JPS61144315A - Manufacture of plastic foam-molded article having different hardness layers - Google Patents

Abstract

PURPOSE:To enable to control easily hardness and a thickness of each of layers of a product to a desired range, by a method wherein after a first foam stock solution has been casted into a mold, a second foam stock solution is made to discharge through high pressure from the upper part of the first foam stock solution. CONSTITUTION:The upper part of a mixing head 7 for casting a first foam stock solution forming a comparatively hard polyurethane foam layer 3 and second foam stock solution becoming of a soft polyurethane foam layer 2 is provided with a hydraulic cylinder and a discharge opening 10 of the foam stock solution on the bottom is opened or closed through a rod 9a of a piston 9 sliding within the hydraulic cylinder. Then the title method is so constituted that the second stock solution is infiltrated into the lower part of the first foam stock solution through discharge pressure of the second stock solution by discharging the second stock solution through high pressure from the upper part of the first foam stock solution casted into a mold. The first and second foam stock solutions are in layers within the mold and a thin and uniform mixture layer is formed on a boundary surface.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a plastic foam molded product having layers of different hardness, a hard layer and a soft layer.
In particular, it relates to a method for producing plastic foam molded articles in which the layers are foam-molded at the same time.

(Prior Art) For example, in cushion pads used for automobile seats, the upper layer that comes into contact with one occupant is formed of flexible plastic foam such as polyurethane foam.
In addition to providing a good feel, it is desirable that the lower layer be formed of a relatively rigid plastic foam to ensure its support.

In such cases, conventionally, the upper layer and the lower layer are separately molded from soft plastic foam and hard plastic foam, respectively, and then bonded together to form a laminate having different hardness.

However, such a manufacturing method not only requires two types of molds, one for the upper layer and the other for the lower layer, but also
There was a problem in that the process was complicated by the adhesion. In addition, in such a case where the upper layer and lower layer are glued together,
Another problem is that the adhesive surface tends to peel off when a horizontal force is applied to the seat cushion due to acceleration, deceleration, direction changes, etc. of the vehicle.

In view of these problems, a method has been proposed in which a layer made of soft plastic foam and a layer made of relatively hard plastic foam are simultaneously foam-molded, as shown in Japanese Patent Application Laid-Open No. 55-98195. There is. In this method, first, a first foaming solution that foams to form a hard plastic foam layer is poured into a mold, and after this first foaming solution foams to some extent, a second foaming solution that becomes a soft plastic foam layer. The second foaming stock solution is injected and the first and second foaming stock solutions are foamed and hardened.

By using such a method, the second foaming stock solution is injected when the first foaming stock solution partially foams and expands inside the mold and its specific gravity becomes small.
The foaming stock solution sinks below the first foaming stock solution to form a layer due to the difference in specific gravity. Therefore, if these first and second foaming stock solutions are foamed and hardened in that state,
It is possible to obtain a single-layer plastic foam molded product of different hardness, in which the lower layer is a soft plastic foam layer and the upper layer is a hard plastic foam layer. When used as a cushion pad for a sheet, the obtained product may be turned upside down.

(Problem to be Solved by the Invention) However, in this way, the first foaming stock solution floats on top of the second foaming stock solution by using the difference in specific gravity between the first foaming stock solution and the second foaming stock solution. In this method, the first foaming stock solution must be foamed and expanded until its specific gravity is reliably lower than that of the second foaming stock solution, and then the second foaming stock solution is injected. According to the publication, the second foaming stock solution is injected when the first foaming stock solution has foamed and expanded to 10% or more of its potential expansion amount.

The time when the foam reaches about 10% of the potential expansion amount is the time when the cell formation of the first foaming stock solution has progressed to a considerable extent. Therefore, if the second foaming stock solution is injected at such a time, the cells in the part of the first foaming stock solution through which the second foaming stock solution passes will be destroyed, and the product formed by the first foaming stock solution will be destroyed. The hard plastic foam layer becomes uneven.

In addition, since the second foaming solution is injected after the first foaming solution has foamed to some extent, it becomes difficult for air mixed in when the second foaming solution is injected to escape, resulting in large air bubbles remaining in the product. If such large air bubbles remain inside the product, cracks are likely to occur at the interface between the cells and the air bubbles, impairing cushioning properties and durability.

Furthermore, since the progress of foaming between the first foaming stock solution and the second foaming stock solution differs significantly, the interface between these becomes uneven, making it difficult to control the thickness, hardness, etc. of each layer of the product. It becomes difficult.

The present invention has been made in view of such problems, and its purpose is to prevent the second foaming solution from forming even when the first foaming stock solution injected into the mold is in a liquid state. The purpose is to enable the stock solution to be injected and to infiltrate below the first foaming stock solution.

Another object of the present invention is to allow the second foaming stock solution to quickly pass through the first foaming stock solution.
The object of the present invention is to reduce the influence exerted on the foaming progress state of a foaming stock solution.

(Means for solving the problem) In order to achieve this object, the present invention discharges a second foaming stock solution under high pressure from above the first foaming stock solution injected into the mold. The discharge pressure causes the second foaming stock solution to infiltrate below the first foaming stock solution.

(Function) In this way, by discharging the second foaming stock solution under high pressure, the second foaming stock solution is able to sneak under the first foaming stock solution without mixing with the first foaming stock solution even if it is in a liquid state. become. The first foaming stock solution and the second foaming stock solution form a layer in the mold, and a thin, uniform mixed layer is formed at the interface between them.

Therefore, if foaming is carried out in this state, the foaming of the first foaming stock solution and the second foaming stock solution will proceed almost simultaneously, and the interface will not be disturbed and the desired hardness and thickness will be achieved. It is possible to obtain a molded product in which plastic foam layers of different hardness are integrally bonded.

(Example) Hereinafter, the present invention will be described in detail based on the drawings.

The figure shows an example in which the method for manufacturing a plastic foam molded product according to the present invention is applied to manufacturing a cushion pad for an automobile seat. FIG. 2 is a vertical cross-sectional view showing the mold used therein and the foaming solution inside the mold at different stages, and FIG. 2 is a perspective view of the mold. Further, FIG. 3 is a circuit diagram showing an example of a foaming stock solution discharging device used in the manufacturing method. Furthermore, FIG. 4 is a cutaway perspective view of a mushroom bud obtained by the manufacturing method.

As is clear from FIG. 4, the target cushion pad l has a center support part 1a that supports the weight of one occupant, and is formed on both sides of the center support part 1a higher than the center support part 1a.
The upper part of the center support part 1a is formed of a soft polyurethane foam layer 2 to softly support the passenger, and the lower part and the side support part 1b are , formed by a relatively rigid polyurethane foam layer 3 to ensure reliable support.

In order to mold such a cushion pad 1, an aluminum alloy mold 4 as shown in FIG. 2 is used. In this mold 4, a lower mold 5 molds the upper surface side of the cushion pad l, and an upper mold 6 molds the lower surface thereof. Therefore, the cushion pad 1 is molded by this mold 4 in an upside-down state.

The mold 4 is heated while being moved inside the kiln by a conveyor or the like. On the moving path, there is a mixing head for injecting into the mold 4 the first foaming stock solution that is foamed once to form a relatively hard polyurethane foam layer, and a mixing head that is foamed to form a relatively hard polyurethane foam layer of 3 degrees. A mixing head for injecting a second foaming stock solution to form layer 2 is provided.

FIG. 3 shows a foaming stock solution discharging device equipped with a mixing head for this purpose. As is clear from this figure, this mixing head 7 has a hydraulic cylinder 8 at the top.
The foaming stock solution discharge port 10 at the lower end is opened and closed by the rod 9a of the piston 9 sliding in the hydraulic cylinder 8, and the hydraulic pressure introduced into the hydraulic cylinder 8 is hydraulic. It is controlled by unit ll. Raw materials are supplied to the lower part of the mixing head 7 from both sides through injection nozzles 121 and 122, respectively. The raw material supplied from one side is a polyol mixture containing a blowing agent, a catalyst, a surfactant, etc. to polyether polyol, which is a lifelong component of the foaming stock solution.
3. It is designed to be pumped from there through an axial plunger pump 141. The raw material supplied from the other side is polyisocyanate, which is the other main component of the foaming stock solution, and is similarly pressure-fed from the second raw material tank 132 via the 7-axis plunger bomb 142. There is. 1. Normally, the piston 9 is pushed down and the discharge port 10 is closed, as shown in FIG.
Each raw material pumped at a pressure of g/cm' is circulated to the raw material tank 13. ．． 132.

When discharging the foaming stock solution, move the piston 9 as shown in the same figure (B).
Raise as shown.

As a result, the discharge port 10 is opened, and the raw materials injected from the injection nozzles 12t and 122 collide under high pressure and are instantaneously stirred. In this way, the foaming stock solution is mixed and formed, and is discharged from the discharge port 10 under the high pressure. The discharge amount is determined by the operating time of the piston 9.

Next, a method for manufacturing a cushion pad 1 having a polyurethane foam index of 2.3 with different hardness using such a mold 4 and a foaming solution discharging device will be described.

First, as shown in FIG. 1(A), the upper mold 6 is opened, and a predetermined amount of the first foam is poured from the first mixing head 71 onto the flat surface 5f of the lower mold 5 at a high position. Inject stock solution 3a. This first foaming stock solution 3a is foamed to form a relatively hard polyurethane foam. The foaming stock solution 3a thus supplied onto the flat surface 5f of the lower mold 5 is
It spreads while flowing down along the inclined surface 5S of the lower mold 5. At this time, since the mold 4 is heated, the foaming system 13a
begins to foam, progressing from a liquid state to a creaming state.

Immediately after discharging the Ml foaming stock solution 3a, the foaming stock solution discharging device of the second mixing head 72 is activated. As a result, the second foaming stock solution 2a is discharged from the rad 72 into the mixing chamber after about 6 seconds. This second foaming stock solution 2a is foamed once to form a flexible polyurethane foam. At the time of discharging the second foaming stock solution 2a, the foaming of the first foaming stock solution 3a has hardly progressed and remains in a liquid state or only partially cleaned. Since the second foaming stock solution 2a is discharged from above at high pressure by the foaming stock solution discharging device as described above, as shown in FIG.
a, and spreads against the surface of the lower mold 5. At this time, the first foaming stock solution 3a is almost in a liquid state, and the second foaming stock solution 2a passes through this in an extremely short time. Almost no traces of the passing of the foaming stock solution 3a remain in the first foaming stock solution 3a, and the air mixed in when the second foaming stock solution 2a is poured becomes bubbles and is transferred to the first foaming stock solution 3a.
Since the air bubbles come out from the top surface of a, the air bubbles will not remain inside.

In this way, the second foaming stock solution 2a becomes the first foaming stock solution 3a.
It infiltrates below and becomes the lower layer. At this time, a thin mixed layer of the first foaming stock solution 3a and the second foaming stock solution 2a is formed on the boundary surface of the foam. The boundary surface becomes smooth and uniform. When the injection of the second foaming stock solution 2a is finished, the upper mold 6 is closed as shown in FIG. 1(C), and one foaming process is allowed to proceed. During this time, by appropriately tilting the mold 4 from the horizontal position, the thickness distribution of the layers of each foaming stock solution 2a, 3a can be adjusted.

If the mold 4 is continued to be heated in this state, the first and second foaming stock solutions 3a and 2a will be cleaned, foamed, and expanded, and the first
The inside of the mold 4 is filled as shown in Figure (D).

During this time, foaming of these foaming stock solutions 2a and 3a proceeds almost simultaneously. Therefore, equal pressure is applied to the boundary surface from both sides, and the boundary surface is not disturbed. Thus, the first and second foaming solutions 3a
, 2a are completely foamed and cured, they become a relatively hard first polyurethane foam layer 3 and a soft second polyurethane foam layer 2, respectively, and these layers 3 and 2 are successively integrated into a laminate. A molded article will be obtained.

When this molded product is removed from the mold 4 and turned upside down, the upper surface of the center support portion 1a is a soft polyurethane foam layer 2, and the surrounding area is a relatively hard polyurethane foam layer, as shown in FIG. 3 cushion pads l can be obtained.

The hardness and thickness of these layers 2 and 3 can be controlled by the raw material blending ratio and amount of the respective foaming stock solutions 2a and 3a. That is, by adjusting the blending ratio of raw materials, the foaming expansion rate and the hardness during natural foaming can be changed. Therefore, if these values are obtained through experiments according to the mixing ratio of each raw material, the theoretical values for the hardness and thickness of each layer 2.3 to be formed can be calculated based on the internal volume of the mold 4, etc. can be determined in advance.

As a result of molding a cushion pad by this method, a desirable cushion pad 1 could be obtained. At this time, the first foaming stock solution 3a and the second foaming stock solution 2a are similar to the usual stock solution for forming polyurethane foam, and the first foaming stock solution 3a contains polyurethane which is harder than the second foaming stock solution 2a. In order to form a foam, we selected a material with a small blending ratio of water and polyisocyanate, or a material with different polyisocyanate components.

Through experiments during this manufacturing process, it was found that the discharge pressure of the second foaming stock solution 2a is desirably 50 kg/crn' or more. If it is lower than 50 kg/arr1'', the first foaming stock solution 3a and the second foaming stock solution 2a are likely to be in a mixed state, causing disturbance in the soft layer 2 and hard layer 3 of the finished product. If the discharge pressure is too high, there is a risk that it will be repelled by the surface of the lower mold 5 during injection and mix, but at a pressure of about 200 kg/crn', such a problem will not occur. Moreover, when the discharge pressure is high, the second foaming stock solution 2a is applied to the surface of the lower mold 5.
Such mixing can be prevented by tilting the direction of discharge.

In addition, in the above embodiment, the first foaming stock solution 3a also
Although the foaming stock solution discharging device equipped with the mixing head 71 discharges the foaming stock solution at high pressure, the first foaming stock solution 3a
It is not necessary to apply a discharge pressure to the mixing head 71. Therefore, all the raw materials may be mixed at the same time and poured onto the lower mold 5 without using the mixing head 71.

Furthermore, after injecting the first foaming stock solution 3a, the second foaming stock solution 2a is discharged after approximately 6 seconds have elapsed, but there is almost no problem even if the discharge timing is slightly shifted before or after. If the time required to operate the foaming stock solution discharge device is shortened, the second foaming stock solution 2a can be discharged earlier.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, the first
After injecting the foaming stock solution into the mold, a second foaming solution is poured from above.
Since the foaming stock solution is discharged under high pressure, the first
Even if the foaming stock solution is in a liquid state, it can be rapidly infiltrated beneath it without mixing with it, and a uniform hard plastic foam layer and a uniform soft plastic foam layer are continuously laminated. A plastic foam molded article having layers of different hardness can be obtained. Then, in the mold, both the first foaming stock solution and the second foaming stock solution are made to form a layer in a liquid state, so no air bubbles remain inside, and furthermore, these foaming solutions occur almost simultaneously. Coupled with this, the boundary surface becomes smooth and undisturbed. Therefore, it becomes easy to control the hardness and thickness of each layer of the product within a desired range.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of a method for manufacturing a cushion pad for an automobile seat using the method for manufacturing a plastic foam molded product having layers of different hardness according to the present invention. (A) to (D) are longitudinal cross-sectional views showing the mold and the state of the foaming solution inside the mold at different stages, respectively. Figure 2 is a perspective view of the mold used for manufacturing the cushion pad. Figure 3. 1 is a circuit diagram showing an example of a foaming stock solution discharging device used in the manufacturing method, and (A) and (B) are an overall diagram showing the state during circulation of the foaming stock solution and a portion showing the state during discharge, respectively. FIG. 4 is a cutaway perspective view of a cushion pad obtained by the manufacturing method. 1... Cushion pad (plastic foam molded product) 2... Soft polyurethane foam layer (second plastic foam layer) 2a... Second foam stock solution 3... Hard plastic foam layer (first plastic foam layer) ) 3a... First foaming stock solution 4... Mold 5... Lower mold 6... Upper mold 7 + 71 + 72... Mixing head $1
Diagram (C) (D)

Claims (1)

[Claims] A first foaming stock solution that is to be foamed to form a relatively hard first plastic foam layer is injected into a mold, and while the first foaming stock solution is being foamed, from above,
Injecting a second foaming stock solution that foams to form a second plastic foam layer that is softer than the first plastic foam layer, and foaming and hardening these first and second foaming stock solutions inside the mold, In a method for manufacturing a plastic foam molded product having layers of different hardness, the second foaming stock solution is discharged at high pressure from above the first foaming stock solution at a stage in the middle of progressing from a liquid state to a creaming state, A method for manufacturing a plastic foam molded article having layers of different hardness, characterized by infiltrating the first foaming stock solution under the discharge pressure.