GB2166127A - Mineral materials and articles made therefrom - Google Patents

Abstract

Flocced mineral materials, and high temperature resistant, water resistant articles prepared therefrom by treating a gellable layered swollen silicate, that has an average charge per structural unit of from -0.5 to -1 and which contains interstitial cations which promote swelling, with a source of at least one species of cations containing aminomethylamineimine cations, especially guanidine derived cations.

Description

SPECIFICATION Mineral materials and articles made therefrom This invention relates to flocced mineral materials, a process for their manufacture, and articles made therefrom, especially sheet materials.

Papers and/or sheets may be produced from water-swellable inorganic materials and, in particular, swollen silicate gels. For example, United States Patent No. 4,239,519 is directed to the preparation of inorganic, crystal-containing gellable, water-swellable sheet silicates and articles, for example papers, fibers, films, boards, and coatings, produced therefrom. These asbestos-free papers and/or sheets exhibit good high temperature stability and good chemical resistance. Furthermore, since asbestos fibers are not utilized in their manufacture, such articles will not have the health hazards which are associated with asbestos containing articles.

U.S. Patent No. 4,239,519 teaches a method for making the precursor gellable silicates used to produce said papers or sheet articles, involving three fundamental steps: (a) a fully or predominantly crystalline body is formed which contains crystals consisting essentially of a lithium and/or sodium water-swellable mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions between those and other structurally compatible species selected from the group of talc, fluortalc, polylithionite, fluorpolylithionite, phlogopite, and fluorphlogopite; (b) that body is contacted with a polar liquid normally water, to cause swelling and disintegration of the body accompanied by the formation of a gel; and (c) the solid:liquid ratio of the gel is adjusted to a desired value depending upon the application therefor.Glass-ceramics are the preferred crystalline starting bodies. Those products are then contacted with a source of large cations, i.e., with an ionic radius larger than that of the lithium cation, to cause macro flocculation of the gel and an ion exchange reaction to take place between the large cations and the Li and/or Na ions from the interlayer of the crystals.

U.S. Patents Nos. 3,325,340 and 3,454,917 teach producing aqueous dispersions of vermiculite flaked crystals which have been caused to swell by the introduction therein of interstitial ions such as (1) alkylammonium cations having between 3 and 6 carbon atoms inclusive in each carbon group such as methylbutylammonium, n-butylammonium, propylammonium and iso-amylammonium, (2) the cationic form of amino-acids, such as lysine and ornithine, and/or (3) lithium.

While the articles, such as papers, sheets and films, prepared by the prior art processes set forth above exhibit excellent heat resistance and are very useful in a wide variety of applications, it has been discovered that they have a certain amount of water sensitivity which is generally exhibited by the articles having a considerable loss of strength and general deterioration of mechanical and electrical properties when exposed to high humidity environments or submerged in water or other polar liquids. This sensitivity to water correspondingly curtails the utility of these articles in certain applications, such as, for example, head gaskets, electrical insulators, environmental protective coatings, and washable and environmentally stable building materials.

It has now been unexpectedly discovered that high temperature, fire-resistant, water-resistant articles, for example, sheet, paper, board, film, fiber and coating articles, may be made from a swollen, layered flocced silicate gel material that is prepared by utilizing exchange cations derived from at least one compound containing an aminomethyleneimine group, especially one based on guanidine orits derivatives. Such articles surprisingly have been found to exhibit, in general, much improved results in tensile strength and puncture resistance tests that are conducted when the articles are wet than do materials that are prepared utilizing prior art exchange cations. Furthermore, the articles made according to the present invention generally display superior electrical and mechanical properties to those of materials made by prior art methods.

With reference to heat resistance, the articles that are produced according to the present invention may be completely stable to temperatures of approximately 350-400"C and maintain their structural stability to approximately 800"C.

The term "water resistant" as used in this specification is not meant to imply any claim that the articles of the present invention are necessarily waterproof or are completely impervious to water. Rather, the term is used to indicate that the materials do not substantially degrade, at least in their tensile strength and puncture resistant properties, when exposed to water.

The articles and the flocced mineral suspensions of the present invention are, in one embodiment of the invention, prepared by utilizing, as a starting material, a water-swellable silicate that has an average charge per structural unit of from about -0.5 to about - 1 and which contains interstitial exchangeable cations that promote swelling. The specific exchangeable cations in the starting material will depend on the silicate being utilized. For example, if a synthetically derived gellable silicate, which is made according to the procedures of U.S. Patent No. 4,239,519, is utilized as a starting material, the exchangeable cations will generally be Li and/or Na ions. If a natural vermiculite dispersion, such as made one according to U.S.Patent No. 3,325,340, is utilized, the exchangeable cations will generally include alkylammonium cations and the other cations specified in U.S. Patent No. 3,325,340. The silicate, whether synthetic or natural in origin, will generally have a morphology represented by thin flakes which are generally disc, strip, and/or ribbons. The flakes will typically have measurements which are from about 500 A to 100,000 A, and preferably 5,000 A to 100,000 A in length, 500 A to 100,000 A in width, and less than 100 A thick. The term "charge per structural unit" as used in this specification refers to an average charge density as specified by G. Lagaly and A. Weiss, "Determination of Layer Charge in Mica-Type Layer Silicates", Proceedings of International Clay Conference, 61-80 (1969) and G.Lagaly, "Characterization of Clays by Organic Compounds", Clay Minerals, 16, 1-21(1981).

The starting silicate may be made according to the aforementioned procedures of U.S. Patents Nos. 4,239,519; 3,325,340; or 3,434,917 or other methods which result in dissociated layer materials with charge densities in the desired ranges.

The silicate is then contacted with a source of cations derived from at least one compound containing the aminomethyleneimine group to effect an ion exchange reaction between the cations and the interstitial ions. As a result of this exchange reaction a floc is formed which may then be utilized to form the articles of the present invention. In another embodiment of this invention, the starting silicate may first be formed into a product, for example a fiber or film, by using theiprocedures of U.S. Patent No. 4,239,519, and a cationic exchange reaction utilizing the above-specified cations may be carried out with the product, for example by immersing the product into a solution containing the above-specified cations. Thus, the ion exchange reaction may be carried out in situ during the actual forming process for the product.

As compounds, and cations derived therefrom, containing the amiomethyleneimine group =N-C(-)=N- there may be mentioned especially those containing the =N-C(-C)=N- or the =N-C(-N)=N- group and resonance structures derived therefrom, in which there is a delocalized double bond. More especially, the cations will have the Formula [R1C(R2)R3] wherein Rt, R2 and R2 are independently selected from NH2 and CH3, provided that at least two of R1, R2 and R3 are NH2, and wherein one or more of the hydrogen atoms on any one or more of R1, R2 and R3 may be replaced by substituents, for example C1 to C5 alkyl, C2 to C5 alkenyl or C2 to C5 alkynyl, and wherein one or more groupings of two of such substituents may be linked to form one or more rings, which may be saturated, unsaturated or aromatic. It will be appreciated that in the cation there will be a positive charge which may be localized on one group or delocalized, giving a resonance structure, depending on the nature of the compound from which the cation is derived.

As examples of compounds from which the cations may be formed there may be mentioned guanidine, aminoguanidine, diaminoguanidine, methylguanidine, tetramethylguanidine, melamine, 2aminopyridine and 2,6-diaminopyridine. The compounds may conveniently be used in the form of their hydrochlorides.

The flocced mineral suspensions of the present invention are prepared, for example, by reacting, generally with agitation, a suitable silicate gel with a source of exchange cations set forth in the Formula above in order to effect an ion exchange between the cations and the interstitial cations in the silicate gel to form exchanged macro flocculated particles. For example, if the exchange cation of choice is guanidinium or melaminium, the silicate will be reacted with the corresponding hydrochloride.

As stated above, one or more exchange cations of the Formula above may be utilized in the cationic exchange reaction. Since the various cations will give floc, and eventually end products, with differing physical properties, the specific cation or combination of cations will be chosen by the practitioner of this invention based on the desired end use.

The flocced mineral suspension will be used to form the desired end products. The specific treatment steps applied to the floc will depend on the particular article being formed. For example, if the articles of the present invention are to be formed into sheet materials, the resultant ion-exchanged floc will be agitated with sufficient shear to produce a particle size distribution which leads to suitable particle packing in the sheet forming operation. Following this process the floc is optionally washed to remove any excess salt solution and the consistency of the flocced slurry is adjusted to from about 0.75% to about 2% solids. To promote better drainage rates on a fourdrinier wire, polyelectrolyte flocculating agents may then be added to the slurry at a level of, for example, from about 0.1% to about 1%, and preferably 0.2%-0.3%, of floc solids. One example of a suitable polyelectrolyte floccuating agent is Polymin P, which is a trademark of BASF Corporation for a polyethylene imine.

The slurry is then fed to a papermaking apparatus where it is dewatered by free drainage and/or vacuum drainage followed by pressing and drying on drum driers. The thus formed sheet material may be used in applications such, for example, as gaskets.

If desired, and depending on the intended end use of the product, additional inert materials may be added to the flocced mineral suspension. For example, if desired one or more fibrous materials, which may be natural or synthetic, organic or inorganic, fibers may be added to the floc to improve its drainage rate and to provide an end product that has improved strength and/or handleability. For example, when the desired end products are gaskets, the fibers of choice are cellulose fibers, glass fibers, and/or Kevlar fibers (Kevlar is a du Pont trademark for an aromatic polyamide fiber). In addition, latex or other binders may be added to the floc to provide a product with improved strength characteristics.

If the cationic exchange reaction is conducted directly on a product formed from the silicate starting material, any desired additional inert materials would be added to the slurry of the silicate starting material prior to the formation of the product and, of course, the subsequent cationic exchange reaction.

In the following Examples, unless otherwise specified, the starting material utilized was a lithium fluorhectorite made according to the procedures described in U.S. Patent No. 4,329,519.

Example 1 This example illustrates both a method of producing a guanidinium exchanged fluohectorite flocced silicate and a formed sheet that was prepared therefrom.

A slurry of guanidinium fluorhectorite was prepared by adding 475 grams of a 10% dispersion of lithium fluorhectorite to 1.4 liters of 1N guanidine hydrochloride solution. The slurry was then agitated with a high shear mixer to reduce the particle size of the resultant floc, washed, analyzed for water content and diluted to give a 2% solids slurry. The slurry was transferred to an 11.5"X11.5" (29 cmX29 cm) hand sheet mold (manufactured by Williams Apparatus Co.) and dewatered. The resultant formed sheet was then wet pressed and dried on a drum drier.

The sheet had good flexibility and performed well in the gasket sealing test.

Example 2 This example illustrates a method of producing films of the present invention wherein the cationic exchange is carried out in situ.

A 10% solids lithium fluorhectorite gelled dispersion was prepared as described in U.S. Patent No. 4,239,519. A film was made of this material by using a 4.5 mil (0.11 mm) Byrd applicator, which was 5 inches (127 mm) wide, to draw down a 4.5 mil (0.11 mm) thick wet film of the dispersion on a glass plate. The glass plate, with the film attached, was then immersed in an 0.25M guanidinium hydrochloride solution to cause cation exchange between the guanidinium cations and the fluorhectorite's interlayer cations. A skin was formed seemingly instantaneously, on the film which indicated such an exchange was taking place. After 10 minutes the film was removed from the plate, washed, in deionized water to remove residual salts, and dried. The film had good flexibility and strength retention when wet.

Examples 3-9 In each of these examples, the procedure of Example 2 was substantially repeated with the exchange cation as specified to form the corresponding film. In Example 7, a 0.1N solution of melamine hydrochloride was employed. In all the other examples, a .25N solution of the respective exchange source was employed: Example Exchange Cation 3 Diaminoguanidine hydrochloride 4 Aminoguanidine hydrochloride 5 Tetramethylguanidine hydrochloride 6 Methylguanidine hydrochloride 7 Melamine hydrochloride 8 2,6-diaminopyridine hydrochloride 9 2-aminopyridine hydrochloride Comparative Examples 1-3 These comparative examples illustrate fluorhectorite films that are made with various prior art exchange cations. 4.5 mil (0.11 mm) thick films of potassium fluorhectorite (KFH) and ammonium florhectorite (NH4FH) were separately prepared by the process specified in U.S. Patent No.

4,239,519. A film was then cast of both the KFH and the NH4FH slurry. A Kymene (a trademark of Hercules, Inc. for a cationic, polyamide-epichlorohydrin resin) fluorhectorite film was also prepared by the procedure of Example 2, except that (1) a 3.0% Kymene solution was used and (2) the lithium fluorhectorite film had to be immersed in the Kymene solution for 2 hours until the resultant exchanged film was sufficiently self-supporting to be removed from the glass plate.

These films, along with the films made in Examples 2-9, were then subjected to tensile strength and puncture resistance tests which were conducted as follows: Tensile Strength Measurements Dry tensile strength measurements were determined using a Instron (trademark) testing machine at 1.5 inch (38 mm) jaw separation and 0.2 inch/min. (5 mm/min.) crosshead speed. Wet strength measurements were made by ringing water-saturated sponges in contact with both sides of the film sample for 10 seconds while the sample was positioned in the Instron clamps just before the strength test was conducted.

Puncture Resistance Measurements A sample of film was secured in a retaining device which held the film securely. A stylus which could be loaded was impinged on the film ip the direction normal to the surface of the film and loaded with increasing weight until the stylus penetrated the film. In the wet test the film in the retaining device was submerged in deionized water for 10 seconds immediately preceding the puncture resistance test.

The data from these tests are shown in the table below.

Puncture Film of Tensile Strength Resistance Example Exchange Dry Wet kg/mm No. Cation Kpsi mPa Kpsi mPa Dry Wet 2 Guanidinium 14 97 9 62 7.1 4.6 3 Diaminoguanidinium 13 90 11 76 14.0 4.2 4 Aminoguanidinium 13 90 11 76 8.9 3.5 5 Tetramethylguani minium 11 76 11 76 13.0 4.4 6 Methylguanidinium 5.2 36 2.8 19 6.6 3.4 7 Melaminiup 19 131 20 138 10.0 3.3 8 2,6-Diaminopyri dinium 13 90 5.3 37 7.9 3.6 9 2-Aminopyridinium 11 76 7.0 48 7.8 3.6 Comparative Example No.

I Kyrnene (protonated) 7.0 48 2.7 19 0.9 0.26 2 Ammonium 3.3 23 1.4 10 3.5 0.68 3 Potassium 1.1 7.6 0.2 1.4 3.3 0.44 The data indicate that the films made according to the procedures of the present invention have markedly superior wet tensile strength and/or superior wet puncture resistance when compared to prior art compositions.

Fire and Smoke Resistance A film prepared according to Example 2 was, after being dried, subjected to fire and smoke resistance tests in accordance to the procedures specified in ASTM-E-662-79. Three separate tests were made and the results are set forth below. The numerical values correspond to the maximum specified optical density as per N.B.S. Technical Note No. 708.

Flaming Smoldering Test No. DM Corr DM Corr 1 2 0 2 1 0 3 1 0 Electrical Properties Films of Examples 2 and 7 and Comparative Example 3 were, when dried, tested for dielectric strength using the procedures of ASTM D149. The results are set forth below.

Dielectric Strength Films of (v/mil) (v/mm) Example 2 5,000 197 Example 7 9,000 354 Comparative Example 2 2,920 115 Comparative Examples 4 and 5 These examples illustrate using, as a starting material, silicate materials which fall outside the scope of the present invention in their charge per structural unit and their physical measurements.

For comparative Example 4, a 10% aqueous dispersion was made from a natural hectorite obtained from the source clay mineral depository of the Clay Minerals Society, Bloomington, Indiana. For Comparative Example 5, a 10% aqueous dispersion was made utilizing sodium montmorillonite obtained from the same source. In each example, a film was drawn down using the procedures set forth in Example 2. The glass plates were then immersed for 10 minutes in a 0.25M guanidine hydrochloride solution. In both instances, a coherent film was not produced.

Example 10 This example illustrates a method of preparing a film of the present invention utilizing a vermiculite starting material: A 10% solids suspension of n-butylammonium vermiculite, which was prepared according to the procedures specified in U.S. Patent No. 3,325,340, was cast as a film on a glass plate according to the procedure set forth in Example 2. The glass plate, with the film attached, was immersed for 10 minutes in a 0.25M guanidinium hydrochloride solution. The resulting film was removed from the plate, washed, and dried. The film displayed wet strength in the tensile strength and puncture resistance tests that a comparable unexchanged vermiculite film does not display.

Example 11 This example illustrates preparing fibers utilizing the method of the invention. A 15% solids suspension of lithium fluorhectorite (prepared as above) was extruded through an 11 mil (0.28 mm) opening needle into a 2N solution of guanidine hydrochloride. The extruded fiber was carried by a porous belt and delivered to a second bath of 2N guanidine hydrochloride. The fiber so produced was washed by submersion in deionized water and dried. The resultant fiber was strong and flexible.

Claims (25)

1. A method of preparing a flocced mineral material which comprises contacting a swollen layered silicate gel that has an average charge per structural unit within the range of from -0.5 to - 1 and contains exchangeable interstitial ions with at least one species of cations containing an aminomethyleneimine group to effect an ion exchange reaction between at least some of the interstitial ions and at least some of the said cations.

2. A method of improving the water resistance of a silicate article, which comprises contacting an article formed from a water-swellable gellable layered silicate that has a charge per structural unit that ranges from -0.5 to - 1 and contains exchangeable interstitial ions with a source of at least one species of cations containing an aminomethyleneimine group to effect an ion exchange reaction between at least some of the said cations and at least some of the interstitial ions.

3. A method as claimed in claim 1 or claim 2, wherein the layered silicate is a synthetic silicate and the interstitial ions are Li+ and/or Na+.

4. A method as claimed in claim 3, wherein said synthetic silicate is prepared by contacting a body consisting essentially of crystals of a water-swellable mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally compatible species selected from the group of talc, fluortalc, polylithionite fluorpolylithionite, phologopite and fluorphlogopite, with a polar liquid for a time sufficient to cause swelling of the crystals accompanied with the formation of a gel.

5. A method as claimed in claim 4, wherein the crystals are fluorhectorite.

6. A method as claimed in claim 4 or claim 5, wherein the polar liquid is water.

7. A method as claimed in claim 1 or claim 2, wherein the silicate is vermiculite and the interstitial ion are selected from alkylammonium cations, the cationic form of amino-acids and u.

8. A method as claimed in any one of claims 1 to 7, wherein the cations containing the aminomethyleneimine group are selected from the group of diaminoguanidine, tetramethyl guanidine, guanidine, aminoguanidine, methyl guanidine and melamine derivatives.

9. A fiocced mineral material which comprises a swollen layered silicate gel that has an average charge per structural unit within the range of from -0.5 to - 1, said silicate containing at least some interstitial cations containing an aminomethyleneimine group.

10. A material as claimed in claim 9, wherein the silicate is synthetically derived.

11. A material as claimed in claim 10, wherein said silicate is prepared by (1) contacting a body consisting essentially of crystals of water-swelling mica containing interstitial lithium and/or sodium ions, said mica being selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally compatible species selected from the group of talc, fluortalc, polylithionite, fluorpolylithionite, phologopite and fluorphlogopite, with a polar liquid for a time sufficient to cause swelling of the crystals accompanied with the formation of a gel, and (2) contacting the thus formed gel with at least one species of cations containing an aminomethyleneimine group to effect an ion exchange reaction between at least some of the lithium and/or sodium ions and at least some of the said cations.

12. A material as claimed in claim 11, wherein the crystals are fluorhectorite.

13. A material as claimed in claim 11 or claim 12, wherein the polar liquid is water.

14. A material is claimed in claim 9, wherein the silicate is vermiculite.

15. A material as claimed in any one of claims 9 to 14, wherein the said cations are selected from the group of diaminoguanidine, tetramethyl guanidine, guanidine, aminoguanidine, methyl guanidine, and melamine derivatives.

16. A water resistant article prepared from a swollen layered silicate that has an average charge per structural unit that ranges from -0.5 to - 1, said silicate containing at least some interstitial cations containing an aminomethyleneimine group.

17. An article as claimed in claim 16 that is prepared from a silicate floc.

18. An article as claimed in claim 16 or claim 17 that is in sheet form.

19. An article as claimed in claim 16 or claim 13 that is in the form of a fiber.

20. An article as claimed in claim 16 or claim 17 that is in the form of a film.

21. A method of preparing a flocced mineral material carried out substantially as described in Example 1 herein.

22. A method of preparing a silicate article, carried out substantially as described in any one of Examples 1 to 11 herein.

23. An ion-exchanged flocced mineral material substantially as described in Example 1.

24. An ion-exchanged silicate article substantially as described in any one of Examples 1 to 11 herein.

25. Any new feature hereinbefore described or any new combination of hereinbefore described features.