JP2019019294A - Method for producing styrenic resin - Google Patents

Abstract

To provide a method for producing a styrenic resin which can produce the styrenic resin having high flowability and high melt tension.SOLUTION: A method for producing a styrenic resin includes: a dispersion step of dispersing nuclear particles containing a styrenic resin into an aqueous medium; an impregnation step of further adding a polymerization initiator and a styrene monomer and impregnating the nuclear particles with the polymerization initiator and the styrene monomer at a temperature at which polymerization of the styrene monomer does not proceed; a polymerization initiation step of raising the temperature of the aqueous medium and initiating the polymerization of the styrene monomer; and an additional impregnation polymerization step of additionally adding a styrene monomer into the aqueous medium, impregnating the nuclear particles with the styrene monomer, and graft polymerizing the styrene monomer with the styrene resin, where an amount of the styrene monomer to be added in the impregnation step is 20-200 pts.wt. and an amount of the styrene monomer to be added in the additional impregnation polymerization step is 50-700 pts.wt. with respect to 100 pts.wt. of the nuclear particles, and a content of the styrene monomer in the nuclear particles in the additional impregnation polymerization step is kept at 10 wt.% or less.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a styrene resin.

Styrenic resins are used as raw materials for various molded products because they are excellent in dimensional stability, molding stability, etc., have high rigidity, and are inexpensive. In general, the melt tension of the resin can be increased by increasing the molecular weight of the styrene-based resin. However, the higher the molecular weight, the lower the fluidity of the resin and the easier it is to reduce the molding processability and productivity.
Various attempts have been made to solve this problem.

  For example, a styrene-based resin composition containing linear polystyrene and hyperbranched polystyrene, (1) The weight average molecular weight (absolute weight average molecular weight) determined by the GPC-MALLS method is 250,000 to 75. (2) The slope in a logarithmic graph with the weight-average molecular weight on the horizontal axis and the radius of inertia of the resin composition determined by GPC-MALLS on the vertical axis is 0.35 to 0.45. It is disclosed that a container having a high melt tension, high fluidity, and a wide range of ratio of depth and opening is produced using the resulting styrene resin composition (see, for example, Patent Document 1).

  In addition to increasing the molecular weight of the styrene resin, as a method for increasing the melt tension of the resin, it is also known that the molecular chain of the polystyrene resin is branched. However, the polyfunctional monomer that is indispensable for branching the molecular chain may cause gelation during the synthesis of the resin. In order to solve such a problem, for example, the following method is disclosed as a method for producing a styrene-based resin composition made of ultra-high molecular weight highly branched polystyrene and linear polystyrene while suppressing gelation. That is, 50 ppm to 5000 ppm of a solvent-soluble polyfunctional vinyl compound copolymer having two or more vinyl groups in one molecule and having a branched structure on an average basis is added to a vinyl monomer essentially containing styrene. A line formed by polymerizing the highly branched ultrahigh molecular weight copolymer and the vinyl monomer produced by polymerizing the solvent-soluble polyfunctional vinyl copolymer and the vinyl monomer by suspension polymerization in water. A method for producing a styrene resin composition containing a polymer is disclosed (for example, see Patent Document 2).

In addition, in order to obtain a polystyrene resin composition for foaming that can improve the weight of the foamed molded product and the productivity at the time of molding, the polystyrene-based resin composition for foaming is composed of a polyfunctional vinyl aromatic compound and a styrene resin. A monomer-derived component is included as a base resin, the polyfunctional vinyl aromatic compound has a molecular weight of 100 or more and less than 1000, and the base resin is polyfunctional in the styrene monomer. It is obtained by polymerizing a monomer mixture containing 50 to 500 ppm of vinyl aromatic compound,
(1) Melt flow rate (MFR: g / 10 minutes) and melt tension value (MT: cN) satisfying the following relational expression at a measurement condition of 200 ° C.
MT ≧ −3 × ln (MFR) +12
(2) Ratio of loss tangent tan δ at an angular frequency ω of 0.01 rad / s and 100 rad / s satisfying the following relational expression 4 ≦ tan δ (ω = 0.01 (rad / s)) / tan δ (ω = 100 (Rad / s)) ≦ 20
(For example, refer to Patent Document 3).
Furthermore, in order to obtain a polystyrene-based resin composition for extrusion foaming that can improve the productivity at the time of molding while reducing elution of styrene and its oligomer into the foam-molded product, a polystyrene-based resin composition for extrusion foaming is used. (1) The top peak molecular weight (Mp) in the molecular weight distribution is 140,000 to 220,000; (2) the proportion of the molecular weight below Mp is 40 to 55% of the whole; (3) the z + 1 average molecular weight is 800,000 to 3.5 million; (4) It is disclosed that the content of an oligomer composed of styrene dimer and styrene trimer is 2000 ppm or less; and (5) the content of styrene is 1000 ppm or less (see, for example, Patent Document 4) ).

JP 2005-281405 A JP 2014-189767 A Japanese Patent Laying-Open No. 2015-193761 Japanese Patent Laying-Open No. 2015-193964

  However, since the styrene resin disclosed in any of Patent Documents 1 to 4 has an absolute weight average molecular weight of several hundred thousand, which is less than one million, the melt tension of the styrene resin is insufficient. Moreover, since the fluidity | liquidity fell when manufacturing a branched resin using a polyfunctional monomer like patent document 3 and 4, it was not excellent in molding workability.

  An object of this invention is to provide the manufacturing method of the styrene resin which can manufacture the styrene resin which has high fluidity | liquidity and high melt tension and which has a branched structure.

That is, the present invention is as follows.
<1> a dispersion step of dispersing core particles containing a styrene resin in an aqueous medium;
A polymerization initiator containing an organic peroxide and a styrene monomer are added to the aqueous medium, and the polymerization initiator and the styrene monomer are added to the core particles at a temperature at which the polymerization of the styrene monomer does not proceed substantially. An impregnation step of impregnating the polymer,
A polymerization initiation step of heating the aqueous medium to initiate polymerization of the styrene monomer;
An additional impregnation polymerization step of adding an additional styrene monomer to the aqueous medium, impregnating the core particles with the styrene monomer, and graft-polymerizing the styrene monomer to a styrenic resin;
Including
The amount of styrene monomer added in the impregnation step is 20 to 200 parts by weight with respect to 100 parts by weight of the core particles,
The addition amount of the styrene monomer in the additional impregnation polymerization step is 50 to 700 weights with respect to 100 parts by weight of the core particles, and the content of the styrene monomer in the core particles in the additional impregnation polymerization step. Is a method for producing a styrenic resin, which is maintained at 10% by weight or less.

<2> The method for producing a styrene resin according to <1>, wherein the aqueous medium has an oxygen concentration at 30 ° C. of 4 mg / L or more.

<3> The method for producing a styrene resin according to <1> or <2>, wherein an average particle size of the core particles in the dispersion step is 0.3 to 1.2 mm.

<4> The 10-hour half-life temperature T _1/2 of the organic peroxide is 85 to 120 ° C., and the temperature of the aqueous medium in the impregnation step is 70 ° C. or more and (T _1/2 -15) ° C. or less. Yes, The temperature of the aqueous medium in the additional impregnation polymerization step is (T _1/2 −10 ° C.) ° C. or more and (T _1/2 +20) ° C. or less, according to any one of <1> to <3>. It is a manufacturing method of this styrene resin.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the styrene resin which can manufacture the styrene resin which has high fluidity | liquidity and has high melt tension and which has a branched structure can be provided.

It is a graph of the simulation result in Examples 1, 5 and 7. 10 is a graph of a simulation result in Example 2. 10 is a graph of simulation results in Example 3. It is a graph of the simulation result in Example 4. 10 is a graph of simulation results in Example 6. 6 is a graph of a simulation result in Comparative Example 1. 10 is a graph of a simulation result in Comparative Example 2. It is an example of the Debye plot obtained when measuring a styrene resin by GPC-MALS method.

The method for producing a styrene resin of the present invention (hereinafter sometimes referred to as “the production method of the present invention”) includes a dispersion step of dispersing core particles containing a styrene resin in an aqueous medium,
A polymerization initiator containing an organic peroxide and a styrene monomer are added to the aqueous medium, and the polymerization initiator and the styrene monomer are added to the core particles at a temperature at which the polymerization of the styrene monomer does not proceed substantially. An impregnation step of impregnating the polymer,
A polymerization initiation step of heating the aqueous medium to initiate polymerization of the styrene monomer;
An additional impregnation polymerization step of adding an additional styrene monomer to the aqueous medium, impregnating the core particles with the styrene monomer, and graft-polymerizing the styrene monomer to a styrenic resin;
Including
The amount of styrene monomer added in the impregnation step is 20 to 200 parts by weight with respect to 100 parts by weight of the core particles,
The addition amount of the styrene monomer in the additional impregnation polymerization step is 50 to 700 weights with respect to 100 parts by weight of the core particles, and the content of the styrene monomer in the core particles in the additional impregnation polymerization step. Is maintained at 10% by weight or less.
The production method of the present invention may further include other steps such as a step of washing the obtained styrenic resin.

High molecular weight is useful as a means of improving the melt tension of styrenic resin and improving strength, but simply increasing the molecular weight reduces the fluidity of the resin and deteriorates the moldability. there were. As a means for improving the strength while maintaining fluidity, it is useful to introduce a branched structure into the molecular chain. A resin having a branched structure has a high degree of entanglement between molecular chains and therefore has a high melt tension and is difficult to break during stretching. As a method of incorporating a branched structure into the molecular chain of the styrene resin, there is a method of polymerizing a styrene monomer in the presence of a polyfunctional monomer such as divinylbenzene as a branching agent. However, such a polymerization method has a problem in that branch points concentrate on the portion where the polyfunctional monomer is polymerized, and a microgel is easily generated. In order to produce more highly branched styrenic resin, if the addition amount of polyfunctional monomer is increased, the polyfunctional monomer is brought into close proximity in the reaction system, and gelation occurs during polymerization. Is likely to occur. Therefore, the addition amount of the branching agent is limited, and it is difficult to produce a styrene resin having a high melt tension while maintaining fluidity.
On the other hand, the reason why the styrene resin having high melt tension and excellent fluidity can be produced by the production method of the present invention having the above configuration is not clear, but is due to the following reason. Inferred.

  The production method of the present invention mainly includes a dispersion step of dispersing the core particles in an aqueous medium, an impregnation step of impregnating the core particles with a polymerization initiator and a styrene monomer, and polymerization for initiating polymerization of the styrene monomer. A starting step and an additional impregnation polymerization step of adding a styrene monomer in the aqueous medium to impregnate the core particles, and graft-polymerizing the styrene monomer to the styrenic resin. In the present invention, in the additional impregnation polymerization step, by maintaining the concentration of the styrene monomer in the core particle as a polymerization reaction field at a specific concentration, while increasing the number of branch points (high branching degree), the high It is considered that the molecular weight can be obtained, and further, the branch points can be separated.

Usually, there are a polymerization initiator and many styrene monomers in the reaction field, and the initiator radicals generated from the polymerization initiator and the polymer chain growth terminal radicals are preferentially related to the vinyl group of the styrene monomer. It is considered that a linear styrene resin is easily formed.
On the other hand, when the concentration of the styrene monomer in the reaction field is low, it is considered that the initiator radical and the polymer chain growth terminal radical are likely to cause not only a polymerization reaction with the styrene monomer but also a hydrogen abstraction reaction of the polymer chain. . As a result, the styrene monomer is graft-polymerized to the radicals on the polymer chain generated by the hydrogen abstraction reaction, or the growing terminal radical of the polymer chain is recombined to form a branched chain in the polymer chain. It is thought that. Furthermore, since the position where the branched chain is generated in the polymer chain is sterically crowded, it is considered that no further branched chain is likely to occur near the generated branch point. That is, it is considered that a hydrogen abstraction reaction occurs again on the polymer chain far from the branch point to the extent that steric hindrance does not occur, and a branched chain is generated. Therefore, it is considered that a styrenic resin having many branched chains can be obtained without causing gelation because branched chains are generated while the branch points are appropriately separated. As described above, according to the production method of the present invention, it is possible to produce a high-molecular-weight styrene resin having a lot of branched chains while suppressing gelation, so that the melt tension is high and the fluidity is maintained. It is considered that the produced styrene resin can be produced.
Hereafter, each process of the manufacturing method of this invention is demonstrated in detail.

[Dispersing process]
In the dispersion step, the core particles containing the styrene resin are dispersed in the aqueous medium.
The method for dispersing the core particles in the aqueous medium is not particularly limited. For example, a suspension agent and, if necessary, a surfactant may be added to the aqueous medium together with the core particles and mixed.

(Nuclear particles)
The core particle includes a styrene resin.
Examples of the styrene resin include a polymer of a styrene monomer, a copolymer of a styrene monomer and another monomer, and a mixture of two or more of these. The structural unit derived from the styrene monomer contained in the copolymer is at least 50% by weight, preferably 60% by weight or more, and more preferably 80% by weight or more.
Specific examples of the styrene resin include polystyrene, rubber-modified polystyrene (impact polystyrene), styrene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, and styrene-methyl methacrylate. Examples thereof include a copolymer and a styrene-maleic anhydride copolymer. Only one type of styrene resin may be used, or two or more types may be used. Among these styrenic resins, it is preferably made of polystyrene from the viewpoint that a hydrogen abstraction reaction is likely to occur and a branched chain is likely to be generated together with the styrene monomer.
The core particle may contain a resin other than the styrene resin, but preferably contains 70% by weight or more of the styrene resin, more preferably contains 85% by weight or more, and consists of a styrene resin. More preferably.

The average particle diameter of the core particles is preferably 0.3 to 1.2 mm. When the average particle diameter of the core particles is 0.3 mm or more, the amount of fine particles contained in the obtained branched styrene-based resin can be reduced, and when it is 1.2 mm or less, the specific surface area increases and the core particles Improves the impregnation of styrene monomer into the water. The average particle diameter of the core particles is more preferably 0.3 to 1.0 mm, and still more preferably 0.3 to 0.5 mm.
The average particle diameter of the core particles means a 63% volume average particle diameter.

(Aqueous medium)
As the aqueous medium, water such as deionized water can be usually used, but it may contain a water-soluble organic solvent such as alcohol as long as the core particles do not dissolve.

(Surfactant)
Examples of the surfactant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. Among these, it is preferable that the surfactant has at least one selected from the group consisting of an anionic surfactant, a cationic surfactant, and a nonionic surfactant. Specifically, alkyl sulfonate (for example, sodium dodecyl sulfonate), alkyl benzene sulfonate (for example, sodium dodecyl benzene sulfonate), polyoxyalkyl ether phosphate, alkyl dimethyl ethyl ammonium ethyl sulfate, higher alcohol, Examples thereof include glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkyl ether, and fatty acid salt.
Only one surfactant may be used, or two or more surfactants may be used.
Furthermore, electrolytes such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium acetate, and sodium succinate may be used together with the surfactant.

(Suspending agent)
Examples of the suspending agent include hydrophilic polymers such as polyvinyl alcohol, methyl cellulose, and polyvinyl pyrrolidone; poorly water-soluble inorganic substances such as tribasic calcium phosphate, magnesium nitrate, magnesium pyrophosphate, hydroxyapatite, aluminum oxide, talc, kaolin, and bentonite. Examples include salts.
Only one type of suspension may be used, or two or more types of suspensions may be used. One or both of the hydrophilic polymer and the sparingly water-soluble inorganic salt may be used, or two or more of them may be used.
When a poorly water-soluble inorganic salt is used as a suspending agent, it is preferable to use an anionic surfactant such as sodium alkyl sulfonate or sodium alkylbenzene sulfonate together.

  The amount of the suspending agent used is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight as a total of the total addition amount of the core particles and the styrene monomer. When the suspending agent composed of the hardly water-soluble inorganic salt and the anionic surfactant are used in combination, the suspending agent is added to the total amount of 100 parts by weight of the total addition amount of the core particles and the styrenic monomer. It is preferable to use 05 to 3 parts by weight and 0.0001 to 0.5 parts by weight of an anionic surfactant.

[Impregnation process]
In the impregnation step, the polymerization initiator containing the organic peroxide and the styrene monomer are contained in the aqueous medium, that is, in the aqueous medium containing the core particles dispersed in the dispersion step and, if necessary, the suspending agent, the surfactant and the like. A monomer is added, and the core particles are impregnated with the polymerization initiator and the styrene monomer at a temperature at which the polymerization of the styrene monomer does not proceed substantially.
Here, the “temperature at which the polymerization of the styrene monomer does not proceed substantially” is a temperature at which the organic peroxide does not substantially decompose, and from the viewpoint of suppressing the decomposition of the organic peroxide, When the 10-hour half-life temperature of the oxide is T _1/2 , the temperature of the aqueous medium in the impregnation step is preferably (T _1/2 -15) ° C. or less, and (T _1/2 -18) ° C. More preferably, it is as follows. From the viewpoint of the impregnation property of the styrene monomer into the core particles, the temperature of the aqueous medium in the impregnation step is preferably 70 ° C. or higher, and more preferably 75 ° C. or higher.
Further, the temperature of the aqueous medium in the impregnation step may be constant as long as it is within the above range, or may be changed by gradually increasing the temperature.
The time for the impregnation step is preferably about 0.5 to 2.0 hours from the viewpoint of sufficiently impregnating the styrene monomer and the polymerization initiator in the core particles, More preferably, it is time.

  The addition amount of the styrene monomer in the impregnation step is 20 to 200 parts by weight, preferably 30 to 180 parts by weight, and more preferably 40 to 160 parts by weight with respect to 100 parts by weight of the core particles. . In the impregnation step, if the amount of styrene monomer added is too small, the core particles cannot be sufficiently plasticized, and the polymerization initiator cannot be sufficiently impregnated with the polymerization initiator. On the other hand, when the addition amount of the styrene monomer is too large, the styrene monomer is polymerized outside the core particles and fine particles are easily generated.

(Polymerization initiator)
The polymerization initiator includes at least an organic peroxide.
Examples of the organic peroxide include benzoyl peroxide, dilauroyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-hexylperoxy-2-ethylhexanoate. Ate, t-amylperoxy-2-ethylhexanoate, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethyl Hexanoate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-butyl Peroxybenzoate, t-amyl peroxyisopropyl carbonate, -Amylperoxy-2-ethylhexyl carbonate, t-hexylperoxyisopropyl carbonate, t-butylperoxy-3,5,5-trimethylhexanoate, 1,1-bis (t-butylperoxy) -3, 3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) -2-methylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) ) Cyclododecane, 2,2-bis (t-butylperoxy) butane, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-hexylper) Oxy) cyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, and the like.
These organic peroxides may be used alone or in combination of two or more.

As the polymerization initiator, an organic peroxide having a 10-hour half-life temperature T _1/2 of 85 to 120 ° C. is preferably used, and a T _1/2 of 90 to 110 ° C. is more preferably used. In addition, when using 2 or more types of organic peroxide as a polymerization initiator, let 10 _1/2 half-life temperature of the organic peroxide with the lowest 10-hour half-life temperature be T1 _{/ 2} . Organic peroxides satisfy these temperature ranges and have high hydrogen abstraction ability, such as t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethylhexyl monocarbonate, t- It is more preferable to use an organic peroxide that generates a t-butoxy radical such as butyl peroxybenzoate or an organic peroxide that generates a cumyloxy radical such as dicumyl peroxide.

The polymerization initiator may contain a polymerization initiator other than the organic peroxide, but from the viewpoint of facilitating the hydrogen abstraction reaction, the polymerization initiator preferably contains 70% by weight or more of the organic peroxide. 85% by weight or more, and more preferably an organic peroxide.
The addition amount of the polymerization initiator is preferably 0.1 to 2.0 parts by weight with respect to 100 parts by weight as the total addition amount of the core particles and the styrene monomer. Within this range, productivity is not excessively lowered and hydrogen abstraction reaction is likely to occur. The addition amount of the polymerization initiator is more preferably 0.2 to 1.5 parts by weight with respect to 100 parts by weight as the total addition amount of the core particles and the styrene monomer.

(Oxygen concentration in aqueous medium)
As the aqueous medium, an aqueous medium having an oxygen concentration at 30 ° C. of 4 mg / L or more is preferably used. Oxygen in the aqueous medium functions as a polymerization inhibitor in the aqueous medium and inhibits the generation of fine particles. Accordingly, the higher the oxygen concentration in the aqueous medium, the higher the yield of the styrene resin. The oxygen concentration at 30 ° C. is more preferably 5 mg / L or more.
The generation of fine particles can also be suppressed by adding 30 to 200 ppm of a water-soluble polymerization inhibitor such as sodium nitrite to the aqueous medium.

[Polymerization start step]
In the polymerization initiation step, the temperature of the aqueous medium in which the core particles impregnated with the polymerization initiator and the styrene monomer are increased, and polymerization of the styrene monomer is started. Specifically, the polymerization of the styrene monomer is preferably started by setting the temperature at which the organic peroxide is substantially decomposed. From the viewpoint of productivity, the temperature of the aqueous medium is preferably (T _1/2 -10) ° C. or higher, and more preferably (T _1/2 -5) ° C. or higher.
The temperature raising time to the temperature is not particularly limited, but the polymerization of the styrene monomer in the core particles proceeds during the temperature rising, and the content of the styrene monomer in the core particles in the additional impregnation polymerization described later. Since it is easy to control the amount to 10% by weight or less, it is preferably 3 hours or more, and more preferably 5 hours or more. On the other hand, from the viewpoint of productivity, it is preferably within 10 hours.

[Additional impregnation polymerization process]
In the additional impregnation polymerization step, the styrene monomer is additionally added in the aqueous medium, that is, in the aqueous medium containing the core particles in which the polymerization of the styrene monomer has started in the core particles after the polymerization start step. The core particles are then impregnated with a styrene monomer and polymerized. At this time, the addition amount of the styrene monomer is 50 to 700 parts by weight with respect to 100 parts by weight of the core particles in the additional impregnation polymerization step. Then, the styrene monomer is intermittently or continuously added so that the content (concentration) of the styrene monomer in the core particles in the additional impregnation polymerization step is maintained at 10% by weight or less.

By passing through the polymerization start step, the styrene monomer starts polymerization using the inside of the core particles as a reaction field. In the additional impregnation polymerization step, by maintaining the content of the styrene monomer in the core particles at 10% by weight or less, not only the polymerization between the styrene monomers but also the styrene monomer in the styrene resin. Graft polymerization tends to occur and a branched chain is formed.
In addition, in the range which does not inhibit the target effect of this invention, content of the styrene monomer in the core particle in an additional impregnation polymerization process can exceed 10 weight%. The time when the content of the styrene monomer in the core particles exceeds 10% by weight is preferably 20% or less, more preferably 10% or less, and more preferably 10% or less of the time of the additional impregnation polymerization step. In all the steps, it is most preferable that the content of the styrene monomer in the core particles is 10% by weight or less. From the viewpoint of highly producing branched chains, the time for the additional impregnation polymerization step is preferably 150 minutes or more, and more preferably 180 minutes or more. From the viewpoint of production efficiency, the upper limit of the additional impregnation polymerization step is preferably about 600 minutes.
The content of the styrene monomer in the core particles in the additional impregnation polymerization step is preferably 8% by weight or less, and more preferably 6% by weight or less.

  The content of styrene monomer in the core particles in the additional impregnation polymerization process can be calculated based on the chemical characteristics of the polymerization initiator used for the polymerization, the polymerization rate of styrene determined from the polymerization temperature, etc. The styrene in the core particles in the additional impregnation polymerization step is adjusted by adjusting the timing and rate of addition (addition ratio) of the styrene monomer so that the desired content is obtained based on the calculated value. The monomer content can be adjusted. Further, the content of the styrene monomer in the actual core particles can be determined by a method described later after extracting the core particles during polymerization from the reaction system.

It is considered that the lower the content of the styrene monomer in the core particles, the more likely to cause not only the polymerization initiation reaction but also the hydrogen abstraction reaction, and the degree of branching is improved. Further, when the ratio of the styrene monomer to the core particles is high, the absolute molecular weight and the degree of branching are likely to be improved.
As described above, it is considered that when the average particle diameter of the core particles is 1.2 mm or less, the specific surface area is increased, the impregnation property of the styrene monomer is improved, and branching is easily generated.

The temperature condition of the additional impregnation polymerization step is not particularly limited, but from the viewpoint of facilitating the hydrogen abstraction reaction, the temperature of the aqueous medium in the additional impregnation polymerization step is (T _1/2 -10) ° C. to (T _1/2 +20). ) ° C., preferably (T _1/2 -5) ° C. to (T _1/2 +10) ° C.
Further, the temperature of the aqueous medium in the additional impregnation polymerization step may be constant as long as it is within the above range, or may be changed by gradually increasing it.

The addition amount of the styrene monomer is 50 to 700 parts by weight with respect to 100 parts by weight of the core particles in the additional impregnation polymerization step. If the addition amount of the styrene monomer is too small in the additional impregnation polymerization step, it will not be possible to generate a branched chain sufficiently. Moreover, when there is too much addition amount of a styrene monomer, it will become easy to superpose | polymerize styrene monomers outside a core particle, and there exists a possibility that the yield of a styrene-type resin may worsen.
The addition amount of the styrene monomer is preferably 100 to 600 parts by weight, more preferably 200 to 550 parts by weight with respect to 100 parts by weight of the core particles in the additional impregnation polymerization step.

  The production method of the present invention can obtain a styrene-based resin having a high degree of branching without using a polyfunctional monomer (branching agent). A sex monomer may be added. The addition amount of the polyfunctional monomer in the aqueous medium is preferably 0.2 parts by weight or less with respect to 100 parts by weight of the core particles through the impregnation polymerization process and the additional addition process, and 0.1 parts by weight or less. More preferably, it is more preferably 0 part by weight. That is, it is preferable not to use a polyfunctional monomer. By not using a polyfunctional monomer, a styrene resin having a higher degree of branching can be obtained.

  In addition to the additional impregnation polymerization step, the production method of the present invention further includes a residual polymerization step of polymerizing a styrene monomer remaining in the styrene resin particles after the additional impregnation polymerization step, and a suspension attached to the obtained styrene resin. A washing step of washing a turbidity agent, a surfactant and the like with water, a coating step of coating a functional component such as an antistatic agent on the surface of the styrene resin, and the like may be included.

The styrene resin obtained by the production method of the present invention has a weight average molecular weight (Mw ′) of 1 million or more, which is determined by GPC-MALS method, and long chain branching per 1000 units of styrene assuming three chain branching. A styrene resin having a branched structure having a degree B _{m, 1000} of 0.3 or more is preferable. Moreover, it is preferable that Z average molecular weight (Mz ') calculated | required by GPC-MALS method is 3 million or more, and it is preferable that long-chain branching degree Bm _{, w} per molecule is 4-20. It is preferable that Moreover, it is preferable that the tetrahydro insoluble content in the styrene resin obtained by the production method of the present invention is 0.1% by weight or less (including 0).
A styrene resin exhibiting such characteristics has a high molecular weight, but has more long chain branches in the molecular chain than a conventional branched styrene resin, and a relatively low molecular weight molecular chain. It is thought that many long-chain branches are present inside.

The GPC-MALS method is a method in which gel permeation chromatography (GPC) and a multi-angle light scattering detector (MALS) are combined. By the GPC-MALS method, the absolute molecular weight and the root mean square radius <R _g ² > of the styrene resin can be measured, and the degree of branching of the styrene resin can be inferred from the measurement result.

(Basic principle of GPC-MALS method)
When a styrene resin solution is prepared by dissolving a styrene resin in a solvent such as tetrahydrofuran and subjected to GPC measurement, a polymer having a larger molecular size elutes first, and therefore, it is classified according to the molecular size. Subsequently, by subjecting the divided styrene resin solution to MALS measurement, the weight average molecular weight (Mw ′) of the styrene resin divided by the molecular size and the root mean square radius <R _g ² > corresponding to the molecular size are obtained. Can be calculated.
Specifically, the styrene resin solution divided by molecular size by GPC is irradiated with laser light, and the intensity of scattered light generated from the styrene resin solution by Rayleigh scattering is measured. Mw ′ and <R _g ² > are calculated from the obtained measurement values using the following equation (1) and the Debye plot shown in FIG.

K ^* : optical parameter (4π ² n ₀ ² (dn / dc) ² / [λ ₀ ⁴ N _A ])
n ₀ : refractive index of solvent dn / dc: concentration increment of refractive index λ ₀ : wavelength of incident light in vacuum N _A : Avogadro number c: sample concentration (g / mL)
R (θ): Rayleigh ratio of excessive scattering Mw ′: weight average molecular weight (g / mole)
P (θ): interference factor P (θ) = (1-2 {(4π / λ) sin (θ / 2)} ² <R _g ² > / 3! +...
λ: wavelength in the measurement system λ ₀ / n _0
<R ^g 2>: mean square radius of gyration _{A 2:} Second virial coefficient

FIG. 8 shows the measurement of styrene resin solutions having different resin concentrations by the GPC-MALS method. The vertical axis (Y axis) is “K ^* c / R (θ)” and the horizontal axis (X axis) is “sin”. ² is an example of a Debye plot plotted as “ ² (θ / 2)”.
From the regression line obtained by the Debye plot and the intercept of the vertical axis (Y-axis intercept), from the weight average molecular weight Mw ′ of the styrene resin divided by molecular size by GPC and the initial slope of the regression line, The root mean square radius <R _g ² > is obtained.
In GPC measurement, since the concentration at each elution time is very dilute, the second when the virial coefficient A ₂ analyzed as 0, the root mean rotating the weight-average molecular weight Mw 'of styrenic resin divided by the molecular size by GPC The radius <R _g ² > can be obtained by the following formulas (2) and (3), respectively.

K ^* c / R ₀ : K ^* c / R (θ) at an angle θ = 0 °
dy / dx: initial slope of the regression line

The number average molecular weight Mn ′, the weight average molecular weight Mw ′, and the Z average molecular weight Mz ′ determined by the GPC-MALS method are absolute molecular weights of the styrene resin.
On the other hand, the number average molecular weight Mn, the weight average molecular weight Mw, and the Z average molecular weight Mz determined by the GPC method using linear polystyrene as a standard substance are relative molecular weights of styrene resins.

In the present invention, the shrinkage factor g of the styrene resin uses a value obtained as follows.
The ratio of the root mean square radius <R _g ² > _{B of the} styrene resin having a branched structure of the present invention to the root mean square radius <R _g ² > _L of the linear styrene resin is defined as a shrinkage factor g, and the following formula (4) ) To (8), the contraction factor g can be obtained. Then, the shrinkage factor g, can be determined degree of long chain branching B _m. In the present invention, the long-chain branching degree is determined on the assumption that the styrene-based resin has a three-chain branching structure.
Shrinkage factor _g w, 1 degree of long chain branching _{B m} per _{molecule, w,} degree of long chain branching _{B m, 1000} per styrene 1000 units is obtained by the following formula (4) to (8).

In the above formula, g _i is the contraction factor in section i; B _{m, i} is the degree of long chain branching in section i; c _i is the concentration in section i.

In addition, the styrene resin obtained by the production method of the present invention has a melt viscosity at 200 ° C. and a shear rate of 100 sec ⁻¹ of 2100 Pa · s or less, and a melt tension at 200 ° C. of 350 mN or more. A styrene-based resin having a ratio of the melt tension (melt tension / melt viscosity [mN / (Pa · s)]) of 0.20 or more is preferable.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. “Parts” and “%” are based on weight unless otherwise specified. The temperature in the autoclave means the temperature of the aqueous medium.

[Preparation of core particles]
(Production Example 1)
In an autoclave with an internal volume of 1 m ³ equipped with a stirrer, 350 kg of deionized water, 2.1 kg of tribasic calcium phosphate (made by Taihei Chemical Industrial Co., Ltd., 20.5% slurry) as a suspending agent, dodecylbenzenesulfone as a surfactant Sodium acetate (10% aqueous solution) 0.158 kg, disodium dodecyl diphenyl ether sulfonate (manufactured by Kao Corporation, Perex SSH 10% aqueous solution) 0.053 kg, and sodium acetate 0.535 kg were added as an electrolyte.
Next, 0.975 kg of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, perbutyl O) and 0.284 kg of t-butyl peroxy-2-ethylhexyl monocarbonate (Kayaku Akzo) as polymerization initiators. Manufactured by Trigonox 117) and 15.4 g of 4-tert-butylcatechol as a polymerization inhibitor were dissolved in 390 kg of styrene, and this was fed into the autoclave while stirring at 110 rpm. After the inside of the autoclave was purged with nitrogen, the temperature was raised and the temperature was raised to 90 ° C. over 1 hour and 15 minutes.

After reaching 90 ° C., the temperature was raised to 100 ° C. over 5 hours. After reaching 100 ° C., the temperature was raised to 115 ° C. over 1 hour and 30 minutes. The temperature was maintained at 115 ° C. for 2 hours and 40 minutes, and then cooled to 40 ° C. over 2 hours. During the temperature increase to 90 ° C., when the temperature reached 60 ° C., 1.95 g of potassium persulfate as a suspending aid was charged into the autoclave.
After cooling, the contents are taken out, tricalcium phosphate adhering to the surface of the styrenic resin particles is dissolved with nitric acid, dehydrated and washed with a centrifuge, and water adhering to the surface of the particles is further removed with an air dryer. Removal of styrene resin particles was obtained.
The obtained styrene resin particles were passed through a sieve to take out particles having a diameter of 0.5 to 1.3 mm (average particle diameter of 0.8 mm), which were designated as core particles 1.
The average particle diameter d63 of the styrene resin particles (the core particles 1 and the core particles 2 described later) was measured by a particle size distribution measuring apparatus “Millitrack JPA” manufactured by Nikkiso Co., Ltd.

(Production Example 2)
In an autoclave with an internal volume of 1 m ³ equipped with a stirrer, 380 kg of deionized water, 6.15 kg of tribasic calcium phosphate (20.5% slurry manufactured by Taihei Chemical Industrial Co., Ltd.) as a suspending agent, dodecylbenzenesulfone as a surfactant 0.499 kg of sodium acid (10% aqueous solution), disodium dodecyl diphenyl ether sulfonate (manufactured by Kao Corporation, 0.166 kg of Perex SSH 10% aqueous solution), and 4 g of potassium persulfate as a suspension aid were supplied.
Next, 0.440 kg of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, perbutyl O) and 0.520 kg of t-butyl peroxy-2-ethylhexyl monocarbonate (Kayaku Akzo) as polymerization initiators. Manufactured by Trigonox 117) was dissolved in 360 kg of styrene, and this was supplied to the autoclave while stirring at 110 rpm. After the inside of the autoclave was purged with nitrogen, the temperature was raised and the temperature was raised to 90 ° C. over 1 hour and 15 minutes.

After reaching 90 ° C., the temperature was raised to 120 ° C. over 6 hours, held at 120 ° C. for 3 hours, and cooled to 40 ° C. over 3 hours.
After cooling, the contents are taken out, tricalcium phosphate adhering to the surface of the styrene resin particles is dissolved with nitric acid, dehydrated and washed with a centrifuge, and water adhering to the surface is removed with an air flow dryer. Thus, styrene resin particles were obtained.
The obtained styrene-based resin particles were sieved to take out particles having a diameter of 0.3 to 0.5 mm (average particle diameter of 0.4 mm) to obtain core particles 2.

[Production of styrene resin]
Example 1
[Dispersion process]
421 kg of deionized water, 2.63 kg of sodium pyrophosphate and 6.56 kg of magnesium nitrate are supplied to an autoclave having an internal volume of 1.5 m ³ equipped with a stirrer, and pyrophosphate as a suspending agent in the autoclave by salt exchange Magnesium was synthesized. After supplying 0.131 kg of sodium alkyl sulfonate (Laomul PS, 40% aqueous solution) as a surfactant and 112 kg of styrene resin particles (nuclear particles 1) obtained in Production Example 1 as core particles to an autoclave The inside of the autoclave was purged with nitrogen. Specifically, the inside of the autoclave was pressurized to 0.3 MPa (G) with nitrogen, and then the gas in the autoclave was released until the pressure in the autoclave reached atmospheric pressure.

[Impregnation process]
Subsequently, it heated up to 80 degreeC, stirring at 50 rpm. After reaching 80 ° C., 84 kg of deionized water, sodium alkylsulfonate (La Kamul PS, 40% aqueous solution) 0.171 kg, 80 kg of styrene (styrene monomer), t-butylperoxy-2-ethylhexyl mono A mixture of 1.58 kg of carbonate (manufactured by Kayaku Akzo, Trigonox 117; described as “BE” in the table, 10-hour half-life temperature T _1/2 99.0 ° C.) 1.58 kg was prepared as an emulsion using a homogenizer. Was fed into the autoclave. Thereafter, the inside of the autoclave was pressurized with nitrogen until it became 0.1 MPa (G), and kept at 80 ° C. for 1 hour.

[Polymerization start step]
Then, it heated up to 105 degreeC over 2 hours.

[Additional impregnation polymerization process]
After reaching 105 ° C., it was held for 5.5 hours. 254 kg of styrene (styrene monomer) was continuously added into the autoclave at a rate of 0.8 kg / min over 5 hours and 10 minutes after the temperature in the autoclave reached 105 ° C.
In addition, when adding styrene, based on the above addition conditions, the chemical characteristics of the polymerization initiator used for the polymerization, and the polymerization rate of styrene calculated from the polymerization temperature, the styrene content in the core particles relative to the elapsed time was calculated by simulation. The amount change and the temperature change were confirmed, and based on the simulation, styrene was additionally added so that the styrene content in the core particles during the addition of styrene would be 10% by weight or less.
The method described later (“Styrene content in core particles during addition of styrene monomer during additional impregnation polymerization step” at the start of additional addition of styrene, at the end of 2.5 hours from the start of addition, and at the end of additional addition The styrene content in the styrenic resin particles was measured by the measurement method "). As a result, the styrene content in the core particles was 6% by weight.

  In FIGS. 1-7, the graph of the simulation result in an Example and a comparative example was shown. The graph shows the elapsed time [Time (hr)] on the horizontal axis, and the content of styrene monomer in the core particles in the additional impregnation polymerization process on the left vertical axis [Amount of Style monomer in a core particle (wt.%). The polymerization temperature [Temperature (° C.)] was plotted on the right vertical axis. In the graph, the change in the styrene content in the core particles with respect to the elapsed time is indicated by a solid line, and the change in polymerization temperature with respect to the elapsed time is indicated by a broken line.

[Residual polymerization step]
After the additional impregnation polymerization step, the aqueous medium was heated to 120 ° C. over 2 hours and held at 120 ° C. for 3 hours to polymerize the unreacted styrene monomer.
[Cooling process]
After the residual polymerization step, the aqueous medium was cooled to 35 ° C. over 6 hours.

  After cooling the inside of the autoclave, the styrene resin particles taken out from the autoclave were washed with dilute nitric acid to dissolve and remove the suspending agent adhering to the surface of the resin particles, washed with water, and further dehydrated with a centrifuge. After coating with 0.01 part by weight of polyoxyethylene lauryl ether as an antistatic agent (value relative to 100 parts by weight of styrene resin), water on the surface of the resin particles was removed by fluid drying (room temperature air, 10 minutes).

(Example 2)
The following points were changed from Example 1. Specifically, the core particles were changed to 66.9 kg of the styrene resin particles (core particles 2) obtained in Production Example 2 from the core particles 1. Further, in the additional impregnation polymerization step, the holding time at 105 ° C. was changed to 6 hours and 10 minutes, the amount of styrene to be additionally added was changed to 299 kg, and styrene was added at a rate of 0.8 kg / min over 6 hours and 10 minutes. Added continuously. When the addition of styrene monomer was started, the styrene content in the styrene resin particles was measured by the method described later at the time of 2.5 hours from the start of addition, and at the end of the addition, respectively. The styrene content was 10% by weight at the start of additional addition, and 6% by weight when 2.5 hours had elapsed from the start of addition and at the end of addition.

(Example 3)
A styrenic resin was prepared in the same manner as in Example 1 except that the temperature was raised from 80 ° C. to 100 ° C. over 2 hours after the impregnation step, and the temperature of the additional impregnation polymerization step was changed to 100 ° C. When the addition of styrene monomer was started, the styrene content in the styrene resin particles was measured by the method described later at the time of 2.5 hours from the start of addition, and at the end of the addition, respectively. The styrene content was 10% by weight at the start of the addition, 9% by weight after 2.5 hours from the start of the addition, and 8% by weight at the end of the addition.

Example 4
The following points were changed from Example 1. Specifically, in the dispersion step, the supply amount of the core particles (core particles 1) was changed to 183 kg. Further, in the additional impregnation polymerization step, the holding time at 105 ° C. is changed to 3 hours, the amount of styrene to be added is changed to 103 kg, and styrene is continuously added at a rate of 0.8 kg / min over 3 hours. Added. When the addition of styrene monomer was started, the styrene content in the styrene resin particles was measured by the method described later at the time of 2.5 hours from the start of addition, and at the end of the addition, respectively. The styrene content was 3% by weight at the start of addition, and 5% by weight after 2.5 hours from the start of addition and at the end of addition.

(Example 5)
The following points were changed from Example 1. In the dispersion step, when the air in the autoclave is replaced with nitrogen before raising the temperature, the autoclave is pressurized to 0.5 MPa (G) with nitrogen, and the gas in the autoclave is changed to atmospheric pressure until the pressure in the autoclave becomes atmospheric pressure. The releasing operation was repeated 3 times. When the addition of styrene monomer was started, the styrene content in the styrene resin particles was measured by the method described later at the time of 2.5 hours from the start of addition, and at the end of the addition, respectively. The styrene content was 6% by weight.

(Example 6)
The following points were changed from Example 1. Specifically, the supply amount of the core particles (core particle 1) was changed to 67 kg. In the additional impregnation polymerization step, the holding time at 105 ° C. was changed to 6 hours 30 minutes, the amount of styrene to be added was changed to 299 kg, and styrene was added at a rate of 0.8 kg / min over 6 hours 10 minutes. Was added continuously. When the addition of styrene monomer was started, the styrene content in the styrene resin particles was measured by the method described later at the time of 2.5 hours from the start of addition, and at the end of the addition, respectively. The styrene content was 10% by weight at the start of additional addition, and 6% by weight when 2.5 hours had elapsed from the start of addition and at the end of addition.

(Comparative Example 1)
A styrenic resin was prepared in the same manner as in Example 1 except that the temperature was raised from 80 ° C. to 90 ° C. over 2 hours after the impregnation step, and the temperature of the additional impregnation polymerization step was changed to 90 ° C. When the addition of styrene monomer was started, the styrene content in the styrene resin particles was measured by the method described later at the time of 2.5 hours from the start of addition, and at the end of the addition, respectively. The styrene content was 19% by weight at the start of addition, 25% by weight after 2.5 hours from the start of addition, and 24% by weight at the end of addition.

(Comparative Example 2)
The following points were changed from Example 1. Specifically, in the dispersion step, the supply amount of the core particles (core particles 1) was changed to 105 kg. The temperature of the impregnation step was changed to 75 ° C., and after reaching 75 ° C., the amount of styrene was changed to 53 kg, and the polymerization initiator was benzoyl peroxide (NIPPER BW manufactured by NOF Corporation, water diluted powder product; 1.79 kg described as “BPO”, 10-hour half-life temperature 73.6 ° C., and t-butylperoxy-2-ethylhexyl monocarbonate (Kayaku Akzo, Trigonox 117, 10-hour half-life temperature 99.0 ° C. ) The emulsion was changed to 0.18 kg, and an emulsion containing 11 g of divinylbenzene added as a branching agent (polyfunctional monomer) was fed into the autoclave. Then, it hold | maintained at 75 degreeC for 2 hours. After maintaining at 75 ° C. for 2 hours, a mixture of 321 kg of styrene and 89 g of divinylbenzene was continuously added at a rate of 2.1 kg / min over 2 hours and 30 minutes while maintaining the temperature. When the addition of styrene monomer was started, when 1.5 hours had elapsed from the start of addition, and at the end of the addition, the styrene content in the styrene resin particles was measured by the method described later. The styrene content was 8% by weight at the start of addition, 58% by weight after 1.5 hours from the start of addition, and 66% by weight at the end of addition. Next, the temperature was raised to 108 ° C. over 2 hours, raised to 112 ° C. over 20 minutes, and raised to 125 ° C. over 2 hours. Then, it hold | maintained at 125 degreeC for 1 hour 30 minutes, and cooled to 35 degreeC over 6 hours.

(Comparative Example 3)
Evaluation was performed using a commercially available product (HP780AN manufactured by DIC) as the styrene resin.

<Evaluation>
The physical properties of the styrene resins of Examples and Comparative Examples were measured by the following methods. The results are shown in Tables 1 and 2.

[Measurement of residual styrene monomer (residual monomer)]
About 1 g of styrene resin was precisely weighed, dissolved in 25 ml of N, N-dimethylformamide (DMF), measured by gas chromatography (GC), calibrated with a calibration curve, and the residual styrene was quantified. The measurement conditions for gas chromatography are as follows.
Equipment used: Gas chromatograph GC-9A manufactured by Shimadzu Corporation
Column packing:
[Liquid phase name] PEG-20M
[Liquid phase impregnation rate] 25% by weight
[Carrier particle size] 60/80 mesh [Carrier treatment method] AW-DMCS (washing, baking, acid treatment, silane treatment)
Column material: Glass column carrier gas with an inner diameter of 3 mm and a length of 3000 mm: N ₂
Detector: FID (hydrogen flame ionization detector)
Quantification: Internal standard method

[Measurement of residual styrene oligomer (styrene dimer + styrene trimer; residual oligomer)]
About 0.1 g of a styrene resin was precisely weighed and dissolved in 10 ml of tetrahydrofuran, and dropped into about 250 ml of n-heptane at 23 ° C. to precipitate the resin. The filtrate from which the resin was filtered was measured with a gas chromatograph mass spectrometer. The measurement conditions for gas chromatograph mass spectrometry are as follows.
Equipment used: Gas chromatograph mass spectrometer GC / MS-QP5050A manufactured by Shimadzu Corporation
Column: DB-5MS manufactured by J & W Scientific, 0.25 mm × 30 m (stationary phase: 5% diphenyl-95% dimethyl-polysiloxane)
Carrier gas: helium, column flow rate 1.6ml / min
Sample injection volume: 1 μL

[Measurement of oxygen concentration in aqueous medium]
The oxygen concentration in the aqueous medium at 30 ° C. immediately before the temperature rise was measured with a handy type dissolved oxygen meter DO-110 (manufactured by Nikko Hansen).

  The melt flow rate (MFR) of the styrene resin was measured under the conditions of a temperature of 190 ° C. and a load of 2.16 kg according to JIS K7210-1: 2014.

(Measurement of melt viscosity)
The melt viscosity of the styrene-based resin at 200 ° C. and a shear rate of 100 sec ⁻¹ was measured using a Capillograph 1D manufactured by Toyo Seiki Co., Ltd. For the measurement, an orifice having an inner diameter of 1 mm and a length of 10 mm was used. Melt viscosity was measured for five measurement samples randomly collected from the obtained styrene resin, and the arithmetic average value of these measured values was taken as the melt viscosity of the styrene resin.

[Measurement of Melt Tension (MT)]
The melt tension of the styrene resin at 200 ° C. was measured by a capillograph 1D manufactured by Toyo Seiki Co., Ltd. For the measurement, an orifice having an inner diameter of 2.095 mm and a length of 8 mm was used. The molten resin extruded in a strand form from the orifice at a piston lowering speed of 10 mm / min was taken out at a take-up speed of 5 m / min through a load measuring section, and the load was measured. In addition, in order to homogenize the obtained styrene-type resin, it performed using the Toyo Seiki lab plast mill, and knead | mixed on the conditions of screw rotation speed 50rpm and resin temperature 200 degreeC was used as a sample for a measurement. If the melt tension of the styrene resin is too high and the melt tension cannot be measured by itself, PS Japan polystyrene “680” is kneaded with the obtained styrene resin at a ratio of 75% by weight and 50% by weight, respectively. Those melt tensions were measured as the measurement samples and extrapolated to obtain the melt tension when the blending amount of “680” was 0% by weight. The value was used as the melt tension of the styrene resin.

[Insoluble matter in tetrahydrofuran (THF insoluble matter)]
Weigh accurately 1 g of styrene resin in styrene resin, add 30 ml of tetrahydrofuran, soak for 24 hours at 23 ° C., shake for 5 hours, and let stand. Next, the supernatant is removed by decantation, and 10 ml of tetrahydrofuran is again added and left to stand. The supernatant is removed by decantation, dried at 23 ° C. for 24 hours, the weight after drying is determined, and the tetrahydrofuran insoluble content is determined by the following formula.
Tetrahydrofuran insoluble content (%) = [weight of insoluble content after drying / weight of sample] × 100

[Molecular weight in terms of polystyrene (GPC)]
The number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) of the styrene resin were measured by gel permeation chromatography (GPC) using linear polystyrene as a standard substance. Specifically, measurement was performed using HLC-8320GPC EcoSEC manufactured by Tosoh Corporation under the conditions of eluent: tetrahydrofuran (THF), flow rate: 0.6 ml / min, and sample concentration: 0.1 wt%. As the column, TSKguardcolumn SuperH-H × 1 and TSK-GEL SuperHM-H × 2 were connected in series. That is, styrene resin was dissolved in tetrahydrofuran (THF), and the molecular weight was measured by gel permeation chromatography (GPC). And the measured value was calibrated with standard polystyrene (straight chain), and the number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z average molecular weight (Mz) of the styrene resin were determined.

[Absolute molecular weight (GPC-MALS)]
The number average molecular weight (Mn ′), weight average molecular weight (Mw ′), and Z average molecular weight (Mz ′) of the styrenic resin were determined by GPC-MALS method [Multi Angle Light Scattering Detector (MALS)]. It was measured. The absolute molecular weight of the styrene resin can be measured by GPC-MALS method. Specifically, Prominence LC-20AD (2HGE) / WS system manufactured by Shimadzu Corporation, multi-angle light scattering detector DAWN HELEOS II manufactured by Wyatt Technology, eluent: tetrahydrofuran (THF), flow rate 1.0 ml It measured on condition of / min. As the column, TSKgel HHR-H × 1 manufactured by Tosoh Corporation and TSKgel GMHHR × 2 connected in series were used. The analysis of the measurement was performed by analysis software ASTRA of Wyatt, and the number average molecular weight (Mn ′), weight average molecular weight (Mw ′), and Z average molecular weight (Mz ′) of the styrene resin were obtained. The analysis was performed using 0.185 ml / g as the refractive index concentration increment dn / dc.

[Shrink factor and long-chain branching degree]
Based on the description of the formula (4) to (8), shrinkage factor _g w, 1 per molecule degree of long chain branching B _{m, w,} the degree of long chain branching B _{m, 1000} per styrene 1000 units was determined by the following formula . In this analysis, the degree of long chain branching was determined assuming triple chain branching. As linear polystyrene, the data of the styrene resin particles obtained in Production Example 1 were used.

[Method for measuring styrene content in core particles during addition of styrene monomer during additional impregnation polymerization process]
In each system at the start of additional addition of styrene monomer, at 2.5 hours from the start, and at the end, the temperature of the reactor was cooled to 30 ° C. within 10 minutes, and the styrene resin particles during polymerization were taken out.
Styrene resin particles were dissolved in N, N-dimethylformamide (DMF), measured by gas chromatography (GC), calibrated with a calibration curve, and the residual styrene in the styrene resin particles was quantified.
The measurement conditions for gas chromatography are as follows.
Equipment used: Gas chromatograph GC-9A manufactured by Shimadzu Corporation
Column packing:
[Liquid phase name] PEG-20M
[Liquid phase impregnation rate] 25% by weight
[Carrier particle size] 60/80 mesh [Carrier treatment method] AW-DMCS (washing, baking, acid treatment, silane treatment)
Column material: Glass column carrier gas with an inner diameter of 3 mm and a length of 3000 mm: N ₂
Detector: FID (hydrogen flame ionization detector)
Quantification: Internal standard method

  As can be seen from Tables 1 and 2, the commercially available styrenic resin (Comparative Example 3) had a low melt tension even though the fluidity was good. Moreover, in all the additional impregnation polymerization steps in the production process, the styrene-based tree (Comparative Examples 1 and 2) produced under the condition that the content of the styrene monomer in the core particles exceeds 10% by weight has high fluidity. However, high fluidity and high melt tension could not be achieved at the same time, such as low melt tension (Example 1) or high melt tension but low fluidity (Example 2).

  According to the method for producing a styrene resin of the present invention, since a styrene resin having a branched structure with high fluidity and high melt tension can be produced, the styrene resin is subjected to extrusion molding, foam molding, By using it for blow molding or as a processing aid for these moldings, it is possible to make the resin difficult to break during stretching.

Claims (4)

A dispersion step of dispersing core particles containing a styrenic resin in an aqueous medium;
A polymerization initiator containing an organic peroxide and a styrene monomer are added to the aqueous medium, and the polymerization initiator and the styrene monomer are added to the core particles at a temperature at which the polymerization of the styrene monomer does not proceed substantially. An impregnation step of impregnating the polymer,
A polymerization initiation step of heating the aqueous medium to initiate polymerization of the styrene monomer;
An additional impregnation polymerization step of adding an additional styrene monomer to the aqueous medium, impregnating the core particles with the styrene monomer, and graft-polymerizing the styrene monomer to a styrenic resin;
Including
The amount of styrene monomer added in the impregnation step is 20 to 200 parts by weight with respect to 100 parts by weight of the core particles,
The addition amount of the styrene monomer in the additional impregnation polymerization step is 50 to 700 weights with respect to 100 parts by weight of the core particles, and the content of the styrene monomer in the core particles in the additional impregnation polymerization step. The manufacturing method of the styrene resin which maintains 10 weight% or less.   The method for producing a styrenic resin according to claim 1, wherein the aqueous medium has an oxygen concentration at 30 ° C. of 4 mg / L or more.   The method for producing a styrene resin according to claim 1 or 2, wherein an average particle size of the core particles in the dispersion step is 0.3 to 1.2 mm. The organic peroxide has a 10-hour half-life temperature T _1/2 of 85 to 120 ° C., and the temperature of the aqueous medium in the impregnation step is 70 ° C. or more and (T _1/2 -15) ° C. or less, The temperature of the aqueous medium in the additional impregnation polymerization step is (T _1/2 -10 ° C) ° C or higher and (T _1/2 +20) ° C or lower. The styrenic resin according to any one of claims 1 to 3. Production method.