CN118667218A - Low-residual-list thermal expansion microsphere and preparation method thereof - Google Patents

Abstract

The invention provides a low-residue single thermal expansion microsphere and a preparation method thereof, comprising the following steps: the monomer, the thermal initiator, the cross-linking agent and the volatile foaming agent are mixed to obtain an oil phase; mixing an aqueous dispersion medium, inorganic salt, a dispersion stabilizer and a dispersion stabilizing auxiliary agent to obtain a water phase; stirring and dispersing the oil phase and the water phase to obtain a suspension solution; the microsphere slurry obtained by the suspension polymerization method is subjected to polymerization reaction of residual monomers by ultraviolet light to prepare thermal expansion microspheres with low residual monomer content; and adding a photoinitiator into the oil phase or microsphere slurry in the step. The thermal expansion microsphere monomer prepared by the invention has low residual quantity, does not influence the foaming performance of the thermal expansion microsphere, and widens the application field of the thermal expansion microsphere.

Description

A kind of low residual heat expansion microsphere and preparation method thereof

Technical Field

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

Background Art

Heat-expandable microspheres are microspheres with a core-shell structure, which are composed of a thermoplastic polymer shell with an expandable substance such as a volatile expander such as aliphatic hydrocarbons. Heat-expandable microspheres have been successfully applied to the fields of plasticine, printing paste, plastics, elastomers, etc. as a light and heavy filler. However, after the preparation of heat-expandable microspheres, there are residual monomers on the surface of the microspheres, the conversion rate of the monomers is low, and the heat-expandable microspheres have odor problems and environmental pollution problems in actual applications.

Among the currently disclosed patents, there are three methods for removing residual monomers of heat-expandable microspheres. One is to increase the monomer conversion rate by introducing a special initiation system before polymerization, such as patent CN111116969 A discloses that a special amphiphilic initiator initiates monomer polymerization at the oil-water interface, and reduces the amount of residual monomer by reducing the water solubility of the monomer, but the amphiphilic initiator has not yet been industrialized or commercialized; patent CN106967195A discloses that monomer polymerization is initiated by γ-ray irradiation to increase the monomer conversion rate and reduce the amount of residual monomer, but γ-ray irradiation polymerization has not yet been industrialized; patent CN113861492A discloses that a reducing agent is added to the water phase and an oxidant is added to the oil phase to form microspheres through interfacial polymerization, and then the temperature is increased for polymerization, but the introduction of a reducing agent in the water phase will increase the cost of water treatment in the later stage; patent CN112430288A adds a combination of a metal photosensitizer and a photoinitiator to the oil phase, and performs a polymerization reaction of oil droplets to form microspheres by light initiation, but the metal photosensitizer has not yet been commercialized. Another method is to post-treat the residual monomers in the aqueous phase after the polymerization reaction. For example, patents CN102775550A and CN116272710A disclose adding a water-soluble thermal initiator after the polymerization reaction and continuing to increase the reaction temperature and extend the reaction time to initiate the polymerization reaction of the residual monomers, which is time-consuming and energy-intensive; patent WO2021198492A1 uses a reagent composed of a group of sulfur-containing oxygen acids, their salts and derivatives to treat the residual monomers of microspheres, but only converts the residual monomers, without achieving the transformation of monomers into polymers, and the water treatment cost is high; patent JP2005254214A heats the microsphere slurry to a temperature where it does not begin to expand in a specific container, so that the residual monomers volatilize, which consumes a lot of energy and is prone to environmental pollution. The third method is to remove the residual monomers from dry powder microspheres. Patent JP2003251169A removes the residual monomers by heating or decompressing the heat-expandable microcapsules, but it consumes a lot of energy and also affects the foaming performance of the microspheres.

Summary of the invention

The purpose of the present invention is to provide a low residual monomer heat-expandable microsphere and a preparation method thereof, so as to overcome the defects of the prior art. Based on the mature industrial technology of heat-expandable microspheres, a small amount of commercial photoinitiator is introduced, and a low-energy ultraviolet light initiation method is adopted to efficiently and greenly remove the residual monomers of the microspheres while maintaining the foaming performance of the heat-expandable microspheres. Among them, the photoinitiator is divided into oil-soluble and water-soluble. The oil-soluble photoinitiator is added to the oil phase before the polymerization reaction, and the water-soluble photoinitiator is added to the microsphere slurry after the polymerization reaction.

When an oil-soluble photoinitiator is used, a monomer, a thermal initiator, a crosslinking agent, a volatile foaming agent and an oil-soluble photoinitiator are mixed to obtain an oil phase; an aqueous dispersion medium, an inorganic salt, a dispersion stabilizer and a dispersion stabilization aid are mixed to obtain a water phase; the oil phase and the water phase are stirred and dispersed to obtain a suspension solution; ultraviolet light is used to initiate the polymerization reaction of residual monomers in the microsphere slurry after suspension polymerization to prepare thermal expansion microspheres with low residual monomer content.

When a water-soluble photoinitiator is used, a monomer, a thermal initiator, a crosslinking agent, and a volatile foaming agent are mixed to obtain an oil phase; an aqueous dispersion medium, an inorganic salt, a dispersant, and a dispersion stabilizing agent are mixed to obtain a water phase; the oil phase and the water phase are stirred and dispersed to obtain a suspension solution; a water-soluble photoinitiator is pre-added to the microsphere slurry after suspension polymerization, and then a polymerization reaction of residual monomers is initiated by ultraviolet light to prepare thermally expandable microspheres with low residual monomer content.

In one aspect, the present invention provides a method for preparing low-residue heat-expandable microspheres, comprising the following steps:

(1) mixing a monomer, an initiator, a cross-linking agent and a volatile foaming agent to obtain an oil phase;

(2) mixing an aqueous dispersion medium, an inorganic salt, a dispersant, and a dispersion stabilizing agent to obtain an aqueous phase;

(3) stirring and dispersing the oil phase and the water phase to obtain a suspension solution;

(4) subjecting the obtained suspension solution to polymerization reaction for 15 to 25 hours at 40 to 80° C. and 0.1 to 0.5 MPa in an inert atmosphere, lowering the temperature of the microsphere slurry to room temperature, initiating the polymerization reaction of the residual monomers with ultraviolet light (when a water-soluble initiator is used, it is necessary to pre-select and add a water-soluble photoinitiator to the microsphere slurry), filtering and drying to obtain heat-expandable microspheres with low residual monomers;

A photoinitiator is added to the oil phase described in step (1) or the microsphere slurry described in step (4).

Furthermore, the photoinitiator in step (1) is an oil-soluble photoinitiator, and the photoinitiator in step (4) is a water-soluble photoinitiator.

Furthermore, the oil-soluble photoinitiator is an oil-soluble cleavage-type free radical photoinitiator, and the water-soluble photoinitiator is a combination of a water-soluble cleavage-type free radical photoinitiator and a water-soluble hydrogen abstraction-type free radical photoinitiator.

Furthermore, the oil-soluble cleavage-type free radical photoinitiator includes one or more of hydroxycyclohexane phenyl ketone (photoinitiator 184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (photoinitiator 1173), benzoin dimethyl ether (photoinitiator BDK), (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (photoinitiator TPO), 4-(N,N-dimethylamino) ethyl benzoate (photoinitiator EDB), 2-methyl-1-[4-methylthiophenyl]-2-morpholinyl-1-propanone (photoinitiator 907), and 2-phenyl-2-N,N-dimethylamino-1-(4-morpholinylphenyl) butanone (photoinitiator 369); the water-soluble The cleavage-type free radical photoinitiator includes 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone (photoinitiator 2959), and the water-soluble hydrogen-abstracting free radical photoinitiator combination includes (4-dibenzoylphenyl)trimethylammonium chloride (photoinitiator BTC), 1-propylamine, 3-(4-benzoylphenoxy)-2-hydroxy-N,N,N-trimethyl chloride (photoinitiator BPQ), 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthene-2-yloxy)-N,N,N-trimethyl-1-propylammonium chloride (photoinitiator QTX) and a combination of tertiary amine substances (N,N-dimethylethanolamine, triethanolamine).

Furthermore, the heat-expandable microspheres include a thermoplastic shell and a volatile expansion agent wrapped in the thermoplastic shell.

Furthermore, the monomer comprises the following components in parts by weight:

40-90 parts of nitrile monomer;

Acrylic monomer 0-60 parts;

Acrylate monomer 5-50 parts.

Furthermore, the nitrile monomer is one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile or fumaronitrile; the acrylic monomer is one or more of acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, α-methylcinnamic acid, maleic acid, itaconic acid, fumaric acid and citraconic acid; the acrylate monomer is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, dicyclopentenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate or isobornyl methacrylate.

Furthermore, the boiling point of the volatile expansion agent is not higher than the softening temperature of the thermoplastic shell, and the volatile expansion agent is a C4-C12 aliphatic hydrocarbon compound.

Preferably, the volatile expansion agent is a C4-C8 straight-chain or branched saturated hydrocarbon compound.

Furthermore, the volatile expansion agent is one or more of isooctane, isopentane, isobutane, neopentane, n-hexane, heptane, petroleum ether and other low molecular weight hydrocarbons, tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane.

Preferably, the volatile expansion agent is one or more of isooctane, isopentane, isobutane, n-hexane and petroleum ether.

Preferably, based on the total weight of the nitrile monomers and the acrylate monomers, the thermoplastic shell further comprises the following components in percentage by weight:

Further, the crosslinking agent is divinylbenzene, ethylene glycol di(meth)acrylate, di(ethylene 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, dipentaerythritol hexa(meth)acrylate, One of 1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1,2-diol-1 or more; the initiator is dihexadecyl peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, dioctanoic acid peroxide, di-(2-ethylhexyl) peroxydicarbonate, dibenzoic acid peroxide, dilauric acid peroxide, didecanoic acid peroxide, tert-butyl peracetate, tert-butyl perlaurate, tert-butyl peroxybenzoate, tert-butyl hydroperoxide, diisopropyl hydroxydicarboxylate, 2,2'-azobis((2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), dimethyl 2,2,-azobis( The dispersion stabilizer is one or more of colloidal silicon dioxide, colloidal clay, calcium carbonate, calcium phosphate, calcium sulfate, calcium oxalate or barium carbonate; the dispersion stabilizing aid is one or more of methyl cellulose, methyl hydroxypropyl cellulose, polyvinyl alcohol, gelatin, polyvinyl pyrrolidone, polyethylene oxide, dialkyl dimethyl ammonium chloride, alkyl trimethyl ammonium chloride, alkyl sodium sulfate, alkyl sodium sulfonate, alkyl dimethyl amino acetate betaine or alkyl dihydroxyethyl amino acetate betaine.

Preferably, the thermoplastic shell is suspended and polymerized in an aqueous dispersion medium containing a dispersion stabilizer and/or a dispersion stabilizing aid, the aqueous dispersion medium is water, and an inorganic salt may be added thereto, the inorganic salt being sodium chloride or sodium sulfate.

Another aspect of the present invention provides a low residual monomer heat-expandable microsphere, which is prepared by the above method.

The low-residue heat-expandable microspheres provided by the present invention can be used in various applications, such as various plastics, elastomers, plasticine, paper/cardboard, etc., and specific applications include: PVC plastics, SBS elastomers, ultra-light clay, Braille paper, lightweight cement, hollow ceramics, emulsion explosives, etc.

The inventors have found that after the polymerization of heat-expandable microspheres is completed, a photoinitiator or a combination of photoinitiators is introduced into the heat-expandable microsphere slurry. Under continuous stirring and irradiation with ultraviolet light, the photoinitiator decomposes to produce a free radical polymerization reaction of a free radical initiator water-soluble monomer, and the water-soluble residual monomer is polymerized to form a polymer, thereby finally obtaining heat-expandable microspheres with a low residual monomer content.

The beneficial effects of the present invention are:

The expandable microspheres prepared by the present invention have significantly reduced residual monomers and do not affect the foaming performance of the heat-expandable microspheres, thereby broadening the application field of the heat-expandable microspheres.

DETAILED DESCRIPTION

The present invention is further described below by way of examples. In the examples listed, unless otherwise specified, all parts and percentages in the examples are parts and percentages by weight, and the analysis of the heat-expandable microspheres was performed using the following methods and instruments: (1) Particle size distribution characteristics analysis:

The particle size distribution of the microspheres was measured by a particle size distribution laser diffraction analyzer LS13320 produced by Bekman Coulter, and the average diameter was measured as the volume average particle size.

(2) Foaming characteristics analysis:

The characteristic of heat-expandable microsphere is measured by the thermomechanical analyzer TMA Q-400 produced by TA Instrument company.The 1.0mg heat-expandable microsphere prepared sample by the aluminum pan of diameter 6.7mm and depth 4.5mm.Then, the aluminum pan of diameter 6.5mm and depth 4.0mm is sealed.According to the TMA extended probe type, the sample temperature is increased to 280 ℃ from ambient temperature with the heating rate of 20 ℃/min, and the power of 0.1N is applied by probe.Analysis is carried out by measuring the vertical displacement of probe.

- Expansion initial temperature (Tstart): The temperature at which the probe displacement starts to increase (°C);

- Maximum foaming temperature (Tmax): the temperature (°C) when the probe displacement reaches the maximum;

- Foaming density (Dmin): ratio of microsphere addition amount to volume after foaming (kg/m ³ ).

(3) Evaluation method of residual monomer content in microspheres:

100 g of microsphere slurry was filtered to obtain a clear liquid, and a small amount of the clear liquid was analyzed by gas chromatography to determine the residual monomer content. We compared the blank example with Examples 1 to 5.

Preparation Example of Blank Heat-Expandable Microspheres:

Aqueous phase:

Oil phase:

Under the condition of 0.5Mpa, the oil phase and the water phase were dispersed by stirring at 7000rpm for 2 minutes with a homogenizer to prepare a suspension solution. The suspension solution was immediately injected into a 1-liter autoclave, the air was replaced by nitrogen, and the autoclave was pressurized to reach an initial pressure of 0.6MPa. Then, the polymerization reaction was carried out at 50-70°C for 20 hours. After the polymerization was completed, the basic thermal expansion microspheres were obtained by filtering, washing and drying. The relevant properties of the microspheres are shown in Table 1.

Table 1

In Table 1, (nitrile monomer) AN: acrylonitrile, (acrylate monomer) MMA: methyl methacrylate, TMPDMA: trimethylolpropane trimethacrylate, LPO: dodecyl peroxide, IP: isopentane.

Example 1

Preparation of Blank Example 1.5 g of photoinitiator 2959 (2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone) was added to the microsphere slurry and dispersed at room temperature for 0.5 hours, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low residual single heat expansion microspheres. The relevant test data are listed in Table 2.

Example 2

Preparation of Blank Example 1.5 g of photoinitiator 2959 (2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone) was added to the microsphere slurry and dispersed at room temperature for 0.5 hours, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 6 hours. The obtained product was filtered and dried to obtain low residual single heat expansion microspheres. The relevant test data are listed in Table 2.

Example 3

Preparation of blank example: 1.9 g BTC ((4-dibenzoylphenyl) trimethylammonium chloride) and 0.6 g N,N-dimethylethanolamine were added to the microsphere slurry and dispersed at room temperature for 0.5 hours, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low residual single heat expansion microspheres, and the relevant test data are listed in Table 2.

Example 4

Preparation of blank example: 1.9 g BTC ((4-dibenzoylphenyl) trimethylammonium chloride) and 0.3 g N,N-dimethylethanolamine were added to the microsphere slurry and dispersed at room temperature for 0.5 hours, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low residual single heat expansion microspheres, and the relevant test data are listed in Table 2.

Example 5

Preparation of blank example: 1.9 g BPQ (1-propylamine, 3-(4-benzoylphenoxy)-2-hydroxy-N,N,N-trimethyl chloride) and 0.6 g N,N-dimethylethanolamine were added to the microsphere slurry and dispersed at room temperature for 0.5 hours, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low residual single heat expansion microspheres, and the relevant test data are listed in Table 2.

Example 6

5 g of photoinitiator 184 (hydroxycyclohexane phenone) was added to the oil phase of the blank example. After the polymerization reaction was completed, the temperature was cooled to room temperature, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low-residue thermal expansion microspheres. The relevant test data are listed in Table 2.

Example 7

15 g of photoinitiator 184 (hydroxycyclohexane phenone) was added to the oil phase of the blank example. After the polymerization reaction was completed, the temperature was cooled to room temperature, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low-residue thermal expansion microspheres. The relevant test data are listed in Table 2.

Example 8

25 g of photoinitiator 184 (hydroxycyclohexane phenone) was added to the oil phase of the blank example. After the polymerization reaction was completed, the temperature was cooled to room temperature, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low-residue thermal expansion microspheres. The relevant test data are listed in Table 2.

Example 9

15 g of photoinitiator 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone) was added to the oil phase of the blank example. After the polymerization reaction was completed, the temperature was cooled to room temperature, and then the microsphere slurry was irradiated with a 100W ultraviolet lamp, and the stirring and irradiation were continued for 4 hours. The obtained product was filtered and dried to obtain low-residue thermal expansion microspheres. The relevant test data are listed in Table 2.

Example 10

15 g of photoinitiator 184 (hydroxycyclohexane phenone) was added to the oil phase of the blank example. After the polymerization reaction was completed, the temperature was cooled to room temperature, and then the microsphere slurry was irradiated with a 100 W ultraviolet lamp, and the stirring and irradiation were continued for 6 hours. The obtained product was filtered and dried to obtain low-residue thermal expansion microspheres. The relevant test data are listed in Table 2.

Through the data in Table 2, we first found that after adding the photoinitiator, the expansion properties of the microspheres were not significantly affected.

Through Example 1, Experimental Example 2, Example 7 and Example 10 in Table 2, we can find that after the polymerization reaction is completed, at room temperature, after adding an equal amount of the same initiator, extending the reaction time can further eliminate the residual monomer, but the reduction is not large.

By comparing Example 3, Example 5 and Example 7 and Example 9, we can also find that when the types of photoinitiators are different, the amount of residual monomers is also different. This is because the molecular weights of the photoinitiators are different. The lower the molecular weight of the initiator, the more free radicals it decomposes, and the higher the initiation efficiency.

By comparing Example 3 and Example 4, it can be seen that the initiation efficiency of the hydrogen abstraction type free radical photoinitiator is related to the amount of the auxiliary initiator used. This is because the initiation reaction of the hydrogen abstraction type free radical photoinitiator requires the participation of the auxiliary initiator to generate free radicals. When the amount of the auxiliary initiator used is small, the initiation efficiency is low.

By comparing Example 6, Example 7 and Example 8, it can be seen that under the same conditions, increasing the amount of photoinitiator can further eliminate residual monomers.

Table 2

According to the method given in the above description, a person skilled in the art can think of various modifications and other embodiments of the present invention. Therefore, the protection scope of the present invention is not limited to the disclosed embodiments, and any appropriate changes or modifications made by a person skilled in the art should be deemed to be within the scope of the patent of the present invention.

Claims (6)

1. A method for preparing low-residue heat-expandable microspheres, comprising the following steps: (1) mixing a monomer, an initiator, a cross-linking agent and a volatile foaming agent to obtain an oil phase; (2) mixing an aqueous dispersion medium, an inorganic salt, a dispersant, and a dispersion stabilizing agent to obtain an aqueous phase; (3) stirring and dispersing the oil phase and the water phase to obtain a suspension solution; (4) subjecting the obtained suspension solution to polymerization reaction for 15 to 25 hours at 40 to 80° C. and 0.1 to 0.5 MPa in an inert atmosphere, lowering the temperature of the microsphere slurry to room temperature, initiating the polymerization reaction of the residual monomers with ultraviolet light, filtering and drying to obtain heat-expandable microspheres with low residual monomers; A photoinitiator is added to the oil phase described in step (1) or the microsphere slurry described in step (4). 2. The method for preparing low-residue heat-expandable microspheres according to claim 1, characterized in that in step (4), a 100W ultraviolet lamp is used to irradiate the microsphere slurry, and stirring and irradiation are continued for 4h-6h. 3. The method for preparing low-residue thermally expandable microspheres according to claim 1, characterized in that the photoinitiator in step (1) is an oil-soluble photoinitiator, and the photoinitiator in step (4) is a water-soluble photoinitiator. 4. The method for preparing heat-expandable microspheres with low residual monomers according to claim 3, characterized in that the oil-soluble photoinitiator is an oil-soluble cleavage-type free radical photoinitiator, and the water-soluble photoinitiator is a combination of a water-soluble cleavage-type free radical photoinitiator and a water-soluble hydrogen abstraction-type free radical photoinitiator. 5. The method for preparing low-residue heat-expandable microspheres according to claim 4, characterized in that the oil-soluble cleavage-type free radical photoinitiator includes hydroxycyclohexane phenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzoin dimethyl ether, (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, ethyl 4-(N,N-dimethylamino) benzoate (photoinitiator EDB), 2-methyl-1-[4-methylthiophenyl]-2-morpholinyl-1-propanone, 2-phenyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)butyl One or more ketones; the water-soluble cleavage-type free radical photoinitiator includes 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and the water-soluble hydrogen-abstraction-type free radical photoinitiator combination includes (4-dibenzoylphenyl)trimethylammonium chloride, 1-propylamine, 3-(4-benzoylphenoxy)-2-hydroxy-N,N,N-trimethyl chloride, 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthene-2-yloxy)-N,N,N-trimethyl-1-propylammonium chloride and a combination of tertiary amine substances. 6. A heat-expandable microsphere with low residual monomers, characterized in that the heat-expandable microsphere with low residual monomers is prepared by any method described in claims 1-5.