CN117924788A - Thermal expansion microsphere and preparation method thereof - Google Patents

Abstract

The invention provides a thermal expansion microsphere and a preparation method thereof. The thermally expandable microspheres comprise a core and a shell; the core comprises a foaming agent; the shell layer comprises a thermoplastic polymer, and the monomer for preparing the thermoplastic polymer comprises an N-hydroxyalkyl acrylamide monomer with a specific structure. The thermal expansion microsphere has longer expansion temperature range, is more stable in the thermal expansion process, is not easy to damage and collapse, and has good thermal stability.

Description

Thermal expansion microsphere and preparation method thereof

Technical Field

The invention belongs to the technical field of polymer microspheres, and particularly relates to a thermal expansion microsphere and a preparation method thereof.

Background

Thermally expandable microspheres refer to microspheres in which the shell softens when heated, and the blowing agent contained therein volatilizes, causing an increase in internal pressure, thereby expanding the microspheres. Thermally expandable microspheres are used as blowing agents, light fillers, etc. in many different fields, for example in the fields of elastomers, thermoplastic elastomers, polymers, putties, primers, plastisols, printing inks, papers, explosives, and cable insulation.

The expanded microspheres are usually used as an additive, and it is necessary to heat a mixture of a base material and the expanded microspheres to expand the mixture during the application process, or to heat-treat the mixture in advance to obtain expanded microspheres for reuse. In either application, the expanded microspheres need to undergo a thermal expansion process. Because of the thermal expansion characteristics of the expanded microspheres, the shell layer must be thermoplastic, which necessarily results in that the shell layer becomes very soft at higher temperatures, loses strength and air tightness, and causes phenomena such as cracking, collapse, leakage of foaming agent, and the like, which affect the performance of the final product. This limits the use of expanded microspheres in some high temperature applications, such as plastic melt extrusion, self-exothermic thermosetting resins, and other processing or use temperature-higher scenes.

Several efforts are currently made to improve the heat resistance of expanded microspheres, and several methods are disclosed. For example, CN104334268B discloses a method for achieving high temperature resistance of microspheres by increasing the softening temperature of the shell polymer by introducing methacrylamide and methacrylonitrile with high glass transition temperature (Tg) as comonomers of the shell. However, the introduction of the high Tg monomer increases the softening point temperature of the polymer shell and is not suitable for expanded microspheres. CN101341227B, CN107001911B discloses a method for preparing high temperature resistant expanded microspheres by utilizing the property that a rigid heat resistant acrylamide structure can be generated by reaction between an acrylic monomer and an acrylonitrile monomer, however, the reaction of acrylic acid and acrylonitrile to generate an imide structure usually needs a temperature of more than 150 ℃ to occur, which limits the application range of the scheme; in addition, the solubility of the acrylic monomer in water is high, which also results in a high residual monomer in the aqueous solution in the reaction system. CN116199933a discloses a scheme of copolymerizing a carboxyl group type monomer and an acrylamide type monomer, and the similar problems described above also exist.

Therefore, developing a method for preparing expanded microspheres which improves the heat resistance of the microspheres and can avoid the defects is an urgent technical problem in the field.

Disclosure of Invention

Aiming at the defects of the prior art, one of the purposes of the invention is to provide a thermal expansion microsphere with a core-shell structure, wherein the thermal expansion microsphere has a longer expansion temperature range, is more stable in thermal expansion process and is not easy to damage and collapse, and the prepared expanded microsphere has good thermal stability.

In order to achieve the purpose of the invention, the following technical scheme is adopted:

A thermally expandable microsphere having a core-shell structure, the thermally expandable microsphere comprising a core and a shell;

the core comprises a foaming agent;

The shell layer comprises a thermoplastic polymer, and the monomer for preparing the thermoplastic polymer comprises an N-hydroxyalkyl acrylamide monomer of the following structural formula (1) and/or formula (2):

Wherein R is a C1-C5 alkyl or alkyl-containing group.

In the technical scheme of the invention, N-methylolacrylamide is used as one of comonomers for preparing the expanded microsphere. The inventor finds that N-methylolacrylamide is a self-crosslinking monomer, the structure of the self-crosslinking monomer contains double bonds capable of undergoing free radical polymerization and also contains condensable hydroxymethyl groups, the double bonds can be introduced into a polymer chain segment through free radical polymerization, and the hydroxymethyl groups connected in the polymer chain segment can undergo condensation reaction under the high-temperature condition to form crosslinking points. The expandable microspheres prepared by the technology do not need to add a large amount of multifunctional crosslinking monomers, retain higher expansion capacity of the microspheres, and can be further crosslinked in the thermal expansion process to increase the strength of the shell and reduce the damage in the expansion process.

In one embodiment of the invention, the proportion of the shell layer in the thermally expandable microspheres is 70 to 95wt%, preferably 70 to 90wt%.

In one embodiment of the present invention, the thermally expandable microspheres have a particle size of 1 to 500. Mu.m, preferably 1 to 200. Mu.m, more preferably 3 to 100. Mu.m, still more preferably 5 to 50. Mu.m.

In one embodiment of the invention, the blowing agent of the core is a low boiling point blowing agent having a boiling point of not more than 100 ℃, preferably one or more of propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, cyclohexane, petroleum ether, n-heptane, isooctane.

In one embodiment of the invention, the microsphere has an expansion temperature range, i.e., the difference between the initial expansion and the maximum expansion temperature, of greater than 40 ℃.

In one embodiment of the present invention, the N-hydroxyalkyl acrylamide monomer used to prepare the thermoplastic polymer in the shell layer comprises one or more of N-methylolacrylamide, N- (1-hydroxyethyl) acrylamide, N- (1-hydroxypropyl) acrylamide, N- (1-hydroxybutyl) acrylamide, N-hydroxyethyl acrylamide, N-hydroxypropyl acrylamide, N-hydroxybutyl acrylamide, N- (1, 2-dihydroxyethyl) acrylamide, N- (1, 3-dihydroxypropyl) acrylamide, N- (hydroxymethyl) methacrylamide; preferably, the N-hydroxyalkyl acrylamide contains 0.01 to 20wt% of oligomers, the oligomers having an average molecular weight of 300 to 5000.

In one embodiment of the invention, the proportion of N-hydroxyalkyl acrylamide monomer in the monomers for preparing the thermoplastic polymer is from 0.1 to 20% by weight, preferably from 1 to 10% by weight.

In one embodiment of the invention, the monomers for preparing the thermoplastic polymer further comprise other monofunctional monomers containing carbon-carbon double bonds and/or polyfunctional monomers containing carbon-carbon double bonds in addition to the N-hydroxyalkyl acrylamide monomer.

In one embodiment of the present invention, wherein preferably the other monofunctional monomer containing a carbon-carbon double bond comprises one or more of acrylonitrile-based monomer, vinyl halide-based monomer, acrylate-based monomer, vinyl pyridine, styrene-based monomer, vinyl ester-based monomer; among them, it is preferable that the acrylonitrile-based monomer contains one or more of acrylonitrile, methacrylonitrile, fumaronitrile, crotononitrile, α -chloroacrylonitrile, or α -ethoxyacrylonitrile, and it is more preferable that acrylonitrile and/or methacrylonitrile; wherein, the preferable acrylic monomer comprises one or more of methyl acrylate, ethyl acrylate, methyl methacrylate, isobornyl methacrylate or ethyl methacrylate; among them, vinyl ester monomer is preferably vinyl acetate; among them, it is preferable that the styrene-based monomer contains styrene and/or α -methylstyrene.

In one embodiment of the invention, the proportion of the other monofunctional monomers containing carbon-carbon double bonds in the preparation monomers of the thermoplastic polymer is from 70 to 99.5% by weight, preferably from 90 to 99% by weight.

In one embodiment of the present invention, wherein the other carbon double bond containing polyfunctional monomer preferably comprises divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1, 4-butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, 1, 3-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1, 10-decanediol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, dimethyloltricyclodecane di (meth) acrylate, triallylmethacrylate, allyl methacrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane triacrylate, polyethylene glycol tri (meth) acrylate, di (meth) oxyacrylate, 3-ethyleneglycol triacrylate or a plurality of triacrylates.

In one embodiment of the invention, the proportion of the other polyfunctional monomers containing carbon-carbon double bonds in the preparation monomers of the thermoplastic polymer is from 0.1 to 1% by weight, preferably from 0.2 to 0.5% by weight.

The invention also aims to provide a preparation method of the thermal expansion microsphere with the core-shell structure.

A method for preparing a thermally-expansive microsphere with a core-shell structure, wherein the microsphere is the microsphere, and the method comprises the following steps:

s1: mixing a foaming agent, a monomer for preparing a thermoplastic polymer and an initiator to obtain an oil phase mixture;

s2: and adding the oil phase mixture into an aqueous phase medium for reaction to obtain the thermal expansion microsphere with the core-shell structure.

In one embodiment of the invention, the initiator of S1 comprises one or more of an organic peroxide type initiator and/or an azo type initiator, preferably behenyl peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, dioctyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, t-butyl peracetate, tertbutyl per month Gui Xianshu, t-butyl benzoin, t-butyl hydroperoxide, cumene ethyl peroxy, diisopropyl hydroxydicarboxylate, 2' -azobisisoheptonitrile, 2' -azobisisobutyronitrile, 1' -azobis (cyclohexane-1-carbonitrile), dimethyl 2,2' -azobis (2-methylpropionate), 2' -azobis (2-methyl-N- (2-hydroxyethyl) propionamide); preferably, the initiator comprises 0.1 to 2wt%, preferably 0.3 to 1wt% of the monomer.

In one embodiment of the invention, the blowing agent as described in S1 is used in an amount of from 5 to 50% by weight, preferably from 10 to 30% by weight, based on the mass of the monomers.

In one embodiment of the invention, the aqueous medium of S2 comprises water, a solid suspending agent and a water-soluble salt; preferably, the solid suspending agent comprises one or more of silica, chalk, bentonite, starch, crosslinked polymers, methylcellulose, gum agar, hydroxypropyl methylcellulose, carboxymethyl cellulose, colloidal clay, calcium phosphate, calcium carbonate, magnesium hydroxide, barium sulphate, calcium oxalate, aluminium hydroxide, ferric hydroxide, zinc hydroxide, nickel hydroxide, manganese hydroxide; preferably, the water soluble salt comprises sodium chloride and/or sodium nitrite.

In one embodiment of the invention, the aqueous medium of S2 further comprises a stabilizing aid; preferably, the stabilizing aid comprises one or more of polyvinylpyrrolidone, sulfonated polystyrene, alginate carboxymethyl fibers, tetramethyl ammonium hydroxide, tetramethyl ammonium chloride, diethanolamine/adipic acid water-soluble condensates, ethylene oxide, urea/formaldehyde water-soluble condensates, polyethylenimine, gelatin, casein, albumin, gelatin proteins, soaps, alkyl sulfates, alkyl sulfonates.

In one embodiment of the invention, the temperature of the reaction of S2 is 40-80℃for 5-30 hours.

In one embodiment of the invention, the reaction further comprises the steps of filtering and drying after the completion of the reaction; preferably, the method of filtration comprises any one or a combination of at least two of bed filtration, positive/negative pressure filtration or spin-on filtration; preferably, the method of drying comprises any one or a combination of at least two of spray drying, tunnel drying, rotary drying, drum drying, flash drying, palladium drying or fluid bed drying.

It is still another object of the present invention to provide a thermally expanded microsphere after heat treatment.

The heat-treated heat-expandable microspheres are the heat-expandable microspheres or the heat-expandable microspheres prepared by the preparation method.

Compared with the prior art, the invention has the following beneficial effects:

The microsphere has higher expansion capacity, the expansion temperature range of the obtained thermal expansion microsphere is longer, the thermal expansion process is more stable, the damage and the collapse are not easy to occur, and the prepared expanded microsphere has better thermal stability and wider application field.

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Examples and comparative examples main raw material sources:

n-methylolacrylamide, industrial grade 98% of Jinan century, which is communicated with chemical industry Co., ltd;

N- (hydroxymethyl) methacrylamide, 60% of the available special chemical (Shanghai) Co., ltd;

N- (2-hydroxypropyl) methacrylamide 98% of Shanghai Ala Biochemical technology Co., ltd;

N- (2-hydroxyethyl) acrylamide, shanghai Ala Biochemical technology Co., ltd;

acrylonitrile (AN): shanghai Ala Biochemical technologies Co., ltd., reagent grade 99%;

Methyl Methacrylate (MMA): shanghai Ala Biochemical technologies Co., ltd., reagent grade 99%;

vinylidene chloride (VDC): shanghai Ala Biochemical technologies Co., ltd., reagent grade 99%;

methacrylonitrile (MAN): 99.5% of Huateng pharmaceutical Co., ltd;

ethylene Glycol Dimethacrylate (EGDMA): shandong Chuang chemical industry Co., ltd, industrial grade 99%;

Trimethylolpropane trimethacrylate (TMPTMA): guangzhou Sanwang chemical materials Co., ltd, industrial grade, 98%;

trimethylolpropane triacrylate (TMPTA), 85% of Shanghai Ala Biochemical technology Co., ltd;

bis (4-t-butylcyclohexyl) peroxydicarbonate) (BCHPC) from Lanzhou auxiliary plant, technical grade 95%;

Dilauryl peroxide (LPO): shanghai Ala Biochemical technology Co., ltd., 98%;

Azobisisobutyronitrile (AIBN): 99% of Shandong kylin chemical industry Co., ltd;

Dibenzoyl peroxide (BPO): noron, inc., industrial grade 75%;

sodium chloride: 99% of Shenghai chemical industry Co., ltd;

potassium chloride: 98% of industrial grade in eastern reagent factories in Liaoning city;

Sodium nitrite: reagent grade 99% of Shanghai Ala Biochemical technologies Co., ltd.

Isopentane: the Ala group Co., ltd, industrial grade 99%;

Isobutane: liaoning Date gas Co., ltd, industrial grade 99%;

Polyvinyl pyrrolidone K30, industrial grade 99% of the high molecular materials of Shenhua, huzhou;

Colloidal silica: the silicon product of Kohn is of the responsibility of Co, industrial grade, and the solid content is 30wt%;

The main test apparatus and method used in the examples and comparative examples:

Polymer particle size test a laser particle sizer was used, model Bettersize 2600, the average particle size expressed as median diameter D50 in volume diameter; particle size distribution is expressed as SPAN, meaning span= (D90-D10)/D50.

The expansion properties of the microspheres were measured using a thermo-mechanical analytical instrument (TMA) model Metreler TMA/SDTA2+ test method of 15 ℃/min. The test steps are as follows: adding 1mg of thermally-expanded microspheres into a 150 mu L ceramic crucible, adding a gasket with a matched diameter above the microsphere layer, preparing a sample, measuring the height of the sample in a state that a force of 0.06N is applied to the sample from above by a presser, heating the sample from 20 ℃ to 300 ℃ at a heating rate of 15 ℃/min in a state that a force of 0.06N is applied by the presser, and measuring the displacement of the presser in the vertical direction; the displacement start temperature in the positive direction was set as the expansion start temperature (Tstart), the temperature at which the maximum displacement amount was exhibited was set as the maximum expansion temperature (Tmax), and the ratio of the maximum height of the expansion process to the initial sample height was set as the expansion ratio.

The true density testing method comprises the following steps: the measurement was performed by a liquid displacement method (archimedes method) using isopropyl alcohol at an ambient temperature of 25 ℃ and a relative humidity of 50%; the specific test steps are as follows: cleaning and drying a volumetric flask with the capacity of 100mL, weighing the volumetric flask with the weight of WB1, adding isopropanol into the volumetric flask, accurately fixing the volume to a scale, and weighing the volumetric flask filled with 100mL of isopropanol with the weight of WB2; further, after washing and drying another volumetric flask having a capacity of 100mL, weighing the volumetric flask to give WS1, adding about 50mL of expanded microspheres to the volumetric flask, weighing the volumetric flask having the thermally expanded microspheres therein to give WS2, adding isopropyl alcohol to the volumetric flask having the thermally expanded microspheres therein to fix the volume to the scale of the volumetric flask (ensuring no air bubbles are introduced during the process), weighing the volumetric flask to give WS3, and finally introducing the obtained WB1, WB2, WS1, WS2 and WS3 into ρ= (WS 2-WS 1) × (WB 2-WB 1)/100 ]/[ (WB 2-WB 1) - (WS 3-WS 2), and calculating the true density of the expanded microspheres.

Preparation example 1

Preparing an aqueous medium: 100g of sodium chloride, 10g of silicon dioxide water dispersing agent (the mass content of silicon dioxide is 30%), 0.2g of polyvinylpyrrolidone and 0.5g of sodium nitrite are added into 500g of deionized water, and the mixture is stirred and mixed uniformly to obtain the aqueous phase medium.

Preparation example 2

Preparing an aqueous medium: 100g of sodium chloride, 10g of magnesium hydroxide water-dispersible colloid (the mass content of magnesium hydroxide is 30%), 0.2g of sodium dodecyl benzene sulfonate and 0.5g of sodium nitrite are added into 500g of deionized water, and the mixture is stirred and mixed uniformly to obtain the aqueous phase medium.

Example 1

2G N-methylolacrylamide (oligomer content 5%, average molecular weight of oligomer 1000), 64g acrylonitrile, 25g vinylidene chloride, 8.5g methyl methacrylate, 0.5g ethylene glycol dimethacrylate, 12g isobutane and 0.5g bis (4-tert-butylcyclohexyl) peroxydicarbonate are uniformly mixed to obtain an oil phase mixture, the oil phase mixture is added into an aqueous phase medium (preparation 1), an oil-in-water emulsion is formed after mechanical high-speed dispersion at 6000rpm, the oil phase mixture is transferred into a reaction kettle, nitrogen is filled into the reaction kettle until the pressure of the system is 0.8MPa (gauge pressure), then the reaction kettle is reacted for 20 hours under the stirring condition of 58 ℃ and 500rpm, the reaction kettle is filtered, washed 3 times by deionized water, and the corresponding thermal expansion microspheres are obtained after drying at 70 ℃.

Example 2

5G N- (hydroxymethyl) methacrylamide (oligomer content 2%, average molecular weight of oligomer 2000), 62.7g acrylonitrile, 24g vinylidene chloride, 8g methyl methacrylate, 0.3g trimethylolpropane trimethacrylate, 12g isobutane and 0.3g azodiisobutyronitrile are uniformly mixed to obtain an oil phase mixture, the oil phase mixture is added into an aqueous phase medium (preparation example 1), an oil-in-water emulsion is formed after mechanical high-speed dispersion at 5000rpm, the oil phase mixture is transferred into a reaction kettle, nitrogen is filled into the reaction kettle until the pressure of the system is 0.8MPa (gauge pressure), then the reaction kettle is reacted for 20 hours under the stirring condition of 60 ℃ and 500rpm, the reaction kettle is filtered, washed with deionized water for 3 times, and dried at 70 ℃ to obtain the corresponding thermal expansion microspheres.

Example 3

18G N- (2-hydroxypropyl) methacrylamide (oligomer content 3%, oligomer average molecular weight 500), 57.4g acrylonitrile, 18g vinyl acetate, 6g methyl methacrylate, 0.6g trimethylolpropane triacrylate, 15g isopentane and 0.8g dilauroyl peroxide were uniformly mixed to obtain an oil phase mixture, the oil phase mixture was added to an aqueous medium (preparation example 1), an oil-in-water emulsion was formed after mechanical high-speed dispersion at 4000rpm, transferred to a reaction kettle, nitrogen was charged into the reaction kettle until the pressure of the system was 0.8MPa (gauge pressure), then reacted for 18 hours under stirring conditions of 60 ℃ and 500rpm, filtered, washed 3 times with deionized water, and dried at 70 ℃ to obtain the corresponding thermally expanded microspheres.

Example 4

0.2G N- (2-hydroxyethyl) acrylamide (oligomer content 18%, oligomer average molecular weight 4500), 38g methacrylonitrile, 61g acrylonitrile, 0.8g ethylene glycol dimethacrylate, 28g isopentane and 1g benzoyl peroxide were uniformly mixed to obtain an oil phase mixture, the oil phase mixture was added to an aqueous medium (preparation 2), an oil-in-water emulsion was formed after mechanical high-speed dispersion at 2500rpm, transferred to a reaction kettle, nitrogen was charged into the reaction kettle until the pressure of the system was 0.8MPa (gauge pressure), then reacted for 10 hours under stirring conditions of 75 ℃ and 500rpm, filtered, washed with deionized water for 3 times, and dried at 70 ℃ to obtain corresponding heat-expandable microspheres.

Example 5

8G N-methylolacrylamide (oligomer content 0.05%, average molecular weight of oligomer 2000), 40.8g acrylonitrile, 45g ethyl acrylate, 6g methyl methacrylate, 0.2g trimethylolpropane triacrylate, 15g isobutane and 0.9g bis (4-tert-butylcyclohexyl) peroxydicarbonate were uniformly mixed to obtain an oil phase mixture, the oil phase mixture was added to an aqueous medium (preparation example 1), and an oil-in-water emulsion was formed after mechanical high-speed dispersion at 5000rpm, transferred to a reaction kettle, nitrogen was charged into the reaction kettle until the pressure of the system was 0.8MPa (gauge pressure), then reacted for 25 hours at 56 ℃ under a stirring condition of 500rpm, filtered, washed with deionized water for 3 times, and dried at 70 ℃ to obtain the corresponding thermally expanded microspheres.

Example 6

1G N- (hydroxymethyl) methacrylamide (oligomer content 5%, average molecular weight of oligomer 3000), 70.5g acrylonitrile, 20g vinylidene chloride, 8g methyl methacrylate, 0.5g trimethylolpropane trimethacrylate, 20g isopentane and 0.6g azobisisobutyronitrile are uniformly mixed to obtain an oil phase mixture, the oil phase mixture is added into an aqueous phase medium (preparation example 1), oil-in-water emulsion is formed after mechanical high-speed dispersion at 4500rpm, the oil phase mixture is transferred into a reaction kettle, nitrogen is filled into the reaction kettle until the pressure of the system is 0.8MPa (gauge pressure), then the reaction is carried out for 15 hours under the stirring condition of 65 ℃ and 500rpm, the reaction kettle is filtered, washed 3 times with deionized water, and the corresponding thermal expansion microspheres are obtained after drying at 70 ℃.

Comparative example 1

In comparison with example 1, the oil phase component was not added with N-methylolacrylamide as comonomer.

65G of acrylonitrile, 25.5g of vinylidene chloride, 9g of methyl methacrylate, 0.5g of ethylene glycol dimethacrylate, 12g of isobutane and 0.5g of bis (4-tert-butylcyclohexyl) peroxydicarbonate are uniformly mixed to obtain an oil phase mixture, the oil phase mixture is added into an aqueous phase medium (preparation example 1), an oil-in-water emulsion is formed after mechanical high-speed dispersion at 6000rpm, the oil phase mixture is transferred into a reaction kettle, nitrogen is filled into the reaction kettle until the pressure of the system is 0.8MPa (gauge pressure), then the reaction kettle is reacted for 20 hours under the stirring condition of 58 ℃ and 500rpm, filtering, washing with deionized water for 3 times, and drying at 70 ℃ to obtain corresponding thermal expansion microspheres.

Comparative example 2

In comparison with example 6, the oil phase component was not added with N- (hydroxymethyl) methacrylamide as a comonomer.

71G of acrylonitrile, 20.5g of vinylidene chloride, 8g of methyl methacrylate, 0.5g of trimethylolpropane trimethacrylate, 20g of isopentane and 0.6g of azobisisobutyronitrile are uniformly mixed to obtain an oil phase mixture, the oil phase mixture is added into an aqueous phase medium (preparation example 1), an oil-in-water emulsion is formed after mechanical high-speed dispersion at 4500rpm, the oil phase mixture is transferred into a reaction kettle, nitrogen is filled into the reaction kettle until the pressure of the system is 0.8MPa (gauge pressure), then the reaction is carried out for 15 hours under the stirring condition of 65 ℃ and 500rpm, the reaction is carried out, the filtration and washing with deionized water are carried out for 3 times, and the corresponding thermal expansion microspheres are obtained after drying at 70 ℃.

The thermally expandable microspheres (examples 1 to 6 and comparative examples 1 to 2) were put into a vessel having a heating function, and the solid mixture powder was suspended therein by rapid stirring, and heat-treated at the corresponding temperature for 3 minutes to perform thermal expansion treatment, to obtain expanded microspheres.

The thermal expansion microspheres obtained in examples 1 to 6 and comparative examples 1 to 2 were subjected to expansion performance test and thermal expansion treatment, and the results are shown in table 1:

TABLE 1

As can be seen from the data of Table 1 comparing examples 1 to 6 with comparative examples 1 to 2, the thermal expansion microspheres prepared from the preparation monomer without introducing N-hydroxyalkyl acrylamide as the shell layer had a narrower expansion temperature range (Tmax-Tstar), both of which were smaller than 40℃and lower Tmax, because the shell layer monomer comprising the polymer had lower strength after heating, and was liable to burst and leak gas at a high Wen Duanhui, and the density of the product after expansion was also significantly higher.

The applicant states that the present invention has been described with reference to the above examples as a thermally expandable microsphere having a core-shell structure and a method for preparing the same, but the present invention is not limited to the above examples, i.e., it is not meant that the present invention must be practiced by relying on the above examples. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of raw materials for the product of the present invention, addition of auxiliary components, selection of specific modes, etc., falls within the scope of the present invention and the scope of disclosure.

Claims (8)

1. A thermally expandable microsphere having a core-shell structure, wherein the thermally expandable microsphere comprises a core and a shell;

the core comprises a foaming agent;

The shell layer comprises a thermoplastic polymer, and the monomer for preparing the thermoplastic polymer comprises an N-hydroxyalkyl acrylamide monomer of the following structural formula (1) and/or formula (2):

Wherein R is a C1-C5 alkyl or alkyl-containing group.

2. The thermally expanded microsphere of claim 1, wherein the proportion of the shell layer in the thermally expanded microsphere is 70 to 95wt%, preferably 70 to 90wt%;

and/or the particle diameter of the thermally expandable microspheres is 1 to 500. Mu.m, preferably 1 to 200. Mu.m, more preferably 3 to 100. Mu.m, still more preferably 5 to 50. Mu.m.

3. The thermally expanded microspheres according to claim 1 or 2, wherein the foaming agent of the core is a low boiling point foaming agent having a boiling point not higher than 100 ℃, preferably one or more of propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, cyclohexane, petroleum ether, n-heptane, isooctane;

And/or the expansion temperature range of the microsphere, namely the difference between the initial expansion degree and the maximum expansion temperature is more than 40 ℃.

4. The thermally expandable microsphere of any one of claims 1-3, wherein the N-hydroxyalkyl acrylamide monomer used to prepare the thermoplastic polymer in the shell layer comprises one or more of N-methylolacrylamide, N- (1-hydroxyethyl) acrylamide, N- (1-hydroxypropyl) acrylamide, N- (1-hydroxybutyl) acrylamide, N-hydroxyethyl acrylamide, N-hydroxypropyl acrylamide, N-hydroxybutyl acrylamide, N- (1, 2-dihydroxyethyl) acrylamide, N- (1, 3-dihydroxypropyl) acrylamide, N- (hydroxymethyl) methacrylamide;

preferably, the N-hydroxyalkyl acrylamide contains 0.01 to 20wt% of an oligomer, the oligomer having an average molecular weight of 300 to 5000;

and/or the proportion of N-hydroxyalkyl acrylamide monomer in the monomer for preparing thermoplastic polymer is 0.1-20wt%, preferably 1-10wt%;

And/or the monomer for preparing the thermoplastic polymer further comprises other monofunctional monomer containing carbon-carbon double bonds and/or polyfunctional monomer containing carbon-carbon double bonds besides the N-hydroxyalkyl acrylamide monomer;

Wherein, preferably, the other monofunctional monomer containing carbon-carbon double bond comprises one or more of acrylonitrile monomer, vinyl halide monomer, acrylic ester monomer, vinyl pyridine, styrene monomer and vinyl ester monomer; among them, it is preferable that the acrylonitrile-based monomer contains one or more of acrylonitrile, methacrylonitrile, fumaronitrile, crotononitrile, α -chloroacrylonitrile, or α -ethoxyacrylonitrile, and it is more preferable that acrylonitrile and/or methacrylonitrile; wherein, the preferable acrylic monomer comprises one or more of methyl acrylate, ethyl acrylate, methyl methacrylate, isobornyl methacrylate or ethyl methacrylate; among them, vinyl ester monomer is preferably vinyl acetate; among them, it is preferable that the styrenic monomer contains styrene and/or α -methylstyrene;

and/or the proportion of other monofunctional monomers containing carbon-carbon double bonds in the preparation monomers of the thermoplastic polymer is 70 to 99.5wt%, preferably 90 to 99wt%;

Wherein, preferably, the other carbon-carbon double bond-containing polyfunctional monomer comprises one or more of divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1, 4-butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, 1, 3-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1, 10-decanediol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, dimethyloltricyclodecane di (meth) acrylate, triallyl formal tri (meth) acrylate, allyl methacrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane triacrylate, tributyl glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 3-acryloxyethylene glycol monoacrylate, triallyl isocyanurate or triallyl isocyanurate;

And/or the proportion of other polyfunctional monomers containing carbon-carbon double bonds in the preparation monomers of the thermoplastic polymer is 0.1 to 1wt%, preferably 0.2 to 0.5wt%.

5. A method for preparing a thermally expandable microsphere having a core-shell structure, the microsphere being according to any one of claims 1 to 4, characterized in that the method comprises the steps of:

s1: mixing a foaming agent, a monomer for preparing a thermoplastic polymer and an initiator to obtain an oil phase mixture;

s2: and adding the oil phase mixture into an aqueous phase medium for reaction to obtain the thermal expansion microsphere with the core-shell structure.

6. The process according to claim 5, wherein the initiator S1 comprises one or more of an organic peroxide initiator and/or an azo initiator, preferably behenyl peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, dioctyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, t-butyl peracetate, butyl perborate Gui Xianshu, t-butyl benzoin, t-butyl hydroperoxide, cumene ethyl peroxy, diisopropyl hydroxydicarboxylate, 2' -azobisisoheptonitrile, 2' -azobisisobutyronitrile, 1' -azobis (cyclohexane-1-carbonitrile), dimethyl 2,2' -azobis (2-methylpropionate), 2' -azobis (2-methyl-N- (2-hydroxyethyl) propionamide);

preferably, the initiator comprises 0.1 to 2wt%, preferably 0.3 to 1wt% of the monomer;

and/or S1, wherein the amount of the foaming agent is 5-50wt%, preferably 10-30wt% of the mass of the monomer.

7. The method of claim 5, wherein S2 the aqueous medium comprises water, a solid suspending agent, and a water-soluble salt;

Preferably, the solid suspending agent comprises one or more of silica, chalk, bentonite, starch, crosslinked polymers, methylcellulose, gum agar, hydroxypropyl methylcellulose, carboxymethyl cellulose, colloidal clay, calcium phosphate, calcium carbonate, magnesium hydroxide, barium sulphate, calcium oxalate, aluminium hydroxide, ferric hydroxide, zinc hydroxide, nickel hydroxide, manganese hydroxide;

Preferably, the water soluble salt comprises sodium chloride and/or sodium nitrite;

and/or, S2 the aqueous medium further comprises a stabilizing aid;

Preferably, the stabilizing aid comprises one or more of polyvinylpyrrolidone, sulfonated polystyrene, alginate carboxymethyl fibers, tetramethyl ammonium hydroxide, tetramethyl ammonium chloride, diethanolamine/adipic acid water-soluble condensate, ethylene oxide, urea/formaldehyde water-soluble condensate, polyethylenimine, gelatin, casein, albumin, gelatin proteins, soaps, alkyl sulfates, alkyl sulfonates;

And/or the reaction temperature of S2 is 40-80 ℃ and the reaction time is 5-30 h.

8. A heat-treated heat-expandable microsphere, which is a heat-expandable microsphere according to any one of claims 1 to 4 or a heat-expandable microsphere produced by the production method according to any one of claims 5 to 7.