Stock material or miscellaneous articles – Ink jet stock for printing – Particles present in ink receptive layer
Reexamination Certificate
2001-02-28
2003-10-14
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Ink jet stock for printing
Particles present in ink receptive layer
C252S184000
Reexamination Certificate
active
06632489
ABSTRACT:
TECHNICAL FIELD
In one aspect, the present invention relates to moniliform (Rosary shaped) silica sol and to a method for producing it.
And in a second aspect, the present invention relates to an ink jet recording medium on which recording is performed with a water-base ink and more particularly to a coating composition for an ink receiving layer containing moniliform silica sol and having high ink absorption and to an ink jet recording medium having such an ink receiving layer.
The moniliform silica sol has a feature in the form of colloidal silica particles thereof and exhibits excellent film formation and porosity when dried on the surface of a solid article and is used in various fields as microfiller for various coating agents, a binding agent, a modifier, a carrier for catalysts and the like.
BACKGROUND ART
A silica sol has a general property that it finally gels from its low viscosity state via its high viscosity state. Accordingly, for silica sol products having the same SiO
2
content, ones having a lower viscosity are evaluated to have a higher stability than others having a higher viscosity. In addition, silica sol containing colloidal silica particles with a more spherical shape has been known to have a lower viscosity. Under this situation, there have heretofore been various proposals for efficiently preparing spherical colloidal silica sols, but there is no proposal up to the present for improving the characteristic of a silica sol by controlling the shape of the colloidal silica particles as dispersed in the silica sol to be non-spherical.
Regarding the shape of the conventional colloidal silica particles, U.S. Pat. No. 2,680,721 mentions three typical types of particles in the drawings as attached thereto. The first is a spherical one as mentioned above, which is shown in
FIG. 1
thereof; the second is a non-spherical one having a ratio of the major axis to the minor axis of almost from
2
to
3
, which is shown in
FIG. 2
, bottom view thereof; and the third is an-amorphous one, which is shown in
FIG. 3
, bottom view thereof. The random-shaped particles of the third type are ones resulting from growth of the fragments formed by cleavage of the chain of a three-dimensional network structure derived from chain-like linkage of smaller silica particles, as so explained in the said U.S. Pat. No. 2,680,721. When attention is-paid to one particle of such type, it is noted that it has a non-spherical shape but the shape is not controlled.
The above-mentioned U.S. Pat. No.2,680,721 has disclosed a method of forming a silica sol comprising spherical colloidal silica particles where a monovalent base is added to spherical silica sol having a particle diameter of 5 nm or more so that the pH value of the sol may be within the range of from 7 to 10.5 and the sol is heated at 160 to 300° C. in the absence of electrolytes.
U.S. Pat. No.2,900,348 has disclosed a method of forming a silica sol where a silica gel formed by adding an acid to an aqueous solution of water glass is washed with water, an alkali is added to the silica gel so that the silica gel may have a pH value of from 9 to 9.5, and the silica gel is then heated at 95 to 100° C. The said method is a so-called peptization method, and the colloidal silica particles of the silica sol prepared by the method has a shape of the above-mentioned second or third type.
U.S. Pat. No. 5,221,497 (corresponding Japanese application: JP-A 1-317115) discloses a method for producing elongated-shaped silica sol containing elongate shaped particles by adding water-soluble calcium salt, magnesium salt or mixtures thereof to an aqueous colloidal solution of active silicic acid or acidic silica sol having a mean particle diameter of 3 to 30 nm in an amount of 0.15 to 1.00 wt. % based on CaO, MgO or both to silica, then adding an alkali metal hydroxide so that the molar ratio of SiO
2
/M
2
O (M: alkali metal atom) becomes 20 to 300, and heating the obtained liquid at 60 to 300° C. for 0.5 to 40 hours. The colloidal silica particles obtained by this method are elongate shaped silica particles that have elongations of a uniform thickness within the range of 5 to 40 nm extending in only one plane.
The ink jet recording process is a process in which ink droplets ejected at high speeds from nozzles are applied onto a recording material to record images/characters. This process is used in various fields such as, various printers, facsimile devices, and computer terminals since it is relatively fast, less noisy and easy full-colorization in recording treatment.
In this process, the ink used contains a large amount of solvent so that a large amount of ink must be used in order to obtain high recording density. In addition, since ink droplets are continuously ejected, there tends to occur a drawback that first ink droplets have not been completely absorbed when next droplets are ejected and the both ink droplets fuse, causing conjugation of ink dots. Therefore, the recording paper and sheet used in this ink jet recording process is required to give printing dots that are high in density, light in hue and sharp and to absorb ink at high rates to cause no blurring.
Paper can absorb ink by itself and hence it is possible to make recording on it as it is by ink jet process. However, to obtain high recording density, it is necessary to provide an ink receiving layer by coating on it. Moreover, to make recording on a sheet that does not absorb ink, such as synthetic paper or PET (polyethylene terephthalate) film used in OHP by an ink jet process, it is indispensable to provide an ink receiving layer by coating on it.
Hitherto, it has been attempted to improve ink absorbability, absorption speed, coloring properties, high density printing, and the like by provision of an ink receiving layer on paper or a sheet by coating thereon a coating agent obtained by using porous pigment, silica sol, alumina sol and the like singly or in admixture and adding an aqueous resin binder thereto and drying.
For example, JP-A 61-19389 proposes an ink receiving layer that comprises anionic spherical colloidal silica and polyvinyl alcohol, and JP-A 60-219084 proposes an ink receiving layer that comprises cationic spherical colloidal silica, precipitated silica powder and an aqueous resin such as polyvinyl alcohol.
JP-A 4-201286 describes an ink receiving layer composition composed mainly of a water-dispersible polymer, colloidal silica linked in a moniliform and/or branched chain forming, and other particulate. JP-A 6-92011 describes an ink receiving layer composition composed of a cation-modified non-spherical colloidal silica and polyvinyl alcohol. JP-A 60-204390 proposes a method of using silica obtained by a gas phase process having a primary particle diameter of 10 to 30 nm after-secondary coagulation thereof. JP-A 7-276789 also proposes an ink receiving layer of a three-dimensional network structure having a porosity of 50 to 80% formed from silica fine particulate having a mean primary particle diameter of 10 nm or less and a water-soluble resin. Further, JP-A 2-276671 proposes an ink receiving layer that comprises a layer composed of porous alumina hydrate having provided thereon a layer of porous fine particulate silica.
Various methods described above generally form vacant spaces in the film of a receiving layer and have ink absorbed therein. At the same time, as a binder itself used for forming the receiving layer, those of the type in which ink is absorbed and held by swelling action are used widely. That is, the ink receiving layer is formed by appropriately mixing the filler having large vacant space and the binder that absorbs ink.
In the above example, the conventional colloidal silica has the drawbacks that the amount of vacant space is too small to absorb ink sufficiently and in addition, making the film thickness larger will lead to the occurrence of cracks in the film or a decrease in the strength of the film.
Where silica powder is used, the amount of ink absorption is sufficiently large. However, it has disadvantages that silica powder itself has
Ema Kiyomi
Kashima Yoshiyuki
Ohmori Yutaka
Watanabe Yoshitane
Grendzynski Michael E.
Hess Bruce H.
Nissan Chemical Industries Ltd.
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