JPS641292B2 - - Google Patents

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, such as:
A method in which a thermoplastic resin is mixed with a chemical blowing agent and molded, and then irradiated with ionizing radiation to cause crosslinking and heated to foam.A method in which a chemical blowing agent and a photosensitizer are mixed in a thermoplastic resin and molded, and then ultraviolet rays are applied Alternatively, a thermoplastic resin is mixed with a chemical blowing agent and a crosslinking agent having a lower decomposition temperature than the blowing agent, and then molded, and then heated to form a crosslinking agent. There are methods such as decomposing and crosslinking, then decomposing a chemical foaming agent and foaming. 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 transported by a transport device such as a belt,
A heating method such as an infrared heater or hot air is used.

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 it over time is used, but even then, if the product is thicker than 10 mm, it is difficult to thermally decompose the chemical foaming agent inside. . Therefore, the maximum thickness of the foam is about 20 mm, and obtaining a crosslinked foam with a thickness greater than that depends on the above-mentioned bonding of the foam. 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 carried out 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 crosslinked foams under pressure has traditionally been
A one- or two-step manufacturing process is used in which a compound made by mixing a thermoplastic resin with a crosslinking agent and a foaming agent is placed in a mold, heated, and foamed, resulting in a thick foam with uniform, fine cells. However, since it is a batch system, productivity does not increase and it is difficult to produce large foams.

The present inventors have arrived at the present invention in order to improve the deficiencies of the methods according to the prior art.

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 the stage before the long land die, and then the temperature at which the blowing agent volatilizes or decomposes or higher in the stage after the long land die is heated. In a method for producing a crosslinked foam in which the foam is heated and then extruded from the long land die and foamed, 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 long land die A crosslinked foam characterized in that a drawing die is provided between the front stage and the rear stage, 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 the 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. In other words, many types of blowing agents that are commonly used in the crosslinking process, which generate crosslinks and reduce the fluidity of the resin, partially volatilize or decompose, forming air bubbles in the resin and delaying the crosslinking. work to do. This is because the thermal conductivity of the resin in which bubbles are formed decreases, making it difficult for sufficient heat to be transmitted to decompose the crosslinking agent. Additionally, if bubbles are formed in the resin before cross-linking can maintain sufficient viscosity for the resin to foam, the cell diameter of the resin foam after molding may become extremely non-uniform. .

In addition, the back pressure that must be applied by the drawing die installed near the exit of the long land die is sufficient to dissolve the gas generated by decomposition of the blowing agent into the resin. In the present invention, a drawing die is provided at an intermediate portion 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 cross-linking is not generated 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 in the resin during the process of foaming is sufficient. . Therefore, the method for applying back pressure using a drawing die or the like provided in the long land die can also be simplified.

The present invention will be explained in detail below.

The crosslinkable thermoplastic resin in the present invention includes:
For example, high-density or low-density polyethylene, polystyrene, polypropylene, polyvinyl chloride, nylon, or copolymers based on these thermoplastic resins, such as ethylene-propylene copolymers,
There are copolymers such as ethylene vinyl acetate copolymer and mixtures thereof, as well as EPR, EPDM,
It can also contain elastomers such as SBR and IIR, as well as rubber. Furthermore, it refers to a mixture of these thermoplastic resins with paraffin or a different type of thermoplastic resin, and additives such as plasticizers, pigments, flame retardants, antistatic agents, and weathering agents.

The present invention can obtain homogeneous cross-linked foams with 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 appropriately selected. Examples include dialkyl peroxide-based ditertiary butyl peroxide, tertiary butyl cumyl peroxide, dicumyl peroxide, α-α-
(bistersialbutylperoxydiisopropyl)benzene, 2,5 dimethyl-2,5-di(tertiarybutylperoxy)hexane,
An organic peroxide such as 2,5-dimethyl 2,5-di(tertiarybutylperoxy)hexyne-3 or a mixture of two or more of these and sulfur, optionally with auxiliary agents such as a crosslinking retarder and crosslinking accelerator. It is a mixture.

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
0.2-2% by weight is used. If it is less than 0.1% by weight, especially when using a crystalline thermoplastic resin, crosslinking will not sufficiently reduce the fluidity of the resin, resulting in a homogeneous cell structure inside the thick crosslinked foam. It tends to be difficult. On the other hand, when the amount is more than 5% by weight, the fluidity of the resin within the extruder is excessively reduced, making it difficult to obtain a crosslinked foam with a homogeneous cell structure.

Further, as the blowing agent used in the present invention, a volatile blowing agent or a decomposable blowing agent that is solid at room temperature and generates gases such as nitrogen, carbon dioxide, and ammonia by chemical thermal decomposition 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 that of the crosslinking agent used, such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, 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. The main parts of the cross-linking agent and the blowing agent are mixed uniformly under temperature and pressure that will not volatilize and decompose and are extruded into the long land dies 2 and 3. Continuous supply of lubricant. As shown in FIG. 2, a slit 2a is formed in the vicinity 4 of the long land die around the entire circumference of the long land die 2 in sliding contact with the resin, so that lubricant can be supplied.

The thermoplastic resin supplied into the long land die is heated under pressure to the front stage part 2 of the long land die.
The foaming agent is then volatilized or decomposed in a post-stage section 3 and extruded under atmospheric or controlled pressure to form a uniformly expanded crosslinked foam.

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

That is, at the stage before the long land die, the blowing agent is decomposed under the back pressure applied by the drawing die 6 installed near the middle of the long land die, and under a pressure that can suppress expansion due to volatilization of the blowing agent. Heating below this temperature decomposes the crosslinking agent and forms crosslinks in the resin. In many types of blowing agents normally used at this stage, a portion of them evaporates or decomposes 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,
Cross-linking is smoothly generated.

As a specific shape element of the drawing die 6, the ratio of the cross-sectional area A of the space in the long land die 2 in the direction perpendicular to the direction of travel of the resin to the cross-sectional area B of the highest drawing part of the drawing die 6 (drawing ratio ) A/B from 100/20
100/98, preferably 2/1 to 10/9.

In addition, the drawing die 6 can provide the same effect as the drawing die, that is, the effect of applying back pressure to the front part 2 of the long land die, by combining two or more drawing dies with drawing ratios outside the above range. It's good to have.

In addition, the degree of crosslinking when crosslinking is generated in the previous 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 xylene boiling point, and is preferably Ten~
By setting it 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. This can be determined based on the decomposition characteristics of the crosslinking agent used, and the pre-stage part 2 is usually 50~
2000cm is suitable, and 200cm to 1000cm is more preferable. Below 50 cm, it is difficult to obtain homogeneous foam cells, while above 2000 cm is not necessary to obtain homogeneous cells.

The reason why the lubricant is supplied 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 resin loses its properties, the pressure of the resin increases, which in turn leads 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 the lubricant, it is usually preferable to use a chemically stable substance that is unlikely to decompose, boil, etc. at the molding temperature of the resin, does not dissolve in the resin, and does not promote deterioration of the resin. Specifically, liquid polysiloxanes (polydimethylsiloxane, polymethylsiloxane, etc.), polyhydric alcohols such as ethylene glycol, and their alkyl esters and alkyl ethers, polyoxyalkylenes, and random, block, and grafts of two or more types of 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.

Then, in the post-stage 3 of the long land die,
The resin is gradually heated to a temperature higher than that at which the foaming agent volatilizes or decomposes, and while the resin is being foamed, it is released from a 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, and particularly when the expansion ratio is 10 times. In order to obtain the above foamed product, the die structure must be such that the volumetric 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 above-mentioned crosslinking is It is sufficient that the length is about 1/5 to 2 times the length of the front part 2 of the
It is about 2/3 times as large.

Since the present invention has the above-mentioned configuration, even if it is a thick foam, it can be made into a uniform constraining body throughout the interior, and furthermore, it can be produced by 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 produced efficiently. It is. Furthermore, even when applied to crystalline polyolefin resins, particularly high-density polyethylene and 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 to form granules. 1.0 parts by weight of a crosslinking agent (Percumil D manufactured by Nippon Oil & Fats Co., Ltd.) was added and mixed and supplied. The extrusion molding machine 1 was 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 showed a temperature of 162°C, and the resin was extruded into the long land die 2 having an inner diameter of 21 mm. The lubricant (Nitsun Unilube manufactured by Nippon Oil & Fats Co., Ltd.) is supplied from the lubricant delivery device 9.
75D-2620) was supplied from the side wall 4 at the entrance of the front stage section 2 of the long land die. In the pre-stage part 2 of the long land die, heating is performed by giving a temperature distribution in four stages of 165°C, 168°C, 172°C, and 175°C in the direction of resin progression, and further, the drawing ratio is 2/5. Back pressure was applied by an intermediate drawing die 6 having 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 rear stage part 3 of the long land die, heating is performed with a temperature distribution in three stages of 185°C, 195°C, and 202°C in order to thermally decompose the foaming agent, and the length of the die is 1 m.
It was hot. An exhaust port is provided at position 7 near the exit of the long land die to drain the lubricant, and
A drawing die 5 is provided at the outlet of the long land die to apply back pressure sufficient to dissolve the gas generated by the decomposition of the blowing agent into the resin, and the drawing ratio A/
B was 4/1. In this way, the molten resin was squeezed and extruded from the die 5 under atmospheric pressure to continuously extrude mold the foam 11. In addition, the resin pressure gauge 10 installed near the exit of the extrusion molding machine has a pressure of 35 kg/
cm ² , and for comparison, the resin pressure when extruding a resin containing no crosslinking agent was 7 Kg/cm ² .

The foam 11 according to this embodiment has a diameter of approximately 3.8 cm.
It has fine bubbles of 20 microns or less, and the density is
It was a rod-shaped foam with a weight of 0.065 g/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 (AC#3, manufactured by Eiwa Kasei Co., Ltd.) were mixed in advance to form granules. 1.0 parts by weight of a crosslinking agent (Percumil D manufactured by Nippon Oil & Fats Co., Ltd.) was added and mixed and supplied. The extrusion molding machine 1 was 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 showed a temperature of 162°C, and the resin was extruded into the long land die 2 having an inner diameter of 21 mm. The lubricant (Nitsun Unilube manufactured by Nippon Oil & Fats Co., Ltd.) is supplied from the lubricant delivery device 9.
75D-2620) was supplied from the side wall 4 at the entrance of the front stage section 2 of the long land die. In the pre-stage part 2 of the long land die, heating is performed by giving a temperature distribution in four stages of 165°C, 168°C, 172°C, and 175°C in the direction of travel of the resin, and the drawing ratio is 2/5.
Applying back pressure with a drawing die 6 having the shape shown in Fig. 3,
At this time, the length of the front stage part 2 of the long land die was 3 m. The resin at the drawing die 6 is crosslinked to the extent that it loses fluidity, and the gel fraction at that time is
It was 43%. Next, in the rear stage section 3 of the long land die, in order to thermally decompose the foaming agent,
Heating was performed with a temperature distribution in three stages: 185°C, 195°C, and 202°C, and the length of the die was 2.5 m.
In this way, the molten resin was extruded from the long land die 3 under atmospheric pressure to continuously extrude mold the foam 11. In addition, the resin pressure gauge 10 provided near the exit of the extrusion molding machine was 20 kg/cm ² .

The foam 11 according to this example has a diameter of approximately 3.8 cm,
It has micro bubbles of 20 microns or less, and the density is 0.065.
It was a rod-shaped foam of g/cc.

Example 3 100 parts by weight of ethylene-vinyl acetate copolymer (EVA-20K, manufactured by Mitsubishi Yuka Co., Ltd.) and 5 parts by weight of a blowing agent (AC#3, manufactured by Eiwa Kasei Co., Ltd.) were kneaded into granules, and a crosslinking agent was added to the resin. (Perc Mill D manufactured by Nippon Oil & Fats Co., Ltd.) 0.8 parts by weight was added and mixed in advance, and molded in the same manner as in Example 2 above, resulting in a density product with a diameter of approximately 3.5 cm and fine cells having a cell diameter of 20 microns or less.
A foam of 0.097 g/cc was obtained.

Example 4 High-density polyethylene (manufactured by Mitsubishi Yuka Co., Ltd.)
JX20) 100 parts by weight of foaming agent (manufactured by Eiwa Kasei Co., Ltd.)
AC# 3) 15 parts by weight were uniformly mixed and granulated through an extruder to form a blowing agent master patch. Add 97 parts by weight of this foaming agent master patch to 3 parts by weight of powder of high-density polyethylene (EY40C manufactured by Mitsubishi Yuka Corporation).
After adding parts by weight to make 100 parts by weight, 0.4 parts by weight of a crosslinking agent (Perhexine 2.5B manufactured by Nippon Oil & Fats Co., Ltd.) was added, mixed uniformly, and then fed to extruder 1 and molded.

The cross-sectional shape of the long land die is rectangular and the total length is
It is 5.3m. For long land dies, the front part 2 is 2.5
m, aperture 60.3, the rear part 3 is divided into three parts, and the first
It consists of five sections: a rear section of 1.0 m, a second rear section of 1.0 m, and a third rear section of 0.5 m. The cross-sectional dimensions of each part are 20 x 100 mm for the front section 2, the minimum cross section of the drawing die 6 15 x 75 mm, the first rear section 20 x 100 mm, and the second rear section.
The size is 25 x 125 mm, and the third rear section is 40 x 200 mm.

Further, at this time, the resin temperature measured by the resin thermometer 8 provided near the exit of the extruder 1 was 164° C., and the resin pressure gauge 10 was 72 Kg/cm ² .

The temperature of each part of the long land die is 163℃, 165℃, 168℃, respectively from the entrance side, where there are 4 points in the front section 2.
At 171℃, the first rear section is 168℃, the second rear section has two points, respectively 165℃ and 166℃, and the third rear section has one point.
It was 165℃.

The cross-sectional dimension of the foam obtained by this molding is 50
It had a rectangular shape of 250 mm and was a continuous board. The density of this foam is 0.302g/cc,
The cells were microscopic with a bubble diameter of 200 microns or less.

In addition, the board obtained by this molding was cut with a band saw.
When sliced into mm-thick pieces, a flexible foam sheet was obtained.

[Brief explanation of drawings]

FIG. 1 is a process example diagram of the present invention, FIG. 2 is an enlarged sectional view of the vicinity of the entrance of a long land die, FIG. 3 is an intermediate drawing die 6, and FIG. 4 is another process example diagram. 1: extruder, 2: front stage part of long land die,
3: Post-stage part of long land die, 4: Lubricating oil supply section, 5: Squeezing die, 6: Intermediate squeezing die, 8: Resin thermometer, 9: Lubricant delivery device, 10: Resin pressure gauge, 11: Foaming body products.

Claims (1)

[Claims] 1. After uniformly mixing a crosslinkable thermoplastic resin, a foaming agent, and a crosslinking agent having a thermal decomposition temperature higher than the melting temperature of the resin, the mixture 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 generate cross-linked bonds, and then the blowing agent is heated to a temperature higher than that at which the blowing agent volatilizes or decomposes at a later stage of the long land die, and then extruded from the long land die. In the manufacturing method of cross-linked foam, in which 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 at the same time, lubricant is supplied between the front stage and the rear stage of the long land die. Set up a die,
A method for producing a crosslinked foam, which comprises applying back pressure in a previous step to prevent the formation of bubbles caused by a foaming agent in a molten resin in a long land die.