Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
COLLECTOR MEMBRANE
Background of the Invention
A printing apparatus for decorating ware is disk
closed in USE Patents 4,508,031 and 4,480,540, filed
December 12, 1981 and US. Patent 4,417,513 filed Septum-
bier 17, 1982. The device includes a flexible membrane
collector. Pressure-sensitive, thermoplastic inks,
especially useful with such a device, are disclosed in
US. Patent 4,472,537, filed September 17, 1982.
The present invention discloses a flexible membrane
material having properties most preferred for quality
print results.
Summary of Invention-
There is disclosed a silicone membrane collector
formed of room temperature vulcanizing silicone material.
The silicone membrane received or collects, by Intimate
contact, a thermoplastic pressure-sensitive ink formula-
lion in the form of a design. The design thus collected
may be deposited onto another surface by intimate
mechanical contact of the membrane therewith. The
membrane may be between 0.2" and 0.02" thick and is
formulated from a silicone material exhibiting a release
characteristic between 20 and 1200 grams from a probe
loaded against the material at about 1050 gm/cm2.
The probe may have a surface area of about .196 cm2;
a dwell time of about 1 sea, a separation speed of about
1 cm/sec, at a temperature of about 20C and a relative
humidity of about 40~.
In another embodiment the present invention provides
a collector membrane for receiving a thermoplastic, pros-
sure-sensiti~Je ink formulation in the form of a design by
intimate contact with a surface carrying such design, and
for depositing the design onto another surface by intimate
mechanical contact therewith, comprising:
a membrane body formed of room temperature vulcan-
icing silicon material,
said silicone material being formulated to have a
I,.
tensile strength of at feat 50 psi and an elonga-
lion of at least 150%, as measured in accordance
with ASTM D-412,
said membrane being between about 0.03" and 0.09"
thick and being formulated from a silicone
material including about 30 to about 50 parts
per weight of dim ethyl selection oil,
said dim ethyl selection oil having a viscosity be-
tweet 20 and 1,000 centistokes, and
said membrane having a hardness of about 50 to 75
points as measured on a Shari dormitory gauge.
Description of the Preferred Embodiment
The present invention utilizes room temperature
vulcanizing (REV) silicones for a collector membrane.
Such materials are generally divided into two classify-
cations, each based upon a particular curing mechanism of
the material. For example, materials known as addition-
cure silicones contain silicone hydrides cross-linkers
which react with vinyl groups when mixed therewith. A
platinum compound is used as a catalyst. There are no
volatile by-products that are produced during the curing
step. The curing proceeds evenly in deep sections and
is heat acceleratable.
Another type, known as condensation-cure silicones,
has a condensation reaction in which an alkoxy cross-linker
reacts with a sullenly group in the presence of a stuns
soap as the catalyst. A volatile alcohol by-product
evaporates as the reaction proceeds.
It is not entirely understood how the composition,
the curing mechanism, the fillers and the degree of cross-
linking affect the surface energy and surface tack. The
surface energy and tack dictate the release properties of
a silicone material. The condensation-cure silicones are
often more releasing, because they generally appear to have
a lower surface tack. Consequently, they are often used
as the first transfer surface or offset surface in a
multiple surface system. On the other hand the addition-
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cure silicones are often less releasing and are generalized as the second transfer surface, i.e., a collector.
The first surface picks up ink from a heated Grover
plate for transfer to the second transfer surface or
collector. Formulation parameters, other than the curing
mechanism, also have significant affects on the release
properties, and thus, condensation and addition types
have overlapping characteristics.
It is known that any given silicone formulation
lo may be made more releasing by adding dim ethyl selection
oil. Although the viscosity, as determined by molecular
weight of the oil, is relatively unimportant, the higher
viscosity oils are usually avoided because they cause
the surface of the silicone to become greasy, and there-
fore susceptible to contamination. The release properties increase, that is the surface energy decreases, as the
amount of oil is increased. A preferred viscosity range
for the oil is between about 20 and 1000 centistokes.
At very high oil levels, the affect on dormitory,
which decreases with increasing oil content, may cancel
any further improvement in the release characteristic
of the material. Extreme values of dormitory interfere
with obtaining a favorable release. A high dormitory
silicone does not conform well to surfaces being printed,
whereas a low dormitory silicone makes it difficult to
exert a sufficient transfer pressure. For these reasons,
dormitory is generally kept within a range of about 30-90
points, as measured on a Shari dormitory gauge, menu-
lectured by Shore Instrument and Manufacturing Company.
The most convenient or preferred working range of duo-
meter is between 50-75 points. For a collector membrane,
the oil may comprise from about 0 to 50~ of the silicone
formulation. A preferred oil content for a typical
membrane formulated from Dow Corning Silas tic L is
between about 30 to 50 parts by weight. Table I shows
that increasing the oil content of the silicone reduces
the tack and dormitory characteristics of Silas tic L.
*Trade Mark
In a prepared embodiment, 40 phi is added to the silicone
(two Shore readings are given.
Table I
Oil Addition Tack Dormitory
(phi)* (grams) Shore-A Shari
0 579 35 78
338
250 10 62
207
164
*phi - parts by weight addition per hundred parts
base resin
The membrane described herein may be prepared by
injecting or pouring liquid unvulcanized material into
a polished metal mold at room temperature. Thereafter,
the material is allowed to cure at room temperature or
is heat accelerated by curing in an oven at a tempera-
lure up to about 200F to form a cohesive body between
about OWE and 0.20" thick. The material may be directly
cast over the support frame, primed with 1200 Dow Corn-
in* primer, or it may be removed from the mold and
either bonded to a support frame (not shown herein, but
see US. Patent No. 4,480,540 referred to above) with a
silicone adhesive, such as General Electric RTV-700,
or mechanically attached to such support frame. The
support frame is generally a metal material with a
centrally located circular hole from 3" to 24'; in
diameter. The membrane is mounted or molded to cover
this circular hole. Upon attachment to the frame, the
membrane may be stretched up to about 25% of its
original size.
In the collector printing process, the membrane is
held by a vacuum against a support or backing member
*Trade Mark
..:....
when printed upon by a series of offset printing
stations. After the print is completely formed upon
the collector membrane surface, the support is removed,
and a silicone pad moves through the hole in the support
frame against the back unprinted) side of the membrane,
urging the membrane against the ware surface to be
decorated. The decoration transfers from the membrane
to the ware surface upon contact therewith.
The membrane thickness should be between about
0.020 and 0.200" . The lower limit is the minimum
thickness providing minimum acceptable mechanical
strength. The upper limit is the maximum thickness
providing minimum acceptable shape conformity. For
example, intimate contact is required for total transfer
from the membrane to the ware. In the case of ware
shapes which have relatively abrupt contour changes,
a membrane with a thickness beyond 0.200" would be
too stiff to be conformed in a manner to prevent air
from being trapped between the membrane and the ware
(see US. Patent No. 4,508,031 referred to above). The
trapped air would then prevent the intimate contact.
A preferred thickness range for membrane would be
between 0.030" and 0.090" .
The tensile strength and the elongation are
measured in accordance with ASTM D-412. The preferred
minimum values for tensile strength and elongation are
50 psi and 150~, respectively.
The most important property of a silicone membrane
collector is its release characteristic To function
as both a receptor for ink and a donor of the same, the
collector membrane must have a release characteristic
within a certain range. Numerous attempts have been
made to quantify such a property. Most attempts have
not been found to be sensitive enough to differentiate
between numerous transfer silicones. A test has been
found for quantifying the surface release characteristics
of REV silicones as illustrated in the attached Tables II
I,.
sly
and III. The preferred equipment for the test is a model
80-2 Pelican* Probe Tack Tester, manufactured by Testing
Machines Inc., Amityville, New York. The test results
in a probe tack reading which measures the force necessary
to separate a metal probe from contact with the silicone
surface. There is good correlation between the test and
observed release characteristics. The test is far less
influenced by the silicone dormitory than other tests.
In general the higher the tack value, the more affinity
the silicone exhibits for pressure-sensitive inks of
the type discussed in US. Patent No. 4,472,537. Table II
summarizes test parameters.
Table II
Parameters of Pelican Probe Tack Test
For Measurement of Silicone Surface Tack*
Parameter Setting
Dwell Time 1 sea
Separation Speed 1 cm~sec
Probe Surface Area .196 cm
Temperature 20C
Relative tumidity 40%
Load 1010 gm/cm2
*Tack is reported as average of 10 readings on 3
samples. Samples are conditioned, after curing,
in an environmentally controlled room for 24 hours
prior to testing.
**1050 gm/cm2 including sample and sample holder
weight
This test has demonstrated its accuracy, in that,
many known silicone materials have been rated in the
cornea' release order. Such correct order has been
demonstrated through actual printing practices. For
*Trade Mark
j
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example, it is known that in order for an ink to trays-
for from one surface to another, the release character
fistic of an ink carrying member must be greater than the
same characteristic of 'the next surface against which
the ink and the transfer member must be urged. In the
past, the ease of release has been theorized to increase
with decreasing surface energy. However, all silicones
have relatively low surface energies, and among various
silicones the ease of release has been found to correlate
with surface tack measurements. Successive transfer
from one surface to another is described in the alone-
mentioned US. Patents. Table III summarizes the
characteristics of commercial REV silicones:
TABLE III
CHARACTERISTICS OF COMMERCIAL REV SILICONES
'~all'are'trade'mar~s)
Category Dormitory
of Release Silicone Cure S G 3 Shore A
High DC 3110 C 1.17 44
GE REV 602 C 1.00 23
GE REV 11 C 1.18 45
SOWS V-54 C 1.18 45
Moderately REV 511 C 1.20 43
High SOWS 04478 C 1.14 25
GE REV 700 C 1.06 31
GE REV 41 C 1.31 43
SOWS 833 C 1.51 40
Moderately Silas tic E A 1.12 42
Low GE REV 615 A 1.01 37
Low Silas tic L A 1.29 36
Silas tic J A 1.29 50
GE REV 630 A 1.28 63
a
TABLE III
- Continued - Tear
Category % Strength
of Release Silicone Rebound Tack
High DC 3110 68 124 20
GE REV 602 70 62 10
GE REV 11 74 83 15
SOWS V-5~ 68 102 18
Moderately REV 511 So 143 25
High SOWS 04478 52 1.59 90
GE REV 700 50 187 125
GE REV 41 73 172 30
SOWS 833 68 170 40
Moderately Silas tic E 60 312 90
Low GE REV 615 57 444 25
Low Silas tic L 44 579 65
Silas tic J 50 514 70
GE REV 630 46 537 85
Tensile
Strength %
(psi) Elongation
High DC 3110 330 150
GE REV 602 100 200
GE REV 11 350 180
SOWS V-54 400 155
Moderately REV 511 350 180
High SOWS 04478 650 275
GE REV 700 600 400
GE REV 41 500 200
WISE 833 800 130
Moderately Silas tic E 700 400
Low ` GE REV 615 900 150
,.;
i--,... ..
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liable IT
- Continued -
Tensile
Category Strength
of Release Silicone (psi) Elongation
Low Silas tic L 550 350
Silas tic 750 175
GE REV 630 800 420
DC - Dow Corning Corp., Michland, MI
SOWS - SOWS Silicone Corp., Adrian, MI
YE - General Electric Co., Water ford, NY
2C - Condensation Cure
A - Addition Cure
3S.G. - Specific Gravity
yin grams as measured on a Pelican probe tack
tester; 1010 gm/cm , 1 sec. dwell, separation
speed 1 cm/sec, 20C, 40-50~ relative humidity.
For a collector silicone to properly function in a
double offset (collector) process of the type described
in US. Patent ~,445,432, it must exhibit intermediate
ink affinity between the first offset silicone surface,
and the ware or substrate surface being printed. Generally,
silicones have good release characteristics and exhibit low
affinities for most inks. A collector silicone, however,
must be chosen to exhibit greater affinity for an ink than
the first offset silicone printing onto the collector. In
terms of the test, herein described, this means that the
collector silicone must be chosen with a higher tack than
the silicone used for the first offset surface, otherwise
transfer onto the collector cannot occur.
The above is true for all inks. However, the absolute
value of the required tack difference between the first off-
set surface and the collector, for consistent transfer be-
tweet surfaces, is dependent upon the chemical nature of
the particular ink employed. Some inks can transfer
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effectively between surfaces with a relatively small tack
difference. Other inks may require a higher tack dip-
furriness to achieve consistent 100% ink transfer. In no
case, however, will a silicone, of a selected tack trays-
for an ink to another silicone of a lower tack.
In actual process operation, the surface tack of a
silicone increases, or its release characteristic de-
creases, with repeated release cycling. Eventually, the
silicone deteriorates to the point where complete transfer
is not obtained, therefore, the process is no longer
operable. At this point, the silicone surface must be
replaced.
Patent applications and patents referred to herein
are assigned to the assignee of the present invention.
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