Water-soluble adhesive for polarizing plate, method for producing the same, and polarizing plate

Abstract

The application provides a water-soluble adhesive for a polarizing plate, a preparation method and a polarizing plate, and belongs to the technical field of polarizing plate adhesives. The adhesive comprises first acetyl-acetylated polyvinyl alcohol and second acetyl-acetylated polyvinyl alcohol, the adhesive has a solid content of 2.0-8.0 wt%, a viscosity of 12-200 mPa s, is suitable for the bonding of iodine-based polarizing plate PVA polarizer and optical protective film, and has the advantages of uniform coating, high bonding strength, strong water resistance, no optical defects and no Mura defects in wet heat aging. The preparation process of the application is simple, stable and controllable, and is suitable for large-scale production of high-end display polarizing plates.

Description

Technical Field

[0001] This invention belongs to the field of polymer adhesives and optical thin film technology, specifically relating to a water-soluble adhesive for preparing polarizers with different grafting rates of acetylated polyvinyl alcohol composites by transesterification, the preparation method, and the polarizer. Background Technology

[0002] OLED (Organic Light Emitting Diode) possesses natural self-emissive properties and, with its outstanding advantages such as ultra-thin and lightweight design, flexibility, ultra-high contrast ratio, and ultra-fast response speed, has been widely used in display terminals, special lighting, and various intelligent electronic devices. In mainstream display technologies, polarizers are the core optical components of liquid crystal displays (LCDs), primarily composed of polyvinyl alcohol (PVA) polarizers bonded to two optical protective films using water-based adhesives. PVA, with its excellent film-forming properties, optical transparency, and water solubility, is widely used as the main raw material for water-based adhesives for polarizers. However, PVA itself has insufficient water resistance and weak adhesive durability, making it difficult to meet the requirements of polarizers under long-term humid and hot conditions. Through acetylation modification, acetylacetyl groups (AA) can be introduced into the side chains of PVA, forming reaction sites that can efficiently crosslink with aldehydes and amines, significantly improving the water resistance and adhesive strength of the adhesive layer. This makes acetylated polyvinyl alcohol (AA-PVA) a core material for preparing high-performance polarizers using water-based adhesives.

[0003] Currently, the preparation and application of AA-PVA still have significant limitations: traditional processes often use diketene as a modifying agent, which has problems such as low safety and easy to cause yellowing of the product; more importantly, most existing technologies use AA-PVA with a single grafting ratio, which makes it difficult to balance the coating fluidity, film uniformity and crosslinking density of water-based adhesives: when the grafting ratio is too high, the system has poor fluidity and is prone to streaks and uneven coating; when the grafting ratio is too low, there are insufficient crosslinking sites, and it is difficult to guarantee water resistance and humid heat stability.

[0004] Because a single grafting ratio of AA-PVA cannot achieve a balance between adhesive performance and process compatibility, its further application in high-end polarizers is limited. Therefore, achieving synergistic performance improvement through compounding AA-PVA with different grafting ratios has become an important direction for improving the overall quality of water-based adhesives. Developing a method for preparing AA-PVA with controllable grafting ratios, safe reaction, and uniform products, and constructing resin compositions with different grafting ratios based on this method, is of great significance for improving the water resistance, stability, and optical reliability of water-based adhesives for polarizers. Summary of the Invention

[0005] The purpose of this invention is to provide a water-soluble adhesive for polarizers, which solves the problem that a single grafting ratio system cannot simultaneously achieve coating flowability, film uniformity, crosslinking strength, and resistance to damp heat by compounding high-grafting-ratio AA-PVA with low-grafting-ratio AA-PVA. High-grafting-ratio AA-PVA (4.0–10.0 mol%) provides high-density crosslinking sites, forming rigid crosslinked regions; low-grafting-ratio AA-PVA (0.3–3 mol%) imparts coating flowability and interfacial wettability, and forms flexible crosslinked regions during curing. The two are compounded in a 1:8 to 8:1 ratio, forming a gradient crosslinking density structure from the interface to the interior of the adhesive layer at the polarizer-protective film interface, effectively reducing internal stress and suppressing Mura defects caused by damp heat aging.

[0006] Another objective of this invention is to provide a method for preparing the water-soluble adhesive, which is safe, odorless, does not use diketene, has a mild reaction, produces a uniform product, and is not prone to yellowing.

[0007] Another objective of this invention is to provide a polarizer that uses the above-mentioned adhesive to form an adhesive layer, exhibiting high optical transparency, no appearance defects, resistance to damp heat aging, and stable polarization performance.

[0008] The present invention provides a water-soluble adhesive for polarizing films, wherein the water-soluble adhesive comprises a mixture of acetylated polyvinyl alcohol with a high grafting rate and acetylated polyvinyl alcohol with a low grafting rate.

[0009] The high grafting rate of acetylated polyvinyl alcohol is 4.0 mol% to 10.0 mol%; the low grafting rate of acetylated polyvinyl alcohol is 0.3 mol% to 3 mol%.

[0010] The adhesive is made by mixing high-graft-rate acetylated polyvinyl alcohol, low-graft-rate acetylated polyvinyl alcohol, metal salt catalyst, crosslinking agent, and deionized water.

[0011] The adhesive is composed of acetylated polyvinyl alcohol with a high grafting rate and acetylated polyvinyl alcohol with a low grafting rate in a mass ratio of 1-8:1-8.

[0012] The adhesive is composed of acetylated polyvinyl alcohol with a high grafting rate and acetylated polyvinyl alcohol with a low grafting rate in a mass ratio of 1:1.

[0013] The adhesive is composed of high-grafted acetylated polyvinyl alcohol, low-grafted acetylated polyvinyl alcohol, metal salt catalyst, crosslinking agent, and deionized water in a mass ratio of 1-8:1-8:0.001-0.1:0.001-0.1:200.

[0014] The adhesive is composed of high-grafted acetylated polyvinyl alcohol, low-grafted acetylated polyvinyl alcohol, metal salt catalyst, crosslinking agent, and deionized water in a mass ratio of 4.5:4.5:0.02:0.01:200.

[0015] The adhesive has a solid content of 2.0–8.0 wt% and a viscosity of 12–200 mPa·s.

[0016] The high-graft-rate acetylated polyvinyl alcohol and the low-graft-rate acetylated polyvinyl alcohol are prepared by transesterification.

[0017] The preparation method of acetylated polyvinyl alcohol involves adding polyvinyl alcohol, dimethyl sulfoxide, and sodium acetate catalyst into a reactor, heating to 90°C to fully dissolve the polyvinyl alcohol, then adding tert-butyl acetoacetate dropwise, followed by post-reaction treatment to obtain the acetylated polyvinyl alcohol resin product. Specifically, the mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of high-grafting-rate acetylated polyvinyl alcohol is 10:10–6; the mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of low-grafting-rate acetylated polyvinyl alcohol is 10:4–1.

[0018] The mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of high grafting rate acetylated polyvinyl alcohol is 10:8; the mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of high grafting rate acetylated polyvinyl alcohol is 10:3.

[0019] The preparation method of the bipolar water-soluble adhesive for polarizing films according to the present invention includes the following steps:

[0020] S1 uses transesterification to prepare high-graft-rate acetylated polyvinyl alcohol and low-graft-rate acetylated polyvinyl alcohol, respectively. After washing and drying, high-graft-rate acetylated polyvinyl alcohol powder or low-graft-rate acetylated polyvinyl alcohol powder is obtained.

[0021] S2 Add high-graft-rate acetylated polyvinyl alcohol powder and low-graft-rate acetylated polyvinyl alcohol powder to deionized water in proportion, heat to 90-98℃ and dissolve for 50-120 min. After complete dissolution, cool to room temperature to obtain a blend.

[0022] S3. Add the formulated amount of metal salt catalyst and crosslinking agent to the blend liquid, stir evenly, and then filter and degas to obtain the polarizer water-soluble adhesive.

[0023] The polarizer described herein, prepared using a bipolar water-soluble adhesive, comprises a polyvinyl alcohol polarizer; an optical protective film adhered to at least one side of the polyvinyl alcohol polarizer; and an adhesive layer disposed between the polyvinyl alcohol polarizer and the optical protective film; characterized in that the polarizer is formed by drying and crosslinking the bipolar water-soluble adhesive; wherein the water-soluble adhesive is prepared by the aforementioned method.

[0024] Compared with the prior art, the advantages of the present invention are as follows:

[0025] First, the present invention uses the transesterification method to prepare AA-PVA compound systems with high and low grafting rates, which avoids the problems of insufficient safety, poor solubility and yellowing of products in traditional processes;

[0026] Second, through the synergistic effect of resins with different grafting rates, a gradient cross-linking network is constructed: with low internal stress and good film toughness, while ensuring good flowability and coatability of the adhesive, it significantly improves the cross-linking density, water resistance and adhesion durability of the cured adhesive layer.

[0027] Third, the polarizer made with this adhesive is free of streaks and defects, and maintains stable optical performance and structural strength even in humid and hot environments, making it more suitable for the long-term use requirements of high-end display devices. Attached Figure Description

[0028] Figure 1. Raw 1H NMR spectrum of the AA-H preparation example;

[0029] Figure 2. Raw 1H NMR spectrum of the AA-L preparation example;

[0030] Figure 3. Raw 1H NMR spectrum data of the AA-D preparation example;

[0031] Figure 4 Comparison of water resistance between the experimental group and the control group;

[0032] Figure 5 Comparison of Mura tests between the experimental and control groups.

[0033] The specific embodiments of the present invention will now be described in detail. It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Example 1

[0034] 1. Preparation of AA-PVA

[0035] High grafting rate acetylated polyvinyl alcohol (AA-H): 100 parts of PVA with an average degree of polymerization of 1700, 2000 parts of dimethyl sulfoxide, and 0.83 parts of sodium acetate catalyst were added to a reactor. The temperature was raised to 90℃ to fully dissolve the PVA. Then, 80 parts of tert-butyl acetoacetate were added dropwise. After post-reaction treatment, a product with a grafting rate of 6.59 mol% was obtained. (Specific details are as follows...) Figure 1 As shown.

[0036] Low grafting rate of acetylated polyvinyl alcohol (AA-L): With the amount of tert-butyl acetoacetate adjusted to 30 parts and other conditions remaining the same, a product with a grafting rate of 2.94 mol% was obtained, as detailed below. Figure 2 As shown.

[0037] Conventional acetylated polyvinyl alcohol (AA-D) involves adding 100 parts of PVA with an average degree of polymerization of 1700 and 60 parts of acetic acid to a reactor, heating to 60°C to allow the PVA to fully swell, and then adding 50 parts of diketene dropwise. After post-reaction processing, a product with a grafting rate of 5.16 mol% is obtained. (Specific details are as follows...) Figure 3 As shown.

[0038] in, Figure 1 , 2 In the NMR spectrum shown in Figure 3, the peaks in the range of 1.2-2.0 ppm correspond to the proton peaks of the methylene group on the polyvinyl alcohol backbone (CH2(VA)), while the peak at 2.18 ppm corresponds to the methyl protons (AA) in the acetoacetyl group. The grafting rate of the dicarbonyl group is obtained by integrating the characteristic peaks at 2.18 ppm and 1.2-2.0 ppm and calculating the ratio of the two integrals. Specifically, as shown in Table 1, the calculation formula is as follows: Grafting rate (%) = integral of the 2.18 ppm peak / (1.5 × (integral of the peaks in the range of 1.2-2.0 ppm)) × 100%.

[0039] Table 1. Calculation results of grafting rates for preparation examples AA-H, AA-L, and AA-D.

[0040]

[0041] Example 2: Polarizing Film Fabrication

[0042] 1. Preparation of polarizer samples

[0043] Experimental Group 1: Adhesive Preparation: Take 4.5 parts by weight of AA-H and 4.5 parts by weight of AA-L, and add them to 200 parts by weight of deionized water. Heat to 95℃ and keep warm for 120 minutes to dissolve, then cool to room temperature. Add 0.02 parts by weight of glyoxal and 0.001 parts by weight of zinc chloride, stir for 30 minutes, filter to remove bubbles, and obtain the adhesive.

[0044] Polarizing film fabrication: A 30 μm thick PVA optical film is sequentially processed through dyeing, cross-linking, stretching, water cutting, water washing, and color correction to obtain a PVA polarizer; subsequently, the aqueous adhesive of this invention is coated onto the upper and lower surfaces of the polarizer, and then bonded to the TAC optical protective films on both sides. The composite film material is then subjected to… The polarizer sample was dried and crosslinked in a gradient temperature controlled oven, cooled, and then rolled up to obtain the target polarizer sample.

[0045] Experimental Group 2: Adhesive Preparation: Take 3 parts by weight of AA-H and 6 parts by weight of AA-L, and add 200 parts by weight of deionized water. The remaining procedures are the same as in Example 1. The polarizer is prepared as above.

[0046] Experimental Group 3: Adhesive Preparation: Take 8 parts by weight of AA-H and 1 part by weight of AA-L, and add 200 parts by weight of deionized water. The remaining procedures are the same as in Example 1. The polarizer is prepared as above.

[0047] Experimental Group 4: Adhesive Preparation: Take 1 part by weight of AA-H and 8 parts by weight of AA-L, and add 200 parts by weight of deionized water. The remaining procedures are the same as in Example 1. The polarizer is prepared as above.

[0048] Comparative Group 1: Only 9 parts by weight of AA-H were used; the remaining components and preparation methods were the same as in Example 1. The polarizer was prepared in the same manner as above.

[0049] Comparative Group 2: Only 9 parts by weight of AA-L were used; the remaining components and preparation methods were the same as in Example 1. The polarizer was prepared in the same manner as above.

[0050] Comparative Group 3: Only 9 parts by weight of AA-D were used; the remaining components and preparation methods were the same as in Example 1. The polarizer was prepared in the same manner as above.

[0051] Example 3 Performance Testing and Evaluation

[0052] 1. Coating appearance: Visually inspect under a 1000 Lux light box to evaluate the "composite texture" defect, as shown in Table 2.

[0053] Table 2 Coating Appearance Inspection

[0054]

[0055] 2. Water Resistance: The prepared polarizer was cut into 90*130mm samples with its absorption axis as the long side. The samples were then adhered to a glass plate with one side flat using OCA adhesive and immersed in deionized water at 40℃ for 24 hours. Afterward, the samples were removed from the water bath and the moisture was wiped off. The polarizer samples were tested before and after the test using a polarizing microscope (Zeiss AxioLab 5). The distance from the end of the short side of the sample (the end of the protective film) to the area where the residual polarizers retain the characteristic color of the polarizer was defined as the shrinkage length, denoted by S.

[0056] Performance rating criteria:

[0057] S < 0.5mm: Excellent, with superior water resistance;

[0058] 0.5mm≤S≤1.0mm: Good, water resistance is average;

[0059] S > 1.0 mm: Poor / Unqualified, poor water resistance.

[0060] The smaller the S value, the better the interfacial bonding stability and water resistance of the adhesive layer; the larger the S value, the more severe the edge shrinkage, whitening and discoloration of the polarizer, and the worse the water resistance of the adhesive. See Table 3 and appendix for details. Figure 4 As shown.

[0061] Table 3 Water resistance data for examples and comparative examples

[0062]

[0063] 3. 500-hour weather resistance optical performance test of polarizer: The prepared polarizer was cut into 30×50 mm samples along the 45° direction of the optical axis. The sample was flatly attached to the glass plate surface on one side using OCA glue. After wiping and cleaning with a lint-free cloth, it was placed in a constant temperature and humidity test chamber (CZ-A-150D type) for damp heat aging. Test conditions: temperature 85 ℃, humidity 85%RH, aging time 500 h.

[0064] Before and after the aging test, the transmittance (T), polarization degree (P), and chromaticity parameters of the samples were measured using a spectrophotometer (Shimadzu UV-2600) in the range of 380 nm to 780 nm. and The changes in each indicator before and after aging are expressed as absolute values, and the calculation formula is as follows:

[0065] ;

[0066] ;

[0067] Where: T0, P0, , —— Optical test values before aging;

[0068] T1, P1, , —— Optical test values after aging.

[0069] The smaller the value, the better the optical stability of the polarizer in a humid and hot environment. Specifically, as shown in Table 4.

[0070] Table 4 Weather resistance data of examples and comparative examples

[0071]

[0072] 4. Conduct a 500-hour Mura test;

[0073] Cut the prepared polarizer sample into a size of 185×250mm (MD×TD) to make a sample, stick one side of it flat on a glass plate with OCA glue, wipe it clean with a lint-free cloth and place it in a thermostatic and humid test chamber (test conditions: temperature 85°C, humidity 85%RH, 500H); place the prepared sample under a uniform backlight source (same size as the sample), and observe the light leakage situation (light leakage, bright spots, unevenness, blueing phenomenon) of the sample in the orthogonal state. Specifically, as shown in Table 5 and the appendix Figure 5 as shown.

[0074] Table 5 Mura data of examples and comparative examples

[0075]

[0076] 5. Interlayer peel strength (tape method): Cut the prepared polarizer with its absorption axis as the long side into a size of 90×130mm to make a sample, stick one side of it flat on a glass plate, stick NITTO 31B special test tape (length 10 - 15cm) on the four corners of the sample, and quickly pull up the tape at an angle of 90 degrees. No delamination is considered qualified; specifically, as shown in Table 6.

[0077] Table 6 Peel strength data of examples and comparative examples

[0078] The test results show that for experimental groups 1 - 4 using the AA-PVA compound system with high and low grafting rates, they have outstanding advantages in coating processing performance, water-resistant adhesion performance, optical stability, and apparent defect control: the sample coating is uniform, without composite lines, the water resistance rating is excellent, and the interlayer peel strength meets the standard; after the humid and hot aging test, the change in light transmittance ΔT, the change in polarization degree Δp, the color difference , All values ​​remained within an extremely low range, and no Mura defects were observed. Among the various performance groups studied, the polarizer exhibited the best overall performance when the AA-H to AA-L quality ratio was 1:1, representing a significant improvement over existing process technologies.

[0079] Comparison between the experimental and control groups reveals that: a single high-grafting-rate system is prone to color difference and bluing after damp heat resistance testing; a single low-grafting-rate system has insufficient water resistance and substandard interlayer peel strength, and is also prone to light leakage and bluing; the single-component water-based adhesive prepared using the diketene process exhibits color deviation and is also prone to bluing after damp heat resistance testing. This compound system effectively balances the resin's rheological properties and cross-linking curing effect, simultaneously improving the adhesive's coating leveling properties, water resistance stability of the adhesive layer, interfacial adhesion strength, and damp heat resistance, solving the industry problem of existing single-grafting-rate systems being unable to simultaneously achieve process adaptability and reliability.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any simple variations or equivalent substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A water-soluble adhesive for polarizing films, characterized in that, The water-soluble adhesive comprises a mixture of acetylated polyvinyl alcohol with a high grafting rate and acetylated polyvinyl alcohol with a low grafting rate.

2. The polarizer water-soluble adhesive according to claim 1, characterized in that, The high grafting rate of acetylated polyvinyl alcohol is 4.0 mol% to 10.0 mol%; the low grafting rate of acetylated polyvinyl alcohol is 0.3 mol% to 3 mol%.

3. The polarizer water-soluble adhesive according to claim 2, characterized in that, The adhesive is made by mixing high-graft-rate acetylated polyvinyl alcohol, low-graft-rate acetylated polyvinyl alcohol, metal salt catalyst, crosslinking agent, and deionized water.

4. The polarizer water-soluble adhesive according to claim 3, characterized in that, The adhesive is composed of acetylated polyvinyl alcohol with a high grafting rate and acetylated polyvinyl alcohol with a low grafting rate in a mass ratio of 1-8:1-8.

5. The polarizer water-soluble adhesive according to claim 4, characterized in that, The adhesive is composed of acetylated polyvinyl alcohol with a high grafting rate and acetylated polyvinyl alcohol with a low grafting rate in a mass ratio of 1:

1.

6. The polarizer water-soluble adhesive according to claim 4, characterized in that, The adhesive is composed of high-grafted acetylated polyvinyl alcohol, low-grafted acetylated polyvinyl alcohol, metal salt catalyst, crosslinking agent, and deionized water in a mass ratio of 1-8:1-8:0.001-0.1:0.001-0.1:

200.

7. The polarizer water-soluble adhesive according to claim 6, characterized in that, The adhesive is composed of high-grafted acetylated polyvinyl alcohol, low-grafted acetylated polyvinyl alcohol, metal salt catalyst, crosslinking agent, and deionized water in a mass ratio of 4.5:4.5:0.02:0.01:

200.

8. The polarizer water-soluble adhesive according to claim 7, characterized in that, The adhesive has a solid content of 2.0–8.0 wt% and a viscosity of 12–200 mPa·s.

9. The polarizer water-soluble adhesive according to claim 8, characterized in that, The preparation methods for the high-graft-rate acetylated polyvinyl alcohol and the low-graft-rate acetylated polyvinyl alcohol are by transesterification.

10. The polarizer water-soluble adhesive according to claim 9, characterized in that, The preparation method of acetylated polyvinyl alcohol involves adding polyvinyl alcohol, dimethyl sulfoxide, and sodium acetate catalyst into a reactor, heating to 90°C to fully dissolve the polyvinyl alcohol, then adding tert-butyl acetoacetate dropwise, followed by post-reaction processing to obtain the acetylated polyvinyl alcohol resin product. Specifically, the mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of high-grafting-rate acetylated polyvinyl alcohol is 10:10–6; the mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of low-grafting-rate acetylated polyvinyl alcohol is 10:4–1.

11. The polarizer water-soluble adhesive according to claim 9, characterized in that, The mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of high grafting rate acetylated polyvinyl alcohol is 10:8; the mass ratio of polyvinyl alcohol to tert-butyl acetoacetate in the preparation of high grafting rate acetylated polyvinyl alcohol is 10:

3.

12. A method for preparing the bipolar water-soluble adhesive for polarizing films according to any one of claims 1 to 10, characterized in that, Including the following steps: S1 uses transesterification to prepare high-graft-rate acetylated polyvinyl alcohol and low-graft-rate acetylated polyvinyl alcohol, respectively. After washing and drying, high-graft-rate acetylated polyvinyl alcohol powder or low-graft-rate acetylated polyvinyl alcohol powder is obtained. S2 Add high-graft-rate acetylated polyvinyl alcohol powder and low-graft-rate acetylated polyvinyl alcohol powder to deionized water in proportion, heat to 90-98℃ and dissolve for 50-120 min. After complete dissolution, cool to room temperature to obtain a blend. S3. Add the formulated amount of metal salt catalyst and crosslinking agent to the blend liquid, stir evenly, and then filter and degas to obtain the polarizer water-soluble adhesive.

13. A polarizer, comprising a polyvinyl alcohol polarizer; an optical protective film adhered to at least one side of the polyvinyl alcohol polarizer; and an adhesive layer disposed between the polyvinyl alcohol polarizer and the optical protective film; characterized in that, The polarizer is formed by drying and cross-linking two water-soluble adhesives. The water-soluble adhesive is prepared by the method described in claim 10.

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