JP4128327B2 - Method for producing optical use film - Google Patents

Description

【００３２】
剥ぎ取り時のフィルム残留揮発分（塩化メチレン及びメタノール）：
湿量基準重量％
ドロー率：
支持体速度Ｖ１、剥離時のフィルム速度Ｖ２としたとき
（（Ｖ２−Ｖ１）／Ｖ１）×１００
剥ぎ取りロールクリアランス：
剥ぎ取りロール外周と支持体表面の最小距離
剥ぎ取りロールラップ角度：
ロール中心をセンターとしたときの、ロールにフィルムがかかっている部分の角度θ
キズ測定法：
１ｍ×５ｍサンプルにおける最大のキズ。
まずルーペ・顕微鏡で長さと幅を概略測定し、大きく強いキズを抽出し、電子顕微鏡あるいは光学顕微鏡で観察。キズの画面を画像処理し、面積を算出した。深さは電子顕微鏡、光干渉計でさらに詳細に測定して求めた。
偏光板適性：
得られたフィルムを偏光膜の両側に保護フィルムとして貼着して作製した偏光板を評価した。
ＬＣＤ適性：
ＬＣＤにフィルムを仮装着して評価した。
評価基準：
透過でキズが認識できない。透明性・ヘイズの低下及び白濁（表面が白っぽくなり、文字等のにじみが認められること）がない。光学特性を乱さない（ＬＣＤ表示時、キズを認識できない。画像に異常（色の変化、欠陥、輝点・暗点）が認められない。
【００３３】
４°の小ラップ角の場合、剥ぎ取りロールでスリップが生じスリキズの長さが増大（面積増）、またロール上でのシワの発生が認められた。
【００３４】
また、セルローストリアセテートフィルム（厚さ８０μｍ、及び４０μｍ）において、キズ（面積４４０〜５６０μｍ^２、深さ０．０５〜０．０８μｍ）のある面、あるいは多い面・強い面を、偏光板作製時、偏光膜側（ＰＶＡ側）にして貼り合わせたところ透過及び反射等の外観検査でキズは認められなかった。また、前記フィルムのキズ面に対して、アクリル系の樹脂で塗布を行った（樹脂層の厚み３〜４μｍ）ところ、やはり透過及び反射でキズは認められなかった。
【００３５】
【発明の効果】
本発明により、キズの限界大きさの明確化、剥ぎ取り時のフィルム剛性の確保及び剥ぎ取りテンション（ドロー率）の低減によるフィルムの幅変化の抑制、剥ぎ取りロールの位置の適正化によるネックイン形状部との接触防止、さらに剥ぎ取りロールのラップ角低減によるフィルムとの接触面積減により、前記微小スリキズを改善して高品質な光学用途にも用いることができる光学用フィルムが得られる。
【図面の簡単な説明】
【図１】 剥ぎ取りロールのラップ角を説明する側面図である。
【符号の説明】
１…フィルム
２…剥ぎ取りロール
θ…ラップ角[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical film, a method for producing the film by a solution casting method, and a polarizing plate on which the film is mounted.
[0002]
[Prior art]
In general, a part of films such as cellulose acetate, polycarbonate and cellophane used as optical films are produced by a solution casting method. In this solution casting method, a polymer solution film cast from a die is solidified while being supported and conveyed by a belt-type or drum-type support, and is peeled off from the support and dried.
[0003]
[Problems to be solved by the invention]
However, when the above-mentioned film is used for high-quality optical applications such as LCD, it has been found that an extremely fine scratch that has not been a problem in the past becomes a problem.
[0004]
An object of the present invention is to provide an optical film that can be used stably for high-quality optical applications such as LCDs and a method for producing the same.
[0005]
[Means for Solving the Problems]
Normally, scratches are generated by slipping between the film and the pass roll or the drive roll. In this case, the holding force is adjusted so that the speed of the film and the peripheral speed of the pass roll or drive roll are the same, but even if this operation is completely performed, minute scratches remain, and the scratches also have extremely uniform optical characteristics. It turned out that it becomes a problem as a required film for polarizing plates.
[0006]
As a countermeasure, peeling rolls and the temperature adjustment of the downstream several rolls, the surface roughness adjustment, change of the roll material (instead of metal roll, ceramic roll Teflon (introduction of such registered trademark) roll) was tried to improve by But that alone did not give enough results. Therefore, as a result of the pursuit of the cause of the occurrence of such minute scratches, the present inventor has found the following.
[0007]
That is, when the film is peeled off from the support after casting, the film is soft, so that neck-in occurs due to the tension at the time of peeling. At this time, when the change in the width of the film occurs on the roll surface, a slip occurs and a minute scratch is generated. Usually, the change in the width of the film occurs in a state where the film is a soft film, and in the case of solution film formation, the change is most prominent at the stripped portion which is a roll conveyance portion where the solvent is the most contained. Therefore, this scratch is most likely to occur on the peeling roll, and in this case, the scratch is usually found on the surface of the film opposite to the support that is in contact with the peeling roll.
[0008]
Therefore, as a countermeasure, the present inventor increased the volatilization rate of the solvent before being peeled off from the support so that the residual volatile content is not more than a certain amount, and the draw rate at the time of peeling is not more than a certain value, and the peeling tension is set. It has been found that if it is reduced, it is possible to produce a film that can be used for high-quality optical applications such as a polarizing plate by suppressing the generation of the fine scratches. Furthermore, it has been found that it is also effective to separate the peeling roll from the support so that the wrap angle of the peeling roll is in a certain range.
[0009]
The present invention has been made based on such knowledge,
When the film is produced by a solution casting method, the residual volatile content of the film when it is peeled off from the support is 10 to 50% (weight% by weight), and the draw rate when the film is peeled off from the support is 8% When peeling the film from the support, the peeling roll is separated from the support by 3 mm or more, and the wrap angle of the peeling roll is 5 ° or more and 150 ° or less, at least one side of the film The maximum flaw size per 5 m ² is 600 μm ² or less, the depth is 0.1 μm or less, and haze is less than 0.7 with one flaw formed by combining one flaw or a plurality of flaws. A method for producing an optical film . ( However, the draw rate is represented by [(V2-V1) / V1] × 100 when the support speed V1 and the film speed V2 at the time of peeling are used .)
It is about.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The optical film of the present invention includes a cellulose ester film, a polycarbonate film and the like. The cellulose ester is typically a lower fatty acid ester of cellulose (eg, cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate). Lower fatty acid means a fatty acid having 6 or less carbon atoms. Cellulose acetate includes cellulose triacetate (TAC) and cellulose diacetate (DAC). The thickness of the film is about 20 to 500 μm, usually about 20 to 300 μm, but the present invention is particularly effective for a thin film, for example, a film having a thickness of about 20 to 120 μm, particularly about 20 to 80 μm. In the present invention, the maximum scratch per 5 m ^{2 on} one or both sides of the film is one single or a plurality of scratches combined, and the area of one scratch regarded as one scratch is 600 μm ² or less, and the depth of the scratch It has been found that by setting the thickness to 0.1 μm or less and haze to less than 0.7, it is possible to obtain a film in which no defect is observed in optical applications. The maximum scratch is preferably a scratch area of 400 μm ² or less, a depth of 0.05 μm or less, and a haze of less than 0.5, and more preferably an area of 200 μm ² or less, a depth of 0.01 μm or less, and a haze of less than 0.3. is there.
[0011]
The film of the present invention is formed by a solution casting method. First, a solution is prepared by dissolving the polymer in a solvent.
[0012]
As the polymer solvent, a lower aliphatic hydrocarbon chloride or a lower aliphatic alcohol is generally used. An example of a lower aliphatic hydrocarbon chloride is methylene chloride. Examples of lower aliphatic alcohols include methanol, ethanol, n-propyl alcohol, isopropyl alcohol and n-butanol. Examples of other solvents are substantially free of halogenated hydrocarbons, acetone, and ketones having 4 to 12 carbon atoms include, for example, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone, carbon Examples of the ester having 3 to 12 atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentyl acetate and 2-ethoxy-ethyl acetate. Examples of alcohols from 1 to 6 include methanol, ethanol, propanol, iso-propanol, 1-butanol, t-butanol, 2-methyl-2-butanol, 2-methoxyethanol, 2-butoxyethanol and the like, and carbon atoms The number is 3 The ethers up to 12 include, for example, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenetole and the like, and cyclic carbonization having 5 to 8 carbon atoms. Examples of hydrogens include cyclopentane, cyclohexane, cycloheptane, and cyclooctane.
[0013]
As the solvent, methylene chloride is particularly preferable. Other solvents may be mixed with methylene chloride. However, the mixing ratio of methylene chloride is preferably 70% by weight or more. Particularly preferred mixing ratios are 75 to 93% by weight for methylene chloride and 7 to 25% by weight for other solvents.
[0014]
The concentration of the polymer in the polymer solution is preferably 10% by weight or more, more preferably 15% by weight or more, and particularly preferably 19% by weight or more. The upper limit of the concentration is determined by the fluidity of the polymer solution and is generally about 30% by weight.
[0015]
Moreover, you may add additives, such as a plasticizer, a ultraviolet absorber, and a degradation inhibitor.
[0016]
The film forming speed v is usually set in the range of 3 m / min to 150 m / min, and preferably in the range of 10 m / min to 100 m / min, but is not limited thereto.
[0017]
When a cellulose ester film such as cellulose acetate is produced by a solution casting method, the residual volatile content of the film at the time of stripping is 50% (weight percent by weight) or less, ensuring film rigidity and supporting the film The draw rate when peeling from the body is set to 8% or less to suppress the width change of the film. The residual volatile content is preferably 40% or less and the draw rate is 5% or less, more preferably 3% or less, and further preferably 1% or less. This residual volatile matter can be adjusted by adjusting the concentration and casting thickness of the polymer solution, the running speed and running distance of the support (belt length and drum diameter), blowing temperature and blowing volume, etc. It is preferable to adjust by the density | concentration of a solution or ventilation temperature, or ventilation volume. The lower limit of the residual volatile content at the time of stripping is not particularly limited, but is practically up to 10%.
[0018]
Next, it is preferable that the peeling roll is separated from the support by 3 mm or more so that the sudden width change portion of the film due to neck-in does not come into contact with the peeling roll. The separation distance is desirably 5 mm or more, and more desirably 8 mm or more. On the other hand, the upper limit of this interval is up to about 100 mm.
[0019]
Moreover, it is preferable that the wrap angle of the peeling roll is 5 ° or more and 150 ° or less. As shown in FIG. 1, the wrap angle is an angle between a line connecting both ends of a portion of the peripheral surface of the peeling roll that is in contact with the film and the center of the roll. When the wrap angle is less than 5 °, the holding force is reduced, the rotation of the peeling roll is caused, and there is a concern that the scratch is increased. Further, if a stripping roll or the like is driven, rotation failure can be prevented, but wrinkles are likely to occur on the roll at a small wrap angle, which is also not preferable. The wrap angle is desirably 30 ° or more and 130 ° or less, and more desirably 45 ° or more and 120 ° or less.
[0020]
The film obtained by the method of the present invention requires extremely uniform optical properties, and can be used as a protective film for a polarizing plate on which a functional film such as an antireflection layer is precisely applied.
[0021]
The polarizing plate is composed of a stretched PVA film and a protective film sandwiching the PVA film, and its performance is greatly affected by the flatness, optical characteristics, and mechanical properties of the protective film. In general, a protective film is required to have a smooth appearance, a uniform thickness, optical characteristics with small anisotropy, moderate strength and flexibility, and physical characteristics with small dimensional change. It is preferable to use the anti-support surface of the film of the present invention as a bonding surface with a polarizing film or a coating surface such as a hard coat because product defects can be avoided.
[0022]
【Example】
[Preparation of raw material dope]
(Preparation of fine particle dispersion a)
Silica (Nippon Aerosil Co., Ltd., “Aerosil R972”) 0.67% by weight
Cellulose acetate (substitution degree 2.8) 2.93% by weight
Triphenyl phosphate 0.23% by weight
Biphenyl diphenyl phosphate 0.12% by weight
Methylene chloride 88.37% by weight
Methanol 7.68% by weight
A solution was prepared and dispersed with an attritor so that the volume average particle size was 0.7 μm.
[0023]
(Preparation of raw material dope A)
Cellulose triacetate (substitution degree 2.8) 89.3% by weight
Triphenyl phosphate 7.1% by weight
Biphenyl diphenyl phosphate 3.6% by weight
17.9 parts by weight of the fine particle dispersion a is added to 100 parts by weight of the solid content.
Dichloromethane 92% by weight
8% by weight of methanol
The dope was prepared by appropriately adding a mixed solvent to be dissolved under stirring. The solid content concentration of the dope was 18.5%. This dope is filtered with a filter paper (Toyo Filter Paper Co., Ltd., “# 63”), and further filtered with a sintered metal filter (Nihon Seisen Co., Ltd., “06N”, nominal pore diameter 10 μm), and further a mesh filter ( It filtered with Nippon Pole Co., Ltd. product "RM", nominal pore diameter 45micrometer.
[0024]
(Preparation of UV absorber solution b)
2 (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole 11.66% by weight
2 (2′-Hydroxy-3 ′, 5′-di-tert-amylphenyl) benzotriazole 5.83% by weight
Cellulose acetate (substitution degree 2.8) 1.48% by weight
Triphenyl phosphate 0.12% by weight
Biphenyl diphenyl phosphate 0.06% by weight
Methylene chloride 74.38% by weight
Methanol 6.47% by weight
An ultraviolet absorber solution was prepared according to the above formulation, and filtered through “Astrpore 10 Filter” manufactured by Fuji Photo Film Co., Ltd.
[0025]
(Preparation of fine particle dispersion / UV absorber solution c)
2 (2′-Hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole 5.40% by weight
2 (2′-hydroxy-3 ′, 5′-di-tert-amylphenyl) benzotriazole 10.79% by weight
Silica (Nippon Aerosil Co., Ltd., “Aerosil R972”) 0.39% by weight
Cellulose acetate (substitution degree 2.8) 2.58% by weight
Triphenyl phosphate 0.28% by weight
Biphenyl diphenyl phosphate 0.14% by weight
Methylene chloride 67.71% by weight
Methanol 10.86% by weight
n-butanol 1.85% by weight
A solution was prepared and dispersed with an attritor so that the volume average particle diameter of the silica particles was 0.6 μm. The solution after dispersion was filtered through “Astropore 10 filter” manufactured by Fuji Photo Film Co., Ltd., and further filtered through a sintered metal filter (manufactured by Nippon Seisen Co., Ltd., “07N”).
[0026]
<Measurement of volume average particle diameter>
The volume average particle size in the fine particle dispersion a and the fine particle dispersion / ultraviolet absorber solution c was measured by “Mastersizer MS20” manufactured by MALVERN.
[0027]
<Measurement of dope solid content concentration>
The dope solid content concentration (%) in the raw material dope A is based on the moisture content,
(Weight loss of dope heated at 120 ° C. for 2 hours) / (original dope weight) × 100
I asked for it.
[0028]
For the above-mentioned dope A, a static mixer is used, and the above-mentioned ultraviolet absorber solution b is added in the dope piping path while adjusting the amount of the ultraviolet absorber to 1.04% by weight with respect to the solid content in the dope. The dope was prepared by mixing.
[0029]
This dope was cast on a stainless steel band as a support. At that time, the temperature and amount of air blown into the housing housing the support were controlled to change the residual film volatile content at the time of peeling as shown in Table 1. Further, the draw rate, the clearance of the peeling roll, and the wrap angle of the peeling roll were also changed as shown in Table 1. The peeled film was dried by a conventional method to obtain a cellulose triacetate film (containing 0.13% by weight of silica, 1% by weight of UV absorber, and 10.7% by weight of plasticizer TPP) having a thickness of 80 μm or 40 μm.
[0030]
Table 1 shows the results of evaluating the area and depth of the maximum scratches per 5 m ^{2 of} each film obtained, the haze, and the suitability of this film for use in polarizing plates and LCDs.
[0031]
[Table 1]

[0032]
Residual volatile content of film after stripping (methylene chloride and methanol):
Humidity reference weight%
Draw rate:
When the support speed V1 and the film speed V2 at the time of peeling are ((V2-V1) / V1) × 100
Peeling roll clearance:
Minimum distance between the outer circumference of the peeling roll and the support surface
The angle θ of the part where the film is on the roll when the roll center is the center
Scratch measurement method:
Maximum scratch in a 1m x 5m sample.
First, measure the length and width roughly with a loupe / microscope, extract large and strong scratches, and observe them with an electron microscope or optical microscope. The scratch screen was image processed and the area was calculated. The depth was determined by measuring in more detail with an electron microscope and an optical interferometer.
Polarizing plate suitability:
The polarizing plate produced by sticking the obtained film as a protective film on both sides of the polarizing film was evaluated.
LCD suitability:
Evaluation was performed by temporarily mounting a film on the LCD.
Evaluation criteria:
The scratches cannot be recognized due to transparency. There is no decrease in transparency, haze, and white turbidity (the surface becomes whitish and bleeding of characters, etc. is observed). Optical characteristics are not disturbed (Scratches cannot be recognized during LCD display. No abnormalities (color change, defects, bright spots / dark spots) are observed in the image.
[0033]
In the case of a small wrap angle of 4 °, slipping occurred on the stripping roll, the length of the scratch was increased (area increase), and wrinkles were observed on the roll.
[0034]
Further, in the cellulose triacetate film (thickness 80 μm and 40 μm), the surface with scratches (area 440 to 560 μm ² , depth 0.05 to 0.08 μm), or a large surface / strong surface, When bonded to the polarizing film side (PVA side), no scratch was observed in appearance inspection such as transmission and reflection. Moreover, when it applied with the acrylic resin with respect to the flaw surface of the said film (thickness of resin layer 3-4 micrometers), the flaw was not recognized by transmission and reflection again.
[0035]
【The invention's effect】
The present invention makes it possible to clarify the limit size of scratches, to ensure film rigidity at the time of peeling, to suppress the change in the width of the film by reducing the peeling tension (draw rate), and to make neck-in by optimizing the position of the peeling roll. By preventing contact with the shape portion and reducing the contact area with the film by reducing the wrap angle of the peeling roll, an optical film that can be used for high-quality optical applications by improving the fine scratches is obtained.
[Brief description of the drawings]
FIG. 1 is a side view illustrating a wrap angle of a peeling roll.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Film 2 ... Stripping roll (theta) ... Wrap angle

Claims (2)

When the film is produced by a solution casting method, the residual volatile content of the film when it is peeled off from the support is 10 to 50% (weight% by weight), and the draw rate when the film is peeled off from the support is 8% When peeling the film from the support, the peeling roll is separated from the support by 3 mm or more, and the wrap angle of the peeling roll is 5 ° or more and 150 ° or less, at least one side of the film The maximum flaw size per 5 m ² is 600 μm ² or less, the depth is 0.1 μm or less, and haze is less than 0.7 with one flaw formed by combining one flaw or a plurality of flaws. A method for producing an optical film . ( However, the draw rate is represented by [(V2−V1) / V1] × 100 when the support speed V1 and the film speed V2 at the time of peeling are used. ) The polarizing plate which mounted | wore with the film obtained by the manufacturing method of Claim 1 as a protective film .

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