1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus that form a toner image and apply a varnish to the toner image, a varnish applicator that applies a varnish to a toner image, and a toner for use in the image forming apparatus.
2. Description of the Background
On the covers of various catalogs and books, images and texts are generally printed. Some of the printed covers need to be protected from water or contamination or to have appropriate gloss in accordance with their purpose of use. In such cases, the surfaces of the printed covers are processed by overprint, vinyl coating, press coating, film pasting, or the like.
Recently, on-demand printing is widely employed because it meets recent demand for a print system which can output variable information at high speed. On the other hand, protective film layers formed with varnishes become popular recently.
On-demand printing apparatuses are of two main types: electrophotographic apparatuses and inkjet apparatuses. Electrophotographic apparatuses that use toner are more widely used for the purpose of printing images.
In electrophotography, an image is formed by adhering a colored powder, what is called toner, to a recording medium. The toner is generally fixed on the recording medium by a fixing device which includes a roller, the surface of which is comprised of a material having excellent releasing property or is coated with a large amount of oil. When a large amount of oil is applied to the surface of the roller, disadvantageously, the oil is likely to contaminate the recording medium such as paper. Additionally, the fixing device is made more complicated and larger because an extra space to contain the oil is necessarily provided.
For the above reasons, there is a need for a more simplified fixing device which does not use oil (hereinafter “oilless fixing device”). Simultaneously, there is a need for a toner applicable to the oilless fixing device. In response to this need, a toner including a wax has been proposed. With respect to the protective film layer, several commercially-available varnishes are used in offset printing. However, some varnishes are incompatible with a wax included in a toner. Such varnishes do not yield sufficient results when used in combination with an electrophotographic apparatus using such a toner including a wax.
In attempting to solve the problem of incompatibility between varnish and wax, Japanese Patent Application Publication No. 2007-277547 discloses a novel varnish composition and its preparing method. The disclosed technique improves the compatibility by covering a print on which a fixing oil is applied with a water-based covering agent including no ammonia and having low static surface tension. Japanese Patent Application Publication No. H10-309876 discloses a resin layer forming device and an image forming apparatus equipped with the device. The resin layer forming device forms a silicone resin layer on a printed surface to protect it from contamination and water and to increase gloss. Japanese Patent No. 2522333 discloses a metal container having printing on its surface and a printing method for metal containers. The disclosed technique employs electrophotography that is capable of efficiently printing wide variety of printings in small amount, in combination with varnish treatment that protects a toner layer and improve gloss of the toner layer.
However, the above-described techniques limit usable types of toner and varnishes to specific combinations. Even when a varnish can be applied to a toner image, in some cases, adhesiveness between the varnish and the toner image is weak and the varnish peels off from the toner image. In such cases, the varnish no longer protects the toner image nor improves gloss of the toner.
In accordance with recent tendency that the mainstream is switching from offset printing to electrophotography that is capable of efficiently printing wide variety of printings in small amount, it is necessary that wider variety of varnishes and toners can be usable in various combinations.