A pressure-sensitive adhesive applied to a protective film for anti-glare type polarizing plates, a protective film and a method for preparing the same

Abstract

The application relates to the technical field of pressure-sensitive adhesive, in particular to a pressure-sensitive adhesive applied to an anti-dazzle type polarizer protective film, a protective film and a preparation method thereof. The pressure-sensitive adhesive of the protective film is a polyurethane modified acrylic polymer, which comprises an acrylic ester polymerized from an acrylic monomer and a curing agent, the acrylic ester synthetic monomer comprises a long-chain ether bond monomer containing a polyether structure repeatable unit, and the number of the repeatable units is greater than or equal to 2. The pressure-sensitive adhesive has excellent initial adhesion and holding adhesion, and the protective film prepared from the pressure-sensitive adhesive can be better attached to the low-polarity surface of the anti-dazzle type polarizer, and has excellent wetting performance on the anti-dazzle type polarizer. In addition, the polyurethane modified acrylic polymer also provides the protective film with good weather resistance, oxidation resistance and ultraviolet resistance, and the protective film of the application has no precipitation and no color difference after aging under the conditions of moisture permeability, high temperature and cold-heat impact, and has excellent performance.

Description

Technical Field

[0001] This invention relates to the field of pressure-sensitive adhesive technology, specifically to a pressure-sensitive adhesive, a protective film, and a method for preparing the same for use in anti-glare polarizer protective films. Background Technology

[0002] With the rapid development of the electronics and logistics industries, the market demands increasingly higher performance from adhesive materials. Pressure-sensitive adhesives (PSA), which bond firmly to substrates with only slight pressure without the need for solvents or heating, have found widespread application in the field of polarizer protective films. Polarizers are one of the core components of liquid crystal displays (LCDs), primarily composed of polyvinyl alcohol (PVA) and cellulose triacetate (TAC) films to achieve light polarization. To prevent polarizers from being scratched, contaminated, or corroded by moisture during manufacturing, transportation, storage, and subsequent processing, a protective film is typically applied to their surface.

[0003] Anti-glare (AG) polarizing films are widely used, often in automotive displays, medical devices, and sunglasses. However, existing protective films for AG polarizing films have several technical drawbacks. First, traditional acrylic protective films often fail to wet the surface of AG polarizing films or exhibit poor adhesion, resulting in poor appearance (such as white fog or bubbles). Second, in harsh environments with high temperature and humidity, small molecule additives (such as antistatic agents) or unreacted monomers in the pressure-sensitive adhesive composition can easily leach onto the surface of the object being coated, causing contamination. Furthermore, after long-term use, some protective films show a significant increase or decrease in peel strength, and color differences may occur after aging.

[0004] To address the aforementioned problems, this invention provides a pressure-sensitive adhesive, a protective film, and a method for preparing the same for use in anti-glare polarizer protective films. Summary of the Invention

[0005] The purpose of this invention is to provide a pressure-sensitive adhesive, a protective film, and a method for preparing the same for use in anti-glare polarizer protective films, in order to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a pressure-sensitive adhesive for use in anti-glare polarizer protective films, wherein the pressure-sensitive adhesive is a polyurethane-modified acrylic polymer, comprising a main adhesive and a curing agent; The main adhesive is made by polymerizing acrylate polymers and polyurethane oligomers; Acrylic polymers contain acrylic monomers, and the acrylic monomers contain long-chain ether monomers with repeatable units of polyether structure, with the number of repeating units being greater than or equal to 2. Polyurethane oligomers are polymerized from polyether polyols and diisocyanate monomers, with the molar ratio of NCO in the diisocyanate to OH in the polyol polymer ranging from 1.05 to 1.35.

[0007] More preferably, the acrylic monomer includes at least one of acrylic acid, butyl acrylate, methacrylic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl acrylate, and hydroxybutyl acrylate.

[0008] More preferably, the long-chain ether monomer is selected from at least one of methoxy polyethylene glycol acrylate and ethoxy polyethylene glycol acrylate.

[0009] Ideally, the acrylic monomers in the main adhesive, by weight, include the following components: 60-65 parts butyl acrylate; 30-35 parts ethoxyethoxyethyl acrylate; 5-10 parts 2-hydroxyethyl acrylate; 1.5-4.5 parts acrylic acid; 230-250 parts ethyl acetate; and 0.2-0.3 parts azobisisobutyronitrile. More preferably, the curing agent is an isocyanate curing agent, which is at least one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer, vinyltriamine, and m-phenylenediamine; the amount used is 0.05~0.15 parts, for example 0.06, 0.08, 0.1, 0.12, 0.15, etc.

[0010] Ideally, the polyether polyol has a molecular weight of 2000-4000, a PDI of 1.2-1.6, and a functionality of 2-4.

[0011] More preferably, the catalyst is one or more of the following: triethylenediamine (TEDA), bis(dimethylaminoethyl) ether, triethylamine, dibutyltin dilaurate, stannous octoate, and bismuth isooctanoate.

[0012] In a more optimized manner, the pressure-sensitive adhesive also contains an antistatic agent and / or a leveling agent; The antistatic agent is at least one of the following: quaternary ammonium salt, lithium bis(trifluoromethanesulfonyl)imide, alkyl sulfonate, inorganic salt and polyol blend, and its dosage is 0.2-0.6 parts by weight; The leveling agent is at least one of polydimethylsiloxane, polyether-modified polysiloxane, and polyether-modified polydimethylsiloxane, and its dosage is 0.001-0.005 parts by weight.

[0013] In a more optimized form, in addition to the above components, it may also contain any necessary and unnecessary components required by conventional pressure-sensitive adhesives without compromising the performance of the invention. For example, antioxidants, plasticizers, fillers, crosslinking agents, etc., may be required.

[0014] This invention provides a polarizer protective film, which is prepared by coating a polymer film substrate with any of the pressure-sensitive adhesives used in anti-glare polarizer protective films as described above, and then curing and aging it. The peel strength of the protective film changed by a factor of 0.8-1.2 before and after aging treatment. Aging time treatment includes low temperature aging treatment, room temperature aging treatment and high temperature and high humidity aging treatment.

[0015] In a more optimized manner, after the protective film is treated at 60°C and 90% relative humidity for 240 hours, the change in peel force is less than 1.2, and there are no exudates on the surface.

[0016] This invention also provides a method for preparing a pressure-sensitive adhesive for polarizer protective films, used to prepare any of the above-mentioned pressure-sensitive adhesives for use in anti-glare polarizer protective films, comprising the following steps: S1: Weigh a certain amount of polyether polyol and diisocyanate, heat the mixture to 40-50°C, react for 2-4 hours under the action of a catalyst, add toluene solvent to dilute and stir evenly to obtain polyurethane oligomer; S2: Weigh out a certain amount of butyl acrylate, long-chain ether monomer, 2-hydroxyethyl acrylate and acrylic acid, add them to ethyl acetate, continuously purge with nitrogen and stir for 30-60 minutes; after stirring, add a certain amount of azobisisobutyronitrile, heat the mixture to 60-70°C, and react for 6-8 hours to obtain the acrylate polymer. S3: Weigh a certain amount of the polyurethane oligomer synthesized in step S1, add it to the mixture in step S2, heat to 80-90°C, and stir until homogeneous. S4: Weigh a certain amount of catalyst and add it to the mixture of S3. React for 1-2 hours under the action of the catalyst to obtain the polyurethane modified acrylic polymer pressure-sensitive adhesive main adhesive. S5: After uniformly mixing the pressure-sensitive adhesive base obtained from S4 with the curing agent and optional additives, it is coated onto the substrate and cured at 120-140°C and aged at 42-48°C to obtain an anti-glare polarizing protective film.

[0017] Ideally, in step S5, the curing time is 2-5 minutes and the aging time is 48-72 hours.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention uses polyurethane-modified acrylic polymer as the main adhesive and introduces polyether monomers into the synthesis of acrylic synthetic monomers. As a highly mobile and flexible monomer, the polyether monomer can improve the wettability of the adhesive after being introduced into the pressure-sensitive adhesive. This protects the macromolecular chains of the adhesive film layer from wetting rough surfaces. The protective film prepared with this pressure-sensitive adhesive can better adhere to low-polarity surfaces such as anti-glare polarizers, and has excellent wetting performance on anti-glare polarizers, thus solving the problem of insufficient adhesion between the protective film and the polarizer surface in the prior art.

[0019] The polyurethane-modified acrylic polymer of the present invention has polyurethane components grafted onto the acrylic side. After crosslinking with an appropriate curing agent, the molecular chain entanglement density of the system can be further increased. When the protective film prepared by this pressure-sensitive adhesive is impregnated onto the rough AG coating surface, the physical and chemical entanglement between the molecular chains themselves and with the micro-nano structure is further enhanced. The protective film wets the surface well and completes the adhesion, while also having excellent tack, making it difficult for it to detach from the rough surface.

[0020] The polyurethane-modified acrylic polymer of the present invention provides the protective film with good weather resistance. The protective film of the present invention shows no exudation or color difference after aging under conditions of moisture permeability, high temperature and thermal shock, and performs excellently. It significantly improves the exudation of the protective film, effectively prevents the exudation of the pressure-sensitive adhesive composition in high temperature and high humidity environments, and solves the problem of easy contamination of the applied object by the protective film in the prior art.

[0021] The polyurethane-modified acrylic polymer of the present invention also provides the protective film with good weather resistance and anti-aging properties, ensuring the stability and durability of the protective film during use, and solving the problem of color difference due to aging in the existing technology.

[0022] The pressure-sensitive adhesive prepared by this invention has good wetting effect, which can effectively improve the interfacial contact between the protective film and the substrate, improve the adhesion performance of the protective film, and reduce the peel force during use. This solves the problem that the peel force of traditional acrylic protective films in the prior art tends to increase over time.

[0023] The protective film preparation method of the present invention is simple and feasible, and the process parameters are easy to control, which helps to ensure the consistency and stability of the product and can meet the requirements of industrial production. Attached Figure Description

[0024] Figure 1 The infrared spectrum of the pressure-sensitive adhesive used in the anti-glare (AG) polarizer protective film prepared in Example 2; Figure 2 The image shows the wetting effect of the anti-glare (AG) polarizer protective film prepared in Example 1. Figure 3The image shows the wetting effect of the anti-glare (AG) polarizer protective film prepared for Comparative Example 1. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The product effects obtained by the present invention were verified through several embodiments and comparative examples. The test results are shown in Table 1. Example 1

[0027] Prepared by the following steps: (1) Weigh a fixed amount of polyether polyol and diisocyanate, wherein the molar ratio of NCO in the diisocyanate to OH in the polyol polymer is 1.2, and heat to 40-50℃. (2) Add 80 ppm of dibutyltin dilaurate catalyst, heat to 50-60℃, react for 2-4 h, add toluene solvent, stir evenly, and obtain polyurethane oligomer; (3) Add 60 parts of butyl acrylate, 30 parts of methoxy polyethylene glycol acrylate, 7.5 parts of hydroxyethyl acrylate and 2.5 parts of acrylic acid to 240 parts of ethyl acetate, purge with nitrogen and stir for 40 minutes; (4) After stirring, add 0.3 parts of azobisisobutyronitrile, heat the mixture to 60°C, and react for 6 hours to obtain the acrylate polymer. (5) Add the polyurethane oligomer synthesized in the second step to the synthesized acrylic polymer, heat the mixture to 80-90℃, and react for 1-2 hours under the action of a catalyst to obtain polyurethane modified acrylic polymer pressure-sensitive adhesive. (6) The prepared polyurethane modified acrylic polymer pressure-sensitive adhesive is mixed with 0.08 parts curing agent, 0.4 parts electrostatic agent and 0.004 parts leveling agent and then coated onto a 38μm PET substrate. After curing at 120-140℃ for 3min and aging at 48℃ for 48H, a protective film with an adhesive layer thickness of 15μm is obtained.

[0028] Example 2 Compared with Example 1, the rest is the same, except that 65 parts of butyl acrylate and 25 parts of methoxy polyethylene glycol acrylate are used in step 3.

[0029] Example 3 The remainder is the same as in Example 1, except that 0.2 parts by mass of azobisisobutyronitrile are added in step 4.

[0030] Example 4 Compared with Example 1, the rest is the same, except that the molar ratio of NCO in the diisocyanate to OH in the polyol polymer in step 1 is 1.1.

[0031] Example 5 Compared with Example 1, the rest is the same, except that no catalyst is added in step 2 and the reaction temperature is 80-100°C.

[0032] Comparative Example 1 The rest is the same as in Example 1, except that methoxy polyethylene glycol acrylate is not used in step 3.

[0033] Comparative Example 2 The remainder is the same as in Example 1, except that 0.6 parts by mass of azobisisobutyronitrile are added in step 42.

[0034] Comparative Example 3 Compared with Example 1, the rest is the same, except for steps (1) and (2), which are acrylic pressure-sensitive adhesive systems.

[0035] Comparative Example 4 The rest is the same as in Implementation 1, except that 0.2 parts of curing agent are added in step 6 to prepare the protective film.

[0036] Comparative Example 5 The rest is the same as in Implementation 1, except that a leveling agent is not added in step 6 to prepare the protective film.

[0037] The specific testing method is as follows: (1) Peel strength: The peel strength was determined by an electronic universal testing machine in accordance with GB / T2792-1998 "Test method for 180° peel strength of pressure sensitive adhesive tape" (the adhered materials are glass plates and the peel rate is 300 mm / min).

[0038] (2) High temperature and high humidity test: Cut the protective film into 150×25mm size, attach it to the surface of the glass plate, put it into a programmable constant temperature and humidity test chamber, and after 240h at 60℃ and 95% humidity, observe whether the protective film surface is detached or has bubbles. If not, it is judged as qualified and the peel strength is tested; if it is, it is judged as unqualified.

[0039] (3) Infrared spectral testing: The pressure-sensitive adhesive of the protective film was tested using a Shimadzu Fourier transform infrared spectrometer (IRTracer-100). The scanning mode was diffuse reflectance, the scanning range was 400-4000 cm⁻¹, and the spectral resolution was 4 cm⁻¹. After infrared spectral scanning, the infrared spectrum was obtained.

[0040] (4) Determination of the wettability of the protective film: The protective film to be tested is attached to the surface of the object to be coated with an AG polarizing film, and the surface is pressed with 25 kgf for 1.5 s. The sample is then removed and the surface is observed. If there are no imprints or black and white marks on the reflected and projected surfaces, it is judged to be OK and has good wettability. Figure 2 As shown; if there are obvious imprints or black and white marks on the surface of the reflection and projection observation, it is judged as NG, and the wetting performance is judged as poor, such as Figure 3 As shown.

[0041] Table 1. Test results of polarizers prepared in each embodiment and comparative example.

[0042] Conclusion Analysis: The test data shows that the peel strength of the protective film for anti-glare (AG) polarizers prepared in Examples 1-5 of this invention is 2.5-3.0 gf / in. The peel strength change factor after 240 hours at 60℃ / 90% humidity is less than 1.2. After 240 hours / 500 hours at 60℃ / 90% humidity, no precipitation or color difference was observed on the surface of the film, indicating good reliability. It has good wetting and adhesion to the surface of the AG polarizer substrate, and the bonded appearance is free of defects such as bubbles. It can meet the current market requirements for bonding AG polarizer substrates in displays, screens, and back panels, as well as the requirements for high temperature and high humidity bonding.

[0043] Compared with Example 1, Comparative Example 1, which did not use methoxy polyethylene glycol acrylate to synthesize monomers, produced a protective film with excessively high peel strength and poor wetting properties, and precipitation also occurred under 60°C / 90% conditions.

[0044] Compared with Example 1, Comparative Example 2 added an excessive amount of initiator, and the protective film prepared by the reaction-prepared pressure-sensitive adhesive had significantly higher peel strength and poorer wetting properties. Precipitation also occurred under 60°C / 90% conditions.

[0045] Compared with Example 1, Comparative Example 3, without polyurethane-modified acrylic polymer system, the protective film prepared by acrylic pressure-sensitive adhesive has significantly excessive peel force and poor wetting performance, and precipitation also occurred under 60℃ / 90% conditions.

[0046] Compared with Example 1, the protective film obtained by adding an excessive amount of curing agent during the preparation of the protective film in Comparative Example 4 did not show precipitation under the conditions of 60°C / 90%, but the peel strength was relatively weak and did not meet the requirements, and the wetting and adhesion to the substrate was also poor.

[0047] Compared with Example 1, Comparative Example 5, which did not add a leveling agent when preparing the protective film, also showed significantly higher peel strength and poorer wetting properties, and precipitation also occurred under 60°C / 90% conditions.

[0048] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A pressure-sensitive adhesive for use in protective films for anti-glare polarizers, characterized in that: The pressure-sensitive adhesive is a polyurethane-modified acrylic polymer, comprising a base adhesive and a curing agent; The main adhesive is polymerized from acrylate polymer and polyurethane oligomer; The acrylate polymer contains acrylic monomers, and the acrylic monomers contain long-chain ether monomers with repeatable units of polyether structure, the number of which is greater than or equal to 2. The polyurethane oligomer is polymerized from polyether polyol and diisocyanate monomer, and the molar ratio of NCO in the diisocyanate to OH in the polyol polymer is in the range of 1.05-1.

35.

2. The pressure-sensitive adhesive for use in anti-glare polarizer protective films according to claim 1, characterized in that: The acrylic monomer includes at least one of acrylic acid, butyl acrylate, methacrylic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl acrylate, and hydroxybutyl acrylate.

3. The pressure-sensitive adhesive for use in anti-glare polarizer protective films according to claim 2, characterized in that: The long-chain ether monomer is selected from at least one of methoxy polyethylene glycol acrylate and ethoxy polyethylene glycol acrylate.

4. The pressure-sensitive adhesive for use in anti-glare polarizer protective films according to claim 1, characterized in that, By weight, the acrylic monomers in the main adhesive include the following components: 60-65 parts butyl acrylate; 30-35 parts ethoxyethoxyethyl acrylate; 5-10 parts 2-hydroxyethyl acrylate; 1.5-4.5 parts acrylic acid; 230-250 parts ethyl acetate; and 0.2-0.3 parts azobisisobutyronitrile.

5. The pressure-sensitive adhesive for use in anti-glare polarizer protective films according to claim 1, characterized in that: The curing agent is an isocyanate curing agent, and the isocyanate curing agent is at least one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer, and diphenylmethane diisocyanate.

6. The pressure-sensitive adhesive for use in anti-glare polarizer protective films according to claim 1, characterized in that: The pressure-sensitive adhesive also contains an antistatic agent and / or a leveling agent; The antistatic agent is at least one of quaternary ammonium salt, lithium bis(trifluoromethanesulfonyl)imide, alkyl sulfonate, inorganic salt and polyol blend, and its dosage is 0.2-0.6 parts by weight; The leveling agent is at least one of polydimethylsiloxane, polyether-modified polysiloxane, and polyether-modified polydimethylsiloxane, and its dosage is 0.001-0.005 parts by weight.

7. A polarizer protective film, characterized in that: The protective film is prepared by coating a polymer film substrate with the pressure-sensitive adhesive used in anti-glare polarizer protective films as described in any one of claims 1-6, and then curing and aging it. The protective film exhibits a peel strength change ratio between 0.8 and 1.2 before and after aging treatment. The aging process includes low-temperature aging, room-temperature aging, and high-temperature and high-humidity aging.

8. A polarizer protective film according to claim 7, characterized in that: After the protective film is treated at 60°C and 90% relative humidity for 240 hours, its peel strength changes by less than 1.2 times, and there are no exudates on the surface.

9. A method for preparing a pressure-sensitive adhesive for polarizing film protection, used to prepare any one of the pressure-sensitive adhesives as described in claims 1-6 for use in anti-glare polarizing film protection, characterized in that, Includes the following steps: S1: Weigh a certain amount of polyether polyol and diisocyanate, heat the mixture to 40-50°C, react for 2-4 hours under the action of a catalyst, add toluene solvent to dilute and stir evenly to obtain polyurethane oligomer; S2: Weigh out a certain amount of butyl acrylate, long-chain ether monomer, 2-hydroxyethyl acrylate and acrylic acid, add them to ethyl acetate, continuously purge with nitrogen and stir for 30-60 minutes; after stirring, add a certain amount of azobisisobutyronitrile, heat the mixture to 60-70°C, and react for 6-8 hours to obtain the acrylate polymer. S3: Weigh a certain amount of the polyurethane oligomer synthesized in step S1, add it to the mixture in step S2, heat to 80-90°C, and stir until homogeneous. S4: Weigh a certain amount of catalyst and add it to the mixture of S3. React for 1-2 hours under the action of the catalyst to obtain the polyurethane modified acrylic polymer pressure-sensitive adhesive main adhesive. S5: After uniformly mixing the pressure-sensitive adhesive base obtained in S4 with the curing agent and additives, the mixture is applied to the substrate and cured at 120-140°C and aged at 42-48°C to obtain the anti-glare polarizing protective film.

10. The method for preparing a pressure-sensitive adhesive for a polarizing film according to claim 9, characterized in that: In step S5, the curing time is 2-5 minutes and the aging time is 48-72 hours.

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