CA1225963A

CA1225963A - Decorative carbon coating and method

Info

Publication number: CA1225963A
Application number: CA000457223A
Authority: CA
Inventors: James D. Flasck
Original assignee: Ovonic Synthetic Materials Co Inc
Current assignee: Ovonic Synthetic Materials Co Inc
Priority date: 1983-06-23
Filing date: 1984-06-22
Publication date: 1987-08-25
Also published as: EP0130754A1; KR850000264A; AU558997B2; IL72125A; AU2977884A; DE3480414D1; IL72125A0; JPS6021373A; ATE47893T1; US4524106A; ZA844706B; PH21197A; EP0130754B1

Abstract

ABSTRACT
Coatings are provided that are especially useful for decorative purposes. In one embodi-ment, black coatings are provided that include a black layer of disordered carbon. The carbon lay-er may be formed by sputtering from a carbon tar-get. The coatings can be characterized as having a high gloss, a high degree of blackness and being non-transparent with good adhesion and physical integrity.

Description

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There are many cases in which it is desir-- able, often for esthetic reasons, to provide a decorative coating on the surface of an article.
Decorative coatings are utilized on innumerable articles used under a variety of conditions. For example, decorative coatings are found on home and office furnishings, such as lamps, chairs, tables and appliances. Decorative coatings are utilized in connection with automobiles on non-functional items such as interior and exterior trim, and on functional items, such as door handles and door lock buttons. Other items included in these cate-gories are, for example, window moldings, body moldings, wheel trim rings, radiator grills, bump-ers, control knobs and levers and other similar parts, just to mention a few.
In the past, silver or similar colors were common for decorative coatings. Such coatings - were~often made~by depositing over the article a ` 20 layer of chrome, for example.
; More recently, there has been a need to pro-vide black decorative coatings~for parts or arti-cles, and in particular black coatings that are very bright and appear highly polished or lus-trous. Black coatings have been provided in the past by applying black paint to the article sur-face, or by black anodizing, which requires an electrochemical reaction.
It would be desirable to provide a black coating of controlled thickness having good adher-ence and high gloss that is suitable for use as a decorative coating. In addition it would be de-, ~ 1 .

~L`Z25963 sirable to provide a coating having a relativelyhigh degree of inertness.
We have found that the above-discussed dis-advantages can be overcome by employing the pres-ent invention, in which thin, non-metallic carbon coatings are provided that are suitable for dec-orative coatings. The coatings can be formed by depositing carbon onto the surface of an article or substrate. ~s used herein, "substrate" and "article" are interchangeable and can include a coating or coatings other than the carbon coatings of the invention. Coatings in accordance with the invention are especially useful as decorative coatings and can be characterized as having a very high gloss. In addition, the coatings can be ex-tremely black and highly opaque (non-transparent).
It is believed that the degree or shade of blackness and gloss of the coatings are related to several factors, which include coating surface morphology, microstructure and thickness and the smoothness of the substrate and the coating compo-sition, as hereinafter described.
In accordance with another aspect of the in-vention, a decorative carbon coating is provided that is formed on a substrate by sputtering. ~en-erally, the decorative coatings of the invention -~orm either the exterior layer on a surface or are otherwise visible (e.g. a transparent coating can be applied over a decorative coating).
In accordance with a more specific aspect of the invention, disordered carbon coatings are pro-vided. It has been discovered that disordered carbon coatings can be deposited on the surface of `` 1225963 an article, which coatings are black and can have a high gloss with essentially featureless surface morphology. The coatings can also exhibit good adherence to the surface to which they are ap-plied. The coatings are preferably amorphous or substantially amorphous. Wit~ respect to gloss, disordered coatings may e~hibit a relatively high degree of specular reflection and a relatively low degree of diffuse reflection with greater disorder resulting in higher gloss. In addition, it is be-lieved that as the disorder increases, integrity and physical stability of the coating is improved.
Any technique that forms a disordered carbon coating having adequate adherence can be utilized in accordance with the invention. Most desirably, the coatings are formed by depositing carbon di-rectly from~an elemental carbon source, such as by transEerring atoms from an elemental carbon target to the substrate. In accordance with a ~ore spe-cific aspect of the invention, a carbon coating isformed by sputtering (non-reactive) using a carbon target. One especially suitable technique is dc magnetron sputtering. It has been discovered that dc magnetron sputtering carbon can provide a dis-ordered, black carbon coating having a high gloss, good substrate adherence and essentially feature-less surface morphology. In addition, sputtering alIows the deposition to take place at relatively low temperatures, such as room temperature. The coatings can, therefore, be deposited on articles that cannot withstand relatively high tempera-ture. Accordingly, suitable materials on which the coating can be deposited include metals and ~L22596;~

nonmetallic materials, including natural and syn-thetic polymers, for example. Thus, the coatings of the invention are particularly suited for ther-moplastic materials, such as ABS ~acrylonitrile-butadiene-styrene) resins, for example~
To a degree, the thickness of the coating de-termines the degree of blackness of the coating.
The optical density of the coating is reLated to its thickness, until a certain thickness is achieved where a thicker coating will not provide a significant increase in optical densityr The smoothness of the substrate surface to which the coating is applied generally has an ef-Eect on the gloss of the coating. Usually, pro-viding a smoother surface results in a coating having a higher gloss. Accordingly, where a high gloss~coatlng is desired, the substrate surface should be relatively smooth.
The composition of the coating determines to a degree the color or shade of the coating. Pref-erably, the coat~ngs essentially contain only car-bon, although it is to be understood that minor amounts of impurities will almost invariably be present. Further, other elements or compounds other than carbon may be present, as long as they do not interfere with the desired color or gloss.
The coatings of the invention can be further characterized in being relatively inert and sta-ble, with good resistance to color change as a re-sult of exposure to ultraviolet radiation, forexample.
In accordance with another aspect of the in vention, a coated article is provided that in -, ~:25~631 cludes a substrate portion and a decorative coat-ing over at least a portion of the substrate. The coating is a thin black layer of disordered car-bon.
Figure 1 illustrates in perspective view an article having a decorative coating in accordance with the invention applied thereon;
Figure 2 illustrates in perspective view another article having a decorative coating in ac-cordance with the invention applied thereon; and Figure 3 illustrates in sectional view acoating in accordance with the invention having a transparent coating applied thereover.
Most desirably, the carbon coatings of the invention are formed by sputtering. One especial-ly useful type of sputtering is dc magnetron sput-tering, although other methods of sputtering or depositing a thin layer of carbon on a surface may be suitable. Dc magnetron is generally preferred because the resulting carbon coatings exhibit good adherence and mechanical integrity.
Generally, prior to sputtering, the surface on which the carbon coating is to be applied should be suitably prepared. Where a high gloss coating is desired, the surface will preEerably be relatively smooth, since this is believed to fa-cilitate the formation of a high gloss coating.
Some surfaces will already be smooth and no treat-ment is required. Where a smoother surface is de-sired, any suitable means can be utilized. Forexample, the surface may be polished. ~lterna-tively, the surface may be precoated with a layer or~layers of polymer material such as a thermo-~ .

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plastic or thermosetting polymer resin or other material which can provide a relatively smooth surface, Epoxy and acrylic resins are examples of such polymer materials. A combination of polish-ing and applying a precoat layer can also be uti-lized.
The surface preparation could also include, depending on the type of substrate, plasma or acid etching. Thereafter, the substrate may be sputter etched, if desired. In general, the surface should be suitable for sputtering and if surface preparation is necessary, any technique which is suitable to prepare the surface for sputtering can be utilized.
After the surface has been suitably prepared as desired, the carbon coating is applied by a suitable method. In accordance with one tech-ni~ue, the coatings are formed by dc magnetron sputtering utilizing a carbon target, and in par-ticular, a high purity, high density graphite tar-get. The sputtering atmosphere can be an inert gas, such as argon. The substrate temperature during sputtering can be very low, such as room temperature. A dc bias voltage may or may not be applied to the substrate. Utilizing a bias volt-age provides improved adhesion of the carbon coat-ing in some cases, although non-uniformity of the coating can begin to occur as the thickness of the coating increases. This is believed to be caused by the corresponding increase of the resistivity of the coating. Such effects are generally ob-served when the thickness of the coating is about 5000A.

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The thickness of the carbon coating can be varied and no minimum thickness is required. ~ow-ever, it is desirable for the thickness of the carbon coating to be in the range of from about - 2000A to about 5000A (10,000A = 1 micrometer).
Coatings which are thinner will be more transpar-ent and the blackness of the coating will be less. Coatings thicker than 5000A can be uti-lized, but for decorative uses, cost may be a limiting factor. The coatings are preferably thick enough to be substantially non-transparent.
The carbon coatings in accordance with the invention are believed to be relatively chemically inert and to generally possess good resistance to degradation from heat and ultraviolet radiation encountered from outdoor atmospheric conditions and other similar environments, for example.
Referring now to the drawings, several arti-cles are depicted to which decorative coatings in ; 20 accordance with the invention are applied. It is, of course, to be understood that the type of arti-cles to which decorative coatings may be applied is virtually limitless, and these illustrations are merely set forth by way of example. In Figure 1, there is illustrated a steel automobile bumper 10 having a decorative coating 12 in accordance with the invention on the surface thereof. Coat-ing 12 is a thin black layer of substantially amorphous carbon and is from about 2000A to about 5000A in thickness and has a high gloss.
In Figure 2, a plastic automobile door look button 14 is illustrated having a decorative coat-ing 16 in accordance with the invention on the surface thereof.

- - ~22S963 A protective overcoat layer may be provided over the carbon coating. For most applications the protective overcoat will be substantially transparent and clear, although it could be color ed, i desired. ~ny such type of material which does not deleteriously affect the carbon layer to an unwanted degree can be used. For example, polymer resins can be used which are thermoplastic or thermosetting. Suitable polymer resins which can be seIected from a wide group of materials.
Included in this group are, for example, poly-urethanes, vinyl polymers and copolymers, copoly-mers of vinylidene chloride and vinyl acetate, co-polymers of vinylidene chloride and acrylonitride, copolymers of vinyl chloride and vinyl acetate, polycarbonates, polyamide, polyesters, ABS copoly-mers and the like. These materials are also suit-ab~e for use as a precoat over the substrate to provide a smoother surface. Any suitable method can be used to apply the overcoat or precoat lay-er. By way~of illustration only, such methods in-clude, for example, spraying, brushing, roller coating, dipping, spin coating, vacuum deposition, electrolysis, electrostatic spraying, or the like.
Referring to Figure 3, there is illustrated an enlarged cross-sectional view of a portion of a substrate 18 having a disordered carbon coating 20 in accordance with the invention. Applied over the surface of coating 20 is a thin layer oE a protective overcoat 22, which serves to protect coating 20 from impact, scratching and abrasion.
Protective overcoat 22 is a polymer resin that is substantially transparent -~ ~2Z5963 As used herein, the term "disordered" in-cludes amorphous, microcrystalline and polycrys-talline (lacking long range order) phases or a mixture of any combination of those phases. By the term "amorphous" is meant a material which has long range disorder, although it may have short or intermediate order or even contain at times some crystalline inclusions.
Example 1 ~ black, amorphous, substantially non-trans-parent carbon coating was formed on the surface of a glass substrate by dc magnetron sputtering. A
target of high purity, high density graphite was utilized. The sputtering atmosphere was ultra high purity argon gas at a pressure of 6 microns (6 x 10~3 torr). The target power was about 30 watts per square inch of target surface and no bias voltage was applied to the substrate. The substrate was at about room temperature during sputtering. The resultant carbon coating was about 2000A thick, had a high gloss and adhered well to the substrate. The composition of the coating was analyzed and it was found that the coating was essentially carbon, with less than 2 atomic percent nitrogen and oxygen being present.
Example 2 Utilizing the procedure of Example 1, a blackj amorphous carbon coating was formed on a steel substrate similar to the coating of Example 1.
Example 3 Utilizing the procedure of Example 1, a black, amorphous carbon coating was formed on a _g_ . . .

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polished nickel substrate similar to the coating - of Example 1.
Example 4 Utilizing the procedure of Example 1, a black, amorphous carbon coating was formed on a tungsten carbide substrate similar to the coating of Example 1.
Example 5 ~ carbon coating was formed as described in ExampIe 1 on an alloy steel substrate, except that the substrate was biased at -500 volts with re-spect to ground.
Example 6 The relative color of black, disordered carbon coatings made in accordance with the invention was measured with a colorimeter. The colorimeter mea-sured the relative amount of incident light that was reflected from the coating surface. The coat-ings~were made as described in Example t and were applied;to various substrates in various thick-nesses. I
A Gardner XL20 Tristimulus~*Colorimeter wasutillzed in making the color measurements which were made in accordance with ASTM E 97-55 (1971) and D 2244-68. The measurements were made using white and black reference standards for calibra-tion. Where a backing was utilized in making the measurements, the backing was on the side of the substrate opposite the side to which the coating was applied. The resul~s are set forth in Table I. ~ ~ ,.

* Trade Mark ~2Z5963 TABLE I
Relative Amount Coating Of Incident ~hickness Light Reflected Sam~le (Angstroms) SubstrateGreen Red Blue - - (White 82.584.6 98.3 Reference) - (Black 0.20.0 0.1 Reference) 1 400 Glass 1.20.9 1.0 1 400 Glass with 0.70.5 0.3 : gray backing

2 2,200 Glass 0.80.5 0.5 2 2,200 Glass with 1.51.6 0.4 white backing 2 2,200 Glass with 0.40.3 0.2 gray backing 2 2,200 Glass with 0.30.1 0.2 black backing

3 2,800 Glass 0.50.2 0.3 3 2,800 Glass with 0.40.2 0.3 gray backing

4 3,200 Glass 0.40.2 0.2 4 3,200 Glass with 0.40.2 0.2 gray backing

5,000 Glass 0.50,2 0.3 5~ 5,000 Glass with 0.50.2 0.3 : gray backing

6 10,000 Glass 0.40,2 0.2 6 10,000 Glass with 0.40.2 0.3 wbite backing

7 : 4,000 Polished nickel1.2 0.9 1.4

8 4,000 Matte finish7.16.5 7.7 Stainless Steel

9 2,800 Matte finish0.40.2 0.3 ABS gray plastic with epoxy precoat and overcoat .~ i .~A

;9~;3 TABLE I - (Continued) Relative Amount Coating Of Incident Thicknéss Liqht Reflected Sample (Angstroms~ SubstrateGreen Red Blue 5,000 Clear polished 0.4 0~2 0.3 ~
plastic with 1.
epoxy precoat and overcoat The foregoing results illustrate the high degree of blackness obtai~ed ~rom relatively thin coatings in accordance with the invention.
: Example 7 The transmittance of Samples 1-6 from Example 6 was determined by measuring the samples with a ' MacB:e~h*TD504 optical densitometer. The ~ollowing results were obtained:
Coating Thickness : j Sample ~Angstroms) _Light Transmittance -: Glass sllde 91.2 1 400 27.5 2 2,200 15.1 i-3 2,800 2.3 4 ~ 3,200 1.7 ~: 5 5,000 0.23 6 10,000 0.02 The Eoregoing results illustrate the high ,;
degree of opacity obtained from relatively thin coatings in accordance with the invention.

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Example 8 The gloss of samples 9 and 10 from Example 6 was measured with a Mallinckrodt*Single ~loss glossmeter in accordance with ~STM Standard D 523, which provides a measurement of specular reflec-tance. The measurements were made relative ~o a black standard having a high gloss. The black standard exhibited reflection values of 92.0 and 1 87.0 for incident white light at angles of inci-dence of 60~ and 20, respectively.
Samples 9 and 10 exhibited reflectance values in excess of 150 for incident white light at both angles of incidence. Such reflectance values in-dicate that the coatings had a very high gloss similar to the gloss of a mirror.

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*Trade Mark '

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A coating applied to a substrate comprising a thin black layer consisting of amorphous carbon formed by dc magnetron sputtering.

2. The coating of claim 1 wherein said layer has a high gloss.

3. The coating of claim 1 wherein said layer is from about 2000.ANG. to about 5000.ANG. thick.

4. The coating of claim 1 further comprising a layer of a substantially transparent protective material over said layer of amorphous carbon.

5. The coating of claim 1 wherein said layer of amorphous carbon is substantially non-transparent.

6. A method of forming a black, amorphous coating consisting of carbon comprising dc magnetron sputtering a layer of black, amorphous carbon on a substrate utilizing a target of high density graphite.

7. The method of claim 6 wherein said sputtered layer has a high gloss.

8. The method of claim 6 wherein said layer is from about 2000.ANG. to 5000.ANG. thick.

9. A coated article comprising:
a substrate; and a decorative coating formed by dc magnetron sputtering over at least a portion of the substrate said coating consisting essentially of a thin black layer of disordered carbon.

10. The article of claim 9 wherein said sputter-ing comprises dc magnetron sputtering with a negative bias voltage applied to the substrate.

11. The article of claim 9 wherein a carbon target is utilized in said sputtering.

12. The article of claim 9 wherein the article is an automobile part.

13. The article of claim 9 wherein said layer is from about 2000.ANG. to about 5000.ANG. thick.

14. The article of claim 9 further comprising a transparent protective coating over said black layer.

15. A method of making a black decorative coating having a high gloss comprising:
providing a relatively smooth surface; and dc magnetron sputtering carbon from a high density graphite target on the smooth surface to form a thin, black layer consisting of amorphous carbon on the surface.

16. The method of claim 15 further comprising applying a bias voltage to the substrate during sputtering.

17. The method of claim 15 wherein said layer is from about 2000.ANG. to about 5000.ANG. thick.

18. The method of claim 15 wherein said rela-tively smooth surface is provided by precoating a substrate with polymer material.