JPS60149427A - Manufacture of container by blow molding - Google Patents

Abstract

PURPOSE:To obtain a container having uniform thickness and excellent transparency by a method in which a bottomed parison of PP resin from injection molding is premolded by blowing in molds whose temperature is specifically regulated for blow molding and for adjusting stretching temperature and molded while being stretched at a regulated stretching temperature. CONSTITUTION:In producing a polypropylene resin container by injection-stretching blow molding, a bottomed parision formed by injection molding is premolded by blowing in molds whose temperature is controlled to a temperature of the range of (Tc-30 deg.C)-(Tc+20 deg.C), where Tc is the crystallization temperature ( deg.C) of polypropylene resin and then molded by blowing while being stretched at a regulated stretching temperature, to obtain an aimed container having good transparency. To make the temperature distribution of the parision uniform, the parision during the blow premolding period is preferably contacted closely with the molds for premolding by blowing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an injection stretch blow-molded container made of polypropylene resin with excellent transparency.

Polypropylene resin is a resin with excellent heat resistance, chemical resistance, safety and hygiene, etc., and its blow molded products have excellent rigidity and impact strength, so it is widely used in food containers, detergent containers, medical containers, etc. There is. However, blow-molded products made of polypropylene resin have the drawback of insufficient transparency, and the market is demanding products that have the same transparency as containers made of polyvinyl chloride resin.

Conventionally, as a method for improving the transparency of polypropylene resin,
A method of adding a nucleating agent, a method of copolymerizing α-ole and fins to propylene, and a method of biaxial stretching are known as processing methods, but in the normal blow molding method, these Even if we take countermeasures, at best we can only get a pale white haze.

On the other hand, recently, in the injection stretch blow molding method, a molding machine that can be applied to polypropylene resin has been developed, and blow molded products have been prototyped. The reality is that this is not the case.

The present inventors investigated a method for manufacturing a polypropylene resin blow-molded container with excellent transparency and no uneven thickness, and found that the temperature of the parison can be adjusted within a specific temperature range by injection stretch blow molding. By pre-blowing in a pre-blow mold that also serves as a stretching temperature adjustment mold, adjusting the stretching temperature, and then stretching-blowing, a polypropylene resin stretch-blow-molded container with excellent transparency and no uneven thickness can be obtained. This finding led to the completion of the present invention.

That is, in the production of an injection stretch blow-molded container made of polypropylene resin, the present invention provides an injection-molded bottomed parison with a temperature between (Tc -30°C) and (Tc + 20°C) relative to the crystallization temperature Tc (°C) of the polypropylene resin. ) An injection stretch blow-molded container made of polypropylene resin with excellent transparency, characterized in that the container is pre-blown in a preliminary blow mold and stretching temperature adjustment mold adjusted to a temperature of This is the manufacturing method.

The injection stretch blow molding method referred to in the present invention means that a bottomed nozzle is first molded by injection molding, and then it is pre-blown in a heated pre-blow mold and stretching temperature adjustment mold to slightly inflate it. In this method, a parison is brought into contact with the inner surface to adjust the stretching temperature, and then the material is transferred into a stretching blow mold, and a blow-molded container is formed there.

In this molding method, the temperature of the preliminary blow mold and stretching temperature adjustment mold is set to the crystallization temperature Tc of the raw material polypropylene resin (
Temperature range from 30°C lower to 20°C higher than (T
Only by adjusting the temperature within the range of (Tc+20°C) - can an injection stretch blow-molded polypropylene resin container with excellent transparency and less uneven thickness be obtained. Preferably, (Tc-20°C) to (Tc
+10°C).

The temperature of the preliminary blow mold and stretching temperature adjustment mold is (Tc-3
If the temperature is below 0°C, the thickness of the molded product will be significantly uneven, and in some cases, the parison will burst due to the blow air pressure during stretching, making it impossible to obtain a good container.

Furthermore, when the temperature exceeds (Tc+20°C), the molded product becomes a pale white haze that is clearly visible to the naked eye, and the breaking strength also decreases.

The temperature adjustment method for the preliminary blow mold and stretching temperature adjustment mold is as follows.
Any method such as using an electric heater or circulating temperature-controlled oil may be used, but the temperature of the mold must be adjusted at the end of the preliminary blowing or immediately before removing the pre-blown parison from the mold. It is sufficient if the temperature is within the above range.

In addition, depending on the shape of the blow molded product, in order to further improve the wall thickness distribution of the blow molded product, the temperature adjustment of the preliminary blow mold and stretching temperature adjustment mold may be divided into several parts (Tc- 30°C) to (Tc+20°C).

Furthermore, in order to make the temperature distribution of the parison uniform, it is desirable to bring the parison into close contact with a preliminary blowing mold and stretching temperature adjustment mold during preliminary blowing.

In order to suitably carry out stretch blowing, the following preliminary blowing conditions are preferred.

Pre-blow stretching ratio: vertical 1.0-1.8 times horizontal 1.2
~2.0 times preliminary blow mold and stretching temperature adjustment mold temperature: (Tc-30
℃)～(Tc+20℃) Preliminary blow air pressure 3～7ky/.

5- Furthermore, the following conditions are preferable for the subsequent stretch blowing.

Stretch blow stretching ratio: vertical 1.2 to 3.5 times horizontal 1.2
~6.0 Injection stretch blow molding machine manufactured by Double Machine ■-ASB-50, ASB
-150, ASB-250, ASB-650, etc.

The polypropylene resin used in the present invention is preferably a random copolymer of propylene and α-olefin, especially ethylene, and may be a blend of small amounts of other resins or elastomers.

Moreover, a nucleating agent may be added if necessary.

In the present invention, a resin obtained by adding additives such as a stabilizer, an antistatic agent, an ultraviolet absorber, a coloring agent, and a nucleating agent to a polypropylene resin and then pelletizing the resin is usually used under the above conditions. By carrying out injection stretch blow molding at the bottom, an injection stretch blow molded polypropylene resin container with a body wall thickness of 0.2 to 6-1.0 mm, excellent transparency, and no uneven thickness is manufactured.

The polypropylene resin injection stretch blow molded container obtained by the present invention not only has excellent transparency, but also has excellent heat resistance, impact resistance, and surface gloss, so it can be used to make food containers, detergent containers, etc. It can be suitably used for shampoo containers, toiletry containers, medical containers, etc.

The present invention will be explained in detail below with reference to Examples.

In addition, the crystallization temperature Tc in the present invention refers to a cooling rate of 1 after completely melting the resin using a differential scanning calorimeter.
This is the peak temperature of the crystallization curve obtained by cooling and solidifying at 0° C./min.

Example 1 As a polypropylene resin, ethylene content was 4% by weight,
An ethylene-propylene random copolymer having a melt flow index (MFI) of 15 f/10 minutes and containing 0.2% by weight of a nucleating agent was used.

The crystallization temperature Tc of this resin was 118°C.

Using an injection stretch blow molding machine AS B-50, the resin was heated to 110°C in a preliminary blow mold and a stretching temperature adjustment mold.
Molded under the following conditions: body diameter 7Qmm, inner volume 500
″ml round bottle was obtained.

Injection molding temperature: 220°C Injection molding mold temperature: 15°C Pre-blow stretching ratio: 1x vertically, 1.4x horizontally Pre-blowing air pressure: 5 kg/ci Stretching Blow stretching ratio:
Stretching length 1.8 times, width 1.2 times Blow air pressure: 9
The resulting bottle had a weight of 209 kg/al, a body wall thickness of about 0.53 mm, excellent transparency, and no uneven thickness.

A test piece was cut out from the body of the resulting bottle, and the haze level was 3.1%, and the breaking strength was 740 b in the longitudinal stretching direction.
y/c4, and the transverse stretching direction was 7 I Oby/al.

The measurement results are summarized in Table 1.

Example 2.3 Comparative Example 1.2 Polypropylene resins with the ethylene content, MFI, and nucleating agent content shown in Table 1 were used, and the temperature of the preliminary blow mold and stretching temperature control mold was adjusted. A round bottle was molded in the same manner as in Example 1 except that the temperature was changed as shown in Table 1.

Table 1 shows the measurement results of the Tc of the resin and the performance of the resulting bottle.

In addition, in Comparative Example 1, the bottle obtained was a pale white and hazy bottle that was clearly visible even when visually observed.

Further, in Comparative Example 2, a bottle with significantly good thickness unevenness could not be obtained.

9-

Claims (1)

[Claims] 1. In the production of polypropylene resin injection stretch blow molded containers, the injection molded bottomed parison is heated to (Tc - 30°C) with respect to the polypropylene resin crystallization temperature Tc (g).
) - (TC+20℃) An injection-stretched polypropylene resin with excellent transparency characterized by preliminary blowing in a preliminary blow mold and stretching temperature adjustment mold adjusted to a temperature of TC + 20°C, and stretch blow molding after adjusting the stretching temperature. A method of manufacturing a blow molded container.