Preparation and photo-patterning characteristics of organic-inorganic hybrid thin film containing latent pigment by using photo-acid-generator (PAG) and microwave irradiation have been investigated. The acrylic thin film modified with methoxysilane containing PAG was formed on a glass substrate and irradiated with ultraviolet rays to promote sol-gel reaction by catalytic action of acid which was generated from PAG. And then the film was hardened with microwave irradiation, yielding organic-inorganic hybrid polymer film having hardness, highly transparency and strong adhesion with a glass substrate. Since this reaction only occurred in the optically (UV) irradiated regions, by exploiting the difference between the adhesivenesses of these regions photo-irradiated through photomask with a glass substrate, it was possible to form a patterned film with pitch of 100 to 50 μm by a simple lift-off method. A pigment-containing film using latent pigments (with subtractive three primary colors of coloring materials) and a patterned film were prepared, and it was possible to make these films multi-colored by varying the mixing ratio of the pigments. This multi-colored film-preparation method is effective for simply and efficiently forming a color-filter film by applying optical and microwave irradiation.
In recent years, organic-inorganic hybrid films―which combine the flexibility and responsiveness of organic substances with the hardness of inorganic substances―are being applied in fields like integrated circuits and optical devices [
The aim of the present study was to develop an easy-to-use optical patterning process and improve the optical characteristics and strength of a color-filter film. By doping a latent pigment into an organic-inorganic hybrid film by utilizing a siloxane-group-linked acrylic resin, a high-performance color-filter film with outstanding transparency, hardness, and durability (such as high adhesiveness) was prepared, and its properties were investigated. Furthermore, as an easy-to-use patterning approach, optical patterning based on a “lift-off” method and formation of a sol-gel film by using a photo-acid generator was investigated. As for an efficient method for curing the film, microwave irradiation was used instead of the conventionally used heat treatment.
As a method for optical patterning of the organic-inorganic hybrid film, irradiation by ultraviolet (UV) light onto a sol-gel film (composed of a chemically modified alkoxide) is known to be available. As for a film prepared by this method, variation of its solubility with regard to the solvent of the UV-irradiated gel film is exploited, and patterns in the film are formed by etching [
Synthetic method of quinacridon (Qn) latent pigment is described below as an example.
Qn pigment 0.30 g (0.96 mmol), di-t-buthyl dicarbonate 0.83 g (3.80 mmol: t-BOC) and 4-dimethylamino- pyridine 0.25 g (2.10 mmol: 4-DMAP) were mixed in N,N-dimethylformamide (70 ml: DMF). The mixed solution was stirred for 24 hours at room temperature. This solution was dropped into water, and the resulting precipitates were filtered and dried. Yellow precipitates were recrystallized from chloroholm and hexane to give Qn latent pigment (Qn-BOC). Yield: 0.190 g (39%).
Indigo latent pigment (Indigo-BOC) and Pigment Yellow 93 latent pigment (PY-BOC) were prepared by a similar method to that of Qn-BOC.
Poly-methacryloxypropyltrimethoxysilane (PMPTMS) was synthesized by block polymerization.
3-methacry-loxypropyltrimethoxysilane (MPTMS) 2.96 g (11.9 mmol) and 1-Hydroxycyclohexylphenylke- tone (HCPK: Photo-polymerization initiator) 0.06 g (0.29 mmol) were mixed and stirred for 5 min at rotating speed 500 rpm. This solution was irradiated with ultraviolet ray (low pressure mercury lamp, emitting wavelength: 254 nm, 185 nm, photo-intensity: 5 mW/cm2) under nitrogen. After 30 min., a stir bar stopped due to high viscosity of the solution because of polymerization. This polymer was diluted with THF and then poured into hexane. After standing in a refrigerator for 24 hours, white precipitate was decanted with hexane and filtered and dried in N2. Yield: 1.586 g (54%).
PMPTMS 20 wt%, triphenylsulfoniumtriflate (PAG) 1.0% and H2O 0.5% were dissolved in THF 58.5%. And then cyclohexanone 20 wt% was added to this solution, resulting in the spin-coating solution for thin film formation. The solution was spin-coated on the glass substrate (30 × 30 × 1.2 mmt) at rotating speed 3000 rpm for 60 sec. to form the thin film. Photomask with 100 μm or 50 μm slit was attached on the film, following to be irradiated with ultraviolet ray using low pressure mercury lamp at photo intensity of 5.0 mW/cm2 for 10 sec. After UV irradiation the film was peeled off by a lift-off method using scotch tape. And then the patterned film was irradiated with microwave (MW, 2.45 GHz, 100 W) for 5 to 10 min. to harden the film.
Latent pigment Qn-BOC 0.70 wt% (Indigo-BOC 1.80 wt%, PY-BOC 1.50 wt%) was added to the PMPTMS so- lution for thin film formation described in 2.3, respectively. By using this solution PMPTMS thin films containing latent pigment were prepared in the same way to the formation method of PMPTMS thin film.
To make multi-coloring thin film the appropriate ratios of Qn-BOC:Indigo-BOC, Qn-BOC:PY-BOC and Indigo-BOC:PY-BOC were mixed and added to the coating solution. The multi-coloring thin films were prepared by using this solution.
Infrared spectroscopy (Shimadzu FT-IR 8400S) and 1H nuclear magnetic resonance spectroscopy (JEOL FT- NMR JNM-ECS400) were used to analyze the structure of latent pigments and organic-inorganic hybrid polymer (PMPTMS). Ultraviolet-Visible spectroscopy (Shimadzu UV2450) was measured to analyze a transparency and absorption characteristics of the films containing latent pigment. The positions of the films containing pigments on chromaticity coordinates were obtained from the values of absorption spectra. Surface morphology of the films was measured with optical microscope (Kyowakogyo ME-LUX2) and laser microscope (Keyence VK-X200). For the evaluation of hardness of the coating films, the dynamic hardness was measured with a dynamic ultra-microhardness tester (Shimadzu DUH 211S) and pencil hardness was evaluated by a tape test conforming to Japan Industrial Standard (JIS K5600).
An outline of the synthesis route for the organic-inorganic-hybrid polymer and formation of a fine pattern are shown in
The chemical structure of the PAG used (triphenylsulfoniumtriflate) and the acid-generation mechanism are shown in
through a photomask, the sol-gel reaction is promoted by the acid catalyst in the UV-irradiated regions only. As a result, as the inorganic polymerization proceeds, the Si-OH groups of the glass surface react with the PMPTMS film, and chemical bonds are formed. The adhesiveness of the PMPTMS film with the glass substrate is thereby improved by this bonding. Exploiting the difference between the adhesiveness of the irradiated regions and that of the non-irradiated regions with the glass substrate makes it possible to form a fine patterning film by means of a simple lift-off method. The MWs (used instead of heat treatment for hardening the film) can act directly on the polarity of molecules in a different manner to heating by thermal convection and heat the interior of the film. As a result, a thin film can be heated efficiently, and processing time can be shortened.
Infrared spectra of MPTMS and photo-polymerized MPTMS (i.e., PMPTMS) are shown in
2830 cm−1. As for photo-radical-polymerized MPTMS (i.e., PMPTMS), the stretching vibration of the C=C bond has disappeared. This result confirms the polymerization of MPTMS.
1H-NMR spectra of PMPTMS (synthesized from MPTMS) and MPTMS are shown in
As for the 1H-NMR spectra of the synthesized PMPTMS, the peaks ascribed to the double-bond protons (at 6.10 ppm and 5.56 ppm) have disappeared, inferring that the double bond has been cleaved. As for the integration ratio of proton number, the proton number of methoxy group with a peak at 3.58 ppm is nine, while the integration ratio of the peaks at 0.65 ppm, 1.73 ppm and 3.90 ppm is 2:2:2, indicating that these peaks are methylene group. That means the three peaks can be ascribed to the alkyl chains of the methacryloxy group. From the peak positions, it is inferred that the 0.65 ppm is peak represents silicon-adjoining -CH2- protons, 1.73 ppm represents -CH2- protons, and 3.90 ppm represents -CH2- protons adjoining a -COO-group. However, a weak peak at 1.10 ppm can also be seen. Although it is likely to be an intermediate -CH2- peak, its proton number does not agree. Moreover, as for PMMA (polymethylmethacrylate) synthesized from MMA (methylmethacrylate), after the C=C (i.e., the main chain) bond is cleaved, the -CH2- peak appears near 1.84 ppm [
The 1H-NMR peaks of the synthesized PMPTMS are similar to those of PMMA with a syndiotactic configuration [
The state of a PMPTMS patterned thin film (width: 100 μm; no organic pigment) prepared by the proposed method is shown in
In the optically irradiated regions, a condensation reaction between the Si-OH group of the glass-substrate surface and the alkoxy group of the PMPTMS is promoted. As a result, adhesion of the film with the glass substrate by formation of chemical bonds becomes extremely strong. In the meantime, in the non-optically irradiated regions, inorganic polymerization does not proceed, chemical bonding with the glass substrate does not occur, and the adhesion with the glass substrate is weak. By exploiting this difference between the adhesivenesses of the respective regions with glass, it is conceivable that a lift-off method could be used for precise patterning. A lift-off method, which forms extremely simple patterns by “peeling off” a tape, does not produce liquid residue or need exclusive-use equipment in the manner of methods like etching; accordingly, it is a low-cost means of forming patterned films.
The absorption spectrum of a thin film formed on glass substrate is shown in
ness of the PMPTMS film. Cross-cut adhesion test (ISO Cross-cut Test) was carried out to evaluate adhesiveness of PMPTMS film on a glass substrate. PMPTMS film showed the value of 25/25 (the number of residual films/the number of cross-cut films), indicating strong adhesiveness. In stark contrast, for acrylic film, which has been used for color filter, both the MW-irradiated film and the heat-treated film at 150˚C showed the values of 0/25, indicating weak adhesiveness. The strong adhesiveness of PMPTMS film would be attributed to the che- mical bonding between PMPTMS film and a glass substrate.
“Multi-coloring” by mixing coloring materials, namely, latent pigments (with three “primary colors” of subtractive mixture) into the synthesized PMPTMS film was investigated. The latent pigments used to form the three subtractive primary colors were cyan (i.e., indigo), yellow (i.e., PY93), and magenta (i.e., quinacridone)). The chemical structures of the pigments are shown in
Changes in the surface color of latent-pigment-containing films (prepared on a glass substrate) after MW irradiation (500 W for 10 min) or heat treatment are compared in
the film produces the three subtractive “primary colors” of the coloring materials (magenta, cyan, and yellow). As for the heat-treated film, heating at 180˚C for 30 min is necessary. The latent pigment is transformed by the MW irradiation (500 W for 5 to 10 min) to active pigment, and a pigment-containing film is formed efficiently by MW irradiation. While hardening the PMPTMS film, the MW irradiation also contributes to forming active pigment from the latent pigment. Moreover, by varying the blend ratio of the latent pigments with the three subtractive “primary colors,” it is possible to produce the three primary colors of light (namely, red, green, and blue) by subtractive mixture. Photographs of the surfaces of films with systematically varied color mixtures of latent pigments are shown in
Changes in absorption spectra when the mixing ratio of latent pigments is changed are shown in
with the three subtractive primary colors of the coloring materials are shown in
An organic-inorganic hybrid film containing latent pigments was prepared by using a photo-acid generator and
MW irradiation and optically patterned by UV light. Acrylic resin combining methoxysilane groups forms a hard and highly transparent thin film as a result of a sol-gel reaction being promoted by an acid generated by a photo-acid generator. Since this reaction only occurs in the optically (UV) irradiated regions, by exploiting the difference between the adhesivenesses of these regions with a glass substrate, it is possible to form a patterned film with pitch of 100 to 50 μm by a simple lift-off method. Moreover, a pigment-containing film using latent pigments (with three primary colors of coloring materials) and a patterned film were prepared, and it was possible to make these films multi-colored by varying the mixing ratio of the pigments. This multi-colored film-pre- paration method is effective for simply and efficiently forming a color-filter film by applying optical and MW irradiation.