Application of alcohol containing 1-4 carbon atoms in improving optical transparency of acetoacetylated polyvinyl alcohol

Abstract

The invention relates to the technical field of polyvinyl alcohol, in particular to application of alcohol containing 1-4 carbon atoms in improvement of optical transparency of acetoacetylated polyvinyl alcohol, and aims to solve the problems that acetoacetylated polyvinyl alcohol prepared in the prior art is poor in water solubility due to non-uniform substitution degree, a finished product prepared after the acetoacetylated polyvinyl alcohol is dissolved in an organic solvent becomes yellow, and the optical transparency of the acetoacetylated polyvinyl alcohol is poor. Therefore, the invention provides the application of the alcohol containing 1-4 carbon atoms in improving the optical transparency of the acetoacetylated polyvinyl alcohol.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl alcohol technology, and more specifically, to the application of an alcohol containing 1 to 4 carbon atoms in improving the optical transparency of acetylated polyvinyl alcohol. Background Technology

[0002] Polyvinyl alcohol (PVA) is an important matrix material for water-based adhesives for polarizing films due to its excellent film-forming properties, transparency, and hydrophilicity. However, the high polarity of its hydroxyl groups limits its water resistance and adhesive durability. Acetylation modification, which grafts acetylacetyl groups (AA) onto the side chains of PVA, not only retains the reactivity of the hydroxyl groups but also endows it with novel crosslinking sites on the ketone carbonyl group. This significantly improves the water resistance of the adhesive layer, making it a key raw material for the preparation of water-based adhesives for polarizing films.

[0003] Polarizing films are known to consist of two layers of triacetate cellulose (TAC) films as protective films, bonded together with a water-based adhesive composed of water-soluble resin and a sandwiched polyvinyl alcohol film (polarizer) through coating and drying. The water-soluble resin used in the preparation of the adhesive serves as the bonding material between the polarizing protective film and the polarizer; its solubility, optical transparency, and other key indicators play a decisive role in the optical performance of the polarizing film. However, the preparation process of acetylated polyvinyl alcohol (AA-PVA) still faces many technical challenges. For example, the acetylation reaction has poor controllability; the reaction after PVA swelling may lead to uneven substitution of the product, resulting in poor solubility of AA-PVA. Furthermore, while the reaction after PVA dissolution can ensure uniform substitution of the product, diketene is unstable in polar solvents and is prone to self-polymerization during the reaction, leading to a yellowing of the product. How to maintain the original optical properties of PVA while ensuring the solubility of AA-PVA is an urgent problem to be solved.

[0004] Therefore, developing a method to stably prepare high-quality AA-PVA and solve the problem of product yellowing is of great practical significance. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that the degree of substitution of acetylated polyvinyl alcohol prepared by the prior art is uneven, resulting in poor water solubility and yellowing of the finished product after dissolving in organic solvents, which affects the optical performance of polarizers. Therefore, this invention provides an application of an alcohol containing 1 to 4 carbon atoms in improving the optical transparency of acetylated polyvinyl alcohol.

[0006] To achieve the above objectives, in a first aspect, the present invention provides the use of alcohols containing 1 to 4 carbon atoms in improving the optical transparency of acetylated polyvinyl alcohol.

[0007] Furthermore, the alcohol containing 1 to 4 carbon atoms is selected from one or more of methanol, ethanol, ethylene glycol, n-butanol, and isopropanol.

[0008] Furthermore, the alcohol containing 1 to 4 carbon atoms is ethylene glycol.

[0009] Secondly, the present invention provides a method for preparing acetylated polyvinyl alcohol, the method comprising: 1) In the presence of an organic solvent, polyvinyl alcohol resin is mixed with an alcohol containing 1 to 4 carbon atoms to obtain a polyvinyl alcohol solution; 2) In an anaerobic environment, react the polyvinyl alcohol solution from step 1) with diketene.

[0010] Furthermore, in step 1), the organic solvent is dimethyl sulfoxide and / or N,N-dimethylacetamide.

[0011] Furthermore, in step 1), the degree of polymerization of the polyvinyl alcohol resin is 500~3000, preferably 800~1500; the degree of alcoholysis is 97~99.999 mol.

[0012] Furthermore, in step 1), the alcohol containing 1 to 4 carbon atoms is selected from one or more of methanol, ethanol, ethylene glycol, n-butanol and isopropanol; preferably ethylene glycol.

[0013] Furthermore, in step 1), the mass ratio of the polyvinyl alcohol resin to the organic solvent is 1:5~20.

[0014] Furthermore, in step 2), the oxygen-free environment is a nitrogen atmosphere and / or an argon atmosphere.

[0015] Furthermore, the mass ratio of the polyvinyl alcohol resin to diketene is 1:0.2~0.6.

[0016] Furthermore, the mass ratio of the diketene to the alcohol containing 1 to 4 carbon atoms is 1:0.0001 to 0.02.

[0017] Furthermore, in step 2), the reaction conditions include: a temperature of 30~130℃ and a time of 2~10h.

[0018] Thirdly, the present invention provides an acetylated polyvinyl alcohol prepared by the preparation method described in the second aspect, wherein the content of structural units having acetylacetyl groups in the acetylated polyvinyl alcohol is typically 0.1 to 20 mol%, preferably 0.3 to 10 mol%, and more preferably 1 to 8 mol%.

[0019] Fourthly, the present invention provides an aqueous adhesive for bonding a polarizer protective film to a polarizer, characterized in that the aqueous adhesive contains the acetylated polyvinyl alcohol described in the third aspect.

[0020] In the above technical solution, the present invention avoids the situation where PVA resin swells in organic acid during the acetylation reaction, resulting in uneven product substitution degree and poor water solubility of the obtained AA-PVA.

[0021] Furthermore, in the preparation method of acetylated polyvinyl alcohol of the present invention, an alcohol containing 1 to 4 carbon atoms is added at 0.1-20 ‰ of the weight of diketene, which effectively solves the problem that the product color turns yellow after the AA-PVA is dissolved in an organic solvent. While ensuring the solubility of AA-PVA, the original optical properties of polyvinyl alcohol are maintained.

[0022] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the 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.

[0025] In a first aspect, the present invention provides the application of alcohols containing 1 to 4 carbon atoms in improving the optical transparency of acetylated polyvinyl alcohol.

[0026] In a preferred embodiment of the present invention, the alcohol containing 1 to 4 carbon atoms is selected from one or more of methanol, ethanol, ethylene glycol, n-butanol and isopropanol, preferably ethylene glycol.

[0027] Secondly, the present invention provides a method for preparing acetylated polyvinyl alcohol, the method comprising: 1) In the presence of an organic solvent, polyvinyl alcohol resin is mixed with an alcohol containing 1 to 4 carbon atoms to obtain a polyvinyl alcohol solution; 2) In an anaerobic environment, react the polyvinyl alcohol solution from step 1) with diketene.

[0028] In a preferred embodiment of the present invention, in step 1), the organic solvent is dimethyl sulfoxide and / or N,N-dimethylacetamide.

[0029] In a preferred embodiment of the present invention, in order to provide a good reaction environment for the reaction of polyvinyl alcohol resin and diketene, the organic solvent needs to have good solubility and stability. In step 1), the degree of polymerization of the polyvinyl alcohol resin is 500~3000, preferably 800~1500; the degree of hydrolysis is 97~99.999 mol%, for example, degree of polymerization of 500, degree of hydrolysis of 97 mol%; degree of polymerization of 600, degree of hydrolysis of 98 mol%; degree of polymerization of 700, degree of hydrolysis of 99 mol%; degree of polymerization of 800, degree of hydrolysis of 97 mol%; degree of polymerization of 1000, degree of hydrolysis of 98 mol%; degree of polymerization of 1500, degree of hydrolysis of 99.999 mol%; degree of polymerization of 2000, degree of hydrolysis of 97 mol%; degree of polymerization of 2500, degree of hydrolysis of 98 mol%; degree of polymerization of 3000, degree of hydrolysis of 99.999 mol%, etc.

[0030] In a preferred embodiment of the present invention, in step 1), the alcohol containing 1 to 4 carbon atoms is selected from one or more of methanol, ethanol, ethylene glycol, n-butanol and isopropanol. The lower alcohol undergoes an esterification reaction with the acetic anhydride in diketene to generate the corresponding ester. This substance has an inhibitory effect on the polymerization of diketene, thereby allowing the product to remain unchanged in color for a long time.

[0031] In a preferred embodiment of the present invention, in step 1), the alcohol containing 1 to 4 carbon atoms is ethylene glycol, wherein ethylene glycol undergoes an esterification reaction with acetic anhydride in diketene to generate ethylene glycol diacetate, which inhibits the polymerization of diketene, thereby preventing the finished product from changing color for a long time.

[0032] In a preferred embodiment of the present invention, in step 1), the mass ratio of the polyvinyl alcohol resin to the organic solvent is 1:5~20.

[0033] In a preferred embodiment of the present invention, in step 2), the oxygen-free environment is a nitrogen atmosphere and / or an argon atmosphere.

[0034] In a preferred embodiment of the present invention, the mass ratio of the polyvinyl alcohol resin to diketene is 1:0.2~0.6.

[0035] In a preferred embodiment of the present invention, the mass ratio of diketene to an alcohol containing 1 to 4 carbon atoms is 1:0.0001 to 0.02.

[0036] In a preferred embodiment of the present invention, the mass ratio of diketene to an alcohol containing 1 to 4 carbon atoms is 1:0.0001 to 0.002, for example, it can be 1:0.0001, 1:0.0005, 1:0.001, 1:0.0015, 1:0.002, etc.

[0037] In a preferred embodiment of the present invention, in order to ensure the smooth progress of the reaction and avoid the self-polymerization of diketene or other side reactions caused by excessively high temperature, and to ensure that the reaction proceeds fully and improve the yield and quality of acetylated polyvinyl alcohol, the reaction conditions in step 2) include: a temperature of 30~130℃ and a time of 2~10h.

[0038] More preferably, in step 2), the reaction conditions include: a temperature of 50~100℃ and a time of 2~8h.

[0039] In a preferred embodiment of the present invention, the preparation method further includes: precipitation, filtration, washing and drying.

[0040] In a preferred embodiment of the present invention, the detergent used for washing is selected from one or more of methanol, ethanol and propanol, which can effectively wash AA-PVA and remove impurities and unreacted substances therein.

[0041] In a preferred embodiment of the present invention, the drying conditions include: a temperature of 40~150℃, a pressure of <20kPa, and a time of 2~12h. If the drying temperature is too high, it will cause resin deterioration, and if it is too low, it will significantly prolong the drying cycle and reduce production efficiency.

[0042] In a preferred embodiment of the present invention, the drying conditions include: a temperature of 50~110℃, a pressure of <15kPa, and a time of 4~12h.

[0043] More preferably, the drying temperature is 60~100°C.

[0044] Thirdly, the present invention provides an acetylated polyvinyl alcohol prepared by the preparation method described in the second aspect, wherein the content of structural units having acetylacetyl groups in the acetylated polyvinyl alcohol is typically 0.1 to 20 mol%, preferably 0.3 to 10 mol%, and more preferably 1 to 8 mol%.

[0045] When the content of acetylacetyl polyvinyl alcohol with acetylacetyl groups in the prepared product is too low, the water resistance tends to decrease; while when the content is too high, long-term storage under high temperature and high humidity conditions will cause the acetylacetyl groups to react and form a cross-linked structure, which tends to decrease the water solubility.

[0046] Fourthly, the present invention provides an aqueous adhesive for bonding a polarizer protective film to a polarizer, characterized in that the aqueous adhesive contains the acetylated polyvinyl alcohol described in the third aspect.

[0047] The present invention will be described in detail below through examples. In the following examples, the pharmaceuticals and agents are all conventional commercially available products.

[0048] In this invention, the room temperature is 15~30℃.

[0049] Example 1 Add 100 parts by weight of polyvinyl alcohol (PVA) resin, 1000 parts by weight of dimethyl sulfoxide (DMSO), and 0.008 parts by weight of ethylene glycol (0.2‰ of the mass of diketene) to a glass instrument equipped with a temperature control system. Stir and dissolve the mixture at 80°C to obtain a homogeneous polyvinyl alcohol solution. Add 40 parts by weight of diketene dropwise under a nitrogen atmosphere. After the addition of diketene is complete, allow the mixture to react for another 1 hour before stopping the reaction. The above product was precipitated with ethanol, washed three times with ethanol, centrifuged, and dried at 15 kPa and 90 °C for 3 h to obtain AA-PVA resin, denoted as B1.

[0050] Example 2 The method described in Example 1 was carried out, except that "0.008 parts by mass of ethylene glycol (0.2‰ of the mass of diketene)" was replaced with "0.02 parts by mass of ethylene glycol (0.5‰ of the mass of diketene)" to obtain AA-PVA resin, denoted as B2.

[0051] Comparative Example 1 The method described in Example 1 was carried out, except that ethylene glycol was not added, and AA-PVA resin, denoted as D1, was obtained.

[0052] Comparative Example 2 The method described in Example 1 was carried out, except that "0.008 parts by mass of ethylene glycol (0.2‰ of the mass of diketene)" was replaced with "0.2 parts by mass of ethylene glycol (5‰ of the mass of diketene)" to obtain AA-PVA resin, denoted as D2.

[0053] Comparative Example 3 Add 100 parts by weight of polyvinyl alcohol (PVA) resin and 20 parts by weight of acetic acid to a glass instrument equipped with a temperature control system, stir to allow the PVA resin to swell, and then add 40 parts by weight of diketene dropwise at 80°C under a nitrogen atmosphere. After the diketene is added, continue the reaction for 1 hour and then stop the reaction. The above product was precipitated with ethanol, washed three times with ethanol, centrifuged, and dried at 15 kPa and 90 °C for 3 h to obtain AA-PVA resin, denoted as D3.

[0054] Detection Example 1 This test example illustrates the determination of insoluble components in AA-PVA resin aqueous solutions: Weigh 5g of the AA-PVA resin prepared in Examples 1-2 and Comparative Examples 1-3 respectively (record sample weight m1), then place it in a clean three-necked flask, add 100 mL of deionized water, stir at 95°C for 1 hour to fully dissolve it, and cool to room temperature. Place the glass dish and 40μm filter paper in an oven at 105 ℃ to dry. After cooling, weigh the glass dish and filter paper together (record data m2). Immediately place the 40μm filter paper into a vacuum filtration device to filter the sample after dissolution. Remove the filtered filter paper and place it in the glass dish. Place the glass dish in an oven at 105 ℃ to dry (for more than half an hour). After drying, weigh the glass dish and filter paper together after cooling (record data m3).

[0055] The insoluble content (%)x = (m3-m2) / m1×100%; the results are shown in Table 1.

[0056] Detection Example 2 This test example illustrates the determination of the transparency of AA-PVA resin aqueous solutions: Weigh 5g of AA-PVA resin prepared in Examples 1-2 and Comparative Examples 1-3 respectively, and place it in a clean three-necked flask. Add 100 mL of deionized water and stir at 95°C for 1 hour to fully dissolve it. Cool the resulting aqueous solution to room temperature and take a uniform sample in a quartz glass (2cm). Measure the transparency (transmittance, wavelength 430nm) of the AA-PVA resin aqueous solution using a spectrophotometer. The results are shown in Table 1.

[0057] Detection Example 3 This test example is used to illustrate the haze of AA-PVA resin aqueous solution: Weigh 5g of AA-PVA resin prepared in Examples 1-2 and Comparative Examples 1-3 respectively, and place it in a clean three-necked flask. Add 100 mL of deionized water and stir at 95°C for 1 hour to fully dissolve it. Cool the resulting aqueous solution to room temperature and take a uniform sample into a sample dish. Measure the haze of the AA-PVA resin aqueous solution with a haze meter. The results are shown in Table 1.

[0058] Detection Example 4 This test example illustrates the determination of the yellow index (YI) value of AA-PVA resin aqueous solution: 5g of AA-PVA resin prepared in Examples 1-2 and Comparative Examples 1-3 were weighed and placed in a clean three-necked flask. 100 mL of deionized water was added, and the mixture was stirred at 95°C for 1 hour to ensure complete dissolution. The resulting aqueous solution was cooled to room temperature to prepare a 1.0 wt% aqueous solution of PVA-based resin. The YI value of the above aqueous solution was determined using a Hach LICO690 liquid colorimeter, and the results are shown in Table 1.

[0059] Table 1

[0060] The test results above show that the AA-PVA resins prepared in Examples 1-2 have significantly different yellow index (YI) values ​​in their aqueous solutions compared to those prepared in Comparative Examples 1-2. The AA-PVA resin in Comparative Example 1, which did not contain ethylene glycol, had a significantly higher yellow index (YI) value in its aqueous solution, along with a significantly lower transparency and a slight increase in haze. The AA-PVA resin in Comparative Example 2, where the amount of ethylene glycol added exceeded the limits specified in this invention, exhibited good solubility, but its transparency decreased slightly, its haze increased slightly, and its yellow index (YI) value was significantly higher. Therefore, adding an appropriate amount of alcohol additive to the reaction system can effectively suppress the increase in the yellow index (YI) value of the AA-PVA resin aqueous solution caused by product yellowing.

[0061] Comparing the AA-PVA resins prepared in Examples 1-2 with those prepared in Comparative Example 3, the PVA in the AA-PVA resin of Comparative Example 3 swelled in acetic acid, resulting in uneven acetylation substitution during the acetylation reaction. This led to poor product solubility, with significantly higher insoluble content and haze in its aqueous solution, and significantly lower transparency. This indicates that the preparation method of the present invention, which involves first dissolving PVA in an organic solvent and then adding diketene, can effectively solve the solubility problem of AA-PVA resin aqueous solutions.

[0062] In summary, this invention prepares AA-PVA by first dissolving PVA in an organic solvent reaction system and then adding a specific amount of alcohol with 1 to 4 carbon atoms. This effectively solves the problem of yellowing of the product while ensuring its solubility, and significantly improves the quality and performance of the product.

[0063] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0064] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0065] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. Application of alcohols containing 1 to 4 carbon atoms in improving the optical transparency of acetylated polyvinyl alcohol.

2. The application according to claim 1, characterized in that, The alcohol containing 1 to 4 carbon atoms is selected from one or more of methanol, ethanol, ethylene glycol, n-butanol, and isopropanol; preferably ethylene glycol.

3. A method for preparing acetylated polyvinyl alcohol, characterized in that, The preparation method includes: 1) In the presence of an organic solvent, polyvinyl alcohol resin is mixed with an alcohol containing 1 to 4 carbon atoms to obtain a polyvinyl alcohol solution; 2) In an anaerobic environment, react the polyvinyl alcohol solution from step 1) with diketene.

4. The preparation method according to claim 3, characterized in that, In step 1), the organic solvent is dimethyl sulfoxide and / or N,N-dimethylacetamide; Preferably, in step 1), the degree of polymerization of the polyvinyl alcohol resin is 500-3000, more preferably 800-1500; the degree of alcoholysis is 97-99.999 mol% More preferably, in step 1), the alcohol containing 1 to 4 carbon atoms is selected from one or more of methanol, ethanol, ethylene glycol, n-butanol and isopropanol; preferably ethylene glycol.

5. The preparation method according to claim 3 or 4, characterized in that, In step 1), the mass ratio of the polyvinyl alcohol resin to the organic solvent is 1:5~20.

6. The preparation method according to any one of claims 3-5, characterized in that, In step 2), the oxygen-free environment is a nitrogen atmosphere and / or an argon atmosphere.

7. The preparation method according to any one of claims 3-6, characterized in that, The mass ratio of polyvinyl alcohol resin to diketene is 1:0.2~0.6; Preferably, the mass ratio of diketene to an alcohol containing 1 to 4 carbon atoms is 1:0.0001 to 0.

02.

8. The preparation method according to any one of claims 3-7, characterized in that, In step 2), the reaction conditions include a temperature of 30~130℃ and a time of 2~10h.

9. An acetylated polyvinyl alcohol prepared by the method according to any one of claims 3-8, characterized in that, The content of acetylated polyvinyl alcohol with acetylated structural units is typically 0.1-20 mol, preferably 0.3-10 mol, and more preferably 1-8 mol.

10. A water-based adhesive for bonding a polarizer protective film to a polarizer, characterized in that, The water-based adhesive contains the acetylated polyvinyl alcohol as described in claim 9.

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