Coating processes – Electrical product produced – Hollow article
Reexamination Certificate
2000-07-11
2002-06-04
Beck, Shrive P. (Department: 1762)
Coating processes
Electrical product produced
Hollow article
C427S067000, C427S430100, C118S408000, C118S410000
Reexamination Certificate
active
06399145
ABSTRACT:
BACKGROUND OF THE INVENTION.
The present invention relates to a method for producing lamps, in which a lamp tube is coated with a coating means and the coating means is dried.
In many sectors of lamp production, it is necessary for substantially tubular lamp vessels or parts thereof to beg coated. The most important application relates to fluorescent layers, for which reason the invention preferably relates to fluorescent lamps. However, this is not necessary; rather, the invention can also relate to reflective layers or other layers which can also be used in the case of other types of lamp.
The invention proceeds in this case from a method in which a liquid, or at least a flowable coating means is applied to the lamp tube and dried thereafter. A solid layer is produced from the flowable coating means by the drying step. Generally, this comes about through vaporization or evaporation of a liquid, in which the remaining coating means had been dissolved or suspended previously.
In the known, so-called flushing of fluorescent lamp glass tubes, fluorescent pastes are applied in a pasty, that is to say viscously flowable, state to the inner wall of a glass tube. In this case, the inner wall of the glass tube which is to be coated is brought into contact with the fluorescent paste, for example by flushing the glass tube. Thereupon, the fluorescent paste is allowed to run off until a relatively thin layer remains on the glass wall. The glass tube is then dried in a oven. An essential quality criterion in this case is to observe a prescribed layer thickness- as consistently as possible. On the one hand, the glass wall is to be completely covered, and penetration of UV radiation through the fluorescent layer is to be avoided, while on the other hand in the case of excessively thick fluorescent layers it is impossible to avoid losses through multiple reflections of visible photons in the fluorescent layers. Furthermore, the material costs of the fluorescent paste play a not unimportant role.
The technical problem on which this invention is based consists in specifying a novel method for coating lamp tubes with a coating means which can be used to achieve particularly uniform layer thicknesses.
SUMMARY OF THE INVENTION.
According to the invention, this problem is solved by means of a method for producing lamps, in which a lamp tube is coated with a coating means and the coating means is dried, characterized in that a liquid level of the coating means is lowered along the lamp tube, and a local drying zone of a layer, left behind by the sinking of the liquid level, of the coating means on the lamp tube tracks the sinking liquid level at a substantially constant time interval.
Thus, according to the invention the running off of the excess coating means from the wall of the lamp tube is achieved in a particularly controlled way by permitting a liquid level to sink. Specifically, it has emerged that drips, or even drops are a substantial cause of layering non-uniformities in conventional methods.
The invention also provides for a drying zone to track the sinking liquid level at a substantially constant time interval. As a result, substantially the same time elapses for all parts of the layer between the sinking of the liquid level at this point and the drying. Specifically, it has further turned out that the non-uniformity of the drying time for different parts of the layer produced is a further main cause of non-uniformities.
Thus, when a coating means which has been rinsed in is allowed to run out, and the entire lamp tube is dried in a oven, it cannot be avoided that the higher lying parts of the layer become thinner than the deeper lying parts, because the coating means which runs off from the higher lying parts stills passes the deeper lying parts. Consequently, a lesser residual layer thickness remains in the higher lying parts than in the deeper lying parts. It is also scarcely possible in the case of the conventional methods to take account of these circumstances with the aid of the drying process by, for example, carrying it out in temporal sequence from top to bottom in a continuous fashion. Specifically, this is because the remains of the coating means which are running out do not prescribe any defined temporal sequence for the drying process. Rather, what happens is more an undefined and statistically varying running out, which does not necessarily leave the same coating thickness on parts of the lamp tube at the same level, because drips or even drops come to be formed, as already mentioned.
The layers are preferably situated inside the lamp tube, the liquid level then being lowered in the lamp tube. For this purpose, the lamp tube is first filled with the coating means, whereupon the coating means then run out as a liquid column, that is to say with a largely defined upper liquid level. It is to be noted in this case that the term “liquid” in the description of this invention also includes viscous, but still flowable, media. Thus, here liquid also means pulp or paste, as long as flowability obtains.
Furthermore, the lamp tube is preferably arranged vertically, as a result of which it is possible to achieve the best uniformity over the circumference of the lamp tube (inner or outer circumference) to be coated.
So far, the discussion has been of a “drying zone” in a general sense. In fact, the invention can also be understood in general such that it is possible to produce in any way a drying zone which is locally defined to the extent that it is possible to talk of tracking in relation to the liquid level at a constant time interval. In general, a drying device is moved relative to the lamp tube in a fashion coordinated with the sinking of the liquid level. However, it is also possible in the case of a fixed relationship between a drying device and the lamp tube to produce a moving drying zone, for example by sequential use of different drying zones in a drying device. The degree of local definition of the drying zones in this case relates also only to the side facing the liquid level. On the other side, on which the coating means at least is dried to such an extent that no more changes in its thickness can take place by flowing processes, no fundamental role is played by the extent to which the drying zone extends or is defined at all. On the side facing the liquid level, as well, the concept of the degree of local definition is not to be understood that there must be a sharp boundary of the drying zone. For all parts of the wall of the lamp tube which are to be coated, it is essentially fully sufficient to have essentially equal time intervals from the liquid level up to a drying which fixes a layer thickness, and so the drying zone is also only to be locally defined to that extent.
The invention is preferably directed to the two variants of the production of such a drying zone. In the first variant, a local heating of the coating means and/or of the lamp tube is carried out. This can be carried out in a favourable way by relative movement between the lamp tube and a oven surrounding the lamp tube, the drying zone generally lying somewhat above the lower edge of the oven. Reference may be made to the first exemplary embodiment for this purpose.
The second variant consists in circulating a gas atmosphere e which serves the purpose of drying. For example, this can be done by introducing into the lamp tube an aerating tube which is essentially parallel to the lamp tube, and tracking with reference to the liquid level. A drying gas can flow in this case through the aerating tube. This can be done by causing the drying gas to flow in through the aerating tube, or else by sucking in or discharging it through the aerating tube and feeding it in another way. In each case, what is important is that there is produced above the liquid level at a certain distance a turbulence zone of the drying gas in which the drying is performed. The turbulence zone is formed below the opening, facing the liquid level, in the aerating tube, and should be deeper-lying than the openings for discharging or
Jerebic Simon
Vollkommer Frank
Beck Shrive P.
Bessone Carlo S.
Cleveland Michael
Patent-Treuhand-Gessellschaft fuer Elektrische Gluehlampen mbH
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