GB1567873A

GB1567873A - Strippable protective coatings

Info

Publication number: GB1567873A
Application number: GB54120/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-01-10
Filing date: 1977-12-29
Publication date: 1980-05-21
Also published as: JPS53111341A; DE2800870A1

Description

(54) STRIPPABLE PROTECTIVE COATINGS (71) I, WALTER HERBERT SPIETH, of 58, Eccleston Crescent, Kleve Hill Park, Sandton, Transvaal, Republic of South Africa, a citizen of the German Federal Republic, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to strippable protective coatings for substrates. In particular the invention relates to a method for providing protective coatings for substrates such as finished metal products and the products coated with this protective material.

In the Applicant's knowledge protective coatings to metal products such as door frames, metal sections and extrusions, motor and electrical spare parts as well as refrigerators and appliances, generally are effected by coating the product with a removable lacquer. This lacquer is easily stripped from the finished product when no longer required. In the Applicant's experience, however, the lacquer tends to lose its protective quality especially when exposed to the elements for a lengthy time or it adheres to the substrate or tends to chip and be broken quite easily and as such does not provide a strippable protective coating which is as effective as it might be.

According to the invention a method of protecting a substrate by providing a protective film thereon includes the steps of coating the substrate with a synthetic resinous powder and heat treating the powder to form an unfoamed film which is removeable from the substrate in peel-off fashion. The term "unfoamed film" herein means a film which is substantially free of gas cavities.

Preferably the powder is of a thermoplastic character.

Suitable materials for the powder may be a polyethylene, a polyvinylchloride, or a polyamide homo-polymer or co-polymer, or a mixture thereof.

In a preferred feature of the invention the substrate is coated with sufficient powder to provide a film of a thickness in excess of 20 microns.

In a further preferred feature of the invention the powder is applied to the substrate by means of an electrostatic spraying process.

Alternatively, the powder may be applied by immersing the substrate in a bath of powder which may be fluidised or static. In this method the substrate is preferably heated prior to immersion to permit the powder to consolidate on the substrate.

The heat treating step preferably comprises heating the powder to a molten, substantially flowable state, and thereafter permitting the molten material to solidify. If desirable, the molten material may be solidified by quenching in a liquid.

Preferably the particle size of the powder is between 30 and 500 microns.

It is further intended to include within the scope of this invention an article having a surface provided with a protective coating in accordance with the method of the invention.

In order more clearly to illustrate the invention some examples thereof are described hereunder.

In practice a protective film in accordance with the method of the invention will, for example, be applied to finished articles of metal, glass, or plastics. Metal articles, other than those of stainless steel, will normally be provided with a finishing coat of paint or enamel prior to the application of the protective film. The protective film will thus serve to protect the finished article during transport, storage, etc.

It is also believed that the film of the invention will find application in manufacturing processes. For example, where polished stainless steel sheeting is to be bent or deformed in a manufacturing process, the film may be applied prior to such bending process to prevent damage to the polished surface.

Some results obtained by applying protective films to articles are set out below.

Example 1): A stainless steel sheet, 22 gge, was coated with a soft type PVC powder (ISOSPRAY) in a cold spray operation, using a GEMA electrostatic spray gun, negative polarity, 95 kV. The panel was subsequently cured in a hot-air convection oven at a temperature of 220"C and, after Ieaving the oven, was quenched with cold water. A uniform film 30 microns thick was obtained which could easily be stripped-off after breaking it at the edge.

Example 2): An aluminium extrusion of irregular shape, 1 m long, average 2 mm thick, was cold sprayed with the PVC powder described in Example 1) at 75 kV, subsequently heat treated 4 1/2 minutes at 3300C, cold water quenched. Uniform film build of 70 microns was obtained which could easily be stripped off.

Example 3): Aluminium extrusion with an anodized surface: treatment and results same as in Example 2) except that in this case the powder used was type "Flamulit" ES PVC 32.

Example 4): Aluminium extrustion with a white Duroplastic*-coated (polyester) finished surface. The object was sprayed with PVC powder at 65 kV, negative polarity, heat treatment and quenching as in Example 2). Result: uniform film of approximately 90 micron, easily strippable.

*Manufacturer's trade name.

Example 5): Object same as Example 4), i.e. polyester powder coated aluminium extrusion. Before spraying, the object was heated up to a temperature of 220 C, it was then coated with a fluid-bed grade polyethylene powder, particle size ranging from 150 - 300 microns (type Flamulit WS PE 21) by means of GEMA electrostatic spray gun, positive polarity, at 75 kV until a visually coherent film was produced on the object surface. The object was subsequently postcured at 220"C for 2 minutes and finally quenched. Result was a uniform film approximately 220 microns thick, which could easily be peeled off after breaking the edge.

Example 6): The methods employed in Examples 4) and 5) were, with equal results, employed also on aluminium and steel articles which had previously been finished off in an industrial baked enamel.

Example 7): A chrome-plated motor car hub cap (Mercedes) was coated alternatively in the methods described under Examples and 5), with results same as described under the respective cases.

Example 8): An electric household iron was switched on until its base plate reached 200"C. The base was then pressed onto a flat bed of static (non-fluidised) polyethylene powder for 2 seconds, then left to cool off.

Result: a fairly even film approximately 300 microns thick which could easily be stripped off after breaking the edge.

Example 9): A vitreous enamel-coated wash basin was treated in the method described under Example 5) with the same result.

Example 10): Part of a steel window frame, 3 mm steel, which had previously been coated with a thermo-setting polyester powder, was taken off the line after leaving the curing oven, then dipped for 3 seconds into a bed of fluidised polyethylene powder (as commercially supplied by A.E. & C.I.), then left to cool off. Result: a rather thick film (500 microns), easily strippable.

Example 11): A motor car crank shaft: the machined surfaces were alternatively treated as in Example 1) and 5) above, with corresponding results. During spraying, the unmachined parts were masked off.

Example 12): A glass plate 0,3 x 0,3 m. 3 mm thick, backed by a steel plate for earthing, was powder coated as described in Example 1), subsequently heat treated in 220"C for 8 minutes, then allowed to cool off. Result: a uniform coat 60 microns thick, easily peeling off.

One may choose between a variety of powders to suit requirements. PVC powders can be used either in a hard or soft setting.

All PVC powders are extremely chemical resistant. The "soft" type PVC powders vary from the "hard" PVC powders in that they have a high degree of elasticity, which renders them suitable protecting surfaces during subsequent manufacturing or deforming stages.

Polyethylene powders, for instance, could be selected for their high mechanical resistances, and durability for the purposes of long-term storage, rough handling during transport and similar. They wouId not be suitable where high flexibility is required.

WHAT I CLAIM IS: 1. A method of protecting a substrate by providing a protective film thereon including the steps of coating the substrate with a synthetic resinous powder, and heat treating the powder to form an unfoamed film which is removeable from the substrate in peel-off fashion.

2. A method according to claim 1 wherein the powder is of a thermoplastic character.

3. A method according to claim 1 or claim 2 wherein the powder is a polyethylene, a polyvinylchloride, or a polyamide homo-polymer or co-polymer, or a mixture thereof.

4. A method according to any one of claims 1 - 3 wherein the substrate is coated with sufficient powder to provide a film of a thickness in excess of 20 microns.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. process to prevent damage to the polished surface. Some results obtained by applying protective films to articles are set out below. Example 1): A stainless steel sheet, 22 gge, was coated with a soft type PVC powder (ISOSPRAY) in a cold spray operation, using a GEMA electrostatic spray gun, negative polarity, 95 kV. The panel was subsequently cured in a hot-air convection oven at a temperature of 220"C and, after Ieaving the oven, was quenched with cold water. A uniform film 30 microns thick was obtained which could easily be stripped-off after breaking it at the edge. Example 2): An aluminium extrusion of irregular shape, 1 m long, average 2 mm thick, was cold sprayed with the PVC powder described in Example 1) at 75 kV, subsequently heat treated 4 1/2 minutes at 3300C, cold water quenched. Uniform film build of 70 microns was obtained which could easily be stripped off. Example 3): Aluminium extrusion with an anodized surface: treatment and results same as in Example 2) except that in this case the powder used was type "Flamulit" ES PVC 32. Example 4): Aluminium extrustion with a white Duroplastic*-coated (polyester) finished surface. The object was sprayed with PVC powder at 65 kV, negative polarity, heat treatment and quenching as in Example 2). Result: uniform film of approximately 90 micron, easily strippable. *Manufacturer's trade name. Example 5): Object same as Example 4), i.e. polyester powder coated aluminium extrusion. Before spraying, the object was heated up to a temperature of 220 C, it was then coated with a fluid-bed grade polyethylene powder, particle size ranging from 150 - 300 microns (type Flamulit WS PE 21) by means of GEMA electrostatic spray gun, positive polarity, at 75 kV until a visually coherent film was produced on the object surface. The object was subsequently postcured at 220"C for 2 minutes and finally quenched. Result was a uniform film approximately 220 microns thick, which could easily be peeled off after breaking the edge. Example 6): The methods employed in Examples 4) and 5) were, with equal results, employed also on aluminium and steel articles which had previously been finished off in an industrial baked enamel. Example 7): A chrome-plated motor car hub cap (Mercedes) was coated alternatively in the methods described under Examples and 5), with results same as described under the respective cases. Example 8): An electric household iron was switched on until its base plate reached 200"C. The base was then pressed onto a flat bed of static (non-fluidised) polyethylene powder for 2 seconds, then left to cool off. Result: a fairly even film approximately 300 microns thick which could easily be stripped off after breaking the edge. Example 9): A vitreous enamel-coated wash basin was treated in the method described under Example 5) with the same result. Example 10): Part of a steel window frame, 3 mm steel, which had previously been coated with a thermo-setting polyester powder, was taken off the line after leaving the curing oven, then dipped for 3 seconds into a bed of fluidised polyethylene powder (as commercially supplied by A.E. & C.I.), then left to cool off. Result: a rather thick film (500 microns), easily strippable. Example 11): A motor car crank shaft: the machined surfaces were alternatively treated as in Example 1) and 5) above, with corresponding results. During spraying, the unmachined parts were masked off. Example 12): A glass plate 0,3 x 0,3 m. 3 mm thick, backed by a steel plate for earthing, was powder coated as described in Example 1), subsequently heat treated in 220"C for 8 minutes, then allowed to cool off. Result: a uniform coat 60 microns thick, easily peeling off. One may choose between a variety of powders to suit requirements. PVC powders can be used either in a hard or soft setting. All PVC powders are extremely chemical resistant. The "soft" type PVC powders vary from the "hard" PVC powders in that they have a high degree of elasticity, which renders them suitable protecting surfaces during subsequent manufacturing or deforming stages. Polyethylene powders, for instance, could be selected for their high mechanical resistances, and durability for the purposes of long-term storage, rough handling during transport and similar. They wouId not be suitable where high flexibility is required. WHAT I CLAIM IS:

1. A method of protecting a substrate by providing a protective film thereon including the steps of coating the substrate with a synthetic resinous powder, and heat treating the powder to form an unfoamed film which is removeable from the substrate in peel-off fashion.

5. A method according to any one of

claims I - 4 wherein the particle size of the powder is between 30 and 500 microns.

6. A method according to any one of claims 1 - 5 wherein the powder is applied to the substrate by means of an electrostatic spraying process.

7. A method according to any one of claims l - 5 wherein the powder is applied to the substrate by immersing the substrate in a fluidised or static hath of powder, the substratc being heated to a sufficient degree to permit the powder to consolidate on the substrate.

8. A method according to any one of claims 1 - 7 wherein the heat treating step comprises heating the powder to a molten, substantially flowable state, and thereafter permitting the molten material to solidify.

9 A method according to claim 8 wherein the molten material is caused to solidify by quenching in a liquid.

l(). A method of protecting a substrate by providing a protective film thereon substantially as herein described with reference to the examples.

l 1. An article provided with a protective film on at least part thereof, substantially in accordance with the method claimed in any one of claims l - 10.