FI62129B - FREQUENCY REFRIGERATION AV ETT AMORFT UTFAELLT KISELDIOXIDPIGMENT - Google Patents

Description

kfta * »* l ΓβΊ« «.INCLUDE JUICAlSU r„ „0 JS&S A UTLÄGGNINGSSKR1FT 6 2 i k. 9 c Patent registered 10 11 1982 (45) Patent na? dcelat ^ (51) Kv.lk.WcL 3 C 09 C 1/30 FINLAND —FINLAND (2.1) Putunttlhukumu · —Pi * untun »Blci» ln | 2756/7 ^ (22) HakamlspUrl — Ai »8knlnj» d »t 20.09.7 ^ ^^ (23) Alkupthrt — GlWfhettdtf 20.09.7 ^ (41) Tulkit lulkMal — Bllrft offuntllf oU. + 0i. 75

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Patent * och register tty releen Antekftn uthgd och utl.ilcrlft * n pubUcured 30 '07.82 (32) (33) (31) Pyr «i« «y« uolk «us — 8« flrd prtorlMt 03.10.73 USA (US) 1 * 02927 (71) JM Huber Corporation, Locust, New Jersey, USA (US) (72) Satish Kumar Wason, Havre de Grace, Maryland, USA (US) (7 * 0 Berggren Oy Ab (5 ^) Process for the preparation of amorphous doped silica pigment -Förfarande för framställning av ett amorft, utfällt small dioxide pigment

The present invention relates to novel silica pigments and, more particularly, to a process for the preparation of synthetic amorphous precipitated silicas having novel and special properties.

As is well known in the art, commercially available silicas can be broadly divided into two basic groups. These groups are those prepared by the liquid phase method and those prepared by the vapor phase method.

Liquid phase silicas include precipitated silicas prepared by acidifying an alkali metal silicate with an acid such as sulfuric acid. Other liquid phase silicas include silica gels and colloidal silicas. Examples of prior art include acidification of a silicate solution to prepare precipitated silicas as disclosed in U.S. Patent Nos. 3,110,606 and 3,582,379.

2,6129 Steam silicas, also called fumes and fumed silicas, are prepared by reacting silicon tetrachloride vapor with oxygen-hydrogen gas at high temperatures to give silica and hydrogen chloride. Pyrogenic silicas have a large external surface area and differ from other dioxides (e.g. gels, precipitated silicas, etc.) prepared by the liquid phase method.

Although precipitated silicas have been used in many applications, several of their properties (such as low abrasion resistance) make them unsuitable for many uses. For example, it is known that conventional synthetic precipitated silicas are unsuitable as polishes and abrasives for use in toothpastes. See, e.g., U.S. Patent No. 3,250,680 and German Patent No. 974,958. U.S. Patent No. 3,538,230 specifically discloses that known amorphous silicas, such as precipitated silica, fumed silica, and aerogels, are unsuitable. for use in toothpastes due to their small particle size and due to the ease with which they disintegrate into smaller particles.

In recent years, previous researchers have developed new methods to produce silica pigments with new and unique properties, e.g., to make them very suitable for use in toothpaste mixtures and to replace phosphate polishes, in order to extend the utility of precipitated silicas.

Accordingly, Finnish Patent Application No. 2754/73 discloses a process for the preparation of silica pigments which can be used as an abrasive or polishing agent in toothpastes, using a salt or electrolyte to prepolymerize alkali metal silicates before acidification with an acid.

According to another invention, there is provided a process for the preparation of precipitated silica pigments which have a high potency and a relative cleaning capacity corresponding to that of the high-quality phosphates used as polishes in toothpastes. According to this patent, pigments are prepared by simultaneously passing a solution of an alkali metal silicate and an acid into an aqueous receiving medium (i.e., water) and keeping the pH of the aqueous receiving medium constant during its precipitation.

The present invention provides a further improvement in the preparation of precipitated silica-containing pigments, the process comprising oxidizing an alkali metal silicate with an acid. Most broadly, the invention is based on the finding that silica pigments with improved properties can be prepared by carefully adjusting the rate of acidification. More specifically, it has been found that silica pigments having a very high structure (to be defined later), good oil absorption capacity and a very large surface area can be prepared by adjusting the acidification and keeping it very slow during the addition of the acid to the alkali metal silicate solution. In this way, precipitation is achieved in a homogeneous environment and in such a way that the extreme values of the particle size can be adjusted. The product obtained has the above-mentioned improved properties, which make it very suitable for use as a thickener in toothpaste mixtures, as a smoothing agent in paints and varnishes, etc.

It should be noted that precipitated silicas have not been used as thickeners and gelling agents in toothpastes. In general, when phosphates are used as polishes and abrasives, a thickening agent such as gum tragacanth has also been used. See, e.g., U.S. Patent No. 2,588,992.

In later years, the use of precipitated silicas (e.g., those mentioned in the above patents) as polishes or abrasives has created the need for and general use of silica-containing substances as thickeners. Specific examples of silicon-based thickeners or gelling agents are disclosed in U.S. Patent No. 3,538,230. The thickeners disclosed in the latter include nCab-O-Sil "(fumed silica) and" Syloid 2W (aerogel).

It is therefore an object of the present invention to provide a process for the preparation of finely divided precipitated silica which can be used as a thickener and / or gelling agent in toothpastes.

H 62129

The invention is therefore directed to the preparation of an amorphous precipitated silica pigment having a very high structure, wet

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data cake moisture content over 85%, oil absorption over 200 cmV. 2,100 g, having an area of more than 250 m / g and having improved chemical and physical properties for use as a thickener in dental preparations, which comprises preparing an aqueous reaction medium containing 10 to 20% by weight of sodium silicate having a SiO2 / Na2O weight ratio of 2.3-3.3, preferably 2.5 + 0.1, the reaction medium is heated to a temperature of 65-77 ° C, preferably 71-7 ° C and most preferably 7 ° C, and sulfuric acid is added, and the process according to the invention is characterized in that the sulfuric acid is a dilute 8-25% by weight solution, that 3-10% by weight of aluminum sulphate is added to the sulfuric acid before it is added to the reaction medium and that the sulfuric acid thus obtained is added to the reaction medium at a rate of 2ΟΟ to 35Ο ml / min 3-0.8 moles of hydrogen ions per minute.

In carrying out the process according to the invention, the alkali metal silicate solution is first introduced into a reaction vessel (equipped with suitable heating and stirring equipment), and the silicate solution is then heated to a temperature in the range of 65-77 ° C, preferably in the range of about 71-7 ° C. The silicate solution can, of course, be prepared in the reaction vessel itself.

In this context, the term "alkali metal silicate" encompasses all conventional forms of alkali metal silicates, such as e.g. metasilicate, disilicates, etc. Water-soluble potassium silicates and sodium silicates are highly preferred, with the latter being most preferred.

In general, sodium silicates are effective in all mixtures with a weight ratio of SiO 2 / Na 2 O of about 1.0 to 0.1. However, very advantageous results are obtained if the SiO 2 / Na 2 O weight ratio is in the range of about 2.3 to 3.3.

After the solution is heated to the above-mentioned temperature, the acidifying agent or acid is added very slowly at a rate of 200-350 ml / min. In conventional processes involving the oxidation of silicate, the addition rates have generally been very high and in the order of 500 ml / min. According to the invention, the rate of addition (at any stage of the oxidation) must not exceed about 350 ml / min.

The acid is preferably a strong mineral acid such as sulfuric acid, nitric acid or hydrochloric acid. However, it can also be used. other acids such as organic acids or their salts (e.g. acetic acid, formic acid, carbonic acid, ammonium carbonate, etc.).

The acid is preferably added as a dilute solution and the best results are obtained if the acidic solution contains about 8-25% by weight of acid based on the total weight of the solution.

Very advantageous results are obtained if the silicate concentration in the initial silicate solution is of the order of about 10 to 20% by weight based on the total weight of the silicate solution.

As can be seen from the above, the starting materials contain an alkali metal silicate and an acid. Important variables in the process are the SiO 2 / Na 2 weight ratio, the reaction temperature and the rate of acid addition to the alkali leach solution.

In this regard, it has also been found that the refractive index of the product (as well as the other properties mentioned above) can be precisely adjusted and maintained if an additive such as aluminum sulphate is premixed with the acid before being introduced into the silicate solution. The aluminum sulphate (preferably as a solution) is thus premixed with the acid before acidification to a concentration of the order of about 3-10% aluminum sulphate, based on the total weight of the acid. Although this additive is preferably a water-soluble aluminum salt such as aluminum sulfate, other salts such as magnesium sulfate may also be used. As mentioned, the additive is premixed with the acid, and the acid / metal salt mixture is then used to acidify the aqueous alkali metal silicate solution.

As mentioned above, the products prepared by the process of the invention have a very high structure. In this context, it should be noted that the term "structure" in this context also means the ability of the silica-containing material to retain water in wet form, i. after the precipitate has been filtered. Commercially purchased silicas contain a high percentage of water (i.e., about 75-85%) and are termed "highly structured silicas." Materials that contain 65-75% water are commonly referred to as "medium silicas." Silicas with a moisture content of more than 85% and always 95% or more in the wet state are termed "highly structured silicas".

6 62129

As mentioned above, it is well known to prepare precipitated and silicas by acidifying aqueous alkali metal silicate with a suitable acidifying agent until a final pH of about 5.6-6.0 is reached. The silica precipitate is then filtered, washed free of salt, dried and ground to the desired fineness.

Looking further at other details of the invention, it can be seen that commercially available sodium silicate solutions can be represented by the formula Na 2 O * x SiO 2, where x is the weight ratio of SiO 2 / Na 2 O. Since the molecular weights of Na 2 O and SiO 2 are approximately the same, weight ratios of sodium silicates are usually used. Water glass is the most common silicate used in the manufacture of silica pigments. The weight ratio of this product is 3.22, which means that it contains 3.22 parts of SiO 2 and 1 part of alkali, i.e. Na20 ta.

In the past, it has been customary to acidify sodium silicate, where the value of x has been in the range of about 3.0 to 3.4. In this prior art, the acid is introduced into the sodium silicate solution until the desired final pH is reached and the product is then recovered using conventional methods.

According to the present invention, the acidification is controlled very precisely, especially at the beginning of the reaction and at the point where the precipitation initially takes place, i.e. with a value of x of approximately 4.2.

The invention is further illustrated by the following examples, which illustrate some highly preferred methods of the invention. These examples merely illustrate, but do not limit, the invention.

Example 1 In this experiment, 45 liters of a sodium silicate solution having a SiO 2 / Na 2 O weight ratio of 2.6 was added to a stirred reaction vessel, and the solution was heated to 74 ° C. The concentration of the silicate solution was 13.3%, the sulfuric acid with a concentration of 11.4% and the aluminum sulfate solution were premixed in a volume ratio of 7: 62129 (0.14 kg / l). This stirred acidifier was then added very slowly to the reactor at a rate of 300 ml / min until a final pH of 5.9 was reached. The product of this example had a very high structure, a cake moisture content of 88%, an oil absorption capacity of 24 ml / 100 g and a surface area of 250 m2 / g.

Example 2

The procedure of Example 1 was repeated except that the rate of addition of the premixed acidifier was 250 ml / min. The product of this example had a very high structure, a wet cake moisture content of '87%, an oil absorption capacity of 230 ml / -100 g and a surface area of 275 m 2 / g.

Example 3

The procedure of Example 1 was repeated except that the rate of addition of the acidulant was 275 ml / min. The product had a very high structure, the moisture content of the wet cake was 86%, the absorbency of the oil was 220 ml / 100 g and the surface area was 265 m / g.

Example 4

The procedure of Example 1 was repeated except that the rate of addition of the acidifying agent was maintained at 225 ml / min until the onset of precipitation at an x value of 4.2. The product of this example had a very high structure, a wet cake moisture content of 89%, an oil absorption capacity of 250 ml / 100 g and a surface area of 280 m2 / g.

Example 5

As a reference, 45 liters of a sodium silicate solution with a SiO 2 / Na 2 O weight ratio of 2.6 was added to a stirred reaction vessel and the solution was heated to 74 ° C. The concentration of the silicate solution was 13.3%. · Sulfuric acid with a concentration of 11.4 # was added to the reactor at a rate of 500 ml / min until a final pH of 5.9 was reached. The product according to this comparative example had only a high structure, with a moisture content of 84% of the wet cake, an oil absorption capacity of 180 ml / 100 g and a surface area of 150 m 2 / g.

As the above examples show, it becomes possible to harden a very high-structure silica pigment only by carefully adjusting the acidification to the initial thickening flux at an x value of 4.2 in the case of sodium silicate with a SiO 2 / Na 2 O weight ratio (x value) of 2.6 and a concentration of 13.3% By adjusting the oxidation to x or 4.2 for as long as practicable, it is possible to adjust the size of the final silica particles and precipitate them in a homogeneous environment, providing controlled micelle formation during the precipitation treatment. This controlled process then provides the production of silicas with improved properties and performance over silicas compared to previous methods.

Comparing the results obtained from the above examples with the corresponding results, it can be seen that the molar to weight ratio SiO 2 / O 2 where M is an alkali metal such as sodium, potassium, etc. is inversely proportional to the molar amount of hydrogen ions obtained by acidification per unit time to achieve controlled micelle formation upon silica precipitation in accordance with the present invention.

In the above examples, when using sodium silicate having a SiO 2 / Na 2 O weight ratio (x value) of 2.6, the most preferred acidification rate is 200 to 350 ml / min, i.e., about 0.4 to 0.8 moles of hydrogen ions per minute.

In general, an acidification rate of an alkali metal silicate in which the molar ratio (or weight ratio) x = SiO 2 / N 2 O, where M is an alkali metal, is from / E ^ 7 / x to 2_ / H ^ 7 / x, where _ / H ^ 7 is the molar concentration of hydrogen ions to be added per minute.

The silicas of the invention were prepared in two 700 kg batches to confirm the values and efficacy of the product of Examples 1-4. These experiments yielded products with the following characteristics:

Test and product A: oil absorption: 237 ml / 100 g

Area: 308 m2 / g

Test and product B: oil absorption: 222 ml / 100 g

Area 259 m 2 / g

The surface area of product A was larger than that of product B because it was finalized at a lower final pH than product B.

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The thickening efficiencies of products A and B were compared in the wetting systems used in typical toothpastes.

Two humidification systems were used. One was labeled "C" and contained a $ 70 sorbitol solution sold by Atlas Chemical Inc., Wilmington, Delaware under the trademark "SORBO", and the other was labeled "D" and consisted of a mixture of 4 5 parts of 7C £: sorbitol solution and 15 parts of 95% glycerol solution.

Products A and B were dispersed by mixing a known weight of each wetting agent C and D until a free-flowing powder was obtained. The silica of Example 5 was also dispersed in wetting agents "C" and "D" for comparison.

The reference silica bound up to 280% "C" and 270% "D".

Product A bound up to 300% "C" and 296% "D". Product B bound up to 294% "C" and 296% "D".

As can be seen, the silicas prepared according to the invention have a superior thickening or drying ability as typical wetting agents compared to previously known silicas.

Thus, the highly structured silicas prepared according to the invention can be used as gelling and thickening agents in various toothpaste and tooth powder mixtures.

The silicas prepared according to the invention can also be used as reinforcing agents, leveling agents in paints and varnishes, and as carriers, flow improvers, liquid desiccants and the like.

For smoothing purposes, 10 g of silica prepared according to the invention (ground in an air mill) was mixed with 350 g of nitrocellulose varnish (corresponding to Military Specification MIL-L-10287A - Amendment 2, Type II, issued August 27, 1959) and mixed for 3 min using Hamilton-Beach mixing device No. 30 at low speed. The varnish containing dispersed silica was tested by the Hegman fine grinding test (5.50) and based on the ease of grinding.

10,621 29

The varnish containing dispersed silica was mixed with and without the use of additional varnish to prepare a stock solution having a solids content of 10%, 3.5% and 1.75% by weight.

Application of the various stock solutions (containing 10%, 3.5% and 1.75% silica in the lacquer) was performed on a glass plate using Spreading Roller No. 34. The glass plates were allowed to dry for 45 min. in dust-free conditions. Using the above method, applications were also performed using stock solutions containing silica prepared by previously known methods.

Using a Gardner polygon gloss meter, the brightness and gloss of the different coatings were measured using angles of 60 ° and 85 °, respectively. These values were compared with those measured by dispersing previously known silicas in a lacquer.

The silicas prepared according to the invention provide purer Hegman values and have better brightness when dispersed in the lacquer. This improved brightness is due to the fact that the silicas prepared according to the invention have a uniform particle size and a more advantageous structure.

The values below show that the novel silicas prepared according to the invention have lower gloss and reflection values than the control samples. Lower gloss and reflection values are cheaper when using products in paints.

smoothness

_60 ° gloss 85 ° reflection_ 10% 3.5% 1.75% 10% 3.5% 1.75%

Silica according to Example 1 8 29 44 28 6l 74

Silica according to Example 5 (comparison) 10 38 54 37 72 82

Although preferred embodiments of the invention have been described in detail above, this description does not limit the invention but may be modified without departing from the scope of the invention.