JP2009051202A - Manufacturing process of optical film, optical film, liquid crystal display device, image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process, etc. of an optical film in which the possibility of breakage in a coupling part is relatively small even if both the sides of the coupling unit are being cut. <P>SOLUTION: A belt-like raw fabric film is sent from a tip side to a stretching device constituted to arrange a nip part for grasping the sent-in belt like film by opening an interval and to stretch this belt-like film in a longitudinal direction in this interval and the rear end side of a preceding end sent raw fabric film and the tip end side of next raw fabric film are coupled by heat sealing, thereby sequentially continuously sending the raw fabric film to the stretching device to stretch the raw fabric film. Before the coupling part of the rear end side of the raw fabric film and the tip side of next raw fabric film is sent in the stretching device, both the sides of the regions including this coupling parts are cut in an arc-shape, and the longitudinal direction length R of the cut region is made 90 to 105% of the interval L of the nip parts. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention mainly relates to a method for producing an optical film used for an image display device such as a liquid crystal display device, an electroluminescence (EL) display device, a plasma display (PD) and a field emission display (FED), and the like. The present invention relates to a manufactured optical film and an image display device such as a liquid crystal display device including the optical film.

Conventionally, as a method for producing this type of optical film, a belt-shaped raw film is fed from the leading end side into a stretching apparatus that stretches the fed belt-shaped film, and stretched by the stretching apparatus. The method to do is adopted.
For example, polarized light is obtained by feeding the leading end of the original film from a raw roll obtained by winding a belt-like polyvinyl alcohol-based raw film into a roll to a stretching device and stretching it while being immersed in a predetermined chemical solution or the like. A film method is employed.

In addition, in this type of optical film manufacturing method, it is very complicated to manually feed the leading end of each original film into a stretching apparatus (for example, between rollers in the apparatus). In addition, it is time-consuming, and the leading end side of the next original film is connected to the rear end side of the preceding original film by heat sealing, and the optical film can be continuously stretched to obtain an optical film. (See Patent Document 1 below).
JP 2004-160665 A

By the way, in the conventional method for producing an optical film, the film width is reduced as a whole by stretching. However, since the width of the connecting portion connected by heat sealing does not decrease so much, the film width is not uniform in the stretching process. As a result, the connecting portion becomes wider than the corresponding width of the stretching apparatus, and various problems may occur, such as the meandering or clogging of the film in the stretching apparatus.
Therefore, according to the present inventor, an attempt is made to cut both sides of the connecting portion in advance before feeding the drawing device.
However, if both sides are cut, the heat-sealed area also decreases, and it is fully predicted that the risk of breakage at the connecting portion may increase in some cases.
In view of the various problems as described above, the present invention is to provide a method for producing an optical film and the like that is relatively less likely to break at the connecting portion while cutting both sides of the connecting portion. And

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by the following means, and have completed the present invention.
That is, the present invention provides a belt-shaped original in a stretching apparatus configured to stretch the belt-like film in the longitudinal direction within the gap, with nip portions for gripping the fed belt-like film being arranged with a space therebetween. By feeding the anti-film from the leading end side and connecting the rear end side of the original raw film and the leading end side of the next original film by heat sealing, the original film is successively successively Is a method for producing an optical film that is drawn into a stretching device and stretched,
Before the connecting portion between the rear end side of the original film and the leading end side of the next original film is fed into the stretching device, both sides of the region including the connecting portion are cut in an arc shape, and the cut region The method of manufacturing an optical film is characterized in that the length R in the longitudinal direction is 90 to 105% of the gap L between the nip portions.
Moreover, this invention provides the optical film manufactured by such a method.
Furthermore, the present invention provides an image display device such as a liquid crystal display device including such an optical film.

  According to the method for producing an optical film of the present invention, it is possible to reduce the risk of breakage due to stretching while sequentially stretching a plurality of original fabric films in the longitudinal direction.

Embodiments of the present invention will be described below.
First, the preferable manufacturing apparatus for enforcing the manufacturing method of the optical film of this embodiment is demonstrated, referring drawings.
As an apparatus for manufacturing an optical film, for example, an apparatus for manufacturing a polarizing film normally supplies an original film from which an original film 1 is fed out from an original roll in which a strip-like polyvinyl alcohol-based original film 1 is wound into a roll. Part 3, a plurality of immersion baths 4 for immersing the fed original film 1 in a predetermined chemical solution, a stretching device 2 for extending the original film 1 in the longitudinal direction (moving direction), and a plurality of immersion baths And a polarizing film take-up unit 10 that winds the film immersed and stretched into a roll shape as a polarizing film.

FIG. 1 and FIG. 2 are schematic perspective views showing an embodiment of a preferable polarizing film manufacturing apparatus.
As shown in FIG. 1, as the immersion bath 4, a swelling bath 4 a in which a swelling liquid for swelling a polyvinyl alcohol-based film is stored in order from an upstream side in the flow direction of the film, and a dyeing liquid for dyeing the swollen film. The stored dye bath 4b, the cross-linking bath 4c stored with the cross-linking agent liquid for cross-linking the constituent polymers of the dyed film, the stretching bath 4d for stretching the film in the bath, and further passed through each immersion bath 4. There are five types of immersion baths 4 called cleaning baths 4f in which cleaning liquid for cleaning the film is stored.

  The manufacturing apparatus of this aspect is provided with a drying device 11, specifically a drying oven, for drying the cleaning liquid adhering to the film on the downstream side in the flow direction of the cleaning bath 4f and on the upstream side of the winding unit 10. Laminating films 12 such as surface protective films (for example, triacetyl cellulose film) wound in a roll shape are disposed on both sides of the film, and the laminating films 12 are disposed on both sides of the polarizing film after drying. It is comprised so that it may be laminated | stacked.

The stretching device 2 is configured to stretch the film 1 by a so-called roll stretching method. That is, it has a nip portion 7 composed of a pair of nip rollers 9 arranged so as to sandwich the fed film 1 therebetween and feed it downstream in the flow direction, with a gap L, and downstream in the flow direction. The film 1 is stretched within the interval L by setting the feeding speed of the side nip portion 7 (specifically, the rotational peripheral speed of the nip roller 9) to be higher than that of the upstream side.
In addition to the nip portion 7, the stretching device 2 includes a plurality of guide rollers 8 that regulate the moving path of the film in order to pass the film through the immersion bath 4, for example.
Specifically, the stretching device 2 includes a plurality of nip portions 7 and guide rollers at a plurality of locations according to each immersion bath 4 so that the film can be stretched at an arbitrary stretching ratio while passing through each immersion bath 4. It is equipped with. Further, in the stretching apparatus 2, each interval L between the nip portion 7 where the stretching is performed and the nip portion 7 is set to a constant value.
In this specification, the gap L between the nip portions is not a linear distance, but a film between a portion of one nip portion 7 that grips the film and a portion of the adjacent nip portion 7 that holds the film. It means the distance along the movement path.

As shown in FIG. 2, the manufacturing apparatus of this aspect is preferably configured so that the rear end side 1 a of the original film 1 is passed through the stretching apparatus 2 and before it is passed through the immersion bath 4. The rear end side 1a of the film 1 and the leading end side 1b of the original film 1 (the next original film 1) that is passed through the stretching apparatus 2 next to the original film 1 are bonded by heat sealing to connect the connecting portion 30. A coupling device (not shown in FIG. 2) for forming is provided.
Here, in this specification, the connection part 30 means the part adhere | attached by heat seal, and when connected by the several linear adhesion part, the area | region between them is shown. It is a concept that also includes In FIG. 2, the connecting portion 30 is shown in black.

3 and 4 are schematic basic configuration diagrams showing the coupling device. In FIG. 3, a side view of the connecting device viewed in the TD direction of the raw film 1 to be connected is shown, and in FIG. 4, a cross-sectional view taken along line AA of FIG. 3 is shown. It is shown.
As shown in FIG. 3, the coupling device includes a plate-like seal bar 21 provided with a heating element 21 a, and a plate-like seal bar receiver 22 disposed so as to face the seal bar 21. The rear end side 1a of the preceding original fabric film 1 and the leading end side 1b of the next original fabric film 1 are overlapped, and the overlapped portion is pressed by the seal bar 21 and the seal bar receiver 22 to be provided in the seal bar 21. By heating the overlapped portion with the generated heating element 21a, the preceding original film 1 and the next original film 1 are connected by thermal bonding.

  The heating element 21a provided in the seal bar 21 is preferably a nichrome wire that is connected to an electric circuit and generates heat when current is supplied. The nichrome wire is on the side that presses the raw film 1. It is arranged on the pressing surface (that is, the surface facing the seal bar receiver 22).

The connecting device is a rubber sheet 24 such as a silicon rubber on a pressing surface of the seal bar receiver 22 (that is, a surface facing the seal bar 21) and a portion facing the heating element 21a provided in the seal bar 21. Is arranged, and the overlapped portion of the raw film 1 is configured to be pressed by the rubber sheet 24 and the portion of the seal bar 21 where the heating element 21a is disposed.
The connecting device is set so that the pressing surface temperature of the seal bar 21 (that is, the temperature of the heating element 21a) is, for example, 55 to 90 ° C., and preferably the sealing time is 1 to 15 seconds. The conditions are set to be
According to such conditions, there is a significant reduction in the possibility of the polyvinyl alcohol-based raw films 1 to be connected to each other being peeled from each other or being broken by heat.

  According to the connecting device, since the plate-like seal bar 21 and the seal bar receiver 22 are connected by heat sealing that presses the overlapped portion of the raw film 1, it is shown in FIG. As shown in FIG. 4 (b), even when unevenness undulations or wrinkles occur in the overlapped portion of the original film 1, these can be connected while correcting them.

In addition, the manufacturing apparatus according to this aspect is configured so that both sides of the region including the connecting portion 30 (that is, both sides in the width direction of the raw film 1) are fed before the connecting portion 30 connected by heat sealing is fed into the stretching device 2. ) Is cut in an arc shape (not shown).
Specifically, as shown in FIG. 5, the raw film is arranged so that the connecting portion 30 is the narrowest portion, in other words, the connecting portion 30 is positioned on the central symmetry line of the cut arcuate cut piece. 1 is provided with cutting means for cutting both sides in the width direction into a substantially arc shape.
The cutting means is set so that the length R in the longitudinal direction of the cut region is 90 to 105%, preferably 95 to 102% of the interval L of the nip portion 7. Preferably, the width A of the connecting portion 30 after cutting (the shortest width A of the connecting portion 30) is 50 to 70% of the original fabric width B, more preferably 55 to 65%, and still more preferably 58. It is set to be -62%.

In the present embodiment, preferred production apparatuses that can be used are as described above. Next, a method for producing an optical film of the present embodiment that can be carried out using the production apparatus as described above will be described.
The manufacturing method of the optical film of this embodiment is as follows. The strip-shaped raw film 1 is fed into the stretching apparatus 2 as described above from the front end side 1b and the rear end side 1a of the original web film 1 is fed in advance. By connecting the leading end side 1b of the next original fabric film 1 by heat sealing, the original fabric film 1 is successively fed into the stretching device 2 and stretched while performing a predetermined treatment to obtain an optical film. Is.

In the present embodiment, examples of the optical film include a polarizing film, and examples of the belt-shaped original film 1 include a polyvinyl alcohol-based original film 1 used for a polarizing film, Examples of the polyvinyl alcohol-based raw film 1 include a polyvinyl alcohol (PVA) film, a partially saponified polyvinyl alcohol film, a dehydrated film of polyvinyl alcohol, and the like.
Usually, these original fabric films 1 are used in the state of the original fabric roll wound by roll shape.

  The polymerization degree of the polymer that is the material of the polyvinyl alcohol-based raw film 1 is generally 500 to 10,000, preferably in the range of 1000 to 6000, and more preferably in the range of 1400 to 4000. Furthermore, in the case of a partially saponified polyvinyl alcohol film, the degree of saponification is preferably 75 mol% or more, more preferably 98 mol% or more, for example, from the viewpoint of solubility in water, and 98.3 to 99. More preferably, it is in the range of 8 mol%.

  As a manufacturing method of the said polyvinyl-alcohol-type raw fabric film 1, what was formed into a film by arbitrary methods, such as the casting method which casts and forms the stock solution melt | dissolved in water or the organic solvent, the casting method, the extrusion method, is used suitably. be able to. The retardation value of the raw film 1 is preferably 5 nm to 100 nm. Moreover, in order to obtain a in-plane uniform polarizing film, it is preferable that the retardation variation in the surface of the polyvinyl alcohol-based raw film 1 is as small as possible, and the in-plane retardation variation of the polyvinyl alcohol-based film as the raw fabric film 1 is In the measurement wavelength of 1000 nm, it is preferably 10 nm or less, and more preferably 5 nm or less.

In the present embodiment, preferably, the original film 1 is wound into a roll shape as described above, and the original film 1 is fed from the original roll and fed into the stretching apparatus 2. A stretching process is performed, and as a process of the stretching process, a process of an immersion process in which a plurality of rollers 8 and 9 regulate the moving path and pass through the plurality of immersion baths 4 is performed.
As the treatment of the dipping process, preferably, as illustrated in FIG. 1, the film is swelled by passing through the swelling bath 4a, etc. while passing through the swelling bath 4a, etc. The film is washed by, for example, a dyeing process for dyeing a film by a crosslinking process, a crosslinking process for crosslinking a film-constituting polymer by passing it through a crosslinking bath 4c, a stretching bath immersion process for facilitating stretching through a stretching bath 4d, and a washing bath 4f. The cleaning process is performed.
In addition, after a washing | cleaning process, a drying process is normally implemented.

As the swelling step, for example, it is immersed in a swelling bath 4a filled with water. As a result, the original film 1 is washed with water, and the surface of the original film 1 can be cleaned of stains and anti-blocking agents, and the original film 1 can be swollen to prevent unevenness such as dyeing unevenness. I can expect.
In the swelling bath 4a, glycerin, potassium iodide or the like may be added as appropriate, and when added, the concentration is 5% by weight or less for glycerin and 10% by weight or less for potassium iodide. Is preferred. The temperature of the swelling bath 4a is preferably in the range of 20-50 ° C, more preferably 25-45 ° C. The immersion time in the swelling bath 4a is preferably 2 to 180 seconds, more preferably 10 to 150 seconds, and particularly preferably 60 to 120 seconds. Further, the polymer film may be stretched in the swelling bath 4a, and the stretching ratio at that time is preferably about 1.1 to 3.5 times including stretching due to swelling.

  As the dyeing process, for example, the film having undergone the swelling process is immersed in a dyeing bath 4b containing a dichroic substance such as iodine to adsorb the dichroic substance to the film.

  A conventionally known substance can be used as the dichroic substance, and examples thereof include iodine and organic dyes. Organic dyes include, for example, Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Sky Blue, Direct First Orange S, First Black, etc. can be used.

  These dichroic substances may be used alone or in combination of two or more. When using the said organic dye, it is preferable to combine 2 or more types from the point which aims at neutralization of the visible region, for example. Specific examples include a combination of Congo Red and Splat Blue G, Splat Orange GL and Direct Sky Blue, or a combination of Direct Sky Blue and First Black.

As the solution of the dyeing bath 4b, a solution in which the dichroic substance is dissolved in a solvent can be used. As the solvent, water can be generally used, but an organic solvent compatible with water may be further added and used.
The concentration of the dichroic substance is preferably in the range of 0.010 to 10% by weight, more preferably in the range of 0.020 to 7% by weight, and in the range of 0.025 to 5% by weight. It is particularly preferable to do this.

  Further, when iodine is used as the dichroic substance, it is preferable to further add an iodide because the dyeing efficiency can be further improved. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples include titanium. The addition ratio of these iodides is preferably 0.010 to 10% by weight, and more preferably 0.10 to 5% by weight in the dye bath. Among these, it is preferable to add potassium iodide, and the ratio (weight ratio) of iodine and potassium iodide is preferably in the range of 1: 5 to 1: 100, and 1: 6 to 1:80. Is more preferable, and a range of 1: 7 to 1:70 is particularly preferable.

  Although the immersion time of the film in the said dyeing | staining bath 4b is not specifically limited, 1-5 minutes are preferable and 2-4 minutes are more preferable. Moreover, it is preferable to make the temperature of a dyeing bath into the range of 5-42 degreeC, and it is more preferable to set it as the range of 10-35 degreeC. Further, the film may be stretched in this dyeing bath, and the accumulated total stretching ratio at this time is preferably about 1.1 to 4.0 times.

  In addition, as a dyeing | staining process, you may employ | adopt the method of apply | coating or spraying the aqueous solution containing a dichroic substance on the said polymer film other than the method of immersing in the dyeing bath 4b as mentioned above, for example. In the present invention, a film formed of a polymer raw material mixed with a dichroic material in advance may be adopted as the raw film 1 to be used without performing the dyeing process.

As the crosslinking step, for example, the film is dipped in a crosslinking bath 4c containing a crosslinking agent to be crosslinked.
A conventionally known substance can be used as the crosslinking agent. For example, boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde can be used. These may be used alone or in combination of two or more. When two or more types are used in combination, for example, a combination of boric acid and borax is preferable, and the addition ratio (molar ratio) is preferably in the range of 4: 6 to 9: 1. A range of 5: 4.5 to 7: 3 is more preferable, and a range of 6: 4 is most preferable.

  As the solution of the crosslinking bath 4c, a solution in which the crosslinking agent is dissolved in a solvent can be used. For example, water can be used as the solvent, but an organic solvent compatible with water may be used in combination. The concentration of the crosslinking agent in the solution is not particularly limited, but is preferably in the range of 1 to 10% by weight, more preferably 2 to 6% by weight.

In the crosslinking bath 4c, an iodide may be added from the viewpoint that uniform characteristics within the plane of the polarizing film can be obtained. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples of the content of iodide when titanium is added include 0.05 to 15% by weight, and more preferably 0.5 to 8% by weight.
As a combination of a crosslinking agent and iodide, a combination of boric acid and potassium iodide is preferable, and a ratio (weight ratio) of boric acid and potassium iodide is in a range of 1: 0.1 to 1: 3.5. It is preferable that the range is 1: 0.5 to 1: 2.5.

The temperature of the crosslinking bath 4c is usually preferably in the range of 20 to 70 ° C., and the immersion time of the polymer film is usually 1 second to 5 minutes, preferably 5 seconds to 4 minutes.
In the cross-linking step, the polymer film may be stretched in the cross-linking bath 4c, and the total stretch ratio accumulated at this time is preferably about 1.1 to 5.0 times.
In addition, as a bridge | crosslinking process, it may replace with the process passed through the bridge | crosslinking bath 4c similarly to the dyeing | staining process, and you may use the method of apply | coating or spraying a crosslinking agent containing solution.

  In the stretching bath soaking step, stretching is performed so that the accumulated total stretching ratio is, for example, about 2 to 7 times in a state of being soaked in the stretching bath 4d.

The solution of the stretching bath 4d is not particularly limited, and for example, a solution to which various metal salts, iodine, boron or zinc compounds are added can be used. As a solvent of this solution, water, ethanol, or various organic solvents can be appropriately used.
Especially, it is preferable to use the solution which added about 2-18 weight% of boric acid and / or potassium iodide, respectively. When boric acid and potassium iodide are used at the same time, the content ratio (weight ratio) is about 1: 0.1 to 1: 4, more preferably about 1: 0.5 to 1: 3. It is preferable to use in.

  As temperature of the said extending | stretching bath 4d, it is preferable to set it as the range of 40-67 degreeC, for example, and it is more preferable to set it as 50-62 degreeC.

  The washing step is a step of washing away unnecessary residues such as boric acid adhering to the previous treatment by passing the film through a washing bath 4f in which water is stored. Iodide is preferably added to the water, for example, sodium iodide or potassium iodide is preferably added. When potassium iodide is added to the water in the washing bath 4f, the concentration is usually 0.1 to 10% by weight, preferably 3 to 8% by weight. Furthermore, the temperature of the cleaning bath 4f is preferably 10 to 60 ° C, more preferably 15 to 40 ° C. Further, the number of times of the cleaning treatment, that is, the number of times of passing through the cleaning bath 4f is not particularly limited, and a plurality of cleaning treatments may be used, and water having different types and concentrations of additives may be stored in the plurality of cleaning baths 4f. You may implement a washing | cleaning process by letting a film pass.

  In addition, when pulling up the film from the immersion bath 4 in each process, in order to prevent the occurrence of dripping, a conventionally known liquid breakage roll such as a pinch roll is used, or the liquid is scraped off by an air knife. Excess water may be removed by such a method.

  As the drying step, an appropriate method such as natural drying, air drying, heat drying or the like can be adopted, but heat drying is usually preferable. The heating and drying conditions are preferably a heating temperature of about 20 to 80 ° C. and a drying time of about 1 to 10 minutes.

In this embodiment, the polarizing film wound in roll shape can be obtained by winding the film which passed through the above processes with a winding roller.
In addition, in this embodiment, you may make it wind up, after laminating | stacking another kind of films for surface protection etc. suitably on the surface one side or both sides of the polarizing film dried at the drying process.

  The final total draw ratio of the polarizing film thus produced is preferably 3.0 to 7.0 times that of the original film 1 and is in the range of 5.0 to 6.5 times. More preferably, it is more preferably in the range of 5.5 to 6.3 times. If the final total draw ratio is less than 3.0 times, it is difficult to obtain a polarizing film having a high degree of polarization, and if it exceeds 7.0 times, the film tends to break.

  The polarizing film can be continuously produced through the above-described steps, but in the present embodiment, the following steps are further performed on the next raw film 1. Before feeding the original film 1 to the stretching device 2, the rear end side 1a of the preceding original film 1 and the leading end side 1b of the next original film 1 are thermally bonded by heat sealing, and the connecting portion 30 is formed.

Specifically, a connecting device as shown in FIG. 3 is used to superimpose the next original film 1 on the rear end side 1a of the preceding original film 1, and the overlapped portion is used as a seal bar 21 and a seal bar holder. While being sandwiched and pressed at 22, the heat is bonded by setting the seal bar temperature, that is, the temperature of the heating element 21 a disposed on the pressing surface side of the seal bar 21 to 55 to 90 ° C.
Even if the heat-bonded portions of the raw film 1 are stretched at a stretch ratio (4 times or more) that is usually required, there is little risk of peeling by sufficient heat-bonding at 55 ° C or higher, and at 90 ° C or lower. If it exists, although the effect | action is not certain, generation | occurrence | production of the bubble by evaporation of the water | moisture content in a film will be suppressed, or there is little possibility that the original fabric film 1 will deteriorate and fracture | rupture.
Here, the heat sealing time (that is, the time during which the seal bar 21 is in contact with the raw film 1) is preferably 1 to 15 seconds, more preferably 2 to 10 seconds.
If the heat sealing time is less than 1 second, the heat sealing may not be sufficiently performed, and it is not necessary to perform the heat sealing for more than 15 seconds.

Further, usually, heat sealing is performed so that the sealed portion is strip-shaped and along the width direction (TD direction) of the original film 1, that is, along the direction orthogonal to the stretching direction. Although not limited, it is usually 1 to 10 mm, preferably 2 to 4 mm.
If the seal width is 1 mm or more, sufficient adhesive strength can be obtained. On the other hand, if the seal width is increased more than necessary, the portion that is hardened and hard to stretch increases, so the possibility of breakage increases. In such a case, such a possibility is extremely small.
The seal width can be appropriately adjusted by adjusting the width of a heating element 21a such as a nichrome wire that contacts the film and heats the film.
Furthermore, although the connection part 30 may be formed by heat-sealing at one place, it may be formed by heat-sealing at two or more places as shown in FIGS.

In the method for producing an optical film of the present embodiment, as described above, after connecting the next raw film 1 by forming the connecting portion 30, both sides of the region including the connecting portion 30 (the width of the original film 1). Cut both sides of the direction in a substantially arc shape.
Specifically, using a cutting device, for example, an area including the connecting portion 30 is arranged on a cutting pedestal, and the cutter formed in a substantially arc shape so as to sandwich the original film 1 is used as the original film 1. The two sides are cut into an arc shape so that the connecting portion 30 becomes the narrowest by being pressed against both sides.
At this time, the length R in the longitudinal direction of the cut region after cutting is preferably 95 to 102% so as to be 90 to 105% of the distance L between the nip portion 7 and the nip portion 7 to be stretched. Cut so that.
By cutting in this way, it is possible to reduce the risk of breakage due to stretching relatively while narrowing the film width at the connecting portion 30.
Preferably, the width A of the connecting portion 30 after cutting (that is, the shortest width A of the connecting portion 30) is 50 to 70% of the original fabric width B, more preferably 55 to 65%, Even more preferably, it is cut so as to be 58 to 62%.
By making it 50 to 70% of the original fabric width B, the breaking strength of the connecting portion 30 can be improved as compared with the case where there is no cutting, and the original fabric film 1 can be stretched at a higher magnification. During the process, the possibility that the connecting part 30 is unexpectedly broken is further reduced.

  In this embodiment, after performing such cutting, the next raw film 1 is fed into the stretching device 2, and if necessary, the stretching ratio is lowered until the connecting portion 30 finishes passing through the stretching device, Sequentially produce polarizing films.

  Although the thickness of the polarizing film manufactured by this embodiment is not specifically limited, It is preferable that it is 5-40 micrometers. If the thickness is 5 μm or more, the mechanical strength will not be reduced, and if it is 40 μm or less, the optical characteristics will not be reduced, and thinning can be realized even when applied to an image display device.

The polarizing film manufactured according to the present embodiment can be used for a liquid crystal display device as a polarizing film laminated on a liquid crystal cell substrate. In addition to a liquid crystal display device, an electroluminescence display device, a plasma display, and It can be used as a polarizing film in various image display devices such as field emission displays.
In practical use, various optical layers can be laminated on both sides or one side to form an optical film, or various surface treatments can be applied to an image display device such as a liquid crystal display device. The optical layer is not particularly limited as long as it satisfies the required optical characteristics. For example, a transparent protective layer for the purpose of protecting a polarizing film, an alignment liquid crystal layer for the purpose of viewing angle compensation, etc. In addition to adhesive layers for laminating other films, polarization conversion elements, reflectors, transflective plates, phase difference plates (including wave plates (λ plates) such as 1/2 and 1/4), viewing angle compensation Films used for forming image display devices such as films and brightness enhancement films can be used.
Examples of the surface treatment include hard coat treatment, antireflection treatment, surface treatment for the purpose of prevention of sticking and diffusion or antiglare.

The manufacturing method of the polarizing film of the present embodiment is as described above, but the present invention is not limited to the present embodiment, and the design can be changed as appropriate within the intended scope of the present invention.
For example, in the present embodiment, a stretching apparatus in which the distances L between the nip portion 7 and the nip portion 7 to be stretched are set to the same value is used, and the longitudinal direction of the cut region with respect to the distance L Although the length R is cut so as to be 90 to 105%, in the present invention, it is not limited to the case of using stretching devices in which the intervals L are set to the same value.
That is, even when a stretching apparatus having a gap L between the nip portion 7 and the nip portion 7 to be stretched is used, the longitudinal length R of the cut region is 90 to 90 for any gap L. As long as it is cut to 105%, it is within the intended scope of the present invention.
Of course, even when the stretching apparatus 2 having only two nip portions 7, that is, when the stretching apparatus 2 having only one spacing L is used, the nip portion 7 was cut with respect to the spacing L. As long as it is cut so that the length R in the longitudinal direction of the region is 90 to 105%, it is within the range intended by the present invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Examples 1-10, Comparative Examples 1-8
Two sheets of polyvinyl alcohol (PVA) raw film 1 (manufactured by Kuraray Co., Ltd., polymerization degree 2400) having a thickness of 75 μm and a width of 50 mm are prepared and stacked on each other to form a coupling device (heating element: nichrome wire) shown in FIG. , Width 3 mm) at two sealing points of 80 ° C. and a sealing time of 10 seconds (dichrome wire interval 10 mm) along the TD direction and heat-sealed along the TD direction, the connecting portion 30 having two linear welded portions 30b. Formed.
Next, as shown in FIG. 5, both sides were cut into a substantially arc shape so that the connecting portion 30 was the narrowest portion.
At this time, the relationship between the longitudinal length R of the cut region and the distance L between the nip portions 7 and the width A of the connecting portion 30 (the shortest width A of the connecting portion, in FIG. 5, the center line 30a of the connecting portion 30). The relationship between the width) and the original fabric width B was adjusted so as to be the relationships shown in Tables 1 and 2, respectively.
In any of the examples and comparative examples, the gap L between the nip portions 7 was set to 50 mm.
Then, the raw film 1 connected to each other is immersed in pure water at 30 ° C. and stretched by a hand stretcher under conditions of a stretching section of 50 mm and a stretching speed of 2 mm / s, and the connected raw film 1 is broken. The stretch ratio until separation was measured. The results are shown in Tables 1 and 2, respectively. Moreover, the results of Table 1 and Table 2 were plotted on a graph and shown in FIGS. 6 and 7, respectively.

  As can be seen from these results, by setting the R / L to 90 to 105%, the breaking strength of the connecting portion 30 can be made relatively excellent, and the A / B (%) is 50. By setting (%) to 70 (%), the breaking strength can be improved as compared with Comparative Example 7 in which cutting is not performed.

The schematic perspective view which shows the one aspect | mode of a manufacturing apparatus. The schematic perspective view which shows the one aspect | mode of a manufacturing apparatus. The schematic side view which shows a connection apparatus. AA line sectional view of Drawing 3. The schematic front view which shows the state which cut | disconnected both sides of the area | region containing the connection part of an original fabric film. The graph which shows the relationship between a draw ratio and R / L. The graph which shows the relationship between a draw ratio and A / B.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Original fabric film, 1a ... Back end side of original fabric film, 1b ... Front end side of original fabric film, 2 ... Stretching device, 7 ... Nip part, 30 ... Connection Part

Claims (6)

A nip portion for gripping the fed belt-like film is arranged at an interval, and a stretching apparatus configured to stretch the belt-like film in the longitudinal direction within the gap is provided with a belt-like original film from the tip side. By feeding and connecting the rear end side of the original film and the front side of the next original film by heat sealing, the original film is successively sent to the stretching device. A method of producing an optical film to be stretched,
Before the connecting portion between the rear end side of the original film and the leading end side of the next original film is fed into the stretching device, both sides of the region including the connecting portion are cut in an arc shape, and the cut region A method for producing an optical film, wherein the length R in the longitudinal direction is 90 to 105% of the gap L between the nip portions.   The manufacturing method of the optical film of Claim 1 which makes the width | variety of the connection part after cut | disconnect 50 to 70% of the original fabric width | variety.   The method for producing an optical film according to claim 1, wherein the original film is a polyvinyl alcohol-based original film.   The optical film manufactured by the manufacturing method of the optical film in any one of Claims 1 thru | or 3.   A liquid crystal display device comprising the optical film according to claim 4.   An image display device comprising the optical film according to claim 4.

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