CA1062985A

CA1062985A - Alumina dispersions

Info

Publication number: CA1062985A
Application number: CA235,603A
Authority: CA
Inventors: Mahlon R. Derolf
Original assignee: PQ Corp
Current assignee: PQ Corp
Priority date: 1973-07-30
Filing date: 1975-09-16
Publication date: 1979-09-25
Also published as: US3935023A

Abstract

ABSTRACT OF THE DISCLOSURE
Stable aqueous dispersions of alumina are formed at concentrations of A1203 of between 18% to 26% on a weight basis by dispersing alumina in a hydrochloric acid solution which is controlled at a temperature below the boiling point of the dispersion, where the A1203/HC1 parts by weight ratio is maintained between 53 and 66 pbw of A1203/1 pbw of HC1, in which the A1203 is provided at 18 to 26% of the total mixture and in which the pH is maintained at 3.5 to 4.2, and simultaneously agitating the mixture to obtain the desired dispersion. Such aqueous dispersions are stable for periods in excess of 6 months and can be used to increase the non-slip characteristics of paper to which it is applied.

Description

11629~35 This invention relates ~o processes for the preparation of stable aqueous dispersions of alumina, It has been'known ~or many years that the'application of dis- ;
persions of finely divided'silica or sols of silica to paper surfaces ~;
increases the friction between'those surfaces. More recently it has been found that the use of dispersions or aerosols of alumina increases friction even more and that such aerosol alumina is more strongly , ` ' attached to the paper so that the non-slip characteristics is maintained '' through three or four passes, even though less alumina is required. For ~ '~
instance, an uncoated paper may have an angle of repose of 29 to 35 in a standard slip testing device. The same paper, treated with a dispersion of colloidal silica may have an angle of repose of 39 to 41, and often better results may be obtained using a lower concentration of alumina as ; ~ ~
the treating liquid than is necessary for silica. These angles depend ' ''~ ' to a large degree on the particular paper employed. ' It is well known that aerosols of alumina are very expensive '' ' compared to sols or dispersions of finely divided alumina. Precipitated ~' " ' colloidal alumina or alumina gel, dispersed with strong acid at a pH of ' 3 is approximately equivalent to the aerosol alumina in performance, but it cannot be formed into disperions of above 10% A1203 which are stable ' for more than one week. These are not really satisfactory for commercial use. It has also been known to increase the stability of such dispersions '~
: . .
by partially removing the acid ions by ion exchange resins. These are also not sufficiently stable at concentrations above 16% A1203.
By a broad aspect of this invention, an improvement is provided ' in a process of forming an aq'ueous alumina dispersion comprising forming '" ' an aqueous solution of HCl and then adding alumina, the improvement ' comprising maintaining the ratio of A1203 to HCl in the dispersion at 53 to 66 pbw of A1203 per 1 pbw of HCl and the pH at 3.5 to 4.2, thereby to provide concéntrations of 18 to 26% A1203 on a weight basis having '' ~ ' stability for at least 6 months. ';
Thus, it has now been found that stable aqueous alumina ` ~

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,r~ 1~6Z9~5 dispersions can be formed at concen-tra~tions up -to 26% A1203 by preparing an aqueous sollltion of i-lCl and thell by adding to this solution, with vigorous mixing, suffici,en-t alumina -to form a dispersion having a concentration of 53 to 66 pbw of A1203 per pbw of HCl. The pH of an 18 to 26% dispersion whi,le preferably between 3.8 to 4.1 can range be-tween 3.5 -to 4.2. An 18%
dispersion will have a viscosity of 4 to 6 centipoises at 25C.
and a 26% dispersion will have a viscosity Or 5 to 7 centipoises at 25C.
By another aspect of this inven-tion, a process '~
is provided for preparing stable aqueous dispersions of alumina at concentra-tions of 18 to 26% A1203 on a weight basis, comprising: ,~
(1) preparing an aqueous solution of hydrochloric acid; (2) controlling the tempera-ture below the boiling poin-t of the ' dispersion; (3) maintaining -the pressure between 0.5 to 5 atmospheres; (4) adding alu~mina to the aqueous soluti'on such that the weight ra-tio of alumina to HCl is 53 to 66 parts alumina to 1 part HCl and the A1203 is 18 -to 26% of the -total mixture;
and the pH is maintained at 3.5 to 4.2 and (5) substantially simultaneously agitating the mixture to obtain -the desired dispersion; especially where the concen~-tration of A1203 is 54 to 65 pbw per 1 pbw of HCl; or where -the concentration of , ' '~
A1203 is 18% and the ratio of A1203 is 54 to 61 pbw of A1203 per 1 pbw of HCl; or where the concentration of A1203 is 26% ' , and the ratio of A1203 is 58 -to 65 pbw of A1203 per 1 pbw of HCl.
In another variant, the temperature is 20 - 80C.; ~ 'and in another, the pressure is a-tmospheric.
In yet another aspect, the alumina is introduced ^
in-to -the mix-ture in the form of alumina monohydrate; while in yet another aspect, the pH is between 3.5 and 4.2 and the . stability is greater than 6 months.

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6~985 - By another aspect of this inven-tion, a s-table aqueous dispersion of alumina is provided hav:ing a concentration of A1203 be-tween 18 and 26%, a ra-tio of A1203 to HCl of 53 to 66 .; :.-pbw of A1203 per 1 pbw of HCl and a pH of 3.5 -to 4.2, particularly with an A1203 concentra-tion of 18% and a ratio of A1203 -to HCl . :.
of 54 to 61 pbw of A1203 per 1 pbw of HCl wi-th a shelf life of 6 ~

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; . ~ `.. : ,'', ' ' ` ' ' : . ' ~ 2a-} ~~~------=' .',' ' ^ -- 106Z~35 `-to 12 months; or with an A1203 concentration of 26% A1203 and a ratio of A1203 to HCl of 58 to 65 p~w of A1203 per 1 pbw'of HCl with a shelf '~
life of 6 months; or having a pH of 3.8'to 4.1. i ' :'-By still another'aspect of this invention, a dried powder is '~
provided'having therein 53 to 66 pbw'A1203 per 1 pbw HCl prepared by drylng the dispersion under conditions that do not alter the A1203-HCl ~ ~ ' ratio. ` ' ' Mixing of the HCl solution and A1203 can take place at any temperature up to the boiling point of the dispersion, but for simpli- ' city of processing equipment, it is preferred to operate between 20 and '~' 80C. Pressure has no notable influence on the process, and while ' ' mixing between 0.5 and 5 atmospheres'is acceptable,'it is preferred to operate at atmospheric pressure.
When an 18% A1203 dispersion is desired as the end product, it has been found necessary to maintain an A1203 to HCl ratio of 54 to 61 ~ ' pbw of A1203 to 1 pbw of HCl. When it is desired to obtain a 26% A1203 ,! . .' :
dispersion, it has been found to be necessary to maintain an A1203 to HCl ratio of'58 to 65 pbw of A1203 to 1 pbw of HCl. When more than 66 ~' ' pbw A1203 are present per pbw of HCl, there is a tendency for the alumina ~'~
to be less dispersible yielding a product that is unsatisfactory. When "' ~ ' less than 53 pbw A1203 per pbw of HCl is utilized in the dispersion mix, ' the shelf life of the resulting product having at least 18% A1203 is ~!~
drastically limited; for example, a dispersion of 18% A1203 prepared s~
from a mixture having S0 pbw A1203 to pbw HCl will have a shelf life of ,. . .
only 20 days. '' The shelf life of this dispersion containing 18 to 26% A1203 when made from a mixture having the aforedescribed A1203jHCl'ratio will be a minimum of 6 months and can be over one year. ~'~
In general, this dispersion is diluted before use to 1 to 5% '' A1203, although much higher concentrations may be used.
Generally the application is 0.05 to 0.3 pounds of alumina ~ ' solids per 1000 square feet of paper or paperboard.
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1062~85 , ` ` . .... . .
For untreated bags or boxes7 wl~ich start to slip at 25, the angle may~be raised'to 40 before slippage if the surface'is treated '! - ' ; ' :
with at least 0~15 pounds of alumina per thousand square feet~ whereas the'use of colloidal silica usually requires'at least 0.3 pounds per ' ' ;
thousand square feet to achieve the'same value. '" ' This dispersion may be applied by known methods. The usual '~-' ' ' .... . ..
methods of application of prior art dispersions are the use of a sponge, ~ ''''' '-a felt, a contact roller or spraying. These methods of application are ~' ~
all suitable for the dispersions of aspects of this invention. ` ' ' ' ' If dispersions prepared according to the processes of aspects ~ ~ ' of the present invention should become dried on the apparatus used in application or on work areas, the dried material can be redispersed in water facilitating cleanup of such apparatus and areas. f'"' ' `,' ' It has further been found that dispersions of one of the " -; ' aspects of this invention wherein the ratio of Al203 to HCl is maintained ~' between 53 and 66 pbw Al203 per pbw of HCl can be dried and redispersed in water at a later time when ready for use. The drying can take place by any known procedure for re ving the water, as long as the conditions `
do not affect the pbw balance between A1203/HCl. Examples of suitable procedures of drying include tray drying, spray drying, double drum ~ '-drying, freeze drying and vacuum evaporation. Rotary dryeLs and fluid ''~' bed dryers are also suitable. An advantage of this drying process is ~' that the resulting powder can be more easily handled and stored than can ' the dispersion. The shelf life on redispersion is equal to that of the `~
original dispersion, i.e., greater than 6 months for the redispersed ' powder having 18 to 26% A1203 in the dispersion. The dispersion may be frozen and rethawed without notable deterioration to the dispersion when ~ -reliquefied. The advantage of freezing the dispersion is that this is a ~ ' procedure whereby the shelf life can be extended indefinitely. The time ~ ' 30 during which the dispersion is frozen does not cause any deterioracion ' and the 6 month minimum shelf life only begins to run when the material " ~' is thawed. A separation of some solids may occur during the freeze-thaw ' .~. " ~ , :

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1i6Z985 cycle; however, t~e dispersion can be returned to its original charac-teristic through Yigorous agitation~
The following examples describe in general the process of pre-paring these dispersions and their use on p~per. These examples are illustrative.
In the following examples, a form of alumina is used which is called "~lumina A". It has a particle si~.e in solution of 5 mu. This alumina contains 90% alumina monohydrate and 10% water by weight.
Impurities in this system total less than 0.9%. The surface area is by the BET method and is 150 to 250 square meters per gram.
EXAMæLE 1 In this example a 10% dispersion was prepared using the prior art procedure. Thus, an acid solution containing 0.8 pbw of concentrated .~r . " .
HCl (37%) and 89.2 pbw of water was prepared at a pH of 102. To this was added, with moderate agitation, 10 pbw of the "Alumina A" described above. Mixing was continued for 15 minutes. A stable dispersion was prepared which had a pH of 2.3 at one hour and stabilized at 3.3 in 24 hours. After 7 weeks, the dispersion was very viscous, but could be redispersed in water.

A dispersion containing 18% A1203 was prepared according to the process of an aspect of this invention as follows: 75.6 pbw of water were mixed thoroughly with 0.9 pbw HCl (37.5%) to form an aqueous acid solution. 25 parts of "Alumina A" was added slowly to this acidic solu-tion while vigorously agitating. The agitation was continued for 15 to 20 minutes after the addition of alumina was complete. The opaque disper-sion had a pH of 3.8 and the ratio of A1203/HCl on a parts by-weight ;
basis was 54/1. The viscosity of this dispersion is 5.4 centipoises at 25C. The dispersion is still stable after a period of 10 mon~hs storage at room temperature.
A dispersion was made by the same process with somewhat less acid at 18% A1203 and a pbw of A1203/HCl of 61/1. The pH of this _ 5 ~

--`` 11D6:;~985 dispersion was 4.05 and the Yiscosity at 25C. was 4.7 cps. The disper-sion was still stable after'one year storage at room temperature.
A dispersion was made by the same process at 18% A1203 and a ratio of A1203/HCl of 58/1. The'pH of this dispersion was 3.95 and the ', viscosity was 5.0 cps. The dispersion was still stable after 11 months storage at room temperature. '~
''EXAMPLR 3 '~ ' A dispersion was made according to the process of Example 2 '' ~ ' , with the following composition: 66.3 pbw of H20, 1.03 pbs HCl (37.5%) '' and 32.7 parts "Alumina A". The'opaque dispersion had a concentration ' ~' , of 25% Al203 and the A1203/HCl ratio was 65/1. The pH was 4.1 and the viscosity was 5.6 cps at 25C. The dispersion was still stable after 7 months storage at room temperature. , , Dispersions were also made at 25% A1203 with A1203/HCl ratios , of 63/1 and 58/1 by the process of Example 2. These opaque dispersions ~ , had pH values of 4.05 and 3.9 respectively. The viscosities were 5.9 and 6.6 cps at 25C. Both dispersions were still stable after 6 months ' storage at room temperature. ,", Slide angle tests were made of these products. These tests were carried out by the standard TAPPI Method 815su 72.
Paper was pre-conditioned at 73F. and 50% relative humidity.
The dispersions were diluted from 1 to 5% A1203 depending on the amount , ' of coating required, and this dilute dispersion of alumina was applied to the paper with a sponge. After coating, the treated paper was again , conditioned at 73F. and 50% relative humidity for 24 hours. Sections of the treated paper were cut'to fit the slide angle tester. The slide angle was measured according to the standard method by raising the tester ' ' ~' with a constant speed motor at a rate of 1.5 per second. The paper was ~,'~ ~!; , placed in cross-grained positiGn. The angle of inclination was observed ' ' at the point when the weight began to slide. The first two slides are ~ , run to precondition the surface and the third slide is the determined value.' - 6 - ,~

~ ~06298S
A colloidal silica as well as the dispersion prepared in this example were diluted to 2% solids, applied'to paper'and tested for slide ~ ,'' -angle as described above. The'slide angle determined with the colloidal silica was 34.5 while the slide angle with the dispersions of the ~`
example were between 36 and 37.5. It ~as found that these test samples , were coated with 0.1 pounds solids per 1000 square feet of paper surface. ',' ', Loadings on the paper surface were determined by measuring the amount of liquid pick-up for a given area of paper coated. `,'' r EXAMPLE 4 , A dispersion was made according to Example 2 with the following '~
composition: 64.9 pbw of water, 1.07 parts HCL (37.5%) and 34.0 parts ', ' , "Alumina A". The opaque dispersion had a concentration of 26% A1203 ~ ;
and the A1203/HCl ratio was 65/1. The pH was 4.1 and the viscosity was 5.7 cps. The dispersion was still stable after 5 months storage at ` ~
room temperature. s, , EXAMPLE 5 ', The dispersion of Example 2 was dried in a laboratory spray ~ ; ' '''' dryer with an inlet temperature of 370C. and an outlet temperature of 125OCD The resulting powder was totally redispersible and the A1203/HCl 20 ratios were 54, 58 and 61/1. The properties and stabilities of these ' ~-dispersions made by re-slurrying this dried powder were the same as the ,~
original dispersions as shown in Example 2.
The dispersions of Example 2 were also dried in an evaporator at temperatures of 60 - 80C. The products of this drying process were equivalent to those of the spray dried powder.
The redispersible powders were aged at room temperature for 6 months and redispersed. The stabilities of these dispersions,were tbe same as those of the original dispersions.
'EXAMPLE 6 The dispersions of Example 3 were frozen and thawed with no apparent effect upon properties and stability of the materia]. Frozen samples'of the dispersion were retained'for 8 months Rnd thawed. The ' ~ ' - .. . - ,, . - .. - . .. .

629~35 stabilities of these dispe~sions were the same as those given in ;~
Example 3. :
Alumina itself is suitable for use in the preparation of the dispersions of aspects of this invention provided it is of a size less than 200 mu and preferably less than 100 mu. :: .
In another example, thereofre, 80 parts by weight of an HCl- .
water solution having 0.3 pbw HCl therein was agitated with 20 pbw ,.
alumina resulting in a stable dispersion containing 20% A1203.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process of preparing stable aqueous dispersions of alumina at concentrations of 18 to 26% A1203 on a weight basis, comprising:
(1) preparing an aqueous solution of hydrochloric acid;
(2) controlling the temperature below the boiling point of the dispersion;
(3) maintaining the pressure between 0.5 to 5 atmospheres;
(4) adding alumina to said aqueous solution such that the weight ratio of alumina to HC1 is 53 to 66 parts alumina to 1 part HC1 and maintaining the pH at 3.5 to 4.2 thereby providing concentrations of 18 to 26%
A1203 on a weight basis of the total mixture;
and (5) substantially simultaneously agitating said mixture to obtain the desired dispersion.

2. The process of claim 1 in which the concentration of A1203 is 54 to 65 pbw per 1 pbw of HC1.

3. The process of claim 1 in which the concentration of A1203 is 18%; and in which the ratio of A1203 is 54 to 61 pbw of A1203 per 1 pbw of HC1.

4. The process of claim 1 in which the concentration of A1203 is 26%; and in which the ratio of A1203 to HC1 is 58 to 65 pbw of A1203 per 1 pbw of HC1.

5. The process of claim 1 in which the temperature is maintained between 20 and 80°C.

6. The process of claims 1, 2 or 3 in which the pressure is atmospheric.

7. The process of claims 4 or 5 in which the pressure is atmospheric.

8. The process of claim 2 wherein the alumina introduced into said mixture is in the form of alumina mono-hydrate.

9. A stable aqueous dispersion of alumina with a concentration of A1203 between 18 and 26% on a weight basis, a ratio of A1203 to HC1 of 53 to 66 pbw of A1203 per 1 pbw of HC1 and a pH of 3.5 to 4.2; the stability thereof being greater than 6 months.

10. The dispersion of claim 9 with an A1203 concentration of 18% and a ratio of A1203 to HC1 of 54 to 61 pbw of A1203 per 1 pbw of HC1 with a shelf life of 6 to 12 months.

11. The dispersion of claim 9 with an A1203 concentration of 26% A1203 and a ratio of A1203 to HC1 of 58 to 65 pbw of A1203 per 1 pbw of HC1 with a shelf life of 6 months.

12. The dispersion of claim 9 with a pH of 3.8 to 4.1.

13. A dried powder having therein 53 to 66 pbw A1203 per 1 pbw HC1 prepared by drying the dispersion of claim 9 under conditions that do not alter the A1203-HC1 ratio.

14. In a process of forming an aqueous alumina dispersion comprising forming an aqueuos solution of HC1 and then adding alumina, the improvement comprising: maintaining the ratio of A1203 to HC1 in the dispersion at 53 to 66 pbw of A1203 per 1 pbw of HC1 and maintaining the pH at 3.5 to 4.2, thereby to provide concentrations of 18 to 26% A1203 on a weight basis having stability for at least 6 months.

15. The process of claim 14 in which the pH is maintained at 3.8 to 4.1.

16. The process of claim 14 in which the weight concentration of A1203 in the dispersion is 18%; and in which the A1203 to HC1 ratio is 54 to 61 pbw of A1203 per 1 pbw of HC1.

17. The process of claim 14 in which the weight concentration of A1203 in the dispersion is 26%; and in which the A1203 to HC1 ratio is 58 to 65 pbw of A1203 per 1 pbw of HC1.

18. The process of claim 14 in which the A1203 to HC1 ratio of the dispersion is 54 to 65 pbw of A1203 per 1 pbw of HC1.