Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-04-27
2001-03-06
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S378000, C427S393500, C427S412100
Reexamination Certificate
active
06197381
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a production method of a recording sheet having a void layer on a support, and specifically to a production method of a recording sheet in which cracking on the surface of the coated layer is minimized.
BACKGROUND OF THE INVENTION
Ink-jet recording is carried out in such a manner that fine droplets of ink are allowed to fly employing various operation principles and are adhered onto a recording sheet such as a sheet of paper to record images and characters. Ink-jet recording exhibits advantages such as relatively high speed, low noise, ease of multicolor production, and the like. Conventional problems of this system regarding clogging of nozzles and maintenance have been solved by improving both aspects of ink and the device, and at present, ink-jet recording has been rapidly applied to a variety of fields such as various printers, facsimile machines, computer terminals, and the like.
Requirements for a recording sheet employed in such ink-jet recording system is that the density of printing dots is high; color tone is bright and clear; ink is rapidly absorbed and when printing dots are superimposed, ink should neither run out nor blot; the diffusion of a printing dot in the lateral direction should not be greater than that needed and the circumference should be smooth and result in no blurring; and the like.
Particularly, at low rates of ink absorption, when recording is carried out by superimposing at least two color inks, on a recording sheet, droplets result in repellence to cause unevenness and in the boundary area of different colors, mutual colors result in blurring. As a result, image quality tends to be markedly degraded. Therefore, it is required that the recording sheet exhibits high ink absorbability.
In order to solve these problems, conventionally, a great number of techniques have been proposed.
For example, Japanese Patent Publication Open to Public Inspection No. 52-53012 describes a recording sheet in which minimally sized paper support is damped with paint employed for surface treatment; Japanese Patent Publication Open to Public Inspection No. 55-5830 describes a recording sheet comprising a support in which an ink absorbing coating layer is provided on the surface of the support; Japanese Patent Publication Open to Public Inspection No. 56-157 describes a recording sheet comprising a covering layer containing non-colloidal silica powder as a pigment; Japanese Patent Publication Open to Public Inspection No. 57-107873 describes a recording sheet comprising an inorganic pigment and an organic pigment in combination; Japanese Patent Publication Open to Public Inspection No. 58-110287 describes a recording sheet which exhibits a void distribution with two peaks; Japanese Patent Publication Open to Public Inspection No. 62-111782 describes a recording sheet composed of an upper porous layer and a lower porous layer; Japanese Patent Publication Open to Public Inspection Nos. 59-68292, 59-123696, 60-18383, etc. describe a recording sheet having amorphous cracking; Japanese Patent Publication Open to Public Inspection Nos. 61-135786, 61-148092, 62-149475, etc. describe a recording sheet having a fine powder layer; Japanese Patent Publication Open to Public Inspection Nos. 63-252779, 1-108083, 2-136279, 3-65376, 3-27976, etc. describe a recording sheet comprising pigments and fine silica particles having specified physical parameters; Japanese Patent Publication Open to Public Inspection Nos. 57-14091, 60-219083, 60-210984, 61-20797, 61-188183, 5-278324, 6-92011, 6-183134, 7-137431, 7-276789, etc. describe a recording sheet containing fine silica particles such as colloidal silica; Japanese Patent Publication Open to Public Inspection Nos. 2-276671, 3-67684, 3-215082, 3-251488, 4-67986, 4-263983, 5-16517, etc. describe a recording sheet containing fine hydrated alumina particles, and the like.
Of these, a recording sheet provided with a void layer composed of fine organic particles having an average diameter of not more than 100 nm and a hydrophilic binder as an ink absorbing layer is preferred, which employs a technique for achieving high ink absorbability and glossiness at the same time.
Further, with such a void layer, a large content of fine inorganic particles with respect to a hydrophilic binder is needed for the formation of voids, and the resulting void layer becomes rigid due to markedly high rigidity. Such a rigid layer is required to obtain high ink absorbability. However, it has been found that during the coating and drying processes of the void layer, cracking readily occurs in the presence of tiny foreign matter, due to low flexibility of the layer and problems are caused in a case of the dry void layer having a thickness of not less than 25 &mgr;m, which is specifically required for ink-jet recording.
It has been found that when a recording sheet having such a void layer is produced, relatively coarse particles such as coarse inorganic particles themselves, coagulum of fine inorganic particles, coagulum of other additives tend to be formed due to various causes during preparing the coating composition, and these coarse particles cause cracking during coating and drying onto a support.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been accomplished. An object of the present invention is to provide a production method of a recording sheet, in which cracking of the coated layer surface due to coarse particles is markedly minimized when a recording paper having a void layer with high gloss is produced. Another object is to provide a production method of the recording sheet, which lowers the production cost, and results in a high void ratio, water resistance and glossiness.
DETAILED DESCRIPTION OF THE INVENTION
The problems of the present invention are solved by each of the following:
1. A production method of a recording sheet which comprises:
coating onto at least one surface of a support with a coating solution so as to form a void layer having a dry thickness of 25 to 60 &mgr;m,
wherein said coating solution comprising;
fine inorganic particles having an average particle diameter of not more than 100 nm, a hydrophilic binder, and not more than 10 coarse particles, per 1 (ml) of said coating solution, having a particle diameter of more than R (&mgr;m) represented by formula (1):
R=80000/L
2
Formula (1)
wherein L represents said dry thickness (&mgr;m) of said void layer.
2. The production method of item 1, wherein said coating solution further comprises a hydrophobic latex having a glass transition temperature of not more than 30° C. and an average particle diameter of not more than 100 &mgr;m, or an emulsion dispersion of hydrophobic organic compound particles having a melting point of not more than 30° C.
3. The production method of item 1, further comprising: filtering said coating solution through a filter which can filter out particles having a diameter of said R (&mgr;m) or more.
4. The production method of item 1, wherein said support is a non-water absorbing support.
5. The production method of item 1, further comprising: cooling said coating solution on the support to not more than 15° C., and drying said coating solution on the support with air blow at a temperature of 20 to 60° C.
6. A production method of a recording sheet which comprises:
coating onto at least one surface of a support with a first coating solution so as to form a first void layer nearest the support;
coating onto said support with at least one coating solution, so as to form void layers having a dry thickness of 25 to 60 &mgr;m including the first void layer, which comprises fine inorganic particles having an average particle diameter of not more than 100 nm and a hydrophilic binder;
wherein the first coating solution comprising fine inorganic particles having an average particle diameter of not more than 100 nm, a hydrophilic binder, and not more than 5 coarse particles, per 1 (ml) of said coating solution, having a particle diameter of more than R (&mgr;m) repr
Okazaki Masaaki
Saito Yoichi
Tsuchiya Masaru
Bierman Jordan B.
Bierman, Muserlian and Lucas
Cameron Erma
Konica Corporation
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