KR20010006245A - Thermal insulating coating employing microencapsulated phase change material and method - Google Patents

Abstract

A method of insulating a substrate from repeated thermal transients and/or thermal impulses applied thereto by proximately absorbing and storing the thermal transients and/or thermal impulses for subsequent removal by radiation. According to the method, a coating (10) is placed in energy absorbing contacting relation with the substrate. The coating (10) includes a base material (20) and a plurality of microcapsules (30) dispersed within the base material (20). The microcapsules (30) may be dispersed throughout the base material (10) and may be submerged therein so that they are substantially space apart from one another. The microcapsules (30) contain a thermal energy absorbing material (40), for example, a phase change material such as a paraffinic hydrocarbons or alternatively, plastic crystals. Articles of manufacture may be produced according to the present invention which employ the above described coating.

Description

Insulation coating using microencapsulated phase change material and its manufacturing method {THERMAL INSULATING COATING EMPLOYING MICROENCAPSULATED PHASE CHANGE MATERIAL AND METHOD}

Stresses on electrical and mechanical systems are known to reduce the reliability of such systems. Excess thermal energy delivered over a short period of time is a type of stress that can shorten the life of components if not handled effectively. For example, it is well known to cool such electronic components and assemblies in order to extend the operating life of the electronic components and assemblies and to prevent breakage of the components. Some techniques are commonly used to cool electronic components, for example, by placing components in a heat sink to remove heat by heat radiation and heat convection. Another method often used with heat sinks is to install a fan or blower near the component to be cooled to circulate air around the component. Another way to cool a component is to enclose the component with a potting compound or a compliant coating that protects the component from harmful effects such as contact with water and / or excessive shock. In general, the potting compound is an epoxy that is semi-flexible with added thixotropic agents and hardeners. The particular epoxy generally used depends on a number of parameters, including the coefficient of thermal expansion of the component. The coefficient of thermal expansion of an epoxy should be similar to the coefficient of thermal expansion of electronic components in order to prevent possible fracture of the electronic components. Another consideration is that the epoxy must be watertight and not electrically or physically react with the component. Thus, providing a coating that can be applied to the exterior of an electronic component or to a package thereof that still maintains the aforementioned advantages of conventional potting compounds while still enhancing conductance that draws thermal energy from the component. Will be commercially valuable.

Similarly, conventional aircraft receive high heat, especially on takeoff. In addition, aircraft that take off and land vertically (so-called "jump jets") receive extremely high amounts of thermal energy during takeoff and landing. The outer shell portion of the aircraft experiences a thermal transient of approximately 177 ° F. in approximately 15 seconds. Naturally, high performance requires a lot of money. Thermal barrier materials are expensive and add to the weight of the aircraft, which means reduced performance and higher costs. Therefore, it would also be commercially valuable to provide a compound that can be applied to an aircraft shell that effectively absorbs large amounts of thermal energy and subsequently protects the underlying aircraft operating system to conduct heat away from the aircraft and conduct it. .

It would also be of significant value if manual systems were developed to prevent bridges, roads, aircraft wings and other structures from freezing under severe cold climatic conditions. Such a system may operate as a thermal capacitor during a relatively warm period and then may need to dissipate stored thermal energy while the temperature is lowered.

Accordingly, it is an object of the present invention to solve the above-mentioned problem.

It is another object of the present invention to provide a heat capacitive coating which extends the life of the component.

It is also an object of the present invention to provide a heat capacitive coating which enhances the reliability of the components.

One object associated with the present invention is to provide a heat capacitive coating that effectively absorbs thermal shock energy and protects the underlying system from the harmful effects of thermal shock.

Another object of the present invention is to provide a method of heat treatment that is more effective than the prior art methods.

It is a further object of the present invention to provide a heat capacitive coating which is cheaper than conventionally available heat handling systems.

It is a further object of the present invention to provide a lighter heat capacitive coating as compared to conventionally available heat handling systems.

Summary of the Invention

The above and other objects are repeated thermal transients applied to the substrate by absorbing and storing thermal and / or thermal shocks applied to the substrate in close proximity to the substrate to subsequently remove heat by radiation. And / or providing a method of insulating the substrate from thermal shock. According to this method, the coating is placed in an energy absorbing contact relationship with the substrate. The coating includes a base material and a plurality of microcapsules dispersed in the base material. This microcapsule contains, for example, a heat energy absorbing substance such as a paraffinic hydrocarbon or a phase shifting substance such as a viscosity crystal.

In accordance with the present invention, articles having the above-described coatings can be produced.

The present invention relates generally to the field of insulating coatings, and more particularly to insulating coatings applied to substrates to protect underlying structures from thermal transients and thermal impulse.

In order to more fully understand the present invention, reference should now be made to the embodiments illustrated in more detail in the accompanying drawings and described below by means of embodiments of the invention.

1 is a cross-sectional view of a microcapsule containing a phase change material in a peripheral shell for use in the present invention.

2 is a cross-sectional view of a substrate such as an aircraft shell, road surface, bridge, electronic component, foam, glass, plastic, etc. coated with a base material incorporating a microencapsulated phase change material according to the present invention.

3 is a graph showing a control sample of an uncovered aircraft shell.

FIG. 4 is a graph showing the result of heating an aircraft shell sample coated to a thickness of 10 mils by a coating made of only a binder.

FIG. 5 is a graph showing the results of heating a 10 mil thick coated outer shell sample with a coating comprised of a binder and a microencapsulated phase change material dispersed therein.

Although the present invention is described in more detail below, it should be understood by those skilled in the art that modifications may be made to the invention described herein while achieving the advantageous results of the present invention. Accordingly, the following description is not intended to limit the invention but should be understood as broad teachings to those skilled in the art.

Looking more particularly at the drawings, in particular Figures 1 and 2, a general embodiment of the present invention is illustrated. The coating, generally designated 10, comprises a flexible polymeric binder 20 and a complete plurality of microcapsules 30 dispersed in the polymeric binder 20 (FIG. 1). The microcapsules 30 contain a temperature stabilization means 40 which will be described in more detail later.

Polymeric binders can take the form of organic plastics, examples of which include, but are not limited to, polyurethanes, nitrile rubbers, chloroprene rubbers, polyvinyl alcohols, silicones, ethylene / vinyl acetate copolymers, acrylics, and the like.

The diameter of the microcapsules can range from about 0.50 microns to about 1000 microns, which is formed according to conventional methods well known to those skilled in the art.

The microcapsules contain a temperature stabilization means or phase inversion material 40, for example eicosane. In addition, viscosity crystals such as 2,2-dimethyl-1,3-propanediol (DMP) and 2-hydroxymethyl-2-methyl-1,3-propanediol (HMP) and the like can be used as temperature stabilization means. Can be. When the viscosity crystals absorb thermal energy, the molecular structure is temporarily transformed without switching the phase of the material.

In another aspect of the present invention, the composition of phase inversion material 40 can be modified to obtain optimal thermal properties for a given temperature range. For example, the melting point of the same type of paraffinic hydrocarbons is directly related to the number of carbon atoms as shown in the table below:

Compound name Carbon atoms Melting point ℃ n-octacoic acid 28 61.4 n-heptacoic acid 27 59.0 n-hexacoic acid 26 56.4 n-pentacoic acid 25 53.7 n-tetracoic acid 24 50.9 n-trichoic acid 23 47.6 n-docosan 22 44.4 n-heneichoic acid 21 40.5 n-eichoic acid 20 36.8 n-nonadecan 19 32.1 n-octadecane 18 28.2 n-heptadecane 17 22.0 n-hexadecane 16 18.2 n-pentadecane 15 10.0 n-tetradecane 14 5.9 n-tridecane 13 -5.5

Each of these materials can be encapsulated separately and is most effective near the indicated melting point. It will be appreciated from the foregoing that the effective temperature of the coating can be adjusted for a particular environment by selecting the phase inversion material required for the corresponding temperature and adding microcapsules containing the material to the coating.

In making the coating 10, the desired encapsulated phase change material is added to the polymer binder (liquid, solution or dispersion), mixed, cured, sprayed, crosslinked or conventionally treated, to give flexibility (or Inflexible) layers are formed according to conventional methods on substrates such as aircraft shells, concrete, road surfaces (eg asphalt), foams, bridge structures or building materials. Typical concentrations of the microencapsulated phase inversion material 30 added to the polymeric binder range from about 30% to about 80% by weight. Incorporating the microcapsules directly into the polymeric binder 30 increases durability because the phase conversion material is protected by a double wall (the first wall is the microcapsules and the second wall is the surrounding polymer matrix itself). . Thus, the phase inversion material is unlikely to flow out of the coating while it is liquid, thereby improving its life and increasing the repeatability of the thermal reaction.

As briefly mentioned above, the substrate may be any type of structure that is repeatedly subjected to a thermal gradient, which is independent of whether it is sudden or relatively gradual. For example, a sudden type of thermal gradient may be sustained in electronic components, such as Pulse Power Thyristors, that have been pulsed in approximately milliseconds or microseconds, or thermal transients may last for approximately 15 seconds. It will be found on jets that take off and land vertically. On the other hand, the thermal gradient can be gradual and can transition over several hours.

For example, bridges (or other structures) absorb thermal energy during the day and emit or radiate energy at night. This often freezes the road dangerously, especially when the sediment sinks in colder climates. The road surface with the coating according to the invention can be kept at temperatures higher than the freezing temperature for longer periods of time, reducing the need for sanding or salting, or in some cases eliminating such a need. In operation, the phase change material is selected to melt during the day to absorb solar energy and, after sunset, to freeze after consuming the stored energy. Thus, given pure results, the formation of ice on the road will be delayed. In another use according to the invention, the coating can be applied to the aircraft wing to eliminate or delay the need for ice making.

In related applications, a high melting point phase change material or viscosity determination may be used at the base of a jet taking off and landing vertically. The coating will protect the base of the aircraft from hot exhaust gases. In the experiments that were conducted, the coating using Polywax 655 as the microencapsulated phase change material was sprayed onto the aircraft shell portion. The film thickness ranged from 0.010 in to 0.100 in and was heated to about 500 ° F. for 15 seconds. The same heating was performed to the corresponding control sample without coating and the control sample coated without the microencapsulated phase inversion material. Experimental results are shown in FIGS. 3 to 5. FIG. 3 shows the results of heating an uncoated (0 mil) control sample that received hot gas at 400 ° C. at 0.50 in. For 20 seconds or less. The upper curve represents the gas temperature, the second line is the surface temperature, and the third curve is the temperature just below the coating, measured with a small thermocouple. Within 15 seconds, the temperature of the uncoated sample reached 270 ° C. 4 shows the case where 10 mil coated samples were heated under the same conditions. The coating was a urethane binder without any microencapsulated phase inversion material. Within 15 seconds, the temperature just below the surface (indicated by the third line from above) reached 190 ° C. As such, it will be appreciated that the urethane film of 0.0100 in may exhibit some degree of protective effect. FIG. 5 is a curve for a 0.010 inch thick film containing phase-encapsulating material microencapsulated at 8% Critical Pigment Volume Concentration (PVC) loading rate. PVC is an industrial indication of the load concentration on the coating. 8% PVC corresponds to approximately 60% by volume or 59% by weight. Under the same experimental conditions, FIG. 5 shows how the temperature just below the surface reaches only 80 ° C. after 15 seconds of heating. In fact, as shown in the figure, the temperature below the surface only reaches 100 ° C. after 20 seconds of heating. This enhanced thermal protection means that a thin coat of microencapsulated phase inversion material can reduce the sample surface temperature by at least 70% from 270 ° C. to 80 ° C. for the same heating level.

With regard to the cooling of the vibrated electronic components, results similar to those obtained above will be obtained in connection with the aircraft shell, thereby enhancing the reliability and life of the components.

While the invention has been described in detail with respect to certain preferred embodiments and their operation, it should be understood that corresponding materials and mechanisms may be changed, modified, and substituted within the spirit and scope of the invention.

Claims (57)

Substrates selected from the group consisting of aircraft shells, electronic component packages, foams, road surfaces, concrete, asphalt, bridge structures and building materials, A polymeric binder, and a plurality of microcapsules dispersed and immersed throughout the binder so as to be surrounded by the polymeric binder, which comprises a temperature stabilizing means selected from the group consisting of phase change materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the surface of the substrate, wherein insulation is enhanced against thermal gradients and thermal transients, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 1, And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 1, Wherein the diameter of the microcapsules ranges from about 0.50 microns to 1000 microns. The method of claim 1, Wherein said coating comprises at least two types of separately encapsulated temperature stabilization means. The method of claim 1, The first preselected portion of the microcapsules contains a first temperature stabilization means and the remaining portion of the microcapsules contains a second temperature stabilization means. The method of claim 1, Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 2, Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 2, Paraffinic hydrocarbon has a melting point of -5.5 ℃ to 61.4 ℃. (a) a substantially rigid structural shell, and (b) a polymer that directly covers and covers at least a portion of the structural shell, and a plurality of microcapsules dispersed throughout the polymer to be covered and enclosed by the polymer, the temperature stabilization selected from the group consisting of phase inversion materials and viscosity crystals Air vehicle shell, which consists essentially of means), with increased insulation against thermal gradients and thermal transients. The method of claim 9, An outer shell of the aircraft comprising a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 9, Aircraft shell with a diameter of the microcapsules ranging from 0.50 microns to 1000 microns. The method of claim 9, And wherein said polymeric binder is selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 10, Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , aircraft shell selected from the group consisting of n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 9, Aircraft shell with a melting point of phase conversion material from about -5.5 ° C to about 61.4 ° C. The method of claim 9, Aircraft shell comprising said coating containing at least two types of separately encapsulated temperature stabilization means. (a) a substrate comprising an electronic component package, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 16, And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 16, Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 16, Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 17, Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 16, A product having a melting point of about -5.5 ° C to about 61.4 ° C. (a) a substrate comprising a foam, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 22, And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 22, Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 22, Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 23, Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 22, A product having a melting point of about -5.5 ° C to about 61.4 ° C. (a) a substrate comprising a road surface, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 28, And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 28, Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 28, Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 29, Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 28, A product having a melting point of about -5.5 ° C to about 61.4 ° C. (a) a substrate comprising concrete, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 34, wherein And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 34, wherein Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 34, wherein Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. 36. The method of claim 35 wherein Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 34, wherein A product having a melting point of about -5.5 ° C to about 61.4 ° C. (a) a substrate comprising asphalt, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 40, And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 40, Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 40, Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. 42. The method of claim 41 wherein Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 40, A product having a melting point of about -5.5 ° C to about 61.4 ° C. (a) a substrate comprising a bridge structure, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 46, And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 46, Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 46, Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 47, Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 46, A product having a melting point of about -5.5 ° C to about 61.4 ° C. (a) a substrate comprising building materials, and (b) a polymeric binder and a plurality of microcapsules dispersed and immersed throughout the polymeric binder so as to be surrounded by the polymeric binder, which contains a temperature stabilizing means selected from the group consisting of phase inversion materials and viscosity crystals; Consisting essentially of a coating covering at least a portion of the substrate surface, Products with enhanced insulation against repeated thermal gradients and thermal transients. The method of claim 52, wherein And said phase converting material comprises a material selected from the group consisting of paraffinic hydrocarbons. The method of claim 52, wherein Wherein the diameter of the microcapsules ranges from 0.50 microns to 1000 microns. The method of claim 52, wherein Said polymer binder selected from the group consisting of polyurethane, nitrile rubber, chloroprene rubber, polyvinyl alcohol, silicone, ethylene / vinyl acetate copolymer and acrylic. The method of claim 53, wherein Paraffinic hydrocarbons are n-octacoic acid, n-heptacoic acid, n-pentacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-eicoic acid, n-nonadecane , n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane. The method of claim 52, wherein A product having a melting point of about -5.5 ° C to about 61.4 ° C.