JP2009149826A - Foamable acrylonitrile-styrene resin particles and foamed molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide foamable acrylonitrile-styrene resin particles having excellent foamability and moldability and having little content of a volatile organic compound, and to provide foamed molded articles therefrom. <P>SOLUTION: The foamable acrylonitrile-styrene resin particles contain an acrylonitrile-styrene copolymer, as a main component, 2-6 wt.% cyclohexane and 2-8 wt.% easily volatile foaming agent except the cyclohexane, and has ≤0.1 wt.% proportion of the volatile organic compound. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to expandable acrylonitrile / styrene resin particles having excellent foamability and moldability while reducing the amount of volatile organic compounds in a resin, and a foam-molded product thereof.

  Acrylonitrile / styrene resin is known to be superior in chemical resistance, oil resistance, mechanical strength, heat resistance, etc. compared to polystyrene, and in the field of foam molding materials, It is being developed for applications that were difficult to adopt.

  As a typical application, its heat resistance and oil resistance are excellent, and its use in automobile interior members is expanding. However, in recent years, in this field, a material having a small amount of volatile organic compounds is required in consideration of the influence on human health. Examples of the volatile organic compound include toluene, xylene, styrene, ethylbenzene and the like. These volatile organic compounds are substances that exhibit high plasticity with respect to foaming acrylonitrile / styrene resin, and are relatively hard, so that foamability and moldability of acrylonitrile styrene resin are difficult to improve. Commonly used for improvement.

As a method for improving foamability and moldability of a resin without using these volatile organic compounds, a method using a high-boiling plasticizer (Patent Document 1) and a method for lowering the molecular weight of the resin are known.
JP-A-2001-164023

  However, the high-boiling plasticizer used in the method of Patent Document 1 has a lower compatibility with acrylonitrile / styrene resin than volatile organic compounds. For this reason, the high boiling point plasticizer bleeds on the surface of the resin particles and the particle surface layer is remarkably plasticized, and a blocking phenomenon occurs in which the particles are welded together during pre-foaming, or the molded product surface melts and the appearance is reduced There was a problem. Further, the method for lowering the molecular weight has a problem of oil resistance and strength reduction when formed into a molded product.

  An object of the present invention is to provide expandable acrylonitrile / styrene resin particles having excellent foamability and moldability and having a small content of volatile organic compounds, and foamed articles thereof.

According to the present invention, the following expandable acrylonitrile / styrene resin particles and foamed molded articles thereof are provided.
1. The main component is an acrylonitrile / styrene copolymer, 2 to 6% by weight of cyclohexane and 2 to 8% by weight of a readily volatile foaming agent other than cyclohexane, and the amount of volatile organic compounds is 0.1% by weight or less. Some expandable acrylonitrile / styrene resin particles.
2. 2. The expandable acrylonitrile / styrene resin particle according to 1, wherein the acrylonitrile / styrene copolymer is 10 to 50% by weight of acrylonitrile and 50 to 90% by weight of styrene.
3. A foam molded product obtained by foaming and molding the expandable acrylonitrile / styrene resin particles described in 3.1 or 2.

  According to the present invention, expandable acrylonitrile / styrene resin particles having excellent foamability and moldability and having a small content of volatile organic compounds, and foamed articles thereof can be obtained.

  The foamable acrylonitrile / styrene resin fat particle of the present invention contains acrylonitrile / styrene copolymer as a main component, and further contains 2 to 6% by weight of cyclohexane and 2 to 8% by weight of other readily volatile foaming agents. By setting it as such foaming agent content, the quantity of the volatile organic compound of this foamable acrylonitrile styrene resin fat particle can be reduced, and the quantity is 0.1 weight% or less.

The composition ratio of acrylonitrile and styrene of the acrylonitrile / styrene copolymer forming the expandable acrylonitrile / styrene resin particles is preferably 10 to 50% by weight of acrylonitrile and 50 to 90% by weight of styrene, more preferably 20 to 40% of acrylonitrile. % By weight and 60-80% by weight of styrene.
If acrylonitrile is less than 10% by weight, the oil resistance tends to decrease, and if it exceeds 50% by weight, foamability and moldability may decrease.
In addition, a composition ratio can be adjusted by adjusting each compounding quantity and superposing | polymerizing until superposition | polymerization is substantially completed.

  Expandable acrylonitrile / styrene resin particles contain cyclohexane as a foaming agent. The content of cyclohexane is 2 to 6% by weight, preferably 2 to 5% by weight, based on the resin particles. If the content is less than 2% by weight, sufficient foamability cannot be imparted to the hard acrylonitrile styrene resin particles, and if it exceeds 6% by weight, the effect of improving foamability is not changed and it is uneconomical.

  It is important that the expandable acrylonitrile / styrene resin particles of the present invention contain a readily volatile foaming agent other than cyclohexane in addition to cyclohexane. The readily volatile foaming agent may be a foaming agent generally used for the production of foamable styrene resin particles, and is a gas or liquid under normal temperature and pressure and does not dissolve acrylonitrile / styrene resin particles. For example, preferred examples include aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane. Particularly, chain or branched aliphatic hydrocarbons having 3 to 6 carbon atoms are particularly effective. Can be mentioned.

  Content of easily volatile foaming agents other than cyclohexane is 2 to 8 weight% with respect to the resin particle, Preferably it is 3 to 7 weight%. If the amount of the foaming agent is less than 2% by weight, it is difficult to impart foamability, and if it exceeds 8% by weight, the effect of improving foamability is not changed and it is uneconomical.

  By setting the content of the foaming agent as described above, the amount of volatile organic compounds in the foamable acrylonitrile / styrene resin particles of the present invention can be reduced, and the amount is 0.1% by weight or less, preferably 0.05. % By weight or less. The volatile organic compound here means an aromatic hydrocarbon, and main objects are toluene, xylene, styrene, and ethylbenzene. The volatile organic compound is contained in the expandable resin particles, for example, due to residual styrene monomer or impurities contained in the monomer.

  The weight average molecular weight of the expandable acrylonitrile / styrene resin fat particles is preferably 200,000 to 500,000, more preferably 300,000 to 400,000. If the weight average molecular weight is less than 200,000, the oil resistance of the molded product may be lowered. In addition, since the mechanical strength of the molded product is lowered, it must be used at a higher density, which is economically disadvantageous because of higher material costs. If the weight average molecular weight exceeds 500,000, foamability and moldability may be deteriorated.

  The expandable acrylonitrile / styrene resin particles of the present invention are obtained by suspension polymerization of acrylonitrile and styrene, and impregnated with styrene and a readily volatile organic compound as a foaming agent. Thereafter, if necessary, dehydration, drying and classification are performed, and then the surface is coated with a coating agent.

  As a specific production method, for example, first, styrene, acrylonitrile, and a polymerization initiator are suspended in an aqueous medium. The dispersion in the aqueous medium is usually performed using an apparatus equipped with a stirring blade. Moreover, it is preferable to disperse | distribute with a dispersing agent.

  The dispersant is not particularly limited as long as it is used for suspension polymerization. For example, an organic dispersant, a hardly soluble inorganic salt, and a surfactant can be used.

  Examples of the polymerization initiator include organic peroxides such as lauroyl peroxide, benzoyl peroxide, t-butyl peroxybenzoate, and t-butyl peroxyisopropyl carbonate.

  The polymerization initiator is added after being dissolved in styrene or a solvent. Examples of the solvent include aromatic hydrocarbons such as ethylbenzene and toluene, and aliphatic hydrocarbons such as heptane and octane.

  Furthermore, fatty acid monoamides such as oleic acid amide and stearic acid amide, fatty acid bisamides such as methylene bis stearic acid amide, ethylene bis stearic acid amide, etc. may be used as dissolved in styrene or the above solvent as a foam regulator.

  The total molecular weight can be adjusted by adjusting the concentration of the polymerization initiator, using a chain transfer agent together, or both. As the chain transfer agent, conventionally known ones such as octyl mercaptan, dodecyl mercaptan, α-methylstyrene dimer can be used.

  The addition of styrene and acrylonitrile may be performed separately or continuously. Further, the addition rate varies depending on the capacity, shape, polymerization temperature and the like of the polymerization apparatus and is appropriately selected.

  In the impregnation with the foaming agent, the foaming agent is press-fitted into the container during or after the polymerization, and the temperature is usually raised to a temperature higher than the softening point of the resin particles, and the resin particles are impregnated.

After the impregnation of the foaming agent is completed, the expandable resin particles can be discharged from the polymerization system and, if necessary, dehydrated and dried, and then coated with the surface coating agent. As the coating agent, those usually used for expandable styrene resin particles can be used. For example, one type or two or more types of zinc stearate, stearic acid monoglyceride, stearic acid triglyceride, castor oil, amide compound, sucrose ester and the like can be used. These additives are preferably used at 0.01 to 0.3% by weight based on the expandable resin particles.
The surface coating agent can be coated on the expandable resin particles with a Henschel mixer, a Redige mixer, or the like.

  The foam-molded article of the present invention is obtained by foaming and molding the above-mentioned expandable acrylonitrile / styrene resin particles with water vapor, hot air, hot water or the like. For foaming and molding, a method used in a normal foamed styrene resin can be applied. For example, there is a method in which expanded particles pre-expanded with steam or the like are filled in a mold having small holes and reheated with steam or the like.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to these.
[Example 1]
A 16 liter autoclave equipped with a stirrer was charged with 6000 g of deionized water, 7.5 g of tricalcium phosphate, and 0.18 g of sodium dodecylbenzenesulfonate, while stirring at 200 rpm. Subsequently, 4320 g of styrene, 1680 g of acrylonitrile, 23.0 g of 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, 6.0 g of t-butyl peroxyisopropyl monocarbonate, α -15.0 g of methylstyrene dimer was charged, and the temperature was raised to 68 ° C after completion of the charging. After completion of temperature increase, 3 g and 4 hours later, 20 g of tricalcium phosphate was added. Subsequently, the mixture was kept at 68 ° C. for 5 hours, then heated to 120 ° C. over 2 hours, and kept for 5 hours to complete the polymerization.

Then, after cooling to 105 ° C., 210 g of cyclohexane and 300 g of butane were sequentially pressed into the autoclave, kept warm for 8 hours, then cooled to room temperature, and the polymerization and blowing agent impregnation steps were completed.
The slurry taken out is washed, dehydrated and dried, then passed through 12 mesh and classified with the remaining 22 mesh, and 0.1% by weight of zinc stearate (as 100% by weight of resin particles) is added to 3000 g of the obtained resin particles. The surface was coated to obtain expandable acrylonitrile / styrene resin particles.

The foamable acrylonitrile / styrene resin particles thus obtained were pre-foamed to a bulk multiple of 60 ml / g, aged for about 18 hours, and then subjected to a molding pressure of 0.08 MPa and a heating time of 15 seconds using a molding machine VS-500 manufactured by Daisen Industry. And molded product thickness 25
A molded product of mm was obtained.

[Example 2]
In Example 1, it carried out like Example 1 except having made cyclohexane 330g.

[Example 3]
In Example 1, in addition to 300 g of butane, 120 g of pentane (iso / normal ratio = 2/8, weight ratio) was added and press-fitted.

[Comparative Example 1]
In Example 1, the same procedure as in Example 1 was carried out except that 60 g of acetylated monoester (Riken Vitamin Co., Ltd., trade name: Riquemal PL-002) was injected and 480 g of butane was further injected without using cyclohexane. It was.

[Comparative Example 2]
In Example 1, it carried out similarly to Example 1 except not using cyclohexane and changing butane to 480g.

[Comparative Example 3]
In Example 1, cyclohexane was not used, 60 g of toluene and 60 g of styrene were injected, and further, butane was changed to 480 g.

Table 1 shows the foamability of the foamable resin particles and the evaluation results of the molded products in Examples 1 to 3 and Comparative Examples 1 to 3. The method for evaluating the characteristics shown in Table 1 is as follows.
(1) Weight average molecular weight It measured by the gel permeation chromatography method on the following conditions, and calculated | required the molecular weight of standard polystyrene conversion.
Column: manufactured by Hitachi Chemical Co., Ltd. Gelpack GL-A100M × 2 eluent: tetrahydrofuran detector: RI detector

(2) Measurement of cyclohexane and readily volatile foaming agent content It measured using the pyrolysis apparatus Nippon Analysis Kogyo's Curie point pyrolyzer JHP-22 type and HITACHI gas chromatography 263-50.
Column: Packed column Unicarbon A-400

(3) Amount of volatile organic compounds (measurement of total amount of toluene, xylene, styrene, ethylbenzene)
This was measured by an internal standard method using a gas chromatography-GC-9A manufactured by SHIMAZU.
Column: Packed column PEG-20MPT
Internal standard: cyclopentanol Solvent: dimethylformamide

(4) Foaming time, amount of blocking generated during foaming The heating time to increase the expansion ratio to 60 ml / g was measured.
In addition, the amount of occurrence of blocking was measured.

(5) Appearance of molded product The appearance of the molded product was visually determined.
○: Good ×: Deformation or shrinkage

(6) Oil resistance test The bottom of the molded product was cut into 100 x 100 mm and used for the test. The test liquid (gasoline or engine oil) was applied, and the state of the surface of the molded article after 168 hours was visually determined.
○: No change △: Swelling or deformation ×: Dissolution

(7) Bending strength A molded product having a density of 0.017 g / ml was measured according to JIS-K-7221.

  The expandable acrylonitrile / styrene resin particles and the foamed molded product of the present invention can be suitably used for packing materials, cushioning materials and the like.

Claims (3)

  The main component is an acrylonitrile / styrene copolymer, 2 to 6% by weight of cyclohexane and 2 to 8% by weight of a readily volatile foaming agent other than cyclohexane, and the amount of volatile organic compounds is 0.1% by weight or less. Some expandable acrylonitrile / styrene resin particles.   2. The expandable acrylonitrile / styrene resin particles according to claim 1, wherein the acrylonitrile / styrene copolymer comprises 10 to 50% by weight of acrylonitrile and 50 to 90% by weight of styrene. A foam molded article obtained by foaming and molding the expandable acrylonitrile / styrene resin particles according to claim 1.