JPH0543500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polyethylene terephthalate container having excellent heat resistance, compressive strength, dimensional stability, appearance, etc.

It has been known to manufacture containers such as cups and trays by thermoforming unstretched polyester sheets by vacuum and/or pressure forming. However, molded products made from unstretched sheets have poor mold release properties, and the side walls of molded products, and sometimes the side walls of deep-drawn products, are highly oriented in the stretching direction, that is, the longitudinal direction, and are therefore susceptible to impact and internal pressure. As a result, vertical cracks are likely to occur, and the heat resistance is also poor, which is not necessarily satisfactory.

On the other hand, methods using biaxially stretched sheets or uniaxially stretched sheets by roll rolling, etc. have been proposed as a method to eliminate the drawbacks of molded products made from unstretched sheets, but biaxially stretched sheets have poor thermoformability. Currently, the anisotropy during thermoforming of uniaxially stretched sheets has not been sufficiently resolved.

In addition, in conventional thermoforming, in order to increase productivity, a pre-formed sheet is preheated and then continuously thermoformed in a mold, resulting in a large amount of scrap such as burrs and post-forming trimming loss. However, there were cases where this resulted in a decrease in production efficiency.

As a method to eliminate this drawback, a thermoplastic resin sheet is cut in advance to form square tablets.
The central part of the tablet is preheated to a temperature within the range of Vikat's softening point or melting point, pressure-formed in a press heated to a temperature within the preheating temperature range of the tablet ±10°C, and then thermoformed to form a container. A method for manufacturing (Japanese Unexamined Patent Publication No. 55-34902) has been proposed.
However, even if this method is applied directly to polyethylene terephthalate, polyethylene terephthalate has a crystallization temperature considerably lower than its melting point, so depending on the temperature settings during preheating or pressure molding, polyethylene terephthalate may may become cloudy due to crystallization, and even with this method, the heat resistance of the container is not improved because the temperature during pressure molding and thermoforming are the same or lower.

Therefore, the present inventor conducted various studies in order to develop a method for manufacturing a polyethylene terephthalate container that has excellent heat resistance, compressive strength, transparency, dimensional stability, gas barrier properties, etc., and does not generate scrap. It has been found that the object of the present invention can be achieved by setting the temperature during compression molding and the temperature during thermoforming of a polyethylene terephthalate sheet separately within specific temperature ranges, and have completed the present invention.

That is, in the present invention, after preheating a single-layer or multi-layer platelet-like body (B) containing amorphous polyethylene terephthalate A as a layer component to a temperature within the range shown by the following formula (1), Tg+10℃≦Tp ₁ ≦Tc ₁ ...(1) (However, in the formula, Tg is the glass transition temperature of polyethylene terephthalate A (℃), and Tp ₁ is the preheating temperature (℃)
and Tc ₁ represents the crystallization temperature (°C) of polyethylene terephthalate A. ) The platelet-shaped body (B) is compression-molded to a thickness of 1/4 to 1/1.1 of the original thickness, and then the molded plate (C) is molded in the range shown by the following formula (2). _After heating to _a temperature _within The present invention provides a method for manufacturing a polyethylene terephthalate container, which is characterized by thermoforming in a mold.

Polyethylene terephthalate A in the present invention
means a crystalline thermoplastic polyester in which 80 mol% or more of the dicarboxylic acid component, preferably 90 mol% or more, is terephthalic acid, and 80 mol% or more, preferably 90 mol% or more of the glycol component is ethylene glycol. It is resin. The remaining dicarboxylic acids include aromatic dicarboxylic acids such as isophthalic acid, diphenyl ether-4,4-dicarboxylic acid, naphthalene-1,4- or 2,6-dicarboxylic acid, Examples include aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, and undecadicarboxylic acid, and alicyclic dicarboxylic acids such as hexahydroterephthalic acid.Other glycol components include propylene glycol, , 4-butanediol, aliphatic glycols such as neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, aromatic dihydroxy compounds such as bisphenol A, and the like. As long as the terephthalic acid and ethylene glycol are within the above range, it may be a copolymer or a mixture of PET and other polyester.

Polyethylene terephthalate A used for thermoforming
Typically, the intrinsic viscosity (IV) measured with a tetrachloroethane/phenol mixed solvent is in the range of 0.5 to 2.0, preferably 0.7 to 1.5.

The platelets (B) made of amorphous polyethylene terephthalate A used in the method of the present invention are made from an amorphous sheet obtained by melt-extruding polyethylene terephthalate from a T-die and then rapidly cooling it into a rectangular shape, e.g. A method of punching small plate-shaped bodies having shapes such as triangular, square, hexagonal, etc., or by injection molding into a cooled mold after melting polyethylene terephthalate, a shape having a circular, square or wall thickness distribution can be formed. It can be obtained by a method of molding a small plate-like body having a shape such as a circle or a square.

The platelet (B) used in the method of the present invention is not limited to a single-layer platelet of the polyethylene terephthalate, but may be made of polyethylene terephthalate or other layers, for example, a dicarboxylic acid component other than terephthalic acid containing 20 moles of the polyethylene terephthalate. polyester copolymers such as polyethylene terephthalate-isophthalate copolymers, polyethylene terephthalate-glycolic acid copolymers, saponified ethylene/vinyl acetate copolymers, polyvinylidene chloride, vinyl chloride/vinylidene chloride copolymers, Polyethylene terephthalate A with polyamide, polycarbonate, etc.
It may also be a laminated platelet with a thermoplastic resin that can be molded at a thermoforming temperature of .

The thickness of the platelets (B) used in the method of the invention is usually in the range from 20 to 0.1 mm, preferably from 10 to 0.5 mm. If the thickness is less than 0.1 mm, the thickness of the molded plate (C) after compression molding will be less than 0.1 mm, and the thickness of the container obtained by thermoforming will be less than 0.05 mm, which is not practical. On the other hand, if it exceeds 20 mm, it becomes difficult to obtain platelets (B) in an amorphous state, and it becomes difficult to manufacture containers due to crystallization during reheating in the next step.

In the present invention, the amorphous polyethylene terephthalate platelet (B) means that polyethylene terephthalate accounts for 20% or more of the total thickness, preferably 5% or more of the total thickness.
polyethylene terephthalate, and its polyethylene terephthalate is in an amorphous state (X
It is in a state in which almost no crystal peaks are observed by line diffraction.

The method for producing a polyethylene terephthalate container of the present invention includes the polyethylene terephthalate A
After preheating the amorphous platelet (B) consisting of the following to a temperature within the range shown by the following formula (1), preferably the following formula (11), Tg+10℃≦Tp ₁ ≦Tc ₁ ... (1) Tg + 20℃≦Tp ₁ ≦Tc ₁ -20℃ ... (11) (However, in the formula, Tg is the glass transition temperature of polyethylene terephthalate A (℃), and Tp ₁ is the preheating temperature (℃)
and Tc ₁ represents the crystallization temperature (°C) of polyethylene terephthalate A. ) Compression molding the platelet (B) to a thickness of 1/4 to 1/1.1, preferably 1/2 to 1/1.5 of the original thickness,
Next, the molded plate (C) is heated to a temperature within the range shown by the following formula (2), preferably the following formula (21), and then Tp ₁ +10°C≦ _Tp2 ≦Tm−30°C ... (2 ) Tp ₁ +30℃≦Tp ₂ ≦Tm−60℃
...(21) (However, in the formula, Tp ₂ represents the heating temperature (°C) and Tm represents the melting point (°C) of polyethylene terephthalate A.) This method is characterized by thermoforming in a mold.

If the preheating temperature Tp ₁ of the platelet (B) is less than Tg + 10°C, the platelet (B) will hardly soften, and the thickness will be reduced to 1/4 to 1/ of the original thickness by compression molding. It is difficult to reduce the thickness to a range of 1.1, whereas when the crystallization temperature (Tc ₁ ) is exceeded, the platelet pair (B) undergoes crystallization;
It becomes cloudy, making subsequent thermoforming difficult and making it impossible to obtain a container with excellent transparency.

When the thickness of the formed plate (C) after compression molding becomes thinner than 1/4 of the original thickness of the platelet-like pair (B), oriented crystallization becomes significant and thermal Formability is extremely reduced. On the other hand, if the ratio is less than 1/1.1, the longitudinal strength of the thermoformed container will not be improved and the container will have poor pressure resistance.

The temperature of the press during compression molding is not particularly limited as long as the temperature of the preheated platelet (B) does not fall outside the range of equation (1), but it is usually between Tg + 5°C and Tc ₁ + 5°C. Within range. At temperatures below Tg + 5°C, the temperature of the preheated platelets (B) tends to be below Tg + 10°C during compression molding, while at Tc ₁ + 5
If it exceeds ℃, there is a risk of exceeding Tc ₁ .

If the heating temperature Tp ₂ of the molded plate (C) formed by compression molding is less than Tp ₁ +10°C, the thermoformability will be poor, and the thermoformed container will be poor in heat resistance, wall thickness uniformity, and transparency. On the other hand, if the temperature exceeds Tm - 30°C, the oriented tension generated during compression molding will relax and disappear, resulting in a low compressive strength.

For thermoforming after heating the molded plate (C) to a temperature within the range shown by formula (2), a known method, that is, a method generally called vacuum forming or pressure forming, can be adopted, but among them, Plug-assisted vacuum and/or pressure forming is preferred.

Polyethylene terephthalate A used in the present invention
Glass transition temperature Tg (℃), crystallization temperature Tg ₁ (℃)
The melting point Tm (℃) was determined by cutting a sample from an amorphous sheet obtained by cooling in a press at 20℃ after compression molding, and using a differential scanning calorimeter (DSC).
It was determined by measuring at a heating rate of °C/min.

The method of manufacturing polyethylene terephthalate containers of the present invention does not generate scrap unlike the conventional method of thermoforming extrusion-molded sheets, and the manufactured containers also have higher heat resistance than conventional polyethylene terephthalate containers. It has excellent properties such as strength, pressure resistance, transparency, dimensional stability, gas barrier properties, and cold resistance, so it can be used as pressure-resistant containers for carbonated drinks, heat-filled containers for juices, kneaded yokan, etc., and gas barriers for alcoholic beverages, frozen foods, etc. It is suitable for a wide range of containers, including containers that require durability and cold resistance.

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded.

Example 1 IV: 1.3, Tg: 75°C, Tc ₁ : 155°C and Tm:
Polyethylene terephthalate (product name) at 260℃
Mitsui PET J055, Mitsui PET resin) was melt extruded at 300℃ and cooled with a cooling roll at 20℃ to a thickness of 4 mm.
A sheet in an amorphous state (almost no crystalline peaks were observed by X-ray diffraction) was obtained. Next, a regular hexagonal small plate (B ₁ ) with a side of 25 mm is cut out from the sheet, and after preheating the small plate (B ₁ ) to 110°C, compression molding (press temperature 105°C) is performed to obtain a diameter of 60 mm.
A circular molded plate (C ₁ ) with mmφ and thickness of 2.3 mm was prepared.
Next, after fixing the peripheral part (5 mm) of the molded plate (C ₁ ) by crimping, heating it to 140°C and vacuum forming it,
A cylindrical container with a flange width of 5 mm, a depth of 100 mm, a diameter of 50 mmφ, and an average side wall thickness of 265 μm was obtained. The obtained container was evaluated by the following method.

Pressure resistance (Kg/cm ² ): Water pressure was applied to determine the maximum pressure that would lead to destruction.

Heat shrinkage rate (%): Calculated from the volume before and after injection of hot water at 90°C.

As a result, the compressive strength was 17Kg/cm ² and the heat shrinkage rate was
It was 0.15%.

Comparative Example 1 Instead of the molded plate (C ₁ ) used in Example 1,
Using a circular platelet (B ₂ ) with a diameter of 60 mmφ cut from an amorphous sheet with a thickness of 2.3 mm obtained in the same manner as in Example 1, 110 mm was used without compression molding.
The container was heated to .degree. C. and vacuum-formed to obtain a container having the same shape as in Example 1. However, the compressive strength was as low as 8 Kg/cm ³ , and when hot water at 90°C was injected, the material was deformed so much that it was not possible to measure the shrinkage rate.

Comparative Example 2 The same procedure as in Comparative Example 1 was carried out except that the heating temperature during vacuum forming of the small plate-shaped body (B ₂ ) of Comparative Example 1 was 140°C. As a result, the platelets (B ₂ ) crystallized during heating, making vacuum forming impossible.

Example 2 Instead of the platelets (B ₁ ) used in Example 1,
Diameter 45mmφ molded at 300℃ using an injection molding machine
and an amorphous circular platelet (B ₃ ) with a thickness of 4 mm.
The small plate-shaped body (B ₃ ) was compression-molded at a preheating temperature of 110° C. (press temperature 105° C.) to form a circular molded plate (C ₃ ) with a diameter of 60 mmφ and a thickness of 2.3 mm. Next, a container having the same shape as in Example 1 was obtained in the same manner as in Example 1, with the heating temperature set to 150°C. The resulting container had a pressure resistance of 18 kg/cm ² and a heat shrinkage rate of 0.15%.

Comparative Example 3 When the molded plate (C ₁ ) used in Example 1 was preheated to 170°C to obtain a molded plate (C ₄ ), crystallization occurred and the heating temperature during vacuum forming was lowered.
Vacuum forming was not possible even at 200℃.

Example 3 IV: 0.88, Tg: 70℃, Tc ₁ : 180℃, Tm: 230
℃ and 10 mol% isophthalic acid polyethylene terephthalate copolymer (trade name Unipet)
RN163, manufactured by Nippon Unipet) was molded at 270° C. using an injection molding machine to obtain an amorphous circular platelet (B ₅ ) with a diameter of 45 mmφ and a thickness of 4 mm. Next, the platelet-shaped body (B ₅ ) was preheated to 130°C and compression molded (pressing temperature 125°C) to give a diameter of 60 mmφ and a thickness of 2.3 mm.
It was made into a circular molded plate (C ₅ ) of mm. Next, vacuum forming was performed in the same manner as in Example 1 at a heating temperature of 190°C to obtain a container having the same shape as in Example 1. The resulting container had a pressure resistance of 16 kg/cm ² and a heat shrinkage rate of 0.23%.

Comparative Example 4 Instead of the small plate-like body (B ₅ ) used in Example 3, a small plate-like body (B ₆ ) having a diameter of 60 mmφ and a thickness of 4 mm molded in the same manner as in Example 3 was used, and compression molding was performed. When vacuum forming was attempted in the same manner as in Example 1 at a heating temperature of 190°C without heating, the platelets crystallized during heating and vacuum forming could not be performed.

Example 4 A regular hexagonal small plate (B ₆ ) with a side of 16.5 mm was cut out from the sheet formed in Example 1, and after preheating the small plate (B ₆ ) to 120°C, compression molding (pressing) was performed. temperature
115°C) to form a circular molded plate (C ₆ ) with a diameter of 60 mmφ and a thickness of 1 mm. Next, the molded plate (C ₆ ) was fixed, heated to 190° C., and vacuum formed in the same manner as in Example 1 to obtain a container having the same shape as in Example 1 (however, the average side wall thickness was 115 μm). The pressure resistance of the obtained container was 9 kg/cm ² despite the thin side wall thickness, and the heat shrinkage rate was
It was 0.06%.

Comparative Example 5 Instead of the molded plate (C ₆ ) used in Example 4,
Using a circular molded plate (C ₇ ) with a diameter of 60 mmφ and a thickness of 0.5 mm that was compression-molded at a preheating temperature of 120°C, it was fixed at 230°C.
℃ and vacuum-formed in the same manner as in Example 1, but it could not be formed into a tight container shape.

Example 5 A regular hexagonal small plate (B ₈ ) with a side of 30 mm was cut out from the sheet formed in Example 1, and the small plate (B ₈ ) was compression molded (press molded) at a preheating temperature of 110°C.
105°C) to form a circular molded plate (C ₈ ) with a diameter of 60 mmφ and a thickness of 3.6 mm. Next, the molded plate (C ₈ ) was fixed and then heated to 110° C. and vacuum-formed in the same manner as in Example 1 to obtain a container having the same shape as in Example 1 (however, the average side wall thickness was 415 μm). The resulting container has a pressure resistance of 21 kg/
cm ² , the heat shrinkage rate was 1.2%.

Example 6 The inner and outer layers are the same polyethylene terephthalate used in Example 1, the middle layer is IV: 0.85, Tg: 55°C,
Coextrusion molding to obtain polyethylene isophthalate without Tc ₁ and without Tm (molding temperature 270℃)
Then, interior/middle layer/outer layer = 1.33mm/1.33mm/
A multilayer sheet (polyethylene terephthalate was also in an amorphous state) with a thickness of 1.33 mm was obtained. Next, a regular hexagonal small plate (B ₉ ) with a side of 30 mm is cut out from the sheet, and after preheating the small plate (B ₉ ) to 90°C, compression molding (press temperature 95°C) is performed to obtain a diameter of 60 mmφ. and thickness
A circular molded plate (C ₉ ) of 3.0 mm was used. Next, the molded plate (C ₉ ) was fixed, heated to 120° C., and vacuum-formed in the same manner as in Example 1 to obtain a container having the same shape as in Example 1 (however, the average side wall thickness was 350 μm). The resulting container had a pressure resistance of 18 kg/cm ² and a heat shrinkage rate of 1.5%.

Comparative Example 6 Instead of the molded plate (C ₉ ) used in Example 6,
A circular plate-like body (B _{10 ) with a diameter of 60 mmφ was cut from an amorphous outer layer sheet with inner layer/intermediate layer/outer layer = 1 mm/1 mm/1 mm (thickness) obtained in the same manner as in Example 6} . A container having the same shape as Example 1 was obtained by heating to 120° C. and vacuum forming without compression molding. The resulting container had a pressure resistance of 14 kg/cm ² , but the container was significantly deformed when hot water at 90°C was poured into it.

Comparative Example 7 The same procedure as in Example 1 was conducted except that the heating temperature during vacuum forming of the molded plate (C ₁ ) of Example 1 was 110°C. The resulting container had a low pressure strength of 8 kg/ ^cm2 ;
When 90°C hot water was injected, the container deformed significantly.

Claims (1)

[Claims] 1. A single-layer or multi-layer platelet-like body (B) containing amorphous polyethylene terephthalate A as a layer component.
After preheating to a temperature within the range shown by the following formula (1), Tg+10℃≦Tp ₁ ≦Tc ₁ (1) (where, in the formula, Tg is the glass transition temperature of polyethylene terephthalate A (℃), Tp ₁ is preheating temperature (℃)
and Tc ₁ represents the crystallization temperature (°C) of polyethylene terephthalate A. ) Compression mold the platelet (B) to a thickness of 1/4 to 1/1.1 of the original thickness, then mold the molded plate (C) as follows.
After heating to a temperature within the range shown by formula (2), Tp ₁ +10℃≦ _Tp2 ≦Tm−30℃ (2) (where, in the formula, Tp ₂ is the heating temperature (℃) and Tm is polyethylene terephthalate A. (represents the melting point (°C) of ) A method for producing a polyethylene terephthalate container characterized by thermoforming in a mold.