JPH0573133B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Object of the Invention The present invention relates to an industrially advantageous method for producing expanded styrenic polymer particles having a narrow particle size distribution. (Industrial Application Field) When using the production method of the present invention, it is possible to obtain a desired particle size and a narrow particle size distribution without going through a suspension polymerization step of a styrene polymer that does not contain a blowing agent. Expandable styrenic polymer particles can be advantageously produced industrially. (Prior Art) Conventionally, various methods have been proposed for producing expandable styrenic polymer particles, but they can be broadly classified into the following two methods. A method in which styrenic polymer particles previously produced by suspension polymerization are impregnated with a blowing agent. A method in which a blowing agent is added during suspension polymerization of a styrenic polymer so that the blowing agent is contained in the resulting polymer particles. The first method requires that styrenic polymer particles be produced in advance by suspension polymerization. Since the styrenic polymer particles obtained by suspension polymerization have a continuous and wide particle size distribution ranging from small particles to large particles, such suspension polymerization is necessary to produce expandable particles by the first method. From the styrenic polymer particles having a wide particle size distribution obtained by the method, only those having a desired particle size are sieved to make the particle sizes uniform, and the particles having the uniform particle size are impregnated with a blowing agent. Therefore, this method requires the following steps: suspension polymerization of styrenic monomer, sieving step, and blowing agent impregnation step, and has the disadvantage of increasing the number of manufacturing steps. Compared to the first method, the second method requires a styrene polymer suspension polymerization step (or a blowing agent impregnation step).
However, in order to impregnate the foaming agent during the suspension polymerization process, particles of all particle sizes produced are impregnated with the foaming agent, and among them, only the foamable particles are impregnated with the foaming agent. Only particles of a size suitable for use as expandable particles are used as expandable particles; remaining particles containing blowing agent with a size unsuitable for use as expandable particles have little use and cannot be disposed of. There was a big problem. That is, among the expandable particles containing a blowing agent produced by the second method, the most commonly used expandable particles are those in the particle size range of 0.5 to 2.0 mm, which are commercially available as standard products. However, particles with particle sizes other than this can hardly be sold commercially as they are non-standard, and this has been a major cause of increasing the production cost of expandable particles obtained by this method. In addition, as a method for improving the drawbacks of the first method and the second method, small particles of a styrenic polymer that does not contain a blowing agent obtained by sieving are suspended in an aqueous medium, and the suspension system is A styrenic monomer in which a polymerization initiator is dissolved is quantitatively added to the polymer, the particles are grown to the desired particle size by suspension polymerization, and then a blowing agent is impregnated to produce an expandable styrenic polymer with a uniform particle size. A method for producing particles was proposed (Special Publication 1977-
Publication No. 2994). This method can produce expandable styrenic polymer particles with a considerably narrower particle size distribution than the conventional method described above, but this method also produces fine powdery polymer particles at a rate of less than 10%. There was a drawback that particles were generated. Furthermore, since this method uses styrenic polymer particles that do not contain a blowing agent, which have been obtained in advance by suspension polymerization and sieved, as a raw material, the number of steps is large. Some drawbacks are unavoidable. (Problems to be Solved by the Invention) The second method is a method for directly obtaining expandable polymer particles, and is advantageous in terms of the number of steps. Particles containing a blowing agent having a particle size unsuitable for use as expandable particles, especially particles with a small particle size such as a particle size of less than 0.5 mm, can be replaced by particles with a particle size that can be advantageously used as expandable particles (e.g. 0.5 to 2.0 mm). It is clear that if a method for converting the particle size into particles with a particle size of mm) is developed, the second method will be industrially significantly more advantageous than the first method. The present invention provides foaming from small particles of an expandable styrenic polymer containing a blowing agent unsuitable for use as expandable styrenic polymer particles, such as the small particles obtained by the second method. The object of the present invention is to provide a method for producing expandable styrenic polymer particles having a particle size suitable for use as expandable styrenic polymer particles. (b) Structure of the Invention (Means for Solving the Problems) As a result of various studies to solve the above-mentioned problems, the present inventors have found that it is not suitable for use as expandable styrenic polymer particles. Small particles of an expandable styrenic polymer containing a blowing agent with an appropriate particle size and arranged within a certain particle size distribution are suspended in an aqueous medium of a polymerization reaction vessel, and By pressurizing the reaction system by vaporizing and supplying a part of the blowing agent to the phase (phase part), foaming of the small particles during the suspension polymerization reaction can be prevented, and a specific low-temperature polymerization initiator can be By conducting a two-stage polymerization reaction of styrenic monomers at low and high temperatures in the presence of a separately added blowing agent while using a specific high-temperature polymerization initiator under specific conditions, this objective can be achieved. I was able to accomplish this. That is, the method for producing expandable styrenic polymer particles of the present invention involves producing small expandable styrenic polymer particles containing a blowing agent whose particle size distribution is within ±20% of the average particle size. A low-temperature polymerization initiator with a decomposition temperature of 50 to 80 °C to obtain a half-life of 10 hours is added to the aqueous suspension system later on to obtain a styrenic monomer suspended in the aqueous medium of the polymerization vessel. Add at least 1/2 of the amount required for polymerization of Styrene containing a high-temperature polymerization initiator whose decomposition temperature is 80 to 120° C. to obtain a half-life of 10 hours and the remainder of the low-temperature polymerization initiator. By continuously or intermittently adding a styrenic monomer containing as a main component, the styrenic monomer is polymerized in the above temperature range (first stage polymerization), and then 100~ 150℃
The temperature is raised to a temperature of This method is characterized by adding a blowing agent so that the amount of foaming agent is 2 to 10% by weight. By using the production method of the present invention, it is possible to use small particles of a uniform particle size of an expandable styrenic polymer containing a blowing agent that is unsuitable for use as expandable styrenic polymer particles. The amount of particles produced is extremely small, and more than 98% by weight of the particles produced have a desired particle size distribution within a narrow range (for example, particle size 0.5 to 2.0 mm).
Expandable styrenic polymer particles having the following properties can be easily produced. The small particles of the expandable styrenic polymer containing a blowing agent used as a raw material in the method of the present invention are smaller particles (for example, particles with a particle size of 0.5 mm or less) than the expandable styrenic polymer particles to be manufactured. The particle sizes are made uniform so that the particle size distribution is within ±20% of the average particle size. If the range of the particle size distribution is wider than the above range, the particle size distribution of the generated expandable styrenic polymer particles will also become wider, which is not preferable. The small particles of the expandable styrenic polymer containing the blowing agent of the raw material may be those obtained by sieving the expandable styrenic polymer particles obtained by the second method,
It may be obtained by various methods, such as those obtained by sieving expandable polymer particles obtained by the method of the present invention. In the method of the present invention, as a polymerization initiator,
Decomposition temperature is 50-80℃ to obtain a half-life of 10 hours
A low-temperature polymerization initiator is used in combination with a high-temperature polymerization initiator whose decomposition temperature is 80 to 120°C to obtain a half-life of 10 hours. Examples of low-temperature polymerization initiators include lauroyl peroxide (decomposition temperature is 62°C to obtain a half-life of 10 hours), azobisisobutyronitrile (decomposition temperature is 63°C), t-butylperoxy-2-ethyl Those that are soluble in styrene monomers are used, such as hexanoate (72.5°C) and benzoyl peroxide (74°C). The low-temperature polymerization initiator is added to the aqueous medium in an amount of 1/2 or more (the entire amount may be sufficient) of the amount required for polymerization of the styrenic monomer, and the rest is added to the styrenic monomer. and use it. Even if the low-temperature polymerization initiator is liquid,
It may be in powder form, but powder form is preferred. If a liquid polymerization initiator is directly added to an aqueous medium, the liquid polymerization initiator will dissolve the styrene polymer particles and cause coagulated particles to be generated. Therefore, a liquid low-temperature polymerization initiator is added to the aqueous medium. In this case, it is desirable to add the mixture while stirring and immediately disperse it into an emulsified state. Examples of high-temperature polymerization initiators include cyclohexanone peroxide (decomposition temperature is 97°C to obtain a half-life of 10 hours), t-butyl peroxybenzoate (decomposition temperature is 104°C), and dicumyl peroxide (decomposition temperature is 117°C). etc., all of which are soluble in styrene monomers are used. The high temperature polymerization initiator is then added to the styrenic monomer and supplied to the polymerization reaction system. Both low-temperature polymerization initiator and high-temperature polymerization initiator
One type of each may be used, or two or more types may be used in combination. The amount of polymerization initiator used is that the low-temperature initiator
0.01 to 1.0% by weight, preferably 0.1 to 0.6% by weight, and the high temperature initiator is based on the styrenic monomer.
0.01-1.0% by weight, preferably 0.05-0.5% by weight. Note that if the amount of low-temperature polymerization initiator added to the aqueous medium is less than 1/2 of the amount required for polymerization of the styrenic monomer added to the polymerization reaction system,
Since the proportion of fine particles in the generated expandable particles increases, in the present invention, the low-temperature polymerization initiator is added to the aqueous medium in an amount greater than 1/2 of the amount required for polymerization of the styrenic monomer. Added. The amount of polymerization initiator required for the polymerization of the styrenic monomer added to the polymerization reaction system is determined based on the molecular weight of the expandable styrenic polymer particles to be produced, which is the optimum molecular weight for the foam moldability of molded objects, expansion ratio, etc. Adjust so that In the method of the present invention, a blowing agent is added to the polymerization reaction system.
The foaming agent is added as a vaporized foaming agent to the space (gas phase) in the polymerization vessel while the temperature is rising to a temperature in the range of 100℃, and the remaining foaming agent undergoes the polymerization reaction in liquid form after the addition of the styrene monomer. Add to system. Adding a portion of the blowing agent to the space of the polymerization reaction vessel by vaporizing it is done by controlling the pressure of the polymerization reaction system by controlling the pressure of the blowing agent contained in the small particles of expandable styrenic polymer suspended in water. This is to maintain the same pressure or higher pressure, thereby suppressing foaming of the foamable small particles due to temperature rise. The amount of the foaming agent that is vaporized and added to the space in the polymerization container is 3 to 15 g per volume ( ) of the space in the polymerization container. If the amount added is too small, it will not be possible to suppress foaming of the foamable small particles previously suspended in water due to the temperature rise during suspension polymerization, and the reaction system will become foamed during the polymerization reaction. This solidifies, making it impossible to produce the final desired expandable styrenic polymer particles. Furthermore, if the amount of the blowing agent added is too large, it may cause the generation of coagulated particles or fine particles. Theoretically, the time to vaporize and add the blowing agent to the space of the polymerization container is until the glass transition temperature (Tg) of the expandable styrenic polymer particles is reached. And the Tg of styrene homopolymer is 103℃,
When a foaming agent is contained, the apparent Tg decreases depending on the content. Therefore, in the present invention, it is added during the temperature rise to a range of 40 to 100°C, preferably when the temperature of the polymerization reaction system reaches 40 to 60°C. In addition, if the foaming agent is added in liquid form to the space of the polymerization container instead of being vaporized, a large amount of fine powdery polymer (for example, 1.5~ (2.0% by weight), and problems such as polymer adhesion to the inner wall of the polymerization container occur. The remainder of the blowing agent is added to the polymerization reaction system in liquid or gas form at an appropriate time after the addition of the styrenic monomer, preferably before the beginning of the second stage polymerization reaction. . The amount of the blowing agent added is such that the amount of the blowing agent contained in the finally obtained expandable styrenic polymer particles is 2 to 10% by weight. The blowing agent used in the production of the expandable styrenic polymer particles of the present invention, that is, the blowing agent that is contained in the small particles of the raw material expandable styrenic polymer, the blowing agent that is vaporized and added to the space of the polymerization container, As the blowing agent added in liquid form to the polymerization reaction system, various blowing agents can be used, and the same blowing agent may be used for each,
There is no problem in using different ones. The blowing agents used in each of these cases include, for example, aliphatic hydrocarbons such as propane, butane, and pentane; alicyclic hydrocarbons such as cyclobutane and cyclopentane; and halogenated hydrocarbons such as methyl chloride and dichlorodifluoromethane. Examples include hydrogen. The styrenic monomer added to the polymerization reaction system in the method of the present invention is a styrene monomer or a monomer mixture containing styrene as a main component, that is, styrene alone or styrene as a main component and a small amount of other monomers. It is a monomer mixture with a monomer. Examples of other monomers include α-methylstyrene, divinylbenzene, acrylonitrile, and carbon atoms of 1 to 1.
Examples include esters of No. 8 alcohol and acrylic acid or methacrylic acid (eg, methyl methacrylate, ethyl acrylate, etc.), monomethyl maleate, monomethyl fumarate, dimethyl maleate, monoethyl itaconate, and the like. In the present invention, a suspension stabilizer is used to suspend small particles of expandable styrenic polymer containing a blowing agent in an aqueous medium. As the suspension stabilizer, for example, polyvinyl alcohol,
Examples include organic suspension stabilizers such as polyvinylpyrrolidone, gelatin, carboxymethylcellulose, and hydroxyalkylcellulose; and inorganic suspension stabilizers such as calcium or magnesium salts of phosphoric acid or carbonate. Particularly preferred are inorganic suspension stabilizers, particularly the combination of tribasic calcium phosphate and the anionic surfactant sodium dodecylbenzenesulfonate as a stabilizing aid. (Examples etc.) Below, Examples and Comparative Examples will be given and further explained in detail. "%" in these examples means % by weight. Example 1 Stirring device 4 with a capacity of 3, blowing agent supply pipe 5, styrene supply pipe 6, drain pipe 8, heating jacket 9,
In a polymerization vessel 1 having the structure shown in the attached drawing and equipped with a thermometer 10, 1000 g of pure water, 5.0 g of tribasic calcium phosphate, 2.0 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate, and 6.13% butane as a blowing agent were added.
165 g of expandable styrene polymer particles 3 sieved to a particle size of 0.5 to 0.37 mm and 3.3 g (total amount) of benzoyl peroxide were added and stirred at 400 rpm to obtain a uniform dispersion liquid 2. This suspension dispersion liquid 2 is heated to 85°C under stirring, and when it reaches a temperature of 40°C, it is poured into the space 7 of the polymerization container at a rate of 7.5% of the volume of the space. A corresponding amount of 14 g of butane was vaporized and fed via line 5. Next, the temperature of the polymerization system was increased to 85℃.
After reaching the same temperature, keep it at the same temperature for 7 hours, and during this time 85
1.65 g of butyl perbenzoate and 16.5 g of cyclohexane were added over 5 hours from the time the temperature reached ℃.
A solution dissolved in 825 g of styrene was continuously added to
It was added at a rate of 165 g per hour. After the addition of the styrene solution was completed, 79 g of butane was added in liquid form, which is an amount equivalent to 8% by weight based on the total amount of foamable styrene polymer particles and styrene monomer as raw materials. The temperature was raised to 1.5 hours to 110°C and maintained at 110°C for 4 hours to complete polymerization. Particle size distribution of expandable styrene polymer particles obtained by cooling after completion of polymerization, then separating water, and drying,
The appearance, volatile content, and state of adhesion of the polymer to the inner wall surface of the polymerization container were as shown in Table 1. In addition, the expanded styrene polymer particles were heated at 98℃.
The density of the pre-expanded particles obtained by heating with 1.0 Kg/cm ² water vapor is shown in Table 1. The pre-expanded particles were filled into the cavity of a mold of 100 mm x 100 mm x 200 mm, and the density of the pre-expanded particles was 0.7 Kg. The surface condition of the foam molded product obtained by foam molding by heating with water vapor of /cm ² for 20 seconds was as shown in Table 1. Example 2 Under the same polymerization conditions as in Example 1, however, the amount of butane added to suppress the foaming of the particles was increased to an amount equivalent to 15 g per volume of the space in the polymerization vessel.
Suspension polymerization was carried out by changing the amount to 28 g. The obtained polymer particles and the same particles were treated in the same manner as in the examples, and the results were as shown in Table 1. Example 3 Under the same polymerization conditions as in Example 1, however, the amount of butane added to suppress the foaming of the particles was changed to 5.6 g, which is equivalent to 3 g per volume of the space in the polymerization container. Polymerization was carried out. The results were as shown in Table 1. Example 4 The same conditions as in Example 1 were used, except that styrene polymer particles containing 5.74% by weight of pentane were used as the raw material foamable small particles, and a foaming agent was supplied to the space for suppressing foaming of the particles. And as a blowing agent to be added later in liquid form, pentane was used in the same amount as the butane in Example 1, respectively, to perform suspension weighting. The results were as shown in Table 1. Example 5 Expandable styrene polymer small particles containing 2.38% by weight of butane were used as the raw material expandable particles, and butane (7.5 g/) was supplied to the space to suppress foaming at a temperature of 60°C. The suspension polymerization was carried out under the same conditions as in Example 1. The results were as shown in Table 1. Comparative Example 1 Suspension polymerization was carried out under the same polymerization conditions as in Example 1, except that 12.9 g of liquid butane, which is added to suppress foaming, was added to the polymerization vessel. The results were as shown in Table 1. Comparative Example 2 Same polymerization conditions as Example 1, but the amount of vaporized butane added to the space was changed to 37g, which is equivalent to 20g/volume of the space, in order to suppress foaming of the particles. Suspension polymerization was carried out.
The results were as shown in Table 1. Comparative Example 3 Under the same polymerization conditions as in Example 1, however, in order to suppress foaming of particles, the amount of vaporized butane added to the space was changed to 4.6 g, which is equivalent to 2.5 g per volume of the space. Suspension polymerization was carried out by changing to In this case, the raw material particles foam during the first temperature rise and the polymerization reaction system solidifies, making it impossible to obtain normal expandable styrene polymer particles even if styrene monomer is added. Nakatsuta. Example 6 Under the same polymerization conditions as in Example 1, except that styrene monomer was added later, 6.19 g of styrene monomer
and 206 g of methyl methacrylate were copolymerized to produce expandable styrenic copolymer particles. The results were as shown in Table 1.

[Table] (c) Effects of the invention The present invention provides the following excellent effects. (i) Unsuitable for use as expandable styrenic polymer particles obtained in the method of producing expandable styrenic polymers by adding a blowing agent during suspension polymerization of styrenic polymers (the second method above), etc. By using appropriate small particles, it is easy to produce excellent expandable styrenic polymer particles that have a desired particle size suitable for use as expandable styrenic polymer particles and have a narrow particle size distribution and uniform particle size. can get. (ii) Therefore, the second method can be implemented industrially advantageously.

[Brief explanation of the drawing]

The accompanying drawing is a longitudinal cross-sectional view of a polymerization vessel used in Examples during suspension polymerization of the present invention. Each symbol in the figure indicates the following. 1
... Main body of polymerization container, 1' ... Lid, 2 ... Suspended aqueous dispersion, 3 ... Expandable styrenic polymer particles,
4... Stirring device, 5... Foaming agent supply pipe, 6... Styrenic monomer and polymerization initiator supply pipe, 7...
Space of polymerization container, 8... drain pipe, 9... heating jacket, 10... thermometer.

Claims (1)

[Scope of Claims] 1. An aqueous medium in a polymerization vessel in which small expandable styrenic polymer particles containing a blowing agent whose particle size distribution is within ±20% of the average particle size are suspended. To,
Decomposition temperature is 50-80℃ to obtain a half-life of 10 hours
A low-temperature polymerization initiator is added in an amount of at least 1/2 of the amount required for the polymerization of the styrenic monomer that will later be added to the aqueous suspension system, and then brought to a temperature of 40 to 100 °C, during which it is vaporized. 3 to 15g of foaming agent (amount of foaming agent)/
A high-temperature polymerization initiator whose decomposition temperature is 80 to 120°C to obtain a half-life of 10 hours after the temperature is increased through a step of supplying at a rate of (space volume of the polymerization container), and the low-temperature polymerization initiator By continuously or intermittently adding a styrenic monomer containing styrene as a main component, the styrenic monomer is polymerized in the above temperature range (the first After that, the temperature is raised to 100 to 150°C to continue the polymerization of the styrenic monomer (second stage polymerization), and after the addition of the styrenic monomer, the product is produced. A method for producing expandable styrenic polymer particles, which comprises adding a blowing agent so that the foaming agent content of the expandable styrenic polymer particles is 2 to 10% by weight. 2. Production of expandable styrenic polymer particles according to claim 1, wherein the vaporized blowing agent initially supplied is added when the temperature of the polymerization reaction system reaches 40 to 60°C. Method.