An Improved Process of Preparing Aluminium Plates for Use in Printing.
Year: 1896

page_text: Date of Application, 19th Oct., 1896-Accepted, 9th Jan., 1897
COMPLETE SPECIFICATION.
[Communicated from abroad by THE CORNWALL PRINTING PRESS COMPANY,
a corporation incorporated under the laws of the State of West Virginia,
87 Nassau Street, New York, State of New York, United States of
America.]
An Improved Process of Preparing Aluminium Plates for Use in
Printing.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of The Agency for
Foreign Patent Solicitors, 322, High Holborn, in the County of Middlesex,
6, Lord Street, Liverpool, and 6, Bank Street Manchester, both in the County
of Lancaster, and Lower Temple Street, Birmingham, in the County of Warwick,
Civil Engineer, do hereby declare the nature of this invention and in what manner
the same is to he performed, to be particularly described and ascertained in and
by the following statement :-
In preparing the ordinary aluminium plates of commerce for use in surface
printing, it is found that the metal is tainted with certain impurities which prevent
its successful use as a printing surface.
The object of the treatment which forms the subject of this invention is to
remove these impurities that are an impediment or drawback and also to render
the plate more porous and sensitive to the design. The first step of the process is,
by mechanical or chemical action, to remove the outer shell or skin of the metal
usually formed in rolling from the ingot and also to get down below any surface
scratches or blemishes on the metal and present a true, even surface for the design.
The next step after the outer shell has been removed is to treat the plate with an
alkaline solution, preferably caustic potash, of strength sufficient to dissolve any
greasy material that may be on the surface or in the metal within reach of the
alkali. The next step is to wash the alkali from the plate with water. The next
step is to dip the plate in a bath of acid for the purpose of removing further
impurities, preferably using a mixture of nitric and hydrofluoric acid which
removes certain grease that the potash does not reach, also dissolving silicon
iron copper, and their oxides or any material that may have been forced into the
plate in the operation of rolling the plate and also any earthy material that has
been incorporated in the plate either in the production of the ingot or the
subsequent production of the plate from the ingot. Then, the acid is removed by
washing in cold water; any remaining trace of acid is then neutralized by dipping.
the plate in a neutralizing solution and the plate washed again.
More in detail, the process is as follows:
A sheet of aluminium of commerce, say, is taken which has on it and in it not
only the ordinary commercial impurities, scratches, and blemishes, but the shell or
skin which is caused by the rolling of the plate. The rolling has compacted the
surface particles more densely than the interior. The said blemishes, scratches
and skin are first removed by buffing or rubbing down the surface, using for this
purpose means which are adapted to the production of the desired grain or surface
finish according to the particular work to which the plate is to be applied; for
example, for a plate which is intended for stipple or line or brush work a buffing
or grinding disc is used having a felt or flannel face and as an abradent powdered
pumice-stone slightly moistened is preferably used, while for producing a plate
which is intended for crayon or grained work, the desired surface is produced by
subjecting the plate to the abrading action of wet powdered grit of some kind

page_text: rolled over the surface of the plate by small quartz pebbles or marbles the size of
which is varied according to the size or character of grain desired.
The plate is then subjected to a bath in an alkaline solution preferably caustic
potash. The strength of the solution depends on whether the solution is used hot
or cold. Ordinarily, at a temperature of seventy degrees the solution may be ten
pounds of caustic soda to twenty gallons of water. The plate must not be left in
long enough to blister it and the length of time it should be left in depends on the
strength of the solution. When the plate has become a peculiar slaty black,
which will be readily recognized by anyone accustomed to the operation, the
treatment has proceeded far enough.
The plate is then removed from the solution and washed in water to remove any
alkali that is upon its surface. Next the plate is put in a solution consisting of
about twenty per centum of concentrated nitric acid of commerce and eighty
per centum of water to which is added hydrofluoric acid until a marked action upon
the plate is noticed. The quantity necessary for this is about one to two per cent.
of hydrofluoric acid.
.: This acid bath removes any grease which may have remained after the alkaline
treatment, any foreign metallic particles such as copper or iron and any grit or dirt
that may have been pressed into the metal by the rolls; also any oxides of
aluminium and silicon. As the plate lies in the bath it is wiped until the dark
surface is entirely removed and the plate has a uniform, brilliant, silvery
aspect.
*The plate is then removed from the acid and very thoroughly washed in water,
preferably using hot water. Any acid remaining on the plate is neutralized by
then washing the plate in a solution of alum, lime-water or any other suitable
neutralizing material. Then the plate is washed in clean water and, upon drying,
the plate is ready for the design.
The above given ingredients and proportions may be varied according to the
result desired; in particular, a small proportion of hydrochloric or a small
proportion of sulphuric acid may be substituted for the hydrofluoric acid and for
the caustic potash, caustic soda or other alkaline material. Preferably, the
re-agents used are those first given above.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed as communicated to me
by my foreign correspondents I declare that what I claim is :-
1. The process of preparing aluminium surface printing plates consisting in
subjecting the plate to an abrading action to remove the outer compressed or
denser surface of the plate and expose an even true surface, substantially as set
forth.
S..
2. The process of preparing aluminium'printing plates consisting in treating the
plate successively with alkali and then with acid to remove the greasy, earthy and
metallic impurities, the presence of which would prevent its successful use in
surface printing, substantially as set forth.
3. The process of preparing aluminium surface printing plates consisting in first
abrading the surface to remove the shell and at the same time give the plate the
desired finish, then treating the plate in an alkaline and then in an acid bath to
remove the impurities, substantially as set forth.
4. The process of preparing aluminium surface printing plates consisting in first
removing the hard shell or skin of the plate and give it the desired finish and then
chemically dissolving out the impurities without impairing the surface finish,
substantially as set forth.
Dated this 19th day of October.
W. P. THOMPSON & Co.,
322 High Holborn, W.C., Agents.