JPH106458A - Nulti-layer polyester sheet and molding using this sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer polyester sheet with outstanding resistance against heat and impact, and high container moldability as well as a molding using this sheet. SOLUTION: This polyester molding is of the multi-layer structure consisting of a surface layer comprising 92-98wt.% of polyethylene terephthalate resin and 2-8wt.% of polyethylene resin with an intrinsic viscosity of at least 0.70dl/g and an inner layer comprising 5-95wt.% of polyethylene terephthalate resin and 5-95wt.% of amorphous resin with an intrinsic viscosity of at least 0.70dl/g. In addition, the multi-layer polyester sheet shows a coefficient of thermal shrinkage of 2-8% by JIS K6734 and the crystallinity index of the surface layer molded using this sheet is 10-40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer polyester sheet suitable for molded articles such as tray containers which are required to have properties such as heat resistance and impact resistance, and containers and molded articles such as trays using the same.

[0002]

2. Description of the Related Art Due to the widespread use of microwave ovens and ovens for home use, food trays that can withstand use at high temperatures, in particular,
As a tray for frozen foods, it is necessary to be able to withstand not only high temperatures but also freezer temperature, and in practical use, it can be used in a wide temperature range from about -20 to about 180 ° C or more. You need to be able to endure. Further, when the sheet is thermoformed and heat set, there are also problems with the formability such as sagging of the sheet at the time of preheating, release from a mold and a molding cycle. At present, crystallized PET (hereinafter referred to as C-PET) has been put to practical use as a heat-resistant food tray.

However, such C-PET also has the disadvantage that the impact resistance at low temperatures is not sufficient, and the container is partially damaged when an impact is applied during movement at the freezing temperature. In addition, due to changes in lifestyle, frozen and heated foods are increasingly required, and there is a need for heat-resistant containers having impact resistance.

As a method for improving such a defect, a patent (JP-A-4-345656) comprising PET and a polyethylene ionomer has been filed.

[0005] However, it cannot be said that sufficient impact resistance is obtained, and there is an unpleasant odor during heating and heat setting, and the heat resistance is inferior.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-layer polyester system suitable for containers such as trays which are required to have heat resistance, impact resistance, good heat moldability and good impact resistance. An object of the present invention is to provide a sheet and a molded product thereof.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a multilayer polyester sheet suitable for containers such as trays which do not have the above-mentioned drawbacks and a molded article thereof. A multilayer polyester sheet excellent in moldability and capable of improving the above-mentioned disadvantages has been found.

That is, the present invention relates to a surface layer composed of 92 to 98% by weight of PET having an IV of 0.70 dl / g or more and 2 to 8% by weight of PE, and a PET of 95 to 95% having an IV of 0.70 dl / g or more.
Multilayer polyester sheet having a multilayer structure having an innermost layer composed of 5% by weight and an amorphous resin of 5 to 95% by weight and having a heat shrinkage of 2 to 8% as measured by JIS method K6734 and excellent in container moldability. Is further molded using the multilayer sheet, and the crystallinity of the surface layer of the molded article is 10 to 40.
% Of a substantially non-oriented multilayer polyester-based sheet molded article.

In the present invention, the PET used for the surface layer has an IV of 0.70 or more, preferably 0.70 or more, in order to prevent the mechanical strength of the obtained multilayer sheet and the occurrence of operation failure due to sagging of the sheet in the sheet preheating step at the time of forming the container. Is 0.80 or more, and PE is 2 to 8% by weight, preferably 3 to 8% by weight from the viewpoint of the crystallization promoting action of PET and the impact resistance of PE.
If it is less than 2% by weight, the effect on crystallization acceleration and impact resistance is significantly reduced, and if it is more than 8% by weight, P
An unusual odor peculiar to E is generated and cannot be used in food containers.

The amorphous resin in the present invention is preferably a resin having excellent impact resistance, for example, cyclohexane dimethanol copolymerized polyester resin, neopentyl glycol copolymerized polyester resin, polycarbonate resin and the like. Is 5% by weight or more, preferably 10% by weight or more, and if the content is less than 5% by weight, PET is mixed with the amorphous resin.
The effect on the impact resistance due to the suppression of crystallization is significantly reduced.

Further, the heat shrinkage of the multilayer polyester sheet is 2 to 8%, preferably 3 to 6%. If the heat shrinkage is less than 2%, sagging of the sheet occurs in the sheet preheating step at the time of molding the container, resulting in operability. When the content is more than 8%, the mold rule becomes poor at the time of molding the container, and a satisfactory container shape cannot be obtained.

[0012] The crystallinity of the surface layer of a molded container or the like is 10 to 40%, preferably 20 to 35%. If the crystallinity is less than 10%, sufficient heat resistance of the container cannot be obtained, and if it is more than 40%, the container becomes overcrystallized, and the impact resistance is significantly reduced.

In the present invention, PET is a homopolymer, and a part of terephthalic acid is converted to 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 You may replace with two or more types.

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

The multilayer polyester sheet of the present invention usually comprises a surface layer (outermost layer of the container when formed into a container), an intermediate layer and an inner layer (the innermost layer when formed into a container).
The ratio of the thickness is as follows: surface layer: intermediate layer: inner layer = 0.5-3: 4-
9: preferably 0.5 to 3. The number of layers is usually three, but may be five or seven.

The multilayer sheet of the present invention can be produced by an ordinary coextrusion extrusion method, and the sheet is formed by multilayer extrusion. Further, the sheet is processed into a container such as a tray by molding such as pressure, vacuum, and compression.

In each layer of the multilayer polyester sheet of the present invention, if necessary, a small amount of other polymers or additives can be mixed as long as the effects of the present invention are not impaired. Examples of these polymers or additives include polyamides, polyolefins other than PE, other polyesters, etc., matting agents such as titanium dioxide and alumina oxide, stabilizers such as phosphoric acid, phosphorous acid and their esters, and antioxidants. Agents, antibacterial agents, ultraviolet absorbers, fluorescent whitening agents or pigments, dyes and the like.

[0018]

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) IV Measurement was performed at a temperature of 30 ° C. using a mixed solvent of phenol / tetrachloroethane = 60/40 (weight ratio).

(2) Impact strength Using a Dupont type drop weight impact test, a cut piece of the tray container adjusted to -10 ° C. was applied with a 76 g weight to a height of 75 cm.
And the number of cracks with respect to the test number of 15 when the weight was dropped from 125 cm.

The used PET, PE, polyethylene ionomer and amorphous resin are as follows. (4) PET Toyobo's IV = 1.00 g / dl PET resin

(5) PE Hi-Zex (high-density PE resin) manufactured by Mitsui Petrochemical Industries, Ltd. (6) Polyethylene ionomer Surlyn (Na ion type polyethylene ionomer resin) manufactured by DuPont (7) Amorphous resin Eastman Cyclohexanedimethanol 32mo
1% copolymerized polyester resin (hereinafter referred to as PET-G), polycarbonate resin manufactured by Sumitomo Dow (hereinafter referred to as PC)

Examples 1 and 2 and Comparative Example 1 Each of the above resins was used in a homemade sheeting machine.
A multilayer sheet having a thickness of 5 mm was obtained. Next, using this sheet, a tray container having a full capacity of 320 cc was obtained with a vacuum pressure air molding machine TVP-33 manufactured by Sanwa Kogyo Co., Ltd. The barrel temperature conditions during sheet molding were all set at 290 ° C, the sheet preheating conditions during container molding were all set at 90% heater output, the mold temperature conditions during container molding were all set at 180 ° C, and the heating time during container molding. Were performed at a setting of 10.5 sec. Table 1 shows the evaluation results of the heat resistance by observing the appearance of discoloration and deformation after leaving the container in a gear oven set at 220 ° C. for 15 minutes.

[0023]

[Table 1]

As is clear from Table 1, the molded article of the multilayer polyester sheet of the present invention has excellent heat resistance. Examples 3 and 4 and Comparative Example 2 Each of the above resins was used to prepare 0.1% by a homemade sheeting machine.
A multilayer sheet having a thickness of 5 mm was obtained. Next, using this sheet, a tray container having a full capacity of 320 cc was obtained using a vacuum pressure air molding machine TVP-33 manufactured by Sanwa Kogyo Co., Ltd. The barrel temperature conditions during sheet molding were all set at 290 ° C, the sheet preheating conditions during container molding were all set at 90% heater output, the mold temperature conditions during container molding were all set at 180 ° C, and the heating time during container molding. Were performed at a setting of 10.5 sec. Furthermore,
This container was subjected to a heat treatment for 30 minutes in a gear oven set at 150 ° C., assuming that the contents were actually put into the container and oven treatment was performed. Table 2 shows the evaluation results of the impact strength of the container.

[0025]

[Table 2]

As is clear from Table 2, the molded article of the multilayer polyester sheet of the present invention shows excellent impact resistance.

[0027]

According to the present invention, there is provided a multilayer structure having a specific structure.
In the surface layer, the crystallization promoting action of PET by mixing PE eliminates fusion to the mold during heat setting,
Heat resistance is imparted to heat-set containers such as trays. In addition, the amorphous resin in the inner layer suppresses crystallization due to heating and heat setting, suppresses the decrease in impact resistance due to crystallization, and makes use of the impact resistance of the amorphous resin itself to make the entire multilayer container resistant to shock. The impact properties are improved. Furthermore, by using the above-mentioned multilayer sheet having a heat shrinkage of 2 to 8%, the sagging property of the sheet at the time of heating and heat setting, and the moldability at the time of heat setting are improved, and the molding cycle can be shortened. Generation of wrinkles in the container,
The thickness unevenness and the like are eliminated, and the moldability of the container is improved. Further, by crystallizing the surface layer to a degree of crystallinity of 10 to 40%, heat resistance that enables use of a microwave oven and an oven can be obtained.

Continued on the front page (72) Inventor Fujio Hirasawa 2-1-1 Katata, Otsu-shi, Shiga Prefecture Toyobo Co., Ltd. Research Laboratory

Claims (2)

[Claims] 1. A surface layer comprising 92 to 98% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.70 dl / g or more and 2 to 8% by weight of a polyethylene resin, and an intrinsic viscosity of 0.70.
dl / g or more of polyethylene terephthalate resin 5 to 9
A multilayer polyester sheet having a multilayer structure having an innermost layer composed of 5% by weight and an amorphous resin of 5 to 95% by weight, and having a heat shrinkage of 2 to 8% as measured by JIS method K6734. 2. A molded article of a multilayer polyester sheet formed from the multilayer polyester sheet according to claim 1, wherein the surface layer has a crystallinity of 10 to 40%.