Patent ID: 12204260

DETAILED DESCRIPTION

In certain liquid electrophotographic printers, a transfer element is used to transfer developed liquid printing fluid (e.g. ink) to a print medium. For example, a developed image, comprising liquid printing fluid aligned according to a latent image, may be transferred from a photo imaging plate (PIP) to a transfer blanket of a transfer cylinder and from the transfer blanket to a desired substrate, which is placed into contact with the transfer blanket. At least two different methodologies may be used to print multi-color images on a liquid electrophotographic printer. Both methodologies involve the generation of multiple separations, where each separation is a single-color partial image. When these separations are superimposed it can result in the desired full color image being formed. In a first methodology, a color separation layer is generated on the PIP, transferred to the transfer cylinder and is finally transferred to a substrate. Subsequent color separation layers are similarly formed and are successively transferred to the substrate on top of the previous layer(s). This is sometimes known as a “multi-shot color” imaging sequence. In a second methodology, a “one shot color” process is used. In these systems, the PIP transfers a succession of separations to the transfer blanket on the transfer cylinder, building up each separation layer on the blanket. Once some number of separations are formed on the transfer blanket, they are all transferred to the substrate together. Both methodologies result in a full color image being formed.

In some electrophotographic printers, an image development unit (such as a binary ink developer (BID)) comprises printing fluid (e.g. liquid ink) which is to be transferred to the PIP. Liquid ink comprises ink particles and a carrier liquid. More than one image development unit can be used, each image development unit comprising different coloured printing fluid. The printing fluid or pigment particles are charged and may be arranged upon the PIP based on a charge pattern of a latent image. Once liquid printing fluid is applied to the latent image on the PIP, an image is formed on the PIP. When the printing fluid is ink, the image comprises ink particles that are aligned according to the latent image.

FIG.1shows an example image development unit100. The image development unit100ofFIG.1is a part of an electrophotographic printer and is movably connected or connectable to a PIP101. As shown inFIG.1, the image development unit100is in the form of a BID100comprising a developer roller1(as shown inFIG.2) which contacts the PIP101to transfer printing fluid (e.g. ink) during a print. In other examples, the image development unit100could take a different form.

FIG.2shows an example developer roller (or roller)1. The developer roller1is for use in the image development unit100ofFIG.1. Like reference numerals inFIGS.1and2indicate like features. The developer roller1comprises a first section2and a second section3. In the example shown inFIG.2, the first section2and the second section3are cylindrical. The first section2comprises a first exterior surface4, the first exterior surface4comprising an electrically-conductive material. In some examples, the first section2is also referred to as an electrically-conductive section. The second section3comprises a second exterior surface5, wherein the second exterior surface5is non-electrically conductive. For example, the second exterior surface5is made entirely of a non-electrically-conductive material. In the example shown inFIG.2, the first exterior surface4and the second exterior surface5are circumferential surfaces of the first section2and the second section3respectively. In some examples, the second section3is also referred to as a non-electrically conductive cap. In the example ofFIG.2, the second exterior surface5comprises the non-electrically-conductive material. In other examples, the second section3is made entirely of the non-electrically-conductive material. In the example ofFIG.2, the non-electrically-conductive material is polyurethane or rubber. In other examples, other non-electrically-conductive materials are used. As shown inFIG.2, the second section3is axially aligned with the first section2and is provided at a first longitudinal end6of the first section2.

In the example shown inFIG.2, the developer roller1comprises a third section7which is axially aligned with the first section2and is provided at a second longitudinal end8of the first section2. In this way, the first section2can be considered a middle section. The third section comprises a third exterior surface9which is non-electrically conductive. In the example ofFIG.2, the third section7is the same as the first section3. For example, the third section7has the same dimensions and comprises the same material as the second section3. In other examples, the third section7has difference properties to the second section3. For example, the third section7may comprise a different material or have a different dimension to the second section3. In some examples, the third section7is also referred to as a non-electrically conductive cap. As shown inFIG.2, the second section3at least partially defines a first longitudinal end16of the developer roller1. The third section7at least partially defines a second longitudinal end17of the developer roller1. The second longitudinal end17of the developer roller1is opposite the first longitudinal end16of the developer roller1. Alternatively, the third section7is omitted.

In the example shown inFIG.2, the first section2is formed on the second section3. For example, the second section3is formed in a mold (as discussed later) and the first section is subsequently formed on the second section3. For example, once the second section3is formed, the first section2can be applied in non-solid form to the second section3, such that when the first section2sets, the first section2is attached to the second section3. In this example, the first section2is formed onto the third section7in the same way. In other examples, the first section2is attached to the second section3and the third section7in any other suitable way. For example, an adhesive can be used to attach the first section2to the second section3and the third section7. In some examples, the first section2and/or the third section7are formed on the second section3. In some examples, there may be a blend in material between the first section2and the second section3, or the first section2and the third section7, when the first section2is formed on the second section3or third section7. Such a blend may occur due to the materials of the respective sections diffusing into each other before the sections have fully set.

FIG.3shows a closer view of a part of the developer roller1ofFIG.2. As shown inFIG.3, the developer roller1comprises a non-electrically-conductive coating15(or layer) on the first exterior surface4and the second exterior surface5. In the example shown inFIG.2, the coating15is also provided on the third exterior surface9. In other examples, the coating15is provided on at least the first exterior surface4. For example, in some examples, the coating15is provided on the first exterior surface4but not the second exterior surface5or the third exterior surface9. In other examples, the coating15is provided on the first exterior surface4and on at least a part of the second exterior surface5and/or on at least a part of the third exterior surface9. In the example ofFIGS.2and3, the coating15comprises polyurethane. In other examples, the coating15comprises any other suitable material. In the example shown inFIG.3, the coating15is retracted from the first longitudinal end16and from the second longitudinal end17of the developer roller1. In other examples, the coating15extends fully across the second exterior surface5to the first longitudinal end16of the developer roller1. The coating15helps with the release of printing fluid from the developer roller1and also helps to control the electrical-conductivity of the developer roller1. For example, the coating15has a formulation that comprises a component to balance adhesion and release of the printing fluid. In some examples, the electrical-conductivity of the developer roller1is determined by a thickness of the coating15. In the example shown inFIGS.2and3, the coating15, the second exterior surface5and the third exterior surface9together define an overall circumferential surface of the developer roller1. In other examples where the coating15covers the first exterior surface4, the second exterior surface5and the third exterior surface9in full (i.e. extends from the first longitudinal end16of the developer roller1to the second longitudinal end17of the developer roller1), the coating15defines the overall circumferential surface of the developer roller1.

As discussed above, as the coating15applied to the developer roller1dries, it can retract from the longitudinal ends16,17of the developer roller1. As shown inFIG.3, this causes a part of the second exterior surface5to be exposed at a circumferential surface of the developer roller1in use. However, as the second exterior surface5is non-electrically conductive, when the developer roller1is provided in an electrostatic print apparatus, arcing is less likely to occur between an electrode of the print apparatus and the second exterior surface5. As such, the second exterior surface5is less likely to soften and melt in use and the chance of gelation is reduced, increasing print consistency of the print apparatus. The same effect can also occur at the third exterior surface9as discussed above in relation to the second exterior surface5.

As shown inFIG.2, the developer roller1comprises a rod10which passes through a center of each of the first section2, the second section3and the third section7. In the example shown inFIG.1, the developer roller1is to rotate about a longitudinal axis of the rod10in use.

In some examples, such as the present example, the first exterior surface4, the second exterior surface5and the third exterior surface9(when provided) comprise the same base material. For example, the first exterior surface4, the second exterior surface5and the third exterior surface9comprise rubber or polyurethane. In this example, the first exterior surface4also comprises electrically-conductive material, while the second exterior surface5and the third exterior surface9are substantially free of electrically-conductive material. In other examples, the first exterior surface4, the second exterior surface5and the third exterior surface9comprise any other suitable material.

FIG.4shows an example of the second section3(or cap) discussed above, before any processing of the second exterior surface5has occurred. The second section3comprises an aperture11which is to receive the rod10. The second exterior surface5of the second section3is non-electrically-conductive. In some examples, the second section3is made entirely of a non-electrically conductive material. In other examples, the second exterior surface5is non-electrically-conductive while a part of the second section3away from the second exterior surface5is electrically-conductive. The third section7is substantially the same as the second section3and has the same properties as discussed above.

FIG.5shows a mold12used to form the second section3(or cap) shown inFIG.2. The use of a mold12, such as that shown inFIG.5, allows the second section3(or end cap) to be pre-produced separately from the first section2. As shown inFIG.5, the mold12comprises a space13into which the material used to form the second section3is inserted. Although the space13is shown having an elongate “D” profile inFIG.5, other shaped profiles can also be used. In one example, the space13has a circular profile. The mold12also comprises a shaped protrusion14which corresponds to the aperture11of the second section3. In some examples, the mold12as shown inFIG.5is also used to form the third section7.

Although it is discussed above that the second section3is formed using a mold12, in other examples, other manufacturing methods are used. In some examples, the second section3and/or third section7are formed using a three-dimensional printer. In other examples, other forms of computer-aided manufacturing can be used, for example using computer numerical control (CNC) machines.

FIG.6shows a flow chart of a method20of making a developer roller1for a print apparatus according to one example. The method20comprises attaching21a non-electrically-conductive cap to an electrically-conductive element, such that the electrically-conductive element and the cap are axially aligned, to form a subassembly. The method20also comprises providing22a non-electrically-conductive coating on an exterior surface of the subassembly, the exterior surface being defined in part by the element and in part by the cap.

In some examples, the subassembly is the developer roller1(or roller) described above in relation toFIG.2. For example, the electrically-conductive element is equivalent to the first section2and the cap is equivalent to the second section3and/or third section7.

As shown inFIG.6, the method20also comprises processing23the exterior surface of the subassembly to create a substantially uniform surface. In this example, the processing23occurs before the providing22the non-conductive coating. In the example ofFIG.6, the processing23comprises grinding the exterior surface such that the subassembly has a substantially circular cross-section. In other examples, other processes can be used that result in a substantially circular cross-section of the subassembly, such as milling or filing. The developer roller1shown inFIG.2has a substantially cylindrical shape with a circular cross-section. In the example ofFIG.2, the developer roller1is initially formed with a non-circular cross-section and is processed to have a circular cross-section, for example by grinding the first exterior surface4, the second exterior surface5and the third exterior surface9. In other examples, the developer roller1is formed with a circular cross-section without the need for further processing to alter the cross-sectional shape of the developer roller1.

As discussed above, the first section2, the second section3and the third section7comprise the same base material. Electrically-conductive material is added to the first exterior surface4such that the first exterior surface4is electrically-conductive. No electrically-conductive material is added to the second exterior surface5and the third exterior surface9, such that the second exterior surface5and the third exterior surface9are non-electrically-conductive.

As shown inFIG.1, the image development unit100comprises the developer roller1(or roller) as discussed in any of the above examples. In some examples, the image development unit100is a binary ink developer. In other examples, a print apparatus, such as a liquid electrographic printer, comprises the image development unit100.

As discussed in the examples above, a developer roller1(or roller) is provided which helps to reduce the chance of the developer roller1melting in use by providing sections of non-electrically-conductive material at the longitudinal ends16,17of the developer roller1. The non-electrically-conductive sections reduce the chance of arcing occurring between an electrode and the developer roller1in use, to reduce the change of the developer roller1melting. This helps to reduce the chance of development roller1becoming damaged, therefore increasing the lifetime of the developer roller1while also improving print quality and/or consistency.

The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with any features of any other of the examples, or any combination of any other of the examples.