JP2001172410A - Polyester-based sheet and molded article using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a polyester-based sheet which has excellent heat resistance, smell retainability and container moldability, and to provide a molded article of the sheet. SOLUTION: This polyester-based sheet comprises 2 to 8 wt.% of a polyethylene resin and 92 to 98 wt.% of a polyethylene terephthalate resin having an intrinsic viscosity of >=0.70 dl/g and has an acetaldehyde (hereinafter AA) content of <=50 ppm, a cyclic trimer (hereinafter CT) content of <=5,000 ppm and a thermal shrinkage rate of 2 to 8%. A polyester-based sheet molded article molded from the polyester-based sheet and having a container crystallinity of 10 to 40% is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyester sheet suitable for a molded article such as a container made of crystallized polyester which is required to have properties such as heat resistance and low odor, and a container such as a tray using the same. About goods.

[0002]

2. Description of the Related Art Polyesters, particularly crystalline polyester resins represented by polyethylene terephthalate (PET), are widely used as polymers for sheets, films and fibers. Further, due to the widespread use of household microwave ovens and ovens, food containers that can withstand use at high temperatures are used. At present, crystallized PET (hereinafter referred to as C-PET) has been put to practical use as a heat-resistant food tray.

[0003] However, such C-PET also has the disadvantage that the properties such as low odor are not sufficient and components that affect the flavor of food are transferred. In addition, containers with better flavor properties are increasingly required due to changes in lifestyles, and heat-resistant containers with low odor have been long-awaited.

[0004] As a method for improving such a defect, a patent (JP-A-9-76327) comprising a production method for reducing the content of acetaldehyde (hereinafter referred to as AA) is known.
Has been filed.

[0005] However, when used as a retort container in combination with a lid material, it cannot be said that sufficient low odor has yet been obtained, and there is an unpleasant odor during heating and heat setting, resulting in poor heat resistance. Therefore, it had a disadvantage of discoloration. Furthermore, there is a problem that the taste becomes worse,
It has not been put to practical use.

[0006] It has been found that the reason for this is that when a retort container combined with a lid material is sealed with the lid, a small amount of aldehyde released from the resin fills the container and cannot be removed. . Furthermore, in the case of a retort container combined with a lid material, there is a step of sterilizing for a long time at a high temperature after putting the contents and closing the lid, and there is a step of heating and cooking in the container itself, and in these steps, In addition, since long-term storage was possible, it was found that the oligomer in the container resin migrated to the contents during the long-term storage, which deteriorated the taste.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have attempted to solve such a conventional problem, and as a method therefor, studied a low-odor C-PET container.
An object of the present invention is to provide a method for packaging foods that can be used in a microwave oven and an oven and has good fragrance retention.

[0008]

That is, the present invention has a structure 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. A polyester sheet having an AA content of 50 ppm or less, a cyclic trimer (hereinafter CT) content of 5000 ppm or less, and a heat shrinkage of 2 to 8%.

Further, according to the present invention, there is provided a molded article having 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.
A polyester having an acetaldehyde (hereinafter, AA) content of 50 ppm or less and a cyclic trimer (hereinafter, CT) content of 5000 ppm or less in the sheet, and having a crystallinity of the molded product body of 10 to 40. % Is a polyester sheet molded product. Furthermore, the above-mentioned molded article is characterized by being sealed by a lid.

The polyester which is the base material of the polyester container of the present invention is polyethylene terephthalate (PE).
T), polyethylene naphthalate (PEN) homopolymer is, of course, part of terephthalic acid is isophthalic acid,
Adipic acid, diphenyl carboxylic acid, diphenyl ether carboxylic acid, sebacic acid, substituted with one or more other dicarboxylic acid components such as naphthalenedicarboxylic acid, and part of the ethylene glycol component is diethylene glycol,
Triethylene glycol, hexamethylene glycol,
PET or PE substituted with one or more other glycol components such as propylene glycol, cyclohexane glycol, neopentyl glycol, butylene glycol, etc.
N copolyesters.

The polyester of this container may contain a lubricating material, but it is preferable that the amount of the lubricating material is small from the viewpoint of impact resistance, and preferably 300 ppm or less. Additives, UV absorbers, stabilizers and pigments can be added as long as the essential properties of the polymer are not changed. The lid material used for the polyester container is a material having low oxygen permeability such as a biaxially stretched PET film, an unstretched nylon film, and a vapor-deposited film.

The present invention relates to a polyethylene terephthalate resin having an intrinsic viscosity of 0.70 dl / g or more, 92 to 98% by weight.
And 2 to 8% by weight of a polyethylene resin,
The sheet has an acetaldehyde content of 50 ppm or less, a CT content of 5000 ppm or less, and JIS method K673.
A polyester sheet having a heat shrinkage of 2 to 8% as measured by the method described in 4, and a polyester sheet molded article formed by the polyester sheet and having a crystallinity of a container of 10 to 40%. .

In the present invention, the intrinsic viscosity of PET is set to an IV of 0.70 or more, preferably 100 or more, in order to prevent mechanical failure of the obtained sheet and occurrence of operation failure due to sagging of the sheet in a sheet preheating step at the time of forming a container. 0.80 or more. The polyolefin (PO) is used in an amount of 2 to 8% by weight, preferably 3 to 6% by weight due to the crystallization promoting effect of PET and the effect of PO on impact resistance. 8% by weight
If the amount is more than that, a peculiar smell peculiar to PE is generated and cannot be used in a food container.

Examples of the PO include polyethylene, polypropylene and various modified products thereof, and polyethylene (PE) is preferred. Examples of polyethylene include high-density PE and low-density PE, and low-density PE is particularly preferable.

The AA content of the polyester sheet is 5
The content is 0 ppm or less, preferably 30 ppm or less, more preferably 20 ppm or less, and most preferably 15 ppm or less. When it is 50 ppm or more, the fragrance retention is significantly reduced. The content of CT is 5000 ppm or less, preferably 3500 ppm or less, more preferably 3000 ppm.
When it is 5000 ppm or more, the fragrance retention and taste are significantly reduced.

The polyester sheet has an AA content of 50
As a method for reducing the content to ppm or less, first, sheet molding is performed using a resin having a low AA content. The AA content of the raw material resin is preferably 40 ppm or less, more preferably 30 ppm or less, further preferably 20 ppm or less, and most preferably 10 ppm or less. Further, the acid value of the resin is preferably at least 10 equivalents / ton, more preferably 15 equivalents / ton, still more preferably 20 equivalents / ton, particularly preferably, in order to reduce the increase in AA due to heat during sheet production. Is 25 equivalents / ton. Also,
It is also important to prevent the increase in AA during molding by lowering the extrusion temperature during sheet production and shortening the residence time.

The polyester sheet has a CT content of 500
As a method for reducing the content to 0 ppm or less, a sheet is formed using a resin having a low CT content. The CT of the resin used is preferably 5000 ppm or less, more preferably 4000 ppm or less, and still more preferably 3000 ppm.
It is as follows. In addition, during sheet molding, C
Since T is generated, it is also preferable to use a resin produced by a method such as reducing the polycondensation catalyst or deactivating the polycondensation catalyst. It is also important to prevent the CT increase during molding by lowering the extrusion temperature during sheet production and shortening the residence time.

Further, the heat shrinkage of the 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 poor operability. If the content is significantly worse than 8%, the mold will be poorly determined at the time of molding the container, and a satisfactory container shape cannot be obtained. As a method of adjusting the heat shrinkage to 2 to 8%, the heat shrinkage is adjusted by adjusting the pressure of the touch roll and the chill roll, the amount of resin discharged from the extruder, and the winding speed of the sheet during sheet production. it can.

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

The degree of crystallinity of a molded container or the like is 1
It is 0 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. During molding, it is necessary to adjust molding conditions so that the crystallinity falls within the above range.

After the processed container is filled with the contents, it is sealed with a lid material. The lid material is not particularly limited, and examples thereof include plastic sheets and films such as polyester, polyolefin, and polyamide, metal foils such as aluminum foil, paper, and laminates thereof. As a sealing method, a method using heat sealing is preferable. As the heat seal material, a polyester heat sealant is preferable from the viewpoint of adhesiveness to C-PET.

If necessary, a small amount of other polymers or additives can be added to the polyester-based sheet of the present invention as long as the effects of the present invention are not impaired. As these polymers or additives, for example, polyamide,
Polyolefins other than PE, other polytesters, matting agents such as titanium dioxide, alumina oxide, stabilizers such as phosphoric acid, phosphorous acid and their esters, antioxidants, antibacterial agents, ultraviolet absorbers, fluorescent brighteners Alternatively, pigments, dyes and the like can be mentioned.

[0023]

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) AA content Sample / distilled water = 1 g / 2 ml was placed in a glass ampoule purged with nitrogen, the upper part was sealed, extracted at 160 ° C. for 2 hours, and cooled, and the amount of AA in the extract was measured. Was measured by high-sensitivity gas chromatography, and the concentration was indicated in ppm.

(3) CT content The sample is dissolved in a mixed solution of hexafluoroisopropanol / chloroform, and further diluted with chloroform. Methanol is added to this to precipitate the polymer, followed by filtration. The filtrate was evaporated to dryness, made up to a constant volume with dimethylformamide, and the cyclic trimer composed of ethylene terephthalate units was quantified by liquid chromatography (HPLC).

(4) Acid value (AV) About 0.5 g of a sample is dissolved in 20 ml of benzyl alcohol, and chloroform is added for dilution. AV was determined by a titration method using a 1 / 50N aqueous potassium hydroxide solution. Phenol red was used as an indicator. (5) Impact strength Using a Dupont-type falling 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.

(5) Heat shrinkage rate Measured according to JIS K6734.

Table 1 shows the used PET and PE resins. The PE resin used was Ultrazex 3010F (low-density PE resin) manufactured by Mitsui Chemicals, Inc.

Examples 1 to 4 and Comparative Examples 1 and 2 Using each of the above-mentioned resins, a homemade sheeting machine was used.
A sheet having a thickness of 5 mm was obtained. Each property of the sheet was evaluated. The results are shown in Table 1. 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 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, and the evaluation results of moldability during molding.

Moldability: Observation of the appearance of the container after molding was performed, and the appearance of the container was evaluated as ○, and the appearance of the container was evaluated as ×. Heat resistance: According to the state of shape change by observation of the appearance in a gear oven , ◎-○-△-×
Were evaluated in the following order. Evaluation of fragrance retention Further, 200 ml of distilled water was placed in the above container, and the thickness was 50
A lid material in which a heat sealant composed of terephthalic acid / isophthalic acid // butanediol / polytetramethylene glycol (65/36 // 83/17 molar ratio) is laminated on a 5 μm biaxially stretched PET film with a thickness of 5 μm is placed and heat sealed. did. The heat treatment was performed for 30 minutes in a gear oven set at 150 ° C. assuming that the contents were actually put and oven treatment was performed (part of the lid was peeled off). Table 1 shows the evaluation results of the flavor retention and taste of the container. As for the fragrance retention and taste, the water in the container after heat treatment was smelled and tasted by 10 panelists.
Or, the case of two persons was evaluated as ○, the case of three to five persons was evaluated as Δ, and the case of six or more persons was evaluated as ×.

As is clear from Table 1, the polyester-based sheet molded article of the present invention shows excellent heat resistance. In addition, it also shows fragrance retention and taste retention.

[0032]

[Table 1]

[0033]

The polyester sheet of the present invention has a structure 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.
A) The content is 50 ppm or less and a cyclic trimer (hereinafter C
T) The content is 5000 ppm or less and the heat shrinkage is 2 to 8
% Polyester sheet, and P
Due to the crystallization promoting action of ET, fusion to the mold during heat setting is eliminated, and heat resistance is imparted to a container such as a tray that has been heated and heat set. Furthermore, the heat shrinkage rate is 2 to 8%
By using the above-mentioned multi-layer sheet, the sagging property of the sheet at the time of heating and heat setting which occurs at the time of heating and heat setting, and the moldability at the time of heat setting are improved, the molding cycle is shortened, the occurrence of wrinkles of the container, thickness unevenness, etc. Is gone,
Container moldability is improved. Further, the crystallinity of the surface layer is set to 10
By crystallizing to 40%, heat resistance that enables use of a microwave oven and an oven is obtained.

Claims (3)

[Claims] 1. A structure 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, wherein the acetaldehyde content of the sheet is 50 ppm or less and the cyclic 3
Monomer content of 5000 ppm or less, and heat shrinkage of 2
8% polyester-based sheet. 2. The molded product has an intrinsic viscosity of 0.70 dl / g.
The above-mentioned structure is composed of 92 to 98% by weight of polyethylene terephthalate resin and 2 to 8% by weight of polyolefin resin, and the acetaldehyde (hereinafter AA) content of the sheet is 5%.
0 ppm or less, and the content of cyclic trimer (hereinafter, CT) is 5
A polyester sheet molded product having a polyester content of 000 ppm or less and a crystallinity of the molded product body of 10 to 40%. 3. The molded article according to claim 2, wherein the molded article is sealed by a lid.