JP7704076B2 - Heat-sealed paper and paper products - Google Patents

Description

This disclosure relates to heat sealable paper and paper products.

Plastic materials have been used primarily for packaging containers such as food trays and pillowcase bags. However, due to environmental concerns, there has been research into using paper as an alternative to plastic containers.

International Publication No. 2015/008703

For the manufacture of packaging bodies using paper, materials having extensibility are preferable from the viewpoint of formability. The present inventors have attempted to form food trays using conventional paper such as that described in Patent Document 1, but have found that wrinkles tend to form in the formed parts. In particular, this is insufficient for forming complex three-dimensional shapes such as deep trays.
The present disclosure relates to a heat seal paper that is highly extensible, has sufficient conformability even when molded into complex three-dimensional shapes, is less likely to cause wrinkles in molded areas, and has excellent heat sealability, and a paper product using the heat seal paper.

That is, the present disclosure relates to the following <1> to <12>.
<1> A heat seal paper having one or more heat seal layers on at least one surface of a paper base material,
The heat seal layer contains a water-dispersible resin binder,
The heat seal paper has a longitudinal tensile stiffness ratio of 1.7 kN m/g to 4.0 kN m/g, and a transverse tensile stiffness ratio of 1.4 kN m/g to 2.9 kN m/g, as measured in accordance with ISO/DIS 1924-3;
The heat seal paper has a longitudinal breaking elongation of 5.0% to 10.0%, and a transverse breaking elongation of 5.0% to 10.0%, as measured in accordance with JIS P 8113:2006.
Heat seal paper.
<2> The tensile stiffness ratio in the longitudinal direction is 2.4 kN m/g to 3.9 kN m/g,
The tensile stiffness ratio in the lateral direction is 1.8 kN·m/g to 2.9 kN·m/g.
The heat seal paper according to <1>.
<3> The heat seal paper according to <1> or <2>, wherein the pulp obtained by defibrating the heat seal paper has a length-weighted average fiber length, measured in accordance with ISO 16065-2:2007, of 1.1 mm to 2.0 mm.
<4> The heat sealable paper according to any one of <1> to <3>, having a basis weight of 40 g/m ² to 130 g/m ² .
<5> The longitudinal breaking elongation is 7.0% to 9.7%,
The transverse breaking elongation is 6.5% to 9.5%.
<1> to <4>, wherein the heat seal paper is a paper having a thickness of 100 nm or less.
<6> The paper base material contains pulp,
The pulp contains softwood kraft pulp,
The heat sealable paper according to any one of <1> to <5>, wherein the content of the softwood kraft pulp in the pulp is 25 mass% or more.
<7> The heat seal paper according to any one of <1> to <6>, wherein the heat seal layer further contains a lubricant.
<8> The heat sealable paper according to <7>, wherein the lubricant comprises at least one wax selected from the group consisting of paraffin wax, carnauba wax, and polyolefin wax.
<9> The heat seal paper according to <7> or <8>, wherein the content of the lubricant in the heat seal layer is 1% by mass or more and 5% by mass or less.
<10> The heat sealable paper according to any one of <1> to <9>, wherein the water-dispersible resin binder has a glass transition temperature of 0° C. or higher and 100° C. or lower.
<11> The heat sealable paper according to any one of <1> to <10>, wherein the water-dispersible resin binder contains at least one selected from the group consisting of a styrene-butadiene copolymer, an olefin-fatty acid vinyl ester copolymer, and an olefin-unsaturated carboxylic acid copolymer.
<12> A paper product obtained by using the heat seal paper according to any one of <1> to <11>.

According to the present disclosure, it is possible to provide heat seal paper that is highly extensible, has sufficient conformability even when molded into complex three-dimensional shapes, is less likely to cause wrinkles in the molded portion, and has excellent heat sealability. Furthermore, according to the present disclosure, it is possible to provide heat seal paper that has excellent moldability in automatic packaging.

Schematic diagram of press processing Example of a tray made from heat-sealed paper

In the present disclosure, the description of a numerical range such as "X or more and Y or less" or "X to Y" means a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be arbitrarily combined.
The machine direction is the machine direction (MD) of the paper base material, which is the same as the direction in which the fibers are oriented. The cross direction is the direction perpendicular to the machine direction (CD). The machine direction of the heat seal paper is the direction corresponding to the MD direction of the paper base material, and the cross direction of the heat seal paper is the direction corresponding to the CD direction of the paper base material.
In addition, "excellent moldability in automatic packaging (hereinafter also referred to as automatic packaging moldability)" means that bags can be continuously manufactured by an automatic packaging machine, and the appearance of the obtained bags is good. More specifically, for example, when a packaging bag is automatically manufactured, the occurrence of wrinkles and poor appearance is suppressed, and sticking to the molding machine (blocking) is suppressed, resulting in excellent moldability, and further, deformation of the bag after manufacturing is suppressed, so that the obtained packaging bag has excellent quality and excellent productivity.

Clupak processing is a process that gives paper stretchability by minutely shrinking it on the papermaking machine. Specifically, for example, a Clupak device equipped with an endless thick elastic rubber blanket with nip rolls is installed in a part of the papermaking machine dryer. A wet paper web is introduced into the Clupak device and compressed by the nip rolls and blanket. At this time, the blanket, which has been stretched beforehand, contracts, shrinking the running paper web (creaping), thereby increasing the breaking elongation. The resulting shrinkage is then dried and fixed so that it does not stretch in the subsequent process.

The inventors have found that the above problem can be solved by controlling the heat seal paper to a specific tensile stiffness index and breaking elongation by Clupac treatment when manufacturing the paper base material used for the heat seal paper. The tensile stiffness index indicates the stiffness of the paper, and the breaking elongation indicates how easily the paper stretches. When the heat seal paper has the above specific tensile stiffness index and breaking elongation, it indicates that the heat seal paper has a moderate stiffness and is somewhat easy to stretch. Therefore, the inventors believe that it is possible to obtain heat seal paper that has high stretchability, has sufficient followability even when molded into complex three-dimensional shapes, and is less likely to cause wrinkles in the molded parts.

The heat seal paper must have a longitudinal tensile stiffness ratio of 1.7 kN·m/g to 4.0 kN·m/g, and a transverse tensile stiffness ratio of 1.4 kN·m/g to 2.9 kN·m/g, as measured in accordance with ISO/DIS 1924-3.
If the tensile stiffness ratio is less than the lower limit, too much stress is applied during molding, making the material prone to wrinkles and tears. On the other hand, if the tensile stiffness ratio is more than the upper limit, the pressure required for molding becomes too high, making molding difficult, and if molding is attempted too forcefully, wrinkles and tears are likely to occur.

The tensile stiffness ratio of heat seal paper can be controlled by the manufacturing conditions of the paper base material used, specifically by the speed difference before and after Clupak treatment, adjusting the density by the nip pressure in calendaring, the type of pulp, etc. Methods for increasing tensile stiffness include reducing the speed difference before and after Clupak treatment, increasing the density by increasing the nip pressure in calendaring, and increasing the fiber length of the pulp. On the other hand, methods for decreasing tensile stiffness include increasing the speed difference before and after Clupak treatment, decreasing the density by decreasing the nip pressure in calendaring, and decreasing the fiber length of the pulp.

The tensile stiffness index in the longitudinal direction of the heat seal paper is preferably 2.4 kN·m/g to 3.9 kN·m/g, more preferably 2.6 kN·m/g to 3.8 kN·m/g, and even more preferably 2.9 kN·m/g to 3.7 kN·m/g.
The tensile stiffness index in the lateral direction of the heat seal paper is preferably 1.8 kN·m/g to 2.9 kN·m/g, more preferably 2.0 kN·m/g to 2.8 kN·m/g, and even more preferably 2.3 kN·m/g to 2.7 kN·m/g.

The ratio of the longitudinal tensile stiffness ratio of the heat seal paper to the transverse tensile stiffness ratio (longitudinal/transverse) is preferably 1.10 or more, more preferably 1.20 or more, and even more preferably 1.22 or more. On the other hand, the upper limit is preferably 1.50 or less, more preferably 1.40 or less, and even more preferably 1.35 or less.

The heat seal paper must have a breaking elongation in the machine direction of 5.0% to 10.0%, and a breaking elongation in the cross direction of 5.0% to 10.0%, as measured in accordance with JIS P 8113:2006.
If the longitudinal and transverse breaking elongations of the heat seal paper are less than the lower limit, the paper will not stretch enough during forming, making it difficult to form. If you try to form it forcibly, it will tear. It will also reduce formability in automatic packaging. On the other hand, if the breaking elongation exceeds the upper limit, the paper will be able to be formed because of the large elongation, but it will be more likely to move and wrinkle, which will cause it to tear.

The breaking elongation of heat seal paper can be controlled by the manufacturing conditions of the paper base material used, specifically, by the basis weight, the speed difference before and after Clupac treatment, the nip pressure during Clupac treatment, etc. Methods for increasing the breaking elongation include increasing the basis weight, increasing the speed difference before and after Clupac treatment, and decreasing the nip pressure during Clupac treatment. On the other hand, methods for decreasing the breaking elongation include decreasing the basis weight, decreasing the speed difference before and after Clupac treatment, and increasing the nip pressure during Clupac treatment.

The longitudinal breaking elongation of the heat seal paper is preferably 6.0% or more, more preferably 7.0% or more, and even more preferably 8.0% or more. The upper limit of the longitudinal breaking elongation is preferably 9.7% or less, more preferably 9.0% or less. For example, it may be 6.0% to 9.7%, 7.0% to 9.7%, or 8.0% to 9.0%.
The lateral breaking elongation of the heat seal paper is preferably 6.0% or more, more preferably 6.5% or more, and even more preferably 7.5% or more. The upper limit of the lateral breaking elongation is preferably 9.5% or less, more preferably 8.5% or less. For example, it may be 6.0% to 9.5%, 6.5% to 9.5%, or 7.5% to 8.5%.

The ratio of the longitudinal breaking elongation of the heat seal paper to the transverse breaking elongation (longitudinal/transverse) is preferably 1.01 or more, more preferably 1.02 or more, and even more preferably 1.05 or more. On the other hand, the upper limit is preferably 1.30 or less, more preferably 1.20 or less, and even more preferably 1.12 or less.

The pulp obtained by disintegrating the heat seal paper preferably has a length-weighted average fiber length, measured in accordance with ISO 16065-2:2007, of 1.1 mm to 2.0 mm, more preferably 1.2 mm to 1.9 mm, and even more preferably 1.3 mm to 1.8 mm. If the length-weighted average fiber length is equal to or greater than the lower limit, the strength is high and tearing during molding is less likely to occur. On the other hand, if the length-weighted average fiber length is equal to or less than the upper limit, the strength is appropriately high and wrinkles during molding can be further suppressed. Therefore, within the above numerical range, moldability can be further improved. The length-weighted average fiber length of the pulp can be controlled by the type of pulp used, etc.

The basis weight of the heat seal paper is preferably 40 g/m ² to 130 g/m ² , more preferably 70 g/m ² to 120 g/m ² , and even more preferably 80 g/m ² to 100 g/m ^2. When the basis weight is equal to or greater than the lower limit, the strength is high and tearing during molding can be more effectively prevented. On the other hand, when the basis weight is equal to or less than the upper limit, the strength is appropriately high and wrinkles during molding can be more effectively prevented. Therefore, within the above numerical range, moldability can be improved.

The thickness of the heat seal paper is preferably 50 μm to 300 μm, more preferably 60 μm to 200 μm, even more preferably 70 μm to 150 μm, and even more preferably 100 μm to 140 μm.

The density of the heat seal paper is preferably 0.40 g/m ³ to 1.10 g/m ³ , more preferably 0.50 g/m ³ to 1.00 g/m ³ , even more preferably 0.60 g/m ³ to 0.90 g/m ³ , and even more preferably 0.70 g/m ³ to 0.80 μmg/m ³ .

[Paper base material]
The basis weight of the paper base material used for the heat seal paper is preferably 30 g/m ² to 120 g/m ² , more preferably 60 g/m ² to 110 g/m ² , and even more preferably 70 g/m ² to 90 g/m ^2. When the basis weight is equal to or greater than the lower limit, the strength is high and tearing during molding can be more effectively prevented. On the other hand, when the basis weight is equal to or less than the upper limit, the strength is appropriately high and wrinkles during molding can be more effectively prevented. Therefore, within the above numerical range, moldability can be improved.

The thickness of the paper substrate is preferably 50 μm to 300 μm, more preferably 60 μm to 200 μm, even more preferably 70 μm to 150 μm, and even more preferably 100 μm to 140 μm.

The density of the paper base material is preferably 0.30 g/m ³ to 1.00 g/m ³ , more preferably 0.40 g/m ³ to 0.90 g/m ³ , even more preferably 0.50 g/m ³ to 0.80 g/m ³ , and even more preferably 0.60 g/m ³ to 0.70 μmg/m ³ .

The tensile stiffness index in the machine direction of the paper substrate, measured in accordance with ISO/DIS 1924-3, is preferably 1.9 kN·m/g to 4.0 kN·m/g, more preferably 2.0 kN·m/g to 3.9 kN·m/g, even more preferably 3.0 kN·m/g to 3.9 kN·m/g, and even more preferably 3.1 kN·m/g to 3.7 kN·m/g.
The tensile stiffness ratio of the paper base material in the transverse direction is preferably 1.5 kN·m/g to 3.0 kN·m/g, more preferably 2.0 kN·m/g to 2.9 kN·m/g, and even more preferably 2.3 kN·m/g to 2.8 kN·m/g. The ratio of the tensile stiffness ratio of the paper base material in the longitudinal direction to the tensile stiffness ratio in the transverse direction (longitudinal direction/transverse direction) is preferably 1.10 to 1.50, more preferably 1.20 to 1.40, and even more preferably 1.25 to 1.35.
By satisfying the above range, the tensile stiffness index of the heat seal paper can be easily adjusted to the desired range, which is preferable.

The breaking elongation in the machine direction of the paper base material, measured in accordance with JIS P 8113:2006, is preferably 5.0% to 10.0%, more preferably 7.0% to 9.7%, and even more preferably 8.0% to 9.0%.
The breaking elongation in the transverse direction of the paper substrate is preferably 4.5 to 10.0%, more preferably 5.0% to 10.0%, even more preferably 6.5% to 9.5%, and even more preferably 7.5% to 8.5%.
The ratio of the breaking elongation in the machine direction to the breaking elongation in the cross direction of the paper base material (machine direction/cross direction) is preferably 1.01 to 1.30, more preferably 1.03 to 1.20, and even more preferably 1.05 to 1.12.
By satisfying the above range, it becomes easier to adjust the breaking elongation of the heat seal paper to a desired range, which is preferable.

The length-weighted average fiber length of the pulp obtained by disintegrating the paper base material, measured in accordance with ISO 16065-2:2007, is preferably 1.1 mm to 2.0 mm, more preferably 1.2 mm to 1.9 mm, and even more preferably 1.3 mm to 1.8 mm.

Next, materials that can be used for the paper base material will be described. The paper base material contains, for example, pulp.
Pulps constituting the paper base material include hardwood kraft pulps such as hardwood unbleached kraft pulp (LUKP) and hardwood bleached kraft pulp (LBKP); softwood kraft pulps such as softwood unbleached kraft pulp (NUKP) and softwood bleached kraft pulp (NBKP); mechanical pulps such as groundwood pulp (GP), pressurized groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), and chemi-ground pulp (CGP); recycled paper pulp;
Examples of the pulp include non-wood fiber pulp such as kenaf, bagasse, bamboo, cotton, etc., and synthetic pulp. These pulps may be used alone or in combination of two or more kinds.

The pulp preferably contains softwood kraft pulp, more preferably contains hardwood kraft pulp and softwood kraft pulp, and even more preferably contains hardwood unbleached kraft pulp and softwood unbleached kraft pulp.

The hardwood kraft pulp content in the pulp is preferably 0% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and even more preferably 13% by mass or more. On the other hand, the upper limit is preferably 75% by mass or less, more preferably 65% by mass or less, even more preferably 60% by mass or less, and even more preferably 57% by mass or less.

The content of softwood kraft pulp in the pulp is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 43% by mass or more. On the other hand, the upper limit is preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 87% by mass or less.

The degree of beating of the pulp is not particularly limited, but the Canadian standard freeness (CSF) is preferably 200 to 800 mL, and more preferably 450 to 700 mL. CSF is measured in accordance with JIS P 8121-2:2012 "Pulp - Freeness test method - Part 2: Canadian standard freeness method."

Additives may be used in the paper base material as necessary. Examples of additives include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents (polyacrylamide, starch, etc.), wet strength agents (polyamide polyamine epichlorohydrin resin, melamine-formaldehyde resin, urea-formaldehyde resin), internal sizing agents (rosin-based, alkyl ketene dimer, etc.), drainage retention improvers (polyacrylamide resin), defoamers, fillers (calcium carbonate, talc, etc.), dyes, etc. These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited and may be within the range commonly used.

[Method of manufacturing paper base material]
An example of a method for producing a paper base material is a method in which a stock containing pulp is made and Clupak treatment is performed during the papermaking process. The stock may further contain additives as necessary. Examples of additives include the additives described above. The stock can be prepared by adding additives to a pulp slurry as necessary. The pulp slurry can be obtained by beating pulp in the presence of water. The pulp beating method and beating device are not particularly limited, and any known beating method and beating device can be used.

The solids concentration of the pulp slurry during beating is not particularly limited, but is preferably about 5 to 40% by mass, and more preferably about 10 to 30% by mass. The pulp content in the paper stock or paper base material is also not particularly limited, and may be within a range that is normally used. For example, it is preferably 60% by mass or more and 100% by mass or less, and more preferably 80% by mass or more and less than 100% by mass, based on the total mass of the paper stock (solids) or paper base material.

In making paper substrates, a known wet paper machine can be appropriately selected and used. Examples of paper machines include Fourdrinier paper machines, gap former paper machines, cylinder paper machines, and short wire paper machines. The Clupak treatment can be carried out by providing a Clupak device capable of carrying out the Clupak treatment in these paper machines. For example, the Clupak treatment can be carried out after papermaking of paper stock and dehydrating it by calendaring.

A known Clupak device can be used. For example, a Clupak device equipped with a nip roll and an endless thick elastic rubber blanket can be mentioned. As described above, in the Clupak process, the paper web is introduced between the nip roll and the blanket, and when the paper web is compressed by the nip roll and the blanket, the blanket, which has been stretched beforehand, is contracted to shrink the paper web and impart a crepe. The Clupak device is usually installed as part of the dryer device of a papermaking machine, and after creping, the paper is dried and fixed. In this manner, a paper base material can be obtained.

In papermaking using the Clupak device, the tensile stiffness index and breaking elongation can be controlled by the difference in papermaking speed before and after the Clupak treatment and the pressure of the nip rolls.
The papermaking speed is not particularly limited, but may be controlled, for example, within the range of preferably 200 to 1000 m/min, more preferably 300 to 800 m/min, and further preferably 400 to 700 m/min. The nip pressure between the nip roll and the blanket during the Clupac treatment is also not particularly limited. For example, it may be appropriately controlled within the range of preferably 5 kN/m to 50 kN/m, and more preferably 10 kN/m to 25 kN/m.
The speed difference before and after the Clupak treatment is not particularly limited, and may be controlled so as to obtain the desired tensile stiffness index and breaking elongation depending on the basis weight and pulp material. It is preferably -45.0% to -10.0%, more preferably -40.0% to -15.0%. Here, the minus sign "-" indicates that the speed after the Clupak treatment is slow.

The nip pressure in the calendar treatment is not particularly limited, and may be controlled to obtain the desired specific tensile stiffness depending on the basis weight, pulp material, speed difference before and after Clupak treatment, etc. It is preferably 100 kN/m to 200 kN/m, and more preferably 130 kN/m to 170 kN/m.

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

(Water-dispersible resin binder)
The heat seal layer contains a water-dispersible resin binder. The water-dispersible resin binder is a resin binder that is not water-soluble (specifically, has a solubility of 10 g/L or less in water at 25° C.) but is finely dispersed in water, such as an emulsion or suspension. By applying a water-based coating to the heat seal layer using the water-dispersible resin binder, a heat seal paper that has excellent redisintegration properties and can be recycled as paper can be obtained. In addition, if the water-dispersible resin binder also falls under the category of the following lubricants, it is classified as a lubricant.

The water-dispersible resin binder is not particularly limited as long as it exhibits the effects of the present invention. Examples of the water-dispersible resin binder include polyolefin resins (polyethylene, polypropylene, etc.), vinyl chloride resins, styrene resins, 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, etc. Examples of the resin include polybutene-1 resin, polybutene-1 resin, vinylidene fluoride resin, vinyl fluoride resin, fluorine resin, polycarbonate resin, polyamide resin, acetal resin, polyphenylene oxide resin, polyester resin (polyethylene terephthalate, polybutylene terephthalate, etc.), polyphenylene sulfide resin, polyimide resin, polysulfone resin, polyethersulfone resin, polyarylate resin, olefin-fatty acid vinyl ester copolymer, olefin-unsaturated carboxylic acid copolymer, and modified products thereof. These may be used alone or in combination of two or more.
Among these, at least one selected from the group consisting of styrene-butadiene copolymers, olefin-fatty acid vinyl ester copolymers, and olefin-unsaturated carboxylic acid copolymers is preferred, and at least one selected from the group consisting of styrene-butadiene copolymers and olefin-unsaturated carboxylic acid copolymers is more preferred.
Furthermore, from the viewpoint of increasing the heat seal peel strength, an olefin-unsaturated carboxylic acid copolymer and an olefin-fatty acid vinyl ester copolymer are more preferable, and from the viewpoints of availability, cost and recyclability, a styrene-butadiene copolymer is more preferable.

Examples of the olefin-unsaturated carboxylic acid copolymer include an ethylene-(meth)acrylic acid copolymer, an ethylene-(meth)acrylic acid alkyl ester copolymer, etc. Among these, an ethylene-(meth)acrylic acid copolymer is preferred, and an ethylene-acrylic acid copolymer is more preferred.
From the viewpoint of increasing the heat seal peel strength, the olefin-fatty acid vinyl ester copolymer is preferably an ethylene-vinyl acetate copolymer.
Therefore, the water-dispersible resin binder contained in the heat seal layer is preferably at least one selected from the group consisting of a styrene-butadiene copolymer, an ethylene-vinyl acetate copolymer, and an ethylene-(meth)acrylic acid copolymer, and more preferably at least one selected from the group consisting of a styrene-butadiene copolymer and an ethylene-(meth)acrylic acid copolymer. The olefin-unsaturated carboxylic acid copolymer may be an ionomer.

The styrene-butadiene copolymer may be either a synthetic product or a commercially available product. Examples of commercially available products include Nipol Latex LX407G51, LX407S10, LX407S12, LX410, LX415M, LX416, LX430, LX433C, and 2507H manufactured by Nippon Zeon Co., Ltd., Nalstar SR-101, SR-102, SR-103, SR-115, and SR-153 manufactured by Nippon A&L Co., Ltd., and Styrene-butadiene Latex 0602 and 0597C manufactured by JSR Corporation.

As the ethylene-(meth)acrylic acid copolymer, either a synthetic product or a commercially available product may be used. Commercially available products include MP498345N, MP4983R, MP4990R, and MFHS1279 manufactured by Michaelman Japan LLC, ZAIXXEN (registered trademark) A and ZAIXXEN (registered trademark) AC manufactured by Sumitomo Seika Chemicals Co., Ltd., and the Chemipearl S series manufactured by Mitsui Chemicals, Inc.

The glass transition temperature of the water-dispersible resin binder is preferably 0° C. or higher, more preferably 10° C. or higher, and even more preferably 15° C. or higher. By using a water-dispersible resin binder having a glass transition temperature equal to or higher than the above lower limit, the occurrence of blocking can be suppressed. From the viewpoint of heat sealability, the glass transition temperature is preferably 100° C. or lower, more preferably 80° C. or lower, even more preferably 60° C. or lower, and even more preferably 50° C. or lower.
The glass transition temperature of the water-dispersible resin binder is measured by a differential scanning calorimeter in accordance with JIS K 7121:1987.

The content of the water-dispersible resin binder in the heat seal layer is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more, and may be 100% by mass or less, preferably 99% by mass or less, more preferably 98% by mass or less. Within the above range, a heat seal paper having high heat seal peel strength can be obtained.

That is, according to one embodiment of the present invention, the content of at least one selected from the group consisting of styrene-butadiene copolymer, olefin-fatty acid vinyl ester copolymer, and olefin-unsaturated carboxylic acid copolymer (preferably ethylene-(meth)acrylic acid copolymer) in the heat seal layer is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass or less, preferably 99% by mass or less, and more preferably 98% by mass or less.

(Lubricant)
From the viewpoint of imparting slipperiness to the heat seal paper and suppressing blocking, the heat seal layer preferably contains a lubricant in addition to the water-dispersible resin binder. A lubricant is a substance that can reduce the friction coefficient of the heat seal layer surface by being blended in the heat seal layer.

The lubricant is not particularly limited, and for example, wax, metal soap, fatty acid ester, etc. can be used. The lubricant may be used alone or in combination of two or more. Examples of waxes include natural waxes such as animal or plant-derived waxes (e.g., beeswax, carnauba wax, etc.), mineral waxes (e.g., microcrystalline wax, etc.), and petroleum wax; and synthetic waxes such as polyolefin wax, paraffin wax, and polyester wax. Examples of metal soaps include calcium stearate, sodium stearate, zinc stearate, aluminum stearate, magnesium stearate, fatty acid sodium soap, potassium oleate soap, castor oil potassium soap, and complexes thereof. Among the above lubricants, paraffin wax, carnauba wax, and polyolefin wax are preferred because they have a relatively low melting point, the wax component is easily formed on the coating layer surface, and have an excellent blocking suppression effect. That is, the lubricant is preferably at least one selected from the group consisting of paraffin wax, carnauba wax, and polyolefin wax.
As the carnauba wax, either a synthetic product or a commercially available product may be used, and an example of a commercially available product may be Cellosol 524 manufactured by Chukyo Yushi Co., Ltd. As the paraffin wax, either a synthetic product or a commercially available product may be used, and an example of a commercially available product may be Hydrin L-700 manufactured by Chukyo Yushi Co., Ltd. As the polyethylene wax, either a synthetic product or a commercially available product may be used, and an example of a commercially available product may be Aquacer 531 manufactured by BYK Corporation.

When the heat seal layer contains a lubricant, the content of the lubricant is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the water-dispersible resin binder, and is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less.

When the heat seal layer contains a lubricant, the content of the lubricant in the heat seal layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 1% by mass or more, and preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less.

In this embodiment, the heat seal layer contains a water-dispersible resin binder, and preferably contains a lubricant in addition to the water-dispersible resin binder. In addition to the water-dispersible resin binder and, if necessary, the lubricant, the heat seal layer may also contain a pigment.

(Pigment)
In this embodiment, the heat seal layer may contain a pigment in addition to the water-dispersible resin binder. By containing the pigment, the problem of the heat seal layer coating surface sticking to the back surface of the heat seal paper and causing peeling (blocking) during the production of the heat seal paper is suppressed, and a heat seal paper with excellent blocking resistance can be obtained.

The pigment is not particularly limited, and examples include various pigments used in conventional pigment coating layers. The pigment may be used alone or in combination of two or more. From the viewpoint of heat seal peel strength and blocking resistance, the pigment preferably has an aspect ratio of 20 or more. The aspect ratio of the pigment is more preferably 25 or more, even more preferably 30 or more, and particularly preferably 60 or more, and from the viewpoint of availability and smoothness of the heat seal layer surface, it is preferably 10,000 or less, more preferably 1,000 or less, and even more preferably 300 or less. The aspect ratio of the pigment means the major axis/minor axis, and may be measured by the method described below.

The pigment is preferably a layered inorganic compound with an aspect ratio of 20 or more. The layered inorganic compound has a flat plate-like shape. If the pigment is flat, the pigment is prevented from protruding from the surface of the heat seal layer, and a heat seal layer with excellent blocking resistance can be obtained while maintaining heat sealability.

The length (average particle size) of the pigment is preferably 0.1 μm or more and 100 μm or less. If the length is 0.1 μm or more, the pigment is likely to be aligned parallel to the paper substrate. Also, if the length is 100 μm or less, there is less concern that part of the pigment will protrude from the heat seal layer. The length of the pigment is more preferably 0.3 μm or more, even more preferably 0.5 μm or more, particularly preferably 1.0 μm or more, and more preferably 30 μm or less, even more preferably 20 μm or less, particularly preferably 15 μm or less.

The length of the pigment contained in the heat seal layer is determined as follows. A magnified photograph is taken of the cross section of the heat seal layer using an electron microscope. The magnification is set so that approximately 20 to 30 pigment particles are contained within the image. The length of each pigment within the image is measured. The average of the lengths obtained is then calculated to determine the length of the pigment. The length of the pigment is sometimes expressed as particle diameter.

The pigment preferably has a thickness of 200 nm or less. The thickness of the pigment is more preferably 100 nm or less, even more preferably 80 nm or less, even more preferably 50 nm or less, and particularly preferably 30 nm or less. Also, it is preferably 5 nm or more, more preferably 10 nm or more. The smaller the average thickness of the pigment, the higher the heat seal peel strength that can be obtained. Here, the thickness of the pigment contained in the heat seal layer is determined as follows. A magnified photograph is taken of the cross section of the heat seal layer using an electron microscope. At this time, the magnification should be such that about 20 to 30 pigments are contained within the screen. The thickness of each pigment within the screen is measured. The average value of the obtained thicknesses is then calculated to be the thickness of the pigment.

Specific examples of pigments 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 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, silicates, colloidal silica, hollow or solid organic pigments, plastic pigments, binder pigments, plastic beads, and microcapsules.

Specific examples of mica include synthetic mica (e.g., swellable synthetic mica), white mica (muscovite), sericite (sericite), phlocopite, biotite, fluorphlogopite (artificial mica), red mica, soda mica, vanadium mica, illite, chin mica, paragonite, and brittle mica. Specific examples of bentonite include montmorillonite.

Specific examples of kaolin include various types of kaolin, such as kaolin, calcined kaolin, structured kaolin, and delaminated kaolin.

Among these, from the viewpoints of heat seal peel strength, blocking resistance, and economy, pigments with an aspect ratio of 20 or more are preferred, and it is more preferred to contain one or more of mica, bentonite, kaolin, and talc, with kaolin being even more preferred.

When the heat seal layer contains a pigment, the amount of pigment is, from the viewpoints of blocking resistance and recyclability, preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more, per 100 parts by mass of the water-dispersible resin binder; on the other hand, from the viewpoints of heat sealability and hot tackiness, it is preferably 200 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 30 parts by mass or less.

When the heat seal layer contains a pigment, the content of the pigment in the heat seal layer is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and even more preferably 8% by mass or more, from the viewpoints of blocking resistance and recyclability, and is preferably 70% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoints of heat sealability and hot tackiness.

(Other ingredients)
The heat seal layer may contain other components in addition to the water-dispersible resin binder and, if necessary, a lubricant and/or a pigment, such as a silane coupling agent, a defoaming agent, a viscosity modifier, a leveling agent such as a surfactant or alcohol, and a colorant such as a coloring dye.

The coating amount (basis weight) of the heat seal layer is not particularly limited, but from the viewpoint of obtaining a packaging bag that is difficult to tear and can be easily opened when opened, it is preferably 3 g/ ^m2 , more preferably 5 g/m2 or ^more , even more preferably 8 g/ ^m2 or more, and preferably 30 g/m2 or ^less , more preferably 20 g/m2 or ^less , even more preferably 15 g/ ^m2 or less.

<Physical properties of heat seal paper>
(Heat seal peel strength)
The heat seal peel strength of the heat seal paper is preferably 2.0 N/15 mm or more, more preferably 3.0 N/15 mm or more, even more preferably 4.0 N/15 mm or more, even more preferably 5.0 N/15 mm or more, and 10 N/15 mm or less, more preferably 9.0 N/15 mm or less, even more preferably 8.0 N/15 mm or less. Furthermore, from the viewpoint of automatic packaging moldability, it is preferably 5.2 N/15 mm or more. The peel strength of the heat seal layer is the peel strength when the heat seal layers are heat sealed together under conditions of 150° C., 0.2 MPa, and 1 second, and is specifically a value measured by the method described in the examples below.
The peel strength can be adjusted by selecting the glass transition temperature and type of the water-dispersible resin binder and the coating amount. For example, by setting the glass transition temperature of the water-dispersible resin binder to 100° C. or less, the resin melts under the specified heat sealing conditions and the heat seal layers are well bonded to each other, so that the desired peel strength can be secured.

(Surface smoothness)
From the viewpoint of improving the heat seal peel strength, the Oken smoothness of the heat seal layer surface of the heat seal paper of this embodiment is preferably 30 seconds or more, more preferably 40 seconds or more, even more preferably 50 seconds or more, and even more preferably 60 seconds or more, and although there is no particular upper limit, it is preferably 500 seconds or less, more preferably 300 seconds or less, and even more preferably 100 seconds or less.
The heat seal layer may be provided on the W side (wire side) or F side (felt side) of the paper substrate, and is not particularly limited. Here, the W side (wire side) is the side that contacts the wire when the paper web is formed, and the opposite side is the F side (felt side).
Furthermore, the Oken smoothness of the side opposite the heat seal layer (for example, the surface of the paper base material when the heat seal layer is provided on only one side of the paper base material and the other side is exposed paper base material) is preferably 3 seconds or more, more preferably 5 seconds or more, from the viewpoint of improving printability, and although there is no particular upper limit, it is preferably 1000 seconds or less, more preferably 300 seconds or less, and even more preferably 100 seconds or less.
The Oken smoothness is measured in accordance with JIS P8155:2010.
The Oken smoothness of the heat seal layer surface and the opposite surface of the heat seal paper can be adjusted within the above range by a supercalendering treatment described later or the like.

The basis weight of the heat seal paper is preferably 40 g/m ² to 130 g/m ² , more preferably 70 g/m ² to 120 g/m ² , and even more preferably 80 g/m ² to 120 g/m ^2. When the basis weight is equal to or greater than the lower limit, the strength is high and tearing during molding can be more effectively prevented. On the other hand, when the basis weight is equal to or less than the upper limit, the strength is appropriately high and wrinkles during molding can be more effectively prevented. Therefore, within the above numerical range, moldability can be improved.

The thickness of the heat seal paper is preferably 60 μm to 350 μm, more preferably 70 μm to 250 μm, even more preferably 80 μm to 200 μm, and even more preferably 100 μm to 150 μm.

The density of the heat seal paper is preferably 0.40 g/m ³ to 1.00 g/m ³ , more preferably 0.60 g/m ³ to 0.90 g/m ³ , and even more preferably 0.70 g/m ³ to 0.85 g/m ³ .

<Method of manufacturing heat seal paper>
The method for producing the heat seal paper of the present embodiment includes a coating step of coating at least one side of the paper substrate obtained as described above with a heat seal layer. The heat seal layer coating liquid (heat seal layer paint) may be applied two or more times.

When forming multiple heat seal layers on a paper substrate, the above method of forming heat seal layers sequentially is preferred, but is not limited to this, and a simultaneous multi-layer coating method may also be used. The simultaneous multi-layer coating method is a method in which multiple types of coating liquids are ejected separately from a slit-shaped nozzle to form a liquid laminate, which is then coated onto the paper substrate to simultaneously form multiple heat seal layers.

There are no particular limitations on the coating equipment used to apply the heat seal layer coating liquid to the paper substrate, and any known equipment may be used. Examples of coating equipment include a blade coater, a bar coater, an air knife coater, a slit die coater, a gravure coater, a microgravure coater, a roll coater, a size press, a gate roll coater, and a shim sizer.

The drying equipment for drying the heat seal layer is not particularly limited, and known equipment can be used. Examples of drying equipment include hot air dryers, infrared dryers, gas burners, and hot plates. The drying temperature can be set appropriately taking into account the drying time, etc.

The solvent for the heat seal layer coating liquid is not particularly limited, and water or an organic solvent such as ethanol, isopropyl alcohol, methyl ethyl ketone, or toluene can be used. Among these, water is preferred as the dispersion medium for the heat seal layer coating liquid from the viewpoint of not causing problems with volatile organic solvents. In other words, the heat seal layer coating liquid is preferably an aqueous composition for the heat seal layer.

The solid content (solid content concentration) of the heat seal layer coating liquid is not particularly limited and may be appropriately selected from the viewpoints of coatability and ease of drying, but is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and is preferably 80% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and even more preferably 40% by mass or less.

The preferred range of the coating weight (after drying) of the heat seal layer is as described above. The heat seal layer may be one layer or two or more layers. When the heat seal layer is two or more layers, the above coating weight represents the total coating weight.

It is also preferable to carry out a supercalendering process after coating and drying the heat seal layer. Here, the supercalendering process is a process in which the paper or the like to be treated is passed between metal rolls or between a metal roll and an elastic roll, which are installed independently of the papermaking process, and heated, pressed, etc. The supercalendering process may be carried out in one stage or in multiple stages, and is not particularly limited.
The supercalendering treatment is preferable because it improves the smoothness of the surface of the heat seal layer, which in turn leads to improved heat seal peel strength and hot tack properties (difficulty in peeling immediately after heat sealing).
It is also preferable because it improves the smoothness of the side opposite the heat seal layer (for example, the surface of the paper base when a heat seal layer is provided on only one side of the paper base and the paper base is exposed on the other side), thereby improving printability.
Furthermore, supercalendering tends to increase the density of the heat seal paper, and as mentioned above, improves the surface smoothness, which is preferable because it improves the feed of the heat seal paper in the packaging machine during bag production and improves processing suitability.

The linear pressure in the supercalendering is preferably 10 kg/cm or more, more preferably 30 kg/cm or more, and even more preferably 50 kg/cm or more, and is preferably 1000 kg/cm or less, more preferably 500 kg/cm or less, and even more preferably 200 kg/cm or less. However, the linear pressure may be appropriately changed depending on the desired smoothness and density.
When heating is performed in the supercalendering process, the heating temperature is not particularly limited, but from the viewpoint of enhancing the effect of the treatment while preventing thermal deterioration of the paper base material or the heat seal layer and sticking of the heat seal layer, the heating temperature is preferably 20° C. or higher, more preferably 30° C. or higher, even more preferably 35° C. or higher, and is preferably 80° C. or lower, more preferably 70° C. or lower, even more preferably 60° C. or lower.

The use of the obtained heat seal paper is not particularly limited, and by forming it into an appropriate molded product, it can be used for paper products such as packaging materials such as wrapping paper, packaging bags, and packaging containers, and various containers such as cups and trays. For example, it can be molded into paper containers such as paper plates, paper cups, and paper trays, and bags for horizontal pillow packaging, vertical pillow packaging, three-sided seal packaging, four-sided seal packaging, bag-feed filling packaging, tube packaging, and stick packaging. The molding method is not particularly limited, and known methods can be used. For example, it can be molded into the desired shape by press molding.

The measurement methods for each physical property are described below.
<Tensile strength>
The tensile stiffness ratios in the longitudinal and transverse directions of the paper base material and the heat seal paper are determined in accordance with ISO/DIS
The measurement is performed in accordance with 1924-3. Specifically, the procedure is as follows. A sample with a test piece length of 150 mm and a test piece width of 15 mm is prepared in both the longitudinal and transverse directions, and the sample is conditioned for one day in an environment of 23±5°C and 50±10% Rh. Then, in that environment, a tensile tester (model RTC-1210A, manufactured by A&D Co., Ltd.) is used to set the sample so that the chuck distance is 100 mm, and the test is performed at a speed of 100 mm/min.

<Breaking elongation>
The longitudinal and transverse breaking elongations of the paper substrate and the heat seal paper are measured in accordance with JIS P 8113:2006 (Testing methods for tensile properties of paper and paperboard).
Specifically, a paper substrate or heat seal paper that has been left to stand for at least one day in an environment of 23±5°C and 50±10% humidity as a temperature and humidity control treatment is cut into a sample having a width of 15 mm and a length of 150 mm. The sample is attached to a tensile tester (model RTC-1210A, manufactured by A&D Co., Ltd.) with a chuck distance of 100 mm, and a tensile test is performed at a speed of 20 mm/min to measure the breaking elongation in each of the MD (longitudinal direction) and CD (transverse direction).

<Length-weighted average fiber length of pulp>
The length-weighted average fiber length of the pulp in the paper base material and the heat seal paper is measured in accordance with ISO 16065-2:2007, specifically as follows:
The paper base material or heat seal paper is cut into a 40 cm square, immersed in ion-exchanged water, and the solid content is adjusted to 2% by mass. After immersion for 24 hours, the paper base material or heat seal paper is defibrated for 30 minutes using a standard defibrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) to defibrate the pulp into fibers.
Using the obtained pulp fiber sample, the "length-weighted average fiber length (ISO)" is measured using a fiber length measuring instrument (model FS-5 with UHD base unit, manufactured by Valmet Co., Ltd.). The "length-weighted average fiber length (ISO)" is the length-weighted average fiber length calculated by selecting fibers having a length of 0.2 mm or more and 7.6 mm or less.

<Basic weight>
The basis weight of the paper base material and the heat seal paper is measured in accordance with JIS P 8124:2011.

<Thickness>
The thickness of the paper base material and the heat seal paper (paper thickness) is measured in accordance with JIS P 8118:2014.

<Density>
The density of the paper base material and the heat seal paper is calculated from the thickness and basis weight obtained by the above-mentioned measuring method.

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate 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 shown below. Furthermore, unless otherwise specified, "parts" refers to "parts by mass." Furthermore, the operations of the examples and comparative examples were carried out at room temperature (20-25°C) and normal humidity (40-50% RH) unless otherwise specified.

Example 1
[Manufacturing of paper base material]
Pulp was prepared by using NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood in a ratio (mass ratio) of NUKP:LUKP = 30:70, and beating the slurry to a CSF (Canadian Standard Freeness) of 600 mL at a slurry concentration of 2 mass% at the time of beating.
Using the above pulp, 0.15 parts of a synthetic sizing agent (SPS400, manufactured by Arakawa Chemical Industries, Ltd.), 1.2 parts of aluminum sulfate, 0.65 parts of a polyacrylamide resin (DS4433, manufactured by Seiko PMC Corporation) as a retention agent, and 0.035 parts of nonionic polyacrylamide (Percoll 47, manufactured by Allied Colloids) as a polymer flocculant (retention agent) were added per 100 parts of pulp in terms of solid content to prepare a paper stock.
Using the above-mentioned paper material, paper was made on a wet papermaking machine (Bellform III, manufactured by Mitsubishi Heavy Industries, Ltd.) equipped with an expansion device (manufactured by Clupac) at a papermaking speed of 600 m/min, a reel moisture content of 6.5%, a nip pressure by calendaring of 150 kN/m, a speed difference before and after Clupac treatment of -37.5%, and a nip pressure between the nip roll and blanket during Clupac treatment of 15 kN/m, to obtain a paper base material with a basis weight of 50 g/ ^m2 and a crepe applied to the paper surface. The paper base material was produced in the following order: papermaking, dehydration by calendaring, and Clupac treatment (including drying).

[Preparation of heat seal layer coating material]
A water dispersion of styrene/butadiene copolymer (SBR) (Nipol Latex LX407S12, solids 46%, glass transition temperature 18°C (catalog value)) (98 parts (solids equivalent)) and a paraffin wax emulsion (Hydrin L-700, solids 30%, manufactured by Chukyo Yushi Co., Ltd.) (2 parts (solids equivalent) were mixed, water was added to the mixture so that the solids concentration was 33%, and the mixture was stirred to prepare a heat seal layer coating material (concentration 33%). The styrene/butadiene copolymer had a solubility in water at 25°C of 10 g/L or less.

[Production of heat seal paper]
The obtained heat seal layer coating material was applied to the W surface of the paper substrate to form a heat seal layer using an air knife coater so that the coating amount of the heat seal layer after drying was 10 g/ ^m2 , and then dried with a dryer at 130 to 160° C. Finally, a chilled roll was brought into contact with the coated surface and a cotton roll was brought into contact with the uncoated surface at a linear pressure of 90 kg/cm, and the rolls were heated to 40° C. to perform one-stage supercalendering to obtain a heat seal paper.

Example 2
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced with a basis weight of 80 g/ ^m2 by adjusting the discharge amount of pulp.

Example 3
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced with a basis weight of 100 g/ ^m2 by adjusting the discharge amount of pulp.

Example 4
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the mass ratio of NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood to NUKP:LUKP = 45:55.

Example 5
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the mass ratio of NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood to NUKP:LUKP = 85:15.

Example 6
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the mass ratio of NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood to NUKP:LUKP = 100:0.

Example 7
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by making paper with a speed difference of -18.0% before and after the Clupac treatment.

Example 8
98 parts (solid content equivalent) of a commercially available aqueous dispersion of ethylene-acrylic acid copolymer A (glass transition temperature 45° C.) and 2 parts (solid content equivalent) of a commercially available aqueous dispersion of carnauba wax were mixed, and water was added to the mixture so that the solid content concentration was 35%, followed by stirring to prepare a heat seal layer coating material (concentration 35%). Heat seal layer formation and supercalendering were performed in the same manner as in Example 4, except that the obtained heat seal layer coating material was used, to obtain a heat seal paper.

<Example 9>
Instead of 2 parts of paraffin wax emulsion (solid content equivalent), 2 parts of polyethylene wax emulsion (Aquacer 531, manufactured by BYK Corporation, solid content concentration 45% by mass)
The heat seal layer was formed and the supercalendering treatment was carried out in the same manner as in Example 4, except that the heat seal layer coating material was prepared by adding 100% ethyl alcohol (calculated as solid content) to the heat seal layer coating material, to obtain a heat seal paper.

Example 10
The heat seal layer was formed and the supercalender treatment was carried out in the same manner as in Example 4, except that no paraffin wax emulsion was added, to obtain a heat seal paper.

Example 11
A heat seal layer was formed and a super calendar treatment was carried out in the same manner as in Example 4, except that an aqueous dispersion of an ethylene/vinyl acetate copolymer (Sumikaflex 470HQ, manufactured by Sumika Chemtex Corporation, solid content 55%, glass transition temperature 0°C (catalog value)) was used instead of the aqueous dispersion of a styrene/butadiene copolymer in the heat seal layer paint, and no paraffin wax emulsion was used, to obtain a heat seal paper.

Example 12
A heat seal layer coating material (concentration 33%) was prepared by mixing 98 parts (solid content equivalent) of an aqueous dispersion of a styrene/butadiene copolymer (Nipol Latex LX407S12, manufactured by Nippon Zeon Co., Ltd., solid content 46%, glass transition temperature 18°C (catalog value)) and 2 parts (solid content equivalent) of a carnauba wax emulsion (ML160RPH, manufactured by Michaelman Co., Ltd., solid content concentration 25% by mass), adding water to the mixture and stirring to obtain a heat seal layer coating material (concentration 33%). Except for this, a heat seal layer was formed and a super calendar treatment was performed in the same manner as in Example 4 to obtain a heat seal paper.

<Example 13>
Aqueous dispersion of styrene / butadiene copolymer (manufactured by Nippon Zeon Co., Ltd., Nipol Latex LX407S12, solid content 46%, glass transition temperature 18 ° C. (catalog value)) 88 parts (solid content equivalent), paraffin wax emulsion (manufactured by Chukyo Yushi Co., Ltd., Hydrin L-700, solid content 30%) 2 parts (solid content equivalent), kaolin (Imeris Contour Extreme, average particle size 8 μm, aspect ratio 80 to 100, dispersed in water so as to have a solid content of 50% by mass) 10 parts (solid content equivalent) were mixed, water was added to the solid content concentration of 33%, and the mixture was stirred to prepare a heat seal layer paint (concentration 33%). Except for this, heat seal layer formation and super calendaring were performed in the same manner as in Example 4 to obtain a heat seal paper.

<Example 14>
A heat seal paper was obtained in the same manner as in Example 4, except that the supercalendering treatment was not carried out after the formation of the heat seal layer.

<Comparative Example 1>
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the nip pressure by the calendar to 100 kN/m.

<Comparative Example 2>
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the nip pressure by the calendar to 180 kN/m.

<Comparative Example 3>
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the nip pressure by the calendar to 200 kN/m.

<Comparative Example 4>
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base was produced without the Clupak treatment.

<Comparative Example 5>
A heat seal paper was obtained under the same conditions as in Example 1, except that the paper base material was produced by changing the speed difference before and after the Clupak treatment to -45.0%.

<Comparative Example 6>
A heat seal paper was obtained under the same conditions as in Example 1, except that the nip pressure by the calendar was changed to 100 kN/m and the paper base material was produced without the Clupak treatment.

<Comparative Example 7>
The paper substrate produced in Example 4 was used as is.

<Evaluation>
[Moldability]
The obtained heat seal paper or paper substrate was used to carry out the following evaluations.
The obtained heat seal paper or paper base material was cut out to obtain an A4 blank sheet 3 with the long side in the machine direction (MD). The blank sheet 3 was pressed with a molding die (1 and 2) and a press molding machine (FVT400, manufactured by Wakisaka Engineering Co., Ltd.) at a pressure of 35 kgf/cm.
The trays were pressed under the conditions of ¹⁰⁰ cm2, a press temperature of 150°C, and a press time of 5 seconds as shown in Fig. 1 to form them into the tray shape shown in Fig. 2. The resulting trays were evaluated for the presence or absence of wrinkles and tears according to the following criteria. As shown in Figs. 1 and 2, the edge of the opening of the tray was evaluated as the formed part 4. The higher the value, the better the result.
5: The molded portion has no tears or wrinkles, and the tray is not distorted.
4: The molded portion is not torn or wrinkled, but the tray is distorted.
3: The molded portion is not torn, but wrinkles are formed on one to three of the four sides of the molded portion.
2: The molded portion is not torn, but wrinkles are formed on all four sides of the molded portion.
1: The molded part is torn.

[Heat seal peel strength]
Two sheets of heat seal paper were stacked so that the heat seal layers faced each other, and heat sealed using a heat seal tester (TP-701-B, manufactured by Tester Sangyo) at 150°C, 0.2 MPa, and 1 second. The heat-sealed test piece was left to stand for 4 hours or more in a room at a temperature of 23°C ± 1°C and a humidity of 50% ± 2%. The heat-sealed test piece was then cut to a width of 15 mm and T-peeled at a tensile speed of 300 mm/min using a tensile tester, and the maximum load recorded was taken as the heat seal peel strength. In Table 3, "-" indicates that the test piece was not bonded and could not be measured.

[Automatic packaging formability]
Using a high-speed horizontal pillow packaging machine (αWrapper FW3410, manufactured by Fujikikai Co., Ltd.), bags were continuously made from heat-sealed paper. No contents were put in the bags, and the bags were formed with empty bags. The following judgments were made based on the appearance and operability. Here, "continuous bag making is impossible" refers to a state in which wrinkles are generated, the bags are twisted so that they cannot be made into bags, or the paper is broken. "Poor appearance" refers to the presence of wrinkles, misalignment of the sealed portion, or deformation of the bags.
A: Continuous bag production was possible, and the appearance of the bags was good.
B: Continuous bag production was possible, but there were slight defects in the appearance of the bags.
C: Continuous bag making was impossible.

The physical properties and evaluation results of Examples 1 to 14 and Comparative Examples 1 to 7 are shown in Tables 1 to 3.

1, 2: Molding die, 3: Blank sheet, 4: Molding part

Claims (12)

A heat seal paper having one or more heat seal layers on at least one surface of a paper substrate,
The heat seal layer contains a water-dispersible resin binder,
The heat seal paper has a longitudinal tensile stiffness ratio of 1.7 kN m/g to 4.0 kN m/g, and a transverse tensile stiffness ratio of 1.4 kN m/g to 2.9 kN m/g, as measured in accordance with ISO/DIS 1924-3;
A heat seal paper, the breaking elongation of which in the longitudinal direction is 5.0% to 10.0%, and the breaking elongation of which in the transverse direction is 5.0% to 10.0%, as measured in accordance with JIS P 8113:2006. The longitudinal tensile stiffness ratio is 2.4 kN m/g to 3.9 kN m/g;
The tensile stiffness ratio in the lateral direction is 1.8 kN·m/g to 2.9 kN·m/g.
The heat seal paper according to claim 1. The heat seal paper according to claim 1, wherein the pulp obtained by disintegrating the heat seal paper has a length-weighted average fiber length of 1.1 mm to 2.0 mm as measured in accordance with ISO 16065-2:2007. The heat seal paper according to claim 1, having a basis weight of 40 g/m ² to 130 g/m ² . The longitudinal breaking elongation is 7.0% to 9.7%,
The transverse breaking elongation is 6.5% to 9.5%.
The heat seal paper according to claim 1. The paper base material contains pulp, and the pulp contains softwood kraft pulp.
2. The heat seal paper according to claim 1, wherein the content of said softwood kraft pulp in said pulp is 25% by weight or more. The heat seal paper of claim 1, wherein the heat seal layer further comprises a lubricant. The heat seal paper according to claim 7, wherein the lubricant comprises at least one selected from the group consisting of paraffin wax, carnauba wax, and polyolefin wax. The heat seal paper according to claim 7, wherein the content of the lubricant in the heat seal layer is 1% by mass or more and 5% by mass or less. The heat seal paper according to claim 1, wherein the glass transition temperature of the water-dispersible resin binder is 0°C or higher and 100°C or lower. The heat seal paper according to claim 1, wherein the water-dispersible resin binder contains at least one selected from the group consisting of styrene-butadiene copolymers, olefin-fatty acid vinyl ester copolymers, and olefin-unsaturated carboxylic acid copolymers. A paper product made using the heat seal paper described in any one of claims 1 to 11.

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