JP2004292558A - Cellulose ester film, production method therefor, and polarizing plate protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a cellulose ester film as a polarizing plate protective film having a low haze, being transparent, being excellent in mechanical strengths (tear strength) and retention, and not becoming hazy under high-temperature high-humidity conditions. <P>SOLUTION: The cellulose ester film is a crosslinked one formed in the presence of a thermally crosslinkable organic compound. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１４２】
本発明の変性セルロースエステルフィルム（実施例１〜１４）は、いずれも良好な性質を示し、特に、寸法安定性が高く、引裂強度の強い、ヘイズの小さい保留性のよいフィルムであることがわかる。また、高湿時の白濁が少なく優れている。
【０１４３】
次いで、各フィルムより偏光板を作製し、以下の評価を行った。
（偏光板の作製）
製膜した全てのセルロースエステルフィルム実施例１〜１４１５、比較例１〜５を、４０℃の２．５ｍｏｌ／ｌの水酸化ナトリウム水溶液で６０秒間表面鹸化処理を行い、３分間水洗して乾燥させた。別に１２０μｍの厚さのポリビニルアルコールをヨウ素１質量部、ホウ酸４質量部を含む水溶液１００質量部に浸漬し、５０℃で４倍に立て方向に延伸した偏光膜を用意した。この偏光膜の両面に上記表面鹸化処理したセルロースエステルフィルムを完全鹸化型のポリビニルアルコール５質量％水溶液を粘着剤として貼り合わせ偏光板１〜１４１５、比較１〜５を作製した。
【０１４４】
（偏光板耐久性）
各々の偏光板から１００ｍｍ×１００ｍｍの大きさの試料を２枚切り出し、８０℃、９０％ＲＨの雰囲気に５０時間曝し、クロスニコルにより偏光板の縁に発生する白抜けの面積を全体の面積に対する面積比として観察して、下記のグレードで評価した。
【０１４５】
Ａ：白抜け部分が全くなかった
Ｂ：白抜けが全体の面積に対して２％未満
Ｃ：白抜け部分が全体の面積に対して２％以上５％未満
Ｄ：白抜け部分が全体の面積に対して５％以上１０％未満
Ｅ：白抜け部分が全体の面積に対して１０％以上あった。
【０１４６】
（偏光板の異物・欠陥）
各々の偏光板から２５ｃｍ×２５ｃｍの大きさに２枚ずつ切りだした試料を、それぞれ５組準備し、クロスニコルにより、異物等による暗黒面に現れる輝きスポット数を観察し、偏光板各試料につき５組の異物の数の平均を下記のレベルで評価した。
【０１４７】
Ａ：全く輝きスポットがなかった
Ｂ：小さな輝きスポットが１〜５個観察された
Ｃ：小さな輝きスポットが６〜５０個観察された
Ｄ：輝きスポットが５１〜９９個観察された
Ｅ：輝きスポットが１００個以上観察された。
【０１４８】
上記各評価の結果を表１に示す。
（リワーク性）
得られた１００×１００ｍｍサイズの偏光板を、ガラス基盤に貼合した。４角の１カ所から偏光板をガラス基盤から少し剥離し、剥離した偏光板を掴みガラス基盤を押さえながら対角方向に剥離していく。同様の操作をそれぞれの偏光板について計１０枚のサンプルで実施し、以下の基準に従い評価を行った。
【０１４９】
◎：１０枚とも完全に剥離できた
○：１枚のみ部分的に剥離残りが生じた
△：２〜５枚で剥離のこりが生じた
×：６枚以上剥離のこりが生じた
評価結果を以下の表 に示す。
【０１５０】
【表２】

【０１５１】
実施例１６
図１に示される複数のドープ液を流延製膜できるダイスを用い、ダイス中央部には前記実施例２において用いたドープ液を、また、ダイス両端部には比較例１で用いたドープ液をそれぞれ流して、前記実施例と同様の製膜に、同様の条件で製膜をおこなった。得られた厚み４０μｍ、１．２５ｍ幅の１０００ｍのロールフィルムを得た。次いでロールフィルムを断裁機にかけ、両端部を１２．５ｃｍずつの幅でカットして、１ｍのロールフィルムとした。切り取った耳返材を、細かく断裁し、前記の実施例２において用いたアセチル置換度２．８８のセルローストリアセテート（数平均分子量１５００００）の１００質量部のうち、２０質量部が置き換わるように用いて実施例２と同様にドープを調製した。
【０１５２】
その結果、増粘もなく実施例２と同様にドープ液が得られた。
このドープを前記同様に、安積濾紙（株）製の安積濾紙Ｎｏ．２４４を使用して濾過した後、更に一晩静置し、脱泡し、次いで日本精線（株）製のファインメットＮＭ（絶対濾過精度１００μｍ）、ファインポアＮＦ（絶対濾過精度５０μｍ、１５μｍ、５μｍの順に順次濾過精度を上げて使用）を使用して濾過圧力１．０×１０^６Ｐａで濾過し製膜に供した。
【０１５３】
濾過して得られた３５℃のドープを用いて、前記同様無端のステンレスベルト上に流延して前記同様に、製膜、乾燥し、乾燥されたウェブを残留溶媒量を０．２質量％で巻き取り、４０μｍのセルロースエステルフィルムを得た。得られたセルロースフィルムについて、前記実施例２のセルロースエステルフィルムと、引裂強度、ヘイズ（濁度）、保留性および高湿時の白濁について比較評価したところ同等の特性を有するフィルムであった。
【０１５４】
また、ドープ液の濾過に用いた安積濾紙（株）製の安積濾紙Ｎｏ．２４４について、また一晩静置後の濾過に用いた日本精線（株）製のファインメットＮＭ（絶対濾過精度１００μｍ）、ファインポアＮＦ等のフィルタの目詰まりもなく、工程上の問題も発生しなかった。
【０１５５】
一方、作製したセルロースエステルフィルムの中央の部分、即ち架橋されたセルロースエステルを含有するフィルムを、細かく断裁した後、前記耳返材と同様に実施例２において用いたアセチル置換度２．８８のセルローストリアセテート（数平均分子量１５００００）の１００質量部のうち、２０質量部が置き換わるように用いて実施例２と同様にドープを調製したところ、不溶解物のかなりの発生があり、又、増粘が大きく、濾紙の目詰まりが起こるため、ドープの濾過が出来なかったため、製膜が同じ条件では出来なかった。また、一部濾過された濾液においても不溶解物がとれず、クリアな溶液とならなかった。
【０１５６】
【発明の効果】
ヘイズ値が低く、透明性があり、機械強度（引き裂き強度）、保留性に優れ、かつ高温高湿化で白濁することのないセルロースエステルフィルムが得られた。
【図面の簡単な説明】
【図１】中央部、両端部と三つに分離したダイスの概略図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cellulose ester film for a polarizing plate protective film having excellent retention and reworkability, and a method for producing the same.
[0002]
[Prior art]
At present, cellulose triacetate films are preferably used for silver halide photographic materials and liquid crystal image display devices because of their transparency and characteristics free from optical defects. Particularly, it is used as a protective film for a polarizing plate in a liquid crystal image display device. The liquid crystal image display device is configured by attaching polarizing plates to both sides of a glass substrate in which a liquid crystal element is incorporated. The polarizing plate has a structure in which a polarizer made of polyvinyl alcohol or the like is sandwiched between protective films on both sides, and the thickness of the protective film is generally about 80 μm. Therefore, one protective film is used for one liquid crystal display device, and the total thickness is about 320 μm. In recent years, there has been a demand for improved portability of liquid crystal display devices, and thinning of a protective film for a polarizing plate is considered to be an effective means for meeting this requirement.
[0003]
However, when the thickness of the protective film for a polarizing plate is reduced, there is a problem that productivity of the liquid crystal display device is reduced. That is, when assembling a liquid crystal display device, a polarizing plate is attached to a glass substrate on which a liquid crystal element is incorporated. At this time, defective products such as a small amount of dust or a misalignment are likely to occur. For this reason, the strength of the polarizing plate cannot withstand the peeling force between the glass substrate and the polarizing plate, so that the polarizing plate is broken on the way and the ninth side cannot be peeled cleanly from the glass substrate.
[0004]
In order to improve such releasability, it was thought that the tear strength of the protective film for a polarizing plate should be improved. As a method for improving the tear strength of a cellulose triacetate film, for example, Patent Document 1 proposes a method of blending a methylene chloride-soluble polyurethane resin. Patent Document 2 discloses a method of blending a polyester-urethane resin.
[0005]
However, according to these methods, the tear strength is certainly improved, but the urethane resin is in the cellulose triacetate dope, the web during drying, or after the film is formed, the cellulose triacetate and the polymer undergo phase separation and the transparency is lowered. As a result, it could not be used for a protective film for a polarizing plate requiring transparency.
[0006]
In particular, when left at high temperature and high humidity, for example, at 80 ° C. and 90% RH for about 48 hours, the film became cloudy and could not be used as a polarizing plate.
[0007]
Further, the cellulose triacetate film containing a urethane resin has a phenomenon that the retardation in the depth direction is reduced. As a result, the viewing angle characteristics of the liquid crystal display device change, and there is a problem that the optical design of the liquid crystal display device must be redesigned in order to correct the change.
[0008]
Further, Patent Document 3 discloses that a polymer is produced by radical polymerization by causing an ethylenically unsaturated monomer and a photopolymerization initiator to be contained in a cellulose ester dope composition, photopolymerizing the ethylenically unsaturated monomer, and being completed by the polymer. There is disclosed a technique capable of imparting water resistance to a cellulose ester film. This means that, in addition to tear strength, stretchability and retention under high humidity and the like are improved by the formation of the photocurable polymer.
[0009]
However, in this method as well, although problems such as haze due to phase separation of the polymer have been improved, curling under high humidity and deterioration of physical properties are major drawbacks. In addition, the retention property refers to a property in which the mass of the film is reduced due to deposition or volatilization of an additive such as a plasticizer outside the film in a high-temperature and high-humidity environment. Due to poor performance, the function of the liquid crystal image display device is deteriorated, and it cannot be said that this has been sufficiently improved even by the above-mentioned technology.
[0010]
On the other hand, in the production of a cellulose ester film, the portion corresponding to the end of the die after forming the film, that is, the end of the formed film roll is not stable in film thickness and the like, and the width of the width is also delicate. Since it has changed, the end is cut off and cut at a constant width to obtain a product roll. Since this part cannot be used as a product, it is mixed again in the dope and used for casting. The cut-off portion at the end of the cellulose ester film whose physical properties have been improved by the cross-linking or the like has different physical properties due to the cross-linking, and therefore cannot be mixed in a usual dope and must be discarded. In the present invention, furthermore, the production method has been devised so that the truncated portion at the end produced in the production of the crosslinked and denatured cellulose ester film, that is, the ear turning material can be reused.
[0011]
[Patent Document 1]
Japanese Patent Publication No. 44-32672
[0012]
[Patent Document 2]
Japanese Patent Publication No. 47-760
[0013]
[Patent Document 3]
JP-A-2002-20410
[0014]
[Problems to be solved by the invention]
An object of the present invention is to provide a cellulose ester film as a protective film for a polarizing plate, which has a low haze value, is transparent, has excellent mechanical strength (tearing strength), excellent retention properties, and does not become cloudy due to high temperature and high humidity. To provide. A second object of the present invention is to provide a cellulose ester film in which a dope containing no isocyanate compound is allowed to flow from both ends of a die so that ear refill materials can be reused.
[0015]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following configurations.
[0016]
1. A cellulose ester film formed into a film in the presence of a thermally crosslinkable organic compound.
[0017]
2. The cellulose ester film according to claim 1, wherein the thermally crosslinkable organic compound is a thermally crosslinkable polymer.
[0018]
3. The cellulose ester film according to claim 1, wherein the thermally crosslinkable organic compound is a polyisocyanate.
[0019]
4. A film obtained by dissolving a polyisocyanate and a cellulose ester in an organic solvent to prepare a dope, casting the dope on a support in the form of a film, and casting the solvent from the support in a state containing at least 10% of a dry solvent. A method for producing a cellulose ester film, which comprises removing the film and heating and drying to accelerate the urethane reaction.
[0020]
5. A cellulose ester film which is formed in the presence of a polyisocyanate and a hydroxyl group-containing compound.
[0021]
6. A polydocyanate, a hydroxyl group-containing compound and a cellulose ester are dissolved in an organic solvent to prepare a dope, and the dope is cast on a support in the form of a film. A method for producing a cellulose ester film, comprising separating a cast film, drying by heating, and accelerating a urethanization reaction.
[0022]
7. The cellulose ester film according to claim 5, further comprising a hydroxyl group-containing ultraviolet absorber.
[0023]
8. 8. The cellulose ester film according to claim 1, wherein the cellulose ester has an elastic modulus of 3500 MPa or more.
[0024]
9. 9. The cellulose ester according to claim 1, wherein the dimensional change when the cellulose ester film is treated at 80 ° C. and 90 RH% for 48 hours is within 0.2%. 10. the film.
[0025]
10. The haze value defined by ASTM-D1003-52 is 2% or less when treated at 80 ± 5 ° C. and 90 ± 10% RH for 48 hours. 10. The cellulose ester film according to 5, 7, 8 or 9.
[0026]
11. In a method for producing a cellulose ester film in which a cellulose ester dope is cast on a support using a die, a cellulose ester dope containing a polyisocyanate and a cellulose ester is supplied from a central portion of the die, and both ends of the die are supplied. A cellulose ester dope containing no polyisocyanate is supplied from the above, and both ends in the width direction of the formed film are made into a cellulose ester film containing no polyisocyanate.
[0027]
12. After saponifying the cellulose ester film according to any one of claims 1 to 3, 5 and 7 to 10, the saponified surface of the cellulose ester film is in contact with the polarizing film, so that both sides of the polarizing film are provided. A method for producing a polarizing plate, comprising laminating.
[0028]
Hereinafter, the present invention will be described in detail.
Cellulose acetate films have been used as protective films for polarizing plates because of their good transparency, no optical distortion, and excellent adhesion to polarizers. An ultraviolet absorber or a plasticizer is added to the protective film for a polarizing plate in order to protect the polarizing film or to impart proper processing to the film itself. However, these additives have a problem in terms of compatibility with the cellulose ester, so that they are easily deposited on the surface by volatilization of the solvent at the time of casting and are easily attached to the surface, and there is a problem in that they have a retention property of causing foreign matter defects. Further, the cellulose ester film has a disadvantage that the mechanical strength is weak and the film is easily torn.
[0029]
In order to solve the above problem, as described in Patent Document 1 (JP-B-44-32672) and Patent Document 2 (JP-B-47-760), a plasticizer is used instead of a plasticizer. Attempts have been made to add polymers having an activating effect, such as urethane resins, polyester-urethane resins, and the like. By these, mechanical strength, moisture permeability and retention are improved, but when polymers are blended, there is a problem that minute phase separation occurs due to poor compatibility between the polymers and the film becomes cloudy.
[0030]
In Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-20410), radical polymerization is carried out by including an ethylenically unsaturated monomer and a photopolymerization initiator in a cellulose ester dope composition and photopolymerizing the ethylenically unsaturated monomer. By doing so, a modified cellulose ester film is imparted with water resistance, tear strength, retention and the like.
[0031]
However, in this method, although problems such as haze due to phase separation of the polymer have been improved, curling under high humidity and deterioration of physical properties have become a major drawback because a considerably different material is mixed. I have.
[0032]
In order to solve these problems, the present inventor does not simply blend a polymer having a plasticizing effect, but thermally cross-links a polymer having a plasticizing effect together with a cellulose ester to form a film. It has been found that it is suitable for obtaining a cellulose ester film having no haze and good retention.
[0033]
Accordingly, in the present invention, a cellulose ester may be formed into a film in the presence of a thermally crosslinkable organic compound, preferably an epoxy group-containing compound, an isocyanate group-containing compound, ethyleneimine, and the like. Since it has a residual hydroxyl group, it reacts with the hydroxyl group and adds a thermally crosslinkable organic compound that forms a crosslink to the cellulose ester dope, casts it into a film, reacts the curing agent during thermal drying, What is necessary is just to form a film by forming thermal crosslinking in a cellulose ester. Thereby, there is no rise in haze due to the minute phase separation, and a cellulose ester film having good retention properties can be obtained. The cellulose ester has a hydroxyl group remaining in its constituent component, and the hydroxyl group participates in the reaction with the crosslinkable organic compound.
[0034]
As a result of repeated studies on various heat-crosslinkable organic compounds, the heat-crosslinkable compound has a heat-crosslinkable polymer, for example, an isocyanate group, or an epoxy group, a crosslinkable group such as an ethyleneiminy group at the terminal. A polymer or the like may be used, and among these thermally crosslinkable compounds, a compound (polyisocyanate compound) having a plurality of isocyanate groups is particularly preferable.
[0035]
Therefore, in the present invention, a crosslinkable compound having a crosslinkable group such as an isocyanate group is added to the cellulose ester dope as a crosslinking agent. By the cross-linking (urethane bond) formed by the reaction with the hydroxyl group in the above, a cellulose ester film having a low haze value, excellent transparency, and excellent moisture permeability, retention and mechanical strength can be obtained.
[0036]
A cellulose ester film is formed by casting a dope containing a cellulose ester from a die onto a support, forming a film, and then winding the film into a roll through processes such as stretching and drying. Because the uniformity of the film is inferior to the part, the ends of the width of the roll are usually cut off at a fixed width, and the cut-out part (return material) is reused, and only the uniform part is used. Is common.
[0037]
In the present invention, a urethane bond is formed in the cellulose ester. In a preferred embodiment, by using a polyisocyanate compound, a compound having a hydroxyl group, and the like together with the cellulose ester (described later), the three react together to form a partially crosslinked cellulose ester polymer. Since these are not pure cellulose esters, both ends of the formed film cannot be reused as cellulose esters.
[0038]
Therefore, as one aspect of the present invention, in the center of the die, a dope containing an isocyanate compound is flowed, and a dope containing no isocyanate compound is flowed from both ends of the die, so that the ear canal can be reused. This is a finished cellulose ester film. As a result, both ends that must be cut off due to unevenness are made of a reusable film consisting essentially of cellulose ester without a urethane cross-linking part, and a uniform film product in the center where ear return materials are cut out The cellulose ester film which is excellent in transparency, has a low haze value, and does not have the problem of cloudiness particularly at high humidity, and has excellent moisture permeability, retention and mechanical strength.
[0039]
The cellulose ester used in the present invention is preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms, for example, cellulose acetate, cellulose propionate, cellulose butyrate and the like, and JP-A-10-45804, JP-A-8-223161. And mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate described in US Pat. No. 2,319,052. Among the above descriptions, particularly preferred lower fatty acid esters of cellulose are cellulose triacetate and cellulose acetate propionate. These cellulose esters can be used alone or as a mixture.
[0040]
In the case of cellulose triacetate, those having an average degree of acetylation (the amount of bound acetic acid) of 54.0 to 62.5% are preferably used, and more preferably cellulose having an average degree of acetylation of 58.0 to 62.5%. Triacetate.
[0041]
Preferred cellulose esters other than cellulose triacetate have an acyl group having 2 to 4 carbon atoms as a substituent, and when the degree of substitution of an acetyl group is X and the degree of substitution of a propionyl group is Y, the following formula (I) And (II) at the same time.
[0042]
Formula (I) 2.6 ≦ X + Y ≦ 3.0
Formula (II) 0 ≦ X ≦ 2.5
Among them, cellulose acetate propionate in which 1.9 ≦ X ≦ 2.5 and 0.1 ≦ Y ≦ 0.9 is preferable. The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by a known method.
[0043]
As the cellulose ester, a cellulose ester synthesized from cotton linter, wood pulp, kenaf or the like can be used alone or as a mixture. In particular, it is preferable to use a cellulose ester synthesized from cotton linter (hereinafter sometimes simply referred to as linter) alone or in combination.
[0044]
If the molecular weight of the cellulose ester is too high, the viscosity of the solution of the cellulose ester will be too high, and the productivity will decrease. Therefore, those having a number average molecular weight (Mn) of 70,000 to 200,000 are preferable. , 100,000 to 200,000 are more preferable,
Crosslinking the cellulose ester increases the molecular weight and increases the modulus, but too much crosslinking makes the cellulose ester film too hard and brittle.
[0045]
In the present invention, the cellulose ester is crosslinked at the time of casting film formation, which will be described later. That is, a crosslinkable compound is added to the dope during film formation, cast to form a film, and the reaction is promoted by heating and drying.
[0046]
As the crosslinking means of the cellulose ester, as described above, there are thermally crosslinkable organic compounds such as isocyanate compounds and epoxy compounds, and further, thermally crosslinkable polymers such as isocyanate groups or crosslinkable epoxy groups. There is a polymer having a group at the terminal. However, preferred is a polyisocyanate compound having a plurality of isocyanate groups and having crosslinkability with respect to cellulose ester.
[0047]
Examples of these polyisocyanate compounds include compounds represented by the following general formula.
[0048]
General formula
O = C = NL- (N = C = O)_v
In the formula, v is 0, 1 or 2, and L represents a divalent linking group having an alkylene group, alkenylene group, arylene group or aralkyl group as a partial structure.
[0049]
These groups may further have a substituent, and preferable examples of the substituent include a halogen (eg, Br and Cl), a hydroxyl group, an amino group, a carboxyl group, an alkyl group, an alkoxyl group and the like.
Examples thereof include isocyanates having an aromatic ring such as 2,4-tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and xylylene diisocyanate; Examples of specific isocyanate compounds which can be obtained from a manufacturer, such as isocyanates of a system, isocyanates obtained by hydrogenating aromatic rings such as hydrogenated TDI and hydrogenated MDI, and the like, are shown below.
[0050]
IC-1 Desmodur N100, Mobay, aliphatic isocyanate
IC-2 Desmodu N3300, Mobay, aliphatic isocyanate
IC-3 Mondur TD-80, Mobay, aromatic isocyanate
IC-4 Mondeux M, Mobay, aromatic isocyanate
IC-5 Montdeux MRS, Mobay, Polymer Isocyanate
IC-6 Desmodu W, Mobay, aliphatic isocyanate
IC-7 Papi 27, Dow, polymer isocyanate
IC-8 Isocyanate T1890, Huels, aliphatic isocyanate
IC-9 Octadecyl isocyanate, Aldrich, aliphatic isocyanate
Further, Coronate 2030, Coronate 2255, Coronate 2513, Coronate 2507, Coronate L, Coronate HL, Coronate HK, Coronate HX, Coronate 341, Coronate MX, Coronate 2067, manufactured by Nippon Polyurethane Co., Ltd., Takenate D103H, Takenate D204EA, Takenate D- 172N, Takenate D-170N, manufactured by Takeda Pharmaceutical Co., Ltd., Sumidur 3200, Sumidur 44V-20, Sumidur IL, manufactured by Sumitomo Bayer Urethane Co., Ltd., and the like. However, the present invention is not limited to these.
[0051]
Further, a polyisocyanate obtained by reacting these isocyanate compounds with an active hydrogen group-containing compound may be used. When an isocyanate having an aromatic ring such as TDI or MDI is used, haze is reduced in a small amount, cloudiness under high humidity conditions is eliminated, retention properties are improved, water absorption elastic modulus is improved, and moisture permeability is also improved. . In addition, a reduction in tear strength can be suppressed with an aliphatic isocyanate.
[0052]
The amount of these used is in the range of 0.01% to 1%, preferably 0.03 to 0.5% by mass relative to the cellulose ester. If the amount is too large, the crosslinking becomes too large and becomes brittle. On the other hand, if the amount is too small, such crosslinks are not formed, and the effects of the present invention cannot be obtained.
[0053]
These thermally crosslinkable organic compounds, particularly polyisocyanate compounds, are more preferably used together with a hydroxyl group-containing compound at the time of film formation by casting.
[0054]
When used together with a hydroxyl group-containing compound, the isocyanate compound also reacts with these hydroxyl group-containing compounds to form a urethane bond to fix the isocyanate compound, improve the plasticizing effect, and to some extent suppress the increase in molecular weight due to crosslinking of the cellulose ester. Thus, as described later, it is considered that there is an effect of suppressing the elastic modulus from becoming too high.
[0055]
The hydroxyl group-containing compound is not particularly limited as long as it reacts with the isocyanate compound as described above, and examples thereof include alcohols and phenols. Among them, an ultraviolet absorber containing a hydroxyl group described later is preferable. It is also preferable to have such a role. However, compounds having two or more hydroxyl groups are particularly preferred. In addition to polyesters having hydroxyl groups at both terminals, polyester ethers containing hydroxyl groups, etc., polyhydric alcohols represented by the following general formula (1) and the like are preferably used together with the heat crosslinkable compound.
[0056]
General formula (1)
R₁-(OH)_n
Where R₁Represents an n-valent organic group, n represents a positive integer of 2 or more, and an OH group represents an alcoholic or phenolic hydroxyl group.
[0057]
Examples of the n-valent aliphatic organic group include an alkylene group (eg, a methylene group, an ethylene group, a trimethylene group, a tetramethylene group), an alkenylene group (eg, an ethenylene group), an alkynylene group (eg, an ethynylene group), a cycloalkylene group (For example, 1,4-cyclohexanediyl group and the like) and alkanetriyl group (for example, 1,2,3-propanetriyl group and the like). The n-valent aliphatic organic group includes those having a substituent (for example, a hydroxyl group, an alkyl group, a halogen atom, etc.). As the aromatic organic group, an arylene group (for example, a phenylene group) is preferable. n is preferably 2 to 20.
[0058]
Examples of preferred polyhydric alcohols include, for example, the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, and aromatic alcohols such as xylylene diol and 1,4-bis (hydroxyethyl) benzene It can be mentioned. Among them, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.
[0059]
Examples of preferred phenolic hydroxyl groups include compounds such as resorcinol and pyrogallol.
[0060]
The molecular weight of the polyhydric alcohol is not particularly limited, but is preferably in the range of 300 to 1500, and more preferably in the range of 350 to 750. From the viewpoint of moisture permeability and compatibility with the cellulose ester, a smaller one is preferable. The polyhydric alcohol may be one kind or a mixture of two or more kinds. Further, all OH groups in the polyhydric alcohol may remain as OH groups, or may be partially esterified or etherified.
[0061]
These compounds containing two or more hydroxyl groups, in addition to the effect of the formation of the urethane compound described above, in the crosslinking of hydroxyl groups and isocyanate remaining in the cellulose ester, the hydroxyl group-containing compound further forms a urethane bond during these crosslinking. It is thought that by penetrating through, the water absorption elastic modulus increases due to an increase in the molecular weight, and also works to relieve excessive hardness and brittleness.
[0062]
The amount of the compound containing a hydroxyl group to be used is in the range of 0.01% to 3%, preferably 0.03 to 1.5% by mass based on the cellulose ester. If the amount is too large, the retention property is deteriorated. If the amount is too small, the resin does not have a plasticizing effect and becomes brittle, so that the effects of the present invention cannot be obtained. Therefore, the amount is preferably about equivalent to about 3 times the amount of the polyisocyanate compound.
[0063]
The polarizing plate protective film thus formed preferably has a high elastic modulus (hereinafter simply referred to as an elastic modulus) at normal temperature and normal humidity such as 23 ° C. and 55% RH, and specifically, 3500 MPa Above, more preferably 4000 MPa or more.
[0064]
In the present invention, the elastic modulus is defined below.
(Elastic modulus)
The sample is conditioned for 24 hours in an environment of 23 ° C. and 55% RH, and the elastic modulus is measured according to the method described in JIS K7127. As the tensile tester, for example, Tensilon RTA-100 manufactured by Orientec Co., Ltd. is used. The test piece is a No. 1 type test piece, and the test speed is 100 mm / min. The elastic modulus is calculated at an elastic modulus analysis start point of 2 MPa and an elastic modulus analysis end point of 60 MPa.
[0065]
Further, by setting the water absorption elastic modulus to a predetermined value (2800 to 4000 MPa, more preferably 2900 to 3800 MPa) in addition to the elastic modulus at normal temperature and normal humidity, the durability is further improved.
[0066]
Further, in the present invention, the water absorption elastic modulus is the elastic modulus measured according to the method described in JIS K7127 within 1 minute after the film is immersed in warm water of 60 ° C. for 30 minutes to sufficiently absorb water, and taken out of the warm water. Point to. The shape of the test piece at this time is a No. 1 type test piece, and the test speed is 100 mm / min.
[0067]
The larger the water absorption elastic modulus is, the smaller the amount of light leakage of the polarizing plate is, which is preferable. However, if it is too large, the film becomes brittle and the tear strength decreases.
[0068]
Control of the molecular weight by the above-mentioned cross-linking of the cellulose ester has a favorable effect in order to keep the elastic modulus in these ranges. In addition, the present invention is also effective in controlling the stretching ratio of the film, controlling the crystallization of the film by controlling the drying temperature during film formation, and adjusting the amount of the plasticizer to be added.
[0069]
The cellulose ester film according to the present invention has improved dimensional stability against high temperature and high humidity, and has a smaller dimensional change rate than the cellulose ester film containing no polymer of the present invention.
[0070]
That is, in the cellulose ester film according to the present invention, the dimensional change after 48 hours when treated at 80 ° C. and 90% RH is less than 0.2% (absolute value is 0.2% or less). preferable.
[0071]
(Measurement of dimensional stability)
After conditioning the cellulose ester film before saponification in a room at 23 ° C. and 55% RH for 24 hours, in the same room, two cross marks are formed on the surface of the cellulose ester film at 100 mm intervals in the longitudinal direction and the width direction of the film. And heat-treated at 80 ° C. and 90% RH for 50 hours, humidified again in a room at 23 ° C. and 55% RH for 24 hours, and between the two marks. Is measured with a cassette meter and the value is set as b, and the dimensional stability is obtained as a dimensional change rate by the following equation. The dimensional change rate is positive when the film is elongated, and is negative when the film is contracted.
[0072]
Dimensional change rate (%) = [(ba) / a] × 100
Further, the cellulose ester film according to the present invention has a haze value (defined by ASTM-D1003-52) of 2% or less when left under these conditions at 80 ± 5 ° C. and 90 ± 10% RH for 48 hours. Preferably, there is.
[0073]
Further, in the present invention, a cellulose ester film having high transparency without a decrease in haze value even at high humidity can be obtained.
[0074]
In the cellulose ester film according to the present invention, in addition to the above, a plasticizer can be used as an additive, and the plasticizer is not particularly limited. Examples thereof include a polyhydric alcohol ester plasticizer and a glycolate plasticizer. An agent, a phosphate ester plasticizer, a phthalate ester plasticizer and the like can be used, and particularly preferred are a polyhydric alcohol plasticizer and a glycolate plasticizer. Further, the addition amount of the phosphate plasticizer is preferably 6% by mass or less.
[0075]
The polyhydric alcohol ester comprises an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. For example, ethylene glycol bis (cyclohexanecarboxylate), ethylene glycol diphenolate and the like can be used.
[0076]
The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. The preferred glycolate-based plasticizer is not particularly limited, and for example, butylphthalylbutyl glycolate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate and the like can be used.
[0077]
Phosphate plasticizers include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like.Phthalate plasticizers include diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate and the like can be used.
[0078]
These plasticizers can be used alone or in combination of two or more.
The use amount of the plasticizer is preferably 4 to 20% by mass, more preferably 6 to 16% by mass, and particularly preferably 8 to 13% by mass based on the cellulose ester. If the added amount of the plasticizer is too large, the film becomes too soft, so that the water absorption elasticity decreases. If the added amount is too small, the moisture permeability of the film decreases.
[0079]
These plasticizers may be added to the dope after dissolving it in an organic solvent such as alcohol, methylene chloride, or dioxolan, or may be added directly to the dope composition. Alternatively, it may be dissolved in an organic solvent and a cellulose ester, and then mixed and added.
[0080]
In the present invention, an ultraviolet absorber may be added.
From the viewpoint of preventing deterioration of the liquid crystal, an ultraviolet absorber having an excellent ability to absorb ultraviolet light having a wavelength of 370 nm or less and having a low absorption of visible light having a wavelength of 400 nm or more is preferably used from the viewpoint of good liquid crystal display properties. In the present invention, the transmittance at a wavelength of 370 nm is particularly preferably 10% or less, more preferably 5% or less, and still more preferably 2% or less.
[0081]
In the present invention, since the compound having a hydroxyl group forms a urethane bond and has a plasticizing effect, an ultraviolet absorber having a hydroxyl group in the molecule is particularly preferably used.
[0082]
The ultraviolet absorber used is not particularly limited as long as it is such an ultraviolet absorber, and examples thereof include an oxybenzophenone-based compound, a benzotriazole-based compound, and a salicylate-based compound. The UV absorber preferably used is preferably a benzotriazole-based UV absorber or a benzophenone-based UV absorber having a high transparency and having an excellent effect of preventing deterioration of a polarizing plate or a liquid crystal element, and has an unnecessary coloring. Less benzotriazole UV absorbers are particularly preferred. Specific examples of the ultraviolet absorbent include, for example, TINUVIN109, TINUVIN171, TINUVIN326, TINUVIN327, and TINUVIN328 manufactured by Ciba Specialty Chemicals Co., Ltd., but are not limited thereto.
[0083]
The amount of the ultraviolet absorber used is not uniform depending on the type of the compound, the conditions of use, and the like. % Is preferable, and 0.6 g to 2.0% by mass is more preferable.
[0084]
Next, a method for producing the cellulose ester film of the present invention will be described.
The production of the cellulose ester film of the present invention comprises the steps of dissolving the cellulose ester and additives in a solvent to form a dope solution, casting the dope solution on a support, and drying the cast dope solution. It is carried out.
[0085]
The concentration of the cellulose ester in the dope solution is preferably higher because the drying load after casting on the support can be reduced, but when the concentration of the cellulose ester is too high, the load at the time of filtration increases, and the filtration accuracy is increased. become worse. The concentration that balances these is preferably 10 to 50% by mass, and more preferably 15 to 35% by mass.
[0086]
The solvent used in the dope solution may be used alone or in combination. However, it is preferable to use a mixture of a good solvent and a poor solvent of cellulose ester in terms of production efficiency. It is preferable in terms of solubility. A preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass of the good solvent and 30 to 2% by mass of the poor solvent.
[0087]
A good solvent and a poor solvent are defined as a solvent that dissolves the cellulose ester used alone as a good solvent, and a solvent that swells or does not dissolve alone as a poor solvent. Therefore, depending on the average degree of acetylation of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as a solvent, it is a good solvent in the case of cellulose acetate ester (bonding acetic acid amount 55%) and cellulose acetate propionate. In the case of cellulose acetate (the amount of bound acetic acid is 60%), it becomes a poor solvent.
[0088]
The good solvent is not particularly limited, but, for example, in the case of cellulostriacetate, organic halogen compounds such as methylene chloride and dioxolanes, and in the case of cellulose-propionate, methylene chloride, acetone, methyl acetate and the like. No.
[0089]
Although the poor solvent is not particularly limited, for example, methanol, ethanol, n-butanol, cyclohexane, acetone, cyclohexanone and the like are preferably used. It is preferable to use a solvent having a boiling point of 80 ° C. or higher, such as n-butanol or cyclohexanone, because the water absorption elasticity can be easily increased by transport in the drying step.
[0090]
As a method for dissolving the cellulose ester when preparing the above-described dope solution, a general method can be used. By combining heating and pressurization, heating can be performed to a temperature higher than the boiling point at normal pressure. It is preferable to perform stirring and dissolution while heating at a temperature not lower than the boiling point of the solvent at normal pressure and within a range in which the solvent does not boil under pressure, so as to prevent the formation of a mass of undissolved material called gel or mamaco. Further, a method in which a cellulose ester is mixed with a poor solvent to wet or swell, and then a good solvent is added to dissolve the cellulose ester is preferably used.
[0091]
Pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.
[0092]
The higher the heating temperature after adding the solvent, the better from the viewpoint of the solubility of the cellulose ester. However, if the heating temperature is too high, the required pressure increases and the productivity decreases. A preferred heating temperature range is 45 to 120 ° C, more preferably 60 to 110 ° C, and even more preferably 70 to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.
[0093]
Next, the cellulose ester solution is filtered using a suitable filter material such as filter paper. It is preferable that the filtration material has a small absolute filtration accuracy in order to remove insolubles and the like, but if the absolute filtration accuracy is too small, there is a problem that the filtration material is likely to be clogged. Therefore, a filter medium having an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium having a range of 0.001 to 0.008 mm is more preferable, and a filter medium having a range of 0.003 to 0.006 mm is further preferable.
[0094]
The material of the filter medium is not particularly limited, and a normal filter medium can be used. However, a plastic filter medium such as polypropylene or Teflon (R) or a metal filter medium such as stainless steel is preferable because the fibers do not fall off.
[0095]
Filtration of the dope solution can be carried out by a usual method. However, a method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and within a range where the solvent does not boil under pressure is used before and after the filtration material. Of the pressure difference (hereinafter sometimes referred to as filtration pressure) is small, which is preferable. A preferred temperature range is 45 to 120 ° C, more preferably 45 to 70 ° C, and even more preferably 45 to 55 ° C.
[0096]
The smaller the filtration pressure, the better. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.
[0097]
In the present invention, the crosslinkable compound, for example, a polyisocyanate compound may be directly dissolved in an organic solvent in the dope and added, or when a hydroxyl group-containing compound is added, it may be sequentially or simultaneously. Before and after the addition. It is preferable that these compounds are mixed as uniformly as possible into a dope solution. However, a solution of an isocyanate compound or a hydroxyl group-containing compound is separately prepared, and the solution is cast immediately before casting on a belt or a drum. Alternatively, the separately prepared solutions of the crosslinking compound or the hydroxyl group-containing compound may be separately or simultaneously mixed with the dope solution.
[0098]
In particular, when the crosslinking reaction proceeds rapidly, for example, it may be sequentially added in-line immediately before the step of casting to a belt or a drum. Thereby, in the casting step, a crosslinking reaction proceeds on a belt or on a drum support and in the web after peeling.
[0099]
Hereinafter, film formation by a casting process of a dope prepared by adding a polyisocyanate or a hydroxyl group-containing compound will be described.
[0100]
As the support in the casting step, a stainless steel endless belt or drum having a mirror-finished surface is preferably used. The temperature of the support in the casting step is preferably from 0 ° C. to a temperature lower than the boiling point of the solvent. A higher temperature is preferable because the drying speed can be increased, but if it is too high, foaming or flatness may be deteriorated. . The preferred support temperature is from 0 to 40 ° C, more preferably from 5 to 30 ° C. The method of controlling the temperature of the support is not particularly limited, and includes a method of blowing hot air or cool air, and a method of bringing a hot water bat into contact with the support. It is preferable to use a hot water vat because the time required for the temperature of the support to become constant is short because heat is efficiently transferred. When using hot air, it may be necessary to use air at a temperature higher than the target temperature.
[0101]
In order for the cellulose ester film to exhibit good flatness, the residual solvent amount when peeled from the support is preferably from 10 to 120%, more preferably from 20 to 40% or from 60 to 120%, particularly preferably. Is 20 to 30% or 70 to 115%. The residual solvent amount is defined by the following equation.
[0102]
Residual solvent amount = ((mass before heat treatment-mass after heat treatment) / (mass after heat treatment)) × 100 (%)
The heat treatment when measuring the amount of residual solvent means that the film is heated at 115 ° C. for one hour.
[0103]
In the present invention, the film is peeled off from a support such as a belt or a drum in a dry state, that is, when the residual solvent amount at the time of peeling is 90% or more and 110% or less, and heated (40 to 150 ° C.). And the time is maintained at 15 to 25 minutes) for promoting the crosslinking reaction. When the amount of the residual solvent in the web is within this range, a urethane-forming reaction is promoted in the film to perform crosslinking, whereby a cellulose ester film having excellent strength can be obtained. In the drying step of the cellulose ester film, the film separated from the support is preferably further dried to reduce the residual solvent amount to 3% or less, more preferably 0.5% or less. In the film drying step, a method of drying while transporting a film by a roll suspension method or a tenter method is generally employed.
[0104]
It is preferable to carry out width holding or stretching by a tenter method in a place where the amount of the residual solvent immediately after peeling from the support is large, from the viewpoint of improving the flatness of the film. When the stretching ratio of the tenter is increased, the water absorption elastic modulus in the width direction increases. The preferred stretching ratio is 0 to 15%, more preferably 1 to 12%. The stretching ratio of 0% means that the width is maintained, and in a place where the amount of the residual solvent is large, the same effect as the stretching can be obtained.
[0105]
The means for drying the film is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, a microwave, or the like, but is preferably performed with hot air in terms of simplicity.
[0106]
The drying temperature is preferably increased stepwise in the range of 40 to 150 ° C, and more preferably in the range of 50 to 140 ° C to improve dimensional stability. Further, it is preferable to dry the film at a softening point of ± 20 ° C. for 10 to 40 minutes from the viewpoint of improving the water absorption elasticity. By controlling the transport tension during drying of the film at a softening point of ± 20 ° C., the water absorption elastic modulus in the casting direction can be controlled. The preferable range of the transport tension is 150 to 350 N / m, and more preferably 200 to 300 N / m.
[0107]
The thickness of the cellulose ester film, for example, when used in a liquid crystal display or the like, a thinner polarizing plate is preferable because it is easy to make the display thinner, but if too thin, moisture permeability, tear strength, etc. to degrade. The film thickness of the cellulose ester film that achieves both of these is preferably 10 to 65 μm, more preferably 20 to 60 μm, and particularly preferably 35 to 50 μm.
[0108]
In the cellulose ester film of the present invention, in addition to the heat-crosslinkable organic compound (preferably a polyisocyanate compound), the hydroxyl group-containing compound, the plasticizer, the ultraviolet absorber, and the like, if necessary, another ultraviolet ray Additives such as an absorbent and a dye or a matting agent may be added.
[0109]
The ultraviolet absorber to be used is not particularly limited, but examples thereof include a cyanoacrylate compound, a nickel complex compound, and an inorganic powder in addition to the hydroxyl group-containing ultraviolet absorber. An ultraviolet absorber having high transparency and less unnecessary coloring is preferable, and these ultraviolet absorbers may be used in combination with the ultraviolet absorber.
[0110]
The method of adding the ultraviolet absorber, including the hydroxyl group-containing ultraviolet absorber, may be added to the dope after dissolving the ultraviolet absorber in an organic solvent such as alcohol, methylene chloride, or dioxolane, or directly in the dope composition. It may be added. Those which do not dissolve in an organic solvent such as inorganic powder are dispersed in an organic solvent and a cellulose ester using a dissolver or a sand mill, and then added to the dope.
[0111]
In the present invention, a blue dye may be added to suppress yellowing of the film. Preferred dyes include anthraquinone dyes.
[0112]
The anthraquinone-based dye can have any substituent at positions 1 to 8 of the anthraquinone. Preferred substituents include an anilino group, a hydroxyl group, an amino group, a nitro group, or a hydrogen atom.
[0113]
The amount of these dyes added to the film is 0.1 to 1000 μg / m in order to maintain the transparency of the film.², Preferably 10 to 100 µg / m²It is.
[0114]
In the present invention, fine particles such as silicon oxide may be added as a matting agent, if necessary. The matting agent fine particles are preferably surface-treated with an organic substance because the haze of the film can be reduced.
[0115]
Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like. The average effect of the primary particles of the fine particles is preferably from 5 to 50 nm, more preferably from 7 to 20 nm, because the larger the average diameter of the fine particles, the greater the matting effect and the smaller the average diameter, the better the transparency.
[0116]
The fine particles of silicon oxide are not particularly limited, and include, for example, AEROSIL 200, 200V, 300, R972, R972V, R972CF, R974, R202, R805, R812, OX50, TT600 manufactured by Nippon Aerosil Co., Ltd., and preferably. AEROSIL 200, 200V, R972, R972V, R974, R202, R805, R812 and the like.
[0117]
The above-mentioned various additives may be batch-added to the dope solution, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the matting agent in-line in order to reduce the load on the filter medium.
[0118]
When the additive dissolving solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in order to improve the mixing property with the dope. The preferred amount of the cellulose ester is 1 to 10 parts by mass, more preferably 3 to 5 parts by mass, based on 100 parts by mass of the solvent.
[0119]
In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), a SWJ (Toray static-type in-pipe mixer Hi-Mixer) or the like is preferably used.
[0120]
When the isocyanate compound is contained in the cellulose ester film, the cellulose ester film is crosslinked and undergoes modification.
[0121]
Therefore, as another embodiment of the present invention, in order to produce the crosslinked cellulose ester film in a form in which ear-return material can be reused, a die for casting on cellulose by the casting is devised. For example, a schematic diagram is drawn in FIG. 1, but the die 1 is divided into a central portion (1a) and both end portions (1b, 1c) so that different dopes can be flowed into each portion. I do. In this way, a dope containing isocyanate is flowed into the die center (1a), and a dope containing no isocyanate compound is flowed from both ends (1b, 1c) of the die. At both ends of the film after the film, a film consisting essentially of a cellulose ester that does not contain a reusable urethane polymer, and a central portion used as a uniform film roll is a crosslinked cellulose ester having a urethane bond. I do.
[0122]
When both ends of the film are cut off as ear-turning material and reused, this part has no cross-linking structure, so it can be reused as usual, and the product part to be cut out and used is cross-linked by urethane bonds. By the formation, a cellulose ester film having excellent moisture permeability, no cloudiness at high humidity, excellent transparency, low haze value, and excellent retention and mechanical strength can be obtained. In addition, ear return materials that do not contain isocyanate compounds at both ends of the die can be reused and utilized.
[0123]
A polarizing plate can be produced by a general method using the cellulose ester film according to the present invention. For example, a polyvinyl alcohol film is roll-oriented, a polarizing film is prepared by adsorbing iodine or a dichroic dye, and the cellulose ester film is alkali-saponified on both surfaces of the polarizing film. There is a method of bonding together. Usually, the lamination is performed so that the stretching direction of the polarizing film and the casting direction (MD direction) of the polarizing plate protective film coincide with each other. The alkali saponification treatment refers to a treatment in which a cellulose ester film is immersed in a high-temperature strong alkaline solution in order to improve the wettability of the aqueous adhesive and improve the adhesiveness.
[0124]
Since the polarizing film is stretched in the uniaxial direction (usually in the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually in the longitudinal direction) shrinks, and the stretching direction is perpendicular to the stretching direction (usually in the width direction). ) To stretch. As the film thickness of the polarizing plate protective film becomes thinner, the expansion and contraction ratio of the polarizing plate becomes larger, and in particular, the amount of shrinkage in the stretching direction of the polarizing film becomes larger. Usually, since the stretching direction of the polarizing film is bonded to the casting direction (MD direction) of the polarizing plate protective film, it is important to suppress the expansion and contraction rate especially in the casting direction when thinning the polarizing plate protecting film. It is.
[0125]
The cellulose ester film of the present invention has high moisture permeability, excellent dimensional stability and excellent tear strength and transparency.For example, when used for a polarizing plate, not only the polarizing plate has few foreign substances and defects, but also rework. Also excellent in properties.
Therefore, it can be advantageously used for liquid crystal display members such as a retardation plate, a reflection plate, a viewing angle widening film, an antiglare film, an antireflection film, and an antistatic film, in addition to the polarizing plate protection film.
[0126]
【Example】
Hereinafter, embodiments of the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.
[0127]
[Example 1]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
Hexamethylene diisocyanate 0.5 parts by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 2]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
Hexamethylene diisocyanate 0.5 parts by mass
1,3-butanediol 5 parts by mass
2- (2'-hydroxy-3 ', 5'-di-t-butyl
Phenyl) bezotriazole 3 parts by mass
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 3]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
Hexamethylene diisocyanate 0.5 parts by mass
2- (2'-hydroxy-3 ', 5'-di-t-butyl
Phenyl) bezotriazole 7 parts by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 4]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.3 parts by mass of 2,4-tolylene diisocyanate (TDI)
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 5]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.3 parts by mass of 2,4-tolylene diisocyanate (TDI)
Hexanetriol 0.2 parts by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 6]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.3 parts by mass of 2,4-tolylene diisocyanate (TDI)
Hexanetriol 0.2 parts by mass
2- (2'-hydroxy-3 ', 5'-di-t-butyl
Phenyl) bezotriazole 3 parts by mass
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 7]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.3 parts by mass of 2,4-tolylene diisocyanate (TDI)
Triethylene glycol 3 parts by mass
2- (2'-hydroxy-3 ', 5'-di-t-butyl
Phenyl) bezotriazole 3 parts by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
Example 8
Degree of substitution of acetyl group 2.00, degree of substitution of propionyl group 0.80, number average
100 parts by weight of cellulose acetate propionate having a molecular weight of 100,000
Hexamethylene diisocyanate 0.2 parts by mass
Ethylphthalylethyl glycolate 4 parts by mass
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methyl acetate
25 parts by mass of ethanol
[Example 9]
Degree of substitution of acetyl group 2.00, degree of substitution of propionyl group 0.80, number average
100 parts by weight of cellulose acetate propionate having a molecular weight of 100,000
Hexamethylene diisocyanate 0.5 parts by mass
2- (2'-hydroxy-3 ', 5'-di-t-butyl
Phenyl) bezotriazole 3 parts by mass
Ethylphthalylethyl glycolate 4 parts by mass
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methyl acetate
25 parts by mass of ethanol
[Example 10]
Degree of substitution of acetyl group 2.00, degree of substitution of propionyl group 0.80, number average
100 parts by weight of cellulose acetate propionate having a molecular weight of 100,000
Hexamethylene diisocyanate 0.5 parts by mass
Hexanetriol 0.2 parts by mass
2- (2'-hydroxy-3 ', 5'-di-t-butyl
Phenyl) bezotriazole 3 parts by mass
Ethylphthalylethyl glycolate 4 parts by mass
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methyl acetate
25 parts by mass of ethanol
[Example 11]
Degree of substitution of acetyl group 2.00, degree of substitution of propionyl group 0.80, number average
100 parts by weight of cellulose acetate propionate having a molecular weight of 100,000
Hexamethylene diisocyanate 0.5 parts by mass
Hexanetriol 0.2 parts by mass
Tinuvin 326 (manufactured by Ciba Specialty Chemicals Co., Ltd.)
3 parts by mass
Ethylphthalylethyl glycolate 4 parts by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methyl acetate
25 parts by mass of ethanol
[Example 12]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.3 parts by mass of 4,4'-diphenylmethane diisocyanate (MDI)
0.2 parts by mass of ethylene glycol
Tinuvin 326 (manufactured by Ciba Specialty Chemicals Co., Ltd.)
3 parts by mass
3 parts by mass of triphenyl phosphate
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 13]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.1 parts by mass of 4,4'-diphenylmethane diisocyanate (MDI)
Tinuvin 326 (manufactured by Ciba Specialty Chemicals Co., Ltd.)
3 parts by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Example 14]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
0.3 parts by mass of 4,4'-diphenylmethane diisocyanate (MDI)
0.2 parts by mass of ethylene glycol
Tinuvin 326 (manufactured by Ciba Specialty Chemicals Co., Ltd.)
3 parts by mass
AEOSIL R-972 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Comparative Example 1]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
Triphenyl phosphate 10 parts by mass
Ethylphthalylethyl glycolate 2 parts by mass
Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 1 part by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Comparative Example 2]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
Triphenyl phosphate 10 parts by mass
Ethylphthalylethyl glycolate 2 parts by mass
Trimethylcetyl ammonium chloride 8 parts by mass
AEROSIL 200V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Comparative Example 3]
Degree of substitution of acetyl group 2.00, degree of substitution of propionyl group 0.80, number average
100 parts by weight of cellulose acetate propionate having a molecular weight of 100,000
Triphenyl phosphate 10 parts by mass
Ethylphthalylethyl glycolate 2 parts by mass
Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 1 part by mass
Benzyltrimethylammonium chloride 1 part by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methyl acetate
25 parts by mass of ethanol
[Comparative Example 4]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
5 parts by mass of vinyl acetate
5 parts by mass of vinyl laurate
Benzoin 1 part by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
[Comparative Example 5]
Cellulose triacetate having an acetyl substitution degree of 2.88 (number average molecular weight 150
000) 100 parts by mass
4 parts by mass of vinyl acetate
3 parts by mass of vinyl stearate
Benzyl acrylate 2 parts by mass
1 part by mass of methyl acrylate
Diethoxybenzophenone 1 part by mass
AEROSIL R972V 0.1 parts by mass
475 parts by mass of methylene chloride
25 parts by mass of ethanol
(Film formation)
Each of the dope compositions having the formulations of Examples 1 to 15 and Comparative Examples 1 to 5 was subjected to film formation as described below. Each dope composition is put into a pressurized and sealed container, heated to 45 ° C., the pressure in the container is set to 1.2 atm, and the cellulose ester is completely dissolved with stirring to obtain a dope composition (hereinafter referred to as “dope”). Got. The temperature of the dope was lowered to 35 ° C. and the mixture was allowed to stand overnight, and this dope was subjected to Azumi Filter Paper No. After filtration using 244, the mixture was left still overnight to remove bubbles. Next, a filtration pressure of 1.0 using Finemet NM (absolute filtration accuracy: 100 μm) and Finepore NF (absolute filtration accuracy: 50 μm, 15 μm, 5 μm in this order, manufactured by Nippon Seisen Co., Ltd.). × 10⁶It was filtered with Pa. Using a 35 ° C. dope obtained by filtration, a film was cast from a hanger-type die onto an endless stainless steel belt at 22 ° C. where the infinity was transferred.
[0128]
In Examples 1 to 15 and Comparative Examples 1 to 3, the air was applied at 40 ° C. and a wind speed of 10 m / sec obliquely at an angle of 40 ° from the air side of the stainless steel belt on the side where the die was located. . Further, for all the webs, the time required from the casting of the dope to the peeling after the web was peeled with the residual solvent amount of 100% by mass was 3 minutes.
[0129]
Thereafter, the web was passed through three rolls, introduced into a tenter drying apparatus that grips both ends of the web with pin clips as described in JP-A-62-115035, and dried at 90 to 115 ° C. Next, the dried web was dried at 110 to 130 ° C., and the dried web was wound at a residual solvent amount of 0.2% by mass to obtain a cellulose ester film of 40 μm.
[0130]
After the web is peeled, crosslinking is sufficiently performed in the cellulose ester film by heating and drying. Thus, cellulose ester films Examples 1 to 15 and Comparative Examples 1 to 3 were produced for each dope.
[0131]
In Comparative Examples 4 and 5, eight 2 kW high-pressure mercury lamps were irradiated from a distance of 15 cm away from the web on the stainless steel belt while blowing air at 40 ° C. to cause photopolymerization to occur in the web. A polymer was formed. 300 mJ / cm total irradiation dose at any position of web on stainless steel belt²After removing the web with the residual solvent amount of 100% by mass (the time required from the dope casting to the peeling was 3 minutes), the web was passed through three rolls, and the mixture was passed through JP-A-62-115035. The web was introduced into a tenter drier in which both ends of the web were gripped with pin clips as described in the gazette, and the web was similarly dried.
[0132]
Each of the obtained cellulose ester films was evaluated as follows.
[0133]
(Measurement of dimensional stability)
After humidifying each cellulose ester film in a room at 23 ° C. and 55% RH for 24 hours, in the same room, two cross marks are formed on the surface of the cellulose ester film at intervals of 100 mm in the longitudinal direction and width direction of the film. Attach the size exactly, measure the distance as a, perform heat treatment at 80 ° C. and 90% RH for 50 hours, adjust the humidity again in a room at 23 ° C. and 55% RH for 24 hours, and place between two marks. The distance is measured with a cassette meter, and the value is set as b.
[0134]
Dimensional change rate (%) = [(ba) / a] × 100
(Tear strength)
The tear strength of the tear load according to the Elmendorf method was measured using a light load tearing device manufactured by Toyo Seiki Co., Ltd. in accordance with JIS K 7128-1991.
[0135]
(Elastic modulus)
The sample was conditioned for 24 hours in an environment of 23 ° C. and 55% RH, and the elastic modulus was measured according to the method described in JIS K7127. The tensile tester used was Tensilon RTA-100 manufactured by Orientec Co., Ltd. The test piece was a No. 1 type test piece, and the test speed was 100 mm / min. In addition, the elastic modulus was calculated at an elastic modulus analysis start point of 2 MPa and an elastic modulus analysis end point of 60 MPa.
[0136]
(Measurement of haze value)
Each film sample is measured using T-2600DA manufactured by Tokyo Denshoku Kogyo Co., Ltd. according to ASTM-D1003-52, and the haze is ranked and evaluated as follows.
[0137]
A: Less than 0.1% haze
B: Haze 0.1% or more and less than 0.5%
C: Haze 0.5% or more and less than 1%
D: Haze 1% or more.
[0138]
(Evaluation of holdability)
Each of the film samples was cut into a size of 10 cm × 10 cm, the mass after being left for 24 hours in an atmosphere of 23 ° C. and 55% RH was measured, and then left for 2 weeks at 80 ° C. and 90% RH. After the treatment, the surface of the sample was gently wiped, the mass after one day of standing at 23 ° C. and 55% RH was measured, and the retention was calculated by the following method.
[0139]
Retention (mass%) = {(mass before standing−mass after standing) / mass before standing} × 100
(Cloudy)
Each film sample was treated in a high-temperature and high-humidity atmosphere at 80 ° C. and 90% RH for 6 hours, and then left in a 23 ° C. and 55% RH atmosphere for 18 hours. After repeating this process a total of 30 times, the metal compound layer side was visually observed to be cloudy. The evaluation was performed on a scale of 1 to 1 when no white turbidity was observed, 5 when severe white turbidity occurred, and 2 to 4 for the rank between them.
[0140]
The evaluation results are shown in Table 1 below.
[0141]
[Table 1]

[0142]
The modified cellulose ester films of the present invention (Examples 1 to 14) all show good properties, and in particular, are films having high dimensional stability, high tear strength, small haze, and good retention. . In addition, there is little cloudiness at the time of high humidity and it is excellent.
[0143]
Next, a polarizing plate was prepared from each film, and the following evaluation was performed.
(Preparation of polarizing plate)
All the formed cellulose ester films of Examples 1-1415 and Comparative Examples 1-5 were subjected to a surface saponification treatment with a 2.5 mol / l sodium hydroxide aqueous solution at 40 ° C for 60 seconds, washed with water for 3 minutes, and dried. Was. Separately, a polyvinyl alcohol having a thickness of 120 μm was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid to prepare a polarizing film stretched in a vertical direction four times at 50 ° C. On both surfaces of the polarizing film, the above-mentioned surface-saponified cellulose ester films were adhered using a completely saponified polyvinyl alcohol 5% by mass aqueous solution as an adhesive to prepare polarizing plates 1-1415 and Comparatives 1-5.
[0144]
(Polarization plate durability)
Two samples of 100 mm × 100 mm in size were cut out from each polarizing plate, exposed to an atmosphere of 80 ° C. and 90% RH for 50 hours, and the area of white spots generated on the edge of the polarizing plate by crossed Nicols was determined with respect to the entire area. Observed as an area ratio, the following grades were evaluated.
[0145]
A: There was no blank area
B: White area is less than 2% of the entire area
C: White area is 2% or more and less than 5% of the entire area
D: White area is 5% or more and less than 10% of the whole area
E: The blank area was 10% or more of the entire area.
[0146]
(Foreign matter / defect of polarizing plate)
Five samples each of which were cut into two pieces each having a size of 25 cm × 25 cm from each polarizing plate were prepared, and crossed Nicols were used to observe the number of shining spots appearing on a dark surface due to foreign substances and the like. The average of the number of the five foreign substances was evaluated at the following levels.
[0147]
A: There was no bright spot
B: 1 to 5 small bright spots were observed
C: 6 to 50 small bright spots were observed
D: 51 to 99 bright spots were observed
E: 100 or more brilliant spots were observed.
[0148]
Table 1 shows the results of the above evaluations.
(Reworkability)
The obtained polarizing plate of 100 × 100 mm size was bonded to a glass substrate. The polarizing plate is slightly peeled off from the glass substrate from one of the four corners, and the polarizing plate is peeled off diagonally while holding the peeled polarizing plate and holding the glass substrate. The same operation was performed for a total of ten samples for each polarizing plate, and evaluation was performed according to the following criteria.
[0149]
：: All 10 sheets were completely peeled off
○: Partial peeling remains only on one sheet
Δ: Peeling residue occurred on 2 to 5 sheets
×: Peeling residue occurred on 6 or more sheets.
The evaluation results are shown in the table below.
[0150]
[Table 2]

[0151]
Example 16
A die capable of casting a plurality of dope liquids as shown in FIG. 1 was used. The dope used in Example 2 was used at the center of the die, and the dope used in Comparative Example 1 was used at both ends of the die. Was flowed, and a film was formed under the same conditions as in the above example. A 1000 m roll film having a thickness of 40 μm and a width of 1.25 m was obtained. Next, the roll film was set in a cutting machine, and both ends were cut into widths of 12.5 cm each to obtain a roll film of 1 m. The cut back ear material was finely cut and used so that 20 parts by mass of 100 parts by mass of cellulose triacetate (number average molecular weight: 150,000) having an acetyl substitution degree of 2.88 used in Example 2 was replaced. A dope was prepared in the same manner as in Example 2.
[0152]
As a result, a dope solution was obtained in the same manner as in Example 2 without thickening.
In the same manner as described above, Azumi Filter Paper No. After filtration using 244, the mixture was allowed to stand still overnight, defoamed, and then Finemet NM (absolute filtration accuracy 100 μm) and Finepore NF (absolute filtration accuracy 50 μm, 15 μm, manufactured by Nippon Seisen Co., Ltd.) Using a filter having a filtration pressure of 1.0 × 10⁶The mixture was filtered with Pa and used for film formation.
[0153]
Using a dope at 35 ° C. obtained by filtration, the film was cast on an endless stainless steel belt in the same manner as described above, and the film was formed and dried in the same manner as described above. To give a cellulose ester film of 40 μm. The resulting cellulose film was compared with the cellulose ester film of Example 2 for tear strength, haze (turbidity), retention, and white turbidity at high humidity.
[0154]
Also, Azumi Filter Paper No. manufactured by Azumi Filter Paper Co., Ltd. used for filtering the dope solution. Regarding 244, there was no clogging of filters such as Finemet NM (absolute filtration accuracy: 100 μm) and Finepore NF manufactured by Nippon Seisen Co., Ltd. which were used for filtration after standing overnight, and there was a problem in the process. Did not.
[0155]
On the other hand, the central portion of the produced cellulose ester film, that is, the film containing the crosslinked cellulose ester was finely cut, and then the cellulose having a degree of acetyl substitution of 2.88 used in Example 2 was used in the same manner as in the case of the ear return material. When a dope was prepared in the same manner as in Example 2 by using 20 parts by mass of 100 parts by mass of triacetate (number-average molecular weight: 150,000), considerable insolubles were generated, and the viscosity increased. Since the filter paper was large and clogging of the filter paper occurred, the dope could not be filtered, so that film formation could not be performed under the same conditions. In addition, insolubles were not removed even from the filtrate partially filtered, and a clear solution was not obtained.
[0156]
【The invention's effect】
A cellulose ester film having a low haze value, being transparent, having excellent mechanical strength (tearing strength) and retention properties, and having no cloudiness due to high temperature and high humidity was obtained.
[Brief description of the drawings]
FIG. 1 is a schematic view of a die separated into a central portion, both end portions and three dies.

Claims (12)

A cellulose ester film formed into a film in the presence of a thermally crosslinkable organic compound. The cellulose ester film according to claim 1, wherein the thermally crosslinkable organic compound is a thermally crosslinkable polymer. The cellulose ester film according to claim 1, wherein the thermally crosslinkable organic compound is a polyisocyanate. A dope is prepared by dissolving a polyisocyanate and a cellulose ester in an organic solvent, the dope is cast on a support in the form of a film, and the film cast in a state containing 10% or more of the solvent is peeled from the support. And heating and drying to promote a urethane-forming reaction. A cellulose ester film which is formed in the presence of a polyisocyanate and a hydroxyl group-containing compound. A polydocyanate, a hydroxyl group-containing compound and a cellulose ester are dissolved in an organic solvent to prepare a dope, and the dope is cast on a support in the form of a film. A method for producing a cellulose ester film, comprising separating a cast film, drying by heating, and accelerating a urethanization reaction. The cellulose ester film according to claim 5, further comprising a hydroxyl group-containing ultraviolet absorber. 8. The cellulose ester film according to claim 1, wherein the cellulose ester has an elastic modulus of 3500 MPa or more. 9. The cellulose ester according to claim 1, wherein the dimensional change when the cellulose ester film is treated at 80 ° C. and 90 RH% for 48 hours is within 0.2%. 10. the film. The haze value defined by ASTM-D1003-52 is 2% or less when treated at 80 ± 5 ° C. and 90 ± 10% RH for 48 hours, wherein the haze value is 2% or less. 10. The cellulose ester film according to 7, 8, or 9. In a method for producing a cellulose ester film in which a cellulose ester dope is cast on a support using a die, a cellulose ester dope containing a polyisocyanate and a cellulose ester is supplied from a central portion of the die, and both ends of the die are supplied. A cellulose ester dope containing no polyisocyanate is supplied from the above, and both ends in the width direction of the formed film are made into a cellulose ester film containing no polyisocyanate. After saponifying the cellulose ester film according to any one of claims 1 to 3, 5 and 7 to 10, the saponified surface of the cellulose ester film is in contact with the polarizing film, so that both sides of the polarizing film are provided. A method for producing a polarizing plate, comprising laminating.

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