JPS5835864B2 - asbestos - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a porous asbestos molded article modified with a polymer.

As an inorganic fibrous material, asbestos has favorable properties such as heat resistance, chemical resistance, and electrical insulation properties.As it is a fiber, asbestos is particularly characterized by the fact that porous molded products can be easily obtained.

Although each asbestos fiber is strong, the adhesion and cohesive force between the fibers are weak, so different binders are used depending on the purpose, but binders are generally used depending on their air permeability, water permeability, etc. significantly reduces the porosity of

Modifying asbestos fibers instead of using binders,
It is desired to obtain an improved porous molded product with increased adhesive strength without significantly reducing air permeability and water permeability.

The purpose of the present invention is to modify the surface of asbestos using a polymeric substance having a secondary transition point and a melting temperature, to increase its adhesive strength, and to obtain a porous molded product using the asbestos. .

Modification of asbestos with such polymeric substances is most commonly carried out by impregnating asbestos with a solution or dispersion of the polymer, but in this case, the polymeric substance binds and simultaneously fills the spaces between asbestos fibers. However, these solutions or dispersions are generally applied or impregnated with these solutions or dispersions after molding, but these methods greatly reduce the porosity of the molded material, making it difficult to mold it after the treatment. It is difficult to use as

As for asbestos molded products using such polymer latex as a binder, a method using rubber latex has been known since ancient times, but in particular,
No. 15 describes a method for making an electrolytic diaphragm using fluororesin latex.

This method is characterized in that asbestos to which 0.5 to 60% by weight of fluororesin is attached is heated after or during molding to partially fuse it.

However, since this method involves melting of the resin, it has the disadvantage that reproducibility cannot be obtained in the heat treatment after molding.

In other words, in Japanese Patent Publication No. 48-32515, it is stated that the water permeability changes greatly when only the heat treatment time is changed, but even under conditions where the temperature, time, etc. are exactly the same, Additional tests conducted by the present inventors revealed that the water permeability varied by 50% or more, and the reproducibility was low.

In addition, when pressurizing the molded product in a heated state using this method, there is a drawback that the water permeability of the molded product is extremely reduced.

The present inventors aimed at making porous molded products of asbestos.
The present invention was achieved as a result of pursuing a reproducible method.

In the present invention, by mixing a polymer latex having a secondary transition point and a melting temperature into an aqueous dispersion of deflated asbestos, 1 to 20 parts by weight of the polymer is applied to the surface of 100 parts by weight of asbestos. This is a method for producing a porous asbestos molded product, which is characterized in that uniformly adhered asbestos fibers are molded, and then pressed and molded at a temperature below the melting temperature and above the secondary transition point of the polymer.

That is, in the present invention, the above-mentioned Japanese Patent Publication No. 48-3251
Completely different from No. 5, this is a method of molding by applying pressure under conditions that do not cause melting of the resin.

The present invention will be explained in detail below.

Asbestos used in the present invention includes chrysotile, anthophyllite, tremolite, amosite, etc., and these materials are mechanically defrosted as appropriate depending on the purpose and then thrown into water.

As for the amount of water used, asbestos is dispersed in at least 5 times the amount of water by weight, preferably 10 times or more by weight.

From the standpoint of work efficiency, it is not desirable to disperse in 1000 times more water, but this is not particularly limited.

After adding it to water, it can also be opened by further applying mechanical stress.

A desired amount of polymer latex is added to an aqueous dispersion of asbestos that has been appropriately opened according to the purpose.

In this polymer latex, the emulsifier may be an anionic surfactant or a nonionic surfactant regardless of the type of polymer.

What is dominant in this invention is the amount of latex.

The amount of polymer having a second-order transition point and melting temperature is:
The amount used is 1 part by weight or more and 20 parts by weight or less per 100 parts by weight of asbestos.

If the amount is less than 1 part by weight, almost no effect will be observed.

Add the latex liquid either thickly or diluted, stirring well.

Surprisingly, the added latex is quickly absorbed by the asbestos and does not remain in the liquid.

This clearly shows that even if latex alone cannot be separated even after being left in water for a long time or even by centrifugation, in systems where asbestos is present, the supernatant liquid from which asbestos is precipitated becomes transparent.

When the polymer weight in the latex liquid is 20 parts by weight or less, most of the polymer is adsorbed.

This adsorption is completely unrelated to the pH after separation. The method of the present invention can be applied to any polymer latex as long as it has a second-order transition point and melting temperature. This method is extremely useful because it allows the use of polymers that would otherwise be difficult to coat asbestos in the absence of a suitable solvent.

Such polymers include polytetrafluoroethylene, polytetrafluoroethylene-hexafluoropylene copolymer polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene-ethylene copolymer, trifluorochloroethylene-ethylene copolymer, Examples include trifluorochloroethylene and polystyrene.

Further, these fluorine-containing resins are particularly preferable for porous bodies that require chemical resistance or heat resistance.

The method of the present invention is characterized in that it does not require salting out, acid precipitation, latex precipitation by solvent or freezing because the polymer latex is adsorbed on asbestos, but these precipitation operations can be used in combination. I can't stand the side.

After adding latex and adsorbing it, salting out, acidic precipitation,
Adsorption can be brought closer to completion by adding a solvent to cause precipitation, or by heating, boiling, etc. separately.

The modified asbestos used in the molded product of the present invention is
Although obtained as a dispersion in water, these can be molded in exactly the same manner as conventional untreated asbestos.

For example, the dispersion can be molded into a sheet by separating water using a sieve or cloth, or it can be further concentrated into a paste state and extruded through a nozzle into a suitable mold.

Of course, other inorganic fillers, polymer powders, fibers, etc. can also be added during molding.

In this molded product, polymers are adsorbed on the surface of asbestos fibers, so if a porous sheet obtained from asbestos adsorbed with polytetrafluoroethylene is used as one material, for example, if a porous sheet made of asbestos with polytetrafluoroethylene adsorbed is used, the polymer will remain on the sheet. Favorable performance such as improved cake releasability can be obtained.

In the next step, the porous molded product must be treated in a dry state at a temperature above the second-order transition point and below the melting temperature of the polymer.

Below the secondary transition point, sufficient adhesion between asbestos cannot be obtained.

For resins that have several secondary transition points, the higher one is preferred; for example, in the case of polytetrafluoroethylene, -100°C, -70°C, =40°C and 130°C.
A second-order transition point has been reported to be at 130°C or higher.

Further, in the case of a crystalline polymer, it is particularly desirable to process the polymer at a temperature equal to or higher than its crystal dispersion temperature.

In the present invention, the pressurizing conditions are 1 k17L/c
Rii or more, 100 to 97 cal or less.

It is difficult to adjust below 1 kg/ca, and 100 kg
/cwt or more, the porosity decreases significantly.

Asbestos moldings treated with heat and pressure are
A remarkable improvement in strength is seen compared to the untreated material.

The improvement in strength is noticeable not only in dry conditions but also in the presence of water.

Untreated asbestos greatly swells in water and has extremely high water permeability, so if the fibers are fixed using the present invention, swelling will be greatly restricted and water permeability will be considerably reduced. In the case of the present invention,
It has greater water permeability than conventional treatment methods for porous asbestos.

Since the molded product obtained in the present invention uses modified asbestos, it is strong and has a wide range of industrial applications such as heat-resistant applications, electrical insulation applications, and diaphragms.

Example 1 Chrysotile made of waste cotton (manufactured by Johns Manpil 4)
T-04) 20f? was dispersed in 500 cc of water.

This material contains polytetrafluoroethylene with a resin content of approximately 60% (
PTFE) emulsion liquid (manufactured by Mitsui Fluorochemical ■,
Teflon 30-J, secondary transition point 130°C, melting temperature 32
7° C.) was diluted in 1 oocc of water, and the mixture containing the required amount of resin was gradually added with thorough stirring.

Thereafter, water was further added to make the total volume 800 cc, and the mixture was stirred uniformly.

The obtained asbestos aqueous dispersion showed a tendency to be somewhat whitish due to its high content of polytetrafluoroethylene, but other than that, there was almost no change in appearance or flow characteristics.

When stirring was stopped and the dispersion was allowed to stand for several hours, the asbestos settled and the supernatant became transparent.

It should be noted that the emulsion used here diluted 100 times with water did not settle even if it was left to stand for more than - day and night.

The resulting dispersion was poured onto a 15 CIrL x 18 cIrL filter, water was removed by gravity filtration, and after pressurization, it was taken out and dried to obtain an asbestos sheet with a thickness of about 1.2ii.

This sheet had almost the same strength as the original asbestos, but it was heated to 250℃ for 1
As a result of pressure molding under a pressure of 5 kg and 10 a to cause adhesion between asbestos fibers, a sheet with strong wet and dry strength was obtained.

At the same time, the water permeability of these samples was measured.

The results are shown in Table 1.

Example 2 In the same manner as in Example 1, an emulsion of asbestos and tetrafluoroethylene-hexafluoropropylene copolymer [Teflon 120 manufactured by Mitsui Polychemicals, secondary transition point 127] was prepared.
℃, melting temperature 270℃] and make a dispersion of 15crr.
It was placed in a filtration device of L x 20 crrL, and after suction filtration, it was taken out and dried to obtain an asbestos sheet with a thickness of about 1.1**.

The strength of this sheet was almost the same as the original asbestos, but it was heated to 250°C.
Pressure molding was performed at a pressure of 15 kg/c77 f to cause adhesion between asbestos fibers, resulting in a strong sheet.

The results are shown in Table 2.

As shown in Table 2, compared to the asbestos sheet of Experiment No. 6' in which no copolymer was added, the sheet of the present invention had comparable wet and dry strength, and also relatively comparable water permeability.

Example 3 500CC glass ampoule, styrene monomer 10
0f, 200 g of water, 0.5 azobisisobutyronitrile
S' and 1.01 of potassium oleate were added, and after purging with N2 gas, polymerization was carried out in a 60°C water bath while shaking for 20 hours.

The resulting latex had almost completely polymerized styrene and had a polystyrene content of 33% by weight.

The polystyrene had a secondary transition point of 100°C and a melting temperature of 150°C.

20 parts by weight of this latex was mixed with 100 parts by weight of chrysotile asbestos in the same manner as in Example 2,
adsorbed to asbestos.

The dispersion was suction filtered, dried, and then pressure molded at a temperature of 120°C.

The results are shown in Table 3.

As mentioned above, both the dry and wet strength were dog-like, and the water permeability was also dog-like.

Comparative Examples 1 to 2 Asbestos sheets treated with polytetrafluoroethylene were prepared in the same manner as in Experiment No. 2 of Example 1.

However, the pressure molding temperature of the sheet was 100° C. below the secondary transition point of polytetrafluoroethylene in Comparative Example 1, and 350° C. above the melting temperature of polytetrafluoroethylene in Comparative Example 2.

The molding pressure was 15ky/cr7L as in Experiment No. 2.

The results are shown in Table 4 along with experiment number 2.

When the polytetrafluoroethylene of Comparative Example 1 was heated to a temperature below the secondary transition point, asbestos was hardly bonded, and both the dry and wet strength showed low values.

Furthermore, heating above the melting temperature of polytetrafluoroethylene increased the strength, but resulted in a membrane with extremely low water permeability.

Claims (1)

[Claims] 1. By mixing a polymer latex having a secondary transition point and a melting temperature into an aqueous dispersion of edged asbestos, 1 to 20 parts by weight of the polymer is uniformly attached to the surface per 100 parts by weight of asbestos. 1. A method for producing a porous asbestos molded product, which comprises molding suspended asbestos fibers, and then pressurizing and molding at a temperature above the secondary transition point and below the melting temperature of the polymer.