JPS6041088B2 - Method for producing ethylene-tetrafluoroethylene copolymer foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a foam made of a tetratetraethylene ethylene copolymer, and more specifically, to a high-temperature decomposition solid foaming agent and a specific heat-resistant 9-cell foam nucleating agent. The present invention relates to a method for producing a foam, which comprises heating and melt-molding the copolymer with the addition of the above-mentioned copolymer.

Ethylene-tetrafluoroethylene copolymers are known as melt-formable materials with excellent heat resistance, chemical resistance, electrical properties, mechanical properties, weather resistance, and flame retardance. It is used in a wide range of applications, including linings, coatings, wire sheathing, and various molded products.

In recent years, foams with closed cells made of various thermoplastic resins have been introduced, and their special properties such as heat insulation, sound insulation, high rigidity, light weight, and low dielectric constant have been introduced to create a variety of products. However, if such a foam is made from an ethylene-tetrafluoroethylene copolymer, in addition to the properties as a foam, the ethylene-tetrafluoroethylene copolymer as described above Combined with the excellent properties of copolymers, foams with extremely superior properties can be obtained, opening up an even wider range of applications.

Various methods have been proposed for producing thermoplastic resin foams.

For example, organic or inorganic chemicals are added to resin, and gases (mainly N2, CO
In this method, an inorganic inert gas such as N2 or CO2 or a volatile organic liquid such as a hydrocarbon is introduced into the melted resin in a molding machine under high pressure in gaseous or liquid form. This method involves blowing the resin into foam using the expansion of dissolved gas as it exits the molding machine, or impregnating the raw resin with a suitable solvent and molding the composition at a temperature higher than the boiling point of the solvent. There are methods of foaming. Fluorine-based resins generally have a high melting point and therefore require a high molding temperature, and no advantageous foaming method has been found to meet this requirement.In particular, there have been few proposals for foaming fluorine-based resins using chemical blowing agent methods. I can't find it.

US Pat. No. 3,072,583 describes a foaming method mainly for tetrafluoroethylene-hexafluoropropylene copolymer. In this method, the resin before the extrusion process is placed in a container, and fluoromethane gas is heated for a certain period of time. The resin is infiltrated at a constant pressure, then put into an extruder and extruded, and foamed by the expansion of the gas contained in the resin as it exits the die. As mentioned above, various methods have been proposed for foaming, but the method of pressurizing gas during the melting process requires a machine with a special structure, making the equipment expensive, and it is difficult to combine liquid or gas with raw resin. The method of soaking and then feeding the resin to a molding machine has its own drawbacks, such as the amount of blowing agent impregnated in the resin changing over time.

In contrast, blowing agents made of chemicals have the advantage that they are powder-like and easy to handle, and can be used with ordinary molding machines. Based on the above-mentioned recognition of the current situation, the present inventor has conducted various studies and studies on effective foaming methods for ethylene-tetrafluoroethylene copolymers, and as a result, has developed an ethylene-tetrafluoroethylene copolymer having a specific melt index.
We have previously discovered that by adding a specific foaming agent and foam nucleating agent to a tetrafluoroethylene copolymer and heating and melt-molding it, a foam containing uniform fine cells can be smoothly and advantageously obtained. The application is currently being filed as Tokusho 32-36081.

The inventor of the present invention has conducted further research and study on the method of manufacturing a foam using a combination of a foaming agent and a foam nucleating agent as described above, and as a result, has obtained the following knowledge.

In other words, the size of the bubbles in the foam and the surface smoothness of the foam largely depend on the type of foam nucleating agent used, and by using a specific foam nucleating agent, it is possible to minimize the bubbles and improve the surface smoothness. It has been found that superior foams are advantageously obtained. Thus, the present invention was completed based on the above findings, and it is possible to prepare an ethylene-tetrafluoroethylene copolymer having a melt index of 0.5 to 8 at the melt-molding temperature of the copolymer. In producing a foam by heating and melt molding with the addition of a decomposable solid foaming agent and a foaming nucleating agent consisting of heat-resistant fine particles with an average particle size of 10 microns or less, turk, sericite, and diatoms are used. The present invention provides a novel method for producing a foam of ethylene tetrafluoroethylene copolymer, which comprises using at least one substance selected from the group consisting of ± as a foam nucleating agent.

It is important that the blowing agent used in the present invention is a solid substance that decomposes at the melt-molding temperature of the specific ethylene-tetrafluoroethylene copolymer, and the term "foaming agent that decomposes at the melt-molding temperature" It includes not only foaming agents whose decomposition starts at the melt-molding temperature, but also foaming agents whose decomposition continues even at the melt-molding temperature even if the decomposition start is below the melt-molding temperature.

Foaming agents that do not decompose at all at the melt-molding temperature or that complete decomposition at a temperature lower than the melt-molding temperature are not included in the "foaming agents that decompose at the melt-molding temperature" in the present invention. By using a blowing agent that decomposes at the melt molding temperature, the generation of decomposed gas continues during hot melt molding, and uniform closed cell formation can be advantageously achieved in exchange for a specific melt index. According to the present invention, first, a foam of ethylene-tetrafluoroethylene copolymer containing uniform and extremely fine cells, for example, cells with a size of 0.1 mm or less, can be produced smoothly and advantageously; It is possible to coat wires that are thin and have excellent insulation properties and mechanical strength, which is advantageous for, for example, coating wires for large-scale high-speed computers.

Second, in addition to the excellent properties of the ethylene-tetrafluoroethylene copolymer (mechanical, electrical, chemical properties, flame retardance, moldability, etc.), it has a low dielectric constant as a foam, lightweight,
Since it has heat insulating properties, sound insulating properties, etc., it is advantageous for a wide range of new applications, such as covering electric wires for audio equipment. Third
In addition, it can be advantageous in terms of extrusion workability and other aspects in foam extrusion molding, etc., compared to conventional gas permeation methods. In particular, when a high-temperature decomposition type organic foaming agent and a fine foaming nucleating agent are combined, the effect of improving workability is exhibited. Furthermore, when using pellets for extrusion molding, etc., prepare a pellet containing a high-temperature organic blowing agent and a pellet containing a foam nucleating agent, mix both pellets in an appropriate ratio, and perform foam extrusion. It is possible to do so. According to the method of the present invention, a foamed product of ethylene-tetrafluoroethylene copolymer can be obtained, and various molded products can be obtained by employing a normal hot melt molding method.

For example, an extruder can be used to continuously mold rod-shaped, pipe-shaped, plate-shaped, sheet-shaped, film-shaped, filament-shaped, and strand-shaped foams, and an injection molding machine can be used to mold foams of various shapes. , molding a hollow foam using a blow molding machine, and further extrusion foaming continuously around a conductor to form an insulated wire covering.
．． The ethylene tetrafluoride copolymer used in the present invention can be produced by catalytic emulsion polymerization in an aqueous medium, suspension polymerization, catalytic solution polymerization, gas phase polymerization, ionizing radiation irradiation polymerization, etc. Products manufactured by various polymerization methods, products with various content ratios of ethylene and tetrafluoroethylene, and products with small amounts of comonomer (propylene, isobutylene, fluoroethylene, etc.) in addition to ethylene and tetrafluoroethylene Vinyl chloride, propylene hexa*, trichlorethylene chloride, vinylidene fluoride, perfluorovinyl ether,
acrylic acid and alkyl esters, methacrylic acid and alkyl esters, perfluoroalkyl ethylene, etc.)
A wide range of substances can be mentioned, including those containing denaturing agents and denaturing agents.

Therefore, the molar ratio of ethylene tetrafluoride is usually 40/60 to 70/3, particularly 45/55 to 60.
A temperature of /4 may be preferably employed. What is particularly important in the present invention is to select an ethylene-tetrafluoroethylene copolymer with an optimal melt index,
If the melt index is too large, the viscosity during melt molding will be too low, making it difficult to maintain the cell structure, and the cells will collect on the surface layer, resulting in non-uniform dispersion. Furthermore, if the melt index is too small, the high viscosity during melt molding will similarly make it difficult to uniformly disperse the bubbles, and more bubbles will escape to the outside, making it impossible to obtain a good foam. In the present invention, the melt index is 0.5 to 8.
1 to 6, preferably 1 to 6, may be employed. The blowing agent used in the present invention is one that decomposes at the melt molding temperature of a specific ethylene-tetrafluoroethylene copolymer, and the decomposition residue does not cause thermal deterioration or significant discoloration of the resin. It is preferable that there is no.

Examples of the blowing agent include inorganic or organic blowing agents that decompose in the temperature range of 260 to 360°C, preferably 270 to 350 qo, and also that Other inorganic or organic blowing agents may be used as long as they are solid foaming agents that decompose.
In the present invention, the advantages of a high-temperature decomposition type organic blowing agent are particularly exhibited when used in combination with a foam nucleating agent.
550, manufactured by United States General Corporation), etc. can be particularly advantageously employed in the present invention. Therefore, basic lead carbonate, zinc carbonate,
Inorganic carbonates such as basic magnesium carbonate can also be used as solid blowing agents in the present invention, but they have drawbacks in extrusion workability and the like. Of course, the above blowing agents may be used alone or in combination of two or more. Regarding the amount of the specific blowing agent added, if it is too small, the foaming will not be effective, and if it is too large, the excellent physical properties of the ethylene-tetrafluoroethylene copolymer will be impaired, so it is not preferable.

Therefore, usually ethylene-tetrafluoroethylene copolymer 1
0.1 to 10 parts by weight of a specific blowing agent,
Preferably, it is appropriate to add and mix in a proportion of 0.2 to 5 parts by weight. The amount of the specific blowing agent to be added depends on the type of ethylene-tetrafluoroethylene copolymer used, the type of blowing agent, the intended molded product, the nucleating agent used, and other molding conditions used. It is desirable to select the optimal amount according to the In the present invention, it is important to use a specific foaming nucleating agent, that is, at least one substance selected from the group consisting of talc, sericite, and sericite as the foaming nucleating agent. By using such a foaming nucleating agent, it is possible for the first time to manufacture a foamed product with excellent surface smoothness by incorporating uniform and extremely fine bubbles, and it is possible to produce a foamed product with excellent surface smoothness. Fine silica, quartz powder, alumina, aluminum hydroxide, magnesium, magnesium hydroxide, calcium carbonate, limestone, kaolin, bentonite, zinc sulfide, molybdenum disulfide,
When using carbon black, graphite, etc. as a foaming nucleating agent, it is difficult to obtain a foam that contains extremely fine bubbles and has excellent surface smoothness. Although it is a hydrous aluminum silicate mineral, although the cell diameter in the foam is reduced to some extent, the surface condition of the foam is poor, and its behavior as a foam nucleating agent is significantly different from that of sericite. What it shows is amazing. All of the specific foaming nucleating agents mentioned above are commercially available in the form of mechanically pulverized fine powders, but the finer the particle size of the powder, the more effective it is as a foaming nucleating agent. Hereinafter, those having an average particle size of preferably 2 microns or less are suitable. Therefore, regarding the amount of the specific foam nucleating agent added, if it is too small, it will not be effective in making the cells fine and uniform, and if it is too large, the extrusion workability or the superiority of the ethylene-tetrafluoroethylene copolymer will be affected. This is not preferable because it will impair the physical properties of the product.

Therefore, usually ethylene-tetrafluoroethylene copolymer 1
It is appropriate to add and mix the specific foam nucleating agent at a ratio of 0.3 to 10 parts by weight, preferably 0.7 to 5 parts by weight, per 0 parts by weight. The amount of the specific nucleating agent to be added depends on the type of ethylene tetrafluoroethylene copolymer, nucleating agent, or combined blowing agent used, the intended molded product, cell density, and other materials used. It is desirable to select the optimum amount depending on the molding conditions, etc. In addition to the above-mentioned specific substance as a foaming nucleating agent, other heat-resistant fine particles such as boron nitride, alumina, titanium oxide, silica, calcium silicate, etc.
Of course, it is also possible to use one or more of carbon black, graphite, zinc sulfide, molybdenum disulfide, magnesium oxide, magnesium hydroxide, calcium carbonate, wollastonite, kaolin, bentonite, etc. in combination. In the present invention, glass fibers, glass powder, asbestos fibers, carbon fibers, etc. It is also possible to contain suitable fillers or reinforcing agents, stabilizers, lubricants, pigments, and other appropriate additives.

These additives make it possible to improve thermal stability, surface hardness, mechanical strength, wear resistance, lubricity, and other properties. The preferred ethylene-tetrafluoroethylene copolymer in the present invention has a flow initiation temperature of 260 to 300oC.
The temperature at which thermal decomposition starts is about 320 to 3600C. Therefore, a suitable melt-molding temperature of the ethylene-tetrafluoroethylene copolymer is in the temperature range between the flow initiation temperature and the thermal decomposition initiation temperature, and is usually 260 to 36
It is about 0°C, especially in the range of about 280 to 350 qo.
Therefore, in the present invention, a foam molding temperature is adopted from the above-mentioned melt molding temperature range. Since such a high molding temperature is employed, conventionally commercially available organic blowing agents such as azo type, nitroso type, and sulfonyl hydrazide type, which complete decomposition at a temperature of 260 qo or less, can be replaced with the ethylene-tetrafluoroethylene type copolymer of the present invention. It cannot be effectively used as a foaming agent for coalescence. In carrying out the present invention, it is desirable that the ethylene-tetrafluoroethylene copolymer, the specific blowing agent, and the foaming nucleating agent be mixed as uniformly as possible. In the case of a fine powder, it is sufficient to simply mix the mixture by grinding, but in the case of a jaw-like or coarse powder, it is desirable to mix the mixture microscopically uniformly by impact-pulverizing the mixture. In addition, when performing foam molding, the optimal temperature conditions are selected depending on the molding method and the shape of the molded product. For example, in the case of extrusion molding, the cylinder temperature may be changed from the powder supply section to the die section in order to gradually decompose the solid foaming agent. It is desirable to set the temperature conditions such that the temperature of the die is raised to the highest temperature in order to complete the decomposition. If the cylinder has two heating zones, the first zone on the raw material supply side usually has a temperature of 260 to 270°C, and the second zone on the die side has a temperature of 270q0
A temperature of about 300 qo and a temperature of about 300 to 350 oo for the dice is adopted. In the case of other molding methods, similar temperature conditions are selected. In a preferred embodiment of the present invention, two types of pellets of ethylene-tetrafluoroethylene copolymer are prepared, and both pellets are mixed in an appropriate ratio and foam molded by heating and melting. It is desirable to implement it. That is, it is desirable to carry out foam molding using a mixture of pellets containing a solid foaming agent and pellets containing a foaming nucleating agent.
In such cases, pellets containing a foaming agent are prepared by extrusion molding at a relatively low temperature where the foaming agent does not decompose, and pellets containing a foaming nucleating agent are prepared using ethylene-4 because of the heat resistance of the nucleating agent. It can be prepared by conventional extrusion of fluorinated ethylene copolymers. By using the two types of pellets prepared in this way, the workability in foam molding and the quality of the foamed molded product are improved.

That is, when handling a powder mixture or a mixture of powder and neck grains, scattering of fine powder and separation between powder and neck grains are eliminated, and fluctuations in extrusion amount due to variations in apparent specific gravity are eliminated. Furthermore, since the ethylene tetrafluoroethylene copolymer and the foaming agent or foam nucleating agent are uniformly melted and kneaded during pellet formation, the bubbles are more uniformly formed during foam molding.
Become minute. When preparing pellets with blowing agent by extrusion molding, it is important to choose appropriate extrusion conditions.

That is, it is necessary to select an extrusion temperature that is sufficient to melt the ethylene-tetraethylene copolymer and below the temperature at which the blowing agent begins to decompose, or below the temperature at which decomposition can be ignored in practical terms. The melt index referred to in the present invention is performed using the melt indexer described in ASTM D-1238-70 at a temperature of 30,000 and a load of 216.
The discharge weight when extruding the copolymer under the conditions of 09/1
It is expressed in 0 minutes. Next, embodiments of the present invention will be described in more detail, but it goes without saying that the present invention is not limited by such explanations.

Examples 1 to 5 and Comparative Examples 1 to 16 Powdered ethylene-tetrafluoroethylene copolymer (melt index 1.3) with a molar ratio of tetrafluoroethylene/ethylene of 53/47 Diisopropyl hydrazodicarboxylate (trade name: Celogen HT500, USA) as a solid blowing agent, based on parts by weight.

0.5 parts by weight (manufactured by Gyal Co., Ltd.) and various foaming nucleating agents shown in Table 1 below.2. parts by weight were added and uniformly dispersed and mixed using a V-blender. Next, these powder compositions were added to the cylinder diameter [D'20 ribs, L/D: 18 (L: screw length)
The material was fed to the hopper of an extruder, and extrusion foam molding of a strand with a diameter of 3 ribs was performed under the conditions that the cylinder part temperature [Zone 1] was 25,000°C, [Zone 2] 280°C, the die part temperature was 310°C, and the screw rotation speed 3 was pm. I did it.

The results are summarized in Table 2. By using the specific foam nucleating agent (Examples 1 to 5), compared to the case where no foam nucleating agent is used (Comparative Example 1) and the case where various other heat-resistant fine particles are used as the foam nucleating agent (Comparative Examples 2 to 16). It is clear that the diameter of the cells in the foam is small, and the color tone and surface smoothness of the foam are good.

Example 6 To 10 parts by weight of granular ethylene-tetrafluoroethylene copolymer (melt index 1.3) having a molar ratio of tetrafluoroethylene/ethylene of 53/47, the following third A pellet containing a foaming agent and a pellet containing a foaming nucleating agent were prepared using the formulation and extrusion conditions shown in the table.

Next, these pellets were mixed at a weight ratio of 1:1 and foamed and extruded. The extrusion conditions and results are summarized in Table 4.
By pelletizing, not only the workability of foam extrusion molding was improved, but also the foaming condition of the foam became even better than in Example 2 because the compound was mixed uniformly.

Table 1 Table 2 Note) 1.75 (true specific gravity)/foam specific gravity Table 3 Table 4 Table Examples 7 to 8 and Comparative Examples 17 to 18 Various melt indexes as shown in Table 5 were used. Celogen HT550 as a solid foaming agent was added to 10 parts by weight of the powdered ethylene-tetrafluoroethylene copolymer.
0.2 parts by weight (manufactured by United States Uniroyal Co., Ltd.) and 2 parts by weight of talc LM-R (manufactured by Tsuchiya Kaolin Industries, Ltd.) as a foaming nucleating agent were added and uniformly dispersed and mixed using a V-blender.

These powders were supplied to the hopper of the extruder shown in Example 1, and extrusion foam molding was performed under the same conditions as in Example 1 into a strand with a diameter of 3 skins. The results are summarized in Table 5.
A good foam could not be obtained with a copolymer having too much or too little melt index. Table 5 Examples 9 to 10 and Comparative Example 19 In Example 1, as the ethylene-tetrafluoroethylene copolymer, the molar ratio of tetrafluoroethylene/ethylene was 5.
A copolymer having a melt index of 8/47 and a melt index of 0.8 was used, basic magnesium carbonate was used as a solid blowing agent, and 5 parts by weight of the solid blowing agent were used per 10 parts by weight of the copolymer. Extrusion foam molding was carried out in the same manner as in Example 1, except that 2 parts by weight of various foam nucleating agents shown in Table 1 above were added, and the results shown in Table 6 below were obtained.

Table 6

Claims (1)

[Claims] 1. Ethylene with a melt index ranging from 0.5 to 8.
A tetrafluoroethylene copolymer is added with a solid foaming agent that decomposes at the melt-molding temperature of the copolymer and a foaming nucleating agent consisting of heat-resistant fine particles with an average particle size of 10 microns or less,
When producing foam by heating and melt-molding,
1. A method for producing an ethylene-tetrafluoroethylene copolymer foam, characterized in that at least one substance selected from the group consisting of talc, sericite, and diatomaceous earth is used as a foaming nucleating agent. 2 The molar ratio of tetrafluoroethylene/ethylene is 40/6
The method for producing a foam according to claim 1, which uses an ethylene-tetrafluoroethylene copolymer having a ratio of 0 to 70/30. 3. The method for producing a foam according to claim 1, wherein the solid blowing agent is added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the ethylene-tetrafluoroethylene copolymer. 4. The method for producing a foam according to claim 1, wherein the foam nucleating agent is added at a ratio of 0.3 to 10 parts by weight per 100 parts by weight of the ethylene-tetrafluoroethylene copolymer. 5
The method for producing a foam according to claim 1, wherein a high temperature decomposition type organic blowing agent is used as the solid blowing agent. 6. The method for producing a foam according to claim 1, wherein a foam nucleating agent having an average particle size of 2 microns or less is used. 7. The method for producing a foam according to claim 1, wherein a foaming agent that decomposes in a temperature range of 260 to 360° C. is used as the solid foaming agent. 8 Flow start temperature is 260-300℃
The method for producing a foam according to claim 1, which uses an ethylene-tetrafluoroethylene copolymer having a thermal decomposition initiation temperature of 320 to 360°C. 9. The method for producing a foam according to claim 1, wherein the foam is heated and melt-molded in a temperature range of 260 to 360°C. 10 A patent claim for carrying out heating melt molding using a mixture consisting of ethylene-tetrafluoroethylene copolymer pellets containing a solid foaming agent and ethylene-tetrafluoroethylene copolymer pellets containing a foaming nucleating agent. A method for producing a foam according to item 1. 11. A method for producing a foam according to claim 1 or 10, wherein extrusion foam molding is performed as heating melt molding.