JP2010155203A - Method and apparatus of drying coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress evaporation or sublimation of additives contained in a coating film and at the same time quickly dry a solvent contained in the coating film. <P>SOLUTION: The apparatus of drying a coating film formed by applying a polymer coating liquid to a support comprises first control means 47 for feedback control of drying conditions of a hot-air drying apparatus 28 to keep the coating film temperature lower than the melting point of a first additive, a vapor drying apparatus 29 for drying the coating film by using hot air containing vapor of a second solvent with a smaller molecular volume than that of the first solvent, a second temperature sensor 51 for measuring the coating film temperature in the vapor drying apparatus 29, and second control means 53 for feedback control of drying conditions of the vapor drying apparatus 29 to keep the coating film temperature lower than the melting point of the first additive based on the measurement results of the second temperature sensor 51. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and apparatus for drying a coating film containing a relatively low-molecular additive, and more particularly to a technique for drying an image forming layer when producing a lithographic printing plate.

  A lithographic printing plate forms a coating film by applying a coating solution such as a photosensitive layer forming solution or a thermosensitive layer forming solution while running a belt-like body such as a support web, a base film, or baryta paper in a certain direction. After drying, it is manufactured by cutting to a predetermined size as required.

  In such a manufacturing process, if the coating film contains impurities such as a solvent (such as an organic solvent), the performance of the coating film is adversely affected. Therefore, it is necessary to sufficiently dry and remove the solvent in the drying process. Conventionally, a general drying technique for drying a coating film with hot air has been used to dry the solvent in the coating film (for example, Patent Document 1).

However, when the solvent is a high-boiling solvent, it takes a long time and high-temperature hot air to dry and remove them, but the high-temperature heating over a long time may cause deterioration of the quality of the coating film and thermal decomposition. . As a method for solving this problem, a drying method using steam-containing hot air by low boiling solvent vapor has been proposed (for example, Patent Document 2). In this method, by using the steam-containing hot air, the high boiling point solvent in the coating film can be removed at a lower temperature and more quickly than in the normal hot air drying method.
JP 2004-205720 A International Publication Number 2007/136005

  However, since the drying method of Patent Document 2 has a high ability to remove and dry, when a relatively low-molecular additive is present in the coating film, such as an image forming layer of a lithographic printing plate, the additive is also evaporated. Alternatively, it sublimates, causing problems such as degradation of the performance of the image forming layer and recondensation of the removed additive on the wall surface of the manufacturing process to cause process contamination.

  Accordingly, there is a need for a coating film drying method and apparatus in which only the solvent, which is an impurity, can be quickly dried and removed in a short time, and necessary additives can be kept in the coating film. However, the conventional drying according to Patent Documents 1 and 2 cannot achieve both rapid drying of the solvent and prevention of evaporation (or sublimation) of the additive.

  The present invention has been made in view of such circumstances, and a coating film capable of quickly drying a solvent contained in the coating film while suppressing evaporation and sublimation of the additive contained in the coating film. An object of the present invention is to provide a drying method and apparatus.

  As a result of earnest research on the above problems, the present inventor has obtained the following knowledge.

  (1) When the temperature reached by the coating film during drying is equal to or higher than the melting point of the additive, not only the solvent but also the additive is removed by evaporation or sublimation in large quantities.

  (2) However, when drying is performed under a low temperature drying condition in which the temperature reached by the coating film is lowered below the melting point of the additive by a normal drying method such as hot air drying, the solvent, particularly the high boiling point solvent, is removed. A long time is required, and productivity is significantly reduced.

  (3) On the other hand, the ultimate temperature cannot be controlled while maintaining a high drying capacity by simply using the steam-containing hot air generated by the low boiling point solvent vapor.

  (4) Therefore, in order to achieve both rapid drying of the solvent and prevention of evaporation (or sublimation) of the additive, the state of the additive at the time of drying is maintained in a solid state, and the drying capacity is increased after the drying point. It is important to use a large steam-containing hot air. This is because there is a large difference between the vapor pressure in the solid state of the additive and the vapor pressure in the liquid state, and in the high viscosity state where the solid content concentration in the coating film after the drying point is large, the drying ability is large. It is considered that the additive is not easily evaporated or sublimated even with hot air containing steam.

  Here, the drying point is a state where the coating film is touched with a cloth and the coating liquid does not adhere to the cloth, the surface glossiness does not change, or the solid content concentration is 60% or more, preferably 70% to 80%. Say dry state.

  The present invention has been made based on the above findings.

  In order to achieve the above object, the invention according to claim 1 supports a polymer coating solution containing at least one additive in a polymer solution obtained by dissolving a polymer resin material in at least one solvent. In the drying method of the coating film applied to the body, when the solvent having the largest molar volume among the solvents is the first solvent and the additive having the lowest melting point is the first additive, A hot air drying step of drying the coating film to a drying point at a coating film temperature lower than the melting point of the first additive, and a second solvent having a molar volume smaller than that of the first solvent immediately after reaching the drying point. And a steam drying step of drying the coating film at a coating film temperature lower than the melting point of the first additive by using steam-containing hot air.

  Here, the additive refers to a solid or a solution thereof at normal temperature (20 ° C.), and does not include a liquid whose melting point is lower than normal. The first additive refers to an additive having the lowest melting point when a plurality of additives are used. Therefore, when one additive is used, the additive becomes the first additive.

  According to the invention of claim 1, immediately after the normal hot air drying to the drying point of the coating film in the hot air drying step, the second having a smaller molar volume than the first solvent contained in the coating film in the vapor drying step. By drying the coating film using hot air containing solvent vapor, the solvent can be removed by drying in a short time.

  Further, in the first and vapor drying steps, the coating film temperature was dried below the melting point temperature of the lowest melting point of the additive, and the viscosity increased after the drying point, that is, the solid content concentration of the coating film increased. Since the steam-containing hot air is used thereafter, the evaporation and sublimation of the additive can be suppressed as much as possible.

  Thereby, the solvent contained in a coating film can be dried rapidly, suppressing the evaporation and sublimation of the additive contained in a coating film. Therefore, it is not necessary to worry about the evaporation and sublimation of the additive during high temperature drying, and the amount of the additive used can be reduced, leading to cost reduction.

  In general, since the molar volume has a correlation with the molecular volume, the molar volume can be expressed by the molecular volume.

A second aspect of the present invention is the method according to the first aspect, wherein in the vapor drying step, Td: coating film temperature [° C.] at the drying point, C: solvent vapor amount [g / m ³ ] of the second solvent, P _Td : coating film temperature The saturated vapor amount [Pa] of the second solvent at Td, R: gas constant, M: molecular weight of the second solvent, and Tm: melting point of the first additive satisfy the formulas 1 and 2. And

0.25 ≦ C × R (273.15 + Td) / (P _Td × M) <1.0 Formula 1
Tm> Td Formula 2
The second aspect of the present invention shows preferable drying conditions in the steam drying process by a relational expression between parameters related to drying. That is, in the vapor drying step, the solvent contained in the coating film is quickly dried while the evaporation and sublimation of the additive contained in the coating film are suppressed by drying under the drying conditions satisfying Formula 1 and Formula 2. The operation can be performed more effectively.

  A third aspect is characterized in that, in the first or second aspect, the coating film is an image forming layer of a lithographic printing plate, and the additive is an additive for improving the sensitivity of the image forming layer.

  This is because the present invention is particularly effective when the coating film is an image forming layer of a lithographic printing plate and the additive is a relatively low-molecular additive used for improving the sensitivity of the image forming layer.

  In order to achieve the above object, the invention according to claim 4 supports a polymer coating solution containing at least one additive in a polymer solution obtained by dissolving a polymer resin material in at least one solvent. In a drying apparatus for a coating film applied to a body, a hot air drying apparatus for drying the coating film to a drying point, a first temperature sensor for measuring a coating film temperature in the hot air drying apparatus, and a measurement result of the first temperature sensor Based on the above, when the solvent having the largest molar volume of the solvent is the first solvent and the additive having the lowest melting point is the first additive, the coating film temperature is the first solvent. A first control means for feedback-controlling the drying conditions of the hot air drying device so as to be less than the melting point of one additive; and a second solvent having a molar volume smaller than that of the first solvent immediately after reaching the drying point. Including steam Based on the steam drying device for drying the coating film using hot air, the second temperature sensor for measuring the coating film temperature in the steam drying device, and the measurement result of the second temperature sensor, the coating film temperature is There is provided a coating film drying apparatus comprising: a second control unit that feedback-controls a drying condition of the steam drying apparatus so as to be lower than a melting point of the first additive.

  Here, the meaning of the drying point is the same as described above. Further, as the first and second temperature sensors for measuring the coating film temperature, a non-contact radiation thermometer or a thermal image device can be suitably used.

  According to a fourth aspect of the present invention, the present invention is configured as an apparatus invention, and in the drying up to the drying point in the hot air drying apparatus, the first control means is based on the measurement result of the first temperature sensor. Drying with hot air so that the coating film temperature is lower than the melting point of the first additive when the solvent having the largest molar volume is the first solvent and the additive having the lowest melting point is the first additive. The drying condition of the apparatus was feedback controlled. Further, in the drying with the steam-containing hot air of the steam drying device, the second control means is configured to cause the coating film temperature to be lower than the melting point of the first additive based on the measurement result of the second temperature sensor. The drying conditions of the drying device are feedback controlled.

  Thereby, the solvent contained in a coating film can be dried rapidly, suppressing the evaporation and sublimation of the additive contained in a coating film.

A fifth aspect of the present invention is the method according to the fourth aspect, wherein the second control means includes: Td: coating film temperature [° C.] at the drying point, C: solvent vapor amount [g / m ³ ] of the second solvent, P _Td : coating film When the saturated vapor amount [Pa] of the second solvent at the temperature Td, R: gas constant, M: molecular weight of the second solvent, Tm: melting point of the first additive, so as to satisfy Equations 1 and 2. The steam drying apparatus is feedback-controlled.

0.25 ≦ C × R (273.15 + Td) / (P _Td × M) <1.0 Formula 1
Tm> Td Formula 2
The fifth aspect of the present invention shows preferable drying conditions in the steam drying apparatus by a relational expression between parameters related to drying. An arithmetic unit that calculates Equations 1 and 2 may be mounted in the second control means so that at least one of the parameters is controlled so as to satisfy Equations 1 and 2.

  According to the coating film drying method and apparatus of the present invention, the solvent contained in the coating film can be quickly dried while suppressing evaporation and sublimation of the additive contained in the coating film.

  Preferred embodiments of a coating film drying method and apparatus according to the present invention will be described below with reference to the accompanying drawings.

  In the following embodiments, the present invention is described as an example in which the present invention is applied to a lithographic printing plate production line. However, the present invention is not limited to the technical field of lithographic printing plates, and is a coating film containing a solvent, particularly a solvent having a large molar volume that is difficult to evaporate, and a relatively low-molecular additive that easily evaporates or sublimes. Applicable to various technical fields for drying.

  FIG. 1 is a diagram in which a coating film drying apparatus according to the present invention is incorporated in a line of a planographic printing plate manufacturing apparatus 10, and an arrow A in FIG. 1 indicates a conveyance direction of a belt-like support 16 (for example, an aluminum plate). Show.

  As shown in FIG. 1, the planographic printing plate manufacturing apparatus 10 mainly includes a delivery device 12, a surface treatment unit 14, a coating unit 18, a drying unit 20, and a winding device 26. A belt-like support 16 wound in a roll shape is attached to the delivery device 12, and this support 16 is delivered from the delivery device 12. The fed support 16 is sent to the surface treatment unit 14, the coating unit 18, and the drying unit 20 in order while being guided by the guide roller 27, subjected to various treatments, and then taken up by the take-up device 26. .

  The configuration of FIG. 1 is an example of a planographic printing plate manufacturing apparatus, and is not limited to this. For example, an application unit for applying the undercoat coating solution may be provided in the front stage of the application unit 18.

  Next, each process part will be described.

  The surface treatment unit 14 is an apparatus that performs various pretreatments necessary for the support 16 before coating. As the pretreatment, a degreasing treatment or a roughening treatment (such as a graining treatment) for improving the adhesion between the support 16 and the image forming layer and imparting water retention to the non-image part, There are anodizing treatment that forms an oxide film on the surface to improve wear resistance, chemical resistance, and water retention, silicate treatment that improves the coating strength, hydrophilicity, and adhesion to the image forming layer of the anodized film. .

  The coating unit 18 is a device that coats the surface of the support 16 with the image forming layer coating solution. As the coating method, for example, a slide bead coating method, a curtain coating method, a bar coating method, a spin coating method, a spray coating method, a dip coating method, an air knife coating method, a blade coating method, a roll coating method, etc. are used. A bead coating method, a curtain coating method, a bar coating method, or the like is preferably used. In FIG. 1, it is illustrated as bar coating.

  The drying unit 20 is a device that dries the coating film (image forming layer) formed on the support 16. The coating film contains at least one additive in a polymer solution in which a polymer resin material is dissolved in at least one solvent, and is contained in the coating film while suppressing evaporation and sublimation of the additive. It is important for the quality of the lithographic printing plate precursor to quickly dry the solvent to be produced. Here, the solvent having the largest molar volume among the solvents contained in the coating film is referred to as a first solvent, and the additive having the lowest melting point among the additives is referred to as a first additive.

As the first solvent, it can be preferably used in the range of 60cm ³ / mol~160cm ³ / mol in molar volume. Moreover, it is preferable that the boiling point of a 1st solvent is 150 degreeC or more. In addition, the specific compound of a 1st solvent is mentioned later.

  Examples of the first additive include cyclic acid anhydrides, phenols, and organic acids added for the purpose of improving the sensitivity of the coating film (image forming layer). Specific compounds of will be described later.

  The drying unit 20 includes a hot air drying device 28, a steam drying device 29, and a cooling unit 30. Each of the hot air drying device 28, the steam drying device 29, and the cooling unit 30 has a tunnel-type box shape, and is configured such that the support 16 passes through the inside thereof. First, the hot air is blown by the hot air drying device 28 to dry the support 16 to the drying point. Then, in the steam drying device 29, after the steam-containing hot air containing the second solvent is blown to the support 16, the cooling unit 30 cools the cool air by blowing it. As a result, a dried coating film (image forming layer) is formed on the support 16.

  By the way, the hot-air drying apparatus 28 of the drying part 20 is provided with the box 40 formed along the conveyance direction of the support body 16, as shown in FIG. The box 40 includes slit-like openings 40A and 40B at both ends, and the support 16 is carried into and out of the box 40 through the openings 40A and 40B.

  In the box 40, a chamber 42 is provided above the support 16, and hot air obtained by heating dry air with a heater 43 is supplied to the chamber 42. A large number of nozzles 44 are provided on the lower surface of the chamber 42, and hot air is blown from the nozzles 44 to the upper surface (coating film surface) of the support 16.

  An exhaust part 46 is provided in the lower part of the box 40, and the exhaust air is exhausted from the exhaust part 46, whereby a downflow of hot air is formed in the box 40.

  Further, at least one non-contact first temperature sensor 45 is disposed on the coating film surface side of the support 16 and the coating film temperature (temperature of the coating film surface) is measured. FIG. 2 shows an example in which a total of three first temperature sensors 45 are arranged on the inlet side, the center, and the outlet side of the box 40. The coating film temperature measured by the first temperature sensor 45 is output to the first control unit 47 to monitor the coating film temperature, and the first control unit 47 includes a first coating film temperature contained in the coating film. The heater is adjusted so as to be lower than the melting point Tm of the additive (the additive having the lowest melting point among the additives), and the temperature of the hot air blown from the nozzle 44 is feedback-controlled. As the 1st temperature sensor 45, a non-contact radiation type thermometer and a thermal image device can be used conveniently.

  Note that the two first temperature sensors 45 are arranged at the inlet and the outlet of the box 40, and the temperature of the hot air blown from the nozzle 44 can be independently controlled based on the measured value from each first temperature sensor 45. preferable. For example, it is used for controlling the drying efficiency based on the difference between the temperature of the coating film surface and the hot air temperature based on the measurement value of the first temperature sensor 45 disposed on the inlet side, and the measurement of the first temperature sensor 45 disposed on the outlet side. Based on the value, the maximum temperature of the coating film surface is monitored to prevent the evaporation and sublimation of additives.

  In this hot air drying device 28, the coating film is dried at a coating film temperature lower than the melting point Tm of the first additive (a state where the coating liquid does not adhere to the cloth when touched with the cloth, a state where the surface gloss does not change, or The coating film is dried until the solid content is 60% or more, preferably 70% to 80%. The dried support 16 is guided by the guide roller 27 and turned upside down, and then sent to the next steam drying device 29.

  FIG. 3 shows a vapor supply / exhaust mechanism for supplying / exhausting solvent vapor to / from the vapor dryer 29. The vapor dryer 29 has a first molar volume smaller than the molar volume of the first solvent contained in the coating film. Two solvents are supplied and exhausted. 4 shows the internal configuration of the steam drying device 29, and FIG. 5 is a cross-sectional view taken along line 5-5 of FIG.

  The vapor drying apparatus 29 shown in these drawings is an apparatus for evaporating and drying a first solvent having a largest molar volume, which has not been completely removed by the hot air drying apparatus 28, among the solvents in the coating film applied to the support 16. It is.

As the second solvent can be suitably used in the range of 10cm ³ / mol~90cm ³ / mol in the molar volume is preferably liquid at ordinary temperature (about 20 ° C.). The boiling point of the second solvent is preferably in the range of 30 ° C to 130 ° C. The difference in molar volume between the first solvent and the second solvent is preferably 40 cm ³ / mol or more. In addition, the specific compound of a 2nd solvent is mentioned later.

  When an organic solvent is used as the second solvent, it is desirable that the concentration used does not fall within the explosion range, and that explosion-proof measures are taken.

  As shown in FIG. 4, the steam drying device 29 includes a hollow box 50, and slit-shaped openings 50 </ b> A and 50 </ b> B are formed on opposite sides of the box 50. The support 16 enters the box 50 through the opening 50A and is conveyed to the outside of the box 50 through the opening 50B. As a material of the box 50, for example, SUS (304, 306, 316, etc.) or iron (SECC, etc.) is preferable, and a heat insulating material such as glass wool, rock wool, ALK24 may be provided inside thereof.

  Inside the box 50, a steam-containing hot air supply unit 52 is provided below the support 16. The supply part 52 is formed in a hollow box shape, and the steam-containing hot air of the second solvent having a molar volume smaller than that of the first solvent is supplied to the inside thereof by the steam supply / exhaust mechanism shown in FIG. Is done.

  As shown in FIG. 3, the steam supply / exhaust mechanism includes a tank 62, a blower 64, and heat exchangers 66, 68, and 70, and a second solvent is stored in the tank 62. The second solvent stored in the tank 62 is heated by the heat exchanger 66 to become steam, the temperature of the second solvent is adjusted by the heat exchanger 68, the air sent from the blower 64 and heated by the heat exchanger 70. And supplied to the supply unit 52.

  Further, at least one non-contact second temperature sensor 51 is disposed on the coating film surface side (lower surface side) surface of the support 16 and the coating film temperature (temperature of the coating film surface) is measured. 3 and 4 show an example in which one second temperature sensor 51 is arranged at the center position of the box 50. FIG. The coating film temperature measured by the second temperature sensor 51 is output to the second control means 53, and the coating film temperature is monitored. The second control means 53 includes a first coating film temperature contained in the coating film. The heat exchangers 68 and 70 are adjusted so as to be less than the melting point Tm of the additive (the additive having the lowest melting point among the additives), and the temperature of the steam-containing hot air supplied to the supply unit 52 is feedback controlled. As the second temperature sensor 51, similarly to the first temperature sensor 45, a non-contact radiation thermometer and a thermal image device can be suitably used.

  In the case of the steam drying device 29, as in the case of the hot air drying device 28, two second temperature sensors 51 are arranged at the inlet and the outlet of the box 50, and measured values from the respective second temperature sensors 51. It is preferable to independently control the steam blown from the supply unit 52 to the box 50 based on the above. For example, it is used for controlling the drying efficiency based on the difference between the temperature of the coating film surface and the vapor temperature based on the measurement value of the second temperature sensor 51 arranged on the inlet side, and the measurement of the second temperature sensor 51 arranged on the outlet side. Based on the value, the maximum temperature of the coating film surface is monitored to prevent the evaporation and sublimation of additives.

  As shown in FIG. 4, a rectifying plate 56 is provided inside the supply unit 52, and the steam-containing hot air of the second solvent is uniformly supplied by the rectifying plate 56. A nozzle 54 is provided above the supply unit 52, and steam-containing hot air is blown from the nozzle 54 toward the lower surface (that is, the coating surface) of the support 16. The nozzle 54 is configured to uniformly blow steam-containing hot air in the width direction of the support 16. For example, the nozzle 54 has a slit in the width direction, and the steam-containing hot air is blown out from the slit. A plurality of nozzles 54 are provided in the transport direction of the support 16, and steam-containing hot air is blown in a predetermined range in the transport direction of the support 16.

  Further, as shown in FIG. 5, the width W of the supply unit 52 is formed to be larger than the width of the support 16, and the steam-containing hot air is blown over the entire width of the support 16. The width W of the supply unit 52 is preferably set to be longer than the length of the zone in which the steam atmosphere is formed (specifically, the interval L between the wind shielding plates 60A and 60B described later), and the ratio W / L is preferably at least 1, and more preferably at least 2. As W / L is larger, L can be reduced to reduce the size of the apparatus, but the residual distribution of the first solvent tends to occur in the width direction. In particular, a residual distribution occurs when W / L is 1 or more, but this embodiment can prevent this.

  The steam-containing hot air is blown out from the nozzle 54 of the supply unit 52 configured as described above, whereby a solvent vapor atmosphere of the second solvent is formed in the box 50. Thereby, drying of the 1st solvent in the coating film of the support body 16 is performed rapidly.

  As shown in FIG. 4, exhaust units 58 </ b> A and 58 </ b> B are provided on the upstream side and the downstream side of the supply unit 52 with respect to the conveyance direction of the support 16. The exhaust parts 58 </ b> A and 58 </ b> B are provided on the lower side of the support 16 like the supply part 52, and suck air downward from the vicinity of the lower surface of the support 16. As shown in FIG. 5, the exhaust parts 58 </ b> A and 58 </ b> B are formed with a width wider than that of the support 16, and preferably with the same width W as the supply part 52. Further, the exhaust units 58A and 58B are connected to the distillation column 72 as shown in FIG. 3, and the exhaust air from the exhaust units 58A and 58B is sent to the distillation column 72. In the exhaust air sent to the distillation column 72, the second solvent and the solvent are separated, and the separated second solvent is returned to the tank 62, while the solvent is recovered. The air volume exhausted from the exhaust units 58A and 58B is set to be larger than the air volume of the solvent vapor-containing hot air of the second solvent blown out from the supply unit 52. Thereby, it is possible to prevent the steam-containing hot air blown from the supply unit 52 from flowing out of the box 50.

  As shown in FIG. 4, a wind shield plate 60 </ b> A is provided between the exhaust unit 58 </ b> A and the supply unit 52, and a wind shield plate 60 </ b> B is provided between the exhaust unit 58 </ b> B and the supply unit 52. The wind shielding plates 60 </ b> A and 60 </ b> B are provided vertically below the support body 16, and are arranged with a predetermined gap amount S on the lower surface of the support body 16. The supply unit 52 and the exhaust units 58A and 58B communicate with each other only through this gap, and the steam-containing hot air blown from the supply unit 52 is exhausted from the exhaust units 58A and 58B through the gap. 4 shows an example in which the wind shielding plates 60A and 60B are integrally provided in the box 50. However, the present invention is not limited to this, and the wind shielding plates 60A and 60B are attached to and detached from the box 50 as separate members. You may attach freely. In that case, the wind shielding plates 60A and 60B may be attached to the box 50 so as to be slidable in the vertical direction, and the height position (that is, the gap amount S) may be adjusted.

  Thus, by providing exhaust parts 58A and 58B on both sides of the supply part 52 with respect to the conveying direction of the support 16, and further providing wind shielding plates 60A and 60B between the supply part 52 and the exhaust parts 58A and 58B. The steam-containing hot air blown out from the supply section 52 flows to the exhaust sections 58A and 58B through the gap between the wind shielding plates 60A and 60B and the support body 16, so that the steam-containing hot air is substantially on the lower surface of the support body 16. It comes in contact evenly. As a result, the first solvent in the film of the support 16 can be uniformly dried in the width direction, and even in the range of “W / L ≧ 1” where uniform drying has been difficult conventionally, The occurrence of residual distribution of one solvent can be prevented.

  Immediately after the above-described hot air drying to the drying point of the coating film by the hot air drying device 28, the vapor content of the second solvent having a smaller molar volume than the first solvent contained in the coating film by the vapor drying device 29 is included. By drying the coating film using hot air, the solvent can be removed by drying in a short time. Further, in the hot air drying device 28 and the steam drying device 29, the coating film temperature is dried at the first point having the lowest melting point of the additive or less than the melting point Tm of the object, and after the drying point, that is, the solid content of the coating film. Since the steam-containing hot air is used after the concentration increases and the viscosity increases, evaporation and sublimation of the additive can be suppressed as much as possible. Thereby, the solvent contained in a coating film can be dried rapidly, suppressing the evaporation and sublimation of the additive contained in a coating film.

  Here, suitable drying conditions in the steam drying apparatus 29 will be described using a relational expression between parameters related to drying.

In the steam drying device 29, Td: coating film temperature [° C.] at the drying point, C: water vapor amount [g / m ³ ], P _Td : saturated vapor amount [Pa] of the second solvent at the coating film temperature Td, R: Gas constant, M: molecular weight of the second solvent (because it is water in the present embodiment, 18), Tm: melting point of the first additive,
0.25 ≦ C × R (273.15 + Td) / (P _Td × M) <1.0 Formula 1
Tm> Td Formula 2
The drying process is performed under the following drying conditions. In this drying condition, “C × R (273.15 + Td) / (P _Td × M)” means a ratio of vapor pressure to saturated vapor pressure (hereinafter referred to as relative vapor pressure ratio). For example, when the second solvent is water, (Equation 1) means that the relative vapor pressure ratio is 1.0 or more (100% or more) and 1.8 or less (180% or less).

  When the drying process is performed under such a drying condition, the second solvent vapor condenses on the surface of the coating film in the form of fine droplets by blowing the steam-containing hot air of the second solvent onto the surface of the coating film. Due to the condensation heat generated by this dew condensation, the coating film where the micro droplets are generated is partially heated and softened, and further, the second solvent droplet pushes away the softened coating film. When passing through the steam-containing hot air zone, minute droplets of the second solvent are instantly evaporated by the heat of the coating film. By passing through such a drying process, the first solvent having a large molar volume can be surely dried and removed.

  Next, the first solvent, the second solvent, and the first additive in the present invention will be specifically described.

[First solvent]
In this embodiment, the largest first solvent is the molar volume of the solvent contained in the coating film, the molar volume is preferably in the range of 60cm ³ / mol~160cm ³ / mol. A high boiling point solvent having a boiling point of 150 ° C. or higher is preferable. Examples of such a large molar volume solvent include the following, but the present invention is not limited thereto.

Specific examples of the first solvent include, for example, γ-butyllactone (molar volume 76 cm ³ / mol, boiling point 204 ° C.), 1,3-dimethyl-2-imidazolidinone (molar volume 109 cm ³ / mol, boiling point 225. 5 ° C.), N, N-dimethylformamide (molar volume 77 cm ³ / mol, boiling point 153 ° C.), tetramethyluric acid (boiling point 175 ° C.-177 ° C.), nitrobenzene (molar volume 103 cm ³ / mol, boiling point 211.3 ° C.) , N-methylpyrrolidone (molar volume 96 cm ³ / mol, boiling point 202 ° C.), N, N-dimethylacetamide (molar volume 93 cm ³ / mol, boiling point 166 ° C.), dimethyl sulfoxide (molar volume 71 cm ³ / mol, boiling point 189 ° C.) ), Etc.

[Second solvent]
In the present embodiment, the second solvent used for the steam-containing hot air in the steam drying device 29 is a solvent having a molar volume smaller than that of the first solvent, and the molar volume is 10 cm ³ / mol to 90 cm ³ /. Those in the mol range are preferred. The boiling point is preferably 30 ° C or higher and 130 ° C or lower. Examples of such second solvent include the following, but the present invention is not limited thereto.

Specific examples of the second solvent include water (molar volume 18 cm ³ / mol, boiling point 100 ° C.), methanol (molar volume 40 cm ³ / mol, boiling point 64.5 ° C.-64.65 ° C.), ethanol (molar volume). 58 cm ³ / mol, boiling point 78.32 ° C., n-propanol (molar volume 75 cm ³ / mol, boiling point 97.15 ° C.), isopropanol (molar volume 77 cm ³ / mol, boiling point 82.3 ° C.), ethyl ether (mol) volume 83cm ³ / mol, boiling point 34.6 ° C.), methyl acetate (molar volume 80 cm ³ / mol, boiling point 57.8 ° C.), acetone (molar volume 73cm ³ /mol,56.2℃), methyl ethyl ketone (molar volume 90cm ³ / mol, boiling point 79.59 ° C.) and the like can be preferably used.

  Moreover, although only a boiling point is shown, as a 2nd solvent, n-butanol (117.7 degreeC), isobutanol (107.9 degreeC), isopropyl ether (68.27 degreeC), methyl-n-propyl ketone (103 3 ° C.), methyl isobutyl ketone (115.9 ° C.), diethyl ketone (102.2 ° C.), ethyl acetate (77.1 ° C.), acetic acid-n-propyl (101.6 ° C.), acetic acid-n-butyl acetate (126.5 ° C.), n-hexane (65.742 ° C.), cyclohexane (80.338 ° C.) and the like can also be used.

[First additive]
For the purpose of improving the sensitivity of the image forming layer, relatively low molecular additives such as molecular cyclic acid anhydrides, phenols, and organic acids are added. In the present invention, the additive refers to a solid at room temperature and does not include a liquid. The first additive is an additive having the lowest melting point when a plurality of additives are used. Therefore, when one additive is used, the additive becomes the first additive.

  Examples of molecular cyclic acid anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 3,6-endooxy-Δ4-tetrahydrophthalic anhydride described in US Pat. No. 4,115,128. Tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, α-phenylmaleic anhydride, succinic anhydride, pyromellitic anhydride and the like can be used.

  As phenols, bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 4-hydroxybenzophenone, 4,4 ′, 4 "-Trihydroxytriphenylmethane, 4,4 ', 3", 4 "-tetrahydroxy-3,5,3', 5'-tetramethyltriphenylmethane and the like.

  Examples of organic acids include sulfonic acids, sulfinic acids, alkyl sulfates, phosphonic acids, phosphoric esters, carboxylic acids and the like described in JP-A-60-88942 and JP-A-2-96755. Yes, specifically, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethyl sulfate, phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipine Examples include acid, p-toluic acid, 3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid, ascorbic acid and the like.

  When the above cyclic acid anhydride, phenols and organic acids are added to the image forming layer, the proportion in the image forming layer is preferably 0.05 to 20% by mass, more preferably 0.1 to 15% by mass. Especially preferably, it is 0.1-10 mass%.

[Other preferred embodiments]
Further, the material and surface treatment of the support used in the production of the lithographic printing plate (original plate) of the present embodiment, the material and formation of the image forming layer (particularly the positive image forming layer), the support and the image forming layer Regarding the material and formation of the undercoat layer, the material and formation of the backcoat layer, and the plate making method, the contents described in JP-A-2007-245478 can be preferably used.

  Next, in the examples where the drying method of the present invention was applied and the comparative examples where the present invention was not applied, the results of drying the first solvent, the results of suppressing the removal of the first additive, and the test results comparing the drying time are as follows. Explained.

(Support)
A strip-shaped aluminum plate (width 1300 mm, thickness 0.24 mm) was used.

(Coating film)
The coating solution was composed of polymethyl acrylate / first solvent gamma butyrolactone (γ-BL) / methyl ethyl ketone (MEK). That is, a coating solution was prepared by dissolving polymethyl acrylate, which is a polymer material, in a mixed solvent of γ-BL (first solvent), which is a high boiling point solvent, and MEK, which is a low boiling point solvent. The mass ratio of γ-BL and MEK was 1: 2. The solid content in the coating solution is 5% by mass.
-Phthalic anhydride (melting point Tm: 131 ° C) was used as an additive contained in the coating film, and was added to the coating solution so as to be 0.5% by mass. As a result, the initial content of the phthalic anhydride contained in the coating film per support m ² before drying is 86 mg / m ² .

(Application conditions)
-While using the bar | burr coating device, the line speed (coating speed) was set to 60 m / min, and the said coating liquid was apply | coated to the support body so that it might become a coating amount of 20 cc / m < ² >.

(Drying conditions)
-Hot air drying apparatus: The drying zone length was set to 30 m, and the hot air of dry air for drying the coating film was changed in the temperature range of 100 to 180 ° C as shown in the table of FIG. The moisture content of the dry hot air is 10 g / m ³ , and the air volume of the hot air is 300 Nm ³ / min.
Steam drying apparatus: The drying zone length was 1 m, water was used as the second solvent for the steam-containing hot air for drying the coating film, and the air volume of the steam-containing hot air was 6 Nm ³ / min. Then, the temperature of the steam-containing hot air was set to 120 ° C. in both the examples and the comparative examples, and the solvent vapor amount was changed in the range of 150 to 400 g / m ³ as shown in FIG.

(Drying test method)
As shown in the table of FIG. 6, for Examples 1 to 3, after coating the coating liquid on the support with the bar coating device, the film temperature at the drying point that is less than the melting point of the first additive in the hot air drying device. The coating film was dried at (90 to 126 ° C.) for 30 seconds. In the table of FIG. 6, the film temperature at the drying point is described, and the intermediate temperature for 30 seconds from the start of drying to the drying point is not described, but the film temperature is gradually increased by hot air. It does not exceed the film temperature indicated by.

The coating film is made to reach the drying point by this hot air drying, and immediately after that, in a steam drying apparatus using steam containing hot air, the temperature is 120 ° C., which is lower than the melting point of the first additive, and the amount of steam (340 to 400 g / The coating film was dried for 1 second at m ³ ).

In Comparative Example 1, after coating the coating solution on the support with a bar coating device, the coating film was heated at a film temperature of 131 ° C. (drying point) at the same melting point (131 ° C.) as the first additive in the hot air drying device. Was dried for 30 seconds. The coating film reaches the drying point by this hot air drying, and immediately after that, in a steam drying apparatus using steam containing hot air, the temperature is 120 ° C. which is lower than the melting point of the first additive, and the amount of steam (380 g / m ^3). The coating film was dried for 1 second.

That is, in Examples 1 to 3 and Comparative Example 1, the drying times of the hot air drying device and the steam drying device are both set to the same 30 seconds and 1 second, while the hot air drying conditions and the drying conditions of the steam-containing hot air are changed. Thus, in Examples 1 to 3 and Comparative Example 1, samples were prepared so that the residual amount of γ-BL as the first solvent was approximately the same, 15 mg / m ² . And content of the phthalic anhydride (additive) which remained in the coating film of the sample created in Examples 1-3 and Comparative Example 1 was measured.

In Comparative Example 2, the film temperature in the hot air dryer was higher than that in Comparative Example 1 to 151 ° C. (drying point), and the coating film was 1 at a temperature of 120 ° C. and a steam amount of 290 g / m ³ in the steam dryer. Dry for 2 seconds.

  In Comparative Example 3, the film temperature in the hot air drying apparatus was further increased to 162 ° C. (drying point) than in Comparative Example 2, and no steam drying apparatus was used.

In Comparative Example 4, the residual amount of γ-BL is 15 mg / m ² which is substantially the same as in Examples 1 to 3 only by hot air drying at a film temperature of 107 ° C. (drying point) which is less than the melting point of the first additive. When the sample was prepared, it was examined how long the drying time was.
(Measurement method of phthalic anhydride in coating film)
The coated film after drying was extracted from the coated support with tetrahydrofuran (THF), and the resulting THF extract was analyzed by high performance liquid chromatography (HPLC). Then, the amount of additive was calculated using the obtained peak and calibration curve.

(Measurement method of residual γ-BL amount)
Three samples of the coated film after drying were cut out together with the support with a diameter of 10 mm and sealed in a vial. This vial was placed in a head spacer (Tekmar 7000HT, GL Science) connected to a gas chromatography (GC390B, GL Science). The vial bottle was heated with the head spacer at 180 ° C. for 5 minutes. The operating conditions of the gas chromatography were performed using a packed column (Silicone DC-550, GL Sciences Inc.), an oven temperature of 180 ° C., and an FID temperature of 180 ° C. Residual solvent vapor evaporated in the vial was automatically introduced into the gas chromatography from the head spacer, and the concentration of the solvent remaining in the coating film was calculated from the obtained peak area and γ-BL calibration curve.

[Test results]
As can be seen from the table in FIG. 6, Examples 1 to 3 satisfying the drying conditions of the present invention are short-time drying of 31 seconds, which is a total of hot air drying and steam drying, and the initial content of phthalic anhydride before drying. (86mg / ^{m 2)} and while almost the same 78~85mg / ^{m 2} is left, it was possible to reduce the residual amount of gamma-BL to about 15~16mg / ^{m 2.}

In contrast, Comparative Example 1 that does not satisfy the drying conditions of the present invention reduced the residual amount of γ-BL to about 14 mg / m ² by short-time drying for 31 seconds, but also the residual amount of phthalic anhydride. It has decreased to 50 mg / m ² .

As in Comparative Example 2, when the film temperature in hot air drying was further increased from that in Comparative Example 1, the residual amount of phthalic anhydride further decreased to 29 mg / m ² .

When the film was dried only under hot air drying conditions where the film temperature was 31 ° C. higher than the melting point of phthalic anhydride as in Comparative Example 3, the residual amount of γ-BL could be reduced to about 15 mg / m ² , but anhydrous The residual amount of phthalic acid has also been greatly reduced to 30 mg / m ² .

  In Comparative Examples 1 to 3, the residual amount of phthalic anhydride was remarkably reduced, and as a result, the photosensitive performance of the finally produced lithographic printing plate was deteriorated.

  Further, as in Comparative Example 4, when only hot air drying was performed at a film temperature of 107 ° C., which is lower than the melting point of phthalic anhydride, the same effects as those of the present invention were obtained with respect to the remaining amounts of γ-BL and phthalic anhydride. However, the drying time was 120 seconds, which was four times that of the present invention. Therefore, it was proved that the production efficiency was significantly reduced in Comparative Example 4.

  As can be seen from the above examples, the coating film drying method and apparatus of the present invention quickly dry the solvent contained in the coating film while suppressing the evaporation and sublimation of the additive contained in the coating film. Can do.

The figure which shows the basic composition of the manufacturing line of the planographic printing plate of this embodiment Explanatory drawing explaining the structure of a hot air drying apparatus Explanatory drawing explaining the steam supply / exhaust mechanism of the steam dryer Explanatory drawing explaining the structure of a steam dryer Sectional view along line 5-5 in FIG. Table showing examples and comparative examples of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Planographic printing plate manufacturing apparatus, 16 ... Support, 18 ... Coating part, 20 ... Drying part, 28 ... Hot air drying apparatus, 29 ... Steam drying apparatus, 30 ... Cooling part, 40 ... Box, 42 ... Chamber, 43 DESCRIPTION OF SYMBOLS ... Heater, 44 ... Nozzle, 45 ... 1st temperature sensor, 46 ... Exhaust part, 47 ... 1st control means, 50 ... Box, 51 ... 2nd temperature sensor, 52 ... Supply part, 53 ... 2nd control means, 54 ... Nozzle, 56 ... Rectifying plate, 58A, 58B ... Exhaust section, 60A, 60B ... Wind shielding plate, 62 ... Tank, 64 ... Blower, 66, 68, 70 ... Heat exchanger, 72 ... Distillation tower

Claims (5)

In a method for drying a coating film in which a polymer coating solution containing at least one additive in a polymer solution obtained by dissolving a polymer resin material in at least one solvent is coated on a support,
When the solvent having the largest molar volume of the solvent is the first solvent and the additive having the lowest melting point is the first additive,
A hot-air drying step in which the coating film is hot-air dried to a drying point at a coating film temperature lower than the melting point of the first additive;
Immediately after reaching the drying point, steam drying is performed by drying the coating film at a coating film temperature lower than the melting point of the first additive by using steam-containing hot air of a second solvent having a smaller molar volume than the first solvent. And a process for drying the coating film. In the vapor drying step, Td: coating film temperature [° C.] at the drying point, C: solvent vapor amount [g / m ³ ] of the second solvent, P _Td : saturated vapor amount of the second solvent at the coating film temperature Td The coating according to claim 1, wherein [Pa], R: gas constant, M: molecular weight of the second solvent, and Tm: melting point of the first additive satisfy Formula 1 and Formula 2. How to dry the membrane.
0.25 ≦ C × R (273.15 + Td) / (P _Td × M) <1.0 Formula 1
Tm> Td Formula 2   The method for drying a coating film according to claim 1 or 2, wherein the coating film is an image forming layer of a lithographic printing plate, and the additive is an additive for improving the sensitivity of the image forming layer. . In a coating film drying apparatus in which a polymer coating solution containing at least one additive in a polymer solution obtained by dissolving a polymer resin material in at least one solvent is coated on a support.
A hot air drying apparatus for drying the coating film to a drying point with hot air;
Based on the first temperature sensor for measuring the coating film temperature in the hot air drying device and the measurement result of the first temperature sensor, the solvent having the largest molar volume is used as the first solvent, and the additive First control means for feedback-controlling the drying conditions of the hot air drying device so that the temperature of the coating film is lower than the melting point of the first additive when the additive having the lowest melting point is the first additive. When,
Immediately after reaching the drying point, a steam drying device for drying the coating film using steam-containing hot air of a second solvent having a smaller molar volume than the first solvent;
A second temperature sensor for measuring a coating film temperature in the steam drying device;
Second control means for feedback-controlling the drying conditions of the steam drying device so that the coating film temperature is lower than the melting point of the first additive based on the measurement result of the second temperature sensor. A coating film drying apparatus characterized by the above. The second control means includes: Td: coating film temperature [° C.] at the drying point, C: solvent vapor amount [g / m ³ ] of the second solvent, P _Td : saturated vapor of the second solvent at the coating film temperature Td Feedback control of the steam dryer so as to satisfy Equation 1 and Equation 2 when the amount [Pa], R: gas constant, M: molecular weight of the second solvent, Tm: melting point of the first additive The apparatus for drying a coating film according to claim 4.
0.25 ≦ C × R (273.15 + Td) / (P _Td × M) <1.0 Formula 1
Tm> Td Formula 2

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