An optical adhesive film for electronic paper lamination and its preparation method

Abstract

The present invention discloses an optical adhesive film for electronic paper lamination and a preparation method thereof. This invention belongs to the field of optical adhesive technology and is prepared by coating with an acrylic resin coating liquid. The raw material components of the acrylic resin coating liquid include an acrylic resin prepolymer, an acrylic acid (ester) monomer, a crosslinking agent, a photoinitiator, a UV absorber, and a color corrector. The acrylic resin prepolymer contains at least: an alkyl acrylate monomer, a hydroxyl acrylate, a strong hydrogen-bonding acrylate functional monomer, and an alkyl nitrogen-containing acrylate monomer. By controlling the amount of each polymerizable monomer component and selecting and controlling the content of the strong hydrogen-bonding acrylate functional monomer, the present invention is highly compatible with plastics, has UV protection, and corrects yellowing, making it ideal for laminating electronic paper and other optical plastic sheets requiring color correction.

Description

Technical Field

[0001] The present invention relates to an optical adhesive film used for electronic paper lamination and a preparation method thereof, and specifically relates to an optical adhesive film used for full lamination of electronic paper, capable of blocking ultraviolet rays and correcting color and a preparation method thereof, belonging to the technical field of optical adhesives. Background Art

[0002] Optically Clear Adhesive (OCA) is primarily used for bonding display modules such as liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs) to touch panels or cover plates. It requires colorless transparency, a light transmittance of over 95%, excellent bonding strength, the ability to cure at room or medium temperatures, and minimal shrinkage upon curing. Currently, it is the optimal adhesive for touch screens.

[0003] Electronic paper is a specialized display technology that utilizes microcapsules or electric field modulation techniques to move color particles on a tiny surface under the influence of an electric field, thereby achieving a flat display of images. It offers numerous advantages, including low power consumption, eye-friendly ease of reading, and immunity to reflections and glare. It is primarily used in e-book readers, smart tags, wearable devices, smart homes, and electronic price tags. With increasing consumer demand for portability, low power consumption, readability, and environmental friendliness, electronic paper display technology holds broad application prospects.

[0004] E-paper primarily consists of components such as a substrate, a conductive layer, a microcapsule layer, a dielectric layer, a protective layer, transparent electrodes, and a control circuit. Optically clear adhesive (OCA) plays a crucial role in e-paper, primarily securing and protecting the various functional components. It secures the outer screen cover to the transparent electrode, the transparent electrodes to each other, the transparent electrodes to the light guide plate, and the light guide plate to the display module. The functional layers of e-paper secured with OCA are typically made of plastics such as polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), and cycloolefin (COP). Beyond the high transmittance, high viscosity, and high filler properties of conventional OCA adhesives, e-paper also places the following additional functional requirements on this type of adhesive: 1) Chromatic aberration correction: Plastic materials are susceptible to free radical generation when exposed to ultraviolet light or high temperatures, leading to aging and deterioration. To mitigate this process, manufacturers typically add large amounts of antioxidants and anti-yellowing agents during production. Although these additives help extend the service life of plastics, they also make the plastic itself slightly yellow, affecting the color display of the electronic paper display module and making it difficult to achieve a pure white display effect. It should also have the function of correcting the yellow color to ensure a purer white display; 2) UV blocking function to prevent the functional layer from being exposed to ultraviolet light during outdoor use, causing photoaging or photoyellowing; 3) High compatibility with plastics, with strong adhesion to plastic sheets and good bubble resistance to ensure long-term and high reliability of bonding; 4) Acid-free, does not corrode the transparent electrode layer, and prevents a decrease in touch sensitivity.

[0005] Regarding optical adhesive films compatible with plastic light guide plates used in electronic paper, some reports indicate that these films generally exhibit good adhesion and bubble rebound resistance. For example, Chinese Patent No. 201310048492.7 discloses an acrylic pressure-sensitive adhesive tape with a 180° peel force on glass exceeding 10 N / 20 mm, a gel fraction exceeding 65%, and a 300% tensile residual stress of 7-16 N / cm². This is achieved by adding a certain amount of a low-molecular-weight polymer with a high glass transition temperature (Tg) to a matrix prepolymer as a tackifying resin. However, monomers with high Tgs are very expensive, and the preparation of the tackifying resin requires solution polymerization and solvent extraction, a complex process. In practical applications, poor compatibility between the tackifying resin and the matrix prepolymer often affects optical performance.

[0006] Another example: Chinese Patent No. 201810863079.9 discloses a pressure-sensitive adhesive film with an adhesive gel fraction between 60% and 95%, resistant to blistering and heat-wet aging. This is achieved by using solution polymerization to polymerize a matrix resin, then adding a large proportion of a multifunctional group and a photoinitiator. After coating, heating, and drying to remove the solvent, the pressure-sensitive adhesive film is formed. Some films may require multiple laminations to form a thicker laminate. After lamination, the pressure-sensitive adhesive film and plastic sheet are exposed to UV light. Chinese patent 202311383316.9 discloses a solvent-free, UV-curable acrylic resin adhesive optical film with a gel fraction of 75% to 98%, a room-temperature elastic modulus of 30,000 to 300,000 Pa, and a room-temperature peel strength of greater than 1500g / 25mm at 180° against glass, and a high-temperature peel strength (85°C) of greater than 600g / 25mm. This optical film combines excellent step-filling properties with excellent bubble-rebound resistance against plastic sheets.

[0007] It can be seen that the existing patents disclosed are all for improving the reliability of bonding with plastics, but there has been no report on optical adhesive films for optically correcting yellowing of plastic sheets. Summary of the Invention

[0008] The present invention aims to provide an optical adhesive film for use in electronic paper bonding and a preparation method thereof. The optical adhesive film is prepared from an acrylic resin coating liquid formed by polymerizing an acrylic resin prepolymer. The acrylic resin prepolymer is polymerized from alkyl acrylate monomers, hydroxy acrylate, strong hydrogen-bonding acrylate functional monomers, alkyl nitrogen-containing acrylate monomers, etc. By controlling the amount of each polymerized monomer component and selecting and controlling the content of the strong hydrogen-bonding acrylate functional monomer, the optical adhesive film can be highly compatible with plastics and has the functions of blocking ultraviolet rays and correcting yellowing. It is very suitable for use in the bonding of electronic paper and other optical plastic sheets that require chromatic aberration correction.

[0009] The present invention is achieved through the following technical solution: an optical adhesive film used for electronic paper bonding is prepared by coating with an acrylic resin coating liquid, wherein the raw material components of the acrylic resin coating liquid include an acrylic resin prepolymer, an acrylic acid (ester) monomer, a crosslinking agent, a photoinitiator, an ultraviolet absorber and a chromaticity corrector.

[0010] The acrylic resin prepolymer contains at least: alkyl acrylate monomers, hydroxy acrylate, strong hydrogen bond acrylate functional monomers and alkyl nitrogen-containing acrylate monomers.

[0011] In the acrylic resin prepolymer, the content of strong hydrogen bond acrylate functional monomer is 1-10%, and the strong hydrogen bond acrylate functional monomer is selected from one or more acid-free monomers selected from acrylamide, methacrylamide, N-hydroxyacrylamide,

[0012] The optical adhesive film meets the following performance indicators:

[0013] UV blocking performance: A;

[0014] Anti-foaming ability: A;

[0015] Haze value: 0~0.5;

[0016] Light transmittance: 280-350nm, <20%;

[0017] B value: -0.1~-0.7;

[0018] Adhesion strength: 1500~2200g.

[0019] In the acrylic resin prepolymer, the mass ratio of alkyl acrylate monomer to hydroxy acrylate is 1:0.9-1:3, and the mass ratio of strong hydrogen bond acrylate functional monomer to alkyl nitrogen-containing acrylate monomer is 1:0.5-5.

[0020] The alkyl nitrogen-containing acrylate monomer is selected from one or more of N-vinyl pyrrolidone, N-vinyl caprolactam, N-isobutoxymethyl acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, and acryloylmorpholine.

[0021] The acrylic resin prepolymer further comprises a coupling agent, an antioxidant or a rust preventive.

[0022] The acrylic acid (ester) monomer is selected from one or more of alkyl acrylate, hydroxy acrylate, carboxyl acrylate, aryl acrylate, and acrylamide.

[0023] A method for preparing the above optical adhesive film is characterized by comprising the following steps:

[0024] S1. An alkyl acrylate monomer, a hydroxyl acrylate, a strong hydrogen bond acrylate functional monomer, and an alkyl nitrogen-containing acrylate monomer are prepared into an acrylate solution, and an acrylic resin solution is obtained by polymerization. The acrylic resin solution contains an acrylic resin prepolymer and an acrylic acid (ester) monomer, and the weight average molecular weight of the acrylic resin prepolymer is 1,000,000 to 5,000,000;

[0025] S2 is added to the acrylic resin solution crosslinking agent, photoinitiator, UV absorber and color corrector, stirred and then vacuum degassed to obtain an acrylic resin coating solution;

[0026] S3. Applying an acrylic resin coating liquid on a polyester release film, and then covering it with another layer of polyester release film to form a viscous liquid layer, which is then cured by ultraviolet light to obtain an optical adhesive film.

[0027] In the step S1, the polymerization method includes UV light polymerization, UV thermal polymerization or solution polymerization.

[0028] During the UV photopolymerization, a photoinitiator is added to the acrylate solution, and after degassing, the solution is irradiated and cross-linked to a final viscosity of 500 to 10,000 cps, thereby obtaining an acrylic resin prepolymer.

[0029] In the step S2, the vacuum degree is controlled at -0.08 to -0.1 MPa during vacuum degassing, and the degassing time is 2 to 5 hours.

[0030] In step S3, the energy density of the UV curing is controlled to be 0.1 to 5 mw / cm 2 , the total curing energy is not less than 500mj.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) The optical adhesive film of the present invention has excellent optical properties and laminating properties, can effectively reduce the presence of air layers in electronic paper, reduce reflection and scattering, improve the clarity and stability of the display effect, and has the advantages of being compatible with plastic cover plates, effectively blocking ultraviolet rays, correcting colors, and improving the yellowing phenomenon of screen display. Specifically:

[0033] The optical film has a haze value of 0-0.5, a transmittance (280-350nm) of less than 20%, and a UV blocking performance of A, thus exhibiting excellent optical properties. Furthermore, the film's B value is between -0.1 and -0.7, which can correct yellowing. This is particularly useful when laminating electronic paper or other optical plastic sheets that require color correction, reducing product yellowing.

[0034] Since the optical film has an anti-foaming ability of A and an adhesive force of 1500 to 2200g, it has excellent bonding performance and is compatible with plastic cover plates;

[0035] Since the optical adhesive film has the above-mentioned optical properties and bonding properties, it can fill the air layer in the electronic paper when bonded, so that the refractive index between the cover and the module can be kept consistent, and there is no obvious interface reflection and scattering problems, which can improve the clarity and stability of the display effect.

[0036] (2) In the present invention, when preparing the optical adhesive film, the mass ratio of the acrylic resin prepolymer used is reasonably controlled to be between 1:0.9 and 1:3. This can avoid the whitening phenomenon caused by insufficient compatibility with other monomers during the dilution process due to a low ratio, and the problem of insufficient bubble resistance after bonding due to a high ratio.

[0037] (3) When preparing the optical adhesive film of the present invention, with respect to the strong hydrogen bond acrylate functional monomers used in the acrylic resin prepolymer, it is not appropriate to use acid-containing monomers such as acrylic acid and methacrylic acid, as these will cause the final product to contain acid, thereby causing corrosion of the circuit during use.

[0038] (4) When preparing the optical adhesive film, the present invention utilizes the introduction of strong hydrogen-bonding acrylate functional monomers to form a complexation with the functional dye subsequently added as a chromaticity corrector, which helps to increase solubility and color fastness. To ensure this functional effect, the addition ratio of the strong hydrogen-bonding acrylate functional monomers should also be reasonably controlled to account for 1 to 10% of the overall mass of the acrylic resin prepolymer. If the addition ratio is too low, no significant complexation effect will be achieved, which will cause the haze value of the OCA product to be too high. If the addition ratio is too high, the internal hydrogen bonds may be too strong, reducing the pressure-sensitive performance.

[0039] (5) In the preparation of optical adhesive films, the present invention considers that acrylamide-based strong hydrogen-bonding acrylate functional monomers are very prone to self-polymerization. Excessive self-polymerized polymers will precipitate in the system, causing whitening and turbidity. Therefore, it is necessary to introduce alkyl nitrogen-containing acrylate monomers to promote the copolymerization characteristics of acrylamide-based strong hydrogen-bonding acrylate functional monomers and to solve the whitening and turbidity problem of the polymerization system. The present invention reasonably controls the mass ratio of strong hydrogen-bonding acrylate functional monomers to alkyl nitrogen-containing acrylate monomers to be 1:0.5-5, avoiding the situation where the addition amount is too low, resulting in insignificant improvement, and the addition amount is too high, resulting in too high a glass transition temperature of the system and reduced pressure sensitivity.

[0040] In summary, the present invention prepares an optical adhesive film with good UV blocking ability. The optical adhesive film has a transmittance of less than 20% between 280 and 350 nm, a B value range of -0.1 to -0.7, a thickness between 0.1 and 0.5 mm, and good resistance to bubble rebound on plastic sheets. It is particularly suitable for laminating plastic sheets that require chromaticity correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a comparison chart of the acrylic resin solutions in Example 1, Example 2 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0042] The objectives, technical solutions and beneficial effects of the present invention are described in further detail below.

[0043] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the claimed invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0044] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0045] Example 1: Preparation of acrylic resin prepolymer

[0046] 2-Ethylhexyl acrylate (40 kg), hydroxyethyl acrylate (30 kg), hydroxypropyl acrylate (20 kg), hydroxyethyl methacrylate (5 kg), acrylamide (2.5 kg), acryloylmorpholine (2.5 kg), and benzoin diethyl ether (photoinitiator BDK, 0.02 kg) were mixed and placed in a 200 L stainless steel reactor. Nitrogen was bubbled in for 20 minutes to deoxygenate. A low-pressure mercury lamp was turned on in the reactor to irradiate the solution. Samples were taken to monitor the viscosity of the reaction system. The reaction was stopped when the solution viscosity reached 3100 cps, resulting in an acrylic resin prepolymer with a weight-average molecular weight of 1.61 million.

[0047] Example 2: Preparation of acrylic resin prepolymer

[0048] 2-Ethylhexyl acrylate (40 kg), hydroxyethyl acrylate (30 kg), hydroxypropyl acrylate (20 kg), hydroxyethyl methacrylate (5 kg), acrylamide (3 kg), dimethylacrylamide (2 kg), and benzoin diethyl ether (photoinitiator BDK, 0.05 kg) were mixed and placed in a 200 L stainless steel reactor. Nitrogen was bubbled through the reactor for 20 minutes to deoxygenate. A low-pressure mercury lamp was turned on to irradiate the solution in the reactor. Samples were taken to monitor the viscosity of the reaction system. The reaction was stopped when the solution viscosity reached 4500 cps, resulting in an acrylic resin prepolymer with a weight-average molecular weight of 1.37 million.

[0049] Comparative Example 1:

[0050] 2-Ethylhexyl acrylate (40 kg), hydroxyethyl acrylate (30 kg), hydroxypropyl acrylate (20 kg), hydroxyethyl methacrylate (3 kg), acrylamide (2 kg), dimethylacrylamide (5 kg), benzoin diethyl ether (photoinitiator BDK, 0.05 kg), and n-dodecyl mercaptan (chain transfer agent, 0.05 kg) were mixed and placed in a 200 L stainless steel reactor. Nitrogen was bubbled in for 20 minutes to deoxygenate. A low-pressure mercury lamp was turned on in the reactor to irradiate the solution. Samples were taken to monitor the viscosity of the reaction system. The reaction was stopped when the solution viscosity reached 3200 cps, resulting in an acrylic resin prepolymer with a weight-average molecular weight of 270,000.

[0051] Comparative Example 2:

[0052] 2-Ethylhexyl acrylate (42 kg), hydroxyethyl acrylate (30 kg), hydroxypropyl acrylate (20 kg), hydroxyethyl methacrylate (5 kg), acrylamide (3 kg), and benzoin diethyl ether (photoinitiator BDK, 0.05 kg) were mixed and placed in a 200-liter stainless steel reactor. Nitrogen was bubbled through the reactor for 20 minutes to deoxygenate. A low-pressure mercury lamp was turned on to irradiate the solution in the reactor. Samples were taken to monitor the viscosity of the reaction system. The reaction was terminated when the solution viscosity reached 4300 cps, resulting in an acrylic resin prepolymer with a weight-average molecular weight of 1.45 million.

[0053] Comparative Example 3:

[0054] 2-Ethylhexyl acrylate (45 kg), hydroxyethyl acrylate (30 kg), hydroxypropyl acrylate (20 kg), hydroxyethyl methacrylate (5 kg), and benzoin diethyl ether (photoinitiator BDK, 0.05 kg) were mixed and placed in a 200-liter stainless steel reactor. Nitrogen was bubbled through the reactor for 20 minutes to deoxygenate. A low-pressure mercury lamp was turned on to irradiate the solution in the reactor. Samples were taken to monitor the viscosity of the reaction system. The reaction was terminated when the solution viscosity reached 3800 cps. The resulting acrylic resin prepolymer had a weight-average molecular weight of 1.38 million.

[0055] By comparing the components and the acrylic resin solutions prepared in Example 1, Example 2 and Comparative Examples 1 to 3, as shown in Tables 1 and Figure 1 As shown (1 to 5 in the figure correspond to Example 1, Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3 respectively).

[0056] Table 1

[0057]

[0058] As can be seen from Table 1 above, adding only the strong hydrogen bond acrylate monomer will cause the acrylic prepolymer solution to turn white, while adding both the strong hydrogen bond acrylate monomer and the alkyl nitrogen-containing acrylate can effectively improve the whitening of the acrylic prepolymer solution.

[0059] Example 3: Preparation of optical adhesive film

[0060] To the acrylic resin solution of Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.2 wt% of the photoinitiator TPO, 0.5 wt% of the ultraviolet absorber UV326, and 0.005 wt% of azo blue were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film I.

[0061] Example 4: Preparation of optical adhesive film

[0062] To the acrylic resin solution of Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.2 wt% of the photoinitiator TPO, 0.5 wt% of the ultraviolet absorber UV326, and 0.01 wt% of azo blue were added. The mixture was thoroughly stirred and mixed, followed by vacuum degassing. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film II.

[0063] Example 5: Preparation of optical adhesive film

[0064] To the acrylic resin solution of Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.2 wt% of the photoinitiator TPO, 0.5 wt% of the ultraviolet light absorber UV326, and 0.015 wt% of phthalocyanine blue were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another layer of 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film III.

[0065] Example 6: Preparation of optical adhesive film

[0066] To the acrylic resin solution of Example 2, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.3 wt% of the photoinitiator TPO, 1 wt% of the ultraviolet absorber UV328, and 0.02 wt% of azo blue were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film IV.

[0067] Example 7: Preparation of optical adhesive film

[0068] To the acrylic resin solution of Example 2, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.3 wt% of the photoinitiator TPO, 0.5 wt% of the ultraviolet light absorber UV328, and 0.02 wt% of azo blue were added. The mixture was thoroughly stirred and mixed, followed by vacuum degassing. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. The sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film V.

[0069] Comparative Example 4:

[0070] To the acrylic resin solution of Comparative Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.3 wt% of the photoinitiator TPO, 0.5 wt% of the ultraviolet light absorber UV328, and 0.005 wt% of methylene blue were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film (①).

[0071] Comparative Example 5:

[0072] To the acrylic resin solution of Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.3 wt% of the photoinitiator TPO, 0.5 wt% of the UV absorber UV328, and 0.005 wt% of azo blue were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film (②).

[0073] Comparative Example 6:

[0074] To the acrylic resin solution of Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.3 wt% of the photoinitiator TPO, and 0.5 wt% of the ultraviolet light absorber UV328 were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film (3).

[0075] Comparative Example 7:

[0076] To the acrylic resin solution of Example 1, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.3 wt% of the photoinitiator TPO, 0.5 wt% of azo blue, and 0.5 wt% of the ultraviolet light absorber UV328 were added. The mixture was thoroughly stirred and then vacuum degassed. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film (4).

[0077] Comparative Example 8:

[0078] To the acrylic resin solution from Comparative Example 2, 0.15 wt% of the crosslinker DPHA (dipentaerythritol hexaacrylate), 0.2 wt% of the photoinitiator TPO, 0.5 wt% of the UV absorber UV326, and 0.01 wt% of azo blue were added. The mixture was thoroughly stirred and mixed, followed by vacuum degassing. The resulting mixture was then coated onto a 100 μm thick PET release film with a release weight of 20 g, resulting in a 150 μm adhesive layer. This was then covered with another 75 μm thick PET release film with a release weight of 10 g to form a sandwich. This sandwich was then irradiated at a wavelength of 405 nm and an illumination of 5000 Lux for 10 minutes to obtain an optically transparent film (5).

[0079] The optically transparent films of Examples 3 to 7 and Comparative Examples 5 to 8 were subjected to relevant functional tests. The specific testing methods are as follows:

[0080] (1) UV blocking performance test

[0081] Test the transmittance within the wavelength range of 280-350nm. If the maximum transmittance is less than 20%, it will be judged as A, otherwise it will be judged as B: cut a 15mm×25mm rectangular test piece from the optical film, tear off the light release film, stick it to the instrument detection port, tear off the heavy film for testing, and use the Shimadzu UV-1900I ultraviolet-visible spectrophotometer from Japan.

[0082] (2) Test of b value and haze value

[0083] The test standards refer to ASTM D1003 and GB / T2410 Plastics Light Transmittance and Haze Test Methods. The specific procedure is to cut a 20mm diameter circular test piece from an optical film sheet, remove the light release film, and stick it to the instrument's detection port. The heavy release film is then removed for testing. The test is performed using the b-value and haze value modes, respectively, using the TH-100 Color Spectrum Transmittance Tester.

[0084] (3) Anti-foaming performance test

[0085] A 100mm x 100mm test piece was cut from the optical adhesive film. After removing the light release film, the test piece was laminated to an optical glass plate (100mm x 100mm, thickness: 1.0mm) using a hand roller with a 2kg roller and a back-and-forth motion. After removing the heavy release film, a PC test piece (PC test piece shape: 100mm x 100mm, thickness: 1.0mm) was pre-laminated under vacuum (lamination conditions: surface pressure 0.5 MPa, vacuum 30 Pa, pressurization lamination time 3 seconds). The sample was then defoamed under pressure (defoaming conditions: pressurization pressure 0.5 MPa, pressurization temperature 50°C, pressurization time 15 minutes). The defoamed sample was placed at 25°C for 24 hours. After 500 hours at 85°C, the sample was observed for the presence of bubbles: no bubbles were rated A, and bubbles were rated B.

[0086] (4) Determination of adhesive strength

[0087] The 180° peel strength test method for pressure-sensitive adhesive tapes, as specified in the national standard GB / T 2792-2014, was used. The specific steps were as follows: The optical adhesive to be tested was cut into 25mm wide test strips. The light release film was peeled off and applied to a clean 2mm thick PC board. The heavy release film was then removed and the strip was attached to a PET support. The strip was then rolled back and forth three times with a manual roller. After standing at room temperature for 30 minutes, the adhesion was tested using a tensile testing machine. Test conditions: peel angle: 180°, tensile speed: 300mm / min, and test temperature: 25°C.

[0088] The test results are shown in Table 2 below.

[0089] Table 2

[0090]

[0091] As can be seen from Table 2 above, the UV blocking performance of the transparent film can be significantly improved by adding a suitable UV absorber; the b value of the film can be adjusted by mixing in a color corrector with good compatibility; and prepolymers with lower molecular weight will reduce the adhesion of the film, which is detrimental to the anti-foaming ability.

[0092] In summary, the present invention adopts alkyl acrylate monomers, hydroxy acrylate, strong hydrogen bond acrylate functional monomers and alkyl nitrogen-containing acrylate monomers in appropriate proportions and types as reaction monomers to prepare an acrylic resin prepolymer with a weight-average molecular weight of 1,000,000 to 5,000,000 and a transparent solution. In the subsequent preparation process of the optical film, it only needs to adjust the solvent, cross-linking agent, photoinitiator, ultraviolet absorber and color corrector in appropriate proportions and types to obtain an optical plastic sheet with excellent optical properties, compatibility with plastic cover plates, UV blocking and improved screen yellowing.

[0093] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. An optical adhesive film for electronic paper lamination, characterized by: The coating is made by coating with an acrylic resin coating liquid, wherein the raw material components of the acrylic resin coating liquid include acrylic resin prepolymer, acrylic acid (ester) monomer, crosslinking agent, photoinitiator, ultraviolet absorber and color corrector. The acrylic resin prepolymer contains at least: alkyl acrylate monomers, hydroxy acrylate, strong hydrogen bond acrylate functional monomers and alkyl nitrogen-containing acrylate monomers. In the acrylic resin prepolymer, the mass ratio of alkyl acrylate monomer to hydroxy acrylate is 1:0.9 to 1:3, the mass ratio of strong hydrogen bond acrylate functional monomer to alkyl nitrogen-containing acrylate monomer is 1:0.5 to 5, the content of strong hydrogen bond acrylate functional monomer is 1 to 10%, and the strong hydrogen bond acrylate functional monomer is selected from one or more acid-free monomers of acrylamide, methacrylamide, and N-hydroxyacrylamide. The optical adhesive film meets the following performance indicators: UV blocking performance: A; Anti-foaming ability: A; Haze value: 0~0.5; Light transmittance: 280-350nm, <20%; B value: -0.1~-0.7; Adhesion strength: 1500~2200g.

2. The optical adhesive film according to claim 1, wherein: The alkyl nitrogen-containing acrylate monomer is selected from one or more of N-vinyl pyrrolidone, N-vinyl caprolactam, N-isobutoxymethyl acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, and acryloylmorpholine.

3. The optical adhesive film according to claim 1, wherein: The acrylic resin prepolymer further comprises a coupling agent, an antioxidant or a rust preventive.

4. The optical adhesive film according to claim 1, wherein: The acrylic acid (ester) monomer is selected from one or more of alkyl acrylate, hydroxy acrylate, carboxyl acrylate, and aryl acrylate.

5. A method for preparing the optical adhesive film according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. An alkyl acrylate monomer, a hydroxyl acrylate, a strong hydrogen-bonding acrylate functional monomer, and an alkyl nitrogen-containing acrylate monomer are prepared into an acrylate solution, and the acrylate solution is polymerized to obtain an acrylic resin solution containing an acrylic resin prepolymer and an acrylic acid (ester) monomer; S2 is added to the acrylic resin solution crosslinking agent, photoinitiator, UV absorber and color corrector, stirred and then vacuum degassed to obtain an acrylic resin coating solution; S3. Applying an acrylic resin coating liquid on a polyester release film, and then covering it with another layer of polyester release film to form a viscous liquid layer, which is then cured by ultraviolet light to obtain an optical adhesive film.

6. The method for preparing the optical adhesive film according to claim 5, wherein: In the step S1, the polymerization method includes UV light polymerization, UV thermal polymerization or solution polymerization.

7. The method for preparing an optical adhesive film according to claim 6, wherein: During the UV photopolymerization, a photoinitiator is added to the acrylate solution, and after degassing, the solution is irradiated and cross-linked to a final viscosity of 500 to 10,000 cps, thereby obtaining an acrylic resin prepolymer.

8. The method for preparing an optical adhesive film according to claim 5, wherein: In the step S2, the vacuum degree is controlled to be -0.08 to -0.1 MPa during vacuum degassing, and the degassing time is 2 to 5 hours.

9. The method for preparing an optical adhesive film according to claim 5, wherein: In step S3, during UV curing, the radiation curing energy density is controlled to be 0.1-5 mw / cm2, and the total curing energy is not less than 500 mj.

10. The method for preparing an optical adhesive film according to claim 5, wherein: The thickness of the optical adhesive film is 0.1-0.5 mm.

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