CA1287472C

CA1287472C - Method for producing a flaky material

Info

Publication number: CA1287472C
Application number: CA000531000A
Authority: CA
Inventors: Kunio Saegusa
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 1986-03-14
Filing date: 1987-03-03
Publication date: 1991-08-13
Anticipated expiration: 2008-08-13
Also published as: US4882133A; JPS62213833A; EP0236952A2; DE3774592D1; JPH0683781B2; EP0236952A3; EP0236952B1; KR870008936A

Abstract

ABSTRACT OF THE DISCLOSURE:
A method for producing flaky materials useful for improving, for example a spreadability and luster of cosmetics and paints or improving mechanical charac-teristics of plastics, which comprises coating the liquid sol of metallic compounds onto a smooth surface to form a coated film; solidifying the said film into gel by means of heating, pH control, hydrolysis or vaporization-removal of a part of the dispersion medium; shrinking the volume of the said film by further vaporization-removal of the dispersion medium from the film; and then scraping off the flaky material from the smooth surface.

Description

1 The present invention relates to a method ~or producing flaky inorganic compounds. ~lore particularl~, it relates to a method for producing ~laky materlalæ
easily and in large amoun~s from the lic~llid ~ol o~
metallic compounds.
Various flaky inorganic materials are so far well known. For example, flaky titanium oxide, flaky alumina, etc. are used, as incorporated in cosmetics and paints, to improve the spreadability and luster thereof, or they are used, as incorporated in plastics, for improvement in the mechanical properties thereof, other objects, etc. Like this, they are finding many applications.
There is known a method for producing the flaky material of titanium compounds by making the film of the compounds attached to a smooth substrate and removing the substrate by dissolution, crushing, etc. (Japanese Patent Publication No. 4731/1955). This method, however, has defects that operation is troublesome because of a necessity to dissolve the substrate, and also that it is difficult to obtain flaky materials having a uniform thickness so that to prepare the materials of the same siæe is very difficult.
There is also proposed a method for producing flaky materials by coating an organic solvent solution ~2~72 l of titanium alkoxide or titanium tetrachloride onto a smooth surface and crac~ing the ormed film by t~e action of steam (U.S. Patent Nos. 2,941,895 and 3,071,4B2).
Flaky inorganic materials composed mainly of titanium compounds can be obtained by these methods, but ~his method has defects that it is impossible to reco~er all the titanium compounds ag flaky materials, and b~$i-1e~;
that ~laky materials obtained in this manner are irregular in size and easy to take irregwlar curly forms.
In order to overcome the foregoing defects, there is proposed a method of coating an organic solvent salution of titanium compounds onto a substrate heated to a high temperature ~Japanese Patent Publication No.
6424/1970). This method, however, has a defect that vaporization and boiling make the generation of extreme irregularity in thickness easy, and therefore that it is very difficult to control the thickness and size.
As described above, in the conventionally well-known methods for producing flaky materials, materials and equipments cost too much to produce cheap flaky materials.
An object of the present invention is to provide a method for producing flak~ inorganic materials which, as compared with the conventionally proposed methods, is capable of using even cheap materials, superior in mass-productivity by simple equipments and operations, and besides produces homogeneous flaky materials.

.... . . . ..

lZ~74~2 According to -the presen-t invention there i~ provided a method Eor producing flaky materials which comprises coa-tirlg a smooth surface with an aqueolls liquid sol o compounds, in a dis-persion medium wherein said compounds are selected from t~s y~oup consisting oE oxideæ and hydroxide~ of one or more met~ls hav:inc3 a vcl:Lenc~ oE 2 or IOOre and b~:Longing to G.~oup :L:CIa, LVA and LVb ~
the Periodic Table and silica to form a coated film; sol-idiEying the film into gel by means of removal of -the dispersion medium by vaporization or by means of adjusting the pH; shrinking the volume of -the said gel by fur-ther vaporization of the dispersion medium from the gel -to produce flaky material; and then scraping the flaky material off the smooth surface.
For the metal of metallic compounds used in the present invention, -there may be given divalent or more-valent metals, preferably metals belonging to Groups IIIa, IVa or IVb of the periodic table, more preferable one or more members selected from the group consisting of aluminum, silicon, titanium, zirconium and tin. Specifically, there are given aluminum compounds such as "` ~287~72 2571~-~7~

alumina, aluminum hydroxide; .silicon compounds such ag silica;
titanium compounds such as titania, ti-tanium hydroxide; zirconium compounds such as zirconium oxide, zirconium hydroxidei arld -t.in compounds such as tin 02ide, tin hydroxide.
These me-tAllic compounds are a liquid or solid At rOOln temperAture. Since they should be a l:Lquid sol at the time o~
use, they are dispersed :In .su:Ltabl.e d:ispers.Lon med:La ~uch a~
water, organic solvents, etc. The sols of metal oxides or metal hydroxides and intermediate state of from metal hydroxides to metal oxides are , ~ ,5.
i ;~

128?~ '7;~
~ 5 1 used because such sols can be yelled ~ m~rel~
vaporiza~ion-removing the dispersion medium, as de~crib~d later~
The dispersion medium used va~ies wi~h the kind of metallic compounds, but the followings are pre~erably used; Water, alcohols ~e.g. methanol, ethanol), aliphatic hydroc rbons ~e.y~ hexan~, d~cane, cyclohexane), aroma~ic hydroca~bons ~e.g. tolu~ne, xylene), ketones (e.g. acetone), and mlxed systems of these solvents.
The concentration ~f metallic compou~d sols varies also with the kind of metallic compound, being not particularly limited. When the concent~ataon is too low, however, the amount o~ dispersion medium to be vaporized becomes large, being not economical. While when the concentration is too high, processability becomes poor. Conse~uently, the sols are gene~ally used in a concentxation o~ from about 2 to about 50 wt.~.
Hereupon, of the commercially available aqueous sols, silica sols include for example ~udox ~S-40 (a trade name of E.I. du Pont Co.), etc., and alumina sols include for example Alumina sol 100 ~a trade name of Nissan Kagaku Kogyo ~o.), etc. Further, as disperse systems in organic solvents, ~ethanol silica sol ~a trade name o~ Nissan Kagaku ~ogyo Co.), etc. are known.
For the preparation of these sols, for example silica sols, the following methods are know~: Ion-:` ?, -- 5 --~Z87~7;Z

1 ~xchange of water glass, neutralization of water glas~with an acid, electro-dialysis of water glass, hydrolysis of ethylsilicate, etc~ Also, for the preparation oE
alumina sols, hydrolysis o hydrolyzable compound~ such as aluminum acetate by means such as heating, etc is well known ~For details, refer to Science o~ no~el industrial materials, Silica and alumina (colloidal products), pp. 59 - 1~7 ; Ch~m:ical handbook ( thi~xd re~lsed edition), Application, pp. 132, edited by Nippon Kagaku-kai].
Further, when special sols are required, theycan be prepared by the well-known methods, for example, described in the foregoing literatures.
For stabilizing the sols, addition of proper pH-regulators, for example small amounts of hydrochloric acid, caustic soda or the like is effective.
In order to make the thickness of coating film uniform, the followings may be added: Polymeric substances such as polyols, ethyl cellulose, etc ;
high-boiling organic substances such as butyl cellosolve, glycerin, etc.; nonionic or anionic surfactants, etc.
The well-known coloring matters comprising iron compounds, nickel compounds, vanadium compounds, chromium compounds, manganese compounds, etc. may also be added.
Metal oxide sols thus prepared are coated onto a smooth surface.
The material of the smooth surface varies 74~

l with the condition of use, but materials resistant to the corrosive action of the sols are preferred. For such materials, there are given for example ceramic materials (e.g. glass, enamel), metallic materials (e g.
stainless steel, aluminum), polymeric materials (e.g polyester, polyimide, nylon, polypropylene), etc.
The shape of the smoo~h su~ac~ .in~lud~ t plates, roll~, belts, sheets, ~ilm~, etc.
When belts, sheets or ~ilms are used, it is desirable -to support them on supporting rolls or apply a definite tension to them in order to cause them to keep a smooth surface. For this purpose, the belts, sheets and films need to have enough strength to resist the tension and enough stiffness not to show extreme defor-mation under the tension. Consequently, the thicknessof the belts, sheets and films is properly determined depending upon the material, and those having a required mechanical strength are U5 ed.
For the purpose of mass production, it is desirable to use endless belts or bulky rolls of sheet or film while unrolling them.
For coating the smooth sur~ace, the well-known coating methods such as dipping, spraying, brushing, etc.
may be used.
2S The mechanism of flaking is not yet clear enough, but the followings may b~ considered: The coating film turns thin film by the removal of the dispersion medium from the metallic compound sol forming the coating film; gelation and then solidi~icaticn of ~2 5374~Z

1 the thin film occur by ~urther removal o~ the dispersion medium and reaction with ~ater, acids, alkalis, etc~; an~
further vaporization of the disperse medium shrinks the volume of the solidified thin film to crack the ~ilm, and thus the thin film turns flake.
Vaporization-removal of the dispersion rnedium from the coating ~ilm ma~ be carri~d out by previowsly heating the smooth surface itself, and when the smooth surface has the form of a roll, it may be carried out by heating the roll by passing a heating medium through the inside thereof. When belts, sheets or films are used, the vaporization-removal may be carried out by passing them through a heating zone wherein the liquid film of . the sol is directly heated by hot air, electric or infrared heaters, high-frequency waves, etc. The heating temperature depends upon the vaporizability of the dispersion medium to be removed, so that it cannot be datermined indis-criminately. Generally, however, a temperature of from room temperature to about 250C is suitable. For example, 2~ in the case of highly vaporizable dispersion media, it suffices to merely blow a room-temperature gas against the coating film.
Depending upon the kind of sol, the sol is gelled by merely heating. For examples o such sol, there are titania sol and alumina sol.
Depending upon the kind of sol, the sol is gelled by merely vaporization-removing the dispersion medium in this manner to turn flake on the substrate.

For examples of such sol, there are given sols of me-tal 7~7Z

1 oxides ~e.g. silica, alumina) or metal hydroxides and intermediate state of from metal hydroxides to rnetal oxides. When the sol is acidic or alkaline, it is yelled by reaction with an alkali or an acid respectively. The alkali used includes ye~eral-purpose alkalis such as ammonia, amines, caustic alkalis, etc. The ~cid use~
includes mineral acids, organic acids, SOx, NOX, etc. In carxying out this gelation with these aLkalis or acids, when the alkalis or acids are of a gaseous form or mist form, the gelation is carried out by blowing them against the thin film. While when the alkalis or acids are contained in solvents, the gelation is carried out by dipping the thin film in the solution together with the substrate or applying the solution to the thin film.
The amount and concentration of these acids or alkalis vary with the kind of metallic sol and desired reaction rate, etc. Generally, however, when the sol is stable in a pH range of from 3 to 4, it suffices to add the alkali of enough amount to make the pH of the sol from 9 to 10 after previous check by the beaker test, etc.
While when the sol is stable in a pH range of from 9 to 10, it suffices to add the acid of enough amount to make the pH
of the sol from 3 to 4 similarly after previous check.
Gelation of the sols of metal alkoxide polymers is carried out by hydrolysis with aqueous solutions containing an acid or alkali. Simultaneously with the gelation, the solvent is vaporized.
In stripping the flaky material from the smooth ~74~/2 1 surface, when the substxate is a hard material such as metals, ceramics, etc., me-thods such as mechanical scraping with a scraper, stripping ~y ultrasonic waves, etc. are used. When the substrate is made o soft polymeric materials, stripping by ultrasonic wa~es is used, and when the smooth surface is flexible, stripping by bending the smooth surface i9 preferabl~ used.
The flakes o~ me~allic, compou~ds thus produced are transparent and have a high luster, so that they can be used even as such. However, depending upon uses, they are finished into inal products by calcination at a temperature of from about 200 to about 1100C, preferably from 500 to 900C.
This calcination converts the metallic compounds to mainly oxides. The flaky inorganic materials produced by the present invention are from about 0.01 to about 10 ~m in thickness. However, depending upon intended uses, they are suitably crushed and used in a length of from about 1 to about 100 ~m in general.
The method of the present invention described above in detail has advantages such that: Flaky metallic compounds which have optical effects (e.g. refractive index, luster) equivalent to those of the conventionally well-known supported-type pigments, can be stripped from the substrate very easily, and have a freely controllable very uniform size and a very smooth surface can be produced on simple equipments and by easy operation using cheap metallic compound sols.

10 -- , lZ1~472 1 The flaky inorganic materials obtained by the method of the present invention can be used as Lustrous pigments for nail enamels, enamel, leather products, cosmetics, etc.; as nacreous pigments used as a ~iller for food-packing ~lastics; for coating ex-terior mekal~
of automobiles; for producing pearl-gla~ed buttons by casting o~ unsatura~ed polyester resin~, etc.
Al~o, because the ~laky inorganic material~ o the present invention have such characteristics that the content of impurities is low and various physical properties of flake such as size, thickness, refractive index, dielectric constant, etc. can be controlled industrially, flaky titanium oxide, flaky alumina, flaky silica, etc. are preferably used as extenders for lS cosmetics and fillers for paints and plastics. In addition to this, because of a further characteristic that the flaky materials have a good free-flowing property, flaky alumina is preferably used as powdery materials for producing tubes of sodium lamp, and flaky titanium oxide is preferably used as powdery materials for producing ceramics products such as condensers, porcelain, etc.
Further, flaky oxides can preferably be used as carriers for catalysts.
Example 1 383 Grams (1 mole~ of zirconium tetrabutoxide was uniformly dissolved in 847 g of butanol, and 90 g (5 moles) of water was mixed with this solution to ,, :. .,.",. .: .,: ,;

." 12~7~.~t72 l prepare a sol. This,sol was taken as a base liquid.
Thls liquid was placed in a breaker, and slide glass was dipped therein and pulled up at a rate o~ 75 cm/min. The slide glass was dried in an air bath at 90C for 30 minutes, and flakes on the slide glass were scraped o~f by means of a scraper and calcined at 900C
for 30 minukes. The ~laky zirconla thus obtained wa~
0.8 ~ in thickness and from 10 to 30 ~ in size.
Example 2 Titanyl sulfate and sulfuric acid were mixed to prepare a solution having a titanium concentration of 0.25 mole/l and a sul~uric acid concentration of 0.9 mole/l. This solution was mixed wlth a 25 wt.~ caustic soda solution with through stirring. The pH of the resulting solution was adjusted to 6 with an aqueous dilute caustic soda solution, and stirring was continued for 24 hours. Thereafter, sodium sulfate was removed by repeating centrifugation and dilution with water, and the titania concentration was adjusted to 2.8 wt.~.
The titania sol solution thus obtained was taken as a base liquid.
This sol solution was placed in a beaker, and slide glass was dipped therein and pulled up at a rate of 250 cm/min. The slide glass was dried in an air bath at 90C for 30 minutes, and flakes on the ~lide glass were scraped off by means of a scraper and calcined at 900C for 30 minutes. The flaky titania thus obtained was from 8 to 40 ~ in size and about 0.5 ~ in thickness.

1~7~ 2 1 Example 3 246 Grams (1 mole) of tributoxyaluminum was dissolved in 302 g of butanol, and 90 g (4 moles) o water was added and reacted to prepare a butanol sol of aluminurn hydroxide. This sol was taken as a base liquid This sol was applied to a stalnl~ss ateel roll of lO cm in diarneter rotating a~ 5 rpm and dri~d, an~
flakes on the roll were recovered by means of a scraper.
The flakes were then calcined at 1200C to obtain flaky alumina of from 5 to 40 ~ in size and of 1 ~ in thickness.
Example 4 260 Grams (1 mole) of stannic tetrachloride was dissolved in 2 kg of water, and a solution of 160 g (4 moles) of caustic soda in 1 kg of water was added dropwise thereto to prepare a tin oxide sol. Sodium chloride was removed from the sol by repeating centrifu-gation and dilution with water and then ion-exchange.
The resulting sol was taken as a base liquid.
This liquid was placed in a beaker, and slide glass was di~ped therein and pulled up at a rate of 75 cm/min. The slide ~lass was dried in an air bath at 90C for 30 minutes, and flakes on the slide glass were scraped off by means of a scraper and calcined at 900C
for 30 minutes. The flaky tin thus obtained was 0.3 in thickness and from 5 to 20 ~ in size.
Example 5 A silica sol (Ludox ~ HS-40; produced by E.I~
du Pont Co~) was diluted with water so that the silica ~LZ~7~7~

1 concentration was 20%, and the resulting sol was taken as a base liquid. This liquid was placed in a ~at, and a roll of 10 cm in diameter was dipped therein at room temperature and rotated at a peripheral speed of 2 m/min. Thereater, a 120C air was blown against the base liquid attached to the roll at a ~low rate o~
1 m/qec. Thus, waker contained in the film of the base liquid was removed, and the gel-form film of silica wa.s formed on the roll. On further removing water, volume shrinkage occurred to form cracks ir. the film and the film turned silica flakes. The flakes were scraped off by means of a scraper made of Swedish steel.
The flakes obtained were calcined at 600C to obtain flaky silica of from 10 to 25 ~ in size and of 2 ~ in thickness.
Example 6 A silica sol with methanol as a dispersion -~ ~ medium (trade name, Methanol silica sol; produced by Nissan Kagaku Kogyo Co.) was adjusted so that the silica concentration was 5%, and the resulting sol was taken as a base liquid. This liquid was flaked on the same equipment as used in Example 5. The flakes ob~ained were calcined at 600C.
Ihus, flaky silica of from 3 to 25 ~ in size and of 0.5 ~ in thickness was obtained.
Example 7 An alumina sol (Alumina sol 100; produced by Nissan Kagaku Kogyo Co.) was diluted with water so that ~rac~

~213~4'7Z
1 the alumina concentration was 10~, and the resulting sol was taken as a base liquid. This liauid was placed in a beaker, and slide galss was dipped therein and pulled up at a rate of 60 cm/min. The slide glass was drîed in an air bath at 90C for 30 minutes, and ~làkes on the slide glass were scraped of~ by means o~ a scraper and calcined at 900C ~or 30 minutes.
~ le ~laky alumina thus obtained was ~rom 8 to 50 ~ in size and about 2 ~ in thickness.

- 15 ~

Claims

1. A method for producing flaky materials which comprises coating a smooth surface with an aqueous liquid sol of compounds in a dispersion medium wherein said compounds are selected from the group consisting of oxides and hydroxides of one or more metals having a valence of 2 or more and belonging to Group IIIa, IVa and IVb of the Periodic Table and silica to form a coated film; solidifying the film into gel by means of removal of the dispersion medium by vaporization or by means of adjusting the pH;
shrinking the volume of the said gel by further vaporization of the dispersion medium from the gel to produce flaky material; and then scraping the flaky material off the smooth surface.

2. A method according to Claim 1, wherein the metal of metallic compound sol is one or two members selected from the group consisting of silicon, aluminum, titanium, tin and zirco-nium.

3. A method according to Claim 1, wherein the dispersion medium is selected from the group consisting of water, alcohols and mixed systems thereof.

4. A method according to Claim 1, wherein the smooth sur-face is formed with a material selected from the group consisting of ceramic materials, metallic materials and polymeric materials.

5. A method according to Claim 1, wherein the smooth sur-face is formed with a material selected from the group consisting of glass, enamel, stainless steel, aluminum, polyester, polyimide, nylon and polypropylene.

6. A method according to Claim 1, wherein the smooth sur-face is shaped into a form selected from the group consisting of flat plates, rolls, belts, sheets and films.

7. A method according to Claim 1, wherein the coated film is formed with a method selected from the group consisting of dipping, spraying and brushing.

8. A method according to Claim 1, wherein the flaky mate-rial is scraped off with a method selected from the group consist-ing of mechanical scraping with a scraper, stripping by ultrasonic waves and bending of the smooth surface.

9. A method according to Claim 1, wherein the flaky material obtained is from about 0.01 to about 10 µm in thickness.