JPS58134720A - Preparation of formed product of foaming resin - Google Patents

Abstract

PURPOSE:To obtain a formed product of a foaming resin having a skin layer free from gas marks by such an arrangement wherein after a product is formed by protrusion filling up process, one side of the product is caused to generate foams by heating it, and a skin layer is formed on the other side of the product. CONSTITUTION:A resin added with a foaming agent is mixed and plasticized by heating it at a temperature lower than the decomposition starting temperature of the foaming agent and it is protruded and filled up in a cavity 6 of a metal mold. Next, one side 6d of the cavity is heated higher than the decomposition starting temperature of the foaming agent and the resin within the cavity 6 is cuased to generate foams from the mold surface 6d and metal molds 4, 5 are caused to open by such a stroke corresponding to the amount of foams to be generated. By this, a foaming resin formed product having a foamed layer at the side facing to the mold surface 6d and a skin layer on the surface of resin contacting with the other side of the mold is obtained. The surface of the foamed layer is melted by heating the mold surface 6d which formed the foamed layer again and a foaming resin formed product having skin layer all over its surface can be obtained.

Description

Detailed Description of the Invention The present invention relates to a foamed resin molded product having a foam layer on one side and a skin layer on the other surface, and a foamed resin molded product whose entire surface is surrounded by a skin layer and has a foam layer inside. This relates to a manufacturing method.

Conventionally, in an injection molding machine, a molten thermoplastic resin containing a blowing agent is injected into a mold at high speed, and the part of the mold in contact with the mold surface is cooled and hardened to form a skin layer. A known method is to open a mold by a certain width to foam the resin inside to obtain a foamed resin molded product whose entire surface is surrounded by a skin layer. According to this method, the foaming rate can be determined to a predetermined size depending on the opening stroke (width) of the mold, and a molded product with a high foaming rate can be obtained relatively easily. However, in this conventional method, the resin generates heat during injection, and the resin is injected and filled into the mold at a temperature higher than the decomposition starting temperature of the foaming agent.
Foaming starts before the part in contact with the mold surface inside the mold is cooled and hardened and a skin layer is formed on the surface,
There was a drawback that gas marks (swirl marks) appeared on the surface of the molded product, making it impossible to obtain a molded product with a good surface.

The present invention provides a manufacturing method capable of forming a highly smooth skin layer without generating gas traces on the surface and obtaining a good foamed resin molded product.

By the way, in the manufacturing method of this type of foamed resin molded product, in order to ensure that the surface is smooth and that no gas traces occur, it is necessary to: ■ not generate gas until the injection is completed; and ■ do not generate gas during injection and when forming the skin of the molded product. There are several ways to prevent this from occurring, such as ■ Preventing gas from scattering from the resin during injection, ■ Correcting and smoothing any unevenness or gas traces that have occurred within the mold, ■ Smoothing the surface after molding. You can see the heat.

The method of the present invention is based on method (2) above, and after injection and filling, one side of the resin thi'i□ is heated to foam from one side, and a long layer is formed on the other side to create a smooth surface without gas traces. This makes it possible to obtain a good foamed resin molded product having a surface.

That is, the first method of the present invention is to plasticize and knead a resin to which a blowing agent has been added using an injection device at a temperature higher than the melting temperature of the resin and lower than the decomposition start humidity of the blowing agent, and then inject and fill the resin into a mold cavity. After that, one of the two opposing mold surfaces of the mold cavity is heated to a temperature higher than the decomposition temperature of the foaming agent, and the resin in the cavity is foamed from this heated mold surface side, and the metal is heated. By opening the mold by a stroke corresponding to the foaming amount, a foam layer of resin is formed on the heated mold surface side and a skin layer is formed on the surface of the resin that is in contact with the other mold surface in the cavity. This is characterized in that the mold is cooled to cool the molded product in the cavity, and the mold is fully opened to take out the molded product.

Further, in the second method of the present invention, after molding the resin foam layer and skin layer in the cavity by the first method, the mold is once cooled to once cool the resin in the cavity, and then the resin foam layer and skin layer are molded in the cavity. By heating the mold surface on which the foam layer has been formed again and melting the surface of the foam layer in contact with this mold surface to form a skin layer, the surface is surrounded by the skin layer and the foam layer is inside the foam resin molding. This method is characterized in that a product is molded, and then the mold is cooled again to cool the molded product, and the mold is fully opened to take out the molded product.

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

1 is a conventionally known injection device, 2 is a stationary plate provided on the front side of the injection device 1, and 3 is opposite to the stationary plate 2 and is slidable in the axial direction by a plurality of tie rods (not shown). The provided movable plates 4 and 5 are a pair of molds that are removably fitted in the axial direction of the U-shaped molds fixed to the opposite surfaces of the fixed plate 2 and the movable plate 3, respectively, and 6 is a pair of molds that are removably fitted in the axial direction. The cavity formed by mold 4.5 is shown.

The mold 4 on the fixed side is a mold surface 6a of the cavity 6.

Form 6b. The mold 5 on the movable side has a core 5b fixed to the mounting plate 5a, and a mold plate 5C is fitted to the core 5b, so that it can freely slide in the axial direction on the mounting plate 5a by means of guide pins and springs (not shown). The mold surface 6 of cavity B is supported by
Form ce' 6d.

The movable mold 5 is set to a clamping position where the mold plate 5c is in close contact with the fixed mold 4 and the tip of the core 5b has entered the cavity 6 by a mold clamping device and a stroke adjustment device (not shown);
An adjustment position where the core 5b is retreated by a stroke of 8 minutes commensurate with the foaming amount of the foaming agent, which will be described later, while the mold plate 5C remains in close contact with the stationary mold 4 from the mold clamping position, for example, the mold surface 6 at the tip of the core.
The position where d is the same surface as the mold surface 60 inside the mold plate 5C,
The core 5b and the mold plate 5C are able to escape from the stationary mold 4 and change their positions to a mold open position where they are separated. For example, the stroke adjusting device is disclosed in Japanese Patent Publication No. 52-2542.
The apparatus disclosed in Japanese Patent No. 9 or Japanese Patent Publication No. 54-11827 is used.

The core 5b is made of a material with high thermal conductivity such as copper, and a heat medium-1 fluid passage 7 is provided inside the core 5b in a portion close to the mold surface 6d. The buttock plate 5a is provided with an inflow lower a and an outflow lower b for the heating medium fluid, which communicate with the passage.

Oil is generally used as the heat transfer fluid, and the inflow lowers a and 7
A hydraulic circuit including a hydraulic pump 8, a switching valve 9, a heater 10, a cooler 11, check valves 11 and 12, etc. is connected to b.
After the oil discharged from the hydraulic pump 8 is supplied to the heater 10 or the cooler 11 to be heated or cooled by switching the switching valve 9, the oil is supplied to the inflow lower a through the check valve 11 or 12, and the passage 7 is The core 5b is configured to be heated or cooled by allowing the core 5b to pass through and returning to the tank 15 from the outflow lower b. 14 is a relief valve. Although the temperature of the heat transfer fluid varies depending on the mold structure, the heater 10 and The performance of the cooler 11 will be considered.

Next, a case will be described in which a foamed resin molded product is manufactured using the apparatus configured as described above.

First, as shown in FIG.
f ””'lj While the tip of the core 5b of the movable mold 5 of the mold clamp L1 is held in the mold clamping position where it enters the cavity 6, a thermoplastic resin to which a foaming agent has been added is injected by the injection device 1. The mixture is plasticized and kneaded and then injected and filled into the cavity 6. However, during plasticization, kneading, and injection filling of this resin, the temperature of the resin is set higher than the melting temperature Tm of the resin, but the temperature is not set higher than the decomposition start temperature T1 of the blowing agent as in the conventional method, but when the decomposition starts. The temperature is controlled to be lower than the temperature Tl. This control is performed by changing molding conditions such as injection speed and increasing the nozzle diameter of the injection device 1. Further, during this injection filling, the pump 8 is stopped and the supply of heat medium fluid to the passage 7 of the core 5b is stopped. In addition, using a 3-position switching valve,
At the neutral position of the switching valve, the pump discharge oil is returned to the tank,
The supply circuit of the heat medium fluid to the core side may be blocked.

In this way, the resin is foamed by plasticizing and kneading the resin to which a foaming agent has been added at a temperature higher than the melting temperature Tm of the resin and lower than the decomposition start temperature Tl of the foaming agent and injected into the cavity 6. The inside of the cavity 6 is filled without any process.

After that, the pump 8 is driven, the switching valve 9 is switched to the right position in the drawing, and the oil as a heat transfer fluid flows into the inflow lower a through the heater 10 and the check valve 12, and the passage 7 in the core 5b is caused to flow into the inlet lower a. By passing through the tank 15, high-temperature oil is supplied to the passage 7, and the core 5b is heated to a temperature equal to or higher than the optimum temperature 72 for decomposing the blowing agent. Note that the stationary mold 4 is kept at normal humidity without being forcibly heated as in the conventional case. As a result, the resin in the cavity 6 contacts the mold surface 6d of the heated core 5b without foaming at the portions in contact with the mold surfaces 6a, 6b of the stationary mold 4 and the mold surface 6C of the mold plate 5C. It will start foaming from the exposed area.

Next, while foaming the resin, the movable mold 5 is moved back by a stroke of 8 minutes commensurate with the foaming amount of the resin. The movable mold 5 is moved back together with the movable platen 6 using a known stroke adjustment device. Then, as shown in FIG. 2, the mold is opened to a position where the mold surface 6d of the core 5b is flush with the surface 6c of the mold fM5c, and the mold is stopped. In this state, the resin is sufficiently foamed. .

Next, by returning the switching valve 9 to the illustrated position, the oil discharged from the pump 8 is transferred to the cooler 11. It flows into the inflow lower a through the inverse ratio valve 12, passes through the passage 7 in the core 5b, and returns to the tank 15, thereby cooling the fluid 5b. At this time, cooling water or the like is supplied to the stationary mold 4 by a known means to cool it. By cooling the molds 4 and 5 in this way, the resin in the cavity 6 is cooled, and then the movable mold 5 is moved back by well-known means to fully open the molds 4 and 5. Remove the resin, that is, the molded product.

As shown in FIG. 6, the molded product thus formed has a skin layer A on the surface side that was in contact with the mold surfaces 6a, 6b of the stationary mold 4 and the mold surface 6c of the mold plate 5c in the cavity 6.
is formed, and a foam layer B is formed on the surface side of the core 5b that was in contact with the mold surface 6d, resulting in a gummy product. According to this molded product, the surface AI and the side surface (peripheral surface) A2 of the skin layer A are kept at a low temperature from beginning to end by the mold surfaces 6a, 6b, and 6c during the molding process. A smooth surface with no gas traces is formed as it is foamed, and gas traces appear only on the surface of the foam layer B. Therefore, by using the foam layer B on the back side, it can be effectively used for covers, etc.

By the way, in the above process, after the resin is foamed in the cavity 6, the mold is cooled, and the resin in the cavity 6 is once cooled, the molded product (at this time, the structure is shown in FIG. 3) is formed. Before taking out the core 5b, the core 5b is heated again using the method described above to melt the surface of the resin (foamed layer) in contact with the mold surface 6d, and then the mold is cooled again to form the cavity 6.
If the resin (molded product) inside is cooled and taken out, a molded product as shown in FIG. 4 will be obtained. This molded product basically has the same structure as the molded product shown in FIG. 5, but the surface of the foam layer B becomes solid due to reheating by the mold surface 6d, and a skin layer is also formed on this surface. A′ is formed, so
It has a foam layer B only on the inside, and the entire surface is surrounded by skin layers A and A', resulting in a stomach i1:1°, which expands its uses compared to the molded product shown in Figure 6. It will be possible.

Example 1 Polyethylene resin was used as the resin material, and P and T amyl dicoating agents were used as the '1 agent. The melting temperature fil Tm of this resin is 160°C, and the characteristics of the blowing agent (
The decomposition performance) is as shown in FIGS. 5a and 5b. Fifth [i
Ja indicates the relationship between temperature and time.

The temperature rise is 5°C/min. In Figure a, the decomposition initiation temperature TI of this foaming agent is 175°C, and the optimum decomposition temperature T2
It can be seen that the temperature is 220°C. Figure 5 shows the relationship between time and gas amount.

A foamed resin molded article was manufactured using the above material and the method of the present invention. The resin temperature at this time was controlled as shown in FIG. In FIG. 6, line I is the temperature of the resin in the injection device 1, ill is the temperature of the resin injected and filled into the mold cavity 6 on the mold surface 6a side, and line drawing is the temperature of the same resin on the mold surface 6d side. The line layer' indicates the temperature of the resin on the mold surface 6d side when it is reheated.

That is, as is clear from FIG. 6, in the first method, the resin mixed with the blowing agent is plasticized and kneaded using the injection device 1 at a temperature lower than the decomposition start temperature 'l+ (175° C.) of the blowing agent, and then , the mold cavity 6 is injected and filled at a temperature lower than the decomposition start temperature T1 and higher than the melting temperature Tm (160° C.) of the resin, and the temperature on the mold surface 6a side of the fixed mold 4 of the cavity 6 is plotted as a line drawing. As shown in the line drawing, the humidity on the mold surface 6d side of the core 5b is close to 220°C (220°C), which is the optimum humidity for decomposition of the foaming agent, while the decomposition start temperature TI is below TI.
10°C), open the mold by a predetermined stroke, then cool the mold to cool the resin, fully open the mold and take out the molded product, as shown in Figure 6. The following foamed resin molded product was manufactured. As a result, the surface AI of skin layer A
A foamed resin molded product with a smooth surface and no gas traces on either side A2 was obtained.

Example 2 After forming a skin layer and a foam layer in the same manner as in Example 1 using the same resin material and foaming agent as in Example 1 above, and before taking out the molded product from the mold, as shown in FIG. After reheating the core 5b and melting the surface of the foam layer to form the skin layer A' as shown in the line drawing ', the mold is cooled to cool the molded product, and the mold is fully opened to mold. The product was taken out, and a foamed resin molded product shown in FIG. 4 was manufactured. As a result, a foamed resin molded product was obtained which had the foamed layer B only inside, the entire surface was surrounded by the skin layers A and A', and had no gas traces on the entire surface and had a smooth surface.

In Examples 1 and 2 above, if high-speed injection is performed when injecting and filling the resin into the mold cavity, the temperature of the resin will exceed the blowing agent's decomposition start temperature T1 or higher, and furthermore, the optimum decomposition temperature 12 or higher. However, as is clear from FIG. 5, if the heat generation is instantaneous, there is no problem even if the optimum decomposition temperature is 12 or higher.

As described above, according to the present invention, a foamed resin molded product having a foam layer on one side and a skin layer on the other side can be easily manufactured. Moreover, there is no gas trace on the skin layer,
It can be molded onto a smooth surface, resulting in a good molded product. Seventh, the problem of gas traces can be solved by controlling the temperature of the mold, and the thickness of the skin layer and the foam layer can be freely controlled.

In addition, mechanically, there is no need to use a nozzle valve in the injection device, and a foamed resin molded product with a good surface can be obtained by improving only the mold.

Furthermore, according to the second method of the present invention, it is possible to obtain a foamed resin molded product having a foamed layer only inside and a skin layer with a smooth surface without gas traces on the entire surface, which increases its versatility. molded products with high commercial value. Furthermore, this molding can be performed using the same mold as in the first method and in a continuous step with the first method, which can also contribute to improving mass productivity.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of a mold used to carry out the method of the present invention, Fig. 2 is a cross-sectional view of the main part of the mold in a state where the mold is opened by a stroke corresponding to the amount of foaming, and Fig. 3 is a cross-sectional view of the main part of the mold. FIG. 4 is a cross-sectional view of a foamed resin molded product molded by the first method of the present invention, FIG. 5 is a cross-sectional view of a foamed resin molded product molded by the second method, and FIGS. FIG. 6, which is a diagram showing the decomposition performance, is a diagram showing an example of controlling the non-resin humidity by the method of the present invention. 1. 1... Injection device, 2... Fixed plate, 3... Movable plate,
4... Fixed side mold, 5... Movable side mold, 5a...
Mounting plate, 5b... Core, 5C... Template plate, 6... Capity, 7 Heat medium fluid passage, 8... Pump, 9... Switching valve, 10... Heater, 11...・Cooler, 12.1
3...Reverse ratio valve. Patent Applicant Kobe Steel, Ltd. - Elm Figure 1 Figure 2 Figure 3 Figure 41 (Figure 5 Figure 6121)

Claims (1)

[Claims] 1. After plasticizing and kneading the resin to which a blowing agent has been added using an injection device at a temperature higher than the melting temperature of the resin and lower than the decomposition start temperature of the blowing agent, and injecting and filling the resin into a mold cavity,
One of the two opposing mold surfaces of the mold cavity is heated above the decomposition temperature of the foaming agent, and the resin in the cavity is foamed from this heated mold surface side, causing the mold to foam. By opening the stroke corresponding to the amount,
Inside the cavity, a foamed resin layer is molded on the heated mold surface side, and a skin layer is molded on the resin surface that is in contact with the other mold surface, and then the mold is cooled to cool the molded product inside the cavity. 7. A method for manufacturing a foamed resin molded product, characterized in that the mold is fully opened to take out the molded product. 2. After plasticizing and kneading the resin to which the foaming agent has been added using an injection device at a temperature higher than the melting temperature of the resin and lower than the decomposition start temperature of the foaming agent, the resin is injected and filled into the mold cavity.
One of the two opposing mold surfaces of the mold cavity is heated above the decomposition temperature of the foaming agent, and the resin in the cavity is foamed from this heated mold surface side, causing the mold to foam. By opening the stroke corresponding to the layer,
Inside the cavity, a foamed resin layer is molded on the heated mold surface side, and a skin layer is molded on the resin surface that is in contact with the other mold surface.Then, the mold is cooled and the resin in the cavity is cooled once. , heating the mold surface on which the foam layer was formed again;
By melting the surface of the foam layer in contact with the mold surface and molding a skin layer, a foamed resin molded product whose surface is surrounded by the skin layer and has a foam layer inside is molded, and then the mold is replaced again. A method for manufacturing a foamed resin molded article, characterized in that the molded article is cooled and the mold is fully opened to take out the molded article.