JPH05295160A - Production of expandable styrene resin particle - Google Patents

Abstract

PURPOSE:To obtain the objective particles which can be produced within a short production time and excels in expandability, moldability, molding strengths and surface smoothness. CONSTITUTION:The particles can be produced by suspension-polymerizing a styrene monomer or a mixture thereof with another copolymerizable vinyl monomer in the presence of a polymerization initiator comprising a peroxyketal- type aliphatic organic peroxide and/or a peroxyester-type aliphatic organic peroxide each having a 10-hr half-life decomposition temperature of 80-95 deg.C and adding a blowing agent to the system at a conversion of 90wt.% or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expandable styrenic resin particles used for packing and packaging materials such as fish boxes and home electric appliances. More specifically, it relates to a method for producing expandable styrenic resin particles which is excellent in foamability during pre-expansion, low-pressure steam fusion property of foamed particles during molding, strength of a molded article, and shortening the manufacturing time.

[0002]

2. Description of the Related Art Conventionally, the expandability during pre-expansion and the low-pressure steam fusion property of expanded particles during molding are determined by the molecular weight of the base resin, the kind and content of the foaming agent, the kind and addition of the plasticizer added. It is known to be affected by the amount and so on. The present inventors have conducted various experiments on the timing of press-fitting of the foaming agent,
Polymerization is completed (polymerization conversion 99.5% by weight) by a method in which a foaming agent is pressed in from the initial stage of polymerization or after the particle size is determined and then a method in which a foaming agent is pressed in at a polymerization conversion of 50 to 90% by weight.
It was found that the foaming characteristics of the obtained resin particles and the quality of the molded product are deteriorated as compared with the method of adding the foaming agent after the above). Specifically, as a foaming property, a blocking substance is generated between particles during foaming at the time of pre-foaming, and productivity is reduced. It was also found that the surface of the molded product was easily melted by the heat of steam during molding, and the strength of the resulting molded product was lowered. As a cause of these, it was found that the foaming agent became a chain transfer agent and the molecular weight of the bead surface was lowered. Therefore, in order to improve the productivity in a short production time, there is a demand for a production method capable of obtaining resin particles which do not have the above-mentioned drawbacks even when a foaming agent is pressed in during polymerization.

Further, the type and the amount of the polymerization initiator used are determined in consideration of the target weight average molecular weight (Mw). On the other hand, from the viewpoint of improving the productivity by increasing the utilization rate of the polymerization apparatus, a polymerization initiator that has a high polymerization rate and quickly reaches a desired degree of polymerization is preferable. Therefore, conventionally, based on such an idea, in order to obtain expandable styrenic resin particles by a suspension polymerization method, polymerization is performed using an organic peroxide such as benzoyl peroxide or t-butyl peroxide. In order to increase the speed, it is necessary to increase the concentration of the polymerization initiator, and the degree of polymerization of the obtained resin particles is extremely lowered, and the resin particles have poor utility as a foam molding material. On the other hand, when the concentration of the polymerization initiator is decreased to increase the molecular weight using such a polymerization initiator,
A long polymerization time was required and the productivity was low. As a solution to this, Japanese Patent Laid-Open No. 60-47037 has been proposed. However, the method using the cyclohexane-based peroxyketal disclosed therein has drawbacks such that the molecular weight becomes too high, the foaming rate is lowered, and the fusion property at the time of low temperature / low pressure steam forming is lowered.

[0004]

SUMMARY OF THE INVENTION As described above, an object of the present invention is to perform a pre-foaming step, even if it is produced in a short production time.
It is intended to provide a method for producing expandable styrenic resin particles which has no problem in the molding step and has good molded products.

[0005]

According to the present invention, a styrene-based monomer or a mixture of a styrene-based monomer and another vinyl-based monomer copolymerizable with the styrene-based monomer is used as a polymerization initiator and has a half-life of 10 hours. While carrying out suspension polymerization using a peroxyketal-based and / or alkylperester-based aliphatic organic peroxide having a decomposition temperature of 80 to 95 ° C. for obtaining
The present invention relates to a method for producing expandable styrenic resin particles, which comprises adding a foaming agent at a polymerization conversion rate of 90% by weight or more.

The styrenic monomer used in the present invention includes styrene, α-methylstyrene, chlorostyrene,
Substituted styrenes such as t-butyl styrene may be mentioned. Examples of the monomer copolymerizable with the styrene monomer include acrylic acid or methacrylic acid esters such as acrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate, dimethyl maleate, diethyl fumarate, divinylbenzene. Etc. can be used. The other monomer copolymerizable with the styrene-based monomer may be used alone or in combination of two or more. Styrene is preferred as the styrene-based monomer.
Further, it is preferable that styrene is contained in an amount of 50% by weight or more in all the monomers.

In the method of the present invention, the decomposition temperature for obtaining a 10-hour half-life as a polymerization initiator is 80 to 95 ° C.
And the peroxyketal-based and / or alkylperester-based aliphatic organic peroxide is used. As the peroxyketal-based organic peroxide, a tetrafunctional or higher functional peroxyketal is preferable because of its excellent effect. Above all,
2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane and di-t-butylperoxyhexahydroterephthalate are particularly effective and are used as preferred ones.

The amount of these polymerization initiators to be used is preferably determined in consideration of the target weight average molecular weight.
The weight average molecular weight (Mw) is 2 in order to obtain expandable styrenic resin particles having excellent expandability, moldability and finished product.
30,000 to 30,000, particularly preferably 23,000
Adjust to 0 to 28,000 (measured by gel permeation chromatography). In this case, the best balance of properties can be achieved. When the weight average molecular weight exceeds these ranges, the strength as a base material increases, but sufficient steaming and molding fusion tends not to be obtained under steam heating conditions during ordinary foam molding. On the other hand, when the weight average molecular weight does not reach these ranges, the mechanical properties tend to deteriorate and the low molecular weight material blocks during foaming, and the skin melts in the high temperature part of the mold during molding (so-called). It tends to cause keloids.

For this reason, the decomposition temperature for obtaining a half-life of 10 hours is 80 to 95 ° C.
Alternatively, the total amount of the alkyl perester-based aliphatic organic peroxide used is preferably 0.005 to 0.4% by weight, and particularly preferably 0.01 to 0.3% by weight, based on the total amount of the monomers. 0.0
If it is less than 05% by weight, the weight average molecular weight becomes too large and a long polymerization time is required. On the other hand, 0.
If it exceeds 4% by weight, the weight average molecular weight is too low, and it is economically excessive.

With these polymerization initiators, a 10-hour half-life of benzoyl peroxide, t-butylperoxy (2-ethylhexanoate), etc., which has a lower decomposition temperature than these polymerization initiators, is obtained. An organic peroxide having a decomposition temperature of 72 to 74 ° C. can also be used together. These are appropriately used depending on the molecular weight of the intended resin. When used, the optimum concentration is 0.4% by weight or less, preferably 0.05 to 0.25, based on all monomers.
% By weight. If it exceeds 0.4% by weight, the molecular weight becomes too small, and it is too economically excessive.

In suspension polymerization, a sparingly soluble inorganic substance, a water-soluble polymer protective colloid or the like can be added to the polymerization system as a dispersant. As a water-soluble polymer protective colloid,
There are polyvinyl alcohol, methyl cellulose and the like, and as the poorly soluble inorganic substances, there are calcium phosphate, magnesium pyrophosphate and bentonite. When a sparingly soluble inorganic substance is used as the dispersant, it is preferable to use a small amount of a surfactant such as sodium dodecylbenzenesulfonate. It is preferable that the amount of the sparingly soluble inorganic substance is 0.01 to 1% by weight with respect to water and the amount of the surfactant is 1 to 300 ppm.

The foaming agent used in the present invention has a boiling point lower than the softening point of the resin to be produced and has a property of not dissolving or slightly swelling the vinyl resin particles. It is suitable. Examples of these blowing agents include chain aliphatic hydrocarbons such as propane, butane and pentane, cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane, halogenated methyl chloride and dichlorodifluoromethane. Hydrocarbons and the like can be mentioned. The amount of the foaming agent used is preferably 3 to 12% by weight, particularly preferably 6 to 8% by weight, based on the weight of all the monomers.

Conventionally, when propane, butane, or pentane is used alone or in combination among the above-mentioned foaming agents, it is preferable to use an organic solvent which dissolves the vinyl monomer during impregnation of the foaming agent. won. Examples of such an organic solvent include ethylene dichloride, trichloroethylene, tetrachloroethylene, benzene, toluene, xylene, ethylbenzene, and the like.
Preferably, it was used in an amount of 0.2 to 0.5% by weight based on all the monomers. However, the addition of such a solvent is not preferable from the viewpoint of health and safety. According to the present invention, good foamability and moldability can be obtained without adding an organic solvent. However, there is no problem using these.

In the suspension polymerization in the present invention, for example, the monomer is first suspended in an aqueous medium in the presence of the above-mentioned polymerization initiator, and the polymerization is usually started at 90 to 100 ° C. for 5 to 7 hours. The polymerization can be carried out by advancing the polymerization, and then, when the conversion of the polymerization is 90% by weight or more, preferably 90 to 98% by weight, the foaming agent is pressed into the reaction system to impregnate the foaming agent. Here, if the polymerization conversion rate is less than 90% by weight, sufficient strength cannot be obtained. The press-in temperature of the foaming agent at this time is 10
It is preferably 0 to 115 ° C. Further, it is preferable that the reaction liquid is heated to 100 to 120 ° C. after pressurizing the foaming agent to impregnate the foaming agent and adjust the residual monomer amount at the same time. In this way, the target expandable styrene resin particles are obtained.

According to the method of the present invention, it is possible to obtain a high-strength molded product that is easy to foam and mold, and at the same time, shorten the manufacturing time. That is, conventionally,
In the case of impregnating with a foaming agent during the polymerization, as compared with the case of injecting the foaming agent after the completion of the polymerization, foaming, the molding characteristics were not balanced, and the strength of the molded article was decreased, According to the method (1), even if the foaming agent is pressed in at a polymerization conversion rate of 90 to 98% by weight, a molded product having strength equal to or higher than that obtained by the method for injecting a foaming agent after completion of polymerization can be obtained.
Moreover, at this time, the time required for the synthesis can be shortened by 10% or more (for example, about 2 hours) with respect to the synthesis time (for example, about 18 hours) when the foaming agent is pressed in after the completion of the polymerization, which improves productivity. It is also advantageous in terms.

[0016]

EXAMPLES Examples of the present invention will be described below. The following parts are parts by weight, and% is% by weight. Examples 1 to 6 In 1200 g of water in a 3 L autoclave equipped with a stirrer,
Disperse or dissolve 2 g of tricalcium phosphate, 10 g of 0.5% sodium dodecylbenzenesulfonate aqueous solution and 0.5 g of sodium sulfate, and then add 2 parts of this aqueous solution.
The stirring was carried out at a rotation speed of 70 rpm. 1.2 g of ethylene bisstearic acid amide as a cell diameter adjusting agent and styrene 120 of an organic peroxide shown in Table 1 as a polymerization initiator.
Dispersed and dissolved in 0 g. This styrene solution was added to the autoclave, the atmosphere in the autoclave was replaced with nitrogen, and the autoclave was sealed. Then, from 90 ℃ to 10
The temperature was raised so as to be between 0 ° C., and suspension polymerization was started at that temperature. After polymerization for 1.5 to 2 hours, 0.05 g of tricalcium phosphate was added to the reaction solution. Further, when the polymerization conversion rate reached 95%, 5 g of tricalcium phosphate was added, the temperature was raised to 105 ° C. over 40 minutes, and 24 g of cyclohexane and 84 g of butane were injected under pressure for 1 hour. Then, it heated up to 115 degreeC over 40 minutes, and hold | maintained at that temperature for 2 hours and 30 minutes. After that, it was cooled to 30 ° C. over 2 hours to obtain expandable polystyrene particles.

Comparative Examples 1 to 4 Organic peroxides other than peroxyketal-based and / or alkylperester-based aliphatic organic peroxides having a decomposition temperature of 80 to 95 ° C. for obtaining a half-life of 10 hours were used. Other than that, the manufacturing was performed in the same manner as in Example 1.

Evaluation and Production of Molded Article The total volatile molecular weight of the obtained particles was measured by weighing 2 g of the sample in an aluminum dish and heating at 180 ° C. for 10 minutes.
{(Weight of sample before heating)-(weight of sample after heating)} /
(Weight of sample) × 100. Also,
The weight average molecular weight and the number average molecular weight were determined by the GPC method.

The expandable polystyrene particles were immersed in boiling water at 100 ° C. for the heating time shown in Table 1 to obtain pre-expanded particles. The specific volume, blocking amount, and presence / absence of contraction (visual observation) of the pre-expanded particles were measured and are shown in Table 1. The pre-expanded particles were packed in a graduated cylinder having a specific volume of 1000 ml, the weight was measured, and the volume / weight was determined.
In addition, 500 g of the pre-expanded particles obtained were blocked.
The shrinkage (y) of the expanded particles is represented by the weight of the blocked particles, y = [(ab) / a] × 100 (%) (where a is after recovery (about 24 after pre-expansion). The volume (ml) after a lapse of time (ml) and b were measured by the volume (ml) immediately after pre-foaming, and the presence or absence of shrinkage is shown in Table 1.

Further, the pre-expanded particles were aged in air at 25 ° C. for 24 hours, and VS heating was performed for 3 seconds using a reduced pressure cooling type molding machine (Diasen Industrial Co., Ltd., Dia VS-300 molding machine). 1; 3 seconds, heating 2; 7 seconds, water cooling 10 seconds,
Allowing to cool for 300 seconds, heating steam pressure is 0.7 kgf / cm
^{Under two} conditions of ² and 1.0 kgf / cm ² , the size is 552 mm length × 335 mm width × 150 mm height, wall thickness 50
A mm-shaped box-shaped molded product was molded. Heating steam pressure 0.
A molded product molded at 7 kgf / cm ³ is divided into
The ratio of cracks in the particles themselves, not in the interfaces between the particles, was evaluated as the internal fusion rate. Heating steam pressure 1.0kgf /
The degree of melting and smoothness of the surface of the molded product molded by cm ³ were visually determined, and a bending strength test (density 0.0166 g / ml) according to JIS-A-9511 was performed. The above results are shown in Table 1.

[0021]

[Table 1]

[0022]

According to the production method of the present invention, expandable styrenic resin particles having good foamability, moldability, molded product strength and surface smoothness can be obtained in a short production time.

Claims (6)

[Claims] 1. A decomposition temperature for obtaining a 10-hour half-life as a polymerization initiator using a styrene-based monomer or a mixture of another vinyl-based monomer copolymerizable with a styrene-based monomer as a decomposition temperature is 80 to Suspension polymerization is performed using a peroxyketal-based and / or alkylperester-based aliphatic organic peroxide at 95 ° C., and the polymerization conversion rate is 90% by weight.
A method for producing expandable styrenic resin particles, which comprises adding a foaming agent as described above. 2. As a polymerization initiator, 2,2-bis (4,4) is used as a peroxyketal-based aliphatic organic peroxide having a decomposition temperature of 80 to 95 ° C. for obtaining a 10-hour half-life. -Di-t-butylperoxycyclohexyl)
The method for producing expandable styrenic resin particles according to claim 1, wherein propane is used. 3. As a polymerization initiator, di-t-butylperoxyhexahydro as an alkyl perester-based aliphatic organic peroxide having a decomposition temperature of 80 to 95 ° C. for obtaining a 10-hour half-life. The method for producing expandable styrenic resin particles according to claim 1, wherein terephthalate is used. 4. A peroxyketal-based and / or alkylperester-based aliphatic organic peroxide having a decomposition temperature of 80 to 95 ° C. for obtaining a 10-hour half-life is used in all monomers. It is 0.005-0.4 weight% with respect to the manufacturing method of the foamable styrene resin of Claim 1, 2 or 3. 5. The expandable styrenic resin according to claim 1, 2, 3 or 4, wherein an organic peroxide having a decomposition temperature of 72 to 74 ° C. for obtaining a 10-hour half-life is also used as a polymerization initiator. Particle manufacturing method. 6. A peroxyketal-based and / or alkylperester-based aliphatic organic peroxide having a decomposition temperature of 80 to 95 ° C. for obtaining a 10-hour half-life is used in all monomers. 0.005 to 0.4% by weight,
The expandable styrenic resin according to claim 5, wherein the amount of the organic peroxide having a decomposition temperature of 72 to 74 ° C. for obtaining a 10-hour half-life is 0.4% by weight or less based on all monomers. Particle manufacturing method.