JPH0458816B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a polyester sheet and a method for producing the same, and more particularly, the present invention relates to a polyester sheet and a method for manufacturing the same, which can be advantageously molded into, for example, ovenable containers with excellent heat deformation resistance and impact resistance. Regarding its manufacturing method. [Prior Art] A sheet made of polyester, particularly polyethylene terephthalate (hereinafter abbreviated as PET), can be molded into a tray or cup shape by thermoforming, and is widely used as a raw material for various containers. Especially modified by polyolefin resin
As described in JP-A No. 59-62660, molded products thermoformed from PET sheets under conditions that allow PET to crystallize have excellent heat resistance and can be used as heat-resistant containers such as ovenable trays. However, the PET containers obtained by this technology are
When used under severe cooking conditions, the impact resistance of the container is extremely reduced, and an improvement has been desired. [Object of the Invention] The present invention has been made against the background of the above circumstances, and its object is to provide a material that has excellent heat resistance and has good impact resistance after being used under severe temperature conditions. An object of the present invention is to provide a polyester sheet that can be shaped into a heated container that maintains an excellent condition, and a method for producing the same. [Object of the Invention] As a result of intensive research into polyester sheets free from the above-mentioned defects, the present inventor has developed a sheet obtained by melt-mixing a specific polyolefin resin with a specific PET in a predetermined ratio under specific conditions. The present invention has been achieved by discovering that the above-mentioned drawbacks can be improved if there is a method. That is, the present invention provides a sheet comprising: (1) about 99 to 90% by weight of polyester mainly composed of polyethylene terephthalate having an intrinsic viscosity of 0.08 or more and about 1 to 10% by weight of polyolefin resin, which are uniformly dispersed; , a polyester sheet characterized in that the average dispersed diameter of the polyolefin resin is 3 μm or less, and (2) about 99 to 90% by weight of a polyester whose main component is polyethylene terephthalate and whose melt viscosity at 300°C is 6000 poise or more. and about 1 to 10% by weight of a polyolefin resin having a melt viscosity of 6000 poise or higher at 300°C are melt-mixed at a temperature higher than the melting point of the polyester resin, extruded into a sheet, and then A method of manufacturing polyester sheets comprising quenching to temperature. In the present invention, polyethylene terephthalate is not only a homopolymer, but also a part of the terephthalic acid component, such as isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl dicarboxylic acid, etc. Aromatic dicarboxylic acids such as sulfonic acid; alicyclic dicarboxylic acids such as hexahydroterephthalic acid, hexahydroisophthalic acid, etc.; aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, etc.; Ρ-β-
With one or more components of other bifunctional carboxylic acids such as oxyacids such as hydroxyethoxybenzoic acid, p-oxybenzoic acid, ε-oxycaproic acid, etc., and/or a portion of the ethylene glycol component, e.g. trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentylene glycol, diethylene glycol, 1,1-cyclohexane dimethylol, 1,4-cyclohexane dimethylol,
Includes copolyesters substituted with one or more components of other glycols such as 2,2-bis(4-β-hydroxyethoxyphenyl)propane, bis(4-β-hydroxyethoxyphenyl)sulfone. The total proportion of copolymerized components in the copolyester is preferably 3 mol % or less based on the total acid components. Among these, a homopolymer of polyethylene terephthalate is preferred. The polyester sheet used in the present invention is a substantially amorphous sheet containing polyethylene terephthalate as its main component, and the intrinsic viscosity of PET constituting the sheet is 0.8 or more. The requirement is that the viscosity is 6000 poise or less at 300°C.
In the polyester sheet, a polyolefin resin is finely dispersed with an average particle size of 3 μm or less, and the olefin resin is particularly a polyethylene resin having a melt viscosity ηa of 6000 poise or more at 300°C. Polyolefin resins with ηa lower than 6000poise, such as general-purpose low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE),
With high-density polyethylene (HDPE), polypropylene (PP), etc., the particles dispersed in PET are large, and the impact strength of PET in the crystallized state is low. Further, in the present invention, the mixing ratio of the polyolefin resin is approximately 1 to 10 wt%, particularly preferably 2 to 5 wt%. If the proportion of polyolefin resin is less than 1%, the effect of improving impact resistance will be poor. Also
When the amount is more than 10wt%, heat resistance decreases. The impact strength of a polyester sheet modified with polyolefin shows a higher impact value as the intrinsic viscosity IV of PET increases when PET is substantially amorphous.
For example, if about 3% of polyolefin is added, IV0.65 regardless of the type of polyolefin.
Approximately 50Kg・cm/cm at IV0.8, 90Kg・cm/cm at IV0.8,
At IV0.95, the impact value is about 130Kg・cm/cm. On the other hand, PET crystallized to some extent (e.g. 20-30
% crystallinity) both the IV and crystallinity of PET are involved in impact resistance. This degree of crystallinity is generally obtained when thermoforming is performed using a PET ovenable tray or a high-temperature mold. However, if the degree of crystallinity of PET is further increased during the thermoforming process in order to further increase the heat resistance of the molded product, or if it is subjected to heat history at high temperatures such as cooking in an oven, The crystallinity of PET is about 40 to 50%, but in such a crystallized state, the impact resistance value is generally low regardless of the IV of PET.
The weight decreases to around 10-20Kg/cm. The present invention has discovered a polyester sheet that can be molded into a molded article with good impact resistance even under such conditions, and the polyolefin resin has a melt viscosity ηa.
6000poise or more, especially ηa
Low density polyethylene of 8000 poise or more is preferred. The polyester sheet of the present invention is thermoformed under specific conditions to obtain molded products in the shape of trays, cups, etc. with excellent heat resistance and impact resistance. Vacuum forming, in which the sheet is softened and pressed against the desired mold, the air in the gap between the mold and the material is eliminated, and the sheet is brought into close contact with the mold using atmospheric pressure, or pressure forming, in which the sheet is brought into close contact with the mold using compressed air at atmospheric pressure or higher. A general term for molding that uses both vacuum and compressed air. As a method for molding a molded product with excellent heat resistance, for example, the crystallization peak temperature of a polyester sheet when heated is T _CI or higher, and the crystallization peak temperature when cooled is T _CD
A sheet is thermoformed in a mold (A) whose weight is maintained within the following range, and then the molded product is further thermoformed using a mold (B) whose weight is maintained at 1 g or less, and then cooled and shaped. Mold (A) and Mold (B) are engraved shapes to obtain molded products with substantially the same shape, but Mold (A) is convex and Mold (B) is molded. It is preferable to have a convex shape with slightly different dimensions taking into account the thickness of the body, or vice versa. Note that the polyester sheet of the present invention may further contain a crystallization nucleating agent for improving moldability and a stabilizer for improving heat-resistant melt stability. [Effects of the Invention] A molded article having excellent heat resistance and impact resistance can be obtained from the polyester sheet of the present invention, and can be advantageously used, for example, as a molding material for containers such as ovenable trays. [Examples] The present invention will be explained in detail below using Examples. The measurement conditions and definitions of the main physical property values are as follows. (1) Intrinsic viscosity [IV]: Measured at 35°C in a solution containing a polyolefin resin in O-chlorophenol or a phenol/tetrachloroethane mixed solvent. (2) [ρ]; Measured at 25°C using a density gradient tube made of carbon tetrachloride and n-heptane. (3) Glass transition temperature [Tg]: 20 by differential calorimeter (DSC-20 model manufactured by Seiko Electronics Co., Ltd.)
Measured at a heating rate of °C/min. (4) Crystallization peak temperature at elevated temperature [ _TCI ]: Measured under the same conditions as Tg. (5) Melting point (polyester) [T _nE ]; Measured under the same conditions as Tg. (6) Crystallization peak temperature during cooling [T _CD ]; Sample held at 290°C for 3 minutes using a differential calorimeter at 20°C/
Measured at a cooling rate of min. (7) Melting point (polyolefin) [T _np ]; Measured under the same conditions as T _CD . (8) Heat shrinkage rate [S _H ]; tray with internal volume V _O at 230℃
Calculated using the following formula from the tray volume V _H when cooled to room temperature after heat treatment in an oven for 10 minutes S _H = V _O − V _H /V _O ×100 [%] (9) Elastic modulus [Y]; Sheet Tensile test specimens punched out from each other were measured according to test method D683. (10) Tensile impact strength [Ti]: The strength of a dumbbell punched from a sample was measured at 20°C using a tensile impact tester manufactured by Tester Sangyo Co., Ltd. (11) Dispersion diameter [D] of polyolefin resin: The fracture surface of the tensile impact strength measurement sample was measured using a scanning electron microscope (JSM20 model manufactured by JEOL-TECHNICS Co.) at a magnification of 1000 to 10000.
Judging from the results of double photography. Examples 1 to 4 and Comparative Examples 1 to 5 Dry chips obtained by drying PET with IV1.12 and ηa12000poise at 160°C for 5 hours with dehumidified hot air, the polyolefin resin shown in Table 1, and the additives shown in Table 1. The mixture was blended in the ratio shown in Table 1, and then fed to a 30 mm diameter screw extruder equipped with a sheet extrusion die at the tip. The mixture was melt-kneaded at an extruder cylinder temperature setting of 240 to 280°C, and the extruded sheet was cooled with a cooling roll to obtain a polyester sheet with a wall thickness of approximately 0.5 mm. of PET in the sheet
IV was 0.94-0.95. The sheet was engraved into a mold (A) using an FC-1APA-W type pressure/vacuum forming machine manufactured by Asano Laboratory to form a concave tray shape with a height of 135 mm, a width of 58 mm, and a depth of 18 mm.
A convex tray mold with a height of 133 mm, a width of 56 mm, and a depth of 18 mm was used as the mold (B), and the heating sheet surface temperature was 160 to 180.
℃, temperature of mold (A) 160℃, contact time with mold (A) 5
Vacuum forming was carried out under the following conditions: the temperature of the mold (B) was 20 to 50° C., and the contact time with the mold (B) was 5 seconds. The tray thus obtained was further heat treated in an oven at 230°C for 10 minutes. Table 1 shows the evaluation results for this tray.

[Table] Examples 5 to 8 and Comparative Examples 6 to 7 Melt index 1.3 for polyolefin resin
A tray was thermoformed and evaluated in the same manner as in Example 1, except that LLDEP was used and the addition ratio was as shown in Table 2. The results are shown in Table-2. The tray obtained from the sheet within the scope of the present invention had good heat shrinkage resistance and impact resistance.

[Table] Examples 9-10 and Comparative Examples 8-9 Sheets and trays were formed in the same manner as in Example 1, except that the IV of the raw material PET chips was changed. The impact strength of the obtained thermoformed tray is shown in Table 3.

【table】

Claims (1)

[Scope of Claims] 1. A sheet comprising approximately 99 to 90% by weight of a polyester mainly composed of polyethylene terephthalate having an intrinsic viscosity of 0.80 or more and approximately 1 to 10% by weight of a polyolefin resin, comprising: A polyester sheet characterized in that the polyolefin resin has a dispersed diameter of 3 μm or less on average. 2 About 99 to 90% by weight of a polyester mainly composed of polyethylene terephthalate having a melt viscosity of 6000 poise or more at 300°C and about 1 to 10% by weight of a polyolefin resin having a melt viscosity of 6000 poise or more at 300°C, the polyester resin A method for producing a polyester sheet, which comprises melting and mixing at a temperature above the melting point of the polyester, extruding it into a sheet, and rapidly cooling it to a temperature below the glass transition temperature of the polyester.