JP2008213412A - Film manufacture facility and solvent recovery method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove effectively and efficiently an additive from a solvent becoming a gas in a film manufacturing portion. <P>SOLUTION: Air of a drying chamber 27 in the film manufacturing portion 27 is sent to an additive removal device 41 of a second solvent recovery portion 19. A temperature of the air when being sent to the additive removal device 41 is in a range which is higher than the boiling point of the solvent 12 and not higher than the boiling point of the additive 13. In the additive removal device 41, an adsorbent sorbing selectively the additive 13 makes contacts with the air from the drying chamber 27. The air from which the additive 13 is removed is sent to an adsorption unit 47 which adsorbs the solvent 12 to desorb. Here, the solvent 12 is separated from the air, becomes a liquid at a condenser 48 and is recovered. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film manufacturing facility and a solvent recovery method for recovering a solvent evaporated by solution casting.

  Cellulose acylate films have been widely used as supports for photographic light-sensitive materials because of their toughness and flame retardancy. Among cellulose acylate films, a TAC film produced from cellulose triacetate (TAC) having an average degree of acetylation of 57.5 to 62.5% is particularly excellent in optical isotropy. The demand for a protective film for a polarizing plate of a liquid crystal display device or an optical compensation film is rapidly increasing.

  The TAC film is generally produced by a solution casting method. This is because the solution casting method can produce a film having more excellent optical properties and physical properties than the melt casting method. As is well known, the solution casting method is a method for producing a film by casting a dope in which a polymer is dissolved in a solvent, peeling it off on a support, and drying it. The solvent evaporated in the drying step is recovered from the viewpoints of environmental protection, human body protection, effective use of resources, and economy, and is reused as a dope raw material.

  In the solution casting drying step, the ambient temperature in the vicinity of the film is raised to a temperature as high as several hundred degrees Celsius or higher in order to dry the film more completely. As a result, the amount of evaporation of the solvent can be increased and the evaporation rate can be increased. On the other hand, the additive which is a component of the dope for inclusion in the film is partially evaporated together with the solvent. Resulting in. Additives are indispensable for improving the performance of the film, and various additives are added to the dope depending on the application or the type of polymer.

  The evaporated solvent is recovered by a condenser, a distillation device, etc., but some additives become liquid or solid with the condensation of the solvent in the condensation process of the solvent, and are removed from the solvent in the subsequent distillation. There are many things that are difficult. A so-called fractionator that divides a mixture into a plurality of substances by distillation needs to increase the number of stages as the fractionation performance increases, so that the structure becomes complicated, maintenance is troublesome, and control is more difficult. There is a problem that it becomes difficult, so it cannot be applied easily.

Accordingly, various methods have been proposed to remove the additive from the solvent. For example, before condensation, the air containing the solvent and the additive is heat exchanged with other substances, so that the temperature of the air is lower than the saturation temperature of the additive and only the additive is added. A method of condensing the liquid into a liquid and collecting it (for example, see Patent Document 1), or in addition to or instead of this method, the liquid additive is further cooled and trapped with a filter as a solid and collected Etc.
JP-A-2005-793

  However, although the method using a heat exchanger can generally separate the solvent and the additive, the additive adheres to the inside of the heat exchanger and becomes a solid, and the performance of the heat exchanger over time However, it is difficult to recover the adhering additive. In addition, gas separation membranes are not sufficient to effectively and efficiently separate specific substances, including filter materials, and when a large amount of solvent must be processed as in solution casting. Is not applicable. Even if a filter having a sufficient processing speed has been proposed, the problem that the separation performance deteriorates with time due to clogging remains as long as the filter is used. In any of the above methods, the solvent and the additive cannot be separated unless the temperature of the air containing the additive and the solvent is lowered to some extent. Therefore, by lowering the temperature of the air, the additive adheres to the separating means and other devices and contaminates them.

  Therefore, in view of the above problems, the present invention provides a film manufacturing method that effectively and efficiently removes an additive from a solvent evaporated with the additive in a solution casting process and prevents contamination of the apparatus by the additive. The object is to propose equipment and solvent recovery method.

  The present invention provides a wet film containing the solvent by casting a dope containing a polymer, a solvent and an additive on a support, and peeling the dope from the support, and drying the wet film to form a film. In a film manufacturing facility comprising a manufacturing unit and a solvent recovery unit that recovers the solvent evaporated by drying the wet film, the solvent recovery unit is configured to reduce the air containing the evaporated solvent from the boiling point of the solvent. In a state where the additive is held at a temperature not higher than the boiling point of the additive, the additive is brought into contact with an adsorbent that adsorbs the additive to remove the additive from the air, and the additive removing device passes through the additive removing device. And a solvent recovery and purification device that recovers and purifies the solvent from the air.

  Furthermore, the present invention provides a gas in a solvent recovery method for recovering a solvent that has become a gas by drying from a film manufacturing section that is dried and cast into a film after casting a dope containing a polymer, a solvent, and an additive. A first contact step of contacting the air containing the solvent with a first adsorbent that adsorbs the additive in a state where the air is held in a temperature range higher than the boiling point of the solvent and lower than the boiling point of the additive; After the first contact step, a second contact step of bringing the air into contact with the second adsorbent that adsorbs the solvent, and contacting the second adsorbent with vapor to cause the second adsorbent to It has a desorption process for desorbing the adsorbed solvent in a gaseous state, and a condensation process for condensing the desorbed solvent.

  The effect is particularly great when the additive is triphenyl phosphate.

  According to the present invention, the additive can be effectively and efficiently removed from the solvent evaporated with the additive in the solution casting process. Furthermore, contamination of the device with the additive can be prevented.

  The present invention will be described in detail below with reference to embodiments. However, the present invention is not limited to the modes described here. FIG. 1 is a schematic view showing a solution casting apparatus as one embodiment of the present invention. In the solution casting apparatus 10, the film production unit 17 for casting the dope 14 containing the polymer 11, the solvent 12, and the additive 13 to form the film 16, and gas inside the film production unit 17. First and second solvent recovery units 18 and 19 are provided for recovering the solvent (hereinafter referred to as solvent gas) 12 for use in manufacturing the dope 14 again.

  The film manufacturing unit 17 stretches a casting die 22 for casting the dope 14 on a continuously running support 21 to form a casting film 14a, and a film 16 peeled off from the support 21 by a roller or the like. A tenter 23 that dries while drying, a drying chamber 27 that is provided downstream of the tenter 23 and advances drying while the film 16 is conveyed by a roller 26 and the like, and a winding chamber 28 that winds the dried film 16 is provided.

[polymer]
The polymer 11 used in the present invention is not particularly limited, and may be a known polymer that can be formed into a film by a solution casting method. In this embodiment, the case where the cellulose acylate widely used for optical uses, such as a protective film for polarizing plates and an optical compensation film, is used is demonstrated as an example. Among cellulose acylates, cellulose acetate, particularly cellulose triacetate having an average degree of acetylation of 57.5% to 62.5% is preferable for producing a film having excellent optical properties. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose, and can be determined according to the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). In the present embodiment, particulate cellulose triacetate is used, and 90% by weight or more of cellulose triacetate has a particle diameter of 0.1 to 4 mm, preferably 1 to 4 mm.

[solvent]
Examples of the solvent include halogenated hydrocarbons, esters, ketones, ethers, and alcohols, but are not particularly limited. As a solvent, one type of compound may be sufficient and the mixture of a some compound may be sufficient. Specific examples of the solvent include halogenated hydrocarbons (eg, dichloromethane), esters (eg, methyl acetate, methyl formate, ethyl acetate, amyl acetate, butyl acetate, etc.), ketones (eg, acetone, methyl ethyl ketone, Cyclohexanone etc.), ethers (eg dioxane, dioxolane, tetrahydrofuran, diethyl ether, methyl-t-butyl ether etc.), alcohols (eg methanol, ethanol etc.) and the like.

[Additive]
An additive contained in the dope includes a plasticizer. Examples of the plasticizer include phosphate esters (for example, triphenyl phosphate (hereinafter referred to as TPP), tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc.) Phthalate esters (eg, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate), glycolate esters (eg, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl) Ethyl glycolate, butyl phthalyl butyl glycolate, etc.) and other plasticizers can be used. Among these, TPP is particularly preferable for producing a highly transparent cellulose acylate film.

  The dope may contain various additives other than the plasticizer. Examples of other additives include an ultraviolet absorber, a release agent, a release accelerator, and a fluorosurfactant. As the ultraviolet absorber, for example, an oxybenzophenone compound, a benzotriazole compound, a salicylic acid ester compound, a benzophenone compound, a cyanoacrylate compound, and a nickel complex compound are preferable, and among them, a benzotriazole compound and a benzophenone compound are preferable. Particularly preferred.

[Solvent recovery process]
In the casting area 29 including the casting die 22, the support 21 and the tenter 23, a large amount of the solvent 12 evaporates from the dope 14, the casting film 14 a and the film 16. The solvent gas thus generated is sent to the first solvent recovery unit 18 connected to the casting area 29 in a state of being contained in the air inside the casting area 29.

  The first solvent recovery unit 18 cools the air sent from the casting area 29 and condenses the solvent gas contained in the air, and passes through the condenser 31 without being condensed. And a heater 32 that warms the cooled air. The solvent 12 recovered by the condenser 31 is sent to the film manufacturing unit 17 and reused as a raw material for the dope 14. Further, the air heated by the heater 32 is returned to the casting area 29 and used, for example, as a drying air for drying the casting film 14 a and the film 16 inside the tenter 23. A heat exchanger 35 is arranged between the casting area 29 and the condenser 31 and between the condenser 31 and the heater 32, so that the low temperature air from the condenser 31 and the high temperature from the casting area 29 are provided. It is preferable to exchange heat with the air. By using the heat exchanger 35, the energy consumption in the condenser 31 and the energy consumption in the heater 32 can be reduced.

  In the drying chamber 27, in order to dry the film 16 as completely as possible, the vicinity of the conveyance path of the film 16 is set to a high temperature of 100 ° C. or more. For this reason, the air inside the drying chamber 27 also contains the solvent 12 evaporated from the film 16 and the additive that has become gaseous as the solvent 12 evaporates. However, the amount of solvent gas contained in the air is smaller than the amount of solvent gas generated in the casting area 29. Therefore, this air is sent to the second solvent recovery equipment 19 connected to the drying chamber 27.

  The second solvent recovery unit 19 includes an additive removal device 41 that selectively removes the additive 13 from the sent air, and the solvent 12 is removed from the air from which the additive 13 has been removed to purify the solvent 12. And a recovery / purification device 43 for the purpose. Further, between the additive removing device 41 and the recovery and purification device 43 and between the recovery and purification device 43 and the drying chamber 27, the air passed through the additive removal device 41 and the air sent from the recovery and purification device 43. A heat exchanger 44 is provided for exchanging heat between the two.

  High temperature air of 100 ° C. or higher is sent to the additive removing device 41 in a state including the solvent gas and the additive 13 that has become a gas. The additive removing device 41 is provided with an adsorbent that adsorbs the additive 13. The air comes into contact with the adsorbent in a state where the temperature is maintained at 100 ° C. or higher, specifically, higher than the boiling point of the solvent and lower than the boiling point of the additive. Thereby, only the additive in the air is adsorbed by the adsorbent. In this way, by first removing the additive from the air in the drying chamber 27, it is possible to prevent the additive from adhering to the solvent recovery equipment and piping provided on the downstream side. In addition, according to this method, the additive can be removed without lowering the temperature of the air, so that the removal of the additive is simple, energy saving is achieved as compared with the recovery by cooling, and the equipment cost is also kept low. Can do. Further, conventionally, many additives are deposited in the downstream heat exchanger 44, the recovery and purification apparatus 43, etc., where it has been necessary to cool the air, so that maintenance and cost such as cleaning are costly. However, according to the present invention, it is possible to reduce these labor and cost. The details of the additive removing device 41 will be described later with reference to another drawing.

  The air from which the additive has been removed is sent to the recovery and purification device 43 to remove the solvent, and then warmed by the heating means and returned to the drying chamber 26. Thereby, since the concentration of the solvent gas and the additive is always kept below the predetermined value in the air in the drying chamber 26, the drying efficiency of the film 16 is prevented from being lowered, and the additive is kept inside the drying chamber 26. The equipment and the film 16 are not contaminated.

  The temperature of the air that has passed through the additive removal device 41 is as high as 100 ° C. or higher, but it is preferable to cool it to about 30 ° C. when it is sent to the recovery and purification device 43. This is to increase the adsorption efficiency by the adsorbent accommodated in the recovery and purification apparatus 43 and to maintain the activity of the adsorbent. Therefore, it is preferable to provide a cooling means for cooling the air between the additive removal device 41 and the recovery and purification device 43. On the other hand, the temperature of about 30 ° C. air coming out of the recovery / purification device 43 can be raised to 100 ° C. or higher when fed into the drying chamber 27. This is for improving the drying efficiency in the drying chamber 27. Therefore, it is preferable to provide a heating means for heating air between the recovery and purification device 43 and the drying chamber 27. In the present embodiment, a heat exchanger 44 having both functions of the cooling means and the heating means is used. This heat exchanger 44 exchanges heat between the air that has passed through the additive removal device 41 and the air that has passed through the recovery and purification device 43, so that each air is controlled by using both temperature control means of the cooling means and the heating means. There are more energy saving effects than cooling and heating each.

  In addition to the heat exchanger 44, a cooling unit and a heating unit may be used. In this case, it is preferable that the heat exchanger 44 exchange heat between the air sent from the additive removing device 41 to the cooling means and the air sent from the recovery and purification device 43 to the heating means. Thereby, size reduction of both a cooling means and a heating means can be aimed at. In the present embodiment, a cooler 45 is used as a cooling means used in addition to the heat exchanger 44. The installation position of the cooler 45 may be in the recovery / purification device 43 or may be outside.

  In the case of using the cooler 45 in addition to the heat exchanger 44, it is preferable to connect a plurality of coolers 45 in parallel to a pipe through which air is sent, and to switch between them. This is because one of the cooling devices 41 is used when an additive is not completely recovered by the additive removing device 41 and the additive is deposited inside the cooling device 41 or when another substance is deposited. This is because the other one can be used for air cooling even if it is washed and air cooling can be carried out continuously.

  The recovery and purification apparatus 43 includes a cooler 45 that cools and condenses the solvent gas, an adsorption unit 47 that adsorbs the solvent gas that has not become liquid in the cooler 45 to the adsorbent, and desorbs the desorbed gas 46. A condenser (condenser) 48 that condenses the desorption gas 46 after being used for desorption, and a purification unit 51 that purifies the solvent that has become liquid in the condenser 48 are provided. A high temperature gas such as water vapor can be used as the desorption gas 46.

  The cooler 45 is preferably used to reduce the load of solvent recovery in the adsorption unit 47, but may not be used when the amount of solvent gas generated in the drying chamber 27 is extremely small. The configuration of the cooler 45 is basically the same as a condenser 48 described later.

  As will be described later, the adsorption unit 47 includes a plurality of adsorption tanks in which an adsorbent is accommodated, and a solvent gas in the air is brought into contact with the adsorbent to remove the solvent from the air. After the adsorption is completed, the desorption gas 46 is sent to desorb the solvent adsorbed on the adsorbent.

  The condenser 48 includes a condenser main body (not shown) for retaining the desorption gas 46 used for desorption, and is continuously fed into the condenser main body to cool the desorption gas. Fluid (not shown) and a circulation unit (not shown) that is provided outside the condenser main body, cools the fluid whose temperature has increased in the condenser main body, and then sends it back to the condenser main body And a tube through which the fluid flows. The fluid is preferably a liquid that is stable at a temperature lower than the boiling point of the solvent, and water is preferable in consideration of handling, availability, and cost. When the desorption gas 46 is fed into the condenser main body, the temperature is lowered below the boiling point by the fluid flowing in the pipe, condenses, and is sent to the purification unit 51 as a liquid.

  The purification unit 51 purifies the liquid solvent by distillation. When a mixture is used as the solvent 12 of the dope 14, the liquid sent to the purification unit 51 is also a mixture and can be recovered for each component by fractional distillation.

  The solvents 12 obtained by the purification unit 51 and the condenser 31 are mixed or reused alone.

  FIG. 2 is a schematic view of the additive removing device 41. The additive removal device 41 includes first and second adsorption towers 71 and 72 for adsorbing and desorbing the additive, and the first and second adsorption towers 71 and 72 exchange heat with piping from the drying chamber 27. It is connected in parallel to the piping to the vessel 44, and either one can be used by switching. The first and second adsorption towers 71 and 72 are provided with temperature controllers 71a and 72a for adjusting the internal temperature. The number of adsorption towers connected in parallel is not limited to 2, and the adsorption tower may be either a fixed bed type adsorption tower or a fluidized bed type adsorption tower.

  The first and second adsorption towers 71 and 72 contain an adsorbent, and the adsorbent is determined according to the type of additive and solvent to be adsorbed. In the present invention, since the additive is adsorbed to the adsorbent at a temperature higher than the boiling point of the solvent and lower than the boiling point of the additive, for example, when the additive is TPP and the solvent is a ketone compound such as dichloromethane, Incombustible materials such as silica gel and zeolite are used as the agent. This is because when general activated carbon is used as the adsorbent, air containing the solvent may ignite. The temperature of the air at the time of adsorption is maintained at a temperature higher than the boiling point of the solvent by the temperature controllers 71a and 72a, thereby keeping the concentration of the additive in the air lower than the saturation concentration. By the adsorption under this temperature condition, the first and second adsorption towers 71 and 72 can adsorb only the adsorbent in contact with the adsorbent while the additive remains in a gas state without adsorbing the solvent, Since the additive is trapped in the fine pores of the adsorbent particles, it is possible to prevent the additive from being precipitated inside the first and second adsorption towers 71 and 72 as a solid.

  When the adsorption of one of the first and second adsorption towers 71 and 72 is completed, the adsorption of the other is started. During the adsorption on the other side, the adsorbent of the adsorption tower that has completed the adsorption is replaced with a new adsorbent. The adsorbent after adsorption is regenerated by activation. This is because high boiling point compounds such as TPP cannot be desorbed with steam.

FIG. 3 is a schematic diagram of the suction unit 47. The adsorption unit 47 includes first to third adsorption towers 91 to 93 that perform adsorption and desorption of solvent gas. The first to third adsorption towers 91 to 93 each contain an adsorbent that adsorbs a solvent gas, for example, activated carbon, and a supply port for putting the desorption gas 46 inside, and the desorption gas 46 outside. There is an outlet for taking out. The supply port and the discharge port are provided so that the desorption gas 46 entering the inside is discharged after contacting the activated carbon. Although the number of adsorption towers is 3 in FIG. 3, the number of adsorption towers is not limited to this.

  In the first to third adsorption towers 91 to 93, the adsorption process for selectively adsorbing the solvent gas from the air passing through the cooler 45 and the desorption process for desorbing the solvent gas from the adsorbent are alternately repeated. To be implemented. And an adsorption | suction process is implemented by switching and using the 1st-3rd adsorption towers 91-93. That is, after the adsorption step is performed in the first adsorption tower 91, the adsorption process is sequentially performed in the second adsorption tower 92 and the third adsorption tower 93, and then again in the first adsorption tower 91. And the desorption process is implemented in the adsorption tower after the adsorption process. In the adsorption process, the air containing the solvent gas passes through the adsorbent area, whereby the solvent gas is adsorbed by the adsorbent, and the air from which the solvent gas has been removed is the first, second, and third adsorption towers. It returns to the drying chamber 27 (refer FIG. 1) through the heat exchanger 44 from 91-93. In the desorption process, a desorption gas 46 of about 100 ° C. is sent to the first to third adsorption towers 56 to 58 to desorb the solvent gas. The desorption gas 46 at about 100 ° C. is sent from the first to third adsorption towers 56 to 58 to the condenser 48 to condense the solvent gas.

  The first to third adsorption towers 91 to 93 are provided with regenerating members 91a to 93a for regenerating the adsorbent, respectively. When the adsorbent that has finished the adsorption process is sent to these regenerating members 91a to 93a, the adsorbent is regenerated by performing desorption treatment with a high-temperature gas such as the desorption gas 46.

  As described above, according to the present invention, it is possible to continuously recover the solvent evaporated in the film manufacturing department, and to effectively and efficiently remove the additive contained in the air by evaporation from the film together with the solvent. Since it can be removed, the reuse rate of the solvent can be improved, and contamination of the film production section and solvent recovery section and film contamination by the additive can be prevented.

It is the schematic of solution casting apparatus. It is the schematic which shows an example of the additive removal apparatus of this invention. It is the schematic which shows an example of an adsorption | suction unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Solution film-forming equipment 14 Dope 18, 19 1st, 2nd solvent collection | recovery part 27 Drying chamber 41 Additive removal apparatus

Claims (3)

Casting a dope containing a polymer, a solvent, and an additive on a support, and removing from the support to form a wet film containing the solvent, and drying the wet film to form a film, In a film production facility comprising a solvent recovery unit that recovers the solvent evaporated by drying the wet film,
The solvent recovery unit is
In a state where the air containing the evaporated solvent is maintained at a temperature higher than the boiling point of the solvent and lower than the boiling point of the additive, the air is brought into contact with an adsorbent that adsorbs the additive, and the additive is removed from the air. An additive removal device to remove,
A solvent recovery and purification device that recovers and purifies the solvent from the air that has passed through the additive removal device;
A film manufacturing facility comprising: In the solvent recovery method for recovering the solvent that has become a gas by the drying, from the film manufacturing section that is dried and casted after the dope containing the polymer, the solvent, and the additive,
First contact is made to contact the first adsorbent that adsorbs the additive in a state in which the air containing the solvent in the form of gas is maintained in a temperature range higher than the boiling point of the solvent and lower than the boiling point of the additive. Process,
A second contact step of bringing the air into contact with a second adsorbent that adsorbs the solvent after the first contact step;
A desorption step of bringing vapor into contact with the second adsorbent and desorbing the solvent adsorbed on the second adsorbent in a gaseous state;
A condensation step of condensing the desorbed solvent;
A solvent recovery method characterized by comprising:   The solvent recovery method according to claim 2, wherein the additive is triphenyl phosphate.

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