JPS62211122A - Manufacture of crosslinking foamed body - Google Patents

Abstract

PURPOSE:To permit the extrusion molding of a foamed body provided with fine cell diameters from low foaming magnification to high foaming magnification by a method wherein lubricating agent is supplied to the part of sliding contact between a die and molten resin from the vicinity of the entrance of a continuous land die to control the back pressure of the molten resin in the continuous land die in a fore stage. CONSTITUTION:A given amount of lubricating agent is supplied from a lubricating agent supplying flange 4 through the slit 5 of the side wall of the entrance in the fore stage 8 of a continuous land die. A lubricating agent extracting flange 13 is provided at the outlet port of the fore stage 8 of the continuous land die to remove the lubricating agent interposing between the resin in the fore stage 8 of the continuous land die and the wall surface of the die while a choking die 21 is provided after the fore stage. A lubricating agent supplying flange 16 is provided at the outlet port of the intermediate section 9 of the continuous land die to supply the lubricating agent again to the interface between the resin and the wall surface of the die. Further, a resin pressure meter 3 and an opening and closing valve 19, provided in the conduit 14 of a lubricating agent extracting flange 13, are utilized for a pressure control system to close the valve 19 automatically when the resin pressure has exceeded a predetermined pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extrusion molding method for crosslinked foam, and more specifically, an extrusion molding method capable of producing a particularly thick crosslinked foam that is homogeneous and has a low expansion ratio to a high expansion ratio. Regarding improvements.

Conventionally, various methods have been known for producing crosslinked foams of thermoplastic resins. For example, after mixing a chemical blowing agent with a thermoplastic resin and molding it, irradiating it with ionizing radiation to crosslink it and heating it. After mixing a chemical foaming agent and a photosensitizer with a thermoplastic resin and molding it,
A method of irradiating ultraviolet rays to cause crosslinking and heating to foam, or a method of mixing a thermoplastic resin with a chemical foaming agent and a crosslinking agent having a lower decomposition temperature than the foaming agent, molding the resin, and then heating the mixture to form the crosslinking agent. decompose and crosslink,
Next, there is a method of foaming by decomposing the colorant using chemical foaming. Although these methods differ in the crosslinking process, they all use a process of foaming by heating under normal pressure using a chemical foaming agent. While being transported by a transport device such as a belt,
A heating method is used, such as an infrared heater or hot air.

In such foaming under normal pressure, when heated rapidly, only the surface of the resin foams, and the foamed area acts as a heat insulating layer and inhibits heat transfer to the inside of the resin. Since it is difficult to thermally decompose the blowing agent, a method of gradually heating the product over time is used, but even then, for thick-walled products of lO■ or more, it is difficult to thermally decompose the chemical foaming agent inside. Become. Therefore, the maximum thickness of the foam is about 20 mm, and in order to obtain a crosslinked foam with a thickness greater than that, it is necessary to bond the foams together. In addition, when heating and foaming during transportation, the foam sticks to the wire mesh endless belt, and the belt in contact with the foam may follow the foam in the traveling direction or lateral direction due to the volumetric expansion of the foam. Because of the difficulty, there is a problem that the foam may fold over or wrinkle. Furthermore, since heating is performed in the atmosphere at a high temperature of 200° C. or higher, thermal oxidative deterioration of the resin progresses at the same time, which poses the problem of adversely affecting the surface layer of the foam.

On the other hand, the production of cross-linked foam under pressure has traditionally been a one- or two-step production process in which a thermoplastic resin mixed with a cross-linking agent and a foaming agent is placed in a mold, heated, and foamed. This method has the characteristic of producing thick-walled foams with uniform, fine cells, but since it is a batch system, productivity does not increase, and it is difficult to produce large-sized foams. have.

The present inventors have previously proposed a method to solve these problems and continuously produce crosslinked foam (Japanese Patent Application No.
52548). That is, the thermoplastic resin is crosslinked and the blowing agent is decomposed in a long land die equipped with a drawing section.
The next step is foaming. According to this method, crosslinked foam can be obtained continuously, but the resin back pressure inside the die reacts sensitively to molding conditions such as temperature and discharge rate, and the amount of lubricant supplied, resulting in stable molding. In order to do so, further improvements were needed.

The present inventors have arrived at the present invention in order to solve this stubborn problem.

That is, the gist of the present invention is that after uniformly mixing a crosslinkable thermoplastic resin, a blowing agent, and a crosslinking agent having a heat content S@ higher than the melting temperature of the resin, the crosslinkable thermoplastic resin is mixed in a long land die. During extrusion, the fluidity of the resin is reduced by thermally decomposing the crosslinking agent to form crosslinks in the stage before the long land die, and then each time the blowing agent decomposes or blows once in the stage after the pure land die. In the method for producing a crosslinked foam, which is heated or depressurized as described above, and then extruded and foamed from the long land die, a lubricant is supplied from near the entrance of the long land die to the sliding contact between the goo and the molten resin. A drawing gou is provided between the front stage and the rear stage of the long land die to apply back pressure to the molten resin in the long land die at the front stage, and is further interposed at the sliding contact portion between the goo and the molten resin. This method of producing a crosslinked foam is characterized in that the amount of lubricant removed is adjusted according to the level of back pressure of the molten resin to control the back pressure of the molten resin.

With this configuration, it is possible not only to obtain a thick foam with a low expansion ratio to a high expansion ratio, but also to extrude a highly elastic foam with a fine cell diameter, and to achieve high productivity. That's what I was able to get.

The present invention will be explained in detail below.

The crosslinkable thermoplastic resin used in the present invention includes, for example, polyethylene, polypropylene, polystyrene, polyvinyl chloride, nylon, etc., or a copolymer mainly composed of the above-mentioned thermoplastic resin, such as ethylene-propylene copolymer, ethylene - Refers to copolymers such as vinyl acetate copolymer, ethylene-vinyl chloride copolymer, vinyl chloride-vinylidene chloride copolymer, and mixtures of these polymers, and further includes synthetic rubber, paraffin or It refers to a mixture of different thermoplastic resins and additives such as plasticizers, pigments, flame retardants, anti-static agents, fillers, and weathering agents, and crosslinking aids such as organic peroxides and polyfunctional monomers.

Furthermore, crosslinkable thermoplastic elastomers other than thermoplastic resins, such as ethylene-propylene copolymer elastomers, styrene-butadiene block copolymer elastomers, etc., and mixtures of the above-mentioned various additives; It also includes mixtures of.

In addition, the blowing agent used in the present invention may be a volatile blowing agent or a blowing agent that is solid at room temperature and that undergoes chemical thermal decomposition to produce nitrogen.
A decomposable blowing agent that generates gases such as carbon dioxide and ammonia is used. As volatile blowing agents, aliphatic hydrocarbons such as butane, pentane, hexane, heftane, aliphatic halogenated hydrocarbons such as methyl chloride, methyl fluoride, etc. are usually used. As a decomposable blowing agent, it is solid at room temperature and has a decomposition temperature higher than the plasticizing temperature of the resin used, and when heated above the G degree, it releases gases such as nitrogen, carbon dioxide, and ammonia. Compounds that decompose as they occur'
a proboscis, such as azodicarbonamide, a metal salt of azodicarbonamide, trihydrazinotriazine, 4
Examples include 14'-oxybisbenzenesulfonyl semicarbazide, 414'-oxybisbenzenesulfonyl hydrazide, N,N'-sility-N, and N'-dinitron terephthalamide. The amount of the blowing agent to be used is not particularly limited and may be determined as appropriate depending on the desired expansion ratio, but it is 1 to 100 parts by weight, preferably 1 to 40 parts by weight, based on 100 parts by weight of the resin. In addition, various foaming aids and nucleating agents can be added to these foaming agents as necessary.

Further, the crosslinking agent used in the present invention has a decomposition temperature higher than the melting start temperature of the thermoplastic resin used, and a crosslinking agent suitable for crosslinking the resin may be selected as appropriate.
Typical examples include dialkyl peroxide-based ditert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, 2,5
-dimethyl-2,5 di(tert-butylperoxy)
Organic peroxides such as hexane, α, α-bis(tert-butylperoxyisopropyl)benzene, or mixtures of two or more of these, and sulfur, and if desired, auxiliary agents such as crosslinking retarders and crosslinking promoters It is a mixture.

Note that the decomposition temperature of the crosslinking agent herein refers to the temperature at which the half-life is 10 minutes or less.

The amount of these crosslinking agents to be used needs to be determined depending on the molecular structure of the thermoplastic resin used, such as the molecular weight, molecular weight distribution, and number of branches, the decomposition temperature of the crosslinking agent, and the degree of crosslinking required. , specifically preferably 0.1 to 5% by weight, more preferably 0.2 to 2% by weight.

0.1g (When the amount is less than 7o, the fluidity of the resin decreases due to crosslinking, especially when using a crystalline thermoplastic resin, and as a result, the inside of the thick crosslinked foam becomes homogeneous. On the other hand, when the amount of paper is more than 5% by weight, the fluidity of the resin in the extruder decreases excessively, making it difficult to obtain a crosslinked foam with a homogeneous cell structure.

The lubricant used in the present invention is usually a chemical agent that does not easily decompose or boil at the molding temperature of the resin, does not dissolve in the resin, and does not accelerate the deterioration of the resin. Stable substances are preferred.

Specifically, liquid polysiloxanes (polydimethylsiloxane, polymethylsiloxane, etc.), polyhydric alcohols such as ethylene glycol and their alkyl esters and alkyl ethers, polyoxyalkylenes, and
A water-soluble surfactant such as a polyhydric alcohol, which can be easily removed after adhering to the surface of a molded article, is particularly preferred, and includes random, block, and graft copolymers of more than one type of alkylene oxide.

Next, the method for extrusion molding the crosslinked foam of the present invention will be described in detail with reference to the process diagrams of FIG.

A crosslinking agent is added to the crosslinkable thermoplastic resin, in particular in an extruder (1
), at a temperature at which the main part of the crosslinking agent does not react, and then a volatile foaming agent is injected in the middle of the cylinder or near the outlet of this extruder (1), mixed again, and then Extrude into a land die (8). Alternatively, a crosslinking agent and a decomposable blowing agent are uniformly mixed into a crosslinkable thermoplastic resin, particularly in an extruder (1), at a temperature at which the main parts of the crosslinking agent and decomposable blowing agent do not decompose. Shakurandai (8)
Push it inside.

A lubricant supply flange (4) capable of continuously supplying lubricant is provided near the entrance of a long land die (8) connected to the extruder (1). The supply 7 flange (4) has a structure as shown, for example, in FIG.
A lubricant can be applied to the outer surface of the resin from a supply device (7) through a conduit (6).

The lubricant may be supplied as long as it can be uniformly leached over the entire inner peripheral surface of the die and coated on the outer surface of the resin. Ceramics with a fine continuous cell structure are also interposed in this pond to leach the lubricant. Various methods such as the above may also be adopted.

The reason why the lubricant is supplied near the entrance (4) of the long land die is that as crosslinking bonds are formed in the resin due to decomposition of the crosslinking agent, the flowability of the resin decreases and the resin pressure increases. The reason for this is to allow the resin to move smoothly within the long land die using the lubricant, since this may lead to damage to the extruder.

The long land die (8) is equipped with a heater (not shown) so that the thermoplastic resin can be heated to a predetermined temperature.

Here, the resin moves while sliding through the long land die (8) under pressure and temperature at which the blowing agent does not explode or decompose, and during this time crosslinks are generated in the resin.

The degree of crosslinking is such that the amount fraction of residual gel (hereinafter referred to as gel fraction) after 10 hours of extraction near the boiling point of xylene is 5% or more, and preferably the gel fraction is determined from the relationship between foaming ratio and gel fraction. By setting the proportion to 10 to 70%, almost all the gas generated by the blowing agent can be used for foaming and expansion.

In addition, the length of the long land die necessary to generate a crosslinking bond with a gel fraction of 5% or more in the resin is determined by the resin temperature in the long land die, the molding speed, and the thermal conductivity of the resin at the molding temperature. It may be determined based on the decomposition characteristics of the crosslinking agent used, and usually 100 crlt to 3.000 crlt is preferred, and more preferably 20 QcIn to 2+0 (1 Ocm).
If it is less than 00 crlt, it is difficult to obtain homogeneous foam cells, while if it is more than 3.000 crlt, it is not necessary to obtain homogeneous cells.

At the position of the long land die that has reached a length sufficient to almost complete the cross-linking of the resin, that is, near the middle of the front stage part (8) and the rear stage part (9) of the long land die, there is a fourth
It is equipped with a drawing die as shown in the figure.

That is, in the pre-stage of the long land die, the blowing agent is heated under the back pressure applied by the drawing die QfJ installed near the middle of the long land die, and under a pressure that can suppress expansion due to volatilization of the blowing agent, or below the decomposition temperature. The resin is heated to decompose the crosslinking agent and form crosslinks in the resin. Many types of blowing agents normally used at this stage will partially volatilize or decompose to form bubbles in the resin, but in the present invention, the back pressure is reduced by the squeezing die C1). Because it is added, the formation of bubbles is not suppressed,
Cross-linking is smoothly generated.

The specific shape elements of the drawing die cl force are the cross-sectional area of the space in the long land die (8) K in the direction perpendicular to the direction in which the resin travels, and the cross-sectional area of the highest drawing part of the drawing die. ■ Ratio (aperture ratio) A/B is 100/20 to 100/9
8, preferably from 2/1 to 10/9.

In addition, the drawing die Qυ is provided with the same effect as the drawing die by combining two or more drawing dies outside the range of the drawing ratio, that is, the effect of applying back pressure to the front part (8) of the long land die. It is also possible.

Furthermore, a lubricant extraction flange α having a structure as shown in FIG. 3, for example, is provided to remove the lubricant present in the resin supplied into the long land die (8).

The resin from which the lubricant has been removed has reduced sliding properties with the long land die (9), resulting in an increase in resistance.
Long land die +8) (9) Increase the back pressure inside.

By decreasing or increasing the degree of lubricant removal in accordance with the level of resin back pressure, that is, the resin back pressure in the long land (8) sensed by the resin pressure gauge (3) can be set to a desired setting. If the pressure becomes higher than
By providing a response system that narrows or closes the opening of the resin back pressure, it is possible to stably control the resin back pressure and prevent the back pressure from increasing more than necessary. This is to prevent the shapeability of the crosslinked resin from deteriorating as the back pressure increases. The desired back pressure melting is usually 5 to 200 #/-, and from the viewpoint of molding stability, it is desirable that this back pressure fluctuation is as small as possible. The length of the long land die (9) required to control the desired back pressure may be determined depending on the shape of the resin, the amount of lubricant extracted, and the molding speed, and is usually 3061 mm.
1 to 500G is suitable.

Next, in the rear stage part (Ill) of the long land die,
In order to volatilize the blowing agent, the resin pressure is reduced or heated above the temperature at which it volatilizes and decomposes. The resin begins to expand in volume due to the volatilization and decomposition of the foaming agent, and expands sequentially as the die cross-sectional area increases in the latter stage of the long land die (II), and finally the foam molding is released from the long land die. Become strict.

Since the present invention has the above-described configuration, even if the foam is thick, it can be made into a highly foamed product that is uniform throughout the interior, and can be produced in a continuous process.

In addition, even though a long die is used, by using the above configuration, the extrusion speed is not reduced, but rather the extrusion speed is increased, and the foam can be efficiently produced. . Even when applied to crystalline polyolefin resins, especially high-density polyethylene resins, which have been considered difficult in the past, it has made it possible to achieve high, homogeneous foaming.

In the following, the invention will be further explained with reference to examples.

Example In the extrusion molding machine (1) shown in Figure 1, 100 parts by weight of high-density polyethylene (JX20 manufactured by Mitsubishi Yuka Co., Ltd.) and 15 parts by weight of a blowing agent (AC+3 manufactured by Eiwa Kasei Co., Ltd.) were mixed in advance to form particles. 0.8 parts by weight of a crosslinking agent (Perbutyl (manufactured by Nippon Oil & Fats Co., Ltd.) was added and mixed with the masterbatch.The extruder (1) was a single screw (L/D=22) at 865 mm. The cross section is 20w x 200
It was extruded into a long land die (8) of m length. Extrusion molding machine (
The resin thermometer near the exit of 1) f2) showed s°C. From the lubricant supply flange (4), lubricant (Nissan Uniloop 75D-3800 manufactured by Nippon Oil & Fats Co., Ltd.) is supplied.
A certain amount of 2) was supplied from the side wall of the entrance of the front part (8) of the long land die through the slit (5). In the long land die (8), the temperature is 170°C in the direction of resin progression.
, 170°C, 173°C, and 175°C. A lubricant extraction flange (13) is provided at the outlet of the front stage part (8) to remove the lubricant from the front stage part (8) of the long land die.
The lubricant interposed between the resin inside and the die wall surface was removed. Furthermore, a drawing die e2D with a drawing ratio of 3/2 was provided after that.

The length of the long land die middle part (9) is 1 m, and the cross section is 20 mm x 200 m, which is the same as the front part (8) of the long land die.
It was a. At the exit of the long land die middle part (9),
A lubricant supply flange was provided to supply lubricant again to the interface between the resin and the die wall.

Furthermore, the resin pressure gauge (3) and lubricant extraction flange α
The opening/closing valve holder provided in the conduit α4 was used as a pressure control system, and the valve tilt was automatically closed when the resin pressure exceeded 20 kg/dG.

In the intermediate portion of the long land die (9), heating was performed by providing a two-stage temperature distribution of 176° C. and 178° C. in the direction of resin travel.

Further, the resin pressure gauge (3) near the exit of the extrusion molding machine (1) at this time showed 20±5 ky/crA, indicating a stable molding target.

Furthermore, the gel fraction of the resin at the outlet of the intermediate portion (9) of the long land die was 41%.

Next, in the rear part Ql at) of the long land die,
In order to thermally decompose the blowing agent, 180°C, 185°C, 1
Heating was performed with a temperature distribution in four stages of 90°C and 190°C, and the length of the die was 3rn.

Further, the cross sections of the long land die rear section Ql) (111) are 30 m x 300 mm and 50 mm x 500 m, respectively, and are designed to expand as the resin expands.

In this way, the resin was extruded from the long land die 0 under atmospheric pressure, and the foam αa could be continuously extruded.

The foam Q3 according to this embodiment is a continuous foam board having a rectangular cross section of 63a + x 62Q;
It has fine bubbles of less than a micron, and the density is 0.02 s.
It was a plate-shaped foam having a skin layer of y/-.

Comparative Example In the example, molding was carried out while the valve holder provided in the lubricant extraction 7-lunge α hot water was fixed in an open position. Resin pressure was controlled by increasing or decreasing the amount of lubricant supplied from the lubricant supply flange (4), but the fluctuations in resin pressure ranged from 5 to 70#/cIIG! : Fluctuations made stable molding difficult.

[Brief explanation of drawings]

FIG. 1 is a sectional side view of a main part showing an embodiment of a device to which the present invention is applied. 1: Extruder 2: Resin thermometer 3: Resin pressure gauge 4: Lubricant supply flange 5 Nislit section 6: Conduit 7: Lubricant supply device 8: Long land die front section 9: Intermediate section 10: Back section (1) 11: I(2) 12: Foamed molded product 13: Lubricant drain flange 14: Conduit 15: Lubricant amount is determined by container 16: Lubricant supply flange 17: Lubricant supply device 18: Conduit 19; Open/close pulp 21: Reprint of drawing die specifications (no changes in content) 22: Pressure control system Figure 2 is a detailed view of the lubricant supply flange Figure 3 is a detailed view of the lubricant extraction 7 flange Figure 4 is a detailed view of the drawing die Patent Applicant Mitsubishi Yuka Co., Ltd. Agent Patent Attorney Hidetoshi Furukawa Agent Masahisa Hase Figure 2 Figure 3 Figure 4 Procedural Amendment (Form) June 3, 1986

Claims (1)

[Claims] After uniformly mixing a crosslinkable thermoplastic resin, a blowing agent, and a crosslinking agent having a thermal decomposition temperature higher than the melting temperature of the resin, the crosslinking agent is extruded into a long land die, and the crosslinking agent is added at a stage before the long land die. The fluidity of the resin is reduced by thermally decomposing it to form cross-linked bonds, and then heating or reducing the pressure to a temperature higher than the temperature at which the blowing agent decomposes or volatilizes at a later stage of the long land die, and then removing it from the long land die. In a method for producing crosslinked foam by extrusion and foaming, a lubricant is supplied from near the entrance of the long land die to the sliding contact area between the die and the molten resin, and a lubricant is supplied between the front stage and the rear stage of the long land die. A drawing die is provided to apply back pressure to the molten resin in the long land die in the previous step, and the amount of lubricant removed at the sliding contact between the die and the molten resin is determined by the level of back pressure of the molten resin. 1. A method for producing a crosslinked foam, characterized by controlling the back pressure of a molten resin by adjusting it according to.