JPH0827124A - Method for improving purity of melamine cyanurate - Google Patents

Abstract

PURPOSE:To improve the purity of melamine cyanurate without carrying out the washing with water by further heating a crude product thereof obtained in the presence of water in obtaining the melamine cyanurate from melamine and cyanuric acid in the presence of water. CONSTITUTION:This method for improving the purity of melamine cyanurate is to heat a crude melamine cyanurate obtained by a method for producing the melamine cyanurate from melamine and cyanuric acid in the presence of water to 220-450 deg.C. If several kinds of impurities are simultaneously contained, they can be removed so far as substances capable of evaporating, subliming or decomposing at <=450 deg.C are included as the impurities contained in the crude melamine cyanurate. The melamine and/or cyanuric acid or water used for the reaction is cited as the impurities. Thereby, a simplified, economical and industrially predominant method for improving the purity of the melamine cyanurate is provided according to this method. The resultant melamine cyanurate is mainly useful as a flame retardant for polyamides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the purity of melamine cyanurate, and more particularly to a method for improving the purity of melamine cyanurate by heating crude melamine cyanurate containing impurities.

[0002]

2. Description of the Related Art Melamine cyanurate is mainly used as a flame retardant for polyamides. In general, when a flame retardant is used for plastic, the flame retardant contaminates the surface of the plastic or the mold during the molding process (mold deposit) or causes a foaming phenomenon. Further, when the molded product is used under high temperature and high humidity conditions, the flame retardant may exude onto the plastic surface (bleed out). Melamine cyanurate is a flame retardant in which these phenomena do not easily occur. However, when impurities such as unreacted melamine and cyanuric acid are contained in melamine cyanurate, phenomena such as mold deposit and bleed-out easily occur. Therefore, it is desirable to use a highly pure melamine cyanurate used as a flame retardant.

Melamine cyanurate was usually prepared by a method in which melamine and cyanuric acid were dissolved in water, respectively, an aqueous solution thereof was mixed and reacted, and a precipitate of the sparingly soluble melamine cyanurate produced was filtered and dried. .

However, when this method is carried out on an industrial scale, (1) the solubility of melamine and cyanuric acid in water is low and a concentrated aqueous solution cannot be prepared, so that the production efficiency is low, and (2) the reaction product is fine particles. However, there is a problem that it is not easy to separate it by filtration or the like.

As an industrial method, a method in which water is mediated instead of the reaction of the above-mentioned aqueous solution, that is, 20 to 2000 parts by weight of water is added to 100 parts by weight of the total amount of solid melamine and solid cyanuric acid. , A method of reacting while stirring or kneading (JP-A-54-555)
87); A method for preparing a powdery homogeneous mixture of melamine and cyanuric acid having an average particle size of 100 μm or less, and then adding 30 to 300% of water based on the mixture to react the mixture (JP-A-54-54). 55588) is disclosed.

[0006] In view of these techniques, the present inventors have further reduced the amount of water added to produce melamine cyanurate, that is, with respect to 100 parts by weight of a mixture of melamine and cyanuric acid having an average particle diameter of 10 µm or less. A method for producing melamine cyanurate, which is characterized by adding less than 20 parts by weight of water and reacting it, has already been proposed.

Further, as a method without using water, a method for producing melamine cyanurate characterized by heating powdered melamine and powdered cyanuric acid at 250 to 500 ° C. in the substantial absence of a liquid medium. Have already proposed. However, this method does not use water, so filtration,
Although there is an advantage that a drying step is unnecessary, the reaction temperature is 250 to 500 ° C. and the reaction must be performed at a high temperature as compared with the method using water, which causes a problem that energy required for the reaction is large. It was

The crude melamine cyanurate obtained by the above-mentioned method using water as a medium generally contains unreacted melamine and / or cyanuric acid. Further, depending on the reaction method, it also contains the pH adjusting agent used in the reaction. Therefore, in order to obtain high-purity melamine cyanurate, washing with water has been performed to remove them. However, washing of melamine cyanurate requires a large amount of water, and the crude melamine cyanurate obtained by the method using water as a medium is in the form of fine particles,
It was very difficult to separate the water used for washing by filtration or the like.

Further, since the melamine cyanurate particles after washing with water contain a considerable amount of water, there is a problem that it takes a long time to dry.

[0010]

Since the conventional washing method uses water, filtration and drying steps are required. Further, the amount of water used for the reaction is large even if it is not washed with water, which causes a problem of wastewater treatment. An object of the present invention is to provide an industrially excellent method for improving the purity of melamine cyanurate, which has a simplified manufacturing process as compared with the conventional technique.

[0011]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the crude melamine cyanurate obtained in the presence of water is further heated to wash it with water. The present inventors have found that the purity of melamine cyanurate is improved even if it is not performed, and completed the present invention. That is, the present invention is characterized in that the crude melamine cyanurate obtained in the method for producing melamine cyanurate from melamine and cyanuric acid is heated at 220 to 450 ° C. in the presence of water. It is a method of improving purity.

Crude melamine cyanurate, which can be improved in purity by the method of the present invention, has an impurity content of 45.
As long as it includes one that evaporates, sublimes, or decomposes at 0 ° C. or less, it can be removed even if several kinds are contained at the same time.

Generally, a crude melamine cyanurate obtained by a reaction using water as a medium, for example, an average particle size of 10 each.
To 100 parts by weight of a 1: 1 equimolar mixture of melamine and cyanuric acid having a size of not more than μm, 15 parts by weight of water is added and the temperature is 200 ° C.
Impurities of the crude melamine cyanurate obtained by stirring for 2 hours are mainly water and reaction raw materials melamine and cyanuric acid. The reaction raw materials melamine and cyanuric acid are mixed because the reaction is not completely progressed or the molar balance of melamine and cyanuric acid is broken during the reaction for some reason.

In the conventional method, the water used in the reaction is partially separated from the crude melamine cyanurate by filtration or the like, and after washing, it is removed at a temperature of about 100 ° C. in the drying step. On the other hand, according to the method of the present invention, after the reaction, excess water is separated by filtration or the like, if necessary, and then water can be removed simultaneously with impurities such as unreacted melamine and / or cyanuric acid.

The amount of water contained in the crude melamine cyanurate that can be removed by the method of the present invention is not particularly limited, but preferably 2 per 100 parts by weight of melamine cyanurate.
The amount is 00 parts by weight or less, more preferably 100 parts by weight or less, and further preferably 50 parts by weight or less. When the amount of water exceeds 200 parts by weight with respect to 100 parts by weight of melamine cyanurate, the time for removing the water becomes long and it is not efficient.

The amount of impurities other than water is not particularly limited, either.
Pure melamine cyanurate in crude melamine cyanurate 1
The amount of impurities other than water is preferably 25 parts by weight or less with respect to 00 parts by weight. If the amount of impurities other than water is 25 parts by weight or less, the melamine cyanurate having a purity of 99% by weight or more can be efficiently obtained. However, if the amount of impurities other than water exceeds 25 parts by weight, the treatment time becomes long and it is not efficient. When compared with the method of carrying out the reaction in the absence of a medium, the economic advantage of the whole process including the reaction step is lost.

When the crude melamine cyanurate contains only one of melamine and cyanuric acid as impurities, it can be removed from the crude melamine cyanurate by sublimating melamine or cyanuric acid like other impurities. it can. On the other hand, when melamine and cyanuric acid are simultaneously contained as impurities, both react with each other to produce melamine cyanurate, thereby improving the purity.

The crude melamine cyanurate capable of improving the purity in the present invention may have any shape such as powder and granules.
The smaller the particle size, the higher the efficiency with which impurities are volatilized, and the higher the efficiency in improving purity.

The heating temperature is 220 to 450 ° C., preferably 240 to 400 ° C., more preferably 280 to 37.
0 ° C. If the heating temperature is lower than 220 ° C, melamine and / or cyanuric acid, which are the main impurities of crude melamine cyanurate, cannot be removed because they do not sublime, and even if both are contained, the reaction is almost impossible. It won't happen. When the heating temperature exceeds 450 ° C, the amount of sublimation of melamine cyanurate itself increases and the loss increases, and the complicated reaction due to the high temperature (heat history)
Cause impurities to increase.

The heating time for making the crude melamine cyanurate containing 25 parts by weight or less of impurities other than water 100% by weight of melamine cyanurate to have a purity of 99% or more depends on the shape of the crude melamine cyanurate. In the case of powder, if the heating temperature is 250 ° C, it is 300 ° C for 1 to 5 hours.
30 minutes to 3 hours, 350 ° C for 10 minutes to 2 hours, 4
It is 5 to 30 minutes at 50 ° C. If the heating time is shorter than the above range, the purity is improved, but sufficient purity cannot be obtained. Further, if the length is longer than the above range, further improvement in purity cannot be expected, and not only the energy required for heating is lost but also the sublimation amount of melamine cyanurate itself increases, which is not efficient.

The apparatus used for heating is not particularly limited,
After carrying out the reaction, heating may be carried out in the reactor as it is, or heating may be carried out in an apparatus different from the reactor.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 In a Henschel mixer having a capacity of 10 liters, industrial melamine (average particle size 20 μm) 0.9 manufactured by Mitsui Toatsu Chemicals, Inc.
7 kg and cyanuric acid manufactured by Shikoku Kasei Co., Ltd., trade name ICA-P
(Average particle size 80 μm) 1.00 kg was charged and mixed at room temperature for 10 minutes. Then, using a jet mill, the whole amount of the mixture was ground at room temperature to obtain 1.91 kg of a finely ground mixture. The average particle size of this finely ground mixture is 3.46μ.
m (measured by laser beam diffraction method based on volume).

50 g of this finely pulverized mixture was put in a magnetic crucible, 7 g of water was added, and the mixture was mixed with a spoon for about 2 minutes at room temperature. Then, the crucible was capped and put in an electric furnace.
It heated at 1 degreeC for 1 hour, and the crude melamine cyanurate was obtained. The composition of this crude melamine cyanurate was 85.2% by weight of melamine cyanurate and 1.3% by weight of water, and the balance was melamine and cyanuric acid.

30 g of this reaction mixture was placed in a magnetic crucible and further heated at 350 ° C. for 90 minutes to obtain 27.8.
g was recovered, of which 99.9% by weight was melamine cyanurate. Also, the water is completely removed,
When treated with a thermobalance (TGA-50H type manufactured by Shimadzu Corporation) at 260 ° C. for 70 minutes in an air stream (100 ml / min), the weight loss rate was 1.74%.

Example 2 The same procedure as in Example 1 was carried out except that the crude melamine cyanurate obtained in Example 1 was used and the heating temperature was 280 ° C. and the heating time was 2 hours. As a result, 28.5 g was recovered. Of these, 99.7% by weight was melamine cyanurate. Also,
Similarly, water was completely removed, and the weight loss rate by the thermobalance was 2.07%.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the crude melamine cyanurate obtained in Example 1 was used and the heating temperature was 150 ° C. and the heating time was 4 hours. As a result, 29.6 g was recovered. It was Although water was completely removed from the obtained mixture, the purity of melamine cyanurate was 87.1%, and heating had almost no effect. Weight reduction rate by thermobalance is 14.4
%Met.

Comparative Example 2 30 g of crude melamine cyanurate obtained in the same manner as in Example 1 was added to 1 liter of water and stirred at 95 ° C. for 30 minutes. Thereafter, vacuum filtration was performed at about 30 mmHg using a glass filter (17G-4) manufactured by TOP having a pore size of 5 to 10 μm, but since clogging occurred on the way and filtration became impossible, the pore size of 20 to 30 μm was again obtained. Vacuum filtration was performed using a glass filter (17G-3) manufactured by the same company. At this time, a part of melamine cyanurate was mixed in the filtrate, and it was impossible to completely recover melamine cyanurate. Obtained melamine cyanurate at 120 ° C
However, it took 8 hours to be completely dried.
As a result, 23.2 g of melamine cyanurate was obtained, and its purity was 99.6% by weight.

Example 3 The raw material melamine and cyanuric acid had a molar ratio of 1.2:
50 g of the mixture of No. 1 (average particle size 4.37 μm) was placed in a magnetic crucible, 20 g of water was further added, and the mixture was mixed with a spoon for about 5 minutes at room temperature. Then, the crucible was covered, put in an electric furnace, heated at 200 ° C. for 2 hours, and then vacuum dried to obtain crude melamine cyanurate. The purity of this crude melamine cyanurate was 83.5% by weight, and all impurities were melamine.

When 30 g of this crude melamine cyanurate was heated in the same manner as in Example 1, 24.3 g was recovered, of which 99.9% by weight was melamine cyanurate. The weight loss rate by the thermobalance was 1.92%.

Example 4 A crude melamine cyanurate was obtained in the same manner as in Example 3 except that the raw material mixture (average particle size 3.88 μm) had a molar ratio of melamine to cyanuric acid of 1: 1.2. Was 82.1% by weight and all impurities were cyanuric acid.

When 30 g of this crude melamine cyanurate was heated in the same manner as in Example 1, 23.6 g was recovered and the purity was 99.8% by weight. The weight loss on the thermobalance was 2.02%.

[0033]

Industrial Applicability According to the present invention, it is possible to provide a simplified and economical method for improving the purity of melamine cyanurate as compared with the conventional method, which is industrially advantageous.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Yoshinaga 1-6-6 Takasago, Takaishi-shi, Osaka Mitsui Toatsu Chemical Co., Ltd.

Claims (4)

[Claims] 1. A crude melamine cyanurate obtained by a method for producing melamine cyanurate from melamine and cyanuric acid in the presence of water, heated at 220 to 450 ° C. How to improve. 2. The method according to claim 1, wherein the crude melamine cyanurate contains impurities that are vaporized by sublimation, evaporation or decomposition at 450 ° C. or lower. 3. The method according to claim 2, wherein the impurities are melamine and / or cyanuric acid. 4. The method according to claim 2, wherein the impurity is water used in the reaction.