CN101847458A - Method for preparing self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste - Google Patents
Method for preparing self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste Download PDFInfo
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- CN101847458A CN101847458A CN 201010145857 CN201010145857A CN101847458A CN 101847458 A CN101847458 A CN 101847458A CN 201010145857 CN201010145857 CN 201010145857 CN 201010145857 A CN201010145857 A CN 201010145857A CN 101847458 A CN101847458 A CN 101847458A
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Abstract
The invention discloses a method for preparing self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste. The method comprises the following steps of: firstly, selecting acrylate monomers, and preparing the self-crosslinking acrylate resin through solution polymerization; secondly, mixing and dispersing superfine aluminum power, low melting point lead-free glass powder, a surface modifier, an aid and an antifoaming agent in the solution, and repeatedly grinding to prepare the electronic aluminum paste. The method for preparing the high-temperature sintered electronic aluminum paste has the characteristics of simple, easy and practicable process, no special equipment, low investment, easy control of product performance and the like.
Description
Technical field
The present invention relates to a kind of preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste.
Background technology
Electric slurry is a class important electron fine chemicals.Can be widely used in numerous industries such as electronics, information, communication, Aero-Space, computer, electrical equipment manufacturing, precision components and solar energy.Its manufacturing technology relates to association areas such as metallurgy, material, chemical industry, electronic technology and silk screen printing.Because the applied range of electric slurry, it is wide to develop related territory, product high in technological content, and therefore, the horizontal developed country of world industry relatively payes attention to the research and development of electric slurry product always.
In recent years, along with the growing tension of conventional energy resources such as coal, oil, natural gas, it is extremely urgent to develop reproducible new forms of energy, and various countries furnish a huge amount of money for to develop various new forms of energy one after another, this wherein the development of solar energy attract attention and with the fastest developing speed with solar cell especially the most.According to statistics, global solar battery industry 1994-2004 increased by 17 times in 10 years, and manufacture of solar cells mainly is distributed in Japan, Europe and the U.S..The global solar battery scale of installing had reached 1744MW in 2006, grew up 19% than 2005, and the whole market output value formally breaks through 10,000,000,000 dollars of high pointes.The global solar battery production reached 3436MW in 2007, had increased by 56% than 2006.The output of global solar battery in 2008 is promoted to 6.85GW, also almost is the growth of multiple.Domestic research to solar cell is started in 1958, and at present, China has become the main manufacture of solar cells state in the whole world.National solar cell yield in 2007 is 1188MW, and output in 2008 continues to improve, and has reached 2,000,000 kilowatts.On industrial pattern, China's solar cell industry has formed certain situation of gathering, and between in March, 2009, ratified building the subsidy of installation photovoltaic generating system, to the photovoltaic generating system more than 500,000 kilowatts, every watt the highest payable 20 yuans (being roughly equal to 2.93 dollars).Because the Chinese government extremely payes attention to solar power generation.China is expected to as the U.S., can start a huge market.Solar energy power generating can occupy the important seat of world energy sources consumption in the near future, not only will substitute the part conventional energy resource, and will become the main body of world energy supplies.
Undoubtedly, be accompanied by shooting up of photovoltaic industry, demand to electric slurry also will increase sharply, especially the thick-film electronic aluminium paste of high temperature sintering type, it is the main slurry that present electrode of solar battery uses, the market demand of following thick-film electronic slurry product will enlarge day by day, but domestic batch process to this series products is close to blank.Especially but aspect the high temperature sintering type thick-film electronic aluminium paste making of top grade, technology and market are almost completely abroad monopolized.
Electric slurry is made up of conductive metal powder, low-melting glass powder, organic carrier and relevant auxiliary agent etc. usually.Wherein organic carrier often adopts polymer and other functional aid compositions such as epoxy resin, polyurethane, cellulose, being the principal element that influences slurry thixotropy, anti-heavy property, levelability, volatility, printability, film forming thickness, slurry viscosity and bin stability etc., also is the key problem in technology that successfully prepares high temperature sintering type thick-film electronic aluminium paste.But because the requirement of the solid content of thick-film electronic aluminium paste is very high,, leaves for and utilize the leeway of the every performance index of secondary solvent adjusting slurry little, cause pulp preparation regulation and control difficulty generally all more than 80%.
Summary of the invention
The object of the present invention is to provide a kind of preparation method of self-crosslinking acrylate resin high-temperature sintered type electronic aluminum paste.
The technical solution used in the present invention is:
This method is at first selected acrylic ester monomer, by the solution polymerization self-crosslinking acrylate resin; Then superfine aluminium power, low-melting point lead-less glasses powder end, surface modifier, auxiliary agent and defoamer are mixed and disperse wherein,, make electronic aluminum paste through grinding repeatedly.
The preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste:
One, the step of self-crosslinking acrylate resin preparation is as follows:,
1. in the reactor of condenser is housed, add mass percent and be 35.0%～85.0% solvent, start blender and add stand-by heat;
2. be that 15.0%～65.0% mix monomer adds in the mixing kettle with mass percent, add mass percent and be 0.1～0.5% initator and stir standby;
When 3. solvent is warming up to 70～90 ℃ in the question response still, in reactor, drip above-mentioned mix monomer, control whole mix monomers and in 1～3h, add, drip afterreaction 1～2h after, cooling, discharging, to obtain self-crosslinking acrylate resin standby;
Two, take by weighing superfine aluminium power and low-melting point lead-less glasses powder, after mixing, add surface modifier and stir, adding mass percent then is 10%～20% self-crosslinking acrylate resin, and auxiliary agent and defoamer, through grinding 5～8h, get the electronic aluminum paste product after the filtration.
Described solvent is diethylene glycol (DEG) ether-ether or any two kinds of mixtures such as butyl carbitol, diethylene glycol dibutyl ether, diethylene glycol methyl ether acetate, DGDE acetate, butyl carbitol acetate.
Described mix monomer is any two kinds and a two or more mixture in methyl methacrylate, Isooctyl acrylate monomer, ethyl acrylate, butyl acrylate, glycidyl methacrylate, N hydroxymethyl acrylamide, hydroxy-ethyl acrylate, this class acrylic compounds of hydroxypropyl acrylate, and described initator is benzoyl peroxide or azodiisobutyronitrile.
The fineness of described aluminium powder is 3～20 μ m; Consumption is 65.0%～80.0% of a silver slurry total amount.
Described low-melting point lead-less glasses powder fineness is 3～20 μ m, and consumption is 5.0%～15.0% of a silver slurry total amount.
Described surface modifier is a silane coupler, and consumption is 0.5%～5.0% of a silver slurry total amount; Described auxiliary agent is terpinol or castor oil and dibutyl phthalate or dioctyl phthalate, and consumption is 0.5%～5.0% of a silver slurry total amount; Described defoamer is tributyl phosphate or silicone oil, and consumption is 0.1%～0.5% of a silver slurry total amount.
The beneficial effect that the present invention has is:
1. given acrylate itself by the selection function monomer and had thixotroping, anti-heavy and suitable multiple functions such as levelability, further regulated the every performance index of electric slurry for secondary solvent regulation and control leeway is provided.
2. because homemade acrylate has the self-crosslinking function, both slight network configuration can be formed, the secondary flow phenomenon of slurry when burning till can be effectively avoided in the temperature rise period in early stage of electric slurry sintering.
3. can be soft in the acrylate by regulating, the toughness of the proportional control polymer of hard monomer etc., avoided that ftractureing appears in electric slurry, the phenomenon of caving in when sintering.
Utilize method provided by the invention to prepare the high-temperature sintering electronic aluminium paste, it is simple, convenient and easy to have technology, need not special installation, to invest for a short time, and properties of product are convenient to characteristics such as control.
Embodiment
Embodiment 1:
At first, the adding mass percent is 38.0% butyl carbitol in the reactor of condenser is housed, and starts blender and adds stand-by heat; Then 39.0% methyl methacrylate, 5.0% Isooctyl acrylate monomer, 15.0% glycidyl methacrylate, 3.0% N hydroxymethyl acrylamide are added in the mixing kettle, add 0.1% benzoyl peroxide and stir, standby; When butyl carbitol is warming up to 75 ℃ in the question response still, in reactor, be added dropwise to above-mentioned mix monomer, control in whole mix monomer 3h and add the acrylate that after 2h is reacted in continuation, cool off, discharging promptly gets self-cross linking type.In addition be that the aluminium powder 65.0% of 3～20 μ m and low-melting point lead-less glasses powder 15.0% that fineness is 3～20 μ m add in the mixer and mix with fineness, the silane coupler KH550 of adding 0.5%, the above-mentioned self-crosslinking acrylate resin 15.0% of back adding stirs, and terpinol 3.0%, dibutyl phthalate 1.0%, tributyl phosphate 0.5%, after mixing, place in the three-roll grinder through grinding 6h repeatedly, with promptly getting product after the filtration of 300 mesh filter screens.
Embodiment 2:
At first, the adding mass percent is 85.0% butyl carbitol acetate in the reactor of condenser is housed, and starts blender and adds stand-by heat; Then 8.0% methyl methacrylate, 2.0% butyl acrylate, 3.0% glycidyl methacrylate, 1.0% N hydroxymethyl acrylamide, 1.0% hydroxy-ethyl acrylate are added in the mixing kettle, add 0.3% azodiisobutyronitrile and stir, standby; When butyl carbitol acetate is warming up to 85 ℃ in the question response still, in reactor, be added dropwise to above-mentioned mix monomer, control in whole mix monomer 2.5h and add the acrylate that after 1h is reacted in continuation, cool off, discharging promptly gets self-cross linking type.In addition be that the aluminium powder 70.0% of 3～20 μ m and low-melting point lead-less glasses powder 10.0% that fineness is 3～20 μ m add in the mixer and mix with fineness, the silane coupler KH560 of adding 0.8%, the above-mentioned self-cross linking type multifunctional acrylic ester resin 16.0% of back adding stirs, and castor oil 2.5%, dioctyl phthalate 0.5%, silicone oil 0.2%, after mixing, place in the three-roll grinder through grinding 5h repeatedly, with promptly getting product after the filtration of 300 mesh filter screens.
Embodiment 3:
At first, adding mass percent in the reactor of condenser is housed is 25.0% diethylene glycol dibutyl ether, 25.0% diethylene glycol methyl ether acetate, starts blender and adds stand-by heat; Then 28.0% methyl methacrylate, 5.0% ethyl acrylate, 5.0% Isooctyl acrylate monomer, 10.0% glycidyl methacrylate, 1.0% N hydroxymethyl acrylamide, 1.0% hydroxypropyl acrylate are added in the mixing kettle, add 0.5% benzoyl peroxide and stir, standby; When diethylene glycol (DEG) ether vinegar mixed solvent is warming up to 88 ℃ in the question response still, in reactor, be added dropwise to above-mentioned mix monomer, control in whole mix monomer 2h and add the acrylate that after 2h is reacted in continuation, cool off, discharging promptly gets the self-crosslinkable type.In addition be that the aluminium powder 78.0% of 3～20 μ m and low-melting point lead-less glasses powder 5.0% that fineness is 3～20 μ m add in the mixer and mix with fineness, the silane coupler KH550 of adding 4.5%, the above-mentioned self-crosslinking acrylate resin 10.0% of back adding stirs, terpinol 1.4%, dibutyl phthalate 1.0%, silicone oil 0.1%, after mixing, place in the three-roll grinder through grinding 8h repeatedly, with promptly getting product after the filtration of 300 mesh filter screens.
Embodiment 4:
At first, adding mass percent in the reactor of condenser is housed is 25.0% diethylene glycol dibutyl ether, 25.0% DGDE acetate, starts blender and adds stand-by heat; Then 25.0% methyl methacrylate, 5.0% ethyl acrylate, 5.0% Isooctyl acrylate monomer, 3.0% N hydroxymethyl acrylamide, 10.0% glycidyl methacrylate, 2.0% hydroxypropyl acrylate are added in the mixing kettle, add 0.5% benzoyl peroxide and stir, standby; When diethylene glycol (DEG) ether vinegar mixed solvent is warming up to 70 ℃ in the question response still, in reactor, be added dropwise to above-mentioned mix monomer, control in whole mix monomer 2h and add the acrylate that after 2h is reacted in continuation, cool off, discharging promptly gets the self-crosslinkable type.In addition be that the aluminium powder 70.0% of 3～20 μ m and low-melting point lead-less glasses powder 5.0% that fineness is 3～20 μ m add in the mixer and mix with fineness, the silane coupler KH550 of adding 1.0%, the above-mentioned self-crosslinking acrylate resin 20.0% of back adding stirs, terpinol 2.0%, dibutyl phthalate 1.5%, silicone oil 0.5%, after mixing, place in the three-roll grinder through grinding 7h repeatedly, with promptly getting product after the filtration of 300 mesh filter screens.
The technical indicator of the electronic aluminum paste product of above-mentioned 4 embodiment is as shown in the table:
| Embodiment | Fineness (order) | Viscosity (mPa.s) | Side's resistance (m Ω/) | Sintering temperature (℃) |
| 1 | 300 | 29200 | 18 | 760 |
| 2 | 300 | 28000 | 17 | 700 |
| 3 | 300 | 27500 | 16 | 750 |
| 4 | 300 | 28700 | 17 | 680 |
Claims (7)
1. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste, it is characterized in that: this method is at first selected acrylic ester monomer, by the solution polymerization self-crosslinking acrylate resin; Then superfine aluminium power, low-melting point lead-less glasses powder end, surface modifier, auxiliary agent and defoamer are mixed and disperse wherein,, make electronic aluminum paste through grinding repeatedly.
2. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste according to claim 1 is characterized in that:
One, the step of described self-crosslinking acrylate resin preparation is as follows:,
1. in the reactor of condenser is housed, add mass percent and be 35.0%～85.0% solvent, start blender and add stand-by heat;
2. be that 15.0%～65.0% mix monomer adds in the mixing kettle with mass percent, add mass percent and be 0.1～0.5% initator and stir standby;
When 3. solvent is warming up to 70～90 ℃ in the question response still, in reactor, drip above-mentioned mix monomer, control whole mix monomers and in 1～3h, add, drip afterreaction 1～2h after, cooling, discharging, to obtain self-crosslinking acrylate resin standby;
Two, take by weighing superfine aluminium power and low-melting point lead-less glasses powder, after mixing, add surface modifier and stir, adding mass percent then is 10%～20% self-crosslinking acrylate resin, and auxiliary agent and defoamer, through grinding 5～8h, get the electronic aluminum paste product after the filtration.
3. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste according to claim 1, it is characterized in that: described solvent is diethylene glycol (DEG) ether-ether or any two kinds of mixtures such as butyl carbitol, diethylene glycol dibutyl ether, diethylene glycol methyl ether acetate, DGDE acetate, butyl carbitol acetate.
4. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste according to claim 1; it is characterized in that: described mix monomer is any two kinds and a two or more mixture in methyl methacrylate, Isooctyl acrylate monomer, ethyl acrylate, butyl acrylate, glycidyl methacrylate, N hydroxymethyl acrylamide, hydroxy-ethyl acrylate, this class acrylic compounds of hydroxypropyl acrylate, and described initator is benzoyl peroxide or azodiisobutyronitrile.
5. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste according to claim 1, it is characterized in that: the fineness of described aluminium powder is 3～20 μ m; Consumption is 65.0%～80.0% of a silver slurry total amount.
6. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste according to claim 1, it is characterized in that: described low-melting point lead-less glasses powder fineness is 3～20 μ m, consumption is 5.0%～15.0% of a silver slurry total amount.
7. the preparation method of self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste according to claim 1, it is characterized in that: described surface modifier is a silane coupler, consumption is 0.5%～5.0% of a silver slurry total amount; Described auxiliary agent is terpinol or castor oil and dibutyl phthalate or dioctyl phthalate, and consumption is 0.5%～5.0% of a silver slurry total amount; Described defoamer is tributyl phosphate or silicone oil, and consumption is 0.1%～0.5% of a silver slurry total amount.
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| CN2010101458574A CN101847458B (en) | 2010-04-13 | 2010-04-13 | Method for preparing self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste |
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| CN2010101458574A CN101847458B (en) | 2010-04-13 | 2010-04-13 | Method for preparing self-crosslinking acrylate resin high-temperature sintered electronic aluminum paste |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103606391A (en) * | 2013-11-08 | 2014-02-26 | 江苏科技大学 | Aluminum slurry composition for solar energy battery |
| CN110246606A (en) * | 2019-06-21 | 2019-09-17 | 广州市儒兴科技开发有限公司 | The electrocondution slurry that a kind of high-performance organic carrier and preparation method thereof is applied with it |
| CN114452686A (en) * | 2022-03-11 | 2022-05-10 | 广州优润合成材料有限公司 | Solvent-free polyacrylate defoaming agent and preparation method thereof |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1545111A (en) * | 2003-11-26 | 2004-11-10 | 廖晓华 | Conductive pulp for terminal electrode of chip capacitor |
| CN1655285A (en) * | 2005-03-08 | 2005-08-17 | 东南大学 | Photosensitive silver slurry for concentration electrode and method for preparing same |
| WO2006038652A1 (en) * | 2004-10-06 | 2006-04-13 | Zeon Corporation | Electrode composition, electrode and battery |
| CN1933189A (en) * | 2005-09-12 | 2007-03-21 | 中芯国际集成电路制造(上海)有限公司 | New method of printing solar cell size |
-
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1545111A (en) * | 2003-11-26 | 2004-11-10 | 廖晓华 | Conductive pulp for terminal electrode of chip capacitor |
| WO2006038652A1 (en) * | 2004-10-06 | 2006-04-13 | Zeon Corporation | Electrode composition, electrode and battery |
| CN1655285A (en) * | 2005-03-08 | 2005-08-17 | 东南大学 | Photosensitive silver slurry for concentration electrode and method for preparing same |
| CN1933189A (en) * | 2005-09-12 | 2007-03-21 | 中芯国际集成电路制造(上海)有限公司 | New method of printing solar cell size |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103606391A (en) * | 2013-11-08 | 2014-02-26 | 江苏科技大学 | Aluminum slurry composition for solar energy battery |
| CN110246606A (en) * | 2019-06-21 | 2019-09-17 | 广州市儒兴科技开发有限公司 | The electrocondution slurry that a kind of high-performance organic carrier and preparation method thereof is applied with it |
| CN114452686A (en) * | 2022-03-11 | 2022-05-10 | 广州优润合成材料有限公司 | Solvent-free polyacrylate defoaming agent and preparation method thereof |
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Address after: Hangzhou City, Zhejiang province 311115 Yuhang Pingyao wind Industrial Park Yangcheng Road No. 15 Patentee after: HANGZHOU DELY TECHNOLOGY CO.,LTD. Address before: Hangzhou City, Zhejiang province 311115 Yuhang Pingyao wind Industrial Park Yangcheng Road No. 15 Patentee before: HANGZHOU DELI TECHNOLOGY Co.,Ltd. |
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