Metal Coated Structure

Abstract

A metal coated structure is disclosed and includes a substrate, an actinic-sensitive coating thereon which becomes adherent upon exposure to actinic radiation and a thin metal coating over the actinic-sensitive coating which will transmit actinic radiation for rendering the actinic-sensitive coating adherent to the substrate and the metal coating. After exposure to actinic radiation, the adhered metal coating is useful per se or provides a basis for further metal coatings such as electroless and electrolytic deposited metal coatings.

Description

BACKGROUND

This invention relates to vacuum deposited metal coatings characterized by excellent adhesion to the substrate coated. Moreover, this invention relates to post-adhering vacuum deposited metal coatings using actinic radiation by a technique herein termed "photogluing."

Vacuum deposited metal coatings have been widely used to provide shaped articles made from plastic for example with metal finishes. The technique of so-called "vacuum metallizing" has thus been used extensively to make interior automobile parts molded from plastic appear to be made from more expensive metal. Bright chrome and aluminum finishes have been extensively used in this and other applications.

A major problem associated with vacuum metallizing which has seriously limited its usefulness in other than decorative applications has been the generally poor adhesion of the metal coating to the substrate coated. Thus, coated articles readily scratch and mar exposing the substrate. Base and top coats have been used but increase the time and cost of vacuum metallizing. Moreover, top coats render the metal coating passive to further metallizing such as by electroless plating.

Etching pretreatments have also been used to improve adhesion but these often involve as much as five or six separate treatment steps which unduly adds to the cost of vacuum metallizing.

The present invention provides a post-coating technique for obtaining excellent adhesion of vacuum metallized coatings. Not only is adhesion greatly improved but also the avenue opened for fabricating further structures using widely practiced metal deposition techniques.

SUMMARY

The metal coated structure of the invention broadly comprises (a) a substrate; (b) an actinic-sensitive coating on said substrate which becomes adherent upon exposure to actinic radiation and (c) a metal layer over said actinic-sensitive material which will transmit actinic radiation for rendering the actinic-sensitive coating adherent to the substrate and the metal coating.

Additionally, the metal layer can have applied thereto a layer of electroless deposited metal after exposure of the actinic-sensitive layer through the metal coating. Following this, the structure may be electroplated over the electroless metal layer.

The process of this invention comprises coating a substrate having an actinic-sensitive layer thereon with a preferably vacuum deposited metal layer which will transmit actinic radiation for rendering the actinic-sensitive layer adherent to the substrate and the metal coating.

The process of the invention also embodies the additional steps of depositing an electroless metal layer on the metal layer and electroplating over the electroless deposited metal.

DESCRIPTION OF THE DRAWING

In the accompanying drawing schematic edge-on views are shown and the thickness of the various layers have been greatly exaggerated for ease of understanding, it being understood that in practice these layers are relatively thin. Also the terms light-sensitive and actinic-sensitive are used interchangeably.

In FIG. 1, substrate 10 is shown having an unexposed light-sensitive layer 12 thereon over which is applied a preferred vacuum deposited metal layer 14.

In FIG. 2, the structure of FIG. 1 is shown positioned below a source 20 of actinic radiation which passes through layer 14 to layer 12 thereby rendering same adherent to substrate 10 and layer 14.

In FIG. 3, a layer of electroless deposited metal 40 is shown applied to the layer 14.

In FIG. 4, the structure of FIG. 3 is shown with an electroplated layer 50 over the electroless layer 40.

DESCRIPTION

In general, the substrate may be virtually any shaped or flat article such as a sheet or a laminate which may be rigid or flexible with varying thicknesses. The substrate may be a synthetic resin, plastic film or sheet, metallic sheets or foils or papers and textiles formed from natural or synthetic fibers or filaments.

The light-sensitive layer or coating used in the structure of this invention must become strongly adherent to both the substrate and the metal layer upon exposure and may be formed from a host of photochemical materials known in the art. Such light-sensitive materials include dichromated colloids, such as those based on organic colloids, gelatin, process glue, albumens, caseins, natural gums, starch and its derivatives, synthetic resins, such as polyvinyl alcohol and the like; unsaturated compounds such as those based on cinnamic acid and its derivatives, chalcone type compounds, stilbene compounds and the like; and photopolymerizable compositions, a wide variety of polymers including vinyl polymers and copolymers such as polyvinyl alcohol, polyvinyl acetals, polyvinyl acetate vinyl sorbate, polyvinyl ester acetal, polyvinyl pyrrolidone, polyvinyl butyrol, halogenated polyvinyl alcohol; cellulose based polymers such as cellulose-acetate hydrogenphthalate, cellulose alkyl ethers; urea-formaldehyde resins; polyamide condensation polymers; polyethylene oxides; polyalkylene ethers; polyhexamethylene adipamide; polychlorophene; polyethylene glycols, and the like. Such compositions utilize as initiators carbonyl compounds, organic sulphur compounds, peroxides, redox systems, azo and diazo compounds, halogen compounds and the like. These and other photochemical materials including their chemistry and uses are discussed in detail in a text entitled Light-Sensitive Systems, Jaromir Kosar, John Wiley and Sons, Inc., New York, 1965. Diazo resins are particularly preferred.

The foregoing photochemicals are often used in the printing plate art where negative working, light-sensitive materials are applied or coated onto a suitable support or substrate and are of such a nature that before exposure to actinic radiation they are soluble in a particular solvent (usually water). When exposed to actinic radiation, however, the material becomes insoluble in the solvent. Other positive working light-sensitive materials function just the opposite, that is, they are insoluble and become soluble upon exposure to actinic radiation.

The criteria for the present invention, however, is not based on relative solubility but on the ability of the photochemical material to become adherent to both the substrate be it hydrophilic, oleophilic or ampholic and the vacuum deposited metal layer upon exposure to actinic radiation.

The thickness of the layer 14 may range from a layer which is atomic in dimension, that is 1 molecule thick up to a thickness of about 1.5 microns. The layer 14 preferably has a thickness of from about 2,000 to about 15,000 Angstroms and more preferably from about 4,000 to about 10,000 Angstroms.

The thickness of the layer 14 can also be expressed as a function of the wave length of the actinic radiation utilized to expose the light-sensitive layer 12. It has been found that generally the thickness of the layer 14 should not be greater than about 10 times the wave length of the actinic radiation and preferably not greater than 5 times the wave length. By definition, actinic radiation is that which will initiate a photochemical reaction and includes x-rays, infrared, visible light and ultraviolet light. Generally, speaking an intense source of visible and/or ultraviolet light is used.

The thickness of the layer 14 must be such that it is capable of transmitting actinic radiation to the light-sensitive coating.

Generally the layer 14 is deposited in thicknesses within the ranges specified above such that there is at least 5 percent and preferably at least 30 percent transparency so as to transmit actinic radiation to the underlying light-sensitive layer.

The layer 14 according to this invention may be vacuum depositable metal elected from the group of the metals of Groups I B, II B, III A, IV A, VI B, VII, of the Periodic Chart. Two or more metals may be used in combination to form the protective coating. Examples of preferred metals include chromium, copper, aluminum, gold, gold alloys, silver, zinc, platinum, iron, cobalt and nickel.

The metal layer 14 has been referred herein as vacuum coated which is the preferred deposition technique. However, metal layer 14 can be applied or deposited using coating techniques which result in uniform deposition of the metal on the light-sensitive layer and which will not adversely affect the light sensitive layer such as by premature exposure. Suitable coating techniques include vacuum coating, sputtering, ion plating, gas plating, and metallized coatings produced by spray metal techniques.

The preferred coating technique is vacuum coating. In vacuum coating, metal particles are deposited by vacuum distillation over the light-sensitive layer to form the metal layer. The substrate with the light-sensitive layer thereon is placed in a coating chamber which is evacuated to eliminate molecular interference between the source of the coating material and the surface to be coated. Readily high vacuum pumps or diffusion pumps may be used to evacuate the coating chamber. The metal is heated intensely, for example, by resistance, induction or electron beam methods, so that it vaporizes and travels from the course to the substrate with the light-sensitive coating thereon. The high vacuum facilitates evaporation of the metal and the absence of air in the coating chamber permits the vaporized metal to travel directly to the relatively cool coated substrate where it condenses to form a layer having a thickness in the range mentioned above. Processes for vacuum coating are well known as disclosed for example in U.S. Pat. Nos. 2,206,020; 2,562,182; 2,622,041; 2,635,579; 2,643,201; 2,664,852; 2,664,853; 2,665,233-9; 2,665,320; 2,963,521; 2,903,544; and 3,562,141.

Metals readily deposited by vacuum coating normally have a deposition constant of at least 5 .times. 10.sup.-.sup.6 grams per square centimeter per second at 1 micron pressure (absolute). Metals especially suited for vacuum coating include aluminum, silver, gold, lead, zinc, chromium, nickel, copper, tin, iron, platinum and the like.

The above-mentioned coating techniques are well known and widely practiced in the art. Details regarding these techniques including vacuum coating in addition to the above mentioned patents may be found in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Interscience Publishers, New York, 1967, Vol. 13, pages 249 through 284.

While vacuum coated articles are useful per se especially where scratch and abrasion resistance is improved as in the present invention, in many instances it is desirable to further reinforce the vacuum coated structure. This can be done by using conventional electrodeposition techniques to deposit further metal coatings over the vacuum metal layer after exposure of the light-sensitive layer therethrough. An especially suitable electrodeposition technique as referred to is electroless plating and is desirable since the initial vacuum metal layer need only be thick enough for the electroless deposited metal to bridge molecules in the layer. Such electroless plating techniques are well-known and widely practiced in the art. For example, vacuum metal layers according to the invention formed from copper, aluminum, nickel, gold, molybdenum, iron, tin, and platinum will catalyze the electroless chemical reduction deposition of copper, nickel, cobalt, lead, platinum, iron, silver, aluminum, gold, palladium, and magnesium among others. Protective layers formed from cobalt, nickel and iron will also catalyze the deposition of chromium. A preferred metal for electroless deposition is copper which can be accomplished by immersing the structure shown in FIG. 2, for example, in an electroless copper bath containing copper salt, complexing agents to keep the copper in solution and a reducing agent. The electroless clad structure of the present invention is shown in FIG. 3, for example.

The structure shown in FIG. 3 may also be utilized to fabricate further structures. This can be accomplished by electroplating the electroless metal layer 40 with layer 50. Electroplating can be carried out using conventional techniques such as set forth in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Interscience Publishers, New York, 1965, Vol. 8, pages 36-74.

The present invention finds particular application in the making of shaped and flat articles from metal, glass, plastic, composites and the like having a metal finish for use as automotive trim, both interior and exterior, machine parts, decorative trim and plaques and the like. Also and very importantly, the present invention makes it possible to replace relatively heavy and expensive "core" materials with cheaper (e.g. plastic for metal), lighter and in many cases stronger or more resilient materials which can be readily metal clad to retain the desirable properties of the metal exterior. Examples are precious metal figures, jewelery and machine parts and more common articles such as automotive bumpers, rails and the like.

The following examples are intended to further illustrate the present invention without limiting the same in any manner.

GENERAL COATING PROCEDURE

Metal layers according to the present invention are vacuum deposited using a bell jar coater in which a single sample is exposed to a resistance heated vapor source while under vacuum. The sample to be coated is held against a plate at distances ranging between about 10 and 20 inches depending on the metal being vacuum coated. A resistance heated tungsten wire or a molybdenum strip formed into a boat shape so as to contain the material to be evaporated is utilized. Between the vacuum source and the work, a moveable baffle is interposed to allow the material being deposited to attain the proper vaporizing temperature prior to exposure and to time the length of the vacuum coating. The baffle prevents the deposition of powdery or non-adherent coatings which can occur before full vaporizing temperature is reached. The bell jar coater is also provided with sight ports to permit measurements of the vapor source temperature and observation of the melt source itself during the coating operation.

In actual operation, an extruded polyethylene sheet is sensitized with a diazo resin and taped to the plate in a darkened room. A small glass slide strip alongside permits ready measurement of the vacuum deposited coating. Care must be taken to keep the sheet shielded from light while placing it in the bell jar coater. Once the coater is closed, the vacuum pump is started and after a vacuum of about 0.1.mu. is achieved the heat is turned on to melt the metal to be vacuum deposited. When the melt reaches the proper vaporizing temperature, the shutter is opened for a period of time sufficient to deposit a coating of the thickness desired.

PHOTOGLUING PROCEDURE

Vacuum coated, presensitized polyethylene diazo resin sheets are exposed to a source of UV light to render the diazo resin adherent to both the polyethylene sheet and the vacuum metal layer. Scratch and abrasion resistance is then tested by dragging a weighted point across the vacuum metal layer. If no metal is removed the specimen is marked as passing the test and, if metal is removed, the specimen is marked as failing the test. Adhesion is tested by applying a pressure sensitive adhesive tape to the vacuum metal layer and then rapidly stripping it off at a right angle by hand. A pass or fail is noted as in the scratch and abrasion resistance test.

EXAMPLES 1-8

Employing the general coating procedure the following materials are vacuum deposited using the conditions indicated: ##SPC1##

The vacuum metal coatings in Examples 1-8 were approximately 45 to 55 percent transparent.

EXAMPLES 9-11

The specimens prepared in Examples 1 and 5 and 6 are each electroless plated with copper after being exposed to UV using a plating bath containing copper sulfate and a reducing agent for the copper. Excellent coatings are obtained.

EXAMPLE 12

An electroless plated sheets prepared according to Examples 9-11 is electroplated with copper using conventional techniques. Excellent quality coatings are obtained.

Claims

What is claimed is:

1. Metal coated structure comprising

a. a substrate;

b. an actinic-sensitive photochemical coating on said substrate which becomes adherent upon exposure to actinic radiation; and

c. a metal layer over said actinic-sensitive coating which will transmit actinic radiation to initiate a photochemical reaction in the actinic-sensitive coating thereby rendering same adherent to the substrate and the metal layer.

2. Structure of claim 1 wherein said metal layer is vacuum deposited.

3. Structure of claim 1 wherein said metal layer is selected from the group of copper, gold, alloys of copper and gold, silver, aluminum, zinc, nickel and chromium.

4. Structure of claim 1 wherein said metal layer has a thickness of from about 4,000 to about 10,000 Angstroms.

5. Structure of claim 1 wherein said metal layer has a thickness of up to about 1.5 microns.

6. Structure of claim 1 wherein said actinic-sensitive material is a diazo resin.

7. Structure of claim 1 wherein a layer of electroless deposited metal is applied to said metal layer after exposure of the actinic-sensitive layer to actinic radiation.

8. Structure of claim 7 wherein said electroless deposited metal is copper.

9. Structure of claim 7 wherein an electroplated metal layer is applied to said electroless deposited metal layer.

10. Structure of claim 1 exposed to actinic radiation.

11. Structure of claim 1 exposed to actinic heat radiation.

12. Process for making a metal coated structure which comprises coating a substrate having an actinic-sensitive photochemical layer thereon with a metal layer which will transmit actinic radiation to initiate a photochemical reaction in the actinic-sensitive layer thereby rendering same adherent to the substrate and the metal coating.

13. Process of claim 12 wherein said metal layer is vacuum deposited.

14. Process of claim 13 wherein the vacuum deposited metal layer has applied thereto a layer of electroless deposited metal after exposure of the actinic sensitive layer to actinic radiation.

15. Process of claim 14 which includes the step of electroplating a metal layer to the electroless deposited metal layer.