JP2000273227A - Polyester resin sheet having antifogging property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin sheet having antifogging property manifesting antifogging property for a long time after forming into a container shape by a thermoforming method. SOLUTION: This resin sheet comprises a polyester sheet having a layer of a copolyester including polyethylene glycol as a diol component manifesting water droplet contact angle of 45-55 deg. and coating an antifogging agent on the surface of the copolyester resin layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an antifogging polyester resin sheet. More specifically, the present invention relates to a sheet having a surface for preventing fogging of the surface due to condensation of water vapor, and which does not deteriorate for a long time even after being formed into a container by a thermoforming method.

[0002]

2. Description of the Related Art Polyethylene terephthalate (hereinafter "P")
Polyester resins represented by "ET" may be used for molding materials for various sheets, containers and the like. Particularly in recent years, the development in the field of molded articles in which vinyl chloride, polystyrene and the like have been frequently used as raw materials has been remarkable. For example, molded articles obtained by thermoforming an unstretched amorphous sheet made of a polyester resin (often referred to as “A-PET sheet”) have begun to be widely used for containers of foods, medicines and the like. .

[0003] Such a polyester resin sheet is excellent in mechanical strength, chemical stability, transparency, water resistance and moldability, but on the other hand, its surface is extremely hydrophobic, so that the temperature and humidity are low. Moisture that condenses in accordance with the change in water does not uniformly wet the (water vapor) surface, but remains as fine water droplets on the surface, and adheres to the entire surface, often causing so-called clouding. For example, when sushi or cake is stored, packaged, and stored in a container formed from such a sheet, water vapor evaporated from the surface of the sushi or cake saturates the inside of the container, and this water becomes small water droplets inside the container. If they are agglomerated and adhered, it is difficult to identify the stored items.
The occurrence of such fogging significantly reduces the commercial value of a container characterized by transparency. This is not only a serious drawback of containers characterized by transparency, but also such unevenly agglomerated and adhered moisture affects foods contained in such containers, resulting in poor quality. , May cause rot.

[0004] Therefore, in order to prevent water droplets from adhering to the surface of the polyester resin sheet, a method of applying various antifogging agents can be considered. As the anti-fog agent, polyglycerin, a fatty acid ester, a sucrose fatty acid ester, a polysaccharide, a hydrophilic polymer, which is an anti-fog agent mainly used for sheets and films of a styrene resin or a polyolefin resin,
Unmodified polyvinyl alcohol and mixtures thereof (for example, JP-A-54-99180;
JP-B-59-19584, JP-B-63-62538, JP-A-9-12751, and JP-A-5-287097.

[0005]

As an example of applying an anti-fogging agent to a polyester resin sheet and using it as an anti-fogging container after thermoforming, the above-mentioned low temperature of sushi, cake, vegetable salad, side dish, etc. is used. Often used as food containers for storage. These foods are placed in anti-fog containers,
It is generally sold at stores such as supermarkets (displayed on refrigerated goods display shelves), but if sold on the same day, about 12 hours of anti-fog properties are sufficient, but Depending on the case, it may be displayed at the store for a longer time, and anti-fogging property for a long time of about 48 hours is desired.

However, when water droplets adhering to the surface of the polyester resin sheet agglomerate and drop (at this time, the anti-fog agent applied to the sheet surface has melted into the water droplets), the water droplets easily fall. In addition, there is a problem that the antifogging agent also drops together with the water droplets, and the antifogging property of the sheet surface is lost. That is, the conventional method shows very good anti-fogging property until a water droplet is generated and falls, but at present, the anti-fogging property has disappeared after the generated water drop starts falling. . At present, the anti-fogging property is maintained for about 3 hours after the display at the store, but after that, the anti-fogging property is often reduced and disappears with the start of dropping of water droplets. Therefore, an object of the present invention is to provide a polyester resin sheet capable of maintaining the anti-fogging property even after the water droplets generated on the sheet surface start falling.

[0007]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies on an antifogging polyester resin sheet, and as a result, formed a copolymer polyester containing polyethylene glycol as a copolymer component on the sheet surface to obtain a hydrophilic polyester resin sheet. It has been found that enhancing the properties has a significant effect on the retention of the antifogging property after applying the antifogging agent to the surface, and the present invention has been achieved. That is, the present invention provides a polyester resin sheet having a copolymerized polyester resin layer surface containing polyethylene glycol (hereinafter referred to as "PEG") as a diol component, wherein the copolymerized polyester resin layer surface is coated with an antifogging agent. It relates to a resin sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester resin in the present invention is represented by terephthalic acid as a carboxylic acid component and polyethylene terephthalate composed of ethylene glycol as a glycol component, and other carboxylic acid components include 2,6-naphthalenedicarboxylic acid, isophthalic acid, and phthalic acid. , Adipic acid, sebacic acid, oxycarboxylic acid (eg, p-oxyethoxybenzoic acid, etc.), and diethylene glycol, 1,4- and 1,3- as other glycol components.
Cyclohexane dimethanol, propylene glycol,
Also included are copolymer resins in which components are replaced with 1,4-butanediol, neopentyl glycol, bisphenol A, bisphenol S, and the like.

The present invention uses the above-mentioned polyester resin sheet, and is characterized in that the sheet has a surface of a copolymerized polyester resin layer containing PEG as a diol component. Specifically, the entire polyester resin sheet may be a PEG copolymerized polyester resin. In addition, PEG copolymerized polyester resin / PE
In some cases, it is constituted as a laminate comprising a surface layer of a PEG copolymerized polyester resin such as T or PEG copolymerized polyester resin / PET / PEG copolymerized polyester resin and another polyester resin layer.

[0010] The weight average molecular weight of the PEG component of the PEG copolymerized polyester resin is usually preferably from 3,000 to 20,000, particularly preferably from 5,000 to 10,000. The copolymerization amount of PEG is usually 3 to 20 mol%, preferably 5 to 15 mol% of the diol component. 5
If the amount is less than mol%, it is difficult to obtain the desired anti-fog property for a long time. If the amount exceeds 20 mol%, the sheets adhere to each other when the sheet is wound into a roll, and blocking tends to occur. The sheet may crack. PE of such PEG copolymerized polyester resin
The monomer components other than G are not particularly limited, but usually terephthalic acid and ethylene glycol are used, and the polymerization method may be carried out according to a generally known polymerization method for PET.

The polyester resin can be formed into a sheet by a conventionally known molding method such as a T-die method.
Specifically, (a) a method of obtaining a sheet with one extruder,
(B) Using two extruders, melt extruding the PEG copolymerized polyester resin and other polyester resins from each other, and using a two-layer or three-layer multilayer T-die, the two-layer or three-layer sheet. How to get a (c)
Using two extruders, the PEG copolymerized polyester resin and other polyester resins are melt-extruded from each, and one or two molten sheets for a base layer and a hydrophilic resin are formed by two or three single-layer T dies. One or two molten sheets for a layer are separately obtained, and they are pressure-bonded and laminated while still in a molten state to obtain a sheet having the two-layer structure or the three-layer structure.

As an extrusion method, a polyester resin is supplied to an extruder after being dried, extruded at a resin temperature usually in the range of 250 to 320 ° C., and cooled and solidified on a casting roll to form a sheet. By providing the extruder with a vent port, the drying step can be omitted or the drying time can be shortened. When cooling and solidifying on a casting roll, the casting roll temperature is usually 0 to 80 ° C., and one or more touch rolls are provided in the vicinity of the casting roll, and the touch roll may be used as a holding roll when sheeting. This is one of the preferred methods. The above-mentioned sheet is usually preferably unstretched, but may be stretched. The thickness of the obtained sheet is usually 0.01 to 0.50 mm, particularly 0.05
０．３0.30 mm. The surface layer made of a PEG copolymerized polyester resin is usually at least 0.005 mm, preferably at least 0.01 mm.

The polyester resin sheet used in the present invention obtained by the above method has a water droplet contact angle on the PEG copolymerized polyester resin layer surface of usually 45 to 55 degrees, preferably 46 to 53 degrees. Since the water contact angle of normal homo PET is usually 60 to 70 degrees, the sheet surface in the present invention usually has a water contact angle smaller than that of the conventional one.
It can be said that the hydrophilicity is high. When the water droplet contact angle is larger than 55 degrees, the initial antifogging property within several hours immediately after the application of the antifogging agent is good, but the intended antifogging property for a long time cannot be maintained. If the water droplet contact angle is smaller than 45 degrees, the sheets are likely to be blocked from each other, and if the sheet is wound into a roll, it becomes difficult to rewind the sheet, which hinders the use of the sheet itself. You. In order to set the contact angle of the water droplet on the sheet surface to a desired value in the above range, the contact angle may be adjusted by a treatment such as corona discharge treatment or high-frequency treatment to make the sheet surface moderately rough.

The antifogging polyester resin sheet of the present invention is obtained by subjecting the surface of a copolymer polyester resin layer containing PEG as a diol component of the sheet obtained by the above method to an antifogging treatment. As the anti-fog agent used in this anti-fog treatment, polyglycerin fatty acid esters and sucrose fatty acid esters, polysaccharides, hydrophilic polymers, unmodified polyvinyl alcohol and the like are suitable. Any of these may be used, or a mixture thereof. Such an antifogging agent is usually added to the sheet surface in a solid content of 0.0
By coating at a rate of 1 to 0.15 g / m ² , a sheet having good antifogging property can be obtained. As a coating method, known methods such as brushing, spraying, a roll coater, a gravure roll coater, a knife coater, a rotor dampening method, and a dipping method can be used. In order to more completely prevent blocking of the sheet, a silicone emulsion or the like may be mixed. On the other hand, a silicone emulsion or the like may be applied to the surface opposite to the anti-fogging treatment surface to prevent blocking. The antifogging polyester resin sheet as described above can be thermoformed by a general thermoforming apparatus and used for molded articles such as containers.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the present invention. In addition, evaluation of the sheet in the following Examples was performed by the method shown below.

(1) Contact angle of water droplet on sheet surface before application of antifogging agent A contact angle meter CA-X manufactured by Kyowa Interface Science Co., Ltd. is used as a water droplet contact angle meter, and ion-exchanged water is used as a liquid to be dropped. used. The amount of water drops dropped on the surface of the polyester resin sheet was about 1.8 μl, and the measurement was performed so that one measurement was completed within 5 seconds after dropping. (2) Anti-fogging property of sheet 300 cc of water was put into a 500 cc beaker, and the upper surface of the beaker was covered with the anti-fogging agent applied surface of the sheet obtained in each of Examples and Comparative Examples facing down, and sealed. did.
This beaker was immersed in a constant temperature water bath installed in a room at room temperature of 5 ° C., and the water temperature in the beaker was kept at 50 ° C. One hour later, the condition in which water vapor condenses on the sheet surface was visually observed, and the evaluation was as follows. Large transparent water droplets are generated, but there is no white haze due to fine water droplets at 5, white light haze is generated at 4, white whit is generated at about 20% of the whole And 3, a state where white haze occurred in about 50% of the whole, and 1 where white haze occurred in about 50% or more of the whole.

(3) Initial anti-fogging property and long-time anti-fogging property of the molded article
0mm x 145mm, bottom 70mm x 120mm, height 50
A container lid having a size of mm and a flange having a width of 15 mm around the opening was formed so that the surface coated with the antifogging agent was inside. Open the molded container lid to 100 mm x 145
300 ° C hot water in a 25 mm high, 25 mm dish-shaped container
The container was placed in a room at room temperature of 5 ° C. The state in which water vapor condenses on the sheet surface was visually observed after 1 hour for the initial antifogging property and 48 hours for the long term antifogging property. The evaluation was performed in the same manner as for the antifogging property of the sheet.

(4) Peeling resistance of anti-fogging agent of molded article obtained by thermoforming method The obtained sheet was formed into a sheet having an opening of 10 mm by using a hot plate forming machine.
0mm x 145mm, bottom 70mm x 120mm, height 50
A container lid having a size of mm and a flange having a width of 15 mm around the opening was formed so that the surface coated with the antifogging agent was inside. 300cc of hot water at 50 ℃ is put into the molded container lid,
Shake for 20 seconds. Then the opening is 100mm x 145m
A dish-shaped container filled with 300 cc of 60 ° C. hot water having a height of 25 mm and a height of 25 mm was covered with the lid of the container so that the surface coated with the antifogging agent was inside, and the container was placed in a room at room temperature of 5 ° C. After one minute, the situation where the water vapor condenses on the top surface of the container lid (the bottom of the molded container) was visually observed. The evaluation was performed in the same manner as for the antifogging property of the sheet.

(5) Sheet Blocking Property Two sheets obtained by coating a surface-treated sheet as shown in the following Examples and Comparative Examples, or an untreated sheet coated with an anti-fogging agent, are stacked at 50 kgf / m ^2. And kept for 24 hours. Thereafter, the load was removed, and the state when the sheet was peeled was evaluated. In the evaluation ○, the sheet can be peeled off with almost no resistance. In the evaluation (1), although there is resistance, the sheet can be peeled off. In the case of the evaluation X, the sheet is blocked and the sheet cannot be peeled off smoothly or the sheet is broken.

Example 1 Terephthalic acid as a dicarboxylic acid component, and a copolymerized PET resin A (intrinsic viscosity 0.74 dl / g) polymerized as 90 mol% of ethylene glycol and 10 mol% of PEG (weight average molecular weight: about 8000) as a diol component. It is supplied to a 65 mmφ twin screw extruder with a vent port (for the skin layer), and homo PET resin B (“NOVA manufactured by Mitsubishi Chemical Corporation”)
PEX ”GS400 grade) is also supplied to a 120 mmφ twin screw extruder (for core layer) with a vent port,
This was carried out by extruding from a T die with a feed block at a resin temperature of 290 ° C. and rapidly cooling on a casting roll at a temperature of 40 ° C. By controlling the discharge rate of each extruder, a three-layer polyester resin sheet having a skin layer thickness of 0.02 mm, a core layer thickness of 0.23 mm, and a total layer thickness of 0.25 mm was prepared.

On this sheet, a sucrose laurate ester (LWA-1570, manufactured by Mitsubishi Chemical Foods, Inc., water 56
A solution prepared by diluting 3 parts by weight of 97 parts by weight of water with a solution of 3 parts by weight of water, 4 parts by weight of ethyl alcohol, and 40 parts by weight of sucrose laurate ester was applied by a bar coater to 2 g / m ^2, and a gear oven was used. For 2 minutes at 60 ° C. to prepare an antifogging polyester resin sheet. Antifogging property of this sheet, initial antifogging property and long-time antifogging property of a molded article obtained from this sheet by a thermoforming method, peeling resistance of an antifogging agent of a molded article obtained by a thermoforming method, and Table 1 shows the evaluation results of the blocking properties of the sheet.

Example 2 The same copolymerized PET resin A as in Example 1 was supplied as a hydrophilic resin component to both of the two extruders in Example 1, and the resin temperature and the like were the same as in Example 1. 0.25mm thick 1
A PET resin sheet having a layer structure was prepared. And Example 1
The same sucrose laurate was applied at ² cc / m ² and dried, and the same anti-fogging PET resin sheet was evaluated in the same manner as in Example 1. The results are shown in Table 1. .

Comparative Examples 1-3 PET resin B was supplied to both of the two extruders of Example 1, and the resin temperature and the like were the same as in Example 1, and the thickness was 0.2 mm.
A 5 mm single-layer PET resin sheet was prepared. Then, the same sucrose laurate ester and Comparative Example 1 In Example 1 were coated to a 2 cc / m ^2, similarly, such that the 3 cc / m ² in Comparative Example 2, Comparative Example 3 4
cc / m ² and apply in a gear oven to 60
C. for 2 minutes, and the solid content of sucrose laurate on the sheet surface was 0.024 g / m in Comparative Example 1, respectively.
² , an antifogging PET resin sheet of 0.036 g / m ² in Comparative Example ² and 0.048 g / m ² in Comparative Example 3 was prepared. Table 1 shows the evaluation results of the sheet. Table 1 shows that the antifogging polyester resin sheet according to the present invention also has good initial antifogging properties and long-time antifogging properties.
Also, it can be seen that the sheet is not blocking.
On the other hand, Comparative Examples 1 and 2 are inferior in anti-fogging property for a long time, and Comparative Example 3 satisfies the anti-fogging property for a long time to some extent, but a sheet blocking phenomenon is observed.

[0024]

[Table 1]

[0025]

The polyester resin sheet of the present invention retains antifogging properties for a long time and is excellent in transparency. Further, the sheet has low blocking properties and good productivity. Such a polyester resin sheet of the present invention is molded and is expected to be widely used as food containers and the like.

Claims (3)

[Claims] 1. An antifogging polyester resin sheet comprising a polyester resin sheet having polyethylene glycol as a diol component and having a copolymer polyester resin layer surface coated with an antifogging agent. 2. The antifogging polyester resin sheet according to claim 1, wherein an antifogging agent is applied to the surface of the copolymerized polyester resin layer having a water droplet contact angle of 45 to 55 degrees. 3. A container formed by thermoforming the antifogging polyester resin sheet according to claim 1.