Method for manufacturing a die

A method for manufacturing an element with a conducting surface and a pattern of insulating spots to be used as a die for the electrolytic production of sieves for screeen printing. The method starts from a conducting surface consisting of or coated with a material that either possesses insulating properties or can be rendered insulating after heating, the surface being patternwise irradiated with short pulses of a high-energy radiation, such that countersunk spots of an insulating substance are obtained on the surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of manufacturing a die, starting 
with a conducting surface, provided with a pattern of an insulating 
material, by means of which die a sieve for screen printing can be 
manufactured in an electrolytic manner. 
2. Description of the Prior Art 
Dies of said type have been used in the art; they comprise a flat or a 
curved surface or they may consist of a closed cylinder, the conducting 
surface being a metal or another material, which is provided with a 
conducting upper layer. 
An electrolytic manufacture of the respective sieve material has also been 
used in the art and is disclosed in the West German Magazine 
"METALLOBERFLACHE" 19th issue, volume 12, December 1965, pages 369-372. 
The respective die comprises a flat or curved sheet and in particular 
cases, also a cylinder having an electrically conducting surface, mostly 
consisting of a metal such as aluminium, copper, steel, nickel or 
chromium, upon which a pattern or grate is applied of insulating parts, 
which pattern corresponds with the pattern of the desired pores in the 
screen printing sieve to be manufactured. The insulating parts upon the 
die surface may be obtained by various different methods, e.g. by means of 
a photographic method, whereby a layer is applied upon the die surface, 
which layer is sensitive to electromagnetic radiation, said layer having 
the desired insulating properties. The layer is subjected to 
electromagnetic radiation through a mask, comprising a positive or 
negative image of the desired perforation pattern, which electromagnetic 
radiation is so carried out that after completion of the same and an 
eventual development, the concerning die surface comprises the desired 
pattern of insulating parts. 
Said method is unsatisfactory, as said insulating parts will slightly 
project above the die surface, such, that on manufacturing the sieve 
material and at the subsequent removal from the die surface, said 
insulating parts will be damaged in such a manner that only one sieve or 
at most a very limited number of sieves may be manufactured upon said die 
surface. It will be obvious that the life of the respective die surface 
will be very restricted, due to the necessity of using an 
electromagnetic-radiation-sensitive product for applying said insulating 
parts. 
Another method, which is used in the art and by means of which it is 
generally possible to obtain considerably more sieve material by means of 
a die surface, than by means of the first mentioned method, is based upon 
the conception to so countersink the desired pattern of insulating parts 
in the die surface, that the top of the points to be insulated is flush 
with the surface of the die material or is even situated slightly 
therebelow. Such a die surface is obtained by first providing a metal 
surface with a pattern of recessed pockets, which are subsequently filled 
with an insulating material, for instance a plastic resin, whereupon the 
entire die surface is polished. Said pattern of recessed pockets may 
either be applied mechanically, for instance by means of impressing or 
cutting, or chemically by etching, or in a physical manner. 
The difficulty with said second method is that it does not render the 
number of sieves to be manufactured upon such a die, to be unlimited, as 
the adherence of the employed plastic resins in the recessed pockets, may 
disadvantageously be impaired as a result of the chemical processes 
occurring during the respective electrolysis. 
SUMMARY OF THE INVENTION 
In view of the foregoing factors and conditions of the prior art it is a 
primary object of the present invention to provide a method which in first 
instance produces a die having a considerably larger life, while 
furthermore the accuracy of manufacturing said die will be increased, 
without the cost price raising above the actual level. 
Said objects are attained in accordance with the present invention in that 
the conducting surface is provided with a material having insulating 
properties, of least after a heating treatment and in that said surface is 
patternwise irradiated with short pulses of a high-energy radiation in 
such a manner that the insulating grate aimed at is accomplished by means 
of said energy pulses. 
The method according to the invention employs the property of high-energy 
radiation in the form of laser radiation or electronic radiation, to wit 
for very strongly locally heating a surface during a very short time. 
Preferably in both cases it is possible to focus high-energy radiation. In 
case of a laser radiation, this is accomplished by means of an optic lens 
system and in case of an electronic radiation by means of magnetic fields. 
An additional beneficial effect of an electronic radiation consists in a 
substantial independence of the nature and color of the surface to be 
irradiated, this contrary to a laser radiation, which is partially 
dependent upon the ratio of absorption and thus upon the wave length of 
the laser radiation to be used. 
Laser beams may both be applied under normal atmospheric pressure as under 
a decreased or an increased gas pressure, the nature of the gas not having 
any influence. Due to the substantially shortwave character of electronic 
radiation, if this can be considered as radiation, a dispersion caused by 
gas molecules is a handicap, so that it is desired to apply a vacuum 
comprised between 0.13 to 1.3 Pa in order to obtain an accurately focused 
radiation point. 
In both cases, manufacturing dies in accordance with the invention with 
short energy pulses having a duration comprised for example from 1.0 to 
0.1 milliseconds, permits obtaining a local heating of the die surface 
during a very short period of time at very high temperatures. Furthermore 
mechanical means will be present displacing the die surface with respect 
to the radiation source in such a manner, that the irradiated parts of the 
die surface form a pattern which corresponds with the desired grate of the 
apertures in the sieve to be manufactured upon said die. 
As an embodiment of the method according to the present invention, the 
example can be given of a metal such as titanium, the surface of which is 
coated with a very thin film, having a thickness of e.g. 50 .mu.m, which 
film contains titanium borides. After a point to point treatment with 
high-energy radiation, the titanium matrix material will show locally 
embedded concentrations of titanium borides, having thicknesses comprised 
between 0.1 and 0.4 mm corresponding to the desired pattern. 
When an electron-beam is used, the invention takes benefit of the fact that 
certain metal derivatives such as, for instance, oxides and silicates, 
have a very low conductivity compared with the metal proper while oxides 
or silicates of such metals will present an excellent adhesion to the 
metal surface. Examples of such oxides formed in situ of the initial 
metal, are aluminium oxide (Al.sub.2 O.sub.3) and titanium oxide 
(TiO.sub.2) although the scope of the present invention is not limited to 
oxides. In said method further use is made of the attribute that chemical 
reactions tend to proceed very rapidly, due to the substantially high 
temperatures which may be attained locally by said high-energy radiation 
so that, notwithstanding the very short pulses, oxidation reactions may be 
completed.

DESCRIPTION OF PREFERRED EMBODIMENTS 
EXAMPLE I 
A polished aluminium sheet 1 as shown in FIGS. 1A-C is irradiated 
point-wise in an atmosphere of pure oxygen under atmospheric pressure, the 
respective radiation points being arranged due to a suitable displacement 
of the work piece of the source of radiation or of both, such that a 
pattern of melting zones 2 is obtained identical to the desired apertures 
in the material to be manufactured (FIG. 1A). The source of radiation is 
an infra-red CO.sub.2 -- laser and the duration of the pulses is one 
millisecond. The diameter of the point hit by the radiation is 50 .mu.m. 
At a sufficient power of the latter source, a pattern of accurately 
defined spots of aluminium oxide 3 is obtained upon the aluminium sheet 1 
(as shown enlarged in FIG. 1B), which spots will adhere strongly to the 
aluminium background. After cooling, the surface is polished, so that it 
becomes smooth (see FIG. 1C). An electrolytic deposit in an acid copper 
both upon the die so manufactured, will show no copper deposit upon the 
aluminium oxide, so that a copper sieve plate is produced having the 
desired pattern of openings. 
EXAMPLE II 
A polished aluminium sheet 4 as shown in FIGS. 2-5 is covered with a thin 
aqueous substance comprising besides a binding agent, a small quantity of 
potassium nitrate and a quantity of sodium silicate (FIG. 2). After having 
dried the applied layer 5, the surface is kept in a vacuum chamber at a 
pressure of 0.13 Pa and subjected to a pulse-shaped bombardment with 
electrons, whereby due to a mechanical displacement of the work piece, the 
bombarded points are arranged in correspondence with a desired pattern 
(FIG. 3). The duration of the pulses is one millisecond and the diameter 
of the focused beam upon the point to be radiated is 70 .mu.m. When the 
respective source of radiation has a sufficient capacity, it will turn out 
that, after having terminated the vacuum, upon the bombarded spots 6, a 
quantity of aluminium oxide is formed, in which likewise aluminium 
silicate is included. 
After having cleaned the respective sheet and having removed the redundant 
covering layer (FIG. 4), the aluminium sheet corresponding to Example I, 
may produce a die by post-polishing (FIG. 5). The rapid oxidation of the 
bombarded spots 6 is caused by oxygen, being emitted due to the heating of 
potassium nitrate, part of which oxygen was converted into ozone causing 
the oxidation of the aluminium upon the bombarded spots to be even 
accelerated. During the reaction, also some silicate was absorbed, thus 
improving the adherence to the aluminium basic material and the closing of 
the oxide layer. Melting and oxidation has penetrated so far, that the 
surface can be polished (FIG. 5). Nevertheless a pattern of insulating 
points 7 will still remain. Instead of grinding off, the basic material of 
the die plate 4 could be raised by a deposit 8 of a suitable material 
(FIG. 6) whereupon finally the surface is polished smooth. 
The application of an electron beam is also based upon the local generation 
of very high temperatures, the circumstances being such that very little 
quantities of a suitable insulating material are melted upon the bombarded 
spots. 
EXAMPLE III 
A nickel sheet is covered with a very thin layer of a substance prepared 
from distilled water, with a mixture of finely ground silicates, which 
are, for instance, used for enameling metal objects, which mixture is 
subsequently dried. The layer thickness after drying amounts to 
approximately 10 .mu.m. 
The nickel sheet to prepared is placed in a vacuum chamber, comprising a 
pulsating electron-beam device and focusing capabilities. Due to a 
suitable movement of the sheet surface with respect to the radiation beam, 
the irradiated spots are arranged in a pattern. The diameter of the 
irradiated spots is 60 .mu.m and the duration of the pulses is 0.5 
millisecond. 
In this example one has taken care that the distribution of the energy 
contents of the beam across the entire surface to be irradiated, is as 
even as possible. At a sufficient energy of the electron-beam comprised 
between 10.sup.5 and 10.sup.7 W/cm2 electron beam-cross-section, the 
enameling powder mixture melts upon the irradiated spots and is firmly 
anchored to the nickel surface. The nickel surface so provided with enamel 
pattern points is polished after a thorough removal of the non-processed 
covering layer. After having passivated the die surface with a 10% 
solution of potassium bichromate, said die is immersed in a nickel bath, 
whereupon a nickel film having a thickness of 50 um is electrolytically 
deposited upon said die. It has turned out that said nickel layer can be 
removed from the die surface and that this sieve comprises a pattern of 
apertures corresponding to the grate of enamelled spots upon which no 
nickel has been deposited. 
EXAMPLE IV 
A sheet of titanium is provided with a coating, and in a vacuum chamber 
subjected to an electron-beam treatment, entirely corresponding to example 
III. After having removed the non-processed enamel mixture, the sheet 
comprising enamel pattern dots is activated by means of 10% hydrochloric 
acid and subsequently disposed in a nickel bath, whereupon 
electrolytically so much nickel is deposited, that the enamel dots 
projecting originally slightly above the titanium surface, do not project 
any longer. 
Subsequently, the entire surface is polished so that enamel points and 
nickel, form one closed surface. 
After having deposited a very thin layer of silver upon the surface in a 
currentless manner, so that a separating layer is formed upon the nickel, 
a number of perforated nickel films can be formed upon the die sheet thus 
obtained. 
It is observed that a method is feasible whereby the surface of the 
material is first locally provided with pockets (analogous to the present 
state of the art) whereupon said pockets are filled with a material, 
Hereafter, energy pulses are directed upon said pockets in such a way that 
the filling material becomes or remains insulating and will adhere upon 
the surface of the die, due to said irradiation.