Coating apparatus – Projection or spray type – With mask or stencil
Reexamination Certificate
2002-07-31
2003-11-25
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
With mask or stencil
C118S314000, C427S374100, C427S421100
Reexamination Certificate
active
06652651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a vehicle lamp having a plastic lens and more particularly to a method for surface treatment of its lens.
2. Description of the Related Art
Transparent lenses or equivalents are now employed in vehicle lamps such as headlamps. However, such a lens becomes fogged with only a few waterdrops sticking to its inner surface and this poses a serious problem in view of its external appearance as quality. Consequently, it has heretofore been contrived to obtain a lens whose inner surface is formed with an antifogging coating film.
In recent years, plastic lenses are increasingly adopted in vehicle lamps such as headlamps. This is because the plastic lenses are lightweight and excellent in shock resistance in comparison with glass lenses; however, as the plastic lenses are poor in scratch resistance, weather resistance and solvent resistance, hard coating films are often formed on their outer surfaces.
From the fact stated above, it is desirable to form antifogging coating films on the inner surfaces and hard coating films on the outer surfaces of transparent lenses or equivalents made of plastic that are adopted as vehicle lamps.
However, the following problem will be posed when it is attempted to form the antifogging coating film and the hard coating film in an offhand manner with the adoption of the aforementioned arrangement.
More specifically, when the hard coating film or the antifogging coating film is formed, a backing jig is employed in order to support a lens. However, as shown in
FIG. 8
, if the hard coat film is formed after the antifogging coating film is formed, there are high possibility that that a lens
6
is scratched because the backing jig
4
may come in contact with the outer surface
6
a
of the lens
6
.
SUMMARY OF THE INVENTION
An object of the present invention made in view of the aforementioned circumstances is to provide a method for surface treatment of a lens of a vehicle lamp so that an antifogging coating film may be formed without scratching the lens when the antifogging coating film is formed on the inner surface of the plastic lens when a hard coating film is formed on the outer surface thereof.
The present invention is intended to accomplish the object above by implementing a method for surface treatment of a lens through the steps carried out in the following proper order.
The method according to the present invention comprises forming a hard coating film on a outer surface of the lens by heating to harden after the hard coating film is applied onto the outer surface of the lens; cooling the lens formed with the hard coating film until the inner surface of the lens has a predetermined temperature; and forming a antifogging coating film on a inner surface of the lens by heating to dry after the antifogging coating film is applied onto the inner surface of the lens.
The “antifogging coating film” may be formed on the whole or part of the inner surface of the lens as long as the film forming range includes a target range where the lens may become fogged.
The “hard coating film” may be formed on the whole or part of the outer surface of the lens as long as the film forming range includes a target range where the scratching of the lens and weather and solvent resistance should be avoided.
As shown in the arrangement above, since the hard coating film is formed before the antifogging coating film is formed according to the present invention, the presence of the hard coating film can prevent the lens from being scratched even though a backing jig is brought into contact with the outer surface of the lens when the antifogging coating film is formed.
Therefore, according to the present invention, the antifogging coating film is formable without scratching the lens even in a case where the antifogging coating film is formed on the inner surface and the hard coating film is formed on the outer surface of the plastic lens.
As the antifogging coating film is formed on the inner surface of the lens according to the present invention, even if a transparent lens or an equivalent is used, the surface-active action of the antifogging coating film prevents poor external appearance that waterdrops sticks to the inner surface of the lens and becomes a water film so that the lens fogs up. On the other hand, the formation of the hard coating film on the outer surface of the lens can improve scratch resistance, weather resistance and solvent resistance of the lens.
Lens elements may or may not be formed on the inner surface of the “lens.” In the latter case, however, as the lens looks foggy even with a few waterdrops sticking thereto, the adoption of the arrangement according to the present invention is specifically effective.
Although the steps of forming the hard coating film, cooling the lens and forming the antifogging coating film constituting a method for surface treatment of the lens may be conducted in different places, the following working effect is achievable by carrying out the whole step in the same clean.
When the aforementioned steps are performed in entirely different places, the number of physical distribution man-hours would be increased to that extent and while the lens formed with the hard coating film is conveyed up to a place where the antifogging coating film is formed, there is the possibility that the lens may be soiled with dirt or scratched. Moreover, the moisture in the air is absorbed by the lens before the antifogging coating film is formed and a whitening phenomenon may occur during the step of forming the antifogging coating film. In other words, since the antifogging coating is hydrophilic, the moisture absorbed into the lens is introduced into the antifogging coating film in the form of waterdrops immediately after the application of the coating and then the moisture in the antifogging coating film is caused to evaporate by heat-drying, so that traces of waterdrops remain to exist. Consequently, there may occur the whitening phenomenon in that the antifogging coating film looks whitish.
On the contrary, performing the whole step mentioned above within the same clean room not only reduces the number of man-hours but also prevents the lens from being soiled and scratched during the conveyance of the lens and also prevents the whitening phenomenon of the antifogging coating film from occurring.
With the arrangement above, the “predetermined temperature” is not restricted to a specific one as long as it is lower than the temperature immediately after hardening by heating during the step of forming the hard coating film. However, setting the inner surface of the lens at temperatures higher than the room temperature of the clean room makes possible the application of the antifogging coating film while the dried condition of the lens is maintained after the heat-hardening process during the step of forming the hard coating film. It is thus prevented to allow the occurrence of the whitening phenomenon in which the lens absorbs the moisture in the air before the coating is applied.
On the other hand, setting the “predetermined temperature” too high causes a phenomenon in which the antifogging coating film is not uniformly formed over the whole area of the antifogging coating film forming area on the inner surface of the lens because the solvent content in the coating is volatilized previously after the antifogging coating film is applied (unsatisfactory leveling). Consequently, it is preferred to set the predetermined temperature at 35° C. or lower.
A method of cooling the lens up to the “predetermined temperature” during the aforementioned cooling step is not restricted in particular but may be what is adoptable in cooling the lens by forcibly blowing cooled air or air thereagainst or by natural cooling depending on the working conditions.
Incidentally, the thickness of the antifogging coating film is also not restricted in particular but may preferably be set at 10 &mgr;m or less for the reason stated below.
Although the antifogging coating film demonstrates its anti
Aikawa Shinji
Anma Hidetaka
Nakamura Koichi
Crispino Richard
Fish & Richardson P.C.
Koito Manufacturing Co. Ltd.
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