GB2200359A

GB2200359A - Corona discharge treatment of plastic film for a paint or lacquer mask

Info

Publication number: GB2200359A
Application number: GB08720224A
Authority: GB
Inventors: Stephanie Horn
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-02-02
Filing date: 1987-08-27
Publication date: 1988-08-03
Anticipated expiration: 2007-08-27
Also published as: DE3865978D1; FR2610222B1; ATE69180T1; DE3702982C2; NO880433L; DK49888A; EP0277552B1; GR3003201T3; DK167245B1; DE3702982A1; DK49888D0; EP0277552A2; GB8720224D0; ES2027708T3; FR2610222A1; EP0277552A3; CA1330965C; GB2200359B; NO880433D0

Abstract

Sheet-like or cap-like mask for paint work on motor vehicles or parts thereof, which is characterised in that a plastic film is used as the mask, at least one surface of which is treated by the corona process. <IMAGE>

Description

A PAINT OR LACQUER MASK The present invention relates to a paint or lacquer mask, for example a mask mountable on a motor vehicle or a part thereof during the performance of a lacquering operation, and to methods of producing and using such a mask.

During lacquering operations in motor vehicle painting, especially when the lacquer colour to be applied is sprayed on, masks are required so that areas not to be lacquered are not coated by paint mist.

Usually, paper, which is absorbent and can take up the excess paint, is used as a masking means. It is, however, disadvantageous that the paper to be used must have a certain strength and a certain quality in order to be suitable for this purpose. If the paper is too thin or too light, the sprayed-on paint can penetrate and reach the surface to be protected. The costs for masking paper are therefore relatively high. This is particularly so in the motor vehicle industry, where great quantities of such masking paper are consumed.

A further disadvantage of such masking paper is that paper saturated by lacquer paint cannot be reused for paper manufacture, due.

to the chemical components of the lacquer paint. The known environmental compatibility of the paper is not the same in the case of wastes contaminated with lacquer. The waste paper must therefore be deposited on special waste tips or burnt.

In DE-PS 16 46 100 there is disclosed a masking hood which is adapted to the shape of a motor vehicle and which includes several portions which can be tilted up. The hood consists of a textile material provided with a surface coating. Masking hoods of that kind are very heavy and difficult to manipulate and can be reused only a limited number of times, since they become stiff in time due to the lacquer residues and no longer adaptible to the vehicle shape. Such hoods are, moreover, very expensive.

Also known are dust protection covers of synthetic material film, which are used in paint shops for covering parked vehicles not subjected to the lacquer operation. The covering in this case, however, is required in order to protect vehicles from airborne lacquer residues so that these do not precipitate on the surfaces of such vehicles.

These covers are not suitable as masks for lacquering operations, since lacquer paint dries very rapidly on the film and peels off on removal of the film. The peeled-off lacquer can fall on the neighbouring, freshly lacquered and still wet surface, which is then spoiled.

Moreover, it is known during lacquering to place masking films of synthetic material over car wheels in order to protect them during the lacquering of the body. Here, too, there is the same problem that the paint on the film peels off on removal of the film and can fall onto the freshly lacquered surfaces. This can mean that the surface has to be cleaned down again, preliminarily treated and relacquered.

It is known to print on synthetic material film, in which case the film must be preliminarily treated by a corona process so that the printing ink to be applied adheres to the film. In this process, the film is passed through an electric field, in which a corona discharge takes place and leads to a surface change in the film. The causes of this surface change have not been explained exactly. Presumably, molecules are broken up in the surface region of the film and can then enter into a firm connection with the printing ink. During the corona discharge, ozone also arises, which possibly combines with the molecules at the surface of the film, whereby the surface tension is reduced.

Moreover, the surface could be roughened through micropores due to the heat arising during the corona discharge so that the printing ink finds a good adhesion base.

The printing process, however, takes place directly after the corona treatment and the printing ink is applied in an extremely thin, barely measurable, layer. For that reason, the problem of a transit time effect on the corona treatment does not arise. The corona treatment need be performed only with an intensity sufficient to allow the ink to immediately adhere.

There is thus a need for a mask for lacquering operations, which reduces or eliminates the above-described disadvantages, is relatively economic to manufacture, is simple and secure to handle and does not require additional aids such as paper webs or the like. Moreover, the mask should preferably be capable of being easily destroyed.

According to a first aspect of the present invention there is provided a paint or lacquer mask comprising a film of plastics material treated at at least one surface thereof by a corona discharge process.

According to a second aspect of the present invention there is provided a method of producing a paint or lacquer mask, comprising the step of treating at least one surface of a film of plastics material by a corona discharge process.

Through this treatment, it is possible for lacquer to adhere to the film without peeling-off when dry. It is of particular significance that the lacquer, even when it forms a layer of appreciable thickness on the film, remains adhering when the film is taken off the vehicle and possibly stressed, in particular creased. This has hitherto not been regarded as possible, since synthetic material films as is known have a wax-like surface to which lacquer does not adhere, but peels off even with slight stressing.

By comparison with paper, the film has a very low weight per unit area so that the waste quantity is smaller. Disposal is therefore simpler than in the case of paper, since the film can be burned and it is only necessary to take care of the lacquer residues. The heating value of the film is relatively high, so that combustion in a heating system is possible. Solid residues, such as in the case of paper, do not arise to such- an extent and the waste gases are not dangerous in the case of polyethylene. Merely the waste gases from the lacquer are to be taken care of.

Preferably, the surface treatment is so performed with the intensity chosen to be so high that a surface tension or wetting tension of at least 45 dynes per square centimetre is attained at the film surface. With this wetting tension, it is ensured that the lacquer adheres in desired manner to the film. Known corona process treatment for the printing on synthetic material film merely achieve wetting tensions of below 40 dynes per square centimetre. The intensity of the preliminary treatment in that case can be of such height, by way of the electrical power per unit area (watts per square centimetre) in the corona treatment and by way of the transit speed of the film during the treatment, that the desired surface tension or wetting tension of at least 45 dynes per square centimetre is attained.

The intensity of the treatment can thus be set through the electrical power per unit area (watts per square centimetre) and through the speed of the film, wherein a high power per unit area (watts per square centimetre) takes care of a high treatment intensity at low speed.

Through choice of these parameters, the treatment can be adapted in simple manner to the particular properties of the film material.

Expediently, the composition of the film synthetic material is such that a surface or wetting tension of at least 45 dynes per square centimetre is achievable after the corona treatment. The maximally achievable surface or wetting tension may be dependent on the material and unable to be increased as desired even in the case of the strongest preliminary treatment. In order to be able to achieve adequate values, it may be desirable to keep the proportion of alubricant as small as possible or to dispense with the use of lubricants completely. The intensity of the preliminary treatment and the small proportion of lubricants both contribute towards achieving the desired result.

Lubricants serve to form the film surface so that an extruded film hose can be opened after production. They are therefore responsible for a wax-like repellent surface which impairs adhesion of lacquer.

Other additives, for example anti-statics, have only a small influence on the adhesion capability of the lacquer. In order further to increase the adhesion capability of the lacquer, chalk can also be added to the film material, so as to provide a relatively rough surface.

The film material can consist of polyethylene, from which film can be economically produced and which can be further processed in simple manner.

The polyethylene film can contain a combination of different polyethylenes and additives and have a composition of, for example, at least 45% by weight of linear polyethylene (LLDPE), 10 to 50% by weight of high density polyethylene (LDPE), 0.5 to 10% by weight of low density polyethylene (HDPE), 0.1 to 5% by weight of oleamides or erucamides or natural silica and up to about 5% by weight of fatty acid esters, dyestuffs, synthetic silica, stabilisers and processing aids, wherein the sum of these components amounts to 100% by weight.

Apart from hoods and tapes, prefabricated moulded parts, for example for the masking of a vehicle bootlid or bonnet, can be produced from the film. Such moulded parts can be tailored to the respective use so as to be able to be mounted in simplest manner without further operating steps, such as cutting to size.

A thus composed film can be blown out to be very thin and, in spite of its small thickness, have good mechanical properties, such as high extensibility and a high tear strength.

If the intensity of the preliminary treatment is selected so that relaxation of the surface properties of the film is taken into consideration, the resulting mask is usable for lacquering operations taking place some time after the preliminary treatment without reduction in its efficacy. In the known printing process, printing takes -place immediately after the preparation. The effect of the preliminary treatment may reduce, however, which was hitherto unknown. Since lacquering operations usually do not take place immediately following the film production, but weeks or months later, it is desirable to structure the preliminary treatment so that a sufficient adhesion base for the lacquer is present even after a relatively long time. In that case, the intensity of the preliminary treatment can be chosen to take such account of relaxation of the surface properties of the treated film that a surface or wetting tension of at least 45 dynes per square centimetre occurs at the film surface after a time interval of about 6 months. It has proved that the surface properties of the film do not significantly change after about 6 months and a quasi-stable state sets in. The usability of the film therefore is not lost even with extended delays between preliminary treatment and use. This long storage life simplifies inventorising and enables cost savings.

The film can be made of a compound material. It then consists of several layers of different material chosen to correspond to the respective task. For example, the side resting on the vehicle can consist of a dull to sticky material so that slipping of the film on the vehicle is excluded. The other side of the film can then be formed of a material which has good adhesion properties or receives them through the preliminary treatment.

The film can also be preliminarily treated on both sides. The treated surface of such a film is not recognisable by the naked eye and treatment of both sides ensures that a surface capable of adhesion is invariably presented outwardly for lacquering operations.

In general, synthetic material films can be produced simply and economically, with very long strips or webs being producible without interruption. These strips can be guided through equipment which operates to provide the corona process. The treatment can thereby take place continuously.

According to a third aspect of the present invention there is provided a method of paint or lacquer coating a first surface portion adjoining or in the region of a second surface portion to be kept free of the paint or lacquer used in the coating process, the method comprising the steps of so covering the second surface portion with a mask according to the first aspect of the invention or produced by a method according to the second aspect of the invention that said at least one surface of the film faces outwardly and spraying paint or lacquer onto the first surface portion.

An embodiment of the mask and an example of the method of the present invention will now be more particularly described with reference to the accompanying drawing, the single figure of which is a schematic illustration of preliminary corona treatment equipment for performance of a method exemplifying the invention.

Referring now to the drawing, there is shown preliminary corona treatment equipment in which a synthetic material film 1 to be treated runs over a roller 2, which is electrically conductive and earthed.

Electrodes 3 are arranged at a certain spacing above the film and are connected by way of a high tension transformer 4 to an alternating current generator 5.

Through the application of a certain electrical power per unit area (watts per square centimetre) at a certain frequency, a corona discharge arises between the film 1 and the electrodes 3. Through this discharge, the surface of the film is changed so that it can later enter into a firm connection with sprayed-on lacquer paint. The surface is roughened by the discharge, whereby micropores arise.

Additionally, a chemical change may occur so that the film can chemically bond with the lacquer. The adhesion of the lacquer to the film 1 is appreciably improved by the treatment and peeling-off of the dried lacquer is largely or entirely excluded.

The intensity of the preliminary treatment is determined on the one hand by the height and frequency of the power per unit area (watts per square centimetre) at the electrodes 3 and on the other hand by the transit speed of the film 1 through the equipment. These parameters can be changed in simple manner for adaptation to the composition of the film material.

The intensity of the preliminary treatment is preferably set so that-a surface or wetting tension of at least 45 dynes per square centimetre is attained at the surface of the film. This value is higher than in the case of known printing processes on films.

It can also be taken into consideration that the maximum achievable values are al-so dependent on the kind of the synthetic material employed.

The material of the film can accordingly be selected so that high surface tensions are achievable. For this purpose, the proportion of the usually added lubricant can be kept as small as possible. Such lubricants normally ensure that the extruded film hose can be opened after production and the adjacent film surfaces separated from each other. The lubricants result in a wax-like surface which is obstructive to the application of lacquer paint. The other additive substances are less significant in this connection.

Polyethylene, which can be processed easily and economically, is particularly suitable for the film. In trials, a preferred combination has proved to be composed of different polyethylenes and oleamides, preferably a mixture of at least 45% by weight of linear polyethylene (LLDPE), 10 to 50% by weight of high pressure polyethylene (LDPE), 0.5 to 10% by weight of low pressure polyethylene (HDPE), 0.1 to 5% by weight of oleamides or erucamides and natural silica, and up to about 5% by weight of fatty acid esters, dyestuffs, synthetic silica, stabilisers and processing means. A film produced of this material mixture is extensible and tear-resistant, can be blown out to be very thin and can be provided with a well adhering surface through the preliminary corona treatment.

It has proved that the surface properties of the film change with time after the preliminary treatment and that the surface tension falls off. The intensity of the preliminary treatment is therefore preferably set so high that an adequate adhesion capability is still present when a lacquer operation is carried out after an extended period of time.

Trials have shown that the intensity of the preliminary treatment should preferably be set so that a surface tension of at least 45 dynes per square centimetre is still present 6 months after the preliminary treatment. After 6 months, according to experience, no further significant change occurs and the surface state of the film remains relatively stable.

The preliminary treatment of the film can be undertaken on both surfaces, in which case a second preliminary treatment station can be provided. The treated surface of the film is not recognisable by the naked eye, so that in the case of a film treated at both sides it is ensured that a treated surface will always be presented outwardly in a masking and lacquering operation.

The film thus treated can be formed into a tape or hood which can be utilised for the.masking of a motor vehicle. On the other hand, a shaped part can also be produced, by which doors, engine hoods, lids and the like can be masked without these parts having to be cut to size individually.

Claims

1. A paint or lacquer mask comprising a film of plastics material treated at at least one surface thereof by a corona discharge process.

2. A mask as claimed in claim 1, wherein the surface tension or wetting tension of said at least one surface is at least equal to 45 dynes per square centimetre.

3. A mask as claimed in either claim 1 or claim 2, wherein the film material comprises a lubricant component present in minimum quantity.

4. A mask as claimed in any one of the preceding claims, wherein the film material comprises chalk.

5. A mask as claimed in any one of the preceding claims, wherein the film material is polyethylene.

6. A mask as claimed in any one of the preceding claims, wherein the film material consists of at least 45% by weight of linear polyethylene.

10 to 50% by weight of high density polyethylene, 0.5 to 10% by weight of lower density polyethylene, 0.1 to 5% by weight of oleamides, erucamides or natural silica, and up to substantially 5% by weight of fatty acid esters, dyestuffs, synthetic silica, stabilisers and processing aids.

7. A mask as claimed in any one of the preceding claims, wherein the mask is one of a hood, a tape and a prefabricated moulded part.

8. A mask as claimed in claim 7, wherein the moulded part is adapted for masking a motor vehicle bonnet or bootlid.

9. A mask as claimed in any one of the preceding claims, wherein the film is a laminate material.

10. A mask as claimed in any one of the preceding claims, wherein the film is treated by a corona discharge process at both sides thereof.

11. A method of producing a paint or lacquer mask, comprising the step of treating at least one surface of a film of plastics material by a corona discharge process.

12. A method as claimed in claim 11, wherein the step of treating is carried out at such an intensity that the surface tension or wetting tension of said at least one surface is at least equal to 45 dynes per square centimetre.

13. A method as claimed in claim 11, wherein the step of treating is carried out at such an electrical power per unit area and at such a transit speed of the film that the surface tension or wetting tension of said at least one surface is at least equal to 45 dynes per square centimetre.

14. A method as claimed in claim 11, wherein the composition of the material of the film is so selected that a surface tension or wetting tension of said at least one surface of at least 45 dynes per square centimetre is achievable by the corona discharge process.

15. A method as claimed in any one of claims 12 to 14, wherein the step of treating is carried out at an intensity taking into account relaxation of the properties of said at least one surface after treatment.

16. A method as claimed in claim 15, wherein the step of treating is carried out at an intensity taking such account of the surface property relaxation that said surface tension or wetting tension of at least 45 dynes per square centimetre is still present six months after treatment.

17. A method as claimed in any one of claims 11 to 16, wherein the step of treating is carried out at both surfaces of the film.

18. A method as claimed in claim 11 and substantially as hereinbefore described with reference to the accompanying drawing.

19. A method of paint or lacquer coating a first surface portion adjoining or in the region of a second surface portion to be kept free of the paint or lacquer used in the coating process, the method comprising the steps of so covering the second surface portion with a mask as claimed in any one of claims 1 to 10 or produced by a method as claimed in any one of claims 11 to 18 that said at least one surface of the film faces outwardly and spraying paint or lacquer onto the first surface portion.