JP2018089986A - Method for producing stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a slit-processed stretched film obtained by laterally stretching an original film while gripping both edges of the original film in the width direction by using clips, and then slitting both edges of the stretched film in the width direction, thereby a long film having uniform width can be produced.SOLUTION: The method for producing a stretched film comprises: a first step of stretching a thermoplastic resin film at least to the width direction while gripping both edges of the thermoplastic resin film in the width direction by using clips to obtain a stretched film; a second step of slitting both edges of the stretched film in the width direction and then passing the slit-processed stretched film through a driving roll; and a third step of further slitting both edges of the stretched film in the width direction after passing thereof through the driving roll.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a stretched film, and more particularly to a method for producing a stretched film slit by slitting both ends in the width direction after stretching (lateral stretching) in the film width direction.

  In an image display device such as a liquid crystal display device, there are various optical films made of a thermoplastic resin such as a polarizer, a protective film for a polarizer, an optical compensation film (such as a retardation film), an antiglare film, and an antireflection film. It is used. Some of these optical films have been subjected to stretching treatment (lateral stretching) in the film width direction in order to increase the toughness of the film or to impart desired optical properties, for example.

  In general, the lateral stretching of the film is carried out by grasping both end portions in the film width direction with clips and supplying them to a tenter or the like. Both ends in the width direction of the laterally stretched film are usually slits to remove the unstretched portion because it was held by a clip during stretching, or to adjust the film width to a desired size. (Trimming) and removed to form an optical film (for example, Patent Documents 1 and 2).

JP 2006-272616 A JP 2010-036414 A

  The film immediately after being laterally stretched by gripping both ends in the width direction with the clip, while the both end portions held by the clip remain thick, the stretched portion is thin. Wrinkles are generated at both ends in the direction and in the vicinity thereof (both end portions gripped by the clip and the inner region adjacent thereto). Moreover, since this thickness difference is not uniform in the film conveyance direction, it has been found that the film causes meandering of the film in the process from being stretched to being wound up. Then, if both ends of the stretched film are slit in a state where such wrinkles and meandering are generated, the wrinkles affect the width of the film after slitting, and the film width does not become uniform over the length direction. It became clear that this occurred.

  An object of the present invention is a method for producing a stretched film slitted by gripping both ends in the width direction with clips and stretching in the film width direction (lateral stretching) and then slitting the both ends in the width direction. Another object of the present invention is to provide a method capable of producing a long film having a wide width.

In order to achieve the above object, the present invention provides a method for producing a stretched film shown below.
[1] A first step of obtaining a stretched film by gripping both ends in the width direction of the thermoplastic resin film with a clip and stretching it at least in the width direction;
After slitting both ends in the width direction of the stretched film, the second step of passing the drive roll,
A third step of further slitting both ends in the width direction of the stretched film after passing through the drive roll;
A method for producing a stretched film.

  [2] The manufacturing method according to [1], wherein in the third step, both widthwise ends are slit in a state where tension is applied to the stretched film after passing through the drive roll.

  [3] The manufacturing method according to [1] or [2], further including a step of winding the stretched film after the third step by a winding device.

  [4] The manufacturing method according to any one of [1] to [3], further including a step of bonding a masking film to the stretched film before the third step.

  [5] The manufacturing method according to any one of [1] to [4], wherein a stretching ratio in the width direction is 1.5 times or more in the first step.

  [6] The manufacturing method according to any one of [1] to [5], wherein the stretched film obtained in the first step has a thickness of a central portion in the width direction of 100 μm or less.

  [7] The production method according to any one of [1] to [6], wherein the thermoplastic resin constituting the thermoplastic resin film is a (meth) acrylic resin or a polystyrene resin.

  According to the method of the present invention, a long slit processed stretched film having a uniform width can be continuously produced.

The present invention is described in detail below.
(1) First Step This step is a step of obtaining a stretched film by gripping both ends of the thermoplastic resin film in the width direction with clips and stretching (laterally stretching) at least in the width direction. Preferably, the thermoplastic resin film is a long film. A long film refers to a film having a length in the film transport direction of 100 m or more. In this case, the thermoplastic resin film is continuously drawn from, for example, a feeding device and continuously conveyed along a conveyance path constructed by a guide roll, a drive roll, etc., and a stretching treatment zone in which a stretching device is arranged. A stretching process is performed at.

  Although there is no restriction | limiting in particular in the kind of resin which comprises a thermoplastic resin film, Since it is preferable that the slit process stretched film obtained by the method of this invention is used as an optical film as illustrated above, an optical film is used. A thermoplastic resin that can be configured is preferred.

  Specifically, the thermoplastic resin film is preferably a thermoplastic resin film having translucency (preferably optically transparent). Specific examples of thermoplastic resins include chain polyolefin resins, cyclic polyolefin resins (such as norbornene resins), polyolefin resins such as polyethylene resins and polypropylene resins; polyester resins such as polyethylene terephthalate; methacrylic acid (Meth) acrylic resins such as methyl resins; cellulose resins such as cellulose triacetate and cellulose diacetate; polycarbonate resins; polyvinyl alcohol resins; polyvinyl acetate resins; polyarylate resins; Polyether sulfone resin; Polysulfone resin; Polyamide resin; Polyimide resin; and mixtures and copolymers thereof.

  In particular, when the thermoplastic resin film is made of a (meth) acrylic resin or polystyrene resin, the toughness of the portion gripped by the clip is low, and this portion on the guide roll becomes difficult when a high transport tension is applied to the film. Since it is easy to break, it is difficult to carry the film immediately after stretching at high tension. Therefore, wrinkles are easily generated in the film immediately after stretching, and the merit of applying the method of the present invention is great.

  The thickness of the thermoplastic resin film is, for example, about 30 to 400 μm, and preferably 50 to 200 μm.

  A tenter method may be used as a method of gripping both ends in the width direction with clips and extending at least in the width direction. The tenter method is a method in which both ends in the film width direction are fixed with clips (chucks) and stretched in an oven while widening the interval between the clips in the lateral direction.

  The stretching treatment in this step is not limited to only transverse stretching, and may be simultaneous biaxial stretching in which stretching or shrinking is performed simultaneously in the longitudinal direction (film length direction). Simultaneous biaxial stretching can be performed by expanding and contracting in the longitudinal direction while expanding the clip interval in the lateral direction in the tenter method.

  A stretching machine (tenter stretching machine) used for the tenter method usually has a zone for performing a preheating step, a zone for performing a stretching step, and a zone for performing a heat setting step, and a mechanism capable of independently adjusting the temperature of each zone. It has.

  A preheating process is a process provided before the process of extending | stretching a thermoplastic resin film, and is a process of heating to temperature sufficient to extend | stretch a thermoplastic resin film. The preheating temperature in the preheating step can be about T-10 ° C. to T + 50 ° C., where T is the phase transition temperature (glass transition temperature or melting point) of the resin constituting the thermoplastic resin film.

The stretching step is a step of stretching the thermoplastic resin film at least in the width direction. The stretching temperature in the stretching step can be about T-10 ° C to T + 50 ° C. The draw ratio in the width direction is, for example, 1.2 to 4 times, and preferably 1.5 to 3 times. The larger the draw ratio is, the greater the difference in thickness between the portion where the film is gripped and the portion where the film is not gripped. Even if it is 5 times or more, and even 2 times or more, a slit processed stretched film having a uniform width can be obtained. The draw ratio is the following formula:
Stretch ratio (times) = (Length after stretching) / (Length before stretching)
More demanded. The length here means the film width in the case of transverse stretching.

  The heat setting step is a step of passing the film through a zone at a predetermined temperature in the oven while maintaining the film width at the end of the stretching step. In the heat setting step, the film may be passed through a predetermined temperature zone in the oven while narrowing the film width from the end of the stretching step. The shrinkage width of the film in the heat setting step can be, for example, 15% or less, more preferably 5% or less. The heat setting temperature can be the same as or lower than the stretching temperature.

  The thickness of the stretched film obtained at this process is the thickness of the center part of the width direction, for example, is about 5-200 micrometers, Preferably it is 10-150 micrometers, More preferably, it is 20-100 micrometers. There is a tendency that wrinkles are more likely to occur in the above-described portion as the thickness of the stretched portion is smaller. However, according to the present invention, even if the thickness of the central portion in the width direction is 100 μm or less, and even 80 μm or less, it is uniform. A slit processed stretched film having a width can be obtained.

(2) Second Step In this step, first, the obtained stretched film is released from the clip, and preferably slits and removes both ends in the width direction while continuously transporting along the transport path. A shear cutter (shear cutter) can be suitably used for the slit.

  The method of the present invention performs slit processing twice (this step and a third step described later) to obtain a slit processed stretched film having a desired width, so both ends to be slit in this step The width (slit width) is such a width that the stretched film after slit processing does not reach the desired width, but at least the portion where the thickness remains larger than the stretched portion, that is, at least Both ends in the width direction held by the clip are slit in this step.

  You may make it wind up sequentially the slit edge part produced | generated by continuously slitting the both ends while conveying a elongate stretched film continuously using a winding device. In this case, in order to stably convey and wind up the long end portion, the slit width is preferably 30 mm or more and 300 mm or less per one end portion, and is preferably 35 mm or more and 200 mm or less per one end portion. More preferred. By setting the slit width to 35 mm or more and 200 mm or less per one end portion, when applying tension to the end portion slit from the winding device, the tension can be uniformly applied to the width direction of the end portion, and this is stabilized. There is a tendency to be able to transport it.

  Similarly, in the second slit processing in the third step, which will be described later, when transporting and winding the slit ends, the slit widths at both ends in this step are The film width after slitting is adjusted to be preferably 60 mm to 600 mm, more preferably 70 mm to 400 mm wider than the final desired film width (film width after the second slit processing).

  In order to keep the slit width as constant as possible, the transport speed of the stretched film during slit processing is preferably 2 to 20 m / min, and more preferably 3 to 15 m / min. For the same reason, the film conveyance speed is preferably as constant as possible during the slit processing, and the variation in the conveyance speed during the slit processing is preferably within a range of ± 1%. The transport speed of the stretched film can be measured with a tachometer or a laser Doppler non-contact tachometer through a rotary encoder.

  Further, the tension applied to the stretched film during slit processing is preferably 5 N / m to 200 N / m, and more preferably 30 N / m to 120 N / m, in order to keep the slit width as constant as possible. . For the same reason, the tension is preferably as constant as possible during slit processing, and more preferably within a range of ± 5%. The tension can be measured by a method of detecting with a load cell attached to the tension pickup roll, a method of calculating the tension from the displacement of the roll, or the like. In the present invention, as will be described later, a driving roll is installed on the downstream side of the slitting process. Therefore, by adjusting the rotational speed of the driving roll, the film conveyance speed and tension during slit processing are maintained at desired values. Control can be easily performed. Alternatively, a dancer roll may be disposed in the vicinity of the drive roll, and the tension may be adjusted by applying pressure to the film via the dancer roll.

  Next, the stretched film subjected to slit processing passes through a drive roll disposed on the downstream side of the slit process in the transport path. The stretched film after the slit processing is more likely to wrinkle during conveyance as the stretched portion has a smaller thickness, but the wrinkle can be eliminated by applying the above tension using a drive roll, A slit processed stretched film having a uniform width can be obtained by the subsequent third step. A plurality of drive rolls may be installed between the slit process in the second step and a third slit process to be described later.

  The drive roll is a roll that can be controlled to rotate, with a drive source connected directly or indirectly, and is a rotatable roll that can apply a driving force for film conveyance and tension to the film to be conveyed. . The drive roll in this invention has the function to control the tension | tensile_strength of the film of the upstream and / or downstream on the conveyance path | route of this drive roll. For example, a drive roll can be used for at least one of a pair of nip rolls that can press the film from above and below. The rotation of the nip roll can be a driving force for film conveyance. By adjusting the rotation speed of the drive roll in the nip roll, it is possible to control the film conveyance speed and the tension applied to the film.

  In addition to the nip roll, a drive roll having a large film holding angle can be used alone to control the tension of the film upstream and / or downstream of the drive roll.

  Another example of the drive roll is a bonding roll. The bonding roll is also composed of a pair of rotatable rolls like the nip roll, but the film is formed by passing a plurality of films (for example, with an adhesive interposed) between the pair of rolls and pressing from above and below. Used for pasting. A drive roll can be used for at least one of the bonding rolls formed of such a pair of rolls. The rotation of the laminating roll can also be a driving force for film conveyance, and the film conveyance speed and the tension applied to the film can be controlled by adjusting the rotation speed.

  Further, a suction roll (suction roll) capable of rotation control can be used as the drive roll. The suction roll has a large number of suction holes formed on the outer peripheral surface, and is a rotatable roll capable of adsorbing a film that contacts the outer peripheral surface by sucking air from the suction holes. Unlike nip rolls and laminating rolls, suction rolls support only one side of the passing film, but the above-mentioned adsorption prevents slipping between the film and the roll, so it absorbs the rotational driving force of the roll. The film can be conveyed while applying tension to the film.

  On the other hand, guide rolls (also referred to as free rolls) that simply support the traveling film and cannot apply a driving force for film transport or tension to the film are not included in the driving rolls. Even if the guide roll is passed after the slitting process, it is difficult to eliminate wrinkles, and the film width varies in the slit process in the subsequent third process.

(3) Third Step This step is a step of further slitting and removing both ends in the width direction of the stretched film after passing through the drive roll, preferably while continuously transporting along the transport path. By this step, a slit processed stretched film having a desired width is obtained. A shear cutter can be suitably used for the slit. When manufacturing a slit processed stretched film by sequentially carrying out the first to third steps while continuously transporting a long thermoplastic resin film, the obtained slit processed stretched film is usually sequentially processed by a winding device. Wind up to make a film roll.

  According to the slit processing of this step performed on the downstream side of the drive roll, the wrinkles are eliminated due to pressing or suction by the drive roll or further tension on the film applied by the drive roll. Therefore, a long slit stretched film having a uniform width can be continuously produced.

  In this step, slitting is preferably performed while tension is applied to the stretched film during slit processing (after passing through the drive roll). Such tension is applied by, for example, the drive roll and the winding device. More specifically, it can be applied by a nip roll including a driving roll and the winding device. It is also possible to control the tension between the nip roll including the drive roll and the winding device by controlling the torque of the powder clutch disposed in the winding device. However, the present invention is not limited thereto, and another drive roll is provided on the downstream side of the drive roll and upstream of the winding device, tension is applied by these drive rolls, and slit processing is performed between these drive rolls. You may make it perform.

  The tension applied to the stretched film at the time of slitting is preferably 5 N / m to 120 N / m, and preferably 30 N / m to 100 N in order to keep the slit width as constant as possible and obtain a stretched film having a uniform width as much as possible. / M is more preferable. For the same reason, the tension is preferably as constant as possible during slitting.

  Moreover, it is preferable to set the conveyance speed of the stretched film at the time of slit processing as 3-20 m / min, in order to keep the slit width as constant as possible and to obtain a stretched film with a uniform width as much as possible, and 5-15 m / min. It is more preferable. For the same reason, the film conveyance speed is preferably as constant as possible during the slit processing, and the variation in the conveyance speed during the slit processing is preferably within a range of ± 1%. The film conveyance speed and tension at the time of slit processing can be easily controlled by the rotation speed of the drive roll or the winding device.

  An accumulator may be installed on the upstream side of the winding device in the transport path. The accumulator is a device for temporarily stopping the film conveyance on the downstream side by accumulating the conveyed film. When such an accumulator is installed, the slit processing in this step is performed on the upstream side of the accumulator.

(4) Other steps [a] Longitudinal stretching step The thermoplastic resin film used in the first step may be subjected to a longitudinal stretching treatment in the film length direction prior to the first step. The longitudinal stretching process includes stretching between rolls in which longitudinal stretching is performed by a difference in peripheral speed between the two nip rolls while passing through an oven between two nip rolls installed at a distance, and heat whose surface is heated. A heat roll that performs longitudinal stretching in a heated state caused by contact with the heat roll by passing between the roll and a guide roll having a different peripheral speed (or a heat roll). Examples include stretching, compression stretching, and stretching using a clip.

  Also in the longitudinal stretching treatment, a preheating step and a heat setting step can be provided as in the transverse stretching treatment. The draw ratio of longitudinal stretching is not particularly limited, and is, for example, 1.2 to 4 times, preferably 1.5 to 3 times.

[B] Winding step As described above, it is usually obtained when a slit processed stretched film is produced by sequentially performing the first to third steps while continuously conveying a long thermoplastic resin film. The slit processed stretched film is sequentially wound by a winding device to form a film roll. Since the obtained film roll has a uniform film width over the length direction, the end faces are uniform and the appearance is excellent.

[C] Bonding process Before the 3rd process, you may provide the process of bonding a masking film to a stretched film. The masking film is also called a protective film or a surface protective film, and is a film for protecting the surface of the stretched film.

  The masking film is usually configured by providing an adhesive layer on one side of a film made of a thermoplastic resin. A masking film is bonded to the surface of the stretched film through this adhesive layer. The thermoplastic resin can be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, a polyester resin such as polyethylene terephthalate or polyethylene naphthalate, and the like.

  Bonding of the masking film can reduce wrinkles during conveyance by increasing the thickness by bonding the masking film to the stretched film or by applying high tension to the stretched film. For this reason, it is preferable to carry out the process upstream of the slit in the third step. In this case, in order to bond a masking film, it is possible to use at least one of the bonding rolls as the drive roll.

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

<Example 1>
Pellets of methyl methacrylate / methyl acrylate (weight ratio 94/6) having a glass transition temperature Tg of 108 ° C. were put into an extruder and extruded from a T-die having a set temperature of 270 ° C. Both sides of the extruded film-like molten resin were sandwiched and cooled by a pair of polishing rolls set at a temperature of 110 ° C. to obtain a long unstretched film having a thickness of 120 μm and a width of 1000 mm as a film roll.

  Subsequently, the unstretched film is continuously fed from the film roll while being conveyed, and a preheating zone (preheating temperature: 110 ° C.), a stretching zone (stretching between rolls, stretching temperature: 120 ° C.), a heat setting zone (heat fixing temperature: 120). C.) was passed in order to obtain a long longitudinally stretched film having a thickness (thickness in the center in the width direction) of 93 μm and a width of 720 mm as a film roll. The draw ratio of this longitudinal drawing was 1.8 times.

  Next, a longitudinally stretched film is continuously fed from a film roll, and a preheating zone (preheating temperature: 120 ° C.), a stretching zone (stretching temperature: 120 ° C.), and a heat setting zone (heat setting temperature: 120 ° C.) are provided. The film was sequentially passed to obtain a continuous biaxially stretched film having a thickness (thickness at the center in the width direction) of 45 μm and a width of 1400 mm. The lateral stretching in the stretching zone was performed by holding a 20 mm portion from both ends in the width direction of the film with a clip and supplying it to a tenter stretching machine to widen the clip interval in the lateral direction. The draw ratio of this transverse drawing was 2.0 times.

  While continuously feeding the obtained sequentially biaxially stretched film, both ends of the film were slit with a width of 50 mm using a shear cutter, and the film width was trimmed to 1300 mm. The film conveyance speed and tension during slit processing were 3 m / min and 80 N / m, respectively.

  The successively biaxially stretched film after slit processing is continuously conveyed and passed through a nip roll (one roll is a drive roll. The same applies to Example 2), and then both ends of the film are passed through. Each film was slit using a shear cutter with a width of 150 mm, the film width was trimmed to 1000 mm, and wound up with a winder to obtain a film roll. The conveyance speed and tension of the film during slit processing were 3 m / min and 100 N / m, respectively.

  When the end surface of the obtained film roll was observed, it was flat without any particularly protruding portion, and the entire end surface was evenly aligned within a range of about ± 0.5 mm.

<Example 2>
"Tretech" is a self-adhesive protective film when the biaxially stretched film is passed through the nip roll sequentially after the first slitting process and then the biaxially stretched film is passed through the laminating roll before the second slitting process. A film roll made of a sequential biaxially stretched film with a masking film was obtained in the same manner as in Example 1 except that (Toray Film Processing Co., Ltd.) was passed through the sequentially biaxially stretched film. When the end surface of the obtained film roll was observed, it was flat without any particularly protruding portion, and the entire end surface was evenly aligned within a range of about ± 0.5 mm.

<Comparative Example 1>
After sequentially producing biaxially stretched films in the same manner as in Example 1, both ends of the film were slit using a shear cutter with a width of 200 mm, respectively, and the film width was trimmed to 1000 mm. The film conveyance speed and tension during slit processing were 3 m / min and 80 N / m, respectively. The sequentially biaxially stretched film after the slit processing was wound as it was with a winder without passing through the nip roll and without performing the second slit processing to obtain a film roll. When the end surface of the obtained film roll was observed, the part which was not uniformly arrange | positioned but protruded 1 mm or more was recognized.

Claims (5)

A first step of obtaining a stretched film by gripping at both ends in the width direction of the thermoplastic resin film with a clip and stretching in the width direction;
After slitting both ends of the stretched film in the width direction while continuously transporting the stretched film, the second step of continuously transporting the slit stretched film and passing the drive roll;
A third step of further slitting both ends in the width direction of the stretched film after passing through the drive roll while continuously transporting the stretched film after passing through the drive roll;
Including
The manufacturing method of a stretched film whose thickness of the center part of the width direction in the stretched film obtained at the said 1st process is 100 micrometers or less.   The manufacturing method according to claim 1, wherein in the third step, both widthwise ends are slit in a state where tension is applied to the stretched film after passing through the drive roll.   The manufacturing method according to claim 1 or 2, further comprising a step of winding the stretched film after the third step by a winding device.   The manufacturing method of any one of Claims 1-3 which further includes the process of bonding a masking film to a stretched film before the said 3rd process.   The manufacturing method of any one of Claims 1-4 whose draw ratio in the width direction is 1.5 times or more in the said 1st process.