Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
465
In the past, letterpress printing plates of the photopolyn-,er type
have nad alumin~,lr~lar and steel substrates. T~ese substrates had various coat-
ings on them including vinyl com~ositions. Sone of the coatinys were clear and
others contained dyes. Some oontaineG black ~yes.
The le-tterpress printing plates of the present invention contain a
substrate that resists elongation muc'n better than the mylar substrates of the
prior art-~hile having rluch better compression properties than tne alur,~num and
steel substrates of the prior art. ~ne letterpress printing plates of tne pre-
sent invention are r~ore easily disposed of after they have been used and the sub-
strate is substantially lighter in weight and is predomLnately cor,~osed of a re-
newable resource, natural pulp. In addition the letterpress printiny plates of
the present invention are less costly.
By an aspect of tne present invention a new type of letterpress photo-
polymer printing plate substrate is provided that is fiberous in character.
mus, one aspect of the invention provides a letterpress printing plate
comprising a fiberous support and a radiation polyr.~erizable relief forming
layer thereover, said fiberous support con~prising fibers that ~lere independently
- colored before incorporation in said fiberous support.
Another aspect of the invention provides a method of preparing letter-
press printing plates cGmprising depositins a liquid relief forl~ing radiationpolyn~rizable cor,~osition onto a substrate comprising a fiberous sheet, solid-
ifying an image in the surface of said composition and air etching said surface,
the irnprovement cor~rising providing the properties in the fiberous sheet of
individually oolored fibers, colored prior to incorporation in said sheet and a
sheet thickness of 5 to 20 mils.
In its preferred form the fibers in the substrate are dyed, prefer-
ably kefore being formed into a sheet. m e preferred fibers are cellulosic in
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character, preferably frorn a natural plant pulp. In its preferred forrn the
substrate is a fil~erous sheet coated with a polyrneric filrn which acts ~ot7n as
an adhesive tie coat and as a sealant for the surface of the sheet. The pre-
ferreci sheet is dyed blaclc and the preferred substrate coating is clear and
preferably a vinyl chloride-vinylidene chloride copolyrner. The preferred plate
has a liquid photocurable polymer over the tie coat.
The letterpress printing plate of the present invention has particular
utility when it is part of a plate production systern e~ploying an air knife or
otller rnechanical and liquid free developing procedure. mus in one aspect the
10 invention is directed to a new procedure for providing print-
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ing plates that include placing a cellulose fiber con-tairling substrate in
position for receipt of a liquid photopolymer printing relief forming layer,
exposing the layer through an image containing negative to actinic light to
solidify portions of the plate corresponding to the image. An air knife is
then used to forcefully strip away the uncured polymer and provide the
desired printing configuration.
BES~' MODE
By this invention a letterpress printing plate of the radiation
polymerized type is provided that has a superior supporting subs-trate. The
unique substrate is in its basic form a fiberous sheet. In one preferred
form the substrate has a coating on at least its face that is to receive the
- radiation polymerizable relief forming layer. This coating provides both a
sealing of the surface of the sheet stock and superior adhesion of the radia-
tion polymerizable relief forming layer. The coating is preferably a solvent
base vinyl resin tie coat, preferably of the vinyl chloride-vinylidene chlo-
ride type.
The fiberous sheet in one preferred form is formed of natural cel-
lulosic pulp. Synthetic plastic fiberous materials may also be used. The
preferred sheet is tag stock. The preferred thickness is 5 to 20 mils. This
is 5 to 20 point stock. The sheet should have a smooth surface and have
relatively low porosity. In a 10 mil thick sheet a basis weight of about
- 150 lb. is appropriate. (Basis weight is the weight of 500 sheets sized 2
inches by 36 inches).
In a preferred form the fibers in the sheet are dyed to provide
more uniform reflectivity. Preferably the fibers are dyed before being in-
corporated into the sheet. However, in some situations the substrate may
have a coated on coloring medium or may be the natural color of the fibers.
- Dark colored substrates generally give the best reflective characteristics.
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Black is most preferred.
The substrate of this invention has particular utili-ty in forming
letterpress printing plates fro~ liquid relief forrning cornposi-tions. ~iquid
c~npositions having chain extended urethane rnonomers witn terminal unsatura-
tion, diacrylate m~onorners and photoinitiators are ideal types. Those con-
taining thiol ~onomers are particularly preferred. Such oompositions are il-
lustrated in United States Patent 3,615,450.
The printing plate of this invention is forrned by positioning the
substrate for receipt of the relief layer o~rnposition. r~nis rnay be done in
any convenient rnanner. A United States Patent depicting oonventional com~
merical equiprnent is United States Patent 3,635,711. The relief layer is pro-
vided on the substrate to forrn the blank printing plate. Thereafter the blank
is imaged conventionally through a negative and the plate is air etc~ned in con-ventional rnanner as is for exarnple shown in United States Patent 3,922,751. Inthe preferred practice of the invention the plate is dry developed or etched
because this better maintains the integrity of the fiberous sheet of the sub-
strate. After the developrnent of the plate it can be installed on a le-tterpress
for the printing operation.
E~lPlE 1
A letterpress printing plate substrate was prepared by coating a
sheet of black tag cover stock with a vinyl chloriae-vinylidene chloride co-
polyrner (SA ~ F310, a product of D~ Chemical Co.). rme black tag cover
stock was n~nufactured by the cylinder process and was 10 point 140 pound
basis weight material and exhibited a smooth surface and had a plate finish.
Tne coating was 4.5-6.5 millogra~s/sq. inch dry weight and was applied from
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a methyl ethyl ketone solvent.
The substrate was positioned in a standard LETTERFLE ~ 290, a prod-
uct of W. R. Grace & Co., plate forming machine and 20 millograms of liquid
LETTERFLE ~ Y polymer, a product of W. R. Grace & Co., photopolymer printing
relief forming material was deposited over the coating in the conventional
manner. The photopolymer printing relief forming material was then cured in
the conventional manner with actinic light projected through a negative on
the plate forming machine. The uncured polymer was then stripped from the
plate by an air knife which was part of the plate forming machine. The plate
was then installed on a letterpress and gave printing results that exceeded
280,000 impressions with no deleterious effects. 70 wraps were applied and
the plates printed well after being cleared. The plate showed little or no
evidence of wear while stereotype plates with comparable impressions showed
signs of wear to visual observation.
EXAMPLE II
A letterpress printing plate substrate was prepared by coating a
sheet natural colored Jute tag cover stock with a vinyl chloride-vinylidene
; chloride copolymer (SAR ~ F310, a product of Dow Chemical Co.). The jute
tag cover stock was manufactured by the cylinder process and was 10 point
149 pound basis weight material containing a small percent of jute fibers and
exhibited a smooth surface and had a plate finish. The coating was 4.5-6.5
millograms/sq. inch dry weight, contained about 2% carbon black on a dry
weight basis and was applied from a methyl ethyl ketone solvent.
The substrate was positioned in a standard LETTERFLE ~ 135, a prod-
; uct of W. R. Grace & Co., plate forming machine and 20 millograms of liquid
LETTERFLE ~ C polymer, a product of W. R. Grace & Co., photopolymer printing
relief forming material was deposited over the coating in the conventional
manner. The photopolymer printing relief forming material was then cured in
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the conventional manner with actinic light projected through a nega-tive on
the plate forming machine. The uncured polymer was then stripped from the
plate by an air knife which was part of the plate forming machine. The plate
was installed on the letterpress and gave printing results that exceeded
20,000 impressions that by visual inspection appeared to be equal to that
produced by plates made in the same way using the conventional aluminum sub-
strate.
