Patent Application
20090290918
The invention relates to a soft pressure roller for use in a printer fusing station. More particularly, the invention relates to a roller having an elastomer composition which provides low composite hardness, very low compression set, and extended life over that of current soft pressure rollers used for printer fusing application.
Laser printers and other electrophotographic image forming devices for both black-and-white and color printing technologies use toner particles to form a desired image on print media. The print media is often paper, although a wide variety of different print media may be employed. Once the toner is applied to the media, the media is advanced along a media path to a thermal fuser. In some image forming devices, the fuser includes a fuser roller and a mating pressure roller. As the media passes between the fuser roller and the pressure roller, the toner is fused to the media through a process using pressure and heat exceeding 300° F. (148° C.).
The interference area between the fuser roller and the pressure roller is often referred to as the nip. It is desirable to maintain a substantially uniform pressure in the nip. Uneven, or non-uniform pressure may result in degraded print quality, wrinkled print media, or other undesirable consequences.
Therefore, it is desirable to develop a roller composition that provides low composite hardness, low compression set, and extended life over that of current soft pressure rollers used for printer fusing application.
NIP formation is created by the intersection of two members under load. The resulting pressure under the nip width formed is an important function to obtain a properly fused image in the printing process. One of the members of the nip fusing systems is a pressure roller. The pressure roller deforms, under load, to create a contact region where pressure and temperature fuse the toner image to the substrate as it passes through the nip region.
A pressure roller is used with another roller or a belt to form the nip region. The amount of pressure and heat that is generated is determined by the design of the fusing system, which is dependent upon the speed of the printer, toner properties, etc. The amount of pressure needed to form the desired nip region is proportional to the composite hardness of the pressure roller.
The hardness or softness of a pressure roller is dependent upon the base material. Critical physical parameters of the material chosen are the hardness, measured in Shore A for harder materials and Asker C for soft materials, compression set expressed in % of permanent deformation, elongation expressed in % of deformation, and tensile strength given in pounds per square inch (psi). Other important properties are dynamic responses under temperature (° C.), pressure, and aging, which also affect roller life performance.
The designs of pressure rollers used in nip forming fusing systems employ a single polymer material on a core or multiple layer configurations. Often fluoropolymer sleeves are bonded to a material for enhanced toner release and wear resistance. When a roller is designed using multiple layers of different polymers, the total hardness, or composite hardness, is a measure of the deformation capability of the roller under pressure. Selection of base materials are chosen from silicone, EPDM, fluorocarbon, and other elastomer polymers. Furthermore, foam structures of these same materials may be utilized, often to achieve a lower composite hardness. The most common polymers are classified as a high consistence elastomer (HCR), a liquid injection material (LIM), a room temperature vulcanized elastomer (RTV), or a foam version of each that incorporates air pockets or voids.
To achieve a roller of very low hardness, physical properties of materials, such as compression set are often compromised, thus contributing to failure modes which affect the performance and or life of the roller in a fusing system environment.
Compression set of a material is critical in fusing system applications and is therefore desired to be as low as possible, less than 10%. Greater compression set introduces issues of loss of nip over time and elevated temperatures. This is one of the issues associated with foam materials, which have a compression set of 50%, but which are often a choice for low hardness pressure rollers. Tensile strength and elongation of materials are values that indicate the strength of a material under pressure in the fusing nip. Accordingly, a material with higher tensile strength and elongation is preferred.
Dynamic properties testing of materials, such as Dynamic Modulus Analysis (DMA) at temperature is a test which indicates the stability of a material to continuous deformation of nip fusing environment. Values from these tests are often considered in the choice of materials suitable for nip formation applications in fusing environments. In general the formulation or chemistry of a polymer that gives the desired softness, may give low physical properties such that the tensile and elongation are very low. This may result in deformation or destruction of the roller under nip forming pressure and thus decreasing the life of the roller. Therefore, a material with the greater tensile and elongation properties is generally preferred. The choice of the materials, and the construction thereof, is critical in the design of the pressure roller.
In view of the foregoing, the pressure roller of the present invention provides a very low composite softness and very low compression set, exhibiting the physical and dynamic properties of a true elastomer. These enhanced properties of the invention result in optimized fusing system parameters, temperature stability and increased life of the roller in printing applications.
The present invention encompasses a pressure roller with a silicone wall thickness between 2 mm and 10 mm having a composite softness of between 15 and 35 Asker C, and a compression set of less than 10%. The present invention also encompasses a pressure roller with a silicone wall thickness between 2 mm and 10 mm having a multilayer construction with a composite hardness between 17 and 60 Asker C.
In another embodiment, the invention includes a pressure roller having a core and a base. The base has an inside diameter and an outside diameter, wherein the inside diameter is molded about the core. The roller is fabricated of a LIM silicone elastomer having a softness of between 15 and 35 Asker C and the distance between the inside diameter and the outside diameter is between 2 mm and 10 mm.
In yet another embodiment, the invention includes a pressure roller having a core and a base. The base has an inside diameter and an outside diameter, wherein the inside diameter is molded about the core. The roller is fabricated of a LIM silicone elastomer having a softness of between 15 and 35 Asker C and the distance between the inside diameter and the outside diameter is between 2 mm and 10 mm. A top coat is disposed about the entire outside diameter. The top coat is fabricated of a polymer having abrasion resistance and surface release properties with a softness between 17 and 40 Asker C.
In an alternative embodiment, the invention includes a pressure roller having an inside diameter and an outside diameter. The roller is fabricated of LIM silicone elastomer having a softness of between 15 and 35 Asker C and the distance between the inside diameter and the outside diameter is between 2 mm and 10 mm. A sleeve having a thickness defined by an interior and an exterior is disposed about the entire outside diameter. The sleeve is fabricated from a fluoropolymer having a thickness of the sleeve is between 20 and 50 microns.
In yet another alternative embodiment, the invention includes a pressure roller having a core and a base. The base is defined by a layer of LIM silicone elastomer having an inside diameter and an outside diameter. The layer of LIM silicone includes a softness of between 15 and 35 Asker C and the distance between the inside diameter and the outside diameter is between 2 mm and 10 mm. The pressure roller also includes a sleeve having a thickness defined by an interior and an exterior. The interior of the sleeve is disposed about the base. The sleeve is fabricated from a fluoropolymer having a thickness between 20 and 50 microns. The composite hardness of the roller is between 20 and 60 Asker C.
The present invention encompasses a pressure roller design in which the composite hardness of the roller is between 15 and 60 Asker C, having a compression set of less than 10% and a base material minimum elongation property of 400%.
With reference to
With respect to
The composite hardness of various pressure roller compositions is given in
The rollers of the preferred embodiment have base elastomer material with physical properties given in
