KR101599375B1 - Expandable polymer particle to form bimodal cell structure and manugacturing method of the same - Google Patents

Abstract

The present invention relates to a foamable polymer particle for providing a foam having a bimodal distribution with a different cell size and a method for producing the same. The foamable polymer particles of the present invention are prepared by dispersing water in a monomolecular liquid droplet before polymerization to form a water domain, suspending the polymer in an aqueous solution, polymerizing the polymer particles in the form of pellets, and adding a foaming agent or a C6 to C10 aromatic hydrocarbon . The foamable polymer particle forms a fine spherical water domain, and the content of water in the particle is 10 to 40 wt%, and the size of the water domain is 20 to 80 microns. The foamable polymer particles obtained by this method have a satisfactory effect of improving the mechanical properties and are capable of forming cells having a double distribution structure having a size range of several tens of microns and several hundreds of microns of each independently in the foaming.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a polymer foamable particle and a method for producing the polymer foamable particle,

The present invention relates to a polymer foamable particle capable of forming a cell structure with a double distribution and a method for producing the same. More particularly, the present invention relates to a process for producing foamable particles comprising the steps of dispersing fine droplets in a monomer droplet and suspending the droplets in an aqueous solution, preparing polymer particles in the form of pellets through a polymerization process, and impregnating a foaming agent or a C6 to C10 aromatic hydrocarbon Method.

The polymer foamable particles are generally prepared by suspension polymerization. Various blowing agents are mixed with the monomers during the polymerization and polymerized at a temperature lower than the foaming temperature of the foaming agent or impregnated with the foaming agent in the polymer particles already prepared under the conditions of the glass transition temperature of the polymer Can be obtained.

The foamed polymer particles thus obtained are pre-expanded by a preceding foaming process, filled in a closed mold having a plurality of small holes, heated and foamed by pressurized steam or the like to fill the voids between the foamed foams, After the ribs are fused together, they are cooled and released from the mold to produce a foam having a cell structure formed of pores having a size of approximately 100 microns.

The foam obtained through such a process forms cells of several tens of microns to several hundreds of microns in size depending on conditions such as the type and content of the blowing agent impregnated or the molecular weight of the polymer particles. Until now, the size of the cells constituting the foam has been recognized as an important factor controlling the heat insulation and mechanical properties of the foam.

The method of producing the foamable polymer particles generally has a monomodal distribution with a certain range of cell sizes generated at the time of foaming, and it is possible to effectively form a bimodal cell structure having different cell size distribution in the foam There is a continuing need for the expandable polymeric particles.

Korean Patent Registration No. 10-0167546

An object of the present invention is to provide a foamable polymer particle capable of forming a foam having a differently distributed cell size and a novel method for producing the same.

Unlike conventional foamed polymer particles which form a cell structure having a uniform distribution with a uniform size after foaming, a large amount of fine water domains are formed in the polymer particles by adding water to the monomer droplets at the time of polymerization, A method of producing a foamable polymer particle through a separate impregnation process. To this end, the method for producing a foamable polymer particle of the present invention comprises: a first step of preparing a monomer mixture in which water is dispersed by previously dissolving 10 to 30% by weight of a polymer resin in a monomer and mixing with water; A second step of preparing the spherical polymer particles through a suspension polymerization process; And a third step of impregnating the produced polymer particles with a foaming agent to produce expandable particles having a water domain.

The foamed polymer particles produced by the method of the present invention can form a cell structure having a dual distribution with different sizes depending on the different foaming properties of the water dispersed in the particles and the foaming agent.

1 is an optical microscope photograph of the foamable polymer particle obtained in Example 1 of the present invention.
Fig. 2 is an optical microscope photograph of a cross section of the foam after foaming of the expandable polymer particle obtained in Example 1 of the present invention. Fig.

The method for producing a polymer foamable particle capable of forming the double cell structure of the present invention is characterized in that a water domain is dispersed in a monomer droplet in a size of several tens of microns to suspend the monomer droplet in an aqueous phase, Forming a polymer particle in which a water domain is present, introducing a foaming agent and a C6-C10 aromatic hydrocarbon, and impregnating the mixture with stirring at a constant temperature and pressure.

In the practice of the present invention, the polymerized polymer particles are selected from the group consisting of styrene; Alkylstyrenes, such as ethylstyrene, methylstyrene and para-methylstyrene; Alpha-alkylstyrenes, such as alpha-methylstyrene, alpha-ethylstyrene, alpha-propylstyrene and alpha-butylstyrene; Halogenated styrenes, such as chlorostyrene, and bromostyrene; And vinyl toluene. Suitable examples of the monomer copolymerizable with the styrenic monomer include acrylonitrile, butadiene, alkyl acrylates such as methyl acrylate, alkyl methacrylate , Such as methyl methacrylate, isobutylene, vinyl chloride, isoprene, and mixtures thereof.

In the present invention, the formed polymer particles preferably have a specific gravity of 1 or more or a gel-like particle having a water domain of at least 10-40% and a water domain of several tens of microns and a degree of polymerization of 80% It says. Preferably, the water has a 10-30% water domain size of 20-50 microns, a degree of polymerization of 90% or more, more preferably 20% of water, and a water domain of 30 microns or more of 95% Is a foamable particle

In one embodiment of the present invention, the polymerization is completed to obtain spherical polymer particles. These polymer particles can be conventionally obtained by emulsion polymerization, bulk polymerization, dispersion polymerization and suspension polymerization methods known in the art. However, considering that the present invention provides the expandable polymer particles, the size and shape of the expandable polymer particles It is preferable to prepare the expanded polymer particles polymerized by suspension polymerization capable of effectively forming a water domain inside.

In a preferred embodiment of the present invention, the foamable polymer particles produced are obtained by impregnation of the first polymer particles obtained by suspension polymerization and introduction of a foaming agent. First, the foaming agent is added to the distilled water in which the stabilizer is dispersed, and then the mixture is heated and stirred at a temperature higher than the softening point of the polymer under pressure. The introduction of the blowing agent is preferably carried out through a separate impregnation step after the first polymerization but it is also possible to add the blowing agent directly into the monomer together with the water during the first polymerization without a separate impregnation step.

The water content and the water domain size dispersed in the monomer during the first polymerization greatly affect the size and distribution of the cells formed after foaming. In the present invention, in general, the effect of facilitating formation of water domains in the monomer Polyvinyl alcohol, a polymeric dispersion stabilizer, was used. Also, by using a monomer in which 10-25% of the polymer was dissolved in the polymerization, the water was effectively prevented from being released into the water phase in the monomer droplet.

The initiator may be a peroxide initiator. The polymerization was carried out using benzoyl peroxide as an initiator and tertiary butyl peroxide, an initiator which decomposes at high temperature, as an auxiliary initiator, maintaining the temperature in the range of 80-95 ^° C for 6-8 hours. The obtained polymer particles are finally obtained through exhaust dewatering, drying, and a separate impregnation process.

In the present invention, a conventional foaming agent is used to impart foamability to the polymer particles and to form a small cell structure in the double-distribution foam, and is preferably added in an amount of 3-10 wt% based on the polymer. Suitable foaming agents include aliphatic hydrocarbon hydrocarbons having 4 to 6 carbon atoms, preferably pentane.

In the present invention, it is preferable to impregnate the polymer particles by heating at a temperature higher than the glass transition temperature (Tg) of the polymer particles so that the polymer particles can be softened so as to impregnate the polymer particles with the foaming agent. In one embodiment of the invention, the heating time may be adjusted to allow the foaming agent to penetrate into the polymer particles as appropriate, and preferably heated for 3 hours or more. When the heating process is carried out for an excessively long time, or when the heating is carried out at an excessively high temperature, the unstiffened monomer may be exhausted, resulting in lowering the foaming property. In one embodiment of the present invention, when the polystyrene type polymer is heated at a temperature of 105 to 130 ^° C. for about 3 to 7 hours, an effective foaming agent can be introduced.

In the practice of the present invention, in order to form a large cell having a large size among the cell structure of the double distribution of the foam, water is dispersed into the monomer in the polymerization process of the monomer. In this case, the method of raising the viscosity of the monomer is effective to prevent the water introduced into the monomer from being separated into the dispersion medium during the polymerization process. For this purpose, the monomer is pre-polymerized to a polymerization conversion ratio of 10% to 30% Or 10-30% of the same polymer is completely dissolved in the monomer.

In the practice of the present invention, water is effectively dispersed in the monomer droplets prior to polymerization to form a water domain in the polymer particle foam. In a dual-distributed cell structure, the small cell is formed by the blowing agent impregnated in the polymer particle, but the large cell is formed in accordance with the foaming of the water domain in the polymer particle in the foaming process. At this time, the cell structure of the double distribution can be effectively controlled depending on the size and dispersion form of the water domain formed in the particle.

It is preferable that the water used is 10-40% of the total monomers used. If the amount of water is excessively large, the viscosity of the monomer droplet falls below the critical point and a large amount of fine particles of 50 microns or less are formed. When the amount of water is small, it is difficult to effectively form a large cell. In the present invention, in order to effectively disperse an appropriate-sized water domain in the monomer droplets, a dispersion stabilizer such as polyvinyl alcohol, polyvinylpyrrolidone and a surfactant such as sodium dodecyl sulfate are used in the water to be used, It is preferable to use 0.5 to 2% by dissolving it in the water content.

In one preferred embodiment of the present invention, the charged water is uniformly distributed in the polymer particles in a domain of several tens of microns in size. Preferably, the water domain size is 20 to 80 microns. When the water domain size is more than 20 to 80 microns, a coalescence phenomenon occurs between the water domains in the foaming, thereby forming a large independent cell and pinhole in the foam. In the following case, And the size distribution becomes ambiguous, the cell structure of the double distribution can not be formed. The foaming conditions of the foamable polymer particles capable of forming the cell structure of the double distribution can be the usual conditions used for foaming the expandable polymer particles, and the conditions are not particularly limited.

The foam obtained through the foaming process of the foamable polymer particles obtained by the present invention can be foamed by a person skilled in the art to have a size range of 20 to 50 microns in each of a small size and 150 to 300 microns in a large size, It has an advantage of having excellent strength and high puffing ratio. 2 is a photograph of a cross section of a foam having a cell structure of double distribution obtained by the present invention, taken by an optical microscope (OM).

In one embodiment of the present invention, a polystyrene particle having a water domain is prepared by using a styrene monomer, and the foamed polystyrene particles are then subjected to a blowing agent impregnation step to complete the final product. FIG. 1 is a view It has a uniformly distributed water domain of 30 to 60 microns in size. In the present invention, if the water present in the polymer particles does not form an independent domain, one large single pore is formed in the foam during foaming, thereby failing to obtain a dual-distributed cell structure.

In addition, known additives used in conventional foam polymer particle production processes may be used in the present invention in addition to usual applications and methods. Specifically, a pH adjuster, an anti-scale agent, a flame retardant, a cell regulator dye and a pigment may be added as needed.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

≪ Example 1 >

(a) Preparation of water-dispersed monomer mixture

Styrene monomers, initiator and polystyrene pellets were mixed and stirred for 1 hour to completely dissolve. Then, pure water in which the dispersion stabilizer was dissolved was added to the monomer mixture and stirred for 10 minutes to form spherical water domains in the monomer. A water / monomer mixture was prepared in the reactor at room temperature using the pure water, styrene monomer, initiator dispersion stabilizer, and polystyrene resin, based on 10 kg. The size of the water domain formed in the resulting monomer mixture ranged from 40-80 microns.

(Manufacturing prescription of monomer / water mixture)

Styrene monomer 56 wt%

0.56 wt% initiator (benzoyl peroxide; Hansol Chemical PEROX-B75)

Polystyrene resin (Mw 380,000) 14%

Water (pure water) 28 wt%

1.4% by weight of a dispersion stabilizer (polyvinyl alcohol Kuraray PVA-217)

0.04 wt% tertiary butyl peroxide (LUPEROX)

(b) Production of polymer particles by polymerization process

A stabilizer was added to water as a dispersion solvent and completely dissolved by stirring. A monomer / water mixture obtained through the above process was added thereto, and polymer particles containing water were polymerized through polymerization for 8 hours at 91 ^° C and 400 rpm . The water in the particles is 40-80 microns in size and forms spherical domains and the average size of the polymer particles is 1000 microns.

 (Manufacturing prescription of polymer particles through polymerization process)

64% by weight of a dispersion solvent (pure water)

0.3% by weight of a dispersion stabilizer (polyvinyl alcohol Kuraray PVA-217)

Water / monomer mixture 35.7 wt%

(c) Impregnation with foaming agent

A stabilizer and a surfactant were added to water as a dispersion solvent, and the solution was completely dissolved by stirring. Then, the above prepared polymer particles having water domains therein were charged, and the temperature was raised. At a point where the internal temperature of the reactor reached 110 ° C, , And the mixture was stirred at 300 rpm for 6 hours to prepare polymer particles impregnated with a foaming agent.

(Blowing agent impregnation)

Dispersion solvent (pure water) 94.395 wt%

5% by weight of the polymer particles prepared above,

0.1% by weight of a dispersion stabilizer (polyvinyl alcohol Kuraray PVA-217)

0.005 wt% surfactant (sodium dodecyl sulfate)

0.5% by weight of a blowing agent (pentane SK)

After the end of the experiment, expandable polymer particles having a size range of 500 to 2000 microns were prepared. The foamable polymer particles were evaluated for appearance through direct observation after drying and observation after foaming, and they are shown in Table 1

≪ Example 2 >

In the monomer mixture preparation step in which the water was dispersed, water was added to the monomers in the same manner, and the same procedure as in Example 1 was carried out except that the water content was changed from 28 wt% to 14 wt%.

≪ Example 3 >

The same procedure was followed as in Example 1 except that water was added to the monomers in the same manner as in the step of producing water-dispersed monomers and the water content was changed from 28 wt% to 42 wt%.

<Example 4>

The procedure of Example 1 was repeated except that the polystyrene resin was dissolved in the monomers in the same manner as in the water-dispersed monomer preparation step, except that the conventional polystyrene resin was used in an amount of 16 wt% to 12 wt%.

&Lt; Example 5 >

The procedure of Example 1 was repeated except that the polystyrene resin was dissolved in monomers in the same manner as in the water-dispersed monomer preparation step, except that 16 wt% to 18 wt% of the conventional polystyrene resin was used

 &Lt; Comparative Example 1 &

The same procedure was followed as in Example 1 except that the monomer mixture was prepared in the same manner as in the monomer mixture preparation step in which water was dispersed, but no water was added.

&Lt; Comparative Example 2 &

Except that the monomer mixture was prepared in the same manner as in the step of preparing the water-dispersed monomer mixture, but the polystyrene resin was not dissolved.

&Lt; Comparative Example 3 &

The procedure of Example 1 was repeated except that the step of impregnating the foaming agent was not included in the preparation of the polymer particles.

The experimental results are shown in Table 1. Table 1 shows comparisons for voiding.

Within the particle
Water domain size (탆) Cell structure after foaming Small cell
size
(탆) Large cell size (㎛) Size size
(탆) Foam drainage Example 1 40-80 Double distribution 30-50 350-400 500-1000 31 Example 2 30-70 Double distribution 20-30 250-350 300-800 26 Example 3 50-80 Double distribution 30-50 400-500 600-1200 34 Example 4 60-80 Double distribution 40-60 450-500 200-600 31 Example 5 30-60 Double distribution 20-40 250-300 600-1500 32 Comparative Example 1 0 Single distribution 70-150 0 700-2000 60 Comparative Example 2 500 ~ Single distribution 30-50 1000 ~ 50-300 15 Comparative Example 3 40-80 Non-foaming 0 0 300-800 0

The foamed polymer particles produced by the method of the present invention form cells by forming independent bubbles in the foaming agent and water impregnated in the foaming process, so that a bimodal foam having different cell size ranges can be obtained. Also, the size of the cells formed after the foaming can be adjusted according to the content of the added water and the polymer resin, so that the cells of the foam can be controlled to have a double distribution structure.

Claims (10)

10 to 30% by weight of the polymer resin is dissolved in the monomer in advance and mixed with water
A first step of preparing a water-dispersed monomer mixture;
A second step of preparing the spherical polymer particles through a suspension polymerization process; And
And a third step of impregnating the produced polymer particles with a foaming agent to produce expandable particles having a water domain.
The method for producing a foamable polymer particle according to claim 1, wherein a dispersion stabilizer is further added in the first step.
delete The method for producing a foamable polymer particle according to claim 1, wherein the amount of water added in the step of preparing the water-dispersed monomer mixture is 10 to 40% by weight.
The method according to claim 1, wherein the size of the water domain generated in the foamable polymer particle ranges from 20 to 80 microns.
10 to 30% by weight of the polymer resin is dissolved in the monomer in advance and mixed with water
A first step of preparing a water-dispersed monomer mixture;
A second step of preparing the spherical polymer particles through a suspension polymerization process;
A third step of preparing the polymer particles by impregnating the polymer particles with a foaming agent; And
And a fourth step of foaming to produce a foam. The method of producing a foam having a dual-distributed cell structure.
A foam produced by the method of claim 6.
8. The foam according to claim 7, wherein the formed double-walled cell structure comprises a large cell formed by water and a small cell formed by vaporization with a foaming agent constitute an outer wall structure of a large cell.
The foam according to claim 8, wherein the area ratio of the large cell to the small cell is in the range of 4 to 7: 6 to 3.
The foam according to claim 8 or 9, wherein the size range of the large cell and the small cell is 200 to 500 and 30 to 80 microns, respectively.

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