JPS6340654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polyester stretch-molded bottle, and more particularly to a method for manufacturing a polyester stretch-molded bottle that has excellent heat resistance, rigidity, and impact resistance.

A plastic bottle is obtained by stretching a parison (preform) made of a saturated polyester resin such as polyethylene terephthalate in the axial direction and expanding it in the circumferential direction with a fluid in a mold. It has come to be widely used as a container with excellent transparency, impact resistance, gas barrier properties, and light weight.

When hot filling plastic bottles with the contents in order to preserve the contents in a sterile state, there is a problem that the bottles may shrink or become deformed. Regarding this problem, although it is possible to improve the dimensional stability at high temperatures by so-called heat setting in the body of the container, where molecular orientation occurs in biaxial directions, in the neck of the bottle, where such molecular orientation does not occur, , the dimensional stabilizing effect of heat setting cannot be expected. However, if the neck of the bottle lacks heat resistance or dimensional stability at high temperatures,
Problems arise in that the neck is deformed during hot overflow filling of the contents, or the screw threads and support ring are deformed when the bottle is capped, making it difficult to securely seal the bottle.

It is already well known that as a means to improve the heat resistance of saturated polyester resin molded products, the molded products are heat treated to increase their crystallinity, and such heat treatment can be applied to the neck of the bottle mentioned above. has already been proposed (Japanese Unexamined Patent Publication No. 54-68385).

However, when the neck of the bottle is crystallized by heat treatment, although the heat resistance is improved, there is a problem that the neck becomes a mechanically brittle structure and the impact resistance etc. are significantly reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a biaxially oriented plastic bottle made of polyethylene terephthalate and having a rigid neck that has an excellent combination of heat resistance, impact resistance, and shape stability (dimensional accuracy). be.

Another object of the present invention is to provide a method for manufacturing a lightweight, impact-resistant plastic bottle suitable for hot filling and forming a reliable sealing structure between the bottle and the lid. .

According to the present invention, the neck forming portion of the parison made of thermoplastic polyester is heated to a crystallization temperature, and the neck forming portion partially crystallizes.
Before the crystallization is completed, the neck forming portion is engaged with the mold, stretched and oriented in the axial direction and the circumferential direction to form the neck, and the formed neck is maintained at the above temperature to complete the crystallization. Then, there is provided a method for producing a polyester stretch blow-molded bottle, which is characterized in that a parison having a molecularly oriented and crystallized neck is heated to an appropriate stretching temperature and then subjected to biaxial stretch blow molding.

The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 showing the overall structure of a plastic bottle according to the present invention, this bottle has a body part 1 integrally molded from polyester, a bottom part 2 connected to the lower end of the body, and a frustum-shaped shoulder connected to the upper end of the body. It consists of a section 3 and a neck section 4 that continues to the upper end of this shoulder section. This bottle is formed by biaxially stretching blow molding a polyester parison mainly composed of ethylene terephthalate units.
That is, the molecules are oriented in the axial direction of the bottle and in the circumferential direction of the bottle.

The neck portion 4 includes a screw 6 or a stepped portion 7 for holding a bottle cap (not shown) attached to the bottle mouth 5 for sealing, or a support for holding the bottle when the bottle cap is engaged in a sealing manner. A ring 8 is provided.

According to the present invention, the polyester constituting the neck portion 4 is given molecular orientation and crystallized.

2-A, 2- showing the main parts of the manufacturing process of the present invention
In Figures B, 2-C and 2-D, first, a bottomed parison (preform) 10 made of polyethylene terephthalate is prepared. This bottomed parison 1
0 is manufactured by injection molding polyethylene terephthalate in a mold, or by pinching off a pipe obtained by extrusion molding polyethylene terephthalate with a split mold and pre-blow molding. First, in FIG. 2-A, the portion of the bottomed parison 10 that is to become the bottle neck, that is, the opening end 11, is heated to the crystallization temperature of polyethylene terephthalate, generally 140 to 210°C, particularly Heat to a temperature of 170-200°C. By this heating, the bottomed parison 1
Crystallization of the polyester begins at the end 11 of 0, and the end 11 becomes somewhat white.

Next, in FIG. 2-B, the bottomed parison 1
The open end of the parison is held by the clamp 13, and the part near the bottom is held by the clamp 14, and the crystallization temperature is adjusted by moving the clamps 13 and 14 in the axial direction of the parison so that the distance between them increases. The neck forming portion 11 that has been heated is mechanically stretched.

Following this axial stretching, the female mold 15 is positioned around the outer periphery of the neck forming portion 11, as shown in FIG. 2-C. This female mold 15 includes the aforementioned screw 6,
A recess 16 corresponding to the stepped portion 7 or the support ring 8 is formed.

Finally, in Figure 2-D, neck forming portion 1
A plunger 17 is forcibly inserted into the inner circumferential portion of 1. The polyester of this neck forming portion 11 is
By inserting the plunger 17, the polyester is subjected to a radially outward ironing process, thereby filling the concave portion 16 of the female mold 15 with polyester without any gaps, and stretching and orienting the polyester in the axial direction and the circumferential direction.

According to the present invention, by crystallizing the polyester of the neck forming portion 11 of the parison 10 and providing molecular orientation, not only the heat resistance and rigidity are significantly improved, but also the molecular orientation This has the advantage that impact resistance is also significantly improved.
In addition, according to the present invention, if the neck forming part is first heated to the crystallization temperature to start crystallization, and then formed into a predetermined neck shape, the screw 6, step part 7, or A significant advantage is that the formation of a support ring 8 is possible. That is, when the neck is first formed and then crystallized, as the density of the polyester in the neck increases due to crystallization, these parts shrink, making it difficult to form a bottle neck with high precision. becomes. On the other hand, according to the present invention, when crystallization is started at the neck forming part and then the neck is formed, extremely high precision forming is possible, and as a result, the sealing workability and sealing of this type of plastic bottle are improved. It becomes possible to significantly improve reliability. Furthermore,
If the neck-forming part is first heated to a crystallization initiation temperature and then this part is stretched, crystallization of the neck-forming part is significantly promoted, and there is also the manufacturing advantage that the process can be completed within a short time.

In the present invention, the stretching ratio of the neck forming part 11 in the axial direction is generally 1.05 to 1.5 times, particularly 1.1 to 1.3 times.
It is desirable to be in the twice range. Additionally, the radial extension due to insertion of the plunger is greatest at the top of the screw or the top of the support ring.
It is preferably in the range of 1.02 to 1.5 times, particularly 1.05 to 1.2 times.

Further, the neck portion 4 is preferably crystallized so that the outermost surface layer has a density of 1.36 g/cc or more, particularly 1.37 g/cc or more. The fact that the polyester of the neck portion 4 is molecularly oriented can be easily confirmed using a fluorescence polarization spectrophotometer.

Instead of stretching in the axial direction by tension as in the specific example shown in the drawings, it may be expanded and stretched in the circumferential direction by pre-blowing, or both can be used in combination. Furthermore, a plunger having an outer diameter larger than the inner periphery of the neck molded portion may be inserted to extend the neck portion in the circumferential direction.

The polyester parison obtained by the method described above is preheated to the stretching temperature prior to stretch blowing. This stretching temperature is a temperature lower than the crystallization temperature of the polyester used and at which the polyester parison can be stretched, and specifically, a temperature of 80 to 130°C, particularly 90 to 110°C is used. .

Stretch blow molding of preheated parison is
This can be carried out by means known per se, such as sequential stretch blow molding or simultaneous stretch blow molding. For example, in the former case, the parison is stretched axially under fluid injection at a relatively low pressure (pre-blowing) and then stretched by circumferential expansion of the container under fluid injection at a relatively high pressure. Let's do it. In the latter case, stretching in the circumferential direction and stretching in the axial direction are simultaneously performed by blowing fluid at high pressure from the beginning. The parison can be easily stretched in the axial direction by, for example, holding the neck of the parison between a mold and a mandrel, applying a stretching rod to the inner surface of the bottom of the parison, and stretching the stretching rod. The stretching ratio of the parison in the axial direction and circumferential direction is
It is desirable to set them to 1.5 to 2.5 times (axial direction) and 1.7 to 4.0 times (circumferential direction), respectively.

The plastic bottle of the present invention is particularly useful for hot filling and long-term storage of juices, mineral water, sauces, ketchup, various sauces, lactic acid bacteria drinks, and the like.

Example: Injection molded polyethylene terephthalate with density 1.34 and intrinsic viscosity 0.75, height 162 mm, body diameter 26 mm,
A bottomed parison with an average body wall thickness of 4 mm was molded. The opening of this parison was heated to a temperature of 160 to 170°C by an infrared heating mechanism, as shown in Figure 2-A. As a result of this heating, the polyester at the edges started to crystallize and became somewhat white. At this point, as shown in Figure 2-B, the opening is longitudinally stretched to 1.15 times, and as shown in Figures 2-C and 2-D, the radial stretching ratio of the support ring is adjusted in the outer and inner neck molds. The neck was formed by stretching it 1.15 times. After the molding was completed, the neck completely turned white and crystallization was completed.

A bottle with an internal volume of 1000 c.c. was obtained by heating the bottomed parison with the neck formed to a stretching temperature of 95 to 100° C. and then using a conventional biaxial stretch blow molding method. The neck density of this bottle was 1.38 g/cc. The resulting bottle was filled to the neck with hot water at 85°C, and after being left for 30 minutes, the radial shrinkage of the neck was 0.4%.
Also, a bottle filled with 5℃ water and sealed is 1.8 in height.
Although it fell upside down from a height of m, no damage occurred.

Comparative Example 1 A bottomed parison with the same resin and dimensions as in Example and also formed with a neck was injection molded, and then this bottomed parison was heated to 95 to 100°C, and then biaxially stretched and blow molded to an internal volume of 1000cm. Got a bottle of .c.

The neck of this bottle was substantially amorphous and had a density of 1.34 g/cc, and when evaluated in the same manner as in the example, there was no fall damage to the neck, but the shrinkage was 4.
% and had poor heat resistance, which caused a practical problem.

Comparative Example 2 A bottomed parison similar to Comparative Example 1 was injection molded,
The neck portion of this bottomed parison was heated to 180°C to crystallize it.

After heating this crystallized bottomed parison to 95 to 100℃, the internal volume is
I got a bottle of 1000c.c. The density of the neck of this bottle was 1.39 g/cc, and when the same evaluation as in the example was conducted, the shrinkage of the neck was 0.4%, which was good.
The drop damage rate was 20%, which caused a practical problem.

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view showing the overall structure of the plastic bottle of the present invention, Fig. 2-A, Fig. 2-B,
Figures 2-C and 2-D are explanatory diagrams of the steps of heating, stretching and shaping the neck of the parison. 1... Torso, 2... Bottom, 3... Shoulder, 4...
Neck, 10... Parison, 12... Heating mechanism, 1
3... Clamp, 14... Clamp, 15... Female mold, 17... Plunger.

Claims (1)

[Claims] 1. Heating the neck-forming part of a parison made of thermoplastic polyester to a crystallization temperature, and engaging the neck-forming part with a mold until the neck-forming part partially crystallizes, but the crystallization is not yet completed. , the neck is formed by stretching and oriented in the axial and circumferential directions, the formed neck is maintained at the above temperature to complete crystallization, and then the parison having the molecularly oriented and crystallized neck is stretched and adjusted to an appropriate temperature. A method for producing a polyester stretch blow molded bottle, which comprises subjecting the bottle to biaxial stretch blow molding.