JPH0735060B2 - Injection molding method for foamed resin moldings - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an injection molding method for a foamed resin molded product, and more specifically to a nozzle of one of a plurality of cavities of a mold in which a molten resin measured in advance is measured. 80% to 95% of the required amount is filled in the cavity that opens to
By filling in one cavity as well,
The present invention relates to an injection molding method for a foamed resin molded product that can suppress the occurrence of product unevenness.

[Prior Art] The conventional method for molding a resin molded product is to use one mold having a plurality of cavities even if one mold is attached to each molding machine and even if a plurality of molded products are simultaneously molded. However, a sufficient amount of resin to fill the cavity is filled with the resin material in the cavity that coincides with the outer shape of the molded product of these molds at a time and under high pressure.

[Problems to be Solved by the Invention] In the above-described conventional molding method, a resin material for filling a cavity of a mold or a plurality of cavities of the mold with a high pressure is used. Since they are all filled at the same time, the amount of resin filled for each operation or for each cavity is not uniform, which results in remarkable unevenness in the quality of the molded product, especially in terms of weight. There was a problem. Moreover, since a high pressure is used to simultaneously fill the mold cavity with a sufficient amount of resin at the same time, a local mold opening phenomenon occurs in the mold, which causes uneven quality of the molded product. there were. In addition, when filling multiple cavities of the mold with resin synchronously,
There was remarkable product unevenness due to this variation in the resin filling amount.

The present invention has been proposed in consideration of such points as a whole, and a uniform amount of resin material is filled in each of a plurality of cavities of a mold to make a uniform foamed resin molding with a small variation in product weight. The object is to provide a method for molding a product.

[Means for Solving the Problems] In order to achieve this object, an injection molding method for a foamed resin molded article according to the present invention is a method in which a synthetic resin charged in a cylinder is rotated by a screw incorporated in the cylinder and rotated. In the injection molding method of a foamed resin molded product that is injected into the mold by forward and backward movement, the total capacity of the mold cavity is set to 80
After pooling the foamable molten resin weighed to be equivalent to ~ 95% in the chamber, the resin flowing out from the cylinder head is connected to each cavity of the mold, and among the multiple nozzles that branch, 80-95% of the required amount of resin in the cavity is injected from one nozzle that is opened, then the injection pressure is reduced and the nozzle is closed, and then the other nozzle is opened. In the same manner as described above, there is an injection molding method for a foamed resin molded product in which the cavity is filled with resin and the process is repeated sequentially.

[Function] A foamable molten resin, which has been weighed in advance so as to correspond to 80 to 95% of the capacity of the mold cavity, is pooled in a chamber, and this resin is passed from the cylinder head to a plurality of molds through roads and nozzles. When supplying to each cavity of the mold, by opening only one nozzle among the nozzles connected to each cavity of the mold to regulate the injection amount and sequentially inject the resin into each cavity of the mold, The injection amount can be accurately and substantially made uniform, and all the molten resin pooled in the chamber can be distributed and filled into individual cavities of the mold.

[Examples] Next, the injection molding method of the foamed resin molded product according to the present invention will be specifically described with reference to the drawings.

FIG. 1 is a schematic vertical sectional view of an injection molding apparatus used in the method of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG.

The injection molding apparatus 1 used in the method of the present invention comprises an injection molding machine groove 2 and a mold assembly 3 connected to the front of the mechanism 2.
It consists of The injection molding machine groove 2 has a cylindrical shape in which a hopper 4 for charging a thermoplastic resin is attached to the center of the injection molding machine groove 2 near the rear end, and a cylinder 5 provided with a heating device (not shown) is arranged around the hopper 4. The cylinder 5 has a built-in screw 8 which is rotated by a driving device 6 composed of, for example, a motor and a speed reducer, and is further moved forward and backward in the cylinder 5 by the operation of a hydraulic cylinder 7 arranged in the rear part of the cylinder 5. ing. A chamber 9 for temporarily storing the molten foaming resin is formed in a cylinder head portion located on the front side of the cylinder 5, and is pooled in the chamber 9 by rotating the screw 8 forward. A predetermined amount of molten resin is injected from the cylinder head.

The amount of resin pooled in the chamber 9 is measured in advance from the total volume of a plurality of cavities of the mold, and the backward stop position of the tip of the screw 8 is determined accordingly, and the resin injection speed is Determined by moving speed.

Next, the fixed side platen 10 is arranged so as to be connected to the mold assembly section 3 and the cylinder head section.
A manifold hold 13 having a plurality of resin guide paths 11 and nozzles 12 therein is assembled in a face-to-face manner. Furthermore, the mold piece 15a of the mold 15 is fixed to the front surface of the manifold hold 13,
Align the nozzle 12 of the manifold hold 13 with the spool 14 of the mold piece 15a. On the other hand, the movable platen 25 to which the mold piece 15b on the other side is fixed is moved to the mold piece 15a side by a hydraulic device or the like, and by a pair of mold pieces 15a and 15b that are in contact with each other, a plurality of pieces that match the outer shape of the molded product are provided therebetween. Mold with cavity 26
15 are assembled.

Further, a needle valve 16 is fitted into each of the nozzles 12 provided in the manifold hold 13, and the needle valve 16 is moved forward and backward by the operation of a nozzle opening / closing cylinder 17 installed at the rear end of the needle valve. This opens and closes the nozzle 12. The positions of the plurality of nozzles 12 are, for example, two positions at the top and bottom as shown in the figure, or one at the center and four at the top, bottom, left and right, for a total of five positions,
The arrangement position can be appropriately selected.

A hydraulic cylinder 7 for moving the screw 8 forward and backward and a needle valve 16 for opening and closing a nozzle for moving the nozzle forward and backward.
The hydraulic circuits 19, 20 and 20 connected to the hydraulic circuits 17 are respectively arranged in the 17, and each hydraulic circuit is connected to each hydraulic tank (not shown). This hollow circuit type has a control valve 21, which changes the direction of oil flow with a solenoid valve.
22 and 22 are provided, and the injection molding work mainly operates on the control panel 23 directly connected thereto.

When operating the molding apparatus 1, first, the control panel 23
Using a computer incorporated in, data such as the injection resin amount, the backward stop position of the screw 8 and the forward / backward moving speed of the screw 8 are input in advance, and the program stored in the computer is started. At this time, the control board 22 controls the forward / backward movement and stop of the needle valve 16 and the screw 8 attached to the nozzle opening / closing cylinder 17 and the hydraulic cylinder 7.

Next, the injection molding method according to the present invention will be described step by step.

(A) When a thermoplastic resin mixed with a foaming agent is supplied to the hopper 4, a predetermined amount of the molten resin is pooled in the chamber 9 in an unfoamed state by the rotation and forward movement of the screw 8.

In this case, the amount of resin pooled is 80 to 95% of the total volume of the multiple cavities of the mold, that is, 80% of the required amount of resin in the cavities.
Approximately 95%, the amount is measured by the resin amount detection sensor, incorporated into the control panel 23, and input to the computer.

That is, as shown in FIG. 3, the foaming agent mixed resin pooled in the chamber 9 is, for example, four cavities A, B,
It is the total amount of resin charged into C and D, but it is 80 to 95% of the total volume of the four cavities. this is,
This is because the molten resin foams in each cavity in the present invention, and the normal expansion ratio is about 1.2 to 1.5.

If the amount of injected resin is less than 80% of the total volume of the cavity (required amount of resin), the cavity cannot be sufficiently filled with the resin, and voids or sink marks are generated in the molded product. On the other hand, if the amount of injected resin exceeds 95% of the total volume of the cavity (required resin amount), the density of the molded product will increase and it will not be possible to obtain a molded product with the expected expansion ratio, and the mold will open. The resin leaks from the gap to cause burrs. Therefore, it is important to pool the foamable molten resin corresponding to 80 to 95% of the total volume of the cavity in the chamber in advance.

In this process, the nozzle 12 of the manifold 13 controls the control valves 21 and 22 to adjust the oil flowing in the hydraulic circuits 19 and 19 and is closed by the needle valve 16 which is in the forward state.

(B) Of the plurality of nozzles 12 of the manihold 13 that have moved forward and are in the closed state, the first needle valve 16 is retracted, one of the nozzles 12 is opened, and the screw 8 that has stopped rotating is The resin is injected into one of the cavities 26 of the mold 15 by advancing to a predetermined speed and position which are input in advance. The injection pressure of this folding resin is 100 to 140 kg / cm ² , and the injection amount is about 80 to 95% of the amount of resin required to fill the mold cavity, preferably
It is controlled in the range of 90-93%.

(C) Subsequently, the control valve 21 is controlled, and the hydraulic circuit is
The speed of the oil flowing through 19 is adjusted so that the forward speed of the screw 8 is smaller than that in the step (B). The injection pressure in this case is 1/5 to 1/10 of the injection pressure in the previous step (B).

(D) At the same time, the control valve 22 is switched to move the first needle valve 16 forward to close the nozzle 12, thereby foam-molding in the cavity.

(E) Subsequently, the second needle valve 16 is retracted to open the other nozzle 12.

(F) The steps (B) to (D) are repeated to inject the resin into the second cavity 26 of the mold. Here, the relationship between the injection pressure and the time in the steps (A) to (F) described above is shown in the model diagram of FIG.

(G) After the mold has cooled, the movable platen to which the mold piece 15b on the other side is attached is moved to open the mold, and the molded product is released from the mold.

In the present invention, the steps (C) and (D) may be activated. The manifold hold 13 is always heated to a constant temperature by a heater (not shown) like the cylinder 5, so that the molten resin does not cool and solidify in the guide passage 11 or the nozzle 12.

The thermoplastic resin used in the present invention is selected from polyethylene, polypropylene, polystyrene, ABS resin, modified polyphenylene oxide, grafted polyphenylene ether, polyamide, polycarbonate, etc., and is in the present invention. Is directed to the production of foam molding using the above resins.

The blowing agent used here is a combination of sodium bicarbonate and an organic acid salt, an organic compound having an N-nitroso group, a diazo group, and a hydrazo group, such as azo. J. Carbon amide,
Examples include dinitrosopentamethylenetetramine, P, P'-oxy-bis (benzenesulfonyl) hydrazide and the like. The amount of the foaming agent added to the resin is 0.1 to 1% by weight,
It is preferably 0.3 to 0.6% by weight.

Next, the results of examining the weight variation surface on the product between the injection molding method according to the present invention and the conventional injection molding method will be disclosed.

Example 1 As shown in FIG. 1, a molding machine equipped with a mold assembly having two cavities in a mold having a mold clamping force of 1,000 tons was used. J. A modified polyphenylene oxide having a specific gravity of 1.1 containing 0.5% by weight of carbon amide is charged and pressure-fed in the screw without being foamed and pooled in a chain bar. The temperature of the cylinder is
The resin set at 280 ° C. and pooled in the chamber is an amount corresponding to about 90% of the total volume of the two cavities.

Then, only the first cavity is opened, and 90% of the volume of this cavity is filled with resin at an injection pressure of 12 Ok.
After filling with g / cm ² , the injection pressure was reduced to ²⁰ kg / cm ² and the nozzle was closed at the same time, subsequently the nozzle of the second cavity was opened and the resin was similarly injected and molded. The foamed resin molded product obtained had a foaming ratio of about 1.34. The results relating to the weight of the 30 molded articles thus obtained are shown in Table 1.

As a comparative example, the same molding machine and material as in Example 1 were used, two nozzles were opened, and the injection pressure was 120 kg / cm.
^{At 2 the} resin was injection molded into the first and second cavities simultaneously. The results relating to the weight of the 30 molded articles thus obtained are shown in Table 1.

Example 2 As shown in FIG. 1, a molding machine equipped with a mold assembly having four cavities in a mold having a mold clamping force of 1,000 tons was used at the tip. J. An acrylonitrile-butadiene-styrene resin containing 0.5% by weight of carbon amide was added and pressure-fed in the screw without being foamed and pooled in the chamber.

In this case, the temperature of the cylinder is set to 200 ° C. and the amount of resin pooled in the chamber is approximately 90% of the volume of the four cavities.

Then, under the same conditions as in Example 1, each cavity was filled with a resin corresponding to 90% of the cavity volume and molded.

As a comparative example, all four cavities were opened and the molten resin pooled in the chamber was injection molded at one time. The results regarding the weight of the 30 molded articles obtained are shown in Table 2.

From the above results, it can be seen that the method of the present invention reduces variations in product weight in each cavity and variations in product weight between cavities, and makes it possible to obtain a homogeneous product.

[Effects] As described above, according to the method of the present invention, the foamable molten resin, which has been measured in advance so as to correspond to 80 to 95% of the total volume of the cavity of the mold, is pooled in the chamber, and the resin is filled in each cavity. 80% to 95% of the cavity volume is sequentially injected into the mold, and the resin can be injected into each cavity of the mold under the same conditions. This has the effect of making it possible to obtain uniform products by reducing variations in product weight between cavities as well as variations.

[Brief description of drawings]

1 is a schematic vertical sectional view of an injection molding apparatus for carrying out the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is a diagram showing a chamber in which a foaming agent mixed resin is pooled, FIG. 4 is a model diagram showing the relationship between injection pressure and time in steps (A) to (F) of the present invention. 1 …… Injection molding device 2 …… Injection molding mechanism section 3 …… Mold assembly section 5 …… Cylinder 8 …… Screw 9 …… Chamber 11 …… Resin guide 12 …… Nozzle 13 …… Many hold 15 …… Mold 15a, 15b …… Mold piece 16 …… Needle valve 26 …… Cavity

Claims (1)

[Claims] 1. An injection molding method for a foamed resin molded article, wherein a synthetic resin charged in a cylinder is injected into the mold by rotation and forward / backward movement of a screw incorporated in the cylinder. After pooling foamable molten resin equivalent to 80 to 95% of the total volume of the cavity in the chamber, the resin flowing out of the cylinder head is continuously dispersed in each cavity of the mold. Of the plurality of nozzles, only one of the nozzles, which is opened, injects the resin in an amount equivalent to 80 to 95% of the required amount of resin in the cavity, and then lowers the injection pressure and closes the nozzle,
Then, one nozzle is further opened to fill the resin in the cavities in the same manner as described above, and this is repeated in sequence to fill the resin in all the cavities. .