JP6752602B2 - Method for manufacturing stretched film - Google Patents

Description

The present invention relates to a method for producing a stretched film.

When producing a stretched film, a method of preparing a film as a material and stretching the prepared film is used, and as a method of stretching the film, both ends of the film are gripped with clips and placed in a heating furnace. A uniaxial stretching method in which the film is conveyed and heat-stretched in either the length direction or the width direction by a clip holding both ends of the film in a heating furnace, or either in the length direction or the width direction. Known are a sequential biaxial stretching method in which heat stretching is performed in one direction and then a heating stretching in the other direction, and a simultaneous biaxial stretching method in which heat stretching is performed simultaneously in two directions in the length direction and the width direction.

In such a uniaxial stretching method or a biaxial stretching method, the film is usually stretched by heating to a required stretching ratio by pulling the film in a heating furnace while holding both ends of the film in the width direction with clips. It is allowed to cool and then cooled. In such a uniaxial stretching method or a biaxial stretching method, both ends in the width direction of the film are gripped by clips. Therefore, in the vicinity of both ends in the width direction of the film, stretching stress caused by heating stretching and after heating stretching While the influence of the shrinkage stress generated at the time of cooling is small, the binding force by the clip is weakened in the central portion in the width direction of the film, and the influence of the above-mentioned stretching stress and shrinkage stress tends to be large. Therefore, in the uniaxial stretching method and the biaxial stretching method, in the film that has undergone heating stretching and cooling, the deformation of the central portion in the width direction of the film is delayed as compared with the deformation of both ends in the width direction (Boeing phenomenon). It is known to occur.

When the above-mentioned Boeing phenomenon occurs, the molecular arrangement of the obtained stretched film becomes non-uniform, and the obtained stretched film has uneven physical properties in the width direction, resulting in optical anisotropy and strength. And durability may decrease.

On the other hand, as a method for homogenizing the molecular arrangement of the film, for example, in Patent Document 1, the thermoplastic film is laterally stretched and then heat-fixed at a temperature 1 to 50 ° C. lower than the temperature at the time of the transverse stretching. A technique for suppressing the boeing phenomenon is disclosed. Further, for example, in Patent Document 2, when an unoriented amorphous resin film is uniaxially stretched in the width direction, a low widening region for reducing the widening speed is provided between the start of widening and the completion of widening. A technique for suppressing the Boeing phenomenon is disclosed.

Japanese Unexamined Patent Publication No. 2008-21334 Japanese Unexamined Patent Publication No. 2005-345816

However, in the techniques of Patent Documents 1 and 2, in order to obtain appropriate processing conditions for homogenizing the molecular arrangement of the film, the manufacturing conditions are set by using a manufacturing apparatus used for manufacturing an actual product. It is necessary to make a trial stretched film many times while changing it, and there is a problem that it takes time and effort to obtain appropriate processing conditions, and there is a problem that it can be applied only to the uniaxial stretching method and the stretching method is limited. It was.

The present invention has been made in view of such an actual situation, and when a film is heat-stretched to produce a stretched film, a heat relaxation treatment for homogenizing the molecular arrangement of the film can be easily and appropriately performed. It is an object of the present invention to provide a method for producing a stretched film, which can be carried out under conditions, whereby a stretched film having excellent optical properties, strength and durability can be obtained.

The present inventors have found that the above object can be achieved by performing a heat relaxation treatment of heating a film that has been heat-stretched and cooled under predetermined conditions, and have completed the present invention.

（上記式（１）中、Ａ、Ｂ、Ｃおよびθ_０は、いずれも、予め、前記熱可塑性樹脂のフィルムを用いて、前記延伸工程と、前記冷却工程と、前記熱緩和工程とを行うというプロセスを試行することにより求められる係数、φ_ｍｉｎは、得ようとする延伸フィルムの配向角（°）、Ｌは、得ようとする延伸フィルムの幅（ｍｍ）） That is, according to the present invention, a stretching step of stretching a film of a thermoplastic resin in one or two directions while heating the film of the thermoplastic resin to a glass transition temperature of T _g or more, and the stretched film are performed. a cooling step of cooling at a temperature below the glass transition temperature T _g, the film after the cooling, and a thermal relaxation step of thermally relaxing by heating at the glass transition temperature T _g above the heat treatment temperature T _r Provided is a method for producing a stretched film, wherein the heat relaxation time in the heat relaxation step is at least t _min (sec), which is the lower limit processing time calculated by the following formula (1).

(In the above formula (1), A, B, C and θ ₀ all carry out the stretching step, the cooling step and the heat relaxation step in advance using the thermoplastic resin film. The coefficient obtained by trying the process , φ _min, is the orientation angle (°) of the stretched film to be obtained, and L is the width (mm) of the stretched film to be obtained).

（上記式（２）中、φ_ｍａｘは、得ようとする延伸フィルムの配向角の制御限界値（°））
本発明の製造方法において、前記熱可塑性樹脂が、非晶性樹脂であることが好ましい。
本発明の製造方法において、前記熱可塑性樹脂が、ポリカーボネートを含有する樹脂であることが好ましい。 In the production method of the present invention, it is preferable that the film cooled in the cooling step is once wound and then the heat relaxation step is performed on the wound film.
In the production method of the present invention, it is preferable that the heat relaxation step is continuously performed from the cooling step on the film cooled in the cooling step.
In the production method of the present invention, in the heat relaxation step, the heat relaxation time is preferably set to the lower limit processing time t _min or more and the upper limit processing time t _max (seconds) represented by the following formula (2). ..

(In the above formula (2), φ _max is the control limit value (°) of the orientation angle of the stretched film to be obtained).
In the production method of the present invention, it is preferable that the thermoplastic resin is an amorphous resin.
In the production method of the present invention, the thermoplastic resin is preferably a resin containing polycarbonate.

Further, according to the present invention, there is provided a method for producing an optical film using a stretched film obtained by the above-mentioned production method.

According to the present invention, when a film is heat-stretched to produce a stretched film, a heat relaxation treatment for homogenizing the molecular arrangement of the film can be easily performed under appropriate conditions. It is possible to provide a method for producing a stretched film capable of obtaining a stretched film having excellent optical properties, strength and durability.

FIG. 1 is a diagram for explaining an example of a method for producing a stretched film. FIG. 2 is a graph for explaining the change in the orientation angle of the film when the heat relaxation treatment is performed. FIG. 3 is a schematic view for explaining a change in the orientation angle of the film when the heat relaxation treatment is performed. FIG. 4 is a graph showing an example of the progress of heat relaxation of the film according to the heat treatment time. FIG. 5 is a graph for explaining the relationship between the width of the film and the orientation angle of the film. FIG. 6 is a graph showing an example of the progress of thermal relaxation of the film according to the heat treatment temperature and the heat treatment time. FIG. 7 is a graph for explaining the relationship between the heat relaxation time and the heat treatment temperature. FIG. 8 is a graph for explaining the difference in the orientation angle of the film when the width of the film is changed. FIG. 9 is a graph for explaining an example of a method of setting the lower limit and the upper limit of the heat treatment temperature and the heat treatment time. FIG. 10 is a diagram (No. 1) for explaining another example of a method for producing a stretched film. FIG. 11 is a diagram (No. 2) for explaining another example of a method for producing a stretched film.

（上記式（１）中、Ａ、Ｂ、Ｃおよびθ_０は、いずれも、前記熱可塑性樹脂の種類および前記延伸工程における延伸条件に応じて決まる係数、φ_ｍｉｎは、得ようとする延伸フィルムの配向角（°）、Ｌは、得ようとする延伸フィルムの幅（ｍｍ）） Method for producing a stretched film according to the present embodiment, a film of thermoplastic resin, while heating above the glass transition temperature T _g of the said thermoplastic resin, a stretching step of stretching in one or two directions, the stretching the film after a cooling step of cooling at a temperature below the glass transition temperature T _g, the film after the cooling, thermal relaxation to thermal relaxation by heating at the glass transition temperature T _g above the heat treatment temperature T _r It is a method for producing a stretched film having a step, and is characterized in that the heat relaxation time in the heat relaxation step is set to a lower limit processing time t _min or more calculated by the following formula (1).

(In the above formula (1), A, B, C and θ ₀ are all coefficients determined according to the type of the thermoplastic resin and the stretching conditions in the stretching step, and φ _min is the stretched film to be obtained. Orientation angle (°), L is the width (mm) of the stretched film to be obtained.

First, an embodiment according to the present invention will be described by taking as an example a scene in which a stretched film is produced by the method shown in FIG. FIG. 1 shows a scene in which a film of a thermoplastic resin is simultaneously stretched in the length direction and the width direction by a simultaneous biaxial stretching device including a pre-tropical zone, a stretching zone, a first cooling zone, a heat relaxation zone, and a second cooling zone. It is a figure which shows. In the example shown in FIG. 1, the film of the thermoplastic resin is preheated in the pre-tropical zone by the simultaneous biaxial stretching device, and is simultaneously stretched in the length direction and the width direction while being heated in the stretching zone, and the first By cooling in the cooling zone, heat is fixed, and in the heat relaxation zone, heat relaxation treatment is performed to make the molecular orientation (orientation angle) of the film uniform, and then cooling is performed in the second cooling zone. Heat fix again.

According to the manufacturing method of the present embodiment, the heat treatment time of the heat relaxation treatment for the film in the above-mentioned heat relaxation zone is set to the lower limit treatment time t _min or more calculated based on the above formula (1), which is convenient. In addition, the molecular arrangement of the film can be made uniform, and a stretched film having excellent optical properties, strength and durability can be obtained.

In the present embodiment, A, B, C and θ ₀ of the above formula (1) are all coefficients, and as a method of obtaining these coefficients, for example, a thermoplastic resin which is a material of a stretched film is used in advance. The above coefficient (1) was obtained by trialing the process of performing heat relaxation treatment after heat stretching and heat fixing using the film of the above, and curve-fitting the result obtained by the trial to the above formula (1). A, B, C and θ ₀ ) can be determined. Then, in the present embodiment, when the obtained coefficients (A, B, C, θ ₀ ) are substituted into the above formula (1) and a stretched film having a desired width L is produced based on the above formula (1). The optimum heat treatment time for the heat relaxation treatment can be calculated.

According to the present embodiment, even when a relatively small-scale stretching device such as a testing machine is used, a process of performing heat stretching, heat fixing, and heat relaxation treatment on a film having a small width is tried. Therefore, the coefficient (A, B, C, θ ₀ ) of the above formula (1) can be obtained, and then it is used in the production of an actual stretched film based on the obtained coefficient and the above formula (1). The lower limit processing time t _min of the heat relaxation treatment in producing a stretched film having a large width can be calculated by using such a large-scale stretching device. That is, according to the present embodiment, the lower limit processing time t _min of the heat relaxation treatment can be easily set by the calculation using the above formula (1) without making a prototype of the repeatedly stretched film using a large-scale stretching apparatus. It can be calculated.
Hereinafter, each step of the method for producing a stretched film according to the embodiment of the present invention will be described with reference to FIG.

<Stretching process>
The stretching step is a step of preheating the film 100 in the pre-tropical zone shown in FIG. 1 and heating and stretching the preheated film 100 in the length direction and the width direction in the stretching zone. Specifically, in the stretching step, first, the film 100 is continuously fed from a roll or the like, the film 100 is gripped at regular intervals by using a plurality of clips 200, and the film 100 is moved by moving each clip 200. Transfer to the simultaneous biaxial stretching device. Next, the film 100 is preheated in the pretropical zone shown in FIG. 1 while being conveyed, and then the clip 200 is heated to a glass transition temperature of T _g or more of the thermoplastic resin constituting the film 100 in the stretching zone. Stretches by pulling in the length and width directions.

In this embodiment, a pair of guide rails (not shown) for moving the clip 200 are installed so as to pass through the simultaneous biaxial stretching device. The pair of guide rails are installed at the position of the clip 200 that grips the upper side of the film 100 and the position of the clip 200 that grips the lower side of the film 100 shown in FIG. They are separated from each other in the width direction of the film 100, and are parallel to each other in the first cooling zone, the heat relaxation zone, and the second cooling zone. Alternatively, in the first cooling zone and the second cooling zone, the distance between the pair of guide rails may be made closer in the width direction in consideration of the shrinkage amount at the time of solidification of the film. In the present embodiment, the clip 200 holding the film 100 can be conveyed and stretched by moving along such a guide rail.

The film 100 can be obtained, for example, by melt-extruding a thermoplastic resin from a T-die.

The thermoplastic resin may be selected according to the intended use of the stretched film to be obtained. For example, an acrylic resin such as polymethylmethacrylate (PMMA), a cyclic olefin copolymer (COC), a polycarbonate (PC), or polyethylene terephthalate. One of polyester resins such as (PET) can be used alone, or a mixed resin of two or more can be used. Among them, the orientation angle can be adjusted by the heat relaxation treatment in the heat relaxation step described later. Acrylic resins are preferable, and polycarbonate (PC) is particularly preferable, from the viewpoint that uniformization can be performed better.

The width of the film 100 before stretching is preferably 280 to 1000 mm, more preferably 400 to 600 mm, and the thickness of the film 100 before stretching is preferably 70 to 250 μm, more preferably 100 to 150 μm. is there.

The heating temperature at the time of preheating by the preheating zone showing the film 100 in FIG. 1, the glass transition temperature _{T g} of the thermoplastic resin constituting the film 100, preferably 10 to 30 ° C. higher temperatures, more preferably 20 to 25 ℃ High temperature.

In the present embodiment, such a film 100 is preheated in the pretropical zone and then stretched in a stretching zone. That is, in the stretched zone, the film 100 is heated to the glass transition temperature _Tg or higher of the film 100, and the clip 200 holding the film 100 is moved along the guide rail so as to spread in the width direction. At the same time, by controlling to widen the distance between the clips 200, the film 100 is pulled in the length direction and the width direction as shown by the arrows shown in FIG. As a result, the film 100 is heat-stretched to a stretch ratio required in the length direction and the width direction.

In the present embodiment, when the film 100 is stretched in the stretch zone, the stretch ratio with respect to the stretch direction (length direction or width direction of the film 100) is preferably within 3 times, more preferably 2.5 times. Within, more preferably within twice.

The width of the stretched film 100 is preferably 500 to 3000 mm, more preferably 1000 to 2000 mm, and the thickness of the stretched film 100 is preferably 10 to 60 μm, more preferably 20 to 40 μm.

<First cooling process>
Next, in the present embodiment, the film 100 stretched in the stretching zone is conveyed to the first cooling zone as shown in FIG. 1, and the glass transition of the thermoplastic resin constituting the film 100 is performed in the first cooling zone. Heat is fixed by cooling at a temperature less than T _g .

Temperature when cooling the film 100 in the first cooling zone, the glass transition temperature _{T g} of the thermoplastic resin constituting the film 100, preferably 10 to 50 ° C. lower temperature, more preferably less 30 to 40 ° C. The temperature.

（上記式（１）中、Ａ、Ｂ、Ｃおよびθ_０は、いずれも、フィルム１００を構成する熱可塑性樹脂の種類および延伸工程における延伸条件に応じて決まる係数、φ_ｍｉｎは、得ようとする延伸フィルムの配向角（°）、Ｌは、得ようとする延伸フィルムの幅（ｍｍ）） <Heat relaxation process>
Next, in the present embodiment, the film 100 cooled in the first cooling zone is conveyed to the heat relaxation zone as shown in FIG. 1, and the glass transition of the thermoplastic resin constituting the film 100 is performed in the heat relaxation zone. Heat relaxation treatment is performed by heating at a heat treatment temperature _Tr of a temperature of T _g or more and a lower limit treatment time of t _min or more represented by the following formula (1). As a result, the film 100 has a uniform molecular orientation and is excellent in optical properties, strength, and durability.

(In the above formula (1), A, B, C and θ ₀ are all coefficients determined according to the type of the thermoplastic resin constituting the film 100 and the stretching conditions in the stretching step, and φ _min is to be obtained. The orientation angle (°) and L of the stretched film to be obtained are the width (mm) of the stretched film to be obtained.

That is, when the film 100 is stretched as shown in FIG. 1, since both ends of the film 100 in the width direction are gripped by the clips 200, the vicinity of both ends of the film 100 in the width direction is caused by heat stretching. While the influence of stretching stress and shrinkage stress generated during cooling after heating and stretching is small, the binding force of the clip 200 becomes weaker at the center of the film 100 in the width direction, and the influence of the above-mentioned stretching stress and shrinkage stress becomes weaker. Becomes larger. Therefore, it is known that in the film 100 stretched as shown in FIG. 1, a phenomenon (Boeing phenomenon) occurs in which the deformation of the central portion in the width direction of the film 100 is delayed as compared with the deformation of the end portion in the width direction. There is.

On the other hand, in the present embodiment, in order to homogenize the molecular orientation (orientation angle) of the film 100 which has been stretched in the stretching step and then heat-fixed in the first cooling step, which has become non-uniform due to the above-mentioned Boeing phenomenon. , The heat treatment temperature _Tr at which the glass transition temperature of the thermoplastic resin constituting the film 100 is T _g or more is appropriately subjected to heat relaxation treatment by heating at the lower limit treatment time t _min or more represented by the following formula (1). , The orientation angle of the film 100 can be made uniform.

In particular, the present inventors have found that the lower limit of the heat treatment time (lower limit treatment time t _min ) when the film 100 is heat-relaxed can be calculated based on the above formula (1), whereby the stretched film can be calculated. An appropriate heat treatment time for making the orientation angle uniform can be easily obtained without using an actual manufacturing apparatus to make a prototype of the stretched film, and the heat relaxation treatment is performed under the conditions of the obtained heat treatment time. As a result, it has become possible to obtain a stretched film having excellent optical properties, strength and durability.

Here, the above formula (1) was obtained as follows based on the knowledge of the present inventors. First, the present inventors examined the relationship between the heat treatment time of the heat relaxation treatment for the film 100 after stretching and the change in the orientation angle of the film 100 in response to the heat relaxation treatment, and found the relationship shown in FIG. It was. FIG. 2 shows both ends of the film 100 using a film 100 having a thickness of 150 μm, a width of 280 mm, and a length of 2,000 mm, which is made of a thermoplastic resin containing polycarbonate as a main component (glass transition temperature T _g is about 130 ° C.). The portions are gripped by clips 200 at intervals of 83 mm, preheated at 150 ° C., stretched at 145 ° C. at a stretching ratio of 1 time in the length direction and 2 times in the width direction, and then cooled at 120 ° C. and 100 ° C. A heat-fixed sample was obtained (the sample after heat-fixing had a width of 525 mm and a length of 1,600 mm), and the obtained sample was subjected to heat relaxation treatment at a temperature of 133 ° C., and then heat-relaxed. It is a graph which measured the state of relaxation of the molecular orientation of a film at the time of heat-fixing by cooling at 100 degreeC. In FIG. 2, before the heat relaxation treatment is performed (indicated by 0 seconds in FIG. 2), the heat relaxation treatment is performed for 42 seconds, the heat relaxation treatment is performed for 84 seconds, and then the heat relaxation treatment is performed for 168 seconds. For each of the samples after this, at each position in the width direction of the film (center in the width direction, position ± 40 mm from the center in the width direction, position ± 80 mm, position ± 120 mm, and position ± 160 mm). The result of measuring the orientation angle (angle from the reference axis of the molecular orientation direction) with the width direction of the film as the reference axis is shown. In FIG. 2, the horizontal axis indicates the position of the film in the width direction (the center in the width direction of the film is 0), and the vertical axis indicates the orientation angle of the film in the width direction.

As shown in FIG. 2, the sample (0 seconds) before the heat relaxation treatment has an orientation angle that increases as the distance from the center position in the width direction of the film (the origin of the graph in FIG. 2) increases, and the width of the film increases. The orientation angle is the largest at both ends of the direction. Similarly, for the samples subjected to the heat relaxation treatment (42 seconds, 84 seconds, and 168 seconds), the heat treatment time of the heat relaxation treatment is long, although the orientation angle increases as the distance from the center position in the width direction of the film increases. Indeed, the size of the orientation angle at each position of the film is small.

From such a result of FIG. 2, the present inventors have obtained the finding that the relationship between the position in the width direction of the film and the orientation angle of the film shown in FIG. 2 can be approximated by a straight line. As a result, it was found that the uniformity of the orientation angle of the film by the heat relaxation treatment proceeds as shown in FIG. That is, as shown in FIG. 3, regarding the relationship between the position in the width direction of the film and the orientation angle of the film, the sample before the heat relaxation treatment is approximated by a broken straight line, and the sample after the heat relaxation treatment is a solid straight line. By performing the thermal relaxation treatment, the angle of the approximate straight line with respect to the horizontal axis becomes smaller (specifically, the angle of the approximate straight line with respect to the horizontal axis becomes smaller from θ ₀ to θ _t ). I found.

（上記式（３）中、θ_０は、熱緩和処理を行う前の配向角近似直線の角度、τは緩和時間（θ＝θ_０／ｅとなる時点のｔの値）） Further, the present inventors further examined the angle of an approximate straight line (hereinafter, referred to as "orientation angle approximate straight line") showing the relationship between the above-mentioned position in the width direction of the film and the orientation angle of the film. The evaluation results when the heat relaxation treatment was performed by changing the heat treatment time using the above-mentioned film of a thermoplastic resin containing polycarbonate as a main component are plotted as shown in FIG. As a result, as shown in FIG. 4, it was found that the angle θ of the alignment angle approximate straight line can be curve-fitted by the general formula (the following formula (3)) expressing the relaxation phenomenon in relation to the heat treatment time t of the heat relaxation treatment. It was. In FIG. 4, in addition to the above-mentioned samples having the heat treatment time of 42 seconds, 84 seconds, and 168 seconds, the evaluation results of the samples having the heat treatment time of 275 seconds were also plotted.

(In the above equation (3), θ ₀ is the angle of the alignment angle approximate straight line before the thermal relaxation treatment, and τ is the relaxation time (the value of t at the time when θ = θ ₀ / e)).

（上記式（４）中、ｔ_ｍｉｎは、配向角近似直線の角度をθ_φにするのに要する熱緩和処理の熱処理時間）） Generally, the more uniform the molecular arrangement of the stretched film, the better the optical properties, strength and durability tend to be. Therefore, for example, depending on the use of the stretched film (optical film or the like), it may be required to suppress the orientation angle of the stretched film to a predetermined standard value or less. For example, as in the example shown in FIG. 5, when a stretched film having a width L is to be obtained, the maximum orientation angle of the stretched film (usually, the orientation angles at both ends of the stretched film in the width direction) is set to a standard value (normally). Target value) It may be required to keep it below φ _min . In this case, as shown in FIG. 5, when the orientation angles at both ends of the stretched film in the width direction are the standard value (target value) φ _min , the angle θ _φ of the alignment angle approximate straight line is the above equation (3). Based on, it can be expressed as the following equation (4).

(In the formula (4), t _min is the heat treatment time of thermal relaxation process which needs the angle of orientation angle approximation line for the theta _phi))

Here, when the above equation (4) is solved for the processing time t _min of the heat relaxation treatment, it can be expressed by the following equation (5).

In the formula (5), the angle theta _phi orientation angle approximate line can be obtained from the graph shown in FIG. 5, represented by the following formula (6).

That is, from the graph shown in FIG. 5 described above, can lead the following expression (7), the equation (7), and solving for the angle theta _phi orientation angle approximate line, the equation (6) is obtained.

Then, the above equation (5) and substituting the angle theta _phi orientation angle approximate line in the formula (6) can be represented by the following formula (8).

In the above formula (8), L is usually a very large value as compared with φ _min (that is, the width L (unit: mm) of the stretched film to be obtained is usually the orientation angle of the stretched film. since the standard value (target value) is a very large value as compared to the phi _min), a 2φ _min / L << 1, _{^{thereby, tan -1 (2φ min / L}} ) is a 2 [phi _min / L Can be approximated. Therefore, in the above equation (8), by approximating tan ^-1 (2φ _min / L) with 2φ _min / L, it can be expressed by the following equation (9).

（上記式（１０）中、ａ、ｂおよびｃは、いずれも、フィルム１００を構成する熱可塑性樹脂の種類および延伸工程における延伸条件に応じて決まる係数、Ｔ_ｒは熱緩和処理を行う際における熱処理温度（℃）、Ｔ_ｇはフィルム１００を構成する熱可塑性樹脂のガラス転移温度（℃）） On the other hand, as a result of diligent studies by the present inventors, the relaxation time τ in the above equation (9) (in the above equation (3), the time t at the time when θ = θ ₀ / e) is as follows. It was found that it can be expressed by the equation (10).

(In the above formula (10), a, b and c are all coefficients determined according to the type of the thermoplastic resin constituting the film 100 and the stretching conditions in the stretching step, and _Tr is the time when the heat relaxation treatment is performed. The heat treatment temperature (° C.) and T _g are the glass transition temperature (° C.) of the thermoplastic resin constituting the film 100.

That is, first, as shown in FIG. 4 described above, a sample of a thermoplastic resin film containing polycarbonate as a main component is stretched at a predetermined magnification and then heat-fixed, and heat relaxation treatment is performed at a heat treatment temperature of 133 ° C. When this was done, the relaxation time τ (time t at the time when θ = θ ₀ / e) was 225 seconds as represented by τ in FIG. On the other hand, when the heat treatment temperature was changed to 135 ° C., 137 ° C. and 140 ° C. and the heat treatment was performed under the conditions of the heat treatment times of 42 seconds, 84 seconds and 168 seconds, the angle of the alignment angle approximate straight line changed. Was plotted in the same manner as in FIG. 4, and the results shown in FIG. 6 were obtained.

Based on the results shown in FIG. 6, the change in the angle of the alignment angle approximate straight line when the heat relaxation treatment is performed at each heat treatment temperature (135 ° C., 137 ° C. and 140 ° C.) is expressed in the above equation (3). Based on the curve fitting, the relaxation time τ (heat treatment time t at the time when θ = θ ₀ / e) is 95.7 seconds (135 ° C.), 28.4 seconds (137 ° C.), and 19.4 seconds, respectively. It became (140 ° C.). In this way, the relaxation time τ when the heat treatment temperature was changed was obtained, and the relationship between the heat treatment temperature and the relaxation time τ was plotted, and the results shown in FIG. 7 were obtained. In addition to the results of the heat treatment temperatures of 135 ° C., 137 ° C. and 140 ° C., FIG. 7 also shows the evaluation results of the relaxation time τ when the heat treatment temperatures are 145 ° C. and 150 ° C. The relaxation times τ when the heat treatment temperatures were 145 ° C. and 150 ° C. were 17 seconds (145 ° C.) and 15 seconds (150 ° C.), respectively.

Here, the present inventors have examined based on the results shown in FIG. 7, and have found that the results shown in FIG. 7 can be curve-fitted using the above equation (10). That is, it was found that the relaxation time τ can be expressed by the above equation (10). From this, it was found that the following equation (1) can be obtained by substituting the relaxation time τ represented by the above equation (10) into the above equation (9). In the following formula (1), the coefficients a, b and c in the above formula (10) have been rewritten as A, B and C, respectively. The relationship between a, b and c and A, B and C is represented by the following equations (11) to (13).

According to the present embodiment, by heat-stretching and heat-fixing using a desired thermoplastic resin film 100 in advance, as shown in FIGS. 2 and 3, the orientation angle approximate straight line before the heat relaxation treatment is obtained. An angle θ ₀ was obtained, and heat relaxation treatment was tried on the film 100 that had been heat-stretched and heat-fixed at different heat treatment temperatures, and the obtained results are shown in FIG. 7 described above. The values of A, B and C in the above equation (1) can be obtained by plotting and curve fitting. These coefficients (A, B, C and θ ₀ ) in the above formula (1) are the types of the thermoplastic resin constituting the film 100 (blending of the thermoplastic resin) and the stretching conditions of the film 100 (for example, It is considered that the film changes depending on the stretching ratio in each of the length direction and the width direction, the heating temperature at the time of stretching, the stretching rate, etc.).

As a result, according to the present embodiment, when the coefficients (A, B, C and θ ₀ ) of the above formula (1) are obtained in advance, a stretched film having a desired width L is to be obtained. The lower limit processing time t _min of the heat relaxation treatment for controlling the orientation angle of the stretched film to a desired standard value (target value) φ _min can be calculated based on the above formula (1).

In the present embodiment, it is desirable that the heat treatment time for performing the heat relaxation treatment is changed according to the width L of the stretched film to be obtained, as shown in FIG. Here, FIG. 8 illustrates a scene in which the maximum orientation angle of the stretched film (usually the orientation angles at both ends in the width direction of the stretched film) is suppressed to a standard value (target value) of φ _min or less. As shown in FIG. 8, when the width of the stretched film is L, the angle of the alignment angle approximate straight line is required to make the orientation angles at both ends of the stretched film in the width direction equal to or less than the standard value (target value) φ _min. the may be less theta _phi, while, when the width of the stretched film is larger than L L ', even to control the angle of the orientation angle approximation line in theta _phi, both widthwise ends of the stretched film The orientation angle of is φ'exceeding the standard value (target value) φ _min .

On the other hand, according to the present embodiment, even when the width L of the stretched film to be obtained is changed, the heat for controlling the orientation angle of the stretched film to the standard value (target value) φ _min or less is applied. The processing time of the relaxation processing (lower limit processing time t _min ) can be easily calculated from the above equation (1). As a result, when the stretched film is actually manufactured, the heat relaxation treatment is performed based on the lower limit treatment time t _min calculated from the above formula (1), which makes it easier and more excellent in optical characteristics, strength and durability. It becomes possible to manufacture a stretched film. In particular, according to the present embodiment, the molecular arrangement of the obtained stretched film can be made uniform with high accuracy by performing the heat relaxation treatment based on the lower limit treatment time t _min calculated from the above formula (1). Therefore, the obtained stretched film can be suitably used, for example, as an optical film in which the demand for uniform molecular arrangement of the stretched film is strict.

The standard value (target value) φ _min of the orientation angle of the stretched film is not particularly limited and may be appropriately set according to the intended use of the stretched film. For example, it is preferably 5 ° or less, more preferably. It is 2 ° or less, more preferably 1 to 0.5 °. By setting the standard value (target value) φ _min of the orientation angle of the stretched film in the above range, the obtained stretched film has excellent optical characteristics, strength and durability.

Here, with reference to FIG. 7 described above, specifically, the coefficients (A, B, C and θ ₀ ) of the above formula (1) are obtained, and based on the above formula (1), the lower limit processing time t _min. An example of the method of obtaining is described.

The graph shown in FIG. 7 is an evaluation result obtained as follows. That is, first, a thickness of 150 [mu] m, width 280 mm, a film of a thermoplastic resin whose main component is polycarbonate length 2,000 mm (glass transition temperature The _{T g} of about 130 ° C.), held with clips 200 at intervals of 83mm After preheating at 150 ° C., the film was stretched at 145 ° C. under the conditions of 1 time in the length direction and 2 times in the width direction (the stretched film had a width L of 525 mm and a length of 1,600 mm. After that, a plurality of films heat-fixed at 120 ° C. and 100 ° C. were prepared. The maximum orientation angle (orientation angle θ ₀ at the end in the width direction) of the prepared film was 3.4 °.

Next, the prepared plurality of films were subjected to heat relaxation treatment at heat treatment temperatures of 133 ° C., 135 ° C., 137 ° C., 140 ° C., 145 ° C. and 150 ° C., respectively, and heat relaxation treatment was performed as shown in FIG. 6 described above. By plotting the angle θ of the alignment angle approximate straight line with respect to the heat treatment time and performing curve fitting based on the above equation (3), the relaxation time τ (time t at the time when θ = θ ₀ / e) is obtained. It was.

Then, the relationship between the obtained relaxation time τ and the heat treatment temperature _Tr of the heat relaxation treatment was plotted as shown in FIG. 7, and the plotted results were curve-fitted based on the above equation (10). The values of a, b, and c, which are the coefficients in the above formula (10), were a = 1444, b = 0.56, and c = 15, respectively. Here, as described above, the obtained values of a, b and c are such that the orientation angle θ ₀ of the widthwise end portion of the film before the heat relaxation treatment is 3.4 °, and the width L of the stretched film is It is a coefficient when it is 525 mm. Further, in the example of FIG. 7, the relaxation time τ (the time until the angle θ of the orientation angle approximate straight line becomes θ ₀ / e) is shown. Therefore, from this, the example of FIG. 7 is shown. Corresponds to the case where the angle θ _φ of the alignment angle approximate straight line in the orientation angle of the film after the heat relaxation treatment (standard value (target value) φ _min of the orientation angle of the stretched film) is set to θ ₀ / e, and is relaxed. The time τ is the lower limit processing time t _min . Note that FIG. 7 shows an example in which the angle θ _φ of the alignment angle approximate straight line at the standard value (target value) φ _min of the orientation angle of the stretched film is θ ₀ / e, but this φ _min can be obtained. It can be arbitrarily set according to the product specifications of the stretched film, and instead of the relaxation time τ, the same figure as in FIG. 7 having the lower limit processing time t _min as the vertical axis is drawn according to the set φ _min. Can be drawn.

Therefore, these values of a, b and c, the width L of the film after stretching, the orientation angle θ ₀ of the widthwise end of the film before the heat relaxation treatment, and the standard values of the orientation angle of the stretched film (target). Value) From the value of φ _min , for example, the values of the coefficients A, B and C can be obtained based on the above equations (11) to (13), and the obtained values of A, B and C can be obtained from the above equations. By substituting into (1), even when the width L of the film to be obtained is changed based on the above formula (1), the orientation angle of the stretched film is set to the standard value (target value) φ _min or less. The lower limit processing time t _min of the heat relaxation treatment for this can be easily calculated.

Further, in the above-mentioned example, a method of obtaining the lower limit processing time t _min of the heat relaxation treatment for setting the maximum orientation angle of the stretched film to the standard value (target value) φ _min or less has been illustrated, but in the present embodiment, the method is exemplified. By replacing the value of φ _min with the control limit value φ _max of the orientation angle of the stretched film to be obtained in the above formula (1), the heat treatment time of the heat relaxation treatment is as shown in the following formula (2). The upper limit value (upper limit processing time t _max ) can also be obtained.

As for the control limit value φ _max in the above equation (2), for example, if the maximum orientation angle of the stretched film is made smaller than the control limit value φ _max , the conditions of the heat relaxation treatment become excessive. Value can be mentioned. Examples of cases where the conditions of the heat relaxation treatment become excessive include cases where the heat treatment time is too long and cases where the heat treatment temperature is too high. If the heat treatment time is too long, the production efficiency of the stretched film is lowered, and the manufacturing cost of the stretched film is increased. Further, if the heat treatment time is too long, the resulting stretched film tends to have a small molecular orientation itself. Therefore, when the stretched film is used as a retardation film, the retardation becomes small and the stretched film becomes a retardation film. Performance may deteriorate. Further, if the heat treatment temperature is too high, the film is easily deformed, which may be deformed by disturbance (such as the wind of an oven used to heat the film) or its own weight, resulting in shape defects. The control limit value φ _max is not particularly limited and may be appropriately set according to the intended use of the stretched film, but is preferably 1 ° or less, more preferably 0.5 ° or less, for example. Further, the control limit value φ _max is preferably 0.3 ° or more from the viewpoint of preventing the conditions of the heat relaxation treatment from becoming excessive.

Here, regarding the film used for the evaluation shown in FIG. 7 described above, a graph of the lower limit processing time t _min when the standard value (target value) φ _min of the orientation angle of the stretched film is set to 5 °, and the orientation of the stretched film. FIG. 10 shows a graph of the upper limit processing time t _max when the angle control limit value φ _max is set to 0.5 °.

In the present embodiment, as shown in FIG. 9, the lower limit treatment time t _min and the upper limit treatment time t _max are obtained in advance, and the heat treatment time when the heat relaxation treatment is performed at a desired heat treatment temperature is shown in FIG. By setting the lower limit processing time t _min or more and the upper limit processing time t _max or less shown in the above, the heat relaxation treatment can be performed under better conditions, thereby improving the optical characteristics, strength and durability. An excellent stretched film can be obtained.

In the present embodiment, the heat treatment temperature of the heat relaxation treatment is not particularly limited, but for example, it prevents the occurrence of shape defects of the stretched film due to disturbance (air of an oven used to heat the film, etc.) or its own weight. From this point of view, the temperature is preferably 0 to 30 ° C. lower, more preferably 5 to 15 ° C. lower than the heating temperature in the stretching step.

Similarly, the heat treatment time of the heat relaxation treatment is not particularly limited, but is preferably 60 seconds or less, more preferably 20 seconds or less, for example, from the viewpoint of preventing a decrease in the phase difference of the obtained stretched film.

<Second cooling process>
Next, in the present embodiment, the film 100 that has undergone the heat relaxation treatment in the heat relaxation zone is conveyed to the second cooling zone as shown in FIG. 1, and the heat constituting the film 100 is formed in the second cooling zone. it is desirable to heat by cooling at a temperature below the glass transition temperature T _g of the thermoplastic resin.

Temperature when cooling the film 100 in the second cooling zone, the glass transition temperature _{T g} of the thermoplastic resin constituting the film 100, preferably 10 to 50 ° C. lower temperature, more preferably less 30 to 50 ° C. The temperature.

In the present embodiment, the stretched film can be obtained as described above. In the present embodiment, the obtained stretched film may be removed by cutting both ends in the width direction, if necessary. As a result, both ends of the stretched film in the width direction, which are particularly thick, can be removed, and the thickness of the entire stretched film can be made uniform.

Further, in the above-described example, as shown in FIG. 1, the thermoplastic resin film 100 is continuously conveyed to the pre-tropical zone, the stretching zone, the first cooling zone, the heat relaxation zone, and the second cooling zone. An example of producing a stretched film by continuously performing a stretching step, a first cooling step, a heat relaxation step, and a second cooling step has been shown, but the present embodiment is not limited to such an example. As shown in 10 and 11, each step may be divided and carried out to produce a stretched film.

For example, in the examples shown in FIGS. 10 and 11, first, as shown in FIG. 10, the thermoplastic resin film 100 is preheated in the pre-tropical zone and heated in the stretching zone in the length direction and the width direction. The film is stretched to 1 and heat-fixed in the first cooling zone, and then the obtained film is once wound up. Next, using the wound film, as shown in FIG. 11, while unwinding the film, the film is heat-relaxed in the heat-relaxation zone while both ends in the width direction of the film are gripped by the clips 200. After the application, the stretched film may be produced by heat-fixing in the second cooling zone.

In the present embodiment, for example, by producing a stretched film using the lines shown in FIGS. 10 and 11 described above, the coefficients (A, B, C and θ ₀ ) of the above formula (1) are obtained. After that, when the stretched film is continuously produced as shown in FIG. 1, the lower limit processing time t _min and the upper limit processing time t _max of the heat relaxation treatment may be calculated from the above formula (1). ..

Further, in the present embodiment, the stretching step in the stretched zone is not limited to the simultaneous biaxial stretching described above, and may be stretched only in one axis (length direction or width direction of the film) or the length of the film. It may be sequentially stretched in the longitudinal direction and the width direction.

Further, in the above-mentioned example, a method of making the orientation angle of the film uniform along the width direction by heat relaxation treatment with the width direction of the film as a reference axis has been illustrated, but in the present embodiment, the film The orientation angle of the film may be made uniform along the length direction by heat relaxation treatment with the length direction as the reference axis.

For example, when the film before stretching is originally oriented along the length direction, or when the stretching ratio in the length direction of the film is higher than the stretching ratio in the width direction of the film in the stretching step. In the film after stretching, the orientation angle of the film may be made uniform in the length direction by the heat relaxation treatment.

Therefore, for example, for a film stretched in a stretching step, the maximum orientation angle (usually, the orientation angles at both ends in the width direction of the film) before the heat relaxation treatment is 30 ° or less with respect to the width direction of the film. In some cases, the width direction of the film is used as the reference axis, and the orientation angle of the film is made uniform along the width direction by the heat relaxation treatment, while the maximum orientation angle before the heat relaxation treatment (usually). , Orientation angle at both ends in the width direction of the film) is 60 ° or more with respect to the width direction of the film, the orientation angle of the film is set to the length by heat relaxation treatment with the length direction of the film as the reference axis. It is preferable to make the film uniform along the direction.

When the orientation angle of the film is made uniform along the length direction by the heat relaxation treatment, the angle θ ₀ of the alignment angle approximate straight line before the heat relaxation treatment in the above equations (1) and (2). , The standard value (target value) φ _min of the orientation angle of the stretched film and the control limit value φ _max of the orientation angle of the stretched film are set by setting an angle with the length direction of the film as a reference axis, and the above equation (1). ) And equation (2), the lower limit processing time t _min and the upper limit processing time t _max can be calculated.

100 ... Film 200 ... Clip

Claims (7)

A stretching step in which a film of a thermoplastic resin is stretched in one or two directions while being heated to a glass transition temperature of T _g or higher of the thermoplastic resin.
A cooling step of cooling the stretched film at a temperature _lower than the glass transition temperature Tg, and
A method for producing a stretched film, which comprises a heat relaxation step of heat-relaxing the cooled film by heating it at a heat treatment temperature _Tr of the glass transition temperature T _g or higher.
A method for producing a stretched film, wherein the heat relaxation time in the heat relaxation step is at least the lower limit processing time t _min (seconds) calculated by the following formula (1).

(In the above formula (1), A, B, C and θ ₀ all carry out the stretching step, the cooling step and the heat relaxation step in advance using the thermoplastic resin film. The coefficient obtained by trying the process , φ _min, is the orientation angle (°) of the stretched film to be obtained, and L is the width (mm) of the stretched film to be obtained). The method for producing a stretched film according to claim 1, wherein the film cooled in the cooling step is once wound, and then the heat relaxation step is performed on the wound film. The method for producing a stretched film according to claim 1, wherein the heat relaxation step is continuously performed on the film cooled in the cooling step from the cooling step. The invention according to any one of claims 1 to 3, wherein in the heat relaxation step, the heat relaxation time is not less than the lower limit processing time t _{min and not} more than the upper limit processing time t _max (seconds) represented by the following formula (2). Method for producing a stretched film.

(In the above formula (2), φ _max is the control limit value (°) of the orientation angle of the stretched film to be obtained). The method for producing a stretched film according to any one of claims 1 to 4, wherein the thermoplastic resin is an amorphous resin. The method for producing a stretched film according to any one of claims 1 to 5, wherein the thermoplastic resin is a resin containing polycarbonate. A method for producing an optical film using a stretched film obtained by the production method according to any one of claims 1 to 6 .

Images