Coating agent for food packaging sheet, food packaging sheet, and food packaging container

Abstract

To provide a coating agent for food packaging sheets enabling formation of a coat layer having superior oil resistance and superior anti-blocking performance under high temperature, and a food packaging sheet and a food packaging container, each made using the coating agent.SOLUTION: A coating agent for a food packaging sheet comprises a polysaccharide and at least one wax (A) selected from the group consisting of polyethylene wax and polypropylene wax. The content of the polysaccharide is 50 to 98 mass% relative to the total 100 mass% of the non-volatile content of the coating agent. The wax (A) has a melting point of 100°C to 180°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a coating agent for food packaging sheets, food packaging sheets, and food packaging containers.

Background Art

[0002] Conventionally, in food packaging sheets and containers, laminate sheets obtained by laminating a resin film on a paper substrate have been widely used for the purpose of preventing oil stains caused by oil components derived from food and sticking of food. However, in recent years, efforts have been made worldwide to reduce the environmental impact, and efforts such as reducing the use of plastics and designing recyclable products have been carried out. Along with this, in food packaging sheets and containers, instead of conventional laminate sheets, the development of paper-coated food packaging sheets in which a coating agent is applied on a paper substrate that is easy to recycle and can reduce the amount of plastic used has been actively carried out.

[0003] As such a packaging sheet, for example, Patent Document 1 discloses a coating agent for paper containing a copolymer having a glass transition temperature of 30°C or lower, carnauba wax, and an aqueous solvent, and coated paper having the same.

[0004] However, in a sheet having such a coating agent, blocking occurs between the sheets during storage or transportation in a high-temperature environment, and defects occur at the blocking occurrence points when peeling the sheets stored in a stacked manner, resulting in oil stains at the defective parts of the substrate or sticking of food, making it difficult to use as a packaging sheet.

[0005] On the other hand, in order to improve the blocking resistance at high temperatures, when a coating agent using a hard acrylic resin is applied to create a packaging sheet, the film-forming property of the resin deteriorates, coating film defects occur, and the oil resistance and food sticking resistance decrease.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 2023-94001 Summary of the Invention Problems to be Solved by the Invention

[0007] The problem to be solved by the present invention is to provide a coating agent for a food packaging sheet capable of forming a coating layer excellent in oil resistance and blocking resistance at high temperatures, a food packaging sheet using the same, and a food packaging container. Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention. The present invention relates to a coating agent for a food packaging sheet containing a polysaccharide and at least one wax (A) selected from the group consisting of polyethylene wax and polypropylene wax, wherein the content of the polysaccharide is 50 to 98% by mass in the total 100% by mass of the non-volatile matter of the coating agent, and the melting point of the wax (A) is 100 to 180°C.

[0009] Preferably, the coating agent for the food packaging sheet contains 2 to 100 parts by mass of the wax (A) with respect to 100 parts by mass of the polysaccharide.

[0010] Preferably, the coating agent for the food packaging sheet contains 10 to 100 parts by mass of the polyethylene wax with respect to 100 parts by mass of the polysaccharide.

[0011] Preferably, the coating agent for the food packaging sheet contains 3 to 50 parts by mass of the polypropylene wax with respect to 100 parts by mass of the polysaccharide.

[0012] Further, the present invention relates to a food packaging sheet having a coating layer formed from the above coating agent for a food packaging sheet on at least one surface of a base material.

[0013] Furthermore, the present invention relates to a food packaging container formed by processing the above food packaging sheet.

Advantages of the Invention

[0014] According to the present invention, it has become possible to provide a coating agent for a food packaging sheet capable of forming a coating layer excellent in oil resistance and blocking resistance at high temperatures, a food packaging sheet using the same, and a food packaging container.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail. In this specification, a numerical range specified using "~" shall include the numerical values described before and after "~" as the lower limit value and the upper limit value. Each of the various components described in this specification is to be construed as being able to be used independently alone or in combination of two or more, unless otherwise noted. Also, a wax (A) having a melting point of 100 to 180°C, which is one or more selected from the group consisting of polyethylene wax and polypropylene wax, may be abbreviated as "wax (A)".

[0016] <Coating Agent for Food Packaging Sheet> The coating agent for a food packaging sheet of the present invention (hereinafter, may be abbreviated as "coating agent") is suitable for coating a substrate such as paper or non-woven fabric to form a coating layer (hereinafter, may be referred to as "coating layer") to produce a coated sheet, and is particularly suitable for producing a coated sheet for packaging food. Further, the coating agent of the present invention can form a coating layer not only excellent in blocking resistance at high temperatures but also having oil resistance and resistance to sticking of food, so it can be suitably used for applications where the coating layer is in direct contact with food. Also, "painting", "coating", and "applying" shall be treated as synonymous.

[0017] The coating agent of the present invention is a coating agent for a food packaging sheet containing a polysaccharide and one or more waxes (A) selected from the group consisting of polyethylene wax and polypropylene wax, wherein the content of the polysaccharide is 50 to 98% by mass in a total of 100% by mass of the non-volatile components of the coating agent, and the melting point of the wax (A) is 100 to 180°C. This coating agent is excellent in heat resistance and film-forming properties, and the sheet and packaging container using this coating agent can achieve both excellent blocking resistance and oil resistance at high temperatures, which was difficult with aqueous coating agents using conventional resins.

[0018] <Polysaccharide> The polysaccharide in this specification is a poly-1,4-glucan ether, which is a polymer in which monosaccharides are linked by glycosidic bonds with a degree of polymerization of 10 or more, and examples include starch, cellulose, pectin, xanthan gum, etc. In the present invention, among them, starch (poly-α-1,4-glucan ether), cellulose (poly-β-1,4-glucan ether) and their derivatives are preferably used. The derivatives here refer to oxides of polysaccharides and compounds obtained by subjecting polysaccharides to ester modification, ether modification, etc. More specifically, they represent oxidized starch, starch acetate, hydroxypropyl starch, carboxymethyl starch, sodium octenyl succinate starch, hydroxypropyl methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, etc.

[0019] The content of the polysaccharide is 50 to 98% by mass in a total of 100% by mass of the non-volatile components of the coating agent. If the content is 98% or less, it is excellent in blocking resistance at high temperatures. On the other hand, if it is 50% or more, performance such as oil resistance and resistance to sticking of food can be exhibited. The preferred content of the polysaccharide is 60 to 95% by mass in a total of 100% by mass of the non-volatile components of the coating agent.

[0020] <Wax (A)> Wax (A) refers to one or more waxes selected from the group consisting of polyethylene wax and polypropylene wax, and having a melting point of 100 to 180°C. As used herein, "polyethylene wax" includes low-density polyethylene wax, high-density polyethylene wax, modified polyethylene wax, low-molecular-weight polyethylene wax, high-molecular-weight polyethylene wax, etc. Also, as used herein, "polypropylene wax" includes modified polypropylene wax, low-molecular-weight polypropylene wax, high-molecular-weight polypropylene wax, etc. Here, "modified" means those whose properties have been changed by chemical and physical treatments such as acid modification, amine modification, and ester modification. Also, "low molecular weight" means those having a molecular weight of several tens of thousands or less, and "high molecular weight" means those having a molecular weight exceeding several tens of thousands.

[0021] Even if each of the selected polyethylene wax and polypropylene wax is not within the range of 100 to 180°C in melting point, Wax (A) may have a melting point within the range of 100 to 180°C as Wax (A). However, it is preferable that the melting points of the selected polyethylene wax and polypropylene wax are each 100 to 180°C. If the melting point is 100°C or higher, it has excellent blocking resistance at high temperatures. On the other hand, if it is 180°C or lower, it can exhibit properties such as oil resistance and resistance to food sticking. The preferable range of the melting point is 110 to 170°C.

[0022] The blending amount of Wax (A) is preferably 2 to 100 parts by mass, more preferably 5 to 100 parts by mass, and even more preferably 5 to 80 parts by mass with respect to 100 parts by mass of the polysaccharide. If it is 2 parts by mass or more with respect to 100 parts by mass of the polysaccharide, it has even more excellent blocking resistance at high temperatures. On the other hand, if it is 100 parts by mass or less, it can further exhibit properties such as oil resistance and resistance to food sticking.

[0023] When only polyethylene wax is used as wax (A), the blending amount of the polyethylene wax is preferably 10 to 100 parts by mass with respect to 100 parts by mass of the polysaccharide. If the amount of the polyethylene wax is 10 parts by mass or more with respect to 100 parts by mass of the polysaccharide, the blocking resistance at high temperatures is further improved. On the other hand, if it is 100 parts by mass or less, performances such as oil resistance and resistance to sticking of food can be further expressed. More preferably, it is within the range of 20 to 80 parts by mass with respect to 100 parts by mass of the polysaccharide.

[0024] When only polypropylene wax is used as wax (A), the blending amount of the polypropylene wax is preferably 3 to 50 parts by mass with respect to 100 parts by mass of the polysaccharide. If the amount of the polypropylene wax is 3 parts by mass or more with respect to 100 parts by mass of the polysaccharide, the blocking resistance at high temperatures is further improved. On the other hand, if it is 50 parts by mass or less, performances such as oil resistance and resistance to sticking of food can be further expressed. More preferably, it is within the range of 5 to 40 parts by mass with respect to 100 parts by mass of the polysaccharide.

[0025] From the viewpoint of the stability of the coating agent over time, it is preferable to use wax (A) that can be obtained in the form of an aqueous dispersion. The average particle diameter of wax (A) in the aqueous dispersion of wax (A) is preferably 10 μm or less, and more preferably 5 μm or less. If it is 10 μm or less, the coating suitability is excellent, and if it is 5 μm or less, the unevenness due to wax spreads uniformly over the entire coating film surface, and the blocking resistance at high temperatures is excellent. Also, the average particle diameter of wax (A) is preferably 0.03 μm or more. If it is 0.03 μm or more, the blocking resistance at high temperatures is excellent. In addition, the average particle diameter referred to in this specification is the median diameter obtained by dynamic light scattering measurement. The average particle diameter is a numerical value obtained by diluting a wax dispersion 500 times with water and measuring about 5 ml of the obtained diluted solution by the dynamic light scattering measurement method (the measuring device is NanoTrack UPA manufactured by Microtrack Bell Co., Ltd., Microtrack MT3300EXII manufactured by Microtrack Bell Co., Ltd.).

[0026] <Liquid medium> The coating agent of the present invention preferably contains a liquid medium, and an aqueous medium is preferable as the liquid medium. Here, the aqueous medium means water or an organic solvent miscible with water. Examples of the aqueous medium include water, alcohols, etc. Among these, water is preferable as the liquid medium.

[0027] <Preservative> In order to prevent spoilage during storage of the coating agent, it is preferable to add a preservative in an amount of about 0.001 to 5% by mass based on 100% by mass of the total non-volatile components of the coating agent.

[0028] <Levelling agent> In order to improve the coating suitability, it is preferable to add a levelling agent in an amount of about 0.01 to 10% by mass based on 100% by mass of the total non-volatile components of the coating agent, if necessary.

[0029] <Defoaming agent> Coating film defects may occur due to bubbles generated during coating. Therefore, it is preferable to add a defoaming agent in an amount of about 0.001 to 10% by mass based on 100% by mass of the total non-volatile components of the coating agent, if necessary.

[0030] <Substrate> There is no limitation on the substrate to which the coating agent of the present invention is applied, but a paper substrate is suitable. When coating only one side of the substrate, a plastic film such as a PET (polyethylene terephthalate) film may be laminated on the other side, or another coating agent may be applied.

[0031] <Coating method> Examples of the coating method include conventionally known coating methods such as offset printing, gravure printing, flexographic printing, comma coater printing, etc.

[0032] After coating the coating agent on the substrate as described above, the volatile components are removed by means such as heating, if necessary, to form a coating layer, whereby the food packaging sheet of the present invention can be obtained.

[0033] Furthermore, by processing the food packaging sheet through cutting, deformation, or the like, food packaging containers such as side dish cups can be obtained.

Example

[0034] Hereinafter, the present invention will be specifically described by way of examples. In the examples, unless otherwise specified, “parts” simply means “parts by mass” and “%” means “mass %”.

[0035] <Preparation of Coating Agent> [Example 1] Into a container equipped with a stirrer, a thermometer, and a reflux condenser, 24 parts of hydroxypropyl starch as a polysaccharide and 42 parts of water were charged, and the internal temperature of the container was raised to 40 ° C and the polysaccharide was dissolved while stirring. After confirming the dissolution of the polysaccharide, heating was stopped, and 29 parts of Chem Pearl W400 (NV (non-volatile content concentration) 40%, manufactured by Mitsui Chemicals, Inc.), which is a polyethylene wax, and 5 parts of water were added to obtain the target coating agent.

[0036] [Examples 2 to 13, Comparative Examples 3 to 5] Coating agents were prepared in the same manner as in Example 1, except that the materials and compounding compositions shown in Table 1 were changed.

[0037] [Comparative Example 1] Into a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, 35.9 parts of water were charged. Separately, 20.4 parts of methyl methacrylate, 19.2 parts of styrene, 0.4 part of acrylic acid, 0.8 part of Emal 0 (sodium lauryl sulfate manufactured by Kao Corporation, with an active ingredient of 97% or more), and 16.2 parts of water were mixed and stirred in advance to prepare an emulsion of ethylenically unsaturated monomers, which was then charged into the dropping funnel. After raising the internal temperature of the reaction vessel to 80 °C and thoroughly performing nitrogen substitution, 3.2 parts of a 5% aqueous solution of potassium persulfate as a polymerization initiator were added. While maintaining the internal temperature at 80 °C, the emulsion of ethylenically unsaturated monomers was dropped from the dropping funnel over 2 hours to conduct emulsion polymerization. After completion of the dropping, the reaction was continued at 80 °C for an additional 3 hours. Then, it was cooled to 50 °C, and 0.2 part of 25% aqueous ammonia was added for neutralization. Further, water was added to adjust the non-volatile content concentration to 40.0% to obtain an aqueous dispersion of styrene-acrylic resin A. The Tg (glass transition temperature) of styrene-acrylic resin A was 103 °C. To 66 parts of the obtained aqueous dispersion of styrene-acrylic resin A, 33 parts of Chemparl W400 (NV40%) and 1 part of water were added to obtain the target coating agent.

[0038] [Comparative Example 2] In the same manner as in Comparative Example 1, the ethylenically unsaturated monomers were changed to 2-ethylhexyl acrylate 20.4 parts, styrene 19.2 parts, and acrylic acid 0.4 part to obtain an aqueous dispersion of styrene-acrylic resin B. The Tg of styrene-acrylic resin B was 1 °C. To 66 parts of the obtained aqueous dispersion of styrene-acrylic resin B, 33 parts of Chemparl W400 (NV40%) and 1 part of water were added to obtain the target coating agent.

[0039] The raw materials in Table 1 are as follows. [Polysaccharides] · Hydroxypropyl starch: manufactured by Nisshin Chemical Co., Ltd., PENON PKW · Cellulose nanocrystal: manufactured by GSI Creos Corporation, DextraCel [Wax (A)] · Chemparl W400: manufactured by Mitsui Chemicals, Inc., an aqueous dispersion (NV40%) of polyethylene wax (melting point 110 °C) · ChemPearl W410: An aqueous dispersion (NV 40%) of polyethylene wax (melting point 110°C) manufactured by Mitsui Chemicals · AQUACER 531: An aqueous dispersion (NV 45%) of polyethylene wax (melting point 130°C) manufactured by BYK · AQUACER 593: An aqueous dispersion (NV 30%) of polypropylene wax (melting point 160°C) manufactured by BYK <Waxes other than Wax (A)> · AQUACER 497: An aqueous dispersion (NV 50%) of paraffin wax (melting point 60°C) manufactured by BYK

[0040] <Preparation of Coated Sheet> The obtained coating agent was applied to one side of commercially available paper (weight 50 g / m 2 ) using a flexographic printing machine to form a coating layer. After application, it was dried in a hot air oven at 100°C for 60 seconds to obtain a coated sheet (food packaging sheet) with a dry coating weight of 5 g / m 2 .

[0041] 《Evaluation Items and Evaluation Methods》 The evaluation items and evaluation methods of the coated sheets obtained in each example and comparative example are as follows.

[0042] <Blocking Resistance> The obtained coated sheets were stacked so that the coated surfaces (coating layers) of the coated sheets were in contact with each other, and left standing at 80°C for 6 hours, 70°C for 6 hours, and 60°C for 24 hours under a pressure of 4 kgf / cm 2 . Then, the ease of peeling between the coated sheets and the state of the coated surface after peeling were observed. [Evaluation Criteria] S: Under the condition of 80°C for 6 hours, the coated sheets are not adhered to each other (extremely good) A: Under the condition of 80°C for 6 hours, the coated sheets adhere to each other, but under the condition of 70°C for 6 hours, the coated sheets are not adhered to each other (good) B: Under the condition of 70°C for 6 hours, the coated sheets adhere to each other, but under the condition of 60°C for 24 hours, the coated sheets are not adhered to each other (usable) C: At 60°C for 24 hours, the coated sheets are stuck together (not usable).

[0043] <Oil resistance> On the surface (coat layer) of the obtained coated sheet where the coating agent was applied, place sliced cheese and heat it in a microwave oven. Immediately after taking it out, observe the state of bleeding of the surface coating, the state of oil seepage, and the state of cheese sticking. The sliced cheese used was "Melting Slices" (registered trademark) manufactured by Snow Brand Milk Products Co., Ltd. [Evaluation criteria] S: The cheese peels off smoothly, and there is only partial dot-like oil staining (extremely good). A: The cheese peels off smoothly, and there is oil staining over the entire area where the cheese was placed (good). B: The cheese does not peel off smoothly, but can be peeled off with force, and there is oil staining over the entire area where the cheese was placed (usable). C: It is difficult to peel off the cheese, and there is oil seepage (not usable).

[0044]

Table 1

[0045]

Table 1

Claims

1. A coating agent for a food packaging sheet, comprising a polysaccharide and one or more waxes (A) selected from the group consisting of polyethylene wax and polypropylene wax, wherein the content of the polysaccharide is 50 to 98% by mass in a total of 100% by mass of the non-volatile components of the coating agent, and the melting point of the wax (A) is 100 to 180°C.

2. The coating agent for a food packaging sheet according to Claim 1, comprising 2 to 100 parts by mass of the wax (A) with respect to 100 parts by mass of the polysaccharide.

3. The coating agent for a food packaging sheet according to Claim 1, comprising 10 to 100 parts by mass of the polyethylene wax with respect to 100 parts by mass of the polysaccharide.

4. The coating agent for a food packaging sheet according to Claim 1, comprising 3 to 50 parts by mass of the polypropylene wax with respect to 100 parts by mass of the polysaccharide.

5. A food packaging sheet having a coating layer formed from the coating agent for a food packaging sheet according to any one of Claims 1 to 4 on at least one surface of a substrate.

6. A food packaging container formed by processing the food packaging sheet according to Claim 5.

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