KR20100103952A - Expandable microsphere for light weight material and manufacturing method thereof - Google Patents

Abstract

PURPOSE: An expandable microsphere and a manufacturing method thereof are provided to secure the excellent dispersibility as a medium for a paint or an ink, and to form a uniform thickness of a shell. CONSTITUTION: A manufacturing method of an expandable microsphere comprises the following steps: forming a water-based disperse medium; forming a polymerizable mixture; homogenizing the water-based disperse medium and the polymerizable mixture; polymerizing the homogenized mixture; and washing the polymerized mixture before a de-aeration process, and drying. The water-based disperse medium is formed with a dispersing stabilizer, an assisted stabilizer, and water.

Description

Expandable microsphere for light weight material and manufacturing method

The present invention relates to a thermally expandable micro spare for a lightweight component material, and more particularly, to a thermally expandable micro spare having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer.

Thermally expandable microspare refers to a plastic capsule in which a liquefied hydrocarbon (foaming agent) is surrounded by a thermoplastic resin as a core material in the microcapsules. When the microcapsules are heated, the thermoplastic resin softens, and the evaporation of the blowing agent increases the internal pressure, resulting in microcapsules having an average particle diameter of 10 to 30 µm that expand to 4 to 5 times the diameter and 50 to 100 times the volume than before foaming. For this reason, these microcapsules are called expandable microspheres or thermal expandable microcapsule.

The heating of the thermally foamable microspare causes softening of the shell material and evaporation of the blowing agent and expansion of the internal pressure. Because the cell material polymer is hard, it is balanced with the internal gas pressure, and at this time, it becomes a micro balloon state.

Further heating causes the thinned shell material to leak due to the pressure of the internal gas and shrinkage because the tensile force of the polymer material is less than the internal gas pressure. Because cell material polymers have excellent soft properties, sudden explosions are unlikely. In addition, there is an advantage that the processing temperature can be lowered because it expands at a lower temperature than 110 ~ 150 ℃ than other blowing agents.

Thermally expandable microspares can generally be prepared by a method of suspension polymerizing a polymerizable mixture containing at least a blowing agent and a polymerizable monomer in an aqueous medium. As the polymerization reaction proceeds, an outer shell is formed by the produced polymer, and a foaming agent is wrapped in the outer shell, thereby obtaining a thermally expandable micro spare having a sealed structure. Suspension polymerization is a polymerization method in which monomer droplets are present in the dispersion medium in the form of oil droplets through mechanical agitation with a suspension stabilizer and polymerized to produce polymer particles. Particles having a particle size of about tens to thousands of microns and polydispersion are usually distributed. Can be obtained. Although the degree of crosslinking is easy to control and the process is simple, it is generally characterized by a wide distribution of particle sizes and a large average particle size. During suspension polymerization, the size and distribution of the produced fine particles appear differently depending on the polymerization conditions.They are affected by the amount of stabilizer, high-speed disperser speed, stirring speed in the reactor, monomer ratio, and other effects such as monomer concentration, stabilizer concentration, and initiator concentration. , Polymerization temperature, concentration of crosslinking agent, and the like are known.

However, although microcapsules have been used in various fields, studies on thermo-expandable microspheres in which a volatile liquid foaming agent is microencapsulated by a polymer have not yet been made in Korea. Thermally expandable microspares are used for paints, plastic fillers, car paints, foamed non-woven fabrics, paper, porous bodies, etc., which are mainly used for foaming inks, and are lightweight. They are slip resistant, lightweight, heat insulating, rigid, and vibration resistant. In order to improve the performance and the like, the practical use for various uses as a functional material is being advanced. As the performance of thermally expandable microspares, it is particularly important to be able to form foam having a sharp foaming uniformity and size. The sharp foaming here means that the foaming start temperature of each particle of the expandable micro spare is almost the same, and the foaming is started simultaneously under the foaming temperature conditions. Therefore, the thermally foamable microspare requires a very spherical particle shape and a very narrow uniformity of particle size distribution.

Therefore, in the present invention, the present invention has been completed by studying the preparation of thermally expandable micro spares having a sharp particle size distribution, having a nearly identical foaming temperature, and capable of uniformly foaming at the same foaming temperature.

According to the present invention, a capsule having a very sharp particle size distribution and a rough surface is prepared using a method of preparing a thermally expandable microspare of suspension polymerization, and has excellent dispersibility in a medium such as paint or ink, and a uniform shell thickness. It is an object to provide an optimal method of making one thermally expandable microspare.

In order to achieve the above object, the present invention comprises the steps of (a) preparing an aqueous dispersion medium; (b) preparing a polymerizable mixture; (c) mixing and homogenizing the aqueous dispersion medium and the polymerizable mixture; (d) polymerizing the homogenized mixture; (e) heat-expandable microfabrication, which includes drying the polymer and washing and degassing the polymer. It is characterized by providing a method for producing a spare and a thermally expandable microspare prepared by the method.

Hereinafter, the present invention will be described in detail.

blowing agent

The blowing agent used in the present invention is a substance which becomes gaseous at a temperature below the softening point of the polymer forming the outer shell, and as such a blowing agent, a low boiling point organic solvent is preferable. For example, ethane, ethylene, propane, propene, n-butane And low molecular weight hydrocarbons such as isobutane, butene, isobutene, n-pentane, isopentane, n-hexane and petroleum ether. These can be used individually or in combination of 2 or more types, respectively, Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, and a mixture of 2 or more types are preferable.

Polymerizable monomer

Until now, the monomers applied to suspension polymerization include vinyl acetate, which is a monomer of polyvinylacetate used for the production of polyvinyl alcohol, and in particular, styrene and methyl methacrylate have been reported by many documents as the most widely known monomers.

The outer shell of the polymer constituting the thermally expandable microspare of the present invention can be formed using various polymerizable monomers such as acrylate ester, (meth) acrylonitrile, vinylidene chloride, vinyl chloride, styrene and the like. Among these, forming an outer shell by the vinylidene chloride copolymer and the (meth) acrylonitrile copolymer is preferable to highly balance the gas barrier property, solvent resistance, heat resistance, foaming property, and the like.

It is preferable that it is a copolymer obtained using 30 weight%-70 weight% of acrylonitrile, 20 weight%-60 weight% of methyl methacrylate, and 1 weight%-10 weight% of methyl acrylate.

Polymerization initiator

In suspension polymerization, azo compounds and organic peroxides are generally used, in which the initiator is insoluble in water and a monomer is used. Especially, benzoyl peroxide and azobis isobutyronitrile (2,2 ') are used. -azobis isobutyronitrile) and azobis divaleronitrile (2,2'-azobis (2,4'-dimethyl valeronitrile)) are widely used.

The polymerization initiator is preferably used in a ratio of 0.1% by weight to 0.5% by weight based on the aqueous dispersion medium.

Crosslinkable monomer

In order to improve foaming property and heat resistance with the said polymerizable monomer, a crosslinkable monomer can be used together. As a crosslinkable monomer, the compound which has 2 or more carbon-carbon double bond is used normally. More specifically, divinylbenzene, di (meth) acrylate ethylene glycol, allyl methacrylate, triallyl isocyanate, triacyl formal, trimethylolpropane trimethacrylate, and pentaerythritol tree ( Meth) acrylate, etc. are mentioned.

Dispersion stabilizer

Suspension polymerization is usually carried out in an aqueous dispersion medium containing a dispersion stabilizer (suspension). Examples of the dispersion stabilizer include silica, calcium phosphate, magnesium hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium carbonate, magnesium carbonate and the like.

In addition, condensation products of diethanolamine and aliphatic dicarboxylic acids, condensation products of urea and formaldehyde, polyethylene oxide, gelatin, methylcellulose, dioctylsulfursuccinate, polyvinyl alcohol, and various emulsifiers may be used as auxiliary stabilizers. .

An aqueous dispersion medium containing a dispersion stabilizer is usually prepared by mixing a dispersion stabilizer or an auxiliary stabilizer with deionized water (distilled water). The pH of the aqueous phase at the time of polymerization is suitably determined according to the type of dispersion stabilizer or auxiliary stabilizer to be used.

Although the usage-amount of colloidal silica changes with the particle diameter, it is preferable to set it as 5 to 20 weight% normally with respect to 100 weight part of polymerizable monomers.

It is preferable to make an auxiliary stabilizer into 0.01 weight%-0.2 weight% with respect to 100 weight part of polymerizable monomers.

It is preferable to make an inorganic salt into 50 weight%-150 weight% with respect to 100 weight part of polymerizable monomers.

Polymerization aid

The polymerization adjuvant plays a role of stably producing thermally expandable microspares while preventing the aggregation of the polymerized particles during the polymerization and not causing the polymer to adhere to the polymerization barrel and effectively removing heat generated by the polymerization. As the nitrite alkali metal salt, stannous chloride, water-soluble ascorbic acid and boric acid, it is preferable to use at least one compound selected from the group consisting of.

It is preferable to make these polymerization aids into 0.01 weight%-0.2 weight% with respect to 100 weight part of polymerizable monomers.

Preparation of Thermal Expansion Microspars by Suspension Polymerization

In order to obtain a thermally expandable microspare having a very sharp particle size distribution, an aqueous dispersion medium and a dispersant are supplied into a double jacket reactor, and both are continuously stirred and dispersed in the reactor, and the resulting dispersion is injected into a constant temperature circulation tank to induce constant temperature. It is desirable to adopt a method of suspension polymerization in a tank.

Suspension polymerization is one of heterogeneous polymerization methods and basically consists of a polymerizable monomer, a polymerization medium, a dispersion stabilizer, and a polymerization initiator. The polymerizable monomer insoluble in water undergoes a reversible process of changing its form through mechanical stirring and dispersing the dispersed particles when the stirring is stopped. At this time, the polymerizable monomer residue is finally formed as a polymer particle through a polymerization process through a decrease in interfacial tension due to the presence of an effective dispersion stabilizer and continuous stirring. Each of the polymerizable monomer residues present in the polymerization medium is surrounded by a dispersion stabilizer and can be regarded as a small bulk polymerization reactor in which only the polymerization initiator and the polymerizable monomer are present. It is known that polymerizable monomer residues are directly converted to produce polymer particles.

The polymerizable monomer in which the polymerizable initiator is dissolved forms dispersion by mechanical stirring in the polymerization medium. This unstable dispersion state in suspension polymerization in which the continuous separation and aggregation occurs is separated into the monomer and the polymer phase, respectively, when stirring is stopped. In suspension polymerization, kinetic forces are applied to liquid phases that do not mix with each other, resulting in the separation of polymerizable monomer residues, each of which has a different size. Although the size of the polymerizable monomer remains small by stirring, the phenomenon of merging with each other due to interfacial tension occurs. It can be estimated that the diameter of the remains remains theoretically constant when the flocculation and separation of these remains reach equilibrium.

During the polymerization reaction, polymerizable monomer residues increase in viscosity as the reaction proceeds to cause agglomeration by collision. Appropriate agitation and dispersion stabilizers in this unstable dispersion state, when the conversion rate of the polymerizable monomer reaches about 30%, an auto-acceleration phenomenon occurs, a sudden temperature runaway, and the conversion rate increases rapidly.

As described above, a capsule having a very sharp particle size distribution and a rough surface manufactured by using the thermally expandable microspare manufacturing method of the suspension polymerization of the present invention may be used as a coating material for weight reduction, including the use of foam ink, Plastic fillers, vehicle coatings, foamed nonwovens, paper, porous bodies and the like.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the scope of the present invention, and ordinary changes by those skilled in the art are possible within the scope of the technical idea of the present invention.

<Examples>

Preparation of Thermally Expandable Microspares

(1) production of aqueous dispersion media

In a 500 ml beaker, 60% by weight of distilled water was added as a polymerization medium, 10% by weight of colloidal silica having a solid content of 40% as a dispersion stabilizer was added, 30% by weight of sodium chloride (NaCl) and 0.02% by weight of sodium nitrite as an auxiliary stabilizer. 0.05 wt% of boric acid as an adjuvant was added thereto and stirred at room temperature to completely dissolve them to prepare an aqueous dispersion medium.

(2) Preparation of polymerizable mixture

In a 500 ml beaker, 52 wt% of acrylonitrile, a dispersing polymerizable monomer, 25 wt% of methyl methacrylate (Samchun Chemical Co., 99%), and 3 wt% of methyl acrylate (Junsei Chemical Co.) were added in this order. Next, 0.3 wt% of trimethacrylic acid trimetholpropane as a crosslinkable monomer and 20 wt% of n-butane as a blowing agent were added, and 0.4 wt% of AIBN (2,2'-azobis isobutyronitrile) as a polymerization initiator was slowly shaken. The initiator was dissolved to prepare a polymerizable mixture.

(3) homogenization

The polymerizable mixture was first added to a double jacket reactor (Lightshoe Chemical), and then an aqueous dispersion medium was added thereto. Thereafter, the homogenization rate of Homogenizer (X520D, Germany) was adjusted to 9900-15000rpm for homogenization. Homogenization time was adjusted to 3-5 minutes.

(4) polymerization

After the homogenization was completed, the double jacket reactor was connected to a constant temperature circulating water tank (CW-20G, Jeio Tech), and polymerization was performed at 57 ° C. At this time, the stirring speed was adjusted to 150 to 200 rpm, and the reaction time was set to 3 to 5 hours, which is a time for generating particles.

(5) washing, dehydration, drying

After the reaction was completed, the filtration and washing were repeated using a centrifuge, followed by drying in a dryer at 30 ° C. (OF-22, Jeio Tech) for at least 12 hours to prepare a thermally expandable microspare of the present invention.

<Test Example>

In order to determine the foaming behavior of the prepared particles, the foaming trend was observed in the dryer. The foaming temperature was 130 ° C., and the amount of particles to be foamed was foamed based on 5 ml. 5 ml of the prepared particles were measured in volume using a measuring cylinder, and then foamed in a plate. The results of observation of the foaming state and the volume are shown in FIGS. 1 and 2.

As can be seen in Figure 1, a) and b) is a manufacturing particle before foaming and c) and d) is a state of the particles after foaming, it was confirmed that the volume difference before and after foaming is about 10 times.

As shown in the electron micrograph before and after the foaming of Figure 2, the particle size of the particle was about 25 ~ 35㎛ before foaming, after foaming the average particle 100㎛ and foamed into uniform particles in the range of 70 to 150 ㎛ mostly and the surface It could be confirmed that the particles are smooth.

1 is an enlarged photograph showing before and after foaming of particles produced by the present invention.

Figure 2 is an enlarged photograph showing the particle size and foaming state of the particles produced by the present invention.

Claims (3)

(a) preparing an aqueous dispersion medium; (b) preparing a polymerizable mixture; (c) mixing and homogenizing the aqueous dispersion medium and the polymerizable mixture; (d) polymerizing the homogenized mixture; (e) a method of manufacturing a thermally expandable micro spare, comprising the step of drying the polymerized product after washing and degassing. The method of claim 1, The aqueous dispersion medium is composed of water, dispersion stabilizer and auxiliary stabilizer, The dispersion stabilizer is a colloidal silica, The auxiliary stabilizer uses sodium nitrite and boric acid; The polymerizable mixture is composed of a polymerizable monomer, a crosslinkable monomer, a blowing agent and a polymerization initiator, The polymerizable monomer may be acrylonitrile, methyl methacrylate, methyl acrylate, The crosslinkable monomer is trimethacrylic acid trimetholpropane, The blowing agent is n-butane, The polymerization initiator is AIBN (2,2'-azobis isobutyronitrile) method for producing a heat-shielding micro-spare, characterized in that using. A thermally expandable micro spare, which is prepared by the method of claim 1 in suspension polymerization of a polymerizable mixture containing at least a blowing agent and a polymerizable monomer in an aqueous dispersion medium.

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