TW202222931A - Method for producing polarizing film - Google Patents

Method for producing polarizing film Download PDF

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TW202222931A
TW202222931A TW110136418A TW110136418A TW202222931A TW 202222931 A TW202222931 A TW 202222931A TW 110136418 A TW110136418 A TW 110136418A TW 110136418 A TW110136418 A TW 110136418A TW 202222931 A TW202222931 A TW 202222931A
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stretching
linking
cross
film
polarizing film
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田邊裕史
高梨啟二
辻嘉久
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日商可樂麗股份有限公司
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
    • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
    • B29C55/04—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique
    • B29C55/06—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique parallel with the direction of feed
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J129/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Adhesives based on hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Adhesives based on derivatives of such polymers
    • C09J129/02—Homopolymers or copolymers of unsaturated alcohols
    • C09J129/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
    • C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
    • C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Organic Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Polarising Elements (AREA)

Abstract

A production method that is for a polarizing film and that subjects a polyvinyl alcohol film to at least a swelling step, a dyeing step, a first crosslinking/stretching step, a second crosslinking/stretching step, and a third crosslinking/stretching step in this order, wherein: the thickness of the polyvinyl alcohol film is 5-100 [mu]m; the average degree of polymerization of a polyvinyl alcohol contained in the polyvinyl alcohol film is 2000-4000; in the swelling step, the polyvinyl alcohol film is swollen through immersion in water at 10-50 DEG C; in the dyeing step, the polyvinyl alcohol film is immersed in an aqueous solution at 10-50 DEG C containing a total of 0.5-3 mass% of iodine and potassium iodide, so that the polyvinyl alcohol film is impregnated with an iodine-based dichroic dye while the polyvinyl alcohol film is uniaxially stretched by a total stretching factor of 2-3; in the first crosslinking/stretching step, the polyvinyl alcohol film is uniaxially stretched in an aqueous solution at a temperature T1 containing 1-5 mass% of boric acid so that, in this step, the stretching factor is 1.1-1.3 and the total stretching factor is 2.5-3.5; in the second crosslinking/stretching step, the polyvinyl alcohol film is uniaxially stretched in an aqueous solution at a temperature T2 containing 1-5 mass% of boric acid so that, in this step, the stretching factor is 1.3-1.8 and the total stretching factor is 4-6; in the third crosslinking/stretching step, the polyvinyl alcohol film is uniaxially stretched in an aqueous solution of temperature T3 containing 1-5 mass% of boric acid so that, in this step, the stretching factor is 1.1-1.3 and the total stretching factor is 4.5-7; and T1, T2, and T3 satisfy formulae (1) and (2). As a result, even in the case where the average degree of polymerization of the PVA is low, a polarizing film that maintains excellent polarizing performance and still has small shrinkage stress while maintaining production stability can be obtained. (1): 25 ≤ T1 ≤ 45 (2): T1 < T2 < T3 ≤ 75.

Description

偏光薄膜之製造方法Manufacturing method of polarizing film

本發明係關於由包含碘系二色性染料之聚乙烯醇薄膜所構成的收縮應力小之偏光薄膜之製造方法。The present invention relates to a method for producing a polarizing film with a small shrinkage stress composed of a polyvinyl alcohol film containing an iodine-based dichroic dye.

在具有光的透射及遮蔽功能的偏光板中所使用之偏光薄膜，為液晶顯示器(LCD)的基本構成要素。許多的偏光板具有在偏光薄膜之表面上貼合三醋酸纖維素(TAC)薄膜等保護薄膜而成之結構，而作為偏光薄膜，現在的主流為用使碘系染料(I 3-或I 5-等)等二色性染料吸附在將聚乙烯醇薄膜(以下也將「聚乙烯醇」稱為「PVA」)單軸拉伸並定向而成的拉伸薄膜上而成之物。此種偏光薄膜係藉由對PVA薄膜施以膨潤步驟、染色步驟、交聯步驟、拉伸步驟、固定化步驟及乾燥步驟之方法等來製造。 The polarizing film used in the polarizing plate with the functions of transmitting and shielding light is the basic component of a liquid crystal display (LCD). Many polarizing plates have a structure in which a protective film such as a triacetate cellulose (TAC) film is laminated on the surface of the polarizing film. - etc.) and other dichroic dyes adsorbed on a stretched film obtained by uniaxially stretching and orienting a polyvinyl alcohol film (hereinafter also referred to as "polyvinyl alcohol" as "PVA"). Such a polarizing film is produced by a method of subjecting a PVA film to a swelling step, a dyeing step, a crosslinking step, a stretching step, an immobilization step, and a drying step.

近年來，LCD大量使用在筆電與行動電話等行動用途上。此種行動機器用的LCD被使用在各種環境下。因此，正尋求在高溫下的收縮應力低且尺寸穩定性優良之偏光薄膜。In recent years, LCDs have been widely used in mobile applications such as laptops and mobile phones. Such LCDs for mobile devices are used in various environments. Therefore, a polarizing film having low shrinkage stress at high temperature and excellent dimensional stability is being sought.

專利文獻1中記載，為了降低偏光薄膜之收縮應力，於第1交聯拉伸步驟中在包含硼酸之50℃的水溶液中進行拉伸後，於第2交聯拉伸步驟中在包含硼酸及碘化鉀之65℃的水溶液中進行拉伸。 [先前技術文獻] [專利文獻] Patent Document 1 describes that, in order to reduce the shrinkage stress of the polarizing film, in the first cross-linking stretching step, after stretching in an aqueous solution containing boric acid at 50° C., in the second cross-linking stretching step Stretching was performed in an aqueous solution of potassium iodide at 65°C. [Prior Art Literature] [Patent Literature]

專利文獻1 WO2017/138551號Patent Document 1 WO2017/138551

[發明欲解決之課題][The problem to be solved by the invention]

然而，在專利文獻1所記載的方法中，由於在染色步驟後以50℃的高溫進行第1交聯拉伸步驟，故若PVA薄膜中所包含的PVA之平均聚合度低，則在第2交聯拉伸步驟中一提高拉伸溫度就會引起薄膜破裂，而有變得難以維持著偏光性能且另一方面降低收縮應力之情形。又，於染色步驟吸附在薄膜上的碘在第1交聯拉伸步驟會溶出，而有變得難以調整成期望的透光率之情形。此外，因溶出的碘使第1交聯拉伸步驟中的硼酸水溶液發生著色的結果，使得第1交聯拉伸步驟中的PVA薄膜發生著色，而有難以維持生產穩定性的情形。However, in the method described in Patent Document 1, since the first crosslinking and stretching step is performed at a high temperature of 50° C. after the dyeing step, if the average degree of polymerization of PVA contained in the PVA film is low, the second As soon as the stretching temperature is increased in the cross-linking stretching step, the film is broken, and it becomes difficult to maintain the polarizing property and on the other hand, the shrinkage stress is reduced. In addition, the iodine adsorbed on the film in the dyeing step is eluted in the first cross-linking and stretching step, and it may become difficult to adjust to a desired light transmittance. In addition, as a result of coloring of the boric acid aqueous solution in the first cross-linking and stretching step by eluted iodine, the PVA film in the first cross-linking and stretching step is colored, and it may be difficult to maintain production stability.

本發明係為了解決上述課題而做，目的為提供一種偏光薄膜之製造方法，該偏光薄膜即使在PVA的平均聚合度低之情形，也維持著生產穩定性，同時維持著優良的偏光性能，且另一方面收縮應力小。 [用以解決課題之手段] The present invention is made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a polarizing film, which maintains production stability and maintains excellent polarization performance even when the average degree of polymerization of PVA is low, and On the other hand, the shrinkage stress is small. [means to solve the problem]

本發明之偏光薄膜之製造方法係藉由提供以下而達成： [1]一種偏光薄膜之製造方法，其係對聚乙烯醇薄膜至少按照以下順序施以膨潤步驟、染色步驟、第1交聯拉伸步驟、第2交聯拉伸步驟、第3交聯拉伸步驟，其中 該聚乙烯醇薄膜的厚度為5～100μm， 該聚乙烯醇薄膜中所包含的聚乙烯醇之平均聚合度為2000～4000， 於該膨潤步驟中，浸漬在10～50℃的水中使該聚乙烯醇薄膜膨潤， 於該染色步驟中，浸漬在合計包含0.5～3質量%的碘及碘化鉀之10～50℃的水溶液中，使碘系二色性染料含浸於該聚乙烯醇薄膜中，並進行單軸拉伸至總拉伸倍率成為2～3倍， 於該第1交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 1之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為2.5～3.5倍， 於該第2交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 2之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.3～1.8倍且總拉伸倍率成為4～6倍， 於該第3交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 3之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為4.5～7倍， 該T 1、T 2及T 3滿足以下的式(1)及(2)： 25≦T 1≦45             (1) T 1＜T 2＜T 3≦75          (2)， [2]如[1]之偏光薄膜之製造方法，其中該T 2及T 3滿足以下的式(3)及(4)： 50≦T 2≦65      (3) 55≦T 3≦75      (4)， [3]如[1]或[2]之偏光薄膜之製造方法，其中進一步在該第3交聯拉伸步驟之後進行第4交聯拉伸步驟，於該第4交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 4之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為5～8倍，T 1、T 2、T 3及T 4滿足以下的式(5)： T 1＜T 2＜T 3≦T 4≦75      (5)， [4]如[3]之偏光薄膜之製造方法，其中該T 4滿足以下的式(6)： 60≦T 4≦75      (6)， [5]如[3]之偏光薄膜之製造方法，其中於該第4交聯拉伸步驟中，最大拉伸應力為10N/mm 2以下， [6]如[1]或[2]之偏光薄膜之製造方法，其係得到收縮應力為50N/mm 2以下之偏光薄膜， [7]如[1]或[2]之偏光薄膜之製造方法，其係得到單體透光率為43.5%時的偏光度為99.80%以上之偏光薄膜。 [發明之效果] The manufacturing method of the polarizing film of the present invention is achieved by providing the following: [1] A manufacturing method of a polarizing film, wherein the polyvinyl alcohol film is subjected to at least a swelling step, a dyeing step, and a first cross-linking step in the following order. The stretching step, the second cross-linking stretching step, and the third cross-linking stretching step, wherein the thickness of the polyvinyl alcohol film is 5-100 μm, and the average degree of polymerization of the polyvinyl alcohol contained in the polyvinyl alcohol film is 2000 ~4000, in the swelling step, the polyvinyl alcohol film is dipped in water at 10 to 50°C to swell the polyvinyl alcohol film, and in the dyeing step, immersed in a 10 to 50°C solution containing a total of 0.5 to 3 mass % of iodine and potassium iodide. The polyvinyl alcohol film is impregnated with an iodine-based dichroic dye in an aqueous solution, and uniaxially stretched until the total stretching ratio becomes 2 to 3 times, and in the first cross-linking stretching step, 1 -5 mass % of boric acid in an aqueous solution at a temperature T 1 , uniaxially stretched until the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 2.5 to 3.5 times, and in the second cross-linking stretching In the stretching step, uniaxial stretching is performed in an aqueous solution containing 1 to 5 mass % of boric acid and at a temperature T 2 until the stretching ratio in this step becomes 1.3 to 1.8 times and the total stretching ratio becomes 4 to 6 times, In this third cross-linking stretching step, uniaxial stretching is performed in an aqueous solution containing 1 to 5 mass % of boric acid and at a temperature of T 3 until the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching is performed. The magnification is 4.5 to 7 times, and the T 1 , T 2 and T 3 satisfy the following equations (1) and (2): 25≦T 1 ≦45 (1) T 1 <T 2 <T 3 ≦75 (2) , [2] The manufacturing method of the polarizing film according to [1], wherein the T 2 and T 3 satisfy the following formulae (3) and (4): 50≦T 2 ≦65 (3) 55≦T 3 ≦75 ( 4), [3] The manufacturing method of the polarizing film according to [1] or [2], wherein a fourth cross-linking and stretching step is performed after the third cross-linking and stretching step, and the fourth cross-linking and stretching step is performed. In the step, in an aqueous solution containing 1 to 5 mass % of boric acid and at a temperature of T 4 , uniaxial stretching is performed until the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 5 to 8 times, T 1. T 2 , T 3 and T 4 satisfy the following formula (5): T 1 <T 2 <T 3 ≦T 4 ≦75 (5), [4] The manufacturing method of the polarizing film according to [3], wherein The T 4 satisfies the following formula (6): 60≦T 4 ≦75 (6), [5] The manufacturing method of a polarizing film according to [3], wherein in the fourth cross-linking stretching step, the maximum stretching The stress is 10 N/mm 2 or less, [6] The manufacturing method of the polarizing film according to [1] or [2], which obtains a shrinkage stress of 50 N/mm 2 or less The polarizing film of [7] is the manufacturing method of the polarizing film according to [1] or [2], which is to obtain a polarizing film with a degree of polarization of 99.80% or more when the light transmittance of the monomer is 43.5%. [Effect of invention]

藉由本發明之製造方法，能得到一種偏光薄膜，其即使在PVA的平均聚合度低之情形，也維持著生產穩定性，同時維持著優良的偏光性能，且另一方面收縮應力小。By the production method of the present invention, a polarizing film can be obtained, which maintains production stability and maintains excellent polarizing performance even when the average degree of polymerization of PVA is low, and on the other hand, has low shrinkage stress.

[用以實施發明的形態][Form for carrying out the invention]

本發明為一種偏光薄膜之製造方法，其係對PVA薄膜至少按照以下順序施以膨潤步驟、染色步驟、第1交聯拉伸步驟、第2交聯拉伸步驟、第3交聯拉伸步驟。其中，特別重要的是於第1交聯拉伸步驟中的溫度T 1、於第2交聯拉伸步驟中的溫度T 2、於第3交聯拉伸步驟中的溫度T 3滿足以下的式(1)及(2)。 25≦T 1≦45           (1) T 1＜T 2＜T 3≦75        (2) The present invention relates to a method for producing a polarizing film, which comprises subjecting a PVA film to at least a swelling step, a dyeing step, a first cross-linking and stretching step, a second cross-linking and stretching step, and a third cross-linking and stretching step in the following order. . Among them, it is particularly important that the temperature T 1 in the first cross-linking and stretching step, the temperature T 2 in the second cross-linking and stretching step, and the temperature T 3 in the third cross-linking and stretching step satisfy the following Formulas (1) and (2). 25≦T 1 ≦45 (1) T 1 ＜T 2 ＜T 3 ≦75 (2)

由後述的實施例與比較例的對比可知，在溫度T 1為50℃之不滿足式(1)的比較例3中，藉由染色步驟吸附至PVA薄膜上的碘會在第1交聯拉伸步驟溶出，因此使第1交聯拉伸步驟的硼酸水溶液發生著色，而難以維持生產穩定性。又，在溫度T 2與溫度T 3為相同溫度之不滿足式(2)的比較例1～3中，所得到的偏光薄膜之收縮應力的降低不充分。相對於此，在溫度T 1為32℃、溫度T 2為約61℃、溫度T 3為約64℃之滿足式(1)及(2)的實施例1～3中，則明顯能製造維持著優良的偏光性能且另一方面收縮應力小之偏光薄膜。因此，採用此種方法之本發明意義重大。 From the comparison between the examples and the comparative examples described later, it can be seen that in the comparative example 3 which does not satisfy the formula ( 1 ) at a temperature T1 of 50°C, the iodine adsorbed on the PVA film by the dyeing step will be in the first cross-linking pull. Since the stretching step is eluted, the boric acid aqueous solution in the first cross-linking stretching step is colored, and it is difficult to maintain production stability. Moreover, in the comparative examples 1-3 which did not satisfy the formula ( 2 ) in which the temperature T2 and the temperature T3 were the same temperature, the reduction of the shrinkage stress of the obtained polarizing film was insufficient. On the other hand, in Examples 1 to 3 satisfying the formulae (1) and (2) in which the temperature T 1 is 32° C., the temperature T 2 is about 61° C., and the temperature T 3 is about 64° C., it is obvious that the production and maintenance can be maintained. It is a polarizing film with excellent polarizing properties and low shrinkage stress on the other hand. Therefore, the present invention using this method is of great significance.

本發明之偏光薄膜之製造中所使用的原材PVA薄膜中所包含的PVA，能使用將1種或2種以上的乙烯酯聚合所得之聚乙烯酯藉由皂化而得之物。作為該乙烯酯，舉例來說有：醋酸乙烯酯、甲酸乙烯酯、丙酸乙烯酯、酪酸乙烯酯、三甲基乙酸乙烯酯、新癸酸乙烯酯、月桂酸乙烯酯、硬脂酸乙烯酯、苯甲酸乙烯酯、醋酸異丙烯酯等，這些之中，從PVA的製造容易性、取得容易性、成本等觀點來看，較佳為醋酸乙烯酯。The PVA contained in the raw material PVA film used for the manufacture of the polarizing film of this invention can use the thing obtained by saponifying the polyvinyl ester obtained by superposing|polymerizing 1 type or 2 or more types of vinyl esters. Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl trimethyl acetate, vinyl neodecanoate, vinyl laurate, and vinyl stearate , vinyl benzoate, propylene acetate, and the like, among these, vinyl acetate is preferred from the viewpoints of ease of production of PVA, ease of acquisition, cost, and the like.

聚乙烯酯，可以是僅使用1種或2種以上乙烯酯作為單體而得者，在不損害本發明之效果的範圍內，也可以是1種或2種以上乙烯酯和能與其共聚之其它單體的共聚物。Polyvinyl esters may be obtained by using only one or two or more vinyl esters as monomers, and may also be one or two or more vinyl esters, together with those that can be copolymerized therewith, within the scope of not impairing the effects of the present invention. Copolymers of other monomers.

作為能與乙烯酯共聚之其它單體，可舉出例如：乙烯、丙烯、1-丁烯、異丁烯等碳數2～30的α-烯烴；(甲基)丙烯酸或其鹽；(甲基)丙烯酸甲酯、(甲基)丙烯酸乙酯、(甲基)丙烯酸正丙酯、(甲基)丙烯酸異丙酯、(甲基)丙烯酸正丁酯、(甲基)丙烯酸異丁酯、(甲基)丙烯酸三級丁酯、(甲基)丙烯酸2-乙基己酯、(甲基)丙烯酸十二烷基酯、(甲基)丙烯酸十八烷基酯等(甲基)丙烯酸酯；(甲基)丙烯醯胺、N-甲基(甲基)丙烯醯胺、N-乙基(甲基)丙烯醯胺、N,N-二甲基(甲基)丙烯醯胺、二丙酮(甲基)丙烯醯胺、(甲基)丙烯醯胺丙磺酸或其鹽、(甲基)丙烯醯胺丙基二甲基胺或其鹽、N-羥甲基(甲基)丙烯醯胺或其衍生物等(甲基)丙烯醯胺衍生物；N-乙烯基甲醯胺、N-乙烯基乙醯胺、N-乙烯基吡咯啶酮等N-乙烯基醯胺；甲基乙烯基醚、乙基乙烯基醚、正丙基乙烯基醚、異丙基乙烯基醚、正丁基乙烯基醚、異丙基乙烯基醚、三級丁基乙烯基醚、十二烷基乙烯基醚、硬脂基乙烯基醚等乙烯基醚；(甲基)丙烯腈等氰乙烯；氯乙烯、偏二氯乙烯、氟乙烯、偏二氟乙烯等鹵乙烯；醋酸烯丙酯、烯丙基氯等烯丙基化合物；馬來酸或其鹽、酯或酸酐；伊康酸或其鹽、酯或酸酐；乙烯基三甲氧基矽烷等乙烯基矽基化合物；不飽和磺酸等。上述聚乙烯酯可具有源自1種或2種以上的前述以外的單體之結構單元。作為前述其它單體，較佳為α-烯烴，其中較佳為乙烯。Examples of other monomers that can be copolymerized with vinyl esters include α-olefins having 2 to 30 carbon atoms, such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or a salt thereof; (methyl) Methyl acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, (meth)acrylate (meth)acrylates such as tertiary butyl acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate; ( Meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N,N-dimethyl (meth) acrylamide, diacetone (meth) base) acrylamide, (meth)acrylamidopropanesulfonic acid or its salt, (meth)acrylamidopropyldimethylamine or its salt, N-methylol (meth)acrylamide or (meth)acrylamide derivatives such as its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether , ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isopropyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether , stearyl vinyl ether and other vinyl ethers; (meth)acrylonitrile and other vinyl cyanide; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and other vinyl halides; allyl acetate, allyl chloride and other allyl compounds; maleic acid or its salts, esters or anhydrides; Iconic acid or its salts, esters or anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids, etc. The said polyvinyl ester may have the structural unit derived from 1 type or 2 or more types of monomers other than the above. As the aforementioned other monomers, α-olefins are preferable, and among them, ethylene is preferable.

聚乙烯酯中所占的，源自其它單體之結構單元的比例，係基於構成聚乙烯酯的全部結構單元之莫耳數，較佳為15莫耳%以下，更佳為10莫耳%以下，再更佳為5莫耳%以下。The proportion of structural units derived from other monomers in the polyvinyl ester is based on the molar number of all structural units constituting the polyvinyl ester, preferably 15 mol % or less, more preferably 10 mol % Below, more preferably, it is 5 mol % or less.

特別是，在該其它單體為如(甲基)丙烯酸、不飽和磺酸等，係能促進所得到的PVA之水溶性的單體之情形，於偏光薄膜之製造過程中為了防止PVA溶解，聚乙烯酯中源自於這些單體的結構單元之比例，基於構成聚乙烯酯的全部結構單元之莫耳數，較佳為5莫耳%以下，更佳為3莫耳%以下。Especially, in the case where the other monomers are monomers such as (meth)acrylic acid, unsaturated sulfonic acid, etc., which can promote the water-solubility of the obtained PVA, in order to prevent the PVA from dissolving during the manufacturing process of the polarizing film, The ratio of the structural units derived from these monomers in the polyvinyl ester is preferably 5 mol % or less, more preferably 3 mol % or less, based on the molar number of all the structural units constituting the polyvinyl ester.

本發明中所使用的PVA，在不損害本發明之效果的範圍內，也可以是藉由1種或2種以上能接枝共聚之單體予以改質而成者。作為該能接枝共聚之單體，可舉出例如：不飽和羧酸或其衍生物；不飽和磺酸或其衍生物；碳數2～30的α-烯烴等。PVA中源自能接枝共聚之單體之結構單元(於接枝改質部分的結構單元)之比例，基於構成PVA的全部結構單元之莫耳數，較佳為5莫耳%以下。The PVA used in the present invention may be modified with one or two or more graft-copolymerizable monomers within the range that does not impair the effects of the present invention. Examples of the graft-copolymerizable monomers include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms. The ratio of the structural unit (structural unit in the graft-modified part) derived from the monomer capable of graft copolymerization in PVA is preferably 5 mol % or less based on the molar number of all the structural units constituting the PVA.

前述PVA，其一部分羥基可以交聯也可以不交聯。另外上述PVA，其一部分羥基也能與乙醛、丁醛等醛化合物等反應形成縮醛結構。In the aforementioned PVA, a part of the hydroxyl groups may or may not be cross-linked. In addition, a part of the hydroxyl groups of the above-mentioned PVA can also react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure.

前述PVA的聚合度係在2000～4000之範圍內。藉由該聚合度為2000以上，於第2交聯拉伸步驟中即便是以高溫拉伸，也能讓PVA薄膜不破裂地拉伸。該聚合度更佳為2200以上。另一方面，藉由該聚合度為4000以下，能降低所得到的偏光薄膜之收縮應力。該聚合度更佳為3500以下，再更佳為3000以下，特佳為小於2500。本說明書中PVA的聚合度意指依據JIS K6726-1994的記載所測定之平均聚合度。其中，偏光薄膜中的PVA雖然包含由硼酸等硼化合物所形成的交聯結構，但只要藉由將硼酸酯水解等而使其解離，則PVA的平均聚合度本身沒有實質上的變化。The degree of polymerization of the aforementioned PVA is in the range of 2,000 to 4,000. Since the degree of polymerization is 2000 or more, the PVA film can be stretched without breaking even if it is stretched at a high temperature in the second cross-linking stretching step. The polymerization degree is more preferably 2200 or more. On the other hand, when the polymerization degree is 4000 or less, the shrinkage stress of the polarizing film obtained can be reduced. The degree of polymerization is more preferably 3,500 or less, still more preferably 3,000 or less, and particularly preferably less than 2,500. The degree of polymerization of PVA in this specification means the average degree of polymerization measured according to the description of JIS K6726-1994. Among them, although PVA in the polarizing film contains a cross-linked structure formed of a boron compound such as boric acid, the average degree of polymerization of PVA itself does not substantially change as long as it is dissociated by hydrolysis of boric acid ester or the like.

PVA的皂化度，從偏光薄膜之偏光性能等的觀點來看，較佳為98莫耳%以上，更佳為98.5莫耳%以上，再更佳為99莫耳%以上。皂化度若小於98莫耳%，則在偏光薄膜之製造過程中PVA變得容易溶出，且溶出的PVA有時會附著在薄膜上使得偏光薄膜之偏光性能降低。其中，本說明書中PVA的皂化度係指PVA所具有之相對於能藉由皂化轉換為乙烯醇單元之結構單元(典型上為乙烯酯單元)與乙烯醇單元的合計莫耳數，該乙烯醇單元的莫耳數所占之比例(莫耳%)。皂化度能依據JIS K6726-1994之記載來測定。其中，原材薄膜中的PVA與所得到的偏光薄膜中的PVA，皂化度實質上相同。The degree of saponification of PVA is preferably 98 mol % or more, more preferably 98.5 mol % or more, even more preferably 99 mol % or more, from the viewpoint of the polarizing performance of the polarizing film and the like. If the degree of saponification is less than 98 mol%, PVA becomes easy to dissolve during the manufacturing process of the polarizing film, and the dissolved PVA sometimes adheres to the film, which reduces the polarizing performance of the polarizing film. Wherein, the saponification degree of PVA in this specification refers to the total molar number of the vinyl alcohol unit and the structural unit (typically vinyl ester unit) that can be converted into a vinyl alcohol unit by saponification. The proportion of the number of moles in the unit (mol%). The degree of saponification can be measured according to the description of JIS K6726-1994. Among them, the PVA in the raw material film and the PVA in the obtained polarizing film have substantially the same degree of saponification.

本發明中所使用的PVA薄膜中之PVA的含有率，從製造期望的偏光薄膜之容易性等來看，較佳在50～99質量%之範圍內。該含有率更佳為75質量%以上，再更佳為80質量%以上，特佳為85質量%以上。又，更佳為98質量%以下，再更佳為96質量%以下，特佳為95質量%以下。The content of PVA in the PVA film used in the present invention is preferably in the range of 50 to 99% by mass from the viewpoint of ease of producing a desired polarizing film. The content is more preferably 75% by mass or more, still more preferably 80% by mass or more, and particularly preferably 85% by mass or more. Moreover, 98 mass % or less is more preferable, 96 mass % or less is still more preferable, and 95 mass % or less is especially preferable.

PVA薄膜，從拉伸它時的拉伸性提升之觀點來看較佳為包含塑化劑。作為該塑化劑，可舉出例如：乙二醇、甘油、丙二醇、二乙二醇、二甘油、三乙二醇、四乙二醇、三羥甲基丙烷等的多元醇等，PVA薄膜可包含1種或2種以上這些塑化劑。這些之中，從拉伸性的提升效果之觀點來看較佳為甘油。The PVA film preferably contains a plasticizer from the viewpoint of improvement in stretchability when it is stretched. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and PVA films. One or more of these plasticizers may be contained. Among these, glycerin is preferable from the viewpoint of the effect of improving stretchability.

PVA薄膜中塑化劑的含量，相對於100質量份的其中所包含之PVA，較佳在1～20質量份之範圍內。藉由該含量為1質量份以上，能更為提升PVA薄膜的拉伸性。另一方面，藉由該含量為20質量份以下，能防止PVA薄膜變得過於柔軟而讓使用性降低。PVA薄膜中塑化劑的含量，相對於100質量份的PVA，更佳為2質量份以上，再更佳為4質量份以上，特佳為5質量份以上。又，塑化劑的含量更佳為15質量份以下，再更佳為12質量份以下。另外，雖視偏光薄膜之製造條件等而定，但PVA薄膜中所包含的塑化劑在製造偏光薄膜時有時會溶出，所以其全部的量未必都殘留在偏光薄膜中。The content of the plasticizer in the PVA film is preferably in the range of 1 to 20 parts by mass relative to 100 parts by mass of the PVA contained therein. When the content is 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the PVA film from being too soft and reducing the usability. The content of the plasticizer in the PVA film is more preferably 2 parts by mass or more, still more preferably 4 parts by mass or more, and particularly preferably 5 parts by mass or more, relative to 100 parts by mass of PVA. Moreover, the content of the plasticizer is more preferably 15 parts by mass or less, and still more preferably 12 parts by mass or less. In addition, although it depends on the production conditions of the polarizing film, the plasticizer contained in the PVA film may be eluted during the production of the polarizing film, so the entire amount may not necessarily remain in the polarizing film.

PVA薄膜視需要也可進一步包含抗氧化劑、防凍劑、pH調節劑、罩護劑、抗著色劑、油劑、界面活性劑等成分。The PVA film may further contain components such as antioxidants, antifreeze agents, pH adjusters, protective agents, anti-coloring agents, oil agents, surfactants, etc., as required.

本發明之製造方法中所使用的PVA薄膜之厚度為5～100μm。藉由厚度為100μm以下，可容易得到薄型的偏光薄膜。PVA薄膜的厚度較佳為60μm以下。另外，為了確保操控性，PVA薄膜的厚度較佳為20μm以上，更佳為30μm以上。另一方面，在厚度小於5μm之情形，除了偏光薄膜之製造變難以外，還變得容易產生染色不均。PVA薄膜的厚度較佳為7μm以上。這裡所說的厚度，在多層薄膜的情形中係指PVA層的厚度。The thickness of the PVA film used in the manufacturing method of this invention is 5-100 micrometers. When the thickness is 100 μm or less, a thin polarizing film can be easily obtained. The thickness of the PVA film is preferably 60 μm or less. In addition, in order to ensure handling properties, the thickness of the PVA film is preferably 20 μm or more, and more preferably 30 μm or more. On the other hand, when the thickness is less than 5 μm, it becomes difficult to manufacture the polarizing film, and uneven dyeing tends to occur. The thickness of the PVA film is preferably 7 μm or more. The thickness referred to here, in the case of the multilayer film, refers to the thickness of the PVA layer.

PVA薄膜可以是單層薄膜，也可以使用具有PVA層與基材樹脂層之多層薄膜。在單層薄膜之情形，薄膜的厚度較佳在上述範圍。另一方面，在多層薄膜之情形，PVA層的厚度可以設為20μm以下，也可以設為15μm以下。多層薄膜中基材樹脂層的厚度通常為20～500μm。The PVA film may be a single-layer film or a multi-layer film having a PVA layer and a base resin layer. In the case of a single-layer film, the thickness of the film is preferably within the above range. On the other hand, in the case of a multilayer film, the thickness of the PVA layer may be 20 μm or less, or 15 μm or less. The thickness of the base resin layer in the multilayer film is usually 20 to 500 μm.

作為PVA薄膜，在使用具有PVA層與基材樹脂層的多層薄膜之情形，基材樹脂必須要能與PVA一起進行拉伸處理。可使用聚酯與聚烯烴樹脂等。其中，較佳為非晶聚酯樹脂，可適當使用聚對苯二甲酸乙二酯或對其共聚間苯二甲酸或1,4-環己烷二甲醇等共聚成分而成之非晶聚酯樹脂。較佳為藉由將PVA溶液塗布於基材樹脂薄膜來製造多層薄膜。此時，為了改善PVA層與基材樹脂層之間的黏著性，可以將基材樹脂薄膜的表面改質、或在兩層間形成黏著劑層。As the PVA film, in the case of using a multilayer film having a PVA layer and a base resin layer, the base resin must be capable of being stretched together with PVA. Polyester and polyolefin resins and the like can be used. Among them, amorphous polyester resin is preferred, and polyethylene terephthalate or an amorphous polyester obtained by copolymerizing isophthalic acid or 1,4-cyclohexanedimethanol with it can be appropriately used resin. Preferably, the multilayer film is produced by applying the PVA solution to the base resin film. At this time, in order to improve the adhesion between the PVA layer and the base resin layer, the surface of the base resin film may be modified, or an adhesive layer may be formed between the two layers.

PVA薄膜的形狀沒有特別限制，從在製造偏光薄膜時能連續供給來看，較佳為長條的PVA薄膜。長條的PVA薄膜之長度(長條方向的長度)沒有特別限制，能依據所製造的偏光薄膜之用途等適當設定，例如可以在5～20,000m之範圍內。The shape of the PVA film is not particularly limited, but it is preferably a long PVA film from the viewpoint of being able to continuously supply the polarizing film. The length of the elongated PVA film (length in the elongated direction) is not particularly limited, and can be appropriately set according to the use of the polarizing film to be produced, for example, within the range of 5 to 20,000 m.

PVA薄膜的寬度沒有特別限制，能依據所製造的偏光薄膜之用途等適當設定。近年來，正在進行液晶電視與液晶顯示器的大畫面化，因此若使PVA薄膜的寬度為0.5m以上、更佳為1m以上，則最適用在這些用途。另一方面，PVA薄膜的寬度如果太寬，則在以實用化的裝置來製造偏光薄膜之情形下會有變得難以均勻拉伸的傾向，所以PVA薄膜的寬度較佳為7m以下。The width of the PVA film is not particularly limited, and can be appropriately set according to the use of the polarizing film to be produced. In recent years, liquid crystal televisions and liquid crystal displays have been increased in size. Therefore, if the width of the PVA film is 0.5 m or more, more preferably 1 m or more, it is most suitable for these applications. On the other hand, if the width of the PVA film is too wide, uniform stretching tends to be difficult when a polarizing film is produced by a practical apparatus, so the width of the PVA film is preferably 7 m or less.

本發明之偏光薄膜係使用以上說明的PVA薄膜作為原料製造。具體來說係至少按照以下順序施以膨潤步驟、染色步驟、第1交聯拉伸步驟、第2交聯拉伸步驟、第3交聯拉伸步驟來製造偏光薄膜。在前述第3交聯拉伸步驟之後，施以洗淨步驟與乾燥步驟也是較佳的。以下對各步驟作詳細說明。The polarizing film of this invention is manufactured using the PVA film demonstrated above as a raw material. Specifically, a swelling step, a dyeing step, a first cross-linking and stretching step, a second cross-linking and stretching step, and a third cross-linking and stretching step are performed at least in the following order to produce a polarizing film. It is also preferable to perform a washing step and a drying step after the third crosslinking and stretching step. Each step is described in detail below.

本發明之製造方法中，首先將PVA薄膜供給至膨潤步驟。在膨潤步驟中，係浸漬在10～50℃的水中使PVA薄膜膨潤。水的溫度較佳為20℃以上，同樣較佳為40℃以下。藉由浸漬在此種溫度範圍內的水中，能有效率且均勻地使PVA薄膜膨潤。將PVA薄膜浸漬在水中的時間，較佳為0.1～5分鐘之範圍，更佳為0.5～3分鐘之範圍。藉由這樣的浸漬時間，能有效率且均勻地使PVA薄膜膨潤。其中，PVA薄膜所浸漬的水不限定於純水，可以是溶解有各種成分的水溶液，也可以是水與水溶性有機溶劑的混合物。膨潤步驟中，較佳對PVA薄膜施以單軸拉伸。在此情形的拉伸倍率沒有特別限定，較佳為1.2～2.8倍。該拉伸倍率更佳為1.5倍以上，同樣更佳為2.5倍以下。In the production method of the present invention, first, the PVA film is supplied to the swelling step. In the swelling step, the PVA film is swelled by immersion in water at 10 to 50°C. The temperature of the water is preferably 20°C or higher, and also preferably 40°C or lower. By immersing in water in such a temperature range, the PVA film can be swelled efficiently and uniformly. The time for immersing the PVA film in water is preferably in the range of 0.1 to 5 minutes, more preferably in the range of 0.5 to 3 minutes. By such immersion time, the PVA film can be swelled efficiently and uniformly. The water in which the PVA film is immersed is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and a water-soluble organic solvent. In the swelling step, the PVA film is preferably subjected to uniaxial stretching. The draw ratio in this case is not particularly limited, but is preferably 1.2 to 2.8 times. The draw ratio is more preferably 1.5 times or more, and likewise more preferably 2.5 times or less.

本發明之製造方法中，係在前述膨潤步驟之後供給至染色步驟。在染色步驟中，係浸漬在合計包含0.5～3質量%的碘及碘化鉀之10～50℃的水溶液中，使碘系二色性染料含浸於PVA薄膜中，並進行單軸拉伸至總拉伸倍率成為2～3倍。藉此，以碘系二色性染料將PVA薄膜染色，並將薄膜中的PVA的分子鏈定向，也將碘系二色性染料定向。In the manufacturing method of this invention, it supplies to a dyeing process after the said swelling process. In the dyeing step, the PVA film is immersed in an aqueous solution containing a total of 0.5 to 3 mass % of iodine and potassium iodide at 10 to 50° C. to impregnate the PVA film with an iodine-based dichroic dye, and uniaxially stretched to a total stretch The elongation ratio becomes 2 to 3 times. Thereby, the PVA film is dyed with the iodine-based dichroic dye, the molecular chains of PVA in the film are aligned, and the iodine-based dichroic dye is also aligned.

染色係藉由將PVA薄膜浸漬於包含碘系二色性染料的染色浴中來進行。染色浴係藉由將碘(I 2)及碘化鉀(KI)與水混合來調製。藉由將碘及碘化鉀與水混合，能產生I 3 -與I 5 -等碘系二色性染料。染色浴中的碘及碘化鉀之合計含量依它們的合計係0.5～3質量%。碘及碘化鉀之合計含量較佳為0.8質量%以上，同樣較佳為2.5質量%以下。藉由在此種濃度範圍染色，能有效率且均勻地染色。碘化鉀相對於碘之質量比(KI/I 2)較佳為10～200，更佳為15～150。染色浴中也可包含硼酸、硼砂等的硼酸鹽等的硼化合物，其含量以硼酸換算通常係小於5質量%，較理想為1質量%以下。 Dyeing is performed by immersing the PVA film in a dyeing bath containing an iodine-based dichroic dye. The dyeing bath is prepared by mixing iodine (I 2 ) and potassium iodide (KI) with water. By mixing iodine and potassium iodide with water, iodine-based dichroic dyes such as I 3 - and I 5 - can be produced. The total content of iodine and potassium iodide in the dyeing bath is 0.5 to 3% by mass in accordance with the total. The total content of iodine and potassium iodide is preferably 0.8 mass % or more, and likewise preferably 2.5 mass % or less. By dyeing in such a concentration range, efficient and uniform dyeing can be achieved. The mass ratio (KI/I 2 ) of potassium iodide to iodine is preferably 10-200, more preferably 15-150. The dyeing bath may contain boron compounds such as boric acid and borate such as borax, and the content thereof is usually less than 5 mass % in terms of boric acid, preferably 1 mass % or less.

染色浴的溫度為10～50℃。該溫度較佳為15℃以上，更佳為20℃以上。又，該溫度較佳為40℃以下，更佳為35℃以下。藉由在此種溫度範圍內染色能有效率且均勻地將PVA薄膜染色。又，作為將PVA薄膜浸漬於染色浴中的時間，較佳為0.1～10分鐘之範圍，更佳為0.2～5分鐘之範圍。藉由在此種時間範圍能夠均勻地將PVA薄膜染色。The temperature of the dyeing bath is 10 to 50°C. The temperature is preferably 15°C or higher, more preferably 20°C or higher. In addition, the temperature is preferably 40°C or lower, more preferably 35°C or lower. The PVA film can be dyed efficiently and uniformly by dyeing in this temperature range. Moreover, as time for immersing the PVA film in the dyeing bath, the range of 0.1 to 10 minutes is preferable, and the range of 0.2 to 5 minutes is more preferable. By being able to dye the PVA film uniformly in this time frame.

於染色步驟中，將PVA薄膜染色並進行單軸拉伸，使總拉伸倍率成為2～3倍。對於具有此種總拉伸倍率的PVA薄膜，接著至少施以3階段的交聯拉伸步驟，能得到具有優良的偏光性能且收縮應力低的偏光薄膜。經過包含膨潤步驟及染色步驟之到目前為止的步驟之總拉伸倍率只要成為2～3倍即可。於染色步驟中的拉伸倍率只要大於1倍即可，更佳為1.05倍以上。In the dyeing step, the PVA film is dyed and uniaxially stretched so that the total stretch ratio becomes 2 to 3 times. For a PVA film with such a total stretching ratio, a polarizing film with excellent polarizing properties and low shrinkage stress can be obtained by applying at least three-stage cross-linking stretching steps. The total stretching ratio through the steps up to now including the swelling step and the dyeing step only needs to be 2 to 3 times. The stretching ratio in the dyeing step may be more than 1 time, more preferably 1.05 times or more.

在本發明之製造方法中，係在前述染色步驟之後供給至第1交聯拉伸步驟、第2交聯拉伸步驟、第3交聯拉伸步驟。藉由施以條件不同的3階段交聯拉伸步驟，能控制所得到的偏光薄膜之結晶狀況及定向狀態，能得到具有優良的偏光性能且收縮應力低之偏光薄膜。如後所述，在第3交聯拉伸步驟之後進行第4交聯拉伸步驟為較佳的實施態樣。以下，對這4個交聯拉伸步驟進行說明。In the manufacturing method of this invention, it supplies to a 1st crosslinking stretching process, a 2nd crosslinking stretching process, and a 3rd crosslinking stretching process after the said dyeing process. By applying three-stage cross-linking and stretching steps with different conditions, the crystalline state and orientation state of the obtained polarizing film can be controlled, and a polarizing film with excellent polarizing performance and low shrinkage stress can be obtained. As will be described later, it is a preferred embodiment that the fourth cross-linking and stretching step is performed after the third cross-linking and stretching step. Hereinafter, these four crosslinking stretching steps will be described.

在第1交聯拉伸步驟中，係在包含1～5質量%之硼酸且溫度T 1為25～45℃之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為2.5～3.5倍。PVA薄膜所浸漬的硼酸水溶液包含1～5質量%的硼酸。硼酸的濃度較佳為1.5質量%以上，同樣較佳為4質量%以下。藉由此種濃度能以適當的速度以硼酸進行分子間交聯反應。其中，硼酸只要是在水溶液中能變成硼酸或硼酸離子者即可，使用硼酸、硼酸鹽中的任一種均可，但較理想為硼酸。在使用硼酸鹽之情形的濃度係以硼酸(H 3BO 3)的質量換算來計算。硼酸水溶液也可含有碘化鉀，在此情形的濃度較佳在0.01～10質量%之範圍內。藉由含有碘化鉀，能調整所得到的偏光薄膜之偏光性能。可以在第1交聯拉伸步驟包含碘化鉀，也可以在後述的第2～4交聯拉伸步驟包含碘化鉀，也可以在全部的步驟中包含。 In the first crosslinking stretching step, uniaxial stretching is performed in an aqueous solution containing 1 to 5 mass % of boric acid and having a temperature T1 of 25 to 45° C. until the stretching ratio in this step becomes 1.1 to 1.3 times and the total draw ratio becomes 2.5 to 3.5 times. The boric acid aqueous solution into which the PVA film is immersed contains 1 to 5 mass % of boric acid. The concentration of boric acid is preferably 1.5 mass % or more, and also preferably 4 mass % or less. With such a concentration, the intermolecular cross-linking reaction with boric acid can proceed at an appropriate rate. Among them, the boric acid may be any one of boric acid and boric acid as long as it can be converted into boric acid or boric acid ion in an aqueous solution, but boric acid is preferable. The concentration in the case of using borate was calculated in terms of the mass of boric acid (H 3 BO 3 ). The boric acid aqueous solution may contain potassium iodide, and the concentration in this case is preferably in the range of 0.01 to 10 mass %. By containing potassium iodide, the polarization performance of the obtained polarizing film can be adjusted. Potassium iodide may be included in the first cross-linking stretching step, potassium iodide may be included in the second to fourth cross-linking and stretching steps described later, or may be included in all the steps.

於第1交聯拉伸步驟中之包含硼酸的水溶液之溫度T 1為25～45℃。也就是說，溫度T 1滿足以下的式(1)。 25≦T 1≦45      (1) The temperature T1 of the aqueous solution containing boric acid in the first crosslinking and stretching step is 25 to 45°C. That is, the temperature T 1 satisfies the following formula (1). 25≦T 1 ≦45 (1)

由後述的實施例與比較例的對比可知，在溫度T 1為50℃之不滿足式(1)的比較例3中，藉由染色步驟吸附至PVA薄膜上的碘會在第1交聯拉伸步驟溶出，因此使第1交聯拉伸步驟的硼酸水溶液發生著色，而難以維持生產穩定性。相對於此，溫度T 1在此範圍之本案發明，即使在PVA的平均聚合度低之情形，也能製造維持著優良的偏光性能且另一方面收縮應力小之偏光薄膜。在溫度T 1低於25℃之情形，以硼酸進行之交聯反應變得不充分，所得到的偏光薄膜之偏光性能恐怕會降低。另一方面，在溫度T 1高於45℃之情形，藉由染色步驟吸附至PVA薄膜上的碘會溶出，因此恐怕會使第1交聯拉伸步驟的硼酸水溶液發生著色，而難以維持生產穩定性。溫度T 1較佳為28℃以上，更佳為30℃以上。又，溫度T 1較佳為40℃以下，更佳為38℃以下。然後，於前述溫度範圍，進行單軸拉伸至拉伸倍率成為1.1～1.3倍且總拉伸倍率成為2.5～3.5倍。總拉伸倍率較佳為2.6倍以上，更佳為3.4倍以下。像這樣，在第一交聯拉伸步驟中，係一邊將溫度T 1維持在上述範圍同時進行一點點單軸拉伸來適當定向，一邊使其進行硼酸交聯反應。藉此，即使在接下來的第2交聯拉伸步驟以後被浸漬於高溫的硼酸水溶液之情形，也不會有PVA自薄膜溶出至硼酸水溶液中、薄膜的強度大幅降低，能拉伸至更高倍率。 From the comparison between the examples and the comparative examples described later, it can be seen that in the comparative example 3 which does not satisfy the formula ( 1 ) at a temperature T1 of 50°C, the iodine adsorbed on the PVA film by the dyeing step will be in the first cross-linking pull. Since the stretching step is eluted, the boric acid aqueous solution in the first cross-linking stretching step is colored, and it is difficult to maintain production stability. On the other hand, the present invention with the temperature T1 in this range can produce a polarizing film with a small shrinkage stress while maintaining excellent polarization performance even when the average degree of polymerization of PVA is low. When the temperature T1 is lower than 25°C, the crosslinking reaction with boric acid becomes insufficient, and the polarizing performance of the obtained polarizing film may be lowered. On the other hand, when the temperature T1 is higher than 45°C, the iodine adsorbed to the PVA film in the dyeing step will be dissolved, so the boric acid aqueous solution in the first cross-linking and stretching step may be colored, making it difficult to maintain production. stability. The temperature T 1 is preferably 28°C or higher, more preferably 30°C or higher. Moreover, it is preferable that temperature T1 is 40 degrees C or less, and it is more preferable that it is 38 degrees C or less. Then, in the aforementioned temperature range, uniaxial stretching is performed until the stretching ratio becomes 1.1 to 1.3 times and the total stretching ratio becomes 2.5 to 3.5 times. The total draw ratio is preferably 2.6 times or more, more preferably 3.4 times or less. In this way, in the first cross-linking and stretching step, the boronic acid cross-linking reaction is carried out while maintaining the temperature T 1 in the above-mentioned range while performing a little uniaxial stretching for proper orientation. Thereby, even if it is immersed in a high-temperature boric acid aqueous solution after the second cross-linking stretching step, PVA will not be eluted from the film into the boric acid aqueous solution, and the strength of the film will not be greatly reduced, and the film can be stretched to a higher level. High magnification.

接下來，在第2交聯拉伸步驟中，係在包含1～5質量%的硼酸且溫度T 2高於第1交聯拉伸步驟的溫度T 1且低於75℃之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.3～1.8倍且總拉伸倍率成為4～6倍。所使用的包含硼酸之水溶液的組成，可使用與第1交聯拉伸步驟中所使用之範圍相同者。 Next, in the second cross-linking and stretching step, it is carried out in an aqueous solution containing 1 to 5 mass % of boric acid and having a temperature T 2 higher than the temperature T 1 of the first cross-linking and stretching step and lower than 75° C. The stretching ratio in this step is uniaxially stretched to be 1.3 to 1.8 times, and the total stretching ratio is 4 to 6 times. The composition of the aqueous solution containing boric acid to be used can be used in the same range as that used in the first crosslinking and stretching step.

於第2交聯拉伸步驟中，包含硼酸的水溶液之溫度T 2高於第1交聯拉伸步驟的溫度T 1且低於75℃。該溫度T 2較佳為50℃以上。又，該溫度T 2較佳為70℃以下，更佳為65℃以下。溫度若過低則會造成收縮應力變大，另一方面溫度若過高則PVA會自薄膜溶出至硼酸水溶液中、偏光度降低。然後，於前述溫度範圍，進行單軸拉伸至拉伸倍率成為1.3～1.8倍且總拉伸倍率成為4～6倍。於第2交聯步驟中的拉伸倍率較佳為1.4倍以上，同樣較佳為1.7倍以下。又，總拉伸倍率較佳為4.1倍以上，同樣較佳為5.9倍以下。也就是說，於高溫的包含硼酸之水溶液中一邊以比較高的倍率拉伸一邊進行硼酸交聯反應，其結果，在接下來的第3交聯拉伸步驟中能防止PVA自薄膜溶出至硼酸水溶液中、破裂。 In the second cross-linking and stretching step, the temperature T 2 of the aqueous solution containing boric acid is higher than the temperature T 1 in the first cross-linking and stretching step and lower than 75°C. The temperature T 2 is preferably 50°C or higher. In addition, the temperature T 2 is preferably 70°C or lower, more preferably 65°C or lower. When the temperature is too low, the shrinkage stress increases, and on the other hand, when the temperature is too high, PVA is eluted from the film into the boric acid aqueous solution, and the degree of polarization decreases. Then, in the aforementioned temperature range, uniaxial stretching is performed until the stretching ratio becomes 1.3 to 1.8 times and the total stretching ratio becomes 4 to 6 times. The draw ratio in the second crosslinking step is preferably 1.4 times or more, and also preferably 1.7 times or less. Moreover, the total draw ratio is preferably 4.1 times or more, and likewise preferably 5.9 times or less. That is, the boric acid cross-linking reaction is carried out while stretching at a relatively high ratio in a high-temperature aqueous solution containing boric acid. As a result, the elution of PVA from the film to boric acid can be prevented in the subsequent third cross-linking stretching step. In aqueous solution, rupture.

接下來，在第3交聯拉伸步驟中，係在包含1～5質量%的硼酸且溫度T 3高於第2交聯拉伸步驟的溫度T 2且為75℃以下之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為4.5～7倍。所使用的包含硼酸之水溶液的組成可使用與第1交聯拉伸步驟所使用之範圍相同者。另外，可以是如圖1所示，以能設定溫度T 2與溫度T 3之程度在1個槽內設置隔板等來進行第2交聯拉伸步驟與第3交聯拉伸步驟，也可以是如圖3所示，在分別的槽中進行第2交聯拉伸步驟與第3交聯拉伸步驟。 Next, in the third cross-linking and stretching step, it is carried out in an aqueous solution containing 1 to 5 mass % of boric acid and having a temperature T 3 higher than the temperature T 2 of the second cross-linking and stretching step and 75°C or lower. The stretching ratio in this step is uniaxially stretched to be 1.1 to 1.3 times, and the total stretching ratio is 4.5 to 7 times. The composition of the aqueous solution containing boric acid to be used can be used in the same range as that used in the first crosslinking and stretching step. In addition, as shown in FIG. 1 , the second crosslinking stretching step and the third crosslinking stretching step may be performed by installing a separator or the like in one tank to such an extent that the temperature T2 and the temperature T3 can be set. As shown in FIG. 3 , the second crosslinking and stretching step and the third crosslinking and stretching step may be performed in separate tanks.

於第3交聯拉伸步驟中，包含硼酸的水溶液之溫度T 3高於第2交聯拉伸步驟的溫度T 2且為75℃以下。也就是說，溫度T 1、T 2及T 3滿足以下的式(2)。 T 1＜T 2＜T 3≦75    (2) In the third cross-linking and stretching step, the temperature T 3 of the aqueous solution containing boric acid is higher than the temperature T 2 in the second cross-linking and stretching step and is 75° C. or lower. That is, the temperatures T 1 , T 2 and T 3 satisfy the following formula (2). T 1 <T 2 <T 3 ≦75 (2)

由後述的實施例與比較例的對比可知，在溫度T 2與溫度T 3為相同溫度之不滿足式(2)的比較例1～3中，所得到的偏光薄膜之收縮應力的降低不充分。相對於此，在溫度T 1為32℃、溫度T 2為約61℃、溫度T 3為約64℃之滿足式(2)的實施例1～3中，則明顯能製造維持著優良的偏光性能且另一方面收縮應力小之偏光薄膜。因此，本發明之製造方法中，滿足上述式(2)是重要的。 From the comparison of Examples and Comparative Examples described later, in Comparative Examples 1 to 3 that did not satisfy the formula (2), in which the temperature T 2 and the temperature T 3 were the same temperature, the reduction of the shrinkage stress of the obtained polarizing film was insufficient. . On the other hand, in Examples 1 to 3 satisfying the formula (2) in which the temperature T 1 is 32° C., the temperature T 2 is about 61° C., and the temperature T 3 is about 64° C., it is clear that excellent polarized light can be produced and maintained. performance and on the other hand a polarizing film with low shrinkage stress. Therefore, in the production method of the present invention, it is important to satisfy the above formula (2).

該溫度T 3較佳為55℃以上，更佳為58℃以上。又，該溫度T 3較佳為75℃以下，更佳為72℃以下。溫度若過低則會造成收縮應力變大，另一方面溫度若過高則PVA會自薄膜溶出至包含硼酸的水溶液中、偏光度降低。然後，於前述溫度範圍，進行單軸拉伸至拉伸倍率成為1.1～1.3倍且總拉伸倍率成為4.5～7倍。於第3交聯拉伸步驟拉伸之薄膜，在高溫的包含硼酸之水溶液中一邊以較高的倍率拉伸一邊進行硼酸交聯反應，能防止PVA自薄膜溶出至硼酸水溶液中、破裂。 The temperature T 3 is preferably 55°C or higher, more preferably 58°C or higher. In addition, the temperature T 3 is preferably 75°C or lower, more preferably 72°C or lower. When the temperature is too low, the shrinkage stress increases, and on the other hand, when the temperature is too high, PVA is eluted from the film into the aqueous solution containing boric acid, and the degree of polarization decreases. Then, in the aforementioned temperature range, uniaxial stretching is performed until the stretching ratio becomes 1.1 to 1.3 times and the total stretching ratio becomes 4.5 to 7 times. The film stretched in the third cross-linking stretching step is stretched in a high-temperature boric acid-containing aqueous solution while the boric acid cross-linking reaction is performed, which can prevent the PVA from being eluted from the film into the boric acid aqueous solution and cracking.

作為上述T 2及T 3，滿足下述式(3)及(4)為較佳的實施態樣。 50≦T 2≦65      (3) 55≦T 3≦75      (4) As the above-mentioned T 2 and T 3 , it is a preferable embodiment that the following formulae (3) and (4) are satisfied. 50≦T 2 ≦65 (3) 55≦T 3 ≦75 (4)

本發明之製造方法中，在前述第3交聯拉伸步驟之後進行第4交聯拉伸步驟為較佳的實施態樣，於前述第4交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 4之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為5～8倍，較佳為T 1、T 2、T 3及T 4滿足以下的式(5)。所使用的包含硼酸之水溶液的組成可使用與在第1交聯拉伸步驟所使用的範圍相同者。另外，可以是如圖2所示，以能設定溫度T 2、溫度T 3及溫度T 4之程度於1個槽內設置隔板等來進行第2交聯拉伸步驟、第3交聯拉伸步驟及第4交聯拉伸步驟，也可以是如圖4所示，在分別的槽中進行第2交聯拉伸步驟、第3交聯拉伸步驟及第4交聯拉伸步驟。 T 1＜T 2＜T 3≦T 4≦75  (5) In the production method of the present invention, it is a preferred embodiment that the fourth cross-linking and stretching step is performed after the third cross-linking and stretching step. % boric acid and an aqueous solution at a temperature of T 4 , perform uniaxial stretching until the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 5 to 8 times, preferably T 1 , T 2 , T 3 and T 4 satisfy the following formula (5). The composition of the aqueous solution containing boric acid to be used may be the same as the range used in the first crosslinking and stretching step. In addition, as shown in FIG. 2 , the second cross-linking stretching step and the third cross-linking stretching step may be performed by providing a separator or the like in one tank to such an extent that the temperature T 2 , the temperature T 3 , and the temperature T 4 can be set. In the stretching step and the fourth cross-linking stretching step, as shown in FIG. 4 , the second cross-linking and stretching step, the third cross-linking and stretching step, and the fourth cross-linking and stretching step may be performed in separate tanks. T 1 <T 2 <T 3 ≦T 4 ≦75 (5)

於第4交聯拉伸步驟中，包含硼酸之水溶液的溫度T 4較佳為第3交聯拉伸步驟的溫度T 3以上且為75℃以下。與第3交聯拉伸步驟的溫度T 3相同之溫度也沒關係。該溫度T 4較佳為60℃以上，更佳為62℃以上。又，該溫度T 4更佳為74℃以下。若溫度過低則會造成收縮應力變大，另一方面溫度若過高則PVA會自薄膜溶出至包含硼酸的水溶液中、偏光度降低。然後，於前述溫度範圍，進行單軸拉伸至成為1.1～1.3倍且總拉伸倍率成為5～8倍。於第4交聯拉伸步驟拉伸之薄膜，係於高溫的包含硼酸之水溶液中一邊以比較高的倍率拉伸一邊進行硼酸交聯反應，能防止PVA自薄膜溶出至包含硼酸的水溶液中、破裂。 In the fourth crosslinking and stretching step, the temperature T4 of the aqueous solution containing boric acid is preferably equal to or higher than the temperature T3 in the third crosslinking and stretching step and 75°C or less. It does not matter if it is the same temperature as the temperature T3 in the third crosslinking and stretching step. The temperature T 4 is preferably 60°C or higher, more preferably 62°C or higher. Moreover, it is more preferable that this temperature T4 is 74 degrees C or less. When the temperature is too low, the shrinkage stress increases, and on the other hand, when the temperature is too high, PVA is eluted from the film into the aqueous solution containing boric acid, and the degree of polarization decreases. Then, in the aforementioned temperature range, uniaxial stretching is performed until it becomes 1.1 to 1.3 times and the total stretching ratio becomes 5 to 8 times. The film stretched in the fourth cross-linking and stretching step is stretched in a high-temperature aqueous solution containing boric acid while being stretched at a relatively high ratio to undergo a cross-linking reaction with boric acid, which can prevent PVA from being eluted from the film into the aqueous solution containing boric acid, rupture.

作為上述T 4，滿足下述式(6)為較佳的實施態樣。 60≦T 4≦75      (6) As the above-mentioned T 4 , it is a preferable embodiment that the following formula (6) is satisfied. 60≦T 4 ≦75 (6)

於第4交聯拉伸步驟，最大拉伸應力較佳為10N/mm 2以下。此處，最大拉伸應力係第4交聯拉伸步驟中，施加在接鄰的輥間之拉伸應力除以原料PVA薄膜的截面積之值。藉由降低最大拉伸應力，可得到收縮應力小的偏光薄膜。最大拉伸應力較佳為8N/mm 2以下，更佳為5N/mm 2以下，再更佳為4N/mm 2以下。而通常最大拉伸應力為1N/mm 2以上。 In the fourth crosslinking and stretching step, the maximum tensile stress is preferably 10 N/mm 2 or less. Here, the maximum tensile stress is a value obtained by dividing the tensile stress applied between adjacent rolls by the cross-sectional area of the raw material PVA film in the fourth crosslinking and stretching step. By reducing the maximum tensile stress, a polarizing film with a small shrinkage stress can be obtained. The maximum tensile stress is preferably 8 N/mm 2 or less, more preferably 5 N/mm 2 or less, and still more preferably 4 N/mm 2 or less. On the other hand, the maximum tensile stress is usually 1 N/mm 2 or more.

於前述第1～4交聯拉伸步驟，在單軸拉伸PVA薄膜之情形，可以在第1～4交聯拉伸步驟中之硼酸水溶液中使用具備相互平行的複數個輥之拉伸裝置，藉由改變各輥間的圓周速率來進行。In the above-mentioned 1st to 4th crosslinking and stretching steps, in the case of uniaxially stretching the PVA film, a stretching device having a plurality of parallel rolls can be used in the boric acid aqueous solution in the 1st to 4th crosslinking and stretching steps. , by changing the peripheral speed between the rollers.

在前述第3交聯拉伸步驟或前述第4交聯拉伸步驟之後，較佳供給至洗淨步驟。於洗淨步驟中，係將薄膜表面不必要的藥品類或雜質除去，調節最終得到的偏光薄膜之光學性能。洗淨步驟能藉由將PVA薄膜浸漬於洗淨浴、將洗淨液散布至PVA薄膜上來進行。作為洗淨液能使用水，但其也能含有碘化鉀。在含有碘化鉀之情形能調整偏光薄膜之色調。碘化鉀的含量較佳為0.1～10質量%。洗淨液的溫度通常為10～40℃，較佳為15～30℃。洗淨浴使用複數槽而不是1槽也沒關係。又，在使用複數槽之情形的各槽中的洗淨液之組成能按照目的來調整。It is preferable to supply to a washing|cleaning process after the said 3rd crosslinking and stretching process or the said 4th crosslinking and stretching process. In the cleaning step, unnecessary chemicals or impurities are removed from the surface of the film to adjust the optical properties of the final polarizing film. The cleaning step can be performed by immersing the PVA film in a cleaning bath and spreading the cleaning solution on the PVA film. As the cleaning solution, water can be used, but it can also contain potassium iodide. In the case of containing potassium iodide, the color tone of the polarizing film can be adjusted. The content of potassium iodide is preferably 0.1 to 10% by mass. The temperature of the cleaning solution is usually 10 to 40°C, preferably 15 to 30°C. It doesn't matter if you use multiple tanks instead of one for the cleaning bath. In addition, when a plurality of tanks are used, the composition of the cleaning liquid in each tank can be adjusted according to the purpose.

前述洗淨步驟再接下去，較佳供給至乾燥步驟。於乾燥步驟的溫度沒有特別限制，較佳為30～150℃，更佳為50～130℃。藉由以上述範圍內的溫度乾燥容易得到尺寸穩定性優良的偏光薄膜。The aforementioned washing step is continued, and it is preferably supplied to the drying step. The temperature in the drying step is not particularly limited, but is preferably 30 to 150°C, more preferably 50 to 130°C. A polarizing film excellent in dimensional stability can be easily obtained by drying at a temperature within the above range.

本發明所得到之偏光薄膜之厚度較佳為1～30μm。在厚度小於1μm之情形有時以高速生產是有困難的，更佳為3μm以上。另一方面，在厚度大於30μm之情形，會有拉伸加工時的拉伸張力變高而裝置損壞的情形，更理想為25μm以下。此處所說的厚度，在多層薄膜之情形中係指PVA層的厚度。The thickness of the polarizing film obtained by the present invention is preferably 1-30 μm. When the thickness is less than 1 μm, it may be difficult to produce at high speed, and it is more preferably 3 μm or more. On the other hand, when the thickness is larger than 30 μm, the stretching tension at the time of drawing processing may become high and the device may be damaged, and it is more preferably 25 μm or less. The thickness referred to here, in the case of the multilayer film, refers to the thickness of the PVA layer.

在所得到的偏光薄膜為PVA的單層薄膜之情形，為了確保操作性，偏光薄膜之厚度較佳為5μm以上，更佳為7μm以上。另一方面，在由多層薄膜構成偏光薄膜之情形，可使偏光薄膜層的厚度為5μm以下，也可為3μm以下。多層薄膜中基材樹脂層的厚度通常為10～250μm。When the obtained polarizing film is a single-layer film of PVA, in order to ensure handleability, the thickness of the polarizing film is preferably 5 μm or more, more preferably 7 μm or more. On the other hand, when the polarizing film is composed of a multilayer film, the thickness of the polarizing film layer may be 5 μm or less, or 3 μm or less. The thickness of the base resin layer in the multilayer film is usually 10 to 250 μm.

本發明所得到的偏光薄膜之單體透光率較佳為42～45%。在單體透光率小於42%之情形，液晶顯示器的亮度會降低。單體透光率更佳為42.5%以上。另一方面，於單體透光率大於45%之偏光薄膜，會難以得到高偏光度的偏光薄膜，單體透光率更佳為44.5%以下。又，本發明之偏光薄膜之偏光度較佳為99.80%以上。偏光度更佳為99.90%以上。The monomer light transmittance of the polarizing film obtained by the present invention is preferably 42-45%. When the light transmittance of the monomer is less than 42%, the brightness of the liquid crystal display will decrease. The single light transmittance is more preferably 42.5% or more. On the other hand, it is difficult to obtain a polarizing film with a high degree of polarization in a polarizing film with a single light transmittance greater than 45%, and the single light transmittance is preferably 44.5% or less. Moreover, the polarization degree of the polarizing film of the present invention is preferably 99.80% or more. The degree of polarization is more preferably 99.90% or more.

本發明所得到之偏光薄膜之收縮應力較佳為50N/mm 2以下。藉由收縮應力小，即使在高溫下使用之情形也會成為尺寸穩定性優良之物。收縮應力更佳為42N/mm 2以下，再更佳為38N/mm 2以下，特佳為35N/mm 2以下。此處收縮應力係指將作為試料的偏光薄膜固定，以80℃維持4小時時的張力除以試料的截面積之值。 The shrinkage stress of the polarizing film obtained by the present invention is preferably 50 N/mm 2 or less. Due to its small shrinkage stress, it has excellent dimensional stability even when used at high temperatures. The shrinkage stress is more preferably 42 N/mm 2 or less, still more preferably 38 N/mm 2 or less, and particularly preferably 35 N/mm 2 or less. Here, the shrinkage stress refers to the value obtained by dividing the tensile force when the polarizing film serving as the sample is fixed and maintained at 80° C. for 4 hours by the cross-sectional area of the sample.

而本發明所得到之偏光薄膜，「單體透光率為43.5%時的偏光度」較佳為99.80%以上，更佳為99.90%以上，再更佳為99.95%以上，特佳為99.98%以上。此值在偏光薄膜之單體透光率(T)不是43.5%之情形中係以假設其為43.5%之情形的偏光度來算出。In the polarizing film obtained by the present invention, the "polarization degree when the light transmittance of the monomer is 43.5%" is preferably 99.80% or more, more preferably 99.90% or more, still more preferably 99.95% or more, and particularly preferably 99.98% above. This value is calculated by assuming the polarization degree of the case where the light transmittance (T) of the polarizing film is not 43.5%.

「單體透光率為43.5%時的偏光度」之計算方法如下。首先，排除表面反射的透光率(T’)與單體透光率(T)之關係是以式(7)表示。此時，PVA的折射率設為1.5，表面的反射率設為4%。透光率(T’)與偏光度(V)與二色性比(R)的關係是以式(8)表示，將式(8)變形為式(9)。此處，二色性比(R)在單體透光率(T)不會大幅變動的範圍，例如在42～45%之範圍，幾乎不會因染料濃度而變動，故可當成常數處理。從而，測量單體透光率(T)及偏光度(V)後，再藉由使用該等之值解出式(7)及(8)即能將偏光膜的二色性比(R)當成常數來算出。由代入該R的式(9)與式(7)，可求取T=43.5(%)時的偏光度(V)。 T’=T/(1-0.04) 2(7) R={-ln[T’(1-V)]}/{-ln[T’(1+V)]}  (8) T’=[1-V] 1/(R-1)/[1+V] R/(R-1)(9) The calculation method of "degree of polarization at a single transmittance of 43.5%" is as follows. First, the relationship between the transmittance (T') excluding surface reflection and the transmittance (T) of the single body is expressed by the formula (7). At this time, the refractive index of PVA was set to 1.5, and the reflectance of the surface was set to 4%. The relationship between the light transmittance (T'), the degree of polarization (V), and the dichroic ratio (R) is represented by the formula (8), and the formula (8) is transformed into the formula (9). Here, the dichroic ratio (R) can be treated as a constant in the range where the light transmittance (T) of the monomer does not change greatly, for example, in the range of 42 to 45%, which hardly changes due to the dye concentration. Therefore, after measuring the light transmittance (T) and the degree of polarization (V) of the monomer, and then solving the equations (7) and (8) by using these values, the dichroic ratio (R) of the polarizing film can be calculated. Calculated as a constant. The degree of polarization (V) when T=43.5 (%) can be obtained from the equations (9) and (7) that are substituted into this R. T'=T/(1-0.04) 2 (7) R={-ln[T'(1-V)]}/{-ln[T'(1+V)]} (8) T'=[ 1-V] 1/(R-1) /[1+V] R/(R-1) (9)

本發明所得到之偏光薄膜，通常係將保護膜貼合在其兩面或一面上來作為偏光板使用。作為保護膜，可舉出光學上透明且具有機械強度者，具體來說可使用例如三醋酸纖維素(TAC)薄膜、醋酸･酪酸纖維素(CAB)薄膜、丙烯酸系薄膜、聚酯系薄膜等。又，作為用於貼合的黏著劑，可舉出PVA系黏著劑、胺基甲酸酯系黏著劑、或紫外線固化型黏著劑等。The polarizing film obtained by the present invention is usually used as a polarizing plate by sticking a protective film on both sides or one side thereof. Examples of the protective film include those that are optically transparent and have mechanical strength. Specifically, for example, triacetate cellulose (TAC) films, cellulose acetate butyrate (CAB) films, acrylic films, polyester films, etc. can be used. . Moreover, as an adhesive used for bonding, a PVA-type adhesive, a urethane-type adhesive, an ultraviolet curable adhesive, etc. are mentioned.

如此進行所得到的偏光板，能使用在高性能的液晶顯示器(LCD)。可提供明亮、偏光特性良好且即使在高溫條件下使用尺寸穩定性同樣優良之偏光板。因此，能適當地使用作為各種高性能LCD、特別是行動用途的LCD用之偏光板。 [實施例] The polarizing plate obtained in this way can be used in a high-performance liquid crystal display (LCD). It can provide a polarizing plate that is bright, has good polarization characteristics and has excellent dimensional stability even under high temperature conditions. Therefore, a polarizing plate for various high-performance LCDs, especially LCDs for mobile use, can be appropriately used. [Example]

以下，以實施例更具體地說明本發明，但本發明並受限於這些實施例。評價方法等係按照以下所示方法進行。Hereinafter, the present invention will be described more specifically with examples, but the present invention is not limited to these examples. The evaluation method etc. were performed according to the method shown below.

[偏光薄膜之光學性能] 從以下的實施例及比較例中所得到之偏光薄膜之寬度方向(TD方向)的中央部，採取偏光薄膜沿機械移動方向(MD方向)4cm、沿寬度方向(TD方向)1.5cm之長方形的測定樣品。對此測定樣品，使用附有積分球之分光光度計(日本分光股份有限公司製「V7100」)，依據JIS Z8722(物體色之測定方法)，進行C光源、2°視野的可見光範圍之發光因數校正後，再測定單體透光率及偏光度。藉由前述方法，算出單體透光率43.5%時的偏光度。 [Optical properties of polarizing films] From the center portion of the polarizing films obtained in the following Examples and Comparative Examples in the width direction (TD direction), a rectangular shape of 4 cm in the mechanical movement direction (MD direction) and 1.5 cm in the width direction (TD direction) of the polarizing film was taken. Assay samples. For this measurement sample, using a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation), according to JIS Z8722 (Method for Measuring Object Color), the luminous factor in the visible light range of C light source and 2° field of view was measured. After calibration, the light transmittance and polarization degree of the monomer were measured again. By the method described above, the degree of polarization when the light transmittance of a single element was 43.5% was calculated.

[偏光薄膜之收縮應力] 收縮應力係使用島津製作所製的附有恆溫槽之Autograph AG-X測定。測定係把以20℃/20%RH調濕18小時的偏光薄膜(長度方向15cm、寬度方向1.5cm)設置於夾頭(夾頭間隔5cm)，在開始拉伸的同時，開始將恆溫槽升溫至80℃。以1mm/min的速度拉伸偏光薄膜，在張力到達2N的時間點停止拉伸，測定在此狀態4小時後的張力。此時，由於軸(shaft)的熱膨脹會使夾頭間的距離改變，所以在夾頭貼上標線貼紙，以能使用影像式伸長計TR ViewX120S將夾頭間的距離僅修正黏貼在夾頭上的標線貼紙所移動之量的方式進行測定。其中，自4小時後的張力之測定值扣除初期張力2N，把所得之值作為偏光薄膜之收縮力，將該值除以樣品截面積之值定義為收縮應力(N/mm 2)。 [Shrinkage stress of polarizing film] The shrinkage stress was measured using an Autograph AG-X with a thermostatic bath manufactured by Shimadzu Corporation. The measurement system is to place a polarizing film (15 cm in the longitudinal direction, 1.5 cm in the width direction) on a chuck (the distance between the chucks is 5 cm) that has been conditioned for 18 hours at 20°C/20% RH, and at the same time as the stretching is started, the temperature of the thermostatic bath is started. to 80°C. The polarizing film was stretched at a speed of 1 mm/min, the stretching was stopped when the tension reached 2 N, and the tension after 4 hours in this state was measured. At this time, the distance between the chucks will change due to the thermal expansion of the shaft, so stick a marking sticker on the chuck, so that the distance between the chucks can only be corrected and pasted on the chuck using the video extensometer TR ViewX120S measured by the amount the reticle sticker moves. The initial tension 2N was deducted from the measured value of tension after 4 hours, and the obtained value was taken as the shrinkage force of the polarizing film, and the value divided by the cross-sectional area of the sample was defined as the shrinkage stress (N/mm 2 ).

[於第4交聯拉伸步驟之最大拉伸應力] 以下的實施例及比較例中，預先求出供給至偏光薄膜之製造的PVA薄膜(未加工的原材薄膜)之薄膜寬度(mm)與薄膜厚度(mm)，將其相乘算出截面積(mm 2)。接下來，於製造偏光薄膜時的第4交聯拉伸步驟中，以張力計測定施加在接鄰的輥間之拉伸應力(N)。將所得到的拉伸應力(N)除以上述求得的截面積(mm 2)，藉此求出第4交聯拉伸步驟中的最大拉伸應力(N/mm 2)。 [Maximum tensile stress in the fourth cross-linking and stretching step] In the following examples and comparative examples, the film width (mm) of the PVA film (unprocessed raw material film) supplied to the production of the polarizing film was determined in advance The cross-sectional area (mm 2 ) was calculated by multiplying the film thickness (mm). Next, in the 4th crosslinking and stretching process at the time of manufacturing a polarizing film, the tensile stress (N) applied between adjacent rolls was measured with a tensiometer. The maximum tensile stress (N/mm 2 ) in the fourth crosslinking and stretching step was obtained by dividing the obtained tensile stress (N) by the cross-sectional area (mm 2 ) obtained above.

[第1交聯拉伸步驟的硼酸水溶液之著色] 關於第1交聯拉伸步驟的硼酸水溶液之著色，採集20cc開始連續拉伸1小時後的硼酸水溶液至30cc的螺旋管中並以目視確認，與連續拉伸前的硼酸水溶液相比，把顏色沒有變化之情形評為○，把顏色發生變化而有碘著色之情形評為×。 [Coloring of boric acid aqueous solution in the first cross-linking stretching step] Regarding the coloring of the boric acid aqueous solution in the first cross-linking stretching step, 20 cc of the boric acid aqueous solution after starting continuous stretching for 1 hour was collected into a 30 cc spiral tube and visually confirmed. Compared with the boric acid aqueous solution before continuous stretching, the color was changed The case where there was no change was rated as ○, and the case where the color was changed and iodine was colored was rated as ×.

[實施例1] 使用包含100質量份的PVA(醋酸乙烯酯聚合物的皂化物、聚合度2400、皂化度99.9莫耳%、乙烯改質2.0莫耳%)、10質量份的作為塑化劑之甘油、0.1質量份的作為界面活性劑之聚氧乙烯月桂基醚硫酸鈉及水之製膜原液，藉由流延製膜，得到厚度45μm的PVA薄膜之卷。對此PVA薄膜，依序進行膨潤步驟、染色步驟、第1交聯拉伸步驟、第2交聯拉伸步驟、第3交聯拉伸步驟、第4交聯拉伸步驟、洗淨步驟及乾燥步驟，藉此製造偏光薄膜。偏光薄膜製造裝置之模式圖示於圖1～4。 [Example 1] 100 parts by mass of PVA (saponification of vinyl acetate polymer, degree of polymerization 2400, degree of saponification 99.9 mol %, ethylene modification 2.0 mol %), 10 parts by mass of glycerin as a plasticizer, 0.1 mass Part of the film-forming stock solution of sodium polyoxyethylene lauryl ether sulfate and water as surfactants was used to form a film by casting to obtain a roll of PVA film with a thickness of 45 μm. For this PVA film, a swelling step, a dyeing step, a first cross-linking stretching step, a second cross-linking and stretching step, a third cross-linking and stretching step, a fourth cross-linking and stretching step, a washing step and A drying step, whereby a polarizing film is produced. Schematic diagrams of the polarizing film manufacturing apparatus are shown in FIGS. 1 to 4 .

具體來說係如下地製造偏光薄膜。首先，於膨潤步驟中，將上述PVA薄膜浸漬在溫度30℃的水中1.6分鐘，同時於長度方向(MD)進行單軸拉伸至原本長度的2倍(第1階段拉伸)。接下來於染色步驟中，浸漬在包含0.06質量%的碘及1.4質量%的碘化鉀之溫度32℃的水溶液中2.3分鐘，同時於長度方向(MD)進行單軸拉伸至原本長度的2.5倍(第2階段拉伸)。接下來於第1交聯拉伸步驟中，浸漬在含有濃度2.6質量%的硼酸且溫度32℃之水溶液2分鐘，同時於長度方向(MD)進行單軸拉伸至原本長度的3倍(第3階段拉伸)。接下來，於第2交聯拉伸步驟中，浸漬在含有濃度2.8質量%的硼酸及5質量%的碘化鉀且溫度60.6℃的水溶液中，同時於長度方向(MD)進行單軸拉伸至原本長度的4.46倍(第4階段拉伸)。接下來，於第3交聯拉伸步驟中，浸漬在含有濃度2.8質量%的硼酸及5質量%的碘化鉀且溫度63.6℃的水溶液中，同時於長度方向(MD)進行單軸拉伸至原本長度的5.27倍(第5階段拉伸)。接下來，於第4交聯拉伸步驟中，浸漬在含有濃度2.8質量%的硼酸及5質量%的碘化鉀且溫度64.6℃的水溶液中，同時於長度方向(MD)進行單軸拉伸至原本長度的6倍(第6階段拉伸)。於第4交聯拉伸步驟中的最大拉伸應力為1.4N/mm 2。接下來於洗淨步驟中，藉由浸漬在含有濃度1.5質量%的硼酸及5質量%的碘化鉀且溫度22℃的水溶液中10秒鐘而洗淨薄膜。接下來於乾燥步驟中，藉由以80℃的乾燥機進行乾燥120秒鐘，而製造厚度14.0μm的偏光薄膜。將各交聯拉伸步驟之條件與於第4交聯拉伸步驟中的最大拉伸應力之值示於表1，將評價結果示於表2。 Specifically, the polarizing film is produced as follows. First, in the swelling step, the PVA film was dipped in water at a temperature of 30° C. for 1.6 minutes and uniaxially stretched in the longitudinal direction (MD) to twice the original length (first-stage stretching). Next, in the dyeing step, it was immersed in an aqueous solution containing 0.06 mass % of iodine and 1.4 mass % of potassium iodide at a temperature of 32° C. for 2.3 minutes, and uniaxially stretched in the longitudinal direction (MD) to 2.5 times the original length ( Stage 2 stretching). Next, in the first cross-linking and stretching step, it was immersed in an aqueous solution containing boric acid with a concentration of 2.6 mass % and at a temperature of 32° C. for 2 minutes, and uniaxially stretched in the longitudinal direction (MD) to three times the original length (the first 3-stage stretch). Next, in the second cross-linking and stretching step, uniaxial stretching was performed in the longitudinal direction (MD) while being immersed in an aqueous solution containing boric acid at a concentration of 2.8 mass % and potassium iodide at a concentration of 5 mass % at a temperature of 60.6° C. 4.46 times the length (stage 4 stretch). Next, in the third cross-linking and stretching step, uniaxial stretching was performed in the longitudinal direction (MD) while being immersed in an aqueous solution containing 2.8 mass % of boric acid and 5 mass % of potassium iodide at a temperature of 63.6° C. 5.27 times the length (Stage 5 stretch). Next, in the fourth cross-linking stretching step, uniaxial stretching was performed in the longitudinal direction (MD) while being immersed in an aqueous solution containing 2.8 mass % of boric acid and 5 mass % of potassium iodide at a temperature of 64.6° C. 6 times the length (stage 6 stretch). The maximum tensile stress in the fourth cross-linking stretching step was 1.4 N/mm 2 . Next, in the washing step, the film was washed by immersion in an aqueous solution containing boric acid having a concentration of 1.5 mass % and potassium iodide of 5 mass % and a temperature of 22° C. for 10 seconds. Next, in the drying step, a polarizing film having a thickness of 14.0 μm was produced by drying with a dryer at 80° C. for 120 seconds. Table 1 shows the conditions of each crosslinking and stretching step and the value of the maximum tensile stress in the fourth crosslinking and stretching step, and Table 2 shows the evaluation results.

[實施例2～3、比較例1～3] 除了如表1所示地變更第1交聯拉伸步驟中包含硼酸的水溶液之溫度、第2交聯拉伸步驟中包含硼酸的水溶液之溫度與總拉伸倍率、第3交聯拉伸步驟中包含硼酸的水溶液之溫度與總拉伸倍率、第4交聯拉伸步驟中包含硼酸的水溶液之溫度與總拉伸倍率以外，與實施例1同樣地製造偏光薄膜。將各交聯拉伸步驟的條件與於第4交聯拉伸步驟中的最大拉伸應力之值示於表1，將評價結果示於表2。又，總拉伸倍率為6.6倍之實施例3與比較例2的評價結果示於表3。另外，表2中的實施例1、2及比較例1、3都是總拉伸倍率為6倍的例子。 [Examples 2 to 3, Comparative Examples 1 to 3] Except for changing the temperature of the aqueous solution containing boric acid in the first cross-linking stretching step, the temperature and total stretching ratio of the aqueous solution containing boric acid in the second cross-linking stretching step, and the third cross-linking stretching step as shown in Table 1 A polarizing film was produced in the same manner as in Example 1, except for the temperature of the aqueous solution containing boric acid and the total stretching ratio, and the temperature and total stretching ratio of the aqueous solution containing boric acid in the fourth cross-linking stretching step. Table 1 shows the conditions of each crosslinking and stretching step and the value of the maximum tensile stress in the fourth crosslinking and stretching step, and Table 2 shows the evaluation results. In addition, Table 3 shows the evaluation results of Example 3 and Comparative Example 2 in which the total draw ratio is 6.6 times. In addition, Examples 1 and 2 and Comparative Examples 1 and 3 in Table 2 are all examples in which the total draw ratio is 6 times.

表1 　 第1交聯拉伸步驟 第2交聯拉伸步驟 第3交聯拉伸步驟 第4交聯拉伸步驟 水溶液 溫度T 1（℃） 拉伸 倍率 （倍） 總拉伸 倍率 （倍） 水溶液 溫度T 2（℃） 拉伸 倍率 （倍） 總拉伸 倍率 （倍） 水溶液 溫度T 3（℃） 拉伸 倍率 （倍） 總拉伸 倍率 （倍） 水溶液 溫度T 4（℃） 拉伸 倍率 （倍） 總拉伸 倍率 （倍） 最大拉伸 應力 (N/mm 2) 實施例1 32 1.19 3 60.6 1.49 4.46 63.6 1.18 5.27 64.6 1.14 6 1.4 實施例2 32 1.19 3 60.6 1.49 4.46 63.6 1.18 5.27 63.6 1.14 6 1.7 實施例3 32 1.19 3 61 1.53 4.6 64 1.22 5.61 64 1.18 6.6 3.5 比較例1 32 1.19 3 60.6 1.49 4.46 60.6 1.18 5.27 60.6 1.14 6 3.3 比較例2 32 1.19 3 61 1.53 4.6 61 1.22 5.61 61 1.18 6.6 5.3 比較例3 50 1.19 3 60.3 1.49 4.46 60.3 1.18 5.27 60.3 1.14 6 2.5 Table 1 1st cross-linking stretching step Second cross-linking stretching step The third cross-linking stretching step The 4th cross-linking stretching step Aqueous solution temperature T 1 (℃) Stretching ratio (times) Total stretch ratio (times) Aqueous solution temperature T 2 (℃) Stretching ratio (times) Total stretch ratio (times) Aqueous solution temperature T 3 (℃) Stretching ratio (times) Total stretch ratio (times) Aqueous solution temperature T 4 (℃) Stretching ratio (times) Total stretch ratio (times) Maximum tensile stress (N/mm 2 ) Example 1 32 1.19 3 60.6 1.49 4.46 63.6 1.18 5.27 64.6 1.14 6 1.4 Example 2 32 1.19 3 60.6 1.49 4.46 63.6 1.18 5.27 63.6 1.14 6 1.7 Example 3 32 1.19 3 61 1.53 4.6 64 1.22 5.61 64 1.18 6.6 3.5 Comparative Example 1 32 1.19 3 60.6 1.49 4.46 60.6 1.18 5.27 60.6 1.14 6 3.3 Comparative Example 2 32 1.19 3 61 1.53 4.6 61 1.22 5.61 61 1.18 6.6 5.3 Comparative Example 3 50 1.19 3 60.3 1.49 4.46 60.3 1.18 5.27 60.3 1.14 6 2.5

表2   偏光薄膜 厚度 (μm) 單體透光率 (%) 偏光度 (%) 偏光度 *1) (%) 收縮應力 (N/mm 2) 第一交聯拉伸步驟的 硼酸水溶液之染色 實施例1 15.7 44.06 99.859 99.980 34.8 ○ 實施例2 16.7 43.96 99.917 99.985 40.2 ○ 比較例1 16.2 43.89 99.958 99.991 44.8 ○ 比較例3 17.3 43.80 99.965 99.988 50.6 × ○：1小時後無變化、×：1小時後有碘染色 *1) 單體透光率為43.5%時的偏光度 Table 2 Polarizing film thickness (μm) Monomer light transmittance (%) Polarization (%) Polarization*1) (%) Shrinkage stress (N/mm 2 ) Dyeing of boric acid aqueous solution in the first cross-linking stretching step Example 1 15.7 44.06 99.859 99.980 34.8 ○ Example 2 16.7 43.96 99.917 99.985 40.2 ○ Comparative Example 1 16.2 43.89 99.958 99.991 44.8 ○ Comparative Example 3 17.3 43.80 99.965 99.988 50.6 × ○: No change after 1 hour, ×: Iodine staining after 1 hour *1) The degree of polarization when the transmittance of a single unit is 43.5%

表3   偏光薄膜 厚度 (μm) 單體透光率 (%) 偏光度 (%) 偏光度 *1) (%) 收縮應力 (N/mm 2) 第一交聯拉伸步驟的 硼酸水溶液之染色 實施例3 14 44.06 99.925 99.991 49.8 ○ 比較例2 14 44.00 99.963 99.995 59 ○ ○：1小時後無變化、×：1小時後有碘染色 *1) 單體透光率為43.5%時的偏光度 table 3 Polarizing film thickness (μm) Monomer light transmittance (%) Polarization (%) Polarization*1) (%) Shrinkage stress (N/mm 2 ) Dyeing of boric acid aqueous solution in the first cross-linking stretching step Example 3 14 44.06 99.925 99.991 49.8 ○ Comparative Example 2 14 44.00 99.963 99.995 59 ○ ○: No change after 1 hour, ×: Iodine staining after 1 hour *1) The degree of polarization when the transmittance of a single unit is 43.5%

1:偏光薄膜製造裝置 2:PVA薄膜卷 3:膨潤步驟 4:染色步驟 5:第1交聯拉伸步驟 6:第2交聯拉伸步驟 7:第3交聯拉伸步驟 8:第4交聯拉伸步驟 9:洗淨步驟 10:乾燥步驟 1: polarizing film manufacturing device 2: PVA film roll 3: swelling step 4: Dyeing step 5: The first cross-linking stretching step 6: Second cross-linking stretching step 7: The third cross-linking stretching step 8: Fourth cross-linking stretching step 9: Cleaning step 10: Drying step

圖1為顯示出偏光薄膜製造裝置的一範例之模式圖。 圖2為顯示出偏光薄膜製造裝置的另一個範例之模式圖。 圖3為顯示出偏光薄膜製造裝置的另一個範例之模式圖。 圖4為顯示出偏光薄膜製造裝置的另一個範例之模式圖。 FIG. 1 is a schematic diagram showing an example of a polarizing film manufacturing apparatus. FIG. 2 is a schematic view showing another example of a polarizing film manufacturing apparatus. FIG. 3 is a schematic view showing another example of a polarizing film manufacturing apparatus. FIG. 4 is a schematic view showing another example of the polarizing film manufacturing apparatus.

無。none.

Claims (7)

一種偏光薄膜之製造方法，其係對聚乙烯醇薄膜至少按照以下順序施以膨潤步驟、染色步驟、第1交聯拉伸步驟、第2交聯拉伸步驟、第3交聯拉伸步驟，其中 該聚乙烯醇薄膜之厚度為5～100μm， 該聚乙烯醇薄膜中所包含的聚乙烯醇之平均聚合度為2000～4000， 於該膨潤步驟中，浸漬於10～50℃的水中使該聚乙烯醇薄膜膨潤， 於該染色步驟中，浸漬於合計包含0.5～3質量%的碘及碘化鉀之10～50℃的水溶液中，使碘系二色性染料含浸於該聚乙烯醇薄膜中，並進行單軸拉伸至總拉伸倍率成為2～3倍， 於該第1交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 1的水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為2.5～3.5倍， 於該第2交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 2的水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.3～1.8倍且總拉伸倍率成為4～6倍， 於該第3交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 3的水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為4.5～7倍， 該T 1、T 2及T 3滿足以下的式(1)及(2)： 25≦T 1≦45       (1) T 1＜T 2＜T 3≦75    (2)。 A method for producing a polarizing film, which comprises subjecting a polyvinyl alcohol film to at least a swelling step, a dyeing step, a first cross-linking and stretching step, a second cross-linking and stretching step, and a third cross-linking and stretching step in the following order, The thickness of the polyvinyl alcohol film is 5-100 μm, and the average degree of polymerization of the polyvinyl alcohol contained in the polyvinyl alcohol film is 2000-4000. In the swelling step, immersion in water at 10-50° C. The polyvinyl alcohol film is swollen, and in the dyeing step, the polyvinyl alcohol film is impregnated with an iodine-based dichroic dye by being immersed in an aqueous solution at 10 to 50° C. containing 0.5 to 3 mass % of iodine and potassium iodide in total. and performing uniaxial stretching until the total stretching ratio becomes 2 to 3 times, and in the first crosslinking stretching step, uniaxial stretching is performed in an aqueous solution containing 1 to 5 mass % of boric acid and at a temperature of T1 The stretching ratio in this step is 1.1 to 1.3 times and the total stretching ratio is 2.5 to 3.5 times. In this second cross-linking stretching step, the aqueous solution containing 1 to 5 mass % of boric acid and having a temperature T 2 In the third cross-linking stretching step, uniaxial stretching is performed until the stretching ratio in this step becomes 1.3 to 1.8 times and the total stretching ratio becomes 4 to 6 times, and in the third cross-linking stretching step, 1 to 5 mass % of In the aqueous solution of boric acid and temperature T 3 , uniaxial stretching is performed until the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 4.5 to 7 times, and the T 1 , T 2 and T 3 satisfy the following Formulas (1) and (2): 25≦T 1 ≦45 (1) T 1 <T 2 <T 3 ≦75 (2). 如請求項1之偏光薄膜之製造方法，其中該T 2及T 3滿足以下的式(3)及(4)： 50≦T 2≦65      (3) 55≦T 3≦75      (4)。 The manufacturing method of the polarizing film according to claim 1, wherein the T 2 and T 3 satisfy the following formulae (3) and (4): 50≦T 2 ≦65 (3) 55≦T 3 ≦75 (4). 如請求項1或2之偏光薄膜之製造方法，其中進一步在該第3交聯拉伸步驟之後進行第4交聯拉伸步驟，於該第4交聯拉伸步驟中，在包含1～5質量%的硼酸且溫度T 4之水溶液中，進行單軸拉伸至該步驟中的拉伸倍率成為1.1～1.3倍且總拉伸倍率成為5～8倍，T 1、T 2、T 3及T 4滿足以下的式(5)： T 1＜T 2＜T 3≦T 4≦75      (5)。 The method for producing a polarizing film according to claim 1 or 2, wherein a fourth cross-linking and stretching step is performed after the third cross-linking and stretching step, and in the fourth cross-linking and stretching step, 1 to 5 Mass % boric acid in an aqueous solution at a temperature of T 4 , uniaxially stretched until the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 5 to 8 times, T 1 , T 2 , T 3 and T 4 satisfies the following formula (5): T 1 <T 2 <T 3 ≦T 4 ≦75 (5). 如請求項3之偏光薄膜之製造方法，其中該T 4滿足以下的式(6)： 60≦T 4≦75      (6)。 The manufacturing method of the polarizing film of claim 3, wherein the T 4 satisfies the following formula (6): 60≦T 4 ≦75 (6). 如請求項3之偏光薄膜之製造方法，其中於該第4交聯拉伸步驟中，最大拉伸應力為10N/mm 2以下。 The method for producing a polarizing film according to claim 3, wherein in the fourth cross-linking and stretching step, the maximum tensile stress is 10 N/mm 2 or less. 如請求項1或2之偏光薄膜之製造方法，其係得到收縮應力為50N/mm 2以下之偏光薄膜。 According to the manufacturing method of the polarizing film of claim 1 or 2, a polarizing film having a shrinkage stress of 50 N/mm 2 or less is obtained. 如請求項1或2之偏光薄膜之製造方法，其係得到單體透光率為43.5%時的偏光度為99.80%以上之偏光薄膜。According to the manufacturing method of the polarizing film of claim 1 or 2, it is to obtain a polarizing film with a degree of polarization of 99.80% or more when the light transmittance of the monomer is 43.5%.
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