Coating processes – With post-treatment of coating or coating material – Gas jet or blast mechanically treats coating
Reexamination Certificate
2000-10-19
2003-09-02
Bareford, Katherine A. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Gas jet or blast mechanically treats coating
C427S356000, C427S358000, C427S359000, C427S361000
Reexamination Certificate
active
06613388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for producing a recording sheet, in particular, for producing a recording sheet having a coloring material receiving layer, which contains inorganic particulates and a water-soluble resin, provided on its substrate, such as a high quality ink jet recording sheet.
2. Description of Related Art
Various types of ink jet methods have been developed up to date; and with their development, various types of ink jet recording sheets have also been developed. Substrates used in these ink jet recording sheets include, for example, not only a variety of resin films but also plain paper, wood free paper (coat paper), and photographic paper. Of these ink jet recording sheets, those provided with a coloring material receiving layer which contains inorganic particulates of fine diameter and a water-soluble resin are now in use as high quality ink jet recording sheets. The recording sheets provided with a coloring material receiving layer containing inorganic particulates and a water-soluble resin also include, for example, those for thermal transfer recording and for electrophotography.
With respect to the production of a recording sheet provided with a coloring material receiving layer containing inorganic particulates and a water-soluble resin, there is disclosed a method in Japanese Patent Laid-Open No. 62-111782 in which a crazing-free recording sheet is produced, while maintaining high ink absorption, high water fastness, and high ink absorption rate, by dividing the coloring material receiving layer into two layers and applying coatings on the layers in sequence. In Japanese Patent Laid-Open No. 8-72388, there is disclosed a method in which a recording sheet of high glossiness is produced by first applying pseudo-boehmite solution to a paper base, second applying silica coating solution to the pseudo-boehmite layer when a water content of the pseudo-boehmite layer is 100 to 450%, and immediately after this, pushing a heated smooth mold against the layer surface. Further, in Japanese Patent Laid-Open No. 11-172597,there is disclosed a method in which a recording sheet of high glossiness is produced by first adjusting a moisture content of its ink coloring material receiving layer formed by applying a coating on a substrate to 200 to 500% by weight, laminating organic polymer films with an arithmetic mean value of surface roughness of 25 nm or less, drying to a moisture content of 5% by weight or lower, followed by stripping the films. In Japanese Patent Laid-Open No. 11-115308, there is disclosed a method in which a recording sheet having high ink absorbability and causing less bleeding and no crazing is produced by providing a coating film of its coloring material receiving layer, which contains inorganic particulates of fine diameter and a water-soluble resin, with a crosslinking agent for crosslinking the water-soluble resin before the above coating film enters its falling drying rate period.
However, in case of the method disclosed in Japanese Patent Laid-Open No. 62-111782, when applying a coating for forming a top layer, such as protective layer, on a sublayer formed by applying/drying a coating for a coloring material receiving layer containing fine particles, bubble trouble is likely to occur, as described in Japanese Patent Laid-Open No. 9-156202, which is a phenomenon that air trapped in voids created in the coloring material receiving layer due to the existence of particulates appears on the protective layer surface of the top layer in the form of traces of bubbles. As a result, the conditions of the coated surface of the recording sheet, as a product, deteriorate, and the smoothness of the same is decreased. Thus the method has a disadvantage in that it is impossible to obtain a recording sheet of high glossiness.
In cases of the methods disclosed in Japanese Patent Laid-Open No. 8-72388 and in Japanese Patent Laid-Open No. 11-172597, the coated surface of a recording sheet is pushed with a mold or laminated with organic polymer films so as to be smoothened; accordingly drying the coating film must be conducted from the back side (the substrate side) of the recording sheet. Thus these methods have disadvantage in that, when using an impermeable film for the substrate of a recording sheet, it is impossible to proceed with drying the coating film.
In case of the method disclosed in Japanese Patent Laid-Open No. 11-115308, in the process of providing a crosslinking agent to an ink coloring material receiving layer, the crosslinking agent is applied on the coloring material receiving layer which does not enter its falling drying rate period yet and is still in the wet state. Accordingly, the conditions of the coated surface of a recording sheet, as a product, may deteriorate depending on the composition and physical properties of the coating solution and on the conditions of coating operation, in particular, the properties of the crosslinking agent, the coating speed, and the coated width; the type of the substrate; and the properties and surface conditions of the coloring material receiving layer containing inorganic particulates and a water-soluble resin in itself. This causes defects in quality, in addition, influences the stability of production because the production is under restrictions of the composition and physical properties of the coating solution as described above. In the cases where a crosslinking agent is applied on the coloring material receiving layer using a slide coater, an extrusion coater or a curtain coater via a bead or curtain film, the bead portion and the curtain film are affected by the entrained wind occurring due to the travel of the substrate and is likely to vibrate; thus the coating of the crosslinking agent is likely to be non-uniform in a direction in which the substrate travels or in a transverse direction of the substrate. In addition, the application of a crosslinking agent is likely to be affected by the wettability by the crosslinking agent on the coloring material receiving layer and affected by the progress of the crosslinking reaction. And when the application of the crosslinking agent is thus destabilized, lines and unevenness are likely to occur on the surface of the products having been subjected to drying. The occurrence of such lines and unevenness not only causes the appearance of the products to deteriorate, but also causes deficiencies in performance, such as glossiness and image quality, of the products as a recording sheet. Particularly in terms of reactivity of the coloring material receiving layer with a crosslinking agent, it is necessary to cure the coloring material receiving layer early by the crosslinking agent, and the reaction is already in progress when a bead is formed; thus the stability in the application of the crosslinking agent is largely affected by the progress of the crosslinking reaction. When using coaters other than those described above, such as roll coater and bar coater, the meniscus of the crosslinking agent solution formed between the roll or bar and the coloring material receiving layer still in the wet state is disturbed depending on the conditions such as wettability by the crosslinking agent on the coloring material receiving layer, reactivity of the coloring material receiving layer with the crosslinking agent and coating speed of the crosslinking agent, which is likely to cause lines and unevenness on the surface of the products having been subjected to drying. When using a dip coater, the amount of the crosslinking agent to be coated cannot be freely controlled. This causes problems in that the formulation and the performance of the crosslinking agent are largely affected, and a worse condition, an excess amount of crosslinking agent applied sags and runs, causing lines on the surface of the products. Further, when using a spray coater for applying a crosslinking agent to the coloring material receiving layer, the traces of the droplets of the crosslinking agent may remain on the p
Kashiwabara Yutaka
Nojo Kazuhiko
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