Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-07-16
2001-09-04
Marcheschi, Michael (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S415000, C106S416000, C106S417000, C106S436000, C106S442000, C106S464000, C106S469000, C106S467000, C106S468000, C106S487000, C106S482000, C106S483000, C106S461000
Reexamination Certificate
active
06284034
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to pigment materials and their use in coating compositions.
Pigment materials such as calcium carbonate and calcined kaolin are employed together with hydrophilic binders such as acrylic and styrene butadiene latices and optionally other ingredients in compositions to coat paper and like materials to provide amongst other things smooth or gloss surfaces which can be printed upon.
Such printing may be carried out using an electrophotographic printer. Dry toner particles providing print information are applied to the coated paper surface by a fuser of a fuser station of such a printer. The toner particles incorporate a thermo-softening polymer and the fuser causes the polymer partially to melt and thereby causes the toner particles to adhere to the surface to be printed. The binders employed in coating compositions may have a relatively low glass transition temperature, eg less than 40° C., and the heat applied by the fuser can cause the binder of the coating composition providing the surface to be printed upon to become soft and sticky. The heat applied may be sufficient that when the printed sheets are stacked or reeled into multiple layers adjacent sheets or layers may adhere together. This can cause later paper handling and/or feeding problems which are of concern to the paper printer.
SUMMARY OF THE INVENTION
According to the present invention in a first aspect there is provided a pigment material for use in a coating composition suitable for coating a sheet material to be printed by an electrophotographic printer which pigment material comprises a blend of Components A and B as follows:
Component A: a fine pigment material suitable for gloss coating of a sheet material the pigment material comprising particles at least 80% by weight of which have an equivalent spherical diameter (“esd”) of less than 2 &mgr;m and having a particle size distribution (“psd”) such that its d
50
value, namely the particle esd value less than which 50% of the particles have an esd, is less than 1am; and
Component B: a coarse pigment material having a psd such that its d
50
value is from 2 &mgr;m to 10 &mgr;m and such that not more than 2% by weight of the particles of the coarse pigment material have an esd greater than 15 &mgr;m;
wherein the weight ratio of Component A to Component B is at least 4:1.
DESCRIPTION OF THE INVENTION
In this specification all pigment psd measurements are as measured in a well known manner by sedimentation of the pigment in a fully dispersed condition in an aqueous medium using a SEDIGRAPH 5100 machine as supplied by Micromeritics Corporation. Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having an esd less than given esd values. From the results obtained using a SEDIGRAPH 5100 machine, a histogram may be constructed of the percentage by weight of particles having an esd within each esd increment in a series of esd increments plotted along one axis. The esd vales of the mid-points of the esd increments plotted in this way may themselves conveniently be on a logarithmic scale. Such a histogram is referred to herein as a “log-normal particle size increment histogram”. An example of such a histogram is FIG. 1 of Assignee's EP-A-0,777,014.
In the pigment according to the first aspect of the invention, the weight ratio of Component A to Component B may be from 4:1 to 100:1, especially from 20:1 to 100:1.
Component A may have a d
50
value of from 0.4 &mgr;m to 0.7 &mgr;m. Preferably, not more than 2% by weight of the articles of Component A have an esd of 5 &mgr;m or more. At least 90% of the particles of Component A may have an esd less than 2 &mgr;m. In some examples of Component A at least 90% by weight of the particles of Component A may have an esd less than lm. Component A may have, on a log-normal particle size increment histogram (as referred to earlier), a histogram peak which at half peak maximum height has a width of from 1.0 to 1.2 along the esd logarithmic scale.
Preferably, not more than 2%, desirably not more than 1% by weight of the particles of Component B have an esd of 10 &mgr;m or more. Desirably, the d
50
value of Component B is from 2 &mgr;m to 5 &mgr;m. Preferably, the particles of Component B are near spherical in shape.
Blending of Component B together with Component A to form the pigment material according to the first aspect of the invention provides a so-called bimodal particle size distribution wherein a secondary peak is seen in the psd in the range 2 &mgr;m to 10 &mgr;m, desirably in the range 2 &mgr;m to 5 &mgr;m, especially when a particle size increment histogram, as described earlier, is constructed.
The pigment material according to the first aspect of the invention when employed in a coating composition helps to provide ‘anti-blocking’, ie to deter or prevent the adhesion between coated layers described earlier. The minor amount of coarse pigment particles present in the coating composition, provided by Component B of the pigment material according to the invention, beneficially causes the coated surface to have localised points of protrusion in the surface profile although surprisingly not substantially reducing the overall surface gloss or substantially harming other properties as illustrated later. These points of protrusion serve to reduce the area of contact between adjacent coated sheets or layers and therefore allow the adjacent sheets or layers to be more easily separated.
The pigment material according to the first aspect should have a psd suitable for use in a paper coating composition to be applied by paper coating machinery, especially modern fast paper coating machinery, without known blade runnability problems such as giving rise to so-called spits, streaks or blade bleeding obtained with certain inferior coating compositions.
The pigment material employed to provide Component A and that employed to provide Component B may each independently be selected from any one or more of the materials known for use in paper coating compositions. Such material may for example comprise one or more (materials having the required particle size properties) of calcium carbonate (synthetic, precipitated material or ground from naturally occurring mineral), calcined kaolin, hydrous kaolin, talc, mica, dolomite, silica, zeolite, gypsum, satin white, titania, calcium sulphate and plastic pigment. Preferably both Component A and Component B are selected from calcium carbonate and calcined kaolin, eg both may be calcium carbonate.
According to the present invention in a second aspect there is provided an aqueous coating composition suitable for coating a sheet material to be printed by an electrophotographic printer which comprises a pigment material according to the first aspect together with a hydrophilic adhesive and optionally other ingredients.
According to the present invention in a third aspect a method of printing paper sheets by an electrophotograhic printing process includes the step of carrying out the printing on coated sheets of the paper wherein the sheets have been coated with a coating composition according to the second aspect.
The sheets which have been printed upon may subsequently be stacked or wound on a reel and may be subsequently re-handled without substantial adhesion between adjacent layers or sheets.
The amount of adhesive or binder present in the coating composition according to the second aspect depends upon whether the composition is to be applied as a relatively dilute or concentrated pigment-containing suspension to the material to be coated. For example, a dilute pigment-containing composition (binder-rich composition) could be employed as a top-coat for underlying more pigment-rich compositions. The adhesive or binder present in the composition may range from 1% to 70% by weight relative to the dry weight of pigment (100% by weight) especially 4% to 50% by weight. Where coating composition is not to be employed as a binder rich composition the adhesive or binder may form from 4% to 30%, eg 8%
Hiorns Anthony Gordon
Jones James Philip Eynon
Preston Janet Susan
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Imerys Minerals Limited
Marcheschi Michael
LandOfFree
Pigment materials and their use in coating compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pigment materials and their use in coating compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pigment materials and their use in coating compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2446111