JP2006350062A - Method for manufacturing polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing film having good transparency, good polarizing property, good uniformity of in-plane optical characteristics and excellent durability with good long running performance. <P>SOLUTION: The polarizing film is an iodine-based polarizing film obtained by stretching a polyvinyl alcohol-based film. In an acid bath crosslinking step with great performance dependency in a manufacturing process for the polarizing film, stretching is carried out by multistage stretching of 4-8 stages and the stretching is controlled on a scale of speed with stretch ratio at each stage as cumulative ratio and each stretch base point as a cumulative ratio base point. A certain angle of gradient is provided to a line connecting cumulative stretch ratios at respective stages precedent to the final stretch crosslinking stage and stretch crosslinking is relaxed at the final stretch crosslinking stage to manufacture the polarizing film. Cumulative stretch ratio at the final stage is preferably 1.5-4.0 times. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image display device such as a liquid crystal display device or a plasma display (PD). In particular, the present invention relates to a method for producing an iodine polarizing film obtained by stretching a polyvinyl alcohol film used for a liquid crystal display device or an electroluminescence (EL) display device, and a polarizing film obtained by this method.

  A polarizing film used for a liquid crystal display device is required to have a high transmittance and a high degree of polarization that are bright and have good optical reproducibility.

  Such a polarizing film is conventionally crosslinked with a polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) film, a dyeing process of dyeing with dichroic iodine or a dichroic dye, boric acid, borax, or the like. After the acid bath cross-linking step, or the acid bath cross-linking step used in combination with uniaxial stretching, it is dried in the hue adjustment and drying step, and is triacetyl cellulose (hereinafter sometimes abbreviated as TAC) film or retardation film, etc. While laminating with the layer which protects a polarizing film, an optical function is improved and a polarizing plate is manufactured. To reiterate, the steps of washing with water, swelling, dyeing, crosslinking, stretching, complementary color, washing, and PVA drying do not have to be performed separately, and may be performed at the same time, and the order of the steps may be arbitrary. .

  In recent years, particularly with the increase in size and performance of liquid crystal display screens, the polarizing film used for them has also been required to be improved in optical properties and in-plane uniformity at the same time as being increased in size. It is an indispensable element as long as the PVA is used as a polarizing film, that the wet stretch production method is frequently used in the final stage of the cross-linking process in the process, and also in the process of using the other processes simultaneously with the stretch cross-linking.

  About the extending | stretching method in an acidic bath bridge | crosslinking process, until now, for example, in patent document 1, in the process with a boron compound, first, it is uniaxially stretched to 4.5 times or less, and then is uniaxially stretched to 2 times or less. It is described that a polarizing film excellent in polarizing property and durability can be obtained. Further, in Patent Document 2, two or more baths containing a crosslinking agent are provided, and the draw ratio of the first bath is 1 to 4 times, and the draw ratio after the second bath is higher than the draw ratio of the first bath. A method for producing a polarizing plate having characteristics of high transmittance and high degree of polarization, which has been difficult in Patent Document 1, by stretching at a high stretching ratio is described. Further, in Patent Document 3, when crosslinking is carried out in a bath containing a crosslinking agent, the stretch ratio before entering the crosslinking bath is in the range of 1 to 5 times (however, before crosslinking, if a crosslinking agent enters the dyeing bath). In addition, the stretching ratio during and after the subsequent crosslinking including the subsequent crosslinking treatment bath is in the range of 1.01 times or more and 4 times or less, and the total stretching ratio from the PVA film forming raw material to the final product is A method for producing a polarizing plate that is 8 times or less is described.

Japanese Patent No. 2512408 JP 2001-290026 A JP 2001-296427 A

  However, in the conventional method, the uniaxiality of the oriented film is lowered and the in-plane uniformity is deteriorated, and it is possible to obtain a polarizing film having uniform optical characteristics (a polarizing film having uniform in-plane optical characteristics and a high degree of orientation). It was difficult. An object of the present invention is to solve the above problems and to provide a method for stably producing a polarizing film having uniform optical characteristics for a long time (hereinafter sometimes abbreviated as long run property). And the polarizing film obtained by this manufacturing method is laminated | stacked with another optical film, and is used for the image display apparatus which applied the said polarizing film or another optical film.

  The present invention pays attention to the stretching cross-linking step of the raw material PVA film, and in the polarizing film manufacturing step, determines the stretching ratio at the time of stretching cross-linking from each step and the magnification of the step one step before the stretching cross-linking step. In addition, in the final stage of the multi-stage stretching and crosslinking process, a polarizing film having excellent optical performance characteristics such as polarization degree and stability and stability can be obtained in the final stage of the multi-stage stretching and crosslinking process while performing stretching and crosslinking within the stable region. As a result, the present invention has been completed.

That is, the present invention
(1) The number of stretch cross-linking steps in the acidic bath cross-linking step in the production of a polyvinyl alcohol (PVA) polarizing film is 4 or more and 8 or less, and the line connecting the cumulative draw ratios up to the last step of the stretch cross-linking (nE-1). Is approximately linear and stretched and cross-linked so that the inclination angle of the straight line to the X-axis is 35 to 43 degrees, and the magnification of 0.85 to 1.80 times in the final stage of stretched cross-linking (nE) A method for producing a polarizing film, wherein the film is stretched and cross-linked.
However, the inclination angle is such that the cumulative draw ratio is Y-axis (origin: maximum draw ratio) and the number of stretch-crosslinking stages is X-axis, the scale width of the cumulative stretch ratio (1 time): the scale width of the stretch-crosslinking stage number (1 stage) ) Is a value measured on a chart of 1: 1.25.
(2) The method for producing a polarizing film according to (1), wherein the stretching crosslinking ratio is adjusted and relaxed so that the stretching ratio is 0.85 to 0.95 times in a subsequent step after the end of the acidic bath crosslinking process. .
(3) The method for producing a polarizing film according to (2), wherein the final stage stretching stress relaxation coefficient (P) represented by the following formula is 0.5 to 1.0.
P = (b−c) / (b−a)
However, a: Cumulative draw ratio of final stage of stretch crosslinking (nE-1)
b: Cumulative draw ratio of the final stage of stretch crosslinking (nE)
c: Cumulative draw ratio of all strokes (cumulative draw ratio after completion of the post-process)
(4) The polarizing film according to (2) or (3), wherein the stretch crosslinking step represented by the following formula, the post-process connection stress relaxation coefficient (L) is −0.1 to 0.3. Production method.
L = c−a
However, a: Cumulative draw ratio of final stage of stretch crosslinking (nE-1)
c: Cumulative draw ratio of all strokes (cumulative draw ratio after completion of the post-process)
(5) The method for producing a polarizing film as described in any one of (1) to (4), wherein an acidic bath cross-linking kit corresponding to the number of stretching stages is used.
(6) The total draw ratio in the production process is 4.5 to 8.0 times, and the total draw ratio in the acidic bath crosslinking process is 1.5 to 4.0 times (1) to (5) The manufacturing method of the polarizing film in any one of.
(7) The method for producing a polarizing film according to any one of (1) to (6), wherein the polymerization degree of the raw material polyvinyl alcohol film is 1700 to 3500.
(8) The transmittance is 43.5% or more and the degree of polarization is 99.95% or more, and the orthogonal transmittance is 0.04% or less manufactured by the method according to any one of (1) to (7). A polarizing film,
Is a summary.

  According to the present invention, the stretching ratio in the step of performing the cross-linking treatment in the production of the polarizing film is manufactured in detail in multiple stages, and the residual stress on the PVA raw film is not affected in the post-process in the final stage of cross-linking (nE). Therefore, it is possible to obtain a polarizing film excellent in optical characteristics such as the degree of polarization regardless of the width of the original film, and to provide a polarizing film optimal for a large-sized image display device free from display spots. Became possible.

  Examples of the polyvinyl alcohol (PVA) -based resin used for the raw material polyvinyl alcohol-based film include PVA and partially formalized PVA. PVA is particularly preferable because of its excellent dyeability with iodine. In addition, a resin that can be produced without emphasizing hydrophilicity and purified by adding several mol% of ethylene or the like by copolymerization in order to improve optical properties can be used. The polymerization degree of the PVA-based resin to be used is generally 100 to 10,000, and a preferable range is 1700 to 3500, and more preferably 2400 to 2600. The saponification degree is preferably 89 mol% or more from the viewpoint of solubility in water, more preferably 95 mol% or more, particularly preferably 99.99 mol% or more, and the sodium acetate content is 0.08 wt% or less. Preferably there is.

  The raw material PVA-based film used in the present invention is produced by an arbitrary method such as a casting method, a casting method, an extrusion method, or the like by dissolving a PVA-based resin powder or a granular solution in which granular resin is dissolved in warm water or an organic solvent. Yes, if it is a PVA-based film, it can be used without any particular limitation regardless of non-stretching / stretching. Moreover, the thickness of a raw material PVA-type film is 75 micrometers and 50 micrometers. In the present invention, commercially available products that satisfy such conditions can be used as they are. The film retardation value in the width direction (abbreviated as TD direction) of the raw material PVA-based film is 35 nm or less, preferably 15 nm or less in terms of the effective total width.

As a method for producing a PVA polarizing film, there is generally a wet stretching method that occupies the mainstream, and is partially coordinating with dry stretching, but the present invention may be abbreviated as a wet stretching method (stretching in solution may be used in some cases). .).
As a manufacturing process of the polarizing film, a method can be appropriately selected according to the optical properties and physical properties of the polarizing film to be obtained. As a process, for example, a raw material PVA-type film is a series of manufacturing processes such as a drying process, a main process excluding a bonding process, adjusting a draw ratio, water washing swelling, iodine dyeing, crosslinking, adjustment dyeing, water washing cooling, etc. In each processing step, it is immersed in each bath containing various solutions and processed. The process order of each treatment process is not limited, except for the crosslinking process.

And in an acidic bath bridge | crosslinking process, the polymer film in the middle of the process which finished the previous process is bridge | crosslinked while being immersed in the adjustment tank liquid containing a crosslinking agent. In the present invention, the number of stretch-crosslinking steps in the acidic bath crosslinking step is 4 or more and 8 or less, and the line connecting the cumulative draw ratios up to the last step (nE-1) of the stretch-bridge is substantially linear, Stretch cross-linking is performed so that the inclination angle to the straight X-axis is 35 to 43 degrees, and the cross-linking is performed at a magnification of 0.85 to 1.80 in the final cross-linking step (nE). Is.
However, the inclination angle is such that the cumulative draw ratio is Y-axis (origin: maximum draw ratio) and the number of stretch-crosslinking stages is X-axis, the scale width of the cumulative stretch ratio (1 time): the scale width of the stretch-crosslinking stage number (1 stage) ) Is a value measured on a chart of 1: 1.25.
In this invention, since it was set as multistage extending | stretching, a draw ratio can be arbitrarily changed in each stage (n1-n8). The number of process steps is 4 to 8 steps, preferably 4 to 6 steps (the steps may be read as tanks) and related conditions, in particular, concentration-temperature-time-magnification (including relaxation) -washing. -There are no particular restrictions on the production-related ratios in all items such as speed. Further, the total draw ratio in the acidic bath stretch crosslinking step is 1.5 to 4.0 cumulative magnification, preferably 2 to 2.7 times. In the n1 stage of the stretch crosslinking step, the magnification is 1. Do not exceed 5 times. The lower limit magnification of the process is 0.95 times. The production process total draw ratio is 4.5 to 8.0 times.
Such multi-stage stretching can be achieved by using a number of pinch rolls corresponding to the number of stretching stages and providing a speed difference between the pinch rolls, but using a crosslinking tank depending on the number of stretching bridge stages, It is preferable to stretch by the speed difference of the pinch rolls in the cross-linking cage because the stretching cumulative magnification, concentration range, immersion time temperature and the like can be appropriately selected as necessary.

Below, the extending | stretching bridge | crosslinking in the acidic bath bridge | crosslinking process of this invention is demonstrated in detail.
For example, when performing multi-stage stretching of 8 stages (if less than 8 stages, the number of stages selected is applicable), each stretch-crosslinking stage is n1 to n8, and the cumulative magnification up to the previous process is A0 (acid bath cross-linking process inlet roll) (Cumulative draw ratio of (base point roll)), the draw ratio of each stage when the draw ratios of the draw bridges at the exit rolls are A1 to A8, and the draw ratio of each draw and bridge stage is α1 to α8. Is as follows.
Cumulative magnification up to the previous process (A0) Base roll of multi-stage stretch cross-linking ratio Multi-stage stretch cross-link 1st exit roll (A1) n1 A1 = A0 * α1 α1: First stage multi-stretch cross-link 2nd exit roll (A2) n2 A2 = A1 * α2 α2: 2nd stage multi-stretch bridged 3-stage exit roll (A3) n3 A3 = A2 * α3 α3: 3rd stage multi-stretch bridged 4-stage exit roll (A4) n4 (nE) A4 = A3 * α4 α4: 4th stage multi-stretch bridged 5-stage exit roll (A5) n5 (nE) A5 = A4 * α5 α5: 5th stage multi-stretch bridged 6-stage outlet roll (A6) n6 (nE) A6 = A5 * α6 α6: 6th stage multi-stretch bridged 7-stage outlet roll (A7) n7 (nE) A7 = A6 * α7 α7: 7th stage multi-stretched bridged 8-stage exit roll (A8) n8 (nE) A8 = A7 * α8 α8: 8th stage magnification However, (nE) means the final stage in the multistage stretching cross-linking, the 4th stage in the case of 4 stages, the 5th stage in the 5 stages, the 8th stage In the case of multi-stage stretching, the eighth stage corresponds. Moreover, let the draw ratio of the post process performed after completion | finish of an acidic bath bridge | crosslinking process be (B0).

And in the present invention, the cumulative draw ratio (A0, A1, A2, A3, A3, A3, A3, ... when AnE) is plotted, it has the greatest feature in that stretch crosslinking is performed so as to satisfy the following requirements. In this case, the scale width of the cumulative stretching ratio (1 time): the scale width of the number of stretched bridges (1 stage) is 1: 1.25.
That is, when plotting the cumulative draw ratio from the base point roll (A0) to the last stage of stretch crosslinking (nE-1), the line connecting the plots is almost linear, that is, at least the difference between the value of each stage and the straight line is , −0.2 to +0.2, preferably −0.05 to +0.1, and the inclination angle of the straight line to the X axis is 35 to 43 degrees, preferably 38 to 40 degrees. Stretch crosslinking is performed, and the stretch crosslinking is performed at a magnification of 0.85 to 1.80 times in the final stretch crosslinking stage (nE).
Specifically, in the case of five-stage multi-stage stretching, the lines connecting the points A0, A1, A2, A3, and A4 (corresponding to the last stage of stretch crosslinking) are almost linear, and the inclination angle is the above It is necessary to satisfy the conditions. Further, in the final stage of stretching and crosslinking (n5), stretching and crosslinking are performed so that A5 = A4 * α5, that is, α5 is 0.85 to 1.80 times. In addition, the inclination angle of 35 to 43 degrees is about 0.6109 to 0.7505 rad when expressed in radians, and is about 0 when expressed in increments of the cumulative draw ratio per step of the stretching and crosslinking stage (when added instead of multiplication). .85 to 1.20 times / stage.

Furthermore, in the present invention, it is preferable to adjust and relax the stretching crosslinking ratio so that the stretching ratio becomes 0.85 to 0.98 times in the subsequent process after the end of the acidic bath crosslinking process.
More specifically, (a) is the cumulative draw ratio of the last stage of stretch crosslinking (nE-1 stage), (b) is the cumulative stretch ratio of the final stage of stretch bridge (nE stage), and the total stroke cumulative stretch ratio (at the end of the post-process). (C), the final stage stretching stress relaxation coefficient (P) represented by the following formula I is in the range of 0.5 to 1.0, preferably 0.6 to 0.9. Thus, it is possible to obtain a polarizing film excellent in optical characteristics such as the degree of polarization and the polarizing film optical characteristics related to the process and quality, such as long run property and quality stability of the process.

P = (bc) / (ba) (I)

Further, when the cumulative draw ratio in the last stage of stretch crosslinking (nE-1 stage) is (a) and the total stretch cumulative draw ratio (cumulative draw ratio at the end of the post-process) is (c), it is expressed by the following formula II. Stretched cross-linking step, post-process connection stress relaxation coefficient (L) is in the range of −0.1 to 0.3, preferably 0.15 to 0.25 when the thickness of the raw material PVA film is 35 to 50 μm. By maintaining the film thickness at the time of passing the process at 13 to 19 μm, the in-plane uniformity can be improved together with the optical characteristics. Moreover, when the thickness of the raw material PVA-based film is 60 to 75 μm, the optical property is maintained and the manufacturing process is more stable by setting the thickness in the range of 0.05 to 0.25, preferably 0.07 to 0.20. Can be secured, and a more excellent polarizing film can be obtained.

L = ca (II)

Crosslinking in the acidic bath crosslinking step is usually 0.01 to 15 parts by weight, preferably 0, per 100 parts by weight of water, with boron compounds such as boric acid and borax, and PVA crosslinking agents such as glyoxal and glutaraldehyde alone or mixed. .5 to 9 parts by weight in an acidic bath composed of an aqueous solution. The aqueous solution further contains auxiliary agents such as iodides such as potassium iodide, lithium iodide, sodium iodide, zinc iodide, lead iodide, copper iodide, calcium iodide, aluminum iodide, and titanium iodide. Addition of 0.01 to 15 parts by weight, preferably 0.5 to 9 parts by weight is particularly preferable from the viewpoint of obtaining in-plane uniform optical characteristics.
Moreover, it is preferable to make the compounding ratio of a PVA crosslinking agent and the said adjuvant into the range of 2: 7-8: 2, especially 6: 4-5: 5-3: 7. In the stretching and crosslinking step, as in the dyeing step, a method of spraying or applying a crosslinking agent or auxiliary agent may be used.

Moreover, about the liquid temperature of an acidic bath, it is 15-75 degreeC by the average temperature in a liquid, Preferably, it is 40-70 degreeC, and the film immersion time in the middle of a process is 5 seconds-25 minutes, Preferably, it is 15 Seconds to 13 minutes are good.
Furthermore, the draw ratio during the stretching and crosslinking process is 1.5 to 4.0 times, preferably 2.5 to 3.2 times as a cumulative ratio, and the film immersion time after the dyeing process in the multistage stretching and crosslinking process. 5 minutes to 25 minutes, preferably 7 minutes to 13 minutes. The cumulative draw ratio in the final stage (nE) of the stretching and crosslinking step is preferably 4.5 to 8.0 times, and the cumulative stretching ratio in the stretching and crosslinking step alone is about 1.0 to 5.0 times. More preferably, about 1.5 to 3.5 times is good.

  That is, the present invention keeps a line connecting the cumulative draw ratios of the respective stretching and crosslinking stages in the acidic bath crosslinking step at a specific inclination angle, and relaxes the angle in the final stretching and crosslinking stage (nE). Even in the post-process after the cross-linking step, the stability of the process is verified by making the pattern satisfy the indices of the final-stage stretch stress relaxation coefficient (P), the stretch cross-linking process, and the post-process link stress relaxation coefficient (L). Improved long run performance. And the polarizing film which was more excellent in optical characteristics, such as the polarization | polarized-light performance which achieves the transmittance | permeability of 43.5% or more, the polarization degree of 99.95% or more, and the orthogonal transmittance | permeability 0-0.04% was able to be obtained. In addition, as an optical film in which one or more optical film layers are laminated on this polarizing film, or for a liquid crystal display device, an electroluminescence (EL) display device, a plasma display (PD), etc. to which the optical film is applied. Can do.

Below, each manufacturing process of a polarizing film is demonstrated.
In the water washing and swelling process, the raw material PVA film is first washed with water on the surface of the raw material film, added foreign substances, etc. in a tank in which the water temperature is kept constant, and further swollen in the tank to cause staining spots and retardation values. To alleviate Boric acid, glycerin, potassium iodide and the like are added to the bath of the swelling tank in this step, and the concentration of boric acid is 1.5 wt% or less. A concentration higher than this is not preferable because it affects the swelling in the film width direction. Moreover, it is preferable that another additive is also 5 wt% or less. The temperature in the swelling tank is 10 to 25 ° C, preferably 15 to 20 ° C. The immersion time in this tank is 10 seconds to 10 minutes, more preferably 3 to 5.5 minutes. In addition, from the viewpoint of in-plane uniformity, and in order to improve the long run property of the subsequent operation, stretching is performed simultaneously with the washing swelling. The draw ratio is related to the adjustment of the raw film TD direction swelling width. The unstretched raw material film has a stretching ratio in the tank (sometimes abbreviated as speed difference rate) of 1.0 to 2.1 times. In the raw material film after stretching, about 0.6 to 1.4 times is preferable.
Furthermore, the swelling ratio in the width direction (TD direction) of the PVA film in the conventional swelling process (hereinafter sometimes abbreviated as the width swelling ratio) is 1.0 to 2.1 times for unstretched raw material PVA-based films. Moreover, in the raw material PVA-based film after the stretching treatment, the width swelling ratio is preferably 0.6 to 1.4 times, and the liquid temperature in the same process tank is 10 to 25 ° C., more preferably 15 to 20 ℃ is good.

  In the dyeing process, the raw material film is immersed in a dyeing tank filled with iodine or other dichroic material to immerse the dichroic material, particularly for the iodine-based dichroic material, only the surface layer of the raw material film. Instead, it penetrates deeply and adsorbs it to the film molecule level. For organic and inorganic dyes, the re-elution into the aqueous solution is only about 0.5 to 30 wt% because the adsorption to the surface layer is stopped, and the elution can be minimized by lowering the temperature. It is important to initiate crosslinking of the surface.

  Conventionally known substances can be used as the dichroic substance, and iodine and organic dyes are good. Examples of dyes include organic dyes such as reds, lemon yellow, blues, and Congo red. And oranges. One of these dichroic substances may be used for dyeing, or two or more kinds may be used in combination. In the case of using organic dyes, it is well known to combine two or more types because of the neutralization of the optical application area. Reds and blues, oranges and blues, etc., and blacks And the like.

  The solution in the dyeing process dissolves the dichroic substance based on water, but a solvent compatible with water may be added in an amount of about 2 to 7 wt%. As such a solvent, a solvent having an OH group such as methyl alcohol or ethyl alcohol is preferably selected. Iodine and organic dyes usually have a concentration range of 0.005 to 20 parts per 100 parts of water and solvent mixed water. Moreover, 0.01-15 parts are more preferable, and 0.018-7 parts are the most preferable.

  In the dyeing process, when iodine is used as the dichroic substance, it is preferable to add an iodide auxiliary in order to further improve the dyeing efficiency. Examples of iodides include potassium iodide, lithium, sodium, zinc, aluminum, lead, copper, barium, calcium, titanium iodide, and the like. The additive ratio of these auxiliaries is preferably 5 to 70 times the iodine ratio, more preferably 15 to 50 times. The use of iodide as an auxiliary agent is widely used as a known technique, and potassium iodide is generally used among them. Along with the concentration ratio, the immersion time in the bath solution of the dyeing bath, the bath temperature, the stretching conditions, and the raw material film dissolution concentration in the bath are also one of the factors that determine the polarizing film performance in the dyeing step.

  Although the immersion time in a dyeing process cannot determine the optical characteristic of a polarizing film by this item alone, it is preferably 0.5 to 25 minutes, and more preferably 2 to 20 minutes. The tank liquid temperature in this step is preferably 5 to 45 ° C, more preferably 10 to 40 ° C. In the dyeing process, as a well-known technique for producing a polarizing film, the stretching process in the process gives a temperature and a dipping time to the iodine so that the dyeing process is stable and the polarizing film has good optical properties. Is obtained. In particular, the polyvinyl alcohol in the dyeing solution is preferably about 0.02 to 0.3 wt%. In addition, the draw ratio in the above process is about 1.05 to 4.5 times as the cumulative draw ratio after unwinding the raw material and the end of the process, and a more preferable state is about 1.8 to 3.5 times.

  In addition, as a dyeing treatment process, iodine or a dichroic dye is dissolved in an aqueous solution and prepared to a predetermined concentration, and the above is applied to or sprayed on the raw polymer film as well as dipping and dyeing. A dichroic substance may be added and mixed in advance as an additive or auxiliary agent in the film production process.

  In the washing process, the number of tanks is not limited. In this process, boric acid or the like is added in an amount of 0.1 to 10.0 parts, preferably 1.0 to 100 parts of water as an auxiliary agent at the time of washing. 9.0 parts may be added. In the same step, 0.01 to 15.0 parts of the additive may be added to 100 parts of the aqueous solution, and preferably 2.0 to 9.0 parts of potassium iodide and the like may be added. In the final part of the step, it is desirable that the aqueous solution is removed as much as possible together with the temperature to remove impurities and foreign matters in the aqueous solution. Further, the use of methyl alcohol, ethyl alcohol or the like as an auxiliary agent as a solvent that has a good water temperature of 5 to 13 ° C. and can be expected to have the ability to improve the next process and improve the quality is not a problem.

  In the film drying step, the polarizing film is obtained by drying the polymer film on which iodine and the dichroic substance have been adsorbed / crosslinked and stretched at 20 to 85 ° C., preferably 40 to 70 ° C. for 1 to 15 minutes with warm air. can get. After immersion in an iodide solution such as potassium iodide having a water temperature of 5 to 65 ° C., preferably 25 to 40 ° C. and having a concentration of 0.1 to 10 wt% in the preceding step of this step, The film surface layer may be dried with cold air at 15 ° C. After the film drying is completed, it is bonded to a protective film, and after the bonding, a polarizing plate is completed through a bonding drying process.

  In the polarizing film manufacturing method of this invention, the film pinch roll aiming at the extending | stretching process arrange | positioned in each process or process is arrange | positioned in air | atmosphere or processing aqueous solution, and the film of each process is extended | stretched in a liquid. When the film is pulled up from the processing liquid on the secondary side of each step, a liquid draining roll known in the prior art is used so as not to cause dripping. Alternatively, the excess aqueous solution may be removed by a method such as blowing off the aqueous solution from the film using an air knife or the like.

  The thickness of the polarizing film manufactured with the manufacturing method of this invention is not specifically limited, It is preferable that it is about 30 micrometers or less. If the thickness is 10 μm or more, the physical strength will not be reduced, and if the thickness is 27 μm or less, the optical properties will not be reduced. .

  In the polarizing film according to the present invention, various optical layers can be laminated in practical use. The optical layer to be used is not limited as long as it satisfies the required optical characteristics. For example, a transparent protective layer for the purpose of protecting the polarizing film on one or both sides of the polarizing film, and a hard coating treatment on the surface of the transparent protective layer opposite to the surface to be bonded to the polarizing film or on one side or both sides of the polarizing film itself Anti-reflection treatment, sticking treatment, surface treatment for the purpose of diffusion and anti-glare, etc., alignment liquid crystal layer for the purpose of visual compensation, etc., adhesive and adhesive layer for laminating other films with optical properties For example. Furthermore, as an optical layer, such as polarized light, orientation conversion element group, reflector, transflective plate, retardation plate (including wavelength plates of 1/2, 1/4, etc., including λ plate), visual compensation, brightness enhancement film, etc. Examples thereof include a laminate in which one, two, or more optical films used for the construction of a liquid crystal screen display device are laminated. In particular, the polarizing plate in which the polarizing film and the transparent protective layer are laminated is a polarizing plate in which a reflecting plate, a reflective polarizing plate in which a semi-transmissive reflecting plate is laminated, a semi-transmissive polarizing plate, or a retardation plate is laminated. A board is generally good. In addition, the optical layer or the optical film may be laminated with the transparent protective layer either before or after being bonded to the polarizing film without any particular limitation.

  As the material of the transparent protective layer provided on one side or both sides of the polarizing film, those showing excellent performance in transparency, mechanical / physical strength, thermal stability, moisture separability, isotropy, etc. are preferable. . Examples of materials and materials that exhibit excellent performance are given below. Polyester polymers such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. Cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, styrene polymers including styrene copolymers, polycarbonate polymers, polyolefin polymers, amide polymers, imide polymers, sulfone polymers Polyether sulfone polymers, polyether ether ketone polymers, vinyl alcohol polymers, vinyl butyral polymers, epoxy polymers, blends of the aforementioned polymers, and the like can be listed as examples of polymers that form a transparent protective layer. The transparent protective layer can be used as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylic urethane epoxy silicone, or the like. Among these, the transparent protective layer to be bonded to the polarizing film according to the present invention is preferably a triacetyl cellulose resin film having a saponified surface.

  When laminating the transparent protective layer on a polarizing film, films having different characteristics may be laminated on each side. The characteristics are not particularly limited to films having different characteristics. For example, hard coat treatment is addressed for the purpose of preventing damage to the polarizing film or the polarizing plate surface on which the polarizing film and the transparent protective layer are laminated. For example, acrylic coating, silicone-based ultraviolet curable resin, etc. As described above, a cured film excellent in hardness, slipperiness and the like can be added to the surface of the transparent protective layer for use. Antireflection and the like are also used in the same manner as described above.

  In the case of bonding the polarizing plate and the transparent protective layer, the bonding treatment is not particularly limited, but a vinyl polymer adhesive or a water-soluble vinyl alcohol polymer such as boric acid, borax, glutaraldehyde, melamine, or oxalic acid. Via an adhesive crosslinker type adhesive. This water-solubility can be used in combination with other additives and catalysts such as acids as necessary.

  The polarizing film of the present invention and the laminated optical material can be provided with an adhesive layer for adhering to other members such as a liquid crystal cell. The member used for the pressure-sensitive adhesive layer is not particularly limited, and an appropriate pressure-sensitive adhesive can be used by a conventionally known technique such as acrylic, polyester, polyether, rubber, or silicone. This pressure-sensitive adhesive prevents firing and peeling phenomenon due to moisture absorption, prevents deterioration of optical characteristics due to thermal expansion, thermal contraction difference, and the like, and warpage of the liquid crystal cell. Further, it is necessary to form an adhesive layer having a low moisture absorption rate and good heat resistance, and a polarizing film or the like having a short drying time is preferable. As the pressure-sensitive adhesive layer, it is possible to use a pressure-sensitive adhesive that contains fine particles regardless of organic or inorganic and exhibits light diffusion. The pressure-sensitive adhesive layer may be provided on a necessary surface if necessary. For a polarizing plate made of a polarizing film and a transparent protective layer as in the present invention, a pressure-sensitive adhesive layer is provided on one surface of the protective layer or on both surfaces of the protective layer as necessary. Just do it. Each layer such as a polarizing plate or a transparent protective layer of an optical member, an optical layer, an adhesive layer, or the like is provided with a UV-absorbing ability such as a salicylate ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, A nickel complex compound or the like may be added.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The present invention is not limited by these examples and comparative examples.

Example 1
Using a raw material polyvinyl alcohol film (degree of polymerization 2600) having a thickness of 75 μm and a film width of 670 mm, a polarizing film having a thickness of 25 μm was obtained through water washing swelling, dyeing, crosslinking, water washing and drying. In the above process, particularly in the cross-linking stretching process, multistage stretching was performed while conveying the film being processed using a plurality of characteristic rolls shown in FIG. The roll was a pinch roll, and in this step, stretching was performed with a difference in rotation speed of each pinch roll (may be abbreviated as “roll circumferential speed difference”).
The conditions including the steps before and after the crosslinking and stretching step were as follows.
<Washing swelling treatment process>
In pure water at 15 ° C., the film was stretched about 1.2 times and the TD (sometimes abbreviated as the film width side) direction swelling was 120%. (No auxiliary additive added.) (Distance between stretches 1350 mm)
<Dyeing process>
Stretched to a cumulative draw ratio of 2.6 times simultaneously with dyeing in a 0.017 wt% iodine aqueous solution (iodine (I ₂ ) / potassium iodide (KI) weight ratio: 1/30) at 30 ° C. Distance 3470 mm).
In the present embodiment, the washing washing swelling treatment step and the dyeing / stretching treatment step are integrated into the previous step.
<Acid bath crosslinking process>
In the acidic bath cross-linking treatment step, 5-stage multi-stretch cross-linking was performed. The acid bath solution has a concentration common to each stage (boric acid 5 wt% + 5 wt% potassium iodide (KI) aqueous solution), and the temperature is 50 ° C. until 1 to 2 stage stretch crosslinking, and 55 until the remaining 3 to 5 stage stretch crosslinking. The immersion time was 480 seconds. Further, the distance between the stretching in this step was 6950 mm (average distance between pinch rolls 1390 mm). Stretch cross-linking was carried out so that the cumulative draw ratio in all steps of polarizing film production at this time was 6.39 times, and the total draw ratio in the acidic bath cross-linking step was 2.5 times. The cumulative draw ratio of this step 5 (stretch cross-linking final step (nE)) is 6.51 times. Table 1 shows various conditions for stretching and crosslinking (coefficients P and L, inclination angle) and the performance of the obtained polarizing film. Moreover, the relationship between each extending | stretching bridge | crosslinking stage at that time and cumulative draw ratio A1-A5 was shown in FIG.
<Post process>
In this example, steps such as washing with water and drying were included as post-steps.
The cumulative draw ratio at the end of the post-process was 6.39 (including the drying process). Moreover, the processing temperature of each post-process was set to 10 degreeC of water-washing processes, adjustment 35 degreeC, and drying 50 degreeC, immersion time was 87 seconds excluding the drying process, and drying time was 60 seconds. Further, the total distance between the pinch rolls in the subsequent process was 3230 mm (however, the distance between the pinch rolls in the drying process of 1620 mm was not included).
In this example, the cumulative draw ratio (a) in the last stage of stretch crosslinking (nE-1 stage) for calculating the coefficients P and L shown in Table 1 is the cumulative draw ratio (A4) in the fourth stage. The cumulative draw ratio (b) of the final stage of the stretch bridge (nE stage) is the fifth stage cumulative draw ratio (A5) = 6.51 times, the total stroke cumulative draw ratio (cumulative draw ratio at the end of the post-process). (C) is 6.39 times.
About the obtained polarizing film optical characteristic in-plane uniformity, as a result of measuring with the sample group shown in FIG. 3, as shown in Table 1, the transmittance is 43.63 to 43.60%, the degree of polarization is 100 to 99.97%, The orthogonal transmittance was 0.0 to 0.02%.

Example 2
The pre-process and post-process were substantially the same as in Example 1, and the acidic bath cross-linking process was stretched and cross-linked under the conditions shown in Table 1. The results are as shown in Table 1. A polarizing film with good optical characteristics and in-plane uniformity was obtained.

Example 3
The pre-process, post-process, etc. were substantially the same as in Example 1, and as shown in Table 1, stretched cross-linking in the acidic bath cross-linking process was performed in four stages. The results are as shown in Table 1. A polarizing film with good optical characteristics and in-plane uniformity was obtained.

Example 4
The pre-process, post-process, etc. were substantially the same as in Example 1, and as shown in Table 1, stretched cross-linking in the acidic bath cross-linking process was performed in six steps. The results are as shown in Table 1. A polarizing film with good optical characteristics and in-plane uniformity was obtained.

Comparative Examples 1 and 2
After performing the previous step in substantially the same manner as in Example 1, the number of stretched crosslinking steps in the acidic bath crosslinking step is set to 5 steps, up to the second step, with an inclination angle of 44 degrees, and in steps 3, 4, and 5, Stretch cross-linking was performed by reducing the stretch ratio and setting the tilt angle to 17 degrees in Comparative Example 1 and 20 degrees in Comparative Example 2. The results are as shown in Table 1. The long run property was good, but the optical properties were insufficient.

Comparative Examples 3 and 4
After performing the pre-process in substantially the same manner as in Example 1, the number of stretch-crosslinking steps in the acidic bath cross-linking step was set to 4 and stretch-crosslinking was performed at the same inclination angle up to the final stretch-crosslinking step. The results are as shown in Table 1, and the long run property and in-plane uniformity were insufficient.

Comparative Example 5
The stretching and crosslinking step was a three-stage stretching, and the stretching and crosslinking were performed as shown in Table 1 with an inclination angle of 47 degrees to the last stage of the stretching and crosslinking and an inclination angle of 44 degrees to the last stage of the stretching and crosslinking. As shown in Table 1, the optical properties were insufficient. In addition, the extending | stretching bridge | crosslinking process film immersion time was 3.8 minutes.

Comparative Example 6
Stretch crosslinking was performed under the conditions shown in Table 1. As shown in Table 1, the optical characteristics were insufficient, and the optical characteristic in-plane uniformity was not achieved at Ty ± 0.05% and Py ± 0.03%.

  As is apparent from the results of Table 1 as a whole, the optical characteristics and the long run properties were both good in the manufacturing methods according to the examples. In particular, with regard to long run properties, film production can be continued from 2 days to 7 days to 11 days. In addition, the transmittance, the degree of polarization, the orthogonal transmittance, and the like showed stable values, and the related in-plane uniformity also showed good values. Therefore, a polarizing film excellent in optical characteristics and in-plane uniformity can be manufactured, suggesting the possibility of future generations and improved durability.

It is explanatory drawing explaining the multistage extending | stretching bridge | crosslinking process in this invention. It is explanatory drawing explaining the inclination angle in this invention, the relaxation coefficient P value, and L value. It is explanatory drawing which shows the sampling method for an optical characteristic measurement.

Claims (8)

In the production of polyvinyl alcohol (PVA) polarizing film, the number of stretch crosslinking steps in the acidic bath crosslinking step is 4 or more and 8 or less, and the line connecting the cumulative stretch ratios up to the last stretch crosslinking (nE-1) is almost linear. The cross-linking is performed so that the inclination angle of the straight line with the X-axis is 35 to 43 degrees, and the cross-linking is performed at a magnification of 0.85 to 1.80 times in the final stage of the cross-linking. A method for producing a polarizing film.
However, the inclination angle is such that the cumulative draw ratio is Y-axis (origin: maximum draw ratio) and the number of stretch-crosslinking stages is X-axis, the scale width of the cumulative stretch ratio (1 time): the scale width of the stretch-crosslinking stage number (1 stage) ) Is a value measured on a chart of 1: 1.25. The method for producing a polarizing film according to claim 1, wherein the stretching crosslinking ratio is adjusted and relaxed so that the stretching ratio is 0.85 to 0.95 times in a subsequent process after the end of the acidic bath crosslinking process. The method for producing a polarizing film according to claim 2, wherein the final stage stretching stress relaxation coefficient (P) represented by the following formula is 0.5 to 1.0.
P = (b−c) / (b−a)
However, a: Cumulative draw ratio of final stage of stretch crosslinking (nE-1)
b: Cumulative draw ratio of the final stage of stretch crosslinking (nE)
c: Cumulative draw ratio of all strokes (cumulative draw ratio after completion of the post-process) The method for producing a polarizing film according to claim 2 or 3, wherein a stretching and crosslinking step and a post-step connection stress relaxation coefficient (L) represented by the following formula are -0.1 to 0.3.
L = c−a
However, a: Cumulative draw ratio of final stage of stretch crosslinking (nE-1)
c: Cumulative draw ratio of all strokes (cumulative draw ratio after completion of the post-process) The method for producing a polarizing film according to any one of claims 1 to 4, wherein an acidic bath cross-linking cage corresponding to the number of stretching stages is used. 6. The total stretching ratio in the production process is 4.5 to 8.0 times, and the total stretching ratio in the acidic bath crosslinking process is 1.5 to 4.0 times. The manufacturing method of the polarizing film of crab. The method for producing a polarizing film according to claim 1, wherein the polymerization degree of the raw material polyvinyl alcohol film is 1700 to 3500. A polarizing film produced by the method according to claim 1, having a transmittance of 43.5% or more, a polarization degree of 99.95% or more, and an orthogonal transmittance of 0.04% or less.

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