JPS6210126A - Microspherical cured melamine resin particle and its production - Google Patents

Abstract

PURPOSE:To facilitate the formation of the titled resin particles surface-treated with a water-insoluble inorganic salt and being excellent in infusibility, etc., by reacting melamine with an aldehyde in the presence of a basic catalyst and a water-soluble inorganic salt in an aqueous medium. CONSTITUTION:Melamine is reacted with an aldehyde (e.g., formalin) in an aqueous medium in the presence of a basic catalyst (e.g., aqueous ammonia or hexamethylenetetramine) and a water-insoluble inorganic salt (e.g., calcium fluoride or magnesium fluoride). In this way, microspherical cured melamine resin particles whose surfaces are coated at least partially with the inorganic salt and which have a particle diameter <=500mum, a true density lower than that of an inorganic substance, a good affinity for an inorganic substance and excellence in mechanical strength, impact resistance, etc., is obtained. These resin particles can be suitably used as a reinforcement, filler or the like for thermoplastic plastics, rubbers, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to microspherical hardened melamine resin particles that are heat infusible and have extremely excellent mechanical strength and impact resistance, and a method for producing the same.

<Prior art> The most common manufacturing method for finely powdered hardened melamine resin is to react melamine and aldehydes in the presence of a basic catalyst, then add a curing agent to cure, and then pulverize. It is something to do. However, such a method requires a crushing step.

There was a problem that the resulting powder was irregular in shape and had a wide particle size distribution.

In order to solve these problems caused by pulverization, a method has been proposed in which fine particles are produced while performing a curing reaction during emulsion polymerization. For example, in Japanese Patent Publication No. 32-5743, melamine and formaldehyde are mixed in the presence of an acid catalyst.
H5-7. React while controlling the temperature at 65 to 75°C,
Japanese Patent Publication No. 43-29159 discloses a method of producing fine spherical hardened melamine particles by rapidly adding a large amount of water and leaving it to stand at the moment when the condensation reaction progresses and a transparent aqueous solution starts to become cloudy. discloses a method for producing fine spherical hardened melamine particles by reacting melamine and formaldehyde in an aqueous medium in the presence of a hydrophilic polymeric protective colloid while controlling the pH to 6.0 to 8.0. Publication No. 50-45852 discloses that the three components of benzoguanamine, melamine, and formaldehyde are mixed at pH 5.
The initial reaction product reacted in steps 1 to 10 is emulsified using a hydrophilic polymeric protective colloid, and then a hardening agent such as an acid is added to harden at 40 to 60°C. A manufacturing method is disclosed.

<Problems to be solved by the present invention> However, there are the following problems in the production method of microcured melamine resin by the conventionally known emulsion polymerization method.
Improvement was desired.

For example, in the method disclosed in Japanese Patent Publication No. 32-5743, the particle size is greatly affected by the pH and the timing of addition of dilution water.
It is necessary to control the pH within an extremely narrow range and to strictly control the timing of addition of dilution water, making it extremely difficult to repeatedly and stably produce a uniform product. In addition, the special public
The method of Publication No. 3-29159 also uses a very narrow range of pH.
In addition, since a protective colloid of a hydrophilic organic polymer is used, secondary coagulation of fine particles during the two reactions is unavoidable, and a pulverization step is necessary.

Although these methods require extremely strict control of the reaction, the reason why it is difficult to stably obtain fine spherical cured particles is said to be due to the high rate of condensation reaction between melamine and formaldehyde.

In JP-A-50-45852, which aims to improve this, an excess of benzoguanamine relative to melamine is used, and nine reactions are controlled by dividing them into two stages: an initial reaction and a curing reaction.

Since the cured resin obtained by this method has a large proportion of benzoguanamine, it should no longer be called a melamine resin but a benzoguanamine resin.

Since benzoguanamine, which is more expensive than melamine, is used, the cost is high and the manufacturing operation is complicated. Furthermore, since a protective colloid of hydrophilic polymer is used,
Secondary coagulation of particles during the curing reaction is unavoidable, and a crushing step is also required.

The present invention solves nine or more conventional problems. That is, the first object of the present invention is as follows.

The present invention provides microspherical hardened melamine resin particles whose surfaces are partially or entirely coated with a substantially water-insoluble inorganic salt. The second object of the present invention is.

The present invention provides a method for easily producing microspherical hardened melamine resin particles.

Means for Solving the Problems As a result of intensive research to solve these problems, the present inventors have found that the above objects can be achieved by using specific inorganic salts as emulsion stabilizers during emulsion polymerization. We discovered this and arrived at the present invention.

That is, in the present invention, part or all of the two surfaces are coated with an inorganic salt that is substantially insoluble in water.

Microspherical cured melamine resin particles characterized by having a particle size of 500 μm or less, and melamine and aldehydes are reacted with a basic catalyst in an aqueous medium in the presence of a substantially water-insoluble inorganic salt. Part or all of the surface is coated with an inorganic salt that is substantially insoluble in water.

This is a method for producing microspherical hardened melamine resin particles having a particle size of 500 μm or less.

The present invention will be further explained in detail below.

The substantially water-insoluble inorganic salts referred to in the present invention are 25
Refers to inorganic salts having a solubility in water of 0.2 g/l or less at °C, such as calcium fluoride, magnesium fluoride, and strontium fluoride.

Calcium phosphate, magnesium phosphate, barium phosphate, aluminum phosphate, barium sulfate.

Examples include calcium sulfate, zinc hydroxide, aluminum hydroxide, iron hydroxide, etc., with calcium fluoride, magnesium fluoride, and strontium fluoride being particularly preferred.

The microspherical hardened melamine resin particles according to the present invention are as follows.

The particle surface is coated with the above-mentioned substantially water-insoluble inorganic salt, and an embodiment thereof will be described below.

Figure 1 is a scanning electron micrograph showing an example of the structure of microspherical hardened melamine resin particles according to the present invention.
Covers the particle surface. The coating of the substantially water-insoluble inorganic salts on the particle surface is effective when reacting melamine and aldehydes in an aqueous medium in the presence of a basic catalyst, as described below. It is formed by allowing inorganic salts to coexist, but by appropriately changing the amount of the inorganic salts that are substantially insoluble in water.

A desired amount of coverage can be obtained.

The microspherical hardened melamine resin particles of the present invention coated with the substantially water-insoluble inorganic salts have a microspherical shape with a particle size of 500 μm or less, as shown in FIG. That is, in the microspherical hardened melamine resin particles of the present invention, each particle is microspherical, and no fusion of the particles is observed, unlike conventional powder or granular particles. in this way.

The reason why the cured melamine resin particles of the present invention have a microspherical shape and no fusion is observed is that the coating of substantially water-insoluble inorganic salts formed in the production method described below prevents fusion during resin production. It is estimated that this is due to

Thus, since the microspherical hardened melamine resin particles of the present invention having the above structure are microspherical particles with a particle diameter of 500 μm or less, they are easy to handle during use.

Next, a method for producing microspherical hardened melamine resin particles of the present invention will be explained.

First, in the second method of the present invention, when melamine and aldehydes are reacted in an aqueous medium in the presence of a basic catalyst, a substantially water-insoluble inorganic salt is allowed to coexist in the reaction system. In the present invention.

A part of melamine can be replaced with melamine analogues such as guanidine and cyanomelamine, benzoguanamine, etc., and one or two of these can also be used in combination. Examples of the aldehydes used in the present invention include formaldehyde in any form such as formalin or paraformaldehyde, as well as furfural, and the molar ratio of the aldehyde to melamine is 1 to 2. Particularly preferred is 1.1 to 1.4.

As mentioned above, calcium fluoride, magnesium fluoride, strontium fluoride, etc. are preferable as substantially water-insoluble inorganic salts, and the amount thereof is 0 to melamine.
．． 2 to 10 ivt%, particularly 0.5 to 3.5 wt% is preferred. In addition, in order to add substantially water-insoluble inorganic salts, the substantially water-insoluble inorganic salts may be directly added as described above.

Furthermore, two or more types of water-soluble inorganic salts may be added such that substantially water-insoluble inorganic salts are produced during the reaction. i.e. 1 eg calcium.

In place of the fluorine compounds of magnesium and strontium, one of the water-soluble inorganic salts is at least one selected from the group consisting of sodium fluoride, potassium fluoride, and ammonium fluoride, and the other is a chloride of calcium, magnesium, and strontium. .

At least one selected from the group consisting of sulfates and nitrates may be added to produce fluorine compounds of calcium, magnesium, and strontium in one reaction.

2. As the basic catalyst used in the method of the present invention, 9 basic catalysts commonly used in the production of melamine resins can be used. 2. For example, aqueous ammonia, hexamethylenetetramine, and alkyl amines such as dimethylamine, diethyltriamine, and 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, and in this case, the amount of water charged is 1. For example, the solid content concentration of the resin is 30 to 7.
It is desirable that the content be 0-t%, preferably 50-60i1t%. In the reaction of the present invention, for example, the heating rate is 0.5 to 1.5° C./min under stirring.

The temperature is gradually increased, preferably at a rate of 0.8-1.2°C/min, until the reaction temperature is 70-90°C, preferably 83-90°C.
The reaction is carried out at 87° C. for 60 to 150 minutes, preferably 80 to 1)0 minutes. After reacting in this manner, the reactant is cooled to 40° C. or lower to obtain a stable solid aqueous emulsion of 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.
Particle size 5 whose surface is coated with substantially insoluble inorganic salts
Solid microspherical cured melamine resin particles of the present invention with a diameter of 00 μm or less are obtained.

The method of the present invention can be carried out either continuously or batchwise; however, it is usually carried out batchwise.

In the method of the present invention, when melamine and aldehydes are reacted in an aqueous medium in the presence of a substantially water-insoluble inorganic salt and a basic catalyst, flame retardants such as phosphorus, talc, etc. are added as necessary. It is possible to coexist with various additives such as additives.

The cured melamine resin obtained by the method of the present invention as described above is a smooth, unfused, microspherical solid particle with a particle size of 500 μm or less, and most of the particles are 10 μm or less.
It has a particle diameter of 0 μm or less, and tends to have a narrower particle size distribution than cured melamine resin particles produced by conventional methods.

<Example> EXAMPLES The present invention will be specifically explained below using examples.

Example 1 1) Add 200 g of melamine to the three flasks.

150 g of 37wt% formalin, 70 g of water, 18 g of hexamethylenetetramine, and 8.4 g of calcium chloride were added with stirring to form a homogeneous solution, and 5.8 g of potassium fluoride was added to this solution with stirring.

The temperature was raised to 85° C. for 60 minutes, and the reaction was carried out for 240 minutes at the same temperature to obtain an emulsion of microspherical hardened melamine resin.

The flask contents were then allowed to cool to 30°C.

After adding 0.51 g of water, the supernatant liquid was removed, and the microspheroidal resin particles in the lower layer were washed with water and air-dried.

Next, this was dried at 50 to 60°C for 24 hours.

Surface coated with water-insoluble inorganic salts, average particle size approximately 1
Microspherical resin particles of 0 μm were obtained. An electron micrograph of this particle showed 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.

In other words, 17! 90g of melamine in 3 flasks
, 130 g of 37 wt % formalin, and 0.52 g of 10 t % sodium carbonate aqueous solution were charged and reacted at a temperature of 94 to 95 °C for 5 hours with stirring, gelation occurred, and polyvinyl alcohol (polymerization degree 500 Even when an aqueous solution obtained by dissolving 8 g of ) in 750 g of water was added, emulsification did not occur, and the entire product hardened and no microparticles were obtained.

<Effects of the Invention> According to the production method of the present invention, microspherical cured melamine resin particles can be obtained very easily and stably. The microspherical hardened melamine resin particles of the present invention have 1 part or all of the surface coated with substantially water-insoluble inorganic salts, 1 particle shape is spherical, and 2 particle diameters are uniform at 500 μm or less; Since it is an organic material, its true specific gravity is lower than that of inorganic materials, and it has the following characteristics: 1. It has good compatibility with organic materials; 1. It has excellent mechanical strength and impact resistance.

Taking advantage of its characteristics, it is used as a reinforcing agent and filler for thermoplastic plastics and rubber, a filler for thermosetting resins, a matting agent for fibers, and a slip improver for films.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph (magnification = 3000 times) showing an example of the structure of microspherical hardened melamine resin particles of the present invention.

Claims (7)

[Claims] (1) Microspherical hardened melamine resin particles characterized in that part or all of the surface is coated with a substantially water-insoluble inorganic salt, and the particle size is 500 μm or less. (2) Microspherical hardened melamine according to claim 1, wherein the substantially water-insoluble inorganic salt is at least one selected from the group consisting of calcium fluoride, magnesium fluoride, and strontium fluoride. resin particles. (3) characterized by reacting melamine and aldehydes in the presence of a basic catalyst and a substantially water-insoluble inorganic salt in an aqueous medium, in which part or all of the surface is substantially immersed in water; A method for producing microspherical hardened melamine resin particles coated with an insoluble inorganic salt and having a particle size of 500 μm or less. (4) Microspherical hardened melamine according to claim 3, wherein the substantially water-insoluble inorganic salt is at least one selected from the group consisting of calcium fluoride, magnesium fluoride, and strontium fluoride. Method for producing resin particles. (5) Microspheric hardening according to claim 4, in which 0.2 to 10 wt% of at least one selected from the group consisting of calcium fluoride, magnesium fluoride, and strontium fluoride coexists with respect to melamine. Method for producing melamine resin particles. (6) A patent claim in which at least one member selected from the group consisting of calcium fluoride, magnesium fluoride, and strontium fluoride is precipitated in a reaction system using two or more water-soluble inorganic salts. A method for producing microspherical cured melamine resin particles according to item 4 or 5. (7) The water-soluble inorganic salt is at least one selected from the group consisting of sodium fluoride, potassium fluoride, and ammonium fluoride, and the group consisting of chlorides, sulfates, and nitrates of calcium, magnesium, and strontium. The method for producing microspherical hardened melamine resin particles according to claim 6, which is at least one selected type.