A precoated web and apparatus including the web for applying offset preventive fluid to a fixing roller

Abstract

 A precoated web (16) and apparatus including the web for applying offset preventive fluid to a fixing roller (10) in an imaging apparatus. The web is precoated with a nonmigrating mixture including an offset preventive fluid such as silicone oil and a thickening agent for the fluid such as a polymer of ethylene, fumed silicon dioxide or an organic gelling agent.

Description

Technical Field

[0001] The invention presented herein relates to contact fixing stations for an imaging apparatus wherein the image is formed by toner particles carried on a receptor sheet which are permanently adhered to the receptor sheet at a fixing station of the apparatus and, more particularly, a precoated web and apparatus including the web for applying offset preventive fluid to the fixing roller and removing toner particles from the fixing roller.

Background Art

[0002] The use of toner particles for forming images on a receptor sheet in various image forming machines, such as office copiers and the like, requires a fixing station within the machine for permanently adhering the toner particles to the receptor sheets. Apparatus for fixing stations which use contact with the toner particles to permanently affix the toner material to the receptor sheet utilize a fixing roller, which contacts the toner, and a back-up roller, at least one of which is driven, to move the receptor sheet between the rollers. One approach relies on the application of heat to the toner material via the fixing roller which is maintained at a temperature sufficient to elevate the temperature of the toner material to a point where the constituents of the toner material coalesce and become tacky. This action causes the toner material to be absorbed to some extent into the fibers of the receptor sheet material which, in many instances, constitutes plain paper. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be permanently bonded to the receptor sheet. By controlling the heat transfer to the toner, virtually no offset of the toner particles from the receptor sheet to the fixing roller is experienced under normal conditions. By careful control of the heat transferred to the toner material, the heat applied to the surface of the fixing roller will not raise the temperature of the surface of the fixing roll above the "hot offset" temperature of the toner particles, which, if present, would cause a splitting action of the toner to result in "hot offset". Splitting occurs when cohesive forces holding the heated toner particles together are less than the adhesive forces tending to offset them to the contacting surface of the fixing roller. Toner particles can also be offset to the fixing roller by an insufficient application of heat and pressure to the toner particles (i.e., "cold" offsetting), by imperfections in the properties of the surface of the fixing roll or by other factors which cause the toner particles to insufficiently adhere to the receptor sheet by the forces which normally hold them to the receptor sheet. In such a case, toner particles may be transferred to the surface of the fixing roller with subsequent transfer to the next receptor sheet or to the back-up roller during periods of time when a receptor sheet is not in the nip presented between the rollers.

[0003] One arrangement for minimizing the "offsetting" problem utilizes a fixing roller with an outer surface or covering of a material that is resistant to the high temperatures involved and will accept an offset preventive fluid, such as silicone oil, which is applied to the outer surface of the fixing roller. The silicone oil forms an interface between the fixing roller surface and the toner images carried on the receptor sheet. The relatively low surface energy of the silicone oil, which is presented to the toner, prevents the toner particles from offsetting to the fixing roller surface. Even with the use of the special coverings for the fixing roller and the application of silicone oil to the covering, some "nonvisual offsetting" (i.e., offsetting of very fine particles of toner) does occur. Such "offsetting" can eventually result in the degradation of the image provided on a receptor sheet and in the case of a heated fixing roller, can reduce its operating life.

[0004] Another fixing station of the contact type applies pressure to the toner particles to permanently affix the toner particles to the receptor sheet. As in the case of the heated fixing roller, some toner is offset to the fixing roller making contact with the toner particles in a pressure fixing apparatus even though an offset preventive fluid, such as silicone oil, is applied to the outer surface of the fixing roller.

[0005] The offsetting problem presented by contact type fixing stations has been solved to a degree by the employment of various oiler/cleaner arrangements for the fixing roller. Wick material supplied with silicone based oil from an oil supply has been employed for applying the silicone based oil to the fixing roller and for cleaning the fixing roller. Another known arrangement uses an oil applicator roller covered with an oil absorbent material that is periodically supplied with oil from an oil supply. Web material, which has been impregnated with silicone oil, has been used which is presented to the fixing roller to provide silicone oil to the outer surface of the fixing roller and also remove any toner material that may be present on the fixing roller.

[0006] The prior art arrangements mentioned for cleaning and applying offset preventive fluid to the fixing roller have not been entirely satisfactory. In the case of wick plus oil supply arrangements, an excessive amount of oil can build up in the wick during inactive periods causing too much oil to be applied to the fixing rollers. A wick clogging problem due to the toner removed is also presented when an oil supply plus wick arrangement is used. While this is overcome by the use of an arrangement using an oil impregnated web material, an oil migration problem is presented when a supply roll of oil impregnated web material is used. Finally, the prior known arrangement using an oil supply plus an oil applicator roller covered with an oil absorbing material requires the use of a complicated arrangement for supplying a controlled amount of oil to the covered roller. If the amount of oil supplied to the fixing roll is not carefully controlled, excessive oil will transfer to the image receptor making a copy objectionable. Contaimination of the oil applicator roll is a problem that is encountered also.

[0007] The problems presented by prior known arrangements have been avoided by the use of apparatus wherein a web member is used which is supplied with an offset preventive fluid from an applicator provided within the imaging apparatus. Cost and space constraints for various imaging apparatus present a problem with respect to the use of such a solution.

Disclosure of Invention

[0008] The invention presented herein provides a solution to the problem of providing a precoated web that is usable in apparatus for supplying offset preventive fluid to the fixing roller of an imaging apparatus. The pre-impregnated web is pre-impregnated by coating the web with a mixture of low-viscosity, offset preventive fluid plus a nonabrasive, nonvolatile thickening agent. Such an arrangement avoids the oil migration problem which has been present in prior efforts made to provide a suitable pre-impregnated web. In addition to providing a solution to the oil migration problem, such an arrangement retains the advantages of apparatus using a pre-impregnated web which include the need for a small number of uncomplicated parts, minimal space, ease of serviceability plus precise coating of the offset preventive fluid and thickening agent onto the web in a manufacturing facility serving to provide consistent deposition of offset preventive fluid onto the fusing roller of the imaging apparatus.

[0009] In one embodiment, the apparatus using the pre-impregnated web includes a supply roll for the web, a driven take-up roll and a pressure roll positioned adjacent the fixing roller of the imaging apparatus between the supply and take-up rolls. The web passes over the pressure roll and in contact with the fixing roll of the imaging apparatus.

[0010] The invention requires the use of a porous web for receiving the mixture of low-viscosity, offset preventive fluid plus a nonvolatile thickening agent. Whether a given mixture is a suitable candidate can readily be determined by testing various mixtures. This can be done without coating a web and checking for migration. Samples of various mixtures can be placed in a small container having a small hole in the center of its bottom and checking for the passage of oil from the hole. If no passage of oil occurs after 14 days, the mixture is considered to be a suitable candidate. Further screening involves coating of a rolled web and checking for gravity migration of the offset preventive fluid at room temperature and also in a heated oven. An optimum ratio of thickener and offset preventive fluid is dependent on the nature of the thickener and the viscosity of the fluid and, in addition, is dependent on the web material, coating weight, web storage conditions, cost and other factors.

Brief Description of the Drawing

[0011] A better understanding of this invention, including its novel features and advantages, will be obtained upon consideration of the following detailed description and accompanying drawing wherein the single figure discloses one form for the apparatus in which the precoated web of the invention is used to supply an offset preventive fluid to a fixing roll of an imaging apparatus.

Detailed Description

[0012] Referring to the single figure of the drawing, apparatus is shown for applying offset preventive fluid to a fixing roller 10, such as can be found in office copy machines currently available. The fixing roller 10 is positioned very close to a back-up fixing roller 12. Either or both the fixing roller 10 and the back-up fixing roller 12 are driven so they move in the same direction at the point where they are positioned close to one another so an unfixed, image bearing receptor sheet 14 presented to the rollers is moved through the rollers causing the unfixed image carried on the receptor sheet 14 to be fixed to the receptor sheet. The apparatus of the invention includes a web supply roll 15 on which a length of precoated web 16 is wound and a driven wind-up roll 18 on which the web 16 is wound as it is used. A driven pressure roll 20 is positioned intermediate the supply roll 15 and wind-up roll 18 and is biased toward the fixing roller 10, such as by a spring 22 which is schematically shown. As can be appreciated, the spring, dependent on its placement, can be a compression, torsion or tension spring. In the drawing, the spring 22 is a compression spring. The web 16 passes from the supply roll 15 and about a portion of the outer surface of the pressure roll 20 so that the web passes between the pressure roll 20 and the fixing roller 10 and thence to the wind-up roll 18. The wind-up roll 18 and pressure roll 20 are driven by a motor drive 24. The coupling needed between the motor drive 24 and rolls 18 and 20 is indicated by dotted lines 28 and 30, respectively. The coupling between the motor drive 24 and wind-up roll 18 is completed via an over-driving slip clutch (not shown). A low torque brake (not shown) is also used with the supply roll 15 to provide a small amount of back tension. In this manner a tension is maintained on the web 16 to keep it in firm contact with the pressure roll 20. The force biasing the pressure roll 20 toward the fixing roller 10 should, in the case of heat fusing, be such as to provide a nip contact width of the web 16 at the fixing roller 10 of about 0.30 cm to 0.64 cm. The nip contact width is less critical when pressure fusing is used. The direction of rotation for each of the various rolls and rollers is indicated by the various arrows in the drawing.

[0013] A nonabrasive, porous material is suitable for the web 16. Paper toweling, such as Fort Howard #289 (Fort Howard Paper Co.); nonwoven carded rayon, such as Scott 6280-8 (Scott Paper Co.) and nonwoven polyesters, such as Pellon 1545 (Pellon Corporation) are examples of suitable materials for the web 16.

[0014] Delivery of an offset preventive fluid, such as silicone oil, to the fixing roller 10 in the arrangement described to this point wherein the web 16 has been precoated with silicone oil has been utilized. United States Patent 3,941,558 is an example of such an arrangement. It has been found that precoating of the web material with only silicone oil is not satisfactory in some applications. Over a period of time, the silicone oil migrates due to gravity to the lower portion of the supply roll so that the amount of silicone oil supplied to fixing roller 10 is not consistently the same. This causes silicone oil to be noticeably transferred to the receptor sheet on which a toner image has been fixed. Oil may also drip from the supply roll and build up on other parts-of the machine below. The migration problem also occurs with respect to the storage of the web rollers prior to use in an apparatus. Reducing the amount of precoated silicone oil prevents oil migration but significantly increases the total web length required.

[0015] In the arrangement embodying the present invention, the web 16 is precoated with a nonmigrating mixture which includes an offset preventive fluid and a thickening agent for the fluid. It is preferred that only that amount of the thickening agent be used that is needed to solve the migration problem, since this maximizes the amount of offset preventive fluid that is available to carry out the offset preventive function. The minimum amount of thickening agent required can be readily estimated by preparing mixtures of various percentages by weight of the thickening agent and placing a sample of each mixture of a predetermined amount in a container having a small hole having a diameter of about 1.6 mm. If there is no loss of the mixture through the hole after a period of time, such as 14 days, the mixture is not likely to present a migration problem. The optimum ratio of thickening agent and offset preventive fluid is dependent on the nature of the thickener and viscosity of the fluid and, in addition, is dependent on web material, coating weight, web storage conditions, cost and other possible factors.

[0016] Using silicone oil as the offset preventive fluid, several suitable thickening agents can be used that are commercially available such as a polymer of ethylene, available from Petrolite Corporation, Tulsa, Oklahoma, under its trademark Polywax; fumed silicon dioxide, available from Cabot Corporation, Tuscola, Illinois, under its trademark "Cab-O-Sil"; and an organic gelling agent, available from New Japan Chemical Company, Ltd., Osaka, Japan, under the product designation "Gel All-D".

[0017] Tests indicate silicone oil ranging from 100 to 1000 centistokes is usable with any one of the thickening agents mentioned. The minimum amount of thickening agent required to provide a nonmigrating coating was found to be three (3) percent by weight. The maximum amount of a thickening agent that can be used is determined by such factors as dispersion stability, coatability of the mixture onto web material, and the fact that too much thickening agent will prevent transfer of silicone oil to the fixing roll. Ten (10) percent by weight is considered to be the maximum concentration for the last two thickening agents mentioned above, while the polymer of ethylene thickening agent can be used with concentrations up to fifty (50) percent by weight. It has also been determined that the preferred molecular weight for the polymer of ethylene is about 300 to 1000.

[0018] The foregoing described arrangement is usable in an imaging apparatus wherein the fixing of the toner image is by heat or pressure. In the case of heat fixing, the fixing roller 10 is heated by a heat source mounted coaxially within the roller and the back-up roller 12 can have a thin silicone rubber coating. In the case of pressure fixing, the fixing roller 10 can be formed of steel with a coating of bubbly chromium. The back-up roller 12 can be of polished steel. In the case of heat fixing, advancement of the web at the rate of about .17 mm/copy is sufficient with a rate of .08 mm/copy sufficient for pressure fixing. The speed at which the web 16 is advanced is dependent on the amount of toner that is removed by the web, the rate at which copies are produced and whether the fixing is by heat or pressure and other factors.

[0019] The coating weight of the mixture precoated onto the web 16 is about 65 grams per square meter to 161 grams per square meter, with about 108 grams per square meter preferred.

[0020] The particulars of the foregoing description are provided merely for purposes of illustration and are subject to a considerable latitude of modification without departing from the novel teachings disclosed therein. Accordingly, the scope of this invention is intended to be limited only as defined in the appended claims, which should be accorded a breadth of interpretation consistent with this specification.

Claims

1. A precoated web (16) adaptable for coating a fixing roller (10) in an imaging apparatus with offset preventive fluid including:

an elongate web of porous material; and

a nonmigrating mixture coated onto said web, said mixture including an offset preventive fluid and a thickening agent for said fluid.

2. A precoated web (16) according to claim 1 wherein said mixture coated onto said web is coated to a coating weight of 65 grams per square meter to 161 grams per square meter.

3. A precoated web (16) according to claim 1 wherein said thickening agent is at least three percent by weight of said mixture.

4. A precoated web (16) according to claim-1 wherein said offset preventive fluid is silicone oiL and said thickening agent is a polymer of ethylene.

5. A precoated web (16) according to claim 4 wherein said thickening agent is three to fifty percent by weight of said mixture.

6. A precoated web (16) according to claim 1 wherein said offset preventive fluid is silicone oil and said thickening agent is fumed silicon dioxide.

7. A precoated web (16) according to claim 6 wherein said thickening agent is three to ten percent by weight of said mixture.

8. A precoated web (16) according to claim 1 wherein said offset preventive fluid is silicone oil and said thickening agent is an organic gelling agent.

9. A precoated web (16) according to claim 8 wherein said thickening agent is three to ten percent by weight of said mixture.

10. Apparatus for applying offset preventive fluid to the fixing roller (10) of an imaging apparatus including a supply roll (15), a take-up roll (18), a precoated web (16) adapted to be transported between the supply roll and the take-up roll, characterized by a pressure roll (20) positioned between the supply roll and the take-up roll with the web (16) positioned between the fixing roll (10) and said pressure roll (20) with said pressure roll adapted to force the web into engagement with the fixing roller (10), the precoated web (16) coated with a nonmigrating mixture including an offset preventive fluid and a thickening agent for said fluid. -

11. Apparatus according to claim 10 wherein said mixture coated onto said web (16) is coated to a coating weight of 65 grams per square meter to 161 grams per square meter.

12. Apparatus according to claim 10 wherein said thickening agent is at least three percent by weight of said mixture.

13. Apparatus according to claim 10 wherein said offset preventive fluid is silicone oil and said thickening agent is a polymer of ethylene.

14. Apparatus according to claim 13 wherein said thickening agent is three to fifty percent by weight of said mixture.

15. Apparatus according to claim 10 wherein said offset preventive fluid is silicone oil and said thickening agent is fumed silicon dioxide.

16. Apparatus according to claim 15 wherein said thickening agent is three to ten percent by weight of said mixture.

17. Apparatus according to claim 10 wherein said offset preventive fluid is silicone oil and said thickening agent is an organic gelling agent.

18. Apparatus according to claim 16 wherein said thickening agent is three to ten percent by weight of said mixture.

Drawing