US3449230A - Manufacture of asbestos products - Google Patents

Description

June 10, 1969 R N ET AL 3,449,230

MANUFACTURE OF ASBESTOS PRODUCTS Filed Nov. 8, 1966 Sheet of 2 s 5 s i g 5 lumuunumwl i 5 i 50/ June 10, 1969 G. F. HERON ET AL MANUFACTURE OF ASBESTOS PRODUCTS orz Sheet Filed NOV. 8, 1966 United States Patent 3,449,230 MANUFACTURE OF ASBESTOS PRODUCTS Gordon F. Heron and John Outram Halstead, Rochdale,

England, assignors to Turner Brothers Asbestos Company Limited, Manchester, England, a British company Filed Nov. 8, 1966, Ser. No. 592,941 Int. Cl. B01d 13/02 US. Cl. 204-180 Claims This invention relates to the manufacture of asbestos articles, that is to say, articles composed essentially of or containing asbestos. The invention is based on the phenomenon of electrophoresis, which involves the passage of a direct current through a dispersion of electrically charged particles between two electrodes, the particles being electrically attracted towards the oppositely charged electrode so that they move towards it and deposit on it.

It is known that if a dispersion is to be subjected to electrophoresis it must contain very highly dispersed particles. These particles are said to be colloidally dispersed, since one of the properties of colloidally dispersed particles is that they are charged and that, accordingly, they may undergo electrophoresis. It is also known that of the three most common types of asbestos, namely chrysotile, amosite and crocidolite, chrysotile can readily be dispersed colloidally in water with an anionic dispersing agent. In the invention anionic dispersions of asbestos are used and they may contain some noncolloidally dispersed asbestos fibres and they may even contain other constituents, either colloidally dispersed or merely intimately mixed, which are not asbestos. The necessary property a dispersion must possess to be usable in the invention in response to electrophoresis is that asbestos fibre in it will be electrically at tracted to an electrode when a current is passed through the dispersion. Whether any given dispersion has this property is readily ascertainable by test.

Chrysotile asbestos is sold in various grades and all grades can be colloidally dispersed.

Fibres of dry chrysotile asbestos are positively charged but when the fibres are opened and dispersed in water by means of anionic dispersing agents (e.g., soaps) their surfaces become negatively charged (due to adsorption of a layer of negative soap anions). Under the influence of a direct current, therefore, the fibres then move towards the anode.

According to the invention the dispersion is passed between two electrodes across which an electric potential difference is applied, whereby constituents are caused to migrate towards the anode, the migrating constituents are collected as a deposit on the anode or on an ion-permeable membrane interposed in their path to the anode, and the deposit is continuously removed from the remainder of the dispersion. Products which may be produced in this way include sheets, tapes and yarns, membranes, such as glass, cloth, coated or impregnated with abestos, and wire and other electrically conducting surfaces coated with asbestos.

It is necessary to pass the dispersion between the electrodes while the process is carried out since if this is not done localised electrolytic effects occurring around the electrodes will interfere with satisfactory deposition of asbestos.

The invention may be carried out in numerous ways. Particularly advantageously the deposit is continuously stripped off the anode as a coherent body. We have surprisingly found that it is possible to produce deposits of such high wet strength that the deposit can be stripped off the anode while it is still immersed in the dispersion. However, the deposit may be carried out of the dispersion on the anode or membrane and then either left in position to form a permanent coating on the electrode or membrane or stripped off. I

3,449,230- Patented June 10, 1969 When the deposit is drawn off the anode or membrane while wet, high wet strength is an extremely important property. For highest wet strength, long fibres should be used. Moreover, we have found that to impart high wet strength it is necessary to deposit a binder with the asbestos. This binder is not required for dry strength in the final product, as is shown by the fact that a product made with it maintains its strength on removal by solvent extraction or by heating to 450 C. of the organic matter in it. This suggests that the very fine, highly opened asbestos fibrils may be giving dry strength to the product by random arrangement and entanglement, a theory which is supported by electron microscopic examination of the deposits.

We find that the fibres are oriented in the direction in which the dispersion flows, and in particular any incompletely opened bundles are deposited parallel to one another. This fact accounts for an observed large difference in strength of electrodeposited asbestos products in directions at right angles to one another. Strengths are much higher in the direction of drawing of continuously deposited materials and the coarse fibres are seen to be aligned in this direction. Alignment is apparently not merely a result of the drawing or flowing motions since alignment occurs in static deposition.

To produce the binder required for high wet strength, we use a water-soluble soap as an anionic dispersing agent. During the electrophoresis process, electrolysis and electroosmosis occur, the electrolysis resulting in the release of cations at the anode and a build-up of acidity there. If the anode does not corrode during the process free fatty acids are formed by reaction of the resultant acid with the water-soluble soap, and these improve the wet strength. Much better wet strength is obtained by a further important feature of the invention, namely the use as the 'anode of a metal which will corrode during the process as a result of electrolytic action. Ions dissolved from such an anode react with the water-soluble soap to yield a water-insoluble soap which acts as a binder. The preferred metals for use as the anode are aluminum and zinc, but copper, lead or iron may also be used.

When high wet strength is not important the electrode can satisfactorily be of materials, for example platinum or carbon, which do not corrode to give ions that form insoluble soaps.

Although the water-soluble soaps serve both as dispersing agents and binder-formers, they do not give wholly satisfactory dispersions when used as the sole dispersing agents. To form the best dispersion and get the highest wet strength, we prefer to use a mixture of soap and another anionic surface-active dispersing agent, for example an alkyl-aryl sulphonate, an alkyl sulphosuccinate or a sulphated higher alcohol. We find a very suitable mixture to be one of 6 parts soap to 1 part of the other anionic dispersing agent. Unless otherwise specified, all parts and percentages quoted in this specification are by weight. Two examples of dispersions which are responsive to electrophoresis are as follows:

EXAMPLE 1 Parts Tap water of hardness of about ppm. ex-

pressed as calcium carbonate (at 60 C.) 1,000 Chrysotile asbestos (Canadian Cassiar A35, length approximately 0.30") Sodium dodecyl benzene sulphonate 1.2 Soap (sodium salts of mixed long-chain fatty acids) 7 If this dispersion is used with an anode of aluminum, zinc or copper the wet strength is good. Equal dry strength may be obtained if the anode is of carbon or platinum.

EXAMPLE 2 The dispersion contains 2% chrysotil asbestos fibre (South African C and G3, length approximately 0.18") and 0.3% sodium dioctyl sulphosuccinate. This dispersion can be deposited on a corrodible or noncorrodible anode, and it requires support until it is dry. It presents the advantage that it yields a deposit containing only about organic matter.

The proportion of the fibre in the dispersion is small, though it may advantageously depend on-the fibre length. With long fibres such as Canadian Cassiar A35 the propor tion in the dispersion may be from 0.5 to 5%. With very short fibres such as Canadian Bells F7M (length approx imately 0.0 the proportion may be as high as and preferably is at least 1% There is an optimum pH of the dispersion for each anode material, so it may be necessary to adjust the pH of the dispersions of Examples 1 and 2 to obtain satisfactory deposition with some anodes;

The dispersion need not consist solely of asbestos fibres, but rather one or more constituents having the same electric charge as the dispersed fibres may also be present in the dispersion, these materials thus undergoing electrophoresis with the asbestos fibres. In particular, the dispersion may contain both chrysotile asbestos fibres and particles of a polymeric material. The proportion of the polymer particles may vary from a very small to a substantial figure.

Particularly useful products, e.g., gaskets, may be made by the codeposition of asbestos and a styrene-butadiene rubber or polytetrafluorethylene. Other useful reinforced polymer compositions may be made by the codeposition of asbestos and a thermoplastic, thermosetting or rubber polymer, examples of suitable polymers being styrene rubbers, copolymers of acrylonitrile and butadiene, copolymers of carboxylic butadiene and acrylonitrile, polyvinyl chloride, polyethylene, polystyrene, polyester resins and various mixtures of these.

Some examples of dispersions which contain polymer particles and are responsive to electrophoresis are as follows:

EXAMPLE 3 The dispersion contains by weight:

2% chrysotile asbestos fibre (Canadian Cassiar A35), 2 /2 polyvinyl chloride added as latex,

0.8% soap,

0.12% sodium dodecyl benzene sulphonate.

This dispersion will give a deposit containing about 34% asbestos, 57% polyvinyl chloride and 9% soap products.

EXAMPLE 4 An equivalent amount of polytetrafluoroethylene is substituted for the polyvinyl chloride in Example 3, and a product of low wet strength but good dry strength is obtained. This deposit must therefore be carried out of the dispersion on a continuous anode or other support.

EXAMPLE 5 The dispersion contains by weight:

5% chrysotile asbestos fibre (Canadian Bells C5R, length approximately 0.06),

% polytetrafluoroethylene (added as a dispersion),

0.5% sodium dioctyl sulphosuccinate.

The dispersion gives deposits containing about 35% asbestos, 63% polytetrafiuoroethylene and 2% other organic matter. These deposits are useful as gasket materials. From this dispersion a deposit of good dry strength but low wet strength is obtained, and the deposit must therefore be carried out of the dispersion on a continuous anode or other support.

The dispersions have a surprisingly high tolerance for charged or uncharged particles and fibes, which may themselves be able to undergo electrophoresis or which may be deposited simply by being mechanically entrained by the deposited fibres. Examples of colloidally dispersible particles which can be added are bentonite, clay, colloidal silica and graphite. Bentonite will also act as a dispersing agent, though it does not produce a satisfactory colloidal dispersion without another dispersing agent. One example is as follows:

EXAMPLE 6 The dispersion contains by weight:

4% bentonite, 3% chrysotile asbestos fibre, 0.15% sodium dioctyl sulphosuccinate.

This dispersion gives a deposit having a low wet strength.

When graphite is colloidally dispersed with the asbestos the product is graphitised asbestos. Such products are known, but when they are made by impregnation the graphite is largely concentrated at the surface, whereas in the product made by the invention it is uniformly dispersed throughout the product. As an example, 20 parts of graphite by weight in the form of a colloidal dispersion may be added to the dispersion of Example 1.

The mechanical entrainment of uncharged constituents is surprising. For example, 20 parts by weight of glass fibres as chopped roving A inch long may be added to the dispersion of Example 1. Broadly, examples of constituents which may be entrained by colloidally dispersed fibres that migrate under electrophoresis are glass fibres (as chopped roving), slag wool and noncolloidally dispersed asbestos fibres, such as fibres of amosite or crocidolite or even of chrysotile.

In order to prevent contamination of the dispersion by bubbles of gas evolved at the cathode it is often preferable to cover the cathode by a membrane, for example a nylon cloth, which is permeable to ions but not to gas bubbles. This cathode membrane separates the liquid around the cathode from the rest of the dispersion between the electrodes.

The shape of the anode on which the deposit is formed depends on the required product. It may be a plate of the width desired for a sheet or tape of asbestos. In order to facilitate drawing of the product off the electrode it is desirable that deposition should occur only on the electrode surface having the shape of the desired product and in order to prevent extraneous deposition the other surfaces are generally shielded. For example, an electrode for the production of sheet or tape may be sunk in a recess in the surface of a larger nonconducting sheet, and the whole then machined to present a fiat surface. Alternatively a backing of nonconducting material may be provided on a very thin electrode, a suitable nonconducting material being polymethyl methacrylate. However, if the plate has two conducting fiat surfaces and is located between two cathodes or within an encircling cathode, sheet or tape can be produced on both surfaces simultaneously.

A particularly suitable anode is a rotary cylinder.

If the deposit does not have sufiicient wet strength to be drawn off without breaking, it may be formed on a flexible band, which may be a membrane that moves over the face of the anode, for instance round a rotary anode, or which may be of metal and thus constitutes the anode.

The invention is useful in the production of yarn. This may easily be made by twisting tape made either in tape form or by slitting wider sheets.

Once the wet deposit has been removed from the dispersion it is not generally necessary to subject it to any special treatment if it has a high wet strength, since strength will be maintained on drying. The drying may occur naturally in air, even when the deposit is rolled up, or it may be forced by heating. Similarly no special treatment is necessary if the deposit is to form a permanent coating on an electrode or membrane. If, however, it has low wet strength it is preferably heated to dry it on leaving the dispersion.

Four apparatus which may be used in carrying out the invention are shown diagrammatically in FIGURES 1 to 4 of the accompanying drawings, each of which shows one apparatus.

In the apparatus shown in FIGURE 1 a box-like container 1 is formed from an aluminum anode 2 and an aluminium cathode 3 separated by insulating blocks 4 and 5. The base of the container thus formed is constituted by a block 6 having a central cavity 7 into which an inlet tube 8 leads and from which a series of passages 9 run to the interior of the container. The cavity in this block is closed by a door 10 which can be removed in order to clean the cavity.

At the upper edge the cathode is shaped to form an overflow weir 11, and the anode is similarly shaped to form an overflow weir 11, and the anode is similarly shaped to form an overflow weir 12. Terminals 13- and 14 are provided for the electrical connections to the anode and the cathode.

In operation the dispersion is pumped through the inlet tube, rises through the passages into the container and flows up between the anode and the cathode, asbestos being deposited on the anode. As soon as the deposit, shown at 15, is thick enough to handle, the upper edge is lifted by hand and drawn upwards over a roller 16 and under a rubber wiper 17. From the roller 16 this deposit is taken beneath a roller 18 and wrapped round it. The roller 18 is frictionally driven by engagement with a positively driven roller 19, and is carried in bearings 20 which are free to rise as the thickness of the sheet wound round it increases, so that at all times the surface speed of the sheet drawn away from the anode remains constant. Dispersion flows over the weir 11 and acid flows over the weir 12.

If the dispersion of Example 1 is passed through the apparatus shown in FIGURE 1, the anode being 8 inches long, and 100 volts-DC are applied across the electrodes to give a current of about 8 amperes, an anodic deposit may be withdrawn at a rate of 5 feet per minute to give a paper which is from 0.0015 to 0.002 inch thick after drying. The tensile strength of a specimen of this paper measured in the direction of movement of the paper was found to be 5 lb. per inch of width.

It will be realised that a layer of acidic liquid is being continuously formed between the deposit and the anode. If this acid is permitted to enter the body of the dispersion between the electrodes it will react with the dispersion and form clots, which are found seriously to interfere with satisfactory operation. It is highly desirable to prevent the acid from escaping from between the deposit and the anode, and this is in effect done by the deposit itself, the edges of which in contact with the insulating blocks 4 and 5 form an acid seal.

In the apparatus, shown in FIGURE 2, a cylindrical anode 72 having end discs 73 of insulating material is rotatably mounted within an open box 74 over a trough formed by a curved cathode 75. An inlet trough 76 extends across the top of the box immediately above one edge 85 of the cathode, and contains an inclined baflle 78 above an inlet 77. Dispersion supplied to the inlet 77 at a uniform rate flows round the lower edge of the baflle 78 and then over the baflle and a weir 87 formed by the edge of this bafile through the gap between the anode and the cathode. Qllll'lt is supplied to the anode through bearings 79 having electrical connections, and to the cathode by a contact '80, and some of the asbestos present in dispersion between the anode and cathode is deposited as a sheet 81 on the anode while excess dispersion flows over a weir 82 formed by the edge of the cathode and down a chute 83. Once an appreciable deposit has formed on the anode its end can be picked off and the deposit drawn slowly upwards. Thereafter the sheet deposit is continuously slowly drawn upwards, this movement causing the anode to rotate and so to present continuously fresh surface to the dispersion. Acid forming in the V- shaped between the upwardly moving deposit and the anode is permitted to flow around the edges of the deposit into the excess dispersion flowing over the weir 82.

Any clots adhering to the deposit should be broken oif, and it may be desirable to trim off the edges and feed them back into the reservoir of dispersion.

It is advantageous to cover the cathode by a membrane 84 of nylon cloth which is permeable to ions but not to gas bubbles. This prevents contamination of the dispersion by evolved gas. Cathode liquid, formed between the membrane and the cathode and containing bubbles of the gas, flows axially off each end of the cathode into the box 74 and leaves through an outlet 86. This cathode liquid is alkaline and advantageously should not reenter the dispersion.

As an example, in an apparatus as shown in FIGURE 2 the anode 72 was approximately 7 inches wide and there was a half-inch space between ,the anode and the cathode membrane 84. The total initial volume of a dispersion of Example 1 in the reservoir and in circulation was approximately 30 litres, the dispersion also containing a sufficient amount, approximately 55 grams, of a mixture of 65 parts oleic acid and 35 parts stearic acid to give the dispersion a pH in the range of 8.5 to 8.7, this pH being the most suitable for the anode, which was of zinc. A current of 5 amps at between 15 and 20 volts DC was applied between the anode and cathode and dispersion was continuously pumped in through the inlet 77 and excess dispersion flowed over the weir 82 back into the reservoir 21. A deposit of wet asbestos paper was formed on the anode and was drawn oft, squeezed to remove excess acidic liquor and then dried. This liquor was returned to the dispersion in the reservoir tank to assist in pH control. After about 20 minutes it was seen by eye that the appearance of the dispersion in the reservoir was changing, and replenishment was started. This replenishment was effected by adding undispersed asbestos fibres, oleic acid and stearic acid, soap, and sodium dodecyl benzene sulphonate as necessary. The process was run continuously for 42 hours, during which time approximately 125 litres of dispersion were added to maintain the level of dispersion in the reservoir tank (ie, 125 litres of dispersion were actually used for deposition.) Approximately 65 litres of cathode liquid were collected and 16 litres of acidic liquid were squeezed from the paper during winding. 3,500 grams of dry paper (0.004 thick) were produced, containing (when dried to 1% moisture content) from 20 to 25% organic matter. This represents deposition of the asbestos in the dispersion.

If the deposit does not have adequate wet strength, then a carrier, which may be an ion-permeable membrane, for example of fine-mesh nylon cloth, is run round the rotary anode and the deposit forms on it and can either be left on it or stripped from it after drying as desired. Alternatively, as shown diagrammatically in FIGURE 3, the anode is replaced by a positively driven roller 64 of insulating material, around which a continuous flexible metal band 65 passes. This band also passes round a roller 66, through a drying box 67 and round another roller 68. The deposit is formed on the band 65, and after being dried in the box 67 is stripped off as shown at 69 and wound into a coil 70. It will be appreciated that in this case the band 65 is itself the anode, and current is supplied to it through a carbon brush 71.

FIGURE 4 shows an apparatus in which a copper wire 50 is continuously coated with asbestos to form a permanent covering. The wire 50 is drawn from a reel 51 through a guide 52 past a contact 53' electrically connected so that the wire becomes the anode. The wire travels onwards past a guide 54 into a pot 55. This pot has a base 56 of waxed cork, through which the wire 50 passes, and its body is made of plastic lined by aluminum foil 57, which forms the cathode and to which an electrical con- 7 nection 58 is taken. The pot 53 has an inlet 59 and outlet 60 for the dispersion, which thus flows in countercurrent to the Wire. The coated wire emerges from the top and is passed through a tubular wiping device 61 and a drying box 62 to be wound into a coil 63.

A suitable dispersion for use in coating wire as shown in FIGURE 4 contains 3% chrysotile asbestos fibres (South African ,HVL4, length approximately 0.10"), 0.75% soap, and 0.12% alkyl aryl sulphonate.

An apparatus similar to that shown in FIGURE 4 may also be used for forming yarn from a paper strip coated with graphite, which constitutes the moving anode. Very short fibres of asbestos can be used to form a deposit on this strip, and the paper coated with asbestos may be twisted to form the yarn.

We claim:

1. A process for the production of an asbestos product comprising the steps of passing an anionic aqueous dispersion of asbestos fibre, that is responsive to electrophoresis between a cathode and an anode, applying an electric potential difference across said cathode and anode, whereby solid constituents are caused to migrate towards the anode, collecting the migrating constituents as a deposit, and continuously removing the deposit from the remainder of the dispersion.

2. A process as claimed in claim 1 in which the deposit is formed on the anode and is continuously stripped off it as a coherent body.

3. A process as claimed in claim 1 in which a binder is deposited with the asbestos.

4. A process as claimed in claim 3 in which the dispersion contains a water-soluble soap as a dispersing agent and the anode is of a metal which corrodes during the process, whereby metal ions are dissolved from the anode and combine with the soap to form a water-insoluble soap as the binder.

5. A process as claimed in claim 1 in which the anode is continuously moved through and out of the dispersion.

6. A process as claimed in claim 1 in which the deposit is formed as a sheet or tape on a plate anode, the sides of the anode being shielded from the dispersion.

7. A process as claimed in claim 1 in which the asbestos dispersion contains other dispersedparticles carrying electric charges such that they undergo electrophoresis and are deposited with the asbestos particles.

8. A process as claimed in claim 7 in which the dispersed particles are polymer particles.

9. A process as claimed in claim 1 in which the disersion contains additional fibres which are entrained by and codeposited with the dispersed asbestos.

10. A process as claimed in claim 1 in which the deposit is formed on an ion-permeable membrane interposed in the path of the migrating constituents to the anode.

References Cited UNITED STATES PATENTS 1,884,110 10/1932 Morehouse 204-181 2,214,876 9/1940 Clark 2041 2,421,652 6/1947 Robinson et al. 117--128.4 2,900,320 8/1959 Metcalfe et a1. 204300 JOHN H. MACK, Primary Examiner.

A. C. PRESCOTT, Assistant Examiner.

US. Cl. X.R. 20418l

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF AN ABESTOS PRODUCT COMPRISING THE STEPS OF PASSING AN ANIONIC AQUEOUS DISPERSION OF ASBESTOS FIBRE, THAT IS RESPONSIVE TO ELECTROPHORESIS BETWEEN A CATHODE AND AN ANODE, APPLYING AN ELECTRIC POTENTIAL DIFFERENCE ACROSS SAID CATHODE AND ANODE, WHEREBY SOLID CONSTITUENTS ARE CAUSED TO MIGRATE TOWARDS THE ANODE, COLLECTING THE MIGRATING CONSTITUENTS AS A DEPOSIT, AND CONTINUOUSLY REMOVING THE DEPOSIT FROM THE REMAINDER OF THE DISPERSION.

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