CN115572499A - Polymer liquid crystal brightness enhancement film and OLED display device - Google Patents
Polymer liquid crystal brightness enhancement film and OLED display device Download PDFInfo
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Abstract
The invention discloses a polymer liquid crystal brightness enhancement film and an OLED display device, belonging to the technical field of OLEDs, wherein the polymer liquid crystal film is a chiral nematic or cholesteric polymer liquid crystal film prepared by mixed crystals of various polymerizable liquid crystals; the concentration of the polymerizable chiral dopant contained in the various polymerizable liquid crystal mixed crystals is different, so that different screw pitches are formed in the polymer liquid crystal brightening film along the direction vertical to the thin film. Different from a cholesteric liquid crystal brightness enhancement film only reflecting specific wavelengths, the brightness enhancement film can enhance the light emitting efficiency of oblique emergent light. The brightness enhancement film is arranged between the phase delay film and the OLED light emitting layer, can reflect left-handed circular polarized light or right-handed circular polarized light, can convert common light into polarized light, and reduces the absorption of the polarizer on emergent light. Under the same energy consumption, the brightness enhancement film can effectively improve the brightness to be more than 30 percent and solve the problem of rapid reduction of the brightness at a large visual angle.
Description
Technical Field
The invention relates to the technical field of OLED, in particular to a high-molecular liquid crystal brightness enhancement film for improving the light emitting efficiency of an OLED display device and the OLED display device.
Background
Organic Light Emitting Diodes (OLEDs) have the advantages of flexible fabrication, low driving voltage, low power consumption, and the like, and have a rapid technological advance and wide application prospects in recent years, making them the hottest display devices in flat panel display, novel lighting, wearable, and intelligent electronic product development.
In the OLED display device, since light emitted from the OLED light-emitting layer is absorbed and dissipated when passing through the circular polarizer, the light emitted from the light-emitting layer of the OLED display is not high in utilization rate, and in order to achieve the use brightness, only the driving current of the light-emitting material in the OLED display can be increased, so that the purpose of increasing the brightness is achieved.
For the light emitting layer of the existing OLED display, when the OLED display is used for outdoor or vehicle-mounted display, the OLED material is required to operate at high power, and the service life of any one material is reduced, so that the whole OLED display fails. Due to the upgrade of hardware of the mobile phone at the present stage and the coming of the 5G era, the mobile phone increases the power consumption of the mobile phone, reduces the standby time, increases the use degree of the battery and most intuitively shows that the use time of the battery is shortened while the performances of the mobile phone in all aspects are improved. In addition, the reflection spectrum of the brightness enhancement film of the current-stage OLED display equipment only aims at a blue waveband or a red-green-blue three-primary-color waveband, the emergence efficiency of the polarizer can be effectively increased only for part of light which vertically or nearly vertically emerges, and the optical brightness enhancement for part of light which obliquely emerges is small. The invention comprehensively improves the utilization rate of visible light wave band light of the light emitting layer of the OLED display.
The special spiral structure of the cholesteric liquid crystal material determines the special optical characteristics thereof, and can split the light of a reflection waveband into left-handed circular polarized light and right-handed circular polarized light, and the left-handed circular polarized light and the right-handed circular polarized light can be changed into linear polarized light after being converted by a phase delay film. The reflection wavelength of the liquid crystal satisfies the Bragg equation, and the central reflection wavelength lambda is proportional to the helix moment p of the liquid crystal material and the average refractive index n thereof: λ = np, due to the dielectric anisotropy, refractive index n, of the liquid crystal material o And n e The average refractive index (n) is (2 n) o +n e )/3. For example, if n =2 of the cholesteric liquid crystal is such that it can reflect normally incident visible light with a visible wavelength λ =550nm, the helix moment should be about 275nm. The relationship between the pitch p of the liquid crystal material and the helical twisting power constant (HTP) of the chiral admixture and the content Xc of the chiral admixture in the liquid crystal composition is that p = [ (HTP) Xc] -1 . According to the average refractive index (n) of the cholesteric liquid crystal material, the central reflection wavelength (lambda) and the spiral twisting force constant (HTP) of the chiral dopant, the concentration of the chiral dopant in the chiral nematic liquid crystal or cholesteric liquid crystal mixed crystal can be calculated, and light with different wavelengths can be reflected by different concentrations of the chiral dopant.
Disclosure of Invention
In order to solve the above technical problems, a primary objective of the present invention is to provide a polymer liquid crystal brightness enhancement film and an OLED display device for improving the light-emitting efficiency of the OLED display device, so as to solve the problems in the prior art that the utilization rate of light emitted from the light-emitting layer of the OLED display is not high, the energy consumption is high, the conventional brightness enhancement film can only enhance a part of visible light with a specific wavelength range, and the gain of the brightness of the oblique emitted light is not large. Since the reflection wavelength λ is proportional to the pitch p of the liquid crystal material and its average refractive index n and the cosine of the incident angle when the light is obliquely incident: λ = nPcos θ. When the emergent light angle is large, the reflection wavelength is blue-shifted, and a brightness enhancement film for reflecting red-shifted wavelength is needed to increase the reflection, so that a chiral nematic or cholesteric liquid crystal film capable of continuously reflecting obliquely emergent visible light is needed to increase the transmittance of the emergent light.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a high molecular liquid crystal brightness enhancement film is a chiral nematic phase or cholesteric phase high molecular liquid crystal film prepared by mixing a plurality of polymerizable liquid crystals;
the concentrations of polymerizable chiral dopants contained in the polymerizable liquid crystal mixed crystals are different, so that different screw pitches are formed in the polymer liquid crystal brightening film along the direction vertical to the film;
the polymer liquid crystal brightness enhancement film can continuously reflect the light of a visible light wave band emergent obliquely and/or an infrared light wave band emergent vertically, and the reflectivity is more than 25%.
Further, the length variation range of the screw pitch is 0.1-0.8 μm. The polymer liquid-based brightening film is internally provided with a plurality of different screw pitches, one screw pitch can reflect visible light with a certain wave band, the multiple screw pitches jointly reflect continuous visible light, and the screw pitches can be uniformly changed or unevenly changed.
Further, each polymerizable liquid crystal mixed crystal is prepared from the following raw materials in percentage by weight:
0.3 to 98.0 percent of polymerizable chiral dopant, 0.3 to 5 percent of initiator and 0 to 98.2 percent of polymerizable liquid crystal monomer. In the invention, the polymerizable liquid crystal monomer comprises a polymerizable nematic liquid crystal monomer and a polymerizable cholesteric liquid crystal monomer.
Still further, the initiator is benzoin dimethyl ether (IRG 651) or other photoinitiator.
Furthermore, the chiral dopant is a non-polymerizable compound monomer or a polymerizable compound monomer, and in the process of preparing the polymer liquid crystal brightness enhancement film, the polymerizable chiral dopant can be subjected to cross-linking polymerization with the polymerizable liquid crystal monomer, and cannot generate phase separation, so that the reliability of a polymer film is more reliable;
the polymerizable chiral dopant is an acrylate or methacrylate compound containing a chiral group R, and the structural general formula of the polymerizable chiral dopant is shown as the following formula (I-1), formula (I-2), formula (I-3), formula (I-4), formula (I-5), formula (I-6), formula (I-7) or formula (I-8):
wherein the chiral group R is
、
、
、
、
、
、
Any one of the above;
x is
、
、
、
Any one of the above;
m is selected from any one of C3-C10 straight chain or branched chain alkyl and substituted or unsubstituted phenyl;
y is any one of H, C-C10 straight chain or branched chain alkyl, C3-C10 straight chain or branched chain alkoxy, C3-C10 straight chain or branched chain alkyl mercapto, C3-C10 straight chain or branched chain alkyl amino, C3-C10 straight chain or branched chain alkyl carboxyl, C3-C10 straight chain or branched chain alkyl cyano.
Furthermore, the polymerizable chiral dopant is any one of a cholesterol derivative liquid crystal polymerizable monomer, an isosorbide derivative polymerizable monomer, a binaphthol derivative polymerizable monomer, a chiral center polymerizable monomer, a double chiral center bond polymerizable monomer and a chiral shaft-containing polymerizable monomer.
Further, the cholesteric derivative liquid crystal polymerizable monomer is:
The isosorbide derivative polymerizable monomer is as follows:
the polymerizable monomer of the binaphthol derivative is as follows:
the chiral center polymerizable monomer is as follows:
the double chiral center bond polymerizable monomer is as follows:
the polymerizable monomer containing the chiral shafts is as follows:
further, the polymerizable liquid crystal monomer is a polymerizable liquid crystal monomer containing a polymerizable group, and the polymerizable group is acrylate or methacrylate.
In the invention, the polymerizable liquid crystal monomer can be mixed with the polymerizable chiral dopant to form a supermolecular helical structure, so that the cholesteric phase or chiral nematic phase liquid crystal film is prepared. The polymerizable liquid crystal mixed crystal contains non-liquid crystal state components, but the mixed crystal phase finally formed after mixing is a cholesteric phase or a chiral nematic phase. The polymerizable chiral dopant has a polymerizable group, and after being doped into liquid crystal mixed crystal, the polymerizable chiral dopant causes a helical arrangement structure of liquid crystal molecules to form chiral nematic phase or cholesteric phase liquid crystal, so that the stability and the reliability of the polymer liquid crystal film can be improved.
Further, the polymer liquid crystal brightness enhancement film is a chiral nematic or cholesteric polymer liquid crystal film obtained by uniformly coating a plurality of polymerizable liquid crystal mixed crystals at the same time to form a coating in interlayer contact, wherein the polymerizable chiral dopants contained in each polymerizable liquid crystal mixed crystal have different concentrations, and a single-layer coating with the polymerizable chiral dopant concentration changing along the direction vertical to the coating along with the diffusion of the polymerizable chiral dopants among the layers is formed, and then the single-layer coating is polymerized. The concentration difference of the chiral dopants between two adjacent layers is 0.01 to 10 percent.
Further, the polymer liquid crystal brightness enhancement film is a multilayer composite brightness enhancement film obtained by sticking and compounding a plurality of chiral nematic or cholesteric polymer liquid crystal films which are prepared in advance and used for reflecting visible light with different wave bands;
or the polymer liquid crystal brightening film is prepared by coating and polymerizing polymerizable liquid crystal mixed crystals containing polymerizable chiral dopants with different concentrations for multiple times on the basis of a layer of chiral nematic or cholesteric polymer liquid crystal film prepared in advance to obtain single-layer brightening films with multiple screw pitches;
each layer of chiral nematic or cholesteric polymer liquid crystal film is formed by polymerizing polymerizable liquid crystal mixed crystals containing polymerizable chiral dopants with different concentrations; the reflection wavelengths of the chiral nematic or cholesteric polymer liquid crystal films between adjacent layers can be connected with each other, and the light with the wavelength range of 435-660nm of each angle is emitted in a continuous reflection and inclination mode. The polymerization is initiated by light, heat or cation.
The preparation of the polymer liquid crystal brightness enhancement film has three modes, specifically as follows:
the first scheme is as follows: a brightness enhancement film is a chiral nematic phase or cholesteric phase polymer liquid crystal film prepared by simultaneously coating a plurality of polymerizable liquid crystal mixed crystals and drying and polymerizing; the concentrations of chiral dopants contained in the various polymerizable liquid crystal mixed crystals are different, and along with the diffusion of the chiral dopants, a pitch gradient is formed in the polymer liquid crystal brightening film along the direction vertical to the thin film, so that the single-layer polymer liquid crystal brightening film is obtained.
Scheme II: or the polymer liquid crystal brightness enhancement film is prepared into a plurality of chiral nematic phase or cholesteric phase polymer liquid crystal films which reflect visible light with different wave bands respectively, and then the different films prepared in advance are pasted and compounded to obtain the multilayer composite brightness enhancement film.
The third scheme is as follows: or on the basis of a layer of chiral nematic or cholesteric polymer liquid crystal film prepared in advance, polymerizable liquid crystal mixed crystals containing chiral dopants with different concentrations are adopted for multiple coating-polymerization, and a single-layer brightness enhancement film with multiple screw pitches is obtained.
The concentrations of chiral dopants in the various polymerizable liquid crystal mixed crystals are different, the prepared thread pitch determines the reflection wavelength, the range of the reflection wavelength can be adjusted according to a formula lambda = np, so that the reflection wavelengths can be just mutually connected, and the visible light wave bands obliquely emergent at various angles and the infrared light wave bands vertically emergent are continuously reflected. The polymer liquid crystal brightness enhancement film continuously reflects visible light through superposition of polymer liquid crystal films with a pitch gradient or multiple pitches; is different from the prior brightness enhancement film which reflects single color or three primary colors.
The thickness of the polymer liquid crystal brightness enhancement film is 3-70 um; the polymer liquid crystal brightness enhancement film inevitably reflects continuously between 435 nm and 660nm, and the continuous reflection visible light wave width is larger than 245nm. Of course, outside the inevitable reflection region, all visible light can be reflected continuously, or part of visible light can be reflected, or a small part of infrared band can be reflected according to the use requirement, and the reflection wavelength is between 380nm and 2000 nm.
In order to enhance the light emitting efficiency of the oblique emergent light of the red, green and blue three primary colors of the OLED display, the reflection bandwidth of the polymer liquid crystal brightness enhancement film is purposefully widened towards the long wave direction, so that the light emitted by the oblique emergent OLED display equipment is improved, the light is not limited to the reflection bandwidth of the red, green and blue three primary colors of the OLED display device, and the reflectivity of the continuous reflection waveband of the polymer liquid crystal brightness enhancement film is larger than 25%.
Furthermore, the polymer liquid crystal brightness enhancement film can increase the light emitting efficiency of oblique emergent light, and the angle range of the oblique emergent light is 0-60 degrees.
The invention also provides an OLED display device, which comprises the polymer liquid crystal brightness enhancement film, wherein the polymer liquid crystal brightness enhancement film is arranged on one side of the light emitting layer of the OLED display device.
Further, the OLED display device further comprises a light emitting layer, a phase retardation film and a linear polarizer along the light emitting direction, and the polymer liquid crystal brightening film is arranged between the light emitting layer and the phase retardation film.
The OLED display device comprises a linear polarizer, a phase delay film, a brightness enhancement film, an OLED light-emitting panel and a metal electrode; the spiral direction in the polymer liquid crystal brightness enhancement film is matched with the absorption axis of the linear polarizer; the light emitted by the organic layer of the OLED display selectively passes through the right-handed circular polarized light and reflects the left-handed circular polarized light through the brightness enhancement film, or passes through the left-handed circular polarized light and reflects the right-handed circular polarized light, the passed circular polarized light is converted into light perpendicular to the absorption axis of the linear polarizer through the phase retardation film to be emitted, the opposite-handed circular polarized light which does not pass through the brightness enhancement film can be reflected by the brightness enhancement film to rebound to the metal electrode, the rotation of the rebounded circular polarized light can be changed through the reflection of the metal electrode, the rotation of the rebounded circular polarized light is converted into the rotation capable of passing through the brightness enhancement film, and the rotation is emitted to the outside through the brightness enhancement film, the phase retardation film and the linear polarizer. Furthermore, the OLED display device also comprises a connecting layer arranged among the luminescent layer, the brightness enhancement film, the phase retardation film and the linear polarizer; the connecting layer is an optical adhesive bonding layer and is required to avoid optical birefringence, stress birefringence and optical interference and diffraction;
further, the light emitting layer is emitted by an organic light emitting diode.
Further, the phase retardation film is a single quarter-phase retardation film or a quarter-phase retardation film and a half-phase retardation film which are combined, and other phase retardation films.
Compared with the prior art, the high polymer liquid crystal brightness enhancement film provided by the invention can effectively solve the problem of rapid reduction of screen brightness caused by increase of a visual angle due to broadening of the reflection bandwidth of the high polymer liquid crystal film.
The invention has the beneficial effects that:
1. the reflection wavelength of the polymer liquid crystal brightness enhancement film for the OLED is 380-2000nm, the emergent light inclined at various angles between 435-660nm is inevitably and continuously reflected, the continuous reflection visible light bandwidth is larger than 225nm, and all or part of visible light or a small part of infrared wave band can be continuously reflected outside an inevitable reflection area; the high-molecular liquid crystal brightness enhancement film is matched with other elements, the aim of enhancing the brightness can be achieved without enhancing the driving current of a luminescent material in an OLED display, the power consumption of a screen is reduced, the high-molecular liquid crystal brightness enhancement film has social significance of energy conservation and environmental protection, and the service life of portable equipment can be prolonged.
2. The high polymer liquid crystal brightness enhancement film disclosed by the invention is matched with other elements, so that the brightness of a screen can be increased under the condition of not increasing the power consumption, and the light-emitting rate of an OLED organic layer is greatly improved. For OLED display devices with the same brightness, the polymer liquid crystal brightness enhancement film provided by the invention can reduce the driving current of the luminescent materials in the OLED display, and can simultaneously prolong the service life of all the luminescent materials in the OLED display. Different from a cholesteric liquid crystal brightness enhancement film only reflecting at a specific wavelength, the polymer liquid crystal film can enhance the light emitting efficiency of oblique emergent light.
3. In the polymeric liquid crystal brightness enhancement film of the present invention, the concentration of the chiral dopant in the cholesteric phase or chiral nematic phase liquid crystal doped with chiral molecules is different between the layers, and thus the concentration difference of the chiral dopant exists in the polymerized cholesteric phase or chiral nematic phase thin film. The concentration of the chiral dopant determines the pitch of a cholesteric phase or chiral nematic phase liquid crystal phase, so that the pitch changes along with the change of the concentration of the chiral dopant in the vertical direction of the brightness enhancement film, the brightness enhancement film can necessarily and continuously reflect light between 435 and 660nm, the bandwidth of the continuously reflected visible light is larger than 225nm, all or part of visible light or a small part of infrared wave band can also be continuously reflected outside a necessary reflection area, and the reflection wavelength is between 380nm and 2000 nm.
4. In the polymer liquid crystal brightness enhancement film, the polymer liquid crystal film is prepared by a multilayer compounding or multilayer coating mode, and because the reflection bandwidth of chiral nematic phase or cholesteric phase liquid crystal is narrow, (the reflection bandwidth is delta lambda = delta nP, delta n is the birefringence index of mixed liquid crystal, and P is the screw pitch of the mixed liquid crystal), the liquid crystal using common birefringence index usually needs 4~5 layers or repeated coating 4~5 times or more, and then the visible light wave band can be continuously reflected. If a large deltan liquid crystal material is used, deltan is more than 0.4, only 2 layers or coating times are needed, and only two pitches exist in the polymer liquid crystal film.
Drawings
FIG. 1 is a schematic view of a brightness enhancement film according to an embodiment of the invention.
Fig. 2 is an exploded view of an OLED display according to an embodiment of the invention.
Fig. 3 is a schematic diagram illustrating a light passing path when light emitted from the OLED display irradiates the circular polarizer according to an embodiment of the present invention.
FIG. 4 is a transmission spectrum of a brightness enhancement film of example 1.
FIG. 5 is a transmission spectrum of a brightness enhancement film of example 2.
In the figure, 1, 2 and 3 are cholesteric phase or chiral nematic phase liquid crystal film layers doped with chiral molecules with different chiral dopant concentrations; 4 is a linear polarizer; 5 is a phase retardation film; 6 is a brightness enhancement film; 7 is a metal electrode; and 8 is a light-emitting layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The brightness enhancement film is a short name of a high polymer liquid crystal brightness enhancement film.
The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
Referring to fig. 1, a polymer liquid crystal brightness enhancement film is a chiral nematic or cholesteric polymer liquid crystal film prepared from a plurality of polymerizable liquid crystals;
according to the weight percentage, each polymerizable liquid crystal mixed crystal is prepared from the following raw materials:
0.3 to 98.0 percent of polymerizable chiral dopant, 0.3 to 5 percent of initiator and 0 to 98.2 percent of polymerizable liquid crystal monomer. In the invention, the polymerizable liquid crystal monomer comprises a polymerizable nematic liquid crystal monomer and a polymerizable cholesteric liquid crystal monomer.
The concentrations of polymerizable chiral dopants contained in the various polymerizable liquid crystal mixed crystals are different, so that different screw pitches are formed in the brightening film along the direction vertical to the thin film; the pitch length varies from 0.1 to 0.8 μm. The brightness enhancement film can continuously reflect light in a visible light wave band and an infrared light wave band, and the reflectivity is larger than 25%.
The chiral dopant is a polymerizable compound monomer with a chiral center or a chiral structure, such as binaphthol, isosorbide and derivatives thereof; the structure and performance profile of the partially chiral dopants is shown in table 1.
TABLE 1 chiral dopant Structure and Performance
The chiral dopant concentration (Xc) depends on the wavelength (λ) to be reflected, the average refractive index (n) of the polymer liquid crystal film, and the helical twisting power constant (HTP) of the chiral dopant. According to the formula λ = nP, P = 1/(htp.xc), λ = n/(htp.xc) is given. The polymerizable chiral monomer applied to the polymer liquid crystal brightness enhancement film provided by the embodiment of the invention is selected according to factors such as solubility, compatibility, refractive index, low haze and low viscosity of the chiral dopant in the liquid crystal mixed crystal.
The initiator is benzoin dimethyl ether (IRG 651). The embodiment of the invention is represented by benzoin dimethyl ether (IRG 651) according to the factors of the initiating mechanism of the initiator, the excitation wavelength, the residue after the reaction, the volatile matters released after the reaction and the like, and the effect of the reagent applied to the polymer liquid crystal brightness enhancement film described in the embodiment of the invention.
The polymerizable liquid crystal monomer is a polymerizable liquid crystal monomer containing any one of the following polymerizable groups: acrylates and methacrylates. The embodiment of the invention uses C6M, C4M, C3M, C B to illustrate the effect.
In the process of preparing the brightness enhancement film, since the reflection bandwidth of the polymeric liquid crystal film is generally 40 to 80nm, in order to widen the reflection bandwidth of the brightness enhancement film, a sufficiently wide pitch gradient is usually formed in the polymeric film or a plurality of polymeric liquid crystal films reflecting different wavelengths are compounded for use. Or a large delta n liquid crystal material is used, the delta n is more than 0.4, and for the reflection bandwidth of 435 to 660nm, only 2 layers or coating is needed.
The preparation method of the brightness enhancement film comprises the following steps:
1) The preparation of the single-layer brightness enhancement film is that the polymerizable liquid crystal mixed crystals with chiral dopants of different concentrations are simultaneously subjected to multi-layer uniform coating to form a coating in contact between layers, liquid crystal molecules are diffused among the coatings, the chiral dopants are also diffused among the layers, and the single-layer coating with the chiral molecule concentration changing is formed in the direction vertical to the coating at a proper time and temperature. Wherein the polymerization process is initiated by light, heat or cations. Specifically, the coating mode is that a gradient flow coating or multilayer extrusion coating or multilayer spraying method is utilized to mix polymerizable liquid crystals doped with chiral molecules with different concentrations, the mixed crystals are simultaneously and uniformly coated on the base film in a multilayer mode, and the cholesteric phase or chiral nematic phase liquid crystal film doped with the chiral molecules is obtained through polymerization. Wherein, the multilayer coating can be 2-8 layers. Forming a cholesteric phase or chiral nematic phase liquid crystal film with a certain pitch gradient through the concentration difference of chiral molecules among the coatings; the concentration difference between the coatings is 0.1 to 15 percent, and the variation range of the pitch gradient is 0.1 to 0.8 mu m. Since the chiral dopant concentration in cholesteric or chiral nematic liquid crystals doped with chiral molecules is different between layers, there is a difference in the concentration of the chiral dopant in the cholesteric or chiral nematic thin film after polymerization. The chiral dopant concentration determines the pitch size of the cholesteric phase or chiral nematic phase liquid crystal phase, the chiral dopant concentration in the cholesteric phase liquid crystal doped with chiral molecules is different between layers, and the pitch is determined by the chiral dopant concentration, so that the pitch size is changed due to the chiral dopant concentration in the vertical direction in the single-layer brightness enhancement film, finally, a pitch gradient is formed in the brightness enhancement film, the concentration and the diffusion time are controlled, the reflection wavelength of the single-layer brightness enhancement film is between 380nm and 2000nm, continuous reflection is inevitable between 435 nm and 660nm, the continuous reflection visible light bandwidth is larger than 225nm, and all or part of visible light or a small part of infrared wave band can be continuously reflected outside a necessary reflection region.
2) The multilayer composite brightness enhancement film comprises a multilayer glued brightness enhancement film and a multilayer coated brightness enhancement film.
a. The multilayer glued brightness enhancement film is formed by sticking and compounding chiral nematic or cholesteric polymer liquid crystal films which are prepared in advance and reflect visible light with different wave bands for multiple times, and the brightness enhancement film capable of continuously reflecting the visible light is formed by multiple kinds of visible light polymer liquid crystal films which reflect the visible light with different wavelengths, and is thicker due to the use of the bonding layer and has the thickness range of 4-60 mu m.
b. The multilayer coating brightness enhancement film is formed by sequentially performing multilayer coating on a base film or a protective film to form brightness enhancement films with different pitches. Firstly, coating a layer of chiral nematic liquid crystal mixed crystal, polymerizing to form a film to form a first layer, coating another liquid crystal mixed crystal which reflects another visible light wavelength again on the basis of the first layer, polymerizing to form a second layer, sequentially coating, and performing multiple coating and polymerization to obtain the multilayer composite high-molecular liquid crystal brightness enhancement film with multiple different pitches. The multilayer composite polymer liquid crystal brightness enhancement film reflects continuous visible light wave bands, the pitch length range of the multilayer composite polymer liquid crystal brightness enhancement film is 0.1-0.8 mu m, the multilayer composite polymer liquid crystal brightness enhancement film inevitably and continuously reflects light between 435-660nm, the continuous reflection visible light wave width is larger than 225nm, all or part of visible light or a small part of infrared wave bands can also be continuously reflected outside an inevitable reflection area, and the reflection wavelength is between 380nm-2000 nm; the number of the composite layers is 2-10, and the larger the number of the composite layers is, the wider the reflection bandwidth is covered.
The brightness enhancement film for an OLED described above will be specifically described below using specific examples.
Example 1
A single-layer polymer liquid crystal brightness enhancement film for an OLED is characterized in that by means of a gradient coating method, polymerizable liquid crystal mixed crystals of chiral dopants with different concentrations are uniformly coated in multiple layers at the same time to form coatings in contact with each other between layers, liquid crystal molecules are diffused among the coatings, the chiral dopants are also diffused among the layers to form a single-layer coating with chiral molecule concentration change in the direction perpendicular to the coating, and then the single-layer polymer liquid crystal brightness enhancement film is obtained through polymerization. The reflection wavelength range of the single-layer brightness enhancement film is 420-700nm, and the reflection bandwidth is 280nm.
In the polymerizable liquid crystal mixed crystal, a polymerizable liquid crystal monomer is selected from C6M, C4M, C M and C6B, the mass ratio of the polymerizable liquid crystal monomer is 1:
C6M：
；
C4M：
；
C3M：
；
C6B：
。
the chiral dopant is S4, and the structure is as follows:
the initiator is IRG651.
The content of the raw materials used for each coating in the single layer brightness enhancement film is shown in table 2. The transmitted spectrum of the single layer brightness enhancement film is shown in figure 4.
TABLE 2 materials and contents of polymerizable liquid crystal mixed crystals in single-layer brightness enhancement film
| Chiral dopants | Initiator | Polymerizable liquid crystal monomer mixed crystal (C6M: C4M: C3M: C6B =1 | |
| First layer | 4.49% | 1% | 94.51% |
| Second layer | 3.73% | 2% | 94.27% |
| Third layer | 3.13% | 2% | 94.87% |
Example 2
A multilayer high-molecular liquid crystal brightness enhancement film for an OLED is prepared by respectively preparing brightness enhancement films for reflecting blue light, cyan light, green light, yellow orange light, red light and near infrared light, and then adhering the multilayer brightness enhancement films together through an adhesive layer to obtain the multilayer brightness enhancement film for continuously reflecting visible light wave bands. The multilayer composite brightness enhancement film has a reflection wavelength range of 420-828nm and a reflection bandwidth of 408nm.
The reflection wavelength range of the brightness enhancement film for reflecting blue light is 420 to 458nm. The liquid crystal mixed crystal for coating is formed by mixing a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and the brightness enhancement film with the reflection wavelength range of 420 to 458nm is obtained by initiating polymerization.
The brightness enhancement film for reflecting the cyan light is formed by mixing a liquid crystal mixed crystal for coating, a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and is subjected to initiated polymerization to obtain the brightness enhancement film with the reflection wavelength range of 458-503 nm.
The brightness enhancement film for reflecting the green light has the reflection wavelength range of 503-559nm, the liquid crystal mixed crystal for coating is formed by mixing a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and the brightness enhancement film with the reflection wavelength range of 503-559nm is obtained by initiating polymerization.
The brightness enhancement film capable of reflecting yellow orange light is characterized in that the reflection wavelength range of the brightness enhancement film capable of reflecting yellow orange light is 559-627nm, a liquid crystal mixed crystal for coating is formed by mixing a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and the brightness enhancement film capable of reflecting yellow orange light is obtained by initiating polymerization.
The brightness enhancement film capable of reflecting red light has a reflection wavelength range of 627-713nm, the liquid crystal mixed crystal for coating is formed by mixing a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and the brightness enhancement film with the reflection wavelength range of 627-713nm is obtained by initiating polymerization.
The brightness enhancement film for reflecting red light and near-infrared light has a reflection wavelength range of 713-828nm, is prepared by mixing a liquid crystal mixed crystal for coating, a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and is subjected to initiated polymerization to obtain the brightness enhancement film with the reflection wavelength range of 700-800 nm. The reflection bandwidth of the chiral nematic and cholesteric liquid crystals increases with wavelength, and the reflection bandwidth is widened because Δ λ = Δ n.P, the wavelength is red-shifted, and the pitch P is enlarged.
In the polymerizable liquid crystal mixed crystal, because S2 has liquid crystallinity and chirality, the monomers can be used in a large proportion, a small amount of polymerizable monomers C6B are selected as required to adjust the pitch and the reflection wavelength, and the structure of S2 is as follows:
a chiral dopant is not used, only a proper amount of liquid crystalline polymerizable monomer is mixed, and IRG651 is selected as an initiator.
The amounts of raw materials used for each layer of the multilayer composite brightness enhancing film are shown in table 3. The pitch of each layer of the polymer liquid crystal film is designed to continuously reflect visible light after matching. The transmitted spectrum of the multilayer composite brightness enhancement film is shown in FIG. 5.
TABLE 3 materials and contents of polymerizable liquid crystal mixed crystals in single-layer brightness enhancement film
| Number of layers | Brightness enhancement film | Reflection wavelength range | Liquid crystalline chiral dopant S2 | Initiator | Polymerizable liquid crystal monomer C6B |
| 1 | Brightness enhancement film for reflecting blue light | 420~458nm | 98.0% | 2.0% | — |
| 2 | Brightness enhancement film for reflecting cyan light | 458-503nm | 88.5% | 2.0% | 9.5% |
| 3 | Brightness enhancement film for reflecting green light | 503-559nm | 80.2% | 2.0% | 17.8% |
| 4 | Brightness enhancement film reflecting yellow orange light | 559-627nm | 72.5% | 3.0% | 24.5% |
| 5 | Brightness enhancement film capable of reflecting red light | 627-713nm | 64.4% | 2.0% | 33.6% |
| 6 | Brightness enhancement film for reflecting infrared light | 713-828nm | 56.7% | 5.0% | 38.3% |
After the film is prepared, liquid optical cement LOCA or an optical adhesive film is used for sequentially pasting the film to prepare a layer of polymer liquid crystal brightness enhancement film.
Example 3
A high-molecular liquid crystal brightness enhancement film for OLED can be coated and polymerized for multiple times by using coating methods such as slit, extrusion, wire rod, scraper, wire rod, reticulate pattern, three-roller five-roller, gravure, micro-concave, air knife, lip type, overturning kiss type or dip coating. The polymer liquid crystal film is prepared by coating one layer each time, the next polymer liquid crystal film is prepared on the upper layer of coating in sequence, and finally, a chiral nematic or cholesteric polymer liquid crystal film with the gradually changed screw pitch is formed in the direction vertical to the coating, and the brightness enhancement film can continuously reflect visible light. The single-layer brightness enhancement film has a reflection wavelength range of 420-690nm and a reflection bandwidth of 270nm.
In the polymerizable liquid crystal mixed crystal system, the pitch size in the mixed crystal is designed, so that the mixed crystal can continuously reflect visible light after being matched. The initiator is IRG651, chiral dopant S4, polymerizable liquid crystal monomer mixed crystal (C6M: C4M: C3M: C6B = 1.
TABLE 4 materials and contents of polymerizable liquid crystal mixed crystals in brightness enhancement films
| Range of reflected wavelengths | Chiral dopant S4 | Initiator | Polymerizable liquid crystal monomer mixed crystal (C6M: C4M: C3M: C6B =1 | |
| First layer | 420~455nm | 5.2% | 2% | 92.8% |
| Second layer | 455-498nm | 4.7% | 2% | 93.3% |
| Third layer | 498-551nm | 4.3% | 2% | 93.7% |
| The fourth layer | 551-615nm | 3.8% | 2% | 94.2% |
| The fifth layer | 615-690nm | 3.4% | 2% | 94.6% |
Comparative example 1
A monochromatic brightness enhancement film for OLED is prepared by uniformly coating polymerizable liquid crystal mixed crystals to form a single-layer coating by one of the methods of slit, extrusion, wire bar, scraper, wire bar, reticulate pattern, three-roller five-roller, gravure, micro-concave, air knife, lip type, turning kiss type or dip coating and the like, and carrying out photo-initiated polymerization to obtain the blue brightness enhancement film. The reflection wavelength range of the blue light brightness enhancement film is 420 to 455nm. The polymerizable liquid crystal mixed crystal for coating is prepared by mixing a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and a brightness enhancement film with the reflection wavelength range of 420 to 455nm is obtained by initiating polymerization.
In the polymerizable liquid crystal mixed crystal, a polymerizable liquid crystal monomer is C6M, and the structure is as follows:
the chiral dopant is S4.
The initiator is IRG651.
The blue light brightness enhancement film comprises a chiral dopant S4, wherein the content of the chiral dopant S4 in the liquid crystal composition is 4.57%, an initiator is IRG651, the mass percent of the initiator is 2%, a rodlike polymerizable liquid crystal monomer is C6M, and the mass percent of the polymerizable liquid crystal monomer is 93.43%.
Comparative example 2
A single-color brightness enhancement film for an OLED is prepared by uniformly coating a polymerizable liquid crystal mixed crystal to form a single-layer coating by a filament rod coating method and carrying out photo-initiated polymerization to obtain the green-light brightness enhancement film. The green light brightness enhancement film has a reflection wavelength range of 492-560nm, and is prepared by mixing a polymerizable liquid crystal mixed crystal for coating as a chiral dopant, an initiator and a polymerizable liquid crystal monomer, and performing initiated polymerization to obtain the brightness enhancement film with a reflection wavelength range of 492-560 nm.
In the polymerizable liquid crystal mixed crystal, a polymerizable liquid crystal monomer is C6M, and the structure is as follows:
the chiral dopant is S4.
The initiator is IRG651.
The green light brightness enhancement film comprises a chiral dopant S4, wherein the content of the chiral dopant S4 in the liquid crystal composition is 3.76%, an initiator selects IRG651, the mass percentage of the initiator is 2%, a polymerizable liquid crystal monomer selects C6M, and the mass percentage of the polymerizable liquid crystal monomer is 94.24%.
Comparative example 3
A single-color brightness enhancement film for an OLED is prepared by uniformly coating polymerizable liquid crystal mixed crystals to form a single-layer coating by a gradient coating method and carrying out photo-initiated polymerization to obtain the red-light brightness enhancement film. The red light brightness enhancement film is characterized in that the reflection wavelength range of the red light brightness enhancement film is 620-700nm, the polymerizable liquid crystal mixed crystal for coating is formed by mixing a chiral dopant, an initiator, a polymerizable monomer and a polymerizable liquid crystal monomer, and the brightness enhancement film with the reflection wavelength range of 620-700nm is obtained by initiating polymerization.
In the polymerizable liquid crystal mixed crystal, a polymerizable liquid crystal monomer is C6M, a chiral dopant is S4, and an initiator is IRG651.
The red light brightness enhancement film comprises a chiral dopant S4, the content of the chiral dopant S4 in the liquid crystal composition is 3.00%, the initiator is IRG651, the mass percentage of the initiator is 2%, the polymerizable liquid crystal monomer is C6M, and the mass percentage of the polymerizable liquid crystal monomer is 95.00%.
The application of the brightness enhancement film is described below.
Referring to fig. 2 to 3, an OLED display device includes a linear polarizer, a phase retardation film, a brightness enhancement film, an OLED light-emitting panel, and a metal electrode;
as shown in fig. 3, when the brightness enhancement film selectively passes through the left-handed circularly polarized light and reflects the right-handed circularly polarized light, light emitted from the OLED light-emitting panel selectively passes through the brightness enhancement film 6 and reflects the right-handed circularly polarized light, the passed left-handed circularly polarized light is converted into light perpendicular to the absorption axis of the linear polarizer 4 through the phase retardation film 5 and emitted, the circularly polarized light which does not pass through the brightness enhancement film 6 and has opposite rotation properties is reflected by the brightness enhancement film 6 and rebounded to the metal electrode 7, the rebounded circularly polarized light has changed rotation properties by reflection of the metal electrode 7, the rebounded circularly polarized light is converted into rotation properties which can pass through the brightness enhancement film 6, and then emitted to the outside through the brightness enhancement film 6, the phase retardation film 5 and the linear polarizer 4. The brightness enhancement film in the embodiment of the invention can reduce the driving current of the luminescent material in the OLED display under the condition of maintaining the same brightness, and has brightness enhancement effect on visible light wave bands, rather than gain only on part of the visible light wave bands. The light utilization rate of the light-emitting layer of the OLED display can be comprehensively improved, and the energy consumption of the OLED display is reduced.
The application of the brightness enhancement film is specifically described below. The circular polarizer is obtained by bonding and compounding a linear polarizer and a phase delay film.
Application example 1
The circular polarizer is bonded with the single-layer polymer liquid crystal brightness enhancement film for the OLED prepared in the embodiment 1, and then bonded and combined with the OLED display panel.
Application example 2
The circular polarizer is bonded with the multilayer polymer liquid crystal brightness enhancement film for the OLED prepared in the embodiment 2, and then bonded with the OLED display panel.
Application example 3
The circular polarizer is bonded with the single-layer polymer liquid crystal brightness enhancement film for the OLED prepared in the embodiment 3, and then bonded and combined with the OLED display panel.
Application comparative example 1
And (3) bonding the circular polarizer and the blue light brightness enhancement film for the OLED prepared in the comparative example 1, and then bonding and combining the circular polarizer and the OLED display panel.
Comparative application example 2
And (3) bonding the circular polarizer and the green light brightness enhancement film for the OLED prepared in the comparative example 2, and then bonding and combining the circular polarizer and the green light brightness enhancement film with the OLED display panel.
Comparative application example 3
And (3) bonding the circular polarizer and the red light brightness enhancement film for the OLED prepared in the comparative example 3, and then bonding and combining the circular polarizer and the red light brightness enhancement film with the OLED display panel.
Application comparative example 4
The circular polaroid is bonded with the OLED display panel without a brightness enhancement film.
In order to further verify that the embodiments of the present invention have the function of the polymer liquid crystal brightness enhancement film, the OLED display devices of application examples 1 to 3 and application comparative examples 1 to 4 of the present invention were subjected to the brightness performance test, and the test results are shown in table 5.
Table 5 test results of luminance performance of OLED display device
From the brightness test results, the application examples 1 to 3 and the application comparative examples 1 to 3 of the invention both have a brightness enhancement effect on the OLED display, wherein the brightness gain of the application example 2 on the OLED display reaches 40%, and the comparison between the application example 1 and the application example 2 shows that the reflection waveband is widened to a long wave, which is beneficial to increasing the light utilization rate of the obliquely emergent visible light part, and the better the brightness enhancement effect on the OLED display. As can be seen from comparison of application examples 1-3 with application comparative examples 1-3, the brightness enhancement film of the present invention has a brightness enhancement function of continuously reflecting visible light, and the brightness enhancement effect is far superior to that of a monochromatic brightness enhancement film.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A high molecular liquid crystal brightness enhancement film is characterized in that the film is a chiral nematic phase or cholesteric phase high molecular liquid crystal film prepared by mixing a plurality of polymerizable liquid crystals;
the concentrations of polymerizable chiral dopants contained in the polymerizable liquid crystal mixed crystals are different, so that different screw pitches are formed in the polymer liquid crystal brightening film along the direction vertical to the film;
the polymer liquid crystal brightness enhancement film can continuously reflect the light of a visible light wave band emergent obliquely and/or an infrared light wave band emergent vertically, and the reflectivity is more than 25%.
2. The polymeric liquid crystal brightness enhancing film according to claim 1, wherein the pitch has a length variation range of 0.1-0.8 μm.
3. The polymer liquid crystal brightness enhancement film according to claim 1, wherein each of the polymerizable liquid crystal mixed crystals is prepared from the following raw materials in percentage by weight:
0.3 to 98.0 percent of polymerizable chiral dopant, 0.3 to 5 percent of initiator and 0 to 98.2 percent of polymerizable liquid crystal monomer.
4. The brightness enhancement film according to claim 3, wherein the polymerizable chiral dopant is a polymerizable compound monomer, and the polymerizable chiral dopant can be cross-linked with the polymerizable liquid crystal monomer without phase separation during the process of preparing the brightness enhancement film;
the polymerizable chiral dopant is an acrylate or methacrylate compound containing a chiral group R, and the structural general formula of the polymerizable chiral dopant is shown as the following formula (I-1), formula (I-2), formula (I-3), formula (I-4), formula (I-5), formula (I-6), formula (I-7) or formula (I-8):
wherein the chiral group R is
、
、
、
、
、
、
Any one of the above;
x is
、
、
、
Any one of the above;
m is selected from any one of C3-C10 straight chain or branched chain alkyl and substituted or unsubstituted phenyl;
y is any one of H, C-C10 straight chain or branched chain alkyl, C3-C10 straight chain or branched chain alkoxy, C3-C10 straight chain or branched chain alkyl mercapto, C3-C10 straight chain or branched chain alkyl amino, C3-C10 straight chain or branched chain alkyl carboxyl, C3-C10 straight chain or branched chain alkyl cyano.
5. The polymer liquid crystal brightness enhancing film according to claim 3, wherein the polymerizable liquid crystal monomer is a polymerizable liquid crystal monomer containing a polymerizable group, and the polymerizable group is acrylate or methacrylate.
6. The polymeric liquid crystal brightness enhancing film according to claim 1, wherein the polymeric liquid crystal brightness enhancing film is a chiral nematic or cholesteric polymeric liquid crystal film obtained by uniformly coating a plurality of polymerizable liquid crystal mixed crystals simultaneously to form a coating layer in contact with each other, wherein each polymerizable liquid crystal mixed crystal contains different polymerizable chiral dopants in concentration, and a single-layer coating layer with the polymerizable chiral dopants in concentration varying along a direction perpendicular to the coating layer is formed along with the diffusion of the polymerizable chiral dopants among the layers, and then the single-layer coating layer is polymerized.
7. The polymer liquid crystal brightness enhancement film according to claim 1, wherein the polymer liquid crystal brightness enhancement film is a multilayer composite brightness enhancement film obtained by sticking and compounding a plurality of chiral nematic or cholesteric polymer liquid crystal films prepared in advance for reflecting visible light with different wave bands;
or the polymer liquid crystal brightness enhancement film is a single-layer brightness enhancement film with various screw pitches obtained by coating and polymerizing for many times by adopting polymerizable liquid crystal mixed crystals containing polymerizable chiral dopants with different concentrations on the basis of a layer of chiral nematic or cholesteric polymer liquid crystal film prepared in advance;
each layer of chiral nematic or cholesteric polymer liquid crystal film is formed by polymerizing polymerizable liquid crystal mixed crystals containing polymerizable chiral dopants with different concentrations; the reflection wavelengths of the chiral nematic or cholesteric polymer liquid crystal films between adjacent layers can be connected with each other and continuously reflect.
8. The polymer liquid crystal brightness enhancement film according to claim 1, wherein the angle of oblique emergent light of the polymer liquid crystal brightness enhancement film is in a range of 0-60 °.
9. An OLED display device, comprising the polymeric liquid crystal brightness enhancement film according to any one of claims 1-7, wherein the polymeric liquid crystal brightness enhancement film is disposed on a light-emitting layer side of the OLED display device.
10. The OLED display device claimed in claim 9, further comprising a light emitting layer, a phase retardation film and a linear polarizer in a light exiting direction, wherein the polymer liquid crystal brightness enhancement film is disposed between the light emitting layer and the phase retardation film.
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