WO2018130176A1

WO2018130176A1 - Composition for thermal insulation coating

Info

Publication number: WO2018130176A1
Application number: PCT/CN2018/072216
Authority: WO
Inventors: Zhijian Lin; Siu Kit LO; Wing Nien Wylie O; Tsang Ming Michael CHOI; Lai To LEUNG; Kwok Keung Paul Ho
Original assignee: Nano And Advanced Materials Institute Limited
Priority date: 2017-01-11
Filing date: 2018-01-11
Publication date: 2018-07-19
Also published as: CN110177846A

Abstract

Provided herein is a coating composition useful for thermal insulation. The coating composition comprises hollow micro-spheres; melamine; and a silicone modified acrylic emulsion. Coatings comprising the coating composition can be non-flammable and thermally stable up to 250°C and can have a thermal conductivity below 0.1 W·m^-1·K^-1.

Description

COMPOSITION FOR THERMAL INSULATION COATING

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 62/498,894, entitled COMPOSITION OF A THERMAL INSULATION COATING SYSTEM, which was filed on January 11, 2017, and is hereby incorporated by reference in its entity.

TECHNICAL FIELD

The present disclosure generally relates to a coating composition useful as a thermal insulation coating.

BACKGROND ART

Domestic and industrial heating applications are responsible for a large portion of global energy consumption. Heating applications typically involve heating a fluid or a gas at a certain temperature in a compartment or piping, such as a reaction vessel, transfer piping, heat exchanger, storage tank, or other equipment. The absence of thermal insulation in these heating applications can increase the energy consumption and cost of the heating process.

Thermal insulation is also used to protect users from exposure to extremely hot surfaces. The American Society for Testing and Materials (ASTM) C1055 standard defines the acceptable limit in an industrial working environment for skin contact on a hot surface to be 60 ℃ for 5 seconds or less.

Thermal insulation can be achieved by a bulk insulation package or by applying a thermal insulation coating system.

Bulk insulation packages typically include three layers: a first layer on the substrate surface for adhesion; a middle functional insulation layer composed of low thermal conductivity materials and a binder; and a top layer optionally be added to protect the thermal insulation coating system from corrosion and/or for aesthetics.

Thermal insulation coating systems are typically formulated by incorporating filler materials with low thermal conductivity and a binder, providing cohesive strength, adhesion to the substrate, flexibility, and stability to constant high service temperature.

Presently, the most common insulation coating for temperature applications under 150 ℃ are usually made of waterborne polymer materials. These coatings can be directly applied to the substrate or over a corrosion inhibiting primer, and then top-coated. The primers provide the corrosion protection in a multi-coat system; the topcoat provides decorative properties and protection to the insulation coating.

For temperature applications over 250 ℃, an inorganic ceramic-based binding material is formulated in the coating. The insulation performance of these coatings, however, is not as good as that of polymer-based coatings.

A need therefore exists for a novel thermal insulation coating with improved performance and eliminate or diminish the disadvantages and problems described above.

SUMMARY OF THE INVENTION

Provided herein is a coating composition comprising hollow micro-spheres; melamine; and a silicone modified acrylic emulsion.

In certain embodiments, the hollow micro-spheres are present at a concentration in a range of 14%-19%w/w in the composition, the melamine is present at a concentration in a range of 21%-28%w/w in the composition, and the silicone modified acrylic emulsion is present at a concentration in a range of 42%-55%w/w in the composition.

In certain embodiments, the hollow micro-spheres comprise glass, a ceramic material or an organic polymer.

In certain embodiments, the hollow micro-spheres have thermal conductivity below 0.1 W·m ^-1·K ^-1.

In certain embodiments, the hollow micro-spheres have a mean particle diameter between 0.5 and 300 microns.

In certain embodiments, the hollow micro-spheres have a density between 0.1 and 5.0 g/cm ³.

In certain embodiments, the coating composition further comprises at least one thickener.

In certain embodiments, the thickener is present at a concentration in a range of 0.15%-1.2%w/w in the composition.

In certain embodiments, the coating composition further comprises at least one extender pigment.

In certain embodiments, the extender pigment is calcium carbonate, crystalline and amorphous silicas, silicate minerals, alumina trihydrate, aluminum oxides, barytes, titanium oxide, lithopone, or a combination thereof.

In certain embodiments, the coating composition further comprises at least one infrared reflective pigment.

In certain embodiments, the infrared reflective pigment is a solid solution comprising corundum and/or hematite in crystalline structure with guest component metal oxides.

In certain embodiments, the thickener is polyether polyurethane.

In certain embodiments, the hollow micro-spheres are glass with a density in a range of 0.2-0.6 g/cm ³ and present at a concentration of 18.2%w/w in the composition, melamine is present at a concentration of 27.2%w/w in the composition, the silicone modified acrylic emulsion is present at a concentration of 54.4%w/w in the composition, and polyether polyurethane is present at a concentration of 0.2%w/w in the composition.

In certain embodiments, the coating composition further comprises water.

In certain embodiments, the hollow micro-spheres are glass with a density in a range of 0.2-0.6 g/cm ³ and present at a concentration of 14.24%w/w in the composition, melamine is present at a concentration of 21.4%w/w in the composition, the silicone modified acrylic emulsion is present at a concentration of 42.8%w/w in the composition, polyether polyurethane is present at a concentration of 0.16%w/w in the composition, and water is present at a concentration of 21.4%w/w in the composition.

Provided herein is a coating comprising any of the aforementioned coating compositions.

These and other aspects, features and advantages of the present disclosure will become more fully apparent from the following brief description of the drawings, the drawings, the detailed description of certain embodiments and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure generally relates to a novel coating composition useful as a thermal insulation coating. Coatings comprising the composition provided herein can be non-flammable, thermally stable up to 250 ℃, and can have low thermal conductivity. The concentration of toxic gases emitted at high temperature from the coatings comprising the compositions provided herein can be below the IDLH (Immediately Dangerous to Life and Health) limit. The coating comprising the compositions provided herein can have low volatile organic compound (VOC) content. The coatings comprising the compositions provided herein can also have good adhesion on various substrates.

In certain embodiments, the composition provided herein comprises hollow micro-spheres, melamine, and a silicone modified acrylic emulsion.

The hollow micro-spheres reduce thermal conductivity of the coating, thus reducing heat flow through the coating. The hollow micro-spheres can be made of glass, ceramic material or organic polymer with low thermal conductivity, for examples, hollow glass micro-spheres (e.g., 3M Scotchlite micro-spheres) , hollow ceramic micro-spheres (e.g., 3M's Z-light Spheres, Cenospheres, fly ash) , hollow micro-spheres made of organic polymer comprising polymers or copolymers of acrylic materials, copolymers of vinylidene chloride and acrylonitrile, cellulosic materials, polymers, natural sugars, synthetic composite or blends thereof.

The hollow micro-spheres may have thermal conductivity below 0.5 W·m ^-1·K ^-1, below 0.1 W·m ^-1·K ^-1, or below 0.05 W·m ^-1·K ^-1. The hollow micro-spheres may have a mean particle size (e.g., diameter) between 0.5 and 300 microns, between 5 and 200 microns, or between 10 and 150 microns. The hollow micro-spheres may have unimodal or polymodal particle size distributions. The hollow micro-spheres may have a density between 0.1 and 5.0 g/cm ³, between 0.1 and 1.0 g/cm ³, or between 0.1 and 0.6 g/cm ³.

The melamine is used as a fire retardant for providing thermal stability of the coating. Melamine release nitrogen gas when the coating is exposed to fire. Melamine containing compounds can be used in the coating compositions. Suitable examples include, but are not limited to melamine, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melamine cyanurate, and the like.

The silicone modified acrylic emulsion is used as a binder. The silicone modified acrylic emulsion can be cured by heat or at ambient conditions.

In certain embodiments, the composition further comprises at least one thickener. The thickener is able to increase the viscosity of the composition for ease of application without substantially changing the thermal insulation properties of the coating. The thickener can be present at a concentration in a range of 0.15%-1.2%w/w in the composition, in a range of 0.55%-1.2 %w/w in the composition, or in a range of 0.68%-0.8%w/w for application on a sandblasted steel substrate by spraying. The thickener can be polyether polyurethane.

In certain embodiments, the composition comprises hollow glass micro-spheres, melamine, silicone modified acrylic emulsion, polyether polyurethane and water. The concentration of polyether polyurethane is tunable to suit different application methods on substrate surfaces.

The examples below provide coating compositions with specific amounts of hollow glass micro-spheres and silicone modified acrylic emulsion, which provide good mechanical strength of the coating with low thermal conductivity. In certain embodiments, the hollow micro-spheres are present at a concentration in a range of 14%-19%w/w in the composition.

In certain embodiments, the composition further comprises at least one extender pigment. As the reflectance characteristics of the coating are described by their solar reflectance spectra, selection of the extender pigment is based on their visible reflectance behavior and their contribution to visible colors (e.g., white, red, green and blue) . The extender pigment having high reflectivity in the infrared region shows advantageous properties. Thus, the extender pigments having a high reflectivity in the infrared region of the electromagnetic spectrum relative to the visible region can be used.

Examples of extender pigments include, but are not limited to, calcium carbonate (both naturally ground and precipitated) , crystalline and amorphous silicas (both natural and synthesized) , silicate minerals (e.g., talcum, kaolin, calcined clay, wollastonite, nepheline syenite, feldspars, micas, attapulgite clay, bentonites and organic-modified bentonites) , alumina trihydrate, aluminum oxides, barytes, titanium oxide, lithopone or a combination thereof.

In certain embodiments, the coating composition further comprises at least one infrared reflective pigment. The infrared reflective pigment is used to reflect radiation from an infrared region of spectrum. The infrared reflective pigment can be solid solutions comprising corundum and/or hematite in crystalline structure with guest component metal oxides (e.g., titanium oxide and other oxides from abundant ores) .

The coating composition can be applied on glass, ceramic, concrete, steel, or sandblasted steel by rolling, brushing, spraying or other conventional methods.

The coating formed from the composition is non-flammable and thermally stable up to 150 ℃, or even up to 250 ℃. The coating has a thermal conductivity value below 0.5 W·m ^-1·K ^-1, or even below 0.1 W·m ^-1·K ^-1. The concentrations of toxic gases emitted at high temperature (up to 250 ℃, or even up to 400 ℃ from the coating) are below the IDLH limit. The toxic gases mentioned include carbon monoxide (CO) , hydrogen cyanided (HCN) , hydrogen fluoride (HF) , hydrogen chloride (HCl) , hydrogen bromide (HBr) , nitrogen oxides (NO _X) including nitrogen dioxide (NO ₂) , and sulfur dioxide (SO ₂) . Furthermore, the coatings prepared from the coating composition can have volatile organic compound (VOC) content below 10 g/L, or even below 100 mg/L.

Example 1

6 grams of silicone modified acrylic emulsion and 0.022 gram of polyether polyurethane thickener were added in a container and the mixture was stirred at a rate of 300 rpm by a mechanical stirrer. After 3 hour, 3 grams of melamine was added and the mixture was mixed under impeller at the rate of 300 rpm for 10 min. 2 grams of hollow glass micro-spheres (density of 0.2 –0.6 g/cm ³) was added and mixed under impeller at the rate of 500 rpm for 10 minutes. The coating material is applied on a sandblasted stainless steel substrate and cured by heat at 120 ℃. It is thermally stable up to 250 ℃. The coating system has good adhesion on the sandblasted steel substrate.

Example 2

6 grams of silicone modified acrylic emulsion, 3 grams of water, and 0.022 gram of polyether polyurethane thickener (0.73%w/w in water) were added in a container and the mixture was stirred at a rate of 300 rpm by a mechanical stirrer. After 3 hour, 3 grams of melamine was added and the mixture was mixed under impeller at the rate of 300 rpm for 10 min. 2 grams of hollow glass micro-spheres (density of 0.2 –0.6 g/cm ³) was added and mixed under impeller at the rate of 500 rpm for 10 minutes. The coating material is applied on a sandblasted stainless steel substrate and cured by heat at 120 ℃. The concentrations of toxic gases emitted at high temperature of this non-flammable thermal insulation coating are measured below IDLH (Immediately Dangerous to Life and Health) limit. The coating has a thermal conductivity of 0.0956 W·m ^-1·K ^-1. It is thermally stable up to 250 ℃. The coating has good adhesion on the sandblasted steel substrate. The volatile organic compound (VOC) content is measured to be below 100 mg/L for high molecular weight hydrocarbons. It can be rolled, brushed or sprayed by conventional methods.

The measured physical properties of coating described in Example 2 are tabulated in Table 1.

Table 1

Comparative Example 1

1 gram of polyurethane modified acrylic acid emulsion as binder, 0.1 gram of polyether polyurethane thickener, 3 grams of polytetrafluoroethylene (PTFE) emulsion as a binder and fire retardant, and 2.5 grams of water were added in a container and the mixture was stirred at a rate of 300 rpm by a mechanical stirrer. After 3 hours, 2 grams of hollow glass micro-spheres (density of 0.2 –0.6 g/cm ³) was added and mixed under impeller at the rate of 500 rpm for 10 minutes. The coating is non-flammable. It is thermally stable up to 250 ℃. However, the cured coating has poor adhesion on a sandblasted steel substrate compared with the others.

A thermal insulation performance test was conducted for Examples 1 &2 and Comparative Example 1. The coating solution from each example was applied on a sandblasted steel substrate and was cured for forming a coating of 4 mm in thickness on the substrate. The substrate with the coating was heated up by a hot plate. Thermocouples were used for measuring temperature of the substrate and the coating. When the temperature of the substrate reached to and was stable at 100 ℃, 150 ℃ and 200 ℃, the temperature of the coating surface was measured respectively. The results are tabulated in Table 2. The lower the coating surface temperature is, the better the thermal insulation performance will be. As shown in Table 2, the thermal insulation performance of the cured coating of Example 1 is identical to that of Example 2, and both of them have good performance. However, the thermal insulation performance of Comparative Example 1 is poorer compared with Example 1 and 2.

Table 2

One or more coatings can be applied to a substrate to form a coating system. The coating system can be used as an exterior surface on a product. Typical applications of the present coating include, but are not limited to, coating for an exterior of construction structures; coating for concrete, wood, plastics or other materials used for walkways; coating of vehicles; coating of products for military applications; coatings for industrial systems (e.g., reaction vessels, transfer piping, heat exchanger, and storage tank) .

Although the invention has been described in terms of certain embodiments, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims which follow.

Claims

A coating composition comprising:

hollow micro-spheres;

melamine; and

a silicone modified acrylic emulsion.
The coating composition of claim 1, wherein the hollow micro-spheres are present at a concentration in a range of 14%-19%w/w in the composition, the melamine is present at a concentration in a range of 21%-28%w/w in the composition, and the silicone modified acrylic emulsion is present at a concentration in a range of 42%-55%w/w in the composition.
The coating composition of claim 1, wherein the hollow micro-spheres comprise glass, a ceramic material or an organic polymer.
The coating composition of claim 1, wherein the hollow micro-spheres have thermal conductivity below 0.1 W·m ^-1·K ^-1.
The coating composition of claim 1, wherein the hollow micro-spheres have a mean particle diameter between 0.5 and 300 microns.
The coating composition of claim 1, wherein the hollow micro-spheres have a density between 0.1 and 5.0 g/cm ³.
The coating composition of claim 1 further comprising at least one thickener.
The coating composition of claim 1, wherein the thickener is present at a concentration in a range of 0.15%-1.2%w/w in the composition.
The coating composition of claim 1 further comprising at least one extender pigment.
The coating composition of claim 9, wherein the extender pigment is calcium carbonate, crystalline and amorphous silicas, silicate minerals, alumina trihydrate, aluminum oxides, barytes, titanium oxide, lithopone, or a combination thereof.
The coating composition of claim 1 further comprising at least one infrared reflective pigment.
The coating composition of claim 11, wherein the infrared reflective pigment is a solid solution comprising corundum and/or hematite in crystalline structure with guest component metal oxides.
The coating system of claim 7, wherein the thickener is polyether polyurethane.
The coating composition of claim 13, wherein the hollow micro-spheres are glass with a density in a range of 0.2-0.6 g/cm ³ and present at a concentration of 18.2%w/w in the composition, melamine is present at a concentration of 27.2%w/w in the composition, the silicone modified acrylic emulsion is present at a concentration of 54.4%w/w in the composition, and polyether polyurethane is present at a concentration of 0.2%w/w in the composition.
The coating composition of claim 13 further comprising water.
The coating composition of claim 15, wherein the hollow micro-spheres are glass with a density in a range of 0.2-0.6 g/cm ³ and present at a concentration of 14.24%w/w in the composition, melamine is present at a concentration of 21.4%w/w in the composition, the silicone modified acrylic emulsion is present at a concentration of 42.8%w/w in the composition, polyether polyurethane is present at a concentration of 0.16%w/w in the composition, and water is present at a concentration of 21.4%w/w in the composition.
A coating comprising the coating composition of claim 1.