CA1080542A

CA1080542A - Process for preparing waterless lithographic printing masters by ink jet printing means

Info

Publication number: CA1080542A
Application number: CA239,477A
Authority: CA
Inventors: Wolfgang H.H. Gunther
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1974-12-16
Filing date: 1975-11-12
Publication date: 1980-07-01
Also published as: FR2294843A1; CH605133A5; JPS5184303A; IT1050066B; GB1479867A; US4003312A

Abstract

ABSTRACT OF THE DISCLOSURE
A master is provided by depositing a silicone or other material which can be rendered ink releasing on a suitable sub-strate by means of an ink jet printing apparatus, and curing the silicone to an elastomeric ink releasing condition. Alternatively, an ink jet printing apparatus can be employed to deposit in image configuration, a catalyst to an uncured silicone on a master substrate, a photopolymer to a cured silicone on a master substrate which photopolymer can be cured to combine with the silicone, or an imaging light insensitive shadow fluid to a light sensitive curable silicone coated on a master substrate whereby the background nonimaged areas can be cured and the shadow fluid and underlying silicone removed to reveal the ink accepting substrate.

Description

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BP~CI~C;ROU~D OF ~HE INVENT:ION
Ink jet printing techniques have recently been sug~ested for duplicating and printing operations which have several advantages over more conventional methods. For 5' example, an optical system is not required which is often expensive and requires a large amount of space in the machine.
Secondly, a pictorial optical input is not re~uired as the graphic information is assembled on a point by point or scan line by scan line basis, electrical or other discrete stimuli substituting for the pictorial optical input. Thirdly, the information guiding the ink jet array is storable and may be transmitted over distances. Fourthly, it is possible to create original documents as distinct from reproduction of existing graphic information. There are some drawbacks, however, Once a document has been created at some cost of time and insirumental sopnisiicaiion, lnulliple copies require t~at the same process be repeated over and over all the while holding the guiding information ln a memory bank and using the electrical circuits to the fullest. Further, to permit high speed operation, rather coarse scan patterns have to be followed, thus sacrificing quality for speed. It is now been discovered t~at the advantages of ink jet printing can be realized and the disadvantages obviated by using the technique to prepare a printing master rather than the ultimate copy.
In this manner, the ink jet printing procedure need not be repeated over and over to make copies thereby limiting the output, but the master can be made more easily and faster than conventional master methods.

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i ' ' ': . ' . - '. , : .': ' BRIEF DESCRIPTION OF THE INVENTION
Briefly, the invention comprises forming an image with an ink jet printing apparatus which comprises discharging ;
the imaging fluid form as droplets and depositing it on an im-aging surface in response to electrical signals which comprise an information pattern. In this manner, the droplets are selectively emitted or deflected in accordance with an informa-tion source. In one embodiment an uncured silicone curable to an ink releasable condition is deposited on an ink accept-ing master substrate and the silicone cured to an in~ releasable condition. By varying the polarity of the incoming video signal, the imaging material can be deposited to form an image either positive or negative in sense. In a second embodiment, a catalyst is deposited in image configuration on an uncured silicone, the silicone cured in image configuration and the uncured silicone removed in the nonimaged areas. Alternatively, ~
a photocurable material which can combine with a cured silicone can be deposited in image configuration on said silicone and the plate subjected to light to bond the imaging material thereto. A further embodiment is to deposit a light insensi-tive shadow fluid on a light sensitive curable silicone, expose the plate to blanket illumination to cure the background non-imaged areas and remove the uncured silicone beneath the light insensitive shadow fluid. In addition, an ink-accepting imag-ing polymer or prepolymer can be applied to an adhesive elasto-mer such as a silicone, which has sites for the covalent attachment of the imaging material, and the materials chemical-ly bonded to one another.
Thus, in accordance with the present teaching, a process is provided for preparing a printing master which comprises coating a master substrate with a silicone having reactive pendant groups and which is curable to an elastomeric D ~
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abhesive ink releasing condition. The resultant coated sub-strate is selectively imaged by discharging an imaging fluid from an ink ~et printing apparatus as droplets by selectively emitting or deflecting the droplets in accordance with an information source. The imaging fluid is an ink-accepting material which has groups reactive with the silicone pendant groups. The silicone is cured to an adhesive ink releasing conditon and the imaging material is grafted to the silicone.
DETAILED DESCRIPTION OF THE IN~ENTION
The types of materials and methods by which the invention can be achieved will now be discussed in detail.

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Substrates which can be employed to prepare the printing master are self-supporting materials to which the silicone can be adhered and which possess su~ficient heat and mechanical stability to permit use under widely varying printing and handling conditions, and which are preferably ink accepting. Exemplary of suitable materials are paper;
metals such as aluminum; and plastics such as polyester, polycarbonate, polysulfone, nylon and polyurethane.
The silicone gums which can be employed to coat the substrate are the conventional types employed heretofore in waterless lithography, which have reactive crosslinking sites or are capable of being cured to an ink releasable elastomeric condition. Exemplary of suitable silicone gums are those having only methyl containing groups in the polymer chain such as polydimethylsiloxane; gums having both methyl and phenyl containing groups or halogenated phenyl and methyl groups in the polymer chain as well as gums having both methyl and vinyl groups, methyl and ~luorine groups, or methyl, phenyl and vinyl groups in the polymer chain with not more than about 5 percent of the total non-Si-0-groups being vinyl, phenyl, or halogenated vinyl or phenyl. Typical pendant groups through which crosslinking can occur include vinyl,hydroxyl, amino, isocyanate and thioisocyanate groups.
Typical silicone gums suitable ~or use in the invention are thermally curable gums, having amino alkane crosslinking sites in the polymer backbone, sold by Union Carbide Corporation under the designation Y-3557 and Y-8053 silicone gums.

In addition to the polysiloxane homopolymers, other abhesive materials can be employed in the invention. For example, block copolymers can be employed prepared from a silicone such as one of the aforesaid homopolymers and a second component such as a vinyl polymer. Typical vinyl polymers include poly(styrene); poly(alpha-methylstyrene);
and poly(N-vinylcarbazole). A preferred block copolymer comprises 10 percent poly(alpha-methylstyrene) and 90 percent poly(dimethylsiloxane) in a suitable solvPnt or mixture of solvents such as a mixture of 20 percent xylene and 80 percent dodecane. Typically the block copolymer would constitute from between about 1 and about 5 percent by weight of the total solvent.
Another abhesive or ink releasing material which can be e~ployed s ~ terpoly~er formed from ethylene and propylene crosslinked with a minor amount of a diene such as 1,4-hexadiene.
A conventional peroxide catalyst such as benzoyl peroxide or dicumyl peroxide can be employed and the unreacted mixture dispensed from an ink jet printing apparatus from a suitable solvent such as hexane, pentane or cyclohexane. The polymer can then be formed by activating the catalyst such as by heat.
For convenience, the following disclosure will describe the invention with reference to abhesive silicones, it being under-stood that other abhesivé materials can be substituted for said silicones.
Any conventional inX jet printing apparatus can be ; employed in which the imaging fluid is discharged and depos-ited as droplets on an imaging surface in response to electrical signals which comprise an information pattern.
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10~0542 ~uitable devices are described in U. S. Patents 3,465,350 to A. B. Dick Company issued September 2, 1969; 3,46S,351 to A. B.
Dick Company issued September 2, 1969; 3,805,273 to the Mead Corporation issued April 16, 1974: 3,673,601 to Walter Simm et al issued June 27, 1972; 3,683,212 to Clevite Corporation issued August 8, 1972; 3,582,954 to Stephen F. Skala issued June 1, 1971;

3,060,429 to Charles R. ~inston issued October 23, 1962; 3,747,120 to Gustaf Erick Stemme issued July 17, 1973; and British Patent 1,042,308.
In preparing the printing master, a suitable abhesive material such as a silicone gum as described, containing pendant reactive groups suitable for crosslinking reactions, is pre-ferably blended with a blocking agent (capping or complexing agent) to convert the gum to a nontacky elastomeric but uncured condition. A variety of blocking agents can be employed by conventional methods. ~or example, gums having pendant amino groups can be reacted with a) an organohalosilane to form a silylamine, b) an organodiisothiocyanate silane to form a silylthiourea, c) an organoisocyanate to form a urea, d) phosgene to form an isocyanate group which can then be blocked with an oxime, e) a hydroxyorganoaldehyde to form an anil and f) an organoisothiocyanate to form a thiourea. Similarly, silicone gums containing pendant hydroxyl groups can be reacted with an isocyanate to form a urethane; gums with pendant isocyanate groups can be reacted with a diamine to form a urea and gums with thioisocyanate groups can be reacted with a diamine to form a thiourea. A variety of solvents can be employed for the reaction between the blocking agent and the silicone gum. It is only necessary that the reactants be at least partially soluble therein. Exemplary of typical solvents are toluene, benzene, tetrahydrofuran, dimethylsulfoxide, .~

108054z dimethylfuran, chlorobenzene, dloxime, chloroform, trichloro-ethylene and the like.
In a preferred embod~ment, a crosslinking agent is incorporated into the silicone gum-solvent solution a~ter the reactive pendant groups of the gum have ~een blocked.
The crosslinking agent must be one which is unreactive at `~
low temperature or it must be blocked so that it is stable -at low temperature. Typical blocked crosslinking agents are the phenol and oxime adducts of diisocyanates. Typical diisocyanates are toluene-2,4-diisocyanate, 4,4'-diiso-cyanato-diphenylmethane, 4,4'-diisocyanato-3,3'-dimethylbiphenyl, poly(m-methylene-p-isocyanatotoluene), hexamethylene diiso-.. . .. .. .. ..
cyanate, bis(2-isocyanato ethyl)-fumarate and tris(2,isocyana-toethyl)trimellitate. Typical blocking agents include alcohols such as ethanol; phenols such as phenol; silanols such as trimethylsilanol and oximes such as acetone oxime.
The blocked isocyanates are prepared by simply mixing together the blocking agent and polyisocyanate and if necessary, warming the mixture gently for a short period ~20 of time. A mutual solvent is preferably employed and to avoid the presence of any free isocyanate groups, it is advisa~le to employ a slight excess of the blocXing agent.
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The blocked silicone-solvent solution which may contain a crosslinking agent is then coated upon a suitable substrate by means of a conventional ink jet apparatus (e.g., A. B. Dick Video Je ~Printer) or conventional means ;
such as draw bar or spray coating (the coating depending f, upon the particular imaging procedure employed) and the silicone film allowed to dry. Drying can be conveniently 30 conducted at room temperature or slightly elevated temperature, to evaporate the solvent. Elevated temperatures can be used when curing is desired. ~`

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When the silicone is applied to the master substrate in image configuration by means of an ink jet printing apparatus, it may be necessary to dilute the silicone gum solution to a viscosity of conventional ink jet printing inks or generally to a concentration of between about 0.5 and 5 percent by weight silicone gum solids. Depending upon the conductivity of the materials employed, it may also be necessary to add a con- ~
ductivity agent such as a tetraalkylammonium salt in order to ~¦
permit the droplets to be given a charge in those ink jet systems requiring charged ink.
Alternatively, the silicone can be applied to the master substrate by conventional means such as draw bar coating and a catalyst deposited in image configuration by L
means of an ink jet printing apparatus, the silicone cur~d in the imaged are,s and the uncureA nonim?ge sil 7 cone rem,~veA
such as by washing with a suitable solvent such as - toluene. ;i Another method of forming the master is to coat a suitable silicone on a master substrate, cure the silicone ~¦
and then image the silicone by depositing in image configura-.j"
tion a curable ink-accepting polymer and curing said polymer.
-~ Preferably the materials are selected so that a grafting -reaction occurs, which generates chemical bonds between the ~, silicone and imaging polymer.
Another method of forming the master is to coat a suitable silicone on a master substrate, cure the silicone and then image the silicone by depositing in image configura-- tion a photocurable polymer by means of an ink jet printing apparatus which photopolymer will combine with the cured . . .

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silicone and be ink accepting in the imaged areas. Exemplary of suitable photopolymers are organic azides which upon the action of light or heat form reactive intermediates called nitrenes which can partially undergo insertion i~to carbon-hydrogen, nitrogen-hydrogen or oxygen-hydrogen bonds as well as form crosslinks with adjacent polymer chains. A typical commercial material is Photozid, sold by Upjohn Company.
Another embodiment of this invention is to apply a light sensitive curable silicone to a master substrate and image the silicone with a light absorbing but non-photosensitive shado~ fluid (e.g. a 2 percent solution of methyl salicylate in iso-propanol) by means for an ink jet printing apparatus followed by blanket illumination of the silicone and removal of the shadow fluid and uncured silicone ~eneath it by con-ventional means such as washing with a suitable solvent.
; Exemplary of suitable organic polysiloxanes whicn ; can be curèd by means of light or electron beams are described , in German OLS 2,207,495. Polymer~ disclosed therein a~e derived from at least one organopolysiloxane such as poly-dimethylsiloxane with an unsaturated residue of the foll'owing ~-;
structure:

HC = C - C - O -wherein R can be hydrogen or a halogen substituted phenyl ij residue while R2 is hydrogen or a methyl residue. The .,'' '`; ~
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unsaturated side chain may be based on acryloxy, methacryloxy, cinnamoloxy, or halo~enated cinnamoyloxy residues. An inhibitor to thermal polymeriæation as well as a sensitizer to specific electromagnetic radiation can be incorporated therein.
The viscosity of fluids discharged by the ink jet printing apparatus can be that of typical ink jet printing inks. Typically a viscosity of that of about water up to about 200 centipoises can be employed, depending upon the materials and type of apparatus employed.
'The silicone masters are ink releasing in the nonimaged areas and can thus be employed on a direct or offset printing . press with conventional inks to provide prints over a long period of operation, without the requirement of a fountain .
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The following examples are illustrative of the invention and preferred embodiments. All parts and percent-ages in said examples and elsewhere in the specification and claims are by weight unless otherwise specified.

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EXAMPLE I
A printing master is prepared and prints made therefrom as follows. Thirty grams of a 1 weight percent solution of poly(dimethyl siloxane) silicone gum (Union Carbide Y-3557) in benzene (which has 0.5 weight percent of aminobutylmethylsilo~ane comonomer units and a molecular weight from 200,000 to 500,000) is mixed with 0;004 gram of dimethyl dichlorosilane (capping agent in an amount excess to the pendant amino groups of the silicone gum) and blended by stirring in an open beaker. To this mixture is added 0.06 gram of a 5 weight percent solution in tetrahydrofuran of the ~-acetone oxime adduct of toluene-2,4-diisocyanate. The resultant solution is then employed in an ink jet printing nozzle like that shown in Figure 1 of U. S. Patent 3,747,120.
The nozzle is mounted in -a Xerox~telecopier apparatus which translates the noz~le sequentially relative to the imaging surface. The information signal is transmitted from another Xerox telecopier which is scanning the document to be reproduced.
The imaging solution is deposited on a 10" x 15" brushed aluminum sheet to form an image negative in sense. The coated sheet is then placed in an air oven maintained at 175C and placed in intimate contact with a metal helf of the oven. After a ; period of 5 minutes, the sheet is removed from the oven and allowed to cool to room temperature. The silicone coating is found to have been converted to a tough highly elastomeric ~ polymer. The plate is then mounted on a Davidson Duo Litho~
-; graphic printing press inked with VanSon 10850 rubber based ink and excellent prints obtained therefrom without the use o a fountain or dampening solution.
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EXAMPLE II
In accordance with the general procedure of Example I, a free radical curable organopolysiloxane prepared from acryloxypropyl trichlorosilane and polydimethylsiloxane, according to the method of German OLS 2,207,495, page 33, is deposited as a one weight percent solution in toluene on a master substrate containing a free radical source. The master - substrate is prepared by dissolving benzoyl peroxide in toluene, the mixture coated on a brushed aluminum sheet and the solvent allowed to dry. The silicone, which is deposited in image configuration in the nonimaged areas, is then cured by heat and excellent prints are obtained ~rom the master in accordance with the procedure of Example I.
EXAMPLE III
; 15 In accordance with the general procedure of Example : I, a printing master is prepared and excellent prints made therefrom employing a paper master substrate (A. B. Dick 3000) and a polydimethylsiloxane having pendant butylnaphthylureido sites prepared by the reaction of naphthylisocyanate and Union Carbide Y-3557 gum.
- EXAMPLE IV
In accordance with the general procedure of Example I, a printing master is prepared and excellent prints made therefrom employing a polydimethylsiloxane elastomer having pendant butyltriphenylsilylimino sites prepared by the reaction of chlorotriphenylsilane and Union Carbide Y-3557 gum.
; EXAMPLE V
A printing master is prepared as follows. A 10 weight percent solution of the siloxane of Example I with capped pendan~ sites and a blocked diisocyanate curing agent is draw ~ ' ~ .

bar coated on a brushed aluminum sheet to a thickness of five microns. The resultant master is then imaged by depositing a reactive polymer in tetrahydrofuran in image configuration from the apparatus of Example I. The toner is prepared by reacting 117.S grams ~0.289 equivalent monomers units) of a random free radical copolymer consisting of 71.8 mole percent styrene and N-butyl methacrylate, 41.0 grams (0.350 mole) 6-aminohexanol and 39.3 grams (0.350 mole) 1,4-diazabicyclo ~2.2.2 octane (DABC0). The mixture is agitated under dry nitrogen at a temperature of approximately 190C and n-butanol collected from a condenser. The toner is purified by quenching in 10 percent hydrochloric acid, dissolving in tetrahydrofuran followed by adding 10 percent hydrochloric acid and removing the liquid phase by decanting it from the gummy polymer. This is repeated several times and the sample dried under reduced pressure. Arter ink jet deposition, the resultant master is then heated to graft the toner to the silicone substrate and . . ~
excellent prints obtained therefrom according to the general procedure of Example I.
EXAMPLE VI
A printing master is prepared as follows. Thirty grams of a 10 weight percent solution of poly(dimethyl siloxane) silicone gum (Union Carbide Y-3557) in benzene (which has 1.5 weight percent of aminobutylmethylsiloxane [comonomer units]
, 25 and a molecular weight from 200,000 to 500,000) is mixed with0.6 gram of a 5 weight percent solution in tetrahydrofuran ~ of the acetone oxime adduct of toluene-2,4-diisocyanate. The 6 ' resultant solution is draw bar coated on a 10`' x 15" aluminum sheet and the solvent allowed to evaporate by maintaining the 30 coated sheet at room temperatur~ for 1 hour. The plate is ~,, .

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then placed in an air oven for two minutes at 180 C to cure the silicone to an elastomeric ink releasing condition. The plate is removed from the oven, allowed to cool to room temperature and imaged with a 20 weight percent acetone solution `-, 5 of Photozia~ Upjohn Co.) light sensitive polymer employing the printer of Example I. The coating is allowed to air dry. After the coat is dry, the plate is subjected to light from a mercury lamp for several minutes to cure and chemically bond the image coating to the silicone. The plate is then mounted on a printing press in accordance with the general procedure of Example I and excellent prints obtained i:;
therefrom without the ~se of any fountain or dampening solution.
EXAMPLE VII
A printing master is prepared and prints made .. j , therefrom as follows. Thirty grams of a 10 weight percent solution or poiy(dimethyl siloxane) sili~one gum (Union Car~idc W-982) in benzene (which has 0.02 weight percent of methyl-. ~
vinylsiloxane ~comonomer ~nits] and a molecular weight from 200,000 to 500,000) is draw bar coated on a 10" x 15" aluminum sheet. The plate is then imaged with a 1% solution of dialkyl peroxide (Lupersol 1~1~ employing an A. B. Dick Videojet printer.
The plate is then placed in an air oven for 2 minutes at 180C to cure the silicone to an elastomeric in~ releasing condition in the imaged areas. The uncured nonimaged areas are then removed by washing the plate with acetone. After allowing , the plate to dry, the plate is mounted on a Davidson Duo ; . Lithographic printing press and excellent prints obtained therefrom employing a conventional ink and no dampening or ~ fountain solution.

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EX~MPLE VIII
A printing master is prepared as follows. A
solution containing 6.6 grams [poly(ethylene propylene-1,4- ;
hexadiene)(63%, 33% and 4% respectively) and ~,3 grams of 1,1-- S bis(t-butyl peroxy)-3,3,5-trimethyl cyclohexane in 200 grams of cyclohexane is deposited on a brushed aluminum sheet in accordance ; with the procedure of Example I. The solvent is allowed to dry and the polymer cured to an elastomeric ink releasable condition by heat in the absence of air at 140C for ~ h~urs.
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EXAMPLE IX
A printing master is made as follows. A block , copolymer of 5~/O by weight polydimethylsiloxane and ~/O
, polystyrene is ~lended with an equal amount of an organopoly- -' siloxane prepared fro~ acryloxypropyltrichlorosilane and dihydroxydimethylsilicone containing 0.5 weight percent hydroguinone sensitizer. The mixture is dissolved in toluene and coated onto a degreased aluminum plate to a thickness of ~ , 8 to 10 microns when dried. The plate i5 dried for 10 minutes ~ '~
at 80C to evaporate the solvent. The plate is then imaged - 20 by depositing a light Lnsensitive shadow fluid o~ a 2% solution of methyl salicylate in iso-propanol, employing a Videcjet~
Printer. The plate is then permanently crosslinked by subjectinc -' it to a high intensity lamp at short distance followed by removal of the uncured silicone under the imaging insensitive fluid by washing with toluene.
EXAMPLE X
An aluminum master substrate having an elastomeric -; ink releasing p~lysiloxane layer, is imaged with the siloxane of Example I employing the ink jet printer, and the resultant master dusted with a particula~e toner comprising styrene/
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n-butyl methacrylate while the imaging silicone is uncured.
The master is then heated to cure the imaging silicone and bond the ink-accepting toner image thereto. Excellent prints are obtained when the master is employed on a printing press.

EXAMPLE XI
` The general procedure of Example I is repeated but for the exception that 'che abhesive material employed is formed from a 2.5% solution of l~/o poly(alpha-methylstyrene) copolymerized with 90% poly~dimethylsiloxane) in a solvent mixture of 8~/o dodecane and 20% xylene; and the solvent allowed to evaporate.
EXAMPLE XII
An aluminum master substrate is coated with the copolymer of Example XI and imaged, after evaporation of the solvent, with a solution of 5% alpha-methylstyrene in xylene employing the ink jet printing apparatus of Example I. After ; the solvent is allowed to evaporate, the mlaster i5 inXed and excellent prints made therefrom.
Having described the invention with reference to these specific embodiments, it is to be understood that , .
; 20 numerous variations can be made without departing from the spirit of the invention, and it is intended to encompass such reasonable variations or equivalents within its scope.

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Claims

T. embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for preparing a printing master compris-ing coating a master substrate with a silicone curable to an elastomeric abhesive ink releasing condition, said silicone having reactive pendant groups, selectively imaging the resultant coated substrate by discharging an imaging fluid from an ink jet print-ing apparatus as droplets by selectively emitting or deflecting said droplets in accordance with an information source wherein the imaging fluid is an ink-accepting material having groups reactive with the silicone pendant groups, curing the silicone to an abhesive ink releasing condition, and grafting the imaging material to said silicone.