JPH0625206B2 - Method for producing polymer-coated sericite particles - Google Patents

Description

The present invention relates to a method for producing polymer-coated sericite particles,
More specifically, the present invention provides a radically polymerizable, at least one ethylenic non-polymerizable molecule in the presence of a fine powder of sericite which is colloidally dispersible in water and has a charge opposite to that of the emulsion polymer in water. The present invention relates to a method for producing polymer-coated sericite particles, which comprises radical emulsion polymerization of a monomer having a saturated bond in water.

The polymer-coated sericite particles are particularly useful as a slurry or paste for producing a sericite-containing foamed polymer, and can be used as a molding material such as compression molding in a dry state, or as a reinforcing material for other resins. it can.

As a method for coating a fine inorganic filler with a polymer, the prior art is known.
The one disclosed in 61-16936 is known. That is, in JP-A-61-16936, the surface characteristics (hydrophilicity) of mineral fibers having an aspect ratio of 5 to 100 as a filler for reinforcing a thermoplastic resin are modified to be hydrophobic, and a thermoplastic resin as a matrix resin is disclosed. In order to improve the affinity with the resin,
A method of suspension polymerizing such mineral fibers is disclosed. According to the description of this publication, the vinyl-based monomer is graft-polymerized on the surface of the mineral fiber in the suspension polymerization,
Polymerization proceeds and the fiber surface is finally covered with the vinyl polymer. Therefore, this method can be said to be a coating method of a fine inorganic material by a chemical means such as a graft polymerization of a vinyl-based monomer onto a mineral fiber.

DISCLOSURE OF THE INVENTION The present invention is different from that by the chemical means described in JP-A-61-16936, based on a physical mechanism, more specifically based on electrical interaction, and nevertheless the surface is It is an object of the present invention to provide a novel method for coating a fine inorganic material with a polymer, which enables uniform coating.

Thus, according to the present invention, radical emulsion polymerization is possible,
In a method of emulsion-polymerizing a monomer having at least one ethylenically unsaturated bond in the molecule in water in the presence of an emulsifier and a radical initiator, the emulsion polymerization can be performed by colloidal dispersion in water. And in the presence of colloidal dispersion of fine powder of sericite having a charge opposite to that of the emulsion polymer produced, removing or without removing excess water from the polymerization system after polymerization, To obtain individual sericite fine powder particles coated with an emulsion polymer in the form of a slurry or paste, and optionally dehydrating and drying the slurry or paste to obtain individually separated polymer-coated particles. A method for producing polymer-coated sericite particles is provided.

In the present invention described above, the monomer to be polymerized is at least 1 in the molecule which can be emulsion-polymerized by a radical initiator.
Any monomer may be used as long as it has one ethylenically unsaturated bond.

Typical examples of such monomers are vinyl monomers, for example ethylene, propylene, vinyl chloride, vinyl bromide, vinylidene chloride, vinyl acetate, acrylonitrile, styrene, α-methylstyrene, acrylic acid. , Methacrylic acid, methyl acrylate, methyl methacrylate, acrylamide, N-methylol acrylamide, 4-vinyl pyridine, N-vinyl pyrrolidone and the like. Also,
The conjugated diene-based monomer is also one of typical monomers that can be used in the emulsion polymerization of the present invention. Examples of this diene monomer include butadiene, isoprene, chloroprene, piperylene and the like. These monomers may be used alone or in a combination of two or more in the method of the present invention.

In the polymerization according to the present invention, the concentration of the monomer that can be used in the polymerization system is within the concentration range used in ordinary emulsion polymerization.
Generally, a concentration of about 5-80% is used.

During the polymerization, the monomer is emulsified in water at a predetermined concentration using an emulsifier. As the emulsifier, a conventional one can be used. Examples of emulsifiers commonly used in the method of the present invention include sodium lauryl sulfate, anionic surfactants such as sodium alkylbenzenesulfonate, alkylammonium halides such as dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide. There are various cationic surfactants and nonionic surfactants such as polyoxyethylene alkyl ether. Such emulsifiers are generally used in the range of about 0.01 to 2% by weight based on the aqueous medium, but may be more or less as long as they are emulsifiable and not harmful.

The aqueous monomer emulsion having a predetermined concentration prepared as described above is then mixed with the fine powder of sericite as an inorganic filler.

The fine powder of sericite to be mixed with the aqueous monomer emulsion in the present invention has a charge opposite to that of the polymer produced in the aqueous emulsion, and can be colloidally dispersed in water. Here, "having an electric charge opposite to that of the polymer in an aqueous emulsion" means not only being charged as such in an aqueous medium itself, but having no electric charge in an aqueous medium as it is. However, by treating the dispersion in water by an appropriate method, for example, an acid, a base or a salt such as AlCl ₃ , Fe ₂ (SO ₄ ) ₃ or Ce (NO ₃ ) ₃・ 6H ₂
It can be charged by adding a salt such as O 2.

The inorganic filler used in the present invention is sericite as a hydrous aluminosilicate clay mineral. Sericite generally has the property of being well wetted by water, so that its fine powder is well dispersed in an aqueous medium, which helps achieve a colloidal state.

In the present invention, sericite is used after being crushed to a particle size such that it is colloidally dispersed in an aqueous emulsion. It is most suitable for the purpose of the present invention that the particle size is in the submicron to micron order, but a larger particle size can be adopted if colloidal dispersion is possible.
Such sericite fine powder can be easily produced by a conventional fine pulverizer and can be used for classification.

The mixing of the aqueous monomer emulsion and the fine powder of sericite is carried out by adding the fine powder of sericite or its aqueous dispersion to the aqueous monomer emulsion and stirring, or vice versa. It can be easily achieved by adding an aqueous monomer emulsion to the liquid and stirring, or by adding a monomer and an emulsifier to an aqueous dispersion of fine powder of sericite and stirring.

When an aqueous dispersion of fine powder of sericite is used for mixing, the concentration of sericite is preferably selected within a range in which the aqueous dispersion forms a suspension, usually about 5 to 80% by weight.
Is used. However, the sericite concentration itself is not a particularly important factor, and even if the sericite is not uniformly suspended, it is dispersed by appropriately stirring,
In this state, the fine powder of sericite is added to the monomer emulsion so that the dispersed state is maintained under stirring, or conversely, the monomer and the emulsifier, or the preformed monomer emulsion is added to the aqueous dispersion. Can be added.

The concentration of sericite in the aqueous monomer emulsion to be subjected to polymerization is basically a concentration at which the dispersed state can be maintained under stirring polymerization conditions. This depends on the desired coating amount of the polymer on the fine powder particles of sericite, the ease of stirring during the polymerization, and the like. The commonly used sericite concentration is about 5-80%, preferably about 10-60% by weight, based on the weight of the mixed system.

The sericite-containing aqueous monomer emulsion obtained as described above is then subjected to a polymerization reaction after adding a radical initiator thereto. As the radical initiator, those generally used for emulsion polymerization of the unsaturated monomer can be used.
A typical example of such an initiator is benzoyl peroxide,
Lauroyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide and other peroxides, potassium persulfate, ammonium persulfate and other persulfates, and azobisisobutyronitrile, 2,2′-azobis (2,4-dimethyl) An azo compound such as valeronitrile, 2,2'-azobis (2-amidinopropane) hydrochloride, etc. A redox initiator commonly used as a radical initiator can also be preferably used. As a typical example, there is a combination of the above-exemplified peroxide with an iron (II) compound such as ferrous ammonium sulfate hexahydrate as a reducing agent, a chromium ion, or a sulfite or hydroxylamine. These radical initiators are usually about 0.05-2.0% by weight of the monomer, more usually about 0.1%.
~ 1.0 wt%, most commonly about 0.4-0.6 wt%. The polymerization can be carried out at room temperature or higher and lower than 100 ° C., that is, lower than the boiling point of water. The polymerization temperature depends, of course, on the type of monomer. Usually about 3
Temperatures in the range 0-70 ° C are employed. Since this radical polymerization is generally an exothermic reaction, the temperature should be controlled so that the reaction does not proceed excessively. The polymerization can be carried out statically on a laboratory scale, but is usually carried out with stirring. In static polymerization, it is generally observed that when the polymerization reaction proceeds to some extent, the formed polymer-coated sericite particles settle to the bottom of the polymerization vessel. In the polymerization under stirring, the polymer-coated sericite particles are usually precipitated when the stirring is stopped after the completion of the polymerization reaction. The completion of the polymerization reaction can be known by confirming that the temperature of the external heating system does not rise above the temperature of the external heating system even if the temperature of the external heating system is raised, and the reaction heat is not generated. In the case of the above-exemplified monomers, the polymerization reaction is generally completed in about several hours to several tens of hours.

Polymers or copolymers of the above monomers generally have a positive or negative charge in water. It is known that the charge of the polymer or the copolymer contributes to the terminal charge of the polymer molecular chain due to the radical initiator or the polarization of the polar group in the polymer molecular chain. This charge is also influenced by the emulsifier used, as is well known. The charge of such a polymer or copolymer in water can be known by measuring the so-called zeta potential.

According to the present invention, individual sericite fine powders are coated with the produced polymer by the above emulsion polymerization. Thus, the mechanism by which the sericite particles are coated with the polymer is that the surface of the sericite particles is oppositely charged, the growing polymer radicals are trapped by electrostatic attraction, and the polymerization is performed on the surface of the sericite particles. Both a mechanism of progress and a mechanism of causing interparticle coagulation by electrical interaction between the colloid particles of sericite and the colloid particles of the polymer are considered.

In the present invention, it has not been confirmed which of the above two mechanisms the formation of the polymer-coated sericite particles is achieved by, or which of the two mechanisms is dominant,
In any case, if the sericite and the polymer do not satisfy the specified charge state, the sericite settles without being substantially covered with the polymer, while the polymer forms a latex and both phases are separated. From the existence, it seems certain that the coating of the sericite particles by the polymer is due to the electrical interaction between the two.

The coating of sericite with such polymers is not fully achieved by suspension polymerization. This is probably because in suspension polymerization, the particle size of the produced polymer is too large to uniformly and densely cover the colloidal particles of sericite.

When stirring is stopped after the completion of emulsion polymerization, the produced polymer-coated sericite particles generally settle to the bottom of the polymerization vessel. The precipitated polymer-coated sericite particles remove excess water from the polymerization vessel,
For example, if it is removed by centrifugation or simple decantation, a slurry or paste is obtained. However, depending on the concentration of sericite and the concentration of polymer, it may be in a slurry state as it is at the end of the polymerization.

The thus obtained aqueous slurry or paste comprising the polymer-coated sericite particles of the present invention is further dehydrated or, without dehydration, or conversely when it is thick for its intended use. Can be used. The most important application of such a slurry or paste is the production of a sericite-containing resin foam by ejecting such a slurry or paste from a sealed container under heat and pressure into a low temperature, low pressure environment.

The polymer-coated sericite particles formed by the above-described method of the present invention remove water from the slurry or paste, and apply reduced pressure through, for example, a filter, suction,
Once removed and dried, it can be converted into discrete polymer coated sericite particles. This does not mean that the polymer particles and the sericite particles are simply mixed in the slurry or paste, but the sericite particles are coated with the polymer, and the coated sericite particles are the slurry. Or means dispersed in the paste.

The coating layer of the coated sericite particles thus formed is very uniform. This is understood from the fact that the sericite particles are very finely and uniformly distributed in the resin foam produced by the method outlined above from the slurry or paste formed as described above,
It is also confirmed by scanning electron micrographs.

As can be seen from the above description, according to the present invention, by a very simple means of emulsion polymerization in the presence of fine powder of sericite, the surface of the polymer-coated sericite particles is uniformly coated with a polymer. It can be manufactured as a slurry or paste. This slurry or paste is particularly useful as a raw material for producing a sericite-containing resin foam, and the slurry or paste is dehydrated,
The polymer-covered sericite particles obtained by drying can be used as a filler for compounding and reinforcing the matrix resin, or as a molding raw material for compression molding or the like.

The present invention has been described in detail above. Next, the present invention will be specifically described with reference to examples. However, these examples merely exemplify the present invention, and the present invention is not limited by these examples.

Example 1 A 1-liter four-necked round-bottomed flask equipped with a mercury-sealing stirrer, a thermometer, a pH probe, and a nitrogen gas blowing tube had a sericite having a particle size of microsands (produced by Kosaka Mine,
100 g (trade name: Microclean) was boiled while blowing nitrogen gas, 500 g of water deoxidized by cooling was added, and the mixture was stirred at about 300 rpm to disperse sericite in water. Of sericite dispersion
The pH was about 4. Add styrene 1 to this sericite dispersion.
00 g and 0.5 g of sodium lauryl sulphate were added and stirred vigorously while bubbling nitrogen gas to form a water emulsion of styrene containing finely divided sericite powder. 1 g of potassium persulfate was added to the obtained styrene water emulsion, the flask was sealed with mercury, and then the flask was heated to 80 ° C. in a warm bath to polymerize while stirring under a nitrogen atmosphere. A small sample was taken after 3 hours of polymerization and examined by scanning electron microscopy as described below, it was observed that the sericite particles were already uniformly coated with the polymer. Polymerization was carried out for a total of 5 hours. The polymerization rate at that time was about 95%.

After the polymerization, a part of water was removed from the polymerization mixture by centrifugation to obtain a homogeneous paste. This paste was useful for the production of foams that were ejected from a high temperature / high pressure state into a low temperature / low pressure environment.

A small sample was taken from the above paste, sufficiently sucked and dehydrated, and then vacuum dried at 80 ° C. for 5 hours to obtain individually separated sericite particles whose surface was coated with polystyrene (PS). When a photograph of the PS-coated sericite particles was taken with a scanning electron microscope at a magnification of 20000, it was found that the entire surface of the sericite particles was uniformly coated with PS along the complicated irregularities and layered structure. .

Comparative Example 1 1 was added to an aqueous dispersion of sericite prepared in the same manner as in Example 1.
After the N-NaOH aqueous solution was added dropwise until the pH of the dispersion became 6 to 7, styrene, sodium lauryl sulfate and potassium persulfate were added in the same manner as in Example 1 and polymerization was carried out at 80 ° C. When the stirring was stopped after 5 hours of the polymerization, it was observed that the sericite particles were settled. Therefore, 2 g of hydroquinone as a polymerization inhibitor was added to the polymerization system to stop the polymerization reaction.
After the termination of the polymerization, when left to stand, sericite particles were precipitated in the lower layer, and it was confirmed that polystyrene was present in the aqueous phase as a latex. The precipitated sericite was taken out, dehydrated, dried and observed by a scanning electron microscope (SEM), but the presence of a polystyrene layer was not substantially observed on the surface of the sericite particles. It is considered that this is because the addition of alkali to the aqueous dispersion of sericite causes the sericite to lose its surface charge and become incapable of electrical interaction with polystyrene.

Example 2 The starting material of Example 1, potassium persulfate, in the same amount of 2,2′-
Polymerization was performed in the same manner as in Example 1 except that azobis (2-amidinopropane) hydrochloride was used instead. After the polymerization, a polymerization sample was taken, dehydrated and dried in the same manner as in Example 1, and then SE
When observed by M, it was found that the sericite was uniformly coated with PS.

Example 3 Polymerization was performed in the same manner as in Example 1 except that the same amount of sodium alkylbenzenesulfonate was used instead of the emulsifier sodium lauryl sulfate of Example 1. After the polymerization, a polymerization sample was collected, dehydrated and dried in the same manner as in Example 1, and then SEM.
When observed by, it was confirmed that the sericite was uniformly coated with PS.

Example 4 Except that 100 g of styrene of Example 1 was replaced with 100 g of a 50/50 mol% mixture of styrene and acrylic acid,
Polymerization was carried out in the same manner as in Example 1. After the polymerization, a polymerization sample was taken, dehydrated and dried in the same manner as in Example 1, and then observed by SEM. It was confirmed that sericite was uniformly coated with the styrene / acrylic acid copolymer.

Example 5 Polymerization was performed in the same manner as in Example 1 except that 100 g of styrene of Example 1 was replaced with 100 g of a 50/50 mol% mixture of styrene and methyl methacrylate. After polymerization,
A polymerized sample was collected, dehydrated and dried in the same manner as in Example 1, and then observed by SEM.
It was found to be uniformly coated with the methyl methacrylate copolymer.

Example 6 To an aqueous dispersion of sericite prepared in the same manner as in Example 1, methyl methacrylate was emulsified at a concentration of 0.5 mol / 1 · H ₂ O. The emulsifier was dodecyltrimethylammonium bromide and was used at a concentration of 1 × 10 ⁻⁴ mol / 1 · H ₂ O.
2,2′-Azobis (2-amidinopropane) hydrochloride was added to the obtained sericite fine powder-containing methyl methacrylate water emulsion at a concentration of 5.0 × 10 ⁻³ mol / 1 · H ₂ O, and the mixture was stirred under a nitrogen atmosphere. While carrying out the polymerization at 60 ° C. for 6 hours. The polymerization rate was about 85%. When the stirring was stopped after the polymerization, the sericite coated with polymethylmethacrylate (PMMA) spontaneously precipitated. When the supernatant was removed by decantation, PMMA-coated sericite particles were obtained in the form of slurry or paste. A small amount of the sample was sufficiently sucked and dehydrated, and then dried at 80 ° C. for 5 hours to obtain individually separated sericite particles whose surface was coated with PMMA. Taking a photograph of these PMMA-coated sericite particles with a scanning electron microscope at a magnification of 20,000,
It was observed that the entire surface of the sericite particles was uniformly coated with PMMA along the complicated irregularities and layered structure.

Example 7 To an aqueous dispersion of sericite prepared in the same manner as in Example 1, 160 g of acrylonitrile and 4 g of sodium lauryl sulfate were added and stirred to form an emulsion. 0.2 g of potassium persulfate and 0.6 g of sodium hydrogen sulfite were added to the obtained emulsion, and polymerization was carried out at 35 ° C. for 8 hours while stirring under a nitrogen atmosphere. Polymerization rate is substantially 10
It was 0%.

After polymerization, when stirring is stopped, polyacrylonitrile (PA
The sericite coated with N) spontaneously settled. When the supernatant was removed by decantation, PAN-coated sericite particles were obtained in the form of slurry or paste. A small amount of the sample was sufficiently sucked and dehydrated in the same manner as in Example 1,
Subsequent vacuum drying gave individually separated resin-coated sericite particles whose entire surface was uniformly coated with PAN.

Example 8 To an aqueous dispersion of sericite prepared in the same manner as in Example 1, 200 g of vinyl acetate and 6 g of sodium lauryl sulfate were added and stirred to form an emulsion. 0.5 g of benzoyl peroxide and ferrous sulfate hexahydrate were added to the obtained emulsion.
1.4 g and sodium pyrophosphate 6.0 g were added, and polymerization was carried out at 40 ° C. for 4 hours while stirring under a nitrogen atmosphere.

When the stirring was stopped after the polymerization, the sericite coated with polyvinyl acetate spontaneously precipitated. When the supernatant was removed by decantation, polyvinyl acetate-coated sericite particles were obtained as a slurry or paste. A small amount of the sample was sufficiently sucked and dehydrated in the same manner as in Example 1, and then vacuum-dried to obtain individually separated resin-coated sericite whose entire surface was uniformly coated with polyvinyl acetate.

Claims (1)

[Claims] 1. A method of emulsion-polymerizing a radical emulsion-polymerizable monomer having at least one ethylenically unsaturated bond in the molecule while stirring in water in the presence of an emulsifier and a radical initiator, The emulsion polymerization is carried out in the presence of colloidally dispersed fine powder of sericite, which is colloidally dispersible in water and has a charge opposite to that of the emulsion polymer to be produced, and an excess amount of the polymer is obtained from the polymerization system. Individual particles of sericite fine powder whose surface is coated with an emulsion polymer are obtained in the form of a slurry or paste, with or without removal of water, and the slurry or paste is dehydrated and dried, if necessary. A process for producing polymer-coated sericite particles, characterized in that the polymer-coated particles separated into the above are obtained.