CN106146807B - A class of polyfluorene-based polymers containing non-conjugated units in the main chain and its preparation method and application - Google Patents

Abstract

The invention discloses a polyfluorene polymer whose main chain contains non-conjugated units and its preparation method and application. The polymer introduces a type of non-conjugated structural unit into the main chain of polyfluorene to realize the induced production beta-phase. As we all know, polyfluorene polymers are one of the most promising blue light polymers, due to their high fluorescence quantum efficiency, relatively good thermal and electrochemical stability, and easy functionalization at the carbon-9 position of fluorene, etc. β‑relative has a profound effect on film morphology, carrier transport, and device performance.

Description

A class of polyfluorene-based polymers containing non-conjugated units in the main chain and its preparation method and application

technical field

The invention belongs to the field of organic optoelectronics, and specifically relates to a polyfluorene polymer whose main chain contains non-conjugated units, a preparation method and application thereof.

Background technique

Polyfluorene materials are promising materials, but they also have some disadvantages. As luminescent materials, homopolyfluorene electroluminescence (EL) has low efficiency and poor spectral stability. This is mainly due to the fact that most of the homopolyfluorenes in light-emitting devices are in the form of amorphous phase, with wide energy band gap and low luminous efficiency. One of the commonly used methods to improve the EL luminescence properties of blue-light polyfluorene is to induce the β phase of polyfluorene. The conjugation length of the β phase of polyfluorene can be extended to about 30 repeating units. It has good planarity and regularity, which is beneficial to Enhanced luminous efficiency and spectral stability. The current methods for inducing the β-phase of polyfluorene include proper structural modification of polyfluorene, selection of solvent during solution processing, and control of solvent volatilization speed. Chen's group capped the main chain of polyfluorene with electron-deficient groups oxadiazole and triazole, respectively, and successfully induced more β-phase.

The polyfluorene polymer involved in the present invention introduces some non-conjugated units into the main chain of the polymer, and induces the β phase of the polyfluorene polymer through chemical methods, which can improve the carrier injection and transmission, improving device efficiency. Its light-emitting device is not only efficient and stable, but also a bluer saturated blue light, which can meet the requirements of full-color display. Therefore, there is great development potential and prospect in the field of organic electronic display.

Contents of the invention

The present invention aims at the problems faced by current polymer light-emitting diodes (PLEDs), and provides a class of polyfluorene polymers whose main chain contains non-conjugated units. Such polymers have better solubility and higher fluorescence quantum yield. Rate, suitable for solution processing and inkjet printing, has good development prospects.

The object of the present invention is also to provide a preparation method of the polyfluorene polymer whose main chain contains non-conjugated units.

The object of the present invention is also to provide the application of the polyfluorene polymer whose main chain contains non-conjugated units in light-emitting diodes.

The purpose of the present invention is achieved through the following technical solutions.

A class of polyfluorene polymers whose main chain contains non-conjugated units, the structural formula is as follows:

In the formula, R is a linear or branched alkyl group or alkoxy group or H atom or aryl group or triphenylamine with a carbon number of _1-20 ; the degree of polymerization n is 1-300; x is a mole fraction, and x> 0 and x<0.05;

Further, the structure of Ar is any one of the following structures.

R is a straight chain or branched chain alkyl group or alkoxy group or H atom or aryl group or triphenylamine with 1-20 carbon atoms.

The above-mentioned preparation method of a polyalkylfluorene polymer whose main chain contains non-conjugated units mainly includes the preparation of non-conjugated structural units and the preparation method of polyfluorene polymers with non-conjugated units. Through the method of Suzuki polymerization, non-conjugated units were introduced into the main chain of polyfluorene to induce β-phase.

The application of the polyalkylfluorene polymer whose main chain contains non-conjugated units in light-emitting diodes and flat panel displays.

The above-mentioned polyalkylfluorene polymer luminescent material whose main chain contains non-conjugated units can be dissolved in common organic solvents. It can be used as a light-emitting layer of a light-emitting diode, and it can be formed into a film by spin-coating, ink-jet printing or printing with an organic solution.

The invention induces β-phase by introducing non-conjugated units into the main chain of polyfluorene. Among them, the β-phase is a more planar configuration with extended conjugation length, which can improve the color purity of polyfluorene polymers and improve device efficiency.

Compared with the prior art, the present invention has the following advantages:

(1) The polyalkylfluorene-based polymer whose main chain contains non-conjugated units according to the present invention induces β-phase by introducing non-conjugated units into the main chain of polyfluorene. Among them, the β-phase is a more planar configuration with extended conjugation length, which can improve the color purity and device efficiency of polyfluorene polymers.

(2) The polyalkylfluorene polymer whose main chain contains non-conjugated units according to the present invention has good solubility, and when it is used as a light-emitting layer, no annealing treatment is required in the preparation of the device, which makes the preparation process simpler.

Description of the drawings:

Figure 1 is a thermal analysis spectrum of polymer P1.

Fig. 2 is a thermal analysis spectrum of polymer P2.

Fig. 3 is a UV-visible absorption spectrum and a fluorescence spectrum of the polymer P3 in a thin film state.

Figure 4 is a cyclic voltammetry (CV) spectrum of polymer P4.

Fig. 5 is a graph of lumen efficiency-current density of polymer P5.

Fig. 6 is the lumen efficiency-current density curve of polymer P6.

Detailed ways

The present invention will be described in further detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto.

Embodiment 1 2, the preparation of 7-dibromofluorene

In a 250 mL three-necked flask, add fluorene (24.5 g, 0.1 mol), iron powder (88 mg, 1.57 mmol), and 100 mL of chloroform. After cooling in an ice-water bath, 35 mL of a bromine (17.6 g, 0.1 mol)/chloroform mixed solution was added dropwise. The temperature in the bottle does not exceed 5°C during the dropwise addition. After the reaction was completed, it was filtered and recrystallized from chloroform to obtain 20.3 g of a white solid with a yield of 83%. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

Example 2 Preparation of 2,7-dibromo-9,9-dioctyl-9H-fluorene

2-Bromofluorene (9.7 g, 0.03 mol), benzyltriethylammonium chloride (0.07 g, 0.3 mmol), 90 mL of dimethyl sulfoxide, and 45 mL of aqueous sodium hydroxide solution (50 wt %) were added to a three-necked flask. Stir at room temperature to form a suspension. 1-Bromo-n-octane (12.5 g, 65 mmol) was added dropwise, and stirring was continued for 3 hours, followed by extraction with ether. The ether phase was washed with saturated aqueous sodium chloride and dried over anhydrous magnesium sulfate. The solvent was evaporated, and the product was purified by column chromatography using petroleum ether as the eluent to obtain a white solid. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

Example 3 Preparation of 2,7-diboronate-9,9-dioctylfluorene

Under an argon atmosphere, 2,7-dibromo-9,9-dioctylfluorene (5 g, 10.65 mmol) was dissolved in 180 mL of refined THF, and 1.6 mol.L ^-1 was gradually added dropwise at -78°C 28mL of n-butyllithium, reacted for 2 hours, then added 25mL of 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborane, at -78°C The reaction was continued for 1 hour, and the temperature was raised to room temperature for 24 hours. The reaction mixture was poured into water, extracted with ethyl acetate, and the organic layer was washed with brine and dried over anhydrous magnesium sulfate. After the solution was concentrated, a light yellow viscous crude product was obtained, which was purified by silica gel column chromatography (petroleum ether/ethyl acetate = 15/1, v/v was selected as the eluent), and the product was placed in the refrigerator for a long time to obtain a white solid. rate of 70%. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

The preparation of embodiment 4 compound M1

Under an argon atmosphere, 2,7-dibromo-9,9-dioctylfluorene (5g, 8.89mmol) and p-bromophenol (1.54g, 8.89mmol) were added to a 250mL two-necked flask, N was added, N-dimethylformamide was used to dissolve it completely, and then potassium carbonate (6.14 g, 44.45 mmol) was added, and the temperature was raised to 110° C. for 16 hours of reaction. The reaction mixture was poured into water, extracted with ethyl acetate, and the organic layer was washed with brine and dried over anhydrous magnesium sulfate. After the solution was concentrated, a light yellow viscous crude product was obtained, which was purified by silica gel column chromatography (petroleum ether/ethyl acetate=10/1, v/v was selected as the eluent). The product was placed in the refrigerator for a long time to obtain a white solid, the product Rate 60%. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

The preparation of embodiment 5 compound M2

Under an argon atmosphere, 2,7-dibromo-9,9-dioctylfluorene (5g, 8.89mmol) and p-bromoaniline (1.53g, 8.89mmol) were added to a 250mL two-necked flask, and toluene was added to make the After it was completely dissolved, palladium acetate (39.92mg, 177.8umol) and tri-tert-butylphosphine (71.94mg, 355.58umol) were added, and the temperature was raised to 110°C for 16 hours of reaction. The reaction mixture was poured into water, extracted with ethyl acetate, and the organic layer was washed with brine and dried over anhydrous magnesium sulfate. After the solution was concentrated, a light yellow viscous crude product was obtained, which was purified by silica gel column chromatography (petroleum ether/ethyl acetate=10/1, v/v was selected as the eluent). The product was placed in the refrigerator for a long time to obtain a white solid, the product Rate 60%. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

The preparation of embodiment 6 compound M3

Under an argon atmosphere, compound M2 (5g, 8.89mmol) and bromine (1.53g, 8.89mmol) were added to a 250mL two-neck flask, toluene was added to dissolve it completely, and then palladium acetate (39.92mg, 177.8umol) was added ) and tri-tert-butylphosphine (71.94mg, 355.58umol), the temperature was raised to 110°C, and the reaction was carried out for 16 hours. The reaction mixture was poured into water, extracted with ethyl acetate, and the organic layer was washed with brine and dried over anhydrous magnesium sulfate. After the solution was concentrated, a light yellow viscous crude product was obtained, which was purified by silica gel column chromatography (petroleum ether/ethyl acetate=10/1, v/v was selected as the eluent). The product was placed in the refrigerator for a long time to obtain a white solid, the product Rate 60%. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

Embodiment 7 dibromophenyl ether

Under an argon atmosphere, phenyl ether (5 g, 29.38 mmol) was added into a 250 ml two-neck flask, and then 50 ml of dichloromethane was added, and stirred under an ice bath to completely dissolve it. Liquid bromine (3.2ml) was then added, and reacted for 16 hours under protection from light. Sodium bisulfite was added to quench liquid bromine, extracted with ethyl acetate, the organic layer was washed completely with brine, and dried over anhydrous magnesium sulfate. After the solution was concentrated, a light yellow viscous crude product was obtained, which was purified by silica gel column chromatography (petroleum ether/ethyl acetate=5/1, v/v was selected as the eluent), and the product was placed in the refrigerator for a long time to obtain a white solid, the product Rate 60%. ¹ H NMR, ¹³ CNMR, MS and elemental analysis results show that the obtained compound is the target product, and its chemical reaction equation is as follows:

The synthesis of embodiment 8 polymer P1

Under an argon atmosphere, 2,7-diboronate-9,9-dioctylfluorene (200 mg, 311.2 μmol), 2,7-dibromo-9,9-dioctylfluorene (167.29 mg, 305.03umol) and dibromodiphenylamine (8.61mg, 2.63μmol) were added to a 100ml two-neck bottle, then 8mL of toluene was added to dissolve it completely, and the gas exchanged three times, then palladium acetate (2.80mg, 12.45μmol) and tricyclohexyl Phosphine (6.98mg, 24.90μmol) was pumped and ventilated three times, then 2ml of tetraethylammonium hydroxide was added, the temperature was raised to 80°C, and the reaction was carried out for 24 hours. Then 30 mg of phenylboronic acid was added for capping, and after 12 hours, 0.1 mL of bromobenzene was used for capping. After continuing to react for 12 hours, add the product dropwise to methanol to precipitate, stir, filter, and then dissolve the crude product in 20 mL of toluene, use 200-300 mesh silica gel as the stationary phase, and use toluene as the eluent for column chromatography. After analysis, the solvent was concentrated under reduced pressure, and precipitated in methanol again, stirred, filtered, and vacuum-dried to obtain a polymer solid. Finally, extract with methanol, acetone, and tetrahydrofuran for 24 hours to remove small molecules. The concentrated tetrahydrofuran solution was dropped into methanol for precipitation, and a fibrous solid was obtained after vacuum drying.

The thermal analysis diagram of the polymer P1 prepared in this example is shown in Figure 1, from which we can see that its decomposition temperature (Td) is 435° C., so the polymer has relatively high thermal stability. Moreover, the polymer has high solubility and is suitable for solution processing and inkjet printing.

The synthesis of embodiment 9 polymer P2

Under an argon atmosphere, 2,7-diboronate-9,9-dioctylfluorene (200 mg, 311.2 μmol), 2,7-dibromo-9,9-dioctylfluorene (167.29 mg, 305.03umol) and compound M1 (7.61mg, 2.63μmol) were added in a 100ml two-necked bottle, and then 8ml of toluene was added to make it completely dissolved, and the gas exchange was performed three times, then palladium acetate (2.80mg, 12.45μmol) and tricyclohexylphosphine ( 6.98mg, 24.90μmol), pumped and ventilated three times, then added 2ml of tetraethylammonium hydroxide, heated to 80°C, and reacted for 24 hours. Then 30 mg of phenylboronic acid was added for capping, and after 12 hours, 0.1 ml of bromobenzene was used for capping. After continuing to react for 12 hours, add the product dropwise to methanol to precipitate, stir, filter, and then dissolve the crude product in 20 mL of toluene, use 200-300 mesh silica gel as the stationary phase, and use toluene as the eluent for column chromatography. After analysis, the solvent was concentrated under reduced pressure, and precipitated in methanol again, stirred, filtered, and vacuum-dried to obtain a polymer solid. Finally, extract with methanol, acetone, and tetrahydrofuran for 24 hours to remove small molecules. The concentrated tetrahydrofuran solution was dropped into methanol for precipitation, and a fibrous solid was obtained after vacuum drying.

The thermal analysis diagram of the polymer P2 prepared in this example is shown in Figure 2, from which we can see that its decomposition temperature (Td) is 455°C, so the polymer has relatively high thermal stability. Moreover, the polymer has high solubility and is suitable for solution processing and inkjet printing.

The synthesis of embodiment 10 polymer P3

Under an argon atmosphere, 2,7-diboronate-9,9-dioctylfluorene (200 mg, 311.2 μmol), 2,7-dibromo-9,9-dioctylfluorene (167.29 mg, 305.03umol) and compound M3 (7.88mg, 2.63μmol) were added in a 100ml two-necked bottle, and then 8ml of toluene was added to make it completely dissolved, and the gas exchange was performed three times, then palladium acetate (2.80mg, 12.45μmol) and tricyclohexylphosphine ( 6.98mg, 24.90μmol), pumped and ventilated three times, then added 2ml of tetraethylammonium hydroxide, heated to 80°C, and reacted for 24 hours. Then 30 mg of phenylboronic acid was added for capping, and after 12 hours, 0.1 ml of bromobenzene was used for capping. After continuing to react for 12 hours, add the product dropwise to methanol to precipitate, stir, filter, and then dissolve the crude product in 20 mL of toluene, use 200-300 mesh silica gel as the stationary phase, and use toluene as the eluent for column chromatography. After analysis, the solvent was concentrated under reduced pressure, and precipitated in methanol again, stirred, filtered, and vacuum-dried to obtain a polymer solid. Finally, extract with methanol, acetone, and tetrahydrofuran for 24 hours to remove small molecules. The concentrated tetrahydrofuran solution was dropped into methanol for precipitation, and a fibrous solid was obtained after vacuum drying.

The ultraviolet-visible absorption spectrum and photoluminescence spectrum of polymer P3 in the film are shown in Figure 3. It can be seen from the figure that the polymer is polymerized at 392nm and 437nm, and the absorption peak of the polymer at 437nm is the β-phase The characteristic absorption peak, so the introduction of non-conjugated units in the main chain of polyfluorene can induce the production of polymer β-phase. The peaks of the photoluminescence spectrum are at 415nm, 439nm, and 468nm.

The synthesis of embodiment 11 polymer P4

Under an argon atmosphere, 2,7-diboronate-9,9-dioctylfluorene (200 mg, 311.2 μmol), 2,7-dibromo-9,9-dioctylfluorene (167.29 mg, 305.03umol) and compound dibromophenylene ether (2.04mg, 2.63μmol) were added into a 100ml two-neck bottle, and then 8ml of toluene was added to dissolve it completely, and the gas exchange was performed three times, then palladium acetate (2.80mg, 12.45μmol) and three Cyclohexylphosphine (6.98mg, 24.90μmol) was ventilated three times, then 2ml of tetraethylammonium hydroxide was added, the temperature was raised to 80°C, and the reaction was carried out for 24 hours. Then 30 mg of phenylboronic acid was added for capping, and after 12 hours, 0.1 ml of bromobenzene was used for capping. After continuing to react for 12 hours, add the product dropwise to methanol to precipitate, stir, filter, and then dissolve the crude product in 20 mL of toluene, use 200-300 mesh silica gel as the stationary phase, and use toluene as the eluent for column chromatography. After analysis, the solvent was concentrated under reduced pressure, and precipitated in methanol again, stirred, filtered, and vacuum-dried to obtain a polymer solid. Finally, extract with methanol, acetone, and tetrahydrofuran for 24 hours to remove small molecules. The concentrated tetrahydrofuran solution was dropped into methanol for precipitation, and a fibrous solid was obtained after vacuum drying.

The cyclic voltammetry curve of the polymer P4 prepared in this embodiment is shown in Figure 4. We calculated the highest occupied molecular orbital energy level (E _HOMO ) and the lowest unoccupied molecular orbital energy level ( _ELUMO ). Wherein, since the oxidation-reduction potential of ferrocene (Fc) has an absolute vacuum energy level of 4.8ev, it is used as a benchmark in the electrochemical test process, through the formula E _HOMO =-e(E _OX +4.8-E _fer ) and E _LUMO =-(E _red +4.8-E _fer ) can calculate the HOMO and LUMO energy levels of the polymer, as can be seen from the test diagram in Figure 4, the oxidation sum of the polymer PCzNIF is 1.42ev, and the E _fer of ferrocene = 0.4, optical bandgap Eg=2.95ev. Therefore HOMO=-5.82ev and LUMO=-2.87ev are calculated.

The synthesis of embodiment 12 polymer P5

Under an argon atmosphere, 2,7-diboronate-9,9-dioctylfluorene (200 mg, 311.2 μmol), 2,7-dibromo-9,9-dioctylfluorene (167.29 mg, 305.03umol) and compound dibromophenylene sulfide (2.54mg, 2.83μmol) were added in a 100ml two-necked bottle, then 8ml of toluene was added to make it completely dissolved, and the air was changed three times, then palladium acetate (2.80mg, 12.45μmol) was added quickly and Tricyclohexylphosphine (6.98mg, 24.90μmol) was ventilated three times, then 2ml of tetraethylammonium hydroxide was added, the temperature was raised to 80°C, and the reaction was carried out for 24 hours. Then 30 mg of phenylboronic acid was added for capping, and after 12 hours, 0.1 ml of bromobenzene was used for capping. After continuing to react for 12 hours, add the product dropwise to methanol to precipitate, stir, filter, and then dissolve the crude product in 20 mL of toluene, use 200-300 mesh silica gel as the stationary phase, and use toluene as the eluent for column chromatography. After analysis, the solvent was concentrated under reduced pressure, and precipitated in methanol again, stirred, filtered, and vacuum-dried to obtain a polymer solid. Finally, extract with methanol, acetone, and tetrahydrofuran for 24 hours to remove small molecules. The concentrated tetrahydrofuran solution was dropped into methanol for precipitation, and a fibrous solid was obtained after vacuum drying.

The polymer P5 obtained in this embodiment is based on the device structure: ITO/PEDOT/EML/CsF/Al, and its lumen efficiency-current density curve is shown in Figure 5. From Figure 5, we can see the maximum lumen of the polymer P5 The efficiency is 2.2cd/A.

The synthesis of embodiment 13 polymer P6

Under an argon atmosphere, 2,7-diboronate-9,9-dioctylfluorene (200 mg, 311.2 μmol), 2,7-dibromo-9,9-dioctylfluorene (167.29 mg, 305.03umol) and compound dibromoaniline (2.44mg, 2.73μmol) were added in a 100ml two-necked bottle, then 8ml of toluene was added to make it completely dissolved, and the air was pumped three times, then palladium acetate (2.80mg, 12.45μmol) and tricyclohexyl Phosphine (6.98mg, 24.90μmol) was pumped and ventilated three times, then 2ml of tetraethylammonium hydroxide was added, the temperature was raised to 80°C, and the reaction was carried out for 24 hours. Then 30 mg of phenylboronic acid was added for capping, and after 12 hours, 0.1 ml of bromobenzene was used for capping. After continuing to react for 12 hours, add the product dropwise to methanol to precipitate, stir, filter, and then dissolve the crude product in 20 mL of toluene, use 200-300 mesh silica gel as the stationary phase, and use toluene as the eluent for column chromatography. After analysis, the solvent was concentrated under reduced pressure, and precipitated in methanol again, stirred, filtered, and vacuum-dried to obtain a polymer solid. Finally, extract with methanol, acetone, and tetrahydrofuran for 24 hours to remove small molecules. The concentrated tetrahydrofuran solution was dropped into methanol for precipitation, and a fibrous solid was obtained after vacuum drying.

The polymer P6 obtained in this example is based on the device structure: ITO/PEDOT/EML/CsF/Al, and its lumen efficiency-current density curve is shown in Figure 6. From Figure 6, we can see the maximum lumen of the polymer P6 The efficiency is 2.13cd/A.

Example 14 Preparation of electroluminescent devices based on polyfluorene-based polymers containing non-conjugated units in the main chain

On the pre-made indium tin oxide (ITO) glass, the square resistance of which is 10-20Ω/□, it is cleaned with acetone, detergent, deionized water and isopropanol in sequence, and treated with plasma for 10 minutes. A film of polyethoxythiophene (PEDOT:PSS) doped with polystyrene sulfonic acid (PEDOT:PSS) was spin-coated on ITO with a thickness of 150 nm.

The PEDOT:PSS film was dried in a vacuum oven at 80°C for 8 hours. Subsequently, the xylene solutions (1wt%) of the copolymers P1, P2, P3, P4, P5, and P6 were spin-coated on the surface of the PEDOT:PSS film with a thickness of 80nm; (1.5nm) and a 120nm thick metallic Al layer. Table 1 shows the photoelectric performance indexes of polyfluorene non-conjugated polymers.

Table 1

It can be seen from Table 1 that the polyfluorene-based polymer whose main chain contains non-conjugated units of the present invention is beneficial to improve the device efficiency of the material.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention All should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (3)

1. the polyfluorene quasi polymer that a kind of main chain contains non-conjugated units, which is characterized in that structural formula is as follows:

In formula, R is the straight chain that carbon atom number is 1-20 or branched alkyl or alkoxy or H atom or aryl or triphenylamine； Polymerization degree n is 1-300；X is molar fraction, x>0 and x<0.05；The structure of the Ar is any one of such as flowering structure:

2. the method for preparing the polyfluorene quasi polymer that a kind of main chain described in claim 1 contains non-conjugated units, feature exist In the method being polymerize by Suzuki introduces non-conjugated units in polyfluorene main chain, and induction generates β-phase.

3. the hair that the polyfluorene quasi polymer that one kind main chain described in claim 1 contains non-conjugated units is applied to light emitting diode Photosphere, which is characterized in that dissolve the polyfluorene quasi polymer that the main chain contains non-conjugated units with organic solvent, then pass through rotation It applies, inkjet printing or printing process form a film.