JPH0732460A - Manufacture of blow-molded item - Google Patents

Abstract

PURPOSE:To provide a manufacture of a blow-molded item with good adhesiveness in the pinched-off part by preventing the inner surface of parison from being degraded by oxidation. CONSTITUTION:The method is characterized in that the cylindrical parison pushed out of an extruder 3 is introduced into the cavity of a mold 2, and upon pushing out the tip end of the cylindrical parison by a predetermined length from the extruder, the tip end of the parison is pinched-off and air is blown into the inside of the parison in order to blow the parison, wherein the parison is pushed out and at the same time inert gas is circulated in the inside of the parison, and after the tip end of the parison is pinched off, the parison is blown by inert gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a blow-molded article, and more particularly to a method for producing a blow-molded article which prevents oxidative deterioration of the inner surface of a parison and has good adhesion at the pinch-off portion.

[0002]

2. Description of the Related Art Conventionally, fuel tanks of automobiles are made of metal such as steel plate, but recently, the purpose of reducing the weight of automobiles and improving the space utilization factor is to use them. So, plastic fuel tanks have come into use. In addition, plastic tubes are being used for automobile heaters, tubes for connecting radiators, etc., and tubes and pipes for general-purpose air conditioners.

In applications such as those for automobiles,
Since heat resistance, heat resistance strength characteristics, impact resistance, gasoline barrier properties, etc. are required, for example, a multilayer structure of polyolefin and polyamide has been used. In such a case, it is usual to use polyolefin as the innermost layer in consideration of the adhesiveness of the pinch-off portion.

However, in the case of manufacturing the above-mentioned multilayer structure by blow molding, it is necessary to mold at a molding temperature of a material having a high melting point (polyamide), which causes the material having a low melting point (polyolefin) to undergo oxidative deterioration, There is a problem that the adhesiveness of the pinch-off portion is significantly reduced, and cracks and the like are likely to occur from that portion.

The above-mentioned problems are not limited to the case of a multilayer blow-molded article, but a single-layer blow-molded article of a polyolefin composition that needs to be molded at a high molding temperature (for example, a polyolefin and another heat-resistant resin). It also occurs in the case of a single layer blow-molded product of a composition or a composition containing glass fiber or the like.

Therefore, it is an object of the present invention to provide a method for producing a blow-molded article which prevents oxidative deterioration of the inner surface of the parison and has good adhesion at the pinch-off portion.

[0007]

As a result of earnest research in view of the above object, the inventors of the present invention, when producing a blow-molded product, pass an inert gas inside a cylindrical parison and According to the present invention, the inventors have found that the blow molding is performed without causing oxidative deterioration on the inner surface of the parison, and that the pinched-off portion has good adhesiveness.

That is, in the method for producing a blow-molded article of the present invention, the cylindrical parison extruded from the extruder is introduced into the cavity of the mold, and the tip of the cylindrical parison has a length longer than that required by the extruder. Just pushed out,
Pinch off the tip of the parison and blow the parison by blowing air into the parison, in which the parison is pushed out and an inert gas is circulated inside the parison, and the tip of the parison is pinched off. After that, the parison is blown with the inert gas.

The present invention will be described in detail below. [1] Blow-Molded Article As a blow-molded article to which the method of the present invention can be applied, it is preferable that at least the innermost surface of the blow-molded article is formed of polyolefin or a composition containing this as a main component. As such a blow-molded product, a single-layer structure product of polyolefin (or a composition containing it as a main component) or a multi-layer structure product of polyolefin and another resin (however, the innermost layer is polyolefin) is preferable. As the other resin, polyamide, polycarbonate, polyester (polyethylene terephthalate, polybutylene terephthalate, etc.), a blend of polyphenylene oxide and polystyrene, or the like can be used. In particular, a multilayer structure product of polyamide and polyolefin is preferable.

As the above-mentioned polyolefin, ethylene,
Propylene, butene-1, hexene-1, 4-methylpentene
-1, etc. homopolymers of α-olefins, copolymers of ethylene and propylene or other α-olefins, or copolymers of two or more of these α-olefins, or homopolymers thereof, It is possible to use a copolymer or a blend of a homopolymer and a copolymer. Moreover, the thing which modified | denatured the said polyolefin with unsaturated carboxylic acid or its anhydride can also be used. Of these, high density polyethylene and polypropylene are particularly preferable.

The above-mentioned high-density polyethylene is 0.93 to 0.97 g /
cm ³ density, 0.1-1.0 g / 10 min, especially 0.1-0.5 g /
10-minute melt index (MI, 190 ° C, 2.16kg load) and 1.0-20g / 10min, especially 3-10g / 10min high-load melt index (HLMI, 190 ° C, 21.6kg)
Those having a load) are preferable.

As the polyamide, hexamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4- or 2,4,4, -trimethylhexamethylenediamine, 1,3- or 1,4-bis ( Aminomethyl) cyclohexane, bis (p-aminocyclohexylmethane),
Aliphatic, alicyclic or aromatic diamines such as m- or p-xylylenediamine and aliphatic or alicyclic diamines such as adipic acid, suberic acid, sebacic acid, cyclohexanedicarboxylic acid, terephthalic acid and isophthalic acid Polyamides produced with aromatic or aromatic dicarboxylic acids, polyamides produced from aminocarboxylic acids such as 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, ε-caprolactam, ω-dodecalactam Polyamides made from lactams such as, and copolyamides consisting of these components, or mixtures of these polyamides. Specifically, nylon 6
(Polyamide 6), Nylon 66 (Polyamide 66), Nylon 610, Nylon 9, Nylon 6/66, Nylon 66 /
610, nylon 6/11, nylon 6/12, nylon 12,
Examples thereof include nylon 46 and amorphous nylon. Of these, nylon 6 and nylon 66 are preferable in terms of good rigidity and heat resistance.

Although the molecular weight is not particularly limited, a polyamide having a relative viscosity η _r (measured in JIS K6810, 98% sulfuric acid) of 0.5 or more is usually used, and among them, those having a relative viscosity of 2.0 or more are excellent in mechanical strength. Is preferred.

Further, in order to improve heat resistance and mechanical strength, glass fibers can be added to the above resin component. The glass fiber is not particularly limited, and chopped strands, rovings and the like can be used. The fiber diameter is preferably about 5 to 30 μm. Further, those subjected to a surface treatment in consideration of the adhesiveness with the resin serving as the matrix are preferable.

In the present invention, each of the above resins includes
For the purpose of its modification, other fillers, heat stabilizers, light stabilizers, flame retardants, plasticizers, antistatic agents, release agents, foaming agents, nucleating agents, and other additives can be added as appropriate. .

[2] Manufacturing Method Next, a method for manufacturing the blow-molded article of the present invention will be described.

FIG. 1 is a schematic diagram showing an example of an apparatus to which the method of the present invention can be applied. The blow-molded product manufacturing apparatus 1 of FIG. 1 includes a mold 2 having a cylindrical cavity 21 (broken line in the figure), an extruder 3, and a die 4 connected to an upper end opening 22 of the mold 2. The die 4 has a gas blowing nozzle (not shown) slightly protruding from the center of the die 4, and the gas blowing nozzle is connected to a blow gas supply device 5. Connected to a source (not shown). A pinch-off mechanism 6 is connected to the lower end opening 23 of the mold 2.

Blow molding is carried out as follows using such an apparatus. First, the resin component is melted and extruded into a cylindrical shape from the die 4. As the extruder 3, an ordinary accumulator type, screw type or the like can be used. The melting temperature of the resin is appropriately set depending on the type of resin used. For example, in the case of a multilayer structure product of polyamide and high-density polyethylene (high-density polyethylene is the inner layer), 200 to 280 ℃, especially 230 to 270 ℃ Is preferred. When high density polyethylene is melt extruded at the above temperature, oxidative deterioration usually occurs. However, according to the method of the present invention as described later, oxidative deterioration does not occur on the inner surface of the parison.

A cylindrical parison is pushed out and an inert gas is jetted from a gas blowing nozzle so as to flow inside the parison. N ₂ gas is generally used as the inert gas. By circulating the inert gas in the parison in this manner, the oxygen concentration in the parison is set to about 10% or less, preferably about 5% or less. If the oxygen concentration exceeds 10%, it becomes difficult to prevent oxidative deterioration.

Subsequently, the cylindrical parison is lowered from the upper end opening 22 of the mold 2. Then, where the tip of the cylindrical parison protrudes from the lower end opening 23 by the required amount,
The tip is pinched off by the pinch-off mechanism 6. In addition,
The pinch-off may be performed by sandwiching the molds 2 and 2'as illustrated in FIG.

Then, the parison is blown up by ejecting an inert gas from the gas blowing nozzle at a pressure of ² to 10 kg / cm ² , and then the mold 2 is opened and the molded product is taken out to obtain a blow molded product. Obtainable.

In the blow-molded article obtained by the method of the present invention, the innermost layer of the polyolefin is kept in the inert gas atmosphere from the time of extrusion to the time of blow-up. However, oxidative deterioration does not occur, and therefore the pinch-off portion has good adhesiveness.

[0023]

In the present invention, when a blow-molded product is manufactured, an inert gas is circulated inside the cylindrical parison, and the blow-molding is performed by this inert gas. It does not occur and the adhesion of the pinch-off part is good. Although the reason why such an effect is obtained is not necessarily clear, it is presumed that the polyolefin produces a low molecular weight component when it is oxidized and deteriorated, and that the low molecular weight component causes poor adhesion. Therefore, it is considered that the adhesion of the pinch-off portion is good because the oxidation deterioration is prevented by circulating the inert gas inside the parison so that the oxygen concentration is 10% or less.

[0024]

The present invention will be described in more detail by the following examples. The following resin components were used as the raw material resin components in the examples and comparative examples. [1] High density polyethylene HDPE-1: [Density 0.95 g / cm ³ , HLMI (190 ° C,
21.6 kg load) 4 g / 10 minutes)] HDPE-2: [density 0.95 g / cm ³ , MI (190 ° C, 2.16)
kg load) 0.1 g / 10 minutes)]

Examples 1 and 2 and Comparative Examples 1 and 2 High-density polyethylene (HDPE-1 or HDPE-2) was extruded and blow-molded (manufactured by BEKUM, BAE1 type) and a mold shown in FIG. The resin temperature shown in Table 1 and N ₂ or air is used as a blow gas, and the blow gas temperature is 20 ° C.
Blow molding was performed with the bottle shown in Fig. 3 (length 200 mm,
An average wall thickness of about 1 mm and a volume of 1 liter) was produced.

The adhesiveness of the pinch-off portion (31 in FIG. 3) of the pipe thus obtained was evaluated. The results are also shown in Table 1.

Table 1 Example 1 Example 2 Comparative Example 1 Comparative Example 2 Types of resin components HDPE-1 HDPE-2 HDPE-1 HDPE-2 Resin temperature (° C) 270 250 270 250 Blow gas N ₂ N ₂ Air Air Adhesiveness ⁽¹⁾ Good Good Bad Bad

(1) Adhesiveness: The pinch-off part (31 in FIG. 3) of the blow-molded product was observed, and the one which was not peeled was good
Those peeled were evaluated as defective.

As is clear from Table 1, the bottles of Examples 1 and 2 produced by the method of the present invention had good adhesion at the pinch-off portion. In addition, when the inner surface of the bottle of each Example and Comparative Example was analyzed by infrared spectroscopy, no abnormality was found in the components in each Example, but Comparative Example 1
In 2 and 2, the presence of a low molecular weight component having a carbonyl group was confirmed. It is speculated that the low molecular weight component having this carbonyl group is caused by oxidative deterioration. In the case of a high-density polyethylene single-layer product, the resin temperature of the high-density polyethylene is usually 180 to 210 ° C., but in the present embodiment, it is assumed that the product is a multilayer structure product with polyamide. Molded at higher temperatures (250 ° C and 270 ° C).

[0030]

As described above in detail, in the present invention,
Inert gas is circulated inside the cylindrical parison, and blow molding is performed with this inert gas, so there is no oxidative deterioration on the inner surface of the parison and blow molding with good adhesion at the pinch-off part. You can get the goods.

The blow-molded product produced by the method of the present invention is suitable for connecting tubes such as containers, automobile heaters, radiators, etc., or tubes and pipes for general-purpose air conditioners.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a blow molding apparatus to which the method of the present invention can be applied.

FIG. 2 is a schematic view showing an example of a mold that can be used in the method of the present invention.

FIG. 3 is a schematic view showing a bottle manufactured by the method of the present invention.

[Explanation of symbols]

 1 ... Blow molding device 2 ... Mold 3 ... Extruder 4 ... Die 5 ... Blow gas supply device 6 ... Pinch off mechanism 21 ... Cavity 22 ... Upper end opening 23・ ・ ・ Bottom opening 30 ・ ・ ・ Bottle 31 ・ ・ ・ Pinch off

Claims (1)

[Claims] 1. A cylindrical parison extruded from an extruder is introduced into a cavity of a mold, and when the tip of the cylindrical parison is extruded from the extruder by a required length, the tip of the parison is extruded. In a method for manufacturing a blow-molded article in which the parison is blown by blowing air into the parison, the inert gas is circulated inside the parison while pushing the parison, and the tip of the parison is A method for producing a blow-molded article, which comprises blowing the parison with the inert gas after pinching off.