JPH0584209B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a thermoforming method for polyester sheets, and more specifically, to a method for thermoforming polyester sheets, which can be advantageously molded into containers with excellent heat deformation resistance that can be used as containers for high-temperature filling such as youth containers. Concerning thermoforming methods. [Prior Art] Molded bodies obtained by thermoforming sheets made of polyester, particularly polyethylene terephthalate, are widely used as containers for foods, beverages, etc.
Particularly in recent years, polyester thermoformed products with improved thermal deformation resistance by increasing crystallinity have come to be used as ovenable trays, as disclosed in JP-A No. 59-62660. Such a heat-resistant polyethylene terephthalate container is usually obtained by thermoforming a sheet using a high temperature mold at a temperature that allows polyethylene terephthalate to crystallize. However, when polyester containers are molded using this method, the sheet sag becomes large when the sheet is heated and softened, causing defects such as wrinkles in the molded product, the shape becomes irregular, and the molded product is removed from the mold. It has drawbacks such as difficult removal operations and insufficient heat resistance of the molded product, and improvements have been desired. [Object of the Invention] An object of the present invention is to provide a method for efficiently molding a polyester molded article having excellent heat resistance, good shape, and uniformity. [Structure of the Invention] As a result of extensive research into a thermoforming method for polyester sheets that does not have the above-mentioned drawbacks, the present inventor has developed a method for heating a polyester sheet of a specific composition to a specific temperature range, and then maintaining it at a specific temperature. The inventors have discovered that the defects can be improved by thermoforming using a certain mold, and have arrived at the present invention. That is, the present invention provides a thermoplastic polyester comprising 50 to 100% by weight of polyethylene terephthalate and 50 to 0% by weight of polybutylene terephthalate.
A polyester sheet obtained from a resin composition in which 5 to 50 parts by weight of a polyolefin resin is melt-mixed to 100 parts by weight is heated at a temperature of sheet heating temperature (T ₁ ), plug mold temperature (T ₂ ), and cavity metal temperature. This is a thermoforming method for a polyester sheet in which the mold temperature (T ₃ ) is thermoformed at a temperature that satisfies the following formulas () to (). TC ₁ ≦T ₁ ≦T _CD ……Formula () T ₂ ≧Tmo ……() T ₃ ≦Tg＋10℃ ……() [However, TC ₁ ：Crystallization start temperature when heating up [℃] T _CD ：Temperature falling Crystallization initiation temperature [°C] Tmo: melting point of polyolefin resin [°C] Tg: glass transition temperature [°C]] In the present invention, polyethylene terephthalate is used not only as a homopolymer thereof but also as a part of the terephthalic acid component, such as isophthalic acid. acids, aromatic dicarboxylic acids such as naphthalene dicarboxylic acid, diphenylcarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, etc.; fats such as hexahydroterephthalic acid, hexahydroisophthalic acid, etc. Cyclic dicarboxylic acids; resin dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, etc.; p-β-
With one or more components of other difunctional 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. Methylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentylene glycol, diethylene glycol, 1,1-dichlorohexane dimethylol, 1,4-cyclohexane dimethylol,
1 of other glycols such as 2,2-bis(4-β-hydroxyethoxyphenyl)propane, bis(4-β-hydroxyethoxyphenyl)sulfone
Includes copolyesters substituted with more than one component. 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. Further, it is preferable that the polyethylene terephthalate has an intrinsic viscosity (IV) of 0.7 or more. Similarly to polyethylene terephthalate, polybutylene terephthalate also includes copolyesters in which a portion of terephthalic acid and/or tetramethylene glycol is replaced with a compound similar to that exemplified as the copolymerization component of polyethylene terephthalate. Among these, homopolymers of polybutylene terephthalate are preferred, and those with an intrinsic viscosity of 0.8 or more are preferred because they cause less sagging during sheet heating. In addition, polyolefin resins include low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) with a melt index (MI) of 0.1 to 1.0.
Medium density polyethylene (MDPE), high density polyethylene (HDPE) and polypropylene (PP) are preferred, especially LDPE with a melt index of 0.1 to 0.5,
LLDPE is preferable in terms of uniform dispersibility with polyester, sheet sagging, etc. The sheet of the present invention contains 5 to 50 parts of such polyolefin resin per 100 parts by weight of thermoplastic polyester.
It is obtained from a resin composition mixed with 20 to 40 parts by weight, preferably 20 to 40 parts by weight. Furthermore, additives or mold release agents having an effect of promoting crystallization may be added to the resin composition used in the present invention. The polyester sheet of the present invention is preferably a substantially amorphous sheet having a density (ρ ₀ ) of 1.35 g/cm ³ or less from the viewpoint of formability during thermoforming. Preferred densities of polyester sheets are those having compositions as shown in Table 1, for example.

〔Example〕

The present invention will be explained in detail with reference to Examples below. The measurement conditions for the main physical property values are as follows. (1) Intrinsic viscosity [IV]; in 0-chlorophenol or phenol/tetrachloroethane mixed solvent
Measured at 35℃. (2) Density [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 initiation temperature upon heating [ _TCI ]: Measured under the same conditions as Tg. (5) Melting point (polyester) [T _nE ]; Measured under the same conditions as Tg. (6) Crystallization onset temperature upon cooling [T _CD ]: A sample held at 290℃ for 3 minutes using a differential calorimeter was heated to 20℃/
Measured at a cooling rate of min. (7) Melting point (polyolefin) [Tmo]; Measured under the same conditions as T _CD . (8) Molding shrinkage rate [S _M ]: Calculated using the following formula from the internal volume of the cup-shaped molded product (V _C ) and the internal volume of the cavity mold [V _M ]. S _M = {(V _M − V _C )/V _M }×100 [%] (9) Filling shrinkage rate [S _F ]; 90°C for a cup with internal volume V _C
After filling the cup with H ₂ O and allowing it to cool to room temperature, measure the internal volume of the cup [V _F ] and calculate it using the following formula. S _F =
{(V _C − V _M )/V _C }×100 [%] (10) Drop failure rate [C _D ]: Place the molded body in a paper cup (similar to a commercially available sake cup) and fill it with H ₂ O. After that, the lid was heat-sealed by coating aluminum foil with adhesive, and then the lid was dropped from a height of 1.5 meters at 0°C with the bottom facing down onto a concrete floor to measure the breakage rate. (11) Shape defects: Observe and evaluate shape defects such as folding wrinkles in the molded product due to sagging of the sheet and poor mold traceability. Examples 1 to 16 and Comparative Examples 1 to 7 IV1.0 polyethylene terephthalate (hereinafter
100 parts of dried chips obtained by drying PET (abbreviated as PET) at 160℃ for 5 hours with hot air, 35 parts of LDPE with a melt index (hereinafter abbreviated as MI) of 0.3, and talc.
After blending 0.4 parts, it was supplied to an extruder with a screw diameter of 30 mm, which was equipped with a die for sheet extrusion at the tip. Extruder cylinder setting temperature 240~280℃
The mixture was melt-kneaded under the following conditions, and the extruded sheet was cooled with a cooling roll to obtain a polyester sheet with a wall thickness of approximately 0.5 mm. The polyester sheet has Tg=75℃, _TnE =250
℃, T _CI = 120 ℃, T _CD = 190 ℃, and ρ ₀ = 1.20 g/cm ³ . The polyester sheet is manufactured by Asano Seisakusho FC-
Engraved shape as a cavity mold by IAPA-W type compressed air/vacuum forming machine, bottom diameter 55mm, top diameter 65mm
A concave cup with a diameter of 84 mm and a depth of 84 mm was air-press-formed using a convex plug mold with a tip diameter of 30 mm, a base diameter of 50 mm, and a length of 77 mm under the conditions shown in Tables 2 and 3. Table 2 shows the results of molding with different temperatures of the plug mold and cavity mold, and Table 3 shows the results of molding with different sheet heating times. As shown in Table 2, when the cavity mold temperature is higher than the (Tg + 10℃) (85℃) of the sheet, the molding shrinkage rate increases, and the plug mold temperature increases.
If the temperature is lower than T _np (92°C), a cup with good heat resistance cannot be obtained. Furthermore, as shown in Table 3, the heating temperature of the sheet is
If the temperature is lower than T _CI (120°C), both the molding shrinkage rate and the filling shrinkage rate will increase, and if the temperature is higher than T _CD (190°C), a molded product with good mold traceability cannot be obtained. On the other hand, it is within the scope of the present invention. Under the conditions of Examples 1 to 16, the moldability and the physical properties and shape of the molded bodies were all good. The sheet temperature was measured using an infrared non-contact temperature measuring device (Heat Spy) manufactured by Bell Howell.

[Table] In the table, - indicates that evaluation was not performed due to poor moldability.

[Table] Examples 17 to 24 and Comparative Examples 8 to 10 LLDPE with an MI of 2.0 and polybutylene terephthalate with an IV of 1.2 (hereinafter referred to as
A 0.5 mm thick polyester sheet having the physical properties shown in Table 4 was obtained by extrusion molding in the same manner as in Example 1, except that PBT (abbreviated as PBT) was mixed in the ratio shown in Table 4.

[Table] The polyester sheet was thermoformed in the same manner as in Example 1 to obtain a cup-shaped thermoformed product. The evaluation results of the molded body are shown in Table-5. In Comparative Examples 8 and 9, where LLDPE is 50 parts or more per 100 parts of polyester, heat resistance is poor.
In the case of Comparative Example 10 in which the proportion of PBT is higher than that of PET, the molding is defective, but within the scope of the present invention shown in Examples 17 to 24, a molded article with good heat resistance, impact resistance, and shape can be obtained. I understand that.

【table】

Claims (1)

[Claims] 1. 50 to 100% by weight of polyethylene terephthalate
and 100 parts by weight of thermoplastic polyester consisting of 50 to 0% by weight of polybutylene terephthalate,
A polyester sheet made of a resin composition prepared by melt-mixing 5 to 50 parts by weight of polyolefin resin,
Sheet heating temperature (T ₁ ), plug mold temperature (T ₂ )
And the cavity mold temperature (T ₃ ) is expressed by the following formula () ~
A thermoforming method for polyester sheets that is thermoformed at a temperature that satisfies (). TC ₁ ≦T ₁ ≦TCD ……Formula () T ₂ ≧Tmo ……() T ₃ ≦Tg＋10℃ ……() [However, TC ₁ ：Crystallization start temperature when temperature rises [℃] T _CD ：When temperature falls Crystallization initiation temperature [°C] Tmo: Melting point of polyolefin resin [°C] Tg: Glass transition temperature [°C]]