JPH01165626A - Polyester sheet and its thermoformed object - Google Patents

Abstract

PURPOSE:To make it possible to form a polyester sheet which is excellent in heat resistance and can give a thermoformed container excellent in impact resistance at a temperature below the freezing point, by melt-mixing a polyester with a specified polyolefin resin at a specified ratio. CONSTITUTION:This polyester sheet is formed by melt-mixing 100 pts.wt. polyester mainly consisting of repeating ethylene terephthalate units with 2-30 pts.wt. polyethylene copolymerized with methyl methacrylate and maleic anhydride. It is desirable that said sheet has a density rho (g/cm<3>) in the range represented by the formula: rho>=(1.36WA+0.94WB)/100 [wherein WA is the rate of the polyester added (wt.%), and WB is the mixing rate of the polyethylene copolymerized with methacrylic acid and maleic anhydride (wt.%)] and a tensile impact strength >=60kg/cm/cm<2>.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a polyester sheet and a thermoformed product thereof;
More specifically, the present invention relates to a polyester sheet and a thermoformed product thereof, which can be used to efficiently form containers with excellent heat deformation resistance and impact resistance for high-temperature filling of food and beverages such as curry (food).

[Prior Art] A sheet made of polyester, particularly polyethylene terephthalate 1--, can be molded into a tray shape or a cup shape depending on the aging form, and is widely used as a raw material for various containers. Polyethylene terephthalate (sometimes abbreviated as PET), especially to which polyolefin resin has been added.
A molded article thermoformed under conditions that allow PET to crystallize from a sheet has excellent heat resistance, as described in JP-A-59-62660, and can be used as a heat-resistant container such as an ovenable tray. However, the PET containers obtained by this technique have the drawback of extremely poor mechanical properties, particularly impact resistance when handled at low temperatures, and improvements have been desired.

[Objective of the Invention] The present invention was made against the background of the above-mentioned circumstances, and its purpose is to provide a method that has excellent heat resistance and impact resistance when used in sub-zero temperature conditions. An object of the present invention is to provide a polyester sheet that can be molded into a thermoformed container with excellent properties, and a thermoformed article obtained from the sheet.

[Structure of the Invention] As a result of intensive research on polyester sheets and thermoformed products thereof that are free from the above-mentioned defects, the present inventors have developed a sheet made by melt-mixing a specific polyolefin resin with PET in a specific ratio, and a sheet thereof. The present inventors have discovered that the above-mentioned drawbacks can be alleviated by using a matured shape formed by thermoforming, and have thus arrived at the present invention.

That is, the present invention provides: (1) A polyester sheet made by melt-mixing 2 to 30 parts by weight of polyethylene copolymerized with methyl methacrylic acid and maleic anhydride to 100 parts by weight of polyester whose main repeating unit is ethylene terephthalate. It is. In particular, the polyester sheet of the present invention has a density ρ (g/cm3) within the following range and a tensile impact strength of at least 60 Ka-cm/cm2.

D≦ (1,36W80.94WB ＞/100
Furthermore, (2) polyethylene 2 to 2, which is obtained by thermoforming the above polyester sheet and is prepared by copolymerizing methyl methacrylic acid and maleic anhydride with 100 parts by weight of polyester whose main repeating unit is ethylene terephthalate. This is a polyester thermoformed product obtained by thermoforming a polyester sheet blended with 30 overlapping parts.

In the present invention, polyester is not only a homopolymer of polyethylene terephthalate, but also a part of the terephthalic acid component, such as isophthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, etc. Aromatic dicarboxylic acids: Alicyclic dicarboxylic acids such as hexahydroterephthalic acid, hexahydroisophthalic acid, etc.: adivic acid. Aliphatic dicarboxylic acids such as cepatic acid, azelaic acid, etc.; one or more other difunctional carboxylic acids such as oxy acids such as p-β-hydroxyethoxybenzoic acid, p-oxybenzoic acid, ε-oxycaproic acid, etc. and/or a part of the ethylene glycol component, such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentyl glycol.

ethylene glycol, 1,1-cyclohexane dimethylol, 1,4-cyclohexane dimethylol.

2,2-bis(4-β-hydroxyethoxyphenyl)
Includes copolyesters substituted with one or more components of other glycols such as propane, bis(4-β-hydroxyethoxyphenyl)sulfone, and the like.

The total proportion of copolymerized components in the copolyester is preferably 3 mol % or less based on the acetic acid component.

Among these, homopolymers to polyethylene terephthalate 1 are preferred.

In the present invention, 2 to 30 parts by weight of polyethylene (hereinafter sometimes abbreviated as Co-PE) obtained by copolymerizing methyl methacrylic acid and maleic anhydride is fused to 100 parts by weight of the PET. If the mixing ratio is lower than 2 parts by weight, the effect of improving the toughness of the thermoformed product at low temperatures will be low, and if it is higher than 30 parts by weight, the toughness improving effect will be poor and the thickness distribution will be poor. This is not preferred because it is difficult to obtain a thermoformed product and the heat deformation resistance of the thermoformed product becomes poor.

A particularly preferable mixing ratio of Co-P E is PET100
The amount is 5 to 15 parts by weight.

The copolymerization ratio of the Co-PE is methyl methacrylic acid (hereinafter sometimes abbreviated as MMA) and maleic anhydride (
(hereinafter sometimes abbreviated as MAH) is 5 to 20 mol% each, the ViCat softening point is 70 to 85°C, and the density is 0.
92 to 0.94 Mcm3, melt flow rate (hereinafter sometimes abbreviated as MFR) of 4 to 8 is PE.
It is extremely finely dispersed in T and has a large effect of improving toughness.

The polyester sheet used in the present invention is a sheet containing polyethylene terephthalate as a main component and blended with the co-pE, and the PET component is substantially amorphous, and the polyethylene terephthalate constituting the sheet has an intrinsic viscosity of 0.6. It is preferable that it is above.

If the intrinsic viscosity (sometimes abbreviated as IV) is lower than 0.6, it is not preferable because the impact strength of the thermoformed product decreases. “The density of the sheet of the present invention is within the range shown by the above formula, is substantially amorphous, and has a tensile impact strength of soKg-cm/cm2 or more.

If the density of the sheet exceeds the above formula, the shapeability of the molded product will be poor when producing the molded product by thermoforming, and if the tensile impact strength is lower than 60K (1-cm/cm2), This is not preferable because the impact strength of the thermoformed product becomes low.Such an amorphous polyester sheet is produced by melt-mixing the composition of the present invention in an extruder, extruding it from a slit-shaped die, and cooling it. It is obtained by rapid cooling with a drum.In addition, PET and Co-P E
The degree of melt-kneading with Co-PE is preferably such that the dispersed particle size of Co-PE is 10 μm or less. Co
- As a means for finely dispersing PE, for example, Co -
It is effective to prepare PE high a degree pellets in advance using an extruder and use them as master pellets during sheet production, or to produce sheets using a twin-screw extruder or a single-screw extruder with a high compression ratio. .

The thermoformed article of the present invention is a molded article obtained by aging the above polyester sheet. Thermoforming in the present invention means
Vacuum forming involves heating and softening the sheet, pressing it against the desired mold, eliminating the air in the gap between the mold and the material, and molding the sheet into close contact with the mold using atmospheric pressure, or using compressed air above atmospheric pressure to adhere the sheet to the mold. A general term for compressed air forming, molding that uses both vacuum and compressed air, etc.

The thermoformed article of the present invention has a low-temperature impact strength of aocm or more and has excellent toughness, but in order to further improve the heat-resistant dimensional stability (also referred to as heat resistance), After heating the polyester sheet to a temperature at which it can be molded, the mold temperature was adjusted to the glass transition temperature of PET (hereinafter TQ).
(sometimes abbreviated as ) or more.

The higher the mold temperature is, the better the heat resistance will be, but if it is too high, the toughness will decrease, which is not preferable.

Although the upper limit of the mold temperature varies depending on the blending ratio of Co-PE, it is preferably in a range where the low-temperature impact strength is 80 cm or more, for example, 130° C. or less.

Note that crystallization nucleating agent 1 may contain a colorant, an inorganic filler, a polymer for improving barrier properties, an ultraviolet absorber, or a stabilizer for improving heat-resistant melt stability, as long as the object of the present invention is not impaired. good.

[Effects of the Invention] The polyester sheet of the present invention can be formed into a thermoformed article with excellent heat resistance and impact resistance, and the thermoformed article can be advantageously used as a container for foods such as curry.

[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]; Insoluble matter in 0-chlorophenol or phenol/tetrachloroethane mixed solvent? Measured at 35°C using solutions delivered to each house.

(2) Density [ρ]: Measured at 25°C using a density gradient tube made of carbon tetrachloride and n-hebutane.

(3) Glass transition temperature [T(l]; Differential calorimeter (DSC-20 manufactured by Seiko Electronics Co., Ltd.)
Measured at a heating rate of 20°C/mi mouth using a mold).

(4) Crystallization peak temperature during temperature rise [TCI]: Measured under the same conditions as IQ.

(5) Melting point (polyester > [TmE]: Tg
Measured under similar conditions.

(6) Crystallization peak temperature when cooling [TCD]; A sample held at 290°C for 3 minutes using a differential calorimeter was
Measured at a cooling rate of min.

(7) Melting point (polyolefin) [TmO];T
Measured under the same conditions as CD.

(8) Heat shrinkage rate [S old; Calculated using the following formula from the tray volume Vl+ when a tray with an internal volume VO is filled with hot water at a predetermined temperature and then cooled to room temperature O-VH 3H=X100[%1V .

(9) Tensile impact strength [Til: The strength of a dumbbell punched out from a sample was measured at 20°C using a tensile impact tester manufactured by Tester Sangyo ■.

(10) Low-temperature impact strength: After filling the tray with water and heat-sealing the lid material, the tray was cooled in a Hitachi WAEC-800) 1-type refrigerator-freezer until the temperature reached -20°C. The tray was dropped onto a concrete floor with the bottom facing downward, and the critical fall height at which the tray would not break was determined.

(11) Formability: A tray-shaped mold was attached to the FC-IAPA-W vacuum-pressure forming machine manufactured by Asano Research Institute, and the separation was performed when vacuum forming was performed at a predetermined mold temperature with various sheet heating conditions. Characteristics such as moldability, sheet sag, and mold traceability are evaluated.

(12) Heat resistant temperature [℃]; Upper limit of hot water temperature at which the hot water shrinkage rate of the tray is within 5%.

Examples 1 to 6 and Comparative Examples 1 to 5 IVo, 81. T975℃ PET pellet at 160℃
'C for 5 hours, the moisture in the pellet is o, oo
Dry pellets of about 5 wt% were obtained.

After blending the dry PET pellets 1 to 1 with the Co-PE or polyolefin resin shown in Table 1 in the proportions shown in Table 1, a die for sheet extrusion was attached to the tip.
The mixture was supplied to an extruder with a screw diameter of 0 mmφ. The extruder cylinder was melt-kneaded at a set temperature of 240 to 280'C, and the extruded sheet was cooled with a cooling roll to give a wall thickness of 0.3
A polyester sheet of mm was obtained. Table 1 shows the density of each sheet and the IV of PET.

The sheet was manufactured by Asano Laboratory FC-IAPA-W type compressed air.
The shape is carved into a vacuum forming machine as a mold, length 135mm.

Equipped with a concave tray type with a width of 58 mm and a depth of 18 mm.
Vacuum forming was carried out under the conditions that the mold temperature was maintained at 80°C and the forming time was 5 seconds. The heat resistance of the tray thus obtained.

Impact resistance and moldability were evaluated. The evaluation results are shown in Table-1.

In addition, the Go-PE or polyolefin shown in Table 1 was used as shown in Table 2.

*1: JIS-5750 *2: JIS-7203 As is clear from the results in Table 1, the sheet of the present invention has good thermoformability, and the thermoformed product obtained from the sheet has Although the heat resistance and low-temperature impact resistance were good, as shown in the comparative example, the blending ratio of Co-PE was outside the range of the present invention, or when a polyolefin different from that of the present invention was used. The thermoformability of the sheet or the performance of the thermoformed product was poor.

Examples 11 to 13 and Comparative Example 6 A polyester sheet 1 was prepared in the same manner as in Example 1, except that the PET was changed to one shown in Table 2, and a molded body was formed by thermoforming in the same manner as in Example 1. Obtained.

Table 3 shows the physical properties of the sheet and the tray.

As is clear from Table 3, the impact strength of the sheet having an IV lower than the range of the present invention and the thermoformed article obtained from the sheet was poor.

Comparative Example 7 A polyester sheet obtained in the same manner as in Example 1 was
After heat treatment at °C, a sheet with a density of 1.35 g/cm3 was obtained. The tensile impact strength of the sheet is 40g-cm7c
m2 was low and could not be thermoformed.

Claims (1)

[Claims] 1. Polyethylene prepared by copolymerizing methyl methacrylic acid and maleic anhydride with 100 parts by weight of polyester whose main repeating unit is ethylene terephthalate.
A polyester sheet obtained by melt-mixing 30 parts by weight of 30 to 30 parts by weight. 2. The sheet according to claim 1, wherein the density ρ (g/cm^3) of the sheet is within the range of the following formula, and the tensile impact strength is 60 kg-cm/cm^2 or more. Polyester sheet. ρ≦(1.36WA+0.94WB)/100 [However,
WA is the blending ratio of polyester [wt%], WB is the blending ratio of polyethylene copolymerized with methacrylic acid and maleic anhydride [wt%]] 3. For 100 parts by weight of polyester whose main repeating unit is ethylene terephthalate, Polyethylene 2 copolymerized with methyl methacrylic acid and maleic anhydride
A polyester thermoformed article obtained by thermoforming a polyester sheet containing 30 parts by weight of the polyester sheet. 4. Hot water deformation temperature is 80℃ or higher, low temperature impact strength is 8.
Claim 3, characterized in that the diameter is 0 cm or more.
The polyester thermoformed article described in .