JPS5854017B2 - Method for manufacturing polyolefin hollow bodies with improved appearance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyolefin hollow bodies with improved appearance such as transparency and surface gloss.

The general method for manufacturing polyolefin hollow bodies is to first extrude a tube-shaped parison from an extruder, sandwich it between molds, and press it against the mold with pressurized fluid to obtain the desired molded product. It is.

In this method, a tube-shaped parison is extruded from an extruder, so it is desirable that there is little drawdown due to its own weight, so a resin with a high molecular weight (low melt index) is preferable as the raw polyolefin. It is used in

However, when such a polyolefin is blow molded under normal molding conditions, fine irregularities, so-called shark skin, occur on the surface of the bottle, resulting in poor transparency and gloss.

This has conventionally been one of the major causes of lowering the commercial value of polyolefins, particularly polypropylene hollow bottles.

Generally speaking, as a countermeasure to this problem, a method has been proposed in the past to raise the temperature of the parison, lower the viscosity of the resin, and reduce the abrasion stress. methods are rarely effective.

There is also a possibility that drawdown of the resin will be promoted.

On the other hand, when polyolefin is stretched at a temperature below its melting point,
It is also known that the clarity of the bottle is significantly improved.

However, this method requires complicated equipment and is therefore disadvantageous in terms of cost.

The object of the present application is to provide a method for producing polyolefin, particularly polypropylene hollow bodies, which have significantly improved appearance such as transparency and surface gloss, using a conventional and simple blow molding machine.

That is, the present invention provides a method for producing a polyolefin hollow body, in which after melting a polyolefin and extruding a parison from a die head, the temperature of the parison is maintained at a temperature higher than the melting point of the polyolefin for at least 5 seconds, and then the parison is extruded. A method for producing a polyolefin hollow body with improved appearance, characterized in that the hollow body is obtained by injecting a pressurized fluid into the hollow body.

In the present invention, polyolefins include ethylene, propylene, 1-7"tene, 1-pentene, 3-methyl-1-
Butene, 1-hexene, 3-methyl-1-pentene, 4
- Homopolymers or copolymers of 4-olefins such as methyl-1-pentene and 1-octene, copolymers of α-olefins and polymerizable monomers other than α-olefins, or derivatives thereof, e.g. , ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, partially or completely saponified product of ethylene-vinyl acetate copolymer, etc., or synthetic rubber such as polybutadiene, polyisobutylene, SBR, etc. to these polyolefins. They may be blended within a range that does not essentially impair the properties of the compound.

Among these, the effect of the present invention is remarkable for resins with good transparency, such as polypropylene, low density polyethylene, etc. Among these, the effect of the present invention is particularly remarkable for resins with good transparency, such as propylene-ethylene with an ethylene content of 2 to 10 mol. Random copolymers are most preferred as raw materials because they have good impact resistance and transparency.

Polyolefin melt index (ASTM-D-
1238-65T) is 001 to 5, especially 0.1
It is desirable that it be in the range of 2 to 2.

If the melt index is less than 0.01, the melt viscosity is too high to extrude a good parison using a normal extruder.

On the other hand, if it exceeds 5, the drawdown of the parison will be large, which is not preferable for the present invention.

The apparatus used in the present invention may be a conventional blow molding apparatus for polyolefins.

To explain the method of the present invention, first, polyolefin is melted using an extruder.

The resin temperature during melting is preferably in the range of 120 to 260°C, particularly 190 to 230°C.

The melted plasticized resin is extruded into a parison from a die head by rotating a screw or using an accumulator.

In a normal method for molding a hollow body, immediately after the above operation, the mold is closed and the parison is clamped between the molds, and then a pressurized fluid is injected into the parison to expand the parison.

The present invention is characterized in that after extruding the parison from the die head, the parison is kept in that state for at least 5 seconds or more, preferably 20 seconds or more, and particularly preferably 30 seconds or more (hereinafter referred to as holding).

In this state, the temperature of the parison gradually decreases, but in the present invention the parison must not solidify during holding.

If the parison solidifies during holding, the parison will expand unevenly and the resulting bottle will have uneven thickness.

Although the atmospheric temperature during holding should be avoided to be extremely high or low, a heating device is usually not required, and the temperature may preferably be room temperature.

It is completely unexpected that such an operation significantly improves the appearance of the molded hollow bottle, such as its surface gloss and haze, as shown in the Examples below.

According to the studies of the present inventors, the above effect is not due to the orientation of polyolefin crystals, but is thought to be due to the strain during extrusion of halinone being relaxed during holding, improving the surface condition of the parison, especially the internal surface. .

Further, the above effect is more remarkable in polypropylene than in polyethylene.

This is considered to be because the molecular weight distribution of polypropylene is generally narrower than that of polyethylene.

The above-mentioned holding may be performed with the mold closed and the parison held between the molds.

It may also be done before the mold is closed. In the latter case, the mold is closed after holding.

Pressurized fluid is then forced into the parison to expand the parison and form a hollow body.

This method itself is known, and the pressurized fluid is nitrogen,
Air, carbon dioxide, and pressurized gas are preferably used.

The inlet pressure of the pressurized fluid is preferably in the range of 1 to 10 degrees.

After the above operations, the mold is opened and the molded product is taken out.

The hollow bodies obtained by the method of the present invention have significantly improved appearance, such as transparency and surface gloss, compared to those obtained by conventional methods.

Therefore, it is particularly suitable for pharmaceutical applications such as infusion containers and eye drop containers that require bottle transparency.

The method of the present invention is effective for producing not only a single-layer polyolefin hollow body but also a multi-layer hollow body with other resins.

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 A polypropylene homopolymer (melt index 0.5) was melted at 220°C using a direct extrusion type blow molding machine (45 mψ, 1 mold, manufactured by Tahara Iron Works), and the melting rate was 1.7 crn/sec from the die head. The parison was extruded at a speed of .

The mold was then immediately closed and held for 10 seconds.

After that, 5 liters of compressed air was blown into the inside of the parison and 400
A test piece was cut from the center of a 1° cylindrical bottle (weighing about 17 g) and tested for light transmittance and haze according to the method of ASTM-D-1003.
The surface glossiness was measured according to the method of No. 523.

The results are shown in Table 1.

Examples 2 to 4 The same procedure as in Example 1 was conducted except that the holding times were 30, 60, and 120 seconds, respectively.

The results are shown in Table 1.

Example 5 The same procedure as in Example 1 was conducted except that the holding time was 5 seconds.

The results are also listed in Table 4.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the holding time was 0.5 seconds.

The results are also listed in Table 1. Examples 6-8 The same procedures as Examples 2-4 were carried out except that the resin was replaced with a propylene-ethylene random copolymer (ethylene content 5.6 mol, melt index 0.5).

The results are shown in Table 2. Example 9 LQ carried out in the same manner as in Example 5 except that the resin was replaced with the propylene-ethylene random copolymer used in Examples 6 to 8.
The results are also listed in Table 2.

Comparative Example 2 The same procedure as Comparative Example 1 was carried out except that the resin was replaced with the propylene-ethylene random copolymer used in Examples 6 to 8.

The results are also listed in Table 2. Examples 10 to 15 80 parts by weight of propylene-ethylene random copolymer (ethylene content 5.6 molar strip, melt index 0.5), 10 parts by weight of low density polyethylene (trade name Mirason M-50. Mitsui Polychemicals fl) Using a composition of 10 parts by weight of ethylene-propylene rubber (ethylene content 82 moles, melt index 2.5), the resin temperature was set at 19%.
The temperature was 0℃, 210℃, and 230℃, and the holding time was 6 hours each.
The same procedure as in Example 1 was performed except that the times were 0 seconds and 120 seconds.

The results are shown in Table 3.

Comparative Examples 3 to 5 The same procedures as Examples 10 to 15 were carried out except that the holding time was 0.5 seconds.

The results are also listed in Table 3.

Example 16, Comparative Example 6 The resin was made of high density polyethylene (melt index: 19
0°C) 0.15, density 0.960 g/cd),
The same procedure as in Example 3 and Comparative Example 1 was conducted except that the temperature of the molten resin during extrusion was 190°C.

The results are shown in Table 4.

Example 17, Comparative Example 7 The resin was made of low density polyethylene (melt index: 19
0°C) 1.9, density 0.920 g/c4) and the temperature of the molten resin during extrusion was 160°C.
, in the same manner as in Comparative Example 1.

The results are shown in Table 4.

Claims (1)

[Claims] 1. In a method for producing a polyolefin hollow body, after melting a polyolefin and extruding a parison from a goohead, the temperature of the parison is maintained at a temperature higher than the melting point of the polyolefin for at least 5 seconds, and then A method for producing a polyolefin hollow body with improved appearance, characterized in that the hollow body is obtained by injecting a pressurized fluid into the parison. 2 Polyolefin melt index (ASTM-
D-1238-65T) 0.1 to 2 of the polyolefin. 3 Polyolefin melt resin temperature is 190 to 23
Claim 1 characterized in that the temperature is in the range of 0°C.
Manufacturing method described in section. 4. The manufacturing method according to claim 1, wherein the extruded parison is held between molds. 5. The manufacturing method according to claim 1, wherein the holding time is at least 20 seconds or more.