JP2018028641A - Method for manufacturing cellulose ester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the surface roughness of a cellulose ester film while suppressing the increase of haze caused by fine particles and stretching.SOLUTION: A method for manufacturing a cellulose ester film comprises a dope preparation step (S11), a flow casting step (S12) and a stretching step. When the degrees of substitution of total acyl groups of cellulose acylates A and B included in a dope are set to TA and TB, respectively, a relation is 2.3≤TA≤2.8 and -1.0≤TB-TA≤-0.3. The added amount of the cellulose acylate B is smaller than that of the cellulose acylate A. The stretching step comprises the first stretching step (S15) of stretching a web in the state that the amount of a residual solvent is more than 1 mass% and 15 mass% or less and the second stretching step (S17) of stretching the web in the state that the amount of residual solvent is 0.02 mass% or more and 1 mass% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a cellulose ester film, in which a cellulose ester film is produced by a solution flow casting method.

  In the production of a cellulose ester film by a solution casting method, a dope containing a cellulose ester resin and a solvent is cast on an endless belt, which is a metal support, and dried on the endless belt to form a web. And after peeling this web from an endless belt, it is extended and dried to make a cellulose ester film. The formed cellulose ester film is finally wound up in a roll shape to become a film original.

  The cellulose ester film formed as described above can be applied to a polarizing plate protective film of a liquid crystal display device, for example. At this time, the cellulose ester resin which comprises a cellulose-ester film may be one type, and may be two or more types. For example, in Patent Document 1, a polarizing plate protective film is formed using two types of cellulose ester resins having different characteristics, and is bonded to a polarizer at high speed without involving air using a photocurable adhesive. It is possible to realize a polarizing plate protective film having high heat resistance and high adhesion to a polarizer. Patent Document 1 discloses that a functional thin film such as a cured layer (hard coat layer) or an antireflection layer may be formed after film formation.

JP 2013-61365 A (refer to claim 1, paragraphs [0009] to [0012], [0120], etc.)

  A polarizing plate protective film with a hardened layer (hereinafter also referred to as an optical film) is formed by, for example, applying a composition for forming a hardened layer on a cellulose ester film and curing it by ultraviolet irradiation to form a hardened layer (coating layer). Can be manufactured. The manufactured optical film is wound into a roll and stored or transported.

  By the way, in the process of manufacturing a polarizing plate, for example, when coating is performed on a cellulose ester film that has been heat-stretched at a high magnification and the optical film is wound up, failure (for example, sticking of an optical film called blocking) frequently occurs. found. When the cause of this failure was investigated, the surface roughness of the cellulose ester film hot stretched at a high magnification was small, and the surface roughness of the cured layer was also reduced following the surface roughness of the underlying cellulose ester film. It is considered that sticking easily occurs and blocking occurs. When blocking occurs in the optical film, local deformation occurs in the optical film at the location where blocking occurs, so it is necessary to reduce blocking as much as possible.

  In order to reduce the blocking of the optical film, it is necessary to ensure the surface roughness of the cellulose ester film that is the base of the cured layer. To that end, the cellulose ester is added by adding fine particles called matting agent to the dope. It is effective to form a film. At this time, in order to reliably reduce the blocking of the optical film, when the addition amount of the fine particles is increased during the production of the cellulose ester film or the fine particles having a large average particle diameter are used, the haze indicating the transparency of the cellulose ester film. Rise (become worse). Moreover, the haze of a film also rises by the stress at the time of high-strength heat stretching. Therefore, it is desired to produce a cellulose ester film so that the surface roughness of the cellulose ester film can be ensured while suppressing an increase in haze caused by fine particles and stretching. However, a method for producing such a cellulose ester film has not been proposed so far.

  The present invention has been made in order to solve the above-mentioned problems, and the object thereof is cellulose capable of ensuring the surface roughness of a cellulose ester film while suppressing an increase in haze caused by fine particles and stretching. It is providing the manufacturing method of an ester film.

  The above object of the present invention is achieved by the following manufacturing method.

1. A method for producing a cellulose ester film by a solution casting film forming method,
A dope preparation step of preparing a dope containing cellulose acylates A and B, fine particles, and a solvent;
Casting a dope on the support to form a web on the support; and
Stretching step to obtain the cellulose ester film by stretching the web,
When the total acyl group substitution degree of the cellulose acylate A is TA and the total acyl group substitution degree of the cellulose acylate B is TB,
2.3 ≦ TA ≦ 2.8
−1.0 ≦ TB−TA ≦ −0.3
And
The amount of cellulose acylate B added is less than the amount of cellulose acylate A added,
The stretching step includes
A first stretching step of stretching the web in a state where the residual solvent amount is greater than 1% by mass and 15% by mass or less;
After the said 1st extending | stretching process, the 2nd extending | stretching process of extending | stretching the said web in the state whose residual solvent amount is 0.02 mass% or more and 1 mass% or less is included, The manufacturing method of the cellulose-ester film characterized by the above-mentioned.

  2. In the plane including the width direction and the conveying direction of the web, the second stretching step extends the web in a direction that forms an angle larger than 0 ° and smaller than 90 ° with respect to the width direction. 2. The method for producing a cellulose ester film as described in 1 above, which comprises a stretching step.

  3. The ratio of the addition amount of the said cellulose acylate B with respect to the sum total of the addition amount of the said cellulose acylate A and B is 1% or more and 5% or less, Manufacture of the cellulose-ester film of said 1 or 2 characterized by the above-mentioned. Method.

  4). 4. The method for producing a cellulose ester film according to any one of 1 to 3, wherein in the first stretching step, the web is stretched in a state where the residual solvent amount is 2% by mass or more and 15% by mass or less.

  5. The method for producing a cellulose ester film according to any one of 1 to 4, wherein the cellulose acylates A and B are cellulose acetate propionate.

  According to said manufacturing method, the surface roughness of a cellulose-ester film is securable, suppressing the raise of the haze resulting from microparticles | fine-particles and extending | stretching.

It is a flowchart which shows the manufacturing process of the optical film which concerns on embodiment of this invention. It is explanatory drawing which shows the structure of the outline of the manufacturing apparatus of the cellulose-ester film by a solution casting film forming method. It is explanatory drawing which shows typically an example of the rail pattern of the tenter which performs diagonal extending | stretching. It is sectional drawing which shows the schematic structure of the said optical film.

  An embodiment of the present invention will be described below with reference to the drawings. In the present specification, when the numerical range is expressed as A to B, the numerical value range includes the values of the lower limit A and the upper limit B.

The method for producing a cellulose ester film of the present embodiment is a method for producing a cellulose ester film by a solution casting film forming method, and is a dope for preparing a dope containing cellulose acylates A and B, fine particles, and a solvent. A preparation step, a casting step of casting the dope on a support to form a web on the support, and a stretching step of stretching the web to obtain the cellulose ester film. And, when the total acyl group substitution degree of the cellulose acylate A is TA and the total acyl group substitution degree of the cellulose acylate B is TB,
2.3 ≦ TA ≦ 2.8
−1.0 ≦ TB−TA ≦ −0.3
It is. Further, the addition amount of the cellulose acylate B is smaller than the addition amount of the cellulose acylate A. The stretching step includes a first stretching step of stretching the web in a state where the residual solvent amount is greater than 1% by mass and 15% by mass or less, and after the first stretching step, the residual solvent amount is 0.02% by mass. And a second stretching step of stretching the web in a state of 1% by mass or less.

  The dope prepared in the dope preparation step contains cellulose acylates A and B, fine particles (for example, a matting agent), and a solvent. The cellulose acylates A and B have the same degree of substitution and addition amount. Is different. When such a dope is cast on the support, the cellulose acylate B and the fine particles are aggregated, and an aggregate larger than the fine particles is locally formed in the web. This is because cellulose acylate B has a relatively low degree of substitution and added amount compared to cellulose acylate A, so that cellulose acylate A becomes “sea” and cellulose acylate B becomes “island”. Among them, it is presumed that cellulose acylate B serving as “islands” and fine particles easily interact, and as a result, cellulose acylate B and fine particles are aggregated to form the above-mentioned aggregates.

  The web on which the aggregate is formed is stretched in a stretching process. Here, if the web is stretched at a high magnification at a time in a state where the residual solvent amount is low, the stress at the time of stretching is large, and the web is forcibly stretched, which may raise haze. Therefore, in the present embodiment, the stretching process is performed in two stages of a first stretching process and a second stretching process. The first stretching step and the second stretching step are transverse stretching (stretching in the film width direction), longitudinal stretching (stretching in the film transport direction), and oblique stretching (stretching in the direction oblique to the film width direction). Either may be sufficient. In the first stretching step, the web is stretched in a state where the residual solvent amount is higher than 1% by mass and as high as 15% by mass or less. Thus, by extending | stretching a web in the state with a high amount of residual solvent in a 1st extending | stretching process, the stress itself at the time of extending | stretching a web can be reduced and the raise of the haze by extending | stretching can be suppressed. In addition, the more desirable range of the residual solvent amount at the time of extending | stretching in a 1st extending | stretching process is 2 mass% or more and 15 mass% or less.

  In the second stretching step, the web is stretched in a state where the residual solvent amount is as low as 0.02% by mass or more and 1% by mass or less. Since the stretching is performed in the first stretching step first, a desired stretching ratio can be realized as the entire stretching process in the second stretching process without increasing the stretching ratio. Therefore, even if it extends in a state with a low amount of residual solvent in a 2nd extending process, the stress at the time of extending | stretching can be reduced and the raise of the haze by extending | stretching can be suppressed.

  Furthermore, in the second stretching step, stretching is performed in a state where the amount of residual solvent is low, so that stretching can be performed while maintaining the aggregated state of cellulose acylate B and fine particles. Thereby, the surface roughness (sliding property) of a cellulose-ester film is securable by the aggregate of cellulose acylate B and microparticles | fine-particles. Therefore, when ensuring the surface roughness, it is not necessary to increase the amount of fine particles added more than necessary or to use fine particles having a large average particle size. Thereby, the surface roughness of the cellulose ester film can be ensured by the cellulose acylate B and the aggregates of the fine particles while suppressing an increase in haze caused by the fine particles.

  That is, according to the above-described method for producing a cellulose ester film, the surface roughness of the cellulose ester film can be ensured while suppressing an increase in haze caused by fine particles and stretching.

  Further, since the surface roughness of the cellulose ester film can be ensured as described above, for example, even when an optical film is produced by forming a coating layer (functional layer) such as a cured layer on the cellulose ester film, the coating layer Can be ensured following the surface roughness of the underlying cellulose ester film. Thereby, even when the manufactured optical film is wound up in a roll shape, blocking in the rolled form of the optical film can be reduced.

  In addition, in order to ensure the surface roughness of the cellulose ester film, for example, when a cellulose ester film is produced using fine particles having a large average particle size, the particle size of the fine particles is large, so that not only the haze of the film increases, Since the fine particles themselves are harder than the above-mentioned aggregates (because they are not flexible like aggregates), when the optical film is wound up, the surface irregularities of the lower film are transferred to the upper film and become transfer scratches. There is concern. By aggregating cellulose acylate B and fine particles as in the present embodiment, a soft and large aggregate can be formed, so that it is possible to suppress the occurrence of transfer scratches during winding while suppressing an increase in haze. .

  In the plane including the width direction and the conveying direction of the web, the second stretching step extends the web in a direction that forms an angle larger than 0 ° and smaller than 90 ° with respect to the width direction. A stretching step may be included. Since the cellulose ester film obtained by obliquely stretching can be bonded to a polarizer to form a circularly polarizing plate, it can be used for various applications. For example, by arranging a circularly polarizing plate on the viewing side of an organic EL (Electro-Luminescence) display device, also called OLED (Organic light-Emitting Diode), external light incident on the OLED is reflected by the metal electrode and emitted to the viewing side. Can be prevented. Further, for example, by arranging the circularly polarizing plate on the viewing side of the liquid crystal display device, even when the user wears polarized sunglasses and visually recognizes the display image of the liquid crystal display device, the unevenness in viewing can be reduced.

  The ratio of the addition amount of the cellulose acylate B to the total addition amount of the cellulose acylates A and B (hereinafter also simply referred to as B ratio) is preferably 1% or more and 5% or less. When the B ratio is within the above range, a sea-island structure is reliably formed between the cellulose acylate A and the cellulose acylate B, and an aggregate of the cellulose acylate B and the fine particles, which become “islands”, is ensured. Can be formed. Thereby, the surface roughness of the cellulose-ester film manufactured can be increased reliably by the said aggregate. A more desirable range of the B ratio is 3% or more and 5% or less.

  The cellulose acylates A and B may be cellulose acetate propionate. In this case, the surface roughness of the cellulose ester film containing cellulose acetate propionate can be ensured.

  The manufacturing method of the optical film of this embodiment includes the manufacturing method of the cellulose-ester film mentioned above, Furthermore, a coating layer is formed on the said cellulose-ester film after the said extending process, and the coating layer formation used as the said optical film A step and a winding step of winding the optical film on which the coating layer has been formed may be included.

  Since the surface roughness of the cellulose ester film manufactured by the manufacturing method of this embodiment is ensured, when the coating layer is formed on the cellulose ester film, the surface roughness of the coating layer can also be secured. Accordingly, when the optical film having the coating layer is wound on the cellulose ester film, blocking of the optical film can be reduced.

  The coating layer may be a cured layer. Blocking can be reduced in the rolled form of the optical film formed with the hardened layer as the coating layer.

[Method for producing optical film]
Hereinafter, the detail of the manufacturing method of the optical film of this embodiment is demonstrated. FIG. 1 is a flowchart showing a manufacturing process of the optical film of the present embodiment. An optical film is manufactured through a cellulose-ester film manufacturing process (S1) and an addition process (S2) in order.

(Cellulose ester film manufacturing process)
The cellulose ester film production step (S1) is a step of producing a cellulose ester film by a solution casting film forming method, and includes a dope preparation step (S11), a casting step (S12), a peeling step (S13), and a first drying. A process (S14), a 1st extending process (S15), a 2nd drying process (S16), a 2nd extending process (S17), a slit embossing process (S18), and a winding process (S19) are included. In addition, an above-described 1st extending process (S15) and 2nd extending process (S17) are corresponded to the extending process which extends | stretches the web formed at the casting process (S12), and obtains a cellulose-ester film. FIG. 2 shows a schematic configuration of a cellulose ester film production apparatus 1 by a solution casting film forming method.

<< Dope preparation process >>
In the dope preparation step (S11), a dope cast on the support 3 (endless belt) is prepared by a preparation unit (not shown). The dope contains at least cellulose acylates A and B, fine particles, and a solvent. Cellulose acylates A and B are, for example, cellulose acetate propionate. The fine particles are a matting agent for forming irregularities on the surface of the cellulose ester film to be produced. As the solvent, for example, methylene chloride or ethanol can be used.

<Casting and peeling process>
In the casting step (S12), the dope prepared in the preparation unit is cast from the casting die 2 onto the support 3, and the dope is dried while being transported by the support 3, thereby forming a casting film. A web 5 is formed. Thereafter, the web 5 is peeled from the support 3 by the peeling roll 4 in the peeling step (S13). More specifically, it is as follows.

  The dope prepared in the preparation unit is fed to the casting die 2 by a conduit through a pressurized metering gear pump or the like, and transferred to the casting position on the support 3 made of a rotationally driven stainless steel endless belt that is infinitely transported. The dope is cast from the casting die 2, thereby forming the web 5 on the support 3.

  The support 3 is held by a pair of rolls 3a and 3b and a plurality of rolls (not shown) positioned therebetween. One or both of the rolls 3a and 3b are provided with a driving device (not shown) for applying tension to the support 3 so that the support 3 is used in a tensioned state.

  The web 5 formed by the dope cast on the support 3 is heated on the support 3, and the solvent is evaporated until the web 5 can be peeled from the support 3 by the peeling roll 4. In order to evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the support 3 by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. That's fine. After drying and solidifying or cooling and solidifying until the web 5 has a peelable film strength on the support 3, the web 5 is peeled off by the peeling roll 4 while having a self-supporting property.

  The residual solvent amount of the web 5 on the support 3 at the time of peeling is preferably in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the support 3 and the like. When peeling at a time when the amount of residual solvent is larger, if the web 5 is too soft, the flatness at the time of peeling is impaired, and wrinkles and vertical lines due to the peeling tension are likely to occur. Therefore, the residual at the time of peeling due to the balance between economic speed and quality. The amount of solvent is determined. The residual solvent amount is defined by the following formula.

Residual solvent amount (mass%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Here, the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

<< First drying process >>
In the first drying step (S14), the peeled web 5 is dried by the first drying device 6. In the 1st drying apparatus 6, the web 5 is conveyed by the some conveyance roll arrange | positioned in zigzag form seeing from the side surface, and the web 5 is dried in the meantime. There is no restriction | limiting in particular in the drying method in the 1st drying apparatus 6, Generally the web 5 is dried using a hot air, infrared rays, a heating roll, a microwave. From the viewpoint of simplicity, a method of drying the web 5 with hot air is preferable.

<< first stretching process >>
In the first stretching step (S15), the web 5 is stretched by the tenter 7 in a state where the residual solvent amount is greater than 1% by mass and 15% by mass or less. The amount of the residual solvent may be realized by the first drying device 6 before the web 5 enters the tenter 7, or by drying in the tenter 7 after the web 5 enters the tenter 7 and before stretching. It may be realized. The stretching direction of the web 5 in the tenter 7 is the conveyance direction (MD direction; Machine Direction) of the web 5, the width direction (TD direction; Transverse Direction) of the web 5 perpendicular to the conveyance direction, and both directions (oblique direction). In this case, the TD direction is set (lateral stretching). In the first stretching step, a tenter method in which both side edge portions of the web 5 are fixed with a clip or the like and stretched is preferable in order to improve the flatness and dimensional stability of the produced film.

<< Second drying step >>
In the second drying step (S16), the web 5 stretched by the tenter 7 is dried by the second drying device 8. The second drying device 8 has the same configuration as that of the first drying device 6, but a different configuration may be adopted.

<< Second stretching process >>
In the second stretching step (S17), the web 5 is stretched by the tenter 9 in a state where the residual solvent amount is 0.02 mass% or more and 1 mass% or less. The amount of the residual solvent may be realized by the second drying device 8 before the web 5 enters the tenter 9 or by drying in the tenter 9 after the web 5 enters the tenter 9 and before stretching. It may be realized. The stretching direction of the web 5 in the tenter 9 is any one of the MD direction, the TD direction, and the oblique direction of the web 5, and here, the oblique direction (oblique stretching). That is, in the tenter 9, the web 5 is positioned at an angle larger than 0 ° and smaller than 90 ° with respect to the width direction in a plane including the width direction (TD direction) and the conveyance direction (MD direction) of the web 5. An oblique stretching process of stretching in the direction to be performed is performed. In the second stretching step, it is desirable to stretch the film by a tenter method from the viewpoint of improving the flatness and dimensional stability of the produced film. After the second stretching step, the web 5 is conveyed toward the cutting unit 10 as the cellulose ester film CF.

  Here, the principle of oblique stretching will be described. FIG. 3 schematically shows an example of a rail pattern of the tenter 9 that performs oblique stretching. The web 5 transported to the tenter 9 is gripped at both ends by the left and right grippers Ci · Co, and is transported in the heating zone as the grippers Ci • Co travel. The left and right grips Ci / Co are opposed to the web 5 in the direction perpendicular to the conveyance direction D1 at the entrance (the position A in the figure) of the tenter 9, and are on the asymmetric rail Ri / Ro. The web 5 gripped at the exit portion (position B in the figure) at the end of stretching is released. Each of the pair of rails Ri and Ro has an endless continuous track, and the gripping tools Ci and Co that release the grip of the web 5 at the outlet of the tenter 9 travel on the outer rail and sequentially enter the inlet. It is supposed to be returned to.

  At this time, since the rails Ri and Ro are asymmetrical in the left and right, in the example of FIG. 3, the left and right gripping tools Ci and Co, which are opposed to each other at the position A in the drawing, move as the rails run on the rails Ri and Ro. The gripping tool Ci traveling on the Ri side (in-course side) has a positional relationship that precedes the gripping tool Co traveling on the rail Ro side (out-course side). Further, since the left and right gripping tools Ci / Co bend and travel along the asymmetrical rails Ri / Ro, the conveyance direction of the web 5 changes from the D1 direction to the D2 direction.

  That is, among the gripping tools Ci and Co that are opposed to each other at the position A in the figure, when one gripping tool Ci first reaches the position B at the end of the stretching of the web 5, the gripping tools Ci and Co are connected. The straight line is inclined by an angle θL (°) with respect to a direction substantially perpendicular to the final conveyance direction (D2 direction) of the web 5. With the above operation, the web 5 is obliquely stretched at an angle of θL with respect to the width direction. Here, “substantially vertical” indicates that the angle is in a range of 90 ± 1 °. By changing the rail pattern, the angle θL can be adjusted in a range of 0 ° <θL <90 °, and the web 5 can be obliquely stretched in a desired direction.

  The tenter 9 may be configured to perform simultaneous biaxial stretching in which the web 5 is stretched in the width direction and simultaneously in the transport direction.

《Slit / embossing process》
In the slit / embossing step (S18), both ends in the width direction of the cellulose ester film CF coming out of the tenter 9 are cut (slit) by the cutting part 10. The part left after cutting constitutes a product part to be a film product. On the other hand, the portion cut from the cellulose ester film CF is collected by a shooter and reused as a part of the raw material for film formation.

  The cellulose ester film CF whose both ends are cut by the cutting part 10 enters the embossed part 11 and is embossed (knurled) at both ends in the width direction. Embossing is performed by pressing a heated embossing roller against both ends of the cellulose ester film CF. Fine irregularities are formed on the surface of the embossing roller. By pressing the embossing roller against both ends of the cellulose ester film CF, the irregularities are formed at both ends. By such embossing, winding deviation and blocking (attachment between films) in the next winding process can be suppressed as much as possible.

《Winding process》
In the winding step (S19), the cellulose ester film CF that has undergone the embossing process is wound by the winding device 12 to obtain the original winding (film roll, original film) of the cellulose ester film CF. That is, in the winding process, the film roll is manufactured by winding the cellulose ester film CF around the core while transporting it. The winding method of the cellulose ester film CF may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress. You can use them properly.

  In the above, the web 5 after the first stretching step is introduced as it is into the tenter 9 of the second stretching step, and finally the cellulose ester film CF is wound up in the winding step. After the subsequent web 5 is dried by the second drying device 8, the film is temporarily wound up as a film, and the wound film is unwound and introduced into the tenter 9 in the second stretching step, and finally wound again. Good. That is, the production of the cellulose ester film CF may be performed continuously from the preparation of the dope to the winding of the cellulose ester film CF, or may be performed by cutting (interrupting) the process halfway.

(Additional process)
Subsequent to the above-described cellulose ester film production step (S1), an addition step (S2) is performed. The adding step (S2) includes a feeding step (S21), a coating layer forming step (S22), and a winding step (S23).

<Feeding process>
In the feeding step (S21), the cellulose ester film CF is fed out from the film roll obtained in S19. In the cellulose ester film manufacturing step (S1) described above, the cellulose ester film CF may not be taken up and the process may proceed directly to the coating layer forming step (S22) shown below. That is, the winding process (S19) and the feeding process (S21) can be omitted.

<< Coating layer formation process >>
In the coating layer forming step (S22), as shown in FIG. 4, the coating layer H is formed on the cellulose ester film CF after the stretching step to obtain an optical film OF. The coating layer H is composed of, for example, a cured layer, but may be composed of other functional layers such as an antistatic layer and an antireflection layer. When the coating layer H is composed of, for example, a cured layer, the coating layer H can be formed by coating the composition for forming a cured layer on the cellulose ester film CF and curing the composition by ultraviolet irradiation.

《Winding process》
In the winding step (S23), the optical film OF on which the coating layer H is formed is wound up by a winding device (not shown). Thereby, the optical film OF can be stored and transported.

[Cellulose ester film]
Next, the detail of the material of the cellulose-ester film of this embodiment is demonstrated. The cellulose ester film according to the present embodiment contains cellulose acylate as a main component. Examples of the cellulose acylate include esters of cellulose and an aliphatic carboxylic acid and / or aromatic carboxylic acid having about 2 to 22 carbon atoms, and in particular, an ester of cellulose and a lower fatty acid having 6 or less carbon atoms. Preferably there is.

  The acyl group bonded to the hydroxyl group of cellulose may be linear or branched, and may form a ring. Furthermore, another substituent may be substituted. In the case of the same substitution degree, birefringence decreases when the number of carbon atoms is large. Therefore, the number of carbon atoms is preferably selected from acyl groups having 2 to 6 carbon atoms. The substitution degree of the propionyl group and the butyryl group The total degree of substitution is 0 or more and less than 3.0. The cellulose acylate preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms.

  Specifically, cellulose acylate includes propionate group, butyrate group or phthalyl group in addition to acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate propionate butyrate or cellulose acetate phthalate. Bound cellulose mixed fatty acid esters can be used. The butyryl group forming butyrate may be linear or branched.

  In the present embodiment, as the cellulose acylate, in addition to cellulose acetate (for example, diacetyl cellulose and triacetyl cellulose), the above-described cellulose acetate butyrate or cellulose acetate propionate is particularly preferably used. In addition, the cellulose acylate may be formed by mixing two or more kinds of resins within a range that satisfies the following conditional expression regarding the degree of substitution. Therefore, the cellulose acylate may be, for example, a mixture of cellulose acetate propionate and cellulose acetate slightly.

In this embodiment, two types of cellulose acylates A and B are used as the cellulose acylate. However, in the cellulose ester film, the amount of cellulose acylate B added is less than the amount of cellulose acylate A added. Here, when the total acyl group substitution degree of cellulose acylate A is TA and the total acyl group substitution degree of cellulose acylate B is TB,
2.3 ≦ TA ≦ 2.8
−1.0 ≦ TB−TA ≦ −0.3
It is. The total acyl group substitution degree refers to the total of the substitution degree of the acetyl group and the substitution degree of the propionyl group or butyryl group. The substitution degree of the acyl group can be measured according to ASTM-D817-96, which is one of the standards formulated and issued by ASTM (American Society for Testing and Materials).

  Thus, by defining the substitution degree and addition amount of cellulose acylates A and B, as described above, in the production of the cellulose ester film, a sea island structure is formed in the web, and the substitution degree and addition amount are more A small amount of cellulose acylate B and fine particles can be agglomerated to ensure the surface roughness of the film with a small amount of fine particles.

  The number average molecular weight of the cellulose acylate is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film becomes strong. More preferably, cellulose acylate having a number average molecular weight of 70,000 to 200,000 is used.

  The weight average molecular weight (Mw) and number average molecular weight (Mn) of cellulose acylate are measured using gel permeation chromatography (GPC). The measurement conditions are as follows. In addition, this measuring method can be used also as a measuring method of the other polymer in this embodiment.

Solvent: methylene chloride;
Column: Three Shodex K806, K805, K803G (made by Showa Denko KK) are connected and used;
Column temperature: 25 ° C .;
Sample concentration: 0.1% by mass;
Detector: RI Model 504 (manufactured by GL Sciences);
Pump: L6000 (manufactured by Hitachi, Ltd.);
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 100000 to 500 samples are used. Thirteen samples are used at approximately equal intervals.

  The cellulose as a raw material for cellulose acylate is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose acylate obtained from them can be mixed and used at an arbitrary ratio. Cellulose acylate can be produced by a known method. Specifically, for example, it can be synthesized with reference to the method described in JP-A-10-45804.

〔Additive〕
The cellulose ester film of this embodiment may contain an additive. Examples of additives that can be used include plasticizers, fine particles, ultraviolet absorbers, retardation adjusting agents, antioxidants, deterioration inhibitors, peeling aids, surfactants, and dyes. In the present embodiment, additives other than the fine particles may be added when preparing the dope solution, or may be added when preparing the fine particle dispersion. Hereinafter, main additives will be described.

(Plasticizer)
As a plasticizer added to the cellulose ester film, a polyester resin can be used. The polyester resin is obtained by polymerizing a dicarboxylic acid and a diol, and 70% or more of the dicarboxylic acid structural unit (the structural unit derived from the dicarboxylic acid) is derived from the aromatic dicarboxylic acid, and the diol structural unit (derived from the diol). 70% or more of the structural unit is derived from an aliphatic diol.

  The proportion of the structural unit derived from the aromatic dicarboxylic acid is 70% or more, preferably 80% or more, more preferably 90% or more. The proportion of the structural unit derived from the aliphatic diol is 70% or more, preferably 80% or more, and more preferably 90% or more. Two or more polyester resins may be used in combination.

  As aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, naphthalenedicarboxylic acid such as 2,7-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, Examples thereof include 3,4'-biphenyldicarboxylic acid and the like and ester-forming derivatives thereof.

  As the polyester resin, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid, and monocarboxylic acids such as benzoic acid, propionic acid, and butyric acid can be used without departing from the object of the present invention.

  Examples of the aliphatic diol include ethylene glycol, 1,3-propylene diol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like, and ester-forming derivatives thereof.

  As the polyester resin, monoalcohols such as butyl alcohol, hexyl alcohol, and octyl alcohol, and polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol can be used as long as the object of the present invention is not impaired.

  A known esterification method or transesterification method can be applied to the production of the polyester resin. Examples of the polycondensation catalyst used in the production of the polyester resin include known antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds such as germanium oxide, titanium compounds such as titanium acetate, and aluminum compounds such as aluminum chloride. Although it can, it is not limited to these.

  Preferred polyester resins include polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer resin, polyethylene-2,6-naphthalene dicarboxylate resin, polyethylene-2, 6-naphthalene dicarboxylate-terephthalate copolymer resin, polyethylene-terephthalate-4,4'-biphenyldicarboxylate resin, poly-1,3-propylene-terephthalate resin, polybutylene terephthalate resin, polybutylene-2,6-naphthalene There are dicarboxylate resins and the like.

  More preferable polyester resins include polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer resin, polybutylene terephthalate resin, and polyethylene-2,6-naphthalene dicarboxylate. Resin.

(Fine particles)
In the present embodiment, a matting agent can be contained in the cellulose ester film as fine particles, whereby the cellulose ester film can be easily conveyed and wound.

  The particle size of the matting agent is preferably primary particles or secondary particles of 10 nm to 0.1 μm. A substantially spherical matting agent having a primary particle acicular ratio of 1.1 or less is preferably used.

  As the fine particles, those containing silicon are preferable, and silicon dioxide is particularly preferable. As fine particles of silicon dioxide preferable for this embodiment, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.) manufactured by Nippon Aerosil Co., Ltd. And commercially available products such as Aerosil 200V, R972, R972V, R974, R202, and R812 can be preferably used. Examples of the polymer fine particles include silicone resin, fluorine resin, and acrylic resin. Silicone resins are preferred, and those having a three-dimensional network structure are particularly preferred. Examples of such resins include Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.).

  The fine particles of silicon dioxide preferably have a primary average particle size of 20 nm or less and an apparent specific gravity of 70 g / L or more. The average diameter of the primary particles is more preferably 5 to 16 nm, and further preferably 5 to 12 nm. A smaller primary particle average diameter is preferred because haze is low. The apparent specific gravity is preferably 90 to 200 g / L or more, and more preferably 100 to 200 g / L or more. Higher apparent specific gravity makes it possible to produce a high-concentration fine particle dispersion, which is preferable because no haze or aggregates are generated.

The amount of the matting agent added in this embodiment is preferably 0.01 to 1.0 g, more preferably 0.03 to 0.3 g, and still more preferably 0.08 to 0.16 g per 1 m ^{2 of} the cellulose ester film.

〔solvent〕
The cellulose ester film of this embodiment is formed by the solution casting film forming method as described above. The organic solvent useful for forming the resin solution (dope composition) when the cellulose ester film is formed by the solution casting film forming method is any one that dissolves the cellulose ester resin and other additives at the same time. Can be used without limitation. For example, as the chlorinated organic solvent, methylene chloride, as the non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, etc. Can, methylene chloride, methyl acetate, ethyl acetate, may be used preferably acetone.

(Coating layer)
The optical film of this embodiment is configured by forming a coating layer on a cellulose ester film. The coating layer can be composed of a functional layer that is formed on a cellulose ester film and exhibits various functions, such as a cured layer, an antireflection layer, and an antistatic layer. Here, a case where the coating layer is formed of a hardened layer (hard coat layer) will be described as an example.

  The hardened layer may have a single layer structure or a laminated structure. The hardened layer may contain an acrylic material. Acrylic materials are synthesized from monofunctional or polyfunctional (meth) acrylate compounds such as (meth) acrylic acid esters of polyhydric alcohols, diisocyanates and polyhydric alcohols, and hydroxy esters of (meth) acrylic acid. Such a polyfunctional urethane (meth) acrylate compound can be used. Besides these, polyether resins having an acrylate functional group, polyester resins, epoxy resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins, and the like can be used.

  In the present embodiment, “(meth) acryl” means both “acryl” and “methacryl”, “(meth) acrylate” means both “acrylate” and “methacrylate”, and “( “Meth) acryloyl” refers to both “acryloyl” and “methacryloyl”. For example, “urethane (meth) acrylate” indicates both “urethane acrylate” and “urethane methacrylate”.

  In particular, UV curable acrylate resins, UV curable urethane acrylate resins, UV curable polyester acrylate resins, UV curable epoxy acrylate resins, UV curable polyol acrylate resins, or UV curable epoxy resins are preferred. Among them, an ultraviolet curable acrylate resin is preferable.

  As the solvent contained in the composition for forming a cured layer used for forming the cured layer, a solvent that dissolves or swells the cellulose ester film in the lower layer is preferable. When the solvent dissolves or swells the cellulose ester film, the composition for forming a cured layer easily penetrates into the inside from the surface of the cellulose ester film, and the adhesion between the cellulose ester film and the cured layer can be improved.

  In addition, a layer in which the resin component of the cellulose ester film and the resin component of the cured layer are mixed is formed near the surface layer of the cellulose ester film, and the refractive index of the cellulose ester film and the cured layer is inclined by the action of this layer. And the occurrence of uneven interference can be prevented.

  The cured layer may contain additives such as an ultraviolet absorber, a photopolymerization initiator, a photosensitizer, and a leveling agent.

  The coating method of the composition for forming a cured layer includes dip coating, spin coating, flow coating, spray coating, roll coating, gravure roll coating, air doctor coating, blade coating, and wire doctor coating. A method such as a method, a knife coating method, a reverse coating method, a transfer roll coating method, a micro gravure coating method, a kiss coating method, a cast coating method, a slot orifice coating method, a calendar coating method, a die coating method, or the like can be employed. Among these, the microgravure coating method is preferable when a uniform thin film layer is formed, and the die coating method is preferable when a thick film layer needs to be formed.

〔Example〕
Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

<Production of cellulose ester film>
(Preparation of fine particle additive solution)
Fine particles (Aerosil R812: manufactured by Nippon Aerosil Co., Ltd., primary average particle diameter: 7 nm, apparent specific gravity 50 g / L)
4 parts by mass Dichloromethane 48 parts by mass Ethanol 48 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.

(Preparation of dope)
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose acylate A (cellulose acetate propionate (CAP), acetyl group substitution degree 1.50, propionyl group substitution degree 1.00, total acyl group substitution degree 2.50, number average Molecular weight Mw: 200,000)
97 parts by mass Cellulose acylate B (cellulose acetate propionate (CAP), acetyl group substitution degree 1.20, propionyl group substitution degree 0.80, total acyl group substitution degree 2.00, number average molecular weight Mw: 200,000)
3 parts by mass An ester compound (terminal group acetyl group) obtained by esterifying a plasticizer (adipic acid: phthalic acid = 70: 30) and 1,2-ethanediol
10 parts by mass Particulate additive solution 10 parts by mass The above is put into a closed container with sufficient agitation, heated to 80 ° C. with stirring, held for 1 hour, cooled to 30 ° C., and filtered with a filter having a pore size of 5 μm. Filtration was performed to obtain a dope.

(Film formation of cellulose ester film 1)
Using the dope, a cellulose ester film (hereinafter also simply referred to as a film) was formed by a solution casting film forming method. More specifically, a dope is cast from a casting die on a metal support driven at an endless speed of 30 m / min, and dried by applying a drying air of 40 ° C. on the support to form a web. Then, it cooled to 10 degreeC and peeled the web from the support body. Thereafter, the web was stretched 20% at 120 ° C. in the TD direction with the residual solvent amount being 10% by mass (first stretching), and dried at 110 ° C. for 30 minutes, and then the residual solvent amount was 0.5% by mass. In this state, the cellulose ester film 1 was formed by performing oblique stretching (second stretching) at a stretching ratio of 1.5 times. The stretch ratio in oblique stretching refers to the ratio between the film width at the tenter inlet before oblique stretching and the film width at the tenter outlet after oblique stretching. Further, the oblique stretching was performed such that the orientation angle (angle formed by the film width direction and the slow axis of the molecule) was about 45 °. The film conveyance speed at this time was 15 m / min, and the film thickness was 35 μm. Then, the film was wound up with a winder.

(Film formation of cellulose ester film 2-18)
The total acyl group substitution degree of the cellulose acylates A and B to be used is changed as shown in Table 1, and the drying conditions of the peeled web are changed. Cellulose ester films 2 to 18 were formed in the same manner as the formation of the cellulose ester film 1 except that the addition ratio of cellulose acylate B was changed as shown in Table 1.

(Measurement of surface roughness)
The surface roughness (arithmetic average roughness) Ra of the cellulose ester films 1-18 produced above was measured using an optical interference type surface roughness meter (manufactured by ZYGO, NewView 5000) according to JIS B0601: 2001. . At this time, in each film, the measurement was performed 10 times, and the average value was defined as the surface roughness Ra.

(Measure haze)
Using a haze meter (Nippon Denshoku Kogyo Co., Ltd., NDH2000), in the environment of 23 ° C. and 50% RH (relative humidity), 10 points of the cellulose ester films 1 to 18 produced above at equal intervals in the width direction. Measurement was performed and the average value was defined as haze value (%).

(Evaluation)
From each value of surface roughness Ra and haze obtained by the said measurement, the cellulose-ester films 1-18 were evaluated comprehensively based on the following evaluation criteria.
"Evaluation criteria"
A: Ra is 5.0 nm or more and haze is less than 0.50%.
O: Ra is 5.0 nm or more and haze is 0.50% or more and less than 0.60%. Or, Ra is 4.0 nm or more and less than 5.0 nm, and haze is less than 0.50%.
Δ: Ra is 4.0 nm or more and less than 5.0 nm, and haze is 0.50% or more and less than 0.60%.
X: Ra is less than 4.0 nm. Or haze is 0.60% or more.

  Table 1 shows the parameters of the cellulose ester films 1 to 18 and the evaluation results.

  From Table 1, in the cellulose ester film 13, the surface roughness Ra is less than 4.0 nm, and the effect of ensuring the surface roughness Ra is small. This is because cellulose acylates A and B are not well separated into a sea-island structure because the difference in the total acyl group substitution degree (TB-TA) between cellulose acylates A and B is too small as -0.1. It is considered that it is difficult to form an aggregate by aggregating cellulose acylate B and fine particles.

  In the cellulose ester film 14, the haze is 0.60% or more. The difference in total acyl group substitution degree (TB-TA) between cellulose acylates A and B is as large as -1.2, and cellulose acylates A and B are well separated into a sea-island structure. Although the effect of ensuring Ra is obtained, it is considered that the haze is increased because the level difference of the haze is remarkably expressed by the clear separation of the sea-island structure.

  In the cellulose ester film 15, the surface roughness Ra is less than 4.0 nm, and the effect of ensuring the surface roughness Ra is small. This is because the residual solvent amount of the web in the first stretching is too high, and even if the increase in haze due to stress during stretching is suppressed, the sea-island structure of cellulose acylates A and B becomes easy to move. It is difficult to form an aggregate having a large diameter, and it is considered that the effect of securing the surface roughness Ra is reduced by the aggregate.

  In the cellulose ester film 16, the haze is 0.60% or more. This is presumably because the residual solvent amount of the web in the first stretching is too low, and the influence of stress during stretching becomes large, which increases the haze.

  In the cellulose ester film 17, the surface roughness Ra is less than 4.0 nm, and the effect of ensuring the surface roughness Ra is small. This is because the amount of residual solvent of the web in the second stretching is too high, and even if the increase in haze during stretching is suppressed, the sea-island structure of the cellulose acylates A and B becomes easy to move. It is considered that it is difficult to maintain an aggregate of acylate B and fine particles in a state where the particle size is large.

  In the cellulose ester film 18, the haze is 0.60% or more. This is because the amount of residual solvent of the web in the second stretching is low, and the sea-island structure of cellulose acylates A and B becomes difficult to move, and as a result, it is easy to maintain an aggregate of cellulose acylate B and fine particles after stretching. However, since the residual solvent amount is low, a load is applied by the film at the time of stretching, and crazing is generated. Therefore, it is considered that the haze is hardly lowered.

  On the other hand, in the cellulose ester films 1 to 12, good results were obtained for both surface roughness Ra and haze (◎, ○ or Δ). This is because, in the production of cellulose ester films 1 to 12, the total acyl group substitution degrees TA and TB of cellulose acylates A and B are 2.3 ≦ TA ≦ 2.8, −1.0 ≦ TB-TA ≦ −. 0.3, the addition amount of cellulose acylate B is less than the addition amount of cellulose acylate A, and in the first stretching, the residual solvent amount is more than 1% by mass and not more than 15% by mass (preferably The web is stretched in a state of 2% by mass or more and 15% by mass or less), and in the second stretching, the web is stretched in a state where the residual solvent amount is 0.02% by mass or more and 1% by mass or less. The aggregate of rate B and fine particles is well formed with a large particle size, and the aggregate can be stretched in a low-stress state while maintaining the aggregate almost without moving. Erareru.

  In addition, in 1st extending | stretching, evaluation is (circle) when the amount of residual solvents is 2 mass% (refer the cellulose-ester film 7), and since evaluation is x when the amount of residual solvents is 0.5 mass% ( The lower limit value of the residual solvent amount in the first stretching can be assumed to be a value between 2% by mass and 0.5% by mass. Based on such consideration, the lower limit value of the residual solvent amount in the first stretching is considered to be 1% by mass which is a value between 2% by mass and 0.5% by mass as described above.

  In addition, when the added amount ratio of cellulose acylate B is increased, cellulose acylate and B are mixed and the sea-island structure is reduced, so that an aggregate having a large particle size is not easily formed, and a surface roughness Ra due to the aggregate is ensured. This makes it difficult to exert the effect (see cellulose ester film 10). From this, it can be said that the addition amount ratio of cellulose acylate B is desirably 1 to 5%.

  In the cellulose ester films 1 to 12, when an aggregate of cellulose acylate B and fine particles was observed with a transmission electron microscope (TEM), the average particle size of the aggregate was about 70 μm. The maximum particle size was about 200 μm.

  INDUSTRIAL APPLICABILITY The present invention can be used for producing a cellulose ester film by a solution flow casting method.

3 Support 5 Web CF Cellulose Ester Film

Claims (5)

A method for producing a cellulose ester film by a solution casting film forming method,
A dope preparation step of preparing a dope containing cellulose acylates A and B, fine particles, and a solvent;
Casting a dope on the support to form a web on the support; and
Stretching step to obtain the cellulose ester film by stretching the web,
When the total acyl group substitution degree of the cellulose acylate A is TA and the total acyl group substitution degree of the cellulose acylate B is TB,
2.3 ≦ TA ≦ 2.8
−1.0 ≦ TB−TA ≦ −0.3
And
The amount of cellulose acylate B added is less than the amount of cellulose acylate A added,
The stretching step includes
A first stretching step of stretching the web in a state where the residual solvent amount is greater than 1% by mass and 15% by mass or less;
After the said 1st extending | stretching process, the 2nd extending | stretching process of extending | stretching the said web in the state whose residual solvent amount is 0.02 mass% or more and 1 mass% or less is included, The manufacturing method of the cellulose-ester film characterized by the above-mentioned.   In the plane including the width direction and the conveying direction of the web, the second stretching step extends the web in a direction that forms an angle larger than 0 ° and smaller than 90 ° with respect to the width direction. The manufacturing method of the cellulose-ester film of Claim 1 including a extending | stretching process.   The ratio of the addition amount of the said cellulose acylate B with respect to the sum total of the addition amount of the said cellulose acylate A and B is 1% or more and 5% or less, The cellulose-ester film of Claim 1 or 2 characterized by the above-mentioned. Production method.   The method for producing a cellulose ester film according to any one of claims 1 to 3, wherein in the first stretching step, the web is stretched in a state where a residual solvent amount is 2% by mass or more and 15% by mass or less.   The method for producing a cellulose ester film according to any one of claims 1 to 4, wherein the cellulose acylates A and B are cellulose acetate propionate.

Images