Coating with photochromic properties, method for producing said coating and use thereof applicable to optical articles and glazed surfaces

Abstract

Coating with photochromic properties, method for producing said coating and use thereof applicable to optical articles and glazed surfaces. The coating is formed by the combination of the following three elements: (1) a polymeric matrix, which is typically rigid and deposited on the surface of interest; (2) hollow, sealed micro- and/or nanocapsules dispersed within said matrix; and (3) solutions of photochromic compounds (chosen from a group comprising spirooxazine, azobenzenes or chromenes) in a liquid solvent that does not react (with the photochromic compound and with the capsule wall), which are encapsulated inside said micro- or nanocapsules.

Claims

1. Coating with photochromic properties applicable to optical articles and glazed surfaces, comprising: a coating formed by a polymeric matrix deposited on a surface of an article, in which photochromic compounds are included, wherein said photochromic compounds are heat reversible photochromic compounds selected from the group consisting of spirooxazine, azobenzenes and chromenes, said photochromic compounds are encapsulated inside hollow and sealed nanocapsules with a diameter between 20-1000 nm, said photochromic compounds are dissolved in a liquid solvent that does not react with the photochromic compounds and does not react with the wall or cortex of the nanocapsules, forming a solution inside the nanocapsules, said nanocapsules are dispersed inside said polymeric matrix, said wall or cortex of the nanocapsules is made of polyamide or melamine and formaldehyde; and said liquid solvent is a liquid solvent non-miscible with water selected from the group consisting of chloroform and toluene.

2. Coating according to claim 1, which comprises nanocapsules which encapsulate one or more different photochromic systems, dissolved in the liquid solvent, such that said systems absorb at different wavelengths.

3. Coating according to claim 1, wherein the polymeric matrix inside which the nanocapsules are dispersed with photochromic solutions may be organic, inorganic or hybrid and comprises polyvinyl alcohol, polyvinyl acetate or polystyrene.

4. Method for producing a coating with photochromic properties applicable to optical articles and glazed surfaces according to claim 1, wherein said method comprises encapsulation of the photochromic compounds in the hollow and sealed nanocapsules in solution in the liquid solvent that does not react with the photochromic compounds and does not react with the wall or cortex of the nanocapsules, and dispersion of said nanocapsules in the polymeric matrix deposited on a surface of an article.

5. Method of using the coating with photochromic properties according to claim 1, wherein said method comprises covering a surface of an article with the coating.

6. Method of using according to claim 5, wherein said article covered with the coating is an optical lens.

7. Method of using according to claim 5, wherein said article covered with the coating is a transparent or translucent glazed surface.

8. Method of using according to claim 5, wherein said article covered with the coating is a reflective glazed surface and suited for being used as a mirror.

9. Method of using according to claim 5, wherein the surface of the article is an optical article, or a glazed surface.

10. Method of using according to claim 5, wherein the covering is applied for temporary staining.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1(A), 1(B), 1(C) and 1(D) show transmission electron microscopy (TEM) images of polyamide capsules of nanometric dimensions (diameters between 20-1000 nm) prepared using (A, B) PVP (25% w/w) or (C, D) Tween 20 (1% w/w) as a stabilizer (bar=(A) 20 nm, (B) 200 nm, (C) 500 nm, (D) 100 nm).

(2) FIGS. 2(A), 2(B), 2(C), 2(D), 2(E) and 2(F) show optical microscopy images of polyamide microcapsules (diameters between 1-100 m) prepared using PVP (20% w/w) as a stabilizer (bar=(A) 50 m, (B) 50 m, (C) 100 m, (D) 200 m, (E) 50 m, (F) 50 m).

(3) FIGS. 3(A), 3(B), 3(C), 3(D), 3(E) and 3(F) show optical microscopy images of polyamide microcapsules (diameters between 1-1000 m) prepared using (A, B) PVA (0.4% w/w) or (C, D) PVP (5% w/w) as a stabilizer (bar=(A) 200 m, (B) 200 m, (C) 200 m, (D) 200 m, (E) 50 m, (F) 200 m).

(4) FIGS. 4(A), 4(B), 4(C), 4(D), 4(E) and 4(F) show the transition absorption spectroscopy measurements carried out to characterize the kinetics of the interconversion process B.fwdarw.A of different photochromes (Photorome I, Photorome III and Disperse Red 13) in: (a) rigid polymeric matrices of PVA and PVAc in which these photochromes have been directly dispersed; (b) polyamide capsules in which these photochromes have been encapsulated in solution.

(5) FIGS. 5(A), 5(B), 5(C), 5(D), 5(E) and 5(F) show the transmission electron microscopy (TEM) images of melamine-formaldehyde capsules of nanometric dimensions (diameters between 20-1000 nm) prepared using SDS (1% w/w) as a stabilizer (bar=(A) 200 nm, (B) 200 nm, (C) 200 nm, (D) 200 nm, (E) 100 nm, (F) 200 nm).

(6) FIGS. 6(A) and 6(B) show TEM microscopy and FIGS. 6(C) and 6(D) show optical microscopy images of melamine-formaldehyde microcapsules (diameters between 1-100 m) prepared using (A, B) PVP (25% w/w), (C) PVP (8% w/w) or (D) PVP (20% w/w) as a stabilizer (bar=(A) 2 m, (B) 5 m, (C) 4 m, (D) 100 m).

(7) FIGS. 7(A), 7(B) and 7(C) show optical microscopy images of melamine-formaldehyde microcapsules (diameters between 100-1000 m) prepared using (A) PVP (2% w/w) as a stabilizer or (B, C) without a stabilizer (bar=(A) 100 m, (B) 100 m, (C) 200 m).

BRIEF DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(8) Examples of Micro/Nanocapsules Synthesized Using Different Methodologies and Which Contain Different Solvents and Photochromes.

(9) Below a number of examples of micro- and nano encapsulation of photochromic compounds dissolved in solvents and their use to form rigid coatings, as proposed by this invention, will be described in detail. These examples are only some, of those carried out in the development of the present invention and the are used to intent to show that: (a) the technology described allows the photochromic compounds to be encapsulated inside micro- and nanocapsules with rigid cortex and which contain liquid solvent; (b) the encapsulated photochromic compounds maintain the optical and interconversion properties which they have when they are found in solution; (c) the optical and interconversion properties of the encapsulated photochromes are maintained when the capsules are dispersed inside a rigid polymeric matrix or directly deposited on a surface; and (d) the process may be considered universal and may be applied to the encapsulation of different types of photochromes and using different solvents, as well as to different types of cortexes of the capsules and rigid external matrices.

Example 1

(10) This first example consists of encapsulating solutions of photochromic compounds inside polyamide capsules. The formation of the polyamide capsules takes place in situ by means of an interfacial polycondensation by means of a methodology which has been derived from the proposal of H. Misawa et al for the synthesis of impermeable microcapsules (Laser Manipulation and Ablation of a Single Microcapsule in Water, H. Misawa, N. Kitamura, H. Masuhara, J. Am. Chem. Soc. 1991, 113, 7859-7863). The monomers which are used in this type of polymerization process are acyl di- or trichlorides (dissolved generally in organic solvents) and polyamines (di- or triamines dissolved in aqueous phase). The first step in the synthesis process of the capsules consists of forming an emulsion obtained by mixing and stirring vigorously an organic solution of the acyl chloride of interest with an aqueous phase which contains a stabilizer (PVA, PVP, etc.). This leads to the formation of small micro- and nano droplets of the organic phase dispersed in the aqueous main phase, the size of which depends on the stirring velocity, the nature and concentration of the stabilizer, the type of organic solvent and the initial ratio between the organic phase and the aqueous phase. Then, the amine of interest is added, which quickly induces the beginning of the interfacial polycondensation process where chemically interlinked polyamide chains are formed around the droplets of the emulsion and trap the organic phase used inside them. This gives rise to the formation of capsules with organic solvent inside, the micro- and nanometric size of which is determined by that of the droplets of the initial emulsion. Furthermore, if the photochrome is dissolved in the initial organic solution, the latter remains encapsulated together with the solvent inside the polyamide capsules once the polycondensation reaction has finished (3-24 hours). In the case of this specific example described here, terc phthaloyl chloride and diethylenetriamine has been used as monomers, and PVP (polyvinylpyrrolidone), PVA (hydrolyzed polyvinyl alcohol) or Tween 20 has been used as stabilizers.

(11) On the other hand and in order to demonstrate that the encapsulation process developed can be applied in a general manner to various types of photochromes which absorb at different regions of the UV-Vis spectrum (.sub.max) and which interconvert by means of different mechanisms, the encapsulation of various types of commercial photochromes in polyamide capsules has been carried out. It should be pointed out that as a function of the type of photochrome encapsulated, the solvent forming the core of the capsule has been varied, thus demonstrating the universality of the method developed in which reference is made to the encapsulated solvent, which in this case, must be non-miscible with water (Table 1).

(12) TABLE-US-00001 TABLE 1 Photochromic systems and solvents encapsulated in polyamide capsules and maximum wavelengths of absorption of the photoinduced (B) states of the photochromes. Commercial Interconversion name mechanism Solvents .sub.max (nm) Photorome I Closed-opened Toluene or CHCl.sub.3 605 Photorome III Closed-opened Toluene 590 Disperse Red 13 Trans-cis Toluene 490

(13) The size of the polyamide capsules prepared has been adjusted by means of the controlled variation of the following experimental conditions: stirring velocity during the emulsification process (600-1500 rpm), nature of the stabilizer (PVA, PVP, Tween 20) and concentration of the stabilizer (PVA: 0.2-0.4%, PVP: 0.4-25%, Tween 20: 1-10%). Varying these parameters has enabled three families of polyamide capsules of different sizes to be prepared, just as it has been determined by means of the electronic and optical microscopy measurements: Nanocapsules with diameter between 20-1000 nm (FIG. 1), Small microcapsules with diameter between 1-100 m (FIG. 2), Large microcapsules with diameter between 100-1000 m (FIG. 3)

(14) The structure of the polyamide capsules prepared has also been analyzed by means of microscopy measurements. As it is observed in FIGS. 1-3, these measurements allow it to be established that the capsules obtained have an outer cortex and an internal cavity, within which the photochrome solutions are expected to be encapsulated. In fact, said capsules have the color typical, of the solutions of the photochrome used in each case, which gives a first indication that their encapsulation has been produced in a satisfactory manner. On the other hand, the capsules are a dry solid which does not show a loss of solvent when they are subjected to a vacuum, nor do they leave a color stain (due to the photochrome) when they are deposited on a surface. However, when compression force was applied to the capsules of that type with larger dimensions (100-1000 m), it was possible to observe in real time by means of optical microscopy the breaking of the capsules and the release of their internal content in the form of solution of the color expected for the photochrome. This demonstrates the encapsulation of the photochromic compound in the form of a solution inside the polyamide capsules.

(15) In turn, relative density measurements have confirmed the presence of the different solvents in the capsules prepared. For example, the capsules containing toluene inside them (d=0.865 g/mL) remain suspended in the upper part of the system when dispersed in the aqueous phase (d=1 g/mL), while they are displaced to the lower part of the vessel when dispersed in acetone (d=0.791 g/mL). In turn, the capsules containing chloroform (d=1.483 g/mL) are deposited on the bottom of the vessel both in the aqueous phase as well as in acetone.

(16) Lastly, the presence of solvent in the capsules prepared by means of proton nuclear magnetic resonance measurements has also been demonstrated. In fact, said measurements have allowed it to be proven that the solvent (toluene or chloroform) is maintained inside the capsules for weeks both if they are preserved in the open air or in an aqueous dispersion. This confirms the impermeability of the cortex of the polyamide capsules and the stability of the system prepared over time.

(17) Once the properties of the capsules (size, impermeability, solvent content, etc.) were characterized, the optical behavior thereof was studied for the purpose of establishing whether the encapsulated photochromic compounds had the same photoactivity as in solution. To this end, the photochromic behavior of the capsules was compared with the photochromic behavior of the solutions of the same material and of the photochromic behavior of the rigid polymeric layers (of polystyrene (PS), polyvinyl acetate (PVAc) and polyvinyl alcohol (PVA)) wherein the photochromic compound is dispersed. Said study was centered on the determination of the thermal interconversion velocity B.fwdarw.A of the system, since the latter is the experimental parameter which is most sensitive to the properties of the environment of the photochrome. The measuring of this parameter was carried out by means of transition absorption spectroscopy which allows the state B of the photochrome to be generated by irradiating the material with a short monochromatic pulse of laser light and subsequently, monitoring the kinetics of the thermal interconversion process B.fwdarw.A by means of absorbance measurements. Said absorbance measurements, may be carried out both at the maximum absorbance of B (for which a deterioration of the signal is observed as B is transformed into A) as well as at the maximum absorbance of A (for which an increase of the signal is observed as B is transformed into A). In either of the two cases, the analysis of the temporal profiles of the change in absorbance measured allows the velocity of the process B.fwdarw.A to be established. In this case, our attention is centered in particular on determining the half-life time of the process (t.sub.1/2), which consists of the time required for the initial concentration of B to decay by 50%. Said parameter and the kinetic profile of the process B.fwdarw.A have been determined for the following samples at ambient temperature. Polymeric layers of PS, PVAc and PVA containing the photochromes of interest in their inside and which have been deposited by drop-casting on a glass surface, Polyamide capsules of various sizes containing the photochromes of interest and which have been deposited directly by drop-casting on a glass surface.

(18) Table 2 and FIG. 4 show the results obtained in the kinetic measurements of the process B.fwdarw.A for the following photochromic systems: Photorome I, Photorome III or Disperse Red 13.

(19) TABLE-US-00002 TABLE 2 Half-life times of the B .fwdarw. A process of various encapsulated photochromes or dispersions in polymeric matrices at room temperature. In the case of the encapsulated samples, the photochromes are dissolved in toluene or chloroform inside the capsules. Photochrome Sample t.sub.1/2 (s) Photororne I Dispersion in PVA >74 Photorome I Dispersion in PS 46 Photororne I Dispersion in PVAc 21 Photororne I In capsules of 20-1000 nm (toluene) 0.92 Photorome I In capsules of 1-100 m (toluene) 0.83 Photorome I In capsules of 100-1000 m (chloroform) 0.71 Photorome III Dispersion in PVA >74 Photorome III Dispersion in PVAc 47 Photorome III In capsules of 20-1000 nm (toluene) 2.50 Photorome III In capsules of 1-100 m (toluene) 2.29 Photorome III In capsules of 100-1000 m (toluene) 2.26 Disperse Red 13 Dispersion in PVAc 31 Disperse Red 13 In capsules of 100-1000 m (toluene) 0.20

(20) From the graphics depicted in FIG. 4 and from the t.sub.1/2 values shown in Table 2, it can be concluded that, independently from the chosen photochromic compound, its thermal reversion kinetics B.fwdarw.A is much more rapid inside the capsules than when the photochrome is dispersed directly in a rigid polymeric matrix. In fact, the behavior measured for the encapsulated systems is very similar to that described in the bibliography for these same photochromes in solution e.g. t.sub.1/2=1.4 s for Photorome I in ethanol solutions at room temperature (Oxidation of photochromic spirooxazines by coinage metal cations. Part I. Reaction with AgNO.sub.3: formation and characterization of silver particles, P. Uznanski, C. Amiens, B. Donnadieu, Y. Coppel, B. Chaudret, New J. Chem. 2001, 25, 1486-1494). Furthermore, said behavior is practically independent from the solvent introduced inside the capsules and from the size of said capsules within the range 20 nm-1000 m. This shows one of the mains contributions of this invention: the optical and interconversion properties of any photochromic system may be maintained if said system is encapsulated in the form of a solution within micro and nanocapsules.

Example 2

(21) The second example which is described in this patent application consists of the encapsulation of photochromic solutions inside melamine and formaldehyde capsules. Again, these capsules are prepared by, means of interfacial polymerization of the corresponding monomers (melamine and formaldehyde), adapting the methodology for the synthesis of impermeable microcapsules developed by S. J. Pastine et al. (Chemicals on Demand with Phototriggerable Microcapsules, S. J. Pastine, D. Okawa, A. Zettl, J. M. J. Frchet, J. Am. Chem. Soc. 2009, 131, 13586-13587). As in the previous example, the synthesis of the capsules starts with the formation of an emulsion which is created when homogenizing (by means of sonication or vigorous magnetic stirring) a mixture formed by an aqueous phase which contains formaldehyde (37% w/w) and an organic phase (typically toluene) which contains the photochrome of interest and the stabilizer (PVP or SDS). Once the emulsion has been prepared, an aqueous melamine solution is added and the pH is adjusted until it reaches an acid medium which facilitates the polycondensation reaction and the formation of the melamine-formaldehyde chemically cross-linked polymer around the micro and nano droplets of organic solvent. In this way, hollow micro and nanocapsules are obtained with solvent inside thereof after about 2 hours, which will contain photochromic compounds if the latter have been initially dissolved in the organic phase.

(22) By varying the experimental parameters, it has been possible to prepare three families of capsules with different sizes containing photochromic solutions inside them, as it has been determined by means of electronic and optical microscopy measurements: Nanocapsules, with a diameter between 20-1000 nm (FIG. 5), Small microcapsules, with a diameter between 1-100 m (FIG. 6), Large microcapsules, with a diameter between 100-1000 m (FIG. 7).

(23) Solutions of one single photochrome (Photorome I, see Table 1) have been introduced in said capsules, given that in the previous example, the universality of the methodology proposed here has already been demonstrated for any type of photochrome, independently from the optical properties and interconversion mechanism between the two states thereof. The properties of the resulting capsules have been studied in a form similar to that which has been carried out in said previous example. Thus, on the one hand, electronic and optical microscopy measurements have allowed the core-shell type structure of these capsules to be established which consist of a melamine-formaldehyde cortex and a hollow internal cavity (see FIGS. 5-7). On the other hand, the presence of solvent inside the capsules has been demonstrated by means of compressing and breaking of, the larger capsules, relative density measurements and proton nuclear magnetic resonance measurements.

(24) The thermal reversion kinetics B.fwdarw.A of the photochromic solutions of Photorome I inside the melamine-formaldehyde capsules has been characterized by means of transition absorption spectroscopy measurements. In this case, our attention has not been centered on researching the dependence of the photochromic behavior on the size of the capsules, since this aspect has been studied extensively in the previous example. However, it is intended to compare the behavior of the photochromic coatings, prepared on the basis of capsules, with those in which the photochromes are directly dispersed without encapsulation. For this purpose, measurements of three different systems have been made: PVA polymeric layers containing Photorome I photochrome dispersed directly inside and which have been deposited by drop-casting on a glass surface, Melamine-formaldehyde capsules, 1-1000 m in size, containing solutions of Photorome I in toluene and which have been deposited directly by drop-casting on a glass surface, PVA polymeric layers containing melamine-formaldehyde capsules, 1-1000 m in size, inside of which solutions of Photorome I in toluene are found and which have been deposited directly by drop-casting on a glass surface.

(25) The half-life times measured for these three systems are shown on Table 3. The following conclusions can be inferred from these data: The thermal reversion kinetics B.fwdarw.A of the Photorome I photochrome is much more rapid inside the melamine-formaldehyde capsules than when it is dispersed directly in a rigid environment such as the PVA polymeric layer, which demonstrates the advantageous aspect of the encapsulation; The thermal reversion kinetics B.fwdarw.A of the Photorome I photochromes is similar both inside the melamine-formaldehyde capsules as well as inside polyamide capsules (see Table 2), which indicates the generality of the methodology which is proposed in this patent in relation to the material with which the cortex of the capsules is prepared; The thermal reversion kinetics B.fwdarw.A of the Photorome I photochrome inside melamine-formaldehyde capsules is independent from the medium in which said capsules are found, whether directly deposited on glass or dispersed inside a rigid PVA matrix; The dispersion of the capsules prepared inside the rigid polymeric matrices allows photochromic coatings with suitable mechanical properties to be obtained and the photoactivity of which reproduces the photoactivity observed for the photochrome in solution, i.e. they maintain rapid B.fwdarw.A interconversion velocities.

(26) TABLE-US-00003 TABLE 3 Half-life time of the B .fwdarw. A process of the Photorome I photochrome in various media at room temperature. Sample t.sub.1/2 (s) Photochrome dispersed in PVA >74 Photochrome in melamine-formaldehyde capsules 2.22 Photochrome in melamine-formaldehyde capsules 2.30 dispersed in PVA

(27) In conclusion, it may be affirmed that different families of micro and nanocapsules which contain inside them different types of photochromic compounds and solvents have been developed. As this invention claims, subsequent studies of transition absorption spectroscopy have demonstrated that the encapsulated photochromes interconvert with a kinetics similar to that observed for the same photochrome in solution, confirming that the encapsulation of these compounds allows their properties to be preserved without them being affected by the presence of a rigid external matrix in which the photochrome capsules are dispersed. This behavior has been observed for various types of capsules (size, material of the cortex), photochromes, solvents and rigid matrices, which demonstrates the universality of the methodology proposed in this invention. This allows the preparation of all types of photochromic coatings based on the encapsulation of solutions of the systems of interest and their subsequent dispersion in rigid polymeric matrices.