JP2594251B2 - Manufacturing method of dicalcium phosphate dihydrate - Google Patents

Description

The present invention relates to a method for producing dicalcium phosphate which improves the water solubility of monofluorophosphate.

Dicalcium phosphate dihydrate has been used as tooth polish in toothpastes and powders for many years.

This material is typically obtained by first reacting slaked lime with phosphoric acid to obtain a dicalcium phosphate dihydrate precipitate, and then separating the dicalcium phosphate dihydrate precipitate from the mother liquor, Afterwards the material is dried and ground to obtain the final product as a fine powder.

One of the first significant problems encountered when using dicalcium phosphate dihydrate in toothpastes is that they tend to form dicalcium phosphate and clump. If this phenomenon occurs in toothpaste, it becomes difficult to extrude the toothpaste from the tube that normally packages the toothpaste.

A second problem is that monofluorophosphate additives have to be used in toothpaste formulations. The monofluorophosphate component has been found to react with dicalcium phosphate, thereby converting the monofluorophosphate component from a water-soluble form to an insoluble form.
It is understood that the beneficial effect of the monofluorophosphate additive in toothpastes is primarily due to the fact that it is derived in a water-soluble form, so that an effective amount of the monofluorophosphate component is stored in a water-soluble state. It has become important to launch toothpaste formulations that can be used.

The phrase "monofluorophosphate-compatible" has been used as a technical term to describe the tendency of such formulations to be able to leave the monofluorophosphate component in a water-soluble state.

The monofluorophosphate compatibility of a particular formulation can be determined by various methods. Preferably, the monofluorophosphate compatibility of the formulation remains in the formulation after actually preparing the formulation, storing the formulation under controlled conditions for a predetermined period of time and then storing under such conditions It is determined by measuring the amount of water-soluble monofluorophosphate. Alternatively, a similar formulation, such as dicalcium phosphate dihydrate to be tested, glycerin and a known amount of a monofluorophosphate component, such as sodium monofluorophosphate, may allow it to be treated for one or more hours.
By holding at an elevated temperature, it ages quickly and the amount of water-soluble monofluorophosphate remaining after such conditioning is determined. Of course, there are many other methods for determining the relative monofluorophosphate compatibility of various samples of dicalcium phosphate dihydrate.

U.S. Pat. No. 2,287,699 teaches that dicalcium phosphate dihydrate is stabilized during the production of dicalcium phosphate by adding a small amount of alkali metal pyrophosphate to the mother liquor at a constant pH. Teaching that a small amount of alkali metal pyrophosphate should be added, especially after the dicalcium phosphate in the mother liquor has settled, and then the entire slurry should be heated briefly while maintaining the pH of the mother liquor above 7. Have been.

 Alternatively, the precipitate can be processed in a continuous washing step.

It is well known to those skilled in the art that other forms of pyrophosphate can also be used to stabilize dicalcium phosphate.

Another method of stabilizing dicalcium phosphate is disclosed in U.S. Pat. No. 2,018,410. This patent teaches that dicalcium phosphate is stabilized by adding a magnesium salt, such as trimagnesium phosphate, magnesium sulfate, magnesium stearate or dimagnesium phosphate, to the dicalcium phosphate.

Concurrent application 106,637 (now a U.S. patent) teaches a method of making a dicalcium phosphate dihydrate composition having an improved monofluorophosphate, which method comprises adding phosphorus to the reaction mixture. Add acid, then about 4.9-
Terminating the reaction within a very narrow pH range of about 5.5.

In view of the teachings of the prior art, surprisingly and unexpectedly, improved monofluorophosphate compatibility can be achieved by adding pyrophosphoric acid and then terminating the reaction at a pH of less than about 4.9. Was found.

According to the present invention, there is provided a method for producing dicalcium phosphate dihydrate having improved monofluorophosphate compatibility, the method comprising the following steps (a), (b) and ( Step c): (a) reacting the slaked lime slurry with phosphoric acid to produce a monocalcium phosphate solution having a steady pH of 1-2: (b) further adding slaked lime slurry and pyrophosphoric acid to the solution; Adding a sufficient amount to produce a dicalcium phosphate dihydrate slurry of greater than about 2.2 and less than about 4.9; and then (c) separating dicalcium phosphate dihydrate from the slurry. Become.

According to the present invention, the following findings have now been obtained: at a pH in the range of greater than about 2.2 and less than about 4.9, an improved product is obtained when the reaction is terminated while co-adding pyrophosphoric acid to the reaction mixture. It has been found that this leads to the formation of dicalcium phosphate dihydrate with fluorophosphate compatibility. This is contrary to the prior art teaching a pH range of 4.9-5.5.

The following findings were also found: during the addition of the lime slurry to the monocalcium phosphate solution, the formation of dicalcium phosphate dihydrate crystals began at about pH 2.2 and was formed at that point. The crystals are said to have a high degree of monofluorophosphate compatibility. However, the yield at this low pH is relatively low.

The dicalcium phosphate dihydrate formed at a pH of about 2.2 to about 3.3 appears to have a very high degree of monofluorophosphate compatibility, but the yield is increased due to the increased pH. Increases as slurry is added. Thus, a higher pH is accompanied by a higher yield.

Crystals formed at a pH higher than about 3.3
It appears that the compatibility with the monofluorophosphate is worse than the crystals formed in step 2, but the overall monofluorophosphate compatibility of the entire mixture of crystals formed is very high even at a final pH of about 4.9. Remain high.

The lime used in the practice of the present invention is the same type of rotary kiln lime or shaft kiln lime used in the normal dicalcium phosphate process.

Slaked lime slurries are used to remove lime from water or circulating mother liquors (ie, those remaining after removing dicalcium phosphate dihydrate from the final slurry), or both.
In an amount of about 100 to about 150 g Cao / l and preferably about 70 ° C. to about 74
Manufactured by mixing at a temperature of ° C. At higher concentrations, the mixture becomes a gelatinous mass which is difficult to handle and if the lime concentration is too low, the yield per reaction vessel size will be reduced.

Next, slaked lime is added to phosphoric acid to obtain a monocalcium phosphate solution.

The acid used is preferably food grade phosphoric acid, preferably at an initial concentration of about 85%. Various amounts of circulating mother liquor are also
Specific amounts can be added to the lime slurry and phosphoric acid, as determined by the preferences of the individual practitioner. The composition range of the monocalcium phosphate solution is approximately as follows: high (wt%) low (wt%) CaO 4 2 P ₂ O ₅ 22 12 pH 21 These ranges are examples of typical ranges And is not intended to be particularly limiting as to the scope of the invention. It should be understood that higher or lower amounts can be used by those skilled in the art provided that the reaction mixture meets the needs of the practitioner.

If the lime slurry and phosphoric acid were introduced together under the specific conditions described above, the reaction would take place and a monocalcium phosphate solution would form. Reaction completion is about 1.0 ~
Indicated by a steady pH of about 2.0. In the present invention, the steady pH refers to a constant pH.

The preparation of the monocalcium phosphate solution can be carried out as a continuous, batch or semi-batch process.

Once the monocalcium phosphate solution is formed, phosphoric acid and additional slaked lime slurry are added to form a dicalcium phosphate dihydrate slurry. This reaction is exothermic and requires external cooling to control the reaction temperature. The reaction temperature should preferably be controlled at or below 50 ° C.

Preferably, the additional slaked lime slurry is first added to the monocalcium phosphate solution until the desired pH is reached, followed by the addition of pyrophosphoric acid. The minimum amount of pyrophosphate to be added is about the amount of dicalcium phosphate dihydrate to be produced.
0.1% by weight, while the maximum amount added should be about 1.0%. Of course, if pyrophosphoric acid is added, pH
Will be slightly reduced. As described above, first, additional slaked lime is added to monocalcium phosphate, and the pH measured after the addition is completed is referred to as "final pH" in the present invention.

Although it is preferred to add the pyrophosphoric acid and slaked lime slurry to the monocalcium phosphate solution in the order described above, it is within the scope of the present invention to add these components out of the order described above. However, after adding these two components, it is important that the final pH be greater than about 2.2 and less than about 4.9 and preferably between about 3.3 and about 4.7.
In the present invention, the pH measured after the addition of the two components (slaked lime slurry and pyrophosphoric acid) is referred to as “final
H ".

The amount of pyrophosphoric acid added should be in the range of about 0.1 to about 1.0%, preferably about 0.3 to about 0.4% by weight of the dicalcium phosphate dihydrate to be produced.

Once the dicalcium phosphate dihydrate slurry is formed as described above, the dicalcium phosphate dihydrate product is separated from the mother liquor. The mother liquor is then circulated or discarded at the beginning of the process.

Separation of dicalcium phosphate dihydrate from the slurry is accomplished by several conventional techniques. These techniques are not particularly limited, but are preferred because the decanting method, including the decanting method, centrifugation, and filtration, is simple.

Stabilizers commonly added to dicalcium phosphate dihydrate are intended to prevent "cake formation" and "clumping" that occurs in unstable dicalcium phosphate dihydrate as a result of dehydration. Many stabilizers useful for this purpose are known. These include, but are not limited to, dimagnesium phosphate, trimagnesium phosphate, magnesium stearate, and magnesium sulfate. The amount of stabilizer added is about 0.5 to about 2% of dicalcium phosphate dihydrate.
It is in the range of about 5.0% by weight. Preferred stabilizers used in the practice of the present invention are dimagnesium phosphate trihydrate,
Trimagnesium phosphate octahydrate, and mixtures thereof.

After drying the dicalcium phosphate dihydrate or alternatively drying the dicalcium phosphate dihydrate and pulverizing, the stabilizer and the stabilizer are dry-dried while the dicalcium phosphate dihydrate is dry-blended. It is preferably added to dicalcium dihydrate. However, it is also within the scope of the present invention to add a stabilizer to the product slurry before separating the dicalcium phosphate dihydrate from them, or to wet the dicalcium phosphate before drying or milling. Addition to the dihydrate is also within the scope of the present invention. Next, the present invention will be described with reference to Examples and Reference Examples for better understanding of the present invention. Nothing in the examples should be construed as limiting the invention within the scope set forth in the claims.

Reference Example 1 A slaked lime slurry (CaO 10.85%) obtained by slaking lime with a circulating mother liquor obtained from dicalcium phosphate dihydrate synthesis was stirred using the circulating mother liquor until the pH reached 5.88. Was added to 750 g of a clear solution of monocalcium phosphate prepared as such. The monocalcium phosphate solution used had a steady pH of about 1.0 to about 2.0. Then 1.13 g of pyrophosphoric acid was added and stirring was continued for another 30 minutes, at which point the final pH was 5.2. The temperature of the mixture was maintained at 40 ° C. during the addition using an external cooling device.

The resulting dicalcium phosphate dihydrate product was recovered from the slurry by filtration, then dried and ground.

A portion of the dicalcium phosphate dihydrate is then mixed with 2% trimagnesium phosphate, based on the weight of the dicalcium phosphate dihydrate, and then a standard containing sodium monofluorophosphate in an amount corresponding to 1000 ppm of fluoride ions. It was used to produce a toothpaste formulation.

The toothpaste formulation was then aged at 49 ° C. for 3 weeks, after which the amount of remaining water-soluble monofluorophosphate was determined.
The results are shown in Table I.

Example 1 A large amount of dicalcium phosphate dihydrate was prepared as described in Reference Example I, except that it was prepared by digesting lime using circulating mother liquor obtained from dicalcium phosphate dihydrate synthesis. Slaked lime slurry (10.85% CaO)
Was added with stirring to 750 g of a clear solution of monocalcium phosphate prepared with the same circulating mother liquor until the pH reached 3.4 ("terminal" pH). The monocalcium phosphate solution used had a steady pH of about 1.0 to about 2.0.

A small amount (1.13 g) of pyrophosphoric acid was added and the slurry was stirred for an additional 30 minutes, after which the final pH was 3.3.
A standard toothpaste formulation was then prepared using the same amounts of ditrimagnesium phosphate and sodium monofluorophosphate and dicalcium phosphate dihydrate as in Reference Example 1, which was aged and aged as in Reference Example 1. The monofluorophosphate compatibility was examined. The results are shown in Table I.

Reference Example 2 Slaked lime slurry was prepared by adding 310 g of calcium oxide and 2400 ml of distilled water.
Was prepared by mixing at temperatures varying from 50 ° C to 78 ° C. The slurry was then passed through a 140 mesh screen and cooled to room temperature. 124g CaO / l slurry
Was found to be contained.

Add the calcium phosphate solution to slaked lime slurry (10.85
It was prepared by% CaO) 358 g and 85% H ₃ PO ₄ 410g of distilled water 608Ml (total amount 1367G) and mixing.

The composition of CaO and P ₂ O _{5 in} the obtained monocalcium phosphate solution is calculated as follows.

358 g of slaked lime slurry (CaO 10.85% :) is 38.
Equivalent to 8 g CaO (358 × 0.1085); 85% H ₃ PO ₄ 401 g is 340.
Equivalent to 9 g H ₃ PO ₄ ; 340.9 × 142/196 = 247 g P ₂ O ₅ 38.8 / 1367 × 100 = 2.83% CaO 247/1367 × 100 = 18.07% P ₂ O ₅ 2.83% CaO obtained here and monocalcium phosphate solution having a 18.07% P ₂ O _5, the constant as is clear from the composition range of monocalcium phosphate solution specification page 10 pH1~
2 range. Therefore, the monocalcium phosphate solution prepared in the above step has a pH of 1-2.

The slaked lime slurry was then added to the monocalcium phosphate slurry at a temperature of 40 ° C. until the pH of the mixture reached 5.8 (the “end pH” is thus 5.8).

Then a 2.0 g quantity of pyrophosphoric acid was added and the mixture was stirred for a further 30 minutes. Final pH was 5.4. The dicalcium phosphate dihydrate product was then recovered by filtration, dried, ground and mixed with trimagnesium phosphate as in Reference Example 1. Then, using a part of the product,
A standard toothpaste formulation was prepared as in the previous Examples and Reference Examples and then aged at 49 ° C. for 3 weeks, after which the amount of remaining water-soluble monofluorophosphate was measured. The results are shown in Table II.

EXAMPLE 2 monocalcium phosphate second solution (pH 1-2), were prepared by mixing the slaked lime slurry 358g and 85% H ₃ PO ₄ 401g of distilled water 608Ml.

The procedure of Reference Example 2 was repeated except that the addition of the slaked lime slurry was terminated at pH 5.0.
pH was 4.7. Then, in order to test the compatibility of the water-soluble monofluorophosphate, a standard toothpaste preparation was prepared using Reference Example 1
Was prepared in exactly the same manner as described in the above section. The results of the monofluorophosphate compatibility test are shown in Table II.

Example 3 The procedure of Example 2 was repeated except that the end pH was 4.5, but the final pH was 4.5.

A standard toothpaste formulation was then prepared in exactly the same manner as described in Reference Example 1 to test for water-soluble monofluorophosphate compatibility. The results of the monofluorophosphate compatibility test are shown in Table II.

Continued on the front page (72) Inventor Helmatt Wilhelm Majoyous Key New York 19960 Nayk Bee Gail Drive 41 (72) Inventor Francis Anthony Via United States New York Yoke Yakuta Unheights Ridge Street 2389 (56) References JP 46-2410 (JP, B1)

Claims (2)

(57) [Claims] (A) reacting slaked lime slurry with phosphoric acid to produce a monocalcium phosphate solution having a steady pH of 1-2, and (b) further adding slaked lime slurry and phosphoric acid to be formed to this solution. 0.1 to 1.0% by weight of pyrophosphoric acid is added to dicalcium dihydrate to form a dicalcium phosphate dihydrate slurry having a pH higher than 2.2 and lower than 4.9, and (c) dicalcium phosphate from the slurry A process for producing dicalcium phosphate dihydrate for improving the compatibility of monofluorophosphate, comprising the step of separating dihydrate. 2. The pH is above 3.3 and up to 4.7.
A method for producing dicalcium phosphate dihydrate according to claim 1.