Coating processes – Interior of hollow article coating – Rotating the article
Reexamination Certificate
1999-06-11
2004-03-23
Beck, Shrive P. (Department: 1762)
Coating processes
Interior of hollow article coating
Rotating the article
C427S231000, C427S236000, C427S240000, C427S385500, C427S393500, C427S425000, C118S052000, C118S055000, C118S320000
Reexamination Certificate
active
06709698
ABSTRACT:
The present invention relates to a method and apparatus for applying a coating such as a paint or a varnish on an article.
BACKGROUND OF THE INVENTION
It is well known to cover the surface of an article of plastics material in a varnish that is designed, for example, to protect decoration provided thereon.
In conventional manner, the varnish is sprayed by means of a spray gun in a painting or varnishing station.
That method requires the use of paints or varnishes that need to be diluted in organic solvents, which solvents must be eliminated prior to polymerization.
Such elimination by evaporation is harmful to the environment.
In addition, solvent evaporation does not make it easy to recycle any paint or varnish that may be recovered.
Finally, the painting or varnishing station is generally situated at a location that is remote from the station where molding takes place, so while the article is being conveyed to the painting or varnishing station, it is exposed to being dirtied, and in some cases there is a risk of the decoration formed thereon being damaged.
There thus exists a need to reduce loss of varnish and to facilitate the operation of varnishing, and more generally to perform the operation of depositing a coating such as paint or varnish on an article in a manner that is more effective.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention provides a novel method of applying a coating such as paint or varnish on a hollow article, in particular an article made of molded plastics material such as the body of a container, a container lid, a stopper, or a flask, with the opening of the flask possibly being narrower than the bottom thereof.
The method includes the operation consisting in depositing a predetermined quantity of coating in the fluid state on the center of a surface of the article, and in spreading it by causing the article to revolve.
By means of the invention, the coating is deposited on the article without needing prior dispersion in the atmosphere in the form of fine droplets.
The invention thus makes it possible to reduce the quantity of paint or varnish that comes into contact with the atmosphere, and thus to reduce losses of solvent by evaporation.
The invention thus makes it possible to use a conventional varnish or paint that does not have organic solvents and that is easy to recycle.
The varnish or paint without solvent is advantageously heated, preferably being raised to a temperature that is higher than ambient temperature, for example a temperature in the range 40° C. to 50° C., for the purpose of increasing its fluidity.
By way of example of a coating that does not have organic solvents, mention can be made of the following composition:
oligomers (urethane/acrylate oligomers);
polyfunctional monomers (acrylates) having strong double bonds; and
photoinitiators (3% to 8%, and preferably 4% to 5%).
The coating can be applied automatically in a closed enclosure, close to the molding station, since said enclosure is more compact than are traditional installations.
This reduces the extent to which the article is at risk during transport of possible dirtying and of damage to decoration on the article, if any.
In a particular implementation of the method of the invention, the surface on which the coating is deposited is situated inside the article, and the quantity of coating that is deposited is sufficient to enable it to rise under the effect of centrifugal force at least some of the way along the side wall of the article.
Surprisingly, the coating deposited on the bottom of the inside surface rises under the effect of centrifugal force along the side wall of the article, even if the side wall is vertical.
It is thus possible by means of the invention to paint an article whose side wall is parallel to the axis of rotation, whether or not the wall is a body of revolution.
Thus, in an implementation of the method of the invention, the side wall of the article is at least in part cylindrical about the same axis as the axis of rotation about which the article is driven.
The side wall of the article can be stepped.
Still in a particular implementation of the method of the invention, a quantity of coating is deposited on the bottom of the article that is sufficient to enable it to cover the top edge of the article after it has moved up along the side wall thereof.
The invention also makes it possible to paint or varnish articles which cannot be painted or varnished by conventional spraying, either because the opening is too small to enable a spray nozzle to be inserted inside the article, or else because the air present in the bottom of the article constitutes a buffer of gas that tends to oppose diffusion of the sprayed aerosol.
The invention thus makes it possible to paint an article of small section or a flask whose opening is narrower than its bottom.
When the coating that is used does not include any solvent, there is no harm in depositing the coating in excess on the surface to be coated since it is easy to recycle any residual quantity of coating that is ejected from the article during rotation thereof without any risk of harming the environment.
After the coating has spread over the inside surface of the article, rotary drive to the article is preferably stopped immediately, e.g. by stopping the drive mechanism, for the purpose of avoiding any coating running over the outside surface of the article.
In a particular implementation of the method of the invention, the coating which spreads under the effect of centrifugal force is deposited on a surface which is itself substantially plane or slightly convex and situated on the outside of the article.
To paint or varnish such a surface, the method advantageously includes the operations consisting in:
depositing a predetermined quantity of coating in the fluid state on the center of said surface, and spreading it by causing the article to spin; and
applying the coating directly on at least a portion of the remainder of the surface of the article.
These two operations can begin simultaneously or they can be performed one after the other, in whichever order is most suitable for the shape of the article that is to be painted or varnished.
The coating can be applied by means of a jet or a spray or by any other means, and it can be applied over the entire outside surface of the article that is not covered by the coating spreading under the effect of centrifugal force.
Advantageously, while the coating for spreading under the effect of centrifugal force is being deposited on the outside surface of the article, its speed of rotation is zero or very small (e.g. less than 5 revolutions per second (rps)) to avoid any risk of coating being thrown off on first contact with the article.
Preferably, on starting up, the speed of rotation of the article increases very quickly so as to avoid any running associated with the shape of the surface over which the coating spreads.
For example, the article can reach a speed of rotation lying in the range 50 rps to 100 rps in less than 1 second.
The coating can be applied directly to the outside surface of the article by means of a nozzle whose position and orientation are adjustable.
Thus, in a particular implementation of the method of the invention, where the substantially plane or slightly convex surface is generally rectangular in shape when observed from above at the moment when it is set into rotation for spreading the coating under the effect of centrifugal force, the means for applying the coating directly to the surface of the article comprise a nozzle that slopes downwards and that is situated slightly above the periphery of said substantially plane or slightly convex surface.
Advantageously, to paint or varnish inside and/or outside surfaces of an article, the coating used is one that is capable of being cured under the effect of ultraviolet radiation.
Curing of the coating deposited on the article is preferably induced while the article is still rotating.
The invention also provides apparatus for applying a coating on an article having at least one surface that
Beck Shrive P.
Jolley Kirsten Crockford
L'Oreal
Oliff & Berridg,e PLC
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