JPH0122841B2 - - 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 does not have a distribution that includes a wide range of particles from small to large diameters, regardless of the stirring, polymerization temperature, time, addition method of styrene monomer and polymerization initiator, etc. It has the following disadvantages. (i) When extruding polymer particles, particles with small diameters and particles with large diameters separate in the raw material hopper or the screw section of the feed section of the extruder, causing fluctuations in the amount of extrusion. (ii) When foaming 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 largely restricted by the expansion rate of the expandable beads, processability such as molding cycles, and product wall thickness, and is mainly used in the field of general-purpose molded products where the wall thickness of molded products is 5 mm to 50 mm. 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 35% 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.
The polymer solution was adjusted to 60,000 CPS, supplied into an aqueous suspension, and subjected to suspension polymerization in the presence of a suspension stabilizer and a foaming agent to create an expandable styrene system with an ideal spherical shape without shrinkage cavities. A method for producing particles is known (Japanese Patent Publication No. 824/1983). 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. Furthermore, a step of dissolving a styrene polymer obtained by polymerization in advance with a vinyl monomer is required. In order to improve the drawbacks of suspension polymerization methods using these polymers as seeds, the present inventors first introduced styrene or a mixture of styrene and other polymerizable ethylenically unsaturated monomers to initiate polymerization. Bulk polymerization is carried out in the presence of a suspension stabilizer until the reaction system has a viscosity of 100 to 10,000 centipoise at 20°C, and the resulting bulk polymer or copolymer solution is fed into an aqueous solution containing a suspension stabilizer, and then suspended. A method for producing styrenic polymer particles characterized by turbidity polymerization was provided (see Japanese Patent Application No. 85631/1983). Although this method improves the above-mentioned drawbacks of the prior art and is an excellent method, it
It turned out that in the future, the entire amount of polymerizable ethylenically unsaturated monomers, mainly styrene, that will be subjected to suspension polymerization will be supplied, so a large bulk polymerization tank will be required, resulting in a large equipment cost. The present invention was made with the aim of improving such drawbacks of the previous application, and first, a polymerizable ethylenically unsaturated monomer mainly composed of styrene was added to a reaction system at 20°C in the presence of a polymerization initiator. Viscosity is 100~10000
The styrene bulk polymer or copolymer solution obtained by bulk polymerization is carried out until it becomes centipoise, and the resulting styrene bulk polymer or copolymer solution is supplied into water containing a suspension stabilizer, and then heated to carry out suspension polymerization of unreacted ethylenically unsaturated monomers. When the polymerization rate of the polymerizable ethylenically unsaturated monomer mainly composed of styrene reaches 40% by weight or more, the polymerizable ethylene mainly composed of styrene initially charged into the reaction system A new polymerizable ethylenically unsaturated monomer mainly composed of styrene is supplied to the suspension reaction system at a ratio of 200 to 900 parts by weight per 100 parts by weight of the sexually unsaturated monomer, and then suspended. The present invention provides a method for producing styrenic polymer particles characterized by completing turbid polymerization. In the practice of the present invention, the ethylenically unsaturated monomer mainly composed of styrene constituting the polymer particles is one whose main component is styrene (50 to 100% by weight), preferably 50% by weight or less, preferably 10% by weight
Other ethylenically unsaturated monomers copolymerizable with styrene may be used in combination in the following proportions. Examples of such monomers include α-methylstyrene, divinylbenzene, acrylonitrile, esters obtained by reacting alcohols having 1 to 8 carbon atoms with acrylic acid or methacrylic acid, such as methyl methacrylate, ethyl acrylate, etc., and monomethyl maleate. , monomethyl fumarate, dimethyl maleate, monoethyl itaconate, and the like. 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°C Lauroyl peroxide (62℃), benzoyl peroxide (74℃), cyclohexanone peroxide (97℃), t-butyl peroxybenzoate (104℃), dicumyl peroxide (117℃), azobisisobutyronitrile The amount of polymerization initiator is preferably styrene monomer or a mixture of styrene monomer and other ethylenic monomer.
0.01 to 5 parts by weight per 100 parts by weight, preferably
It is 0.01-0.6 parts by weight. As the method for adding the polymerization initiator, since two types of polymerization, bulk polymerization and suspension polymerization, are carried out in the present invention, the following methods (a) to (c) can be considered. (a) The entire amount of polymerization initiator required for bulk polymerization and suspension polymerization is dissolved and supplied in an ethylenically unsaturated monomer mainly composed of styrene before bulk polymerization. (b) The required amount of polymerization initiator for each of bulk polymerization and suspension polymerization is dissolved in the ethylenically unsaturated monomer mainly composed of styrene supplied to the reaction system, and then added. (c) A polymerization initiator in an amount necessary for suspension polymerization is dissolved in a styrene bulk polymer solution or copolymer solution obtained by bulk polymerization, and this is supplied into water containing a suspension stabilizer. In the bulk prepolymerization of the present invention, the viscosity of the reaction system at 20°C is 100 to 10,000 centipoise, preferably
This is continued until the temperature reaches 200 to 5000 centipoise. Polymerization temperature is 70-110℃ for 1.5-10 hours, preferably 2-10 hours.
Do it for 5 hours. At this time, 10 to 40% by weight, preferably 20 to 40% by weight of the ethylenic monomer mainly composed of styrene.
35% by weight is prepolymerized. When the bulk polymer reaches the above viscosity, the bulk polymer solution is fed into an aqueous medium containing a suspension stabilizer under stirring to form a suspension. This suspension is 60-130℃, preferably 60-90℃
is heated with stirring to a temperature of Adjustments are made so that the above is achieved. When the polymerization rate reaches 40% by weight or more, 70~
Adjust the temperature of the suspension reaction system to a temperature of 90°C, and add a new ethylenically unsaturated monomer mainly composed of styrene (50 to 100% by weight) to the suspension reaction system continuously or intermittently. Suspension polymerization is carried out at a temperature of 70 to 130°C for 3 to 10 hours, preferably 4 to 6 hours at a temperature of 120 to 130°C, to complete the polymerization. Examples of the above-mentioned suspension stabilizers include organic suspension stabilizers such as polyvinyl alcohol, polyvinylpyrrolidone, gelatin, carboxymethyl cellulose, and hydroxyalkyl cellulose, and phosphoric acid or carbonic acid.
Examples include inorganic suspension stabilizers such as Ca and Mg salts.
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 addition, when using an ethylenically unsaturated monomer other than styrene, the type and amount of the unsaturated monomer to be subjected to bulk polymerization and the unsaturated monomer newly added to be subjected to suspension polymerization are They may be the same or different. The weight ratio (phase ratio) of ethylenically unsaturated monomers such as styrene and their polymers to water in suspension polymerization is 0.8 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. Therefore, the degree of bulk polymerization of polymerizable ethylenically unsaturated monomers mainly composed of styrene is
The reason why we created a bulk polymerization solution with a centipoise (CPS) of 10,000 centipoise (CPS) is that at less than 100 CPS, there is a difference in particle size distribution compared to when styrenic polymer particles are obtained only by suspension polymerization without the bulk polymerization step. In addition, if it exceeds 10,000 CPS, the viscosity is high, and the work of transferring the bulk polymerization solution to a suspension system becomes difficult. In addition, the supply timing of the ethylenically unsaturated monomer mainly composed of styrene that is newly added to the suspension reaction system should be adjusted to 40% by weight or more of the ethylenically unsaturated monomer mainly composed of styrene in the reaction system. The reason why the time point was set at the time when was polymerized is as follows. The suspended oil droplets formed from the bulk polymerization liquid in the suspension system by stirring quickly and uniformly absorb newly supplied oil droplets of ethylenically unsaturated monomers mainly composed of styrene. , the resulting styrenic polymer particles have a narrow particle size distribution. If there are oil droplets that are not absorbed, they will themselves undergo suspension polymerization to form small-sized styrene-based polymer particles, and this and large-sized styrene-based polymer particles with the bulk polymer solution oil droplets as cores. coexist, resulting in a wide particle size distribution, which is undesirable. The rate at which the newly supplied oil droplets of the ethylenically unsaturated monomer mainly composed of styrene are absorbed into the oil droplets of the bulk polymerization solution is The higher the concentration of coalescence, the faster it is. Therefore, in order to minimize the chance that the newly supplied styrenic unsaturated monomer independently forms styrenic polymer particles with a small particle size, it is necessary to The polymerization rate should be more than 40% by weight. Generally, new ethylenically unsaturated monomers mainly composed of styrene are fed to the suspension reaction system in a polymerized state of 40 to 70% by weight, preferably 40 to 55% by weight. 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 impregnating it or by supplying a blowing agent into the reaction system during bulk polymerization or suspension polymerization and performing the polymerization step. Generally, it is convenient to supply a blowing agent during suspension polymerization in terms of the polymerization process, but when the diameter of the resulting expandable particles is small, the blowing agent may dissipate in the particle receptacle and during storage. In view of this, it is preferable to impregnate the particles with a 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 below, the styrenic polymer particles obtained by carrying out the present invention have a high proportion of particles that fall into a commercial grade of 45% or more, and the particle size distribution of the particles is also narrowly sieved. is easy. Furthermore, the content of particles with a particle size of 0.42 mm or less and particles with a particle size of 2.83 mm or more, which are inferior products, is also small, so it has the advantage of being extremely low. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 200g of styrene and 0.4g of benzoyl peroxide were added into a 0.5mm polymerization vessel, and after replacing the air in the vessel with nitrogen gas, the temperature was heated to 80°C while stirring at 250rpm.
The temperature rose to The styrene solution, which was heated at the same temperature for 2 hours and subjected to bulk polymerization, was transferred under stirring at 350 rpm 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. did. 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, a part of the bulk polymerization solution heated at 80°C for 2 hours was sampled and measured using a B-type viscometer (manufactured by Tokyo Keiki).
When the viscosity at 20℃ was measured using
It was 150 centipoise. In addition, as a result of infrared analysis of the sampled liquid, the styrene polymerization rate of the above solution (comparison of absorption of 1632 cm ^-1 to 1602 cm ^-1 )
was 16.0% by weight. In addition, in the suspension system, the styrene polymerization rate immediately before the addition of styrene was 42.5% by weight.
It was hot. The weight average molecular weight of the styrene polymer finally obtained was 310,000. Example 2 In Example 1, the polymerization was completed under exactly the same conditions except that the time from the start of the suspension polymerization to the addition of the styrene solution was changed to 3 hours. 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. 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 7 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 time from the start of suspension polymerization to the addition of the styrene solution was 0 hours and 1 hour, respectively.
Polymerization was completed under exactly the same conditions except that the time was changed. 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 1000 g of styrene and 2 g of benzoyl peroxide were added into the polymerization vessel of Comparative Examples 3 and 4, and after replacing the air in the vessel with nitrogen gas, the temperature was raised to 80°C while stirring at 250 rpm. The styrene solution was heated at the same temperature for 2 hours (Comparative Example 3) or 6 hours (Comparative Example 4) and polymerized in bulk.
It was transferred into 1000 g of pure water containing 2.5 g of tricalcium phosphate and 0.025 g of sodium dodecylbenzenesulfonate under stirring at 350 rpm. 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. In addition, when heating at 80℃ for 3 hours, sampling a part of the bulk polymerization liquid, and measuring the viscosity at 20℃ using a Tokyo Keiki B-type viscometer, it was 150CPS.
and 14000CPS. Further, when the sampled liquid was analyzed by infrared rays, the styrene polymerization rate of the above solution was 16% by weight and 50% by weight. 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 First, a polymerizable ethylenically unsaturated monomer mainly composed of styrene was bulk polymerized in the presence of a polymerization initiator until the viscosity of the reaction system at 20°C was 100 to 10,000 centipoise. A styrene bulk polymer or copolymer solution is fed into water containing a suspension stabilizer and then heated to initiate suspension polymerization of unreacted ethylenically unsaturated monomers, resulting in styrene-based polymerization. When the polymerization rate of the ethylenically unsaturated monomer reaches 40% by weight or more, add 100 parts by weight of the styrene-based polymerizable ethylenically unsaturated monomer initially charged into the reaction system. , a styrene product characterized in that a polymerizable ethylenically unsaturated monomer mainly composed of styrene is newly supplied to a suspension reaction system at a ratio of 200 to 900 parts by weight, and the suspension polymerization is subsequently completed. Method for producing polymer particles.