Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/66—Additives characterised by particle size
  • C09D7/69—Particle size larger than 1000 nm
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/004—Reflecting paints; Signal paints
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/66—Additives characterised by particle size
  • C09D7/67—Particle size smaller than 100 nm
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/66—Additives characterised by particle size
  • C09D7/68—Particle size between 100-1000 nm

Definitions

• the present invention relates to an infrared reflective coating for use in construction applications.
• the present invention relates to an infrared reflective coating comprising particles encapsulated by hydrophobic polymers and methods for making thereof.
• US RE34145 discloses a stable aqueous suspension of discrete finely divided solid particles which are encapsulated by a water-insoluble polymer. But such encapsulation comprises a step of polymerization which will result in a complicated reaction process and significantly increase the cost.
• the waterborne coating could not achieve a high loading for inorganic components.
• the limited total inorganic loading ( ⁇ 35wt.%) in the previous acrylic emulsion based coating system potentially restricts high solar reflectance, i.e. above 85%, since the inorganic components contribute mostly to the reflectance property in a coating.
• the introduction of hollow materials in a coating potentially leads to the impact resistance issue which may result from abrasion, e.g. scuffing.
• the collapse of hollow microspheres may also impair the durability/life time of a coating.
• reflectance and its durability There is tradeoff between reflectance and its durability.
• the initial high solar reflectance easily leads to the poor performance after long-term application in an exterior architectural system due to the instable components in a coating or not good weather-ability property.
• the introduction of functional fillers such as hollow microspheres increases the cost of a formulated coating as compared with conventional coatings.
• the present inventors have sought to solve the problem of providing an infrared reflective coating achieving high reflection rate and improved durability at low cost for use in construction applications and have discovered an infrared reflective coating which overcomes abovementioned problems associated with achieving high reflectance and notably enhanced durability at a low cost.
• the present invention provides an aqueous dispersion comprising a) primary inorganic particles having an average size of 0.25 ⁇ - ⁇ , preferably ⁇ - ⁇ ; b) secondary inorganic particles having an average size of Inm-lOOOnm, preferably 10nm-500nm; and c) a hydrophobic polymer, d) a surfactant, and e) water, wherein the primary inorganic particles and the secondary inorganic particles are encapsulated by the hydrophobic polymer, and wherein the average size ratio of the primary particles to the secondary particles is from 5: 1 to 10000: 1.
• the hydrophobic polymer may be, for example, a silicon containing polymer such as a polysiloxane.
• the present invention provides an aqueous dispersion comprising 2-5 ⁇ Si0 2 , 15 ⁇ 40nm Ti0 2 and a mixture of polydimethylsiloxane (PDMS) having a viscosity of 80000 mPa-s(i.e. centipoise) and PDMS having a viscosity of lOOOOmPa s, wherein said Si0 2 and Ti0 2 are encapsulated by the PDMS mixture.
• PDMS polydimethylsiloxane
• the present invention provides a process for preparing the aqueous dispersion of the present invention, said process comprising mixing said hydrophobic polymer with said primary particles and said secondary particles before adding water and a surfactant.
• the process further comprises pre-treating said primary particles and said secondary particles with a coupling agent.
• the present invention provides an infrared reflective coating composition
• an infrared reflective coating composition comprising the aqueous dispersion of the present invention.
• the coating compositions may further comprise known binder polymers for roof or thermal insulation wall coatings, such as acrylic and styrene acrylic emulsion or latex polymers.
• the infrared reflective coating composition further comprises a crosslinker and a catalyst.
• the present invention provides a process for preparing the infrared reflective coating composition of the present invention comprising the following steps in such an order: a) mixing the hydrophobic polymer with the particles under stirring; b) adding a surfactant and water under stirring; and c) adding a crosslinker and a catalyst.
• the present invention provides a building structure, such as a roof or a thermal insulation wall, comprising an infrared reflective coating made from the infrared reflective coating composition of the present invention.
• the present invention provides a process for preparing a building structure, such as a roof or a thermal insulation wall, including an infrared reflective coating of the present invention, comprising: adding a crosslinker and a catalyst into the aqueous dispersion of the present invention to obtain a coating composition, and applying the coating composition onto the outer surface of the building structure.
• Average particle size could be measured by a Coulter LS230 Particle Size Analyzer using the DC200 optical model (available from Beckman Coulter).
• a Coulter LS230 measures particle size distributions by laser diffraction to produce a particle-size distribution weighted by the volume (or mass) of the dispersed droplets/particles.
• Laser particle size analysis is based on the principle that particles scatter and diffract light at certain angles based on their size, shape, and optical properties. Its measurement principle could be found at: https://www.beckmancoulter.corn/wsrportal/wsr/ industrial/particle-techno logies/laser- diffraction/index.htm.
• a coating system is developed to achieve super solar reflectance property by introducing micro-nano hierarchical structured material including primary particles with micron size level, secondary particles with nano size level and a hydrophobic polymer as an encapsulant (may also act as a binder polymer).
• micro-nano hierarchical structured material is obtained by mechanically mixing solid particles (both primary particles and secondary particles) with the hydrophobic polymer without the presence of water. After thoroughly mixing, the solid particles will be encapsulated by the encapsulant (the hydrophobic polymer), and every primary particle encapsulated by the polymer will be surrounded by secondary particles encapsulated by the polymer.
• a surfactant and water will be added into such micro-nano hierarchical structured material under stirring to obtain aqueous dispersion, and then a curing agent and a catalyst could be added to obtain the coating composition of the present invention.
• the preparation processes will be specified in the following parts.
• Suitable solid particles used herein are inorganic non-metallic or metallic particles with a size level of nano and micron and are stable in aqueous media, such as fillers used in coatings.
• Fillers are commonly inorganic materials including pigments used in a coating, preferably mineral oxide, such as Si0 2 , quartz, Ti0 2 , ZnO, MgO, alumina, cerium oxide, Fe 2 0 3 , anhydrous CaS0 4 , alumino silicates (for example, clays and zeolites), or metallic materials used in a coating, such as aluminum, copper, nickel, and zinc.
• pigments used in a coating preferably mineral oxide, such as Si0 2 , quartz, Ti0 2 , ZnO, MgO, alumina, cerium oxide, Fe 2 0 3 , anhydrous CaS0 4 , alumino silicates (for example, clays and zeolites), or metallic materials used in a coating, such as aluminum, copper, nickel,
• solid particles used in the inventive coating system are inorganic non- metallic particles. More preferably, primary particles are chosen from CaC0 3 , Quartz, ZnO, MgO, anhydrous CaS0 4 , alumina, cerium oxide, Fe 2 0 3 , and alumino silicates, such as clays and zeolites; secondary particles are chosen from alumina, CaC0 3 , cerium oxide, Fe 2 0 3 , Ti0 2 , fume silica, and precipitate silica.
• Primary particles such as Si0 2 , have an average size of 0.25 ⁇ -100 ⁇ , preferably 0.5 ⁇ -20 ⁇ , more preferably 0.75 ⁇ -15 ⁇ , even more preferably ⁇ - ⁇ , even further more preferably 2 ⁇ -5 ⁇ , and is used in a loading range of 15-50%, preferably 20-40%), more preferably 25-35%) by weight of the total weight of the dispersion.
• Secondary particles such as Ti0 2 , have an average size of Inm-lOOOnm, preferably 5nm-750nm, more preferably 10nm-500nm, even more preferably 15nm-40nm, and is used in a loading range of 1-35%, preferably 3-25%, more preferably 5-20%, even more preferably 10-15% by weight of the total weight of the dispersion.
• the average size ratio of the primary particles to the secondary particles is at least 5: 1, preferably at least 10: 1, more preferably at least 50: 1, even more preferably at least 100: 1, even further more preferably at least 300: 1, even further more preferably at least 1000: 1, even further more preferably at least 5000: 1, and even further more preferably at least 10000: 1
• the hydrophobic polymer may include a homopolymer or a copolymer, which may include, but is not limited to, block, random, statistical, periodic, gradient, star, graft, comb, (hyper)branched or dendritic polymers.
• a hydrophobic polymer could be judged in its wetting ability, such as contact angel or surface energy (surface tension). Normally a polymer having a static contact angle of water ( ⁇ ) of more than 90 degree, or a surface tension ( ⁇ ) of less than 35N-m _1 (Newton-meter -1 )could be used in the present invention. DI water static contact angle measurements are performed using an OCA 20 contact angle instrument (DataPhysics Company). A 5.0 ⁇ , drop is placed on the coating surface and a snapshot of the drop is taken. The baseline is visually determined. Five random locations on each panel are measured, from which the average is calculated.
• Preferred polymers could be at least one chosen from Si-containing hydrophobic polymers, fluorine containing hydrophobic polymer, and hydrocarbon hydrophobic polymers. More preferably, the hydrophobic polymer may be at least one chosen from polytetrafluoroethylene, polytrifluoroethylene, polyvinylfluoride, fluoroalkyl functional polymer, polyolefms, such as polyethylene and polypropylene, polysiloxanes. Even more preferably, the hydrophobic polymer may be polydimethylsiloxane (PDMS).
• PDMS polydimethylsiloxane
• the hydrophobic polymer should have a content being enough to encapsulate the solid particles when mixing with them.
• the loading range of the hydrophobic polymer is 5-50%, preferably 7-30%, more preferably 10-25%) by weight of the total weight of the dispersion.
• the weight ratio of inorganic components to organic components in the mixture of the solid particles and the hydrophobic polymer could be 30:70- 95:5, preferably 40:60-90: 10, more preferably 75:25-25:75, even more preferably 50:50- 85: 15.
• the weight ratio of said primary inorganic particles plus said secondary inorganic particles to said hydrophobic polymer could be 60:40-90: 10, and more preferably 75:25- 85: 15.
• hydrophobic polymer could also play a role as a binder in the present invention for binding solid particles together in a dried coating layer; or another roof coating binder polymer, such as a known rubbery acrylic emulsion copolymer can be included as a binder.
• the hydrophobic polymer of the present invention could be a mixture of two PDMS polymers having different viscosities, such as 80000 mPa-s and 10000 rnPa-s respectively (measured by Brookfield DV-I/RV (25°C, test spindle No.3, test speed 12RPM, both available from GE CTC), having a ratio of one to the other of 1 :30-30: 1 , preferably 1 :20- 20: 1, more preferably 1 : 10-10: 1.
• the aqueous dispersion could further comprise a binder polymer, which could be added into the dispersion after the solid particles are encapsulated by the hydrophobic polymer.
• this film-forming binder polymer serves to form a film (i.e. a dried coat) of paint which bonds to the surface and also binds together all the nonvolatile components of the paint including particularly solid particles encapsulated by the hydrophobic polymer in the present invention.
• the binder polymer is hydrophobic and can be the hydrophobic polymer (encapsulant) as mentioned above.
• the binder polymer may be acrylic and styrene acrylic emulsion or latex polymers, preferably hydrophobic acrylics, such as acrylic latex NeocarTM Acrylic 820 (Neocar is a trademark of Dow Chemical).
• a coupling agent could be used to pre-treat the solid particles before mixing with the hydrophobic polymer.
• the coupling agent is capable of reacting with the inorganic particles and with the resin matrix of a hydrophobic polymer.
• coupling agents are silane couplers, which lead to a significant improvement of encapsulation of solid particles by the hydrophobic polymer.
• suitable coupling agents are organotrialkoxysilanes, titanates, and zirconates. More preferably the coupling agent is methacryloxypropytrimethoxysilane (available from Aldrich CAS. 2530-85-0).
• encapsulated or “encapsulation” means at least 50%, preferably at least 60%, at least 70%, at least 80%, at least 90%, or 100% of the surface of the solid particles is covered by a thin layer of the hydrophobic polymer.
• the encapsulating polymer layer can be adjusted according to the substrate type.
• the thickness of the layer formed on the surface of solid particles is normally at nano level, such as 0.2-500nm, preferably 0.5-200 nm, even more preferably 2-20nm.
• a TEM (Transmission Electron Microscope) image shows that the thickness of the PDMS thin layer encapsulated on Si0 2 particles is around 20nm.
• Encapsulation could be achieved through many ways.
• the polymer could be absorbed to the solid particles, or through other physico-chemical actions, such as electrovalent or covalent bond connection.
• the solid particles are encapsulated by the polymer through a mechanically mixing process, such as thoroughly mixing under stirring.
• encapsulation of the solid particles by the hydrophobic polymer could be achieved by stirring for at least 30 minutes, or even longer time, such as 1 hour, 1.5 hours, or 2 hours.
• Encapsulation could be judged by measuring the weight of certain volume (such as 5ml or 10ml) of the mixture of solid particles and the hydrophobic polymer during mixing. After the weight becomes constant, thorough mixing and encapsulation are achieved.
• the hydrophobic polymer includes functional groups, such as hydroxyl group or amine group, and therefore could be cross-linked upon addition of a curing agent.
• the encapsulated particles could bind to each other by curing under the presence of the curing agent (crosslinker) and a catalyst.
• curing agents include substances or mixtures of substances added to a polymer composition to promote the curing reaction. Through such curing reaction, a low molecular weight resin/hardener system could form a cross-linked network.
• the curing agent is tetraethyl orthosilicate (TEOS).
• the dispersion of the present invention may further include conventional additives used in the coating art.
• additives may include, but are not limited to, stabilizing agents, wetting agents, surfactants, anti-static agents, antifoam agents, anti block agents, wax- dispersion pigments, neutralizing agents, thickeners, compatibilizers, brighteners, rheology modifiers, biocides, fungicides, additional surfactants, frothing agents, dispersants, fire retardants, pigments, reinforcing fibers, antifoam agents, antioxidants, preservatives, acid scavengers, leveling agents and the like.
• Aqueous dispersion can be formed by many methods recognized by those having skill in the art.
• the aqueous dispersion may be formed by emulsion polymerization, mixing under shear force or melt kneading, such as melt kneading by twin-screw extruder as disclosed in WO2005021638A.
• the process for preparing the aqueous dispersion according to the present invention may comprise, in order: a) mixing the hydrophobic polymer with the solid particles including the primary particles and said secondary particles and stirring thoroughly for at least 30 minutes, preferably 1 hour or 2 hours, to achieve encapsulation; and b) adding water, a surfactant and other additives under stirring to form an aqueous dispersion.
• step a) the mixing can be conducted without the presence of water and step b) is followed after encapsulation is achieved.
• the process for preparing the aqueous dispersion according to the present invention further comprises pre-treating said primary particles and said secondary particles with a coupling agent before mixing them with the hydrophobic polymer.
• the aqueous dispersion of the present invention may be used to produce a solar reflective coating.
• a crosslinker and a catalyst could be added into the aqueous dispersion to form a coating composition.
• Other additives may also be incorporated into the composition, which may include dyes, antioxidants, UV stabilizers, biocides, thickeners, viscosity enhancers, etc.
• the composition could then be applied, such as by brushing, onto the outer surface of a substrate, such as a roof or a wall. Upon evacuation of the water therein, solid particles will bind to each other through the curing of the encapsulated hydrophobic polymer and an infrared reflective coating is formed.
• a coating system with multi-functional performance (infrared reflectance, dirt pick-up resistance, and hydrophobic property) is provided.
• the inventive coating achieves more than 85% of solar reflectance, especially for even more than 90% of near infrared reflectance. Therefore, the improved infrared reflectance (in the wavelength of 700-2500nm) is achieved by the inventive formulated coating.
• the inventive coating also achieves a specific micro structure e.g. roughness of surface morphology, which results in a synergistic effect on multiple reflection /scattering and thus super solar/infrared reflectance in the inventive formulated coatings.
• the inventive coating also gives improved dirt pick-up resistance; probably from a modified hydrophobic coating surface upper layer having a contact angle of more than 135°, more preferably from 135 to 145°, which potentially provides easy or self cleaning properties, so as to enhance the durability/lifetime for solar reflectance and other properties in formulated coatings.
• the coating is made using simple and cost-effective manufacturing processes and raw materials as above-mentioned.
• step b) 0.35 g dry coal ash (without water) is brushed homogenously on the surface of our samples.
• a series of Si0 2 -Ti0 2 /polydimethylsiloxane (PDMS) hybrid particle coatings with different PDMS loading range level were fabricated by mechanical dispersion processes.
• the PDMS loading level can be adjusted to achieve different coating properties.
• the coating composition was applied manually on a glass substrate and was dried at room temperature for further testing.
• Example 2 Inventive Examples and Solar Reflectance Property
• Coating formulations of the present invention with key components are shown in Table 2.
• Table 2 the total loading range of inorganic particles (Si0 2 & Ti0 2 ) and binder PDMS is fixed at 51.05 % by weight of the total weight of the dispersion.
• the binder is composed of two kinds of PDMS with different viscosity (molecular weight). Both PDMS with different viscosities are available from GE CTC.
• Inventive Samples 1 and 3 having a larger particle size (5 ⁇ ) of Si0 2 provide higher solar reflectance especially for higher near infrared reflectance than Samples 2 and 4 with smaller particle size (2 ⁇ ) of Si0 2 .
• the binder in Samples 1 and 2 with a higher weight ratio (3: 1) of high viscosity PDMS to low viscosity PDMS achieved a much higher solar reflectance (>89%), especially for super near infrared reflectance (>93%), than Sample 3 and 4 having such a lower weight ratio (1 :3).
• Dirt pick-up resistance has a significant correlation to the long-term performance of coatings which reflect solar radiation.
• DPR is considered as the lifetime /durability of reflectance.
• the standard method for testing DPR is altered by using dry dust to replace the wet dust (refer to the aforementioned Test Methods part).
• the DPR performance for all inventive and comparative examples is listed in Table 3 based on the altered method.
• Samples in this invention provide excellent dirt pick-up resistance, indicating long lasting durability for reflectance property ( ⁇ 7.5% loss in reflectance after DPR testing).
• the enhancement of DPR property might result from the hydrophobic surface of inventive formulated coating with 135-145° of contact angle as shown in the last column of Table 3.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Materials Engineering (AREA)
• Wood Science & Technology (AREA)
• Organic Chemistry (AREA)
• Nanotechnology (AREA)
• Paints Or Removers (AREA)

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Citations (4)

• 2011
  • 2011-08-31 WO PCT/CN2011/079199 patent/WO2013029252A1/en active Application Filing
  • 2011-08-31 CN CN201180072968.XA patent/CN103748179B/zh active Active

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