JP2010091811A - High contrast polarizing plate and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display apparatus which has contrast higher than before. <P>SOLUTION: A polarizing plate contains a polarizing film which is formed by adsorption alignment of a dichroic dye on a polyvinyl alcohol resin film. In the polarizing film, polarizing film simplex contrast (S<SB>CR</SB>(λ)) at each wavelength defined by following formula (1) satisfies relations expressed by formulas (2), (3). Tp(λ) denotes transmittance (%) of the polarizing film measured in a parallel Nicol relation with incident linearly polarized light of wavelength λnm. Tc(λ) denotes transmittance (%) of the polarizing film measured in a cross Nicol relation with incident linearly polarized light of wavelength λnm. Both are measured values obtained by polarizing ultraviolet visible light absorption spectrum measurement by a spectrophotometer. Formula (1): S<SB>CR</SB>(λ)=T<SB>//</SB>(λ)/T<SB>L</SB>(λ). Formula (2): [(S<SB>CR</SB>(550)+S<SB>CR</SB>(600))/2]≥30,000. Formula (3): 3,000≤S<SB>CR</SB>(450)<30,000. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a high-contrast liquid crystal display device with clear display and a polarizing plate used therefor.

  A polarizing film is widely used as a film obtained by adsorbing and orienting a dichroic dye on a polyvinyl alcohol resin film. An iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic direct dye as a dichroic dye, and the like are known. These polarizing films are usually made into a polarizing plate by attaching a transparent protective film such as triacetyl cellulose or cycloolefin via an adhesive made of an aqueous solution of a polyvinyl alcohol resin on one or both surfaces thereof.

  A polarizing plate is widely used as an optical component for liquid crystal display devices. The market of liquid crystal display devices is expanding as display screens for liquid crystal televisions, personal computer monitors, notebook computers, mobile phones, and the like. In particular, mobile phones have become widespread regardless of generation, and progress has been remarkable. In particular, improvement in display quality is required along with weight reduction, thinning, and cost reduction. In addition, the spread rate of LCD televisions has recently been remarkably increasing, and this also requires improved display quality along with cost reduction.

In such display quality, there is a characteristic called contrast,

Display device contrast = (Luminance when displaying white) / (Luminance when displaying black)

It is a numerical value defined by. Here, the luminance is an index of brightness measured with a commercially available luminance meter, for example, a color luminance meter (BM-5A) sold by TOPCON Co., Ltd. or a spectroradiometer (SR-UL1). ) Etc. These are numerical values that are devised so as to match the sensitivity of the human eye by applying correction called visibility correction. Visibility correction will be described in detail later. When contrast is high, black and white becomes clear and a clearer image can be obtained. Therefore, it is generally used as an indicator of visibility in this field.

One method for improving the contrast is to improve the polarization performance of a polarizing plate, which is an essential member of a liquid crystal display device. The polarization performance referred to here is a numerical value mainly called a single transmittance and a degree of polarization, and is a numerical value defined by the following formula.

Single transmittance (λ) = 0.5 × (Tp (λ) + Tc (λ))

Polarization degree (λ) = 100 × (Tp (λ) −Tc (λ)) / (Tp (λ) + Tc (λ))

Here, Tp (λ) is the transmittance (%) of the polarizing film measured in the relationship between the linearly polarized light having the incident wavelength λnm and the parallel Nicol, and Tc (λ) is crossed with the linearly polarized light having the incident wavelength λnm. It is the transmittance | permeability (%) of the polarizing film measured by the relationship of Nicol, and is a measured value obtained by the polarized ultraviolet visible absorption spectrum measurement by a spectrophotometer. In addition, the single transmittance (λ) and polarization degree (λ) obtained for each wavelength are subjected to sensitivity correction called visibility correction, and the visibility correction single transmittance (Ty) and visibility correction polarization degree ( Py). Visibility correction will be described in detail later. Ty and Py can be easily measured with, for example, a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

  Until now, there was still room for improving the Py and Ty of the polarizing plate. Therefore, the contrast of the liquid crystal display device was improved by improving the polarizing performance of the polarizing plate by improving Py. The polarization performance is almost saturated, and is approaching the theoretical limit value. Therefore, it cannot be expected that the polarization performance greatly improves. In terms of Ty and Py values measured with V7100, the polarization performance of the best type of polarizing plate in recent years is Py = 99.996% and Ty = 42.5%. It is practically difficult to produce a plate stably. For example, when the degree of polarization is increased, the transmittance is lowered and darkened. Conversely, when the degree of polarization is increased, the degree of polarization is decreased.

  However, on the other hand, the demand for improving the contrast of liquid crystal display devices is still increasing, and it can be said that a breakthrough based on a new concept that fundamentally breaks away from the above-described improvement method is necessary.

  An object of the present invention is to provide a liquid crystal display device having a higher contrast than conventional ones. Moreover, it aims at providing the polarizing plate for achieving it, and the method of manufacturing the polarizing plate.

In order to solve the above-mentioned problems, the present inventors have conducted intensive research going back to the principle and principle of numerical values called contrast, and as a result, the visibility correction, which is an index based on the evaluation of a single polarizing plate as in the past With the idea of single transmittance and visibility correction polarization degree, etc., we notice the reason why it is not possible to achieve higher contrast than this, and understand the light emission characteristics of the liquid crystal display device and specify the characteristics for each wavelength of the polarizing plate As a result, the inventors have found an epoch-making method capable of further increasing the contrast as a liquid crystal display device, and have reached the present invention. Specifically, the present inventors have realized that it is important to have a specific relationship between the light emission wavelength characteristics of the backlight and the wavelength dependence of the polarizing film single-piece contrast (S _CR ) of the polarizing plate, leading to the present invention. . Moreover, it succeeded in finding the method for manufacturing the polarizing plate which has such a characteristic.

That is, the present invention is a polarizing plate including a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film, and the polarizing film at each wavelength defined by the following formula (1) of the polarizing film The polarizing plate is characterized in that the single contrast (S _CR (λ)) satisfies the relationship of the following formulas (2) and (3).

(here,

Tp (λ) is the transmittance (%) of the polarizing film measured in the relationship between the linearly polarized light with the incident wavelength λnm and the parallel Nicol, and Tc (λ) is crossed with the linearly polarized light with the incident wavelength λnm. It is the transmittance | permeability (%) of the polarizing film measured by the relationship of Nicol, and is a measured value obtained by the polarized ultraviolet visible absorption spectrum measurement by a spectrophotometer. )

[(S _CR (550) + S _CR (600)) / 2] ≧ 30,000 (2)

3,000 ≦ S _CR (450) <30,000 (3)

Whether the polarizing plate of the present invention is obtained by laminating a cellulose acetate resin film on one surface of the polarizing film via an adhesive layer and a cycloolefin resin film on the other surface via an adhesive layer. Alternatively, a cellulose acetate-based resin film may be laminated on one surface of the polarizing film via an adhesive layer, and a self-adhesive protective film that may be peeled off via an adhesive layer on the other surface. preferable. The adhesive layer is preferably formed from a water-based adhesive.

The polarizing plate of the present invention is a polarizing plate used in a liquid crystal display device including a backlight and a liquid crystal cell, and the liquid crystal display device has only the liquid crystal cell on the backlight and the backlight is turned on. In the spectrum measured in the state, it is preferable that the blue emission peak wavelength (Bmax) and the red emission peak wavelength (Rmax) satisfy the following formula (4).

(Rmax−550) <(550−Bmax) (4)

Moreover, this invention is a manufacturing method of the said polarizing plate, Comprising: A polarizing film which laminates | stacks a film on both surfaces of a polarizing film with a moisture content of 9% or more, and heat-processes at the temperature of 70 degreeC or more within 40 second immediately after lamination | stacking. It also relates to the manufacturing method of the board.

Furthermore, the present invention is a liquid crystal display device comprising a backlight, a liquid crystal cell and the polarizing plate,
In a spectrum measured with only the liquid crystal cell mounted on the backlight and the backlight is turned on, the blue emission peak wavelength (Bmax) and the red emission peak wavelength (Rmax) satisfy the following formula (4). The present invention also relates to a liquid crystal display device.

(Rmax−550) <(550−Bmax) (4)

  The polarizing plate of the present invention has a backlight and a liquid crystal cell (color filter) even if the polarizing plate alone has the same visibility correction polarization degree (Py) and visibility correction single transmittance (Ty) as the conventional polarizing plate. ), The contrast of the screen of the liquid crystal display device can be significantly improved as compared with the case where a conventional polarizing plate is used.

The present invention will be specifically described below.
In a normal liquid crystal display device, when the light emitted from the backlight through the color filter of the liquid crystal cell is examined, it is not uniform at all wavelengths, and there are strengths for each wavelength. This strength is determined by the emission spectrum from the backlight and the design of the color filter.

  The shape of the emission spectrum is determined to some extent depending on the type of backlight, and the shape varies depending on the type. For example, there is a cold cathode fluorescent lamp (CCFL) type having an emission spectrum as shown in FIG. 1, a light emitting diode (LED) having an emission spectrum as shown in FIG. . Since the principles of light emission are different from each other, the spectrum shape is also characteristic to some extent.

  On the other hand, since the design of the color filter of the liquid crystal cell is important for the color creation of the display device, there is a difference in design for each company. Usually, there are many things composed of three colors of red (R), green (G), and blue (B).

  It should be noted that Rmax, Gmax, and Bmax, which are the peak wavelengths of the three colors R, G, and B, cannot always be designed at equal intervals in the spectrum created by the combination of the backlight and the liquid crystal cell (color filter). . This is a problem of color creation as a display device, and is derived from the wavelength characteristics of the backlight and the color filter. For example, in the case of a mobile phone using a white LED, it is preferable that Bmax is about 450 nm, Gmax is about 550 nm, and Rmax is about 600 nm from the viewpoint of color creation and backlight characteristics.

  The definitions of Rmax (red light emission peak wavelength), Gmax (green light emission peak wavelength), and Bmax (blue light emission peak wavelength) will be described. An LED backlight type such as a cellular phone is shown in FIG. As shown in Fig. 1, the peak is clear and very easy to understand, but in the CCFL type backlight seen in large LCD TVs, as shown in Fig. 1, one color is composed of multiple fine peaks. Some are. Bmax is a peak having a maximum integrated area among emission peaks having a peak position between 380 and 500 nm. A minute jump such as noise is not counted as a peak, and a peak position may be determined by performing an appropriate fitting method such as normal distribution approximation as necessary. Gmax may be selected in the same manner from the peak position in the range of 500 to 570 nm and Rmax in the range of the peak position from 570 to 700 nm.

  Here, the concept of visibility correction is introduced. The sensitivity of the human eye is highest for light with a wavelength of about 550 nm, and the light with a wavelength farther from it has a lower sensitivity. Taking this into consideration is the concept of the visibility correction, and the visibility correction luminance is calculated by multiplying the actual spectrum by a symmetrical distribution distribution curve that is symmetrical as shown in FIG. . The peak of this correction curve is at a position of 550 nm, which means that the light of this wavelength has the highest sensitivity of the luminance meter and the human eye. Conversely, the sensitivity decreases as the wavelength is far from 550 nm. To go. For example, assuming that the visibility correction rate at 550 nm is 1.0, there is only a ratio of 0.04 or less at 450 nm, that is, light having a wavelength of 450 nm is 1/25 of light at 550 nm even with the same light emission amount. This means that only the brightness is measured.

When the backlight is viewed again in consideration of these, the interval between 550 nm and Bmax is about 100 nm, but the interval between 550 nm and Rmax is only about 50 nm. That is, there is a relationship of the following formula (4).

(Rmax−550) <(550−Bmax) (4)

This means that when a numerical value is measured as luminance, blue light is measured much weaker than red light. Conversely, the red peak contributes significantly more to the luminance than the blue peak.

  In particular, in the case of a mobile application such as a mobile phone or PDA using a white LED or the like as a backlight, this tendency can restrict the peak on the long wavelength side in principle. Often the relationship is more pronounced. However, large TVs designed with CCFL or the like are often preferable from the viewpoint of color creation, etc., because they satisfy equation (4).

  According to the present invention, the polarizing plate applied to the liquid crystal display device having the backlight as described above is designed in consideration of wavelength dependency, so that the contrast of the display device can be improved without improving Ty and Py of the polarizing plate. Can be drastically improved.

  This indicates that even in the polarizing plate applied to such a display device, the importance for each wavelength is different, and when combined with the above-mentioned backlight, the polarization performance in the red region is emphasized. It is efficient that it is.

  Current polarizing plates tend to pursue polarization performance in a form that cares for the entire wavelength region of visible light. In particular, the visibility correction single transmittance and the visibility correction polarization degree, which are indexes of conventional polarization performance, are numerical values to which visibility correction has been applied, as the name suggests. This visibility correction is the curve itself of FIG. In this index, for example, a polarizing plate having a spectrum of orthogonal transmittance (Tp (λ)) as shown in FIG. 4 (having a relatively uniform orthogonal transmittance at all wavelengths of B, G, and R) Even a polarizing plate having a spectrum of orthogonal transmittance (Tp (λ)) as shown in FIG. 5 (transmittance at G and R wavelengths is low and transmittance at B wavelengths is high) Since the sensitivity decreases symmetrically around 550 nm, both values are similar when the visibility correction is applied.

  However, when considering the characteristics of the backlight and the color filter as described above, the red wavelength region has a larger contribution to the luminance, and therefore the type of polarizing plate as shown in FIG. 5 is more preferable. It can be said.

  In order to increase the visibility correction polarization degree, it is necessary to improve the polarization degree in the whole wavelength range, so it is quite difficult to achieve the theoretical limit value. When the viewpoint was switched to the direction of improvement to the type shown in FIG. 5, there was room for improvement, which could be a big breakthrough.

FIGS. 6 and 7 respectively show the polarizing film single contrast (S _CR (λ)) defined by the above formula (1) for the polarizing film having the spectrum of the orthogonal transmittance Tc (λ) as shown in FIGS. It is the shown graph. Since the polarizing film single-piece contrast (S _CR (λ)) is a ratio of the maximum value to the minimum value of the transmittance of natural light in a state where two polarizing plates are stacked, rather than indexes such as orthogonal transmittance and polarization degree, It is an index that is considered to be closer to the superiority or inferiority of contrast of an actual liquid crystal display device.

(Measurement method of contrast of polarizing film alone)
Hereinafter, it describes about the measuring method of polarizing film single-piece | unit contrast ( _SCR ((lambda))).

<Measurement device>
A spectrophotometer is used as a measuring device for Tp (λ) and Tc (λ). In order to evaluate the Tc (λ) value more correctly, it is necessary to use a spectrophotometer capable of measuring up to a higher absorbance region. In the present invention, it is necessary to use an apparatus capable of measuring an absorbance of about 7-8. There is. Examples of such a spectrophotometer include a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

As a method for entering linearly polarized light, a method using a polarizing prism made of calcite is generally known. In the present invention, the extinction ratio of the polarizing prism is set to 10 ⁻⁵ or less.

<Measurement sample>
In the polarizing plate, a transparent protective film is often bonded to one or both sides of the polarizing film, but the transparent protective film has retardation characteristics, and its slow axis is parallel to the absorption axis of the polarizing film. If they are pasted together, the incident linearly polarized light becomes elliptically polarized light due to the retardation characteristics of the transparent protective film, and the above Tp (λ) and Tc (λ) cannot be measured correctly. When evaluating such a polarizing plate, it is necessary to measure by separating the transparent protective film from the polarizing plate. When the transparent protective film has substantially no retardation characteristics, or even if the transparent protective film has retardation characteristics, it is bonded so that its slow axis is parallel or perpendicular to the absorption axis of the polarizing film. In this case, the Tp (λ) and Tc (λ) can be measured correctly without separating the transparent protective film from the polarizing plate.

<Measurement>
Using the above spectrophotometer, linearly polarized light (wavelength λ nm) is incident on the polarizing film, and the transmittance (parallel transmittance: Tp (λ)) measured in the relationship between the linearly polarized light and parallel Nicol is measured. The transmittance (orthogonal transmittance: Tc (λ)) measured in the relationship is measured at each wavelength. Further, S _CR (λ) is obtained from the measured Tp (λ) and Tc (λ) according to the above equation (1).

(Characteristics of polarizing film)
The polarizing plate used in the liquid crystal display device according to the present invention is characterized in that the polarizing film simple substance contrast (S _CR (λ)) of each wavelength defined by the above formula (1) satisfies the relationship of the following formula (2). It is necessary to be.

[(S _CR (550) + S _CR (600)) / 2] ≧ 30,000 (2)

Here, [(S _CR (550) + S _CR (600)) / 2] in the above formula (2) is 30000 or more, preferably 40000 or more, the contrast of the display device is improved. On the other hand, when the value is less than 30000, there is a problem that the contrast of the display device cannot be obtained. S _CR (550) and S _CR (600) are each independently preferably 30,000 or more, more preferably 40000 or more.

Conversion from a polarizing plate having _SCR (λ) characteristics as shown in FIG. 6 to a polarizing plate of the type having _SCR (λ) characteristics as shown in FIG. 7 is performed at 550 nm or 600 nm. S _CR is increased but, S _CR in the vicinity of 450nm becomes possible to decrease the contrary,

[(S _CR (550) + S _CR (600)) / 2]> S _{CR (450)}

It becomes a relationship. This is because, for example, in the case of a polarizing film in which iodine is adsorbed and oriented, the high-temperature and high-humidity treatment described later increases the ratio of I ₅ out of iodine in the polarizing film, thereby increasing absorption on the high wavelength side. This is because the absorption on the low wavelength side is reduced by decreasing the ratio of I ₃ . Incidentally, there is also a phenomenon that the degree of orientation of itself iodine by high-temperature and high-humidity treatment slightly increased, also observed increase in overall S _CR by this.

  As described above, even when the contrast of the polarizing film alone at the wavelength of the B (blue) region is lowered, when applied to an LED backlight or a color filter that contributes little to blue, there is not much problem if the visibility correction is taken into consideration. Therefore, priority is given to the contrast of the polarizing film alone at wavelengths in the R (red) and G (green) regions, thereby improving the contrast of the screen of the liquid crystal display device.

  This is because the contrast characteristics of the display device are pursued from a viewpoint completely different from the viewpoints such as Ty and Py that have been required for the polarizing plate in the past, and the polarizing performance is near the theoretical limit at present. It can be said that this is a breakthrough for increasing the contrast of display devices.

(Preparation method of polarizing plate)
Although the polarizing plate of this invention can be produced as follows, for example, it is not limited to this.

(1) Polarizing film production process The polyvinyl alcohol-type resin which comprises a polarizing film is normally obtained by saponifying a polyvinyl acetate type resin. The saponification degree of the polyvinyl alcohol-based resin is usually 85 mol% or more, preferably 90 mol% or more, and more preferably 99 to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymers. Etc. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually in the range of 1000 to 10000, preferably in the range of 1500 to 5000.

  These polyvinyl alcohol resins may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Usually, as a starting material for producing a polarizing film, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of 20 to 100 μm, preferably 30 to 80 μm is used. Industrially, the practical width of the film is 1500 to 4000 mm. The unstretched film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, uniaxially stretched in the steps up to boric acid treatment, and finally dried to obtain a polarizing film having a thickness of, for example, 5 ~ 50 μm.

  There are roughly two methods for producing a polarizing film. In the first method, a polyvinyl alcohol-based resin film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of a swelling treatment step, a dyeing treatment step, a boric acid treatment step and a water washing treatment step, and finally drying. How to do it. In the second method, an unstretched polyvinyl alcohol-based resin film is solution-treated with an aqueous solution in the order of a swelling treatment step, a dyeing treatment step, a boric acid treatment step and a water washing treatment step, and the boric acid treatment step and / or the previous step. In this method, uniaxial stretching is performed in a wet process, followed by drying.

  In any method, the uniaxial stretching may be performed in one step or in two or more steps. As a stretching method, a known method can be adopted. For example, stretching between rolls in which stretching is performed with a difference in peripheral speed between two nip rolls for transporting a film, for example, a hot roll as described in Japanese Patent No. 2731813 There are a stretching method and a tenter stretching method. The order of the steps is basically as described above, but there are no restrictions on the number of treatment baths, treatment conditions, and the like. Moreover, you may add the process which is not described in the said 1st and 2nd method for another objective. Examples of such processes include immersion treatment with an aqueous iodide solution not containing boric acid (iodide treatment) or immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment) after boric acid treatment. Can be mentioned.

  The swelling treatment step is performed for the purpose of removing foreign matter on the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The processing conditions are determined within a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When the film previously stretched in the gas is swollen, for example, the film is immersed in an aqueous solution at 20 to 70 ° C, preferably 30 to 60 ° C. The immersion time of the film is 30 to 300 seconds, preferably 60 to 240 seconds. In order to swell the unstretched raw film from the beginning, the film is immersed in an aqueous solution of 10 to 50 ° C., preferably 20 to 40 ° C., for example. The immersion time of the film is 30 to 300 seconds, preferably 60 to 240 seconds.

  In the swelling process, since the film is likely to swell in the width direction and wrinkles into the film, a known wide roll (expander roll), spiral roll, crown roll, cross guider, bend bar, tenter clip, etc. It is preferable to convey the film while removing the wrinkles of the film with a widening device. In order to stabilize the film transport in the bath, the water flow in the swelling bath is controlled by an underwater shower, EPC (Edge Position Control device: a device that detects the edge of the film and prevents the film from meandering), etc. It is also useful to use together. In this step, since the film swells and expands in the film transport direction, it is preferable to take measures such as controlling the speed of the transport roll before and after the treatment tank in order to eliminate the sag of the film in the transport direction. In addition to pure water, the swelling treatment bath used is boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water-soluble An aqueous solution to which an organic solvent, alcohol or the like is added in an amount of 0.01 to 0.1% by weight can also be used.

  The dyeing process with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. The processing conditions are determined within a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When iodine is used as the dichroic dye, for example, iodine / potassium iodide / water = 0.003 to 0.2 / 0.1 in a weight ratio of 10 to 45 ° C., preferably 20 to 35 ° C. An immersion treatment is performed for 30 to 600 seconds, preferably 60 to 300 seconds, using an aqueous solution having a concentration of 10/100. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. Any dye containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, dichroic dye / water = 0.001 to 0.1 / by weight ratio under a temperature condition of 20 to 80 ° C., preferably 30 to 70 ° C. A 100-concentration aqueous solution is used for 30 to 600 seconds, preferably 60 to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used in combination.

  As described above, the film may be stretched in a dyeing tank. Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling treatment step, a widening roll (expander roll), a spiral roll, a crown roll, a cross guider, a bend bar and the like can be installed in the dyeing bath and / or at the bath entrance / exit.

  The boric acid treatment is performed by immersing a polyvinyl alcohol resin film dyed with a dichroic dye in an aqueous solution containing 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain 1 to 30 parts by weight of iodide. Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  The boric acid treatment is carried out for water resistance by crosslinking or hue adjustment (for example, to prevent bluish tint). When boric acid treatment is performed for water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde can be used in addition to boric acid or together with boric acid, if necessary. In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color treatment or re-dyeing treatment.

  This boric acid treatment is performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but can be carried out under the following conditions. When the raw film is subjected to swelling treatment, dyeing treatment, boric acid treatment, and boric acid treatment is aimed at water resistance by crosslinking, boric acid is added in an amount of 3 to 10 parts by weight with respect to 100 parts by weight of water. A boric acid treatment bath containing 1 to 20 parts by weight of iodide is used, and is usually performed at a temperature of 50 to 70 ° C, preferably 55 to 65 ° C. The immersion time is 90 to 300 seconds. In addition, when performing the dyeing | staining process and a boric-acid process to the film extended | stretched previously, the temperature of a boric-acid processing bath is 50-85 degreeC normally, Preferably it is 55-80 degreeC.

  You may make it perform the boric-acid process for hue adjustment after the boric-acid process for water resistance. For example, when the dichroic dye is iodine, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. Usually, it is carried out at a temperature of 10 to 45 ° C. The immersion time is usually 3 to 300 seconds, preferably 10 to 240 seconds. The subsequent boric acid treatment for adjusting the hue is usually performed at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than the boric acid treatment for water resistance.

  These boric acid treatments may consist of a plurality of steps and are usually carried out in 2 to 5 steps. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above-described range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of steps, respectively.

  In the boric acid treatment step, the film may be stretched as in the dyeing treatment step. The final cumulative draw ratio is 4 to 7 times, preferably 4.5 to 6.5 times. The cumulative stretching ratio here means how long the reference length in the length direction of the original film is in all the films after the completion of the stretching process. For example, it is 1 m in the original film. If the portion is 5 m in all the films after the stretching treatment, the cumulative stretching ratio at that time is 5 times.

  After the boric acid treatment, a water washing treatment is performed. The water washing treatment is performed by immersing a polyvinyl alcohol resin film treated with boric acid for water resistance and / or hue adjustment in water, spraying water as a shower, or combining immersion and spraying. The water temperature in the water washing treatment is usually 2 to 40 ° C., and the immersion time is 2 to 120 seconds.

  Here, in each step after the stretching treatment, tension control may be performed so that the tension of the film becomes substantially constant. Specifically, when stretching is completed in the dyeing process, tension control is performed in the subsequent boric acid treatment process and the water washing process. When stretching is completed in the previous process of the dyeing process, tension control is performed in subsequent processes including the dyeing process and the boric acid process. When the boric acid treatment step is composed of a plurality of boric acid treatment steps, the film is stretched in the boric acid treatment step from the beginning or the first to the second step, and the next boric acid treatment step after the boric acid treatment step in which the stretching treatment is performed. Tension control is performed in each step from the acid treatment step to the water washing step, or the film is stretched in the boric acid treatment step from the first to the third stage, and the boric acid next to the boric acid treatment step in which the stretching treatment is performed. It is preferable to perform tension control in each process from the treatment process to the water washing process, but industrially, the film was stretched in the boric acid treatment process from the first or the first to the second stage, and the stretching process was performed. It is more preferable to perform tension control in each step from the boric acid treatment step next to the boric acid treatment step to the water washing step. In addition, when performing the above-described iodide treatment or zinc treatment after the boric acid treatment, tension control can also be performed for these steps.

As the nip roll for controlling the tension and the guide roll for controlling the film conveyance direction, a rubber roll, a stainless steel polishing roll, a sponge rubber roll, and the like can be used. The rubber roll is made of NBR or the like, and its hardness is preferably 60 to 90 degrees, more preferably 70 to 80 degrees on the JIS Shore C scale measured by the test method of JIS K 6301. The stainless steel polishing roll is preferably made of SUS304, SUS316, or the like, for the purpose of making the film thickness uniform. As the sponge rubber roll, the hardness of the sponge is 20-60 degrees on the JIS Shore C scale measured by the test method of JIS K 6301, further 25-50 degrees, the density is 0.4-0.6 g / m ³ , It is preferable that it is 0.42-0.57 g / cm < ³ >.

  The tension in each step from the swelling treatment to the water washing treatment may be the same or different. The tension on the film in the tension control is not particularly limited, and is 150 to 2000 N per unit width. / M, preferably within the range of 600 to 1500 N / m. When the tension is less than 150 N / m, the film is likely to be wrinkled. On the other hand, when the tension exceeds 2000 N / m, problems such as film breakage and life reduction due to bearing wear occur. The tension per unit width is calculated from the film width near the entrance of the process and the tension value of the tension detector. In addition, when tension control is performed, there are cases where the film is inevitably slightly stretched or shrunk, but in the present invention, this is not included in the stretching process.

  At the end of the polarizing film manufacturing process, a drying process is performed. The drying treatment is preferably carried out in a large number of stages by changing the tension little by little, but is usually carried out in 2 to 3 stages due to restrictions on equipment. When performed in two stages, the tension in the front stage is preferably set in the range of 600 to 1500 N / m, and the tension in the rear stage is preferably set in the range of 250 to 1200 N / m. When the tension becomes too large, the film breaks more, and when it becomes too small, the generation of wrinkles increases, which is not preferable. Moreover, it is preferable to set the drying temperature of a front | former stage from the range of 30-90 degreeC, and the drying temperature of a back | latter stage from the range of 40-100 degreeC. If the temperature is too high, the film will be ruptured and the optical properties will be deteriorated. If the temperature is too low, streaks will increase, which is not preferable. The drying treatment temperature can be 60 to 600 seconds, for example, and the drying time in each stage may be the same or different. If the time is too long, it is not preferable in terms of productivity, and if the time is too short, drying is insufficient, which is not preferable.

  In this way, the polyvinyl alcohol resin film is subjected to uniaxial stretching, dyeing treatment with a dichroic dye, and boric acid treatment to obtain a polarizing film. The thickness of this polarizing film is usually in the range of 5 to 40 μm.

(2) Method for imparting characteristics satisfying formulas (2) and (3) to the polarizing film In the polarizing plate of the present invention, the polarizing film used has the characteristics represented by the following formula (2). A polarizing film having this property can be obtained by maintaining the polarizing film in a specific environment. That is, it is necessary to hold the polarizing film in a state where at least shrinkage in the flow direction (absorption axis direction) is suppressed and in a high temperature and high humidity environment.

[(S _{CR (550)} + S _{CR (600)} ) / 2] ≧ 30,000 (2)

In a state where the shrinkage of the polarizing film is not suppressed, the polarizing film produced by uniaxial stretching greatly shrinks and the polarizing performance is lost. The state in which the shrinkage of the polarizing film is suppressed is a method of holding the polarizing film in a high-temperature and high-humidity tank while maintaining the tension, a state in which the film is laminated on both surfaces of the polarizing film having a high moisture content, and the polarizing film has a high moisture content. And a method of imparting a high temperature. The tension in the former is 15 × 10 ⁴ N / m ² to 1500 × 10 ⁴ N / m ² , more preferably 150 × 10 ⁴ N / m ² to 1200 × 10 ⁴ N / m ² . If it is less than 15 × 10 ⁴ N / m ² , the polarization performance tends to be lost, and if it is 1500 × 10 ⁴ N / m ² or more, it tends to break.

  In the case of the latter, shrinkage | contraction of a polarizing film is suppressed by laminating | stacking films, such as the below-mentioned transparent protective film, on both surfaces of a polarizing film. In addition, since this method simply places the polarizing film in a high-temperature and high-humidity environment by heating the laminated polarizing plate, a high-temperature and high-humidity tank is installed when the polarizing film is held in a high-temperature and high-humidity environment. There is no need to do this, and it is convenient and preferable.

  The high temperature and high humidity environment refers to an environment having a temperature of 40 ° C. to 90 ° C. and a humidity of 50% to 95% RH, and more preferably a temperature of 60 ° C. to 80 ° C. and a humidity of 60% to 90% RH. . When the temperature is lower than 40 ° C. or when the humidity is lower than 50% RH, it is difficult to obtain the characteristics described in the formula (3) because the temperature and humidity are insufficient. When the temperature is 90 ° C. or higher, the polarizing film is deteriorated and easily becomes blue-stained, and when the humidity is 95% RH or higher, condensation tends to occur.

  The exposure time in a high temperature and high humidity environment is 10 seconds to 1200 seconds, more preferably 20 seconds to 600 seconds. If the time is short, a sufficient treatment effect cannot be obtained, and if it is too long, the polarizing film is deteriorated, and it is easy to cause a blue discoloration.

  In the method of laminating films on both sides of a polarizing film and applying a high temperature while the moisture of the polarizing film is high, it is difficult to quantify the temperature and humidity environment to which the polarizing film is exposed. Define the conditions for doing so. Such temperature is 70 ° C. or higher, preferably 75 ° C. or higher, and is usually 100 ° C. or lower, preferably 90 ° C. or lower. When the temperature is too low, a sufficient treatment effect cannot be obtained, and when the temperature is too high, the polarizing film is deteriorated, and it is not preferable because it is easily discolored.

  Such treatment imparts a high temperature within 40 seconds, preferably within 30 seconds, more preferably within 20 seconds, immediately after bonding. If the time until the high temperature is applied is long, the moisture of the polarizing film is lowered, and it becomes difficult to obtain a treatment effect.

  The time for applying the high temperature after bonding is 10 seconds to 1200 seconds, more preferably 20 seconds to 600 seconds. If the time is short, a sufficient treatment effect cannot be obtained, and if it is too long, the polarizing film is deteriorated, and it is easy to cause a blue discoloration.

  A polarizing film having a high moisture content is a polarizing film having a moisture content of 9% or more, preferably 10% or more. If it is lower than 9%, it is difficult to obtain a treatment effect even if a film is laminated on both sides of the polarizing film and a high temperature is applied. If the moisture content is too high, wrinkles and the like are generated when the films are laminated on both sides of the polarizing film, which is not preferable. The upper limit of the moisture content is usually 20% or less, more preferably 15% or less.

The moisture content of the polarizing film is determined by the following formula based on the value measured with an infrared moisture meter IM-3SCV MODEL-1900 (L) manufactured by Fuji Work.

Moisture content = (1/28) * (1.2145 * measured value−941.662)

This equation is a relational expression obtained from the fact that the value of the moisture content of the polarizing film having a different moisture content and the moisture content obtained from the change in the moisture content before and after the heat treatment at 105 ° C. are almost linear. is there.

  A polarizing film having a moisture content within the preferred range described above can be obtained, for example, by controlling the drying temperature and drying time of the polarizing film, and a polarizing film having a low moisture content lowers the temperature of the drying furnace, and / or Alternatively, it can be obtained by shortening the drying time, and a polarizing film having a high moisture content can be obtained by increasing the temperature of the drying furnace and / or lengthening the drying time.

  In the present invention, when the performance of the formula (3) is to be obtained, in the method of laminating films on both sides of the polarizing film and applying a high temperature in a state where the polarizing film has a high water content, the above-described temperature, time, and moisture content are used. The combination of is important.

  After drying, the film can be further cured at room temperature or slightly higher, for example, at a temperature of about 20 to 50 ° C. for about 12 to 600 hours. The temperature during curing is generally set lower than the temperature employed during drying.

(3) Lamination of a film such as a transparent protective film on a polarizing film As a method of laminating a film such as a transparent protective film on both sides of the polarizing film, the film is laminated directly or via an adhesive layer. When a film is laminated | stacked only on the single side | surface of a polarizing film, even if it gives high temperature after that, since a polarizing film is hard to be hold | maintained in a high-humidity environment, it is unpreferable.

  The film may be laminated by laminating the polarizing film and the film one by one successively or simultaneously on both sides using a roll or the like. From the viewpoint of production efficiency, it is preferable that both surfaces are bonded simultaneously. The bonding temperature is usually in the range of about 15 to 30 ° C. When laminating through the adhesive layer, for example, apply the adhesive uniformly on the surface of the polarizing film and / or the transparent protective film, overlap the other film on the application surface, and paste with a roll, The method of drying etc. are mentioned. Usually, the adhesive is applied at a temperature of 15 to 40 ° C. after its preparation.

  As an adhesive in the case of using an adhesive, a water solvent adhesive, an organic solvent adhesive, a hot melt adhesive, a solventless adhesive, or the like can be used. Examples of the aqueous solvent-based adhesive include a polyvinyl alcohol-based resin aqueous solution and an aqueous two-component urethane emulsion adhesive, and the organic solvent-based adhesive includes, for example, a two-component urethane adhesive. Examples of the adhesive include a one-pack type urethane adhesive and an epoxy adhesive.

  When an aqueous polyvinyl alcohol resin solution is used, the polyvinyl alcohol resin used as an adhesive includes a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as vinyl acetate and this. And vinyl alcohol copolymers obtained by saponifying a copolymer with another copolymerizable monomer, and modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups. A polyhydric aldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, a zinc compound, or the like may be added to the adhesive as an additive. When such an aqueous adhesive is used, the adhesive layer obtained therefrom is usually 1 μm or less, and even when the cross section is observed with a normal optical microscope, the adhesive layer is practically not observed.

  A photo-curing adhesive can also be used as the adhesive. Examples of the photo-curable adhesive include epoxy resin, acrylic resin, okitacene resin, urethane resin, polyvinyl alcohol resin, and the like to which a radical polymerization initiator and / or a cationic polymerization initiator are added. Especially, what added the cationic polymerization type initiator to the mixture of the alicyclic epoxy resin and the epoxy resin which does not have an alicyclic structure is preferable.

When joining a polarizing film and the film bonded to it using a photocurable adhesive, after joining, a photocurable adhesive is hardened by irradiating an active energy ray. The light source of the active energy ray is not particularly limited, but an active energy ray having a light emission distribution at a wavelength of 400 nm or less is preferable. Specifically, the low-pressure mercury lamp, the medium-pressure mercury lamp, the high-pressure mercury lamp, the ultrahigh-pressure mercury lamp, the chemical lamp, and the black light lamp A microwave excited mercury lamp, a metal halide lamp, or the like is preferably used. The light irradiation intensity to the photocurable adhesive is appropriately determined depending on the composition of the photocurable adhesive and is not particularly limited. However, the irradiation intensity in the wavelength region effective for activating the polymerization initiator is 0.1 to 6000 mW. / Cm ² is preferable. When the irradiation intensity is 0.1 mW / cm ² or more, the reaction time does not become too long, and when it is 6000 mW / cm ² or less, it is caused by heat radiated from the light source and heat generated when the photocurable adhesive is cured. There is little risk of yellowing of the epoxy resin and deterioration of the polarizing film. The light irradiation time to the photo-curing adhesive is controlled for each photo-curing adhesive to be cured and is not particularly limited, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is It is preferably set to be 10 to 10,000 mJ / cm ² . When the cumulative amount of light to the photo-curing adhesive is 10 mJ / cm ² or more, a sufficient amount of active species derived from the polymerization initiator can be generated to allow the curing reaction to proceed more reliably, and at 10,000 mJ / cm ² or less. In some cases, irradiation time does not become too long and good productivity can be maintained. The thickness of the adhesive layer after irradiation with active energy rays is usually about 0.001 to 5 μm, preferably 0.01 μm or more, preferably 2 μm or less, more preferably 1 μm or less.

  When the photocurable adhesive is cured by irradiation with an active energy ray, it is preferable to perform the curing under conditions where various functions of the polarizing plate such as the degree of polarization, transmittance, and hue of the polarizing film do not deteriorate.

  When laminating the film on both surfaces of the polarizing film, the film is preferably a transparent protective film when laminated via an adhesive layer.

  Examples of transparent protective films include cycloolefin resin films, cellulose acetate resin films, polyester resin films such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, polycarbonate resin films, acrylic resin films, and polypropylene films. Examples thereof include films that have been widely used in the art, such as resin films.

  Cycloolefin-based resins may be commercial products such as Topas (manufactured by Ticona), Arton (manufactured by JSR Corporation), ZEONOR (manufactured by Nippon Zeon Co., Ltd.), ZEONEX (manufactured by Nippon Zeon Corporation). ) And Apel (Mitsui Chemicals) can be preferably used. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. In addition, for example, commercially available cycloolefin resin films such as Essina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), Zeonoa Film (manufactured by Optes Co., Ltd.), etc. You may use goods.

  The cycloolefin resin film may be uniaxially stretched or biaxially stretched. By stretching, an arbitrary retardation value can be given to the cycloolefin-based resin film. Stretching is usually performed continuously while unwinding the film roll, and the film is stretched in a heating furnace in a roll traveling direction, a direction perpendicular to the traveling direction, or both. As the temperature of the heating furnace, a range from the vicinity of the glass transition temperature of the cycloolefin resin to the glass transition temperature + 100 ° C. is usually employed. The draw ratio is usually 1.1 to 6 times, preferably 1.1 to 3.5 times.

  When the cycloolefin-based resin film is stretched, the stretching direction is arbitrary, but those that are 0 °, 45 °, and 90 ° with respect to the flow direction of the film are common. The retardation characteristics of a film having a stretching direction of 0 ° are completely uniaxial, and the retardation characteristics of films having 45 ° and 90 ° are often weakly biaxial. The characteristics affect the viewing angle of the display device, but may be appropriately selected depending on the type of liquid crystal display device to be applied and the type of composite polarizing plate. As the phase difference value, what is usually called λ / 4, λ / 2, or the like is often used. In many cases, the phase difference range is 90 to 170 nm for λ / 4 and 200 to 300 nm for λ / 2.

  When the cycloolefin-based resin film is in a roll state, the films tend to adhere to each other and easily cause blocking. Therefore, the protective film is usually bonded to roll. In addition, since cycloolefin resin films generally have poor surface activity, surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment is performed on the surface to be bonded to the polarizing film. Is preferred. Among these, plasma treatment and corona treatment that can be performed relatively easily are preferable.

  The cellulose acetate-based resin that can be used for the transparent protective film is a part of cellulose or a complete acetate ester, and examples thereof include triacetyl cellulose, diacetyl cellulose, and cellulose acetate propionate.

  As such a cellulose ester resin film, an appropriate commercially available product such as Fujitac TD80 (Fuji Film Co., Ltd.), Fujitac TD80UF (Fuji Film Co., Ltd.), Fujitac TD80UZ (Fuji Film Co., Ltd.) KC8UX2M (manufactured by Konica Minolta Opto Co., Ltd.), KC4UY (manufactured by Konica Minolta Opto Co., Ltd.) and the like can be suitably used.

  In addition, a cellulose acetate-based resin film imparted with retardation characteristics is also preferably used. As a commercially available cellulose acetate-based resin film imparted with such retardation characteristics, WV BZ 438 (manufactured by Fuji Film Co., Ltd.), KC4FR-1 (manufactured by Konica Minolta Opto Co., Ltd.) and the like can be mentioned. Cellulose acetate is also called acetyl cellulose or cellulose acetate.

  The cellulose resin film is subjected to a saponification treatment in order to enhance the adhesion to the polarizing film, particularly when the cellulose resin film is laminated with the polarizing film using an aqueous adhesive. As the saponification treatment, a method of immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide can be employed.

  The surface of the cycloolefin-based resin film or the cellulose acetate-based resin film may be subjected to a surface treatment such as an antiglare treatment, a hard coat treatment, an antistatic treatment, or an antireflection treatment, depending on the application. Further, a liquid crystal layer or the like may be formed in order to improve the viewing angle characteristics.

  When laminating films on both sides of the polarizing film, it is more preferable that at least one of the films is a resin film having low moisture permeability. When the moisture permeability is low, the polarizing film is easily held in a high humidity environment when it is laminated and given a high temperature.

The moisture permeability is preferably 400 (g / m ² · 24 hr) or less, preferably 300 g or less, more preferably 100 g or less, and even more preferably 50 g or less in an environment of 40 ° C. and 90% RH.

  When a transparent protective film is in a roll state, the films tend to adhere to each other and easily cause blocking. Therefore, usually, the roll end part is subjected to uneven processing, a ribbon is inserted into the end part, or the protective film is attached. What was pasted together and made into a roll is used.

  The transparent protective film is preferably thin, but if it is too thin, the strength is lowered and the processability is poor. On the other hand, when it is too thick, problems such as a decrease in transparency and a longer curing time after lamination occur. Therefore, the suitable thickness of a transparent protective film is 5-200 micrometers, for example, Preferably it is 10-150 micrometers, More preferably, it is 20-100 micrometers.

  When laminating films directly on both sides of the polarizing film, the film is preferably a peelable protective film. The protective film is peeled off when it is no longer necessary, for example, when an adhesive layer is formed on the polarizing film surface of the polarizing plate.

  The peeling force between the protective film and the polarizing film is 0.01 to 5 N / 25 mm, preferably 0.01 to 2 N / 25 mm, more preferably 0.01 to 0.5 N / 25 mm. When the peeling force is less than 0.01 N / 25 mm, the protective film may be partially peeled off because the adhesion between the polarizing film and the protective film is small. Moreover, since it will become difficult to peel a protective film from a polarizing film when peeling force exceeds 5 N / 25mm, it is unpreferable.

  As the material of the protective film, polyethylene resin, polypropylene resin, polystyrene resin, polyethylene terephthalate resin, etc., which are easy to handle and secure a certain degree of transparency, can be preferably used. Or the film which shape | molded 2 or more types in the single layer or the multilayer form can be used as a protective film.

  As such a protective film, specifically, sanitect (sold by Sanei Kaken Co., Ltd.) in which an adhesive layer is formed on the surface of the polyethylene resin film, an adhesive layer is formed on the surface of the polyethylene terephthalate resin film. Commercial products such as E-mask (manufactured by Nitto Denko Corporation) and MASTACK (manufactured by Fujimori Kogyo Co., Ltd.) in which an adhesive layer is formed on the surface of the polyethylene terephthalate resin film.

  Among them, the self-adhesive protect film having adhesiveness to the polarizing film alone is simple because it does not need to protect the pressure-sensitive adhesive layer on the surface of the protect film, and can be used more suitably. As a commercial item of the self-adhesive resin film which shows suitable peeling force with respect to the said polarizing film, the Tretec (made by Toray Industries, Inc.) etc. which consist of polyethylene resins can be mentioned, for example.

  The transparent protective film preferably has fewer defects such as fish eyes. If there is a defect, the shape is transferred to the polarizing film, which may be a defect of the polarizing film.

  In the polarizing plate produced as described above, an optical film having an optical function other than the polarizing plate may be laminated on the protective film surface or the pressure-sensitive adhesive layer surface. Examples of such an optical film include an optical compensation film coated with a liquid crystal compound on the surface of a substrate, an optical compensation film that is oriented, and a reflection type polarized light that transmits a certain kind of polarized light and reflects polarized light having the opposite property. Film, phase difference film made of polycarbonate resin, phase difference film made of cyclic polyolefin resin, film with antiglare function having an uneven shape on the surface, film with surface antireflection function, reflection film having reflection function on the surface, reflection Examples thereof include a transflective film having both a function and a transmission function. Commercially available products corresponding to an optical compensation film coated with a liquid crystal compound on the substrate surface and oriented are WV film (Fuji Film Co., Ltd.), NH film (Shin Nippon Oil Co., Ltd.), NR Examples include films (manufactured by Nippon Oil Corporation). For example, DBEF (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) is a commercially available product corresponding to a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties. , APF (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) and the like. Moreover, as a commercial item corresponding to the phase difference film which consists of cyclic polyolefin resin, for example, Arton Film (made by JSR Corporation), Essina (made by Sekisui Chemical Co., Ltd.), Zeonore Film (made by Optes Co., Ltd.) Etc.

  When such other optical films are provided on the protective film side of the polarizing plate described above, both are usually laminated via an adhesive. In this case, the same adhesive as described above can be used as the pressure-sensitive adhesive, but the storage elastic modulus may not be so large. Moreover, when providing another optical film in the adhesive layer side of an above-described polarizing plate, an optical film is adhere | attached by the adhesive layer. In this case, it is usual to provide an adhesive layer for bonding to the liquid crystal cell on the outside of the optical film.

  In order to obtain a polarizing plate having a desired shape and transmission axis, the polarizing plate with the pressure-sensitive adhesive layer produced by the production method of the present invention usually has a form of a large roll material or sheet material. Then, it is cut (chip cut) by a cutting tool having a sharp blade. For this reason, in the polarizing plate chip obtained by cutting, a state in which the polarizing film is exposed to the outside at the outer peripheral end portion occurs.

  When the polarizing plate chip in this state is subjected to a durability test such as a heat shock test, for example, compared with a polarizing plate that is generally used, that is, a polarizing plate in which both surfaces of the polarizing film are protected with a cellulose resin film or the like. There is a tendency that problems such as peeling and cracking are likely to occur. In order to avoid such problems, it is preferable to continuously cut the outer peripheral end face of the polarizing plate chip obtained by the present invention by a fly-cut method or the like.

(Lamination of polarizing plate to liquid crystal cell)
The polarizing plate manufactured by the above manufacturing method is bonded to the liquid crystal cell of a liquid crystal display device through an adhesive layer.

  Such an adhesive layer uses various adhesives that have been used for pasting liquid crystal cells and polarizing plates, such as acrylic, rubber, urethane, silicone, and polyvinyl ether adhesives. In general, those formed are used. In addition, energy ray curable adhesives and thermosetting adhesives may be used, and among these, acrylic adhesives based on acrylic resins having excellent transparency, weather resistance, heat resistance, etc. are preferred. .

  When the pressure-sensitive adhesive layer is directly formed on the surface of the polarizing film, one having a storage elastic modulus of 0.15 to 1 MPa in a temperature range of 23 to 80 ° C. is preferable. In other cases, such a high elasticity is used. The thing which does not have a rate may be sufficient.

  Acrylic adhesive is not particularly limited, but (meth) acrylic such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate. An acid ester base polymer or a copolymer base polymer using two or more of these (meth) acrylic acid esters is preferably used. Furthermore, polar monomers are copolymerized in these base polymers. Examples of polar monomers include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, glycidyl (meth) ) A monomer having a functional group such as a carboxy group, a hydroxyl group, an amide group, an amine group or an epoxy group, such as acrylate.

  These acrylic pressure-sensitive adhesives can of course be used alone, but usually a crosslinking agent is used in combination. Crosslinking agents include divalent or polyvalent metal salts that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups Examples thereof include polyepoxy compounds and polyol compounds that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Of these, polyisocyanate compounds are widely used as organic crosslinking agents.

  The energy ray curable adhesive has the property of being cured by irradiation with energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with energy rays to adhere to an adherend such as a film. It is a pressure-sensitive adhesive that has the property of being adhered and cured by irradiation with energy rays to adjust the adhesion. As the energy ray curable adhesive, it is particularly preferable to use an ultraviolet curable adhesive. The energy beam curable pressure-sensitive adhesive generally comprises an acrylic pressure-sensitive adhesive and an energy beam polymerizable compound as main components. Usually, a crosslinking agent is further blended, and if necessary, a photopolymerization initiator and a photosensitizer can be blended.

  In addition to the base polymer and the cross-linking agent described above, the pressure-sensitive adhesive composition includes, for example, natural products and the like in order to adjust the pressure-sensitive adhesive force, cohesive force, viscosity, elastic modulus, glass transition temperature, etc. Appropriate additives such as synthetic resins, tackifier resins, antioxidants, ultraviolet absorbers, dyes, pigments, antifoaming agents, corrosion inhibitors, and photopolymerization initiators can also be blended. Further, a pressure-sensitive adhesive layer exhibiting light scattering properties can be formed by containing fine particles.

  The thickness of the pressure-sensitive adhesive layer is preferably 1 to 40 μm. However, in order to obtain a thin polarizing plate that is the object of the present invention, it is desirable to apply a thin film within a range that does not impair the workability and durability characteristics. It is more preferably 3 to 25 μm from the viewpoint of maintaining excellent processability and suppressing dimensional change of the polarizer. If the pressure-sensitive adhesive layer is too thin, the tackiness is lowered, and if it is too thick, problems such as sticking out of the adhesive tend to occur.

  As described above, the pressure-sensitive adhesive directly formed on the surface of the polarizing film preferably has a storage elastic modulus in the temperature range of 23 to 80 ° C. of 0.15 to 1 MPa. A pressure-sensitive adhesive used in a normal image display device or an optical film therefor has a storage elastic modulus of about 0.1 MPa at most, and in comparison with this, a preferable storage elastic modulus of the pressure-sensitive adhesive used in the present invention. 0.15 to 1 MPa is a high value. In addition, a storage elastic modulus can be measured using a commercially available viscoelasticity measuring apparatus, for example, DYNAMIC ANALYZER RDA II (made by REOMETRIC).

  In addition, in the manufacturing method of the polarizing plate of this invention, it does not restrict | limit especially as a method of forming an adhesive layer in a polarizing film, Each component including the above-mentioned base polymer is provided in the other surface of a polarizing film. After forming a pressure-sensitive adhesive layer by applying a solution containing, a separator that has been subjected to a release treatment such as a silicone-based separator may be laminated, or a pressure-sensitive adhesive layer is formed on the separator Then, it may be transferred to a polarizing film and laminated. Moreover, when forming an adhesive layer in a polarizing film, you may perform an adhesion | attachment process, for example, a corona treatment, etc. to at least one of a polarizing film and an adhesive layer as needed. In addition, the surface of the formed pressure-sensitive adhesive layer is usually protected by a separator film that has been subjected to a release treatment, and the separator film is bonded to a liquid crystal cell or other optical film before the polarizing plate is bonded. It is peeled off.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited by these examples.

[Example 1]
(Preparation of polarizing film)
A polyvinyl alcohol film having an average degree of polymerization of about 2400 and a saponification degree of 99.9 mol% or more and a thickness of 75 μm is uniaxially stretched about 5 times in a dry method and further kept in a tension state, and 1 After dipping for 1 minute, it was immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.1 / 5/100 at 28 ° C. for 60 seconds. Thereafter, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 10.5 / 7.5 / 100 at 72 ° C. for 300 seconds. Subsequently, it was washed with pure water at 10 ° C. for 5 seconds, and then dried at 60 ° C. for 75 seconds and then at 75 ° C. for 30 seconds, and iodine with a moisture content of 10.9% was adsorbed and oriented. A polarizing film was obtained.

(Preparation of adhesive)
Separately, in 100 parts by weight of water, 3 parts by weight of a carboxyl group-modified polyvinyl alcohol (Kuraray Poval KL318 (manufactured by Kuraray Co., Ltd.)) and a water-soluble polyamide epoxy resin (Smiles Resin 650 (manufactured by Sumika Chemtex Co., Ltd.)) An aqueous adhesive (A) containing a polyvinyl alcohol resin as a main component was prepared by dissolving 1.5 parts by weight of an aqueous solution having a solid content concentration of 30%, and a carboxyl group-modified polyvinyl alcohol and a water-soluble polyamide epoxy. The adhesive (B) was prepared with 2 parts by weight and 1.0 part by weight of resin, respectively.

(Preparation of polarizing plate)
Using the adhesive (A), a saponified triacetyl cellulose film having a thickness of 40 μm (KC4UY, manufactured by Konica Minolta Opto Co., Ltd.) is used on one surface of the polarizing film obtained previously. On the other surface, a norbornene-based retardation film (Zeonor film ZD14-141158-A1340 (manufactured by Optes Co., Ltd.), thickness: 32 μm) previously corona-treated is coated with the adhesive (B). And was bonded by a nip roll. While maintaining the tension of the bonded product at 430 N / m, after 5 seconds have passed from bonding at room temperature, the polarizing plate is successively dried at 60 ° C. for 11 seconds, 80 ° C. for 141 seconds, and 70 ° C. for 93 seconds. Got.

[Example 2]
(Preparation of polarizing film)
A polarizing film having a moisture content of 13.9% was obtained in the same manner as in Example 1 except that drying was performed at 40 ° C. for 60 seconds and 50 ° C. for 25 seconds.

(Preparation of polarizing plate)
Other than performing continuous drying at 60 ° C. for 9 seconds, 80 ° C. for 113 seconds, and 70 ° C. for 75 seconds in succession after 4 seconds from pasting at room temperature while maintaining the tension of the bonded product at 430 N / m. Obtained a polarizing plate in the same manner as in Example 1.

[Example 3]
(Preparation of polarizing film)
A polarizing film having a moisture content of 13.9% was obtained in the same manner as in Example 1 except that drying was performed at 40 ° C. for 60 seconds and 50 ° C. for 25 seconds.

(Preparation of polarizing plate)
While maintaining the tension of the bonded product at 430 N / m, after 4 seconds have passed from bonding at room temperature, it is sequentially dried at 60 ° C. for 9 seconds, 90 ° C. for 39 seconds, 80 ° C. for 74 seconds, and 70 ° C. for 75 seconds. A polarizing plate was obtained in the same manner as in Example 1 except that the above was performed continuously.

[Comparative Example 1]
(Preparation of polarizing film)
A polarizing film having a moisture content of 8.7% was obtained in the same manner as in Example 1 except that the film was dried at 90 ° C. for 106 seconds.

(Preparation of polarizing plate)
While maintaining the tension of the bonded product at 430 N / m, after 4 seconds have passed from bonding at room temperature, drying is performed in order of 10 seconds at 50 ° C, 43 seconds at 65 ° C, 83 seconds at 80 ° C, and 84 seconds at 70 ° C. A polarizing plate was obtained in the same manner as in Example 1 except that the above was performed continuously.

[Comparative Example 2]
(Preparation of polarizing film)
A polarizing film having a moisture content of 10.6% was obtained in the same manner as in Example 1.

(Preparation of polarizing plate)
Other than performing continuous drying at 50 ° C. for 10 seconds, 65 ° C. for 43 seconds, and 80 ° C. for 167 seconds in succession after 4 seconds have passed from bonding at room temperature while maintaining the tension of the bonded product at 430 N / m. Obtained a polarizing plate in the same manner as in Example 1.

[Comparative Example 3]
(Preparation of polarizing film)
A polarizing film having a moisture content of 8.7% was obtained in the same manner as in Example 1 except that the film was dried at 90 ° C. for 106 seconds.

(Preparation of polarizing plate)
While maintaining the tension of the bonded product at 430 N / m, after 4 seconds passed from bonding at room temperature, drying was performed in order of 10 seconds at 50 ° C., 43 seconds at 70 ° C., 83 seconds at 80 ° C., and 84 seconds at 90 ° C. A polarizing plate was obtained in the same manner as in Example 1 except that the above was performed continuously.

[Measurement of _SCR of each polarizing plate]
For the polarizing plate samples obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the phase difference film is peeled off, and the triacetyl cellulose film having substantially no phase difference characteristic is still bonded. manufactured by JASCO Corporation spectrophotometer (model number: V7100) at a wavelength of 450 nm, 550 nm, was measured S _CR of the polarizers in the 600 nm. The results are shown in Table 2.

(Contrast evaluation of liquid crystal display devices)
Table 1 shows the results of measuring Bmax and Rmax by measuring the emission spectrum of a mobile phone module (without a polarizing plate) composed of a white LED backlight and a VA liquid crystal cell. Bmax and Rmax of the mobile phone module satisfy the above formula (4). The polarizing plates produced in Examples 1 to 3 and Comparative Example 1 were bonded to both sides of the liquid crystal cell of this module, and the contrast of the liquid crystal display of the liquid crystal display device (mobile phone) incorporating this module was made by TOPCON Co., Ltd. The spectroradiometer (SR-UL1). The results are shown in Table 2. Although the liquid crystal display device using the polarizing plates of Examples 1 to 3 has a very good contrast ratio, the liquid crystal display device using the polarizing plate of the comparative example can obtain only a low contrast ratio compared to the examples. There wasn't.

It is a graph which shows an example of the emission spectrum measured by putting a color filter on a CCFL type backlight. It is a graph which shows an example of the emission spectrum measured by putting a color filter on LED type backlight. It is a graph which shows an example of a visibility correction curve. It is a graph which shows the orthogonal transmittance | permeability spectrum of the polarizing film used for the conventional polarizing plate. It is a graph which shows the orthogonal transmittance | permeability spectrum of the polarizing film used for the polarizing plate of this invention. It is a graph which shows the polarizing film single-piece | unit contrast of the polarizing film similar to FIG. It is a graph which shows the polarizing film single-piece | unit contrast of the polarizing film similar to FIG.

Claims (7)

A polarizing plate comprising a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film, wherein the polarizing film has a single contrast (S _CR (S _CR ) at a wavelength λ nm defined by the following formula (1) of the polarizing film. λ)) satisfies the following formulas (2) and (3).

(here,

Tp (λ) is the transmittance (%) of the polarizing film measured in the relationship between the linearly polarized light with the incident wavelength λnm and the parallel Nicol, and Tc (λ) is crossed with the linearly polarized light with the incident wavelength λnm. It is the transmittance | permeability (%) of the polarizing film measured by the relationship of Nicol, and is a measured value obtained by the polarized ultraviolet visible absorption spectrum measurement by a spectrophotometer. )

[(S _CR (550) + S _CR (600)) / 2] ≧ 30,000 (2)

3,000 ≦ S _CR (450) <30,000 (3)
  The polarizing plate according to claim 1, wherein a cellulose acetate-based resin film is laminated on one surface of the polarizing film via an adhesive layer, and a cycloolefin-based resin film is laminated on the other surface via an adhesive layer.   The polarizing plate according to claim 1, wherein a cellulose acetate-based resin film is laminated on one surface of the polarizing film via an adhesive layer, and a self-adhesive protective film that can be peeled off is laminated on the other surface.   The polarizing plate according to claim 2, wherein the adhesive layer is formed from a water-based adhesive. A polarizing plate used in a liquid crystal display device including a backlight and a liquid crystal cell,
The liquid crystal display device has a blue emission peak wavelength (Bmax) and a red emission peak wavelength (Rmax) represented by the following formula (4) in a spectrum measured with only the liquid crystal cell mounted on the backlight and the backlight is turned on. The polarizing plate according to claim 1, wherein:

(Rmax−550) <(550−Bmax) (4)
  It is a manufacturing method of the polarizing plate of Claims 2-4, Comprising: A film is laminated | stacked on both surfaces of a polarizing film with a moisture content of 9% or more, and it heat-processes at the temperature of 70 degreeC or more within 40 second immediately after lamination | stacking. Manufacturing method of polarizing plate. A liquid crystal display device comprising a backlight, a liquid crystal cell, and the polarizing plate according to claim 1,
In a spectrum measured with only the liquid crystal cell mounted on the backlight and the backlight is turned on, the blue emission peak wavelength (Bmax) and the red emission peak wavelength (Rmax) satisfy the following formula (4). A liquid crystal display device.

(Rmax−550) <(550−Bmax) (4)

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