Metallized aluminium profiles, compositions and method therefor

Abstract: Metallic coating compositions for aluminum profiles providing stability and weather and chemical resistance even when applied as a single coat suitable for use inter alia with the Ransburgh turbo-disc electrostatic spray system comprising: a) a highly elastic cross-linking polyacrylate coating resin; b) a suspending agent; c) a plasticizer; d) a polar solvent mixture of i) butyl alcohol; ii) butyl glycol; and iii) aromatic solvents; e) a pigment mixture of i) non-leaving metallic pigment; and ii) colour pigment; a method of coating aluminum profiles and aluminum profiles coated therewith.

Description: The present invention concerns a method of coating aluminium profiles with metallic finishes. The invention also provides metallizing coating compositions for use on aluminium profiles with such method. Aluminium profiles are used extensively in applications such as window and door frames, display counters and partitions. Such aluminium profiles come in several finishes, among which are metallic finishes such as the well-known silver-metallic and gold or bronze metallic finishes. Recently a brown-metallic finish has become popular as well. These finishes involve anodizing the aluminium. Alternatively, aluminium profiles have been coated with paints which are baked onto the aluminium. To anodize aluminium, it has to undergo an electro-chemical process which is rather complex, expensive and limits the colours obtainable. Aluminium profiles that are painted require first to undergo a preliminary process of undercoating in order to provide a suitable surface for the paint to adhere to, since paints do not adhere well to aluminium. Although many advances and developments have taken place in the coating industry, including the art of finishing aluminium profiles, there are a number of problems that have as yet not been overcome. First of all the finished aluminium profiles, which are used for so many diverse applications, require special resistance against degradation by light, chemicals, corrosive atmospheric gases and other pollutants, because they are used so much under outdoor conditions in displays and window frames where ultra-violet light, industrial gases and other weather conditions deteriorate the coating and the aluminium. This is particularly true for use of aluminium near coastal areas, where oxygen and salt water in the air subjects the profiles to severe corrosion. A further problem is caused by the fact that modern household and sanitary cleaning materials contain bleaches and alkali which react with aluminium and deteriorate its surface. These problems dictate that the aluminium profiles for use in such applications must have complete protection from contact between any corrosive atmosphere and the aluminium. This protection is very difficult to achieve in profiles with intricate channels and grooves, as is the case with aluminium profiles. Yet the demand for aluminium profiles for such applications is ever-increasing, particularly for profiles with metallic finishes at a reasonable price. It is the object of the present invention to provide an economic method for coating aluminium profiles with a metallic finish. Another object of the present invention is to provide a continuous process for making metallic coating aluminium profiles. It is a further object of the present invention to provide a highly stable, uniformly coated aluminium profile having a metallic finish. A still further object of this invention is to provide uniformly coated, metallic finish aluminium profiles of up to six metres in length. Yet another object is to provide a metallic finish coating composition for application to aluminium profiles. The above objectives are obtained by the method which will be described in details as follows. The method of this invention involves the use of the Ransburgh turbo-disc electrostatic spray system for coating aluminium profiles with a specially formulated coating composition. The Ransburgh turbo-disc electrostatic sprayer is a known apparatus for painting aluminium profiles with regular paints. In this system the profiles are hung vertically on a track moving in a closed circuit. The paint operation is carried out electrostatically. The vertically hung aluminium profiles are moved continuously along a track from station to station until they get to the paint chamber. In this chamber there is a hydraulic piston which moves vertically up and down, whose movement with respect to speed and distance is controlled. At the lower end of this hydraulic piston there is a controlled high speed revolving disc plate. Paint is transferred via suitable tubing onto this spinning disc in measured quantities and is thus sprayed onto the aluminium profile. An electrostatic charge is imparted onto the paint at the disc while it is being sprayed, while the aluminium profile is charged with an opposite electrostatic charge as it moves along the track circling the disc. The electrostatic charges can be controlled as far as intensity and time. The opposite electrostatic charges on the paint and on the aluminium profile assure that the paint is attracted to all parts of the profile and the thickness of the coating is controlled by the mechanical and electrical parameters of the system. As the spinning disc slowly moves up and down with the hydraulic piston in a uniform manner adjacent the vertical profile, the coating on the entire length of the profile is controlled to be applied uniformly. This electrostatic attraction between paint and aluminium profile also is responsible for the coating to take place not only on the surface of the profile facing the disc, but also on the sides and rear of the profile, since the paint as it is sprayed in the direction of the profile is attracted to all parts thereof. This enables complex profiles, having numerous grooves and protrusions, to be uniformly coated with the spray paint. The Ransburgh spray system is not in itself new and has been used for coating with ordinary paints. Such paints which are pigmented opaque do not present any particular difficulty in formulation for this application. Metallic finishes on base surfaces, such as plastic and metals, are known and their use in corrosion resistant applications is widespread on steel surfaces of automobiles. Such anti-corrosion metallic finishes on steel surfaces require numerous coats, one on top of another, in order to produce the desired metallic effect. Furthermore, these finishes are designed for use on large, smooth surfaces and not on intricate profiles with channels and grooves. Aluminium surfaces, on the other hand, are not very amenable to being metallized with such coatings, since the coatings used on steel surfaces do not adhere well to aluminium surfaces and are not suitable for use with intricate profiles. We have discovered coating compositions suitable for metallizing aluminium profiles and which are particularly suitable for use with the Ransburgh spray system. The novel compositions provide metallic-finished aluminium profiles with only a single coat of paint. The novel coating compositions of this invention comprise - a) a coating consisting of highly elastic crosslinking polyacrylate resin; b) a suspending agent; c) a plasticizer: d) polar solvent mixture of butyl alcohol, butyl glycol, and a mixture of aromatic solvents; and e) a mixture of pigments consisting of a non-leaving metallic pigment and a coloured pigment. Suitable resins for the novel metallic coating compositions are, for example, Larodur 145 (TM) acrylic resin. Suspending agents can be, among others, treated montmorillonite such as Bentone 34 (TM) or pyrogenic silicic acid such as Aerosil R 972. The non-leaving metallic pigment, for example, may be Stapa (TM) and the colour pigment may be, for example, brass-copper power Resist LT stabil (TM), Lamp black Printex G (TM), Hostapermgelb H4G (TM) and Hosta-permorange GR (TM), just to cite a few. Suitable proportions of the coating composition are as follows: A mixture of acrylate and polyester coating resins (solid) 28-35 parts Suspending agent 0.5 - 1 parts Plasticizer 2-5 parts Solvents: Butyl alcohol 16-20 parts Butyl glycol 3-5 parts Aromatic solvents 28-32 parts Total solvent 47-57 parts Metal pigment: Non-leaving metallic pigment 0.5-12 parts Colouring pigment: Carbon black 1-6 parts Metallic colour pigment 4-12 parts Total pigments 5.5-30 parts. A preferred combination contains in the colours, silver metallic resin 35 parts suspending agent 1 part plasticizer 3 parts solvent mixed 47 parts Al non-leaving metallic pigment 6 parts colour pigments in the colour eloxal brown Ton 13 Klil 6 parts resin 35 parts suspending agent 1 part plasticizer 3 parts solvent mixed 47 parts brass copper power metallic pigments 10 parts colour pigments 4 parts This novel coating composition provides the following advantages when applied to aluminium profiles with the Ransburgh spray system. The coating composition is non-dripping, i.e. when used in this system the paint does not flow in the object surface but stays put at the spot that it contact initially. This leads to smooth uniform thickness. The particular combination of resins provides just the right balance of strong corrosion-resistant coating which adheres permanently to the aluminium. The specific solvent system in this composition is particularly critical, in that it provides just the right degree of evaporation and drying to prevent running of the paint on the profile surface and avoids pinholes, often caused by too quick drying. This coating composition gives high weather and chemical resistance and is extremely stable. The thickness of this coat on the aluminium can range from 20 - 60 millimicrons and preferably 30 - 40 millimicrons when dry. Aluminium profiles subjected to such a single coat of metallic paint as defined above are much less expensive than the anodized aluminium profiles and yet provide a very similar surface appearance, particularly the brown or dark bronze look.

Claims: A metallic coating composition for aluminium profiles providing stability and weather and chemical resistance even when applied as a single coat suitable for use inter alia with the Ransburgh turbo-disc electrostatic spray system comprising: A coating composition according to claim 1 as follows: A mixture of acrylate and polyester coating resins 28-35 parts Suspending agent 0.5-1 parts Plasticiser 2-5 parts Solvents: Butyl alcohol 16-20 parts Butyl glycol 3-5 parts Aromatic solvents 28-32 parts Total solvent 47-57 parts Metal pigment: Non-leaving metallic pigment 0.5-12 parts Colouring pigment: Carbon black 1-6 parts Metallic colour pigment 4-12 parts Total pigment 5.5-20 parts. A composition as in claims 1 and 2 wherein the resin is Larodur 145 (TM). A composition as in claims 1 to 3 wherein the suspending agent is selected from bentonite and aerosil. A composition as in claims 1 to 4 wherein the non-leaving metallic pigment is STAPA (TM). A composition as in claims 1-5 wherein the colour pigment is a mixture of carbon black and Hostapermgelb H4G (TM) and Hostapermorange GR (TM). A method of coating aluminium profiles with a metallic finish having high stability and weather and chemical resistance comprising subjecting the said profiles to coating by the Ransburgh Turbo-disc electrostatic spray system with compositions of claims 1-6. Aluminium profiles having coated metallic finishes of uniform thickness of 20-60 millimicrons, said profiles being weather and chemical resistant, manufactured with coatings of claims 1 to 6. A method of coating aluminium profiles according to claim 7 wherein said coating is applied to a uniform thickness of 20-60 millimicrons.

Inventors: NIR ZVI, RENTSCH WOLFGANG, NIR, ZVI, RENTSCH, WOLFGANG
Applicants: KLIL IND LTD, KLIL INDUSTRIES LTD.
Application year: 1990
Main classification: C09D5
IPC codes: C09D133, C09D5, B05D7, B05D5