JPH11129422A - Multi-layer polyester sheet and molding using the sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer polyester sheet which shows high heat resistance and impact resistance and superb container moldability, and a molding using this sheet. SOLUTION: This multi-layer polyester sheet is of such a multi-layer structure that a surface layer consists of 92-98 wt.% of PET resin with a proper viscosity of 0.70 dl/g or more and 2-8 wt.% of polyolefin resin, and at least, one layer of an intermediate layer consists of 95 wt.% or less of a PET resin with a proper viscosity of 0.70 dl/g or more, 0.3-5 wt.% of polyolefin resin and 5 wt.% or more of non-crystalline resin. In addition, the multi-layer polyester sheet shows a degree of heat shrinkage of 2-8% as measured by the JIS method K 6734. The multi-layer polyester molding is obtained by molding the sheet and shows 10-40% crystallization of the surface layer.

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 a molded article such as a tray container which is required to have properties such as heat resistance and impact resistance, and a container such as a tray using the same. Related to molded products.

[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, especially trays for frozen foods, can withstand use at high temperatures. In addition, it is necessary to withstand the freezer temperature, and practically, it is necessary to withstand use in a wide temperature range from about -20 to about 180 ° C or more. Further, when the sheet molded article is thermoformed and heat set, there are problems in formability such as sagging of the sheet at the time of preheating, mold release from the mold and a molding cycle. At present, as a tray for heat-resistant food, crystallized polyethylene terephthalate (hereinafter C-PE) is used.
T) has been put to practical use. However, such C-PET also has a disadvantage that the impact resistance at a low temperature is not sufficient, and the container is partially damaged when an impact is applied during movement at a 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 remedying such a defect, a container comprising poly (ethylene terephthalate) (PET) and polyethylene ionomer (JP-A-4-345656).
No.) has been proposed. However, in such articles,
It cannot be said that sufficient impact resistance is obtained, and it has a disadvantage that it has an unpleasant odor during heating and heat setting, and discolors as heat resistance. Due to these drawbacks, they have not been put to practical use, and improvements are desired.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-layer polyester system having heat resistance, impact resistance and good container moldability, which is suitable for tray containers requiring heat resistance and impact resistance. An object of the present invention is to provide a sheet and a molded product thereof.

[0004]

SUMMARY OF THE INVENTION In view of the above problems, the present invention relates to a multilayer polyester sheet suitable for a tray container free from the above-mentioned drawbacks and a molded product thereof. The inventors have found a multilayer polyester sheet which is excellent in properties, impact resistance and container moldability and can improve the above-mentioned disadvantages, and has reached the present invention. That is, the present invention provides an IV of 0.70 dl /
a surface layer comprising 92 to 98% by weight of PET and 2 to 8% by weight of a polyolefin resin having an IV of 0.7 g or more
/ G of at least 95% by weight of PET, 0.3 to 5% by weight of polyolefin resin, and at least one intermediate layer composed of at least 5% by weight of amorphous resin, as measured by JIS method K6734. Heat shrinkage 2-8
% Of a multilayer polyester sheet excellent in container moldability and a molded article thermoformed from the sheet.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The PET used for the surface layer and the intermediate layer in the present invention is intended to prevent the occurrence of operation failure due to the mechanical strength of the obtained molded product and the sagging of the sheet in the sheet preheating step during container molding. Therefore, the IV is preferably 0.70 or more, more preferably 0.80 or more. The polyolefin resin used for the surface layer is 2 to 8% by weight from the viewpoint of the crystallization promoting action of PET and the effect on the impact resistance of the polyolefin resin.
Preferably it is 3 to 6% by weight, and if it is less than 2% by weight, the effect on crystallization acceleration and impact resistance is remarkably reduced, and 8% by weight.
If the amount is larger than the above, an unpleasant odor peculiar to the polyolefin resin is generated and cannot be used in a food container.

The amorphous resin used for the intermediate layer may be any resin as long as the resin itself is excellent in impact resistance. Examples thereof include cyclohexane dimethanol copolymer polyester resin and neopentyl glycol copolymer. Polyester resins, polycarbonate resins, polyester-polyether block copolymer resins, and the like are preferable, and the amount of these added is 5% by weight or more, preferably 10% by weight or more, and less than 5% by weight. The effect on impact resistance is significantly reduced.

The polyolefin resin used in the intermediate layer is 0.3 to 5% by weight, preferably 0.5 to 4% by weight. When the content is less than 0.3% by weight, the moldability of the obtained multilayer molded container is poor, so that the thickness distribution and the like are poor.

Further, the heat shrinkage of the multilayer sheet is 2 to 8%,
Preferably, it is 3 to 6%, and if it is less than 2%, the sheet will sag in the sheet preheating step at the time of forming the container, and the operability will be remarkably deteriorated. And a satisfactory container shape cannot be obtained. The crystallinity of the surface layer is 10 to 40%, preferably 20 to 40%.
If it is less than 10%, sufficient heat resistance of the container will not be obtained, and if it is more than 40%, the container will be in an overcrystallized state and the impact resistance will be significantly reduced.

In the present invention, PET is not limited to homopolymer, but part of terephthalic acid is 2,6-naphthalenedicarboxylic acid, isophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, hydroxybenzoic acid, diphenyldicarboxylic 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. It may be replaced with more than species.

In addition, a part of ethylene glycol is converted into a small amount of cyclohexane dimethanol, diethylene glycol,
1,2-propylene glycol, trimethylene glycol
, Tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentylene glycol, 1,4-bishydroxybenzene and polyalkylene glycols such as polyethylene glycol and polytetraethylene glycol. Methylene glycol, polypropylene glyco-
May be replaced by one or more of them. Also,
Tri- or higher functional compounds, such as glycerin, pentaerythritol, trimellitic acid, 5-hydroxyisophthalic acid, may be used to some extent with the polymer being substantially linear, and monofunctional compounds such as p-phenyl Pheno
, Benzyloxybenzoic acid, naphthalene monocarboxylic acid, polyethylene glycol monomethylene ether and the like.

The polyolefin resin used in the present invention is polymerized from an olefin monomer having 2 to 6 carbon atoms and has a function of accelerating crystallization of polyethylene terephthalate resin. Resin, high-density polyethylene resin, linear low-density polyethylene resin, polypropylene resin and the like. Particularly, a polyethylene resin is preferable.

The non-crystalline resin in the present invention is an amorphous resin compatible with PET, and the non-crystalline resin is preferably an amorphous copolyester resin. Among the amorphous copolymerized polyester resins, a more preferred resin is a cyclohexanedimethanol copolymer resin, which is composed of a terephthalic acid-based dicarboxylic acid component and ethylene glycol 95 to 10 mol%, It is a copolymerized polyester resin containing 5-90 mol% of 1,4-cyclohexanedimethanol as a glycol component. In this copolymerized polyester resin, a part of terephthalic acid is converted to isophthalic acid, 2,6-naphthalenedicarboxylic acid, hexahydroterephthalic acid, hydroxybenzoic acid, diphenylene-
One or more of terdicarboxylic acid, adipic acid, sebacic acid and the like may be substituted. Part of ethylene glycol and 1,4-cyclohexanedimethanol are replaced by diethylene glycol, hexamethylene glycol.
, Trimethylene glycol, tetramethylene glycol
And polyalkylene glycols, for example, one or more of polyethylene glycol, polytetramethylene glycol and the like. Further, a compound having three or more functions, for example, glycerin, pentaerythritol,
Trimellitic acid or the like may be used to some extent because the polymer is substantially linear.

The multilayer polyester sheet and the molded article of the present invention may contain a small amount of other polymers or additives if necessary. In this case, however, the multilayer polyester sheet and the molded article may be mixed. It is preferable to perform the treatment within a range that does not substantially change the properties. Examples of these polymers or additives include polyamides, modified polyolefins, other polyesters, matting agents such as titanium dioxide and alumina oxide, stabilizers such as phosphoric acid, phosphorous acid and esters thereof, and higher fatty acid amides. Dispersants, antioxidants, antibacterial agents, ultraviolet absorbers, fluorescent brighteners or pigments,
Dyes and the like.

As an example of the multilayer polyester sheet of the present invention, there is a three-layer structure. In this case, the surface layer (the outermost layer of the container when formed as a container), the intermediate layer and the inner layer (the innermost layer when formed as a container). , The surface layer in the present invention), and the thickness ratio is surface layer: intermediate layer: inner layer = 0.5-3: 4-9:
It is preferably from 0.5 to 3. The number of layers is usually three, but may be five or seven.

The method for producing the multilayer sheet of the present invention can be generally carried out by an extrusion method using a coextrusion 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 pressurization, vacuum and compression.

[0016]

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 phenol / tetrachloroethane = 60/40 (weight ratio) as a solvent. (2) Impact strength The cut-out piece of the tray adjusted to -10 ° C was subjected to a 76 g weight to a height of 75 c using a Dupont drop weight impact test.
m, the number of cracks relative to the test number of 15 when dropped from 125 cm. The used PET, polyethylene (PE), polyethylene ionomer and amorphous resin are as follows. (3) PET Toyobo Co., Ltd. IV = 1.00 g / dl PET resin

(4) PE High-density PE resin (Hi-Zex manufactured by Mitsui Petrochemical Industry Co., Ltd.) (5) Polyethylene ionomer Na-ion type polyethylene ionomer resin (Surline manufactured by DuPont) (6) Non-polyester Crystalline resin Cyclohexane dimethanol About 32 mol% copolymerized polyester resin (Kodar manufactured by Eastman Chemical Co., Ltd.)
PETG6763, hereinafter referred to as PET-G), polycarbonate
Bonnet 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. The thickness ratio between the surface layer and the intermediate layer was 22:56:22 (all the following Examples and Comparative Examples have this thickness ratio). Next, using this sheet, a full filling capacity of 3 was produced with a vacuum pressure air molding machine TVP-33 manufactured by Sanwa Kogyo.
A 20 cc tray container was formed. The barrel temperature conditions during sheet molding were all set at 290 ° C.
The preheating conditions were all set at a heater output of 90%, the mold temperature conditions during container molding were all set at 180 ° C., and the heating time during container molding was all set at 10.5 seconds. 220 ° C
Table 1 shows the evaluation results of the heat resistance by observing the appearance of discoloration and deformation after being left in the set gear oven for 15 minutes.

[0019]

[Table 1] As is clear from Table 1, the multilayer polyester sheet molded article of the present invention shows excellent heat resistance.

Examples 3 to 6 and Comparative Examples 2 to 5 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 with a full injection capacity of 320 cc was molded by a vacuum pressure air molding machine TVP-33 manufactured by Sanwa Kogyo. In addition, all barrel temperature conditions during sheet molding were set at 290 ° C, all sheet preheating conditions during container molding were set at 90% heater output, and all mold temperature conditions during container molding were set at 180 ° C. The heating time in molding the container was all set at 10.5 seconds. Further, 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 contained and the oven treatment was performed. Table 2 shows the evaluation results of the impact strength of the container. As is evident from Table 2, the multilayer polyester sheet molded article of the present invention shows excellent impact resistance. In addition, the containers of the multilayer polyester sheets of Examples 3 to 6 had good moldability and containers having a uniform thickness were obtained.
However, the formability of the container from the sheet of Comparative Example 4 was poor, and the shape of the obtained container was also poor.

Example 7 and Comparative Examples 6 and 7 A multi-layer sheet having a thickness of 0.5 mm and a heat shrinkage of 5% was obtained using a home-made sheeting machine using each of the above resins. Further, as a comparative example, a multilayer sheet having the same thickness of 1% and 10% in heat shrinkage was obtained by slightly changing the sheeting conditions. The sheet forming machine and conditions are the same as those in the first embodiment. Table 3 shows the results such as operability during container molding. As is clear from Table 3, the operability of the multilayer polyester sheet of the present invention at the time of forming the container is good, and the shape of the obtained container is also good.

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

According to the present invention, there is provided a multilayer structure having a specific structure.
In the surface layer, the fusion of PET to the mold during heat setting is eliminated due to the crystallization promoting action of the PET by mixing the polyolefin resin, and heat resistance is imparted to a container such as a tray heated and heat set. In addition, the amorphous resin and the polyolefin resin in the inner layer can prevent the impact resistance from being reduced, and the polyolefin resin in the inner layer can improve the moldability and provide a multilayer container having a uniform thickness. Furthermore, the heat shrinkage rate 2
By using the above-mentioned multilayer sheet which is 8%, heating,
The sagging property of the sheet at the time of heat setting at the time of heat setting and the mold determining property at the time of heat setting are improved, the molding cycle is shortened, wrinkles are not generated on the container, the thickness unevenness is eliminated, and the container formability is improved. Be improved. The crystallinity of the surface layer is 1
Microwave oven, O-
Heat resistance that allows the use of buns is obtained.

Claims (4)

[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 polyolefin resin, and 95% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.70 dl / g or more. % Or less, polyolefin resin 0.3
And a multilayer structure having at least one intermediate layer composed of at least 5% by weight and at least 5% by weight of an amorphous resin.
A multilayer polyester sheet having a heat shrinkage of 2 to 8% as measured by 6734. 2. The multilayer polyester sheet according to claim 1, wherein the polyolefin resin according to claim 1 is a polyethylene resin. 3. The amorphous resin according to claim 1, comprising terephthalic acid as a dicarboxylic acid component as a main component, 95 to 10 mol% of ethylene glycol as a glycol component and 5 to 90 mol% of 1,4-cyclohexanedimethanol. The multilayer polyester sheet according to claim 1, wherein the multilayer polyester sheet is a copolymerized polyester resin containing: 4. A multilayer polyester sheet according to any one of claims 1 to 3, wherein the surface layer has a crystallinity of 10 to 4.
A molded article of a multilayer polyester sheet characterized by being 0%.