JP2004161989A - Styrene-based expandable resin particle, foamed bead and expansion molding product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide styrene-based expandable resin particles having good appearance of molding product and excellent in expansion molding properties and to provide a method for producing the resin particles and to provide styrene-based foamed beads and expansion molding products. <P>SOLUTION: The method for producing the styrene-based expandable resin particles comprises advancing polymerization reaction while keeping the interior of a reacting tank in a low oxygen concentration from the start of polymerization in suspension polymerization of a styrene-based monomer and impregnating a readily volatile foaming agent before or after completion of polymerization reaction. In the styrene-based expandable resin particles obtained by the production method, the expandable molding product having good appearance can be obtained, because the occurrence of a low molecular weight product is suppressed in the outermost layer part. <P>COPYRIGHT: (C)2004,JPO

Description

【００４０】
【発明の効果】
本発明によれば、成形品の外観が良好で、発泡成形性に優れたスチレン系発泡性樹脂粒子とその製造方法、さらに、スチレン系発泡ビーズ及び発泡成形品を提供できる。
【図面の簡単な説明】
【図１】本発明の発泡ビーズの最表面層部分と表面層部分を説明するための図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to styrene-based foamable resin particles and a method for producing the same, and further relates to styrene-based foam beads and foam molded articles.
[0002]
[Prior art]
Styrene-based foamable resins are used in many food containers, packing materials, cushioning materials, and the like, because of their excellent heat insulating properties, economic efficiency, and hygiene. These foamed molded articles are manufactured by a method in which styrene-based foamable resin particles are heated by steam or the like, pre-expanded to a desired bulk density, passed through an aging step, filled in a molding die, and then heated and foamed again. Is done. The styrene-based expandable resin particles are required to have excellent foam moldability and have a good appearance of the molded product when formed.
[0003]
Conventionally, in order to improve the appearance of a foam molded product, it is necessary to completely eliminate voids between the beads when heating and foaming styrene foam beads filled in a molding die. . However, it was difficult to completely eliminate voids between beads. Therefore, in order to reduce the voids as much as possible, improvements in characteristics of the styrene-based expandable resin particles themselves and improvements in molding technology including functions of a molding machine and the like have been made.
[0004]
For example, in improving the characteristics of the styrene-based expandable resin particles themselves, a method of adjusting the type and amount of a plasticizer that plasticizes the resin particles, and an adjustment such as reducing the molecular weight have been performed. However, these methods have a drawback that the heat resistance of the resin particles is reduced, and the surface of the molded body is melted by heating and foaming at the time of molding to increase voids.
[0005]
In the improvement of molding technology including the function of a molding machine and the like, a control method in a heating process is examined for a molding machine, and a method of using steam more efficiently is adopted. Further, in a molding die, a method of similarly using steam more effectively by increasing the number of slits is being studied. However, these methods have a drawback that it is difficult to improve all of them at once, because a great amount of money is added to the cost of remodeling the machine and the cost of remodeling the mold.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a styrene-based foamable resin particle having a good appearance of a molded article and excellent foam moldability, a method for producing the same, a styrene-based expanded bead, and a foamed molded article.
[0007]
[Means for solving the problems]
According to the first aspect of the present invention, in the suspension polymerization of a styrenic monomer, at least at the latter stage of the polymerization, the polymerization reaction is advanced while maintaining the inside of the reaction tank at a low oxygen concentration, and before the completion of the polymerization reaction or the polymerization. After the completion of the reaction, there is provided a method for producing styrenic expandable resin particles impregnated with a blowing agent.
[0008]
According to the second aspect of the present invention, in suspension polymerization of a styrene-based monomer, from the start of polymerization, the polymerization reaction is advanced while maintaining the inside of the reaction tank at a low oxygen concentration, and before the completion of the polymerization reaction or during the polymerization reaction. After the completion, there is provided a method for producing styrene-based expandable resin particles, characterized by impregnating a readily volatile blowing agent.
[0009]
According to a third aspect of the present invention, there is provided styrene-based expandable resin particles obtained by the above-described method.
[0010]
According to a fourth aspect of the present invention, there is provided styrene-based expanded beads obtained by expanding the styrene-based expandable resin particles.
[0011]
According to a fifth aspect of the present invention, there is provided a styrenic foam molded article obtained by molding the above-mentioned styrenic foam beads.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The styrene-based expandable resin particles, expanded beads and expanded molded products of the present invention will be described in detail.
In the production method of the present invention, a styrene monomer is subjected to suspension polymerization.
As a styrene monomer, styrene or styrene as a main component, styrene derivatives such as α-methylstyrene, chlorostyrene, vinyltoluene, acrylates such as methyl acrylate, methyl acrylate, butyl acrylate, and methacrylic acid A mixed monomer with methacrylates such as methyl acrylate, ethyl methacrylate and butyl methacrylate can be used.
[0013]
A conventionally known method can be employed for suspension polymerization.
In the method of polymerizing a styrene monomer without a nucleus, generally, a styrene monomer in which a catalyst such as an organic peroxide is dissolved is dispersed in an aqueous medium containing a dispersant to generate radicals. I do.
[0014]
As the dispersant, a sparingly soluble inorganic salt and a surfactant may be used in combination, or a conventionally known dispersant such as an organic dispersant may be used.
As the hardly soluble inorganic salt, magnesium phosphate, tricalcium phosphate and the like can be used. As the surfactant, any of sodium oleate, sodium dodecylbenzenesulfonate, and other anionic surfactants and nonionic surfactants generally used for suspension polymerization can be used. As the organic dispersant, polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose and the like can be used.
As the organic peroxide, a conventionally known organic peroxide having a 10-hour half-decomposition temperature of 50 to 100 ° C. can be used. For example, there are lauroyl peroxide, benzoyl peroxide, t-butylperoxybenzoate, t-butylperoxyisopropyl carbonate and the like. The organic peroxide is preferably used in an amount of 0.001% by weight to 0.5% by weight based on the polymerizable monomer. One or more organic peroxides can be used.
[0015]
The overall molecular weight can be adjusted by adjusting the catalyst concentration, using a chain transfer agent, or both.
As the chain transfer agent, conventionally known ones such as octyl mercaptan, dodecyl mercaptan and α-methylstyrene dimer can be used. The addition amount of the chain transfer agent is preferably 20 ppm to 100 ppm based on the polymerizable monomer.
[0016]
In the production method of the present invention, at least at the latter stage of the polymerization, the reaction is carried out while keeping the inside of the reaction tank at a low oxygen concentration, and the volatile reaction agent is impregnated before the completion of the polymerization reaction or after the completion of the polymerization reaction.
In this method, the inside of the reaction tank may be set to a low oxygen concentration from the start of polymerization or during the polymerization. Preferably, the low oxygen concentration is obtained when the polymerization rate is 60% or more, more preferably 60% or more and less than 97%.
In general, when the polymerization proceeds in a state where oxygen is present in the reaction tank, the amount of the low molecular weight material formed in the styrene resin particles increases. In particular, in the latter stage of polymerization, a small amount of the remaining polymerization catalyst and radicals are stopped, so that a low-molecular-weight product is easily formed on the surface layer of the styrene-based resin particles, thereby impairing the appearance of a molded article.
On the other hand, in the production method of the present invention, since the inside of the reaction tank is kept at a low oxygen concentration from the latter stage of the polymerization or from the start of the polymerization, it is possible to suppress the generation of such low-molecular-weight products. The oxygen concentration is preferably kept below 7% by volume, more preferably below 1% by volume. The oxygen concentration can be adjusted by replacing with an inert gas such as nitrogen.
[0017]
The suspension polymerization temperature is generally between 80C and 95C. The polymerization temperature is preferably 90 ° C. or higher from the industrial production efficiency of reducing the amount of styrene monomer remaining in the finally obtained styrene foamable resin particles.
[0018]
In the production method of the present invention, it is preferable to start polymerization when the hydrogen ion concentration of the aqueous dispersion is 8 to 10, and to add at least one or more hardly soluble inorganic salts at a polymerization rate of 20 to 50%. The aqueous dispersion is preferably a continuous phase.
If the hydrogen ion concentration is outside the above range, the particle size distribution at the end of suspension polymerization may not be sharp. The hydrogen ion concentration can be adjusted with a basic inorganic salt.
Further, for the same reason, a sparingly soluble inorganic salt can be added at a polymerization rate of 20% to 50%.
The poorly soluble inorganic salt can be added at least once or more, for example, two or three times. Further, the sparingly soluble inorganic salt can be added after the polymerization is further advanced.
[0019]
The readily volatile blowing agent impregnates the styrenic resin particles before or after the completion of the polymerization reaction.
The volatile volatile foaming agent is selected from aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane and cyclopentane. In addition, as a foaming aid, an alicyclic hydrocarbon such as cyclohexane or an aromatic hydrocarbon can be used in combination with a readily volatile foaming agent in addition to an aliphatic hydrocarbon.
[0020]
In the polymerization, solvents, plasticizers, foam cell nucleating agents, fillers, flame retardants, flame retardant aids, lubricants, coloring agents, etc., additives used when producing styrene-based foamable resin particles are required. They may be used as appropriate.
[0021]
After the impregnation of the styrene-based expandable resin particles with the blowing agent is completed, the styrene-based expandable resin particles are discharged from the polymerization system, and are further dehydrated and dried, and then can be coated with a surface coating agent as necessary. As such a coating agent, those used for conventionally known expanded styrene resin particles can be applied. Examples include zinc stearate, triglyceride stearate, monoglyceride stearate, hardened castor oil, amide compounds, silicones, antistatic agents and the like.
[0022]
In the production method of the present invention, a seed polymerization method using styrene foamable resin particles or recycled styrene resin particles as a core can be applied. Also in this method, as described above, the oxygen concentration is controlled to be low.
[0023]
Generally, in styrene-based expandable resin particles produced by suspension polymerization, the weight-average molecular weight (molecular weight) is determined by the amount of the polymerization catalyst, and the molecular weights of the particle center, the intermediate part, and the surface part are almost constant. However, when the polymerization proceeds without reducing the oxygen concentration in the reaction tank by controlling it, as described above, a low-molecular-weight product is easily formed on the styrene-based resin particle surface layer, and thus the styrene-based expanded beads in the styrene-based expanded beads are used. When the molecular weights are compared in the range of the foam cell size, the molecular weight at the outermost surface decreases.
However, in the styrene-based expandable resin particles produced according to the present invention, since the generation of such low-molecular-weight products is suppressed, the appearance is lower than that of a foam molded article produced by ordinary polymerization without controlling the oxygen concentration. Can obtain a good foam molded article.
[0024]
The average particle diameter of the styrene-based expandable resin particles of the present invention is usually 0.05 to 2.0 mm.
[0025]
The styrene foam beads of the present invention are produced by foaming styrene foam resin particles. Further, the styrene-based foam molded article of the present invention is manufactured by molding the foam beads.
Generally, styrene-based expandable resin particles are pre-expanded to a predetermined bulk density by heating with steam or the like, and then subjected to an aging step to produce expanded beads. Thereafter, the foamed beads are filled in a molding die, and are again subjected to heat foam molding to produce a foam molded article.
[0026]
In the present invention, it is possible to improve the appearance of a molded product obtained from the styrene-based expandable resin particles while maintaining the expandability of the expandable resin particles. The molded article of the present invention can be suitably used for food containers, packing materials, cushioning materials and the like.
[0027]
【Example】
The characteristic evaluation methods in the examples and comparative examples are as follows.
(1) Weight average molecular weight (molecular weight)
The molecular weight of the styrene-based expandable resin particles was measured by expanding the particles.
The styrene-based foamable resin particles were foamed in saturated steam at a bulk factor of 80 ml / g.
The molecular weight of the styrene foam beads was measured as follows.
First, 5 to 6 foamed beads (average particle diameter: 3.0 mm) were prepared, and each was cut in half. Next, as shown in FIG. 1, the layer portion 2 and the layer portion 3 are separated under a microscope by a thickness of one foam cell at equal intervals from the surface of the foam bead 1 cut in half toward the center. I cut it out while checking. The molecular weights of the outermost surface layer portion (layer portion 2) and the surface layer portion (portion of layer portions 2 and 3) were measured. The outermost layer portion is a portion for one foam cell, and the surface layer portion is a portion for two foam cells. The molecular weight of the surface layer portion was determined as the average of the molecular weights of the layer portions 2 and 3.
In the present embodiment, one foam cell in the outermost layer indicates a size of about 50 to 100 μm, and two foam cells in the surface layer indicates a size of about 100 to 200 μm.
The molecular weight was measured by gel permeation chromatography (GPC) using the following apparatus and conditions.
Measuring device: Hitachi, Ltd. Eluent: THF, flow rate: 2 ml / min Detector: UV 220 nm
Column: Two GL-R400M manufactured by Hitachi Chemical Co., Ltd.
(2) Foaming foamability was measured by measuring the bulk density (foaming degree) of foaming in boiling water at 100 ° C. for 3 minutes when the amount of volatile components in the styrene-based foamable resin particles was 7.0% by weight. .
[0029]
(3) Appearance (surface smoothness)
The styrene-based foamable resin particles were foamed using an HBP-700 foaming machine manufactured by Hitachi Techno Plant Co., Ltd. to have a bulk density of 60 ml / g to obtain foamed beads. Further, the foamed beads were subjected to a steam pressure of 0.08 MPa using a VS-500 molding machine manufactured by Daisen Industries Co., Ltd. to obtain a molded product of 550 mm × 335 mm × 150 mm. A black printing ink was lightly applied to the surface of the molded article with a roller, and the surface was applied to an image processing apparatus. At this time, since the printing ink was not applied to the voids on the surface portion, the area of the black portion with respect to the entire application area was determined, the surface smoothness was used, and this was used as the evaluation value of the appearance.
[0030]
Example 1
In a 14-liter autoclave attached to a stirrer, 6,000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were charged and charged with stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 6,000 g of styrene, 20.8 g (wet 75%) of benzoyl peroxide, 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
[0031]
After completion of the charging, the inside of the polymerization tank was sealed, and the blowing pipe was opened. Then, nitrogen was flowed, and the blowing pipe was closed when the oxygen concentration reached 6.5% by volume. The temperature was raised to 90 ° C., and 2 hours and 3 hours after completion of the temperature increase, 3 g of tricalcium phosphate was added. At this time, the polymerization rates were 34% and 43%, respectively.
[0032]
Subsequently, when the temperature was maintained at 90 ° C. for 3 hours, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again. As a result of measuring the oxygen concentration in the polymerization tank at this time, it was 5.8% by volume. Thereafter, the temperature was raised to 100 ° C. over 1 hour.
[0033]
Subsequently, 90 g of cyclohexane and 420 g of butane (isobutane / normal butane ratio = 4/6) were injected in 1 hour after 1 hour, and the temperature was kept for 4 hours. Then, it cooled to room temperature and took out from the autoclave.
[0034]
The taken-out slurry was subjected to washing, dehydration, and drying, followed by passing through 14 mesh and classifying with 26 mesh remaining. Further, zinc stearate 0.08%, castor hardened oil 0.05%, dimethyl silicone The surface was coated with 0.02% to obtain styrene foamable resin particles (average particle diameter: 0.85 mm). Table 1 shows the measurement results of the molecular weight and the properties.
[0035]
Example 2
From the completion of the charging to the completion of the polymerization at 90 ° C., nitrogen was continuously flown into the polymerization tank, and the same procedure as in Example 1 was carried out except that the oxygen concentration in the polymerization tank was controlled at 0.1% by volume or less. System expandable resin particles (average particle diameter: 0.85 mm) were obtained. Table 1 shows the measurement results of the molecular weight and the properties.
[0036]
Comparative Example 1
In a 14-liter autoclave attached to a stirrer, 6,000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were charged and charged with stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 6,000 g of styrene, 20.8 g (wet 75%) of benzoyl peroxide, 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
[0037]
After completion of the charging, the temperature was raised to 90 ° C., and the blowing pipe was opened to proceed with polymerization. At this time, the oxygen concentration in the polymerization tank was 20.7% by volume. Two hours and three hours after completion of the heating, 3 g of tricalcium phosphate was added. At this time, the polymerization rates were 33% and 42%, respectively.
[0038]
Subsequently, when the temperature was maintained at 90 ° C. for 3 hours, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again. As a result of measuring the oxygen concentration in the polymerization tank at this time, it was 15.8% by volume. Thereafter, the temperature was raised to 100 ° C. over 1 hour. After the impregnation with the foaming agent, the same procedure as in Example 1 was carried out to obtain styrene-based foamable resin particles (average particle diameter: 0.85 mm). Table 1 shows the measurement results of the molecular weight and the properties.
[0039]
[Table 1]

[0040]
【The invention's effect】
According to the present invention, it is possible to provide a styrene-based expandable resin particle having a good appearance of a molded article and excellent foam moldability, a method for producing the same, a styrene-based expanded bead, and a foamed molded article.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an outermost surface layer portion and a surface layer portion of a foamed bead of the present invention.

Claims (7)

In suspension polymerization of styrenic monomers,
At least during the late stage of the polymerization, the polymerization reaction proceeds while maintaining the inside of the reaction tank at a low oxygen concentration,
A method for producing styrene-based expandable resin particles in which a foaming agent is impregnated before or after completion of the polymerization reaction. In suspension polymerization of styrenic monomers,
From the start of polymerization, the polymerization reaction is promoted while maintaining the inside of the reaction tank at a low oxygen concentration.
A method for producing styrenic foamable resin particles, comprising impregnating a readily volatile foaming agent before or after completion of the polymerization reaction. The method for producing styrene-based expandable resin particles according to claim 1 or 2, wherein the low oxygen concentration is 7% by volume or less. In the suspension polymerization of the styrene-based monomer, polymerization is started at a hydrogen ion concentration of the aqueous dispersion of 8 to 10,
The method for producing styrene-based expandable resin particles according to any one of claims 1 to 3, wherein the sparingly soluble inorganic salt is added at least once or more at a polymerization rate of 20% to 50%. A styrene-based expandable resin particle obtained by the production method according to claim 1. A styrene-based expanded bead obtained by expanding the styrene-based expandable resin particles according to claim 5. A styrene foam molded article obtained by molding the styrene foam beads according to claim 6.

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