JPS591232A - Method for producing crosslinked foam - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 thermoplastic resin with an iponic foaming agent and molding the mixture, irradiation with ionizing radiation causes crosslinking. A method in which a thermoplastic resin is mixed with a chemical foaming agent and a photosensitizer and then molded, and then irradiated with ultraviolet rays to crosslink and foamed by heating. Alternatively, there is a method in which a crosslinking agent having a decomposition temperature lower than that of the foaming agent is mixed and molded, followed by heating to first decompose the crosslinking agent and cause crosslinking, and then decompose the chemical foaming agent and foam. Although these methods differ in the crosslinking process, they all agree that they use a chemical foaming agent and foam by heating under normal pressure. While being transferred by a transfer device such as a pelt,
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 foaming agent, a method of gradually heating the product over time is used, but even then, if the product is thicker than 10m, it becomes difficult to thermally decompose the chemical foaming agent inside. . Therefore, the maximum thickness of the foam is about 20 sam, and in order to obtain a crosslinked foam with a thicker thickness, 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 manufacturing process in which a compound of 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. This led to the invention.

That is, the gist of the present invention is to uniformly mix a crosslinkable thermoplastic resin, a blowing agent, and a crosslinking agent having a thermal decomposition temperature higher than the melting temperature of the resin, and then extrude the mixture into a long land die. , the fluidity of the resin is reduced by thermally decomposing the crosslinking agent to form crosslinks in a stage before the long land die, and then at a temperature higher than that at which the blowing agent volatilizes or decomposes in a stage after the long land die. In a method for producing a crosslinked foam in which the foam is heated to a temperature of A cross-linked foam characterized in that a drawing die is provided between the front stage and the rear stage of the land die, and back pressure is applied in the front stage to prevent bubbles caused by the foaming agent from forming in the molten resin in the long land die. This is a manufacturing method.

The present invention includes a crosslinking process in which the crosslinking agent is decomposed at a temperature below the volatilization or decomposition temperature of the blowing agent at a temperature before the long land die to form crosslinks and reduce the fluidity of the resin; An intermediate drawing die is provided to separate the foaming process from the subsequent foaming process in which the foaming agent is heated to a temperature higher than the temperature at which the foaming agent evaporates or decomposes. That is, many kinds of blowing agents that are commonly used in the crosslinking process that generate crosslinking bonds and reduce the fluidity of the resin partially volatilize or decompose to form bubbles in the resin.
It acts to retard cross-linking. This is because the thermal conductivity of the resin with the formation of air bubbles decreases, making it difficult to transfer enough heat to decompose the crosslinking agent. Furthermore, if bubbles are formed in the resin before the crosslinking can maintain sufficient viscosity for the resin to foam, the cell diameter of the resin foam after molding may become extremely non-uniform. Take.

In addition, the back pressure that must be applied by the 9-diaphragm die provided near the exit of the long land die is sufficient to dissolve the gas generated by decomposition of the blowing agent into the resin, whereas the present invention In this method, a drawing die was provided in the middle between the front stage and the rear stage of the long land die to apply back pressure to the molten resin in the front stage, so that the process of forming crosslinks in the front stage The back pressure that must be applied can be kept low because the back pressure that is sufficient to dissolve the gas generated by partial volatilization or decomposition of the blowing agent that occurs in the resin is sufficient. Therefore, the method of applying back pressure such as a drawing die provided in the long land die can also be simplified.

The present invention will be explained in detail below.

Examples of the crosslinkable thermoplastic resin in the present invention include high-density and low-density polyethylene, polystyrene, polypropylene, polyvinyl chloride, and nylon, or copolymers mainly composed of these thermoplastic resins, such as ethylene-propylene copolymer. Combined.

Which copolymers such as ethylene vinyl acetate copolymers and their mixtures are used as Asho or EPR%EPDM, SBR, I
It can also contain elastomers such as IR, as well as rubber and the like. Furthermore, it refers to a mixture of these thermoplastic resins with paraffin or different thermoplastic resins, and additives such as plasticizers, pigments, flame retardants, antistatic agents, and weathering agents.

The present invention can obtain homogeneous cross-linked foams of polyolefin resins and other crystalline thermoplastic resins with a range of expansion ratios from low to high. It has the characteristic of being able to be molded into thick cross-linked foams.

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 ditertiary-butyl peroxide, tertiary-butylcumyl(-oxide), dicumyl peroxide,
α-α-(bisterstiarybutylbaroxydiisoglobil)benzene, 2 tablespoons 5 dimethyl-2,5-di(tert-butyl peroxy)hexane, 2,5-dimethyl 2,5 di(tert-butyl peroxy) An organic peroxide such as oxy)hexyne-3 or a mixture of two or more of these and sulfur are mixed with auxiliary agents such as a crosslinking retarder and a crosslinking accelerator, if desired.

Note that the decomposition temperature of the crosslinking agent herein refers to the temperature at which the half-life is 1 minute or more.

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.

When the amount is less than 0.1% by weight, especially when using a crystalline thermoplastic resin, the fluidity of the resin is insufficiently reduced due to crosslinking, and as a result, homogeneous bubbles form inside the thick crosslinked foam. They tend to be difficult to structure. On the other hand, when the amount of paper is more than 5% by weight, the fluidity of the resin in the extruder is excessively reduced, making it difficult to obtain a crosslinked foam with a homogeneous cell structure.

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, heptane, etc. and aliphatic halogenated hydrocarbons such as methyl chloride and methyl fluoride are usually used. Degradable blowing agents include those having a decomposition temperature higher than the decomposition temperature of the crosslinking agent used, such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisinbutyronitrile, p-p'-oxybis These blowing agents include benzenesulfonyl hydrazide, and various auxiliary agents can be used as necessary for these blowing agents. Moreover, two or more types of these blowing agents can also be used in combination.

Next, the method for extrusion molding the crosslinked foam of the present invention will be described in detail with reference to the process diagram in FIG. Inside, the main parts of the crosslinking agent and foaming agent are mixed uniformly under temperature and pressure that will not volatilize and decompose, and extruded into the long land dies (2) and (3). Lubricant is continuously supplied to the vicinity of the land die population (4). As shown in FIG. 2, slits 2a are formed around the entire circumference of the long land die (2) in sliding contact with the long land die (4) to enable supply of lubricant.

The thermoplastic resin fed into the long land die is subjected to substantial cross-linking under pressurized conditions in the front stage (2) of the long land die, and is then treated with a blowing agent in the rear stage (3) of the long land die. It is volatilized or decomposed and extruded under atmospheric or controlled pressure to form a uniformly foamed crosslinked foam.

A drawing die (6) is provided near the middle square between the front stage part (2) and the rear stage part (3) of the long land die.

That is, in the pre-stage of the long land die, the foaming is carried out under the back pressure applied by the drawing die (6) K provided near the middle of the long land die, and under a pressure that can suppress expansion due to volatilization of the blowing agent. The crosslinking agent is decomposed by heating below the decomposition temperature to 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 drawing die (6). Because it is added, no bubbles are formed and crosslinking is smoothly generated.

The specific shape elements of the several-second die (6) include the cross-sectional area (■) of the space in the long land die (2) 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 (6). (b) Ratio (aperture ratio) A/B is 100/20~Zoo
/98 Preferably it is 2/1 to 10/9.

By combining two or more several-second dies outside the range of the drawing ratio, the magnifying drawing die (6) has the same effect as the drawing die, that is, back pressure is applied to the front part of the long land die (2). Any material is acceptable as long as it provides the effect of

In addition, the degree of crosslinking when crosslinking is generated in this preliminary step is such that the residual gel weight fraction (hereinafter referred to as gel fraction) is 5% or more after 10 hours of extraction near the boiling point of xylene. By setting the proportion to preferably 10 to 70%, almost all of the gas generated by the blowing agent can be used for foaming and expansion.

In addition, the length of the long land die required to progress crosslinking to the extent that the resin loses fluidity 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 can be determined based on the decomposition characteristics of the crosslinking agent to be used, and usually the pre-stage part (2) is preferably 50 to 2,000 cm, and more preferably 200 cat to 1,000 cm.・505+
Below it is difficult to obtain homogeneous foam cells, while above 2,000 cm is not necessary to obtain homogeneous cells.

The reason for supplying the lubricant near the entrance (4) of the long land die is that as the crosslinking agent decomposes and crosslinks are formed in the resin, the flowability of the resin decreases, and as the crosslinking progresses further, the flowability of the resin decreases. As the flowability of the resin decreases, the resin pressure increases, leading to damage to the extruder.Also, as the flowability of the resin decreases, it becomes difficult to shape the resin as required. This is to allow the resin to move smoothly. As a lubricant,
Generally, it is preferable to use a chemically stable substance that is unlikely to cause decomposition, boiling, etc. at the molding temperature of the resin, does not dissolve in the skeleton resin, and does not accelerate the deterioration of the resin. Specifically, liquid polysiloxanes (polydimethylsiloxane, polymethylsiloxane, etc.), polyhydric alcohols such as ethylene glycol and their alkyl esters, alkyl ethers, polyoxyalkylenes, and random, block, and grafts of two or more alkylene oxides. Copolymers etc. are used. Among these, preferred are water-soluble surfactants such as polyhydric alcohols, which are easy to remove after adhering to the surface of the molded article.

Next, in the subsequent step (3) of the long land die, the resin is gradually heated to a temperature higher than the temperature at which the foaming agent volatilizes or decomposes, and the resin is foamed while being released from the long land die to obtain a crosslinked foam.

In the step (3) after the long land die, it is preferable to use a long land die having an area change that somewhat suppresses the tendency of the resin to expand in volume due to foaming. When trying to obtain a foam, the die structure must be such that the volume expansion due to foaming can be absorbed in stages.

The length of the rear part (3) of the long land die necessary for thermally decomposing the foaming agent mixed in the resin varies depending on the thickness of the resin, but usually the length of the long land die necessary for the crosslinking is The length may be about 1/5 to 2 times the length of the front part (2) of , and preferably about 1/3 to 2/3 times.

Since the present invention has the above-mentioned configuration, even if the foam is thick, it can be made uniform throughout the inside, and furthermore, it can be produced through a continuous process. In addition, even though a long die is used, by using the configuration described above, the extrusion speed can be improved without reducing the extrusion molding speed, and the foam can be efficiently produced. be. Furthermore, even when applied to crystalline polyolefin resins, especially high-density polyethylene/polypropylene resins, which have been considered difficult in the past, it has become possible to achieve high, homogeneous foaming.

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

Example 1 In the extrusion molding machine (1) shown in Fig. 1, 100 parts by weight of low density polyethylene (LK50, manufactured by Mitsubishi Yuka Co., Ltd.) and 7 parts by weight of a blowing agent (AC''3, manufactured by Eiwa Kasei Co., Ltd.) were mixed in advance. The granulated material was mixed with 1.0 parts by weight of a crosslinking agent (Percumil D manufactured by Nippon Oil & Fats Co., Ltd.) and supplied.
1) is heated from outside the cylinder with an electric heater, and the resin thermometer (8) near the exit of the extrusion molding machine (1) measures 162°C.
was extruded into a long land die (2) with an inner diameter of 21w+. A certain amount of lubricant (Nissan Uniloop 75D-2620 manufactured by NOF Corporation) is supplied from the lubricant delivery device (9) to the side wall of the entrance of the front stage part (2) of the long land die (
4). In the pre-stage part (2) of the long land die, the temperature is 165°C, 168°C,
Heating was performed with a temperature distribution in four stages of 172°C and 175°C, and back pressure was applied with an intermediate drawing die (6) having a drawing ratio of 2/5 and the shape shown in Fig. 3, and at this time, The length of the front stage part (2) of the long land die was 2 m. The resin at the intermediate drawing die (6) was crosslinked to the extent that it lost fluidity, and the gel fraction at that time was 35%. Next, in the latter stage part (3) of the long land die, in order to thermally decompose the blowing agent, the temperature is 185°C, 195°C, and 202°C.
Heating was performed with a temperature distribution in three stages, and the length of the die was 1 m.

A drain is provided at a position (7) near the exit of the long land die to draw out the lubricant, and at the exit of the long land die, sufficient pressure is applied to dissolve the gas generated by the decomposition of the foaming agent into the resin. ■■■-■ A low drawing die (5) was installed to provide back pressure, and its ratio A/B in seconds was 4/1.In this way, the molten resin was drawn from the drawing die (5) under atmospheric pressure. Extruded foam (II) could be continuously extruded.The resin pressure gauge (6) installed near the exit of the extruder was 35 Kf/cIII, and for comparison, no crosslinking agent was included. The resin pressure when extruding the resin is 7 K.
It was f/cd.

The foam α force according to this example has a diameter of %i3.8clI
4, has microbubbles of 20 microns or less, and has a density of 0.
It was a rod-shaped foam of 065t/cC.

Example 2 In the extrusion molding machine (1) shown in Fig. 4, 100 parts by weight of low-density polyethylene (LK50, manufactured by Mitsubishi Yuka Co., Ltd.) and 7 parts by weight of a blowing agent (AC3, manufactured by Eiwa Kasei Co., Ltd.) were mixed in advance to form particles. and a crosslinking agent (Percumil D manufactured by Nippon Oil & Fats Co., Ltd.)
) 1.0 part by weight was added and mixed and supplied. The extrusion molding machine (1) is heated from the outside of the cylinder with an electric heater, and the resin thermometer (8) near the exit of the extrusion molding machine (1) measures 162.
℃ and extruded into a long land die (2) with an inner diameter of 21 m. A certain amount of lubricant (Nissan Uniloop 75D-2620 manufactured by NOF Corporation) is supplied from the lubricant delivery device (9) to the side wall of the entrance of the front stage part (2) of the long land die (
4). In the pre-stage part (2) of the long land die, the temperature is 165°C, 168°C,
Heating is performed with a temperature distribution in four stages of 172°C and 175°C, and back pressure is applied with a drawing die (6) having a drawing ratio of 2/5 and the shape shown in Fig. 3. The length of the front stage part (2) of the shakuland die was 3 m.

The resin at the drawing die (6) was crosslinked to the extent that it lost fluidity, and the gel fraction at that time was 43%.

Next, in the rear stage part (3) of the long land die,
In order to thermally decompose the blowing agent, 185°C, 195°C, 2
Heating was performed with a temperature distribution in three stages of 0.2°C, and the length of the die was 2.5 m. In this way, it was possible to continuously extrude the molten resin through the long land die (3) under atmospheric pressure to form a foam. In addition, the resin pressure gauge (7) installed near the exit of the extrusion molding machine is 20K.
It was f/-.

The foam α) according to this example has a diameter of 'i 3.8 ty.
m, has fine bubbles of 20 microns or less, and has a density of 0.
0659/C! : It was a rod-shaped foam.

Example 3 Ethylene-vinyl acetate copolymer (Mitsubishi Yuka Co., Ltd. E)
VA-20K) and 5 parts by weight of a blowing agent (AC3 manufactured by Eiwa Kasei Co., Ltd.) were kneaded into granules.
After preliminarily adding and mixing 0.8 parts by weight of Percmill D (manufactured by Nippon Oil & Fats Co., Ltd.), the same molding as in Example 2 was carried out, and the resulting product had fine cells with a diameter of 3.5 cm and a cell diameter of 20 microns or less. A foam having a density of 0.097 t/cr was obtained.

Example 4 High-density polyethylene (JX20 manufactured by Mitsubishi Yuka Co., Ltd.) 1
00 parts by weight of foaming agent (AC3 manufactured by Eiwa Kasei Co., Ltd.) 15
Parts by weight were uniformly mixed and granulated through an extruder to obtain a blowing agent masterbatch. High-density polyethylene (EY4 manufactured by Mitsubishi Yuka Co., Ltd.) was added to 97 parts by weight of this blowing agent masterbatch.
After adding 3 parts by weight of powder of 0 C) to make 100 parts by weight, a crosslinking agent (Perhexine 2.51 manufactured by NOF Corporation) was added.
Add 0.4 parts by weight of () and mix uniformly, then use an extruder (
1) and molded.

The cross-sectional shape of the long land die is rectangular, and the total length is 5.3 m. Is the front part (2) of the long land die 2.5f? t
, the aperture (6) is 0.3m, and the rear part (3) is divided into three parts.
It consisted of five sections: a first rear section of 1.0 m, a second rear section of 1.0 m, and a third rear section of 110.5 m. The cross-sectional dimensions of each part are: the front part (2) is 20 x 100 m, the minimum cross section of the drawing die (6) is 15 x 75 pieces, and the first rear part is 20 x 1
00sm+*Second rear section 25X125m, third rear section 4
It is 0x200■.

Further, at this time, the resin temperature measured by the resin thermometer (8) installed near the exit of the extruder (1) was 164° C., and the resin pressure gauge o1 was 72V4/alI.

The temperature of each part of the long land die is 163°C and 165°C, respectively, from the four points in the front stage (2) inlet side.

168°C, 171°C, and 168°C in the first rear section.

The temperatures were 165°C and 166°C at two points in the second rear stage, respectively, and 165°C at one point in the third rear stage.

The cross-sectional dimensions of the foam obtained by this molding are 50 x 25
It had a rectangular shape of 0 Wm and a continuous board shape. Further, the density of this foam was 0.302 t/cC, and the foam had fine cells with a bubble diameter of zoo microns or less.

Furthermore, when the board obtained by this molding was sliced into 3-inch thick slices with the edge of a belt, a flexible foamed sheet was obtained.

[Brief explanation of the drawing]

Fig. 1 is a side view of the process of the present invention, Fig. 2 is an enlarged sectional view near the entrance of the long land die, and Fig. 3 is an intermediate drawing die (6).
, FIG. 4 is a side view of another process. 1: Extruder 2: Pre-stage section of long land die 3: Post-stage section of long land die 4: Lubricating oil supply section 5: Drawing die 6: Intermediate drawing die 8; Resin thermometer 9: Lubricant delivery device 10: Resin pressure gauge 11: Foam product

Claims (1)

[Claims] l) After uniformly mixing a crosslinkable thermoplastic resin, a blowing agent, and a crosslinking agent having a thermal decomposition temperature 9 times higher than the melting temperature of the resin, the mixture is extruded into a long land die, and the mixture is extruded into a long land die in the pre-stage of the long land die. The fluidity of the resin is reduced by thermally decomposing the crosslinking agent to generate crosslinks, and then the blowing agent is heated to a temperature higher than the temperature at which the blowing agent volatilizes or decomposes at a later stage of the long land die, and then the long land die In a method for producing crosslinked foam that is extruded and foamed from a land die, 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 the lubricant is supplied to the sliding contact area between the die and the molten resin. A method for producing a crosslinked foam, characterized in that a drawing die is provided in the middle, and a back pressure is applied in a previous stage to prevent bubbles caused by the foaming agent from forming in the molten resin in the long land die.