JPS6230132A - Pellet for expansion molding - Google Patents

Abstract

PURPOSE:Pellets for expansion molding, obtained by adjusting the apparent specific volume of synthetic resin pellets containing a foaming agent to the same or almost the same apparent specific volume of expanded resin prepared by expanding the pellets. CONSTITUTION:Pellets for expansion molding obtained by previously applying synthetic resin powder, containing no foaming agent and having a high softening point to a mold 4 by slush molding, melting the powder to set a skin material 5, setting a reinforcing material 7 with a gap 6 for forming an expansion layer above the skin material 5, filling synthetic resin pellets 3, particularly vinyl chloride resin, containing a foaming agent and having almost the same apparent specific volume as that of the expanded resin prepared by melt expanding the pellets 3 in an amount calculated for filling in the cavity of the mold 4 from the specific volume value of the apparent specific volume in the mold 4 and heating the pellets 3 to a temperature at which the skin material 5 and reinforcing material are not melted but the pellets 3 are melt expanded to form the expansion layer 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to pellets for foam molding used in foam molding of synthetic resins.

(Prior Art) Conventionally, as a manufacturing method for synthetic resin molded parts that require cushioning properties, such as pads for automobile instrument panels, a skin material that will become the skin is first set in an insert molding mold. Next, there is a method in which a reinforcing material is set on top of the reinforcing material with a predetermined gap, and finally, a foamable urethane resin is injected and foamed between the reinforcing materials.

The foamable urethane resin has a high expansion ratio, and since it is liquid and can be injected into the mold, it has good fluidity in the mold. Therefore, when foamable urethane resin is foamed in a mold, the foamed urethane resin flows between the skin material and the reinforcing material, bonding them together, and as a result,
The solidified foamed urethane resin layer becomes a component of an excellent molded part.

However, at present, foamable urethane resin is a relatively expensive raw material resin. Therefore, attempts have been made to obtain molded parts by a method similar to the above method using a resin having a lower order than the same resin as a raw material resin. For example, an attempt is made to use expandable vinyl chloride resin in place of expandable urethane resin.

(Problems to be Solved by the Invention) However, there is no convenient solvent for vinyl chloride resin that can cause the resin to flow and cause foaming, and the resin cannot be used as a solution resin.

Therefore, as shown in FIG. 9, a gap 25 in which a foamed resin layer is to be formed is provided between the skin material 22 set in the cavity of the insert mold 21 and the reinforcing material 24 set thereon. There is no choice but to adopt a method of supplying cylindrical vinyl chloride resin pellets 23 containing a foaming agent into the gap 25 to cause foaming.

However, when a sufficient amount of vinyl chloride resin pellets 23 are placed in the gap 25 to fill the gap during foaming, the entire gap 25 becomes chlorinated as shown in FIG. There is a problem that the foamed layer 26 of vinyl resin does not fill the area. This is because the foamed vinyl chloride resin melt does not have good fluidity, and therefore does not rise to the upper part of the gap 25.

In particular, a complex skin material 22 is formed by a so-called slush molding method in which powder such as vinyl chloride resin is melted and adhered to the cavity of a complex insert molding die 21, and then a reinforcing material 24 having a relatively simple shape is formed. When inserting into the mold 21 and creating a gap 25 with a considerable distance between the skin material 22 and the reinforcing material 24, the high-density vinyl chloride resin may rise to the bottom surface of the reinforcing material 24. do not have.

An object of the present invention is to provide a pellet for foam molding which foams to fill a predetermined cavity even when pellets are put into a mold and foamed.

Structure of the Invention (Means for Solving Problems) The present invention provides synthetic resin pellets 1 to 1 containing a blowing agent, the apparent specific volume of which is a foamed resin obtained by melting and foaming the pellets. The purpose is to solve the above-mentioned problems by creating pellets for foam molding that have the same or almost the same apparent specific volume.

Note that the apparent specific volume of a synthetic resin pellet here means the volume of the pellet including the space created between the pellets per unit weight, and the specific volume of a foamed resin pellet means the volume of the pellets including the spaces created between the pellets per unit weight. It means the volume of foamed resin including.

(Function) Since the apparent specific volume of the synthetic resin pellet containing the foaming agent is the same or almost the same as the apparent specific volume of the foamed resin obtained by melting and foaming the same pellet, it is possible to The foamed layer obtained by foaming the pellets occupies the same volume in the cavity as the space occupied by the pellets before foaming.

(Example) Next, a first example in which the present invention is embodied in pellets of vinyl chloride resin will be described based on FIGS. 1 to 6.

A commercially available vinyl chloride resin to which a blowing agent has been added is melt-extruded as a strand (not shown) through a die 1 having an opening 2 shown in FIG. 1 at a temperature low enough to prevent the blowing agent from foaming, and then rapidly cooled. The strands were cut to produce pellets 3 having a star-shaped cross section as shown in FIG.

This pellet 3 was placed in a container with a constant volume in a normal state without being compressed, and the volume and weight of the pellet were measured, and the apparent specific volume was determined to be approximately 3 crn3/gr.

This pellet 3 was placed in a heatable container and foamed at a higher temperature than the temperature at which the strand was manufactured to produce a foam molded test piece. Then, when the apparent specific volume was measured, it was almost the same as the apparent specific volume of the pellet.

From this value of apparent specific volume, mold 4 as shown in Fig.
Calculate the amount of pellets 3 that should be filled into the cavity of
As shown in FIG. 4, pellets 3 were filled into the cavity. In addition, in FIG. 4, only the pellets 1 to 3 are drawn in a perspective view to show the state in which the pellets 3 are filled into the mold 4.

In addition, a vinyl chloride resin powder that does not contain a blowing agent and has a high softening temperature (in this example, it can withstand 150'C) is placed in the cavity of the mold 4 by so-called slush molding, and then melted. By doing so, the skin material 5 having a substantially constant thickness is set in the cavity.
Moreover, above it, glass fiber filled AS (acrylic nitrile styrene) is inserted through the gap 6 where the foam layer is to be formed.
A reinforcing material 7 made of resin was set.

Then, using a heater, the skin material 5 and reinforcing material 7 are heated to a temperature (15
The pellet 3 was heated at 0'C) to melt and foam. Then, the space occupied by the pellets 3 is occupied by the foamed layer 8 formed by melting and foaming, and as a result, the foamed layer 8 from the pellets 3 has a skin material 5 and a reinforcing material 7 as shown in FIG. The gap 6 between them was completely filled.

Therefore, it has become possible to obtain a foam layer 8 that can fill the gap 6 between the skin material 5 and the reinforcing material 7, regardless of its size.

As a result, when determining the shape of the reinforcing material 7, there is no need to consider the shape of the mold, and the shape can be freely designed.

Moreover, the molded parts made from the pellets 3 according to the present invention were comparable in properties to the molded parts made of conventional urethane resin as a foam layer.

Next, a second embodiment in which the cross-sectional shape of the pellet is changed to another shape will be described based on the W-piece in FIG. 6.

Similarly to the first embodiment, the cross section as shown in FIG.
Pellets 3 of vinyl chloride resin having a letter shape were produced. In producing the pellets 3, a hollow torpedo tube was used to extrude vinyl chloride resin while blowing air from the tip, thereby producing pellets 3 with a hollow cross section.

As a result of attempting foam molding using the pellets 3 in the same manner as in the first example, the volume of the foam layer 8 slightly decreased. A product similar to one example was obtained.

As described above, the present invention is designed to reduce the apparent specific volume of the foamable synthetic resin pellet 3 so that the foamed resin can easily spread to every corner of the cavity. This is an excellent invention in which the apparent specific volume is the same or almost the same as that of the resin. The configuration of the present invention is not limited to the above-mentioned embodiments, and can be implemented, for example, in the following manner.

(1) The present invention can be applied to any resin that cannot be injected and foamed in a molding die in a solution or molten state while containing a foaming agent.

(2) The foaming agent may be contained in the pellets 3,
It may be attached to or coated on the surface of the pellet 3. In the former case, it is necessary to prevent the foaming agent from foaming entirely.

(3) The cross-sectional shape of the pellet 3 is selected to be, for example, a diagonal shape, an S-shape, etc., as shown in FIGS. 7 and 8, within a limit that does not significantly impair the effects of the present invention.

(4) The pellets 3 of the present invention can be applied to any foam molding method in which the resin pellets 3 are simply put into a mold and heated and foamed, but preferably, the method of the first embodiment is applicable. It is better to apply this method to foam molding that uses a mold with a complex cavity. In particular, the gap 2 between the skin material 5 set in advance to have a certain thickness in the cavity and the reinforcing material 7 set above the cavity.
Even if it is adapted to a molding method that forms a foam layer 8 on 5,
The pellets 3 of the present invention are melted and foamed to form a foam layer 8 that fills the entire gap 25 and has the effect of adhering the two.

Effect of the invention A3 of the present invention exhibits the following excellent effects.

Even if the resin has poor melt flowability, if pellets from the resin are placed in a mold and heated, they will occupy the same volume in the mold cavity as the pellets occupied in the cavity and foam. and fills the cavity in the same way as a highly fluid resin. Therefore, regardless of the size of the cavity, the foam layer can be formed to fill the entire cavity.

[Brief explanation of the drawing]

Fig. 1 is a partial front view showing the vicinity of the opening of the die used to manufacture the pellets of the first embodiment, Fig. 2 is a perspective view of the pellets of the first embodiment, and Fig. 3 is a cross section of the mold. Figure 4 is a cross-sectional view showing the mold filled with pellets, Figure 5 is a cross-sectional view showing the completed foam molding, Figure 6 is a perspective view of the pellets of the second embodiment, and Figure 7 is a cross-sectional view showing the pellets filled in the mold. The figure is a front view of another pellet, Figure 8 is a front view of yet another pellet, Figure 9 is a sectional view showing a conventional pellet packed into a foam mold, and Figure 10 is a front view of a conventional pellet. It is a sectional view showing the point where foam molding is completed after use. pellet 3゜

Claims (1)

[Claims] 1. A synthetic resin pellet containing a blowing agent,
A pellet for foam molding, characterized in that its apparent specific volume is the same or almost the same as the apparent specific volume of a foamed resin obtained by melting and foaming the pellet. 2. A pellet for foam molding according to claim 1, wherein the synthetic resin is a vinyl chloride resin.