JPS6356245B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a vinyl polymer having a desired shape and a narrow particle size distribution. Vinyl polymers are generally produced by methods such as suspension polymerization and emulsion polymerization. In the former method, methyl cellulose, polyvinyl alcohol, and
Gelatin and the like are used, and in addition to adding a dispersion stabilizer, it is necessary to stir during polymerization in order to prevent destruction of the dispersion state. For example, the vinyl chloride polymer obtained by this method is usually porous and has a large particle size ranging from several tens of microns to over a hundred microns with significant unevenness on the particle surface, and also has a wide particle size distribution. In the latter method, emulsifiers (surfactants)
Since a water-soluble polymerization initiator is used, the particle size becomes extremely small and spherical, with a particle size of about 2 μm or less, and when a plasticizer is added to form a paste sol, the viscosity is extremely high. Microsuspension polymerization is used as a method to obtain polymers with particle sizes between these two, but because of the use of emulsifiers in the polymerization, the resulting polymers have an extremely wide particle size distribution. Controlling the diameter was extremely difficult and required advanced technology. Incidentally, the particle size distribution of the polymers obtained by these methods expressed as quantity average particle diameter/number average particle diameter is around 2. As a result of various studies with the aim of obtaining a polymer with a narrow particle size distribution having a particle size of several microns to several tens of microns by a simple method, the present inventors conducted suspension polymerization of vinyl monomers in an aqueous medium. In this process, an oil-soluble polymerization initiator is dissolved in a vinyl monomer, water containing the above-mentioned dispersant, which is not normally referred to as a surfactant, is added thereto, stirred at high speed, and then dissolved in a conventional manner. They discovered that a polymer with a narrow particle size distribution could be obtained by polymerization, and as a result of extensive research on the method of adding vinyl monomers, they were able to obtain the desired particle shape and size from several microns to several tens of microns. The present invention was accomplished by discovering that a vinyl polymer having the following properties can be obtained. A method similar to the method of the present invention is described in JP-A No. 53-97680, but this method is simply a fine suspension polymerization, and since a surfactant is used in the method, the particle size is extremely wide. Only polymers with a certain distribution can be obtained. Therefore, the gist of the present invention is to provide a method for producing a vinyl polymer by polymerizing vinyl monomers containing an oil-soluble polymerization initiator in an aqueous medium containing a dispersant. 40 of the total amount
~90%, apply high-speed shearing force to the polymerization system using a polymerization initiator, disperse vinyl monomer into fine particles, and then polymerize. When the polymerization conversion rate of vinyl monomer reaches 30% or more, vinyl The present invention resides in a method for producing a vinyl polymer characterized by adding the remainder of the monomer. To explain the present invention in detail, vinyl monomers include, but are not particularly limited to, vinyl chloride, vinyl acetate, acrylic esters, methacrylic esters, styrene, vinyltoluene, methoxy Examples include vinyl monomers that are insoluble or poorly soluble in water, such as styrene, and these can be used alone or in combination. Furthermore, the vinyl monomer used in the method of the present invention may be a mixture of the above vinyl monomer and a copolymerizable monomer such as butadiene. In particular, the method of the present invention uses vinyl chloride or a mixture containing vinyl chloride as the main component and other copolymerizable monomers such as vinyl acetate, methyl acrylate, etc. in an amount of up to about 20% by weight. is preferred. Any polymerization initiator may be used as long as it generates radicals upon thermal decomposition, such as dialkyl or diaryl peroxide,
Examples include peroxy acid esters and diacyl peroxides, specifically lauroyl peroxide, isononanoyl peroxide, decanoyl peroxide, benzoyl peroxide, tert-butyl peroxypivalate, di-
tert-butyl-cyclohexyl peroxydicarbonate, diethyl peroxydicarbonate,
Examples include dicyclohexyl peroxydicarbonate and diisopropyl peroxydicarbonate. Although these peroxides depend on the decomposition temperature, those having a relatively large number of carbon atoms in the alkyl group, aryl group or acyl group, particularly those having 5 or more carbon atoms, are highly lipophilic and are preferred. The amount of initiator used is not necessarily limited, but
Usually, the amount is 0.1 to 1 part by weight per 100 parts by weight of the vinyl monomer, and it is preferable that the entire amount is added and dissolved in the vinyl monomer initially charged. If the polymerization initiator has a high affinity for water, the polymerization product tends to adhere to the walls of the polymerization tank, and fine particles are likely to be generated, making it difficult to obtain the desired particle size and resulting in poor reproducibility. Become. The dispersant used in the method of the present invention is a polymeric dispersant, such as polyvinyl alcohol, partially saponified polyvinyl alcohol, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, casein, starch, gelatin, etc. Among these, polyvinyl alcohol and partially saponified polyvinyl alcohol are most suitable for obtaining a polymer with a narrow particle size distribution. The amount of dispersant used is preferably slightly changed depending on the desired particle size, but
It is difficult to make a general determination because it varies depending on the conditions during dispersion, such as shear stress and shear rate, but it is usually used in the range of 0.1 to 3 parts by weight per 100 parts by weight of the vinyl monomer. The dispersant is used after being dissolved in water, but it is not necessary to add the entire amount before the dispersion treatment, and it can also be added after the dispersion treatment. In order to apply shear force to the polymerization system prior to the start of polymerization, the monomer containing the initiator and the water containing the dispersant are predispersed by gentle stirring, and then a high-speed stirrer,
Forcibly disperse into minute droplets using a high-speed pump, colloid mill, high-pressure injection nozzle, etc. These dispersers have a shear rate of 10 ⁵ to
A dispersion machine having a flow rate of the order of 10 ⁶ min ^-1 is particularly preferred, and suitable examples of such a dispersion machine include a high-speed pump type homogenizer, a turbine type homomixer, and a colloid mill. The particle size of the dispersed droplets is determined mainly by the strength of the shearing force, but it can also be slightly changed depending on the type and amount of the dispersant. Fine particles (droplets) can be formed by various methods such as reducing the amount of the agent and adding the reduced amount after dispersion treatment. After the dispersion treatment, a dispersant may be added if necessary, but this addition is preferably carried out before polymerization, and addition during polymerization is not particularly necessary since very few new particles are generated during polymerization. It should be added only when absolutely required to maintain stability. The bath ratio during dispersion treatment, that is, the ratio of vinyl monomer to water (monomer/water), is preferably smaller than 1 in volume ratio, and the closer it is to 1, the more it is 1 or more, under the same dispersion conditions. In this case, the particle size of the monomer droplets increases. The ratio of monomer to water during dispersion treatment is 1:1
It is preferable that it is 5. The method of the present invention can be carried out, for example, as follows. First, the pre-stirring tank contains the entire amount of water and oil-soluble polymerization initiator containing dispersant, and the total amount of
A vinyl monomer equivalent to 40 to 90% is injected, and a shear force is applied through a high-speed pump etc. sealed in a pre-stirring tank while performing weak stirring to obtain the desired particle size of the vinyl polymer. In consideration of particle shrinkage during polymerization, the vinyl monomer is dispersed into micro droplets (particles) in the range of 0.5 to 70 microns, preferably 2 to 60 microns, particularly 5 to 40 microns. Preferably, the droplets are as uniform in size as possible. The dispersant is transferred to a polymerization tank and polymerized in a conventional manner at a temperature in the range of 5 to 80°C, preferably 40 to 70°C, and when the polymerization conversion rate of the initially charged monomer reaches 30% or more, vinyl monomers are added. The polymerization is continued by adding the residual polymer continuously, in multiple portions, or all at once, and after the polymerization is completed, the vinyl polymer is separated and dried by a conventional method. I'll do it. The polymerization temperature is preferably a constant temperature depending on the desired degree of polymerization of the vinyl polymer. To explain specifically using vinyl chloride as an example,
Reduce the initial amount of vinyl chloride to 40 to 75% of the total amount,
A dispersant containing desired droplets, preferably 45 to 60%, is polymerized at a predetermined temperature, and when the polymerization conversion rate of the initially charged vinyl chloride is between 30 and 50%, the polymerization of vinyl chloride containing no polymerization initiator is performed. A portion of the remaining amount is added, and as the polymerization of vinyl chloride progresses, the remaining amount of vinyl chloride is added in 2 to 3 portions. Polymerization conversion rate is 30~
When it is between 50% and 50%, as the polymerization of vinyl chloride progresses, the droplet shrinks slightly and maintains its spherical shape, and the added vinyl chloride further polymerizes on top of the spherical particles, resulting in a droplet. Polyvinyl chloride polymer has a thickness of several μ~
It becomes a perfect sphere with a uniform particle size in the range of several tens of microns (narrow particle size distribution). In addition, if the initial charge amount of vinyl chloride is set to 50 to 90%, especially 60 to 80% of the total charge amount, and vinyl chloride is added when the polymerization conversion rate is 50% or more and preferably 70%, almost the entire particle is The polymer has a shape similar to that of a spherical particle with one or several depressions on the surface, and has a narrow particle size distribution.
On the other hand, if the entire amount of vinyl chloride is charged at the beginning,
The polymer forms various irregular shapes with wrinkles and irregularities. The method of the invention is suitable for producing particles in the range 2-70μ, especially 10-50μ. According to the method of the present invention, by appropriately selecting the initial amount of vinyl monomer charged, the timing of adding vinyl monomer, and the addition method, it is possible to obtain droplets that are slightly smaller than those dispersed by applying shear force. Alternatively, a vinyl polymer having a large desired shape and desired particle size can be obtained, and the particle size distribution of the polymer is extremely narrow. In addition, after dispersing by applying shear force, very few new particles are generated during polymerization, so there is no need to add a dispersant during polymerization, which not only facilitates particle size control but also improves reproducibility. The polymerization process is extremely easy, and it does not require any special modifications to the polymerization tank. Polymerization can be carried out with a minimum amount of adhesion to the can wall. Particles with a surface shape suitable for the purpose can be obtained, and the polymerization operation is extremely simple. . Even in post-polymerization treatments such as separation, washing, and drying, operations are easy because the particle size is uniform, and polymerization aids such as dispersants can be easily removed by simple filtering and repeated washing with water. have. The vinyl polymer thus obtained has a clean particle surface and good interparticle fusion, and has extremely high utility value as a sinterable molding material. Also,
In particular, the vinyl chloride polymer obtained by the method of the present invention can be selected from particles with uniform particle sizes ranging from perfectly spherical to recessed particles, and from several microns to tens of microns, and is therefore suitable for reducing the viscosity of paste resins. It can be used as a compounded resin. The method of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it departs from the gist thereof. In the examples, the particle size was measured by the centrifugal sedimentation method if the particle size was small (approximately 10μ or less), and by the natural sedimentation method if the particle size was large, and the particle shape was observed using an optical and scanning electron microscope. . Example 1 After dissolving 2.5 g of lauroyl peroxide in 250 g of vinyl chloride monomer in an autoclave,
1200 ml of water containing 3.75 g of polyvinyl alcohol (PVA) was introduced under pressure, and the mixture was stirred at room temperature with a stirrer rotating at 300 rpm. Next, the contents were stirred at a rotation speed of 2700 r.pm using a turbine-type high-speed stirrer (homo mixer).
Apply shear force for 30 minutes to uniformly disperse, and then heat at 55°C.
The mixture was heated to initiate polymerization. The rotation speed during polymerization is
It was set to 300r.pm. Initial monomer conversion rate is approximately 40%
60g of vinyl chloride monomer was added 1 hour after the temperature reached 1 hour, and 65g and 125g were added at 2 and 3.5 hours.
added to each. Internal pressure is 5.9Kg/cm ² in 6.8 hours
The residual monomer was purged. The obtained vinyl chloride polymer was perfectly spherical and had a weight average particle size of 16.4μ, and the particle size ratio expressed as weight average particle size/number average particle size was 1.32, indicating an extremely narrow particle size distribution. Moreover, the particle size was almost the same as the particle size measured by microscopic observation. Examples 2 to 5 Polymers were obtained in the same manner as in Example 1, except that the homomixer treatment conditions and the amount of PVA were changed. All of the particles obtained were perfectly spherical. Weight average particle size, particle size distribution (weight average/number average)
are shown in Table 1.

[Table] Example 6 2.5 g of lauroyl peroxide was dissolved in 350 g of vinyl chloride monomer in an autoclave.
Next, 1200ml of water containing 3.75g of PVA was injected,
The mixture was stirred at 300 rpm at room temperature. The contents were treated with a homomixer at 2700 rpm for 30 minutes to apply shearing force to disperse them, and then heated to 55°C to initiate polymerization. Stirring during polymerization was 300 rpm. Two hours after the polymerization conversion rate of the initially charged monomer reached approximately 55%, 50g of vinyl chloride monomer was added, and in the third hour, 100g of vinyl chloride monomer was added.
Added g. Polymerization was completed in 6.5 hours. The obtained vinyl chloride polymer had a shape close to a spherical shape with 2 to 3 depressions in the spherical particles, and the weight average diameter was
At 15μ, the distribution was 1.2. Further, throughout Examples 1 to 6, there was only a small amount of deposits on the inner wall of the autoclave, and the slurry was extremely easy to drain after the polymerization was completed, and drainage was good. Reference Example The viscosity lowering properties of the polyvinyl chloride polymers obtained in Examples 1 to 6 against paste resin at 23°C were measured using a B-type viscometer (Table 2). The paste sol was prepared by adding 50 parts by weight of dioctyl phthalate (DOP) to 100 parts by weight of paste resin (registered trademark VINICA P-450) or 60 parts by weight mixed with 40 parts by weight of the polymer obtained by the method of the present invention. The addition mixture was made into a sol. Viscosity measurement is 3.5sec ^-1 and
It was conducted at a shear rate of 35 sec ^-1 and the viscosity was expressed in poise.

[Table] As is clear from the examples, according to the method of the present invention, an appropriate amount of dispersant is selected and shearing force is applied to disperse fine particles.
By uniformly dispersing it, it is possible to obtain a desired uniform particle size in the range of 2 to 70μ, and as shown in the reference example, it exhibits the effect of significantly reducing the viscosity of paste resin when blended with it. It can be seen that it has extremely high utility value as a blended resin for reducing the viscosity of paste resin.

Claims (1)

[Claims] 1. In a method for producing a vinyl polymer by polymerizing a vinyl monomer containing an oil-soluble polymerization initiator in an aqueous medium containing a dispersant, the initial charge amount of the vinyl monomer is The amount should be 40 to 90% of the total amount charged, and the polymerization initiator should be used to apply high-speed shearing force to the polymerization system to disperse the vinyl monomer into fine particles and then polymerize, so that the polymerization conversion rate of the vinyl monomer is 30% or more. 1. A method for producing a vinyl polymer, which comprises adding the remainder of the vinyl monomer when it has matured. 2. The method for producing a vinyl polymer according to claim 1, wherein the remainder of the vinyl monomer is added continuously. 3. The method for producing a vinyl polymer according to claim 1, wherein the remainder of the vinyl monomer is added in several portions. 4. The method for producing a vinyl polymer according to claim 1, wherein the remainder of the vinyl monomer is added at once. 5. The method for producing a vinyl polymer according to claim 1, wherein the vinyl monomer is vinyl chloride or a mixture of vinyl chloride and a monomer copolymerizable therewith. 6 Set the initial amount of vinyl monomer to 40 to 40% of the total amount.
75% and the remainder of the vinyl monomer is added when the polymerization conversion rate is between 30 and 50%. Method of manufacturing coalescence. 7. Set the initial charge amount of vinyl monomer to 50 to 50% of the total charge amount.
90%, and when the polymerization conversion rate becomes greater than 50%, the remainder of the vinyl monomer is added. Production method.