HK1098728B - Composition for thermal insulation layer - Google Patents

Description

Composition for thermal insulation layer

Cross Reference to Related Applications

This application claims priority to U.S. provisional application No.60/519,400, filed 11/12/2003, which is incorporated herein by reference.

Background

The present invention relates to thermal insulation, and more particularly, to coating compositions for forming a thermal insulating layer on a substrate, methods of forming such thermal insulating layers, and methods for preparing such compositions.

Unplanned heat transfer results in inefficient use of energy by consumers as well as in industrial facilities, and increased financial costs. Examples of such undesired heat transfer are: increased heat from building structures that absorb solar radiation; heat loss from improperly insulated pipes and other structures, etc. Long term heat transfer may cause degradation of the material that transfers heat. Another effect of unintended heat transfer is loss of worker productivity due to burns or frostbite caused by contact with uninsulated or insufficiently insulated equipment. At a minimum, thermal and cold stresses in the workplace reduce worker productivity.

Methods of mitigating unintended heat transfer are known under the heading "insulation" and are generally identified by the composition of the solid portion that makes up the insulation. Examples include: polyurethane foam, fiberglass batting, rock wool, loose-fill vermiculite or perlite, blow-in cellulose, polystyrene foam, polyisocyanate foam, acrylic coatings, coatings containing ceramic particles or microspheres, and the like.

Each of the above insulation methods suffers from one or more of the following problems: loss of insulation due to penetration of dust, moisture, mold and mildew after installation; when these materials are used on metal surfaces, corrosion occurs due to the accumulation of moisture under the insulator, particularly condensation caused by the temperature difference generated at the interface between the insulator and the substrate; and insufficient insulation, particularly in the case of surface coatings.

It is an object of the present invention to provide an insulator in the form of a thin layer or coating, which is a protective layer characterized by low thermal conductivity and excellent and uniform adhesion to the substrate, thereby protecting the metal substrate from corrosion and protecting all substrates from mold and mildew. This layer is formed by applying a liquid coating composition characterized by good storage stability. The work of the present inventors resulted in the coating composition of the present invention satisfying the above object.

The coating composition of the invention contains highly porous particles of a material obtained by drying a wet sol-gel. Such materials include, but are not limited to, materials known as aerogels and xerogels. In its conventional meaning, the term "aerogel" is used to describe a material obtained by drying a wet sol-gel at a temperature above the critical temperature and a pressure above the critical pressure. Under such conditions, removal of the gel liquid, e.g. water, from the sol-gel results in a porous structure without damaging the gel structure, thereby obtaining a high porosity. Traditionally, the product obtained by drying under conditions below critical conditions is called a "xerogel", which has a low porosity, wherein at least some of the pore structure is destroyed during the drying process. Since the process of drying under supercritical conditions is very energy intensive and costly, attempts have been made to produce xerogels which approximate the properties of aerogels. Such xerogels are suitable for use in the compositions of the present invention. For example, U.S. Pat. No.5,565,142 describes "an ultra-porous xerogel which is dried at a pressure from vacuum-to-below supercritical pressure, but which has the properties of an aerogel which is typically dried at supercritical pressure. This is achieved by reacting the internal pore surfaces of the wet gel with an organic substance to change the contact angle of the fluid meniscus in the pores during drying.

Silica aerogels were the first aerogels studied intensively. However, aerogels and xerogels may have a wide range of chemical compositions. Other inorganic aerogels, as well as aerogels prepared from organic polymers, sometimes referred to as "carbon aerogels," can be used in the present invention. Inorganic xerogels and organic xerogels are suitable as compositions of the invention provided they have properties similar to aerogels.

Aerogels and xerogels may also be surface treated to alter their properties. For example, silica aerogels can be rendered less hydrophilic by converting surface-OH groups to-OR groups (where R is an aliphatic group). U.S. Pat. No.6,806,299, the contents of which are incorporated herein by reference in their entirety, discloses the preparation of hydrophobic organic aerogels. These chemically modified aerogels, as well as chemically modified xerogels having properties similar to aerogels, are also suitable for use in the compositions of the present invention.

Aerogels are known to have excellent thermal insulation properties, and xerogels with porosity and pore structure similar to aerogels are also good insulators. In known uses of insulation, aerogel particles have been compressed into panels or packed in closed containers or flexible bags, optionally with the use of binders. In another application, U.S. patent publication 2003-0215640 describes "a heat resistant aerogel insulation composite comprising an insulation base layer comprising hydrophobic aerogel particles and an aqueous binder, and a heat reflective top layer comprising a protective binder and an infrared reflecting agent. The insulation layer "preferably contains a foaming agent" and "a small amount of an aqueous binder is suitably used as needed to obtain the desired amount of mechanical strength. "

U.S. patent publication 2004-0077738a1 describes "an aerogel-hollow particle binder composition comprising an aqueous binder, hydrophobic aerogel particles, and hollow, non-porous particles, as well as an insulation composite comprising the aerogel-hollow particle binder composition and methods of making the insulation composite". The composition "preferably contains a foaming agent" and "a small amount of an aqueous binder is suitably used as needed to obtain the desired amount of mechanical strength".

Prior to the work conducted by the present inventors forming the subject of the present patent application, aerogel and xerogel particles have not been successfully used as primary insulating agents embedded in thin layers or coatings that are firmly adhered to substrates, formed by coating film-forming liquid compositions that have good storage stability and do not thicken excessively upon storage. In addition, in the present invention, aerogel and xerogel particles thermal insulation is not reduced by other components of the coating composition, such as the particle fine pore structure damage and/or pore invasion and saturation results. In addition, aerogel and xerogel particles in the coating formed from the composition of the present invention are protected from damage and degradation by environmental conditions by the physical properties inherent to the coating.

Summary of The Invention

It is a first object of the present invention to provide a coating composition containing highly porous particles of a material obtained by drying a sol-gel as an insulating agent and which forms a coating having the same structural and performance integrity even in harsh application environments, as found in industrial and manufacturing applications. The insulation layer of the present invention is impervious to moisture penetration, dust, mold and insects, which cause a significant loss of insulation of conventional insulation when used in a location where the insulation is exposed to weather or environmental conditions. The insulation of the present invention can also withstand without damage or compression significant physical impacts that are other common causes of failure of loose insulation materials.

It is another object of the present invention to provide a thermal insulation layer which is flame retardant in addition to having the characteristics described in the first object of the present invention.

It is a further object of the present invention to provide a thermal insulation layer which, in addition to having the characteristics set forth in any of the above objects of the invention, also protects the substrate from corrosion.

It is another object of the present invention to provide a thermal insulation layer that protects a substrate against mold and mildew in addition to having the characteristics set forth in any of the above objects of the present invention.

Detailed Description

The curable coating composition of the present invention is made from highly porous particles dispersed in a film-forming resin system containing a film-forming polymer and in the presence of a stabilizer as defined below. The particles are particles of a material obtained by drying a wet sol-gel and have a porosity of at least 80% and a particle size in the range of 5 μm to 4.0 mm.

The present invention provides a curable coating composition for forming a thermal insulation layer, wherein the composition comprises:

(a) highly porous particles of a material obtained by drying a wet sol-gel, said particles having a porosity of at least 80% and a particle size in the range of 5 μm to 4.0 mm; and

(b) a film-forming resin system comprising a film-forming polymer,

wherein the particles (a) are dispersed in a resin system (b) and the resin system (b) contains at least one stabilizer having an average molecular weight in the range of from about 1,000 to about 4,000 selected from the group consisting of ethylene oxide-propylene oxide block copolymers, poly C' s₂C3 alkoxylated C₁₂-C₁₈Saturated or unsaturated fatty alcohols, poly C₂Hydrogenated or partially hydrogenated castor oil alkoxylated at C3, poly C₂-C3 alkoxylated hydrogenated or partially hydrogenated soybean oil, polydimethylsiloxane C₂-C3 alkoxylates and C₁₂-C₁₈At least one of sorbitan esters of saturated or unsaturated fatty acids,

the amount of particles (a) is in the range of 2 to 6% by weight based on the weight of the composition and the amount of stabilizer is in the range of about 50% to about 90% by weight based on the weight of the highly porous particles.

The present invention also provides a method of preparing a coating composition for forming a heat insulating layer, the method comprising the steps of:

(a) a resin system is provided comprising a film forming polymer and at least one stabilizer having an average molecular weight in the range of from about 1,000 to about 4,000 selected from the group consisting of ethylene oxide-propylene oxide block copolymers, poly C₂C3 alkoxylated C₁₂-C₁₈Saturated or unsaturated fatty alcohols, poly C₂Hydrogenated or partially hydrogenated castor oil alkoxylated at C3, poly C₂-C3 alkoxylated hydrogenated or partially hydrogenated soybean oil, polydimethylsiloxane C₂-C3 alkoxylates and C₁₂-C₁₈Sorbitan of saturated or unsaturated fatty acidsAt least one of an alcohol ester, and

(b) adding to the resin system obtained in step (a) highly porous particles of a material obtained by drying a wet sol-gel, said particles having a porosity of at least 80% and a particle size in the range of 5 μm to 4.0mm, and mixing the resulting composition at a low shear rate,

wherein the amount of the particles is in the range of 2 to 6 wt% based on the weight of the composition and the amount of the stabilizer is in the range of about 50% to about 90 wt% based on the weight of the highly porous particles.

(i) Highly porous particles

The highly porous particles used in the composition are made of a material obtained by drying a sol-gel and have a porosity of at least 80% and a particle size in the range of 5 μm to 4.0 mm. The chemistry and preparation of such sol-gel derived materials is well documented in the chemical literature, which discloses various methods of drying the sol-gel and modifying its surface properties.

Highly porous particles suitable for use in the compositions of the present invention include, but are not limited to, aerogel particles prepared by a process of drying a wet sol-gel at supercritical pressure, and xerogel particles prepared by a process of drying a wet sol-gel at a pressure below supercritical pressure. Particles of amorphous silica aerogels or xerogels as well as particles of carbon aerogels or xerogels may be used.

The size of the highly porous particles suitable for use in the present invention is in the range of 5 μm to about 4.0 mm. In one embodiment of the present invention, ultrafine particles having a particle size in the range of 5 μm to 1,200. mu.m, preferably 5 μm to 500. mu.m, more preferably 5 μm to 15 μm are used. In another embodiment of the invention, particles having a size in the range of about 0.5mm to about 4mm are used.

The highly porous particles used in the present invention have a porosity of at least 80%, preferably at least 90%, which is a measure of the proportion of the volume of the particle occupied by air.

The shape of the particles is not particularly limited, and includes irregular shapes as well as smooth and symmetrical shapes.

Highly porous particles typically have small pores with a pore size of no more than 50 μm. In one embodiment of the invention, the particles are characterized by a pore size of about 20 μm.

By virtue of having a high porosity and a small particle size, particles suitable for use in the present invention have a large surface area, for example in the range of 600-800 m²In the range of/g.

The aerogel or xerogel from which the highly porous particles are made may be hydrophobic or hydrophilic. In one embodiment of the invention, the aerogel or xerogel is a non-metal oxide aerogel or xerogel in which the hydrogen atoms of the terminal-OH groups are substituted with non-polar groups that render the aerogel or xerogel hydrophobic. In another preferred embodiment, the aerogel or xerogel is a carbon aerogel or xerogel of an organic compound in which the hydrogen atoms of the terminal-CH groups are substituted with non-polar groups that render the aerogel or xerogel hydrophobic.

Aerogels and xerogels suitable for use in the present invention may be prepared by methods known in the art and are available from commercial suppliers.

(ii) Resin system

Resin systems suitable for use in the coating compositions of the present invention may be aqueous systems or solvent-based systems and contain at least one known film-forming polymer. The chemistry and preparation of suitable film-forming polymers is well known and the polymers are available from a variety of commercial manufacturers. Examples of suitable film-forming polymers include, but are not limited to, acrylic polymers, acrylic styrene copolymers, vinyl acrylic copolymers, epoxy acrylic copolymers, acrylic vinyl acetate copolymers, alkyds, styrene butadiene copolymers, cellulose acetate polymers, and polyester polymers. One of ordinary skill in the art can select the polymer in view of the particular application.

In one aspect of the invention, the resin system is an aqueous emulsion of a film-forming polymer selected from the group consisting of acrylic polymers, acrylic styrene copolymers, vinyl acrylic copolymers, epoxy acrylic copolymers, acrylic vinyl acetate copolymers, styrene butadiene copolymers and cellulose acetate polymers.

In another aspect of the invention, the resin system is solvent-based. Suitable solvents include, but are not limited to, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, acetates, glycol ethers and glycol ether esters. Specific examples are hexane, toluene, xylene, isopropanol, ethyl acetate and diethylene glycol monoethyl ether. One of ordinary skill in the art can select a suitable solvent-based system in view of the particular application.

(iii) Stabilizer

In the case of particles dispersed in the composition of the invention having a very high porosity and a corresponding low density, their maximum loading in the dispersion is rather low. Typically, it is difficult to incorporate particles into the dispersion in excess of 0.1 to 0.5% by weight of the solid content of the dispersion, and in particular, such particles are shear sensitive so mixing at high shear rates will disrupt their structure. In addition, many of these particles, particularly silica, obtained by drying sol-gels are thixotropic, and thus loading the dispersion with 1% by weight, based on the solid content of the dispersion, may raise the viscosity of the dispersion to about 25,000 centipoise, which is unsuitable for coating applications.

In the compositions of the present invention, the above problems are alleviated by the use of a stabilizer that is added to the composition prior to incorporation of the highly porous particles. The stabilizer is selected from ethylene oxide-propylene oxide block copolymer, poly C₂C3 alkoxylated C₁₂-C₁₈Saturated or unsaturated fatty alcohols, polyC₂Alkoxylation of hydrogenated or partially hydrogenated castor oil with C3, poly C₂Alkoxylation of hydrogenated or partially hydrogenated soya oil, polydimethylsiloxane C by C3₂-C3 alkoxylates and C₁₂-C₁₈At least one of sorbitan esters of saturated or unsaturated fatty acids.

The first group of stabilizers, Ethylene Oxide (EO) -Propylene Oxide (PO) block copolymers, described above, are symmetrical copolymers having two EO blocks of the same chain length surrounding the PO block. The ratio of EO and PO in the copolymer can vary. An example of such a copolymer has EO₁₃-PO₃₀-EO₁₃And (5) structure.

The average molecular weight of the stabilizers suitable for use in the present invention is from about 1,000 to about 4,000, preferably from about 2,000 to 3,000.

The total amount of stabilizer used is in the range of about 50% to 90% by weight, preferably 60% to 80%, more preferably 65% to 75%, based on the weight of the highly porous particles.

The chemistry and preparation of stabilizers suitable for use in the present invention are known, and a variety of suitable stabilizers are available from commercial suppliers. Examples of these commercial products are listed in the following table.

Trade mark	Manufacturer(s)	Directory
			PLURONICS	BASF	EO-PO copolymer
TERGITOL	Dow	EO-PO copolymer
			RHODASURF	Rhodia	Polyethoxylated fatty alcohols
ANTAROX	Rhodia	Polyethoxylated fatty alcohols
			CREMOPHOR	BASF	Polyethoxylated (polyethoxylated) castor oil
SILWET	Crompton	Polydimethylsiloxane alkoxides
			TWEEN	Amersham Biosciences	Sorbitan esters of fatty acids

Without being bound to any theory of the mechanism by which the above stabilizers help to stabilize the coating composition, the inventors of the present invention have noted that the effect of the stabilizers may be related to the long aliphatic chains in their molecules and their molecular weight ranges.

(iv) Other additives

The composition may contain other additives known in the art, as may be determined by one of ordinary skill in the art, to improve the "lay flat" properties of the coating and composition. These additives include, but are not limited to: a surfactant; a leveling agent; rheology modifiers such as thickeners; suds suppressors or defoamers; a coalescing agent; a curing agent (in the case where the resin in the composition is not itself cured); and an extender.

The composition may optionally contain whitening pigments. If titanium dioxide (TiO) is used in the composition of the invention₂) It is a common whitening pigment, which must be in the rutile form to prevent chalking of the composition. In one embodiment of the invention, the coating composition contains rutile in an amount of from 5 to 15% by weight, preferably from 10 to 12% by weight, based on the weight of the composition.

The coating composition may contain one or more flame retardants, which may be selected by one of ordinary skill in the art. Examples of flame retardants include, but are not limited to, polymer grade montmorillonite clays or aluminosilicates, chlorinated phosphate esters, and bromoaryl ethers/phosphates.

The coating composition may also contain one or more bactericides, mildewcides, or biocides, which can be selected by one of ordinary skill in the art. Examples of bactericides, mildewcides, and biocides include, but are not limited to, 4, 4-dimethyloxazolidine, 3, 4, 4-trimethyloxazolidine, modified barium metaborate, orthophenylphenol, 2, 4, 5-trichlorophenol, and dehydroacetic acid.

The coating composition may also contain one or more corrosion inhibitors, which may be selected by one of ordinary skill in the art. Examples of corrosion inhibitors include, but are not limited to, mercaptobenzothiazole and salts thereof, and benzothiazole derivatives containing a hydrophobic group.

Further examples of these additives can be found in and selected from the following documents: the raw Materials Index, the National Paint & Coatings Association, 1500Rhode Island Avenue, N.W., Washington, D.C.20005, which is incorporated herein by reference in its entirety.

(iv) Preparation of the composition

According to the present invention, it is necessary to add the highly porous particles to the resin system and gently mix under low shear conditions after the other components of the composition have been blended at higher and moderate to high shear rates. In the most preferred method, the highly porous particles are mixed in a separate container with a stabilizer under very low shear conditions (and if necessary, a very small amount of water to form a uniform paste). Once a homogeneous paste is obtained, it is immediately added slowly with stirring to the blend of the remaining components, characterized by very low shear forces.

In some embodiments of the invention, time can be saved by omitting the separate pre-mixing of the highly porous particles and the stabilizing agent, and slowly adding the highly porous particles to a pre-mix of all other components of the composition, including the stabilizing agent. This simplified approach may be used, for example, when higher amounts of stabilizer are used in the composition.

Whichever method is used, the mixing of very fine, highly porous particles must be carried out in a closed container, since the particles form a fluffy powder that tends to escape into the atmosphere, thus posing a health hazard to the operator and increasing costs due to the waste of valuable materials.

When the optional whitening pigment is used in the coating composition, the pigment is ground to the desired particle size and mixed into the resin system prior to the addition of the highly porous particles.

The present invention provides a method of incorporating into a coating composition a highly porous particle in an amount sufficient to provide good insulation of a coating formed from the composition, and to prevent excessive thickening of the composition during standby.

The compositions of the present invention have a Brookfield viscosity of no greater than about 12,000 centipoise, preferably no greater than about 10,000 centipoise. Thus, the composition can be sprayed and otherwise processed in the same manner as conventional coating compositions.

The compositions of the present invention have excellent storage stability with less than 10% increase in viscosity after 3 months of storage aging. The composition can be applied to the substrate by conventional means, for example by brush, roller or spray. The composition may be applied directly to the substrate or may be applied over a conventional primer layer that is first applied to the substrate. A conventional topcoat may optionally be applied over the layer of the composition of the present invention.

The compositions of the present invention can be used to insulate a variety of substrates, including, but not limited to, roofs, ceilings, walls, containers, tanks, pipes, trucks, boats, barges, and ships.

The following examples further illustrate aspects of the invention. It is to be understood that these embodiments do not limit the present invention, and that various changes may be made by those skilled in the art without changing the essential features and basic concept of the present invention. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight unless otherwise indicated.

Example 1

Clear coating compositions were prepared from the components shown in the table below.

Components	Name (R)	Based on the weight of the composition%
			1	Water (W)	35.24
2	ACRYSOL RM825	0.39
			3	Propylene glycol	0.48
4	BYK 025	0.13
			5	TAMOL 165	0.85
6	ARMOREZ IC2954	46.95
			7	Dibutyl phthalate	0.73
8	Dipropylene glycol n-butyl ether	6.78
			9	AMP-95	0.29
10	ACRYSOL RM8251	0.48
			11	PLURONIC L62	2.90
12	BYK 025	0.23
			13	NANOGEL 07N	4.55

⁽¹⁾Thickening agent (Rohm)& Haas)

⁽²⁾Defoaming agent (BYK Chemie USA)

⁽³⁾Dispersing agent (Rohm)& Haas)

⁽⁴⁾Self-crosslinking epoxy acrylic acid copolymer (MeadWestvaco)

⁽⁵⁾Neutralizer, Co-dispersant (The Dow Chemical Co.)

⁽⁶⁾EO-PO copolymer (BASF)

⁽⁷⁾Silica aerogel (Cabot)

Components 1 and 2 were mixed in a Cowles mixer for 5 minutes. Components 3, 4 and 5 were then added and mixed for 5 minutes, after which components 6-12 were added with mixing just until a homogeneous dispersion was obtained. In the final step, silica aerogel particles (component 13) are slowly added and mixed under cover at a low speed not exceeding 500 rpm/hr. A clear liquid coating composition is obtained.

The insulation properties of coatings prepared from the composition having a thickness of 0.048 inches were measured by ASTM method ASTM C-518. The results shown below show that the coating has outstanding insulation properties.

Thermal conductivity: 0.058Btu/hr ft ℉

R-value of 048/(12x.058) of 0.069hr ft²℉/Btu

t_Average＝170℉

Example 2

White coating compositions were prepared from the components shown in the table below.

Components	Name (R)	Based on the weight of the composition%
			1	Water (W)	2.63
2	Propylene glycol	0.42
			3	BYK 025	0.11
4	TAMOL 731-A	0.74
			5	CR 800TiO(rutile)	13.4
6	ARMOREZ IC2954	39.47
			7	Dibutyl phthalate	0.63
8	Dipropylene glycol n-butyl ether	7.7
			9	AMP-95	0.25
10	PLURONIC L62	2.51
			11	BYK 025	0.20
12	SURFYNOL 104-BC	0.84
			13	Water (W)	2.16
14	NANOGEL TLD201	3.94

⁽¹⁾Defoaming agent (BYK Chemie USA)

⁽²⁾Dispersing agent (Rohm)& Haas)

⁽³⁾Self-crosslinking epoxy acrylic acid copolymer (MeadWestvaco)

⁽⁴⁾Neutralizer, Co-dispersant (The Dow Chemical Co.)

⁽⁵⁾EO-PO copolymer (BASF)

⁽⁶⁾Wetting and defoaming agents (Air Products and Chemicals)

⁽⁷⁾Silica aerogel (Cabot)

The components 1-4 were mixed at low speed for 10 minutes in a vortex mixer. Component 5 (rutile form of TiO)₂Powder) slow rotationMove to a vortex mixer. The mixture was covered and dispersed at high speed to a Hegman 6 consistency. The mixing speed was reduced and components 6-13 were added with continued mixing just until a homogeneous dispersion was obtained. In the final step, silica aerogel particles (component 14) are slowly added and mixed under cover at a low speed of no more than 500 rpm/hr. A white liquid coating composition was obtained. [ viscosity 3,600-]

The insulation properties of coatings prepared from the composition having a thickness of 0.058 inches were measured by ASTM method ASTM C-518. The results shown below show that the coating has outstanding insulation properties.

Thermal conductivity: 0.187Btu/hr ft ℉

R-value of 058/(12x.187) of 0.026hr ft²℉/Btu

t_Average＝180℉

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims (25)

1. A curable coating composition for forming a thermal insulating layer, wherein the composition comprises:

(a) highly porous particles of a material obtained by drying a wet sol-gel, said particles having a porosity of at least 80% and a particle size in the range of 5 μm to 4.0 mm; and

(b) a film-forming resin system comprising a film-forming polymer,

wherein the particles (a) are dispersed in a resin system (b) and the resin system (b) contains at least one stabilizer having an average molecular weight in the range of 1,000 to 4,000An agent selected from the group consisting of ethylene oxide-propylene oxide block copolymers, poly C₂C3 alkoxylated C₁₂-C₁₈Saturated or unsaturated fatty alcohols, poly C₂Hydrogenated or partially hydrogenated castor oil alkoxylated at C3, poly C₂-C3 alkoxylated hydrogenated or partially hydrogenated soybean oil, polydimethylsiloxane C₂-C3 alkoxylates and C₁₂-C₁₈At least one of sorbitan esters of saturated or unsaturated fatty acids,

the amount of the particles (a) is in the range of 2 to 6% by weight based on the weight of the composition, and the amount of the stabilizer is in the range of 50 to 90% by weight based on the weight of the highly porous particles.

2. The composition according to claim 1, wherein the particles are at least one selected from the group consisting of aerogel particles prepared by a process in which a wet sol-gel is dried under a supercritical pressure and xerogel particles prepared by a process in which a wet sol-gel is dried under a pressure lower than the supercritical pressure.

3. A composition according to claim 1, wherein the particles have a particle size in the range of from 5 μm to 15 μm.

4. The composition according to claim 1, wherein the particles have a particle size in the range of 5 μm to 500 μm.

5. The composition according to claim 1, wherein the particles have a particle size in the range of 5 μm to 1,200 μm.

6. A composition according to claim 1, wherein the particles have a particle size in the range of from 0.5mm to 4.0 mm.

7. The composition of claim 1, wherein the particles have a porosity of at least 90%.

8. The composition according to claim 1, wherein the particles are amorphous silica aerogel particles.

9. A composition according to claim 1, wherein the particles are amorphous silica xerogel particles.

10. The composition according to claim 1, wherein said particles are carbon aerogel particles.

11. A composition according to claim 1, wherein the particles are carbon xerogel particles.

12. The composition according to claim 1, wherein the resin system is aqueous.

13. A composition according to claim 12, wherein the particles are hydrophobic.

14. The composition according to claim 1, wherein the resin system is solvent-based.

15. A composition according to claim 14, wherein the particles are hydrophilic.

16. The composition according to claim 1, wherein the film-forming polymer is selected from the group consisting of acrylic polymers, acrylic styrene copolymers, vinyl acrylic copolymers, epoxy acrylic copolymers, acrylic vinyl acetate copolymers, alkyds, styrene butadiene copolymers, cellulose acetate polymers and polyester polymers.

17. The composition according to claim 12, wherein the resin system is an aqueous emulsion of a film-forming polymer selected from the group consisting of acrylic polymers, acrylic styrene copolymers, vinyl acrylic copolymers, epoxy acrylic copolymers, acrylic vinyl acetate copolymers, styrene butadiene copolymers and cellulose acetate polymers.

18. The composition according to claim 1, further comprising rutile in an amount of 5 to 15% by weight based on the weight of the composition.

19. The composition of claim 1, further comprising a flame retardant.

20. A method of forming a thermal insulating layer on a substrate, the method comprising the step of applying the composition of claim 1 to the substrate.

21. A method of preparing a coating composition for forming a thermal insulation layer, the method comprising the steps of:

(a) a resin system is provided comprising a film forming polymer and at least one stabilizer having an average molecular weight in the range of 1,000 to 4,000 selected from the group consisting of ethylene oxide-propylene oxide block copolymers, poly C₂C3 alkoxylated C₁₂-C₁₈Saturated or unsaturated fatty alcohols, poly C₂Hydrogenated or partially hydrogenated castor oil alkoxylated at C3, poly C₂-C3 alkoxylated hydrogenated or partially hydrogenated soybean oil, polydimethylsiloxane C₂-C3 alkoxylates and C₁₂-C₁₈At least one of sorbitan esters of saturated or unsaturated fatty acids, and

(b) adding to the resin system obtained in step (a) highly porous particles of a material obtained by drying a wet sol-gel, said particles having a porosity of at least 80% and a particle size in the range of 5 μm to 4.0mm, and mixing the resulting composition at a low shear rate,

wherein the amount of the particles is in the range of 2 to 6 wt% based on the weight of the composition and the amount of the stabilizer is in the range of 50 to 90 wt% based on the weight of the highly porous particles.

22. A method according to claim 21, wherein the highly porous particles are premixed slowly and under low shear with a stabilizer and, if desired, water in an amount sufficient to obtain a homogeneous paste, and the obtained paste is added to the resin system.

23. The method according to claim 21, wherein a whitening agent is mixed with the resin system prior to step (b).

24. The method of claim 21, wherein the particles have a porosity of at least 90%.

25. The method of claim 21, wherein the particles are silica aerogel particles.