Method for producing stretched film
阅读说明：本技术 拉伸膜的制造方法 (Method for producing stretched film ) 是由 平田聪 清水享 山本真士 村冈敦史 于 2019-01-10 设计创作，主要内容包括：本发明拉伸膜的制造方法包括：采用间距在纵方向上变化的可变间距型的左右的夹具分别抓持长条状的膜的左右端部,并且改变在左右的夹具中的至少一者的夹具间距,从而斜向拉伸该膜；从夹具松开该膜并冷却该膜；和使用非接触方式的加热手段在将该膜加热至Tg-30℃～Tg-10℃的同时向该膜在长度方向上施加100N/m～400N/m的张力。(The method for producing a stretched film of the present invention comprises: gripping left and right end portions of a long film with left and right clamps of a variable pitch type whose pitch varies in the longitudinal direction, respectively, and changing the clamp pitch of at least one of the left and right clamps, thereby obliquely stretching the film; releasing the film from the clamp and cooling the film; and applying a tension of 100N/m to 400N/m to the film in a longitudinal direction while heating the film to Tg-30 ℃ to Tg-10 ℃ by using a heating means of a non-contact manner.)
1. A method of manufacturing a stretched film, comprising:
the long film is obliquely stretched by:
gripping the left and right ends of the film with a variable-pitch type left and right gripper configured such that the gripper pitch varies in the longitudinal direction; and
changing a clip pitch of a clip of at least one of the left and right clips;
releasing the film from the clamp and cooling the film; and
applying a tension of 100N/m to 400N/m to the film in a longitudinal direction while heating the film to Tg-30 ℃ to Tg-10 ℃ by a heating means in a non-contact manner.
2. The manufacturing method according to claim 1, wherein the heating means is a hot air type heating means.
3. The production method according to claim 1 or 2, wherein a thermal conductivity from the heating means to the film is 50W/m-K to 500W/m-K.
4. The production method according to any one of claims 1 to 3, wherein the application of the tension is performed by adjusting the tension applied to the film between conveying rollers.
5. The production method according to any one of claims 1 to 4, wherein a material for forming the film comprises a polycarbonate-based resin, a polyester carbonate-based resin, a cycloolefin-based resin, a cellulose-based resin, or a mixture thereof.
6. The production method according to any one of claims 1 to 5, wherein the obliquely-stretched film is stretched so that an in-plane retardation Re (550) of the film is 100nm to 180 nm.
7. A method of manufacturing an optical stack, comprising:
a long stretched film obtained by the manufacturing method according to any one of claims 1 to 6; and
the optical film and the stretched film are continuously laminated while conveying the optical film and the stretched film in a long form while aligning the longitudinal directions of the optical film and the stretched film with each other.
8. The method for producing an optical laminate according to claim 7,
wherein the optical film is a polarizing plate, and
wherein the stretched film is a lambda/4 plate.
Technical Field
The present invention relates to a method for producing a stretched film and a method for producing an optical laminate.
Background
For the purpose of improving display characteristics and preventing reflection, circular polarizing plates have been used in image display devices such as liquid crystal display devices (LCDs) or organic electroluminescent display devices (OLEDs). A circularly polarizing plate is typically obtained by laminating a polarizer and a phase difference film (typically, a λ/4 plate) in such a manner that the absorption axis of the polarizer and the slow axis of the phase difference film may form an angle of 45 °. Heretofore, a retardation film has been typically produced by subjecting to uniaxial stretching or biaxial stretching in the longitudinal direction and/or the transverse direction, and therefore, in many cases, the slow axis thereof appears in the transverse direction (width direction) or the longitudinal direction (length direction) of the original film. As a result, in order to produce the circularly polarizing plate, the following needs to be performed. The phase difference film was cut at an angle of 45 ° to the width direction or the longitudinal direction, and the resulting sheet material 1 was laminated 1 by 1.
In order to solve such a problem, a technique of causing the slow axis of the retardation film to appear in an oblique direction has been proposed, which involves stretching a long film in an oblique direction by: gripping left and right ends (ends in the width direction) of the film with left and right variable-pitch clamps having a clamp pitch that varies in the longitudinal direction; and the jig pitch of at least one of the left and right jigs is changed (for example, patent document 1). However, when the obliquely stretched film obtained by such a technique is wound up on a roll, wrinkles (wrinkle) or wrinkles (crumple) sometimes occur. In addition, when the obliquely stretched film is bonded to another optical film, uneven coating or uncoated portions of the adhesive or the pressure-sensitive adhesive may occur, and wrinkles or wrinkles may occur.
Reference list
Patent document
[PTL 1]JP 4845619 B2
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to solve the above-mentioned problems occurring when a obliquely stretched film is wound up and when it is laminated with another optical film.
Means for solving the problems
According to an embodiment of the present invention, there is provided a method of manufacturing a stretched film, including: the long film is obliquely stretched by: gripping left and right ends of the film with left and right variable-pitch clamps having a clamp pitch that varies in the longitudinal direction, respectively, and changing the clamp pitch of at least one of the left and right clamps; releasing the film from the clamp and cooling the film; and applying a tension of 100N/m to 400N/m to the film in a length direction while heating the film to Tg-30 ℃ to Tg-10 ℃ by a heating means in a non-contact manner.
In one embodiment, the heating means is a hot air heating means.
In one embodiment, the thermal conductivity from the heating means to the film is from 50W/mK to 500W/mK.
In one embodiment, applying tension is performed by adjusting the tension applied to the film between the transport rollers.
In one embodiment, the film-forming material includes a polycarbonate-based resin, a polyester carbonate-based resin, a cycloolefin-based resin, a cellulose-based resin, or a mixture thereof.
In one embodiment, the obliquely stretched film is stretched in such a manner that the in-plane retardation Re (550) of the film is 100nm to 180 nm.
According to another embodiment of the present invention, there is provided a method of manufacturing an optical stack, including: obtaining a long stretched film by the manufacturing method; and continuously attaching the optical film and the stretched film while conveying the optical film and the stretched film in a long form while aligning the longitudinal directions of the optical film and the stretched film with each other.
In one embodiment, the optical film is a polarizing plate and the stretched film is a λ/4 plate.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a predetermined tension is applied to an obliquely stretched film in the longitudinal direction thereof while heating it to a predetermined temperature. Therefore, the above-described problems occurring when the stretched film is wound up and when it is laminated with another optical film are solved, and therefore a stretched film excellent in quality can be obtained.
Drawings
Fig. 1 is a schematic plan view for explaining the overall constitution of one example of a stretching apparatus which can be used for the production method of the present invention.
Fig. 2 is a schematic cross-sectional view of a circularly polarizing plate using a retardation film obtained by the production method of the present invention.
Fig. 3 is a schematic view for explaining a measuring method of sag (sagging amount).
Detailed Description
The inventors of the present invention have studied the cause of the above-described problem occurring when the obliquely stretched film is wound up and when it is laminated with another optical film, and as a result, have found that: sagging occurs at one or both ends in the width direction of the stretched film during conveyance of the stretched film by the rollers, and winding or lamination of the film in a state having sagging causes generation of wrinkles or wrinkles; and the application of the adhesive or pressure-sensitive adhesive to the film in a state having sag causes the generation of coating unevenness or uncoated portions. Specifically, as shown in fig. 3, the
The reason why the drooping occurs is presumed as follows. That is, in the oblique stretching, one end portion and the other end portion of the film are different from each other in, for example, timing, number of times, order, and the like of stretching or shrinking, and therefore, the stretching processes at both end portions become asymmetric with each other with respect to the center in the width direction. In addition, the thermal histories of the two end portions may be different from each other. As a result, the amount of deformation and the properties of the obliquely stretched film become nonuniform in the width direction. Further, even when the jig is released after the film is fixed by cooling to a temperature below its Tg, the film slightly shrinks when the jig is released because its shape is not sufficiently stabilized. In this case, the shrinkage amount becomes nonuniform in the width direction of the film. As a result of the foregoing, sagging may occur in the film after the oblique stretching (for example, at the end portion, particularly at the end portion).
The relationship between the amount of deformation and the amount of sagging of the end portion was studied in the following manner: the length and the amount of sagging of the end portions and the center portion in the width direction of the film were measured in a state where the film sagging at the end portions was set up on conveying rollers having an inter-roller distance of 1000 mm. As a result, it was found that the sagging amount reached about 10mm when the length of the end portion was only 0.25mm longer than the length (the distance between the rollers was 1000mm) of the portion having no sagging (the center portion in the width direction). As shown in fig. 3, the maximum distance (L) was obtained by measuring the distance from the
In the present invention, a predetermined tension is applied to the obliquely stretched film in the longitudinal direction thereof while heating it to a predetermined temperature. Therefore, the drooping is reduced, and as a result, the above-described problem caused by the drooping is solved. Now, preferred embodiments of the present invention are described. However, the present invention is not limited to these embodiments.
A. Method for producing stretched film
The method for producing a stretched film of the present invention comprises: the long film is obliquely stretched by: gripping the left and right ends (ends in the width direction) of the film with a variable-pitch type left and right gripper having a gripper pitch that varies in the longitudinal direction, and changing the gripper pitch of at least one of the left and right grippers (oblique stretching step); releasing the film from the jig and cooling the film (releasing-cooling step); and applying a tension of 100N/m to 400N/m in the longitudinal direction to the film while heating the film to Tg-30 ℃ to Tg-10 ℃ by a heating means in a non-contact manner (tension applying step). As used herein, the term "jig pitch in the longitudinal direction" means a distance between centers of jigs adjacent to each other in the longitudinal direction in the moving direction. Now, each step will be described in detail.
[ oblique stretching step ]
First, an example of a stretching apparatus applicable to the manufacturing method of the present invention will be described with reference to fig. 1. Fig. 1 is a schematic plan view for explaining the overall constitution of one example of a stretching apparatus which can be used for the production method of the present invention. The stretching apparatus 100 has, on both left and right sides, an annular ring (end loop)10L and an annular ring 10R each provided with a plurality of clamps 20 for gripping the film in such a manner that the rings can be bilaterally symmetrical to each other, when viewed in a plan view. In this specification, the left annular ring is referred to as "left annular ring 10L" and the right annular ring is referred to as "right annular ring" when viewed from the inlet side of the membrane. The clamps 20 of the left and right annular rings 10L and 10R are each guided by the reference rail 70 to move cyclically in an annular manner. The left annular ring 10L is cyclically moved in the counterclockwise direction, and the right annular ring is cyclically moved in the clockwise direction. In the stretching apparatus, a grip area a, a preheating area B, a stretching area C, and a releasing area D are provided in this order from the inlet side of the sheet toward the outlet side of the sheet. These regions mean regions in which the film to be stretched is held, preheated, obliquely stretched, and unwound substantially separately, and do not mean mechanically or structurally independent blocks. In addition, the following facts should be noted: the ratio between the lengths of the regions is different from the actual length ratio. Further, a region (not shown) for performing any appropriate process may be provided between the stretching region C and the releasing region D as necessary. Examples of such treatments include machine direction shrinking treatments and cross direction stretching treatments, and the like.
In the grip area a and the preheating area B, the left and right annular rings 10L and 10R are configured to be substantially parallel to each other while being spaced apart from each other by a distance corresponding to the initial width of the film to be stretched. In the stretch zone C, the left and right annular rings 10L and 10R are constituted in the following manner: the distance separating the rings from each other may be gradually enlarged from the preheating region B side toward the releasing region D until the distance corresponds to the stretched width of the film. In the unclamp region D, the left and right annular rings 10L and 10R are configured to be substantially parallel to each other while being spaced apart from each other by a distance corresponding to the stretched width of the film.
The gripper (left gripper) 20 of the left annular ring 10L and the gripper (right gripper) 20 of the right annular ring 10R are cyclically movable independently of each other. For example, the driving sprockets 11 and 12 of the left annular ring 10L are rotationally driven in the counterclockwise direction by the electric motors 13 and 14, and the driving sprockets 11 and 12 of the right annular ring 10R are rotationally driven in the clockwise direction by the electric motors 13 and 14. As a result, a traveling force is applied to the jig carrying member (not shown) of each drive roller (not shown) engaged with the driving sprockets 11 and 12. Thus, the left annular ring 10L is cyclically moved in the counterclockwise direction, and the right annular ring 10R is cyclically moved in the clockwise direction. The left and right annular rings 10L and 10R can be each independently cyclically moved by driving the left and right electric motors independently of each other.
Further, the jig (left jig) 20 of the left annular ring 10L and the jig (right jig) 20 of the right annular ring 10R are each of a variable pitch type. That is, the jig pitches of the left and right jigs 20 and 20 in the longitudinal direction may each independently vary with their movements. The variable pitch type configuration can be realized by adopting a driving mode such as a pantograph mode, a linear motor mode, or a motor/chain mode. For example, patent document 1 describes a zoom apparatus mode connection mechanism in detail.
A stretched film, for example, a retardation film having a slow axis in an oblique direction can be produced by obliquely stretching the film using the stretching apparatus as described above.
Specifically, in the grip area a (the entrance of the stretching apparatus 100 into which the film is taken), both side edges of the film to be stretched are gripped with the grippers 20 of the left and right annular rings 10L and 10R at a constant gripper pitch equal to each other or at a gripper pitch different from each other, and the film is supplied to the preheating area B by the movement of the left and right annular rings 10L and 10R (substantially, the movement of each gripper carrying member guided by the reference rail 70).
In the preheating zone B, as described above, the left and right annular rings 10L and 10R are configured to be substantially parallel to each other while being spaced apart from each other by a distance corresponding to the initial width of the film to be stretched, and thus the film is heated substantially without transverse stretching or longitudinal stretching. However, the distance between the left and right jigs (the distance in the width direction) may be slightly enlarged so as to avoid inconveniences such as: the film sags due to preheating and thus comes into contact with the nozzle inside the oven.
In the preheating, the film was heated to a temperature T1 (. degree. C.). The temperature T1 is preferably equal to or greater than the glass transition temperature (Tg) of the film, more preferably equal to or greater than Tg +2 ℃, and still more preferably equal to or greater than Tg +5 ℃. Meanwhile, the heating temperature T1 is preferably equal to or less than Tg +40 ℃, more preferably equal to or less than Tg +30 ℃. The temperature T1 is, for example, 70 to 190 c, preferably 80 to 180 c, although the temperature varies depending on the film to be used.
The time required for the temperature of the film to rise to the temperature T1 and the time for which the temperature thereof is kept at the temperature T1 may be appropriately set depending on the constituent material of the film and the conditions for producing the film (for example, the conveying speed of the film). The temperature rise time and the holding time can be controlled by, for example, adjusting the moving speed of the jig 20, the length of the preheating zone, the temperature of the preheating zone, and the like.
In stretch zone C, the film is obliquely stretched by: the jig pitch of at least one of the left and right jigs 20 in the longitudinal direction is changed. For example, as shown in the figure, the diagonal stretching may be performed while increasing the distance between the left and right jigs (the distance in the width direction). Alternatively, unlike the illustrated example, the diagonal stretching may be performed while maintaining the distance between the left and right clamps.
In one embodiment, the bias stretching may be performed in the following manner: in a state in which a position where the jig pitch of one jig among the left and right jigs starts to increase or decrease and a position where the jig pitch of the other jig starts to increase or decrease are set to different positions in the longitudinal direction, the jig pitch of each side jig is increased or decreased to a predetermined pitch.
In another embodiment, the bias stretching may be performed in the following manner: while the clamp pitch of one of the left and right clamps is fixed, the clamp pitch of the other clamp is increased or decreased to a predetermined pitch and then restored to the original clamp pitch.
In yet another embodiment, the bias stretching may be performed in the following manner: (i) the distance between the clamps on one side of the left and right clamps is increased, and the distance between the clamps on the other side is reduced; and (ii) changing the jig pitch of each side jig in such a manner that the reduced jig pitch and the increased jig pitch become a predetermined pitch equal to each other.
As a specific mode for performing the oblique stretching, those described in patent document 1, JP2013-54338A, JP2014-194482A, JP 2014-.
The bias stretching may typically be performed at a temperature T2. In the case where Tg represents the glass transition temperature of the resin film, the temperature T2 is preferably from Tg-20 ℃ to Tg +30 ℃, more preferably from Tg-10 ℃ to Tg +20 ℃, particularly preferably about Tg. The temperature T2 is, for example, 70 to 180 c, preferably 80 to 170 c, although the temperature varies depending on the resin film to be used. The difference between the temperature T1 and the temperature T2 (T1-T2) is preferably + -2 ℃ or higher, more preferably + -5 ℃ or higher. In one embodiment, T1> T2, therefore, a film heated to a temperature T1 in a pre-heat zone can be cooled to a temperature T2.
The longitudinal shrinkage treatment and the transverse stretching treatment are performed after the oblique stretching. For these treatments after the oblique stretching, refer to paragraphs 0029 to 0032 of JP 2014-194483A.
[ unclamping-Cooling step ]
In the unclamping region, the clamp holding the film is unclamped and the film is cooled. The release of the clamp is typically performed after cooling the film to a temperature equal to or less than Tg. If necessary, the film is subjected to heat treatment to fix its stretched state (heat fixation), and cooled to a temperature equal to or less than Tg, and then the jig is released.
The film is cooled, for example, to a temperature of less than Tg-30 deg.C, preferably equal to or less than Tg-35 deg.C, more preferably equal to or less than Tg-40 deg.C. In one embodiment, the film is cooled to a temperature of less than Tg-30 deg.C, preferably equal to or less than Tg-35 deg.C, more preferably equal to or less than Tg-40 deg.C, and then the clamps are released. In another embodiment, the clamps are released at a film temperature of Tg to Tg-30 deg.C, and then the film is further cooled to a temperature of less than Tg-30 deg.C, preferably equal to or less than Tg-35 deg.C, more preferably equal to or less than Tg-40 deg.C. When the stretched film is sufficiently cooled to complete the deformation of the film which causes sagging, the deformation can be adjusted to be bilaterally symmetric in the tension applying step, thereby appropriately reducing the sagging. In the latter embodiment, the cooling of the film after releasing the clamps may be performed in the release region (in other words, in the oblique stretching apparatus), or may be performed during the conveyance of the film to the tension applying step after the film has been sent out from the outlet of the stretching apparatus.
The heat treatment may typically be carried out at a temperature T3. The temperature T3 varies depending on the film to be stretched. In some cases, T2 ≧ T3, and in other cases, T2< T3. In general, when the film is an amorphous material, T2 ≧ T3, and when the film is a crystalline material, the crystallization treatment can be performed by setting T2 and T3 in such a manner that T2 can be smaller than T3. When T2 is not less than T3, the difference between the temperatures T2 and T3 (T2-T3) is preferably 0 ℃ to 50 ℃. The heat treatment time is typically 10 seconds to 10 minutes.
[ tension applying step ]
In the tension applying step, a tension of 100N/m to 400N/m is applied to the stretched film released from the jig in the longitudinal direction while heating the film to Tg-30 ℃ to Tg-10 ℃. When a predetermined tension is applied in such a temperature range, it is possible to reduce the sag while suppressing the variation in optical characteristics (e.g., phase difference, axis angle, and the like) of those obtained by the oblique stretching. In one embodiment, the amount of sagging reduced by the tension applying step (the amount of sagging of the stretched film before the tension applying step — the amount of sagging after the tension applying step) is, for example, 6mm or more, preferably 8mm or more, more preferably 10mm or more, and further preferably 12mm or more. The sag of the stretched film after the application of tension is preferably less than 8mm, more preferably 6mm or less, and further preferably 5mm or less.
The stretched film is heated by a non-contact heating means. The use of the heating means in a non-contact manner can prevent the generation of wrinkles or scars (flaw). Examples of the heating means in the non-contact manner include a hot air type heating means, a near infrared heating means, a far infrared heating means, a microwave heating means, and the like.
The thermal conductivity from the heating means to the stretched film is preferably 50W/mK to 500W/mK, more preferably 100W/mK to 300W/mK. When the thermal conductivity falls within the above range, generation of wrinkles or scars upon heating the stretched film can be prevented. The thermal conductivity can be determined as follows.
Method for measuring thermal conductivity
Heating means of the object was set from room temperature (T) in a state where the thermocouple was fixed to the filmini) To a predetermined set temperature (T)set) And the temperature change of the film during this process is measured. The mixture is cooled to room temperature (T)ini) And a set temperature (T)set) Substituted into the following equation (1), and solved by factoring in the temperature dependence of specific heat, thereby being transformed into equation (2). Next, equation (2) is fitted to the temperature change data of the film, thereby finding the thermal conductivity.
(wherein ρ is density [ kg/m ]3]、Cp: specific heat [ J/kgK ]]T: time [ sec ]]T: film temperature [ K ]]V: volume [ m ]3]H: thermal conductivity coefficient [ J/kgK]、Tset: set temperature [ K]、Tini: initial temperature [ K ]]S: area [ m ]2]A, b: temperature constant of specific heat, d: film thickness [ m ]])
The heating temperature (film temperature) is from Tg-30 ℃ to Tg-10 ℃, preferably from Tg-25 ℃ to Tg-10 ℃, more preferably from Tg-20 ℃ to Tg-10 ℃. When the heating temperature is less than Tg-30 ℃, the sag reducing effect becomes insufficient. Meanwhile, when the heating temperature exceeds Tg-10 ℃, the change in optical characteristics increases.
The tension applied to the stretched film is 100N/m to 400N/m, and may preferably be 120N/m to 380N/m, more preferably 150N/m to 350N/m. When the tension falls within the above range, only the non-sagging portion of the film takes the tension, with the result that the non-sagging portion extends very slightly while the length of the sagging portion thereof is constant, thereby having a length close to the sagging portion. As a result, it is possible to suitably reduce the sag while avoiding the change in optical characteristics and the breakage of the film. Meanwhile, when the tension is less than 100N/m, the sag reducing effect may become insufficient. In addition, when the tension exceeds 400N/m, the stretched film may break.
The application of tension is preferably performed between the transport rollers. Specifically, the tension may be applied by: the tension applied to the stretched film between the conveying rollers is measured, and the rotation speed of each conveying roller, for example, is controlled in such a manner that the tension can take a desired value. Herein, the conveying roller encompasses a nip roller, a feed roller, a suction roller, and the like.
The time for applying the tension can be appropriately set according to the film formation material, the sagging amount, and the like. This time may be, for example, 5 seconds to 60 seconds.
After the application of the tension is completed, the tension applied to the film is removed, and the film may be wound on a roll in a conventional manner.
B. Film to be stretched
In the production method of the present invention, any suitable film may be used. Examples thereof are films that can be used as phase difference films. As a constituent material of this film, for example: polycarbonate-based resins, polyvinyl acetal-based resins, cycloolefin-based resins, acrylic-based resins, cellulose ester-based resins, cellulose-based resins, polyester carbonate-based resins, olefin-based resins, and polyurethane-based resins. Among them, a polycarbonate-based resin, a polyvinyl acetal-based resin, a cellulose ester-based resin, a polyester-based resin, or a polyester carbonate-based resin is preferable because a retardation film exhibiting so-called reverse wavelength dispersion dependency (reverse wavelength dispersion dependency) can be obtained by using any of these resins. These resins may be used alone or in combination according to the desired characteristics.
Any suitable polycarbonate-series resin is used as the polycarbonate-series resin. A preferred example thereof is a polycarbonate resin comprising a structural unit derived from a dihydroxy compound. Specific examples of the dihydroxy compound include 9, 9-bis (4-hydroxyphenyl) fluorene, 9-bis (4-hydroxy-3-methylphenyl) fluorene, 9-bis (4-hydroxy-3-ethylphenyl) fluorene, 9-bis (4-hydroxy-3-n-propylphenyl) fluorene, 9-bis (4-hydroxy-3-isopropylphenyl) fluorene, 9-bis (4-hydroxy-3-n-butylphenyl) fluorene, 9-bis (4-hydroxy-3-sec-butylphenyl) fluorene, 9-bis (4-hydroxy-3-tert-butylphenyl) fluorene, 9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, 9, 9-bis (4-hydroxy-3-phenylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) phenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-methylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-isopropylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-isobutylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-tert-butylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-cyclohexylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-phenylphenyl) fluorene, 9, 9-bis (4- (2-hydroxyethoxy) -3, 5-dimethylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-tert-butyl-6-methylphenyl) fluorene, and 9, 9-bis (4- (3-hydroxy-2, 2-dimethylpropoxy) phenyl) fluorene, and the like. The polycarbonate resin may contain a structural unit derived from the above dihydroxy compound and a structural unit derived from a dihydroxy compound such as isosorbide, isomannide, isoidide, spiroglycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), or bisphenols.
The details of the polycarbonate-series resin as described above are described in, for example, JP 2012-67300A and JP 3325560B2, the descriptions of which are incorporated herein by reference.
The glass transition temperature of the polycarbonate-based resin is preferably 110 ℃ or higher and 250 ℃ or lower, more preferably 120 ℃ or higher and 230 ℃ or lower. When the glass transition temperature is too low, the heat resistance of the resin tends to deteriorate, and therefore the resin may cause dimensional change after it is formed into a film. When the glass transition temperature is too high, the molding stability of the resin at the time of molding the resin into a film may be deteriorated. In addition, the transparency of the film may be impaired. The glass transition temperature was determined in accordance with JIS K7121 (1987).
Any suitable polyvinyl acetal resin can be used as the polyvinyl acetal resin. Typically, the polyvinyl acetal resin can be obtained by subjecting at least 2 kinds of aldehyde compounds and/or ketone compounds to condensation reaction with a polyvinyl alcohol resin. Specific examples of polyvinyl acetal resin and detailed production methods are described in, for example, JP 2007-161994A, the description of which is incorporated herein by reference.
The refractive index characteristic of the retardation film obtained by stretching the film to be stretched is preferably such that it shows a relationship of nx > ny. Further, the retardation film preferably functions as a λ/4 plate. The in-plane retardation Re (550) of the retardation film is preferably 100nm to 180nm, more preferably 135nm to 155 nm. In this specification, nx represents a refractive index in a direction in which an in-plane refractive index becomes maximum (i.e., a slow axis direction), ny represents a refractive index in a direction orthogonal to the slow axis in a plane (i.e., a fast axis direction), and nz represents a refractive index in a thickness direction. Further, Re (. lamda.) represents the in-plane retardation of the film measured at 23 ℃ with light having a wavelength of. lamda.nm. Thus, Re (550) represents the in-plane retardation of the film measured at 23 ℃ with light having a wavelength of 550 nm. Re (λ) is found by the equation "Re (λ) ═ nx-ny) × d", where "d" represents the thickness (nm) of the film.
The in-plane retardation Re (550) of the retardation film can be made to fall within a desired range by appropriately setting the oblique stretching conditions. For example, a method for producing a retardation film having an in-plane retardation Re (550) of 100nm to 180nm by oblique stretching is disclosed in detail in JP2013-54338A, JP2014-194482A, JP 2014-238524A or JP 2014-194484A and the like. Therefore, the person skilled in the art can set appropriate oblique stretching conditions based on the disclosure.
The slow axis direction of the retardation film is preferably 30 ° to 60 ° or 120 ° to 150 °, more preferably 38 ° to 52 ° or 128 ° to 142 °, further preferably 43 ° to 47 ° or 133 ° to 137 °, particularly preferably about 45 ° or about 135 °, with respect to the longitudinal direction of the film.
The retardation film preferably exhibits so-called inverse wavelength dispersion dependence. Specifically, the in-plane retardation satisfies the relationship of Re (450) < Re (550) < Re (650). Re (450)/Re (550) is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.95. Re (550)/Re (650) is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.97.
The absolute value of the photoelastic coefficient of the retardation film is preferably 2 × 10-12(m2/N)～100×10-12(m2/N), preferably 10 × 10-12(m2/N)～50×10-12(m2/N)。
C. Optical laminate and method for producing optical laminate
The stretched film obtained by the production method of the present invention can be used as an optical laminate by laminating with another optical film. For example, the retardation film obtained by the production method of the present invention can be suitably used as a circular polarizing plate by being laminated with a polarizing plate.
Fig. 2 is a schematic cross-sectional view of an example of such a circularly polarizing plate. The circular polarizing plate 200 of the illustrated example includes a polarizer 210, a 1 st protective film 220 disposed on one side of the polarizer 210, a 2 nd protective film 230 disposed on the other side of the polarizer 210, and a
The retardation film obtained by the manufacturing method of the present invention is long and has a slow axis in an oblique direction (a direction of, for example, 45 ° with respect to the longitudinal direction). In many cases, the long polarizing plate has an absorption axis in the longitudinal direction or the width direction. Therefore, the use of the retardation film obtained by the production method of the present invention ensures the use of a so-called roll-to-roll process and ensures the production of a circular polarizing plate with extremely excellent production efficiency. The roll-to-roll method refers to a method involving: the respective films are continuously laminated while being conveyed by rollers in a long form with their longitudinal directions aligned with each other.