GB1593720A

GB1593720A - Strippable wax coatings and method for their application

Info

Publication number: GB1593720A
Application number: GB2609878A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-07-22

Description

(54) STRIPPABLE WAX COATINGS AND METHOD FOR THEIR APPLICATION (71) We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPlJ B.V., a Company organised under the laws of the Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the fpllowing statement: This invention relates to wax coatings, and in particular those which have to be removed at the end of their useful life, for example, the protective wax coating given to new motor cars.

An important feature of the wax coatings with which the invention is concerned is that they should be removable without great difficulty or expense. On the other hand they must completely cover the article and should be impervious.

Conventionally a very thin coat of a relatively hard petroleum-derived wax is sprayed onto the article using an emulsion of the wax in a solvent such as a white spirit. When the wax has to be removed from the article even quite thin coatings, e.g. those thinner than 20 microns, can present considerable difficulties and steam and/or solvents have to be used.

In view of the growing concern for protection of the environment and for the improvement of working conditions, the use of solvents for the application of wax coatings, as for their removal, is becoming less acceptable, and in pure cost terms, more and more expensive.

However it is not possible to apply a smooth non-porous wax coating using conventional spray equipment without using a large quantity of solvent.

The present invention relates to a method of providing an article with a strippable protective coating thicker than 0.1 mm and not more than 3 mm thick of a wax formulation having a mineral oil content between 10 and 60, preferably between 30 and 60% w, comprising streaming the formulation in a molten state through one or more elongate openings to produce a continuous film of the formulation, and passing the article through the film.

This invention furthermore relates to articles coated by this method.

As compared with conventional spraying in which the liquid is conventionally broken up into an array of tiny droplets and projected towards the object to be coated, the present process comprises forming a substantially continuous film or curtain of the wax formulation and applying it as such to the article.

This can be achieved by streaming it through an elongated opening or a line of openings.

Ideally, the opening or openings are in the form of a slit having a width of 0.05 to 0.5, preferably 0.1 to 0.3 mm, and being from several millimeters to two or three metres in length or longer. The width of the opening may even be varied over its length to take account of the geometry of the article to be coated.

A principal advantage of applying the wax formulation in an unbroken film is that it can be applied evenly over the whole of the article without gaps or lines and to give a smooth appearance. It also permits an extremely rapid application without any after treatment being necessary.

If the wax formulation is sprayed using conventional equipment but without a solvent the droplets lose their heat very rapidly and have virtually solidified by the time they reach the surface to be coated. This means that a smooth, non-porous coating cannot be obtained without some subsequent heat treatment.

The temperature at which the formulation is applied should be between 10 "C above the congealing point of the wax formulation and 150 OC and preferably between 120 and 130 OC.

The actual temperature chosen will depend upon the viscosity of the formulation and the geometry of the coating equipment used and of the article to be coated. Generally, the article will be coated using a film of wax formulation which is forced through the opening(s) under a pressure of 2-100 bar, preferably 440 bar, and falling under gravity. The opening(s) will ideally be placed 200-400 mm above the article.

The width of the nozzle is chosen taking into account inter alia the speed at which the article is moved across the nozzle and the desired coating thickness.

Rather high pressures (up to, say, 100 bar) may be necessary if the opening(s) are in a vertical or substantially vertical plane.

The coating in accordance with the invention can be stripped, if required, even ininiediately after its application by peeling or by scraping it off the object because the oil content of the formulation, which migrates or sweats to the interface between the coating and the article, reduces adhesion or sticking. Thus, such a thicker coating can be made readily removable, for example by peeling, unlike a conventional (IlltlCh thinner) coating. In addition, it does not require the use of a solvent for its application or for its removal.

For a non-porous coating to be peelable or strippable without difficulty the optimum coating thickness appears to be between 0,5 and 1,5 mm though in certain circumstances it may be possible to reduce the thickness to 0,1 mm. Coatings in excess of 3 mm thick are not favoured.

Using the invention there need not be any substantial loss of the formulation during its application, and in view of the absence of a solvent makes any cost difference over convention. By the way of example a standard size family car would require some 5 kg wax at a coating thickness of 0.5 mm. Tlie coating equipment would normally deliver between 2 and 60 kg/min of the formulation per meter length of the opening, and the process can be carried out with the same high degree of automation as at present.

Tlie required toughness of the coating will depend upon its purpose, and in particular the temperature of the environment where it is to be used, arid its applied thickness, but in general tlie coating should have a penetration at 25 OC below 80 admin (0,1 mm) according to ASTM D 1321 and preferably should be in the region of 15-40 drill.

The wax element of the formulation should have a congealing point of at least 50 OC, and may comprise a petroleum wax such as a paraffin wax or a microcrystalline wax either substantially free of oil or alternatively in the form of a slack wax or petrolatum. Naturallyoccurring and synthetic waxes can also be used.

The oil content which is dependent very much upon the type of wax used will generally constitute approximately the same proportion of the formulation on a weight basis as the wax element. It may either result frond the choice of a slack wax as the wax component, and/or the mixi1lg of a substantially oil-free wax with a suitable oil, having, say a viscosity greater than 1 mm2/s at 25 C.

But the effect of the oil is to reduce the toughness of the wax. This can be corrected by the inclusion of one or more additives in the formulation which can be used not only to achieve the desired toughness, but also eventually to improve other properties of the formulation, such as its adhesion and/or pourability. These additives may represent 10 to 50% w of the formulation and preferably between 25% and 35% w.

Various additives may be suitable, for example, natural or synthetic resins, polypropylene, and polyethylene and mixtures thereof or co-polymers of propylene and ethylene or esters with ethylene. For example, 30% w of a low molecular weight polyethylene (MW 120020000) may achieve the desired effect in a typical formulation.

Another very suitable additive is a co-polymer of vinyl acetate with ethylene, wherein the vinyl acetate represents between 10 to 50 preferably 25 to 40% w of the copolymer. Such an additive can also increase adhesion due to its polarity. A combination of different additives may enable the same or improved properties to be obtained more economically.

The additive or additives are added to the wax in a known way such as mixing them into the wax above their respective melting points, or by rolling the wax and the additives together.

In some instances in order to obtain a smoother or more regular coating, the article may be heated, e.g. by infra red radiation, either before during or immediately after application, e.g. to a temperature between the melting point of the formulation and 10 "C above its melting point. Where it is heated to a temperature slightly above the melting point of the formulation it may permit a thinner, peel able coating to be obtained even more economically.

FXAAIPLE I 1. A formulation for a wax coating for protection of new motor cars leaving the pro duction line comprised 30% w microcrystalline wax with a congealing point of 63 "C and having an oil content of less than 1% '7O w with 40S, deasphalted oil. The required toughness was obtained by including in the formulation 30W w of low molecular weight, low density polyethylene.

The formulation was heated to 130 OC and applied to a metal surface by streaming it through a horizontal opening 0.5 mm wide, 70 mm long at a pressure of 4 bar and moved slowly over the surface at a height of 400 mm.

A smooth uniform coating of 1 mm thick was produced, which could be stripped without solvents at ambient temperature.

2. A similar test was carried out with a formulation comprising 45% bright stock slack wax (30cm w oil content), 25% w bright stock and 30% w copolymer of ethylene and vinyl acetate. The vinyl acetate component of the copolymer represented 33% w. Satisfactory results were obtained using the same technique, but using an opening of 0.15 mm wide situated 200 mm above the test article. The wax was at a pressure of 20 bar and at 120 OC to 130 OC.

On cooling the resulting 1 mm thick coating could be peeled off the metal without diffi culty.

3. In a further series of tests the formulation comprised 40who w petrolatum (containing approx. 35% w oil), 10% w paraffin wax (less than 1% oil and congealing point 54 OC), 20% w low viscosity index oil, 25% w of the ethylene vinyl acetate copolymer used in example 2 above, and 5% w low molecular weight, low density polyethylene. The formulation was applied as in example 2 above and produced a 1 mm thick peelable coating.

WHAT WE CLAIM IS:- 1. A method of providing an article with a strippable protective coating thicker than 0,1 mm and not more than 3 mm thick of a wax formulation having mineral oil content between 10 and 60% w comprising streaming the formulation in a molten state through one or more elongated openings to produce a continuous film of the formulation, and passing the article through the film.

2. A method as claimed in claim 1 in which the oil content of the formulation is between 30 and 60% w.

3. A method as claimed in claim 1 or claim 2 in which the coating is between 0,5 mm and 1,5 mm thick.

4. A method as claimed in any preceding claim in which the coating has a penetration below 80dmin (ASTM D 1321 at 25 OC).

5. A method as claimed in claim 4 in which the coating has a penetration in the range of 15 to 40 dmin.

6. A method as claimed in any preceding claim in which the formulation contains an additive or additives to increase the toughness of the coating.

7. A method as claimed in claim 5 in which the total amount of the additive or additives included comprise(s) between 10% and 50% w of the formulation and preferably 25 to 35% w.

8. A method as claimed in claim 7 in which the additive comprises a co-polymer of ethylene and vinylacetate wherein the vinyl acetate represents 10% to 50% w of the co-polymer.

9. A method as claimed in claim 8 in which the vinyl acetate represents 25% to 40% w of the co-polymer.

10. A method as claimed in claim 7 in which the additive comprises a low molecular weight polyethylene of molecular weight 1200 to 20000.

11. A method as claimed in any preceding claim in which the formulation is applied at a temperature between 10 "C above the congealing point of the formulation and 150 OC.

12. A method as claimed in claim 11 in which the formulation is applied at between 120 OC and 130 OC.

13. A method as claimed in any preceding claim in which the formulation is applied at a pressure of between 2 and 100 bar.

14. A method as claimed in any preceding claim in which the formulation is applied at a pressure of at between 4 and 40 bar.

15. A method as claimed in any preceding claim in which the coating is heated during or immediately after its application to a temperature between the melting point of the formulation and 10 OC above its melting point.

16. A method as claimed in claim 15 in which the coating is heated by infra red heating means.

17. A method as claimed in any preceding claim in which the opening or opening(s) are in the form of a slit having a width of between 0.05 and 0.5 m.

18. A method as claimed in claim 17, in which the opening or opening(s) are in the form of a slit having a width of between 0.1 and 0.3 mm.

19. A method as claimed in any preceding claim in which the opening or opening(s) is (are) 200400 mm from the article.

20. An article when coated by the method claimed in any preceding claim.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. vinyl acetate copolymer used in example 2 above, and 5% w low molecular weight, low density polyethylene. The formulation was applied as in example 2 above and produced a 1 mm thick peelable coating. WHAT WE CLAIM IS:-

1. A method of providing an article with a strippable protective coating thicker than 0,1 mm and not more than 3 mm thick of a wax formulation having mineral oil content between 10 and 60% w comprising streaming the formulation in a molten state through one or more elongated openings to produce a continuous film of the formulation, and passing the article through the film.

20. An article when coated by the method claimed in any preceding claim.