阅读说明：本技术 一种可膨胀微球及其制备方法 (Expandable microsphere and preparation method thereof ) 是由 崔宾 于 2021-09-30 设计创作，主要内容包括：本发明公开一种可膨胀微球及其制备方法,其中,所述可膨胀微球包括以下原料组分：可聚合单体、交联剂、偶氮二异丁腈、分散剂、水相阻聚剂和发泡剂；其中,所述可聚合单体包括丙烯腈、甲基丙烯酸甲酯和甲基丙烯酸,所述可聚合单体中,所述甲基丙烯酸甲酯的质量分数为60～70％,所述甲基丙烯酸的质量分数为6～9％,通过对原料组分的设计,使制得的可膨胀微球能够具有较高的起始膨胀温度,耐热性能较好；同时,丙烯腈的添加量较少,从而使其在应用过程中不容易黄变和破裂。(The invention discloses expandable microspheres and a preparation method thereof, wherein the expandable microspheres comprise the following raw material components: polymerizable monomers, a cross-linking agent, azodiisobutyronitrile, a dispersing agent, a water-phase polymerization inhibitor and a foaming agent; the polymerizable monomer comprises acrylonitrile, methyl methacrylate and methacrylic acid, the mass fraction of the methyl methacrylate in the polymerizable monomer is 60-70%, the mass fraction of the methacrylic acid is 6-9%, and the prepared expandable microspheres can have a high initial expansion temperature and good heat resistance through the design of raw material components; meanwhile, the addition amount of acrylonitrile is small, so that the acrylonitrile is not easy to yellow and crack in the application process.)

1. An expandable microsphere is characterized by comprising the following raw material components:

polymerizable monomers, a cross-linking agent, azodiisobutyronitrile, a dispersing agent, a water-phase polymerization inhibitor and a foaming agent;

the polymerizable monomer comprises acrylonitrile, methyl methacrylate and methacrylic acid, wherein in the polymerizable monomer, the mass fraction of the methyl methacrylate is 60-70%, and the mass fraction of the methacrylic acid is 6-9%.

2. The expandable microsphere of claim 1, wherein the blowing agent comprises at least one of isooctane, isopentane, n-octane, n-hexane, and n-pentane.

3. The expandable microsphere of claim 1, wherein the aqueous phase polymerization inhibitor comprises sodium nitrite.

4. The expandable microspheres of claim 1, wherein the mass ratio of the polymerizable monomer, the crosslinking agent, the azobisisobutyronitrile, the dispersing agent, the aqueous phase polymerization inhibitor, and the foaming agent is 80: 0.1-0.2: 1-3: 5-10: 0.4-0.5: 20 to 30.

5. The expandable microsphere of claim 1, wherein the crosslinking agent comprises trimethylolpropane trimethacrylate.

6. The expandable microsphere of claim 1, wherein the dispersant comprises at least one of magnesium hydroxide, silica, calcium hydroxide, barium hydroxide, and nickel hydroxide.

7. A process for the preparation of expandable microspheres according to any one of claims 1 to 6, comprising the steps of:

uniformly mixing a polymerizable monomer, a cross-linking agent, a foaming agent and azodiisobutyronitrile to obtain an oil phase composition;

uniformly mixing water, inorganic salt and alcohol, and adding a neutral silicon solution, a dispersing agent and a water-phase polymerization inhibitor to obtain a water-phase composition;

mixing the oil phase composition and the water phase composition and uniformly stirring to obtain a suspension;

and carrying out suspension polymerization reaction on the suspension liquid for 8-13 h at the temperature of 60-65 ℃ in the nitrogen atmosphere to obtain the expandable microspheres.

8. The method for preparing expandable microspheres according to claim 7, wherein the mass ratio of the water, the salt, the alcohol, the neutral silicon solution and the dispersing agent is 300: 70-80: 25-35: 1-2: 5 to 10.

9. The method for preparing expandable microspheres according to claim 7, wherein the mass ratio of the water phase composition to the oil phase composition is 10-14: 3.

10. the method for preparing expandable microspheres according to claim 7, wherein in the step of mixing the oil phase composition with the water phase composition and stirring them uniformly to obtain a suspension:

the stirring speed of the stirring is 4000-7000 rpm, and the stirring time is 5-12 min.

Technical Field

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

Background

The expandable microsphere is a microsphere with a core-shell structure, which is formed by taking a thermoplastic polymer as a shell and taking an expandable substance as a core. Wherein the expandable substance is generally a liquid having a boiling point not higher than the softening temperature of the thermoplastic polymer. At normal temperature, the shell of the microsphere is hard and the particles are tiny; when heated, at a temperature above the glass transition temperature of the shell (i.e., the thermoplastic polymer), the gas pressure within the shell increases and the thermoplastic shell softens, causing the microspheres to expand and increase in volume significantly; upon cooling, the polymer shell does not retract, i.e., the volume of the microspheres remains in the expanded state. The temperature at the beginning of expansion is called T_{Start of}And the temperature at which maximum expansion is reached is called T_{Maximum of}。

Because the special structure of the expandable microspheres endows the expandable microspheres with good foaming performance, the expandable microspheres are widely applied to the foaming processing of thermoplastic resin, rubber or thermoplastic elastomer. However, the foaming process of thermoplastic resins such as polyvinyl chloride, polystyrene, polyethylene, thermoplastic polyurethane, etc. requires a high temperature (160 to 200 ℃) and a long time for the operation. T of the current expandable microspheres_{Start of}The temperature is low, namely the heat resistance is poor; in addition, the high acrylonitrile content causes the expandable microspheres to be easily yellowed and cracked during the resin foaming process, thereby limiting the application thereof.

Disclosure of Invention

The invention mainly aims to provide expandable microspheres and a preparation method thereof, and aims to solve the problems that the existing expandable microspheres are easy to yellow and crack.

In order to achieve the above purpose, the present invention provides an expandable microsphere, which comprises the following raw material components:

polymerizable monomers, a cross-linking agent, azodiisobutyronitrile, a dispersing agent, a water-phase polymerization inhibitor and a foaming agent;

the polymerizable monomer comprises acrylonitrile, methyl methacrylate and methacrylic acid, wherein in the polymerizable monomer, the mass fraction of the methyl methacrylate is 60-70%, and the mass fraction of the methacrylic acid is 6-9%.

Optionally, the blowing agent comprises at least one of isooctane, isopentane, n-octane, n-hexane, and n-pentane.

Optionally, the aqueous phase polymerization inhibitor comprises sodium nitrite.

Optionally, the mass ratio of the polymerizable monomer, the crosslinking agent, the azobisisobutyronitrile, the dispersing agent, the aqueous phase polymerization inhibitor and the foaming agent is 80: 0.1-0.2: 1-3: 5-10: 0.4-0.5: 20 to 30.

Optionally, the crosslinker comprises trimethylolpropane trimethacrylate.

Optionally, the dispersant comprises at least one of magnesium hydroxide, silica, calcium hydroxide, barium hydroxide, and nickel hydroxide.

Further, the invention also provides a preparation method of the expandable microspheres, which comprises the following steps:

sequentially adding a polymerizable monomer, a cross-linking agent, a foaming agent and azodiisobutyronitrile and uniformly mixing to obtain an oil phase composition;

uniformly mixing water, inorganic salt and alcohol, and adding a neutral silicon solution, a dispersing agent and a water-phase polymerization inhibitor to obtain a water-phase composition;

mixing the oil phase composition and the water phase composition and uniformly stirring to obtain a suspension;

and carrying out suspension polymerization reaction on the suspension liquid for 8-13 h at the temperature of 60-65 ℃ in the nitrogen atmosphere to obtain the expandable microspheres.

Optionally, the mass ratio of the water, the salt, the alcohol, the neutral silicon solution and the dispersant is 300: 70-80: 25-35: 1-2: 5 to 10.

Optionally, the mass ratio of the water phase composition to the oil phase composition is 10-14: 3.

optionally, in the step of mixing the oil phase composition and the water phase composition and stirring them uniformly to obtain a suspension:

the stirring speed of the stirring is 4000-7000 rpm, and the stirring time is 5-12 min.

According to the technical scheme provided by the invention, a polymerizable monomer, a cross-linking agent, azodiisobutyronitrile, a dispersing agent, a water-phase polymerization inhibitor and a foaming agent are used as raw materials, wherein the polymerizable monomer comprises acrylonitrile, methyl methacrylate and methacrylic acid, the mass fraction of the methyl methacrylate is 60-70%, and the mass fraction of the methacrylic acid is 6-9%, so that the prepared expandable microspheres can have a high initial expansion temperature and good heat resistance; meanwhile, the addition amount of acrylonitrile is small, so that the acrylonitrile is not easy to yellow and crack in the application process.

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, 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 related drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic flow chart of an embodiment of a method for preparing expandable microspheres according to the present invention.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In addition, the meaning of "and/or" appearing throughout includes three juxtapositions, exemplified by "A and/or B" including either A or B or both A and B. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention. 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.

The foaming process of thermoplastic resins such as polyvinyl chloride, polystyrene, polyethylene, thermoplastic polyurethane, etc. requires operation at a relatively high temperature (160-200 ℃) and a relatively long time. T of the current expandable microspheres_{Start of}The temperature is low, namely the heat resistance is poor; in addition, the high acrylonitrile content causes the expandable microspheres to be easily yellowed and cracked during the resin foaming process, thereby limiting the application thereof.

In view of the above, the present invention provides an expandable microsphere, which in one embodiment comprises the following raw material components: polymerizable monomers, a cross-linking agent, azodiisobutyronitrile, a dispersing agent, a water-phase polymerization inhibitor and a foaming agent;

the polymer prepared from methacrylic acid (MAA) monomer has high glass transition temperature, but has high solubility in water, can diffuse to a water phase in the initial polymerization stage, and changes interfacial tension and reaction droplet viscoelasticity, which can affect the appearance of the prepared expandable microspheres, thereby affecting the performance of the expandable microspheres. In the present embodiment, in the polymerizable monomer, the mass fraction of the methacrylic acid is 6 to 9%, the mass fraction of the methyl methacrylate is 60 to 70%, and it is understood that the mass fraction of the acrylonitrile is 21 to 34%. The solubility of methyl methacrylate is lower than that of methacrylic acid, and a proper amount of methacrylic acid is added, so that the prepared microspheres are coated with the foaming agent, and the core-shell structure is complete, so that the microspheres have better expansion performance; meanwhile, the heat resistance is good.

By using Azobisisobutyronitrile (AIBN) as an initiator, the aqueous phase polymerization can be initiated to generate secondary polymer particles which are adsorbed on the surface of the microsphere, and meanwhile, the phase separation process in the polymerization process can be accelerated, which is beneficial to forming the microsphere with the core-shell structure.

By adding the aqueous phase polymerization inhibitor, aqueous phase polymerization can be properly inhibited, so that more and fine polymer fragments are prevented from being adsorbed on the surface of the microsphere, and the surface of the prepared expandable microsphere with the core-shell structure is smooth.

According to the technical scheme provided by the invention, polymerizable monomers, a cross-linking agent, azodiisobutyronitrile, a dispersing agent, a water-phase polymerization inhibitor and a foaming agent are used as raw materials, the polymerizable monomers comprise acrylonitrile, methyl methacrylate and methacrylic acid, the mass fraction of the methyl methacrylate is 60-70%, and the mass fraction of the methacrylic acid is 6-9%, so that the prepared expandable microspheres can have a high initial expansion temperature and good heat resistance; meanwhile, the addition amount of acrylonitrile is small, so that the acrylonitrile is not easy to yellow and crack in the application process.

The present invention is not limited to a specific kind of the blowing agent, as long as the blowing agent is a liquid having a boiling point lower than that of the thermoplastic polymer shell, and in the present embodiment, the blowing agent includes at least one of isooctane, isopentane, n-octane, n-hexane, and n-pentane.

Wherein the cross-linking agent comprises trimethylolpropane trimethacrylate (TMPTMA), and the TMPTMA is used as the cross-linking agent, so that more cross-linking points can be formed, the mechanical strength of the shell of the prepared expandable microsphere is harder, and the T is higher_{Start of}And T_{Maximum of}Higher.

In one embodiment, the dispersant comprises at least one of magnesium hydroxide, silica, calcium hydroxide, barium hydroxide, and nickel hydroxide.

Further, the mass ratio of the polymerizable monomer, the crosslinking agent, the azobisisobutyronitrile, the dispersing agent, the aqueous phase polymerization inhibitor and the foaming agent is 80: 0.1-0.2: 1-3: 5-10: 0.4-0.5: 20 to 30. In this way, the aqueous polymerization agent can be added in an appropriate amount to restrict aqueous polymerization, and the inhibition of polymerization in the oil phase is small. Under the above proportion, the prepared expandable microspheres have a core-shell structure with good morphology, good heat resistance and expansion performance, and are not easy to yellow and crack in the application process.

Further, the present invention also provides a method for preparing expandable microspheres as described above, referring to fig. 1, in one embodiment, the method comprises the following steps:

step S10, uniformly mixing the polymerizable monomer, the cross-linking agent, the foaming agent and the azobisisobutyronitrile to obtain an oil phase composition;

in one embodiment, step S10 includes: and uniformly mixing the polymerizable monomer and the crosslinking agent, sequentially adding azodiisobutyronitrile and the foaming agent, and uniformly mixing to obtain the oil phase composition.

Step S20, uniformly mixing water, inorganic salt and alcohol, and adding a neutral silicon solution, a dispersing agent and a water-phase polymerization inhibitor into the mixture to obtain a water-phase composition;

through the mutual matching of the salt, the aqueous phase polymerization inhibitor, the neutral silicon solution and the dispersant, the obtained aqueous phase composition is uniformly dispersed and is not easy to agglomerate, and the dissolution of methyl methacrylate and methacrylic acid in water can be reduced.

Wherein the mass ratio of the water, the salt, the alcohol, the neutral silicon solution and the dispersing agent is 300: 70-80: 25-35: 1-2: 5 to 10.

In one embodiment, step S20 includes: adding water and salt into a reaction kettle, uniformly mixing, adding alcohol, uniformly mixing, adding a neutral silicon solution, uniformly mixing, adding a dispersing agent and a water-phase polymerization inhibitor, and uniformly mixing to obtain a water-phase polymer.

It is understood that step S10 may be performed before step S20, after step S20, or simultaneously.

Step S30, mixing the oil phase composition and the water phase composition and uniformly stirring to obtain a suspension;

if the stirring speed is higher, the particle size of the prepared expandable microspheres is smaller, and the distribution is narrower, so that the expandable microspheres are more favorable for foaming, but if the stirring speed is too high, the microsphere structure can be damaged. In the embodiment, the stirring speed of the stirring is 4000-7000 rpm, and the stirring time is 5-12 min, so that the prepared expandable microspheres have small particle size, narrow distribution and complete core-shell structure.

When the mass ratio of the water phase composition to the oil phase composition is too small, liquid drops are easy to adhere and agglomerate, the particle size distribution of microspheres is increased, the viscosity of suspension is also high, heat dissipation, stirring and material flowing are difficult, and the polymerization reaction cannot be normally carried out; when the mass ratio of the aqueous phase composition to the oil phase composition is too large, the production efficiency is lowered, and for comprehensive consideration, in this embodiment, the mass ratio of the aqueous phase composition to the oil phase composition is 10 to 14: 3, the prepared expandable microspheres have small particle size and relatively high production efficiency.

And S40, carrying out suspension polymerization reaction on the suspension liquid at the temperature of 60-65 ℃ for 8-13 h in a nitrogen atmosphere to obtain the expandable microspheres.

The polymerization reaction temperature is controlled to be 60-65 ℃, so that the polymerization reaction speed is proper, and the prepared expandable microspheres have good foaming performance, wide foam stabilizing temperature range and low possibility of cracking in the using process. Meanwhile, through the design of raw materials, the suspension polymerization reaction can be completed within 8-13 h, and the time is short.

An example of the method for preparing expandable microspheres according to the invention is given below:

(1) adding a polymerizable monomer (a mixture of acrylonitrile, methyl methacrylate and methacrylic acid) and a crosslinking agent into a reaction kettle, uniformly mixing, sequentially adding azodiisobutyronitrile and a foaming agent, and uniformly mixing to obtain an oil phase composition, wherein the mass ratio of the polymerizable monomer to the crosslinking agent to the azodiisobutyronitrile to the foaming agent is 80: 0.1-0.2: 1-3: 20-30%, wherein in the polymerizable monomer, the mass fraction of the methyl methacrylate is 60-70%, and the mass fraction of the methacrylic acid is 6-9%;

(2) adding water and salt into a reaction kettle, uniformly mixing, adding alcohol, uniformly mixing, adding a neutral silicon solution, uniformly mixing, adding a dispersing agent and a water-phase polymerization inhibitor, and uniformly mixing to obtain a water-phase polymer, wherein the mass ratio of the water to the salt to the alcohol to the neutral silicon solution to the dispersing agent to the water-phase polymerization inhibitor is 300: 70-80: 25-35: 1-2: 5-10: 0.4 to 0.5;

(3) mixing the oil phase composition and the water phase composition, and stirring at 4000-7000 rpm for 5-12 min to obtain a suspension, wherein the mass ratio of the water phase composition to the oil phase composition is 10-14: 3;

(4) and carrying out suspension polymerization reaction on the suspension liquid for 8-13 h at the temperature of 60-65 ℃ in the nitrogen atmosphere to obtain the expandable microspheres.

The technical solutions of the present invention are further described in detail below with reference to specific examples and drawings, it should be understood that the following examples are merely illustrative of the present invention and are not intended to limit the present invention.

Example 1

(1) Adding a polymerizable monomer (a mixture of acrylonitrile, methyl methacrylate and methacrylic acid) and methyl propane trimethacrylate into a reaction kettle, uniformly mixing, sequentially adding azobisisobutyronitrile and a foaming agent (a mixture of n-octane and isopentane), and uniformly mixing to obtain an oil phase composition, wherein the mass ratio of the polymerizable monomer to the trimethylolpropane trimethacrylate to the azobisisobutyronitrile to the foaming agent is 80: 0.1: 3: 30, in the polymerizable monomer, the mass fraction of the methyl methacrylate is 70%, and the mass fraction of the methacrylic acid is 8%;

(2) adding water and salt into a reaction kettle, uniformly mixing, adding alcohol, uniformly mixing, adding a neutral silicon solution, uniformly mixing, adding magnesium hydroxide and sodium nitrite, and uniformly mixing to obtain a water-phase polymer, wherein the mass ratio of the water to the salt to the alcohol to the neutral silicon solution to the dispersant to the sodium nitrite is 300: 75: 30: 1.5: 7: 0.4;

(3) mixing the oil phase composition and the water phase composition, and stirring at 7000rpm for 7min to obtain a suspension, wherein the mass ratio of the water phase composition to the oil phase composition is 13: 3;

(4) and carrying out suspension polymerization reaction on the suspension for 8h at 65 ℃ in the nitrogen atmosphere to obtain the expandable microspheres.

Example 2

(1) Adding a polymerizable monomer (a mixture of acrylonitrile, methyl methacrylate and methacrylic acid) and trimethylolpropane trimethacrylate into a reaction kettle, uniformly mixing, sequentially adding azobisisobutyronitrile and a foaming agent (a mixture of n-octane and n-hexane), and uniformly mixing to obtain an oil phase composition, wherein the mass ratio of the polymerizable monomer to the trimethylolpropane trimethacrylate to the azobisisobutyronitrile to the foaming agent is 80: 0.2: 1: 20, in the polymerizable monomer, the mass fraction of the methyl methacrylate is 60%, and the mass fraction of the methacrylic acid is 6%;

(2) adding water and salt into a reaction kettle, uniformly mixing, adding alcohol, uniformly mixing, adding a neutral silicon solution, uniformly mixing, adding barium hydroxide and sodium nitrite, and uniformly mixing to obtain a water-phase polymer, wherein the mass ratio of the water to the salt to the alcohol to the neutral silicon solution to the barium hydroxide to the sodium nitrite is 300: 70: 25: 1: 5: 0.45 of;

(3) mixing the oil phase composition and the water phase composition, and stirring at 4000rpm for 12min to obtain a suspension, wherein the mass ratio of the water phase composition to the oil phase composition is 14: 3;

(4) and carrying out suspension polymerization reaction on the suspension for 10h at the temperature of 60 ℃ under the nitrogen atmosphere to obtain the expandable microspheres.

Example 3

(1) Adding a polymerizable monomer (a mixture of acrylonitrile, methyl methacrylate and methacrylic acid) and trimethylolpropane trimethacrylate into a reaction kettle, uniformly mixing, sequentially adding azobisisobutyronitrile and n-pentane, and uniformly mixing to obtain an oil phase composition, wherein the mass ratio of the polymerizable monomer to the trimethylolpropane trimethacrylate to the azobisisobutyronitrile to a foaming agent is 80: 0.17: 2: 27, the mass fraction of the methyl methacrylate in the polymerizable monomer is 67%, and the mass fraction of the methacrylic acid is 9%;

(2) adding water and salt into a reaction kettle, uniformly mixing, adding alcohol, uniformly mixing, adding a neutral silicon solution, uniformly mixing, adding a dispersing agent (a mixture of calcium hydroxide and magnesium hydroxide) and sodium nitrite, and uniformly mixing to obtain a water-phase polymer, wherein the mass ratio of the water to the salt to the alcohol to the neutral silicon solution to the dispersing agent to the sodium nitrite is 300: 80: 20: 2: 10: 0.5;

(3) mixing the oil phase composition and the water phase composition, and stirring at 6000rpm for 5min to obtain a suspension, wherein the mass ratio of the water phase composition to the oil phase composition is 10: 3; (ii) a

(4) And carrying out suspension polymerization reaction on the suspension for 13h at 63 ℃ in a nitrogen atmosphere to obtain the expandable microspheres.

Example 4

(1) Adding a polymerizable monomer (a mixture of acrylonitrile, methyl methacrylate and methacrylic acid) and a crosslinking agent into a reaction kettle, uniformly mixing, sequentially adding azodiisobutyronitrile and a foaming agent, and uniformly mixing to obtain an oil phase composition, wherein the mass ratio of the polymerizable monomer to the crosslinking agent to the azodiisobutyronitrile to the foaming agent is 80: 0.2: 2: 25, in the polymerizable monomer, the mass fraction of the methyl methacrylate is 65%, and the mass fraction of the methacrylic acid is 7%;

(2) adding water and salt into a reaction kettle, uniformly mixing, adding alcohol, uniformly mixing, adding a neutral silicon solution, uniformly mixing, adding a dispersing agent and a water-phase polymerization inhibitor, and uniformly mixing to obtain a water-phase polymer, wherein the mass ratio of the water to the salt to the alcohol to the neutral silicon solution to the dispersing agent to the water-phase polymerization inhibitor is 300: 75: 30: 2: 10: 0.4;

(3) mixing the oil phase composition and the water phase composition, and stirring at 5000rpm for 10min to obtain a suspension, wherein the mass ratio of the water phase composition to the oil phase composition is 12: 3;

(4) and carrying out suspension polymerization reaction on the suspension for 10h at 65 ℃ in a nitrogen atmosphere to obtain the expandable microspheres.

Comparative example 1

The procedure was as in example 1 except that the polymerizable monomer in step (1) was modified so that the polymerizable monomer was a mixture of methyl methacrylate and acrylonitrile in a mass ratio of methyl methacrylate to acrylonitrile of 70: 22.

Comparative example 2

The procedure was as in example 1 except that no aqueous phase polymerization inhibitor was added in the step (2).

The expandable microspheres obtained in examples and comparative examples were subjected to performance tests, and the results are shown in table 1.

Table 1 results of performance testing

As can be seen from Table 1, the particle size of the expandable microspheres prepared by the embodiment of the invention is 10-30 μm, the initial expansion temperature is 160-180 ℃, the maximum expansion temperature is 210-220 ℃, the expandable microspheres can turn yellow after more than 16 minutes at 220 ℃, the expandable microspheres can crack after more than 22 minutes, the expansion ratio is good, the surfaces of the microspheres are smooth, and the morphology structure is good. While comparative example 1, to which methacrylic acid was not added, had lower initial and maximum expansion temperatures than those of examples and was more likely to yellow and crack at high temperatures, comparative example 2, to which an aqueous phase polymerization inhibitor was not added, had a poor microsphere morphology and also had lower initial and maximum expansion temperatures than those of examples.

Therefore, by designing the raw materials, the proportion among the raw materials and the preparation process, the prepared expandable microspheres have good morphology and structure, better heat resistance and expansion performance, wide application range and obvious competitive advantage, and are not easy to yellow and crack in the application process.

The above is only a preferred embodiment of the present invention, and it is not intended to limit the scope of the invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the scope of the present invention.