CN-113334808-B - Method for manufacturing polarizing film

Abstract

The invention aims to reduce fluctuation of optical characteristics of a polarizing film in the width direction. A method for producing a polarizing film from a polyvinyl alcohol resin film, comprising a treatment step of bringing a treatment liquid into contact with the polyvinyl alcohol resin film to thereby treat the film, and a washing step of bringing a washing liquid into contact with the polyvinyl alcohol resin film to thereby wash the film, wherein the washing step is a step of washing the polyvinyl alcohol resin film in such a manner that the washing liquid is divided into one end portion including one end in the width direction of the polyvinyl alcohol resin film, the other end portion including the other end in the width direction, and a central portion inside the one end portion and the other end portion in the width direction, based on the width of the polyvinyl alcohol resin film, and then the washing of the one end portion is made to be greater than the washing of the other end portion, and the washing of the other end portion is made to be greater than the washing of the central portion.

Inventors

• GU CHUANCHUN
• SHIRAKAWA KEIICHI

Assignees

• 住友化学株式会社

Dates

Publication Date

20260508

Application Date

20210226

Priority Date

20200302

Claims (3)

1. 1. A method for producing a polarizing film from a polyvinyl alcohol resin film, comprising, in order: A treatment step of treating the polyvinyl alcohol resin film by bringing a treatment liquid into contact with the polyvinyl alcohol resin film, and A washing step of bringing a washing liquid into contact with the polyvinyl alcohol resin film to wash the film, The washing step is a step of washing the polyvinyl alcohol resin film such that, after dividing the polyvinyl alcohol resin film into one end portion including one end in the width direction of the polyvinyl alcohol resin film, the other end portion including the other end in the width direction, and a central portion which is inward in the width direction with respect to the one end portion and the other end portion, the washing degree of the one end portion is made greater than the washing degree of the other end portion, and the washing degree of the other end portion is made greater than the washing degree of the central portion, The polyvinyl alcohol resin film has a fluctuation in thickness in the width direction, The washing step includes the operation of continuously discharging the washing liquid from the discharge ports toward the polyvinyl alcohol resin film using a washing apparatus having a plurality of discharge ports for discharging the washing liquid, In the operation of continuously discharging the washing liquid, the polyvinyl alcohol resin film is conveyed upward in a vertical direction, In the washing step, the operation of continuously discharging the washing liquid is performed such that the height position of the discharge port for discharging the washing liquid toward the center portion is lower than the height positions of the discharge ports for discharging the washing liquid toward the other end portion and the one end portion, and the height position of the discharge port for discharging the washing liquid toward the other end portion is lower than the height position of the discharge port for discharging the washing liquid toward the one end portion, The washing step is performed so as to satisfy i) below and at least any one of a 1) and b 1) below: i) When the temperature of the washing liquid contacting the one end portion is T1, the temperature of the washing liquid contacting the other end portion is T2, and the temperature of the washing liquid contacting the center portion is T3, the T1, T2, and T3 satisfy a relationship of T1> T2> T3, wherein the units of T1, T2, and T3 are set to be °c, a1)1≤T1-T2≤15 b1)2≤T2-T3≤30。
2. 2. The method for producing a polarizing film according to claim 1, wherein the washing step is performed so as to satisfy the i) and c 1) below: c1)3≤T3≤25。
3. 3. the method for producing a polarizing film according to claim 1 or 2, wherein the washing step is performed so as to satisfy ii) described below, Ii) when the amount of the washing liquid per unit width and unit time in contact with the one end portion is M1, the amount of the washing liquid per unit width and unit time in contact with the other end portion is M2, and the amount of the washing liquid per unit width and unit time in contact with the central portion is M3, the M1, M2, and M3 satisfy a relationship of M1> M2> M3, Wherein the units of M1, M2 and M3 are L/(m.multidot.min).

Description

Method for manufacturing polarizing film Technical Field The present invention relates to a method for producing a polarizing film from a polyvinyl alcohol resin film. Background Conventionally, a polarizing film is known in which a polyvinyl alcohol resin film is aligned by adsorbing a dichroic dye. The polarizing film can be used as a material of a polarizing plate, for example. The polarizing plate is generally produced by bonding a protective film such as triacetyl cellulose to at least one surface of a polarizing film, preferably to both surfaces thereof, via an adhesive formed from an aqueous solution of a polyvinyl alcohol resin. Polarizing plates are used as display screens in liquid crystal display devices (LCDs) such as liquid crystal televisions, monitors for personal computers, and cellular phones. In the production process of a polarizing film, a work for suppressing fluctuation of optical characteristics in the width direction of the polarizing film has been conventionally performed. For example, japanese patent application laid-open publication No. 2013-140345 (patent document 1) and taiwan patent publication No. 201142375 (patent document 2) propose that, in the case of manufacturing a polarizing film by washing a polyvinyl alcohol resin film with water after each treatment such as dyeing, fluctuation of the optical characteristics is suppressed by making the washing temperature at both widthwise end portions of the polarizing film different from the washing temperature at the widthwise central portion of the polarizing film. Prior art literature Patent literature Patent document 1 Japanese patent application laid-open No. 2013-140345 Patent document 2 taiwan laid-open patent publication No. 201142375 Disclosure of Invention Problems to be solved by the invention The purpose of the present invention is to provide a method for manufacturing a polarizing film, which is capable of reducing fluctuations in the optical characteristics of the polarizing film in the width direction. Means for solving the problems The present invention provides a method for producing a polarizing film shown below. [1] A method for producing a polarizing film from a polyvinyl alcohol resin film, comprising, in order: A treatment step of treating the polyvinyl alcohol resin film by bringing a treatment liquid into contact with the polyvinyl alcohol resin film, and A washing step of bringing a washing liquid into contact with the polyvinyl alcohol resin film to wash the film, The washing step is a step of washing the polyvinyl alcohol resin film, after dividing the polyvinyl alcohol resin film into one end portion including one end in the width direction of the polyvinyl alcohol resin film, the other end portion including the other end in the width direction, and a central portion which is inward in the width direction with respect to the one end portion and the other end portion, so that the degree of washing of the one end portion is greater than the degree of washing of the other end portion, and so that the degree of washing of the other end portion is greater than the degree of washing of the central portion. The method for producing a polarizing film according to [ 2 ], wherein the washing step is performed so as to satisfy the following i). I) The T1, the T2 and the T3 satisfy the relation of T1> T2> T3, when the temperature of the washing liquid contacting the one end portion is T1℃, the temperature of the washing liquid contacting the other end portion is T2℃, and the temperature of the washing liquid contacting the central portion is T3℃. The method for producing a polarizing film according to [ 3 ], wherein the washing step is performed so as to satisfy the above i) and at least any one of the following a 1) and b 1). a1)1≤T1-T2≤15 b1)2≤T2-T3≤30 The method for producing a polarizing film according to [ 4 ] or [ 3 ], wherein the washing step is performed so as to satisfy the above-mentioned i) and the following c 1). c1)3≤T3≤25 The method for producing a polarizing film according to any one of [1 ] to [ 4 ], wherein the washing step is performed so as to satisfy the following ii). Ii) when the liquid amount of the washing liquid per unit width and unit time contacting the one end portion is M1[ L/M/min ], the liquid amount of the washing liquid per unit width and unit time contacting the other end portion is M2[ L/M/min ], and the liquid amount of the washing liquid per unit width and unit time contacting the central portion is M3[ L/M/min ], the M1, M2, and M3 satisfy a relation of M1> M2> M3. The method for producing a polarizing film according to any one of [ 1] to [ 5 ], wherein the washing step comprises the operation of continuously discharging the washing liquid from the discharge port toward the polyvinyl alcohol resin film by using a washing apparatus having a plurality of discharge ports for discharging the washing liquid. The method for producing a polarizing film according to item [ 7 ], wherein i