JP2011025564A - Method and apparatus for manufacturing recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for manufacturing a recording sheet, which can perform stable coating and in which coating problem such as stripe does not occur even when quickly applying a film-hardening coating liquid for hardening an ink absorbing layer onto the ink absorbing layer containing inorganic fine particles and a water-soluble resin within a range of 100-250 m/min using a coating head of an extrusion type during manufacturing the recording sheet. <P>SOLUTION: When quickly applying a film-hardening coating liquid for hardening an ink absorbing layer onto the ink absorbing layer dried into a half-dry state within a range of 100-250 m/min using a coating head 42 of an extrusion type, a viscosity of the film-hardening coating liquid at the shearing speed of 1,000 sec<SP>-1</SP>is adjusted to be 5 mPa s or less, a lip clearance D between the downstream side lip 48A of the coating head 42 and a surface of the ink absorbing layer is set within the range of 500-1,000 μm, and the upstream side pressure of a coating liquid bead 52 during coating is reduced within the range of 0.1-0.2 kPa from the atmospheric pressure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and apparatus for producing a recording sheet, and in particular, on an ink absorbing layer containing inorganic fine particles and a water-soluble resin on a support, the ink absorbing layer is hardened while the ink absorbing layer is in a dry state. The present invention relates to a technique for manufacturing a high-quality inkjet recording sheet including a coating step of coating a hardened coating solution at high speed.

  Currently, various ink jet methods have been developed, and various ink jet recording sheets have been developed accordingly. Among these recording sheets for inkjet, a recording sheet provided with an ink absorbing layer containing fine inorganic particles and a water-soluble resin is a high-quality inkjet recording sheet (hereinafter referred to as “high quality”). Used as a recording sheet). Other recording sheets provided with an ink absorbing layer containing inorganic fine particles and a water-soluble resin include thermal transfer recording sheets and electrophotographic recording sheets.

  As a manufacturing method of this high quality recording sheet, the present applicant has proposed the manufacturing method and apparatus of Patent Document 1. In this method and apparatus, an ink absorbing layer containing inorganic fine particles and a water-soluble resin is applied and formed on a support, and then an ink absorbing layer and an upper layer such as a cross-linking agent layer are applied excessively on the ink absorbing layer in a dry state. . That is, the upper layer is excessively applied on the ink absorbing layer by a wet-on-wet method so as not to damage the fluid ink absorbing layer. Then, within 30 seconds after the upper layer is applied and formed, smoothing and metalling processing is performed with an apparatus such as a bar, a blade, or an air knife to smooth the film surface and adjust the coating amount of the upper layer.

  However, in the method for producing a recording sheet disclosed in Patent Document 1, stable coating can be performed regardless of any coating method such as curtain coating, bar coating, roll coating, slide bead coating, and extrusion coating. The maximum coating speed that can be applied is 20 m / min. In order to further increase the coating speed, it is necessary to increase the supply coating amount to more than twice the required coating amount to stabilize the coating solution bead, and then to scrape off a large amount of the coating solution in the subsequent smoothing and metering treatment. There is a problem of not getting.

  From this background, the present applicant has proposed a recording sheet manufacturing method and apparatus disclosed in Patent Document 2. In this recording sheet manufacturing method, an extrusion type coating head is used, and a suction chamber is provided on the upstream side of the coating head when viewed from the running direction of the support so that the degree of decompression relative to the atmospheric pressure is increased on the upstream side of the bead. The coating is performed under reduced pressure so as to be over 0 kPa and 2.0 kPa or less. Thereby, in the Example, the coating speed of the polyvinyl alcohol (PVA) coating liquid used as the upper layer could be increased to about 100 m / min.

JP 2001-113820 A JP 2006-247574 A

  However, today, due to the widespread use of inkjet recording apparatuses, the amount of recording sheets (recording materials) used is increasing, and the upper layer coating speed applied on the ink absorbing layer is limited to 100 m / min. 2 has a problem in terms of productivity. Therefore, there is a demand for a method for manufacturing a recording sheet that can be applied at a higher speed than Patent Document 2 to improve productivity.

  In particular, when a hardened coating liquid that hardens the ink absorbing layer is applied as an upper layer, a part of the ink absorbing layer after the hardened coating liquid is applied adheres to the lip tip of the coating head. Since the adhering matter is cured to become a protrusion, application trouble such as a streak failure in which streaks are generated in the ink absorption layer due to the protrusion is likely to occur. Once a coating trouble such as a streak failure occurs, the recording sheet production line must be stopped and the coating head cleaned, etc., resulting in a significant reduction in productivity.

  Therefore, when a hardened coating solution is used as the upper layer, unlike the PVA coating solution described above, stable coating must be given the highest priority over productivity, so that a coating speed of 100 m / min can be achieved. The fact is not.

  The present invention has been made in view of such circumstances, and at the time of manufacturing a recording sheet, an ink is absorbed using an extrusion type coating head on an ink absorbing layer containing inorganic fine particles and a water-soluble resin. Even if a hardened coating solution for hardening the layer is applied at a high speed in the range of 100 to 250 m / min, stable coating can be performed without causing coating troubles such as streak failure. It is an object of the present invention to provide a recording sheet manufacturing method and apparatus capable of increasing productivity.

In order to achieve the above object, according to the first aspect of the present invention, after an ink absorbing layer containing inorganic fine particles and a water-soluble resin is applied and formed on a belt-like support that is continuously wound around and supported by a backup roller, Recording including a coating process in which a hardened coating liquid for hardening the ink absorbing layer is applied at a high speed in a range of 100 to 250 m / min on the ink absorbing layer in a dry state using an extrusion type coating head. In the coating process, the viscosity of the hardened coating solution is adjusted to 5 mPa · s or less at a shear rate of 1000 sec ⁻¹ before coating the hardened coating solution. The lip clearance between the downstream lip of the coating head and the surface of the ink absorbing layer applied to the support is set to 500 to 500 before applying the liquid adjusting step and the hardening coating solution. Formed between the lip tip of the coating head and the support body during the clearance setting step of setting the range of 1000 μm and the coating for applying the adjusted hardening coating liquid on the ink absorbing layer. A suction chamber provided on the upstream side of the coating head as viewed from the running direction of the support so that the upstream pressure of the coating liquid bead is reduced in the range of 0.1 kPa to 0.2 kPa with respect to atmospheric pressure. And a depressurizing step for controlling the degree of vacuum of the recording sheet.

Claim 1 of the present invention finds a condition for performing stable coating even when a hardened coating liquid is applied at a high speed in a range of 100 to 250 m / min on an ink absorbing layer in a dry state, The viscosity of the hardened coating solution at a shear rate of 1000 sec ⁻¹ is adjusted to 5 mPa · s or less, and the lip clearance between the downstream lip of the coating head and the ink absorbing layer surface is set in the range of 500 to 1000 μm. In addition, when the pressure on the upstream side of the coating solution bead during coating is reduced within a range of 0.1 kPa to 0.2 kPa with respect to atmospheric pressure, stable coating of the hardened coating solution can be achieved.

  Therefore, when a recording sheet is produced according to the present invention, a hardened coating solution for hardening an ink absorbing layer using an extrusion type coating head on an ink absorbing layer containing inorganic fine particles and a water-soluble resin. Even if it is applied at a high speed in the range of 100 to 250 m / min, stable application that does not cause application trouble such as streak failure can be performed, so that the productivity of high quality recording sheets can be increased.

  In the manufacturing method of this invention, it is preferable that the surface tension of the said hardening coating liquid is 30-60 mN / m. By making the surface tension of the hardened coating liquid in the range of 30 to 60 mN / m, stable formation of the coating liquid bead, which is an important element of stable coating, can be further improved.

  In the manufacturing method of the present invention, the slit clearance of the coating head may be set to more than 50 μm and not more than 500 μm, and the thickness of the downstream lip may be set to more than 30 μm and not more than 500 μm when viewed from the running direction of the support. preferable.

  By setting the slit clearance of the coating head and the thickness of the downstream lip within the above ranges, it is possible to further improve the stable formation of the coating liquid bead, which is an important factor for stable coating. In this case, the slit clearance is more preferably more than 50 μm and not more than 300 μm, particularly preferably more than 50 μm and not more than 200 μm. Further, the thickness of the downstream lip is more preferably more than 30 μm and not more than 300 μm.

  In the production method of the present invention, after excessively applying the hardened coating liquid onto the ink absorbing layer, smoothing and metalling treatment is performed within 30 seconds to adjust the coating amount and smoothen the coating film surface. It is preferable.

  By performing the smoothing / metalling treatment, it is possible to repair the poor surface condition of the lower ink absorbing layer and the deterioration of the surface condition caused by bubble failure of the hardened coating liquid layer as the upper layer. This is because the repair effect is reduced when the value exceeds.

In order to achieve the above object, the present invention provides an ink absorbing layer containing inorganic fine particles and a water-soluble resin on a belt-like support that is wound around and supported by a backup roller and continuously runs. Recording including a coating apparatus that applies a high-speed coating of a hardened coating solution for hardening the ink absorbing layer on the ink absorbing layer in a dry state using an extrusion type coating head in a range of 100 to 250 m / min. The coating apparatus is a manufacturing apparatus for a sheet, wherein the coating apparatus has a viscosity of ¹ to 5 mPa · s at a shear rate of 1000 sec ⁻¹ before the coating liquid is applied. The lip clearance between the downstream lip of the coating head and the surface of the ink absorbing layer applied to the support is 5 before applying the coating liquid adjusting device to be adjusted and the hardened coating liquid. Clearance setting means for setting in a range of 00 to 1000 μm, and provided on the upstream side of the coating head as viewed from the running direction of the support, and applying the adjusted hardening coating liquid onto the ink absorbing layer During the coating, the upstream pressure of the coating solution bead formed between the lip tip of the coating head and the support is reduced in the range of 0.1 kPa to 0.2 kPa with respect to atmospheric pressure. And a suction chamber for controlling the recording sheet.

  The present invention constitutes the invention as an apparatus.

  According to the recording sheet manufacturing method and apparatus of the present invention, an ink absorbing layer is formed using an extrusion-type coating head on an ink absorbing layer containing inorganic fine particles and a water-soluble resin when the recording sheet is manufactured. Even if the hardening coating liquid for hardening the film is applied at a high speed in the range of 100 to 250 m / min, stable coating can be performed without causing coating troubles such as streak failure. Therefore, productivity in manufacturing a high quality recording sheet can be remarkably increased.

Schematic diagram showing the overall configuration of a manufacturing apparatus for carrying out the method for manufacturing a recording sheet of the present invention Explanatory drawing explaining the whole structure of the extrusion-type coating device in this invention Explanatory drawing explaining conditions, such as a lip clearance of the coating device in this invention Explanatory drawing explaining the coating angle of the coating head The conceptual diagram which shows another aspect which shows the whole structure of the manufacturing apparatus for enforcing the manufacturing method of the recording sheet of this invention

  Hereinafter, preferred embodiments of a recording sheet manufacturing method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a conceptual diagram showing an example of the overall configuration of a manufacturing apparatus for carrying out the recording sheet manufacturing method of the present invention.

[Application of coating liquid for ink absorbing layer]
As shown in FIG. 1, the support 12 delivered from the delivery device 10 is first coated with an ink absorption layer coating solution containing inorganic fine particles and a water-soluble resin by an ink absorption layer coating device 14.

FIG. 1 shows a case where a slide coating apparatus is used as the ink absorbing layer coating apparatus 14, and the coating liquid is supplied to a manifold 18 formed in the coating head 16 of the slide coating apparatus so as to extend in the width direction of the support 12. After being spread, it is pushed out to the slide surface 22 through the slit 20 and flows down the slide surface 22. The coating liquid flowing down the slide surface 22 forms a coating liquid bead in a gap portion between the slide surface tip and the support body 12 engaged and supported by the coating roll 24, and the support body 12 is interposed via the coating liquid bead. It is applied on top. Thereby, an ink absorption layer having a coating amount of, for example, about 100 to 300 g / m ² is formed on the support 12.

  In FIG. 1, a slide coating device is used as the ink absorbing layer coating device 14, but other coating devices such as an extrusion coating device, a curtain coating device, and a bar coating device can also be used.

  Examples of inorganic fine particles used in the present invention include silica fine particles, colloidal silica, calcium silicate, zeolite, kaolinite, halloysite, muscovite, talc, calcium carbonate, calcium sulfate, boehmite, pseudoboehmite and the like. Can do. From the viewpoint of not reducing transparency, the refractive index is preferably in the range of 1.40 to 1.60. Among these, silica fine particles are particularly preferable. The average primary particle diameter of the inorganic fine particles is 20 nm or less, preferably 10 nm or less, particularly preferably 3 nm or less, and the refractive index is preferably around 1.45.

  Examples of water-soluble resins used in the present invention include, as hydrophilic structural units, resins having hydroxyl groups, such as polyvinyl alcohol (PVA), cellulose resins [methyl cellulose (MC), ethyl cellulose (EC), Hydroxyethylcellulose (HEC), carboxymethylcellulose (CMC), etc.], chitins, and starch; resins having an ether bond, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), and polyvinylids Mention may be made of ether (PVE); and polyacrylamide (PAAM) and polyvinylpyrrolidone (PVP), which are resins having amide groups or amide bonds. In addition, as a dissociable group, polyacrylate, maleate, alginate and gelatin having a carboxyl group; polystyrenesulfonate having a sulfonic acid group, amino group, imino group, tertiary amine and fourth group Mention may be made of polyallylamine (PAA), polyethylenimine (PEI), epoxidized polyamide (EPA), polyvinylpyridine and gelatins having a quaternary ammonium salt.

  In addition, as the support 12 used in the present invention, a resin film such as WP paper or PET can be suitably used, but other high quality paper or the like may be used. A support having a width of 500 mm to 2000 mm can be suitably used.

[Drying of ink absorbing layer]
Next, the support 12 on which the ink absorbing layer is formed travels through the drying zone of the drying device 26 and the ink absorbing layer is dried to a freshly dried state.

  In the process of drying the ink absorbing layer by the drying device 26, the drying temperature is 20 to 180 ° C., preferably 30 to 150 ° C., for about 0.5 to 5 minutes before the drying speed enters the decreasing range. dry. Then, a hardened coating solution described below is applied before the rate of drying rate reduction or in a raw dry state where the moisture content of the ink absorption layer (indicated by moisture / solid weight%) is in the range of 200 to 600%. . The moisture content of the ink absorption layer in the dry state is more preferably in the range of 200 to 500%, and particularly preferably in the range of 250 to 450%.

[Application of hardening coating solution]
Next, an excessively thickened coating solution for hardening the ink absorbing layer is applied wet-on-wet by an extrusion-type coating device 28 disposed on the outlet side of the drying device 26. Is done.

The required coating amount of the hardened coating solution finally applied onto the ink absorbing layer is preferably in the range of 5 to 100 cc / m ² .

Examples of the hardening agent contained in the hardening coating solution used in the present invention include boric acid and borates (for example, orthoborate, InBO ₃ , ScBO ₃ , YBO ₃ , LaBO ₃ , Mg ₃ ( BO ₃ ) ₂ , Co ₃ (BO ₃ ) ₂ ], diborate [eg Mg ₂ B ₂ O ₅ , Co ₂ B ₂ O ₅ ], metaborate [eg LiBO ₂ , Ca (BO ₂ ) ₂ , NaBO ₂ , KBO ₂ ], tetraborate [eg Na ₂ B ₄ O ₇ .10H ₂ O], pentaborate [eg KB ₅ O ₈ .4H ₂ O, Ca ₂ B ₆ O ₁₁ .7H ₂ O, CsB ₅ O ₅ ], glyoxal, miramine formaldehyde [eg, methylol melamine, alkylated methylol melamine], methylol urea, resole resin, polyisocyanate, and the like. Of these, boric acid or borates are particularly preferred.

  FIG. 2 shows an extrusion type coating apparatus 28 for applying a hardening coating solution.

  As shown in FIG. 2, the hardened coating solution is supplied to the manifold 44 of the coating head 42 and expanded in the support width direction, and then discharged from the lip tip 48 through the slit 46. The discharged hardening coating liquid is liquid-cross-linked to the surface of the belt-like support 12 that is wound around and supported by the backup roller 50 and continuously runs (in the present invention, the ink absorbing layer is applied), and then the support 12. A coating liquid bead 52 is formed between the two. Then, the hardened coating liquid is applied on the ink absorbing layer in a dry state through the coating liquid bead 52. In addition, a suction chamber 54 that depressurizes the upstream side of the coating liquid bead 52 is provided on the upstream side of the coating head 42 as viewed from the traveling direction of the support 12.

  In the application of the hardening coating solution, it is important to satisfy the following conditions (1) to (3) in order to stably apply the hardening coating solution at a high speed in the range of 100 to 250 m / min. Become.

(1) Before applying the hardened coating solution, the hardened coating solution supplied to the coating device 28 has a viscosity at a shear rate of 1000 sec ⁻¹ by a coating solution adjusting device (for example, a coating solution adjusting tank) (not shown). Is adjusted to 5 mPa · s or less.

  When the viscosity exceeds 5 mPa · s and the coating speed is 100 m / min or more, the coating liquid bead 52 is suddenly pulled by the traveling support 12 and the bead width becomes narrower than the support width. To do. If the bead width is further narrowed, the coating solution bead 52 is cut, so that a liquid running out phenomenon occurs, and the hardened coating solution is not applied to the support 12.

  As a method of adjusting the viscosity of the hardening coating solution, a method of adjusting the concentration of the hardening agent dissolved in the solvent or a method of adding a viscosity adjusting agent can be preferably employed.

  (2) As shown in FIG. 3, the lip clearance D between the downstream lip 48A at the lip tip 48 of the coating head 42 and the surface of the ink absorbing layer coated on the support 12 is set in the range of 500 to 1000 μm. To do.

  That is, if the lip clearance is narrowed to less than 500 μm and the coating speed is set to 100 m / min or more, the support 12 is likely to float from the backup roller 50 due to the accompanying air generated when the support 12 travels. The ink-absorbing layer applied to the surface easily comes into contact with the lip tip 48 (especially the downstream lip 48A) of the application head 42, causing streak failure. In addition, the ink absorbing layer formed on the convex surface portion such as a ridge formed on the support 12 is likely to come into contact with the lip tip 48 of the coating head 42, resulting in streak failure. On the other hand, if the lip clearance D is increased beyond 1000 μm, the coating solution bead 52 cannot be stably formed.

  As a means for adjusting the lip clearance D, for example, the coating head 42 is mounted on a slide table (not shown), and the slide table is slid with respect to the roller surface of the backup roller 50, whereby the lip clearance D is set to 500 to 1000 μm. Means for adjusting the range can be suitably used.

  (3) During the application of applying the adjusted hardening coating liquid onto the ink absorbing layer, the degree of vacuum of the suction chamber 54 is controlled, and the lip tip 48 of the application head 42 and the support 12 are controlled. The upstream pressure of the coating liquid bead 52 formed therebetween is adjusted so as to be reduced within a range of 0.1 kPa to 0.2 kPa with respect to the atmospheric pressure. In this case, the upstream pressure of the coating liquid bead 52 may be adjusted in advance before the start of application, or may be adjusted immediately after the start of application. In short, what is necessary is just to be in the state adjusted during application | coating.

  That is, the coating solution bead cannot be stabilized when the pressure on the upstream side of the coating solution bead 52 during coating is reduced to less than 0.1 kPa with respect to the atmospheric pressure. On the other hand, if the pressure on the upstream side of the coating solution bead 52 during coating exceeds 0.2 kPa with respect to the atmospheric pressure and the degree of vacuum is increased, the coating solution bead is pulled into the suction chamber, resulting in liquid breakage and inability to apply. .

  Furthermore, in order to stably apply the hardened coating solution at a high speed in the range of 100 to 250 m / min, the following conditions (4) to (7) should be added to the above conditions (1) to (3). Is preferred.

  (4) It is preferable that the surface tension of the hardening coating liquid is 30 to 60 mN / m. Thereby, the coating liquid bead 52 important for stable coating can be formed more stably. The surface tension of the hardening coating solution can be adjusted by adding an appropriate surfactant to the coating solution.

  (5) As shown in FIG. 3, the slit clearance A of the coating head 42 is set to be more than 50 μm and not more than 500 μm, and the thickness B of the downstream lip when viewed from the running direction of the support 12 is more than 30 μm and not more than 500 μm. It is preferable to set to. The slit clearance A and the thickness B of the downstream lip are set in advance when the coating head is manufactured.

  (6) As shown in FIG. 3, the overbite amount C of the upstream lip 48B of the coating head 42 is preferably more than 0 μm and 500 μm or less. This overbite amount C is also set in advance when the coating head 42 is manufactured.

  (7) As shown in FIG. 1, after excessively applying the hardened coating liquid onto the ink absorbing layer, smoothing and metalling treatment is performed within 30 seconds to adjust the coating amount and smooth the coating film surface. It is preferable to do.

  Here, the smoothing and metering process will be described in detail.

  As shown in FIG. 1, immediately after application of the hardened coating solution, smoothing and metering is performed by a smoothing and metering device 30 (shown in FIG. 1 in a bar system). In this case, it is preferable to perform the smoothing / metalling treatment with the bar 30A immediately after application of the hardening coating solution, preferably within 30 seconds. As a result, the poor surface state of the lower ink absorbing layer and the deterioration of the surface state due to foam failure of the hardened coating liquid layer (coating failure such as streaks and unevenness) are repaired. A coated surface having a good and high glossiness can be formed.

  As a smoothing and metering device for performing the smoothing and metering treatment, there are a bar type, an air knife type and a blade type.

  The bar method is a method in which the bar 12 is arranged in the width direction of the support 12 that travels in the axial direction of the bar of the round bar and is brought into contact with the application surface formed on the support 12. A round bar shape of 200 mm, preferably 5 to 50 mm is preferable. In addition, the bar is rotated in the same direction as the support 12 or in the opposite direction at a peripheral speed within 50% of the speed at which the support 12 travels. The wrap angle (θ) of the support 12 to the bar at this time is suitably within 0 to 30 degrees. Also, when the bar and the coating surface come into contact with each other by forming a groove between the wound wires by winding the wire etc. according to the required coating amount, or by engraving the groove in the bar itself, surplus The coating liquid is metallized by being taken into the groove.

In the air knife method, the longitudinal direction of the slot-like air nozzle that blows knife-like air is arranged in the width direction of the traveling support 12, and the knife-like air from the air nozzle is applied to the coating surface. In this method, the coated surface layer is scraped off while leveling the coated surface. The speed of air blown from the air nozzle is in the range of 10 to 150 m / sec, and the air pressure is preferably in the range of 0.01 to 10 kg / cm ² , particularly preferably in the range of 0.5 to ⁵ kg / cm ² . Further, it is preferable that the distance from the tip of the air nozzle to the uppermost application surface is set in the range of 1 to 30 mm, and the angle formed by the air nozzle and the application surface is set in the range of 1 to 50 degrees.

In the blade system, the width direction of the blade is arranged in the width direction of the support 12 and brought into contact with the coating surface formed by coating on the support 12, so that the coating surface layer portion is made uniform while smoothing the coating surface. This is a scraping method. The blade used for this is made of a flexible resin material, and the pressure applied to the coating surface is preferably 0.01 to 10 kg / cm ² , particularly preferably in the range of 0.1 to 5 kg / cm ² . Good.

  However, the above conditions for the bar method, air knife method, and blade method are as follows: a) required coating amount, b) the degree of curing by the hardened coating liquid layer (upper layer) of the ink absorbing layer (lower layer), c) ink absorbing layer It is further preferable to adjust within the range of the above conditions according to the composition and physical properties of the coating solution and the hardened coating solution, and d) the time from application and formation of the hardened coating solution to the smoothing and metalling treatment.

  In addition, the angle of the coating head 42 with respect to the traveling support 12 may be arbitrary, but the coating liquid bead 52 is formed with the coating liquid discharged from the coating head 42 on the portion of the support 12 that is wound around and supported by the backup roller 50. It is preferable to set the angle of the coating head 42 so that the bead pressure can be kept high. This is because it is preferable for stable bead formation to reduce the pressure on the upstream side of the coating solution bead 52 in the suction chamber 54 in a state where the bead pressure is high.

  Therefore, it is preferable to adjust the direction of the coating head 42 so that the coating angle of the coating head 42 with respect to the backup roller 50 is in a range of ± 30 degrees. Here, as shown in FIG. 4, the application angle is defined as 0 ° when the direction of the slit 46 of the coating head 42 is directed to the center Q of the backup roller 50. Then, when the application point of the coating liquid to the support 12 supported around the backup roller 50 from the lip tip 48 is supported as a swing point P, the direction of the slit 46 is swung to the running direction side of the support 12. Was expressed as a positive painting angle θ1, and an angle when swung in the opposite direction was represented as θ2 and a negative coating angle.

[Drying and winding after smoothing and metalling]
Next, the coating layer that has been subjected to the smoothing and metalling treatment (the ink absorption layer after the coating of the hardened coating solution has been applied) is hot-air dried with a wind of about 180 ° C. by the drying device 26. In this case, in the case of the air-permeable support 12 such as paper, a casting drum 32 may be used as shown in FIG.

  Then, the support 12 dried by the drying device 26 is taken up by the winding device 34. Thereby, a recording sheet is manufactured. Reference numeral 36 denotes a guide roller that forms a travel path of the support 12.

As described above, according to the recording sheet manufacturing method of the present invention, the viscosity of the hardened coating solution at a shear rate of 1000 sec ⁻¹ is adjusted to 5 mPa · s or less, and the downstream lip 48A of the coating head 42 is used. The lip clearance D between the surface and the ink absorbing layer surface is set in the range of 500 to 1000 μm, and the upstream pressure of the coating liquid bead 52 during coating is 0.1 kPa or more and 0.2 kPa or less with respect to atmospheric pressure. By reducing the pressure within the range, stable coating of the hardening coating solution can be achieved.

  Therefore, when a recording sheet is produced according to the present invention, a hardened coating solution for hardening an ink absorbing layer using an extrusion type coating head on an ink absorbing layer containing inorganic fine particles and a water-soluble resin. Even if it is applied at a high speed in the range of 100 to 250 m / min, stable application that does not cause application trouble such as streak failure can be performed, so that the productivity of high-quality recording sheets can be increased.

  In FIG. 1, both the ink absorbing layer and the hardened coating liquid layer are dried by one drying device 26. However, the ink absorbing layer and the hardened coating liquid layer are dried by another drying device. May be. Further, when applying the hardening coating solution, the support 12 may be provided with an undercoat layer for improving the coating adhesion, wettability and the like of the support 12. In this case, the moisture content of the undercoat layer is preferably 10% or less. The reason is that the dry state of the ink absorbing layer when applying the hardened coating solution is important for the stable application of the hardened coating solution, and an undercoat layer having a high water content other than the ink absorbing layer is formed on the support 12. This is because the influence of the ink absorbing layer on the moisture content becomes large, and the ride of the hardened coating solution becomes worse.

  In addition, depending on how the application conditions (1) to (6) are set, a stable application liquid bead can be obtained even when the required application amount and the supply application amount of the hardened application liquid forming the upper layer are the same. It is possible to form and apply. Thereby, in the embodiment of the present invention, the smoothing and metering device 30 is provided. However, the smoothing and metering device 30 may be omitted.

  The recording sheet manufacturing method that satisfies the conditions of the present invention and the recording sheet manufacturing method that does not satisfy the conditions were tested for differences in coating properties and continuous coating stability.

[Preparation of ink absorbing layer coating solution]
As the ink absorbing layer coating solution, one having the composition shown in Table 1 was prepared.

  The detailed composition of the water-soluble resin in Table 1 is as follows. The “part” indicating the blending ratio is shown per ink absorption layer coating solution.

  Polyvinyl alcohol (“JM33” (degree of saponification 95.5%, degree of polymerization 3300), 1.8 parts of Nippon Vinegar Poval Co., Ltd., water-soluble cellulose (“HPC-SSL”, made by Nippon Soda Co., Ltd.) 0.1 part, 23.0 parts of ion-exchanged water, 0.55 part of diethylene glycol monobutyl ether (“Butizenol 20P”, manufactured by Kyowa Hakko Chemical Co., Ltd.), surfactant (“Emulgen 109P”, Kao Corporation) Made) is 0.6 part.

[Preparation of polyaluminum chloride solution]
A cationic compound solution (in-line solution) is often added in-line to the ink-absorbing layer coating solution for the purpose of improving the water resistance of the ink-absorbing layer. In this example, the cationic compound solution has the composition shown in Table 2 below. A polyaluminum chloride solution was prepared. The “part” indicating the blending ratio is shown per ink absorption layer coating solution.

[Formation of ink absorption layer]
Then, the mixture was in-line mixed polyaluminum chloride Table 2 solution 11.4 g / ^{m 2} (coating amount) with a static mixer in the ink absorbing layer coating solution 165 g / ^{m 2} of Table 1 (coating amount), the corona discharge An ink absorption layer was formed on the surface of the treated water-impermeable support by applying an extrusion type coating apparatus.

  Next, the coated and formed ink absorbing layer is dried in a hot air drying apparatus at a drying temperature of 80 ° C. and a drying wind speed of 3 to 8 m / sec. Dry until. The ink absorbing layer exhibited a constant rate of drying during this period.

Then, after applying 13 g / m ² (application amount) of the curing agent coating liquid having the composition shown in Table 3 on the ink absorption layer, the ink absorption layer was dried by a hot air drying apparatus at a drying temperature of 72 ° C. for 10 minutes. It became hardened.

[Test method]
The test shows three conditions: viscosity of the hardened coating solution at a shear rate of 1000 sec ^-1 (condition 1), lip clearance (condition 2), and upstream pressure of the coating solution bead (degree of decompression) (condition 3). The coating property and the continuous coating stability when the hardened coating solution was continuously applied for 30 minutes at a coating speed of 250 m / min. Moreover, it implemented similarly at the application | coating speed | rate of 100 m / min, and it checked just in case that there was no problem when the application | coating speed was reduced. Moreover, the influence when changing the coating liquid surface tension was confirmed.

  (Remarks) Since the upstream pressure is a degree of pressure reduction with respect to atmospheric pressure, it is shown with a minus sign. In addition, the evaluation of “−” in the continuous application stability indicates that the evaluation cannot be performed because the application property was “x” and application was impossible.

  Example 1 is a case where the three conditions of the present invention are satisfied and the process is performed under conditions close to the lower limit value or the lower limit value in the range of Conditions 1-3.

  Example 2 is a case where the three conditions of the present invention are satisfied and an intermediate numerical value in the range of conditions 1 to 3 is used.

  Example 3 is a case where the three conditions of the present invention are satisfied and the process is performed under the condition of the upper limit value in the range of Conditions 1-3.

  Comparative Example 1 is a case where the lower limit of Condition 3 is not satisfied among the three conditions of the present invention.

  Comparative example 2 is a case where the upper limit of condition 3 out of the three conditions of the present invention is exceeded.

  Comparative Example 3 is a case where the lower limit of Condition 2 is exceeded among the three conditions of the present invention.

  Comparative example 4 is a case where the upper limit of condition 2 out of the three conditions of the present invention is exceeded.

  The comparative example 5 is a case where the upper limit of the condition 1 out of the three conditions of the present invention is exceeded.

  Example 4 is a case where the coating speed of Example 2 was reduced to 100 m / min.

  Example 5 is a case where the coating speed of Example 3 was reduced to 100 m / min.

  Comparative Example 6 is a case where the coating speed of Comparative Example 5 was reduced to 100 m / min.

  Example 6 is a case where the coating liquid surface tension is outside the lower limit.

  Example 7 is a case where the coating liquid surface tension is the lower limit.

  Example 8 is a case where the coating liquid surface tension is the upper limit.

  Example 9 is a case where the surface tension of the coating solution deviates from the upper limit.

[Test results]
The coating evaluation in the examples and comparative examples was performed on two items of coating properties and continuous coating stability.

(Evaluation of applicability)
The applicability was evaluated as to whether the liquid could be applied without running out of liquid, and was determined as follows based on the number of liquid running out during the coating operation.

○: No liquid breakage, △ ... Occasional liquid breakage, X: Liquid runout at all times and application not possible (evaluation of continuous application stability)
The continuous application stability was evaluated as follows to determine whether the application could be performed stably without the occurrence of application defects due to streak failure, and was determined based on the degree of streak failure.

○… No streak failure, ×… Streak failure is observed (evaluation result)
As can be seen from the coating properties and continuous coating properties in Table 4, the viscosity of the hardened coating solution (5 mPa · s or less), the lip clearance (500 to 1000 μm), and the upstream pressure of the coating solution bead (0.1 kPa or more and 0 In Examples 1 to 3, which satisfy all three conditions (depressurization in a range of 0.2 kPa or less), both applicability and continuous application stability were evaluated as ◯ even at a high speed application of 250 m / min. Incidentally, Examples 4 and 5 in which the coating speed was reduced to 100 m / min under the conditions of Examples 2 and 3 were evaluated as good for both coating property and continuous coating stability.

  On the other hand, Comparative Examples 1 to 6 lacking even one of the above three conditions were evaluated as x for coating property or continuous coating stability at high speed coating of 250 m / min. Incidentally, Comparative Example 6 in which the coating speed was reduced to 100 m / min under the conditions of Comparative Example 5 was evaluated as x for coating properties. Moreover, Example 6 and Example 9 in which the coating liquid surface tension deviated from the upper limit or the lower limit were evaluated as Δ for applicability.

  DESCRIPTION OF SYMBOLS 10 ... Delivery apparatus, 12 ... Support body, 14 ... Coating apparatus for ink absorption layer, 24 ... Coating roll, 26 ... Drying apparatus, 28 ... Coating apparatus for upper layer, 30 ... Bar type smoothing and metering apparatus, 32 ... Casting Drum, 34 ... winding device, 42 ... coating head, 44 ... manifold, 46 ... slit, 48 ... lip tip, 48A ... downstream lip, 48B ... upstream lip, 50 ... backup roller, 52 ... bead, 54 ... suction Chamber, A ... Slit clearance, B ... Downstream lip thickness, C ... Upstream lip overbite amount, D ... Lip clearance

Claims (5)

An ink-absorbing layer containing inorganic fine particles and a water-soluble resin is applied and formed on a belt-like support that is continuously wound around and supported by a backup roller, and then an extrusion-type coating is applied on the ink-absorbing layer in a dry state. A method for producing a recording sheet comprising a coating step of applying a hardened coating solution for hardening the ink absorbing layer using a head at a high speed in a range of 100 to 250 m / min,
In the coating process,
A coating liquid adjusting step of adjusting the viscosity of the hardened coating liquid at a shear rate of 1000 sec ⁻¹ to 5 mPa · s or less before applying the hardened coating liquid;
A clearance setting step of setting a lip clearance between the downstream lip of the coating head and the surface of the ink absorbing layer applied to the support in a range of 500 to 1000 μm before applying the hardening coating solution. When,
During the application of applying the adjusted hardening coating liquid onto the ink absorbing layer, the upstream pressure of the coating liquid bead formed between the lip tip of the coating head and the support is atmospheric pressure. Pressure reduction step of controlling the degree of vacuum of the suction chamber provided on the upstream side of the coating head as viewed from the traveling direction of the support so that the pressure is reduced in the range of 0.1 kPa to 0.2 kPa. A method for producing a recording sheet, comprising:   2. The method for producing a recording sheet according to claim 1, wherein a surface tension of the hardening coating solution is 30 to 60 mN / m.   The slit clearance of the coating head is set to more than 50 μm and not more than 500 μm, and the thickness of the downstream lip is set to more than 30 μm and not more than 500 μm when viewed from the running direction of the support. 2. A method for producing a recording sheet according to 2.   The coating film surface is smoothed by adjusting the coating amount by performing a smoothing / metalling treatment within 30 seconds after the hardened coating liquid is applied excessively on the ink absorbing layer. A method for producing a recording sheet according to any one of 1 to 3. An ink-absorbing layer containing inorganic fine particles and a water-soluble resin is applied and formed on a belt-like support that is continuously wound around and supported by a backup roller, and then an extrusion-type coating is applied on the ink-absorbing layer in a dry state. A recording sheet manufacturing apparatus including a coating apparatus that applies a high-speed coating of a hardened coating liquid that hardens the ink absorbing layer using a head in a range of 100 to 250 m / min,
In the coating device,
A coating liquid adjusting device that adjusts the viscosity of the hardened coating liquid at a shear rate of 1000 sec ⁻¹ to 5 mPa · s or less before applying the hardened coating liquid;
Clearance setting means for setting the lip clearance between the downstream lip of the coating head and the surface of the ink absorbing layer applied to the support to a range of 500 to 1000 μm before applying the hardening coating solution. When,
The lip tip of the coating head and the lip tip of the coating head are provided on the upstream side of the coating head as viewed from the traveling direction of the support, and the coated hardened coating solution is coated on the ink absorbing layer. A suction chamber that controls the upstream pressure of the coating solution bead formed between the support and the support so that the pressure is reduced in the range of 0.1 kPa to 0.2 kPa with respect to the atmospheric pressure. A recording sheet manufacturing apparatus.

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