JPH11228727A - Expandable styrene-based resin particle and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an expandable styrene-based resin particle having excellent expansability at low temperatures and to provide a method of preparing the same. SOLUTION: An expandable styrene-based resin particle is prepared from a styrene-based resin particle with an average particle diameter of 0.2-1.2 mm and a weight average molecular weight of 1,50, 000-500,000 at a foam initiating temperature of 50-70 deg.C and a maximum foaming temperature of 80-110 deg.C and contains 3-10 wt.% of a blowing agent based on an aliphatic hydrocarbon of 5 or fewer carbons having a side chain. The styrene-based resin particle is preferably a styrene-based polymer or a copolymer of styrene, an acrylate and/or a methacrylate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expanded styrene resin particles having excellent expandability at low temperatures and a method for producing the same.

[0002]

2. Description of the Related Art Styrofoam, which has excellent heat insulating properties, economy, hygiene and the like, has been widely used as foam plastic used for food containers and packing cushioning materials. Since the production process of styrofoam includes various processes using heat, such as pre-foaming, molding, and drying, improvement of thermal efficiency and energy saving measures relating to these processes are indispensable. In particular, in the foaming and molding steps, there is a demand for a low-temperature foamable styrene-based resin having excellent foamability at low temperatures. Normally, commercially available expandable styrene resin particles are premised on using steam as a heat medium, and therefore, a material suitable for foaming at 100 ° C. or higher is used.

Conventionally, methods for imparting higher foaming properties at low temperatures include a method of reducing the molecular weight of styrene-based resin particles, the addition of a plasticizer for the purpose of lowering the apparent glass transition point, and a method of lowering the glass transition point. It has been common to copolymerize with a monomer having an effect of causing such an effect.

The weight average molecular weight supplied to the expandable styrene resin particles is about 15 to 300,000. If the weight average molecular weight is less than this, the strength of a styrene molded article is low, so that it is not general and has a sufficient strength. It was difficult to exhibit excellent foaming properties at a low temperature, which is the object of the present invention, in a molecular weight within the range of obtaining.

In the method of imparting low-temperature foaming properties by adding a plasticizer, not only is it difficult to obtain sufficient low-temperature foaming properties due to the difference in compatibility, but also the balance between the softening of the resin and the escape rate of the foaming agent. And it is difficult to obtain low-temperature expandable expandable styrene resin particles that can withstand practical use.

For the above reasons, as a method for foaming styrene resin particles at a low temperature, a method has been proposed in which styrene is used as a base material and a monomer for lowering the glass transition point is copolymerized therewith. For example, Japanese Patent Publication No. 46-42
No. 2236 and Japanese Patent Application Laid-Open No. 60-156736, that by using styrene-acrylate copolymerization to lower the glass transition temperature, a good molded product can be obtained with a smaller amount of a foaming agent, or It is disclosed that foam molding can be performed at a low temperature. However, in this polymerization method, not only sufficient low-temperature foaming property cannot be obtained, but also
Since it is difficult to form stable oil droplets during aqueous suspension polymerization, it is difficult to obtain resin particles having a targeted particle size range in high yield. In addition, a general foaming agent has a problem that it is difficult to obtain industrially stable foamability.

[0007]

Therefore, the present invention shows excellent foaming performance with hot water, because energy can be saved from a difference in heat capacity by using hot water as a heat medium.
Another object of the present invention is to provide expandable styrene-based resin particles having a long performance expression period to the market more economically.

[0008] In giving low-temperature foaming performance to the expandable styrene resin particles, an acrylate ester and / or
The composition for efficient expression of low-temperature foaming properties by a copolymer with methacrylic acid ester and methacrylic acid ester, to obtain selectively the desired particle size range in high yield, and to remove the blowing agent from the copolymer The challenge is to provide a property with less scattering.

The present inventors have conducted intensive studies, and as a result, it has been found that styrene and acrylate and / or methacrylate mixed in a predetermined amount are impregnated with specific styrene-based resin particles as a nucleus, and that polymerization is carried out. By impregnating a foaming agent mainly composed of an aliphatic hydrocarbon having 5 or less carbon atoms having a side chain in the latter half or after completion of polymerization, a low-temperature foamable copolymer can be obtained more effectively and more economically. This led to the present invention.

[0010]

According to the present invention, styrene resin particles having an average particle diameter of 0.2 to 1.2 mm and a weight average molecular weight of 150,000 to 500,000 are used. Blowing agent 3 to 5 or less containing aliphatic hydrocarbon as a main component
The present invention relates to expandable styrene resin particles containing 10% by weight, having a foaming start temperature of 50 to 70 ° C and a maximum foaming temperature of 80 to 110 ° C.

In the present invention, the styrene-based resin particles are preferably styrene-based resin particles or styrene-based resin particles which are copolymers with styrene, acrylates and / or methacrylates.

The present invention also provides a method of dispersing expandable styrene resin particles having an average particle diameter of 0.33 to 0.9 times the average particle diameter of the styrene resin particles in an aqueous dispersion medium containing no foaming agent. When copolymerized resin particles are obtained by impregnating and polymerizing a monomer of styrene and an acrylic acid ester or / and a methacrylic acid ester, the number of carbon atoms having a side chain is 5 or less after or after the completion of the polymerization. The present invention relates to a method for producing expandable styrenic resin particles impregnated with a foaming agent containing an aliphatic hydrocarbon as a main component.

[0013]

Next, expandable styrene resin particles of the present invention and a method for producing the same will be described. In the present invention, first, styrene-based resin particles are used as nuclei and polymerized while impregnating styrene with an acrylate or / and methacrylate to produce copolymer resin particles. The styrene-based resin particles serving as a core here are styrene homopolymer or a copolymer containing styrene as a main component, and the particle diameter is 0.1% of the target expandable styrene-based resin particle diameter.
Those having a particle diameter of 33 to 0.9 times are used. The polymerization method and the granulation method are not particularly limited, but spherical polymer particles obtained by suspension polymerization are preferable, and it is preferable that the particle size is previously adjusted by classification or the like.

The impregnation and polymerization in the present invention are carried out in an aqueous dispersion medium containing a dispersant. As the dispersant, one or more of conventionally known dispersants such as poorly soluble inorganic compounds such as calcium phosphate and calcium carbonate, and organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone, carboxymethylcellulose, and hydroxyethylcellulose can be used. .

The acrylate and / or methacrylate, which are copolymer components in the present invention, are selected from monomers that copolymerize with styrene to lower the glass transition temperature as compared with styrene homopolymer. Examples of such a monomer include acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate and 2-ethylhexyl acrylate, and methacrylates such as butyl methacrylate and 2-ethylhexyl methacrylate. is there. These copolymer compositions have a content of 10 to 90 with respect to the monomers to be impregnated and polymerized.
It is preferably selected from the range of weight%.

In the present invention, the ratio between the styrene resin particles and the monomer to be impregnated and polymerized is determined by the target particle size and the particle size of the nucleus.
The amount of the core particles is preferably 5 to 60% by weight. 5
If it is less than the weight%, stable control of the particle size is difficult,
Even if low-temperature foaming properties can be imparted, there is a tendency that there is a problem in strength and dissipation of the foaming agent, and if it exceeds 60% by weight, it tends to be difficult to impart sufficient low-temperature foaming properties.

The polymerization temperature in the present invention is determined from the decomposition temperature of the organic peroxide used and the boiling point of the monomer.
The temperature is preferably in the range of 0 ° C to 120 ° C. Possible organic peroxides include lauroyl peroxide, benzoyl peroxide, t-butyl peroxy benzoate, t-butyl peroxy isopropyl carbonate, and the like.

The average particle diameter of the styrene resin particles in the present invention is 0.2 to 1.2 mm, and 0.3 to 1.2 m
m is preferred. If the average particle diameter is less than 0.2 mm, it is difficult to impart sufficient foaming properties,
If it exceeds m, coalesced particles are likely to be generated during the synthesis, and it is difficult to obtain a target yield. The weight average molecular weight of the styrene resin particles in the present invention is 150,000 to 500,000 in terms of polystyrene, and the weight average molecular weight is preferably 100,000 to 500,000. When the weight average molecular weight is less than 150,000, it is difficult to obtain sufficient strength as a foam, and when it exceeds 500,000, it becomes difficult to impart low temperature foamability.

As the blowing agent used in the present invention, an aliphatic hydrocarbon having a side chain and having 5 or less carbon atoms such as isobutane and isopentane is used as a main component. The foaming agent is contained at 3 to 10% by weight. If the amount of the foaming agent is less than 3% by weight, it is difficult to impart sufficient foaming properties, and if the amount of the foaming agent exceeds 10% by weight, the plasticity becomes strong, resulting in problems such as generation of irregular shapes and united particles. is there. The foaming temperature in the present invention is such that the foaming start temperature is 50 to 70 ° C and the maximum foaming temperature is 80 to 110 ° C. Foaming start temperature is 5
If the temperature is lower than 0 ° C., there is a problem that the styrene resin cannot be softened and foaming does not start. If the temperature exceeds 70 ° C., the styrene resin has a problem that the softening becomes large and the styrene resin shrinks. If the maximum foaming temperature is lower than 80 ° C., there is a problem that good foamability cannot be imparted. If the maximum foaming temperature exceeds 110 ° C., there is a problem that the foamed particles themselves shrink and cannot impart good foamability.

As the foaming aid in the present invention, plasticizers such as hydrocarbons having 6 or more carbon atoms, aromatic hydrocarbons, 2-ethylhexyl adipate (DOA), 2-ethylhexyl phthalate (DOP), and epoxidized soybean oil are used. It can be used as appropriate.

The low-temperature expandable styrene resin particles according to the present invention are preferably coated with a surface coating agent. As the surface coating agent, conventionally known coating agents such as metal soaps and fatty acid amides for the purpose of preventing solidification at the time of prefoaming, glycerides for promoting heat fusion, and antistatic agents can be applied.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.
In addition, the measurement of the physical property was performed by the following method. Quantitative method of residual monomer: Bubbling agent content by gas chromatography method: Measuring method of foaming onset temperature and maximum foaming temperature by pyrolysis gas chromatograph method: Thermal decomposition analyzer (TMA, Seiko) The heating rate was 10 ° C./min, and the measurement range was 30 to 170 ° C. Foaming performance in hot water: Foamable polystyrene resin particles were put into a water bath at 80 ° C, foamed, dried, and the density was measured.

[0023]

Example 1 <Preparation of Step 1 dispersion> In a 2 liter beaker, 1,000 g of pure water in which 3.0 g of polyvinyl alcohol (PVA KH-20 manufactured by Nippon Synthetic Chemical Co., Ltd.) was dissolved
Then, 450 g of styrene and 150 g of butyl acrylate in which 3.0 g of benzoyl peroxide and 0.5 g of t-butyl perbenzoate were dissolved were added, and the mixture was dispersed with a homomixer to prepare a dispersion. <Step 2-1 Suspension Polymerization> A 3-liter autoclave equipped with a stirrer was charged with 600 g of pure water, 6 g of tricalcium phosphate as a dispersant, and 400 g of polystyrene particles (average diameter 0.28 mm, high pace 7SB manufactured by Hitachi Chemical Co., Ltd.), and 85
The temperature was raised to ° C. After the temperature was raised to 85 ° C., 12 g of a 1% by weight aqueous solution of dodecylbenzenesulfone soda was added, and subsequently, the monomer dispersion prepared in Step 1 was added dropwise over 240 minutes to carry out impregnation and polymerization. After completion of the dropwise addition, the temperature was further maintained for 1 hour at the same temperature, and then the temperature was raised to 115 ° C. and maintained for 3 hours to complete the polymerization. <Step 2-2 Impregnation with foaming agent>
After cooling to 0 ° C, isobutane 8% by weight was injected,
It was kept warm for another 5 hours. After the completion of the heat retention, the mixture was cooled to 30 ° C. and taken out of the autoclave. <Step 3 Post-treatment> The obtained slurry is washed, dehydrated,
Through a drying step, low-temperature expandable styrene-based copolymer particles 10
50 g were obtained. To 1000 g of the obtained copolymer particles, 1.0 g of zinc stearate and 1.0 g of stearic amide were mixed and coated. <Evaluation (1)> The properties of the obtained low-temperature expandable styrene resin were as follows. Residual monomer amount: 0.31% by weight, weight average molecular weight: 280,000 Isobutane content: 6.3% by weight, average particle diameter 0.37 mm <Evaluation (2)> Evaluation of low-temperature foaming properties revealed a thermomechanical analysis. Foaming start temperature and maximum foaming temperature are 56
° C and 103 ° C. Further, the bulk density of the foamed particles when kept in warm water at 80 ° C. for 10 minutes was 0.05 g / ml.

[0024]

Example 2 In the preparation of the dispersion of Step 1 in Example 1, 300 g of styrene and 3 parts of butyl acrylate were used.
Low-temperature expandable styrene resin particles were prepared in the same manner as in Example 1 except that the amount was changed to 00 g. Table 1 shows the evaluation results.

[0025]

Comparative Example 1 Expandable styrene resin particles were prepared in the same manner as in Example 1 except that the whole amount was suspension-polymerized with styrene alone without using butyl acrylate in the preparation of the dispersion in Step 1 in Example 1. did. Table 1 shows the evaluation results.

[0026]

Comparative Example 2 Expandable styrene resin particles were produced in the same manner as in Example 1 except that 850 g of styrene and 150 g of butyl acrylate were copolymerized by suspension polymerization without using core particles. Table 1 shows the evaluation results.

[0027]

Comparative Example 3 Expandable styrene resin particles were prepared in the same manner as in Example 1 except that normal butane was used as the blowing agent. Table 1 shows the evaluation results.

[0028]

[Table 1]

[0029]

The expanded styrenic resin particles of the present invention can save energy due to the difference in heat capacity by using hot water as a heat medium, exhibit excellent foaming performance with hot water, and have a long period of exhibiting the performance. In addition, the expandable styrene resin particles can be marketed more economically.

Claims (3)

[Claims] 1. An aliphatic hydrocarbon having a side chain of 5 or less carbon atoms using styrene resin particles having an average particle diameter of 0.2 to 1.2 mm and a weight average molecular weight of 150,000 to 500,000. Containing 3 to 10% by weight of a foaming agent having as a main component a foaming start temperature of 50 to 70 ° C and a maximum foaming temperature of 80 to 110.
Expandable styrenic resin particles manufactured at ℃. 2. The expandable styrene resin particles according to claim 1, wherein the styrene resin particles are a styrene polymer or a copolymer of styrene, an acrylate and / or a methacrylate. 3. A method for dispersing expandable styrene resin particles having an average particle diameter of 0.33 to 0.9 times the average particle diameter of the styrene resin particles in an aqueous dispersion medium containing no foaming agent. And copolymerizing acrylic acid and / or methacrylic acid ester monomers to obtain copolymer resin particles while impregnating the same, the latter half or after completion of the polymerization, the aliphatic having 5 or less carbon atoms having a side chain. The method for producing expandable styrene resin particles according to claim 1 or 2, wherein the expandable styrene resin particles are impregnated with a blowing agent containing a hydrocarbon as a main component.