TWI893600B - Innovative barrier-film free quantum dot optical film structure and method for manufacturing thereof with cardo polymer - Google Patents

Abstract

An innovative barrier-film free quantum dot optical film structure and method for manufacturing thereof with cardo polymer are provided. The quantum dot optical film includes: a quantum dot thin film layer including a solvent-free UV photosensitive resin composition and a quantum dot material, wherein the quantum dot material is dispersed in the solvent-free UV photosensitive resin composition, wherein the solvent-free UV photosensitive resin composition includes resin, monomer, and photo-initiator, wherein the resin includes a cardo polymer oligomer, based on total 100 wt % of the solvent-free UV photosensitive resin, the content of the resin ranges from 20 wt% to 65 wt%; the content of the monomer ranges from 5 wt% to 20 wt%; and the content of the photoinitiator ranges from 1 wt% to 15 wt%.

Description

Novel barrier-free quantum dot film of polycarboxylic acid polymer and its manufacturing method

The present invention relates to a quantum dot film and a method for manufacturing the same, and more particularly to a quantum dot film and a method for manufacturing the same that utilizes fluorene resin oligomers to eliminate the need for a moisture barrier film.

In recent years, quantum dot components and elements have been used in displays and other optical devices, such as LCD displays, LED devices, and backlight modules. They offer benefits such as improved display quality, brightness, color rendering index (CRI), and color gamut.

However, due to their nanoscale size, quantum dots are easily affected by external factors such as heat, water, moisture, oxygen, and volatiles. Therefore, a barrier film is required outside the quantum dot film to prevent fluorescence quenching caused by oxygen and moisture degradation.

In recent years, developments in quantum dots and related technologies have primarily focused on enhancing quantum dot properties, color variation, and the display capabilities of quantum dot-based optical devices. While the stability of optical film materials used for quantum dots is key to the widespread application of quantum dot optical materials, research on enhancing quantum dot stability has been limited to modifying the ligands on the core, shell, and surface of the quantum dots.

On the other hand, the effectiveness of other optical materials used for quantum dot stabilization has rarely been examined.

In the past, developing resins compatible with quantum dot films required the use of a multi-layer barrier film due to the nanoscale size of quantum dots and their high surface area. This resulted in a strong affinity for water and oxygen. This barrier film is essentially an inorganic oxide layer applied or sputtered onto the PET surface. Specifically, a layer of silicon dioxide or aluminum oxide is applied to the PET surface to achieve a water and oxygen barrier. However, barrier films are prohibitively expensive, increasing the cost of quantum dot films and significantly hindering their widespread application. Existing quantum dot films without barrier films have shown poor reliability testing (RA) performance.

Therefore, there is a need to provide improved materials with quantum dots that can reduce and/or avoid the stability issues associated with quantum dots without the need for barrier materials, thereby resolving the problems associated with existing technologies.

One object of the present invention is to provide a composition for use in photosensitive optical composite materials that can improve fluorescence quenching caused by oxygen and moisture-induced degradation in conventional quantum dot films.

Another object of the present invention is to provide a composition for photosensitive optical composite materials that can improve fluorescence quenching caused by oxygen and moisture-induced degradation, increase reliability, and extend service life.

Another object of the present invention is to provide a photosensitive optical composite material that does not require a barrier film and can improve fluorescence quenching caused by oxygen and moisture-induced degradation, thereby increasing stability and extending service life.

To achieve the above objectives, the present invention provides a quantum dot film comprising: a quantum dot film layer comprising a solvent-free UV-sensitive resin composition and a quantum dot material. The quantum dot material is dispersed in the solvent-free UV-sensitive resin composition, wherein the solvent-free UV-sensitive resin composition comprises a resin, a monomer, and a photoinitiator, wherein the resin comprises a fluorene resin oligomer and another resin. The other resin is a polyurethane-acrylate resin (PU acrylic resin) or an epoxy-acrylate resin (epoxy acrylic resin). Based on 100 weight percent of the total weight of the solvent-free UV-sensitive resin composition, the solvent-free UV-sensitive resin composition comprises 20 to 65 weight percent of the resin; 5 to 20 weight percent of the monomer; and 1 to 15 weight percent of the photoinitiator.

The present invention also provides a photosensitive optical composite composition containing a cardo polymer, wherein the photosensitive optical composite composition comprises a luminescent material, a cardo polymer, a monomer, a photoinitiator, and a light scattering agent. The cardo polymer comprises a fluorene resin oligomer. Based on 100 weight percent of the total weight of the photosensitive optical composite composition, the photosensitive optical composite composition comprises 0.1 to 5 weight percent of the luminescent material; 10 to 60 weight percent of the cardo polymer; 0 to 20 weight percent of a polyurethane-acrylate monomer or an epoxy-acrylate monomer; 1 to 5 weight percent of the light scattering agent; and 1 to 15 weight percent of the photoinitiator.

In some embodiments, the resin is a cardo polymer mainly composed of a fluorene framework.

In some embodiments, the fluorene framework has the following structural formula:

In some embodiments, the monomer comprises a monomer selected from the group consisting of (3',4'-epoxycyclohexane)-methyl-3,4-epoxycyclohexane carboxylate (trade name: Daicel 2021P), ethoxylated bisphenol A diacrylate, and dipentaerythritol hexaacrylate (DPHA).

In some embodiments, the monomer further comprises an epoxy acrylic resin such as a bisphenol A modified acrylic resin, an epoxy monomer, an acrylate monomer, or a methacrylate monomer.

In some embodiments, the photoinitiator comprises a free radical initiator, such as diphenyl(2,4,6-trimethylbenzyl)phosphine oxide (TPO), α-hydroxyisobutylbenzene (photoinitiator 1173 (UVC-1173)), 1-hydroxycyclohexylphenyl ketone (photoinitiator 184 (UVC-184)), or benzoin diethyl ether (photoinitiator 651 (UVC-651)). In some embodiments, the photoinitiator further comprises a cationic initiator, such as iodonium, (4-methylphenyl) [4-(2-methylpropyl)phenyl] hexafluorophosphate (trade name OMNIRAD 250).

In some embodiments, the quantum dot film further comprises a polyester layer, wherein the quantum dot thin film layer is disposed on the polyester layer.

In addition, the present invention also provides a method for manufacturing a quantum dot film, comprising the following steps: mixing a resin, a monomer, and a photoinitiator to prepare a solvent-free UV-sensitive resin composition, wherein the resin comprises a fluorene resin oligomer and another resin, wherein the other resin is a polyurethane-acrylate resin or an epoxy-acrylate resin, wherein the total weight of the UV-sensitive resin composition is 1000 ppm. Based on 100 weight percent, the solvent-free UV-sensitive resin composition comprises 20 to 65 weight percent of the resin; 5 to 20 weight percent of the monomer; and 1 to 15 weight percent of the photoinitiator. A quantum dot material is added to the solvent-free UV-sensitive resin composition to form a quantum dot resin composition; and the quantum dot resin composition is formed into a quantum dot film.

In some embodiments, the resin is a cardo polymer mainly composed of a fluorene framework.

1: Quantum dot film

10: Base material layer

11: Quantum dot materials

20: Polyester layer

3: Method for manufacturing the quantum dot film of the present invention

S31~S33: Steps

[Figure 1] is a schematic structural diagram of the first embodiment of the quantum dot film of the present invention.

[Figure 2] is a schematic structural diagram of the second embodiment of the quantum dot film of the present invention.

[Figure 3] is a schematic diagram of the process for manufacturing the quantum dot film of the present invention.

As used herein, reference to a variable's numerical range is intended to indicate that the variable is equal to any value within that range. Thus, for a variable that is inherently discontinuous, the variable is equal to any integer value within the numerical range, inclusive. Similarly, for a variable that is inherently continuous, the variable is equal to any real value within the numerical range, inclusive. By way of example, and not limitation, a variable described as having a value between 0 and 2 takes on the value 0, 1, or 2 if the variable is inherently discontinuous, whereas it takes on the value 0.0, 0.1, 0.01, 0.001, or any other real value ≥ 0 and ≤ 2 if the variable is inherently continuous.

To facilitate understanding of the design principles of the present invention, the following describes the details and implementation principles of the quantum dot film and its manufacturing method.

1 , the present invention provides a quantum dot film comprising a quantum dot film layer 1 . The quantum dot film layer 1 comprises a substrate layer 10 formed of a solvent-free UV-sensitive resin composition and a quantum dot material 11 . The quantum dot material 11 is dispersed in the solvent-free UV-sensitive resin composition of the substrate layer 1. The solvent-free UV-sensitive resin composition comprises a resin, a monomer, and a photoinitiator. The resin comprises a fluorene resin oligomer and another resin, wherein the other resin is a polyurethane-acrylate resin (PU acrylic resin) or an epoxy-acrylate resin (epoxy acrylic resin). Based on the total weight of the solvent-free UV-sensitive resin composition as 100 weight percent, the solvent-free UV-sensitive resin composition comprises 20 to 65 weight percent of the resin; 5 to 20 weight percent of the monomer; and 1 to 15 weight percent of the photoinitiator.

Preferably, the resin is a cardo polymer mainly composed of a fluorene skeleton, wherein the fluorene skeleton is shown in the following formula: .

In some embodiments, the fluorene framework has the following structural formula: For example, 9,9-bis(4-hydroxyphenyl)fluorene has the following structure: .

It should be noted that this resin can also be used in combination with polyurethane resin (PU resin), polyurethane-acrylate resin (PU acrylic resin), epoxy resin, epoxy-acrylate resin (epoxy acrylic resin), and acrylate resin (acrylic resin).

The monomer comprises a monomer selected from the group consisting of (3',4'-epoxycyclohexane)-methyl-3,4-epoxycyclohexane carboxylate (Daicel 2021P), ethoxylated bisphenol A diacrylate, and dipentaerythritol hexaacrylate (DPHA).

Optionally, the monomer may be combined with another monomer, including a bisphenol A modified acrylate, an epoxy monomer, an acrylic acid monomer, or a methacrylic acid monomer.

The photoinitiator may be diphenyl (2,4,6-trimethylbenzyl) phosphine oxide (photoinitiator TPO).

In addition, this photoinitiator can also be used in combination with other free radical photoinitiators, such as ethyl 2,4,6-trimethylbenzylphenylphosphonate (photoinitiator TPO-L), α-hydroxyisobutylbenzene (photoinitiator 1173), 1-hydroxycyclohexylphenyl ketone (photoinitiator 184), or benzoin diethyl ether (photoinitiator 651). Furthermore, this photoinitiator can also be used in combination with the cationic photoinitiator iodonium, (4-methylphenyl) [4-(2-methylpropyl)phenyl] hexafluorophosphate (trade name OMNIRAD 250).

The solvent-free UV-sensitive resin composition may further contain a light-scattering material to increase the light scattering path or enhance brightness by utilizing a refractive index difference. The light-scattering material may include inorganic material particles, a nitride, or an organic polymer material. For example, the inorganic material particles may include _one or a combination of _SiO2 , _TiO2 , _ZnO2 , _SrSO4 , and BaSO4; the nitride may be BNx, etc.; and the organic polymer material may include polystyrene polymer, polymethyl methacrylate polymer, acryl crosslinked polymer, acryl-styrene crosslinked polymer, benzoguanamine-formaldehyde polymer, melamine-formaldehyde condensation polymer, benzoguanamine-melamine-formaldehyde condensation polymer, or a combination thereof (such as MBX-8 from Sekisui Chemical Co., Ltd. or MS from Nippon Catalyst Co., Ltd.).

Examples of quantum dot materials include cadmium-containing or cadmium-free quantum dot concentrates (diluted with isobornyl acrylate (IBOA)), phosphors, or perovskite. Quantum dot materials include, but are not limited to, silver indium sulfide (AgInS ₂ , AIS), copper indium sulfide (CuInS ₂ ,CIS), cadmium selenide (CdSe), cadmium sulfide (CdS), cadmium telluride (CdTe), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), zinc oxide (ZnO), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), cadmium selenide sulfide (CdSeS), cadmium selenide telluride (CdSeTe), cadmium telluride sulfide (CdSTe), zinc selenide sulfide (ZnSeS), zinc telluride selenide (Zn SeTe), zinc telluride sulfide (ZnSTe), mercury selenide sulfide (HgSeS), mercury selenide telluride (HgSeTe), mercury telluride sulfide (HgSTe), cadmium zinc sulfide (CdZnS), cadmium zinc selenide (CdZnSe), cadmium zinc telluride (CdZnTe), cadmium mercury sulfide (CdHgS), cadmium mercury selenide (CdHgSe), cadmium mercury telluride (CdHgTe), mercury zinc sulfide (HgZnS), mercury zinc selenide (HgZnSe), telluride Mercury zinc (HgZnTe), cadmium zinc selenide (CdZnSeS), cadmium zinc selenide telluride (CdZnSeTe), cadmium zinc telluride (CdZnSTe), cadmium mercury selenide (CdHgSeS), cadmium mercury selenide telluride (CdHgSeTe), cadmium mercury telluride (CdHgSTe), mercury zinc selenide (HgZnSeS), mercury zinc selenide telluride (HgZnSeTe), mercury zinc telluride (HgZnSTe), gallium nitride (GaN), gallium phosphide (GaP), Gallium arsenide (GaAs), gallium antimonide (GaSb), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), gallium phosphide nitride (GaNP), gallium arsenide nitride (GaNAs), gallium antimonide nitride (GaNSb), gallium arsenide phosphide (GaPAs), gallium antimonide phosphide (GaPSb), Aluminum (AlNP), aluminum arsenide nitride (AlNAs), aluminum antimony nitride (AlNSb), aluminum arsenide phosphide (AlPAs), aluminum antimony phosphide (AlPSb), indium phosphide nitride (InNP), indium arsenide nitride (InNAs), indium antimony nitride (InNSb), indium arsenide phosphide (InPAs), indium antimony phosphide (InPSb), gallium aluminum phosphide nitride (GaAlNP), gallium aluminum arsenide nitride (GaAlNAs), gallium aluminum antimony phosphide nitride (GaAlNSb), Gallium aluminum arsenide (GaAlPAs), gallium aluminum antimony phosphate (GaAlPSb), gallium indium phosphate nitrogen (GaInNP), gallium indium arsenide nitrogen (GaInNAs), gallium indium antimony nitride (GaInNSb), gallium indium arsenide phosphate (GaInPAs), gallium indium antimony phosphate (GaInPSb), indium aluminum phosphate nitrogen (InAlNP), indium aluminum arsenide nitrogen (InAlNAs), indium aluminum antimony nitride (InAlNSb), indium aluminum arsenide phosphate (InAlPAs), indium aluminum antimony phosphate (In AlPSb), tin sulfide (SnS), tin selenide (SnSe), tin telluride (SnTe), lead sulfide (PbS), lead selenide (PbSe), lead telluride (PbTe), tin selenide sulfide (SnSeS), tin selenide telluride (SnSeTe), tin telluride sulfide (SnSTe), lead selenide sulfide (PbSeS), lead selenide telluride (PbSeTe), lead telluride sulfide (PbSTe), lead tin sulfide (SnPbS), lead tin selenide (Sn [0014] The present invention also provides a novel nanostructured crystalline silicon (NCM) comprising: a quartz crystal (CsC), a quartz crystal (CsPbC), a _quartz crystal ( _{CsPbS ...}

In some embodiments, the fluorescent powder may include, but is not limited to: sulfide fluorescent powder, such as zinc _sulfide ( _ZnS ), cadmium sulfide (CdS), strontium sulfide (SrS), and calcium sulfide (CaS); halogenated phosphate fluorescent powder, such as calcium halogenated phosphate; _phosphate fluorescent powder, such as strontium phosphate ( _Sr2P2O7 ), _barium phosphate ( _Ba2P2O7 ), and calcium zinc phosphate ((Ca, Zn) ₃ ( _PO4 ) ₂ ); silicate fluorescent powder, such as _zinc silicate ( _Zn2SiO4 ), and calcium silicate ( _CaSiO3 ); tungstate fluorescent powder, such as magnesium tungstate (MgWO4 ₎ ; ), calcium tungsten oxide (CaWO ₄ ); aluminate fluorescent powders, such as barium magnesium aluminate (BaMg ₂ Al ₁₆ O ₂₇ ), barium magnesium aluminate (CeMgAl ₁₁ O ₁₉ ), and strontium aluminate (Sr ₄ Al ₁₄ O ₂₅ ); fluoride fluorescent powders, such as potassium fluorosilicate (K ₂ SiF ₆ :Mn ₄ ⁺ ); oxide fluorescent powders, such as yttrium oxide (Y ₂ O ₃ ) or luminium oxide (La ₂ O ₃ ).

In addition, as shown in FIG2 , the quantum dot film 1 further includes a polyester layer 20 , wherein the quantum dot film layer 10 is disposed on the polyester layer 20 . The polyester layer can be a polyethylene terephthalate (PET) film.

Next, referring to FIG3 , a schematic diagram of the process of manufacturing the quantum dot film of the present invention is shown. Method 3 for manufacturing a quantum dot film comprises the following steps: (step S31) mixing a resin, a monomer, and a photoinitiator to prepare a solvent-free UV-sensitive resin composition, wherein the resin comprises a fluorene resin oligomer, and based on 100 weight percent of the total weight of the UV-sensitive resin composition, the solvent-free UV-sensitive resin composition comprises 20 to 65 weight percent of the resin; 5 to 20 weight percent of the monomer; and 1 to 15 weight percent of the photoinitiator; (step S32) adding a quantum dot material to the solvent-free UV-sensitive resin composition to form a quantum dot resin composition; and (step S33) forming the quantum dot resin composition into a quantum dot film.

The following will illustrate the manufacturing method of the present invention in detail by way of examples.

First, prepare a solvent-free UV resin composition by thoroughly mixing the resin, monomer, initiator, and/or light scattering material in a high-speed blender or homogenizer for, for example, 10 to 30 minutes. The resin is primarily a fluorene resin, with other resins such as, but not limited to, polyurethane resins (PU resins), polyurethane-acrylate resins (PU acrylic resins), epoxy resins, epoxy-acrylate resins (epoxy acrylic resins), and acrylate resins (acrylic resins) used in combination, with the resin ratio ranging from 20 to 65%. The monomer can be Daicel 2021P, ethoxylated bisphenol A diacrylate, or DPHA. Additionally, monomers can be used in combination, such as, but not limited to, bisphenol A-modified acrylic monomers, epoxy monomers, acrylic acid, and methacrylic acid monomers. The monomer ratio is 5 to 20%. The main structure of the photoinitiator is the photoinitiator TPO, and can be used in combination, such as, but not limited to, free radical photoinitiators TPO-L, photoinitiator 1173 (UVC-1173), photoinitiator 184 (UVC-184), photoinitiator 651 (UVC-651), and cationic free radical OMNIRAD 250. The photoinitiator ratio is 1 to 15%.

Next, add the photoluminescent material (such as quantum dot concentrate or fluorescent powder) to the prepared UV adhesive and mix thoroughly using a high-speed blender or homogenizer (e.g., for 10 to 30 minutes) to form the quantum dot adhesive.

The quantum dot paste is then coated onto a carrier to form the quantum dot film of the present invention. Optionally, the carrier can be a polyethylene terephthalate (PET) film. Alternatively, the carrier can include glass, a release film, another polymer film (such as polycarbonate (PC), acrylic, or cellulose triacetate (TAC)), or a metal film. In some embodiments, the carrier can include one or more microtextures, and the microtexture(s) can include at least one of bevels, rhombuses, concave-convex grooves, semicircular shapes, circular shapes, or photonic crystals. It should be noted that after the quantum dot film is formed, the carrier can be removed or not.

Example 1

Table 1 shows the components and ratios of the quantum dot film optical composite material.

First, all the ingredients in Table 1 are mixed to form a mixture S1. This mixture is then stirred in a high-speed mixer or homogenizer for 15 to 30 minutes to uniformly disperse the CdSe/ZnS quantum dot material throughout the mixture. This mixture S1 is then placed between two polyethylene terephthalate (PET) substrates using a roll-to-roll process. The film is then exposed to ultraviolet light (UV mercury lamp, illuminance 300 to 2200 mW, total exposure dose not exceeding 1100 mJ) to form an optical film. This optical film comprises a composition S2 of the optical composite material between two PET substrates. As shown in Figure 1, the luminescent CdSe/ZnS material 10 is dispersed within the acrylic polymer 11. The precursor for preparing the acrylic polymer 11 includes a cardo polymer, an acrylate monomer, a light scattering agent, and an initiator, as shown in Table 2. Alternatively, monomer 1 can be a polyurethane-acrylate monomer, and monomer 2 can be an epoxy-acrylate monomer.

The inventors analyzed the high-temperature and high-humidity reliability (RA) performance of PET quantum dot films loaded with cardo polymer (Example 1; Tables 3 and 4) and without cardo polymer (Comparative Example; Tables 3 and 4). The results are shown in Tables 3 to 6, respectively.

Example 1: Reliability Performance of PET Quantum Dot Film Loaded with Cardol Polymer

Comparative Example 1: RA Performance of PET Quantum Dot Film Without Cardopolymer Loading

Comparative Example 2: RA Performance of Quantum Dot Barrier Film Without Cardopolymer Loading

Based on the above analysis, quantum dot films using the UV resin composition of this invention in combination with a fluorene-based cardo polymer and the monomers taught by this invention can significantly improve the RA test results of the PET film (i.e., after 1000 hours of high-temperature and high-humidity reliability testing at 85°C and 60°C/90% RH) to industry-standard standards (Δx, Δy < 0.010, ΔL no less than 85%).

Therefore, this invention conducts RA verification on the presence or absence of fluorene resin oligomers and the use of PET and barrier films. This confirms the effectiveness of this invention and its ability to significantly reduce the cost of quantum dot films, thereby enhancing their competitiveness and market application.

1: Quantum dot film

10: Base material layer

11: Quantum dot materials

Claims (9)

A new type of barrier-free quantum dot film based on polycarbamate polymer, comprising: A quantum dot film layer comprises a solvent-free UV-sensitive resin composition and a quantum dot material, wherein the quantum dot material is dispersed in the solvent-free UV-sensitive resin composition. The solvent-free UV-sensitive resin composition comprises a resin, a monomer, and a photoinitiator, wherein the resin comprises a fluorene resin oligomer and another resin, wherein the other resin is a polyurethane-acrylate resin or an epoxy-acrylate resin. Based on 100 weight percent of the total weight of the solvent-free UV-sensitive resin composition, the solvent-free UV-sensitive resin composition comprises 20 to 65 weight percent of the resin, 5 to 20 weight percent of the monomer, and 1 to 15 weight percent of the photoinitiator. The quantum dot film as described in claim 1, wherein the resin is a cardo polymer mainly having a fluorene framework. The quantum dot film of claim 2, wherein the fluorene framework has the following structural formula: . The quantum dot film of claim 1, wherein the monomer comprises a monomer selected from the group consisting of (3', 4'-epoxyhexane)-methyl-3,4-epoxyhexane carboxylate, ethoxylated bisphenol A diacrylate, and dipentaerythritol hexaacrylate. The quantum dot film as described in claim 4, wherein the monomer further comprises a bisphenol A modified acrylic resin, an epoxy monomer, an acrylic monomer or a methacrylic monomer. The quantum dot film of claim 1, wherein the photoinitiator comprises diphenyl (2,4,6-trimethylbenzyl) phosphine oxide. The quantum dot film as described in claim 6, wherein the photoinitiator further comprises ethyl 2,4,6-trimethylbenzylphenylphosphonate, α-hydroxyisobutylbenzene, 1-hydroxycyclohexylphenyl ketone or benzoin diethyl ether. The quantum dot film as described in claim 6, wherein the quantum dot film further comprises a carrier, wherein the quantum dot thin film layer is disposed on the carrier. A method for producing a novel barrier-free quantum dot film based on a polycarboxylic acid polymer comprises the following steps: Mixing a resin, a monomer, and a photoinitiator to prepare a solvent-free UV-sensitive resin composition, wherein the resin comprises a fluorene resin oligomer and another resin, wherein the other resin is a polyurethane-acrylate resin or an epoxy-acrylate resin. Based on 100 weight percent of the total weight of the solvent-free UV-sensitive resin composition, the solvent-free UV-sensitive resin composition comprises 20 to 65 weight percent of the resin; 5 to 20 weight percent of the monomer; and 1 to 15 weight percent of the photoinitiator. Adding a quantum dot material to the solvent-free UV-sensitive resin composition to form a quantum dot resin composition; and forming the quantum dot resin composition into a quantum dot film.