Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1994-06-16
1995-11-14
Hoke, Veronica P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
106189, 106195, 427415, 427421, 427469, 427485, 427486, 524361, 524363, 524376, 524389, 524391, B32B 904, C09D10118, C09D17504, C09D16708, C09D13310, C09D13308
Patent
active
054667364
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to spray paints, for use in particular in electrostatic spraying.
BACKGROUND
Electrostatic spray heads are described in ICI's U.K. patent specifications Nos. 1 569 707, 2 018 601 and numerous others. Liquid supplied to the head is broken up essentially by the action of a high voltage field to form charged droplets, which are then attracted to and deposit on an earthed target such as a plant crop. The current passing, which is minute and harmless, is supplied for example by dry cells. No impellant gas or mechanical action is involved in transport of the spray.
Spraying of paint is mentioned in the above patents, but without discussion of paint compositions or other aspects of successful application of the electrostatic principle to paint.
DEVELOPMENT OF THE INVENTION
We have sought to apply electrostatic spray generation to paint and other associated products where normally they have been applied using aerosol dispensing systems. We have found that by using the electrostatic system, material can be applied more efficiently with a greater degree of control and accuracy and generate a surface finish comparable to that given by an aerosol.
Further, especially as the use of a propellant is not required, a considerable reduction in emissions of solvents and other volatile constituents is achieved when compared to an aerosol spray system.
The inherent advantages of electrostatic paint spraying over aerosol paint spraying can be defined thus: adjacent areas. compared to a typical aerosol spray paint. This is because no propellant is required to generate the spray and the paint itself requires a lower proportion of solvent in use, and also because of the inherent transfer efficiency of the system.
Typically an automotive spray paint aerosol may contain 22% propellant, 70% solvent, and 8% paint solids compared to the present formulations that contain no propellant and at least double that solids content. Calculations have demonstrated that if used for a similar application, then the system detailed can reduce emissions of volatile organic compounds (VOC's) by up to three quarters when compared to those emitted during application of a paint via an aerosol.
In order to achieve satisfactory results attention will be paid to characteristics of the paint, such as viscosity, resistivity, solids content and drying time, and the operating characteristics of the spray gun, such as voltage and flow rate. However we have found that the viscosity and resistivity of the paint formulation are key points.
In the context of the present invention, paint formulations consist essentially of pigment, resin, and solvent. The pigment, resin and other non-volatile elements together are the solids of the final paint coat, the pigment giving colour and the resin, which may for example be a nitrocellulose, alkyd, polyurethane, or-acrylic, acting to bind the system, promoting adhesion, gloss, flexibility and wear resistance of the film.
The solvent is largely or wholly lost by evaporation from the deposited coat (in some systems part becomes incorporated in the resin), but is essential to formation of the spray and its deposition as a paint coat.
In the spraying, the paint must of course be thin enough to form a spray and not merely dust on the work but equally not so thin that it forms runs and sags. However there are special requirements in electrostatic spraying. Ideally the paint fed to the head is broken up, by the electrostatic forces in the head, into a diverging spray that is uniform and of close particle size distribution, and thus the resistivity and viscosity of the paint formulation have to be considered in relation to the generation and transport of the spray.
Specifically, the following observations have been made in the development of the formulation.
If viscosity is too low, sags form in the paint film on the work. If it is too high then no proper spray cloud forms and spidery filaments of paint are left between droplets on the surface; alternatively a spray cloud may be form
REFERENCES:
patent: 3267057 (1966-08-01), Spiller
patent: 3348965 (1967-10-01), Drum
patent: 3796590 (1974-03-01), Spiller
patent: 4151152 (1979-04-01), Schmitt et al.
patent: 4276212 (1981-06-01), Khanna et al.
patent: 4638031 (1987-01-01), Bouboulis
patent: 4739006 (1988-04-01), Bouboulis
patent: 4752502 (1988-06-01), Winchester
Ahmed Nighat
Grayson Julia P.
Outhwaite Alan C.
Spowage Mark J.
Hoke Veronica P.
The Morgan Crucible Company plc
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