Source: http://www.google.com/patents/US5112453?dq=6948823
Timestamp: 2014-04-24 22:48:38
Document Index: 491190754

Matched Legal Cases: ['art17', 'art20', 'art 15', 'art25', 'art  15', 'art  20', 'art 1', 'art 1', 'art 1']

Patent US5112453 - Method and apparatus for producing etched plates for graphic printing - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsThere is provided an apparatus and a process for using same for etching a metallic object (22), suitably a plate to prepare a metallic printing plate. The object is partially covered by a resist surface (14) wherein the exposed portions (16) of said metal, will be exposed to the action of an electrolytic...http://www.google.com/patents/US5112453?utm_source=gb-gplus-sharePatent US5112453 - Method and apparatus for producing etched plates for graphic printingAdvanced Patent SearchPublication numberUS5112453 APublication typeGrantApplication numberUS 07/788,244Publication dateMay 12, 1992Filing dateNov 5, 1991Priority dateOct 31, 1990Fee statusPaidPublication number07788244, 788244, US 5112453 A, US 5112453A, US-A-5112453, US5112453 A, US5112453AInventorsOmri M. Behr, Marion R. BehrOriginal AssigneeBehr Omri M, Behr Marion RExport CitationBiBTeX, EndNote, RefManPatent Citations (6), Referenced by (35), Classifications (18), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetMethod and apparatus for producing etched plates for graphic printingUS 5112453 AAbstract There is provided an apparatus and a process for using same for etching a metallic object (22), suitably a plate to prepare a metallic printing plate. The object is partially covered by a resist surface (14) wherein the exposed portions (16) of said metal, will be exposed to the action of an electrolytic etchant force. The apparatus comprises a bath (10) for an aqueous electrolyte (12), an electrode (23), suitably but not critically metallic, immersible in said electrolyte, which will serve as the cathode, a source of direct current voltage (32), which may further be associated with adjustment means (38) for controlling the applied voltage. The voltage should be adjustable to operate accurately within a rather narrow voltage range, such that the minimum voltage shall be at least that of the ionization potential of the metal of the metal object in the electrolyte chosen and the maximum shall not substantially exceed the sum of the decomposition voltage of the aqueous electrolyte and the over-voltage of the cathode selected.
We claim: 1. A process of etching a roughened surface directly onto a metallic object, the original surface whereof is partially covered by a resist surface and causing the thus exposed portions of said metal object to be subjected to the action of an etchant force in an electrolytic bath containing an aqueous electrolyte, an electrode and a source of direct current voltage having a positive pole and a negative pole, comprising the steps ofa) immersing said metallic object to be etched in said bath proximate to but spaced from said electrode, b) connecting the negative pole of said direct current voltage source to said electrode and the positive pole to said metal object whereby said electrode becomes the cathode and said metal object becomes the anode and c) applying direct current voltage, wherein the improvement comprisesproviding the applied voltage so that it shall be at least that of the ionization potential of the metal of the object in the electrolyte chosen and shall not substantially exceed the sum of the decomposition voltage of the aqueous electrolyte and the over-voltage of the cathode selected, whereby hydrogen evolution is avoided and applying said selected voltage until the desired depth of metal has been removed from the exposed portions of the anode and the desired degree of roughness attained thereon. 2. A process of claim 1 wherein said direct current voltage source additionally comprises a means for adjusting the voltage.
RELATED APPLICATIONS This application is a continuation in part of applicants' co-pending application Ser. No. 07/606,871 filed Oct. 30, 1990 now U.S. Pat. No. 5,102,520.
FIELD OF THE INVENTION Environmentally acceptable etching of metals.
BACKGROUND OF THE INVENTION The art of etching metal plates in order to produce a reproducible image is centuries old. The basic principle involves putting a resist coating on the surface of a clean smooth metal plate, removing a portion of this resist with a suitable tool such as a needle and then immersing the metal plate for a predetermined time in an acid bath in order to bite or remove a portion of the metal which is exposed thereby. The resist is then dissolved off, usually by means of a solvent, and a printing ink rubbed into the surface of the plate. The plate is then rubbed with a cloth to remove all or substantially all of the ink that does not reside within the grooves caused by the etching process. The plate is then laid face up on a suitable surface, covered with a suitably prepared, usually moist paper sheet and pressure applied thereto, usually by means of roller press. This procedure causes the ink to be transferred from the grooves in the metal plate on to the paper to give the printed image.
SUMMARY OF THE INVENTION The solution of the problem posed by traditional anodic etching procedures is solved by operating in a very narrow voltage range wherein the minimum voltage is controlled by that potential necessary to convert the metal of the etched object or plate into ionic form and the maximum is that voltage above which hydrogen gas is generated at the cathode.
This voltage adjustment means should be able to operate accurately within a rather narrow voltage range, suitably between about 0.3 and about 2.5 volts with a sensitivity of about .+-01 v, preferably 0.001 v. This is required because the voltage range for the process is such that the minimum voltage shall be at least that of the ionization potential of the metal of the metal plate in the electrolyte chosen and the maximum shall not substantially exceed the decomposition voltage of the aqueous electrolyte plus the overvoltage of the cathode selected. The term "substantially" as used herein, means that if the stated voltage is exceeded this excess is such that there shall be no observable generation of hydrogen at the cathode or oxygen at the anode.
As in the conventional preparation for etching, the rear face of the plate (or object) is covered with a resist material. Zinc plates for etching are usually sold with such a resist backing painted thereon. Where this is not initially present as in copper plates or solid objects, the rear surface may be covered with paint, hard ground or where flat with adhesive polymeric sheets (sold under the trade name Con-Tact Corporation of North Carolina, U.S.A., for example). Since sharp edges are well known to concentrate electric current, care should be taken to coat the edges which are present. Where embossment or large surface aquatinting by the direct method is desired, the front face can be covered with such adhesive polymeric sheet and the areas to be treated cut away.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side-elevational representation of an apparatus of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side-elevational view of an apparatus of the present invention showing all of the possible monitoring and condition adjustment mechanisms. The mode of connecting the detecting mechanism to the adjusting mechanisms to provide automatic feed-back and adjustment upon change of preset conditions, would be apparent to one skilled in the art.
The temperature is not critical, provided that it does not interfere with the adhesion of the resist to the metal plate. Thus operative temperatures will range from the freezing point of the electrolyte to about 30 C. However, at this higher temperature some softening of certain resists may begin. Therefore, it is preferable not to exceed 26 pumping system is not employed, circulation of the electrolyte can be enhanced by bubbling air through sintered disk 44 via inlet tube 25. Care should be taken however that the flow of air is not so intense as to cause loss of electrolyte by spattering.
The voltage at which the process is operated depends upon a combination of the constituents of the electrolyte, the nature of the metal plate and the nature of the electrode. The voltage should be sufficiently high to enable to metal of the metal plate to be converted into the ions. The voltage relative to a standard hydrogen electrode (O v.) will range from -1.42 volts for gold (Au -3e=Au.sup.+++), to +0.76 volts for zinc (Zn -2e=Zn.sup.++). The specific voltages may noted from the known reduction potentials. The upper limit for the cell is the highest voltage at which hydrogen is not generated at the cathode. Generally speaking, this is a function of the relationship between the material of the cathode and the electrolyte. For copper in copper sulphate, for example, this theoretically lies in the region of approximately 1.7 volts. However, there is an additional, incompletely understood, phenomenon, known as over-voltage, which raises the voltage at which hydrogen may be generated by a further amount, usually about 0.5 volts.
EXAMPLES General Experimental Conditions The examples set forth below were carried out under certain general conditions. The cathode was a plate of the same metal as that of the anode plate to be etched. The metals used were zinc and copper. The back part of the anode was covered with a resist of transparent adhesive plastic known commercially as "Con-Tact bottom edges of the plate by about 0.3". The juncture of the plastic with the front part of the plate was sealed with a thin film polyacrylic solution. The remaining part of the front of the plate was covered with Le Franc and Bourgeois hard ground #3764, on which, when dry the design to be etched was drawn.
EXAMPLE 1 ______________________________________a) Metal: Copper (18 Gage)  Electrolyte: 0.2 M Copper Sulfate.pH 4.0Time in min.     voltage mA                                Comment______________________________________ 0        1.00    52      22   Full picture exposed10        1.06    48      "    Tower blocked20        1.04    15      "    Tree blocked30        1.03    15      "    Pond + Path blocked40        1.03    15      "    House/Mts Left.______________________________________
______________________________________b) Metal: Zinc (20 Gage)  Electrolyte: 0.2 M Zinc Sulfate.pH 4.0Time in min.     voltate mA                                Comment______________________________________ 0        .503    25      22   Full picture exposed15        .503    25      "    Tower blocked35        .502    25      "    Tree blocked55        .503    22      "    Pond + Path blocked75        .502    18      "    House/Mts Left.______________________________________
EXAMPLE 2 The process was carried out in the general manner except that in place of hard ground a second layer of Con-Tact face. An outline of a head, about 2 mm wide was drawn and the drawn segment cut out with a sharp blade to expose the copper.
______________________________________Metal: Copper (18 Gage)  Electrolyte: 0.2 M Copper Sulfate.pH 3.5Time in hrs.     voltage mA                                Comment______________________________________0         1.09    50      22   Start17        1.04    45      "    Breakthrough noted at                          sharp angles on figure28.7      1.08    30      "    ca. 10% not cut                          through29.7      1.05    40      "    complete cut.______________________________________
EXAMPLE 3 In place of hard ground, rosin was dusted on the plate and partially melted in the conventional manner to provide an aquatint resist. The anode was about 4" square as was the cathode. At 20 minute intervals segments of the plate were covered with stop out varnish.
______________________________________Metal: Copper  Electrolyte: 0.2 M Cupric Sulfate. pH: 4.0Time in min.     voltage mA                                 Comment______________________________________ 0        0.80    250     22    Start20        0.68    250     "     Voltage reduced to                           prevent current                           exceeding 250 mA40        0.68    250     "60        0.72    240     "80        0.71    160     "     Stop______________________________________
The Con-Tact with gasoline and the plate then printed in the conventional manner by rubbing ink into the etched lines on the plate, cleaning the surface of the plate, laying damp paper over the inked side of the plate and running through a French Tool bed/roller press. A clear differentiation of different shades of grey were noted between the segments.
EXAMPLE 4 In accordance with the general method, a copper plate was cleaned successively with acetone, isopropyl alcohol, and soap-and-water, to remove all traces of grease, and immersed in the bath with a jet projecting electrolyte "parallel" to and between the anode and the cathode. After each interval, the anode was removed from the bath and brushed with a soft brush under a stream of water to remove the brown/purple residual copper and dried. A segment of the plate was coated with a stop out varnish formulated for electroplating (MICCROSHIELD manufactured by Miccro Products, Tolber Div., Pyramid Plastics Inc., Hope, Ark., U.S.A.). The resultant plate is illustrated in FIG. 8.
______________________________________Metal: Copper  Electrolyte: 0.75 M Cupric Sulfate. pH: 4.0Time in min.     voltage mA                                 Comment______________________________________ 0        0.49    730     26    Start 15       0.49    730     " 30       0.49    620     " 60       0.49    620     "120       0.49    360     "240       0.49    450     "420       0.49    480     "660       0.49    380     "975       0.49    310     "1335      0.49    140     "     Excess pitting. Stop______________________________________
The Con-Tact with (MICCROSTRIP B Pyramid Plastics Inc., Hope, Ark., U.S.A.) and the plate then printed in the conventional manner by rubbing ink into the roughened areas on the plate, cleaning the surface of the plate, laying damp paper over the inked side of the plate and running through a French Tool bed/roller press. A clear differentiation of different shades of grey were noted between the segments.
EXAMPLE 5 The process was carried out in the general manner except that in place of hard ground a layer of soft ground was coated on the plate and a paper heart outline and a pair of small leaves were placed on the soft ground and pressed in with the roller/bed press. The plate was backed with spray enamel and edged with hard ground.
______________________________________Metal: Copper (18 gage)  Electrolyte: 0.2 M Cupric Sulfate.pH: 3.5Time in min.      voltage   mA                                    Comment______________________________________ 0         1.03      80     22      Start25         1.03      80     "______________________________________
EXAMPLE 6 The process was carried out in the general manner except that in place of hard ground a layer of soft ground was coated on the plate an open weave patterned muslin cloth with a paper figure outline placed thereon and pressed in with the roller/bed press. The plate was backed with spray enamel and edged with hard ground.
______________________________________Metal: Copper (18 gage)  Electrolyte: 0.2 M Cupric Sulfate.pH: 3.5Time in min.      voltage   mA                                   Comment______________________________________a)      0      1.06      120  22     Start  15       .98      160  "b)      0      1.06      150  22     Start  20      1.06      150  "______________________________________
EXAMPLE 7 In accordance with the general procedure two copper plates were prepared whereon two areas of 4 cm.sup.2 on each plate were blocked out under the hard ground resist, the Con-Tact sheeting. (a) One such area was exposed on each plate and the plates were then etched at 0.5 V and ca. 22 C. for 30 minutes in baths of 0.75M Copper sulfate and ammonium sulfate respectively and the amperage tracked. (b) The experiments were repeated in that on the plate to be immersed in ammonium sulfate the second area was exposed and the initial area was blocked with stop out varnish. (c) The experiments were repeated in that on the plate to be immersed in copper sulfate the second such area was also exposed leaving the first open and on the other plate the second area was again exposed (the first still being blocked with stop out varnish.
______________________________________Time in min.    mA Cu++    mA (NH.sub.4).sup.+                                                          Comment______________________________________a)    0      120        70       22    Start 1      100        40       " 2       90        40       "15       80        30       "20                 30       "30       80        30       22    stopb)    0                 60       22    Start 1                 50       " 2                 50       "10                 50       "20                 50       "30                 50       "     Stopc)    0      200        70       22    Start 1      160        70       " 2                 50       "10                 40       "15      160        40       "30      160        40       "     Stop______________________________________
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