Coating processes – Spraying
Reexamination Certificate
2003-05-01
2004-05-11
Pianalto, Bernard (Department: 1762)
Coating processes
Spraying
C427S475000
Reexamination Certificate
active
06733842
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the high-speed rotary application of liquid coating agents, wherein the coating agents are formed from at least two liquid components during the course of high-speed rotary application.
BACKGROUND OF THE INVENTION
When producing liquid coating agents, various liquid components must often be mixed together which, depending upon the viscosity and/or density of the liquid components to be mixed, may cause difficulties. A further complicating factor may arise if there is also a significant difference in the proportions by volume to be mixed of such components. This problem will immediately become clear as shown in the following examples. For example, it may be very problematic to mix a large volume of a highly fluid, low-density component with a small volume of a relatively viscous, high-density component, or a large volume of a highly fluid, high-density component with a small volume of a relatively viscous, low-density component.
The process according to the invention described below provides a surprisingly efficient solution to the above-described problems. The process eliminates the mixing problem from the coating production stage and instead relocates the mixing operation to the coating application stage and there overcomes the above described problems. The quality of the coatings obtained with the process according to the invention is very high.
SUMMARY OF THE INVENTION
A first embodiment of the invention relates to a process for the high-speed rotary application of a liquid coating agent onto a substrate, wherein the process comprises the steps:
(a) directly supplying at least two, preferably only two, liquid components in a specified quantity ratio which determines the qualitative and quantitative composition of the coating agent to at least one high-speed rotary atomizer,
(b) high-speed rotary atomizing the components directly supplied in step (a) to the at least one high-speed rotary atomizer and
(c) applying the material atomized in step (b) onto a substrate,
wherein at least one of the components used in step (a) differs from at least one further component used in step (a) with regard to density by 0.05 to 2 g/cm
3
and/or with regard to flow time (DIN EN ISO 2431, DIN 4 cup, 20° C.) by 15 to 150 seconds.
The second embodiment of the invention relates to a process for the high-speed rotary application of a liquid coating agent onto a substrate, wherein the process comprises the steps:
(a) preparing a premix from at least two, preferably only two, liquid components in a specified quantity ratio which determines the qualitative and quantitative composition of the coating agent,
(b) supplying the premix from step (a) to at least one high-speed rotary atomizer,
(c) high-speed rotary atomizing the premix supplied in step (b) to the at least one high-speed rotary atomizer and
(d) applying the material atomized in step (c) onto a substrate,
wherein at least one of the components used in step (a) differs from at least one further component used in step (a) with regard to density by 0.05 to 2 g/cm
3
and/or with regard to flow time (DIN EN ISO 2431, DIN 4 cup, 20° C.) by 15 to 150 seconds.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In the first embodiment, the coating agent is formed and applied from at least two liquid components virtually in a single operation. The at least two liquid components are directly supplied to the at least one high-speed rotary atomizer, for example, via a T-piece which is arranged immediately upstream from the feed orifice of the high-speed rotary atomizer(s) or is a component of the high-speed rotary atomizer(s). During coating of a substrate, the at least two liquid components are supplied to the at least one high-speed rotary atomizer in a specified quantity ratio which determines the qualitative and quantitative composition of the liquid coating agent, for example, using suitable metering devices, such as, for example, gear pumps.
In the second embodiment of the process according to the invention, the at least two liquid components are not directly supplied to the at least one high-speed rotary atomizer. Instead, the process comprises the additional, preceding step of producing a premix from components, as are directly supplied to the at least one high-speed rotary atomizer in step (a) of the first embodiment. Before application, the coating agent is initially prepared by mixing at least two liquid components in a specified quantity ratio which determines the qualitative and quantitative composition of the coating agent to form a premix, after which it is supplied to the at least one high-speed rotary atomizer and only then is it atomized and applied. Relative to the degree of mixing in the premix, the degree of mixing is increased on atomization and/or application. Premixing may proceed either continuously or discontinuously, but continuous premixing is preferred for the purposes of industrial mass-production coating. Continuous premixing may here be achieved in conventional manner, for example, by means of a multicomponent mixing unit, in particular, a two-component mixing unit, for example, a conventional static mixer, such as, a Kenics mixer, as is conventionally used in automotive original coating. During coating of a substrate, the at least two liquid components are supplied to the multicomponent mixing unit in a specified quantity ratio which determines the qualitative and quantitative composition of the liquid coating agent, for example, using suitable metering devices, such as, for example, gear pumps.
The term “premix” used in connection with the second embodiment refers to the mixture of the at least two liquid components of the liquid coating agent with a greater or lesser degree of mixing or homogenization which varies as a function of the nature of the premixed components. The term “premix” is intended to relate to the mixture which is fed into the high-speed rotary atomizer(s) and does not mean the mixture after having entered the bell dish of the rotary atomizer(s).
In both embodiments of the process according to the invention, at least two, preferably no more than four, but preferably only two, liquid components are used in step (a) in a specified quantity ratio which determines the qualitative and quantitative composition of the coating agent. With regard to the quantity ratio, it is generally the case that the proportion by volume of the component with the largest proportion by volume is at most one hundred times, preferably at most ten times, as large as the proportion by volume of the component with the smallest proportion by volume.
The coating agent, i.e. the atomized material obtained in step (b) of the first embodiment or in step (c) of the second embodiment, is applied onto the substrate by high-speed rotary application, preferably by electrostatically-assisted high-speed rotary application. In the case of electrostatic support, the coating agent may be charged directly by means of the high-speed rotary bell or by external charging. The coating agent may be applied in one or more spray passes to any substrate, such as, for example, automobile bodies or body parts. The high-speed rotary atomizer(s) may be passed by means of an automatically controlled machine or a coating robot over the substrate surfaces to be coated.
Examples of high-speed rotary atomizers include conventional rotary bells suitable for the application of liquid coatings and are made of metal, for example, aluminum, titanium or refined steel, wherein the circular spray edges of the atomizers have a diameter of, for example, 5 cm to 12 cm. Examples of such rotary bells include the ECO-M bell (manufactured by DÜRR GmbH, Bietigheim Bissingen, Germany) or the G1 atomizer (manufactured by ABB Flexible Automation, Friedberg, Germany). The spray edges of the rotary bells may be unserrated, but are preferably serrated, and more preferably straight-, cross- or diagonally-serrated.
The circumferential velocity of the spray edge lies in the range of 3,000 to 25,000 m/min, preferably 10,000 to 25,
Becker Michael
Doessel Karl-Friedrich
Holfter Dirk
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Pianalto Bernard
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