JP4424634B2 - Expandable resin particles and foamed molded products - Google Patents

Description

【００３７】
【発明の効果】
本発明により、ポリスチレン換算重量平均分子量が１５万を越える高分子量樹脂粒子でも良好な発泡性を示し、易揮発性発泡剤の保持性もよく、また、得られる成形品の強度も強い発泡性樹脂粒子が提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an expandable resin particle and an expanded molded product thereof. More specifically, the present invention relates to an expandable resin particle having good retention of a readily volatile foaming agent and having a molded article using resin particles having high strength, and an expanded molded article obtained using the same.
[0002]
[Prior art]
Currently, wooden boxes for container use are used in all fields of the industry, but demand is limited because of the constraints of the protection of wood resources and the balance with characteristics such as production cost, weight, and thermal insulation. is decreasing. Various plastic containers are used as an alternative material, but the present situation is that the disposal depends on incineration. In addition, the plastic box has a high combustion heat amount of about 10,000 cal / g, which has the problem of damaging the incinerator. Furthermore, polystyrene-based resins generate black smoke during natural combustion, which has an environmental problem.
[0003]
As a solution to this problem, a polypropylene-based resin blended and filled with an inorganic substance has been proposed. This reduces the combustion heat per unit weight, but tends to lower the combustion efficiency as a molded product with the same function. There was also an environmental problem due to the increase in ash content. Therefore, regarding incineration of molded products, methyl methacrylate is the main component as expandable resin particles that do not generate black smoke, resin residue, ash, etc., are low in calories burned, and exhibit a combustion form similar to wood. Various thermoplastic resin particles have been proposed.
[0004]
As a method for producing thermoplastic resin particles mainly composed of methyl methacrylate, a vinyl polymer having a low homopolymer glass transition temperature and copolymerization has been conventionally used to improve foamability in addition to methyl methacrylate monomer. A method is employed in which a monomer is subjected to suspension polymerization in an aqueous medium to which an organic or inorganic dispersant is added. In addition, the molecular weight modifier at this time is usually added only once together with the methyl methacrylate monomer and the copolymerizable vinyl monomer when the polymerization rate is 0% or more and less than 25%.
[0005]
When the methyl methacrylate monomer is polymerized alone by the above suspension polymerization method, the polydispersity (Mw / Mn Mw: weight average molecular weight, Mn: number average molecular weight) determined from the polystyrene equivalent molecular weight is 2. In order to obtain resin particles having good foamability due to a decrease in resin fluidity around 0, it is necessary to reduce the weight average molecular weight to about 100,000. It is also already known to impregnate polymer particles thus obtained with a readily volatile foaming agent to obtain thermoplastic resin particles mainly composed of foamable methyl methacrylate. However, the molded article thus obtained has a problem that it becomes a very brittle foamed molded article.
[0006]
In the above-mentioned suspension polymerization method, in order to improve foamability, homopolymers having low glass transition temperature and copolymerizable vinyl monomers are copolymerized. Methacrylic acid esters such as n-butyl methacrylate, i-butyl methacrylate, 2-ethylhexyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate and the like. Some thermoplastic resin particles mainly composed of methyl methacrylate produced by copolymerization of these methacrylic acid esters have improved foaming properties and can provide good molded products.
[0007]
However, although the thermoplastic resin particles have improved foamability, they have the disadvantage that the retention of the easily volatile foaming agent is poor and the foaming power decreases in a short time. Furthermore, there is a disadvantage that the bending strength of the molded product when formed into a molded product is considerably inferior to that of a molded product using general-purpose polystyrene resin particles.
[0008]
[Problems to be solved by the invention]
As a result of diligent examination of the above problems, the present inventors showed good foamability even with high molecular weight resin particles having a polystyrene-equivalent weight average molecular weight exceeding 150,000, good retention of easily volatile foaming agents, and An object of the present invention is to provide expandable resin particles having a strong molded product using resin particles and a foam molded product using the same.
[0009]
[Means for solving problems]
The present invention is copolymerized by suspension polymerization in a proportion of 85 to 97 wt% of methyl methacrylate and acrylonitrile 3-15 wt%, a foamable resin particles containing a volatile blowing agent, the foamable resin particles The polystyrene-reduced weight average molecular weight is 150,000 to 500,000, and the polydispersity (Mw / Mn, Mw: weight average molecular weight, Mn: number average molecular weight) determined from the polystyrene equivalent molecular weight is 3.0 or more and 7.0 or less . It is an object of the present invention to provide expandable resin particles and a foam molded product using the same.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In general, suspension polymerization is performed by dispersing a vinyl monomer in which an organic peroxide is dissolved as a polymerization initiator in an aqueous dispersion medium containing a dispersant. In the present invention, methyl methacrylate is similarly used. Suspension polymerization is carried out by mixing 85 to 97% by weight and 3 to 15% by weight of acrylonitrile.
The methyl methacrylate in the present invention may be a copolymer of a vinyl monomer copolymerizable with methyl methacrylate. Examples of the copolymerizable vinyl monomer include methacrylic acid esters such as n-butyl methacrylate, i-butyl methacrylate and 2-ethylhexyl methacrylate, and acrylic acid such as n-butyl acrylate and 2-ethylhexyl acrylate. Examples include esters.
In the present invention, the polydispersity of 3.0 or more and 7.0 or less is obtained by selecting the polymerization temperature, the kind and amount of the polymerization initiator, the composition of the monomer, the addition timing of the chain transfer agent, the amount of use thereof, and the like. be able to.
[0011]
As the polymerization initiator used in the present invention, a conventionally known organic peroxide having a decomposition temperature (10 hour half-life temperature) of 110 ° C. or less can be applied. Such organic peroxides include octanoyl peroxide (62 ° C), lauroyl peroxide (62 ° C), stearoyl peroxide (62 ° C), benzoyl peroxide (74 ° C), t-butylperoxy-2ethylhexa Noate (72 ° C), bis (t-butylperoxy) trimethylcyclohexane (90 ° C), bis (t-butylperoxy) cyclohexane (91 ° C), t-butylperoxybenzoate (105 ° C), t-butyl Examples include peroxyisopropyl carbonate (97 ° C.). These organic peroxides are preferably used in an amount of 0.3 to 0.6% by weight based on the total amount of monomers.
These organic peroxides can usually be used in combination of two or more kinds in order to obtain copolymer particles having a high polymerization rate.
[0012]
The polymerization temperature in the present invention is preferably from 50 to 110 ° C., more preferably from 60 to 95 ° C., from the polymerization rate. The polymerization time is determined by the type and amount of the polymerization initiator, the composition of the monomer, the polymerization temperature, the timing of addition of the chain transfer agent and the amount used, and is usually 4 to 7 hours.
[0013]
As the dispersant used in the suspension polymerization, those conventionally used widely as dispersants can be applied. This includes water-soluble cellulose derivatives such as polyvinyl alcohol, alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose, water-soluble polymers such as sodium polyacrylate and polyvinyl pyrrolidone, and difficulties such as tricalcium phosphate and magnesium phosphate. There are soluble inorganic substances. The water-soluble polymer is preferably added in an amount of 0.05 to 1% by weight relative to the total amount of monomers, and the sparingly soluble inorganic substance is preferably added in an amount of 0.05 to 0.5% by weight.
[0014]
Further, an anionic surfactant such as sodium dodecylbenzenesulfonate can be added as a dispersion aid. This is preferably used in combination when a hardly soluble inorganic substance is used as a dispersant. The amount used is preferably 0.001 to 0.02% by weight based on the total amount of monomers.
[0015]
In addition, an electrolyte such as sodium chloride, sodium sulfate, sodium hydrogen sulfite, sodium carbonate, sodium hydroxide, sodium hydrogen carbonate or the like may be added to the aqueous medium in order to adjust the particle size of the polymer obtained in suspension polymerization. it can. The amount of electrolyte used is preferably 0.001 to 1% by weight based on the total amount of monomers.
[0016]
The polystyrene equivalent weight average molecular weight of the resin particles according to the present invention is 15 to 500,000 . If the weight average molecular weight is less than 150,000, the strength of the foamed molded product tends to be inferior, and if it exceeds 500,000, it tends to be difficult to obtain sufficiently high foamability.
[0017]
The polymerization rate in the present invention is generally determined by the selection of the polymerization temperature and the type of organic peroxide, but is preferably 95% or more.
[0018]
Further, in the present invention, it is preferable to add the chain transfer agent by dividing it at least twice in the suspension polymerization step.
[0019]
In the present invention, the chain transfer agent is added at least once when the polymerization rate is 0% or more and less than 25% in the polymerization step, and at least once when the polymerization rate is 25% or more and 65% or less. It is preferable.
[0020]
In the present invention, the total amount of chain transfer agent to be added when the polymerization rate is 25% or more and 65% or less in the polymerization step is the amount of chain transfer agent added when the polymerization rate is 0% or more and less than 25%. It is preferable to increase the weight ratio by 5 times or more.
[0021]
As the chain transfer agent used in the present invention, sulfur compounds such as t-dodecyl mercaptan and n-octyl mercaptan, alphamethylstyrene dimer, and the like can be applied. The amount of chain transfer agent added at the initial stage of polymerization is preferably 0.01 to 0.1% by weight, more preferably 0.015 to 0.05% by weight, based on the total amount of monomers. . The amount of chain transfer agent added when the polymerization rate is 25% or more and 65% or less is preferably 0.05 to 0.7% by weight, more preferably 0.15%, based on the total amount of monomers. ˜0.5 wt%.
[0022]
For the impregnation of the foaming agent into the resin particles in the present invention, the formulation generally used for expandable styrene resin particles can be applied as it is. As the foaming agent that can be used, a readily volatile organic compound that is liquid or gas at normal temperature and normal pressure and does not dissolve the resin composition can be used. Such as aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane, cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane, methyl chloride, ethyl chloride, trichlorotrifluoroethane, dichloromethane. And halogenated aliphatic hydrocarbons such as difluoroethane.
[0023]
The amount of these volatile foaming agents used is preferably in the range of 4 to 10% by weight with respect to the polymer because of foamability. The impregnation of the polymer particles with the easily volatile foaming agent can be performed during the polymerization or after the completion of the polymerization. In the middle of the polymerization, the polymerization rate is 50% or more, preferably 70% or more. The impregnation under suspension polymerization is preferably performed at 90 to 130 ° C.
[0024]
A plasticizer can be present during the impregnation of the readily volatile blowing agent into the polymer. As the plasticizer, an organic solvent capable of dissolving or swelling the polymer can be used, and the boiling point thereof is preferably a temperature not lower than about 10 ° C. and not higher than 150 ° C. below the softening point of the polymer.
[0025]
Examples of plasticizers include aromatic hydrocarbons such as ethylbenzene, toluene, styrene, benzene and xylene, halogenated hydrocarbons such as 1,2-dichloropropane and trichloroethylene, dioctyl adipate, dioctyl phthalate, dibutyl sebate, butyl stearate, Examples include epoxidized soybean oil and vegetable oil. The plasticizer is preferably used in an amount of 0.5 to 6% by weight based on the polymer.
[0026]
The resin particles according to the present invention are impregnated with a foaming agent, dehydrated and dried, and then coated with various additives.
In the foaming process of the present invention, an agglomeration inhibitor can be used to prevent agglomeration in primary foaming. Examples of the agglomeration inhibitor include silicones, metal soaps such as zinc stearate and calcium stearate, and higher fatty acid amides such as ethylene bisamide and stearic acid amide. The agglomeration inhibitor is preferably used in an amount of 0.05 to 0.5% by weight based on the expandable resin particles.
In the molding process, a fusion accelerator can be used to improve the fusion of the resin particle body. Examples of the fusion promoter include triesters, diesters, monoesters, sucrose esters, castor oil and the like of higher fatty acids such as stearic acid triglyceride and oleic acid glyceride. The fusion accelerator is preferably used in an amount of 0.005 to 0.2% by weight based on the expandable resin particles.
[0027]
Coating of these additives on the resin particles is not particularly limited and can be performed by a conventionally known means. For example, it can be performed by a riboblender, a V-type blender, a Henschel mixer, a Redige mixer, or the like.
[0028]
Foaming of the expandable resin particles according to the present invention is performed with water vapor, hot air, hot water or the like. As the method, the foaming method of styrene resin widely used in industry can be applied as it is.
[0029]
Molding of the expandable resin particles according to the present invention can be performed by a conventional method of molding a styrenic resin, in which pre-expanded particles are fed into a closed mold and heated or decompressed.
[0030]
The foam obtained from the expandable resin particles according to the present invention exhibits good foamability, good retention of a readily volatile foaming agent, and a foam molded article using the foam has high strength.
[0031]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
[Example 1]
<Polymerization reaction>
In a 16 liter autoclave attached to a stirrer, 8000 g of pure water, 8.0 g of tricalcium phosphate, 0.12 g of sodium dodecylbenzenesulfonate, and 0.40 g of sodium hydrogen sulfite were charged while stirring at 200 rpm. Subsequently, 3800 g of methyl methacrylate, 200 g of acrylonitrile, 26.7 g of benzoyl peroxide (manufactured by NOF Corporation: NIPPER B), t-butyl peroxyisopropyl carbonate (manufactured by NOF Corporation: perbutyl I) 2 while stirring in the same manner. 0.0 g, 1.6 g of n-octyl mercaptan (manufactured by Kao Corporation: thiocalcol 08) were mixed and dissolved, purged with nitrogen gas, and heated to 60 ° C.
After 2.5 hours of completion of temperature increase, 4.0 g of tricalcium phosphate was added. Next, the mixture was kept at 60 ° C. for 1.3 hours, and when the polymerization rate reached about 50%, 1-6.0 g of n-octyl mercaptan was added, and the mixture was further kept for 2 hours, followed by 4.0 g of tricalcium phosphate and dodecyl. 0.20 g of sodium benzenesulfonate was added. Subsequently, the temperature was kept at 90 ° C. for 5 hours to complete the polymerization reaction.
[0032]
<Impregnation of foaming agent>
After completion of the polymerization, 6.0 g of tricalcium phosphate was added, and then the temperature was raised to 110 ° C. In a state where the temperature was kept at 110 ° C., 280 g of butane as a blowing agent was press-fitted and further kept for 8 hours, and then cooled to room temperature and taken out from the autoclave.
<Post-processing>
After the taken-out slurry was washed, dehydrated and dried, particles having a particle size between 18 mesh and 36 mesh were collected to obtain 3630 g of resin particles. To the obtained resin particles, 0.73 g of dimethyl silicone, 5.45 g of zinc stearate, and 2.36 g of castor hydrogenated oil were sequentially added and mixed to coat the surface, thereby obtaining expandable resin particles.
<Foam molding>
The obtained expandable resin particles were pre-foamed with a small pre-foaming machine using steam as a heat medium so that the bulk density was 0.03 g / ml, and aged for 1 day, and then a polystyrene foam molding machine (Daisen CVS). -300), a box-shaped product was obtained at a steam pressure of 0.07 MPa.
[0033]
<Evaluation>
Table 1 shows the molecular weight (polystyrene equivalent weight average molecular weight, polydispersity), foaming degree, bending strength and appearance of the molded product of the obtained expandable resin particles. The physical properties were measured according to the following method.
Molecular weight: Measured by gel permeation chromatography (GPC).
Foaming degree: Expressed by the expansion ratio (ml / g) when held in boiling water for 3 minutes when the amount of volatile components of the foamable resin particles was 8.0% by weight.
Molded product bending strength: The test method conformed to JIS-K-7221.
Molded product appearance: visually.
[0034]
[Comparative Examples 1 and 2]
As shown in Table 1, suspension polymerization and impregnation with a blowing agent were carried out in the same manner as in Example 1 except that the composition of the monomer was changed. The test results are shown in Table 1.
[0035]
[Comparative Example 3]
<Polymerization reaction>
In a 16 liter autoclave attached to a stirrer, 8000 g of pure water, 8.0 g of tricalcium phosphate, 0.12 g of sodium dodecylbenzenesulfonate, and 0.40 g of sodium hydrogen sulfite were placed while stirring at 200 rpm. Subsequently, 3800 g of methyl methacrylate, 200 g of acrylonitrile, 26.7 g of benzoyl peroxide (manufactured by Nippon Oil & Fats Co., Ltd .: Nyper B), t-butyl peroxyisopropyl carbonate (manufactured by Nippon Oil & Fats Co., Ltd .: perbutyl I) 2 while stirring similarly 0.0 g, n-octyl mercaptan (Kao Co., Ltd .: Thiocalcol 08) (4.0 g) was mixed and dissolved, purged with nitrogen gas, and heated to 60 ° C.
Two hours after completion of the temperature increase, 4.0 g of tricalcium phosphate was added. After keeping the temperature for 2.5 hours, 4.0 g of tricalcium phosphate and 0.20 g of sodium dodecylbenzenesulfonate were added. Subsequently, the temperature was kept at 90 ° C. for 5 hours to complete the polymerization reaction. After impregnation with the foaming agent, the same procedure as in Example 1 was performed. As a result, only expanded particles having a low expansion degree were obtained.
[0036]
[Table 1]

[0037]
【The invention's effect】
According to the present invention, a foamable resin which exhibits good foamability even with high molecular weight resin particles having a polystyrene-equivalent weight average molecular weight exceeding 150,000, has good retention of a readily volatile foaming agent, and has a strong molded product. Particles are provided.

Claims (3)

Expandable resin particles copolymerized by suspension polymerization in a proportion of 85 to 97% by weight of methyl methacrylate and 3 to 15% by weight of acrylonitrile and containing a readily volatile foaming agent,
The polystyrene equivalent weight average molecular weight of the expandable resin particles is 150,000 to 500,000,
A foamable resin particle having a polydispersity (Mw / Mn, Mw: weight average molecular weight, Mn: number average molecular weight) determined from a polystyrene-equivalent molecular weight of 3.0 or more and 7.0 or less.   2. The expandable resin particles according to claim 1, wherein the readily volatile foaming agent is an aliphatic hydrocarbon, and the content thereof is 4% by weight or more and less than 10% by weight.   A foam molded product obtained by using the expandable resin particles according to claim 1.