Herein are described phase change ink apparatuses, and more specifically, a dual-layer transfix pressure member, for use in offset printing or ink jet printing apparatuses. In embodiments, the dual-layer transfix pressure member can be used in high speed printing machines. In embodiments, the transfix pressure member includes a substrate, an intermediate layer thereon, and an outer layer positioned on the intermediate layer and wherein the layer(s) have certain moduli and thickness. In embodiments, the layers can be used in combination with phase change inks such as solid inks.
Ink jet printing systems using intermediate transfer, transfix or transfuse members are well known, such as that described in U.S. Pat. No. 4,538,156. Generally, the printing or imaging member is employed in combination with a printhead. A final receiving surface or print medium is brought into contact with the imaging surface after the image has been placed thereon by the nozzles of the printhead. The image is then transferred and fixed to a final receiving surface by the imaging member in combination with a transfix pressure member, or in other embodiments, by a separate fuser and pressure member.
More specifically, the phase-change ink imaging process begins by first applying a thin liquid, such as, for example, silicone oil, to an imaging member surface. The solid or hot melt ink is placed into a heated reservoir where it is maintained in a liquid state. This highly engineered ink is formulated to meet a number of constraints, including low viscosity at jetting temperatures, specific visco-elastic properties at component-to-media transfer temperatures, and high durability at room temperatures. Once within the printhead, the liquid ink flows through manifolds to be ejected from microscopic orifices through use of proprietary piezoelectric transducer (PZT) printhead technology. The duration and amplitude of the electrical pulse applied to the PZT is very accurately controlled so that a repeatable and precise pressure pulse can be applied to the ink, resulting in the proper volume, velocity and trajectory of the droplet. Several rows of jets, for example four rows, can be used, each one with a different color. The individual droplets of ink are jetted onto the liquid layer on the imaging member. The imaging member and liquid layer are held at a specified temperature such that the ink hardens to a ductile visco-elastic state.
After depositing the image, a print medium is heated by feeding it through a preheater and into a nip formed between the imaging member and a pressure member, either or both of which can also be heated. A high durometer synthetic transfix pressure member is placed against the imaging member in order to develop a high-pressure nip. As the imaging member rotates, the heated print medium is pulled through the nip and is pressed against the deposited ink image with the help of a transfix pressure member, thereby transferring the ink to the print medium. The transfix pressure member compresses the print medium and ink together, spreads the ink droplets, and fuses the ink droplets to the print medium. Heat from the preheated print medium heats the ink in the nip, making the ink sufficiently soft and tacky to adhere to the print medium. When the print medium leaves the nip, stripper fingers or other like members, peel it from the printer member and direct it into a media exit path.
To optimize image resolution, the transferred ink drops should spread out to cover a predetermined area, but not so much that image resolution is compromised or lost. The ink drops should not melt during the transfer process. To optimize printed image durability, the ink drops should be pressed into the paper with sufficient pressure to prevent their inadvertent removal by abrasion. Finally, image transfer conditions should be such that nearly all the ink drops are transferred from the imaging member to the print medium. Therefore, it is desirable that the imaging member has the ability to transfer the image to the media sufficiently.
The imaging member is multi-functional. First, the ink jet printhead prints images on the imaging member, and thus, it is an imaging member. Second, after the images are printed on the imaging member, they can then be transfixed or transfused to a final print medium. Therefore, the imaging member provides a transfix or transfuse function, in addition to an imaging function.
In order to ensure proper transfer and fusing of the ink off the imaging member to the print medium, certain nip temperature, pressure and compliance are required. Unlike laser printer imaging technology in which solid fills are produced by sheets of toner, the solid ink is placed on the imaging member one pixel at a time and the individual pixels must be spread out during the transfix process to achieve a uniform solid fill. Also, the secondary color pixels on the imaging member are physically taller than the primary color pixels because the secondary pixels are produced from two primary pixels. Therefore, compliance in the nip is required to conform around the secondary pixels and to allow the primary pixel neighbors to touch the media with enough pressure to spread and transfer. The correct amount of temperature, pressure and compliance is required to produce acceptable image quality.
Currently, the transfix pressure roller for commercial products such as, for example, Phaser 840, 850, 860, 8200 and 8400, which produce up to 24 images per minute, comprises a substrate, a polyether-based polyurethane or nitrile-butadiene rubber (NBR) intermediate layer having a hardness of from about 60 to about 74 Shore D, and having a thickness of from about 2.2 to about 5.3 mm, and an outer layer comprising a polyester-based polyurethane or nitrile butadiene rubber (NBR), having a hardness of from about 80 to about 82 Shore A, and a thickness of from about 0.24 to about 0.38 mm, and wherein the outer layer has a convex profile. A three-layer transfix pressure roller sold commercially, such as that in the Phaser 380, which produces up to 3 prints per minute, comprises a crowned profile substrate, a polyether-based polyurethane first intermediate layer having a Shore A hardness of about 40 Shore A, and a thickness of about 2.2 mm to 5.7 mm, a second intermediate layer comprises a polyether-based polyurethane having a Shore D hardness of 80D and a thickness of 2.54 mm, and an outer layer comprising polyether-based polyurethane having a hardness of 82 Shore A and a thickness of 0.38 mm. A single layer transfix pressure roller sold, for example, as Phaser 340, 350 or 360, and produces up to 6 prints per minute, comprises a substrate, a millable gum polyether-based polyurethane material having a hardness of 35 Shore D and a thickness of 2.6 mm, wherein the layer has a convex profile.
The transfix pressure member aids in transfer and fixing from the imaging member, at a pressure of approximately 500 psi. The pressure exerted at the nip in known machines is from about 500 to about 700 psi. However, the present transfix pressure member must allow for exertion at the nip of from about 750 to about 4,000 psi, or from about 800 to about 3,000 psi, or from about 800 to about 2,000 because the present transfix pressure member is designed for use in high-pressure, high-speed machines.
Therefore, as the process speed goes up for high-speed machines, the size of the roll and the required pressure increases to enable high speed printing with desired image quality. This requires that the applied load on the transfix pressure member must be increased from 1,100 pounds to from about 2,000 to about 4,000 pounds to provide the same image quality. As the pressure requirement is increased, the design of the transfix pressure member requires that the layers on the member become thinner and harder for a given applied load on the member. As the layers become thinner and harder, the ability to keep uniform pressure across the nip, while maintaining the necessary nip profile for paper handling, becomes more and more difficult. In addition, the member sees reasonably high temperature variations, print liquids, and ink components, which could adversely affect its function and print quality. The design of the currently sold transfix pressure roller is not sufficient to meet these needs.
Therefore, it is necessary to provide a transfix pressure member design which provides desired image quality, roll life, and acceptable cost, as a compromise between the member dimensions, material properties (both physical and chemical), layer designs, surface morphology, core and layer profiles, member fabrication processes, and interlayer bonding. It is desired to optimize the transfix system performance at lower loads and with desired print quality.