U.S. patent number 3,906,536 [Application Number 05/166,414] was granted by the patent office on 1975-09-16 for apparatus for processing printing plates precoated on both sides.
Invention is credited to Robert C. Graham.
United States Patent |
3,906,536 |
Graham |
September 16, 1975 |
Apparatus for processing printing plates precoated on both
sides
Abstract
An apparatus for simultaneously processing two sides of an
offset printing plate, including a developer solution dispenser for
dispensing developer solution onto two sides of the plate, a
developer section, a washing section, a gumming section and
transport rollers for propelling the plates through the apparatus.
The improvement lies primarily in the developer section which
includes two free-floating pads of a soft material mounted in a
manner to receive a plate between them and reciprocatable
transversely to the direction of plate travel.
Inventors: |
Graham; Robert C. (Florham
Park, NJ) |
Family
ID: |
22603206 |
Appl.
No.: |
05/166,414 |
Filed: |
July 27, 1971 |
Current U.S.
Class: |
396/624; 396/612;
396/627; 118/120 |
Current CPC
Class: |
G03F
7/3042 (20130101) |
Current International
Class: |
G03F
7/30 (20060101); G03d 003/08 () |
Field of
Search: |
;95/89R,89A,94R
;118/109,120 ;15/29R ;354/297,319,325,328,339 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Braun; Fred L.
Attorney, Agent or Firm: Bryan; James E.
Claims
What is claimed is:
1. In an apparatus for simultaneously processing two sides of an
offset printing plate, including means for dispensing developer
solution onto two sides of the plate, developer means, washing
means, gumming means and means for propelling the plate through the
apparatus, the improvement comprising a developer means which
includes a pair of opposed pad means, of a soft material, mounted
in a manner to receive a plate between them, the upper one of said
pad means being free-floating, whereby the pressure applied to a
plate passing between said pad means is essentially the weight of
said upper pad means assembly, and said pad means being
reciprocatable transversely to the direction of plate travel.
2. In an apparatus for simultaneously processing two sides of an
offset printing plate, including means for dispensing developer
solution onto two sides of the plate, developer means, washing
means, gumming means and means for propelling the plate through the
apparatus, the improvement comprising a developer means which
includes a pair of opposed pad means, of a soft material, mounted
in a manner to receive a plate between them and curved away from
each other on the side where the plate enters between them, the
upper one of said pad means being free-floating, whereby the
pressure applied to a plate passing between said pad means is
essentially the weight of said upper pad means assembly, and said
pad means being reciprocatable transversely to the direction of
plate travel.
3. An apparatus according to claim 2 including means for
introducing a spray of developer between the curved portions of the
pad means.
4. An apparatus according to claim 2 in which the pad means are
fabricated of velour type cloth covered rubber.
5. An apparatus according to claim 2 in which the two pad means
reciprocate in directions opposite to each other.
6. An apparatus according to claim 2 in which the plate is a
subtractive presensitized plate.
Description
This invention relates to an apparatus for simultaneously
processing two sides of a printing plate, for example a
planographic printing plate as is used in the lithographic printing
process. It has long been known in the lithographic industry that a
subtractive presensitized offset printing plate may be developed by
what is known as the "hand developing process." In this process,
the carrier, which is usually a thin sheet of aluminum, is first
coated by the manufacturer with a light-sensitive coating usually
containing, among other things, one or more resins and the plate is
then sold in the presensitized condition to the customer.
Some printing plates are available with such a subtractive coating
on two sides thereof. In this case, the customer exposes one side
at a time or, in suitable equipment, both sides simultaneously
through a master to a source of strong light such as a carbon arc,
for example. The light-sensitive coating when subjected to such a
light is converted in such a manner that, after development, the
image areas are retained on the plate surface and the non-image
areas are removed. After development, for example by rubbing a
developing agent into the surface of the plate by means of a
sponge, the plate may be fixed and/or washed and finally a coating
of gum arabic or similar material is applied to the surface of the
plate to protect the image-free areas thereof. The plate is then
ready for the printing press.
Where this hand developing process is employed to produce a
printing plate, the following procedure is generally followed: From
a typewritten set-up or make-up equivalent to the material to be
printed and provided in any desired manner including typed
articles, pictures of various kinds of art work of different sizes
and the like, all assembled onto a suitable cardboard or other
support, a master is prepared in the conventional manner. The image
of the master is then transferred onto the sensitized printing
member, such as is described above, by a suitable exposure
means.
The printing member thus prepared is then subjected to a developing
operation using the "chemistry" prescribed by the manufacturer of
the printing member. This "chemistry" is worked into the exposed
coating by hand rubbing, for example with a sponge, and the
non-image areas are subtracted or removed from the carrier leaving
an exact replica of the image on the plate carrier. The printing
member is then fixed and/or washed and a solution of gum arabic, or
a similar solution, is applied to the plate surface, resulting in a
printing plate which is ready for the press.
As described above, some plates have a light-sensitive coating on
two sides of the carrier or support, thus resulting in advantages
to the printer who is then able to print two different jobs from a
single printing member. This means that each side of the printing
member must be exposed, as described above, and each side must be
hand developed and processed in a sink, as described above.
The disadvantages of hand development of offset printing plates are
numerous. The process is slow and expensive. Uniformity of pressure
in applying the developing solution to remove the undesired coating
is almost impossible to attain and exposure to the developing
solution is uneven. Thus, defective printing often results from an
inadequate development or under-development of an area or from
applying varying pressure by hand, which may adversely affect the
desired printing image. Drying of the developer on certain portions
of the plate before it can be rubbed in to remove the undesired
coating also may leave a residue on the plate. A further difficulty
with the hand method is in the application of the developing
solution. It is presently the practice of the craftman to pour a
quantity of developer onto a developing sponge or pad and onto the
center of the plate, which quantity is supposedly sufficient to
process the plate, and the craftman then works his sponge from the
"reservior." This procedure may lead to a high degree of
contamination of the processing fluids by the removed
photosensitive coating as well as a change in the chemistry of the
fluid because of evaporation, which will, in turn, either reduce
the efficiency of the chemistry resulting in incomplete removal of
the undesired coating in highly critical areas of halftones, or
increase its potency resulting in image attack.
Further, the development of a two-sided plate by developing one
side at a time in a sink and turning the plate over can result in
damage to the first developed side by pieces of contaminated
material in the sink being forced back into the image or non-image
areas of the first developed side when the second side is
developed. These defects may not become apparent until the plate is
clamped into a printing press and the expense of developing the
plate has been incurred. All of these problems become more critical
with increasing plate sizes.
The present invention overcomes the difficulties associated with
the conventional hand developing of a two-sided plate by providing
an enclosed developer apparatus which includes a receiving station
for receiving a printing plate, a continuous transport system, a
dispensing station in which developer is applied onto two sides of
the plate simultaneously and evenly over the complete surface of
the two sides, a rubbing or scrubbing station wherein two slightly
curved, free floating velour type cloth coated pieces of rubber are
mounted one above and one below the plate in a manner such as to
facilitate easy entrance of the plate between the two scrubbing
devices, the two scrubbing devices being mounted for reciprocation
transversely across the surface of the plate in directions opposite
to each other. When no plate is in the developing system, the two
scrubbing devices rub against each other.
Prior to entering the scrubbing unit, developer is applied onto
both sides of the plate. Developer is also introduced into the
opening or nip between the scrubbing pads. By reciprocating the
slightly curved, floating pads in directions opposite to each other
and by introducing developer into the nip of the scrubbing pads,
the removed coating which would eventually foul the scrubbing pads
is effectively and continuously scrubbed and washed away. Nip rolls
carry the plate into the developing apparatus and nip rolls removed
excess developer from the plate and carry it into a washing station
which washes the top and bottom of the plate effectively with or
without mechanical scrubbing action. Another pair of nip rolls
removes excess water from the plate and passes the plate into a
gumming station where a gum solution is applied to both surfaces of
the plate and which, in turn, is metered by a pair of soft rubber
squeegee rolls in intimate contact with each other to minimize the
amount of protective material applied, consistent with the
requirement to protect the plate. The plate then passes into a
drying station where warm air is blown onto the top and bottom of
the plate before it exits from the apparatus.
The apparatus according to the present invention provides a uniform
and even processing on the top and bottom of the plate without
scratching or otherwise damaging the image. Also, by including
means for recirculating the developer, it is continuously filtered
and used to exhaustion, resulting in additional savings to the
user.
The invention will be further illustrated by reference to the
accompanying drawings in which:
FIG. 1 is a schematic view of the apparatus of the present
invention, and
FIG. 2 is a detail view of the scrubbing or rubbing apparatus.
Referring to FIG. 1, a planographic printing plate sensitized on
both sides and imaged on both sides by exposure to a desired
master, is inserted into the apparatus at the point of the arrow 2.
Alternatively two plates, each sensitized and exposed only on one
side thereof may be inserted back to back into the apparatus. The
inserted plate passes over the trigger mechanism 4 and thus
actuates the entire apparatus. The plate then passes through a pair
of feed rolls 6, then through a first pair of shielded developer
dispensers 8, and through a second pair of developer dispensers 10,
which introduces developer into the free-floating reciprocating
scrubber pads 14 and 16 respectively. The upper pad 14 is mounted
on the upper reciprocator shaft 18 and the lower scrubber pad is
mounted on the lower reciprocator shaft 20. The upper scrubber pad
is guided at its lower end in its transverse reciprocating movement
by the guide 22 and the lower scrubber pad is guided in its
transverse reciprocating movement by the guide 24. Both of the
guides 22 and 24 cooperate with fixed guide means on the frame of
the apparatus, not shown. After passing through the scrubber pads,
the plate passes between a third pair of developer dispensers 26
which remove any residual coating which may still adhere to the
surface. The plate then passes between the developer
transport-squeegee rolls 28 which remove excess developer and
propel the plate or plate assembly between the water wash tubes 30
to the rinse transport-squeegee rolls 32. This pair of rolls now
assumes the propulsion of the plate or plate assembly and passes it
between the gum dispensing tubes 34 to the gum applicator
transport-squeegee rolls 36. These rolls, in turn, pass the plate
between a pair of air-drying tubes 38 to the exit rolls 40, which
guide the now developed, rinsed, gummed, and dried planographic
printing plate or plate assembly out of the apparatus in condition
for mounting on a press.
Referring to FIG. 2, a plate 42 is shown as it passes between the
upper and lower scrubber pads 14 and 16 respectively. As noted
above and as shown in FIG. 2, the pads 14 and 16 are free-floating,
being secured to the upper and lower shafts 18 and 20,
respectively, and travel freely at their unsecured ends by means of
the guides 22 and 24. These pads may be made of any desired soft
material which does not harm the surface of the plate and, as noted
above, velour-covered rubber has been found to give good
results.
As will be seen from FIG. 2, the scrubbing pads 14 and 16 are
curved away from each other at the leading edges 44 and 46,
respectively, the leading edges being those edges through which the
plate 42 first passes as it travels from left to right, as shown in
FIG. 2. The upper and lower reciprocator developer sprays 10
introduce sprays into the entrance nip of the scrubber pads 14 and
16 so that the removed coating is effectively and continuously
washed away. The upper and lower developer dispensers 26 remove any
residual coating which may still adhere to the plate surface prior
to the entry of the plate into the developer transport-squeegee
rolls.
The scrubbing pads 14 and 16 are reciprocated, by means not shown
in the drawings, in directions opposite to each other.
The entire apparatus is enclosed in a housing, not shown.
The operating conditions of the scrubber or rubbing means may be
widely varied depending, for example, upon the plate size, plate
travel speed, and the like. However, the pad reciprocation rate may
be in the range of 300 to 400 strokes per minute, with 350 strokes
per minute providing excellent results. The pad stroke may be in
the range of 1 to 3 inches and a stroke or travel of 1.25 inches
has been found to give excellent results. The plate travel speed
may be in the range of 24 to 60 inches per minute, with a speed of
36 inches per minute providing excellent results.
The total pad contact area per plate side is approximately 90
square inches for a processor accommodating 32-inch plates, and 100
square inches per plate side for a processor accommodating 48-inch
plates, but the pad to plate contact area is, of course, relative
to the plate size.
The length of the pad contact with the plate may be in the range of
2 to 4 inches or more, and a length of about 2.5 inches has been
found to give excellent results. The pressure of the pad contact
with the plate may be in the range of about 0.08 to 0.3 psi or more
and a pressure of about 0.12 psi has been found to give excellent
results. This pressure results in a total pressure of 10.8 pounds
per plate side in an apparatus for processing 32-inch plates and
15.6 pounds per plate side in an apparatus for processing 48-inch
plates.
It will be obvious to those skilled in the art that many
modifications may be made within the scope of the present invention
without departing from the spirit thereof, and the invention
includes all such modifications.
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