Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-08-17
2004-07-06
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S416000, C106S428000
Reexamination Certificate
active
06758895
ABSTRACT:
The present invention relates to particulate mineral materials having improved properties and their use in application compositions.
Particulate mineral materials find use in a variety of applications including pigments, fillers and extenders for use in paints, plastics, polymers, paper making and paper coating.
Particulate minerals may exist in a hydrous form; Such minerals may include, for example, kaolin clay, ball clay, talc, mica, and vermiculite. Kaolin is a well-known mineral which comprises mainly the mineral kaolinite obtained by processing material obtained from natural sources. Alternatively, kaolins may be produced in a calcined or chemically aggregated form. Calcined kaolins are obtained by processing hydrous kaolins at high temperatures, e.g. greater than 800° C. Chemically aggregated kaolins are composites having a micro structure resembling that of calcined kaolins produced by treating hydrous kaolins with chemicals. Calcined and chemically aggregated kaolins can show benefits such as improved opacity in application compositions compared with hydrous kaolins. However, such benefits are obtained only with certain disadvantages such as additional cost of production of these materials and a deleterious effect on other properties of the host composition.
The present invention is concerned with improving one or more properties of hydrous minerals. In particular, it is concerned with improving the opacity, without significantly hindering the overall combination of properties shown by such materials in host compositions.
According to the present invention in a first aspect there is provided a particulate hydrous mineral suitable for use as an opacifying pigment, filler or extender which has a shape factor which is greater than S, where S is given by Equation 1 as follows:
S
=(
d
50
/0.036)+20 Equation 1;
where d
50
is the mean particle size of the particles of the mineral measured in microns (micrometers).
The shape factor and the d
50
value are measured by known procedures as described later.
We have found surprisingly and beneficially that the particulate mineral according to the invention shows an unusually high opacity compared with prior art particulate hydrous minerals and this can be obtained with acceptable or no changes in other beneficial properties in a host composition.
The particulate hydrous mineral material of the invention may be selected from the group consisting of kaolin, ball clay, talc, mica, and vermiculite. It is especially preferred that the particulate hydrous mineral is a kaolin.
The invention allows particulate hydrous mineral, and particularly hydrous kaolin, to be employed as an extender in a matt paint composition to provide an opacity which matches or approaches that which may be achieved using more expensive extenders such as calcined and chemically aggregated kaolins. Furthermore, this opacity improvement may be obtained without other disadvantages caused by use of calcined and chemically aggregated koalins.
The sheen, mud crack resistance and stain resistance of the composition are adversely affected by addition of calcined and chemically aggregated kaolins but the adverse effect on such properties can be much less using the particulate hydrous mineral, and most particularly hydrous kaolin, according to the invention. This surprising result was not predictable.
The combination of benefits shown by the particulate hydrous mineral, and most preferably the hydrous kaolin, according to the invention is not obtained with prior art hydrous minerals (and kaolins). We believe that the unusually high opacity shown by the hydrous kaolin of the invention is produced by an unusually high porosity. The mineral (particularly kaolin) porosity can be measured in a well known manner by oil absorption as described later. Without wishing to be bound by any particular theory, we believe that the high porosity results from the unusually thin kaolinite platelets which constitute the particles of the new product having properties defined by Equation 1 earlier. A collection of such platelets can exist in a form in which at least some of such platelets do not lie flat in stacks but can be arranged with their axes in a variety of different planes causing significant voids to exist between the platelets to contribute to the porosity.
The particulate mineral of the invention preferably has a fine particle size, a high shape factor, and a steep particle size distribution which are believed to enhance the opacity of the mineral in an application composition.
“Shape factor” as used herein is a measure of an average value (on a weight average basis) of the ratio of mean particle diameter to particle thickness for a population of particles of varying size and shape as measured using the electrical conductivity method and apparatus described in GB-A-2240398/U.S. Pat. No. 5,128,606/EP-A-0528078 and using the equations derived in these patent specifications. “Mean particle diameter” is defined as the diameter of a circle which has the same area as the largest face of the particle. In the measurement method described in EP-A-0528078 the electrical conductivity of a fully dispersed aqueous suspension of the particles under test is caused to flow through an elongated tube. Measurements of the electrical conductivity are taken between (a) a pair of electrodes separated from one another along the longitudinal axis of the tube, and (b) a pair of electrodes separated from one another across the transverse width of the tube, and using the difference between the two conductivity measurements the shape factor of the particulate material under test is determined.
The mean particle size or d
50
value and other particle size properties referred to herein for the particulate mineral according to the invention are as measured in a well known manner by sedimentation of the particulate material 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 a size, referred to in the art as the ‘equivalent spherical diameter’ (esd), less than given esd values. The mean particle size d
50
is the value determined in this way of the particle esd at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d
50
value.
The value of d
50
for the preferred particulate kaolin according to the invention may for example be in the range 0.4 &mgr;m to 3 &mgr;m, especially 0.5 &mgr;m to 2.0 &mgr;m. For example, particulate kaolin of English (Cornish) origin may have a d
50
value of from 0.5 &mgr;m to 1.0 &mgr;m. Particulate kaolins having some other origins may have a larger d
50
value.
It is not necessary for the preferred particulate kaolin of the invention to have a shape factor which is high, e.g. above 40. However, if the shape factor is less than 40 the d
50
value must be less than about 0.6 &mgr;m to satisfy the above relationship expressed in Equation 1. If the d50 value is greater than 1 &mgr;m then the shape factor must be greater than about 50 to satisfy the above relationship of Equation 1. Similarly, if the d50 value is greater than 2 &mgr;m then the shape factor must be greater than about 75. Preferably, the particulate kaolin has a shape factor of at least 40, in many cases at least 60, e.g. a shape factor in the range 70 to 140, especially from 80 to 120. In all cases, however, the shape factor is greater than S where S is defined by the relationship with d
50
value given in Equation 1 above.
Preferably, the oil absorption of the preferred particulate kaolin is at least 50 grammes of linseed oil per 100 grammes of kaolin. (This may be measured in the manner described in Method A).
It is preferred that the particulate mineral, which is preferably a hydrous kaolin, according to the present invention has a shape factor which is greater than S where S is defined by Equation 2 as follows:
S
=(
d
50
/0.036)+25 Equation 2.
Finnegan Henderson Farabow Garrett & Dunner LLP
Imerys Minerals Limited
Koslow C. Melissa
Manlove Shalie
LandOfFree
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