JPS6143174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously producing a foam, and more specifically, the present invention relates to a method for continuously producing a foam, and more specifically, a foam made of a thermoplastic resin 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 molded body into a foamed body using a molded body having properties as a raw material. In addition, as long as the molded product has the above properties, the foam can be continuously produced in any shape, such as plate, rod, irregular shape, or tube. be.

Various proposals have been made in the past as a method for manufacturing a plate-shaped foam by heating and foaming a molded body made of a thermoplastic resin such as polyethylene and having a property of being foamable when heated, that is, a so-called foaming ability. For example, there is a so-called vertical foaming method in which foaming is performed by heating the molded product while vertically descending, or a so-called horizontal foaming method in which the molded product is first heated on a support belt and then foaming is completed in a free state. Are known. The above-mentioned method has an advantage over a method of foaming in a liquid heat medium in that a molded product having foaming ability can be foamed in air, but there are drawbacks as described below. .

In other words, in the vertical foaming method, the unfoamed molded product is heated and foamed while being hung vertically.
The molded product softened by heating stretches under its own weight, and the foamed cells are stretched in the length direction of the molded product. Such foams shrink when heated during subsequent processing, resulting in poor dimensional stability of the product.

On the other hand, in the horizontal foaming method, it is difficult to support the molded product heated on the support belt at the stage where it is separated from the support belt immediately before or immediately after the start of foaming.

By the time the molded body is separated from the support belt, it has begun to foam, and it is naturally wider and wider than the original molded body.
At the excessive stage where the length and thickness increase and the state changes from an unfoamed state to a foamed state, the molded product becomes wavy and uneven. It is difficult to support a molded body or a foamed body in such a state even by means such as a jet of air, and it is difficult to stably support or move the molded body or foamed body. In addition, 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, etc. A foaming method that uses the above methods in combination is also being considered. In other words, a foaming method in which the molded product 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. This method also consumes a large amount of energy and requires a large-scale device due to preheating in a horizontally supported state.
Furthermore, as the thickness of the molded product increases, heat conduction into the interior of the molded product becomes poorer, resulting in an increase in the scale of the device.

The present invention was made in order to eliminate the drawbacks of the conventional foaming method as described above.
It is an object of the present invention to provide a method in which the elongation of a foam is minimized, support can be easily provided during the foaming stage, and foaming can be carried out using a small-scale device. Therefore, the present invention allows a continuously supplied thermoplastic resin molded body having foaming ability to be directly fed from an extruder in a high temperature range above the extrusion temperature so that the surface of the molded body does not come into contact with other utensils and is perpendicular to the extruder. The gist is a method for continuously manufacturing a foam, which is characterized by foaming while descending in the direction, then heating again while supporting it horizontally, and finally heating the inside of the molded body with high frequency to complete foaming. It is something to do.

As mentioned above, the thermoplastic resin molded product used in the present invention has the property of being softened by heating, generating heat by applying high frequency, and then foaming as the foaming agent contained therein decomposes. It refers to a molded body made from a thermoplastic resin having the following properties, and the shape of the molded body includes shapes called plate, rod, irregular shape, and tube. There are no restrictions on the thickness, length, width, or other dimensions of the molded body, but those having dimensions that are normally employed are preferably used.

Further, the means for producing the above-mentioned molded body is not particularly limited, and it may be produced by extrusion molding or the like, and a continuous elongated body is particularly preferable. However, thermoplastic resins such as polyvinyl chloride and ethylene
There is no limitation as long as it can generate internal heat due to high frequency, such as vinyl chloride copolymer.

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

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 suitable 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 of vertically lowering the molded body.

In the same figure, the foaming device is composed of a vertical foaming chamber 1, a horizontal foaming chamber 2, and a high frequency device 8, and each of the above 1 and 2 is provided with a pair of heaters 3 and 4 in the chamber. . As the heaters 3 and 4, for example, infrared lamps, electric heaters, hot air blowing devices, etc. are used.

The thermoplastic resin molded body 14 having the foaming ability as described above is continuously fed into the foaming chamber 1 from the extruder 16 . As shown in the figure, the foaming chamber 1 is provided vertically, and is designed so that the molded article can pass between a pair of heaters 3 in the foaming chamber 1 without coming into contact with other objects on its surface. 1, the molded body becomes a foamed body 15. The molded product foams in the foaming chamber 1, and in order to cause foaming, it is heated to a temperature higher than the decomposition temperature of the foaming agent contained in the molded product, as is usually done. The temperature at this time cannot be unambiguously determined either, and varies depending on the type of resin of the molded product, the type of foaming agent, etc.

When foaming begins in earnest in the foaming chamber 1, the volume of the molded body increases, and the width, length, and wall thickness of the molded body increase. By doing so, the molded body 14 or foamed body 15 can be moved without coming into contact with other utensils. Therefore, the surface of the foam 15 in a softened state is manufactured into a product without any damage. The molded product foamed as described above is then supplied to the heating chamber 2, where it is further foamed and then passed through the plate gap 4 of the high-frequency device to form a stable foamed product 6, which is then manufactured into a product. and taken out from the foaming device by a take-up roll 13. Similarly to the foaming chamber 1, the foaming chamber 2 is also provided with a heater 4, which heats the foam 15 to further promote the decomposition of the foaming agent. Also foaming chamber 2
are arranged horizontally, and an endless belt 5 is provided inside the chamber to horizontally support the foam. Furthermore, instead of the endless belt 5, it is also possible to horizontally support the foam 15 by floating the foam 15 with an airflow jetting upward, and in this case, the jetting airflow can be hot air. This allows preheating and support to be performed simultaneously.

An air jet device 9 is provided in the heating chamber 2 to prevent the foam 15 from adhering to the endless belt 5. Furthermore, an air jet device 10 is provided inside the bending portion where the foam 15 moves from a state in which it moves vertically to a state in which it moves horizontally.
5 is folded. Reference numeral 12 denotes a partition wall between the foaming chamber 1 and the foaming chamber 2, which prevents the temperatures in both chambers from interfering with each other.

The purpose of the high frequency device 8 is to separate the unreacted foaming agent in the center of the foam 15.

The length of the foaming chamber 1, that is, the descending distance of the molded product can be determined as appropriate depending on the type of molded product, the supply rate, and the foaming behavior. Generally, it is preferable that the foam is moved horizontally with wrinkles caused by foaming removed.

As described in detail above, the present invention involves foaming a molded product directly from an extruder while lowering the molded product vertically in a temperature range higher than the extrusion temperature without the surface of the molding coming into contact with other utensils, and then supporting it horizontally. Since it adopts the steps of heating again and finally heating the inside of the molded body with high frequency to complete foaming, the following effects are achieved. Thermal efficiency is high because the foam is sent directly from the extruder to the heating chamber, and since the molded product is foamed while hanging vertically without coming into contact with other utensils, 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 produced. Furthermore, by applying high frequency heating in the final stage, the unreacted blowing agent in the center of the foam can be decomposed. It is clear that this is particularly effective in the case of thick molded bodies.

In addition, since it is supported horizontally after foaming, the weight of the foam that is applied to the molded product during the foaming process is reduced, and the foam is not stretched along its length, which in turn improves dimensional stability. It is possible to produce a foam with good quality. Further, when carrying out the method of the present invention, the foaming step can be carried out by moving in the vertical direction, so 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 and 4 are heating chambers, 5 is an endless belt, 6 is a foam, and 8 is a high frequency device.

Claims (1)

[Scope of Claims] 1. A thermoplastic resin molded body having a foaming ability that is continuously supplied from an extruder is made so that the surface of the molded body is perpendicular to other objects without welding to other objects in a temperature range higher than the extrusion temperature. A method for continuously producing a foam, which is characterized by foaming while descending in a direction, then supporting it horizontally, heating it again, and finally heating the inside of the molded body with high frequency to complete foaming. 2. The method according to claim 1, wherein the thermoplastic resin is a resin that can generate heat by high frequency. 3. The method according to claim 2, wherein the resin capable of generating heat by high frequency is a vinyl chloride resin composition.