Anti-fog resin sheet and its secondary molded product

Abstract

To provide an anti-fogging resin sheet that exhibits good anti-fogging properties, has excellent adhesion between the anti-fogging layer and the thermoplastic resin sheet, and the anti-fogging layer is difficult to peel off from the thermoplastic resin sheet, and further has an anti-fogging layer formed using an anti-fogging agent that has excellent storage stability of the solution. [Solution] On at least one surface of the thermoplastic resin sheet, This is an anti-fogging resin sheet in which an anti-fogging layer is formed, comprising an anti-fogging agent that contains at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and a cellulose derivative (C), but does not contain sucrose fatty acid esters.

Description

[Technical Field]

[0001] This invention relates to an anti-fogging resin sheet and its secondary molded product, which is used in food packaging containers and various other containers. [Background technology]

[0002] Resin sheets extruded using various thermoplastic resins are secondarily molded by heat molding using vacuum forming machines, pressure vacuum forming machines, hot plate pressure forming machines, etc. The resulting secondarily molded products are widely used for lightweight food packaging containers and packaging for other items. Among these resin sheets, transparent resin sheets, such as those made of polystyrene, polyethylene terephthalate, and polypropylene, are widely used as lids for lunch boxes and prepared food containers due to their transparency. However, this lid material has the problem of the inner surface fogging up due to water vapor generated from the contents.

[0003] As a means of solving the above problems, for example, an anti-fogging styrene resin sheet has been proposed in which an anti-fogging agent consisting of sucrose fatty acid ester, polyvinyl alcohol, and fatty acid salt is coated onto a styrene resin sheet (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-222868 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present inventors evaluated an anti-fogging resin sheet obtained by applying an anti-fogging agent to a thermoplastic resin sheet such as a styrene resin sheet as described in Patent Document 1 above. As a result, as shown in the comparative example below, it was found that in an anti-fogging resin sheet in which an anti-fogging layer consisting of an anti-fogging agent containing sucrose fatty acid ester, polyvinyl alcohol, and a fatty acid salt having 12 to 17 carbon atoms is formed on a thermoplastic resin sheet, the adhesion between the anti-fogging layer and the thermoplastic resin sheet is poor, and the anti-fogging layer is prone to peeling off the thermoplastic resin sheet.

[0006] Furthermore, the inventors investigated the storage stability of a solution containing polyvinyl alcohol and a fatty acid salt having 12 to 17 carbon atoms, and found that it was not sufficient. They concluded that further improvements are necessary to obtain an antifogging agent with superior storage stability.

[0007] The present invention aims to provide an anti-fogging resin sheet that exhibits good anti-fogging properties, has excellent adhesion between the anti-fogging layer and the thermoplastic resin sheet, and the anti-fogging layer is difficult to peel off from the thermoplastic resin sheet, and further has an anti-fogging layer formed of an anti-fogging agent that has excellent storage stability of the solution. [Means for solving the problem]

[0008] The inventors have conducted extensive research to solve the above problems and have found that when an anti-fogging resin sheet is formed using an anti-fogging agent containing at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and a cellulose derivative (C), but without sucrose fatty acid ester, an anti-fogging resin sheet is obtained that exhibits good anti-fogging properties, has excellent adhesion between the anti-fogging layer and the thermoplastic resin sheet, and the anti-fogging layer is less likely to peel off the thermoplastic resin sheet. In particular, the inventors have found that including the cellulose derivative (C) in the anti-fogging agent results in even better storage stability of the solution. Accordingly, as described above, when an anti-fogging resin sheet having an anti-fogging layer formed using an anti-fogging agent containing the above components (A) to (C) but not containing sucrose fatty acid ester is formed, it is found that an anti-fogging resin sheet can be obtained that exhibits good anti-fogging properties, has excellent adhesion between the anti-fogging layer and the thermoplastic resin sheet, the anti-fogging layer is difficult to peel off from the thermoplastic resin sheet, and furthermore, has an anti-fogging resin sheet having an anti-fogging layer formed with an anti-fogging agent that has excellent storage stability of the solution, thus completing the present invention.

[0009] In other words, the present invention encompasses the following embodiments. [1] On at least one surface of the thermoplastic resin sheet, An anti-fogging resin sheet having an anti-fogging layer formed by an anti-fogging agent containing at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and a cellulose derivative (C), but without sucrose fatty acid esters. [2] The anti-fogging resin sheet according to [1], wherein the degree of saponification of the polyvinyl alcohol (B) is 70 to 85 mol%. [3] The anti-fogging resin sheet according to [1] or [2], wherein the cellulose derivative (C) is methylcellulose or hydroxypropylmethylcellulose. [4] The viscosity of the 2% by mass aqueous solution of the cellulose derivative (C) at 20°C is 20-60 mm 2 An anti-fogging resin sheet as described in any one of items [1] to [3], which is / s. [5] The anti-fogging resin sheet according to any one of [1] to [4], wherein a release layer made of silicone oil (E) is formed on the other side of the thermoplastic resin sheet opposite to the side on which the anti-fogging layer is provided. [6] The anti-fogging resin sheet according to any one of [1] to [5], wherein the thermoplastic resin sheet is a styrene-based resin sheet. [7] A secondary molded product obtained by molding an anti-fogging resin sheet as described in any one of items [1] to [6]. [Effects of the Invention]

[0010] The present invention provides an anti-fogging resin sheet that exhibits good anti-fogging properties, has excellent adhesion between the anti-fogging layer and the thermoplastic resin sheet, and the anti-fogging layer is difficult to peel off from the thermoplastic resin sheet, and further has an anti-fogging layer formed of an anti-fogging agent that has excellent storage stability of the solution. [Modes for carrying out the invention]

[0011] The present invention will be described in detail below. The following description of the constituent elements is illustrative for illustrating the present invention, and the present invention is not limited to these elements.

[0012] (Anti-fog resin sheet) The anti-fogging resin sheet of the present invention comprises a thermoplastic resin sheet and an anti-fogging layer. The anti-fogging layer is formed on at least one surface of the thermoplastic resin sheet. The anti-fogging layer is formed using an anti-fogging agent. The anti-fogging resin sheet of the present invention may further have a release layer. The release layer is preferably formed on the side of the thermoplastic resin sheet opposite to the side with the anti-fogging layer.

[0013] <Thermoplastic resin sheet> The resin type of the thermoplastic resin sheet serving as the base material of the anti-fog resin sheet of the present invention is not particularly limited, but it is preferably transparent. For example, styrene resins such as polystyrene, crystalline polystyrene, styrene-butadiene copolymer, styrene-isoprene-styrene copolymer, styrene-isoprene-butadiene-styrene copolymer, styrene-ethylene-butadiene-styrene copolymer, transparent styrene-butadiene-(meth)acrylic acid alkyl ester copolymer, styrene-(meth)acrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-(meth)acrylic acid alkyl ester copolymer, etc., propylene resins such as polypropylene, propylene-butadiene copolymer, ethylene-propylene copolymer, etc., polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyamide resins represented by nylon 6, polyester resins represented by polyethylene terephthalate, etc. are preferred.

[0014] Also, within a range that does not inhibit the transparency of the anti-fog resin sheet of the present invention, two or more of these resins may be mixed and used. Furthermore, these thermoplastic resin sheets may be multi-layered sheets of two or more layers using one or more of these resins. Furthermore, these thermoplastic resin sheets may be subjected to a stretching treatment in a uniaxial or biaxial direction.

[0015] Furthermore, biaxially stretched polystyrene-based resin sheets are often heat-formed using a hot plate pressure-air forming machine. In this case, when a conventional anti-fog agent is used, the anti-fog property of the formed body during heat forming tends to be significantly reduced. However, in the anti-fog resin sheet of the present invention, even when a biaxially stretched polystyrene-based resin sheet is used as the base material, a secondary molded product having excellent anti-fog property can be obtained. From the viewpoint of compatibility with a general-purpose hot plate pressure-air forming machine, a polystyrene-based resin sheet is preferred as the base material for the anti-fog resin sheet of the present invention, and a biaxially stretched polystyrene-based resin sheet is most preferred.

[0016] The thickness of these thermoplastic resin sheets is not particularly limited, but is preferably 0.05 to 1.0 mm from the viewpoint of the rigidity and strength of the secondary molded product when the anti-fogging resin sheet is secondary molded.

[0017] In the resin used for these thermoplastic resin sheets, various fine particles for causing protrusions on the surface of the resin sheet can be added within a range that does not impair the transparency of the resin sheet for the purpose of preventing blocking of the anti-fogging resin sheet. Examples of the fine particles include resin cross-linked beads such as styrene-based resin cross-linked beads, (meth)acrylate-based resin cross-linked beads, and polyurethane-based resin cross-linked beads, inorganic fine particles such as silica, hydrophobized silica, spherical silica, soft calcium carbonate, titanium oxide, and talc, and rubber fine particles. Examples of the rubber fine particles include a method of using a rubber-containing resin in combination, and the rubber-containing resin used here is different from the thermoplastic resin that is the base material of the anti-fogging resin sheet. Examples of the rubber-containing resin include impact-resistant polystyrene (HIPS), styrene-acrylonitrile-butadiene copolymer (ABS), styrene-ethylene-butadiene-styrene copolymer (SEBS), styrene-butadiene-(meth)acrylate copolymer (MBS), and impact-resistant (meth)acrylate (HI-PMMA).

[0018] <Anti-fogging layer> The anti-fogging layer is formed using an anti-fogging agent. The anti-fogging agent contains at least one kind (A) selected from sodium oleate and potassium oleate, polyvinyl alcohol (B), and a cellulose derivative (C), and does not contain sucrose fatty acid ester.

[0019] <<At least one kind (A) selected from sodium oleate and potassium oleate>> Sodium oleate and potassium oleate (A) are known as anionic surfactants, and in the present invention, commercially available products can usually be used.

[0020] <<Polyvinyl alcohol (B)>> Polyvinyl alcohol (also known as PVA) (B) is a homopolymer composed of vinyl alcohol units or a copolymer composed of vinyl alcohol units and vinyl acetate units, with a vinyl alcohol unit content of 50% by mass or more. As the polyvinyl alcohol (B), the product of partial saponification of polyvinyl acetate is preferred, and a degree of saponification of 70 to 85 mol% is preferred. The preferred degree of saponification is determined from the viewpoint of obtaining a significant improvement in anti-fogging properties without degrading the appearance of the anti-fogging resin sheet. For example, by setting the degree of saponification to 85 mol% or less, water solubility is improved, and when the anti-fogging agent coating is formed by applying an aqueous solution, the uniformity of the dispersion of polyvinyl alcohol in the coating can be improved. Also, by setting the degree of saponification to 70 mol% or more, good anti-fogging properties are obtained. If the degree of saponification is high, the stability of the anti-fogging solution deteriorates. Therefore, within the preferred range described above, it is possible to effectively prevent the anti-fogging solution from becoming unstable. Furthermore, the viscosity of a 4% by mass aqueous solution of polyvinyl alcohol (B) at 20°C is preferably 4 to 30 mPa·s, more preferably 4 to 25 mPa·s, even more preferably 4 to 15 mPa·s, even more preferably 4 to 9 mPa·s, particularly preferably 4 to 8 mPa·s, and particularly more preferably 4.5 to 6.0 mPa·s. The viscosity of the polyvinyl alcohol is preferably 4 mPa·s or more and 30 mPa·s or less, as described above, from the viewpoint of obtaining an anti-fogging improvement effect and ease of mixing with oleate salts.

[0021] <<Cellulose derivative (C)>> There are no particular restrictions on the cellulose derivative, but it is preferable to use methylcellulose (MC) or hydroxypropyl methylcellulose (HPMC), which are commonly used for applications such as water retention, thickening, bonding, adhesion, and surfactant properties. Methylcellulose can be produced, for example, by reacting alkali cellulose obtained by alkali treatment of cellulose (pulp) with methyl chloride. Hydroxypropyl methylcellulose can be produced, for example, by reacting methyl chloride with propylene oxide. Hydroxypropyl methylcellulose is obtained by substituting not only methyl groups but also hydroxypropyl groups with alkali cellulose.

[0022] The viscosity of a 2% by mass aqueous solution of cellulose derivative (C) at 20°C is 20-60 mm². 2 A value of / s is preferable. Within this range, it is possible to effectively prevent the anti-fogging liquid from becoming unstable.

[0023] <<Sucrose fatty acid esters not included>> As shown in the comparative example below, in an anti-fogging resin sheet in which an anti-fogging layer consisting of an anti-fogging agent containing sucrose fatty acid ester, polyvinyl alcohol, and a fatty acid salt having 12 to 17 carbon atoms is formed on a thermoplastic resin sheet, a problem arises in which the adhesion between the anti-fogging layer and the thermoplastic resin sheet is poor, and the anti-fogging layer is prone to peeling off the thermoplastic resin sheet. Therefore, the anti-fogging agent of the present invention does not contain or substantially contains sucrose fatty acid esters. "Substantially contained" means, for example, that the content is less than 10 ppm, which is the lower limit of general measurement when the sucrose fatty acid ester content is measured using a high-performance liquid chromatography (HPL) measurement method. Here, sucrose fatty acid esters refer to those obtained by transesterifying sucrose with lower alcohol esters of fatty acids, such as fatty acid methyl esters. Specifically, examples include sucrose stearate, sucrose palmitate, sucrose laurate, and sucrose oleate.

[0024] The anti-fogging agent according to the present invention contains at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and a cellulose derivative (C), and does not contain sucrose fatty acid esters. In mixed systems of sucrose fatty acid ester and sodium oleate, or sucrose fatty acid ester and potassium oleate, the adhesion between the anti-fogging layer applied to the thermoplastic resin sheet and the thermoplastic resin sheet is poor. For example, when the thermoplastic resin sheet is rolled up, the anti-fogging agent is transferred to the opposite side, leading to problems such as reduced transparency and deterioration of anti-fogging properties due to surface roughness of the coating. However, the present invention can effectively prevent such problems. In this invention, since the composition used as an anti-fogging agent contains at least one selected from highly water-soluble sodium oleate and potassium oleate, the handling properties during coating are good, and the coating layer can be formed in good condition. It is believed that the formation of this good condition coating layer also contributes to maintaining and improving the anti-fogging properties of the anti-fogging resin sheet.

[0025] Furthermore, in this invention, since the composition used as an anti-fogging agent contains a cellulose derivative (C), the storage stability of the anti-fogging agent solution can be improved. For example, by forming an anti-fogging layer using an anti-fogging agent with excellent storage stability in solution, a layer with good film formation can be formed. By preventing the separation of the anti-fogging agent, for example, whitening of the sheet after coating can be prevented, and an anti-fogging resin sheet with a good sheet appearance can be obtained.

[0026] The content ratio of at least one (A) selected from sodium oleate and potassium oleate according to the present invention is preferably 0.01 to 20 parts by mass, and more preferably 0.05 to 10 parts by mass, per 100 parts by mass of aqueous solution containing the anti-fogging agent of the present invention. The content ratio of polyvinyl alcohol (B) according to the present invention is preferably 0.05 to 20 parts by mass, and more preferably 0.05 to 10 parts by mass, per 100 parts by mass of aqueous solution containing the anti-fogging agent of the present invention. The content ratio of the cellulose derivative (C) according to the present invention is preferably 0.05 to 10 parts by mass, and more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the aqueous solution containing the anti-fogging agent of the present invention.

[0027] Furthermore, the content ratio of at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and cellulose derivative (C) in the anti-fogging agent according to the present invention is preferably at least one selected from sodium oleate and potassium oleate (A): polyvinyl alcohol (B): cellulose derivative (C) = 90 parts by mass to 20 parts by mass: 5 parts by mass to 75 parts by mass: 5 parts by mass to 75 parts by mass, more preferably 80 parts by mass to 30 parts by mass: 5 parts by mass to 65 parts by mass: 5 parts by mass to 65 parts by mass, and even more preferably 60 parts by mass to 40 parts by mass: 5 parts by mass to 55 parts by mass: 5 parts by mass to 55 parts by mass.

[0028] In particular, in the present invention, it is more preferable from the viewpoint of improving anti-fogging properties that the composition used as an anti-fogging agent contains a relatively high proportion of highly water-soluble oleates, and from the viewpoint of the appearance of the sheet after coating, it is preferable that the oleates are contained in a relatively low proportion. For example, it is preferable that at least one selected from sodium oleate and potassium oleate (A): polyvinyl alcohol (B) = 30 parts by mass:70 parts by mass to 70 parts by mass:30 parts by mass. Furthermore, in the present invention, it is preferable that the composition used as an anti-fogging agent contains, for example, at least one selected from sodium oleate and potassium oleate (A):cellulose derivative (C) = 95 parts by mass: 5 to 60 parts by mass: 40 parts by mass. Furthermore, in the present invention, it is preferable that the composition used as an anti-fogging agent contains, for example, polyvinyl alcohol (B):cellulose derivative (C) = 90 parts by mass:10 to 50 parts by mass:50 parts by mass.

[0029] In the present invention, if component (A) contains a combination of multiple types of sodium oleate and potassium oleate, the content of component (A) shall be the total amount of all components used as component (A), and if component (C) contains multiple types of cellulose derivatives, the content of component (C) shall be the total amount of all components used as component (C).

[0030] <Release layer> In the present invention, a release layer can be formed on the other side of a thermoplastic resin sheet where an anti-fogging layer is provided, by applying a release agent. As a release agent, silicone oil (E) can be used. From the standpoint of safety and cost-effectiveness, this silicone oil (E) has a viscosity of 1 million to 500,000 mmHg at 25°C. 2 Dimethylpolysiloxane in the range of / s is preferred.

[0031] Furthermore, when applying silicone oil (E) to the surface of a thermoplastic resin sheet, it is preferable to use it in the form of a silicone emulsion. It is preferable that the average particle size of the silicone oil (E) in the silicone emulsion be 1 μm or less. That is, if the average particle size exceeds 1 μm, uniform application becomes difficult, and the appearance of the anti-fogging resin sheet deteriorates.

[0032] Furthermore, since the appearance of the sheet and secondary molded product is good, it is preferable to apply the silicone oil (E) used in the present invention to the other side of the surface coated with the anti-fogging agent. In other words, if silicone oil (E) is mixed into the anti-fogging agent and applied, there is a problem that the appearance of the sheet and secondary molded product deteriorates, so the amount of silicone oil (E) blended with 100 parts by mass of aqueous solution containing the anti-fogging agent of the present invention must be 10.0 parts by mass or less. Moreover, it is preferable to have 5.0 parts by mass or less, and it is particularly preferable that the anti-fogging agent does not contain silicone oil.

[0033] Furthermore, it is possible to add antistatic surfactants, lubricants, etc., to the silicone emulsion containing the silicone oil (E) used in the present invention.

[0034] <Method for manufacturing anti-fog resin sheets> The present invention provides a method for producing an anti-fogging resin sheet, for example, by applying a solution-type anti-fogging agent (anti-fogging composition) containing at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and a cellulose derivative (C), but without sucrose fatty acid esters, to at least one surface of a thermoplastic resin sheet, and then drying the solvent to form an anti-fogging layer.

[0035] The method for producing the anti-fogging resin sheet of the present invention is not particularly limited, but it is preferable to apply an anti-fogging agent consisting of an aqueous solution to at least one surface of a thermoplastic resin sheet obtained by forming a film of a thermoplastic resin by a known method. Specifically, one method involves hydrophilizing one surface of the thermoplastic resin sheet, then applying the anti-fogging agent according to the present invention to this treated surface, and drying the solvent to form an anti-fogging layer.

[0036] The antifogging agent used in the manufacturing method of the antifogging resin sheet of the present invention can be applied using known methods such as a spray coater, roll coater, gravure roll coater, knife coater, air knife coater, rotor dampening coater, or applicator method, and there are no particular limitations.

[0037] The amount of antifogging agent applied to the antifogging resin sheet of the present invention is preferably adjusted to a predetermined amount in order to improve the antifogging effect and prevent appearance defects due to uneven application. Specifically, the amount of solid content applied after drying, i.e., the mass of the antifogging layer per unit area of ​​the antifogging resin sheet, is 5 to 1,000 mg / m². 2 Preferably, it is 5-150 mg / m² 2 It is particularly preferable that this be the case.

[0038] Quantitative analysis of the amount of anti-fogging agent applied can be performed using a Fourier transform infrared spectrophotometer (multiple internal reflection method) [FTIR analysis method (ATR method)].

[0039] Furthermore, known methods for hydrophilizing the surface of thermoplastic resin sheets include acid treatment, flame treatment, and corona treatment. The wettability of the surface of the thermoplastic resin sheet subjected to these hydrophilization treatments is preferably 38 mN / m or higher, and more preferably in the range of 45 to 60 mN / m in order to uniformly apply the antifogging agent and obtain a sufficient antifogging effect. Here, the wettability is a value measured by the method described in JIS K6768-1999.

[0040] (Secondary molded product) By molding the anti-fog resin sheet of the present invention by means of vacuum forming, pressure vacuum forming, hot plate pressure forming, etc., secondary molded products suitable for food containers such as bento boxes, prepared food containers, sushi containers, and sashimi containers, and especially for anti-fog transparent lids for such food containers, can be produced. [Examples]

[0041] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0042] (Example 1) Potassium oleate (A-2) 0.9% by mass, polyvinyl alcohol (B-1) (saponification degree 74 mol%, viscosity of 4% aqueous solution at 20°C 4.7 mPa·s) 0.66% by mass, methylcellulose (C-1) (viscosity of 2% aqueous solution 50 mm 2 0.1% by mass of ( / s) was mixed and dissolved in 98.34% by mass of water to obtain anti-fogging agent (1).

[0043] Next, a 0.21 mm thick biaxially oriented polystyrene resin sheet (Sandic Sheet 510, manufactured by Sandic Co., Ltd.) without surface coating was subjected to corona treatment with a wetting tension of 50 mN / m on one side, and a roll coater was used to apply an anti-fogging agent with a solid content of 50 mg / m² to the corona-treated surface.2 To achieve this, the anti-fogging agent (1) was appropriately diluted with water and applied, then dried with a hairdryer to obtain an anti-fogging resin sheet (1) on which an anti-fogging layer was formed on a polystyrene resin sheet. The amount of anti-fogging agent applied was determined by measuring the infrared absorption spectrum of the sheet surface using the multiple internal reflection method (ATR method) with a Fourier transform infrared spectrophotometer (FTIR), and then performing quantitative analysis based on a calibration curve created from standard samples with known application amounts.

[0044] The obtained anti-fogging resin sheet (1) was evaluated according to the following method for its appearance, anti-fogging properties, anti-fogging properties of the deep-drawn molded product, adhesion to the sheet, and storage stability of the anti-fogging agent solution.

[0045] (Evaluation of the appearance of anti-fogging resin sheets) The sheets were visually inspected after the anti-fogging agent was applied, and the presence or absence of whitening was evaluated. The lower the degree of whitening, the better the appearance of the anti-fogging resin sheet. [Evaluation Criteria] ○: The sheet did not turn white after application and maintained its transparency. △: The sheet is slightly whitened after application, but this is at a level that does not affect practical use. ×: The sheet has turned white after application, and its transparency has been significantly reduced.

[0046] (Evaluation of anti-fogging properties of secondary molded products) A secondary molded product (1) was obtained by molding an anti-fogging resin sheet (1) using a hot plate pressure molding machine with a hot plate temperature of 125°C and the mold shown below. • Mold dimensions: 94mm (height) x 94mm (width) x 30mm (depth), corners: 2R Next, to evaluate the anti-fogging properties assuming use in a high-temperature food container to observe the contents from the outside, the high-temperature anti-fogging properties of the secondary molded product were evaluated in the following manner. Specifically, a base material (obtained by secondary molding of a thermoplastic resin sheet) identical in shape to the secondary molded product was prepared, a piece of paper printed with a 15mm square grid pattern was placed on top, 100mL of 90°C water was poured into the base material, the top was covered with the secondary molded product obtained in the above example, and left at 23°C for 5 minutes. The distortion of the grid pattern visible through the secondary molded product, as well as the degree of water droplets adhering to the top surface and the inside of the four corners, were observed visually. The less fogging there is on the secondary molded product, or the less distortion there is in the grid pattern visible to the naked eye, the better the anti-fogging properties of the anti-fogging resin sheet. [Evaluation Criteria] ◎: The secondary molded product is free from cloudiness, and the checkerboard pattern is clearly visible without distortion over 85% or more of the secondary molded product's surface area. ○: The secondary molded product is free from cloudiness, and the checkerboard pattern is clearly visible without distortion over more than 50% of the secondary molded product's surface area. △: The secondary molded product is free of cloudiness, but the checkerboard pattern appears distorted over a larger area than 15% of the secondary molded product. ×: Small water droplets adhere to the top surface or corners of the secondary molded product, causing fogging.

[0047] (Evaluation of anti-fogging properties of deep-drawn molded products) As a deep-drawn molded product (secondary molded product), a deep-drawn secondary molded product (1) was obtained by molding an anti-fogging resin sheet (1) to the size shown below using a hot plate pressure molding machine with a hot plate temperature of 125°C. Mold dimensions: 94mm (height) x 94mm (width) x 50mm (depth), corners: 2R The method for evaluating anti-fogging properties is as described above (Evaluation of anti-fogging properties of secondary molded products).

[0048] (Evaluation of adhesion between the anti-fogging agent and the sheet) The adhesion between the anti-fogging layer, which consists of an anti-fogging agent, and the thermoplastic resin sheet (also known as the adhesion of the anti-fogging agent to the sheet) was evaluated. The surface of the anti-fog resin sheet (1) was rubbed with a finger, and the presence or absence of peeling of the anti-fog agent and the presence or absence of clouding of the sheet were evaluated. [Evaluation Criteria] ○: The anti-fog coating does not peel off, and the sheet does not become cloudy. △: There is slight peeling of the anti-fog coating, but it does not affect practical use. ×: The anti-fog agent peeled off the sheet, causing the sheet to become cloudy.

[0049] (Evaluation of storage stability of anti-fogging agent solutions) The anti-fogging agent (1) was left at 23°C, and the number of days until suspended particles or sediment could be visually observed was evaluated.

[0050] The evaluation results for Example 1 are shown in Table 1-1. The anti-fogging resin sheet (1) exhibited good sheet appearance, anti-fogging properties, anti-fogging properties of deep-drawn molded products, adhesion, and liquid stability. In Table 1-1, since the mixture contains 0.9% by mass of potassium oleate, 0.66% by mass of polyvinyl alcohol, and 0.1% by mass of methylcellulose, the amounts of potassium oleate are expressed as 0.9 / (0.9+0.66+0.1)=54 (by mass), polyvinyl alcohol as 0.66 / (0.9+0.66+0.1)=40 (by mass), and methylcellulose as 0.1 / (0.9+0.66+0.1)=6 (by mass) (other examples and comparative examples are expressed similarly).

[0051] (Examples 2) to (Examples 14) In Example 1, anti-fogging agents (2) to (14) were obtained in the same manner as in Example 1, except that the types and proportions of components contained in the anti-fogging agent were changed as shown in Tables 1-1 to 1-3. Hereinafter, Tables 1-1 to 1-3 will be collectively referred to as "Table 1". Next, using the obtained anti-fogging agents (2) to (14), anti-fogging resin sheets (2) to (14) and secondary molded products (2) to (14) were obtained in the same manner as in Example 1, and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. The ingredients listed in Table 1 are as follows (the same applies to Table 2). • Sucrose fatty acid ester (sucrose laurate ester (monoester 70%, HLB 15)) · Polyvinyl alcohol (B-1) (saponification degree 74 mol%, 20 °C viscosity of 4 mass% aqueous solution 4.7 mPa·s) · Polyvinyl alcohol (B-2) (saponification degree 88 mol%, 20 °C viscosity of 4 mass% aqueous solution 23 mPa·s) · Polyvinyl alcohol (B-3) (saponification degree 80 mol%, 20 °C viscosity of 4 mass% aqueous solution 4.5 mPa·s) · Polyvinyl alcohol (B-4) (saponification degree 88 mol%, 20 °C viscosity of 4 mass% aqueous solution 5.5 mPa·s) · Methyl cellulose (C-1) (methyl cellulose, viscosity at 20 °C of 2 mass% aqueous solution 50 mm 2 / s) · Methyl cellulose (C-2) (hydroxypropyl methyl cellulose, viscosity at 20 °C of 2 mass% aqueous solution 25 mm 2 / s) · Methyl cellulose (C-3) (hydroxypropyl methyl cellulose, viscosity at 20 °C of 2 mass% aqueous solution 100 mm 2 / s) · Methyl cellulose (C-4) (hydroxypropyl methyl cellulose, viscosity at 20 °C of 2 mass% aqueous solution 3 mm 2 / s) · Methyl cellulose (C-5) (methyl cellulose, viscosity at 20 °C of 2 mass% aqueous solution 4 mm 2 / s)

[0052] (Comparative Example 1) 1.3 mass% of sucrose laurate (monoester 70%, HLB 15), 0.6 mass% of polyvinyl alcohol (saponification degree 74 mol%, 20 °C viscosity of 4% aqueous solution 4.7 mPa·s), and 1.0 mass% of sodium oleate were mixed and dissolved in 97.1 mass% of water to obtain Comparative Antifogging Agent (1). Next, using the obtained Comparative Antifogging Agent (1), in the same manner as in Example 1, a Comparative Antifogging Resin Sheet (1) and a Comparative Secondary Molded Product (1) were obtained and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2-1. The Comparative Antifogging Resin Sheet (1) had good antifogging properties but poor adhesion to the sheet. In Table 2, since the product contains 1.3% by mass of sucrose laurate, 0.6% by mass of polyvinyl alcohol, and 1.0% by mass of sodium oleate, the amounts are expressed as follows: sucrose fatty acid ester (sucrose laurate) = 1.3 / (1.3+0.6+1.0)=45, polyvinyl alcohol = 0.6 / (1.3+0.6+1.0)=21 (by mass), and sodium oleate = 1.0 / (1.3+0.6+1.0)=34 (by mass).

[0053] (Comparative Example 2) to (Comparative Example 8) Comparative anti-fogging agents (2) to (8) were obtained in the same manner as in Comparative Example 1 and Example 1, except that the types and proportions of components contained in the anti-fogging agent were changed as shown in Tables 2-1 to 2-2. Hereinafter, Tables 2-1 to 2-2 will be collectively referred to as "Table 2". Next, using the obtained comparative anti-fogging agents (2) to (8), comparative anti-fogging resin sheets (2) to (8) and comparative secondary molded products (2) to (8) were obtained in the same manner as in Comparative Example 1 and Example 1, and evaluated in the same manner as in Example 1 and Comparative Example 1. The evaluation results are shown in Table 2.

[0054] [Table 1-1]

[0055] [Table 1-2]

[0056] [Table 1-3]

[0057] [Table 2-1]

[0058] [Table 2-2]

[0059] The anti-fogging resin sheets of the examples exhibited good sheet appearance, anti-fogging properties, anti-fogging properties of deep-drawn molded products, adhesion, and storage stability of the anti-fogging agent solution. The comparative anti-fogging resin sheet had good anti-fogging properties, but it had poor adhesion to the sheet, and the storage stability of the anti-fogging agent liquid used to form the anti-fogging layer of the anti-fogging resin sheet was poor.

[0060] As shown in Table 1, the anti-fogging resin sheets obtained in the examples all satisfied the requirements of good sheet appearance, good anti-fogging properties, good anti-fogging properties of deep-drawn molded products, good adhesion, and good storage stability of the anti-fogging agent solution.

Claims

1. On at least one surface of the thermoplastic resin sheet, An anti-fogging resin sheet having an anti-fogging layer formed by an anti-fogging agent containing at least one selected from sodium oleate and potassium oleate (A), polyvinyl alcohol (B), and a cellulose derivative (C), but without containing sucrose fatty acid esters.

2. The anti-fogging resin sheet according to claim 1, wherein the degree of saponification of the polyvinyl alcohol (B) is 70 to 85 mol%.

3. The anti-fogging resin sheet according to claim 1, wherein the cellulose derivative (C) is methylcellulose or hydroxypropylmethylcellulose.

4. The viscosity of the 2% by mass aqueous solution of the cellulose derivative (C) at 20°C is 20 to 60 mm. ２ The anti-fogging resin sheet according to claim 3, wherein the value is / s.

5. The anti-fogging resin sheet according to claim 1, wherein a release layer made of silicone oil (E) is formed on the other side of the thermoplastic resin sheet opposite to the side on which the anti-fogging layer is provided.

6. The anti-fogging resin sheet according to claim 1, wherein the thermoplastic resin sheet is a styrene-based resin sheet.

7. A secondary molded product obtained by molding an anti-fogging resin sheet according to any one of claims 1 to 6.

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