Expandable microsphere with temperature resistance and preparation method thereof

Abstract

The preparation method comprises the following steps: mixing a monomer, an initiator, a cross-linking agent, a volatile foaming agent and an auxiliary agent to obtain an oil phase; mixing a water-based dispersion medium, inorganic salt, a dispersion stabilizer and a dispersion stabilizing aid to obtain a water phase; stirring the oil phase and the water phase to disperse the oil phase and the water phase to obtain a suspension solution; the expandable microspheres are prepared through a suspension polymerization method. The temperature resistance of the prepared expandable microspheres is obviously improved, meanwhile, the foaming performance of the expandable microspheres is not affected, and the application field of the expandable microspheres is widened.

Description

Technical Field

[0001] The invention relates to the field of polymer materials, and in particular to a temperature-resistant expandable microsphere and a preparation method thereof. Background Art

[0002] As a light and heavy filler, expandable microspheres have been successfully applied to the fields of plasticine, printing paste, plastics, elastomers, etc. 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 expansion agent such as aliphatic hydrocarbons. During the thermal expansion process of expandable microspheres, since the shell layer is in a highly elastic state under high temperature environment, the gaseous aliphatic hydrocarbons contained in the expandable microspheres can easily penetrate from the inside of the shell layer to the outside of the shell layer, thereby causing the collapse of the expandable microspheres and affecting the application effect of the expandable microspheres. In various high-temperature environment applications, the temperature resistance of expandable microspheres is an important indicator.

[0003] In order to improve the temperature resistance of expandable microspheres under high temperature conditions, in the currently disclosed patent technologies, specific raw materials (monomers, cross-linking agents, post-treatment agents, initiators) are usually used to modify the temperature resistance of expandable microspheres. Patent CN110724299A improves the temperature resistance of microspheres by combining monomers with epoxy groups and imidazole cross-linking agents, but the starting temperature and maximum foaming temperature of expandable microspheres show obvious changes, which restricts the application of expandable microspheres to a certain extent. Patent CN118179391A introduces a post-treatment agent (ESRA additive) into the slurry in the later stage of suspension polymerization, and improves the temperature resistance of microspheres by catalyzing the reaction between functional groups during the thermal expansion of expandable microspheres by the post-treatment agent. However, there are problems such as large amount of post-treatment agent used, difficulty in sewage treatment in the later stage, and high water treatment cost. Patent CN111701546A prepares expandable microspheres by adding organic acid or organic anhydride in the late stage of the polymerization reaction of expandable microspheres, so that the expandable microspheres have excellent high temperature resistance, but the introduction of organic acid or organic anhydride will also increase the cost of sewage treatment in the later stage, and will also cause odor problems in the application of microspheres. Patent CN111116969A introduces amphiphilic peroxide initiators and uses the interfacial polymerization formed by amphiphilic peroxides to prepare expandable microspheres with good morphological structure and excellent temperature resistance, but the preparation process of amphiphilic peroxide initiators is complicated, the preparation cost is high, and industrial amplification and commercialization are difficult. Patent CN111116970A combines an oil-soluble oxidant or an oil-soluble reducing agent with a matching water-soluble reducing agent or a water-soluble oxidant, and initiates the interfacial polymerization of oil-phase monomers containing carbon-carbon double bonds through redox combination to prepare expandable microspheres with good morphological structure and excellent temperature resistance.

[0004] Therefore, how to improve the temperature resistance of expandable microspheres under high temperature conditions without affecting the rise temperature and maximum foaming temperature of the expandable microspheres is an urgent problem to be solved at this stage. Summary of the invention

[0005] The purpose of the present invention is to provide a temperature-resistant expandable microsphere and a preparation method thereof, so as to overcome the defects of the prior art.

[0006] On one hand, the present invention provides a method for preparing expandable microspheres with temperature resistance, comprising the steps of mixing a monomer, an initiator, a crosslinking agent, a volatile foaming agent and an auxiliary agent to obtain an oil phase; mixing an aqueous dispersion medium, an inorganic salt, a dispersion stabilizer and a dispersion stabilizing auxiliary agent to obtain a water phase; stirring the oil phase and the water phase to disperse the oil phase and the water phase to obtain a suspension solution; and preparing the expandable microspheres by a suspension polymerization method.

[0007] A method for preparing temperature-resistant expandable microspheres comprises the following steps:

[0008] (1) Mixing monomers, initiators, crosslinking agents and volatile foaming agents to obtain an oil phase;

[0009] (2) mixing an aqueous dispersion medium, an inorganic salt, a dispersion stabilizer, and a dispersion stabilization aid to obtain an aqueous phase;

[0010] (3) stirring the oil phase and the water phase to disperse the oil phase and the water phase to obtain a suspension solution;

[0011] (4) After the obtained suspension solution is polymerized for 15 to 25 hours in an inert atmosphere at 40 to 80° C. and a pressure of 0.1 to 0.5 MPa, the temperature of the microsphere slurry is lowered to room temperature, filtered and dried to obtain temperature-resistant expandable microspheres;

[0012] The initiator is a combination of 4,4'-azobis(4-cyanopentanol) and 4,4'-azobis(4-cyanopentanol).

[0013] Furthermore, the expandable microspheres include a thermoplastic shell and a volatile expansion agent wrapped in the thermoplastic shell.

[0014] Furthermore, the monomer comprises the following components in parts by weight:

[0015] 40-90 parts of nitrile monomer;

[0016] 5-50 parts of acrylamide monomer;

[0017] 5-50 parts of acrylic acid ester monomer.

[0018] Furthermore, the nitrile monomer is one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile or fumaronitrile; the acrylamide monomer is one or more of N,N-dimethylacrylamide, N-(isobutoxymethyl)acrylamide, N-tert-butylacrylamide, diacetoneacrylamide; the acrylate monomer is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, dicyclopentenyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, butyl methacrylate or isobornyl methacrylate.

[0019] 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.

[0020] Preferably, the volatile expansion agent is a C4-C8 straight-chain or branched saturated hydrocarbon compound.

[0021] 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.

[0022] Preferably, the volatile expansion agent is one or more of isooctane, isopentane, isobutane, n-hexane and petroleum ether.

[0023] 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:

[0024] Cross-linking agent 0.1wt%~5wt%;

[0025] Initiator 1 wt%~5 wt%;

[0026] Additives 0.1wt%~0.5wt%;

[0027] Dispersion stabilizer 0.1~0.5%;

[0028] Dispersing and stabilizing agent 0.1~0.5%;

[0029] Inhibitor 0.01~0.1%;

[0030] Inorganic salt 1%-3%.

[0031] 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, triallyl formal tri(meth)acrylate, allyl methacrylate, trimethylolpropane tri(meth)acrylate, tributylene glycol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate. The invention relates to a polymer composition comprising the following: ester, PEG#600 di(meth)acrylate, 3-acryloyl glycol monoacrylate, triacyl formal, triallyl isocyanate, triallyl isocyanurate, divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, or tetraethylene glycol divinyl ether; the dispersion stabilizer is one or more of colloidal silica, 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; the polymerization inhibitor is one or more of sodium nitrite, cuprous chloride, and ferric chloride.

[0032] 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.

[0033] Another aspect of the present invention provides a heat-resistant expandable microsphere, which is prepared by the above method.

[0034] The heat-resistant expandable microspheres provided by the present invention can be used in various applications in high-temperature environments, and specific applications include: rubber applications, plastic applications, water-based printing pastes, and the like.

[0035] The inventors have found that after an initiator combination is introduced into the oil phase, free radicals generated by the thermal decomposition of the initiator combination initiate polymerization of the oil phase monomers to form polymer molecular chains with end groups (carboxyl groups or hydroxyl groups). During the thermal expansion of the expandable microspheres, due to the continuous movement of the polymer molecular chains, a reaction will occur between the end groups, that is, a dehydration condensation reaction will occur between the carboxyl groups and the hydroxyl groups to form an extension of the polymer molecular chain. The temperature resistance of the microsphere shell after chain extension is significantly improved, and finally expandable microspheres with temperature resistance are obtained.

[0036] The beneficial effects of the present invention are:

[0037] The heat resistance of the expandable microspheres prepared by the present invention is significantly improved, and the foaming performance of the expandable microspheres is not affected, thereby broadening the application field of the expandable microspheres. DETAILED DESCRIPTION

[0038] The present invention is further described below by way of examples. In the examples listed, unless otherwise stated, all parts and percentages in the examples are parts and percentages by weight, and the analysis of expandable microspheres was performed using the following methods and instruments:

[0039] (1) Particle size distribution characteristics analysis:

[0040] 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.

[0041] (2) Foaming characteristics analysis:

[0042] 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.

[0043] - Expansion initial temperature (Tstart): The temperature at which the probe displacement starts to increase (°C);

[0044] - Maximum foaming temperature (Tmax): the temperature (°C) when the probe displacement reaches the maximum;

[0045] - Foaming density (Dmin): the ratio of the amount of microspheres added to the volume after foaming (kg / m 3 ).

[0046] (3) Evaluation method of temperature resistance of expandable microspheres: In the TMA test of expandable microspheres, there is a temperature difference when the microspheres expand to half of the maximum foaming height, that is, the temperature between Tstart and Tmax at which the microspheres expand to half of the maximum foaming height (T 1 / 2左 ) and the temperature at which the microspheres expand to half of their maximum foaming height after exceeding Tmax (T 1 / 2右 ) between the temperature (ΔT). The temperature resistance of the microspheres is judged by ΔT. The larger the ΔT, the better the temperature resistance of the expandable microspheres.

[0047] Example of Preparation of Blank Expandable Microspheres

[0048] Aqueous phase:

[0049] 280g water (aqueous dispersion medium);

[0050] 10g sodium chloride (inorganic salt);

[0051] 0.1g sodium nitrite (inhibitor);

[0052] 0.5g 50wt% silica aqueous solution (dispersion stabilizer);

[0053] 0.5 g of 5 wt% aqueous solution of methyl hydroxypropyl cellulose (average molecular weight 26000 g / mol) (dispersion stabilizing agent);

[0054] 0.2g sodium dodecyl sulfate (dispersion stabilization aid);

[0055] Oil phase:

[0056] 150g acrylonitrile (monomer);

[0057] 15g methyl methacrylate (monomer);

[0058] 15g N,N-dimethylacrylamide (monomer);

[0059] 10g vinyl acetate (monomer);

[0060] 2g dodecanoyl peroxide (initiator);

[0061] 0.6 g trimethylolpropane tri(meth)acrylate (crosslinker);

[0062] 50g isopentane (volatile swelling agent);

[0063] Under the condition of 0.5Mpa, the oil phase and the water phase were dispersed by stirring at 2000rpm 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 60-75°C for 20 hours. After the polymerization was completed, the basic expandable microspheres were obtained by filtering, washing and drying. The relevant properties of the microspheres are shown in Table 1.

[0064] Table 1

[0065]

[0066] In Table 1, (nitrile monomer) AN: acrylonitrile, (acrylate monomer) MMA: methyl methacrylate, (acrylamide monomer) DMAA: N,N-dimethylacrylamide, vinyl acetate: VA; (cross-linking agent) TMPDMA: trimethylolpropane trimethacrylate; (foaming agent) IP: isopentane; (initiator) LPO: dodecanoyl peroxide.

[0067] Comparative Example 1

[0068] 1.8 g ACVA initiator was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank case, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres. The relevant test data are listed in Table 2.

[0069] Comparative Example 2

[0070] 1.61 g of AHVA was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres, and the relevant test data are listed in Table 2.

[0071] Example 1

[0072] An initiator combination of 1 gram of ACVA and 0.89 gram of AHVA was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank case, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres, and the relevant test data are listed in Table 2.

[0073] Example 2

[0074] An initiator combination of 1.4 g ACVA and 1.25 g AHVA was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank case, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres, and the relevant test data are listed in Table 2.

[0075] Example 3

[0076] An initiator combination of 1.8 g ACVA and 1.61 g AHVA was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank case, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres, and the relevant test data are listed in Table 2.

[0077] Example 4

[0078] An initiator combination of 1.8 g ACVA and 1.25 g AHVA was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank case, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres, and the relevant test data are listed in Table 2.

[0079] Example 5

[0080] An initiator combination of 1.4 g ACVA and 1.6 g AHVA was used as the oil phase initiator, and the types and addition amounts of other materials remained the same as those of the blank case, and then water-oil phase emulsification and suspension polymerization were performed. The obtained product was filtered and dried to obtain temperature-resistant expandable microspheres, and the relevant test data are listed in Table 2.

[0081] Through the blank examples and comparative examples 1 and 2 in Table 2, we can find that: when ACVA or AHVA is used alone as an initiator, the temperature resistance data of the microspheres does not increase significantly, but after ACVA and AHVA are combined as oil phase initiators (Example 3), the ΔT of the microsphere TMA foaming increases, that is, the temperature resistance of the microspheres is improved. Through Example 1, Example 2, and Example 3 in Table 2, we can find that: as the amount of ACVA and AHVA combined is continuously increased, the temperature resistance data of the microspheres also increases, and the TMA foaming density gradually decreases. Through Example 2, Example 4, and Example 5 in Table 2, we can see that: after increasing the amount of ACVA or AHVA, the temperature resistance data of the microspheres is not much different, and the foaming density of the microspheres increases. This is caused by the decrease in the molecular weight of the shell polymer after the increase in the initiator.

[0082] Table 2

[0083]

[0084] In Table 2, ACVA: 4,4'-azobis(4-cyanovaleric acid), AHVA: 4,4'-azobis(4-cyanopentanol).

[0085] 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

1. A method for preparing temperature-resistant expandable microspheres, comprising the following steps: (1) Mixing monomers, initiators, crosslinking agents and volatile foaming agents to obtain an oil phase; (2) mixing an aqueous dispersion medium, an inorganic salt, a dispersion stabilizer, and a dispersion stabilization aid to obtain an aqueous phase; (3) stirring the oil phase and the water phase to disperse the oil phase and the water phase to obtain a suspension solution; (4) After the obtained suspension solution is polymerized for 15 to 25 hours in an inert atmosphere at 40 to 80° C. and a pressure of 0.1 to 0.5 MPa, the temperature of the microsphere slurry is lowered to room temperature, filtered and dried to obtain temperature-resistant expandable microspheres; The initiator is a combination of 4,4'-azobis(4-cyanopentanol) and 4,4'-azobis(4-cyanopentanol).

2. The method for preparing expandable microspheres according to claim 1, characterized in that: The expandable microspheres include a thermoplastic shell and a volatile expansion agent wrapped in the thermoplastic shell.

3. The method for preparing expandable microspheres according to claim 1, characterized in that: The monomer comprises the following components in parts by weight: 40-90 parts of nitrile monomer; 5-50 parts of acrylamide monomer; 5-50 parts of acrylic acid ester monomer.

4. The method for preparing expandable microspheres according to claim 1, characterized in that: 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.

5. A temperature-resistant expandable microsphere, characterized in that: The expandable microspheres are prepared by the method according to any one of claims 1 to 4.

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