JP7392244B1 - Heat seal paper and packaging - Google Patents

Abstract

An object of the present invention is to provide a heat-sealing paper with excellent bag-making properties and a package using this heat-sealing paper. [Solution] The paper base material has a heat seal layer on at least one outermost surface, and the paper base material is a heat seal paper having an elongation at break in the MD direction of 2.0% or more and 5.5% or less. , a package using this heat seal paper. [Selection diagram] None

Description

The present invention relates to heat seal paper and a package using the same.

In recent years, there has been a growing trend to move away from oil and plastics due to environmental issues such as plastic waste and global warming, and the use of resin materials derived from fossil resources and non-biodegradable resin materials in industrial products is increasing. It is desired to reduce the amount as much as possible.
In such a trend, it is desired to reduce the environmental impact of packaging as well. For example, it is possible to reduce the thickness of the packaging material using plastic film, but such thin packaging materials are less easy to handle during the packaging forming process, and are more likely to be damaged at the thermocompression bonding part. This makes it more likely that cracks and tears will occur. Furthermore, although the amount of resin used has decreased, the problem that resin remains semi-permanently without being decomposed when released into the environment remains the same.

Patent Documents 1 and 2 propose the use of heat-seal paper in which a heat-seal layer is laminated on a paper base material as a packaging material. Depending on the type of heat-sealable resin, these are decomposed in the environment, so the environmental load can be significantly reduced. However, heat-seal paper has significantly different physical properties compared to plastic film, so if heat-seal paper is passed through a bag-making machine under the same operating conditions as plastic film, the paper may meander, break, or become unusable. In some cases, problems such as folding, wrinkling, and flexing occur in the packaged product, and the inability to form bags in the desired shape, necessitating optimization of operating conditions such as slowing down the line speed.

Japanese Patent Application Publication No. 2020-163675 JP2021-046234A

An object of the present invention is to provide a heat-seal paper with excellent bag-making properties and a package using this heat-seal paper.

Means for solving the problems of the present invention are as follows.
1. having a paper base material and a heat sealing layer on at least one outermost surface,
A heat seal paper, wherein the paper base material has an elongation at break in the MD direction of 2.0% or more and 5.5% or less.
2. 1. The paper base material has a basis weight of 70 g/m ² or more and 120 g/m ² or less. Heat seal paper as described in .
3. 1. The paper base material has a density of 0.6 g/cm ³ or more and 0.8 g/cm ³ or less. or 2. Heat seal paper as described in .
4. 1. The heat-sealing layer is a coating layer of a water-dispersible resin or a water-soluble resin. or 2. Heat seal paper as described in .
5.1. or 2. A package using the heat seal paper described in .

The heat seal paper of the present invention can be used as a substitute for conventional packaging materials made of resin films. The heat-sealable paper of the present invention can be passed through a conventional bag-making machine used for making plastic film bags to form bags in a desired shape.
Since the heat seal paper of the present invention is mainly made of paper, the amount of resin material used can be significantly reduced.

"Heat seal paper"
Heat seal paper has a paper base material and a heat seal layer on at least one outermost surface.
-Paper base material The paper base material is a base material on which a heat seal layer is formed on at least one surface thereof. The paper base material is a sheet mainly made of pulp, and the base paper is obtained by making paper from paper stock containing pulp, fillers, various auxiliary agents, etc., or it is coated with a sealing layer, an ink-receiving layer, etc. on at least one surface of the base paper. One or more functional layers such as a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, a gas barrier layer, etc. can be used.

The paper base material of the present invention has an elongation at break in the MD direction of 2.0% or more and 5.5% or less. The paper base material of the present invention has excellent bag-making properties and impact resistance because the elongation at break is 2.0% or more and 5.5% or less. If this elongation at break is less than 2.0%, it will be easy to tear when it is made into a package, and it will not be possible to increase the tension when passing through the bag making machine, so it will not be able to be conveyed as specified and cut. Discrepancies in spacing may occur. If this elongation at break exceeds 5.5%, the heat-sealing layer will not be able to follow the elongation of the paper base material, causing minute cracks in the heat-sealing layer, which may reduce the heat-sealing strength. The amount of shrinkage after cutting increases, and wrinkles are particularly likely to occur in the center seal portion. The elongation at break in the MD direction is more preferably 2.5% or more, even more preferably 3% or more, and more preferably 5% or less, and 4.5% or less. is more preferable, and even more preferably 4% or less. The elongation at break of the paper base material is measured in accordance with JIS P8113:2011.

The paper base material of the present invention preferably has a ratio of elongation at break in the CD direction to elongation at break in the MD direction (CD/MD) of 1.0 or more and 2.5 or less. When the elongation at break ratio (CD/MD) is within this range, the elongation at break is well balanced in the longitudinal and lateral directions, making it difficult to tear and improving impact resistance. This ratio of elongation at break (CD/MD) is preferably 2.2 or less, more preferably 1.9 or less. Note that paper tends to stretch in the CD direction because the pulp is oriented in the MD direction, and the elongation at break in the CD direction is larger than the elongation at break in the MD direction.

The paper base material of the present invention preferably has a thickness of 100 μm or more and 160 μm or less. A paper base material has inferior strength compared to a plastic film, but by using a paper base material with a thickness of 100 μm or more and 160 μm or less, it becomes easy to make a package with excellent strength. The thickness of the paper base material is preferably 110 μm or more, more preferably 120 μm or more, and preferably 155 μm or less, more preferably 150 μm or less. The thickness of the paper base material is measured in accordance with JIS P8118:2014.

The paper base material of the present invention preferably has a basis weight of 70 g/m ² or more and 120 g/m ² or less from the viewpoints of strength, shape retention, flexibility, etc. The basis weight of the paper base material is more preferably 75 g/m ² or more, even more preferably 80 g/m ² or more, and more preferably 110 g/m ² or less, 100 g/m ² It is more preferable that it is the following. The basis weight of the paper base material is measured in accordance with JIS P8124:2011.

The paper base material of the present invention preferably has a density of 0.6 g/cm ³ or more and 0.8 g/cm ³ or less from the viewpoints of strength, shape retention, flexibility, etc. The density of the paper base material is more preferably 0.62 g/cm ³ or more, more preferably 0.75 g/cm ³ or less, and even more preferably 0.7 g/cm ³ or less. . The thickness of the paper base material is calculated from the density and basis weight.

It is preferable that the paper base material of the present invention has a tensile stiffness in the MD direction of 450 kN/m or more and 850 kN/m or less from the viewpoints of shape retention, shock absorption, and the like. The tensile stiffness of paper substrates is measured according to ISO/DIS 1924-3.
It is preferable that the paper base material of the present invention has a bending resistance in the CD direction of 65 mN or more and 100 mN or less from the viewpoints of bag-making properties, shape retention properties, and the like. The bending resistance of paper substrates is measured according to ISO 2493.

Pulps include chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached pulp (NUKP), sulfite pulp, stone grind pulp, and thermoplastic pulp. Mechanical pulp such as mechanical pulp, wood fibers such as deinked pulp and waste paper pulp, non-wood fibers obtained from kenaf, bamboo, hemp, etc. can be used, and two or more types can also be used in combination. Among these, it is preferable to use unbleached pulp. Unbleached pulp has longer and thicker fibers than bleached pulp, so it can improve the strength of the base paper. Specifically, the amount of unbleached chemical pulp such as LUKP and NUKP relative to the total pulp is preferably 80% by weight or more, and it is more preferable that the amount of unbleached chemical pulp is 100% by weight. Further, the amount of NUKP added to the total unbleached pulp is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight. In addition, the paper base material only needs to have a tensile stiffness in the MD direction of 450 kN/m or more and 850 kN/m or less, and unbleached kraft paper, Clupac paper, semi-Clupaque paper, etc. whose main pulp is unbleached chemical pulp may be used. You can also do it.
The freeness of the pulp (Canadian standard freeness: CSF) is preferably 600 ml or less, more preferably 550 ml or less, and 500 ml or less from the viewpoint of the strength of the paper base material. More preferred.

Fillers include talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide. , inorganic fillers such as calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, calcium sulfate, etc., organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, micro hollow particles, and other fillers known for paper manufacturing. can be used. Note that the filler is not an essential material and may not be used.

Various auxiliary agents include rosin, alkyl ketene dimer (AKD), sizing agents such as alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationized starches, various modified starches, urea, etc. Formalin resin, dry paper strength enhancer such as melamine/formalin resin, wet paper strength enhancer, retention agent, freeness improver, coagulant, sulfuric acid, bulking agent, dye, optical brightener, pH adjuster, Examples include antifoaming agents, ultraviolet inhibitors, antifading agents, pitch control agents, slime control agents, etc., and can be appropriately selected and used as required.

The base paper manufacturing (paper making) method is not particularly limited, and twin paper machines such as Fourdrinier paper machine, cylinder paper machine, short wire paper machine, gap former type, hybrid former type (on-top former type), etc. It is possible to select a known manufacturing (paper making) method or paper machine such as a wire paper machine, and it is also possible to perform the Kurupack treatment using a gap former type paper machine equipped with a Kurupack device. In addition, the pH during papermaking may be any of the acidic region (acidic papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), and alkaline region (alkaline papermaking). Afterwards, an alkaline chemical may be applied to the surface of the paper layer. Further, the base paper may have one layer or may be composed of two or more layers.

Furthermore, it is possible to treat the surface of the base paper with various chemicals. Examples of the agents used include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water resistance agents, water retention agents, thickeners, lubricants, etc. These can be used alone or in combination of two or more. Furthermore, these various drugs and pigments may be used in combination. Pigments include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin. Inorganic pigments such as white and organic pigments such as solid type, hollow type, or core-shell type can be used alone or in combination of two or more types.
The method of surface treatment of the base paper is not particularly limited, but known coating equipment such as a rod metering size press, pound type size press, gate roll coater, spray coater, blade coater, curtain coater, etc. can be used. .

Furthermore, one or more functional layers such as a filler layer, an ink-receiving layer, a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, and a gas barrier layer can be formed on at least one surface of the base paper. The functional layer may be either a coating layer or a laminate layer, but a coating layer is preferred from the viewpoint of maintaining the flexibility of the paper base material.

- Heat-sealing layer The heat-sealing layer is a layer that imparts heat-sealing properties, and specifically, it is a layer that can be bonded to an object to be bonded by applying heat and pressure. Since the heat-sealable paper of the present invention has heat-sealability, it can be easily formed into a package, maintains the shape of the package, and ensures sealing performance.

The heat-sealing layer is provided on the outermost surface of at least one of the heat-sealing papers. The heat-sealing layer may be either a coating layer or a laminate layer, but a coating layer is preferable because it has excellent deformation followability.
The thermoplastic resin contained in the heat seal layer is not particularly limited, and may include ethylene-vinyl acetate resin, styrene-acrylic ester copolymer resin, acrylic resin, ethylene-acrylic resin, polyolefin resin (polyethylene, polypropylene, etc.) , thermoplastic resins used for heat sealing such as polyester resins (polyethylene terephthalate, polyethylene succinate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl alcohol resins, polyvinyl acetate resins, polylactic acid resins, etc. It can be used without any restrictions. Among these, ethylene-vinyl acetate resins, styrene-acrylic acid ester copolymer resins, acrylic resins, and ethylene-acrylic resins are preferred from the viewpoint of heat seal strength. Furthermore, biodegradable resins such as polyvinyl alcohol, polylactic acid, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) are preferred from the standpoint of reducing the environmental burden if they are discharged as trash.
The heat-sealing layer can contain additives such as an anti-blocking agent, a silane coupling agent, and an antifoaming agent. As the anti-blocking agent, pigments, waxes, metal soaps, etc. can be used without particular limitations. In the heat-sealing paper of the present invention, when the heat-sealing layer is a coating layer, it preferably contains an antifoaming agent. By including an antifoaming agent, a uniform coating layer can be obtained, thereby improving heat sealability.

When the heat seal layer is a coating layer, the dry weight of the heat seal layer is preferably 3 g/m ² or more and 20 g/m ² or less per side. If the dry weight is less than 3 g/m ² , heat sealability may be reduced. Moreover, even if the dry weight exceeds 20 g/m ² , the heat sealability is hardly improved and the cost increases. The heat-sealing layer may be one layer or may be composed of two or more layers. By configuring the heat-sealing layer as a multilayer of two or more layers, defects such as coating unevenness can be reduced compared to the case of a single layer. When the heat-sealing layer is composed of two or more layers, it is preferable that the total dry weight of all the heat-sealing layers is within the above range, and the dry weight coating amount per layer is 2 g/m It is preferable that it is ² or more.
When the heat seal layer is a laminate layer, the thickness of the heat seal layer is preferably 20 μm or more and 100 μm or less. If the thickness is less than 20 μm, heat sealability may not be ensured. Moreover, if the thickness exceeds 100 μm, it is not preferable from the viewpoint of cost.

When the heat seal layer is a coating layer, the coating method is not particularly limited, and coating can be performed using a known coating device and coating system. For example, examples of the coating device include a blade coater, a bar coater, an air knife coater, a curtain coater, a spray coater, a roll coater, a reverse roll coater, a size press coater, a gate roll coater, and the like.
The coating system may be either a water-based coating using a solvent such as water or a solvent-based coating using a solvent such as an organic solvent, but water-based coating is preferred from the viewpoint of safety and hygiene. In the case of aqueous coating, a water-dispersible resin or a water-soluble resin is used as the thermoplastic resin, and therefore the heat-sealing layer is preferably a coating layer of a water-dispersible resin or a water-soluble resin.
When the heat-sealing layer is a laminate layer, the formation method thereof is not particularly limited, and for example, various methods such as extrusion lamination, wet lamination, dry lamination, etc. can be appropriately used to laminate.

"Packaging"
The package of the present invention uses the heat seal paper of the present invention described above.
The shape of the package is not particularly limited, and may be a vertical pillow packaging bag, a horizontal pillow packaging bag, a side-sealed bag, a two-sided sealed bag, a three-sided sealed bag, a gusset bag, a bottom gusseted bag, a stand bag, or the like. Since the packaging body of the present invention is mainly made of paper, it is easier to tear compared to packaging materials using conventional resin packaging materials.

EXAMPLES The features of the present invention will be explained in more detail below with reference to Examples and Comparative Examples. The materials, usage amounts, proportions, processing details, 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.

The raw materials used in the examples and comparative examples are as follows.

[Example 1]
<Preparation of heat seal layer paint>
100 parts of ethylene-acrylic acid copolymer (manufactured by Mitsui Chemicals, Chemipearl S500, water dispersion with a solid content of 43%), 0.2 parts of antifoaming agent (manufactured by BASF, Formstar SI 2213, solid content 100%) were mixed, water was added and stirred so that the solid content concentration was 33%, and a heat seal layer coating material (concentration 33%) was obtained.
<Manufacture of heat seal paper>
The obtained heat seal layer paint was applied to unbleached kraft paper (manufactured by Shin Tokai Paper Co., Ltd., thickness 143 μm) with a basis weight of 91.1 g/m ² and a coating amount of 6.0 g/m after drying of the heat seal layer. Coating was performed using an air knife coater to form a heat-sealing layer so that the film thickness was ² m2.

[Example 2]
Heat seal paper was obtained in the same manner as in Example 1 except that the paper base material was changed to unbleached kraft paper (manufactured by Shin Tokai Paper Co., Ltd., thickness 130 μm) with a basis weight of 85.6 g/m ² .
[Example 3]
The paper base material was changed to unbleached kraft paper (manufactured by Shin Tokai Paper Co., Ltd., thickness 149 μm) with a basis weight of 96.7 g/m ² , and the coating amount of the heat seal layer after drying was 7.5 g/m ² A heat seal paper was obtained in the same manner as in Example 1 except for the following.
[Example 4]
The paper base material was changed to unbleached kraft paper with a basis weight of 96.0 g/m ² (manufactured by Shin Tokai Paper Co., Ltd., thickness 146 μm), and the coating amount of the heat seal layer after drying was 7.5 g/m ² A heat seal paper was obtained in the same manner as in Example 1 except for the following.

[Comparative example 1]
Heat seal paper was obtained in the same manner as in Example 1, except that the paper base material was changed to unbleached kraft paper (manufactured by Shin Tokai Paper Co., Ltd., thickness 130 μm) with a basis weight of 88.6 g/m ² .

[Comparative example 2]
Heat seal paper was obtained in the same manner as in Example 1, except that the paper base material was changed to unbleached kraft paper (manufactured by Shin Tokai Paper Co., Ltd., thickness 143 μm) with a basis weight of 99.4 g/m ² .

The obtained paper base material or heat seal paper was evaluated as follows. The results are shown in Table 1.
- Tensile stiffness Measured using an L&W tensile tester in accordance with ISO/DIS1924-3:.
- Breaking elongation Measured using an L&W tensile tester in accordance with the second part constant speed elongation method in accordance with JIS P8113:2006.
- Bending resistance value Measured using L&W BENDING TESTER in accordance with ISO 2493.

・Heat-sealing strength Two square test pieces of 100 mm on a side were cut out from the obtained heat-sealing paper, the coating layers were brought into contact with each other, and the pressure was applied at a temperature of 130°C, a pressure of 2 kgf/cm ² , and a time of application. Heat sealed in 0.5 seconds.
When the heat-sealed test piece was peeled off by hand, the peeled portion was visually observed.
1: Peeling occurs within the paper base material (paper base material is destroyed).
2: Most of the sample peels off within the paper base (paper base is destroyed).
3: Peeling occurs between coating layers.

The obtained heat seal paper was cut into a width of 310 mm and wound into a roll. This was carried out using a horizontal pillow packaging machine (Omori Kikai Kogyo Co., Ltd., S-5000X BX). 900 horizontal pillow bags were made under conditions of seal and top seal temperatures of 160°C and evaluated according to the following criteria. In addition, if the heat seal paper broke during manufacturing, manufacturing was discontinued at that point.

・Transportability OK: The heat seal paper can be transported as specified.
NG: Misalignment occurs in the conveyance of the heat seal paper.
・Wrinkles on center seal part (N=100)
1: There are no wrinkles, or there are slight wrinkles that are hard to notice unless you look carefully.
2: Although small wrinkles occur, they are localized and do not pose a problem in terms of appearance (OK for practical use).
3: Some wrinkles are large enough to be noticed at a glance (not suitable for practical use).

The heat-sealing papers of Examples 1 to 4 according to the present invention have a heat-sealing strength that can withstand practical use, can be transported as specified in a bag-making machine, and have wrinkles in the center seal portion that are at a level that is acceptable for practical use. We were able to manufacture horizontal pillow bags.
The heat-sealing paper of Comparative Example 1 had poor heat-sealing strength, and some of the resulting horizontal pillow bags had large wrinkles in the center seal area.
The heat-seal paper of Comparative Example 2 could not be conveyed as specified, and some sheets were not cut at intervals of 150 mm.

Claims (5)

having a paper base material and a heat sealing layer on at least one outermost surface,
The paper base material has an elongation at break in the MD direction of 2.0% or more and 5.5% or less, a bending resistance in the CD direction of 65 mN or more and 100 mN or less , and a density of 0.6 g/cm3 or more and 0.6 g/cm3 ^or more. A heat seal paper characterized in that it has a weight of 75 g/cm ³ or less . The heat seal paper according to claim 1, wherein the paper base material has a basis weight of 70 g/m ² or more and 120 g/m ² or less. The heat-sealing paper according to claim 1 or 2, wherein the heat-sealing layer is a coating layer of a water-dispersible resin or a water-soluble resin. The heat seal paper according to claim 1 or 2, wherein the thickness of the paper base material is 120 μm or more and 160 μm or less. A package using the heat seal paper according to claim 1 or 2.