Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-07-26
2001-03-13
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S442000, C106S443000, C106S446000, C427S214000, C427S215000
Reexamination Certificate
active
06200375
ABSTRACT:
The present invention concerns a titanium dioxide pigment that presents a surface treatment adapted for use in high quality exterior paints.
Titanium dioxide is used in paint compounds because of its pigment properties.
Titanium dioxide pigments are generally treated with mineral compounds to improve their application properties such as dispersibility, whiteness, and coverage power.
These treatments also make it possible to improve the quality of titanium dioxide based paints over time while retaining the original physicochemical characteristics of the paint despite its outdoor exposure, specifically its gloss, color stability, and the mechanical properties of the film.
In addition to its pigment function, titanium dioxide pigment is known for its absorption of UV rays. It protects the organic matrix into which it is introduced (paints, plastics) against surface degradation from the effect of rays of this type.
At the same time, titanium dioxide contains photocatalytic properties that degrade the existing organic compounds when they are exposed to the effect of those same UV rays. This degradation is characterized by chalking of the paint.
Mineral processes are also designed to avoid direct contact between the titanium dioxide and the organic components of the matrix. To this end, it is known to use a silica and/or aluminum based mineral treatment. However, it has been observed that such surface treatments were insufficient when the pigment was used in paint compounds for exterior coats with strong exposure to sunlight.
A goal of the present invention is to present a titanium dioxide pigment that has a mineral surface treatment which exhibits good behavior in exterior paints over time, most particularly in terms of low chalking and good gloss retention.
To this end, the invention concerns a titanium dioxide pigment containing a titanium dioxide core covered sequentially with a layer of zirconium hydroxide or oxyhydroxide, then a layer of titanium hydroxide or oxyhydroxide, then a layer of a phosphate and silica coprecipitate, followed by a layer of aluminum oxyhydroxide.
The invention also concerns a process for the preparation of this pigment consisting of the following operations:
an aqueous suspension of titanium dioxide pigments if formed,
in a first step, a layer of zirconium hydroxide or oxyhydroxide is precipitated on the surface of the pigment;
in a second step, a layer of titanium hydroxide or oxyhydroxide is precipitated on the surface of the pigment;
in a third step, a layer of phosphate and silica are coprecipitated on the surface of the pigment;
in a fourth step, a layer of aluminum oxyhydroxide is precipitated on the surface of the pigment;
the pigment is recovered from the suspension.
Lastly, the invention concerns the use of this pigment in paints and plastics.
Other details and advantages of the invention will become more obvious to the reader as the description and examples are read.
The invention thus concerns a titanium dioxide pigment containing a titanium dioxide core, covered sequentially with a layer of zirconium hydroxide or oxyhydroxide followed by a layer of titanium hydroxide or oxyhydroxide, then a layer of a phosphate and silica coprecipitate, and finally a layer of aluminum oxyhydroxide.
For the entire description, the different layers covering the titanium dioxide present a general thickness of between 50 and 100 Å. These layers can be discontinuous, surrounding the titanium dioxide more or less evenly.
The pigment according to the invention is routinely covered with:
0.5 to 1.5 wt-% zirconium hydroxide or oxyhydroxide, expressed as ZrO
2
,
0.05 to 1 wt-% titanium hydroxide or oxyhydroxide, expressed as TiO
2
,
0.2 to 1.5 wt-% phosphate, expressed as P
2
O
5
,
0.2 to 1.5 wt-% silica, expressed as SiO
2
,
2 to 4 wt-% aluminum oxyhydroxide, expressed as Al
2
O
3
,
the percentages being expressed as wt-% in ratio to the titanium dioxide core.
The invention also concerns a process for treating the surface of this titanium dioxide pigment. The process includes the following steps:
an aqueous suspension of titanium dioxide pigments is formed;
in a first step, a layer of zirconium hydroxide or oxyhydroxide is precipitated on the surface of the pigment;
in a second step, a layer of titanium hydroxide or oxyhydroxide is precipitated on the surface of the pigment;
in a third step, a layer of a phosphate and silica are coprecipitated on the surface of the pigment;
in a fourth step, a layer of aluminum oxyhydroxide is precipitated on the surface of the pigment;
the pigment is recovered from the suspension.
The process, then, consists of forming an initial layer of zirconium hydroxide or oxyhydroxide or oxyhydroxide directly on the surface of the pigment, followed by a second layer of titanium hydroxide or oxyhydroxide, then a third layer that is a phosphate or silica coprecipitate, and lastly a layer of aluminum oxyhydroxide.
According to the invention procedure, one starts with an aqueous suspension of titanium dioxide pigments containing titanium dioxide, the majority of which are preferably in rutile form. This suspension may be formed by any method known in the profession, as for example sulfate or chlorine processes.
The concentration of titanium dioxide pigments in this suspension varies routinely between 100 and 500 g/l.
This dispersion may possible contain a dispersant in order to disperse and stabilize it. It can be obtained specifically by grinding a titanium dioxide dispersion with the aid of the said dispersant. The dispersant may be selected from among the following: amino 2-methyl 2-propanol 1; potassium or sodium tetrapyrophosphate; potassium or sodium hexametaphosphate; polymer alkaline salts; or polyacrylic acid copolymers such as ammonium salts or polyacrylic acid sodium. In the event dispersants with a phosphate base are used, they may be present generally in a concentration of 0.1 to 0.5 wt-% in ratio to the titanium dioxide weight, expressed as P
S
O
5
.
The surface treatment process is generally performed at a temperature greater than 60° C. This temperature is maintained for the entire process, but one may also simply raise the temperature of the original dispersion above 80° C. then continue the treatment without a heat source.
The first treatment step consists of depositing a layer of zirconium hydroxide or oxyhydroxide onto the surface of the pigment through precipitation.
During this first step, a layer of zirconium hydroxide or oxyhydroxide is routinely precipitated from a compound that can be hydrolyzed from zirconium chosen from among zirconium sulfate, zirconium orthosulfate, zirconium chloride, or zirconium oxychloride.
The amount of hydrolyzable zirconium compound introduced during this first step is generally between 0.5 and 1.5 wt-% in ratio to the titanium dioxide core to be treated, expressed as ZrO
2
, and preferably between 0.2 and 1.5%.
The second treatment step consists of depositing a layer of titanium hydroxide or oxyhydroxide onto the surface of the pigment of precipitation.
During this second step, a layer of titanium hydroxide or oxyhydroxide is routinely precipitated from a compound that can be hydrolyzed from titanium chosen from among titanium chloride, titanium oxychloride, or titanium sulfate.
The amount of hydrolyzable titanium compound introduced during the second step generally comprises between 0.05 and 1 wt-% in ratio to the titanium dioxide core to be treated, expressed as TiO
2
.
To obtain precipitation of hydroxides, the first two steps are performed at a pH routinely between 4 and 6, preferably 5. The pH can generally be controlled by the addition of an acid and/or a base such as sulfuric acid, hydrochloric acid or acetic acid, and soda or potassium.
The third processing step consists of depositing a layer of a phosphate and silica coprecipitate onto the surface of the pigment by precipitation.
During this third step, a layer of a phosphate and silica coprecipitates are routinely precipitated from compounds that can be hydrolyzed from phosphorus and silicium chosen from among:
phosphoric aci
Guez Anny
Steiner Caroline
Bell Mark L.
Faison Veronica F.
Kalow & Springut LLP
Millennium Inorganic Chemicals, S.A.
LandOfFree
Titanium dioxide, preparation and use does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Titanium dioxide, preparation and use, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Titanium dioxide, preparation and use will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2547349