JPS62185721A - Production of expandable styrene polymer particle - Google Patents

Abstract

PURPOSE:To obtain advantageously the titled polymer particles of a desired particle diameter and a narrow particle diameter distribution, by suspension- polymerizing a styrene monomer in two stages of different temperatures in the presence of a blowing agent by using both of low-temperature-decomposable and high-temperature-decomposable polymerization initiators. CONSTITUTION:Small particles of a blowing agent-containing expandable styrene polymer having a particle diameter distribution adjusted to a range within an average particle diameter + or -20% are suspended in an aqueous medium. A low-temperature-decomposable polymerization initiator whose decomposition temperature for obtaining a 10hr-half life is 50-80 deg.C is added to the suspension, and the blowing agent is vaporized in the course of bringing the temperature to a first-stage polymerization temperature and is fed at a rate of 3-15g per liter of the space capacity of the polymerization vessel. A styrene monomer to which a high-temperature decomposable polymerization initiator whose decomposition temperature for obtaining a 10hr-half life is 80-120 deg.C and a blowing agent are added to the reaction system, and the whole is subjected to the first- stage polymerization at 40-100 deg.C and subjected to a second-stage polymerization at 100-150 deg.C to obtain the titled polymer particles.

Description

DETAILED DESCRIPTION OF THE INVENTION (-) OBJECTS 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 prepared in advance by suspension polymerization are impregnated with a blowing agent.

■ Adding a blowing agent during suspension polymerization of styrenic polymers,
A method of incorporating a blowing agent into the produced polymer particles.

The first method requires the production of cystyrene polymer particles 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, in order to produce expandable particles by the first method, such W , sieving only those having a desired particle size from styrenic polymer particles having a wide particle size distribution obtained by turbidity polymerization, making the particle sizes uniform, and impregnating the particles with a blowing agent. become. Therefore, this method requires the following steps: Mfta 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 does not require a styrenic polymer suspension polymerization step (or a blowing agent impregnation step),
This method has the advantage of requiring fewer steps, but since it is impregnated with a blowing agent during the suspension polymerization process, particles of all particle sizes produced are impregnated with the blowing agent, and among them, they are suitable for use as expandable particles. Only particles with a diameter that is suitable for use as expandable particles are used as expandable particles, and residual particles containing a blowing agent with a particle size that is inappropriate for use as expandable particles have little use and pose a major problem in their disposal. there were. That is, among the expandable particles containing a blowing agent produced by the second method, the most commonly used expandable particles are 0.5 to 2. O
Particles with a particle size in the range 2 and 3 are commercially available as standard products, but particles with particle sizes other than this are rarely commercially available as non-standard products, which is why this method cannot be used. This was a major cause of increasing the production cost of expandable particles.

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 with a polymerization initiator dissolved in it is added quantitatively to the styrene monomer, the particles are grown by suspension polymerization to the desired particle size, and then a foaming agent is impregnated to form an expandable styrenic monomer with a uniform particle size. A method for producing polymer particles was proposed (% Kosho 49
-2994 publication). This method can produce expandable styrenic polymer particles with a considerably narrower particle size distribution than the conventional method described above;
(This method had the disadvantage that fine powder-like monomerized particles were produced at a ratio of less than 11%. Furthermore, this method had the disadvantage that styrene particles containing no blowing agent, which were obtained in advance by suspension polymerization and obtained by sieving, Since this is a method that uses polymer particles as a raw material, the disadvantage of increasing the number of steps as described above is unavoidable.

(Problems to be Solved by the Invention) The second method is a method for directly obtaining foamable polymer particles, and is advantageous in terms of the number of steps. Blowing agents and particles that have a particle size unsuitable for use as particles, especially particles with a particle size of 0.5
If a method could be developed to convert particles with a small particle size, such as less than It is clear that the second method is industrially significantly more advantageous than the first method. The present invention provides small particles of expandable styrenic polymer containing a blowing agent that is unsuitable for use as expandable styrenic polymer particles, such as the small particles obtained by the second method, It is an object of the present invention 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 found that 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 carrying out 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, I was able to achieve my goal.

That is, the method for producing expandable styrenic polymer particles of the present invention involves producing small particles of expandable styrenic polymer containing a blowing agent whose particle size distribution is within ±201 of the average particle size. A large part (or even all) of a low temperature polymerization initiator having a decomposition temperature of 50 to 80°C to obtain a half-life of 10 hours is added to the aqueous medium of the polymerization vessel in which the initiator is suspended.

During the temperature rise to the first stage polymerization temperature, a blowing agent is vaporized in the space of the polymerization container in an amount to completely suppress the foaming of the small particles of the expandable styrenic polymer. l(
After supplying the remaining part of the low-temperature polymerization initiator and a high-temperature polymerization initiator whose decomposition temperature is 80 to 120 °C to obtain a half-life of 10 hours, The added styrenic monomer containing styrene as a main component is added continuously or intermittently, and the amount of blowing agent necessary for foaming the finally obtained expandable styrenic polymer particles is added to the polymerization reaction system. 10 below the decomposition temperature to obtain a half-life of 10 hours for the low-temperature polymerization initiator.
The first stage polymerization reaction is carried out at a temperature within the range of 20 °C higher than the decomposition temperature from 100 °C lower, and then the second stage polymerization reaction is carried out at a temperature of 100 to 150 °C. This method is characterized by the following:

By using the production method of the present invention, small particles of an expandable styrenic polymer containing a blowing agent unsuitable for use as expandable styrenic polymer particles with uniform particle sizes can be used. The amount of particles produced is extremely small, with 98% of the particles produced.
Expandable styrenic polymer particles having a desired particle size distribution within a narrow range (for example, particle size 0.5 to 2.01111+1) 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 particles smaller than the expandable styrenic polymer particles to be produced (for example, particles with a particle size of 0.5 mm). (below), and the particle sizes are made uniform so that the particle size distribution is within the range of ±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 formed expandable styrenic polymer particles will also become wider, which is not preferable. Small particles of expandable styrenic polymer containing a blowing agent of such a raw material are
It may be obtained by sieving the expandable styrenic polymer particles obtained by the second method, or it may be obtained by sieving the expandable styrenic polymer particles obtained by the method of the present invention etc. There is no problem even if it is obtained by various methods.

In the method of the present invention, the polymerization initiator is a low-temperature polymerization initiator whose decomposition temperature is 50 to 80°C to obtain a half-life of 10 hours, and a low-temperature polymerization initiator whose decomposition temperature is 80 to 80°C to obtain a half-life of 10 hours. A high temperature polymerization initiator of 120'C is used in combination.

Examples of low-temperature polymerization initiators include lauroyl 4-oxide (decomposition temperature is 62°C to obtain a half-life of 10 hours), azobisisobutyronitrile (decomposition temperature is 63°C),
), t-putilno J? -Oxy-2-ethylhexanoate (72.5°C), benzoyl peroxide (74°C), etc., which are both soluble in the styrene polymer, are used. 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 remainder is added to the styrenic monomer. and use it. The low-temperature polymerization initiator may be in liquid form or powder form, but powder form is preferable. If a liquid polymerization initiator is added to the aqueous medium, the liquid polymerization initiator will dissolve the styrene polymer particles and cause coagulated particles to be generated. When adding it, it is desirable to add it while stirring and immediately disperse it into an emulsified state.

Examples of high-temperature polymerization initiators include cyclohexanone oxide (decomposition temperature is 97°C to obtain a half-life of 10 hours), t-butylno-f-oxybenzoate (decomposition temperature is 104°C), and dicumyl/4-oxide (decomposition temperature is 97°C to obtain a half-life of 10 hours). 117
℃), 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.

One type of each of the low-temperature polymerization initiator and the high-temperature polymerization initiator may be used, or two or more types may be used in combination.

The amount of the polymerization initiator used is such that the low temperature initiator is 0.01 to 1.0% by weight, preferably 0. The content of the high temperature initiator is 0.01 to 1.0% by weight, preferably 0.05 to 50.5% by weight, based on the styrenic monomer. 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, fine particles in the generated expandable particles Since the proportion of 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. 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, and a part of the blowing agent enters the space (gas phase) of the polymerization vessel while the temperature is raised to the first stage polymerization temperature. It is added as a vaporized blowing agent, and the remaining blowing agent is added in liquid form to the polymerization reaction system after the addition of the styrenic monomer.

Adding a part of the blowing agent to the space of the polymerization reaction vessel while the temperature is being raised to the first-stage polymerization temperature is necessary to maintain the pressure of the polymerization reaction system by suspending the pressure in the water at one valve. In order to maintain the pressure at a pressure equal to or higher than the partial pressure of the blowing agent contained in the cloudy small particles of foamable styrenic polymer, thereby suppressing the foaming of the small foamable particles due to temperature rise. It is. The amount of the foaming agent to be vaporized and added to the space in the polymerization container is approximately 15 g per volume (1) of the space in the polymerization container.

If the amount added is too small, it will not be possible to prevent the foamable small particles suspended in water from foaming due to the temperature rise during suspension polymerization, and the reaction system will solidify due to foaming during the polymerization reaction. It becomes impossible to produce the final target 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 determined by the glass transition temperature (Tg) of the expandable styrenic polymer particles.
Until it reaches . And T of styrene homopolymer
g is 103° C., and if a foaming agent is contained, the apparent Tg decreases depending on the content. for that,
In the present invention, it is added during the temperature rise of the first stage polymerization reaction, preferably when the temperature of the polymerization reaction system reaches 40 to 60°C.

Note that if the foaming agent is added in liquid form instead of vaporized and added to the space of the polymerization container, a large amount of fine powdery polymer (for example, 1 .5
~2.0% by weight), and problems such as the polymer adhering to the inner wall surface of the polymerization vessel occur.

The remainder of the blowing agent is added to the polymerization reaction system in liquid or gaseous form at an appropriate time after the addition of the styrene monomer, for example, from before the start of the first stage polymerization reaction to the beginning of the second stage polymerization reaction. It is. The amount of the blowing agent to be 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 to be added in liquid form to the polymerization reaction system, various blowing agents can be used.The same blowing agent may be used for each, or different blowing agents may be used. do not have. 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, esters of alcohols having 1 to 8 carbon atoms with acrylic acid or methacrylic acid (for example, methyl methacrylate, ethyl acrylate, etc.), monomethyl maleate, Examples include monomethyl 7-maleate, dimethyl maleate, and monoethyl itaconate.

In the present invention, a suspension stabilizer is used to suspend small particles of expandable styrenic polymer containing a blowing agent in an aqueous aqueous body. The FIB 1% stabilizer includes, for example, polyvinyl alcohol, polyvinylpyrrolidone, gelatin, carol, etc. Examples include organic suspension stabilizers such as oxymethyl cellulose and hydroxyalkyl cellulose; and inorganic suspension stabilizers such as calcium or magnesium salts of phosphoric acid or carbonate. Especially inorganic′! A turbidity stabilizer is preferred, especially the combination of tricalcium phosphate and anionic surfactant as a stabilizing aid with sodium dodecylbenzenesulfonate.

(Examples etc.) Below, Examples and Comparative Examples will be given and further explained in detail. "CH" in these examples means % by weight.

Example 1 Stirring device (4) with 31 containers, blowing agent supply pipe (5), styrene supply pipe (6), drainage '♂ (8), heating jacket)
(9) Into 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, and 1% aqueous solution of sodium dodecylbenzenesulfonate 2.0 g, 1659 sifted expandable styrene polymer particles (3) containing 6.13% butane as a blowing agent and having a particle size of 0.5 to 0.37 mm, and 3.3 g (total amount) of benzoyl peroxide were added. , 400 r
A uniform dispersion (2) was obtained by stirring at pm. .

This suspension dispersion (2) is heated to 85°C under stirring, and when it reaches the 40°C heating box, the space in the polymerization container (
7), the volume of the same space is 7.5. ! 14 g of butane, which is an amount corresponding to a ratio of 9/l, was vaporized into a tube (5/l).
). Next, after the temperature of the polymerization system reached 85°C, it was kept at the same temperature for 7 hours, and from the time when it reached 85°C during this period, over a period of 5 hours, butyl perbenzony) 1
．． 651! and cyclo to Φsan 16.5. jil 82
A solution of 5 fI in styrene was added continuously at a rate of 165 g per hour.

After the addition of the styrene solution was completed, 799 butane was added in liquid form in an amount equivalent to 8% by weight based on the total amount of the raw material expandable styrene polymer particles and styrene monomer.
Raise the temperature from 85℃ to 9110℃ over 1.5 hours, 1
The polymerization was completed by holding at 10° C. for 1 hour.

After completion of polymerization, the particle size distribution, appearance, and volatile content of the expandable styrene polymer particles obtained by cooling, separating water, and drying, as well as the state of adhesion of the polymer to the inner wall surface of the polymerization container, are shown in Table 1. It was as shown.

In addition, this expanded styrene polymer particle fI: 98°C, 1,
If the density of the pre-expanded particles obtained by heating with 0 kg/- of steam is shown in Table 1, then the pre-expanded particles are
The surface condition of the foam molded product obtained by filling the cavity of a 00111111X 100 fi

Example 2 The same polymerization conditions as in Example 1 were used, except that the amount of butane added was changed to 28 g, which corresponds to 1511/l with respect to the volume of the space in the polymerization container, in order to suppress foaming of the particles. Suspension polymerization was carried out. The obtained polymer particles and the same particles were treated in the same manner as in the examples, and the results are 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 set at 978 g, which corresponds to 39/L with respect to the volume of the space in the polymerization container. Turbid polymerization was carried out. The results are shown in Table 1.

Example 4 The conditions were the same as in Example 1, except that styrene polymer particles containing 5.74% by weight of styrene were used as foamable small particles as the raw material, and the particles were supplied to a space for suppressing foaming. As a blowing agent and a blowing agent that is later added in liquid form,
In each case, a suspension type test was carried out using the same amount of pentane as the butane used in Example 1. The results are shown in Table 1.

Example 5 Expandable styrene polymer small particles containing 2.38 wt.
It was added when the temperature reached 60°C during the temperature rise to the first stage polymerization temperature, and the other conditions were the same as in Example 1. I1 polymerization was carried out. The results are shown in Table 1.

Comparative Example 1 A 'jB f74 polymerization was carried out under the same polymerization conditions as in Example 1, except that 12.9 grsr of butane in liquid form was added to the mixing vessel to suppress foaming. The results are shown in Table 1.

Comparative Example 2 The same polymerization conditions as in Example 1 were used, except that the amount of vaporized butane added to the space was 20 f! to the volume of the space in order to suppress foaming of the particles. 37. of the amount corresponding to /l.
9 to carry out suspension polymerization.

The results are 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 an amount equivalent to 2.59/l K based on the volume of the space. 4.6
! Suspension polymerization was carried out by changing to i.

In this case, the raw material particles foam before reaching the first stage polymerization temperature, and the polymerization reaction system solidifies, resulting in normal expandable styrene polymer particles even when added with styrene monomer. I couldn't do that.

Example 6 The polymerization conditions were the same as in Example 1, except that the styrene monomers added later were 6.199% of styrene monomer and 206% of methyl methacrylate. ! 9 monomer mixture and! Copolymerization was performed to produce expandable styrenic copolymer particles. The results are shown in Table 1.

(C) Effect of the invention The present invention provides the following excellent effects.

(1) 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. using suitably small particles and having a desired particle size suitable for use as expandable styrenic polymer particles;
In addition, eroded expandable styrenic polymer particles with uniform particle sizes and a narrow particle size distribution can be easily obtained.

0i) Therefore, the second method can be carried out industrially advantageously.

[Brief explanation of drawings]

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. DESCRIPTION OF SYMBOLS 1... Body of polymerization container, 1'... Lid, 2... Suspended aqueous dispersion, 3... Expandable styrenic polymer particles, 4
... Stirring device, 5... Blowing 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)

[Claims] 1) A polymerization vessel in which small particles of an expandable styrenic polymer containing a blowing agent whose particle size distribution is within ±20% of the average particle size are suspended. Most (or all) of the low-temperature polymerization initiator whose decomposition temperature is 50 to 80°C to obtain a half-life of 10 hours is added to the aqueous medium, and the temperature is raised to the first stage polymerization temperature. A blowing agent in an amount that suppresses foaming of the small particles of the expandable styrenic polymer is vaporized in the space of the polymerization container at a ratio of 3 to 15 g (amount of blowing agent)/l (volume of space of the polymerization container). Styrene containing styrene as a main component is supplied with the remainder of the low-temperature polymerization initiator and a high-temperature polymerization initiator with a decomposition temperature of 80 to 120° C. to obtain a half-life of 10 hours. The above-mentioned low-temperature type monomer is added continuously or intermittently, and a blowing agent in an amount necessary for foaming the finally obtained expandable styrenic polymer particles is added to the polymerization reaction system. 10 of polymerization initiators
The first stage polymerization reaction is carried out at a temperature ranging from 10°C below the decomposition temperature to 20°C above the decomposition temperature to obtain a half-life of
A method for producing expandable styrenic polymer particles, which comprises raising the temperature to a temperature of 00 to 150°C to carry out a second-stage polymerization reaction. 2) The time to add the vaporized blowing agent, which is added to suppress the foaming of the suspended small particles of the expandable styrenic polymer, is when the temperature of the polymerization reaction system reaches 40 to 60°C. A method according to claim 1. 3) The method according to claim 1 or 2, wherein the blowing agent is added in an amount of 2 to 10% by weight in the finally obtained expandable styrenic polymer particles.