Heat seal paper

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

[Technical Field]

[0001] This invention relates to heat-sealable paper. [Background technology]

[0002] In recent years, plastic waste has become a major issue due to concerns that plastics released into the environment as waste do not decompose semi-permanently and have a negative impact on ecosystems. As a countermeasure, it has been proposed to replace plastics with biomass-derived materials and biodegradable materials such as paper. On the other hand, conventionally, when paper packaging materials are molded into packaging materials, bags, containers, boxes, cups, lids, etc. for food and other products, it is common practice to laminate thermoplastic resins, such as polyethylene, polypropylene, and polymethylpentene, onto the packaging material using methods such as extrusion lamination to impart heat-sealability.

[0003] However, these thermoplastic resin laminates have a density of 10-30 g / m². 2 Currently, a considerable amount of thermoplastic resin is used, and the reduction in plastic content is insufficient. For this reason, packaging paper is currently available in which a water or solvent dispersion containing a thermoplastic resin dispersion is coated onto a paper substrate, thereby reducing the thickness and volume of the laminated coating layer (Patent Document 1, etc.). However, heat is required during the paint drying process when laminating coating layers, and when molding paper packaging materials into food packaging, bags, containers, boxes, cups, and lids. If heat remains after each process (the thermoplastic resin remains soft), blocking occurs, resulting in product defects. Furthermore, coated paper is stored wound in rolls until it is molded, and blocking can occur during long-term storage at room temperature. Therefore, there is a need to provide packaging paper that combines good blocking resistance with suitable heat-sealability. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6580291 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a heat-sealable paper that is suitable for use in packaging applications such as packaging materials, bags, containers, boxes, cups, and lids, and that has good heat-sealing properties and good blocking resistance. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. A paper substrate and a heat-sealable coating layer comprising at least a thermoplastic resin and a pigment, The heat-sealable coating layer is characterized by containing 50 to 150 parts by mass of pigment per 100 parts by mass of thermoplastic resin. 2. The amount of the heat-sealable coating layer applied is 5 g / m². 2 More than 20g / m 2 The heat-sealable paper described in 1, characterized in the following way. 3. The heat-sealable coating layer consists of two or more adjacent layers. The heat-sealable paper according to 1. or 2., characterized in that the outermost layer has a lower pigment content per 100 parts by mass of thermoplastic resin compared to the entire coating layer, and contains 20 parts by mass or more and 80 parts by mass of pigment per 100 parts by mass of thermoplastic resin. 4. The amount of coating applied to the outermost layer is 2 g / m². 2 The heat-sealable paper described in 3., characterized by the above. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a heat-sealable paper that is suitable for packaging applications, has good heat-sealing properties, and possesses good blocking resistance. The heat-sealable paper of the present invention has excellent disintegration properties and is easy to recycle. [Modes for carrying out the invention]

[0008] The present invention comprises a paper substrate and a heat-sealable coating layer (hereinafter also referred to as the coating layer) containing at least a thermoplastic resin and a pigment. This invention relates to heat-sealable paper in which the heat-sealable coating layer contains 50 to 150 parts by mass of pigment per 100 parts by mass of thermoplastic resin.

[0009] (Paper base material) Paper substrates are obtained by papermaking a paper stock containing pulp, fillers, various auxiliary agents, etc. When using the heat-sealable paper of the present invention for applications that come into contact with food, it is preferable to use materials for the paper substrate that are approved as food additives or have obtained FDA certification, or otherwise conform to food safety standards.

[0010] As the pulp, chemical pulps of wood such as softwood bleached kraft pulp (NBKP), softwood unbleached kraft pulp (NUKP), hardwood bleached kraft pulp (LBKP), hardwood unbleached kraft pulp (LUKP), sulfite pulp (SP), etc., mechanical pulps of wood such as ground pulp (GP), refiner ground pulp (RGP), stone ground pulp (SGP), chemiground pulp (CGP), semi-chemical pulp (SCP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc., non-wood pulp obtained from kenaf, bagasse, bamboo, hemp, straw, etc., wastepaper pulp obtained by using wastepaper as a raw material and removing the ink contained in the wastepaper in a deinking process, etc., known pulps can be appropriately blended and used. Among these, chemical pulps such as LBKP and NBKP, which are less likely to be contaminated with foreign substances, are preferred, and it is also preferred that the blending amount of wastepaper pulp is small. Specifically, the blending amount of chemical pulp is preferably 80% or more, and particularly preferably 100%. Also, the blending amount of wastepaper pulp is preferably 10% or less, more preferably 1% or less, and most preferably not contained.

[0011] As the filler, known fillers such as inorganic fillers such as 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, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, calcium sulfate, etc., and organic fillers such as urea-formalin resin, polystyrene resin, phenol resin, micro hollow particles, etc. can be used. Note that the filler is not an essential material and may not be used.

[0012] Examples of various auxiliaries include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide-based polymers, polyvinyl alcohol-based polymers, cationized starch, various modified starches, dry paper strength enhancers such as urea-formalin resin and melamine-formalin resin, wet paper strength enhancers, retention aids, drainage improvers, flocculants, sulfate bands, bulking agents, dyes, fluorescent brighteners, pH adjusters, defoamers, UV inhibitors, anti-fading agents, pitch control agents, slime control agents, etc. These can be appropriately selected and used as needed.

[0013] The method for manufacturing (papermaking) the paper base material is not particularly limited, and known manufacturing (papermaking) methods and papermaking machines such as Fourdrinier machines, cylinder machines, twin-wire machines such as short-formers, gap former types, and hybrid former types (ontopper types) can be selected. Also, the pH during papermaking can be in any of the acidic region (acidic papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), or alkaline region (alkaline papermaking). After papermaking in the acidic region, an alkaline agent can be applied to the surface of the paper layer. Further, the paper base material may be a single layer or may be composed of multiple layers of two or more layers.

[0014] Furthermore, the surface of the paper base material can be treated with various agents. 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, thickening agents, lubricants, etc. These can be used alone or in combination of two or more. Further, these various agents and pigments may be used in combination. Examples of pigments include inorganic pigments such as 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, satin white, etc., and organic pigments such as solid type, hollow type, or core-shell type, etc. These can be used alone or in combination of two or more.

[0015] The method of surface treatment of the paper substrate is not particularly limited, and known coating devices such as rod metering size presses, pond size presses, gate roll coaters, spray coaters, blade coaters, curtain coaters, etc. can be used. Examples of the paper substrate obtained in this way include various known ones such as fine paper, medium paper, coated paper, one-sided glossy paper, kraft paper, one-sided glossy kraft paper, bleached kraft paper, glassine paper, cardboard, white cardboard, liner, etc.

[0016] The basis weight of the paper substrate can be appropriately selected according to various desired qualities, handling properties, etc., but it is preferably 20 g / m 2 or more and 600 g / m 2 or less. In the case of heat-sealing paper used for applications such as bags, lids, and flexible packaging materials, it is preferably 30 g / m 2 or more and 150 g / m 2 or less. Also, in the case of heat-sealing paper used for applications such as containers, boxes, cups, etc., it is more preferably 150 g / m 2 or more and 350 g / m 2 or less. Note that a flexible packaging material is a packaging material composed of a highly flexible material, and generally, it is a packaging material made of a thin and flexible material such as paper, film, aluminum foil, etc., used alone or laminated, and is used in forms such as vertical pillow packaging bags, horizontal pillow packaging bags, side-seal bags, two-side seal bags, three-side seal bags, gusset bags, bottom gusset bags, stand-up bags, etc. Also, the density of the paper substrate can be appropriately selected according to various desired qualities, handling properties, etc., but usually, it is preferably 0.5 g / cm 3 or more and 1.0 g / cm 3 or less.

[0017] (Heat-sealing coating layer) The heat-sealable coating layer comprises at least a thermoplastic resin and a pigment. In addition to the thermoplastic resin and pigment, the heat-sealable coating layer may also contain dispersants, thickeners, flow modifiers, defoamers, antifoaming agents, mold release agents, penetrating agents, colorants, UV absorbers, antioxidants, lubricants (such as waxes), etc., which may be incorporated into the heat-seal layer. The coating layer may be provided on both sides of the heat-sealable paper, but is provided on at least one side. The coating layer has heat-seal properties and can be bonded to the object by heating and pressurizing. Because the coating layer has heat-seal properties, the heat-sealable paper of the present invention is particularly useful in packaging applications such as packaging materials for food, bags, containers, boxes, cups, and lids, as it facilitates molding into packaging forms, maintaining shape, and ensuring airtightness.

[0018] ·Thermoplastic resin As the thermoplastic resin, any resin used in the papermaking field for forming heat seal layers can be used without particular limitation. For example, a resin with a glass transition temperature of 100°C or less can be used. Preferably, the glass transition temperature of the thermoplastic resin is between -20°C and 85°C. Preferably, the melting point of the thermoplastic resin is between 80°C and 120°C. Examples of thermoplastic resins that can be used include polyolefin resins such as (meth)acrylic resin (PMMA), low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP); polyvinyl alcohol resins such as polyvinyl acetate (PVAc) and fully saponified or partially saponified polyvinyl alcohol (PVA); polyester resin (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 acrylic acid ester copolymer resin; and polylactic acid resin. Furthermore, thermoplastic resins can be used by mixing one or more types. Among these, it is preferable to include acrylic resins, polyolefin resins, polyvinyl alcohol resins, ethylene acrylic acid copolymer resins, and ethylene vinyl acetate copolymer resins, which have high heat sealability, and it is more preferable to include polyolefin resins, and it is particularly preferable to consist of only these.

[0019] Pigments The pigments are not particularly limited and can include inorganic pigments such as 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, as well as organic pigments such as solid, hollow, or core-shell types. Furthermore, one or more pigments can be used in combination. Among these, kaolin is preferred due to its excellent dispersibility and stability with thermoplastic resins. The average particle size (D50) of the pigment used in this invention is preferably 10 μm or less, and more preferably 5 μm or less. Furthermore, the average particle size (D50) of the pigment is preferably 0.1 μm or more. In this invention, the average particle size refers to the 50% volume average particle size (median diameter), which is measured by laser diffraction and can be measured using a Malvern Mastersizer 3000 or similar instrument.

[0020] The heat-sealable paper of the present invention has a coating layer containing 50 to 150 parts by mass of pigment per 100 parts by mass of thermoplastic resin, based on dry mass. This range of pigment content relative to thermoplastic resin provides an excellent balance between heat-sealability and blocking resistance. Furthermore, a pigment content of 50 parts by mass or more per 100 parts by mass of thermoplastic resin results in excellent disintegration properties and easy recycling. The pigment content relative to thermoplastic resin is more preferably 70 parts by mass or more, and more preferably 130 parts by mass or less.

[0021] It is preferable that the coating layer consists of two or more layers. By providing multiple coating layers, coating defects such as uneven coating can be reduced compared to the case of a single layer. In this case, it is preferable that the composition of the outermost layer among the two or more coating layers has a smaller amount of pigment per 100 parts by mass of thermoplastic resin (a larger amount of thermoplastic resin) compared to the composition of the entire coating layer, and contains 20 parts by mass or more and 80 parts by mass of pigment per 100 parts by mass of thermoplastic resin. It is more preferable that the amount of pigment per 100 parts by mass of thermoplastic resin in the outermost layer is 1 part by mass or more less than the amount of pigment per 100 parts by mass of thermoplastic resin in the entire coating layer, and even more preferable that it is 3 parts by mass or more less. Furthermore, it is more preferable that the outermost layer contains 30 parts by mass or more and 70 parts by mass of pigment per 100 parts by mass of thermoplastic resin. Specifically, when the coating layer consists only of a thermoplastic resin and a pigment, if the amount of pigment blended per 100 parts by mass of thermoplastic resin in the entire coating layer is 80 parts by mass, then it is preferable that the amount of pigment blended per 100 parts by mass of thermoplastic resin in the outermost layer be 20 parts by mass or more and less than 80 parts by mass. Also, if the amount of pigment blended per 100 parts by mass of thermoplastic resin in the entire coating layer is 50 parts by mass, then it is preferable that the amount of pigment blended per 100 parts by mass of thermoplastic resin in the outermost layer be 20 parts by mass or more and less than 50 parts by mass.

[0022] The method for applying the coating layer is not particularly limited and can be applied using known coating equipment and coating systems. For example, coating equipment includes blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters, gate roll coaters, etc. Coating systems include water-based coating using solvents such as water, and solvent-based coating using solvents such as organic solvents. Since the heat-sealable paper of the present invention may be used in applications that come into contact with food, etc., water-based coating is preferable from the viewpoint of food safety. The viscosity, solid content concentration, etc., of the coating solution can be adjusted as appropriate depending on the coating equipment, coating system, etc. used.

[0023] The coating amount (dry mass) of the coating layer is 5 g / m² per side. 2 More than 20g / m 2 The following is preferable: Coating amount of 5 g / m² per side. 2 Below this level, the heat sealability decreases. Also, the coating amount is 20 g / m² per side. 2 Beyond this limit, heat sealability hardly improves, and costs increase. When the coating consists of two or more layers, it is preferable that the total coating amount of all layers be within the above range. Also, when there are two or more coating layers, the coating amount (dry mass) of the outermost layer should be 2 g / m² per side. 2 Preferably, it is 3 g / m 2 It is more preferable that the above conditions are met.

[0024] The heat-sealable paper of the present invention may have a coating layer and a paper substrate, and may have other layers such as a sealing layer, a printing layer, a light-shielding layer, a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, or a gas barrier layer. Preferably, a sealing layer is provided between the coating layer and the paper substrate. By providing a sealing layer, the occurrence of coating defects such as pinholes and streaks in the coating layer can be reduced, and water resistance and oil resistance can be improved. The heat-sealable paper of the present invention can be used as a heat-sealable paper for packaging purposes such as packaging materials for food, bags, containers, boxes, cups, and lids. [Examples]

[0025] (Evaluation method) (1) Heat sealability (Heat sealing conditions) Two 100mm square test pieces were cut from the obtained heat-sealable paper, and the coated layers were brought into contact with each other. The test was then conducted at a pressurized temperature of 130°C and a pressurized pressure of 2 kgf / cm². 2 With a pressurization time of 0.5 seconds It was heat-sealed. The heat-sealable suitability of the test specimens was evaluated by visually observing the peeled area after manually separating them, according to the following criteria. A: Delamination within the paper substrate (the paper substrate is destroyed) B: There are areas where delamination has occurred within the paper substrate and areas where delamination has occurred between the coating layer. C: Delamination between coating layers

[0026] (2) Blocking properties This evaluation simulates the adhesion of a heated coating layer to various equipment during product manufacturing or processing. A heated roll press (roll pressure 0.5 MPa, processing speed 2 m / min, arbitrary roll temperature) was used to pass a humidified sample (23°C, RH 50%) through the metal roll so that the coated surface was in contact with the metal roll. The degree of adhesion of the coated surface to the metal roll was then evaluated. An evaluation of A or B indicates no practical problems. [Evaluation Criteria] A: At a roll temperature of 70°C, no adhesion was observed, and no damage to the coated surface was seen. B: At a roll temperature of 60°C, no adhesion was observed, and no damage to the coated surface was seen. C: At a roll temperature of 60°C, damage to the coated surface is observed, such as the coating layer adhering to the metal roll and the coating layer being removed from the metal roll.

[0027] (3) Dissociability The obtained heat-sealed paper was disintegrated using a pulp disintegration tester (manufactured by Kumagai Riki Kogyo Co., Ltd., compliant with JIS P8220) under the conditions of a concentration of 2.5%, a water volume of 2000 ml, a water temperature of 40°C, and a disintegration time of 20 minutes, without pre-swelling of the test specimens. After disintegration, the disintegration solution was diluted with water to a concentration of 0.5%. The diluted dissociation solution was subjected to a slit screen (0.15 mm width) to remove foreign matter, and the residue rate was calculated from the mass of residue on the screen. [Criteria for evaluating residue rate] A: No residue remains at all, or the amount of remaining residue is less than 10% by mass of the heat-sealing paper that was put in. B: The amount of remaining residue is between 10% and 20% by mass of the heat-sealing paper that was put in. C: The amount of remaining residue is 20% or more of the mass of the heat-sealing paper that was put in.

[0028] "Example 1" (Preparation of coating liquid for coating layer) A thermoplastic resin (polyolefin resin manufactured by Dow Chemical: RHOBARR320) and kaolin (manufactured by Imerys: KCS, standard white kaolin, D50: 4.6 μm) were prepared in a solid content mass ratio of 100.0 / 50.0 parts, respectively, to obtain a coating solution for a coating layer with a solid content concentration of 50% by mass. (Preparation of heat-sealable paper) Paper base material (basis weight 50g / m 2 On one side of the bleached kraft paper, apply a coating liquid for the coating layer at a dry weight of 10.0 g / m². 2 The paper was coated and dried using the barblade method to obtain heat-sealable paper.

[0029] [Example 2] Heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the coating layer was set to 100.0 / 150.0.

[0030] [Comparative Example 1] Heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the coating layer was set to 100.0 / 10.0. [Comparative Example 2] Heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the coating layer was set to 100.0 / 20.0. [Comparative Example 3] Heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the coating layer was set to 100.0 / 30.0. [Comparative Example 4] Heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the coating layer was set to 100.0 / 300.0. [Comparative Example 5] Heat-sealable paper was obtained in the same manner as in Example 1, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the coating layer was set to 100.0 / 500.0.

[0031] [Table 1]

[0032] [Example 3] (Preparation of coating liquid for undercoat layer) A thermoplastic resin and kaolin (Imeris Co., Ltd.: KCS, standard white kaolin) were prepared in a solid content mass ratio of 100.0 / 100.0 parts each to obtain a coating liquid for the undercoat layer. (Preparation of coating liquid for the top coating layer) A thermoplastic resin and kaolin (Imeris Co., Ltd.: KCS, standard white kaolin) were prepared in a solid content mass ratio of 100.0 / 20.0 parts, respectively, to obtain a coating liquid for the top coating layer. (Preparation of heat-sealable paper) Paper base material (basis weight 50g / m 2 On one side of the bleached kraft paper, apply the undercoating liquid by dry weight at a rate of 5.0 g / m². 2 After coating using the barblade method and drying, the top coating liquid is applied at a dry weight of 5.0 g / m². 2 The paper was coated and dried using the barblade method to obtain heat-sealable paper.

[0033] [Example 4] Heat-sealable paper was obtained in the same manner as in Example 3, except that the mass ratio of thermoplastic resin to kaolin in the coating liquid for the top coating layer was set to 100.0 / 80.0. [Example 5] A coating solution for the coating layer was obtained in the same manner as in Example 3, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the undercoat layer was 100.0 / 60.0, and the mass ratio of thermoplastic resin to kaolin in the coating solution for the topcoat layer was 100.0 / 50.0.

[0034] [Comparative Example 6] A coating solution for the coating layer was obtained in the same manner as in Example 3, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the undercoat layer was 100.0 / 250.0, and the mass ratio of thermoplastic resin to kaolin in the coating solution for the topcoat layer was 100.0 / 100.0. [Comparative Example 7] A coating solution for the coating layer was obtained in the same manner as in Example 3, except that the mass ratio of thermoplastic resin to kaolin in the coating solution for the undercoat layer was 100.0 / 60.0, and the mass ratio of thermoplastic resin to kaolin in the coating solution for the topcoat layer was 100.0 / 10.0.

[0035] [Table 2]

Claims

1. The material comprises a paper substrate and a heat-sealable coating layer containing at least a thermoplastic resin and a pigment. The heat-sealable coating layer consists of two or more layers. The heat-sealable coating layer, as a whole, contains 50 to 150 parts by mass of pigment per 100 parts by mass of thermoplastic resin. The outermost layer of the heat-sealable coating layer has a lower pigment content per 100 parts by mass of thermoplastic resin compared to the entire heat-sealable coating layer, and contains 20 parts by mass or more and 80 parts by mass of pigment per 100 parts by mass of thermoplastic resin. A heat-sealable paper characterized in that the thermoplastic resin includes a polyolefin resin.

2. The amount of the heat-sealable coating layer applied is 5 g / m². ２ 20g / m or more ２ The heat seal paper according to claim 1, characterized in that it is as follows.

3. The amount of coating on the outermost layer is 2 g / m ２ The heat seal paper according to claim 1 or 2, characterized in that it is as described above.

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