JPH0453724A - Manufacture of crosslinked foam and production equipment used therefor - Google Patents

Abstract

PURPOSE:To obtain a method for continuously manufacturing thick-walled crosslinked foam, the diameters of cells of which are uniform and minute and the surface of which is smooth, under stable state by a method wherein wires are stretched so as to circulatingly move through the interior and exterior of a die in order to apply braking force to partially foam- molded body to the direction opposite to its extrusion direction by means of the tension of the wires. CONSTITUTION:Wires 4 and 4, which are made into an integral body together with partially foam-molded body 7 moved in a die 2 at both the sides of the body, is moved to downstream direction (or direction indicated with the arrow P). Especially, in a cooling zone 2c, partially foam-molded body 7 is cooled and brought into hardened state, resulting in bonding the wires 4 and 4 integrally with the partially foam-molded body 7, which moves in the cooling zone 2c. By adjusting the tension of the wires 4 and 4 or by so-called back-tensioning, the rate of movement of the partially foam-molded body 7 in the die 2 is retarded, resulting in applying braking force to the partially foam-molded body 7. By the application of the braking force to the partially foam-molded body 7, the pressure of resin is heightened in a heating zone 2b, resulting in preceding the crosslinking of resin composition under high pressure. As a result, foam, which has neither warpage nor crack and has minute and uniform cells, can be stably manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a crosslinked foam and a production apparatus used therefor. The present invention relates to a method for continuously producing a crosslinked foam in a stable state, and a production apparatus used therefor.

(Prior Art) Various methods are known for producing foams using resin compositions containing thermoplastic resins, blowing agents, and crosslinking agents 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, crosslinking and
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 the small cell diameter provides the foam with low shrinkage, improved crack resistance, and a smooth surface, giving it a luxurious feel as a whole.

In order to meet such demands, a method has been proposed in which a resin composition is filled into a closed mold having a rectangular cross-sectional shape, heated, and foamed under pressure. With this method, it is certainly possible to obtain a thick-walled foam having uniform, fine cells, but this method has to be carried out in a batch manner, which poses the problem of low productivity.

Moreover, in the case of this method, there is a problem in that unless pressure is applied evenly within the mold, the crosslinking reaction will not proceed uniformly and, under the influence of this, the foaming will also not proceed uniformly.

As a method for solving these problems, for example, there is a method as disclosed in Japanese Patent Application Laid-Open No. 53-69274. In this method, the resin composition is completely processed from crosslinking to foaming in a long land die connected to an extruder, and then the crosslinked foam is continuously taken out from the die outlet. .

(Problem to be Solved by the Invention) However, the method disclosed in the above publication requires a very long die, and as foaming progresses, the die structure in the longitudinal direction is gradually changed. This not only complicates the structure of the die, but also makes it extremely difficult to produce foams with a certain thickness or with a foaming ratio that can be freely changed depending on the purpose of use. There's a problem.

The present invention solves the problems of the above method, and achieves uniform cell diameter and
The object of the present invention is to provide a method for continuously producing fine crosslinked foam with a smooth surface and a thick wall in a stable state, and a production apparatus used therefor.

(Means/effects for solving the problem) In order to achieve the above object, in the present invention, a resin composition containing a thermoplastic resin, a foaming agent, and a crosslinking agent as essential components is used in a molding area, a heating area, and a cooling area. By extruding into a die in which regions are continuously formed, and in the molding region and/or the heating region, the crosslinking agent is decomposed and at the same time at least a part of the foaming agent is decomposed to generate bubbles. A partially foamed molded product is molded, and then the obtained partially foamed molded product is cooled in the cooling region to a temperature below the softening point of the partially foamed molded product, and then extruded from the die, and the extruded partially foamed molded product is In the method for producing a crosslinked foam that is foamed by heating under normal pressure, the partially foamed molded product has an expansion ratio of M4. When the expansion ratio of the crosslinked foam to be finally obtained is Mt, M, , Mt
is 0.05≦M+/M! ≦0.35 (However, Mt >
M+≧1.05), and at least one wire is introduced from the molding region, passes through at least one side of each region, and then is led out from the cooling region. A crosslinked foam body is stretched so as to circulate inside and outside the die, and the tension of the wire body applies a braking force to the partially foamed molded body in a direction opposite to the extrusion direction thereof. and thermoplastic resins.

An extruder for a resin composition containing a foaming agent and a crosslinking agent as essential components; A die connected to the extruder and in which a molding area, a heating area, and a cooling area are successively formed in this order; and a heating furnace, wherein at least one wire body is introduced from the molding region, passes through at least one side of each region, and then is led out from the cooling region. Provided is an apparatus for producing a crosslinked foam, characterized in that the crosslinked foam is stretched so as to circulate around the outside.

Hereinafter, the method and manufacturing apparatus of the present invention will be explained in detail based on the drawings.

First, FIG. 1 is a schematic plan view showing an example of the apparatus of the present invention. In the figure, the entire apparatus is connected to an extruder 1 for resin composition and an outlet 1a of this extruder 1, and a molding area 2
A, a die 2 consisting of a heating region 2b and a cooling region 2c, and a heating furnace 3 located downstream of the die 2 are arranged in series.

On both sides of the die 2, a wire body 4.4, which will be described later and circulates between the inside and outside of the die, is stretched, and at the outlet of the die 2, a lubricant removing part 5, which will be described later, is attached. ,
The lubricant removing portion 5 is connected to wire body extracting portions 6, 6, which extend from the outlet thereof in a widened manner toward both sides.

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 molded into a desired shape in the molding area 2a, converted into a partially foamed molded product 7 in the heating area 2b, cooled in the cooling area 2C, and extruded from the die 2. . During extrusion, both sides of the partially foamed molded body 7 are partially removed, and the central part is transferred to the heating furnace 3, where it is heated to a predetermined temperature to become a product as a foamed body 8.

In this overall flow, the thermoplastic resin, foaming agent, and crosslinking agent, which are essential components, are uniformly mixed in the extruder 1 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 thermoplastic resins 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, appropriate amounts of known additives such as pigments, antioxidants, ultraviolet absorbers, flame retardants, antistatic agents, antifungal agents, antibacterial agents, and inorganic fillers can be added to this thermoplastic resin. .

The blowing agent to be used may be a decomposition type blowing agent that thermally decomposes during the heating process in the die described later to generate gases such as nitrogen and carbon dioxide, such as azodicarbonamide,
Examples include dinitrosopentamethylenetetramine, 4.4°-oxybisbenzenesulfonylhydrazide, and 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. Examples include 5-dimethyl-2,5-di(t-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.

A resin composition formed by uniformly mixing the above-mentioned components is continuously extruded from the outlet 1a of the extruder 1 to the die 2.

As described above, the die 2 has a projection area 2 in its longitudinal direction.
A, a heating area 2b, and a cooling area 2C are successively constructed in this order.

The resin composition extruded from the outlet 1a of the extruder 1 is first molded into a predetermined shape in the molding area 2a.

At this time, if the die shape of the molding area 2a is appropriately selected, a molded product having an arbitrary shape such as a sheet shape or a rod shape can be obtained.

The molded product that has passed through the molding area 2a is then transferred to the heating area 2b.
I will move to. The molded body moving within the heating area 2b is heated to a predetermined temperature by a heating means (not shown). As a result, the crosslinking agent contained in the molded body is thermally decomposed and crosslinking of the thermoplastic resin progresses. At the same time, a part of the foaming agent in the molded body is decomposed to form cell nuclei that are uniformly dispersed inside the molded body, and the molded body is converted into a partially foamed molded body 7.

The degree of crosslinking in the partially foamed molded product 7 obtained in this process is such that the residual gel weight fraction is 5% or more when extracted with a xylene solution at 120°C for 24 hours. That's good. This is because in the case of a crosslinked state in which the residual gel weight fraction is less than 5%, the cell diameter of the finally obtained foam tends to become coarse.

Regarding the initial decomposition of the blowing agent in this process, die 2
The expansion ratio of the partially foamed molded product obtained by extrusion from
3. The expansion ratio of the crosslinked foam to be finally obtained is M,
Then, between M1 and Ml, 0.05≦M/M!
≦0.35 (However, M t > M + ≧1, 05
) The blowing agent is decomposed so as to satisfy the following relationship.

Ml/M! In the case of a partially foamed molded product with <o. Also, Ml/M! This is because, in the case of a partially foamed molded article having a diameter of >0.35, when it is extruded from the die 2, natural expansion occurs to a large extent, making the skin rough.

The amount of decomposition of the blowing agent is controlled by appropriately selecting the temperature of the heating region 2b.

The partially foamed molded product 7 that has passed through the heating area 2b moves to the next cooling area 2c. In this region, the partially foamed molded body 7 is cooled and its shape, the state of cell nuclei, etc. are maintained.

The cooling temperature at this time needs to be lower than the softening point of the partially foamed molded product 7. If the cooling is insufficient and the temperature is too high to soften, when the partially foamed molded product 7 is extruded from the die 2, the pressure of the gas contained inside the molded product 3 will cause the partially foamed molded product 7 to soften. This is because the material expands naturally and causes surface roughness.

Note that a lubricant is press-fitted from a lubricating pump 9 through a lubricating pipe 9a to the boundary between the forming area 2a and the heating area 2b, so that the lubricant is applied to the outer periphery of the molded object moving from the forming area 2a to the heating area 2b. It is preferable to attach.

This is a process in which the molded body moves as a partially foamed body within the heating area 2b and the cooling area 2c, and as the crosslinking of this molded body progresses, the melt viscosity of the partially foamed body 7 increases and The frictional resistance between the area 2c and the inner wall of the die increases, and the partially foamed molded product 7 no longer moves downstream, resulting in an increase in the head load on the extruder 1, leading to damage to the extruder 1. This is to prevent

That is, by attaching a lubricant to the outer periphery of the molded body from the molding region 2a, the heating region 2b and the cooling region 2
The frictional resistance between the inner wall of the die c and the partially foamed molded article 7 is reduced, and smooth movement toward the downstream side is ensured.

The lubricant used for this purpose is one that does not decompose or evaporate at the temperature of the heating area 2b.
In addition, it must be chemically stable, without dissolving in the molded product, and without causing deterioration of the molded product. For example, liquid polysiloxane, polyhydric alcohol such as ethylene glycol, alkyl ester, alkyl ether, polyoxyalkylene, etc. can be used.

The lubricant injected from the molding region 2a follows the movement of the partially foamed molded body 7 and reaches the lubricant removal section 5 disposed at the downstream end of the die 2, from where it is passed through the pipe 9b. After being suctioned and removed from the partially foamed molded body 7 by the suction pump 10, it is filtered and then injected into the molding area 2a again by the oil pump 9.

If this lubricant removal operation is not performed, the lubricant will be introduced into the heating furnace 3 while adhering to the partially foamed molded body 7, resulting in the inconvenience that the surface appearance of the obtained foamed body 8 will be significantly impaired. .

Now, in this device, the partially foamed molded product 7 that is about to move downstream at a predetermined extrusion speed is controlled by a wire body 4.4 that is stretched so as to circulate inside and outside the die 2. Power is added.

Here, the wire body 4.4 is introduced from the upstream exterior of the molding region 2a to both sides of the inside of the die 2, passes through the molding region 2a, the heating region 2b and the cooling region 2c in the longitudinal direction of the die 2, and is cooled. A pulley 12a that rotates freely so as to perform a circular movement in which it is led out from the region 2c and then introduced into the molding region 2a again via the tension control section 11;
12b.

12c.

This wire body may be an ordinary wire or stranded wire having a circular cross section, or may be in the form of a tape.

Furthermore, it is preferable that the surface of these wire bodies is made uneven so as to increase the contact area with the partially foamed molded body 7 moving through the die 2, as will be described later.

As shown in FIG. 2, which is a schematic cross-sectional view taken along the line ■-■ in FIG. 7 and moves in the downstream direction (arrow p direction). In particular, in the cooling region 2C, the partially foamed molded product 7 is cooled and hardened, so the wire bodies 4, 4 are in close contact with and integrated with the partially foamed molded product 7 moving in this cooling region 2c.

Therefore, when no tension is applied to the wire bodies 4.4, the wire bodies 4, 4 follow the moving speed of the partially foamed molded body 7 and move in circulation. However, by adjusting the tension of the wire bodies 4, 4 and applying so-called back tension, the moving speed of the partially foamed molded product 7 within the die 2 is slowed down, and a braking force is applied to this partially foamed molded product 7. be able to.

By applying such a braking force to the partially foamed molded body 7, the pressure of the resin increases in the heating region 2b, and crosslinking of the resin composition proceeds under high pressure. Conventionally, due to unstable pressure, when foaming progresses randomly and converts into a partially foamed molded product, if crosslinking does not progress uniformly in the longitudinal and width directions of the resulting partially foamed molded product, When extruded from the cooling area 2c of the die 2, the entire body frequently curves or cracks appear on the surface, causing difficulty in extrusion, but the method of the present invention eliminates such inconveniences. At the same time, fine cell nuclei generated as a result of the decomposition of the foaming agent in the heating region 2b are uniformly and stably held in the partially foamed molded product 7.

This braking force must not be such a force as to completely stop the movement of the extruded partially foamed molded product 7 toward the downstream side, but must be a force that is sufficient to slow down the moving partially foamed molded product 7. This force varies depending on the state of the partially foamed molded product 7 being extruded, so it cannot be determined unambiguously, but it is generally 30 to 30% for the cross section of the partially foamed molded product 7.
Preferably, the force is such that a pressure of 50 kg/crl is applied.

In order to adjust this braking force, a pressure gauge 13 is disposed at the position of the heating region 2b of the die 2, and the pressure within the region 2b is actually measured, and the measured value is sent to the path 13a.

13a to the tension control unit 9, where it is compared with a preset tension so that the two become equal.
The capacity in the tension control 11.11 is adjusted. Thereby, the partially foamed molded body 7 can be moved while the pressure inside the heating region 2b of the die 2 is kept constant at the set value.

In addition, tension control parts 11.1 located outside both sides of the die 2
1 can be controlled independently, it is possible to adjust the imbalance in the moving speed of both sides of the partially foamed product 7 separately in response to the state of the partially foamed molded product 7 moving in the heating region 2b. become able to.

As shown in FIG. 2, the partially foamed molded product 7 extruded from the cooling region 2c has wire bodies 4, 4 on both sides thereof.
are embedded in one piece.

Therefore, cutters 14.14 are arranged on both sides of the outlet of the lubricant removal section 5 with the cutting edges facing upstream of the device, and the partially foamed molded product 7 extruded from the cooling area 2c is cut by the cutters 14.14. It is continuously cut and separated into a main body 7a of the partially foamed molded body and both side parts 7a, 7b in which the wire body 4.4 is integrated.

The separated side parts 7a, 7b each pass through a wire body extraction section 6.6, and in the process the partially foamed molded body around the wire bodies 7, 7 is removed.

Then, only the wire bodies 7, 7 are pulled out via the wires 2a, 12a, and the tension control unit 11. Moving on to II.

On the other hand, the main body 7a is introduced into the heating furnace 5 under normal pressure,
By heating the foam to a temperature higher than the decomposition temperature of the remaining foaming agent, uniform foaming centering around the cell cores progresses, resulting in the foam 8 having the desired cell diameters that are uniform and fine.

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

That is, first, low density polyethylene (Ml1, 02
710 minutes, 100 parts by weight of density 0.920g/c111), 10 parts by weight of azodicarbonamide, and 1.0 parts by weight of dicumyl peroxide were put into extruder 1, melted and mixed at 140°C, and then extruded into die 2. did.

In die 2, the length of the molding area 2a was 200 m and the temperature was 140°C, and the length of the heating area 2b was 800 m and the temperature was 170°C. A certain amount of diethylene glycol was injected from an oil pump 9 between the molding area 2a and the heating area 2b.

The length of the cooling region 2C is 600 m, the temperature is 70° C., the internal pressure of the heating region 2b is set to 25 kg/cJ, and while monitoring the pressure with the pressure gauge 13, the tension control section 11 of the wire body 4.4 is set. .11 is operated, the diethylene glycol adhering to it is removed by the lubricant removal section 5, and both side parts 7b, 7b are cut and removed over the width IO, and the main body 7a of the partially foamed molded product is removed from the cooling area. Extruded continuously.

This foaming ratio M1 was 2. During this continuous operation, the pressure in the heating area 2b of the die 2 is 25±1kg/
Controlled within the cd range.

Moreover, the residual gel weight fraction of the obtained main body 7a was 43%.

Next, the main body 7a of the partially foamed molded product was introduced into a heating furnace 3 at a temperature of 200° C. to decompose the remaining foaming agent, and a foamed product 8 having an expansion ratio M of 16 was continuously produced. M, and M
, the relationship is M +/M t = 0.125.

The obtained foam 8 has a smooth appearance, a stable wall thickness of 21 cm, a density of 0.067 g/cn, and an average cell diameter of 12
It was 0 μm.

Example 2 The composition of the resin composition used was low density polyethylene (M+
2.0 g/10 min, density 0.920 g/'ci) 70
Part by weight, linear low density polyethylene (Ml1, 5g/
l Omin, density 0.920g/C1) 30 weight 1 part,
10 parts by weight of azodicarbonamide and 0.6 parts by weight of dicumyl peroxide, the temperature of the molding area 2a was 150°C, and the temperature of the heating area 2b was 175°C.
The main body 7a of the partially foamed molded product was continuously extruded from the cooling region 2c in the same manner as in Example 1, except that.

The residual gel weight fraction of the partially foamed product obtained was 49%.

Next, this partially foamed molded product was introduced into a heating furnace at 200° C. to continuously produce a foamed product. The obtained foam has a smooth appearance, a wall thickness of 20M, a stable structure, and a density of 0.
075 g/Cf1r, and the average bubble diameter was 110 μm.

Comparative Example 1 A crosslinked foam was produced under the same conditions as in Example 1 without operating the tension horn control section 11.11.

The pressure in the heating region 2b of the die was 5 kg/cd or less, and it was not possible to increase the pressure higher than this. Furthermore, the extruded state of the foam was unstable at 4°, and a phenomenon in which the partially foamed molded product 7 meandered from side to side was also observed.

The foamed body 8 obtained by foaming the main body 7a at the same temperature as in Example I had coarse pores with an average pore diameter of 380 μm.

(Effects of the Invention) As is clear from the above explanation, according to the method of the present invention and the manufacturing apparatus of the present invention, by adjusting the tension of the wire body penetrating the inside of the die, As a result, the desired pressure can be applied inside the die by braking the movement of the partially foamed product, which stabilizes the flow state of the partially foamed molded product as it moves within the heating area, and crosslinking progresses uniformly in the process, preventing bending and It is possible to stably produce a foam that has no cracks and has fine, uniform cells.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view showing an example of the apparatus of the present invention, and FIG. 2 is a schematic cross-sectional view taken along the line -■ in FIG. 2a... Molding area, 2b... Heating area, 2C...
cooling area, 3... heating furnace, 4... wire body, 5...
・Lubricant removal part, 6... Wire body extraction part, 7...
Partially foamed molded product, 7a... Main body of partially foamed molded product, 7
b... Side part of partially foamed molded product, 8... Foam, 9...
... Oil supply pump, 9a ... Oil supply pipe, 9b ... Suction pipe, lO ... Suction pump, 11- ... Tension control section, 12a, 12b, 12c ... Pulley, 13.
...Pressure gauge, 13a...Pressure path, 14...Cutter.

Claims (2)

[Claims] (1) A resin composition containing a thermoplastic resin, a foaming agent, and a crosslinking agent as essential components is extruded into a die in which a molding region, a heating region, and a cooling region are continuously formed, and the molding region or/and In the heating region, the crosslinking agent is decomposed and at the same time at least a portion of the blowing agent is decomposed to generate bubbles to form a partially foamed molded product, and then the partially foamed molded product obtained is transferred to the cooling region. In the method for producing a crosslinked foam, the partially foamed molded product is cooled to a temperature below the softening point of the partially foamed molded product, and then extruded from the die, and the extruded partially foamed molded product is heated and foamed under normal pressure. When the expansion ratio is M_1 and the expansion ratio of the crosslinked foam to be finally obtained is M_2, M_1 and M_2 are 0.05≦M_1/M_2≦0.
35 (however, M_2>M_1≧1.05), and is a partially foamed molded product that is introduced from the molding region, passes through at least one side of each region, and then extracted from the cooling region. At least one wire body is stretched so as to circulate inside and outside the die, and the tension of the wire body applies a braking force to the partially foamed molded product in a direction opposite to the extrusion direction thereof. Characteristic method for producing crosslinked foam. (2) An extruder for a resin composition containing a thermoplastic resin, a foaming agent, and a crosslinking agent as essential components; connected to the extruder, and a molding region, a heating region, and a cooling region are successively formed in this order. a die; a heating furnace connected to the die; and at least one wire introduced from the molding region, passed through at least one side of each region, and then led out from the cooling region. An apparatus for producing a crosslinked foam, characterized in that the body is stretched so as to circulate inside and outside the die.