JP6549424B2 - Method of producing stretched film - Google Patents

Description

  The present invention relates to a method for producing a stretched film from a long polyvinyl alcohol resin film.

  The polarizing plate is widely used as a polarizing element or the like in an image display device such as a liquid crystal display device. As a polarizing plate, one having a structure in which a transparent resin film (protective film or the like) is bonded to one side or both sides of a polarizing film using an adhesive or the like is general.

  The polarizing film is mainly treated by immersing a raw film made of a polyvinyl alcohol-based resin in a dyeing bath containing a dichroic dye such as iodine, and then dipped in a crosslinking bath containing a crosslinking agent such as boric acid The film is manufactured by uniaxially stretching the film in any of the steps as well as subjecting it to Uniaxial stretching includes dry stretching in which the stretching is performed in the air before the immersion treatment, and wet stretching in which the stretching is performed in a liquid such as the dyeing bath and the crosslinking bath.

  The polyvinyl alcohol-based resin film to be subjected to dry stretching may have its moisture content adjusted in order to enhance stretchability. For example, Japanese Patent Application Laid-Open No. 2002-333521 (Patent Document 1) describes that the moisture content of a polyvinyl alcohol-based resin film to be subjected to dry stretching is 10% or less by drying (paragraph [0016]) .

  Regarding adjustment of the moisture content of a film, for example, in JP-A-2004-160846 (Patent Document 2), a polyvinyl alcohol-based film is produced by cast film formation, and then water vapor is sprayed from both sides of the film in a humidity controller. It is described that the humidity control (humidification) process is performed (paragraph [0057]).

JP, 2002-333521, A JP 2004-160846 A

  An object of the present invention is to provide a method for producing a stretched film using a polyvinyl alcohol-based resin film whose moisture content has been adjusted by a new method.

The present invention provides the following method for producing a stretched film.
[1] A step of continuously introducing a long polyvinyl alcohol resin film into a humidifier to obtain a humidified film,
Dry stretching the humidifying film derived from the humidifying device to obtain a stretched film;
Including
The method for producing a stretched film, the step of obtaining the humidifying film includes the step of adjusting the moisture content of the humidifying film by changing the transport path length of the polyvinyl alcohol-based resin film in the humidifying device.

[2] The humidifying device includes a chamber capable of adjusting the relative humidity inside, and a plurality of guide rolls disposed in the chamber and defining a transport path of the polyvinyl alcohol-based resin film,
At least one of the plurality of guide rolls is a movable guide roll capable of positional movement,
The manufacturing method according to [1], wherein the step of adjusting the moisture content includes adjusting the position of the movable guide roll.

[3] The step of obtaining the humidifying film is
Detecting the moisture content of the humidifying film derived from the humidifying device;
Controlling the position of the movable guide roll based on the detection result obtained in the detecting step;
The method according to [2], further comprising

  [4] The manufacturing method according to [3], wherein in the step of detecting the moisture content, the moisture content is detected in-line while conveying the humidifying film derived from the humidifying device.

  [5] The manufacturing method according to any one of [2] to [4], wherein the movable guide roll is movable in parallel in a direction inclined from the horizontal direction.

[6] The chamber includes a first chamber into which the polyvinyl alcohol resin film is introduced, and a second chamber from which the humidifying film is led out,
The manufacturing method according to any one of [2] to [5], wherein the relative humidity in the second room is higher than the relative humidity in the first room.

  [7] The manufacturing method according to [6], wherein each of the first chamber and the second chamber is provided with the movable guide roll.

  ADVANTAGE OF THE INVENTION According to this invention, the method of manufacturing a stretched film using the polyvinyl alcohol-type resin film in which the moisture content was adjusted by the new method can be provided.

It is a flowchart which shows an example of the manufacturing method of the stretched film which concerns on this invention. It is a schematic sectional drawing which shows an example of the humidification apparatus used suitably by process S10 which obtains a humidification film, and a humidification system containing this. It is a schematic sectional drawing which shows an example of the position movement direction of a movable guide roll. It is a schematic sectional drawing which shows another example of the humidification apparatus used suitably by process S10 which obtains a humidification film, and a humidification system containing this.

<Production method of stretched film>
Referring to FIG. 1, the method for producing a stretched film according to the present invention is
Step S10 of continuously introducing a long polyvinyl alcohol-based resin film (hereinafter also referred to as a PVA film) into a humidifying device to obtain a humidified film;
Dry-stretching the humidified film derived from the humidifying device to obtain a stretched film S20;
including.

(1) Step S10 of obtaining a humidifying film
Step S10 of obtaining a humidified film is a step of continuously introducing a long PVA film into a humidifying device to obtain a humidified film, and referring to FIG. 1, a conveyance path of the PVA film in the humidifying device. A step S101 of adjusting the moisture content of the humidified film by changing the length is included.

(1-1) Polyvinyl alcohol-based resin film As polyvinyl alcohol-based resin which comprises a PVA film, what saponified polyvinyl acetate type resin can be used. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth) acrylamides having an ammonium group, and the like. In addition, "(meth) acryl" represents at least 1 sort (s) chosen from the group which consists of an acryl and methacryl. The same applies to other terms with "(meth)".

  The degree of saponification of the polyvinyl alcohol resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, and more preferably 98.0. It is in the range of -100.0 mol%. When the obtained oriented film is used as a raw material of a polarizing film as saponification degree is less than 80.0 mol%, the water resistance and moist heat resistance of the polarizing plate containing the said polarizing film may fall.

Saponification degree is the ratio of acetic acid group (acetoxy group: -OCOCH ₃ ) contained in polyvinyl acetate resin, which is a raw material of polyvinyl alcohol resin, changed to hydroxyl group in the saponification process in unit ratio (mol%) It is represented and the following formula:
Degree of saponification (mol%) = 100 × (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups)
Defined by The degree of saponification can be determined in accordance with JIS K 6726 (1994). The higher the degree of saponification, the higher the proportion of hydroxyl groups, and thus the lower the proportion of acetate groups that inhibit crystallization.

  The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and still more preferably 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol resin can also be determined in accordance with JIS K 6726 (1994). When the average degree of polymerization is less than 100, it is difficult to obtain a polarizing film having preferable polarization performance when using the obtained stretched film as a raw material of a polarizing film, and when it exceeds 10000, the solubility in a solvent is deteriorated. Film formation can be difficult.

  The PVA film is formed by forming the polyvinyl alcohol resin described above. The film forming method is not particularly limited, and a known method such as a melt extrusion method or a solvent casting method can be adopted. The thickness of the PVA film is, for example, about 10 to 150 μm, preferably 100 μm or less, more preferably 65 μm or less, still more preferably 50 μm or less, and particularly preferably 35 μm or less (eg 30 μm or less, further 20 μm or less).

  The PVA film can contain an additive such as a plasticizer. Preferred examples of the plasticizer are polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triglycerin glycol, triglycerin, tetraethylene glycol, trimethylolpropane, polyethylene glycol etc. . The PVA film can contain one or more plasticizers. The content of the plasticizer is usually 5 to 20 parts by weight, preferably 7 to 15 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin constituting the PVA film.

(1-2) Humidifying Device FIG. 2 is a schematic cross-sectional view showing an example of a humidifying device suitably used in step S10 of obtaining a humidified film and a humidifying system including the same. The humidifying device 3 shown in FIG. 2 is a device for continuously humidifying the long PVA film 1 (increasing the moisture content), and includes a chamber 4 capable of adjusting the relative humidity inside. The chamber 4 has an inlet 5 for introducing the long PVA film 1 to be humidified into the chamber 4 and an outlet 6 for discharging the humidified film (humidified film) 2 from the chamber 4. And.

  A plurality of guide rolls 7 and 8 are disposed in the chamber 4. The guide rolls 7 and 8 are rolls for guiding the PVA film 1 in the chamber 4 and define a transport path of the PVA film 1 in the chamber 4. The PVA film 1 continuously introduced from the inlet 5 into the chamber 4 under the humidified environment is continuously (in a state of being wound around the outer periphery of each of the guide rolls 7 and 8) along the transport path. It is transported. In this transport process, the PVA film 1 is humidified by being placed in the chamber 4 in a humidified environment for a certain residence time. The humidified film 2 is continuously taken out from the outlet 6 and subjected to the step S20 of obtaining the next stretched film. Alternatively, the humidified film 2 drawn out from the outlet 6 may be temporarily wound up in a roll shape, and thereafter, the humidified film 2 may be unwound from the film roll to be subjected to step S20 of obtaining a stretched film. Preferably, the humidifying film 2 is subjected to the step S20 of obtaining a stretched film without being wound up once.

  In the humidifying device 3, the guide roll group installed in the chamber 4 is movable guide rolls 8 (two in the example of FIG. 2) capable of position movement, and non-movable guide rolls 7 (not shown) capable of position movement. 3) in the example of 2. The “movable guide roll capable of position movement” refers to a guide roll capable of moving the arrangement position of the rotation axis of the guide roll in the chamber 4. The non-movable guide roll 7 and the movable guide roll 8 may be independently drive rolls or free rolls. The drive roll is a roll that can give a driving force for film transport to the film in contact with it, a roll to which a roll drive source such as a motor is connected directly or indirectly, a suction roll (suction roll Roll etc. The free roll simply plays a role of supporting a film which is traveling, and refers to a roll which can not provide a driving force for film transport.

  According to the humidifying device 3 having the movable guide roll 8, the transport path length of the PVA film 1 in the humidifying device 3 (chamber 4) can be freely changed by position adjustment of the movable guide roll 8. The change of the conveyance path length of the PVA film 1 means the change of the residence time in the humidifier 3 (chamber 4). Therefore, by adjusting the position of the movable guide roll 8, the humidified state (moisture content) of the obtained humidified film 2 can be controlled. That is, in the case where the humidifying device 3 is used, the step S101 of adjusting the moisture content of the humidifying film 2 includes adjusting the position of at least one movable guide roll 8 which the humidifying device 3 has.

  In the conventional film humidifying apparatus, generally, as described in Patent Document 2, the humidified state (moisture content) of the obtained humidified film is adjusted by controlling the humidifying environment in the humidifying apparatus. However, it is not easy to precisely adjust the humidification state of the humidification film by controlling the humidification environment in the humidifier, and it takes a certain amount of time to adjust the humidification environment in the humidifier to a desired environment. There is also a problem that much film loss occurs before obtaining a humidified film having a humidified state (water content). According to the humidifying device 3 suitably used in the present invention, the transport path length of the PVA film 1 in the chamber 4 and hence the residence time can be changed in a short time, so that the humidified state of the humidified film 2 Even in the case where the desired humidification state (moisture content) is changed, etc., the humidification film 2 having the desired humidification state (moisture content) can be provided in a short time. . Moreover, according to the humidifying device 3 that changes the transport path length by the position movement of the movable guide roll 8, the transport path length, and hence the residence time can be precisely controlled, so the humidified state (moisture content) of the humidified film 2 Can be precisely adjusted. Precise adjustment of the moisture content can improve the stretchability (especially, suitability for dry stretching) of the PVA film 1 in the step S20 of obtaining a stretched film.

  The numbers of the non-movable guide rolls 7 and the movable guide rolls 8 included in the humidifying device 3 are not limited to the example shown in FIG. 2 as long as at least one movable guide roll 8 is provided. All of the guide rolls provided in the humidifying device 3 may be the movable guide rolls 8. The humidifying device 3 has two or more movable guide rolls 8 because the change in the transfer path length (the difference between the maximum transfer path length and the minimum transfer path length) can be further increased and the transfer path length can be more precisely controlled. Is preferred.

  Positional movement of the movable guide roll 8 can be performed using, for example, a mechanism such as a ball screw, a hydraulic cylinder, a pneumatic cylinder, a hydraulic cylinder, an electric cylinder, a linear actuator or the like.

  The positional movement of the movable guide roll 8 is, for example, a positional movement such that the transport path length of the PVA film 1 can be changed as shown in FIG. Including. The parallel movement means that the rotation axes of the movable guide roll 8 before and after the position movement are parallel. The direction of position movement of the movable guide roll 8 is not particularly limited, and may be parallel to the horizontal direction as shown in FIG. 3 or horizontal as shown in FIG. It may be a direction inclined from the direction. In the case where the humidifying device 3 has two or more movable guide rolls 8, these movable guide rolls 8 may be movable in the same direction or may be movable in different directions. Further, the movable distances of these movable guide rolls 8 may be the same or different.

  The positional movement direction of the movable guide roll 8 being inclined from the horizontal direction is advantageous in reducing the occupied area (installation floor area) of the humidifying device 3. A preferred example of the direction inclined from the horizontal direction is the vertical direction. That is, in this case, the movable guide roll 8 is a roll that can move up and down in the vertical direction (vertical direction). For example, the conveyance direction of the PVA film 1 can be horizontal in the introduction into the chamber 4 of the PVA film 1 to be humidified, and the conveyance direction of the humidification film 2 is also horizontal in the delivery of the humidification film 2 from the chamber 4 In this case, the vertical direction is a direction perpendicular to the conveyance direction of the PVA film 1 or the humidifying film 2.

  The chamber 4 is capable of adjusting the internal relative humidity by adjusting the internal moisture. By continuously passing the long PVA film 1 through the chamber 4, the PVA film 1 can be humidified (increase in water content) continuously. The relative humidity in the chamber 4 can be set in accordance with the desired humidification state (moisture content) of the humidification film 2. The relative humidity in the chamber 4 is, for example, 20% or more, preferably 30% or more, and may be 40% or more.

  The relative humidity is usually 99% or less, preferably 95% or less. If the relative humidity is too high, condensation may occur on the surface of the PVA film 1 depending on the temperature of the PVA film 1. If dew condensation occurs on the surface of the PVA film 1, the temperature of the PVA film 1 does not rise to the desired value in the dew condensation portion due to the latent heat of evaporation of water, and as a result, the desired humidification state (moisture content) is not achieved in the dew condensation portion Sometimes. In addition, if dew condensation occurs on the surface of the PVA film 1, dew marks may be generated later to adversely affect the appearance quality of the humidifying film 2, and hence the stretched film or the polarizing film. Condensation marks refer to drying marks that are formed after condensation occurs and which are dried.

  The chamber 4 is preferably capable of adjusting the internal temperature as well as the relative humidity inside. By appropriately raising the temperature of the PVA film 1, the PVA film 1 can be efficiently humidified. The internal temperature can be raised by the supply of hot air or the like. For temperature control of the PVA film 1, instead of or in combination with hot air, an infrared heater, a halogen heater, a panel heater or the like is used, or a heat roll is used as at least one of the guide rolls 7 and 8 It can also be done. The heat roll here means a heat source (for example, a heat medium such as hot water or an infrared heater) provided therein to increase the surface temperature.

  The internal temperature of the chamber 4 when humidifying the PVA film 1 and the temperature of the PVA film 1 are usually 35 ° C. or higher, preferably 40 ° C. or higher, and more preferably 45 ° C. or higher. By the internal temperature and the temperature of the PVA film 1 being 35 ° C. or higher, the efficiency of the humidification process can be enhanced. On the other hand, the internal temperature of the chamber 4 and the temperature of the PVA film 1 are preferably 150 ° C. or lower, since the internal temperature and the temperature of the PVA film 1 may cause thermal degradation of the PVA film 1. The temperature is more preferably the following, more preferably 100 ° C. or less, and particularly preferably 90 ° C. or less.

  The residence time of the PVA film 1 in the chamber 4 can be controlled by adjusting the position of the movable guide roll 8 according to the desired humidification state (moisture content) of the humidification film 2. The residence time of the PVA film 1 is, for example, about 5 to 500 seconds.

  FIG. 4: is a schematic sectional drawing which shows another example of the humidification apparatus suitably used by process S10 which obtains a humidification film, and a humidification system containing this. The humidifying device 3 shown in FIG. 4 has the same configuration as the humidifying device 3 shown in FIG. 2 except that it includes a chamber consisting of a plurality of chambers. Specifically, in the humidifying device 3 shown in FIG. 4, the chamber is composed of a first chamber 4 a including the inlet 5 of the PVA film 1 and a second chamber 4 b including the outlet 6 of the humidifying film 2. There is. The first chamber 4a and the second chamber 4b can independently adjust the relative humidity in the room, and can preferably adjust the internal temperature together with the relative humidity in the room.

  Preferably, each of the first chamber 4 a and the second chamber 4 b includes at least one of the above-described movable guide rolls 8 so that the transport path length of the PVA film 1 in each chamber can be freely changed. All of the guide rolls provided in the first chamber 4 a may be the movable guide rolls 8, and all of the guide rolls provided in the second chamber 4 b may be the movable guide rolls 8. Each of the first chamber 4a and the second chamber 4b has two or more movable guide rolls 8 because the change in the transfer path length can be increased and the transfer path length can be more precisely controlled. preferable. The plurality of movable guide rolls 8 included in the first chamber 4a and the second chamber 4b may be movable in the same direction, or may be movable in different directions. Further, the movable distances of these movable guide rolls 8 may be the same or different.

  The relative humidity in the second chamber 4 b on the outlet 6 side is preferably higher than the relative humidity in the first chamber 4 a on the inlet 5 side. By passing the second chamber 4b having a high relative humidity after passing the first chamber 4a having a low relative humidity, the PVA film 1 can be humidified more efficiently.

  The humidifying device 3 may be composed of three or more chambers, such as providing a third chamber between the first chamber 4a and the second chamber 4b shown in FIG. The three or more chambers preferably are capable of independently adjusting the relative humidity of the room, and more preferably are capable of adjusting the internal temperature together with the relative humidity of the room. In addition, each chamber is preferably provided with at least one of the above-described movable guide rolls 8 so that the transport path length of the PVA film 1 in each chamber can be freely changed. It is preferable that each chamber have two or more movable guide rolls 8 in that the change in the transfer path length can be made larger and the transfer path length can be controlled more precisely. The plurality of movable guide rolls 8 included in three or more chambers may be movable in the same direction, or may be movable in different directions. Further, the movable distances of these movable guide rolls 8 may be the same or different.

  In the case where the humidifying device 3 is used, the step S10 of obtaining the humidified film preferably refers to step S102 of detecting the moisture content of the humidifying film 2 drawn from the humidifying device 3 with reference to FIG. And controlling the position of the movable guide roll 8 based on the detection result obtained in step S101. Steps S102 and S103 can be performed using a humidification system including the humidification device 3 described above.

  As shown in FIGS. 2 and 4, the humidifying system includes a humidifying unit provided with the above-described humidifying device 3, a detecting unit 10 that detects the moisture content of the humidifying film 2 drawn from the humidifying device 3, and a detecting unit 10. And a control unit 20 connected to the movable guide roll 8 included in the humidifying device 3 and controlling the position of the movable guide roll 8 based on the detection result of the detection unit 10. Step S102 can be performed by the detection unit 10, and step S103 can be performed by the control unit 20.

  The method for producing the humidifying film 2 including the series of steps S101 to S103 is advantageous for continuously and stably producing the humidifying film 2 having a desired moisture content. That is, according to this method, based on the detection result obtained in the detecting step S102, the position of the movable guide roll 8 so that the moisture content of the humidifying film 2 becomes a desired value (or within the desired range). The conveyance path length of 1 can be feedback controlled.

  The specific flow of step S10 of obtaining a humidified film including a series of steps S101 to S103 is, for example, as follows. First, by adjusting the transport path length of the PVA film 1 in the humidifying device 3, the humidified film 2 whose moisture content is adjusted is manufactured (step S101). Next, the moisture content of the humidified film 2 derived from the outlet 6 is detected by the detection unit 10 (step S102), and it is determined whether the moisture content detection value is within a desired value or a desired range. This determination may be performed by the detection unit 10 or may be performed by the control unit 20. When the moisture content detection value is within the desired value or the desired range, the control unit 20 maintains the position of the movable guide roll 8 without changing it in step S103. On the other hand, when the moisture content detection value is not within the desired value or the desired range, the control unit 20 adjusts the position of the movable guide roll 8 in step S103 to change the transport path length of the PVA film 1 in the chamber 4. Specifically, when the detected moisture content is larger than the desired value or the desired range, the control unit 20 shortens the transport path length of the PVA film 1 so that the detected moisture content is higher than the desired value or the desired range. If it is smaller, the position of the movable guide roll 8 is adjusted so that the transport path length of the PVA film 1 becomes longer. Then, preferably after changing the transport path length of the PVA film 1, the moisture content of the humidified film 2 is again detected by the detection unit 10, and it is determined whether the moisture content detection value is within a desired value or a desired range. Check. The above control is repeated until the moisture content detection value falls within the desired value or the desired range.

  Preferably, the detection unit 10 detects the moisture content of the humidifying film 2 continuously or continuously at certain time intervals, and accordingly, the control unit 20 provides feedback regarding the position of the movable guide roll 8. Control is performed continuously or continuously at certain time intervals.

  In adjusting the position of the movable guide roll 8 to change the transport path length of the PVA film 1 in the chamber 4, the change amount of the transport path length of the PVA film 1 and the change amount of the moisture content of the humidifying film 2 The correlation may be checked in advance, and the change amount of the transport path length may be determined based on this. When the humidifying device 3 is provided with a plurality of movable guide rolls 8, the change amount of the conveyance path length of the PVA film 1 is a predetermined value for the movable guide rolls 8 to be moved and the number thereof, and the movement distance of each movable guide roll 8. It is appropriately selected to be

  It is preferable that the detection part 10 can detect a moisture content in-line, conveying the humidification film 2 derived | led-out from the humidification apparatus 3, As such a thing, using a moisture absorption meter of infrared absorption type suitably Can. As the above-mentioned moisture content detection value, the moisture content by an infrared absorption type moisture meter may be adopted, or the correlation between the moisture content by an infrared absorption type moisture meter and the moisture content according to the dry weight method is shown A calibration curve may be prepared in advance, and the moisture content according to the dry weight method converted by this calibration curve may be adopted as the moisture content detection value.

The moisture content according to the dry weight method is as follows, where W1 is the weight of the film when dried at 105 ° C. for 2 hours, and W0 is the weight of the film before drying:
Moisture content by dry weight method (% by weight) = {(W0-W1) / W0} x 100
It is sought according to

  The control unit 20 can receive a signal from the detection unit 10, and can be a computer or the like that controls the position of the movable guide roll 8 based on this.

  Although not shown, the film humidifying system can include a heating device for heating the PVA film 1 disposed on the upstream side of the humidifying device 3. By introducing the PVA film 1 through the heating device and then introducing it into the humidifying device 3, dew condensation on the surface of the PVA film 1 which may occur when introduced into the humidifying device 3 can be more effectively suppressed or prevented. The heating device is a heating chamber capable of adjusting the internal temperature (hot air oven etc. capable of raising the internal temperature by the supply of hot air), one or more heat rolls, a heater (infrared heater, halogen heater, panel heater etc.) And so on.

  The heating temperature of the film 1 by a heating apparatus is 50-150 degreeC, for example, Preferably it is 60-130 degreeC, More preferably, it is 70-120 degreeC. In order to effectively suppress or prevent condensation on the surface of the PVA film 1 when introduced into the humidifying device 3, the heating temperature of the PVA film 1 by the heating device is the internal temperature of the chamber 4 when the PVA film 1 is humidified. And the temperature of the PVA film 1 in the chamber 4 is preferably 10 ° C. or more, more preferably 20 ° C. or more.

  The heat treatment of the PVA film 1 by the heating device is usually performed under a relative humidity environment lower than the relative humidity in the chamber 4.

  The humidifying device used in the step S10 of obtaining the humidifying film is not limited as long as the conveying path length of the PVA film in the humidifying device can be changed, and the humidifying device of the humidifying device 3 having the movable guide roll 8 is not limited. In addition, for example, it is equipped with one or more guide rolls that define a transfer path of PVA film, which can move the relative humidity inside the chamber into the adjustable chamber or out of the chamber. The transport path length of the PVA film in the chamber may be freely changed by the introduction and removal of the guide roll. However, it is preferable to use the humidifier 3 which has the said movable guide roll 8 from a viewpoint of the simplicity of installation.

  The moisture content of the obtained humidifying film 2 depends on the thickness of the humidifying film 2, but is preferably 4 to 15% by weight, more preferably 5 to 13% by weight, and 7% by weight or more, further 8% by weight It may be% or more.

(2) Step S20 of obtaining a stretched film
Step S20 of obtaining a stretched film is a step of obtaining a stretched film by dry-stretching the humidified film 2. Dry stretching means stretching performed in the air, usually longitudinal uniaxial stretching. In dry stretching, a film is passed between a heat roll whose surface is heated and a guide roll (or a heat roll) having a circumferential speed different from that of the heat roll, and heating is performed using the heat roll. Hot roll drawing which performs longitudinal drawing under; between rolls performing longitudinal drawing by the circumferential speed difference between these two nip rolls while passing a heating means (such as an oven) between two nip rolls placed at a distance. Stretching; tenter stretching; compression stretching etc. can be mentioned. The stretching temperature (surface temperature of the heat roll, temperature in the oven, etc.) is, for example, 80 to 150 ° C., preferably 100 to 135 ° C.

  The stretching ratio of the humidifying film 2 is preferably 3.5 times or more, more preferably 4 times or more, from the viewpoint of the optical properties (particularly, polarization properties) of the polarizing film when using the stretched film as a raw material of the polarizing film. It is. The stretching ratio is usually about 8 or less.

  The stretched film continuously obtained as a long film may be wound once to be a film roll, or may be continuously supplied to the next step such as a polarizing film forming step without winding.

<Production of Polarizing Film and Polarizing Plate>
The stretched film obtained by the production method according to the present invention can be suitably used as a raw material of a polarizing film. The polarizing film is a step of adsorbing a dichroic dye by dyeing a stretched film with a dichroic dye; a step of crosslinking treatment of the film to which the dichroic dye is adsorbed; and a step of washing with water after the crosslinking treatment It can be manufactured through. As the dichroic dye, iodine or a dichroic organic dye can be used.

  As a method of dyeing a stretched film with a dichroic dye, for example, a method of immersing the stretched film in an aqueous solution (dyeing solution) containing a dichroic dye is employed. The stretched film is preferably subjected to immersion treatment (swelling treatment) in water before dyeing treatment.

  In the case of using iodine as the dichroic dye, usually, a method of dyeing by immersing a stretched film in an aqueous solution containing iodine and potassium iodide is employed. The content of iodine in the aqueous dyeing solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous staining solution is usually about 20 to 40 ° C.

On the other hand, in the case of using a dichroic organic dye as the dichroic dye, usually, a method of dyeing by immersing a stretched film in a dyeing aqueous solution containing a water-soluble dichroic organic dye is employed. The content of the dichroic organic dye in the aqueous dyeing solution is usually 1 × 10 ⁻⁴ to 10 parts by weight, preferably 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. The aqueous dyeing solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous staining solution is usually about 20 to 80 ° C.

  The crosslinking treatment after dyeing with the dichroic dye can be carried out by immersing the dyed film in an aqueous solution containing a crosslinking agent. A preferred example of the crosslinking agent is boric acid, but other crosslinking agents such as boron compounds such as borax, glyoxal, glutaraldehyde and the like can also be used. The crosslinking agent may use only 1 type and may use 2 or more types together.

  The amount of the crosslinking agent in the crosslinking agent-containing aqueous solution is usually 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. When using iodine as a dichroic dye, it is preferable that this crosslinking agent containing aqueous solution contains potassium iodide. The amount of potassium iodide in the crosslinking agent-containing aqueous solution is usually 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. The temperature of the crosslinking agent-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

  The cross-linked film is usually washed with water. The water washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 1 to 40 ° C.

  In one or more treatments of swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment, the film may be subjected to wet stretching, if necessary.

  After washing with water, the film is dried to obtain a polarizing film. The drying process may be drying with a hot air dryer, drying by contacting with a heat roll, drying with a far infrared heater, and the like. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 50 to 90 ° C. The thickness of the polarizing film is usually about 2 to 40 μm. From the viewpoint of thinning of the polarizing plate, the thickness of the polarizing film is preferably 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less.

  A polarizing plate can be obtained by bonding a thermoplastic resin film to one side or both sides of a polarizing film through an adhesive layer. The thermoplastic resin film is a film composed of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin. The thermoplastic resin constituting the thermoplastic resin film is, for example, polyolefin resin such as chain-like polyolefin resin (polypropylene resin etc.), cyclic polyolefin resin (norbornene resin etc); triacetyl cellulose, diacetyl cellulose Cellulose-based resins such as: polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate-based resins; (meth) acrylic-based resins such as methyl methacrylate-based resins; polystyrene-based resins; polyvinyl chloride-based resins; Acrylonitrile styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyacetal resin; modified polyphenylene ether resin; Hong resins; poly (ether sulfone) resins; polyarylate resin; polyamideimide resin; may be a polyimide resin or the like.

  Examples of linear polyolefin resins include homopolymers of linear olefins such as polyethylene resins and polypropylene resins, and copolymers of two or more types of linear olefins. More specific examples are polypropylene resins (polypropylene resins which are homopolymers of propylene, copolymers mainly composed of propylene), polyethylene resins (polyethylene resins which are homopolymers of ethylene), and ethylene (Copolymer)).

  Cyclic polyolefin resin is a general term for resin polymerized as cyclic olefin as a polymerization unit. Specific examples of cyclic polyolefin resins include ring-opened (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and linear olefins such as ethylene and propylene (typically Are random copolymers), graft polymers obtained by modifying these with unsaturated carboxylic acids and derivatives thereof, and hydrides thereof. Among them, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer as the cyclic olefin is preferably used.

  Cellulose-based resin means that part or all of hydrogen atoms in hydroxyl groups of cellulose obtained from raw material cellulose such as cotton linta and wood pulp (hardwood pulp, softwood pulp) are substituted with acetyl group, propionyl group and / or butyryl group Or cellulose organic acid ester or cellulose mixed organic acid ester. For example, those composed of cellulose acetate, propionate, butyrate, mixed esters thereof and the like can be mentioned. Among them, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate and cellulose acetate butyrate are preferable.

  The polyester-based resin is a resin other than the above-mentioned cellulose-based resin having an ester bond, and is generally made of a polycondensate of polyvalent carboxylic acid or derivative thereof and polyvalent alcohol. Divalent dicarboxylic acid or its derivative can be used as polyvalent carboxylic acid or its derivative, For example, a terephthalic acid, an isophthalic acid, a dimethyl terephthalate, dimethyl naphthalene dicarboxylic acid etc. are mentioned. Divalent diol can be used as polyhydric alcohol, For example, ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexane dimethanol etc. are mentioned. Examples of suitable polyester-based resins include polyethylene terephthalate.

  A polycarbonate-based resin is an engineering plastic comprising a polymer in which monomer units are bonded via a carbonate group, and is a resin having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called a modified polycarbonate in which the polymer skeleton is modified to lower the photoelastic coefficient, or a copolymerized polycarbonate having a wavelength dependency improved.

  The (meth) acrylic resin is a polymer containing a structural unit derived from a (meth) acrylic monomer. The polymer is typically a polymer containing a methacrylic acid ester. Preferably, the proportion of structural units derived from methacrylic acid esters is 50% by weight or more based on all structural units. The (meth) acrylic resin may be a homopolymer of methacrylic acid ester, or may be a copolymer containing a structural unit derived from another polymerizable monomer. In this case, the proportion of constituent units derived from other polymerizable monomers is preferably 50% by weight or less based on all structural units.

  As a methacrylic acid ester which can comprise a (meth) acrylic-type resin, methacrylic acid alkyl ester is preferable. Examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate And methacrylic acid alkyl esters having 1 to 8 carbon atoms in the alkyl group such as 2-hydroxyethyl methacrylate. The carbon number of the alkyl group contained in the methacrylic acid alkyl ester is preferably 1 to 4. In the (meth) acrylic resin, only one kind of methacrylic acid ester may be used alone, or two or more kinds thereof may be used in combination.

  As said other polymerizable monomer which can comprise (meth) acrylic-type resin, acrylic acid ester and the compound which has a polymerizable carbon-carbon double bond in another molecule can be mentioned. The other polymerizable monomers may be used alone or in combination of two or more. As acrylic acid ester, acrylic acid alkyl ester is preferable. As acrylic acid alkyl ester, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate And alkyl acrylates having 1 to 8 carbon atoms in the alkyl group such as 2-hydroxyethyl acrylate. The carbon number of the alkyl group contained in the acrylic acid alkyl ester is preferably 1 to 4. In the (meth) acrylic resin, only one acrylic ester may be used alone, or two or more acrylic esters may be used in combination.

  Examples of the compound having a polymerizable carbon-carbon double bond in another molecule include vinyl compounds such as ethylene, propylene and styrene, and vinyl cyan compounds such as acrylonitrile. The compound which has a polymerizable carbon-carbon double bond in another molecule may be used individually by 1 type, and may use 2 or more types together.

  The thermoplastic resin film can be a protective film for protecting a polarizing film. The thermoplastic resin film can also be a protective film having an optical function such as a retardation film or a brightness enhancement film. For example, by stretching (uniaxial stretching or biaxial stretching, etc.) a thermoplastic resin film made of the above material, or forming a liquid crystal layer or the like on the film, a retardation to which an arbitrary retardation value is imparted It can be a film. The thermoplastic resin film may have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflective layer, an antistatic layer, and an antifouling layer laminated on the surface thereof.

  The thickness of the thermoplastic resin film is usually 1 to 100 μm, but is preferably 5 to 60 μm and more preferably 5 to 50 μm from the viewpoints of strength and handleability, thinning of a polarizing plate and the like.

  As an adhesive used for bonding the polarizing film and the thermoplastic resin film, a water-based adhesive, an active energy ray-curable adhesive or a thermosetting adhesive can be used, and preferably a water-based adhesive, an active energy ray It is a curable adhesive.

  The water-based adhesive is one in which the adhesive component is dissolved in water or dispersed in water. The aqueous adhesive preferably used is, for example, an adhesive composition using a polyvinyl alcohol resin or a urethane resin as a main component.

  When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin can be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol or completely saponified polyvinyl alcohol, or a carboxyl group-modified polyvinyl alcohol It may be a modified polyvinyl alcohol resin such as acetoacetyl group modified polyvinyl alcohol, methylol group modified polyvinyl alcohol, or amino group modified polyvinyl alcohol. The polyvinyl alcohol-based resin is a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable therewith. It may be a polyvinyl alcohol copolymer obtained by saponification treatment of the united body.

  The water-based adhesive containing a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of a polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol resin in the adhesive is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of water.

  An adhesive comprising an aqueous solution of a polyvinyl alcohol resin is a curable component such as a polyvalent aldehyde, a melamine compound, a zirconia compound, a zinc compound, a glyoxal, a glyoxal derivative, a water-soluble epoxy resin, or the like to improve adhesion. It is preferred to contain a crosslinking agent. As a water-soluble epoxy resin, for example, a polyamide polyamine epoxy resin obtained by reacting epichlorohydrin with a polyamide amine obtained by the reaction of a polyalkylene polyamine such as diethylene triamine and triethylene tetramine and a dicarboxylic acid such as adipic acid Can be suitably used. Commercially available products of such polyamide polyamine epoxy resin include "Sumirez Resin 650" (Taoka Chemical Industry Co., Ltd.), "Sumirez Resin 675" (Taoka Chemical Industry Co., Ltd.), "WS-525" (Japan) PMC Co., Ltd. product etc. are mentioned. The amount of the curable component or crosslinking agent added (the total amount of both the curable component and the crosslinking agent when added together) is usually 1 to 100 parts by weight, preferably 100 parts by weight of the polyvinyl alcohol resin. 1 to 50 parts by weight. When the addition amount of the curable component and the crosslinking agent is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol resin, the effect of improving the adhesiveness tends to be small, and the addition amount is polyvinyl If it exceeds 100 parts by weight with respect to 100 parts by weight of the alcohol-based resin, the adhesive layer tends to become brittle.

  Moreover, as a suitable example in the case of using a urethane resin as a main component of an adhesive agent, the mixture of a polyester type ionomer type urethane resin and the compound which has a glycidyloxy group can be mentioned. A polyester-based ionomer-type urethane resin is a urethane resin having a polyester skeleton, into which a small amount of ionic component (hydrophilic component) is introduced. Such an ionomer-type urethane resin is suitable as a water-based adhesive because it is directly emulsified in water without using an emulsifier to form an emulsion.

  An active energy ray-curable adhesive is an adhesive that cures upon irradiation with active energy rays such as ultraviolet light, visible light, electron beams, and X-rays. When using an active energy ray curable adhesive, the adhesive layer of the polarizing plate is a cured product layer of the adhesive.

  The active energy ray-curable adhesive can be an adhesive containing, as a curable component, an epoxy-based compound which is cured by cationic polymerization, and preferably, an ultraviolet-curable adhesive comprising such an epoxy-based compound as a curable component It is an agent. The epoxy compound as referred to herein means a compound having an average of one or more, preferably two or more epoxy groups in the molecule. The epoxy compounds may be used alone or in combination of two or more.

  Specific examples of epoxy compounds that can be suitably used are hydrogenated epoxy compounds obtained by reacting epichlorohydrin with an alicyclic polyol obtained by subjecting the aromatic ring of an aromatic polyol to a hydrogenation reaction ( Glycidyl ethers of polyols having alicyclic rings); aliphatic epoxy compounds such as aliphatic polyhydric alcohols or polyglycidyl ethers of alkylene oxide adducts thereof; epoxy groups bonded to alicyclic rings in the molecule 1 The alicyclic epoxy-type compound which is an epoxy-type compound which has more than one is included.

  The active energy ray-curable adhesive can contain, as a curable component, a (meth) acrylic compound which is radically polymerizable instead of or together with the above-mentioned epoxy compound. (Meth) acrylic compounds are (meth) acrylate monomers having at least one (meth) acryloyloxy group in the molecule; obtained by reacting two or more functional group-containing compounds, at least two in the molecule And (meth) acryloyloxy group-containing compounds such as (meth) acrylate oligomers having a (meth) acryloyloxy group of

  When the active energy ray-curable adhesive contains an epoxy compound curable by cationic polymerization as a curable component, it preferably contains a photo cationic polymerization initiator. Examples of the cationic photopolymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; and iron-allene complexes. When the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth) acrylic compound, it is preferable to contain a photoradical polymerization initiator. Examples of photo radical polymerization initiators include acetophenone initiators, benzophenone initiators, benzoin ether initiators, thioxanthone initiators, xanthones, fluorenones, camphorquinones, benzaldehydes, anthraquinones and the like.

  Prior to bonding a thermoplastic resin film to a polarizing film, the bonding surface of the polarizing film and / or the thermoplastic resin film is subjected to plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, saponification treatment Such surface activation treatment may be performed. The surface activation treatment can enhance the adhesion between the polarizing film and the thermoplastic resin film.

  1 polyvinyl alcohol-based resin film (PVA film), 2 humidified film (humidified film), 3 humidifier, 4 chambers, 4a chamber first chamber 4b chamber second chamber 5 inlet port 6 outlet port 7 non-movable guide roll, 8 movable guide roll, 10 detector, 20 controller.

Claims (6)

A step of continuously introducing a long polyvinyl alcohol resin film into the humidifying device to obtain the humidified film;
Dry stretching the humidifying film derived from the humidifying device to obtain a stretched film;
Including
Wherein the step of obtaining a humidifying film look including the step of adjusting the moisture content of the humidified film by changing the conveying path length of the polyvinyl alcohol resin film in said humidifier,
The humidifying device includes a chamber capable of adjusting the relative humidity inside, and a plurality of guide rolls disposed in the chamber and defining a transport path of the polyvinyl alcohol resin film.
At least one of the plurality of guide rolls is a movable guide roll capable of positional movement,
The process of adjusting the moisture content includes adjusting the position of the movable guide roll . In the step of obtaining the humidifying film,
Detecting the moisture content of the humidifying film derived from the humidifying device;
Controlling the position of the movable guide roll based on the detection result obtained in the detecting step;
Further comprising, process of claim 1. The manufacturing method according to claim 2 , wherein in the step of detecting the moisture content, the moisture content is detected in-line while conveying the humidifying film derived from the humidifying device. The manufacturing method according to any one of claims 1 to 3 , wherein the movable guide roll is movable in parallel in a direction inclined from the horizontal direction. The chamber includes a first chamber into which the polyvinyl alcohol resin film is introduced, and a second chamber from which the humidification film is discharged.
The manufacturing method according to any one of claims 1 to 4 , wherein the relative humidity in the second room is higher than the relative humidity in the first room. The method according to claim 5 , wherein each of the first chamber and the second chamber comprises the movable guide roll.

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