JPH0250925B2 - - Google Patents

Description

Detailed Description of the Invention The present invention utilizes a polymerizable composition (mixed solution) containing an inorganic filler with a low viscosity in which the inorganic filler is uniformly dispersed in a radically polymerizable vinyl monomer. The present invention relates to a method for producing narrow polymer particles.

The molded product of polymer particles obtained according to the present invention is excellent in easy incineration, rigidity, and dimensional stability.

It is known to add a high content of inorganic fillers to polymers to improve rigidity, dimensional stability, electrical properties, easy incineration, etc. A common method for this addition is to mix the molten polymer and the inorganic filler using a roll, kneader, extruder, plastic bender, or the like.

However, with this method, it generally becomes difficult to prepare a homogeneous mixture as the amount of inorganic filler added increases. If kneading is carried out for a long time in order to improve the dispersion of the inorganic filler in the polymer, the polymer will deteriorate.

As a method to improve these drawbacks, an inorganic filler is added to a radically polymerizable vinyl monomer such as styrene, and this is polymerized to create a polymer composition in which the filler is uniformly dispersed in the polymer. A method of obtaining the item is proposed. However, even with this method, if the filler content is 10% by weight or more, the filler tends to settle and it is difficult to obtain a uniform dispersion, and the composition generally becomes grease-like or clay-like. It is virtually impossible to transfer this composition to a polymerization reactor and to polymerize the composition.

The purpose of the present invention is to solve various molding problems caused by the wide particle size distribution of polymer particles obtained by suspension polymerization of vinyl monomers such as styrene. The object of the present invention is to provide a method for stably producing narrow polymer particles. For example, styrenic polymer particles are produced by suspension polymerization of styrene monomers in the presence of a polymerization initiator and a suspension stabilizer. The particle size distribution of the particles obtained by this suspension polymerization does not have a distribution that includes a wide range of particles from small to large diameters, regardless of the stirring, polymerization temperature, time, addition method of styrene monomer and polymerization initiator, etc. It has the following disadvantages.

(i) When extruding polymer particles, particles with small diameters and particles with large diameters separate in the raw material hopper or the screw section of the feed section of the extruder, causing fluctuations in the amount of extrusion.

(ii) When foaming the foamable polymer beads (particles) obtained by impregnating the particles with a blowing agent during or after suspension polymerization into a molded product, the weight of the molded product may vary due to the difference in expansion ratio between the beads. may be uneven, or the heating and cooling times during molding may be inconsistent.

Generally, expandable polymer beads with a small particle size have a small expansion force and short heating and cooling times. As the particle size increases, the expansion force increases and the time required for cooling also increases.

The appropriate viscosity of expandable polymer beads is greatly restricted by the expansion rate of the expandable beads, processability such as molding cycles, and product wall thickness, and is mainly used in the field of general-purpose molded products where the wall thickness of molded products is 5 mm to 50 mm. and the wall thickness is 100
It can be divided into two categories: block-shaped beads of mm or larger, and the latter naturally has a larger bead diameter. However, the reality is that even in these two fields, particles are sieved into grades within several particle size ranges depending on the application.

When these beads are obtained by suspension polymerization of styrene monomers containing an inorganic filler, the particle size distribution of the beads, which is due to the aggregation of fillers together in a styrene solution, does not contain fillers. The reality is that they are wider than beads. The object of the present invention is to provide a method for solving such particle size distribution problems.

The present inventors added an inorganic filler to vinyl monomer at 10%.
As a result of intensive study to solve the above-mentioned drawbacks when blending at a ratio of % by weight or more, we found that by subjecting the inorganic filler to silane coupling treatment in a vinyl monomer solution (substantially containing no water), vinyl monomer In addition to facilitating the dispersion of the inorganic filler in the polymer,
It has been found that the viscosity of the dispersion decreases. In addition, when the same effect as that obtained by blending a polymer of vinyl monomer soluble in vinyl monomer is brought about by bulk polymerization, the dispersion stability of the inorganic filler in the mixture is further improved. Heading, the invention was completed.

That is, in producing polymer particles containing 10 to 80% by weight of an inorganic filler, the present invention involves mixing the inorganic filler, a silane coupling agent, and a silane coupling promoter in a vinyl monomer solution. The viscosity of the reaction system at 20° C. is adjusted to 100 to 10,000 centipoise by preliminarily bulk polymerizing 5 to 45% by weight of vinyl monomer to the mixed solution obtained in the presence of a polymerization initiator. The present invention provides a method for producing polymer particles, characterized in that the prepared pre-bulk polymerization solution is supplied into water containing a suspension stabilizer, and then heated to carry out suspension polymerization of vinyl monomers. .

In the embodiments of the present invention, the vinyl monomer is a radically polymerizable vinyl monomer that is liquid at room temperature, and specifically includes styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; acrylic acid; Esters obtained from acrylic acid such as methyl and n-butyl acrylate and lower alcohols having 1 to 8 carbon atoms; methyl methacrylate, acrylonitrile, vinyl acetate, maleic anhydride, vinyl chloride, etc. can be used. Among these, the effect of lowering the viscosity of the present invention is remarkable in the case of styrene and methyl methacrylate.

These may be used alone or in combination of two or more.

Inorganic fillers include inorganic fine powders with an average particle size of 0.1 to 100μ, such as silica, alumina, iron oxide,
Metal oxides such as zinc oxide and magnesium oxide; Metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and iron hydroxide; Metal powders such as iron powder and aluminum powder; Other asbestos powder, glass powder, calcium carbonate, carbonate These include magnesium, sodium sulfate, diatomaceous earth, and glass fiber.

Among these, when metal hydroxides are used, the viscosity of the dispersion becomes extremely low.

These may be used alone or in combination of two or more.

As the silane coupling agent, commonly used ones can be used.

Specifically, the general formula, RnSiX _3- n ...... () (wherein R is a monovalent hydrocarbon, a halogenated hydrocarbon group, for example, an alkyl group such as methyl, ethyl, propyl, octyl, decyl, Aryl groups such as phenyl, benzyl, tolyl, chloropropyl,
represents a haloalkyl group such as 3,3,3-trifluoropropyl or promophenyl; It represents an alkoxy group, etc.; n is 0, 1 or 2. ) In addition to the compounds represented by formulas, there are silane compounds having alkoxy groups represented by the following formulas () to ().

(In the formula, R ¹ is H or CH ₃ , R ² is a straight chain or branched alkyl group with 4 or less carbon atoms, R ³ is OR ² or a straight chain or branched alkyl group with 4 or less carbon atoms, or phenyl, A is (It is a straight chain or branched alkylene group having 6 or less carbon atoms.) Specific compound names include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, and methyltrimethoxysilane. Propoxysilane, methyltriptoxysilane, ethyltriethoxysilane, ethyltributoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, trimethylmethoxy Silane compounds without double bonds such as silane, trimethylethoxysilane, trimethylpropoxysilane, trimethylbutoxysilane, tripropylmonochloropropylsilane;
Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxyethyltripropoxysilane, methacryloxymethyltrimethoxysilane, methacryloxyethyltriethoxysilane, Thacryloxyethyltripropoxysilane, Methacryloxypropyltrimethoxysilane, Methacryloxypropyltriethoxysilane, Methacryloxypropyltripropoxysilane, Acryloxymethyltrimethoxysilane, Acryloxymethyltriethoxysilane, Acryloxymethyltripropoxysilane, Acrylic Vinyl silane compounds such as loxethyltrimethoxysilane, acryloxyethyltriethoxysilane, acryloxyethyltripropoxysilane, acryloxypropyltrimethoxysilane, acryloxypropyltriethoxysilane, acryloxypropyltripropoxysilane; N-aminomethyl- Aminomethyltrimethoxysilane, γ-
glycidopropylmethyldipropoxysilane, β
-glycidoxyethylethyldiethoxysilane and the like.

These may be used alone or in combination of two or more.

Examples of silane coupling accelerators include dibutyltin dilaurate, stannous acetate, stannous octenoate,
Carboxylic acid salts such as lead naphthenate, zinc octenoate, iron 2-ethylhexanoate, cobalt naphthenate; titanate esters such as tetrabutyl titanate, tetranonyl titanate, bis(acetylacetonitrile) di-isopropyltitanate, etc. ; Organometallic compounds such as chelates; Organic bases such as ethylamine, hexylamine, dibutylamine, etc. can be used.

The ratio of each of these components is such that the inorganic filler accounts for 10 to 80% by weight, preferably 20 to 70% by weight of the mixed solution, and the silane coupling agent is the proportion of the inorganic filler.
The silane coupling promoter is incorporated in an amount of 0.1 to 5% by weight, preferably 1 to 3% by weight, and 0.01 to 2% by weight of the inorganic filler. Preferably, the viscosity of the mixed solution obtained by pre-bulk polymerization of the mixed solution is 10-10.
Adjust to 10,000 centipoise (cps).

If the proportion of the inorganic filler in the mixed solution is less than 10% by weight, the effect of improving the mechanical strength and dimensional stability of the polymer will not be sufficient. Furthermore, instead of relying on the method of the present invention, it can also be prepared by, for example, a method in which the surface of an inorganic filler is modified with ethyl acrylate, methyl methacrylate, etc., and then kneaded with a molten polymer.

Furthermore, if the amount exceeds 80% by weight, it is difficult to uniformly disperse the inorganic filler in the vinyl monomer, and the viscosity of the mixed solution is high, making it difficult to handle the mixed solution.

Next, the silane coupling agent is used as an inorganic filler.
It is used in a proportion of 0.1 to 5% by weight, preferably 1 to 3% by weight. If it is less than 0.1% by weight, it is difficult to uniformly disperse the filler, and it is also difficult to expect the resulting mixed solution to have a reduced viscosity. Further, even if the amount exceeds 5% by weight, it is difficult to expect further effects of lowering dispersibility and viscosity, and it is economically disadvantageous to use a large amount of the expensive silane coupling agent.

In addition, the silane coupling promoter improves filler
It is used in a proportion of 0.01 to 2% by weight. 0.01% by weight
If it is less than this, the silane coupling reaction will be too slow to be practical. Further, even if the amount exceeds 2% by weight, it is economically disadvantageous because no further promotion of the silane coupling reaction can be expected.

The mixed solution of the present invention is prepared by first mixing the vinyl monomer and the inorganic filler, then adding the silane coupling agent and the silane coupling promoter, and stirring and mixing uniformly. .

A mixed solution containing a silane coupling agent is
The reason why the viscosity is lower than that of a mixed solution of an inorganic filler and vinyl monomer that does not contain the coupling agent is unknown, but it is presumed as follows.

If the inorganic filler is simply dispersed in the vinyl monomer, the inorganic filler has poor affinity for the vinyl monomer, so multiple fillers aggregate together, and the inorganic filler occupies the mixed solution. The volume apparently increases. On the other hand, when a silane coupling agent is blended, the inorganic filler and the silane coupling agent combine, giving the filler affinity with the vinyl monomer and suppressing aggregation of the fillers. The filler is uniformly dispersed in the vinyl monomer solution, and the apparent increase in the volume occupied by the inorganic filler in the mixed solution is small.

Therefore, when the same amount of inorganic filler is blended,
A mixed solution containing no silane coupling agent has a higher viscosity.

Furthermore, the smaller the average particle diameter of the inorganic filler, the more likely it is to aggregate, and the higher the viscosity of the mixed solution becomes.

Although the mechanism of modification of the inorganic filler by the silane coupling agent in the present invention is not clear, for example, when a silane compound having an alkoxy group is used as the silane coupling agent and a metal hydroxide is used as the inorganic filler, It is presumed that a dealcoholization reaction occurs and the coupling agent is chemically bonded to the filler. A silane coupling promoter is blended to promote this coupling reaction and prepare a uniform dispersion in a short time.

In the present invention, a radical polymerization initiator necessary for polymerization is added to the inorganic filler-containing polymerizable mixed solution during or after its preparation.

Such initiators include benzoyl peroxide, lauryl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-di(peroxybenzoate)hexyne-3,
Organic peroxides such as butyl perbenzoate and azo compounds such as azobisisobutyronitrile and dimethyl azocyisobutyrate can be used.

These polymerization initiators are 0.1 to 5% of vinyl monomer.
It is used in a proportion of 0.5 to 1% by weight, preferably 0.5 to 1% by weight.

Furthermore, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, and a rubber substance soluble in the vinyl monomer are blended as necessary.

The mixed solution containing the polymerization initiator is subjected to preliminary bulk polymerization and suspension polymerization (continuous bulk polymerization) to form polymer particles in which the inorganic filler is uniformly dispersed. It is also possible to produce expandable polymer beads by supplying a blowing agent such as n-butane, isobutane, pentane, etc. before or during the polymerization.

Alternatively, expandable beads may be produced by impregnating polymer particles obtained by preliminary bulk polymerization/suspension polymerization with an expanding agent.

A polymerization method that is particularly suitable for producing polymer particles with a narrow particle size distribution is to prepare a mixed solution in the presence of a polymerization initiator of 5 to 45% by weight of vinyl monomer, preferably
20~35% by weight preliminary bulk polymerization is carried out at 20°C in the reaction system.
The viscosity in 100~10000cps, preferably 200~
This is a method in which the preliminarily bulk polymerization solution is prepared at 5000 cps, and then the obtained preliminary bulk polymerization solution is supplied into water containing a suspension stabilizer, and this is heated to carry out suspension polymerization of unreacted vinyl monomers.

Performing preliminary bulk polymerization before suspension polymerization further prevents precipitation of the inorganic filler in the reaction system, and facilitates the transfer of the preliminary bulk polymerization solution to the suspension polymerization reactor and the suspension polymerization.

In this preliminary bulk polymerization, when the vinyl monomer is styrene, the polymerization temperature is 70 to 110°C, and the polymerization is carried out for 1.5 to 10 hours, preferably 2 to 5 hours. At this time, 5 to 45% by weight, preferably 20 to 35% by weight of the styrene monomer is prepolymerized.

The viscosity of the preliminary bulk polymerization solution at 20℃ is 100~
Upon reaching 10,000 poise, the prebulk polymerization solution is fed under stirring into an aqueous medium containing a suspension stabilizer to form a suspension and is heated for 2 to 10 hours at a temperature of 60 to 140 °C, preferably 80 to Suspension polymerization is carried out at a temperature of 130° C. for 4 to 6 hours to complete the polymerization.

Examples of the above-mentioned suspension stabilizers include organic suspension stabilizers such as polyvinyl alcohol, polyvinylpyrrolidone, gelatin, carboxymethyl cellulose, and hydroxyalkyl cellulose, and phosphoric acid or carbonic acid.
Examples include inorganic suspension stabilizers such as Ca and Mg salts.
When an inorganic material such as tertiary calcium phosphate is used, an anionic surfactant such as sodium dodecylbenzenesulfonate may be used in combination as a stabilizing agent.

The amount of suspension stabilizer used is 0.1 to 3% by weight of the bulk polymer or copolymer solution, and the stabilizing agent is 0.002 to 3% by weight of water.
It is 0.05% by weight.

The weight ratio (phase ratio) of the bulk polymer or copolymer solution to water in suspension polymerization is
0.5-2.0, preferably 1.0-1.5. Phase ratio is 1
When the number is 1 or more, the batch size of the reactor becomes smaller, which is more economical, and the resulting particles contain less water and are easier to dry. Furthermore, if the phase ratio exceeds 2.0, stirring becomes difficult as the polymerization progresses.

A molded article obtained by injection molding, extrusion molding, or roll molding of the inorganic filler-containing polymer particles obtained by carrying out the present invention has excellent rigidity and dimensional stability.

The above has described a method for producing polymer particles that do not contain a swelling agent, but when producing polymer particles that contain a swelling agent, the obtained polymer particles are impregnated with a swelling agent after the suspension polymerization described above. Alternatively, it can be obtained by supplying an expanding agent into the reaction system during preliminary bulk polymerization or suspension polymerization and carrying out the polymerization step. In general, it is convenient to supply an expanding agent during suspension polymerization from the standpoint of the polymerization process, but when the diameter of the resulting expandable particles is small, the expanding agent may dissipate during particle sieving and storage. In view of this, it is preferable to impregnate the particles with a swelling agent after suspension polymerization.

Such expansion agents include, for example, propane,
Examples include aliphatic hydrocarbons such as Norman-butane, isobutane, Norman-pentane, isopentane, neopentane, and hexane, alicyclic hydrocarbons such as cyclobutane and cyclopentane, and halogenated hydrocarbons such as methyl chloride and dichlorodifluoromethane. , these may be used alone or in combination of two or more. The swelling agent has a swelling agent content of 5 in the produced particles.
It is normal to supply the amount to about 20% by weight.

In the styrenic polymer particle group obtained by the example of the present invention, 45% of the particles fall into the commercial grade.
This is high, and the particle size distribution is narrow, making it easy to sieve.

Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that parts and percentages in the examples are based on weight unless otherwise specified.

Example 1 To 100 parts of styrene, 40 parts of aluminum hydroxide (manufactured by Showa Light Metal Co., Ltd., trade name "Hygilite") having an average particle size of 17 μm was added at 20° C. under stirring. Then,
1.0% phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-103") and 0.2% dibutyltin dilaurate were added to aluminum hydroxide for 15 minutes at 20°C. A homogeneous mixed solution was obtained by stirring.

The viscosity of this mixed solution at 20°C (measured with a Tokyo Keiki B-type viscometer) was 5 cps.

Add benzoyl peroxide to this mixed solution.
0.3 parts and t-butyl perxybenzoate 0.2
After adding 50% of the dispersion, the dispersion was transferred to an autoclave and heated to 80°C.

Preliminary bulk polymerization was carried out at the same temperature for 2.5 hours to obtain a styrene bulk polymerization solution. The styrene polymerization rate (ratio of 1632 cm ^-1 to infrared absorption of 1602 cm ^-1 ) of this solution was 21.2%.

In addition, this styrene pre-bulk polymerization solution at 20℃
The viscosity was 3070 cps, and when this solution 1 was transferred into a cylindrical graduated cylinder and left to stand, the settling time for the supernatant to become 20% by volume was 20 hours.

This pre-bulk polymerization solution of styrene was added to 200 parts of water in which 0.6 parts of polyvinylpyrrolidone was dissolved.
The mixture was stirred at 300 rpm, and then the temperature of the suspension polymerization reactor was raised from 80°C to 125°C over 7 hours.
Furthermore, stirring was continued for 1 hour at 125°C to complete suspension polymerization and produce polymer particles.

The obtained polymer particles had a particle size of 0.59 to 1 mm in 53%, and an average particle size of 0.81 mm. Also,
The aluminum hydroxide content in the particles was 24.9% (theoretical value was 25.6%).

Claims (1)

[Claims] 1. In producing polymer particles containing 10 to 80% by weight of an inorganic filler, the inorganic filler, silane coupling agent, and silane coupling promoter were mixed in a vinyl monomer solution. The mixed solution is mixed with vinyl monomers in the presence of a polymerization initiator.
The viscosity of the reaction system at 20° C. is adjusted to 100 to 10,000 centipoise by carrying out 45% by weight pre-bulk polymerization, and then the obtained pre-bulk polymerization solution is supplied into water containing a suspension stabilizer and heated. A method for producing polymer particles, which comprises carrying out suspension polymerization of vinyl monomers.