MX2007005300A - Photochromic composite based on titania sol/acrylic resin having thermochromic and anticorrosive additional properties. - Google Patents

Abstract

Produced is an organic/inorganic composite material based on acrylic/titania resin, which is obtained by mixing a titania sol resulting from the sol-gel method along with a methacrylate polymethyl. The composite presents reversible photocrhomic properties upon exposure to UV light (1=380 nm) and sunlight. Also presents reversible thermochromic properties upon exposure to temperatures higher than 100 °C.

Description

PHOTOCROMIC COMPOSITE OF ACRYLIC RESIN / SUN OF TITANIA WITH ADDITIONAL THERMOCROMIC AND ANTICORROSIVE PROPERTIES AND LUMINESCENCE OF ACRYLIC RESIN / SOL DE TITANIA FIELD OF THE INVENTION The present invention is related to the industry of production of objects in which a shadowing of any of its surfaces is required, for example in ophthalmic lenses, measuring devices, architectural decoration, on metals, concrete, wood, etc. It also applies to where a color change is required when exposed to a temperature range.

BACKGROUND OF THE INVENTION The materials that change color before a stimulus, have been studied extensively due to the large number of applications they have. This stimulus can be a source of energy such as thermal, radiative, mechanical, electrical or chemical, classified according to their response to this stimulus, such as thermochromic, photochromic, luminescent, atomic-chromic, electrochromic or chromogenic materials, respectively.

The origin of this effect is due to different physical and chemical principles, in this work we focus on photochromic and thermochromic materials.

In this section we focus on the properties and nature of photochromic materials, in a second part of the procurement processes related to the material of interest in this work and (and the first part?). cCo-mo complement to the classification the properties and nature of thermochromic materials.

Among the photochromic materials can be divided into three classes that are organic, inorganic and organic-inorganic.

Organic photochromic materials In recent years, a large number of organic photochromic materials have been developed, among these photochromic compounds are azobenzene, thio-indigo, dithizone metal complexes, spiro-pyranes, spiroxazines, dihydropyrenes, spirothiopyrans, oxazines, trifen il methane, viologens, etc. [Patent US 5,208,132].

Organic photochromic systems can be subdivided according to the type of reaction. Geometric isomerism gives rise to different optical properties, for example, azobenzene (C12H10N2) undergoes photoisomerization, where the cis form has a higher absorbance than the trans form [(Thermochromism; JHDay; Chem.Rev. V.63 p. 65-80 (1963) and The Physics and Chemistry of Color; K. Naassau; John Wiley &Sons. (1983) ISBN 047-186776-4) put [] or ()].

Cycloaddition can cause photochromism, such as the reversible formation of the endoperoxide (C28H14O) from the red compound dibenzo perylene-8,6-dione (C28H14O2) [The Physics and Chemistry of Color; K.Nassau; John Wiley & Sons. (1983)] [J. H. DAY, op. cit]. (put the same bibliographic reference format [] or () The dissociation both heterolytic (photolysis of triphenyl methyl chloride) and homolytic (photolysis of bis (2,4,5-triphenyl imidazole) to form the free radical purple red color), both can produce photochromism. UV (ultra violet) light can excite polycyclic aromatics, such as 1, 2,5,6-dibenzacridene (C21H13N) at its triple state that has a different absorption spectrum [1,2]. The viologens undergo redox reactions and exhibit photochromic properties when they are in a crystalline state and are exposed to UV. The most popular photochromic materials undergo reversible electrocyclic reactions, including the indolino-spiropyrans and indolino-spiroxazines ([Thermochromism; JHDay; Chem.Rev. V.63 p.65-80 (1963) and The Physics and Chemistry of Color; K.Nassau; John Wiley &Sons. (1983) ISBN 047-186776-4]) · Inorganic photochromic materials Among the great variety of inorganic photochromic materials are silver halides, polyoxometalates and transition metal oxides.

The principles on which the inorganic photochromic materials are based are usually transitions in their valence bands caused by vacancies induced by defects, impurities, functionalization of groups.

Examples of silver halides, these are made from fine suspensions (10-20 nm), crystals that are dispersed through a glass that has cooled slowly. Its most common application is as fotogray lenses [Patent US 5,208,132], Polyoxometalates are clusters of transition metals that form complexes that interact with water, protons and organic substances present in solution, when illuminating with UV light the complex can initiate electron transfer, which will change the valence state of the metal in the cluster through the oxidation of its organic components. Examples of these are W03 and 0O3, which present photo and electrochromism [Solid State ionics 165 (2003) 117-121 Solid State ionics 165: 117-121 (2003)]. A direct effect of the particle size and the isoelectric point of the metal oxides in their photochromic properties is also known, which is reflected in a shift towards the blue in the absorption peaks due to the transfer of electrons between the different valence states of the atoms. W ions located in sites adjacent [Physics of the Soüd State, 41, 7 (1999) 1210-1215Ph ysics of the Solid State, 41, 7: 1210-1215 (1999)].

Among the oxides of transition metals that exhibit the photochromic effect, titania is considered as the universal semiconductor par excellence, as well as the ZrÜ2, S1O2, etc.

One of the best known principles that govern the presence of this phenomenon is the generation of vacancies and electron-hole pairs, Clark [W. Clark and P. Broadhead; Optical absorption and photochromism n iron-doped rutile, 1969] shows the first evidence that the coloring process is interpreted as the optical transfer of an electron from the valence band of a Fe3 + center where there is an adjacent vacancy of the anion iron, most of the resulting holes are trapped by Fe3 + ions at sites without an adjacent vacancy.

Another case is that of work [J. Phys. C: Solid State Phys., 5 (1972) J. Phys. C: Solid State Phys., Vol. 5, 1972.] show that the iron incorporated in a rutile network substitutes Ti + directly for Fe3 + and thus creates oxygen vacancies to maintain the neutrality of the charge, they they show the evidence that indicates that the Fe3 + adsorbed on the surface of the BOD, forms acceptor states on the surface.

Another variation of the semiconductor principle is found in [Patent JP 08-074411] where, to obtain the photochromic effect, they use titanium dioxide in the form of rutile that in solution and with temperature they cover it with anatase, which results in a change of color in the material by exposing it to UV light, which disappears when it is removed from the radiation source.

Cases that depend on the sun of titania are shown in [Journal of Materials Science Letters 20, 2001, 485-486 Journal of Materials Science Letters 20: 485- 486 (2001)] in which the O-Ti-0 networks from the sol-gel passing from T3 + to Ti + when activated by UV light.

Photochromic organic-inorganic materials As can be seen, the transition metal oxides (OMT) can have the effect by themselves, thanks to impurities, defects, etc. But there is also the case in which the photochromic effect is due to the presence of an additional matrix to the OMT that gives rise to that electronic transfer thanks to a real link or a Van der Waals type interaction existing between them, by example, a polymer. Many polymers are currently not found in this work [Journal of Nanoscience and Nano-technology, 6, 2: 459-463 (2006) Journal of Nanoscience and Nanotechnology, Volume 6, Number 2, February 2006, pp. 459-463 (5)] performed nanocompositions of TiO? in rutile phase and polyvinyl alcohol, polyvinyl pyrrolidone or polyvinyl pyridine, during exposure to UV light, the nanocomposites turned blue due to the partial reduction of Ti (IV) to Ti (lll), this color remained even after removing the source of radiation even in spite of the sensitivity of Ti (III) to atmospheric oxygen, in contrast, when put in water they returned to their original color. The coloring and discoloration cycles were repeated ten times, due to the nanometric size of the TiC particles high resolution blue structure patterns were formed in the polymeric material.

Yang [J. Phys. D: App. Phys. 37 (2004) 1987-1992J. Phys. D: App. Phys. 37: 1987-1992 (2004)] found that when H3PW11M0O40 was mixed with PVA the polymer acted as an electron donor and polyoxometalate as electron acceptor where the reduction occurs under UV radiation.

The same case [Patent JP19980312308] in which when mixing Ti02 with PVA in a medium of hydrocarbon oil for a cosmetic gives rise to the reversible photochromic effect when exposed to sunlight.

Processes for obtaining photochromic materials based on titania In the field of processes for obtaining titania that possess photochromic properties, the first and most popular are those that start from a mixing process with metallic impurities with thermal treatment. In the process shown in [US Patent 4134853] they start from anatase dispersed in distilled water to which they add 10% Fe203 and 1% PbN03l dry it and bake it at 1000 ° C thereby reducing Fe203 to FeO and PbN03 to PbO by integrating them into the crystal structure of the titania allowing it to change color when exposed to UV light. In this class of processes are other similar ones with variations such as baking in the presence of a sodium compound and an aromatic compound [Patent JP 05-140527] or the temperature of obtaining the titania compound [Patent JP19910291856] .

From this, it was observed that the photochromic property of the titania could be obtained in other ways. At work [Patent JP 08-074411] a process for obtaining a titania-based photochromic pigment consisting of adding titanium sulfate and sodium hydroxide to a hot aqueous suspension of titania in rutile phase and heating from 100 to 700 is shown ° C, this gives as an anatase coated rutile product that exhibits reversible photochromism. In the work [Journal of Materials Science Letters 20, 2001, 485-486 Journal of Materials Science Letters 20: 485-486 (2001)] by means of the sol-gel process and the hydrolysis of titanium butoxide they obtain photochromism by Ti networks. -O-Ti generated.

There are so many known processes to obtain titania or functionalize it to take us to a specific property can be from the same dust and receive a mechanical treatment, radiative (de-excitation by emission of photons), chemical or thermal to obtain the desired property, or starting from an organometallic or inorganic precursor that through a process allows us to break the ionic bond MC that can be anhydrous or through hydrolysis. Specifically, those that start from the sol-gel, exist from those that use simple hydrolysis to obtain networks of (-O-Ti-O) n [Journal of Materials Science Letters 20, 2001, 485-486 Journal of Materials Science Letters 20: 485-486 (2001)], those that have an intermediate stage in its process which is the esterification to give chemical stability to the titanium precursor and react at the desired speed [Malasyan Journal of Chemistry 2003, 5, 1, 86-91], [Materials Chemis-try and Physics 83 (2004) 169-177 Malaysian Journal of Chemistry, 5, 1: 86-91 (2003)], [Materials Chemistry and Physics 83: 169-177 (2004)], up to which their process consists of the previous stages and additionally have a process of peptization, grinding, heat treatment [J. Mater. Chem., 2005, 15, 412-418J. Mater. Chem., 15: 412-418 (2005)]. In the case of functionalization of titania from powders, there are also those that receive chemical and electrochemical processes [J. Phys Chem. 1995, 99, 11974-11980J. Phys Chem., 99: 11974-11980 (1995)], heat treatments [U. S. Patent 4134853], [Patent JP 08-074411], [Patent JP 05-140527], It has been found, although not very commonly that the photochromic effect can be found in hybrids or titania and polymer composites. Among the processes that have been found, the same case [Patent JP19980312308] in which when mixing T02 with PVA in a medium of hydrocarbon oil for a cosmetic gives rise to the reversible photochromic effect when exposed to sunlight.

In the work [Journal of Nanoscience and Nanotechnology, Volume 6, Number 2, February 2006, pp. 459-463 (5) Journal of Nanoscience and Nanotechnology, 6, 2: 459-463 (2006)] obtain a process of obtaining nanocomposites of titania particles in rutile phase by a high temperature process, which they mixed with conductive polymers such as polyvinyl pyrrolidone, polyvinyl pyridine and polyvinyl alcohol in aqueous dispersion which resulted in a material with photochromic properties.

Apart from the previous work to obtain photochromic titania with polymer, the only way to obtain them is by mixing a titania that already has photochromic and embed in a polymeric matrix [Patent U. S. 4134853] which could obtain properties with polymers of different nature to the above as acrylates, polyesters, etc.

However, it has been observed that in certain conditions the photochromic material tends to build on the polymeric material in which it was incorporated, from which it is deduced that the functions of the photochromic material are influenced by the local environment that surrounds it and that the migration It can deteriorate them. One method to reduce it is to link the photochromic material to the polymeric, it is thought that they can be polymerized with what they would have a lower tendency to obtain, however, this link can cause the discoloration speeds of the material to decrease (US Patent 5,258. 300], An alternative to this problem has been the sol-gel chemistry since it offers a versatile access to chemically design new organic-inorganic hybrid materials from the properties of the individual components depending obviously on their nature, but the synergy between them extends them being the nature of the interactions that can lead us to an unknown property.

Among the processes to perform this link, for example in the case of wanting to link titania with acrylate-type polymers, there are several routes, some have in common the use of polymerization with in-sítu particles, obtaining in turn the titania particles, usually through a process of sol-gel with esterification, peptization at temperature, grinding and heat treatment to finally polymerize adding to the medium and monomers and carry out the process at 60-80 ° C for a period of between 12 and 72 hrs ([J. Mater. Chem., 2003, 13, 1475-1479, Mater.Chem., 13: 1475-1479 (2003)], [Colloid Polym, Sci. 2005) 284: 243-250Colloid Polym, Sci. 284: 243-250 (2005)], [Journal of Macromolecular Science, Part B: Physics, 45: 53-60, 2006 Journal of Macromolecular Science, Part B: Physics, 45: 53-60 (2006)]).

There are others that start from the sol-gel process of titania complexing the medium with binders or acetates by hours or days to stabilize the titania, to subsequently make the polymerization ([Polym Int 51: 1013-1022 (2002)], [Journal of Polymer Science: Part B: Polymer Physics, Vol. 42, 3682-3694 (2004)]). In other cases they require the intervention of the plasma technique to cause the polymer to be absorbed on the surface of the titania [Plasma Science and Technology, 7, 4 (2005) 2955-2958Plasma Science and Technology, 7, 4: 2955-2958 (2005)] or gamma radiation intervention to polymerize MMA on the surface of the titania particle with prior preparation [Journal of Nanoparticle research (2006) 8: 137-139 Journal of Nanoparticle Research, 8: 137-139 (2006)] .

Classification of thermochromic materials The mechanism responsible for thermochromism involves a change in the electronic state of a molecule, the electronic energy of the complexes of transition metals can be disturbed by changes in (i) electronic configuration, (ii) coordination geometry, (iii) coordination number, (iv) molecular movement of ligands, among others [Bloomquist, DR; Wíllett, R. D. Co-ord. Chem. Rev. 1982, 47, 125. Soné, K .; Fukuda, Y. Inorganic Thermochro-mism. (Inorganic Chemistry Concepts, Vol. 10). Springer: Berlin. 1987].

Examples of (ii) are observed in structural isomers of coordination compounds such as the nickel complexes which possess the two structural isomers [Arai, N .; Sorai, M .; Seki.S. Bull. Chem. Soc. Japan, 45: 2398 (1972) S. Bull. Chem. Soc. Japan 1972, 45, 2398], An example of thermochromism due to molecular movement of ligands (iv) is observed in the planar square complex of the Copper (II) complex [Yamakí, S .; Fukuda, Y .; I sounded, K.Chem. Lett. 269 (1982) Chem. Lett. 1982, 269].

Among the complexes that give rise to the phenomenon of spine overlap (¡) The complexes of Fe (i I) are found, one of them is a complex at room temperature. S is in the high spin state and is black turning blue when it reaches 160 ° K in the low spin state. [Haddad, M. S .; Federer, W. D .; Lynch, M. W .; Hendrickson, D. N.J. Am. Chem. Soc., 102: 1468 (1980). Inorg. Chem., 20: 123 (1981) J. Am. Chem. Soc. 1980.102, 1468. Haddad, M. S .; Lynch, M.W .; Federer, W. D .; Hendrickson, D. N. Inorg. Chem. 1981, 20, 123].

Some complexes of copper (II) and nickel (II) as well as salts of sopropylammonium show the case (iii). Studies show that the low temperature phase corresponds to a triclinic crystal and that the high temperature phase corresponds to an orthorhombic crystal [Roberts, S.A .; Bloomquist, D. R.; Wiilett, R. D .; Dodgen, H.W. J. Am. Chem. Soc. 1981, 103.2603J. Am. Chem. Soc, 103: 2603 (1981)].

STATE OF THE ART As can be seen, there is a great variety of photochromic materials whose physicochemical principles are very different and based on these interesting properties are obtained. Organic photochromic materials exhibit excellent coloration and tonality, but because of the great need to improve their characteristic absorption in the visible part of the spectrum, which may be the basis for effective coloration, the molecular structure must frequently contain an electron. -unlocated, the molecules that are associated with this type of electronic structure are polycyclic aromatic hydrocarbons, azoquinolines and heterocyclic pigments, are often carcinogenic that penetrate the skin and have a high risk of toxicity [US Pat. No. 6,461,594].

Another of the main problems that photochromic compounds face alone is that they lose stability when they are repeatedly exposed to intermittent or continuous radiation in the presence of air, this leads to decomposition in a few days and then does not give a good response to light [Patent US 5,208,132]. To address these problems, additives or additives are added to other polymeric materials that increase the resistance to them that are not always compatible because the photochromic material-matrix interactions in their photochromic response can be strongly modified by the presence of polar groups since they can cause complexation, protonation, matrix rigidity and steric hindrance thereof [Journal of Sol-Gel Science and Technology 19, 31-38, 2000 Journal of Sol-Gel Science and Technology 19: 31-38 (2000)].

In the case of titania base photochromic materials based on metal doping, they require very high temperature processes, which implies a high process cost and also, if you want to protect them from the environment, they must be embedded in a polymeric matrix , with probability of phase incompatibility and modification of the performance of the final material due to the titania-matrix interactions [US Patent 4134853].

In the case of processes for obtaining functionalized photochromic titania ([Patent JP 08-074411]), in the case of the sol-gel process or the powders, they may require esterification, peptization at temperature, grinding and thermal thermal treatment. [J. Mater. Chem., 2005, 15, 412-418 J. Mater. Chem., 15: 412-418 (2005)], these processes require a high use of thermal and mechanical energy in addition to requiring considerable time to be carried out.

In the case of the processes of obtaining photochromic titania based on their interaction with polymers ([Journal of Nanoscience and Nanotechnology, Volu-me 6, Number 2, February 2006, pp. 459-463 (5) Journal of Nanoscience and Nanotechnology, 6, 2: 459-463 (2006)], [Patent JP19980312308]), has certain limitations because the polymers that allow the effect are known conductive polymers because of their high cost or in the case of PVA very soluble in water and fragile for applications where the mechanical properties of the material are decisive.

Among the great variety of polymers that have good mechanical, optical, aesthetic and protective properties, the acrylates family stands out, but for the photochromic effect to be present, the photochromic titania in this matrix should be imbibed with the aforementioned problems. that in several of these processes, embedding in the matrix requires a polymerization process, these processes are known to be polluting due to the volatility and toxicity of the monomers from which they start due to the temperatures and times managed, in addition to the difficulty of control of molecular weight ([J. Mater. Chem., 2003, 13, 1475-1479Mater.Chem., 13: 1475-1479 (2003),], [Co-lloid Polym. Sci. (2005) 284: 243-250Colloid Polym, Sci. 284: 243-250 (2005)], [Journal of Macromolecular Science, Part B: Physics, 45: 53-60, 2006 Journal of Macromolecular Science, Part B: Physics, 45: 53-60 (2006)] ), ([Polym Int 51: 1013-1022 (2002)], [Journal of Polymer Science: Part B: Polymer P hysics, 42: 3682-3694 (2004) Journal of Polymer Science: Part B: Polymer Physics, Vol. 42, 3682-3694 (2004)]) or requiring the intervention of the plasma or gamma radiation technique to link it ( [Plasma Science and Technology, 7, 4 (2005) 2955-2958Plasma Science and Technology, 7, 4: 2955-2958 (2005)], [Journal of Nanoparticle research (2006) 8: 137-139Journai of Nanoparticle re-search, 8: 137-139 (2006)].) For these reasons, a material is invented whose synthesis includes a semiconductor harmless to health and the environment such as titania, which is instantly functionalized when, in the presence of a high-evaporation point ester, it comes into contact and without any other means of transfer of energy rather than simple agitation at room temperature, with a polymer of the acrylate type known for its protective and versatile properties, this significantly reduces the synthesis times of the material thanks to the synergic process of its three components based on a physicochemical foundation giving as resulting in a photochromic material mainly with thermochromic, luminescent and additional protective properties (such as thermal and electrical insulation, as well as resistance to abrasion and corrosion). Not actually cases have been reported in which a polymer that does not have this facility to donate electrons of origin to the photochromic effect. In this work, we find the way that PMMA polymer of a different nature to conductive polymers and PVA, allows the electronic transfer of ??? 2 that gives origin to the photochromic effect.

OBJECTIVE OF THE INVENTION The object of the present invention is the creation of a composite material with photochromic properties upon exposure to UV light and thermochromic material properties in a certain temperature range. Its applications are as a substitute for smart window as coating on glass or acrylic, registration band (stay in cinemas, parking lots, etc.), sensors in bacterial issues, identification of false bills, such as dosimeters in tanning chambers, dosimeter in sun exposure , artistic applications involving change of white or translucent to coffee especially exposed to sunlight that are resistant to this as for example paintings, sculptures, murals in exteriors of buildings, as sensor of UV exposure both solar and lamp as for example on beach bands that warn of overexposure or as of time elapsed from exposure, such as flat or strip thermometer, battery testers or indicators on boats when the contents change temperature in clothes.

DETAILED DESCRIPTION OF THE INVENTION According to the background, the present invention has the objective of providing a photochromic material by exposure to UV that does not deteriorate its photochromic properties with additional thermochromic properties that do not deteriorate very quickly even under sun exposure and whose synthesis is easy and rapid being its low environmental impact as a final product.

The contribution that is protected is the formulation of a photochromic composition material whose characteristic composition consists of a semiconductor dissolved in a polymer in the presence of an ester that involves the method and all the components present. The contribution of the present photochromic material is that it contains three materials that individually do not have this characteristic.

The present inventors disclose the following. When a semiconductor such as titania, has OH groups on the surface or forms Ti-O-Ti chains and comes into contact with a polymer of the acrylate type in the middle of an ester, it is immediately functionalized, so that it can make a transition of bands generating a vacancy of O when exposed to UV light, which is physically observed in the sample due to the typical brown color of Ti3 +, and then returning to the typical color of T44 + that is white after a certain time of having been removed from the light source. When this compound is ex- posed to a certain temperature range (in the range between 90 and 180 ° C), its functionalization changes irreversibly obtaining a permanent brown color, because the OH groups disappear completely not allowing the return to its original color. This irreversible change is carried out without degradation of the organic polymer. This functionalization has as a tertiary effect the emission of light that is caused by carbonyls adjacent to T1O2, which occurs at the same time as the first phenomenon. All these fundamental principles on which the new invention is based, give it the technical properties of reversible photochromism, (at room temperature up to 100 C), irreversible thermochromism, luminescence and also, with homogeneous properties and protected from the environment by the presence of the polymer, available in the form of liquid, powder, volume and coating; being for the latter case possible to achieve high homogeneity, good adhesion on various types of surface, allow both thermal and electrical insulation, as well as resistance to corrosion and abrasion, for example, in combination with particles of alumina or zirconia .

The functionalizable semiconductor par excellence is the titania, although also other metal oxides or semiconductors susceptible to present the effect are ZnO and ZrÜ2. The titania can be obtained functionalized from precursors of titanium alkoxides such as titanium isopropoxide, tita-nio butoxide, titanium terbutoxide, titanium tetrachloride, titanium ethoxide among others. The hydrolysis of the titania can be carried out via aqueous or anhydrous. Other functionalization methods for semiconductors can be chemical, electrochemical, plasma, etc., and may contain additional functional groups such as (S, N, P, F, Na, K).

The polymers useful in the present invention can be all those of the acrylate and co-polymer family from monomers or polymerized from methyl methacrylate, butyl methacrylate, phenoxyethyl acrylate, lauryl acrylate, acrylamide, 2-naphthyl methacrylate, 2-carboxymethyl acrylate. , 2-butoxyethyl acrylate, 2-ethoxyethyl acrylate, trimethylsilyl methacrylate, vinyl acrylate, allyl methacrylate, vinyl acrylate, acrylic acid, methacrylic acid, 2-ethylacrylic acid, trimethylsilyl acrylate, poly (propylene glycol) methacrylate, mono-2 - (methacryloyloxy) ethyl maleate, among others. The polymers used can be of molecular weights of 104,000 to 106, synthesized by radical polymerization, among others, with initiators such as AIBN and PBO, copolymerized with any other polymer of any family, since the main interaction is given by the acrylate group.

The esters useful in the present invention are of the family of the alkanoates such as diethyl oxalate, dibutyl propionate, benzyl benzoate, butyl butyrate, dibutyl malonate, diethyl succinate, dimethyl carbonate, ethyl forma, tributyrin, among others.

The proportions of the semiconductor must be from 1 to 99% to obtain the effect. The ester can be in 20 to 80% in the total volume.

The photochr material should be prepared, for example, in the following manner. The polymer is dissolved in the ester in a proportion of 1 to 99% w / v until a homogeneous mixture is obtained. TO this mixture is added to the functionalized semiconductor in a proportion that can be from 1 to 99% by volume of the dissolved polymer and is stirred until a homogeneous mixture is obtained. The semiconductor may be previously dissolved, depending on the case, in a solvent to obtain a finer dispersion and an acid, base, electrolyte or pH regulator may have been added in order to vary its zeta potential. A coupling agent can be added to the final mixture or semiconductor to be compatible with other substances or substrates where it is to be applied. A surfactant can be added if you want to make it compatible with another material in which it is not miscible.

Examples of functionalized semiconductor solvents are isopropanol, ethanol, butanol, propanol in proportions of 1-80% volv / v.

Examples of modifiers of the zeta potential or that change the pH can be HN03, HCI, NaOH, KOH, etc.

Examples of the coupling agents may be the titanates, silanes and zirco-natives.

According to the invention, the additives may be added to the semiconductor or to the final mixture. Examples of useful additives are plasticizers, solvents, antioxidants, infrared radiation absorbers, fats and oils, waxes, additional resins.

Example 1 Titanium isopropoxide is dissolved in isopropyl alcohol and left on ultrasound, then water is added and again subjected to ultrasound and removed. Polymethyl methacrylate is dissolved in diethyl oxalate and left in a water bath with constant stirring obtaining a uniform and transparent mixture. The first preparation is added directly to the second, stirred and a homogenous mixture is obtained. This is known as the photochr material 1.

EXAMPLE 2 The same procedure of Example 1 is repeated with the exception of using the polymers polymethyl methacrylate co-ethyl acrylate (PMMA-co-EA), polymethyl methacrylate co-methacrylic acid (PMMA-co-AMA), polymethyl methacrylate co-butyl methacrylate (PM A-co-BMA), (PMMA, pm2x104) and (PMMA, p.106), in place of the polymethyl methacrylate polymer (PMMA, p.m 3.5x105).

Example 3 The same procedure as in Example 1 with the exception that during the preparation of the T1O2 sol-gel the pH modifiers HNO3, NaOH, KOH, HCI, and 10% phosphate buffer are added instead of simple distilled water.

Example 4 With the synthesis of the titania, it is mixed in different proportions with the polymethyl methacrylate (20/80 and 20/50), in the following table and with the deposit and exp procedures. to UV Example 56 The photochr material 1 is made and the coupling agent MPMS previously hydrolyzed in acid is added to the end, this is added as 5% of the composition of the formulation 1. It is poured on an acrylic substrate and left to dry . It is exposed to UV lamp of 360 nm of 15 W for 5 minutes and darkens with a grayish-brown hue, it takes to return 20 minutes to its original color. The same response times and physical characteristics were obtained by exposing it to solar radiation. This test was done repeatedly achieving the same results without problems. This final composite obtained is mixed with sol-gel of S1O2 achieving miscibility. The use of agents to reinforce properties is evidenced.

Photochr test with light exposure UVI example 2 PMMA-co-BMA is dissolved in diethyl oxalate 20/50 ratio w / v. 5% by volume of the dissolved polymer is added. It is stirred until a homogeneous mixture is obtained and poured onto an acrylic substrate. It is left to dry at room temperature. It is exposed to 360 nm UV lamp of 15 W for 5 minutes and darkens with a grayish-brown hue, it takes 20 minutes to return to its original color. The same response times and physical characteristics were obtained by exposing it to solar radiation. This test was done repeatedly achieving the same results without problems. The use of another polymer is evident. As shown in the following table: The sample of the photochromic material with both 5% Ti02 (semitransparent) and 20% present a quantitative photochromic change and a return as shown in the table.

Test for the study of what effect of pH is mixed with polymethyl methacrylate (PMMA) in proportion 1. Tests were done by adding the pH modifying agent at the end of the composition as during the synthesis of titania. This shows that any pH modifying agent does not interfere with the photochromic effect.

Test for the study of the effect of several wavelengths The samples of example 1 are exposed to UV light of 260 and 360 nm and sunlight for half an hour. The samples are removed and a change to brown is observed, more pronounced as the wavelength decreases or the power increases.

Test for the study of the effect of the temperature of synthesis The mixture of polymethyl methacrylate and titania is made at different temperatures to see change in its viscosity, in the curve shown below. Subsequently, it is deposited and exposed to UV light. The effect is observed with the same intensity in the samples for all the mixing temperatures.

Test for the study of the effect of the physical state of the hybrid The sample is exposed to UV according to preparation 1 in the liquid state, as a coating, as a body, as a powder dried at a temperature. The effect is present.

Application 1 Use of photochromic material as a coating Deposit and drying on acrylic substrate It is poured onto the substrate by draining and allowed to drain until a uniform coating is obtained. It is left to dry at room temperature and with low relative humidity or alternatively in the latter case, a treatment is applied with a dryer or left under environmental conditions for a longer time until its consolidation.

Exposure conditions to UV light of photochromic material Exposure to UV lamp of 360 nm or shorter wavelength of 15 W for 5 minutes. The reversibility time is measured and the degree of absorption is evaluated by means of colorimetry on the L, a, b scale. For solar exposure, a photochromic change will be obtained under direct exposure, depending on the time and intensity of this.

Application 12 (photochromic window) An acrylic window of 2x2 m was covered and exposed to sunlight, the effect lasted all the time that the sun was at its peak, decreasing as the sun decreased the intensity of radiation. Checking the photochromic effect The formulation of Example 1 is carried out and deposited by means of casting as a coating on acrylic. It is left to dry until a semitransparent film is obtained. It is exposed to UV lamp of 360 nm of 15 W for 5 minutes and darkens with a grayish-brown hue, it takes to return 20 minutes to its original color (after removing the UV light). The same response times and physical characteristics were obtained by exposing it to solar radiation. This test was done repeatedly achieving the same results without problems.

Application 2 (thermochromism) The formulation is made with 20% semiconductor and is deposited in a deep container to make the three-dimensional body. This is milled to obtain Take the powder. It is subjected to temperature for 15 minutes from 60 ° C to 110 ° C in a conventional oven, a slight change to beige color is observed from 70 ° C and gradually increases its intensity until it turns brown at 110 ° C. Putting as evidence the irreversible thermochromic property. A thermal analysis is performed that indicates that there is a transformation in this temperature range and two others probably lower at 130 and 170 ° C Application 3 (Anticorrosive) A 304 steel plate is coated with the 5% photochromic material and with PMMA-co-BMA and impedance tests are carried out. The resistances are 106 and 108 showing good resistance to corrosion in saline medium, preserving the photochromic effect repeatedly and without problems.

Comparison of functional versus non-functional example The formulation of Example 1, when exposed to a UV lamp of 360 nm of 15 W for 5 minutes and darkened with a grayish-brown color, takes 20 minutes to return to its original color. The same response times and physical characteristics were obtained by exposing it to solar radiation. This test was done repeatedly achieving the same results without problems. Compared with the formulation of Example 2, it does not exhibit the photochromic effect when exposed to UV light, furthermore its resistance to corrosion by impedance tests is much lower than that of Example 1.

Claims (20)

1. Preparation process of a photochromic composition characterized by consisting of two stages, the first being the preparation of titania functionalized with OH groups and of a polymer of the acrylate type in a medium type ester and the second the mixture of both. Considered an innocuous, fast, simple and cheap process due to the ability to carry out the second stage, which is the most critical, instantaneous and with the possibility of being carried out at room temperature with very low emission of volatiles according to to ecological regulations and whose final product is very stable in its storage life.

2. Preparation process of a photochromic composition according to claim 1, wherein the process of synthesis of the titania can be by any means remaining available with the same functional groups.

3. Preparation process of a photochromic composition according to claim 1, wherein the polymer synthesis process can be by any polymerization route, prepolymerization, copolymerization, mixture or variations in the synthesis conditions thereof.

4. Preparation process of a photochromic composition according to claim 1, wherein the order of addition of the ester medium can be during any of the stages of the process.

5. Process for preparing a photochromic composition as claimed in claim 1, characterized by the intervention of radiative and non-radiative energy transfer, sound or inelastic collisions.

6. Preparation process of the photochromic composition as claimed in 1 characterized by the variation of the isoelectric point of the sun of titania

7. Preparation process of a photochromic composition as claimed in claim 1, characterized by any variation to the synthesis times.

8. Preparation process of a photochromic composition as claimed in claim 1, characterized by any variation in the amounts and proportions of the formulation.

9. Preparation process of the photochromic composition as claimed in any of claims 1 to 4, characterized in that it is mixed with any other material or compound.

10. A composite material with a reversible photochromic change before UV exposure comprises a mixture of three essential elements: functionalised titania (??? 2), polymer of the acrylate group and carboxylic ester, where the environment of the two components surrounding the titania allow make a transition to Ti + when exposed to sunlight or UV, giving it properties of reversible photochromic material; which also has properties of irreversible thermochromic material in a temperature range due to the loss of OH groups generating Ti-O-Ti bonds. Additionally, the composite material constituted of polymer and functionalized titania is a semitransparent, anticorrosive, thermal and electrical insulator material.

11. A photochromic material according to claim 1, wherein the ester medium used can be any di or carboxylic acid, ketoster, acetate or beta hydroxy acid derivative.

12. A photochromic material according to claim 1, characterized by the use of another alkoxide precursor, particles or clusters in the preparation of functionalized titania

13. A photochromic material according to claim 1, wherein the majority polymer is of the acrylate group or copolymers synthesized by any route and with any molecular weight.

14. A photochromic material according to claim 1, characterized by replacing the OH functionality of the titania with any other available or establishing a stable meta character, the Ti-O-Ti bonds being the origin of the irreversible thermochromic phenomenon.

15. A photochromic material whose preparation process is according to claim 1, characterized by the participation of other solvents or non-flocculating or dispersing media in the composition, with, without or in combination with another element that changes the texture of the sun. titania

16. A photochromic material whose composition according to claim 1, characterized in that in any part of the process its composition is modified with acid or alkaline compound or combinations that modify the pH either of the sol-gel or of the final mixture.

17. A photochromic material according to claim 1, with availability in any of its configurations (paint, coatings, monoliths, fibers, mesoporous materials).

18. A photochromic material according to claim 1, wherein the T1O2 component when exposed to sunlight or UV has a transition from Ti3 + to Ti4 + which is reflected in a brown hue.

19. A photochromic material according to claim 1, whose response to UV light is rapid and its return to its original color depends on the inten- of the radiative source and the exposure time, having control in both responses.

20. The use of the photochromic composition of claims 10 to 19 in any technological, scientific, scaling at industrial or commercial level. SUMMARY An organic-inorganic composite material of acrylic resin / titania prepared by mixing a titania sol produced by the sol-gel process with polymethyl methacrylate is produced. This presents reversible photochromic properties when exposed to UV light (? = 380 nm) and sunlight. It also has reversible thermochromic properties when exposed to a temperature. (greater than 100 C)