EP4692456A1

EP4692456A1 - Heat-sealable paper and packaging bag

Info

Publication number: EP4692456A1
Application number: EP24779821.8A
Authority: EP
Inventors: Shiori KOYAMA; Yasutomo Noishiki; Misaki WAKABAYASHI
Original assignee: Oji Holdings Corp
Current assignee: Oji Holdings Corp
Priority date: 2023-03-30
Filing date: 2024-03-21
Publication date: 2026-02-11
Also published as: WO2024203699A1; JPWO2024203699A1; CN120882931A; AU2024245362A1

Abstract

To provide heat-sealable paper excellent in the heat sealing property and blocking resistance. Heat-sealable paper containing a heat-sealable layer on one surface of a paper substrate, wherein the heat-sealable layer contains a water-dispersible resin and a wetting agent, the water-dispersible resin contains a water-dispersible resin having a glass transition temperature of 0°C or more, a content of the wetting agent is 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin, and a surface roughness (RzJIS) of a surface opposite to a surface having the heat-sealable layer of the heat-sealable paper is 12.0 µm or more.

Description

Technical Field

The present invention relates to heat-sealable paper and a packaging bag using the heat-sealable paper.

Background Art

Packages using a heat sealing method have been widely used for packaging foods, medicines, medical devices, etc., other than packaging general industrial products.
In recent years, the problem of plastic waste is getting worse. Of the world's plastic production amount, the packaging sector accounts for a large portion of the plastic production amount, which is one of the causes of plastic waste. Plastics do not decompose semi-permanently, and their garbage turns into microplastics in the natural environment, which has a serious adverse effect on the ecosystem. As a countermeasure, it has been proposed to replace plastics with paper.
For example, JP 7070785 B discloses heat-sealable paper having at least one heat-sealable layer on at least one surface of a paper substrate, wherein the heat-sealable layer contains a water-dispersible resin binder; the heat-sealable layer further contains a lubricant; when two such heat-sealable layers are heat-sealed to each other under conditions of 150°C and 0.2 MPa for one second, a hot tack peeling distance is 150 mm or less and the heat sealing peel strength is 2 N/15 mm or more; and a pulp recovery rate after re-pulping is 85% or more.
In addition, JP 2022-175023 A discloses heat-sealable paper, wherein the heat-sealable paper has at least one heat-sealable layer on at least one surface of a paper substrate; the heat-sealable layer contains a pigment having an aspect ratio of 20 or more and a heat-sealable resin; when two such heat-sealable layers are heat-sealed to each other under conditions of a sealing pressure of 0.2 MPa, a sealing temperature of 140°C, and sealing time of 1 second, a peel strength is 3 N/15 mm or more; the Oken air resistance is 2,000 seconds or more; and water repellency on both surfaces is R6 or more.

Summary of Invention

The applications of packages using the heat sealing method are expanding, and there is a demand for achieving heat-sealable paper that has excellent blocking resistance during storage and the like and is suitable for various applications.
An object of the present invention is to provide heat-sealable paper excellent in the heat sealing property and blocking resistance and a packaging bag using the heat-sealable paper.
The object of the present invention can be achieved by the following configurations <1> to <9>.

<1> Heat-sealable paper containing a heat-sealable layer on one surface of a paper substrate, wherein
- the heat-sealable layer contains a water-dispersible resin and a wetting agent,
- the water-dispersible resin contains a water-dispersible resin having a glass transition temperature of 0°C or more,
- a content of the wetting agent is 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin, and
- a surface roughness (RzJIS) of a surface opposite to a surface having the heat-sealable layer of the heat-sealable paper is 12.0 µm or more.
<2> The heat-sealable paper according to <1>, wherein the wetting agent contains at least one selected from the group consisting of an acetylene wetting agent, an acrylic wetting agent, and a silicone wetting agent.
<3> The heat-sealable paper according to <1> or <2>, wherein the water-dispersible resin contains a styrene-butadiene copolymer.
<4> The heat-sealable paper according to any one of <1> to <3>, wherein the water-dispersible resin contains a styrene-butadiene copolymer, and the wetting agent contains an acetylene wetting agent.
<5> The heat-sealable paper according to any one of <1> to <4>, having a basis weight of 50 g/m² or more and 140 g/m² or less.
<6> The heat-sealable paper according to any one of <1> to <5>, wherein the paper substrate is extensible paper.
<7> The heat-sealable paper according to any one of <1> to <6>, wherein a basis weight of the heat-sealable layer is 7 g/m² or more and 21 g/m² or less.
<8> The heat-sealable paper according to any one of <1> to <7>, wherein, when two such heat-sealable layers are heat-sealed to each other under conditions of 160°C, 0.3 MPa, and 0.5 seconds, a heat sealing peel strength is 6.0 N/15 mm or more.
<9> A packaging bag using the heat-sealable paper according to any one of <1> to <8>.

Description of Embodiments

Hereinafter, the preferable embodiments of the present invention will be described. In this description, "X to Y" showing a range means a range of "X or more and Y or less". When numerical ranges are stated stepwise, the upper and lower limits of each numerical range can be combined arbitrarily. In this description, unless otherwise specified, operations and measurements of physical properties and the like are performed under the conditions of room temperature (20 to 25°C)/relative humidity of 40 to 50%RH. Further, the term "(meth)acrylic" collectively refers to acrylic and methacrylic. In addition, the "wetting agent" includes a leveling agent.

<Heat-sealable paper>

The heat-sealable paper of the present embodiment (hereinafter also referred to simply as "heat-sealable paper") is heat-sealable paper containing a heat-sealable layer on one surface of the paper substrate, the heat-sealable layer contains a water-dispersible resin and a wetting agent, the water-dispersible resin contains a water-dispersible resin having a glass transition temperature of 0°C or more, a content of the wetting agent is 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin, and a surface roughness (RzJIS) of a surface opposite to a surface having the heat-sealable layer of the heat-sealable paper is 12.0 µm or more. The heat-sealable paper of the present embodiment is excellent in the heat sealing property and blocking resistance.
Hereinafter, the surface having the heat-sealable layer of the paper substrate is also referred to simply as the "coated surface". In addition, the surface opposite to the surface having the heat-sealable layer of the paper substrate or the heat-sealable paper is also referred to as the "non-coated surface " for convenience. However, in this case, a form having a coated layer on a surface opposite to the surface having the heat-sealable layer of the paper substrate or the heat-sealable paper is not excluded. Note that, when a layer is not formed on the surface opposite to the surface having the heat-sealable layer of the paper substrate by coating or the like, the surface opposite to the surface having the heat-sealable layer of the paper substrate is a non-coated surface.
When a heat-sealable layer, which contains a water-dispersible resin having a glass transition temperature of 0°C or more and a wetting agent, is formed, the wettability between the paper substrate and the heat-sealable layer coating liquid is improved when the heat-sealable layer is formed, the water-dispersible resin is uniformly absorbed into the paper substrate, the adhesion between the heat-sealable layer and the paper substrate increases, and an excellent heat sealing property can be achieved by heating or the like. It is thought that when the amount of the wetting agent is controlled to an range of 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin and the surface roughness (RzJIS) on the non-coated surface is increased to 12.0 µm or more, a desired heat sealing property can be achieved by heating or the like, and blocking between the heat-sealable layer and the non-coated surface can be suppressed during storage (particularly when the heat-sealable layer is coated, then wound in a roll, and stored in a pressure-bonded state). Note that, the effect of the present invention is not limited by the above mechanism.

[Paper substrate]

(Raw material pulp)

The pulp constituting the paper substrate is not particularly limited, and known pulps can be used. Specifically, examples thereof include unbleached pulps such as unbleached hardwood kraft pulp (LUKP) and unbleached softwood kraft pulp (NUKP); chemical pulps such as bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP); mechanical pulps such as Groundwood Pulp (GP), Pressurized Groundwood Pulp (PGW), Refiner Mechanical Pulp (RMP), ThermoMechanical Pulp (TMP), ChemiThermoMechanical Pulp (CTMP), ChemiMechanical Pulp (CMP), and ChemiGroundwood Pulp (CGP); waste paper pulps; non-wood fiber pulps such as kenaf, bagasse, bamboo, and cotton; and synthetic pulps. These pulps may be used individually by one type or in combination of two or more types. Among them, from the viewpoint of obtaining heat-sealable paper having a desired surface roughness (RzJIS) on the non-coated surface, at least one selected from the group consisting of unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), bleached hardwood kraft pulp (LBKP), and bleached softwood kraft pulp (NBKP) is preferable, at least one selected from the group consisting of unbleached hardwood kraft pulp (LUKP) and unbleached softwood kraft pulp (NUKP) is more preferable, and unbleached softwood kraft pulp (NUKP) is still more preferable.
A main component of pulp constituting the paper substrate used in the heat-sealable paper of the present embodiment is preferably softwood pulp, and is more preferably unbleached softwood kraft pulp (NUKP). The "main component of pulp constituting the paper substrate is softwood pulp (or unbleached softwood kraft pulp)" means that the content of the softwood pulp (or unbleached softwood kraft pulp) in the pulp constituting the paper substrate is more than 50% by mass, and the content of the softwood pulp (or unbleached softwood kraft pulp) is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass. The softwood pulp has a long average fiber length, and use of a paper substrate containing softwood pulp as raw material pulp is preferable because heat-sealable paper that has a desired surface roughness (RzJIS) on the non-coated surface can be obtained. In addition, use of unbleached softwood kraft pulp (NUKP) as pulp constituting a paper substrate is advantageous because the strength of the pulp fiber itself is higher than that of bleached softwood kraft pulp (NBKP) or unbleached hardwood kraft pulp (LUKP), and thus the obtained paper substrate has higher strength and elongation.
The raw material pulp constituting the paper substrate is preferably one or more selected from the group consisting of Bleached Kraft Pulp and Unbleached Kraft Pulp, and is more preferably Unbleached Kraft Pulp.
From the viewpoint of obtaining heat-sealable paper having desired surface roughness (RzJIS) and an arithmetic mean roughness (Ra) on the non-coated surface, Clupak paper (extensible paper) that has been subjected to Clupak processing for shrinking paper strip is preferably used as the paper substrate. The extensible paper refers to paper that has an elongation of 5% or more in the longitudinal direction or in the transverse direction measured according to JIS P 8113:2006, and examples thereof include kraft paper type-5 Nos. 1 and 2 described in JIS P 3401:2000.

(Basis weight)

The basis weight of the paper substrate is not specifically limited, and is preferably 40 g/m² or more and 130 g/m² or less from the viewpoint of the following. The basis weight of the paper substrate is preferably 40 g/m² or more, more preferably 50 g/m² or more, still more preferably 60 g/m² or more, and even still more preferably 70 g/m² or more, from the viewpoint of obtaining heat-sealable paper having a desired strength, and is preferably 130 g/m² or less, and more preferably 110 g/m² or less, from the viewpoint of the bag making processability and economic efficiency. When the basis weight of the paper substrate falls within the above preferable range, the heat-sealable paper of the present embodiment is suitable for application of packaging bags.
The basis weight of the paper substrate is measured according to JIS P 8124:2011.

(Thickness)

The thickness of the paper substrate is not specifically limited, and is preferably 50 µm or more and 200 µm or less from the viewpoint of the following. The thickness of the paper substrate is preferably 50 µm or more, more preferably 60 µm or more, still more preferably 80 µm or more, and even still more preferably 100 µm or more, from the viewpoint of obtaining heat-sealable paper having a desired strength, and is preferably 200 µm or less, more preferably 180 µm or less, and still more preferably 160 µm or less, from the viewpoint of the bag making processability and economic efficiency. When the thickness of the paper substrate falls within the above preferable range, the heat-sealable paper of the present embodiment is suitable for application of packaging bags.
The thickness of the paper substrate is measured according to JIS P 8118:2014.

(Density)

The density of the paper substrate is not specifically limited, and is preferably 0.3 g/cm³ or more and 1.0 g/cm³ or less from the viewpoint of the following. The density of the paper substrate is preferably 0.3 g/cm³ or more, and more preferably 0.5 g/cm³ or more, from the viewpoint of obtaining heat-sealable paper having a desired strength, and is preferably 1.0 g/cm³ or less, more preferably 0.9 g/cm³ or less, and still more preferably 0.75 g/cm³ or less, from the viewpoint of the bag making processability and economic efficiency. When the density of the paper substrate falls within the above preferable range, the heat-sealable paper of the present embodiment is suitable for application of packaging bags.
The density of the paper substrate is calculated from the basis weight and the thickness of the paper substrate obtained from the above measurement methods.

(Stockigt degree of sizing)

The Stockigt degree of sizing on the non-coated surface of the paper substrate is not specifically limited, and is preferably 30 seconds or more and 100 seconds or less from the viewpoint of the following. The Stockigt degree of sizing on the non-coated surface of the paper substrate is preferably 30 seconds or more, more preferably 40 seconds or more, and still more preferably 50 seconds or more, from the viewpoint of improving strength when it is used as a packaging bag, and specifically from the viewpoint of maintaining the strength when the paper substrate is in contact with water, and the upper limit thereof is not specifically limited, and is preferably 100 seconds or less, more preferably 90 seconds or less, still more preferably 85 seconds or less, and even still more preferably 80 seconds or less, from the viewpoint of economic efficiency.
The Stockigt degree of sizing of the coated surface of the paper substrate is not specifically limited, and is preferably 30 seconds or more and 100 seconds or less from the viewpoint of the following. The Stockigt degree of sizing on the coated surface of the paper substrate is preferably 100 seconds or less, more preferably 90 seconds or less, still more preferably 85 seconds or less, and even still more preferably 80 seconds or less. When the Stockigt degree of sizing on the coated surface of the paper substrate is equal to or lower than the upper limit, the heat-sealable layer is appropriately wetted and spread on the paper substrate, and a uniform heat-sealable layer can be obtained, resulting a good heat sealing peel strength. On the other hand, the preferable lower limit and its reasons are the same as those of the Stockigt degree of sizing on the non-coated surface.
The Stockigt degree of sizing is measured according to JIS P 8122:2004.
Note that, the Stockigt degree of sizing of the paper substrate can be controlled by the type and the amount of the surface sizing agent used.

[Heat-sealable layer]

The heat-sealable paper according to this embodiment contains a heat-sealable layer on one surface of the paper substrate. The heat-sealable layer is a layer that contains a water-dispersible resin and a wetting agent and is melted and adheres by heating, ultrasonic waves, or the like. The heat-sealable paper of the present embodiment preferably has a heat-sealable layer on the uppermost layer on one surface of the paper substrate. The heat-sealable paper of the present embodiment may include, for example, a clay coat layer, a gas barrier layer and/or a water vapor barrier layer between the paper substrate and the heat-sealable layer, but preferably has the heat-sealable layer directly on one surface of the paper substrate.

(Water-dispersible resin)

The water-dispersible resin is a resin binder that is not water-soluble (specifically, the solubility in water at 25°C is 10 g/L or less) but is finely dispersed in water like an emulsion or a suspension.
The water-dispersible resin contains a water-dispersible resin having a glass transition temperature of 0°C or more.
The water-dispersible resin having a glass transition temperature of 0°C or more is not specifically limited except that it has a glass transition temperature of 0°C or more, as long as it exerts the effects of the present invention, but examples thereof include polyolefin resins (such as polypropylene), vinyl chloride resins, styrene resins, styrene-butadiene copolymers, styrene-unsaturated carboxylic acid copolymers (such as styrene-(meth)acrylic acid copolymer), acrylic resins, acrylonitrile-styrene copolymers, acrylonitrile-butadiene copolymers, ABS resins, AAS resins, AES resins, vinylidene chloride resins, polyurethane resins, poly(4-methyl pentene-1) resins, poly(butene-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, polyether sulfone resins, polyarylate resins, olefin/unsaturated carboxylic acid copolymers, and modified products thereof. These may be used individually by one type or may be used in combination of two types or more. Among them, styrene-butadiene copolymers are more preferable from the viewpoint of the heat sealing property, blocking resistance, and cost of the heat-sealable paper.
The styrene-butadiene copolymer may be any of synthetic product and commercially available product, and examples of the commercially available product include Nipol latex LX407G51, LX407S10, LX407S12, LX410, LX415M, LX416, LX430, LX433C, 2507H, available from Zeon Corporation, Nalstar SR-102, SR-103, SR-115, and SR-153, available from NIPPON A&L INC., and styrene butadiene latex 0602 and 0597C, available from JSR Corporation.
The glass transition temperature of the water-dispersible resin is 0°C or more from the viewpoint of blocking resistance. The glass transition temperature of the water-dispersible resin is preferably 0°C or more and 80°C or less, is preferably 3°C or more, and more preferably 6°C or more, and is more preferably 70°C or less, still more preferably 60°C or less, even still more preferably 50°C or less, further more preferably 40°C or less, even further more preferably 30°C or less, and even further more preferably 20°C or less.
The glass transition temperature of the water-dispersible resin, which is equal to or higher than the above lower limit, is preferable, from the viewpoint of blocking resistance, and the glass transition temperature of the water-dispersible resin, which is equal to or lower than the upper limit, is preferable, from the viewpoint of the heat sealing property.
As the glass transition temperature of the water-dispersible resin binder, a value measured with a differential scanning calorimeter (measurement method) is used.
The content of the water-dispersible resin in the heat-sealable layer is preferably 60% by mass or more and 99% by mass or less, is more preferably 70% by mass or more, and still more preferably 80% by mass or more, and is more preferably 98% by mass or less. When the content of the water-dispersible resin in the heat-sealable layer falls within the above range, heat-sealable paper having a high heat-sealable strength can be obtained.
According to one embodiment of the present invention, the content of the styrene-butadiene copolymer in the water-dispersible resin is preferably 85% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, and is preferably 100% by mass or less.
The water-dispersible resin may contain a water-dispersible resin having a glass transition temperature of less than 0°C, and the content of the water-dispersible resin having a glass transition temperature of less than 0°C in the water-dispersible resin is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less (lower limit 0% by mass).

(Wetting agent)

The heat-sealable layer contains a wetting agent.
Examples of the wetting agent include acetylene wetting agents, acrylic wetting agents, and silicone wetting agents. From the viewpoint of the heat sealing property and blocking resistance, the wetting agent preferably contains one selected from the group consisting of acetylene wetting agents, acrylic wetting agents, and silicone wetting agents, and more preferably contains an acetylene wetting agent.
In addition, from the viewpoint of the heat sealing property and blocking resistance, the above water-dispersible resin preferably contains a styrene-butadiene copolymer, and the wetting agent preferably contains an acetylene wetting agent.
The acetylene wetting agent is a compound that has an acetylene backbone, and examples thereof include compounds that have an acetylene backbone and a functional group such as a hydroxy group. Among them, acetylene glycol wetting agents are preferable. Examples of the acetylene glycol wetting agents include acetylene glycol and alkylene oxide (e.g., ethylene oxide, propylene oxide) adducts of acetylene glycol, alkylene oxide adducts of acetylene glycol (alkylene group having 2 to 10 carbon atoms) are preferable, and ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol are more preferable.
As the acetylene wetting agents, either synthetic products or commercially available products may be used. Examples of the commercially available products include "MEIKASURF S-28" available from MEISEI CHEMICAL WORKS, LTD. and "Surfynol series" available from Nissin Chemical Industry Co., Ltd.
The acrylic wetting agent is a compound that has an acryloyl backbone.
As the acrylic wetting agents, either synthetic products or commercially available products may be used. Examples of the commercially available products include "MODAFLOW AQ3025" available from Allnex and "POLYFLOW WS" available from Kyoeisha Chemical Co., Ltd.
The silicone wetting agent is a compound that has a siloxane backbone.
As the silicone wetting agents, either synthetic products or commercially available products may be used. Examples of the commercially available products include "POLYFLOW KL-401" available from Kyoeisha Chemical Co., Ltd. and "DISPARLON LS-460" available from Kusumoto Chemicals, Ltd.
The wetting agent may be used individually by one type or may be used in combination of two types or more.
The content of the wetting agent in the heat-sealable layer is 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin, from the viewpoint of the following. With respect to 100 parts by mass of the water-dispersible resin, the content of the wetting agent in the heat-sealable layer is 0.04 parts by mass or more, preferably 0.06 parts by mass or more, and more preferably 0.08 parts by mass or more, from the viewpoint of the heat sealing property, and is 1.2 parts by mass or less, preferably 0. 7 parts by mass or less, and more preferably 0.4 parts by mass or less, from the viewpoint of blocking resistance.
The content of the wetting agent in the heat-sealable layer is preferably 0.01% by mass or more and 3.0% by mass or less from the viewpoint of the following. The content of the wetting agent in the heat-sealable layer is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, still more preferably 0.03% by mass or more, even still more preferably 0.04% by mass or more, further preferably 0.06% by mass or more, and even further preferably 0.08% by mass or more, from the viewpoint of the heat sealing property, and is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, still more preferably 1.2% by mass or less, even still more preferably 1.0% by mass or less, further preferably 0.7% by mass or less, and even further preferably 0.4% by mass or less, from the viewpoint of blocking resistance.
According to one embodiment of the present invention, the total content of the acetylene wetting agent, the acrylic wetting agent, and the silicone wetting agent in the wetting agent is preferably 85% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, and is preferably 100% by mass or less.
According to another embodiment of the present invention, the content of the acetylene wetting agent in the wetting agent is preferably 85% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, and is preferably 100% by mass or less.

(Lubricant)

From the viewpoint of blocking resistance, the heat-sealable layer preferably contains a lubricant in addition to the above water-dispersible resin and wetting agent. The lubricant is a substance that can reduce the coefficient of friction on the surface of the heat-sealable layer by being mixed in the heat-sealable layer.
The lubricant is not specifically limited, and waxes, metal soaps, fatty acid esters, and the like can be used, for example. One of the lubricants may be used alone, or two or more of them may be used in combination. Examples of the waxes include natural waxes including animal or plant-derived waxes (such as beeswax and carnauba wax), mineral waxes (such as microcrystalline wax), and petroleum wax; and synthetic waxes including polyolefin wax, paraffin wax, polyester wax, and the like. Examples of the metal soaps include calcium stearate, sodium stearate, zinc stearate, aluminum stearate, magnesium stearate, fatty acid sodium soap, potassium oleate soap, castor oil potassium soap, composites thereof, and the like. Among the lubricants, carnauba wax and paraffin wax are preferable since the melting point is comparatively low, and wax components are easily formed on the surface of the coating layer, and the effect of suppressing blocking is excellent. That is, the lubricant is preferably at least one selected from the group consisting of carnauba wax and paraffin wax. The carnauba wax to be used may be any of synthetic products and commercially available products, and examples of the commercially available products include Selosol 524 and the like, available from Chukyo Yushi Co., Ltd. The paraffin wax to be used may be any of synthetic products and commercially available products, and examples of the commercially available products include Hidorin L-700 and the like, available from Chukyo Yushi Co., Ltd.
In the case where the heat-sealable layer contains a lubricant, the content of the lubricant in the heat-sealable layer is preferably 0.2 parts by mass or more and 15 parts by mass or less, more preferably 0.5 parts by mass or more, and still more preferably 1 part by mass or more, and is more preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, with respect to 100 parts by mass of the water-dispersible resin binder.
In the case where the heat-sealable layer contains a lubricant, the content of the lubricant in the heat-sealable layer is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.2% by mass or more, and still more preferably 0.5% by mass or more, and is more preferably 10% by mass or less, and still more preferably 5% by mass or less.

(Pigment)

In the present embodiment, the heat-sealable layer may contain the above water-dispersible resin, the wetting agent, and, if necessary, a pigment in addition to the lubricant. Containing the pigment suppresses such a problem that the coated surface of the heat-sealable paper sticks to the non-coated surface of the heat-sealable paper to cause peeling (blocking) when the heat-sealable paper is produced and stored, and therefore the heat-sealable paper having excellent blocking resistance is obtained.
Specific examples of the pigment include mica, bentonite, kaolin, pyrophyllite, talc, smectite, vermiculite, chlorite, septe chlorite, serpentine, stilpnomelane, montmorillonite, heavy calcium carbonate (ground calcium carbonate), light calcium carbonate (synthetic calcium carbonate), composite synthetic pigment 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 hollow or solid organic pigments, binder pigments, plastic beads, microcapsules, and the like. These may be used individually by one type or may be used in combination of two types or more.
Specific examples of mica include synthetic mica (such as swelling synthetic mica), white mica (muscovite), silk mica (sericite), phlogopite (phlogopite), black mica (biotite), fluorine phlogopite (artificial mica), red mica, soda mica, vanadium mica, illite, tin mica, paragonite, and brittle mica. Further, specific examples of bentonite include montmorillonite.
Specific examples of kaolin include various kaolins such as kaolin, calcined kaolin, structured kaolin, and delaminated kaolin.
Among them, especially, one or more selected from the group consisting of calcium carbonate and kaolin is preferably included from the viewpoint of blocking resistance.
When the heat-sealable layer contains a pigment, the content of the pigment in the heat-sealable layer is preferably 10 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin from the viewpoint of the following. With respect to 100 parts by mass of the water-dispersible resin, the content of the pigment in the heat-sealable layer is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, and even still more preferably 40 parts by mass or more, from the viewpoint of blocking resistance, and is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and still more preferably 120 parts by mass or less, from the viewpoint of the heat sealing property.
When the heat-sealable layer contains a pigment, the content of the pigment in the heat-sealable layer is preferably 5% by mass or more and 70% by mass or less, from the viewpoint of the following. The content of the pigment in the heat-sealable layer is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, and even still more preferably 25% by mass or more, from the viewpoint of blocking resistance, and is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less, from the viewpoint of the heat sealing property.

(Other components)

The heat-sealable layer may contain other components in addition to the water-dispersible resin, the wetting agent, the lubricant, and the pigment. Examples of the other components include silane coupling agents; defoaming agents; viscosity modifiers; and colorants such as coloring dyes.
When the heat-sealable layer contains the above other components, the content of the other components is not specifically limited, and the total content of the other components is preferably 0.01 parts by mass or more and 5 parts by mass or less, more preferably 3 parts by mass or less, and still more preferably 1 part by mass or less, and is more preferably 0.1 parts by mass or more, with respect to 100 parts by mass of the water-dispersible resin.

[Basis weight, thickness, and physical properties of heat-sealable paper]

(Basis weight)

The basis weight of the heat-sealable paper is not specifically limited, and is preferably 50 g/m² or more and 140 g/m² or less, from the viewpoint of the following. The basis weight of the heat-sealable paper is preferably 50 g/m² or more, more preferably 55 g/m² or more, and still more preferably 60 g/m² or more, from the viewpoint of obtaining a desired strength, and is preferably 140 g/m² or less, more preferably 130 g/m² or less, and still more preferably 120 g/m² or less, from the viewpoint of easy production and bag making processability of the heat-sealable paper. When the basis weight falls within the above preferable range, the heat-sealable paper of the present embodiment is suitable for application of packaging bags.
The basis weight of the heat-sealable paper is measured according to JIS P 8124:2011.

(Thickness)

The thickness (paper thickness) of the heat-sealable paper is not specifically limited, and is preferably 60 µm or more and 220 µm or less, from the viewpoint of the following. The thickness (paper thickness) of the heat-sealable paper is preferably 60 µm or more, more preferably 80 µm or more, and still more preferably 100 µm or more, from the viewpoint of obtaining a desired strength, and is preferably 220 µm or less, more preferably 200 µm or less, and still more preferably 180 µm or less, from the viewpoint of easy production and bag making processability of the heat-sealable paper. When the thickness falls within the above preferable range, the heat-sealable paper of the present embodiment is suitable for application of packaging bags.
The paper thickness of the heat-sealable paper is measured according to JIS P 8118:2014.

(Density)

The density of the heat-sealable paper is not specifically limited, and is preferably 0.3 g/cm³ or more and 1.0 g/cm³ or less, from the viewpoint of the following. The density of the heat-sealable paper is preferably 0.3 g/cm³ or more, and more preferably 0.5 g/cm³ or more, from the viewpoint of obtaining a desired strength, and is preferably 1.0 g/cm³ or less, more preferably 0.9 g/cm³ or less, and still more preferably 0.75 g/cm³ or less, from the viewpoint of easy production and bag making processability of the heat-sealable paper. When the density falls within the above preferable range, the heat-sealable paper of the present embodiment is suitable for application of packaging bags.
The density of the heat-sealable paper is calculated from the basis weight and the thickness of the paper substrate obtained from the above measurement methods.

(Oken smoothness)

From the viewpoint of blocking resistance, the Oken smoothness on the non-coated surface of the heat-sealable paper of the present embodiment is preferably 50 seconds or less, more preferably 30 seconds or less, and still more preferably 10 seconds or less, and the lower limit, which is not specifically limited, is preferably 1 second or more. The Oken smoothness of the heat-sealable paper is measured according to JIS P 8155:2010. The Oken smoothness on the non-coated surface of the heat-sealable paper can be controlled by the conditions such as the fiber length and the beating degree of pulp, the pressure treatment in the papermaking step, and Clupak processing. For example, when pulp having a long fiber length or pulp having a low beating degree is used, the Oken smoothness tends to decrease. In addition, when the difference between the production speed at the inlet side and the production speed at the outlet side of a Clupak processing device is increased, the Oken smoothness tends to decrease.

(Surface roughness (RzJIS))

From the viewpoint of blocking resistance, the surface roughness (RzJIS) on a surface (non-coated surface) opposite to a surface having a heat-sealable layer of the heat-sealable paper of the present embodiment is 12.0 µm or more, preferably 12.5 µm or more, and more preferably 13.0 µm or more. The upper limit is not specifically limited, and is preferably, for example, 16.0 µm or less. When the RzJIS on the non-coated surface is equal to or higher than the lower limit, it is thought that relatively large roughness exists on the non-coated surface, which can suppress blocking. The surface roughness (RzJIS) on the non-coated surface of the heat-sealable paper is measured according to JIS B 0601:2013. The surface roughness (RzJIS) on the non-coated surface of the heat-sealable paper can be controlled by the conditions such as the fiber length and the beating degree of pulp, the pressure treatment in the papermaking step, and Clupak processing. For example, when pulp having a long fiber length or pulp having a low beating degree is used, the surface roughness (RzJIS) tends to increase. In addition, when the difference between the production speed at the inlet side and the production speed at the outlet side of a Clupak processing device is increased, the surface roughness (RzJIS) tends to increase. In the present specification, the surface roughness (RzJIS) of a surface opposite to a surface having the heat-sealable layer of the heat-sealable paper is a ten point height of roughness profile in the MD direction and the ten-point average roughness in the CD direction obtained by measuring the line roughness in the MD direction and the CD direction according to JIS B 0601:2013, and is specifically a value measured by the method described in Examples.

(Arithmetic average roughness (Ra))

The arithmetic average roughness (Ra) on the non-coated surface of the heat-sealable paper of the present embodiment is preferably 2.0 µm or more, more preferably 2.5 µm or more, and still more preferably 3.0 µm or more, from the viewpoint of blocking resistance. The upper limit, which is not specifically limited, is preferably, for example, 5.0 µm or less. The arithmetic average roughness (Ra) on the non-coated surface of the heat-sealable paper is measured according to JIS B 0601:2013. The arithmetic average roughness (Ra) on the non-coated surface of the heat-sealable paper can be controlled by the conditions such as the fiber length and the beating degree of pulp, the pressure treatment in the papermaking step, and Clupak processing. The tendency is the same as that of the surface roughness (RzJIS). In the present specification, the arithmetic average roughness (Ra) on a surface opposite to a surface having a heat-sealable layer of the heat-sealable paper is an arithmetic mean of the arithmetic average roughness in the MD direction and the arithmetic average roughness in the CD direction obtained by measuring the line roughness in the MD direction and the CD direction according to JIS B 0601:2013, and is specifically a value measured by the method described in Examples.
Regarding the RzJIS and the Ra, although the paper substrate has an orientation, blocking is a phenomenon that occurs on the entire non-coated surface, so the arithmetic average of the measured value in the MD direction and the measured value in the CD direction is used.

(Heat sealing peel strength)

The peel strength of the heat-sealable layer of the heat-sealable paper of the present embodiment is preferably 6.0 N/15 mm or more and 12.0 N/15 mm or less, more preferably 6.5 N/15 mm or more, and still more preferably 7.0 N/15 mm or more, and is more preferably 11.0 N/mm or less, and still more preferably 10.0 N/15 mm or less. The peel strength of the heat-sealable layer is a peel strength when two heat-sealable layers are heat-sealed to each other under conditions of 160°C, 0.3 MPa, and 0.5 seconds, and is specifically a value measured by the method described in Examples below.
The peel strength can be adjusted by selecting the glass transition temperature and type of the water-dispersible resin, and the type and amount of the wetting agent.

The production method of the heat-sealable paper of the embodiment is not specifically limited. For example, the production method includes a coating step of coating a heat-sealable layer coating liquid to one side (preferably a wire side (highly smooth surface)) of the extensible paper, which is the paper substrate. Note that, the heat-sealable layer coating liquid (heat-sealable layer coating material) may be coated two or more times.
In the case of forming multiple heat-sealable layers on the paper substrate, the method of sequentially forming the heat-sealable layers is preferable, but there is no limitation to this, and a simultaneous multilayer coating method may be employed. The simultaneous multilayer coating method is a method of discharging multiple types of coating liquids separately from slit-shaped nozzles to form a liquid laminate and applying the laminate to the paper substrate to form multiple heat-sealable layers simultaneously.
The application equipment for applying the heat-sealable layer coating liquid to the paper substrate is not specifically limited, and known equipment may be used. Examples of the application equipment include blade coaters, bar coaters, air knife coaters, slit die coaters, gravure coaters, micro gravure coaters, roll coaters, size presses, gate roll coaters, Sym-sizers, and the like.
The drying equipment for drying the heat-sealable layer is not specifically 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. Further, the drying temperature may be appropriately set in consideration of the drying time.
It is preferable to adjust the conditions at the time of forming the heat-sealable layer so that the formation of the heat-sealable layer does not affect the surface roughness (RzJIS) on the non-coated surface of the paper substrate.
The solvent for the heat-sealable layer coating liquid is not specifically limited, and water or an organic solvent such as ethanol, isopropyl alcohol, methyl ethyl ketone, and toluene can be used. Among these, water is preferable as a dispersion medium for the heat-sealable layer coating liquid, since there is no problem of volatile organic solvents. That is, the heat-sealable layer coating liquid is preferably an aqueous composition for heat-sealable layers.
The solid content (solid content concentration) of the heat-sealable layer coating liquid is not specifically limited and may be appropriately selected from the viewpoint of the coating property and ease of drying but is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more, and still more preferably 30% by mass or more, and is more preferably 65% by mass or less, and still more preferably 50% by mass or less.
The basis weight of the heat-sealable layer (when the heat-sealable layer is provided by coating, the coating amount (after drying)) is preferably 7 g/m² or more and 21 g/m² or less, more preferably 8 g/m² or more, and still more preferably 9 g/m² or more, and is more preferably 19 g/m² or less, and still more preferably 17 g/m² or less. The heat-sealable layer may be one layer or two or more layers. When the number of the heat-sealable layer is two or more, the aforementioned coating amount is the total coating amount.

[Applications]

The heat-sealable paper according to the present embodiment can be favorably used as a packaging bag for foods, household goods, commodities (soaps and diapers), and the like. Accordingly, the present invention also provides a packaging bag using the heat-sealable paper.

Examples

The features of the present invention are described in more detail below by way of Examples and Comparative Examples. The materials, the amounts used, the ratios, the processing contents, the processing procedures, and the like described in the following Examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific Examples described below. Furthermore, the operations of the Examples and Comparative Examples were performed at room temperature (20 to 25°C) and normal humidity (40 to 50% RH) unless otherwise specified.

[Example 1]

(Preparation of heat-sealable layer coating liquid)

One hundred parts by mass (in terms of solid content) of an aqueous dispersion of a styrene-butadiene copolymer (available from Zeon Corporation, Nipol LATEX LX407S12, solid content 46% by mass, glass transition temperature 18°C), 3 parts by mass (in terms of solid content) of a lubricant (available from Chukyo Yushi Co., Ltd., Hidorin L-700, solid content 30% by mass), 0.05 parts by mass (in terms of active component) of an acetylene glycol wetting agent (available from MEISEI CHEMICAL WORKS, LTD., MEIKASURF S-28, active component 20% by mass), and 0.4 parts by mass (in terms of active component) of a defoaming agent (available from SAN NOPCO LIMITED, SN0215, active component 15% by mass) were mixed, and water was added and stirred so that the solid content concentration was 38% by mass, to thereby prepare a heat-sealable layer coating liquid (concentration 38% by mass).

(Coating of heat-sealable layer coating liquid)

The obtained heat-sealable layer coating liquid was coated, with a bar coater, on the coated surface of paper substrate (extensible paper) of 100% by mass of unbleached softwood kraft pulp (NUKP) having a basis weight of 100 g/m², a thickness of 150 µm, a density of 0.67 g/cm³, a Stockigt degree of sizing on the coated surface (wire side, high smooth surface) of 73 seconds, a Stockigt degree of sizing on the non-coated surface (felt side, low smooth surface) of 79 seconds, and a surface roughness (RzJIS) on the non-coated surface (felt side, low smooth surface) of 14.9 µm, so that the coating amount of the heat-sealable layer after drying was 14 g/m², and then, it was dried at 140°C for 25 seconds to form a heat-sealable layer, obtaining heat-sealable paper.

[Example 2]

Heat-sealable paper was obtained in the same manner as in Example 1 except that the amount of the acetylene glycol wetting agent added was changed to 0.1 parts by mass (in terms of active component) in the preparation of the heat-sealable layer coating liquid of Example 1.

[Example 3]

Heat-sealable paper was obtained in the same manner as in Example 1 except that the amount of the acetylene glycol wetting agent added was changed to 0.2 parts by mass (in terms of active component) in the preparation of the heat-sealable layer coating liquid of Example 1.

[Example 4]

Heat-sealable paper was obtained in the same manner as in Example 1 except that the amount of the acetylene glycol wetting agent added was changed to 1.0 part by mass (in terms of active component) in the preparation of the heat-sealable layer coating liquid of Example 1.

[Example 5]

Heat-sealable paper was obtained in the same manner as in Example 3 except that the acetylene glycol wetting agent was changed to the acrylic wetting agent (available from Allnex, MODAFLOW AQ3025, active component 25% by mass) in the preparation of the heat-sealable layer coating liquid in Example 3.

[Example 6]

Heat-sealable paper was obtained in the same manner as in Example 3 except that the acetylene glycol wetting agent was changed to the silicone wetting agent (available from Kyoeisha Chemical Co., Ltd., POLYFLOW KL-401, active component 100% by mass) in the preparation of the heat-sealable layer coating liquid in Example 3.

[Example 7]

Heat-sealable paper was obtained in the same manner as in Example 3 except that the paper substrate was changed to extensible paper of 100% by mass of unbleached softwood kraft pulp having a basis weight of 88 g/m², a thickness of 135 µm, a density of 0.65 g/cm³, a Stockigt degree of sizing on the coated surface (wire side, high smooth surface) of 75 seconds, a Stockigt degree of sizing on the non-coated surface (felt side, low smooth surface) of 70 seconds, and a surface roughness (RzJIS) on the non-coated surface (felt side, low smooth surface) of 13.8 µm in the coating of the heat-sealable layer coating liquid of Example 3.

[Example 8]

Heat-sealable paper was obtained in the same manner as in Example 3 except that the paper substrate was changed to extensible paper of 100% by mass of unbleached softwood kraft pulp having a basis weight of 88 g/m², a thickness of 135 µm, a density of 0.65 g/cm³, a Stockigt degree of sizing on the coated surface (felt side, low smooth surface) of 60 seconds, a Stockigt degree of sizing on the non-coated surface (wire side, high smooth surface) of 60 seconds, and a surface roughness (RzJIS) on the non-coated surface of 13.4 µm in the coating of the heat-sealable layer coating liquid of Example 3.

[Comparative Example 1]

Heat-sealable paper was obtained in the same manner as in Example 1 except that the acetylene glycol wetting agent was not used in the preparation of the heat-sealable layer coating liquid of Example 1.

[Comparative Example 2]

Heat-sealable paper was obtained in the same manner as in Example 1 except that the amount of the acetylene glycol wetting agent added was changed to 0.03 parts by mass (in terms of active component) in the preparation of the heat-sealable layer coating liquid of Example 1.

[Comparative Example 3]

Heat-sealable paper was obtained in the same manner as in Example 1 except that the amount of the acetylene glycol wetting agent added was changed to 1.5 parts by mass (in terms of active component) in the preparation of the heat-sealable layer coating liquid of Example 1.

[Comparative Example 4]

Heat-sealable paper was obtained in the same manner as in Example 3 except that the paper substrate was changed to unbleached light-duty packaging paper of 100% by mass of unbleached softwood kraft pulp having a basis weight of 100 g/m², a thickness of 155 µm, a density of 0.65 g/cm³, a Stockigt degree of sizing on the coated surface (wire side, high smooth surface) of 36 seconds, a Stockigt degree of sizing on the non-coated surface (felt side, low smooth surface) of 30 seconds, and a surface roughness (RzJIS) on the non-coated surface (felt side, low smooth surface) of 10.4 µm in the coating of the heat-sealable layer coating liquid of Example 3.

[Comparative Example 5]

Heat-sealable paper was obtained in the same manner as in Example 3 except that the aqueous dispersion of the styrene-butadiene copolymer was changed to an aqueous dispersion of a styrene-butadiene copolymer (available from NIPPON A&L INC., Nalstar SR-110, solid content 46% by mass, glass transition temperature -27°C) in the preparation of the heat-sealable layer coating liquid in Example 3.

Measurements and evaluations of the following items were performed on the paper substrates and the heat-sealable papers produced in Examples and Comparative Examples.

(Basis weight)

The basis weights of the paper substrate and the heat-sealable paper were measured according to JIS P 8124:2011.

(Thickness)

The thicknesses of the paper substrate and the heat-sealable paper were measured according to JIS P 8118:2014.

(Density)

The densities of the paper substrate and the heat-sealable paper were calculated from the basis weight and the thickness obtained from the above measurement methods.

(Stockigt degree of sizing)

The Stockigt degrees of sizing on the coated surface and on the non-coated surface of the heat-sealable paper were measured according to JIS P 8122:2004.

(Oken smoothness)

The Oken smoothness on the non-coated surface of the heat-sealable paper was measured according to JIS P 8155:2010.

(Ten-point average roughness (RzJIS))

The ten-point average roughness (surface roughness (RzJIS)) on the non-coated surface of the heat-sealable paper was measured according to JIS B 0601:2013.
The measurement was performed using "one-shot 3D shape measuring device VR-3000/VR-3200" and analysis application "VR-H2A" built in VR-3000, available from KEYENCE. The observation conditions were a magnification 80x and a field of view of 3.8 mm × 2.9 mm. Linear roughness was measured in the MD direction and the CD direction at any five locations on the sample, and the arithmetic mean of the measured values of the ten-point average roughness in the MD direction and the measured values of the ten-point average roughness in the CD direction for the five locations was considered as the ten-point average roughness RzJIS of the sample.
Specifically, a sample of approximately A4 size was cut from the heat-sealable paper, and the sample was placed along the edge of the stage with the non-coated surface of the sample facing upward, so that the CD direction of the sample coincided with the depth direction of the stage equipped in VR-3200. The autofocus for measurement was performed at observation magnification 80x, and an observation image of 3.8 mm transverse × 2.9 mm longitudinal was obtained. Regarding the observation image obtained here, the transverse direction corresponds to the MD direction of the sample, and the longitudinal direction corresponds to the CD direction of the sample. A horizontal line (a straight line in the transverse direction) was selected at any position on the obtained observation image, line roughness analysis was performed, and the ten-point average roughness in the MD direction was automatically measured. In addition, a vertical line (a straight line in the longitudinal direction) was selected at any position on the obtained observation image, line roughness analysis was performed, and the ten-point average roughness in the CD direction was automatically measured. The same measurement as above was performed by changing the measurement positions, and the ten-point average roughness in the MD direction and the ten-point average roughness in the CD direction were measured at any five locations on the sample, and the arithmetic mean of these measured values was calculated to obtain the ten-point average roughness (RzJIS) of the sample.

(Arithmetic average roughness (Ra))

The arithmetic average roughness (Ra) on the non-coated surface of the heat-sealable paper was measured according to JIS B 0601:2013. Using the same measuring device and observation conditions as those of the ten-point average roughness measurement, line roughness analysis was performed in the MD direction and the CD direction at any five locations on the sample, and the arithmetic mean of the measured values of the arithmetic average roughness in the MD direction and the measured values of the arithmetic average roughness in the CD direction for the five locations was considered as the arithmetic average roughness (Ra) of the sample.

(Heat sealing peel strength)

Two sheets of heat-sealable paper in a set were laminated with the heat-sealable layers facing each other, and were heat-sealed using a heat seal tester (TP-701-B, available from TESTER SANGYO CO,. LTD.) under the conditions of 160°C, 0.3 MPa, and 0.5 seconds. The heat-sealed test specimen was left to stand indoors at temperature of a temperature 23°C±1°C and relative humidity 50%±2% for four hours or more. Subsequently, the test specimen heat-sealed was cut into a width of 15 mm and T-peeled using a tensile tester at a tensile speed of 300 mm/min, and the maximum load recorded was taken as a heat sealing peel strength.

(Blocking resistance)

The heat-sealable paper was cut to a 9 cm square. Then, sheets of the heat-sealable paper were stacked so that the coated surface and the non-coated surface faced each other, pressed at a temperature of 40°C and a pressure of 46 kg/cm² using a press machine (MINI TEST PRESS-10, model MP-SNH, available from TOYO SEIKI SEISAKU-SHO, LTD.), and maintained in that state for 15 hours. After 15 hours, the sample was removed from the press machine and peeled by hand. The condition of the sample after peeling was confirmed and evaluated based on the following criteria. A and B can be judged as being usable for practical use.

[Evaluation criteria]

A: Neither paper peeling nor fuzzing was found.
B: No paper peeling was found, but fuzzing was slightly found.
C: Paper peeling was found.

[Table 1-1]

Table 1-1

			Comparative Example 1	Comparative Example 2	Example 1	Example 2	Example 3	Example 4	Comparative Example 3
	Paper	Type	Extensible paper	Extensible paper	Extensible paper	Extensible paper	Extensible paper	Extensible paper	Extensible paper
	Basis weight	g/m²	100	100	100	100	100	100	100
	Density	g/cm³	0.67	0.67	0.67	0.67	0.67	0.67	0.67
Paper substrate	Thickness	µm	150	150	150	150	150	150	150
Paper substrate	Stockigt degree of sizing (coated surface)	Second	73	73	73	73	73	73	73
	Stockigt degree of sizing (non-coated surface)	Second	79	79	79	79	79	79	79
		Type	S12	S12	S12	S12	S12	S12	S12
		Resin type	SBR	SBR	SBR	SBR	SBR	SBR	SBR
	Water-dispersible resin	Glass transition temperature (°C)	18	18	18	18	18	18	18
		Solid content in parts	100	100	100	100	100	100	100
	Lubricant	Solid content in parts	3	3	3	3	3	3	3
Heat-sealable layer		Type	-	Acetylene
Heat-sealable layer		Type	-	MEIKASURF S-28
	Wetting agent	Solid content in parts	0	0.03	0.05	0.1	0.2	1.0	1.5
		Content in heat-sealable layer (% by mass)	0.00	0.03	0.05	0.10	0.19	0.96	1.43
	Defoaming agent	Solid content in parts	0.4	0.4	0.4	0.4	0.4	0.4	0.4
	Coating amount	g/m²	14	14	14	14	14	14	14
	Oken smoothness on non-coated surface	Second	8	8	8	8	8	8	8
	Arithmetic average roughness (Ra) on non-coated surface	µm	4.2	4.2	4.2	4.2	4.2	4.2	4.2
Heat-sealable paper	Ten-point average roughness (RzJIS) on non-coated surface	µm	14.9	14.9	14.9	14.9	14.9	14.9	14.9
Heat-sealable paper	Basis weight	g/m²	114	114	114	114	114	114	114
	Thickness	µm	164	164	164	164	164	164	164
	Heat sealing peel strength	N/15mm	3.5	4.9	7.1	7.9	8.3	8.7	8.3
	Blocking resistance	-	A	A	A	A	A	B	c

[Table 1-2]

Table 1-2

			Example 5	Example 6	Example 7	Example 8	Comparative Example 4	Comparative Example 5
	Paper	Type	Extensible paper	Extensible paper	Extensible paper	Extensible paper	Unbleached light-duty packaging paper	Extensible paper
	Basis weight	g/m²	100	100	88	88	100	100
Paper substrate	Density	g/cm³	0.67	0.67	0.65	0.65	0.65	0.67
	Thickness	µm	150	150	135	135	155	150
	Stockigt degree of sizing (coated surface)	Second	73	73	75	60	36	73
	Stockigt degree of sizing (non-coated surface)	Second	79	79	70	60	36	79
		Type	S12	S12	S12	S12	S12	SR-110
		Resin type	SBR	SBR	SBR	SBR	SBR	SBR
	Water-dispersible resin	Glass transition temperature (°C)	18	18	18	18	18	-27
		Solid content in parts	100	100	100	100	100	100
	Lubricant	Solid content in parts	3	3	3	3	3	3
Heat-sealable layer		Type	Acrylic	Silicone	Acetylene
Heat-sealable layer		Type	MODAFLOW AQ3025	POLYFLOW KL-401	MEIKASURF S-28
	Wetting agent	Solid content in parts	0.2	0.2	0.2	0.2	0.2	0.2
		Content in heat-sealable layer (% by mass)	0.19	0.19	0.19	0.19	0.19	0.19
	Defoaming agent	Solid content in parts	0.4	0.4	0.4	0.4	0.4	0.4
	Coating amount	g/m²	14	14	14	14	14	14
	Oken smoothness on non-coated surface	Second	8	8	4	4	13	8
	Arithmetic average roughness (Ra) on non-coated surface	µm	4.2	4.2	4.0	3.7	2.9	4.2
Heat-sealable paper	Ten-point average roughness (RzJIS) on non-coated surface	µm	14.9	14.9	13.8	13.4	10.4	14.9
Heat-sealable paper	Basis weight	g/m²	114	114	102	102	114	114
	Thickness	µm	164	164	149	149	169	164
	Heat sealing peel strength	N/15mm	6.5	7.8	7.3	8.9	10.1	8.5
	Blocking resistance	-	A	A	A	A	c	c

(Notes of Tables)

S12: LX407S12 available from Zeon Corporation
SBR: Styrene-butadiene copolymer
SR-110: Nalstar SR-110 available from NIPPON A&L INC.

It is found from Tables 1-1 and 1-2 that the heat-sealable paper, which includes a heat-sealable layer on one surface of a paper substrate, wherein the heat-sealable layer contains a water-dispersible resin and a wetting agent, the water-dispersible resin contains a water-dispersible resin having a glass transition temperature of 0°C or more, a content of the wetting agent is 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin, and a surface roughness (RzJIS) on the non-coated surface is 12.0 µm or more, is excellent in the heat sealing property and blocking resistance (Examples 1 to 8). In addition, it is found that the heat-sealable paper, in which the water-dispersible resin contains a styrene-butadiene copolymer having a glass transition temperature of 0°C or more and a wetting agent contains an acetylene wetting agent, is more excellent in the heat sealing property (comparison between Example 3 and Examples 5 and 6).
On the other hand, the heat-sealable paper in which the heat-sealable layer contains a water-dispersible resin but contains no wetting agent, and the heat-sealable paper, in which the heat-sealable layer contains a water-dispersible resin and a wetting agent, but the content of the wetting agent is less than 0.04 parts by mass (0.03 parts by mass) with respect to 100 parts by mass of the water-dispersible resin, have poor heat sealing property (Comparative Examples 1 and 2). In addition, the heat-sealable paper, in which the heat-sealable layer contains a water-dispersible resin and a wetting agent but the content of the wetting agent is more than 1.2 parts by mass (1.5 parts by mass) with respect to 100 parts by mass of the water-dispersible resin, has poor blocking resistance (Comparative Example 3). The heat-sealable paper, in which the surface roughness (RzJIS) on the non-coated surface was less than 12.0 µm (10.4 µm), has poor blocking resistance (Comparative Example 4). Moreover, the heat-sealable paper, in which the heat-sealable layer contains a water-dispersible resin and a wetting agent but the glass transition temperature of the water-dispersible resin is less than 0°C (-27°C), has poor blocking resistance (Comparative Example 5).

Claims

Heat-sealable paper comprising a heat-sealable layer on one surface of a paper substrate, wherein
the heat-sealable layer comprises a water-dispersible resin and a wetting agent,

the water-dispersible resin comprises a water-dispersible resin having a glass transition temperature of 0°C or more,

a content of the wetting agent is 0.04 parts by mass or more and 1.2 parts by mass or less with respect to 100 parts by mass of the water-dispersible resin, and

a surface roughness (RzJIS) of a surface opposite to a surface having the heat-sealable layer of the heat-sealable paper is 12.0 µm or more.
The heat-sealable paper according to claim 1, wherein the wetting agent comprises at least one selected from the group consisting of an acetylene wetting agent, an acrylic wetting agent, and a silicone wetting agent.
The heat-sealable paper according to claim 1 or 2, wherein the water-dispersible resin comprises a styrene-butadiene copolymer.
The heat-sealable paper according to any one of claims 1 to 3, wherein the water-dispersible resin comprises a styrene-butadiene copolymer, and the wetting agent comprises an acetylene wetting agent.
The heat-sealable paper according to any one of claims 1 to 4, having a basis weight of 50 g/m² or more and 140 g/m² or less.
The heat-sealable paper according to any one of claims 1 to 5, wherein the paper substrate is extensible paper.
The heat-sealable paper according to any one of claims 1 to 6, wherein a basis weight of the heat-sealable layer is 7 g/m² or more and 21 g/m² or less.
The heat-sealable paper according to any one of claims 1 to 7, wherein, when two such heat-sealable layers are heat-sealed to each other under conditions of 160°C, 0.3 MPa, and 0.5 seconds, a heat sealing peel strength is 6.0 N/15 mm or more.
A packaging bag using the heat-sealable paper according to any one of claims 1 to 8.