JPH0193317A - Injection molding method - Google Patents

Abstract

PURPOSE:To beautifully finish the appearance of a molded product and shorten the cycle time by coating a foamed material with a coating agent to make a double structure and kneading and dispersing a foaming agent for which required temperature and required retaining time to generate foaming action with molten resin. CONSTITUTION:A foamed material 17 is constituted with a coating agent 16 to make a double structure in a manner to be mixed with molten resin 13 without foaming reaction occurring in a heating cylinder 2 during plasticizing the resin, not foamed at the molten resin temperature of a section of fast cooling speed in a mold after being injected into the mold and foamed at the molten resin temperature of the slow cooling speed, and a foaming agent 14 for which required temperature and required retaining time are adjusted is kneaded and dispersed with the molten resin. The same is injected in this state into the mold through a heating cylinder 2, and the difference of foaming reaction is provided by the difference of the cooling speeds of the molten resin in the mold and molded. As the molding can be carried out in the non-foaming state just after filling into a product section in the mold in the process, a product of a thin wall or complicated shape of a projected section can be molded and the cycle time can be shortened because of the localized foaming.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of injection molding using foaming.

[Conventional technology]

Conventional injection molding machines for foam molding include an injection mechanism that melts and injects injection molding materials such as thermoplastic raw materials or thermosetting resins using a heating cylinder equipped with a screw, and a mold that is heated to high pressure. A mold clamping mechanism that tightens with
It consists of a control mechanism that automatically moves these, causing the resin to fall from a hopper into a heating cylinder, and the foaming agent to fall from a separate hopper into the heating cylinder, kneading the foaming agent into the plasticized resin, and moving the screw forward. A molding method in which a foaming agent such as urethane foam or foamed polyethylene is added to the molding material to create a sponge-like plastic molded product. There is also a so-called sandwich molding method, in which a molding material that will become the skin layer is first press-fitted, and then an internal molding material containing a foaming agent is press-fitted, but both have the following drawbacks.

(1) The air pressure during foaming prevents the formation of whiskers in the molding material being cooled, but since the foaming extends to the surface layer, the appearance becomes dirty.

(2) Since the entire product is foamed, it has air insulation properties and the cycle time becomes longer.

(3) Foaming has already occurred at the time of filling (inside the screw), and the effective injection pressure is low, making it difficult to fill thin-walled areas.
Shape is limited.

[Problems to be Solved by the Invention] In view of the above-mentioned circumstances, the present invention provides an injection method that can finish the appearance of molded products neatly, can mold even thin-walled parts and products with complex shapes, and can shorten cycle time. The object of the present invention is to provide a molding method.

[Means for solving problems]

The injection molding method of the present invention for solving the above problems includes:
During the plasticization of the resin, it is mixed in the molten resin without causing a foaming reaction in the heating cylinder, and after being injected into the mold, the molten resin does not foam at the temperature of the part of the mold where the cooling rate is high, and the cooling rate is low. The foam material is coated with a coating agent to form a double structure so that it foams at the temperature of the molten resin in the slow part of the process.
A foaming agent prepared at the required temperature and for a required holding time to cause a foaming reaction is mixed and dispersed in the molten resin, and is injected into the mold through the heating cylinder, and the molten resin is mixed in the mold. The feature is that molding is performed by giving different foaming reactions due to differences in cooling rates.

[For production]

Although the resin melts inside the screw in the heating cylinder, the reaction temperature of the blowing agent has not been reached, so the blowing agent is mixed in the molten resin. The temperature of the molten resin rises further during the process of being injected into the mold through the heating cylinder, exceeding the reaction temperature of the blowing agent, but since the time until it is injected into the mold is short, The foaming agent does not foam.

In the process of cooling and solidifying the molten resin injected into the mold through the heating cylinder, the molten resin near the mold surface (the resin layer outside the molded product) is rapidly cooled, and therefore the molten resin near the mold surface The foamed resin solidifies in the foaming agent mixed therein. As a result, a molded product can be obtained that has a clean surface, that is, a molded product appearance, and has no decrease in strength. On the other hand, the molten resin inside the mold (resin layer inside the molded product) is slowly cooled and the temperature is lowered (in a low state), and the foaming agent in the molten resin has enough time to foam. The temperature will be maintained above the reaction temperature, and the foaming agent will react and foam.

The molten resin in the mold is expanded from the inside by the foaming pressure during this foaming. This expansion makes it possible to prevent the occurrence of "sink marks" caused by contraction of the resin when it is cooled.

〔Example〕

Hereinafter, an injection molding method as an embodiment of the present invention will be explained with reference to the drawings. As shown in FIGS. 1 to 3, an injection molding machine suitable for carrying out the present invention is equipped with Heating cylinder 2, nozzle 3, fixed plate 4, fixed mold 5, movable mold 6, sprue 7, heater 8, runner 9
, a gate 10, a cavity 11, and other known elements constitute a molding machine main body.

The molding machine main body includes a cooling blower air passage 12 for blowing air into the heating cylinder 2 and absorbing the shear heat generated in the cylinder 2, and a hopper for supplying resin 13 and foaming agent 14 as molding materials. A configuration consisting of 15 is attached.

Further, as the foaming agent 14, the resin 13 melts during plasticization in the heating cylinder 2, but the foaming agent 14 has a boiling point higher than the melting point of the resin 13, which does not cause a foaming reaction. Furthermore, due to the difference in the cooling rate of the molten resin in the cavity 11, foaming does not occur at the resin temperature in the part where the cooling rate is fast (temperature of the rapidly cooled molten resin), and the resin temperature in the part where the cooling rate is slow ( The foaming agent 14 is adjusted to the required temperature and required holding time to cause the foaming reaction so that the foaming agent 14 foams at the temperature of the slowly cooled molten resin.

Specifically, for example, as shown in Figure 2, when heat is applied for a certain period of time and above a certain temperature, that is, the resin is heated at a certain temperature (temperature of the resin in the area where the cooling rate is slow) or above for a certain period of time. The foamed substance 17 is coated with a coating agent 16 made of a plastic material, which is the same material as the molding material but has a higher molecular weight and a melting point higher than that of the molding material, and is solidified into granules. 14 (for example, azodicarboxylic acid amide or sodium bicarbonate).

Next, the injection molding operation in this example will be explained. First, after clamping the fixed mold 5 and the movable mold 6, the resin 13 and the coated foaming agent 14 are sent from the hopper 15, cross-dispersed by the rotation of the screw 1 in the heating cylinder 2, and melted from the nozzle 3. The resin is injected and the foaming agent 14 coated with the molten resin is mixed in.

That is, in this embodiment, the injection of the molten resin and the supply of the blowing agent are carried out on the same axis, and the coated blowing agent 14 is directly mixed into the molten resin flowing on the same axis (the sprue 7) from the vertical direction.

The molten resin mixed with the coated blowing agent 14 was then press-fitted into the cavity 11, and the molten resin mixed with the coated blowing agent 14 in the cavity 11 was then cooled and solidified according to a conventional general method. rear,
Release the mold.

Next, FIG. 3 shows temperature changes inside the heating cylinder and inside the mold.

In addition, the symbol J in FIG. 3 indicates the melting point of the coating material,
K indicates the melting point of the molding material, and L indicates the boiling point of the blowing agent.

Further, the symbol ■ in FIG. 3 indicates the temperature change area inside the screw 1, the symbol ■ indicates the temperature change area when passing the nozzle 3, the symbol ■ indicates the temperature change area when the sprue 7 passes, and the symbol ■ indicates the temperature change area when passing the nozzle 3. The temperature change area when passing through the launch 9 is shown, the code V shows the temperature change area when passing through the gate 10, and the code ■ shows the temperature change area during the filling of the molded product and the shrinking process.

Furthermore, the solid line ■ shows the temperature change of the molding material near the mold skin, the broken line ■ shows the temperature change at the foaming limit point inside the coating material, and the -dot-dashed line ■ shows the temperature change of the molding material inside the molded product. Shows temperature change.

In the cooling and solidifying step, the melting point of the resin 13 as the molding material is K.
Therefore, resin 13 melts, but coating agent 1
6. Since the foamed material 17 absorbs the shear heat generated by blowing air through the blower air path 3, it does not reach the reaction temperature as in region I. By injecting the kneaded mixture of molten resin and foaming agent into the mold, when it passes through the nozzle 3, the temperature rises as shown in the area ■, and the temperature change when passing through the sprayer is in the area ■, and when it passes through the runner 9, the temperature rises as shown in the area ■. The temperature change is in the region (2), the temperature change when passing through the gate 10 is in the region V, and the temperature change in the product section in the mold and after the product section is filled is in the region (2).

That is, the temperature changes as shown by the solid line (■) in the area close to the mold, and the temperature changes as shown in the dashed line (■) in the annealing section inside the product inside the mold, which causes whiskers. As the limit line of thermal work when the coating agent 16 melts and reacts, the temperature changes as indicated by the broken line (■).Therefore, a foaming reaction occurs at the dashed line (2) above the dashed line (4), and on the other hand,
In the solid line ■ below the broken line ■, no foaming reaction occurs. In other words, the amount of thermal work at the foaming boiling point of 3 or higher is the area APB near the mold skin, which does not result in foaming, and the area APC in one direction, which results in foaming.

In this way, it is possible to mold in a non-foamed state during or immediately after filling the product part in the mold, so it is possible to mold products with complex shapes with thin walls and convex parts, and also to obtain molded products with a beautiful appearance. can.

In addition, as a means to prevent the slow cooling part of the resin from pulling on the rapidly cooling part after gate sealing, the gate 10 is made wider and the injection pressure is increased, which reduces the number of cracks and warps. will also decrease.

Furthermore, since foaming is performed only locally, the cycle time can be significantly shortened compared to normal foaming.

In this embodiment, the molding material 13 and the coated foaming agent 14 are placed separately in the hopper 15, but the foaming agent 14 may be mixed into the molding material 13.

Further, the foamed material 17 may be used alone without being coated.

[Effects of the Invention] As described in detail above, the injection molding method of the present invention can mold in a non-foamed state during or immediately after filling the product part in the mold, so it is possible to mold the product in a non-foamed state. In addition to being able to form a molded product with a beautiful appearance, this method also has the advantage that the cycle time can be significantly shortened compared to normal foaming because it foams only locally.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view showing an injection molding machine suitable for carrying out an injection molding method as an embodiment of the present invention, Fig. 2 is a sectional view showing a blowing agent, and Fig. 3 is a schematic sectional view showing the inside of the heating cylinder and the injection molding machine. FIG. 3 is a relationship diagram showing temperature changes within the mold. DESCRIPTION OF SYMBOLS 1... Screw, 2... Heating cylinder, 3... Nozzle, 4... Fixed plate, 5... Fixed mold, 6... Movable mold, 7... Sprue, 8... ...Heater, 9...Runner, 10...Gate, 11...Cavity, 12
... Blower air passage, 13 ... Resin, 14 ... Foaming agent, 15 ... Hopper, 16 ... Coating agent, 1
7... Foamed material, ■... Temperature change area inside the screw, ■... Temperature change area when passing through the nozzle, ■... Temperature change area when passing through the sprue, ■... Temperature change area when passing through the runner. Temperature change area, ■...Temperature change area when passing through the gate, ■
...Temperature change area during molded product filling and shrinkage process,■
...Temperature change in the molding material near the mold skin, ■...Temperature change at the foaming limit inside the coating material, ■.
...Temperature change of the molding material inside the molded product, J...Melting point of the coating material, K...Melting point of the molding material, L...Boiling point of the blowing agent. Procedural amendment September 7, 1986

Claims (1)

[Claims] During the plasticization of the resin, it is mixed in the molten resin without causing a foaming reaction in the heating cylinder, and after being injected into the mold, the molten resin does not foam at the temperature of the part of the mold where the cooling rate is high, and the cooling rate is low. The foam material is coated with a coating agent to form a double structure so that it foams at the temperature of the molten resin in the slow part of the process.
A foaming agent prepared at the required temperature and for a required holding time to cause a foaming reaction is mixed and dispersed in the molten resin, and is injected into the mold through the heating cylinder, and the molten resin is mixed in the mold. An injection molding method characterized in that molding is performed by imparting a difference in foaming reaction due to a difference in cooling rate.