JPH0447926A - Apparatus for producing crosslinked foamed body - Google Patents

Abstract

PURPOSE:To continuously produce a thick crosslinked foamed body having a uniform and fine foam size and a smooth surface in a stable state by performing the crosslinking and partial foaming of a resin composition under pressure in a molten state by arranging belt bodies driven so as to circulate along the inside and outside of a long die to two opposed surfaces of the inner wall of the long die. CONSTITUTION:The tensions of belt bodies 4, 4 are controlled to apply back tension to the belt bodies, 4, 4 and the moving speed of the partially foamed body in a long die 2 is made slow to apply braking force to the foamed body 6. The crosslinking and foaming of a molten resin composition are simultaneously advanced in a heating part 2c by said braking force and the resin composition is converted to the partially foamed body but, in such a case that obtained partially foamed body is not uniformly advanced in crosslinking in its longitudinal or lateral direction, the partially foamed body is extruded from a cooling part 2d to eliminate trouble such that the curving of the whole or the generation of cracks from the surface of the foamed body frequently occurs to bring about extrusion difficulty and, at the same time, minute foaming nuclei generated by the decomposition of a foaming agent in the heating part 2c are uniformly and stably held in the foamed body 6.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for producing crosslinked foam, and more specifically,
The present invention relates to a production device for continuously producing in a stable state a crosslinked foam having uniform and fine cell diameters, a smooth surface, and a thick wall.

(Prior Art) Various methods are known for producing a foam using a thermoplastic resin composition containing a blowing agent and a crosslinking agent as essential components. Among these methods, for example, the resin composition is molded into a predetermined shape such as a sheet, and the resulting molded product is subjected to heat treatment under normal pressure to first decompose the crosslinking agent in the molded product and convert it into a thermoplastic resin. There is a method of proceeding with crosslinking, and then decomposing the foaming agent to foam the crosslinked product.

However, in the case of this method, the crosslinking 9
Since foaming is progressed, the cell diameter of the obtained foamed product is usually as large as 100 μm or more, and the problem of deterioration in appearance is unavoidable.

Incidentally, recently, there has been an increasing demand for foams having a cell diameter of about 70 to 90 μm. This is because by reducing the cell diameter, the foam has low shrinkage, improved crack resistance, and a smooth surface, giving the foam a luxurious feel as a whole.

In order to meet these demands, a polyolefin resin molded product containing a blowing agent and a crosslinking agent is heated under pressure.
A method has been proposed in which a part of the blowing agent is decomposed at the same time as the crosslinking agent is decomposed or after the crosslinking agent is decomposed to generate foaming nuclei, and then heated and foamed under normal pressure (Japanese Patent Application Laid-Open No. 134719/1983). (see publication). However, in the case of this method, when using conventional pressurizing equipment, such as Roto Cure, which wraps the polyolefin resin molding around the roll surface and presses it with a belt from above, the resin flows out from both sides. Unable to apply pressure evenly. Further, there is a problem that the resin adheres to the belt or roll surface, making it difficult to remove it, and furthermore, when the pressure is returned to normal pressure in a heated state, bubbles tend to become coarse. Similarly, in the method of sandwiching a polyolefin resin molded product between two parallel plates and pressing them from both sides, industrial equipment that enables this has not yet been developed.

Further, when foaming nuclei are generated at a pressure of 1 to 10 kg/cj as described in JP-A-58-134719, a foam having sufficiently fine bubbles is not obtained.

In order to solve the problems of the above method, for example,
JP-A-180611 discloses the following method.

In this method, a mixture of resin compositions is extruded through a T-die to form a sheet-like molded product, which has a rectangular cross section, and an endless belt that circulates inside and outside is disposed on the upper and lower surfaces of its inner wall. The foam is then transferred into a long mold and heated under pressure to crosslink and simultaneously generate foaming nuclei.
In this method, the mold is cooled at the outlet of the mold, continuously taken out, and then heated in a heating furnace under normal pressure.

(Problems to be Solved by the Invention) In the case of the above-described method, the mixed resin composition is first formed into a non-crosslinked sheet-like molded product using a T-die, and then transferred to a mold, where it is partially molded. It is foaming. In that case,
Inside the mold, it is necessary to uniformly apply pressure and heat to the moving sheet-shaped molded body. This is because if this pressure is not uniform, crosslinking in the sheet-like molded product will not proceed uniformly, and therefore the foaming nuclei that will be generated will not be uniform.

However, in the above method, the object to be pressurized in the mold is a sheet-shaped molded product that is thin, has a large area on the top and bottom surfaces, and has a rectangular cross section, and it is difficult to apply pressure uniformly on the top and bottom surfaces. It is quite difficult. This is a problem caused by the fact that a resin composition melt-kneaded in an extruder must be partially molded into a sheet using a T-die.

In addition, in order to control the pressure on the sheet-shaped molded product in the mold, it has been considered to provide a choke bar at the outlet of the T-die and thereby control the internal pressure of the mold. In the case of this method, the sheet-like molded product may slip or slip on the choke bar, and the speed at which it is transferred into the mold becomes unstable.

The present invention solves the above-mentioned problems and is extruded from an extruder,
By directly crosslinking and partially foaming the molten resin composition under pressure, a crosslinked foam with uniform and fine cell diameters, a smooth surface, and a thick wall can be produced in a stable state. The purpose is to provide manufacturing equipment for continuous manufacturing.

(Means/effects for solving the problem) In order to achieve the above object, the present invention provides an extruder for a resin composition containing a thermoplastic resin 9 as an essential component, a blowing agent and a crosslinking agent; A long die having a rectangular cross-sectional shape and having at least a continuous heating section and a cooling section; and a heating furnace connected to the long die. The crosslinked foam manufacturing apparatus is characterized in that a belt body is disposed on two opposing surfaces of the inner wall of the long die to circulate and drive the inside and outside of the long die. provided.

Hereinafter, the manufacturing apparatus and its operation will be explained in detail based on the drawings.

First, FIG. 1 is a schematic side view showing one example of the device of the present invention. In the figure, the entire apparatus includes an extruder 1 for a resin composition, a long die 2 connected to an outlet 1a of the extruder 1, and equipped with at least a heating section and a cooling section in this order, and a long die 2. The heating furnace 3 located downstream of the heating furnace 3 is arranged in series.

Belt bodies 4, 4, which will be described later, are stretched over the upper and lower parts of the long die 2, and which circulate and move between the inside and outside of the long die 2.

First, the produced crosslinked foam moves through the apparatus as a whole as follows. That is, the resin composition extruded from the extruder 1 is directly introduced into the long die 2 in a molten state, where it is partially foamed in the heating section, cooled in the cooling section, extruded from the long die 2, and heated. Furnace 3
The product is transferred to the foam body 5, where it is heated to a predetermined temperature to become a product as a foam 5.

In this overall flow, in the extruder 1, the essential components of the thermoplastic resin 2, the blowing agent and the crosslinking agent, are uniformly mixed to prepare a resin composition having a predetermined composition. This uniform mixing is performed at a temperature at which neither the blowing agent nor the crosslinking agent decomposes.

Examples of the thermoplastic resin used include polyethylene;
Ethylene copolymers such as polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer; polyvinyl chloride alone or a mixture thereof can be mentioned. In addition, this thermoplastic resin is further added with known pigments and antioxidants.

Ultraviolet absorber, flame retardant, antistatic agent, anti-mold agent.

Appropriate amounts of additives such as antibacterial agents and inorganic fillers can also be blended.

The blowing agent to be used may be a decomposition-type blowing agent that is thermally decomposed to generate gases such as nitrogen and carbon dioxide during the heating process in the long die 2 described below, such as azodicarbonamide, dinitrosopentamethylenetetramine, 4
．． 4'-oxybisbenzenesulfonyl hydrazide,
Examples include azobisisobutyronitrile.

The blending amount of these blowing agents is appropriately selected depending on the expansion ratio of the desired foam, but is usually set within the range of 5 to 30 parts by weight per 100 parts by weight of the above-mentioned thermoplastic resin. Further, if necessary, appropriate amounts of various auxiliary agents and nucleating agents may be added to these foaming agents.

As the crosslinking agent, which is the third essential component of the resin composition, those having a decomposition temperature higher than the melting start temperature of the thermoplastic resin are used, such as dicumyl peroxide, di-t-butyl peroxide, t-Butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-
Examples include di(1-butylperoxy)hexyne-3.

The blending amount of these crosslinking agents is appropriately selected depending on the degree of crosslinking in the intended foam, the molecular structure of the thermoplastic resin, etc., but is usually 0.2 to 5.0 parts by weight per 100 parts by weight of the thermoplastic resin. Set within the range of parts by weight.

The above-mentioned components are uniformly melted and mixed in an extruder 1.

Then, the molten resin composition is directly extruded into the long die 2 from the outlet 1a while remaining in a molten state.

As shown in FIG. 2, the inside of the long die 2 consists of a heating section 2c located upstream of the long die 2 and a cooling section 2d following it. It is controlled by a control system. That is, the molten resin composition introduced through the inlet 2a is transferred to the heating section 2c.
During the process of moving the
After being heated to a temperature of 100° C. and undergoing crosslinking and partial foaming in this process, the partially foamed product 6 is cooled while moving through the cooling section 2d, and reaches a temperature of about 25° C. at the outlet 2b.

Moreover, belt bodies 4, 4 are introduced into the upper and lower parts of the long die 2 from the inlet side of the long die 2, move while slidingly contacting the upper surface 2e and lower surface 2f of the inner wall, and then are led out from the outlet side. It is arranged so as to be driven in circulation via 7a and 7b.

Then, as shown in Fig. 5, the inner wall surface 2 of the long die is
A lubricant 8.8 is press-fitted between the belt bodies 4, 4 and the belt bodies 4, 4, and the inner wall surfaces 2e, 2 of the long die.
By reducing the frictional resistance between f, the belt bodies 4, 4 can move smoothly inside the long die 2.

It is preferable that the surfaces of the belt bodies 4, 4 that come into sliding contact with the inner wall of the long die are smooth, but on the other hand, by making the surface on the side of the partially foamed body 6 rough, the contact with the partially foamed body 6 is improved. It is preferable to increase the frictional resistance.

It is preferable that the belt members 4, 4 are usually made of a rough surface made of a highly corrosion-resistant nickel alloy, and a fluororesin is provided on the sliding surface, and these are integrated. Incidentally, the timing belt may be formed by providing unevenness on the surface on the sliding contact side.

The belt bodies 4, 4 are in pressure contact with the upper and lower surfaces of the partial foam body 6 in the long die 2, and especially in the cooling section 2d, since the partial foam body 6 is cooled and hardened, the belt body 4. 4 conveys the partial foam body 6 in the downstream direction (in the direction of arrow p) in a state in which it is in close contact with and integrated with the partial foam body 6 moving through the cooling section 2d. .

Therefore, when no tension is applied to the belt bodies 4, 4, the belt bodies 4, 4 are driven in circulation following the moving speed of the partially foamed body 6 defined by the extrusion speed from the extruder 1. However, by adjusting the tension of the belt bodies 4, 4,
By applying so-called pack tension, the moving speed of the partial foam body 6 within the long die 2 is slowed down,
A braking force can be applied to this partially foamed body 6.

By applying such a braking force to the partially foamed body 6,
When crosslinking of the molten resin composition progresses in the heating section 2c and at the same time foaming progresses to convert it into a partial foam, if the crosslinking does not progress uniformly in the longitudinal direction or width direction of the resulting partial foam, When it is extruded from the cooling section 2d of the long die 2, the inconvenience that the entire body frequently curves or cracks occur on the surface, causing difficulty in extrusion, is eliminated, and at the same time, foaming in the heating section 2c Fine foaming nuclei generated as the agent decomposes are uniformly and stably held in the partially foamed body 6.

This braking force must not be a force that completely stops the movement of the extruded partial foam body 6 toward the downstream side, but must be a force that is sufficient to slow down the moving partial foam body 6. This force varies depending on the state of the partially foamed body 6 being extruded, so it cannot be determined unambiguously, but it is preferably about 20 to 25 kg/car.

In order to adjust this braking force, a pressure gauge 9 is inserted into the long die 2 as shown in FIG.
The pressure inside the wheel 7 is measured, and based on the measured value, the pressure inside the wheel 7 is measured.
a and 7b are moved up and down to adjust the tension of the belt bodies 4 and 4.

From the partially foamed product 6 extruded from the outlet 2b of the long die, the belt members 4, 4, which are integrated at the top and bottom surfaces, are separated and then introduced into the heating furnace 3 under normal pressure, where the remaining foam is removed. By being heated to a temperature higher than the decomposition temperature of the agent, uniform foaming centered around the foaming core progresses, resulting in the foam 5 having the desired cell diameter uniform and fine.

The separated belt bodies 4, 4 move outside the long die 2, are again introduced into the die from the upstream side of the long die 2, and convey the partially foamed body again in the manner described above.

Note that the locations where the belt bodies 4, 4 are disposed are not limited to the upper and lower surfaces of the inner wall of the long die 2, but may also be provided on both sides of the inner wall of the long die 2.

(Examples of the Invention) Example 1 A crosslinked foam was manufactured using the manufacturing apparatus shown in FIG.

That is, first, low density polyethylene (MI 1.Og
/10 minutes, density 0.920g/aIF) 100 parts by weight,
6 parts by weight of azodicarbonamide and 1.0 parts by weight of dicumyl peroxide were charged into an extruder 1, melt-mixed at 140° C., and then extruded in a molten state into a long die 2 having a diameter of 3 m.

The long die 2 has a cross-sectional shape with a width of 300 am.
, a rectangular shape with a thickness of 15 m+, and the internal temperature distribution was controlled as shown in FIG. Note that the length of the heating section 2c is approximately 1
The length of the cooling section 2d was approximately 600 m+.

A certain amount of diethylene glycol was injected as a lubricant 8 between the inner wall of the die and the molten resin composition from an oil pump.

Back tension was applied to wheels 7a, 7a, wheels 7b, 7b were left in a free state, and the pressure indicated by pressure gauge 9 was set to 35 kg/cd.

The moving speed of the belt body 4.4 was approximately 15ao/win. In this state, the long die 2 was continuously operated while monitoring the internal pressure with the pressure gauge 9.

The foam obtained from heating furnace 5 (temperature: 200° C.) had a smooth appearance, a stable wall thickness of 25 mm, and an average cell diameter of 80 μm.

Comparative Example After extruding the same polyethylene resin as in the example into a sheet using an extruder, it was immediately fed into a heating furnace and heated for 22 hours.
A crosslinked polyethylene foam of a comparative example was obtained by heating at 0°C to cause crosslinking and foaming.

The surface of the obtained foam was uneven, and the cell diameter was 400 μm or more and non-uniform.

(Effects of the Invention) As is clear from the above explanation, according to the apparatus of the present invention, the molten resin composition prepared in the extruder is directly introduced into the long die, and there, the conveyance rate of the partially foamed material is Since the desired pressure can be applied inside the die by controlling the temperature, the fluid state of the partially foamed body moving in the heating section is stabilized, and crosslinking progresses uniformly in the process. As a result, it is possible to stably produce a foam having fine and uniform cells without bending or cracking.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing an example of the apparatus of the present invention, FIG. 2 is a schematic side view showing an example of a long die, and FIG.
4 is a graph showing an example of temperature distribution inside the long die, and FIG. 5 is a partial side view of the long die. l...Extruder, 1a...Extruder outlet, 2...Long die, 2a...Long die inlet, 2b...Long die outlet, 2c...Heating section, 2d...Cooling Part, 2e... Upper surface of long die inner wall, 2f... Lower surface of long die inner wall, 3... Heating furnace, 4... Belt body,
5... Foam, 6... Partial foam, 7a, 7b...
・Wheel, 8...Lubricant. Figure 1

Claims (1)

[Scope of claims] An extruder for a resin composition containing a thermoplastic resin, a blowing agent, and a crosslinking agent as essential components; and a long die in which a cooling section is continuously provided; and a heating furnace that is connected to the long die; and a heating furnace connected to the long die; The apparatus for producing a crosslinked foam is characterized in that a belt member is disposed for circulating and driving the inside and outside of the long die.