CN115260896B

CN115260896B - Preparation and application of transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating

Info

Publication number: CN115260896B
Application number: CN202210673685.0A
Authority: CN
Inventors: 陶劲松; 谢静怡; 刘浩
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2022-06-14
Filing date: 2022-06-14
Publication date: 2023-02-14
Anticipated expiration: 2042-06-14
Also published as: CN115260896A

Abstract

The present invention belongs toIn the field of flexible electronics, the preparation and application of a transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating are disclosed. The invention prepares the flexible hard coating by adding filler particles for enhancing the hardness and the scratch resistance into the organic-inorganic hybrid coating, and the prepared CNC/ZrO ₂ the/GPTMS-PSQ coating has excellent surface hardness, scratch resistance, excellent optical performance and good surface smoothness. The pencil hardness can reach 5H, and the relation among the hardness H, the equivalent elastic modulus E and the elastic recovery coefficient We obtained by a nano indentation experiment meets the following conditions: H/E is more than or equal to 0.1 and We is more than or equal to 60 percent. The coating had a light transmission of 86.68% at 550nm and a roughness of only 2.68nm. The coating is solidified on the cover plate, the cover plate shows good flexibility, and the mobile phone can still work normally when being pasted on a mobile phone for writing and marking.

Description

Preparation and application of transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating

Technical Field

The invention belongs to the field of flexible electronics, and particularly relates to a preparation method and application of a transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating.

Background

Foldable devices have attracted considerable attention due to portability and to meet user demands for large-sized screens. The cover plate serves as an interface for human-computer interaction in the foldable device and plays a role in protecting internal components. There are two main types of materials currently available as cover plates for flexible OLED displays, ultra-thin glass (UTG) and Colorless Polyimide (CPI). The flexibility of the CPI allows for smaller radius bends than the inherent high stiffness and fragility of UTG. However, CPI has a low surface hardness and is easily mechanically damaged by the external environment. Therefore, it is of great and realistic significance to study the material of the cover plate to achieve high hardness and scratch resistance.

To overcome the disadvantages of low surface hardness and poor scratch resistance of polymer cover plates, various surface protective coatings have been extensively studied. It has been found that for a flexible hard coating requiring both hardness and toughness, in addition to the requirement that the coating is not susceptible to cracking, the hardness H and equivalent Young's modulus E should satisfy H/E0.1 or more and the elastic recovery We 60 or more. Surface protective coatings currently applied to polymeric membranes can be broadly divided into three broad categories, organic, inorganic and organic-inorganic hybrid coatings. (1) Although the common organic coatings such as polyurethane, multifunctional acrylate and the like have good adhesion with a substrate, the self hardness of the coatings is not high enough, and the effect of improving the hardness of the substrate is limited. Moreover, such coatings are not flexible enough to be suitable for use on flexible decking. (2) Inorganic wear-resistant coatings such as titanium nitride (TiN), molybdenum disulfide (MoS 2) composite coatings and the like can be deposited on the polymer film by a vapor deposition technology to protect the film. However, the inorganic material has poor bonding property with the substrate, poor flexibility and opacity, which limits the application of the inorganic material in the field of flexible display. (3) The organic-inorganic hybrid coating is a current research hotspot because the glass-like wear resistance and the plastic-like flexibility can be simultaneously realized, and is expected to be used as a flexible touch screen cover plate coating. At present, most organic-inorganic hybrid coatings are based on Polysilsesquioxane (PSQ) containing Si-O-Si bonds, and although the coatings have flexibility and wear resistance, the hardness of the organic components is still far lower than that of ceramics and metals due to the lower hardness of the organic components and the limited volume fraction of the inorganic components. Although the three materials have respective advantages, the three materials still have the defects of poor flexibility, low hardness, poor hardness improvement effect on the surface of the polymer and the like. Therefore, it is a challenge to provide coatings with high surface hardness and scratch resistance while maintaining their flexibility and high transparency.

In the prior art, the preparation of a composite flexible hard coating which has the advantages of flexibility, transparency, high hardness and scratch resistance so as to obtain a report that the composite flexible hard coating can be used for protecting a flexible OLED display cover plate is not found.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention mainly aims to provide a preparation method of a transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating.

The invention also aims to provide the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating prepared by the method.

The invention further aims to provide application of the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating in a flexible OLED cover plate.

The purpose of the invention is realized by the following scheme:

a preparation method of a transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating comprises the following steps:

(1) Preparation of CNC (nanocellulose): adding cotton fibers into an oxalic acid solution for hydrolysis, adding water to stop the reaction, filtering the oxalic acid remaining on the surface of the product, washing with water to remove the oxalic acid, centrifuging, collecting supernatant, and dialyzing to obtain CNC suspension;

(2) Surface modification of CNC: adding acid into a mixed solvent containing ethanol and water to adjust the pH =3-5, adding a modified monomer after uniform mixing, stirring and hydrolyzing for 1-2h, then adding the CNC suspension obtained in the step (1) for reaction, purifying after the reaction is finished, and dispersing by butanone to obtain the CNC suspension with the modified surface;

(3)ZrO ₂ preparation of (zirconia): adding n-butyl zirconium into benzyl alcohol, stirring for dissolving, placing into a polytetrafluoroethylene lining filled with water in advance for hydrothermal reaction, adding ethanol after the reaction is finished, ultrasonically dispersing the product, centrifuging, and collecting supernatant containing light blue substances, namely ZrO ₂ A suspension;

(4) Preparation of GPTMS-PSQ (polysilsesquioxane): adding monomers, water and a catalyst for synthesizing polysilsesquioxane into a three-neck flask, and heating and stirring to crosslink the monomers; then adding a solvent to dissolve the GPTMS-PSQ, and carrying out rotary evaporation on the supernatant to remove redundant solvent and impurities to obtain GPTMS-PSQ for low-temperature (3-4 ℃) storage;

(5)CNC/ZrO ₂ preparation of/GPTMS-PSQ (nanocellulose/zirconia/polysilsesquioxane) coating: directly blending and stirring the CNC suspension liquid after surface modification with the prepared GPTMS-PSQ, and adding the ZrO prepared in the step (3) ₂ Uniformly stirring the suspension, dropwise adding a photoinitiator, continuously stirring uniformly, coating the coating on glass or colorless polyimide, removing the solvent in an oven, and carrying out ultraviolet curing to obtain the CNC/ZrO ₂ a/GPTMS-PSQ coating.

The mass fraction of the oxalic acid solution in the step (1) is 30-70 wt.%, preferably 50wt.%, and the mass ratio of the cotton fiber to the oxalic acid solution is 1:10-15, preferably 1:10; the hydrolysis is carried out at 90-110 deg.C for 1-3h, preferably at 100 deg.C for 1h.

The centrifugal collection in the step (1) is to centrifuge for 3-5 times at 8000-10000rpm for 10min each time until no CNC exists in the supernatant, and collect all the supernatants; wherein the lower layer is large fiber with insufficient oxidation degree, and nano-scale CNC is dispersed in the supernatant.

The mixed solvent containing ethanol and water in the step (2) is used for slowly hydrolyzing the modified monomer, and the ethanol plays a role in dissolving assistance, so that the stability of the hydrolyzed solution is ensured, and the hydrolyzed monomer is prevented from being subjected to polycondensation. Wherein the mass ratio of ethanol to water is 8-10:1, preferably 9:1.

the acid used in the step (2) for adjusting the pH value by adding acid can be at least one of weak acids such as glacial acetic acid, dilute hydrochloric acid, oxalic acid and the like;

the modified monomer in the step (2) is at least one of gamma-Glycidoxypropyltrimethoxysilane (GPTMS), gamma-aminopropyltriethoxysilane and 2- (3, 4-epoxycyclohexane) ethyltrimethoxysilane, and is preferably gamma-Glycidoxypropyltrimethoxysilane (GPTMS).

The mass ratio of the modified monomer to the CNC suspension liquid in the step (2) is 1:3-1:5, wherein the solid content of the CNC suspension is 0.2-0.5%, preferably 0.215%;

the reaction in the step (2) is carried out at 25-30 ℃ for 36-48h; the purification is to remove the solvent by centrifugation, wash the solvent with butanone and disperse the solvent with butanone.

The dosage of the n-butyl zirconium and the benzyl alcohol in the step (3) meets the requirement that the dosage of the added substance is 0.0025-0.012mol per 12mL of the benzyl alcohol; the temperature of the hydrothermal reaction is 120-160 ℃, preferably 140 ℃, and the time of the hydrothermal reaction is 12-48h, preferably 24h.

The monomer for synthesizing the polysilsesquioxane in the step (4) is one of gamma-Glycidoxypropyltrimethoxysilane (GPTMS), gamma-aminopropyltriethoxysilane and 2- (3, 4-epoxycyclohexane) ethyltrimethoxysilane, and preferably gamma-Glycidoxypropyltrimethoxysilane (GPTMS). More preferably, the modifying monomer in step (2) is the same as the monomer for synthesizing polysilsesquioxane herein.

The catalyst in the step (4) is a basic catalyst, preferably at least one of Amberlite IRA-400 chloride form, ammonia water and sodium hydroxide; the mass ratio of the using amount of the catalyst to the monomer for synthesizing the polysilsesquioxane is 1:15-1:20; the molar ratio of water to monomers for the synthesis of polysilsesquioxane is 1.5:1. when the catalyst is solid, the method also comprises the step of removing the solid catalyst by centrifugation before removing the redundant solvent and impurities by rotary evaporation of the supernatant.

The reaction temperature of the crosslinking in the step (4) is 80-90 ℃, and is preferably 85 ℃; the reaction time is 0.5h-4h; the solvent is one of butanone, tetrahydrofuran and acetone, preferably butanone.

The rotary evaporation temperature of the supernatant in the step (4) is 60-70 ℃, and preferably 65 ℃.

The surface-modified CNC suspension, GPTMS-PSQ and ZrO described in the step (5) ₂ The amount of the suspension is such that: the mass of the CNC subjected to surface modification accounts for 0.1-0.35% of the mass of the GPTMS-PSQ; zrO (ZrO) ₂ The mass of the compound accounts for 0.1-0.7% of the mass of the GPTMS-PSQ; wherein the solid content of the CNC suspension liquid after surface modification is preferably 0.5-1%; zrO (ZrO) ₂ The solid content of the suspension is 0.5-1.5%.

The photoinitiator in the step (5) is at least one of triaryl sulfonium hexafluoroantimonate mixture, diaryl iodonium salt I-250 and mixed triaryl hexafluoro phosphonium phosphate sulfonium salt cation initiator; the photoinitiator dripped in the step (4) accounts for 1% -3% of the mass of GPTMS-PSQ, and is preferably 2%; the ultraviolet curing time is 15-25min, preferably 20min; the wavelength of an ultraviolet lamp is 365nm, the curing temperature is room temperature, and the temperature of the oven for removing the solvent is 60-65 ℃.

The transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating prepared by the method.

The transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating is applied to a flexible OLED cover plate, especially a mobile phone touch screen cover plate.

The mechanism of the invention is as follows:

the preparation of flexible hard coatings by adding filler particles to organic-inorganic hybrid coatings that enhance hardness and scratch resistance may provide a solution for this. Nanocrystalline Cellulose (CNC), a novel nanomaterial isolated from cellulose by physical or chemical means, has been widely used as a filler for polymer-reinforced mechanical properties, has an ultra-high young's modulus, and has the potential to enhance coating hardness. And the CNC has smaller nano-particle size and higher surface activity, so the CNC has good compatibility with polymers and is beneficial to keeping good optical transmittance. Nano zirconium dioxide (ZrO) ₂ ) The inorganic ceramic material has good chemical stability and high hardness, has good wear resistance, and can be used as a filler for enhancing the scratch resistance of polymers. ZrO (ZrO) ₂ The preparation method in the laboratory is various, and ZrO with controllable shape and size can be realized by adjusting reaction time, pressure, precursor and other factors ₂ The preparation of the nano particles can meet different application requirements. ZrO of small particle diameter ₂ The nanofiller is beneficial for maintaining good optical transmittance of the polymer matrix. Thus, CNC, zrO ₂ The composite material is compounded with an organic-inorganic hybrid coating with flexibility, and is expected to enhance the surface hardness and scratch resistance of a flexible hard coating under the condition of keeping the optical performance.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) The invention prepares CNC/ZrO ₂ The GPTMS-PSQ coating has excellent surface hardness and scratch resistance. The pencil hardness can reach 5H, and the relation among the hardness H, the equivalent elastic modulus E and the elastic recovery coefficient We obtained by a nano indentation experiment meets the following conditions: H/E is more than or equal to 0.1 and We is more than or equal to 60 percent. The scratch resistance of the coating is also improved by observing the coating through an optical microscope.

(2) CNC/ZrO prepared by the invention ₂ the/GPTMS-PSQ coating has excellent optical performance and good surface smoothness. The coating had 8 at 550nmThe light transmittance of 6.68 percent is only 2.68nm, the requirement that the roughness of the flexible electronic cover plate is less than 5nm is met, and the flexible electronic cover plate can be used as a protective coating of a flexible touch screen cover plate.

(3) The coating is solidified on the cover plate, the cover plate shows good flexibility, and the mobile phone can still work normally when being pasted on a mobile phone for writing and marking.

Drawings

FIG. 1 is a schematic representation of CNC/ZrO produced from raw materials ₂ A GPTMS-PSQ coating and a process diagram for obtaining a transparent, high-hardness, scratch-resistant composite coating that can be used for flexible touch screen cover plates.

FIG. 2 shows ZrO prepared in example 1 ₂ SEM and AFM images of (a).

Fig. 3 is a comparison of real images before and after modification and a red spectrogram of the CNC prepared in example 1.

FIG. 4 is a graph of GPTMS-PSQ, weight average molecular weight, FT-IR without curing, FT-IR before and after 4 hours of reaction and pencil hardness, and load-displacement curve for various reaction times prepared in example 1.

FIG. 5 is a pictorial representation, a micro-topographical representation, an AFM representation, a transmittance and hardness comparison of CNC/GPTMS-PSQ of different CNC contents prepared in example 1.

FIG. 6 shows the different ZrO prepared in example 1 ₂ Content of ZrO ₂ The microcosmic appearance and the light transmittance of the GPTMS-PSQ coating are shown.

FIG. 7 shows the different ZrO prepared in example 1 ₂ Content of ZrO ₂ Optical microscopy of the scratched surface of the/GPTMS-PSQ coating.

FIG. 8 shows CNC/ZrO prepared in example 1 ₂ The infrared spectrum, the light transmittance, the micro appearance, the flatness, the load-displacement curve and the hardness contrast chart of the/GPTMS-PSQ coating.

FIG. 9 shows CNC/ZrO prepared in example 1 ₂ Folding and curling of the/GPTMS-PSQ coating, optical microscopic picture after scratching and application.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.

The reagents used in the examples are commercially available without specific reference. Oxalic acid (Fuchentianjin chemical Co., ltd.); double loop qualitative filter paper (Hangzhou Wohua filter paper Co., ltd.); zirconium n-butoxide (80 wt% n-butanol solution, shanghai Aladdin Biotechnology Co., ltd.); benzyl alcohol (Fochen Tianjin chemical reagent, inc.); gamma-Glycidoxypropyltrimethoxysilane (GPTMS) (97%, shanghai Michelin Biochemical technology Ltd); amberlite IRA-400 chloride form (shanghai mclin biochem technologies ltd); triarylsulfonium hexafluoroantimonate mixture (50 wt%, shanghai Michelin Biochemical technologies, inc.); absolute ethanol (national group chemical reagent); glacial acetic acid (shanghai runjie chemical limited); butanone (Guangzhou chemical reagent factory)

In this example, zrO was analyzed by Multimode 8 Atomic Force Microscope (AFM) of Bruker, germany ₂ Morphology and composite coating surface roughness; observation of ZrO by EVO18 Scanning Electron Microscope (SEM) from Zeiss, germany ₂ Morphology, cross-sectional morphology of the composite coating; the German Bruker Tensor27/Hyperion infrared spectrum (FT-IR) instrument tests and analyzes the functional groups of the substances; testing the light transmittance by using a U.S. LAMBDA1050 ultraviolet-visible spectrophotometer; the pencil hardness of the coating was tested using a QHQ-A pencil hardness tester, china precision instruments, inc.; microscopic image of scratched coating was observed by BX51 research grade upright microscope of OLYMPUS corporation, japan; agilent 1260THF gel chromatography, USA, analyzes the molecular weight of the coating; the TTX-NHT3 nanoindenter analysis of Anton Paar, austria load-displacement curves.

Examples CNC/ZrO from raw materials ₂ The process of the/GPTMS-PSQ transparent hard coating applied to the touch screen cover plate is shown in figure 1. Firstly, carrying out surface modification on the prepared CNC suspension liquid (a) to change hydroxyl on the surface of the suspension liquid into epoxy group, and obtaining the modified CNC (b). Hydrolysis was carried out using (c) GPTMS as a reaction monomerPolycondensing to obtain (d) GPTMS-PSQ as matrix material. In order to improve the wear resistance of the coating, (e) ZrO is prepared by adopting a steam phase hydrolysis combined hydrothermal method ₂ And applied, and then CNC and ZrO are processed ₂ And GPTMS-PSQ, coating on the substrate, and curing with ultraviolet lamp under the action of photoinitiator to obtain (f) CNC/ZrO ₂ the/GPTMS-PSQ transparent hard protective coating. The coating cured on the CPI substrate is useful in (g) flexible OLED display devices, and the composite coating has good (h) transparency, (i) scratch resistance, and (j) enhanced surface hardness.

Example 1: CNC/ZrO ₂ Preparation and application of/GPTMS-PSQ coating

(1) Preparation and surface modification of CNC

First, 100g of oxalic acid solution with the mass fraction of 50% is prepared. At 100 ℃,10 g of cotton fibers were added to the above solution for hydrolysis reaction. After 1 hour of reaction, 400mL of deionized water was added to the solution to stop the reaction. And (4) carrying out suction filtration on the residual oxalic acid on the surface of the product by using a vacuum pump, and washing by using deionized water. Finally centrifugation at 10000rpm and collection of supernatant, repeat this step until the supernatant is essentially CNC free. The collected supernatant was dialyzed against deionized water until the liquid conductivity approached that of deionized water.

The surface modification of CNC is carried out by using GPTMS, and the specific method is as follows: adding 14.4g of absolute ethyl alcohol and 1.6g of deionized water into a three-neck flask, adding glacial acetic acid into the solution to adjust the pH value to 4, adding 4g of GPTMS after uniform mixing, and stirring for hydrolysis for 1h. Then 20g of CNC suspension with solid content of 0.215% is added, and stirring is continued for 48h at room temperature, so that the CNC suspension modified by GPTMS is obtained. And centrifuging the modified solution to remove water, centrifuging and washing the solution with butanone solution for three times, and finally dispersing the solution in butanone by CNC ultrasonic, wherein the solid content is adjusted to 0.5%.

(2)ZrO ₂ Preparation of

12mL of benzyl alcohol solution is weighed into a beaker, 0.0025mol of n-butyl zirconium is added under the condition of continuous stirring, and the mixture is fully dissolved and then is filled into an unsealed glass vial. Adding 15mL of deionized water into the polytetrafluoroethylene lining in advance, placing a glass vial containing the solution into the polytetrafluoroethylene lining, and placing the glass vial into the polytetrafluoroethylene liningThe reaction is carried out in an oven at the temperature of 140 ℃ for 24h, and then the reaction product is taken out and cooled. Adding ethanol into the reacted substance, and performing ultrasonic treatment to precipitate white ZrO ₂ And (4) dispersing the solid. The supernatant, in which a pale blue material appeared, was collected by centrifugation at 10000rpm for ten minutes using a centrifuge. Adding ethanol into the centrifuged precipitate again, performing ultrasonic dispersion, centrifuging at 10000rpm, and continuously collecting supernatant to obtain the small-particle-size ZrO dispersed in the blending solution of the benzyl alcohol and the ethanol ₂ And labeling and storing after measuring the solid content.

(3) Preparation of GPTMS-PSQ

In a three-necked flask, 20g of GPTMS, 2.28g of deionized water and 1g of Amberlite IRA-400 in the form of chloride (as a catalyst) were added, and the temperature of the thermostatic oil bath was raised to 85 ℃ and vigorously stirred at this temperature for 0.5h, 1h, 2h, 3h and 4h, respectively, to hydrolyze and crosslink GPTMS to form GPTMS-PSQ. Subsequently, 10g of butanone was added to the crosslinked GPTMS-PSQ, and the solution was completely dissolved. The resulting solution was centrifuged at 5000rpm for 10min to precipitate the solid catalyst, and the supernatant was taken out. Filling the obtained upper layer uniform solution into a conical flask, vacuumizing and stirring at 65 ℃ for 10min, removing redundant solvent and impurities in the solution, and storing at low temperature.

(4) Preparation of CNC/GPTMS-PSQ coating

Taking 1g of GPTMS-PSQ prepared for 4h of reaction, adding 0.3g of butanone, stirring uniformly, adding 0g, 0.2g, 0.5g and 0.7g of CNC butanone solution with solid content of 0.5% after surface modification, respectively, as GPTMS-PSQ, 0.1 CNC/GPTMS-PSQ, 0.25% CNC/GPTMS-PSQ and 0.35% CNC/GPTMS-PSQ (wherein the percentage is 0.35% in 0.35% CNC/GPTMS-PSQ, referring to the percentage of the weight of CNC in GPTMS-PSQ), stirring for 10min, dropwise adding 0.02g of triarylsulfonium hexafluoroantimonate mixture (as a photoinitiator), stirring for 10min, dropwise coating each sample on CPI film and glass, baking for 20min in an oven at 60 ℃, and volatilizing the solvent. And finally, under the irradiation of an ultraviolet lamp of 365nm for 20min, completely curing the coating to obtain the CNC/GPTMS-PSQ transparent hard coating.

(5)ZrO ₂ Preparation of/GPTMS-PSQ coating

Adding 0.3g butyl into 1g of GPTMS-PSQThe ketone is stirred evenly, and ZrO with different mass and known solid content is added into the mixture ₂ ，ZrO ₂ The addition amounts are respectively 0.1%, 0.3%, 0.5%, 0.7% of the mass of GPTMS-PSQ, respectively, and respectively 0.1% ₂ /GPTMS-PSQ、0.3％ZrO ₂ /GPTMS-PSQ、0.5％ZrO ₂ GPTMS-PSQ and 0.7% ZrO ₂ GPTMS-PSQ, 0.02g of triarylsulfonium hexafluoroantimonate mixture (as a photoinitiator) was added dropwise after stirring for 10min, and after stirring for 10min, each sample was separately applied dropwise to CPI film and glass, and dried in an oven at 60 ℃ for 20min to volatilize the solvent. Finally irradiating for 20min with 365nm ultraviolet lamp to cure the coating completely to obtain ZrO ₂ the/GPTMS-PSQ transparent hard coating.

(6)CNC/ZrO ₂ Preparation of/GPTMS-PSQ coating

Taking 1g of the prepared GPTMS-PSQ, adding 0.3g of butanone, stirring well, adding thereto 0.25% CNC (0.25% means percentage by mass of GPTMS-PSQ) and 0.5% ZrO ₂ (0.5 percent is the mass percentage of GPTMS-PSQ), 0.02g of triaryl sulfonium hexafluoroantimonate mixture (used as a photoinitiator) is added dropwise after being stirred uniformly, the mixture is continuously stirred for 10min, then the mixture is added dropwise on a CPI film and glass, the CPI film and the glass are dried in an oven at 60 ℃ for 20min, and the solvent is volatilized. Finally, the coating is completely cured under the irradiation of an ultraviolet lamp of 365nm for 20min to obtain ZrO ₂ the/GPTMS-PSQ transparent hard coating.

And (3) performance testing:

(1)ZrO ₂ performance of

ZrO prepared in example 1 ₂ The Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) of the nanoparticles are shown in FIG. 2, wherein (a) of FIG. 2 is ZrO ₂ In FIG. 2, (b) is ZrO ₂ AFM graph of (1). ZrO (ZrO) ₂ The nano particles are spherical and have smaller particle size of about 10nm, and the agglomeration phenomenon is more serious. The nano particles have small size, the transparency can not be obviously reduced, and the subsequent application is facilitated.

(2) Surface modification of CNC

The CNC prepared in example 1 has abundant hydroxyl groups on the surface, has very poor compatibility with the coating, and is easy to generate precipitates, so that we prepared the CNCThe prepared CNC is subjected to surface modification. The CNC modification results are shown in figure 3. As can be seen from fig. 3 (a), the CNC suspension is relatively clear and transparent and appears bluish. The modified GPTMS can be dispersed in butanone, the suspension is white, no precipitate is generated after standing for 24h, the successful modification of CNC by GPTMS is indirectly shown, and the groups on the surface of CNC are changed. Fig. 3 (b) is FT-IR image contrast before and after GPTMS modified CNC. It can be seen from the figure that the infrared spectra of the CNC before and after modification are approximately the same. At 3417cm ^-1 The stretching vibration peak of hydroxyl appears nearby and is 2904cm ^-1 And 1639cm ^-1 Peaks appearing at 1060cm were C-H bond stretching vibration and O-H bending vibration absorbing water, respectively ^-1 The peak is the C-O-C stretching peak. Modified CNC at 819cm compared to unmodified CNC ^-1 New Si-O-Si or Si-O-C absorption peaks appeared, demonstrating that CNC has been successfully modified.

(3) Characterization of GPTMS-PSQ

The actual images of the GPTMS-PSQ coatings prepared in example 1 at different reaction times are shown in fig. 4 (a), and the coatings at the reaction times are yellowish, clear and transparent, and have excellent light transmittance. In order to investigate the effect of the reaction time on the polymerization degree of the coating, the molecular weight of GPTMS-PSQ after the reaction at different times was examined, and the results are shown in fig. 4 (b). As can be seen from the graph, the molecular weight of GPTMS-PSQ increases with the increase of the reaction time, which indicates that the degree of polymerization between GPTMS monomers gradually increases with the increase of the reaction time. Figure 4 (c) compares FT-IR images of GPTMS monomer and GPTMS-PSQ coating uncured at different reaction times. From the FT-IR image, it can be seen that the FT-IR curves of GPTMS-PSQ after 0.5h and 1h of reaction are substantially consistent with GPTMS monomer, and in combination with the change of weight average molecular weight, it is indicated that 0.5h and 1h of reaction are too short for forming GPTMS-PSQ protective coating, and only a small portion of monomer is polymerized. In fact, we have uv cured coatings with different reaction times, but coatings reacted for 0.5h and 1h did not form complete coatings after 20min uv curing, indicating that the degree of crosslinking was not sufficient. Starting from the reaction time 2h, a complete protective coating can be formed after curing on the glass slide. KnotFrom the FT-IR curve, the FT-IR curve changes from 2h to GPTMS monomer, which is mainly represented by 1087cm ^-1 The sharp peak of Si-O disappears and is at 1105cm ^-1 And 1035cm ^-1 Two broad Si-O-Si doublets are present and as the reaction time increases, the doublets become more pronounced and symmetrical. FIG. 4 (d) compares FT-IR images of GPTMS-PSQ coatings before and after curing after 4h of reaction. As can be seen from the figure, the FT-IR curves before and after curing are substantially unchanged, since the main change before and after curing is the ring-opening of the epoxy groups by the photoinitiator.

To compare the effect of reaction time on coating hardness, the coating hardness was tested at different reaction times using a pencil hardness tester. Since the reaction times of 0.5h and 1h failed to form a complete coating, the test was started from reaction 2h regardless of the pencil hardness of both, and the results are shown in (e) of fig. 4. As can be seen from the graph, the pencil hardness of the coating after the reaction for 2H reached 3H, and the pencil hardness showed a tendency to increase as the reaction time increased. This is because the degree of crosslinking between monomers increases with the progress of the reaction, and the oligomers gradually change into a network-like or body-type structure substance having a high degree of crosslinking, and the movement of the molecular chain is gradually hindered, thereby increasing the hardness thereof. Fig. 4 (f) shows the load-displacement curve obtained after nanoindentation test of the GPTMS-PSQ coating after 4h reaction. During the experiments we observed that the coating surface did not leave any indentations after loading and unloading, which indicates that the coating is more elastic. It can be seen from the data in the figure that after unloading, the curve has smaller hysteresis and has good elastic recovery capability. However, the surface hardness is as low as 189.4MPa, which is not favorable for obtaining a coating material with high hardness. The coating after 4h reaction has high crosslinking degree, so the coating is selected as a substrate material for subsequent research.

(4) Characterization of CNC/GPTMS-PSQ

The modified CNC has good compatibility with GPTMS-PSQ when the addition amount is less, a real object diagram of the CNC/GPTMS-PSQ composite coating with 0 percent, 0.1 percent, 0.25 percent and 0.35 percent of CNC added is shown in (a) of figure 5, coatings with different CNC addition amounts are clear and transparent, no obvious agglomeration phenomenon exists, and high optical performance is shown. From the sectional SEM image in (b) of fig. 5, it can be observed that both GPTMS-PSQ and 0.1% CNC/GPTMS-PSQ were dense and smooth, indicating that CNC had good dispersibility in the matrix and good compatibility with the substrate due to no or less addition of CNC. After 0.25% cnc was added, a small amount of agglomeration phenomenon on the cross section could be observed. With the continuous increase of CNC, the agglomeration phenomenon is more obvious. The surface roughness of each CNC/GPTMS-PSQ composite coating was analyzed by AFM, and the results are shown in (c) of fig. 5. With the increase of CNC, the surface roughness of each CNC/GPTMS-PSQ coating was 0.956nm,0.493nm,0.496nm and 0.825nm, respectively, and the surface roughness of the coating tended to increase as a whole, but GPTMS-PSQ without CNC addition had a large viscosity at the time of coating, and many bubbles were easily generated, and thus the roughness was higher than that of other samples.

The change in transmittance is as shown in (d) of fig. 5, the optical transmittance of the coating shows a slight decrease tendency with the addition of CNC, and the more the CNC is added, the worse the optical performance, which is attributed to the agglomeration of part of the unmodified CNC in the substrate. To investigate the effect of CNC on coating hardness, we performed tests using a pencil hardness meter, and the results are shown in (e) of fig. 5. When 0.1% of cnc was added, since the added amount of the filler was too small, and the pencil hardness was a characterization performed macroscopically, it did not show a significant increase in hardness. But when 0.25% and 0.35% CNC was added, the pencil hardness increased from the original 4H to 5H, suggesting that the addition of CNC had a positive effect on increasing the hardness of the coating. Since the coatings applied to the cover plates must have good optical transmittance while considering the influence of surface hardness, we selected 0.25% cnc/GPTMS-PSQ coatings having both good hardness and optical properties as the best subjects for subsequent studies.

(5)ZrO ₂ Characterization of/GPTMS-PSQ

FIG. 6 shows the respective ZrO layers in example 1 ₂ Content of ZrO ₂ The cross section microscopic appearance and the light transmittance of the/GPTMS-PSQ coating. As shown in FIG. 6 (a), with ZrO ₂ The more can be seen in the cross section of the coatingThe more ZrO ₂ And (3) granules. When ZrO 2 ₂ When the amount of (A) is from 0.1% to 0.5%, no significant ZrO appears ₂ And (3) granules. Until the amount of addition reached 0.7%, agglomerated ZrO could not be observed ₂ Is present. This is because ZrO ₂ Has smaller primary particle size and is partially agglomerated ZrO after ultrasonic treatment before use ₂ Dispersed, and can be well coated after being added into GPTMS-PSQ, so that the dispersion can be well carried out when the addition amount is less. FIG. 6 (b) shows ZrO in different addition amounts ₂ Light transmittance of the/GPTMS-PSQ coating on the CPI substrate. With ZrO ₂ The increase of the content gradually reduces the optical transmittance of the coating. When ZrO ₂ ZrO coated with GPTMS-PSQ ₂ When the amount of the compound added was 0.1%, the transmittance at 550nm was 93.66%. And ZrO ₂ the/GPTMS-PSQ coating was added at 0.5% ZrO ₂ Then, the transmittance can still reach 92.43%.

For the sake of clarity of comparison, we added different amounts of ZrO ₂ ZrO of ₂ The surface scratch resistance of the/GPTMS-PSQ coating is analyzed, and the observation result of an optical microscope is shown in FIG. 7. It can be observed that, after being scratched with 800-mesh sandpaper under a weight of 100g, scratches were left on the coating surface, compared to when ZrO was added ₂ The surface of the GPTMS-PSQ was scratched more clearly, and more chips of the damaged coating appeared, indicating that the depth of scratching by the sandpaper was greater, and thus it was seen that the abrasion resistance was worse than that of the other samples. Adding 0.3%, 0.5% and 0.7% of ZrO ₂ ZrO of ₂ Scratches also appear on the/GPTMS-PSQ coating, but mostly are shallow marks and do not damage the coating deeply, probably because of ZrO ₂ The addition of (2) has a reinforcing effect on the surface hardness of the coating, thereby improving the scratch resistance of the coating. However, the scratch resistance effect is not very remarkable because of the small amount of addition. ZrO like CNC/GPTMS-PSQ coatings with CNC added alone as filler ₂ The relation between balanced optical performance and scratch resistance performance also needs to be considered simultaneously in the/GPTMS-PSQ coating, and by combining the results, the adding amount of CNC which is finally selected is 0.25 percent, and ZrO is finally selected ₂ Addition amount of (2) is 0.5% for CNC/ZrO ₂ Preparation and characterization of a/GPTMS-PSQ coating.

(7)CNC/ZrO ₂ Characterization of/GPTMS-PSQ

In conjunction with the above studies, we finally determined the 0.25% CNC and 0.5% ZrO ₂ The results of the analysis of the filler for the hardness and scratch resistance of GPTMS-PSQ are shown in FIG. 8. FIG. 8 (a) characterizes CNC/ZrO ₂ The FT-IR curve for the/GPTMS-PSQ coating is essentially identical to that for GPTMS-PSQ, probably because less filler was added and the functional groups of the individual fillers are not shown in the curve. CNC/ZrO ₂ The optical transmittance of the/GPTMS-PSQ coating is shown in figure 8 (b), and at 550nm, the transmittance of the coating can reach 86.68 percent and still meet the requirement>85% of optical requirements. (c) and (d) of FIG. 8 are CNC/ZrO ₂ Cross-sectional SEM images of/GPTMS-PSQ coatings and roughness data of the surface. It can be seen from the figure that slight agglomeration occurred in the coating due to the higher addition of the two filler particles, although the epoxy groups of the CNC surface that was partially modified successfully were ring-opened to the epoxy groups of GPTMS-PSQ under uv light, there may still be some unmodified CNC and CNC or ZrO ₂ Agglomeration occurs in between. The root mean square of the surface roughness of the coating can be calculated from the surface height data to be 2.68nm. For analysis of CNC/ZrO ₂ The surface hardness of the/GPTMS-PSQ coating is measured by a pencil hardness test, and the result shows that CNC/ZrO ₂ The pencil hardness of the/GPTMS-PSQ coating is still 5H, and no ZrO is added ₂ This is probably because of ZrO ₂ Is not added in a large amount and thus cannot be expressed on a macroscopic level. To verify the effectiveness of filler particles on enhancing coating hardness, we compared GPTMS-PSQ and CNC/ZrO on a microscopic level using nanoindentation experiments ₂ The surface hardness of the/GPTMS-PSQ coating varied, and the results are shown in (e) and (f) of FIG. 8. In the nano indentation experiment, the surfaces of the two materials are observed to have no visible indentation after 5mN loading and unloading. It can also be seen from the load-displacement curve that the hysteresis of both curves is very small, indicating a strong elastic recovery. For flexible hard nanocomposite coatings with enhanced toughness, it is desirable to meet a low equivalent Young's modulus E ^* And a high elastic recovery coefficient W _e . The key parameters are mainly two, and are respectively H/E ^* Not less than 0.1 and W _e More than or equal to 60 percent, thereby leading the coating to have good crack resistance. According to the load-displacement curve, the W of the two materials is calculated _e All values exceed 80%. FIG. 8 (f) compares the hardnesses H and E of two materials ^* The result shows CNC/ZrO ₂ The surface hardness of the/GPTMS-PSQ coating was greater than GPTMS-PSQ, which is consistent with the results obtained with pencil hardness. Calculate the H/E of both ^* The results are 0.12 and 0.14, respectively, both ≧ 0.1. This indicates that both materials meet the requirements of a flexible hard coating. But, in comparison, CNC/ZrO ₂ The hardness of the/GPTMS-PSQ coating is improved, H/E ^* Value sum W _e The higher the value. Thus, we performed CNC and ZrO on the synthesized coatings ₂ Is necessary.

(8)CNC/ZrO ₂ Flexibility and application analysis of/GPTMS-PSQ

To observe the flexibility of the coating, we measured CNC/V-ZrO ₂ the/GPTMS-PSQ was coated on CPI and PET film, respectively, and cured, and the coating was observed after curling and folding, and the result is shown in fig. 9 (a). After the coating is curled and folded with small radius, the surface of the coating is intact, and failure phenomena such as fracture, falling and the like do not occur, which shows that the coating has good flexibility. FIG. 9 (b) is a view of CNC/ZrO viewed under an optical microscope ₂ Scratching of/GPTMS-PSQ coatings (CNC/ZrO) ₂ GPTMS-PSQ on glass slides for scratch test), it can be seen that after the sand paper was scratched, no more deep scratches appeared, due to the improved hardness of the coating and the better elastic recovery. Finally, we attached the coating cured on the CPI to the smartphone screen and performed a writing test, as shown in fig. 9 (c), which indicated that the phone display was able to function properly, indicating that the prepared coating has the potential for use as a phone cover protective material.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating is characterized by comprising the following steps:

(1) Preparing nano-cellulose: adding cotton fibers into an oxalic acid solution for hydrolysis, adding water to stop the reaction, filtering the oxalic acid remaining on the surface of the product, washing with water to remove the oxalic acid, centrifuging, collecting supernatant, and dialyzing to obtain a nano cellulose suspension;

(2) Surface modification of nanocellulose: adding acid into a mixed solvent containing ethanol and water to adjust the pH to be 3-5, adding a modified monomer after uniform mixing, stirring and hydrolyzing for 1-2h, then adding the nano-cellulose suspension obtained in the step (1) for reaction, purifying after the reaction is finished, and dispersing with butanone to obtain the nano-cellulose suspension with the modified surface;

(3) Nano ZrO ₂ The preparation of (1): adding n-butyl zirconium into benzyl alcohol, stirring for dissolving, placing into a polytetrafluoroethylene lining filled with water in advance for hydrothermal reaction, adding ethanol after the reaction is finished, ultrasonically dispersing the product, centrifuging, and collecting supernatant with light blue substance, namely ZrO ₂ A suspension;

(4) Preparation of polysilsesquioxane: adding monomers for synthesizing polysilsesquioxane, water and a catalyst into a three-neck flask, and heating and stirring to crosslink the monomers; then adding a solvent to dissolve the polysilsesquioxane, and performing rotary evaporation on the supernatant to remove redundant solvent and impurities to obtain polysilsesquioxane for storage;

(5) Preparing a nano-cellulose/ceramic/siloxane flexible hard coating: directly blending and stirring the nano-cellulose suspension subjected to surface modification with the prepared polysilsesquioxane, and adding the ZrO prepared in the step (3) ₂ Stirring the suspension, adding photoinitiator, stirring, coating on glass or colorless polyimide, removing solvent in oven, and ultraviolet curingObtaining a nano cellulose/ceramic/siloxane flexible hard coating;

the modified monomer in the step (2) is at least one of gamma-glycidoxypropyltrimethoxysilane, gamma aminopropyltriethoxysilane and 2- (3, 4-epoxycyclohexane) ethyltrimethoxysilane;

the mass ratio of the modified monomer to the nano cellulose suspension in the step (2) is 1:3-1:5, wherein the solid content of the nano-cellulose suspension is 0.2-0.5%;

the reaction in the step (2) is carried out at 25-30 ℃ for 36-48h;

the dosage of the n-butyl zirconium and the benzyl alcohol in the step (3) meets the condition that the amount of the added substance is 0.0025-0.012mol per 12mL of the benzyl alcohol; the temperature of the hydrothermal reaction is 120-160 ℃, and the time of the hydrothermal reaction is 12-48 h;

the monomer for synthesizing polysilsesquioxane in the step (4) is at least one of gamma-glycidoxypropyltrimethoxysilane, gamma-aminopropyltriethoxysilane and 2- (3, 4-epoxycyclohexane) ethyltrimethoxysilane.

2. The method for preparing the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating according to claim 1, characterized in that:

the mass fraction of the oxalic acid solution in the step (1) is 30-70 wt.%, and the mass ratio of the cotton fiber to the oxalic acid solution is 1:10-15 parts of; the hydrolysis is carried out at 90-110 ℃ for 1-3h.

3. The method for preparing the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating according to claim 1, characterized in that:

the catalyst in the step (4) is an alkaline catalyst.

4. The method for preparing the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating according to claim 3, characterized in that:

in the step (4), the catalyst is at least one of Amberlite IRA-400 chloride, ammonia water and sodium hydroxide.

5. The method for preparing the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating according to claim 1, characterized by:

the mass ratio of the using amount of the catalyst in the step (4) to the monomer for synthesizing the polysilsesquioxane is 1:15-1:20; the molar ratio of water to polysilsesquioxane-synthesizing monomers was 1.5:1;

the reaction temperature of the crosslinking in the step (4) is 80-90 ℃; the reaction time is 0.5h-4h; the solvent is one of butanone, tetrahydrofuran and acetone.

6. The method for preparing the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating according to claim 1, characterized in that:

the surface-modified nano-cellulose suspension, polysilsesquioxane and ZrO described in step (5) ₂ The amount of the suspension is such that: the mass of the surface modified nano-cellulose accounts for 0.1-0.35% of that of the polysilsesquioxane; zrO (ZrO) ₂ The amount of (B) is 0.1-0.7% of the weight of the polysilsesquioxane.

7. The method for preparing the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating according to claim 1, characterized in that:

the photoinitiator in the step (5) is at least one of triaryl sulfonium hexafluoroantimonate mixture, diaryl iodonium salt I-250 and mixed triaryl hexafluoro phosphonium phosphate sulfonium salt cation initiator; the photoinitiator dripped in the step (4) accounts for 1-3% of the weight of the polysilsesquioxane; ultraviolet curing time is 15-25min; the curing temperature was room temperature.

8. A transparent scratch resistant nanocellulose/ceramic/silicone flexible hardcoat prepared by the method of any one of claims 1-7.

9. The transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating of claim 8 on a flexible OLED cover plate.

10. The application of the transparent scratch-resistant nanocellulose/ceramic/siloxane flexible hard coating of claim 8 in a cover plate of a touch screen of a mobile phone.