Heat-sealable paper, packaging paper

Abstract

The present invention provides a heat-sealable paper that can be manufactured with high productivity and that, after waste paper thereof is disintegrated in water, can be reused as is in a papermaking machine provided with an on-machine coating machine.　The heat-sealable paper of the present invention has a paper base material and a heat-sealable component adhered to one or both sides of the paper base material. The heat-sealable component includes a thermoplastic resin, and the Oken-type air permeability of the surface to which the heat-sealable component is attached is more than 700 seconds and less than 100,000 seconds.

Description

Technical Field

[0001] The present invention relates to heat-sealing paper and packaging paper. This application claims priority based on Japanese Patent Application No. 2022-108890 filed with the Japan Patent Office on July 6, 2022, and incorporates its content herein.

Background Art

[0002] Heat-sealing paper having a heat-sealing layer containing a thermoplastic resin may be used as packaging paper in various fields such as, for example, food, medical products, and electronic components (for example, Patent Documents 1 to 5). These heat-sealing layers are provided by covering the surface of a paper base material by applying or thermally laminating a resin layer containing a thermoplastic resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to improve the productivity of heat-sealing paper, it is effective to use a paper-making machine equipped with an on-machine coater. In a paper-making machine equipped with an on-machine coater, a coating layer is provided on the surface of the paper obtained from a pulp slurry, and then the heat-sealing paper is collected by a winding device. However, unevenness in paper and coating thickness is likely to occur at both ends of the winding in the width direction. As a result, waste paper is generated when the ends of the heat-sealed paper are removed by the slitter. In addition to this, waste paper can also be generated during the operation of the paper machine, for example, when adjusting the quality at the start of papermaking and when changing windings.

[0005] The inventors believed that if the waste paper generated during the operation of a paper machine equipped with an on-machine coating machine could be disintegrated with water and reused as pulp raw material, the productivity of heat-sealed paper could be further increased and production costs could be further reduced. However, in conventional heat-sealed paper such as those described in Patent Documents 1-5, when disintegrated with water, the coating film consisting of the heat-seal layer remains in the water as film fragments several millimeters in size. These film fragments become foreign matter in subsequent processes, causing blockages and defects. Therefore, unless special equipment is used, waste paper cannot be reused as raw material in a paper machine equipped with an on-machine coating machine even if it is disintegrated with water.

[0006] This invention provides heat-sealable paper that can be manufactured with high productivity by allowing waste paper to be separated with water and then reused in a paper machine equipped with an on-machine coating machine. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] Heat-sealable paper comprising; a paper substrate; and a heat-seal component attached to one or both sides of the paper substrate; wherein the heat-seal component contains a thermoplastic resin; and the Wang-Ren air permeability of the surface to which the heat-seal component is attached, as measured in accordance with JIS P 8117:2009, is greater than 700 seconds and less than or equal to 100,000 seconds. [2] The heat seal paper according to [1], wherein the surface to which the heat seal component is attached has a Wang Ken smoothness of 30 seconds or more. [3] The heat-sealable paper of [1] or [2], wherein the thermoplastic resin is at least one selected from the group consisting of biodegradable resins and non-petroleum-derived resins. [4] A heat-sealing paper according to any of [1] to [3], wherein the total content of thermoplastic resin in the heat-sealing component is 90% by mass or more. [5] A heat-sealable paper according to any of [1] to [4], wherein the heat-sealing component further comprises a polyacrylate salt; the content of the polyacrylate salt is 0.1 to 3.0% by mass relative to the total content of the thermoplastic resin in the heat-sealing component. Packaging paper equipped with one of the heat-sealable papers [6][1] to [5]. [Effects of the Invention]

[0008] According to the present invention, a heat-sealable paper is provided that can be manufactured with high productivity by allowing waste paper to be separated with water and then reused in a paper machine equipped with an on-machine coating machine. [Modes for carrying out the invention]

[0009] <Terms, etc.> "Wangyan-style air permeability" refers to air permeability measured in accordance with JIS P 8117:2009. "Wang Gan-style smoothness" refers to the smoothness measured in accordance with JIS P 8155:2010. In this specification, the "~" symbol indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively. The lower and upper limits of the numerical ranges disclosed herein can be combined in any way to create new numerical ranges.

[0010] <Heat sealable paper> The heat-sealable paper of the present invention comprises a paper substrate and a heat-sealing component attached to one or both sides of the paper substrate. In the heat-sealable paper of the present invention, the air permeability of the surface to which the heat-sealing component is attached is 100,000 seconds or less according to the Oken method, so it is considered that the heat-sealing component is attached to the paper substrate as a discontinuous film with appropriately sized pores on the surface. Therefore, when the heat-sealing component is disintegrated, it becomes extremely fine, and most of it is discharged outside the production system. Thus, waste paper can be disintegrated with water and reused as pulp raw material in a paper machine equipped with an on-machine coating machine, enabling productive manufacturing. Furthermore, in the heat-sealable paper of the present invention, the air permeability of the surface to which the heat-sealing component is attached is greater than 700 seconds, more preferably 1000 seconds or more. Because the air permeability of the surface to which the heat-sealing component is attached is greater than 700 seconds according to the Oken method, sufficient heat-sealing properties are exhibited.

[0011] Conventionally, heat-sealable papers with an air permeability exceeding 100,000 seconds, such as laminated paper, are difficult to decompose because they have a continuous layer of resin. Even if they do decompose, the resin layer remains in the water as film fragments, so if they are reused in a paper machine equipped with an on-machine coating machine, defects and contamination may occur, potentially negatively impacting the operation of the production line. In contrast, in the present invention, since the Wangyan air permeability is 100,000 seconds or less, the surface to which the heat-sealing component is attached has good breathability and is considered to be a discontinuous layer with an appropriate number of pores on the surface. Furthermore, even if a continuous layer consisting of the heat-sealing component is partially formed, the thickness of that layer is considered to be extremely thin. Therefore, when the heat-sealable paper of the present invention is disintegrated in water, the heat-sealing components remain attached but are finely dispersed in the water. As a result, problems are unlikely to occur even if waste paper is disintegrated in water and reused as pulp raw material in a paper machine equipped with an on-machine coating machine. Consequently, the heat-sealable paper of the present invention can be manufactured with high productivity.

[0012] (Paper base material) The paper base material is mainly composed of pulp. The paper base material may be any commonly used paper and is not particularly limited. For example, a paper base material mainly composed of wood pulp can be mentioned. Also, a paper base material mainly composed of pulp that is easily dispersed in water by mechanical disintegration action is preferred. Here, "mainly composed of pulp" means that the pulp content in the paper base material is 70% by mass or more. The pulp content in the paper base material may be 80% by mass or more, 90% by mass or more, or 100% by mass.

[0013] Examples of the paper base material include, for example, bleached kraft paper, unbleached kraft paper, fine paper, cardboard, liner paper, coated paper, one-sided coated paper, glassine paper, and graphan paper. Among them, in terms of the heat-sealing property of heat-sealing paper, bleached kraft paper, unbleached kraft paper, coated paper, and one-sided coated paper are preferred.

[0014] The pulp of the paper base material is not particularly limited. Any pulp for papermaking can be used. For example, chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood sulfite pulp (LBSP), and softwood sulfite pulp (NBSP) can be mentioned. In addition, there are also unbleached pulps, semi-bleached pulps, and bleached pulps such as stone ground pulp (GP), pressure stone ground pulp (PGW), refiner ground pulp (RGP), chemiground pulp (CGP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP). Sulfite pulp, waste paper pulp, etc. can also be mentioned.

[0015] The paper base material may further contain various internal additives. Examples of the internal additives include, for example, sizing agents, fillers, paper strength enhancers, yield improvers, pH adjusters, drainage improvers, water resistance agents, softeners, antistatic agents, defoaming agents, slime control agents, dyes, and pigments.

[0016] The disintegration freeness (water permeability) of paper substrates, measured in accordance with JIS P8121:2012, is preferably 200-600 ml, more preferably 220-500 ml, and even more preferably 250-450 ml, from the viewpoint of heat sealability. Disintegration freeness is the Canadian standard freeness measured in accordance with JIS P8121:2012 of pulp obtained by disintegrating paper after papermaking in accordance with JIS P8220-1.

[0017] The basis weight of the paper substrate is 20-500 g / m². 2 Preferably, 30-350 g / m² 2 More preferably, 35-200 g / m 2 This is even more preferable. If the basis weight of the paper substrate is above the lower limit of the aforementioned numerical range, the strength of the heat-seal paper tends to improve. If the basis weight of the paper substrate is below the upper limit of the aforementioned numerical range, the moldability of the heat-seal paper tends to improve. The basis weight of paper substrates is measured in accordance with JIS P 8124.

[0018] The thickness of the paper substrate is preferably 20 to 650 μm, more preferably 30 to 450 μm, and even more preferably 35 to 250 μm. If the thickness of the paper substrate is above the lower limit of the above numerical range, the strength of the heat-sealable paper tends to improve. If the thickness of the paper substrate is below the upper limit of the above numerical range, the delamination properties tend to improve further. In addition, the moldability of the heat-sealable paper tends to improve. The thickness of the paper substrate is measured in accordance with JIS P 8118.

[0019] In the paper substrate, the surface to which the heat-sealing component adheres is preferably 30 seconds or more, more preferably 50 seconds or more, and even more preferably 100 seconds or more. When the surface to which the heat-sealing component adheres is 30 seconds or more than the lower limit, heat-sealable paper with excellent heat-sealing properties is more likely to be obtained. There is no particular upper limit to the surface to which the heat-sealing component adheres is 30 seconds or more. Considering that the air permeability of heat-sealable paper is 100,000 seconds or less, an upper limit of about 2000 seconds is considered to be the upper limit. The Wangyan method of smoothness is measured in accordance with JIS P 8155:2010.

[0020] The paper substrate may further have an optional layer, such as a clay coat layer, on one or both sides, or on at least a portion thereof, as needed. The clay coat layer is for sealing and smoothing the paper substrate. Examples of clays include kaolin, talc, and mica.

[0021] (Heat seal component) The heat-sealing component contains a thermoplastic resin. Therefore, the heat-sealing paper exhibits heat-sealing properties within a practical heating temperature range. Examples of thermoplastic resins include polyethylene, polypropylene, olefin-unsaturated carboxylic acid copolymers, biodegradable resins, acrylic resins, ethylene vinyl alcohol, polystyrene resins, polycarbonate resins, polyacetal resins, polyester resins, polyamides, styrene-butadiene latex, polyvinyl alcohol, and polyvinylidene chloride. The thermoplastic resin may also be a non-petroleum-derived resin. Thermoplastic resins may be used individually or in combination of two or more types.

[0022] Examples of olefin-unsaturated carboxylic acid copolymers include ethylene-acrylic copolymers. Examples of acrylic monomers that form the constituent units of olefin-acrylic copolymers include: Unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butentricarboxylic acid; Alkyl unsaturated polycarboxylates having at least one carboxyl group, such as monoethyl itaconate, monobutyl fumarate, and monobutyl maleate; Examples include unsaturated sulfonic acid monomers and their salts, such as acrylamidepropanesulfonic acid, sodium sulfoethyl acrylate, and sodium sulfopropyl methacrylate. Acrylic monomers may be used individually or in combination of two or more types.

[0023] Olefin-unsaturated carboxylic acid copolymers can be obtained, for example, by emulsion polymerization of an olefin such as ethylene with an acrylic monomer. Commercially available olefin-unsaturated carboxylic acid copolymers may be used. Examples of commercially available olefin-unsaturated carboxylic acid copolymers include Zyxene AC (aqueous dispersion of ethylene-acrylic acid copolymer ammonium salt, with an acrylic acid copolymerization ratio of 20 mol%), a product of Sumitomo Seika Co., Ltd.

[0024] Examples of biodegradable resins include polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), and poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBH). Biodegradable resins may be used individually or in combination of two or more types.

[0025] In terms of availability, polylactic acid and polybutylene succinate are preferred as biodegradable resins, with polylactic acid being more preferred. Polylactic acid may be a homopolymer of L-lactic acid, a homopolymer of D-lactic acid, a copolymer of L-lactic acid and D-lactic acid, or a copolymer of L-lactic acid, D-lactic acid, and monomers copolymerizable with these. Examples of monomers copolymerizable with L-lactic acid and D-lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid, but are not limited to these examples. One monomer copolymerizable with L-lactic acid and D-lactic acid may be used alone, or two or more may be used in combination. Commercially available polylactic acid may be used. Examples of commercially available polylactic acid include Randy PL-1000 and Randy PL-3000 (aqueous dispersions of polylactic acid) from Miyoshi Oil & Fat Co., Ltd., and Rezem Y225 (aqueous dispersion of polylactic acid) from Chukyo Oil & Fat Co., Ltd.

[0026] Non-petroleum-derived resins are not particularly limited and include various thermoplastic resins. Examples include biomass-derived polyolefins, biomass-derived polyesters, biomass-derived polyamides, biomass-derived polyurethanes, and biomass-derived cellulose acetates. As for the biomass, plant-derived materials are preferred. Examples include corn-derived biomass and sugarcane-derived biomass. Non-petroleum-derived resins may be used individually or in combination of two or more.

[0027] Examples of biomass-derived polyolefins include polymers of various olefins such as ethylene and propylene, and copolymers of these olefins, but are not limited to these examples. Among these, biomass-derived polypropylene and biomass-derived polyethylene are preferred, and biomass-derived polyethylene is more preferred.

[0028] Commercially available biomass-derived polyolefins may be used. Examples of commercially available biomass-derived polyolefins include SBC818 (biomass low-density polyethylene) and SGF4950 (biomass high-density polyethylene) from Braschem.

[0029] In biomass-derived polyesters, either or both of the alcohol units and carboxylic acid units are derived from biomass. Examples of alcohols include diols. Examples include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, decanediol, and 2-ethyl-butyl-1-propanediol. However, the alcohols are not limited to these examples. Furthermore, one type of alcohol may be used alone, or two or more types may be used in combination. Examples of carboxylic acids include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and their derivatives. However, the carboxylic acids are not limited to these examples. Furthermore, a single carboxylic acid may be used, or two or more may be used in combination.

[0030] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, and phthalic acid. Examples of derivatives of aromatic dicarboxylic acids include lower alkyl esters of aromatic dicarboxylic acids (e.g., methyl esters, ethyl esters, propyl esters, butyl esters, etc.). However, aromatic dicarboxylic acids are not limited to these examples. Examples of aliphatic dicarboxylic acids include chain-like or alicyclic dicarboxylic acids having 2 to 40 carbon atoms. Examples include, but are not limited to, oxalic acid, succinic acid, glutaric acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, dodecanediic acid, dimer acid, azelaic acid, dodecadicarboxylic acid, and cyclohexanedicarboxylic acid. Examples of derivatives of aliphatic dicarboxylic acids include lower alkyl esters of aliphatic dicarboxylic acids (e.g., methyl esters, ethyl esters, propyl esters, butyl esters, etc.). Acid anhydrides of aliphatic dicarboxylic acids such as succinic anhydride are also examples.

[0031] Commercially available biomass-derived polyesters may be used. An example of a commercially available biomass-derived polyester is CB602AB (biopolyethylene terephthalate) from FENC Corporation.

[0032] From an environmental perspective, at least one thermoplastic resin selected from the group consisting of biodegradable resins and non-petroleum-derived resins is preferred. Since biodegradable resins and non-petroleum-derived resins are often expensive, there is also the significant technical significance of applying the present invention, namely the significant benefit of improved productivity due to improved disintegrability.

[0033] If the thermoplastic resin has a melting point, it is preferably 130 to 180°C, more preferably 140 to 170°C, and even more preferably 150 to 160°C. When the melting point of the thermoplastic resin is within the above range, the adhesive strength of the heat-seal paper after heat sealing can be further enhanced. Also, because the melting point is higher than the typical drying temperature in the manufacturing process, the resin of the heat-seal component is less likely to form a continuous film. Therefore, the heat-seal paper disintegrates easily in water, and even when reused in the papermaking process of a paper substrate in a paper machine equipped with an on-machine coating machine, defects caused by the heat-seal component are less likely to occur. The melting point of thermoplastic resins is measured using a differential scanning calorimeter (DSC). If the heat seal component contains two or more types of thermoplastic resins, the melting point of the thermoplastic resin is defined as the mass average value measured for a mixture of multiple thermoplastic resins.

[0034] The total content of thermoplastic resin in the heat seal component is preferably 90% by mass or more, more preferably 90-99% by mass, and even more preferably 95-99% by mass. When the total content of thermoplastic resin in the heat seal component is above the lower limit of the above numerical range, the heat sealability tends to improve. When the total content of thermoplastic resin in the heat seal component is below the upper limit of the above numerical range, blocking and excessive foaming tend to be suppressed.

[0035] The heat-sealing component can enhance the adhesive strength of the heat-sealing paper after heat sealing, and therefore, it is preferable to further include a polyacrylate salt. Examples of polyacrylate salts include sodium salts, potassium salts, and ammonium salts of acrylic acids such as polyacrylic acid, maleic acrylic acid copolymer, and sulfonic acrylic acid copolymer, but the invention is not limited to these examples. When the heat seal component contains a polyacrylate, the polyacrylate content is preferably 0.1 to 3.0% by mass, more preferably 0.2 to 2.0% by mass, and even more preferably 0.5 to 1.5% by mass, relative to the total content of the thermoplastic resin in the heat seal component. If the polyacrylate content is above the lower limit of the aforementioned numerical range, good heat sealability is likely to be obtained. If the polyacrylate content is below the upper limit of the aforementioned numerical range, a heat sealability improvement effect commensurate with the amount added will be obtained.

[0036] The heat-sealing component may optionally contain other auxiliary agents besides thermoplastic resins. Examples of auxiliary agents include defoamers, thickeners, polysaccharides, neutralizing agents, plasticizers, preservatives, pH adjusters, crosslinking agents, antiblocking agents, lubricants, and dyes. However, the auxiliary agents are not limited to these examples.

[0037] (Properties of heat-sealing paper) The Wang Ken air permeability of the surface to which the heat-sealing component is attached is 100,000 seconds or less. Preferably, the Wang Ken air permeability is 60,000 seconds or less, more preferably 50,000 seconds or less, and even more preferably 10,000 seconds or less. The fact that the Wang Ken air permeability of the heat-sealing paper is below the above upper limit suggests that there are appropriately discontinuous portions of the thermoplastic resin, which is the heat-sealing component attached to the surface of the paper substrate. In such a state, even if the heat-sealing paper is disintegrated in water and reused in the papermaking process of the paper substrate, defects caused by the heat-sealing component are less likely to occur. In terms of disintegrability, a lower Wang Ken air permeability of the heat-sealing paper is better, but the lower limit is greater than 700 seconds, and more preferably 1,000 seconds or more, considering its use as heat-sealing paper. The Wangyan method air permeability is measured in accordance with JIS P 8117:2009.

[0038] The residue rate of the heat-sealing paper is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.3% or less. When the residue rate of the heat-sealing paper is below the above upper limit, the residue is less likely to cause problems in the process after disintegration, and the disintegrated slurry can be easily returned to the raw material. The residue rate of heat-sealing paper is measured as follows: The heat-sealing paper is immersed in water to a solid content concentration of 2.0% by mass. Then, the slurry obtained by dissociating the paper for 30 minutes using a pulp dissociation tester compliant with JIS P 8220 is processed on a flat screen with a mesh size of 0.25 mm, and the dry mass of the residue (reject) is measured. The residue rate is calculated by dividing the dry mass of the residue by the dry mass of the heat-sealing paper and multiplying the result by 100.

[0039] In heat-sealable paper, the Wang Ken smoothness of the surface to which the heat-sealing component is attached is preferably 30 seconds or more, more preferably 100 seconds or more, and even more preferably 200 seconds or more. When the Wang Ken smoothness of the surface to which the heat-sealing component is attached is above the lower limit, the surface smoothness is high and the heat-sealing performance is easily improved. There is no particular upper limit to the Wang Ken smoothness of the surface to which the heat-sealing component is attached. Considering that the Wang Ken air permeability is 100,000 seconds or less, an upper limit of about 1,000 seconds is considered to be the upper limit.

[0040] The amount of thermoplastic resin deposited on a paper substrate per unit area is 1 to 10 g / m² per side. 2 Preferably, 2-8 g / m 2 More preferably, 3-6 g / m 2 This is even more preferable. If the amount of thermoplastic resin adhering per unit area is above the lower limit of the aforementioned numerical range, the heat sealability tends to improve. If the amount of thermoplastic resin adhering per unit area is below the upper limit of the aforementioned numerical range, blocking and contamination during the process tend to be suppressed.

[0041] The thickness of the heat-sealing component adhering to the surface of the paper substrate fibers is thought to be approximately 10 μm or less, but is not particularly limited. The thickness of the heat-sealing component on the surface of the paper substrate fibers can be confirmed by microscopic observation of the fiber cross-section. In a cross-sectional view perpendicular to the plane of the heat-sealing paper, a heat-sealing layer consisting of heat-sealing components may be observed, but it is thought that such a heat-sealing layer may not always be clearly visible.

[0042] In heat-sealable paper, the heat-sealing component may be attached to one side of the paper substrate or to both sides. For further reduction of production costs, it is preferable that the heat-sealing component be attached to one side of the paper substrate.

[0043] (Manufacturing method for heat-sealable paper) Heat-sealable paper can be manufactured by applying heat-sealing components to one or both sides of a paper substrate so that the Wangyan air permeability is 100,000 seconds or less. Methods to achieve a Wangyan-type air permeability of 100,000 seconds or less include, for example, the following: • Use a thermoplastic resin with a melting point of 130-180°C. • Ensure the decomposition-freeness of the paper substrate is 200 ml or more.

[0044] The paper substrate can be manufactured, for example, by making paper using various paper machines, forming wet paper, and drying it. The paper machine is not particularly limited. Examples include a long-wire paper machine, a gap former type paper machine, a cylinder-wire paper machine, and a short-wire paper machine. Furthermore, a paper machine equipped with an on-machine coating machine is preferred because it makes it easier to obtain the effects of the present invention.

[0045] For the preparation of pulp slurry for papermaking, it is preferable to disintegrate the pulp and beat it using a refiner and beater to give the pulp appropriate flexibility and fluffiness. However, the pulp beating method is not particularly limited. The disintegration freeness (water permeability), which is an indicator of the degree of pulp beating, is preferably 200 to 600 ml, more preferably 220 to 500 ml, and even more preferably 250 to 450 ml, from the viewpoint of the air permeability of heat-sealed paper and the physical properties of the paper. The beaten pulp may be mixed with internal additives such as sizing agents and paper strength enhancers as needed, dispersed in water, and a pulp slurry of a concentration suitable for papermaking may be prepared.

[0046] The wet paper obtained from the paper machine is preferably dried using a multi-stage cylinder dryer, an air dryer, or a Yankee dryer.

[0047] The heat-sealable paper of the present invention can be manufactured, for example, by applying a coating liquid containing a heat-sealing component to one or both sides of a paper substrate, and then drying it. As the coating liquid, an aqueous dispersion of thermoplastic resin or an aqueous emulsion containing thermoplastic resin is preferred. When an aqueous dispersion or emulsion of thermoplastic resin is used as the coating liquid, the air permeability of the heat-sealing paper tends to be 100,000 seconds or less. The coating solution may further contain auxiliary agents as optional components in addition to the thermoplastic resin. The details and preferred embodiments of the thermoplastic resin and auxiliary agents are the same as those already described.

[0048] The method of applying the coating solution is not particularly limited. Various coating devices that are generally available can be used. Examples of coating machines include blade coaters, air knife coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, slot die coaters, gravure coaters, champlex coaters, brush coaters, slide bead coaters, two-roll size press coaters, pound size press coaters, rod metering size press coaters, blade metering size press coaters, short dwell coaters, gate roll coaters, and nip coaters with calenders. In particular, on-machine coating machines are preferred in terms of productivity. Examples of preferred on-machine coating machines include blade coaters, bar coaters, gate roll coaters, rod metering size press coaters, blade metering size press coaters, and pound size press coaters.

[0049] The heat-sealable paper may be subjected to a smoothing treatment as needed. The smoothing treatment can be performed on-machine or off-machine using a smoothing device such as a standard supercalender, gloss calender, or soft calender. The paper substrate may be smoothed before the coating liquid is applied, as long as it does not impair the effects of the invention. The heat-sealed paper is then wound into a roll. For example, to match the width of the wound paper to the width of a processing machine in a subsequent process, the ends of the roll may be removed using a slitter. The waste paper at both ends has a Wangyan air permeability of 100,000 seconds or less, so it disintegrates easily. Furthermore, the heat-sealing component adheres to the surface of this waste paper as a discontinuous film with a moderate number of pores. Therefore, after disintegrating with water, it can be reused directly in a paper machine equipped with an on-machine coating machine.

[0050] (Mechanism of action) In the heat-sealable paper described above, the air permeability of the surface to which the heat-sealing components are attached is 100,000 seconds or less according to the Oken method, resulting in excellent disintegration properties. Furthermore, waste paper generated after the heat-sealing components are attached by an on-machine coating machine, as well as other waste paper generated during the operation of the paper machine, can be reused as is. As a result, the number of sheets produced per unit of raw pulp increases, the productivity of heat-sealable paper is improved, paper production costs can be further reduced, and even lower costs can be achieved.

[0051] (Application) The applications of heat-sealable paper are not particularly limited. For example, it can be used as a material for packaging paper in various fields. For instance, it may have applications in fields such as food, medical products, electronic components, hygiene products, agricultural materials, and building materials. [Examples]

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following description.

[0053] <Raw materials> (Aqueous emulsion containing thermoplastic resin) • Aqueous emulsion 1: Polylactic acid (Chukyo Oil & Fat Co., Ltd. product "Rezem Y225", melting point 150℃) • Aqueous emulsion 2: Polylactic acid (Chukyo Oil & Fat Co., Ltd. product "Rezem W990", melting point 140℃) • Aqueous emulsion 3: Polylactic acid (Miyoshi Oil & Fat Co., Ltd. product "PL1005", melting point 160℃) • Aqueous emulsion 4: Polyolefin resin (Mitsui Chemicals product "Chemipearl", melting point 91℃) • Aqueous emulsion 5: Polyolefin resin (Sumitomo Seika Co., Ltd. product "Zyxen AC", melting point 80-95°C)

[0054] (Polyacrylate) • Polyacrylates: Polyacrylate-based sulfonates (Sunopco product "SN Thickener 615")

[0055] (Antifoaming agent) • Antifoaming agent: Mineral oil-based mixture (Sunopco product "Noptam 777F")

[0056] <Example 1> Aqueous dispersions with the compositions shown in Table 1 were prepared using aqueous emulsion 1. The blending ratios of polyacrylate and defoamer shown in Table 1 are values ​​when the solid content of the thermoplastic resin in aqueous emulsion 1 is set to 100% by mass. Using pulp made from LBKP that had been beaten to a disintegration-freeness of 250 ml, a pulp slurry was obtained by adding 1.5% by mass of aluminum sulfate (homemade), 0.55% by mass of rosin sizing agent (Arakawa Chemical Co., Ltd. product, Sizing Pine G), and 0.5% by mass of cationized starch (Oji Corn Starch Co., Ltd. product, GELTRON18) as internal additives. The pulp slurry was then prepared with a basis weight of 66 g / m². 2 The base paper produced by the papermaking process was used as the paper substrate. An aqueous dispersion was applied to the felt surface of this paper substrate on-machine using a rod metering size press coater, and then dried to obtain heat-sealable paper with a heat-seal component attached to one side.

[0057] <Examples 2-11, Comparative Examples 1-3> The basis weight of the paper substrate, the smoothness of the surface to which the heat-sealing component adheres, and the composition of the aqueous dispersion were changed in each example to match those shown in Tables 1 and 2, respectively. Except for these points, the aqueous dispersion was applied on-machine using a rod metering size press coater under the same conditions as in Example 1, and then dried to obtain heat-sealable paper with the heat-sealing component adhered to one side. Note that Example 4 is Reference Example 1, and Example 11 is Reference Example 2.

[0058] <Measurement methods, evaluation methods> (Oken-style air permeability of a surface with heat-sealing components attached) In accordance with JIS P 8117:2009, the air permeability of the surface to which the heat sealant component was attached was measured using the Ouken method.

[0059] (Estimated thickness of heat-sealing component (μm)) The thickness of the heat-sealing component attached to the heat-sealing paper in each example was estimated by dividing the mass of the heat-sealing component per unit area attached to the heat-sealing paper by the density of the heat-sealing component.

[0060] (Oken-style smoothness of the surface to which heat-sealing components are attached) In accordance with JIS P 8155:2010, the smoothness of the surface to which the heat sealant component was attached was measured using the Ouken method.

[0061] (Heat sealable) Two heat-sealable papers from each example were placed on top of each other with the sides to which the heat-sealing components were attached facing each other. They were then heat-bonded using a heat seal tester (Tester Sangyo Co., Ltd. product "TP701B") under conditions of 160°C, 0.2 MPa, and 1 second, and the heat sealability was evaluated according to the following criteria. A: When the adhesive is peeled off, the paper substrate is destroyed (material breakage). B: When the adhesive is peeled off, there is resistance, but no breakage occurs (interfacial delamination). C: When peeling off the adhesive, there is almost no resistance.

[0062] (blocking) Two heat-sealable papers from each example were placed on top of each other, with the side containing the heat-sealing component facing the side without the heat-sealing component. Then, they were pressed together using a hot press (Toyo Seiki Co., Ltd. product "MP-WNL") at 40°C, 4.6 MPa, and for 6 hours. The blocking properties of the pressed area were evaluated according to the following criteria. A: There is almost no resistance when peeling off the crimped part. B: When the crimped area is peeled off, there is some resistance, but the paper substrate is not damaged. C: When the crimped area is peeled off, the paper substrate is destroyed (material breakage).

[0063] (Dissociability) Heat-sealed paper from each example was used as a sample, and the sample was immersed in water so that the solid content concentration of the sample was 2.0% by mass. The slurry obtained by dissociating the paper for 30 minutes using a pulp dissociation tester compliant with JIS P 8220 was processed on a flat screen with a mesh size of 0.25 mm, and the dry mass of the residue (reject) was measured. The residue rate was calculated by dividing the dry mass of the residue by the dry mass of the sample and multiplying the result by 100, and the dissociability was evaluated according to the following criteria. A: The residue rate is less than 1%. B: The residue rate is 1% or more but less than 3%. C: The residue rate is 3% or higher.

[0064] <Result> The measurement and evaluation results for each example are shown in Tables 1 and 2.

[0065] [Table 1]

[0066] [Table 2]

[0067] The blending ratios of polyacrylates and defoamers shown in Tables 1 and 2 are based on the solid content of the thermoplastic resin in the aqueous emulsion being 100% by mass. Examples 1 to 11 yielded heat-sealable paper with excellent decomposition properties. Because the Wangyan air permeability is less than 100,000 seconds, film fragments are less likely to remain after the waste paper is decomposed with water. Therefore, it is considered that the paper can be reused directly in a paper machine equipped with an on-machine coating device. In contrast, in Comparative Examples 1 and 2, the Oken-style air permeability was too high to measure, exceeding 100,000 seconds. Therefore, the disintegration properties were insufficient. If waste paper is disintegrated with water and then reused as pulp raw material, the film fragments in the water become foreign matter, causing blockages and defects, which is thought to disrupt the operation of the paper machine. In Comparative Example 3, the Oken-style air permeability was too low, which is thought to be why sufficient heat sealability could not be obtained. [Industrial applicability]

[0068] According to the present invention, a heat-sealable paper is provided that can be manufactured with high productivity by allowing waste paper to be separated with water and then reused in a paper machine equipped with an on-machine coating machine.

Claims

1. Paper substrate and A heat-sealing component attached to one or both sides of the aforementioned paper substrate, It has, The heat-sealing component includes a thermoplastic resin. The Wangyan air permeability of the surface to which the heat-sealing component is attached, measured in accordance with JIS P 8117:2009, is greater than 700 seconds and less than or equal to 100,000 seconds. The thermoplastic resin comprises polylactic acid having a melting point of 130 to 180°C and a polyacrylate salt. A heat-sealing paper in which the content of the polyacrylate is 0.1 to 3.0% by mass relative to the total content of the thermoplastic resin in the heat-sealing component.

2. The heat-sealing paper according to claim 1, wherein the surface on which the heat-sealing component is attached has a Wang Ken smoothness rating of 30 seconds or more.

3. The heat-seal paper according to claim 1 or 2, wherein the total content of thermoplastic resin in the heat-seal component is 90% by mass or more.

4. Packaging paper comprising the heat-sealable paper according to claim 1 or 2.

Images