JPH0610234B2 - Microspherical cured melamine resin particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to fine spherical cured melamine resin particles having extremely excellent thermal infusibility, mechanical strength and impact resistance, and a method for producing the same.

<Prior Art> The most general method for producing a finely powdered cured melamine resin is to react melamines and aldehydes in the presence of a basic catalyst, then add a curing agent to cure the mixture, and then pulverize it. To do. However, such a method has a problem that a pulverization step is required, the obtained powder has an irregular shape, and the particle size distribution is wide.

For the purpose of solving these problems caused by pulverization, a method of producing fine particles while performing a curing reaction during emulsion polymerization has been proposed. For example, Japanese Examined Patent Publication (Kokoku) No. 32-5743 discloses melamine and formaldehyde in the presence of an acid catalyst.
The reaction is carried out while controlling the pH at 5 to 7 and the temperature at 65 to 75 ° C.
A method for producing fine spherical hardened melamine particles which have been hardened by rapidly adding a large amount of water and leaving it at the moment when the condensation reaction proceeds and the transparent aqueous solution starts to become turbid, is also disclosed in Japanese Patent Publication No. 43-29159. Is a method for producing fine spherical hardened melamine particles, which comprises reacting melamine and formaldehyde in the presence of a hydrophilic polymer protective colloid in an aqueous medium while controlling the pH to 6.0 to 8.0. JP-A-50-45852 discloses that three components of benzoguanamine, melamine and formaldehyde are added in a pH range of 5 to 1
Production of a finely cured resin containing benzoguanamine as a main component, in which the initial reaction product reacted at 0 is emulsified with a hydrophilic polymer protective colloid, and then a curing agent such as an acid is added and cured at 40 to 60 ° C. The law is disclosed.

<Problems to be Solved by the Present Invention> However, there are the following problems in the method for producing a micro-cured melamine resin by a conventionally known emulsion polymerization method,
Improvement was desired.

For example, in the method disclosed in Japanese Examined Patent Publication (Kokoku) No. 32-5743, the particle size greatly depends on the pH and the time of addition of the dilution water.
Therefore, it is necessary to control the extremely narrow range and strictly control the time of addition of dilution water, and it is extremely difficult to repeatedly manufacture a uniform product stably. In addition, Japanese Patent Publication No. 43-
In the method of Japanese Patent No. 29159, not only does pH control in an extremely narrow range are required, but also a protective colloid of a hydrophilic organic polymer is used, so secondary coagulation of fine particles during the reaction cannot be avoided, and the pulverization process is is necessary.

It is considered that these methods require extremely strict control of the reaction, but it is difficult to stably obtain fine spherical hard particles because the condensation reaction rate of melamine and formaldehyde is high.

In JP-A-50-45852, which is aimed at this improvement, an excess of benzoguanamine with respect to melamine is used, and the reaction is controlled in two stages of an initial reaction and a curing reaction. Since the cured resin obtained by this method has a large ratio of benzoguanamine, it should be called benzoguanamine resin instead of melamine resin anymore.Because benzoguanamine which is more expensive than melamine is used, the cost is high and the manufacturing operation is also difficult. It's complicated. Furthermore, since a protective colloid of hydrophilic polymer is used, secondary coagulation of particles during the curing reaction cannot be avoided,
A grinding process is also required.

The present invention solves the above conventional problems. That is, the first object of the present invention is to provide fine spherical cured melamine resin particles whose surface is partially or wholly coated with a substantially water-insoluble inorganic salt. A second object of the present invention is to provide a method for easily producing fine spherical hardened melamine resin particles.

<Means for Solving Problems> As a result of earnest research to solve such problems, the inventors of the present invention can achieve the above object by using a specific inorganic salt as an emulsion stabilizer during emulsion polymerization. The inventors have found that and reached the present invention.

That is, the present invention is a microspherical cured melamine resin characterized in that a part or all of the surface is coated with a substantially water-insoluble inorganic salt containing a fluorine atom and has a particle size of 500 μm or less. Particles and a basic catalyst in an aqueous medium, characterized by reacting melamine and aldehydes in the presence of substantially water-insoluble inorganic salts containing a fluorine atom, part or all of the surface It is a method for producing fine spherical cured melamine resin particles coated with a substantially water-insoluble inorganic salt containing a fluorine atom and having a particle size of 500 μm or less.

Hereinafter, the present invention will be described in more detail.

The substantially water-insoluble inorganic salt containing a fluorine atom referred to in the present invention has a solubility in water at 25 ° C. of 0.2.
It refers to inorganic salts containing fluorine atoms of g / g or less, and examples thereof include calcium fluoride, magnesium fluoride, and strontium fluoride.

The microspherical cured melamine resin particles according to the present invention are obtained by coating the surface of the particles with the above-mentioned substantially water-insoluble inorganic salts, and the embodiments thereof will be described below.

FIG. 1 is a scanning electron micrograph showing an example of the structure of the fine spherical cured melamine resin particles of the present invention, in which substantially water-insoluble inorganic salts containing extremely fine fluorine atoms are deposited on the surface of the particles. , Covering the particle surface. The coating of the particle surface of the water-insoluble inorganic salt containing substantially this fluorine atom, as described below, when reacting melamine and aldehydes in an aqueous medium in the presence of a basic catalyst, fluorine atom Is formed by coexisting substantially water-insoluble inorganic salts containing, by changing the addition amount of the substantially water-insoluble inorganic salts containing a fluorine atom, etc., the desired coating amount Can be

The fine spherical hardened melamine resin particles of the present invention coated with the substantially water-insoluble inorganic salt exhibit fine spherical particles having a particle size of 500 μm or less, as shown in FIG. That is, unlike the conventional powdery or granular particles, the fine spherical cured melamine resin particles of the present invention have a fine spherical shape, and no fusion of particles is observed. Thus, the cured melamine resin particles of the present invention exhibit a fine spherical shape and no fusion is observed because the coating of the substantially water-insoluble inorganic salt containing a fluorine atom formed in the production method described later. It is presumed that this is to prevent fusion during resin production.

Thus, since the fine spherical cured melamine resin particles of the present invention having the above-mentioned constitution are fine spherical particles having a particle size of 500 μm or less, they can be easily handled during use.

Next, a method for producing the fine spherical cured melamine resin particles of the present invention will be described.

First, in the method of the present invention, when reacting melamine and an aldehyde in an aqueous medium in the presence of a basic catalyst, the reaction system is allowed to react with a substantially water-insoluble inorganic salt containing a fluorine atom. Let In the present invention, a part of melamine can be replaced with guanamine, a melamine homologue such as cyanomelamine, or benzoguanamine.
It is also possible to use one kind or a mixture of two kinds thereof. Further, as the aldehydes used in the present invention,
For example, not only formaldehyde in any form such as formalin or paraformaldehyde but also furfural and the like can be mentioned, and the molar ratio of aldehydes to melamine is 1 to 2, and particularly 1.1 to 1.4 is preferable.

As the substantially water-insoluble inorganic salt containing a fluorine atom, calcium fluoride, magnesium fluoride, strontium fluoride and the like are preferable as described above, and the amount thereof is 0.2 to 10 wt% with respect to melamine, particularly 0.5 ~
3.5 wt% is preferred. In addition, in order to add the substantially water-insoluble inorganic salt, the substantially water-insoluble inorganic salt may be directly added as described above, and the above-mentioned substantially water-insoluble inorganic salt may be added during the reaction. Two or more kinds of water-soluble inorganic salts may be added so that the above inorganic salts are produced. That is, for example, in place of the fluorine compound of calcium, magnesium, or strontium, at least one selected from the group consisting of sodium fluoride, potassium fluoride, and ammonium fluoride in one of the water-soluble inorganic salts and calcium, magnesium in the other. It is also possible to add at least one selected from the group consisting of strontium chloride, sulfate and nitrate to produce a fluorine compound of calcium, magnesium and strontium during the reaction.

Further, as the basic catalyst used in the method of the present invention, a basic catalyst used in the usual production of melamine resin can be used, and examples thereof include aqueous ammonia, hexamethylenetetramine and dimethylamine, diethyltriamine, alkylamines such as polyethyleneimine. Etc. The molar ratio of these basic catalysts to melamine is preferably 0.02 to 0.2.

The reaction of the present invention is carried out in an aqueous medium. In this case, as the charged amount of water, for example, the solid content concentration of the resin is 30 to 7
It is desirable to set it to 0 wt%, preferably 50 to 60 wt%. The reaction of the present invention is carried out, for example, under stirring with a temperature rising rate of 0.5 to 1.5 ° C./min, preferably 0.8 to 1.2.
℃ / min, gradually raise the temperature, reaction temperature 70 ~
The reaction is carried out at 90 ° C., preferably 83 to 87 ° C. for 60 to 150 minutes, preferably 80 to 110 minutes. After the reaction in this way, the reaction product is cooled to 40 ° C. or lower to obtain a stable solid aqueous emulsion of the melamine resin.

Next, this aqueous emulsion is separated into solid and liquid by a conventional method such as filtration or centrifugation, and then washed and dried,
The surface is coated with a substantially insoluble inorganic salt, and the particle size is 5
Solid microspherical cured melamine resin particles of the present invention having a size of 00 μm or less are obtained.

The method of the present invention can be carried out by either a continuous method or a batch method, but is usually carried out by the batch method.

In the method of the present invention, when reacting melamine and aldehydes in the presence of a basic catalyst and a substantially water-insoluble inorganic salt containing a fluorine atom in an aqueous medium, a flame retardant such as phosphorus, if necessary. Various additives such as fillers such as talc and talc can be made to coexist.

As described above, the cured melamine resin obtained by the method of the present invention is a smooth, non-fusing, fine spherical solid particle having a particle size of 500 μm or less, most of which is 10 μm.
The particle size distribution is 0 μm or less, and the particle size distribution tends to be narrower than that of the cured melamine resin particles produced by the conventional method.

<Examples> Hereinafter, the present invention will be specifically described with reference to Examples.

Example 1 In a three-necked flask of 1, 200 g of melamine, 37 wt%
150 g of formalin, 70 g of water, 18 g of hexamethylenetetramine, and 8.4 g of calcium chloride were added with stirring to form a uniform solution, and 5.8 g of potassium fluoride was added to this solution under stirring, and the mixture was heated to 85 ° C. for 60 minutes. Raise
The reaction was carried out at the same temperature for 240 minutes to obtain an emulsion of fine spherical hardened melamine resin.

Next, the contents of the flask were lowered to 30 ° C., and 0.5
After adding water, the supernatant was removed, and the microsphered resin particles in the lower layer were washed with water and air dried. Then this is 50
After drying at -60 [deg.] C. for 24 hours, fine spherical resin particles having an average particle size of about 10 [mu] m whose surface was coated with a water-insoluble inorganic salt were obtained. The electron micrograph of these particles had the same shape and surface condition as in FIG.

Comparative Example 1 Melamine resin particles were produced according to the method described in JP-A-50-45852.

That is, 90 g of melamine in a three-necked flask of 1,
37 wt% formalin 130 g, 10 wt% sodium carbonate aqueous solution 0.52 g were charged, and the mixture was stirred at 94 to 95 ° C.
When the reaction was carried out at the temperature of 5 hours, gelation occurred, and even if an aqueous solution obtained by dissolving 8 g of polyvinyl alcohol (polymerization degree 500) in 750 g of water was added, emulsification did not occur, and the whole was hardened to form fine particles. I couldn't get it.

<Effect of the Invention> According to the production method of the present invention, stable microspherical cured melamine resin particles can be obtained very easily. The fine spherical cured melamine resin particles of the present invention are such that a part or all of the surface thereof is coated with a substantially water-insoluble inorganic salt containing a fluorine atom, the particle shape is spherical, and the particle size is 5
It has the following characteristics: it has an average particle size of less than 00 μm, its true specific gravity is smaller than that of an inorganic substance because it is an organic substance, it has good compatibility with organic substances, and it has excellent mechanical strength and impact resistance. Taking advantage of its features, it is used as a reinforcing agent for thermoplastics and rubber, a filler, a filler for thermosetting resin, a matting agent for fibers, a slip improving agent for films, and the like.

[Brief description of drawings]

FIG. 1 is an electron micrograph (magnification: 3000 times) showing an example of the structure of the fine spherical cured melamine resin particles of the present invention.

Front page continuation (72) Inventor Tadashi Ishikura 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Central Co., Ltd. Central Research Institute (72) Inventor Ritsuko Yotsui 23 Uji Kozakura, Uji City, Kyoto Unitika Central Co. Ltd. Central Research Center Examiner Kunihiko Sato (56) References Japanese Patent Publication Sho 56-8845 (JP, B2) Japanese Patent Publication Sho 53-46239 (JP, B2)

Claims (7)

[Claims] 1. A part or all of the surface is coated with a substantially water-insoluble inorganic salt containing a fluorine atom,
And fine spherical cured melamine resin particles characterized by having a particle size of 500 μm or less. 2. The substantially water-insoluble inorganic salt containing a fluorine atom is at least one selected from the group consisting of calcium fluoride, magnesium fluoride and strontium fluoride. The minute spherical cured melamine resin particles according to item 1. 3. A part of the surface, or a part of the surface, which comprises reacting melamine with an aldehyde in the presence of a basic catalyst and a substantially water-insoluble inorganic salt containing a fluorine atom in an aqueous medium. All are coated with substantially water-insoluble inorganic salts containing fluorine atoms, and have a particle size of 500
A method for producing fine spherical cured melamine resin particles having a size of not more than μm. 4. The substantially water-insoluble inorganic salt containing a fluorine atom is at least one selected from the group consisting of calcium fluoride, magnesium fluoride and strontium fluoride. A method for producing the microspherical cured melamine resin particles according to item 3. 5. Calcium fluoride, magnesium fluoride,
The method for producing fine spherical cured melamine resin particles according to claim 4, wherein at least one selected from the group consisting of strontium fluoride coexists with 0.2 to 10 wt% with respect to melamine. 6. Calcium fluoride, magnesium fluoride,
The method according to claim 4 or 5, wherein at least one selected from the group consisting of strontium fluoride is precipitated in the reaction system by using two or more kinds of aqueous inorganic salts. A method for producing fine spherical cured melamine resin particles. 7. The inorganic salt of the aqueous solution is sodium fluoride,
At least one selected from the group consisting of potassium fluoride and ammonium fluoride, calcium, magnesium,
The at least one selected from the group consisting of chloride, sulfate and nitrate of strontium.
Item 10. A method for producing fine spherical cured melamine resin particles according to the item.