Color thermal printer

Details Color thermal printer Color thermal printer

2001-03-05

2003-06-24

Nguyen, Lamson (Department: 2861)

Incremental printing of symbolic information

Thermal marking apparatus or processes

Record receiver driving means

Reexamination Certificate

active

06583804

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color thermal printer for recording a full-color image by use of a plurality of thermal heads. More particularly, the present invention relates to a color thermal printer capable of increasing recording speed, decreasing non-recording area and density unevenness caused by deviations in feeding speed.
2. Background Arts
There are various color thermal printers, some examples of which are a direct thermal recording type and a thermal transfer printing type. Any of the types incorporates a thermal head in which a great number of heating elements are arranged in line. A thermosensitive recording sheet (hereinafter referred to as recording sheet) for use in a direct thermal recording type includes cyan, magenta and yellow thermosensitive coloring layers formed on a support in this order listed. In recording, the heating elements are pressed onto the recording sheet and is driven to record respective color image to respective coloring layers, to produce a full-color image. In the thermal transfer type, a color ink sheet of great length is used, in which yellow, magenta and cyan ink areas are formed in cyclic fashion. The ink is thermally transferred to a recording sheet, to produce a full-color image.
In the color thermal printer, there are plural recording types: a three-pass type in which a recording sheet is passed three times under one thermal head; and a one-pass type in which a recording sheet is passed one time under plural thermal heads. The one-pass type has advantages in shorter time required for printing the same image than the three-pass type, so the one-pass type is used to a color thermal printer for business use that is required to print many sheets continuously.
FIG. 10
illustrates a conventional color thermal printer of the one-pass type. A continuous recording sheet
2
is set in the feeder of the printer as a recording sheet roll
3
. A feeding roller
4
draws the recording sheet
2
from the recording sheet roll
3
and feeds it toward a feeding passage. There are a plurality of conveyor roller sets
5
in the feeding passage. Between adjacent conveyor roller sets
5
, yellow, magenta and cyan thermal heads
6
to
8
are provided to record respective color images to the yellow, magenta and cyan coloring layers. Below the thermal heads
6
to
8
, three platen rollers
9
to
11
are provided to support the thermal heads
6
to
8
. Two fixation lamps
12
and
13
are provided for fixing the yellow and magenta coloring layers after thermal recording.
The conveyor roller set
5
includes a capstan roller
15
and a pinch roller
16
. The capstan roller
15
is rotated by a conveyor motor. The pinch roller
16
is pressed to the capstan roller
15
, and rotates subsidiary to the capstan roller
15
. The pinch roller
16
is made of a soft and high-frictional material, like a rubber or the like, so as to ensure to feed the recording sheet
2
without slipping. Also, the platen rollers
9
to
11
are made of a soft and high-frictional material like a rubber, so as to ensure to nip the recording sheet
2
. Thus, the capstan rollers
15
and the thermal heads
6
to
8
are slightly inserted into the deformed pinch rollers
16
and the platen rollers
9
to
11
respectively.
In the one-pass type, during the recording of the yellow image to the yellow recording layer, the magenta recording thermal head
7
comes in contact with, and presses, the recording sheet
2
. Since the recording sheet
2
receives the pressing force from the magenta recording thermal head
7
, a load to the recording sheet
2
is rapidly increased. Thus, the feeding speed of the recording sheet
2
decreases, so that density unevenness is likely to occur.
In order to solve the problem, U.S. Pat. No. 5,818,494 (corresponding to JPA 8-67020) discloses a color thermal printer to decrease the load to the recording sheet by changing the pressing force of the thermal head gradually in pressing and releasing the recording sheet. In addition, JPA 8-174876 discloses a color thermal printer to keep the load constant by pressing and releasing three thermal heads simultaneously.
In the conventional one-pass type, conveyor roller set is provided between two adjacent thermal heads. Thus, long feeding passage required for placing plural conveyor roller sets, makes recoding time longer. In the thermal printer of U.S. Pat. No. 5,818,494, since the load to the recording sheet
2
is increased by increasing the pressing force gradually, density unevenness is likely to occur.
In the thermal printer of JPA 8-174186, the cyan thermal head is provided in the position furthest from the recording sheet roll
3
, and the yellow thermal head is the nearest. Since print operation begins when the front end of the recording sheet reaches the cyan thermal head, a leader portion of the recording sheet
2
having a length between the yellow and cyan thermal heads is of no use.
Moreover, since surfaces of the pinch rollers
16
are deformed by the capstan rollers
15
, the recording sheet
2
is waved near the conveyor roller sets
5
. Since the platen rollers
9
to
11
are also deformed, the recording sheet
2
has waved areas. Since these waved areas work as obstacles for feeding, feeding speed changes largely when the load to the recording sheet
2
increases. In addition, it requires much time before the feeding speed comes up to a certain value.
SUMMARY OF THE INVENTION
An object of the invention is to provide a color thermal printer and a color thermal recording method for increasing recording time and decreasing non-recording area.
Another object of the invention is to decrease density unevenness caused by deviation in feeding speed.
To achieve the above objects, a color thermal printer of the present invention includes a feeding passage for guiding a recording material from a roll toward an outside of the printer, feeding means for feeding the recording material in an advancing direction and a recording direction along the feeding passage, a plurality of thermal heads for recording the image to the recording area, a plurality of platens that are disposed opposite to respective thermal heads, and a elastic members for covering surfaces of respective platens. The elastic members are deformed by pressing force of respective thermal heads, so the feeding passage is bent toward the thermal head at positions where the thermal heads presses the platens, so as to form a V-shape.
The feeding means is disposed at a position upstream of the thermal heads and comprised of a capstan roller and a pinch roller for nipping and feeding the recording material. The pinch roller is covered with a elastic material which is deformed by pressing force of said capstan roller, so the feeding passage is bent toward the capstan roller at a position where the capstan roller presses the pinch roller, so as to form a V-shape. By bending the feeding passage, the recording material is kept from being waved, so it is possible to reduce deviation in feeding speed even when the load to the recording material is changed largely.
In the embodiment, the thermal heads includes cyan, magenta and yellow thermal heads arranged in this order listed. When a print command is produced, the recording material is fed in the advancing direction. When the recording material reaches a print start position where a rear end of the recording area passes the yellow thermal heads, the recording material is stopped and the thermal heads press the recording material simultaneously. Afterwards, the recording material is fed back to the recording direction, and the thermal heads are driven to record respective color image. When respective color image is recorded, each thermal head is moved away from the recording material gradually to decrease pressing force gradually, so that deviation in load to the recording material is decreased.


REFERENCES:
patent: 4358776 (1982-11-01), Mitsui
patent: 4734704 (1988-03-01), Mizutani et al.
patent: 4780729 (1988-10-01), Murakami et al.
patent: 499

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