Pretreatment process and application of TAC film

Abstract

The invention discloses a pretreatment process and application of a TAC film, the pretreatment process of the TAC film comprises the step of carrying out alkali washing on the TAC film by using alkali liquor, the alkali liquor uses a sodium hydroxide aqueous solution with the mass fraction of 9%-11%, the temperature of the alkali liquor is 45-55 DEG C, and the alkali washing time is 5-8 s.According to the pretreatment process of the TAC film, the defects in the prior art are overcome, and the TAC film can be recycled. By adjusting the concentration and the temperature of the sodium hydroxide aqueous solution used in the alkali washing process, on the premise of ensuring that a coating on the surface of the TAC film is not damaged, separation of crystals on the film surface in the alkali washing process of the TAC film is effectively avoided, the problems of aggregation and accumulation of the crystals separated out in the alkali washing process on a clamping roller are solved, and the service life of the TAC film is prolonged. The number of membrane surface defects after alkali washing and water washing of the TAC membrane is greatly reduced, and continuous and stable operation of a TAC membrane alkali washing system is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of TAC film processing, and in particular to a pretreatment process and application of a TAC film. Background Art

[0002] TAC film (triacetyl cellulose film) has excellent optical properties. It is compounded with dyed and stretched PVA (polyvinyl alcohol) film to play a supporting and protective role. After compounding with TAC film, PVA film is used to make polarizer. Since the composite glue of TAC film and PVA film is water-based glue, and the surface energy of TAC film is low, the water-based composite glue has poor adhesion to its surface. Therefore, before the two are compounded, the surface of TAC film needs to be treated with alkaline solution saponification to improve its hydrophilicity and improve the composite fastness of TAC film and PVA film. For functional TAC film, after its alkaline washing treatment, crystalline precipitation will occur on the surface. Crystallized pollutants are easy to gather on the conveyor roller, causing damage to the surface of the subsequent alkaline-washed TAC film, resulting in a decrease in product yield. In addition, crystalline pollutants will produce broken bright spot defects after the TAC film is compounded with PVA film. Summary of the invention

[0003] The purpose of the present invention is to provide a TAC film pretreatment process and application, which overcomes the shortcomings of the prior art.

[0004] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0005] A TAC film pretreatment process comprises the step of using an alkali solution to wash the TAC film, wherein the alkali solution is a 9%-11% sodium hydroxide aqueous solution by mass fraction, the alkali solution has a temperature of 45°C-55°C, and the alkali washing time is 5s-8s.

[0006] Furthermore, the tension value of the TAC film during alkali washing is 210N-240N.

[0007] Furthermore, after the alkali washing, the TAC membrane is washed with water at least twice, the washing temperature is 20°C-25°C, and the tension value of the TAC membrane during the washing is 210N-240N.

[0008] Furthermore, the TAC film is further dried after being washed, and the tension value of the TAC film during drying is 160N-180N.

[0009] Furthermore, after the TAC film is dried, a winding step is also included, and the tension value of the TAC film during winding is 220N-230N.

[0010] The TAC film prepared by the TAC film pretreatment process can be used in polarizers.

[0011] Compared with the prior art, the implementation effects of the present invention are as follows: the present invention adjusts the concentration and temperature of the sodium hydroxide aqueous solution used in the alkali washing process, and under the premise of ensuring that the surface coating of the TAC membrane is not damaged, by reducing the sodium hydroxide concentration and increasing the alkali washing temperature, effectively avoiding the precipitation of crystals on the membrane surface during the alkali washing of the TAC membrane, avoiding the aggregation and accumulation of crystals precipitated during the alkali washing process on the nip roller, greatly reducing the number of membrane surface defects after alkali washing and water washing of the TAC membrane, and ensuring the continuous and stable operation of the TAC membrane alkali washing system. DETAILED DESCRIPTION

[0012] The technical solutions in the present invention are described clearly and completely below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] Example 1

[0014] The TAC film is unwound, and the speed ratio between the nip rollers used to convey the TAC film is adjusted to ensure that the tension value of the TAC film during unwinding is maintained at 220N. The unwound TAC film first enters the alkali washing tank. The solution used for alkali washing is a sodium hydroxide aqueous solution containing 9% by mass, and the temperature during alkali washing is 55°C, the alkali washing time is 8s, and the tension value of the TAC film during alkali washing is 210N. By reducing the sodium hydroxide concentration of alkali washing, the sodium hydroxide remaining on the surface of the TAC film after alkali washing can be effectively reduced, and at the same time, a large amount of sodium acetate and sodium carbonate produced by the reaction during alkali washing can be avoided, which greatly reduces the problem of crystallization on the surface of the TAC film after alkali washing. In addition, the present invention maintains a tension of 210N during the alkali washing process of the TAC film, so that the film surface can produce a certain stretching, increase the surface area of ​​the TAC film, and weaken the crystallization effect.

[0015] After alkali washing, the TAC film is sent to a water tank with a temperature of 20°C for washing. The tension value of the TAC film during the washing process is 210N. The film is washed three times, each washing time is 5s, and three washings are performed using three sequentially arranged water tanks. The present invention adopts low-temperature water washing to further inhibit the precipitation of sodium hydroxide, sodium acetate, and sodium carbonate crystals during the washing process. After washing, the TAC film is sent to an oven for drying. The tension value of the TAC film during drying is 160N. The film can be rolled up after drying. The tension value of the TAC film during rolling up is 220N.

[0016] Example 2

[0017] The TAC film is unwound, and the speed ratio between the nip rollers used to convey the TAC film is adjusted to ensure that the tension value of the TAC film during unwinding is maintained at 240N. The unwound TAC film first enters the alkali washing tank. The solution used for alkali washing is an aqueous solution of sodium hydroxide containing 11% by mass, and the temperature during alkali washing is 45°C, the alkali washing time is 5s, and the tension value of the TAC film during alkali washing is 240N. By reducing the concentration of sodium hydroxide in alkali washing, the sodium hydroxide remaining on the surface of the TAC film after alkali washing can be effectively reduced, and at the same time, a large amount of sodium acetate and sodium carbonate produced by the reaction during alkali washing can be avoided, which greatly reduces the problem of crystallization on the surface of the TAC film after alkali washing. In addition, the present invention maintains a tension of 240N during the alkali washing process of the TAC film, so that the film surface can produce a certain stretch, increase the surface area of ​​the TAC film, and weaken the crystallization effect.

[0018] After alkali washing, the TAC film is sent to a water tank at a temperature of 25°C for washing. During the washing process, the tension value of the TAC film is 240N. It is washed three times, and each washing time is 8s. The three washings use three water tanks set in sequence. After washing, the TAC film is sent to an oven for drying. During drying, the tension value of the TAC film is 180N. After drying, it can be rolled up. During rolling, the tension value of the TAC film is 230N.

[0019] Example 3

[0020] The TAC film is unwound, and the speed ratio between the nip rollers used to convey the TAC film is adjusted to ensure that the tension value of the TAC film during unwinding is maintained at 230N. The unwound TAC film first enters the alkali washing tank. The solution used for alkali washing is an aqueous solution of sodium hydroxide containing 10% by mass, and the temperature during alkali washing is 50°C, the alkali washing time is 6s, and the tension value of the TAC film during alkali washing is 220N. By reducing the sodium hydroxide concentration of alkali washing, the sodium hydroxide remaining on the surface of the TAC film after alkali washing can be effectively reduced, and at the same time, a large amount of sodium acetate and sodium carbonate produced by the reaction during alkali washing can be avoided, which greatly reduces the problem of crystallization on the surface of the TAC film after alkali washing. In addition, the present invention maintains a tension of 220N during the alkali washing process of the TAC film, so that the film surface can be stretched to a certain extent, the surface area of ​​the TAC film is increased, and the crystallization effect is weakened.

[0021] After alkali washing, the TAC film is sent to a water tank at a temperature of 23°C for washing. The tension value of the TAC film during the washing process is 225N. It is washed three times, each washing time is 8s, and three washings are performed using three water tanks set in sequence. After washing, the TAC film is sent to an oven for drying. During drying, the tension value of the TAC film is 170N. After drying, it can be rolled up. The tension value of the TAC film during rolling up is 225N.

[0022] Example 4

[0023] The TAC film is unwound, and the speed ratio between the nip rollers used to convey the TAC film is adjusted to ensure that the tension value of the TAC film during unwinding is maintained at 230N. The unwound TAC film first enters the alkali washing tank. The solution used for alkali washing is a sodium hydroxide aqueous solution containing 10% by mass, and the temperature during alkali washing is 51°C, the alkali washing time is 7s, and the tension value of the TAC film during alkali washing is 225N. By reducing the sodium hydroxide concentration of alkali washing, the sodium hydroxide remaining on the surface of the TAC film after alkali washing can be effectively reduced, and at the same time, a large amount of sodium acetate and sodium carbonate produced by the reaction during alkali washing can be avoided, which greatly reduces the problem of crystallization on the surface of the TAC film after alkali washing. In addition, the present invention maintains a tension of 225N during the alkali washing process of the TAC film, so that the film surface can produce a certain stretching, increase the surface area of ​​the TAC film, and weaken the crystallization effect.

[0024] After alkali washing, the TAC film is sent to a water tank at a temperature of 20°C for washing. The tension value of the TAC film during the washing process is 230N. It is washed three times, each washing time is 6s, and three washings are performed using three water tanks set in sequence. After washing, the TAC film is sent to an oven for drying. During drying, the tension value of the TAC film is 170N. After drying, it can be rolled up. The tension value of the TAC film during rolling up is 230N.

[0025] Example 5

[0026] The TAC film is unwound, and the speed ratio between the nip rollers used to convey the TAC film is adjusted to ensure that the tension value of the TAC film during unwinding is maintained at 230N. The unwound TAC film first enters the alkali washing tank. The solution used for alkali washing is a sodium hydroxide aqueous solution containing 9% by mass, and the temperature during alkali washing is 53°C, the alkali washing time is 7s, and the tension value of the TAC film during alkali washing is 235N. By reducing the sodium hydroxide concentration of alkali washing, the sodium hydroxide remaining on the surface of the TAC film after alkali washing can be effectively reduced, and at the same time, a large amount of sodium acetate and sodium carbonate produced by the reaction during the alkali washing process can be avoided, which greatly reduces the problem of crystallization on the surface of the TAC film after alkali washing. In addition, the present invention maintains a tension of 235N during the alkali washing process of the TAC film, so that the film surface can produce a certain stretching, increase the surface area of ​​the TAC film, and weaken the crystallization effect.

[0027] After alkali washing, the TAC film is sent to a water tank at a temperature of 22°C for washing. During the washing process, the tension value of the TAC film is 215N. It is washed three times, and each washing time is 7s. The three washings use three water tanks set in sequence. After washing, the TAC film is sent to an oven for drying. During drying, the tension value of the TAC film is 170N. After drying, it can be rolled up. During rolling, the tension value of the TAC film is 220N.

[0028] Comparative Example 1

[0029] The difference from Example 5 is that the solution used for alkali washing is an aqueous solution containing 13% by mass of sodium hydroxide, and the temperature for alkali washing is 40°C, the alkali washing time is 5s, and the tension value of the TAC membrane during the alkali washing process is 165N; after alkali washing, the TAC membrane is sent to a water tank at a temperature of 40°C for water washing. The tension value of the TAC membrane during the water washing process is 170N, and it is washed three times, with each washing time of 7s.

[0030] Comparative Example 2

[0031] The difference from Example 5 is that the solution used for alkali washing is a sodium hydroxide aqueous solution containing 13% by mass, the temperature during alkali washing is 40° C., the alkali washing time is 5 s, and the tension value of the TAC film during the alkali washing process is 165N.

[0032] Comparative Example 3

[0033] The difference from Example 5 is that after the alkali washing, the TAC membrane is sent to a water tank at a temperature of 40° C. for washing. During the washing process, the tension value of the TAC membrane is 170N. The membrane is washed three times, and each washing time is 7 seconds.

[0034] The TAC films of Example 5 and Comparative Examples 1-3 were used to manufacture polarizing layers (the polarizing layer was a dyed PVA film after the TAC films were laminated on both sides), and then the broken bright spot defects of the manufactured polarizing layers were tested. During the test, 5 samples were taken from each sample, each with a size of 1m*1m. The samples were placed on a table with backlight, and the number of broken bright spots of each sample was recorded. Finally, the average value of the broken bright spot defects of each sample was taken. The results are shown in the following table:

[0035] Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Number of broken bright spots (pcs / m 2 )]]> 1.4 7.2 5.8 3.8

[0036] It can be seen that the present invention effectively avoids the precipitation of crystals on the membrane surface during the alkali washing process of the TAC membrane by controlling the tension of the TAC membrane during the alkali washing process, reducing the concentration of sodium hydroxide, increasing the alkali washing temperature, and coordinating low-temperature water washing, thereby greatly reducing the number of membrane surface defects after the alkali washing and water washing of the TAC membrane, ensuring the quality of the TAC membrane after alkali washing, and ensuring the continuous and stable operation of the TAC membrane alkali washing system. In addition, it should be noted that the tension values ​​of the TAC membrane referred to in the present invention are all tension values ​​in the TAC transmission direction.

[0037] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A TAC film pretreatment process, characterized in that: The method comprises the steps of using alkaline solution to wash the TAC film, wherein the mass fraction of the alkaline solution is 9%-11% of a sodium hydroxide aqueous solution, the temperature of the alkaline solution is 45°C-55°C, and the washing time is 5s-8s.

2. A TAC film pretreatment process according to claim 1, characterized in that: The tension value of TAC film during alkali washing is 210N-240N.

3. A TAC film pretreatment process according to claim 1, characterized in that: After the TAC membrane is alkali washed, it is washed with water at least twice. The washing temperature is 20°C-25°C. The tension value of the TAC membrane during the washing is 210N-240N.

4. A TAC film pretreatment process according to claim 3, characterized in that: After the TAC film is washed, a drying step is also included. During the drying, the tension value to which the TAC film is subjected is 160N-180N.

5. A TAC film pretreatment process according to claim 4, characterized in that: After the TAC film is dried, the process of winding the film is also included. During the winding process, the tension value of the TAC film is 220N-230N.

6. The TAC film prepared by the process according to any one of claims 1 to 5, characterized in that: Application in polarizer.