JP2001260215A - Producing method for vessel consisting of crystalline polyester sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method, in which in the case of producing a vessel of a crystalline polyester sheet, good mold decision properties and mold release characteristics are simultaneously revealed and productivity is enhanced by shortening of a molding cycle and decrease of a failure generation rate. SOLUTION: In the method for obtaining the vessel by heating and softening a polyester sheet mainly consisting of polyethylene terephthalate and thereafter molding the same, the polyester vessel is produced by molding the sheet heated till such a state that degree of crystallinity becomes 5-14% by a molding die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a crystalline polyester container from a crystalline polyester sheet mainly composed of polyethylene terephthalate, and more particularly, to a method for forming a polyester container excellent in heat resistance and impact resistance. The present invention relates to a manufacturing method capable of simultaneously exhibiting mold-fixing property and mold-releasability, and improving productivity by shortening a molding cycle and reducing a defect occurrence rate.

[0002]

2. Description of the Related Art With the widespread use of microwave ovens and ovens for home use, food trays that can withstand use at high temperatures are widely used. As a typical heat-resistant food tray, crystallized PET (hereinafter referred to as C-PET) has been put to practical use. Since C-PET is an environmentally friendly material, its use as a heat-resistant tray for gratin, doria, confectionery and the like has been expanding in recent years.

[0003] As a method of manufacturing a container using C-PET, a polyester sheet is preheated by a heater or the like which is not in contact with the sheet, heat-softened to a moldable state, and the heat-softened sheet is heated to about 160 to 200 mm. There is known a method in which crystallization is performed simultaneously with molding in a high-temperature mold heated to about ° C.

[0004] However, in the above-mentioned forming process, there are problems such as sagging of the sheet at the stage of preheating the sheet, releasability at the stage of removing the container from the high-temperature mold, and determination of the shape of the container. For example, when the sheet is excessively heated and softened, the mold temperature is as high as about 160 to 200 ° C., so that the container comes into close contact with the mold, which causes a problem such as deformation at the time of mold release. on the other hand,
When the heating time is shortened to solve the above-described problem, the releasability is improved, but the rigidity of the sheet lowers the mold definition. Since these cause a decrease in container productivity and an increase in the rate of occurrence of defective containers, improvement thereof has been desired.

As a method for solving such a problem, a two-stage pressing method using a high-temperature and low-temperature mold has been proposed (Japanese Patent Laid-Open No. 4-85019, Japanese Patent Publication No. Hei 4-85019).
No. 34931). However, the above-described method still has a problem that the molding cycle becomes long and a problem of molding defects such as deformation and scratches of the molded product.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problems at the time of molding, and at the same time, achieves good moldability and mold releasability, and improves productivity by shortening the molding cycle and reducing the incidence of defects. It is an object of the present invention to provide a method for producing a polyester container, which enables the above.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by setting the crystallinity of the polyester sheet at the time of molding to a predetermined range. The inventors have found that the above-mentioned problems are solved, and have reached the present invention.

That is, the present invention is as follows. 1. A method for obtaining a container by heating and softening a polyester sheet mainly composed of polyethylene terephthalate, wherein the sheet heated to a state where the crystallinity is 5 to 14% is formed by a molding die. Manufacturing method of polyester container. 2. Crystalline polyester sheet has an intrinsic viscosity of 0.70 dl
2. The method for producing a polyester container as described in 1 above, wherein the polyethylene terephthalate and the polyolefin resin are contained in a ratio of 92/8 to 99/1 (weight ratio) of polyethylene terephthalate / polyolefin resin in a ratio of 92/8 to 99/1 (weight ratio). 3. 3. The method for producing a polyester container according to 1 or 2, wherein the polyolefin resin is polyethylene having a melt flow rate of 2 g / 10 min or less as measured by ASTM method D1238.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The polyester sheet in the present invention is mainly composed of polyethylene terephthalate (hereinafter referred to as PET). PET means 80 units of ethylene terephthalate.
% Of terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, hydroxybenzoic acid,
Diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxy ethane dicarboxylic acid, 3,5-dicarboxybenzene sulfonic acid, oxalic acid, succinic acid, glutaric acid, sebacic acid, etc. and one of their ester-forming derivatives or It may be replaced with two or more types.

In addition, a part of ethylene glycol is converted to a small amount of cyclohexanedimethanol, 1,2-propylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentylene glycol, 1,4-bis It may be replaced with one or more of hydroxybenzene and polyalkylene glycol such as polyethylene glycol, polytetramethylene glycol, and polypropylene glycol. In addition, tri- or higher functional compounds, such as glycerin, pentaerythritol, trimellitic acid, 5-hydroxyisophthalic acid, may be used to some extent in a substantially linear polymer, and monofunctional compounds,
For example, it may be replaced with p-phenylphenol, benzyloxybenzoic acid, naphthalene monocarboxylic acid, polyethylene glycol monomethylene ether, or the like.

The polyester sheet of the present invention may contain a small amount of other polymers or additives, if necessary. In this case, however, the mixing is carried out within a range that does not substantially change the properties of the polyester sheet. It is preferred to do so. As these polymers or additives, for example,
Polymers such as polyamides and polytesters, matting agents such as titanium dioxide and alumina oxide, stabilizers such as phosphoric acid, phosphorous acid and their esters, antioxidants, antibacterial agents, ultraviolet absorbers, fluorescent brighteners or pigments And dyes.

The above-mentioned PET has an intrinsic viscosity (hereinafter referred to as IV) in order to prevent the occurrence of operation failure due to the sagging of the sheet in the sheet preheating step at the time of sheet preheating during molding.
Is 0.70 or more, preferably 0.80 or more.

The polyester container described in the present invention can be molded by any method conventionally known as a method for molding a polyester container. Examples include, but are not limited to, vacuum forming, plug assist forming, air slip forming, compressed air forming, snapback forming, lever draw forming, and a combination thereof.

In the present invention, the crystallinity of the polyester sheet is determined by rapidly cooling the heat-softened sheet using a cooled iron plate, a cooled mold, liquid nitrogen, water, and the like, and then using a hydrometer, a density gradient, and the like. It can be calculated by measuring the specific gravity using a tube or measuring the heat of fusion using a differential scanning calorimeter (DSC).

In the present invention, when the polyester sheet is molded in a molding die, the crystallinity of the sheet is 5 to 14%, preferably 6 to 12%. Crystallinity of the sheet, the temperature at the time of heating the polyester sheet,
The time is adjusted to the above-mentioned range by appropriately optimizing the time. If the average crystallinity is less than 5%, the container is in close contact with the mold and cannot be released quickly or is often undesirably deformed. On the other hand, if it is more than 14%, the release properties are excellent, but the sheet is hard, so that the container is often not formed according to the mold, which is not preferable.

The polyolefin resin in the polyester sheet used in the present invention is used in a proportion of PET / polyolefin resin = 92/8 to 99/1 (weight) from the viewpoint of a crystal nucleating agent during thermoforming and imparting impact resistance. Ratio), and is preferably 94/6 to 98/2. When the use ratio of the polyolefin resin is more than 8% by weight, a peculiar smell peculiar to the polyolefin resin is generated, and when it is less than 1% by weight, the effect of the polyolefin resin to impart a crystal nucleating agent and impact resistance is not sufficient.

As the polyolefin resin, a crystal nucleating agent and a polypropylene resin having an effect of imparting impact resistance,
Polystyrene resin, polyethylene resin, ethylene-maleic anhydride-acrylate copolymer, ethylene-
Maleic anhydride graft, butadiene-alkyl acrylate-alkyl methacrylate copolymer, ethylene-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate-vinyl acetate copolymer, ethylene-glycidyl methacrylate-alkyl acrylate copolymer Modified polyolefin resins such as polymers are exemplified. These may be used alone or in combination of two or more, but are preferably polyethylene resins (hereinafter referred to as PE). In addition,
The polyethylene resin may be either high density or low density.

It is desirable that the polyolefin resin has a melt flow rate (hereinafter, referred to as MFR) of 2 g / 10 min or less, preferably 1 g / 10 min or less, in view of the effect of imparting impact resistance and the dispersibility with PET. However,
For the modified polyolefin resin having a reactive site,
This is not the case.

The degree of crystallinity of the container obtained from the polyester sheet of the present invention is 10 to 40%, preferably 20 to 3%.
5%. If the degree of crystallinity is less than 10%, sufficient heat resistance as a container cannot be obtained, and if it is more than 40%, an overcrystallized state is obtained, and the impact resistance is remarkably reduced.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The main methods for measuring physical properties are as follows. (1) Intrinsic viscosity (IV) Measured at a temperature of 30 ° C. with a mixed solvent of phenol / tetrachloroethane = 60/40 (weight ratio). (2) Melt flow rate (MFR) (g / min) Measured by ASTM method D1238. (3) Crystallinity of heat-softened sheet before molding The heat-softened sheet was molded using a mold cooled to a surface temperature of 20 to 40 ° C to obtain a container. The cut section of the container was used as a sample, and was calculated from the average value of the specific gravities of the five samples based on a standard method. (4) Mold Determining A case where the molded container was molded according to the mold was evaluated as “O”, and a case where the molded container was not molded according to the mold, and one having distortion was evaluated as “X”. (5) Release Property When the container was released from the high-temperature mold, the case where the container was deformed due to close contact with the mold was evaluated as x, and the case where it was not performed was evaluated as ○.

The PET and polyethylene used are as follows. (A) PET resin with IV = 1.00 g / dl (b) Low density polyethylene with MFR of 1.0 g / 10 min

[Examples 1 to 3 and Comparative Examples 1 to 3] Each of the above resins was mixed at a ratio (weight ratio) of (a) / (b) = 96/4, and 0.5 mm with a homemade sheeting machine. A sheet molded product having a thickness was obtained. Barrel temperature condition during sheet molding is 2
90 ° C. Next, using this sheet, a tray container having a full injection capacity of 320 cc was obtained using a mold for baking container with a vacuum pressure air molding machine TVP-33 manufactured by Sanwa Kogyo Co., Ltd. Sheet preheating at the time of container molding was performed using a heater heated to 520 to 530 ° C. The preheating time was appropriately set, and the mold temperature was 180 ° C. The molding results and the crystallinity are shown in Table 1. It can be seen that when the crystallinity is less than 5%, the mold releasability is poor, and when the crystallinity is more than 14%, the moldability is poor.

[0023]

[Table 1]

[0024]

It can be seen that the method for producing a polyester container of the present invention imparts good mold-determining properties and releasability simultaneously when molding a crystalline polyester container. That is, the present invention improves the heat resistance and impact resistance of a polyester container, improves the sagging property of the sheet during heating and the mold setability during heat setting, shortens the molding cycle, and reduces wrinkles. The occurrence of defects such as generation and uneven thickness is reduced, and the moldability of the container is improved.
In addition, a heat-resistant container that can be used in a microwave oven and an oven can be obtained by crystallizing to a crystallinity of 10 to 40%.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29K 23:00 B29K 23:00 67:00 67:00 B29L 22:00 B29L 22:00 F-term (Reference) 4F208 AA03 AA24 AC03 AG07 AH55 AH58 AR17 AR18 AR20 MA01 MA02 MB01 MC01 MG01 MH06 MK02 4J002 AC022 BB032 BB072 BB122 BB212 BC032 BH022 BN142 CF061 GG01

Claims (3)

[Claims] 1. A method of obtaining a container by heating and softening a polyester sheet mainly composed of polyethylene terephthalate to obtain a container, wherein the sheet heated to a state where the crystallinity is 5 to 14% is formed by a molding die. A method for producing a polyester container, comprising: 2. A crystalline polyester sheet comprising polyethylene terephthalate having an intrinsic viscosity of 0.70 dl / g or more and a polyolefin resin in a ratio of polyethylene terephthalate / polyolefin resin = 92/9 to 99/1 (weight ratio). The method for producing a polyester container according to claim 1, wherein 3. The polyolefin resin according to ASTM method D12.
The method for producing a polyester container according to claim 1, wherein the polyethylene is a polyethylene having a melt flow rate of 2 g / 10 min or less as measured by No. 38.