1. Field of the Invention
The present invention relates to a recording medium, a substrate for a recording medium, production processes thereof, and an image forming process using the recording medium. In particular, the present invention relates to a recording medium, which can provide a clear or bright and high-quality recorded image in a surface coated part region thereof and can prevent the occurrence of a phenomenon called cockling in which a printed surface is waved by an aqueous ink, and a production process of the recording medium.
2. Related Background Art
An ink-jet recording system often used in recent years is a system in which fine droplets of an ink are flown by any one of various working principles to apply them to a recording medium such as paper, thereby making a record of images, characters and/or the like. Recording apparatus, to which this recording system is applied, are quickly spread as recording apparatus for various images in various applications including information instruments because they have features that recording can be conducted at high speed and with a low noise, multi-color images can be formed with ease, printing patterns are very flexible, and neither development nor fixing is unnecessary. Further, they begin to be widely applied to a field of recording of full-color images because images formed by a multi-color ink-jet system are comparable in quality with multi-color prints by a plate making system and photoprints by a color photographic system, and such images can be obtained at lower cost than the usual multi-color prints and photoprints when the number of copies is small.
With the enlarged utilization of the ink-jet recording system, further improvements in recording properties such as speeding up and high definition of recording, and full-coloring of images are required, so that recording apparatus and recording methods are improved. In order to meet such requirements, a wide variety of recording media have heretofore been proposed. For example, there have been proposed paper for ink-jet recording, in which a coating layer having good ink absorbency is provided on a surface of a substrate (for example, Japanese Patent Application Laid-Open No. S55-5830), and the use of amorphous silica as a pigment in an ink-receiving layer laminated on a substrate for recording medium (for example, Japanese Patent Application Laid-Open No. S55-51583).
With the diversification of uses, it has also been required to reduce the occurrence of curling or cockling of printed articles for the purpose of improving the quality of recorded images. These phenomena are both considered to be caused due to the occurrence of expansion or shrinkage and distortion on a recording medium by absorption of an ink. In the present invention, the cockling means a phenomenon that a printed surface of a recording medium is made irregular or waved. As means for avoiding this cockling phenomenon, there have heretofore been proposed the following methods.
(1) Japanese Patent Application Laid-Open Nos. H3-38376, H3-199081, H7-276786 and H8-300809 describe recording media using paper having an underwater elongation and a wetted elongation within respective specified ranges. However, since the technical ideas described in these documents are based on the premise that water is evenly given to the whole of a recording medium, they cannot cope with a case where states applied with a liquid differ with portions.
(2) Japanese Patent Application Laid-Open No. H10-46498 discloses a crosslinking treatment in which a water-proofing agent, a polymer, a size and the like are used to form a bound structure between fibers, and also discloses to the effect that the degree of floating after 10 seconds from printing is controlled to 1 mm or small. Japanese Patent Application Laid-Open No. 2002-201597 has proposed a recording medium in which cellulose fiber is shrunk by a mercerization treatment that a treatment with an alkali is conducted on the whole surface, and discloses to the effect that friction with an ink-jet recording head is avoided. Incidentally, these proposals are both those for recording media on which no ink-receiving layer is provided.
(3) The constitution that an ink-receptive layer containing a water-repellent component in Japanese Patent Application Laid-Open No. 2000-158805 and a void layer formed of a thermoplastic resin such as polyurethane in Japanese Patent Application Laid-Open No. 2002-154268 are respectively provided as intermediate layers for barrier preventing penetration of inks between an ink-receiving layer and a substrate is described. Since these intermediate layers both act as a barrier preventing penetration of inks, the quantity of inks absorbed is reduced, and an ink-absorbing speed is lowered when the quantity of inks printed is great because the inks printed do not penetrate into the substrate, so that ink overflowing and/or bleeding may be caused in some cases.
(4) Proposals for the solution, which are different from the methods in the above-described publicly known documents, include the following proposals. Namely, the proposals comprise providing an additional structure on a recording medium. A recording medium, in which ink-receptive layers are provided on both surfaces of a substrate, a recording medium, in which a back coat layer is provided on a surface opposite to an ink-receiving layer, and a recording medium, in which substrates are laminated on each other into a two-layer structure, are described in Japanese Patent Application Laid-Open Nos. H2-270588, 2001-253160 and 2002-2092, respectively.
(5) On the other hand, Japanese Patent Application Laid-Open No. 2002-211121 discloses a recording medium, in which an aqueous solution containing a cationic resin and an alumina hydrate is coated on an ink-receiving surface of a single-layer fibrous structure composed mainly of a fibrous material containing no filler and making no use of a size (non-sized). It is described that according to the structure disclosed in this document, the cationic resin and alumina hydrate can be caused to exist on the surface of the fibrous material, thereby surely trapping an anionic colorant, so that an excellent image can be formed without causing cockling and very great curling upon formation of a 100% solid-printed image.
(6) Japanese Patent Application Laid-Open No. 2001-246840 discloses a recording medium, in which an ink-receiving layer having an inorganic pigment and a binder is formed in a coating weight of 1 to 10 g/m2 on a base material composed mainly of pulp fiber. In Comparative Example 2, it is described that when an ink-receiving layer containing no binder was formed on a base material subjected to a sizing treatment, an alumina hydrate that is an inorganic pigment entered pulp fiber, and the surface of the pulp was scarcely coated with the alumina hydrate.
The present inventors have carried out an investigation on various kinds of the recording media proposed in the prior art documents mentioned above and found, on all the recording media, a phenomenon that new cockling or curling is caused when printing is conducted in an ink quantity exceeding 100% in particular. When the state thereof has been analyzed, it has been found that the number of portions undergoing cockling substantially increases, so that the cockling is conspicuous. The present inventors have also found that when a quantity of an ink applied to a recording medium is increased to 2 times or 3 times to form an image, the ink-absorbing capacity of the recording medium itself is lowered, so that ink overflowing and/or bleeding may be caused in some cases to fail to achieve good image quality.
The present inventors have paid attention to the fibrous materials of the substrates to carry out research and investigation. As a result, the following facts have been confirmed. Since the alumina hydrate and cationic resin are coated on the fibrous material by on-machine coating in Japanese Patent Application Laid-Open No. 2002-211121, the alumina hydrate is limited by the application of the cationic resin to the surface of the fibrous material and partially scattered. It has been confirmed that the cockling-inhibiting effect by the alumina hydrate is not sufficiently brought about on the recording medium disclosed in this document as described below.
In Japanese Patent Application Laid-Open No. 2001-246840, the substrate containing pulp and a filler and size-pressed is used. Accordingly, when the alumina hydrate is applied without using a binder like Comparative Example 2 of this document, the alumina hydrate cannot be applied to the surface of the substrate fiber, but only fills in voids formed by the pulp. It has been thus confirmed that this constitution does not bring about the cockling-inhibiting effect as described below.
As described above, it has been confirmed that when images are formed by printers for conducting high-speed printing in recent years, or the like, even the various kinds of recording media proposed in the prior art documents are not always satisfied from the viewpoints of image quality, curling, cockling, conveyability and the like.
It is a principal object of the present invention to solve the novel problems on the basis of such new findings.
The present inventors have sought a phenomenon by deformation of fiber, such as swelling and elongation, that is a cockling producing mechanism and considered that it is caused by excessive absorption of water by the fiber and a high degree of freedom of displacement within an allowable space. Accordingly, the present inventors have sought means that a water-holding capacity of the fiber itself can be diffused so as to be optimized, and at the same time the degree of freedom of displacement can also be controlled, thus leading to completion of the present invention.
It is thus a first object of the present invention to provide a recording medium having an ink-receiving layer that can solve the above-described new problem caused by conducting printing in an ink quantity exceeding 100%, permits forming an image high in density and bright in color tone and can settle the cause of the occurrence of new curling or cockling, and a production process of the recording medium.
A second object of the present invention is to provide a substrate (including a case where the substrate itself functions as an ink-receiving layer) for a recording medium for preventing ink overflowing even in an ink quantity exceeding 100%, permitting forming an image high in density and bright in color tone and settling the cause of the occurrence of new curling or cockling, and a production process of the substrate for a recording medium.
The above objects can be achieved by the present invention described below.