EP0528803A1

EP0528803A1 - Method of masking

Info

Publication number: EP0528803A1
Application number: EP19910906023
Authority: EP
Inventors: John O'rourke
Original assignee: Ford Werke GmbH; Ford France SA; Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Werke GmbH; Ford France SA; Ford Motor Co Ltd; Ford Motor Co
Priority date: 1990-03-15
Filing date: 1991-03-15
Publication date: 1993-03-03
Also published as: GB2241907A; GB9005789D0; WO1991013692A1

Abstract

Afin de masquer une partie de la surface d'un article avant de le peindre, l'on forme une crête (16) sur la surface (18, 20) de l'article à l'endroit où doit se trouver la limite de la couche de peinture. Ensuite, on arrose la totalité de l'article d'une substance de masquage (24) de sorte qu'une couche à épaisseur réduite soit formée au niveau de la crête. Lorsque ladite substance est sèche, on peut la détacher de la surface (20) de l'article et l'on pourra voir que la couche située d'un côté de la crête se sépare de la couche située de l'autre côté de la crête en laissant intacte et prête à l'usage la substance de masquage située d'un côté de la crête (16). On peut ensuite peindre l'article avant d'enlever la substance de masquage de l'autre côté de ladite crête (16).In order to mask part of the surface of an article before painting it, a crest (16) is formed on the surface (18, 20) of the article at the point where the limit of the coat of paint. Then, the entire article is sprayed with a masking substance (24) so that a reduced thickness layer is formed at the crest. When said substance is dry, it can be detached from the surface (20) of the article and it can be seen that the layer located on one side of the ridge separates from the layer located on the other side of the ridge leaving the masking substance located on one side of the ridge (16) intact and ready for use. The article can then be painted before removing the masking substance on the other side of said crest (16).

Description

Method of masking

FIELD OF THE INVENTION

This invention relates to a method of masking an article to be spray coated so that the coating can be applied to an unmasked part of the article, and not to a masked part of the article. The invention is particularly, but not exclusively, intended for use with a spray painting process.

DESCRIPTION OF PRIOR ART

It is known to carry out such masking by attaching a layer of masking material over the part of the article to be masked. However where this masking layer is applied manually using sheet material and self-adhesive tape, it is difficult to ensure that it is applied regularly and correctly to produce an even edge to the painted area. This is a particular problem for mass-production. It is also known to apply a maskant to a surface using spray application, followed by the use of a blade to cut a clean edge at the place where the masking is to be effective.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method of masking part of an article which is to have a sprayed coating applied to a first region and another surface finish on a second region, comprising the steps of designing the article surface and/or the desired sprayed coating so that an edge of the coating is to coincide with a surface irregularity on the article surface which divides the first region from the second region, spraying the whole article surface with a sprayable masking material (hereinafter called a maskant) in such a way that a reduced thickness of maskant exists on an area of the surface associated with the irregularity, and peeling part of the maskant, as a sheet, from the first region of the article in such a manner that the maskant separates along the irregularity.

The surface irregularity preferably includes an edge with a radius of less than 0.5 mm. The use of an edge allows the formation of an area of reduced thickness through the surface tension of the liquid maskant which, on application, migrates away from the edge to reduce its

10 surface area.

The area where a reduced thickness of maskant exists may be a layer of maskant which is thinner than the remainder of the maskant, or may be an area entirely devoid of 15 maskant.

The sprayed coating will normally be paint, but the invention can also be used with other types of sprayed coating. 20

Preferably the maskant is sprayed to give a coating over the major part of the article with a thickness of at least 85 microns.

25 According to a second aspect of the invention, there is provided a method of painting part of an article, the method comprising the steps of designing the article surface and/or the desired paint coating so that an edge of the coating is to coincide with a surface irregularity

30 on the article surface, spraying the whole article surface with a sprayable maskant, peeling part of the maskant, as a sheet, from said part of the article in such a manner that the mask material separates along the irregularity, leaving part of the maskant adhered to the article surface

35 on one side of the irregularity, painting the article surface, including both sides of the irregularity, and then peeling the remainder of the maskant from the article. The area of reduced thickness is preferably formed by directing the spraying operation relative to the ridge so that a part of the surface extending alongside the ridge is partially or wholly shielded from the spray. For example if part of the surface alongside the ridge is parallel with the direction from which the spray approaches the surface, then an area of reduced thickness will be formed on that part of the surface.

The mask material on one side of the ridge can be removed simply by pulling it off and the material will then tear along the area of reduced thickness so that the mask material on the other side of the ridge remains in place. Subsequently the article can be painted, and once the paint has dried the remainder of the mask material can be peeled off, leaving a sharp edge to the painted area.

Sprayable materials suitable for paint masking are known. One such material is a strippable or peelable coating manufactured by the 3M's company and sold under the number YR43. This is an aqueous coating material which can be sprayed onto a plastics article to provide a thick film. The film has sufficient adhesion to plastics surfaces such as polycarbonate or polypropylene to prevent paint penetrating between the film and the surface, but the dry film strength and the adhesion to the surface are such that the film can be peeled off as a continuous sheet.

We have now found that if a ridge is incorporated in the surface of the article, then when the film is peeled off, the film on one side of the ridge separates from the film on the other side of the ridge, i.e. the film on one side of the ridge can be peeled off whilst the film on the other side remains intact.

According to a third aspect of the invention, there is provided a method of masking part of an article before applying a sprayed coating to the article, the method comprising the steps of designing the article surface and/or the desired coating so that an edge of the coating is to coincide with a sharp ridge on the article, spraying the whole article surface with a sprayable maskant, and peeling part of the mask material, as a sheet, from said part of the article in such a manner that the mask material separates along the sharp ridge.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of part of an article to be masked and then painted;

Figures 2, 3, 4 and 5 are successive stages in the masking and pointing process shown in relation to a cross section through the article surface of Figure 1; and

Figure 6 shows part of a motor vehicle bumper which has a surface configuration adapted for use in the method of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a component surface on an enlarged scale. The surface is formed with two parallel valleys 12, 14 separated by a sharp ridge 16. The ridge 16 is below the major surface of the component so that it is not exposed at the front surface of the component.

The technology to design such a groove into a moulded article such as a vehicle bumper is in itself well known and styling lines running horizontally across the bumper are often used by vehicle stylists. The modification of such a line to incorporate a sharp ridge would not be difficult.

In use, where the area 18 of the surface on one side of the ridge 16 is to be painted a different colour or finished differently from the surface 20 on the other side, then the procedure illustrated in Figures 2, 3, 4 and 5 is followed.

First of all as shown in Figure 2 a continuous layer 24 of a sprayable strippable maskant is applied to the whole of the surface. The maskant, being a low-viscosity liquid on application, will run away from the ridge 16 as a consequence of the surface tension of the liquid which tries to establish a minimum surface area for the liquid across the ridge. As a result, a very thin layer of maskant will remain on the ridge 16 itself, with a thicker layer remaining on all other parts of the surface.

A suitable sprayable maskant is the 3M,'s coating known under the designation YR43. This can be sprayed as a 50% solution in water and should be sprayed at a density to produce a dry film thickness of 130 to 170 microns.

Once dry, this material can be peeled off the surface in one continuous strip by lifting a corner of the film using a finger nail or the like. If a corner on the surface 20 is lifted and the film stripped off it will be found that the film tears at the reduced thickness part of the film 24 which will be located immediately adjacent the ridge 16. The part of the film on one side of the ridge therefore separates from the part of the film 27 on the opposite side of the ridge. Pulling off the film will result in the condition shown in Figure 3 where the surface 18 is masked but the surface 20 is not, and the edge of the mask material lies reliably along the ridge 16 which is a feature of the moulded surface. The rest of the process is conventional. A layer of paint 26 is applied over the whole surface as shown in Figure 4. In fact the paint 26 may not cover the whole of the masked surface 18, but will be sprayed at full application thickness up to the ridge 16 and beyond. Once the paint has dried sufficiently, the mask film on the right hand side 18 of the surface is pulled off to leave the surface in the condition as shown in Figure 5 with one side properly painted and the other side unpainted. The surface may be left in this condition or, if it is desired to paint the surface 18 in a contrasting colour, then the process shown in the above four Figures can be repeated to produce an interface between the two colours along the ridge 16.

The ridge 16 has been described as "sharp", and the actual form of the. ridge is significant. The method described here depends on the creation of an area of reduced thickness along the line of the ridge. The thickness reduction must be such that the surface is still covered, but at a layer thickness substantially less than that over the remainder of the surface so that the film tears readily along the ridge where the film is at its thinnest. The thickness reduction occurs as a result of the influence of the surface tension of the liquid when it iε sprayed onto the surface.

Figure 6 shows a moulded-in ridge 30 forming part of the outer skin of a bumper moulding 32. The ridge itself is located at the bottom of a recess 34 which runs along the bumper surface. The separation line caused by the tearing of the maskant film will therefore lie at the bottom of the recess, so that any imperfections in the interface between two areas will not be too noticeable, and the presence of the ridge 30 itself will not be noticeable. Where painting is desired on both sides of the ridge, then the contours of either side of the ridge are preferably the same. In Figure 6, the ridge 30 may have a radius of 0.06 mm and a height of 0.6 mm. The depth of the recess can be 2 mm.

It will be appreciated that many different surface formations could be used to produce the desired area of reduced thickness in the sprayed coating, and that the configurations shown are merely examples of such formations.

Claims

1. A method of masking part of an article which is to have a sprayed coating applied to a first region and another surface finish on a second region, comprising the steps of designing the article surface and/or the desired sprayed coating so that an edge of the coating is to coincide with a surface irregularity on the article surface which divides the first region from the second region, spraying the whole article surface with a sprayable masking material (hereinafter called a maskant) in such a way that a reduced thickness of maskant exists on an area of the surface associated with the irregularity, and peeling part of the maskant, as a sheet, from the first region of the article in such a manner that the maskant separates along the irregularity.

2. A method as claimed in Claim 1, wherein the surface irregularity includes an edge with a radius of less than

0.5 mm.

3. A method as claimed in Claim 1 or Claim 2, wherein the area where a reduced thickness of maskant exists is covered by a layer of maskant thinner than the remainder of the maskant.

4. A method as claimed in claim 1 or Claim 2, wherein the area where a reduced thickness of maskant exists is devoid of maskant.

5. A method as claimed in any preceding claim, wherein the sprayed coating is paint.

6. A method as claimed in any preceding claim, wherein the maskant is sprayed to give a coating of at least 85 microns.

7. A method of painting part of an article, the method comprising the steps of designing the article surface and/or the desired paint coating so that an edge of the coating is to coincide with a surface irregularity on the article surface, spraying the whole article surface with a sprayable maskant, peeling part of the maskant, as a sheet, from said part of the article in such a manner that the mask material separates along the irregularity, leaving part of the maskant adhered to the article surface on one side of the irregularity, painting the article surface, including both sides of the irregularity, and then peeling the remainder of the maskant from the article.

8. A method as claimed in Claim 7, wherein the painting is carried out by spraying.

9. A method as claimed in Claim 7 or Claim 8, wherein sprayable maskant is applied a second time to the article, part of the mask material is stripped from the area which has not been painted, that area is painted, and the remainder of the mask material is then peeled off.

10. A method as claimed in any preceding claim, wherein the sprayable maskant is the 3M strippable coating YR43.

11. A method of masking part of an article before applying a sprayed coating to the article, the method comprising the steps of designing the article surface and/or the desired coating so that an edge of the coating is to coincide with a sharp ridge on the article, spraying the whole article surface with a sprayable maskant, and peeling part of the mask material, as a sheet, from said part of the article in such a manner that the mask material separates along the sharp ridge.