Thermal expansion microsphere and preparation method thereof

Abstract

The invention provides a thermal expansion microsphere as well as a preparation method and application thereof, and the preparation method comprises the following steps: fully and uniformly mixing a hydrophobic olefinic monomer, a hydrophilic olefinic monomer, an initiator, a foaming agent and a cross-linking agent to obtain a required oil phase; mixing an emulsifier, a co-emulsifier, a water-phase polymerization inhibitor and deionized water, and uniformly stirring to obtain a water phase; and mixing the oil phase and the water phase, homogenizing at a high speed, stirring to obtain an emulsion, and carrying out gradient heating reaction for 9-24 hours to obtain the thermal expansion microspheres. The prepared microspheres are uniform in particle size distribution, the active ingredients of the microspheres are close to 100%, inorganic impurity particles such as silicon dioxide are not contained, and the microspheres are expected to be applied to preparation of ultralow-defect CMP polishing pads.

Description

Technical Field

[0001] The invention belongs to the field of polymer and semiconductor materials, and particularly relates to a thermal expansion microsphere and a preparation method thereof. Background Art

[0002] Thermal expansion microspheres are polymer particles with a core-shell structure, which are formed by a thermoplastic polymer as a shell and a low-boiling-point foaming agent as a core. When heated to a certain temperature, the polymer shell softens due to heat, and the foaming agent inside vaporizes, so that the volume of the microspheres can expand to dozens of times before foaming. After cooling, the hardness of the polymer shell recovers without shrinking, and the microspheres can maintain their volume after foaming. As an ideal lightweight filler and physical foaming agent, thermal expansion microspheres have been widely used in CMP polishing pads, coating printing, foam industry, textile industry, construction, automobile manufacturing, and aerospace.

[0003] Thermally expanded microspheres account for less than 5% of the mass of CMP polishing pads, but they occupy more than 30% of the volume of finished polishing pads. Their main function is to form pores inside the polishing pad that carry the polishing liquid and provide micro-reaction sites required for chemical corrosion. Therefore, the physical and chemical properties of thermally expanded microspheres play a vital role in indicators such as polishing pad removal rate, polishing defects, and flattening efficiency. At present, thermally expanded microspheres for CMP polishing pads are often added with colloidal silica, insoluble salts such as calcium carbonate, or metal hydroxides such as magnesium hydroxide sol as dispersants during the synthesis process. These dispersants are often difficult to remove after the reaction and will adhere to the surface of the microspheres and be brought into the finished polishing pads. These inorganic particles have a high hardness and may scratch the surface of the wafer during the polishing process, thereby causing defects. Therefore, reducing or even removing inorganic impurity particles in the microspheres is of great significance for improving the defect control ability of CMP polishing pads. Summary of the invention

[0004] The purpose of the present invention is to obtain a thermally expandable microsphere polymer, which is synthesized by emulsion polymerization. During the polymerization process, there is no need to add inorganic particles such as silica or magnesium hydroxide as dispersants, so that the prepared microspheres do not contain hard inorganic particles such as silica or metal hydroxides, fundamentally eliminating the introduction of hard inorganic impurity particles in the microspheres, and can be used to prepare ultra-low defect CMP polishing pads.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing heat-expandable microspheres, the preparation method comprising the following steps:

[0007] The hydrophobic olefinic monomer, the hydrophilic olefinic monomer, the initiator, the foaming agent and the cross-linking agent are fully mixed to obtain an oil phase;

[0008] The emulsifier, the co-emulsifier, the water phase inhibitor and the deionized water are mixed and stirred to obtain a water phase;

[0009] The oil phase and the water phase are mixed and homogenized at high speed to obtain an emulsion, the emulsion is heated to 40° C. to 80° C. and stirred for reaction for 9 h to 24 h, the material is discharged after cooling, and the heat-expandable microspheres are obtained by filtering and drying.

[0010] The preparation method does not use an inorganic solid particle dispersant, and the inorganic solid particle dispersant is one or a combination of silicon dioxide, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, calcium phosphate, iron oxide, calcium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate.

[0011] Furthermore, the temperature is increased in a gradient manner, and the gradient temperature increase is specifically: reacting at 40°C to 60°C for 4h to 6h, and then increasing the temperature to 60°C to 80°C at a rate of 2°C / min to 4°C / min to react for 5h to 19h;

[0012] And / or, the conditions of the high-speed homogenization are: a homogenization speed of 10 Hz to 40 Hz, a time of 10 min to 40 min, and a stirring speed of 1000 rpm to 3000 rpm;

[0013] In the preparation method of the present invention, a gradient temperature increase method is adopted, so that the prepared expandable microspheres can have uniform particle sizes and better stability.

[0014] Furthermore, the hydrophobic olefinic monomer is selected from one or a combination of styrene, vinyl chloride, and butadiene olefinic monomers;

[0015] And / or, the hydrophilic olefinic monomer is selected from one or a combination of acrylate, acrylonitrile, acrylic acid, acrylamide, and vinyl sulfonic acid olefinic monomers;

[0016] And / or, in the present invention, the hydrophobic olefinic monomer is preferably a styrene monomer, and the hydrophilic olefinic monomer is preferably an acrylate;

[0017] Furthermore, based on 100 parts by mass of the hydrophobic olefinic monomer, 30 to 50 parts of the hydrophilic olefinic monomer, 0.5 to 1 part of the initiator, 20 to 50 parts of the foaming agent, 1 to 5 parts of the crosslinking agent, 10 to 30 parts of the emulsifier, 10 to 20 parts of the co-emulsifier, 3 to 7 parts of the aqueous phase inhibitor, and 300 to 500 parts of deionized water.

[0018] And / or, the emulsifier is selected from one or a combination of allyl polyethylene glycol, allyl sulfoalkoxy succinic acid diester sodium salt, allyl-2-propyl ethanesulfonate sodium, vinyl-2-propyl ethanesulfonate sodium, polyoxyethylene nonylphenol ether acrylate, sodium dodecyl sulfate, sodium dodecyl sulfonate, and tert-dodecyl mercaptan.

[0019] And / or, the foaming agent is selected from one or more combinations of C4-C8 straight-chain or branched alkanes, preferably one or more combinations of n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, n-octane and isooctane; further, one or more combinations of isobutane, n-pentane, isopentane, neopentane, isohexane and n-hexane are preferred; further, one or more combinations of isobutane, n-pentane and isopentane are preferred;

[0020] And / or, the inhibitor is one or a combination of sodium nitrite, potassium dichromate, water-soluble ascorbic acid, citric acid or sodium sulfide; further, preferably one or a combination of sodium nitrite, water-soluble ascorbic acid, citric acid; further, preferably the inhibitor is sodium nitrite;

[0021] And / or, the co-emulsifier is selected from one or more combinations of methanol, ethanol, ethylene glycol, propylene glycol, glycerol, n-butanol and isobutanol; further, preferably one or more combinations of methanol, ethanol, ethylene glycol, propylene glycol; further, preferably methanol and ethanol;

[0022] And / or, the crosslinking agent is selected from one or more combinations of divinylbenzene, diallyl phthalate, trimethylolpropane trimethacrylate, vinyl triethoxysilane, diethylene glycol divinyl ether, triethylene glycol divinyl ether, triacyl formal, triallyl isocyanurate or divinyl ether; further, preferably one or more combinations of divinylbenzene, diallyl phthalate, trimethylolpropane trimethacrylate, vinyl triethoxysilane; further, preferably one or more combinations of divinylbenzene and trimethylolpropane trimethacrylate;

[0023] And / or, the initiator is selected from one or more combinations of sodium persulfate, potassium persulfate, ammonium persulfate, azobisisobutyronitrile (AIBN), azobisisoheptanitrile (ABVN), and azoisobutylcyanoformamide (V30); further, preferably, one or more combinations of sodium persulfate, azobisisobutyronitrile (AIBN), and azobisisoheptanitrile (ABVN);

[0024] The second aspect of the present invention provides a heat-expandable microsphere, which is prepared by the above method.

[0025] The third aspect of the present invention provides a use of the heat-expandable microspheres obtained by the above preparation method in preparing a CMP polishing pad.

[0026] Beneficial effects:

[0027] 1. The present invention provides an emulsion polymerization method for preparing expandable microspheres without using an inorganic solid particle dispersant. The prepared microspheres have a smooth surface, a perfect core-shell structure and a uniform particle size, which solves the problem that in the process of preparing microspheres by adding inorganic solid particles as dispersants, inorganic particles adhere to the surface of the microspheres and are brought into the finished polishing pad, which may scratch the surface of the wafer during the polishing process;

[0028] 2. By using two different types of monomers, hydrophilic olefinic monomers and hydrophobic olefinic monomers, it is possible to form expandable microsphere products with uniform particle size and excellent performance;

[0029] 3. By carrying out emulsion polymerization in a gradient temperature rising manner, expandable microspheres with uniform particle size and better stability can be obtained, thereby further improving the quality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of the heat-expandable microspheres prepared in Example 1;

[0031] Figure 2 Particle size distribution diagram of heat-expandable microspheres prepared in Example 3 DETAILED DESCRIPTION

[0032] Hereinafter, the specific embodiments of the heat-expandable microspheres and preparation methods and applications thereof according to the present invention will be described in detail, but the present invention is not limited to the embodiments comprising the following examples and is explained, and various changes can be made within the scope of being able to achieve the purpose of the invention and not exceeding the gist of the invention.

[0033] In the following examples, unless otherwise specified, the raw materials, reagents or processing techniques used are all commercially available raw materials or conventional processing techniques commonly used in the art.

[0034] The present invention provides a method for preparing heat-expandable microspheres, comprising the following steps:

[0035] The hydrophobic olefinic monomer, the hydrophilic olefinic monomer, the initiator, the foaming agent and the cross-linking agent are fully mixed to obtain an oil phase;

[0036] The emulsifier, the co-emulsifier, the water phase inhibitor and the deionized water are mixed and stirred to obtain a water phase;

[0037] The oil phase and the water phase are mixed and homogenized at high speed to obtain an emulsion; the emulsion is heated to 40° C. to 80° C. and stirred for reaction for 9 h to 24 h, the material is discharged after cooling, and the thermal expansion microspheres are obtained by filtering and drying;

[0038] In the preparation method of the present invention, no inorganic solid particle dispersant is used, so no inorganic solid impurity particles are introduced into the microspheres. These inorganic solid particle dispersants include silicon dioxide, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, calcium phosphate, iron oxide, calcium sulfate, calcium oxalate, calcium carbonate, barium carbonate, magnesium carbonate, etc. The use of inorganic solid particle dispersants can be either directly added or formed by reaction, such as a process in which sodium hydroxide or potassium hydroxide reacts with calcium chloride or magnesium chloride to form inorganic solid particle dispersants such as calcium hydroxide or magnesium hydroxide.

[0039] In the present invention, a gradient heating method is adopted, and the gradient heating method is specifically: reacting at 40℃~60℃ for 4h~6h, and then heating to 60℃~80℃ at a rate of 2℃ / min~4℃ / min for 5h~19h; in the preparation method of the present invention, the gradient heating method is adopted, which can make the prepared expandable microspheres have uniform particle size and better stability. The conditions for high-speed homogenization are: homogenization speed of 10Hz~40Hz, time of 10min~40min, stirring speed of 1000rpm~3000rpm;

[0040] In the present invention, by using a combination of hydrophobic olefinic monomers and hydrophilic olefinic monomers, microspheres with good air tightness, excellent foaming performance and expansion ratio can be obtained. Olefinic monomers are polymerizable organic monomers containing double bonds; hydrophilic olefinic monomers refer to monomeric compounds that can combine with water molecules or form hydrogen bonds with water. The molecular structures of these monomers contain polar groups such as carboxyl, ester, cyano, etc., which are easy to interact with water molecules. In the present invention, hydrophilic olefinic monomers include acrylates, acrylonitriles, acrylic acid, acrylamides, and vinyl sulfonic acid olefinic monomers, such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, acrylamide, methacrylamide, vinyl sulfonic acid, etc. Hydrophobic olefinic monomers are opposite to the definition of hydrophilic olefinic monomers, and their molecular structures mainly contain non-polar groups, which are more soluble in neutral and non-polar solutions (such as organic solvents), thereby showing hydrophobic properties. In the present invention, the hydrophobic olefinic monomers include styrene, vinyl chloride, butadiene and other olefinic monomers, such as styrene, 2-phenyl-1-propylene, 3-phenylpropylene, vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, butadiene and the like.

[0041] In the present invention, the hydrophobic olefinic monomer is preferably a styrene monomer, and the hydrophilic olefinic monomer is preferably an acrylate;

[0042] In the present invention, based on 100 parts by mass of the hydrophobic olefinic monomer, 30 to 50 parts of the hydrophilic olefinic monomer, 0.5 to 1 part of the initiator, 20 to 50 parts of the foaming agent, and 1 to 5 parts of the crosslinking agent; 10 to 30 parts of the emulsifier, 10 to 20 parts of the co-emulsifier, 3 to 7 parts of the aqueous phase inhibitor, and 300 to 500 parts of deionized water; the emulsifier is selected from allyl polyethylene glycol, allyl sulfoalkoxy succinic acid diester sodium salt, allyl-2-propyl ethane sulfonate sodium, vinyl-2-propyl ethane sulfonate sodium, polyoxyethylene nonylphenol ether propylene One or more combinations of olefinic acid esters, sodium dodecyl sulfate, sodium dodecyl sulfonate, and tert-dodecyl mercaptan; the foaming agent is selected from one or more combinations of C4-C8 straight-chain or branched alkanes, preferably one or more combinations of n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, n-octane and isooctane; further, one or more combinations of isobutane, n-pentane, isopentane, neopentane, isohexane, and n-hexane are preferred; further, one or more combinations of isobutane, n-pentane, and isopentane are preferred; the inhibitor is sodium nitrite, potassium dichromate, water-soluble ascorbic acid, citric acid or sodium sulfide One or several combinations thereof; further, preferably sodium nitrite, water-soluble ascorbic acid, citric acid, one or several combinations thereof; further, preferably the polymerization inhibitor is sodium nitrite; the co-emulsifier is selected from one or several combinations of methanol, ethanol, ethylene glycol, propylene glycol, glycerol, n-butanol and isobutanol; further, preferably one or several combinations of methanol, ethanol, ethylene glycol, propylene glycol; further, preferably methanol and ethanol; the crosslinking agent is selected from divinylbenzene, diallyl phthalate, trimethylolpropane trimethacrylate, vinyl triethoxysilane, diethylene glycol divinyl ether, triethylene glycol divinyl ether, triacyl formal, triallyl isocyanuric acid ester or divinyl ether; further, preferably divinyl benzene, diallyl phthalate, trimethylolpropane trimethacrylate, vinyl triethoxysilane one or several combinations; further, preferably divinyl benzene, trimethylolpropane trimethacrylate one or several combinations; the initiator is selected from sodium persulfate, potassium persulfate and ammonium persulfate, azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), azoisobutylcyanoformamide (V30) one or several combinations; further, preferably sodium persulfate, azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN) one or several combinations;

[0043] <Heat-expandable microspheres>

[0044] In the present invention, the heat-expandable microspheres have a core-shell structure, the shell layer is a thermoplastic polymer, and the core is a low-boiling-point foaming agent; the heat-expandable microspheres of the present invention do not contain inorganic solid particles, and the solid content of the effective components is zero.

[0045] <Emulsifiers and dispersants>

[0046] Emulsifiers and dispersants are commonly used chemical additives that play an important role in the dispersion and emulsification of substances.

[0047] Emulsifiers are usually composed of a molecule with hydrophilic and hydrophobic properties, in which one polar group interacts with water molecules, while the other non-polar group interacts with oils and fats. This structure enables the emulsifier to form a thin film at the oil-water interface, wrapping the oil molecules in it to achieve the effect of oil-water emulsification;

[0048] Dispersants are composed of one or more lipophilic or hydrophilic molecules that can interact with the surface of dispersion particles to form a stable dispersion system.

[0049] <Inorganic solid particle dispersant>

[0050] In the present invention, the inorganic solid particle dispersant includes silicon dioxide, alkaline metal hydroxides, insoluble salts, etc., such as silicon dioxide, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, calcium phosphate, iron oxide, calcium sulfate, calcium oxalate, calcium carbonate, barium carbonate, magnesium carbonate, etc. The use of the inorganic solid particle dispersant can be either directly added or formed by reaction, such as the process of reacting sodium hydroxide or potassium hydroxide with calcium chloride or magnesium chloride to generate inorganic solid particle dispersants such as calcium hydroxide or magnesium hydroxide.

[0051] The preparation process of the heat-expandable microspheres of the present invention does not include the process of using an inorganic solid particle dispersant.

[0052] <Hydrophilic Olefin Monomer and Hydrophobic Olefin Monomer>

[0053] Olefin monomers are polymerizable organic monomers containing double bonds; hydrophilic olefinic monomers refer to monomeric compounds that can combine with water molecules or form hydrogen bonds with water. The molecular structures of these monomers contain polar groups such as carboxyl, ester, cyano, etc., which are easy to interact with water molecules. In the present invention, hydrophilic olefinic monomers include acrylates, acrylonitriles, acrylic acid, acrylamides, and vinyl sulfonic acid olefinic monomers, such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, acrylamide, methacrylamide, vinyl sulfonic acid, etc. Hydrophobic olefinic monomers are opposite to the definition of hydrophilic olefinic monomers, and their molecular structures mainly contain non-polar groups, which are more easily dissolved in neutral and non-polar solutions (such as organic solvents), thereby showing hydrophobic properties. In the present invention, hydrophobic olefinic monomers include olefinic monomers such as styrenes, vinyl chlorides, butadienes, such as styrene, vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, butadiene, etc.

[0054] <Steady Bubble Temperature Range>

[0055] The stable foaming temperature range refers to the difference between the starting temperature of the expansion of the heat-expandable microspheres and the temperature at which the maximum expansion is reached, which means that the heat-expandable microspheres can foam without breaking within this temperature range.

[0056] <Test Method>

[0057] 1. Thermal expansion microsphere particle size analysis (DLS)

[0058] Take an appropriate amount of foamed microsphere sample and add it to the laser particle size analyzer to obtain the average particle size, the percentage of particles within each size range and the particle size distribution curve. The median particle size (D50 value) is determined as the average particle size, and the dispersion of the particle size distribution is calculated using (D90-D10) / D50.

[0059] 2. Volume expansion ratio test

[0060] The volume expansion ratio of the microspheres was tested using an optical microscope hot stage. The particle sizes of 200 microspheres before foaming were measured and their average particle size was calculated as d0. The particle sizes of 200 microspheres after foaming were measured and their average particle size was calculated as d1. The volume expansion ratio of the microspheres was (d1 / d0)^ 3 .

[0061] 3. Test of solid active ingredients in thermal expansion microspheres

[0062] In the present invention, the solid effective components of the heat-expandable microspheres are calculated by the ash residue method, which is not less than 99%, calculated based on the total weight of the heat-expandable microspheres. The "ash residue" of the microspheres solid content of the present invention is determined by the following method: after sampling, calcining at 900°C in a muffle furnace for 9 hours, and measuring the proportion of the remaining ash to the sampled amount.

[0063] 4. Test of concentrated foaming temperature, expansion starting temperature, maximum expansion temperature and stable foaming temperature range

[0064] Use a polarizing microscope with a hot stage (DM4P), the heating rate of the hot stage is 10℃ / min, the temperature range is from room temperature to 250℃, the objective lens magnification is 10 times, and record the expansion temperature of the first ball and the expansion temperature when it reaches the maximum. Steady bubble temperature range = T 最大 -T 开始 The temperature at which more than 80% of the microspheres reach the maximum expansion ratio is recorded as the concentrated foaming temperature T 发泡 .

[0065] Example

[0066] Example 1

[0067] The embodiment of the present invention provides a method for preparing heat-expandable microspheres, the preparation method comprising the following steps:

[0068] Step 1: 100 g of styrene monomer, 40 g of ethyl methacrylate, 0.7 g of initiator sodium persulfate, 45 g of blowing agent isobutane, and 1.5 g of cross-linking agent divinylbenzene are mixed uniformly to obtain an oil phase;

[0069] Step 2: 475 g of deionized water, 20 g of sodium dodecyl sulfate emulsifier, 13 g of ethanol co-emulsifier, and 5 g of sodium nitrite as an aqueous phase inhibitor were mixed to obtain an aqueous phase;

[0070] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1200 rpm, time of 30 min, and temperature of 45° C.;

[0071] Step 4: Start stirring at a speed of 3000 rpm, react the emulsion at 50°C to 55°C for 3 h, then heat to 70°C to 75°C at a rate of 3°C / min and react for 7 h, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0072] Example 2

[0073] Step 1: 100 g of styrene monomer, 40 g of ethyl methacrylate, 1 g of initiator sodium persulfate, 45 g of blowing agent n-pentane, and 1.2 g of cross-linking agent trimethylolpropane trimethacrylate were mixed uniformly to obtain an oil phase;

[0074] Step 2: 450 g of deionized water, 16 g of sodium vinyl-2-propyl ethanesulfonate, 10 g of methanol, and 5 g of sodium nitrite, an aqueous phase inhibitor, are mixed to obtain an aqueous phase;

[0075] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1400 rpm, time of 20 min, and temperature of 50° C.;

[0076] Step 4: Start stirring at a speed of 2500 rpm, react the emulsion at 50°C to 55°C for 4 hours, then heat to 70°C to 75°C at a rate of 3°C / min and react for 7 hours, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0077] Example 3

[0078] Step 1: 100 g of styrene monomer, 40 g of ethyl methacrylate, 1 g of initiator azobisisoheptanenitrile (ABVN), 45 g of foaming agent isopentane, and 1.5 g of crosslinking agent vinyltriethoxysilane are mixed uniformly to obtain an oil phase;

[0079] Step 2: 450 g of deionized water, 16 g of emulsifier tert-dodecyl mercaptan, 10 g of co-emulsifier ethanol, and 7 g of aqueous phase inhibitor sodium nitrite were mixed uniformly to obtain an aqueous phase;

[0080] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1400 rpm, time of 20 min, and temperature of 50° C.;

[0081] Step 4: Start stirring at a speed of 2500 rpm, react the emulsion at 45°C to 50°C for 4 hours, then heat to 65°C to 70°C at a rate of 3°C / min and react for 7 hours, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0082] Example 4

[0083] The embodiment of the present invention provides a method for preparing heat-expandable microspheres, the preparation method comprising the following steps:

[0084] Step 1: 100 g of styrene monomer, 30 g of ethyl methacrylate, 0.5 g of initiator azobisisobutyronitrile (AIBN), 20 g of blowing agent isobutane, and 5 g of cross-linking agent divinylbenzene are mixed uniformly to obtain an oil phase;

[0085] Step 2: 325 g of deionized water, 10 g of emulsifier allyl polyethylene glycol, 20 g of co-emulsifier methanol, and 3 g of aqueous phase inhibitor citric acid are mixed uniformly to obtain an aqueous phase;

[0086] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1200 rpm, time of 30 min, and temperature of 45° C.;

[0087] Step 4: Start stirring at a speed of 3000 rpm, react the emulsion at 50°C to 55°C for 3 h, then heat to 70°C to 75°C at a rate of 3°C / min and react for 7 h, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0088] Example 5

[0089] Step 1: 100 g of styrene monomer, 50 g of ethyl methacrylate, 1 g of initiator AIBN, 50 g of blowing agent isobutane, and 1 g of cross-linking agent triethylene glycol divinyl ether are mixed uniformly to obtain an oil phase;

[0090] Step 2: 450 g of deionized water, 30 g of emulsifier sodium lauryl sulfate, 12 g of co-emulsifier ethanol, and 3 g of water-soluble ascorbic acid as a water phase inhibitor are mixed uniformly to obtain an aqueous phase;

[0091] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1200 rpm, time of 30 min, and temperature of 45° C.;

[0092] Step 4: Start stirring at a speed of 3000 rpm, react the emulsion at 50°C to 55°C for 3 h, then heat to 70°C to 75°C at a rate of 3°C / min and react for 7 h, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0093] Example 6

[0094] Step 1: 100 g of styrene monomer, 40 g of ethyl methacrylate, 1 g of initiator sodium persulfate, 45 g of foaming agent n-hexane, and 1 g of cross-linking agent diallyl phthalate are mixed uniformly to obtain an oil phase;

[0095] Step 2: 450 g of deionized water, 30 g of sodium salt of allyl sulfoalkoxy succinate diester as an emulsifier, 12 g of methanol as an auxiliary emulsifier, and 3 g of sodium nitrite as an aqueous phase inhibitor are mixed uniformly to obtain an aqueous phase;

[0096] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1200 rpm, time of 30 min, and temperature of 45° C.;

[0097] Step 4: Start stirring at a speed of 3000 rpm, react the emulsion at 50°C to 55°C for 3 h, then heat to 70°C to 75°C at a rate of 3°C / min and react for 7 h, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0098] Application Example 1

[0099] The heat-expandable microspheres prepared in Example 1 and the isocyanate prepolymer obtained by reacting 40wt% TDI, 10wt% HMDI, 10wt% DEG and 40wt% PTMG-1000 are mixed and dispersed, and then mixed with a curing agent dichloroaniline methane (MOCA), and then transferred to a casting machine and cast into a conventional mold. After the casting is completed, the surface of the mixture in the mold is solidified and has no fluidity, and then cured in an oven at 110°C for 16 to 20 hours. After the aging is completed, the mixture is cooled to room temperature and cut into polishing pad slices, thereby obtaining a low-defect polishing pad containing the heat-expandable microspheres of the present invention.

[0100] Comparative Example 1

[0101] Step 1: 100 g of styrene monomer, 40 g of ethyl methacrylate, 0.7 g of initiator sodium persulfate, 45 g of blowing agent isobutane, and 1.5 g of cross-linking agent divinylbenzene are mixed uniformly to obtain an oil phase;

[0102] Step 2: 475 g of deionized water, 20 g of dispersant silicon dioxide, 13 g of co-emulsifier ethanol, and 5 g of aqueous phase inhibitor sodium nitrite were mixed uniformly to obtain an aqueous phase;

[0103] Step 3, mixing the oil phase and the water phase, and homogenizing at high speed to obtain an emulsion, wherein the conditions for high-speed homogenization are: stirring speed of 1200 rpm, time of 30 min, and temperature of 45° C.;

[0104] Step 4: Start stirring at a speed of 3000 rpm, react the emulsion at 50°C to 55°C for 3 h, then heat to 70°C to 75°C at a rate of 3°C / min and react for 7 h, cool, filter, and then dry at 60°C to obtain the thermally expandable microspheres.

[0105] Comparative Example 2

[0106] This comparative example provides a method for preparing heat-expandable microspheres. The preparation process is the same as that of Example 1, except that in step 1, only 140 g of styrene monomer is added, and no ethyl methacrylate monomer is added.

[0107] Comparative Example 3

[0108] This comparative example provides a method for preparing heat-expandable microspheres. The preparation process is the same as that of Example 1, except that in step 1, only 140 g of ethyl methacrylate monomer is added, and no styrene monomer is added.

[0109] Comparative Example 4

[0110] This comparative example provides a method for preparing heat-expandable microspheres. The preparation process is the same as that of Example 1, except that step 4 is: starting stirring at a stirring speed of 3000 rpm, heating the emulsion at 70°C to 75°C for 10 hours, cooling, filtering, and then drying at 60°C to obtain the heat-expandable microspheres.

[0111] Take the heat-expandable microspheres in the examples and comparative examples, use a sampling spoon to gently take 1 / 3 spoon of the sample and add it to the feeding chamber, and then use a laser particle size analyzer to analyze the median particle size as shown in the following table.

[0112] Table 1 Particle size test:

[0113]

[0114]

[0115] Table 2 Foaming performance, volume expansion rate and solid content test:

[0116]

[0117] As can be seen from Table 2, the embodiment does not use inorganic solid particle dispersants such as silicon dioxide, and the particle size distribution discreteness, foaming temperature and volume expansion ratio of the microspheres obtained by emulsion polymerization are comparable to those of Comparative Example 1 using inorganic solid particle dispersants. However, after the microspheres in Comparative Example 1 are calcined in a muffle furnace, a small amount of solid residues remain, and the main component is silicon dioxide, while the microspheres in the embodiment have basically no solid residues and a smooth surface, indicating that the microspheres in the embodiment do not contain inorganic impurities such as silicon dioxide, thereby effectively avoiding scratches on the wafer surface by inorganic hard particles introduced by the microspheres during the polishing process.

[0118] In addition, the present invention uses hydrophilic olefinic monomer ethyl methacrylate and hydrophobic olefinic monomer styrene as monomers for preparing expandable microspheres by emulsion polymerization, and can obtain expandable microspheres with uniform particle size, high expansion ratio and wide stable bubble temperature range. Higher expansion ratio and wider stable bubble temperature range show that heat expandable microspheres have better foaming performance. Comparative Examples 2 and 3 use only one monomer, and the air tightness of the polymer shell of the obtained microspheres is poor, and the foaming performance, volume expansion ratio and stable bubble temperature range of the microspheres all show poor effects compared with the embodiments. At the same time, the present invention designs a reaction process of gradient heating, which is better in uniformity of microsphere particle size and higher in stability than the single temperature reaction preparation.

Claims

1. A method for preparing heat-expandable microspheres, characterized in that: The preparation method comprises the following steps: The hydrophobic olefinic monomer, the hydrophilic olefinic monomer, the initiator, the foaming agent and the cross-linking agent are fully mixed to obtain an oil phase; The emulsifier, the co-emulsifier, the water phase inhibitor and the deionized water are mixed and stirred to obtain a water phase; The oil phase and the water phase are mixed and homogenized at high speed to obtain an emulsion; the emulsion is heated to 40° C. to 80° C. and stirred for reaction for 9 h to 24 h, the material is discharged after cooling, and the thermal expansion microspheres are obtained by filtering and drying; The preparation method does not use an inorganic solid particle dispersant, and the inorganic solid particle dispersant is one or a combination of silicon dioxide, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, calcium phosphate, iron oxide, calcium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate.

2. The method for preparing heat-expandable microspheres according to claim 1, characterized in that: The temperature is increased in a gradient manner, which is as follows: reacting the emulsion at 40°C to 60°C for 4h to 6h, then increasing the temperature to 60°C to 80°C at a rate of 2°C / min to 4°C / min and reacting for 5h to 19h; and / or, the high-speed homogenization conditions are as follows: a homogenization speed of 10Hz to 40Hz, a time of 10min to 40min, and a stirring speed of 1000rpm to 3000rpm.

3. A method for preparing heat-expandable microspheres according to claim 1 or 2, characterized in that: Taking the mass fraction of the hydrophobic olefinic monomer as 100 parts, the hydrophilic olefinic monomer as 30-50 parts, the added amount of the initiator as 0.5-1 parts, the added amount of the foaming agent as 20-50 parts, the added amount of the crosslinking agent as 1-5 parts; the added amount of the emulsifier as 10-30 parts, the added amount of the co-emulsifier as 10-20 parts, the added amount of the water phase inhibitor as 3-7 parts, and the added amount of the deionized water as 300-500 parts.

4. A method for preparing heat-expandable microspheres according to any one of claims 1 to 3, characterized in that: The hydrophobic olefinic monomer is selected from one or a combination of styrene, vinyl chloride, and butadiene olefinic monomers; and / or, the hydrophilic olefinic monomer is selected from one or a combination of acrylate, acrylonitrile, acrylic acid, acrylamide, and vinyl sulfonic acid olefinic monomers; preferably, the hydrophobic olefinic monomer is a styrene monomer, and the hydrophilic olefinic monomer is an acrylate.

5. The method for preparing heat-expandable microspheres according to any one of claims 1 to 4, characterized in that: The emulsifier is selected from one or a combination of allyl polyethylene glycol, allyl sulfoalkoxy succinic acid diester sodium salt, allyl-2-propyl ethanesulfonate sodium, vinyl-2-propyl ethanesulfonate sodium, polyoxyethylene nonylphenol ether acrylate, sodium dodecyl sulfate, sodium dodecyl sulfonate, and tert-dodecyl mercaptan.

6. The method for preparing heat-expandable microspheres according to any one of claims 1 to 5, characterized in that: The foaming agent is selected from one or more combinations of C4-C8 straight-chain or branched alkanes, preferably one or more combinations of n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, n-octane and isooctane.

7. The method for preparing heat-expandable microspheres according to any one of claims 1 to 6, characterized in that: The inhibitor is one or a combination of sodium nitrite, potassium dichromate, water-soluble ascorbic acid, citric acid or sodium sulfide; and / or the co-emulsifier is one or a combination of methanol, ethanol, ethylene glycol, propylene glycol, glycerol, n-butanol and isobutanol.

8. The method for preparing heat-expandable microspheres according to any one of claims 1 to 7, characterized in that: The crosslinking agent is selected from one or more combinations of divinylbenzene, diallyl phthalate, trimethylolpropane trimethacrylate, vinyl triethoxysilane, diethylene glycol divinyl ether, triethylene glycol divinyl ether, triacyl formal, triallyl isocyanurate or divinyl ether; and / or, the initiator is selected from one or more combinations of sodium persulfate, potassium persulfate, ammonium persulfate, azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), and azoisobutylcyanoformamide (V30).

9. A heat-expandable microsphere, characterized in that: The heat-expandable microspheres are prepared by the method according to any one of claims 1 to 8.

10. Use of the heat-expandable microspheres according to claim 9 in preparing a CMP polishing pad.

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