Note: Descriptions are shown in the official language in which they were submitted.
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SUN 118 (RUTH)
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COMPRESSIBLE CO~IPOSITE PRINTING PLATE
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Back~round of the InYention
Many surfa~ss which require being printed
or decora~ed for identification, sales, or other purposes
are not smooth and are not always of uni~orm thicknesses.
In some printing processes, such as lithographic offset,
dry of~set, gravure, or letter press printing, the uneven-
ness is sometimes overcome by using substantial printing
pressure to press into the substrate and thereby
momentarily squeeze and relocate the unevenness, or, in
the case o of ~set, to absorb the unevenness into the
rubber blanket which carries the image area inX to the
substrate.
An increase in printing pressure is not
possible in-printing ~here the plate material is relatively
- soft, often having a durometer range of about 65-100, The
plate material is softer than the substrate being printed
upon a~d the plate itself ~ill be compressed or squ~ezed,
which caus~s an undesirable de~ormation or growth in the
area o~ the image being printed.
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Various methods have been devised for use
in printing to overcome the problems of uneven
surfaces and uneven thic~nesses with their resulting
deformation or "cupping" of the printed material. One
such device is a resilient printing plate described in
U.S. Patent 3,425,347, a cross-section of which is set
forth in Figure 1 here~f. Such printing p.late includes a
curved metallic backing member 1 usually made of brass
- and a layer of soft rubber 2 whose surface contacting
the backing member is discontinuous so as to provide a
plurality of uniformly spaced projections 3 and the other
surface being connected to a layer of a hard rubber 4 which
has an outer printing surface 5. The printing plate is made
by partially vulcanizing rubber layers 2 and 4 together in
a molding.press, cooling the resulting plate, afix;ng
the soft rubber plate to the metallic backing material and
then cpmpleting the curing process~ The combination of the
spaced projections and the procedure of partially curing
the rubber plate ~ith the subsequent co~npletion of the ..
curing process after the plate has been mounted on the
bac~ing material is said to substantially reduce cupping
of the printed sur~ace normally e:ncountered in bending a
fully cured rubber plate. When heat is applied to the
partially cured rubber in the curved position during the
Z5 second curin~ operation, the nerve or memory of $he rubber
formula is relaxed and sets to the diameter of the curve.
The projections 3 are positioned on the surface furthes~ -
from the printing surface 5 i~ order to compensate ~or any
compression generated throughout the entire thickness of
the rubber body.
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The resilient printing plate of Patent
3,425,347 involves a number of inconveniences. These
result from the fac~ that the rubber layers 2 and 4
must be jointly partially cured and completion of the
vulcanization of the composite rubber structure must be
accomplished a~ainst a curved metallic bacXing surface,
The individual hard prin~ing layer and soft cushioning
layer cannot be separately produced and particularly an
inventory o so~t cushion layer 2 cannot be maintained.
Additionally, the required use o~ the curved metallic
backing layer 1 requires that *he metallic material be
dedicated to this purpose.
Accordingly, it is the object of this
invention to provide an improved printing plate which
will produce a high fideli~y and sharpness in printing
without haloing, cupping, unevenness, or other imperfections
which can be produced without requiring a special partial
cure subsequent cure procedure 9 or the use of a dedicated
curved or 1at backing material or any special backing
material. This and other objects of the invention will
become apparent from the follo~ing detailed description
in conjunction with the drawings of which
Figure 1 is a cross-section ~f a printing
plate of the prior art as heretofore described;
Figure 2 is a cross-section of a printing
plate produced in accordance with the present invention;
Figure 3 is a plan vie~ of a section of the
soft ~ushion layer of the instant printing plate; and
Figure 4 is a plan view, partially cut away,
of one embodiment of a printing plate in accordance with
the present invention.
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SU~I~IARY OF Tl-IE INVENTION
This invention relates to a compressible
composite relief type printing plate and more particularly
to relatively soft letter press type relief printing
plates such as flexographic printing plates. The printing
plate has a layer of a relatively hard rubbery material
haviIlg an outer printing sur~ace and an inner support
surface, a layer of a relatively so~t rubbery material
having a surface which is discontinuous in the peripheral
direction to provide a plurali~y of spaced projections
integral wi~h the soft rubbery material and of substantially
the same height to define a mountin~ surface, the mount;ng
surface and the inner support surface being secured to-
gether by an adhesive. The compressibility of the plate
permits it to absorb excess pressures exerted against tlle
ink ~ransfer image producing lands o-~ the printing plate
so t}-at the integrity of the amount and size of images
~rans~erred to t}le surface being printed remains sub-
stantially constant even though the thickness thereo~
may vary up to 0.008 inch in random patterns.
DESCRIPTION OF I'~-IE INVENTION
With reference to Figures 2, 3 and 4, the
printing plate 101 has two layers 102, 103 o rubber-
li~e material. Any oE the rubbery materials heretoore
used ~or printing plates can be used to make layers 102
and 103. For e~ample, the rubber-like material can be
natural rubber, butyl rubber, ethylene-propylene rubber,
and the li~e, or harder materials such as the photo-
~ polymers or "Dycril~ Such materials must be moldable
and, in the case o~ the rubber and soft pla5tic com~ounds,capable of being vulcanized. As is conventional, the
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rubbery material of prin~ing layer 10~ is harder relative
to the rubbery material of cushion layer 103. For example,
layer 102 can have a durometer rating of 50 to 90 while
cushion layer 103 has a durometer rating of Z0 to 30.
Printing layer 102 is -formed by melting a
suitable moldable relatively hard rubbery material in a
mold which is the mirror image of the orm to be printed
and vulcanizin~ the material after it fills the mold
cavity. The mold is made usually by photoengraving
techniques or other similar etching techniques and is
constructed from such ma~erials as zinc, copper, or
sometimes a special glass material. Layer 102 is made
by placing the moldable plate ma~erial in contact with
the mold and applying heat and pressure in a special
press. The plate material softens~ fills the cavity o
the mold and accepts the exact configuration of the
mold~ The vulcanizing cycle is adjusted so that the
plate~~aterial is maintained for a su-fficient time at
a high enougll temperature to completely cure. As a
result, the molded printing layer 102 has integral
upraised printing lands 104 molded into its top or
outer printin~ surace 105. The o~posite or inner surface
106 of layer 102 is relatively smooth.
The cushion layer 103 is prepared in the
same manner, i.e., by vulcanizin~ an appropriate ~ubbery
material in a mold but in this case one surface 107 of
layer 103, which is intended to be inounted to the printing
cylinder, is relatively smooth while the opposite surface
108 is discontinuous in the peripheral direction. The
discontinuancies provide a plurality of spaced projections
or pedestals 109 which are spaced sufficieTLtly from one
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- another to prevent the setting up of compressive forces
in the peripheral direction at the mounting surface.
Thus, a two-dimensional ~attern of spaced projections 109
integral with layer 103 and being of substantially the
same height is provided to define a mounting surface.
The cross-section of projections 109 can ta~e any desired
form such as circular 109a, ring-like lO9b, square 109c,
or rectangular lO9d as shown in Figure 3.
The individual platforms 109 are usualIy
spaced apart from each other by a distance which is
preferably less than one-half of the thickness of plate
101 and the pattern of pedestals is usually, although not
necessarily, uniform. The height of projections 109 is
preferably about one-quarter to one-half the thic~ness o
layer 103 or about one-eightll to one-quarter of the
thickness of plate 101. The projections 109 should ~ccupy
from 25 to 75% of the area corresponding to the area to
be printed and preferably about 40 to 60% of that area.
In one preferred embodiment, projections 109 l~ere in
the form of 144 pedestals of circular cross-sect:Lon per
square inch and covered about 50~ of the surface area in a
uniform pattern. As sho~n in the cut-a~ray portion of
Figure 4~ projections 109 need not occupy the entire
surface 108 of cushion layer 103 but only that area
corresponding to the area o layer 102 ~hich carries
printing lands 104.
Printing layer 102 and cushion layer 103
are joined by adhesively bonding mounting surface 108
of layer 103 to the inner support surface 106 of layer
102. It is necessary to adhere the t~-~o layers 102, 103
by means of a suitable adhesive 110 since it has been
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found that attempts to vulcanize the mounting surface 108
of soft rubber layer 103 to the inner surface 106 of printing
layer 102 has resulted in the destruction of the projections
109. Although any adhesive material which will bond mounting
surface lQ8 to inner surface 106 can be used, it is preferred
to use a material which is known in the trade as "Sticky Back".
Sticky back is a double-sided adhesive tape, about 0.005-
0.020 inch thick and having a caliber variation of about
0.003-0.005 inch, and is substantially incompressible, i.e.,
it does not significantly yield when pressure is applied to
the printing plate. It is commercially available, e.g., from
the 3M Company as ScotchTM brand double-coated tape.
By constructing the instant plate as described above,
cupping and other deformities of the printing when applied to
such materials as thermo-formed or vacuum formed cups whose
thickness is irregular can be substantially eliminated.
Accordingly, the printing plates of the present invention are
particularly adapted for printing of such materials in such
printing equipment as the process decorators described in
U.S. Patent 3,645,201, copending application Serial No. 917,115,
filed June 19, 1978, and the like. By virtue of the ins-tant
construction, cushion layer 103 can be performed and stored
or stockpiled for a substantial period of time before being
adhered to printing layer 102. Additionally, because pedestals
109 are disposed substantially at the middle of plate 101 and
layer 102 is harder than layer 103, deformities due to ex-
pansion of printing lands 104 are substan-tially avoided.
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- It will be appreciated that various changes
and modifications can be made in the printing plate of
the present invention without departing from the spirit
and scope thereof. The various embodiments which have
been described in this specification were intended to
be illustrative only and not ~o be limitin~.
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