JP2516474B2 - Modified acidic sodium metaphosphate composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to sodium acid metaphosphate having improved hygroscopicity and powder fluidity, and is used as a modifier.
It relates to a modified acidic sodium metaphosphate composition to which a Group II metal compound is added.

[Prior Art] Sodium acid metaphosphate is a condensed phosphate of a polymer obtained by melting and dehydrating and condensing a reaction product of phosphoric acid and sodium hydroxide or sodium carbonate in an amount less than equimolar to phosphoric acid. It is a generic term for a mixture, and it has various compositions depending on the production conditions such as the molar ratio of the raw materials, the temperature and the time during the reaction.

Neutral sodium metaphosphate obtained by dehydration condensation of phosphoric acid and equimolar sodium hydroxide is also a mixture of polymer condensed phosphates, but there is a big difference in properties between the two, and sodium acid metaphosphate Has a different utility than neutral sodium metaphosphate.

That is, neutral sodium metaphosphate is well known to have an excellent sequestering ability, and is widely used in cleaning agents, water treatment agents, food industry, dyeing industry, etc.,
Acidic metaphosphate has a unique stable PH buffering action and unique properties as an acidic powder in addition to the same sequestering effect, which is a remarkable feature.

The difference between the two is due to the difference in molecular structure. Neutral salt has a stable linear or cyclic structure, whereas sodium acid metaphosphate has a highly reactive hydroxyl group in the molecule. This is due to the fact that it has a net-like structure containing many active sites.

Such high reactivity combined with PH buffering action and sequestration action, sodium acid metaphosphate has a wide range of uses as an extremely useful substance.

[Problems to be Solved by the Invention] However, on the other hand, sodium acid metaphosphate is inevitably accompanied by handling problems due to its high reactivity.

That is, sodium acid metaphosphate has extremely strong hygroscopicity, and powder particles lose adhesiveness and fluidity due to moisture absorption, making it difficult to maintain good use characteristics as a powder, which is a major drawback. Has become.

The strong hygroscopicity of sodium acid metaphosphate is derived from its unique molecular structure as described above, and neutral sodium metaphosphate has a linear molecular structure, and the phosphorus atom is almost neutralized. On the other hand, sodium acid metaphosphate is known to be a molecule having a network structure that expands in multiple dimensions, in addition to the presence of a number of highly reactive hydroxyl groups with incomplete neutralization of phosphorus atoms, The phosphorus atom located at the branch point of this network structure is extremely unstable in structure and easily reacts with a water molecule to undergo hydrolytic cleavage to form a hydrophilic and highly reactive end group. It exhibits hygroscopicity and reactivity peculiar to salt.

Therefore, the hygroscopic reaction of sodium acid metaphosphate is
It tends to accelerate, and even when it is stored tightly in a moisture-resistant packaging material, it immediately absorbs moisture when opened, and the particle surfaces become viscous candy-like particles that bind to each other to form a lump. . As a result, not only does it hinder handling such as a large amount of adhesion to the container and difficulty in uniform powder mixing,
Dispersion at the time of dissolution is disturbed, solubility and reactivity are lowered, and the original characteristics are not utilized.

For example, the hygroscopicity of sodium acid metaphosphate is a major obstacle even when it is used as a deflocculating agent or binder for refractories, for which the usefulness of sodium acid metaphosphate has recently been drawing attention. The action as a deflocculating agent in castable refractories is due to its ion sequestering ability, and therefore highly reactive sodium acid metaphosphate shows excellent performance, but the dissolution obstacle due to the formation of lumps is It reduces the effective concentration of condensed phosphate in the refractory material and prevents the development of effective peptization. In addition, the refractory for spraying, which is indispensable for maintenance and repair of steelmaking furnaces,
Water is mixed with a powder mixture consisting of a refractory material and a binder to form a slurry and sprayed. The reactivity of the binder greatly affects the performance of the obtained refractory material.
In particular, in a semi-dry spray material that uses water as a nozzle mix, the curing reaction by the binder is performed in an extremely short time, and bond formation with strong adhesiveness is required, so the reactivity of the binder is particularly important. Is. Although highly reactive sodium acid metaphosphate shows excellent performance, the effect of the decrease in solubility and reactivity due to moisture absorption and lump formation is remarkable.

Sodium acid metaphosphate has a wide range of applications as an acidic condensed phosphate having a stable PH buffering action and a high metal sequestering ability, but it always suffers from a handling drawback of powder fluidity loss due to moisture agglomeration. This is an obstacle to use, and there is a problem in that it cannot be fully utilized.

However, the disadvantage of sodium acid metaphosphate is that only the characteristics and the back and forth of it are strong, and although there is a strong demand for sodium acid metaphosphate having low hygroscopicity and good powder fluidity, there is still a definitive solution. Not found.

Therefore, the object of the present invention is to suppress the hygroscopic reactivity of the surface of sodium acid metaphosphate particles to improve the flow characteristics, and at the same time to improve the dispersion solubility, which has been modified to solve this problem. The purpose is to provide sodium acid metaphosphate.

[Means for Solving the Problem] The present inventors, while continuing research for solving the above-mentioned problems, treated powdered sodium acid metaphosphate with a certain Group II metal compound to give a powder. It was found that the hygroscopicity of the surface of the particles is drastically reduced, and modified sodium acid metaphosphate can be obtained which maintains stable powder fluidity for a long period of time.

That is, the present invention is based on 100 parts by weight of powdered sodium acid metaphosphate having a Na ₂ O / P ₂ O ₅ molar ratio of less than 1, and at least 0.5 parts by weight of oxides of calcium, magnesium or zinc and hydroxide. A modified acidic sodium metaphosphate composition, characterized in that one or more compounds selected from the group consisting of compounds, carbonates, basic carbonates, phosphates and hydroxyphosphates are added. is there.

 Hereinafter, the present invention will be described in detail.

In the present invention, acidic sodium metaphosphate is obtained by melting phosphoric acid and sodium hydroxide or sodium carbonate in an amount less than equimolar to phosphoric acid and a reaction product at a temperature of 400 ° C. to 750 ° C., and dehydrating and condensing the same. It is a powder of glassy material, Na ₂ O / P ₂ O ₅ molar ratio is less than 1, P ₂ O ₅ content 70
~ 77% (w / w).

Such sodium acid metaphosphates all show strong hygroscopic reactivity, especially those with a small Na ₂ O / P ₂ O ₅ molar ratio are remarkable, and quickly become sticky due to moisture in the air, and powder As a result, it has the property of lowering the fluidity.

However, according to the present invention, there is an effect that the above-mentioned sodium acid metaphosphate particles can be modified to obtain a more stable powder product.

The Group II metal compound which can be used in the present invention is selected from oxides, hydroxides, carbonates, basic carbonates, phosphates and hydroxyphosphates of calcium, magnesium or zinc. It can be used as a mixture of two or more species.

The addition amount is at least 0.5 parts by weight with respect to 100 parts by weight of sodium acid metaphosphate, and if the addition amount is less than 0.5 parts by weight, a sufficient modifying effect cannot be obtained. There is no particular limitation on the upper limit of the amount added, but a sufficient effect is usually obtained with an amount of 5% or less. Addition of a large amount brings about a decrease in sequestering ability of metal ions and adverse effects due to mixing of different components, so it is desirable to select the type and amount of the additive according to the application.

Since the refractory material is intentionally blended with a calcium compound or a magnesium compound, the present invention is particularly purposeful, and these group II metal compounds are useful as food additives. There are many, and there is no problem in using additives.

In carrying out the present invention, a predetermined amount of a fine powder of a Group II metal compound is added to sodium acid metaphosphate powder,
Although it is sufficient to mix with sufficient stirring and no special treatment is required, it is desirable that 80% or more of the particles of the group II metal compound are composed of fine particles of 10 μm or less. If there are many coarse particles having a size of more than 10 μm, the modifying effect is relatively lowered, and thus the addition amount becomes large, which is not efficient, and the unfavorable effect of the additives becomes apparent.

Although the mechanism of modifying the additive in the present invention is not clear, the effect of preventing the moisture absorption of the Group II metal compound used as an additive (modifying agent) is not due to the blocking effect by merely adhering to the particle surface. That is, even if a similar treatment is carried out with a hydrophobic powder that is generally used as a fluidization modifier, for example, silicic acid anhydride or alumina fine particles, such a moisture resistance effect is not obtained, and the limited II Obviously, this can only be achieved by group metal compounds. Further, even with some moisture absorption, even in the case of sodium acid metaphosphate whose fluidity is partially reduced, the fluidity is quickly recovered by the addition of the Group II metal compound of the present invention, and the subsequent powder properties are remarkably improved. , It was confirmed to stabilize. From these points, in the present invention, the added Group II metal compound is
It is considered that the active sites of the sodium acid metaphosphate particles are chemically acted, and as a result, the surface of the particles is modified and the hygroscopic reaction is suppressed.

The modified sodium acid metaphosphate of the present invention is characterized in that the effect of improving powder fluidity is extremely stable and lasts for a long period of time. From this point as well, addition of a Group II metal compound is simple. It can be understood that the active site having high reactivity with water is chemically concealed and blocked by the additive, not the effect of physical mixing.

The Group II metal compounds used as additives (modifiers) in the present invention are all sparingly soluble substances, but do not remain as insoluble components at the time of dissolution of sodium acid metaphosphate, and upon dissolution use No problem at all.

As described above, according to the present invention, the powder fluidity of sodium acid metaphosphate is improved, the handling problem is greatly improved, and the use effect associated therewith is remarkable.

For example, in a refractory for spraying, as described above,
At the time of its use, it is mixed with a predetermined amount of water and applied as a slurry to the repair surface, etc., but in order to improve adhesion to the repair surface, a binder with a high curing reaction rate and a high slurry viscosity increase rate is used. It has been demanded. Since the modified sodium acid metaphosphate according to the present invention has good powder fluidity, when used as a binder, the dispersibility in the refractory composition is good, and the curing reaction is accelerated by the addition of water. Has the advantage that a high-viscosity slurry having a strong adhesive force can be obtained in a short time, and the fire resistance of the resulting connective structure also becomes high.

Further, in castable refractories, a deflocculating agent having a strong dispersing action, which shows a deflocculating action quickly even if added in a small amount, is desired, but the modified sodium acid metaphosphate according to the present invention is a highly condensed phosphate. Therefore, the dispersing action is extremely large, and since the powder fluidity is improved and the powder is well dispersed in the composition, the peptizing action can be promptly expressed by adding a small amount.

[Examples] Examples of the present invention will be described below and described in more detail.

Example 1. To 100 g of sodium acid metaphosphate having a Na ₂ O / P ₂ O ₅ molar ratio of 0.52 and a P ₂ O ₅ content of 75.3%, the compounds shown in Table 1 were added as an additive and mixed with sufficient stirring. Then, after standing at 20 ° C. and 80% RH for a predetermined time, the moisture absorption amount and the powder fluidity were measured. The results are shown in Table 1.

Example 2 As in Example 1, except that sodium acid metaphosphate having a Na ₂ O / P ₂ O ₅ molar ratio of 0.71 and a P ₂ O ₅ content of 72.3% was used, the results are shown in Table 1. The compound was added and the moisture absorption and the powder fluidity were measured in the same manner. The results are shown in Table 1.

The "moisture absorption amount" and "fluidity" in Table 1 are as follows.

[Amount of moisture absorption] Place 5g of sample in an open container with an inner diameter of 55m / m and a height of 30m / m.
After left at a temperature of 80% RH for a predetermined time, the weight difference before and after was measured, and this was expressed as a moisture absorption amount in% by weight. It was difficult to obtain an accurate measurement value of the powdery sodium acid metaphosphate without addition because the surface layer portion became sticky due to moisture absorption to prevent the diffusion of water into the inside. (Displayed values are
It is a reference value. ) [Fluidity] The sample left to stand at 20 ° C and 80% RH for a predetermined time was observed to flow out from an hourglass-shaped glass funnel with an outlet hole diameter of 10 m / m. Those that flow out quickly are indicated by a circle, and those that do not pass are indicated by a cross.

As is clear from Table 1, the addition (modifying agent) in the present invention exhibits low hygroscopicity and fluidity which are not caused by the addition of silicic acid anhydride, aluminum oxide and barium sulfate.
Further, it can be understood that even if the additive (modifier) in the present invention is added in an amount of less than 0.5 part by weight, the above effect does not occur.

[Effects of the Invention] Powdery sodium acid metaphosphate has strong hygroscopicity, so that the particle surface becomes sticky, and there is a drawback that it forms a fixed lump and quickly loses fluidity. Although it was a significant obstacle during handling work, the modified sodium acid metaphosphate according to the present invention is a good modified product showing low hygroscopicity and stable flow characteristics for a long time without impairing the original characteristics. Therefore, this facilitates the handling of sodium acid metaphosphate, significantly reduces the trouble in use, and improves the usefulness.

Claims (1)

(57) [Claims] 1. At least 0.5 with respect to 100 parts by weight of powdered sodium acid metaphosphate having a Na ₂ O / P ₂ O ₅ molar ratio of less than 1.
Parts by weight of oxides of calcium, magnesium or zinc,
Modified acidic metaphosphoric acid, characterized in that one or more compounds selected from the group consisting of hydroxides, carbonates, basic carbonates, phosphates and hydroxyphosphates are added. Sodium composition.