Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-11-16
2003-06-24
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S478200, C428S327000, C428S323000, C428S325000, C428S328000, C428S331000, C428S206000
Reexamination Certificate
active
06582802
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink jet recording medium (hereinafter referred to as a recording medium, an ink jet recording sheet, or a recording sheet) having a ink absorbing layer, and specifically to an ink jet recording medium in which brittleness and water resistance of a coated layer is improved.
BACKGROUND OF THE INVENTION
In recent years, ink jet recording has resulted in rapid progress of image quality, which is nearly approaching that of the conventional photography. In order to achieve the quality of conventional photography, improvement has been carried out in the aspect of recording sheets. Recording sheets, which are prepared by applying a fine void layer onto a support having high surface smoothness, exhibit excellent ink absorbing and drying properties. Thus said sheet is becoming one of recording sheets which result in image quality approaching conventional photography.
In order to obtain such high quality print images, a high ink absorbing rate is required. When the ink absorbing rate is low, before being absorbed perfectly, ink droplets unite with each other to result in spottiness.
In recent high-speed printing, from the viewpoint of image quality, it is essentially required that an ink absorbing layer comprises a void structure.
Since the ink absorbing layer comprises said void structure, ink droplets are temporarily absorbed into voids. Thus, even immediately after printing, the surface exhibits almost a dried state. However, since ink solvents (for example, water and organic solvents) remain in the void structure, the resultant coated layer not always bears sufficient strength compared to that before printing. As a result, a problem has occurred in which the surface tends to be abraded during handling immediately after printing.
Said problem tends to occur particularly when a non-water absorbing support, which does not absorb ink solvents, is employed.
In order to enhance the coating strength of an ink absorbing layer, heretofore, regarding ink jet recording sheets, hardening a hydrophilic binder using hardeners has been widely carried out in the same manner as those commonly employed.
In the case of recording sheets which comprise a so-called swelling type ink absorbing layer, in which ink is absorbed utilizing swelling properties of a hydrophilic binder, when hardened by the addition of a hardener, it is difficult to carry out sufficient hardening due to a decrease in ink absorbability. Further, in most cases, it was impossible to place a printed sheet on a previously printed one for the time being after printing. On the contrary, it has been discovered that recording sheets comprising a void structure, containing an ink absorbing layer (hereinafter occasionally referred to as a porous ink absorbing layer), has almost no such limitations, but rather, the more hardened, the higher the ink absorbability tends to be.
For this reason, it is considered that in a recording sheet having a void structure comprising an ink absorbing layer, the swellability of a hydrophilic binder forming a void structure is further restricted, and in the upper region (namely the side nearer the surface) of the ink absorbing layer, hindrance of ink penetration due to swelling of the hydrophilic binder is restricted.
Accordingly, in ink jet recording sheets having a void structure comprising an ink absorbing layer, in accordance with an increase of hardening of said ink absorbing layer, it is possible to increase ink absorbability and to enhance water resistance of said layer.
Since in the ink absorbing layer comprising the void structure, ink droplets are temporarily absorbed into said void layer, even immediately after printing, the surface exhibits almost a dried state. However, since ink solvents (for example, water and organic solvents) remain in the void structure, the resultant layer not always bears sufficient strength compared to that before printing. As a result, a problem has occurred in which the surface tends to be abraded during handling immediately after printing.
Heretofore, it has been well known that in ink jet recording sheets, hydrophilic binders are hardened.
For example, U.S. Pat. No. 4,592,951 discloses an ink jet recording sheet comprising polyvinyl alcohol which is hardened employing boric acid based cross linking agents; Japanese Patent Publication Open to Public Inspection No. 10-119423 discloses an ink jet recording sheet comprising fine inorganic particles and boric acid based hardeners or epoxy based hardeners; and Japanese Patent Publication Open to Public Inspection No. 11-115308 discloses a method in which after applying a coating composition comprising fine inorganic particles and a hydrophilic resin, a cross linking agent is supplied before decreasing drying, and described as preferable hardeners are boric acid salts, aldehydes, polyisocyanates, methylolurea, and boric acid salts are listed as specifically preferable hardeners. In addition, Japanese Patent Publication Open to Public Inspection No. 11-198519 describes an ink jet recording sheet employing specific epoxy based hardeners.
However, when hardening is carried out employing conventional methods known in the art, side effects occur. Thus it is hard to describe that sufficient effects have been obtained.
For example, in the case of the use of inorganic hardeners such as boric acid salts, and the like, when the used amount of said hardeners increases to carry out sufficient hardening to achieve the desired layer strength, the resultant layer is more brittle and tends to result in cracking at low humidity.
On the other hand, when hardeners such as epoxy based and aldehyde based or polycyanate based hardeners are employed in an amount to obtain sufficient layer strength, hardening of the hydrophilic binder itself proceeds sufficiently. However, the void ratio of ink jet recording sheets, having a void structure comprising ink absorbing layer decreases and the ink absorbing amount also tends to be decreased. Thus it has been impossible to obtain the high layer strength while maintaining a high ink absorbing amount.
The inventors of the present invention have noticed that as the ink receiving layer having a void structure is hardened, the rate of ink absorption tends to increase. Then it has been assumed that in the upper portion (the side nearer the surface) of the void layer, the hindrance of ink penetration is restricted due to the fact that the swell ability of hydrophilic binders comprising said void structure is further restricted. Namely it has been discovered that as the ink receiving layer having said void structure of an ink jet recording sheet is hardened, the ink absorbability increases and at the same time, the hydrophilicity of the layer is enhanced.
However, when hardening is carried out employing the aforementioned conventional methods known in the art, it has been found that side effects occur, and it is impossible to obtain sufficient physical properties of the resultant layer. For example, it has been found that when hardeners such as borates and the like are employed in an amount which is necessary for obtaining sufficient water resistance, the brittleness of the resultant layer is degraded, and when stored under hard circumstance at a relatively low temperature, cracking tends to occur.
Further, it has been found that when an image receiving layer forming coating composition, comprising epoxy based, aldehyde based, or polyisocyanate based hardeners is coated, due to the instability of these hardeners against water, sufficient hardening is not obtained in an amount which theoretically results in sufficient hardening. However, it has also been found that when the excessive amount of those is employed, ink is not sufficiently absorbed probably due to a decrease in the void ratio of the void layer.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an ink jet recording medium which exhibits high ink absorbability and desired water resistance without degrading layer brittleness through sufficiently hardening the
Ohbayashi Keiji
Tachibana Kimie
Tsubaki Yoshinori
Kelly Cynthia H.
Konica Corporation
Muserlian Lucas & Mercanti
Nguyen Kimberly T.
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