EP0978386B1 - Thermal transfer printer - Google Patents

Description

The invention relates to a thermal transfer printing device for a franking and / or addressing machine.
In thermal transfer printing, the print carrier on the side of the counter roll and an ink ribbon on the side of the thermal print head are usually guided between a thermal print head and a counter roller arranged opposite it, the print head having a correspondingly large force on the ink ribbon and this must again rest on the print carrier, to transfer the melted ink particles from the ink ribbon to the print carrier.
The dye can be bound on the ink ribbon in a wax layer or more recently in a layer made of polyimide.
An office printer based on the thermal transfer printing principle works with constant pressure conditions, such as the same pressure force for the thermal print head, single sheets with prescribed paper type, in particular paper thickness and constant paper guidance.

In contrast, franking and / or addressing machines often change the nature of the letters, in particular their thickness and rigidity due to different fillings and the paper quality of the envelopes.
The pressure conditions become particularly critical when processing airmail, since the envelopes used are often very soft and delicate. A gentle operation would be possible by reducing the pressure force, but the print quality would then deteriorate accordingly. On the contrary, in the case of the so-called soft letters, the contact pressure even has to be increased compared to the normal letters in order to achieve the same print quality. However, higher contact pressures result in greater wear on the thermal print head and consequently in a correspondingly shorter service life and can also lead to damage to the letters.

It is a thermal printer, compare EP 0 787 592 A1, in which the letters are guided lying flat along the broad side of a thermal print head. The heating elements are arranged in the middle of the plate-shaped printhead in a row transversely to the transport direction of the letter, which is pressed together with the ink ribbon against the heating elements by means of a spring-mounted roller. The broad side is much larger in relation to the area with the heating elements, so that the ribbon and letter can be held against each other even longer after printing.
This lettering is gentle on paper due to the large area, but the color particles are more difficult to separate from the ribbon. Compensation is only possible through a longer thermal exposure time, which in turn means a lower transport speed. Due to the larger contact area, a larger contact pressure is also required, which in turn causes the thermal print head to wear out more quickly.

The situation is similar with another franking machine, see EP 0 724 234 A2, in which the heating element series is more in one End of the plate-shaped thermal print head is moved. The common one Away from ribbon and letter after thermal exposure is still too long because the ribbon is only through a subsequent deflection roller is guided away from the letter.

A thermal transfer printing device is also known, see EP 0 434 340 B1, in which the heating elements on one edge of a Thermal print head are attached and the same only with this edge in the direction of a counter roller. The ribbon is placed over one of the Edge downstream roller swung away from the letter. Here too the ink ribbon stays too long on the letter. in addition comes through that with a small radius of curvature Edge of the thermal print head the letter is so mechanically stressed will that for envelopes made of thin paper and with multiple layers softer filling folds up to damage can occur. This also has a correspondingly poorer print quality Episode.

Finally, a thermal printer is also known, see EP 0 329 478, in which the heating elements are attached directly to the narrow end edge of a flat thermal printing head and the ink ribbon is led away from the printing medium immediately after the heating element print bar. In this way, favorable conditions are created with regard to the detachment of ink particles, but use for multi-layer print carriers, such as soft letters, is associated with the risk of wrinkles.
This thermal print head represents the so-called "corner edge type", while the two solutions described at the beginning correspond to the so-called "flat type".

The purpose of the invention is to improve the functional properties and an enlargement of the area of application.

The invention has for its object a device of the type mentioned at the outset, with which regardless of the Condition of the letters and at high transport speeds same good print quality is achieved. In addition, the Wear of the thermal print head can be kept as low as possible.

According to the invention, this object is achieved according to the main claim. Further advantageous features of the invention can be found in the subclaims.
The combination of a commercially available thermal print head of the corner edge type with the shell designed according to the invention enables, contrary to expectations, the use of such a thermal print head and the use of its advantages - good color particle detachment and lower pressure force - for franking and / or addressing machines.
The arrangement of the shell on the underside of the thermal print head and its extension right up to the print bar ensures gentle pre-smoothing of the letters without the pressure force between the thermal print head and counter roller having to be increased for good print quality. Due to the lower pressure force, the thermal print head itself is spared, thereby extending its service life.

Fig. 1

Eine perspektivische Ansicht einer erfindungsgemäßen Thermotransfer-Druckvorrichtung von vorn rechts,

Fig. 2

eine perspektivische Ansicht eines Thermodruckkopfes mit einer Schale an der Unterseite mit Detail von unten rechts,

Fig. 3

einen Längsschnitt durch die Vorrichtung nach Fig. 1, teilweise im Detail.

The invention is explained in more detail below using the exemplary embodiment.
Show it:

Fig. 1

A perspective view of a thermal transfer printing device according to the invention from the front right,

Fig. 2

a perspective view of a thermal print head with a shell on the underside with detail from the bottom right,

Fig. 3

a longitudinal section through the device of FIG. 1, partially in detail.

The illustration is for simplification and easier understanding partially carried out schematically.

1, a letter A is arranged between an ink ribbon 4 and a counter roller 3. A thermal print head 1 and a shell 2 located on the underside thereof lie against the ink ribbon 4.
The thermal print head 1 is of the corner-edge type and only touches the ink ribbon 4 with its edge 12, to which a printing strip 11 comprising individual heating elements 111 is attached, see also FIG. 2.
The tray 2 touches the ink ribbon 4 with its bottom surface 21 only in an area that is adjacent to the edge 12 or pressure bar 11. The shell 2 extends on the two outer edges to just before the edge 12 and is provided with rounded corners 212.

At least in the area in contact with the ink ribbon 4, the shell 2 and the thermal print head 1 are made wider than the ink ribbon 4. The letter A is gently smoothed due to the rounded edges of the tray 2.
The shell 2 expediently consists of a rustproof metal, the bottom surface 21 being smoothed in the sliding area of the ink ribbon 4 or the letter A. A version with a plastic, acetal copolymer or with a Teflon-coated metal is also possible.
The ribbon 4 is guided in front of the tray 2 around a deflection roller 5 so that the lower edge of the deflection roller 5, bottom surface 21 and pressure bar 11 lie in one plane, see also FIG. 3. The ink ribbon 4 is in a conventional ribbon cassette, not shown stored with a supply reel for fresh and a take-up reel for used ribbon. From the unwinding spool, the ink ribbon 4 passes around the deflection roller 5 along the bottom surface 21 to the edge 12 with the pressure bar 11, around the latter to the winding spool in the direction of the arrow.
The counter roller 3 is axially parallel under the edge 12. Both are adjustable relative to one another under pressure force in accordance with the pressure required for the heat effect on the ink ribbon 4 in order to achieve a reliable transfer of the color particles onto the letter. Deflection roller 5 and counter roller 3 are rotated according to the direction of the arrow shown. In the case of the counter roller 3, an elastic covering 31 with a good coefficient of friction is applied to a solid base body 32, which in turn surrounds an axis 33.

2, the shell 2 is docked onto the underside 13 of the thermal print head 1 largely with the same contour.
The pressure bar 11 consists of equidistant heating elements 111 attached to the edge 11, as can be clearly seen in the magnifying glass view. Depending on the control pattern, the colored elements on the ink ribbon 4 are partially dissolved with the heating elements 111 and then the colored particles are transferred to the letter A by means of adhesion.

In Fig. 3 it can be seen how the shell 2 by means of a single screw connection 23 attached to the thermal print head 1 and with the rounded Edge 211 via an insulation layer 22 on the underside 13 the same is supported near the edge 12. The heating elements 111 include the edge 12 in the form of the pressure bar 11.

Reference symbols used

1

Thermal printhead

11

print bar

111

Heater / e

12

Edge with the pressure bar 11

13

Bottom of the thermal print head 1

2

Bowl

21

Bottom surface of the shell 2 in the pressure bar area

211

Edge of the shell 2 in the pressure bar area

212

Corners of the shell 2 in the area of the edge 12

22

insulation layer

23

Screw connection to the thermal print head 1

3

counter-roller

31

Counter roller coating 3

32

Base body of the counter roller

33

Counter roller axis 3

4

ribbon

5

idler pulley

A

letter

Claims (7)

1. A thermal transfer printing device for franking and/or addressing machines having the following characteristics:

   there is provided a thermal print head (1) of the Comer-Edge type the heating elements (111) of which form a print bar (11) at an edge (12) that is closest faced with a counter roller (3) parallel to its axis and that the ink tape (4) is guided around directly away from the letter (A);

   on the lower side (13) of the thermal print head (1) that faces the counter roller (3), there is provided a shell (2) that extends directly up to the print bar (11) and the area of the bottom surface (21) of which that is adjacent to the print bar (11) is arranged almost level with the print bar (11);

   the thermal print head (1) including the shell (2) and the counter roller (3) are arranged in a manner relatively adjustable to each other.
2. A device according to Claim 1, characterised in that the shell (2), in the area adjoining the print bar (11), is rounded on its edge (211) towards the thermal print head (1) and that it is wider than thermal print head (1) and has rounded comers (212) in continuation of edge (12).
3. A device according to Claim 1, characterised in that the counter roller (3) is longer than the print bar (11), but shorter than the length of edge (12) of the thermal print head (1).
4. A device according to Claim 1, characterised in that the shell (2) is detachably fixed to the thermal print head (1).
5. A device according to Claims 1 and 2, characterised in that the shell (2) is made of a rustproof metal and, in the area adjoining the print bar (11), is supported by the thermal print head (1) through an insulating layer (22); and that the bottom face (21) of the shell (2) is smoothened in that area.
6. A device according to Claims 1 and 2, characterised in that the shell (2) is made of a synthetic material with a low coefficient of friction, such as acetate copolymer with Teflon.
7. A device according to Claims 1 and 2, characterised in that the shell is made of a metal, such as aluminium, with Teflon coating.

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