GB1567491A - Coating and dyeing metal articles - Google Patents

Description

(54) COATING AND DYEING METAL ARTICLES (71) We, TEXTRON INC., a corporation organised and existing under the laws of the State of Delaware, of 40 Westminster Street, Providence, Rhode Island, 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 invention relates to the coating and dyeing of metal articles.

The prior art, as exemplified in U.S.

Patents No. 2,042,451, No. 2,334,000, No.

2,535,794, No. 3,544,351, No. 3,615,894 and No. 3,647,567, includes a number of coatings and processes for producing various coatings including colored coatings, on metal articles. Presently in the manufacture of textile articles with metal fastener elements, such as slide fasteners with metal sliders, the elements are coated with liquid enamel paints which include pigments selected to produce coatings of the desired color when the paints dry or solidify, while the textile portions of the articles are dyed separately from the metal elements; then the enameled fastener elements are attached to the articles to produce completed color-coodinated articles.The separate enameling of the metal slider elements requires the maintenance of an inventory of numerous different colors and shades of slide fasteners and paints as well as complex general planning to coordinate the production activity of the fasteners; often purchasers of the slide fasteners, such as garment makers, request colors which are not in inventory; and supplying such noninventoried fasteners introduces delays, interruptions, and/or inefficiency in the production activity.

The above U.S. Patent No. 2,334,000 discloses a particular slide fastener and process wherein a metal slider is coated with a white enamel, assembled on white tapes, and then subjected to a dye process to form a colored slide fastener. There have also been previous attempts to form dyeable metal sliders by coatng with a polymer; such coatings have been made from dry powder epoxy coatings and from nylon coatings, dry powder nylon coatings being well known in the prior art. The formation of a suitable dye coating on sliders and dyeing of the coating have generally not been commercially successful; the prior art coatings were unevenly dyed, did not readily pick up colors from dyes, or often resulted in colors from certain dyes which substantially differ from or conflict with the colors produced in the slide fastener tapes.Also, the prior art coatings could not withstand the acid mediums employed in many conventional dye processes, or easily chipped and peeled off and thus could not withstand the handling, such as tumble drying, normally given to garments.

The prior art contains a number of prior art processes utilizing baths, including electrostatically charged pigmented powder sprays, of powdered polymer resins, including epoxy resins and nylon resins, for producing polymer films or coatings on metal articles. U.S. Patents No. 3,028,251, No. 3,058,951, No. 3,321,438, No.

3,442.856, No. 3.506,598, No. 3,102,823 and No. 3,758,633 disclose particular epoxy resins for coatings. The powder resins generally contain pigments, such as titanium dioxide and the like, for producing a coating of a desired color. Some of the polymer coatings, particularly the epoxy coatings, have been known for their adherence, durability and resistance to chemical attack.

However, the required powder bath coating equipment and its limited suitability for being repeatedly and conveniently changed to produce different colored coatings along with the higher cost of materials has pre vented any extensive adoption of pigment colored powder bath coating color matching metal fastener elements for dyed articles.

Primer coatings such as the phenol for maldehyde coating disclosed in U.S. Patent No. 3.h97,331 have been used to incrcase the corrosion rcsistance and paint adhesion of metal articles.

Dyes in the prior art have been successfully utilized to color a variety of materials including fabrics nnd, 'is illustrated in U.S.

Patent No. 2,X54,3()7, phosphate treated metal surfaces. The dyes have been divided into a number of general classes, such as acid dyes, direct dyes, disperse dyes, mordint dyes, fiber reactive dyes, basic dyes, and azoic dyes, according to their use or propertics. Acid dyes are water-soluble anionic dyes th;lt are applied to nitrogenous fibers such as wool. silk, nylon and modified acrylic fibers, l'rom acid or ncutral baths; attachmcnt ol color groups to the fiber is attributcd ;;tt legist partly to salt formation between 'illionic groups in the dyes and cationic gU()llpS in the fiber. Active amino groups cxhibil a basic nature which has been attributed to their ability to attract and dissociate I proton from HzO thus forming a cationic group and a free hydroxyl ion.

Direct dyes are also considered to be generally anionic in nature and substantive to cellulosic fibers in the presence of an electrolyte such as salt. Disperse dyes are substantially water-insoluble dyes held in aqueous solution by anionic dispersing agents. The disperse dyes are generally believed to migrate from the dispersion, sometimes with the aid of a carrier, into the fibers where the dyes remain due to their insolubility; in nylon fibers hydrogen bonds between amino groups in disperse dyes and carbonyl groups in the nylon fibers may contribute to fixation. Mordant dyes and azoic dyes generally require the reaction of two components in situ in the fiber to produce an insoluble molecule.In the dyeing of nylon rugs and carpets, benzyl alcohol is conventionally included in dye solutions to increase the dye pick-up in the nylon rugs and carpets. Although the prior dyeing art is extensive. the various properties of dyes and their application to various materials is not completely understood.

The invention provides a method of forming a colored coating on a metal article comprising steps of forming a first coherent layer of white polymer on the article, forming a second coherent layer of clear polymer on the first layer, said clear polymer being dyeable and having for each polymer molecule an average of at least 0.5 proton acceptor groups providing for dye pick-up, and dyeing the second coherent layer of clear polymer.

The invention extends also to the coated and dyed metal article, specifically a slidingclasp fastener clasp or other fastening member color-match dyed with a textile.

Preferably the second layer is formed by depositing a coating of a powdered nylon on the first layer, and heating the coating sufficiently to convert the powdered coating into a coherent film.

l'referably, the first layer is formed by depositing on the metal article a coating of powdered nylon containing white pigment, and heating such coating sufficiently to convert the powdered coating into a coherent film.

Preferably the proton acceptor groups are basic quaternisable derivatives of ammonia.

Preferably the dyeable polymer is a clear nylon resin, the first layer being formed from a nylon resin containing a white pigment. An epoxy resin, a polyester copolymer resin or an acrylic copolymer resin may however be used.

Both exemplary embodiments and general aspects of the invention are given in the following description.

In the drawings: Figure I is a plan view of a slide fastener including a metal slider to be color coated in accordance with the invention.

Figure 2 is a perspective view of the metal slider of Figure 1.

Figure 3 is a detailed cross-section view of a portion of the slider of Figure 2 after one step in the coating process.

Figure 4 is a view similar to Figure 3 after a final step in the coating process.

Figure 5 is a detailed cross-section of a portion of a slider after one step in a modified coating process.

Figure 6 is a view similar to Figure 5 after a further step in the modified coating process.

Figure 7 is a view similar to Figures 5 and 6 after a still later step in the modified coating process.

Figure 8 is a view similar to Figures 5, 6 and 7 after a still later step in the coating process.

Figure 9 is a view similar to Figures 5, 6, 7 and 8 illustrating in detail a cross-sectional view of a slider in a modified coating process.

An article, such as a slide fastener shown in Figure 1 manufactured in accordance with the invention, has a metal element or member, such as a slider 12, with a colored coating matching the color of other portions of the article, such as textile stringer tapes 14 and 16. A dyeable polymer film 18, Figure 4, is formed on the slider 12 by first coating with a powdered polymer resin 20, Figure 3, and then heating the powdered resin to convert the coating 20 into the coherent film 18. The slider 12 is assembled on fastener elements 21 and 22 of the tapes 14 and 16 which are initially undyed. The article may include other undyed portions, such as a textile garment (not shown) having a seam opening to which the fastener is secured for opening and closing the seam.

Then the entire article including the polymer coated metal slider 12 is subjected to a dyeing process, as indicated by the stipling in Figure 4, to form a colored article which has the color of the polymer film 18 on the metal slider 12 matching the color of the rest of the article including the textile tapes 14 and 16.

In addition to the described slide fastener many other elements and members, such as buttons, buckles, clasps, snaps, nuts, bolts, hooks, other fasteners, furnishing, etc. can also be formed with dyeable polymer coatings. Where the dyeable metal members are to be color-coordinated or matched with other portions of an article, the members can be dyed separate from such other portions when such other portions are already colored or will not be suitably dyed by the same dye. Also the dyeable coatings can be applied by processes other than the described dry powdered coating process.

It has been discovered that polymer coatings containing proton acceptor groups, result in substantially improved color pickup when subjected to dye solutions. Metal members or articles having such polymer coatings when subjected to a dye process, will pick-up substantially more color from a dye than a polymer coating not having such a substantial quantity of available proton acceptor groups. Certain polymer coatings, such as coatings produced from nylon resins and from an epoxide resin and an amine, produce colors which closely match the colors produced in synthetic textile materials, such as those made from any of the common nylon fibers and the common polyester fibers, when dyed together.

The term "proton acceptor group" includes those basic acting radicals, such as the quaternizable derivatives of ammonia including the primary, secondary and tertiary amine groups, which are believed capable of attracting and dis-associating a proton from H20 to form a cationic group and a free hydroxyl ion. Amines form a covalent bond with a proton and thereby become "quaternized".

The polymer resin can be, for example, an epoxy resin, a nylon resin, or a copolymer resin containing a polyester or an acrylic resin. All of the resins when formed into a film must have a quantity of active or untransformed proton acceptor groups equal to at least 0.5 times the quantity of polymer resin molecules, irrespective of cross-linking and additive chain-linking during hardening, to produce acceptable dye pick-up. Preferrably the quantity of active proton acceptor groups is at least equal to the quantity of polymer resin molecules, and especially preferrably greater than 1.1 or even 1.9 times the quantity of polymer resin molecules.Some resins such as the nylons contain active proton acceptor groups while other resins such as the epoxides, polyesters and acrylics often must contain other materials, such as crosslinking or curing agents or copolymers, with active proton acceptor groups.

There are several nylon resins commercially available and which can be dyed.

Among the nylons, nylon-li, nylon12, nylon-6, nylon-6,6 and copolymer nylon-6,6 and nylon-6,10 have been used in making film coatings utilizing a powder deposition process. Nylon11 and nylon-12 have a greater differential between their melting temperature and their decomposition temperature and have been found to be favored for producing nylon coatings by powder coating processes.

Polyesters suitable for coating and dyeing include the condensation products of polycarboxylic acids and polyols and, in particular, aliphatic, aromatic and heterocyclic polycarboxylic acids and aliphatic, aromatic and heterocyclic polyols. More particularly, polyesters suitable for coatings and dyeing processes, in accordance with the invention include the condensation products of aliphatic, aromatic and heterocyclic dicarboxylic acids and aliphatic, aromatic and heterocyclic diols. Those deserving of special mention are the polyethylene terephthalates such as the condensation products of ethylene gylcol with terephthalic acid or dimethyl terephthalate. Polyesters containing only hydroxyl and carboxyl groups can be made dyeable by including a curing agent, such as an amine, or an amine copolymer in the coating composition applied to the metal article to be dyed.

Also useful in the production of dyeable coatings on metal articles are the polymethacrylates and the polymethylmethacrylates. Such materials can be crosslinked to produce dyeable films in metal articles by including in the coating composition an amine cross-linking agent. Also, the acrylic resins containing amine resins or epoxy resins with amine curing agents form films on metal article suitable for dyeing,; As used herein, the term "epoxy resins is intended to include resins containing one or more epoxide groups. Typical and representative of those epoxy resins containing one or more epoxy groups are those resins disclosed in U.S. Patents No. 3,028,251, No. 3,058,951, No. 3,102,823, No.

3,321.438, No. 3,442,856, No. 3,506,598 and No. 3.758.633. The aforementioned references illustrate the wide variety of epoxy resins which can be used as filmforming materials, as a powder liquid, suitable for use in the manufacture of the dyeable films of the invention. Among the epoxy resins which have been found to be satisfactory, both as to durability and dye color pick up are those epoxides made by the reaction of epichlorohydrin (1-chloro2,3-epoxy-propane) and polyols or hydroxyl containing compounds such as 2,2'-bis(phydroxyphenyl) propane (bis-phenol A); phenol-formildehyde, novalac resins, resorcinal, glyccrol and the like.

Curing agents are included in the epoxy resin compositions or must be mixed therewith to either promote homopolymerization or form a copolymer therewith. Heating may be required to cure the epoxy resin or the reaction may occur at room temperature. Conveniently the curing agent has proton acceptor groups to contribute the basic radicals in the cured film. A large number of curing agents are described in the prior art as cxemplified in U.S. Patents No.

3,028,251, No. 3,058.951, No. 3,321,438, No. 3.442.856. No. 3,506,598, No.

3,102,823 and No. 3.758,633. Suitable agents are found in the quaternizeable derivatives of ammonia such as the amines including the mono-, di-, and poly-primary, secondary and tertiary amines which can be aliphatic. cycloaliphatic, or aromatic in nature.

In powder epoxy resin compositions the curing agents are generally included in the compositions and require heating to cure the resin. Such heat-activated curing agents are mixed with the epoxide in any suitable manner, i.e.. a solid curing agent powder mixed with a solid epoxide powder, or the curing agent may be incorporated with the epoxide in a partially reacted solid epoxy resin commonly referred to as B-stage resin.

One commonly employed solid curing agent is dicyandiamide which also contributes the necessary proton acceptor groups.

Additionally the polymer resin material may contain other ingredients, such as heat-activated catalysts, pigments, fillers and the like. Where the color (particularly the lighter colors) of a polymer film on a metal element is to closely match a garment when dyed together with the garment, a white pigment, such as titanium dioxide is included in the polymer resin.

A wide variety of dyes in various classes of dyes have been found to produce colors with excellent intensity and uniformity in the polymer film 18. Examples of dyes classified as acid dyes in the Colour Index, Third Edition, 1973, by The Society of Dyers and Colourists, Great Britain, and the American Association of Textile Chemists and Colorists. U.S.A., and which have been found suitable include: Colour Index No. 15510 Acid Orange Colour Index No.

18950 Acid Yellow 40; Colour Index No.

17025 Acid Violet 1; and Colour Index No.

42655 Acid Blue 90. Particular disperse dyes which have been found suitable include FORON (Trade Mark) Brilliant Yellow SE-6GFL from Sandoz Inc., Hanover, New Jersey, U.S.A., classified as Colour Index Disperse Yellow 49; FORON Red E-g from Sandoz Inc. classified as Colour Index Disperse Red 65; RESOLIN (Trade Mark) Yellow 7 GL from Bayer Akticngesellschaft, Leverkusen, Germany, classified as Colour Index Disperse Yellow 73; and RESOLIN Blue FBLD from Bayer classified as Colour Index Disperse Blue 71.

Additional suitable dyes include FORON Brilliant Blue E-GFLN from Sandoz; RE SOLIN Scarlet PGG from Bayer; and DURONYL Yellow G from Ciba-Geigy Corporation, Andsley, New York, U.S.A.

classified as Colour Index Acid Orange 1.

Dyes sold in the United States under the Trademark RIT have also been found to produce acceptable color in the polymer coatings. Anionic dyes such as acid dyes and direct dyes in aqueous solutions are believed to be fixed by salt formation with the cationic sites produced by the proton acceptor groups in the polymer film. Other types of dyes, such as disperse dyes, azoic dyes and mordant dyes are believed to be at least aided by the presence of the proton acceptor groups in penetration or reaction to become fixed in the polymer film.

In powder coatings, it has been found that it may be necessary to limit the temperature used during heating the coating 20 of powdered polymer resin to form the film 18. If the temperature is allowed to exceed a predetermined temperature, substantially all the proton acceptor groups may undergo irreversible transformation, either by decomposition, becoming buried in the polymer film structure, reaction such as crosslinking, or the like, and the dyeability of the polymer film is substantially impaired. This predetermined temperature is generally substantially less than the temperature at which the polymer is degraded in strength, i.e. the temperature at which depolymeriza- tion or oxidation can occur. However, the temperature must be allowed to exceed the melting point of the powdered solid polymer resin to allow the powder to coalesce into a coherent film. The duration of the heating should also be limited to less than a predetermined duration since substantially complete transformation of the proton acceptor groups in polymer resins can occur at lower elevated temperatures over extended periods of time. Transformation of at least some of the proton acceptor groups in certain polymer resins, such as the epoxy resins, may be necessary to allow cross linking reaction during the heating cycle; but the heating must be stopped short of substantially complete transformation to allow a sufficient quantity of the proton acceptor groups to remain untransformed or active.For epoxy resins with quaternizable derivatives of ammonia or amine curing agents, nylons, and copolymers with amine materials, the temperature is maintained generally below about 205"C (400 F) and preferably should not exceed about 1900C (375"F); and heating at a temperature approaching 1900C should be limited to about 25 minutes, longer time periods being acceptable for lower temperatures, and higher temperatures acceptable only for shorter periods.

The employment of smaller particles of powdered polymer resin aids in the color pick-up from dye solutions; this is particu arl noticeable with resins such as nylon-11 and nylon-12 which are formed somewhat deficient in active proton acceptor groups.

The milling of the polymer resin to produce the finely divided particles is belived to produce a change in chemical structure of the polymer which results in more active proton acceptor groups being available.

Generally, powders having an average particle size less than about 200 microns and preferrably less than about 150 microns produce superior results. The small particle size has another advantage in producing films on small articles such as sliders in that thinner dyeable films are possible using smaller particle powders, the thinner films interfering less with slider operation in slide fasteners than the thicker films produced by prior art coatings. For sliders, the coating should have a thickness generally in the range of about 12 to 153 microns (0.5 to 6 mils) and preferrably in the range of about 22 to 127 microns (0.9 to 5 mils). Preferred thicknesses are above 25 microns, desirably above 38 microns.

Preferrably the powder coating 20 on the metal element 12 is applied by an electrostatic spray process although other powder applying processes may be employed. Films formed from electrostatic powder sprays are generally superior in being more even, and thinner than films formed by other processes. The solid powders are preferrably melted and/or reacted in an oven to form the films but other heating techniques may be used with good results.

One particular advantage of having sliders formed with a dyeable coating is that a garment, such as a dress, of one color could be dyed to a new color and the metal slider will be dyed to the new color along with the rest of the garment.

The adherence and durability of the coating 18 is improved by first treating the metal article 12 with a conventional treatment used to form suitable base surfaces for conventional painting processes and the like; prior to treating, it may be necessary or desirable to initially clean and degrease the metal articles. Typical treatment processes for articles made from alloys which are principally zinc or aluminium include dipping the article in a chromating solution, such as (1) a concentrated sodium dichromate solution which is slightly acidified with sulfuric acid, (2) a chromic acid solution containing one or more mineral acids (i.e.

sulfuric acid, nitric acid, etc) and a low molecular weight organic acid (i.e. formic acid, acetic acid, etc), or (3) any of the several commercial chromating solutions which are acceptable for treating zinc or aluminium. Where the article is a ferrous alloy, the article can be subjected to a phosphoric treating process. Typical phosphoric treating processes include treating with (a) solutions containing phosphoric acid, stabilizers such as dihydrogen phosphate and accelerating agents such as copper salts, nitrates, etc., (2) phosphoric acid solutions containing phosphates of iron, manganese, and zinc, and (3) any of several commercially available phosphoric treating solutions suitable for treating ferrous metals.It is generally believed that the chromate and phosphoric treating processes produce complexes at the metal surfaces which improve the bonding of many materials.

In nylon coated articles it has been found that improved dye pick-up is achieved in nylon coatings on metal articles if the second nylon coating is subjected to a benzyl alcohol treatment prior to dyeing.

The benzyl alcohol treatment is readily accomplished by dipping the coated parts into benzyl alcohol heated to a temperature in the range of from 71"C (160"F) to 880C (190"F). At a temperature of 71"C a treatment time of two hours is required for improved dye pick-up while at temperatures of 88"C only forty-five minutes is required.

For optimum results a benzyl alcohol treatment of the coated metal article at a temperature of 88"C (190"F) for a period of one hour is recommended.

Nylon films, particularly clear films of nylon-11 and nylon-12, formed by powder deposition processes on metal members are somewhat deficient in dye pick-up compared to dye pick-up by the nylons commonly used in textile materials. The benzyl alcohol treatment has been found to improve the dye pick-up in nylon films on sliders such that the nylon coated metal sliders closely match the dye pick-up in common nylon textiles. The reason that benzyl alcohol renders the nylon film more dyeable is not understood; it could be a reaction rendering the film surface more penetrable by the dye solution or rendering the proton acceptor groups more active.

A modified coated article or slider, illustrated in Figures 5, 6, 7 and 8, includes a primer or base layer of film 30, such as a phenol aldehyde polymer layer or a polyester layer, on the metal article 12 under the dyeable polymer film 18. Phenol aldehyde layers are generally formed by dipping in a liquid solution of a phenol aldehyde resin, spinning to remove excess solution and then heating to evaporate the solvent and cure or polymerize the phenol aldehyde resin.

Polyester layers are formed by a powder deposition process similar to the process for forming the layer 18 in Figure 4; such polyester however need not necessarily be dyc;able. Suitable polyesters include the polyethylene terephthalates with a curing agent such as isophorone isocyanide.

Phenol aldehyde primer layers are formed as thin as possible while still completely covering the article 12. Generally films of phenol aldehyde less than about 13 microns (0.5 mils) thick and preferrably about 2.5 to 5 microns (0.1 to 0.2 mils) thick will cover the article sufficiently to provide a good base for the polymer film 1X.

Polyester primer layers formed from powder deposition techniques are thicker than the phenol aldehyde layers, and should generally have a thickness within the range from 12 to 127 microns (0.5 to 5 mils) and preferrably in the range from 20 to 39 (0.9 to 1.5 mils).

Both phenol aldehyde and polyester primer layers improve the adherence and durability of the dyeable polymer film 18 and impart improved resistivity against a tendency for the polymer film 18 to blister and become loosened from the article 12 when subjected to an acidic dye solution.

Cross-linking type polymer resins, such as epoxy resins, in the film 18 may be improved in toughness and durability by grafting or cross-linking across the interface between the layer 30 and the film 18 to render the polymer film 18 more adherent and thus less likely to chip or crack during subsequent processing and handling.

A modified dyeable article or slider for a slide fastener, illustrated in Figure 9, includes a white pigmented polymer underlayer or film 31 on the metal member with a clear dyeable polymer layer or film 32, similar to film 18 in Figures 4, 7 and 8 on top of the white underlayer 31. The layers 31 and 32 are preferrably formed in a manner similar to the layer 18 such as by an electrostatical spraying and heating process.

For sliders, the layers 31 and 32, In Figure 9, each should have a thickness generally greater than about 2.5 microns (1 mil) to produce coherent films covering the metal member, and generally less than about 127 microns (5 mils) to avoid interference with slider operation. Preferrably each of the layers 31 and 32 is at least 38 microns (1.5 mils) in thickness.

Clear dyeable polymer layers, particularly clear nylon layers with an underlying white layer have been found to pick-up dark colors, such as the blacks, to closely match the color picked-up nylon textiles.Dyeing dark colors in white pigmented layers is deficient due to a lightening of color by white pigment.

EXAMPLE I (Comparative) A batch of metal sliders for slide fasteners are coated by an electrostatic spray with epoxy resin powder No. 89-910 from Pratt and Lambert, Inc., Buffalo, New York, U.S.A. The epoxy resin powder No.

89-910 has an average particle size less than 2()0 microns and includes an epoxide formed from epichlorohydrin and Bis-phenol A and having a epoxy equivalent weight from 740-800, dicyandiamide as a curling agent, an accelerator, and a titanium dioxide pigment. The quantity of dicyandiamide is stoichmetrically more than 1.1 times the quantity of epoxide. Then the sliders are placed in a convection type oven having a temperature of about 182"C (360"F) for a period of about 25 minutes to form a polymerized film of approximately 51 microns (2 mils) on the external surfaces of the slider. The sliders are then assembled on slide fastener tapes made of nylon 6,6.

Different groups of the assembled slide fasteners are subjected to the following dye solutions, respectively, in conventional dye processes: (a) ORCO Acid Orange from Ciba-Geigy (Colour Index 15510), (b) DUPONT Milling Yellow (Colour Index No. 18950), (c) ORCO Acid Violet from Ciba-Geigy (Colour Index No. 17025), (d) DURONYL Yellow G from Ciba-Geigy (e) RESOLIN Blue FBLD from Bayer, (t) RESOLIN Scarlet PGG from Bayer, and (g) Acid Blue 90 (Colour Index No. 42655).

The dye pick-up is generally good in the slide fasteners and the colors of the coatings on the sliders are generally excellent in compatability to the fastener tapes.

EXAMPLE 2 (Comparative) A batch of zinc bodied sliders is treated by immersing in DUCHROME 115 P from DuTone Chemicals Co., Inc. Waukegan, Illinois, U.S.A. for about 60 seconds.

DUCHROME 115 P is a chromating solution. Different portions of the treated batch of sliders are then coated with polymer films and dyed used the materials and techniques of Examples 1, 2 and 3, respectively. The colored coatings have improved adherence to the sliders when subjected to tumbling as compared to the respective coatings in Examples 1, 2 and 3.

EXAMPLE 3 A batch of metal sliders for slide fasteners are coated by an electrostatic spray of a polyethylene terephthalate polyester dry resin powder paint No. 3081-125 from Pratt and Lambert, Inc., Buffalo, New York, U.S.A. The polyethylene terephthalate polyester resin powder has a hydroxyl number of 55, an equivalent weight of 1000 and an average particle size of less than 200 microns. The polyethylene terephthalate polyester resin powder also contained a phorone isocyanide as a curing agent and a titanium dioxide pigment.After the coating operation is completed, the sliders are paced in a convection type oven and the powdered film cured at 400"F for a period of time of about 20 minutes to provide a cured polymer film having an average thickness of about 28 microns (1.1 mils) on the external surfaces of the slider. A film of epoxy resin is then applied on top of the polyester film for dyeing, using the materials and techniques of comparative Example I. In tests, the sliders with the base polyethylene terephthalate polyester films were found to be extremely resistant against damage, including impact or chipping, which may occur during commercial dye processing.

EXAMPLE 4 A batch of zinc bodied sliders is treated with a chromating solution in a manner similar to comparative Example 2. The batch of sliders are then coated electrostatically with a nylon-li powder containing a white pigment. The white powder coated sliders are heated in an oven at a temperature of about 204"C (400 F) for about five minutes to melt the white nylon-11 powder and form a coherent white film having a thickness of about 38 microns (1.5 mils).

The white nylon coated sliders are then coated electrostatically with a clear nylon-11 powder containing an anti-oxidant and which is subsequenly melted in an oven at a temperature of about 204"C (400 F) for about five minutes to form a non-yellowing, free from orange peel smooth clear polymer coating having a thickness of about 51 microns (2 mils) on the white underlayer.

The clear nylon coatings are then treated by immersing the sliders for about one hour in a benzyl alcohol bath which is maintained at a temperature of about 82"C. Subsequently the sliders are assembled on slide fastener tapes of nylon-6,6 and the assembled slide fasteners are, respectively, subjected to various nylon dye solutions including disperse dyes, acid neutral dyes and acid type dyes. The dye pick-up in the polymer coatings on the sliders is very good and closely matches the color of the tapes even for the color black.

It is noted that the nylon-ll coated sliders treated with benzyl alcohol show improved dye pick-up to a considerable extent compared to nylon coated sliders not treated with benzyl alcohol.

Equally good results are obtained using a clear nylon-12 powder for the nylon11 powder above.

Attention is directed to the related disclosure and claims of our application serial No.

1 519 613, having regard to the provisions of the Patents Act 1949, Section 9.

WHAT WE CLAIM IS: 1. A method of forming a colored coating on a metal article comprising steps of forming a first coherent layer of white polymer on the article, forming a second coherent layer of clear polymer on the first layer, said clear polymer being dyeable and having for each polymer molecule an average of at least 0.5 proten acceptor groups providing for dye pick-up, and dyeing the second coherent layer of clear polymer.

2. A method as claimed in claim 1 wherein the second layer is formed from a clear nylon resin.

3. A method as claimed in claim 2 wherein the first layer is formed from a nylon resin containing a white pigment.

4. A method as claimed in claim 2 wherein the second layer is formed by depositing a coating of a powdered nylon on the first layer, and heating the coating sufficiently to convert the powdered coating into a coherent film.

5. A method as claimed in claim 4 wherein the powdered nylon is selected from the group consiting of nylong 11 and nylon 12.

6. A method as claimed in claim 4 wherein the powdered nylon has an average particle size less than 200 microns.

7. A method as claimed in claim 2 including the step of treating the second layer of clear nylon with benzyl alcohol to render the second layer more susceptible to dye.

8. A method as claimed in claim 7 wherein the treating step includes dipping the article with the first and second layers into benzyl alcohol at a temperature within the range from 71" to 88"C for a period of forty-five minutes to two hours.

9. A method as claimed in claim 4 wherein the first layer is formed by depositing on the metal article a coating of powdered nylon containing white pigment, and heating such coating sufficiently to convert the powdered coating into a coherent film.

10. A method as claimed in claim 4 wherein sufficient nylon is deposited on the metal article to form a coherent film after

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

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. Examples 1, 2 and 3. EXAMPLE 3 A batch of metal sliders for slide fasteners are coated by an electrostatic spray of a polyethylene terephthalate polyester dry resin powder paint No. 3081-125 from Pratt and Lambert, Inc., Buffalo, New York, U.S.A. The polyethylene terephthalate polyester resin powder has a hydroxyl number of 55, an equivalent weight of 1000 and an average particle size of less than 200 microns. The polyethylene terephthalate polyester resin powder also contained a phorone isocyanide as a curing agent and a titanium dioxide pigment.After the coating operation is completed, the sliders are paced in a convection type oven and the powdered film cured at 400"F for a period of time of about 20 minutes to provide a cured polymer film having an average thickness of about 28 microns (1.1 mils) on the external surfaces of the slider. A film of epoxy resin is then applied on top of the polyester film for dyeing, using the materials and techniques of comparative Example I. In tests, the sliders with the base polyethylene terephthalate polyester films were found to be extremely resistant against damage, including impact or chipping, which may occur during commercial dye processing. EXAMPLE 4 A batch of zinc bodied sliders is treated with a chromating solution in a manner similar to comparative Example 2. The batch of sliders are then coated electrostatically with a nylon-li powder containing a white pigment. The white powder coated sliders are heated in an oven at a temperature of about 204"C (400 F) for about five minutes to melt the white nylon-11 powder and form a coherent white film having a thickness of about 38 microns (1.5 mils). The white nylon coated sliders are then coated electrostatically with a clear nylon-11 powder containing an anti-oxidant and which is subsequenly melted in an oven at a temperature of about 204"C (400 F) for about five minutes to form a non-yellowing, free from orange peel smooth clear polymer coating having a thickness of about 51 microns (2 mils) on the white underlayer. The clear nylon coatings are then treated by immersing the sliders for about one hour in a benzyl alcohol bath which is maintained at a temperature of about 82"C. Subsequently the sliders are assembled on slide fastener tapes of nylon-6,6 and the assembled slide fasteners are, respectively, subjected to various nylon dye solutions including disperse dyes, acid neutral dyes and acid type dyes. The dye pick-up in the polymer coatings on the sliders is very good and closely matches the color of the tapes even for the color black. It is noted that the nylon-ll coated sliders treated with benzyl alcohol show improved dye pick-up to a considerable extent compared to nylon coated sliders not treated with benzyl alcohol. Equally good results are obtained using a clear nylon-12 powder for the nylon11 powder above. Attention is directed to the related disclosure and claims of our application serial No.

1 519 613, having regard to the provisions of the Patents Act 1949, Section 9.

WHAT WE CLAIM IS: 1. A method of forming a colored coating on a metal article comprising steps of forming a first coherent layer of white polymer on the article, forming a second coherent layer of clear polymer on the first layer, said clear polymer being dyeable and having for each polymer molecule an average of at least 0.5 proten acceptor groups providing for dye pick-up, and dyeing the second coherent layer of clear polymer.

2. A method as claimed in claim 1 wherein the second layer is formed from a clear nylon resin.

3. A method as claimed in claim 2 wherein the first layer is formed from a nylon resin containing a white pigment.

4. A method as claimed in claim 2 wherein the second layer is formed by depositing a coating of a powdered nylon on the first layer, and heating the coating sufficiently to convert the powdered coating into a coherent film.

5. A method as claimed in claim 4 wherein the powdered nylon is selected from the group consiting of nylong 11 and nylon 12.

6. A method as claimed in claim 4 wherein the powdered nylon has an average particle size less than 200 microns.

7. A method as claimed in claim 2 including the step of treating the second layer of clear nylon with benzyl alcohol to render the second layer more susceptible to dye.

8. A method as claimed in claim 7 wherein the treating step includes dipping the article with the first and second layers into benzyl alcohol at a temperature within the range from 71" to 88"C for a period of forty-five minutes to two hours.

9. A method as claimed in claim 4 wherein the first layer is formed by depositing on the metal article a coating of powdered nylon containing white pigment, and heating such coating sufficiently to convert the powdered coating into a coherent film.

10. A method as claimed in claim 4 wherein sufficient nylon is deposited on the metal article to form a coherent film after

heating having a thickness greater than 25 microns.

11. A method as claimed in claim 10 wherein sufficient nylon is deposited on the metal article to form a coherent film after heating having an average thickness greater than 38 microns.

12. A method of forming a colored coating on a metal article with a white polymer first layer and a clear polymer outer layer, substantially as herein described in Example 3 or 4.

13. A metal article, having a colored coating formed by the method of any preceding claim, as such or when associated with a colour match dyed textile article.