JPS5833432A - Method for blow molding of polypropylene - Google Patents

Abstract

PURPOSE:To obtain a molded product excellent in transparency by a method wherein a heater is provided to the mandrel and/or the core of a blow molding die and the temp. of the core is kept higher than that of an outer die to carry out the blow molding of polypropylene. CONSTITUTION:A heater 5 is provided to the mandrel 1 and/or the core of a blow molding die to heat the same and the temp. of the core 2 is kept higher than that of an outer die 3 to carry out the blow molding of polypropylene. The temp. of the core 2 is pref. kept 5-100 deg.C higher than that of the outer die 3. By this method, a molded product excellent in transparency is obtained and the draw-down property of a parison during blow molding is improved and the molded product with reduced deviation of a wall thickness is obtained.

Description

[Detailed description of the invention] The present invention relates to a method for forming a raw molded product.

Mechanical properties of polypropylene blow molded containers, III
11 Due to its excellent heat resistance and chemical resistance, it is used in a wide range of applications such as food containers, pharmaceutical containers, detergent containers, etc. However, in terms of transparency, although it is better than polyethylene, it is inferior to polyvinyl chloride and polyethylene terephthalate, and further improvements are required in order for it to be widely used as a base material for transparent containers.

One way to improve the transparency of polypropylene is to add a small amount of a nucleating agent such as aluminum aluminum butyl benzoate. In the case of injection molding (
4. Unlike blow molding, the mold is pressed against a smooth mold surface under high pressure. It is easy to obtain a 1.1ν-shaped product with good transparency because the surface of the shaped product tends to be smooth, and because the group 5-shaped product is rapidly cooled through the mold, the crystal nuclei are small and torn. However, due to the advantages of blow molding, JJy is
．． If you do the shape, you will not be able to obtain sufficient transparency. Therefore, when molding is carried out at a higher resin temperature, the gloss and surface smoothness are improved, and the transparency is also improved. Otherwise, the surface of the molded product becomes avatar-like, resulting in a product with a low value per song.

The inventors of the present invention carefully investigated the reason why blow-molded products with excellent transparency cannot be obtained within the normal molding temperature range, and found that the cause lies in the condition of the inner surface of the blow-molded product. As a result, by installing a heater in the mandrel and/or core of the blow molding die and performing blow molding of polypropylene by maintaining the temperature of the core higher than the temperature of the outer die, the transparency of the molded product obtained can be improved. We have found that this is a significant improvement and have arrived at the present invention.

In the present invention, the drawdown properties of the parison during blow molding are significantly improved, and a molded product with less uneven thickness can be obtained.

When blow molding polypropylene using a conventional blow molding die that heats the die by installing a heater only on the outside of the die, the temperature of the core is lower than the temperature of the outer die9. The transparency of the polypropylene molded product is not good. By installing a heater on the mandrel and/or the core to maintain the temperature of the core at a higher temperature than that of the outer die and performing blow molding as in the present invention, a polypropylene molded product with outstanding transparency can be obtained. The temperature of the core is preferably 5 to 100°C, preferably 10 to 50°C higher than the temperature of the outer die.

If the temperature is low, the effect of improving transparency will be reduced, and if the gap is too high, drawdown will be less likely to occur, although this will vary depending on the wall thickness and molding speed.

The mandrel, core and outer die of the blow molding die referred to in the present invention are parts 1, 2 and O, respectively, as shown in the structural example of a general blow molding die as shown in FIG. The place to install the heater is a mandrel,
The heater may be installed at either one or both locations on the core, but it is preferable to install the heater at the core where it has the least effect on drawdown performance. The method of installing the heater is not particularly limited, but one example is shown in FIG. In the example in Figure 2,
The heater uses a trick heater with a power of 200 V and 350 W. A hole is made inside the core and filled with thermocement. Temperature is normally adjusted using an external shearing resistor.

Tree brother 1! Polypropylene in IJ pζ refers to glopylene homopolymer, propylene and other α-olefins,
For example, it also includes copolymers with ethylene, butene-1, etc., and resin mixtures that are blended with other resins such as polyethylene or rubber, etc., which have these as main components, but
Among them, from the viewpoint of transparency, it is particularly preferable to use propylene 7-ethylene random co-topolymer.

Therefore, these polypropylenes contain a nucleating agent, tlI=,
The composition may also contain commonly used additives such as antifouling agents, antistatic agents, ultraviolet absorbers, and pigments.

In order to explain the present invention in more detail, practical examples will be described below, but first the test method used in the examples will be described.

Haze measurement: AsTMDlo[] using Tokyo Denshoku haze meter
It was measured according to method 3.

Measuring the total haze of the bottle body: The haze value is obtained by cutting out the bottle body and measuring the test piece as it is.

Measuring the haze inside the bottle body: The haze value measured by cutting off the bottle body and applying liquid paraffin to the inner surface of the bottle is subtracted from the total haze value.

Measurement of transparency: Hold the bottle 2 or m apart from the universal visual acuity chart, look through the bottle at the legible lowercase letters of the universal visual acuity chart up to '', and express the visual acuity value at that time.

The larger the value, the better the transparency.

Judgment of drawdown: Extrude the parison under the conditions of a scree rotation speed of 39 rpm+ and a temperature of 220° C., and obtain a relationship diagram between the extrusion characteristic j and the parison length. If linearity is observed up to a parinon length of 30 cm, it is determined that there is no drawdown.

Example 1 Blow molding was performed under the following temperature conditions using a 40 mmφ blow molding machine manufactured by Japan Steel Works, Ltd. Screw speed: 59 rpm, cylinder temperature: 180°C, 200°C, 2
20℃, Gui temperature 220℃, outer die temperature 220℃, core temperature 260℃. Further, a cartridge heater was inserted into the core and heated by the method shown in FIG.

As the polypropylene, a propylene-ethylene random copolymer with M,
．． One containing 1 weight crack was used.

The molded product was molded into a round bottle with a body wall thickness of approximately 0.8 mm, and the drawdown properties during molding, haze and transparency of the bottle were measured. The results are shown in Table 1, and a bottle with good transparency and no drawdown was obtained.

Example F+2 A bottle was molded at a core temperature of 310° C. and using the same machine as in Example 1, and as a result, a bottle with good transparency as shown in Table 1 was obtained.

A bottle was molded in the same manner as in Example 1 except that the hifter was embedded in the matdrel instead of the core and the core temperature was 260°C. As a result, as shown in Table 1, a bottle with good transparency was obtained. Got a bottle,.

Comparative Example 1 Molding without putting a heater inside the core, and the outside was Example 1
A round bottle was molded in the same manner as above, but only a bottle with poor transparency was obtained. The measurement results are shown in Table-1. The temperature of the core under these molding conditions was 200°C.

Table 1 Example 4 Bottles were molded in the same manner as in Example 1 and Example 1 and 1 of 4 types of visibility except that the core temperature was 360°C.
I got dabinwo. When we evaluated the drawdown properties, we found that there was a slight drawdown, and the wall thickness of the bottle was slightly thinner, but the commercial value as a container was 1)j:1. Got wet.

[Brief explanation of the drawing]

FIG. 1 shows an example of the structure of a v-molding gou suitable for carrying out the method of the present invention, and No. 21 shows an example of a device v1 related to the core heating mechanism. It is. In the figure 1...Mandrel 2...Core 2...Outer die 4.Scree 5...Heater 6
...Thermocouple patent mill 1 Mitsui Toatsu Chemical Co., Ltd. Figure 1

Claims (1)

[Claims] A polypropylene blow molding method characterized by installing a heater in the mandrel and/or core of the blow molding die to maintain the temperature of the core higher than the temperature of the outer die.