GB2067471A - Fuser roll and method of manufacture thereof - Google Patents

Abstract

A copy machine fuser roll comprises a silicone rubber compound incorporating a high viscosity silicone oil, the viscosity being at least 1,000 centistokes (20,000 MW). Accordingly, the fuser roll needs less frequent replacement because of offsetting problems. Preferably, the oil e.g. a polydimethylsiloxane, is incorporated in the composition used for moulding the roll.

Description

SPECIFICATION Fuser roll and method of manufacture thereof The final process step in a conventional electrostatic copy machine is the fixing or fusing of the toner powder image to the paper substrate. Toner is a pigmented thermoplastic which must be heated above its softening point to develop particle-toparticle and particle-to-paper adhesion in orderto produce a permanent copy. Fuser rolls of silicone rubber are typically employed in this fusing process.

The fuser roll is typically one of a pair of pinch rollers between which the paper with toner image thereon is passed during the fusing process. The fuser roll is typically a silicone rubber roll. Depending on the design of the particular electrostatic copier involved, the pair of pinch rolls may both be silicone rubber rolls, or one of the rolls may be silicone rubber and one of the rolls may be, for example, a steel roll our a steel roll coated with polytetrafluoroethylene (PTFE).

The silicone rubber fuser roll and/orthe other roll in a pair of pinch rolls may be directly or indirectly heated, and the fuser roll may either come into contact with the front side of the paper on which the toner is located or it may come into contact with the rear side of the paper.

Regardless of the particular configuration in which a fuser roll is employed in a particular machine, the silicone rubber fuser roll comes into contact, either directly or indirectly, with the toner. The toner must be released from the fuser roll as each copy is made in order for the succeeding copy to pass cleanly through the fusing operation. That is, unless the toner is adequately released from the fuser roll, the next succeeding copy made by the machine will pick up traces of the residual toner material on the fuser roll, and that succeeding copy will be dirty, ghosted or otherwise defective. This problem of toner adherence resulting in defective copying is sometimes referred to as "offsetting".

Offsetting is not the only cause of fuser roll failure.

By way of example, picker fingers may damage the roll, or the roll may be impaired by exposure to heat.

However, offsetting is one of the principal factors in fuser roll failure, and it is often the limiting factor in fuser roll life. Thus, the life expectancy of a fuser roll is often measured by the number of copies which can be made by the fuser roll before it fails to release toner adequately, i.e. before unacceptable adherence of toner particles to the silicone rubber fuser roll in encountered.

Conventional practice in the prior art to combat the offsetting problem is to create a thin film of silicone fluid on the outer surface of the fuser roll to promote release of toner particles. This has been achieved in the prior art by incorporation of a relatively low viscosity (about 100 cs.) silicone fluid in the silicone rubber compound from which the fuser roll is made. A thin film of silicone fluid is established on the outer surface of the roll as the result of migration of the fluid through the rubber to the roll surface. The fuser roll performs satisfactorily as long as an adequate coating of silicone fluid appears on the surface of the roll. The rate of migration of this low viscosity silicone oil is such that the roll becomes depleted of the oil relatively quickly, and replacement of the roll is required.By way of example, one manufacturer of electrostatic copying machines specifies that the fuser roll should be changed after 50,000 copies. While other potential sources of roll failure may be considered in setting thatfigure, a prime consideration isthoughtto be that the supply of silicone oil in the roll will be deplated to the level that adherence of toner particlews to the roll is likely to occur at around 50,000 copies.

The requirement to replace the fuser roll because of offsetting is, of course, an element of operating expense of copy machines that manufacturers and users would like to see reduced in frequency. That is, it is highly desirable to extend the life of fuser rolls by increasing the number of copies that can be made before offsetting is expected to become a problem, and it is the object of the present invention to provide such a fuser roll and a method of manufacture thereof.

In accordance with the present invention, there is provided a fuser roll including a generally cylindrical body of silicone elastomeric material, and an amount of high viscosity silicone oil incorporated in said body of elastomeric material, the viscosity of said silicone oil being at least 1,000 centistokes.

More particularly, a polydimethylsiloxane oil of approximately 1,000 cs (about 20,000 MW) is incorporated in the silicone rubber compound of the fuser roll. The incorporation of this high viscosity polydimethylsiloxane fluid has resulted in an unexpectedly dramatic increase in the roll life of silicone rubber fuser rolls before release of toner particles becomes a problem. Fuser rolls made in accordance with this invention have a life expectancy of up to several hundred thousand copies in some cases before toner release becomes a problem. The high viscosity polydimethylsiloxane fluid is incorporated in the silicone rubber roll in the ratio of from 5 to 50 parts per one hundred parts of silicone rubber.

There is also provided a method of forming a rubber roll including the steps of forming a mixture having from 99-101 parts silicone elastomer, 8-20 parts curative, 5-50 parts of silicone oil having a viscosity of not less than 1000 cs, and pouring said mixture into a mold and curing to form a roll.

Referring now to the drawings, wherein like elements are numbered alike in the several figures: Figure 1 is a prospective view of a silicone rubber fuser roll made in accordance with the present invention, and Figures 2 and 3 show one of typical arrangements known in the art for employing a silicone rubber fuser roll.

Referring first to the drawings, Figure 1 shows the general configuration of a typical silicone rubber fuser roll, indicated generally at 10. The fuser roll has a central metal shaft 10 to which is bonded an outer generally cylindrical layer of silicone elastomeric material 14. Since the subject matter of the present invention relates to the composition of the silicone material from which the fuser roll is formed and the resultant improved fuser roll, it will be understood by those skilled in the art that the outward appear ance of a silicone fuser roll of the present invention will not be different from one of the prior art. As would be true with the prior art fuser rolls and the fuser roll of the present invention, the roll is preferably formed in a highly polished mold with the use of low shrinkage materials.The use of a highly polished mold results in a mirror finish on the outer surface of the roll without the need for any post grinding operations; i.e., grinding operations after formation of the roll. The roll would be formed in the appropriate mold by the general steps of (1) positioning center shaft of mandrel 12 in the mold, (2) filling the mold with the uncured silicone compound, (3) curing the roll at about 1 000C for about 15 minutes and (4) post curing in an oven for about 2 hours at about 205"C.

Referring to Figures 2 and 3, a schematic representation is shown of the typical fuser roll installation in which a silicone fuser roll 10 constitutes one of a pair of pinch rolls in conjunction with a second roll 16 which, in this case, is a metal cylinder with a polytetrafluoroethylene coating on the outer surface. In the configuration of Figures 2 and 3, rolls 10 and 16 rotate in opposite directions in the directions indicated by the arrows to draw a sheet of paper 18 between the nip of the rolls. The surface of paper 18 in contactwith roll 16 has an electrostatically formed toner image thereon. Unfused toner particles are indicated by the dot segments 20 to the left of the nip of the rolls, while fused toner particles are indicated by the flat lines 22 to the right of the nip of the rolls.

The toner particles are fused by heating either or both of rolls 10 or 16 as the paper passes through the nip of the rolls. Some of the toner particles from the paper are picked up by roll 16 as the paper passes through the nip of the rolls. The picking up of these particles, indicated as flattened and partially fused particles 24 on the surface of roll 16, is undesirable because it contaminates the surface of roll 16 (i.e., the surface of the roll tends to get dirty). In an effort to keep the surface of roll 16 clean, a cleaning web 26 in the form of a continuously rotating belt may be brought into contact with the surface of roll 16 to wipe the surface of the roll. However, not all of the residual toner particles on the surface of roll 76 are wiped of by cleaning web 26.Some of the particles oftonercontinueto adhere to the surface of roll 16 and are transferred to roll 10 in a transfer process referred to in the art at "offsetting", as shown in Figure 3. If the surface of silicone roll 10 retains the toner particles deposited thereon, fuser roll 10 will then either "dirty" the back of the next sheet of paper passing through the nip of the rolls, or the rolls will pass the toner particles back and forth in repeat offsetting steps whereby both surfaces of succeeding sheets of paper will be dirtied.

As indicated previously, the configuration shown in Figures 2 and 3 is only one of several possible arrangements employing silicone elastomer fuser rolls as one of a pair of pinch rolls at the fuser sta tion. However, the problem of adherence of toner particles to the surface of silicone fuser rolls has been a persistent problem which has limited fuser roll life of most machines. Prior art fuser rolls have typically incorporated a low viscosity (in the range of 100 to 250 cs) silicone oil to promote release of toner particles from the surface of the roll. This result, i.e., promoting release of the toner particles on the surface of the roll, is achieved by forming a thin film of the low viscosity silicone oil on the outer surface of the roll.In some instances in the prior art, the film has been formed bydirectdepositofthe lowviscositysilicone oil on the surface of the roll, while in other embodiments the low viscosity silicone oil has been incorporated in the compound from which the roll is made, and the silicone oil migrates to the surface of the roll to form the film. However, once the oil is depleted, the roll must either be replaced, or in some circumstances may be serviced to reestablish the surface film.

It has also been discovered that the useful life of silicone rubber fuser rolls can be significantly extended to produce upto several hundred thousand copies in some instances by a significant departure from prior art practice. More specifically, it has been discovered that use of a very high viscosity silicone oil incorporated in the compound from which the roll is formed results in a significant extension of the useful life of the fuser roll. A measured amount of polydimethylsiloxane oil having a viscosity of greater than 1,000 centistokes (approximately 20,000 MW) is incorporated in the compound from which the roll is made. It has been discovered that this high viscosity polydimethylsiloxane oil will still migrate to the surface of the fuser roll to form a satisfactory film to promote release of fuser particles.Moreover, it has been discovered that the rate of migration of this high viscosity oil is synergistically lowerthan would be expected merely from the difference in viscosity between the high viscosity oil which is employed and the low viscosity oil used in the prior art. It appears that because the molecules of polydimethylsiloxane oil (1,000 cs) are so much larger than prior art silicone oil of 100 cs that the large polydimethylsiloxane molecules actually become entangled with each other and with the molecules of the silicone rubber of the roll. This apparent molecular entanglement results not only in a drastic reduction in the rate of diffusion of the silicone oil, but is also promotes retention of an effective film on the surface of the roll.Thus, the useful life of the roll is dramatically and synergistically increased, both by promoting the retention of an effective release film of silicone oil on the surface of the roll and by establishing a rate of silicone oil migration which is significantly lower than the prior art, but still adequate to maintain the required film on the surface of the roll.

It must be stressed that while it is believed the theory of molecular entanglement correctly explains and helps understanclthe reasons for the unex pected improvements achieved by the invention, it is not certain that that theory is correct, and it not wished to be bound by that theory.

The high viscosity silicone oil used in the present invention consists of linear polymers of dimethyl siloxane of the type [(CH3)2SiO-} where x is an integergreaterthan 2 and having the structural unit

The specific composition or structure of the base silicone elastomer material is not new to this invention. Rather, it will be understood that any silicone elastomer material suitable for forming fuser rolls may be used in the present invention.The base silicone elastomer material may be of the type where vulcanization is by an energy activated cure, or it may be of the room temperature vulcanization type (row). In accordance with the present invention, the high viscosity (about 1,000 cs or more) Non Newtonian PDMS oil is incorporated in the silicone elastomer compound from which the fuser roll is formed in the proportion of from 5 to 50 parts per 100 parts of the base silicone elastomer compound.

A particularly preferred formula for the practice of the present invention is as follows: TABLE 1 Material Weight (gms.) Silicone elastomer (1 ) 100 Curative (2) 13 PDMS oil ( > 1000 cs) (3) 30 Iron oxide powder 1 These ingredients were mixed, poured into a mold, and cured to form a silicone rubber fuser roll of the general type shown in Figure 1. That roll was then installed as the fuser roll in a Royal RBC II electrostatic copy machine. According to the manufacturer, the life expectancy of prior art silicone rubber fuser rolls (impregnated with low viscosity silicone oil) in that machine was about 50,000 copies. The fuser roll of the present invention has functioned in that machine to make over 250,000 copies without encountering any significant problem of toner release.

Tests have also shown that a useful range of proportions of the foregoing Table 1 compound ingredients may be established as follows: Table2 Material Weight (gms) Silicone Elastomer 100 t 1 Curvative 13 + 5 PDMS oil ( > 1000 cs) 30 + 225 Iron oxide powder 1 t b.s These ranges were established as the result of the following test procedure. Eleven compounds were formed having the compositions set forth in Table 3.

TABLE 3 Material 1 2 3 4 5 6 7 8 9 10 11 Silicone Elastomer 100 100 100 100 100 100 100 100 100 100 100 Curative 10 10 10 10 10 10 11 12 13 14 15 PDMS oil ( > 1000 cs) 0 10 20 30 40 50 10 20 30 40 50 Iron oxide powder 1 1 1 1 1 1 1 1 1 1 1 (1) Silastic J-RTV polydimethylsiloxane elastomer (70,000 cs) available from Dow Corning (2) Silastic J-PDMS curing agent with functional groups for crosslinking and a platinum catalyst, available from Dow Corning (3) DC200 - polydimethylsiloxane oil (1,000 ca, 20,000 MWJ, available from Dow Corning.

Each of these eleven test sample compounds were mixed by hand, degassed, cast into tensile sheets 152 x 152 x 2,54 mm, cured at 70 C for from 30 to 60 minutes, post cured for 24 hours at room temperature, and cut into 25,4 x 152 mm specimen strips.

The fully cured strips were dusted with toner powder and put into an oven at 1000C for 5 minutes, then removed from the oven and allowed to cool to room temperature. A metal spatula was then used to try to lift the toner off. With test sample 1 (no PDMS oil), the toner would not come off. The ease of removal of toner increased directly with increased amounts of PDMS oil.

In these tests, specimens 1-6 were first formed. It was noted that the mechanical properties of the specimen strips deteriorated in specimens 4, 5 and 6 as the amount of PDMS oil was increased above 20 parts per 100 parts. The specimens of tests, 4, 5 and 6 were markedly inferior in tear and tensile characteristics compared to those of tests 1-3. It is suspected that this occurred because the PDMS oil was present in sufficient amounts to dilute the curative and reduce the probabilities of crosslinking between the curative and the silicone elastomer. Accordingly, test specimens 7-11 were formed with additional curative added in all cases in the amount of one additional part of curative per ten parts of PDMS oil to keep the overall proportions of 10 parts of curative per 100 parts of silicone elastomer and PDMS oil.

The specimens of tests 7-11 had acceptable tear and tensile characteristics comparable to tests 1-3.

Thus, it was determined that the amount of high viscosity PDMS oil to be added to a silicone elastomer compound should be limited to about 20 parts per 100 parts of silicone elastomer unless the amount of curative is increased to maintain a ratio of approximately 10 partsofcurative per 100 parts of silicone elastomer and PDSM high viscosity oil. It will be noted that the added curative in the system does not effect any significant curing of the supplemental high viscosity PDMS oil, since that oil is essentially non-reactive.

Additional testing was also done similar to that shown in Table 3 to form compounds having less than 10 and more than 50 parts of PDMS high viscos ity oil per 100 parts of silicone elastomer. Those tests showed that (1) it was necessary to have a minimum of 5 parts of such PDMS oil per 100 parts of silicone elastomerto get any noticeable toner release effect, and (2) it was necessary to limit the supplemental PDMS oil to not more than 50 parts per 100 parts of silicone elastomerto prevent the oil from bleeding out and forming an unacceptable tacky surface on the roll.

It was also determined that the range of curative should be from 8 to 20 parts of curative per 100 parts of silicone elastomer. Less than 8 parts resulted in poor cure and more than 20 parts resulted in curing too fast.

As previously indicated, fuser rolls made in accordance with this invention have shown remarkable improvements in life span. That is, such fuser rolls are capable of making several hundred thousand copies before toner release (or conversely, undesired sticking oftonertothe roll) becomes a problem requiring service or replacement of the roll.

Claims (17)

1. A fuser roll including a generally cylindrical body of silicone elastomeric material, and an amount of high viscosity silicone oil incorporated in said body of elastometic material, the viscosity of said silicone oil being at least 1,000 centistokes.

2. Afuser roll as claimed in claim 1, wherein the amount of high viscosity silicone oil is from 5 to 50 parts per 100 parts of silicone elastomeric material.

3. A fuser roll as claimed in claims 1 or 2, wherein said silicone oil is polydimethylsiloxane.

4. A roll for use in material handling equipment, the roll having a rubber body having the following proportional composition: Material Weight (proportional) Silicone elastomer 99-101 Curative 8-20 Silicone oil ( > 1000 cs) 5-50

5. A roll as claimed in claim 4, wherein the amount of curative is maintained in the ratio of about 10 parts of curative per 100 parts of silicone elastomer and silicone oil.

6. A roll as claimed in claims 4 or 5, wherein the elastomer is polydimethylsiloxane elastomer, and the oil is polydimethylsiloxane oil.

7. A roll as claimed in any of claims 4 to 6, including from 0.5-1.5 parts of iron oxide powder

8. A roll as claimed in any of claims 4 to 7, wherein the composition is approximately: Material Weight (proportional) Silicone elastomer 100 Curative 13 Silicone oil ( > 1000 cs) 30

9. A roll as claimed in claim 8, including about one part iron oxide powder.

10. A method of forming a rubber roll including the steps of forming a mixture having from 99-101 parts silicone elastomer, 8-20 parts curative, 5-50 parts of silicone oil having a viscosity of not less than 1000 cs, and pouring said mixture into a mold and curing to form a roll.

11. A method as claimed in claim 10, wherein the step of form ing a mixture includes adding from 0.5 to 1.5 parts of iron oxide.

12. A method as claimed in claim 10 wherein the step of forming a mixture includes maintaining the curative in the ratio of about 10 parts of curative per 100 parts of silicone elastomer and silicone oil.

13. A method as claimed in any of claims 10 to 12, wherein the silicone elastomer is polydimethylsiloxane elastomer, and the silicone oil is polydimethylsiloxane oil.

14. A method as claimed in claim 13, wherein the step offorming a mixture includes forming a mixture having about 100 parts silicone elastomer, about 13 parts curative and about 30 parts silicone oil.

15. A method as claimed in claim 14, wherein the step of forming the mixture also includes adding about 1 part iron oxide powder.

16. A roll substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. A method substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.