulp and 0 to 10 parts by mass of softwood pulp in the total pulp. Further, in addition to the hardwood pulp, it is preferable to add softwood pulp in order to increase the strength of the folding process. For example, it is preferable to use 50 to 100 parts by mass of softwood pulp and 0 to 50 parts by mass of hardwood pulp in the total pulp. Moreover, you may use only softwood pulp as pulp.

As the paper base material, one containing a filler can also be used. Examples of the filler include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, and aluminum hydroxide. The filler content in the paper substrate is, for example, 1 to 30 parts by mass with respect to 100 parts by mass of the dry mass of the pulp. For example, it is preferable to contain 1 to 10 parts by mass of light calcium carbonate with respect to 100 parts by mass of dry mass of pulp.

Further, the paper base material may contain various known additives for papermaking in addition to pulp and filler. Examples of the papermaking additive include an internal paper strength enhancer such as a sizing agent and a wet paper strength enhancer, a bulking agent, a yield improver, a drainage improver, a coloring dye, a coloring pigment, a fluorescent whitening agent, and fluorescence. There are decoloring agents, pitch control agents, etc. Further, a water-soluble polymer such as starch, polyvinyl alcohol, or polyacrylamide may be applied.

The paper-based paper-making method is not particularly limited, and is a long-net paper machine, a long-net multi-layer paper machine, a circular net paper machine, a circular net multi-layer paper machine, a long-net circular net combination multi-layer paper machine, and twin wire paper. It can be manufactured with various paper machines such as machines. Further, in the present invention, the paper base material may be a single-layer paper, a multi-layer paper, or a laminated product having a plurality of layers.

The paper base material may be provided with one or more coating layers other than the heat seal layer, and may be provided with, for example, a pigment coating layer containing a pigment and an adhesive. As the pigment in the pigment coating layer, a known pigment used for the coating layer of general printing coated paper can be used, and for example, calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), Kaolin (including clay), calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous soil, aluminum hydroxide, hydroxide Examples thereof include inorganic pigments such as magnesium, acrylic, styrene, vinyl chloride, nylon itself, and organic pigments (so-called plastic pigments) obtained by copolymerizing these. For example, as the pigment, a combination of 20 to 40 parts by mass of kaolin and 60 to 80 parts by mass of heavy calcium carbonate can be used. Further, as the adhesive, a known adhesive used for the coating layer of general printing coated paper can be used, for example, butadiene-based copolymerized latex, cross-linking agent-modified starch, oxidized starch, enzyme-modified starch, and the like. Stars such as esterified starch, etherified starch, cationic starch, amphoteric starch, water-soluble polymers such as gelatin, casein, soybean protein, polyvinyl alcohol, vinyl acetate, ethylene vinyl acetate, polyurethane resin, acrylic resin, Examples of synthetic resins such as polyester-based resin and polyamide-based resin can be exemplified. The blending ratio of the pigment and the adhesive in the pigment coating layer is not particularly limited, but it is preferably 5 to 50 parts by mass of the adhesive with respect to 100 parts by mass of the pigment. For example, as the adhesive, a combination of 1 to 5 parts by mass of phosphoric acid esterified starch and 5 to 15 parts by mass of styrene-butadiene latex can be used with respect to 100 parts by mass of the pigment. The pigment coating layer may contain various auxiliaries as long as the desired effect of the present invention is not impaired. For example, a viscosity modifier, a softener, a gloss imparting agent, a water resistant agent, a dispersant, and a flow modifier. , UV absorbers, stabilizers, antistatic agents, cross-linking agents, sizing agents, optical brighteners, colorants, pH adjusters, antifoaming agents, plasticizers, preservatives may be included. The coating amount of such a pigment coating layer is, for example, ² to 40 g / m 2 in terms of solid content per one side of the paper substrate. As one of the embodiments of the wrapping paper of the present invention, the heat seal layer may be provided on such a pigment coating layer, and in another embodiment, the pigment coating layer is provided on only one surface. The heat seal layer may be provided on the surface of the paper base material provided with the above on which the pigment coating layer is not provided.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Further, "parts" and "%" in the example indicate "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of copies added is a value in terms of solid content.

(Example 1)
(Preparation of paper substrate)
Canadian Standard Freeness 500ml csf 100 parts of broadleaf bleached kraft pulp, 5 parts of light calcium carbonate (trade name: TP-221BM, manufactured by Okutama Kogyo Co., Ltd.), cationized starch (trade name: Neotac 20T, manufactured by Nippon Food Processing Co., Ltd.) 0.3 Part, modified rosin sizing agent (acidic sizing agent) (trade name: Harsize NES-500, manufactured by Harima Kasei Co., Ltd.) Add water to 0.2 parts to prepare the paper material, and use a long net multi-cylinder paper machine. A base paper having a basis weight of 193 g / m ^{2 was prepared.} Oxidized starch (trade name: M-200, manufactured by Sansho Co., Ltd.) is applied to this base paper by a size press so that the dry coating amount per both sides is 2 g / m ^2, and the paper is dried to have a basis weight of 195 g / m ^2. Paper substrate was obtained.

(Making wrapping paper)
Water-based ionomer emulsion (trade name: Chemipal S-300, manufactured by Mitsui Chemicals, Inc., composition: metal salt of ethylene / methacrylic acid copolymer, self-emulsifying emulsion, microtrack method) on one side of the paper substrate obtained above. (Average particle size 0.5 μm) is coated with an air knife coater so that the dry coating amount is 5 g / m ² , dried to provide a heat seal layer, and a wrapping paper having ^{a basis weight of 200 g / m 2 is applied.} Made. The degree of sutekihito size was 50 seconds.

(Example 2)
A wrapping paper was prepared in the same manner as in Example 1 except that the pulp was 100 parts of unbleached kraft pulp made of softwood. The degree of sutekihito size was 60 seconds.

(Example 3)
A wrapping paper was produced in the same manner as in Example 1 except that the amount of the rosin sizing agent added was 0.05 parts. The degree of sutekihito size was 10 seconds.

(Example 4)
A wrapping paper was prepared in the same manner as in Example 1 except that the amount of the modified rosin sizing agent was 0.5 parts. The degree of sutekihito size was 250 seconds.

(Example 5)
A wrapping paper was prepared in the same manner as in Example 1 except that the amount of cationized starch was 0.1 part. The degree of sutekihito size was 51 seconds.

(Example 6)
A wrapping paper was prepared in the same manner as in Example 1 except that the pulp was 40 parts of softwood kraft pulp and 60 parts of hardwood kraft pulp. The degree of sutekihito size was 54 seconds.

(Example 7)
A wrapping paper was prepared in the same manner as in Example 1 except that the cationized starch was changed to 0.6 parts. The degree of sutekihito size was 54 seconds.

(Comparative Example 1)
Low-density polyethylene (Petrosen DLZ19A, manufactured by Tosoh Corporation) is laminated on one side of the paper substrate produced in Example 1 with an extraction coater (melt extruder) so that the coating amount is 30 g / m ^2. A heat-sealing layer was provided to prepare a wrapping paper. Stekihito sized was not measurable (water impermeable).

(Comparative Example 2)
A wrapping paper was prepared in the same manner as in Example 1 except that the modified rosin sizing agent was not added. The degree of sutekihito size was 0 seconds.

The wrapping papers obtained in each Example and Comparative Example were evaluated by the methods shown below. The results obtained are shown in Table 1.

Nice human size degree
Measured according to JIS P 8122.

(2) Z-axis strength (JPAPAN TAPPI No. 18-1)
JAPAN TAPPI No. Measured according to 18-1.

(3) Tensile breaking elongation in the vertical direction Measured according to JIS P-8113.

(4) Longitudinal tensile strength Measured according to JIS P-8113.

(5) Heat-sealing strength Two sheets of the obtained wrapping paper are cut into a size of 8 mm in width and 15 cm in length, and the front and back surfaces of the wrapping paper are overlapped to form a heat-sealing device (manufactured by Palmec, model number: PTS-). Under 100), heat sealing was performed under certain conditions (adhesion width: 4 mm, temperature: 180 ° C., pressure 0.4 MPa, pressing time 0.5 seconds, pitch: 4 mm). Next, the heat-sealed sample was measured for peel strength under certain conditions (peeling speed: 100 mm / min, peeling length: 10 cm) with a peel strength tester (manufactured by Shimadzu Corporation, model number: Autograph AGS-X). The heat seal strength (gf / 4 mm) was used. The higher the number, the better.

(6) Adequacy for paste processing A carton was manufactured with a potato carton making machine. The adhesiveness of the glued portion was visually inspected and evaluated as follows.
◎: Completely adhered ○: There is a part that is not adhered slightly, but it is a practical level.
Δ: There is a part that is not adhered, so it is not practical.
×: Not adhered at all and cannot be put into practical use.

(7) Folding suitability A carton was manufactured with a potato carton making machine. The cracks and tears in the folded part were visually inspected and evaluated as follows.
⊚: There is no crack in the bent part and it is practical.
〇: There are slight cracks in the bent part, but it is practical.
Δ: There is a crack in the bent part, so it is not practical.
×: There is a remarkable crack in the bent part, which is not practical.

As shown in Table 1, Examples 1 to 8 are preferable because the heat-sealing suitability and the glue-pasting process suitability are at the same level as those of the polylami paper of Comparative Example 1. Further, Comparative Example 2 was inferior in sheet seal suitability and glue-pasting process suitability because the wrapping paper had a nice human size of less than 5 seconds.

Claims (5)

A wrapping paper having at least one heat-sealing layer on at least one surface of a paper base material, the heat-sealing layer containing an ionomer, and the dry coating amount of the heat-sealing layer is 2 to 10 g in all layers. / ^{m 2,} wherein a wrapping basis weight of ^{80 g} / m 2 to 500 g / ^{m 2} of paper, the packaging material, wherein the Stöckigt sizing degree of the packaging material is not less than 5 seconds. The wrapping paper according to claim 1, wherein the Z-axis strength (JPAPAN TAPPI No. 18-1) of the wrapping paper is 150 kN / m ^{2 or more.} The wrapping paper according to claim 1 or 2, wherein the wrapping paper has a longitudinal tensile elongation at break of (JIS P-8113) of 1% or more. The wrapping paper according to any one of claims 1 to 3, wherein the wrapping paper has a longitudinal tensile strength of (JIS P-8113) of 5 kN / m or more. The wrapping paper according to any one of claims 1 to 4, wherein the base material contains 0.01 to 1.0 parts of an acidic rosin sizing agent with respect to 100 parts by mass of pulp.