Apparatus for applying a primer coating with the aid of vacuum

Apparatus for application of primer with the aid of vacuum, includes a reservoir (26) for liquid primer, an applicator nozzle (14) having an applicator chamber (16) and a suction chamber (18), a supply system (24, 26) for supplying primer from the reservoir (28) to the applicator chamber (16), a suction system (30, 32) for withdrawing air and primer from the suction chamber (18) and a separator (34) for separating primer from the withdrawn air and recirculating the separated primer into the reservoir (28), wherein the separator (34) is a cyclone.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for applying a primer coating with the aid of vacuum, comprising a reservoir for liquid primer, an applicator nozzle having an applicator chamber and a suction chamber, a supply system for supplying primer from the reservoir to the applicator chamber, a suction system for withdrawing air and primer from the suction chamber, and a separator for separating primer from the withdrawn air and for recirculating the separated primer into the reservoir.

When work pieces such as plastic profiles for windows, doors and the like are to be provided with a surface decor, e.g. a layer of lacquer or a coating such as a film coating, it is convenient that, at first, a primer is applied to the surfaces which are to be coated with the decor in order to assure a sufficient adhesion of the lacquer or adhesive that will be applied later. An apparatus with the features indicated above, which apparatus is manufactured and distributed by the applicant, has turned out to be particularly useful for applying the primer. In the known apparatus, the separator is formed by a baffle onto which the withdrawn mixture of air and liquid will impinge so that the liquid will be caught at the baffle and will drip down whereas air substantially free of primer will be exhausted.

However, during extended operation, several effects, especially the evaporation of solvent components of the primer and precipitations of solid pigments from the primer, result in a gradual change of the composition of the primer recirculated in the system so that the primer will be usable only for a limited time. Moreover, increased accumulation of precipitations in the system results in short cleaning intervals. It is an object of the invention to provide an apparatus which permits to extend the usage time of the primer.

SUMMARY OF THE INVENTION

According to the invention, this object is solved by using a cyclone as separator.

As is known, a cyclone which is used also for example for separating dust from dust-laden air, generates a rapidly rotating air vortex which has the effect that the air and the solid components suspended therein are separated by centrifugal action. In the apparatus according to the invention, the cyclone effects a separation of air and liquid (primer).

Surprisingly, it has turned out that, by using a cyclone as separator, the evaporation losses can be reduced drastically. In the apparatus according to the invention, the contents of vapours of organic solvents in the exhaust air amounts to only about 10% of the value that has been achieved with conventional separators in the form of a baffle. Moreover, the invention significantly reduced the precipitation and accumulation of solid components such as pigment particles from the liquid primer. While continuous operation (24 hours a day) of a conventional apparatus having a baffle-type separator required a cleaning of the separator system already after two days on the average, in order to remove solid components precipitated from the primer, the invention permits to extend these cleaning intervals to about 5 days.

Next to a reduction of the maintenance work and a reduction of emissions of noxious substances into the ambient air the invention has the main advantage that the primer retains its original composition as specified by the supplier for a substantially longer period of time. This is particularly important because suppliers of primer warrant the effectiveness of the primer as adhesion promoter only on condition that the composition of the primer, when it is used, stably fulfils the specifications of the supplier. With the apparatus according to the invention, these specifications can be fulfilled for an extended period of time, so that the primer recirculated in the system needs to be exchanged less frequently.

The apparatus according to the invention is particularly advantageous for aqueous primers, especially aqueous dispersion primers, i.e. primers in which water is the main component of the solvent. Although these primers typically contain also organic solvent additives, their flash point is generally above 90° C. and, consequently, significantly above the limit of 55° C. that is required pursuant to the pertinent anti-explosion guidelines. Thus, no anti-explosion measures are necessary in the suction and separator system.

When these primers are used, the suction and separator system can be operated at an underpressure of approximately 10 kPa without causing any significant evaporation of components parts of the primer. Consequently, it is also an object of the invention to provide a method for applying aqueous primer with use of the apparatus that has been described above.

DETAILED DESCRIPTION

In the example shown, the work pieces are profiles10, e.g. plastic profiles for doors or windows, which are fed in the direction of an arrow A in the drawing on a roller-type conveyer12and move past a stationary applicator nozzle14for primer. The applicator nozzle14has an applicator chamber16and a suction chamber18which are separated by a partition wall20and both open-out into parallel slots22a,22bthat face the surface of the profile10. The slots22a,22bare slightly spaced apart from the surface of the profile10and extend in a direction normal to the plane of the drawing over a certain width that corresponds to the contour of the surface of the profile10where the primer is to be applied.

A pump24and a duct26form a supply system with which liquid primer is sucked from a reservoir28and supplied to the applicator chamber16. A suction blower30and a duct32form a suction system with which a mixture of air and liquid primer is withdrawn from the suction chamber18. Primer from the applicator chamber16is discharged onto the surface of the profile10through the slot22aof the applicator nozzle14, and, simultaneously, ambient air is sucked into the suction chamber18through a gap formed between the applicator nozzle14and the surface of the profile10. Concurrently, excess primer is withdrawn from the surface of the profile10and entrained into the suction chamber18. From there, the mixture of air and liquid is discharged via the suction system. A continuous layer of primer having a uniform and reproducible layer thickness is left on the surface of the profile10.

A separator34which is formed by a cyclone is interposed between the duct32and the suction blower30. The separator34has an outer casing36with a cylindrical upper part and a conical, downwardly tapered lower part. A vertical inner tube38is arranged coaxially in the casing36and is connected to the suction side of the suction blower30. At the top end, the casing36is closed except for a feedthrough for the inner tube38. The tapered lower end of the casing36opens-out in a top wall of the reservoir28that is configured as a closed, air-tight container and is divided into two chambers42,44by a dam40. The chamber42is disposed below the separator34whereas the duct26is connected to the chamber44so as to suck liquid primer from this chamber. Thus, in the example shown, the suction system including the separator34and the reservoir28form a closed system into which air can enter only via the applicator nozzle14. The power for the suction blower30is adapted such that an underpressure of about 5-15 kPa, preferably about 10 kPa is maintained in this system.

The primer is an aqueous primer that is essentially free of highly volatile components that would apt to rapid evaporation at the given underpressure.

The mixture of air and liquid primer withdrawn from the suction chamber18enters tangentially into the cylindrical top part of the separator34from the duct32, so that a vortex flow is induced in the outer casing36of the separator, the vortex flow spiraling downward in the conical lower part of the casing36. The liquid components suspended in the air are urged outwardly by centrifugal action and are deposited on the internal wall of the outer casing36but have only a relatively small velocity component in the direction normal to the wall of the casing. This prevents the droplets of liquid from being finely sputtered when they impinge onto the wall, thereby avoiding an increased evaporation rate and a drying-out and precipitation of solid pigments. The primer that has efficiently but gently been separated from the air in this way runs down along the internal wall of the casing36and drips into the chamber42of the reservoir28whereas the air that is essentially free of liquid is withdrawn via the inner tube38.

In this example, the chamber42serves as a sedimentation tank in which dried solids that may be produced in a small amount in the course of time can settle as a sediment46. The dam40prevents the sediment46from entering into the chamber44whereas the liquid primer flows over the dam into the chamber44and can again be supplied to the applicator nozzle14.