阅读说明：本技术 一种含化学发泡剂的可膨胀微球及其制备方法 (Expandable microsphere containing chemical foaming agent and preparation method thereof ) 是由 成晓军 刘利利 于 2020-12-11 设计创作，主要内容包括：本发明提出了一种含化学发泡剂的可膨胀微球及其制备方法,属于材料制备技术领域,所述含化学发泡剂的可膨胀微球由聚合物树脂外壳和壳内所包含的芯材构成,所述聚合物树脂外壳由单体在引发剂、交联剂的存在下聚合而成,所述芯材由不参与自由基聚合的物理发泡剂和化学发泡剂组成。本发明通过采用化学发泡剂和物理发泡剂作为可膨胀微球的主要芯材,解决了可膨胀微球在一段时间后发泡剂泄露的问题,此外,使用本发明的技术手段,可以精准控制微球的起始发泡温度。(The invention provides an expandable microsphere containing a chemical foaming agent and a preparation method thereof, belonging to the technical field of material preparation. The invention solves the problem of foaming agent leakage after a period of time by adopting the chemical foaming agent and the physical foaming agent as the main core materials of the expandable microspheres, and in addition, the initial foaming temperature of the microspheres can be accurately controlled by using the technical means of the invention.)

1. An expandable microsphere containing a chemical foaming agent, which is characterized by comprising a polymer resin shell and a core material contained in the shell, wherein the polymer resin shell is formed by polymerizing monomers in the presence of an initiator and a crosslinking agent, and the core material consists of a physical foaming agent and a chemical foaming agent which do not participate in free radical polymerization.

2. Expandable microspheres with chemical blowing agent according to claim 1, wherein the monomers are selected from the group consisting of airtight monomers, acrylate monomers, amide monomers and other olefin monomers, in combination or in combination.

3. The expandable microspheres with chemical blowing agent according to claim 2, wherein the gas-tight monomer is selected from one or more of acrylonitrile, methacrylonitrile, crotononitrile, fumaronitrile, vinylidene chloride; the acrylate monomer is selected from one or a mixture of methyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, isopropyl methacrylate, vinyl acetate and isobornyl methacrylate; the amide monomer is selected from one or a mixture of acrylamide, methacrylamide, N-hydroxymethyl acrylamide and N, N-dimethylacrylamide; the other olefin monomer is selected from one or a mixture of styrene, N-methyl pyrrolidone, sodium styrene sulfonate, maleic anhydride and N-vinyl maleimide.

4. Expandable microspheres with chemical blowing agent according to claim 1, wherein the chemical blowing agent is selected from the group consisting of azo compounds, sulfonyl hydrazides, nitroso compounds.

5. Expandable microspheres with chemical blowing agent according to claim 4, wherein the azo compound is selected from one or a combination of several of azobisisobutyronitrile, diisopropyl azodicarboxylate, diethyl azodicarboxylate and azoaminobenzene; the sulfonyl hydrazide compound is N, N-dimethyl-N, N-dinitrosoterephthalamide; the nitroso compound is selected from one or a combination of a plurality of benzene sulfonyl hydrazide, p-toluene sulfonyl hydrazide and 4, 4-bis benzene sulfonyl hydrazide oxide; the physical foaming agent is C3-C12 alkane.

6. Expandable microspheres with chemical blowing agent according to claim 1, wherein the physical blowing agent is added in an amount of 0.03-0.08% of the total mass of the microspheres; the addition amount of the chemical foaming agent is 1-2% of the total mass of the microspheres.

7. Expandable microspheres with chemical blowing agent according to claim 1, wherein the initiator comprises oil soluble initiators and water soluble initiators.

8. Expandable microspheres with chemical blowing agent according to claim 1, wherein the oil soluble initiator is selected from LOP, BPO, AIBN, ABVN, DCP, EHP, the reaction temperature is between 30 and 50 ℃, EHP or ABVN; selecting AIBN at the reaction temperature of 50-70 ℃; selecting LOP and BPO at a reaction temperature of above 70 ℃; the dosage of the initiator is 0-10% of the total mass of the reaction system.

9. A method for the preparation of expandable microspheres with chemical blowing agent according to any of the claims 1-8, comprising the steps of:

s1, preparing an oil phase: mixing a monomer, a cross-linking agent, a chemical foaming agent, a physical foaming agent and an initiator, adding the mixture into an oil phase kettle, stirring for 0.5-1h until the mixture is uniformly mixed, and adjusting the pressure of the oil phase kettle to obtain an oil phase;

s2, preparation of a water phase: sequentially adding deionized water, inorganic salt and surfactant into a water phase kettle, and stirring for 0.5-1h at normal pressure until the mixture is uniformly mixed to obtain a water phase;

s3, preparing expandable microspheres: and (4) uniformly mixing the oil phase obtained in the step S1 and the water phase obtained in the step S2, transferring the mixture into a homogenizing kettle for homogenizing for 0.5-1h, then heating to 30-80 ℃, reacting for 20-24h, performing suction filtration, and drying to obtain expandable microsphere powder.

10. The method according to claim 9, wherein the preparation of the aqueous phase in step S2 specifically comprises: preparing a magnesium sulfate solution and a sodium hydroxide solution, then dropwise adding the magnesium sulfate solution into the sodium hydroxide solution under stirring, adding a surfactant after dropwise adding, and continuously stirring for 0.5-1h to obtain a magnesium hydroxide alkaline water phase, wherein the pH value is 8-10; the concentration of the magnesium sulfate solution is 0.1-0.2mol/L, and the concentration of the sodium hydroxide solution is 0.4-0.8 mol/L; the addition amount of the surfactant is 0.01-1% of the total mass of the system.

11. The method according to claim 9, wherein the preparation of the aqueous phase in step S2 specifically comprises: adding silica sol, hydrochloric acid and a surfactant into deionized water, and then violently stirring for 0.5-1h to obtain an acidic silica sol water phase, wherein the pH is 3-5, and the mass ratio of the silica sol to the electrolyte to the deionized water is (3-5): 1: (15-25); the addition amount of the surfactant is 0.01-1% of the total mass of the system.

12. The method according to claim 9, wherein an inorganic dispersant, a thickener, a molecular weight modifier, and a pH modifier are further added to the preparation of the aqueous phase in step S2; the inorganic dispersant is selected from one or a combination of more of silicon dioxide, titanium dioxide, silver chloride, calcium carbonate, barium sulfate, magnesium hydroxide, ferric hydroxide, cupric hydroxide, cuprous oxide, cupric oxide, magnesium hydroxide and aluminum hydroxide; the thickening agent is selected from one or more of carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene and polyvinylpyrrolidone; the molecular weight regulator is selected from one or two of dodecyl mercaptan and isopropanol; the pH regulator is selected from one or more of sodium hydroxide, ammonia water, sodium bicarbonate and hydrochloric acid.

Technical Field

The invention relates to the technical field of material preparation, in particular to expandable microspheres containing a chemical foaming agent and a preparation method thereof.

Background

The expandable microspheres are high molecular plastic microspheres with a core-shell structure, which are formed by an airtight thermoplastic polymer shell and a hydrocarbon (C4-C12 alkane) as a core. At room temperature, the hydrocarbon is confined by the polymer shell and exists in the core in a two-phase coexistence state, and when the microspheres are heated, the hydrocarbon is vaporized and the pressure inside the microspheres increases, and at the same time, when the polymer shell reaches its glass transition temperature (T)_g) When this occurs, the shell becomes soft and malleable. When the internal pressure of the microspheres exceeds the yield strength of the polymer, the microspheres begin to expand and the density decreases dramatically as the mass remains constant and the volume increases dramatically. The expansion of which is dependent on the type and amount of hydrocarbon and the T of the polymer_gAnd controlling the factors. After the microsphere is expanded, the thermoplastic shell is thinned from a thick layer, the volume is increased by more than 80 times, the density is obviously reduced, most of hydrocarbon escapes from the core, and the shell is kept in an expanded state at room temperature.

The expandable microsphere is a plastic particle synthesized by suspension polymerization and consists of an airtight shell and a foaming agent sealed in the airtight shell. When the microspheres are heated, irreversible foaming occurs, and pre-expanded microspheres (ultra-light materials) are generated. The ultra-light material is widely applied to the industrial fields of aerospace, high-speed rail, automobiles and the like, coatings, heat-insulating materials, sealing materials and the like as a light filler. The automotive industry uses ultra-lightweight materials in underbody coatings, tires, composites, and adhesives.

Microsphere synthesis and foaming techniques are reported in US3615972, EP486080, EP566367, CN201610792097.3, CN201510483687.3, CN201280073857.5, CN 2012100109302.3 and the like. Due to the difference of the synthesis process, the microspheres can be divided into low-temperature, medium-high temperature, high-temperature and ultrahigh-temperature microspheres according to the foamable temperature range of the microspheres. The fast-thinking technologies (shanghai) ltd may provide various different forms of expandable microspheres, including expanded and unexpanded forms, of dry powders and filter cakes, of which low-temperature WU1501 and high-temperature DU608 brands are best known.

US3615972, which first reported a synthesis method of expandable microspheres, describes in detail a method for preparing microspheres in different aqueous environments in a microsphere polymerization process, and also has an effect on functional monomers such as styrene when a core-shell structure of expandable microspheres is formed. Although it is described about the preparation of expandable microspheres based on physical blowing agents in general, no detailed approach is given in the further investigation of expandable microspheres.

CN102137878B expandable microspheres formed by suspension polymerization using an infusion growth method. The microspheres consist of a continuous, gas-impermeable shell surrounding a blowing agent. The shell includes a first polymer layer formed from a primary monomer and includes a chemically reactive monomer and a high T_gA second layer inside the monomer. By adopting the synthesis method, the microspheres can be made to carry cations, so that the application of the microspheres in paper pulp is increased. However, due to the complex synthesis method, the synthesized microspheres are mainly used for papermaking, and the application range is limited.

CN108503881A is prepared from (methyl) acrylonitrile and (methyl) acrylic acid as comonomers, and is subjected to free radical suspension polymerization in a small-size form under the action of a suspending agent, wherein an AC foaming agent is used in the material forming process, so that a PMI material with higher strength is prepared. The application method of the chemical foaming agent, such as the AC foaming agent, is a common application method of the chemical foaming agent, and the chemical foaming agent is added at the later stage of material forming, and is foamed through heating to obtain the porous foam material.

Initial foaming temperature (T) of expandable microspheres_start) With the maximum foaming temperature (T)_max) The boiling point and the saturated vapor pressure of the blowing agent in the shell are determined together with the elastic modulus of the shell. The initial foaming temperature is dependent on the type of blowing agent used, and the boiling point of common physical blowing agents is generally related to the foaming temperature. Due to the influence of the shell layer,the microspheres may experience premature or delayed foaming. The shell of the cryomicrosphere generally contains (meth) acrylonitrile (T)_g120 ℃ C.), methyl acrylate homolog (T)_g< 120 ℃), so that the shell glass transition temperature of the microsphere is below 120 ℃ according to the Fox formula. The high-temperature microsphere formula generally contains monomers such as (methyl) acrylic acid and the like, so the shell layer glass transition is higher. In general, expandable microspheres begin to foam before the glass transition temperature, and it is difficult to precisely control the initiation temperature.

The synthesis method of the expandable microspheres has been reported in a large number of patents, the synthesis method of the expandable microspheres based on a physical foaming agent tends to be mature, the preparation technology of the expandable microspheres is further improved, and the synthesis method of the expandable microspheres is expanded.

Disclosure of Invention

The invention aims to provide expandable microspheres containing a chemical foaming agent and a preparation method thereof, wherein different core materials of the chemical foaming agent are adopted, and the expandable microspheres can be successfully prepared only by using a small amount of C3-C12 physical foaming agent, and the combination mode of the chemical foaming agent and the physical foaming agent ensures the core-shell structure of the expandable microspheres, and can utilize the chemical foaming agent to quickly release gas after reaching the decomposition temperature, so that the microspheres start to foam after the decomposition temperature of the chemical foaming agent is taken as the starting foaming temperature of the microspheres and is not limited to the situation that the shell layer reaches the glass transition temperature, and the application mode and the application field of the microspheres are expanded.

The technical scheme of the invention is realized as follows:

the invention provides expandable microspheres containing a chemical foaming agent, which consists of a polymer resin shell and a core material contained in the shell, wherein the polymer resin shell is formed by polymerizing monomers in the presence of an initiator and a crosslinking agent, and the core material consists of a physical foaming agent and a chemical foaming agent which do not participate in free radical polymerization. The core material is composed of substances which do not participate in free radical polymerization, and the core material occupies the volume in the microsphere because the core material does not participate in reaction, thereby providing conditions for the formation of the core-shell structure of the microsphere.

As a further improvement of the invention, the monomer is selected from one or a mixture of more of airtight monomer, acrylate monomer, amide monomer and other olefin monomer; the airtight monomer is selected from one or a mixture of acrylonitrile, methacrylonitrile, crotononitrile, fumaronitrile and vinylidene chloride, and the dosage of the airtight monomer is 20-60% of the total mass of the system, preferably 40-50%; the acrylate monomer is selected from one or a mixture of methyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, isopropyl methacrylate, vinyl acetate and isobornyl methacrylate, and the dosage of the acrylate monomer is 20-60%, preferably 30-45% of the total mass of the system; the amide monomer is selected from one or a mixture of more of acrylamide, methacrylamide, N-hydroxymethyl acrylamide and N, N-dimethyl acrylamide, and the dosage of the amide monomer is 0-50%, preferably 5-35%, and more preferably 10-30% of the total mass of the system; the other olefin monomer is selected from one or more of styrene, N-methyl pyrrolidone, sodium styrene sulfonate, maleic anhydride and N-vinyl maleimide, and the dosage of the other olefin monomer is 20-60 percent of the total weight of the system, preferably 30-45 percent.

The airtight monomer can completely encapsulate the core material by the expandable microspheres and prevent the core material from escaping. The acrylic ester monomer can increase the plasticity of the spherical shell and reduce the glass transition temperature of the spherical shell, has good copolymerization with the airtight monomer, and has the effect of obviously improving the performance of the expandable microsphere shell. The amide monomer can remarkably improve the hydrophilicity of the expandable microspheres, induce phase separation and accelerate the formation process of the microsphere shell. Other olefin monomers can have different effects on the spherical shell of the copolymer, can be used as main monomers and can also be used as functional modified monomers.

As a further improvement of the invention, the chemical foaming agent is selected from one or a combination of several of azo compounds, sulfonyl hydrazine compounds and nitroso compounds; the azo compound is selected from one or a combination of a plurality of azodiisobutyronitrile, diisopropyl azodicarboxylate, diethyl azodicarboxylate and azoaminobenzene; the sulfonyl hydrazide compound is N, N-dimethyl-N, N-dinitrosoterephthalamide; the nitroso compound is selected from one or a combination of a plurality of benzene sulfonyl hydrazide, p-toluene sulfonyl hydrazide and 4, 4-bis benzene sulfonyl hydrazide oxide; the physical foaming agent is C3-C12 alkane, including but not limited to isopentane, isohexane, isooctane, n-octane;

as a further improvement of the invention, the addition amount of the physical foaming agent is 0.03-0.08% of the total mass of the microspheres. The addition amount of the chemical foaming agent is 1-2% of the total mass of the microspheres.

The crosslinking agent is used for increasing the rigidity of the spherical shell and supporting the spherical shell, and the structure of the crosslinking agent is generally acrylate containing 2-3 functional groups. The cross-linking agent is selected from one or a combination of more of divinylbenzene, triallyl cyanurate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate and 1, 4-butanediol diacrylate; the amount of the crosslinking agent is 0 to 10%, preferably 0.01 to 5%, more preferably 0.5 to 3% by mass of the total mass of the reaction system.

The initiator comprises oil-soluble initiator and water-soluble initiator, and mainly plays a role in initiating polymerization reaction, and the suspension polymerization is preferably oil-soluble initiator selected from LOP, BPO, AIBN, ABVN, DCP and EHP.

Depending on the reaction temperature, generally the reaction temperature is below 30-50 ℃ and low temperature initiators such as bis (2-ethylhexyl) peroxydicarbonate (EHP), Azobisisoheptonitrile (ABVN) and the like are generally used. When the reaction temperature is 50-70 deg.C, medium temperature initiator such as Azobisisobutyronitrile (AIBN) can be used, and when the reaction temperature is above 70 deg.C, high temperature initiator such as dilauroyl peroxide (LOP), dibenzoyl peroxide (BPO), etc. can be selected. The amount may be in the range of 0-10%, preferably 0.01-5%, more preferably 0.5-3%. The amount of the initiator is 0 to 10%, preferably 0.01 to 5%, more preferably 0.5 to 3% of the total mass of the reaction system.

The invention further provides a preparation method of the expandable microsphere containing the chemical foaming agent, which is characterized by comprising the following steps of:

s1, preparing an oil phase: mixing a monomer, a cross-linking agent, a chemical foaming agent, a physical foaming agent and an initiator, adding the mixture into an oil phase kettle, stirring for 0.5-1h until the mixture is uniformly mixed, and adjusting the pressure of the oil phase kettle to obtain an oil phase;

s2, preparation of a water phase: sequentially adding deionized water, inorganic salt and surfactant into a water phase kettle, and stirring for 0.5-1h at normal pressure until the mixture is uniformly mixed to obtain a water phase;

s3, preparing expandable microspheres: and (4) uniformly mixing the oil phase obtained in the step S1 and the water phase obtained in the step S2, transferring the mixture into a homogenizing kettle for homogenizing for 0.5-1h, then heating to 30-80 ℃, reacting for 20-24h, performing suction filtration, and drying to obtain expandable microsphere powder.

The homogenization rotation speed is 500-10000rpm, preferably 500-5000rpm, and more preferably 1000-2000 rpm.

As a further improvement of the present invention, the preparation of the aqueous phase in step S2 specifically includes: preparing a magnesium sulfate solution and a sodium hydroxide solution, then dropwise adding the magnesium sulfate solution into the sodium hydroxide solution under stirring, adding a surfactant after dropwise adding, and continuously stirring for 0.5-1h to obtain a magnesium hydroxide alkaline water phase, wherein the pH value is 8-10; preferably, the concentration of the magnesium sulfate solution is 0.1-0.2mol/L, and the concentration of the sodium hydroxide solution is 0.4-0.8 mol/L; the addition amount of the surfactant is 0.01-1% of the total mass of the system.

The other preparation methods such as barium sulfate, calcium carbonate, copper oxide and the like can be prepared according to the preparation method of inorganic double decomposition reaction.

As a further improvement of the present invention, the preparation of the aqueous phase in step S2 specifically includes: adding silica sol, hydrochloric acid and a surfactant into deionized water, and then stirring vigorously for 0.5-1h to obtain an acidic silica sol water phase with a pH of 3-5, wherein preferably the mass ratio of the silica sol to the electrolyte to the deionized water is (3-5): 1: (15-25); the addition amount of the surfactant is 0.01-1% of the total mass of the system.

As a further improvement of the invention, the surfactant is selected from cationic, anionic, nonionic and polymeric surfactants, preferably anionic surfactants, and is selected from one or more of sodium dodecyl benzene sulfonate, sodium diisooctyl succinate sulfonate, sodium dibutyl naphthalene sulfonate, sodium p-methoxy fatty amide benzene sulfonate, low-carbon-chain coconut oil, sodium alpha-alkenyl sulfonate, sodium fatty alcohol ether sulfate and sodium methyl palmitate sulfonate.

As a further improvement of the present invention, in the step S2, an inorganic dispersant, a thickener, a molecular weight regulator, and a pH regulator are further added in the preparation of the aqueous phase; the inorganic dispersant is selected from one or a combination of more of silicon dioxide, titanium dioxide, silver chloride, calcium carbonate, barium sulfate, magnesium hydroxide, ferric hydroxide, cupric hydroxide, cuprous oxide, cupric oxide, magnesium hydroxide and aluminum hydroxide; the thickening agent is selected from one or more of carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene and polyvinylpyrrolidone; the molecular weight regulator is selected from one or two of dodecyl mercaptan and isopropanol; the pH regulator is selected from one or more of sodium hydroxide, ammonia water, sodium bicarbonate and hydrochloric acid.

In the invention, water provides an environment for suspension polymerization, an oil-in-water system is formed, and heat generated in the polymerization process is removed.

Dispersed phase: water as the main dispersed phase may further comprise other solvents, such as alcohols. The mass of water is 1 to 10 times, preferably 2 to 5 times, more preferably 3 to 4 times that of the oil phase.

Inorganic dispersant: the inorganic dispersant is adsorbed on the surface of oil drops and plays a role in preventing coalescence. The inorganic dispersant is selected from nano solid particles, and the addition amount of the inorganic dispersant is 0.5-10%, preferably 0.5-5%, and more preferably 1-3% of the total mass of the water phase. The inorganic salt serves to reduce the solubility of the monomers in the aqueous phase and is added in an amount of 0.5 to 50%, preferably 1 to 30%, more preferably 1 to 20% of the total mass of the aqueous phase.

Surfactant (b): the surfactant can promote the adsorption of the inorganic dispersant on the interface of oil drops, and the anionic surfactant and metal ions form stable ionic bonds, so that the stable adsorption of the inorganic dispersant on the oil drops is maintained to the greatest extent. The amount added is 0.01 to 5%, preferably 0.1 to 5%, more preferably 1 to 3% of the total mass of the aqueous phase.

Thickening agent: the thickening agent can increase the viscosity of the water phase, improve the suspension property of the inorganic dispersant and further improve the stability of suspended oil drops, and the addition amount of the thickening agent is 0.01-5%, preferably 0.1-5%, and more preferably 1-3% of the total mass of the water phase.

Molecular weight regulator: a small amount of a substance having a large chain transfer constant is added to the polymerization system. The chain transfer agent is called molecular weight regulator because of its strong chain transfer ability, the molecular weight can be obviously reduced by adding small amount of molecular weight regulator, and the molecular weight can be controlled by regulating its dosage. The amount added is 0.01 to 5%, preferably 0.1 to 5%, more preferably 1 to 3% of the total mass of the aqueous phase.

pH regulator: the pH regulator is used for regulating the pH value of the water phase, so that the nano inorganic dispersant and the surfactant are combined to stabilize the fine oil drops in the continuous water phase, the pH regulator reduces the interfacial tension between the monomer drops and water, and promotes the dispersion of the drops.

Firstly, the nano inorganic dispersant is flocculated with the help of a co-stabilizer (comprising a surfactant, a thickening agent and an inorganic salt which have a synergistic effect on oil drop stabilization), and then the flocculate is adsorbed on an oil-water interface (part of which can be wetted by an organic phase and a water phase) to prevent oil drops from coalescing. The addition of salts has a great influence on the stability of the emulsion. The flocs must be amphiphilic to adsorb at the oil-water interface, otherwise they attract other monomer droplets and coalescence occurs. The commonly used water phase pH regulator can be selected according to requirements, such as a silica sol water phase system, which belongs to an acidic water phase, and needs hydrochloric acid and the like for regulation, and the dosage of the commonly used water phase pH regulator is that the pH of the water phase is regulated to about 3-5. The magnesium hydroxide aqueous phase belongs to an alkaline aqueous phase, and needs sodium hydroxide, ammonia water, sodium bicarbonate and the like for adjustment, and the dosage of the magnesium hydroxide aqueous phase is generally to adjust the pH of the aqueous phase to about 8-10.

As a further improvement of the present invention, the oil phase tank pressure in step S1 is adjusted to 0 to 15MPa, preferably 0 to 10MPa, more preferably 5 to 8 MPa.

The invention has the following beneficial effects: the invention solves the problem of foaming agent leakage after a period of time by adopting the chemical foaming agent and the physical foaming agent as the main core materials of the expandable microspheres, and in addition, the initial foaming temperature of the microspheres can be accurately controlled by using the technical means of the invention.

The expandable microspheres can be successfully prepared by adopting different chemical foaming agent core materials and a small amount of C3-C12 physical foaming agent, the combination mode of the chemical foaming agent and the physical foaming agent ensures the core-shell structure of the expandable microspheres, and the chemical foaming agent can be utilized to rapidly release gas after reaching the decomposition temperature, so that the microspheres start to foam after the decomposition temperature of the chemical foaming agent is taken as the initial foaming temperature of the microspheres and are not limited to the shell layer reaching the glass transition temperature, and the application mode and the application field of the microspheres are expanded.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic diagram of the structure of expandable microspheres containing a chemical blowing agent;

FIG. 2 is a graph showing the test of the foaming properties of the microspheres of example 3;

wherein, 1, chemical foaming agent; 2. a microsphere shell; 3. a solid dispersant.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

All the examples are parts by mass.

Example 1

S1, preparing 1kg of 0.15mol/L magnesium sulfate solution, preparing 1kg of 0.6mol/L sodium hydroxide solution, then dropwise adding magnesium sulfate into the sodium hydroxide solution under vigorous stirring, after dropwise addition, keeping the pH at 9, adding 0.05% of surfactant sodium dodecyl benzene sulfonate, and continuing stirring for 0.5h to obtain a magnesium hydroxide alkaline water phase;

s2, taking 1000 parts of the magnesium hydroxide alkaline water phase prepared by the method as a water phase, 60 parts of acrylonitrile, 30 parts of methyl methacrylate, 10 parts of methyl acrylate, 1 part of azobisisoheptonitrile, 0.5 part of divinylbenzene, 0.05 part of isobutane, and 1 part of azobisisobutyronitrile (decomposition temperature 98-110 ℃), uniformly mixing to obtain an oil phase, wherein the polymerization temperature is 45 ℃, and the polymerization time is 20 hours, and then preparing the expandable microspheres containing the azobisisobutyronitrile serving as a chemical foaming agent according to the preparation method of the expandable microspheres. The particle diameter of the microsphere is 20um and T_s＝100℃，T_max＝140℃。

Example 2

S1, adding 400g of silica sol and 0.05% of surfactant dibutyl naphthalene sodium sulfonate into 2kg of deionized water, adjusting the pH to 4 by using HCl solution, and then violently stirring for 0.5h to obtain an acidic silica sol water phase;

s2, taking 1000 parts of the silica sol water phase prepared by the invention as a water phase, 60 parts of acrylonitrile, 30 parts of methyl methacrylate, 10 parts of methyl acrylate, 1 part of azobisisoheptonitrile, 0.5 part of divinylbenzene, 0.05 part of isobutane, and 1 part of azobisisobutyronitrile (decomposition temperature 98-110 ℃), uniformly mixing to obtain an oil phase, wherein the polymerization temperature is 45 ℃, and the polymerization time is 20 hours, and then preparing the expandable microspheres containing the azobisisobutyronitrile as a chemical foaming agent according to the preparation method of the expandable microspheres. The particle diameter of the microsphere is 16um and T_s＝105℃，T_max＝136℃。

As azobisisobutyronitrile belongs to a class of initiators, the polymerization temperature is selected to be 45 ℃ to prevent early thermal decomposition.

Example 1 and example 2, in which the aqueous phase was replaced, the microspheres obtained from the basic magnesium hydroxide aqueous phase had a larger particle size than the acidic aqueous phase; because the particle size is small, the shell layer of the microsphere is thin, and the maximum foaming temperature is low.

Comparative example 1

S1, adding 400g of silica sol and 0.05% of surfactant dibutyl naphthalene sodium sulfonate into 2kg of deionized water, adjusting the pH to 4 by using HCl solution, and then violently stirring for 0.5h to obtain an acidic silica sol water phase;

s2, taking 1000 parts of the silica sol water phase prepared by the method as a water phase, uniformly mixing 60 parts of acrylonitrile, 30 parts of methyl methacrylate, 10 parts of methyl acrylate, 1 part of azobisisoheptonitrile, 0.5 part of divinylbenzene, 0.05 part of isobutane and 20 parts of a physical foaming agent isobutane to obtain an oil phase, wherein the polymerization temperature is 45 ℃, the polymerization time is 20 hours, and then preparing the expandable microspheres containing isobutane according to the preparation method of the expandable microspheres. The particle diameter of the microsphere is 17um and T_s＝90℃，T_max＝140℃。

The expandable microspheres prepared by replacing different foaming agents in example 1 and comparative example 1 show that the microspheres begin to expand after reaching the glass transition temperature after being heated, and the initial expansion temperature is advanced to 90 ℃, while the microspheres prepared by using azobisisobutyronitrile as a foaming agent in example 1 have an initial foaming temperature of 105 ℃, and the initial foaming temperature of the microspheres can be accurately controlled by using a chemical foaming agent around the decomposition temperature of the azobisisobutyronitrile.

Isobutane exists in the microspheres in a gas-liquid coexisting form and can gradually permeate out of the shell, and azodiisobutyronitrile is hardly decomposed at normal temperature, so that the problem of foaming agent leakage is solved.

Example 3

S1, preparing 1kg of 0.15mol/L magnesium sulfate solution, preparing 1kg of 0.6mol/L sodium hydroxide solution, then dropwise adding magnesium sulfate into the sodium hydroxide solution under vigorous stirring, after dropwise addition, keeping the pH at 9, adding 0.05% of surfactant sodium dodecyl benzene sulfonate, and continuing stirring for 0.5h to obtain a magnesium hydroxide alkaline water phase;

s2, taking 1000 parts of the magnesium hydroxide alkaline water phase prepared by the invention as a water phase, 60 parts of acrylonitrile, 30 parts of methyl methacrylate, 10 parts of methacrylic acid and 1 part of azodiisoheptanonitrile,0.5 part of divinylbenzene, 0.05 part of isopentane and 1 part of 4, 4-oxybis-benzenesulfonylhydrazide as a chemical foaming agent (the decomposition temperature is 140-. The particle size of the microspheres is 24um and T_s＝135℃，T_max＝165℃。

It is clear from fig. 2 that the microspheres started up very quickly at 135 ℃, indicating that the effect of the chemical blowing agent was achieved and that precise control of the microsphere initiation temperature was successfully achieved.

Example 4

S1, preparing 1kg of 0.15mol/L magnesium sulfate solution, preparing 1kg of 0.6mol/L sodium hydroxide solution, then dropwise adding magnesium sulfate into the sodium hydroxide solution under vigorous stirring, after dropwise addition, keeping the pH at 9, adding 0.05% of surfactant sodium dodecyl benzene sulfonate, and continuing stirring for 0.5h to obtain a magnesium hydroxide alkaline water phase;

s2, taking 1000 parts of the magnesium hydroxide alkaline water phase prepared by the invention as a water phase, 60 parts of acrylonitrile, 10 parts of methyl methacrylate, 30 parts of methacrylic acid, 0.05 styrene, 1 part of lauroyl peroxide, 0.5 part of divinylbenzene, 0.05 part of isopentane, 1 part of 1, 3-benzenesulfonylhydrazide as a chemical foaming agent (the decomposition temperature is 150 ℃ and 200 ℃), uniformly mixing to obtain an oil phase, wherein the polymerization temperature is 65 ℃ and the polymerization time is 20h, and then preparing the expandable microspheres containing the 1, 3-benzenesulfonylhydrazide as the chemical foaming agent according to the preparation method of the expandable microspheres. The particle diameter of the microsphere is 30um and T_s＝200℃，T_max＝260℃。

Due to the increased methacrylic acid content, the hydrophilicity of the microspheres is increased and the particle size of the microspheres is also increased.

In example 3 and example 4, the encapsulation of the chemical foaming agent in the microspheres is realized by changing different oil phase formulas, and the foaming temperature is different due to the different decomposition temperature of the used chemical foaming agent.

According to the invention, research shows that a chemical foaming agent which can be decomposed at a certain temperature can be used and dissolved in oil phases such as acrylonitrile, and then the chemical foaming agent can be gradually separated out from the oil phase after a microsphere shell is generated and further remains in the microsphere shell without participating in free radical polymerization in the process of gradually generating a polymer from the oil phase.

The invention provides a simple synthesis method, which uses a chemical foaming agent, namely a solid foaming agent dissolved in oil phase monomers such as acrylonitrile, Methyl Methacrylate (MMA), methacrylic acid (MAA) and the like, wherein the chemical foaming agent is gradually separated out from the monomers along with the reaction, and remains in a microsphere shell together with the foaming agent, and the expandable microsphere with the chemical foaming agent encapsulated in the shell is generated after suspension polymerization. In the process of foaming the microspheres, the chemical foaming agent decomposes to generate gas with increasing temperature, thereby foaming the microspheres.

Compared with the prior art, the expandable microsphere adopts the chemical foaming agent and the physical foaming agent as the main core materials of the expandable microsphere, so that the problem of foaming agent leakage after a period of time of the expandable microsphere is solved, and in addition, the initial foaming temperature of the microsphere can be accurately controlled by using the technical means of the invention.

The expandable microspheres can be successfully prepared by adopting different chemical foaming agent core materials and a small amount of C3-C12 physical foaming agent, the combination mode of the chemical foaming agent and the physical foaming agent ensures the core-shell structure of the expandable microspheres, and the chemical foaming agent can be utilized to rapidly release gas after reaching the decomposition temperature, so that the microspheres start to foam after the decomposition temperature of the chemical foaming agent is taken as the initial foaming temperature of the microspheres and are not limited to the shell layer reaching the glass transition temperature, and the application mode and the application field of the microspheres are expanded.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.