CA1216112A - Collector membrane - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In a printing apparatus using a collector membrane, certain formulations of room temperature vulcanizing silicone materials form membranes with superior performance.
The preferred release characteristic of the material is set forth in terms of the time it takes a test element to roll along an inclined plane having an adhesive material thereon.

Description

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-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 *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 .

~21~

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 SOWS V-5~ 68 102 18 Moderately REV 511 So 143 25 High SOWS 04478 52 1.59 90 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 Tensile Strength %
(psi) Elongation High DC 3110 330 150 Moderately REV 511 350 180 High SOWS 04478 650 275 Moderately Silas tic E 700 400 Low ` GE REV 615 900 150 ,.;
i--,... ..

liable IT
- Continued -Tensile Category Strength of Release Silicone (psi) Elongation Low Silas tic L 550 350 Silas tic 750 175 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 , 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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Claims (12)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A collector membrane comprising: a material formed of room temperature vulcanizing silicone material, said membrane for receiving thereon by intimate contact a thermoplastic, pressure-sensitive ink formulation in the form of a design by intimate contact with a surface carrying said design, the membrane for depositing the design onto another surface by intimate mechanical contact therewith, the membrane being between 0.02 and 0.2" thick and being 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 having a surface area of about .196 cm2; a dwell time of about 1 sec, a separation speed of about 1 cm/sec, at a temperature of about 20°C and a relative humidity of about 40%.

2. A silicone membrane as set forth in claim 1 wherein the material has a hardness of about 50 to 75 points as measured on a Shore-OO durometer gauge.

3. A silicone membrane as set forth in claim 1 wherein the silicone material includes dimethyl siloxane oil in an amount up to about 50% of the silicone formu-lation.

4. A silicone membrane as set forth in claim 3 wherein the silicone is Dow Corning Silastic L containing from about 30 to about 50 parts per weight of said oil.

5. A silicone membrane as set forth in claim 4 wherein said oil has a viscosity between 20 and 1000 centistokes.

6. A silicone membrane as set forth in claim 1 wherein the membrane is between 0.030 and 0,090" in thickness.

7. A silicone membrane as set forth in claim 6 wherein said membrane is stretched up to about 25%.

8. A silicone membrane as set forth in claim 1 wherein the silicone material is formulated to have a tensile strength of at least 50 PSI and an elongation of at least 150%, measured in accordance with ASTM
D-412.

9. A collector membrane for receiving a thermo-plastic, pressure-sensitive 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, com-prising:
a membrane body formed of room temperature vulcan-izing silicone material, said silicone material being formulated to have a tensile strength of at least 50 psi and an elongation 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 dimethyl siloxane oil, said dimethyl siloxane oil having a viscosity between 20 and 1,000 centistokes, and said membrane having a hardness of about 50 to 75 points as measured on a Shore-OO durometer gauge.

10. A silicone membrane as defined in claim 9 wherein said silicone material is formulated so as to exhibit a release characteristic of between 20 and 1200 grams from a probe loaded against the material at about 1050 grams/cm2, with the probe having a surface area of about 0.196 cm2, a dwell time of about 1 second, and a separation speed of about 1 cm/second, at a temperature of about 20°C, and a relative humidity of about 40%.

11. A silicone membrane as defined in claim 9 wherein said membrane is stretchable up to about 25%
greater than its original size.

12. A silicone membrane as set forth in claim 1 wherein the silicone material is formulated so as to exhibit a release characteristic of between 120 and 1200 grams.