Coating agent for food packaging sheets, food packaging sheets

Abstract

To provide a coating agent for food packaging sheets that can form a coating layer with excellent coating properties, oil resistance, and blocking resistance at high temperatures, and a food packaging sheet using the same. [Solution] A coating agent for food packaging sheets comprising a natural wax (A) and a polysaccharide (B), wherein, in 100% by mass of the coating agent, the proportion of the natural wax (A) is 20% by mass or more and 50% by mass or less, and the proportion of the polysaccharide (B) is 0.1% by mass or more and 10% by mass or less, and the amount of the polysaccharide (B) is 0.2 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the natural wax (A), the melting point of the natural wax (A) is 50°C or more and 90°C or less, and the viscosity measured at 25°C using a B-type viscometer is 50 mPa·s or more and 500 mPa·s or less.

Description

[Technical Field]

[0001] This invention relates to a coating agent for food packaging sheets and to food packaging sheets. [Background technology]

[0002] Traditionally, laminated sheets, made by laminating a resin film onto a paper base, have been widely used in food packaging sheets and containers to prevent oil stains from food-derived oil components and to prevent food from sticking. However, in recent years, there has been a global demand for efforts to reduce environmental impact, and efforts are being made to reduce plastic usage and design recyclable products. Accordingly, in food packaging sheets and containers, there is a growing trend to develop paper-coated food packaging sheets (hereinafter simply referred to as packaging sheets or sheets), which are easier to recycle and reduce plastic usage, as an alternative to conventional laminated sheets.

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

[0004] However, sheets using such coating agents can develop problems when stored or transported in high-temperature environments, such as blocking between sheets. When sheets that have been stored stacked together are separated, defects occur at the point of blocking, leading to oil stains or food sticking to the defective areas, making them unsuitable for use as packaging sheets.

[0005] On the other hand, when packaging sheets are made by coating them with a hard acrylic resin to improve blocking resistance at high temperatures, the film-forming properties of the resin deteriorate, leading to coating defects and a decrease in oil resistance and food adhesion resistance.

[0006] In addition, Patent Document 2 discloses barrier paper having a barrier layer containing a polymer binder and a wax based on vegetable oil. However, there is a problem that a coating agent mainly composed of wax easily penetrates into paper, and it becomes difficult to exhibit oil resistance under coating conditions with a low coating amount.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] The problem to be solved by the present invention is to provide a coating agent for a food packaging sheet that can form a coating layer excellent in coating properties, oil resistance, and blocking resistance at high temperatures, and a food packaging sheet using the same.

Means for Solving the Problems

[0009] 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 natural wax (A) and polysaccharide (B), wherein in 100% by mass of the coating agent, the proportion of the natural wax (A) is 20% by mass or more and 50% by mass or less, the proportion of the polysaccharide (B) is 0.1% by mass or more and 10% by mass or less, with respect to 100 parts by mass of the natural wax (A), the polysaccharide (B) is 0.2 parts by mass or more and 50 parts by mass or less, the melting point of the natural wax (A) is 50°C or more and 90°C or less, and the viscosity measured using a B-type viscometer at 25°C is 50 mPa·s or more and 500 mPa·s or less.

[0010] Preferably, the natural wax (A) is at least one selected from the group consisting of plant-derived waxes and animal-derived waxes.

[0011] Furthermore, the present invention relates to a food packaging sheet having a base sheet and a coating layer formed on the base sheet from the above-mentioned food packaging sheet coating agent.

[0012] Preferably, the base sheet of the food packaging sheet is paper. [Effects of the Invention]

[0013] The present invention provides a coating agent for food packaging sheets that can form a coating layer with excellent coating properties, oil resistance, and blocking resistance at high temperatures, as well as a food packaging sheet using the same. [Modes for carrying out the invention]

[0014] The present invention will now be described in detail. In this specification, numerical ranges specified using "~" include the numbers before and after "~" as the lower and upper limits. Unless otherwise noted, the various components described in this specification may be used independently, individually, or in combination of two or more.

[0015] <Coating agent for food packaging sheets> The coating agent for food packaging sheets of the present invention (hereinafter sometimes abbreviated as "coating agent") is suitable for forming a coating layer on a substrate such as paper or nonwoven fabric to produce a coated sheet, and is particularly suitable for producing coated sheets for packaging food. Furthermore, the coating agent of the present invention not only has excellent blocking resistance at high temperatures, but can also form a coating layer that has oil resistance and resistance to food adhesion, so it can be suitably used in applications where the coating layer and food come into direct contact. In addition, "painting," "coating," and "application" shall be treated as synonymous.

[0016] The coating agent of the present invention contains natural wax (A) and polysaccharide (B). In 100% by mass of the coating agent, the proportion of natural wax (A) is 20% by mass or more and 50% by mass or less, and the proportion of polysaccharide (B) is 0.1% by mass or more and 10% by mass or less. With respect to 100 parts by mass of natural wax (A), the polysaccharide (B) is 0.2 parts by mass or more and 50 parts by mass or less. The melting point of the above natural wax (A) is 50°C or more and 90°C or less, and at 25°C, the viscosity measured using a B-type viscometer is 50 mPa·s or more and 500 mPa·s or less. The B-type viscosity is measured at a rotational speed of 60 rpm using a No. 2 rotor. When the viscosity exceeds 500 mPa·s, it can be measured by changing the rotor to No. 3 or No. 4. This coating agent is excellent in coating properties, heat resistance, and film-forming properties. The coated sheet 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.

[0017] <Natural wax (A)> Examples of the natural wax (A) include waxes derived from animals such as beeswax (bead wax), shellac wax, and carnauba wax, waxes derived from plants such as carnauba wax, candelilla wax, rice wax, wood wax, and soy wax, waxes derived from crude oil such as paraffin wax, microcrystalline wax, and slack wax, and waxes derived from minerals such as montan wax, ceresin, and ozokerite. It is preferable to use at least one of the animal-derived wax and the plant-derived wax.

[0018] The melting point of the natural wax (A) may be within the range of 50°C or more and 90°C or less, but it is preferably 55°C or more and 80°C or less. If the melting point is 50°C or more, it is excellent in blocking resistance at high temperatures. On the other hand, if it is 90°C or less, the film-forming property is excellent even under drying conditions at about 100°C, which is a general drying temperature after coating, so water resistance and oil resistance can be exhibited.

[0019] The blending amount of the natural wax (A) is 20% by mass or more and 50% by mass or less, preferably 25% by mass or more and 40% by mass or less, in 100% by mass of the coating agent. If it is 20% by mass or more in 100% by mass of the coating agent, it becomes easy to increase the coating amount by one application, and it is easy to exhibit water resistance and oil resistance. On the other hand, if it is 50% by mass or less, the stability as a coating agent can be ensured, and the coating property becomes good.

[0020] From the viewpoint of the stability of the coating agent over time, it is preferable to use the natural wax (A) that can be obtained in the form of an aqueous dispersion. The average particle diameter of the wax particles in the aqueous dispersion of the natural wax (A) is preferably 1 μm or less. If it is 1 μm or less, the film-forming property is excellent and it is easy to exhibit oil resistance. There is no particular lower limit for the average particle diameter of the wax particles, but it exceeds 0 μm because it has a finite value. In addition, the average particle diameter referred to in this specification is the median diameter obtained by the laser diffraction scattering measurement method.

[0021] <Polysaccharide (B)> The polysaccharide (B) in this specification is a polymer in which monosaccharides are linked with a polymerization degree of 10 or more by glycosidic bonds, and examples include starch (α-1,4-glucan), cellulose (β-1,4-glucan), curdlan (β-1,3-glucan), dextran (α-1,6-glucan), glycogen, chitin, nigellan, agarose, carrageenan, heparin, alginic acid, hyaluronic acid, pectin, xyloglucan, xylan, glucomannan, levan, α-1,2-glucan, α-1,3-glucan, β-1,2-glucan, β-1,6-glucan, xanthan gum, tamarind seed gum, etc. In addition, starch, cellulose and their derivatives such as oxidized starch, acetylated starch, hydroxypropyl starch, carboxymethyl starch, sodium octenyl succinate starch, hydroxypropyl methylcellulose, carboxymethylcellulose, hydroxyethylcellulose can also be used.

[0022] The amount of polysaccharide (B) is preferably 0.1% to 10% by mass, and more preferably 0.2% to 8% by mass, based on 100% by mass of the coating agent. If the amount is 0.1% by mass or more, the thickening effect of polysaccharide (B) prevents the coating agent from penetrating too deeply into the paper, making it easier to exhibit water resistance and oil resistance. On the other hand, if the amount is 10% by mass or less, the stability of the coating agent can be ensured, resulting in good coating properties and stable oil resistance of the coated sheet.

[0023] Furthermore, the amount of polysaccharide (B) added is preferably 0.2 parts by mass or more and 50 parts by mass or less, and more preferably 0.4 parts by mass or more and 25 parts by mass or less, per 100 parts by mass of natural wax (A). If the amount is 0.2 parts by mass or more, the thickening effect of polysaccharide (B) prevents the coating agent from penetrating the paper too much, making it easier to exhibit water resistance and oil resistance. On the other hand, if the amount is 50 parts by mass or less, the effect of the water-soluble polysaccharide on water resistance is small, and a coating film with good water resistance can be formed.

[0024] <Viscosity> The viscosity of the coating agent, as measured using a B-type viscometer at 25°C and a shear rate of 60 rpm, should be between 50 mPa·s and 500 mPa·s, preferably between 50 mPa·s and 300 mPa·s. If the viscosity is 50 mPa·s or higher, the coating agent does not penetrate the paper too much, making it easier to exhibit water and oil resistance. On the other hand, if the viscosity is 500 mPa·s or lower, the stability of the coating agent is ensured, resulting in good coating properties and stable oil resistance of the coated sheet.

[0025] <Liquid media> The coating agent of the present invention preferably contains a liquid medium, and an aqueous medium is preferred as the liquid medium. Here, an aqueous medium means water or an organic solvent that is miscible with water. Examples of aqueous media include water, alcohols, etc. Among these, water is preferred as the liquid medium.

[0026] <Preservatives> To prevent spoilage during storage of the coating agent, it is preferable to add a preservative at a concentration of approximately 0.001 to 5% by mass of the total non-volatile content of the coating agent (100% by mass).

[0027] <Leveling agent> To improve coating suitability, it is preferable to add a leveling agent in an amount of approximately 0.01 to 10% by mass of the total non-volatile content of the coating agent, as needed.

[0028] <Antifoaming agent> Defects in the coating film may occur due to bubbles generated during the coating process. Therefore, it is preferable to add an antifoaming agent of about 0.001 to 10% by mass, based on 100% by mass of the total non-volatile content of the coating agent, as needed.

[0029] <Food packaging sheets> As described above, after applying the coating agent onto the base sheet, the food packaging sheet of the present invention is obtained by removing volatile components by means such as heating as necessary to form a coating layer.

[0030] <Base sheet> There are no restrictions on the type of substrate sheet to which the coating agent of the present invention is applied, but paper is suitable.

[0031] <Coating equipment> Coating equipment includes knife coaters, comma coaters, roll coaters, bar coaters, gravure coaters, and flexo coaters.

[0032] <Application amount> The preferred amount of coating agent to apply varies depending on the substrate sheet used, but the amount applied after drying is 2 to 10 g / m². 2 Preferably, the range is 3-8 g / m 2 It is more preferable that it be within that range. [Examples]

[0033] The present invention will be specifically described below with reference to examples. In the examples, unless otherwise specified, "parts" refers to "parts by mass," and "%" refers to "mass percent." Also, "non-volatile content concentration" will be abbreviated as "NV."

[0034] <Preparation of coating agent> [Example 1] In a container equipped with a stirrer, thermometer, and reflux condenser, 0.5 parts of tamarind seed gum (Glyloid S, manufactured by MP5 Food & Chemical Co., Ltd.) and 29.5 parts of water were charged. 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 70 parts of Eurica Coat SW166HS-B (non-volatile content concentration 40%, melting point 62°C, manufactured by Eurica), an aqueous dispersion of soybean-derived wax, were added while stirring. The resulting coating agent had a B-type viscosity of 250 mPa·s, and the average particle size of the wax particles was 0.4 μm.

[0035] [Examples 2-10, Comparative Examples 1-5] The coating agents were prepared in the same manner as in Example 1, except that the materials and formulations shown in Table 1 were changed.

[0036] [Comparative Example 6] 35.9 parts of water were charged into a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping tank, and reflux valve. Separately, 20.4 parts of methyl methacrylate, 19.2 parts of styrene, 0.4 parts of acrylic acid, 0.8 parts of Emal 0 (sodium lauryl sulfate, active ingredient 97% or more, manufactured by Kao Corporation), and 16.2 parts of water were pre-mixed and stirred to prepare an emulsion of ethylenically unsaturated monomers, which was then charged into the dropping tank. After raising the internal temperature of the reaction vessel to 80°C and thoroughly purging with nitrogen, 3.2 parts of a 5% aqueous solution of potassium persulfate was added as a polymerization initiator, and while maintaining the internal temperature at 80°C, the emulsion of ethylenically unsaturated monomers was added dropwise from the dropping tank over 2 hours to carry out emulsion polymerization. After the dropwise addition was complete, the reaction was continued for a further 3 hours while maintaining the temperature at 80°C. Then, it was cooled to 50°C and neutralized by adding 0.2 parts of 25% aqueous ammonia. Further water was added to adjust the non-volatile content to 40% to obtain an aqueous dispersion of styrene-acrylic resin A. The glass transition temperature (Tg) of styrene-acrylic resin A was 103°C. To 10 parts of the obtained aqueous dispersion of styrene-acrylic resin A, 90 parts of Euroca Coat SW166HS-B (NV 40%) were added to obtain a coating agent.

[0037] [Comparative Example 7] In Comparative Example 6, the ethylenically unsaturated monomer was changed to 20.4 parts of 2-ethylhexyl acrylate, 19.2 parts of styrene, and 0.4 parts of acrylic acid. The reaction and preparation were carried out in the same manner as in Comparative Example 6 to obtain an aqueous dispersion of styrene-acrylic resin B with a non-volatile content of 40%. The Tg of styrene-acrylic resin B was 1°C. To 70 parts of the obtained aqueous dispersion of styrene-acrylic resin B, 30 parts of Euroca Coat SW166HS-B (NV 40%) were added to obtain the desired coating agent.

[0038] The raw materials listed in Table 1 are as follows: <Natural wax (A)> • Eurica Coat SW166HS-B: Aqueous dispersion of soy-derived wax (melting point 62°C) manufactured by Eurica (NV 40%). • Topscreen BW200: Aqueous dispersion of plant-derived wax (melting point 57°C) manufactured by Solenis (NV 40%). • AQUACER2650: Manufactured by BYK, an aqueous dispersion of carnauba wax (melting point 84°C) (NV30%) • AQUACER497: Manufactured by BYK, aqueous dispersion of modified paraffin wax (melting point 55°C) (NV50%) <Waxes other than natural wax (A)> • Chemipearl W400: Aqueous dispersion of low molecular weight polyethylene wax (melting point 110°C) manufactured by Mitsui Chemicals, Inc. (NV 40%) <Polysaccharide (B)> • Grilloid S: MP5 Food & Chemicals, tamarind gum seed • PENON PKW: Manufactured by Nippon Denshi Kagaku Co., Ltd., hydroxypropyl starch • CMC2260: Carboxymethylcellulose, manufactured by Daicel Chemicals, Inc.

[0039] <Melting point of wax> The melting point of the wax was measured using a DSC (Differential Scanning Calorimeter, TA Instruments). Specifically, 3 mg of the dried sample was accurately weighed and placed in an aluminum pan, along with an empty aluminum pan used as a reference. These pans were then placed in a DSC measuring holder, and the temperature of the endothermic peak in the resulting DSC curve, obtained under a heating rate of 10°C / min, was defined as the melting point of the wax.

[0040] <Average particle size of wax> The coating agent obtained in each example was diluted 500 times with water, and approximately 5 ml of the diluted solution was measured using laser diffraction scattering measurement (measurement device: Microtrac MT3000II, manufactured by Microtrac Bell Co., Ltd.). The median diameter (median value) was taken as the average particle diameter.

[0041] <B-type viscosity of coating agent> The coating agents obtained in each example were adjusted to 25°C and measured using a B-type viscometer at a shear rate of 60 rpm.

[0042] <Manufacturing of coated sheets> The resulting coating agent is applied to a commercially available thin paper (basis weight 30 g / m²) as a base sheet. 2 Using a bar coater #6 to #12 on one side of the surface, the coating amount after drying is approximately 4g / m². 2 The coating was applied in such a manner. After coating, the coated sheet was obtained by drying it in a hot air oven at 80°C for 30 seconds.

[0043] Evaluation items and evaluation methods The evaluation items and evaluation methods for the coated sheets obtained in each example and comparative example are as follows.

[0044] <Stability of coating agent> The coating agent for food packaging sheets obtained above was placed in a screw-top bottle and left to stand at 40°C for one month. The state after redispersion and the rate of change in viscosity were then observed. The viscosity of the coating agent before and after the time elapsed was measured using the same method as described above. [Evaluation Criteria] S: No separation was observed, and viscosity remained unchanged (good). A: Separation is not observed, but the viscosity has slightly changed (change rate is less than ±20%) (usable) B: Separation is not observed, but the viscosity has significantly changed (change rate is ±20% or more) (not usable) C: Cannot be redispersed (not usable)

[0045] <Blocking resistance> The obtained coated sheets were stacked so that the coated surfaces (coat layers) of the coating agent faced each other, and placed in a thermo-hygrostat at 50°C - 80% RH under a pressure of 4 kgf / cm 2 and left standing for 24 hours. Then, the ease of peeling between the coated sheets and the state of the coated surface after peeling were observed. [Evaluation criteria] S: The coated sheets are not adhered to each other (good) A: The coated sheets are slightly adhered to each other but can be easily peeled off (usable) B: The coated sheets are adhered to each other, and a part of the sheet is damaged during peeling (not usable) C: The coated sheets are firmly adhered to each other and cannot be peeled off (not usable)

[0046] <Water resistance> For the coated surface of the obtained coated sheet, a water resistance test was conducted for 10 minutes in accordance with JIS P8140 (Water absorption test method: Cobb method). [Evaluation criteria] S: The water absorption after 10 minutes is less than 10 g / m 2 (good) A: The water absorption after 10 minutes is 10 g / m 2 or more and less than 15 g / m 2 (usable) B: The water absorption after 10 minutes is 15 g / m 2 or more and less than 20 g / m 2 (not usable) C: The water absorption after 10 minutes is 20 g / m 2 or more (not usable)

[0047] <Oil resistance> To evaluate the oil resistance of the obtained coated sheets, a few drops of salad oil were placed on the coated surface, and the state of staining on the surface and the state of oil seepage to the back were observed. [Evaluation Criteria] S: No stains after 10 minutes (good) A: After 10 minutes, a stain is visible, but there is no bleed-through (usable). B: After 5 minutes, no leakage was observed, but after 10 minutes, leakage occurred (unusable). C: A glitch occurred in less than 5 minutes (unusable).

[0048] [Table 1]

[0049] As can be seen from Table 1, the food packaging sheets using the coating agents obtained in Examples 1 to 10 exhibited excellent blocking resistance, water resistance, and oil resistance, demonstrating performance that fully met practical requirements. On the other hand, the food packaging sheets using the coating agents obtained in Comparative Examples 1 to 7 showed inferior physical properties in blocking resistance, water resistance, or oil resistance, and the results were not satisfactory for practical use.

Claims

1. A coating agent for food packaging sheets comprising a natural wax (A) and a polysaccharide (B), In the coating agent, the proportion of the natural wax (A) is 20% by mass or more and 50% by mass or less. The proportion of the aforementioned polysaccharide (B) is 0.1% by mass or more and 10% by mass or less. The amount of polysaccharide (B) is 0.2 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the natural wax (A). The melting point of the aforementioned natural wax (A) is 50°C or higher and 90°C or lower. A coating agent for food packaging sheets, wherein the viscosity measured using a B-type viscometer at 25°C is between 50 mPa·s and 500 mPa·s.

2. The coating agent for food packaging sheets according to claim 1, wherein the natural wax (A) is at least one selected from the group consisting of plant-derived waxes and animal-derived waxes.

3. A food packaging sheet having a base sheet and a coating layer formed on the base sheet from the food packaging sheet coating agent described in claim 1 or 2.

4. The food packaging sheet according to claim 3, wherein the base sheet is paper.

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