WO2023157217A1

WO2023157217A1 - Heat seal paper

Info

Publication number: WO2023157217A1
Application number: PCT/JP2022/006582
Authority: WO
Inventors: 匡史岡本; 健太渡辺
Original assignee: 日本製紙株式会社; ジュウジョウサーマルオーユー
Priority date: 2022-02-18
Filing date: 2022-02-18
Publication date: 2023-08-24

Abstract

The present invention addresses the problem of providing a heat seal paper which is suitably used in packaging applications such as packaging materials, bags, containers, boxes, cups and lid materials, and which has heat sealing adequacy and good blocking resistance. The present invention provides, as a means for solving the problem, a heat seal paper which comprises a paper base material and a heat sealable coating layer that contains at least a thermoplastic resin and a pigment, wherein the heat sealable coating layer contains 50 parts by mass to 150 parts by mass of the pigment relative to 100 parts by mass of the thermoplastic resin.

Description

heat seal paper

The present invention relates to heat seal paper.

In recent years, plastic waste has been raised as a major problem because there is concern that plastic that has flowed into the environment as waste will not be decomposed semi-permanently and will adversely affect the ecosystem. As a countermeasure, it has been proposed to replace plastic with paper, which is a biomass-derived material and a biodegradable material.
On the other hand, conventionally, when paper packaging materials are molded into food packaging materials, bags, containers, boxes, cups, lids, etc., heat is applied to polyolefin resins such as polyethylene, polypropylene, and polymethylpentene. It is common practice to laminate a plastic resin on a packaging material by an extrusion lamination method or the like to impart heat-sealability.

However, these thermoplastic resin laminates use about 10 to 30 g/m ² of thermoplastic resin, and the amount of plastic is not sufficiently reduced. For this reason, currently, packaging paper is provided in which the laminated coating layer is thinned and reduced in weight by coating a paper base material with a water or solvent dispersion containing a thermoplastic resin dispersion (patent Reference 1, etc.).
However, heat is applied during the paint drying process when laminating coating layers by coating, and when forming paper packaging materials into food packaging materials, bags, containers, boxes, cups, lid materials, etc. There is a need. At this time, if heat remains after each step (thermoplastic resin remains softened), blocking occurs, resulting in product defects. Coated paper is wound into a roll and stored until it is formed, but there is a problem that blocking occurs during long-term storage at room temperature. Therefore, it is necessary to provide a wrapping paper having both good blocking resistance and heat-sealability.

Japanese Patent No. 6580291

An object of the present invention is to provide a heat-sealable paper that is suitable for packaging applications such as packaging materials, bags, containers, boxes, cups, lids, etc., and has good blocking resistance as well as heat-sealability.

Means for solving the problems of the present invention are as follows.
1. having a paper substrate and a heat-sealable coating layer containing at least a thermoplastic resin and a pigment;
A heat-sealable paper, wherein the heat-sealable coating layer contains 50 parts by mass or more and 150 parts by mass or less of a pigment with respect to 100 parts by mass of a thermoplastic resin.
2. 1. The coating weight of the heat-sealable coating layer is 5 g/m ² or more and 20 g/m ² or less. Heat-sealing paper described in .
3. The heat-sealable coating layer consists of two or more adjacent layers,
The outermost layer contains less pigment per 100 parts by mass of the thermoplastic resin than the entire coating layer, and contains 20 parts by mass or more and 80 parts by mass or less of the pigment per 100 parts by mass of the thermoplastic resin. 1. or 2. Heat-sealing paper described in .
4. 3. The coating weight of the outermost layer is 2 g/m ² or more. Heat-sealing paper described in .

According to the present invention, it is possible to provide a heat-sealable paper having heat-sealability and good blocking resistance, which is suitable for packaging applications. The heat-sealable paper of the present invention has excellent disaggregation properties and is easy to recycle.

The present invention has a paper substrate and a heat-sealable coating layer (hereinafter also referred to as a coating layer) containing at least a thermoplastic resin and a pigment,
It relates to a heat-sealable paper in which a heat-sealable coating layer contains 50 parts by mass or more and 150 parts by mass or less of a pigment with respect to 100 parts by mass of a thermoplastic resin.

(Paper substrate)
The paper base material is obtained by making a paper stock containing pulp, fillers, various auxiliary agents, and the like.
When the heat-sealable paper of the present invention is used for applications that come into contact with food, each material of the paper substrate is approved as a food additive or certified by the FDA, and conforms to food safety. is preferably used.

As pulp, softwood bleached kraft pulp (NBKP), softwood unbleached kraft pulp (NUKP), hardwood bleached kraft pulp (LBKP), hardwood unbleached kraft pulp (LUKP), sulfite pulp (SP), etc. Wood Chemical Pulp, Ground Pulp (GP), Refiner Ground Pulp (RGP), Stone Ground Pulp (SGP), Chemi-Ground Pulp (CGP), Semi-Chemical Pulp (SCP), Thermo-Mechanical Pulp (TMP), Chemi-Thermomechanical Mechanical pulp of wood such as pulp (CTMP), non-wood pulp obtained from kenaf, bagasse, bamboo, hemp, straw, etc., waste paper pulp made from waste paper and the ink contained in waste paper is removed in the deinking process, etc. , known pulps can be appropriately mixed and used. Among these, chemical pulps such as LBKP and NBKP, which are less likely to be contaminated with foreign matter, are preferred, and the blending amount of waste paper pulp is preferably small. Specifically, the chemical pulp content is preferably 80% or more, and particularly preferably 100%. Also, the content of waste paper pulp is preferably 10% or less, more preferably 1% or less, and most preferably not included.

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, and aluminum hydroxide. , inorganic fillers such as calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, calcium sulfate, urea-formalin resins, polystyrene resins, phenolic resins, organic fillers such as fine hollow particles, etc. can be done. Note that the filler is not an essential material and may not be used.

Various auxiliaries include sizing agents such as rosin, alkylketene dimer (AKD), alkenylsuccinic anhydride (ASA), polyacrylamide-based polymers, polyvinyl alcohol-based polymers, cationized starch, various modified starches, urea- Formalin resin, dry paper strength enhancer such as melamine/formalin resin, wet paper strength enhancer, retention agent, drainage improver, coagulant, aluminum sulfate, bulking agent, dye, fluorescent whitening agent, pH adjuster, Antifoaming agents, anti-ultraviolet agents, anti-fading agents, pitch control agents, slime control agents and the like can be exemplified, and can be appropriately selected and used as necessary.

The method of manufacturing the paper substrate (papermaking) is not particularly limited, and may be a fourdrinier paper machine, a cylinder paper machine, a short-mesh paper machine, a gap former type, a hybrid former type (on-top former type), or the like. A known manufacturing (papermaking) method and papermaking machine, such as the twin wire papermaking machine, can be selected. The pH during papermaking may be in the acidic region (acidic papermaking), quasi-neutral region (quasi-neutral papermaking), neutral region (neutral papermaking), or alkaline region (alkaline papermaking). After that, the surface of the paper layer may be coated with an alkaline chemical. Moreover, the paper base material may be composed of one layer, or may be composed of multiple layers of two or more layers.

Furthermore, it is possible to treat the surface of the paper substrate with various chemicals. Examples of 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, and the like. These can be used alone or in combination of two or more. Furthermore, these various agents and pigments may be used in combination. Pigments include kaolin, clay, engineered kaolin, delaminated clay, ground calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin. Inorganic pigments such as white and organic pigments such as solid-type, hollow-type, or core-shell-type pigments can be used alone or in combination of two or more.

The method of surface treatment of the paper substrate is not particularly limited, but a known coating apparatus such as a rod metering size press, a pound size press, a gate roll coater, a spray coater, a blade coater and a curtain coater can be used. can be done.
Paper substrates thus obtained include woodfree paper, medium-quality paper, coated paper, one-sided glossy paper, kraft paper, one-sided glossy kraft paper, bleached kraft paper, glassine paper, paperboard, white paperboard, liner, and the like. Various known ones can be exemplified.

The basis weight of the paper base material can be appropriately selected according to the desired quality, handleability, etc., but is preferably 20 g/m ² or more and 600 g/m ² or less. In the case of heat-sealable paper used for applications such as bags, lids, and soft packaging materials, the weight is preferably 30 g/m ² or more and 150 g/m ² or less. In the case of heat-sealable paper used for applications such as containers, boxes, and cups, it is more preferable to have a weight of 150 g/m ² or more and 350 g/m ² or less. Flexible packaging materials are packaging materials that are made of highly flexible materials. In general, they are packaging materials that are composed of thin and flexible materials such as paper, film, and aluminum foil, either alone or laminated together. , vertical pillow packaging bag, horizontal pillow packaging bag, side seal bag, two side seal bag, three side seal bag, gusset bag, bottom gusset bag, stand bag, etc.
The density of the paper base material can be appropriately selected depending on the desired quality, handleability, etc., but is usually preferably 0.5 g/cm ³ or more and 1.0 g/cm ³ or less.

(Heat-sealable coating layer)
The heat-sealable coating layer contains at least a thermoplastic resin and a pigment. In addition to the thermoplastic resin and the pigment, the heat-sealable coating layer contains dispersants, thickeners, fluidity improvers, antifoaming agents, foam inhibitors, mold release agents, penetrating agents that can be incorporated in the heat seal layer. agents, colorants, UV absorbers, antioxidants, lubricants (wax, etc.), and the like. Although the coating layer can be provided on both sides of the heat-sealable paper, it is provided on at least one side.
The coating layer has heat-sealability and can be adhered to an object to be adhered by applying heat and pressure. Since the coating layer has heat-sealability, the heat-sealable paper of the present invention can be molded into a packaging form or shaped particularly in packaging applications such as packaging materials such as food, bags, containers, boxes, cups, and lid materials. It becomes easy to maintain the airtightness and to ensure the airtightness.

- Thermoplastic resin As the thermoplastic resin, those used for forming a heat seal layer in the papermaking field can be used without particular limitation. For example, those having a glass transition temperature of 100 ° C. or less are used. be able to. The glass transition temperature of the thermoplastic resin is preferably -20°C or higher and 85°C or lower. Also, the melting point of the thermoplastic resin is preferably 80° C. or higher and 120° C. or lower. Examples of thermoplastic resins include (meth)acrylic resins (PMMA), low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and polyolefin-based resins such as polypropylene (PP). Resins, polyvinyl alcohol resins such as polyvinyl acetate (PVAc), fully saponified or partially saponified polyvinyl alcohol (PVA), polyester resins (PET), ethylene acrylic acid copolymer resin (EAA), ethylene methacrylic acid copolymer Resin (EMAA), ethylene methyl acrylate copolymer resin (EMA), ethylene vinyl acetate copolymer resin (EVA), styrene acrylate copolymer resin, polylactic acid resin, and the like can be used. Moreover, the thermoplastic resin can be used singly or in combination of two or more. Among these, acrylic resins, polyolefin resins, polyvinyl alcohol resins, ethylene acrylic acid copolymer resins, and ethylene vinyl acetate copolymer resins with high heat-sealability are preferably included, and among these, polyolefin resins are included. is more preferable, and it is particularly preferable to consist only of these.

・Pigments Pigments are not particularly limited, and kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid. , silicates, colloidal silica, and satin white, and organic pigments such as solid-type, hollow-type, or core-shell-type pigments. In addition, pigments can be used singly or in combination of two or more. Among these, kaolin is more preferable because it is excellent in dispersibility and stability with thermoplastic resins.
The average particle size (D50) of the pigment used in the present invention is preferably 10 μm or less, more preferably 5 μm or less. Also, the average particle size (D50) of the pigment is preferably 0.1 μm or more. In the present invention, the average particle size means a 50% volume average particle size (median size), which is measured by a laser diffraction method, and can be measured by Mastersizer 3000 manufactured by Malvern.

In the heat-sealable paper of the present invention, the coating layer contains 50 parts by mass or more and 150 parts by mass or less of the pigment with respect to 100 parts by mass of the thermoplastic resin in dry mass. When the blending amount of the pigment with respect to the thermoplastic resin is within this range, the heat-sealing property and blocking resistance are well balanced. Further, when the amount of the pigment compounded is 50 parts by mass or more with respect to 100 parts by mass of the thermoplastic resin, the disaggregation property is excellent and recycling is easy. The amount of the pigment compounded with respect to the thermoplastic resin is more preferably 70 parts by mass or more, and more preferably 130 parts by mass or less.

The number of coating layers is preferably two or more. By providing a plurality of coating layers, coating defects such as coating unevenness can be reduced as compared with the case of a single layer. At this time, the composition of the outermost layer of the two or more coating layers has a smaller amount of pigment per 100 parts by mass of the thermoplastic resin than the composition of the entire coating layer (a large amount of the thermoplastic resin) ), and preferably contains 20 parts by mass or more and 80 parts by mass or less of the pigment with respect to 100 parts by mass of the thermoplastic resin. The amount of the pigment blended with respect to 100 parts by mass of the thermoplastic resin in the outermost layer is more preferably 1 part by mass or more less than the blended amount of the pigment with respect to 100 parts by mass of the thermoplastic resin in the entire coating layer, and is more preferably 3 parts by mass. It is more preferable that it is less than or equal to. Further, the outermost layer more preferably contains 30 parts by mass or more and 70 parts by mass or less of pigment with respect to 100 parts by mass of the thermoplastic resin. Specifically, when the coating layer consists only of a thermoplastic resin and a pigment, and the amount of the pigment is 80 parts by mass with respect to 100 parts by mass of the thermoplastic resin in the entire coating layer, the thermoplastic resin in the outermost layer The amount of the pigment blended with respect to 100 parts by mass of the resin is preferably 20 parts by mass or more and less than 80 parts by mass. It is preferable that the amount of the pigment compounded with respect to 100 parts by mass of the thermoplastic resin in the outermost layer is 20 parts by mass or more and less than 50 parts by mass.

The coating method of the coating layer is not particularly limited, and the coating can be performed using a known coating device and coating system. Examples of coating equipment include blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters and gate roll coaters. Examples of the coating system include water-based coating using a solvent such as water, and solvent-based coating using a solvent such as an organic solvent. Since the heat-sealable paper of the present invention may be used in applications where it comes into contact with food or the like, water-based coating is preferred from the standpoint of food safety.
The viscosity, solid content concentration, and the like of the coating liquid can be appropriately adjusted according to the coating apparatus, coating system, and the like to be used.

The coating amount (dry mass) of the coating layer is preferably 5 g/m ² or more and 20 g/m ² or less per side. If the coating amount is less than 5 g/m ² per one side, the heat-sealability is lowered. Also, even if the coating amount exceeds 20 g/m ² per side, the heat-sealability is hardly improved and the cost increases. When the coating layer is composed of multiple layers of two or more layers, it is preferable to make the total coating amount of all the coating layers within the above range. When the number of coating layers is two or more, the coating amount (dry mass) of the outermost layer is preferably 2 g/m ² or more per side, more preferably 3 g/m ² or more.

The heat-sealable paper of the present invention may have a coating layer and a paper substrate, and other layers such as a filling layer, a printing layer, a light-shielding layer, a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, and a gas barrier layer. It can have layers, and preferably has a filler layer between the coating layer and the paper substrate. By having the filling layer, it is possible to reduce the occurrence of coating defects such as pinholes and streaky unevenness in the coating layer, and to improve water resistance and oil resistance.
The heat-sealable paper of the present invention can be heat-sealable paper used for packaging such as food packaging materials, bags, containers, boxes, cups, lids, and the like.

(Evaluation method)
(1) Heat sealability (heat seal conditions)
Two 100 mm square test pieces were cut out from the obtained heat-sealed paper, and the coating layers were brought into contact with ^each other. It was heat sealed with
When the heat-sealed test piece was manually peeled off, the peeled portion was visually observed, and the heat-sealability was evaluated according to the following criteria.
A: Detachment within the paper base (paper base is destroyed)
B: There is a part that is peeled within the paper substrate and a part that is peeled between the coating layers C: Peeling between the coating layers

(2) Blocking property This evaluation assumes sticking when the heated coating layer comes into contact with equipment during manufacturing or processing of the product.
Pass the humidity-conditioned sample (23 ° C., RH 50%) through a hot roll press (roll pressure 0.5 MPa, processing speed 2 m / min, arbitrary roll temperature) so that the coated surface and the metal roll are in contact, The degree of sticking of the coated surface to the metal roll was evaluated. If the evaluation is A or B, there is no practical problem.
[Evaluation criteria]
A: When the roll temperature is 70°C, no sticking is observed, and no damage to the coated surface is observed. B: No sticking is observed, and no damage to the coated surface is observed when the roll temperature is 60°C. C: When the roll temperature is 60°C, the coating layer sticks to the metal roll, and damage to the coating surface is observed, such as the coating layer being removed by the metal roll.

(3) Disaggregation The obtained heat-sealed paper was subjected to a disaggregation test with a pulp disaggregation tester (manufactured by Kumagai Riki Kogyo Co., Ltd., in accordance with JIS P8220) with a concentration of 2.5%, a water volume of 2000 ml, a water temperature of 40°C, and a disaggregation time of 20. The specimens were disaggregated without pre-swelling at the conditions of 10 minutes. After maceration, the maceration solution was diluted with water to a concentration of 0.5%.
A slit screen (0.15 mm width) was used to remove foreign matter from the diluted disaggregation solution, and the residue ratio was calculated from the mass of residue on the screen.
[Residual rate evaluation criteria]
A: No residue remains, or the amount of remaining residue is less than 10% by mass of the heat-sealed paper mass.
B: The amount of remaining residue is 10% by mass or more and less than 20% by mass of the heat-sealed paper mass.
C: The amount of remaining residue is 20% by mass or more of the heat-sealed paper mass put in.

"Example 1"
(Preparation of coating solution for coating layer)
Thermoplastic resin (manufactured by Dow Chemical Co., Ltd. polyolefin resin: RHOBARR320) and kaolin (manufactured by Imerys: KCS, standard white kaolin, D50: 4.6 μm) in a solid content mass ratio of 100.0/50.0 parts, respectively to obtain a coating liquid for a coating layer having a solid content concentration of 50% by mass.
(Preparation of heat seal paper)
On one side of a paper base material (basis weight of 50 g/m ² bleached kraft), the coating liquid for the coating layer is coated by a bar blade method so that the coating amount is 10.0 g/m ² in terms of dry mass, and dried. and heat-sealed paper was obtained.

[Example 2]
A heat seal paper was obtained in the same manner as in Example 1, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the coating layer was changed to 100.0/150.0.

[Comparative Example 1]
A heat seal paper was obtained in the same manner as in Example 1, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the coating layer was changed to 100.0/10.0.
[Comparative Example 2]
A heat seal paper was obtained in the same manner as in Example 1, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the coating layer was changed to 100.0/20.0.
[Comparative Example 3]
A heat seal paper was obtained in the same manner as in Example 1, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the coating layer was changed to 100.0/30.0.
[Comparative Example 4]
A heat seal paper was obtained in the same manner as in Example 1, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the coating layer was changed to 100.0/300.0.
[Comparative Example 5]
A heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the coating layer was changed to 100.0/500.0.

[Example 3]
(Preparation of coating solution for under coating layer)
A thermoplastic resin and kaolin (manufactured by Imerys: KCS, standard white kaolin) were prepared so that the solid content mass ratio was 100.0/100.0 parts, respectively, to obtain a coating solution for an under coating layer. .
(Preparation of coating solution for top coating layer)
A thermoplastic resin and kaolin (manufactured by Imerys: KCS, standard white kaolin) were prepared so that the solid content mass ratio was 100.0/20.0 parts, respectively, to obtain a coating solution for the top coating layer. .
(Preparation of heat seal paper)
On one side of a paper substrate (bleached kraft with a basis weight of 50 g/m ² ), the coating liquid for the under coating layer is coated by a bar blade method so that the coating amount is 5.0 g/m ² in terms of dry mass. After drying, the coating liquid for the top coating layer was applied by a bar blade method so that the coating amount was 5.0 g/m ² in terms of dry weight, and dried to obtain a heat-sealable paper.

[Example 4]
A heat-sealable paper was obtained in the same manner as in Example 3, except that the mass ratio of the thermoplastic resin and kaolin in the coating liquid for the top coating layer was changed to 100.0/80.0.
[Example 5]
The mass ratio of the thermoplastic resin and kaolin in the coating solution for the under coating layer is 100.0/60.0, and the mass ratio of the thermoplastic resin and kaolin in the coating solution for the top coating layer is 100.0/ A coating solution for a coating layer was obtained in the same manner as in Example 3, except that the value was 50.0.

[Comparative Example 6]
The mass ratio of the thermoplastic resin and kaolin in the coating solution for the under coating layer is 100.0/250.0, and the mass ratio of the thermoplastic resin and kaolin in the coating solution for the top coating layer is 100.0/ A coating solution for a coating layer was obtained in the same manner as in Example 3, except that the value was 100.0.
[Comparative Example 7]
The mass ratio of the thermoplastic resin and kaolin in the coating solution for the under coating layer is 100.0/60.0, and the mass ratio of the thermoplastic resin and kaolin in the coating solution for the top coating layer is 100.0/ A coating solution for a coating layer was obtained in the same manner as in Example 3, except that the value was 10.0.

Claims

having a paper substrate and a heat-sealable coating layer containing at least a thermoplastic resin and a pigment;
A heat-sealable paper, wherein the heat-sealable coating layer contains 50 parts by mass or more and 150 parts by mass or less of a pigment based on 100 parts by mass of a thermoplastic resin.
The heat-sealable paper according to claim 1, wherein the heat-sealable coating layer has a coating weight of 5 g/m2 or more and 20 g/m2 or less.
The heat-sealable coating layer consists of two or more layers,
The outermost layer contains a smaller amount of pigment per 100 parts by mass of the thermoplastic resin than the entire heat-sealable coating layer, and 20 parts by mass or more and 80 parts by mass of the pigment per 100 parts by mass of the thermoplastic resin. 3. The heat-sealable paper of claim 1 or 2, comprising:
4. The heat-sealable paper according to claim 3, wherein the coating amount of the outermost layer is 2 g/m2 or more .