Heat seal paper and packaging bag

Abstract

To provide heat-seal paper excellent in anti-blocking property under a high temperature / high humidity condition and having high peel strength, yielding a packaging bag excellent in drop resistance, and a packaging bag using the heat seal paper.SOLUTION: A heat-seal paper comprises one or more heat-seal layers at least on one surface of a paper substrate, with the heat-seal layer containing a water-dispersible resin binder, paraffin wax, and calcium carbonate, the water-dispersible resin binder containing a styrene-butadiene copolymer, the content of the paraffin wax in the heat-seal layer being 6 pts. mass or more and 14 pts. mass or less relative to 100 pts. mass of the water-dispersible resin binder, and the content of the calcium carbonate in the heat-seal layer being 4 pts. mass or more and 19 pts. mass or less relative to 100 pts. mass of the water-dispersible resin binder.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to heat-sealing paper and a packaging bag using the same.

Background Art

[0002] Packages using the heat-sealing method are widely used not only for packaging general industrial products but also for packaging foods, pharmaceuticals, medical devices, etc.

[0003] In recent years, the problem of plastic waste has been worsening. Among the world's plastic production, the plastic production in the packaging container sector is large, which has caused plastic waste. Plastics are not decomposed semi-permanently, and the waste is micro-plasticized in the natural environment, having a serious adverse impact on the ecosystem. As a countermeasure, it has been proposed to replace plastics with paper.

[0004] For example, Patent Document 1 aims to provide a water- and oil-resistant heat-sealing paper having water resistance, oil resistance, heat-sealing suitability, and capable of long-term storage, and is characterized in that it has a coating layer containing a thermoplastic resin, a wax, and an inorganic flat pigment on at least one surface of a paper substrate. A water- and oil-resistant heat-sealing paper is disclosed. Further, Patent Document 2 aims to provide a heat-sealing paper having heat-sealing suitability and good blocking resistance, which is preferably used for packaging applications such as packaging materials, bags, containers, boxes, cups, lid materials, etc., and has a coating layer containing a thermoplastic resin on at least one surface of a paper substrate, and the basis weight of the paper substrate is 20 g / m 2 above 600 g / m 2 below, and the coating layer contains one or more selected from wax or pigment as an anti-blocking agent, and the thermoplastic resin contained in the coating layer contains an ethylene acrylic acid copolymer resin. A heat-sealing paper is disclosed.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2022-24664 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2023-10964 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] The water- and oil-resistant heat-sealing paper of Patent Document 1 has heat-sealing suitability and can be stored for a long time, but the strength after heat-sealing has not been sufficiently studied. Also, regarding the package using the water- and oil-resistant heat-sealing paper, the difficulty of bag breakage (drop resistance) when dropped has not been studied. The heat-sealing paper of Patent Document 2 has heat-sealing suitability and blocking resistance, but the strength after heat-sealing has not been sufficiently studied. Also, the drop resistance of the package using the water- and oil-resistant heat-sealing paper has not been studied. Further, the blocking resistance during storage has not been sufficiently studied.

[0007] An object of the present invention is to provide a heat-sealing paper that is excellent in blocking resistance during storage, has a high heat-sealing peel strength, and is excellent in the drop resistance of the resulting packaging bag, and a packaging bag using the heat-sealing paper. MEANS FOR SOLVING THE PROBLEMS

[0008] The problems of the present invention can be solved by the following <1> to <10>. <1> A heat-sealable paper having one or more heat-sealing layers on at least one surface of a paper substrate, wherein the heat-sealing layer contains a water-dispersible resin binder, paraffin wax, and calcium carbonate, the water-dispersible resin binder contains a styrene-butadiene copolymer, the content of the paraffin wax in the heat-sealing layer is 6 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder, and the content of the calcium carbonate in the heat-sealing layer is 4 parts by mass or more and 19 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder. <2> The heat-sealable paper according to <1>, wherein the glass transition temperature of the styrene-butadiene copolymer is 0°C or higher and 100°C or lower. <3> The heat-sealable paper according to <1> or <2>, wherein the content of the styrene-butadiene copolymer in the water-dispersible resin binder is 50% by mass or more. <4> The heat-sealable paper according to any one of <1> to <3>, wherein the melting point of the paraffin wax is 70°C or higher and 100°C or lower. <5> The heat-sealable paper according to any one of <1> to <4>, wherein the average particle diameter of the calcium carbonate is 0.5 μm or more and 5.0 μm or less. <6> The heat-sealable paper according to any one of <1> to <5>, wherein the sharpness index of the particle size distribution of the calcium carbonate is 1.0 or more and 3.0 or less. <7> The heat-sealable paper according to any one of <1> to <6>, wherein the calcium carbonate is amorphous particles. <8> The heat-sealable paper according to any one of <1> to <7>, wherein the main component of the pulp constituting the paper substrate is softwood unbleached kraft pulp. <9> The heat-sealable paper according to any one of <1> to <8>, wherein the paper substrate is stretched paper. <10> A packaging bag made using the heat-sealable paper according to any one of <1> to <9>.

Advantages of the Invention

[0009] According to the present invention, there are provided a heat-sealing paper excellent in blocking resistance during storage, having a high heat-sealing peel strength, and excellent in the drop resistance of the resulting packaging bag, and a packaging bag using the heat-sealing paper.

Mode for Carrying Out the Invention

[0010] <Heat-sealing paper> The heat-sealing paper of the present embodiment (hereinafter, also simply referred to as "heat-sealing paper") is a heat-sealing paper having one or more heat-sealing layers on at least one surface of a paper base material, wherein the heat-sealing layer contains a water-dispersible resin binder, paraffin wax, and calcium carbonate, the water-dispersible resin binder contains a styrene-butadiene copolymer, the content of the paraffin wax in the heat-sealing layer is 6 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder, and the content of the calcium carbonate in the heat-sealing layer is 4 parts by mass or more and 19 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder. The heat-sealing paper of the present embodiment is excellent in blocking resistance during storage, has a high heat-sealing peel strength, and is excellent in the drop resistance of the resulting packaging bag.

[0011] Since the heat-sealing layer contains a water-dispersible resin binder, the heat-sealing paper of the present embodiment can exhibit heat-sealing properties. Further, since the water-dispersible resin binder contains a styrene-butadiene copolymer, the heat-sealing peel strength can be increased, and the drop resistance of the resulting packaging bag can be made excellent. In addition, when the heat-sealing layer contains paraffin wax in an amount of 6 parts by mass or more with respect to 100 parts by mass of the water-dispersible resin binder, it is possible to prevent the heat-sealing layer-coated surface and the surface on the opposite side of the heat-sealing layer-coated surface from sticking to each other, and to make the blocking resistance excellent. On the other hand, by setting the content of paraffin wax to 14 parts by mass or less, it is possible to prevent the heat-sealing peel strength from decreasing and to make the drop resistance of the resulting packaging bag excellent. Also, although the reason is not clear, when the heat-sealing layer contains 4 parts by mass or more of calcium carbonate with respect to 100 parts by mass of the water-dispersible resin binder, for example, when stored in a rolled state, it prevents the heat-sealing layer coating surface from sticking to the surface on the opposite side of the heat-sealing layer coating surface, and particularly can provide excellent blocking resistance during storage under high-temperature and high-humidity conditions. On the other hand, by setting the content of calcium carbonate to 19 parts by mass or less, it prevents the heat-sealing peel strength from decreasing, and can provide excellent drop resistance for the resulting packaging bag. Note that the effects of the present invention are not limited by the above mechanism.

[0012] In this specification, the longitudinal direction of the heat-sealing paper means the direction corresponding to the papermaking direction (MD direction) of the paper base material, and the transverse direction of the heat-sealing paper means the direction perpendicular to the papermaking direction of the paper base material (CD direction). Hereinafter, the configuration and physical properties of the water-resistant paper of the present embodiment will be described in more detail. In this specification, the numerical range represented by "X to Y" means a numerical range including X as the lower limit value and Y as the upper limit value. When the numerical ranges are described stepwise, the upper and lower limits of each numerical range can be arbitrarily combined. Also, "(meth)acrylic" is a general term including both acrylic and methacrylic.

[0013] [Paper base material] (Raw pulp) The pulp constituting the paper base material is not particularly limited, and known pulp can be used. Specifically, unbleached pulp such as hardwood unbleached kraft pulp (LUKP) and softwood unbleached kraft pulp (NUKP); chemical pulp such as hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP); groundwood pulp (GP), pressurized groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemimechanical pulp (CMP), chemigroundwood pulp (CGP), etc.; wastepaper pulp; non-wood fiber pulp such as kenaf, bagasse, bamboo, cotton, etc.; synthetic pulp, etc. These pulps may be used alone or in combination of two or more. Among these, from the viewpoint of improving the drop resistance of the obtained packaging bag, it is preferably to contain at least one selected from the group consisting of hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood bleached kraft pulp (LBKP), and softwood bleached kraft pulp (NBKP), more preferably to contain at least one selected from the group consisting of hardwood unbleached kraft pulp (LUKP) and softwood unbleached kraft pulp (NUKP), and even more preferably to contain softwood unbleached kraft pulp (NUKP).

[0014] The main component of the pulp that constitutes the paper base material used in the heat-sealing paper of this embodiment is preferably softwood pulp, and more preferably unbleached kraft pulp of softwood (NUKP). "The main component of the pulp that constitutes the paper base material is softwood pulp (or unbleached kraft pulp of softwood)" means that the content of softwood pulp (or unbleached softwood pulp) in the pulp that constitutes the paper base material exceeds 50% by mass. The content of softwood pulp (or unbleached kraft pulp of softwood) is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass. Softwood pulp has a long average fiber length, and by using a paper base material using softwood pulp as the raw material pulp, a heat-sealing paper can be obtained in which the drop resistance of the resulting packaging bag can be improved, which is preferable. Furthermore, when unbleached kraft pulp of softwood (NUKP) is used as the pulp that constitutes the paper base material, the strength of the pulp fibers themselves is higher than that of bleached kraft pulp of softwood (NBKP), unbleached kraft pulp of hardwood (LUKP), etc., so there is an advantage that the strength and elongation of the resulting paper base material are increased.

[0015] The raw material pulp that constitutes the paper base material preferably contains one or more selected from the group consisting of bleached kraft pulp and unbleached kraft pulp, and more preferably contains unbleached kraft pulp.

[0016] (Grammage) The grammage of the paper base material is not particularly limited, but from the viewpoints of improving the drop resistance of the resulting packaging bag and the ease of processing the packaging bag, it is preferably 50 g / m 2 or more and 150 g / m 2 or less, more preferably 60 g / m 2 or more, still more preferably 70 g / m 2 or more, and more preferably 120 g / m 2 or less, still more preferably 110 g / m 2 or less. The grammage of the paper base material is measured in accordance with JIS P 8124:2011.

[0017] (Thickness) The thickness of the paper base material is not particularly limited, but from the viewpoints of improving the drop resistance of the resulting packaging bag and the ease of processing the packaging bag, it is preferably 60 μm or more and 200 μm or less, more preferably 80 μm or more, still more preferably 100 μm or more, and more preferably 180 μm or less, still more preferably 160 μm or less. The thickness of the paper base material is measured in accordance with JIS P 8118:2014.

[0018] (Density) The density of the paper base material is not particularly limited, but from the viewpoints of improving the drop resistance of the resulting packaging bag, the ease of processing the packaging bag, and the moldability, it is preferably 0.3 g / cm 3 or more and 1.0 g / cm 3 or less, more preferably 0.4 g / cm 3 or more, still more preferably 0.5 g / cm 3 or more, and more preferably 0.9 g / cm 3 or less, still more preferably 0.8 g / cm 3 or less. The density of the paper base material is calculated from the basis weight and thickness of the paper base material obtained by the above-described measurement method.

[0019] (Optional components) The paper base material may contain, if necessary, for example, internal auxiliary agents such as anionic, cationic or amphoteric retention aids, drainage improvers, dry paper strength enhancers, wet paper strength enhancers, sizing agents, fixing agents, fillers, etc., water resistance agents, dyes, fluorescent brighteners and other optional components.

[0020] Examples of the wet paper strength enhancer include polyamide polyamine epichlorohydrin, urea formaldehyde resin, melamine formaldehyde resin and the like.

[0021] Examples of the sizing agent include internal sizing agents such as rosin sizing agent, synthetic sizing agent, petroleum resin-based sizing agent, and surface sizing agents such as styrene / acrylic acid copolymer and styrene / methacrylic acid copolymer. The content of the sizing agent is not particularly limited, but is preferably 3.0% by mass or less per raw material pulp (dry mass).

[0022] Examples of the fixing agent include vanadium sulfate and polyethyleneimine. The content of the fixing agent is not particularly limited, but is preferably 3.0% by mass or less per raw material pulp (dry mass).

[0023] Examples of the filler include inorganic fillers such as talc, kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, white carbon, bentonite, zeolite, sericite, and smectite, and organic fillers such as acrylic resins and vinylidene chloride resins.

[0024] From the viewpoint of improving the drop resistance of the obtained packaging bag, the paper base material is preferably Kurapak paper (stretched paper) subjected to a Kurapak treatment for shrinking the paper sheet. That is, in the heat-seal paper of the present embodiment, the paper base material is preferably stretched paper. The stretched paper refers to paper having a longitudinal or transverse elongation of 5% or more measured in accordance with JIS P 8113:2006, and Kraft papers No. 1 and No. 2 described in JIS P 3401:2000 are exemplified.

[0025] [Heat-seal layer] The heat-seal paper of the present embodiment has at least one heat-seal layer on at least one surface of the paper base material. The heat-seal layer is a layer that melts and adheres by heating, ultrasonic waves, or the like.

[0026] (Water-dispersible resin binder) The heat-seal layer contains a water-dispersible resin binder. The water-dispersible resin binder is not water-soluble (specifically, the solubility in water at 25°C is 10 g / L or less), but is a resin binder that is finely dispersed in water in the form of an emulsion or suspension. By applying the heat-seal layer with a water-dispersible resin binder by aqueous coating, a heat-seal paper excellent in re-dissociability and recyclable as paper can be obtained. When the water-dispersible resin binder also falls under the following lubricants, it shall be classified as a lubricant.

[0027] [Styrene-butadiene copolymer] The water-dispersible binder resin contains a styrene-butadiene copolymer. By containing the styrene-butadiene copolymer, the heat seal peel strength can be increased, and the resulting packaging bag can have excellent drop resistance. Also, the styrene-butadiene copolymer is preferable from the viewpoints of easy availability, cost, and recyclability.

[0028] As the styrene-butadiene copolymer, either a synthetic product or a commercially available product may be used. Commercially available products include Nipol latex LX407G51, LX407S10, LX407S12, LX410, LX415M, LX416, LX430, LX433C, 2507H manufactured by Nippon Zeon Co., Ltd.; Narstar SR-101, SR-102, SR-103, SR-115, SR-153 manufactured by Nalco Chemical Japan Co., Ltd.; Styrene butadiene latex 0602, 0597C manufactured by JSR Corporation; Styronal DD718ap, Styronal ES7902, Styronal 304, etc. manufactured by BASF Japan Ltd.

[0029] The glass transition temperature of the styrene-butadiene copolymer is preferably 0°C or higher and 100°C or lower, more preferably 5°C or higher, still more preferably 10°C or higher, and more preferably 80°C or lower, still more preferably 60°C or lower, even more preferably 50°C or lower, still more preferably 40°C or lower, even more preferably 30°C or lower, and particularly preferably 20°C or lower. By using a styrene-butadiene copolymer having a glass transition temperature of the above lower limit value or higher, the occurrence of blocking can also be suppressed. And by using a styrene-butadiene copolymer having a glass transition temperature of the above upper limit or lower, a heat-seal paper excellent in heat seal peel strength can be obtained, which is preferable. The glass transition temperature of the styrene-butadiene copolymer shall adopt the value measured by a differential scanning calorimeter.

[0030] The content of the styrene-butadiene copolymer in the water-dispersible resin binder is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and even more preferably 100% by mass, from the viewpoint of improving the heat-seal peel strength and the drop resistance of the resulting packaging bag.

[0031] 〔Other water-dispersible resin binders〕 The heat-seal layer may contain, if necessary, a water-dispersible resin binder other than the above styrene-butadiene copolymer (also referred to as "other water-dispersible resin binders" in this specification). The other water-dispersible resin binders are not particularly limited, and examples include polyolefin resins (such as polyethylene and polypropylene), vinyl chloride resins, styrene resins other than styrene-butadiene copolymers, styrene-unsaturated carboxylic acid copolymers (for example, styrene-(meth)acrylic acid copolymers), acrylic resins, acrylonitrile-styrene copolymers, acrylonitrile-butadiene copolymers, ABS resins, AAS resins, AES resins, vinylidene chloride resins, polyurethane resins, poly-4-methylpentene-1 resins, polybutene-1 resins, vinylidene fluoride resins, vinyl fluoride resins, fluorine resins, polycarbonate resins, polyamide resins, acetal resins, polyphenylene oxide resins, polyester resins (such as polyethylene terephthalate and polybutylene terephthalate), polyphenylene sulfide resins, polyimide resins, polysulfone resins, polyethersulfone resins, polyarylate resins, olefin-unsaturated carboxylic acid copolymers, and modified products thereof. These may be used alone or in combination of two or more. When other water-dispersible resin binders are contained in the water-dispersible resin binder, the content of the other water-dispersible resin binder in the water-dispersible resin binder is not particularly limited as long as the effects of the present invention are achieved, but is preferably less than 50% by mass, more preferably less than 30% by mass, still more preferably less than 10% by mass, even more preferably 5% by mass or less, and still more preferably 0% by mass.

[0032] From the viewpoint of further improving the heat-seal peel strength and drop resistance, the content of the water-dispersible resin binder in the heat-seal layer is preferably 75% by mass or more, more preferably 80% by mass or more, still more preferably 85% by mass or more. From the viewpoint of further improving the blocking resistance, it is 91% by mass or less, preferably 89% by mass or less, more preferably 87% by mass or less. Similarly, from the viewpoint of further improving the heat-seal peel strength and drop resistance, the content of the styrene-butadiene copolymer in the heat-seal layer is preferably 75% by mass or more, more preferably 80% by mass or more, still more preferably 85% by mass or more. From the viewpoint of further improving the blocking resistance, it is 91% by mass or less, preferably 89% by mass or less, more preferably 87% by mass or less.

[0033] (Paraffin wax) In the heat-seal paper of this embodiment, the heat-seal layer contains paraffin wax. By containing paraffin wax, it is possible to prevent the heat-seal layer coating surface and the surface on the opposite side of the heat-seal layer coating surface from sticking to each other, and the blocking resistance can be made excellent. In addition, paraffin wax acts as a so-called lubricant and can reduce the friction coefficient of the surface of the heat-seal layer. Therefore, blocking during the production of heat-seal paper and sticking to the molding machine of heat-seal paper are suppressed, and the effect of improving the automatic packaging formability is also achieved.

[0034] As the paraffin wax, either a synthetic product or a commercially available product may be used. Examples of commercially available products include Hydrin L-700 manufactured by Chukyo Yushi Co., Ltd., Aquacer 539 manufactured by BYK, and the like.

[0035] In the heat-sealing layer, the content of paraffin wax is 6 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder. When the content of paraffin wax is 6 parts by mass or more, it is possible to prevent the heat-sealing layer coating surface and the surface on the side opposite to the heat-sealing layer coating surface from sticking to each other, and to obtain excellent blocking resistance. On the other hand, when the content of paraffin wax is 14 parts by mass or less, it is possible to prevent the heat-sealing peel strength from decreasing and to obtain excellent drop resistance of the resulting packaging bag. From the viewpoint of further improving the blocking resistance, the content of paraffin wax in the heat-sealing layer is preferably 6.5 parts by mass or more, more preferably 7 parts by mass or more, still more preferably 7.5 parts by mass or more with respect to 100 parts by mass of the water-dispersible resin binder, and from the viewpoint of further improving the heat-sealing peel strength and the drop resistance, it is preferably 12 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 9 parts by mass or less. Also, from the viewpoint of further improving the blocking resistance, the content of paraffin wax in the heat-sealing layer is preferably 5% by mass or more, more preferably 6% by mass or more, still more preferably 6.5% by mass or more, and from the viewpoint of further improving the heat-sealing peel strength and the drop resistance, it is preferably 11% by mass or less, more preferably 10% by mass or less, still more preferably 8% by mass or less.

[0036] The melting point of the paraffin wax contained in the heat-sealing layer is preferably 70°C or higher, more preferably 75°C or higher, still more preferably 80°C or higher, even more preferably 85°C or higher, and preferably 100°C or lower, more preferably 95°C or lower. When the melting point of the paraffin wax is within the above range, the paraffin wax is likely to be present on the surface of the heat-sealing layer, and the blocking resistance during storage can be further improved.

[0037] 〔Other lubricants〕 The heat-sealing layer may contain, if necessary, a lubricant other than the above paraffin wax (also referred to as "other lubricants" in this specification). Other lubricants are not particularly limited. For example, waxes other than the above paraffin wax, metal soaps, fatty acid esters, etc. can be used. Examples of waxes other than the above paraffin wax include natural waxes such as waxes derived from animals or plants (e.g., beeswax, carnauba wax, etc.), mineral waxes (e.g., microcrystalline wax, etc.), petroleum waxes; synthetic waxes such as polyolefin waxes, polyester waxes, etc. Examples of metal soaps include calcium stearate, sodium stearate, zinc stearate, aluminum stearate, magnesium stearate, sodium fatty acid soap, potassium oleate soap, potassium castor oil soap, and composites thereof. These may be used alone or in combination of two or more. The content of other lubricants in the heat-sealing layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, even more preferably 1% by mass or less, and even more preferably 0% by mass.

[0038] (Calcium carbonate) In the heat-sealing paper of the present embodiment, the heat-sealing layer contains calcium carbonate as a pigment. By containing calcium carbonate, it is possible to prevent the heat-sealing layer coating surface and the surface on the opposite side of the heat-sealing layer coating surface from sticking to each other, and to provide excellent blocking resistance during storage, particularly during storage under high-temperature and high-humidity conditions.

[0039] In the heat-sealing layer, the calcium carbonate content is 4 parts by mass or more and 19 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder. When the calcium carbonate content is 4 parts by mass or more, it is possible to prevent the heat-sealing layer coating surface and the surface on the opposite side of the heat-sealing layer coating surface from sticking to each other, and to obtain excellent blocking resistance during storage, particularly under high-temperature and high-humidity conditions. On the other hand, when the calcium carbonate content is 19 parts by mass or less, it is possible to prevent the heat-sealing peel strength from decreasing and to obtain an excellent drop resistance of the resulting packaging bag. In the heat-sealing layer, the calcium carbonate content is preferably 5 parts by mass or more, more preferably 6 parts by mass or more, still more preferably 7 parts by mass or more, and preferably 16 parts by mass or less, more preferably 12 parts by mass or less, still more preferably 10 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder. From the viewpoint of blocking resistance, the calcium carbonate content in the heat-sealing layer is preferably 3.5% by mass or more, more preferably 4.5% by mass or more, still more preferably 6% by mass or more, and from the viewpoints of heat-sealing peel strength and drop resistance, it is preferably 15% by mass or less, more preferably 12% by mass or less, still more preferably 9% by mass or less, even more preferably 8% by mass or less.

[0040] The average particle diameter of the calcium carbonate is preferably 0.5 μm or more and 5.0 μm or less. When the average particle diameter is 0.5 μm or more, appropriate unevenness can be imparted to the heat-sealing layer, and the blocking resistance during storage can be further improved. In addition, when the average particle diameter is 5.0 μm or less, the concern that a part of the calcium carbonate protrudes from the heat-sealing layer is reduced, and the decrease in the heat-sealing peel strength can be suppressed, so that the drop resistance of the resulting packaging bag can be further improved. The average particle diameter of the calcium carbonate is more preferably 0.8 μm or more, still more preferably 1.0 μm or more, even more preferably 1.2 μm or more, and more preferably 4.5 μm or less, still more preferably 3.0 μm or less, even more preferably 2.0 μm or less. The average particle diameter of calcium carbonate is determined as the particle diameter (D50) at which the cumulative frequency is 50% by volume in the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer.

[0041] The sharpness index of the particle size distribution of calcium carbonate is determined by the following calculation formula based on the volume particle size distribution measured with a laser diffraction / scattering particle size distribution analyzer. (Sharpness index) = {(D90 - D10) / D50} Here, in the above calculation formula, D50 is the particle diameter at which the cumulative frequency is 50% by volume in the volume-based particle size distribution, D90 is the particle diameter at which the cumulative frequency is 90% by volume in the volume-based particle size distribution, and D10 is the particle diameter at which the cumulative frequency is 10% by volume in the volume-based particle size distribution. The closer the value of the above calculation formula is to 1.0, the narrower the width of the particle size distribution, and the sharper the particle size distribution. The larger the value, the wider the width of the particle size distribution, and the broader the particle size distribution. The sharpness index of the particle size distribution of calcium carbonate is preferably 1.0 or more, more preferably 1.5 or more, still more preferably 2.0 or more, and preferably 3.0 or less, more preferably 2.5 or less. When the sharpness index of the particle size distribution of calcium carbonate is within the above range, although the cause is not clear, it is considered that appropriate unevenness is imparted to the heat seal layer by the calcium carbonate particles, and the blocking resistance during storage is further improved.

[0042] The specific surface area of calcium carbonate is not particularly limited, but is preferably 5 m 2 / g or more and 20 m 2 / g or less. When the specific surface area is within the above range, adsorption of moisture in the air, etc. to calcium carbonate is suppressed, so the quality of the heat seal layer can be stabilized, and the blocking resistance during storage is further improved. The specific surface area of calcium carbonate is measured with a BET specific surface area analyzer.

[0043] In the heat-sealing paper of this embodiment, the calcium carbonate contained in the heat-sealing layer is preferably amorphous particles. Since the calcium carbonate is amorphous particles, the blocking resistance during storage is further improved. In addition, in this specification, amorphous particles mean inorganic particles having no specific shape. For example, in the present invention, amorphous particles of calcium carbonate can be obtained by pulverizing calcium carbonate having a large particle size and then classifying it.

[0044] In the heat-sealing paper of this embodiment, the calcium carbonate preferably contains at least one selected from heavy calcium carbonate (ground calcium carbonate) and light calcium carbonate (synthetic calcium carbonate), and more preferably contains heavy calcium carbonate. By using heavy calcium carbonate, the blocking resistance during storage is further improved. From the viewpoint of further improving the blocking resistance, the content of heavy calcium carbonate in the heat-sealing layer is preferably 3.5% by mass or more, more preferably 4.5% by mass or more, still more preferably 6% by mass or more, and from the viewpoint of further improving the heat-sealing peel strength and drop resistance, it is preferably 15% by mass or less, more preferably 12% by mass or less, still more preferably 9% by mass or less, and even more preferably 8% by mass or less.

[0045] 〔Other pigments〕 The heat-sealing layer may contain pigments other than the above calcium carbonate (also referred to as "other pigments" in this specification) as required. Specific examples of other pigments include mica, bentonite, kaolin, pyrophyllite, talc, smectite, vermiculite, chlorite, septarian chlorite, serpentine, stilpnomelane, montmorillonite, composite synthetic pigments of calcium carbonate and other hydrophilic organic compounds, satin white, lithopone, titanium dioxide, silica, barium sulfate, calcium sulfate, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, silicate, colloidal silica, plastic pigments of organic pigments that are hollow or dense, binder pigments, plastic beads, microcapsules, and the like. These may be used alone or in combination of two or more. The content of other pigments in the heat-sealing layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably 6% by mass or less, more preferably 4% by mass or less, still more preferably 2% by mass or less, even more preferably 1% by mass or less, and most preferably 0% by mass.

[0046] <Physical properties of heat-sealing paper> (Grammage) The grammage of the heat-sealing paper is not particularly limited, but from the viewpoints of improving the drop resistance of the obtained packaging bag and ease of processing of the packaging bag, it is preferably 50 g / m 2 or more and 180 g / m 2 or less, more preferably 70 g / m 2 or more, still more preferably 90 g / m 2 or more, and most preferably 140 g / m 2 or less, still more preferably 120 g / m 2 or less. The grammage of the heat-sealing paper is measured in accordance with JIS P 8124:2011.

[0047] (Thickness) The thickness of the heat-sealing paper is not particularly limited, but from the viewpoints of improving the drop resistance of the resulting packaging bag and the ease of processing the packaging bag, it is preferably 60 μm or more and 220 μm or less, more preferably 80 μm or more, still more preferably 100 μm or more, even more preferably 120 μm or more, yet more preferably 140 μm or more, and more preferably 200 μm or less, still more preferably 180 μm or less. The thickness of the heat-sealing paper is measured in accordance with JIS P 8118:2014.

[0048] (Density) The density of the heat-sealing paper is not particularly limited, but from the viewpoints of improving the drop resistance of the resulting packaging bag and the ease of processing the packaging bag, it is preferably 0.3 g / cm 3 or more and 1.0 g / cm 3 or less, more preferably 0.4 g / cm 3 or more, still more preferably 0.5 g / cm 3 or more, even more preferably 0.6 g / cm 3 or more, and more preferably 0.9 g / cm 3 or less, still more preferably 0.75 g / cm 3 or less. The density of the heat-sealing paper is calculated from the basis weight and thickness of the heat-sealing paper obtained by the above-described measurement method.

[0049] (Heat-sealing peel strength) The heat-sealing peel strength of the heat-sealing paper is preferably 6.0 N / 15 mm or more and 30.0 N / 15 mm or less, more preferably 6.1 N / 15 mm or more, still more preferably 6.2 N / 15 mm or more, and more preferably 20.0 N / 15 mm or less, still more preferably 10.0 N / 15 mm or less, from the viewpoints of improving the drop resistance of the resulting packaging bag and the ease of manufacturing. The heat-sealing peel strength is the peel strength when the heat-sealing layers are heat-sealed under the conditions of 160 °C, 0.2 MPa, and 1 second, and specifically, it is the value measured by the method described in the examples below.

[0050] [Method for producing heat-sealing paper] The manufacturing method of the heat-sealing paper of this embodiment is not particularly limited. For example, there is a manufacturing method including a cooking step of performing a cooking treatment on raw pulp, a beating step of beating a dispersion containing 20% by mass or more and 45% by mass or less of the cooked raw pulp, a papermaking step of making paper from the beaten raw pulp, and a coating step of coating at least one surface of the paper base material obtained by the above method with at least one layer of a heat-sealing layer. Each step of the manufacturing method will be described below.

[0051] (Cooking step) The cooking step is a step of performing a cooking treatment on raw pulp. By the cooking step, it is preferable that the copper number of the raw pulp is 30 or more and 60 or less. Although not particularly limited, it is preferable to treat the raw chips used as the material of the raw pulp with a chemical solution containing sodium hydroxide, and as the treatment method with the chemical solution containing sodium hydroxide, a known treatment method using a known chemical solution can be used.

[0052] The raw chips used as the material of the raw pulp preferably contain softwood pulp as the main component. "Raw chips containing softwood pulp as the main component" means those in which the content of softwood in the raw chips exceeds 50% by mass, and the content of softwood is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass.

[0053] The raw pulp may or may not be bleached. The raw pulp is preferably at least one selected from the group consisting of unbleached kraft pulp and bleached kraft pulp, and more preferably unbleached kraft pulp.

[0054] (Beating step) The beating process is a process of beating a dispersion containing preferably 20% by mass or more and 45% by mass or less of the steamed raw material pulp. The method of beating is not particularly limited, but it is preferable to disperse the steamed raw material pulp in water to prepare a dispersion with the above raw material pulp concentration and then beat it. The beating method is not particularly limited, and for example, it can be carried out using a beater such as a double disk refiner, a single disk refiner, or a conical refiner.

[0055] By beating a dispersion containing 20% by mass or more and 45% by mass or less of the steamed raw material pulp, a paper base material having impact resistance and processability and a heat-sealing paper using the paper base material can be obtained, and the productivity is excellent.

[0056] (Paper-making process) The paper-making process is a process of making paper from the beaten raw material pulp. The paper-making method is not particularly limited, and examples include an acid paper-making method in which papermaking is carried out at a pH of around 4.5, a neutral paper-making method in which papermaking is carried out at a pH of about 6 to about 9, etc. In the paper-making process, if necessary, papermaking process chemicals such as a pH adjuster, an antifoaming agent, a pitch control agent, and a slime control agent can be appropriately added. The paper-making machine is also not particularly limited, and examples include a continuous paper-making machine such as a fourdrinier type, a cylinder type, or an inclined type, or a multi-layer combined paper-making machine combining these.

[0057] The paper base material used for the heat-sealing paper of the present embodiment can be obtained by a method including the above-described steaming process, beating process, and paper-making process. After the paper-making process, if necessary, it may have a Kurpack process of shrinking the paper web using Kurpack equipment. As the Kurpack equipment, known ones can be used. Note that the manufacturing method of the paper base material used for the heat-sealing paper of the embodiment is not limited to the above method.

[0058] Also, in the present embodiment, the method for manufacturing the heat-sealing paper may include a surface treatment step of treating the surface of the paper base material with a chemical. Examples of the chemical used in the surface treatment step include sizing agents, water resistance agents, water retention agents, thickening agents, lubricants, and the like. As the apparatus used in the surface treatment step, a known apparatus can be used.

[0059] The method for manufacturing the heat-sealing paper of the present embodiment includes a coating step of coating a heat-sealing layer on at least one surface of the paper base material obtained as described above. Note that the heat-sealing layer coating liquid (heat-sealing layer paint) may be coated two or more times.

[0060] When forming a plurality of heat-sealing layers on the paper base material, the above method of sequentially forming the heat-sealing layers is preferable, but it is not limited thereto, and a simultaneous multilayer coating method may be adopted. The simultaneous multilayer coating method is a method of simultaneously forming a multilayer heat-sealing layer by discharging a plurality of types of coating liquids separately from slit nozzles to form a liquid laminate and coating it on the paper base material.

[0061] The coating equipment for coating the heat-sealing layer coating liquid on the paper base material is not particularly limited, and known equipment may be used. Examples of the coating equipment include blade coaters, bar coaters, air knife coaters, slit die coaters, gravure coaters, microgravure coaters, roll coaters, size presses, gate roll coaters, simsizers, bar coaters, and the like.

[0062] The drying equipment for drying the heat-sealing layer is not particularly limited, and known equipment can be used. Examples of the drying equipment include hot air dryers, infrared dryers, gas burners, hot plates, and the like. Also, the drying temperature may be appropriately set in consideration of the drying time and the like.

[0063] The solvent of the heat-sealing layer coating liquid is not particularly limited, and water or organic solvents such as ethanol, isopropyl alcohol, methyl ethyl ketone, and toluene can be used. Among these, from the viewpoint of not causing problems with volatile organic solvents, water is preferable as the dispersion medium of the heat-sealing layer coating liquid. That is, the heat-sealing layer coating liquid is preferably an aqueous composition for the heat-sealing layer.

[0064] The solid content (solid concentration) of the heat-sealing layer coating liquid is not particularly limited and may be appropriately selected from the viewpoints of coatability and ease of drying. Preferably, it is 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more, still more preferably 25% by mass or more, and more preferably 60% by mass or less, still more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0065] The preferable range of the coating amount (after drying) of the heat-sealing layer is as described above. The heat-sealing layer may be a single layer or two or more layers. When the heat-sealing layer has two or more layers, the above coating amount represents the total coating amount.

[0066] After coating and drying the heat-sealing layer, supercalendering treatment may be performed. Here, the supercalendering treatment is installed independently of papermaking. Generally, paper or the like to be treated is passed between metal rolls or between a metal roll and an elastic roll, and heating, pressurization, etc. are performed. The supercalendering treatment may be performed in one stage or multiple stages and is not particularly limited.

[0067] <Use> The heat-sealing paper according to this embodiment can be suitably used as a packaging bag for foods, daily sundries, books, daily necessities (soap, detergent, diaper), etc. Therefore, the present invention also provides a packaging bag using the above heat-sealing paper.

[0068] [Packaging Bag] The packaging bag of the present embodiment is made using the heat-sealing paper of the above-described present embodiment. That is, the packaging bag of the present embodiment is heat-sealing paper having one or more heat-sealing layers on at least one surface of a paper substrate, wherein the heat-sealing layer contains a water-dispersible resin binder, paraffin wax, and calcium carbonate, the water-dispersible resin binder includes a styrene-butadiene copolymer, the content of the paraffin wax in the heat-sealing layer is 6 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder, and the content of the calcium carbonate in the heat-sealing layer is 4 parts by mass or more and 19 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder, and is formed using at least the heat-sealing paper. Since the packaging bag of the present embodiment is made using the heat-sealing paper of the above-described present embodiment, it has excellent heat-sealing peel strength at the heat-sealing portion and excellent drop resistance. The packaging bag according to the present embodiment can be suitably used as a packaging bag for foods, daily sundries, books, daily necessities (soap, detergent, diaper), and the like.

Examples

[0069] Examples are given below to specifically explain the present invention, but the present invention is not limited to these examples. Unless otherwise specified, the following operations were performed under the conditions of 23°C and a relative humidity of 50%RH. Also, in the examples and comparative examples, "parts" and "%" indicate "parts by mass" and "mass%", respectively, unless otherwise specified.

[0070] [Example 1] <Preparation of Heat-Sealing Layer Coating>[ 100 parts (in terms of solid content) of an aqueous dispersion of a styrene-butadiene copolymer (manufactured by BASF Japan Ltd., Styronal DD718ap, glass transition temperature 12°C), 8 parts (in terms of solid content) of a paraffin wax emulsion (manufactured by BYK, Aquacer539, melting point 90°C), heavy calcium carbonate (manufactured by Fimatic Co., Ltd., FMT-65, amorphous, average particle size 1.65 μm, sharpness index of particle size distribution 2.26, specific surface area 8m 2 / g) The 8 parts were mixed, water was added to adjust the solid content concentration to 28%, and the mixture was stirred to prepare a heat-seal layer coating (concentration 28%).

[0071] <Manufacture of Heat-Seal Paper> As the base paper of the heat-seal paper, extensible paper cement (manufactured by Oji Materia Co., Ltd., extensible paper, 100% by mass of softwood unbleached kraft pulp, basis weight 100 g / m 2 , thickness 150 μm, density 0.65 g / cm 3 ) was used. The heat-seal layer coating was applied with a bar coater so that the coating amount after drying of the heat-seal layer would be 10 g / m 2 , and dried at 140 °C for 25 seconds to form a heat-seal layer, resulting in a heat-seal paper with a basis weight of 110 g / m 2 , thickness 160 μm, density 0.69 g / cm 3 .

[0072] [Example 2] In the preparation of the heat-seal layer coating liquid of Example 1, except that heavy calcium carbonate was changed to FMT-90 (manufactured by Fimatic Co., Ltd., amorphous, average particle size 1.15 μm, sharpness index of particle size distribution 1.90, specific surface area 11 m 2 / g), a heat-seal paper was obtained in the same manner as in Example 1.

[0073] [Example 3] In the preparation of the heat-seal layer coating liquid of Example 1, except that heavy calcium carbonate was changed to light calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., Hakuenka PZ, average particle size 3.9 μm, sharpness index of particle size distribution 1.29, specific surface area 15 m 2 / g), a heat-seal paper was obtained in the same manner as in Example 1.

[0074] [Example 4] In the preparation of the heat-seal layer coating liquid of Example 1, except that heavy calcium carbonate was changed to light calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., Tunex-E, average particle size 4.1 μm, sharpness index of particle size distribution 1.38, specific surface area 7 m 2 / g), a heat-seal paper was obtained in the same manner as in Example 1.

[0075] [Example 5] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of the paraffin wax emulsion was changed to 6 parts (in terms of solid content).

[0076] [Example 6] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of the paraffin wax emulsion was changed to 13 parts (in terms of solid content).

[0077] [Example 7] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of heavy calcium carbonate (FMT-65) was changed to 4 parts.

[0078] [Example 8] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of heavy calcium carbonate (FMT-65) was changed to 18 parts.

[0079] [Comparative Example 1] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of the paraffin wax emulsion was changed to 10 parts (in terms of solid content) and heavy calcium carbonate (FMT-65) was not added.

[0080] [Comparative Example 2] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of heavy calcium carbonate (FMT-65) was changed to 10 parts and the paraffin wax emulsion was not added.

[0081] [Comparative Example 3] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of the paraffin wax emulsion was changed to 5 parts (in terms of solid content).

[0082] [Comparative Example 4] In the preparation of the heat-sealing layer coating liquid of Example 1, heavy calcium carbonate was changed to kaolin (produced by Imerys, Valifine HX, average particle size 9 μm, sharpness index of particle size distribution 3.15, specific surface area 12.8 m 2 / g), and a heat-sealing paper was obtained in the same manner as in Example 1.

[0083] [Comparative Example 5] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of the paraffin wax emulsion was changed to 15 parts (in terms of solid content).

[0084] [Comparative Example 6] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of heavy calcium carbonate (FMT-65) was changed to 3 parts.

[0085] [Comparative Example 7] In the preparation of the heat-sealing layer coating liquid of Example 1, a heat-sealing paper was obtained in the same manner as in Example 1, except that the addition amount of heavy calcium carbonate (FMT-65) was changed to 20 parts.

[0086] [Comparative Example 8] In the preparation of the heat-sealing layer coating liquid of Example 1, paraffin wax was changed to carnauba wax (produced by Michelman, Michem Emulsion 67135, melting point 83 °C), and a heat-sealing paper was obtained in the same manner as in Example 1.

[0087] [Evaluation] [Measurement of Heat-Sealing Peel Strength] Two sheets of heat-sealing paper were overlapped with the heat-sealing layers facing each other, and heat-sealed under the conditions of 160 °C, 0.2 MPa, and 1 second using a heat-sealing tester (manufactured by Tester Sangyo Co., Ltd., TP-701-B). The heat-sealed test piece was allowed to stand in a room at a temperature of 23 °C ± 1 °C and a humidity of 50% ± 2% for 4 hours or more. Subsequently, the heat-sealed test piece was cut into a width of 15 mm, and T-peel separation was performed at a tensile speed of 300 mm / min using a tensile testing machine, and the maximum load recorded was taken as the heat-sealing peel strength.

[0088] <Blocking resistance 1> Five samples of heat-sealing paper cut into 9 cm squares were prepared and stacked with the heat-sealing layers facing upward. The stacked samples were sandwiched between the upper and lower plates set at 40 °C of a press machine (manufactured by Toyo Seiki Co., Ltd., MINI TEST PRESS-10, model MP-SNH), pressed at a pressure of 46 kg / cm 2 and allowed to stand in an environment with a relative humidity of 40 - 50% RH for 15 hours. After 15 hours, the samples were taken out of the press machine and peeled by hand. The appearance of the surfaces of the four paper substrates in contact with the heat-sealing layer of the peeled samples was visually confirmed and evaluated according to the following criteria. If it is A, B, or C, it can be judged that it is usable in practice. 〔Evaluation criteria〕 A: There is no paper peeling or fluffing on the surfaces of all paper substrates, and they are smooth. B: There is no paper peeling on the surfaces of all paper substrates, but fluffing is observed on less than 30% of the surfaces of one or more paper substrates. C: There is no paper peeling on the surfaces of all paper substrates, but fluffing is observed on 30 - 70% of the surfaces of one or more paper substrates. D: There is no paper peeling on the surfaces of all paper substrates, but fluffing is present on more than 70% of the surfaces of one or more paper substrates, and the surface is rough. E: Fluffing and paper peeling occur on the surfaces of one or more paper substrates.

[0089] <Blocking resistance 2> Prepare 5 samples of the heat-sealing paper cut into 2.5 cm squares, stack them with the heat-sealing layer facing upward, and use a blocking tester (manufactured by Eagle Corporation, EGCO-201) to press at a pressure of 8 kg / cm 2 and leave it standing in an environment of 40 °C and a relative humidity of 90% RH for 15 hours together with the blocking tester. After 15 hours, take out the samples from the blocking tester and peel them by hand. Visually check the surfaces of the four paper substrates that were in contact with the heat-sealing layer of the peeled samples and evaluate them according to the following criteria. If it is A, B, or C, it can be judged as usable in practice. 〔Evaluation Criteria〕 A: There is no paper peeling or fuzzing on the surfaces of all the paper substrates, and they are smooth. B: There is no paper peeling on the surfaces of all the paper substrates, but fuzzing is observed on less than 30% of the surfaces of one or more paper substrates. C: There is no paper peeling on the surfaces of all the paper substrates, but fuzzing is observed on 30 - 70% of the surfaces of one or more paper substrates. D: There is no paper peeling on the surfaces of all the paper substrates, but fuzzing is present on more than 70% of the surfaces of one or more paper substrates, and the surfaces are rough. E: Fuzzing and paper peeling occur on the surfaces of one or more paper substrates.

[0090] <Drop Test> Stack two sets of A4-sized heat-sealing papers with the heat-sealing layers facing each other, and use a heat-sealing tester to seal three sides under the conditions of 160 °C, 0.2 MPa, and 1 second. Put 1 kg of gravel in a plastic bag with a chuck, and seal the last side under the same conditions to obtain a packaging bag. In accordance with JIS Z0217:1998, repeatedly drop the same sample vertically from a height of 1.2 m onto a concrete floor with a vinyl sheet attached until the packaging bag breaks. The vinyl sheet had a thickness of 2 mm, a composition of 30% polyvinyl chloride resin, 17% bis(2-ethylhexyl) phthalate, 48% calcium carbonate, and 5% others. Check the number of drops when the packaging bag breaks and evaluate it according to the following criteria. If it is A, it has excellent drop resistance. 〔Evaluation Criteria〕 A: Even when the number of drops is 10 or more, the bag did not break. E: Broke the bag with less than 10 dropping times

[0091]

Table 1

[0092] From Table 1, it can be seen that the heat-sealing papers of Examples 1 to 8 are excellent in blocking resistance under high-temperature and high-humidity conditions and have high heat-sealing peel strength. Also, it was confirmed that the packages using the heat-sealing papers of Examples 1 to 8 are difficult to break the bag and are excellent in drop resistance. On the other hand, Comparative Examples 1 and 2 that do not contain either paraffin wax or calcium carbonate, Comparative Example 3 with a paraffin wax content of less than 6 parts by mass, Comparative Example 4 that contains kaolin instead of calcium carbonate, Comparative Example 6 with a calcium carbonate content of less than 4 parts by mass, and the heat-sealing papers of Comparative Example 8 that contain carnauba wax instead of paraffin wax were inferior in blocking resistance under high-temperature and high-humidity conditions. Also, the heat-sealing papers of Comparative Example 5 with a paraffin wax content exceeding 14 parts by mass and Comparative Example 7 with a calcium carbonate content exceeding 19 parts by mass were inferior in heat-sealing peel strength, and the resulting packaging bags were likely to break and were inferior in drop resistance.

Claims

1. A heat-sealable paper having one or more heat-sealing layers on at least one surface of a paper substrate, wherein the heat-sealing layer contains a water-dispersible resin binder, paraffin wax, and calcium carbonate, the water-dispersible resin binder includes a styrene-butadiene copolymer, the content of the paraffin wax in the heat-sealing layer is 6 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder, and the content of the calcium carbonate in the heat-sealing layer is 4 parts by mass or more and 19 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin binder. A heat-sealable paper.

2. The heat-sealable paper according to claim 1, wherein the glass transition temperature of the styrene-butadiene copolymer is 0°C or higher and 100°C or lower.

3. The heat-sealable paper according to claim 1, wherein the content of the styrene-butadiene copolymer in the water-dispersible resin binder is 50% by mass or more.

4. The heat-sealable paper according to claim 1, wherein the melting point of the paraffin wax is 70°C or higher and 100°C or lower.

5. The heat-sealable paper according to claim 1, wherein the average particle diameter of the calcium carbonate is 0.5 µm or more and 5.0 µm or less.

6. The heat-sealable paper according to claim 1, wherein the sharpness index of the particle size distribution of the calcium carbonate is 1.0 or higher and 3.0 or lower.

7. The heat-sealable paper according to claim 1, wherein the calcium carbonate is amorphous particles.

8. The heat-sealable paper according to claim 1, wherein the main component of the pulp constituting the paper substrate is softwood unbleached kraft pulp.

9. The heat-sealable paper according to claim 1, wherein the paper substrate is stretch paper.

10. A packaging bag made using the heat-sealable paper according to any one of claims 1 to 9.

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