JPS624301B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polyester containers. More specifically, the object is to provide a container made of polyethylene terephthalate that has excellent drop impact resistance. Containers made of polyester have recently attracted attention as containers for carbonated beverages, foods, cosmetics, and the like. In particular, containers made of polyethylene terephthalate,
Unlike polyvinyl chloride resin containers, there is no concern about the negative effects on human health caused by plasticizers or residual monomers, and compared to containers made of polyethylene or polypropylene, there is less permeability to gases such as oxygen and carbon dioxide. It has advantages such as excellent transparency, and is useful as containers for beverages, foods, cosmetics, etc. Conventionally, methods for obtaining such polyester containers have been
It is shown in specifications such as U.S. Patent No. 3,733,309, U.S. Pat. However, polyester containers obtained by these methods are suitable for storing liquids under pressure, such as those for carbonated drinks, and are too thick and costly to fill with general foods. , it is difficult to replace conventionally used containers. On the other hand, if you try to reduce the cost by reducing the wall thickness, the drop impact resistance will deteriorate, and to avoid this, it will be necessary to significantly increase the degree of polymerization of the raw material polyester, which will increase the polymerization cost and make molding difficult. It is difficult to use as a substitute for conventional containers because of disadvantages such as increased cost. As a result of intensive research into polyester containers that do not have such drawbacks, the inventor of the present invention set the wall thickness of the curved portion between the body and the bottom of the container to a value within a specific range, and determined that the wall thickness change at the bottom of the container If the refractive index in the thickness direction of the bottom of the container is kept within a certain range without making it too large, it is possible to provide excellent impact resistance without increasing the wall thickness of the container, and it is also possible to achieve extremely high impact resistance. The inventors have discovered that it is not necessary to use a polymer with a certain degree of polymerization, and have arrived at the present invention. That is, the present invention provides a container made of polyethylene terephthalate having an intrinsic viscosity of 0.50 to 0.70, in which the wall thickness of the curved portion between the body and the bottom of the container is 0.1 mm to 0.6 mm, and the bottom The ratio of the wall thickness Amm of the thickest part of the bottom to the wall thickness Bmm of the smallest wall thickness of the bottom satisfies A/B≦15, and when the container is held upright on a horizontal surface, This polyester container has improved drop impact resistance and has a refractive index of 1.50 to 1.55 in the thickness direction of the bottom portion of the container that contacts the horizontal surface. Polyethylene terephthalate as used in the present invention is a polyester that can be obtained by polymerizing terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative, but in a small proportion (for example, about 20 mol% or less).
Other dicarboxylic acid and/or glycol components may be copolymerized. The dicarboxylic acids that may be copolymerized include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, naphthalene dicarboxylic acids, diphenyl dicarboxylic acids, diphenoxyethane dicarboxylic acids, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid,
Examples include aliphatic or alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. In addition, glycol components include trimethylene glycol, tetramethylene glycol, propylene glycol,
Aliphatic or alicyclic glycols such as neopentylene glycol, hexamethylene glycol, dodecamethylene glycol, cyclohexanedimethanol, etc., bisphenols, hydroquinone,
Examples include 2,2-bis(4-β-hydroxyethoxyphenyl)propane and other aromatic diols. Furthermore, oxyacids such as P-hydroxyethoxybenzoic acid and -oxycaproic acid may be used, and lower alkyl esters thereof and other ester-forming derivatives may also be used. The polyethylene terephthalate includes:
A polyfunctional compound such as trimethylolpropane, pentaerythritol, trimellitic acid, trimesic acid, etc. may be copolymerized in an amount of 2 mol % or less based on the dicarboxylic acid component or diol component. The copolymerized polyethylene terephthalate preferably has a softening point (Picato softening point measured after heat treating a polymer chip at 140°C for 1 hour) of 220°C or higher (particularly preferably 230°C or higher). Such polyethylene terephthalate has an intrinsic viscosity of 0.50 or more, preferably 0.55 or more. Polymers having an intrinsic viscosity lower than 0.45 are not preferred because the drop impact resistance of the container is poor even if the wall thickness and refractive index are within the range specified in the present invention. Also, the intrinsic viscosity of the polyethylene terephthalate should be 0.70 or less. Intrinsic viscosity is 0.65
The following are preferred. If the intrinsic viscosity is higher than 0.70, not only does polymerization take a long time or require the complicated process of solid phase polymerization, which increases polymerization costs, but the resin has poor flowability and is difficult to use in containers (e.g. bottles). This is undesirable because it may cause distortion, significant unevenness in thickness, or areas with poor transparency at the bottom, etc., resulting in a deterioration in appearance and quality. In the container of the present invention, the wall thickness of the curved portion between the body and the bottom is set to 0.1 mm to 0.6 mm. If the wall thickness of this part is less than 0.1 mm, the drop impact resistance of that part will be too weak, which is undesirable. Further, if the wall thickness includes a portion thicker than 0.6 mm, surprisingly, the drop impact strength is also significantly weakened, which is not preferable. The reason for this is unknown, but if the wall thickness of this part is thicker than 0.6 mm, cracks will occur from this part and the container will tend to burst when the container is dropped. The thickness of the curved portion is preferably 0.15 mm to 0.5 mm, particularly preferably 0.2 mm to 0.5 mm. In addition, for the bottom of the container of the present invention, the ratio of the wall thickness Amm at the thickest part and the wall thickness Bmm at the smallest wall thickness (therefore, A≧B) is A/B≦. Make it 15. If A/B is greater than 15, cracks are likely to occur at the bottom where the wall thickness starts to decrease from the thickest part when the container is dropped, which is undesirable. A/B is preferably 12 or less, particularly preferably 10 or less. When the container of the present invention is stood upright on a horizontal surface, the refractive index in the thickness direction of the portion of the bottom of the container that contacts the horizontal surface is 1.50 to 1.55. Whether the refractive index is smaller than 1.50 or larger than 1.55,
This is not preferred because impact resistance decreases. In order to manufacture the container of the present invention, the following method may be adopted, for example. That is, raw material polyethylene terephthalate is injection molded to create a cylindrical preform with a bottom for blow molding. It is preferable that the thickness of the obtained preform at the bottom is equal to or thinner than the thickness of the straight body, and it is preferable that the density of the bottom is almost the same as that of the straight body. The preform is heated to 80 to 150°C, preferably 85°C.
After heating to a temperature range of ~120°C, it is fixed in a mold, stretched in the axial direction by a stretching rod, and fluid such as air or nitrogen is injected to expand it to the container mold, where it is cooled and solidified in the mold. During stretching, the temperature at the bottom of the preform is equal to or about 5 to 10°C higher than the temperature at the body of the preform.
Increase the degree. For this purpose, when heating the preform, it is preferable to heat not only from the side of the preform but also from the bottom side of the preform and control the temperature to be within the above temperature range. In addition, by allowing the heated preform to cool for 3 to 10 seconds before stretching the preform with a stretching rod after heating is completed and before blowing, the temperature gradient between the bottom and body of the preform is made gentler. It is preferable to reduce the temperature difference in the thickness direction of the preform. Furthermore, it is preferable that the blowing be carried out after or just before the completion of stretching the preform.
It is preferable to start blowing at least after the preform has been stretched by 50% or more. Furthermore, the material used for the stretching rod has a thermal conductivity of 1 Kcal/m·hr·°C or less. In addition, the blow mold lowers the temperature of the part corresponding to the bottom of the container by about 10
It is better to keep it at a higher temperature. However, it goes without saying that the containers of the present invention are not limited to those obtained by such a method. The container of the present invention is crystalline and has excellent appearance such as drop impact resistance, transparency, and gloss, and when used as a container for food or cosmetics, there is little change in taste or adhesion of odor, and the amount of water and other substances that permeate is small. It has the advantage of being Hereinafter, the present invention will be explained in detail with reference to Examples. In addition,
The main measurement methods used in the present invention are as follows. Γ Intrinsic viscosity [η]: Value measured at 35°C using 0-chlorophenol as a solvent. ΓRefractive index in the thickness direction n _z : The refractive index in the thickness direction of a sample cut from the bottom of the container was measured using a sodium D line at a temperature of 25°C using an Atsube refractometer equipped with a polarizing plate. value. Examples 1 to 6 and Comparative Examples 1 to 5 Polyethylene terephthalate chips with [η] = 0.65 and a softening point of 259°C were heat-dried at 160°C for 4 hours in a hot air dryer (the moisture content of the chips was brought to 0.008%). . Using this chip, the outer diameter was
A bottomed preform with a length of 28 mm, a length of 160 mm, a wall thickness of 2 mm, and a weight of 33 g was molded. The molding conditions were: cylinder temperature 260-280℃, injection pressure 800Kg/cm ² , cycle.
The mold temperature was set to 20°C (water-cooled) for 35 seconds. After preheating the obtained bottomed preform for a predetermined period of time in a heating tube (one that can set different temperatures for heating the body and bottom of the preform), The preform was transferred into a blowing mold having a cavity in the shape of a food container bottle with a diameter of 28 mm, and stretched in the axial direction with a stretching rod (a nylon rod was used in the example, and a stainless steel rod was used in the comparative example). At the same time, it was expanded in the circumferential direction with compressed air to produce a bottle with an internal volume of 1 liter. As a result of molding under various molding conditions, bottles with the quality shown in Table 1 were obtained. After filling the resulting bottle with 900 ml of water at a temperature of 10°C and sealing it, the bottle was dropped onto a concrete floor with its bottom facing down to test its drop impact strength. The test was initially carried out at a height of 1 m above the concrete floor, and the test was repeated by increasing the height by 10 cm each time until the bottle was destroyed. The results obtained are shown in Table 1.

[Table] Regarding drop impact strength, a drop of 1.5 m or less will cause practical problems. As shown in Table 1, the cases within the scope of the present invention have excellent drop impact resistance, whereas the cases of Comparative Examples 1 to 5 were all broken at 1.5 m or less, which is a practical problem. I understand that. Examples 7 to 12 and Comparative Example 6 Bottles were obtained in the same manner as Examples 1 to 6, except that polyethylene terephthalate chips with different [η] were used. The resulting bottles were dropped in the same manner as in Examples 1 to 6 to test impact resistance. Table 2 shows the molding conditions and results.

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Claims (1)

[Scope of Claims] 1. A container in which a body made of polyethylene terephthalate having an intrinsic viscosity of 0.50 to 0.70 is biaxially stretched and oriented crystallized, and the curve between the body and the bottom of the container is The wall thickness of the bottom part is 0.1 mm to 0.6 mm, and the wall thickness of the thickest part of the bottom part is A mm,
The ratio of the wall thickness Bmm of the smallest wall thickness of the bottom part satisfies A/B≦15, and the thickness of the part of the bottom part of the container that comes into contact with the horizontal surface when the container is stood upright on the horizontal surface. A polyester container with improved drop impact resistance and a refractive index in the transverse direction of 1.50 to 1.55.