JPH0627217B2 - Method for producing red phosphorus flame retardant - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a red phosphorus flame retardant, and particularly to a method for producing a red phosphorus flame retardant having a high degree of stability.

<Background of the Invention> Red phosphorus is known as a flame retardant for synthetic resins and is added to various resins, but commercially available red phosphorus is rarely used as it is, and in many cases, some stabilization treatment is required. It has been subjected.

This is because red phosphorus itself is unstable with respect to heat, friction, shock, etc., so it is likely to be dangerous during storage and handling, and when kneading with synthetic resin, and further reacts with moisture and oxygen in the air. To produce a harmful substance or to have poor compatibility with a synthetic resin and lack in use stability. For this reason, a coating treatment with an inorganic substance or an organic substance is usually performed.

However, in recent years, the demands on the physical properties of synthetic resin materials have become more severe, and red phosphorus-based flame retardants have also been required to have higher stability.

In thermosetting resins, red phosphorus-based flame retardants are used to make the insulation materials of high-voltage electronic parts flame-retardant, but with the miniaturization of electric equipment and higher voltage, improvement in insulation performance is required. It is difficult to deal with the red phosphorus-based flame retardant materials.

That is, since the conventional red phosphorus flame retardant is not sufficiently stabilized, it is gradually deteriorated by a small amount of moisture in the compounded resin to generate a corrosive substance, which deteriorates the resin with time, and It has been pointed out that it corrodes the metals that make up the epoxy, resulting in poor insulation and reduced performance, and also reduces durability and reliability. Improvement is required.

On the other hand, thermoplastic resins are often used in molded products, devices, housings of devices, etc., but since the molding temperature is high,
Red phosphorus flame retardants that are unstable at high temperatures and ignite or generate phosphine are rarely used, and halogen flame retardants are mainly added.

However, since halogen-based flame retardants generate a large amount of harmful gas when smoked, it is not possible to use additives that generate such a large amount of pollutant gas as interest in fire stability of synthetic resins increases. However, it is clear that there is a problem not only in terms of human safety but also in the maintenance of equipment and machinery, and there is little smoke or harmful gas generated during combustion, and there is little danger of fire safety and low pollution. It is desired to develop a far superior red phosphorus flame retardant which has improved heat resistance stability and can be used as a thermoplastic resin.

<Purpose of the Invention> The present inventors have addressed the problem of stabilization of red phosphorus flame retardants in such a situation, and there is a limit to the conventional method by only surface treatment of red phosphorus particles. As a result of repeated studies on the stabilization of red phosphorus from a completely different angle, it was obtained by a manufacturing method different from conventional red phosphorus,
The surface state and physical properties of red phosphorus particles are completely different from those of conventional products.Red phosphorus having a specific shape is extremely stable and can be used as a flame retardant by itself, and it is remarkably stable by further surface treatment. It has been found that the heat resistance is improved, and the moisture resistance, corrosion resistance, and heat resistance are far superior to those of conventional red phosphorus flame retardants.

Therefore, it is an object of the present invention to provide a method for producing a red phosphorus flame retardant having improved stability and safety.

<Structure and Operation and Effect of the Invention> The present invention includes (1) heating yellow phosphorus to 250 to 600 ° C., converting a part of the yellow phosphorus into red phosphorus, and the content of red phosphorus is 70% by weight or less. Forming a fluid mixture (conversion reaction step), (2) removing unconverted yellow phosphorus from the fluid mixture (separation step), (3) from the obtained spherical particles and / or aggregate particles thereof. A red phosphorus-based flame retardant, characterized in that, after adding water to the powdery red phosphorus to form a suspension, the suspension is coated with a thermosetting resin and / or a metal hydroxide (surface modification treatment step). The present invention is intended to provide the above-mentioned objective "red phosphorus flame retardant having improved stability and safety".

Hereinafter, the manufacturing method of the present invention will be described in detail in comparison with the conventional method.

Red phosphorus is produced by thermal conversion of yellow phosphorus, but as a conventional method for producing red phosphorus, a method of continuing the heat treatment of the raw material yellow phosphorus at a temperature near its boiling point for several days to complete the conversion reaction is taken. There is. (Hereafter, this conventional method is referred to as "complete conversion method".
Say. ) In this case, the red phosphorus forms as a cake-solid, tightly set and integral mass.

However, in order for red phosphorus to exhibit flame retardant curing in a synthetic resin, it needs to be in powder form, and therefore, in the case of ordinary red phosphorus produced as an integral lump from a conversion kettle, the crushing step is It is indispensable.

On the other hand, in the production method of the present invention, since the conversion processing conditions are different, red phosphorus is directly obtained as a powder composed of fine particles, and a crushing step is not required.

That is, in the production method of the present invention, first, the raw material yellow phosphorus is placed in a reaction vessel in which an inert gas is replaced and heated to melt to start the conversion reaction. Next, when the conversion to red phosphorus progresses and reaches a predetermined conversion rate (conversion rate of 70% by weight or less), this reaction is stopped, and unconverted yellow phosphorus is removed by an arbitrary method ( Hereinafter, it will be referred to as "partial conversion method"), and as a result, it will not be formed as a lump as in the conventional complete conversion method, but will be formed as powdery red phosphorus.

The present inventors have completed the present invention by discovering that powdered red phosphorus obtained by such a partial conversion method has remarkably higher stability than conventional ground red phosphorus.

According to the study by the present inventors, the conversion of yellow phosphorus to red phosphorus begins at a relatively low temperature, becomes remarkable near the boiling point, and the reaction rate increases with an increase in temperature. In the low temperature region, red phosphorus is produced as spherical fine particles in molten yellow phosphorus, but as the temperature rises, the fine particles form aggregates and the particle size increases.

Particle growth is also observed with extended reaction time. Therefore, if the reaction temperature is too high, or the reaction time is too long, the reaction proceeds excessively and most of the yellow phosphorus is converted to red phosphorus, so red phosphorus cannot exist as particles, It becomes a condensed lump, and powdery red phosphorus cannot be obtained.

The present inventors have to suppress the excessive conversion reaction, in order to obtain red phosphorus as a powder consisting of fine particles, it is necessary to convert while maintaining the fluidity of the reaction mixture at 250 ~ 600 ℃, It was found that the fluidity of the reaction mixture can be maintained by setting the conversion to 70% or less.

The conversion rate changes depending on the temperature and the reaction time.
The shorter the reaction time, the lower the reaction time. Therefore, the conversion rate can be set arbitrarily by adjusting the treatment temperature and time, but by suppressing the conversion rate to 70% or less, the reaction mixture becomes fluid and the red phosphorus obtained after the separation of unconverted yellow phosphorus is obtained. Will produce a sphere-like powder.

When the reaction temperature is less than 250 ° C, the reaction rate is extremely low, which is not preferable as a practical production condition.
If it exceeds, the conversion rate becomes too high, the reaction is difficult to control, the fluidity of the reaction mixture is suddenly lost, and a lump is formed, and powdery red phosphorus is obtained without going through the crushing step as in the conventional method. Can't do it.

Particles of powdered red phosphorus obtained by the partial conversion method of the present invention,
As described above, the lower the reaction temperature and the shorter the reaction time, that is, the lower the conversion rate, the smaller the particle size. On the contrary, when the reaction time is long and the conversion rate is high, the degree of aggregation of particles increases and the particle size becomes large, but the aggregate particles obtained from the fluid reaction mixture in the method of the present invention are aggregate red phosphorus. In contrast, since the bonding property is extremely weak, it is brittle and easily crumbles, and does not require a treatment such as crushing, and easily disintegrates into powder by a simple mechanical treatment.

Moreover, it is clear from the measurement results that the stability of the aggregate particles is not lost even by such a disintegration treatment, and the powdered red phosphorus obtained by disintegrating the aggregate particles still shows high stability. .

Therefore, the powdery red phosphorus obtained by the method of the present invention also includes the powdery red phosphorus obtained by disintegrating the aggregate particles.

The particle size of powdery red phosphorus obtained by the partial conversion method of the present invention is
The particle size distribution is several μm to 100 μm, and the particle size distribution is narrower and more uniform than the red phosphorus obtained by pulverizing the massive red phosphorus obtained by the conventional complete conversion method (hereinafter referred to as “pulverized red phosphorus”). It is characterized by high price.

In the method of the present invention, since the conversion of yellow phosphorus to red phosphorus is carried out by a partial conversion method different from the conventional complete conversion method, a step of removing unreacted yellow phosphorus (separation step) is required. Any method such as a distillation method, a filtration method and a solvent extraction method can be used.

The distillation method is a method in which the yellow phosphorus content is distilled off under reduced pressure or normal pressure in an inert gas after the reaction is stopped (after the conversion reaction step), and the filtration method is after the reaction mixture is put into water or an aqueous solution. The red phosphorus is filtered off, and the attached yellow phosphorus is washed with an alkaline solution and dried.The solvent extraction method is a method of extracting yellow phosphorus from the reaction mixture using a yellow phosphorus-soluble solvent. , These can also be used in combination of two or more methods. In either case, the separated yellow phosphorus can be recycled to the conversion reaction step to red phosphorus again.

As a surface modification treatment of red phosphorus, when red phosphorus is coated with a thermosetting resin or a metal hydroxide, it is convenient to continuously carry out the conversion reaction step and the coating treatment step. According to the method (1), this can be preferably implemented.

That is, in the method of the present invention, after completion of the conversion reaction to red phosphorus,
The unconverted yellow phosphorus is separated and removed from the reaction mixture, and water is directly injected into the obtained red phosphorus to make powdered red phosphorus into a slurry, or it is directly pumped with nitrogen gas or the like to perform a coating step (surface modification treatment step ) And have the advantage that this coating process can be easily continued.

On the other hand, in the conventional complete conversion method, the red phosphorus produced in the conversion tank is solidified into a solid lump, and a complicated process of crushing the lump is indispensable, and also on the side wall of the tank. Since it is fixed, it has a drawback that a labor-intensive take-out operation is required. Usually, the lumpy red phosphorus in the conversion tank is dug up by using an excavator, etc., and powdering is performed through a complicated procedure of crushing with a crusher after coarsely granulating with a crusher, and thus the conversion reaction as in the present invention. It is impossible to connect the process, the separation process, and the surface modification treatment process (coating process) by a series of directly connected processes.

Further, unconverted yellow phosphorus is likely to be included and remain in the solidified red phosphorus obtained by the conventional complete conversion method, which may deteriorate the quality of red phosphorus or cause ignition in the subsequent step. In the method of the present invention, since red phosphorus is produced in the form of powder, it is easy to remove unconverted yellow phosphorus by distillation and such a problem does not occur.

Thus, in the method of the present invention, a high-quality red phosphorus flame retardant can be easily and economically produced by a series of simplified production steps that do not include a dangerous pulverization step. Most importantly, the red phosphorus obtained by the method of the present invention has a high stability which far exceeds that of conventional stabilized red phosphorus.

The sphere-like red phosphorus obtained by this partial conversion method is further surface-treated with a thermosetting resin and / or a metal hydroxide such as aluminum hydroxide or zinc hydroxide to improve its stability. The problem of deterioration of the synthetic resin due to the addition of the red phosphorus flame retardant is almost eliminated, and almost perfect moisture resistance and corrosion resistance are imparted. In addition, the heat resistance is significantly improved, and it can be safely used as a flame retardant for thermoplastic resins.

Such unique stability of the red phosphorus flame retardant of the present invention is
It is considered that the surface state of the red phosphorus particles produced by the method of the present invention is significantly different from that of the conventional pulverized product (pulverized red phosphorus).

That is, in the granular material obtained by crushing a solidified aggregate like a conventional crushed red phosphorus, the particle surface has a complicated shape composed of sharp ridges and crushed surfaces. The red phosphorus particles obtained by the method described above have almost no crushing surface or ridgeline because they do not go through the crushing process, and it is said that they are composed of particles with spontaneously continuous sphere-like surfaces and their aggregates. It could be confirmed by observation with a microscope.

Therefore, the particles of crushed red phosphorus have many active points on the crushed surface of the surface, and the reaction with moisture and oxygen is active, whereas
The red phosphorus of the present invention has almost no active sites, its surface is extremely stable, and the reaction with moisture or oxygen hardly occurs. As a result, the moisture resistance stability and heat resistance stability are remarkably improved.

Further, even during surface treatment with a thermosetting resin or a metal hydroxide, crushed red phosphorus has uneven coating due to the state of the surface and exposed crushed surfaces tend to remain. Since it is carried out uniformly and completely, there is a definite difference in the stability of the coated red phosphorus.

As a method for surface treatment with a thermosetting resin and / or a metal hydroxide, known means (for example, JP-A-61-291644) is used.
Japanese Patent Laid-Open Publication No. 61-219706).

Of these, thermosetting resins include phenol / formalin type, urea / formalin type, melamine / formalin type,
Formalin-based resins such as furfuryl alcohol / formalin-based, aniline / formalin-based, and polyhydric alcohol / polybasic acid-based resins are suitable, and red containing 10 to 100 parts by weight of red phosphorus to 100 parts by weight of water. 1 to 35 parts by weight of resin synthetic raw material or initial condensate in 100 parts by weight of red phosphorus in an aqueous suspension of phosphorus.
Add parts by weight and stir for 1 hour at 40 to 100 ° C.

At this time, if necessary, a polymerization catalyst and a filler such as aluminum hydroxide, magnesium hydroxide or titanium hydroxide can coexist.

The addition of the filler improves the mechanical strength of the resin coating and has a concealing effect against the purple-red color peculiar to red phosphorus, and thus the application of the red phosphorus flame retardant can be expanded.

Further, for coating with a metal hydroxide, for example, in the case of coating with aluminum hydroxide or zinc hydroxide, an aqueous solution of aluminum or zinc sulfate or chloride is added to an aqueous suspension of red phosphorus, and then a sodium hydroxide solution is used. Aluminum hydroxide or zinc hydroxide is adsorbed on the red phosphorus particles by neutralization or metathesis with ammonium bicarbonate. In this case, the aqueous suspension of red phosphorus is preferably 10 to 100 parts by weight of red phosphorus with respect to 100 parts by weight of water, the concentration of the metal salt solution in water is 5 to 30%, and the amount of hydroxide formed is 100% by weight of red phosphorus. 1 to 30 parts by weight is preferable per part by weight.

Further, as the surface modification treatment step (coating step) of the present invention,
A resin that has been coated with a metal hydroxide and then double-coated with a thermosetting resin has the best stability and does not deteriorate even under severe conditions. Has almost no effect due to the addition of the red phosphorus flame retardant over a long period of time. When performing double coating, the coating amount of metal hydroxide is 0.1 to 100 parts by weight of red phosphorus.
30 parts by weight is preferred.

As a conventional technique related to the method for producing red phosphorus, a method is known in which the above-mentioned complete conversion method is replaced with the thermal conversion into red phosphorus and the evaporation of yellow phosphorus at the same time.

For example, JP-A-60-141608 discloses that heat conversion into red phosphorus is performed at a boiling point to evaporate yellow phosphorus, vapor of yellow phosphorus is discharged from a reaction vessel, and is collected by a condenser. According to this method, red phosphorus is obtained as a soft and friable mass,
Further, it is described that the desired particle morphology can be obtained with almost no manipulation, which shows the similarity to the present invention.

However, in the method for producing red phosphorus according to this conventional technique, it is essential that the conversion of red phosphorus and the evaporation of yellow phosphorus are performed simultaneously. Therefore, (1) the conversion reaction step to red phosphorus (red phosphorus) Content of 70% by weight
The following steps of forming a fluid mixture, that is, a step of forming a fluid mixture with a conversion rate to red phosphorus of 70% or less), and (2) a separation step of removing yellow phosphorus, are configured as separate steps. The method of the present invention is clearly different from the method of the present invention.

Moreover, the above-mentioned prior art merely discloses that the obtained red phosphorus product is “porous and soft”.
There is nothing about obtaining red phosphorus having physical properties suitable for the red phosphorus flame retardant intended in the present invention (see Table 1 below).

In addition, as another conventional technique, Japanese Patent Publication No. 59-19044 discloses a rotary ball mill set at a predetermined temperature for the purpose of obtaining a high-purity red phosphorus so that a conversion reaction occurs at a high rate. Yellow phosphorus is gradually introduced to carry out the conversion reaction,
After the conversion is completed, a method of adding water and further wet milling is described.

According to this method, red phosphorus is powdered by incorporating a pulverizing means in the manufacturing process, which is clearly different from the present invention in which partial conversion which does not require the pulverizing step is essential. Further, since the pulverization treatment is included, powdery red phosphorus composed of spherical particles as in the present invention cannot be obtained.

<Effects of the Invention> As shown in Tables 1 and 2 below, all of the red phosphorus flame retardants produced by the method of the present invention have a high ignition point and excellent heat resistance stability as compared with those of conventional ground red phosphorus. In addition, the moisture resistance stability has also been greatly improved, and since there is almost no generation of phosphine or formation of corrosive acidic substances due to the reaction with water,
As a highly safe flame retardant for thermoplastic resin,
It is most suitable and extremely useful as a flame retardant for insulating resins for high-voltage electronic parts, which requires high quality stability in terms of corrosion resistance.

In addition, the method of the present invention does not require a crushing step in terms of steps and can be continuous in steps, so that it is advantageous in terms of equipment, labor, cost, etc. as compared with the conventional method, and has excellent economic efficiency. Is to have.

<Example> (Example 1) 500 g of yellow phosphorus was placed in a stainless steel container in which nitrogen gas had been replaced and sealed, and after heating at 270 ° C for 4 hours, unconverted yellow phosphorus was removed. 211 g of powdery red phosphorus having an average particle diameter of 50 μm was obtained (conversion rate to red phosphorus: 42.2%).

The red phosphorus was suspended in 400 ml of water, 150 ml of 10% aqueous solution of aluminum sulfate was added, 50 ml of 5% aqueous solution of sodium hydroxide was added dropwise with sufficient stirring, and the mixture was heated to 50 ° C. and kept for 30 minutes. This was filtered, washed with water and dried to obtain 217 g of a red phosphorus flame retardant.

(Example 2) 100 g of yellow phosphorus was placed in a high-pressure reaction vessel in which nitrogen gas was replaced, and the vessel was sealed, heated to 480 ° C in 30 minutes, kept at that temperature for 10 minutes, and then cooled. Unconverted yellow phosphorus was removed to obtain 68 g of powdery red phosphorus (conversion rate to red phosphorus: 68%). This red phosphorus is 10
The residue was 22% in the 0mesh sieve test, but it became 100mesh whole by pulverizing with a finger.

Next, suspend this in 200 ml of water, 3 g of phenol, 37%
6 g of formalin was added, heated to 80 ° C., and 2 g of 85% phosphoric acid was added with stirring. After heating and stirring at the same temperature for 1 hour, the mixture was allowed to cool, filtered and dried to obtain 72 g of a red phosphorus flame retardant.

(Example 3) 200 g of yellow phosphorus was placed in a reaction vessel in which nitrogen gas had been replaced and sealed, and after heating at 280 ° C for 1.5 hours, unconverted yellow phosphorus was removed.
36 g of powdery red phosphorus having an average particle diameter of 28 μm was obtained (conversion rate to red phosphorus: 18%).

This is suspended in 100 ml of water and 8 m of 8% aluminum sulfate aqueous solution
After adding l and stirring, 10% 15% ammonium bicarbonate aqueous solution
l was added dropwise and heated at 60 ° C. for 10 minutes.

Next, add 2 g of phenol and 4 g of 37% formalin, and add 80 ° C.
1 g of 85% phosphoric acid was added with stirring. After continuing stirring at the same temperature for 1 hour, the mixture was allowed to cool, filtered and dried to obtain 39 g of a red phosphorus flame retardant.

Table 1 shows the physical properties of the red phosphorus obtained in Examples 1 to 3 and Table 2 shows the stability of the red phosphorus flame retardant.

Comparative Example 1 Commercially available ground red phosphorus (the physical properties of which are shown in Table 1) was coated in the same manner as in Example 1 above.

The stability of the obtained red phosphorus flame retardant is shown in Table 2.

Comparative Example 2 The commercially available ground red phosphorus used in Comparative Example 1 was coated in the same manner as in Example 2.

The stability of the obtained red phosphorus flame retardant is shown in Table 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 61-291644 (JP, A) JP-A 61-219706 (JP, A) JP-A 60-141608 (JP, A) JP-B 59- 19044 (JP, B2)

Claims (1)

[Claims] 1. Yellow phosphorus is heated to 250 to 600 ° C., a part of the yellow phosphorus is converted into red phosphorus to form a fluid mixture having a red phosphorus content of 70% by weight or less. After removing unconverted yellow phosphorus, water is added to the powdery red phosphorus composed of the obtained spherical particles and / or aggregate particles thereof to form a suspension, and then thermosetting resin and / or metal water is added. A method for producing a red phosphorus flame retardant, which comprises coating with an oxide.