JP2015163907A - Polarizing plate protective film and polarizing plate including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate protective film having a high stress at break and bending strength, and a polarizing plate including the polarizing plate protective film and having excellent reworkability.SOLUTION: The polarizing plate protective film comprises at least a resin (A) and a resin (B) having different degrees of solubility with an organic solvent from each other, and has a film thickness of 15 to 100 μm. In an evaluation test of solubility in a given amount of a resin, in a given amount of a solvent, and at a given temperature, the polarizing plate protective film exhibits the following characteristics: when the polarizing plate protective film is dissolved under given conditions by using a solvent (a), which is a good solvent with respect to the resin (A) but is a poor solvent with respect to the resin (B), in at least a minimum amount necessary to solely and completely dissolve the resin (A), an undissolved portion is left in the polarizing plate protective film, and a mass of the resin (A) included in the undissolved portion is 10% or more with respect to the mass of the resin (A) included in the polarizing plate protective film before dissolution.

Description

  The present invention relates to a polarizing plate protective film and a polarizing plate provided with the same.

  The demand for liquid crystal display devices is expanding in applications such as liquid crystal televisions and personal computer liquid crystal displays. A liquid crystal display device generally includes a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, and the like are sandwiched between glass plates, and two polarizing plates provided on both sides of the liquid crystal cell. Each polarizing plate is usually configured by sandwiching a polarizer between two polarizing plate protective films, and a cellulose ester film such as triacetyl cellulose is used as the polarizing plate protective film.

  In recent years, there has been a demand for an increase in the size and thickness of a display. However, if the triacetyl cellulose film (TAC film), which is a protective film, is thinned in order to make the polarizing plate thin, there is a problem that the moisture permeability deteriorates or the dimensional stability is lowered, especially in a thin film of less than 40 μm. Due to the significant decrease in physical properties, it was difficult to realize a thin polarizing plate.

  Furthermore, the liquid crystal panel is manufactured by attaching a polarizing plate to the surface of the liquid crystal cell. However, depending on the situation such as poor attachment or defective polarizing plate, it is necessary to remove and reattach the polarizing plate (also called rework). There is a case. In order to be able to rework, the stress at the breaking point of the film is high, and it is necessary to have a characteristic that does not break even by bending, but it is becoming difficult to ensure reworkability as the polarizing plate becomes larger and thinner. .

  In order to improve the strength of the polarizing plate, attempts have been made to improve the adhesion between the polarizer and the polarizing plate protective film, and to increase the strength of the polarizing plate protective film. For example, in manufacturing a polarizing plate roll in Patent Document 1, unevenness of a polarizer at the roll core and outside of the roll is suppressed, and adhesion with the polarizer is improved even under weak saponification conditions. A technique for improving the reworkability of a polarizing plate has been proposed.

  Patent Document 2 uses an acrylic resin and a cellulose ester resin, which are excellent in transparency and dimensional stability and have a low hygroscopic property, and are improved in brittleness, which is a drawback of acrylic resins, and are suitable for polarizing plate protective films. Has been proposed. However, it has been found that this optical film does not have sufficient stress at break and bending strength, causing problems in reworkability.

  As displays become thinner and larger, these technologies are not sufficient in reworkability, and a polarizing plate having further excellent reworkability has been desired.

JP 2012-047662 A International Publication No. 2009/047924

  The present invention has been made in view of the above-mentioned problems and situations, and the problem to be solved is the provision of a polarizing plate protective film having a high stress at break and bending strength, and the reworkability provided with the polarizing plate protective film. It is to provide an excellent polarizing plate.

  As a result of repeated studies by the present inventor, the cause of the above problem of the resin composed of the acrylic resin and the cellulose ester resin is that the molecules of the acrylic resin and the cellulose ester resin do not form a film in a uniform compatible state. Yes, I thought that if each molecule was entangled, it would behave like one molecule in the entangled state to form a uniform layer. As a result of studying a composition obtained by performing an operation in which molecules are entangled when mixing the resin, the polarizing plate protective film containing the resin A and the resin B is an average of the resin A and the resin B as reworkability. In other words, the heel also behaved as if it were another resin, and it was found that the stress at break and the bending strength may be greatly improved. As a parameter for confirming the situation, evaluation was made by paying attention to solubility in a solvent. Usually, even when an amount of a solvent in which the resin A is completely dissolved is used, the resin A in the polarizing plate protective film does not dissolve and is insoluble. The part may remain, and in the solubility evaluation test, by specifying a specific numerical range for this insoluble part, it is found that a polarizing plate protective film having a high stress at break and bending strength can be obtained, The present invention has been reached.

  That is, the said subject which concerns on this invention is solved by the following means.

  1. A polarizing plate protective film having at least a resin A and a resin B having different solubility in an organic solvent and having a film thickness in the range of 15 to 100 μm, and dissolving at a certain amount of resin, a certain amount of solvent, and a certain temperature In the property evaluation test, the resin A is a good solvent, but the resin B is a poor solvent at least the minimum amount required to completely dissolve the resin A alone. When the polarizing plate protective film containing the constant amount of the resin A is dissolved at the constant temperature, the insoluble part remains and the mass of the resin A contained in the insoluble matter is The polarizing plate protective film is characterized by being 10% or more based on the mass of the resin A contained in the polarizing plate protective film before dissolution.

  2. The polarized light according to item 1, wherein the mass of the resin A contained in the insoluble part is 50% by mass or more based on the mass of the resin A contained in the resin composition polarizing plate protective film. Board protection film.

  3. The polarizing plate protective film according to Item 1 or 2, wherein the resin A is a cellulose ester resin or a cellulose ether resin.

  4). The polarizing plate protective film according to any one of Items 1 to 3, wherein the resin A is a cellulose ester resin or a cellulose ether resin, and the resin B is an acrylic resin.

  5. A polarizing plate comprising the polarizing plate protective film according to any one of items 1 to 4.

  By the above means of the present invention, it is possible to provide a polarizing plate protective film having high breaking stress and high bending strength, and a reworkable polarizing plate provided with the polarizing plate protective film.

  The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.

  In the solubility evaluation test, even when an amount of solvent that completely dissolves the resin A is used, the resin A in the polarizing plate protective film composed of the resin A and the resin B may not be dissolved and an insoluble part may remain. This is probably because the molecules of the resins A and B are entangled and the behavior of one molecule is developed. That is, the interaction between the constituent molecules of the resin A and the constituent molecules of the resin B is stronger than the interaction between the constituent molecules of the resin A and the solvent molecules, and there is a structural entanglement between the two. It is thought that it was inhibited. For this reason, it is considered that the stress at break increased. Further, even when stress such as bending is applied due to molecular entanglement, it is considered that the entanglement is loosened to some extent, the bending strength is increased, and cracks are less likely to occur.

NMR chart of resin

  The polarizing plate protective film of the present invention is a polarizing plate protective film having at least a resin A and a resin B having different solubility in an organic solvent and having a film thickness in the range of 15 to 100 μm, and having a certain amount of resin, In a certain amount of solvent and solubility evaluation test at a constant temperature, the resin A is a good solvent, but the resin B is a poor solvent. When the polarizing plate protective film containing the certain amount of the resin A is dissolved at the certain temperature using at least the minimum amount required to dissolve in the undissolved part, and the insoluble matter remains in the insoluble matter. The mass of the resin A contained in the resin is 10% or more with respect to the mass of the resin A contained in the polarizing plate protective film before the dissolution. This feature is a technical feature common to the inventions according to claims 1 to 5.

  Moreover, it is preferable that the resin A is a cellulose ester resin or a cellulose ether resin because an effect of entanglement of the resin can be easily obtained by ingenuity of the blending method and the resin A can be easily insolubilized.

  In addition, it is preferable that the resin A is a cellulose ester resin or a cellulose ether resin, and the resin B is an acrylic resin because an entanglement effect can be easily obtained and insolubilization can be easily achieved.

  The polarizing plate protective film of the present invention can be suitably included in a polarizing plate.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

  When a film is produced by blending the resin A and the resin B, the characteristics of the resin A and the resin B are expressed as average values only by blending normally. That is, the reworkability is generally the average value of the resin A and the resin B. However, although it was the same composition, it showed the behavior as if it became another resin, and found that the stress at break and the bending strength could be greatly improved.

  This is because the molecules of the resins A and B are entangled and the polymer molecules interact with each other, so that a behavior like that of a single molecule is developed, and the mechanical strength, particularly the breaking stress and the bending strength are improved. Conceivable. Furthermore, when stress such as bending is applied due to molecular entanglement, it is considered that cracks are less likely to occur because the entanglement is loosened to some extent.

  As a parameter for confirming the situation, evaluation was made by paying attention to solubility in a solvent. Usually, even when an amount of a solvent in which the resin A is completely dissolved is used, the resin A in the polarizing plate protective film does not dissolve and is insoluble. It was found that some parts may remain. In the solubility evaluation test, the entanglement can be quantitatively detected, and by defining a specific numerical range for the insoluble part where the resin A and the resin B are entangled, the stress at break and the bending strength It was found that a polarizing plate protective film having a high thickness and a polarizing plate having excellent reworkability using the polarizing plate protective film can be obtained.

  In the present invention, the reworkability means that after a polarizing plate protective film and a polarizer are bonded together to produce a polarizing plate, the polarizing plate is once bonded to a glass substrate of a liquid crystal cell, and then the polarizing plate is peeled off again. It means the ability to re-paste.

[Solubility evaluation test]
In the present invention, a solvent a which is a good solvent for the resin A but a poor solvent for the resin B in a certain amount of resin, a certain amount of solvent, and a solubility evaluation test at a certain temperature. The polarizing plate protective film containing the predetermined amount of the resin A is used at the constant temperature, using at least the minimum amount required for completely dissolving the resin A contained in the polarizing plate protective film alone. When dissolved, the insoluble part remains and the mass of the resin A contained in the insoluble material is 10 with respect to the mass of the resin A contained in the polarizing plate protective film before the dissolution. % Or more.

  The technical significance of this feature is presumed as follows.

  Under the condition where the resin A alone is completely dissolved, it is considered that the resin A constituent molecules are relatively uniformly dispersed in the solvent due to the interaction between the constituent molecules of the resin A and the solvent molecules. .

  On the other hand, the polarizing plate protective film containing at least the resin A and the resin B having different solubility in the organic solvent is used at least at the minimum amount required for completely dissolving the resin A alone at the constant temperature. When dissolved, the insoluble part remains and the mass of the resin A contained in the insoluble material is 10% with respect to the mass of the resin A contained in the polarizing plate protective film before the dissolution. If this is the case, the interaction between the constituent molecules of the resin A and the solvent molecules is stronger than the interaction between the constituent molecules of the resin A and the constituent molecules of the resin B, and there is a structural entanglement between them. It is thought that dissolution of A was inhibited.

  Therefore, the results of the solubility evaluation test are considered to reflect the interaction between the constituent molecules of the resin A and the constituent molecules of the resin B and the ease of structural entanglement between the two. Furthermore, this evaluation result shows the interaction between the constituent molecules of the resin A and the constituent molecules of the resin B when the resin A and the resin B are mixed (blended) regardless of the presence of the solvent, and the structural entanglement between the two. It can be considered as an index for inferring ease based on various experimental results described later.

  In the present invention, “good solvent” refers to a solvent in which a base resin having a molecular weight of 10,000 or more dissolves in a range of 10 g or more with respect to 100 ml of the good solvent at 23 ° C. and no turbidity is observed. The “poor solvent” refers to a solvent that dissolves a base resin having a molecular weight of 10,000 or more in a range of 5 g or less with respect to 100 ml of the poor solvent at 23 ° C.

  The good solvent and the poor solvent differ from each other when the target resin is different. In the solubility evaluation test, a solvent a that is a good solvent for the resin A but a poor solvent for the resin B is used.

  In the practice of the present invention, it is preferable to select and set an evaluation condition for the evaluation test of the solubility of the polarizing plate protective film according to the solubility of the resin A and the resin B. In particular, it is preferable to select and set based on appropriate conditions for the resin A alone to be completely dissolved in the solvent a.

  However, in the solubility evaluation test, the resin A and the resin B to be evaluated are evaluated under the same conditions. Therefore, in the evaluation test of each evaluation sample, a certain amount of resin and a certain amount of solvent are used. It is necessary to evaluate with.

  For example, when a cellulose ester resin is used as the resin A, it is preferable to employ the following conditions as a certain amount of resin, a certain amount of solvent, and a certain temperature.

  In the present invention, the certain amount of resin used in the solubility evaluation test refers to 50 g of a base resin constituting a mass ratio of 10% by mass or more with respect to the polarizing plate protective film.

  The “constant amount of solvent” refers to 100 ml of solvent used to dissolve 50 g of the base resin.

  “Constant temperature” refers to 23 ° C.

  An evaluation test is performed by regarding each of the base resins having a mass ratio of 10% or more constituting the polarizing plate protective film as the resin A. Even when there are three or more kinds of base resins having a mass ratio of 10% or more, each resin is regarded as a resin A and an evaluation test is performed.

  The amount for completely dissolving the resin A alone is determined by the following method.

  50 g of Resin A is stirred in 100 ml of solvent at a temperature of 23 ° C. for 30 minutes. By measuring the mass of the insoluble portion, the amount of the resin dissolved in 100 ml of the solvent, that is, the solubility can be determined. From this solubility, the minimum amount of solvent required to dissolve a certain amount of resin is calculated.

  In addition, it is determined whether the resin is a good solvent or a poor solvent. When 50 g of resin is completely dissolved, the minimum amount required to completely dissolve 50 g of resin is determined to be 100 ml.

  The evaluation test of the solubility of the polarizing plate protective film was carried out at 23 ° C. using 10 g of the polarizing plate protective film and the above-obtained at least the minimum amount of solvent a required for completely dissolving the resin A. Perform an evaluation test.

  The amount of resin A contained in the polarizing plate protective film is calculated from the original blend ratio, and the minimum amount required for complete dissolution determined above is determined for this resin amount. For example, when the blend ratio of the resin A is 80% and there is no other additive, 8 g of the resin A is contained in the polarizing plate protective film 10 g. When the solubility determined above is 16 g / 100 ml, the minimum amount required to completely dissolve the resin A8 g contained in 10 g of the polarizing plate protective film is 50 ml.

  The resin is formed into a film having a thickness of 100 μm or less so that it can be easily dissolved, cut into an appropriate size, and stirred at a temperature of 23 ° C. for 30 minutes. If the dissolution time is too short, insoluble parts may remain due to the dissolution rate, and if the stirring time is lengthened, the soot in the insoluble part will behave like a single molecule. This is because the mass of the insoluble part may become inaccurate. After stirring for 30 minutes, the insoluble part is taken out and the amount of resin A in the insoluble part is measured.

  An evaluation test is performed by regarding each of the base resins having a mass ratio of 10% or more constituting the polarizing plate protective film as the resin A. Even when there are three or more kinds of base resins having a mass ratio of 10% or more, each resin is regarded as a resin A and an evaluation test is performed.

  In the present invention, in the evaluation test of the solubility of the polarizing plate protective film, the mass of the resin A contained in the insoluble portion is 10% by mass or more based on the mass of the resin A contained in the polarizing plate protective film before dissolution. If so, the effect of the present invention can be exhibited. Preferably, it is 30% by mass or more with respect to the mass of the resin A before dissolution, and more preferably 50% by mass or more with respect to the mass of the resin A before dissolution. The upper limit is not particularly limited, but in order to increase this ratio, it takes about 80% because the blending takes a long time or molecules may be cut by shearing during blending.

  Quantitative analysis of the insoluble part can use NMR to estimate the degree of insolubilization of the blended resin from the total integral value of the protons at the peaks unique to each resin and the proportion of protons in the insoluble matter. . The measurement of NMR can be performed using, for example, FT-NMR Lambda400 manufactured by JEOL.

  It should be noted that during the solubility evaluation test, it should be noted that the solvent does not evaporate and that the agitation is too strong to scatter.

[Selection of good and poor solvents]
Although it is a good solvent for the resin A, the solvent a that is a poor solvent for the resin B can be obtained by conducting the solubility evaluation test described above.

  Such a solvent varies depending on the target resin, but can be selected from the following solvents through a solubility evaluation test.

  For example, the chlorinated organic solvent is methylene chloride, chloroform, and the non-chlorinated organic solvent is methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, gamma. Butyrolactone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3 3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane Dimethyl sulfoxide (DMSO), acetonitrile and the like, methylene chloride, methyl acetate, acetic acid Chill, acetone, may be used preferably acetonitrile.

〔resin〕
In the present invention, the resin used as the resin A and the resin B is preferably a thermoplastic resin. These resins are used as a base resin. For example, it can be obtained by conducting the above-described solubility evaluation test from the following resins.

  Examples of the thermoplastic resin include cellulose ester resin, cellulose ether resin, polycarbonate resin, polyether sulfone resin, acrylic resin, polysulfone resin, polyarylate resin, polyethylene resin, polystyrene resin, polyvinyl chloride resin, polyamide resin, polyimide resin. , Polyester resin, polyether ketone resin, polyamideimide resin, polyesterimide resin, and alicyclic olefin polymer. Among these, a cellulose ester resin, a cellulose ether resin, an acrylic resin, a polycarbonate resin, and a polyester resin are preferable from the viewpoint of manifesting the effects of the present invention. More preferred are cellulose ester resins, cellulose ether resins and acrylic resins.

  Hereinafter, particularly preferred resins will be described in detail.

〔acrylic resin〕
Acrylic resins that can be used in the present invention also include methacrylic resins. Although it does not restrict | limit especially as resin, What consists of 50 mass% or more of polymethylmethacrylate or a methylmethacrylate unit, and the other monomer unit copolymerizable with this is preferable.

  Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, acrylic acid, methacrylic acid, and the like. Saturated acids, maleic acids, fumaric acids, unsaturated divalent carboxylic acids such as itaconic acid, aromatic vinyl compounds such as styrene, α-methylstyrene, and nucleus-substituted styrene, α, β- such as acrylonitrile, methacrylonitrile, etc. Examples thereof include unsaturated nitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and the like. These may be used alone or in combination of two or more.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. n-Butyl acrylate is particularly preferably used.

  The acrylic resin used for the polarizing plate protective film of the present invention has a weight average molecular weight (Mw) of 80,000 or more, particularly in terms of brittleness as a polarizing plate protective film and transparency when mixed with, for example, a cellulose ester resin. Preferably there is. The weight average molecular weight (Mw) of the acrylic resin is more preferably in the range of 80,000 to 1,000,000, particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000. Although the upper limit of the weight average molecular weight (Mw) of an acrylic resin is not specifically limited, It is a preferable form that it shall be 1 million or less from a viewpoint on manufacture.

  The weight average molecular weight of the acrylic resin according to the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin in this invention, You may use any well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. Regarding the polymerization temperature, suspension or emulsion polymerization may be carried out within a range of 30 to 100 ° C., and bulk or solution polymerization may be carried out within a range of 80 to 160 ° C. Furthermore, in order to control the reduced viscosity of the produced copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  A commercially available thing can also be used as an acrylic resin of this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. .

[Cellulose ester resin]
The cellulose ester resin that can be used in the present invention is preferably a cellulose ester resin substituted with an acyl group.

  Cellulose ester resin is an acyl group having an acyl group with a total substitution degree of 2.0 to 3.0 and a carbon number of 3 to 7, particularly from the viewpoint of improving brittleness and transparency when mixed with an acrylic resin, for example. The degree of substitution is 1.2 to 3.0, and the degree of substitution of the acyl group having 3 to 7 carbon atoms is preferably in the range of 2.0 to 3.0.

  When the acyl group of the cellulose ester resin is an acyl group other than those having 3 to 7 carbon atoms, that is, an acetyl group or an acyl group having 8 or more carbon atoms, the total degree of substitution is preferably 1.3 or less. .

  Further, the total substitution degree of the acyl group of the cellulose ester resin is more preferably in the range of 2.5 to 3.0.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the said cellulose ester resin has an aromatic acyl group as a substituent, it is preferable that the number of the substituents X substituted to an aromatic ring is 0-5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is in the range of 1.2 to 3.0. For example, since the benzyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  In the said cellulose ester resin, having a structure which has at least 1 sort (s) of a substituted or unsubstituted C3-C7 aliphatic acyl group is used as a structure used for the cellulose resin of this invention.

  The cellulose ester resin of the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, that is, having 3 carbon atoms. Or what has an acyl group of 4 as a substituent is preferable.

  Among these, cellulose ester resins that are particularly preferred are cellulose acetate propionate and cellulose propionate.

  The portion not substituted with an acyl group is usually present as a hydroxy group. These can be synthesized by known methods.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester resin of the present invention is 75000 or more, particularly from the viewpoint of improvement in compatibility with acrylic resin, brittleness and heat resistance, and is preferably in the range of 75,000 to 300,000. More preferably, it is in the range of ˜240,000, particularly preferably in the range of 160000 to 240,000.

[Cellulose ether resin]
Cellulose ether can also be used suitably. Examples include, but are not limited to, methylcellulose, ethylcellulose, carboxymethylcellulose, carboxymethylethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and the like.

  Of these, cellulose ether resins having an alkyl group substitution degree of 2.0 to 2.80 such as cellulose methyl ether, cellulose ethyl ether, and cellulose propyl ether are more preferable.

  The cellulose ether resin may be used alone or in combination with the cellulose ester resin. When used in combination, the content of the cellulose ether resin and the cellulose ester resin is not particularly limited, assuming that the total of the cellulose ether resin and the cellulose ether resin is 100% by mass. It is preferably within the range of 20% by mass, and more preferably within the range of 85 to 97% by mass of cellulose acylate and 3 to 15% by mass of cellulose ether.

  The molecular weight of the cellulose ether resin to be used is not particularly limited. For example, in the case of cellulose acylate such as cellulose acetate propionate or cellulose acetate butyrate, or cellulose ether resin such as ethyl cellulose, the number average molecular weight is 30,000 to 150. 1,000 (polystyrene equivalent) is preferably used. If the molecular weight is less than 30,000, the film becomes brittle, which is not preferable.

[Combination of Resin A and Resin B]
The combination of the resin A according to the polarizing plate protective film of the present invention can be obtained by conducting the solubility evaluation test described above. The combination of resins is not particularly limited as long as the combination satisfies the requirements for the solubility evaluation test. For example, the following combinations of resins can be subjected to the solubility evaluation test.

  In the polarizing plate protective film of the present invention, the resin A is preferably a cellulose ester resin or a cellulose ether resin. Examples of the good solvent for the cellulose ester resin or the cellulose ether resin include acetonitrile, tetrahydrofuran (THF), dichloromethane and the like. A solvent that is a poor solvent is selected for the other resin B to be combined, and a solubility evaluation test is performed using the solvent to select the resin A according to the polarizing plate protective film of the present invention. It is preferable that the resin A is a cellulose ester or a cellulose ether resin because an effect of entanglement of the resin can be easily obtained by ingenuity of the blending method, and the resin A can be easily insolubilized.

  Furthermore, it is preferable that the resin A according to the protective film for polarizing plate of the present invention is a cellulose ester resin or a cellulose ether resin, and the resin B is an acrylic resin because an entanglement effect is easily obtained and insolubilization is facilitated.

  The acrylic resin and the cellulose ester resin are preferably contained in a mass ratio of 95: 5 to 30:70. More preferred is a mass ratio of 95: 5 to 50:50, and still more preferred is a mass ratio in the range of 90:10 to 60:40.

  The weight average molecular weight (Mw) of the acrylic resin, the weight average molecular weight (Mw) of the cellulose ester resin and the degree of substitution in the polarizing plate protective film of the present invention are classified using the difference in solubility in the solvent of both resins. Then, it is obtained by measuring each.

  The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the polarizing plate protective film of the present invention is preferably 55% by mass or more of the polarizing plate protective film, more preferably 60% by mass or more, Most preferably, it is 70 mass% or more.

  When using a resin or additive other than the acrylic resin and the cellulose ester resin, it is preferable to adjust the addition amount in a range that does not impair the effect of the polarizing plate protective film of the present invention.

  These resins can be synthesized by a known method.

[Resin blending method]
The polarizing plate protective film of the present invention is not dependent on the resin blending method, and the expression of the effect is determined by the solubility evaluation test of the polarizing plate protective film described above. A polarizing plate protective film using a resin blended by the method is preferable.

<Solvent addition kneading method>
In the solvent addition kneading method, the molecules of the resin A and the resin B are compared with each other by kneading in a swollen state using a small amount of solvent of about 2 to 20% by mass with respect to the resin, compared to the kneading method without using a normal solvent. This is a kneading method for increasing the interaction.

<Combined grinding method>
The pulverization combined method is a method of increasing the mixing efficiency by pulverizing the resin in advance with a ball mill or the like, reducing the particle size with a disperser, and then kneading and pelletizing.

<High shear method>
The high shear method is a kneading method in which the shear rate is increased and the interaction between molecules is increased as compared with a normal blend method. For example, the shear rate is preferably about 4000 sec ⁻¹ or more. The polarizing plate protective film of this invention can contain additives, such as a plasticizer, a ultraviolet absorber, antioxidant, other than resin as base resin mentioned above.

[Plasticizer]
In the polarizing plate protective film of the present invention, a plasticizer can be used in combination in order to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

  The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester and polyester types, and the molecular weight is preferably in the range of 100 to 10000, but preferably in the range of 600 to 3000, the plasticizing effect is large.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 mPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the polarizing plate protective film of the present invention. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

[Ultraviolet absorber]
The polarizing plate protection of the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole, 2-hydroxybenzophenone and salicylic acid phenyl ester. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine A hybrid system having both structures can be mentioned, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

〔Antioxidant〕
In this invention, what is generally known can be used for a polarizing plate protective film as antioxidant. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used. For example, those including those commercially available from BASF Japan under the trade names of “IrgafosXP40” and “IrgafosXP60” are preferable.

  The phenolic compound preferably has a 2,6-dialkylphenol structure. For example, BASF Japan Ltd., “Irganox 1076”, “Irganox 1010”, and ADEKA “ADEKA STAB AO-50” are trade names. What is marketed is preferable.

  The phosphorous compounds are, for example, from Sumitomo Chemical Co., Ltd., “Sumilizer GP”, ADEKA Co., Ltd., “ADK STAB PEP-24G”, “ADK STAB PEP-36”, “ADK STAB 3010”, BASF Japan Co., Ltd. IRGAFOS P-EPQ ", commercially available from Sakai Chemical Industry Co., Ltd. under the trade name" GSY-P101 "is preferred.

  As the hindered amine compound, for example, those commercially available from BASF Japan Ltd. under the trade names “Tinuvin 144” and “Tinvin 770” and ADEKA Co., Ltd. under the name “ADK STAB LA-52” are preferable.

  As the sulfur compound, for example, those commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer TPL-R” and “Sumilizer TP-D” are preferable.

  The above-mentioned double bond compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer GM” and “Sumilizer GS”.

  Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

  The amount of these antioxidants and the like to be appropriately added is determined in accordance with the process at the time of recycling, but generally 0.05 to 20% by mass, preferably with respect to the resin as the main raw material of the film Is added in the range of 0.1 to 1% by mass.

  These antioxidants can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

[Other additives]
Furthermore, an antistatic agent can be added to the polarizing plate protective film of the present invention to impart antistatic performance to the optical film.

  For the polarizing plate protective film of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphates, halogen-containing condensed phosphonates, halogen-containing phosphites, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

[Production method of polarizing plate protective film]
The manufacturing method of a polarizing plate protective film is demonstrated.

  The polarizing plate protective film may be a film produced by the solution casting method or a film produced by the melt casting method, but is preferably a film produced by the melt casting method.

  The solution casting method forms a film by casting a solution dissolved in a solvent and evaporating and drying the solvent. Therefore, the equipment investment and the production cost for the production line such as the removal of the solvent and the recovery of the evaporated solvent are enormous.

  In the film formation by the melt casting method, since the solvent is not used, the above-described drying load and equipment load do not occur. However, when the film is formed by the melt casting method, fine foaming is likely to occur at the time of molding, so that optical properties such as haze, transmittance, and retardation are deteriorated, and a coating failure is likely to occur in a post-processing step. When the resin used for the polarizing plate protective film of the present invention is melt cast, not only the mechanical strength is increased, but also the occurrence of haze and the like is reduced, the optical characteristics are improved, and the coating failure can be reduced.

[Melt casting method]
<Melted pellet manufacturing process>
A mixture of resin, particulate matter, plasticizer, and other additives containing resin A and resin B that has passed the solubility evaluation test, which is used for melt extrusion, is usually kneaded in advance and pelletized. preferable. The kneading method is preferably the blending method described above.

  Pelletization may be performed by a known method. For example, a polymer, a plasticizer, and other additives that form a film are supplied to an extruder with a feeder, and are kneaded using a single-screw or twin-screw extruder. Extruded into a shape, water-cooled or air-cooled and cut.

  It is important for the raw materials to be pre-dried before extrusion in order to prevent decomposition of the raw materials. In particular, since the polymer that forms the polarizing plate protective film is easy to absorb moisture, it is dried for 3 hours or more in a range of 70 to 140 ° C. with a dehumidifying hot air dryer or vacuum dryer, and the moisture content is set to 300 ppm or less, and further to 100 ppm or less. It is preferable.

  The additives may be mixed before being supplied to the extruder, or may be supplied by individual feeders. A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly.

  Mixing of the antioxidants may be performed by mixing solids, and if necessary, the antioxidant may be dissolved in a solvent and impregnated with a polymer that forms a polarizing plate protective film, or mixed. You may spray and mix.

A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Further, if the contact with air, such as the exit from the feeder unit or die, it is preferable that the atmosphere such as dehumidified air and dehumidified N ₂ gas.

  The extruder is preferably processed at as low a temperature as possible so that the resin can be pelletized so that the resin does not deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

  A film is formed using the pellets obtained as described above.

<Process for extruding molten mixture from die to cooling roll>
The produced pellets are extruded using a single-screw or twin-screw type extruder with a melting temperature Tm of about 200 to 350 ° C., filtered by a filtration device to remove foreign matters, and then cast from a T die into a film. Then, it solidifies on the cooling roll and casts while pressing with the elastic touch roll.

  When introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition or the like under vacuum or reduced pressure or in an inert gas atmosphere. Tm is the temperature of the die exit portion of the extruder.

  When foreign matter such as scratches or plasticizer aggregates adheres to the die, streak-like defects may occur. Such defects are also referred to as die lines, but in order to reduce surface defects such as die lines, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

  The inner surface that contacts the molten resin such as an extruder or a die is preferably subjected to surface treatment that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material having a low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

  There is no particular limitation on the cooling roll, but it is a roll having a structure in which a heat medium or a coolant body in which the temperature can be controlled flows with a high-rigidity metal roll, the size of which is not limited, but a melt-extruded film The diameter of the cooling roll is usually about 100 mm to 1 m.

  Examples of the surface material of the cooling roll include carbon steel, stainless steel, aluminum, and titanium. Further, in order to increase the hardness of the surface or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

  The surface roughness of the chill roll surface is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable that the surface processed is further polished to have the above-described surface roughness.

  Examples of the elastic touch roll include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97 / 028950, JP-A-11-235747, JP-A-2002-36332. No. 2005-172940 and JP-A 2005-280217. A thin-film metal sleeve-covered silicon rubber roll can be used.

  When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

  The film obtained as described above is preferably stretched by a stretching operation after passing through the step of contacting the cooling roll.

  As a method of stretching, a known roll stretching machine or tenter can be preferably used. The stretching temperature is usually preferably performed in the temperature range of Tg to Tg + 60 ° C. of the resin constituting the film.

  The thickness of the polarizing plate protective film of the present invention is in the range of 15 to 100 μm. When it becomes thinner than 15 μm, the strength of the polarizing plate protective film is lowered and the reworkability is inferior. On the other hand, if the thickness of the polarizing plate protective film exceeds 100 μm, not only the cost is increased but also the bending strength is lowered and the reworkability is lowered.

  Before winding, the end may be slit and cut to the width to be the product, and knurling (embossing) may be applied to both ends to prevent sticking and scratching during winding. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing. In addition, since the film has deform | transformed and cannot use as a product normally, the holding | grip part of the clip of both ends of a film is cut out and reused.

〔Polarizer〕
When using the protective film for polarizing plates of this invention, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back surface side of the protective film for polarizing plate of the present invention, and is bonded to at least one surface of a polarizer produced by dipping and stretching in an iodine solution.

  Although the polarizing plate protective film of the present invention may be used on the other surface or another polarizing plate protective film may be used, it is preferable to use the polarizing plate protective film of the present invention on both sides.

  Commercially available protective films include cellulose ester films (for example, Konica Minoltac KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KV8UY-HA, KV8UX-RH Advanced Layer Co., Ltd.) is preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. Preferably, a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded is suitably used.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The concentration of the pressure-sensitive adhesive solution may be appropriately determined depending on the film thickness after adhesion, the coating method, the coating conditions, and the like, and is usually in the range of 0.1 to 50 mass%.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

(Preparation of base resin)
<Base resin A>
The following resins A (A-1 to A-4) were prepared as the base resin A by a known method.
A-1
Cellulose acetate propionate: acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 200000
A-2
Polylactic acid: Terramac TE-2000 (manufactured by Unitika Ltd.)
A-3
Polycarbonate: Panlite L-1225LM (manufactured by Teijin Chemicals Ltd.)
A-4
Cellulose ether resin: Etocel 45 (Nisshin Kasei Co., Ltd.)
<Base resin B>
The following resins B (B-1 to B-3) were prepared as the base resin B by a known method.
B-1
PMMA (polymethyl methacrylate): weight average molecular weight Mw = 100000
B-2
MMA (methyl methacrylate) / MA (methyl acrylate) copolymer: MMA / MA = 95/5 (molar ratio), weight average molecular weight Mw = 100000
B-3
MMA (methyl methacrylate) / IBMA (isobornyl methacrylate) copolymer: MMA / IBMA = 90/10 (molar ratio), weight average molecular weight Mw = 100000
Example 1
<< Preparation of Resin Composition 1 and Polarizing Plate Protective Film 1 >>
The following resin A, resin B and additives were blended in the following proportions.
Resin A (A-1) 20.00 parts by mass Resin B (B-1) 80.00 parts by mass additive GSY-P101 (manufactured by Sakai Chemical Industry Co., Ltd.) 0.25 parts by mass Irganox 1010 (BASF Japan Ltd.) Manufactured) 0.50 parts by mass Sumizer GS (manufactured by Sumitomo Chemical Co., Ltd.) 0.24 parts by mass The blending method of the resin A and the resin B was performed by the following blending method 1.

<Blend method 1 and film formation>
Blend method 1 is a solvent addition kneading method.

Resins A-1 and B-1 were mixed in a V-type mixer for 30 minutes, and a twin-screw extruder (screw outer diameter 15 mmφ, screw length to screw diameter ratio (L / D) = 30, shear rate 300 sec ^{− 1} ) from the hopper.

  At this time, methanol is supplied to the liquid addition nozzle installed at the position immediately before the kneading disk by using a plunger pump so as to be 5% with respect to the resin composition, and methanol is supplied from the liquid addition nozzle into the cylinder. Injected.

  The resin is heated to 230 ° C., melted, extruded from a strand die mounted on a twin screw extruder, and cut to form a cylindrical resin A-1, resin B-1 having a length of 4 mm and a diameter of 3 mm, and The pellet of the resin composition 1 which blended the additive was produced. The pellets were dried with a hopper at 100 ° C. for 4 hours. The water content at this time was 520 ppm.

  The pellets were formed into a film using the following single screw extruder. In the single screw extruder, the number of rotations of the screw was adjusted so that the screw diameter was 20 mm, L / D = 30, and the extrusion amount was 1 kg / h.

  Nitrogen gas was sealed from the vicinity of the material supply port, and the inside of the extruder was kept in a nitrogen atmosphere. The extruder and T-die were set at a temperature of 250 ° C. The T-die is a coat hanger type, has a width of 150 mm, has an inner wall plated with hard chrome, and has a mirror finish with a surface roughness of 0.1S. The lip gap of the T die was set to 1 mm.

  The extruded film was taken up with a cast roll having a surface temperature of 120 ° C., cooled to room temperature, and formed into a film having an average film thickness of 110 μm before stretching.

  Subsequently, the film was heated to 165 ° C., stretched 2.1 times in the MD (Machine Direction) direction and 2.1 times in the TD (Transverse Direction) direction, and wound to prepare a polarizing plate protective film 1 having an average film thickness of 25 μm. .

<< Preparation of Resin Compositions 2-16 and Polarizing Plate Protective Films 2-16 >>
Resin compositions 2 to 16 and a polarizing plate protective film were prepared by changing only resin A-1 and resin B-1, and blending method and film forming method as shown in Table 1, in the same manner as in the preparation of resin composition 1. 2-16 were produced.

  The blending method and film forming method are shown below.

<Blend method 2 and film formation>
Blending method 2 is a pulverization combined method.

  Resin A, Resin B and additives were mixed at 2300 r / min for 60 seconds using a Henschel mixer. Then, it grind | pulverized at 50 degreeC with the stirring type ball mill at another process, and the average particle diameter was 10 micrometers. As a stirring ball mill, a high-speed planetary mill, Hijie, manufactured by Kurimoto Steel Corporation was used. The mixed and pulverized thermoplastic resin composition was dried at 100 ° C. for 4 hours. The water content at this time was 510 ppm.

This resin was introduced from a hopper of a twin screw extruder (screw outer diameter 15 mmφ, screw length to screw diameter ratio (L / D) = 30, shear rate 300 sec ⁻¹ ). The resin was heated to 250 ° C., melted, and extruded from a T die attached to a twin screw extruder to produce a film. The T-die is a coat hanger type, has a width of 150 mm, has an inner wall plated with hard chrome, and has a mirror finish with a surface roughness of 0.1S. The lip gap of the T die was set to 1 mm.

  The extruded film was taken up with a cast roll having a surface temperature of 120 ° C., cooled to room temperature, and formed into a film having an average film thickness of 110 μm before stretching. Subsequently, the film was heated to 165 ° C., stretched 2.1 times in the MD (Machine Direction) direction and 2.1 times in the TD (Transverse Direction) direction, and wound to prepare a polarizing plate protective film having an average film thickness of 25 μm.

<Blend method 3 and film formation>
Blend method 3 is a high shear method.

Resin A, resin B, and additives were mixed in a V-type mixer for 30 minutes, then charged from the hopper of a DSM twin-screw kneader and kneaded at 250 ° C. for 15 minutes. At this time, the shear rate was set to 4000 sec ⁻¹ by adjusting the distance between the screw and the cylinder and the screw rotation speed.

  After kneading for 15 minutes, it was extruded from a T-die (coat hanger type, width 55 mm, lip interval 1 mm) attached to the injection port.

  The extruded film was taken up by a cast roll having a surface temperature of 120 ° C. and cooled to room temperature to obtain a film having a width of 50 mm. The average film thickness of the polarizing plate protective film was adjusted to 25 μm by adjusting the extrusion amount of the resin and the take-up speed.

<Blend Method 4 and Film Formation (Comparative Example)>
Blending method 4 is a normal pelletizing method.

Resin A, resin B and additives were mixed in a V-type mixer for 30 minutes, and a twin-screw extruder (screw outer diameter 15 mmφ, screw length to screw diameter ratio (L / D) = 30, shear rate 300 sec ^{− 1} ) from the hopper.

  Resin is a resin composition in which cylindrical resins A and B having a length of 4 mm and a diameter of 3 mm are blended by extruding and cutting a resin from a strand die mounted on a twin-screw extruder by heating and melting at 230 ° C. A pellet was prepared. The pellets were dried with a hopper at 100 ° C. for 4 hours. The water content at this time was 520 ppm.

  The pellets were formed into a film using the following single screw extruder. In the single screw extruder, the number of rotations of the screw was adjusted so that the screw diameter was 20 mm, L / D = 30, and the extrusion amount was 1 kg / h. Nitrogen gas was sealed from the vicinity of the material supply port, and the inside of the extruder 1 was kept in a nitrogen atmosphere. The temperature of the extruder 1 and the T die was set to 250 ° C. The T-die is a coat hanger type, has a width of 150 mm, has an inner wall plated with hard chrome, and has a mirror finish with a surface roughness of 0.1S. The lip gap of the T die was set to 1 mm.

  The extruded film was taken up with a cast roll having a surface temperature of 120 ° C., cooled to room temperature, and formed into a film having an average film thickness of 110 μm before stretching. Subsequently, the film was heated to 165 ° C., stretched 2.1 times in the MD (Machine Direction) direction and 2.1 times in the TD (Transverse Direction) direction, and wound to prepare a polarizing plate protective film having an average film thickness of 25 μm.

[Solubility evaluation test]
The polarizing plate protective film 1 will be described as an example.

(Solvent a)
Resin A (A-1) is a poor solvent and Resin B (B-1) is a good solvent a. Therefore, 5 g, 10 g, and 50 g of Resin A-1 and Resin B-1 respectively. And 100 ml of the target solvent, each was stirred with a stirrer for 30 minutes at a temperature of 23 ° C., and a solubility evaluation test was performed. As a result, 15% by mass of acetonitrile was dissolved in resin A-1, and 3% by mass was dissolved in resin B-1, which was found to be solvent a according to the present invention.

  When a 10 g sample of the polarizing plate protective film 1 was similarly subjected to a solubility evaluation test using the minimum amount of acetonitrile required to completely dissolve the resin A-1 using this acetonitrile, an insoluble portion remained. It was.

  Since resin A-1 is a good solvent, A-1 is usually not included in the insoluble matter. However, by blending by blending method 1, resin A-1 that should be dissolved does not dissolve and is not dissolved. It can be seen that the resin A-1 and the resin b-1 are entangled in the melt.

(Quantitative analysis of insoluble part)
The insoluble portion, resin A-1, and resin B-1 were measured for proton NMR using FT-NMR Lambda400 manufactured by JEOL. This will be described below with reference to the drawings. FIG. 1 is an NMR of the resin.

  That is, the NMR chart of the resin B-1 alone shown in FIG. 1B has no peak at 5.5 to 4 ppm, and the NMR chart of the resin A-1 shown in FIG. Since peak 1 is observed at 4 ppm, this peak is considered to be a peak peculiar to resin A-1. Since the peak 2 peculiar to the resin A-1 is observed in both the NMR chart of the insoluble matter shown in FIG. 1C and 5.5 to 4 ppm, the resin A-1 is present in the insoluble matter. I understand that.

  From the integral value of the proton of the resin A-1 and the integral value of the peak, the ratio of the integral value of the proton of the insoluble matter and the integral value of the peak, and the respective mass ratios, the blended resin A-1 As a result, it was found that it was 70% of the resin A-1 before the solubility evaluation test.

  This is because the interaction between the constituent molecule of the resin A-1 and the constituent molecule of the resin B-1 is stronger than the interaction between the constituent molecule of the resin A-1 and the solvent acetonitrile, and the structural entanglement between the two. Therefore, it is considered that dissolution of resin A-1 by acetonitrile was inhibited. Therefore, the result of the solubility evaluation test is considered to reflect the interaction between the constituent molecules of the resin A-1 and the constituent molecules of the resin B-1 and the ease of structural entanglement between the two. It is done. Furthermore, this evaluation result shows the interaction between the constituent molecules of the resin A and the constituent molecules of the resin B when the resin A and the resin B are mixed (blended) regardless of the presence of the solvent, and the structural entanglement between the two. It may be an index for inferring ease.

  Similarly, as a result of conducting a solubility evaluation test on the combination of resin A and resin B of other polarizing plate protective films, it was found that dimethyl sulfoxide and tetrahydrofuran can be applied in addition to acetonitrile. That is, for the polarizing plate protective films 2 to 8, 12, 15, and 16, acetonitrile is used as the solvent a according to the present invention, the polarizing plate protective films 9 and 13 are dimethyl sulfoxide, and the polarizing plate protective films 10 and 14 are In the same manner, each of the polarizing plate protective films 2 to 16 was subjected to a solubility evaluation test using tetrahydrofuran. As a result, an insoluble portion remained, and the insoluble portion was quantitatively analyzed using NMR as described above. Went. As a result, the ratio of the insoluble part of the resin A was shown in Table 1.

[Evaluation of roll dirt]
When film-forming the resin compositions 1-16, the polarizing plate protective film was produced continuously for 2 hours. The degree of dirt on the cast roll at this time was visually evaluated.
○: Dirt is not recognized Δ: Slightly dirty X: Dirt [Evaluation of bubbles and perforations]
Similarly, after producing a polarizing plate protective film continuously for 2 hours, the failure of bubbles and perforations was evaluated by visual observation. Note that the perforation is a failure in which bubbles are stretched and appear continuously dotted.
○: No bubbles or perforations are observed Δ: Slight bubbles or perforations are present ×: There are bubbles or perforations [Evaluation of haze]
Each of the polarizing plate protective films 1 to 16 was measured according to JIS K-7136 using a haze meter (NDH2000 type, manufactured by Nippon Denshoku Industries Co., Ltd.).

[Evaluation of stress at break]
The following evaluation was performed using a Tensilon tester (ORITC Corporation, RTC-1225A).

  The polarizing plate protective film was cut out at 70 mm (TD: width direction) × 10 mm (MD: longitudinal direction), and the tensile stress at break was measured at a rate of 50 mm / min at a chuck length of 50 mm in an environment of 23 ° C. and 55%.

[Evaluation of bending strength]
The polarizing plate protective film was cut out at 100 mm (TD) × 10 mm (MD), folded at the central part in the vertical direction once into a mountain fold and a valley fold, and this evaluation was measured three times. It was evaluated as follows. In addition, breaking of evaluation here represents having broken into two or more pieces.

○: Cannot be folded 3 times ×: Can be folded at least once out of 3 times Table 1 shows the above evaluation results.

  From the results of Table 1, the polarizing plate protective films 1 to 11 of the present invention are good solvents for the base resin relative to the comparative polarizing plate protective films 12 to 16, even though they are good solvents, It can be seen that the proportion of insolubilized resin is high, and the stress at break and the bending strength are good. Further, it can be seen that the polarizing plate protective film of the present invention produced by the melt casting method has few roll stains, bubbles and perforation failures when forming a film-like material, and has good haze.

(Example 2)
<< Production of Polarizing Plates 1-16 >>
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution at 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. . This was washed with water and dried to obtain a polarizing film.

  Subsequently, according to the following processes 1-5, the polarizing film and the produced said polarizing plate protective films 1-16 were bonded together, and the polarizing plates 1-16 were produced, respectively.

  Step 1: Polarizing plate protective films 1 to 16 were each immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried.

  Similarly, a commercially available cellulose ester film was immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried.

  Process 2: The above-mentioned polarizing film was immersed for 1 to 2 seconds in the polyvinyl alcohol adhesive tank of 2 mass% of solid content.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and the same polarizing plate protective film that had been subjected to alkali treatment in Step 1 was sandwiched between the two, and laminated.

Process 4: It bonded together at the speed | rate of about 2 m / min with the pressure of 20-30 N / cm < ² > with the two rotating rollers. At this time, care was taken to prevent bubbles from entering.

  Step 5: The sample prepared in Step 4 in a dryer at 80 ° C. was dried for 2 minutes to prepare polarizing plates 1 to 16, respectively.

[Evaluation of reworkability]
About the polarizing plates 1-16, it cut to the magnitude | size of 100 mm x 100 mm, respectively, and affixed on the glass plate using the base material-less double-sided tape LUCIACS CS9621T (made by Nitto Denko Corporation). After aging at 23 ° C. and 55% for 24 hours, the polarizing plate was peeled off from the glass plate by hand, and the state of the film at that time was evaluated as follows.
○: The film can be peeled cleanly without being broken. Δ: The film is sometimes broken, but can be removed somehow. ×: The film is immediately broken and cannot be peeled. The results are shown in Table 2.

  Table 2 shows that the polarizing plates 1-11 of this invention are excellent in reworkability compared with the comparative polarizing plates 12-16.

(Example 3)
In the production of the polarizing plate protective film 1 of Example 1, the thickness of the film before stretching was changed by adjusting the extrusion amount of the resin by changing the screw rotation speed of the single screw extruder, and the average film thickness after stretching. However, it adjusted so that it might become 12 micrometers, 15 micrometers, 100 micrometers, and 120 micrometers, respectively, and produced the polarizing plate protective film, respectively. Next, in the same manner as in the production of the polarizing plate 1 described in Example 2, a corresponding polarizing plate was produced. When the reworkability of these polarizing plates was evaluated in the same manner as in Example 2, a polarizing plate prepared from a polarizing plate protective film having a thickness of 12 μm and a polarizing plate prepared from a polarizing plate protective film having a protective film thickness of 120 μm In the evaluation of the reworkability of the plate, the film was immediately cut off and could not be peeled off. On the other hand. The polarizing plate (protective film) having a thickness of 10 to 100 μm of the present invention showed the same performance as the polarizing plate 1 of Example 2 and was good.

1, 2 Proton peak peculiar to Resin A-1

Claims (5)

  A polarizing plate protective film having at least a resin A and a resin B having different solubility in an organic solvent and having a film thickness in the range of 15 to 100 μm, and dissolving at a certain amount of resin, a certain amount of solvent, and a certain temperature In the property evaluation test, the resin A is a good solvent, but the resin B is a poor solvent at least the minimum amount required to completely dissolve the resin A alone. When the polarizing plate protective film containing the constant amount of the resin A is dissolved at the constant temperature, the insoluble part remains and the mass of the resin A contained in the insoluble matter is The polarizing plate protective film is characterized by being 10% or more based on the mass of the resin A contained in the polarizing plate protective film before dissolution.   2. The polarized light according to claim 1, wherein the mass of the resin A contained in the insoluble part is 50% by mass or more based on the mass of the resin A contained in the resin composition polarizing plate protective film. Board protection film.   The polarizing plate protective film according to claim 1, wherein the resin A is a cellulose ester resin or a cellulose ether resin.   The polarizing plate protective film according to any one of claims 1 to 3, wherein the resin A is a cellulose ester resin or a cellulose ether resin, and the resin B is an acrylic resin.   A polarizing plate comprising the polarizing plate protective film according to any one of claims 1 to 4.

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