JP2003105004A - Method of manufacturing styrene resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a styrene resin having very little elusion or a volatile content because of its low content of low molecular components with a high productivity by improving workability, working stability, and mechanical characteristic of the resin. SOLUTION: In this method of manufacturing a styrene resin, a continuous anion polymerization process where a feed having a composition of 1.0 kg styrene monomer, 0.5-2 kg cyclohexane solvent, and 0.5-200 mmol organic lithium compound is continuously supplied at the same time or batchwise from a side of a reactor R1 having a backmixing flow and from the other side of the reactor R1 the reactant is continuously removed is contained, the inner temperature of the reactor R1 is controlled not lower than 60 deg.C but lower than 80 deg.C by removing polymerization heat with an attached reflux condenser under a reduced pressure, polymerization is carried out controlling the average ratio of the monomer to lower than 5% of the total of the styrene monomer, the cyclohexane solvent, and the styrene polymer in the reactor R1, and the obtained styrene polymer solution is evaporated and dried.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a styrene resin having a low content of styrene low-molecular components such as styrene oligomer, styrene monomer and residual hydrocarbon solvent, and excellent processability and thermal stability. The present invention relates to a method capable of continuous stable production for a long period of time without the formation of accumulated substances such as polystyrene gel. The obtained styrene resin can be preferably used for various applications such as molding materials such as electric material materials, miscellaneous goods materials, food container materials and food packaging materials, especially food container materials and food packaging materials.

[0002]

2. Description of the Related Art Styrene resins have many excellent physical properties such as light weight, high rigidity, resistance to water, and excellent electrical insulation. In addition, it also has excellent moldability, which enables easy and mass production of molded products of various shapes.
Taking advantage of these features, it is used in large quantities for various purposes such as electrical product materials, sundries, food containers, and packaging materials. Generally, the styrene resin is produced by two types of reaction mechanism, that is, a thermal radical polymerization method or a radical polymerization method using an initiator. Further, there are two types of manufacturing processes, a bulk polymerization method and a suspension polymerization method, but the bulk radical polymerization method is currently the mainstream because it is difficult for impurities such as a dispersant to enter and is advantageous in cost. There is.

However, it is well known that radical polymerization generally accompanies the formation of oligomers during resin production and that styrene monomers are likely to remain. For example, review literature (En
cyclopedia of chemical technology, Kir k-Othmer, Th
According to ird Edition, John Wily & Sons, Vol. 21, p. 817), styrene dimer,
It is said that the amount is about 1% by weight with the by-product of oligomer such as styrene trimer. Further, the specific oligomer component is mainly composed of 1-phenyl-4- (1'-phenylethyl) tetralin and 1,2-diphenylcyclobutane, and additionally 2,4-diphenyl-1-butene and 2,4,6-. Triphenyl-1-hexene is said to be present.

Generally, in the bulk radical polymerization process, polymerization is usually carried out at 80 to 180 ° C., and then the solvent and unreacted monomers contained therein are removed by heating and volatilization to recover the polymer. However, the radical polymerization method cannot achieve a high degree of conversion of the monomer into a polymer, and even after devolatilizing this by heating, in general, a relatively large amount of unreacted styrene monomer remains in the styrene resin. Remain. For this reason, measures have been developed to devise a devolatilization process, for example, a method of azeotropically removing residual styrene monomer with water by volatilizing by heating, then adding and mixing water and then devolatilizing again. However, we have not yet reached the level where we are fully satisfied. Further, oligomers such as dimer and trimer of styrene, which are by-produced, are difficult to volatilize, so that most of them generally remain in the polymer.

When the styrene resin produced in this manner is analyzed, residues derived from the raw materials, impurities and by-products during polymerization are detected. Specifically, styrene, α-methylstyrene, n-propylbenzene, isopropylbenzene, 2,4-diphenyl-1-butene, 1,2-diphenylcyclobutane, 1-phenyltetralin, 2,
4,6-triphenyl-1-hexene, 1,3,5-triphenylcyclohexane, 1-phenyl-4- (1 '
-Phenylethyl) tetralin and the like are contained in the styrene resin. As described above, the styrene resin of the radical polymerization method which is widely used at present contains a large amount of low molecular components such as styrene monomer and styrene oligomer due to the manufacturing method. Furthermore, these radical polymerization styrene resins are generally inferior in stability, and the amount of low molecular components such as styrene monomer and styrene oligomer in the resin increases due to mechanical history or thermal history during molding. Cheap. The low molecular weight component newly generated during the molding process has the same problem as the low molecular weight component generated during the polymerization. For example, when it is used for electric product materials, miscellaneous goods materials, food packaging materials and food container materials, low molecular components contained in the resin cause various problems.

Specifically, such a styrene resin containing a large amount of low molecular weight components generally does not have sufficient thermal stability during molding and processing and is inferior in heat resistance represented by rigidity during heating. Further, there is a case where an oily substance adheres to a mold or a molded product during the molding process. The low molecular component contained in the resin is
In some cases, the printing may be difficult to print or the printing may be easily peeled off because it may diffuse or bleed from the inside of the molded product to the surface. Furthermore, when used in food containers and food packaging, low-molecular components contained in the resin material may elute or volatilize, and reduction thereof is desired. In contrast to these radical polymerization methods, a method for producing a styrene resin by an anionic polymerization method using organic lithium or the like has also been known for a long time in the art. For example, US Pat. No. 5,391,655, US Pat. No. 5,089,572, US Pat. No. 4,883,846, US Pat.
48,222, U.S. Pat. No. 4,205,016.
U.S. Pat. No. 4,200,713, U.S. Pat. No. 4,016,348, U.S. Pat.
954,894, U.S. Pat. No. 4,859,74.
Detailed description is given in the specification No. 8.

To summarize these US patent techniques, a method of lowering the degree of dispersion in the anionic polymerization method (US Pat. No. 4,883,846), a continuous polymerization method in producing polystyrene by the anionic polymerization method, etc. Associated with manufacturing apparatus of US Pat. No. 4,016,3
48, U.S. Pat. No. 4,748,222, U.S. Pat. No. 5,391,655), a method for producing an initiator used in an anionic polymerization system and application examples (U.S. Pat. No. 4,205). , 016, U.S. Pat. No. 5,0.
89,752). U.S. Pat. No. 4,859,748 discloses a method of controlling the anionic polymerization reaction of styrene in a continuous stirred tank reactor. However, in the anionic polymerization method technology of these styrene resins, there is no disclosure regarding the styrene-based low-molecular component according to the object of the present invention.

Furthermore, in recent years, Japanese Patent Laid-Open No. 10-110
Japanese Patent Publication No. 074 discloses that a polymer having a small number of oligomers can be obtained by anionic polymerization using an organolithium as an initiator. In the description of Reference Example 2, according to a batch polymerization method of a styrene monomer using organic lithium,
A monodisperse polymer having a narrow molecular weight distribution can be obtained, and a dimer content of 1 pp can be obtained by adding an antioxidant and then drying.
m, a styrene polymer having a trimer content of 170 ppm is obtained. Further, it is disclosed that the styrene polymer obtained by the anionic polymerization method thus obtained can be used for food packaging materials and the like.

Food Hygiene Magazine, Vol. 39, No. 3, 199 (1
In 998), it is reported that styrene dimers and styrene trimers are eluted from food grade polystyrene products.
International application PCT / JP97 / 00796 relates to a method for producing a vinyl polymer, an initiator for anionic polymerization of vinyl monomers, and a styrene resin composition. In the description of this specification, when a polymer in which the styrene trimer present in the obtained styrene polymer is 250 ppm or less is used in a food packaging material, migration to foodstuffs is negligible. Disclosure. Further, JP-A-2000-143725 relates to a styrene polymer by an anionic polymerization method and a method for producing the same,
A styrene polymer having a styrene dimer content of 80 ppm or less and a styrene trimer content of 800 ppm or less, a method for producing the same, and use for a food application are disclosed.

As described above, the following items (a) to (c) have already been known. (A) A styrene polymer can be obtained by an anionic polymerization method using organic lithium. (B) The styrene polymer obtained by the anionic polymerization method using organic lithium has a lower content of styrene dimer and styrene trimer than the styrene polymer obtained by the radical polymerization method. (C) A styrene polymer obtained by using organolithium can be used as a resin material in various applications, particularly in food container materials and food packaging materials.

However, the styrene resins obtained by these anionic polymerization methods have some problems, and have not been widely used for various uses as styrene resin materials at present. That is, there are the following problems (d) to (f). (D) The styrene resin of the anionic polymerization method using organic lithium is more expensive to manufacture than the styrene resin of the bulk radical polymerization method. (E) When anionic polymerization is carried out at high temperature and high monomer concentration in order to increase productivity and achieve cost reduction, styrene low-molecular components, particularly dimers and trimers, are increased,
Loss of one of the major characteristics of anion-polymerized styrene resin. (F) The styrene resin of anionic polymerization method using organic lithium generally has a narrow molecular weight distribution and is inferior in processability.

Each of the problems in the above-mentioned prior art will be specifically described below. One of the main reasons for the high cost in the production of the item (d) is that the anionic polymerization method is inferior in productivity. That is, in the bulk radical polymerization method, the monomer concentration is 90% by weight or higher, whereas in the anionic polymerization method, particularly in the batch process anionic polymerization method, the monomer concentration is usually 25% by weight. Limited to less than about%. This is mainly due to the difficulty in removing the heat of polymerization in the anionic polymerization method, and the production at a low monomer concentration is inferior in productivity. That is, in the anionic polymerization method using organic lithium, the deactivation of the initiator occurs remarkably at a high temperature exceeding 120 ° C. Therefore, in order to complete the reaction sufficiently, it is necessary to suppress the polymerization temperature to 120 ° C. or lower by removing heat.
However, at a high monomer concentration, the polymerization rate and the viscosity of the polymerization solution increase significantly. Therefore, the amount of heat generation and the rate of heat generation increase, and the heat removal property decreases, making temperature control difficult.

This can be solved by applying heat removal in a laboratory-level reactor. However, this is a serious problem in a large-scale plant reaction tank where the heat transfer area is relatively reduced, and batch polymerization at a high monomer concentration is extremely difficult. In order to avoid this, there is an idea to lower the monomer concentration to absorb the heat of polymerization by the latent heat of the temperature rise of the polymerization system. However, also in this case, the monomer concentration is naturally limited, and in order to control the temperature in the batch polymerization method, the monomer concentration is usually limited to less than about 25% by weight. Therefore, in the anionic polymerization method, a low monomer concentration lowers the productivity and becomes a major cause of high cost.

As a measure for fundamentally solving the heat removal problem in high-concentration polymerization, there is proposed a method of continuous polymerization using a special reactor having a high heat removal capacity. For example, US Pat. No. 4,85
Japanese Patent No. 9,748 discloses a method of continuously flowing a high concentration monomer of 30 to 80% by weight into a tubular circulation type reaction tank having a large surface area and a high heat removal capacity to carry out anionic polymerization. ing. Although high monomer concentration anionic polymerization can be achieved by such a method, another problem remains. That is,
The flow of the high-viscosity polymer solution in the thin tube becomes unstirred. Polymerization in such a non-stirring tube-type reaction tank causes gelation depending on the conditions and eventually the tube-type reaction tank is blocked, which is a fatal drawback.

The item (e) is a problem of low molecular weight styrenic components, especially dimers and trimers. Unlike the radical method, it is generally said that the anionic polymerization method does not produce styrene dimers or trimers. However, as a result of diligent studies by the present inventor, even in anionic polymerization using organolithium, it is possible that not less than a considerable amount of dimer and trimer are formed at a practical polymerization temperature and monomer concentration. Clarified.
In addition to the dimer and trimer of styrene, it was also clarified that a styrene-based low-molecular component peculiar to the anionic polymerization method occurs. This is mainly produced by reacting a specific solvent or a trace amount of impurities contained in the solvent or monomer with a styrene monomer in the coexistence of organic lithium. Have. That is, as a result of examination by the present inventors, it is clear that even in the anionic polymerization method, there is a problem that the obtained styrene resin contains a styrene-based low molecular component having a molecular weight of 140 to 400 in a nonnegligible amount. Became.

The inferior processability of the styrene resin of the anionic polymerization method in the item (f) is mainly due to the narrow molecular weight distribution.
The molecular weight distribution of the polymer obtained by batch polymerization or continuous polymerization in a tubular reactor is generally very narrow. For example, the above-mentioned JP-A-10-110074, in the description of Reference Example 2, has a narrow molecular weight distribution (Mw / Mn = 1.04) by a batch polymerization method of a styrene monomer using organic lithium, A monodisperse polymer is obtained. A polymer having a narrow molecular weight distribution is inferior in molding and processability and is usually not preferable. As one measure for expanding the molecular weight distribution, a method of adding a coupling agent after the completion of polymerization to achieve polydispersion is known. That is, it is a method of polymerizing a polymer having a slightly low molecular weight in advance and coupling it to partially jump the molecular weight to expand the molecular weight distribution in a polydisperse form.

However, the polymerization of the low molecular weight polymer before the coupling requires a large amount of the organolithium initiator. Also, a coupling step is required after the polymerization. That is, there is a problem in that the manufacturing cost is increased due to the increase in the amount of catalyst used and the complicated manufacturing process. Moreover, in order to achieve a sufficient broadening of the molecular weight distribution, it is necessary to use a trifunctional or higher-functional polyfunctional coupling agent. The polymer polydispersed by such a method has a long-chain branched structure and exhibits specific fluidity, and it is usually not preferable in sheet extrudability and foaming property, and there are problems in molding and processability. . As another measure for expanding the molecular weight distribution, a technique of partially deactivating the initiator by dividing feed of the polymerization initiator or adding alcohol or the like is also known.

In the case of divided feed of the polymerization initiator, for example, two-stage divided feed, as a result, the molecular weight distribution can be expanded as a blend composition of a polymer having a high molecular weight and a polymer having a low molecular weight. The same effect can be obtained in the case of partial deactivation of the initiator by the deactivating agent during the polymerization. However, even this method has some problems. For example, the obtained polymer is a resin having a composition containing a large amount of low-molecular components, and such a resin has problems such as poor mechanical properties and heat resistance. Also,
There is also a problem that it is difficult to control the molecular weight and the molecular weight distribution, the manufacturing process is complicated, and the productivity is reduced.

[0019]

The problem to be solved by the present invention is to improve the processability, process stability and mechanical properties of the resin, and to reduce the amount of elution or volatilization due to the low content of low molecular components. It is to provide a method for producing a small amount of styrene resin with high production efficiency. That is, the present invention intends to achieve the solution to the following problems (g) to (j) all at once in the method for producing a styrene resin using organic lithium. (G) Achieving a highly productive continuous polymerization process. (H) Improve the processability of styrene resin by expanding the molecular weight distribution. (I) Reduction of styrene monomer contained in the obtained styrene resin. (J) Molecular weight of 140 contained in the obtained styrene resin
Reduction of low molecular weight styrenic components in the range of up to 400.

[0020]

The present invention, which is a means for solving the problems, is also shown in the claims. That is, according to the present invention, a raw material system having the following composition (A) is continuously charged from one of the reaction tanks R1 having a reverse mixing flow in a batch or in a divided manner, and the production system is continuously supplied from the other reaction tank R1. The internal temperature of the reaction tank R1 is adjusted to 60 by removing the heat of polymerization by using a reflux condenser attached under reduced pressure, which includes a continuous anionic polymerization process of drawing out into
C. or more and less than 80.degree. C., and controlling the average ratio of the styrene monomer, cyclohexane solvent and styrene polymer present in the reaction vessel R1 to less than 5% by weight. Method for producing styrene resin obtained by polymerization and devolatilization drying of the obtained styrene polymer solution: (A) Styrene monomer 1.0 kg Cyclohexane solvent 0.5-2 kg Organic lithium compound 0.5-200 mmol .

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a styrene resin of the present invention, the styrene resin is produced by an anionic polymerization method using an organolithium initiator. The process of anionic polymerization is limited to continuous polymerization. That is, a method for producing a styrene resin including a continuous polymerization process in which a raw material system is continuously charged from one of the reaction tanks R1 having a reverse mixing flow in a batch or divided manner and the production system is continuously withdrawn from the other reaction tank R1. Limited to In the method for producing a styrene resin of the present invention, polymerization is carried out by using a polymerization process of the reaction tank R1 alone or a composite polymerization process in which the reaction tank R1 is followed by one or more reaction tanks connected in series. You can It is necessary that the reaction tank R1 has a reverse mixing flow as a mixed state. Back-mixing flow means that a part of the raw material system fed to the reaction vessel mixes in the opposite direction to the flow. The most preferred reaction vessel having a backmixing flow is a reaction vessel having a complete mixing flow.

The most preferred composite polymerization process is a composite polymerization process in which a substantially complete mixing continuous reaction tank R1 and then a plug flow continuous reaction tank R2 are connected in series.
It is difficult to efficiently achieve a high conversion rate in a reaction vessel having a reverse mixing flow or a reaction vessel of complete mixing because of its mixing property. It is preferable to connect another reaction vessel to this in series or in multiple vessels. The reverse mixing flow here is not limited to a narrow sense. This means a mixed state in which the initiator has a broad residence time distribution, which significantly widens the molecular weight distribution of the polymer. Specifically, it means a mixed state in which the molecular weight distribution of the obtained polymer, that is, the ratio Mw / Mn of the weight average molecular weight and the number average molecular weight is 1.5 or more.

The specific definition of the reverse mixing flow or the complete mixing flow is the prior application of the present inventors, Japanese Patent Application No. 2001-136.
No. 262. Specifically, the reaction tank R
The weight average molecular weight of the polymer in the solution at each site in 1 is preferably 0.7 to 1.3 times the average weight average molecular weight in all reaction vessels, more preferably 0.8 to
The mixed state has a distribution range of 1.2 times, particularly preferably 0.9 to 1.1 times. The narrow distribution means that the molecular weights of the polymers present in the respective parts of the reaction tank are not biased and the inside of the tank is made uniform by stirring. It is possible to broaden the molecular weight distribution of the polymer in a reaction vessel having a reverse mixing flow or a complete mixing, and efficiently convert the remaining monomers in the reaction vessel of the next plug flow. The broadening of the molecular weight distribution helps improve the processability of the resin, and the complete conversion of the monomer results in the conversion of the monomer and low-molecular components derived from the monomer mixed in the resin after devolatilization and drying into the low-molecular weight product. Is preferably 99.9% or more, more preferably 99.99% or more, particularly preferably 99.995% or more.

In the method for producing a styrene resin of the present invention, it is necessary to control the average monomer concentration in the reaction vessel R1 to be less than 10% by weight. That is, it is necessary to control the ratio of the styrene monomer, the hydrocarbon solvent and the styrene polymer to less than 10% by weight based on the total amount. Preferably less than 5% by weight, more preferably 3
It is less than wt%, particularly preferably less than 2 wt%. That is, even though the fed styrene monomer concentration exceeds 33% by weight, the monomer concentration in the polymerization field is 10%.
It is necessary to control the operation to be less than wt%, and the remaining 15 wt% or more coexists as a polymer in the solution. In a stable continuous polymerization process this value does not change at all times. On the other hand, in the batch polymerization method, the monomer concentration at the beginning of the reaction naturally matches the feed composition, and decreases with time.
Further, in the continuous polymerization method in a plug flow type reaction vessel without a back-mixing flow, the monomer concentration at the feed site matches the feed composition and decreases as it moves to the extraction section. That is, the substantial monomer concentration in the polymerization field is close to the feed composition.

In the method for producing a styrene resin of the present invention, the concentration of the monomer present in the reaction vessel R1 also depends on the mixed state, but basically, the feed rate and composition of the raw material system and the reaction vessel Determined by polymerization rate. The reduction of the concentration of the monomer existing in the reaction vessel of the completely mixed flow can be achieved by, for example, suppressing the monomer feed rate in proportion to the polymerization rate. Since the polymerization rate of anionic polymerization is proportional to the first power of the monomer concentration, the side reaction proportional to the second power or the third power of the monomer concentration is to lower the substantial monomer concentration in the polymerization field. Thus, it can be suppressed to an extremely low level. Probably because the production rate of oligomers such as styrene dimer and styrene trimer is proportional to the multiplier of the monomer concentration, it can be significantly reduced by suppressing the monomer concentration.

In the method for producing a styrene resin of the present invention, an organic lithium compound is used as a polymerization initiator. The organolithium compound is a so-called lithium organometallic compound having a carbon-lithium bond. More specifically, alkyllithium, alkyl-substituted phenyllithium compounds and the like can be mentioned. Preferred examples of alkyllithium include ethyllithium, n-propyllithium, n
-Butyl lithium, sec-butyl lithium, tert
-Butyl lithium, benzyl lithium, etc. are mentioned.
The amount of the organolithium initiator used depends on the molecular weight of the polymer to be obtained. That is, the molecular weight of the polymer is basically determined by the monomer amount and the composition ratio of the organolithium initiator. The amount of organolithium used per 1 kg of monomer is in the range of 0.5 to 200 mmol. Preferably 1-100 mmol,
It is particularly preferably in the range of 2 to 20 mmol.

If the amount of organolithium is reduced below this range, the polymerization rate will be reduced, and the molecular weight of the resulting polymer will be undesirably increased. Further, increasing the amount of organolithium beyond this upper limit increases the production cost, and extremely reduces the molecular weight of the resulting polymer, etc.
After all it is not preferable. In the method for producing a styrene resin of the present invention, the main component of the monomer used is styrene. However, a small amount of other copolymerizable monomer other than styrene may be contained. Examples of this include vinyl aromatic hydrocarbons other than styrene, conjugated dienes, and the like. The use of these polymerized monomers may be useful for adjusting the heat resistance, softening temperature, impact strength, rigidity, processability, etc. of the resin.

The polymerization solvent used in the method for producing a styrene resin of the present invention is a hydrocarbon solvent which is inactive to an organolithium initiator and is capable of dissolving a monomer and a produced polymer, and which is liquid at the time of polymerization. Examples of the solvent include a solvent that can be kept and easily removed by volatilization in the desolvation step after polymerization. Specifically, cyclohexane can be preferably used. However, since cyclohexane has a relatively high freezing point of 6.5 ° C., it is solidified in the condenser depending on the condensation temperature in the devolatilization step, and the devolatilization ability is significantly reduced. Therefore, cyclohexane 85-9
9% by weight and other aliphatic hydrocarbons having 5 to 7 carbon atoms 15 to 1
Mixing the weight% can be preferably used in the sense of preventing the coagulation of cyclohexane in the condenser. Further preferred range is 10 to 2% by weight of other aliphatic hydrocarbons having 5 to 7 carbon atoms, and particularly preferred range is 7 to 3% by weight.

The mixing amount of other hydrocarbon having 5 to 7 carbon atoms is 1
If it is less than wt%, the effect of lowering the freezing point cannot be sufficiently expected,
If it exceeds 15% by weight, the solubility of the styrene polymer in the solvent decreases, which is not preferable in some cases. Carbon number 5
Specific examples of the other hydrocarbons of 7 include n-hexane, isohexane, a mixture of C6 aliphatic hydrocarbons called industrial hexane, methylcyclopentane, n-pentane, isopentane, methylcyclohexane, cyclohexene and the like, and mixtures thereof. Can be mentioned. The amount of the polymerization solvent used is in the range of 0.5 to 2 kg per 1 kg of the monomer.
It is preferably in the range of 0.67 to 1.5 kg. When the amount of the polymerization solvent used is small, heat removal and stirring become difficult, and when the amount of the polymerization solvent used is large, the amount of the solvent to be removed after the polymerization increases, and the amount of thermal energy used increases, which is not preferable.

In the method for producing a styrene resin, the solution viscosity during polymerization is generally extremely high, although it depends on the monomer concentration of the raw material system. Therefore, it is difficult to remove the heat of polymerization only by the jacket attached to the ordinary reaction tank. In addition, a local temperature rise occurs depending on the conditions. In the present production method, a reflux condenser attached under a reduced pressure is used to remove the heat of polymerization, so that the internal temperature of the reaction tank R1 is uniformly kept within the range of the polymerization temperature of 60 ° C or higher and lower than 80 ° C. Controlled. In order to control the heat of polymerization to 60 ° C. or lower, the degree of pressure reduction in the reaction tank must be raised, which is not preferable because the foaming due to the heat of polymerization becomes severe. Further, if the polymerization temperature is 80 ° C. or higher, the amount of styrene oligomers produced increases, which is not preferable for the purpose of the present invention. Further, in order to enhance the heat removal capacity of the equipment, known heat removal methods can be used at the same time. For example, a method of arranging a heat removal coil in the reaction tank or providing an external circulation jacket separately from the reaction tank jacket can be preferably used.

After the polymerization, carbon-lithium bonds basically remain at the ends of the polymer. If this is left as it is, it is subjected to air oxidation or thermal decomposition at the finishing stage and the like, which causes deterioration of stability and coloring of the obtained styrene resin. After the polymerization, it is preferable to stabilize the active terminal of the polymer, that is, the carbon-lithium bond. For example, it is preferable to add a compound having an oxygen-hydrogen bond such as water, alcohol, phenol, carboxylic acid, etc., and an epoxy compound, an ester compound, a ketone compound, a carboxylic acid anhydride, a compound having a carbon-halogen bond, or the like also has the same effect. Can be expected. The amount of these additives used is preferably about 0.1 to 10 times equivalent to the carbon-lithium bond. If it is too large, not only is it disadvantageous in terms of cost, but mixing of residual additives may be an obstacle.

It is also possible to increase the molecular weight of the polymer and further to form a branched structure in the polymer chain by performing a coupling reaction with a polyfunctional compound utilizing a carbon-lithium bond. The coupling agent used in such a coupling reaction can be selected from known ones. Examples of the coupling agent include polyhalogen compounds, polyepoxy compounds, mono- or polycarboxylic acid esters, polyketone compounds, mono- or polycarboxylic acid anhydrides, and silicon or tin alkoxy compounds. Specific examples include silicon tetrachloride, di (trichlorosilyl) ethane, 1,3,5-tribromobenzene, epoxidized soybean oil, tetraglycidyl 1,3-bisaminomethylcyclohexane, dimethyl oxalate, trimellitic acid tri-. 2-ethylhexyl,
Examples include pyromellitic dianhydride and diethyl carbonate. Further, an alkaline component derived from organic lithium, such as lithium oxide or lithium hydroxide, can be neutralized and stabilized by adding an acidic compound. Examples of such acidic compounds include carbon dioxide, boric acid, various carboxylic acid compounds and the like. Addition of these may improve the turbidity due to water absorption and coloring of the obtained styrene resin.

The molecular weight of the styrene polymer contained in the styrene resin of the present invention is generally 50,000 in terms of weight average molecular weight.
0 to 1,000,000, preferably 100,000 to 6
0,000, particularly preferably 200,000-40
It is in the range of 10,000. If the weight average molecular weight is too low, various mechanical properties of the resin, such as impact strength and thermal rigidity, are deteriorated, which is not preferable. Further, when the weight average molecular weight is high, resin molding and processability are deteriorated, which is also not preferable. The molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight and the number average molecular weight of the styrene polymer contained in the styrene resin of the present invention is in the range of 1.5 to 5.0, preferably in the range of 2 to 4. Is. If the molecular weight distribution is too narrow, processability and specific resin performance, such as impact strength and foaming characteristics, are deteriorated, which is not preferable. In addition, when it is too wide, the specific resin performance, for example, the flow characteristics during molding, the rigidity during heating, and the like are deteriorated, which is also not preferable. The styrene resin of the present invention may contain various stabilizers publicly used for the styrene resin in order to improve its thermal or mechanical stability, antioxidant property, weather resistance and light resistance. . Examples thereof include phenol stabilizers, phosphorus stabilizers, nitrogen stabilizers, and sulfur stabilizers.

JP-A-7-292188 discloses that the addition of 2,4,6-trisubstituted phenol is particularly advantageous as a method for stabilizing polystyrene. Preferred examples of 2,4,6-trisubstituted phenol include 2,6-di-t-butyl-4-methylphenol and triethylene glycol-bis- [3- (3-t-butyl-
5-Methyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3- (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 1,
3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, n
-Octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2-t-butyl-
6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 [1-
(2-Hydroxy 3,5-di-t-pentylphenyl)]-4,6-di-t-pentylphenyl acrylate, tetrakis [methylene 3- (3,5-di-t-butyl-4-hydroxyphenyl)] Propionate] methane, 3,9 bis [2- {3- (t-butyl-4-hydroxy-5-methylphenyl) propynyloxy} -1,
1-Dimethylethyl] -2,4,8,10-tetraoxa [5,5] undecane, 1,3,5-tris (3 ′,
5'-di-t-butyl-4'-hydroxybenzyl)-
s-Triazine-2,4,6 (1H, 2H, 3H) -trione, 1,1,4-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4'-butylidenebis (3-methyl-6-t-butylphenol) and the like.

Specific preferred examples of the phosphorus-based stabilizer include:
Tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl)-
4-, 4'-bisphenylene phosphite, tris (nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, bis (2,4, di-t-butylphenyl) pentaerythritol phosphite, bis (2 , 6, di-t-butyl-4-methylphenyl) pentaerythritol phosphite, 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite, tetrakis (2,4-di-t) -Butylphenyl)
4,4'-bisphenylene-di-phosphite and the like can be mentioned.

The amount of 2,4,6-trisubstituted phenol used is usually 1 part by weight or less based on 100 parts by weight of the styrene resin. However, in the styrene resin of the present invention, it is particularly preferable that the amount is 0.01 part by weight or more and less than 0.05 part by weight. When the amount of 2,4,6-trisubstituted phenol used is less than 0.01 part by weight, the effect of improving thermal or mechanical stability, oxidation resistance, weather resistance, etc. is not sufficiently exhibited. On the other hand, if the amount is more than 0.05 parts by weight, there is an increased concern that the stabilizer itself or its decomposition products may migrate or elute, depending on the use or processing conditions of the styrene resin. These stabilizers can also be mixed after resin recovery. However, the addition at the solution stage after the polymerization is particularly preferable because the mixing is easy and the deterioration of the resin in the solvent recovery step can be suppressed.

After completion of the polymerization, unreacted monomers and solvents are volatilized and recovered from the polymer solution. A known method can be used for volatilization removal. As the devolatilization device, for example, a method of flushing in a vacuum tank or a method of removing volatilization from a vent port using an extruder can be preferably used. Depending on the volatility of the solvent, the temperature is generally 150-300.
° C, preferably 180-260 ° C, particularly preferably 20
Volatile components such as a solvent and a residual monomer are volatilized and removed at 0 to 240 ° C., a degree of vacuum is preferably 0 to normal pressure, and more preferably 100 Pa to 50 KPa. A method of connecting a plurality of devolatilization devices in series and arranging them in series is effective for advanced volatilization. A method of adding water between the first stage and the second stage to enhance the volatility of the second stage can also be preferably used.

Molecular weight 1 contained in the styrene resin of the present invention
Styrene low molecular weight component in the range of 40 to 400 is 1000
must be less than 500 ppm and the non-styrene oligomer component therein must be less than 500 ppm. The low molecular weight styrene component is preferably less than 600 ppm, more preferably less than 400 ppm, particularly preferably 160 pp.
It is less than m. The content of the non-styrene oligomer component therein is preferably less than 300 ppm, more preferably 100.
It is less than ppm, particularly preferably less than 40 ppm. The styrene low molecular weight component having a molecular weight of 140 to 400 contained in the styrene resin of the present invention comprises a styrene oligomer component and a non-styrene oligomer component. Specifically, the styrene oligomer component mentioned here is a dimer or trimer of styrene. The non-styrene oligomer component has 1 phenyl group excluding these styrene oligomers.
It is a low molecular weight component having a molecular weight of 140 to 400 having 3 units.

The styrene dimer has a molecular weight of 208 and is composed of 2,4-diphenyl-1-butene and cis-1,2-
Examples thereof include diphenylcyclobutane and trans-1,2-diphenylcyclobutane. The styrene trimer has a molecular weight of 312 and is 2,4,6-triphenyl-1-
Hexene, 1-phenyl-4- (1'-phenylethyl) tetralin (including 4 isomers), 1,3,5
-Triphenyl-cyclohexane etc. are mentioned. The non-styrene oligomer component is a hydrocarbon compound having 1 to 3 aromatic rings in the molecule. Specifically, 1,3-diphenylpropane, 1,3-diphenylbutane, 2,4-diphenylpentane as a hydrocarbon compound having two aromatic rings, and 1,3 diphenylpentane as a hydrocarbon compound having three aromatic rings
3,5-triphenylpentane, 1,3,5-triphenylhexane, 1,2,4-triphenylcyclopentane and the like can be mentioned.

These non-styrene oligomer components are formed mainly by reacting a specific solvent and impurities contained therein with a styrene monomer in the presence of organic lithium, and have a structure which can no longer be called a styrene oligomer. Have. For example,
One or two molecules of styrene are added to the contained toluene to produce 1,3-diphenylpropane or 1,3,5-triphenylpentane. In addition, one or two molecules of styrene are added to ethylbenzene to produce 1,3-diphenylbutane and 1,3,5-triphenylhexane. In addition, the generation mechanism such as the decomposition and generation of the styrene resin is not always clear.
-Triphenylcyclopentane, 2,4-diphenylpentane, 1,2-diphenylcyclopropane, etc. are also found in the styrene resin after heating and devolatilization.

The styrene monomer contained in the styrene resin of the present invention is preferably less than 200 ppm. More preferably less than 100 ppm, particularly preferably 20 pp
m, most preferably less than 10 ppm. The residual hydrocarbon solvent contained in the styrene resin of the present invention is 2000.
It is preferably less than ppm. More preferably 10
It is less than 00 ppm, particularly preferably less than 300 ppm, most preferably less than 100 ppm. When the content of these low-molecular components, that is, styrene monomer, styrene-based low-molecular component and residual hydrocarbon solvent is high, the thermal stability during molding and processing of the styrene resin is not sufficient, and the rigidity during heating is poor. It is inferior in heat resistance. The low-molecular component contained in the resin diffuses or bleeds from the inside of the molded product to the surface, which makes it difficult to print or peels off the print. Further, there may be a problem that a low molecular component contained in the resin is eluted or volatilized. In particular, when the amount of the styrene-based low molecular weight component is large, there is a case where an oily substance adheres to a mold or a molded product during the molding process.

The styrene monomer content is less than 20 ppm and the styrene low molecular weight component having a molecular weight of 140 to 400 is 200.
ppm or less and 100 pp of non-styrene oligomer component
When it is m or less, almost no diffusion or elution is observed, which is particularly preferable. In the method for producing a styrene resin of the present invention, the styrene resin from which volatile components such as a solvent have been devolatilized and removed can be finished into pellets by a known method. If necessary, the styrene resin of the present invention may be mixed with a resin additive known to be used in styrene resin materials. Examples thereof include dyes, pigments, fillers, lubricants, release agents, plasticizers and antistatic agents. Further, the styrene resin of the present invention can be mixed with other known resins, if necessary, as long as the characteristics are not lost. Preferred examples thereof include polystyrene obtained by radical polymerization, high-impact polystyrene, polyphenylene ether, and AB.
S, styrene-conjugated diene block copolymers and hydrogenated products thereof.

The styrene resin of the present invention can be molded by a known resin molding method. Specific resin molding methods include injection molding, compression molding, extrusion molding, blow molding, vacuum molding and the like. Further, it is also possible to mold a foam molded body by combining with various foam molding techniques.
The styrene resin of the present invention is preferably used for various known uses of the styrene resin such as electric appliance materials, miscellaneous goods materials, toy materials, foam insulation materials for homes, tatami core materials, food container materials, and food packaging materials. be able to. Taking advantage of the extremely low content of the styrene monomer and the styrene-based low-molecular component, it can be particularly preferably used for food containers and food packaging applications that come into direct contact with foods. Specific examples of food containers and packaging include, for example, injection molding, injection blow molding, lactic acid beverage containers obtained by biaxially stretching into a sheet, pudding containers, jelly containers, soy sauce bottles and other food containers,
Examples thereof include food trays obtained by foam molding, food containers such as instant noodle bowls, lunch boxes and beverage cups, and food packages such as fruit and vegetable packaging and seafood packaging obtained by sheet processing.

[0044]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to Examples and Comparative Examples. However, it goes without saying that these are examples and do not limit the technical scope of the present invention in any way. Example 1 Actual capacity 2 equipped with reflux condenser and stirrer
A reaction vessel R1 which is a completely mixed type of liter and a plug flow type reaction vessel R2 having a capacity of 1 liter and equipped with a stirrer were connected in series. A 40/60 weight ratio mixture of styrene monomer and cyclohexane (containing 5 wt% n-hexane) as a polymerization solvent was fed to the reaction tank R1 at a flow rate of 1.78 Kg / hour. Separately, a cyclohexane solution of n-butyllithium as an organic lithium initiator was fed to the reaction tank in an amount corresponding to 8 mmol per 1 kg of styrene monomer.

The absolute pressure in the reaction vessel R1 was reduced to 500 mmHg, and the heat generated during the polymerization was removed by refluxing the polymerization solvent to the reflux condenser. The temperature of the reaction solution was stable at 70 ° C. The temperature of the reaction tank R2 was controlled at 70 ° C. The reaction liquid flowing out of the reaction tank R1 was subsequently passed through the reaction tank R2 by plug flow. Reaction tank R1
The average conversion rate of monomer to resin at the time of flowing out from
6%, the conversion rate after passing through the reaction tank R2 was 99.99% or more.

The polymer solution thus obtained is deactivated at the anion active end by adding water in an amount twice the amount of lithium, and further an equimolar amount of carbon dioxide gas is added.
The produced lithium hydroxide was neutralized, and 0.04 parts of a non-volatile 2,4,6-trisubstituted phenol-based stabilizer was added and mixed. Then, the polymer solution was heated at 220 ° C. in a depressurized flushing tank to remove volatile components. Further, 0.5% by weight of water was added to and mixed with the polymer, and then the remaining volatile components were removed through an extruder equipped with a vacuum vent at 220 ° C. The molecular weight distribution (indicated by the ratio Mw / Mn of the weight average molecular weight and the number average molecular weight) of the polymer of the styrene resin thus obtained, the styrene monomer, the styrene low molecular weight component and the residual hydrocarbon solvent (cyclohexane) Was analyzed by gas chromatography. The results of the analysis are shown in Table 1 (styrene monomer is abbreviated as monomer).

Example 2 Cyclohexane alone was used as a polymerization solvent, and a mixed solution of a monomer / solvent at a ratio of 50/50 by weight was used. The absolute pressure in the reaction tank R1 was reduced to 470 mmHg, and the temperature in the reaction tank R2 was 70%.
Controlled to ° C. Other conditions were the same as in Example 1. The results are shown in Table 1. Comparative Example 1 A reaction vessel R1 equipped with a stirrer and having a capacity of 2 liters, which is a complete mixing type (without an accompanying reflux condenser), and a stirrer equipped with a 1 liter capacity plug flow type reaction vessel R2, were connected in series. Combined The temperature of both reaction vessels was controlled at 100 ° C. In the reaction tank R1, a mixture of styrene monomer and cyclohexane as a polymerization solvent in a weight ratio of 60/40 was added to 1.
It was fed at a flow rate of 78 Kg / hr. Separately, a cyclohexane solution of n-butyllithium as an organic lithium initiator was fed to the reaction tank in an amount corresponding to 8 mmol per 1 kg of styrene monomer.

The reaction liquid flowing out of the reaction tank R1 was subsequently passed through the reaction tank R2 by plug flow. Reaction tank R
The conversion rate of the monomer to the resin at the time of flowing out from 1 was 98% on average, and the conversion rate after passing through the reaction tank R2 was 99.99% or more. The anion active terminal was deactivated by adding methanol in an amount of 3 times the amount of lithium in the obtained polymer solution. Then, the polymer solution was heated at 240 ° C. in a depressurized flushing tank to remove volatile components. Furthermore, 0.5% by weight of water is added to the polymer,
After mixing, the remaining volatile components were removed by passing through an extruder with a vacuum vent at 250 ° C. The molecular weight distribution (indicated by the ratio Mw / Mn of the weight average molecular weight and the number average molecular weight) of the polymer of the styrene resin thus obtained, the styrene monomer, the styrene low molecular weight component and the residual hydrocarbon solvent (cyclohexane) The content was analyzed by gas chromatography. The results of the analysis are shown in Table 1.

Comparative Example 2 Ethylbenzene was used as the polymerization solvent and the temperature in both reaction tanks was adjusted to 1
The same operation as in Comparative Example 1 was carried out except that the temperature was set to 22 ° C. Comparative Example 3 The stirring speed of Example 1 was reduced and the stirring blade shape was changed to
The flow of the reaction vessel R1 was set to the plug flow state, and the other conditions were the same as in Comparative Example 1 and the operation was performed. Comparative Example 4 A reactor having a capacity of 2 liters equipped with a stirrer was charged with 0.75 Kg of styrene monomer at room temperature and 0.1% as a polymerization solvent.
Charge 75 kg of ethylbenzene and 0.57 mmol of n-butyllithium as an organolithium initiator. Then, when the temperature was gradually raised with stirring, the temperature was raised from about 50 ° C. due to internal heat generation, and the final temperature reached 133 ° C. Then, the temperature was gradually lowered to 100 ° C., and the reaction was continued for a total of 1.5 hours. The treatment after the polymerization was carried out under the same conditions as in Comparative Example 1.

Comparative Example 5 In a reactor having a capacity of 2 liters equipped with a stirrer, 1.35 Kg of styrene monomer and 0.
Charge 15 kg of ethylbenzene. Then, the temperature was gradually raised with stirring to carry out thermal radical polymerization at 130 to 140 ° C. for 6 hours, and then continued at 160 ° C. for 2 hours. The treatment after the polymerization was carried out under the same conditions as in Comparative Example 1. 1) Moldability Evaluation A 1.2 mm thick sheet was injection-molded using the styrene resin obtained above at a resin temperature of 240 ° C. and a mold temperature of 50 ° C. Further, the moldability was evaluated in the state of the flow mark of the molded sheet. The evaluation criteria are shown below. ◯: No flow mark is recognized. Δ: A slight flow mark is recognized. X: Flow marks are noticeable.

2) Evaluation of mold contamination property After the above-mentioned sheet molding was carried out for 500 shots, the surface of the mold was strongly wiped with gauze, and the state of adhesion of the oily substance to the gauze was evaluated. The evaluation criteria are shown below. ◯: No adhesion of oily substance is observed. X: Slight adhesion of oily substance is recognized. 3) Foaming characteristics Using the above-mentioned styrene resin, 0.1 part by weight of talc was added to 100 parts by weight of styrene resin, which was introduced into the first-stage extruder and was plasticized at about 220 ° C. weight%
It was pressed in and impregnated. Then, send it to the second stage extruder,
A styrene resin foamed sheet was prepared by extruding a product whose temperature was adjusted to a viscosity suitable for foaming through a die at about 130 ° C.

After sufficiently curing the sheet, its thickness and performance were measured or evaluated. The average thickness of the styrene resin foam sheet was about 2.5 mm. The evaluation criteria are shown below. ◯: Bubble size is uniform and independent. Δ: Bubble size is slightly uneven, and some continuous bubbles are present. X: The size of the bubbles is non-uniform, and some partially continuous bubbles are present.

4) Measurement of Elution Amount The 1.2 mm-thick sheet obtained by the above injection molding was cut, 2 ml of n-heptane solvent was added per 1 cm ^{2 of} surface area, and it was immersed and eluted at 25 ° C. for 1 hour to elute. Then, it moved to the glass container and analyzed and evaluated this solution as an eluate. (1) Method for analyzing styrene monomer and hydrocarbon solvent The above eluate was quantitatively analyzed by applying a gas chromatography mass spectrometer. (2) Method of analyzing styrene low-molecular component After concentrating 50 ml of the above-mentioned eluate, 2 ml using hexane
Then, the volume of the solution was adjusted to 1, and the sample was quantitatively analyzed by applying a gas chromatography mass spectrometer. The evaluation results are summarized in Table 2.

[0054]

[Table 1]

[0055]

[Table 2]

As is apparent from Table 1, Examples 1 and 2
The styrene resin according to Comparative Example 5 was compared with the styrene resin by radical polymerization of Comparative Example 5 as well as the styrene resin by anionic polymerization methods of Comparative Examples 1 to 4, and the amount of styrene low-molecular component and residual styrene monomer contained therein. Is extremely low. Further, as is clear from Table 2, the styrene resins of Examples 1 and 2 are excellent in resin performance indicated by moldability, mold staining property and foaming property, and in the elution test, monomer and styrene low molecular weight compounds are used. No elution of components was detected.

[0057]

The method for producing a styrene resin of the present invention is a method for producing a styrene resin which reduces the contents of monomers and styrene low-molecular components in the resin and is excellent in mechanical properties and processing stability of the resin. Is provided. The resulting styrene resin has excellent mechanical properties and processing stability, and also has improved thermal stability. For example, the mold contamination by an oily substance during molding is remarkably improved, the molding and processability, particularly the foaming property is improved, and the volatilization from the resin material and the amount of eluted components are remarkably reduced.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hironori Suezawa             Asahi Kasei Co., Ltd. 3-13-1, Shiodori, Kurashiki City, Okayama Prefecture             Inside the company (72) Inventor Hiroshi Shirai             Asahi Kasei Co., Ltd. 3-13-1, Shiodori, Kurashiki City, Okayama Prefecture             Inside the company F-term (reference) 4J011 AA05 DA04 DB13 DB23 DB26

Claims (5)

[Claims] 1. A raw material system having the following composition (A) is continuously charged from one of the reaction tanks R1 having a reverse mixing flow in a batch or in a divided manner, and a production system is continuously supplied from the other reaction tank R1. The internal temperature of the reaction tank R1 is adjusted to 60 by removing the heat of polymerization by using a reflux condenser attached under reduced pressure, which includes a continuous anionic polymerization process of drawing out into
C. or more and less than 80.degree. C., and controlling the average ratio of the styrene monomer, cyclohexane solvent and styrene polymer present in the reaction vessel R1 to less than 5% by weight. A method for producing a styrene resin, which is obtained by polymerizing, and devolatilizing and drying the obtained styrene polymer solution. (A) Styrene monomer 1.0 kg Cyclohexane solvent 0.5-2 kg Organic lithium compound 0.5-200 mmol. 2. The production method according to claim 1, wherein the obtained styrene resin has the following characteristic (B). (B) The weight average molecular weight of the styrene polymer contained in the styrene resin is in the range of 50,000 to 1,000,000, and the molecular weight distribution (Mw / Mn)
Is in the range of 1.5 to 5.0, and the styrene low molecular component contained in the styrene resin has a molecular weight of 140 to 400 (however, the styrene low molecular component is composed of a styrene oligomer component and a non-styrene oligomer component). Is 16)
It is less than 0 ppm, and the content of the non-styrene oligomer component therein is less than 40 ppm. 3. The production method according to claim 1, wherein the polymerization is carried out by a composite polymerization process in which one or more reaction tanks R2 are connected in series after the reaction tank R1. 4. The cyclohexane-based solvent comprises 85 to 99% by weight of cyclohexane and 15 to 1% by weight of another aliphatic hydrocarbon having 5 to 7 carbon atoms. The manufacturing method described. 5. A styrenic resin having the following characteristics a) to d), which is obtained by the production method according to any one of claims 1, 3 and 4. a) The styrene polymer contained in the styrene resin has a weight average molecular weight of 50,000 to 1,000,000 and a molecular weight distribution (Mw / Mn) of 1.5 to 5.0. b) The styrene-based low-molecular weight component contained in the styrene resin having a molecular weight of 140 to 400 (however, the styrene-based low-molecular weight component is composed of a styrene oligomer component and a non-styrene oligomer component) is less than 160 ppm, and Less than 40 ppm of non-styrene oligomer component. c) 100p of styrene monomer contained in styrene resin
less than pm. d) The cyclohexane solvent contained in the styrene resin is 2
Less than 000 ppm.