JP4593827B2 - Polarizing film manufacturing method and manufacturing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for producing a polarizing film made of polyvinyl alcohol (hereinafter sometimes abbreviated as “PVA”). In particular, the present invention relates to a technique for producing a highly accurate polarizing film that can be used for liquid crystal display applications.
[0002]
[Prior art]
Conventionally, as a polarizing film, a uniaxial or biaxially stretched film of PVA, which adsorbs iodine, is well known. A dichroic dye oriented film obtained by adsorbing and orienting a dichroic dye on a PVA film is generally well known.
[0003]
By the way, when manufacturing a PVA polarizing film, it can be roughly divided into two types of stretching methods, a dry stretching method and a wet stretching method, and both techniques are actually adopted, but these are considered to be merits and demerits. It is coming. In other words, in the case of dry stretching, the hydrogen bonds between PVA molecules can be relaxed to some extent to suppress the neck-in phenomenon during uniaxial stretching, thus suppressing the occurrence of film thickness unevenness and the uniformity of light transmittance. The advantages that can be expected can be pointed out. However, in the case of dry stretching, by relaxing the hydrogen bond, an intermolecular shift occurs during the sustaining axis stretching, and the polarization performance (molecular orientation) does not increase at a ratio of increasing the stretching ratio, so that the polarization is further improved. If the draw ratio is increased, the film is likely to break.
[0004]
The wet stretching method for PVA film also has advantages and disadvantages. The advantages of the dry stretching method described above are generally the disadvantages of the wet stretching method, and the disadvantages of the dry stretching method are generally the advantages of the wet stretching method.
[0005]
An object of the present invention is to develop a stretching technique that makes the best use of the advantages of the dry stretching method and the wet stretching method in manufacturing the PVA polarizing film, in other words, avoids both problems as much as possible.
[0006]
[Problems of the prior art]
As a conventional technique, according to a dry stretching method, Japanese Patent Application Laid-Open No. 8-240715 discloses a film made of PVA having a polymerization degree of 2000 to 10,000 is uniaxially stretched in a dry manner and is immersed in an aqueous solution containing boric acid at 70 to 85 ° C. after dyeing. Although a method has been disclosed, this PVA polarizing film is inferior in mechanical strength, and has a problem that breakage tends to occur when it is formed on a polarizing plate or used as a polarizing plate. In the method described in JP-A-4-215603 in which a PVA polarizing film is post-treated with a boron compound, in-plane contrast spots are generated on the polarizing plate, and thus the problem of poor optical characteristics cannot be solved.
[0007]
Thus, in the dry stretching method, even if the stretching ratio is increased, the molecular orientation does not increase so much, and if the stretching ratio is increased to further increase the polarization, the film breaks, so it cannot be said to be a stable production method. There was a problem.
[0008]
The present invention employs a means for combining the dry stretching method and the wet stretching method as a solution to this problem, but it is not a simple compromise method, but a technique that takes advantage of both. In particular, for a high-precision TFF-LCD required for liquid crystal applications, a polarizing film having good contrast performance is desirable, and it is necessary to provide a PVA film manufacturing technique that can meet this demand.
[0009]
In the present invention, as a production method, basically, first, stretching in the air (stretching in the gas phase. In order to distinguish it from dry stretching performed in a dry state and stretching in liquid phase performed in a water bath, “in-air stretching” is used. In the presence of a swelling agent such as water, an aqueous solution, or alcohols, the iodine complex salt colorant is dyed (including a dye fixing process) to provide polarization performance. Wet stretching is performed, the swelling agent is removed by a drying means, and if necessary, complementary color processing and stretching fixing processing are added to complete the production of the polarizing film.
[0010]
It is also possible to stretch in the air a PVA film containing iodine after being dyed, but in this case, it will be followed by the dyeing process and the dry stretching process, which is sufficient during the stretching of the prior art. It is not recommended because it is difficult to solve the problem that the correct molecular arrangement does not occur.
[0011]
Therefore, in the present invention, the PVA film is first molecularly aligned to some extent by stretching in the air, and thereafter, the PVA film containing a polarizing agent such as iodine is wet-stretched. This manufacturing method is based on the result of finding that it is easy to obtain a high-quality film with improved thickness as a polarizing film and less thickness spots and molecular orientation spots.
[0012]
In addition, after obtaining a polarizing film, it is requested | required to ship in the completed state in actual production. Therefore, in order to be able to be applied immediately to the liquid crystal display cell, the polarizing film is subsequently subjected to a laminating process in which a PVA film is laminated with a triacetate film, an adhesive layer is applied so that the adhesive layer can be attached to the liquid crystal display cell. A layer coating treatment process, a finishing process for cutting to a predetermined specification size, and a winding process are added.
[0013]
Furthermore, taking the application into consideration, a supplementary polarizing plate for liquid crystal display cells is required, but as a countermeasure against this, the PVA film of the present invention is first stretched in the air and then continued. In the swelling treatment, it is known that the swelling treatment is effective when boric acid is added to water instead of mere water (see Japanese Patent Laid-Open No. 10-153709). Is possible. In addition, it is preferable in terms of process that an iodine dyeing process is performed after the swelling process and then wet stretching is performed.
[0014]
In order to obtain a uniform product having appropriate molecular orientation and no spots as a polarizing film, it is necessary to skillfully combine air stretching and wet stretching. Only in this way can a high-quality product be produced efficiently and rationally. In the prior art, there was a tendency to use inefficient wet stretching with emphasis on quality, or to select a dry stretching method with emphasis on production efficiency and low cost, but the dry method is better. Rather than discussing whether or not it is, understanding the characteristics of both and combining them effectively makes it possible to bring out superior performance not found in the prior art.
[0015]
[Problems to be solved by the invention]
The means for hot stretching the film made of polyvinyl alcohol in the air is to first apply a controlled temperature and humidity to the film. Since PVA film is a hydrophilic polymer, it is extremely sensitive to water. In an atmosphere where water droplets are present, unlike when immersed in water, water molecules adhere nonuniformly to the film surface, and the relaxed state of hydrogen bonds becomes irregular. In this state, when the film is subjected to tension, the non-uniformity is further promoted. In order to avoid this phenomenon, in the present invention, the film must be guided to an atmosphere where there is no water droplets or condensation on the film surface. Usually, no condensation is observed on the surface of the hydrophilic film polymer. This is because water droplets are absorbed immediately. However, as described above, the presence of water droplets causes a non-uniform swelling action. It is necessary to pay particular attention to avoiding water droplets, and this is an important guideline for implementing the present invention.
[0016]
Therefore, in order to make the surface of the film or the like not dewed at all, the inside and outside (the surroundings) of the air stretching apparatus are preliminarily humidified (preheated under unsaturated steam).
[0017]
At that time, the relative humidity is maintained in steps of about 80-90-95% and heated. In the stretching operation, in the stretching chamber, the PVA film is exposed to the same conditions as the humidity control apparatus or more dried conditions, and immediately stretched to a predetermined magnification.
[0018]
In addition, the temperature around the stretching roll group, the ceiling of the steam bath, and the wall of the stretching tub is not higher than the steam temperature so that condensation does not occur at all on the ceiling and wall of the steam bath as well as the stretching roll group. Maintain 0.5-5 ° C higher and control temperature precisely.
[0019]
Furthermore, it is preferable to provide a treatment, for example, a dry air spraying means, for cooling the stretched film with dry air at a position immediately after coming out of the steam atmosphere (bath), for example, to suppress the formation of condensation accompanying cooling and heat dissipation.
[0020]
Completely avoiding overheating is often a necessary treatment because a film stretched at a high stretch ratio is easily broken. Therefore, facilities that pay attention to temperature control are provided so that overheating does not occur.
[0021]
Further, it may be required to completely adjust the tension. In the above-described highly stretched film, if the tension is too high, the film tends to break. Therefore, for example, a device such as a dancer roll, which is a buffer means that can change the distance between the roll axes in the middle, is required.
[0022]
In the present invention, the steps of first subjecting the PVA film to air stretching, then subjecting it to swelling treatment and dyeing treatment, and further subjecting it to wet stretching are usually carried out in this order. By applying this stretching means, a high-functional and high-quality polarizing film can be obtained.
[0023]
[Means for solving the problems]
In order to achieve the above-described problems, the invention according to claim 1 includes a step of swelling a polarizing film substrate made of polyvinyl alcohol resin, a step of iodine-staining the polarizing film substrate subjected to swelling treatment, and iodine. A stretching step for uniaxially stretching the dyed polarizing film substrate, a colorant fixing step for fixing an iodine staining agent to the polarizing film substrate that has undergone the stretching step, and a water washing of the polarizing film substrate that has undergone the coloring agent fixing step It is a manufacturing method of the polarizing film for liquid crystal cells which consists of a polyvinyl alcohol resin including the washing process and the drying process which dries the polarizing film base material which passed through the washing process. In the first aspect of the present invention, the film surface is kept free of condensation as the stretching step, preheated under unsaturated steam to maintain a relative humidity of about 80-95%, and then the same atmosphere or more dried. In the conditions, it is characterized by an in-air stretching method comprising immediately stretching the polarizing film substrate.
[0024]
In order to obtain a polarizing plate having a high contrast suitable for a liquid crystal display cell, the invention according to claim 2 is carried out before or after stretching in the air during the production of the polarizing film for a liquid crystal cell according to claim 1. In the water washing (swelling) step of the film substrate, a water washing (swelling) treatment is performed using an aqueous boric acid solution. When the film substrate that has been stretched in air is subjected to a washing (swelling) treatment containing boric acid, it has a contrast superior to that obtained by washing (swelling) a conventional film that has been stretched in water only with a boric acid solution. There is an effect that a polarizing film is obtained.
[0025]
According to a third aspect of the present invention, in order to obtain a polarizing plate having a high contrast for a liquid crystal display, in the production of the polarizing film for a liquid crystal display cell according to the first aspect, the water washing (swelling) step is iodinated. A water washing (swelling) treatment is performed using an aqueous potassium solution. In this case as well, it is desirable that the air stretching is completed before the water washing (swelling) step, but of course, water washing treatment may be performed after the air stretching step. In the air stretching, the neck-in is small during stretching, and the state of molecular orientation in the width direction of the film base material is not greatly different between the center and both ends, so that a uniform polarizing plate is obtained as a result. The homogeneity of the film stretched in the air in the present invention is a significant difference when compared with a film substrate subjected only to water bath stretching, and is an excellent point of the film stretched in the air. Thus, according to the present invention, there is an advantage that a polarizing film having a high degree of contrast can be obtained.
[0026]
The invention of claim 4 is a manufacturing apparatus capable of carrying out uniaxial stretching in the air, and means for swelling a polarizing film substrate made of polyvinyl alcohol resin, and iodine-staining the swollen polarizing film substrate Dyeing means, stretching means for uniaxially stretching the iodine-stained polarizing film substrate, colorant fixing means for fixing the iodine dyeing agent to the polarizing film substrate that has undergone the stretching process, and polarizing film that has undergone the colorant fixing process In a means for producing a liquid crystal cell comprising a polyvinyl alcohol resin, the stretching means is in contact with the polarizing film base material, including a water washing means for washing the base material with water and a drying means for drying the polarizing film base material that has undergone the water washing step. Heating means capable of maintaining at least 0.5 ° C. higher than the water vapor temperature capable of keeping the surface completely dew-free over all means A means for pre-heating the polarizing film substrate under unsaturated steam and drying (heating while maintaining the relative humidity at about 80-95%); and a means for immediately stretching the polarizing film substrate. Features.
[0027]
In the invention according to claim 5, the production apparatus can perform one-stage stretching in the air, the stretching ratio is in the range of 1: 2 to 8, and the stretching ratio when the stretched film is wet-stretched is 1: 1. comprising a stretching satisfies stretching apparatus comprising about .5～5.0, moreover in the range of the stretching temperature is 60 to 120 ° C. in air, accurately be maintained at a predetermined temperature, atmospheric pressure (outside vapor bath apparatus It is characterized in that it has an air stretching means that can maintain a high pressure (including the case of a high pressure that can be released).
[0028]
Embodiment
Below, the manufacturing method and manufacturing apparatus of this invention are demonstrated with reference to drawings.
[0029]
FIG. 1 shows an outline of an apparatus for producing a PVA polarizing film according to the present invention. The arrangement of this apparatus shows an embodiment in which a PVA film is first stretched in the air without adsorbing iodine, but of course, an embodiment in which iodine is adsorbed and in the air or wet stretching is also envisaged.
[0030]
In FIG. 1, the process starts from the step of conditioning the unstretched PVA film. The mill roll (unstretched PVA film) is unwound from the unwinder to adjust the humidity, but before the mill roll is mounted on the unwinder, after the mill roll is received, the humidity control tank <humidity control warehouse> It is also possible to adjust the humidity over a wide range. In the present invention, this humidity control step also serves as dust removal processing in a clean room (clean unit). Of course, the dust removal treatment can be performed in a humidity control tank <humidity control warehouse>.
[0031]
The PVA film that has undergone the humidity conditioning treatment is guided to a stretching process, where it is stretched and oriented under predetermined conditions. In-air stretching is advantageous in that the shrinkage (neck-in) in the film width direction is small and the thickness unevenness in the width direction is small, so that the method of the present invention carried out at the initial stage of the stretching process is excellent.
[0032]
The PVA stretched film that has been stretched in the air is then subjected to a swelling treatment in the presence of water or a swelling agent in a swelling step. By this treatment, the PVA stretched film is completely immersed in the water bath. The PVA stretched film that has been subjected to the swelling treatment is dyed in iodine, potassium iodide aqueous solution (composition of iodine / potassium iodide / water).
[0033]
The dyed PVA stretched film is washed with water and subjected to an operation to remove the unreacted (undyed) free colorant and the like. With the iodine colorant fixed to the PVA molecule (film), wet stretching is performed this time. A polarizing film is obtained by this stretching treatment.
[0034]
The polarizing film is subjected to a water washing treatment again and then wound up in a dried state through a dryer.
[0035]
FIG. 2 is a flowchart showing the entire process. The above-mentioned air-stretched PVA film becomes a wet-stretched polarizing film dyed with an iodine colorant, and is wound or laminated with a highly transparent film such as cellulose triacetate. The adhesive layer coating process in which an adhesive is applied, and the finishing process in which a desired size is cut are shown.
[0036]
FIG. 3 is an explanatory diagram illustrating the dry stretching apparatus in some detail. The unrolled mill roll 21 is dedusted and conditioned in clean units 22, 23 and 24 that create an atmosphere of controlled temperature and humidity. Next, the film is guided to a stretching apparatus, where it is stretched in a range of about 1 to 2 (stretching ratio) by appropriately setting the ratio of the peripheral speeds of the nip roller 25 and the stretching high-speed roller 27. . The stretching temperature at this time is selected in the range of 60 to 120 ° C., but a higher stretching temperature is generally selected for a material having a high molecular weight <polymerization degree> of PVA forming the film.
[0037]
In the stretching zones 25, 26, and 27 into which the film is introduced, the film surface is kept free from condensation as a stretching process, and the film is preheated and dried (with a relative humidity of 80− under an unsaturated vapor). Then, the polarizing film substrate is immediately stretched while being exposed to saturated steam in the steam bath 36. A seal box is provided in each of the inlet 34 where the unstretched film is introduced and the outlet 35 where the stretched film is led out.
[0038]
Thus, when uniaxially stretching a PVA film between rolls having different peripheral speeds, first, in-air hot stretching at 60 to 120 ° C. is performed in a state where the film is not wet. For example, complete dry heating is performed so that the film or device is not condensed, preheating for drying (preheating under unsaturated steam), humidity conditioning 24, 25 (relative humidity is maintained at about 80-95% and heating is performed. ), And stretched immediately under the same atmospheric conditions. During this stretching, sealing is performed with dry air 35 just before the exit of the stretched film to suppress the formation of condensation due to cooling. Furthermore, it is added that complete avoidance of overheating and complete tension adjustment. The dry stretched PVA film is subsequently subjected to swelling treatment, dyeing and wet stretching to become a polarizing film. The group of rolls 26, 26,... Are maintained at a surface temperature that is at least 0.5 ° C. to 5 ° C. higher than the stretching temperature so that condensation does not occur.
[0039]
The dry stretching of the present invention can be once wound up by a winder 32 as shown in FIG. At that time, it is also possible to draw another film from the roll 31 so as to follow the PVA stretched film, and to wrap the film through the rollers 27 and 28 and wind it simultaneously with the auxiliary film.
[0040]
Needless to say, the PVA film can be continuously produced by the apparatus shown in FIG.
[0041]
As described above, the present invention substantially follows the conventional technology except for the humidity control apparatus including the air stretching apparatus and the clean unit. As a further explanation, the preheating range of the heating roller can be set to 50 to 120 ° C., and the setting temperature is set to a desired temperature with an accuracy of 0.5 ° C. The heating time until reaching the predetermined stretching temperature can be achieved by adjusting the residence time of the clean unit or adjusting the running speed of the film.
[0042]
Although it is desirable to immediately cool the stretched film in order to maintain the molecular orientation, it is also necessary to prevent condensation, and it is effective to cover the outlet with a seal box using dry air. Similar effects can be achieved in tension management.
[0043]
【Example】
<Reference example>
Drawing conditions and physical properties will be described.
[0044]
As a raw material polyvinyl alcohol film, Kuraray Co., Ltd. “Vinylon (registered trademark)” film VF-XS # 7500 was used.
[0045]
An aqueous iodine solution (composition of iodine / potassium iodide / water = 0.05 / 5/100) was used as the staining solution.
[0046]
The measurement of the degree of polarization was calculated by measuring the light transmittance in the polarizing plate at five points using a spectrophotometer after drying the stretched film in accordance with Japan Electronic Machinery Industry Standard (EIJL) LD-201-1983.
[0047]
Washing after dyeing was performed with pure water at 25 ° C. containing 1% of boric acid (HBO ₃ ).
[0048]
Wet stretching was carried out in 30 ° C. pure water containing 1% boric acid (HBO ₃ ) at a feed rate of 3 m / min, and the roll speed on the winding side was increased according to the stretch ratio.
[0049]
Using the air-stretching apparatus shown in FIG. 1 for the vinylon film, the humidity control and stretching atmosphere conditions are 80 ° C. and 93% relative humidity, and the feed rate is 1 m / min, the take-up speed is 6 m / min, and 6.0 times. Stretched. Then, it was dyed and washed with pure water. Then, after drying for 5 minutes with 50 degreeC warm air, the optical characteristic was implemented about the stretched film.
[0050]
The stretched film had a light transmittance of 42.2%, a degree of polarization of 99.9%, and a light transmittance of 0.04%.
<Example 1>
The 6-fold stretched film obtained in the reference example was dyed again, washed with pure water, then wet-stretched 1.7 times again, and then dried with hot air at 50 ° C. for 5 minutes. Regarding the physical property values of the obtained redrawn film, the light transmittance was 43.1%, the degree of polarization was 99.9%, and the in-plane variation of the light transmittance was 0.21%.
<Example 2>
In the reference example, the humidity was adjusted and the internal temperature of the stretching apparatus was maintained at 70 ° C. and 95% relative humidity, the film was stretched at a take-up speed of 3 m / min (stretching ratio 3 times), and further wet-stretched 2.5 times. Regarding the physical property values of the obtained redrawn film, the light transmittance was 43.3%, the degree of polarization was 99.9%, and the in-plane variation of the light transmittance was 0.40%.
[0051]
【The invention's effect】
Because it is a PVA film manufacturing technology that draws out the advantages of both air-stretching and wet-stretching, neck-in phenomenon can be suppressed during uniaxial stretching. There is an effect that the uniformity is excellent.
[0052]
Since wet stretching is used in combination, the stretching ratio can be increased, and the polarization performance (molecular orientation) can be sufficiently enhanced. In addition, there is no concern that the film breaks as in the case of the dry stretching method, and the effect of enabling stable production is achieved.
[0053]
Furthermore, since the neck-in phenomenon can be suppressed in the stretching in the air, a polarizing film having a high degree of contrast and excellent uniformity in the molecular orientation state in the width direction of the film can be obtained.
[Brief description of the drawings]
FIG. 1 shows an outline of an apparatus for producing a PVA polarizing film according to the present invention.
FIG. 2 is a flowchart showing an overall process including the present invention.
FIG. 3 is an explanatory diagram of a PVA polarizing film in-air stretcher according to the present invention.
[Explanation of symbols]
20 In-air stretching process 21 Unwinder 22 Humidity control device 23 Clean unit 25 Low speed side stretching roller 26 Heating roller 27 High speed side stretching roller 28 Laminating roller 29 Guide roller 30 In-air stretching bath (stretching zone)
31 Different film supply roll 32 Winder 34 Entrance seal box 35 Exit seal box 36 Steaming device 37 Ceiling heating condensation prevention device 38 Wall heating condensation prevention device 42 Swelling process 44 Dyeing process 46 Washing / fixing process 48 Wet stretching process 52 2nd washing process 54 Drying process 62 Laminating process 64 Adhesive layer sticking affirmation 66 Finishing process

Claims (5)

A polarizing film substrate made of a polyvinyl alcohol resin is stretched uniaxially before being dyed with iodine, a step of swelling treatment, a step of dyeing the swollen polarizing film substrate with iodine, and iodine dyed A stretching step for uniaxially stretching the polarizing film substrate, a colorant fixing step for fixing an iodine dye to the polarizing film substrate that has undergone the stretching step, and a water washing step for washing the polarizing film substrate that has undergone the coloring agent fixing step with water In the production of a polarizing film for a liquid crystal cell comprising a polyvinyl alcohol resin, including a drying step of drying a polarizing film substrate that has undergone a washing step,
While maintaining the state without completely condensing the film surface as a stretching step, characterized in that to Drying preheated under unsaturated vapor, it succeeded in exposing the polarizing film substrate to saturated steam in the steam bath, immediately stretched A method for producing a polarizing film.   2. The method for producing a polarizing film according to claim 1, wherein the water washing process is performed using a boric acid aqueous solution in the water washing step.   The method for producing a polarizing film according to claim 1, wherein a washing process is performed using a potassium iodide aqueous solution in the washing step. A polarizing film substrate made of a polyvinyl alcohol resin is uniaxially stretched before being dyed with iodine, a means for swelling treatment, a dyeing means for dyeing the swollen polarizing film substrate with iodine, and iodine dyed Stretching means for uniaxially stretching the polarizing film substrate, colorant fixing means for fixing the iodine dyeing agent to the polarizing film substrate that has undergone the stretching process, and water washing means for washing the polarizing film substrate that has undergone the colorant fixing process with water In the means for producing a polarizing film comprising a polyvinyl alcohol resin, including a drying means for drying the polarizing film substrate that has undergone the water washing step,
The stretching means carried out in the air can be maintained at a temperature at least 0.5 ° C. higher than the water vapor temperature that can maintain a state in which no condensation occurs on the surface of all the means in contact with the polarizing film substrate. Heating means,
Means you Drying preheated polarizing film substrate under non-saturated vapor,
Means for guiding the polarizing film substrate to the steam bath;
Apparatus for producing a polarizing film characterized in that a polarizing film substrate subjected to the unsaturated vapor, comprising a means capable of immediately stretch. The apparatus for producing a polarizing film according to claim 4 is capable of at least one step of stretching in the air, the stretching ratio is in the range of 1: 2 to 8, and the stretched film is re-stretched in a wet or aqueous solvent. The stretching ratio is about 1: 1.5 to 5.0, and the air stretching temperature can be maintained at a predetermined temperature in the range of 60 to 120 ° C., and includes an air stretching means that can be maintained at normal pressure. An apparatus for manufacturing a polarizing film for a liquid crystal cell.

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