JPS638892B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously manufacturing a foam, and more specifically, the present invention relates to a method for continuously manufacturing a foam, and more specifically, a foam is made of a thermoplastic resin and is foamed by heating and foamed by internal heat generation by applying high frequency. The present invention relates to a method of continuously forming a foamed body from a molded body having the properties that can be obtained.

Further, the molded product having the above-mentioned properties is characterized in that a foamed product can be continuously produced regardless of the shape of the molded product, such as plate, rod, irregular shape, or tube.

Various proposals have been made in the past as a method for producing a plate-shaped foam by heating and foaming a molded body made of a thermoplastic resin such as polyethylene and having the property of being foamable by heating, that is, the ability to foam.

For example, there is the so-called vertical foaming method, in which the molded product is heated and foamed while falling vertically, or the so-called horizontal foaming method, in which the molded product is first heated on a support belt and then foamed in a free state. The law is known. The method described above has an advantage over the method of foaming in a liquid heat medium in that a foamable molded article can be foamed in air.

However, in the horizontal foaming method, it is difficult to support the molded article heated on the support belt at the stage when it is separated from the support belt immediately before or immediately after the start of foaming. At that stage, foaming has already begun, and naturally the width, length, and thickness of the molded product increase compared to the original molded product, and in the transitional stage from an unfoamed state to a foamed state, the molded product exhibits a wavy state and becomes uneven. occurs. It is difficult to support a molded body or foamed body in such a state even by means such as jet air, and it is difficult to stably support or move the body. Furthermore, when implementing this method, the length of the entire device increases, it is necessary to prepare a large-scale device, and it is not practical if there are restrictions on the site or the like.

In the vertical foaming method, an unfoamed molded product is suspended vertically and heated to foam, but in order to foam the inside, a high heating temperature or a long heating distance is required. Therefore, the softened molded body stretches under its own weight, and therefore, the bubbles after foaming are in a state of being stretched in the length direction of the molded body. Such foams shrink when heated during subsequent processing, resulting in poor dimensional stability of the product. A foaming method that uses the above methods in combination is also being considered. In other words, the molded body is preheated while being supported horizontally, then foamed while falling or rising vertically in a higher temperature range than the preheating temperature, and then heated again while being supported horizontally to complete foaming. It is the law.

This method also consumes a large amount of energy due to preheating in a horizontally supported state, increases the length of the device, and requires a large-scale device.
Furthermore, as the thickness of the molded product increases, heat conduction into the interior of the molded product becomes poorer, resulting in a corresponding increase in the scale of the apparatus.

The present invention has been made to overcome the drawbacks of the conventional foaming methods as described above, and provides a method using an apparatus that can freely maintain the foaming ratio uniformly up to a maximum of about 20 times. The purpose is to

That is, in the present invention, a continuously supplied thermoplastic resin molded body having foaming ability is extruded from an extruder at a temperature as low as possible to prevent stretching of the molded body after foaming, and then extruded in a temperature range higher than the extrusion temperature. The inside of the molded body is gradually foamed while being lowered vertically without the surface of the molded body coming into contact with other utensils, and the inside of the molded body is heated with high frequency while the molded body is lowered vertically to complete the foaming. The gist of this paper is a method for continuously producing a foam, which is characterized by its characteristics.

As mentioned above, the thermoplastic resin molded article used in the present invention can be softened by heating, generate heat by applying high frequency, and then foam as the foaming agent contained therein decomposes. It refers to a molded body of thermoplastic resin having properties, and the shape of the molded body includes shapes called plate, rod, irregular shape, and tube.

Further, the means for producing the molded body is not particularly limited, and it may be manufactured by extrusion molding or the like, and a continuous elongated body is particularly preferable.
Thermoplastic resins used in the present invention are limited to those that can generate internal heat under high frequency, such as polyvinyl chloride, vinyl chloride resin compositions containing gel components, ethylene-vinyl chloride copolymers, and thermoplastic elastomers. Not done.

It goes without saying that the thermoplastic resin molded article having foamability as described above may contain a plasticizer, a stabilizer, a foaming aid, a pigment, etc., as necessary, in addition to the foaming agent.

Next, in order to explain the present invention more specifically, the present invention will be explained in detail with reference to the drawings showing an example of an apparatus for carrying out the present invention.

FIG. 1 is a longitudinal sectional view showing an apparatus used in the method of the present invention, which employs a method in which a molded body is vertically lowered.

In the figure, the foaming device is composed of vertical foaming chambers 1 and 2, and 1 has a heater 3 installed in it.
A pair of high frequency devices 4 are provided in pair 2.
As the heater, for example, an infrared lamp, an electric heater, a hot air blower, or the like is used.

The thermoplastic molded body 5 having the above-mentioned foamability is fed into the foaming chamber 1 at a temperature that allows continuous extrusion from the extruder 6, preferably at a temperature as low as possible. As shown in the figure, the foaming chamber 1 is provided vertically, and the molded article is configured to pass between a pair of heaters 3 in the foaming chamber 1 without its surface coming into contact with other utensils. There, it gradually foams to form the foam 7. In order to cause foaming, the foaming chamber is heated to a temperature at which foaming is gradually carried out above the decomposition temperature of the foaming agent contained in the molded article, as is usually done. The temperature at this time cannot be unambiguously determined either, but varies depending on the type of resin of the molded article, the type of blowing agent, etc.

When foaming begins in earnest in the foaming chamber 1, the volume of the molded body increases, and therefore the width, length, and wall thickness of the molded body increase. can be moved without coming into contact with other objects. Therefore, the surface of the foam 7 in a softened state is manufactured into a product without any damage.

This molded body is then supplied to the heating chamber 2, and is stabilized by passing through the plate gap 4 of the high frequency device.
If desired, it can be made into a product with a high magnification foam 8,
Take-off roll 9 passes through support rolls 10 and 11
It is picked up by the company and taken out as a product.

The high frequency device 4 is intended to decompose unreacted blowing agent in the foam 7, especially in the center.

Regarding the lengths of the foaming chambers 1 and 2, that is, the descending distance, it is natural to think that the shorter the length, the better, since there is a concern that the foamed bubbles may stretch due to their own weight.
In this method, the molded product is gradually foamed especially in the foaming chamber 1, and the unfoamed part (especially the center part) is foamed in the next foaming chamber 2 by high frequency, so the temperature of the foaming chamber 1 is lower than that of the conventional vertical type Since the heating temperature is lower than that for foaming, the length can be shortened, and the center of the foam is allowed to fall unfoamed for a long time, it is possible to prevent the foamed cells from stretching due to their own weight.

The length and heating temperature of these foaming chambers are appropriately determined depending on the type of molded product and foaming behavior. Although it is natural that the temperature of the extruded resin is below the foaming temperature of the blowing agent, it is preferably kept as low as possible.

As explained in detail above, the present invention involves extruding a molded product from an extruder at a temperature that allows extrusion, and gradually foaming the molded product while lowering the molded product vertically in a high temperature range without contacting other utensils. This method employs a process of heating the foam with high frequency while lowering the foam to complete foaming. Therefore, it has the following effects.

Thermal efficiency is high because the foam is sent directly from the extruder to the foaming chamber, and since the molded product is foamed while hanging vertically without coming into contact with other objects, the molded product to be foamed can freely foam. This prevents wrinkles that occur during the process of increasing the volume of the molded product from being crushed by external force or causing them to come into contact with each other. Therefore, the surface of the foam in a softened state is not damaged, and a foam with good surface condition can be manufactured. In addition, since the molded body is gradually foamed in the heating and foaming chamber, and the center portion in particular is hung in an unfoamed state, it is possible to prevent the bubbles from stretching due to their own weight. In the final stage, the unreacted foaming agent is decomposed using high frequency waves, making it possible to produce uniform foamed cells with a high expansion ratio.

Furthermore, when carrying out the method of the present invention, the foaming step can be carried out by moving in the vertical direction, so although a little height is required, the apparatus can be installed even in a narrow site, which is suitable.

[Brief explanation of the drawing]

FIG. 1 shows an example of an apparatus for carrying out the present invention, and the main parts in the figure are numbered as follows. 1 and 2 are foaming chambers, 3 is a heater, 4 is a high frequency device, 5 is a molded product, 6 is an extruder, 7 and 8 are foams,
9 is a take-up roll, and 10 and 11 are support rolls.

Claims (1)

[Claims] 1. A thermoplastic resin molded body having a foaming ability that is continuously extruded from an extruder is foamed while falling vertically into a region higher than the extrusion temperature, and the inside of the molded body is further heated with high frequency. Heat to complete foaming,
A method for producing a foam characterized by continuously obtaining a product by cooling and solidifying. 2. The method for producing a foam according to claim 1, wherein the thermoplastic resin is a resin that can generate heat using high frequency waves. 3. The method for producing a foam according to claim 2, wherein the resin capable of generating heat by high frequency is a vinyl chloride resin composition.