CN101781479B - Environment-friendly nano ceramic film coating with self heat radiating function and preparation method thereof - Google Patents
Environment-friendly nano ceramic film coating with self heat radiating function and preparation method thereof Download PDFInfo
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- CN101781479B CN101781479B CN2009101999549A CN200910199954A CN101781479B CN 101781479 B CN101781479 B CN 101781479B CN 2009101999549 A CN2009101999549 A CN 2009101999549A CN 200910199954 A CN200910199954 A CN 200910199954A CN 101781479 B CN101781479 B CN 101781479B
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Abstract
The invention provides an environment-friendly nano ceramic film coating with a self heat radiating function and a preparation method thereof, belonging to the field of functional coating. The formula of the coating is as follows: 15-65% of alumina sol, 15-65% of silica sol, 4-20% of cobalt oxide, 3-27% of pigment, 3-27% of packing, 5-25% of anti-settling agent and the like. The preparation method comprises the following steps: respectively weighing the corresponding alumina sol, cobalt oxide, pigment, packing, anti-settling agent and the like, mixing, dispersing at high speed and grinding to obtain a component a; weighing the silica sol with a corresponding weight as a component b; and mixing the component a and the component b, standing and aging to obtain the ceramic film coating. The coating and the preparation method thereof are based on inorganic film forming raw materials, and the cobalt oxide is added to ensure that the invention has the characteristics of high-temperature resistance, fast heat radiation, far infrared radiation and the like, simultaneously has the quality of an enamel surface, strong decoration, safety and no toxicity, and is an environment-friendly high-temperature resistant coating.
Description
Technical field
The invention belongs to field of functional coatings, relate to a kind of environment-friendly nano ceramic film coating and preparation method thereof with self heat dissipation function.
Background technology
At present, high-temperature resistant coating is mainly used in the engine and the semiconductor devicess such as military equipments such as vapor pipe, machine gun artillery, unicircuit and electronics of the vehicles such as automobile train.This class coating adopts synthetic resins to form the coating pellicle usually, and its resistance toheat is generally relatively poor, and, under the condition of high temperature, also environment and health are caused multiple detrimentally affect through regular meeting.For example, locomotive for track traffic, when burst accident occurring, if fire-cureed by high temperature or can not in time dredge away unnecessary heat in locomotive inside, be arranged on the organic coating of inwall, objectionable impurities or evaporable obnoxious flavour that high temperature is produced down will cause great health threat to the passenger who does not in time run away.
Along with the high speed development of nanosecond science and technology, nano material progressively is applied in paint field.For example, China granted patent CN1243062C, a kind of protection against corrosion blackwash technology of adding multiple nano composite oxide has been reported in high-temperature flame-proof blackwash and method for making thereof and application, and this technology is mainly used in aluminum silicate fiber and goods thereof or other high-temperature flame-proofs, lagging material top layer.United States Patent (USP) 5759746, Fabrication process using a multi-layerantireflective layer and Japanese Patent 10-330937, Formation ofsubstantially flat coating have all reported by add the technology that a small amount of nanometer oxide material improves the performance of coating in coating.
In view of the above-mentioned state of the art, the present invention proposes a kind of environment-friendly nano ceramic film coating and preparation method thereof, in order to realize a kind of chinafilm that has from the high temperature resistant function of dispelling the heat.
Summary of the invention
The object of the present invention is to provide a kind of environment-friendly nano ceramic film coating and preparation method thereof, in order to realize a kind of chinafilm that has from the high temperature resistant function of dispelling the heat.
A kind of environment-friendly nano ceramic film coating with self heat dissipation function, it is to form according to following prescription:
Wherein, aforesaid ratio is by the proportion unfolded, and total amount is 100%.
Further, described this environment-friendly nano ceramic film coating with self heat dissipation function also has following technical characterictic:
Described aluminium colloidal sol is the aqueous dispersion type alumina in Nano level, and its granularity is 10-40nm.
Described silicon sol is an aqueous dispersion type nano level silicon oxide, and its granularity is 10-40nm.
Described cobalt oxide is a nanometer grade cobalt oxide, and its granularity is 15-40nm.
Described pigment mainly is functional pigment, for copper-chrome black, ferrimanganic are black, titanium manganese brown, siderochrome palm fibre, cobalt blue, titanium nickel yellow, titanium are green, titanium dioxide, wollastonite powder, and one or more the mixture in the mill base of candle light bronze or the allotment of various color pigments.
Described filler comprises one or more the mixture in nano-sized crystal powder silicon-dioxide, potassium titanate crystal whisker, the aluminum oxide.
Described anti-settling agents etc. comprise one or more mixture of sodium bentonite in the inorganic bentonite, calcium-base bentonite, lithium bentonite, hydrogen base bentonite (atlapulgite).
A kind of preparation method with environment-friendly nano ceramic film coating of self heat dissipation function, it can be realized by following step:
Step 1, according to the described ratio of above-mentioned prescription, take by weighing aluminium colloidal sol, cobalt oxide, pigment, filler and the anti-settling agent etc. of respective component respectively, after the initial stage of the carrying out mixing, begin to carry out high speed dispersion, then it is ground until its fineness and reaches below the 15 μ m, with this part raw material as a component;
Step 2 according to the described ratio of above-mentioned prescription, takes by weighing the silicon sol of respective component, with it as the b component;
Step 3 during use is carried out a component and b component simply mechanically mixing and is left standstill slaking, forms described ceramic film coating.
Further, described a kind of preparation method with environment-friendly nano ceramic film coating of self heat dissipation function also has following technical characterictic:
Described high speed dispersion adopts high speed dispersor band dentation dispersion impeller to realize that with rotating speed 900-1000r/min jitter time is 2-3h.
Described grinding adopts basket type sand mill to realize that milling time 6-8h generally reaches below the 15 μ m until its fineness.
Advantage of the present invention:
Under the prerequisite that does not change original coating preparation technology, by adding a spot of nanometer cobalt oxide powder body material, give full play to their heat radiation certainly, far infrared release action, prepare coating with high heat dispersion, and, its far infrared release efficiency is up to more than 92%, and it has health-care effect to human body.The present invention is a filmogen with nanoscale alumina sol, nano silicone colloidal sol, chemical bond after the film forming is based on " Si=O " and " Al=O ", be the inorganic molecule structure fully, because its granularity is between nano level, in follow-up application and moulding process, can utilize the viscosity and the sticking power of this colloid self, replace traditional organic solvent and caking agent filler etc., having natural safety non-toxic, is a kind of environment-friendly type thermostable coating.
In addition, by this preparation method with environment-friendly nano ceramic film coating of self heat dissipation function, the top coat that makes has high thermal conductivity, high temperature resistant, far infrared characterization, has the enamel quality simultaneously, and is very bright and clean, and hardness is also very high.And, in the preparation process of coating, do not add any organism or toxic ingredient, without any the composition that health is had potential threat yet.In application, can replace present widely used teflon coatings fully, also can be applied in the anti-combustion of other various needs, high temperature resistant, hardness is high, the application of paints field of good weatherability.
Embodiment
Specific embodiment 1:
Environment-friendly nano ceramic film coating with self heat dissipation function of the present invention can constitute according to following prescription:
These components are 1000kg altogether altogether.
Aluminium colloidal sol wherein is the aqueous dispersion type alumina in Nano level, and its granularity is chosen as 15nm.
Silicon sol wherein is an aqueous dispersion type nano level silicon oxide, and its granularity is 20nm.
Cobalt oxide wherein is a nanometer grade cobalt oxide, and its granularity is 30nm.
Pigment wherein is chosen as copper-chrome black, has fabulous chemical resistance, outdoor weatherability, and thermostability, photostabilization, and have no perviousness, no transport property.
Filler wherein is chosen as nano-sized crystal powder silicon-dioxide, and this whisker granularity is little, dispersed strong, helps to realize in coating mixed uniformly purpose.
Anti-settling agent wherein can be selected the sodium bentonite in the inorganic bentonite for use, and this composition can play a role to the moulding of whole coating, the lifting of smooth finish.
Specific embodiment 2:
Environment-friendly nano ceramic film coating with self heat dissipation function of the present invention can constitute according to following prescription:
These components are 1000kg altogether altogether.
Aluminium colloidal sol wherein is the aqueous dispersion type alumina in Nano level, and its granularity is chosen as 25nm.
Silicon sol wherein is an aqueous dispersion type nano level silicon oxide, and its granularity is 15nm.
Cobalt oxide wherein is a nanometer grade cobalt oxide, and its granularity is 20nm.
Pigment wherein is chosen as titanium dioxide, and its strong covering power, particle are evenly tiny, is easy to disperse and stable performance.
Filler wherein is chosen as aluminum oxide, and this aluminum oxide is a nanometer grade powder, and is dispersed extremely strong, is easy to realize in coating uniform mixing, simultaneously, because the nano effect of himself, helps optimizing the performance of coating.
Anti-settling agent wherein can be selected the lithium bentonite in the inorganic bentonite for use, has high physical chemistry and dispersiveness, and moulding of coating etc. is played an important role.
Specific embodiment 3:
Environment-friendly nano ceramic film coating with self heat dissipation function of the present invention can constitute according to following prescription:
These components are 1000kg altogether altogether.
Aluminium colloidal sol wherein is the aqueous dispersion type alumina in Nano level, and its granularity is chosen as 35nm.
Silicon sol wherein is an aqueous dispersion type nano level silicon oxide, and its granularity is 25nm.
Cobalt oxide wherein is a nanometer grade cobalt oxide, and its granularity is 10nm.
Pigment wherein is chosen as cobalt blue, has fabulous opacifying power, the color transparency and high tinting strength, thermostability, photostabilization, very high light reflective.
Filler wherein is chosen as potassium titanate crystal whisker, and this whisker is dispersed strong, helps to realize in coating all and the blended purpose, simultaneously, because the intensity of whisker self, helps strengthening the force of cohesion of coating.
Anti-settling agent wherein can be selected the calcium-base bentonite in the inorganic bentonite for use, can strengthen the water tolerance of coating, improves intensity and the sticking power and the dispersiveness of coating, strengthens the stability of coating.
Environment-friendly nano ceramic film coating with self heat dissipation function of the present invention, it can be realized by following step:
Step 1 according to the described ratio of embodiment, takes by weighing aluminium colloidal sol, cobalt oxide, pigment, filler and the anti-settling agent etc. of respective component respectively, after the initial stage of the carrying out mixing, begin to carry out high speed dispersion, it ground until its fineness reach below the 15 μ m then, with this part raw material as a component;
Step 2 according to the described ratio of embodiment, takes by weighing the silicon sol of respective component, with it as the b component;
Step 3 is carried out a component and b component thorough mixing and is left standstill slaking during use, forms described ceramic film coating.
Described high speed dispersion adopts high speed dispersor band dentation dispersion impeller to realize that with rotating speed 900-1000r/min jitter time is 2-3h.
Described grinding adopts basket type sand mill to realize that milling time 6-8h generally reaches below the 15 μ m until its fineness.
By the environment-friendly nano ceramic film coating that this preparation technology obtained, be glass water quality shape in appearance;
Aspect burning, for not firing, add under the thermal conditions smokeless;
Aspect thermotolerance, can resist 500-800 ℃ high temperature;
Aspect hardness, can reach 9H;
The weathering resistance aspect was greater than 30 years;
Acidproof, alkaline-resisting, anti-solvent that, aspect the heat-resisting water, heat-resisting wet goods, also all show good.
Constructional method:
The pre-treatment of metal base: skimming treatment, sandblasting in case of necessity.
Application mode: aerial spraying, dip-coating, brushing etc.
As an example, on the metallic surface, before the construction, need carry out surface cleaning to metal base and handle, make its surface clean, no-sundries, no rust staining, specifically can be by sandblasting be carried out in the metallic surface, and mode such as degreasing decontamination processing realizes.Two before spraying, can adopt 300 purpose filter screens to filter to ceramic film coating.
More than be the description of this invention and non-limiting, based on other embodiment of inventive concept, all among protection scope of the present invention.
Claims (10)
1. the environment-friendly nano ceramic film coating with self heat dissipation function is characterized in that, this coating is made up of following prescription:
Wherein, aforesaid ratio is by the proportion unfolded, and total amount is 100%.
2. a kind of environment-friendly nano ceramic film coating with self heat dissipation function according to claim 1 is characterized in that: described aqueous dispersion type alumina in Nano level, its granularity are 10-40nm.
3. a kind of environment-friendly nano ceramic film coating with self heat dissipation function according to claim 1 is characterized in that: described aqueous dispersion type nano level silicon oxide, its granularity is 10-40nm.
4. a kind of environment-friendly nano ceramic film coating with self heat dissipation function according to claim 1 is characterized in that: described nanometer grade cobalt oxide, its granularity are 15-40nm.
5. a kind of environment-friendly nano ceramic film coating according to claim 1 with self heat dissipation function, it is characterized in that: described pigment, for copper-chrome black, ferrimanganic are black, titanium manganese brown, siderochrome palm fibre, cobalt blue, titanium nickel yellow, titanium are green, titanium dioxide, wollastonite powder, and one or more the mixture in the mill base of candle light bronze or the allotment of various color pigments.
6. a kind of environment-friendly nano ceramic film coating with self heat dissipation function according to claim 1 is characterized in that: described filler comprises one or more the mixture in nano-sized crystal powder silicon-dioxide, potassium titanate crystal whisker, the aluminum oxide.
7. a kind of environment-friendly nano ceramic film coating according to claim 1 with self heat dissipation function, it is characterized in that: described anti-settling agent comprises one or more mixture of sodium bentonite in the inorganic bentonite, calcium-base bentonite, lithium bentonite, hydrogen base bentonite.
8. preparation method with environment-friendly nano ceramic film coating of self heat dissipation function is characterized in that this method includes following step:
Step 1, according to the described ratio of aforesaid claim 1, take by weighing aqueous dispersion type alumina in Nano level, nanometer grade cobalt oxide, pigment, filler and the anti-settling agent of respective component respectively, the initial stage of carrying out is carried out high speed dispersion after mixing, then it is ground until its fineness and reaches below the 15 μ m, with this part raw material as a component;
Step 2 according to the described ratio of aforesaid claim 1, takes by weighing the aqueous dispersion type nano level silicon oxide of respective component, with it as the b component;
Step 3 is carried out a component and b component thorough mixing and is left standstill slaking during use, forms described ceramic film coating.
9. a kind of preparation method according to claim 8 with environment-friendly nano ceramic film coating of self heat dissipation function, it is characterized in that: described high speed dispersion, adopt high speed dispersor band dentation dispersion impeller to realize that with rotating speed 900-1000r/min jitter time is 2-3h.
10. a kind of preparation method with environment-friendly nano ceramic film coating of self heat dissipation function according to claim 8 is characterized in that: described grinding, and adopt basket type sand mill to realize that milling time is 6-8h.
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| CN102690536B (en) * | 2011-03-21 | 2016-09-14 | 上海宜瓷龙新材料股份有限公司 | A kind of environmental-friendly ceramic paint for building aluminum curtain walls and preparation method thereof |
| CN102911535B (en) * | 2012-10-31 | 2014-09-10 | 华南理工大学 | Ceramic membrane cooling coating for LED radiator and preparation method of ceramic membrane cooling coating |
| CN103756445A (en) * | 2014-01-15 | 2014-04-30 | 芜湖市宝艺游乐科技设备有限公司 | Heat dissipating coating for fibrolite LED lamps |
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| CN104250481A (en) * | 2014-09-05 | 2014-12-31 | 天长市巨龙车船涂料有限公司 | Refreshing environment-friendly paint |
| CN104263112A (en) * | 2014-09-05 | 2015-01-07 | 天长市巨龙车船涂料有限公司 | Fluorine-containing styrene-acrylic coating |
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| CN104403382B (en) * | 2014-11-14 | 2016-08-24 | 曾锦秋 | Enamel paint of a kind of aqueous high-temperature-resistant and preparation method thereof and construction method |
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| CN105985669A (en) * | 2016-04-27 | 2016-10-05 | 广东工业大学 | Waterborne nano ceramic paint and preparation method thereof |
| CN109439038A (en) * | 2018-11-22 | 2019-03-08 | 常州天瑞新材料科技有限公司 | A kind of environmentally friendly ceramic film coating suitable for fibre surface |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1583889A (en) * | 2004-06-14 | 2005-02-23 | 华东理工大学 | High-temperature resistant energy-saving coating for metal |
| KR20090044224A (en) * | 2007-10-31 | 2009-05-07 | 한국전기연구원 | Binder sol |
| CN101445677A (en) * | 2008-12-19 | 2009-06-03 | 上海瓷龙化工有限公司 | Thin ceramic coating and production method thereof |
| CN101481554A (en) * | 2009-01-22 | 2009-07-15 | 广州化工研究设计院 | High-hardness high temperature resistant non-fluoride aqueous nonstick coating |
-
2009
- 2009-12-04 CN CN2009101999549A patent/CN101781479B/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1583889A (en) * | 2004-06-14 | 2005-02-23 | 华东理工大学 | High-temperature resistant energy-saving coating for metal |
| KR20090044224A (en) * | 2007-10-31 | 2009-05-07 | 한국전기연구원 | Binder sol |
| CN101445677A (en) * | 2008-12-19 | 2009-06-03 | 上海瓷龙化工有限公司 | Thin ceramic coating and production method thereof |
| CN101481554A (en) * | 2009-01-22 | 2009-07-15 | 广州化工研究设计院 | High-hardness high temperature resistant non-fluoride aqueous nonstick coating |
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