JP2573656B2 - Extrusion foam molding of thermoplastic resin - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an extrusion foam molding method for producing a foam molded article of a styrene resin such as polystyrene paper (PSP) or synthetic wood.

(Prior art)

Using an extruder, a thermoplastic resin containing a foaming agent plasticized and melted by a screw is extruded to a low pressure range from a die connected to a resin passage in the extruder to produce synthetic wood and PSP. .

In this extrusion foam molding method, a gear pump is attached to the resin passage of the extruder and the die as shown in FIG. 1 in order to increase the extrusion pressure without increasing the resin temperature so as to improve the mixing between the foaming agent and the molten resin. (JP-B-48-42460, JP-A-62-268622, JP-A-58-268622).
−63431). If necessary, a static mixer may be arranged in series between the gear pump and the die (Japanese Patent Laid-Open No. 58-63).
431).

The structure of this type of extrusion device is the structure shown in FIG. In the figure, 1 is an extruder, 2 is a gear pump, 3 is a static mixer, 4 is a die (circular die shown), 5 is an extruded cylindrical sheet, 6 is a popper for supplying resin particles, 7
Is a screw, 8 is a foaming agent supply pipe, and 9 is a resin passage.

The resin particles supplied from the hopper are melt-plasticized by an extruder, mixed with a volatile expanding agent supplied from a foaming agent supply pipe provided in the middle of the extruder, and further pressurized by a gear pump through a resin passage. , Through a static mixer and die to atmospheric pressure and form a foam.

The extrusion pressure of the resin is reduced to, for example, 30 by increasing the pressure of the gear pump.
It is rapidly increased and 200~300kg / cm ² G from ~100kg / cm ² G. After the extrusion pressure is reduced by 20 to 35% in the static mixer (screen), the pressure is released from the die into the atmosphere (0 kg / cm ² G).

When the foaming agent is a thermal decomposition type foaming agent, it is contained in the resin particles and supplied from the hopper, so that the foaming agent supply pipe 8 is unnecessary.

The gears 10, 10 'of this type of gear pump 2 were of the spur type as shown in FIGS.

The extruder equipped with this gear pump is mainly used for forming non-foamed yarn and sheet, and is also used for forming polyolefin resin sheet such as polypropylene, high-density polyethylene and linear linear polyethylene, and for manufacturing polyamide yarn. ing.

[Problems to be solved by the present invention]

The present inventors have attempted to increase the discharge capacity by adding a gear pump to a device for producing a polystyrene extruded foam sheet. In the production of a foamed sheet, unless the resin temperature at the die outlet is set to 165 ° C. or lower, the cells of the foamed sheet do not become closed cells, resulting in a decrease in sheet strength. It has been confirmed that the use of a gear pump makes it possible to lower the resin pressure in the extruder, to suppress the resin temperature in the extruder, and to increase the discharge rate as a result.

However, when the gear pump gear is a spur gear,
There is a problem that the thickness distribution of the foam sheet obtained is large. That is, it is considered that the cause is that the fluctuation width of the resin discharge amount per unit time in the extrusion direction is large. Furthermore, the resulting foamed sheet also had remarkable results in variations in bending strength, appearance, and the like.

As a result of the inventor's intensive study of this problem,
At the position of the point A shown in FIG. 3 (a), the resin pressure intermittently and rapidly drops locally, and the foaming agent in the molten resin is partially vaporized and the flow of the molten resin is stopped. It is considered to be due to the fluctuation.

In the present invention, conventionally, when a spur gear pump is attached, the fluctuation of the discharge amount is large, and the fluctuation width of the thickness distribution of the obtained foam sheet is increased by using a helical gear. An object of the present invention is to obtain a desired purpose by reducing the deflection width of the thickness distribution.

The reason is that by using a helical gear, the intermittent gas release of the resin pressure at the position of point A shown in FIG. 3A becomes continuous, thereby evaporating the foaming agent in the molten resin. It is considered that this is because it is possible to prevent

[Specific means to solve the problem]

In the present invention, instead of a spur gear pump,
A helical gear pump having two or more spiral (helical) gears is used. The effect of using this helical gear pump is that the weight average molecular weight of the thermoplastic resin (▲ ▼)
Is particularly remarkable when a high molecular weight polystyrene of 2.5 × 10 ^{5 to} 3.7 × 10 ⁵ is used.

That is, the present invention provides a resin passage between an extruder and a die,
Using a resin extrusion molding device equipped with a helical gear pump, a styrene resin containing a foaming agent plasticized and melted by a screw is stirred by a helical gear pump, and then extruded from a die to a lower pressure range than the pressure in the resin passage to foam. The present invention provides an extrusion foam molding method for a thermoplastic resin, characterized in that the method comprises the steps of:

The helical gear pump 2 'shown in FIG. 2 is used. In the figure, 9 is a resin introduction passage, 10, 1
0 'is a spiral gear, 11 is a drive shaft, and 12 is a bearing.

Number average molecular weight (▲ ▼) for styrene resin
1.8 × 10 ^{5 to} 3.7 × 10 ⁵ , number average molecular weight (▲ ▼) 6.
0 × 10 ^{4 to} 1.2 × 10 ⁵ polystyrene, styrene / butadiene / styrene block copolymer, styrene / butadiene / styrene block copolymer, styrene / butadiene
Styrene copolymer, styrene / acrylonitrile copolymer, styrene / methyl methacrylate copolymer, styrene / α-methylstyrene copolymer, styrene / α-methylstyrene / acrylonitrile copolymer, alone or in combination of two or more Used in combination.

A part (50% by weight or less) of the styrene resin is converted to a metal salt of a polyphenylene ether, an ethylene / vinyl acetate copolymer, or an ethylene / methacrylic acid copolymer (Zn ⁺⁺ , K ⁺ , Na).
⁺ , Li ⁺ , Al ⁺⁺⁺ ), ethylene / propylene copolymer rubber or the like.

The resin generally has a melt viscosity of 5,000 to 20,000 poise, the extrusion pressure of the resin is 30 to 100 kg / cm ² , and the outlet pressure of the helical gear pump is generally 150 to 300 kg / cm ² . The angle of the meshing gear of the helical gear is 5 to 20 degrees.

Examples of the foaming agent include volatile swelling agents such as butane, heptane, pentane, dichlorodifluoromethane, trichloromonofluoromethane, dichlorodifluoroethane, and methyl chloride;
A pyrolytic foaming agent such as azodicarbonic amide is used.

The amount used for 100 parts by weight of the styrene resin is 2 to 15 parts by weight for the volatile expanding agent and 1 to 5 parts by weight for the pyrolytic foaming agent. To obtain a highly foamed sheet, a volatile expanding agent is preferred.

In addition to the resin and the foaming agent, the nucleating agent is 0.1 to 3% by weight,
0.1 to 3% by weight of pigment and 0.05 to 1% by weight of higher fatty acid may be used. The nucleating agent helps to uniformly adjust the cell diameter of the foam, and includes talc, magnesium carbonate, perlite, calcium silicate, calcium carbonate,
Inorganic nucleating agents such as silicon oxide, baryta and vermiculite, and organic acids such as citric acid, tartaric acid, boric acid and oxalic acid are used. Examples of metal salts of higher fatty acids include higher fatty acids having 12 to 22 carbon atoms, for example, metal salts (Ca, Na, K, Li, Zn, Al) such as capric acid, stearic acid, and palmitic acid. Particularly, zinc stearate, aluminum stearate and calcium stearate are preferred.

The metal salt of the higher fatty acid improves the processability when extruding the sheet and also improves the flexibility of the foam sheet. By using this helical gear pump, it is possible to foam even at a discharge rate higher by 5 to 20% without increasing the resin temperature than when a gear pump is not attached, and the obtained sheet has small wall thickness fluctuation and bending strength. Also, there was no problem in the appearance and the like.

In the following, an example in which a helical gear is used as a gear pump in the configuration of FIG. 1, an example in which a spur gear is used as a gear pump, and a comparative example-2 in which a gear pump is not used as Comparative Example-1. The effects of the present invention will be described.

(Examples, etc.)

As the extruder, an extruder having a built-in two-stage screw with a screw 65 mmφ and L / D33 with a dal image was used.

As the gear pump, in the embodiment, a helical gear pump shown in FIG. 2 (14 teeth of gear, spiral angle of helical gear 7 degrees, capacity 10.2 cm ³ / vev) is used.
In Comparative Example 1, a gear pump having a spur gear shown in FIG. 3 (30 gear teeth, capacity 50 cm ³ / rev) was used. In Comparative Example 2, extrusion molding of a polystyrene foam sheet was performed without using a gear pump.

As the die, a circular yoke having a diameter of 75 mmφ was used.

The following high molecular weight polystyrene (a) and low molecular weight polystyrene (b) were used as the resin.

(B) High molecular weight polystyrene ▲ ▼ 3.5 × 10 ⁵ ▲ ▼ 1.0 × 10 ⁵ (b) Low molecular weight polystyrene ▲ ▼ 2.4 × 10 ⁵ ▲ 7.2 × 10 ⁴ Supply polystyrene particles from the hopper of the extruder,
Extruder compression zone temperature C ₁ 220 ℃, C ₂ 220 ℃, C ₃ 150
℃, C ₄ 150 ℃, the die temperature is set to 150 ℃, butane is supplied from the blowing agent supply nozzle provided in the middle of the extruder (C ₃ parts) so that it becomes 3% by weight of polystyrene, and the wall thickness is 2mm Of polystyrene paper (expansion ratio 10 times) was manufactured.

The temperature control works effectively and a closed-cell polystyrene paper is obtained. The extrusion amount and the thickness variation in the extrusion direction when the resin temperature at the die outlet reaches 160 ° C. are as shown in Table 1 below ( See also FIG. 4).

It is understood that the addition of the helical gear pump can increase the discharge rate by 17.9% in the case of high molecular weight polystyrene as compared with the case where the gear pump is not attached, thereby improving the productivity.

In the case of low molecular weight polystyrene, the rate of increase in discharge rate is about 8.2%.

FIG. 4 shows the results of examining the thickness variation in the extrusion direction at intervals of 15 seconds when a high molecular weight polystyrene was used and when a gear pump was not used.

A helical gear pump was installed (Example) in comparison with the fluctuation width of the discharge amount when no gear pump was installed (Comparative Example 2) or when a spur gear pump was installed (Comparative Example 1).
It can be understood that the fluctuation width of the ejection amount at the time of performing is small.

〔effect〕

By attaching the helical gear pump to a conventional foam extruder, (1) the discharge rate can be increased and the productivity of the foam sheet can be improved.

(2) Since the variation width of the discharge amount in the extrusion direction is small, the thickness variation width of the obtained foam sheet is also small.

There are advantages.

[Brief description of the drawings]

1 is a plan view of a resin extrusion molding apparatus, FIG. 2 is a perspective view of a helical gear pump with a part cut away, FIG. 3A is a plan view of a gear pump having a spur gear, and FIG. FIG. 4 is a side view of a gear pump provided with (a spur gear tooth is omitted in the drawing), and FIG. 4 is a diagram showing a change in wall thickness in the extrusion direction of a polystyrene foam sheet.

Claims (2)

(57) [Claims] A styrene resin containing a foaming agent plasticized and melted by a screw is stirred by a helical gear pump using a resin extrusion molding apparatus having a helical gear pump disposed in a resin passage between an extruder and a die. A method for extruding and foaming a thermoplastic resin, wherein the resin is extruded from a die to a pressure lower than the pressure in the resin passage and foamed. 2. The number average molecular weight of a styrene resin (▲
▼) is 6.0 × 10 ^{4 to} 1.2 × 10 ⁵ , weight average molecular weight (▲
2. The extrusion foam molding method according to claim 1, wherein (▼) is from 1.8 × 10 ^{5 to} 3.7 × 10 ⁵ .