WO2012101306A1

WO2012101306A1 - Formulation comprising silicon microparticles, as a pigment that can absorb visible uv radiation and reflect ir radiation

Info

Publication number: WO2012101306A1
Application number: PCT/ES2012/070034
Authority: WO
Inventors: Marie Isabelle RODRÍGUEZ; Roberto Fenollosa Esteve; Francisco Javier Meseguer Rico; Alberto Gonzalo PÉREZ-ROLDÁN TACUMI
Original assignee: Consejo Superior De Investigaciones Científicas (Csic); Universidad Politécnica De Valencia; Ona Investigación, S.L.
Priority date: 2011-01-25
Filing date: 2012-01-24
Publication date: 2012-08-02
Also published as: WO2012101306A4; ES2386126A1; ES2386126B1

Abstract

The invention relates to a formulation characterised in that it comprises silicon microparticles having a size between 0.010 µm and 50 µm in diameter, and to the use thereof as a pigment that can absorb visible UV radiation and reflect IR radiation.

Description

Formulation comprising silicon microparticles as a pigment absorbing UV-visible radiation and

IR radiation reflective

Field of the Invention

The present invention refers to sunscreen radiation protective preparations, effective against UV-visible radiation, as well as IR thermal radiation.

State of the art prior to the invention

The solar radiation that reaches the surface of the earth after an important part has been absorbed by the atmosphere, covers a range of wavelengths between 295 nm and 2500 nm. According to the energy of the photons that are involved, three main areas in the spectrum are distinguished: the ultraviolet zone (295-400 nm), the visible zone (400-700nm) and the infrared zone (700-2500nm).

The visible zone represents approximately 50% of the energy emitted by sunlight, 45% corresponds to the IR range. Although only the remaining 5% of the energy is in the form of ultraviolet photons, these are energetic enough to break numerous chemical bonds of organic materials, mainly composed of carbon-hydrogen bonds, such as wood, plastics, and even asphalt, and produce its deterioration

On the other hand, infrared radiation results in heating of exposed surfaces. Specifically, the absorption of the rays of wavelengths between 700nm and llOOnm (near infrared) results in an increase in temperature. This heating tends to favor the chemical reactions that lead to deterioration, loss of volume or softening of the materials. In addition, continuous changes in temperature of greater or lesser amplitude can even cause the material to rupture due to the stresses to which they are subjected. Apart from the degradation of the elements exposed to thermal radiation (such as plastics, wood, cement ...), the increase in temperature induces an increase in energy costs and consumption in buildings and homes

(such as vehicles) exposed to solar radiation. In urban areas, the irradiation of heat absorbed by the walls and roofs of buildings causes an increase in the temperature of the outside air. The use of paints, varnishes and coatings with reflective properties of infrared thermal radiation can minimize these inconveniences. They incorporate in their composition inorganic particles that do not absorb but reflect (or otherwise transmit) the radiation in the near infrared range. Therefore, the mechanism is different from that of insulating ceramics or polymeric laminar structures that are characterized by their weak thermal conductivity. These are materials with higher refractive indices than the medium in which they are dispersed in that area of the electromagnetic spectrum, which causes a diffuse reflection of the IR. In general, they are usually metal oxides

(for example, in the paint described in US2005 / 0215685) that sometimes metal particles or alloys can be incorporated forming a crystalline structure of the corundum-hematite type (US6616744).

They give the preparations mechanical stability, opacity and generally a dark color. However, to achieve light colors in paints and / or coatings, titanium dioxide (Ti0 ₂ ) is frequently used, although its effectiveness as a reflector of IR thermal radiation is minimal. However, patent GB2453343 proposes incorporating white alumina (in particular, white corundum) in the paint composition, in order to obtain at the same time infrared reflectivity characteristics close to those of metal or alloy particles, at the same time as a light color.

There is a whole range of inorganic crystalline compounds (many of them already used in the ceramic industry) that in addition to having good qualities such as Pigment providing color, also have near IR reflective properties. Bendiganavale et al. in "Recents Patents on Chemicals Engineering" they have evaluated the reflectivity of several of these commercial pigments. Color can also be provided by coating white pigments (TIO ₂ , Zn) with organic dye molecules, obtaining dispersions of IR radiation reflective elements.

(for the inorganic component) as described by Yanagimoto et al. (US20036521038) or flakes of conductive oxides or metals coated with a transparent or colored layer that gives them mechanical or chemical stability

(O'Keefe Eoin, US7455904B2). Even in the case of aluminum and mica flakes in which the color has been incorporated into the metal surface, military camouflage applications may be presented (Sutter Christopher et al., US6468647).

Some metals or semiconductors that have high infrared reflectivity are transparent to visible light, but only in the form of a very thin sheet, which can only be used in window coverings. As an alternative to gold, high cost, or non-noble metals that lack stability against corrosion, thin semiconductor films such as cadmium stannate (Cd ₂ Sn0 ₄ ) doped or not doped with copper are used

(Haacke Gottfried, US3998752) or binary compounds such as copper, silver, nickel or tin sulfide (Bulletin of the National Autonomous University of Mexico UNAM-DGCS-014, "They develop solar filters for buildings in UNAN").

However, in the case of metals, another approach used in obtaining thermal radiation reflective compounds for incorporation in paints and coatings formulations is to deposit a thin uniform metallic layer (silver in general) on the surface of the microspheres (filled or hollow) of glass (such as those marketed by the company Sherperd Color Co.) or coated glass flakes such as those patented by Merck GmbH (Anselman Ralf et al. US7226503), although the Main application is rather for aesthetic purposes, since they produce a glowing effect in sunlight. However, the combination of hollow microspheres (glass, ceramics, polymers) with pigments reflecting IR radiation decreases thermal conductivity and increases IR reflectivity in preparations (Shelhorn, Anthony D., US20050126441).

Another motivation for the development of pigments capable of reflecting infrared radiation is its application in paints and coatings that protect the material from the heat that is released from the fire, a fundamental factor also to prevent its spread. In most cases, white or light coatings are used using titanium dioxide (Ti0 ₂ ) as pigment. In US5811180, Berdahl P. proposes as reflective pigments of infrared radiation emitting fire, highly reflective aluminum (or other metal) flakes, or mica flakes coated with a layer of suitable thickness of a high index material. refraction such as Fe ₂ 03, T1O ₂ (anatase and rutile), Cr ₂ 03, ZnS, Sb ₂ 03, Zr0 ₂ or ZnO. Some calculations show that particle size (1-2 microns) reverses a crucial importance in efficiency in reflecting infrared radiation.

The present invention proposes the use of metallic silicon powder with microparticles of the appropriate size for application as an IR radiation reflecting pigment in the preparation of paints, varnishes and thermal protective coatings. Such preparations also absorb UV-visible radiation (intrinsic property of silicon), providing, at low cost, protection of any surface over a wide range of electromagnetic radiation.

Description of the invention

The present invention relates, first of all, to a formulation characterized in that it comprises silicon microparticles with a size between 0.010 and m and 50 and m, preferably between 0.1 and m and 50 and m in diameter, more preferably, between 0.1 and 20 and 20 and even more preferably between 1 and 20 and 20.

For the purposes of this patent, microparticles, particles of varied shapes and micrometer size, preferably between 0.010 and m and 50 and m, and more preferably between 0.1 and 50 and m in diameter are understood. Said silicon microparticles are characterized by having a high refractive index (n = 3.5).

Preferably, the percentage of said silicon microparticles in the formulation is preferably comprised between 0.1% and 30% by weight, more preferably 0.1% and 10% by weight and more preferably, between a 0.8% and 5% by weight.

In a particular embodiment of the invention, said microparticles can be obtained from silicon powder, preferably, by a grinding and sieving process, preferably, wet, to obtain particle sizes between 0.010 and m and 50 and m, preferably between 0.1 and m and 50 and m in diameter, more preferably, between 0.1 and 20 and 20 and even more preferably between 1 and 20 and 20. Additionally, prior to incorporation into the formulation, they may have undergone a surface modification treatment, such as an increase in hydrophilicity, or the anchoring of some pigment providing color. Thus, for example, it is possible to add anilines, to give color, or siloxane bonds to give hydrophilicity to the particles.

Thus, in a particular embodiment of the invention, the described formulation may also comprise at least one additional component active against IR radiation and UV-visible radiation, said component being preferably selected from conventional pigments.

It is also the object of this invention to use said formulation as a pigment absorbing UV-visible radiation and reflecting IR radiation, in a range of wavelengths between 0.7 and 180 mm. In a particular embodiment of the invention, said IR radiation may consist of near IR radiation or thermal radiation, between wavelengths of 0.7 ym to 3 ym, preferably 0.7 ym to 1.1 ym. In another particular embodiment of the invention, said IR radiation may consist of thermal radiation emitted by fire, in the range of 1 ym to 20 ym, and more particularly in the range of 1 ym to 8 ym.

Thus, it is a further object of the invention, the use of said formulation in preparations for the protection of surfaces against solar radiation, and more specifically, against thermal IR radiation and UV-visible radiation. It is, therefore, a further object of the invention a coating comprising as active principle the described formulation, said formulation being characterized in that it comprises silicon microparticles of high refractive index and with a size between 0.010 and m and 50 and m in diameter , preferably between 0.1 and 50 ym. Thus, the use of the described formulation for the preparation of heat-protective compositions emitted by solar radiation or fire is object of this invention.

Preferably, it is an object of the invention to use said formulation as a pigment reflecting IR radiation, preferably in the form of paints, varnishes, lacquers, putty, cements, ceramic frits, enamels, polymeric or textile films, etc. ..

Protected surfaces can be elements of buildings such as roofs, walls, pavements, windows, doors, as well as elements in plastic, wood and metal surfaces such as the interiors of civil or military vehicles, etc.

For the preparation of paints, varnishes, coatings, etc., IR and UV-visible radiation protectors, the usual formulations of said products can be used, incorporating silicon microparticles of the appropriate size. The paints may preferably be plastic with resins vinyl or acrylic emulsified in water, or fatty paints composed of resins in oil.

In a particular embodiment in which the formulation is used in preparations for the protection of heat from fire, the silicon microparticles can act as pigments reflecting the thermal radiation emitted by the fire in the range between 1 and 20 and 20, and more preferably between 1 and 8 ym.

Also, in a further particular embodiment in which the formulation is used in paint preparations, coatings, etc. intumescent, protective of thermal radiation emitted by fire, the usual formulations of these products can be used, but incorporating silicon microparticles of the appropriate size as active pigment, or in combination with chemical fire retardants, such as those described in R.I. Ensminger (Pigment Handbook, vol. II, Temple C. Patton, John Wiley & Sons, 1988).

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For a person skilled in the art, other objects, advantages and features of the invention will be derived partly from the description, and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and not by way of limitation of the present invention.

Description of the figures

Figure 1 shows the diameter distribution (centered at 1 millimeter) of the silicon powder particles used in example 1 and example 2.

Figure 2 shows an effective Mié scattering section, calculated according to the particle diameter distribution of Figure 1, and considering a spherical shape of the particles. Figure 3 shows the diameter distribution (centered on 2.5 microns) of the silicon powder particles used in example 3 and example 4.

Figure 4 shows an effective Mié scattering section, calculated according to the particle diameter distribution of Figure 3, and considering a spherical shape of the particles.

Figure 5 shows a comparison between optical transmission spectra obtained in the near IR range of samples prepared in the form of an oil / water emulsion (O / W), with silicon microparticles (0.8% by weight with the size distribution of figure 1). Likewise, a sample prepared according to the same procedure with 0.8% by weight of titania particles (T1O ₂ , P-25 Degussa) on glass substrates (11 mg / cm ² ) is presented.

Figure 6 shows a comparison between optical transmission spectra obtained in the near IR range of samples prepared in the form of PVA film (Polyvinyl alcohol, 98% hydrolyzed), and a PVA film with embedded silicon microparticles (2% in weight with the size distribution of figure 1).

Figure 7 shows a comparison between optical transmission spectra obtained in the near IR range of a commercial white paint sample, and a sample with the same commercial white paint with embedded silicon microparticles (2% by weight with the size distribution of figure 3).

Figure 8 shows a comparison between optical transmission spectra obtained in the near IR range of a sample of a commercial varnish, and a sample with the same commercial varnish incorporating silicon microparticles in different percentages (2% and 5% by weight, with the size distribution of figure 3).

Optical transmission measurements are presented, as well as experiments measuring the reflectivity of the preparations. Examples

The present invention is illustrated below by means of different tests, which show the specificity and effectiveness of silicon microparticles as a pigment reflecting the thermal radiation of the near IR. Through these examples, the optical properties of various preparations are presented incorporating silicon microparticles of different average sizes. Infrared optical transmittance measurements have been performed using Fourier transform spectroscopy (FTIR).

The optical measurements presented have been made on thin layers of the different preparations containing the particles of silicon pigments, of identical thickness, on glass substrates, or loose.

The amounts of preparation applied on the substrates vary between 2 and 11 mg / cm ² .

The silicon microparticles used were obtained by treatment of dust (or "fines") of purified silicon of particle size smaller than 100 ym (Ferroatlantica, SA). The powder was subjected to grinding to obtain particles as loose as possible and smaller sizes, in order to optimize the performance in the next wet sieving process. In the following examples, silicon particles of average size of 1 and m (figure 1) and 2.5 ym (figure 3) were collected. If the particles are assimilated into spheres, the average Wed scattering section to which they give rise in the near infrared and which is responsible for shielding the solar infrared radiation can be calculated. Figure 1 shows the diameter distribution (centered at 1 m) of the silicon powder particles used in example 1 and example 2 and Figure 3 shows the diameter distribution (centered at 2.5 microns) of the Silicon powder particles used in example 3 and example 4. Figures 2 and 4 illustrate this scattering for particles of size 1 mm and 2.5 mm respectively. Specifically, Figure 2 shows an effective Mié scattering section, calculated according to the particle diameter distribution of Figure 1, and considering a spherical shape of the particles. Similarly, Figure 4 shows an effective Mié scattering section, calculated according to the particle diameter distribution of Figure 3, and considering a spherical shape of the particles.

The average chemical analysis of the silicon particles used is as follows:

Table 1 shows the amounts of impurities in ppm of the starting silicon powder particles used.

Example 1

This example shows the optical properties of an oil-in-water (O / W) emulsion with silicon particles as a pigment reflecting infrared thermal radiation in the range between 850 nm and 3 microns. The results of the optical transmissions of the preparation on glass plates are shown, which are compared with those of an identical preparation but incorporating particles of titania.

Preparation of the oil-in-water emulsion (O / W) 0.3% by weight of methylcellulose is dissolved in water at 70 ° C, with stirring. Once a homogeneous solution is obtained, 4% by weight of self-emulsifiable glyceryl monostearate is added, maintaining stirring.

Silicon particles with the size distribution according to the curve of Figure 1, obtained after a process of grinding and sieving silicon powder, were added to the preparation under strong stirring. mechanical (3000 rpm). 0.8% by weight with respect to the total weight of the emulsion was used.

After 20 minutes, mineral oil was added gradually (between 20-30% by weight with respect to the total weight) while maintaining vigorous stirring for an additional 15 minutes.

Optical measurements in the infrared range

For optical measurements, 11 mg / cm ² of preparation is spread evenly on a glass object holder.

Samples prepared in the form of an emulsion (O / W), containing 0.8% by weight of silicon microparticles of the present invention, were analyzed optically by infrared spectroscopy, in the range between 0.85 and m and 3 and m , considering the glass substrate as a reference. Very good attenuation of thermal infrared radiation (near infrared) is observed, obtaining optical transmission values varying between 4% and 10% over the measured range (see figure 5).

By comparison, a sample was prepared according to the same preparation and characterization procedure as detailed in example 1, but replacing the silicon microparticles with titania microparticles (TIO ₂ , P-25 Degussa), that is, with the same weight percentage as silicon microparticles. They are shown in the experimental results of optical transmission obtained.

Figure 5 compares the results of optical transmission measured in the near IR range between 0.85 and 3 and 3 m, of samples prepared in the form of an oil / water emulsion (11 mg / cm ² on glass), containing particles of silicon (0.8% by weight with the size distribution of Figure 1), with an identical emulsion prepared with titania particles (T1O ₂ , P-25 Degussa) in the same percentage by weight (0.8%) than that of silicon particles and with the same thickness on glass substrates (llmg / cm ² ). It is observed how the emulsion with silicon particles produces a greater attenuation of the infrared radiation than the emulsion with titania particles.

Example 2

This example describes the preparation of a polymeric film containing silicon microparticles as an infrared reflective pigment, and its properties in the near infrared range between 0.85 and m and 4 and m. The results of the optical transmissions of a film with and without incorporated silicon particles are shown.

Preparation of polyvinyl alcohol (PVA) film

30 mg of polyvinyl alcohol (98% hydrolyzed) are dissolved in 3 ml of distilled water. The solution is poured into a plastic box of dimensions 32x32x7 mm, and allowed to dry at 70 ° C, before peeling off the uniform PVA film that forms.

Preparation of the PVA film with silicon particles 30 mg of polyvinyl alcohol (98% hydrolyzed) are dissolved in 3 ml of distilled water. 2% by weight of medium-sized silicon particles centered at 1 and m are then added under stirring according to the distribution shown in the curve of Figure 1 and obtained after a silicon powder milling and sieving process whose chemical composition is shown in table 1.

The solution is poured into a plastic box of dimensions 32x32x7 mm, and allowed to dry at 70 ° C before peeling off the uniform film that forms brown.

Optical measurements in the infrared range

Both the sample in the form of PVA film and the PVA film with 2% by weight of silicon particles and IR reflective pigments were optically analyzed. The measurements were made by infrared spectroscopy in the range between 0.85 and m and 4 and m, considering air as a reference. Figure 6 compares the results of optical transmission in the near infrared range of the sample in the form of PVA film (Polyvinyl alcohol, 98% hydrolyzed), with the sample of PVA film with 2% by weight of particles of silicon with the size distribution of Figure 1 as IR reflective pigment. It is observed how the introduction of silicon particles in the polymeric film composition drastically lowers the optical transmission in the near and middle infrared range.

Example 3

This example describes the preparation of a sample composed of an aqueous white paint to which 2% of medium-sized silicon particles centered at 2.5 and m and with a size distribution illustrated in Figure 3 are incorporated. show the optical properties in the range of infrared measured between 0.85 and 2 and 2.

Preparation of an aqueous paint with silicon particles

It is based on a commercial white aqueous paint to which 2% by weight of silicon particles of size distribution are added under stirring according to the curve of Figure 3 and centered on 2.5 microns. The silicon particles with said distribution were obtained by a process of grinding and sieving silicon powder whose composition is defined in Table 1.

The optical transmission results in the near IR range of the commercial aqueous white paint sample and the same paint incorporating silicon particles by 2% by weight with the size distribution of Figure 3 are shown in Figure 7. observes an attenuation of between 8% and 36% of the upper infrared radiation for the paint sample containing silicon particles that act as pigments reflecting infrared radiation. Example 4

This example describes the use of silicon particles of the present invention as a pigment reflecting IR radiation in varnishes. The results of the optical transmissions of the preparations are shown and compared according to the percentage of silicon particles introduced into the varnish.

Preparation of a varnish with different percentages of silicon microparticles

It is based on a commercial acrylic varnish to which 2% by weight of 2.5 and m silicon particles with size distribution according to the curve of Figure 3 is added under stirring. Said particles were obtained by a milling and sieving process before of its incorporation in the varnish.

Another sample is prepared according to the same procedure but increasing the percentage by weight of silicon microparticles incorporated in the preparation to 5%.

Optical measurements in the infrared range

For optical measurements, 8 mg / cm ² of the preparations are spread on a glass holder.

Samples of varnishes with and without silicon particles object of the invention were optically analyzed, by infrared spectroscopy in the range between 0.85 and m and 2.5 and m, considering the glass substrates as reference.

Figure 8 offers a comparison of the infrared radiation attenuation in the near IR range of a sample of a commercial varnish, and a sample with the same commercial varnish incorporating silicon microparticles in different percentages (2% and 5% by weight , with the size distribution of Figure 3, and with an average size of 2.5 microns). From wavelengths greater than 1 m, this attenuation is about 50% for a load of 2% by weight of silicon particles, and of approximately 90% for a varnish with 5% by weight of silicon particles, indicating the effectiveness as a pigment reflecting the infrared radiation of the silicon particles of the present invention.

Example 5

In this last example of the present invention, an experiment is described to evaluate the thermal protection provided by a sample that incorporates silicon particles in its composition as a reflective pigment of thermal infrared radiation. For that purpose, samples whose preparation and characterization have been described in example 3 of this document were used.

A copper plate (thermal conductor) is coated with a layer of 8 mg / cm ² of the aqueous white paint used in example 3. In another identical plate 6 mg / cm ² of the same white paint containing 2% was deposited. weight of silicon particles, described in example 3.

The 2 samples were heated by a Xenon lamp placed at an equidistant distance from the 2 samples. After 1 minute the temperature at the back of the samples was measured, repeating the experiment several times and allowing the samples to cool to room temperature.

Table 2 shows the values of the temperature measurements.

Table 2 shows the temperatures of surfaces painted with paint with and without silicon particles incorporated. In that example, a difference of approximately 10 ° C is observed between the temperature of the copper plate coated with white paint and the copper plate coated with white paint containing 2% silicon particles. This data represents a 19% decrease in temperature on surfaces protected with a paint including 2% of silicon particles of medium size 2.5 microns.

Claims

1. Formulation characterized in that it comprises silicon microparticles with a size between 0.01 and m and 50 and m in diameter.

2. Formulation according to claim 1, wherein the size of the silicon microparticles is between 0.1 and m and 50 and m in diameter.

3. Formulation according to claim 1, wherein the size of the silicon microparticles is between 0.1 and 20 and 20 in diameter.

4. Formulation according to any one of the preceding claims, wherein the percentage of silicon microparticles is comprised between 0.1% and 30% by weight.

5. Formulation according to claim 4, wherein the percentage of silicon microparticles is between 0.1% and 10% by weight.

6. Formulation according to claim 4, wherein the percentage of silicon microparticles is between 0.8% and 5% by weight.

7. Formulation according to any one of the preceding claims, wherein the silicon microparticles comprise at least one additional component active against IR radiation and against UV-visible radiation.

8. Formulation according to claim 7, wherein said active component is a pigment.

9. Use of a formulation according to any one of claims 1 to 8, as a pigment absorbing UV-visible radiation and reflecting IR radiation.

10. Use according to claim 9, wherein the IR radiation is about near-IR radiation in a range of wavelengths between 0.7 and 3 and 3.

11. Use according to claim 9, wherein the IR radiation is about near IR radiation in a range of wavelengths between 0.7 and 1.1 mm.

12. Use according to claim 9, wherein the IR radiation is heat radiation emitted by the fire in a wavelength range between 1 and 20 and 20 m.

13. Use according to claim 11 and 12, wherein the thermal radiation emitted by the fire comprises a range of wavelengths between 1 and m and 8 and m.

14. Use of a formulation according to any one of claims 1 to 8, for the preparation of heat-protective compositions emitted by solar radiation and / or fire.

15. Use of a formulation according to any one of claims 1 to 8, for the preparation of a product selected from a group consisting of paints, varnishes, lacquers, putty, cements, ceramic frits, enamels and polymeric or textile films , as well as any of its combinations.

16. Use according to claim 15, wherein the product is used for application on roofs, walls, floors, windows, doors and elements in plastic, wood and metal surfaces, as well as any combination thereof.

17. Use according to claim 14, wherein when The preparation is of a protective composition of heat emitted by fire, the formulation is used alone or in combination with at least one chemical fire retardant compound.