EP0809675A1

EP0809675A1 - Fluoroelastomer and silicone blend compositions and fuser member containing same

Info

Publication number: EP0809675A1
Application number: EP96906456A
Authority: EP
Inventors: Chris F. Delrosario; Carl A. Aufdermarsh
Original assignee: Ames Rubber Corp
Current assignee: Ames Rubber Corp
Priority date: 1995-02-16
Filing date: 1996-02-15
Publication date: 1997-12-03
Also published as: WO1996025461A1; CA2211544A1

Abstract

A blend of a cured fluoroelastomer and silicone suitable for the outer suface layer of a fuser member which does not require the use of mercapto functional active release agents to prevent offset is provided. The fluoroelastomer component of the compositions contain at least 23.4 mole percent hexafluoropropylene, and preferably do not contain any metal oxide. The blend can be prepared by dissolving the fluoroelastomer in a solvent and adding a siloxane and catalyst and allowing the siloxane to cure. Alternatively, the siloxane can be added to the fluoroelastomer in the solvent in the presence of a catalyst and then added to the fluoroelastomer in the solvent.

Description

FLUOROELASTOMER AND SILICONE BLEND COMPOSITIONS AND FUSER MEMBER CONTAINING SAME

BACKGROUND OF THE INVENTION

This invention relates to blends of fluoroelastomer and silicone, and more particularly to blends of polysiloxane particles dispersed in a matrix of fluoroelastomer vulcanizate suitable for use in fusing applications and to fuser members with improved copy life having a top coat of the blend.

A fuser member is designed to apply direct heat and pressure to a toner image on a recording medium. The surface top coat permits toner to be fixed to the recording medium without adhering to the fuser member surface and can withstand continuous exposure to high temperatures, silicone oils, toners, toner additives and paper product residue without unacceptable physical degradation.

In general, when forming images by xerographic processes, an image formed of a heat fusible toner powder is selectively disposed on a web-like surface of a recording medium, such as paper, by electrostatic forces. Toner powders are commonly formed of a mixture of thermoplastic and/or thermosetting resin carriers and additives such as amorphous carbon and magnetic particles. They are conventionally fixed to the recording paper by direct contact with a fuser member such as a roller which applies pressure and heat at temperatures between about 200 to 400°F.

The fusing process is conventionally accomplished by feeding a recording medium having the toner image thereon between the nip where two mated rollers meet. One or both of the rollers are heated, typically by an internal heat source within the roller, so that the surface temperature of the roller will be above the softening point of the resinous carrier of the toner.

The recording medium with the toner image thereon is fed between the two rollers which press towards each other to apply direct heat and pressure to the toner image. The amount of pressure and the length of time that the toner is heated determines the degree of fusing. The actual temperature range suitable for fixing toner images to recording paper is referred to as the "fusing window". The fusing window, T_w can be defined by the formula:

T_w ⁼ T_0FF - T_MIN wherein T_0FF is the hot offset temperature and T_MIN is the minimum fusing temperature.

Hot offset temperature is the temperature at which the cohesive forces within the molten toner layer are less than the adhesive forces between the toner and roller surface so that toner adheres to the fuser roller. T_MIN is the minimum temperature at which toner can be acceptably fixed to the recording paper. This temperature range is dependent on the raw materials, type of toner, release agents and the pressure applied by the rollers. It is important that the toner is fixed without "offset" occurring, in order to produce copies of acceptable quality. For commercial applications, a fusing window of at least 30°F is acceptable for some applications. However, it is preferable to have as large a fusing window as possible. Thus, a 60°F fusing window is desirable and a 100°F fusing window is particularly ideal. Conventional fusing systems have drawbacks . Softened toner generally has an affinity for the surface of the fuser roller it contacts. When toner adheres to the surface of a fuser roller, it can unintentionally be deposited on an unselected portion of the recording medium during the next rotation of the roller. This phenomenon is referred to as "offset. "

To prevent offset, a thin coating of a release agent such as polysiloxane fluid is commonly spread over the surface of the fuser roller which contacts the surface of the toner image. The polysiloxane fluid reduces the surface free energy of the roller surface and decreases the affinity of the toner for the roller. Surface energy values for several conventional fuser roller materials are set forth below in Table I.

TABLE I Surface Energy of Fuser Roller Materials Fuser Roller Surface Surface Energy nMn

Polytetrafluoroethylene (PTFE) 18.0-18.5 Polyvinylidene fluoride (PVF₂) 21-22

Polysiloxane Compounds 28-29

Polyfluorocarbon Elastomers 35-37

Polysiloxane Release Agents 19-21

When compounding or formulating fluorocarbon elastomers, metal oxides are typically included to act as an acid acceptor, cure activator, reinforcing filler and/or as an additive to promote improved chemical resistance. Commercially available fuser rollers generally have a fluoroelastomer surface which contains metal oxide particles in at least the fluoroelastomer surface layer. U.S. Patent Nos. 4,257,699, 4,264,181 and 4,272,179 describe fuser rollers in which additional metal oxide filler particles beyond that needed to promote cure of the material are added to the fluoroelastomer surface material to increase the metal oxide content of the surface of the fuser rollers. Fluoroelastomers described in U.S. Patent No. 5,035,950 have high hexafluoropropylene (HFP) content and contain only so much metal oxide as is necessary to effect cure of the high fluorine content material. This patent is assigned to the assignee herein and the contents are incorporated herein by reference.

These issued patents also describe that use of a polymer release agent having mercapto functional groups applied to the surface of a fuser roller having metal oxide filler decreases problems associated with offset. When the metal- containing filler in the elastomer surface layer is present in sufficient amount, it interacts with the polymeric release agent to produce an active release film. This active release film prevents the thermoplastic resin toner from contacting the elastomeric material itself and accordingly, offset is avoided.

Although this active release mechanism has proven to be commercially acceptable, it nevertheless has drawbacks. Release agent fluids having mercapto functional groups are expensive. They can also present an unpleasant odor in the office environment and interfere with the ability to write or type on the copy sheet. The copy life of the high HFP compositions is at some risk, particularly in fusing systems using standard dimethylpolysiloxane release fluids.

Accordingly, it is desirable to provide an improved fusing system with improved copy life which overcomes the shortcomings of the conventional fuser systems described above.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a blend of polysiloxane particles dispersed in a fluoroelastomer particularly well suited for the topcoat of a fusing member for applying heat and pressure to fix toner to a recording medium is provided. The fluoroelastomer material are those having high molar content of hexafluoropropylene (HFP) , with a molar content above about 23.4 mole per cent. The fluoroelastomer and silicone blend can be formed by a first insitu method, wherein a hydropolysiloxane is crosslinked in the presence of a catalyst in a fluoroelastomer which has been dissolved in a suitable solvent. In a second pre-reaction method, the hydropolysiloxane is crosslinked in a solvent in the presence of a catalyst and a fluoroelastomer is then added. A fusing member having a fluoroelastomer and silicone blend surface prepared in accordance with the invention has advantages over conventional fusing members in fusing systems using dimethylpolysiloxane release fluids, by providing increased copy life and avoiding the need to use expensive mercapto functional active release agents to prevent offset. Accordingly, it is an object of the invention to provide an improved fluoroelastomer and silicone blend composition.

Another object of the invention is to provide an improved fuser member having a topcoat of fluoroelastomer and silicone blend for fixing toner to a recording medium.

A further object of the invention is to provide a fuser member having a fluoroelastomer and silicone blend topcoat for fusing without the need to use mercapto functional release agents.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the composition possessing the features, properties and the relation of constituents and the article possessing the features, properties, and the relation of elements, which are all exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a fuser roller test assembly; FIG. 2 is a cross-sectional view of a single layer fuser roller constructed in accordance with an embodiment of the invention;

FIG. 3 is a cross-sectional view of a multi-layer fuser roller constructed in accordance with another embodiment of the invention;

FIG. 4 are the results of an X-ray analysis of the surface of a cut cross-section of a film of a fluoroelastomer and silicone blend prepared in accordance with the invention; FIG. 5 are the results of an X-ray analysis of an individual dispersed particle in the film analyzed in FIG. 4; and

FIG. 6 is a Thermogram showing the Dynamic Mechanical Thermal Analysis of the film of FIG. 4 measured on a plastic backing, and measured by Differential Scanning Calorimetry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fusing member constructed in accordance with an embodiment of the invention includes a fluoroelastomer and silicone blend topcoat surface. The fusing member can be a roller, a belt, a flat surface or another substrate having a suitable shape for fixing toner images to a recording medium, such as paper, at elevated temperatures under pressure. A preferred fusing member is a fuser roller having a metal core that can be hollow, covered with the fluoroelastomer and silicone blend material. A heating element can be included within the metal core to heat the fluoroelastomer and silicone blend surface. The fuser roller can be used to fix toner powder to a recording medium, such as paper, without offset and without relying on the interaction between metal oxides in a fluoroelastomer and mercapto functional release agent fluids.

The outer layer of the fusing member is of a fluoroelastomer material having high molar content of HFP

(hexafluoropropylene) with the molar content of HFP is above about 23.4 mole percent, preferable above about 30.0 mole percent. The fluoroelastomer preferably is a copolymer of HFP and VF₂ (vinylidene fluoride) monomer, and includes more HFP monomer than VF₂ monomer, so that the weight ratio of VF₂ to HFP is less than about 1.40, and above about 0.70. A copolymer of VF₂ and HFP based on the monomer content described would contain between about 65 to 71 percent total fluorine by weight. Preferred silicone material for preparation of the composition are hydropolysiloxane oligomers having weight average molecular weights ranging from about 500 to 10,000 and preferably between about 500 and 2,000. The hydropolysiloxane is preferably present in the composition between about 10 to 40% by weight.

The preferred polysiloxane phase is selected from dimethylpolysiloxane copolymers which can be described and specified as:

MD^_yM, wherein M = Me₃Si0_1/2

D = Me₂SiO D^x= H(Me)SiO, or

H₂C=CH(Me)SiO, or R(Me)SiO, and wherein R = alkoxy, or

R = acetoxy, or R = ketoxy, or D^x= HO(Me)SiO, and wherein x + y = 1, and x = 0 to 0.99 y = .01 to 1.0 The weight average molecular weight of the aforementioned copolymers can vary from about 550 to 120,000, with the most preferred range being between about 2000 to 60,000.

The silicone copolymer phase can be insitu crosslinked in the presence of the fluoroelastomer phase, or crosslinked independently in solvent and added to the fluoroelastomer phase. In either case suitable crosslink agents must be present to crosslink the silicone copolymer. Suitable crosslinking agents include water, vinyl silanes and hydrosilanes, plus catalysts appropriate to the chemistry, i.e. Sn (IV) salts for condensation reactions and Pt salts for addition systems.

The fluoroelastomer composition can also include cure additives, such as hexafluoropropylidine diphenol, triphenyl benzylphosphonium chloride/bromide and acid acceptors, including metal oxides in some. The effectiveness of compositions prepared in accordance with the invention are due to inclusion of the silicone phase and including higher amounts of HFP than is conventional. The high HFP content relates to the associated reduction in surface energy at the expense of other properties conventionally considered to be more important.

As noted above, the top coat compositions can be prepared in two ways. The first, or "insitu" method, follows a sequence whereby the fluoroelastomer is first put into solution by dissolving in an appropriate solvent, such as methyl ethyl ketone (MEK) , methyl isobutyl ketone (MIBK) , ethyl acetate, and the like. A typical solids by weight content ranges from about 10 to 40 percent of the solution. A hydropolysiloxane and a platinum catalyst is then added to the fluoroelastomer solution and lightly agitated until thoroughly mixed. The mixture is allowed to stand until evolution of hydrogen is completed after which time the mixture is ready for use as coating material for fabrication of fusing members. The second, or "pre-reaction" method, follows a sequence whereby hydropolysiloxane in the presence of ketone base solvent, distilled water and platinum salt complex is first refluxed for about 1 to 2 hours at slightly above the boiling point of the solvent, allowed to cool after which time the fluoroelastomer components is added and agitated until the fluoroelastomer component is dissolved. The "pre-reaction" method can also be prepared as a two component system whereby the fluoroelastomer component as in the in-situ method is first dissolved in solvent prior to blending with the pre-reacted silicone component. The latter method of preparation (pre- reaction) generally allows higher proportion of silicone component to be added in the composition. A fuser roller test assembly 100 is shown generally in FIG. 1. Roller 100 applies heat and pressure to fuse a quantity of toner particles 12 on a sheet of paper 13 between a fuser roller 20 and a pressure roller 30. Fuser roll test assembly 100 also includes a release agent application unit 11 including a wick 15 for applying release agent to the surface of fuser roller 20. A stripper finger 16 facilitates the separation of paper 13 from roller 20.

FIG. 2 is a cross-sectional view of a fuser roller 200 constructed in accordance with an embodiment of the invention. Fuser roller 200 includes a hollow middle core 201 covered with a fluoroelastomer surface layer 202. A second fuser roller 300 is shown in cross-sectional view in FIG. 3. Fuser roller 300 includes an insert 302 covered with a base coat 303 having a tie coat 304 disposed thereon and a topcoat 302 disposed on tie coat 304. Base coat 303 is preferably 0.5 to 5 mil thick and the overall coating (either surface layer 202 or combined layers 303, 304, and 302) should be between about 3 to 8 mils thick. The following Examples describe fluoroelastomer and silicone blend compositions and fuser members having a topcoat of the composition prepared in accordance with the invention.

These examples are presented for purposes of illustration only, and are not intended to be construed in a limiting sense.

Example 1

A composition containing 75% by weight of an incorporated cure copolymer of VF₂ and HFP having 37% mole percent HFP with a VF₂/HFP mole ratio of 1.7, and 25% by weight hydropolysiloxane having molecular weight of 1610 was prepared by first dissolving the components in MEK. Using an appropriate amount of MEK to make a 10% solids mixture, the two solutions were blended with addition of approximately 0.1% chloroplatinic acid as a catalyst. The mixture was then allowed to stand at room temperature until evolution of hydrogen was completed prior to use as a coating material for fabrication of a fuser roller sample.

Fabrication of the fuser roller sample was made using a 38mm diameter aluminum insert that has been degreased, sandblasted, degreased and an epoxy based adhesive (Thixon 300/301) applied by spraying approximately 0.01 to 0.02mm thickness. The fluoroelastomer silicone mixture was applied to the prepared insert by spraying to a thickness build-up of 0.30mm. The sample was then allowed to dwell at room temperature for 12 to 24 hours after which it was then exposed to a curing cycle of 1 hour each at 100°C, 121°C, 149°C, 176°C, plus 16 hours @ 204°C. using an air circulating oven. The cured sample was then ground to have a final coating thickness of 0.2mm. The roller prepared in the foregoing manner was placed in a fuser assembly shown in FIG. 1. When used with a linear polydimethysiloxane release fluid of 250 CSTKS viscosity the roller showed excellent release of thermoplastic resin toner and excellent copy life.

Example 2

A fuser roller is prepared in accordance with Example 1, except that an inner layer of fluoroelastomer compound consisting of 100 parts of fluoroelastomer described in Example 1, 15 parts of MgO, 2 parts of Ca(OH)₂ and 20 parts of MT black was applied to the insert by similar spraying manner to a thickness build-up of 0.07mm before applying the top layer composition described in Example 1. The roller was then placed in a fuser assembly shown in FIG. 1 and used with a linear polydimethysiloxane release fluid of 250 CSTKS viscosity. The roller showed excellent release of thermoplastic toner resin, excellent copy life and no sign of coating delamination from the aluminum insert during the test period. Example 3 A composition containing 75% by weight of an incorporated cure copolymer of VF₂ and HFP having 37% mole percent HFP with a VF₂/HFP mole ratio of 1.7 and 25% by weight hydropolysiloxane having molecular weight of 1610 was prepared using the pre-reaction method. In this method, 77.8 g of hydropolysiloxane (M.W. 1610), 724.5 g of MEK, 6.6 g of distilled water and 3.3 cc of chloroplatinic acid (0.1% solution) was refluxed at about 80°C. for 2 hours then allowed to cool. In preparing an approximately 2 liter spray solution, the hydropolysiloxane solution was charged with 2060 g of MEK after which the fluoroelastomer component was blended until fully dissolved. A fuser roller having a top coat sample was then prepared using the construction described in Example 2. The roller used in a similar manner as sample described in Examples 1 and 2 gave similar results with no evidence of flat spots in the coating when the two rollers are left in contact statically overnight. Example 4 A composition containing 75% by weight of an incorporated cure polymer of VF₂ and HFP having 44 mole percent HFP with a VF₂/HFP mole ratio of 1.2 and 25% by weight hydropolysiloxane having molecular weight of 1610 was prepared using the pre-reaction method described in Example 3. A fuser roll of this composition using the methods used in Example 3 showed excellent release from the thermoplastic toner with no hot offset observed when this roller is heated at 185°C. to fix toner to paper.

Example 5 A fuser roller was prepared in accordance with

Example 3 , except that the outermost layer or topcoat composition was modified to include 4.2 percent by weight of dicinnamylidene - 1,6 hexanediamine to the fluoroelastomer component. The roller prepared in the foregoing manner was placed in a fuser assembly shown in FIG. 1 and used with a linear polydimethysiloxane release fluid of 250 CSTKS viscosity. The roller showed excellent toner release properties, absence of flat spots and no hot off-set observed when this roll was heated at 185°C. to fix toner to paper.

Example 6

The rollers prepared in Examples 1-5 were tested for roller life. The materials utilized and the roller life results tested are set forth in the following Table II.

TABLE II Material Description Roller Life Type of Release Media

Mercapto- Standard

Run Elastomer Additives functional Polvdimethyl- Polydimethyl- siloxane siloxane

Copolymer of VF₂ 2 PHR MgO/4 PHR NO TEST MADE 6,000 and HFP with 65.9% Ca(OH). fluorine

II Copolymer of VF₂ 2 PHR Mgθ/4 PHR NO TEST MADE 12,000 and HFP containing Ca(OH)₂ phosphonium salt accelerator and bisphenol crosslin er with 69.6% fluorine

III Copolymer of VF₂ #3 CURE/NO 185,000^* NO TEST and HFP containing METAL OXIDE phosphonium salt accelerator and bisphenol crosslinker with 69.6% fluorine

IV Copolymer of VF₂ 2 PHR MgO/4 PHR NO TEST MADE 21, 000 and HFP containing Ca(OH) , phosphonium salt accelerator and bisphenol crosslinker with 70% fluorine

Copolymer of VF₂ #3 CURE/NO 225,000^* 115,000 and HFP containing METAL OXIDE phosphonium salt accelerator and bisphenol crosslinker with 70% fluorine

VI Copolymer of VF₂ 35 PHR SiH/NO NO TEST MADE 206,000^* and HFP containing METAL OXIDE phosphonium salt accelerator and bisphenol crosslinker with 69.6% fluorine

Life test conducted using Xerox 1065 machine

Designates failure mode due to delamination or adhesion related Fuser roller samples were formed by covering a 1.5 inch standard aluminum insert with a 4 mil thick fluoroelastomer base coat covered with a 2 mil thick topcoat of the materials shown below in Table II. The sample fuser rollers were prepared by first mixing the base coat material and topcoat material in a two roll mixing mill. The base coat compound was formulated by combining 100 parts VITON E-60

(DuPont) fluoroelastomer, 30 parts thermal carbon black filler,

12 parts magnesium oxide (as an activator/acid accepter) and 5.5 parts blend CURATIVE 20 (DuPont) and CURATIVE 30 (DuPont).

The mixed starting materials were dissolved in a 50:50 blend of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) solvents to approximately a 15% solid concentration. The aluminum insert was precured with a primer layer of THIXON 300/301 adhesive and then sprayed with the base coat solution to a thickness of about 5-6 mils. The coated sample was maintained at room temperature to permit residual solvent to evaporate and then cured in a circulating oven for up to 24 hours at a temperature of 150 to 450° F. The sample was then ground to a base coat thickness of 3-4 mils. After washing the sample with solvent, it was over sprayed with a 15% solid topcoat solution to yield a coating having a thickness of 4 to 5 mils. Residual solvent was permitted to evaporate and the sample was subjected to final curing in a hot air circulating oven for up to 24 hours at 450° F. The topcoat was then ground to a thickness of 2 to 3 mils.

Fusing tests herein were carried out by passing an 8.5 x 11.5 inch 75g/m² sheet of paper having toner particles thereon between fuser roller 20 and pressure roll 30 to fuse toner 12 to paper 13. Fuser roller life is indicated by the number of sheets of paper that can be successfully fused before failure by either offset, mechanical failure or some other difficulty.

The above procedure was followed for each of the six Runs shown in Table II, except that the topcoat composition was changed as set forth in the Table and the insert was a standard two inch insert. All fuser roller samples were installed and tested in a Xerox 1065 copier. The results of each copy life test are shown in the Table. These demonstrate the advantages of a high fluorine content fluoroelastomer and dispersed silicone film topcoat for fusing applications.

By comparing Runs I and II, it can be seen that including a high HFP percentage is associated with 100% increase in roller life. Run IV having 70% F shows a further 75% increase in roller life compared to Run II and a 250% increase over Run I with 66% F. The most dramatic increase can be seen by comparing Runs III, V and VI. Elimination of metal oxide within the fuser roll surface material leads to a further significant increases in roller life. The increase in Runs III and V is due to use of a mercapto-functional polydimethylsiloxane release oil. Essentially equivalent results to Runs III and V were obtained in Run VI with a standard polydimethylsiloxane oil were the top coat was a high fluorine content fluoroelastomer and silicone blend prepared in accordance with the invention. During conventional fluoroelastomer cross-linking, metal oxides are used to generate unsaturation in the polymer material. However, the reaction is generally not easy to control and accordingly, it has been common to employ excess metal oxides to achieve acceptable results. However, this typically generates excess unsaturation. The unsaturation in the cured polymer material increases the surface energy and may decrease fuser roller life by promoting oxidation of the release surface before offset occurs. The metal particles at the roller surface also increase the surface energy.

Additional efforts to increase copy life in accordance with the invention include making the surface of the fusing roller compatible with a standard dimethylpolysiloxane release media. Thus, the blend prepared in accordance with the invention incorporates high concentrations of silicone dispersed in a matrix of fluoroelastomer vulcanizate. Analysis of the fluoroelastomer and polysiloxane blends prepared in accordance with the invention confirm they are physical mixture without any evidence of covalent bonding between the fluoroelastomer and polysiloxane.

The following Examples 7, 8 and 9 reports on the analysis of the resulting films of fluoroelastomer and silicone blends prepared in accordance with the invention. Example 7 A cured fluoroelastomer of 75% copolymer of VF₂ and

HFP containing phosphonium salt accelerator and bisphenol cross linker with 70 weight percent fluorine, 25% polydimethylsiloxane (a hydropolysiloxane oligomer) as in Example 1 and a platinum catalyst was dissolved in MEK. The solution was spray-coated on a substrate, air-dried overnight and subjected to a stepped post cure cycle ending with heating for 24 hours at 400°F. The 100 micron film so prepared was a dry, pale tan, translucent elastomer which appeared to be under-cured.

Microscope and X-ray Analysis

Photomicrographs of both the film surface and a cut cross-section low magnification indicated mud-cracking. At higher magnification a grainy topography was visible with numerous particles under the surface appearing to be about 0.1 μm or less in diameter. The cross-section featured voids and numerous particles ranging broadly in size from less than 0.1 μm to as much as 10 μm. Many were smoothly ovoid in shape. The appearance of the voids and particles suggested very poor interfacial adhesion. X-ray analysis of the ovoid shaped particles showed the presence of C, 0 and Si as shown in FIG. 4.

Additional SEM analysis was performed and photomicrographs of the cross-section confirmed the existence of voids and dispersed particles. X-ray analysis of an individual particle as shown in FIG. 5 indicated the presence of considerable silicon, along with carbon and oxygen, but fluorine was not detected. This leads to the conclusion that the particles are polysiloxane moieties derived from the hydropolysiloxane. The absence of fluorine shows that they are uncontaminated with fluoroelastomer. Analysis of a smooth area in the film free of larger polysiloxane particles (but not of subsurface graininess) detected fluorine along with carbon, oxygen and silicon. This is the fluoroelastomer matrix. The presence of oxygen and silicon shows polysiloxane is also present, possibly as dispersed particles 0.1 micron or smaller in diameter and/or as an oil on the surface. Efforts to prepare a clean cross- section by potting in plastic and polishing failed to produce a usable specimen precluding determination of the microstructure of the matrix by TEM (Transmission Electron Microscopy) analysis.

Thermal Analyses

FIG. 6 is a Thermogram showing the DMTA (Dynamic Mechanical Thermal Analysis) of the film supported by a plastic backing. The lower tan δ curve shows three thermal transitions centered at -80°, -3° and +17°C. The first transition is very broad and is assigned to the mixture of polydisperse polysiloxanes derived from the hydropolysiloxane. The transition at -3°C corresponds to the glass transition temperature (T_g) of the fluoroelastomer. This was the normal T_g expected for this polymer. The peak at +17°C may be a third order transition and is not believed to be significant because it was not confirmed in the DSC discussed below.

A Thermogram was measured on the plastic backing alone after removal of the film. This did not exhibit any feature showing that the backing did significantly affect the transitions observed in the Thermogram of FIG. 6. A Thermogram obtained by Differential Scanning Calorimetry confirmed the normal fluoroelastomer T_g at -2.3°C.

These thermal data provide strong evidence that the polysiloxane does not modify the fluoroelastomer phase at the molecular level as set forth above. If significant amounts of polysiloxane grafts, crosslinks or even dispersed plasticizer were present they would be expected to shift the T_g of the fluoroelastomer, most probably toward a lower temperature.

Thus, the data support the conclusion that covalent bonding between fluoroelastomer and polysiloxane is either non-existent or, if present, each segment exists in perfectly pure, separate domains at an extremely low and insignificant level.

Example 8

Other experiments revealed information about the nature of the polysiloxane material dispersed in the film.

Sample films from the formulation utilized in Example 7 were prepared in both the un-cured and the fully-cured state and were coded Ex 8-A.

A second set of un-cured and fully cured films was prepared by a modified make-up procedure. A solution of polydimethylsiloxane oligomer and Curative 50 was prepared and aged for 72 hours before mixing with a solution of the fluoroelastomer L of Example 7. The Pt catalyst was then added to the combined solution which was sprayed immediately. Sample films coded Ex 8-B were obtained in both the un-cured and fully-cured state. Extraction of the four films with boiling methylene chloride was performed. The amounts of extractable material were reported as follows:

EXTRACTABLES, Wt. % FILM Un-Cured Cured

Ex 8-A 3.1 0.3 Ex 8-B 13.0 0.5

Both cured films contained only traces of extractable material . Considerably more material was extracted from the un-cured versions, especially Ex 8-B. In un-cured Ex 8-A, only about 10% of the added polydimethylsiloxane (which is soluble in methylene chloride) was recoverable by extraction with methylene chloride. In Ex 8-B about 50% was recovered. This indicates that the Pt catalyst in Ex 8-A promotes transformation of the siloxane to products which are insoluble in methylene chloride. Example 9 A control experiment was used to investigate further the interaction between polymethylsiloxane and MEK. A 10% solution of the siloxane in MEK was treated with 0.1% Pt catalyst and allowed to stand a few hours before evaporating the MEK. The residue weighed only 12% more than the siloxane originally charged. This shows that addition of MEK is not extensive.

Additional test tube experiments showed that the reaction is extremely slow in the absence of a catalyst. The siloxane is recovered unchanged after standing overnight at room temperature. Addition of Pt catalyst to a fresh solution causes slow evolution of a gas, presumably hydrogen. Gas evolution continued for at least 5 hours, but ceased after standing overnight. When the clear, colorless solution was allowed to evaporate it deposited a viscous oil and a small amount of gelatinous solid. It is believed that by carefully controlling the curing of metal-oxide free polymer material, sufficient cross¬ linking is achieved to cure the polymer and also provide acceptable mechanical properties, without creating excessive unsaturation and without any residual material to increase the surface energy of the fuser roll. Metal free fluoroelastomer compositions utilized in some aspects of the invention include sufficient sites for cross-linking, but not excessive sites which would oxidize, thereby increasing surface energy and impede toner release. Furthermore, without residual metal oxide particles, the compositions inherently yield a polymer surface having lower surface energy, making it well suited for fusing applications.

The effectiveness of compositions prepared in accordance with the invention as a fusing material is a result of the complimenting properties of the two elastomers specific to fusing applications. The fluoroelastomer segments provides a toughness to the coating while the silicone segments provides a desirable silicone rich surface best suited for fusing systems utilizing silicone oil as a release agent in the fusing process.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method, and in the composition and article set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Particularly it is to be understood that in said claims, ingredients or compounds recited in the singular are intended to include compatible mixtures of such ingredients wherever the sense permits.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A blend of a polysiloxane material dispersed in a fluoroelastomer matrix, comprising: a cured fluoroelastomer component having at least about 23.4 mole percent hexafluoropropylene (HFP) content, and a polysiloxane material having a weight average molecular weight of from about 500 to 10,000 blended into the fluoroelastomer and present in an amount between about 10 and 40 weight percent, based on the total weight of the blend.

2. The fluoroelastomer and polysiloxane blend of claim 1, wherein the fluoroelastomer is a copolymer of HFP and vinylidene fluoride (VF₂) , formulated to include more HFP monomer than VF₂ so that the weight ratio of VF₂ to HFP is less than 1.40 and above 0.70.

3. The fluoroelastomer and polysiloxane blend of claim 1, wherein the HFP content is above about 30.0 mole percent.

4. The fluoroelastomer and polysiloxane blend of claim 1, wherein the polysiloxane is present in an amount between about 25 and 30 weight percent.

5. The fluoroelastomer and polysiloxane blend of claim 1, wherein the polysiloxane is a hydropolysiloxane oligomer.

6. The fluoroelastomer and polysiloxane blend of claim 1, wherein the polysiloxane has a molecular weight from about 500 to 2, 000.

7. The fluoroelastomer and polysiloxane blend of claim 1, wherein the siloxane has the general formula:

MD^_y , wherein M = Me₃Si0_1/2 D = Me₂SiO D^x= H(Me)SiO, or

H₂C=CH(Me)SiO, or R(Me)SiO, and wherein R = alkoxy, or R = acetoxy, or R = ketoxy, or D^α= HO(Me)SiO, and wherein x + y = 1, and x = 0 to 0.99 y = .01 to 1.0.

8. The fluoroelastomer and polysiloxane blend of claim 7, wherein the siloxane oligomer is hydropolysiloxane.

9. A fuser member for fixing toner particles to a recording medium, comprising a substrate and an outer layer of a blend of: a cured fluoroelastomer component having at least about 23.4 mole percent hexafluoropropylene (HFP) content, and a polysiloxane oligomer having a weight average molecular weight of from about 500 to 10,000, the polysiloxane blended into the fluoroelastomer and present in an amount between about 10 and 40 weight percent, based on the total weight of the blend.

10. The fuser member of claim 9, wherein the substrate includes a substrate carrier and an intermediate layer of a cured fluoroelastomer and the fluoroelastomer and polysiloxane blend is dispersed on the intermediate layer.

11. The fuser member of claim 9, wherein the siloxane has the general formula;

MD^_yM, wherein M = Me₃Si0_1/2 D = Me₂SiO D^x= H(Me)SiO, or

H₂C=CH(Me)SiO, or R(Me)SiO, and wherein R = alkoxy, or R = acetoxy, or R = ketoxy, or D= HO(Me)SiO, and wherein x + y = 1, and x = 0 to 0.99 y = .01 to 1.0.

12. A method of preparing a blend of a polysiloxane dispersed in a cured fluoroelastomer, comprising: dissolving a fluoroelastomer having at least about 23.4 mole percent hexafluoropropylene (HFP) content in a suitable solvent; adding a polysiloxane oligomer and catalyst to the fluoroelastomer solution; agitating the solution until mixed; allowing the siloxane to form hydropolysiloxane by evolution of hydrogen; and curing the fluoroelastomer and polysiloxane.

13. The method of claim 12, wherein the polysiloxane has the general formula:

MD_j-D¹^, wherein M = Me₃Si0_1/2 D = Me₂SiO D¹" H(Me)SiO, or

H₂C=CH(Me)SiO, or R(Me)SiO, and wherein R = alkoxy, or R = acetoxy, or R = ketoxy, or D¹* HO(Me)SiO, and wherein x + y = 1, and x = 0 to 0.99 y = .01 to 1.0.

14. A method of preparing a blend of a polysiloxane dispersed in a cured fluoroelastomer, comprising; mixing a polysiloxane oligomer and catalyst in a solvent; refluxing the solvent solution to form a hydropolysiloxane; adding a fluoroelastomer having at least about 23.4 mole percent hexafluoropropylene (HFP) content to the siloxane solution; and curing the blend by heating to remove the solvent .

15. The method of claim 14, where the polysiloxane has the general formula:

MD-I^_yM, wherein M = Me₃Si0_1/2 D = Me₂SiO D^x= H(Me)SiO, or

H₂C=CH(Me)SiO, or R(Me)SiO, and wherein R = alkoxy, or R = acetoxy, or R = ketoxy, or D^x= HO(Me)SiO, and wherein x + y = 1, and x = 0 to 0.99 y = .01 to 1.0.