GB1559355A - Coating of metal articles - Google Patents

Description

(54) COATING OF METAL ARTICLES (71) We, THE EMPIRE PLATING COMPANY, a Corporation organized and existing under the laws of the State of Ohio, United States of America, of 8800 Evarts Road, Cleveland, Ohio 44104, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the protective coating of metal articles to improve their corrosion resistance and/or their appearance.

There are numerous techniques which are well known in the metal finishing art for applying metal coatings to metal surfaces of articles. One technique called "mechanical plating" is not widely used despite the fact that it is relatively simple to practise and despite the fact that it obviates many of the pollution problems incurred in such other techniques as electrolytic plating. Among the reasons that explain the limited use of mechanical plating are the facts that its processes are relatively time consuming and uneconomical to utilise in the plating of very thin coatings, and that mechanically plate surfaces often have undesirably poor corrosion resistance and cosmetically unattractive appearances.Mechanically plated coatings have, accordingly, been thought to be unsatisfactory for many applications, and little, if any, consideration has been given to the utilisation of mechanical plating methods in applications which require relatively high corrosion resistance and/or an exceptionally good appearance.

Several approaches have been taken to enhance the corrosion-resistance and appearance of non-mechanically plated articles. One approach has called for an application of phosphate coating to a metal surface followed by an application of oil or paint over the phosphated surface. Another approach has called for the passivation of certain metal surfaces by chromating techniques. U.S. patents nos: 3,961,993 and 3,790,355 describe still more advanced techniques wherein polymeric coating of plated metal articles has been employed to aid in obtaining good corrosion resistance. In accordance with methods described in these patents, articles having a metal surface composed typically of aluminium, iron, zinc, brass and copper alloys are either electroplated with zinc, cadmium, nickel or chromium, or are phosphated and are then chromated, rinsed and coated with a polymeric substance.

According to the invention a method of making a metal article resistant to corrosion comprises the steps of plating the metal article with at least one layer of a plateable metal by mechanical plating, applying a corrosion inhibiting chromate coating to the metal plated article, rinsing the resulting chromate coated surface to flush away excess chromating solution remaining thereon, coating the rinsed surface with a polymer to form a polymeric layer on the rinsed surface and curing the polymeric layer to form a hard film.

The plateable metal may be appplied solely by mechanical plating or in at least two layers, one being applied by mechanical plating and another by electrolytic plating. Either the mechanically plated layer or the electrolytically plated layer may be applied in direct contact with the article.

In the practical application of a method according to the present invention, metal articles to be coated are first cleaned in any suitable conventional manner. As an example, one cleaning technique which is particularly useful where electroplating is the first treatment to which the metal articles is subjected, involves tumbling t"e article in a caustic soda solution or passing an electric current through such a solution with the metal article constituting the anode. After cleaning in this manner, the article is rinsed in cold water, is then dipped in a dilute acid solution and is again rinsed in cold water.When the article is composed of ferrous metal or copper alloys, a 10% sulfuric acid solution or a 25% hydrochloric solution is sufficient to neutralise the caustic soda. When the article is composed of zinc, a very weak acid solution is preferably used.

In certain instances, where even better cleaning of a ferrous metal article is desired or where its surface is to be activated, the article may be reversely treated in an alkaline cyanide bath, i.e. by passing a current through the bath for about 30 seconds while the article is the anode in the circuit, and then reversing the current flow for about 30 seconds while the article is the cathode in the circuit. Following this reverse treatment, the article is rinsed in water if it is to be plated promptly thereafter, or it may be rinsed in a dilute sodium cyanide solution to prevent rusting when it is not to be plated promptly. Where the first treatment to which the metal article is subjected is mechanical plating, an exemplary cleaning procedure is disclosed in U.S.Patent No.~3,330,769. It will be appreciated, however, that the manner in which the metal surfaces are cleaned forms no part of the instant invention and any suitable cleaning process may be used.

The cleaned metal article is then plated. Depending upon its intended usage the plating may be accomplished using only mechanical plating methods. Alternatively, plating can be accomplished by a combination of both mechanical and electrolytic techniques. If the plating is to be accomplished by both mechanical and electrolytic techniques, either the mechanically applied metal layer or the electrolytically applied metal layer can be in direct contact with the metal surface of the article. In this connection, in accordance with the present invention, the article may have a surface formed of any metal capable of being plated, by either technique, even including the typically difficult to plate metal sufaces.The particular metal constituting the metal surface may, in some cases, dictate a preference as to whether the mechanically applied plating layer or the electrolytically applied plating layer is placed in direct contact with the surface. It has been found, for examp1e, that an electrolytically applied metal plate is most effective in direct contact with surfaces of iron, zinc, and copper alloys and is preferably applied to surfaces, for example, only after tEe surface is first coated with a metal such as copper.

For plating using mechanical techniques, the coating metal may be any metal known to be advantageously plated in this manner, e.g., lead, tin, cadmium, zinc, copper, aluminum, nickel, titanium, gold, silver, and mixtures or alloys of the foregoing. For electrolytic plating, the coating metal is preferably cadmium or zinc although nickel, chromium, or brass plated layers may also be advantageously applied.

Both electrolytic and mechanical plating are well known techniques and, therefore, no detailed description of either process is included herein. However, use of the term "electrolytic plating" herein refers to electrolytically applied metal plating using conventional means, as by making the metal article the cathode in an electrolytic bath. Cadmium or zinc coating metals are advantageously applied from well known cadmium cyanide or zinc cyanide baths.

However, cadmium or zinc alkaline or acid baths are equally effective. Any suitable conventional bath composition may be used for depositing nickel or chromium layers, for example, a nickel sulfate, nickel chloride, boric acid bath may be used for the nickel deposition and a chromic acid-sulfate bath may serve for the chromium deposition. Where barrel plating techniques are used, a current density of about 0.1 to about 10 amperes per square foot is suitable. Where rack plating techniques are used, a current density of about 2 to about 100 amperes per square foot is suitable. The plating action is continued until between about a 0.0002 to about a 0.005 inch layer of the plated metal has been deposited on the article or on the previously applied mechanically plated layer.

As is known in the art, the term "mechanical plating" as used herein generally consists in the utilization of particles of metal dust which are hammered, impacted or otherwise pressure applied to the surface of various articles, thereby forming a permanent metallic coating. The hammering or impacting is typically effected by the use of spheroidal or non-spheroidal impacting media such as round iron or steel shot, crushed shot, nailed clippings, cut iron pellets, Alundum chips, silicon carbide, sand, metal turnings, or the articles being plated if sufficiently small, e.g., nuts and bolts. Basically, an impacting medium is placed in a ball mill along with a charge of the metal dust or particles, and the articles to be coated. The ball mill is then tumbled sufficiently to produce a hammering of the particles onto the articles. The coating results from a build up of layers of mecllanically bonded particles. Often, there is also included a sustantial quantity of promoter substances in a liquid carrier, including filmforming materials and metal deoxidizers, to enhance and promote the plating process. This latter feature, known as wet plating, produces a substantially superior coating. Coating without liquids is known as dry plating.

In a typical dry plating procedure, the articles to be plated are mixed with the metal, e.g., zinc, dust or powder and steel shot in a tumbling container preferably sealed to exclude air. In this case aqueous or other liquid suspending medium is omitted. The tumbling of the container subjects the articles to direct contact with the zinc particles under conditions of rubbing, attrition and impact, removing or penetrating surface films and bonding the metal surfaces together. The exclusion of oxygen tends to avoid recurrence of oxide film and the clear metal surfaces of the zinc particles become attached directly to the metal of the articles accumulating and confirming the particles as a covering base layer of zinc grains having strong adhesion to the metal article and strong cohesion to each other at their areas of contact.Upon this adhering base layer the continued tumbling of the dry mixture deposits and attaches the zinc particles by their clear surfaces giving strong zinc-to-zinc bonding and rapidly building up the assembled coating to desired thickness with the flattened particles interfitted and overlapping and generally parallel to the base surface. This intensified bonding action adapts this procedure to a variety of metal coatings and at room temperature is effective to form relatively thick deposits, e.g., up to about .006 inches, in short treatment times.

In a typical wet process, plating catalysts and promoters, e.g., deoxidizers, are included in the mill. Typical of such additives are the fatty acids, organic carboxylic acids such as citric, tartaric and amino acids, protective colloids, such as gums, and numerous other liquids well known to the art.

"Mechanical plating", as intended by use of that term herein, is exemplified in the following patents which are believed to be generally indicative of the state of the art: U.S.

Patent Nos. 2,640,001; RE 23,861; 2,689,808; 2,723,204; 2,788,297; 3,013,892; 3,23,127; 3,093,501; 3,132,043; 3,164,448; 3,251,711; 3,268,356; 3,328,197; 3,400,012; 3,442,691; 3,443,985; 3,460,977; 3,479,209; 3,601,087.

Following application of the metal plate, by mechanical plating alone or in combination with electroplating, the plated article is given a chromate corrosion inhibiting coating in such a manner as to convert the metal surface thereof into a clear, stain-free finish with corrosion resisting properties. Chromating, per se, is well known and virtually any of the conventional, chromating processes, e.g., clear or yellow chromating are suitable for use herein. However, one chromating process which has been found to be quite effective involves dipping the plated article in an aqueous solution consisting essentially of chromic acid, nitric acid, acetic acid and sulfuric acid.A particularly preferred formulation for such a solution includes the following ingredients in the indicated approximate percentages by weight: Chromic acid 30% Nitric acid 20% Acetic acid 13% Sulfuric acid 3% Water 34% To use this formulation it is best to further dilute it in water such that the dip solution includes from 1 to 10% by weight of the above formulation with the balance being water.

Still another effective chromating material consists of about 90 S98 % chromium trioxide and about 2-10% sodium bisulfate dissolved in water, the useful concentration of this chromating material being between about 4 and 16 ounces per gallon of water. The article to be chromated is thoroughly rinsed to free it from alkali and is then dipped into chromating solution for between about 10 to about 25 seconds. Preferably the solution should be at a temperature between about 65"F. and about 95"F.

When the metal article is formed of a material subject to hydrogen embrittlement, such as high carbon steels, the conventional wisdom in the art has dictated that electroplating is not an acceptable processing step unless followed by a heating step to relieve hydrogen embrittlement. In accordance with the present invention, the embrittlement problem may, to a great degree, be alleviated by applying a mechanically plated layer directly over the high carbon steel to shield the steel from the possibility of embrittlement upon subsequent electroplating.

However, where it is not desirable to electropilate because the mechanically plated layer is believed too porous to risk embrittlement, or for other reasons, the metallic article can be phosphated as by washing the article in an alkaline cleaner, rinsing it in water, coating it in a phosphating bath typically including zinc and phosphate compounds which in solution combine to give a zinc phosphate coating, whereafter the article is rinsed in water. In conventional phosphating a weak chromate rinse is typically employed to seal the phosphate coating. However, in the instant case the chromating step hereinbefore described, practiced following phosphating, will achieve the same result.

Upon removing the article from the chromating bath, it is thoroughly rinsed with water.

The chromated surface is then ready to receive a thermosetting or thermoplastic polymer coating thereover.

A hydrophobic thermosetting polymer is applied, e.g., by dipping, spraying or other well known polymer application techniques, over the chromated surface and the article is heated at a temperature between about 300"F. and about 400"F until the polymer has been baked and has become a hard film. The heating time depends somewhat on the thickness of the metal article and its variations in thickness. Preferably, the heating is continued long enough for all polymeric coated surface portions of the metal article to be brought to about the above-specified range of temperatures.

A preferred hydrophobic thermosetting film-forming polymer composition, including approximate weight percentages, is as follows: Hexamethoxyl methyl melamine 15.3% Ethyl Acrylate 16.0% Methacrylic Acid 1.0% Chromium Trioxide 0.1% Water 67.6% Other film forming compositions which may be used include the hexamethoxy methyl melamine of the foregoing composition with equivalents of the other ingredients thereof.

It has been found that uniformity of the thermosetting polymer coat and its abrasion resistance can be substantially improved by applying a plurality of polymer coatings prior to heat setting the polymer. It is preferable to apply each successive polymer coating after the previous coat has become tacky. Depending on the type of polymer coating used, the second coating can be applied almost instantly, or may require a few seconds delay between coating applications. Vastly superior results have been found where two polymer coatings are applied prior to heat setting the polymer. Added polymer coatings prior to heat setting have produced additional protective benefits.

An alternative polymer coating over the chromated surface can be applied by dipping the articles in a solution of a thermoplastic polymer and then air drying the applied polymer layer until it cures to a hard, transparent film.

A preferred thermoplastic film-forming polymer composition is as follows, in approximate percentages by weight: Polyvinyl acetate above 95% Potassium dichromate up to 2% Surfactant up to 2% Alkalinity agent-to pH from above 7 to 10 Other thermoplastic polymers as well as combinations, copolymers and the like of polyvinyl acetate and other compatible polymers are also suitable for use herein, as are equivalents of the dichromate.

Corrosion protective films applied in accordance with the present invention, wherein the metallic plate is applied by mechanical techniques and, preferably, by successive mechanical and electrolytic techniques, complemented with a hard, polymeric film, have evidenced improved and unexpected results in terms of the extent of abrasion and corrosion protection.

Salt spray tests suggest that exended corrosion free article life, superior to that attainable with any previously known protective polymer or other films, is attained by practicing the new present invention.

Example I To demonstrate the improved corrosion protection properties attainable with the present invention a number of fastener batches (4 fasteners per batch) were plated with zinc by electrolytic and/or mechanical techniques, then clear or yellow chromated, and thereafter coated with thermoplastic or thermoset polymer Aayers. Where both electrolytically and mechanically applied layers are present, the mechanically applied layer underlies (was applied prior to) the electrolytically applied layer. Each batch was subjected to a standard neutral salt spray 5% solution test. The number of hours required before white salt deposits formed on the first and last fastener of each batch of fasteners is recorded in columns (2) and (3) of Table I. The number of hours required before red rust was detected on the first and last fastener of each batch of fasteners is recorded in columns (4) and (5) of Table I.

The following symbols are used in column (1) of Table I to indicate the corrosion protection treatments applied sequentially to the fasteners: A - electrolytic application of .0002" zinc layer B - mechanical application of .0007" zinc layer CC - application of clear chromate layer YC - application of yellow chromate layer I - application of thermoset polymer layer II - application of theremoplastic polymer layer ( )n - indicates application of "n" coatings Table Coating Salt Spray (hours) Procedure Plate Salts Red Rust (1) (2) (3) (4) (5) A 12 24 18 26 B 16 30 89 194 B+CC 16 30 89 194 B+YC 95 164 240 506 B+CC+I 27 51 112 210 B+CC+II 22 62 140 241 B+CC+(I)2 1)2 72 91 195 294 B+CC+(II)2 69 96 175 317 B+YC+I 180 260 456 610 B+YC+II 143 206 311 494 B+YC+(I)2 255 410 507 720 B+YC+(II)2 187 304 410 570 B+A 89 94 220 281 B+A+CC 97 110 241 306 B+A+YC 400 460 690 840 B+A+CC+I 120 156 381 501 B+A+CC+II 118 161 340 520 B+A+CC+(I)2 170 210 435 590 B+A+CC+ 11)2 161 217 498 625 B +A +YC +I 421 501 731 892 B+A+YC+II 491 560 738 862 B+A+YC+(I)2 461 541 810 X 920 B+A+YC+(II)2 517 610 790 920 It is most noteworthy from the foregoing data that application of a zinc plate comprised of combined electrolytically applied and mechanically applied layers exhibits a surprisingly greater corrosion resistance than would have been expected based upon the data obtained for only electrolytically applied or only mechanically applied layers.This is particularly so after the combined zinc layer has been chromated and/or polymerically coated.

Example II The procedure of Example I was repeated except that fasteners were plated with cadmium.

Where both electrolytically and mechanically applied layers are present, the mechanically applied layer underlies (was applied prior to) the electrolytically applied layer. The number of hours required before red rust was detected is recorded in Table II.

In addition to the symbols used in Table I, the following symbols are used in Table II: C - electrolytic application of .0002" cadmium layer D - mechanical application of .0005 " cadmium-tin layer (due to use of tin promoter, preferably utilizing a powder metal mixture of about 50 percent cadmium (+ 10%) and 50 percent tin (+ lO5'o) by weight)).

Table II Coating Salt Spray (hours) Procedure Red Rust (1) (4) (5) C 39 62 D 901 991 D+CC 1272 1608 D+YC 241 1300 D+CC+I 312 1608 D+CC+II 936 1608 D+CC+ 1)2 363 963 D+CC+(II)2 1016 1811 D+YC+I 310 1267 D +YC+II 1017 1710 D+YC+ 1)2 398 1341 D+YC+ 11)2 1200 1721 D+C 961 1106 D+C+CC 1306 1608 D+C+YC 300 1402 D+C+CC+I 468 1608 D+C+CC+II 1216 1608 D+C+CC+ 1)2 468 1608 D+C+CC+(II)2 1346 1608 D+C+YC+I 468 1608 D+C+YC+II 1216 1608 D+C+YC+ 1)2 468 1608 D+C+YC+ 11)2 1346 1608 It appears from the Table II data that there is a discernible improvement in corrosion resistance properties when the metal layer is applied by a combination of electrolytic and mechanical application techniques. However, the improvement is not nearly as striking as in Example I. It is also noteworthy that significantly improved cadmium resistance to salt spray is attainable with thermoplastic polymer protective layers over the applied metal layer as compared with theremosetting polymer protective layers.

In an effort to compare the type of results which obtain where the mechanically applied layer underlies the electrolytically applied layer (as per Examples I and II) and the situation where the electrolytically applied layer underlies the mechanically applied layer, further tests have been run as will be described in Examples III and IV.

Example III The procedure of Example I was repeated except that, where both electrolytically and mechanically applied layers are present, the electrolytically applied layer underlies (was applied prior to) the mechanically applied layer. The results are summarized in Table III where the same symbols used in Table I apply:: Table III Coating Salt Spray (hours) Procedure White Salts Red Rust (1) (2) (3) (4) (5) A+B 97 103 241 300 A+B+CC 110 131 251 333 A+B+YC 441 467 770 916 A+B+CC+I 131 171 390 510 A+B+CC+II 119 160 381 533 A+B+CC+(I)2 1)2 198 251 498 697 A+B+CC+(II)2 182 199 512 644 A+B+YC+I 431 500 780 956 A+B+YC+II 510 571 751 873 A+B+YC+(I)2 500 525 869 949 A+B+YC+ (11)2 522 615 843 923 Example IV Similarly, the procedure of Example II was repeated except that, where both electrolytically and mechanically applied layers are present, the electrolytically applied layer underlies (was applied prior to) the mehanically applied layer.The results are sunimarized in Table IV where the same symbols used in Table II app1y: Table IV Coating Salt Spray (hours) Procedure Red Rust (1) (4) (5) C+D 954 1202 C+D+CC 1496 1610 C+D+YC 681 1500 C+D+CC+I 521 1694 C+D+CC+II 1230 1710 C+D+CC+ 1)2 490 1690 C+D+CC+H)2 1494 1723 C+D+YC+I 517 1608 C+D+YC+II 1219 1694 C+D+YC+(I)2 493 1590 C+D+YC+(II)2 1393 1828 It appears from a comparison of the results in Table I and III, and from a comparison of the results in Tables II and IV, that little signficant corrosion resistance difference obtains if the electrolytically applied layer is applied either prior to or following the mechanically applied layer.Differences are noted, however, in that where the electrolytic layer is applied last, the resulting finish has a more pleasing appearance; whereas where the mechanical layer is applied last, the combined coating layers appear to exhibit a better degree of adherence to the substrate. Accordingly, there are detectable difrerences in the two types of resulting finishes.

WHAT WE CLAIM IS: 1. A method of making a metal article resistant to corrosion comprising the steps of plating the metal article with at least one layer of a plateable metal by mechanical plating, applying a corrosion inhibiting chromate coating to the metal plated article, rinsing the resulting chromate coated surface to flsh away excess chromating solution remaining thereon, coating the rinsed surface with a polymer to form a polymeric layer on the rinsed surface and curing the polymeric layer to form a hard film.

2. A method according to claim 1 wherein the plateable metal is applied solely by mechanical plating.

3. A method according to claim 1 wherein the plateable metal is applied in at least two layers, one being applied by mechanical plating and another by electrolytic plating.

4. A method according to claim 3 wherein the mechanically plated layer is applied in direct contact with the article.

5. A method according to claim 3 wherein the electrolytically plated layer is applied in direct contact with the article.

6. A method according to any one of the precding claims wherein a phosphate coating is applied to the metal plated article prior to the chromate coating application.

7. A method according to any one of the preceding claims wherein the applied polymeric layer is a hydrophobic thermosetting polymer and curing of the polymeric layer is achieved by heating the article to a suffic-ently high temperature and for a sufficiently long time to convert the polymeric layer to a hard film.

8. A method according to claim 7 wherein the step of polymer coating the chromated surface is carried out in a number of coating steps to apply the polymer in sequential layers, where after the polymer coats are cured together during heating of the article to provide a film of substantially uniform thickness.

9. A method according to any one of claims 1 to 6 wherein the applied polymeric layer is a thermoplastic polymer and curing of the polymeric layer is achieved by drying the polymer layer in air at ambient temperature for a time sufficient to convert the polymeric layer to a hard film.

10. A method according to any one of the preceding claims wherein the plateable metal comprises zinc, cadmium, nickel or chromium.

11. A method according to claim 10 wherein the plateable metal is zinc and the chromate coating is yellow chromate.

12. A method according to claim 10 wherein the plateable metal is cadmium and the polymeric layer is a thermoplastic polymer.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. (was applied prior to) the mehanically applied layer. The results are sunimarized in Table IV where the same symbols used in Table II app1y: Table IV Coating Salt Spray (hours) Procedure Red Rust (1) (4) (5) C+D 954 1202 C+D+CC 1496 1610 C+D+YC 681 1500 C+D+CC+I 521 1694 C+D+CC+II 1230 1710 C+D+CC+ 1)2 490 1690 C+D+CC+H)2 1494 1723 C+D+YC+I 517 1608 C+D+YC+II 1219 1694 C+D+YC+(I)2 493 1590 C+D+YC+(II)2 1393 1828 It appears from a comparison of the results in Table I and III, and from a comparison of the results in Tables II and IV, that little signficant corrosion resistance difference obtains if the electrolytically applied layer is applied either prior to or following the mechanically applied layer. Differences are noted, however, in that where the electrolytic layer is applied last, the resulting finish has a more pleasing appearance; whereas where the mechanical layer is applied last, the combined coating layers appear to exhibit a better degree of adherence to the substrate. Accordingly, there are detectable difrerences in the two types of resulting finishes. WHAT WE CLAIM IS:

1. A method of making a metal article resistant to corrosion comprising the steps of plating the metal article with at least one layer of a plateable metal by mechanical plating, applying a corrosion inhibiting chromate coating to the metal plated article, rinsing the resulting chromate coated surface to flsh away excess chromating solution remaining thereon, coating the rinsed surface with a polymer to form a polymeric layer on the rinsed surface and curing the polymeric layer to form a hard film.

2. A method according to claim 1 wherein the plateable metal is applied solely by mechanical plating.

3. A method according to claim 1 wherein the plateable metal is applied in at least two layers, one being applied by mechanical plating and another by electrolytic plating.

4. A method according to claim 3 wherein the mechanically plated layer is applied in direct contact with the article.

5. A method according to claim 3 wherein the electrolytically plated layer is applied in direct contact with the article.

6. A method according to any one of the precding claims wherein a phosphate coating is applied to the metal plated article prior to the chromate coating application.

7. A method according to any one of the preceding claims wherein the applied polymeric layer is a hydrophobic thermosetting polymer and curing of the polymeric layer is achieved by heating the article to a suffic-ently high temperature and for a sufficiently long time to convert the polymeric layer to a hard film.

8. A method according to claim 7 wherein the step of polymer coating the chromated surface is carried out in a number of coating steps to apply the polymer in sequential layers, where after the polymer coats are cured together during heating of the article to provide a film of substantially uniform thickness.

9. A method according to any one of claims 1 to 6 wherein the applied polymeric layer is a thermoplastic polymer and curing of the polymeric layer is achieved by drying the polymer layer in air at ambient temperature for a time sufficient to convert the polymeric layer to a hard film.

10. A method according to any one of the preceding claims wherein the plateable metal comprises zinc, cadmium, nickel or chromium.

11. A method according to claim 10 wherein the plateable metal is zinc and the chromate coating is yellow chromate.

12. A method according to claim 10 wherein the plateable metal is cadmium and the polymeric layer is a thermoplastic polymer.