DE2222972A1 - Coating compositions - Google Patents

Description

PATENT LAWYERS

DR ₁ -ING. H. FINCKE DIPL. -1 NQ. H . BOHR DIPL.-ING. S. STAEGER

MUNICH 5, Müllerstrasse 31

Telephone: »26 6060

Folder 22886 Case P 23867

Dr.

1 May 0, 1972

Imperial Chemical Industries ltd, London ,. Great Britain

Coating compositions Priority: May 10, 1971 - Great Britain

The invention relates to coating compositions and in particular to such coating compositions containing polytetrafluoroethylene in aqueous dispersion, to a process for the preparation of these compositions and to substrates which have been coated with these compositions ο

It is a process used to coat certain metals Polytetrafluoroethylene (PTPB) known in which a mixture of

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Chromic and phosphoric acid is added to a polytetrafluoroethylene diaper- · sion, which is stabilized with sodium lauryl sulfate, in order to produce a primer dispersion. The primer dispersion is sprayed on to a degreased metal surface, and the coating is dried and calcined at 250 ⁰ O. Then a top covering made of a polytetrafluoroethylene dispersion is sprayed onto the primer surface and then dried and sintered.

This process has the disadvantage that the polytetrafluoroethylene dispersion and the acid that are used in the primer must be stored separately until they are needed, since the mixture of these substances has a short shelf life o The term "short shelf life" means that the mixture of the dispersed polymeric material and the acid is unstable when it is stored at room temperature. This instability manifests itself in several stages. Within about 24 st, the mixture begins to separate into two distinct Sohiohten, wherein the upper layer j.st clear _o Dae mixture is thick and within 14 days, the mixture becomes so thick that it can no longer be injected "The process is irreversible ο No suitable mixture can be restored by vigorous stirring, for example, "This is a problem that has been unsolved in Teohnik for a long time",

The storability can be extended by storage at low temperatures, for example at 5 to 8 ⁰ C, but this often makes coolable storage facilities necessary.

According to the invention there is now a coating composition proposed, which consists of an aqueous dispersion of a polyfluorocarbon and an acid and which thereby is characterized as being 1 to 90 wt .- ^ of an acidic material

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contains which is selected from at least one of the acids chromic, phosphoric, nitric, sulfuric and hydrochloric acid, being the percentage based on the combined weight of polyfluorocarbon and acid, and that it is sufficient to stabilize the dispersion. lot

contains a stabilizer, wherein the stabilizer consists of a surface-active material which is selected from water-soluble sulfonated surface-active agents of the formula R ~ (SO ₅ » _m X _{n y} where R is an alkyl group having at least 6 atoms, an alkyl-substituted phenyl group or an alkyl-substituted diphenyl ether group , X and m and η equal Sindo The surfactant material is preferably in an amount up to 15 parts by weight jC, in particular in an amount of 1 to 10 wt _o is hydrogen, a metal ion or an ammonium or substituted ammonium ion - # , based on the weight of the polyfluorocarbon (for example PTFE) in the composition, present "A mixture of chromic and phosphoric acids is preferred as the acid" ^! If a mixture of these acids is used in a PTFE dispersion, then that it is possible through the use of one or more sulfonated surfactants as defined above is to achieve a better storage life, as is the case with PTFE dispersions which contain the same amounts of these acids and which are stored under the same conditions, but are stabilized with sodium lauryl sulfate, as was previously used for PTFE Dispersions were used to which a mixture of these acids had to be added to prepare a coating composition. This is a surprising result o This improvement makes it possible to store PTFE coating compositions according to the invention in the ready-mixed state before use. This is of considerable advantage and brings with it considerable convenience,

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The invention also encompasses substrates made using Coated coating suspensions according to the invention been sincL

With the term "chromic acid" are chromium trioxide, CrO-, as well as

one made by dissolving this material in water Acid meant The chromic acid concentrations used here are expressed by the equivalent amount of trioxide (CrO,) ο

As used herein, the term "phosphoric acid" includes orthophosphoric acid; H * PO, _S and their hydrates and all oxides of phosphorus meant which, when dissolved in sufficient water, H »P0. or produce hydrates of the same »

An aqueous dispersion of a polyfluorocarbon for the Use according to the invention can be made by the techniques heretofore known for the preparation of such dispersions. An aqueous medium containing a water-soluble free radical catalyst and a suitable fluorinated surfactant material can be incorporated into one stirred reactor are introduced, which then the reactor continuously with a fluorocarbon or a fluorocarbon mixture is pressurized and the polymerization is carried out until a dispersion with the desired pesticide content is created »

Because of the high cost of fluorinated emulsifiers, the Concentration normally used in this process only provides the concentration absolutely necessary to achieve the desired To achieve solids content in the dispersion without the risk of coagulation during the polymerization process., If the If the dispersion is to be further concentrated or handled in the presence of air, then it is noted that this dispersion

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is protected by the addition of further stabilizers. In the preparation of compositions according to the invention, the stabilization can be carried out by adding one or more of the sulfonated surface-active agents defined above, _{or the like}

In a modified process for making dispersions of fluorocarbon polymers, can polymerization be initiated in the absence of a surfactant? whereupon after the start of the reaction but before the amount of polymer 10 Grew "~ #, based on the weight of the polymers and the aqueous phase exceeds, a fluorinated surfactant is added to continue the polymerization is ₀

In the preparation of the compositions according to the invention are the dispersions prepared by, for example, the processes described above before the addition of the acid or the Acids stabilized, but if necessary, a further stabilization can be made by adding one or more of the water-soluble sulfonated surface active agents defined above. The concentration of this surface-active material should be sufficient and the dispersion sufficient for the addition of the acid or acids to stabilize. These The concentration is preferably up to 15% by weight, in particular 1 to 10 weight percent based on the weight of the fluorocarbon in the dispersion. Then the acid or acids are added to the dispersion to make the coating composition to manufacture ,,

Fluorocarbon polymers that can be used in the compositions are polytetrafluoroethylene; Mixed polymers of tetrafluoroethylene and other monomers such as ethylene, vinyl chloride and hexafluoropropene (such as Z ₀ B ₀ FKP resins) j

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Polychlorotrifluoroethylene; Copolymers of chlorotlfluoroethylene and other monomers such as vinylidene fluoride and vinylidene chloride; Polyvinylidene fluoride; Mixed polymers of Vinylidene fluoride with monomers such as hexafluoropropene; and Polyvinyl fluoride ο Of particular interest are compositions the polytetrafluoroethylene contained

Sulphonated surfactants, which can be prepared according to the Invention for the manufacture of a coating composition of the type described have proven useful with a good shelf life are sulfonated aliphatic Hydrocarbons with 10 to 20 carbon atoms, dodecylbenzenesulfonic acid and the sodium salt thereof, isopropylamine dodeoyl benzene sulfonate and the sodium salt of dodecyldiphenyl ether disulfonic acid, An alkyl sulfonate, which predominantly consists of the mono sulfonates, is particularly preferred consists of hydrocarbons with 14 to 16 carbon atoms. Suitable materials are under the trademark "Warolat U" and "Mersolat" from Farbenfabriken Bayer AG, Leverkusen, Germany, expelled,

The sulfonated surface-active agents should preferably have a high water solubility ^{at temperatures down to 0 ° C.} Commercial surfactants usually contain impurities such as electrolytes. It is preferred that the surfactants used in the compositions described herein should contain only minor amounts of contaminants »

The concentration of the surfactant, which eur Achieving a usable shelf life required depends on the concentration of the composition Acid and, to a certain extent, also by the nature of the

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surfactant. It has been found that when the sulfonate group is linked to a low molecular weight hydrocarbon moiety, the surface active properties of the compound (for the same weight) are inferior to those of a compound containing a higher molecular weight hydrocarbon moiety when, on the other hand, the high molecular weight carbon moiety , then the proportion by weight is of Sulfonatteils lower, and the effectiveness of the compound (at the same Gewioht) less Tut the purposes of the invention have the sulfonates optimal · properties when the hydrocarbon portion of the surfactant contains 6 to 30 Kohlenetoffatome, and a satisfactory "shelf-life is obtained when a concentration between 1 and 10 wt% based on the weight of the polymer in the composition is used. Aliphatic hydrocarbon sulfonates having 10 to 20 carbon atoms are preferred and provide compositions with a satisfactory shelf life when present in concentrations between 1 and 8 weight percent based on the weight of the fluorocarbon polymer in the composition.

An inventive composition is prepared in purposeful manner in moderate _f that an aqueous solution or a fluoroethylene added to a dispersion of polytetrafluoroethylene "· several sulfonated surface-active agents of the type mentioned above, before concentrating the dispersion to a high polymer content. Additional sulfonated surfactant can be added after the desired level of concentration is achieved by any of the conventional methods. The acid or the acid mixture can then be obtained in concentrations between 1 and 90% by weight

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on the combined © weight of polytetrafluoroethylene polymer in the dispersion and the oleic acid, c

Other additives such as buffers, pigments and fillers can also be added to the compositions of the invention be o

The compositions of the invention can be applied to a variety of substrates as coverings such as e.g. Glass, for example for non-stick cookware and non-stick autoclave liners; Ferrous metal such as cast iron, _0, mild steel and stainless steel; Aluminum and aluminum alloys; and composite surfaces, such as metals with a covering, for example made of ceramic, glass or metal frit low friction on industrial devices, such as molds, rolls, stirrers, mixers, chutes, funnels and welding jaws, on en household ₉ such as Bügele is enplatt s, and are set to 'canting Eugen as used zobo saw blades, *

The invention will now be explained in more detail by the following examples

example 1

100 parts by weight of a polytetrafluoroethylene dispersion with a solids content of 18.3% by weight, based on the dispersion, and a mean diameter of 0.18 / i,

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was mixed with 3.66 parts of a 15 weight percent solution of "Warolat U". The average diameter of the PTFE particles is based on the number of particles, wherein the .Durchmesser are determined from the projected areas of the particles ₀ An average diameter, such as is obtained in this way _P is referred to as "particle size", "" U Warolat "is an alkyl sulfonate, which can be obtained from Farbenfabriken Bayer AG, Leverkusen, Germany. It should be noted that the alkyl groups of this material contain 14 to 16 carbon atoms and that the material contains a high content of monosulfonating molecules * Das Mixture was concentrated to a pesticide content of 66.8 # by electrode canting, analysis of the dispersion showed that it contained a "Warolat U" content of 1.12% by weight, based on the weight of the polymer in the dispersion "Warolat U" and water were added to bring the polymer content to 55 wt .- ^ of the dispersion and to bring the concentration of "Warolat U" to 2.25 wt .- #, based on au f daa weight of the polymer, to increase.,

An acid mixture was prepared which contained 20% by weight of 88% phosphoric acid, 15% by weight of chromium trioxide and 65% by weight of water. 47 parts by weight of this mixture was added to 100 parts by weight of Polytetrafluoräthylendispersion, and then a further 10 parts by weight of water were added, the composition was thoroughly mixed and then stored at about 25 ⁰ C in stoppered bottles ,, It has been found that the - ^ robe after 3 Months had separated in two layers “The upper layer was a clear red layer, and the lower layer was a yellow colored layer, which contained sedimented polymer. When shaken, the mixture turned back into a homogeneous orange-colored dispersion

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transformed; it therefore had a good shelf life,

For comparison, a similar acid / dispersant mixture was prepared, which dispersion occurred 2.25 parts by weight sodium "löuryl sulfate in place of the" Warolat U "contained. After a 3-month storage at 25 ⁰ C, a separation was in two layers . the upper layer was dark brown, indicating a reaction between the acid and the surfactant. the lower layer was brown, by shaking, it was not possible to obtain a homogeneous dispersion, since the polytetrafluoroethylene was coagulated irreversibly ₀

Example 2

A polytetrafluoroethylene dispersion with a particle size of 0.21 / 6, a solids content of $ 55.0 and a "Warolat U". Salary of 2.25 Gev; A dispersion / acid mixture was prepared using this dispersion as in Example 1, using the same acid mixture and the same proportions of dispersion and acid became. Could be storage tests over a period of 3 months showed that the mixture sedimented but easily returned to a homogenous mixture dispersed showed Warolat U "from" A comparative test using sodium-lauryl = eulfat anetelle "means that the polymer dispersion was coagulated ₀

Example 3

In a further group of experiments, polytetrafluoroethylene dispersions, containing "Warolat U", prepared as described in Examples 1 and 2. These dispersions were with the acid solution described in Example 1

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mixed in the ratio of the 68.Gewichtsteilen 55 $ solids containing dispersion to 32 parts by weight of Säurelösungo The stability of the acid / dispersant mixture was monitored during 41 days at 25 ⁰ C by dee di.e change in the viscosity measured and mixtures a visual assessment of the mixture was also made. For comparison purposes, a = acid / PTFE Diepersion mixture (weight ratio 32ί68) containing sodium lauryl sulfate was contained in place of "Warulat U", at 25 ⁰ C. The dispersion had stored before the addition of the acid 54.7 wt. - ^ PTFE (particle size _{0 0} IIjU) and 2.4 wt .- ^ sodium lauryl sulfate, based on PTFE. Ford B2 = cups were determined at 25 ⁰ C after the Umschüttein mixtures ,, the details of the Ford cup are beschriebenο in British standard 1733 (1955)

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NJ

co 00

Dispersion Viscosity (ertO after
41 days colour after
41 days Lower class after
41 days Δ *
B *
σ * after
1 day 52
49
- Pt upper layer Red
Red
Brown after
1 day yellow
yellow
Brown ⁴ p ...
50
44 ■ - after
1 day yellow
yellow
yellow j
j Red ,
Red
Red

* Dispersion A contained 2.25 wt. # "Warolat U", based on the PTFE; the PTFE possessed a particle size of 0.21ft;

Dispersion B contained 2.25% by weight of "Warolat U", based on the PTFE; the PTFE had a particle size of 018

Dispersion C contained 2.42% by weight of sodium lauryl sulfate, based on PTFE; the PTFE had a particle size of 017

ro

It was not possible to measure the viscosity due to coagulation of the dispersion.

ro

CD

-j fs)

The acid / diapersion mixtures A and B, which were stored for 41 days all primers were used to coat aluminum panels for their suitability. For comparison a freshly prepared acid / dispersion mixture containing dispersion C was used *

Each of the mixtures was sprayed onto aluminum panels which had been previously on sandblasted with alumina of a grain size of 0.25 · The plates were further heated in an oven for 5 min at 80 ⁰ C and then 10 min at about 25O ° O. In this and in other examples, the thickness of the first deposits was approximately 2 [beta]. it was determined using a "Peraascope". The thickness was determined from the difference between the "Permascope" reading on the coated panel and the "Permascope" reading on the sandblasted aluminum panel itself. The latter averaged approximately 16 / s. On. these first covering was applied a conventional pigmented top coating of polytetrafluoroethylene, and the plates were dried at 8O ⁰ C and then for about 10 min to 400 ⁰ G heated to sinter the PTFE · The thickness of the final coatings including the first coverings in this and in the other examples it was about 17/4,; it was determined by the increase in the "Permaecope" reading compared to the "Peraascope" reading on the base substrate. The adherence of the coverings was determined by the following procedure. A cross-hatch pattern of sections was cut through the pavement using a razor blade. The cuts were made over an area of approximately 625 ma to produce squares of approximately 3nx3> i. Then an adhesive tape responding to pressure was pressed firmly over the cross-hatched surface and then torn back at an angle of 45 ° to the direction of application. This procedure was made with fresh tape

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repeated up to a maximum of 15 times or until the topping Showed signs of peeling away from the metal. Using dleaee process, all three coverings withstood the 15 times The tape tears off without any covering being peeled off.

The acid / dispersion mixtures based on A and B were stored at 25 ° C for a total of 9 months, during which time they were checked periodically. They were then agitated by shaking and tested as primers as above. At the end of this storage period, the homogenized mixture still had the usual orange color and no PTFE had coagulated. The viscosities of the shaken mixtures, which were determined by the flow times through the * Ford B2 beaker, were 56 and 54 seconds for samples A and B. The primers were tested as above, that is, on sandblasted aluminum with a pigmented one PTFE top layer. Excellent adhesion results were obtained, that is to say that the coverings withstood the 15 times that the tape was torn off without failure. The same result was also achieved if the coated plates were ^{immersed 8 st at 200 6} G in boiling oil and cleaned and the experiments were repeated.

Example 4

Using an aqueous PTFE dispersion that is 65 "? Containing wt .-% PTFE with an average particle size of 0.18 / * and was stabilized with 1.25 wt .-% "Warolat U", based on PTFE, samples were prepared, each with 55 wt .- % PTFE and "Warolat U" concentrations, based on PTFE, of 1.25 »2.25, 3» 5 »5 * 0 and 10.0% by weight *. These samples were mixed with a CrOx / HxPO ^ mixture, as indicated in Example 1, and with more water in the ratio

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of 100 parts by weight of dispersion, 47 parts by weight of acid and 10 parts by weight of water. Were these samples were stored at 30 ⁰ C 101 days Qlasflaschen (sample 3 "5%" Warolat U "was 91 days stored), they during which, at intervals of about 30 days examined for coagulum, after they had been shaken before. No coagulum was found. At the end of the storage period, the samples were shaken again. Again there was no coagulum to be found. There was a slight color gradient from orange to orange-brown when the samples were viewed one after the other according to their "Warolat U" content, the sample with 10 % "Warolat U", based on PTFE, being the darkest, ie slightly brown. The samples with "Warolat U" contents, based on PTFE, of 1.25, 2.25s 3 * 5 and 5.0% by weight were kept at 25 ° C. for a further 2 months and then shaken (no Coagulate can be seen) and tested as a primer as above. The adhesion results were excellent, ie the coverings withstood the tape tearing off 15 times without the covering coming off, and "was both before and after" immersion of the plates in hot oil at 200 ° C. for 8 hours and then afterwards Clean.

Example 5

To samples of an aqueous PTFE'Dispersion, the 37 * 6 parts by weight J PTFE (particle size 0.12 / f) containing aqueous solutions of the following stabilizers were (15 wt -.% Active material) were added so that the weight of the active stabilizer each time made 2.25 wt .- X, based on the PTFE (except for stabilizer No. 2, where the concentration was 1.125 wt .- *).

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No. ₂ . sulfated castor oil, Na-
triumphal
Sodium dodecyl diphenyl
ether-dieulfonate Trade name 1.
2 * Sodium diisobutyl sulfo-
succinate Türklsch red oil soda
finish
Dowfax 2-1 3. Isopropylamine dodecylbenzene
sulfonate Manoxol IB 4th Sodium dodecyl benzene
eulfonate Nansa XB94 5. Dodecylbenzenesulfonic acid Nansa HS 80 / S 6th Alkyl sulfonate Nansa SSA 7th Sodium lauryl sulfate Varolat U 8th. Sodium decyl sulfate Empicol 9. Empicol

Then the CrO, / H, PO ^ acid mixture described in Example 1 was added in an amount of 47 parts by weight to 55 parts by weight of FXPE. The finished mixtures thus each contained approx. 2? Wt% PTFE.

Samples were stored in glass bottles at 30 ° C. for 26 days, during which time they were periodically examined for deposition, color changes and the formation of PTFE coagulum. However, no sample was shaken during this time. At the end of the storage period, the bottles were shaken to homogenize the contents. Samples containing the stabilizers numbered 1, 3, 8 and 9 showed a large amount of nicate-dispersible polymer coagulate and a dark brown color in the upper liquid layers. Samples with the stabilizers of the numbers 2, 4 and 5 showed a slightly darker color (now orange-brown), as it was the case in the original mixtures (bright orange color \ which indicated that some reaction between the acids and the Stabl-

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However, there was only a small amount of non-dispersible polymer in the bottles "which was easy to use" Samples with stabilizers # 6 and # 7 appeared unchanged in color, although similar small amounts of non-dispersible a polymer were present. It was believed that it was a consequence of prolonged storage without affecting the mixtures.

A duplicate set of samples 33 Vague at 25 ⁰ Cgelagert had been, showed similar results. Samples with the stabilizers numbered 1, 3 »β and 9

contained a lot of coagulate and had a dark color. Samples with the buzzers 4, 5 and 6 appeared somewhat darker than the original mixtures. Samples with the numbers 2 and 7 appeared unchanged in terms of color * In the samples with the numbers 4, 5 and 6, however, about nondispersible polymer was present. However, the amount was insufficient to represent a substantial loss of polymer content or to cause difficulties in using the composition. After a further one-month storage at 25 ° C., all samples were again poured over. The mixture of old Stabilisatornummep 5 "which previously bti 30 ⁰ C had been stored, then showed coagula. The samples with the numbers 2, 4, 5 »6 and 7 (originally stored at 25 ° C) and the numbers 2, 4, 6 and 7 (original storage at 30 ° 0) were all tested, with the Substrate type, top covering and other conditions were used as described in Example 3. In all nine samples, excellent fieetulates were obtained in terms of adhesion before and after treatment with hot oil. The appearance of the top covering was also very satisfactory *

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Claims (1)

- 18 -patent claims 1. BeBChichtungasbueamneneetZung, which contains an aqueous dispersion of a polyfluorocarbon and a satire, characterized in that it contains 1 to 90 wt .-% of an acidic material which is composed of at least one of the acids chromium, phosphorus, nitric, sulfur uni Hydrochloric acid is selected, whereDAi is the percentage based on the combined weight of polyfluorocarbon and acid, and that it further contains an amount sufficient to stabilize the dispersion of a stabilizer, the stabilizer consisting of a surface-active material which consists of water-soluble sulfonated surface-active agents Formula R- (SOx) ^ X _{n is} selected, where R is an alkyl group with at least 6 atoms, an alkyl-substituted phenyl group or an alkyl-substituted diphenyl ether group, Z is hydrogen, a metal ion or an ammonium or substituted ammonium ion and m and η are the same are. 2. Composition according to claim 1, characterized in that that it contains 1 to 10% by weight, based on the weight of the polyfluorocarbon, of the surfactant material. ?. Composition according to claim 1, characterized in that that the surface-active material is a sulfonated aliphatic ·? Hydrocarbon having 10 to 20 carbon atoms or a SaIs thereof and in a concentration between 1 and 8% by weight, based on the weight of the polyfluorocarbon. 209847/1132 M- " Composition according to claim 1 or 2, characterized in that the surface-active material is an alkyl sulfonate, which consists predominantly of monostilfonates of hydrocarbons with 14 to 16 carbon atoms. 5 «Composition according to claim 1 or 2, characterized in that that the surface-active material consists of dodecylbenzenesulfonic acid or the sodium salt of this acid. 6. Composition according to claim 1 or 2, characterized in that that the surface-active material consists of a sodium salt of dodecyldiphenyl ether disulfonic acid. 7 * Composition according to claim 1 or 2, characterized in that that the surface-active material of isopropylamine-dodecylbenzene-8ulfonat consists. 8. Composition according to any one of the preceding claims, characterized in that the acid consists of a mixture of Chromic acid and phosphoric acid. 9. Composition according to one of the preceding claims, characterized in that the polyfluorocarbon is made from FITFE consists. 10. Composition according to one of the preceding claims <> characterized in that it has been prepared by making the surface-active material into a dispersion of the polyfluorocarbon before concentrating the dispersion is added, then the dispersion is concentrated, if necessary, additional surfactant is added and then the acid or the acid mixture adds. 209847/1 1 32