U.S. patent application number 13/505485 was filed with the patent office on 2012-08-30 for paper laminates comprising tungsten treated titanium dioxide having improved photostability.
This patent application is currently assigned to E.I. Dupont De Nemours and Company. Invention is credited to John Davis Bolt, Eugene Michael McCarron, III, Charles David Musick.
Application Number | 20120216976 13/505485 |
Document ID | / |
Family ID | 43568707 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120216976 |
Kind Code |
A1 |
Bolt; John Davis ; et
al. |
August 30, 2012 |
PAPER LAMINATES COMPRISING TUNGSTEN TREATED TITANIUM DIOXIDE HAVING
IMPROVED PHOTOSTABILITY
Abstract
This disclosure relates to a resin-impregnated, opaque,
cellulose pulp-based sheet comprising an inorganic particle,
wherein the inorganic particle comprises at least about 0.002% of
tungsten, based on the total weight of the inorganic particle, and
has a photostability ratio (PSR) of at least about 2, as measured
by the Ag.sup.+ photoreduction rate, and color as depicted by an L*
of at least about 97.0, and b* of less than about 4. The disclosure
also relates to paper laminates prepared from these
resin-impregnated, opaque, cellulose pulp-based sheets.
Inventors: |
Bolt; John Davis; (Kingston,
TN) ; McCarron, III; Eugene Michael; (Chadds Ford,
PA) ; Musick; Charles David; (Waverly, TN) |
Assignee: |
E.I. Dupont De Nemours and
Company
Wilmington
DE
|
Family ID: |
43568707 |
Appl. No.: |
13/505485 |
Filed: |
November 9, 2010 |
PCT Filed: |
November 9, 2010 |
PCT NO: |
PCT/US10/55902 |
371 Date: |
May 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61384892 |
Sep 21, 2010 |
|
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|
Current U.S.
Class: |
162/164.6 ;
162/164.3; 162/164.7; 162/165 |
Current CPC
Class: |
D21H 27/30 20130101;
D21H 17/37 20130101; D21H 17/67 20130101; D21H 21/285 20130101;
D21H 17/48 20130101; D21H 17/52 20130101; D21H 17/53 20130101 |
Class at
Publication: |
162/164.6 ;
162/164.3; 162/164.7; 162/165 |
International
Class: |
D21H 17/57 20060101
D21H017/57; D21H 17/56 20060101 D21H017/56; D21H 17/48 20060101
D21H017/48; D21H 17/36 20060101 D21H017/36; D21H 17/37 20060101
D21H017/37; D21H 17/52 20060101 D21H017/52; D21H 17/55 20060101
D21H017/55 |
Claims
1. A resin-impregnated, opaque, cellulose pulp-based sheet
comprising an inorganic particle, wherein the inorganic particle
comprises at least about 0.002% of tungsten, based on the total
weight of the inorganic particle, and has a photostability ratio
(PSR) of at least about 2, as measured by the Ag.sup.+
photoreduction rate, and color as depicted by an L* of at least
about 97.0, and b* of less than about 4.
2. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 1 wherein the inorganic particle is an inorganic metal oxide
or mixed metal oxide particle.
3. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 2 wherein the inorganic metal oxide particle is titanium
dioxide.
4. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 further comprising a resin.
5. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 4 wherein the resin is a thermosetting resin.
6. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 5 wherein the thermosetting resin is a polymer of diallyl
phthalate, epoxide, urea formaldehyde, urea-acrylic acid ester.
copolyester, melamine formaldehyde, melamine phenol formaldehyde,
dicyandiamide-formaldehyde, urethane, unsaturated polyester,
curable acrylic and phenol formaldehyde or mixtures thereof.
7. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein the amount of the titanium dioxide in the
resin-impregnated, opaque, cellulose pulp-based sheet is up to and
including about 60 wt. %, based on the total dry weight of the
cellulose pulp-based sheet prior to resin impregnation.
8. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 7 wherein the amount of the titanium dioxide in the the
resin-impregnated, opaque, cellulose pulp-based sheet ranges from
about 20 to about 40 wt. %, based on the total dry weight of the
cellulose pulp-based sheet prior to resin impregnation.
9. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein tungsten is present in the amount of at least about
0.004%, based on the total weight of the inorganic particle.
10. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein the photostability ratio (PSR) is at least about
4.
11. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein L* is at least about 98.
12. resin-impregnated, opaque, cellulose pulp-based sheet of claim
3 wherein b* is less than about 3.
13. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein tungsten is added to the titanium dioxide particle
by cooxidation or post-oxidation.
14. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein tungsten is added to the titanium dioxide particle
from an alloy comprising tungsten.
15. The resin-impregnated, opaque, cellulose pulp-based sheet of
claim 3 wherein the titanium dioxide particle further comprises
alumina in the amount of about 0.06 to about 5% based on the total
weight of the titanium dioxide particle.
16. A paper laminate prepared from a resin-impregnated, opaque,
cellulose pulp-based sheet comprising an inorganic particle,
wherein the inorganic particle comprises at least about 0.002% of
tungsten, based on the total weight of the inorganic particle, and
has a photostability ratio (PSR) of at least about 2, as measured
by the Ag.sup.+ photoreduction rate, and color as depicted by an L*
of at least about 97.0, and b* of less than about 4.
17. The paper laminate of claim 16 further comprising a dried
overlay.
18. The paper laminate of claim 16 wherein the inorganic particle
in the coating composition is an inorganic metal oxide or mixed
metal oxide particle.
19. The paper laminate of claim 18 wherein the inorganic metal
oxide particle is titanium dioxide.
20. The paper laminate of claim 16 wherein tungsten is present in
the amount of at least about 0.004%, based on the total weight of
the inorganic particle.
21. The paper laminate of claim 19 wherein the titanium dioxide
particle further comprises alumina in the amount of about 0.06 to
about 5% based on the total weight of the titanium dioxide
particle.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Disclosure
[0002] The present disclosure relates to resin-impregnated, opaque,
cellulose pulp-based sheet and paper laminates, and more
particularly to resin-impregnated, opaque, cellulose pulp-based
sheet and paper laminates prepared therefrom comprising
tungsten.
[0003] 2. Background of the Disclosure
[0004] Paper laminates are in general well-known in the art, being
suitable for a variety of uses including table and desk tops,
countertops, wall panels, floor surfacing, tableware and the like.
Paper laminates have such a wide variety of uses because they can
be made to be extremely durable, and can be also made to resemble
(both in appearance and texture) a wide variety of construction
materials, including wood, stone, marble and tile, and can be
decorated to carry images and colors.
[0005] Typically, the paper laminates are made from papers by
impregnating the papers with resins of various kinds, assembling
several layers of one or more types of laminate papers, and
consolidating the assembly into a unitary core structure while
converting the resin to a cured state. The type of resin and
laminate paper used, and composition of the final assembly, are
generally dictated by the end use of the laminate.
[0006] Decorative paper laminates can be made by utilizing a
printed decorative paper layer as upper paper layer and various
support paper layers in the unitary core structure. The decorative
paper is typically highly opaque so that the appearance of the
support layers below the decorative paper does not adversely impact
the appearance of the decorative paper laminate. A decorative paper
is also known as a decor paper.
[0007] To achieve required abrasion, scuff, and mar resistance,
typically, a separate overlay is used as the top layer for paper
laminates. An overlay usually comprises the same resin as the one
that is used for the resin impregnated decorative paper.
[0008] A paper laminate has been made by applying to the outer
layer of a composite structure a mixture of an additive amount of a
fluorourethane additive, available from E. I. du Pont de Nemours
and Company and a melamine resin slurry. Paper laminates may be
produced by both low- and high-pressure lamination processes.
[0009] Various methods can be employed to provide paper laminates
by low-pressure lamination. For example, a single opening, quick
cycle press can be used where one or more resin-saturated paper
sheets are laminated to a sheet of plywood typically with a 1A
face, particle board, or fiberboard.
[0010] In a high-pressure lamination process, a melamine overlay
and a melamine resin-impregnated decor paper are usually laminated
onto a phenolic sheet, which provides additional mechanical
support. For example, a "continuous laminator" can be used where
one or more layers of the resin-saturated paper are pressed into a
unitary structure as the layers move through continuous laminating
equipment between plates, rollers or belts. One or two laminated
sheets (continuous web or cut to size) may be pressed onto a
particle or fiberboard, etc. and a "glue line" used to bond the
laminated sheet to the board. Single or multiple opening presses
may also be employed which contain several laminates.
[0011] The decor paper in such paper laminates generally comprises
a resin-impregnated, cellulose pulp-based sheet, with the pulp
being based predominantly on hardwoods such as eucalyptus,
sometimes in combination with minor amounts of softwood pulps.
Pigments (such as titanium dioxide) and fillers are added in
amounts generally up to and including about 45 wt. % (based on the
total dry weight prior to resin impregnation) to obtain the
required opacity. Other additives such as wet-strength, retention,
sizing (internal and surface) and fixing agents may also be added
as required to achieve the desired end properties of the paper. The
resin can be a thermosetting resin selected from the group
consisting of a polymer of diallyl phthalate, epoxide, urea
formaldehyde, urea-acrylic acid ester. copolyester, melamine
formaldehyde, melamine phenol formaldehyde,
dicyandiamide-formaldehyde, urethane, curable acrylic, unsaturated
polyester and phenol formaldehyde and mixtures thereof.
[0012] Titanium dioxide pigments are prepared using either the
chloride process or the sulfate process. In the preparation of
titanium dioxide pigments by the vapor phase chloride process,
titanium tetrachloride. TiCl.sub.4, is reacted with an oxygen
containing gas at temperatures ranging from about 900.degree. C. to
about 1600.degree. C., the resulting hot gaseous suspension of
TiO.sub.2 particles and free chlorine is discharged from the
reactor and must be quickly cooled below about 600.degree. C., for
example, by passing it through a conduit, i.e., flue, where growth
of the titanium dioxide pigment particles and agglomeration of said
particles takes place.
[0013] It is known to add various substances, such as silicon
compounds and aluminum compounds, to the reactants in order to
improve the pigmentary properties of the final product. Aluminum
trichloride added during the process has been found to increase
rutile in the final product, and silicon tetrachloride that becomes
silica in the final product has been found to improve carbon black
undertone (CBU), particle size and pigment abrasion. It is useful
to be able to add elements to the titanium dioxide particles.
However, the process and materials to be added to improve
properties of the titanium dioxide particles may be hazardous.
[0014] One method of adding elements to the surface of a particle
is by impregnation with a solution containing the element. This is
difficult to do with pyrogenically prepared metal oxide particles
since the properties of the pyrogenically produced metal oxides
change upon contact with a liquid medium.
[0015] A need exists for a low cost approach for preparing paper
laminates comprising pyrogenically prepared metal oxide particles,
particularly titanium dioxide particles, comprising elements such
as tungsten that provide improved photostability without changing
the color of the product.
SUMMARY OF THE DISCLOSURE
[0016] In a first aspect, the disclosure provides a
resin-impregnated, opaque, cellulose pulp-based sheet comprising
inorganic particles, typically inorganic metal oxide or mixed metal
oxide particles, more typically titanium dioxide (TiO.sub.2)
particles, comprising at least about 0.002% of tungsten, more
typically at least about 0.004% of tungsten, and still more
typically at least about 0.01% of tungsten, and most typically at
least about 0.05% of tungsten, based on the total weight of the
inorganic particles, wherein the inorganic particles, have a
photostability ratio (PSR) of at least about 2, more typically at
least about 4, and still more typically at least 10, as measured by
the Ag.sup.+ photoreduction rate, and color as depicted by an L* of
at least about 97.0, more typically at least about 98, and most
typically at least about 99.0, and b* of less than about 4, and
more typically less than about 3. Typically the inorganic
particles, more typically inorganic metal oxide or mixed metal
oxide particles, and most typically titanium dioxide particles,
comprising tungsten may further comprise alumina in the amount of
about 0.06 to about 5% of alumina, more typically about 0.2% to
about 4% of alumina, still more typically about 0.5% to about 3% of
alumina, and most typically about 0.8% to about 2%, based on the
total weight of the inorganic particles.
[0017] In a second aspect, the disclosure provides a paper laminate
comprising a resin-impregnated, opaque, cellulose pulp-based sheet,
wherein the resin-impregnated, opaque, cellulose pulp-based sheet
comprises inorganic particles, typically inorganic metal oxide or
mixed metal oxide particles, more typically titanium dioxide
(TiO.sub.2) particles, comprising at least about 0.002% of
tungsten, more typically at least about 0.004% of tungsten, and
still more typically at least about 0.01% of tungsten, and most
typically at least about 0.05% of tungsten, based on the total
weight of the inorganic particles, wherein the inorganic particles,
have a photostability ratio (PSR) of at least about 2, more
typically at least about 4, and still more typically at least 10,
as measured by the Ag.sup.+ photoreduction rate, and color as
depicted by an L* of at least about 97.0, more typically at least
about 98, and most typically at least about 99.0, and b* of less
than about 4, and more typically less than about 3. Typically the
inorganic particles, more typically inorganic metal oxide or mixed
metal oxide particles, and most typically titanium dioxide
particles, comprising tungsten may further comprise alumina in the
amount of about 0.06 to about 5% of alumina, more typically about
0.2% to about 4% of alumina, still more typically about 0.5% to
about 3% of alumina, and most typically about 0.8% to about 2%,
based on the total weight of the inorganic particles. The paper
laminate further comprises a dried overlay.
BRIEF DESCRIPTION OF THE DRAWING
[0018] FIG. 1 is a schematic illustration showing the process for
preparing titanium dioxide (TiO.sub.2).
DETAILED DESCRIPTION OF THE DISCLOSURE
[0019] This disclosure relates to a paper laminate comprising a
resin-impregnated, opaque, cellulose pulp-based sheet, wherein the
resin-impregnated, opaque, cellulose pulp-based sheet comprises
inorganic particles, typically inorganic metal oxide or mixed metal
oxide particles, more typically titanium dioxide (TiO.sub.2)
particles, comprising at least about 0.002% of tungsten, more
typically at least about 0.004% of tungsten, and still more
typically at least about 0.01% of tungsten, and most typically at
least about 0.05% of tungsten, based on the total weight of the
inorganic particles. These inorganic particles have a
photostability ratio (PSR) of at least about 2, more typically at
least about 4, and still more typically at least 10, as measured by
the Ag.sup.+ photoreduction rate, and color as depicted by an L* of
at least about 97.0, more typically at least about 98, and most
typically at least about 99.0, and b* of less than about 4, and
more typically less than about 3. Typically the inorganic
particles, more typically inorganic metal oxide or mixed metal
oxide particles, and most typically titanium dioxide particles,
comprising tungsten may further comprise alumina in the amount of
about 0.06 to about 5% of alumina, more typically about 0.2% to
about 4% of alumina, still more typically about 0.5% to about 3% of
alumina, and most typically about 0.8% to about 2%, based on the
total weight of the inorganic particles, and the paper laminate
made therefrom.
[0020] The paper laminate typically comprises a dried overlay and a
base sheet wherein at least one of the dried overlay and the base
sheet can comprise a resin-impregnated, opaque, cellulose
pulp-based sheet. The base sheet can comprise a phenolic core or
engineered wood comprising substrate such as particle or fiber
board. The dried overlay and the base sheet can be laminated
together utilizing a low pressure or a high pressure lamination
process. The paper laminate may further comprise components to make
it abrasion resistant.
Resin-Impregnated, Opaque, Cellulose Pulp-Based Sheet:
[0021] The resin-impregnated, opaque, cellulose pulp-based sheet is
also known in the industry as Decor paper. The cellulose pulp used
in the pulp-based sheet comprises pulp predominantly from hardwoods
such as eucalyptus, sometimes in combination with minor amounts of
softwood pulps. Pigments (such as titanium dioxide, more typically
rutile titanium dioxide comprising tungsten and in addition
alumina) and fillers can be added in amounts generally up to and
including about 60 wt. %, more typically about 20% to about 40%,
(based on the total dry weight prior to resin impregnation) to
obtain the required opacity. Other additives such as wet-strength,
retention, sizing (internal and surface) and fixing agents may also
be added as required to achieve the desired end properties of the
Decor paper. Resins used to impregnate the papers are typically
thermosetting resins. Examples of suitable thermosetting resins
include, without limit, polymers of diallyl phthalate, epoxide,
urea formaldehyde, urea-acrylic acid ester. copolyester, melamine
formaldehyde, melamine phenol formaldehyde,
dicyandiamide-formaldehyde, urethane, unsaturated polyester,
curable acrylic and phenol formaldehyde and mixtures thereof. In
some situations, the resin used to impregnate this decorative sheet
may contain abrasive inorganic particles selected from the group
consisting of aluminum oxide or silicon oxide and mixtures
thereof.
[0022] This resin impregnated, opaque, cellulose pulp-based sheet
may contain a print, pattern design or solid color and these are
generated using known techniques. Some such techniques include
various well-known analog and digital printing methods to impart
desired coloration and designs as required for the particular end
use. Analog printing methods such as screen printing are
particularly suitable for large runs and repetitive patterns.
Digital printing methods such as inkjet printing are particularly
suitable for short runs and customized patterning.
[0023] Some suitable resin-impregnated, opaque, cellulose
pulp-based sheets are available from Mead Westvaco (11013 West
Broad Street, Glen Allen, Va. 23060), as, solid colored Duoply.RTM.
papers or printbase Primebase.RTM. papers.
Dried Overlay
[0024] The dried overlay can be wear resistant and the dried
overlay can be used in both low pressure and high pressure
lamination processes to provide improved resistance to abrasive
wear. The dried overlay can be of varying thickness and can be low
opacity, more typically substantially optically transparent.
[0025] The dried overlay can comprise a thermosetting resin or can
be a resin-impregnated, opaque, cellulose pulp-based sheet as
described above. The thermosetting resin used in the dried overlay
can be subjected to a pre-cure step prior to the lamination process
which also includes a curing step. The term "pre-cure" is used to
mean that the cure of the resin particles has been advanced either
to the maximum degree possible or at least to a stage of cure where
the melt viscosity of the cured resin particles is sufficiently
high to prevent these particles from melting and flowing under
usual laminating conditions and thus undesirably saturating into
the decor paper or other resin-impregnated, opaque, cellulose
pulp-based sheet, during the lamination step to form the paper
laminate.
[0026] The resins are typically thermosetting resins. Examples of
suitable thermosetting resins include, without limit polymer of
diallyl phthalate, epoxide, urea formaldehyde, urea-acrylic acid
ester. copolyester, melamine formaldehyde, melamine phenol
formaldehyde, dicyandiamide-formaldehyde, urethane, curable
acrylic, unsaturated polyester and phenol formaldehyde and mixtures
thereof. More typically the resin used in the dried overlay is a
formaldehyde-melamine polymer.
[0027] Especially when the dried overlay is not a resin
impregnated, opaque, cellulose pulp-based sheet, the resin used to
impregnate the resin-impregnated opaque cellulose pulp-based sheet
typically has the same or substantially the same index of
refraction as the resin in the dried overlay. More typically, the
resin used in the dried overlay is the same resin used to
impregnate the resin-impregnated opaque cellulose pulp-based
sheet.
[0028] The dried overlay further comprises a binding material,
selected from a group consisting of microcrystalline cellulose,
carboxyl methyl cellulose, sodium alginate and mixtures
thereof.
[0029] Optionally, the dried overlay further comprises mineral
particles, usually ranging is size from about 20 to about 35 .mu.m,
comprising aluminum oxide, silicon oxide, or the mixture thereof,
to further improve abrasion resistance.
[0030] The dried overlay can be transparent after curing.
[0031] The dried overlay can be made by processes well known in the
paper making industry, by forming a suspension of the resin and the
binding material together and drying the suspension to form the
dried overlay. Optionally additional ingredients can be employed
such as the mineral particles and opacifier, if the dried overlay
is to be opaque.
[0032] The dried overlay can also be made by applying a thick layer
of pre-cured thermosetting resin particles to the decorative sheet,
as disclosed in U.S. Pat. No. 5,545,476.
[0033] Some suitable dried overlays, specifically the
melamine-containing overlays are commercially available form
Wilsonart International of Fletcher North Carolina.
Other Components of the Paper laminate
[0034] The paper laminate can comprise other components such as a
phenolic core sheet, engineered wood sheet, such as particle board
or fiber board or plywood. The phenolic core sheet typically
comprises a plurality of phenolic resin-impregnated Kraft papers
which are laminated together. Glues can also be included usually as
seam sealants, for example, a hot wax-oil emulsion. Other suitable
glues are made of acrylic polymer, polyvinylacetate, and
polychloroprene and commercially available from Wilsonart
International of Fletcher N.C.
Treated Particle:
[0035] It is contemplated that any inorganic particle, and in
particular inorganic particles that are photoactive, will benefit
from the treatment of this disclosure. By inorganic particle it is
meant an inorganic particulate material that becomes dispersed
throughout a final product such as a polymer melt or coating or
paper laminate composition and imparts color and opacity to it.
Some examples of inorganic particles include but are not limited to
ZnO, ZnS, BaSO.sub.4, CaCO.sub.3, TiO.sub.2, Lithopane, white lead.
SrTiO.sub.3, etc.
[0036] In particular, titanium dioxide is an especially useful
particle in the processes and products of this disclosure. Titanium
dioxide (TiO.sub.2) particles useful in the present disclosure may
be in the rutile or anatase crystalline form. They are commonly
made by either a chloride process or a sulfate process. In the
chloride process. TiCl.sub.4 is oxidized to TiO.sub.2 particles. In
the sulfate process, sulfuric acid and ore containing titanium are
dissolved, and the resulting solution goes through a series of
steps to yield TiO.sub.2. Both the sulfate and chloride processes
are described in greater detail in "The Pigment Handbook", Vol. 1,
2nd Ed., John Wiley & Sons, NY (1988), the teachings of which
are incorporated herein by reference. The particle may be a pigment
or nanoparticle.
[0037] By "pigment" it is meant that the titanium dioxide particles
have an average size of less than 1 micron. Typically, the
particles have an average size of from about 0.020 to about 0.95
microns, more typically, about 0.050 to about 0.75 microns and most
typically about 0.075 to about 0.50 microns. By "nanoparticle" it
is meant that the primary titanium dioxide particles typically have
an average particle size diameter of less than about 100 nanometers
(nm) as determined by dynamic light scattering that measures the
particle size distribution of particles in liquid suspension. The
particles are typically agglomerates that may range from about 3 nm
to about 6000 nm.
[0038] The titanium dioxide particle can be substantially pure
titanium dioxide or can contain other metal oxides, such as
alumina. Other metal oxides may become incorporated into the
particles, for example, by co-oxidizing, post-oxidizing,
co-precipitating titanium compounds with other metal compounds or
precipitating other metal compounds on to the surface of titanium
dioxide particles. These are typically hydrous metal oxides. If
co-oxidized, post-oxidized, precipitated or co-precipitated the
amount of the metal oxide is about 0.06 to about 5%, more typically
about 0.2% to about 4%, still more typically about 0.5% to about
3%, and most typically about 0.8% to about 2%, based on the total
weight of the titanium dioxide particles. Tungsten may also be
introduced into the particle using co-oxidizing, or post-oxidizing.
If co-oxidized or post-oxidized at least about 0.002 wt. % of the
tungsten, more typically, at least about 0.004 wt. %, still more
typically at least about 0.01 wt. % tungsten, and most typically at
least about 0.05 wt. % may be present, based on the total particle
weight.
Process for Preparing Treated Titanium Dioxide Particles
[0039] The process for producing titanium dioxide particle
comprises: [0040] a) mixing of chlorides of, titanium, tungsten or
mixtures thereof; wherein at least one of the chlorides is in the
vapor phase; [0041] (b) oxidizing the chlorides of, titanium,
tungsten or mixtures thereof; and [0042] (c) forming titanium
dioxide (TiO.sub.2) particles comprising at least about 0.002% of
tungsten, more typically at least about 0.004% of tungsten and
still more typically at least about 0.01% of tungsten, and most
typically at least about 0.05% of tungsten, based on the total
weight of the titanium dioxide particles. These titanium dioxide
particles have a photostability ratio (PSR) of at least 2, more
typically at least 4, and still more typically at least 10, as
measured by the Ag.sup.+ photoreduction rate, and color as depicted
by an L* of at least about 97.0, more typically at least about 98,
and most typically at least about 99.0, and b* of less than about
4, and more typically less than about 3. Typically the titanium
dioxide particles comprising tungsten further comprise alumina in
the amount of about 0.06 to about 5% of alumina, more typically
about 0.2% to about 4% of alumina, still more typically about 0.5%
to about 3% of alumina, and most typically about 0.8% to about 2%,
based on the total weight of the titanium dioxide particles.
[0043] Methods known to one skilled in the art may be used to add
tungsten to the titanium dioxide particles. In one specific
embodiment, tungsten may be added to the titanium dioxide particle
from an alloy comprising tungsten. As shown in FIG. 1, the alloy 11
and chlorine 12 are added to the generator 10. This reaction can
occur in fluidized beds, spouting beds, packed beds, or plug flow
reactors. The inert generator bed may comprise materials such as
silica sand, glass beads, ceramic beads, TiO.sub.2 particles, or
other inert mineral sands. The alloy comprising aluminum, titanium
or mixtures thereof and tungsten, 11, reacts in the generator 10
according to the following equations:
2Al+3Cl.sub.2.fwdarw.2AlCl.sub.3+heat
Ti+2Cl.sub.2.fwdarw.TiCl.sub.4+heat
W+3Cl.sub.2.fwdarw.WCl.sub.6+heat
Al.sub.12W+21Cl.sub.2.fwdarw.12AlCl.sub.3+WCl.sub.6+heat
[0044] The heat of reaction from the chlorination of the aluminum
or titanium metal helps provide sufficient heat to drive the
kinetics of the reaction between chlorine and one or more of the
other elements.
[0045] Titanium tetrachloride 17 may be present during this
reaction to absorb the heat of reaction. The chlorides formed
in-situ comprise chlorides of the tungsten and chlorides of
aluminum such as aluminum trichloride, chlorides of titanium such
as titanium tetrachloride or mixtures thereof. The temperature of
the reaction of chlorine with the alloy should be below the melting
point of the alloy but sufficiently high enough for the rate of
reaction with chlorine to provide the required amount of chlorides
to be mixed with the TiCl.sub.4.
[0046] Typical amounts of chlorine used in step (a) are about 0.4%
to about 20%, more typically about 2% to about 5%, by weight, based
on the total amount of all reactants. Typical amounts of titanium
tetrachloride are about 75% to about 99.5% added in step (a) and
(b), and more typically about 93% to about 98%, by weight, based on
the total amount of all reactants.
[0047] The reaction of chlorine with the alloy occurs at
temperature of above 190.degree. C., more typically at temperature
of about 250.degree. C. to about 650.degree. C., and most typically
at temperatures of about 300.degree. C. to about 500.degree. C. In
one specific embodiment where the metal is Ti the reaction occurs
at temperature of above 50.degree. C. (bp of TiCl.sub.4=136.degree.
C.), more typically at temperature of about 200.degree. C. to about
1000.degree. C., and most typically at temperatures of about
300.degree. C. to about 500.degree. C.
[0048] The chlorides formed in the in-situ step 13 flows into an
oxidation reactor 14 and titanium tetrachloride 15 is then added to
the chlorides, such that titanium tetrachloride is present in a
major amount. Vapor phase oxidation of the chlorides from step (a)
and titanium tetrachloride is by a process similar to that
disclosed, for example, in U.S. Pat. Nos. 2,488,439, 2,488,440,
2,559,638, 2,833,627, 3,208,866, 3,505,091, and 7,476,378. The
reaction may occur in the presence of neucleating salts such as
potassium chloride, rubidium chloride, or cesium chloride.
[0049] Such reaction usually takes place in a pipe or conduit,
wherein oxygen 16, titanium tetrachloride 15 and the in-situ formed
chlorides comprising chlorides of tungsten and chlorides of
aluminum such as aluminum trichloride, chlorides of titanium such
as titanium tetrachloride or mixtures thereof 13 are introduced at
a suitable temperature and pressure for production of the treated
titanium dioxide. In such a reaction, a flame is generally
produced.
[0050] Downstream from the flame, the treated titanium dioxide
produced is fed through an additional length of conduit wherein
cooling takes place. For the purposes herein, such conduit will be
referred to as the flue. The flue should be as long as necessary to
accomplish the desired cooling. Typically, the flue is water cooled
and can be about 50 feet (15.24 m) to about 3000 feet (914.4 m),
typically about 100 feet (30.48 m) to about 1500 feet (457.2 m),
and most typically about 200 feet (60.96 m) to 1200 feet (365.76 m)
long.
[0051] The following Examples illustrate the present disclosure.
All parts, percentages and proportions are by weight unless
otherwise indicated.
EXAMPLES
[0052] Photostability ratio (PSR) is the rate of photoreduction of
Ag+ by TiO.sub.2 particles without tungsten (control samples)
divided by the rate of photoreduction of Ag+ by the otherwise same
TiO.sub.2 particles comprising tungsten. The rate of photoreduction
of Ag+ can be determined by various methods. A convenient method
was to suspend the TiO.sub.2 particles in 0.1 M AgNO.sub.3 aqueous
solution at a fixed ratio of TiO.sub.2 to solution, typically 1:1
by weight. The suspended particles were exposed to UV light at
about 0.2 mW./cm.sup.2 intensity. The reflectance of visible light
by the suspension of TiO.sub.2 particles was monitored versus time.
The reflectance decreased from the initial value to smaller values
as silver metal was formed by the photoreduction reaction,
Ag.sup.+->Ag.sup.o. The rate of reflectance decrease versus time
was measured from the initial reflectance (100% visible reflectance
with no UV light exposure) to a reflectance of 90% after UV
exposure; that rate was defined as the rate of Ag.sup.+
photoreduction.
[0053] Color as measured on the CIE 1976 color scale, L*, a*, and
b*, was measured on pressed pellets of dry TiO.sub.2 powder.
Comparative Example 1
[0054] Titanium dioxide made by the chloride process comprising
1.23% alumina by weight and having an L*a*b* color index of (99.98,
0.60, 2.13) and a rate of Ag.sup.+ photoreduction of 0.0528
sec.sup.-1 was fired under flowing oxygen at 4.degree. C./min to
1000.degree. C. and held at temperature for 3 hours; furnace cooled
to 750.degree. C. and held at temperature for 1 hour; furnace
cooled to 500.degree. C. and held at temperature for 3 hours;
furnace cooled to 250.degree. C. and held at temperature for 3
hours; and finally furnace cooled to room temperature. After firing
the sample had an L*a*b* color index of (99.15, -0.45, 2.17) and a
rate of Ag.sup.+ photoreduction of 0.1993 sec.sup.-1.
Comparative Example 2
[0055] Titanium dioxide made by the chloride process comprising
0.06% alumina by weight and having an L*a*b* color index of (99.43,
-0.58, 1.36) and a photoractivity rate of 0.3322 was fired under
flowing oxygen at 4.degree. C./min to 1000.degree. C. and held at
temperature for 3 hours; furnace cooled to 750.degree. C. and held
at temperature for 1 hour; furnace cooled to 500.degree. C. and
held at temperature for 3 hours; furnace cooled to 250.degree. C.
and held at temperature for 3 hours; and finally furnace cooled to
room temperature. After firing the sample had an L*a*b* color index
of (97.71, -0.03, 1.89) and a photoactivity rate of 0.2229
sec.sup.-1.
Example 3
[0056] Titanium dioxide similar to that described in Comparative
Example 1 was well mixed with various amounts of ammonium
tungstate, (NH.sub.4).sub.10W.sub.12O.sub.415H.sub.2O, to give
samples having the W contents listed below. These samples were
fired as described in Comparative Example 1. After firing the
samples had L*a*b* color and photostability ratios (PSR) as given
in the following table:
TABLE-US-00001 W (wt. %) L* a* b* PSR 0.0 99.15 -0.45 2.17 1.0 0.34
99.00 -0.71 2.72 3.0 1.72 98.56 -0.82 3.17 10.4 3.44 98.41 -0.90
3.11 211.4
[0057] The increased incorporation of W clearly enhanced
photostability up to roughly a factor of 200 while the color was
only minimally affected.
Example 4
[0058] Titanium dioxide similar to that described in Comparative
Example 1 was impregnated via incipient wetness with various
amounts of ammonium tungstate,
(NH.sub.4).sub.10W.sub.12O.sub.415H.sub.2O, to give samples having
the W contents listed below. These samples were fired as described
in Comparative Example 1. After firing the samples had L*a*b* color
and photostability ratios as given in the following table:
TABLE-US-00002 W (wt. %) L* a* b* PSR 0.0 98.16 0.02 2.09 1.0 0.34
97.97 -0.02 2.53 2.2 1.72 97.52 -0.15 2.79 10.0 3.44 97.41 -0.53
3.34 67.4
[0059] The increased incorporation of W clearly enhanced
photostability up to roughly a factor of 67 while the color index
was only minimally affected.
Example 5
[0060] Titanium dioxide similar to that described in Comparative
Example 2 was well mixed with amounts of ammonium tungstate,
(NH.sub.4).sub.10W.sub.12O.sub.415H.sub.2O, to give samples having
the W contents listed below. These samples were fired as described
in Comparative Example 1. After firing the samples had L*a*b* color
and photostability ratios as given in the following table:
TABLE-US-00003 W (wt. %) W L* a* b* PSR 0.0 0.0 97.71 -0.03 1.89
1.0 0.34 1x 97.73 -0.21 2.19 4.3 1.72 5x 97.18 -0.56 1.94 139.0
3.44 10x 97.03 -0.83 2.45 113.8
[0061] The increased incorporation of W clearly enhanced
photostability up to roughly a factor of 140 while the color index
was only minimally affected.
Comparative Example 6
[0062] Titanium dioxide similar to that described in Comparative
Example 1 was well mixed with various amounts of ammonium
molybdate, (NH.sub.4).sub.6Mo.sub.7O.sub.244H.sub.2O, to give
samples having the Mo contents listed below. These samples were
fired as described in Comparative Example 1. After firing the
samples had L*a*b* color and photostability ratios as given in the
following table:
TABLE-US-00004 Mo (wt. %) L* a* b* PSR 0.0 98.76 -0.37 2.48 1 0.18
94.08 -3.45 17.96 314.8 0.91 93.77 -4.47 30.45 no rate 1.83 91.89
-5.27 35.82 no rate
[0063] The increased incorporation of Mo clearly enhanced
photostability to the point where, at the higher Mo concentrations,
the photostability ratio could not be determined. However, the
material took on a decidedly yellow coloration clearly compromising
its use as a white pigment.
Comparative Example 7
[0064] Titanium dioxide similar to that described in Comparative
Example 1 was impregnated via incipient wetness with various
amounts of ammonium molybdate,
(NH.sub.4).sub.6Mo.sub.7O.sub.244H.sub.2O, to give samples having
Mo to Al atomic ratios of 0.1, 0.5, and 1.0 versus 0.0 for the
undoped control. These samples were fired as described in
Comparative Example 1. After firing the samples had L*a*b* color
and photostability ratios as given in the following table:
TABLE-US-00005 Mo (wt. %) L* a* b* PSR 0.0 97.79 -0.19 2.57 1.0
0.18 92.62 -3.61 24.15 862.3 0.91 92.66 -4.21 31.63 1188.0 1.83
90.74 -4.92 37.94 no rate
The incorporation of Mo clearly enhanced photostability to the
point where, at the highest Mo concentration, the photostability
ratio could not be determined. However, the material took on a
decidedly yellow coloration clearly compromising its use as a white
pigment.
Example 8
[0065] Whatman #1 filter paper is impregnated with a slurry
consisting of 10 wt. % of the dry titanium dioxide samples having W
contents as listed in Example 3 and a 50 wt. % aqueous solution of
Kauramin.RTM. 773 impregnating resin (melamine formaldehyde
powder). The impregnated paper is dried in a convection oven at
230.degree. F. Laminate lay-ups are constructed between two steel
caul plates. From the bottom up, the construction is as follows:
[0066] a) single overlay sheet (LK2050FK MELAMINE IMPREGNATED 20#
BASE WEIGHT, WHITE OVERLAY) [0067] b) single white backing sheet
(L2028050 MELAMINE IMPREGNATED 80# BASE WEIGHT, WHITE BACKER)
[0068] c) three sheets of Kraft paper (C99N5OCG PHENOLIC
IMPREGNATED 99# BASE WEIGHT, KRAFT PAPER) [0069] d) single white
backing sheet (see (b) above) [0070] e) two sheets of the Whatman
#1 filter paper impregnated with TiO.sub.2 slurry [0071] f) single
overlay sheet (see (a) above)
[0072] The laminate is formed using a Carver press heated to
300.degree. F. under a force of 36,000 pounds for six minutes.
* * * * *