JPH0122843B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing styrenic polymer particles having a narrow particle size distribution. Styrenic polymer particles obtained by practicing the present invention are particularly useful as particles for expandable styrenic polymer beads. Conventionally, styrenic polymer particles have been produced by suspension polymerizing 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 remains 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 beads obtained by impregnating particles with a blowing agent during or after suspension polymerization is used to foam a molded product, the weight of the molded product may be uneven due to the difference in expansion ratio between the beads. , Heating time and cooling time during molding are not constant. Generally, expandable beads with a small particle size have a small expansion force and short heating and cooling times. As the particle size increases, the distension force increases and the time required for cooling also increases. The appropriate particle size of expandable beads is greatly restricted by the expansion rate of the expandable beads, processability such as molding cycle, 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. There are two types of block type products with a wall thickness of 100 mm or more, but the latter naturally has a larger bead diameter. however,
In these two fields as well, the reality is that particles are sieved into grades within several particle size ranges shown in Table 1 below, depending on the application.
Even if the suspension polymerization conditions are optimally selected, the amount of the obtained particle group suitable for one grade is at most about 30% by weight (see Comparative Example 5). As a means to improve this drawback of the conventional suspension polymerization method, styrene polymer particles that have been sieved in advance are suspended in water, and styrene monomer in which a polymerization initiator is dissolved is quantitatively added to this suspension system. However, a method has been proposed in which styrenic polymer particles of uniform particle size are produced by growing the particles to a desired particle size by suspension polymerization (Japanese Patent Publication No. 46-2987). Although this method can produce styrenic polymer particles with a considerably narrower particle size distribution than conventional methods, it has the following drawbacks. (i) It is necessary to align the particle size range of the styrene polymer particles that serve as seeds. (ii) 8-13% by weight of substandard fine particles are produced. On the other hand, when a styrenic polymer is dissolved in an ethylenically unsaturated monomer such as styrene, the viscosity at 25℃ is 15~15.
60,000 centipoise (CPS), this polymer solution was supplied into an aqueous suspension, and suspension polymerized in the presence of a suspension stabilizer and a blowing agent to form an ideal spherical shape without shrinkage cavities. A method for producing expandable styrenic particles is known (Japanese Patent Publication No. 824/1982). Although this publication describes that expandable particles having an ideal spherical shape can be produced, there is no description whatsoever regarding the particle size distribution of the resulting particles. In addition, in the particles obtained by this method, the production ratio of non-standard large particles reaches 3 to 5% by weight, and gelation often occurs depending on the type of vinyl monomer that dissolves polystyrene. It has its drawbacks. In order to improve the drawbacks of these conventional methods, the present invention provides a method for producing styrenic polymer particles with a narrow particle size distribution, with fewer non-standard products, and with the amount of particles contained in one grade being 50% or more. , a styrenic polymer is dissolved in a styrene monomer to prepare a polymer solution with a viscosity of 100 to 10,000 centipoise at 20°C, this polymer solution is supplied and dispersed in water containing a suspension stabilizer, and then polymerization is initiated. Suspension polymerization is started in the presence of the suspension reaction system, and when the amount of unpolymerized styrene monomer in the suspension reaction system becomes 60% by weight or less of the sum of the polymer and styrene monomer, the polymerization in the suspension reaction system is started. A styrenic polymer characterized in that styrene monomer is newly supplied to the suspension reaction system at a ratio of 200 to 900 parts by weight to 100 parts by weight of the combined styrene monomer and the suspension polymerization is subsequently completed. A method for producing coalesced particles is provided. In the practice of this invention, the styrenic polymer dissolved in the styrene monomer generally has a molecular weight of 10
A homopolymer of styrene of 10,000 to 600,000 styrene, or styrene as the main component (50% by weight or more, preferably 90% by weight)
above) and is a copolymer of this and other ethylenically unsaturated monomers. This styrenic polymer is
Preferably, it is economical to use styrenic polymer particles obtained by carrying out the present invention, especially polymer particles of inferior quality. Examples of ethylenically unsaturated monomers that can be copolymerized with styrene as the copolymer component include α-methylstyrene, divinylbenzene, acrylonitrile, and alcohols having 1 to 8 carbon atoms reacted with acrylic acid or methacrylic acid. The resulting esters include, for example, methyl methacrylate, ethyl acrylate, etc., monomethyl maleate, monomethyl fumarate, dimethyl maleate, monoethyl itaconate, and the like. These styrenic polymer particles are dissolved in styrene monomer and have a viscosity of 100~100℃ at 20℃.
It is adjusted to 10,000 CPS, preferably 100 to 5,000 CPS. At this time, it is also possible to replace a part of the styrene monomer (50% by weight or less, preferably 10% by weight or less) with another ethylenically unsaturated monomer copolymerizable with styrene. As such ethylenically unsaturated monomers, those mentioned above can be used, and the ethylenically unsaturated monomers constituting the styrenic polymer particles may be the same or different. Therefore, the viscosity at 20°C of a styrenic polymer solution dissolved in styrene monomer is 100~
The reason for setting 10,000 CPS is that at less than 100 CPS, there is no difference in particle size distribution compared to when styrenic polymer particles are obtained only by suspension polymerization without this dissolution step, whereas at more than 10,000 CPS, the viscosity decreases. This is because it is expensive and the work of transferring the polymer solution to the suspension system becomes troublesome. A styrenic polymer solution whose viscosity is adjusted to 100 to 10,000 CPS is fed into an aqueous medium containing a suspension stabilizer under stirring to form a suspension. This suspension is 60-130℃, preferably 70-100℃
The mixture is heated to a temperature of 100% with stirring in the presence of a polymerization initiator, and pre-suspension polymerization of ethylenically unsaturated monomers mainly consisting of styrene is carried out. In this pre-suspension polymerization, the amount [A] of polymerizable ethylenically unsaturated monomers mainly composed of unpolymerized styrene in the suspension reaction system is 60% by weight or less, preferably 45 to 60% by weight of the sum of the polymer obtained in [B] and the unreacted styrene-based ethylenically unsaturated monomer [A], preferably 45 to 60% by weight {[A]/ [A]+
[B]}, and then, based on the sum of 100 parts by weight of the unreacted styrene-based ethylenically unsaturated monomer [A] and polymer [B] in the suspension reaction system. , 200 to 900 parts by weight, preferably 200 to 900 parts by weight of a new ethylenic monomer mainly composed of styrene.
500 parts by weight is continuously or intermittently fed to a suspension reaction adjusted to a temperature of 70 to 90 °C, and 70
3-10 hours at a temperature of ~130℃, preferably 120~
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, polyvinyl pyrodrine, gelatin, carboxymethyl cellulose, and hydroxyalkyl cellulose, and phosphoric acid or carbonic acid.
Examples include inorganic suspension stabilizers such as Ca and Mg salts.
Among them, inorganic ones are preferable, especially tertiary ones.
It is preferable to use calcium phosphate in combination with sodium dodecylbenzenesulfonate, an anionic surfactant as a stabilizing agent. The amount of the suspension stabilizer used is 0.1 to 3% by weight of the styrenic bulk polymer or copolymer solution, and the amount of the stabilizing agent is 0.002 to 0.05% by weight of the water. In suspension polymerization, the weight ratio (phase ratio) of ethylenically unsaturated monomers such as styrene and their polymers to water is 1.0 to 2.0, preferably 1.0 to 2.0.
It is 1.5. Setting the phase ratio to 1 or more allows the batch size of the reactor to be smaller than setting it to less than 1, which is economical, reduces water content in the obtained particles, and facilitates drying. Furthermore, if the phase ratio exceeds 2.0, stirring becomes difficult as the polymerization progresses. In addition, the polymerization initiator is generally a radical polymerization initiator whose decomposition temperature is 50 to 155°C to obtain a half-life of 10 hours, and specifically, for example, t-butyl peroxyvivalate (55 ℃),
Lauroyl peroxide (62℃), benzoyl peroxide (74℃), cyclohexanone peroxide (97℃), t-butyl peroxybenzoate (104℃), dicumyl peroxide (117℃), azobisisobutyronitrile etc., those that can be dissolved in styrene monomer are preferred. The amount of polymerization initiator is styrene monomer or a mixture of styrene monomer and other ethylenic monomers.
0.01 to 5 parts by weight per 100 parts by weight, preferably
It is 0.01-0.6 parts by weight. As a method for adding the polymerization initiator, the following method (a) or (b) can be considered in the present invention. (a) The total amount of polymerization initiator required for suspension polymerization,
Styrenic polymer particles are dissolved in an ethylenically unsaturated monomer mainly composed of styrene and supplied. (b) An ethylenically unsaturated monomer mainly composed of styrene that dissolves styrenic polymer particles, and an ethylenically unsaturated monomer mainly composed of styrene that is newly supplied to the suspension reaction system after pre-suspension polymerization. A polymerization initiator is dissolved separately in the polymer. Of the feeding methods (a) and (b), the method (a) makes it possible to obtain styrenic polymer particles having a narrower particle size distribution. In the present invention, the supply timing of the ethylenically unsaturated monomer mainly composed of styrene newly added to the suspension reaction system is adjusted to The amount of is 60% by weight
The reason for the following is as follows. Suspended oil droplets formed from a styrenic polymer solution in a suspension system by stirring quickly and uniformly absorb newly supplied oil droplets of ethylenically unsaturated monomers mainly composed of styrene. Upon absorption, the resulting styrenic polymer particles have a narrow particle size distribution. If there are oil droplets that are not absorbed, they themselves undergo suspension polymerization, forming styrene polymer particles with a small particle size, and these and styrene polymer particles coexist.
The particle size distribution becomes wide, which is not preferable. The rate at which the oil droplets of the ethylenically unsaturated monomer mainly composed of styrene newly supplied to the reaction suspension system are absorbed into the oil droplets of the styrenic polymer solution is determined by The higher the concentration of coalescence, the faster it is. Therefore, we are trying to maximize the opportunity for newly supplied ethylenically unsaturated monomers mainly composed of styrene to independently form styrenic polymer particles with small particle diameters.
To reduce the amount, the amount of unreacted ethylenic monomer mainly composed of styrene in the suspension should be 60% of the sum of the polymer and the unsaturated ethylenic monomer mainly composed of unreacted styrene. This should be done when the percentage is below %. Therefore, in the method of adding a polymerization initiator, the reason why the method (a) in which the entire amount of the polymerization initiator is supplied to the ethylenically unsaturated monomer mainly composed of styrene that dissolves the styrenic polymer particles is preferable is also self-explanatory. As will be understood, oil droplets of styrene-based ethylenically unsaturated monomer (without polymerization initiator) freshly fed into the reaction suspension system were previously dissolved in styrene monomer. This is because it prevents the oil from polymerizing independently before it associates with the oil droplets (including the polymerization initiator) of the styrenic polymer. The method for producing styrenic polymer particles that do not contain a blowing agent has been described above, but when producing polymer particles that contain a blowing agent, a blowing agent is added to the obtained polymer particles after the suspension polymerization described above. It can be obtained by supplying a blowing agent into the reaction system during impregnation or dissolving the polymer particles, or during suspension polymerization, and performing the polymerization step. Generally, it is convenient to supply a blowing agent during suspension polymerization from the viewpoint of the polymerization process, but when the diameter of the resulting expandable particles is small,
Considering that the blowing agent dissipates in the particles and during storage, it is preferable to impregnate the particles with the blowing agent after suspension polymerization. Such blowing agents include, for example, propane,
Examples include aliphatic hydrocarbons such as normal butane, isobutane, normal 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 blowing agent has a blowing agent content of 5 in the generated particles.
It is normal to supply the amount to about 20% by weight. As can be understood from the results of the examples described later, the styrenic polymer particles obtained by carrying out the present invention have a high proportion of particles that fall into the commercial grade of 50% or more, and the particle size distribution of the particles is also narrowly sieved. is easy. Furthermore, it has the advantage that the content of particles with particle diameters of 0.42 mm or less and particles with particle diameters of 2.83 mm or more, which are inferior products, is extremely low. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 40 g of styrene homopolymer having a degree of polymerization of 1500 was dissolved in 160 g of styrene monomer to prepare a polymer solution having a viscosity of 540 CPS at 20°C. 0.32 g of benzoyl peroxide was added to this polymer solution to obtain a polymer solution. The polymer solution [] was transferred into a No. 3 autoclave containing 1000 g of pure water containing 2.5 g of tertiary calcium phosphate and 0.025 g of sodium dodecylbenzenesulfonate at 80° C. under stirring at 350 rpm. Next, the temperature of the above suspension was raised to 90℃, and at the same temperature
After maintaining the temperature for an additional 4 hours, styrene in which 0.2% by weight of benzoyl peroxide was dissolved was continuously added quantitatively over 4 hours at a rate of 200 g per hour, and then the temperature was increased from 90°C to 120°C. After raising the temperature over 5 hours, the mixture was further heated at the same temperature for 1 hour to complete polymerization. Table 1 shows the particle size distribution of the styrene polymer particles obtained by cooling, separating water, and drying. In addition, the polymer solution [] was analyzed by infrared absorption spectrum, and from the ratio of absorption of 1632 cm ^-1 to 1602 cm ^-1 , the styrene of the polymer solution [] was calculated based on the assumption that the polymer solution was obtained by polymerizing styrene. When the polymerization rate was determined, the polymerization rate was equivalent to 20.0% by weight. In addition, the polymer solution obtained by pre-suspension polymerization at 90°C for 2 hours was similarly analyzed by infrared absorption spectrum, and the polymerization rate was determined to be 43.7% by weight.
It was hot. This means that the amount of unreacted styrene monomer in the presuspension system before new styrene is added is
This corresponds to 56.3% by weight. Example 2 Same as Example 1 except that the amount of benzoyl peroxide added to the styrene monomer in which the styrene homopolymer was dissolved was 4.7 g, and it was not added to the styrene monomer newly added to the suspension reaction system. Styrene polymer particles having the particle size distribution shown in Table 1 were obtained. Example 3 Polymerization was carried out in the same manner as in Example 1, except that 70 g of pentane was added to the reaction system 6 hours after the start of suspension polymerization, and expandable styrenic polymer particles having the particle size distribution shown in Table 1 were obtained. Obtained. The blowing agent content in the polymer particles was 6.2% by weight. When this was pre-foamed for 3 minutes in a steam bath maintained at a temperature of 97°C, beads with an apparent specific gravity of 17.5g/ were obtained. Comparative Examples 1 and 2 In Example 1, the preliminary suspension polymerization time after the start of suspension polymerization until the addition of the styrene solution was
Polymerization was completed under exactly the same conditions except that the time was changed to 0 hours and 1 hour. Table 1 shows the particle size distribution of the obtained styrene polymer particles, the viscosity and polymerization rate of the bulk polymerization solution, and the polymerization rate immediately before addition of the styrene solution. Comparative Examples 3 and 4 Polymer solutions with viscosities of 150 CPS and 14000 CPS at 20°C were obtained by varying the amount of styrene monomer used to dissolve the styrene homopolymer. Add 5.0 g of benzoyl peroxide to 200 g of this polymer solution, and add this solution to 1000 g of pure water containing 2.5 g of tribasic calcium phosphate and 0.025 g of sodium dodecylbenzenesulfonate at 350 rpm.
The mixture was transferred at 70°C under stirring. Next, the temperature of the above suspension was raised to 90℃, and from 90℃
After continuously increasing the temperature to 120℃ for 5 hours, further increasing the temperature to 125℃
The temperature was raised to 1, and the polymerization was completed by heating at the same temperature for 2 hours. After cooling, the water was separated and the particle size distribution of the styrenic polymer particles obtained by drying is shown in Table 1. 1000 g of pure water containing 2.5 g of tertiary calcium phosphate and 0.025 g of sodium dodecylbenzenesulfonate was supplied into the polymerization vessel of Comparative Example 5-3, and then nitrogen gas was introduced into the polymerization vessel to replace the air. Into this vessel, 1002 g of styrene in which 2 g of benzoyl peroxide was dissolved was fed under stirring, and the temperature was raised to 90°C over 30 minutes. Styrenic polymer particles having the following properties were obtained.

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Claims (1)

[Claims] 1 Dissolve the styrene polymer in styrene monomer to prepare a polymer solution with a viscosity of 100 to 10,000 centipoise at 20°C, supply and disperse this polymer solution in water containing a suspension stabilizer, and then initiate polymerization. Suspension polymerization is started in the presence of the suspension reaction system, and when the amount of unpolymerized styrene monomer in the suspension reaction system becomes 60% by weight or less of the sum of the polymer and styrene monomer, the polymerization in the suspension reaction system is started. Add new styrene monomer to 100 parts by weight of the combined and styrene monomer.
A method for producing styrenic polymer particles, which comprises supplying styrenic polymer particles to a suspension reaction system in a proportion of 200 to 900 parts by weight, and subsequently completing suspension polymerization.