JPH05116390A - Platen roller for heat transfer type recorder - Google Patents

Abstract

PURPOSE:To prevent extension of a circumferential length at the time of bringing a thermal head into pressure contact, and to prevent degrading in quality of a picture, particularly generation of color deviation, by forming a thin layer made of at least resin having a high elastic modulus on a peripheral surface of an elastic layer of a platen roller. CONSTITUTION:A platen roller 10 comprises a shaft 10a made of metal, etc., an elastic layer 10b applied coaxially on the outer periphery of the shaft 10a, a thin layer (a high elastic modulus resin layer) 10c made of resin having a high longitudinal elastic modulus and covering the outer periphery of the layer 10b, and a thin layer (a high frictional layer) 10d made of a material having a high frictional coefficient such as rubber, etc., and applied on the outer periphery of the layer 10c. The layer 10c is formed by laminating resin having a high longitudinal elastic modulus. The higher the modulus is, the higher an effect of preventing an elongation of a circumferential length of the layer 10b becomes, but the layer 10b is scarcely deformed, and hence its thickness is reduced thereby making a pressure uniform at the time of bringing into pressure contact. Since the elastic material such as rubber, etc., of the layer 10d is sufficiently reduced in thickness the deformation at the time of bringing into pressure contact does not become a problem and can be ignored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a thermal transfer recording apparatus, and more particularly to an improvement in a platen roller which receives a pressure from a thermal head via an ink sheet and recording paper.

[0002]

2. Description of the Related Art In a thermal transfer recording apparatus, a thermal head having a large number of minute heating elements is pressed against the surface of a recording sheet through an ink sheet, and the heating elements are selectively heated according to a print signal. The image is transferred onto a recording paper by melting or sublimating the ink on the ink sheet.
In order to press the thermal head against the ink sheet and recording paper with a necessary and sufficient pressure to perform good printing, place a platen roller on the opposite side of the thermal head sandwiching the ink sheet and recording paper, and It is necessary to pinch the ink sheet and the recording paper with the platen roller.

FIG. 2 (a) is a schematic structural explanatory view of a conventional thermal transfer recording apparatus, and FIG. 2 (b) is a sectional view of a platen roller, in which an ink sheet 3 and an image receiving sheet 4 (recording sheet) are recorded by a platen roller 1 and a thermal head 2. The paper is pressed and the minute heating element at the tip of the thermal head 2 generates heat to record an image on the image receiving sheet 4. The image receiving sheet 4 is conveyed by the frictional force between the contact surfaces of the two as the platen roller rotates. As shown in FIG. 2B, the platen roller 1 has a structure in which an elastic layer 1b made of rubber or the like having a thickness of about 1 mm is integrated with the outer circumference of a shaft 1a made of metal or the like.

The platen roller 1 having such a structure
The following two points are required for the function. That is, 1. 1. The thermal head 2 presses the ink sheet 3 and the image receiving sheet 4 with a pressure as uniform as possible over the entire pressure contact surface of the outer peripheral surface (a narrow strip-shaped pressure contact surface extending in the axial direction). That is, the image receiving sheet 4 is conveyed at a constant speed.

However, the conventional platen roller 1 shown in FIG. 2 (b) cannot sufficiently exhibit the second function. That is, FIG. 3 is a view showing a deformed state of the elastic layer 1b of the platen roller due to the thermal head 2 being in pressure contact, and the ink sheet and the image receiving sheet are omitted for simplification of description. Platen roller 1 when not pressurized
Maintains a circular cross-sectional shape as shown by the broken line,
When the thermal head 2 is pressed, it elastically deforms as shown by the solid line. A general rubber material forming the elastic layer 1b has a Poisson's ratio of about 0.5, and its volume hardly changes even if it is deformed. Therefore, the plater roller expands laterally by the amount of compression. Therefore, the point AB before pressurization
The distance between the points A ′ and B ′ is expanded to the length between points A ′ and B ′ after the pressurizing deformation, and the length between points A and B is less than the length between points A and B <point A ′.
-The length between B'is. The expansion of the length in the lateral direction is not necessarily uniform in each part of the pressure contact region extending in the axial direction of the platen roller.

However, when the platen roller 1 makes one revolution in the direction of the arrow, the time required to move from the point A to the point B of the elastic layer 1b on the peripheral surface when no pressure is applied and the point A'when pressure is applied.
The time required to move from point to point B'is constant. That is, the peripheral speed of the portion A′-B ′, which is pressed by the thermal head 2 and expanded laterally, increases as the amount of compressive deformation increases. Since the conveying speed of the image receiving sheet 4 is determined by the peripheral speed of the platen roller 1 at the thermal head pressure contact portion, the image receiving sheet increases as the pressure contact load with the thermal head 2 increases as shown in FIG. The conveyance speed of No. 4 will increase. Therefore, when the pressure contact load of the thermal head 2 varies in the axial direction, the image receiving sheet 4 is obliquely fed.

Similarly, the conveying speed of the image receiving sheet 4 also changes depending on the load acting on the image receiving sheet 4, and the larger the load acting in the opposite direction to the conveying direction of the image receiving sheet 4, the lower the conveying speed. .. FIG. 5 is a diagram showing a change in the transport speed of the image receiving sheet when the load acting in the transport direction has a negative value. The load acting in the transport direction has a negative value, and the load is thermal energy given from the thermal head. Since it changes depending on the amount, when high density recording is performed,
The conveyance speed of the image receiving sheet is different from that when low density recording is performed, and color misregistration occurs.

Japanese Patent Laid-Open No. 2-29361 discloses an example in which a hard layer is provided on the surface of an elastic body of a platen roller and the surface is made into a flat connection surface. However, an elastic body made of rubber or the like is used. Due to the deformation as described above, problems such as an increase in circumferential length still occur. Further, since the outer periphery of the platen roller is slippery, a recording paper conveyance failure is likely to occur.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and the conveyance speed of the image receiving sheet is changed due to the variation of the pressure contact load from the thermal head, the load acting on the image receiving sheet, etc. It is an object of the present invention to provide a platen roller for a thermal transfer recording apparatus that can prevent deterioration, particularly color misregistration.

[0010]

To achieve the above object, the present invention is a thermal transfer recording apparatus for carrying out image recording by conveying an image receiving sheet by a frictional force acting between the platen roller and the image receiving sheet, and an elastic layer of the platen roller. At least a thin layer made of a resin having a high elastic coefficient is formed on the peripheral surface to prevent the circumferential length from being extended during the pressure contact of the thermal head. A high friction layer, which is a thin layer made of a material having a friction coefficient of 1 or more, is formed, and further, a thin layer having an adhesive property is formed on the outer peripheral surface of the thin layer made of the resin having the high elastic coefficient. I am trying.

The present invention will be described in detail below with reference to the illustrated embodiments.

FIG. 1 is a sectional view showing the construction of the platen roller of the present invention, and FIG. 2 (a) is also referred to for the overall view of the recording section including this platen roller.

The platen roller 10 has a shaft 10a made of metal or the like, an elastic layer 10b coaxially covering the outer circumference of the shaft 10a with a thickness of several mm, and a longitudinal elastic modulus covering the outer circumference of the elastic layer 10b. And a thin layer (high-friction resin layer) 10c made of a material having a high coefficient of friction such as rubber on the outer periphery of the high-elasticity resin layer 10c.

The high elastic resin layer 10c is made of a resin such as PET or aramid and has a longitudinal elastic modulus (tensile) of several tens to several hundreds of kg.
/ Mm @ 2 is laminated to a thickness of about 10 to 100 .mu.m, and the high elastic resin layer 10c prevents the elastic layer 1b from being stretched by the pressure contact of the thermal head. The higher the longitudinal elastic modulus is, the higher the effect of preventing the elongation of the circumferential length becomes, but the deformation becomes difficult, but the wall thickness is made thin so that the pressure at the time of pressure contact is made uniform.

The high-friction layer 10d is formed by laminating an elastic material such as rubber so as to have a thickness of several tens of μm and is laminated.
It is necessary that the coefficient of friction between and is at least 1. Since the high-friction layer 10d has a sufficiently thin wall thickness, deformation during pressure contact does not pose a problem and can be ignored. In addition, as a material forming the high-elasticity resin layer 10c,
The high-friction layer 10d is not necessarily required if a material having a friction coefficient with the image receiving sheet 4 of 1 or more is used. Further, instead of the high friction layer 10d, a thin layer made of a substance having an adhesive property such as a silicone rubber adhesive may be formed.

As described above, in the present invention, the thin layer (high elastic resin layer) 10c made of resin having a high elastic coefficient is uniformly coated on the peripheral surface of the elastic layer 10b of the platen roller 1, so that the thermal head Preventing the increase of the conveying speed of the image receiving sheet due to the extension of the circumference of the elastic layer 10b due to the pressure contact, the variation of the pressure contact load in the pressure contact area in the axial direction of the platen roller, and the difference in the load such as the heating temperature, It is possible to prevent deterioration of image quality such as color shift. When rubber is arranged on the outer peripheral surface of the roller as in the prior art described in the above publication, even if it is hard rubber, the order of the longitudinal elastic modulus is significantly different from that of the resin of the present invention, so the elongation of the circumferential length is prevented. There is no effect to do.

Further, a thin layer (high friction layer) made of a material having a coefficient of friction with the image receiving sheet of 1 or more is formed on the outer peripheral surface of the high elastic resin layer 10c.
Since 10d is formed, it is possible to prevent the occurrence of slippage between the image receiving sheet and the platen roller, resulting in poor conveyance.

Further, if a thin layer made of an adhesive material is formed on the outer peripheral surface of the high-elasticity resin layer 10c, slippage between the image receiving sheet and the platen roller 1 can be effectively prevented.

[0019]

As described above, according to the present invention, the conveyance speed of the image receiving sheet is changed due to the variation of the pressure contact load from the thermal head, the load acting on the image receiving sheet, etc., and as a result, the image quality is deteriorated. It is possible to prevent color shift or the like from occurring.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a platen roller according to an embodiment of the present invention.

FIGS. 2A and 2B are a schematic configuration explanatory view of a printing unit of a conventional thermal transfer recording apparatus and a sectional view of a platen roller.

FIG. 3 is a cross-sectional view illustrating a problem of a conventional platen roller.

FIG. 4 is a diagram showing a relationship between a pressure contact load of a thermal head and an image receiving sheet speed.

FIG. 5 is a diagram showing a change in image receiving sheet speed when a negative load is applied.

[Explanation of symbols]

1 ... Platen roller, 2 ... Thermal head, 3
... Ink sheet, 4 ... Image receiving sheet 4 (recording paper), 10 ... Platen roller, 10a ... Shaft, 1
0b ... Elastic layer, 10c ... Thin layer made of resin having high longitudinal elastic coefficient (high elastic resin layer), 10d ... Thin layer made of material having high friction coefficient (high friction layer)

Claims (3)

[Claims] 1. A thermal transfer recording apparatus for carrying out image recording by conveying an image receiving sheet by a frictional force acting between the platen roller and the image receiving sheet, wherein a resin having at least a high elastic modulus is formed on a peripheral surface of an elastic layer of the platen roller. A platen roller for a thermal transfer recording apparatus, characterized in that a thin layer is formed to prevent the circumferential length from expanding when the thermal head is pressed. 2. A high-friction layer, which is a thin layer made of a material having a coefficient of friction with the image-receiving sheet of 1 or more, is formed on an outer peripheral surface of the thin layer made of a resin having a high elastic coefficient. The platen roller of the thermal transfer recording apparatus according to 1. 3. A platen roller for a thermal transfer recording apparatus, wherein an adhesive thin layer is formed on an outer peripheral surface of the thin layer made of a resin having a high elastic coefficient.