JP6886883B2 - Manufacturing method of styrene resin - Google Patents

Description

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

Styrene-based 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. Generally, by increasing the molecular weight of the styrene-based resin, the melt tension of the resin can be increased, but the higher the molecular weight, the lower the fluidity of the resin, and the more easily the moldability and productivity are lowered.
Various attempts have been made to solve this problem.

For example, it is a styrene resin composition containing linear polystyrene and multi-branched polystyrene, and (1) the weight average molecular weight (absolute weight average molecular weight) obtained by the GPC-MALLS method is 250,000 to 75. (2) The slope in the logarithmic graph with the weight average molecular weight as the horizontal axis and the inertial radius of the resin composition obtained by GPC-MALLS as the vertical axis is 0.35 to 0.45. It is disclosed that a styrene-based resin composition obtained from the above is used to produce a container having a high melt tension, high fluidity, and a wide range of depth to opening ratio (see, for example, Patent Document 1).

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

Further, in order to obtain a polystyrene-based resin composition for foaming that can reduce the weight of the foam-molded product and improve the productivity during molding, the polystyrene-based resin composition for foaming is made of a polyfunctional vinyl-based aromatic compound and a styrene-based resin. The monomer-derived component is contained as a base resin, the polyfunctional vinyl-based aromatic compound has a molecular weight of 100 or more and less than 1000, and the base material resin is polyfunctional in the styrene-based monomer. Obtained by polymerizing a monomer mixture containing 50 to 500 ppm of a vinyl-based aromatic compound.
The base resin is subjected to (1) melt flow rate (MFR: g / 10 minutes) and melt tension value (MT: cN) satisfying the following relational expression under measurement conditions 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 that satisfies the following relational expression 4 ≦ tan δ (ω = 0.01 (rad / s)) / tan δ (ω = 100) (Rad / s)) ≤20
(See, for example, Patent Document 3).
Further, in order to obtain a polystyrene-based resin composition for extrusion foaming that can improve productivity during 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) Top peak molecular weight (Mp) in molecular weight distribution is 140,000 to 220,000; (2) Ratio of molecular weight below Mp is 40 to 55% of the total; (3) z + 1 average molecular weight is 800,000 to 3.5 million; It is disclosed that (4) the content of an oligomer composed of a styrene dimer and a styrene trimer is 2000 ppm or less; and (5) the content of styrene is 1000 ppm or less (see, for example, Patent Document 4). ).

Japanese Unexamined Patent Publication No. 2005-281405 Japanese Unexamined Patent Publication No. 2014-189767 Japanese Unexamined Patent Publication No. 2015-193761 Japanese Unexamined Patent Publication No. 2015-193764

However, since the styrene-based 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-based resin is insufficient. Further, when a branched resin is produced using a polyfunctional monomer as in Patent Documents 3 and 4, the fluidity is lowered, so that the molding processability is not excellent.

An object of the present invention is to provide a method for producing a styrene-based resin, which has high fluidity and high melt tension and can produce a styrene-based resin having a branched structure.

That is, the present invention is as follows.
<1> A dispersion step of dispersing nuclear 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 nuclear particles at a temperature at which the polymerization of the styrene monomer does not substantially proceed. The impregnation process of impregnating the monomer and
A polymerization initiation step of raising the temperature of the aqueous medium to initiate polymerization of the styrene monomer, and
An additional impregnation polymerization step of adding a styrene monomer to the aqueous medium, impregnating the nuclei with the styrene monomer, and graft-polymerizing the styrene monomer to the styrene resin.
Including
The amount of the styrene monomer added in the impregnation step is 20 to 200 parts by weight with respect to 100 parts by weight of the nuclear particles.
The amount of the styrene monomer added in the additional impregnation polymerization step is 50 to 700 weight with respect to 100 parts by weight of the nuclear particles, and the content of the styrene monomer in the nuclear particles in the additional impregnation polymerization step. Is a method for producing a styrene-based resin, which maintains the content of 10% by weight or less.

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

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

<4> When 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 higher (T _{1 /} 2-15) ° C. or lower. There, according to the any one of the temperature of the aqueous medium _(T 1/2 -10 ℃) ℃ or higher _(T 1/2 +20) ℃ or less <1> to <3> in the additional impregnation polymerization step This is a method for producing a styrene-based resin.

According to the present invention, it is possible to provide a method for producing a styrene-based resin, which can produce a styrene-based resin having a branched structure having high fluidity and high melt tension.

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

The method for producing a styrene-based resin of the present invention (hereinafter, may be referred to as "the production method of the present invention") includes a dispersion step of dispersing nuclear particles containing the styrene-based 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 nuclear particles at a temperature at which the polymerization of the styrene monomer does not substantially proceed. The impregnation process of impregnating the monomer and
A polymerization initiation step of raising the temperature of the aqueous medium to initiate polymerization of the styrene monomer, and
An additional impregnation polymerization step of adding a styrene monomer to the aqueous medium, impregnating the nuclei with the styrene monomer, and graft-polymerizing the styrene monomer to the styrene resin.
Including
The amount of the styrene monomer added in the impregnation step is 20 to 200 parts by weight with respect to 100 parts by weight of the nuclear particles.
The amount of the styrene monomer added in the additional impregnation polymerization step is 50 to 700 weight with respect to 100 parts by weight of the nuclear particles, and the content of the styrene monomer in the nuclear 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 cleaning the obtained styrene resin.

High molecular weight is useful as a means to improve the melt tension and strength of the styrene resin, but simply increasing the high molecular weight causes a problem that the fluidity of the resin decreases and the moldability deteriorates. there were. It is useful to introduce a branched structure into the molecular chain as a means of improving the strength while maintaining the fluidity. A resin having a branched structure has a high degree of entanglement between molecular chains, so that the melt tension is high and it is difficult to break during the stretching process. As a method of incorporating a branched structure into the molecular chain of a 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, in such a polymerization method, there is a problem that branching points are concentrated on the portion where the polyfunctional monomer is polymerized and microgels are easily formed. When the amount of the polyfunctional monomer added is increased in an attempt to produce a more highly branched styrene resin, the polyfunctional monomers are brought close to each other in the reaction system, resulting in gelation during polymerization. Is likely to occur. Therefore, the amount of the branching agent added is limited, and it is difficult to produce a styrene-based resin having a high melt tension while maintaining fluidity.
On the other hand, it is not clear 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, but it is due to the following reason. Inferred.

The production method of the present invention mainly comprises a dispersion step of dispersing the nuclear particles in an aqueous medium, an impregnation step of impregnating the nuclear particles with a polymerization initiator and a styrene monomer, and a polymerization of initiating the polymerization of the styrene monomer. It has a start step and an additional impregnation polymerization step of additionally adding a styrene monomer to an aqueous medium to impregnate the nuclear particles and graft-polymerizing the styrene monomer to a styrene-based resin. In the present invention, in the additional impregnation polymerization step, the concentration of the styrene monomer in the nuclear particles which is the reaction field of the polymerization is maintained at a specific concentration, so that the number of branching points is increased (high degree of branching) and high. It is considered that the molecular weight can be adjusted and the branch points can be separated from each other.

Normally, a polymerization initiator and many styrene monomers are present in the reaction field, and the initiator radicals generated from the polymerization initiator and the growth-terminal radicals of the polymer chain are preferential to the vinyl group of the styrene monomer. It is considered that a linear styrene-based resin is likely to be formed because it reacts with.
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 growing terminal radical of the polymer chain are likely to cause not only the polymerization reaction with the styrene monomer but also the hydrogen abstraction reaction of the polymer chain. .. As a result, the styrene monomer is graft-polymerized to the radical on the polymer chain generated by the hydrogen abstraction reaction, or the growing terminal radical of the polymer chain is recombined to generate a branched chain in the polymer chain. It is thought that. Further, since the position where the branched chain is generated in the polymer chain is in a sterically crowded state, it is considered that further branched chain is unlikely to be generated near the formed branch point. That is, it is considered that the hydrogen abstraction reaction occurs again on the polymer chain away from the branch point to the extent that steric hindrance does not occur, and the branched chain is generated. Therefore, it is considered that a styrene-based resin having many branched chains can be obtained without gelation because the branched chains are generated while the branched points are appropriately separated from each other. As described above, according to the production method of the present invention, it is possible to produce a styrene-based resin having a large number of branched chains and a high molecular weight while suppressing gelation, so that the melt tension is high and the fluidity is maintained. It is considered that the styrene-based resin produced can be produced.
Hereinafter, each step of the production method of the present invention will be described in detail.

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

(Nuclear particles)
The nuclear particles include a styrene resin.
Examples of the styrene-based 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 or more, 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 resistant polystyrene), styrene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methacrylate copolymer, and styrene-methyl methacrylate. Examples thereof include copolymers and styrene-maleic anhydride copolymers. Only one type of styrene resin may be used, or two or more types may be used. Among these styrene-based resins, polystyrene is preferable because a hydrogen abstraction reaction is likely to occur and a branched chain is likely to be formed together with the styrene monomer.
The nuclei particles may contain a resin other than the styrene resin, but preferably contain 70% by weight or more of the styrene resin, more preferably 85% by weight or more, and are made of the styrene resin. Is even more preferable.

The average particle size of the nuclear particles is preferably 0.3 to 1.2 mm. When the average particle size of the nuclear particles is 0.3 mm or more, the amount of fine particles generated in the obtained branched styrene resin can be reduced, and when the average particle size is 1.2 mm or less, the specific surface area becomes large and the nuclear particles. The impregnation property of the styrene monomer to the resin is improved. The average particle size of the nuclear particles is more preferably 0.3 to 1.0 mm, and even more preferably 0.3 to 0.5 mm.
The average particle size of the nuclear particles means a 63% volume average particle size.

(Aqueous medium)
As the aqueous medium, water such as deionized water can be usually used, but a water-soluble organic solvent such as alcohol may be contained as long as the nuclear particles are not dissolved.

(Surfactant)
Surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Among these, the surfactant preferably has at least one selected from the group consisting of anionic surfactants, cationic surfactants, and nonionic surfactants. Specifically, alkyl sulfonates (eg, sodium dodecyl sulfonate), alkylbenzene sulfonates (eg, sodium dodecylbenzene sulfonate), polyoxyalkyl ether phosphate, alkyldimethylethylammonium ethyl sulfate, higher alcohols, Examples thereof include glycerin fatty acid ester, sorbitan fatty acid ester, polyooxyethylene alkyl ether, and fatty acid salt.
Only one type of surfactant may be used, or two or more types may be used.
Further, an electrolyte such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium succinate and the like may be used together with the surfactant.

(Suspension)
Examples of the suspending agent include hydrophilic polymers such as polyvinyl alcohol, methyl cellulose and polyvinylpyrrolidone; and poorly water-soluble inorganic substances such as calcium tertiary phosphate, magnesium nitrate, magnesium pyrophosphate, hydroxyapatite, aluminum oxide, talc, kaolin and bentonite. Examples include salt.
Only one type of suspending agent may be used, or two or more types may be used. Only one kind of each one or both of the hydrophilic polymer and the poorly water-soluble inorganic salt may be used, or two or more kinds of each may be used.
When a poorly water-soluble inorganic salt is used as the suspending agent, it is preferable to use an anionic surfactant such as sodium alkylsulfonate or sodium alkylbenzene sulfonate in combination.

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

[Immersion process]
In the impregnation step, a polymerization initiator containing an organic peroxide and styrene monomer in an aqueous medium, that is, in an aqueous medium containing nuclear particles dispersed by the dispersion step and, if necessary, a suspending agent, a surfactant and the like. A quantity is added to impregnate the nuclei with the polymerization initiator and the styrene monomer at a temperature at which the polymerization of the styrene monomer does not substantially proceed.
Here, the "temperature at which the polymerization of the styrene monomer does not substantially proceed" is a temperature at which the organic peroxide does not substantially decompose, and from the viewpoint of suppressing the decomposition of the organic peroxide, the organic peroxide is present. when the 10-hour half-life temperature of the oxide was _{T 1/2,} preferably to a temperature of the aqueous medium _(T 1/2 -15) ℃ below in the impregnation _{step, (T} 1/2 -18) ℃ The following is more preferable. From the viewpoint of impregnation of the styrene monomer into the nuclei particles, the temperature of the aqueous medium in the impregnation step is preferably 70 ° C. or higher, 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 of the impregnation step is preferably about 0.5 to 2.0 hours, preferably 1.0 to 2.0 hours, from the viewpoint of sufficiently impregnating the styrene monomer and the polymerization initiator into the nuclear particles. It is more preferable to set the time.

The amount of the styrene monomer added 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 nuclear particles. .. If the amount of the styrene monomer added is too small in the impregnation step, the nuclear particles cannot be sufficiently plasticized, and the polymerization initiator cannot be sufficiently impregnated into the nuclear particles. On the other hand, when the amount of the styrene monomer added is too large, the styrene monomer is polymerized outside the nuclear particles and fine particles are likely to be generated.

(Polymerization initiator)
The polymerization initiator contains at least an organic peroxide.
Examples of the organic peroxide include benzoyl peroxide, dilauroyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, and 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-amylperoxyisopropyl carbonate, t-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- Examples thereof include trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane, and 2,2-bis (4,5-di-t-butylperoxycyclohexyl) propane.
Only one kind of these organic peroxides may be used, or two or more kinds may be used.

As the polymerization initiator, it is preferable to use an organic peroxide having a 10-hour half-life temperature T _1/2 of 85 to 120 ° C., and more preferably to use _{an organic peroxide having a T 1/2 of 90 to 110 ° C.} When two or more kinds of organic peroxides are used as the polymerization initiator, the 10-hour half-life temperature of the organic peroxide having the lowest 10-hour half-life temperature is T _1/2 . Further, as the organic peroxide, those satisfying these temperature ranges and having high hydrogen extraction ability, for example, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-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 cumyl oxy radical such as dicumyl perkiside.

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 composed of an organic peroxide.
The amount of the polymerization initiator added is preferably 0.1 to 2.0 parts by weight based on 100 parts by weight of the total amount of the nuclear particles and the styrene monomer added. Within this range, the productivity is not excessively lowered and the hydrogen abstraction reaction is likely to occur. The amount of the polymerization initiator added is more preferably 0.2 to 1.5 parts by weight with respect to 100 parts by weight of the total amount of the nuclear particles and the styrene monomer added.

(Oxygen concentration in aqueous medium)
As the aqueous medium, it is preferable to use an aqueous medium having an oxygen concentration of 4 mg / L or more at 30 ° C. Oxygen in the aqueous medium functions as a polymerization inhibitor in the aqueous medium and inhibits the generation of fine particles. Therefore, 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.
Further, the generation of fine particles can also be suppressed by adding a water-soluble polymerization inhibitor, for example, sodium nitrite at 30 to 200 ppm to the aqueous medium.

[Polymerization start process]
In the polymerization initiation step, the temperature of the aqueous medium in which the polymerization initiator and the nuclear particles impregnated with the styrene monomer are dispersed is raised to initiate the polymerization of the styrene monomer. Specifically, it is preferable to initiate the polymerization of the styrene monomer by setting the temperature at which the organic peroxide is substantially decomposed. From the viewpoint of productivity, it is preferred that the temperature of the aqueous medium and _(T 1/2 -10) ℃ temperatures _above, and more preferably to _(T 1/2 -5) ℃ or higher.
The temperature rise time to the temperature is not particularly limited, but the polymerization of the styrene monomer in the nuclear particles is promoted during the temperature rise, and the styrene monomer in the nuclear particles is contained in the additional impregnation polymerization described later. Since the amount can be easily controlled 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 step]
In the additional impregnation polymerization step, the styrene monomer is additionally added to the aqueous medium, that is, the aqueous medium containing the nuclear particles in which the polymerization of the styrene monomer has started in the nuclear particles through the polymerization initiation step. Then, the nuclei are impregnated with the styrene monomer and polymerized. At this time, the amount of the styrene monomer added is 50 to 700 parts by weight with respect to 100 parts by weight of the nuclear particles in the additional impregnation polymerization step. Then, the styrene monomer is added intermittently or continuously so as to maintain the content (concentration) of the styrene monomer in the nuclear particles in the additional impregnation polymerization step to 10% by weight or less.

By going through the polymerization initiation step, the styrene monomer initiates polymerization with the inside of the nuclear particles as a reaction field. Then, in the additional impregnation polymerization step, by maintaining the content of the styrene monomer in the nuclei particles at 10% by weight or less, not only the polymerization between the styrene monomers but also the styrene monomer in the styrene resin is added. Graft polymerization is likely to occur, and branched chains are generated.
The content of the styrene monomer in the nuclear particles in the additional impregnation polymerization step can exceed 10% by weight as long as the objective effect of the present invention is not impaired. 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. Most preferably, the content of the styrene monomer in the nuclear particles is 10% by weight or less in all the steps. From the viewpoint of highly producing branched chains, the time of the additional impregnation polymerization step is preferably 150 minutes or more, more preferably 180 minutes or more. From the viewpoint of production efficiency, the upper limit of the time of the additional impregnation polymerization step is preferably about 600 minutes.
The content of the styrene monomer in the nuclear 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 the styrene monomer in the nuclear particles in the additional impregnation polymerization step can be calculated based on the chemical properties of the polymerization initiator used for the polymerization, the polymerization rate of styrene obtained from the polymerization temperature, and the like. By adjusting the timing of additional addition of the styrene monomer and the addition rate (addition ratio) so as to obtain the desired content based on the calculated value, styrene in the nuclear particles in the additional impregnation polymerization step. The content of the monomer can be adjusted. Further, the actual content of the styrene monomer in the nuclear particles can be determined by extracting the polymerized nuclear particles from the reaction system and using a method described later.

It is considered that the lower the content of the styrene monomer in the nuclear particles, the easier it is for not only the polymerization initiation reaction but also the hydrogen abstraction reaction to occur, and the degree of bifurcation is improved. Further, when the ratio of the styrene monomer to the nuclear particles is high, the absolute molecular weight and the degree of bifurcation are likely to be improved.
As described above, it is considered that when the average particle size of the nuclear 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 conditions of the additional impregnation polymerization step are not particularly limited, but the temperature of the aqueous medium in the additional impregnation polymerization step is (T _{1 /} 2-10) ° C. to (T _1/2 +20) from the viewpoint of facilitating the hydrogen abstraction reaction. ) ° C., more 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 the temperature.

The amount of the styrene monomer added is 50 to 700 parts by weight with respect to 100 parts by weight of the nuclear particles in the additional impregnation polymerization step. If the amount of the styrene monomer added in the additional impregnation polymerization step is too small, it becomes impossible to sufficiently generate branched chains. On the other hand, if the amount of the styrene monomer added is too large, the styrene monomers tend to polymerize outside the nuclear particles, and the yield of the styrene resin may deteriorate.
The amount of the styrene monomer added is preferably 100 to 600 parts by weight, more preferably 200 to 550 parts by weight, based on 100 parts by weight of the nuclear 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), but as long as gelation during polymerization does not occur, it is polyfunctional. A sex monomer may be added. The amount of the polyfunctional monomer added to the aqueous medium is preferably 0.2 parts by weight or less, preferably 0.1 part by weight or less, based on 100 parts by weight of the nuclear particles through the impregnation polymerization step and the additional addition step. Is more preferable, and 0 part by weight is further preferable. That is, it is preferable not to use a polyfunctional monomer. By not using the 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 comprises a residual polymerization step of polymerizing the styrene monomer remaining in the styrene resin particles after the additional impregnation polymerization step, and a suspension attached to the obtained styrene resin. It may include a cleaning step of washing the turbidant, the surfactant and the like with water, a coating step of coating the surface of the styrene resin with a functional component such as an antioxidant, and the like.

The styrene-based 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 the GPC-MALS method, and is a long-chain branch per 1000 units of styrene assuming a three-chain branch. It is preferable that the styrene resin has a branched structure in which degrees B _{m and 1000 are 0.3 or more.} Further, the Z average molecular weight (Mz') determined by the GPC-MALS method is preferably 3 million or more, and the long chain branching degree B _{m, w} per molecule is preferably 4 to 20. Is preferable. Further, it is preferable that the tetrahydro-insoluble content in the styrene resin obtained by the production method of the present invention of the present invention is 0.1% by weight or less (including 0).
The styrene-based resin exhibiting such characteristics has a higher molecular weight, but has more long-chain branched chains in the molecular chain than the conventional branched styrene-based resin, and has a relatively low molecular weight. It is considered that many long-chain branched chains are present in the chain.

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 turning 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 results.

(Basic principle of GPC-MALS method)
When a styrene-based resin is dissolved in a solvent such as tetrahydrofuran to prepare a styrene-based resin solution and subjected to GPC measurement, the polymer having a larger molecular size elutes first, so that the polymer is classified according to the molecular size. Subsequently, the separated styrene resin solution was subjected to MALS measurement to obtain the weight average molecular weight (Mw') of the styrene resin divided by the molecular size and the root mean square radius of gyration <R _g ² > corresponding to the molecular size. Can be calculated.
Specifically, the styrene resin solution divided by the molecular size by GPC is irradiated with laser light, and the scattered light intensity generated from the styrene resin solution by Rayleigh scattering is measured. _{From the obtained measured values, Mw'and <R g} ² > are calculated using the following formula (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 dn / dc of the solvent: Concentration increment of the refractive index lambda _0: Wavelength _{N A} of the incident light in a vacuum: Avogadro number c: sample concentration (g / mL)
R (θ): Rayleigh ratio of overscattering 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 >: Root mean square radius of gyration A ₂ : Second virial coefficient

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

K ^* c / R ₀ ^{: K *} c / R (θ) at an angle θ = 0 °
dy / dx: Initial gradient of regression line

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

Further, 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 turning radius <R _g ² > _{B of the} styrene resin having the branched structure of the present invention and the root mean square turning radius <R _g ² > _L of the linear styrene resin is the shrinkage factor g, and the following equation (4) )-(8), the contractile factor g can be obtained. Then, the long chain branching degree B _m can be obtained from the contraction factor g. In the present invention, the degree of long-chain branching 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 shrinkage factor in the interval _i; B _m, i is the long chain branching index in the interval i; c _i is the concentration in the interval i.

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

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. “Part” and “%” are based on weight unless otherwise specified. The temperature in the autoclave means the temperature of the aqueous medium.

[Preparation of nuclear particles]
(Manufacturing 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 tricalcium phosphate (20.5% slurry manufactured by Taihei Kagaku Sangyo Co., Ltd.) as a suspending agent, and dodecylbenzene sulfonate as a surfactant. 0.158 kg of sodium acid (10% aqueous solution), 0.053 kg of dodecyldiphenyl ether sulfonate disodium (manufactured by Kao, Perex SSH 10% aqueous solution), and 0.535 kg of sodium acetate as an electrolyte were added.
Then, as a polymerization initiator, 0.975 kg of t-butylperoxy-2-ethylhexanoate (manufactured by Nippon Oil & Fats Co., Ltd., perbutylO) and 0.284 kg of t-butylperoxy-2-ethylhexyl monocarbonate 0.284 kg (Akzo Corporation). , Trigonox 117), 15.4 g of 4-tert-butylcatechol as a polymerization inhibitor was dissolved in 390 kg of styrene, and this was supplied into an autoclave while stirring at 110 rpm. After replacing the inside of the autoclave with nitrogen, the temperature was started to rise 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. It was kept at 115 ° C. for 2 hours and 40 minutes, and then cooled to 40 ° C. over 2 hours. During the temperature rise to 90 ° C., when the temperature reached 60 ° C., 1.95 g of potassium persulfate was put into the autoclave as a suspension aid.
After cooling, the contents are taken out, the tricalcium phosphate adhering to the surface of the styrene resin particles is dissolved with nitric acid, dehydrated and washed with a centrifuge, and the moisture adhering to the surface of the particles is removed with an air flow dryer. The particles were removed to obtain styrene resin particles.
The obtained styrene-based resin particles were sieved, and particles having a diameter of 0.5 to 1.3 mm (average particle diameter of 0.8 mm) were taken out and used as nuclear particles 1.
The average particle size d63 of the styrene-based resin particles (the nuclear particles 1 and the nuclear particles 2 described later) was measured by a particle size distribution measuring device "Millitrack JPA" manufactured by Nikkiso Co., Ltd.

(Manufacturing 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 tricalcium phosphate (20.5% slurry manufactured by Taihei Kagaku Sangyo Co., Ltd.) as a suspending agent, and dodecylbenzene sulfonate as a surfactant. 0.499 kg of sodium acid (10% aqueous solution), 0.166 kg of disodium dodecyldiphenyl ether sulfonate (manufactured by Kao, Perex SSH 10% aqueous solution), and 4 g of potassium persulfate as a suspension aid were supplied.
Then, as a polymerization initiator, 0.440 kg of t-butylperoxy-2-ethylhexanoate (manufactured by Nippon Oil & Fats Co., Ltd., perbutyl O) and 0.520 kg of t-butylperoxy-2-ethylhexyl monocarbonate 0.520 kg (chemical drug Axo) Trigonox 117) was dissolved in 360 kg of styrene and supplied to an autoclave while stirring at 110 rpm. After replacing the inside of the autoclave with nitrogen, the temperature was started to rise 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, the tricalcium phosphate adhering to the surface of the styrene resin particles is dissolved with nitric acid, dehydrated and washed with a centrifuge, and the moisture adhering to the surface is removed with an air flow dryer. To obtain styrene-based resin particles.
The obtained styrene-based resin particles were sieved, and particles having a diameter of 0.3 to 0.5 mm (average particle diameter of 0.4 mm) were taken out and used as nuclear particles 2.

[Manufacturing 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 were supplied to an autoclave having an internal volume of 1.5 m ^{3 equipped with a stirrer, and pyrophosphate as a suspending agent was supplied in the autoclave by salt exchange.} Magnesium was synthesized. After supplying 0.131 kg of sodium alkylsulfonate (manufactured by Kao Co., Ltd., Latemul PS, 40% aqueous solution) as a surfactant and 112 kg of the styrene-based resin particles (nuclear particles 1) obtained in Production Example 1 as nuclear particles to an autoclave. , The inside of the autoclave was replaced 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.

[Immersion process]
Then, the temperature was raised to 80 ° C. with stirring at 50 rpm. After reaching 80 ° C, 84 kg of deionized water, 0.171 kg of sodium alkylsulfonate (manufactured by Kao, Latemul PS, 40% aqueous solution), 80 kg of styrene (styrene monomer), t-butylperoxy-2-ethylhexyl mono A mixture of 1.58 kg of carbonate (Trigonox 117 manufactured by Kayaku Akzo Corporation; described as "BE" in the table, 10-hour half-life temperature T _1/2 99.0 ° C.) was prepared as an emulsion by a homogenizer, and the emulsion was prepared. Was supplied into the autoclave. Then, 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 process]
Then, the temperature was raised to 105 ° C. over 2 hours.

[Additional impregnation polymerization step]
After reaching 105 ° C., it was kept for 5.5 hours. Over 5 hours and 10 minutes after the temperature in the autoclave reached 105 ° C., 254 kg of styrene (styrene monomer) was continuously added into the autoclave at a rate of 0.8 kg / min.
When adding styrene, the styrene content in the nuclear particles with respect to the elapsed time was simulated by simulation based on the above addition conditions, the chemical properties of the polymerization initiator used for the polymerization, and the polymerization rate of styrene calculated from the polymerization temperature. 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 was 10% by weight or less.
At the start of the additional addition of styrene, 2.5 hours after the start of the addition, and at the end of the additional addition, the methods described later (“Styrene content in the nuclei during the addition of the styrene monomer during the additional impregnation polymerization step” When the styrene content in the styrene-based resin particles was measured by the above-mentioned method, the styrene content in the nuclei particles was 6% by weight.

Figures 1 to 7 show graphs of simulation results in Examples and Comparative Examples. In the graph, the horizontal axis is the elapsed time [Time (hr)], and the left vertical axis is the content of styrene monomer in the nuclear particles in the additional impregnation polymerization step [Amount of Style monomer in a core particle (wt.%). ], The vertical axis on the right side is the polymerization temperature [Temperature (° C.)]. In the graph, the change in the styrene content in the nuclear particles with respect to the elapsed time is shown by a solid line, and the change in the polymerization temperature with respect to the elapsed time is shown 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 kept 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-based resin particles taken out from the autoclave were washed with dilute nitrate to dissolve and remove the suspending agent adhering to the surface of the resin particles, washed with water, and further dehydrated by a centrifuge. After coating with 0.01 part by weight of polyoxyethylene lauryl ether as an antistatic agent (value with respect to 100 parts by weight of styrene resin), moisture 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 the first embodiment. Specifically, the nuclear particles were changed from the nuclear particles 1 to 66.9 kg of the styrene-based resin particles (nuclear particles 2) obtained in Production Example 2. 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 the ratio of styrene was 0.8 kg / min over 6 hours and 10 minutes. Was added continuously. When the styrene content in the styrene resin particles was measured by the method described later at the start of the additional addition of the styrene monomer, 2.5 hours after the start of the addition, and at the end of the additional addition, the styrene content in the styrene resin particles was measured. The styrene content was 10% by weight at the start of the additional addition, and 6% by weight at the lapse of 2.5 hours from the start of the addition and at the end of the additional addition.

(Example 3)
A styrene-based resin was produced 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 styrene content in the styrene resin particles was measured by the method described later at the start of the additional addition of the styrene monomer, 2.5 hours after the start of the addition, and at the end of the additional addition, the styrene content in the styrene resin particles was measured. The styrene content was 10% by weight at the start of the additional addition, 9% by weight after 2.5 hours from the start of the addition, and 8% by weight at the end of the additional addition.

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

(Example 5)
The following points were changed from the first embodiment. In the dispersion step, when the air in the autoclave is replaced with nitrogen before the temperature rise, the inside of the autoclave is pressurized to 0.5 MPa (G) with nitrogen, and the gas in the autoclave is released until the pressure in the autoclave reaches atmospheric pressure. The release operation was repeated 3 times. When the styrene content in the styrene-based resin particles was measured by the method described later at the start of the additional addition of the styrene monomer, 2.5 hours after the start of the addition, and at the end of the additional addition, the styrene content in the styrene-based resin particles was measured. The styrene content was 6% by weight in each case.

(Example 6)
The following points were changed from the first embodiment. Specifically, the supply amount of nuclear particles (nuclear particles 1) was changed to 67 kg. Further, in the additional impregnation polymerization step, the holding time at 105 ° C. was changed to 6 hours and 30 minutes, the amount of styrene to be additionally added was changed to 299 kg, and the ratio of styrene was 0.8 kg / min over 6 hours and 10 minutes. Was added continuously. When the styrene content in the styrene resin particles was measured by the method described later at the start of the additional addition of the styrene monomer, 2.5 hours after the start of the addition, and at the end of the additional addition, the styrene content in the styrene resin particles was measured. The styrene content was 10% by weight at the start of the additional addition, and 6% by weight at the lapse of 2.5 hours from the start of the addition and at the end of the additional addition.

(Comparative Example 1)
A styrene-based resin was produced 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 styrene content in the styrene resin particles was measured by the method described later at the start of the additional addition of the styrene monomer, 2.5 hours after the start of the addition, and at the end of the additional addition, the styrene content in the styrene resin particles was measured. The styrene content was 19% by weight at the start of the additional addition, 25% by weight when 2.5 hours had passed since the start of the additional addition, and 24% by weight at the end of the additional addition.

(Comparative Example 2)
The following points were changed from the first embodiment. Specifically, in the dispersion step, the supply amount of nuclear particles (nuclear particles 1) was changed to 105 kg. The temperature of the impregnation process 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 (Niper BW manufactured by Nippon Oil & Fats Co., Ltd., water-diluted powder product; in the table. Described as "BPO", 10-hour half-life temperature 73.6 ° C.) 1.79 kg, and t-butylperoxy-2-ethylhexyl monocarbonate (Chemical Axo, Trigonox 117, 10-hour half-life temperature 99.0 ° C.) ) Was changed to 0.18 kg, and an emulsion to which 11 g of divinylbenzene was added as a branching agent (polyfunctional monomer) was supplied into the autoclave. Then, it was kept at 75 degreeC for 2 hours. After holding at 75 ° C. for 2 hours, a mixture of 321 kg of styrene and 89 g of divinylbenzene was continuously added at a ratio of 2.1 kg / min over 2 hours and 30 minutes while keeping the temperature unchanged. When the styrene content in the styrene resin particles was measured by the method described later at the start of the additional addition of the styrene monomer, 1.5 hours after the start of the addition, and the end of the additional addition, the styrene content in the styrene resin particles was measured. The styrene content was 8% by weight at the start of the additional addition, 58% by weight after 1.5 hours from the start of the addition, and 66% by weight at the end of the additional addition. Then, the temperature was raised to 108 ° C. over 2 hours, 112 ° C. over 20 minutes, and 125 ° C. over 2 hours. Then, it was held at 125 ° C. for 1 hour and 30 minutes, and cooled to 35 ° C. over 6 hours.

(Comparative Example 3)
As a styrene resin, a commercially available product (HP780AN manufactured by DIC Corporation) was used for evaluation.

<Evaluation>
The physical characteristics 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)]
Approximately 1 g of styrene-based resin was precisely weighed, dissolved in 25 ml of N, N-dimethylformamide (DMF), measured by gas chromatography (GC), calibrated by a calibration curve, and 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 material:
[Liquid phase name] PEG-20M
[Liquid phase impregnation rate] 25% by weight
[Carrier particle size] 60/80 mesh [Carrier treatment method] AW-DMCS (washing with water, firing, 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 (Flame Ionization Detector)
Quantitative: internal standard method

[Measurement of residual styrene oligomer (styrene dimer + styrene trimmer; residual oligomer)]
About 0.1 g of the styrene-based resin was precisely weighed, dissolved in 10 ml of tetrahydrofuran, and added dropwise to about 250 ml of n-heptane at 23 ° C. to precipitate the resin. The filtrate obtained by filtering the resin 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 x 30 m (stationary phase: 5% diphenyl-95% dimethyl-polysiloxane)
Carrier gas: helium, column flow rate 1.6 ml / 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 in accordance with JIS K7210-1: 2014.

[Measurement of melt viscosity]
The melt viscosity of the styrene resin at 200 ° C. and a shear rate of 100 sec ^{-1 was measured by Capillograph 1D manufactured by Toyo Seiki Co., Ltd.} An orifice having an inner diameter of 1 mm and a length of 10 mm was used for the measurement. The melt viscosities were measured on five measurement samples randomly collected from the obtained styrene resin, and the arithmetic mean 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 Capillograph 1D manufactured by Toyo Seiki Co., Ltd. An orifice having an inner diameter of 2.095 mm and a length of 8 mm was used for the measurement. The molten resin extruded from the orifice in a strand shape at a piston descent speed of 10 mm / min was taken up through a load measuring unit at a take-up speed of 5 m / min, and the load was measured. In order to homogenize the obtained styrene-based resin, a lab plast mill manufactured by Toyo Seiki Co., Ltd. was used, and a sample kneaded under the conditions of a screw rotation speed of 50 rpm and a resin temperature of 200 ° C. was used as a measurement sample. If the melt tension of the styrene resin is too high to measure the melt tension by itself, PS Japan polystyrene "680" is kneaded into the obtained styrene resin at a ratio of 75% by weight and 50% by weight, respectively. The melt tension of these was measured as a measurement sample, and the melt tension was obtained when the blending amount of "680" was 0% by weight by extrapolation, and the value was taken as the melt tension of the styrene resin.

[Insoluble in tetrahydrofuran (THF insoluble)]
1 g of the styrene resin in the styrene resin is precisely weighed, 30 ml of tetrahydrofuran is added, the mixture is immersed at 23 ° C. for 24 hours, shaken for 5 hours, and allowed to stand. Next, the supernatant is removed by decantation, 10 ml of tetrahydrofuran is added again and allowed 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 matter (%) = [weight of insoluble matter after drying / weight of sample] x 100

[Polystyrene equivalent molecular weight (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 a gel permeation chromatography (GPC) method using linear polystyrene as a standard substance. Specifically, the measurement was carried out 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, TSKguardcolum SuperH-H x 1 and TSK-GEL SuperHM-H x 2 were connected in series and used. That is, the styrene resin was dissolved in tetrahydrofuran (THF), and the molecular weight was measured by gel permeation chromatography (GPC). Then, the measured values were calibrated with standard polystyrene (straight chain) to determine the number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) of the styrene resin, respectively.

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

[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 calculated on the assumption that it was a three-chain branch. As the linear polystyrene, the data of the styrene-based resin particles obtained in Production Example 1 was used.

[Method for measuring styrene content in nuclei particles during addition of styrene monomer during additional impregnation polymerization step]
In each system at the start, 2.5 hours, and end of the additional addition of the styrene monomer, the temperature of the reactor was cooled to 30 ° C. within 10 minutes, and the styrene resin particles being polymerized were taken out.
Styrene-based resin particles were dissolved in N, N-dimethylformamide (DMF), measured by gas chromatography (GC), calibrated by a calibration curve, and residual styrene in the styrene-based 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 material:
[Liquid phase name] PEG-20M
[Liquid phase impregnation rate] 25% by weight
[Carrier particle size] 60/80 mesh [Carrier treatment method] AW-DMCS (washing with water, firing, 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 (Flame Ionization Detector)
Quantitative: internal standard method

As can be seen from Tables 1 and 2, in the commercially available styrene resin (Comparative Example 3), the melt tension was small even though the fluidity was good. Further, in all the additional impregnation polymerization steps of the production process, the styrene-based trees (Comparative Examples 1 and 2) produced under the condition that the content of the styrene monomer in the nuclear 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-based resin of the present invention, a styrene-based resin having a branched structure having high fluidity and high melt tension can be produced. By using it for blow molding or the like, or as a processing aid during these moldings, it is possible to make it difficult for the resin to break during stretching.

Claims (4)

A dispersion step of dispersing nuclear particles containing 85% by weight or more of 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 nuclear particles at a temperature at which the polymerization of the styrene monomer does not substantially proceed. The impregnation process of impregnating the monomer and
A polymerization initiation step of raising the temperature of the aqueous medium to initiate polymerization of the styrene monomer, and
An additional impregnation polymerization step of adding a styrene monomer to the aqueous medium, impregnating the nuclei with the styrene monomer, and graft-polymerizing the styrene monomer to the styrene resin.
Including
The amount of the styrene monomer added in the impregnation step is 20 to 200 parts by weight with respect to 100 parts by weight of the nuclear particles.
The amount of the styrene monomer added in the additional impregnation polymerization step is 50 to 700 weight with respect to 100 parts by weight of the nuclear particles, and the content of the styrene monomer in the nuclear particles in the additional impregnation polymerization step. A method for producing a styrene-based resin, which maintains the content at 10% by weight or less. The method for producing a styrene-based resin according to claim 1, wherein the aqueous medium has an oxygen concentration of 4 mg / L or more at 30 ° C. The method for producing a styrene-based resin according to claim 1 or 2, wherein the average particle size of the nuclear particles in the dispersion step is 0.3 to 1.2 mm. The 10-hour half-life temperature T _1/2 of the organic peroxide is 85 to 120 ° C., the temperature of the aqueous medium in the impregnation step is 70 ° C. or higher (T _{1 /} 2-15) ° C., and the above. additional impregnation temperature of the aqueous medium in the polymerization process _(T 1/2 -1 0) ℃ or higher _(T 1/2 +20) of ° C. or less according to any one of claims 1 to 3 styrene resin Production method.

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