METHOD AND APPARATUS FOR TWO-LAYERED COATING OF COPPER FOILS WITH MELTABLE COATING

Abstract: A method is described which is characterised in that copper foils are twice-coated with meltable coating means in such a way that the copper foil (19) is guided approximately half encirclingly about a heatable roll (1), and coated by means of two heatable roll-type coating units (2, 4 & 3, 5) in such a way that in a first coating operation, there is applied from the melt an ultravioletly and thermally hardenable solvent-free coating means and in a second coating operation, a solvent-free, only thermally hardenable, meltable coating means is applied over the first coating means, and in that the first binding agent layer is cross-linked by radiation by ultraviolet radiators disposed downstream. There is furthermore described an apparatus for execution of the method.

Description: METHOD AND APPARATUS FOR TWO-LAYERED COAΗNG OF COPPER FOILS WITH MELTABLE COAΗNG In order to manufacture sequential multi-layers, it is necessary to press or to laminate copper foils coated with dialectical resins onto printed circuit boards. In this connection, the resin must have a very good flowability, in order to be able to fill, free of air-bubbles, the gaps between conductors. An opposing requirement resides in the fact that the vertical spacing between the conductor levels must be constant, in order to guarantee a uniform insulation spacing. In order to be able to meet this requirement, the resin must have as little flowability as possible. Preferably, the resin should not change, under the effect of temperature and pressure, its layer thickness obtained on the copper foil. In order to be able to meet these opposing requirements, coating methods have been described, in which solvent-containing resin was applied to the copper foil in a first coating process, the solvent was dried and the resin was pre-hardened up to the C-stage under the influence of temperature. The C-stage means, in regard to epoxy resins, that all epoxy groups are crosslinked and that no more free epoxy groups are detectable. The foil coated in this manner is then coated a second time with the same epoxy resin solution. This second layer must be capable of flowing under application of pressure and temperature. Accordingly, it is only dried and, if required, pre- hardened up to the imminent B-stage. For a dryer temperature of 160°C and a dryer length of 10 metres with a gelling time of 180 seconds at 160°C, the first coating requires a coating speed of three metres per minute . In view of the above, the present invention seeks to provide a method, and an apparatus in which a drying and pre-hardening is not necessary after the first coating, and which thus achieves coating speeds of greater than 10 metres per minute. A method of this kind has been described in P195 39 193.4. Here there were used powdered resins having different melting point and a first layer was applied having a high melting point as well as a second layer having a low melting point. This method is very difficult to control in particular because of the high melting temperatures and coating temperatures, since the hardening reaction sets in and unacceptable processing times are obtained. According to the present invention, there is provided a method for the two layered coating of copper foils with meltable coating means, characterised in that a copper foil is guided approximately half encirclingly about a heatable roll, and coated by means of two heatable roll-type coating units in such way that in a first coating operation, there is applied from the melt an ultravioletly and thermally hardenable solvent-free coating means and in a second coating operation, a solvent-free, only thermally hardenable, meltable coating means is applied over the first coating means, and in that the first binding agent layer is crosslinked by radiation by ultraviolet radiators disposed downstream. According to a second aspect of the- present invention there is provided a method for the multi- layered coating of foils with meltable coating means, characterised in that a foil is guided approximately half encirclingly about a heatable roll and coated by means of two heatable roll-type coating units in such a way that in a first coating operation, there is applied from the melt a first solvent-free coating means which is hardenable by exposure to ultraviolet radiation and by heating and in a second coating operation, a second solvent -free, only thermally hardenable, meltable coating means is applied over the first coating means, and in that the first coating means is crosslinked by radiation by ultraviolet radiators disposed downstream. Preferably, there is used, for the first coating, an ultravioletly and thermally hardenable epoxy resin which may be melted on at temperatures under 100°C. At this temperature, a hardening reaction only takes place so slowly that the coating process is not impaired. For a better understanding of the present invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawing. For the purpose of coating, the copper foil is placed about a heated roll, winding around half of the roll. This roll (1) should have as large a diameter as possible. A diameter is advantageous which corresponds to about twice the diameter of the applicator rolls (2) and (3) . To the surface of this heated foil roll (1 ) there are applied roll-type coating units, one each in the horizontal axis- and in the vertical axis. The first heatable roll-type coating unit comprises the metering roll (4) and the applicator roll (2) . This roll pair forms a gap, into which the melted resin is metered from a heated resin supply vessel (6) disposed above the gap . In the vertical axis of the foil roll (1) there is disposed a second roll-type coating unit comprising the applicator roll (3) and the metering roll (5) . Above this roll pair there is disposed a second heated resin supply vessel (7) , out of which a second melted, only thermally hardenable resin is supplied to the roll pair (5,3) . The second coating is applied wet-on-wet to the first layer. On completion of coating, the foil (9) is drawn tangentially off the foil roll (1) at an angle of 45° and the varnish layer (8) is radiated by an - 4 - ultraviolet radiator (10) . This radiation may also be further intensified by a vertical deflection of the foil (9) . Cooled deflection rolls (11) , (12) & (13) are required for this purpose. Between the rolls (11) S_ (12) there is disposed an ultraviolet radiator and between the rolls (12) & (13) an infrared radiator. After cooling off to ambient temperature, the foil (9) is wound up on a winding station (14) . The temperatures of the applicator rolls (2) & (3) are chosen so that there is produced, from the mean of the applicator roll temperature (2) &. (3) and the temperature of the foil roll (1) , a mean coating temperature at which the epoxy resin to be applied has a melt viscosity of approx. 5,000 to 15,000 mPa . s . The ultraviolet radiation after the double coating ensures that the first varnish layer (17) is crosslinked by radiation. The second varnish layer (8) is smoothed by the heating, but does not harden. A defined pre-hardening of the second layer (8) is achieved by the infrared radiator (16) . The present invention is to be explained with reference to the following example: Example: Coating means 1 45.00 parts by weight Rϋtapox VE 4704 R by Bakelite 36.00 parts by weight Mg ( OH) 2 15.00 parts by weight cresol novolak 3.00 parts by weight 2-ethylanthraquinone, BASF 0.50 parts by weight 2-ethyl-4-methylimidazole, BASF 0.50 parts by weight helio fast green 100.00 parts by weight 100 % by weight Coating means 2 53.00 parts by weight Rϋtapox 0400 by Bakelite 18.00 parts by weight Rύtapox 0164 by Bakelite 28.00 parts by weight cresol novolak 0.50 parts by weight 2-ethyl-4-methylimidazole 0.50 parts by weight helio fast green 100.00 parts by weight 100 % by weight Electrolytic copper foil thickness 17.5 μm The coating means 1 is put into the supply vessel (6) which is preheated to 60°C. The applicator roll (2) and the metering roll (4) are brought to a temperature of 60°C. The foil roll (1) is brought to a temperature of 70°C. The costing means 2 is put into the varnish supply tank (7) which is brought to a temperature of 100°C. The applicator roll (3) and the metering roll (5) are heated to 100°C. The applicator roll (2) &. (3) are provided with a 3 nm thick rubber coating which is profiled. The profiling amounts to 125 grooves per 25 mm. The varnish film divides in the middle. 25 μm of layer thickness are applied in each coating operation. The coating speed is 15 metres per minute. The ultraviolet hardening of the first layer is carried out in 2 x 10 seconds. The ultraviolet radiators (10) & (15) each have a length of 2,500 mm. The deflection rolls (11) , (12) & (13) are cooled to 5 -6- °C. The roll surface is teflon coated. Coating plant : Foil roll diameter 500 mm, chromium-plated (1) Metering rolls (4,5), diameter 250 mm Applicator rolls, rubber-coated, 3 mm LURA 2105, Shore A 40, by Lύraflex Diameter 250 mm Ultraviolet radiator, 10 kW, wavelength 350 nm, length 2,500 mm (10, 15)

Claims: CLAIMS 1. A method for the two layered coating of copper foils with meltable coating means, characterised in that a copper foil (19) is guided approximately half encirclingly about a heatable roll (1) , and coated by means of two heatable roll-type coating units (2,4) & (3,5) in such way that in a first coating operation, there is applied from the melt an ultravioletly and thermally hardenable solvent-free coating means and in a second coating operation, a solvent-free, only thermally hardenable, meltable coating means is applied over the first coating means, and in that the first binding agent layer is crosslinked by radiation by ultraviolet radiators disposed downstream. 2. A method as claimed in Claim 1, characterised in that the mean value of the temperatures of the applicator rolls (2 & 3) and of the foil roll (1) produces a temperature at which the coating means reaches a viscosity of 5,000 " to 15 , 000- mPa. s . 3. An apparatus for execution of the method according to Claim 1, characterised in that on a heated roll having a preferred diameter of 200 to 600 mm, two roll-type coating units comprising heatable applicator rolls (2) (3) having a preferred diameter of 100 to 300 mm are disposed in such a way that the first applicator roll (2) touches the foil (19) in the horizontal axis of the foil roll (1 ) and the second applicator roll (3) does so in the vertical axis. 4. An apparatus as claimed in Claim 3 , characterised in that the diameter of the foil roll (1) is approximately twice as large as the diameter of the applicator rolls (2 & 3) . 5. An apparatus as claimed in Claim 3 , characterised in that ultraviolet radiators (10,15) are disposed after the roll-type coating unit (3,5). 6. A method for the multi-layered coating of foils with meltable coating means, characterised in that a foil is guided approximately half encirclingly about a heatable roll and coated by means of two heatable roll-type coating units in such a way that in a first coating operation, there is applied from the melt a first solvent-free coating means which is hardenable by exposure -to ultraviolet radiation and by heating and in a second coating operation, a second solvent-free, only thermally hardenable, meltable coating means is applied over the first coating means, and in that the first coating means is crosslinked by radiation by ultraviolet radiators disposed downstream.

Inventors: SCHAEFER HANS JUERGEN, SCHAEFER, HANS, JUERGEN
Applicants: ELECTRA HOLDINGS LTD, SCHAEFER HANS JUERGEN, ELECTRA HOLDINGS LTD., SCHAEFER, HANS, JUERGEN
Application year: 1999
Main classification: B05D3
IPC codes: B05C1, B05C9, B05D1, B05D3, B05D7, H05K3