FI61910B - SAETT ATT FRAMSTAELLA AMORFA UTFAELLDA KISELSYRAPIGMENT - Google Patents

Description

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Patani- och registratyralaan 'Antokin utkgd ech utUkriftm publicerad 30.06.82 (32) (33) (31) «uolkeui —Begird prior It« t 03.10.73 USA (US) U03129 (71) J.M. Huber Corporation, Locust, New Jersey, USA (72) Satish Kumar Wason, Havre de Grace, Maryland, USA (7U) Berggren Oy Ab (5U) Method for producing amorphous precipitated silica pigment - Sätt att framställa amorfa utfällda kiselsyrapigment This invention relates to silicic acid pigments and to a unique process for preparing synthetic precipitated silicic acids having a unique combination of physical and chemical properties.

As is known in the art, doped silica pigments can be prepared by acidifying an aqueous silicate solution with an acid such as sulfuric acid, hydrochloric acid, etc. Examples of prior methods involving acidifying a silicate solution to prepare silica-containing pigments are disclosed in U.S. Pat. the nature and properties, sometimes referred to herein as silicas, depend on the particular conditions used, such as precipitation pH, reaction temperature, etc. Nevertheless, previously known pigments are characterized and have the following properties: fine structure, high wet cake moisture content, high oil absorption, low oil absorption valley wear, large surface area and low compaction density. In this sense, and due to properties such as high oil absorption, high surface area 2,61910, etc., these pigments have been widely used as reinforcing pigments in rubber, papermaking, moisture control agents, etc.

However, the high moisture content of the wet cake is detrimental in the sense that the drying and filtration rates increase, thus increasing the overall cost of the final product. For example, in the conventional production of silica pigments (as defined above), the moisture content of the wet cake of the product (after filtration of the precipitated reaction mass) is approximately 82%. This means that only 18 parts of dry pigments can be recovered from 100 parts of a wet cake.

Furthermore, the low abrasion capacity of the known silica and silicate pigments makes them unsuitable for many purposes. For example, it is well known that conventional synthetic precipitated silicic acids are not suitable as polishes and abrasives for toothpaste preparations.

See German Patent 97-958; French Patent 1,130,627; English Patent 995,351; Swiss Pat. which lead to poor cleaning ability.

In this sense, the main function of abrasives or polishes in toothpaste is to remove dirt, food debris and bacterial plaque from the tooth surface. Ideally, the polish should provide a maximum cleaning effect at acceptable levels of abrasion and should be miscible in amounts of about 15-50% with the other ingredients in the toothpaste recipe. Examples of known polishing agents are aluminas, thermoplastic resins (such as melamine-formaldehyde resins), zirconium silicates and various phosphate salts or compounds such as betatricalcium orthophosphate. Typical examples of phosphate wedges are disclosed in U.S. Patents 3,169,096; 3,359,170 and 3 M2 604.

Overall, the present invention relates to the preparation of finely divided precipitated silicas which, due to their new and unique properties, can be used as polishes in dental paste preparations. It is therefore an object of the invention to provide a process for the preparation of an amorphous, precipitated silica pigment having improved chemical and physical properties, such as good abrasion and cleaning ability when used in dentifrice preparations, to prepare an aqueous reaction medium containing an electrolyte in an amount of 3 to 15% by weight. based on the total weight of the reaction medium, an acidic solution and an alkali metal silicate, namely sodium silicate, potassium silicate or lithium silicate having a molar ratio of SiO 2: X 2 O of about 2.3 to 3.3, wherein X in the formula means lithium or potassium, are added simultaneously to the aqueous reaction medium. , a solution having a concentration of 0.1 to 0.3 kg / l, wherein the acidic solution contains sulfuric acid, nitric acid or hydrochloric acid 10 to 25% by weight based on the total weight of the acidic solution and the electrolyte is the sodium, potassium or lithium salt of the acid used, and adding silicate to the aqueous reaction medium it is not continued to maintain a substantially constant pH until the precipitation of the pigment is substantially complete, after which the precipitated pigment is recovered, and the invention is characterized in that the pH of the aqueous medium is adjusted to a predetermined value of 8-10.4 before the addition of alkali metal silicate. the value at which the pigment must be precipitated.

The invention is described in more detail below with application examples.

As described above, silica pigments are traditionally prepared by acidifying an aqueous silicate solution with an acid.

That is, the silicate solution is charged to the reactor, after which the solution is acidified by feeding acid. However, very recently (and before going into the details of the invention) a method has been developed, as described in Finnish Patent Application No. 2754/73, for preparing silica-containing pigments with improved properties, in which a salt or electrolyte is used to prepolymerize an alkali metal silicate solution before acidification. According to the teachings of this patent, an alkali or alkaline earth metal salt is first added to a solution of an alkali metal silicate, such as sodium silicate, the latter becoming prepolymerized by the addition of a salt.

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Said silicate solution is then heated to a temperature in the range of about 37-93 ° C, and preferably in the range of about 66-79 ° C. An acidifying agent or acid, e.g. sulfuric acid, is next fed to the reactor until the precipitation of silicate is complete. The reaction or precipitation is carried out at a pH in the range of about 6.5 to 11.0. At the end of the precipitation, an excess of acid is preferably added to bring the pH of the pigment to between about 5.5 and 6.5 and the reaction mass is filtered, washed and dried. In a first embodiment of the process disclosed in this patent, a solution of whole salt-induced polymerized silicate is initially added to the reactor. In another embodiment, half or two-thirds of the silicate is initially charged to the reactor and the remainder of the silicate is added with acid.

In contrast, according to the present invention, an aqueous receiving medium, i. water is first charged to the reactor. The electrolyte is then added to water and the pH of the aqueous electrolyte medium is adjusted to be the same as where the pigment precipitation is to be performed. In the practice of the invention, the precipitation pH should be between 8 and 10.4. Aqueous solutions of acid and silicate (described in detail in 5

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more specifically below) is added simultaneously in such a way and at such a rate that the reaction or precipitation is carried out at a preset constant pH. When the pigment is completely precipitated and depending on the final or intended use of the pigment, the pH can be lowered or adjusted by adding acid, etc. Although the product of the above-mentioned Finnish patent application No. 275 ^ / 73 has high abrasion ability and can be advantageously used in tooth cleaning preparations, that the products prepared according to the method of the present invention have a significantly improved cleaning ability or effect, the latter being the same or equivalent to the high-quality toothpaste phosphate polishing agents. In addition, and as mentioned above, when the products are used in toothpaste preparations, they have miscibility with fluorides (i.e., fluoride is available in soluble form and not converted to e.g. insoluble salt, etc.), which is better and does not suffer from the disadvantages of known phosphates such as calcium pyrophosphate.

As can be seen from the above, and to go into other details specific to the practice of the invention, the starting materials are the electrolyte, the alkali metal silicate and the acid. As used herein, the phrase alkali metal silicate encompasses all common forms of alkali metal silicates, such as, for example, metasilicates, disilicates, etc. Water-soluble potassium silicates and sodium silicates are particularly preferred. Due to the relatively low cost, sodium silicates are recommended. Sodium silicates are effective in all compositions with a molar ratio of SiO 2 to Na 2 O of about 1.0-4. With this in mind, commercially available sodium silicate solutions are more or less polymerized depending on their silica / sodium oxide (SiO 2 / Na 2 O) ratios. For example, sodium metasilicate solution (molar ratio 1), which is known to be primarily monomeric in nature, is both monomeric and polymeric in nature as a water glass (molar ratio 3.3). As the silicic acid / sodium oxide molar ratio of sodium silicate increases, so does the polymer / monomer ratio of its silicate anions. Although sodium silicates having a SiO 2 / Na 2 O molar ratio of 1 to 4 may be used, particularly advantageous results are obtained if the SiO 2 / Na 2 O ratio is between about 2.0 and 3.3, or more preferably about 2.0 to 2, B.

Although commercially available silicate solutions may be more or less polymerized depending on their silica / sodium oxide (SiO 2 / NapO) ratios, it has also been found that particularly advantageous and 6 61910 Preferred results are obtained if a sulfate salt or electrolyte is added to the silicate solution - or to the receiving medium. In other words, the silicate solution itself can be prepolymerized, as described in Finnish Patent Application No. 275V73. In addition, and instead of simply mixing the salt with the silicate solution, the silicate itself may be the product obtained by reacting silica with hydroxide in the presence of a sulfate filler to produce polysilicate.

Although the acidifying agent or acid is preferably a strong mineral acid such as sulfuric acid, nitric acid and hydrochloric acid, it is to be understood that other acids such as organic acids, e.g. acetic acid, formic or carbonic acid and carbonic acid salts such as ammonium carbamate may be used. As mentioned above, the acidulant and silicate are preferably added as dilute solutions thereof. The recommended results are obtained if the acid solution is about 10 to 25% by weight relative to the acid, based on the total weight of the solution. Particularly advantageous and thus recommended results are obtained if the concentration of the silicate solution is of the order of about 120-300 g / l.

As is known in the art, the word electrolyte refers to ionic or molecular substances which, when in solution, decompose or dissociate to form ions or charged particles. As used herein (and referring to an electrolyte that is added to water before feeding acid and silicate solutions), the word electrolyte is intended to have its general meaning. However, in carrying out the invention, and again as mentioned above, the electrolyte must be compatible with the acid and the silicate. Thus, if sodium silicate and sulfuric acid are used, the preferred electrolyte would be sodium sulfate.

If hydrochloric acid is used as the acid (again using sodium silicate), then the electrolyte would be sodium chloride. If the combination of silicic acid is potassium silicate and sulfuric acid, the electrolyte would be potassium sulfate, etc. Other examples of electrolytes are sodium nitrate, sodium acetate, etc. However, it should be noted that the electrolyte must not be a salt. The amount of electrolyte used should be in the range of 3 to 15% by weight based on the weight of water originally added to the reaction (receiving means).

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the temperature used is not critical and is the same as in the known processes described above. In a preferred embodiment, the electrolyte-containing receiving medium is heated to a temperature range of 37-93 ° C before the silicate and acid are fed.

As should be readily apparent to those skilled in the art, no special hardware is required in the method described herein. With this in mind, however, the reactor must be equipped with a heating device, e.g., a steam jacket, to maintain the desired reaction temperatures and must have sufficient agitators to provide strong backflow of the bulk of the liquid and thus avoid high concentration zones of incoming reagents. It is desirable to combine the reagents together to effect the immediate reaction of all feed material to a reasonable extent to the fullest extent possible, as this promotes the uniformity of the products obtained. Storage tanks (for reagents) connected to the reaction vessel by tubes equipped with flow control devices can also be fabricated. The reaction vessel may be provided with an outlet pipe leading to a filter, which may be of a conventional design. After precipitation, the filtered mass is washed and dried. Such steps may also be performed in conventional equipment and it is, of course, to be understood that they do not form part of the present invention.

If the pigments of the invention are used in toothpaste preparations, the toothpaste (in the form of a toothpaste) may contain wetting agents and binders to impart a uniform structure and good flowability to the toothpaste. Glycerin, sorbitol, corn syrup, glucose and the like can be used as carriers. Examples of binders include gum tragacanth, sodium carboxymethylcellulose, etc. The above-mentioned substances as well as special recipes and ingredients for toothpaste preparations are well known in the art and are described in several publications such as U.S. Patents 2,994,642 and 3,538,230.

Before proceeding to specific examples, it should be noted that as used herein, the term "structure" is intended to encompass and define the ability of a silicic acid material to retain water in a wet cake.When silicas such as the conventional precipitated silicas mentioned above retain a high percentage of water, i.e., 75-85%, they are known and are referred to as finely divided silica

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dit. Materials that retain less than 75% and preferably about 50-70% water in their wet cake are referred to as coarse silicas.

The invention is further illustrated by the following examples, which show particularly preferred embodiments of the method and composition. Although the examples are intended to illustrate this invention, they are not intended to limit it to itself.

Example 1 In this experiment, dry sodium sulfate was added to 37.8 liters of water in a 760 liter reactor so that the concentration of sodium sulfate in the reaction medium was 10%. The pH of the reaction medium was adjusted to 9.0 by the addition of sodium silicate. The reaction medium was then heated to 66 ° C. Sodium silicate having a SiO 2 / Na 2 O molar ratio of 2.5 and a concentration of 240 g / l and sulfuric acid having a concentration of 11.4 were then added to the reaction medium at 756 ml / min and 453 ml / min, respectively, so that the standard precipitation The pH of 9.0 was maintained.

The sodium silicate solution used in this example also contained 7% sodium sulfate, which was added to the solution before it was fed to the reactor. After 30 minutes, the precipitation was complete. Excess acid was added until the pH of the slurry was 5.4. The reaction slurry was boiled at 77 ° C for 20 minutes after which it was filtered, washed, dried and ground in the usual manner. The wet cake had a moisture content of 51% in the product prepared in this example; surface area 173 m2 / g; density 152 g / dm3 and valley wear (mg wire loss) 70.2. It was further found that the relative purification number (ROS) of the product was 100, which was the same as that of the phosphate polishing agent disclosed in U.S. Patent 3,359,170 and better fluoride stability.

Example 2

Example 1 was repeated except that the reaction temperature was maintained at 79 ° C and the precipitation pH was 10.0. The cooking temperature was 92 ° C. The input was otherwise handled in the usual manner. The properties of the product were essentially the same as in Example 1.

Example 3

Example 1 was repeated except that the reaction temperature was maintained at 85 ° C and the batch was boiled at 92 ° C. The batch was otherwise handled in the usual manner. The properties of the product were essentially the same as in Example 1.

Example A

In the series of experiments, the general procedure of Examples 1-3 was repeated except that the precipitation pH, although kept constant in each experiment, ranged from 8.0 to 10.4. The results were essentially the same except that it was found that the intrinsic properties of the substance could be adjusted within predetermined limits by varying the pH. In all cases, the products had a low wet cake moisture content, were coarse-grained, had relatively low oil absorptions, and higher valley wear compared to a control experiment to prepare conventional precipitated silica by neutralizing 148 g / L sodium silicate (37.8 L) with 11.4 # sulfuric acid. The latter valley wear was found to be 2.5 compared to even 167.8 (Example 3) with the products of the invention.

Example 5

The general procedures of Examples 1-4 were repeated except that sulfuric acid was replaced with nitric acid, hydrochloric acid, acetic acid and formic acid. The results were essentially the same as in Examples 1-4. Corresponding salts (e.g. sodium nitrate, sodium chloride, etc.) were also used as the electrolyte initially charged to the reactor (instead of sodium sulfate).

Example 6

The general procedures of Examples 1-5 were repeated in a series of experiments except that the 2,5-silicate of Examples 1-5 was replaced with aqueous sodium silicates having molar ratios (SiO 2 / Na 2 O) in the range of 1-3. The results were generally the same as in Examples 1-5 except that it was found that the use of alkali metal silicates with a SiO 2 / Na 2 O molar ratio between about 2.0-2.0 resulted in excellent properties (as defined above).

Example 7

The procedures of Examples 1-6 were repeated except that the amount of salt used as the electrolyte in the aqueous receiving medium was varied between 3 and 15% by weight (about every 5%). The results were essentially the same as in the examples above.

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Example 8

The procedure of Example 1 was repeated except that the sodium silicate solution contained no sulfate before it was fed to the reactor. It was found that although the valley wear was relatively high compared to the control experiment (see Example * 0, the cleaning effect was approx.

85 (RCS) compared to 100 for the product of Example 1.

It can be seen from the above examples that the process of the present invention produces silicas with lower wet cake moisture, rougher texture, lower oil absorption, higher density and higher valley wear than conventional products. In addition (and this was really unexpected) the cleaning effect of these new products when used in toothpaste was found to be very high and similar to that of known phosphates. The cleaning effect was also about LO% higher than with products made in accordance with the teachings of Finnish Patent Application No. 2754/73. The valley wear of the latter and the products of the present invention are similar.

This new process also results in silicas, which have lower manufacturing costs than ordinary precipitated silicas. For example, the average wet cake moisture of the silicas prepared according to the new process (Examples 1-8) is approximately 53% compared to 8% of ordinary silica. % By weight. This means that 47 parts of dry silica can be recovered from 100 parts of a wet cake. Thus, according to the new process, 29 parts more dry silicic acid or an addition of (29/18) x 100 or about 160% is obtained. The new process results in silicas with better drying and filtration rates and therefore significantly lower manufacturing costs than precipitated silicas prepared by the conventional method.

It can be seen from the above that the present invention provides a truly significant and simplified process for the preparation of silica pigments with new and unique properties.

Although preferred methods and composition-embodiments have been described herein for purposes of illustration, it is to be understood that the invention is not limited thereto. For example, as described in Finnish Patent Application No. 2754/73, the refractive index of the precipitated pigment can be adjusted by adding an adductive component (such as aluminum, magnesium, etc.) to provide an abrasive or polishing agent.

Claims (1)

il 61910 sex in a clear translucent or transparent toothpaste preparation. In this embodiment, the acid is premixed with a solution of an adductant (such as aluminum sulfate) and the acid-metal salt mixture is then used to acidify the alkali metal silicate. A process for preparing an amorphous, precipitated silica pigment having improved chemical and physical properties, such as good abrasion and cleaning ability when used in dentifrices, to prepare an aqueous reaction medium containing an electrolyte in an amount of 3 to 15% by weight based on the total weight of the reaction medium. an acidic solution and a solution of an alkali metal silicate, namely sodium silicate, potassium silicate or lithium silicate having a molar ratio of 3102 ^ 2 ^ of about 2.0-3.3, wherein X in the formula is 0, is added to the aqueous reaction medium at the same time. , 1-0.3 kg / l, wherein the acidic solution contains sulfuric acid, nitric acid or hydrochloric acid 10-25% by weight based on the total weight of the acidic solution and the electrolyte is the sodium, potassium or lithium salt of the acid used, the addition of acid and silicate to the aqueous reaction medium is continued that maintained essentially constant pH until the precipitation of the pigment is substantially complete, after which the precipitated pigment is recovered, characterized in that the pH of the aqueous medium is adjusted to a predetermined value of 8-10.4, which is the value at which the pigment is precipitated, before the addition of the alkali metal silicate. accordingly. In the case of amorphous compounds, such as chemical or physical agents, the nature of the slurry and the preparation of the reaction medium in the preparation of the reaction medium, the color of the reactants of the electrical reactants in 3 to 15 days , reacting with water-containing reactants with the addition of alkali metal and the addition of alkali metal silicate, certain sodium silicate, potassium silicate or lithium silicate with molar silica SiC 2, X lithium, vilken alkalimetallilikatlösnings concentration up to 0.1-0.3 kg / l, varvid den den Sura lösningen innehäller 10-25 vikt- #