DK141620B - Process for making asbestos fibers. - Google Patents

Description

(11) PREFERRED EMBODIMENT U1620 C OA B 31/08 // D 06 M 13/30 Π A Μ Μ Δ D 1 / (61> lnt-cl · 3 C OA B 31 / AO C 04 B 43/04 UAIMIVIAnlv C OA B 15/16 d 06 mh / 06 "(21) Application No 5955 / 7Ο (22) Filed on Nov. 23, 1970 (23) Running Dec. 23. HOV., 1970 (44) The application submitted and 1θ" gele submit a reading published on * s

Dl REPORT OF THE PATENT AND TRADEMARKET (30) Priority requested from the

Nov 24 1969, 879549, US

(71) JOHNS-MANVILLE CORPORATION, Johns-Manville Research & Engineering Uenfcer, Manville, New Jersey 08835, US · (72) Inventor: Thomas Harry Sadler, 318 "A" Street, Middlesex, New Jersey, US.

(74) Plenipotentiary in the proceedings:

International Patent Bureau._ (54) Process for making ash fiber.

The invention relates to a process for the production of asbestos fibers having good filtration properties, and in particular to asbestos fibers intended for the production of asbestos cement products.

Although the specific embodiments of the present invention are directed to a method of producing fibers intended for the manufacture of asbestos cement articles by filtration of particulate lined materials from a slurry containing asbestos fibers, hydraulic cement and silica, and for the production of asbestos cement pipes using chrysotile as the majority of such slurry fiber content, it is to be understood that the invention includes within its scope the manufacture of fibers for use in the manufacture of many different asbestos-containing articles.

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Asbestos has been used for many years in many common products, such as thicker and thinner asbestos cement slabs, shavings, pipes, etc., and paper and thick cardboard produced by so-called "wet" or "dry" processes which include filtration methods or percolation-type processes in which a liquid, typically water, is removed from a pulp or body containing asbestos fibers. Examples of such processes are the wet processes, which usually include the formation of an aqueous slurry of asbestos fibers as well as Portland cement in water, outflow of the slurry onto a filter element upon which the dispersed solid materials of the slurry can be collected, removal of the water in the slurry through the filter element by filtration, and subsequent removal of the formed mass of asbestos fibers and cement from the filter element. Due to the inhibition of the filtration caused by the asbestos fibers and the finely divided cement particles, there are in practice a great deal of the thicknesses of the resulting layers which can be collected on filter elements in this way. Thus, as the collected mass builds up on the filter element, the filtration rate is rapidly reduced, making it impossible to form larger thickness structures at such a throughput rate as may be required in industrial manufacture.

In a conventional dry process for forming asbestos cement articles, the dry materials such as asbestos, silica, cement and pigment are mixed together and formed into portions by weight. Sufficient water is added to each portion to form a plastic paste which can be molded, calendered and pressed or extruded prior to standard ashest cement curing operations.

The filtration properties of chrysotile asbestos fibers vary substantially with the location of the source or mine as well as with the type, quality and consistency varying from the relatively fast filtering "hard" fiber to the slowly filtering "soft" fiber. A typical example of the latter class of fibers is certain asbestos materials found in Quebec, Canada. The filtration properties of chrysotile asbestos are of critical importance in determining the suitability or usefulness of a particular fiber or fiber blend in wet and dry manufacturing modes, and these properties are especially crucial in the conventional wet-machine processes usually used in the manufacture of asbestos cement pipes, sheets. , clothing and paper products as well as molded or pressed products.

A large number of treatment methods have been proposed in the past to increase the filtration rate of the slowly filtering fibers. They include thermal treatment of the fiber, application of various coatings to the fiber, use of organic coagulants as well as inorganic saline solutions, and further soaking in sodium silicate solutions followed by dewatering with an acid treatment to maximize the accelerating effect of the sodium silicate on hydraulic cement. However, despite the disadvantages associated with the use of the slower filtering fiber in wet machine processes, very few of these treatment methods to improve the filtration properties of asbestos fibers have been extensively used. Two of these methods are described below.

It has previously been found that a non-foaming anionic dispersant can be added to a slurry or paste containing asbestos fibers in order to increase the rate at which water can be removed from the slurry or paste. This method produces the desired results, namely increased filtration rates, but it has been found that the effect of the non-foaming anionic dispersant is not cumulative. That is, although increased filtration rates are obtained by adding the dispersant up to a certain weight percent level, further addition of the dispersant, once this level is reached, does not result in further increase of the filtration rate. Thus, there is an upper limit to the maximum filtration rate for a given slow-filtering asbestos fiber obtainable by this process.

The silicate treatment of asbestos fibers gives increased filtration rates, but results in significant decreases in the strength of products in which the treated fiber is incorporated when large amounts of silicate are added to achieve greatly increased filtration rates. A preferred silicate treatment method, which is used commercially but which may nevertheless result in asbestos cement products with reduced strength at high silicate content, is described in U.S.A. U.S. Patent No. 3,173,831. This process, in which a silicate solution is sprayed onto asbestos fibers, greatly improves the filtration properties of chrysotile asbestos fibers, but has a strengthening effect on asbestos cement products. Therefore, for practical purposes, it is desirable to reach a compromise consisting of a 0.4-0.6 wt.% Silicate treatment which improves the filtering properties of the fiber without causing a prohibitive decrease in the strength of the product. Larger amounts of silicate progressively improve filtration properties but result in strength losses which render the higher amounts of silicate unusable.

While adding a non-foaming anionic dispersant or applying approx. 0.4-0.6% by weight of silicate or less thus used commercially to obtain increased rates of production of asbestos cement articles from slowly filtering asbestos fibers, said natural process limitations have prevented slurries or pastes from being obtained in these processes. which provides fast filtration as well as strong products.

Accordingly, the invention has for its object to provide an effective method for making asbestos fibers, thereby greatly increasing the filtration rate of slurries or pastes containing asbestos fibers, which method does not have the detrimental effect on the product strength which would result from a silicate treatment and most other known treatments for improving the filtration properties of asbestos fibers, thereby providing treated asbestos fibers which provide increased rates of production in wet and dry processes for producing asbestos cement products such as pipes, sheets, cladding, insulation and the like from slowly filtering asbestos fibers.

In the process of the invention for the production of asbestos fibers with improved filtration properties, a spray of an aqueous solution of an alkali metal silicate is applied to the asbestos fibers while suspended in air or other gas for application of between 0.4 and 4.0% by weight of solid particles. of the alkali metal silicate on the fibers, and the process is characterized in that additional 0.05-5.0% by weight of a non-foaming anionic dispersant such as a sulfonic acid derivative, calculated as a powder or aqueous, is applied to the asbestos fibers thus treated. resolution.

The combined treatment using alkali metal silicate as well as a non-foaming anionic dispersant is not only cumulative in its effect on the filtration rate of asbestos fibers, but quite unexpectedly, it does not diminish the strength of products made from the treated fibers, as is the case with fibers treated with the same amount of alkali metal silicate alone.

The dual treatment method of the invention allows the use of over 100% more alkali metal silicate than the 0.4-0.6% by weight which was previously considered to be the commercially practicable upper limit. For example, chrysotile fibers are treated with 1% sodium silicate but without dispersant, possessing improved filtration properties compared to untreated fibers, but asbestos cement products made from such silicate treated fibers are weaker than products made from untreated fibers and are unsatisfactory from a strength point of view.

On the other hand, fibers treated with 1% sodium silicate as well as a non-foaming anionic dispersant in the dual treatment: process of the present invention have filtration properties better than the properties of fibers treated with 1% sodium silicate, and they also provide products which have similar or better strength properties when compared to products made from unprocessed fiber.

By using fibers treated by the process of the invention, the rate of manufacture of products from an asbestos cement slurry or paste is dramatically increased, and the strength losses in asbestos cement products made from the slurry or paste which would otherwise result from the incorporation of silicate treated asbestos fibers to which more than about 0.4-0.6% by weight of solid silicate is applied is eliminated.

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The process of the invention comprises, as a first step, the application of alkali metal silicate to the surface of the asbestos fibers. An aqueous solution containing alkali metal silicate is sprayed onto the asbestos fibers while the fibers are kept in a gaseous suspension. This spraying procedure has been found to be particularly desirable for the application of alkali metal silicates to asbestos fibers if the fiber is then to be packaged and transported or stored before use.

The preferred method of applying alkali metal silicates to asbestos fibers is described in U.S.A. U.S. Patent No. 3,173,831. Generally, the spraying technique disclosed in U.S.A. U.S. Patent No. 3,173,831 is the preferred first step of the present process and consists of applying a sprayable aqueous solution of alkali metal silicates consisting of conventional commercially available grades of sodium and / or potassium silicates having an alkali metal ratio of about 0.60 to approx. 3.75 moles per moles of alkali metal.

The silicate solution is applied to the fibers in the form of a finely divided, atomized spray. Although the concentration of alkali metal silicate in the aqueous solution of the patent is stated to be in the range of approx. 3 to approx. 20% by weight, it has been found that in the process of the present invention, significantly higher concentrations such as e.g. 30% and higher alkali metal silicate content.

During the spraying, the fibers are kept substantially separated, suspended in air or other gas, such as the condition usually prevailing in an asbestos fiber former, or when the fibers pass through a fan or fan. Alkali metal silicate solutions of the above concentrations can be effectively sprayed in a finely divided or atomized state from typically commercial equipment without clogging. Application of the silicate solution in the form of a finely divided spray to the fibers during vigorous movement thereof allows large amounts of the aqueous solution to be applied without producing visible wetting or bonding of the fibers.

Up to 15-20 percent of the aqueous silicate solution, based on the fiber weight, can be sprayed onto the air-suspended fiber. The total amount of solution applied depends on the concentration of the solution. In order to produce the useful effects of the process of the present invention, up to 4% by weight of solid alkali metal silicate compounds, preferably from 0.5% by weight, to about 4% by weight are applied. 2.0% by weight, on the fiber.

As mentioned above, the application of alkali metal silicates to the surface of asbestos fibers in amounts of at least about 0.4% by weight, relative to the fiber, significantly improves the filtration properties of the treated fiber compared to untreated fiber. However, alkali metal silicate at these weight percentages has so far tended to significantly reduce the strength of the products in which the silicate treated fiber is incorporated.

According to the invention, a non-foaming anionic dispersant 6 141620 is added to the silicate treated asbestos fibers for dual treatment of the fibers. This results in an increased filtration rate of slurries or pastes containing the double-treated asbestos fiber relative to the filtration rate of slurries or pastes containing only silicate-treated fibers, and in an improvement in the strength of asbestos cement products made from the double-treated fibers relative to the strength. of similar asbestos products made from only silicate treated fibers. By the addition of the non-foaming anionic dispersant to the silicate treated fibers, the strength loss that would otherwise result from the use of silicate treated fibers is reduced.

The addition of the dispersant to the silicate treated fibers can be accomplished by numerous physical methods. An aqueous solution of the dispersant can be sprayed onto the silicate-treated fibers while suspended, using methods similar to those described above for use in the silicate treatment. The dispersant may also be added as a dry, finely divided solid and blown onto the silicate treated asbestos fiber.

It has been found that a large number of non-foaming anionic dispersants are effective in increasing the filtration capacity of asbestos cement slurries or pastes, and in counteracting the strength loss in asbestos cement articles which would otherwise be the result of a prior silicate treatment of asbestos fibers.

Preferred dispersants include a sodium salt of condensed naphthalene sulfonic acid marketed by Rohm and Haas under the trademark "Tamol SN", hereinafter sometimes referred to simply as Tamol, and sodium lignosulfonate marketed by the Marathon division of American Can Company under the trademark "Marasperse N-22 ".

Other suitable dispersants include a sulfonated benzimidazole derivative of a higher fatty acid marketed by Ciba Chemical and Dye Company, Inc. under the trademark "Ultravon WC," a sugar-free calcium lignosulfonate marketed by Lake States Yeast & Chemical Division, St. Regis Paper Company under the trademark "Toranil B"> sodium alkyl naphthalene sulfonate marketed by National Aniline Dividion, Allied Chemical Corporation under the trademark "Naccosol A", an alkylaryl sodium sulfonate marketed by the National Aniline Division, Allied Chemical Corporation under the trademark "Naccotan A sodium condensate salt" marketed by Jacques Wolf and Company, Division of Nopco Chemical Company under the trademark "Lomar PW", the sodium salt of a condensed naphthalene sulphonate marketed by Jacques Wolf and Company, Division of Nopco Chemical Company under the trademark "Nopcosant", the sodium salt of polymerized alkyl naphthalene sulphonic acid marketed by Dewey Almy Chemical Division, WR Grace and Company under the trademark "Darvan II, J, the sodium salt of polymerized, substituted alkylbenzenesulfonic acid marketed by Dewey and Almy Chemical Division, WR Grace and Company under the trademark" Darvan # 2 ", the sodium salt of polymerized alkylene aphthalene sulfonic acid 141620 7 marketed by Dewey and Almy Chemical Division, WR Grace and Company under the trademark "Darvan # 15", the monocalcium salt of polymerized alkylarylsulfonic acids marketed by Dewey and Almy Chemical Division, WR Grace and Company under the trademark "Daxad # 21", sodium salts of polymerized , substituted alkylbenzenesulfonic acids marketed by Dewey and Almy Chemical Division, WR Grace and Company under the trademark "Daxad # 23", sodium salts of substituted alkylbenzenesulfonic acids, and suspending agent marketed by Dewey and Almy Chemical Division, WR Grace and Company under the trademark "Daxad # 27 ", sodium salts of substituted alkylbenzenesulfonic acids and suspending agent marketed by Dewey and Almy Chemical Division, WR Grace and Company under the trademark" Darvan # 3 ", and a group comprising sulfonated naphtha 1 mono-formaldehyde polymers such as a sulfonated condensate of naphthalene -formaldehyde marketed by New York Color and Chemical C ompany, Division of American Dyewood, Inc. under the trademark "Syntan NNC", the sodium salt of a sulfonated naphthalene formaldehyde condensate marketed by Dyestuff and Chemicals Division, General Aniline and Film Corporation under the trademark "Blancol", and the sodium salt of a sulfonated naphthalene formaldehyde condensate marketed by Dyestuff and Chemicals Film Corporation under the trademark "Blancol N". The above materials including Tamol and Marasperse are classified as dispersants in the publication: Detergents and Emulsifiers, 1964 Annual, Copyright 1964 by John W. McCutcheon, Inc.

The non-foaming anionic dispersant added in the second step of this dual treatment process is effective in generating beneficial results at very low concentrations of approx. 0.05 to 5.0% by weight based on the dry weight of the asbestos fiber. Larger amounts of the non-foaming anionic dispersant can be used, but the addition of additional amounts is superfluous and offers no additional benefits. Furthermore, as the amount of the dispersant increases, the dispersant begins to act in its normally intended manner as a dispersant and affects the harmful rate of production by which asbestos cement articles can be produced. The amount of dispersant used should not lower the surface tension of the asbestos cement slurry or paste for approx. 65-67 dynes / cm compared to the surface tension of ordinary water of approx. 72 dynes / cm, thereby preventing any tendency for the slurry to foam further. The exact amount of dispersant required to produce the desired results varies with the percentage of the particulate solid in the slurry or paste into which the asbestos fiber is to be incorporated, as well as the particulate matter of the particulate solid.

The asbestos fibers prepared by the above process comprise at least about 0.4% by weight of solid silicate which at least partially covers the surface of the asbestos fibers, as well as a non-foaming anionic dispersant distributed on the silicate treated fibers. The fibers can be compressed during packaging operations and, during shipment and long storage periods, retain their ability to increase production rates as well as to form strong asbestos cement articles.

According to a preferred embodiment of the present process, chrysotile asbestos fibers are first coated by spraying an aqueous solution of sodium silicate on the fibers to deposit about 10%. 0.75% by weight of solid silicate and then coated with approx. 0.4% by weight of the non-foaming anionic dispersant Tamol.

Portland cement is the most important hydraulic cement material used to make asbestos cement articles from fibers made by the process of the invention. Other hydraulic cements, e.g. pozzolance cement, calcium aluminate cement, and calcium sulfate cement, however, can be used, if desired, to replace at least part of the Portland cement.

Suitable asbestos cement articles can be made using mixtures consisting essentially of the cement and the asbestos fibers. However, it is often desirable from a cost point of view as well as for the structural properties of the finished products to incorporate additional silicon-containing materials into the aqueous slurries and pastes so that they will form part of the final shaped articles. As a result, sand, powdered silica, ground mica, ground feldspar and the like may be present in the slurry or paste.

The following examples are intended to illustrate the method of the invention. The exact methods, conditions, materials and / or properties given are to be understood as examples and not to be construed as limiting the scope of the invention. All percentages listed are percentages by weight unless otherwise stated.

Examples 1-4

A chrysotile asbestos fiber extracted in Quebec, Canada is treated in accordance with the dual treatment method of the invention. The filtration properties of the resulting fiber are compared with untreated fiber as well as fiber treated with silicate alone in the following Table 1.

An atomized 30% silicate solution is sprayed onto the fibers tested while the fibers are transported in an air stream. The dispersant, the sodium salt of condensed naphthalene sulfonic acid (Tamol) in dry powder form, is blown into the cyclone used to collect the silicate-treated fibers.

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The treated fibers are tested for their "Fiberator Index value" resulting from a "Standard Johns-Manville Corporation filtration test" used to determine the production rate properties of a fiber for use in wet machine operations. The sample is different from a wet permeability sample that simply measures the amount of time a given portion of liquid passes through a filter mat or through a formed filter cake.

"Fiberator Index value" is an empirical value obtained by using a test apparatus comprising a top open vessel with a side inlet opening, a side outlet opening, a bottom outlet and a net covering the bottom outlet. A filtrate collection flask connected to a vacuum source is connected to the bottom outlet of the container to enable the creation of a vacuum on a filter cake formed on the grid.

In the test method, an aqueous asbestos cement slurry is caused to flow through the container, and particles in the slurry build up to form a filter cake on the web. Vacuum draws the water through the cake of built-up material on the web and into the collection flask.

The amount of water that is collected in the collection flask over a given period of time is measured as is the case for the thickness of the material that builds up on the web. The number of milliliters of water collected is multiplied by a factor of 0.0833 and the dry weight in g of the material collected on the web is multiplied by a factor of 4.0. The average value of the products obtained by these multiplication processes is the "Fiberator Index". It is an empirical value that allows accurate prediction of the true filtration properties of an aqueous slurry of fibrous materials when the slurry is subjected to a rotary vacuum cylinder moving through a vessel. containing the slurry, which is the procedure used in a conventional commercially available wet machine for making asbestos cement products.

The fibers tested with the results shown in Tables 1 and 2 were of quality 4, which was determined in accordance with the standard Quebec Asbestos Mining Association (QAMA) grading system.

Table 1

Example Fiber Treatment "Fiberator Index" 1 (No treatment) 51 2 (0.57 «silicate) 59 3 (17c silicate) 78 4 (17. silicate + 0.377 Tamol) 87

Comparison of the results of Example 4 comprising fibers treated according to the invention with the results of the other examples shows that one index of filtration capacity is drastically increased by the dual treatment method according to the invention.

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Examples 5-8 In these examples, chrysotile asbestos fibers, while suspended in air, are initially sprayed with a 20% aqueous solution of sodium silicate to apply 1% by weight of solid silicate. Then 0.4% by weight of Tamol is applied to the fiber, either by blowing dry powder into the cyclone used to collect the silicate-treated fiber prior to its packaging, or by recycling the silicate-treated fiber past the zone used for initial application. spraying of the silicate, and spraying an aqueous solution of Tamol on the ► silicate treated fiber. The above weight percentages are calculated in relation to the weight of untreated asbestos fiber.

The treated fibers are incorporated into a 7% solids containing slurry of the type commonly used for the manufacture of asbestos cement pipes and processed on a small wet machine. The solids in the slurry comprise approx. 207th

fiber, 327. silica and 48% Port land cement.

The small wet machine is a conventional type of machine for making a garment, which machine has a mixing tank in which a slurry comprising asbestos fibers, hydraulic cement and silica as the particulate material is produced. The solids forming the slurry are filtered on a cylindrical form in a vessel and transferred as a continuous layer or filter mat onto a felt which leads the layer to a collection roller in which the layer is rolled up in several layers. Once the desired number of layers have been formed on the pickup roller, a longitudinal cut is produced and the laminated layers are removed from the pickup roller as a unit plate which is then pressed and subjected to conventional asbestos cement curing operations.

The following Table 2 shows that fibers subjected to the dual treatment method of the invention, Examples 7 and 8, possess a desired combination of superior filtration properties and the ability to produce strong asbestos cement articles.