Sealant materials for toner cartridges

Abstract: A release agent composition for use in an electrophotographic process is disclosed. This composition includes a specifically-defined heat-stable silicone oil-silicone wax random copolymer. The copolymer has a melting point such that it is liquid on the hot fuser roll, but solidifies at room temperature on the printed page. A random silicone copolymer, in the form of a paste or pliable caulk, which is useful for sealing leaks in toner cartridges is also disclosed. Finally, the method for preparing these copolymers is disclosed.

Description: The present invention relates to electrophotographic printing and specifically to a sealant used in toner cartridges. BACKGROUND OF THE INVENTION In the process of electrophotography, the light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with a subsequent rendering of that latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of paper, with subsequent affixing of the image thereto. Print quality issues can arise as the result of toner leaks from the print cartridge. The toner cartridge is a replaceable supply used in printers and photocopiers. Its function is to hold a supply of the toner in a reservoir and then transfer the toner from that reservoir onto the developer roll, where it is present as a monolayer. The toner is then transferred onto the photoconductor in a pattern corresponding to the image to be printed, based on a charge distribution created on the photoconductor surface. Toner cartridges are well-known in the electrophotographic art and are, for example, described in EP 0864945A. Careful transfer of the toner is critical to obtaining good printed images. Leaking toner will result in poor image quality, as well as soiling of the user's hands, clothing and office. A particularly troublesome spot on the cartridge, where toner leakage is likely to occur, is at the ends of the developer roll. In fact, toner cartridges frequently utilize specific seals, such as the J-seal, to prevent toner leakage at the ends of the developer roll. Despite that, some leakage still occurs due to variability in cartridge parts and assembly. A liquid or grease seal could be considered for use at the ends of the developer roll. However, that could cause problems since such materials tend to migrate and migration of the sealant into the print area can cause contamination of the developer roll, the photoconductor and the charge roll, thereby causing print defects. Therefore, it is an object of the present invention to provide a silicone copolymer which, when formulated to have a paste or caulk-like consistency, serves as an effective sealant for use on toner cartridges, which does not migrate, is easy to apply and can be spread as a thin layer. SUMMARY OF THE INVENTION The present invention relates to a random silicone copolymer, which may be used as a sealant in a toner cartridge, having the formula: wherein x represents from 0.988 to 0.995 of the copolymer, y represents from 0.005 to 0.012 of the copolymer, and R comprises from 70% to 100% of C 15 -C 60 alkyl and from 0% to 30% of C 2 -C 14 alkyl groups. Preferred copolymers have a molecular weight (weight average) of from 80,000 to 250,000. The copolymers are in the form of a paste or caulk and have a viscosity of from 300 to 700 Pa (3,000 to 7,000 centipoise) at about 93°C. Toner cartridges which utilize these copolymers as a sealant are also claimed. DETAILED DESCRIPTION OF THE INVENTION In this formula, x is preferably from 0.990 to 0.992, and most preferably about 0.99, molar percent of the copolymer. y is preferably from 0.008 to 0.010, and most preferably about 0.01 molar percent of the copolymer. The C 2 -C 14 alkyl R group is preferably a hexyl group. Both of the alkyl components may be halogenated, preferably fluorinated. It is preferred that the major component in R be C 30 -C 45 alkyl, most preferably C 36 alkyl (triacontyl). The copolymer should also preferably be heat stable. The molecular weight (weight average) of the copolymer is from 80,000 to 250,000, preferably from 80,000 to 150,000, most preferably about 110,000. The copolymer useful as a sealant has the consistency of a paste or pliable caulk. For each particular sealant copolymer, it is within the knowledge of one of ordinary skill in the art to vary the values of x and y and the copolymer's molecular weight to achieve the desired viscosity. The copolymer may be used in combination with antioxidants. This silicone copolymer material is useful for sealing leaks, for example in a toner cartridge, especially at the ends of the developer roll. The structure of such cartridges is well-known in the art as, for example, disclosed in EP 0864945A. To accomplish this sealant function an effective amount (from about 5 mg to 40 mg, preferably 10 mg) is placed on each end of the developer roll. The roll is then turned, wetting the surface of the roll with the copolymer. The copolymer is easy to apply. This thin layer of the copolymer acts to effectively seal toner leaks and the copolymer does not migrate into the print area, in use. The copolymer may be synthesized by any method known in the art. The steps generally will include the copolymerization of the cyclic siloxane (D4) and silicone hydride components to form a silicone prepolymer and then grafting the long chain alkene group onto that prepolymer. An example of a reaction which can be used to accomplish this follows: The melt viscosity of the copolymer may be effectively influenced by controlling the crosslinking of the copolymer while it is being prepared. Crosslinking agents which may be used for this purpose include divinyl-terminated polydimethyl siloxane. This approach is useful when a higher molecular weight copolymer is desired. The result of this procedure is to increase the copolymer viscosity in a controlled manner making the flow rate of the copolymer wax product more controllable. When a lower molecular weight copolymer is desired, from 0.1 to 0.5 weight percent (preferably about 0.26%) of a chain-stopper material may be added to the step 1 reaction. Effective chain-stoppers include any low molecular weight PDMS, such as hexamethyl disiloxane (HMDS). It is preferred that this reaction take place in the presence of bentonite. After the step 2 reaction is completed, it is preferred that the reaction be quenched with a volatile low molecular weight 1-alkene (e.g., C 2 -C 14 alkenes)such as 1-hexene. This quenching step replaces any hydrides in the material synthesized with the short alkyl chain to prevent further reaction of any hydrides, such as self-crosslinking. Up to about 30% of the y groups on the copolymer can be so substituted - greater amounts can adversely affect viscosity of the material. It has surprisingly been found that when the effective amount of reaction catalyst (see step 2 above) is added stepwise to the reaction mixture over the course of the reaction, the reaction goes further toward completion than if the catalyst had all been added at one time. The following example is intended to illustrate the present invention and is not intended to be limiting thereof. EXAMPLE A copolymer of the present invention useful as a sealant is synthesized as follows: Step 1 In a 1000mL four-neck round bottom flask equipped with thermometer, condenser, mechanical stirrer, and septum, add 213.05 g of D4, 1.93 g of PMHS, 0.62 g of dried bentonite (F-20X at 100°C for four hours), and 0.744 g of HMDS (967 µL). Fill the reaction flask with nitrogen. Slowly heat the mixture to 90°C with 500 RPM stirring. Hold at 90°C for 18 hours. To remove any unreacted D4, heat the mixture under high vacuum at 125°C. The viscosity of the material should reach 500 Pa (5,000 cps). The content of hydride is measured by proton NMR and is about 1 molar percent. Step 2 Cool the reaction flask from step 1 to room temperature. Then add 26.5 g of triacontene (e.g., Gulftene 30 +, commercially available from Chevron, a mixture of alkene materials having an alpha-olefin content greater than 60%, and an average chain length of about 36) and 400 mL toluene (dried with molecular sieves). Fill the reaction mixture with nitrogen. Heat to 75°C, measure IR of a solution aliquot, and add 50 µL of PC072 (Platinum, 1,3- diethenyl-1,1,3,3-tetramethyldisiloxane complex) (time = 0 min). At 20 minutes add 50 µL of PC072 and measure IR. Continue to add 50 µL every 20 minutes taking IR of aliquot until percent hydride (%H) reaches 25-30% of original (time = 0 min.) hydride integration from IR (no less than 40 min. addition; nor more than 60 min. addition). When the % hydride reaches 25-30% add 50 mL of hexene and 50 µL of PC072 (quench time = 0 min.). At 30 minutes add another 50 µL of PC072. Continue monitoring by IR until the % hydride is below 10% of original hydride integration (normally 1 hour). Procedure for adding antioxidant From step 2, add in 3% Cyanox STDP, 0.6% Irganox 1010,0.9% Mark 2112 antioxidants based on amount of wax (if assumed 214.3 g wax produced: 7.24 g STDP, 1.45 g 1010, and 2.17 g 2112). Heat (100°C) and stir until mixed (1 hour). Pour into oven dish, dry in explosion proof oven ( ~ 75°C) overnight. Cyanox and Irganox are trade marks. A small quantity of the material synthesized above is used to seal the ends of the developer roll in the developer section of the printing cartridge. This sealing operation prevents the toner from leaking into the transfer section of the cartridge. The material is inside the cartridge where it cannot be touched by the customer; it is not released during the printing process. To apply the material, the cartridge assembly person takes a small amount of the material (about 10 mg) on the end of a tool that is like a flat screwdriver and places that amount of material on each end of the developer roll. The roll is then turned to distribute the material around the roll, forming a thin layer, sealing the end of the roll to prevent toner from escaping.

Claims: A random silicone copolymer having the formula: wherein x represents 0.988 to 0.995 of the copolymer, y represents from 0.005 to 0.012 of the copolymer, and R comprises from 70% to 100% of C 15 -C 60 alkyl and from 0% to 30% of C 2 -C 14 alkyl groups, the alkyl groups being optionally halogenated. A random silicone copolymer according to claim 1 having a molecular weight (weight average) of from 80,000 to 250,000. A random silicone copolymer according to claim 2 which is in the form of a paste or caulk. A random silicone copolymer according to claim 3 having a viscosity of from 300 to 700 Pa (3,000 to 7,000 centipoise) at about 93°C. A random silicone copolymer according to claim 4 wherein x is from 0.990 to 0.992 and y is from 0.008 to 0.010. A random silicone copolymer according to claim 5 having a molecular weight of from 80,000 to 150,000. A random silicone copolymer according to claim 6 wherein x is about 0.99 and y is about 0.01. A random silicone copolymer according to claim 7 having a molecular weight of about 110,000. A random silicone copolymer according to claim 8 wherein R comprises from 70% to 100% by weight C36 alkyl. A random silicone copolymer according to claim 4 wherein R comprises from 70% to 100% by weight C36alkyl. A toner cartridge which incorporates the random silicone copolymer according to any preceding claim as a sealant. A toner cartridge which incorporates the random silicone copolymer according to Claim 4 as a sealant. A toner cartridge which incorporates the random silicone copolymer according to Claim 9 as a sealant. A toner cartridge which includes a developer roll having from 5 mg to 40 mg of the random silicone copolymer according to Claim 4 as a sealant at each end of said developer roll. A toner cartridge which includes a developer roll having from 5 mg to 40 mg of the random silicone copolymer according to Claim 9 as a sealant at each end of said developer roll. A toner cartridge according to Claim 15 wherein about 10 mg of said random silicone copolymer is present at each end of said developer roll.

Inventors: BEACH BRADLEY L, CURRY STEPHEN A, DOWLEN KATHRYN E, WARD EARL D II, BEACH, BRADLEY L., CURRY, STEPHEN A., DOWLEN, KATHRYN E., WARD, EARL D., II
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL, INC.
Application year: 1998
Main classification: C08G77
IPC codes: C08L83, C08G77, C09K3, G03G15, C09J183, C08G81