Document ZnL9vNax3dKjbNBoBK8Znj6M0
BROOKES & MARTIN
CHARTERED PATENT AGENTS
TRADE MARK AGENTS
EUROPEAN PATENT ATTORNEYS
RICHARD C. MARTIN, M.A.Camt am.
r ec eiv ed
DAVtO C. WOODCRAFT, .8a.,lCMtJ
CfttC E.BARNARO, C.Rn o ,M.1.R,E., C.Dift A.F, JOHN F, SYMONDS, LL.B.Lena, SOLICITOR
MAR 2^ 199U
JOHN H. BLAKE, B.SC.,{Ch c m>
HUGH R. WRIGHT, ma o mh . PETER C. SANDERS. B.Se.
DJ
DONALD J. ATTFIELO, B-S.C.CeM.M.R.S.C.(BIRM|NGHAM)
RECEIVEDASSISTED BY!
TIMOTHY M,A.RICKARD, a..FM.D,
GRAHAM F. MATTHEWS, B AnC-EMO. F.I.E.E Co n s u l t a n t ) H. NICHOLAS MATTHEWS, Hinar. T.M. A.(QbJ43ULTANT) GEOFFREY E. BROOME (c o n s u l t a n t
MAR 2 0 1990
Ornce Ma n a g e r - A. J. JELLY ACCOUNTS-MRS C. OLSIN<~T`
^p a t e n t r e c o r d s
CENTER
v
Mr. David J. Gould E.I. DU PONT DE NEMOURS AND COMPANY Legal Department, Patent Records Center 1007 Market Street Wilmington, Delaware 19898 U.S.A.
e l k 287541
TELEPHONES (Ol) 242 963* FACSIMILE (Ol) 831 0588 LDX 318
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OUR REF YOUR REF
DCW/VSW
15 March 1990
Dear David,
European Patent Application No Your reference : CH-1370_________
J
f87 303 682.6
I am pleased to report that the above application has been
accepted and I enclose a copy of the notice of acceptance under
Rule 51(4).
I also enclose a copy of the text of the
application in the form in which the EPO propose to grant the
application. This corresponds with the form of the application
as amended in January of this year.
We have a term of four months expiring on 8 July 1990 for making any last minute voluntary amendments to the application.
If I do not hear from you by 8 June 1990. I will indicate approval of the present text proposed for grant.
Yours sincerely.
DAVID CT WOODCRAFT
FILE CHECKED
Enel:
APR 9 1990
TUNBRIDGE WELLS: I BOYNE PARK. TUNBRIDGE WELLS, KENT. TN4 GEL. TL.(O602) 510600 TELEX 957078 FACSIMILE (OG02) 510666 BIRMINGHAM: PRUDENTIAL BUILDINGS, 5 ST. PHILIP'S PLACE. BIRMINGHAM, B3 2AF. TEL (0211236 6262 TELEX 3353BI FACSIMILE (021) 2001473 MUNICH: 15 ZWEIBRUCKENSTRASSE, 3 000 MUNICH 22. TEL (069} 22 20 IQ
N 30925
Europaisches Patentamt
Eui^fean Patent Om&s
Generaldirektion 2 Directorate General 2
Office europden des brevets
Direction generate 2
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rWoodcraft, David Charles
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G-BANDE BSETAGHE
Datum/Date
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LJ
Zeichen/RefJFtef
DCH/CH-137 0
Anmeldung Nr,/Application No./Demande n//Patent Nr./Patent No./Brevet n
87303682.6-* /
AnmelderiAppllcantfDemandeur/tPatentinhaber/Proprietorfntulalre
i,I. .DU PGKX DE KEfUOUES AED COHPAHI
COMMUNICATION UNDER RULE SI (4) EPC
You are hereby informed that the Examining Division intends to grant a European patent on the basis of the above application with the text and drawings as indicated below:
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of the published Mtent application
received on
_2~jL...... with letter of..
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of the published patent application
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With the following amendments to the abovS^mentioneq documents
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A copy of the relevant documents is enclosed.
The title of the invention in the three official languages of the European Patent Office, the international patent classification, the designated Contracting States and the registered name of the applicant are shown on the attached EPO Form 2056.
You are requested to state your approval of the text specified above within four months of this notification. Failure to do so will result in refusal of the application under Article 97 (1) EPC (Rule 51 (5) EPC).
Further information concerning the acceptability of amendments or the filing of a separate set of claims for one or more designated Contracting States that have entered a reservation under Article 167 (2) (a) EPC will be found in the Guidelines for Examination in the EPO, C-VI, 4.8 to 4.10 and 15.1.2 to 15.1.4 (July 1987).
Enclosures: EPO Form 2056 /.SW... copies
.-infant
ormalities Officer, Tel.: (089) 2399
Registered letter EPO Form 2004.110.87
N 30925.01
DUP050449386
EUROPAISCHES PATENTAMT
EUROPE) PATENT
OFFIC^P
OFFICE EUROPEEN DES BREVETS
/
Generaldirektion 2 Directorate General 2 Direction Generals 2
Woodcraft, David Charles BROOKES & MARTIN High Holborn House 52/54 High Holborn London, WC1V 6SE GRANDE BRETAGNE
n
dtstraQe 27 Munchen 2
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Zeichen/Ref./Ref.
DCW/CH-1370
Anmelder/Applicant/Demandeur//Paten!lnhaber/Proprletor/Titulaire
E.I. DU PONT DE NEMOURS AND COMPANY
Datum/Date
j
8. b. 3
Anmeldung Nr./Application No./Demande n* .//Patent Nr./Paient No./Brevel n1.
87303682.6-2112
For the intended grant of a European patent, (1) the title of the invention in the three official languages of the European Patent Office, (2) the International Patent Classification and (3) the de signated Contracting States and the applicant's registered name, address and country of residence or principal place of business are set out below.
(1)
- Titandioxid-Pigment, beschichtet mit durch Boroxid modifizierten Siliziumoxiden - Titanium dioxide pigment coated with boria-modified silica - Bioxyde de titane pigmentaire revetu de silice modiflee par de l'oxyde de bore
(2) CLASS STRING: C09C1/36, C09C3/06
(3) BE-DE-ES-FR-GB-NL E.I. DU PONT DE NEMOURS AND COMPANY 1007 Market Street Wilmington Delaware 19898/US
EPO FORM 2056 06.82 (Annex to EPO Form 2004)
7006030 08/06/88
DUP050449387
87303682.6
CH-1370
''
' /I; TIrT.IlB /'I 71 -i
:
Titanium DioxideiPigment- Coate,d wi^tW ^oria^Modi^fifed 'S-ilica 5 BACKGROUND OF THE INVENTION^
The present invention relates generally to coated Ti02 particles for use as pigments, and particularly to Ti02 particles having densified silica coatings. 3.0 Ti02 has a high refractive index for its density, which renders it a superior pigment for use in coatings, e.g., paints. HoweWg, TiOj is photoactive; exposure to ultraviolet radiation"*results in generation
of free radicals.on the surface of Ti02 particl^. 15 Thus, where a TiOj pigment is employed in a paint
exposed to sunlight, free radicals are generated which can migrate to the film-forming component of the paint, resulting in coating degradation or failure.
Therefore, minimizing free radical migration 20 is desireable in order to provide lightfast and stable
pigments for coating use. A widely-used approach to the
problem of providing lightfastness involves coating Ti02 particles with a layer of densified silica. The following patent references disclose conventional silica 25 coating densification techniques.
Werner, V. S. Patent 3,437,502, discloses Ti02 pigment having high opacity and dispersibility, which is obtained by applying a dense silica coating to Ti02 followed by topcoating with alumina. The silica coating 30 is applied by increasing the pH of a slurry of TiOj particles to above 7. A predetermined quantity of sodium silicate is then added to the slurry, resulting
in a rise in pH of the slurry to above 8, generally above 11. The pH is then gradually reduced over a 35 period of several hours by addditon of dilute acid, and
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the resulting silica-coated particles are cured at pH 6.0 to 7.5, at 60 to 100C, for 30 minutes to several hours. The resulting product is then coated with alumina.
West, U. 5. Patent 4,125,412, discloses preparation of durable Ti02 pigments by slurrying silica-coated Ti02 particles at pH 9 to 10.5 while maintaining slurry temperature at 80 to 100C.
European Patent Application 73,340 describes a similar method for coating Tio2 particles with amorphous dense silica prior to topcoating with alumina. Silica is applied by adding a soluble silicate to a Ti02 slurry at a temperature of at least 85C and at a pH of from 9.8 to 10.1. The slurry is then neutralized in at least three neutralization steps by addition of acid.
Common to the teachings of the foregoing references is a requirement for relatively high temperatures and high alkalinity during the silica densification step. An extremely lightfast white pigment for use in paint systems can be made by depositing 4-6 weight percent amorphous dense silica on rutile Ti02 pigment. To coat the base Ti02 pigment with this quantity of dense silica requires several hours at 85-90C, during which mineral acids are used to precipitate silica from Na2Sio3. This high temperature coating operation requires use of steel tanks, since less costly fiberglass tanks are not rated for use in the 85-90C temperature range. Methods for providing dense coatings of more than 4 weight percent silica at lower temperatures, e.g., 65-60C, to allow use of fiberglass tanks, would be of significant interest to the Ti02 pigment industry.
It has now been found that codeposition of B202 with Si02 provides dense silica coatings at process temperatures which permit use of fiberglass slurry tanks. The boria-containing pigments resulting from
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this process are highly lightfast, and exhibit excellent gloss and dispersibility.
SUMMARY OF THE INVENTION
5 The present invention provides a pigment consisting essentially of Ti02 particles bearing coatings comprising Si02 and B2o3. In a Process aspect, the present invention provides a process for preparing Tio2 particles bearing coatings of boria-modified
10 silica, comprising: (a) forming an aqueous slurry of rutile Ti02
at a temperature from about 65C to about 90C; (b) adjusting pH of the slurry to the range
7-10.5; 15 (c) adding a predetermined quantity of a
solution comprising Na2Si03 and B203, under conditions which maintain silicate and boria ions in solution;
(d) gradually lowering pH of the slurry to. 20 about 7.5-8.5 by addition of acid, thereby
depositing a coating of silica and boria; and (e) curing the resulting coated pigment at a
temperature from about 65C to about 90C for a period of at least 15 minutes. 25
DETAILED DESCRIPTION OP THE INVENTION In accordance with the present Invention,
B2O3 is codeposited with Si02 on Ti02 particles, providing lightfast, durable pigments. The Ti02 30 particles making up the pigments bear dense silica coatings, yet are produced at temperatures significantly lower than those required by other silica densification processes capable of providing dense silica coatings at greater than 4 weight percent. 35 In practice, silica/boria layers are codeposited from a master solution of Na2Si03 and
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Na2B2C>4. A standard acid solubility test can be to measure effectiveness of coating densification. in addition to enhanced densification of Si02 in the presence of B203, an imPcovement in pigment brightness 5 is provided.
The Ti02 used to prepare the pigment of the invention can be of the conventional rutile variety, prepared by either the chloride or sulfate process.
The amount of silica or silica topcoated with 10 alumina which the particles bear as coatings can be
varied depending primarily upon the pigment's intended use. Generally, the silica coatings will constitute from 2-10% of the total pigment weight, and an alumina topcoat, if present, will constitute 0.5-5% of the total 15 weight of the particles. Preferably, the silica coating constitutes 4-8% of the total weight of the pigment particles. Preferably, the alumina topcoat, if present, constitutes 1-4% of the total weight.
The amount of alumina the particles bear as 20 coatings, expressed as percent by weight, is calculated
by first determining the alumina content of the coated pigment by ion plasma spectroscopy. The alumina content of the uncoated rutile Ti02 is similarly determined, and the alumina content attributable to the coating is 25 determined by computing the difference between coated and uncoated alumina contents.
The pigment of the present invention can be prepared from an aqueous slurry containing 200-450 grams per liter Ti02- This slurry is brought to 65-90C and 30 is held at that temperature throughout the preparation procedure. The slurry is adjusted to pH 7-10.5, and a sufficient quantity of solution containing Na2Si03 and Na2B204, or, separate solutions of Na25i03 and Na2B20^, is added to provide a coating of the desired composition 35 and weight. Upon addition of the Na2Si03 and Na2B204 solution(s), pH of the slurry increases to about 11.
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Generally, slurry pH must be maintained above about 10 to maintain silicate and boria ions in solution.
Generally, the weight and composition of the coatings to be deposited will be determined by the 5 composition of the master Na2Si03/Na2B204 solution, the quantity added to the slurry containing Ti02, and quantity of TiC>2 in the slurry. For Ti02 slurries containing 400 g/L 7102, about 40-S0 mL of a master aqueous solution, containing 400 g Si02 equivalent and 10 40 g B203 equivalent per liter, should be added per liter Ti02 slurry to provide coatings approximating 5% of pigment weight. The compositions of the coating solutions can be varied as required to provide variations in coating weight and composition. 15 The coatings applied to Ti02 particles in accordance with the present invention can contain from 60-95 percent by weight Si02 and 0.5-30% by weight B203, based upon coating weight. Preferably, coatings will contain 80-90 percent by weight Si02 and 2-20 percent by 20 weight B2<>3.
Upon addition of the coating solutions, the pH of the Ti(>2 slurry will rise to the range 10.5-11.5. Over a period of 2-4 hours, 15% aqueous HC1 or other mineral acid is added to gradually decrease slurry pH to 25 about 8.0. As acid is added, Si02/B203 will be deposited and densified on the surfaces of the Ti02 particles. After all acid is added, the pigment should be cured at 65-90C for 30 minutes.
Xf desired, alumina can be precipitated on 30 silica/boria coated Ti02 particles by adding enough
sodium aluminate to the slurry, at a temperature from about 50-90C, to provide a concentration of about 2-8% by weight of the Ti02. Acid, normally sulfuric or hydrochloric, is added at the same time to maintain the 35 pH of the slurry within the range 6-9 as the alumina is precipitated. After addition of aluminate is complete,
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the slurry is allowed to cure, with continuous stirring, for 15-30 minutes.
The resulting pigment is then separated from the liquid by filtration or centrifugation, washed with 5 water, and dried.
Coating compositions can be prepared with the pigments of the invention in conventional ways, e.g., by blending the pigment with a film-forming component and a liquid carrier. 10 The following examples illustrate particular aspects of the present invention. In the examples, all parts and percentages are by weight and all degrees are Celsius unless otherwise indicated.
Example 1 15 In a large plastic vessel equipped with
stirring apparatus and a pH probe, 9000 parts water are mixed with 3000 parts rutile Ti02.
The resulting slurry is heated to 75, and the pH is adjusted to about 7.5 by addition of NaOH. 400 20 parts of an aqueous solution containing 400 parts Si02 equivalent (as Na2Si03) and 40 parts B23 equivalent (as Ha2B204) per 1000 parts water are added. The pH of the resulting mixture is then determined, and sufficient 15% aqueous HCl is added, over a period of about 3 hours, to 25 reduce the slurry pH to about 8.0. After all HCl has been added, the slurry is cured for 30 minutes at pH 8.0 and 75.
The resulting coating, which constitutes about 5.5% by weight of the total pigment, contains Si02 and 30 B202 in a ratio by weight of about 90:10.
A coating of 2.5% hydrous alumina is then deposited on the pigment by simultaneous gradual addition of 200 mL NaAl02 solution (containing NaAl02 equivalent to 400 g Al203 per liter solution} and HCl, 35 such that the pH of the slurry is continuously maintained from about 7.0 to about 7.5.
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The resulting coated pigment is cured by holding for about 30 minutes at ambient temperature and pH 7.5. The pigment is then filtered from the slurry, washed free of salts with water, and air-dried. The 5 pigment is then micronized, using 3 lbs. superheated steam per lb. pigment. The resulting pigment is suitable for use in paint systems where lightfastness is required.
Example 2 10 In this series of experiments, several batches
of pigment were prepared to evaluate the effect of codeposition and various processing temperatures upon acid solubility. Generally, acid solubility is inversely related to chalk-fade resistance for Ti02 15 pigments.
The pigments described below were prepared by procedures substantially similar to that described in Example 1, above, except that processing temperatures were varied as indicated in Table 1, below. Acid 20 solubilities were determined as follows.
10 ml> 66% sulfuric acid is added to a test tube containing a magnetic stirring bar, and the tube is placed in an aluminum heating block and heated to 175. A 0.2000 g pigment sample is added to the tube, and 25 digested for 1 hour with stirring. At the conclusion of the digestion period, the tube containing the pigment sample is cooled by pouring the acid mixture into a beaker of ice, and the residue in the tube and beaker is washed with distilled water. The pigment residue in the 30 tube and beaker is collected in a 100 mL volumetric flask, the volume made up to 100 mL by addition of distilled .water, and the contents mixed thoroughly. The contents of the volumetric flask are then filtered, and 10 ml. of the resulting filtrate are added to a 25 mL 35 volumetric flask, to which 2 mL 20t hydrogen peroxide, and sufficient 10% sulfuric acid to make 25 mL, are
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added. The resulting solution is allowed to stand one hour. Absorbance of the solution is 'then read at 400 nm
using a 10 ns cell path. Soluble Ti02 is determined by
reference to a previously prepared spectrophotometric
5 curve obtained by measurement of samples containing known quantities of dissolved TiOj.
Table 1
Acid Solubility; (% dissolved TiOQ
10 Processing
Temp. (C)
Coating Composition;
100% SiO.,
9o% SiO^/16%
90 80 15 70 65
0.11 0.27 3.34 6.0
0.10 0.12 0.17 0.22
Example 3 A mill base is made by mixing
20
Figment of Example 1
387 parts
alkyd resin
(Syntex 3145j
Celanese Coatings Co.) 149.6 parts
25 n-butanol xylol
9.4 parts 79 parts.
This mixture is sand ground, and then the sand is filtered from the mill base. A paint is made by 30 mixing 100 parts of the mill base with the following:
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xylol
1.4 parts
alkyd resin
(Syntex 3145;
5 Celanese Coatings Co.) 71.8 parts melamine resin solution
(Cymel 248-8, 55%
solids, American
Cyanamid Co.)
38.5 parts.
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