JPH11292524A - Non-crystalline calcium phosphate slurry, its preparation and non-crystalline calcium phosphate particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain non-crystalline calcium phosphate particles excellent in dispersibility in water and an org. solvent and to prepare a non-crystalline calcium phosphate slurry less liable to cause precipitation over a long period of time. SOLUTION: A calcium component such as calcium hydroxide is added to water, pressurized to be comminuted and dispersed while passing through a medium mixing will to prepare a slurry, a phosphoric acid component such as an aq. phosphoric acid soln. is added to the slurry, while the slurry is pressurized to be comminuted and dispersed while passing through the medium mixing mill, to form non-crystalline calcium phosphate and finally the pH is adjusted to 6-8 to prepare the objective non-crystalline calcium phosphate slurry. This slurry is dried to obtain the objective non-crystalline calcium phosphate particles. The objective non-crystalline calcium phosphate slurry is also prepd. by dispersing the calcium phosphate particles in water or an org. solvent compatible with water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to amorphous calcium phosphate particles excellent in dispersibility in water or an organic solvent compatible with water, and amorphous calcium phosphate particles which are not easily aggregated or precipitated for a long period of time. The present invention relates to a calcium phosphate slurry and a method for producing the same.

[0002]

2. Description of the Related Art Amorphous calcium phosphate is a substance widely distributed in the form of phosphate rock, animal bones, and the like. This amorphous calcium phosphate is applied to materials for artificial bones, tooth repair materials, etc., taking advantage of its high affinity with living organisms, or to ion exchange materials, pigments, cosmetics, UV inhibitors, etc. Applied. Fine particles of amorphous calcium phosphate are used as a stabilizer for maintaining a suspended state of a monomer or a polymer in an aqueous medium during the production of a polymer by a suspension polymerization method, or during the production of a plastic film. It is also used as an anti-blocking agent.

[0003] However, amorphous calcium phosphate is usually aggregated by van der Waals force, ionic charge, etc., despite the fact that the primary particles produced during its production are fine particles of 0.1 μm or less. And an aggregate having a particle size of about 4 to 100 μm, and the dispersibility is reduced.

Accordingly, amorphous calcium phosphate having a particle size of submicron or several microns, specifically, an average particle size of about 0.1 to 4 μm, such as the above-mentioned stabilizer for suspension polymerization and antiblocking agent. In a field that requires a process, a step of breaking up the generated aggregates is required, and there is a problem that it takes time and effort.

When the dispersibility of the slurry is low, the following problem occurs. For example, since suspension polymerization is generally performed in a batch process, when the slurry is transported through a pipe of an industrial plant, or when the slurry stays in the pipe between a batch process and the next batch process, Slurry is separated. As a result, the pipes become clogged and need to be cleaned frequently, the concentration of the slurry cannot be kept constant, and the particle size and the degree of polymerization of the polymerization product tend to vary.

[0006] The ease of separation of the slurry is, for example, that the slurry is poured into a pipe of a certain diameter and allowed to stand, and the volume of the sediment is reduced.
The time until the volume of the slurry becomes half of the volume immediately after the injection, that is, the so-called sedimentation half-life can be used as an index. In a suspension polymerization plant or the like, the sedimentation half-life of the slurry needs to be at least about 3 hours, and a longer sedimentation half-life is more preferable.

[0007]

As a method for improving the dispersibility of a slurry in a calcium phosphate compound such as amorphous calcium phosphate, various means have been tried in the past. JP-A-7-102006 discloses a method in which a slurry obtained by synthesizing hydroxyapatite in water is strongly sheared with a homogenizer or the like to redisperse the slurry.

However, in order to stably maintain a highly dispersed state for a long period of time without coagulating hydroxyapatite, that is, without separating the slurry, it is necessary to continuously carry out strong shearing treatment. Was difficult. Further, the slurry of amorphous calcium phosphate obtained by the method disclosed in the above publication has a long sedimentation half-life of about 1 hour, which is insufficient for actual use in suspension polymerization.

[0009] Japanese Patent Application Laid-Open No. 9-142817 discloses that a slurry obtained by synthesizing hydroxyapatite is subjected to strong shearing treatment using a bead mill and redispersed, and the sedimentation half-life is about 5 to 25 minutes. Japanese Patent Application Laid-Open No. 9-301708 discloses a method for lengthening the length of apatite. After once synthesizing apatite, the obtained apatite particles are re-dispersed in an organic solvent compatible with water, and the apatite thus obtained is obtained. A method is disclosed in which a slurry is supplied to a stirring mill and pulverization and dispersion treatment is performed until particles having a particle diameter of 3 μm or more substantially disappear.

However, even when the method disclosed in the above publication is used, the sedimentation half-life is insufficient at about 1 hour or less.

Accordingly, an object of the present invention is to provide a method for producing an amorphous calcium phosphate slurry which can be highly dispersed in water and an organic solvent and can maintain the dispersion state for a long time.

Another object of the present invention is to provide an amorphous calcium phosphate slurry and amorphous calcium phosphate particles which can be highly dispersed in water and an organic solvent and can maintain the dispersion state for a long period of time.

[0013]

In order to produce amorphous calcium phosphate, a method of adding a phosphoric acid aqueous solution or a phosphoric acid component such as sodium phosphate to a slurry of a calcium component such as calcium hydroxide or calcium carbonate has conventionally been used. Is used. However, this method causes an imbalance between the dissolution rate of calcium ions in water and the addition rate of phosphoric acid,
The unreacted calcium component forms aggregates, and the inside forms unreacted particles.

When the amorphous calcium phosphate particles thus obtained are used as they are, no particular problem occurs. However, since the crushing treatment is performed to adjust the particle size, the aggregates are crushed to expose the unreacted calcium component inside, and as a result, the pH of the slurry increases, and the dispersion stability increases. Decrease.

On the other hand, the inventors of the present invention have been conducting studies to solve the above-mentioned problems, and as a result, the increase in pH promotes the separation and precipitation of amorphous calcium phosphate particles in the slurry. However, it has been found that the dispersion stability is lowered and that the use of the thus obtained amorphous calcium phosphate particles as a stabilizer for suspension polymerization has an adverse effect such as a decrease in the polymerization rate.

Further, the present inventors can suppress the generation of unreacted aggregates by performing sufficient pulverization at the stage of synthesizing the particles of amorphous calcium phosphate, and improve the dispersibility in water or an organic solvent. The idea was obtained that a slurry of amorphous calcium phosphate which was good and hard to form aggregates could be obtained. As a result of repeated studies on various pulverization methods, the present invention was completed.

That is, according to the method for producing an amorphous calcium phosphate slurry of the present invention, a calcium component is added to water;
After performing a whole-shear treatment and pulverizing and dispersing the slurry to prepare a slurry, a phosphoric acid component is added to the slurry while further performing a full-shear treatment to form amorphous calcium phosphate particles. ８8.

According to the method for producing an amorphous calcium phosphate slurry of the present invention, it is possible to efficiently obtain a slurry which hardly causes agglomeration and can maintain a highly dispersed state for a long period of time.

In the present invention, "all shearing treatment" means
The operation of applying pressure to the slurry to pulverize and disperse the slurry is performed while the slurry is passed through a medium stirring mill.

Examples of the medium stirring mill include a flow tube mill such as a disper mill, a homogenizer, a sand grinder, and a pearl mill; and a stirring mill such as a stirring tank mill.

[0021] The amorphous calcium phosphate slurry of the present invention is characterized by being produced by the above-described method for producing an amorphous calcium phosphate slurry.

That is, the amorphous calcium phosphate slurry of the present invention is prepared by adding a calcium component to water, subjecting the resultant slurry to a full-shear treatment and pulverizing and dispersing the slurry. To form amorphous calcium phosphate particles, and finally adjust the pH to 6 to
It was adjusted to 8.

In the amorphous calcium phosphate slurry of the present invention, the calcium component is reacted with the phosphoric acid component while being pulverized and dispersed by a full-shear treatment, whereby the formation of unreacted aggregates is sufficiently suppressed. I have. Also, by adjusting the final pH to 6-8,
It is highly dispersed, and it is difficult to form aggregates such as secondary particles.

In addition, according to the above-mentioned slurry, the sedimentation half-life of the amorphous calcium phosphate particles can be made 3 hours or more, as described in Examples below.

Further, even if the slurry is further stirred, subjected to a full shearing treatment, or the amorphous calcium phosphate particles in the slurry are pulverized, the formation of unreacted aggregates is sufficiently suppressed. As a result, the pH of the slurry is unlikely to increase, so that a highly dispersed state can be maintained.

The amorphous calcium phosphate particles of the present invention include:
The above amorphous calcium phosphate slurry of the present invention is dried.

According to the above-mentioned amorphous calcium phosphate particles of the present invention, it is possible to obtain a slurry which can be easily dispersed in water or an organic solvent and maintains a highly dispersed state for a long period of time.

Another amorphous calcium phosphate slurry of the present invention is obtained by dispersing the above-mentioned amorphous calcium phosphate particles of the present invention in an organic solvent compatible with water.

According to the above slurry, even if the dispersion medium is an organic solvent compatible with water, a high degree of dispersion can be obtained, and aggregates such as secondary particles are hardly formed.

In the other amorphous calcium phosphate slurry of the present invention, since the formation of unreacted aggregates is sufficiently suppressed in the same manner as described above, the slurry is further stirred or subjected to full shearing. Even if a treatment is performed or the amorphous calcium phosphate particles in the slurry are pulverized, the pH of the slurry is hardly increased, and a highly dispersed state can be maintained.

The pH cannot be measured with a slurry using an organic solvent compatible with water as a dispersion medium.
In the present invention, the pH was measured after adding about 2 parts by weight of water to 100 parts by weight of the slurry, and the result was defined as the pH of the slurry.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the method for producing an amorphous calcium phosphate slurry of the present invention, first, a calcium component such as calcium hydroxide, calcium carbonate, calcium hydrogen phosphate or the like is added to water, and a stirring mill (eg, a disper mill, a homogenizer, a stirring mill) is used. The calcium component is pulverized and dispersed by supplying it to a mill or the like and subjecting it to a full shearing treatment. Next, the amorphous calcium phosphate is generated by reacting with a phosphoric acid component such as phosphoric acid and sodium phosphate while further performing the entire shearing treatment, and finally the pH of the slurry is adjusted to 6 to 8.

When calcium hydroxide is used as the calcium component, an aqueous phosphoric acid solution is used as the phosphoric acid component. On the other hand, when calcium carbonate or calcium hydrogen phosphate is used as the calcium component, sodium phosphate is used as the phosphoric acid component.

The amount of the calcium component when the calcium component is added to water and subjected to the whole shearing treatment is not particularly limited, but is usually 0.01 to 80% by weight, preferably 10 to 50% by weight. Is set in the range. When the amount is less than the above range, the production efficiency of the amorphous calcium phosphate particles is low, and the production efficiency is low. Conversely, if the amount exceeds the above range, the calcium component may not be sufficiently pulverized. In addition, there is a possibility that agglomeration due to the interaction of the generated amorphous calcium phosphate particles is likely to occur.

The stirring mill used for the whole shearing treatment includes a whole type, a screw type, a flow tube type (disk type), a stirring tank type, an annular type, and the like. May be used. Among them, a full-type disper mill, a mighty mill (manufactured by Inoue Seisakusho), a dyno mill (manufactured by Shinmaru Enterprises), a high-pressure homogenizer, and the like are preferably used.

In the whole shearing treatment in the present invention,
The processing time by the agitating mill may be usually set to 10 to 240 minutes, preferably about 10 to 120 minutes.

When a high-pressure homogenizer is used as the stirring mill, the pressure is set to 300 to 500 kg / cm.
^Second , the outflow speed of the slurry may be set to about 250 to 450 kg / hour.

When a mighty mill is used as a stirring mill, the amount of sand mill beads is
0 to 60%, convection time to 5 to 10 minutes, discharge amount to 3 to
What is necessary is just to set each to 10 kg / hour.

In the present invention, the amorphous calcium phosphate (A
Morphous Calcium Phosphate is represented by the formula: Ca ₃ (PO ₄ ) ₂ .nH ₂ O. In this amorphous calcium phosphate, part of Ca is, for example, barium, strontium,
It may be substituted by an atom such as zinc, magnesium, sodium, potassium, iron, aluminum and titanium. A part of PO ₄ is, for example, VO ₄ , SiO ₄ , CO ₃
And the like, may be substituted with one or more of such atomic groups. In addition,
An antibacterial metal ion may be added to the slurry of the present invention, and the antibacterial metal ion may be adsorbed on the amorphous calcium phosphate particles to impart antibacterial properties to the obtained porous particles.
Such antibacterial metal ions include gold, silver, zinc,
Copper, tin, lead, arsenic, platinum, iron, antimony, nickel,
Aluminum, barium, cadmium, ions such as manganese, and the like, may be used alone,
A mixture thereof, a metal compound, or an aqueous solution thereof may be used. The amorphous calcium phosphate according to the present invention has a ratio of CaO to P ₂ O ₅ (CaO / P ₂
O ₅ ) is in the range of 1.25 to 1.37 by weight, and the primary particles are acicular, columnar, plate-like, rice-grain-like, or oval.

The amorphous calcium phosphate particles obtained by the production method of the present invention have an average particle size of 4 μm or less before being dispersed in water or an organic solvent compatible with water, and have particles having a size of 15 μm or more. Will not do. Further, by adding to water or an organic solvent having compatibility with water and dispersing the mixture with a stirring mill or the like, the average particle size is 0.1 to 4 μm.
m.

That is, in the amorphous calcium phosphate particles and the amorphous calcium phosphate slurry of the present invention, the secondary particles constituting the coarse particles of 4 μm or more are removed, and almost all of the primary particles are in the state of the primary particles. Has become. Further, even if the slurry of the present invention is further subjected to full-shear dispersion or the like with a stirring mill, the pH does not increase due to unreacted aggregates, and the pH is maintained in the range of 6 to 8.

Examples of the organic solvent compatible with water in which the amorphous calcium phosphate is dispersed include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and butanediol;
Examples include monohydric alcohols such as ethanol and propanol. These solvents may be used by directly mixing water, a dispersant, a surfactant and the like, if necessary.

Examples of the dispersant include polymerized phosphate dispersants such as sodium hexametaphosphate and sodium tripolyphosphate. The amount of the dispersant added is not particularly limited, and the dispersant can be used within the usual range of the amount added.

The amount of amorphous calcium phosphate particles in water as a dispersion medium or in an organic solvent compatible with water,
That is, the solid content concentration of the slurry differs depending on the use, and is not particularly limited. However, if the solid content of the slurry is too low, the dispersion effect may be insufficient. Conversely, if the solid content of the slurry is too high, the viscosity of the slurry becomes high, and reaggregation due to the interaction of particles may occur.

The solid content of the slurry is preferably 0.01 to 50% by weight when the dispersion medium is water, preferably 10 to 50% by weight.
More preferably, it is -20% by weight. In the case of an organic solvent compatible with water, the content is preferably 0.01 to 90% by weight, and more preferably 30 to 50% by weight.

The use of the amorphous calcium phosphate slurry and the amorphous calcium phosphate particles of the present invention is not particularly limited. For example, polyester fiber raw materials, polyurethane raw materials, adhesives, inks, brake oils, polyethylene terephthalate Examples include (PET) resin raw materials, antifreeze, pharmaceuticals, cosmetic raw materials, electrolytic capacitor pastes, and alkyd resin raw materials. When used as a raw material for polyester or the like, a slurry system is suitable as it is, but if necessary, the solvent can be removed and used as a powder.

[0048]

The present invention will be described below with reference to examples and comparative examples.

[Preparation of Amorphous Calcium Phosphate Slurry] Example 1 Calcium hydroxide 500 was added to 9.5 liters of ion-exchanged water.
g was added and supplied to a disper mill (Disper mill manufactured by Hosokawa Micron Corp.). Then, the rotation speed 800
By circulating for 10 minutes at a condition of 0 rpm and a processing amount of 500 liter / hour, a full shearing treatment was performed, and calcium hydroxide was pulverized and dispersed.

The suspension of calcium hydroxide thus obtained was subjected to a full shearing treatment under the same conditions as described above.
An 8% phosphoric acid aqueous solution was added over 1 hour. Thus,
Finally, a slurry of amorphous calcium phosphate whose pH was adjusted to 7.5 was obtained. In addition, the reaction temperature of calcium hydroxide and phosphoric acid was adjusted in the range of 20 to 60 ° C.

Next, the obtained slurry was dehydrated, dried and pulverized to obtain amorphous calcium phosphate particles.

Further, the particles and ethylene glycol were supplied to a disper mill at a ratio of 50:50, circulated for 30 minutes under the same conditions as described above, and subjected to a full shearing treatment.
A highly dispersed amorphous calcium phosphate slurry was obtained.

Example 2 In the same manner as in Example 1, calcium hydroxide was pulverized and dispersed, reacted with phosphoric acid, dehydrated, dried and pulverized.
Amorphous calcium phosphate particles were obtained.

Next, the particles and water were supplied at a ratio of 10:90 to a high-pressure homogenizer (a homogenizer manufactured by MANTONGAULIN), and the pressure was 400 kg / cm.
^{2. A} full-dispersion shearing treatment was performed at a discharge rate of 300 kg / hour to obtain a highly dispersed amorphous calcium phosphate slurry.

Example 3 Calcium hydroxide 200 was added to 9.0 liters of ion-exchanged water.
g was added and supplied to a stirring mill (Mighty mill manufactured by Inoue Seisakusho Co., Ltd.). Next, a 5% phosphoric acid aqueous solution was added over 90 minutes while performing a full-shear treatment under the conditions of a bead volume of 50% with respect to the Bethel capacity, a convection time of 8 minutes, and a discharge rate of 6 kg / hour. A slurry of amorphous calcium phosphate whose pH was adjusted to 7.5 was obtained. In addition,
The reaction temperature was adjusted in the same range as in Example 1.

Next, the obtained slurry was dehydrated, dried and pulverized to obtain amorphous calcium phosphate particles.

Further, the particles and ethylene glycol were supplied at a ratio of 50:50 to a stirring mill (described above), and circulated for 10 minutes under the same conditions as described above to perform a full-shear treatment to obtain a high dispersion An amorphous calcium phosphate slurry was obtained.

Example 4 Amorphous calcium phosphate particles obtained in Example 1 and cyclohexanone were supplied at a ratio of 50:50 to a disper mill (described above) and circulated for 10 minutes under the same conditions as in Example 1. The whole was subjected to a shearing treatment to obtain a highly dispersed amorphous calcium phosphate slurry.

The average particle size of the particles present in the amorphous calcium phosphate slurry obtained in Example 4 was 0.27 μm.

Comparative Example 1 A commercially available aqueous hydroxyapatite slurry (trade name “Supertight” manufactured by Nippon Chemical Industry Co., Ltd.) was supplied to a high-pressure homogenizer (described above), and the whole mixture was subjected to the same conditions as in Example 2. Shearing was performed.

The slurry thus obtained had a pH of 9.2.
It was 3.

Comparative Example 2 Commercially available hydroxyapatite fine particles (manufactured by Mitsui Toatsu Co., Ltd.) and water were supplied to a stirring mill (the above-mentioned mighty mill) at a ratio of 10:90 (weight ratio). A full shearing treatment was performed under the same conditions as in Example 3.

The pH of the slurry thus obtained was 10.
52.

Comparative Example 3 Commercially available hydroxyapatite fine particles (manufactured by Goodenheim)
And ethylene glycol in a ratio of 10:90 (weight ratio)
And supplied to a stirring mill (the above-mentioned mighty mill), and subjected to full shearing treatment under the same conditions as in Comparative Example 2.

The pH of the slurry thus obtained was 10.
It was 3.

[Measurement of Particle Size Distribution] The particle size distributions of the slurries obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were measured.
The results are shown in Tables 1 and 2 together with the average particle size of each slurry.

[0067]

[Table 1]

[0068]

[Table 2] As is clear from Tables 1 and 2, in Examples 1 to 3, the average particle size is in the range of 0.1 to 4 μm, and the particle size is 0.1 μm.
m, no more than 4 μm, or very little.

On the other hand, in Comparative Examples 1 to 3, the particle size was 4 μm.
m in many cases, and it was confirmed that aggregation occurred with an increase in pH. The average particle size also exceeded 4 μm in Comparative Examples 1 and 3.

[Measurement of Sedimentation Half-Life] A slurry (dispersion solution: water) immediately after the reaction of calcium hydroxide and phosphoric acid in Examples 1 to 3 and an amorphous After obtaining the powder of the porous calcium phosphate, the sedimentation half-life was measured by the following method using the slurry (dispersion liquid: ethylene glycol) obtained by subjecting it to the full shear treatment again.

The slurry obtained in Example 4 (dispersion: cyclohexanone), the slurry obtained in Comparative Examples 1 and 2 (dispersion: water), and the slurry obtained in Comparative Example 3 (dispersion: Using ethylene glycol), the sedimentation half-life was measured by the following method.

Further, in Example 2 and Comparative Examples 1 to 3, the slurry was dewatered and dried to obtain particles, and then the particles were used to disperse ethylene glycol in a slurry (Example 2, Comparative Examples 1 to 3). A slurry (Comparative Example 3) using 1 and 2) and water as a dispersion liquid was prepared, and the sedimentation half-life was measured by the following method.

The method for measuring the sedimentation half-life is as follows. First, the amorphous calcium phosphate slurry is put into a 100 ml settling tube in a sufficiently dispersed state. Then
This is allowed to stand at 25 ° C., and the time until the volume of the precipitate reaches 50 ml is measured, and this time is defined as the sedimentation half-life.

Table 3 shows the measurement results of the sedimentation half-life.

[0075]

[Table 3] As is clear from Table 3, in Examples 1 to 3, when the dispersion was water, an extremely long sedimentation half-life of 1 month or more was obtained, and when the dispersion was ethylene glycol, the precipitation An extremely excellent dispersion state, which does not even occur, was observed. Further, even when dispersed in cyclohexanone as in Example 4, the sedimentation half-life was extremely long, exceeding 3 hours.

On the other hand, Comparative Examples 1 to 3 all had insufficient sedimentation half-lives of about 1 hour or less, which were insufficient.

[Measurement of pH in Ethylene Glycol] To 500 ml of the slurry (dispersion medium: ethylene glycol) obtained in Example 1 was added 10 ml of water, and the mixture was stirred.
The pH was measured to be 7.4.

Further, 10 ml of water was added to 500 ml of a slurry (dispersion medium: ethylene glycol) using the particles obtained in Comparative Example 1 and stirred, and the pH was measured to be 9.3.

Further, 10 g of calcium hydroxide was added to 100 ml of water, stirred for 10 minutes, and the filtrate obtained by removing the calcium hydroxide by filtration was mixed with the slurry obtained in Example 1 (dispersion medium: ethylene glycol). ) 500ml
When 10 ml of the mixture was added, the pH became 8.3.

Here, the time-dependent changes in the particle size distribution of the three slurries were examined. Table 4 shows the results.

[0081]

[Table 4] As is clear from Table 4, when calcium hydroxide contained in the filtrate was added to the slurry or unreacted calcium hydroxide was disintegrated, and the pH was inclined toward the alkali side, the time required for aggregation was large. Was found to accelerate.

[0082]

As described above in detail, according to the method for producing amorphous calcium phosphate of the present invention, the amorphous calcium phosphate is easily dispersed in water and an organic solvent and is maintained in a state of being highly dispersed in water and an organic solvent for a long time. Amorphous calcium phosphate and a slurry of amorphous calcium phosphate that can be obtained can be obtained efficiently. The amorphous calcium phosphate and the slurry obtained in this manner are suitably used, for example, as a stabilizer for suspension polymerization.

Claims (5)

[Claims] 1. A calcium component is added to water, subjected to a whole shearing treatment and ground and dispersed to form a slurry. Then, a phosphoric acid component is added to the slurry while further subjecting the slurry to an amorphous shearing treatment. A method for producing an amorphous calcium phosphate slurry, comprising generating calcium phosphate particles and finally adjusting the pH to 6 to 8. 2. The method for producing an amorphous calcium phosphate slurry according to claim 1, wherein the calcium component is calcium hydroxide and the phosphoric acid component is an aqueous solution of phosphoric acid. 3. An amorphous calcium phosphate slurry produced by the production method according to claim 1. 4. Amorphous calcium phosphate particles obtained by drying the amorphous calcium phosphate slurry according to claim 3. 5. An amorphous calcium phosphate slurry comprising the amorphous calcium phosphate slurry particles according to claim 4 dispersed in an organic solvent compatible with water.