JP5104741B2 - Grainy foreign matter judgment method of cellulose ester film - Google Patents

Description

  The present invention relates to a cellulose ester film used for a protective film for a polarizing plate and the like, and more particularly to a method for producing a cellulose ester film in which grainy foreign matter is unlikely to be produced and a method for judging grainy foreign matter.

  In recent years, as liquid crystal display devices (LCD) are used in various places, higher productivity (increased production) is also demanded for liquid crystal display elements used in LCDs, that is, polarizing plates. In addition, liquid crystal display devices (LCDs) are becoming thinner, and there is a demand for thinner polarizing plates used in LCDs.

  By the way, cellulose triacetate (TAC) films are mainly used as protective films for polarizing plates of LCDs. However, as the productivity of polarizing plates increases, such cellulose ester films for LCDs are becoming increasingly expensive. As productivity increases, the load on the quality of the cellulose ester film increases, and fine foreign matter (called grainy foreign matter in this specification) may be visible on the film during production. There was a problem that it was not preferable because the appearance was impaired. And, when the appearance of the cellulose ester film is impaired by such a grainy foreign material, it is not possible to endure the use as a protective film for a polarizing plate, but the external appearance of the film is impaired by the precipitation of the foreign material, There was a problem that the appearance of the original winding state deteriorated, leading to poor appearance of the polarizing plate, and further deterioration of the visibility of the liquid crystal display.

  Examples of prior patent documents related to the generation of foreign matters in such a cellulose ester film include the following.

  The invention described in Patent Document 1 was previously proposed by the present applicant and relates to an optical film including a cellulose ester film suitable as a protective film for a polarizing plate such as a liquid crystal display. In particular, the invention aims to reduce foreign matter observed under the orthogonal state of the polarizing plate, which is called bright spot foreign matter. And in this invention of the optical film proposed previously, it is disclosed that the amount of Fe component contained in the cellulose ester film is 1 ppm or less. Further, Patent Document 1 discloses that the amount of Ca component contained in the cellulose ester film is 60 ppm or less, and that the amount of Mg component contained in the cellulose ester film is 15 to 70 ppm. Has been.

  The invention described in Patent Document 2 has been previously proposed by the present applicant, and relates to an optical film including a cellulose ester film suitable as a protective film for a polarizing plate such as a liquid crystal display. In particular, the invention improves the surface quality and optical isotropy problems of the film, improves the processability of the film, specifically, improves the cutting characteristics when punching the film into a desired shape during production. Was aimed at. And in this invention of the optical film proposed previously, Mw / Mn = 3.0-5.0 is disclosed by ratio of the weight average molecular weight (Mw) of a TAC film and a number average molecular weight (Mn).

  The invention of the cellulose ester film described in Patent Document 3 aims to provide a cellulose ester film that has high transparency and excellent processing characteristics and can be produced with high productivity. And invention of patent document 3 is a cellulose ester film manufactured by the casting film forming method containing the cellulose ester and the plasticizer of 2-40 mass%, Comprising: The plasticizer in the film surface of an at least one side Is present in the range of 87 to 96% by mass of the amount of plasticizer present in the cellulose ester film.

In the invention described in Patent Document 4, in the semiconductor industry where pattern processing is becoming finer, it is necessary to surely detect finer foreign matters that lead to pattern defects. The present invention relates to a foreign matter inspection apparatus that can satisfactorily detect foreign matter adhering to the surface on which a regular drawing pattern is formed, and in particular, a foreign matter detection apparatus using infrared transmission is disclosed.
JP 2000-313766 A JP 2000-314811 A JP 2000-336179 A JP-A-5-93695

  However, the inventions described in Patent Documents 1 to 3 are all aimed at preventing the generation of foreign substances and preventing the precipitation (bleed out) of plasticizers, ultraviolet absorbers, etc. Therefore, there is a problem that the improvement effect is insufficient for the grainy foreign matter.

  Further, the invention described in Patent Document 4 uses infrared rays and does not use visible light, so there is a problem that the visual appearance and the determination result may be different.

  In any case, according to the prior art, the improvement of the grain-like foreign matter that seems to be caused by the minute foreign matter is insufficient, and the grain-like foreign matter cannot be detected and judged by a simple method. There was a problem that had to rely on.

  An object of the present invention is a cellulose ester film used as a protective film for a polarizing plate, which solves the above-described problems of the prior art, and can prevent the occurrence of grainy foreign matter. An object of the present invention is to provide a protective film for a polarizing plate that hardly occurs.

  Moreover, according to the cellulose-ester film used as a protective film for polarizing plates of this invention, a grainy foreign material can be detected and determined by a simple method.

  Furthermore, the appearance of a polarizing plate produced using the cellulose ester film of the present invention as a protective film for polarizing plate can be improved, and the visibility of a liquid crystal display (liquid crystal display device) produced using this polarizing plate is improved. can do.

To achieve the above object, the present invention is as follows.
1. A method for producing a cellulose ester film having a thickness of 20 to 60 μm used for a polarizing plate protective film, wherein the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is 0.95 to 1.05. A method for producing a cellulose ester film, characterized by adjusting to the above.
2. A method for determining grainy foreign matter in a cellulose ester film having a thickness of 20 to 60 μm used for a polarizing plate protective film, wherein the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is 0.95 to 1. .05. A method for determining grainy foreign matters in a cellulose ester film, wherein the one that becomes .05 is selected.

  According to the cellulose ester film of the present invention, with a high productivity (increased production) of a liquid crystal display element, that is, a polarizing plate, a cellulose ester film having a thickness of 20 μm or more and 60 μm or less used as a protective film for a polarizing plate, It is possible to prevent the occurrence of grainy foreign matter, and it is difficult for the grainy foreign matter to occur.

  Further, according to the cellulose ester film used as the protective film for polarizing plate of the present invention, the occurrence of grainy foreign matters can be easily evaluated by microscopic observation, and the result of microscopic observation and the use of visible light are utilized. The results of the visual appearance evaluation are consistent with each other, and the accuracy of quantification can be increased and the evaluation can be made reliably by microscopic observation.

  And according to the cellulose ester film of the present invention, it is possible to suppress the occurrence of grainy foreign matter in the film, and since the improvement effect on the grainy foreign matter is great, unexpectedly, the transparency of the cellulose ester film The appearance (color) of the original roll state of the film is beautiful, and a high-quality protective film for a polarizing plate can be made highly productive.

  Furthermore, the appearance of a polarizing plate produced using the cellulose ester film of the present invention as a protective film for polarizing plate can be improved, and the visibility of a liquid crystal display (liquid crystal display device) produced using this polarizing plate is improved. can do.

  Hereinafter, the present invention will be specifically described.

  The cellulose ester film used in the protective film for polarizing plate according to the present invention is characterized in that the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is 0.95 to 1.05.

Here, the spectral transmission density is defined as follows. That is, when the spectral transmittance T (%) is set, the spectral transmission density = −log (T / 100)
In the present invention, the spectral transmission density is determined by measuring the spectral transmittance of the cellulose ester film with a spectrophotometer and measuring the transmittance at a wavelength of 500 nm and a wavelength of 600 nm.

  More specifically, the spectrophotometer U-3200 (manufactured by Hitachi, Ltd.) is used to measure the spectral absorption spectrum of the cellulose ester film, and the spectral transmission at a wavelength of 500 nm and a wavelength of 600 nm of the cellulose ester film. The ratio is measured and obtained from each spectral transmittance at a wavelength of 500 nm and a wavelength of 600 nm.

  As a result of intensive studies to improve the above-described conventional problems, the present inventor has found that the observation state of grainy foreign matters varies depending on the difference in color on the back of the field of view when the cellulose ester film is observed with a microscope. It was. Although visible light is not affected by light having a wavelength of 400 to 500 nm or light having a wavelength of 600 to 700 nm, it is known to be greatly affected by light having a wavelength of 500 to 600 nm. It was found that the transmission density at a wavelength of 600 nm is characteristic, and that the grainy foreign matter can be improved by defining the ratio of these. Further, the present inventors have found that the evaluation of the grain-like foreign matter can be performed by substitution instead of visual appearance evaluation but by quantification with high accuracy by microscopic observation, and have led to the present invention. That is, even in the case of a cellulose ester film as a thin optical film, the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is set to a range of 0.95 to 1.05. The present inventors have found that a cellulose ester film having a thickness of 20 μm or more and 60 μm or less used as a protective film can prevent the occurrence of grainy foreign matters and can improve the above conventional problems.

  According to the cellulose ester film of the present invention, with a high productivity (increased production) of a liquid crystal display element, that is, a polarizing plate, a cellulose ester film having a thickness of 20 μm or more and 60 μm or less used as a protective film for a polarizing plate, Generation | occurrence | production of a grain-like foreign material can be prevented, and the protective film for polarizing plates which a grain-like foreign material cannot produce easily can be provided.

  Further, according to the cellulose ester film used as the protective film for polarizing plate of the present invention, the occurrence of grainy foreign matters can be easily evaluated by microscopic observation, and the result of microscopic observation and the use of visible light are utilized. The results of the visual appearance evaluation are consistent with each other, and the accuracy of quantification can be increased and the evaluation can be made reliably by microscopic observation.

  And according to the cellulose ester film of the present invention, it is possible to suppress the occurrence of grainy foreign matter in the film, and since the improvement effect on the grainy foreign matter is great, unexpectedly, the transparency of the cellulose ester film The appearance (color) of the original roll state of the film is beautiful, and a high-quality protective film for a polarizing plate can be made highly productive.

  Furthermore, the appearance of a polarizing plate produced using the cellulose ester film of the present invention as a protective film for polarizing plate can be improved, and the visibility of a liquid crystal display (liquid crystal display device) produced using this polarizing plate is improved. can do.

  Next, in the cellulose ester film of the present invention, the content of the magnesium compound in the cellulose ester film is 30 ppm or less as a magnesium atom in a mass ratio with respect to the film mass, and the content of the calcium compound in the cellulose ester film is the film mass. It is 30 ppm or less as a calcium atom by mass ratio with respect to.

  In this case, the detection probability of magnesium atoms detected when the cellulose ester film is analyzed and measured by an inductively coupled plasma emission spectrometer (ICP-AES) has a mass ratio of 30 ppm or less with respect to the cellulose ester film, and calcium atoms. The detection probability is 30 ppm or less by mass ratio with respect to the cellulose ester film.

  Further, in the cellulose ester film according to the present invention, the magnesium compound content is 80 ppm or less as magnesium atoms in a mass ratio to the cellulose ester, and the calcium compound content of the cellulose ester is calcium in a mass ratio to the cellulose ester. It is 80 ppm or less as an atom.

  In this case, the detection probability of magnesium atoms detected when the cellulose ester film is analyzed and measured by an inductively coupled plasma emission spectrometer (ICP-AES) is 80 ppm or less by mass ratio to the cellulose ester film, and The detection probability is 80 ppm or less by mass ratio with respect to the cellulose ester film.

  Examples of the cellulose ester that is the main component of the cellulose ester film of the present invention include cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, and cellulose acetate propionate.

  In the case of cellulose triacetate, cellulose triacetate having a polymerization degree of 250 to 400 and a bound acetic acid amount of 54 to 62.5% is particularly preferable, and a base strength having a bound acetic acid amount of 58 to 62.5% is strong and more preferable. As the cellulose triacetate, either cellulose triacetate synthesized from cotton linter or cellulose triacetate synthesized from wood pulp can be used alone or in combination.

  In the cellulose ester film of the present invention, when the weight average molecular weight of the cellulose ester is Mw and the number average molecular weight is Mn, the ratio of the weight average molecular weight to the number average molecular weight: Mw / Mn is 1.0 to 5. 0. The ratio of the weight average molecular weight to the number average molecular weight: Mw / Mn is preferably 1.7 to 3.0.

  The cellulose ester is preferably substantially cellulose triacetate, and the average molecular weight of cellulose triacetate can be measured using gel permeation chromatography, so that the number average molecular weight (Mn) and weight average can be measured using this. Molecular weight (Mw) can be calculated.

  The measurement conditions for the average molecular weight are as follows.

Using the apparatus and materials shown below, the weight average molecular weight (Mw) and average molecular weight (Mn) of cellulose triacetate are measured by gel permeation chromatography, and the molecular weight distribution Mw / Mn is calculated.
Gel permeation chromatography solvent (eluent): dichloromethane Column name: Showa Denko GPCk806-GPCk805-GPCk803 (3)
Sample concentration: 0.1 (mass%)
Flow rate: 1.0 (ml / min)
Sample injection volume: 100 (μl)
Standard sample: polystyrene (Mw: 5,000,000-6,700,000)
Temperature: 25 ° C
Detection: RI (Suggested refractometer)
Ratio of weight average molecular weight (Mw) and number average molecular weight (Mn) of cellulose triacetate: If Mw / Mn is less than 1.0, the tear strength of the film is lowered, which is not preferable. Further, when the ratio: Mw / Mn exceeds 5.0, the dimensional stability and slipperiness of the film deteriorate, which is not preferable.

  Examples of the cellulose ester solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and n-butyl alcohol, lower aliphatic chlorinated hydrocarbons such as cyclohexane, dioxane, and methylene chloride. Can be used.

  As a solvent ratio, for example, methylene chloride is preferably 70 to 95% by mass, and other solvents are preferably 5 to 30% by mass. The concentration of the cellulose ester is preferably 10 to 50% by mass.

  The heating temperature with the addition of the solvent is preferably a temperature not lower than the boiling point of the solvent used and in a range where the solvent does not boil, for example, preferably 60 ° C. or higher and 80 to 110 ° C. The pressure is determined so that the solvent does not boil at the set temperature.

  After dissolution, it is taken out from the container while cooling, or extracted from the container with a pump or the like and cooled with a heat exchanger or the like, and used for film formation.

  The cellulose ester film according to the present invention contains additives such as a plasticizer and an ultraviolet absorber in addition to the cellulose ester and the solvent.

  Additives such as a plasticizer and an ultraviolet absorber may be mixed with a solvent in advance and dissolved or dispersed, and then added to the solvent before dissolving the cellulose ester, or may be added to the dope after dissolving the cellulose ester.

  Although it does not specifically limit as a plasticizer which can be used by this invention, In a phosphate ester type | system | group, a triphenyl phosphate (TPP), a biphenyl diphenyl phosphate (BDP), a tricresyl phosphate, a cresyl diphenyl phosphate, an octyl diphenyl phosphate, For phthalate esters such as trioctyl phosphate and tributyl phosphate, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, etc. Rubutyl glycolate, ethyl phthalyl ethyl glycolate (EPEG), methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycol Preferably alone or in combination rates.

  The above plasticizers may be used in combination of two or more as required. By containing these plasticizers, a film having excellent dimensional stability and water resistance can be obtained, which is particularly preferable.

  In the present invention, in order to make the water absorption rate and moisture content within a specific range, the preferable addition amount of the plasticizer is 12% by mass or less with respect to the cellulose ester. When two or more kinds of plasticizers are used in combination, the total amount of these plasticizers may be 12% by mass or less.

  Although it does not specifically limit as an ultraviolet absorber which can be used by this invention, it is excellent in the ability to absorb the ultraviolet-ray with a wavelength of 370 nm or less from the point of prevention of deterioration of a liquid crystal, and visible light with a wavelength of 400 nm or more from the point of favorable liquid crystal display property. Those that absorb as little as possible are preferably used.

  Examples of commonly used compounds include, but are not limited to, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like.

  The fine particles added as a matting agent for the purpose of improving the slipperiness and preventing blocking after winding of the cellulose ester film of the present invention may be added to the main dope. Is preferable. Add to additive solution and add to film. Moreover, although it may be contained in the main dope, any fine particles can be used.

  As fine particles used in the present invention, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated calcium silicate. Mention may be made of aluminum silicate, magnesium silicate and calcium phosphate. Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.), and can be used. Among these, fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  Examples of these are those commercially available under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above, Nippon Aerosil Co., Ltd.). Can do.

  Furthermore, the silicon dioxide fine particles are preferably silicon dioxide fine particles having a primary average particle diameter of 20 nm or less and an apparent specific gravity of 70 g / liter or more. Examples of the silicon dioxide fine particles that satisfy these requirements include Aerosil 200V and Aerosil R972V, which are particularly preferable because they have a great effect of reducing the friction coefficient while keeping the turbidity of the film low.

  In the present invention, the fine particles are used in an amount of 0.04 to 0.4 mass% added to the cellulose ester. Preferably, it is 0.05-0.3 mass%, More preferably, it is 0.05-0.2 mass%.

  In the present invention, a dope obtained by dissolving cellulose ester is cast on a support (casting process), and then heated to remove a part of the solvent (drying process on the support), and then from the support. It peels and the peeled film is dried (film drying process), and a cellulose-ester film is obtained.

  As the support in the casting process, a support in which a belt-like or drum-like stainless steel is mirror-finished is used. The temperature of the support in the casting process can be cast in a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, but the dope is gelled by casting on a support at 5 to 30 ° C. Therefore, it is preferable to cast it on a support at 5 to 15 ° C.

  In the drying process on the support, the dope is cast, once gelled, and when the time from casting to peeling is 100%, the dope temperature is set to 40 to 70 ° C. within 30% from casting. Thus, the evaporation of the solvent is promoted, and it can be peeled off from the support as quickly as possible, and the peel strength is further increased. The dope temperature is preferably set to 55 to 70 ° C. within 30%. This temperature is preferably maintained at 20% or more, more preferably 40% or more.

  For drying on the support, it is preferable to peel from the support with a residual solvent amount of 60 to 150% because the peel strength from the support becomes small, and more preferably 80 to 120%. The dope temperature at the time of peeling is preferably 0 to 30 ° C., because the base strength at the time of peeling can be increased and the base breakage at the time of peeling can be prevented, and 5 to 20 ° C. is more preferable.

  In the film drying step, the film peeled off from the support is further dried, and the residual solvent amount is 3% by mass or less, preferably 1% by mass or less, more preferably 0.5% by mass or less. It is preferable for obtaining a good film. In the film drying process, generally, a roll suspension system, a pin tenter system, or a clip tenter system is used for drying while transporting the film. For the liquid crystal display member, it is preferable to dry while maintaining the width by a tenter method in order to improve the dimensional stability.

  The means for drying the film is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to carry out with hot air in terms of simplicity. The drying temperature is preferably divided into 3 to 5 stages in the range of 40 to 150 ° C and gradually increased, and more preferably in the range of 80 to 140 ° C in order to improve dimensional stability. These steps from casting to post-drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas.

  The winder related to the production of the cellulose ester film of the present invention may be a commonly used winder such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress. It can be wound up by the method.

  Although the thickness of the cellulose ester film according to the present invention is not particularly limited, it is usually preferably 60 μm or less because it is used for a protective film for a liquid crystal display element used for an LCD, that is, a polarizing plate. A cellulose ester film having a thickness of 20 to 60 μm or less is preferred.

  The reason is that, when a cellulose ester film having a thickness of 60 μm or less is used as, for example, a protective film for a polarizing plate, more stringent performance is required for quality.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.
Examples 1-3
(Preparation of dope solution)
A dope solution of cellulose triacetate was prepared as follows.
Cellulose triacetate (TAC): 100kg
Tinuvin 326 (Ciba Japan): 0.3kg
Tinuvin 171 (Ciba Japan): 0.5kg
Tinuvin 109 (Ciba Japan): 0.5kg
Ethyl phthalyl ethyl glycolate (EPEG): 2.8 kg
Triphenyl phosphate (TPP): 9.7 kg
Aerosil 200V (Nippon Aerosil Co., Ltd.): 0.09kg
Methylene chloride: 320kg
Ethanol: 20kg
These were put into an airtight container and completely dissolved while maintaining agitation at 80 ° C. under pressure.
(Production of film sample)
After the dope solution was filtered, it was cast on a support made of a stainless steel endless belt from a die at a dope temperature of 33 ° C. using a belt casting apparatus (not shown). After holding on the support for 60 seconds, it was peeled off from the support and dried while being conveyed by a number of rolls. At this time, using a clip tenter, the film was dried while being stretched 1.07 times in the width direction. After drying, a cellulose triacetate (TAC) film having a film thickness of 41 μm was obtained by winding up into a roll.

  In Examples 1 to 3, different types of cellulose triacetate (TAC) having different detection probabilities of calcium atoms and magnesium atoms were used.

  Next, for the cellulose triacetate (TAC) films obtained in Examples 1 to 3, a spectrophotometer U-3200 (manufactured by Hitachi, Ltd.) was used to measure the spectral absorption spectrum. The spectral transmittance of the film at a wavelength of 500 nm and a wavelength of 600 nm was measured.

When this transmittance T (%), the spectral transmission density is
Spectral transmission density = -log (T / 100)
Therefore, the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm was calculated by this equation, and the obtained results are shown in Table 1 below.

About the cellulose triacetate (TAC) film obtained in the said Examples 1-3, it analyzed with the inductively coupled plasma emission spectrometer (ICP-AES), measured the detection probability of the calcium atom and the magnesium atom, and obtained. The results are shown in Table 1.
Comparative Examples 1 and 2
For comparison, different cellulose triacetate films having different detection probabilities of calcium atoms and magnesium atoms as shown in Table 1 below were prepared. And about the cellulose triacetate (TAC) film obtained by these comparative examples 1 and 2, the ratio of the spectral transmission density in wavelength 500nm with respect to the spectral transmission density in wavelength 600nm was calculated like the case of the said Examples 1-3. The results obtained are shown in Table 1 below.

Next, for each of the cellulose triacetate films of Examples 1 to 3 and Comparative Examples 1 and 2 according to the present invention, generation of grainy foreign matters in the film, transparency of the film, coloring (external appearance) of the original film, and liquid crystal Display visibility was measured, and the obtained results are shown in Table 1.
(Evaluation of grainy foreign matter)
For the evaluation of the grainy foreign matter of the cellulose triacetate film, each cellulose triacetate film cut into a size of 40 cm square after the production was observed by visually observing the grainy foreign matter visible on the surface of the film under visible light, From the extent of the occurrence, the following sensitivity evaluation was performed.
◎: Grainy foreign matter is not observed at all ○: Grainy foreign matter is slightly observed △: Grainy foreign matter is observed a lot ×: Grainy foreign matter is observed very much (transparency Evaluation)
Further, the transparency of the cellulose triacetate film was observed in the state of a single wafer film. That is, the spectral transmittance at 400 nm and the wavelength of 500 nm of the single wafer dry film was used as an index. Evaluation was performed according to the following evaluation criteria.
Wavelength 500nm Wavelength 400nm
○: 93.5% or more 70.0% or more Δ: less than 93.5% less than 70.0% (evaluation of film original winding appearance)
The original appearance of the cellulose triacetate film was observed in the normal original winding state, and the degree of coloring was evaluated according to the following evaluation criteria.
○: Almost no color Δ: Slight yellow coloration is observed (evaluation of visibility)
A polarizing plate was prepared using each cellulose triacetate film as a protective film for a polarizing plate. Each produced polarizing plate was attached to a liquid crystal panel for evaluation. At this time, the antireflection layer was disposed so as to face outward.

The polarizing plates on both the front and back sides of the color liquid crystal display (Model VL-1530S manufactured by Fujitsu Limited) were peeled off, and each of the prepared polarizing plates was pasted so as to be the same as the original polarizing plate with the absorption axis. This was left to stand at 40 ° C. and a humidity of 90% RH for 1 month, and then the contrast of the screen was visually evaluated, and the visibility was determined according to the following criteria.
○: No decrease in contrast is observed Δ: A decrease in contrast is recognized at the periphery of the screen

  As is clear from the results in Table 1, according to the cellulose triacetate films of Examples 1 to 3 of the present invention, the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is within the scope of the present invention. For each cellulose triacetate film, the occurrence of grainy foreign matter was very small, the transparency of the film was good, and the original film was not colored. Furthermore, when the cellulose triacetate film according to the present invention is used as a protective film for a polarizing plate to produce a polarizing plate and the produced polarizing plate is attached to a liquid crystal panel for evaluation, the liquid crystal display has excellent visibility. I understand.

On the other hand, in the cellulose triacetate films of Comparative Examples 1 and 2, the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is out of the scope of the present invention. The appearance of the film was poor, the appearance of the original film was deteriorated, and a polarizing plate was prepared using the cellulose triacetate film of Comparative Example as a protective film for polarizing plate. The visibility of the liquid crystal display was poor when the prepared polarizing plate was attached to a liquid crystal panel for evaluation.
Examples 4 and 5
The cellulose triacetate film according to the present invention, the content of the magnesium compound shown by the mass ratio with respect to the film mass, the content of the calcium compound, and the content of the magnesium compound in the cellulose triacetate that is the main raw material of the cellulose triacetate film, Cellulose triacetate films were prepared using different cellulose triacetates as shown in Table 2 below.

  Next, as in the case of Examples 1 to 3 above, for each cellulose triacetate film of Examples 4 and 5 according to the present invention, the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is calculated, The occurrence of grainy foreign matter on the film, the transparency of the film, the color (external appearance) of the original roll film, and the visibility of the liquid crystal display were measured, and the results obtained are shown in Table 2 below.

As is apparent from the results in Table 2 above, according to the cellulose triacetate films of Examples 4 and 5 of the present invention, the ratio of the spectral transmission density at the wavelength of 500 nm to the spectral transmission density at the wavelength of 600 nm is within the scope of the present invention. In each cellulose triacetate film, the occurrence of grainy foreign matters was very small, the transparency of the film was good, and the original film was not colored. Furthermore, when the cellulose triacetate film according to the present invention is used as a protective film for a polarizing plate to produce a polarizing plate and the produced polarizing plate is attached to a liquid crystal panel for evaluation, the liquid crystal display has excellent visibility. I understand.
Examples 6-8
A cellulose triacetate film is produced in the same manner as in Example 1, but the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of cellulose triacetate, which is the main component of the film, is Mw / Mn as follows. Cellulose triacetate films were made using different cellulose triacetates as shown in Table 3. Here, the average molecular weight of the cellulose triacetate is measured using the gel permeation chromatography, and the number average molecular weight (Mn) and the weight average molecular weight (Mw) are calculated using this, and the weight of the cellulose triacetate is calculated. Ratio of average molecular weight (Mw) and number average molecular weight (Mn): Mw / Mn was calculated.

  Next, for each of the cellulose triacetate films of Examples 6 to 8 according to the present invention, the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is calculated, and the occurrence of grainy foreign matters in the film and the transparency of the film are calculated. Properties, coloring of the original film (appearance), and liquid crystal display visibility were measured in the same manner as in Examples 1 to 3 above, and the results obtained are shown in Table 3.

  As apparent from the results in Table 3, according to the cellulose triacetate films of Examples 6 to 8 of the present invention, the ratio of the spectral transmission density at the wavelength of 500 nm to the spectral transmission density at the wavelength of 600 nm is within the scope of the present invention. For each cellulose triacetate film, the occurrence of grainy foreign matter was very small, the transparency of the film was good, and the original film was not colored.

  Furthermore, when the cellulose triacetate film according to the present invention is used as a protective film for a polarizing plate to produce a polarizing plate and the produced polarizing plate is attached to a liquid crystal panel for evaluation, the liquid crystal display has excellent visibility. I understand.

  Although the cellulose triacetate with Mw / Mn = 1.5 used in Example 8 of the present invention has good quality, it leads to cost increase of the cellulose triacetate film and is not practical.

Claims (1)

A method for determining grainy foreign matter of a cellulose ester film having a thickness of 20 to 60 μm used for a polarizing plate protective film,
A method for determining grainy foreign matters in a cellulose ester film, wherein the ratio of the spectral transmission density at a wavelength of 500 nm to the spectral transmission density at a wavelength of 600 nm is 0.95 to 1.05.