Coating processes – Immersion or partial immersion
Reexamination Certificate
2001-12-19
2003-06-10
Barr, Michael (Department: 1762)
Coating processes
Immersion or partial immersion
C427S402000, C427S372200, C427S258000
Reexamination Certificate
active
06576299
ABSTRACT:
BACKGROUND OF THE INVENTION
When a photoreceptor is dip coated, the layer thickness increases slowly to a target value after the takeup speed reaches a constant value. The resulting non-uniformity in layer thickness is called “sloping.” “Sloping” of the deposited layer over the imaging area of the photoreceptor is undesirable since it can degrade the performance of the photoreceptor. To prevent the deposited layer from exhibiting “sloping” in the imaging area, one can use a longer substrate to provide a longer non-imaging area so that the “sloping” of the deposited layer occurs only in the non-imaging area while the deposited layer exhibits relatively uniform thickness in the imaging area. However, a longer substrate and a longer non-imaging area increase costs since more materials have to be used in the substrate and the deposited layer or layers. Thus, there is a need, which the present invention addresses, for new methods to eliminate or reduce the above described problem.
Coating methods and apparatus are described in Petropoulos et al., U.S. Pat. No. 5,633,046; Herbert et al., U.S. Pat. No. 5,683,742; Swain et al., U.S. Pat. No. 6,132,810; Petropoulos et al., U.S. Pat. No. 5,578,410; and Crump et al., U.S. Pat. No. 5,385,759.
SUMMARY OF THE INVENTION
The present invention is accomplished in embodiments by providing a coating method for a substrate defining a deposition region and an optional uncoated region, wherein the deposition region includes an intermediate region disposed between a first end region and a second end region, the method comprising:
(a) dip coating a first layer of a coating solution including a liquid medium and a coating material only over the first end region; and
(b) dip coating a second layer of the coating solution over the first layer, the intermediate region, and the second end region in the recited sequence.
There is also provided in embodiments a coating method for a substrate defining a deposition region and an optional uncoated region, wherein the deposition region includes an intermediate region disposed between a first end region and a second end region, the method comprising:
(a) dip coating a first layer of a coating solution including a liquid medium and a coating material only over the first end region;
(b) removing at least a portion of the liquid medium in the first layer, resulting in an at least partially dried first layer; and
(c) dip coating a second layer of the coating solution over the at least partially dried first layer, the intermediate region, and the second end region in the recited sequence.
DETAILED DESCRIPTION
As used herein, the phrase “coating solution” encompasses any fluid composition including the liquid medium and the coating material regardless of the extent that the coating material may be dissolved in the liquid medium.
The substrate employed in the present invention defines a deposition region and an optional uncoated region, wherein the deposition region includes an intermediate region disposed between a first end region and a second end region. In embodiments where the present invention fabricates the substrate into an electrostatographic imaging member (e.g., a photoreceptor), one or more of the first end region, the second end region, and the optional uncoated region may correspond to a non-imaging area of the imaging member, whereas the imaging area of the imaging member includes at least the intermediate region and optionally one or both of the first end region and the second end region. In embodiments, the first end region, the second end region, and the optional uncoated region correspond to the non-imaging area of the imaging member, and the intermediate region corresponds to the imaging area.
The method involves dip coating a first layer of a coating solution including a liquid medium and a coating material only over the first end region. In embodiments, while dip coating of only the first end region is occurring, the intermediate region and the second end region are in contact with the coating solution; this can be accomplished for example by contacting the entire deposition region with the coating solution and then creating relative motion between the substrate and the coating solution to move only the first end region above the coating solution meniscus while the intermediate region and the second end region remain immersed in the coating solution below the coating solution meniscus.
In other embodiments, while dip coating of only the first end region is occurring, the intermediate region and the second end region are not in contact with the coating solution; this can be accomplished for example by using an elevating coating apparatus such as that described in Crump et al., U.S. Pat. No. 5,385,759, the disclosure of which is totally incorporated herein by reference, and pushing only the first end region through the reservoir apparatus to contact the coating solution, thereby depositing the first layer only on the first end region. The first end region is then pushed back in the opposite direction to prevent contact of the intermediate region and the second end region with the coating solution in the reservoir apparatus.
Subsequently, the method involves dip coating a second layer of the coating solution over the first layer, the intermediate region, and the second end region in the recited sequence.
The phrase “dip coating” encompasses the following techniques to deposit layered material onto a substrate: moving the substrate into and out of the coating solution; raising and lowering the coating vessel to contact the coating solution with the substrate; positioning the substrate in a vessel containing the coating solution and then draining the coating solution from the vessel.
The substrate may be moved into and out of the solution at any suitable speed including the takeup speed indicated in Yashiki et al., U.S. Pat. No. 4,610,942, the disclosure of which is hereby totally incorporated by reference. The dipping speed to contact the substrate with the coating solution may range for example from about 50 to about 3,000 mm/min and may be a constant or changing value. The takeup speed to withdraw the substrate from the coating solution may range for example from about 50 to about 500 mm/min and may be a constant or changing value. Any suitable dipping speed and takeup speed, including those discussed herein, can be used to deposit the first layer, the second layer, and any other desired layers.
The thickness of the first layer depends upon for instance the takeup speed, the immersion time in the coating solution, and the drying time. Illustrative takeup speeds and drying times are discussed herein. Any suitable immersion time may be employed such as from 0 to about 3 minutes, and particularly from 0 to about 30 seconds. The first layer has a thickness ranging for example from about 0.05 to about 50 micrometers, and particularly from about 1.5 to about 20 micrometers.
The thickness of the second layer depends upon for instance the takeup speed. Illustrative takeup speeds are discussed herein. The second layer has a thickness ranging for example from about 0.05 to about 75 micrometers, and particularly from about 3 to about 40 micrometers.
Unless otherwise indicated, the disclosed thickness values for the various layers are dry thickness values.
In embodiments, the second layer exhibits a substantially uniform thickness over the entire deposition region, particularly over the intermediate region. The phrase “substantially uniform thickness” indicates that the dry coating thickness over the deposition region varies by no more than about 10%, particularly no more than about 5%, based on the largest thickness value of the second layer.
In embodiments, the present method further involves depositing (by for example dip coating) a third layer including a different coating material over the entire deposition region prior to the dip coating of the first layer.
In embodiments, the present method removes at least a portion of the liquid medium in the first layer, resulting in an at least partially dried first
Chen Cindy C.
Pan Sean X.
Barr Michael
Soong Zosan S.
Xerox Corporation
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