阅读说明：本技术 一种热膨胀微球及其制备方法 (Thermal expansion microsphere and preparation method thereof ) 是由 柯伟强 于 2021-07-23 设计创作，主要内容包括：本发明公开了一种热膨胀微球及其制备方法,所述热膨胀微球具有复合微球结构,包含外层和内层,其中外层为聚合物层,内层为包含若干小微球及固体颗粒的混合层,所述小微球包含壳材及芯材,所述固体颗粒与芯材接触后发生化学反应并释放出气体。本发明通过化学反应进行发泡,从而可以不使用市面上常见的低沸点烷烃发泡剂,在不影响发泡效果的前提下,解决了传统发泡剂的出油问题,是一种性能良好,能够运用于日常生活用品的热膨胀微球,其可以运用于TPE发泡日用材料中,并且由于其不出油的特性,能够用于制作贴身使用的材料。本发明采用的是二段发泡的方式,最终发泡结构更加的稳定。(The invention discloses a thermal expansion microsphere and a preparation method thereof, wherein the thermal expansion microsphere has a composite microsphere structure and comprises an outer layer and an inner layer, wherein the outer layer is a polymer layer, the inner layer is a mixed layer containing a plurality of small microspheres and solid particles, the small microspheres comprise a shell material and a core material, and the solid particles are in contact with the core material and then undergo chemical reaction to release gas. The foaming agent disclosed by the invention is foamed through a chemical reaction, so that a common low-boiling-point alkane foaming agent on the market is not used, the problem of oil production of a traditional foaming agent is solved on the premise of not influencing the foaming effect, and the foaming agent is a thermal expansion microsphere which has good performance, can be applied to daily necessities, can be applied to TPE (thermoplastic elastomer) foaming daily materials, and can be used for manufacturing materials used next to the skin due to the characteristic of no oil production. The invention adopts a two-stage foaming mode, and the final foaming structure is more stable.)

1. The heat expansion microsphere is characterized by having a composite microsphere structure and comprising an outer layer and an inner layer, wherein the outer layer is a polymer layer, the inner layer is a mixed layer comprising a plurality of small microspheres and solid particles, the small microspheres comprise a shell material and a core material, and the solid particles are in contact with the core material and then undergo a chemical reaction to release gas.

2. The thermally expandable microspheres according to claim 1, wherein the thermally expandable microspheres have a particle size of 30 to 50 μm and the microspheres in the inner layer have a particle size of 0.5 to 3 μm.

3. The thermally expandable microspheres according to claim 1, wherein said outer layer is obtained by polymerizing a double bond-containing polymerizable monomer.

4. The thermally expandable microsphere according to claim 1, wherein the shell material of said microsphere is PMMA.

5. A thermally expandable microsphere according to claim 4, wherein PMMA has a molecular weight of 30 to 50 ten thousand.

6. The thermally expandable microsphere of claim 1, wherein the core material of said microsphere is an organic acid.

7. The thermally expandable microsphere of claim 6, wherein the organic acid is acetic acid.

8. The thermally expandable microspheres of claim 6, wherein the solid particles are calcium carbonate.

9. The thermally expandable microsphere according to claim 1, wherein the preparation method of said microsphere comprises the steps of:

dissolving PMMA in an organic solvent, and adding an organic acid, a dispersing agent and an emulsifying agent;

stirring, adding water, controlling the temperature of the solution to be between 10 and 20 ℃, and continuously stirring until the solution is emulsified uniformly;

after the emulsion is evenly emulsified, the emulsion is spread and dried at the temperature of 25-35 ℃ until the organic solvent is completely removed, so that a small organic acid microsphere aqueous solution coated with PMMA is obtained, and then the small organic acid microsphere aqueous solution coated with PMMA is dehydrated, so that the small organic acid microsphere coated with PMMA is obtained.

10. The method for producing thermally expandable microspheres according to claim 9, comprising the steps of:

(1) mixing a lipophilic bi-component polymerizable monomer, an initiator, an emulsifier, PMMA-coated organic acid-containing microspheres, a polymerization initiator, calcium carbonate and water, and emulsifying in advance to obtain a to-be-titrated solution for later use;

(2) adding water and hydrophilic monomer containing double-building polymerizable monomer into a reactor in advance, stirring and heating, slowly dripping the solution to be titrated in the step (1) into the system, preserving heat and curing for a period of time after dripping is finished, and finishing the reaction;

(3) and removing water in the system by using a freeze-drying method to obtain the thermal expansion microspheres.

Technical Field

The invention relates to the field of foaming materials, in particular to a thermal expansion microsphere and a preparation method thereof.

Background

The heat expansion microsphere mainly comprises a polymer shell and a core material capable of expanding under heating, the volume of the heat expansion microsphere can expand by tens of times when the heat expansion microsphere is heated, and the characteristic enables the heat expansion microsphere to have important application values in the aspects of light weight, patterning, three-dimensional and the like of materials.

In recent years, when the thermal expansion microspheres are applied to the foaming industry, compared with the original foaming agent, the thermal expansion microspheres have the advantage of uniform foam, but the main foaming component of the thermal expansion microspheres on the market at present is low-boiling-point alkane, the alkane can be changed from solid or liquid into gas after high-temperature foaming, and the volume expansion occurs, but when the foaming process is finished and enters a cooling process, the gaseous alkane can be recovered to the solid or liquid, and in the subsequent use, the small-molecular component can slowly permeate to the surface of a substance, so that the oil is produced commonly by people, the influence is small in the industrial use, and great discomfort can be produced when the thermal expansion microspheres are made into daily living goods for use.

In addition, the preparation method of the thermal expansion microspheres has more domestic and foreign patents and literature reports at present, and is mainly prepared by a suspension polymerization method. The foaming ability of the thermally expandable microspheres is influenced by a plurality of factors, such as the composition of the foaming agent, the composition of the shell wall polymer, the ratio of the foaming agent to the shell wall polymer, the size and distribution of the microspheres, and the like, so that the regulation and control of the foaming performance of the microspheres are complex. And high expansion ratio and excellent high-temperature foam stabilizing performance are difficult to be considered, so that the preparation of the heat-resistant high-temperature thermal expansion microspheres is difficult.

In view of the above problems, there is no effective solution, and further development of a thermally expandable microsphere material and a preparation process thereof is needed.

Disclosure of Invention

The purpose of the invention is as follows: in order to solve the above problems, an object of the present invention is to provide thermally expandable microspheres which have a good foaming effect and do not allow an oil substance to bleed out after foaming, and a method for preparing the same.

The technical scheme of the invention is as follows:

a thermal expansion microsphere has a composite microsphere structure and comprises an outer layer and an inner layer, wherein the outer layer is a polymer layer, the inner layer is a mixed layer containing a plurality of microspheres and solid particles, the microspheres comprise a shell material and a core material, and the solid particles are in contact with the core material and then undergo chemical reaction to release gas.

As a further scheme of the thermal expansion microsphere, the particle size of the thermal expansion microsphere is 30-50 μm, and the particle size of the small microsphere in the inner layer is 0.5-3 μm.

As a further scheme of the thermal expansion microsphere, the outer layer of the thermal expansion microsphere is obtained by carrying out polymerization reaction on polymerizable monomers containing double bonds.

As a further proposal of the thermal expansion microsphere, the shell material of the microsphere used in the invention is PMMA.

In a further embodiment of the thermally expandable microspheres of the present invention, the shell material of the microspheres used in the present invention is preferably ultra-high molecular weight PMMA having a molecular weight of 30 to 50 ten thousand, in order to provide sufficient expandability of the shell material.

Specifically, the preparation method of the PMMA with the molecular weight exceeding is as follows:

stirring water and a dispersant uniformly, raising the temperature to 60-80 ℃, then preserving the temperature, dripping a mixed solution containing methyl methacrylate and an initiator into an aqueous solution containing the dispersant for polymerization reaction, separating out the polymerized ultrahigh molecular weight PMMA from the system, and filtering to obtain the required ultrahigh molecular weight PMMA.

In the preparation process of the PMMA with the ultrahigh molecular weight, the addition amount of water is 80-90% of the total mass of the raw materials.

In the preparation process of the PMMA with ultrahigh molecular weight, the dispersant is preferably gelatin, and the addition amount of the gelatin is 0.5-2% of the total mass of the raw materials.

In the preparation process of the PMMA with the ultrahigh molecular weight, the initiator is preferably benzoyl peroxide, and the addition amount of the benzoyl peroxide is 0.02-0.05% of the total mass of the raw materials.

As a further scheme of the thermal expansion microsphere, a core material wrapped in the small microsphere used in the invention is organic acid; specifically, the organic acid is preferably acetic acid.

As a further aspect of the thermally expandable microspheres of the present invention, the method for preparing the microspheres used in the present invention comprises the steps of:

dissolving the prepared PMMA with ultrahigh molecular weight in an organic solvent, and adding an organic acid, a dispersing agent and an emulsifying agent;

stirring, adding water, controlling the temperature of the solution to be between 10 and 20 ℃, and continuously stirring until the solution is emulsified uniformly;

after the emulsion is evenly emulsified, the emulsion is spread and dried at the temperature of 25-35 ℃ until the organic solvent is completely removed, so that a small organic acid microsphere aqueous solution coated with PMMA is obtained, and then the small organic acid microsphere aqueous solution coated with PMMA is dehydrated, so that the small organic acid microsphere coated with PMMA is obtained.

Specifically, the dispersant is preferably polyvinyl alcohol, the emulsifier is preferably sodium dodecylbenzenesulfonate, and the organic solvent is preferably a low-boiling organic solvent such as dichloromethane.

As a further embodiment of a thermally expandable microsphere according to the present invention, the other solid particles used in the present invention are calcium carbonate.

The PMMA-coated organic acid microspheres of the present invention can release organic acid under heating, and the action principle of the present invention is explained as follows by taking acetic acid as a representative of organic acid:

acetic acid can react with calcium carbonate to form CO₂Gas and calcium acetate, then the calcium acetate can be decomposed under the heating condition to generate acetone gas and calcium carbonate, and then the calcium carbonate continuously reacts with acetic acid. Acetic acid is finally and completely converted into carbon dioxide and acetone gas, and no residue exists in the system, so that the problem of oily substances permeating to the surface can be effectively avoided.

The invention adopts a two-stage foaming mode, and the final foaming structure is more stable.

As a further proposal of the thermal expansion microsphere, the polymer layer used in the invention is obtained by in-situ polymerization reaction of polymerizable monomers containing double bonds.

Specifically, the bireformable polymerizable monomer may be selected from one or more of acrylic acid, methacrylic acid, acrylonitrile, acrylamide, styrene, vinyl acetate, N-vinyl pyrrolidone, butyl acrylate, isooctyl acrylate, N-hexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, phenoxyethyl acrylate, and tetrahydrofurfuryl acrylate, nonylphenol polyoxyethylene ether (meth) acrylate, tripropylene glycol diacrylate, 1, 6-hexanediol diacrylate, bisphenol a diacrylate.

As a further aspect of the thermally expandable microspheres of the present invention, a method for preparing composite microspheres used in the present invention comprises the steps of:

(1) mixing the lipophilic bi-monomer, emulsifier, PMMA-coated organic acid-containing microspheres, polymerization initiator, calcium carbonate and water, and emulsifying in advance to obtain a to-be-titrated solution for later use;

(2) adding water and hydrophilic monomer containing double-building polymerizable monomer into a reactor in advance, stirring and heating, slowly dripping the solution to be titrated in the step (1) into the system, preserving heat and curing for a period of time after dripping is finished, and finishing the reaction;

(3) and removing water in the system by using a freeze-drying method to obtain the composite microspheres.

The chemical reaction of the present invention is a two-stage reaction, which is capable of releasing gas.

The foaming agent disclosed by the invention is foamed through a chemical reaction, so that a common low-boiling-point alkane foaming agent on the market is not used, the problem of oil production of a traditional foaming agent is solved on the premise of not influencing the foaming effect, the foaming agent is a thermal expansion microsphere which has good performance, can be applied to daily necessities, can be particularly applied to TPE (thermoplastic elastomer) foaming daily materials, and can be used next to the skin due to the characteristic of no oil production.

The technical scheme provided by the invention has the beneficial effects that:

the invention solves the problem that two mutually reactive substances can not coexist before foaming by using a composite microsphere technology, thereby achieving good foaming effect, and because solid particles contained in the inner layer of the thermal expansion microsphere can circularly participate in the reaction, the volume expansion multiple cannot be influenced by the change of the addition amount of the solid particles, thereby ensuring the homogeneity of the product.

Drawings

FIG. 1 is a GPC chart of the ultrahigh molecular weight PMMA-1 prepared in Synthesis example 1 of ultrahigh molecular weight PMMA of the present invention.

FIG. 2 is a GPC chart of the ultrahigh molecular weight PMMA-2 prepared in Synthesis example 2 of ultrahigh molecular weight PMMA of the present invention.

FIG. 3 is a GPC chart of the ultra-high molecular weight PMMA-2 prepared in ultra-high molecular weight PMMA synthesis example 3 of the present invention.

FIG. 4 is a 200-fold microscopic observation image of an aqueous solution 1 of PMMA-coated organic acid microspheres prepared in example 1 of the present invention.

FIG. 5 is a 200-fold microscopic observation image of an aqueous solution 2 of PMMA-coated organic acid microspheres prepared in example 2 of the present invention.

FIG. 6 is a 500-fold microscopic observation image of aqueous solution 3 of PMMA-3 coated organic acid microspheres prepared in example 2 of the present invention.

Detailed description of the invention

The present invention will be further described below by way of specific examples.

In the following examples, those whose operations are not subject to the conditions indicated, are carried out according to the conventional conditions or conditions recommended by the manufacturer. The raw materials used in the scheme of the invention are purchased from Chinese medicine reagents and an Allantin reagent.

Synthesis example 1 of ultra-high molecular weight PMMA

Adding 90g of water and 1g of gelatin into a reaction bottle, stirring uniformly, raising the temperature to 70 ℃, keeping the temperature, dropwise adding a mixed solution containing 9g of methyl methacrylate and 0.01g of benzoyl peroxide into an aqueous solution of the gelatin to perform polymerization reaction, and controlling the dropwise adding speed by using a peristaltic pump to uniformly dropwise add for about 3 hours.

The polymerized PMMA is precipitated from the system in the dropping process, and suspended in the system under the action of stirring and dispersing agent, after all reactions are completed, the PMMA-1 with ultrahigh molecular weight is obtained by filtering, the molecular weight Mw is 384435, and the GPC spectrogram thereof is shown in figure 1.

Synthesis example 2 of ultra-high molecular weight PMMA

89.5g of water and 1.5g of gelatin were added to a reaction flask, stirred uniformly, heated to 80 ℃ and then kept warm, and a mixed solution containing 9g of methyl methacrylate and 0.03g of benzoyl peroxide was added dropwise to an aqueous solution of gelatin to carry out a polymerization reaction, and the dropping speed was controlled by a peristaltic pump, and the mixture was dropped uniformly over about 3 hours.

The polymerized PMMA is separated out from the system in the dropping process, the PMMA is suspended in the system due to the action of stirring and dispersing agent, the required PMMA-2 with ultrahigh molecular weight is obtained by filtering after all reactions are finished, the molecular weight Mw is 304193, and the GPC spectrogram thereof is shown in figure 2.

Synthesis example 3 of ultra-high molecular weight PMMA

Adding 90g of water and 1g of gelatin into a reaction bottle, stirring uniformly, raising the temperature to 75 ℃, keeping the temperature, dropwise adding a mixed solution containing 9g of methyl methacrylate and 0.02g of benzoyl peroxide into an aqueous solution of the gelatin to perform polymerization reaction, and controlling the dropwise adding speed by using a peristaltic pump to uniformly dropwise add for about 3 hours.

The polymerized PMMA is precipitated from the system in the dropping process, the PMMA is suspended in the system due to the action of stirring and dispersing agent, the required ultrahigh molecular weight PMMA-3 is obtained by filtering after all reactions are finished, the molecular weight Mw is 346492, and the GPC spectrogram thereof is shown in figure 3.

Example 1

Dissolving 5g of PMMA-1 in 10g of dichloromethane, adding 95g of acetic acid as a core material, adding 1g of polyvinyl alcohol as a dispersing agent, and adding 0.5g of sodium dodecyl benzene sulfonate as an emulsifying agent;

after stirring uniformly, adding 400g of water, controlling the temperature of the solution to be between 10 and 20 ℃, and continuously stirring for 2 hours to ensure that the solution is emulsified uniformly;

after the emulsion is evenly emulsified, the emulsion is flatly laid in a tray and dried at the temperature of 35 ℃ until dichloromethane is completely removed, and the PMMA-coated organic acid microsphere aqueous solution 1 is obtained. FIG. 4 is a microscopic view of an aqueous solution 1 of PMMA-coated organic acid microspheres.

Example 2

Dissolving 5g of PMMA-2 in 10g of dichloromethane, adding 95g of acetic acid as a core material, adding 1g of polyvinyl alcohol as a dispersing agent, and adding 0.5g of sodium dodecyl benzene sulfonate as an emulsifying agent;

after stirring uniformly, adding 400g of water, controlling the temperature of the solution to be between 10 and 20 ℃, and continuously stirring for 2 hours to ensure that the solution is emulsified uniformly;

after the emulsion is evenly emulsified, the emulsion is flatly laid in a tray and dried at the temperature of 35 ℃ until dichloromethane is completely removed, and a PMMA-coated organic acid microsphere aqueous solution 2 is obtained. FIG. 5 is a microscopic view of an aqueous solution 2 of PMMA-coated organic acid microspheres.

Example 3

Dissolving 5g of PMMA-3 in 10g of dichloromethane, adding 95g of acetic acid as a core material, adding 1g of polyvinyl alcohol as a dispersing agent, and adding 0.5g of sodium dodecyl benzene sulfonate as an emulsifying agent;

after stirring uniformly, adding 400g of water, controlling the temperature of the solution to be between 10 and 20 ℃, and continuously stirring for 2 hours to ensure that the solution is emulsified uniformly;

after the emulsion is evenly emulsified, the emulsion is flatly laid in a tray and dried at the temperature of 35 ℃ until dichloromethane is completely removed, and a small microsphere aqueous solution 3 of PMMA-coated organic acid is obtained. FIG. 6 is a microscopic view of an aqueous solution 3 of PMMA-coated organic acid microspheres.

Example 4

And dehydrating the PMMA-1 coated organic acid microsphere aqueous solution 1 to obtain the PMMA coated organic acid microsphere 1.

Adding 5g of isoborneol methacrylate, 2g of styrene, 3g of methyl methacrylate, 1g of sodium dodecyl benzene sulfonate, 70g of small microspheres of PMMA-coated organic acid 1, 0.3g of polymerization initiator azobisisobutyronitrile and 20g of calcium carbonate into a reactor, adding 200g of deionized water, stirring at the rotating speed of 1500 revolutions per minute, controlling the temperature of the system to be not more than 20 ℃, and continuously emulsifying for 1 hour to obtain a to-be-titrated solution for later use.

Adding 400g of water, 3g of acrylamide and 2g of acrylic acid into a reactor in advance, stirring and heating to 60 ℃, slowly dripping the pre-emulsified liquid to be titrated into the system, ensuring that the liquid to be titrated is dripped into the reactor at a constant speed for about 3 hours by using a peristaltic pump in the dripping process, and preserving heat at 60 ℃ after finishing drippingAging for 1 hr, and performing infrared spectrum test at 1640cm^-1The reaction is considered to be complete after the double bond peak completely disappears;

and (3) removing water from the obtained water dispersion by using a freeze dryer to obtain the required thermal expansion microspheres A-1.

Example 5

And dehydrating the PMMA-1 coated organic acid microsphere aqueous solution 1 to obtain the PMMA coated organic acid microsphere 1.

Adding 5g of isoborneol methacrylate, 2g of styrene, 3g of methyl methacrylate, 1g of sodium dodecyl benzene sulfonate, 80g of small microspheres of PMMA-coated organic acid 1, 0.3g of polymerization initiator azobisisobutyronitrile and 10g of calcium carbonate into a reactor, adding 200g of deionized water, stirring at the rotating speed of 1500 revolutions per minute, controlling the temperature of the system to be not more than 20 ℃, and continuously emulsifying for 1 hour to obtain a to-be-titrated solution for later use.

Adding 400g of water, 3g of acrylamide and 2g of acrylic acid into a reactor in advance, stirring and heating to 60 ℃, slowly dripping the pre-emulsified liquid to be titrated into the system, ensuring that the liquid to be titrated is dripped into the reactor at a constant speed for about 3 hours by using a peristaltic pump in the dripping process, preserving heat and curing for 1 hour at 60 ℃ after finishing dripping, carrying out infrared spectrum test, and aging at 1640cm^-1The reaction is considered to be complete after the double bond peak completely disappears;

and (3) removing water from the obtained water dispersion by using a freeze dryer to obtain the required thermal expansion microspheres A-2.

Example 6

And dehydrating the PMMA-2 organic acid coated microsphere aqueous solution 2 to obtain the PMMA coated organic acid coated microsphere 2.

Adding 4g of butyl methacrylate, 3g of isooctyl acrylate, 3g of 1, 6-hexanediol diacrylate, 1g of sodium dodecyl benzene sulfonate, 75g of PMMA-coated organic acid microspheres 2, 0.3g of polymerization initiator azobisisobutyronitrile and 15g of calcium carbonate into a reactor, adding 200g of deionized water, stirring at the rotating speed of 1500 revolutions per minute, controlling the temperature of the system to be not more than 20 ℃, and continuously emulsifying for 1 hour to obtain a solution to be titrated for later use.

Adding 400g of water, 2g of hydroxyethyl acrylate and 3g of acrylic acid into a reactor in advance, stirring and heating to 60 ℃, slowly dripping the pre-emulsified liquid to be titrated into the system, ensuring that the liquid to be titrated is dripped into the reactor at a constant speed for about 3 hours by using a peristaltic pump in the dripping process, preserving heat and curing for 1 hour at 60 ℃ after finishing dripping, carrying out infrared spectrum test, and aging at 1640cm for 1 hour^-1The reaction is considered to be complete after the double bond peak completely disappears;

and (3) removing water from the obtained water dispersion by using a freeze dryer to obtain the required thermal expansion microsphere B-1.

Example 7

And dehydrating the PMMA-2 organic acid coated microsphere aqueous solution 2 to obtain the PMMA coated organic acid coated microsphere 2.

Adding 5g of phenoxyethyl acrylate, 3g of styrene, 2g of bisphenol A diacrylate, 1g of sodium dodecyl benzene sulfonate, 70g of small microspheres of PMMA-coated organic acid 2, 0.3g of polymerization initiator azobisisobutyronitrile and 20g of calcium carbonate into a reactor, adding 200g of deionized water, stirring at the rotating speed of 1500 revolutions per minute, controlling the temperature of the system not to exceed 20 ℃, and continuously emulsifying for 1 hour to obtain a solution to be titrated for later use.

Adding 400g of water, 1g of N-vinyl pyrrolidone and 4g of acrylic acid into a reactor in advance, stirring and heating to 60 ℃, slowly dripping the pre-emulsified liquid to be titrated into the system, ensuring that the liquid to be titrated is dripped into the reactor at a constant speed for about 3 hours by using a peristaltic pump in the dripping process, carrying out infrared spectrum test after heat preservation and curing for 1 hour at 60 ℃ after finishing dripping, and carrying out infrared spectrum test at 1640cm^-1The reaction is considered to be complete after the double bond peak completely disappears;

and (3) removing water from the obtained water dispersion by using a freeze dryer to obtain the required thermal expansion microspheres B-2.

Example 8

And dehydrating the PMMA-3 coated organic acid microsphere aqueous solution 3 to obtain the PMMA coated organic acid microsphere 3.

5g of nonylphenol polyoxyethylene ether (methyl) acrylate, 4g of styrene, 1g of tripropylene glycol diacrylate, 1g of sodium dodecyl benzene sulfonate, 80g of PMMA-coated organic acid microspheres 3, 0.3g of polymerization initiator azobisisobutyronitrile and 10g of calcium carbonate are added into a reactor, 200g of deionized water is added, stirring is carried out at the rotating speed of 1500 revolutions per minute, the temperature of the system is controlled not to exceed 20 ℃, and after 1 hour of continuous emulsification, a solution to be titrated is obtained for later use.

Adding 400g of water, 1g of acrylonitrile and 4g of methacrylic acid into a reactor in advance, stirring and heating to 60 ℃, slowly dripping the pre-emulsified liquid to be titrated into the system, ensuring that the liquid to be titrated is dripped into the reactor at a constant speed for about 3 hours by using a peristaltic pump in the dripping process, preserving heat and curing for 1 hour at 60 ℃ after finishing dripping, carrying out infrared spectrum test, and aging at 1640cm for 1 hour^-1The reaction is considered to be complete after the double bond peak completely disappears;

and (3) removing water from the obtained water dispersion by using a freeze dryer to obtain the required thermal expansion microsphere C-1.

Example 9

And dehydrating the PMMA-3 coated organic acid microsphere aqueous solution 3 to obtain the PMMA coated organic acid microsphere 3.

Adding 5g of butyl methacrylate, 3g of phenoxyethyl acrylate, 2g of cyclohexyl acrylate, 1g of sodium dodecyl benzene sulfonate, 85g of small microspheres of PMMA-coated organic acid 3, 0.3g of polymerization initiator azobisisobutyronitrile and 5g of calcium carbonate into a reactor, adding 200g of deionized water, stirring at the rotating speed of 1500 revolutions per minute, controlling the temperature of the system to be not more than 20 ℃, and continuously emulsifying for 1 hour to obtain a solution to be titrated for later use.

Adding 400g of water, 2g of acrylamide and 3g of methacrylic acid into a reactor in advance, stirring and heating to 60 ℃, slowly dripping the pre-emulsified liquid to be titrated into the system, ensuring that the liquid to be titrated is dripped into the reactor at a constant speed for about 3 hours by using a peristaltic pump in the dripping process, preserving heat and curing for 1 hour at 60 ℃ after finishing dripping, carrying out infrared spectrum test, and aging at 1640cm for 1 hour^-1The reaction is considered to be complete after the double bond peak completely disappears;

and (3) removing water from the obtained water dispersion by using a freeze dryer to obtain the required thermal expansion microsphere C-2.

The above-mentioned embodiments are merely illustrative of the principles and effects of the present invention, and some embodiments may be used, not restrictive; it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept of the present invention, and these changes and modifications belong to the protection scope of the present invention.

The invention tests the volume expansion rate and the residual quantity of organic acid of the thermal expansion microspheres A-1, A-2, B-1, B-2, C-1 and C-2 respectively prepared in the above examples 4-9, and the test results are shown in Table 1, and the specific test method is as follows:

volume expansion rate test: adding 10g of thermal expansion microspheres into a container externally connected with a pressure gauge, heating the system to 200 ℃, testing the final pressure condition, and converting the volume expansion rate by calculation.

Testing the residual quantity of organic acid: and (3) cooling the pressure container to room temperature, opening the pressure release valve, discharging gas, adding a certain amount of water, uniformly stirring, filtering out solid particles, and testing the acetic acid residue of the aqueous solution by using a headspace gas chromatography.

Table 1:

	rate of volume expansion	Acetic acid residual amount
			Example 4	18 times of	Not detected out
Example 5	21 times of	Not detected out
			Example 6	18 times of	Not detected out
Example 7	17 times of	Not detected out
			Example 8	23 times of	Not detected out
Example 9	24 times that of	Not detected out

The test results show that the thermal expansion microsphere provided by the invention has good foaming effect, can ensure that the volume expansion rate reaches 18-24 times, does not contain any residue, and has good performance and market prospect.