Antifogging agent for resin sheet coating

Abstract

To provide an antifogging agent for resin sheet coating which enables formation of a coating film excellent in antifogging property and its sustainability under low temperature and high temperature conditions on a resin sheet, and can maintain similar effects for a molded article obtained by molding the resin sheet.SOLUTION: An antifogging agent for resin sheet coating contains (A) a surface active agent and (B) hydroxypropyl methylcellulose, wherein (A) the surface active agent is an alkali metal salt of an oleic acid and / or an alkali metal salt of a lauryl sulfonic acid, and (B) the hydroxypropyl methylcellulose satisfies the following conditions 1 to 3. Condition 1: A degree of substitution of a methoxy group exceeds 1.4. Condition 2: a substituted molar number of a hydroxy propoxy group exceeds 0.2. Condition 3: Viscosity of 2 mass% aqueous solution at 20°C is 30 to 2,000 (mm2 / s).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an anti-fogging agent for resin sheet coating that prevents fogging on the surface of a resin sheet.

Background Art

[0002] Conventionally, transparent packaging containers formed by thermoforming a transparent resin sheet have been used for the main body, lid, etc. of packaging containers for various foods used in bento boxes, etc. And, the transparent packaging container is required to be excellent in low-temperature anti-fogging property that prevents dew condensation under low-temperature conditions such as when packaging a food containing a large amount of moisture and storing it in a refrigerator, and high-temperature anti-fogging property that prevents fogging caused by water vapor generated under high-temperature conditions such as when packaging a high-temperature food.

[0003] Polystyrene has been widely used for packaging containers for high-temperature foods, but recently, transparent packaging containers made of olefin resins such as polypropylene have been used. However, since the surface polarity of the resin sheet using an olefin resin is extremely low, its affinity with surface treatment agents such as anti-fogging agents is low. For this reason, the resin sheet coated with a conventional anti-fogging agent and the molded product obtained by molding it have particularly poor high-temperature anti-fogging property, and there has been a problem that even if the high-temperature anti-fogging property is good, its effect does not last.

[0004] As conventional techniques related to anti-fog agents for resin sheet coating, there are a surface treatment agent for synthetic polymer films composed of a specific vinyl copolymer and a specific lubricant and contained in a ratio of the vinyl copolymer / the lubricant = 30 / 70 to 90 / 10 (weight ratio) (Patent Document 1), an anti-fog sheet in which an anti-fog agent layer containing (A) a surfactant, (B) a hydrophilic acrylic copolymer, and (C) a copolymer composed of an oxyethylene skeleton is formed on at least one surface of a resin sheet (Patent Document 2), an anti-fog resin sheet having an anti-fog agent layer containing specific amounts of each component of (A) a surfactant, (B) a polyoxyethylene-polyoxypropylene block copolymer, and (C) a hydrophilic acrylic copolymer on at least one surface of a resin sheet (Patent Document 3), etc. However, from the viewpoint of solving the above problems, a more excellent anti-fog agent for resin sheet coating is required.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide an anti-fog agent for resin sheet coating that can form a coating film excellent in anti-fog properties and its persistence under low-temperature and high-temperature conditions on a resin sheet, and can maintain the same effect even in a molded product obtained by molding the resin sheet.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using a specific surfactant and a hydrophilic cellulose derivative as an anti-fogging agent for resin sheet coating. Based on these findings, the present inventors have further conducted studies and completed the present invention.

[0008] That is, the present invention consists of the following (1) and (2). (1) An anti-fogging agent for resin sheet coating containing (A) a surfactant and (B) hydroxypropylmethylcellulose, wherein (A) the surfactant is an alkali metal salt of oleic acid and / or an alkali metal salt of lauryl sulfate, and (B) the hydroxypropylmethylcellulose satisfies the following conditions 1 to 3. An anti-fogging agent for resin sheet coating. Condition 1: The degree of substitution of the methoxy group exceeds 1.4 Condition 2: The number of moles of substituted hydroxypropoxy groups exceeds 0.2 Condition 3: The viscosity of a 2% by mass aqueous solution at 20°C is 30 to 2000 (mm 2 / s) (2) An anti-fogging resin sheet in which a coating film containing the anti-fogging agent for resin sheet coating described in (1) above is formed on at least one surface of the resin sheet.

Effects of the Invention

[0009] The anti-fogging agent for resin sheet coating of the present invention can form a coating film excellent in anti-fogging property and its persistence under low-temperature and high-temperature conditions on the resin sheet, and can maintain the same effect on the molded article obtained by molding the resin sheet.

Modes for Carrying Out the Invention

[0010] The (A) surfactant [hereinafter also referred to as the (A) component] used in the present invention is an alkali metal salt of oleic acid and / or an alkali metal salt of lauryl sulfate.

[0011] Examples of the alkali metal salts of oleic acid as component (A) include potassium oleate, sodium oleate, etc., and sodium oleate is preferred. Examples of the alkali metal salts of lauryl sulfate as component (A) include potassium lauryl sulfate, sodium lauryl sulfate, etc., and sodium lauryl sulfate is preferred.

[0012] The hydroxypropyl methylcellulose used in the present invention [hereinafter also referred to as component (B)] is a water-soluble cellulose ether obtained by substituting the hydroxyl groups in cellulose with methoxy groups and hydroxypropoxy groups, and satisfies the following conditions 1 to 3.

[0013] [Condition 1] The hydroxypropyl methylcellulose of component (B) has a degree of substitution of methoxy groups exceeding 1.4, preferably exceeding 1.6, more preferably exceeding 1.8. When the degree of substitution of methoxy groups is 1.4 or less, the coatability of the anti-fogging agent on the resin sheet is poor, a stable coating film cannot be obtained, and good anti-fogging properties cannot be obtained, which is not preferable. There is no particular limitation on the upper limit value of the degree of substitution of methoxy groups, but it can be, for example, 2.8. Here, the degree of substitution of methoxy groups refers to the average number of hydroxyl groups substituted with methoxy groups per glucose ring unit of cellulose.

[0014] [Condition 2] The hydroxypropyl methylcellulose of component (B) has a substitution mole number of hydroxypropoxy groups exceeding 0.2, preferably exceeding 0.22, more preferably exceeding 0.24. When the substitution mole number of hydroxypropoxy groups is 0.2 or less, the hydrophilicity of the coating film formed on the resin sheet is insufficient, and good anti-fogging properties cannot be obtained, which is not preferable. There is no particular limitation on the upper limit value of the substitution mole number of hydroxypropoxy groups, but it can be, for example, 1.6. Here, the substitution mole number of hydroxypropoxy groups refers to the average mole number of hydroxypropoxy groups added per glucose ring unit of cellulose.

[0015] The degree of substitution of the methoxy group and the number of moles of hydroxypropoxy group substitution in Conditions 1 and 2 can be determined by measuring the amount of methoxy group or hydroxypropoxy group in the sample by a method conforming to the method for measuring the degree of substitution of "hydroxypropylcellulose" and "methylcellulose" in the 17th Revised Japanese Pharmacopoeia, and converting this into the number of moles.

[0016] [Condition 3] (B) The hydroxypropylmethylcellulose of the component has a viscosity of 30 to 2000 (mm 2 / s) at 20 °C in a 2% by mass aqueous solution, preferably 30 to 1000 (mm 2 / s), more preferably 40 to 500 (mm 2 / s), and even more preferably 40 to 200 (mm2 / s). If the viscosity is less than 30 (mm 2 / s), the persistence of the anti-fogging property is weak, which is not preferable. Also, if the viscosity exceeds 2000 (mm 2 / s), in addition to not being able to obtain a stable coating film, when the resin sheet is secondary molded, peeling of the coating film occurs, etc., and the followability is insufficient, and a good anti-fogging property cannot be obtained, which is not preferable.

[0017] The viscosity at 20 °C of the 2% by mass aqueous solution in Condition 3 can be measured using an Ubbelohde viscometer in accordance with the capillary viscometer method of the viscosity measurement method of the general test method described in the 17th Revised Japanese Pharmacopoeia.

[0018] Examples of the hydroxypropylmethylcellulose of component (B) include Methocel SE-50 [trade name; degree of substitution of methoxy group: 1.9; number of moles of hydroxypropoxy group substitution: 0.25; viscosity at 20 °C in a 2% by mass aqueous solution: 50 (mm 2 / s); manufactured by Shin-Etsu Chemical Co., Ltd.], Methocel 60SH-50 [trade name; degree of substitution of methoxy group: 1.9; number of moles of hydroxypropoxy group substitution: 0.25; viscosity at 20 °C in a 2% by mass aqueous solution: 50 (mm 2 / s); manufactured by Shin-Etsu Chemical Co., Ltd.], etc., which are commercially manufactured and sold, and these can be used in the present invention.

[0019] The contents of component (A) and component (B) in the anti-fogging agent for resin sheet coating of the present invention are not particularly limited. However, from the viewpoint of fully exerting the effects of the present invention, for example, based on 100% by mass of the total amount of component (A) and component (B), the amount of component (A) is 40 to 90% by mass, preferably 50 to 80% by mass, and the amount of component (B) is 10 to 60 parts by mass, preferably 20 to 50 parts by mass.

[0020] The total amount of component (A) and component (B) in 100% by mass of the anti-fogging agent for resin sheet coating of the present invention varies depending on the use of the resin sheet and the desired anti-fogging property, etc., and is not uniform. There is no particular limitation, but for example, it is 3 to 25% by mass, preferably 5 to 15% by mass.

[0021] In the anti-fogging agent for resin sheet coating of the present invention, other substances other than component (A) and component (B) can be blended within a range that does not inhibit the effects of the present invention. For example, surfactants, defoamers, anti-foaming agents, antioxidants, plasticizers, leveling agents, ultraviolet absorbers, colorants, flame retardants, lubricants, preservatives, viscosity modifiers, thickeners, etc. can be mentioned.

[0022] Examples of the surfactant include nonionic surfactants such as glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, polyethylene glycol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid amide, polyoxyethylene (hydrogenated) castor oil ether, polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene block copolymer, and polyvinyl alcohol; and anionic surfactants such as fatty acid salts (excluding alkali metal salts of oleic acid), polyoxyethylene alkyl ether carboxylates, alkyl sulfate esters (excluding alkali metal salts of lauryl sulfate), polyoxyethylene alkyl ether sulfate esters, alkylbenzene sulfonates, alkyl sulfocarboxylates, alkyl phosphate esters, and polyoxyethylene alkyl ether phosphate esters.

[0023] The anti-fogging agent for resin sheet coating of the present invention is obtained by diluting component (A) and component (B) with water and / or an organic solvent (for example, ethanol, isopropanol, etc.). Specifically, component (A), component (B), water and / or an organic solvent can be mixed using a known device such as a stirrer or an emulsifier to prepare a transparent solution or suspension. The above mixing is preferably carried out under a temperature condition of 20 to 70 °C until component (A) and component (B) are dissolved in water and / or an organic solvent to obtain a transparent solution.

[0024] An anti-fogging resin sheet obtained by forming a coating film on at least one surface of a resin sheet using the anti-fogging agent for resin sheet coating of the present invention (hereinafter, also simply referred to as "anti-fogging agent") is also one form of the present invention.

[0025] There is no particular limitation on the type of resin sheet used in the anti-fog resin sheet of the present invention, but it is preferably a resin sheet used for a transparent container for food packaging. For example, an unstretched sheet of a thermoplastic resin such as a polystyrene-based resin, a polyester-based resin such as amorphous polyethylene terephthalate (A-PET), a polypropylene-based resin, a polylactic acid-based resin, and a polyvinyl chloride-based resin, a uniaxially or biaxially stretched sheet, etc. may be mentioned. Among these, a biaxially stretched polystyrene-based resin (OPS) sheet, an unstretched A-PET sheet, and an unstretched polypropylene-based resin sheet are preferable. The thickness of the resin sheet is preferably 0.1 to 0.7 mm.

[0026] The anti-fog resin sheet of the present invention can be produced, for example, by adjusting the surface tension of the resin sheet surface to a range of 50 to 60 mN / m by a known surface treatment method such as corona discharge treatment, or by performing a treatment such as high-frequency treatment as desired, and then, on one of its surfaces, diluting an anti-fog agent with water to adjust the total content of components (A) and (B) to 0.1 to 5% by mass, contacting and attaching an aqueous solution, and then drying with a hot air dryer or the like to form a coating film.

[0027] Examples of the above contact treatment include methods such as coating (roll coating such as gravure roll coating, spray coating, etc.), dipping, etc., and preferably the method of coating.

[0028] The amount of the anti-fog agent adhered to the resin sheet in the above contact treatment (coating amount), in terms of the amount of the coating film obtained by drying after the contact treatment, is preferably 5 to 1000 mg / m 2 and more preferably 10 to 200 mg / m 2 . When the coating amount is within the above range, it is preferable because the anti-fog property is good and adverse effects such as poor appearance due to whitening of the resin sheet can be avoided.

[0029] The anti-fogging resin sheet of the present invention is mainly formed into a container body and / or a lid body or the like by a thermoforming method such as a vacuum forming method or a pressure air forming method so that the coating film becomes the inner surface, and is used as the container body and / or the lid body of an anti-fogging food packaging container.

[0030] The present invention will be described below with reference to examples, which are merely for explaining the present invention and do not limit the present invention.

Examples

[0031] <Preparation of anti-fogging agent for resin sheet coating> (1) Raw materials [(A) Surfactant] A-1: Sodium oleate (trade name: Nonsal ON-A; manufactured by NOF Corporation) A-2: Sodium lauryl sulfate (trade name: Emal 2FG; manufactured by Kao Corporation) A-3: Sodium laurate (trade name: Sodium laurate; manufactured by Fujifilm Wako Pure Chemical Corporation) A-4: Diglycerin laurate (trade name: Poem DL-100; manufactured by Riken Vitamin Co., Ltd.)

[0032] [(B) Hydroxypropyl methylcellulose] B-1: Methocel SE-50 (trade name; manufactured by Shin-Etsu Chemical Co., Ltd.) B-2: Methocel 90SH-100 (trade name; manufactured by Shin-Etsu Chemical Co., Ltd.) B-3: Methocel 65SH-50 (trade name; manufactured by Shin-Etsu Chemical Co., Ltd.) B-4: Methocel 60SH-15 (trade name; manufactured by Shin-Etsu Chemical Co., Ltd.) B-5: Methocel 60SH-4000 (trade name; manufactured by Shin-Etsu Chemical Co., Ltd.)

[0033] The degree of substitution of the methoxy group, the number of moles of substituted hydroxypropoxy groups, and the viscosity (mm 2 / s) of a 2% by mass aqueous solution at 20 °C of the (B) hydroxypropyl methylcellulose (B-1 to B-5) used in the preparation of the anti-fogging agent for resin sheet coating are shown in Table 1.

[0034] [Table 1]

[0035] (2) Formulation of the anti-fog agent for resin sheet coating Table 2 shows the formulations of (A) surfactant and (B) hydroxypropyl methylcellulose used in the preparation of the anti-fog agent for resin sheet coating.

[0036] [Table 2]

[0037] (3) Preparation method of the anti-fog agent for resin sheet coating 90 mL of ion-exchanged water was added to a 300 mL four-necked flask and heated to 70 °C. Then, 1 / 10 of the amounts of component (A) and component (B) described in Table 1 were added, and stirring was carried out at 300 rpm for 30 minutes using a stirrer (model: BL-600; manufactured by Shin-Tong Scientific Co., Ltd.; equipped with a three-blade stirring impeller with a diameter of 38 mm, one stage). Further, while cooling to 45 °C at 300 rpm using the same stirrer, stirring was continued. After confirming that the contents of the flask were in a transparent state, the anti-fog agent for resin sheet coating (Examples 1 to 4 and Comparative Examples 1 to 9) was obtained.

[0038] [Preparation of the resin sheet for evaluation and the resin molded article for evaluation] (1) Preparation of the resin sheet for evaluation The anti-fog agent for resin sheet coating (any one of Examples 1 to 4 and Comparative Examples 1 to 9) was diluted with water so that the total content of component (A) and component (B) was 1% by mass to prepare an anti-fog agent diluted solution. Next, the anti-fog agent diluted solution was applied to a surface corona-treated biaxially stretched polystyrene resin (OPS) sheet (thickness: 200 μm) cut to a width of 23 cm and a length of 32 cm using a bar coater (No. 3) so that the coating amount after drying was 50 mg / m 2 ². After coating, it was dried in a constant temperature bath at 70 °C for 3 minutes. The dried resin sheet was cut into a circle with a diameter of 70 mm to prepare the resin sheet for evaluation (Test Pieces 1 to 13).

[0039] (2) Preparation of Resin Molded Articles for Evaluation A 23 cm wide and 32 cm long anti-fogging agent-coated sheet prepared in the same manner as the resin sheet for evaluation was heated by a small vacuum forming machine (model: 450DT; manufactured by Formech) equipped with a cup-shaped female mold with a diameter of 80 mm, a bottom shape of 40 mm, and a height of 25 mm so that the sheet temperature was above the softening point, and then brought into contact with the above mold and adhered under a vacuum of -0.8 Bar or more for 3 seconds. Thereafter, it was released from the mold to produce cup-shaped resin molded articles for evaluation (test pieces 14 to 26).

[0040] <Evaluation of Resin Sheet for Evaluation and Resin Molded Articles for Evaluation> (1) Low-temperature Anti-fogging Property Evaluation of Resin Sheet for Evaluation A resin sheet for evaluation (any one of test pieces 1 to 13) was placed on the upper surface of a 200 mL beaker with a diameter of 67 mm containing 100 mL of water at 20°C with the anti-fogging agent-coated surface facing inward, fixed to the beaker using adhesive tape, and then the beaker was placed in a 5°C showcase. After 5 minutes and 1 hour, the occurrence of fogging on the inner surface of the resin sheet for evaluation and the adhesion of liquid films and water droplets were visually evaluated according to the evaluation criteria in Table 3 as initial anti-fogging property and anti-fogging continuity, respectively. The results are shown in Table 4.

[0041] (2) High-temperature Anti-fogging Property Evaluation of Resin Sheet for Evaluation A resin sheet for evaluation (any one of test pieces 1 to 13) was placed on the upper surface of a 200 mL beaker without a bottom (obtained by cutting off the bottom of a 200 mL beaker with a diameter of 67 mm) with the anti-fogging agent-coated surface facing inward, fixed to the beaker using adhesive tape, and then the beaker was placed in a constant temperature water bath at a water temperature of 60°C so that the resin sheet for evaluation did not come into contact with the warm water. After 5 minutes and 3 hours, the occurrence of fogging on the inner surface of the resin sheet for evaluation and the adhesion of liquid films and water droplets were visually evaluated according to the evaluation criteria in Table 3 as initial anti-fogging property and anti-fogging continuity, respectively. The results are shown in Table 4.

[0042] (3) Low-temperature Anti-fogging Property Evaluation of Resin Molded Articles for Evaluation An evaluation resin molded product (any one of Test Pieces 14 to 26) was placed on the upper surface of a 200 mL beaker with a diameter of 67 mm containing 100 mL of water at 20°C, with the anti-fogging agent-coated surface facing inward. The beaker was placed in a 5°C showcase, and the occurrence of fogging on the inner surface of the evaluation resin molded product and the adhesion of liquid films and water droplets after 5 minutes and 1 hour were visually evaluated according to the evaluation criteria in Table 3 as initial anti-fogging property and anti-fogging continuity, respectively. The results are shown in Table 5.

[0043] (4) High-temperature anti-fogging property evaluation of the evaluation resin molded product An evaluation resin molded product (any one of Test Pieces 14 to 26) was placed on the upper surface of a 200 mL beaker without a bottom (obtained by cutting off the bottom of a 200 mL beaker with a diameter of 67 mm), with the anti-fogging agent-coated surface facing inward. The beaker was placed in a constant temperature water bath at a water temperature of 60°C so that the evaluation resin molded product did not come into contact with the warm water. The occurrence of fogging on the inner surface of the evaluation resin molded product and the adhesion of liquid films and water droplets after 5 minutes and 3 hours were visually evaluated according to the evaluation criteria in Table 3 as initial anti-fogging property and anti-fogging continuity, respectively. The results are shown in Table 5.

[0044]

Table 3

[0045]

Table 4

[0046]

Table 5

[0047] From the results in Tables 4 and 5, the evaluation resin sheets (Prototype 1 to 4) using Examples 1 to 4 as the anti-fog agent for resin sheet coating were excellent in both initial anti-fog property and anti-fog sustainability at low and high temperatures. Also, the evaluation resin molded products (Prototype 14 to 17) using Examples 1 to 4 as the anti-fog agent for resin sheet coating showed similarly excellent results. Therefore, it can be said that the anti-fog resin sheet of the present invention maintains the anti-fog property even after molding and has good followability during molding.

[0048] On the other hand, in Comparative Example 1, neither the evaluation resin sheet nor the evaluation resin molded product exhibited anti-fog property. In Comparative Examples 2 and 4, although anti-fog property was exhibited, it was insufficient, resulting in some water droplets remaining. In Comparative Examples 3, 6, and 9, the performance tended to deteriorate after molding, and it is considered that the followability during molding was insufficient. In Comparative Example 5, the anti-fog sustainability in the high-temperature anti-fog property evaluation was insufficient. In Comparative Examples 7 and 8, the coatability of the anti-fog agent was poor, resulting in insufficient anti-fog property overall.

Claims

1. An anti-fogging agent for resin sheet coating containing (A) a surfactant and (B) hydroxypropyl methylcellulose, wherein (A) the surfactant is an alkali metal salt of oleic acid and / or an alkali metal salt of lauryl sulfate, and (B) the hydroxypropyl methylcellulose satisfies the following conditions 1 to 3, the anti-fogging agent for resin sheet coating. Condition 1: The degree of substitution of methoxy groups exceeds 1.4 Condition 2: The number of moles of substituted hydroxypropoxy groups exceeds 0.2 Condition 3: The viscosity at 20 °C of a 2% by mass aqueous solution is 30 to 2000 (mm ２ / s)

2. An anti-fogging resin sheet in which a coating film containing the anti-fogging agent for resin sheet coating according to Claim 1 is formed on at least one surface of the resin sheet.

Images