IL110683A - Paint compositions for high infra-red reflectivity with a low gloss property while controlling the colour in the visible range - Google Patents

Description

Paint compositions for high infra-red reflectivity with a low gloss property while controlling the colour in the visible range. o-nK-KHDiPK amro nm:n. ΓΠΤΠΠ yas 'TWDH / The present invention relates to paint compositions for high infra-red reflectivity. More particularly, the invention relates to paint compositions useful for the thermal infra-red region and maintaining a low gloss property.

BACKGROUND OF THE INVENTION.

Paints are generally defined as liquids, or pastes comprising a suspension of a pigment in oil or water.

As known, thermal infra-red region of the electromagnetic spectrum refers to waves whose wavelength exists roughly between 3 to 14 micrometers. Applications of thermal infra-red radiation exist in many systems and sub-systems for household applications, such as: radiative cooling or heating; for industrial uses, such as: solar collectors, heat exchangers; for military purposes, such as: homing devices, surveillance,night vision devices and camouflage devices , etc Almost all the paints known in the art include in addition to pigments, a solvent system which comprises volatile liquids added in order to dissolve the paints components. The three main constituents of paints are: (a) Pigments, having the function to give the paint the opacity, colour and added durability. (b) Binders, which impart film forming properties and . fulfill the optical requirements at visible light. (c) Fillers also known as extenders, which have the property to aid in protecting the paint from weathering of the dyes and also to reduce the gloss of a paint.

There are cases when it is most desirable that the layer of the film resulted from a binder, should possess a low gloss property, which is generally achieved by adding a filler material, such as calcium carbonate, silicate, colloidal silica, etc. These filler materials are actually used in most of the cases where no particular requirements on their absorption in the infra-red range is imposed. However, in case of films produced by paints which posses a high reflectance in the thermal infra-red range of 3 to 12 micrometers, these materials are not suitable.

In our prior Israeli Patent Application Number 092550, there were described paint compositions useful for high reflective means, which provide a colour in the visible range and high reflectivity in the range of 3 to 14 jjm. The compositions were characterized by the presence of a suitable carrier, selected from thermosetting or thermoplastic compounds such as epoxy, acrylic, silicone, polyvinyl chloride, etc.

Paints comprising aluminum metal are widely used for various purposes due to particular properties thereof. One important property, known as non-leafing is its wettability which enables its dispersion throughout a paint film. Paints containing aluminum paste, or zinc paste having a low infra-red emittance useful as anti-corrosion coatings are claimed in the U.S. Patent Number 4,356,036 Low infra-red emlssivity paints based on the presence of two or more metals are also known. Thus according to the U.S. Patent Number 4,131,593, mixtures comprising tantalum pentoxide, cadmium titanate and barium titanate are suggested as pigments to be used for low infra-red emlssivity paints. The emlssivity mentioned is close to zero in the visible range, but over 0.9 at 8um the paints are characterized by a high gloss. no, _ 4 _ Compositions for producing low infra-red coating in the range of 2 to 15 microns, are claimed in the U.S. Patent Number 4,289,677. The compositions comprise coarse non-leafing aluminum powder, in the orde of 100 mesh, cobalt metal, cobalt oxide, titanium oxide in a medium of silicone alkyd resin and a mineral spirit thinner as. One of the · d i sad vantages of the aluminum powder is the fact that each particle is coated by a thin polar oxide film which is quite hydrophilic in its nature and tends tc adhere to polar groups and inorganic salts present in the compositions. Also, this patent does not refer at all to the gloss requirement for such compositions.

It is an object of the present invention to provide paint compositions which possess an increased reflectivity in the thermal infra-red region. It is another object of the present invention to provide paint compositions which possess an increased reflectivity in the thermal infrared region while' controlling the colour in the visible i range and are maintaining a low gloss. - 4a - 110,683/2 In the Israeli Patent number 56485, it is described a paint composition for the spectrally selective coating of metal surfaces, comprising a pigment and a binder, said pigment comprising at least one metal oxide in a powder form having a good transparency for heat radiation. The binder after conditioning as described in the specification is holding the pigment in place on a metal surface, such that a layer of the paint composition, after having been applied to the metal surface and conditioned, gives such metal surface at least a medium selectivity.

It is an object of the present invention to provide paint compositions which possess an increased reflectivity in the thermal infra-red region. It is another object of the present invention to provide paint composition which possess an increased reflectivity in the thermal infrared region, while controlling the colour in the visible range and are maintaining a low gloss.

BRIEF DESCRIPTION OF THE INVENTION The invention relates to paint compositions, which impart an increase in the reflectivity at the thermal infra-red 5 1 10 , 683 / 2 region , while controlling the colour in the visible range and are maintaining a low gloss which comprise: (a) a binder selected from resins or copolymers such as, alkyds, polyurethanes, vinyl and epoxy compounds, silicones, acrylic resins and mixtures thereof; ( ) an extender selected from polyolefins, substituted polyolefins and fluorinated polyolefins, (c ) a pigment selected from a metal oxide calcined at a temperature of above 600 degrees C and a non-leafing paste of a metal flakes or any mixture thereof, and ( d) an organic solvent to dissolve the components in the paint compositions.

The most preferred pigments are those where the non-leafing paste contains flakes or a metal selected from aluminum, nickel , copper and zinc, whose particle size are smaller than 220 mesh.

The invention is based on the discovery that when the above constituents are utilized as a paint composition, even in a one layer system, the reflectivity achieved is substantially increased.

According to a preferred embodiment, the weight ratio percentage of a polyolefin to a binder is between 0.03 to 0.3 and the ratio of a polyolefin to the metallic pigment is between 0.05 to 0.5.

DETAILED DESCRIPTION OF THE INVENTION.

In contrast to the prior art, which in order to achieve an increased reflectivity, a particular substrate possessing a high reflectivity property has to be used , according to the present invention the nature of the substrate is immaterial. It was found that contrary to some prior references which are suggesting paints based on a metal powder in a certain range of particles size, the compositions suggested according to the present invention are in the form of a paste containing a volatile hydrocarbon, such as a mineral spirit, in an amount of at least 20%. In this manner, the metal particles are protected against oxidation ,their surface area will be more hydrophobic and thus will bond to different groups of the constituents in the composition. As a result, the optical and radiometric reflectances imparted by the flakes are substantially increased. However, in case of aluminum powder, each particle in the flake is coated by a thin porous oxide film, which is quite hydrophilic in its nature and tends to adhere to polar groups and inorganic salts which are present in the composition. The consequence of this matter is that the gloss and infra-red emissivity will be substantially reduced.

It was found according to the present invention, that the metal oxide used in the pigment composition, should be calcined at a temperature of at least 600°C, in order to impart a high reflectivity to the paint composition. It seems that the calcination of above 600 degrees C, produces a solid solution which is transparent in the thermal infra-red region and thus will impart to the paint a film possessing a high reflection in that region. On the other hand, when the calcination of the metal oxide is carried out at a temperature below 600 degrees C, the paints obtained with the respective pigment are not transparent in the thermal infra-red region.

The metal to be used may be selected from cobalt, aluminum, nickel, copper, and magnesium or a mixture thereof, the preferred one being that according to the respective colour required.

The paints according to the present invention contain the following main components: pigment, binder, extender and an organic solvent system. Other auxiliary additives which may be present, will be selected from thickeners, plasticizers, dryers, surface active agents, fungicides, biocides, fire retardants etc.

The binders, may be selected from polymeric resins or polymer precursors which are capable to provide film-forming properties, although inorganic substances or ceramic may also be utilized. Generally, the amount of the binder present in the paint compositions, according to the - 8 - present invention will be in the range of between 10% to 45% by weight.

The pigments dispersed in the paint compositions imparting the high reflectivity, may be selected from two main types: metal oxides calcined at a temperature of above 600°C and non-leafing metallic flakes.

The best results are achieved when the metal oxides are transparent in the infra-red radiation and possess a particles size below 325 mesh. Generally the amount of of this component is between 25% to 45% by weight of the composition.

The non-leafing metallic flakes, are in the form of a paste in a mineral spirit or another volatile hydrocarbon, to afford a high reflectivity. The preferred metals in said flakes are selected from aluminum, nickel, copper and zinc whose particles size are smaller than 220 mesh. The paste imparts to the flakes particular characteristic surface properties and protects said surface against oxidation.

The preferred amount of the non-leafing paste should be in the range of between 12% to 35% by weight of the composition.

The pigments impart to the paint the optical properties and sometimes also opacity , durability, corrosion protection and mechanical strength. Extenders, are paint additives which are incorporated in the paint in order to modify certain properties, such as gloss, flow, levelling, permeability and mechanical characteristics. The most preferred extenders useful for the present compositions are polyolefins, substituted polyolefins and fluorinated polyolefins. Generally, the amount of the extender will be in the range of between 2% to 8% by weight..

The ratio between the binder and the powder content in the composition, i.e. pigment and extender, will determine the contrast ratio and gloss; a composition with a low binder content and a high pigment content, will result in a composition with a low gloss.

Another component in the paint composition is the organic solvent system, added in order to dissolve the components of the paint. Generally, the amount of solvent is in the range of between 13% to 30% by weight. Also, the concentration of the solvent determines the viscosity of the entire composition. - 10 - Other additives which optionally may be incorporated, are selected from anti-setting, dryers and anti-floating reagents as known in the art. Generally the amount of these additives are in the range of between 5% to 12% by weight of the composition.

The reflectivity in the infra-red can be adjusted according to a specific requirement. Generally, the reflectivity will be in the range of between 0.1 to 0.7.

The paint compositions according to the present invention are useful for a broad range of industrial applications, agricultural uses, military uses and residential uses. The invention will be hereafter illustrated by a number of Examples being understood that these Examples are presented only for a better understanding of the invention without limiting its scope as covered by the appended Claims.

In the Examples the amount mentioned and concentrations are by weight, unless otherwise stated. - 11 - EXAMPLE 1.

A paint composition was prepared from the following components: 40 g of a medium oil soya bean alkyd NVC 55%; 17 g of a non-leafing aluminum paste; 15 g of polyethylene, as extender; 10 g of xylene, as solvent medium; 3 g of an organo-metal lie dryer, and 0. 5 g of anionic wetting agent.

The reflectivities in the thermal infra-red region were as follows: - 0.47 for the range of betwwen 3 to 5 urn, and - 0.33 for the range of between 8 to 12 μπι.

A comparative experiment was carried out using the same amounts of components, but instead of the polyethylene as extender, 15 g of talc were used. The reflectivity in this case was as follows: r- 0.41 for the range of between 3 to 5 urn, and - 0.27 for the range of between 8 to 12 pm. - 12 - EXAMPLE 2.

A paint composition was prepared using the components and the amounts as in Example 1, but to the aluminum paste an amount of 17 g of a black calcined pigment, was added. The reflectivity in the thermal infra-red region was as f ol lows : - 0.39 for the range of between 3 to 5 urn, and - 0.31 for the range of between 8 to 12 urn.

A comparative experiment was carried out, without adding the aluminum paste, and the reflectivity in this case was as follows: - 0.12 for the range of between 3 to 5 jjm, and - 0.08 for the range of between 8 to 12 jjm.

The beneficial effect of an increased infra-red reflectivity imparted by the incorporation of the aluminum paste is evident.

EXAMPLE 3.

A paint composition was prepared using the same components and amounts as in Example 1, but it was added also 30 g of black carbon calcined at a temperature of about 900°C. - 13 - The reflectivity in the range of 3 to 5 um and gloss were as follows : reflectivity gloss 0.39 3 A comparative experiment was carried out, wherein instead of the black carbon calcined at 900°C, an amount of 3 g of common black carbon was added.

The reflectivity in the range of 3 to 5 um and gloss were as follows: reflectivity gloss 0.27 5 EXAMPLE 4.

A paint composition was prepared as in Example 3 using the same components and amounts, but adding also 17 g of non-rleafing aluminum paste.

The reflectivity in the thermal infra-red region and gloss were as folows: reflectivity gloss 3-5 um 0.39 3 8-12 pm 0.31 A comparative experiment was carried out, without adding the non-leafing aluminum paste and instead of 8 g of - 14 - polyethylene as extender, an amount of 8 g of talc was added.

The reflectivity in the thermal infra-red region and gloss were as follows: ■.·*'■' reflectivity gloss 3-5 um 0.08 30 8-12 um 0.09 The synergistic effect resulted by the presence of the non-leafing aluminum paste and the polyolefin extender is evident.

Claims (11)

- 15 - 110,683/3

1. C L A I M S :- 1. Paint compositions which impart an increase .in the reflectivity at the thermal infra-red region, while controlling the colour in the visible range and are maintaining a low gloss, which comprise: (a) a binder selected from resins or copolymers such as alkyds, polyurethanes, vinyl ic and epoxy compounds, silicones, acrylic resins and mixtures thereof; (b) an extender selected from polyolefins and substituted polyolefins; (c) a pigment selected from a metal oxide calcined at a temperature of above 600°C and a paste of metal flakes or any mixture thereof, and d) an organic solvent system to dissolve the components in the paint composition.

2. The paint compositions according to Claim 1, wherein the metal in said flakes is selected from aluminum, zinc and n ckel .

3. The paint compositions according to Claim 2, wherein the particles size of said metal flakes is smaller than 220 mesh. - 16 -

4. The paint compositions according to Claims 1 to 3, wherein said solvent contains a volatile hydrocarbon.

5. The paint compositions according to Claims 1 to 4, wherein the amount of non-leafing paste is in the range of between 12% to 35% by weight of the composition.

6. The paint compositions according to Claim 1, wherein the metal oxide, is an oxide of a metal selected from the group consisting of cobalt, aluminum, nickel, copper, and magnesium or any mixture thereof,

7. The paint compositions according to Claim 6, wherein said metal oxides are transparent in the infra-red radiation and their particles size are below 325 mesh.

8. The paint compositions according to Claims 6 and 7, wherein the amount of the metal oxide is in the range of between 25% to 45% by weight of the composition.

9. The paint compositions according to Claims 1 to 8, wherein the amount of binder is in the range of between 10% to 45% by weight of the composition. ,

10. The paint compositions according to Claims 1 to 10, wherein the amount of the extender is in the range of between 2% to 8% by weight of the composition. - 17 -

11. The paint compositions according to Claims 1 to 10, wherein the amount of solvent is in the range of between 12% to 30¾ by weight of the composition. 12, Paint compositions which impart an increase in the reflectivity at the thermal infra-red region, substantially as described in the specification and in any one of Claims 1 to 11. For the Applicants, Patent Attorney