JP2007260570A - Method for drying coating film and method for producing planographic printing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the productivity and quality stability of a product by restraining a defective coating caused by the agglomeration and precipitation of a solute in a coating liquid from being generated at a drying step. <P>SOLUTION: The method for drying a coating film formed on the surface of a traveling aluminum web 14 by applying the coating liquid prepared by dissolving the solute in a mixed solvent containing two or more solvents having different boiling points comprises a step of rapidly drying the coating film so that the amount of the solvent remaining in the coating film becomes ≤500 mg/m<SP>2</SP>within 30 seconds after the saturated amount of the solute to be dissolved in the mixed solvent contained in the coating film when dried becomes equal to or lower than that of the solute to be dissolved in the mixed solvent contained in the coating film before dried when the solubility of the solute in a high boiling point solvent is higher than that of the solute in other solvents having different boiling points. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for drying a coating film and a method for producing a lithographic printing plate, and more particularly to a method for drying various coating films formed by coating on a continuously running strip.

  Magnetic recording materials such as lithographic printing plates, various optical films, silver salt films, photographic paper, and video tape base films are used for photosensitivity while running strips such as support webs, base films, and baryta paper in a fixed direction. A coating solution such as a conductive coating solution, a heat-sensitive coating solution, a photosensitive emulsion coating solution, or a magnetic coating solution is applied and dried, and the dried product is cut into a predetermined size as necessary.

  As a drying method and a drying apparatus for drying a coating film formed by coating on a belt-like body, for example, the following are proposed.

  In patent document 1, it is made to dry until it is touch-dried at the temperature of 150-190 degreeC and the temperature of a wind speed of 3-30 m / sec, making it run continuously, the strip | belt material with which the coating liquid containing an organic solvent was apply | coated, Then, with a heating roll There has been proposed a method for drying a photographic photosensitive strip characterized by evaporating residual solvent in a coating film.

  Further, in Patent Document 2, a belt-like support on which a photosensitive coating liquid containing an organic solvent is applied and a photosensitive coating layer is formed with the photosensitive coating liquid is continuously run by the first heating unit. The photosensitive coating layer is dried until it is dry to the touch, and the support and the photosensitive coating layer are heated by the second heating means provided on the downstream side of the first heating means. There has been proposed a method for producing a lithographic printing plate comprising a drying / heating step for promoting the curing of the lithographic printing plate.

According to this, it is described that the heating conditions for the support and the photosensitive coating layer in the heating / drying process of the lithographic printing plate can be quickly changed in a wide range and can be heated in a non-contact manner.
Japanese Examined Patent Publication No. 6-49175 JP 2002-14461 A

  However, for example, when a coating solution containing two or more solvents having a large difference in boiling point is applied to the web and dried, such as a photosensitive coating solution for a lithographic printing plate, the solute dissolved in the coating solution is in the middle of drying. In some cases, the particles agglomerate and precipitate and locally solidify or become foreign matter specific points, resulting in coating failure. Thereby, there has been a problem that the productivity and quality stability of the product are lowered.

  On the other hand, in the conventional methods including the above-mentioned Patent Documents 1 and 2, no consideration and countermeasures have been taken to suppress coating failure due to solute precipitation in the coating solution.

  Such coating failures are not limited to the field of lithographic printing plates, but in other technical fields, coating and drying coating films formed by coating a coating solution in which a solute is dissolved in a solvent containing a solvent having a large boiling point difference. Even when it is used, it may cause a product quality failure.

  The present invention has been made in view of such circumstances, and can suppress the occurrence of coating failure due to aggregation and precipitation of solutes in the coating film in the drying process, and can improve product productivity and quality stability. It is an object of the present invention to provide a method for drying a coating film and a method for producing a lithographic printing plate.

In order to achieve the above object, claim 1 of the present invention applies and forms a coating solution in which one or more types of solutes are dissolved in a mixed solvent containing two or more types of solvents having different boiling points on the surface of a continuously running belt. In the drying method of the applied film, the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film at the time of drying is equal to or less than the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film before drying. There is provided a method for drying a coating film, comprising a rapid drying process in which the amount of residual solvent in the coating film is reduced to 500 mg / m ² or less within 30 seconds from the time point.

  In drying a coating film containing a mixed solvent in which two or more kinds of solvents having different boiling points are mixed, the solvent on the low-boiling side mainly evaporates first, and the mixing ratio of the solvent on the high-boiling side increases. High boiling solvents evaporate mainly. Simultaneously with the evaporation of the solvent, the saturated dissolution amount of the solvent decreases. Therefore, the saturated dissolution amount that the mixed solvent has is rapidly reduced by the evaporation of the low boiling point solvent, and then gradually decreases with the evaporation of the high boiling point solvent. The solute begins to precipitate from the time when the saturated dissolution amount of the mixed solvent is equal to or less than the dissolution amount that had been dissolved from the initial stage (before drying), but at that point the evaporation of the high boiling point solvent is the main and the drying rate is When the speed is low, the solute aggregates and precipitates in the high boiling point solvent. Thereby, it becomes the foreign material singular point which solidified locally, and a failure arises in the coating film surface.

As a result of diligent research on a drying method in which such a coating failure does not occur, the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film at the time of drying is the saturation of the solute with respect to the mixed solvent in the coating film before drying. It is possible to prevent aggregation and precipitation of solutes by performing rapid drying to reduce the amount of residual solvent in the coating film to 500 mg / m ² or less within 30 seconds from the time when it becomes less than the dissolution amount, and drying and solidifying the coating film. I found.

  The present invention has been made based on such knowledge. According to claim 1, the occurrence of coating failure due to aggregation and precipitation of solute in the coating film in the drying process is suppressed, and the productivity and quality of the product are reduced. Stability can be improved.

Here, the saturated dissolution amount is a value per unit volume at the drying temperature. In addition, the residual amount of the solute in the mixed solvent in the coating solution at the time of drying remains in the coating solution within 30 seconds from the time when the saturated dissolved amount of the solute in the mixed solvent in the coating solution before drying is equal to or less than 30 seconds. It is more preferable to dry so that the amount of solvent is 200 mg / m ² or less.

  A second aspect of the present invention is characterized in that, in the first aspect, the difference in boiling point between the solvent having the lowest boiling point and the solvent having the highest boiling point is 50 ° C. or more among the mixed solvents in the coating film before the drying. .

  Thus, when drying a coating film containing two or more kinds of solvents having a large difference in boiling point, the solute is likely to aggregate or precipitate, and the present invention is particularly effective.

  A third aspect of the present invention is the method according to the first or second aspect, wherein a solvent having a boiling point higher by 50 ° C. or more than the solvent having the lowest boiling point is 10% to 90% of the mixed solvent in the coating film before drying. % Is included.

  Thus, when drying a coating film containing a solvent having a boiling point of 50 ° C. or more higher than the solvent having the lowest boiling point in the mixed solvent in the range of 10% to 90% with respect to the mixed solvent, the solute Are easily aggregated and precipitated, and the present invention is particularly effective.

  A fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the rapid drying process is performed by adjusting a heating temperature of the belt-shaped body and / or an amount of drying air.

  According to claim 4, by adjusting the heating temperature of the strip and / or the amount of drying air, the drying speed of the solvent having a high boiling point among the mixed solvents can be increased, and the solute aggregation and precipitation can be further increased. It can be reliably suppressed. Here, the heating temperature of the belt is preferably set within the boiling point temperature ± 150 ° C. of the high-boiling solvent, and the air volume of the drying air depends on the surface of the coating film to be obtained. It is preferable that the air volume be large as long as it is acceptable (not generated).

  A fifth aspect of the present invention is characterized in that, in any one of the first to fourth aspects, a drying process having a drying condition different from that of the rapid drying process is provided before and / or after the rapid drying process.

  As a result, the drying conditions can be efficiently divided into several stages, so that the productivity and quality stability of the product can be improved.

  A sixth aspect of the present invention is the case of any one of the first to fifth aspects, in the case of a coating solution in which two or more kinds of solutes are dissolved in a mixed solvent containing two or more kinds of solvents having different boiling points. A solute that is highly soluble in the low-boiling side solvent and has a low solubility in the low-boiling side solvent, and a solute that is highly soluble in the low-boiling side solvent and low in the high-boiling side solvent, respectively. It contains more than seeds.

  Thereby, in a system including a high-boiling solvent and a low-boiling solvent, a favorable coating film surface shape can be obtained even by drying a coating solution with high precipitation by evaporation of the low-boiling solvent.

  A seventh aspect is characterized in that the method for drying a coating film according to any one of the first to sixth aspects is applied to a method for producing a lithographic printing plate.

  Thereby, a lithographic printing plate having excellent quality stability such as surface quality can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the coating failure resulting from aggregation and precipitation of the solute in a coating film in a drying process can be suppressed, and product productivity and quality stability can be improved.

  Hereinafter, preferred embodiments of a method for drying a coating film and a method for producing a lithographic printing plate according to the present invention will be described in detail with reference to the accompanying drawings. The present invention can be applied to any step of drying a coating film coated on a support (strip-shaped body), and is not particularly limited. However, in the present embodiment, photosensitive coating of a lithographic printing plate production line is possible. An example applied to the layer drying step will be described.

  FIG. 1 is a diagram for explaining the overall configuration of a lithographic printing plate production line 10 as an example to which a coating film drying method according to the present invention is applied. Hereinafter, the web conveyance direction is indicated by an arrow A.

  As shown in FIG. 1, the planographic printing plate production line 10 includes a web delivery machine 12, and a belt-like aluminum web 14 is wound around the web delivery machine 12 in the form of a web roll 16. It is set. The aluminum web 14 set in the web delivery machine 12 is sent out from the web roll 16, guided by a plurality of transport rollers 17, 17..., And then sent to the surface treatment device 18. In the surface treatment apparatus 18, a surface treatment for improving the coating property and adhesion of the photosensitive compound applied to the surface of the aluminum web 14 is performed. The surface-treated aluminum web 14 is sent to the water washing apparatus 20 where it is washed.

  The cleaned aluminum web 14 is sent to the first coating device 22, and a photosensitive coating solution is applied to the upper surface (surface to be processed) of the aluminum web 14. 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. It is not limited. And it is sent to the 1st drying apparatus 24 to which this invention is applied, a drying process is performed, and the application surface of the aluminum web 14 is dried.

  The aluminum web 14 dried by the first drying device 24 is sent to the second coating device 26. Then, the protective layer coating solution or the photosensitive coating solution is applied by the second coating device 26. The protective layer coating solution is formed on the photosensitive coating layer in order to block oxygen from the photosensitive coating layer and prevent contamination of the surface of the image forming layer with a lipophilic substance. The protective layer can be easily removed during printing and contains a resin selected from water-soluble organic polymer compounds. The photosensitive coating liquid has a function of improving sensitivity and printing performance in addition to protecting the lower photosensitive coating layer.

  Next, the aluminum web 14 to which the protective layer coating solution has been applied is subjected to a drying process by a second drying device 28 to which the present invention is applied.

  The aluminum web 14 on which the protective layer has been formed is conveyed from the second drying device 28 by a plurality of conveying rollers 31, 31,... And then wound into a web roll 34 by a web winder 32. The materials for the aluminum web 14 and the photosensitive coating layer used in this embodiment will be described later.

  Next, a method for drying a coating film, which is a characteristic part of the present invention, will be described. Hereinafter, since the first and second drying devices 24 and 28 have the same configuration, description of the second drying device 28 will be omitted, and the first drying device 24 will be described. FIG. 2 is a diagram illustrating an example of the configuration of the first drying device 24 in the present embodiment.

  The first drying device 24 includes a drying box 36 formed along the conveying direction of the aluminum web 14. At both ends of the drying box 36, slit-shaped openings through which the aluminum web 14 enters and exits are formed. Inside the drying box 36, there are provided transport rollers 37 for transporting the aluminum web 14 on which the photosensitive coating solution is applied. A plurality of nozzles 44a, 44b, 44c are arranged above the drying box 36 so that hot air is blown out.

  In the present embodiment, the inside of the drying box 36 is divided into three drying zones (a first drying zone 38, a second drying zone 40, and a third drying zone 42) in the transport direction.

  As in this embodiment, the photosensitive coating solution dissolves solutes such as dyes in a mixed solvent containing at least two types of solvents having a large boiling point difference (hereinafter, low boiling point solvent and high boiling point solvent are used). It has been made. In addition, since the solute used here is difficult to dissolve in the solvent on the low boiling point side and includes extremely easily dissolved in the solvent on the high boiling point side, the photosensitive coating solution contains the high boiling point solvent. . Specific examples of the low boiling point solvent, the high boiling point solvent, and the solute will be described later.

  Thus, when drying a coating solution containing a low-boiling solvent and a high-boiling solvent, the solute is likely to precipitate or aggregate in the high-boiling solvent due to the difference in drying speed between the low-boiling solvent and the high-boiling solvent. Therefore, the drying immediately before the solute starts to be precipitated, that is, the saturated dissolution amount of the solute in the mixed solvent in the coating film at the time of drying starts to become smaller than the saturated dissolution amount of the solute in the mixed solvent in the coating film before drying. It is important to increase the drying rate from the elapsed time point (hereinafter referred to as the saturation dissolution point), thereby promoting the drying of the high boiling point solvent and suppressing the precipitation and aggregation of the solute.

  In the above, when the difference in boiling point between the lowest boiling solvent and the highest boiling solvent in the mixed solvent contained in the coating solution is 50 ° C. or more, more preferably when the difference in boiling point is 70 ° C. or more. The solute tends to precipitate or aggregate in the film. In addition, when drying a coating solution containing a solvent having a boiling point higher than the lowest boiling point solvent by 50 ° C. or more in a range of 10% to 90% with respect to the entire mixed solvent, a solute is precipitated particularly in the coating film. Easy to agglomerate and aggregate. Therefore, the present invention is particularly effective when drying a coating film formed by coating such a coating solution.

  In the first drying zone 38, the coating film can be dried up to just before the saturation dissolution point under a mild condition that does not cause unevenness in the coating film. In the second drying zone 40, it is possible to rapidly dry from the saturation dissolution point to a state immediately before the drying point (set point). In the third drying zone 42, the residual solvent in the coating film can be further dried immediately before the drying point. In this embodiment, an example in which three drying zones having different drying conditions are provided in one drying apparatus will be described, but the present invention is not limited to this, and three or more drying zones are provided in one drying apparatus. Or a plurality of drying zones may be configured as separate devices.

  As a drying means in the first drying zone 38, the second drying zone 40, and the third drying zone 42, a publicly known drying means can be used. For example, hot air drying, a heated object is directly contacted with an object to be dried. Conducted electric heat (for example, heating the transport roller), radiant heat transfer (for example, a halogen heater) that does not bring the heating means into contact with the object to be dried, induction heat transfer (for example, the support is self-heated by a high-frequency coil), etc. There is no particular limitation. Moreover, the method of heating a to-be-dried material in the vapor | steam of a low boiling-point solvent is also employable. The various drying means described above may be used in combination.

  Here, the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film before drying can be calculated as follows. Although the method differs depending on the solute, for example, when the solute has absorptivity, first, using each solvent constituting the coating solution and a solute such as a dye, create a solution in which the solvent amount and the solute solubility are changed, and filtration Thereafter, the absorbance is measured. A saturated dissolution amount of a dye or the like that dissolves in each solvent is obtained from the obtained absorption peak. That is, the saturated dissolution amount of the solute per weight of each solvent is obtained. The absorbance can be measured using a known absorptiometer, for example, a spectrophotometer U-3400 manufactured by Hitachi, Ltd.

  Next, the saturated dissolution amount of the solute in the mixed solvent in which each of the above solvents is mixed can be theoretically calculated using the data for each of the above solvents, or the data can be obtained by the same method as described above using the mixed solvent. .

  In addition, regarding the evaporation rate of each solvent and the evaporation rate of the mixed solvent, the solvent is evaporated under the desired drying conditions, the weight of the remaining liquid or the volatile gas concentration is measured by gas chromatography, and evaporation rate data (solvent amount reduction rate) ) Further, regarding the evaporation rate of each solvent under the mixing condition, the mixed solvent is evaporated under the above-mentioned desired drying condition, and the composition of the remaining liquid is analyzed by weight and gas chromatography to obtain the evaporation rate.

  Then, based on the coating speed on the production line, the drying conditions, the evaporation speed of each of the obtained solvents, the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film at the time of drying is the coating before drying under each transport condition. The time that is less than the amount of solute dissolved in the mixed solvent in the film is predicted.

  Thus, an offline test is performed in advance, and the saturation dissolution point can be determined by the drying time from the start of drying until the solute starts to precipitate. In this embodiment, the method for determining the saturated melting point offline has been described. However, the method is not limited to this, and the saturated melting point may be determined online.

  The set point refers to the state of the coating film that is undried more than the drying point, and refers to the state where there is no fluidity and only the surface layer portion is not dried. Specifically, a state having a viscosity of 5000 mPa · s or more is shown.

  The drying point means that the surface of the coating film is rubbed with a stick with a cloth wrapped around the tip in the drying zone, the coating liquid does not adhere to the cloth wrapped around the stick, and no change in the surface gloss of the coating film is observed. The position of the drying zone that reaches the dry state.

  Here, the drying conditions in each drying zone can be controlled by drying temperature, drying time, air volume (in the case of hot air drying), humidity, conveyance speed, and the like. In particular, in the second drying zone 40, in order to promote the drying of the high boiling point solvent, it is preferable to set the drying temperature within the boiling point temperature ± 80 ° C. of the high boiling point solvent.

  Next, the operation of the first drying device 24 will be described with reference to FIG. FIG. 3 is a graph for explaining an example of the change in the amount of residual solvent contained in the photosensitive coating solution with respect to the drying time. In addition, the figure is a figure which represented the change of the amount of residual solvents as an image, and is not limited to this.

  First, the aluminum web 14 coated with a photosensitive coating solution and having a photosensitive coating layer formed on the surface thereof is carried into a drying box 36.

  Next, in the first drying zone 38, the photosensitive coating layer is dried to the saturation dissolution point by hot air drying. Here, the low-boiling point solvent is mainly evaporated, and the drying conditions are preferably dried at the boiling point temperature of the low-boiling point solvent ± 30 ° C. for 2 to 15 seconds. As a result, as shown in FIG. 3, during the drying time T1, the amount of residual solvent in the photosensitive coating layer gradually decreases.

  Next, the aluminum web 14 that has passed through the first drying zone 38 is conveyed into the second drying zone 40. In the second drying zone 40, a drying temperature at which the high boiling point solvent is easily evaporated is set. Here, it is rapidly dried from the saturation dissolution point to the set point state. Thereby, as shown in FIG. 3, during the drying time T2, the amount of residual solvent in the photosensitive coating layer rapidly decreases. In particular, in the present invention, it is preferable to set the drying conditions so that the drying time T2 in the second drying zone 40 is 30 seconds or less, preferably 20 seconds or less.

  Next, the aluminum web 14 that has passed through the second drying zone 40 is conveyed into the third drying zone 42. In the third drying zone 42, hot air drying is performed. Here, drying is performed while reducing and adjusting the amount of residual solvent in the photosensitive coating layer from the set point or dry point state where the undried portion remains on the surface layer. As a result, as shown in FIG. 3, during the drying time T3, the residual solvent amount in the photosensitive coating layer is dried until the desired amount is reached.

  As described above, by applying the coating film drying method according to the present invention, it is possible to suppress the occurrence of coating failure due to aggregation and precipitation of solutes in the coating film in the drying process, and to improve product productivity and quality stability. Can be improved.

  As mentioned above, although embodiment of the drying method of the coating film which concerns on this invention was described, this invention is not limited to the said embodiment, Various aspects can be taken.

  For example, an example has been described in which a plurality of nozzles 44a, 44b, and 44c are disposed in the first drying zone 38, the second drying zone 40, and the third drying zone 42 in the first drying device 24, respectively, and hot air drying is performed. The drying means in each drying zone is not limited to the above, and different drying means can be used. For example, the first and third drying zones may be hot air drying, and the second drying zone may be drying by radiant heat transfer such as a far-infrared heater instead of hot air drying, or drying by hot air drying and radiant heat transfer. May be used in combination.

  Moreover, although the example which dries the coating film apply | coated on the web of the strip | belt-shaped body which runs continuously was demonstrated, it is not limited to this, When drying the coating film apply | coated on the support body which does not run continuously Is also applicable.

  Moreover, although the example which applies this invention to the drying process of the photosensitive coating layer for lithographic printing plates was demonstrated, it is not limited to this, Other various optical films, silver salt films, photographic paper, and video Magnetic recording materials such as tape base film are photosensitive coating solution, heat sensitive coating solution, photosensitive emulsion coating solution, magnetic layer coating while running strips such as support web, base film and baryta paper in a certain direction. The present invention can also be preferably applied to a step of drying a coating film formed by coating a liquid or the like.

[Support]
The support is a plate that is stable in strength, for example, paper, paper laminated with plastic (for example, polyethylene, polypropylene, polystyrene, etc.), metal plate (for example, aluminum, zinc, copper, etc.), Plastic films (eg, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc.), and the above metals are laminated Or vapor-deposited paper or plastic film.

  As the lithographic printing plate support of the present embodiment, a polyester film or an aluminum plate is preferable, and among them, an aluminum plate that has good dimensional stability and is relatively inexpensive is particularly preferable. A suitable aluminum plate is a pure aluminum plate or an alloy plate containing aluminum as a main component and containing a trace amount of foreign elements, and may be a plastic film on which aluminum is laminated or vapor-deposited. Examples of foreign elements contained in the aluminum alloy include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The content of foreign elements in the alloy is at most 10% by weight.

  Particularly suitable aluminum in the present embodiment is pure aluminum, but completely pure aluminum is difficult to manufacture in terms of refining technology, and therefore may contain slightly different elements. The thickness of the aluminum plate used in the present embodiment is about 0.1 mm to 0.6 mm, preferably 0.15 mm to 0.4 mm, and particularly preferably 0.2 mm to 0.3 mm. Moreover, although the aluminum web 14 wound up by roll shape was used in this form, it does not necessarily need to be able to run continuously.

  When an aluminum alloy is used as the aluminum plate, for example, the following method can be employed. First, a molten aluminum alloy adjusted to a predetermined alloy component content is subjected to a cleaning process and cast according to a conventional method. In order to remove unnecessary gas such as hydrogen in the molten metal, the cleaning process includes a flux process, a degassing process using argon gas, a chlorine gas, etc., a filtering process, or a process combining the degassing process and the filtering process. Done. This cleaning treatment is preferably performed in order to prevent defects caused by foreign matters such as non-metallic inclusions and oxides in the molten metal and defects caused by gas dissolved in the molten metal.

  Next, casting is performed using the molten metal that has been cleaned as described above. As for the casting method, there are a method using a solid mold typified by a DC casting method and a method using a driving mold typified by a continuous casting method. Then, hot rolling and cold rolling are performed to obtain a rolled aluminum plate. The flatness of the aluminum plate finished to a predetermined thickness, for example, 0.1 to 0.5 mm by the above steps may be further improved by a correction device such as a roller leveler or a tension leveler.

[Coating film]
The coating film is not particularly limited, and various coating films such as a photosensitive coating layer, a heat-sensitive coating layer, and a magnetic coating layer can be used.

  The photosensitive coating layer for lithographic printing plates in the present embodiment is intended for organic solvent-based layers having photosensitivity or heat sensitivity, and specifically, a photosensitive coating mainly composed of naphthoquinone diazide and a phenol resin. A conventional positive printing plate having a layer, a conventional negative printing plate having a photosensitive coating layer mainly composed of a diazonium salt and an alkali resin or a urethane resin, an ethylenically unsaturated compound, a photopolymerizable initiator, and a binder resin. Photopolymer type digital direct printing plate with photosensitive coating layer, thermal positive type digital direct printing plate with photosensitive coating layer mainly composed of phenol resin, acrylic resin and IR dye, thermal acid generator, thermal crosslinking agent, Thermal negative digital direct with photosensitive coating layer made of reactive polymer and IR dye Photosensitive coating layer is subject in the plate. Also applicable are organic solvent-based photosensitive coating layers in thermal ablation type untreated printing plates, thermal thermal fusion untreated printing plates, and lithographic printing plates using the silver salt diffusion transfer method.

  Here, as an organic solvent, ethylene dichloride, cyclohexanone, methyl ethyl ketone, methanol, ethanol, propanol, ethylene glycol monomethyl ether, 1-methoxy-2-propanol, 2-methoxyethyl acetate, 1-methoxy-2-propyl acetate, dimethoxy Examples include ethane, methyl lactate, ethyl lactate, N, N-dimethylacetamide, N, N-dimethylformamide, tetramethylurea, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, γ-butyrolactone, and toluene. It is not limited.

These solvents are used alone or in combination, and the concentration of the above components (total solid content including additives) in the solvent is preferably 1 to 50% by mass. Moreover, although the coating amount (solid content) on the support obtained after coating and drying varies depending on the application, it is generally preferably 0.5 to 5.0 g / m ² for the photosensitive printing plate.

[Low boiling solvent]
As the low boiling point solvent used in the present embodiment, those having a boiling point of 30 ° C. or more and less than 140 ° C. are preferable. Examples of such a low boiling point solvent include the following, but the present invention is not limited thereto. The boiling point is described in parentheses.

  Methanol (64.5 ° C-64.65 ° C), ethanol (78.32 ° C), n-propanol (97.15 ° C), isopropanol (82.3 ° C), n-butanol (117.7 ° C), iso Alcohols such as butanol (107.9 ° C), ethers such as ethyl ether (34.6 ° C), isopropyl ether (68.27 ° C), acetone (56.2 ° C), methyl ethyl ketone (79.59 ° C), Ketones such as methyl-n-propyl ketone (103.3 ° C.), methyl isobutyl ketone (115.9 ° C.), diethyl ketone (102.2 ° C.), methyl acetate (57.8 ° C.), ethyl acetate (77. 1 ° C), esters such as acetic acid-n-propyl (101.6 ° C), acetic acid-n-butyl (126.5 ° C), n-hexane (68.742 ° C), cyclohexa Hydrocarbons such as (80.738 ° C.), water and the like.

[High boiling point solvent]
The high boiling point solvent used in this embodiment preferably has a boiling point of 140 ° C. or higher. Examples of such high boiling point solvents include the following, but the present invention is not limited to these. The boiling point is described in parentheses.

  γ-butyllactone (204 ° C.), acetamide (222 ° C.), 1,3-dimethyl-2-imidazolidinone (225.5 ° C.), N, N-dimethylformamide (153 ° C.), tetramethyluric acid (175 ° C.) -177 ° C), nitrobenzene (211.3 ° C), formamide (210.5 ° C), N-methylpyrrolidone (202 ° C), N, N-dimethylacetamide (166 ° C), dimethyl sulfoxide (189 ° C) and the like.

[Solute]
The solute used in this embodiment is not particularly limited. For example, a dye, a urethane resin, a photosensitive coating solution, a heat-sensitive coating solution, a photosensitive emulsion coating solution, a magnetic coating solution, and various coating materials. A phenol resin, an acrylic resin, a monomer, an emulsion, a magnetic substance, etc. are mentioned.

  Next, examples will be described in detail, but the present invention is not limited to the following examples.

  Solvents A, B, C and D in Table 1 used in this example are as follows, and the saturated dissolution amount in Table 1 is the saturated dissolution amount of ethyl violet dye (solute) at a temperature of 130 ° C.

Solvent A: Methyl ethyl ketone Solvent B: Methyl isobutyl ketone Solvent C: 1-methoxy-2-propanol Solvent D: γ-butyrolactone

Next, about the mixed solvent of Table 1, the coating liquid which melt | dissolved the ethyl violet dye and the acrylic resin as a solute on each condition of Tables 2-4 was mixed and dissolved at normal temperature, and was prepared. The prepared photosensitive coating solution is applied onto an aluminum web 14 having a thickness of 0.3 mm so as to have a photosensitive coating layer of 2.0 g / m ^2, and hot air is then used using the first drying device 24 of FIG. Dried.

At this time, the drying time was changed, and the drying time T2 required from the saturation dissolution point to the set point was measured. The set point was a point where the amount of residual solvent in the photosensitive coating layer was 500 mg / m ² or less. The residual solvent amount was measured as follows.

(Measurement method of residual solvent amount)
From the sample in which the photosensitive coating layer was formed on the aluminum web 14, the entire aluminum web 14 was cut out to 30 mm × 10 mm and sealed in a vial bottle. The vial was put into a dedicated device and heated at 180 ° C. for 5 minutes, and then a part of the gas in the vial was taken out by a syringe equipped in the device and analyzed by gas chromatography. The concentration of the solvent remaining in the coating film was calculated from the peak area of the obtained chromatogram and a calibration curve prepared in advance.

  Furthermore, it visually evaluated whether the photosensitive coating layer after drying had precipitation of solid content. In this evaluation, the case where there was no solid content precipitation was evaluated as “◯”, the case where there was a slight solid content precipitation but a level where there was no practical problem, Δ, and the case where there was a large amount of solid content precipitation as “X”. The results are shown in Tables 2-4.

  As shown in Table 2, in the case of the mixed solvent 1 using only the low boiling point solvent, the drying time T2 was 30 seconds or less even when the drying temperature was 80 ° C. Moreover, precipitation of solid content was not recognized by the photosensitive coating layer (Examples 1-1 to 1-4).

  Next, as shown in Table 3, in the case of the mixed solvent 2 containing the high boiling point solvent C, if the drying temperature was 150 ° C. or higher, the drying time T2 to the set point was 15 seconds or shorter. Also, no solid content was observed in the photosensitive coating layer after drying. On the other hand, when the drying temperature was 100 ° C. or lower, the drying time T2 to the set point took 35 seconds or more. Moreover, precipitation of solid content was recognized by the photosensitive coating layer after drying (Examples 2-1 to 2-4).

  Next, as shown in Table 4, in the case of the mixed solvent 3 containing the high boiling point solvent D, if the drying temperature was 180 ° C. or higher, the drying time T2 to the set point was 30 seconds or shorter. Also, no solid content was observed in the photosensitive coating layer after drying. On the other hand, when the drying temperature was 140 ° C. or lower, the drying time T2 to the set point was 40 seconds or more, and when the drying temperature was further lowered, the drying time T2 was significantly increased. Moreover, many precipitation of solid content was recognized with the drying time T2 in the photosensitive coating layer after drying (Examples 3-1 to 3-4).

  As described above, by setting the drying conditions such as the drying temperature so that the drying time T2 from the time when the solute begins to precipitate to the set point is 30 seconds or less, the occurrence of solute precipitation and aggregation is suppressed. Can do. Moreover, it turned out that it is more preferable to set a drying condition so that drying time T2 from the point which a solute begins to precipitate to the set point may be 20 seconds or less.

It is a figure explaining the whole structure of the manufacturing line of the lithographic printing plate which is an example to which the drying method of the coating film which concerns on this invention is applied. It is explanatory drawing explaining the structure of an example of the drying apparatus in this embodiment. It is a graph figure in the drying apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Planographic printing plate production line, 14 ... Aluminum web, 24 ... 1st drying apparatus, 28 ... 2nd drying apparatus, 38 ... 1st drying zone, 40 ... 2nd drying zone, 42 ... 3rd drying zone, 44a , 44b, 44c ... nozzle

Claims (7)

A method for drying a coating film in which a coating solution in which one or more types of solutes are dissolved in a mixed solvent containing two or more types of solvents having different boiling points is applied to the surface of a continuously running belt.
Within 30 seconds from the time when the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film at the time of drying becomes equal to or less than the saturated dissolution amount of the solute with respect to the mixed solvent in the coating film before drying. A method for drying a coating film, characterized by having a rapid drying process in which the amount of residual solvent is 500 mg / m ² or less.   2. The method for drying a coating film according to claim 1, wherein a difference in boiling point between the solvent having the lowest boiling point and the solvent having the highest boiling point is 50 ° C. or more among the mixed solvent in the coating film before drying.   Among the mixed solvents in the coating film before drying, a solvent having a boiling point higher by 50 ° C. or more than the solvent having the lowest boiling point is contained in a range of 10% to 90% with respect to the mixed solvent. The method for drying a coating film according to claim 1 or 2.   The method of drying a coating film according to any one of claims 1 to 3, wherein the rapid drying process is performed by adjusting a heating temperature and / or an amount of drying air of the strip.   The method for drying a coating film according to any one of claims 1 to 4, further comprising a drying step having a drying condition different from that of the quick drying step before and / or after the quick drying step.   In the case of a coating solution in which two or more solutes are dissolved in a mixed solvent containing two or more solvents having different boiling points, it is highly soluble in a high boiling point solvent and low dissolved in a low boiling point solvent. 1 or 5 each including 1 or more types of the solute which shows the property, and the solute which is highly soluble in the solvent of a low boiling point side, and low solubility in the solvent of a high boiling point side. The drying method of the coating film of 1.   A method for producing a lithographic printing plate, wherein the method for drying a coating film according to any one of claims 1 to 6 is applied.

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