JP2008137350A - Manufacturing method of film, film manufactured by this method, and retardation film manufactured by using this film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a manufacturing method for obtaining a film having a low thickness variation in a flow direction of the film and having a high thickness precision, and to provide a film manufactured by this method and a retardation film without thickness variation and/or variation in phase difference. <P>SOLUTION: In the manufacturing method of the film, melted thermoplastic resin is extruded from a T die 1 in a film shape, and supplied between a cooling roll 2 and a touch roll 3, and the film is manufactured by sandwiching and pressing with two rolls 2 and 3. The film 4 extruded from the T die is contacted with one of the rolls (the cooling roll 2) before sandwiching and pressing the film with two rolls 2 and 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film used for optical applications, display fields, and the like, and more specifically, a method for producing a film obtained by extrusion molding, a film produced by this method, and a retardation film produced using this film About.

  In recent years, a phase difference film is used for a liquid crystal display used in a large amount for a notebook computer, a mobile phone, an instrument of a car, a machine, and the like for the purpose of compensating for optical distortion resulting from the birefringence of the liquid crystal.

  In this retardation film, when the thickness accuracy of the film is poor, streaky color unevenness due to retardation unevenness occurs, which adversely affects the quality of the liquid crystal display, which is a serious problem.

  In particular, in a retardation film having a thickness of 50 μm or less, when the variation in retardation value of the retardation film is 0.7 nm / 5 mm or more, stripe-shaped color unevenness is easily recognized.

  In order to reduce such retardation unevenness, it is necessary to reduce the thickness unevenness of the retardation film, and for that purpose, a film having high thickness accuracy is formed in the extrusion process of the film that is the original film of the retardation film. It will be necessary.

  Therefore, as a method for producing a film used as a raw material for a retardation film, a method of forming a film by sandwiching a film with two rolls when an amorphous thermoplastic resin is formed by a melt extrusion method has been conventionally used. (For example, refer to Patent Document 1 and Patent Document 2).

In the film manufacturing methods described in these prior art documents, first, a molten thermoplastic resin is extruded into a film form from a die attached to an extruder. Then, the extruded film is supplied between the cooling roll and the touch roll, and the film is manufactured by sandwiching between the two rolls.
JP 2004-149639 A JP 2004-330651 A

In the phase difference film, the phase difference unevenness in the film flow direction, that is, the stripe-like color unevenness in the direction parallel to the film width direction is caused by the occurrence of thickness unevenness at random cycles in the film flow direction.

  By the way, generally a retardation film is manufactured by extending | stretching the film used as an original fabric in a fixed direction.

When the film is stretched, if the stretching direction is the same direction (longitudinal stretching) as the film flow direction, the thickness unevenness in the film flow direction is alleviated and the thickness unevenness interval increases. In the state molded as a phase difference film, the color unevenness is hardly noticeable.

On the other hand, when the stretching direction is a direction parallel to the film width direction (transverse stretching or tenter stretching), there is no effect of reducing thickness unevenness in the film flow direction, and color unevenness is noticeable in the state of being formed as a retardation film. It becomes like this.

Therefore, there is a strong demand for a method for producing a retardation film that improves the thickness unevenness in the flow direction of the film, which occurs at random cycles, and has no streak-like color unevenness.

  However, a method for producing a film by supplying a thermoplastic resin extruded from a T die into a film shape between two rolls of a cooling roll and a touch roll as in the above-described conventional example, and sandwiching and pressing between the two rolls. In this case, a phenomenon has occurred in which a lip mark (horizontal stage) is generated when the extruded film comes into contact with the edge portion of the lip end of the T die. This lip mark is a cause of uneven thickness that occurs in the flow direction of the film.

  Such a lip mark has a low resin viscosity at the lip tip and the resin viscosity is low and easily deforms. Therefore, the section from the lip tip of the T die to the contact point where the extruded film first contacts the cooling roll (hereinafter referred to as the lip mark). It is strongly expressed when the film vibrates in “air gap”).

  By the way, in order to reduce the thickness unevenness in the film width direction, the tangent line where the film extruded from the T die first contacts the cooling roll is set to coincide with the tangent line of the two rolls, and the thermoplasticity is set. It is known that it is effective to cool the resin uniformly and rapidly.

  However, in such a film manufacturing method, when a cooling roll and an elastic touch roll are used as a roll for pinching the film, the touch roll is elastically deformed at the pinching portion. And the peripheral speed fluctuation becomes large.

  Therefore, when the film extruded from the T-die first comes into contact with the touch roll, the film vibrates due to the influence of the rotation fluctuation of the touch roll.

  Even when the rotation fluctuation of the touch roll is small, when the film is guided on the tangent line between the cooling roll and the touch roll, the film is always kept in contact with the cooling roll and the touch roll due to influences such as free vibration of the film and disturbance due to air current. It is difficult to keep the first contact on the tangent line. For this reason, the first contact with the cooling roll or the first contact with the touch roll is repeated at random cycles, resulting in film tension fluctuations and film vibrations.

  Furthermore, it is difficult to draw the film while maintaining a straight shape parallel to the tangent line between the cooling roll and the touch roll due to the parallelism error between the T die lip and the cooling roll and the influence of flare in the air gap. Therefore, also in the film width direction, the film extruded from the T-die first contacts the cooling roll or first touches the touch roll is repeated at random cycles, resulting in fluctuations in the film tension. Vibration occurs.

  Furthermore, because of the following factors, the contact position between the film extruded from the T-die and the cooling roll fluctuates, so that film vibration with a random period may occur in the air gap.

  That is, since the effective width of the touch roll is set shorter than the film width in order to make the touch roll surface uniformly contact with the film surface in the film width direction, both ends of the film are not sandwiched by the touch roll. The contact position of the cooling roll does not become constant due to the fluctuation caused by the neck-in of the part. Alternatively, when the outer diameters of the two rolls are different, air entrainment occurs when the film comes into contact with the roll, and the smaller the roll radius of curvature, the greater the entrainment of air at the contact point. The contact position is lowered, and the contact position is likely to fluctuate.

The present invention was devised in view of such circumstances, and has a small thickness unevenness in the flow direction of the film, a film manufacturing method with high thickness accuracy, a film manufactured by this method, and a film manufactured using this film. The present invention provides a retardation film free from streak-like color unevenness.

  In order to achieve the above object, the present invention manufactures a film by extruding a molten thermoplastic resin from a T-die into a film shape and supplying it between two rolls, and sandwiching the pressure between these two rolls. In the method, the film extruded from the T die is brought into contact with one of the rolls before being sandwiched between the two rolls.

According to the present invention, since the film extruded from the T-die always comes into contact with either one of the rolls first, this film does not first come into contact with either of the two rolls in a random cycle, As a result, there is no occurrence of fluctuations in film tension. Thus, since the film tension does not fluctuate, the vibration of the film in the air gap is prevented. Therefore, it is possible to prevent the generation of lip marks due to the contact between the edge portion of the lip end of the T die and the extruded film, and to reduce the thickness unevenness generated in the film flow direction.

  Further, according to the present invention, the two rolls are composed of a roll having no elasticity and a roll having elasticity, and the roll first brought into contact with the film extruded from the T die is a roll having no elasticity. It is characterized by.

  According to the present invention, the film extruded from the T-die is pinched by the elastic roll, so that the film is closely pressed against the film surface and the pressing force on the film is dispersed and uniformed in the width direction. It becomes difficult for thickness unevenness to occur in the film.

In addition, the film extruded from the T-die always comes into contact with a roll that does not always have elasticity,
Since the roll having elasticity is not initially contacted, it is possible to prevent the occurrence of film vibration due to the influence of rotational fluctuation caused by the elastic deformation of the roll. Therefore, the generation of lip marks due to the contact between the edge portion of the tip end of the lip of the T die and the film can be prevented, and the thickness unevenness generated in the film flow direction can be reduced.

  Note that an elastic touch roll is preferably used as the roll having elasticity, and the rotational runout accuracy of the outer peripheral surface is preferably 100 μm or less. Further, the hardness of the touch roll rubber layer is preferably set such that the durometer hardness measured in accordance with JIS K 6253 is in the range of 50A to 80A.

  Further, the rotational runout accuracy of the outer peripheral surface of the roll having no elasticity is preferably 30 μm or less.

  Further, the lip clearance of the T die is preferably narrow, and the film take-up speed is preferably fast. The lower temperature of the thermoplastic resin is preferable because the film tension increases. This resin temperature is preferably controlled by the mold temperature and set to the glass transition temperature Tg + 100 ° C. to Tg + 130 ° C. of the resin.

  When manufacturing such a film in a clean room, in order to prevent the film from shaking due to the airflow in the room, the pressure fluctuation in the room should be set to 2 Pa or less, and the supply air velocity of the room air conditioning should be set to 0.4 m / s or less. Is preferred.

  In the above configuration, it is effective to set the two rolls to different outer diameters, and to form a roll with which the film extruded from the T-die first comes into contact with a larger diameter than the other roll.

Further, the present invention is a film produced by any one of the methods described above, wherein the average thickness d is 200 μm or less, and the thickness unevenness in the film flow direction is 3.3 × 10 ⁻³ dμm / 5 mm or less. It is characterized by that.

  In this film, when the thermoplastic resin is a norbornene-based resin, the film can be excellent in optical characteristics and excellent in thickness accuracy.

Furthermore, the present invention is a retardation film produced by stretching the above film in at least a lateral uniaxial direction, and the retardation unevenness in the flow direction of the retardation film after stretching the film is an average level. When the phase difference is Rnm, it is 3.3 × 10 ⁻³ Rnm / 5 mm or less.

  In this case, as a method of stretching the film that becomes the original film of the retardation film in the lateral uniaxial direction, for example, while the film is continuously passed through the heating furnace, the film is widened at a predetermined speed and magnification in the lateral direction. After cooling and solidifying.

  According to the present invention, the thickness unevenness in the flow direction of the film is small, the film manufacturing method with high thickness accuracy, the film manufactured by this method, and the stripe-shaped color unevenness manufactured using this film are free from It becomes possible to provide a phase difference film.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  1 and 2 show a schematic configuration of a film production apparatus for carrying out the method of the present invention. In the figure, 1 is a T die, 2 is a cooling roll, and 3 is a touch roll.

  This manufacturing apparatus extrudes the molten thermoplastic resin from the T die 1 into a film shape and supplies it between the cooling roll 2 and the touch roll 3, and sandwiches the pressure between these two rolls 2 and 3. The extruded film 4 is configured to be brought into contact with the cooling roll 2 before being pressed between the two rolls 2 and 3.

  The T die 1 is attached to the extruder A, the cooling roll 2 is a roll having no elasticity, and the touch roll 3 is a roll having elasticity.

  In addition, the cooling roll 2 is formed to have a larger diameter than the touch roll 3, and as shown in FIG. 1, after the film 4 extruded from the T die first contacts the cooling roll 2, They are designed to come into contact with each other and to be sandwiched between these two rolls 2 and 3.

  Thus, since the film 4 extruded from the T-die 1 always comes into contact with the cooling roll 2 first, the film 4 may first come into contact with either the cooling roll 2 or the touch roll 3 at a random cycle. Therefore, there is no fluctuation in the tension of the film that occurs. Thus, since the film tension does not fluctuate, the occurrence of film vibration in the air gap (symbol g in FIG. 1) is prevented. Accordingly, it is possible to prevent the generation of lip marks due to the contact between the edge portion of the lip tip of the T die 1 and the film 4 and to reduce the thickness unevenness generated in the film flow direction.

  As described above, the present invention uses the manufacturing apparatus described above to extrude the molten thermoplastic resin from the T-die 1 into a film shape, and before the film 4 is pressed between the cooling roll 2 and the touch roll 3, A film is produced by bringing them into contact with each other.

  Next, using the manufacturing apparatus described above, a film is manufactured, and the obtained film is stretched to manufacture a retardation film. However, Examples 1 to 4 and Comparative Example 1 are manufactured. This will be described with reference to Table 1.

  First, the thermoplastic norbornene-based resin (manufactured by ZEON Corporation, trade name “ZEONOR1420”, Tg = 135 ° C.) is used as the thermoplastic resin as the raw material of the films of Examples 1 and 2 and Comparative Examples 1 to 4. Pre-dried at a temperature of 110 ° C. for 3 hours.

  The melt viscosity (measured by a flow characteristic tester (capillograph)) was 1520 Pa · s at 280 ° C.

  The production was performed in a clean room, and the room was ventilated at a supply air velocity of 0.2 m / s.

  Furthermore, the specifications of the manufacturing apparatus used are as follows.

  As the extruder A, a single-screw extruder having a diameter of 100 mm and L / D = 32 was used.

  The T die 1 having an effective width of 1900 mm was used.

  The cooling roll 2 adopts a three-roll system, an outer diameter of 300 mm, an effective width of 1800 mm, a material of S45C, a surface of HCr plated finish, and a heat medium circulation heating method with a rotational runout accuracy of 15 μm or less. The temperature control mechanism (using oil as a heat medium) is provided.

  The touch roll 3 has three outer diameters of 200 mm, 300 mm, and 350 mm. Each has an effective width of 1800 mm, a rubber layer thickness of 5 mm, a rubber hardness of 60 A (measured with a Type A durometer (“GS-719N” manufactured by Teclock Co., Ltd.)), and a metal sleeve made of nickel and having a thickness of 0.25 mm. Has a Cr plating finish, and the rotational runout accuracy is set to 50 μm / 360 ° or less and 5 μm / 20 ° or less (measured by a laser displacement meter system (“LK035” manufactured by Keyence Corporation)).

  Using a manufacturing apparatus having such specifications, a film was manufactured by extrusion molding under the following extrusion molding conditions.

  The extrusion speed from the extruder A is 100 kg / h, the temperature of the T die 1 is 280 ° C., the lip gap of the T die 1 is 0.8 mm, the air gap is 90 mm, the temperature of the cooling roll 2 is 120 ° C., and the touch roll 3 The temperature is 100 ° C. and the effective width of the film is 1600 mm.

(Example 1)
The manufacturing conditions of Example 1 will be described.

(A) The roll to which the film 4 extruded from the T die first comes into contact is the cooling roll 2.
(B) The outer diameter of the touch roll is 200 mm.

(Example 2)
The manufacturing conditions of Example 2 are the same as in Example 1 (b), that is, the outer diameter of the touch roll is 300 mm, and the other conditions are the same as in Example 1.

(Example 3)
The manufacturing conditions of Example 3 are the same as in Example 1 (a), that is, the roll in which the film 4 first comes into contact is the touch roll 3, and the other conditions are the same as in Example 1.

Example 4
The manufacturing conditions of Example 4 are the same as those of Example 1 (b), that is, the outer diameter of the touch roll is 350 mm, and other conditions are the same as those of Example 1.

(Comparative Example 1)
The manufacturing condition of Comparative Example 1 is that of Example 1 (a), that is, the film 4 is first brought into contact with the tangent line of the cooling roll 2 and the touch roll 3, and the other conditions are the same as in Example 1 above. .

Here, about each film manufactured on the manufacturing conditions of Examples 1-4 mentioned above and Comparative Example 1, the thickness (average) of a film and the film flow direction thickness nonuniformity were measured, and the film after extending | stretching these films Was evaluated by examining the stripe-like unevenness by visual inspection.

  The film was stretched in the lateral uniaxial direction under the following conditions.

  The stretching method uses a tenter clip method, the stretching ratio is 2 times, the traveling speed in the film length direction is 10 m / min, the stretching zone length is 7 m, the strain rate is 0.024 / sec, the preheating temperature is 150 ° C. The temperature was 145 ° C., the heat treatment temperature was 140 ° C., and the cooling temperature was 100 ° C.

  Moreover, about the thickness measurement of the obtained film, it measured with the film thickness measuring device (the Seiko EM company make, brand name "Millitron1240").

  Regarding the measurement of the thickness unevenness in the film flow direction, the film width direction center part is taken from an arbitrary position to a section of 1000 mm in the flow direction, the thickness of 1001 points is measured at intervals of 1 mm in the flow direction, and the maximum of 6 consecutive points is measured. The difference between the value and the minimum value was obtained, and the average value of all the obtained values was determined as thickness unevenness.

  For striped unevenness after stretching, a film stretched in the transverse uniaxial direction is attached to a transparent glass having a size equivalent to A4 size, and the presence or absence of streaky unevenness is visually evaluated through a polarizing plate. What was possible was evaluated with ◎, what was hardly visible with ○, slightly visible with Δ, and clearly visible with ×.

  Here, the results will be described with reference to Table 1. First, the thickness of the film was equal to 69.5 μm in each of Examples 1 to 4 and Comparative Example 1. Further, the thickness unevenness in the flow direction is 0.1 (μm / 5 mm) in Examples 1 and 2, 0.4 (μm / 5 mm) in Example 3, 0.3 (μm / 5 mm) in Example 4, and comparison. Example 1 was 0.5 (μm / 5 mm). And as for the stripe-shaped nonuniformity by visual observation of the film after extending | stretching, Example 1 and 2 was (double-circle), Example 3 was (triangle | delta), Example 4 was (circle), and the comparative example 1 was x.

  As mentioned above, although the Example as an example of manufacturing conditions was described about embodiment of this invention, it is not restricted to the Example mentioned above.

  The present invention relates to a method for producing a film having a small thickness unevenness in the flow direction of the film and a high thickness accuracy, a film produced by this method, and a retardation film having no stripe-like color unevenness produced using this film. Applicable to.

It is the schematic which shows typically a part of manufacturing apparatus of the film which concerns on this invention. It is the schematic which shows typically the whole manufacturing apparatus of the film which concerns on this invention.

Explanation of symbols

1 T-die 2 Cooling roll 3 Touch roll 4 Film extruded from T-die

Claims (6)

In the method of producing a film by extruding a molten thermoplastic resin from a T die into a film shape and supplying it between two rolls, and sandwiching between these two rolls,
Before the film extruded from the T-die is pressed between the two rolls, it is brought into contact with either one of the rolls. The two rolls are composed of a roll having no elasticity and a roll having elasticity,
The method for producing a film according to claim 1, wherein the roll first brought into contact with the film extruded from the T-die is a roll having no elasticity. The two rolls are set to different outer diameters,
The method for producing a film according to claim 1 or 2, wherein the roll first brought into contact with the film extruded from the T-die is formed to have a larger diameter than the other roll. A film produced by the method according to any one of claims 1 to 3,
A film having an average thickness d of 200 μm or less and a thickness unevenness in the film flow direction of 3.3 × 10 ⁻³ dμm / 5 mm or less.   The film according to claim 4, wherein the thermoplastic resin is a norbornene resin. A retardation film produced by stretching the film according to claim 4 or 5 in at least a lateral uniaxial direction,
The retardation film, wherein the retardation unevenness in the flow direction of the retardation film after stretching the film is 3.3 × 10 ⁻³ Rnm / 5 mm or less when the average retardation is Rnm.

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