Plastic Articles Containing Suspended Photochromic Dye Molecules

Abstract

The present invention provides a plastic article containing suspended photochromic dye molecules, and the said suspended photochromic dye molecules suspended in liquid micro-droplets of a suspension medium, and the said micro-droplets of the said suspension medium containing the said suspended photochromic dye molecules are embedded inside a solid polymer matrix, and the said solid polymer matrix is formed by polymerization of liquid polymer precursors. The invented structure of a plastic article containing suspended photochromic dye molecules exhibits fast response time and enhances photochromic performance.

Claims

1. a plastic article containing suspended photochromic dye molecules, and the said suspended photochromic dye molecules suspended in liquid micro-droplets of a suspension medium, and the said micro-droplets of the said suspension medium containing the said suspended photochromic dye molecules are embedded inside a solid polymer matrix, and the said solid polymer matrix is formed by polymerization of liquid polymer precursors.

2. the said plastic article containing suspended photochromic dye molecules of claim 1 is in a film form.

3. the said plastic article containing suspended photochromic dye molecules of claim 1 is coated on a transparent substrate

4. the said plastic article containing suspended photochromic dye molecules of claim 1 is sandwiched between two identical transparent substrates

5. the said plastic article containing suspended photochromic dye molecules of claim 1 is sandwiched between two different transparent substrates

6. the said suspended photochromic dye molecules suspended in liquid micro-droplets of a suspension medium of claim 1 are spirooxazine-type compounds, or spiropyran-type compounds or pyran-type compounds or a mixture of any of these compounds

7. the said suspended photochromic dye molecules suspended in liquid micro-droplets of a suspension medium of claim 1 are selected from reversacol plum red, reversacol oxford blue, and reversacol rush yellow or a mixture of any of these photochromic dye molecules

8. the said micro-droplets of the said suspension medium containing the said suspended photochromic dye molecules are embedded inside a solid polymer matrix of claim I are substantially disconnected from one to another.

9. the said suspension medium containing the said suspended photochromic dye molecules are embedded inside a solid polymer matrix of claim 1 is esters, or oils, or aromatic or alcohols, or aromatic esters, or plasticizer, and or a mixture of any these chemicals.

10. the said suspension medium containing the said suspended photochromic dye molecules are embedded inside a solid polymer matrix of claim 1 is phthalate (dioctyl phthalate, or dibutyl phthalate, or diisooctyl phthalate, or butyloctyl phthalate), or isophthalate (dioctyl isophthalate), or oleate (butyl oleate,or n-propyl oleate, for example), or adipate (dioctyladipate, etc.), or benzoate (diethyl glycol dibenzoate, etc.), or a trimellitate (triethyl, triisodecyl etc) and or a mixture of any of these listed chemicals.

11. the said solid polymer matrix is formed by polymerization of liquid polymer precursors of claim 1, wherein the said polymeric matrix is polyorganosiloxane, or polybutadiene, or polystyrene, or poly(cyclopropene), or polyamide, or polyolefin, or silicone gum, or polyacrylamide, or polyurethane, or polyacrylates, or polymethacrylates, or polyethers, or polymethylstyrenes, or alkyd resins, or polyamides, or polyurethanes, or polycarbonates, or epoxy resins and or any mixture of these polymers.

12. the said solid polymer matrix is formed by polymerization of liquid polymer precursors of claim 1, wherein the said polymeric matrix comprises a polyorganosiloxane.

13. a liquid emulsion to make the said plastic article containing suspended photochromic dye molecules of claim 1, comprises the said suspended photochromic dye molecules suspended in liquid micro-droplets of a suspension medium, and liquid polymer precursors to form the said solid polymer matrix of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows transforming of molecular configuration a photochromic molecule upon photo activation, where the molecule is a typical family of spiro-naphthoxazines, and the color changing from colorless in the left to plum red in the right.

[0017] FIG. 2 presents schematically the photochromic plastic film, where the photochromic plastic film (200) consists liquids microdroplets (220) embedded in a polymeric matrix (210), and the said liquids microdroplets (220) containing photochromic molecules (230), and the said photochromic molecules (230) can be either in a solution form or in a dispersion form.

[0018] FIG. 3 presents schematically the photochromic light controlling device, wherein, a layer of photochromic layer (200) is sandwiched between two transparent substrates (100 and 300). The photochromic layer (200) consists liquids microdroplets (220) embedded in a polymeric matrix (210), and the said liquids microdroplets (220) containing photochromic molecules (230), and the said photochromic molecules (230) can be either in a solution form or in a dispersion form. The said two transparent substrates (100 and 300) can be the same or different materials. In one example, two identical transparent substrates are selected; therefore, the transparent substrate (100) is equivalent to transparent substrate (300).

[0019] FIG. 4 is the absorption spectra of a photochromic plastic film exampled in this invention with and without UV activation.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention provides a solid photochromic plastic article, comprising a solid polymeric matrix having liquid microdroplets embedded inside the said solid polymeric matrix and the said liquid microdroplets containing photochromic molecules, and the said photochromic molecules are capable of reversibly transforming their chemical configurations upon photo activation and the transformed molecular configuration having different absorption spectrum in the visible region comparing to these untransformed molecular configuration, so exhibiting different color .

[0021] To better understand this invention, FIG. 2 presents a schematic view of a photochromic plastic film made according to this invention. In FIG. 2, the photochromic plastic film(200) consists liquids microdroplets(220) embedded in a polymeric matrix(210), and the said liquids microdroplets(220) containing photochromic molecules(230), and the said photochromic molecules(230) can be either in a solution form or in a dispersion form. In the state that no UV is applied on the film, the photochromic molecules dissolved in the microdroplets are in a molecular configuration with no visible color or called bleached state, so the light can pass through. When UV is applied on the film, the photochromic molecules dissolved in the microdroplets are transformed their molecular structure to another configuration with color or called colored state, then the light is significantly cut off.

[0022] In FIG. 3, the photochoromic plastic film consists of a light control layer(200) sandwiched between the two transparent substrates (100) and (300), and the light control layer (200) consists of polymeric matrix(210) containing light control microdroplets(220). In the state that no UV is applied on the film, the photochromic molecules dissolved in the light control droplets are bleached, the light can pass through. When UV is applied on the film, the photochromic molecules dissolved in the light control droplets are colored then the light is significantly cut off.

[0023] Many organic photochromic molecules are well known, including azobenzene-type compounds, thioindigo-type compounds, triarylmethanes-type compounds, stilbenes-type compounds, nitrones-type compounds, naphthopyrans-type compounds, quinones-type compounds, dithizone metal complexes, spiropyran-type compounds, spirooxazine-type compounds, fulgide-type compounds, dihydropyrene compounds, spirothiopyran-type compounds, 1,4-2H-oxazine, triphenylmethane-type compounds, viologen-type compounds, pyran-type compounds, etc. Of these compounds, spiropyran-type compounds, spirooxazine-type compounds and pyran-type compounds are excellent in the sensitivity to coloring and in the color density. However, these compounds involve a low rate of color reversion and reduce the color density or decolorize at a temperature higher than room temperature. Also, these organic photochromic compounds are so low in the stability to light that the compounds may decompose in a few days and become non-responsive to light, when coloring or decolorizing repeatedly occurs on intermittent irradiation or are subjected to continuous irradiation in air. To obviate this serious drawback, a hindered amine-type compound has been added to a high molecular-weight synthetic resin matrix along with the organic photochromic material to provide a resin matrix. However, the organic photochromic material containing the hindered amine-type compound in this form remains insufficient in the resistance to light although higher in this property than when free of a hindered amine-type compound, and is low in the sensitivity to coloring and in the rate of color reversion and poor in the color density because the organic photochromic compound is present as dispersed in the resin.

[0024] In this invention, the photochromic molecules are encapsulated in liquid microdroplets to obviate the above serious drawbacks, and these liquid microdroplets containing the said photochromic molecules are further embedded inside a polymeric matrix. The liquid in microdroplets protects the photochromic molecules from light, air and other chemicals, and while provides photochromic molecules a freedom for reversibly transforming their chemical configurations upon photo activation, Examples of organic photochromic compounds useful in the invention are conventional compounds such as spirooxazine-type compounds, spiropyran-type compounds and pyran-type compounds, etc. More specifically in one embedment, reversacol plum red (from Vivimed Labs Ltd.) was chosen as an example of phtochromic molecules for the fabrication of photochromic light control film with the improved structure in this invention.

[0025] Many solvents can be used as liquid dispersion medium to dissolve or disperse the photochromic molecules and to constitute microdroplets inside a polymeric matrix, therefore, the dispersion medium in this respect is also referred as the suspension medium. Suitable liquid suspension media are described in U.S. Pat. Nos. 1,951,664; 2,290,581; 3,625,869; 4,247,175; 4,442,019; and 6,936,193, for examples including esters, oils, aromatic alcohols, and aromatic esters. These suspension media can be used for dissolving or dispersing the photochromic molecules to make the solid plastic photochromic articles according to this invention. Further in accordance with an aspect of the invention, the liquid suspending medium is preferably incompatible or at most partially compatible with the selected polymeric matrix, and is inert with respect to the suspended or dissolved the photochromic molecules. Furthermore in order to reduce the amount of haze of the photochromic film, the difference of refractive index between the suspending medium and the polymeric matrix must not exceed 0.02. The suspending medium in the present invention can also be a plasticizer such as a phthalate including but not limiting to dioctyl phthalate, dibutyl phthalate, diisooctyl phthalate, butyloctyl phthalate, an isophthalate such as dioctyl isophthalate, an oleate such as butyl oleate, or n-propyl oleate, an adipate such as dioctyladipate, a benzoate such as diethyl glycol dibenzoate, or a trimellitate such as triethyl, or triisodecyl. In one embedment of this invention, diisooctyl phthalate was chosen as an example of the liquid dispersion medium to dissolve the photochromic molecules. To simplify the description of these examples of this invention, the microdroplets constructed by the dispersion medium containing photochromic molecules are also refereed as the light control droplets, LCD for short. In the embodiments exampled in this invention, the solid form of polymeric matrix(PM) is mostly formed by polymerization of the corresponding monomers or oligomers, referred as precursors(PPM) by photo-polymerization; thus a emulsion containing PPM, light control droplets and photoinitiator is formulated such that this emulsion can be coated onto a transparent substrate by traditional coating methods including doctor-blade coating, screen printing, slot-die coating, and then the wet coated layer is subsequently solidified (or named cured) by exposure to a ultraviolet(UV) irradiation.

[0026] The liquid cross-linkable oligomer or polymer(PPM) and the liquid dispersion medium(LDM) are so chosen that the components of one will not deleteriously affect the other. Moreover, the cross-linking, agent used'to form the cross-linked polymer matrix, the by-products of the cross-linking reaction, if any, and the cross-linking conditions, e.g. temperature, pressure etc. must also be compatible with and not adversely affect the light control droplets(LCD).

[0027] The preferable liquid cross-linkable oligomers suitable as precursors of polymer matrix(PPM) include cross-linkable polyorganosiloxane, polybutadiene, polystyrene, poly(cyclopropene), polyamide, polyolefin, silicone gum, polyacrylamide, polyurethane, and the like. The preferable precursors of polymer matrix may inherently have functional groups that enable it to be cross-linked, such as a polyacrylamide, or it may comprise a polymeric chain that has been modified to include such functional groups, such as a dihydroxy terminated polydimethylsiloxane. Cross-linkable functional groups are known in the art and include polyacrylates, polymethacrylates, polyethers, polymethylstyrenes, alkyd resins, polyamides, polyurethanes, polycarbonates, epoxy resins, and the like. Further the preferable PPM may have two or more cross-linkable functional groups per molecule, and may even comprise a large number of such groups provided that the solubility requirements previously stated herein are met. Such cross-linkable functional groups may be located not only at or near the ends of the main chain but also along the main chain and may be substituted either directly to the main chain or on groups pendant from the main chain. In one embedment of this invention, liquid photo-curable polysiloxane was chosen as an example to form the polymeric matrix layer.

[0028] According to this invention as illustrated in FIG. 2, the said polymeric matrix layer is preferably a high light transmittance plastic material. More preferably, the said polymeric matrix 210 can be formed by photo-curing, so the shrinkage of this layer can be technically controlled. Still more preferably, the said polymeric matrix layer is a cross-linked polysiloxane formed from liquid siloxane copolymer with ethylenically unsaturated bond by photo-curing method described in U.S. Pat. Nos. 6,900,923 and 7,791,788. As stated above, the photo-curable polysiloxane which is used to form the polymeric matrix layer 200 is referred as the polymeric matrix precursor(PPM) in this invention. The optical transmittance is related to the thickness of the layer, and such, a thickness is preferably between 50-1000 m, more preferably, 100-250 m.

[0029] Practically according to this invention, the said precursors of polymer matrix material(PPM), the said light control droplets(210) material are formulated into an emulsion, The emulsion can be applied onto the surface of a substrate by conventional coating methods to form a wet coated layer, and then the wet coated layer can be solidified by photo-polymerization of precursors of polymer matrix via a conventional ultraviolet (UV) irradiation.

[0030] Still in common, the layer 100 is transparent substrates, which are commercially available as PVDF, PET, Polyimide(PI), and polymer carbonate(PC).

[0031] Hereinafter, the present invention will be more specifically described by way of examples, and these examples are not to be constructed as limiting the present invention in any manner.

EXAMPLES

[0032] In the following examples, the commercially PET film was selected as the transparent substrates, and the light transmittance of the PET film is 90%. The selected polymeric matrix precursor is a liquid siloxane copolymer with ethylenically unsaturated bond, which is synthesized by following similar method that described in U.S. Pat. Nos. 6,900,923 and 7,791,788. The selected dispersion medium is diisooctyl phthalate. The selected photochromic molecular dye is Reversacol plum red which is commercially available from Vivimed Labs Ltd. All chemicals used in the examples are purchased from Sigma-Aldrich company unless otherwise specified. The doctor blade coater (Model: MSK-AFA-III-110, MTI Corporation) was used to coat the photochromic light control emulsion onto the selected substrate. The UV light source is a commercially available metal halide lamp having a cumulative light dose of 500 mJ/cm.sup.2.

Example 1

[0033] In a 50 ml glass flask, 0.02 g of photo initiator(PI), bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide, was first dissolved in 5 g of acetone. Then 20 g of the elected precursor of polymeric matrix(PPM) was added. After thoroughly mixing by shaking, acetone was subsequently removed by a rotary evaporator to yield a liquid solution, referred as PPM-PI, which is reserved for further use in formulating the photochromic light control emulsion.

[0034] In another 50 ml glass flask, 0.08 g of reversacol plum red(from Vivimed Labs Ltd.), used as photochromic dye molecule(PD), was first dissolved in 20 g isoamyl acetate. Then 10 g of diisooctyl phthalate, as dispersion medium(DM), was added. After thoroughly mixing by shaking, isoamyl acetate was subsequently removed by a rotary evaporator to yield a liquid suspension referred as PD-DM.

[0035] The photochromic emulsion(PCE-1) was then formulated by mixing 10 g of PD-DM liquid suspension prepared above with 12.5 g of PPM-PI solution prepared above in a separate 50 ml glass flask.

[0036] In this example, the photochromic emulsion(PCE-1) prepared above was coated onto the selected PET film by the doctor blade to produce a wet thickness of 200 m at room temperature under a coating speed of 10 mm/s. The coated wet emulsion was exposed to the UV light source for 40 seconds to yield a solid light control layer on PET sheet (referred as LCL/PET). Another fresh sheet of PET without light control layer was finally laminated with this LCL/PET at room temperature to complete the assembly of the photochromic device or referred the solid plastic photochromic article(PCD-1). Thus, PCD-1 was made according to this invention, where photochromic molecule molecules are suspended in a liquid medium, and the liquid medium form micro-droplets inside a solid polymer matrix, therefore yields a solid plastic article containing suspended photochromic molecules.

Example 2

[0037] In this example, a comparative example is prepared as follows. In a 50 ml glass flask, 2 g of PMMA was first dissolved in 20 g of acetone. Then 40 mg of reversacol plum red(from Vivimed Labs Ltd.) was added to the PMMA solution to form a photochromic emulsion (PCE-2). The photochromic emulsion (PCE-2) prepared above was coated onto the selected PET film by dip coating to produce a wet thickness of 200 um at room temperature. The coated wet emulsion was dried in air for about 1 hour to yield a photochromic dye containing PMMA layer coating on the PET substrate, which is referred as a comparative photochromic device(PCD-2). PCD-2 was not made according to this invention where dye molecules are not suspended in a polymeric material in any form of micro-droplets.

Example 3

[0038] In this example, devices made in the Example and Example 2 are tested and evaluated in parallel. First, PCD-1 and PCD-2 were exposed to outdoor sunlight at the same time. Under the same condition, PCD-1 exhibited color change from colorless to pink in few seconds while PCD-2 did not observed any color change with a minute. Secondly, the absorption spectrum of the PCD-1 and PCD-2 was further measured by an Oceanview spectrometer. FIG. 4 presents visible light transmittance spectra of the PCD-1 under an irradiation of xenon lamp (CHF-XM35-500W, ON State) and without irradiation of the xenon lamp (OFF-State). From FIG. 4, it can be seen that PCD-1 prepared according to this invention exhibited excellent light transmittances at OFF-State but significantly shield light in the wavelength of 430 to 65 0nm when it is in ON-state. No such a photochromic effect was observed from PCD-2 prepared in a way different from this invention.