JPS6134430B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing melamine cyanurate. More specifically, the present invention relates to a method for industrially producing melamine cyanurate from melamine and cyanuric acid easily and at low cost.
Melamine cyanurate has the reaction formula

As shown in [Table], it is thought to be an addition salt of an organic compound produced by a neutralization reaction between the base melamine acid and cyanuric acid, but recently this melamine cyanurate has been used as a nitrogen-containing difficult-to-use compound for polyamide resin. It has been found that it has superior properties as a refractory agent than conventionally used melamine and cyanuric acid. The conventional general method for synthesizing melamine cyanurate is to mix an aqueous melamine solution and an aqueous cyanuric acid solution to immediately cause a neutralization reaction between the melamine and cyanuric acid, producing hardly soluble melamine cyanurate as a precipitate. It was a method (hereinafter referred to as an aqueous solution reaction method) in which it could be separated by operations such as separation and drying. However, when this method is carried out on an industrial scale, the production efficiency is low because the solubility of melamine and cyanuric acid in water is low and it is not possible to prepare a concentrated aqueous solution. It has been difficult to put it into practical use because it is difficult to separate and requires a long time to dry because the separated melamine cyanurate particles contain a considerable amount of water. Taking these circumstances into consideration, the present inventors have conducted extensive research to develop an industrially viable method for producing melamine cyanurate. When is a poorly soluble solid, the reaction occurs at the interface between the solid starting material and the liquid, and the solid reaction product covers the surface of the solid starting material, inhibiting the progress of the reaction. , melamine, which is a uniform mixture of melamine particles and cyanuric acid particles with a certain average particle size or less.
When a powder mixture of cyanuric acid was prepared and a much smaller amount of water was added to the mixture than the amount of water required to dissolve the melamine and cyanuric acid in the mixture, the reaction proceeded in a solid-liquid coexistence system and the melamine was dissolved. The present invention was achieved by discovering that cyanurate is produced. That is, in producing melamine cyanurate from melamine and cyanuric acid, the present invention
First, a powder homogeneous mixture of melamine and cyanuric acid with an average particle size of 100μ or less is prepared, and then 30 to 300% water based on the weight of the mixture is added to the mixture to cause the melamine and cyanuric acid to react. The present invention provides a method for producing melamine cyanurate. Melamine used as a starting material in the present invention has the structural formula Cyanuric acid is a compound represented by the structural formula There are two possible tautomers, as shown in
Although the keto form is called isocyanuric acid, the name cyanuric acid used in the present invention does not mean only the enol form, but includes both the enol form and the keto form. Melamine and cyanuric acid in the present invention are
When melamine and cyanuric acid are uniformly mixed, the average particle size of the powder mixture must be 100μ or less, preferably 60μ or less. The average particle size in the present invention refers to the longest length of one particle in all directions, and the average particle size of one particle in all directions is the particle size.
This is the average particle size obtained by averaging the individual particle sizes. If the average particle size of the melamine/cyanuric acid mixture powder exceeds 100μ, no matter how uniformly the melamine and cyanuric acid are mixed, the reaction rate after adding water will be extremely slow, and furthermore, the reaction will not occur at a certain reaction rate. This is not preferable because it may stop.
The smaller the particle size is, the more preferable it is. Any known method may be used to reduce the average particle size of the melamine/cyanuric acid mixture powder to 100μ or less, but as an example,
A method of mixing fine powders of melamine and cyanuric acid with an average particle size of 100μ or less, pulverizing and mixing melamine and cyanuric acid with an average particle size of more than 100μ, and reducing the average particle size of the melamine/cyanuric acid mixture powder after mixing to 100μ or less. For example, the method of In the present invention, any known method can be used to uniformly mix melamine and cyanuric acid. However, in order to mix melamine fine powder and cyanuric acid fine powder, which have extremely small particle sizes, sufficiently uniformly in a short time, a high-speed stirring type mixer such as the Henschel mixer or a product known as the Flush Mixer is used. It is preferable to mix using a disc rotating mixer. In addition, the above-mentioned high-speed stirring mixer, rotary disc mixer, ball mill, pan mill, etc. are used to mix powders, powders, or lumps of melamine and cyanuric acid with an average particle size of more than 100μ while pulverizing them. It will be done. The mixing ratio of melamine and cyanuric acid of the present invention is preferably 1:1 in molar ratio because melamine cyanurate is produced by equimolar reaction. However, if the produced melamine cyanurate is used as a flame retardant, the molar ratio must be strictly 1:1.
It is not necessary that the molar ratio be such that a trace amount of excess melamine or cyanuric acid remains. Furthermore, the mixing molar ratio of melamine and cyanuric acid may be intentionally set in order to obtain a mixture of melamine cyanurate and melamine or a mixture of melamine cyanurate and cyanuric acid all at once. Also, when mixing melamine and cyanuric acid, depending on the intended use of melamine cyanurate, dispersants, lubricants, heat stabilizers, pigments, etc. may be added and mixed at the same time, as long as they do not inhibit the reaction between melamine and cyanuric acid. I can't help it. The amount of water added to the melamine-cyanuric acid mixture of the present invention is from 30 to 300% by weight of the mixture. If the amount of water is less than 30% by weight, the water will not be sufficiently dispersed throughout the mixture and the reaction rate will be extremely slow, making it impractical. If the amount of water exceeds 300% by weight, after the reaction is complete,
This is not preferable because it becomes necessary to separate melamine cyanurate before drying and purifying it, which only makes the solid-liquid separation operation troublesome. The temperature of the water added is 0℃
Any temperature between ~100℃ is acceptable. Furthermore, the pH of the water may be weakly acidic or slightly alkaline as long as it does not inhibit the production of melamine cyanurate. The method of adding water to the melamine/cyanuric acid mixture to react melamine and cyanuric acid in the present invention is a well-known method of stirring, kneading, or kneading a viscous mixture containing water, or a paste-like or slurry-like mixture. This method or the method of leaving it as is. Stirring, kneading, and kneading have a higher reaction rate than leaving the mixture to stand, but one of the features of the present invention is that the reaction proceeds sufficiently practically even if the mixture is left to stand. The reaction time varies depending on the amount of water added, the particle size of the melamine/cyanuric acid mixture, and whether a stirring operation or the like is added, but when the reaction time is left to stand, it is preferably several hours to about one week. When water is added to the mixture and reacted, a method of accelerating the reaction by heating can also be used. In the present invention, the reaction rate between melamine and cyanuric acid is preferably 100%, but not necessarily 100%.
%, but 50% or more, preferably 80% or more is sufficient. The reaction rate can be measured by (1) taking advantage of the fact that cyanuric acid is easily soluble in dimethylformamide, whereas melamine and melamine cyanurate are poorly soluble; A method of extracting cyanuric acid using cyanuric acid and calculating the production rate of melamine cyanurate from the remaining amount of cyanuric acid. (2) First, the reaction product including unreacted substances is washed with dimethylformamide to remove cyanuric acid, Another method is to wash the reaction product with hot water to remove melamine, isolate melamine cyanurate, and determine the reaction rate. The method for producing melamine cyanurate of the present invention includes:
Compared to the aqueous solution reaction method, the process of mixing powder, adding water, allowing it to stand, drying, and pulverizing is required, so the equipment is simpler and smaller in scale, and the separate steps required with the aqueous solution reaction method are not required. It is excellent in terms of productivity and economy, and is extremely advantageous industrially. EXAMPLES Examples are shown below to explain the present invention in more detail, but the present invention is not limited thereto. Example 1 2.52Kg (20mol) of melamine powder with an average particle size of 40μ
and 2.58 kg (20 mol) of cyanuric acid powder with an average particle size of 30μ were mixed for 3 minutes in a Henschel mixer with an internal volume of 20 μm, taken out, and the particle size was examined, and the average particle size was 35μ. 300 g of the mixture was placed in eight two-container beakers, water was added to each beaker in the proportions shown in Table 1, and the mixture was left at room temperature for 24 hours and 72 hours. After standing, the reaction product was directly heated and dried, and the reaction rate was measured. The reaction rate is measured by taking advantage of the fact that cyanuric acid is soluble, whereas melamine and melamine cyanurate are poorly soluble in dimethylformamide. Unreacted cyanuric acid is extracted from the reactant with dimethylformamide, and the reaction rate is determined from the amount of unreacted cyanuric acid. was calculated. The results are shown in Table 1.

[Table] Example 2 Melamine and cyanuric acid having different average particle sizes as shown in Table 2 were prepared, and 20 moles of each were mixed using the Henschel mixer used in Example 1 for the mixing time shown in Table 2. After mixing and removal, the particle size was examined. Next, each mixture was placed in 20 plastic buckets, 7.65 kg of water (150% by weight to mixture) was added to each, and the mixture was left at room temperature for 24 hours and 72 hours. After standing, the reaction product was heated and dried, and the reaction rate was determined in the same manner as in Example 1. The results are shown in Table 2.

[Table] Comparative Example For comparison, an aqueous solution reaction method was carried out. First, prepare two 200 liter tanks with steam heating jackets and stirrers, fill each with 100 ounces of water, add 2.52 kg (20 moles) of melamine to one tank,
2.58Kg (20mol) of cyanuric acid in the other tank
and heat each tank with steam to bring the liquid temperature to about 85.
℃ and dissolved the melamine and cyanuric acid. Next, the melamine aqueous solution was poured into a cyanuric acid aqueous solution tank and stirred for 30 minutes. Next, the reaction solution containing the produced melamine cyanurate as a precipitate was passed through a centrifugal filtration machine to obtain melamine cyanurate in the form of a paste with a water content of about 150%. This pasty melamine cyanurate was dried by heating to obtain 5.01 kg of melamine cyanurate. As you can see from this comparative example, in order to obtain 5 kg of melamine cyanurate using the aqueous solution reaction method, even if the solubility is increased by heating, 200 ml of water and two 200 ml tanks are required, and additional equipment is required after the reaction. be. In contrast, as can be seen from Examples 1 and 2, the method of the present invention requires a maximum of 20 Henschel mixers and 15 water to obtain 5 kg of melamine cyanurate, and about 20 containers required to leave the mixture. After the reaction, the water content of the reactant is at most 300%, so melamine cyanurate can be obtained simply by heating and drying without any additional operations.

Claims (1)

[Claims] 1. When producing melamine cyanurate from melamine and cyanuric acid, first the average particle size is
A method of producing melamine cyanurate, which is characterized by preparing a powder homogeneous mixture of melamine and cyanuric acid with a size of 100μ or less, and then adding 30 to 300% water based on the weight of the mixture to react the melamine and cyanuric acid. Production method.