Device for wet coating, in particular printed circuit boards, with lacquer

A device for wet coating, in particular printed circuit boards, with lacquer using at least one applicator roller (20, 21) and sparing at least one edge area of the printed circuit boards. The device uses a doctor blade arrangement situated between a lacquer reservoir and the printed circuit board that can move in an axial direction, one edge of which touches the applicator roller (20, 21). The doctor blade arrangement is designed can also remove excess lacquer, for example, photo-resistant lacquer from a multilayer board, from both longitudinal edges of the printed circuit board without any residue. This is also possible for multilayer boards of varying widths in particular. By laterally displacing the lacquer from the respective peripheral edges of both applicator rollers (20, 21) that are to kept free of lacquer, this lacquer is directly fed back into a lacquer reservoir via the outer edge area of the pertaining applicator roller without leading to an accumulation of lacquer, dirtying and breaking-down of the machine.

BACKGROUND OF THE INVENTION
 1. Technical Field
 The invention relates to a device for wet coating, in particular printed
 circuit boards, with lacquer by means of at least one application roller,
 leaving at least one edge area of the printed circuit board free and
 employing a doctor blade arrangement.
 2. Prior Art
 Such an arrangement is known from DE-GM 85 03 321, it is essentially used
 to obtain a lacquer-free gripping edge in multi-layer printed circuit
 boards which are coated on one or both sides, in particular with variable
 coating widths, in the course of a rolling method. A more detailed
 description of this problem can also be found in DE-PS 44 17 518.
 The doctor blade arrangement in accordance with the first-mentioned utility
 model consists of two independent strippers, which leave the problem of
 what to do with the lacquer stripped off in the area of the circumference
 of the roller. If no reasonable solution is provided for this, this known
 solution can lead to accumulations of lacquer at undesired places,
 soiling, and interference with the operation of the entire device.
 BRIEF SUMMARY OF THE INVENTION
 The essential object of the invention therefore is to further develop such
 doctor blade arrangements in such a way that they can be adapted to modern
 roller designs (cyclical processes) and permit the controlled displacement
 of the lacquer from the circumferential area of the application roller.

DETAILED DESCRIPTION OF THE INVENTION
 The attainment of the object in accordance with the invention can be found
 in a first embodiment by means of a perspective basic representation in
 FIG. 1:
 In a known manner, the multi-layer board 10 to be coated is passed between
 two application rollers 20 and 21, which are arranged one above the other
 and rotate in opposite directions, or is respectively taken along by them,
 so that the photo-resist lacquer, for example, which adheres there is,
 evenly distributed from the circumference of the application roller 20, 21
 to the multi-layer board 10. In this connection it is known to leave a
 first edge F1/F2 of the printed circuit board 10 free of the coating in
 that the application roller 20 and the metering roller 30 cooperate in
 this area (on the right in FIG. 1) in such a way that coating of this edge
 F1 by the upper application roller 20, and of the lower edge F2 by the
 lower application roller 21 is prevented. This is without problems
 regarding any formats of printed circuit boards, since the edge of the
 printed circuit board 10, which is on the right in FIG. 1, can always be
 appropriately aligned.
 However, with printed circuit boards of varying width the upper edge R1, or
 respectively the lower edge R2 on the opposite longitudinal side of the
 printed circuit board 10, takes up a changing relative position in respect
 to the circumference of the application roller 20, 21, so that it is
 necessary here to free a circumferential area S1, S2 of the application
 rollers 20, 21 from applied lacquer, whose axial position on the
 application rollers 20, 21 can be variably set.
 The doctor blade arrangement 40 has only been represented in principle in
 FIG. 1, these are two strippers which are placed wedge-like in respect to
 each other and have curved stripping edges 45, 46 (FIG. 3), forming an
 angle in the range of 40.degree. to 50.degree. in respect to each other.
 Here, the radius of the curved stripping edge 45, 46 is of such a
 dimension that, in the relative positioning of the stripper 40, 41
 represented in FIG. 1, it rests, or respectively can be placed, against
 the circumference of the application rollers 20, 21.
 A first, upper lacquer reservoir 60 is located between the upper
 application roller and the upper metering roller, and correspondingly a
 second, lower lacquer reservoir 61 between the lower application roller 21
 and the lower metering roller 31. The metering rollers 30 and 31 can be
 adjusted in relation to the application rollers 20, 21 in such a way that
 a variable roller gap is formed, by means of which the thickness of the
 lacquer application on the multi-layer board 10 can be defined.
 The relative arrangement of the two strippers 40, 41, which are inclined
 wedge-shaped in respect to each other, on the one hand and, on the other,
 in respect to the application rollers 20, 21, and the arrangement of the
 lacquer reservoirs 60, 61 now has been selected to be such that, when the
 device is operated, i.e. when the application rollers 20, 21 rotate in the
 direction of the arrow, the lacquer from the lacquer reservoir which has
 already been applied is laterally pushed away in a circumferential area S1
 on the upper application roller 20, or respectively S2 on the lower
 application roller 21, which is intended to be shown by the
 non-cross-hatched circumferential areas of the application rollers 20, 21
 in FIG. 1. A lacquer flow V1, or respectively V2, results from this
 lateral displacement of the lacquer, which is represented by the arrows in
 FIG. 1 and FIG. 2. In this case it is of essential importance that the
 excess lacquer from the circumferential areas S1, S2, which are to be made
 lacquer-free, is directly returned via the outer edge areas of the
 associated application roller to one of the two lacquer reservoirs 60, 61.
 By displacing the doctor blade arrangement, consisting of the strippers 40
 and 41, in the direction of the longitudinal axes of the rollers, the
 relative position of the stripped-of circumferential area S1, S2 can be
 defined in a simple manner in such a way, that the desired lacquer-free
 upper edge R1, or respectively lower edge R2, is created on the
 multi-layer board 10.
 The structural embodiment as a part of the doctor blade arrangement R of
 the strippers 40, 41, which have been only schematically represented in
 FIG. 1 for better understanding, is shown in greater detail in FIGS. 2 and
 3.
 Both strippers 40 and 41 are seated on a common guide block 50, which can
 be displaced by means of a spindle drive 51, by means of this the above
 mentioned axial displacement and therefore the definition of the
 stripped-off circumferential area S1, S2 on the application rollers is
 provided. Here, the doctor blade suspension has been made resilient so
 that, even with an application roller moved upward in a cyclical manner,
 the strippers 40, 41 always remain in contact in order to immediately
 achieve a lacquer-free edge at the start of the multi-layer board 10. The
 strippers 40, 41 can be rapidly changed for cleaning, even if strippers
 must be used which are correspondingly adapted to the reduced roller
 diameter occurring when the application rollers are re-ground.
 The strippers are centered and adjusted on the work side of the guide block
 50. During the cyclical movement, the upper stripper 40 is pushed downward
 by the upper metering roller 30 and thereby creates the required contact
 pressure on the lower application roller 21. In order not to transfer
 these pressure forces to the spindle drive 51, the upper stripper 40 is
 resiliently seated on the guide block 50, as already mentioned above.
 The fine adjustment of the strippers can be accomplished by means of
 screws.
 The fixed-in-place metering rollers 30, 31 in the sectional view in FIG. 2
 have been provided with different cross sections, which brings about two
 advantages:
 First, a drip edge is created, so that no cleaning agent can run down along
 the shell of the metering rollers during cleaning and result in soiling,
 furthermore, an enlargement of the lower lacquer reservoir 61 is achieved
 by means of the positioning of the lower metering roller 31, which is
 advantageous during continuous operation.