Coating processes – Electrical product produced – Cellulosic or fibrous base
Reexamination Certificate
2001-12-27
2003-12-09
Pianalto, Bernard (Department: 1762)
Coating processes
Electrical product produced
Cellulosic or fibrous base
Reexamination Certificate
active
06660325
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the application of aqueous multi-component coating compositions, particularly aqueous two-component coating compositions.
BACKGROUND OF THE INVENTION
Typically, aqueous multi-component coating compositions are prepared just prior to their application by mixing components that had been previously stored separately from one another. Generally speaking, the components of aqueous multi-component coating compositions are miscible with one another only after a great deal of difficulty, thereby necessitating the use of equipment requiring a high input of energy. The completely mixed aqueous multi-component coating compositions ready for application are aqueous dispersions, wherein binders and/or hardeners form one or more disperse phases in a continuous aqueous phase.
The quality of a coating applied from an aqueous multi-component coating composition, with regard to technological and/or optical properties, depends upon the degree of mixing of the components prior to application. It is generally known that greater homogeneity of such a mixture, for example a finer dispersion, corresponds to an increase in the quality of the coating with regard to properties, such as, appearance, leveling and gloss. In order to achieve good mixing properties, measures had to be taken in terms of the formulation such as, for example, making use of hydrophilized components, however, these measures restrict the developers of aqueous multi-component coating compositions in their freedom to develop a formulation with regard to the components that may be utilized.
Typically, mixing equipment for two-component coatings present in automotive OEM (Original Equipment Manufacturing) coating plants, (e.g. static mixers such as Kenics mixers), do not routinely provide the necessary mixing quality for the application of aqueous multi-component coating compositions.
EP-A-0 685 544 and WO 01/05860 disclose processes, operating on the principle of jet dispersion, for the preparation of aqueous two-component polyurethane coating agents. Both components of the aqueous two-component polyurethane coating agent are pressed through fine nozzles at high pressure and depressurized, wherein the mixing process is characterized by the use of a dynamic mixer, which requires considerable input of energy during mixing. However, these processes have several disadvantages such as, for example, the use of elaborate mixing technology which requires large amounts of space, general preparation work for the jet dispersion devices, and considerable amounts of energy and maintenance in order to operate the jet dispersion devices.
It is a desire within the industry to utilize a process that incorporates the simple and conventional technology of static mixers rather than the elaborate mixing technology of dynamic mixers. Therefore, it is an object of the present invention to provide a process for the application of coatings comprising aqueous multi-component coating compositions, where the process permits a high level of coating quality without the use of elaborate mixing technology such as dynamic mixers (i.e., nozzle jet dispersers) when mixing the components, such that the conventional multi-component mixing installations present in coating plants for industrial-scale production line coating, for example, in automotive production line coating, may be used.
SUMMARY OF THE INVENTION
The present invention relates to a process for the application of aqueous multi-component coating compositions;, comprising at least two components, to a substrate. More specifically, the process comprises the steps of:
(a) preparing a premix of an aqueous multi-component coating composition comprising at least two components, preferably two components, and optionally water;
(b) high-speed rotary atomizing the premixture using at least one high-speed rotary atomizer, each having one spray edge, wherein each spray edge has a circumferential velocity ranging from 10,000 to 25,000 m/min; and
(c) applying the atomized premixture to a substrate.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The process of the present invention relates to the application of aqueous multi-component coating compositions, and particularly aqueous two-component coating compositions, to a substrate. These coating compositions are prepared, just prior to their application, by premixing a particular ratio of at least two components, which are initially stored separately from one another. The components may be premixed in a ratio determined by the stoichiometry of the cross-linking reaction in order to obtain a suitable aqueous multi-component coating composition. These components, namely a binder and a cross-linking agent, are stored separately from one another in order to prevent a premature cross-linking reaction.
More specifically, the process comprises the steps of:
(a) preparing a premix of an aqueous multi-component coating composition comprising at least two components, preferably two components, and optionally water;
(b) high-speed rotary atomizing the premixture using at least one high-speed rotary atomizer, each having one spray edge, wherein each spray edge has a circumferential velocity ranging from 10,000 to 25,000 m/min; and
(c) applying the atomized premixture to a substrate.
The term “premix” as used herein, refers to the ready-to-apply mixture of the components of an aqueous multi-component coating composition with its relatively low degree of homogenization as it is fed into the rotary atomizer(s). The term shall only apply to that mixture which is fed into the rotary atomizer(s) and shall not mean the same mixture after having entered the bell dish of the rotary atomizer(s).
Application of the premix to a substrate is performed using high-speed rotary atomization, preferably electrostatically supported high-speed rotary atomization. In the case of electrostatic support, the aqueous multi-component coating composition may be charged directly by means of the high-speed rotary bell or by external charging. The premixed aqueous multi-component coating compositions 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 10,000 to 25,000 m/min. Thus, this means, for example, where the spray edge has a diameter of 6.5 cm, the rotational speed (measured as revolutions per minute) will be in the range from 50,000 to 120,000 min
−1
. In cases where the spray edge diameter is in the lower range of values, the rotational speed tends to lie in the upper range of values and vice versa such as, for example, where the spray edge has a diameter of 5 cm, the rotational speed will be in the range from 65,000 to 156,000 min
−1
. In each case, the 10,000 to 25,000 m/min range for the circumferential velocity of the spray edge is 10% to 150% higher than is used in the art for the rotary atomizing application of aqueous multi-component coating compositions. The greater circumferential velocity of the spray edge according to the present invention provides a coating having a satisfactory appearance, satisfactory leveling properties and a high level of gloss, in spite of the fact that the aqueous multi-component coating comp
Holfter Dirk
Laack Birgit
Deshmukh Sudhir G.
E. I. du Pont de Nemours and Company
Pianalto Bernard
LandOfFree
Process for the application of aqueous multi-component... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the application of aqueous multi-component..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the application of aqueous multi-component... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3144069