KR100249767B1 - Method of manufacturing foaming stylene resin particle - Google Patents

Abstract

The present invention relates to a method for producing high productivity foamed styrene resin particles having excellent mechanical strength, and using pentane as a blowing agent and adding polyethylene waxes having different average molecular weights in combination to form a uniform bubble, and by suspension polymerization method. After preparing expandable styrene resin particles having a molecular weight of 250000 to 270000 g / mol, mineral oil and glyceryl tri-stearate are added to provide a uniform foam structure and excellent mechanical strength. It relates to a manufacturing method.

Description

Method for producing expanded styrene resin particles

The present invention relates to a method for producing high productivity foamed styrene resin particles having excellent mechanical strength, and more particularly, by using pentane as a blowing agent and adding polyethylene waxes having different molecular weights as nucleating agents for bubble control by suspension polymerization. The present invention relates to a method for producing high productivity foamed styrene resin particles having uniform foam structure and excellent mechanical strength by adding mineral oil and glycerin tri-stearate, respectively, after preparing the expandable styrene particles.

Foamable synthetic resin particles, preparation of such particles, foaming and processing of these particles in various forms are well known. Most of the expandable particles currently used are expandable polystyrene particles, which are used in molded articles such as foamed plastic cups, foam coolers, and various types of cargo pads. Such expandable polystyrene particles are usually composed of volatile fluid blowing agents, polystyrenes with aliphatic hydrocarbons such as chlorofluorocarbons, and generally have various forms of expandable particles having various sizes ranging from less than 1 mm to several mm. These foams can be used to produce foamed products used for packaging.

In general, methods for preparing expanded styrene resin particles include suspension polymerization and emulsion polymerization. Among them, suspension polymerization is widely used commercially. In this case, a suspension stabilizer is added to a water pressure polymerization tank and polymerization is performed under stirring. The catalyst applied styrene monomer is dispersed. After the high temperature polymerization to obtain a spherical polystyrene resin, the spherical expanded styrene resin particles are obtained by impregnating low boiling point hydrocarbons such as pentane, butane and propane at a temperature above the softening point in the same polymerization tank in which the polymerized styrene resin particles are sealed.

The present invention, in the production of expanded styrene resin particles, by using polyethylene wax having a different average molecular weight from each other to control the bubble size, to maintain the average molecular weight within a certain range to improve the mechanical strength, pentane, mineral oil and glyceryl tree The use of stearate provides a method for producing expanded styrene resin particles having a very short molding cycle time.

1 is a schematic of the molding cycle time (Cycle-Time) and the mechanical strength shown in Table 2.

That is, the present invention provides a polyethylene wax having a mean molecular weight of 500 to 1500 g / mol and 2000 to 3000 g / mol, respectively, of 0.1 to 0.2 phm (part per hundred monomer), 0.05 in the method for producing expandable styrene resin particles. To 0.1 phm was added to polymerize, and 5.0 to 6.0 phm of pentane was added as a blowing agent to prepare expandable styrene resin particles having an average molecular weight of 250000 to 270000 g / mol, followed by 0.1 to 0.3 phr of mineral oil and glyceryl tri-stearate, respectively. (part per hundred resin) is added to provide a method for producing high productivity foamed styrene resin particles having a uniform bubble structure and excellent mechanical strength.

Hereinafter, the present invention will be described in detail.

In the present invention, the bubble size of the expanded styrene resin particles is added by adding 0.1 to 0.2phm and 0.05 to 0.1phm of polyethylene wax having an average molecular weight of 500 to 1500 g / mol and 2000 to 3000 g / mol, respectively. The average molecular weights are 1000 and 2000 g / mol, respectively, and the addition amounts are 0.1 phm and 0.05 phm, respectively.

The foam structure of the foamed resin shows an inherent bubble structure according to the molecular weight and content of the nucleating agent used to control the bubbles. The smaller the molecular weight and content of the nucleating agent, the finer and uneven bubble structure, and the larger and uniform the molecular weight and content. It has the characteristic of showing bubble structure.

Therefore, if the average molecular weight of the polyethylene wax used as the nucleating agent of the expanded styrene resin particles in the present invention is less than 500g / mol disperse finely into the styrene molecules, and loses the role as a nucleating agent, if larger than 3000g / mol is compatible with styrene Apart from this, there is no microstructure distribution between the polyethylene wax and the styrene resin particles, and thus loses its role as a nucleating agent. That is, the ability of the polyethylene wax nucleating agent is lost if the compatibility with the styrene resin particles is too large or too small.

Further, in the present invention, by using a combination of polyethylene waxes having different average molecular weights, respectively, it is possible to produce a uniform and fine bubble structure of 80 to 100 µm, preferably 100 µm. When polyethylene wax having an average molecular weight of 500 to 1500 g / mol is used alone, the bubble size is 40 to 100 μm, the bubble structure is non-uniform, the bubble holding ability decreases, and the polyethylene having an average molecular weight of 2000 to 3000 g / mol is used. When the wax is used alone, the bubble size is 150 to 200 μm, the bubble structure is uniform, and the bubble holding ability is good, but the flexural tensile strength is sharply dropped, which is very hard, fragile, and the moldability decreases.

As such, when the size of the bubble structure is 80 to 120 µm, preferably 100 µm, the compressive and flexural tensile strength is excellent. Therefore, if the foam structure of the foamed resin is smaller than the above range, the compressive strength is difficult to apply to products requiring load resistance, such as fish box packaging material, and if it exceeds the above range, the flexural tensile strength drops sharply and is very hard. It is fragile and moldability deteriorates.

In the present invention, in order to make a highly productive foamable styrene resin having a very short cycle cycle time, 5.0 to 6.0 phm of pentane was used as the foaming agent. ) It is very important to be careful not only because it has a great influence on other properties but also on other properties such as foamability, welding, and appearance of molded products. Low blowing point hydrocarbons such as propane, butane and pentane are commonly used as blowing agents. Pentane, which has low vapor pressure and good affinity with polystyrene resin, is used to make a highly productive foamed styrene resin with a very short molding cycle time. It was applied to 5.0 to 6.0phm in consideration of other physical properties such as foamability, fusion, molded article appearance.

The styrene resins thus obtained are characterized by styrene copolymers such as styrene homopolymers or copolymers of styrene and acrylonitrile or copolymers of styrene and α-methylstyrene and have a molecular weight of 250000 to 270000 g / mol. If the molecular weight is less than 250000 g / mol, the mechanical strength is lowered, and if the molecular weight is higher than 270000 g / mol has a disadvantage of relatively high melt viscosity and foaming properties.

In addition, in order to make the high-productivity foamable styrene resin, the present invention removes the water of less than 0.5% by the fluidized bed drying, and then added 0.1 to 0.3 phr of mineral oil and glyceryl tri-stearate, respectively. These additives are dispersed on the particle surface through the mixer and act as a surface plasticizer during foaming to make a fine hole in the surface of the foam granules, and play an important role in making the molding cycle time very fast during molding by accelerating the external diffusion of unnecessary foaming agent after foaming. do. If the content of mineral oil and glyceryl tri-steareart is out of the scope of the present invention, the molding cycle time is shortened, but the flowability is poor, causing problems in commercialization.

As the styrene monomer used in the present invention, a styrene monomer, a mixture of acrylonitrile or α-methylstyrene mainly composed of styrene monomers was used.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

EXAMPLE

10 kg of styrene monomer was added in the pre-dissolution tank 1, and 40 g and 20 g of polyethylene waxes having a molecular weight of 1000 g / mol and 2000 g / mol were added thereto while stirring at 110 rpm. It is left to cool to.

130 g of benzoyl peroxide and 62 g of t-butylperbenzoate were dissolved in 30 Kg of styrene monomer in the preliminary dissolution tank 2 and dissolved over 30 minutes. The solution made in the preliminary dissolution tank 1 was quenched and stirred for 30 minutes to prepare a dispersion.

Separately, add 40 kg of pure water in a 100L pressure vessel, add 250 g of tricalcium phosphate and 110 g of hydroxyethyl cellulose as a dispersant to prepare a suspension. The polymerization is carried out until the polymerization rate is 95% while the temperature is maintained at and maintained at 캜. After that, the reactor is sealed and then heated at 110 ° C., and 2 kg of pentane is introduced at a rate of 1 g / min. When the addition is completed and the temperature is 110 ℃ is maintained for 6 hours so that the content of unreacted styrene monomer up to 3000ppm or less. At this time, the blowing agent to be introduced is impregnated into the glass transition foamed styrene resin particles are made of expandable styrene resin particles.

After cooling to 45 ° C. or less, the residual blowing agent is released. At this time, when the pressure of the reactor drops to the normal pressure, it is discharged and the foamed styrene resin particles can be soaked in a slurry state.

The obtained polymerized product is separated from water by dehydration, and the water on the particle surface is removed to 0.3% or less through fluid bed drying, and then sorted and stored by particle size. Among them, a polymer having a particle size of 0.80 mm is added to a mixer and stirred for 30 minutes by adding 0.2 phr of mineral oil and 0.2 phr of glyceryl tri-stearate to obtain high productivity foamed styrene resin particles having excellent mechanical strength.

The final product thus obtained was foamed at 50 times magnification using a foaming machine (model name: HLC-901) specially manufactured by Daegong Co., Ltd., and the bubble structure was shown in Table 1, and the vacuum molding machine manufactured by Daegong Co., Ltd. The molding cycle time was measured while molding with (model name: DKM-90VS), and is shown in Table 2. In addition, in order to measure the mechanical strength, the compression and flexural strength were measured by U.T.M (model name AUTOGRAPH 2000 A) manufactured by Shimadzu, Japan, and the results are shown in Table 2 below.

Comparative Example 1

Except that the addition amount of the benzoyl peroxide in the pre-dissolution tank 2 was prepared in the same manner as in the expanded styrene resin particles in the same manner as in Example and performed the same analysis and the results are shown in Table 1, Table 2 together.

Comparative Example 2

Except for using polyethylene wax having an average molecular weight of 1000 g / mol in the preliminary melting tank 1, foamed styrene resin particles were prepared in the same manner as in Example, and the same analysis was performed, and the results are shown in the following Tables 1 and 2.

Comparative Example 3

Foamed styrene resin particles were prepared in the same manner as in Example, except that 2 kg of butane was added at a rate of 1 g / min as the blowing agent added in the pressure vessel, and the results were analyzed through the following Tables 1 and 2 Together.

[Comparative Example 4]

Foamed styrene resin particles were prepared and analyzed in the same manner as in Example, except that only 0.2 phr of glyceryl tri-stearate was used instead of mineral oil and glyceryl tri-stearate, and the results were analyzed. It is shown together in Table 1, Table 2.

[Comparative Example 5]

Except for the addition of 0.4hpr mineral oil and 0.4hpr glyceryl tri-stearate in comparison with the Example was prepared in the same manner as in the expanded styrene prepared by the analysis and the results are shown in Table 1, Table 2 is shown together.

1 is a diagram illustrating the molding cycle time and mechanical strength of Examples and Comparative Examples 1 to 5, and it can be seen that the molding cycle time and mechanical strength of the embodiment were excellent. Even if the molding cycle time and the mechanical strength are similar, in the case of Comparative Example 5 there is a disadvantage in poor productability.

TABLE 1

Property Analysis Method

(1) Molecular weight: It measured by gas adsorption chromatography.

(2) Bubble structure: Measured by scanning microscope.

TABLE 2

[Property evaluation method]

(1) Foamability: After adding a small amount of foamable polystyrene to the foamer in which the steam pressure flows into 0.5㎏ / ㎠, measure the expansion ratio after 300 seconds.

Expansion ratio = 1 / density (volume / weight)

(2) Molding cycle time (C / T): The molding cycle time is calculated by the process of filling, heating, cooling, and releasing.

(3) Fusion: When the foamed polystyrene molded product is dried and cut into half of its length, the entire expanded granules in the solid line are drawn when the solid line is drawn in the horizontal (2cm) × vertical (2cm) area about 2cm away from the surface. The fusion is calculated by the ratio of the number to the torn foam granules.

Fusion = (number of torn foam in solid line / total number of foam in solid line) × 100

(4) Flowability: It is evaluated visually simply by grasping the fluidity of the expandable polystyrene resin beads when the expandable polystyrene resin beads are transferred to the foamer during preliminary foaming.

(5) Compressive strength: Measure the compressive strength at the time of YS point after compressing the center of the specimen by using universal testing machine (Universal trsting machine) to dry foamed polystyrene resin specimen after pre-expanding (67 times).

(6) Flexural strength: Measure the flexural strength at the time of YS point after compressing the center of the specimen by using universal testing machine (Universal trsting machine) by molding after foaming (67 times) pre-foamed.

As described above, the expanded styrene resin particles prepared according to the present invention have a molecular weight of 250000 to 270000 g / mol, a uniform bubble structure of 100 μm, a very short cycle time during molding, excellent economic efficiency, and excellent mechanical strength. It can be used for products that require a certain mechanical strength, such as, especially when applied to products requiring load resistance, such as fish box packaging material has an excellent effect of showing excellent physical properties.

Claims (3)

In the production of expandable styrene resin particles, 0.1 to 0.2 phm of polyethylene wax having an average molecular weight of 500 to 1500 g / mol and polyethylene glycol 0.05 to 0.1 phm having an average molecular weight of 2000 to 3000 g / mol are combined with the styrene monomer. To prepare the expandable resin particles having a molecular weight of 250000 to 270000g / mol by suspension polymerization using a pentane 5.0 to 6.0phm as a blowing agent, by adding 0.1 to 0.3 phr of mineral oil and glyceryl tri-stearate, respectively Method for producing expanded styrene resin particles, characterized in that. The method for producing expanded styrene resin particles according to claim 1, wherein the expandable styrene resin is a styrene copolymer such as a styrene homopolymer or a copolymer of styrene and acrylonitrile or a copolymer of styrene and α-methylstyrene. . The method for producing expanded styrene resin particles according to claim 1, wherein the styrene monomer is a styrene monomer or a mixture with acrylonitrile or α-methylstyrene mainly composed of styrene monomers.

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