JP2010082993A - Method of solution film-forming - Google Patents

Abstract

An object of the present invention is to produce a film having no axial misalignment.
A dope 11 is cast onto a casting drum 32, and the casting film 33 is cooled and solidified by the casting drum. The casting film 33 is peeled off as the wet film 12 containing the solvent and dried to produce the retardation film 17. A wind shielding plate 41 is provided in the vicinity of the gelling position where the casting film 33 gels so as to face the casting drum 32. In the area upstream of the gelling position, the air flow is controlled so that the relative speed with respect to the peripheral speed of the casting drum 31 is a wind speed suppressed to 5 m / second or less. In the area downstream of the gelation position, the air flow is controlled so that the wind speed is higher than that of the upstream area.
[Selection] Figure 1

Description

  The present invention relates to a solution casting method for producing a polymer film for use in an optical product such as a liquid crystal display.

  The required performance for liquid crystal displays has been increasing in recent years, and the required performance is only increasing for a plurality of polymer films constituting the liquid crystal display. In recent years, the brightness of liquid crystal displays has become higher and the screen has become larger, and this has led to stricter demands on the uniformity of optical properties for polymer films such as retardation films. It is becoming

  The non-uniformity of the optical characteristics of the polymer film, that is, the optical unevenness includes non-uniformity in the direction of the slow axis (so-called axial misalignment). When the polymer film is manufactured continuously, that is, in a long length, the slow axis becomes symmetrical with respect to the center in the width direction of the polymer film as a result of receiving a mechanical force in the manufacturing process. That is, the direction of the slow axis is not a constant direction in the width direction or the longitudinal direction. When light is incident on a polymer film having such an axial shift, the desired polarization cannot be achieved, and so-called light leakage occurs in which light that should not be transmitted is transmitted.

  Conventionally, in order to eliminate optical unevenness, a method of making the film flatter by making the thickness more uniform and smoothing the surface has been proposed. For example, Patent Document 1 discloses a first static pressure above a casting film when it starts to be formed on a traveling support, and a second above a position where a predetermined time passes after the casting film is formed. By making the difference from the static pressure within a predetermined range, the thickness is made uniform, thereby eliminating optical unevenness. Moreover, Patent Document 2 attempts to make the thickness uniform by gelling the exposed surface of the cast film immediately after formation to generate a gel layer having a contraction force larger than that of the dope used for casting. .

  In addition, Patent Document 3 casts a dope on a support whose surface is cooled to form a casting film, and the casting film when the solvent content is within a predetermined range, from the exposed surface side, By pressing a roller at a predetermined temperature, the productivity of the film is improved and the thickness unevenness is eliminated.

By the way, the production of polymer films is on the rise due to the rapid increase in demand for liquid crystal displays. However, increasing the number of production facilities takes a great deal of cost and time to start operation, and therefore it is desirable to increase production using existing facilities. In solution casting, the cast film is solidified by drying on the support (hereinafter referred to as dry casting method), and the cast film is solidified by cooling on the support. There is a method (hereinafter referred to as “cooling casting method”), and the cooling casting method is remarkably superior when compared with the production efficiency, that is, the production amount per unit time.
JP 2007-223307 A JP 2006-297922 A JP 2008-012839 A

As described above, there are both optical unevenness due to thickness unevenness and axial misalignment, and optical unevenness cannot be eliminated simply by eliminating thickness unevenness. However, as in Patent Documents 1 to 3, eliminating the thickness unevenness is effective in eliminating the axial misalignment, although a certain effect is observed in the retardation, particularly in the optical unevenness as in-plane retardation Re non-uniformity. There is no. Note that Re is a value obtained by the following equation (1). In this formula (1), Nx is the refractive index in the X axis that is the slow axis direction on the surface of the retardation film, Ny is the refractive index in the Y axis that is the fast axis direction, and d is the film thickness (nm). It is.
Re = (Nx−Ny) × d (1)

  And if importance is attached to the productivity of the polymer film, it can be said that the cooling casting method is preferable to the dry casting method as described above, but there is a problem that the axial deviation appears more prominently by the cooling casting.

  In view of the above problems, an object of the present invention is to provide a solution casting method for producing a polymer film having no axial misalignment.

  In order to solve the above-mentioned problems, the solution casting method of the present invention is a method in which a dope containing a polymer and a solvent is flown out of a casting die to form a casting film on a peripheral surface of a drum rotating at a predetermined peripheral speed. A gelling step in which the flow rate of the air flowing on the cast film is maintained at a relative speed with respect to the peripheral speed of 5 m / sec at most, and the cast film is cooled by a drum to be gelled, and the gel A blowing process that advances drying of the casting film by blowing air having a relative speed larger than that of air flowing on the casting film in the forming process to the gelled casting film, and the casting that has undergone the blowing process The film has a stripping process for stripping the film from the drum as a wet film containing a solvent, and a drying process for drying the wet film to form a film.

  Suppressing the inflow of air downstream from the gelling position to the upstream side by a wind shielding member provided near the gelling position where the casting film gels so as to face the peripheral surface of the drum. In the drying step, the wet film is dried at a drying rate such that the reduction rate of the wet film thickness is suppressed to 400 μm / min at the maximum until the solvent residual ratio of the wet film reaches 60%. It is preferable.

  According to the present invention, a polymer film having no axial misalignment can be produced.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described here.

As the polymer, a known polymer that can be made into a polymer film by a solution casting method can be used. Among the polymers, cellulose acylate is preferable, and among cellulose acylates, the ratio of esterifying the hydroxyl group of cellulose with carboxylic acid, that is, the substitution degree of acyl group (hereinafter referred to as acyl group substitution degree) is represented by the following formula (I). Those satisfying all the conditions of (III) to (III) are more preferable. In (I) to (III), A and B are both acyl group substitution degrees, the acyl group in A is an acetyl group, and the acyl group in B has 3 to 22 carbon atoms.
2.5 ≦ A + B ≦ 3.0 (I)
0 ≦ A ≦ 3.0 (II)
0 ≦ B ≦ 2.9 (III)

  Glucose units constituting cellulose and having β-1,4 bonds have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer in which some or all of these hydroxyl groups are esterified, and hydrogen of the hydroxyl groups is substituted with acyl groups having 2 or more carbon atoms. Since the degree of substitution is 1 when esterification of one hydroxyl group in the glucose unit is 100%, in the case of cellulose acylate, the hydroxyl groups at the 2nd, 3rd and 6th positions are each 100% ester. The degree of substitution is 3.

  Here, the substitution degree of the acyl group at the 2-position of the glucose unit is DS2, the substitution degree of the acyl group at the 3-position is DS3, and the substitution degree of the acyl group at the 6-position is DS6. The total acyl group substitution degree determined by DS2 + DS3 + DS6 is preferably 2.00 to 3.00, more preferably 2.22 to 2.90, and even more preferably 2.40 to 2.88. . DS6 / (DS2 + DS3 + DS6) is preferably 0.32 or more, more preferably 0.322 or more, and further preferably 0.324 to 0.340.

  There may be only one kind of acyl group, or two or more kinds. When there are two or more acyl groups, it is preferable that one of them is an acetyl group. DSA + DSB, where DSA is the sum of the substitution degrees of the hydrogens of the hydroxyl groups at the 2nd, 3rd and 6th positions with the acetyl group, and DSB is the sum of the substitution degrees other than the acetyl groups at the 2nd, 3rd and 6th positions The value of is preferably 2.2 to 2.86, particularly preferably 2.40 to 2.80. DSB is preferably 1.50 or more, and particularly preferably 1.7 or more. Further, it is preferable that 28% or more of the DSB is a substituent at the 6-position hydroxyl group, more preferably 30% or more, still more preferably 31% or more, and particularly preferably 32% or more is a substituent at the 6-position hydroxyl group. Preferably there is. The 6-position DSA + DSB value of cellulose acylate is preferably 0.75 or more, more preferably 0.80 or more, and particularly preferably 0.85 or more. By using the cellulose acylate as described above, a dope having a preferable solubility and a dope having a low viscosity and a good filterability can be produced. In particular, when a non-chlorine organic solvent is used, the above cellulose acylate is preferable.

  The acyl group having 2 or more carbon atoms may be an aliphatic group or an aryl group, and is not particularly limited. For example, there are cellulose alkylcarbonyl ester, alkenylcarbonyl ester, aromatic carbonyl ester, aromatic alkylcarbonyl ester, etc., and these may each further have a substituted group. Propionyl group, butanoyl group, pentanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, iso-butanoyl group, t-butanoyl group, cyclohexane Examples thereof include a carbonyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, and a cinnamoyl group. Among these, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a t-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and a propionyl group and a butanoyl group are particularly preferable.

  The present invention is particularly effective when the cellulose acylate is a product of esterification of cellulose obtained from wood pulp. Cellulose obtained from wood pulp has the advantage that it is easier to obtain and easier to secure than cellulose obtained from cotton linter. However, cellulose acylate obtained by esterifying cellulose from wood pulp generally has lower tear strength and inferior film transport stability than cellulose acylate obtained by esterifying cellulose from cotton linter. is there. When a film is produced from such a cellulose acylate using wood pulp as a raw material according to the present invention, the effect of increasing the tear strength becomes more remarkable.

  The details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148, and these descriptions can also be applied to the present invention.

  The dope can contain a retardation increasing agent. A retardation raising agent is not specifically limited, For example, what is described in Paragraph [0030]-[0142] of Unexamined-Japanese-Patent No. 2006-235383 can be used. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, UV absorbers, optical anisotropy control agents, dyes, matting agents, release agents, etc., paragraph [0196] of JP-A-2005-104148. To [0516] paragraphs, and these descriptions can also be applied to the present invention.

  Solvents for producing the dope include aromatic hydrocarbons (for example, benzene, toluene, etc.), halogenated hydrocarbons (for example, dichloromethane, chlorobenzene, etc.), alcohols (for example, methanol, ethanol, n-propanol, n-). Examples include butanol, diethylene glycol, etc., ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl acetate, ethyl acetate, propyl acetate, etc.) and ethers (eg, tetrahydrofuran, methyl cellosolve, etc.). Here, the dope is a polymer solution or dispersion obtained by dissolving a polymer in a solvent or dispersing in a dispersion medium.

  As a solvent for cellulose acylate, a halogenated hydrocarbon having 1 to 7 carbon atoms is preferable among these solvents, and dichloromethane is most preferable. And from the viewpoint of properties such as the solubility of TAC, the peelability of the cast film from the support, the mechanical strength of the film, and the optical properties of the film, one or several kinds of alcohols having 1 to 5 carbon atoms are selected. It is preferable to use it mixed with dichloromethane. At this time, the content of the alcohol is preferably 2% by weight to 25% by weight and more preferably 5% by weight to 20% by weight with respect to the whole solvent. Preferable specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, etc. Among them, methanol, ethanol, n-butanol, or a mixture thereof is preferably used.

  For the purpose of minimizing the influence on the environment, the dope may be manufactured without using dichloromethane. As the solvent in this case, an ether having 4 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, and an ester having 3 to 12 carbon atoms are preferable, and these may be appropriately mixed and used. These ethers, ketones and esters may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as a solvent. The solvent may have another functional group such as an alcoholic hydroxyl group in the chemical structure.

  The method for producing the dope to be cast is not particularly limited. However, the present invention is particularly effective when the cast film comprising the cast dope is solidified by cooling and peeled off, that is, when the cooling casting method is performed. For this, it is preferable to produce the dope so that the concentration of solids such as cellulose acylate is higher than the dope when the cast film is dried and peeled off (in the case of the dry casting method). As this method, a so-called flash concentration method is preferably used. The flash concentration method is a method in which a dope having a concentration lower than a target concentration is once formed, and a part of the solvent is evaporated by blowing out the dope 11 with a known flash device.

  The dope to be cast preferably has a cellulose acylate concentration of 5 to 40% by weight, more preferably 15 to 30% by weight, and more preferably 17 to 25% by weight. The following range is more preferable.

  In addition, about the raw material in the solution casting method which obtains a TAC film, a raw material, the additive dissolution method, the filtration method, the defoaming, and the addition method, [0517] Paragraph [0616] Paragraph of JP, 2005-104148, A In detail, these descriptions can also be applied to the present invention.

[Film production equipment and method]
FIG. 1 is a schematic view showing a solution casting apparatus 10 for producing a polymer film. However, the present invention is not limited to the solution casting apparatus 10. In the following explanation, cellulose acylate is used as the polymer component of the dope, and the polymer film to be manufactured is described as an example of a retardation film used for a liquid crystal display, but other polymers are used for other applications. A polymer film may be produced.

  The solution casting apparatus 10 holds a casting chamber 13 for casting a dope 11 in which TAC is dissolved in a solvent to form a wet film 12 containing the solvent, and both end portions of the wet film 12. A tenter 18 for widening the wet film 12, an edge-cutting device 21 for cutting off both end portions of the wet film 12, and a drying chamber that dries the wet film 12 over a plurality of rollers 22 and transports the wet film 12 to form a retardation film 17. 23, a knurling roller pair 27 for embossing the side ends, and a winding chamber 28 for winding the retardation film 17 are provided in this order from the upstream side.

  The casting chamber 13 includes a casting die 31 that continuously flows out the guided dope 11 and a dope outlet of the casting die 31 so that the dope 11 is cast on the peripheral surface. And a casting drum 32 as a support that rotates in the circumferential direction.

  A temperature controller (not shown) for controlling the temperature of the casting die 31 is attached to the casting die 31 so that the temperature of the dope 11 flowing out toward the casting drum 32 is maintained at a predetermined temperature. The casting drum 32 is rotated by driving means (not shown). By continuously flowing out the dope 11 from the casting die 31 onto the circumferentially rotating casting drum 32, the dope 11 is cast on the circumferential surface of the casting drum 32 to form a casting film 33. The

  The casting drum 32 is provided with a heat transfer medium circulation device (not shown) that supplies a heat transfer medium having a predetermined temperature to the casting drum 32 and controls the peripheral surface temperature of the casting drum 32. A flow path (not shown) for the heat transfer medium is formed inside the casting drum 32, and the temperature of the peripheral surface of the casting drum 32 is increased by passing the heat transfer medium through the flow path. It is held at a predetermined value. The surface temperature of the casting drum 32 is appropriately set according to the type of solvent, the type of solid component, the concentration of the dope 11, and the like.

  A decompression chamber 34 that sucks air is provided on the upstream side of the casting die 31 in the rotation direction of the casting drum 32. By sucking air by the decompression chamber 34, the upstream area of the dope 11 that has flowed out as a bead is decompressed to a pressure lower than that of the downstream area.

  On the downstream side of the casting die 31 in the rotation direction of the casting drum 32, a wind shielding plate 41 as a wind shielding member is provided in a posture standing up against the peripheral surface of the casting drum 32. The wind shielding plate 41 suppresses the air flow so that the air flow in the upstream area and the air flow in the downstream area do not affect each other. A known labyrinth is provided at one end of the wind shield plate 41 facing the casting drum 32, whereby the air flowing on the casting film 33 is upstream and downstream of the wind shield plate 41. The wind shielding effect is enhanced.

  The wind shielding plate 41 can be displaced in the rotation direction of the casting drum 32, that is, in the direction along the circumferential surface of the casting drum 32, and is displaced by the shift mechanism 42.

  Between the casting die 31 and the wind shielding plate 41, a blower duct 44 that flows out air and a suction duct 45 that sucks air are provided. The suction duct 45 is disposed in the vicinity of the casting die 31, and the air duct 44 is disposed on the upstream surface of the wind shielding plate 41. Further, a similar air duct 46 and suction duct 47 are provided downstream of the wind shielding plate 41. The air duct 46 is disposed in the vicinity of the stripping position where the casting film 33 is stripped from the casting drum 32, and the suction duct 46 is disposed on the downstream surface of the wind shielding plate 41. As a result, an air flow can be generated on the casting film 33 so that the wind is directed toward the traveling direction of the casting film 33 on the upstream side and the downstream side of the wind shielding plate 41. Further, since the air duct 44 and the suction duct 47 are displaced together with the wind shield plate 41, the position of the wind shield plate 41 is changed, and the range of each area upstream and downstream of the wind shield plate 41 is changed. In addition, the air flow in each area can be effectively controlled.

  A controller (not shown) for independently controlling the air blowing speed in the air duct 42.45 and the air sucking air speed in the suction ducts 43, 46 is provided in each air duct 42, 45 and the suction ducts 43, 46. Thereby, the velocity of the air flowing on the casting film 33 can be controlled independently.

  The casting chamber 13 has a temperature control device (not shown) for keeping the internal temperature at a predetermined value, and a condenser (condenser) for condensing and recovering the solvent evaporated from the dope 11 and the casting film 33. (Not shown). A recovery device (not shown) for recovering the solvent condensed and liquefied by the condenser is provided outside the casting chamber 13.

  The tenter 18 provided downstream of the casting chamber 13 is provided with a blower duct 51 that extends in the conveyance direction of the wet film 12 and sends out temperature-adjusted air to the wet film 12 from above. The air duct 51 is divided into a plurality of sections in the transport direction of the wet film 12, and a slit (not shown) extending in the width direction of the wet film 12 is formed in each section so as to face the transport path. ing. And air flows out from each of these slits. This air is sent to the air duct 51 by a blower 47 connected to the air duct 51. The blower 47 is provided with a controller (not shown) for controlling on / off of air delivery from the slits of each section of the air duct 51, air volume, wind speed, air temperature and humidity. In addition, the temperature and humidity of the air sent out and the air outflow conditions are controlled independently.

  The ear clip device 21 is provided with a crusher 52 for finely cutting the side edge scraps of the wet film 12 that has been cut off.

  An adsorption recovery device (not shown) for adsorbing and recovering the solvent evaporated from the wet film 12, that is, the solvent gas, is connected to the drying chamber 23. A cooling chamber (not shown) is provided downstream of the drying chamber 23. The knurling application roller pair 27 applies knurling to both end portions of the retardation film 17 by embossing. Inside the winding chamber 28, a winding roll 56 for winding the retardation film 17 and a press roller 57 for controlling the tension at the time of winding are provided.

  Next, an example of a method for producing the retardation film 17 using the solution casting apparatus 10 will be described. The dope 11 is cast by continuously flowing out from the casting die 31 to the traveling casting drum 32 cooled by the heat transfer medium. The temperature of the dope 11 at the time of casting is preferably constant in the range of 30 to 35 ° C., and the surface temperature of the casting drum 32 is preferably constant in the range of −10 to 10 ° C. The temperature of the casting chamber 13 is preferably set to 10 ° C. to 30 ° C. by a temperature controller.

  A casting bead is formed from the casting die 31 to the casting drum 32, and a casting film 33 is formed on the casting drum 32. In order to stabilize the state of the casting bead, the upstream area of the bead is controlled by the decompression chamber 34 so as to have a predetermined pressure value. The pressure in the upstream area with respect to the bead is preferably 2000 Pa to 10 Pa lower than the downstream area.

  The casting film 33 is cooled by the casting drum 32 to form a gel. Then, once the casting film 33 has been formed so as to have self-supporting properties, that is, when the casting film 33 has reached a hardness that can be peeled off, the casting film 33 is peeled off from the drum 32. The peeling is performed by pulling the wet film 12 from the downstream side of the casting drum 32 and supporting the wet film 12 on a roller 43 provided in the conveyance path.

  The wind shield plate 41 is disposed to face the casting drum 32 so as to be in the vicinity of a position where the casting film 33 gels (hereinafter referred to as a gelling position). In the area upstream of the gelation position, the air flow rate from the air duct 44 is set so that the flow velocity of the air flowing on the casting film 33, that is, the wind velocity, is maintained at 5 m / second, that is, 5 m / second or less at most. The suction air speed by the suction duct 45 is controlled. The flow velocity of the air flowing on the casting film 33 is a relative speed with respect to the circumferential speed of the casting drum 32. Then, on the casting film 33, the air blowing speed from the air duct 44 and the suction air speed by the suction duct 45 are controlled so as not to follow the casting film 33. . On the upstream side of the gelling position, the flow velocity of the air flowing on the casting membrane 33 is preferably maintained in the range of 0 to 5 m / second, and is preferably maintained in the range of 0 to 4 m / second. More preferably, it is more preferably maintained in the range of 0 m / second to 2 m / second. Thus, it is preferable to keep the air flow in the vicinity of the casting film 33 as low as possible until the gel is formed, and the 0 (zero) wind speed is conveyed to the gel position. It is most preferable to keep it constant on the road from the viewpoint of the effect of preventing the occurrence of shaft misalignment.

  The casting film 33 is 0 (zero) when a value obtained by (storage elastic modulus) / (loss elastic modulus) is formed, and this value gradually increases as it accumulates. In the present invention, “gelled” means when the value of (storage elastic modulus) / (loss elastic modulus) is 1, and the gelation position is the position where this value has reached 1. . The storage elastic modulus and the loss elastic modulus may be obtained with a rheometer (for example, MCR301 manufactured by Anton Paar Physica). In advance, the storage elastic modulus and the loss elastic modulus due to the change over time of the casting film are obtained, the ratio between the two is obtained, and each value is made to correspond to the conveyance path by the casting drum 32. An approximate position is required.

  If the range of the wind speed is within the above range, the gelation of the casting film 33 progresses in the conveyance section from the position where the casting film 33 is formed, that is, the position where the dope 11 reaches the gel 32 to the gelation position. The wind speed may be gradually increased according to the degree. According to this method, both the prevention of axial misalignment and the promotion of gelation of the cast film are achieved in a well-balanced manner. The wind speed in this case may be increased stepwise or continuously. For example, on the conveyance path until the value of (storage elastic modulus) / (loss elastic modulus) becomes 0.3, the wind speed is 1 m / second, and the value of (storage elastic modulus) / (loss elastic modulus) is 0.3. In the conveyance path from the reached position to the position where the value of (storage elastic modulus) / (loss elastic modulus) reaches 0.6, the wind speed is 3 m / second, and the value of (storage elastic modulus) / (loss elastic modulus) is In the conveyance path from the position reaching 0.6 to the gelation position, the wind speed is set to 5 m / sec. This method has a greater effect of preventing axial deviation than making the wind speed constant at 5 m / sec in the conveyance path from the position where the casting film 33 is formed to the gelling position.

  By suppressing the wind speed in the area upstream of the gelling position as described above, the occurrence of unevenness due to abrupt drying of the exposed surface is suppressed, thereby preventing axial misalignment.

  On the other hand, on the downstream side of the gelling position, the flow velocity of the air flowing on the casting film 33 is made larger than that in the area upstream of the gelling position. Thereby, drying of the cast film 33 which gelatinized is advanced. Preferably, the air flows out from the blower duct 46 so as to blow against the casting film 33. As a result, the cast film 33 that has gelled can be quickly wound, and can be peeled off from the support while the exposed surface smoothed on the upstream side of the gelling position is held. The wind speed in the area downstream of the gelling position is preferably constant in the range of 10 m / second to 30 m / second relative to the peripheral speed of the casting drum 32.

  Control of the wind speed on the downstream side of the gelling position is performed by the air blowing speed from the air duct 46 and the suction air speed by the suction duct 47.

  An anemometer (not shown) is provided in the vicinity of the conveying path of the casting film 33 on both the upstream side and the downstream side of the wind shielding plate 41, and thereby flows on the casting film 33. Air flow can be detected.

  As described above, the wind speed on the casting film 33 before and after the casting film is gelled is independently controlled. That is, it is good to make the wind speed as low as possible during gelation, and to make the wind speed higher after gelation than before gelation. Thereby, the retardation film 17 without an axial shift can be manufactured.

  And in this invention, since the wind-shielding board 41 is provided facing the gelation position, it can suppress that the air downstream from a gelation position flows into an upstream. Thereby, it is possible to prevent the downstream air having a high wind speed from affecting the upstream area of the gelation position where the wind speed should be suppressed.

  According to this method, even when the production speed of the retardation film 17 is increased to 35 m / min or more, and further to a range of 45 m / min or more and 120 m / min or less, no axial deviation occurs.

  In the present embodiment, the wind shielding plate 41 is provided only in the vicinity of the gelling position, and the wind speed is controlled independently for the two areas of the upstream side and the downstream side, but the number of the wind shielding plates 41 is further increased. Also good. That is, a plurality of wind shielding plates 41 may be arranged in the rotation direction of the casting drum 32 and the wind speed may be controlled for each space partitioned by the wind shielding plates 41. For example, the conditions of the wind speed on the upstream side of the gelation position and the wind speed on the downstream side should be within the range of the above conditions, so that the wind speed sequentially increases from the upstream area to the downstream area. To do. Thereby, since wind speed control is made more elaborately according to the progress degree of the gelation of the casting film 33, the inhibitory effect of the axis | shaft deviation expression in the phase difference film 17 further increases.

  Further, a wind shielding plate 41 is provided inside the chamber by using a chamber that is provided along the peripheral surface of the casting drum 32 so as to cover the casting film 33 and partitions a space for controlling air feeding from the outside. By providing this, the wind speed control effect can be further enhanced, and the axial displacement suppression effect is enhanced.

  The higher the production rate, the higher the solvent residual rate at the time of stripping. Therefore, it is preferable to cool so that the cooling rate, that is, the amount of change in temperature that falls per unit time increases. When the solvent residual ratio is higher than 320%, the cast film 33 is not hard enough to be transported even if the cast film 33 is cooled, or is not hard enough to start widening in the tenter 18. It may tear when widening. In addition, the fact that the solvent residual ratio at the time of stripping is small means that the solvent is dried on the casting drum 32, so that the significance of the cooling casting is low. Therefore, the solvent weight of the casting film 33 at the time of peeling is preferably 180% or more and 320% or less when the weight of the solid content is 100%. Thus, in the present invention, the solvent residual ratio (unit:%) is a value based on the dry amount, and specifically, when the weight of the solvent is x and the weight of the casting film 33 or the wet film 12 is y. And {x / (y−x)} × 100.

  When the wet film 12 peeled off from the casting drum 32 in a state of containing the solvent is guided by the tenter 18, both end portions thereof are held by pins as holding means and conveyed downstream. During this conveyance, the wet film 12 is promoted to dry by the air sent out from the air duct 51.

  The temperature of the wet film 12 is controlled by the air that flows out from the air duct 51. The slit of the air duct 51 is provided in the vicinity of the conveyance path of the wet film 12, and the temperature of the air that flows out and the temperature of the wet film 12 may be regarded as the same temperature. The temperature condition and width control in the tenter 18 will be described later with reference to another drawing.

  It is preferable to dry the wet film 12 within a predetermined drying speed until the solvent residual rate reaches 60 wt% with the tenter 18 from the peeling position where the drum 32 is peeled off. This drying speed is preferably determined based on the rate of decrease in the thickness of the wet film 12. The reduction rate of the thickness of the wet film 12 can be represented by a thickness that decreases per minute, and a preferable drying rate is 400 μm / min or less. In other words, the shaft misalignment can be more reliably suppressed by stripping off at a drying speed of 400 μm / min at the maximum and then drying until the solvent residual ratio reaches 60% by weight. In addition, from the viewpoint of more reliably suppressing the axial displacement, the drying speed from the stripping position until the solvent residual rate reaches 60% by weight should be constant at 300 μm / m rather than constant at 400 μm / m. Is more preferable, and it is more preferable to make it constant at 200 μm / m.

  The thickness of the wet film 12 may be measured by providing a plurality of well-known thickness measuring instruments that measure the thickness in a non-contact manner in the conveyance path.

  The tenter 18 applies tension to the wet film 12 in the width direction. When the width is widened at this time, the wet film 12 exhibits high Re, and when the drying proceeds, the retardation film 17 is obtained.

  The wet film 12 from the tenter 18 is cut and removed by the edge-cutting device 21 at both side ends held by the pins. The separated both ends are sent to the crusher 52 by a cutter blower (not shown). By the crusher 52, the side end portion is crushed into chips. Since this chip is reused for dope manufacturing, the raw material can be effectively used.

  On the other hand, the wet film 12 from which both ends have been removed is sent to the drying chamber 23 and further dried. In the drying chamber 23, the wet film 12 is conveyed while being wound around the roller 22. The internal temperature of the drying chamber 23 is not particularly limited as long as the wet film 12 does not deteriorate by heating.

  In addition, it is more preferable that the drying chamber 23 is divided into a plurality of sections in the conveyance direction of the wet film 12 in order to change the blowing temperature. In addition, when a predrying chamber (not shown) is provided between the ear opener 21 and the drying chamber 23 and the wet film 12 is preliminarily dried, the temperature of the wet film 12 is prevented from rapidly rising in the drying chamber 23. Therefore, the shape change of the wet film 12 in the drying chamber 23 can be suppressed.

  A first roller 61 that conveys the wet film 12 to the drying chamber 23 is provided upstream of the drying chamber 23, and the retardation film 17 is conveyed from the drying chamber 23 to the winding chamber 28 downstream of the drying chamber 23. A second roller 62 is provided. The first roller 61 and the second roller 62 are each provided with a controller (not shown) that independently controls the rotational speed in the circumferential direction. The controller rotates at a predetermined rotational speed and wets in contact with the circumferential surface. The film 12 or the retardation film 17 is conveyed.

  The solvent gas generated by evaporation in the drying chamber 23 is adsorbed and recovered by an adsorption recovery device. The air from which the solvent component has been removed is sent again as dry air into the drying chamber 23.

  The retardation film 17 is imparted with knurling to both end portions by a knurling roller pair 27. In addition, it is preferable that the height of the unevenness | corrugation of the knurled location is 1 micrometer-200 micrometers.

  The retardation film 17 is wound up by a winding roll 56 in the winding chamber 28. It is preferable to wind the film while applying a desired tension to the film 62 by the press roller 57. It is more preferable to gradually change the tension from the start to the end of winding, thereby preventing excessive winding in the film roll. The length of the phase difference film 17 to be wound is preferably 100 m or more. The width of the retardation film 17 to be wound is preferably 600 mm or more, and preferably 1400 mm or more and 2500 mm or less. However, the present invention is applied even when the width is larger than 2500 mm. The present invention is also applied to the production of a thin film having a thickness of 15 μm to 100 μm.

  From casting die, decompression chamber, support structure, peeling method, stretching, drying conditions for each process, handling method, curling, winding method after flatness correction, solvent recovery method, film recovery method, etc. This is described in detail in paragraphs [0617] to [0889] of JP-A-2005-104148. These descriptions can be applied to the present invention.

  FIG. 2 is a schematic view of the inside of the tenter 18. Inside the tenter 18, a pin plate 72 having a large number of pins 71 as holding means for the wet film 12 at positions on both side ends of the wet film 12 along the conveyance path of the wet film 12, A chain 73 that travels endlessly with a pin plate 72 attached thereto, a rail 76 that determines the track of the chain, and a drying device 51 (see FIG. 1) are provided. The rail 76 is provided with a shift mechanism 77. When the wet film 12 sent to the tenter 18 reaches a predetermined position, pins 71 are inserted and held at both ends. The shift mechanism 77 moves the rail 76 in the width direction of the wet film 12, whereby the chain 73 is displaced. The pin plate 72 on the chain 73 moves in the width direction of the film 12 while holding the wet film 12, and tension is applied to the wet film 12 in the width direction.

  The wet film 12 immediately after being peeled off from the casting drum 32 contains a large amount of solvent and is very unstable. Therefore, the wet film 12 is difficult to transport with a roller and can withstand gripping by a clip. Can not. Therefore, as in this embodiment, when the both ends of the wet film 12 are pierced with the pins 71, the wet film 12 can be stably held and transported.

  FIG. 3 is an explanatory view of the wet film 12 from the start of holding by the pin of the tenter 18 to the release of holding by the pin of the tenter 18. The arrow line Y is the conveyance direction of the wet film 12. In the tenter 18, tension is applied to the wet film 12 in the width direction indicated by the arrows X1 and X2. In the tenter 18, a position where the holding of the wet film 12 by the pin 71 (see FIG. 2) is started is a holding start position PS, and a position where the holding is released is a holding release position PE. Although the tenter 18 has an inlet on the upstream side of the holding start position PS and an outlet on the downstream side of the second position, the illustration is omitted in FIG.

  The solvent gradually evaporates from the wet film 12 until it reaches the holding start position after being peeled off from the casting drum 32 at the first position P1, and further evaporated by the outflow of dry air from the air duct 51 in the tenter 18. The solvent residual ratio of the wet film 12 is further lowered. The position at which the solvent residual ratio is 60% by weight is the first position P1, the position at which 40% by weight is the second position P2, and the position at which 10% by weight is the third position P3.

  Until reaching the first position P1, as described above, the drying speed of the wet film 12 is reduced to 400 μm / min or less.

  In the tenter 18, the temperature of the air blown out from the air duct 51 is adjusted so that the temperature of the wet film 12 is in the range of 80 ° C. or higher and (Tg + 50) ° C. or lower between the second position P2 and the third position P3. That is, the temperature of the wet film 12 is once in the range of 80 ° C. or more (Tg + 50) ° C. during the time when the solvent residual ratio becomes 40 wt% to 10 wt%. It may be continuous while the residual ratio is from 40% by weight to 10% by weight, or may be intermittent. This step is a step for promoting the crystallization of TAC when the polymer contained in the wet film 12 is TAC, and will be referred to as a crystallization step in the following description.

  And while maintaining the temperature of the wet film 12 in the above temperature range with the tenter 18, it is preferable not to widen the film 12, which is to keep the width constant and to reduce the width. Either of these may be used. The contraction width can be implemented by holding the wet film 12 with a tension smaller than the contraction force of the wet film 12.

  The wet film 12 that has undergone the temperature holding step is spread in the width direction with a pin. When the tenter 18 does not apply tension in the width direction indicated by the arrows X1 and X2 in the tenter 18, the wet film 12 is loosened by its own weight or contracts in the width directions X1 and X2 as the solvent evaporates. Therefore, in addition to the purpose of preventing looseness, in the present invention, the wet film 12 is widened by applying tension in the width directions X1 and X2 in order to express Re more. The tension is preferably applied to the wet film 12 symmetrically with respect to the center in the width direction of the wet film 12. This is because the molecular orientation is uniformly controlled in the width direction of the wet film 12.

  By applying tension, the width of the wet film 12 that was the width L1 (hereinafter referred to as the first width) when entering the tenter 18 is increased to L2 (hereinafter referred to as the second width). The width L2 may be held so as not to change thereafter as shown in FIG. 3, or may be further reduced after the holding. Even when the second width L2 is maintained and when the width is reduced from the second width L2, tension is applied to the wet film 12 in the width directions X1 and X2. In the case of reducing the width, the width is controlled by adjusting the balance between the contraction force and the tension by the pin by utilizing the contraction force of the wet film 12 that naturally contracts when not held by the pin. In addition, in FIG. 3, code | symbol KL represents the position of the center part side in the width direction of the wet film 12 among the holding | maintenance parts of the wet film 12 hold | maintained with a pin, and 1st width L1 and 2nd width L2 are Both are the distances between the holding target lines KL on both sides.

  A position where the first width L1 starts to be widened to the second width L2 is a fourth position P4, and a position where the widening is finished is a fifth position P5. The widening is performed after the crystallization step. Therefore, for example, when the crystallization step is finished when the solvent residual ratio is 20 wt%, the timing of the start of widening may be before the solvent residual ratio reaches 10 wt%. The fourth position P4 is upstream of the third position P3. Note that the end timing of widening is not particularly limited.

  The temperature of the wet film 12 at the time of widening from the fourth position P4 to the fifth position P5 is preferably in the range of 120 ° C. or higher and 190 ° C. or lower when dichloromethane is used as the solvent component.

  Furthermore, the widening ratio from the fourth position P4 to the fifth position P5 is preferably 10% or more and 60% or less. Here, the widening rate (unit:%) is a value obtained by 100 × (L2−L1) / L1. By performing widening at the above-mentioned widening ratio after the crystallization step, even when the retardation film 12 having a high Re of 50 nm or more is formed by cooling casting, it can be stably conveyed.

  Moreover, although this embodiment shows the case where cooling casting is implemented using the casting drum 32 as a casting support body, it replaces with this aspect and can also use it as a band which carries out a continuous travel. Good. Furthermore, the same effect can be obtained as an aspect of dry casting regardless of the drum and the band. However, the present invention has the above-mentioned effect particularly remarkable in the case of cooling casting.

It is the schematic of the solution casting apparatus which implemented this invention. It is the schematic which shows the holding | maintenance state of the film in a tenter. It is the schematic which shows the widening and contraction width of the film in a tenter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Solution casting apparatus 11 Dope 12 Wet film 17 Phase difference film 18 Tenter 23 Drying chamber 32 Casting drum 41 Wind shield plate 44, 46 Air duct 45, 47 Suction duct 61, 62 First and second rollers

Claims (3)

A casting process in which a dope containing a polymer and a solvent flows out of a casting die to form a casting film on the peripheral surface of a drum rotating at a predetermined peripheral speed;
A gelling step of maintaining the relative velocity of the air flowing on the casting membrane with respect to the peripheral speed to be at most 5 m / sec, cooling the casting membrane with the drum, and gelling;
A blowing process that advances drying of the casting film by blowing air having the relative speed larger than the air flowing on the casting film in the gelling process to the gelled casting film,
A stripping step of stripping the cast film that has undergone the blowing step from the drum as a wet film containing the solvent;
A solution casting method comprising: drying the wet film to form a film.   By the wind-shielding member provided in the vicinity of the gelling position where the cast film gels so as to oppose the peripheral surface of the drum, the air downstream from the gelling position flows into the upstream side. The solution casting method according to claim 1, wherein   In the drying step, the wet film is dried at a drying rate such that the reduction rate of the wet film thickness is suppressed to 400 μm / min at the maximum until the solvent residual ratio of the wet film reaches 60%. 3. The solution casting method according to claim 1, wherein the solution is formed into a film.

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