KR20160125396A - Stretched film manufacturing method - Google Patents

Abstract

The present invention relates to a thermoplastic resin film comprising a first step of holding a thermoplastic resin film in a width direction at both ends in a width direction and stretching the thermoplastic resin film at least in a width direction to obtain a stretched film, a second step of slitting both widthwise ends of the stretched film, And a third step of further slitting both end portions in the width direction of the stretched film after passing through the drive roll.

Description

STRETCHED FILM MANUFACTURING METHOD [0002]

The present invention relates to a method for producing a stretched film, and more particularly, to a method for producing a stretched film that is slit-processed by stretching both transverse direction ends after stretching in the film width direction.

BACKGROUND ART Various optical films made of a thermoplastic resin such as a polarizer, a protective film for a polarizer, an optical compensation film (a retardation film and the like), an antiglare film, an antireflection film and the like are used for an image display apparatus such as a liquid crystal display. Some of these optical films are subjected to stretching treatment (transverse stretching) in the film width direction, for example, to increase the toughness of the film or to impart desired optical characteristics.

The transverse stretching of the film is generally carried out by gripping both ends of the film in the width direction and supplying the film to a tenter or the like. Since the widthwise both ends of the transversely stretched film are normally grasped by a clip at the time of stretching, in order to remove the unstretched portion or to adjust the film width to a desired size, And is removed to give an optical film (for example, Japanese Unexamined Patent Application Publication No. 2006-272616 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2010-036414 (Patent Document 2)).

Patent Document 1: Japanese Patent Application Laid-Open No. 2006-272616 Patent Document 2: Japanese Patent Application Laid-Open No. 2010-036414

The film immediately after transversely stretched by holding both ends in the width direction in the transverse direction is thick at both ends held by the clip while the stretched portion is thinned by the difference in thickness, Wrinkles are generated in both end portions gripped and inner regions adjacent to these portions). In addition, since the thickness difference is not uniform throughout the film transport direction, it is found that the film thickness is a factor of meandering of the film in the process from the stretching to the winding. If the both ends of the stretched film are slit while the wrinkles or serpentine are generated, the wrinkles may affect the width of the film after the slit is not uniform in the longitudinal direction, It became clear.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a slit-processed stretched film by stretching both transverse direction end portions in a film width direction (transverse stretching) and then slitting both end portions in the transverse direction, ) Of the film of the present invention.

Means for Solving the Problems In order to achieve the above object, the present invention provides a process for producing a stretched film described below.

 [1] A method for producing a stretched film, comprising: a first step of holding a thermoplastic resin film at both ends in a width direction thereof with a clip and stretching the film at least in a width direction,

A second step of slitting both end portions in the width direction of the stretched film and then passing the driving roll,

A third step of further slitting both end portions in the width direction of the stretched film after passing through the drive roll

To form a stretched film.

[2] The manufacturing method according to [1], wherein in the third step, both ends in the width direction are slit while tensile force is applied to the stretched film after passing through the driving roll.

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

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

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

[6] The production method according to any one of [1] to [5], wherein the stretched film obtained in the first step has a thickness in the width direction central portion of 100 m 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, it is possible to continuously produce an elongated slit-processed stretched film having a uniform width.

Hereinafter, the present invention will be described in detail.

(1) First step

The present step is a step of holding both ends of the thermoplastic resin film in the width direction with a clip and stretching at least in the width direction (transverse stretching) to obtain a stretched film. Preferably, the thermoplastic resin film is a long film. The term " long film " refers to a film having a length of at least 100 m in the film transport direction. In this case, the thermoplastic resin film is continuously fed from a feeding device, continuously fed along a conveyance path constructed by a guide roll, a driving roll, or the like, and is subjected to a stretching process in a stretching process zone where the stretching device is disposed .

The type of the resin constituting the thermoplastic resin film is not particularly limited, but it is preferable that the slit stretched film obtained by the method of the present invention is used as the optical film as exemplified above. Therefore, It is preferably a thermoplastic resin.

Specifically, the thermoplastic resin film is preferably a thermoplastic resin film having translucency (preferably optically transparent). Specific examples of the thermoplastic resin include polyolefin resins such as a chain polyolefin resin, a cyclic polyolefin resin (norbornene resin and the like), a polyethylene resin and a polypropylene resin; Polyester-based resins such as polyethylene terephthalate; (Meth) acrylic resins such as methyl methacrylate resins; Cellulosic resins such as cellulose triacetate and cellulose diacetate; Polycarbonate resin; Polyvinyl alcohol-based resin; Polyvinyl acetate resin; Polyarylate resins; Polystyrene type resin; Polyether sulfone type resin; Polysulfone resins; Polyamide based resin; Polyimide resin; And mixtures and copolymers thereof.

In the present specification, the term " (meth) acryl " means at least one selected from acrylic and methacrylic.

In particular, when the thermoplastic resin film is composed of a (meth) acrylic resin or a polystyrene resin, since the toughness of the portion gripped by the clip is low and a high transporting tension is applied to the film, It is difficult to carry the film immediately after it with a high tension force. Therefore, wrinkles easily occur in the film immediately after stretching, and the merit of applying the method of the present invention is large.

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

As a method of holding both ends in the width direction with a clip and drawing at least in the width direction, a tenter method can be mentioned. The tenter method is a method in which both ends of the film in the width direction are fixed with clips (chucks), and the intervals between the clips are extended in the transverse direction while stretching in an oven.

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

The stretching machine (tenter stretching machine) used in the tenter method usually has a zone for performing a preheating process, a zone for performing a stretching process, and a zone for performing a heat setting process, and a mechanism capable of independently controlling the temperature of each zone Respectively.

The preheating step is a step provided prior to the step of stretching the thermoplastic resin film, and is a step of heating to a temperature sufficient for stretching the thermoplastic resin film. The preheating temperature in the preheating step may be about T-10 占 폚 to T + 50 占 폚, 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 may be about T-10 占 폚 to T + 50 占 폚. The draw ratio in the width direction is, for example, 1.2 to 4 times, preferably 1.5 to 3 times. The larger the stretch 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. As a result, wrinkles tend to occur in the above-mentioned portion. However, according to the present invention, the stretch ratio is 1.5 times or more, A slit-processed stretched film having a uniform width can be obtained. The stretching magnification is calculated by the following formula:

   Drawing magnification (times) = (length after stretching) / (length before stretching)

. The length referred to herein means the film width in the case of transverse stretching.

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

The thickness of the stretched film obtained in this step is, for example, about 5 to 200 占 퐉, preferably 10 to 150 占 퐉, more preferably 20 to 100 占 퐉 in terms of the thickness at the center in the width direction. The thickness of the elongated portion tends to be more likely to be wrinkled in the above-mentioned portion. However, according to the present invention, even if the thickness in the widthwise central portion is 100 mu m or less, or even 80 mu m or less, A processed stretched film can be obtained.

(2) Second step

In the present step, the obtained stretched film is released from the clip, and preferably, both ends in the width direction are slit and removed while continuously conveying along the conveying path. For the slit, a shear cutter may suitably be used.

The method of the present invention is to obtain a slit-processed stretched film having a desired width by performing a slit process twice (the main process and the third process described below) in total, so that the width (slit width) , The portion of the stretched film after the slit processing is not wide enough to reach a desired width but the portion of the film which is thicker than at least the stretched portion, that is, at least both ends in the width direction gripped by the clip, do.

The slit end portions generated by successively slitting the both end portions of the elongated stretched film while continuously transporting them may be sequentially wound by using a winding device. In this case, in order to stably carry and wind the long end, the slit width is preferably 30 mm or more and 300 mm or less per one end, and more preferably 35 mm or more and 200 mm or less per one end . By setting the slit width to 35 mm or more and 200 mm or less per one end, when tension is applied to the slitted end portion from the winding device, it is possible to uniformly apply a tension to the width direction of the end portion, There is a tendency.

Likewise, in carrying out the second slit processing in the third step to be described later and carrying and winding the slit end, in order to facilitate this, in order to facilitate this, the slit width at both end portions in the present step is set to be the film width 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 transporting speed of the stretched film at the time of slit processing is preferably 2 to 20 m / min, more preferably 3 to 15 m / min. For the same reason, the film transport speed is preferably as constant as possible during slit processing, and the fluctuation of the transport speed during slit processing is preferably within a range of 1%. The conveying speed of the stretched film can be measured by a tachometer through a rotary encoder, a laser Doppler type non-contact tachometer or the like.

The tension applied to the stretched film at the time of slit processing is preferably 5 N / m to 200 N / m and preferably 30 N / m to 120 N / m to maintain the slit width as constant as possible . For the same reason, the tension is preferably as constant as possible during slit processing, more preferably within a range of 5%. The tension can be measured by a method of detecting by a load cell associated with the tension pickup roll or by a method of calculating the tension from the displacement of the roll. In the present invention, since the drive roll is provided on the downstream side of the slit process as described later, by controlling the rotation speed of the drive roll, the control for maintaining the film transport speed and the tension at the slit processing at a desired value Can be easily performed. Further, a dancer roll may be disposed in the vicinity of the drive roll, and the tension may be adjusted by pressing it on the film through the dancer roll.

Subsequently, the slit-processed stretched film passes through a driving roll disposed on the downstream side of the slit process in the conveying path. The stretched film after the slit processing is liable to cause wrinkles to occur during conveyance as the thickness of the stretched portion becomes smaller. However, wrinkles can be removed by applying the above tension using a driving roll, A slit-processed stretched film having a uniform width can be obtained. A plurality of drive rolls may be provided between the slit processing of the second step and the third slit processing path described later.

The driving roll is a rotatable roll that is directly or indirectly connected to a driving source, and is a rotatable roll capable of imparting a driving force for film transportation and a tension to the film to be transported. The drive roll in the present invention has a function of controlling the tension of the film on the upstream and / or downstream side on the transport path of the drive roll. For example, a drive roll can be used for at least one of the pair of nip rolls capable of pressing the film from above and below. The rotation of the nip roll can be the driving force of the film transportation. It is possible to control the film conveying speed and the tension applied to the film by adjusting the rotation speed of the drive roll in the nip roll.

Further, in addition to the nip roll, the tension of the film on the upstream side and / or the downstream side of the driving roll may be controlled by using a single driving roll having a large holding angle of the film.

Another example of a driving roll is a bonding roll. The joining roll is also composed of a pair of rolls rotatable in the same manner as the nip roll. The joining rolls are used for passing a plurality of films between a pair of rolls (for example, with an adhesive interposed therebetween) and pressing them from above and below. A driving roll may be used for at least one of the pair of rolls. The bonding roll can also be a driving force for film transportation, and the film transport speed and the tension applied to the film can be controlled by adjusting the rotation speed of the bonding roll.

As the drive roll, a suction roll (suction roll) capable of rotation control can also be used. The suction roll is a rotatable roll capable of sucking a film in contact with the outer circumferential surface by sucking air from the suction hole and forming a large number of suction holes on the outer circumferential surface. Unlike the nip roll or the bonding roll, the suction roll supports only one side of the film to be passed. Since the film and the roll can be prevented from slipping by the adsorption, the rotational driving force of the roll can be transferred to the adsorbed film , Whereby the film can be transported while applying tension to the film.

On the other hand, a guide roll (also referred to as a pre-roll) that does not merely support a running film and can not impart a driving force for film transportation or tension to the film is not included in the driving roll. Even after passing through the guide roll after the slitting process, it is difficult to eliminate the wrinkles, and the film width varies in the slitting process in the subsequent third process.

(3) Third step

The present step is preferably a step of continuously slitting and removing both ends in the transverse direction of the stretched film after passing through the drive roll, while continuously transporting along the transport path. By this step, a slit-processed stretched film having a desired width can be obtained. A sheer cutter can be suitably used for the slit. In the case where the slit processing stretched film is produced by successively carrying out the first to third steps while continuously transporting the elongated thermoplastic resin film, the slit stretched film thus obtained is usually wound in turn by a winding device to form a film roll.

According to the slit process of the present step performed on the downstream side of the drive roll, since the wrinkles are relieved due to the pressing or sucking by the drive roll or the tension applied to the film by the drive roll, A long slit-processed stretched film having a uniform width can be continuously produced.

In this step, slit processing is preferably performed in the state that a tension is applied to the stretched film at the time of slit processing (after passing the drive roll). Such a tension can be applied, for example, by the drive roll and the winding apparatus , More specifically, it can be applied by the nip roll including the driving roll and the winding device. By controlling the torque of the powder clutch disposed in the winding device, it is also possible to control the tension between the nip roll including the driving roll and the winding device. However, the present invention is not limited to these, and a separate driving roll may be provided on the downstream side of the driving roll and on the upstream side of the winding device, tension may be applied by these driving rolls, and slit processing may be performed between these driving rolls .

The tension applied to the stretched film at the time of slit processing is preferably 5 N / m to 120 N / m in order to keep the slit width as constant as possible and to obtain a stretched film as uniform as possible, And more preferably N / m to 100 N / m. Also for the same reason, it is preferable that the tension be as constant as possible during slit processing.

The transporting speed of the stretched film at the time of slit processing is preferably 3 to 20 m / min, preferably 5 to 15 m / min, in order to keep the slit width as constant as possible and to obtain a stretched film of as uniform width as possible. / Min is more preferable. For the same reason, the film transport speed is preferably as constant as possible during slit processing, and the fluctuation of the transport speed during slit processing is preferably within a range of 1%. The film conveying speed and tension at the time of slit processing can be easily controlled by the rotation speed of the driving roll or the winding device.

An accumulator may be provided on the upstream side of the winding device in the conveying path. The accumulator is a device for temporarily stopping the transport of the film on the downstream side by accumulating the transported film. In the case of installing such an accumulator, slitting of the present step is performed on the upstream side of the accumulator.

(4) Other processes

[A] longitudinal stretching process

The thermoplastic resin film provided in the first step may be longitudinally stretched in the longitudinal direction of the film prior to the first step. As the longitudinal stretching treatment, roll stretching in which longitudinal stretching is performed by a difference in peripheral velocity between the two nip rolls while passing through an oven between two nip rolls provided at a distance, For example, thermal roll stretching, longitudinal stretching, compression stretching, and stretching using a clip, which are subjected to longitudinal stretching under a heating condition caused by contact with a hot roll, by passing between a guide roll (or thermal roll)

Also in the longitudinal stretching process, the preheating process and the heat setting process can be provided similarly to the transverse stretching process. The stretching magnification of longitudinal stretching is not particularly limited and is, for example, 1.2 to 4 times, preferably 1.5 to 3 times.

[B] Coiling process

As described above, when the elongated thermoplastic resin film is continuously conveyed and the first to third steps are sequentially performed to produce a slit-stretched film, the slit-stretched film thus obtained is usually wound by a winding device in succession, Roll. The obtained film rolls have uniform end faces because the film width is uniform over the lengthwise direction, and the appearance is excellent.

[C] Bonding process

Before the third step, a step of bonding a masking film to the stretched film may be provided. 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 constituted by forming a pressure-sensitive adhesive layer on one side of a film made of a thermoplastic resin. The masking film is bonded to the surface of the stretched film through the adhesive layer. The thermoplastic resin may be, for example, a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, or a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate.

The joining of the masking film can increase the thickness by joining the masking film to the stretched film, and it is possible to apply a high tension to the stretched film, so that wrinkles during conveyance can be reduced. Therefore, It is preferable to perform this operation on the upstream side. In this case, in order to bond the masking film, it is possible to use at least one of the bonding rolls as the driving roll.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

≪ Example 1 >

Pellets of methyl methacrylate / methyl acrylate (weight ratio 94/6) having a glass transition temperature Tg of 108 DEG C were fed into an extruder and extruded from a T-die at a set temperature of 270 DEG C. Both sides of the extruded film-form molten resin were sandwiched between a pair of polishing rolls set at a temperature of 110 占 폚 and cooled to obtain a long unoriented film having a thickness of 120 占 퐉 and a width of 1000 mm as a film roll.

Subsequently, the unstretched film was continuously conveyed from the film roll while being fed, and the film was continuously conveyed in a preheating zone (preheating temperature: 110 占 폚), a stretching zone (roll stretching, stretching temperature: 120 占 폚) ) To obtain a longitudinally stretched film having a thickness of 93 mu m and a width of 720 mm as a film roll (thickness in the width direction central portion). The stretching magnification of this longitudinal stretching was 1.8 times.

(Stretching temperature: 120 占 폚), heat-setting zone (heat-setting temperature: 120 占 폚) were successively transferred from the film roll in the order of To obtain a longitudinally stretched biaxially stretched film having a thickness (thickness in the width direction central portion) of 45 m and a width of 1400 mm. The transverse stretching in the stretching zone was carried out by gripping a portion of 20 mm from both ends in the transverse direction of the film with a clip and feeding it to a tenter stretching machine to widen the interval of the transverse direction in the transverse direction. The draw ratio of this transverse stretching was 2.0 times.

Both successive end portions of the film were slit with a shear cutter at a width of 50 mm each while continuously conveying the obtained continuous biaxially stretched film, and the film width was trimmed to 1300 mm. The transporting speed and the tension of the film at the time of slit processing were 3 m / min and 80 N / m, respectively.

After passing through the slit-processed continuous biaxially stretched film continuously, the film was passed through a nip roll (one roll was a drive roll, the same also in Example 2), and then the both ends of the film were each sheared at a width of 150 mm Slit using a cutter, trimmed to a film width of 1000 mm, and wound with a winder to obtain a film roll. The transporting speed and the tension of the film during the slit processing were 3 m / min and 100 N / m, respectively.

Observation of the end face of the obtained film roll revealed that it was flat without any protruding part, and the entire end face was uniformly in the range of about +/- 0.5 mm.

 ≪ Example 2 >

After passing through the nip roll after the first slit processing, the continuous biaxially stretched film was allowed to pass through the nip roll, and then passed through the bonding rolls before the second slit processing, the self-adhesive system protective film "Torretec" A film roll made of a sequential biaxially stretched film to which a masking film was adhered was obtained in the same manner as in Example 1 except that the film was passed over a continuous biaxially stretched film. Observation of the end face of the obtained film roll revealed that it was flat without any protruding part, and the entire end face was uniformly in the range of about +/- 0.5 mm.

≪ Comparative Example 1 &

After the continuous biaxially stretched film was produced in the same manner as in Example 1, both ends of the film were slit with a shear cutter each having a width of 200 mm, and the film width was trimmed to 1000 mm. The transporting speed and the tension of the film at the time of slit processing were 3 m / min and 80 N / m, respectively. The biaxially stretched film after the slit processing was wound on a take-up machine without passing through the nip roll and without being subjected to the second slit processing to form a film roll. As a result of observing the end faces of the obtained film roll, the portions which did not coincide uniformly and protruded by 1 mm or more were seen.

Claims (7)

A first step of holding both ends of the thermoplastic resin film in the width direction with a clip and stretching at least in the width direction to obtain a stretched film,
A second step of slitting both end portions in the width direction of the stretched film and then passing the driving roll,
A third step of further slitting both end portions in the width direction of the stretched film after passing through the drive roll
To form a stretched film. The manufacturing method according to claim 1, wherein, in the third step, both ends in the width direction are slit while tension is applied to the stretched film after passing through the driving roll. The 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 method according to any one of claims 1 to 3, further comprising a step of bonding a masking film to the stretched film before the third step. The production method according to any one of claims 1 to 4, wherein the stretching ratio in the width direction in the first step is 1.5 times or more. The production method according to any one of claims 1 to 5, wherein the thickness of the stretched film obtained in the first step in the width direction central portion is 100 占 퐉 or less. The production method according to any one of claims 1 to 6, wherein the thermoplastic resin constituting the thermoplastic resin film is a (meth) acrylic resin or a polystyrene resin.