JPH0516255A - Method for producing thermoplastic resin foam molded article - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing a thermoplastic resin foam-molded product, which enables good shape quality of the foam-molded product, particularly filling property of the lower ridge. [Structure] A molding die 1 composed of a female die 2 and a male die 3 is closed to form a cavity-4. Drain valve 12a, 12
b and 12c are opened, the filling gun opening 8 is opened, and compressed air is jetted to fill the cavity 4 with the pre-expanded resin particles A, which is an air-filling step. Next, drain valve 1
2a, 12b, and 12c are closed, the decompression device 13 is operated to discharge the air in the cavity-4, and a vacuum filling step of filling the pre-foamed resin particles A into the cavity-4 is performed to perform heat molding.

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 thermoplastic resin foam-molded article, which has good shape quality of the foam-molded article, and particularly good filling property at the lower ridge.

[0002]

2. Description of the Related Art Conventionally, in a method for producing a thermoplastic resin foam-molded article, as a method for filling pre-expanded resin particles in a cavity, the pre-expanded resin particles are sucked by a suction force generated by jetting compressed air. Air filling method for filling the cavity into the cavity, and a vacuum filling method for filling the cavity by accelerating the suction of the pre-expanded resin particles by reducing the pressure while discharging the air inside the cavity (JP-A-1- No. 127323) is known.

[0003]

Of the above filling methods,
In the air-filling method, compressed air is ejected to perform filling for a preset time.Therefore, the location where the pre-expanded resin particles cannot be completely supplied within the set time due to fluctuations in the pressure of the compressed air, or for some reason Therefore, even if the pre-expanded resin particles are not supplied from the pre-expanded resin particle hopper into the cavity, the supply of the pre-expanded resin particles is stopped at the set time. There is a risk that the foam may not be filled, resulting in defective shape quality of the foam-molded product. Further, if the set time is set longer than necessary in order to prevent such a state, there is a problem that the filling time becomes long and the consumption of compressed air also increases.

On the other hand, in the vacuum filling method, the pre-expanded resin particles are not sufficiently supplied to the lower ridges in the cavity, so that a particularly light weight molded product (foaming ratio 80 2 times or more), the filling property of the lower ridge corner becomes poor, and shrinkage occurs.
As shown in (b), there is a possibility that the lower ridge corner may be missing.

The present invention has been made in view of the above problems, and has an advantage of a vacuum filling method that effectively eliminates the drawbacks of the air-filling method and the vacuum filling method, that is, can shorten the filling time. It is an object of the present invention to provide a method for producing a thermoplastic resin foam-molded article, which maintains the above-mentioned properties as much as possible and also makes the shape quality of the foam-molded article good.

[0006]

In order to achieve the above object, the present invention sufficiently fills the pre-expanded resin particles in the lower ridges in the cavity by air-filling, and then vacuum-fills. By doing so, the entire interior of the cavity is sufficiently filled with the pre-expanded resin particles.

That is, according to the present invention, a molding die composed of a female mold and a male mold is closed, pre-expanded resin particles are filled in the formed cavity, and then the molding die is heated. In a method for producing a foam-molded article, air-filling is performed to fill pre-expanded resin particles in a cavity by jetting compressed air, and then a decompression device is driven to expel air in the cavity-pre-expanded resin. A method for producing a thermoplastic resin foam-molded article, characterized by performing vacuum filling for filling particles into a cavity.

[0008]

The method for producing a thermoplastic resin foam molded article of the present invention will be described in detail with reference to the drawings.

An apparatus used in the method for producing a thermoplastic resin foam-molded article of the present invention is shown in FIG.

In FIG. 1, reference numeral 1 denotes a molding die used in the manufacturing method of the present invention. The molding die 1 is composed of two molds, a female mold 2 and a male mold 3. Is the recess inner wall 4a
And a steam chamber 5a are formed, and the male mold 3 is formed with a lid inner wall 4b and a steam chamber 5b. Then, the female mold 2 and the male mold 3 are matched and closed to form a cavity-4 as a space surrounded by the recess inner wall 4a and the lid inner wall 4b.

A large number of flow holes 6 are formed in the inner wall 4a of the recess and the inner wall 4b of the lid so that steam and air for heating the pre-expanded resin particles A can flow, but the pre-expanded resin particles A cannot pass through. There is.

A filling gun 7 is fitted in the female mold 2, and a filling gun opening 8 is formed in the inner wall 4a of the recess. In addition, from the compressed air supply passage 9, the cylinder 7a of the filling gun 7
Compressed air flows in, and the pre-expanded resin particle hopper
The pre-expanded resin particles A are supplied into the cylinder 7a from the pre-expanded resin particle supply passage 11 from the nozzle 10.

Next, the method for producing the thermoplastic resin foam-molded article of the present invention will be described in the order of steps.

The first step of the present invention is an air-filling step.

First, the drain valves 12a, 12b, 12c are opened, compressed air is jetted from the compressed air supply passage 9 into the cylinder 7a of the filling gun 7, and the pre-expanded resin particles A are spared by the suction force generated by this. Expanded resin particle hopper
10 is sucked into the cylinder 7a of the filling gun 7 through the pre-foaming resin particle supply passage 11 and is supplied into the cavity 4 through the filling gun opening 8.

As described above, the drain valves 12a, 1 below the cavity-4 are provided through the filling gun opening 8 above the cavity-4.
By the flow of compressed air to 2b and 12c, the pre-foamed resin particles A also flow, and the pre-foamed resin particles A are sufficiently filled up to the lower ridge of the cavity-4.

When the filling amount of the pre-expanded resin particles A becomes 5% by weight or more, preferably 10 to 25% by weight of the whole, the jetting of the compressed air is stopped, and at the same time, the drain valves 12a, 12.
Close b and 12c to complete air-filling.

The second step is a vacuum filling step.

When the air-filling in the first step is completed, the depressurizing device 13 is operated to discharge the air in the steam chambers 5a, 5b and the cavity-4. At this time, the flow rates of the air supplied by the filling gun 7 and the gas discharged by the decompression device 13 are set equal to each other, so that the steam chambers 5a and 5b.
Further, the pre-expanded resin particles A are continuously filled in the cavity 4 while the air pressure in the cavity 4 is maintained near atmospheric pressure.

When the filling is almost completed, it becomes difficult for the air to freely flow in the cavity-4, while the pressure reducing device 13 is used.
Due to this, the air in the steam chambers 5a, 5b is forcibly discharged continuously, so that the steam chambers 5a, 5b are discharged.
The inside is gradually depressurized.

Here, by detecting the degree of pressure reduction in the steam chambers 5a, 5b by the pressure detector 14, the degree of filling of the pre-expanded resin particles A in the cavity 4 can be determined. Therefore, when the predetermined degree of pressure reduction is reached, if the operation of the pressure reducing device 13 and the filling gun 7 is stopped and the vacuum filling is completed, the filling amount of the pre-expanded resin particles A in the cavity-4 is set to the predetermined amount. You can

It is to be noted that the time until the predetermined pressure reduction degree is set is set in advance in a timer, and if the predetermined pressure reduction degree is not reached even after the time has elapsed, an alarm is issued. In other words, if the pre-expanded resin particle A is not supplied from the pre-expanded resin particle hopper 10 for some reason, an alarm is issued and an abnormality in the filling of the pre-expanded resin particle A can be detected. There is no danger of producing defective molded products.

After that, the open valve 15 is opened to return the inside of the cavity 4 and the steam chambers 5a and 5b to the atmospheric pressure. Then, the compressed air is ejected from the compressed air supply passage 9,
The pre-expanded resin particles A remaining in the cylinder 7a are returned to the pre-expanded resin particle hopper 10 (so-called blowback), the piston 7b of the filling gun 7 is advanced and the filling gun opening 8 is closed, and all filling is performed. The process is completed.

The predetermined degree of pressure reduction is generally -0.01.
~ -0.80 kg / cm ² G, preferably -0.10
-0.30 kg / cm ² G.

The pre-expanded resin particles filled in the cavity 4 can be molded by a method similar to the molding method generally used in the method for manufacturing a thermoplastic resin foam molded article of this type. .

As the pre-expanded resin particles A used in the production method of the present invention, polystyrene expanded particles are preferable, but metal of polypropylene, polyethylene, ethylene / vinyl acetate copolymer, ethylene / (meth) acrylic acid copolymer. It can also be applied to expanded particles of thermoplastic resin such as salt, α-methylstyrene / styrene / acrylonitrile copolymer, styrene-grafted polyethylene copolymer, styrene-grafted polypropylene and cross-linked resins thereof. Furthermore, pre-expanded particles obtained from a composition obtained by blending ethylene / propylene copolymer rubber or polyisoprene rubber with these resins or mixtures may be used. The pre-foamed resin particles may or may not be crosslinked. The pre-expanded particles have a bulk density of 5 to 100 g /
1, preferably 10-65 g / l, particle size 0.5-2
The thickness is 0 mm, preferably 2 to 8 mm.

Next, a case where a molded product is actually manufactured by the method for manufacturing a thermoplastic resin foam-molded product of the present invention will be given and described in more detail.

(Example 1) In order to fill the pre-expanded resin particles in the cavity-4, air-filling was first performed for 6 seconds, and then vacuum filling was performed for 48 seconds. As the pre-expanded resin particles, polystyrene pre-expanded particles JP-200 (85 times foamed product) manufactured by Mitsubishi Petrochemical Badisher Co., Ltd. was used. The predetermined degree of pressure reduction was set to -0.20 kg / cm ² G, and when this was reached, the pressure reduction device 13 was stopped, the open valve 15 was opened, and the pressure inside the cavity-4 was returned to atmospheric pressure. Thereafter, compressed air is ejected from the compressed air supply passage 9 to return the pre-expanded resin particles A remaining in the cylinder 7a to the pre-expanded resin particle hopper-10, and the piston 7b of the filling gun 7 is advanced to open the filling gun. 8 closed. Next, steam was supplied to the steam chambers 5a and 5b to heat the pre-expanded resin particles A to 115 ° C., which was held for 40 seconds, and then cooled to take out the molded product. The obtained molded product has a size of 1830 × 925 × 420 mm,
The evaluation result of shape quality is

[Table 1] As shown in.

[0029]

[Table 1]

(Example 2) In order to fill the pre-expanded resin particles into the cavity-4, air-filling was first performed for 15 seconds, and then vacuum filling was performed for 40 seconds. Other conditions were the same as in (Example 1), and a molded product was manufactured.

Comparative Example 1 In order to fill the pre-expanded resin particles in the cavity-4, only vacuum filling was carried out for 52 seconds. Other conditions were the same as in (Example 1), and a molded product was manufactured.

(Comparative Example 2) In order to fill the pre-expanded resin particles in the cavity-4, vacuum filling was first performed for 10 seconds, and then air-filling was performed for 45 seconds. Other conditions were the same as in (Example 1), and a molded product was manufactured.

[0033]

As shown in Table 1, according to the method for producing a thermoplastic resin foam-molded product of the present invention, the filling time at the lower ridge portion was made good while maintaining the filling time almost the same as in the case of vacuum filling. A molded product could be manufactured.

Incidentally,

The weight ratio in each filling method in Table 1 is calculated by measuring the filling speed in each filling method in advance.

[0035]

EFFECTS OF THE INVENTION According to the method for producing a thermoplastic resin foam-molded product of the present invention, it is possible to obtain a molded product in which the filling time of the lower ridge is good while maintaining the filling time almost the same as in the vacuum filling. It can be manufactured.

Further, since the filling of the pre-expanded resin particles is completed when the inside of the cavity reaches a predetermined degree of reduced pressure, a defective molded product with insufficient filling is not produced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a molding die and a piping system used in a method for producing a thermoplastic resin foam-molded article of the present invention.

FIG. 2 is an external perspective view of a foam-molded article, in which (a) shows a good shape quality and (b) shows a bad shape.

[Explanation of symbols]

1 Mold for molding 2 female 3 male type 4 cavities 4a Inner wall of recess 4b lid inner wall 5a Steam chamber 5b steam chamber 7 Filling gun 9 Compressed air supply path 10 Pre-expanded resin particle hopper 11 Pre-expanded resin particle supply path 13 Pressure reducing device 14 Pressure detector a Pre-expanded resin particles

Claims (3)

[Claims] 1. A molding die comprising a female die and a male die is closed, pre-expanded resin particles are filled in the formed cavity, and the molding die is heated to obtain a foamed molded article. In the method for producing, pre-expanded resin particles are filled with air by blasting compressed air into the cavity, and then the decompressor is driven to discharge the air in the cavity to form pre-expanded resin particles into the cavity. A method for producing a thermoplastic resin foam-molded article, which comprises performing vacuum filling for filling the inside. 2. A depressurized state in the cavity caused by the filling of the pre-expanded resin particles is detected, and the filling of the pre-expanded resin particles is completed when a predetermined degree of reduced pressure is reached. The method for producing a thermoplastic resin foam-molded article according to claim 1. 3. A safety measure is provided to interrupt the molding process due to insufficient filling of the pre-expanded resin particles when the predetermined degree of pressure reduction is not reached within the set time. Method for producing thermoplastic resin foam molded article.