A method for increasing the width of a polarizing film

Abstract

The application discloses a method for improving the width of a polarized film, which comprises the following steps: after the production raw material PVA element of the polarized film is washed, the PVA element is pre-dried and shaped, and then is sent into an oven for drying; the pre-drying and shaping is performed by using two corresponding hot air pipes, the two hot air pipes are located on the upper surface and the lower surface of the PVA element respectively, the hot air pipes are not in contact with the PVA element, and the two hot air pipes respectively blow out hot air streams with a temperature of 80 DEG C to 120 DEG C towards the upper surface and the lower surface of the PVA element; the method overcomes the defects of the prior art, the width shrinkage rate of the PVA element before and after drying is less than 10%, and the polarization degree and the transmittance of the PVA element are ensured.

Description

Technical Field

[0001] This invention relates to the field of polarizing film technology, specifically to a method for improving the width of a polarizing film. Background Technology

[0002] Polyvinyl alcohol (PVA) film is a key raw material in the production of polarizing films. After washing, swelling, stretching, dyeing, and washing again, PVA elements are formed. During these processes, the PVA film undergoes a stretching ratio of 5-7 times in the length direction. Currently, increasing the width of polarizing films is generally achieved by increasing the width of the PVA elements (the dyed PVA film). Increasing the width of the PVA elements is mainly achieved by increasing the width of the original film (PVA film) or decreasing its stretching ratio. However, increasing the width increases production costs, while decreasing the stretching ratio results in a relatively thicker PVA element, which affects the optical performance of the polarizer and does not meet the requirements of some high-performance products. Summary of the Invention

[0003] The purpose of this invention is to provide a method for increasing the width of a polarizing film, overcoming the shortcomings of the prior art.

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

[0005] A method for improving the width of a polarizing film includes the following steps: washing PVA elements, the raw material for producing the polarizing film, with water, pre-drying and shaping them, and then sending them into an oven for drying. The pre-drying and shaping uses two corresponding hot air pipes, which are located on the upper and lower surfaces of the PVA elements respectively. The hot air pipes do not contact the PVA elements, and the two hot air pipes blow hot air at a temperature of 80℃-120℃ towards the upper and lower surfaces of the PVA elements respectively.

[0006] Furthermore, the distance between the hot air duct and the PVA element is 4cm-8cm, and the flow velocity of the hot air flowing out of the hot air duct is 2m / s-5m / s.

[0007] Furthermore, after pre-drying and shaping, the PVA elements are placed in an oven for drying within 20-40 seconds.

[0008] Furthermore, the oven is provided with at least four drying sections, and the temperatures of the four drying sections are 50℃-60℃, 55℃-65℃, 65℃-75℃, and 75℃-85℃ respectively.

[0009] Furthermore, the speed of the PVA element passing between the two corresponding hot air pipes is 8m / min-15m / min.

[0010] Furthermore, the width of the PVA element after oven drying is not less than 90% of the width of the PVA element after washing and pre-drying.

[0011] Compared with the prior art, the implementation effect of this invention is as follows: After washing PVA elements, this invention uses a pre-drying and shaping device to rapidly bake the surface of the PVA elements at high temperature, so that the moisture on the surface of the PVA elements evaporates quickly and the shaping is achieved early. When the PVA elements enter the drying oven, since most of the surface moisture has evaporated, the width of the PVA elements is less affected by the drying oven, thereby increasing the width of the PVA elements. The width shrinkage rate of the PVA elements before and after drying is less than 10%, and the polarization degree and transmittance of the PVA elements are guaranteed. Detailed Implementation

[0012] 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.

[0013] Example 1

[0014] A 2000mm wide PVA film is stretched 5.7 times along its length during washing, swelling, stretching, dyeing, and washing again to obtain a 1683mm wide PVA element. The PVA element is then pre-dried and shaped by passing it through two corresponding hot air pipes at a speed of 12m / min. The hot air pipes have several 4mm vent holes, with the vent holes on both sides of the PVA element facing the upper and lower surfaces of the PVA element, respectively. The distance between the hot air pipes and the PVA element is 6cm. Hot air at a temperature of 100℃ is blown out of the vent holes towards the upper and lower surfaces of the PVA element, with a flow rate of 3m / s.

[0015] After passing through the hot air duct, the PVA particles are dried in an oven for 30 seconds. The oven has four drying sections with temperatures of 55℃, 60℃, 70℃, and 80℃ respectively. After drying in the oven, the width of the obtained PVA particles is 1519mm, the shrinkage rate in the width direction of the PVA particles is 9.74%, the transmittance is 41.4, and the polarization is 99.999.

[0016] Example 2

[0017] A 2000mm wide PVA film is stretched 6.0 times along its length during washing, swelling, stretching, dyeing, and washing again to obtain a 1656mm wide PVA element. The PVA element is then pre-dried and shaped by passing it through two corresponding hot air pipes at a speed of 15m / min. The hot air pipes have several 5mm air vents, with the air vents on both sides of the PVA element facing the upper and lower surfaces of the PVA element, respectively. The distance between the hot air pipes and the PVA element is 4cm. Hot air at a temperature of 80℃ is blown out of the air vents towards the upper and lower surfaces of the PVA element, with a flow rate of 5m / s.

[0018] After passing through the hot air duct, the PVA particles are dried in an oven for 20 seconds. The oven has four drying sections with temperatures of 50℃, 55℃, 65℃, and 75℃ respectively. After drying in the oven, the width of the obtained PVA particles is 1494mm, the shrinkage rate in the width direction of the PVA particles is 9.76%, the transmittance is 41.4, and the polarization is 99.999.

[0019] Example 3

[0020] A 2000mm wide PVA film is stretched 5.5 times its length during washing, swelling, stretching, dyeing, and washing again to obtain a 1698mm wide PVA element. The PVA element is then pre-dried and shaped by passing it through two corresponding hot air pipes at a speed of 8m / min. The hot air pipes have several 3mm air vents, with the vents on both sides of the PVA element facing the upper and lower surfaces of the PVA element, respectively. The distance between the hot air pipes and the PVA element is 8cm. Hot air at a temperature of 120℃ is blown out of the vents towards the upper and lower surfaces of the PVA element, with a flow rate of 2m / s.

[0021] After passing through the hot air duct, the PVA particles are dried in an oven within 40 seconds. The oven has four drying sections with temperatures of 60℃, 65℃, 75℃, and 85℃ respectively. After drying in the oven, the width of the obtained PVA particles is 1531mm, the shrinkage rate in the width direction of the PVA particles is 9.83%, the transmittance is 41.4, and the polarization is 99.997.

[0022] Comparative Example 1

[0023] The difference from Example 1 is that no airflow flows out from the air outlets of the two hot air pipes, the width of the obtained PVA element is 1273mm, the shrinkage rate in the width direction of the PVA element is 15.13%, the transmittance is 41.3, and the polarization is 99.997.

[0024] A comparison of Comparative Example 1 and Example 1 clearly shows that after pre-drying and shaping treatment, the shrinkage rate in the width direction of the PVA element decreased by more than 5%, effectively increasing the width of the PVA element. Simultaneously, the optical properties of the PVA element remained largely unchanged, ensuring its performance. During the pre-drying and shaping process, the high-temperature, high-speed airflow rapidly heated the surface of the PVA element due to the high-temperature, high-speed disturbance. When the PVA element surface was briefly heated to a high temperature, the attraction between water molecules and polymer chains decreased significantly, allowing surface moisture to be carried away by the dry, high-speed air. Under this high-temperature condition, the PVA element underwent a cross-linking reaction due to its material properties, eliminating overall internal stress. Therefore, the width direction of the PVA element was successfully shaped. Since the internal stress was eliminated during the pre-drying and shaping process, the shrinkage rate in the width direction of the PVA element was reduced, preventing significant shrinkage after drying in the oven. Therefore, the overall width direction of the PVA element was wider than before the pre-drying and shaping treatment. During the subsequent drying process in the oven, the moisture inside the PVA particles continuously permeates to the surface, then evaporates and diffuses into the air until the moisture content of the PVA particles reaches equilibrium with the moisture in the surrounding air.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of increasing the web width of a polarizing film, characterized by, The method comprises the following steps: after the production raw material PVA element of the polarized film is washed, pre-drying and shaping are performed, then the PVA element is sent into an oven for drying, the pre-drying and shaping is performed by using two corresponding hot air pipes, the two hot air pipes are respectively located on the upper surface and the lower surface of the PVA element, the hot air pipes are not in contact with the PVA element, and the two hot air pipes respectively blow hot air streams with a temperature of 80-120 DEG C to the upper surface and the lower surface of the PVA element. The distance between the hot air pipes and the PVA element is 4-8 cm, the flow rate of the hot air streams flowing out of the hot air pipes is 2-5 m / s, and the speed of the PVA element when passing through the two corresponding hot air pipes is 8-15 m / min.

2. The method of increasing the web width of a polarizing film according to claim 1, wherein: After the pre-drying and shaping, the PVA element enters the oven for drying within 20-40 s.

3. The method of increasing the web width of a polarizing film according to claim 2, wherein: The oven is provided with at least four drying sections, and the temperatures of the four drying sections are 50-60 DEG C, 55-65 DEG C, 65-75 DEG C and 75-85 DEG C in sequence.

4. The method of increasing the web width of a polarizing film according to claim 1, wherein: The width of the PVA element after drying in the oven is not less than 90% of the width of the PVA element before washing and pre-drying and shaping.