CN111171221A - Method for preparing thermal expansion microspheres by using SPG emulsion membrane technology - Google Patents
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
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Abstract
The invention provides a method for preparing thermal expansion microspheres by utilizing SPG technology, which comprises the following steps: 1) preparing an oil phase containing monomers: mixing a vinyl monomer combination, a cross-linking agent, an initiator, and a blowing agent for polymerization to form a thermoplastic polymer to form an oil phase; the monomers in the monomer combination are monomers without benzene aromatic structures; 2) preparing a water phase: adding a solid suspending agent, a dispersion stabilizing auxiliary agent, an inhibitor and an electrolyte into deionized water to form a water phase; 3) dispersing: applying pressure to the oil phase to disperse the oil phase into the flowing water phase through an SPG emulsion membrane to obtain a dispersion liquid; 4) polymerization: introducing the dispersion liquid drops into a high-pressure polymerization reaction kettle for polymerization reaction to prepare heat expansion microspheres; the core-shell structure expanded microsphere synthesized by the invention has the advantages of uniform particle size, controllable size and high foaming agent coating efficiency, and can effectively improve the traditional production process.
Description
Technical Field
The invention provides a preparation method of thermal expansion microspheres, which is to obtain an oil phase droplet dispersion with narrow particle size distribution by using an SPG emulsion membrane technology, and further prepare the thermal expansion microspheres with uniform size by using the oil phase droplet dispersion through the existing suspension polymerization method. The core-shell structure expanded microsphere prepared by the method has the advantages of uniform particle size, controllable size and high foaming agent coating efficiency.
Background
Thermally expandable microspheres are formed of a shell of a thermoplastic polymer and a core of an alkane as a blowing agent, typically the thermoplastic polymer forming the shell has a softening temperature above the boiling point of the blowing agent, so that when heated the shell softens and the propellant evaporates, increasing the internal pressure, resulting in significant expansion of the microsphere. The initial temperature of expansion is called TstartThe temperature at which maximum expansion is reached is called Tmax。
Thermally expanded microspheres may be sold in different forms, such as dried granules, aqueous slurries, partially dewatered wet cakes, and the like. In addition, thermally expandable microspheres are also sold in both unexpanded and expanded states, with significant differences in density and appearance. The microspheres are used as foaming agents in many different applications and are one of the raw materials that are not available in the fields of paper making, printing, inks, foamed plastics, automotive lightweight materials, building insulation, textile and artificial leather.
The synthesis of thermally expandable microspheres is well established and patents have been made earlier in the 70's of the last century to study the synthesis of thermally expandable microspheres (US2615972), and since then for decades the skilled man has continued to study in depth the different polymerization and expansion processes of thermally expandable microspheres, such as US4287308, US6235800, US6509381, and EP 1054034, EP1408097, and japanese patent JP1987-286534, etc. These patents are described in detail in the influence of the composition and properties of the polymer monomer, the use of a crosslinking agent, the selection of an initiator, the screening of a dispersion medium, the polymerization temperature and pressure, the expansion foaming technique, etc., respectively, but they have a common problem in that there is only a few patents investigating how to prepare thermally expandable microspheres having uniform size. The common method is to select a high-speed mechanical dispersion mode to disperse the water phase and the oil phase to form liquid drops with different sizes; the selection of suitable dispersants and dispersing aids stabilizes the already formed oil phase droplets against aggregation between the droplets. The method inevitably causes the size of the liquid drop to be in a normal distribution rule and uneven in size, so that the sizes of the polymerized microspheres are also inconsistent, and the foaming performance is further influenced.
The SPG membrane is a novel inorganic membrane developed by SPG corporation of japan in 1981, and has uniform and uniform minute pore sizes, and the pore sizes are easily changed as with special function glasses. The conventional method for preparing emulsion particles is to mix two immiscible liquids under the action of a proper amount of surface active ingredients by stirring to prepare an emulsion, but the emulsion droplets are polydisperse and have diameters which can be different by several times or even tens of times. In the SPG emulsion membrane technology, the oil phase dispersed phase permeates through the pores of the microporous membrane under the action of nitrogen pressure to form droplets on the membrane surface, and the droplets are peeled off from the membrane surface after the diameter of the droplets reaches a certain value under the flushing action of the aqueous phase continuous phase flowing along the membrane surface, thereby forming an emulsion. The control of the particle size and the distribution of the emulsion can be better realized by utilizing the SPG membrane with uniform pore size. The diameter of the micropores of the membrane is relatively uniform, so that the droplets of the prepared emulsion are relatively uniform, the stability of the droplets can be kept as long as the composition of the water phase is adjusted, the emulsion droplets with good monodispersity can be prepared, and the corresponding polymer microparticles are obtained after polymerization. Therefore, the SPG film can prepare emulsion or emulsion beads with uniform size, and is an effective means for preparing the polymer microspheres.
Patents CN105037603, CN200810020545.3 and CN201010017686.7 all provide similar preparation methods for preparing monodisperse copolymer microspheres with uniform particle size and controllable size by membrane emulsification, which can easily control the morphology and properties of the product, and increase the uniformity and yield of the particle size distribution of the product. However, the monomers used in the above patents are limited to mono-or poly-alkenyl styrene monomers, such as styrene, ethylstyrene, chloromethylstyrene or chloroacetylated styrene, etc., and the monodisperse copolymerized microspheres prepared by copolymerizing such monomers are microspheres with solid structures and do not have thermal expansion properties; and the oil phase combination in the process of carrying out the membrane emulsification technology does not contain raw materials with low boiling point. Considering that a low-boiling-point raw material as a foaming agent is one of the essential raw materials of the thermal expansion microsphere, the invention researches how to efficiently mix the low-boiling-point raw material with a vinyl monomer without a benzene series and prepare the copolymerization microsphere with uniform particle size, controllable size and high foaming agent coating efficiency.
Disclosure of Invention
The invention aims to provide a method for preparing thermal expansion microspheres by using an SPG (Shirasu Porous Glass) technology so as to prepare single-core structure thermal expansion microspheres with uniform particle size distribution.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing thermally expandable microspheres using SPG technology, wherein the method comprises:
1) preparing an oil phase containing monomers: mixing a vinyl monomer combination, a cross-linking agent, an initiator, and a blowing agent for polymerization to form a thermoplastic polymer to form an oil phase; wherein the monomers in the monomer combination are monomers without benzene aromatic structures;
2) preparing a water phase: adding a solid suspending agent, a dispersion stabilizing auxiliary agent, an inhibitor and an electrolyte into deionized water to form a water phase;
3) dispersing: applying pressure to the oil phase to disperse the oil phase into the flowing water phase through an SPG emulsion membrane to obtain a dispersion liquid;
4) polymerization: and introducing the dispersion liquid drops into a high-pressure polymerization reaction kettle for polymerization reaction to prepare the thermal expansion microspheres.
In the invention, a monomer, a cross-linking agent, an initiator and a foaming agent are mixed to obtain an oil phase, the oil phase is introduced into an assembled container by utilizing an SPG emulsion membrane, corresponding pressure is applied to the oil phase in the container, and the oil phase is mixed with an aqueous solution dissolved with a dispersing agent through the SPG membrane to form a continuous dispersion phase. Unlike typical solid microspheres, the shell of the expanded microsphere needs to have good barrier properties, and acrylonitrile monomers become an indispensable monomer component. Meanwhile, the shell of the expanded microsphere needs higher glass transition temperature, so that a monomer structure containing benzene series is less used. In order to reduce the dissolution and diffusion of acrylonitrile in the water phase, an electrolyte with salting-out effect is required to be added into the water phase, so that the solubility of acrylonitrile in water is reduced; meanwhile, in order to reduce the polymerization of the dissolved monomer in the aqueous phase, a water-soluble free inhibitor is required to be added into the aqueous phase. The above measures are all to make the monomer carry out polymerization reaction in the interior of the liquid drop, and avoid the monomer dissociated in the water phase from self-polymerization to form flocculent impurities.
In the invention, a water phase mixed by a solid suspending agent, a dispersion stabilizing auxiliary agent, a water-soluble free inhibitor and an electrolyte is subjected to mechanical stirring or a circulating system to give a certain flow velocity, and an oil phase passing through an SPG film is fully dispersed to prepare a liquid drop dispersed phase with uniform size for the next polymerization reaction.
Unlike the conventional stirring and homogenizing method, the SPG membrane emulsification method is a technique of manufacturing microbeads by penetrating an oil phase into a water phase through an inorganic porous membrane under a certain pressure using a porous membrane. The principle is that the oil phase is pressurized by nitrogen to pass through an emulsion film, the water phase forms a certain flow velocity in the stirring process, the oil phase passing through the emulsion film leaves the emulsion film in droplets with certain size due to the shearing force of the continuously flowing water phase, the newly formed droplets maintain the shape of spheres through a dispersing agent in the water phase, and then solid particles are formed through the polymerization process.
The SPG emulsification membrane method can prepare liquid drops with uniform sizes, and can prepare thermal expansion microspheres with different particle sizes according to the pore size of the SPG membrane. The pore diameter of the SPG emulsion membrane is preferably 1-30um, and the diameter range of the final thermal expansion microspheres is 0.1-30 um; the pore size of the SPG emulsion membrane is more preferably 5-20um, and the diameter of the final heat-expandable microspheres is in the range of 0.1-20 um.
The pressurization method according to the present invention is preferably performed by pressurizing with nitrogen gas so that the oil phase smoothly passes through the pores of the SPG film and is further dispersed into the water phase to form droplets. Said pressure is preferably a pressure of 0.5-5.0bar, more preferably a value of 1.0-5.0bar, such as 2 or 4 bar.
In a specific embodiment, the monomer, the cross-linking agent, the foaming agent and the initiator are mixed and then are filled into an SPG oil phase tank, and a pressure of 0.5-5.0bar is added to continuously disperse in the aqueous solvent dissolved with the dispersing agent to prepare uniform liquid drops. The SPG membrane emulsifier can be of an internal pressure type, an external pressure type and the like, and the assembled container can be made into a flat tube shape, a cylinder type and the like, but is not limited to the above. In view of the low boiling point of the oil phase components, the assembled container is preferably a totally enclosed system including an oil phase mixing tank, an SPG oil phase tank, an aqueous phase tank, and an SPG membrane.
The polymerization method of the thermally-expansible microballs to which the present invention relates can be carried out by a conventional method for preparing thermally-expansible microballs, which is well known and known to those skilled in the art, and is not particularly limited.
The SPG emulsion membrane method can disperse the oil phase in the water phase to form liquid drops with uniform size. Wherein the oil phase comprises a mixture of unsaturated monomers, foaming agents, initiators, crosslinking agents and the like, and the water phase comprises an aqueous solution of dispersing agents and the like dissolved in water. Wherein the weight ratio of oil phase to aqueous phase is preferably from 1: 1 to 1: 10, more preferably from 1: 4 to 1: 9, such as 1: 5 or 1: 8.
In one embodiment, the oil phase obtained in step 1) contains the monomer combination in an amount of 48.9 to 89.8 wt.%, preferably 55 to 88 wt.%, such as 55 wt.%, 70 wt.% or 80 wt.%; the amount of cross-linking agent is 0.1 to 3 wt%, such as 0.6 wt%, 0.8 wt%, 1 wt% or 2 wt%; the initiator is present in an amount of 0.1 to 2 wt%, such as 0.5 wt%, 0.6 wt% or 1 wt%; the blowing agent is present in an amount of 10 to 50 wt.%, such as 20 wt.%, 30 wt.% or 35 wt.%.
In the present invention, "wt%" and "wt%" may be used interchangeably.
The unsaturated monomers (i.e., monomer combination) to which the present invention relates include one or more mixtures of vinylidene chloride, acrylonitrile, methacrylonitrile, esters of methacrylic acid. In one embodiment, the monomer combination comprises 0 to 30 weight percent vinylidene chloride, 20 to 80 weight percent acrylonitrile, 0 to 10 weight percent methacrylonitrile, and 0 to 50 weight percent of an ester of methacrylic acid. Wherein the ester of methacrylic acid comprises one or more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate and isobornyl methacrylate.
The unsaturated monomer preferably contains from 5 to 30% by weight of vinylidene chloride, for example 10% or 18% by weight. Further, the unsaturated monomer preferably contains 30 to 80 wt% of acrylonitrile, more preferably 35 to 70 wt%, such as 40 wt%, 50 wt% or 65 wt%. Further, the unsaturated monomer preferably contains 5 to 50% by weight of the monomer combination consisting of esters of methacrylic acid, more preferably 5 to 35% by weight, such as 8%, 20% or 30% by weight.
The esters of methacrylic acid preferably have only one carbon-carbon double bond, possible esters of methacrylic acid including, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, isobornyl methacrylate and mixtures thereof, of which methyl methacrylate is preferred.
The unsaturated monomer may be free of methacrylonitrile, but if methacrylonitrile is included, the amount of methacrylonitrile is preferably from 0.5 to 8 wt%, more preferably from 1 to 5 wt%, such as 1.5 wt%, 2 wt% or 4 wt%.
In the present invention, the oil phase also contains 0.1 to 3 wt.% of a cross-linking agent, which may be one or more cross-linking polyfunctional monomers, including difunctional monomers and/or trifunctional monomers. The selected difunctional monomer is preferably added in an amount of 0.1 to 3% by weight, particularly preferably 0.5 to 2.9% by weight, such as 0.8% by weight, and includes one or more of divinylbenzene, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, allyl methacrylate, and the like. The selected trifunctional monomer is preferably added in an amount of 0.1 to 1 wt.%, particularly preferably 0.1 to 0.8 wt.%, such as 0.3 wt.%, and comprises one or more of pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, triallylisocyanate, and the like.
The blowing agent of the present invention is an alkane or mixture of alkanes, preferably having a boiling point not higher than the glass transition temperature of the thermoplastic polymer shell. Alkanes having a boiling point of-20 to 60 ℃ are preferred, and alkanes having a boiling point of-15 to 40 ℃ are more preferred. The foaming agent can be one or more of butane, isobutane, isopentane, n-hexane and cyclohexane. Wherein the blowing agent combination comprises 20 to 100 weight percent of isobutane, 0 to 30 weight percent of isopentane, 0 to 10 weight percent of n-butane, 0 to 10 weight percent of n-hexane and 0 to 30 weight percent of cyclohexane. Preferred blowing agents contain isobutane and may be used alone or in admixture with one or more other alkanes, wherein the preferred amount of isobutane in the mixture is from 60 to 100 wt%, more preferably from 80 to 100 wt%.
The initiator of the present invention may be conventional radical polymerization initiator including one of organic peroxides, azo compounds and their mixture. The initiator can be one of dilauroyl peroxide, dibenzoyl peroxide, tert-butyl hydroperoxide, di (4-tert-butylcyclohexyl) peroxydicarbonate, azobisisobutyronitrile, azobis (2, 4-dimethylvaleronitrile) and a mixture thereof. In one embodiment, the initiator may be added to the oil phase in an amount of 0.2 to 2 wt%, preferably 0.4 to 2 wt%, such as 0.5 wt%, 1 wt% or 2 wt%.
In the aqueous phase of the present invention, the solid suspending agent mainly serves to disperse the suspension and stabilize the uniform droplets passing through the SPG emulsion membrane from secondary aggregation, and preferably constitutes 0.5 to 5 wt%, more preferably 0.8 to 4 wt%, such as 1.0 wt%, 1.4 wt%, or 2.5 wt% of the aqueous phase. The dispersing agent may be selected from starch, derivatives of cellulose, silica, colloidal clays, metal oxides or hydroxides. A pH of preferably 1 to 6 is suitable if the solid suspending agent is starch, cellulose derivatives, silica, colloidal clays, and a pH of preferably 5 to 12 is suitable if the solid suspending agent is a metal oxide or hydroxide. It is to be noted that although solid suspending agents are added to the aqueous system, they can be washed off in a subsequent step, so that they are substantially absent from the final product.
To optimize the dispersion, small amounts of one or more dispersion stabilizing aids, preferably from 0.2 to 5% by weight, more preferably from 0.8 to 4% by weight, for example 0.8%, 1% or 3% by weight, based on the aqueous phase, are also added, which may be selected from alkylsulfonates and alkylsulfates, such as sodium dodecylsulfate, polyvinyl imides, polyvinyl alcohols, polyvinyl pyrrolidones, amphoteric substances, such as gelatin, proteinaceous substances.
The aqueous solution according to the invention may contain, in addition to the dispersion stabilizing aid, an electrolyte and an inhibitor for preventing the monomer from leaving the outside of the drops and polymerizing. The electrolyte is not particularly limited and includes one or more of lithium chloride, sodium chloride, potassium chloride, calcium chloride, lithium sulfate, sodium sulfate, potassium sulfate, and is used in an amount of preferably 0.1 to 10% by weight, more preferably 2.5 to 10% by weight, such as 2.5%, 5% or 8% by weight, based on the proportion to the aqueous phase. The inhibitor serves to prevent the microspheres from becoming mutually enriched during the polymerization process, preferably an alkali metal nitrite, including one or more of sodium nitrite and potassium nitrite, is preferably used in an amount of 0.001 to 0.8% by weight, more preferably 0.01 to 0.6% by weight, such as 0.01%, 0.05% or 0.08% by weight, based on the proportion of the aqueous phase.
The polymerization process to which the present invention relates can be carried out following the same principles as in the patents mentioned above. For example, in one embodiment of the present application, a dispersion of uniformly sized droplets prepared using the SPG emulsion membrane technique is stirred for a period of time and then transferred to a high pressure reaction vessel in a closed system for polymerization. The polymerization temperature may be 40 to 100 ℃, preferably 40 to 80 ℃; the polymerization pressure may be from 1.0 to 20 atmospheres, preferably from 2 to 8 atmospheres; the polymerization time may be 4 to 30 hours, preferably 15 to 28 hours.
When the polymerization process is complete, the microspheres are typically obtained as an aqueous dispersion or aqueous slurry, and may then be dewatered for use by conventional means, such as compression filtration, rotary filtration, centrifugal filtration, bed filtration, and the like. It may then be dried by conventional methods such as rotary drying, air-blast drying, spray drying, tray drying, and the like.
The thermally expandable microspheres prepared in the present invention refer to microspheres that have not been previously expanded, i.e., unexpanded, thermally-initiated expanded microspheres.
The average particle size of the thermally expandable microspheres prepared according to the present invention is related to the pore size of the SPG membrane, and is generally in the range of 1 to 100 microns, preferably 1 to 50 microns, and more preferably 5 to 40 microns.
Initial foaming temperature T of thermally expandable microspheresstartAnd maximum expansion temperature TmaxThe initial foaming temperature T is dependent on the type and ratio of monomers and blowing agentstartGenerally between 70-180 ℃, preferably 80-150 ℃, more preferably 80-130 ℃; maximum expansion temperature TmaxGenerally between 120 and 240 ℃, preferably between 120 and 200 ℃, more preferably in the range of 120 to 170 ℃.
Compared with the traditional homogenization process, the method has the advantages that the particle size of the microspheres prepared by the SPG membrane emulsification method is more uniform, the content of the microspheres in the applicable particle size range is higher, and the use efficiency of the reaction kettle is improved. Meanwhile, the phenomenon that the manufactured microspheres are shriveled or the foaming agent is not coated in the traditional process is reduced, the material waste is effectively reduced, the coating efficiency of the foaming agent is improved, and the expansion performance of the expanded microspheres is further improved, such as the reduction of the maximum foaming density.
Detailed Description
The process provided by the present invention is described in further detail below, but the present invention is not limited thereto.
Raw material source/type
| Name of reagent | Reagent shorthand | Purity of | Suppliers of goods |
| Polyethylene glycol | PEG | Experiment purity | Chemistry of Dow |
| Acrylonitrile | AN | Chemical purity | Wanhua chemistry |
| Methacrylonitrile | MAN | Chemical purity | Wanhua chemistry |
| Vinylidene chloride | VDC | Chemical purity | Chemical engineering of Nantong Xiangtai |
| Methyl radicalAcrylic acid methyl ester | MMA | Chemical purity | Wanhua chemistry |
| Methacrylic acid butyl ester | BMA | Chemical purity | Wanhua chemistry |
| Ethylene glycol dimethacrylate | EGDMA | Analytical purity | Chemical industry of Xilong |
| Trimethylolpropane trimethacrylate | TMPTMA | Analytical purity | Chemical industry of Xilong |
| Azobisisobutyronitrile | AIBN | Analytical purity | Chemical industry of Xilong |
| Isobutane | IB | Analytical purity | Jinling petrochemical |
Test method
The particle size and particle size distribution of the thermally expanded microspheres were determined by laser light scattering on a wet sample on a Bettersize 2000LD laser particle size analyzer. The average particle size is expressed as the volume diameter median diameter D50 and the particle size distribution is expressed as the SPAN.
The amount of blowing agent of the thermally expanded microspheres was determined by thermogravimetric analysis (TGA) on Mettler TGA/DSC 1. All samples were dried as much as possible prior to analysis to exclude interference from moisture and residual monomers. The analysis was carried out under a nitrogen atmosphere, starting at 30 ℃ and at a heating rate of 20 ℃/min.
The expansion properties of the thermally expandable microspheres were tested on Mettler TMA/SDTA 2+ LN/600 using a heating rate of 20 deg.C/min and a load of 0.06N. T isstartStarting temperature for foaming, and TmaxTMA-density, temperature at maximum foaming, of microspheres at TmaxDensity of the particles.
Example 1
An aqueous dispersion medium was prepared by the following method: 50g of sodium chloride, 8.6g of magnesium hydroxide, 5g of polyethylene glycol, 0.2g of polyvinylpyrrolidone and 0.5g of sodium nitrite are added into 545g of deionized water, and the mixture is stirred and mixed uniformly to prepare an aqueous medium. On the other hand, 60g of acrylonitrile, 28g of vinylidene chloride, 12g of methyl methacrylate, 1.3g of ethylene glycol dimethacrylate, 0.8g of azobisisobutyronitrile and 50g of isobutane as a blowing agent were prepared as an oil phase mixture. The prepared oil phase mixture was put on an air cylinder container assembled with an SPG membrane of 8.0um pore size, and a pressure of 3.5bar was applied to prepare continuously dispersed oil phase droplets. After stirring the uniformly sized droplet dispersion phase at 1000rpm for 1 hour, it was transferred to an autoclave and reacted at 60 ℃ for 24 hours with a pressure of 3MPa and a stirring rate of 500 rpm. And then, centrifugally separating the polymer, washing the polymer for 2 to 3 times by using deionized water, and drying the polymer in an oven to obtain the dried thermal expansion microspheres.
Examples 2 to 13
The compositions of the water phase and the oil phase of the examples are shown in Table 1, and the other experimental modes used were the same as those in example 1 described above except that the raw material ratios were different. The results are shown in Table 1.
Comparative examples 1 to 3
The differences between the comparative examples and the examples include that the proportions of the water phase raw materials in the comparative examples 1 to 3 are the same as those in the example 1, and the proportions of the oil phase raw materials in the comparative examples 1 to 3 are shown in Table 2 and are the same as those in the examples 1/6/12, respectively; comparative examples 1-3 were dispersed before polymerization in a different manner, not by the SPG emulsification method, but by mechanical stirring at 8000rpm for 10 minutes and then by transferring to 1000rpm and continuing stirring for 1 hour. The results appear in table 2.
In table 1 above:
PEG: polyethylene glycol
PVP: polyvinyl pyrrolidone
SDS (sodium dodecyl sulfate): sodium dodecyl sulfate, C12H25SO3Na
AN: acrylonitrile
MAN: methacrylonitrile
VDC: vinylidene chloride
MMA: methacrylic acid methyl ester
BMA: methacrylic acid butyl ester
EGDMA: ethylene glycol dimethacrylate
TMPTMA: trimethylolpropane trimethacrylate
AIBN: azobisisobutyronitrile
IB: isobutane
TABLE 2 summary of data for comparative examples 1-3
As shown in Table 1, comparative examples 1 to 5, in which the same oil phase component was used and different water phase components were changed, had some influence on the properties of the thermally expandable microspheres produced by the SPG method. After the polyvinylpyrrolidone is removed and replaced by the polyethylene glycol with the same amount, the SPAN SPAN value of the microsphere is increased to a certain extent, which shows that the polyvinylpyrrolidone plays a role in controlling the particle size distribution as a dispersion stabilizing auxiliary agent in the system. After the sodium dodecyl sulfate with equal mass is used for replacing the polyvinylpyrrolidone, the SPAN SPAN value of the microsphere is greatly increased, the coating amount of the foaming agent is reduced, and the irreplaceability of the polyvinylpyrrolidone in an aqueous phase system is also proved.
On the premise that the aqueous phase system is consistent, comparing the data of examples 1/6/12 in table 1 and comparative examples 1/2/3 in table 2, the difference of the average particle size of the thermal expansion microspheres is not large, but the SPAN value is greatly different, and the SPAN value of the thermal expansion microspheres manufactured by using the SPG method is basically within 1.5, which shows that the particle size distribution is narrower; compared with the prior art, the expanded microspheres prepared by the common homogeneous stirring method have wider particle size distribution, SPAN SPAN values are all larger than 2.1, and the nonuniformity of the particle size distribution is obviously reflected. On the other hand, the thermally expandable microspheres produced by the SPG method also covered more blowing agent than the products produced by the conventional homogeneous stirring method, for example, the blowing agent content in the better performing examples 1 and 6 was about 25%, while the value in the same monomer composition of comparative examples 1 and 2 was less than 20%, and the conventional homogeneous method was significantly insufficient in terms of the blowing agent covering amount compared to the blowing agent content of about 33% in the initial charge ratio.
In addition, in the index of TMA-density, the maximum density (TMA-density) of microspheres produced using the SPG method after the end of expansion is also significantly lower than that of ordinary homogenization methods, which may be caused by two reasons. First, if the size of the microspheres itself is not uniform, the capsules may exist in a large or small state, and the foaming agent coated inside the microspheres is difficult to stabilize on the core, thereby affecting the expansion properties of the microspheres, resulting in breakage or depression during expansion and further increasing the density after expansion. The thermally expandable microspheres produced by the SPG process ensure a more uniform size of the microspheres (SPAN value). Secondly, data in the table show that the content of the foaming agent coated inside the microspheres is obviously higher than that of the foaming agent coated inside the microspheres by a common homogenization method, so that the expansion degree of the microspheres is higher, the final density is lower, and the side proves that the coating efficiency of the foaming agent is obviously improved.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all equivalent modifications made by the present invention in the light of the present specification, or directly/indirectly applied to other related technical fields are included in the scope of the present invention.
Claims (10)
1. A method for preparing thermally expandable microspheres using SPG technology, the method comprising:
1) preparing an oil phase containing monomers: mixing a vinyl monomer combination, a cross-linking agent, an initiator, and a blowing agent for polymerization to form a thermoplastic polymer to form an oil phase; wherein the monomers in the monomer combination are monomers without benzene aromatic structures;
2) preparing a water phase: adding a solid suspending agent, a dispersion stabilizing auxiliary agent, an inhibitor and an electrolyte into deionized water to form a water phase;
3) dispersing: applying pressure to the oil phase to disperse the oil phase into the flowing water phase through an SPG emulsion membrane to obtain a dispersion liquid;
4) polymerization: and introducing the dispersion liquid drops into a high-pressure polymerization reaction kettle for polymerization reaction to prepare the thermal expansion microspheres.
2. The method of claim 1, wherein the combination of vinylic monomers used to polymerize to form the thermoplastic polymer is a mixture of one or more of acrylonitrile, vinylidene chloride, methacrylonitrile, and methacrylate; wherein the monomer combination comprises 0 to 30 weight percent of vinylidene chloride, 20 to 80 weight percent of acrylonitrile, 0 to 10 weight percent of methacrylonitrile, and 0 to 50 weight percent of methacrylate; preferably, the methacrylate is one or more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate and isobornyl methacrylate.
3. The method of claim 1 or 2, wherein the blowing agent is one or more of n-butane, isobutane, isopentane, n-hexane, and cyclohexane; preferably, the blowing agent consists of 20 to 100% by weight of isobutane, 0 to 30% by weight of isopentane, 0 to 10% by weight of n-butane, 0 to 10% by weight of n-hexane and 0 to 30% by weight of cyclohexane; and/or the presence of a gas in the gas,
the cross-linking agent is one or more of cross-linking difunctional monomer and cross-linking trifunctional monomer; preferably, the crosslinking difunctional monomer is one or more of divinylbenzene, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, etc., and the crosslinking trifunctional monomer is one or more of pentaerythritol triacrylate, pentaerythritol trimethacrylate, trimethylolpropane trimethacrylate, etc.; and/or the presence of a gas in the gas,
the initiator is one or more of organic peroxides and azo compounds; preferably, the azo compound initiator is one or more of azobisisobutyronitrile and azobis (2, 4-dimethylvaleronitrile), and the organic peroxide initiator is one or more of tert-butyl hydroperoxide, dibenzoyl peroxide and bis (4-tert-butylcyclohexyl) peroxydicarbonate.
4. A process according to any one of claims 1 to 3 wherein the solid suspending agent is one or more of starch, methylcellulose, silica, colloidal clay, metal oxide or hydroxide.
5. The method according to any one of claims 1 to 4, wherein the dispersion stabilizing aid is one or more of polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, alkyl sulfate and sulfonate.
6. The method of any one of claims 1-5, wherein the inhibitor is one or more of potassium dichromate, sodium nitrite, potassium nitrite, and lithium nitrite.
7. The method according to any one of claims 1 to 6, wherein the electrolyte is one or more of a halide, a sulfate compound, a carbonate compound of alkali and alkaline earth metals; preferably; the electrolyte is one or more of sodium chloride, magnesium chloride, ammonium chloride, sodium sulfate, magnesium sulfate and sodium carbonate.
8. The process according to any of claims 1 to 7, characterized in that the electrolyte content in the aqueous phase obtained in step 2) is from 0.1 to 10% by weight, preferably from 2.5 to 10% by weight; the content of solid suspending agent in the aqueous phase is 0.5 to 5% by weight, preferably 0.8 to 4% by weight; the content of the dispersion stabilizing aid in the aqueous phase is from 0.2 to 5% by weight, preferably from 0.8 to 4% by weight; the inhibitor is present in the aqueous phase in an amount of 0.01 to 0.8% by weight, preferably 0.01 to 0.6% by weight.
9. The process according to any one of claims 1 to 8, characterized in that the oil phase obtained in step 1) has a content of said combination of monomers of from 49.8 to 89.8% by weight, preferably from 55 to 88% by weight; the content of the cross-linking agent is 0.1 to 3 wt%; the content of the initiator is 0.1 to 2 wt%; the content of the foaming agent is 10 to 50% by weight.
10. The method of any of claims 1-9, wherein the SPG emulsification membrane has a pore size of between 1 and 30 microns and the applied pressure is between 0.5 and 5.0 bar.
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| CN116987467A (en) * | 2023-09-26 | 2023-11-03 | 太仓斯迪克新材料科技有限公司 | Compressed low-rebound high-level difference filling pressure-sensitive adhesive, pressure-sensitive adhesive tape and preparation method |
| CN116987467B (en) * | 2023-09-26 | 2023-12-15 | 太仓斯迪克新材料科技有限公司 | Compressed low-rebound high-level difference filling pressure-sensitive adhesive, pressure-sensitive adhesive tape and preparation method |
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