1. Field of the Invention
The present invention relates to a printing method and a printer with a platen. More particularly, the present invention relates to a printing method and a printer with a platen, in which a thermal head can contact recording material in a reliably stable manner.
2. Description Related to the Prior Art
A thermal printer with type of a direct thermal recording is constituted by at least one platen roller for supporting thermosensitive recording material, and a thermal head including an array of plural heating elements. The recording material includes at least one thermosensitive coloring layer. The thermal head and the recording material are transported in a manner relative to one another, while the thermal head applies heat to the recording material to develop color on the recording material one line after another. There are various types of platen devices including the platen roller, which is constituted by a rubber roller member, and has a shape of a rod with a diameter of several centimeters.
According to the prior art, the platen roller is constituted by a rubber member, and becomes deformed according to a convexly curved surface of the heating element array of the thermal head. There is an area with high contact pressure in the vicinity of the central top of the heating element array of the thermal head. However areas distant from the central top of the heating element array have only small contact pressure. A problem exists in that an amount of conducted heat is likely to change due to changes in the contacting pressure. Coloring density is also changed due to changes in the amount of the conduced heat, to create irregularities in the density or color.
It is conceivable to increase hardness of the rubber material for the purpose of increasing pressure of the contact between the recording material and the thermal head. However another problem arises in that a depth of sinking of the heating element array into the recording material is decreased. The area of the contact is decreased, and also becomes subjected to the influence of changes in the pressure due to eccentricity of the platen roller and irregularities on its surface.
In view of the foregoing problems, an object of the present invention is to provide a printing method and a printer with a platen, in which a thermal head can contact recording material in a reliably stable manner.
In order to achieve the above and other objects and advantages of this invention, a printer includes a recording head for image recording to recording material in application of pressure to the recording material. A platen device supports the recording material during the pressure application of the recording head to the recording material, the platen device including first, second and third plates serially laid on one another and secured to one another, the first plate being rigid, the second plate being resilient, and the third plate having higher rigidity than the second plate, having a smooth surface, and contacting the recording material.
In a preferred embodiment, the printer is a thermal printer, the recording head is a thermal head for thermal recording by applying heat energy to the recording material.
Furthermore, the first plate is produced from metal, the second plate is produced from rubber, and the third plate is produced from resin.
The resin is polyethylene terephthalate.
Furthermore, a carriage transports the thermal head and the platen device relative to another thereof, wherein the thermal head affects the thermal recording during transportation of the carriage.
The thermal head includes one array of heating elements arranged in a main scan direction, and the carriage relatively transports the thermal head and the platen device in a sub scan direction crosswise to the main scan direction.
The carriage transports the thermal head.
In another preferred embodiment, the carriage transports the platen device.
Furthermore, there is a head support unit on which the thermal head is mounted. At least one guiding roller is secured to the head support unit, rotatable about an axis extending in the main scan direction, pressed against the recording material with the thermal head, for stabilizing orientation of the thermal head transported relative to the recording material.
At least one guiding roller comprises first and second guiding rollers disposed upstream and downstream from the thermal head with reference to the sub scan direction.
In another preferred embodiment, at least one guiding roller comprises first and second guiding rollers arranged in the main scan direction so that the thermal head is disposed therebetween.
The second plate is 0.5-10 mm thick, and the third plate is 0.05-0.5 mm thick.