Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates -to a method of printing on material
in sheet or web form on which material direct printing by the
transfer method is not possible.
For printing on textiles and other materials which have
good receptivity for subliming inks the transfer printing process
has been very successful in recent years. This process is based
on transferring special inks from a printed paper, the so-called
transfer paper, in a calender or press to the textile web by the
action of heat and pressure, the special inks used for this pur- .
pose subliming into and being bonded to the textile fabric~
This transfer printing process has hitherto been success- `
; ful for only a very limited range of materials, mainly textiles,
because these havegood receptivity for the printing inks. For
example it would not be possible to print on wood or sheet metal
by the transfer printing process known hitherto.
Materials of this kind are at present printed after suit- -
able pretreatment, for example after applying a coa-ting of var-
nish to the surface which is to be printed. The varnish must how-
ever contain a plasticiser, which has the disadvantage that after
a time the printed image smudges because the plasticiser begins to
diffuse. Printing on wood is currently effected by very expensive
presses.
The problem underlying the present invention is that of
enabling the transfer printing process to be applied to materials
in sheet or web form whatever their composition.
According to the invention there is provided a method of
pretreating material in sheet or web form which material is to be
used for printing by the transfer method, said method comprising
; applying electrostatically a polyester powder to a surface to be
printed of a base material on which base material direct printing
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by the transfer method is not possible, and bonding the polyester
powder to the base material by heating, so that -transfer printing
can be effected on that surface.
By coating the surface of the base material with poly-
ester, the surface is prepared for transfer prin-ting, so that con-
ventional printing by the transfer process is immediately possible
on materials pre-treated by the method of the invention. The ~ ~
field of application of the transfer printing process is consid- ~ ;
erably widened since the invention makes possible printing on
materials which could only be printed hereto at high cost and in
some cases with unsatisfactory results. This is because pre- `;
treatment of the base materials makes available all the advantages
of the transfer printing process, particularly low investmen-t
cost, speed, high printing quality - even in colour shading - and
inexpensive printing.
For printing on surfaces of materials which are only
slightly or not at all electrically conductive it is preferable
to apply to the base material a medium having good electrical
conductivity before applying the polysster powder. This medium
makes the surface electrically conductive. If the mediwm is an
adhesive, it will effect additional bonding between the surface
and the plastics material.
The method of the invention can be applied continuously ;-
or discontinuously in a press. ~-
In order that thç invention may be more clearly under- -
stood an embodiment thereof will now be described, by way of
example, with reference to the accompanying single drawing which
shows diagrammatically the essential components of a
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continuously operating installation for printing on a web
o~ material.
Polyester powder is contained in a reservoir 1 of
electrically conductive material. The reservoir 1 is conn-
ected to the negative pole of a high-voltage source and has
sieve openings in its bottom surface. Powder passing through
these sieve openings is thus negatively charged. A web 2 of
material to be printed travels under the reservoir. In the
embodiment described the web is of sheet metal, for example
aiuminium. The web of material is positively charged. The
passage of the powder through the bottom of the reservoir 1
can be assisted in known manner by rotating brushes. The
sense of connection o~ the reservoir and web o~ material
to the high-voltage source may be reversed. Flocking
¦ installations of this kind are kno~ and the installation will
not be described in greater detail. The voltage between the
electrodes of the flocking installa-tion is preferably between
80 and 100 Kv~ During operation a current of about 0.5 to 5
milliamperes flows. The reservoir 1 represents in general an
electrostatic flocking installation, which could also be in the
form o~ a gun. The electrostatic forces can be assisted in known
manner by compressed air and other means, for example rotating
brushes. The plastics powder applied by the electrosta-tic forces
to the web 2 of material is represented by the arrows 3.
When printing is to be on a web of material which is only
slightly or not at all electrically conductive, a medium
having good electrical conductivity~ preferably a suitable
adhesive, which can be connected to direct voltage, is
applied to the web before it reaches the reservoir 1. This
electrically conductive medium bonds the plastics powder to
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the webO A metal plate may also be provided under the web
in the region of the reservoir 1. A uniform layer of elec-
trostatic powder can thus be deposited on the surface of the
web. Polyester powder is particularly suitablep because
polyester accepts the transfer inks~ Pigmented polyester
powder may be used if it is desired to print by the transfer
process on a co oured layer of plastics materialO Polyester
powder is also preferred in order to obtain printing which
does not fade when exposed to light and is resistant to
abrasion.
A conveyor device 4 for the web includes a drying tunnel
5 which is si-tuated downstream of the elec-trostatic coating
installation represented by the reservoir 1. In the tunnel
$ the web 2, coated with plastics powder and optionally with
adhesive, is heated to a temperature between about 150C and
220C. The plastics powder is thereby sintered.
The treated web then passes to a transfer printing
station 6. Transfer printing paper 7 passes around two rol-
lers 8 which are in intimate contact with the web 2 to be
printed. The print is thus transferred from the transfer
printing paper 7 to the surface of the web 2. This transfer
is effected by the application of heat and pressure. The used
trans~er printing paper is fed away as indicated at 9. ~uring
the printing process an endless bel-t 10 is applied against
the printing paper 7.
At the end of these stages sf the process the printed
web 2 emerges.
The method of the invention may also be carried out
discontinuously, in a press in similar manner to the contin-
uous method just described7 Pieces o~ web or sheets of
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electrically Gonductive material are prepared by electro
statically coating of their surfaces with the plastics
material, followed by sintering and finally printing by a
transfer process in the press.
When printing webs of non-conductive material the
electrostatic coating step is preceded by coating with an
adhesive or other electrically conductive medium.
Surfaces printed in this manner are abrasicn resistant
and fast to light and comply with foodstuffs regulàtions.
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