CA1302035C - Silicone-covered roll and method for its production - Google Patents

Abstract

Abstract of the Disclosure This invention provides a silicone elastomer-covered roll consisting essentially of a central roll axle that is in contact with an inner layer of cured silicone elastomer having a hardness value no greater than 30 on the JIS A scale and an outer layer of cured silicone material having a hardness in excess of that of the inner layer. The roll is resistant to assuming a permanent compression set during use, in addition to exhibiting excellent soiling resistance. In particular, when used as a fixing roll in an electrophotographic copier, the contact area with the hard roll can increase, resulting in a clear image on the copy paper.

Description

13~ 5 ROLL COVERED WITH SILICONE MATERIAL
AND METHOD FOR PRODUCING ~AME

Thi~ invention relate~ to a roll covered with a silicone materia~ ~uitable for the variouæ applications, including transfer rolls, heating roll~, pressure rolls, and ~leaning roll~, typically found in electrophotographic copier~ and facsimlle devices. More par~icularly, thi6 invention relat~ to ~uch rollg that ~ontain a ~urface layer of cured silicone material that i B harder than the underlying rubber and to a method for producin~ these rolls.
Contact thermal fixing i~ widely u6ed, for example, in el~ctrophotographic copier~. In contact thermal fixing, ~n image is electrophotographically ~ormed on the photoreceptor by toner ( a thermopla~tic resin powder), sub~equently transferred to the transfer ~heet and then fixed in a fixing element to generate the copy.
- Conta~t thermal ~ixing omploy~ a device referred to a~ a heat-flxing roll a6 embly compri~in~ a bard heated roll, whose ~urface ha~ both heat resistance and relea~ibility, and a ~oft pressure roll, which posse se~ heat resistance, relea~ibllity, and flexibility. To ~ix a toner image the&e two heat-ix~ng rOllB are pre~8ed together at a deslgned pre~sure, and the image-carrying transfer paper i6 pas~ed between the rolls~ Und2r these conditions the so~t roll should undergo an inerea~e i~;conta~t area while in ~ontact with .

r ~3~21D3~i the hard roll in order to obtain a clear imag~. A
problem encountered with prior ar~ ~oft roll6 i~ their tendency to as~ume a permanent set ~ecause they are continually being deformed.
With reqard to the 60ft roll~ us~ed for paper advance in, for example, fac~imile devices, ~oiling of the original occur6 as a re~ult of use and accumulation o powder from the paper and other 60urces, with the result that the quality of the image is adversely affected.
In attempting to solve these problems, rolls have been proposed in which a relatively hard material such as a fluorinated resin or a flexible metal i8 additionally coated around the outer circumference of a low-hardnes~ rubber.
Japane~e Patent Publication No. 20232/80, published on April 19, 1980, di~close a roller comprising a metal core, an under-coat of a æpecified organo~iloxane composition that ~l~o includes an allyl ester of a polybasic acid, a metal ~alt of a fatty acid and an alkoxysilane, and an outer coating of a ~ilicone rubber.
Research Di~clo~ure Nos. 2178,033 and 217,034, publiRhed by Kenneth Mason Publications, Ltd. on April 20, 1982 and U.S. Pat. No. 4,430,406, which issued to J.
Newkirk et al. on~May 4, 1983 disclose a roller compri~ing an i~ner layer of a ~ilicone elastomer and an outer layer of an elastomeric organic fluoropolymer or a fluorosilicone that resi~t6 a~sorption of fusel oil absorbed by the inner lRyer. An intermediate layer has a compo~ition that changes continuously or ln a step-wi.e manner from that of the inner layer to that of ~he outer layer.

, ~3~2~35 West German Pat. No. 3,539,377, which issued on May 22, 1986 describes a roller having an elastic silicone rubber layer that is coated with a ~intered fluorinated organic resin such as polytetrafluoroethylene.
Japanese Patent Publication No. 26070/61, which was published on February 5, 1986, is directed to a heat fixing roll comprising a layer of silicone rubber sponge and a hard layer formed on the outer surface of the sponge rubber.
U.S. Pat. No. 4,329,565, which issued to Namiki et al. on May 11, 1982, discloses a fixing roll comprising a layer of resilient material that is overlaid with a layer of offset-preventing material containing from 1 to 5 percent of a thermally conductive metal powder. The offset-preve~ting material can be a silicone, fluorosilicone or organic resin.
Japanese Patent Publication No. 56854/57, which ` --`
issued on April 5,~1982 discloses a roller formed from a heat hardenable silicone rubber that is coated with a layer of anti-~tatic material prepared by adding a peroxide and either sodium sulfate or a sulonamide to a heat hardenable silicone rubber.
Canadian Pat. No. 1,116,549, which issued on January l9, 1982 discloses a fuser roll for a copier consisting essentially of a thermally conductive metal tube coated with a thin layer of a cured silicone rubber.
The rubber layer exhibits a thickness of about 0.25 mm.
and is expo~ed to ultra-violet radiation under an inert atmosphere following curing.

i3~2~:~S

Japanese P~tent Publication ~o. 38957/61, which was publi~hed on August 20, 19B7 discloses forming a roller by molding a silicone rubber on a metal core, in~erting the roller into a tube formed from a fluorinated resin and heating the resultant composite to shrink the resin tuba on to the 6ilicone rubber layer.
Japanese Patent Publication No. 28213, which i6sued on Febxuary 6, 1987, ~isclosP6 a method for forming a cvpier roll by placing a heat-resistant resin tube and a central core in a mold, pouring in a heat resistant material ~uch as a curable silicone rubber composition between the tube and the core to form an intermediate layar that is then vulcanized to form an elastomer.
Japanese Patent Publ~cation No. 26027/87, which was publi~hed on June S, 1987 discloses a fixing roll comprising a metal roll, an inner layer of a sili~one rubber and an outer layer of a fluoro~ilicone rubber.
U.S. Pat. No. 4,149,7~7, which iR~ued to G.
Imperial on April 17, 1979 and U.S. Pat. No. 4,083,092, which issued to ~mperial et al. on April 11, 1978 disclose a fixing roll comprising a rigid core, an organic rubber layer adhered to the core and an outar protective ~leeve. The ~leeve haæ a high flex life and blocks air from reaching and oxidizing the rubber.
Soft rolls known in the art, including the 6ilicone rubber-covered rolls, suffar from the problems of 1) not increa6ing in contact area along the line of contact between ~he ~oft roll and the aforementioned hard roll 2 ) and ~suming a permanent compres6ion set. As a result, there i~ a ~trong tendency for the copy image to be unclear.

i , ~L3~;~1D3~;

The present inventors carefully studied methods for eliminating these problems, and developed the present inven^tion as a consequence.
An objective of the present invention is to provide a soft roll coated with a silicone material which is not subject to permanent set during use and which has an excellent resistance to soiling. This invention also provides a method ~or preparing these rolls.
A particular object of the present inven~ion is to provide a soft roll whose contact area with an adjacent hard roll can expand along the line of contact with a hard roll. This provides a clear copy image when the rubber-covered roll is used as a fixer roll in an electrophotographic device.
Another objective is to provide a method ~or the production of these soft rolls.
The aorementioned objectives can be achieved by a roll wherein a first layer of cured silicone material having a hardness no greater than 30 on the JIS
A scale is formed on a roll axle and covered with a second layer of cured silicone material having a hardness greater than that of the first layer.
The present invention resides in an improvement in an unheated roll for a copier or facsimile device comprising a metal roll axle coated with a cured silicone rubber, which improvement comprises:
a. the presence on said roll of an inner layer of cured silicone rubber having a first and a second surface and a hardness of less than 30 on the Japanese Industrial Standards (JIS) A scale, wherein said first surface is in contact with said axle and said second surface is in contact with an outer layer of cured silicone rubber exhibiting a hardness greater than that of said inner layer, where said roll is formed by ~L30~35 1) coating the interior surface of a mold with an organohydrogenpolysiloxane having at least 3 silicon-~onded hydrogen atoms per molecule, 2) mounting said roll axle in said mold, 3) introducing into said mold a curable liquid silicone rubber composition that will yield said cured silicone rubber having a hardness no greater than 30 on the JIS A scale, and 4) curing said organohydrogenpolysiloxane and said liquid silicone rubber composition by heating.

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~3~2~35 The pres0nt invention also provides a preferred method for preparing the present silicone-covered roll.
In accordance with this method an organopolysil~xane having at least 3 silicon-bonded hydrogen atoms in each molecule is applied to the interior surface of a mold. A
roll axle is then introduced into the interior of this mold, followed by introduction of a liguid silicone composition that is convertible t~ the aforementioned elastomeric cured material having a hardness no greater than 30 on the JIS A scale. As the final step the organopolysiloxane and liquid silicone rubber composition are thermally cured.
No specific restrictions apply to the roll axle used in the present invention. The axle is formed from a metal typically used as a roll core metal. The surface of the axle can be treated with an anticorrosive agent or a primer.
The inner layer of the present roll is adjacent to the roll axle and consists essentially of an elastomeric cured silicone material having a hardness no greater than 30 on the JIS A scale. This material is obtained from an organopolysiloxane-based composition that cures either at room temperature or upon heating.
The cured silicone material is not specifically restricted, and includes silicone gels and conventional silicone rubbers. The hardness of the cured material must be no greater than 30 on the JIS A scale, measured as specified in JIS C 2123. The hardness of the cured silicone material is preferably no more than 20, and most preferably no more than 10.
If the hardness value of the inner layer exceeds 30 on the JIS A scale the roll will not exhibit the advantages of the present invention.

~L3~2~3~;

The thickness of the inner layer is not specifically restricted, and will depend upon the end use application of the roll.
An outer layer of cured silicone material having a hardness in excess of that of the aforementioned inner layer of cured silicone material is the characterizing feature of the present rolls. The principal component of the cured surface layer is at least one organopolysiloxane. Preferably the organopolysiloxanes present in the inner and outer layers are identical.
No specific restrictions apply to the outer layer other than the fact that a tacky semi-cured material or cured gel material is undesirable. Concrete examples of cured materials suitable for use as the outer layer are silicone rubbers and silicone resin~.
The cured outer layer must be harder than the cured inner layer. A hardness value in the range of 35 to 90 on the JIS A scale is preferred for the outer layer. When the hardness of the outer layer is less than that of the cured inner layer, the roll will have a tacky surface, and will not exh'bit the desired resistance to soiling and development of a permanent compression set.
The cured outer layer preferably has a thickness of approximately 1/10 to 1/1000 that of aforementioned inner layer. The thickness of the outer layer is preferably no greater than 1,000 microns.
The mold used to manufacture the silicone-covered roll in accordance with the present method can be formed from metal, silicone rubber, or a synthetic resin such as a polyester or nylon. These materials are typically used as mold materials for silicone rubber compositions : ~`

~L3~2~3S

No specific res~ictions apply to the mold so lvng a~ the curable lisuid ~ilicone rubber comp~sition can flow into the mold and be ~ubsequently cured.
In accordance with a preferred method for preparing the present roll an organopolysiloxane containing at lea~t 3 silicon bonded hydro~en atom~ is applied to t~e interior ~urface of the mold, the roll axle i~ placed in-~he center of the mold cavity and the cavity is ~ubsequently filled with a cur~ble liquid æilicone composition that will form the inner layer of ~; the roll upon curing. The organopolysiloxane is in contact with and cures together with the curable liquid Eilicone composition during molding to form the hard outer layer o~ the roll. Although thi~
organopolys~loxane must have at least 3 ~ilicon-bonded hydrogen atom~ in each molecule, it can be used in combination with an organopolysiloxane having 2 : ~ilicon-bonded hydrogen atoms in each molecule to vary the h~rdnes~ of ~he outer layer.
The molecular structure of the organopolysiloxane containing at least three -silicon-bonded hydrogen atoms per molecule is not ~pecifically restxicted. The molecular structure of thi6 molecule may be ~traight chain, branch-containing straight chain, or cyclic. When a harder and tougher outer layer must be formed at the 6urface of the ~ilicone~covered roll, it is pre~erable to use a branched ~: organopolysiloxane, for example, a copolymer composed of ~CH337HSiOl~2 and SiO4/2 units, or a copolymer o~
(C~3)3silJ2' ~CH3)2Hsiol/2~ and SiO4/2 Non-limiting examples of the organopoly~ilox~ne ingredient include but are not limited to trimethylsiloxy-terminated me~hylhydrogenpolysiloxanes.

7.

~:

s trimethylsiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymers, dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymers, d:Lmethylsiloxane-methylhydrogensiloxane cyclic copolymers, copolymerscomposed of (CH3)2HSiol/2 and Sio4/2 units, and copolymers composed of (CH3)3SiOl/2l (CH3)2HsiOl/2~ and SiO4/2 units.
The organopolysiloxane can be applied to the inner surface of the mold by any of the known conventional means, including spraying, brushing and sponge coating. No specific restrictions apply to tha quantity of organopolysiloxane, applied to the inner mold surface, as long as a continuous, dry film is formed on the mold surface.
The curable liquid silicone composition that forms the inner elastomer layer of the present roll can be a liquid or paste at room temperature, and is based on a reactive group-containing liquid organopolysiloxane, a crosslinker and~or a curing catalyst. The composition is capable of curing into a rubbery elastomer or gel at room temperature or with heating. It can be of the "sag" or "non-sag" type.
The curing mechanism of this composition is not critical, and can be an addition-reaction mechanism, organoperoxide-based radical reaction-curing mechanism, or condensation-reaction mechanism. Compositions that cure by means o~ an addition reaction are preferred in order to obtain a faster and more uniform curing.
Particularly preferred addition-curable liquid silicone compositions for use in preparing the inner elastomer layer comprise (A) an organopolysiloxane having at least i~

~3~2~3S

2 lower alkenyl groups in each molec~lle; (B) an organopolysilo~ane having at least 2 silicon-bonded hydroyen atoms in each molecule, in a quantity such that the molar ratio of the total quantity of silicon-bonded hydrogen atoms in the present component to the total quantity of all lower alkenyl groups in component ~A) is from 0.1 to 1; and (C) a concentration of a platinum-type catalyst equivalent to from 0.1 to 1,000 weight parts platinum metal for each one million weight parts of the total of components (A) and (B).
Component (A) of the preferred curable compositions is the principal component of the composition. Curing of the composition proceeds by the addition reaction of component (A) with component (B) under the catalytic activity of component (C). Component (A~ must contain at ].east 2 silicon-bonded lower alkenyl radicals-in each molecule. These lower alkenyl radicals .
are exempli~ied by vinyl, allyl, and propenyl.
The alkenyl radicals of ingredient (A) can be present at any location in the molecule, but are preferably present at least at the molecular terminals.
The molecular configuration of this component can be straight chain, branch-containing straight chain, cyclic, or network, but is preferably straight chain, possibly slightly branched. No specific restriction applies to the molecular weight of this component. Also, while the viscosity may range from that of low-viscosity liquids to very high-viscosity gums and thus i~ not specifically restricted, the viscosity at 25C is preferably at least 100 centipoise (0.1 Pa.s) in order to obtain a cured material in the form of a rubbery elastomer. Examples of this alkenyl-substituted organopolysiloxane include but ~l3~

are not limited to methylvinylpolysiloxanes, methylvinylsiloxane-dimethylsiloxane copolymers, dimethylvinylsiloxy-terminated dimethylpolysiloxanes, dimethylvinylsiloxy-terminated dimethylsiloxane-methylphenylsiloxane copolymers, dimethylvinylsiloxy-terminated dimethylsilo~cane-diphenylsiloxane-methylvinylsiloxane copolymers, trimethylsiloxy-terminated dimethylsiloxane-methylvinylsiloxane copolymers, trimethylsiloxy-terminated dim thylsiloxane-methylphenylsiloxane-methylvinylsiloxane copolymers, dimethylvinylsiloxy-terminated methyl(3,3,3-trifluoropropyl)polysiloxanes, dimethylvinylsiloxy-terminated dimethylsiloxane--methyl(3,3,3-trifluoropropyl)siloxane copolymer~, and polysiloxane~ consisting essentially of 2 ( H3)2Si1/2~ (CH3)3siol/2~ and SiO4/2 units Combinations of the above organopolysiloxanes can also be used in the present invention.
. Component tB) of the preferred compositions or preparing the inner elastomer layer of the present rolls is a crosslinker for component (A). Curing proceeds by the addition of the silicon-bonded hydrogen atoms in this component with the lower alkenyl groups in component (A) under the catalytic activity of component (C). This component (B) must contain at least 2 silicon-bonded hydrogen atoms in each molecule in order to function as a crosslinker.
The molecular structure of component (B) is not specifically restricted, and can be straight chain, branch-containing straight chain, or cyclic. The molecular weight of this component is likewise not specifically restricted, however the viscosity of this 1~

~L3~2Q135 component, me~ured at 25bC., i6 preferably 1 to SO,OOO
centipoi~e ~0.001 to 50 P~.~) in order to obtain goQd mi~cibility with component (A).
The concentration of component ~B) is preferably one ~hat will provide a molar ratio of ~ilicon-bonded hydrogen atoms to all lower alkenyl radical~ in c~mpo~ent (A) of from 0.1 to l. MGst preferably t~iB ratio i6 fro~ 0.~ to 0.6. 'rhe crosslinking density will be too low at molar ratios below 0.1, re~ulting in un6ati~factory curing. On the other hand, the cro~lin~ing den~ity of the cured inner layer will be too high when the molar ratio 8i licon-bonded hydrogen atoms to total alkenyl radicals exceeds 1, and it will be difficult to orm a hard covering layer at the ~urace o~ the ~l$cone-covered roll.
It will be unders~ood that when the curable compo~ition u~ed to form the inner-elastomer layer incl~d~ an additional organopoly~iloxane containing a large concentration of alkenyl radicals for the purpo~e of providing rei~forcement or other properties to the cured elastomer, th~ amount of organopolysiloxane containing siliton-bonded hydrogen atom i8 preferably ~ufficient to react with thee2 additional alkenyl radicals.
Examples ~f component (B~ include but are not limited to trimethyl~iloxy-terminated methylhydroge~poly~ilox~ne > trimethyl~iloxy-terminated dimethylsiloxane-methylhydrogen~iloxane copolymers, dimethylhydrogensiloxy-terminated dimethyl~iloxane-methylhydrogen~iloxane copolymer~, 1~

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~30;~35 .
dimethylsiloxane-methylhydrogensiloxane cyclic copolymers, copolymers composed of (CH3~2HSiO1/2 and SiO4/2 units, and copolymers composed of (CH3)3$iO1~2, (CH3)2HsiOl/2~ and SiO4/2 units.
Component (C) of the preerred curable compositions is a catalyst for the addition reaction of silicon-bonded hydrogen atoms with alkenyl radicals.
Non-limiting examples of this component include chloroplatinic acid, including solutions of this catalyst in alcohol or ketone and these solution following aging, chloroplatinic acid-olefin complexes, chloroplatinic acid-alkenylsiloxane complexes, chloroplatinic acid-diketone complexes, platinum black, and platinum supported on a carrier.
Component ~C) is present in an amount equivalent to from 0.1 to 1~000 weight parts of platinum-group metal for each one million parts by weight (ppm) of the total guantity of components (A~ and`~~BF.'`~
The crosslinking reaction will not proceed satisfactorily at below O.l ppm, while exceeding 1,000 weight parts is uneconomical. In the typical case, the preferred catalyst concentration is equivalent to approximately 1 to 100 ppm of platinum-group metal.
The curable liquid silicone compositions used to form the inner layer of the present roller can include at least one filler to adjust the fluidity and/or improve the mechanical strength of the molded article.
These fillers are exemplifi~d by reinforcing fillers such as precipitated silica, fumed silica, calcined silica, and fumed titanium dioxide, and by non-reinforcing fillers such as quartz powder, diatomaceous earth, asbestos, aluminosilicic acid, iron oxide, zinc oxid~, 13012~35 and calcium car~onat~. The ~urface of the filler can optionally be treated with a~ organo~ilicon compound, for example, hexamethyldisilazane, trimethylchloro~ilane~ or a hydroxyl terminated polydimethyl~iloxane.
Ths prasent curable liguid 6ilicone compogition~ can al~o include ~mall or very ~mall amount~
of inhibitor~ for the curing reactionr BO long a~ the~e inhibitor~ do not adversely affect the objectives of the pre~en~ invention. Non-limiting ~xample~ of ~uch inhibitors include acetylenic compounds, hydrazines, triazole , phosphineR, and mercaptans.
Other optional inqredients that can be pre~ent in the curable precursor of the elastomeric inner layer include but are not limited to pigment8, heat stabilizers, flame retardants, plaBticizer~ and organopolyciloxanes having 1 alkenyl radical i~ each molecule that are added to reduce the modulus of the cured ela~tQmeris inner.layer.
A second ciaa of preferred curable ligui~
organosiloxana compositions cure by means of a free radical reaction and include an organoperoxide as the curing ~gent. The~e ~ompo~itions include a vinyl group-containin~:diorganopolysiloxane that is li~uid at room temperature and a catalytic quantity of organoperoxide. Optional ingredients include but are not limited to inorganic filler6 ~uch as fumed silica and precipitated silica, heat stabilizers, and pigments. The organoperoxide preferably has a decomposition temperature in the range of ~25 to ~100C.
Compressio~ molding, transfer molding, and in~ection molding are typically used to mold liquid cilicone rubber composit on~, and can be u3ed to introduce the pre~ent curable liguid silicone rubber compo~ition into the in~erior of the mold ~nd thermally cure them.

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131[~2~

When the temperature used to cure the curable llquid 6ilicone ma~erial is too low, the curing rate will be reduced ~nd the productivity will be low. On the other hand, when the molding ~emperature il3 to~ high, ~he re~ul~ing ~ilicone ela6tomer molding will ~stick to the i~terior surface of the mold, thus generat:ing problems in de-moldinq. Ac a con~eguence, the molding temperature æhould be within the range of from 50 to 220~C and preferably in the range of 50 to 170C.
The sllicone-covered roll of the present lnvention finds use in various applications, ~or example, as the transfer roll~, fixing rolls, or c~eaning rol}s used in electrophotographic copiers, and as paper-advance roll~ in ac~imile devices.
The following examples describe preerred e~bodiment~ of the prssent rolls, and should not be -~nterpreted as limiting the scQpe of the invention a~ ~ _ de~ined in.the accompanying claims. Unless otherwise ~pecified.all part~ ~nd percen~age~ are by weight a~d vi~coæities were measured at 25~C.

Example 1 100 Part6 of a dimethylvinylsiloxy-terminated dimethylpoly~iloxane having a viscosity o~ 2000 centipoise (2 Pa.s) and a vinyl content of 0.23 wt%, 25 part~ dry-me~hod silica having a ~pecific ~urface area o~
200 sguare meter~ per gram, and 0.5 parts tximethyl~iloxy-terminated methylhydrogen-poly iloxane having a ~i6cosity of 10 centipvi~e (0.01 Pa . ~) and a SiH ~ilicon-~onded hydrogen content of 0.9%
were blended to homcgeneity to provide a mixture having a vi~co~ity o~ 5~000 poise (500 Pa.~j at a ehear rate of 1~

,. 1~

: ., ~l3(~13~i Bec 1, A curable liquid ~ilicone composition of this invention wa~ obtained by bl~nding this ~uxture together with 0.1 par~ of a ~olution of chloroplatinic acid in i opropanol. The solution contained 3 percent of platinum.
A metal mold designed for the moldi~g of ~ilicone ela~tomer-covered rolls and having a chromium-plated interior ~urface was coated on it~
interior surface with a trimethylsiloxy-terminated methylhydrogenpoly6iloxane having a vi6cosity of 10 centi~tokes (10 5 m2/sec.) and a silicon bonded hydrogen atom content of 1.0 wt% to yield a uniform coating density o~ 0.2 g per square meter.
A cylindrical iron roll axle was al50 prepared, and coated with a primer consisting essentially of an organopoly~iloxane gum~ an organopolysiloxane resin, ethyl ~ilicate, a ~ethylhydro~enpoly6iloxane. and an organotita~ate ~ster. The primer was applied ~o th~
ur~ace of the roll and subs~quently cured.
The primed roll axle wa~ mounted in~ide the aforementioned metal mold, and the liguid ~ilicone ~omposition prepared as described in the preceding portion of thi~ ~xample was then injected into the cavity and thermally cured at 150C for lO rninutes. After cooling, ~he obtained ~ilicone~-covered roll wa~ removed and the interior portion o~ the coating was expo~ed by cutting lnto the coating u~ing a knife.
The hardness of the $nterior and exterior layers of the roll coating was then mea6ured using the JIS A scale with the following results: surface layer hardness - 50, inner layer hardne6s = 10. The thickness of the outer layer wa~ ~.5 mm.

~13~2~35 The resiliency of the rubber layer wa~ 10% and the permanent compree6io~ ~et was 15%. Th~ compreC6ion æet value was o~tained by compressing the rub~er layer to 75% of its initial thicknesR for a period of 72 hour~
while heating the roll at a temperature of lB~C.
When this ~ilicone ela~tomer-covered roll wa~
u~ed a~ the pressure roll in the fixing roll of an electroph~tographic copier, ~he copy paper wa~ not creased, and the copied image was clear.

Example 2 100 Part~ of a dimethylvinyl6iloxy-terminated dimethylpolysiloxane having a vi~cosity of ~000 centipoi~e (2 Pa. 5 ) and a vinyl content of 0.23 wt%l ~0 parts dry-method silica having a ~pecific surface area of 200 ~guare meterC per gram, 0.4 parts trimethylsiloxy-terminated methylhydrogenpoly6i}0xane having a SiH
content of ~.0 wt%, and Ool part of a ~olution of chloroplatinic acid 801ution in isopropanol (plati~um content = 3 percent) were blended t9 homogeneity to produce a curable liguid ~ilicone compo6itio~ of thi~
invention. The ~ame methylhydrogenpoly6iloxane described in the preceding Example 1 wa~ ~prayed on the interior ~urface of ~n m~tal injection mold. The mold was heated to a temperature of 120C at which time an iron roll core was mounted in the interior of the~mold, and the liquid silicone ~ompo~ition prepared as above was the~ injected and cured. The hardne s values of the exterior and interior lay~r~ o~ the resultant ilicone elastomer-covered roll of thi invention were mea~ured a described in the preceding Example 1, and were 38 and 3, respectively, measured using the JIS A ~cale. When this roll was u~ed a~ a paper-advance roll in a fac6imile device neither the roll ~urface nor ~he image were ~oiled.
1~
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Example 3 100 Part~ of a dimethylvinylsiloxy-terminated dimethylpoly iloxane having a visc06ity of 2000 centipoise (2 ~. 8) and a vinyl conten~ of 0.23 wt%, 15 part of carbon blaok having a specifiG ~urface area of 70 ~quare meters per gram (available as Denka Bl~ck*~rom Denki Kagaku Kogyo ~abu~hi~i ~aisha) and Q.4 parts of a trimethyl~iloxy-terminated methylhydrv~enpoly~iloxane having a vi6cosity of 10 centipoige ~0.01 Pa.~) and a #ilicon-bond~d hydrogen atom ~ontent of 1.0 wt% were blended to ha~eneity of yield a mixture having a viscosity of 800 po~se ~80 Pa.~) at a shear rate of 100 ~ec 1. To this mixture wa~ added 0.1 part of the chloroplatinic acld ~olution described in the preceding Example 1 to produce a curabl~ liquid silicone rub~er composit~on of this invention.
A cylindrtcal metal mold having a chromium~
plated inner ~urface was coated with a cylindrical -~preformed polyester film and a 10% fiolution in toluene of a trimethyl~iloxy-terminated methylhydrogenpolysiloxane exhibiting a viscosity o~ 10 cer.tistokes (lxlO 5 m2~ec~
and eo~taining 1 percent of ailicon- bond~d hydrogen was sprayed on the expo~ed surface of the film to produce a c~ating density o~ 5 gram~ per ~guare meter. The coating was then dried. An alumi~um roll axle was then inserted into the cavity'~ interior, and the liguid ~ilicone rubber comps~ition prepared a~ described in the precedin~
portion o~ ~hi~ Example wa~ then in~ected and thermally cured at 139C for 5, minutes. ~e re~ultin~ molding wa~
a silicone-covered roll having an inner gel layer (hardness = 5) and a 0.4 mm-thick hard cover~ng layer at *Trad ~ rk 1)3~;

the surface. This silicone elastomer-covered roll of this invention was used as the pressure roll in the fixing rolls of an electrophotographic copier. No permanent compression set in the roll was observed, and the copied image was clear.

,~

2~

Claims (4)

1. In an unheated roll for a copier or facsimile device comprising a metal roll axle coated with a cured silicone rubber, the improvement which comprises:
a. the presence on said roll of an inner layer of cured silicone rubber having a first and a second surface and a hardness of less than 30 on the Japanese Industrial Standards (JIS) A scale, wherein said first surface is in contact with said axle and said second surface is in contact with an outer layer of cured silicone rubber exhibiting a hardness greater than that of said inner layer, where said roll is formed by 1) coating the interior surface of a mold with an organohydrogenpolysiloxane having at least 3 silicon-bonded hydrogen atoms per molecule,

2) mounting said roll axle in said mold,

3) introducing into said mold a curable liquid silicone rubber composition that will yield said cured silicone rubber having a hardness no greater than 30 on the JIS A scale, and

4) curing said organohydrogenpolysiloxane and said liquid silicone rubber composition by heating.

2. A roll according to claim 1 wherein the liquid silicone rubber composition comprises:
(A) an organopolysiloxane containing at least 2 silicon-bonded lower alkenyl radicals in each molecule, (B) an organopolysiloxane having at least 2 silicon-bonded hydrogen atoms in each molecule, in a quantity such that the molar ratio of the total quantity of silicon-bonded hydrogen atoms in the present component to the total quantity of all lower alkenyl groups in component (A) is from 0.1 to 1; and (C) a platinum-type catalyst in an amount equivalent to from 0.1 to 1,000 parts by weight of platinum metal for each one million parts by weight of the total of components (A) and (B).

3. A roll according to claim 2 where said lower alkenyl radical is vinyl and said organopolysiloxane having at least 2 silicon-bonded hydrogen atoms in each molecule is a polymethylhydrogensiloxane.

4. A roll according to claim 3 where said vinyl radicals are present in a dimethylvinylsiloxy-terminated polydimethylsiloxane.