GB2338207A

GB2338207A - Method and apparatus for producing a thermal transfer print by means of a tape-like transfer film

Info

Publication number: GB2338207A
Application number: GB9905819A
Authority: GB
Inventors: Alfons Schuster; Armin Weichmann; Bernhard Feller; Dirk Probian; Michael Mueller; Thomas Hartmann
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1998-03-13
Filing date: 1999-03-12
Publication date: 1999-12-15
Anticipated expiration: 2019-03-12
Also published as: DE19811028B4; DE19811028A1; CA2265311C; JPH11314387A; GB9905819D0; GB2338207B; CA2265311A1

Abstract

In a method and apparatus for producing a thermal transfer print, especially a printing forme, by controlled heating of a surface layer by means of one or more laser beams from a laser writing head 2 so as to apply the selected area elements to a substrate 1a, use is made of a tape-like transfer film 8 with a width small in relation to the substrate width. The transfer film is transported continuously tangentially between the substrate 1a and the laser beam or beams L, close to the substrate surface, during the imaging operation in order to write a track. As each track is written the film is moved over the width of the substrate simultaneously and in synchrony with the movement of the laser writing head 2. In order not to have to change the tape too often, and to provide increased versatility, the tape width b of the transfer film 8 is sufficiently large for a number of imaging tracks 14 to be used alongside one another, an as yet unused track being selected for each imaging operation.

Description

2338207 Method and apparatus for producing a thermal transfer print by

means of a tape-like transfer film The invention relates to a method and an apparatus for producing a thermal transfer print, especially a printing forme or a proof, by controlled imagewise heating of' a surface layer by means of one or more laser beams and applying the selected area elements to the substrate.

The substrate may be a print material, such as. paper, an intermediate 'carrier to be transferred subsequently to the print material or a printing forme, that is to say a printing plate or, in particular, a seamless printing-forme cylinder or a seamlessprinting-forme sleeve.

Coating a substrate in this way, in particular by means of a laser, is disclosed by DE 44 30 555 Cl. This publication de scribes a method and an apparatus which enables simple production of a printing forme, especially on a seamless printing-forme cylinder with a smooth surface, and allows it to be integrated into the printing machine, without the gases which are produced in the laser imaging operation noticeably interfering with the material transfer from the thermal transfer film, that is to say the inaging quality.

A tape-like transfer film having a tape width which is only a fraction of the substrate width is transported here between the substrate and the imaging unit, in the direct vicinity of the substrate surface, by means of the tape transport mechanism, and the tape transport mechanism, together with the imaging unit and coupled. electronically or mechanically, is mounted on a traversing unit, so that the transfer film can be moved over the substrate width uniformly with the movement of the imaging unit.

In conjunction with the laser-induced thermal imaging unit, which is controlled in a known way by means of a control unit in accordance with an image to be transferred and which, for each image point, introduces heat onto the thermal transfer film, and thus performs a dot-by-dot transfer of the ink-accepting coating of the transfer tape, it is thus possible for the complete substrate, in particular the complete seamless printing-forme cylinder, to be imaged all round.

However, at those points which have already been transferred during an imaging operation, the transfer tape can in principle not be reused, analogously to a carbon ribbon in a conventional typewriter. Hence, in the invention cited, the tape ca n be used only once per section. In order to achieve a number of imaging operations without changing the tape, a very great tape length is therefore necessary. However, the tape length directly influences the diameter of the reel, so that even in the case of a very small number of imaging operations per tape, the reel becomes unfavourably large.

The object of the present invention is therefore to make it possible to carry out a larger number of imaging operations without changing the transfer tape.

According to the invention, this object is achieved by the characterizing part of the generic method claim and the generic apparatus claim.

Use is made of a transfer tape of a width which is a multiple of the width of the writing tracks of the laser imaging unit, and it is thus possible to write a number of tracks alongside one another for various imaging operations. This enables the same section of the transfer tape to be used for a number of imaging operations. In this case., the position of the point or points of incidence of the laser beam or beams, that is to say the writing track of the laser on the transfer tape, has to be shifted in each case, so that the tracks do not overlap and, an unused track is used for each imaging operation.

It is of course nevertheless possible for the tape lengths to. be a multiplelthe lengths needed for the imaging operation, so that via a combination of tracks located alongside one another and after one another, a large number of imaging operations per tape becomes possible. The tape is changed only when all the tracks have been used up.

Exemplary embodiments of the invention are explained below with reference to the drawing, in which, in highly schematic form:

Fig 1 shows a side view of a thermal transfer 20 apparatus for implementing the inventive method with a first tape guide mechanism, Fig. 2 shows a perspective view of a possible way of bringing the transfer film into contact with the substrate surface, Fig. 3 shows a perspective view of a second tape guide mechanism, and Fig. 4 shows a sketch in a perspective view to explain the lateral shifting of the transfer tape in relation to the laser beam.

The addressing, the construction and the mode of action of a printing head which emits one or more laser beams are known per se and therefore do not need more detailed explanation in the present connection.

p J> 4 Fig. 1 shows a substrate cylinder 1 to whose surface a substrate la has been applied. A tape transport mechanism, comprising a supply roll 4 and a wind-up roll 5 (the identification of the supply roll 4 and of the wind-up roll 5 is merely representative of one running direction of the tape-like thermal transfer film 8, in the opposite direction these would of course have to be supply roll 5 and wind-up roll 4), two contact rolls 6a, 6b and two guide rolls 7a, 7b guide a tape-like thermal transfer film 8, referred to below as transfer tape, close to the substrate cylinder 1 or in contact with the substrate la.

A laser writing unit 2 focuses one. or more beams onto the transfer tape (8). In the preferred arrangement, the laser writing unit 2 and the tape guide mechanism 4, 5, 6, 7 are jointly arranged on the traversing unit 3, by means of which they can be moved over the width B of the substrate cylinder 1.

This arrangement is 'shown in perspective form in Fig. '2. In the exemplary embodiment, the transfer film preferably has a tape width of 20 mm. and a thickness of about 12 gm. By comparison, the width B of a substrate cylinder is typically 700 mm. - The imaging track is typically about 1 mm.

Fig. 4 shows the multiple use of the transfer tape via the provision of unused tracks. According to the invention, this is achieved by the tape 8 having a width b which is a multiple of the imaging width t. The transfer tape is then divided up into imaging tracks 14a, 14b, 14c and one track is provided for each imaging operation.

For this purpose, it must be possible for the transfer tape 8 to be shifted in a defined way, indicated by the arrows 15, in relation to the laser beam or beams L. Overall, for one imaging operation, the apparatus of - B --- course still traverses over the substrate cylinder width B in synchronism with the laser imaging unit and writes one track 16 for each cylinder revolution, until the entire area to be imaged has been covered.

As a result of the unavoidable inaccuracies in tape guidance, it is not possible for one track to adjoin the next precisely. For this reason, a safety margin a is observed and is selected to be somewhat greater than the maximum lateral movements of the transfer tape which occur. Hence, the track width s of the laser imaging unit plus'the safety margin a is needed for one imaging operation, and n = INT(b/(s + a)) imaging operations alongside one another are possible, where INT(x) is equal to the largest integer less than x.

During the imaging operation, the tape is unwound from the supply roll 4 and wound up on the wind-up roll 5. Following the imaging operation, in a position where there is no contact between the transfer tape 8 and substrate la or substrate cylinder 1, the transfer tape is then wound back 'again, shifted to a track which has not yet been used, that is to say by at least the distance s + a, and is then ready for the next imaging operation. The tape is changed only when all the tracks have been used up.

It is of course not necessary for the written tracks to be located directed alongside one another in each case:

it may prove to be expedient, for example, to write the furthest right track first, then the furthest left, then the second furthest right, then the second furthest left and so on, or beginning from the centre to use first the most central, then the one to the lef t, then the one to the right of the centre and so on. A different, more irregular sequence of the tracks may also be expedient for reasons connected with winding up the tape cleanly and with reel stability.

- i- ?B 4: 1.'.

A development of this invention is provided by enlarging the tape reel, so that a number of successive imaging operations are possible. In combination with imaging of tracks lying alongside one another, the number of possible successive imaging operations is multiplied by the number of possible imaging operations alongside one another.

Such a large number or such an irregular sequence of tracks must of course be managed by means of a software program which in each case pos.itions a free track and then also indicates and effects complete utilization and hence changing of the tape.

One variant for mechanical direct coupling of the tape transport mechanism and laser imaging unit is independent mechanical traversing of the tape transport mechanism and laser imaging unit, the synchronous movement being achieved electronically. In this case, the tape transport mechanism and the laser imaging unit each have their own traversing drive, and the synchronous shifting is achieved by means of electronic coupling. Shifting the transfer tape in relation to the laser imaging head in order to provide unused tracks is then readily possible simply by changing the distance between the tape transport mechanism and laser imaging unit.

A further exemplary embodiment of an apparatus for implementing the method for laser-induced thermal transfer is shown by Fig. 3. Here, the tape transport mechanism comprises a supply roll 10 and a wind-up roll 11, each arranged in a fixed position (of course, the identification 10 and 11 for the supply wind-up roll can again be exchanged here), the two rolls 6a, 6b, arranged axially parallel to the substrate cylinder 1, for bringing the transfer film 8 into contact with the substrate surface, and two further deflection rolls 12a, 12b. The contact rolls roll and 8:^ -, f' 7 6a, 6b and deflection rolls 12a, 12b can be traversed, together with the laser imaging unit 2, along the width B of the substrate cylinder 1 by means of a traversing unit, in a fixed arrangement in relation to each other but independently of the supply roll 10 and the wind-up roll 11, which are arranged in a fixed position.

In order to position different tracks, it is additionally possible for the deflection rolls 12a, 12b and the contact rolls 6a, 6b to be shifted in a defined way in relation to the laser imaging unit, shown symbolically in Fig. 3 by the short arrows 15.

CIAII4S is 1. A method of producing a thermal transfer print,especially a printing forme, by controlled imagewise heating of a surface layer by means of one or more laser beams from a laser writing head (2) in order to apply selected area elements to a substrate (1a) in a track of a predetermined width, the surface layer being provided on a tape-like transfer film (8) with a width (b) which is small in relation to the substrate width (R), this transfer film being transported continuously between the substrate (1a) and the laser beam or beams (L), close to the substrate surface, during the imaging operation and being moved over the substrate width (B) simultaneously and in synchrony with the movement of the laser writing head (2); characterised in that the width (b) of the transfer tape (8) is sufficiently large for a number of imaging tracks (14) to be used alongside one another and in that an as yet unused track is selected for each imaging operation-

Claims

2. A method according to Claim 1, in which the length of the transfer tape

(8) permits a number of successive imaging operations.

3. An apparatus for implementing the method according to Claim 1, including a laser imaging unit (2) which emits one or more laser beams (L) and can traverse over the width (B) of the substrate, a tape transport mechanism for gui ding a tape-like transfer film (S) whose width (b) is small in relation to the substrate width (3), a traversing unit (3) coupled to the laser imaging unit (2) and co-operating with the tape transport mechanism, it being possible, by means of the traversing unit (3),.for at least that part of -g- the transfer film (8) which outputs the area elements to be moved over the substrate width (B) uniformly with the movement of the imaging unit (2), characterised in that the transfer tape has a width (b) accommodating a number of imaging tracks (14) alongside one another, and by the provision of a means for positioning the tape in such a way that, during the imaging operation, the laser beam or beams strike a track which has not yet been used.

is 4. Apparatus according to Claim 3, in which the tape transport mechanism comprises a supply roll (4, 10) and a wind-up roll (5, 11) and at least two rollers (6a, 6b), arranged axially parallel to the substrate width (B), for bringing the transfer film (8) into contact with the substrate surface, the tape transport mechanism (4, 5, 6) and the printing head (2) are mounted on a common traversing unit (3) and are coupled mechanically, and in the tape transport mechanism or at least the rollers (6a, 6b) for bringing the transfer films (8) into contact with the substrate surface (1a) can be shifted in a defined way in relation to the laser imaging unit (2) and hence to the laser beams (L).

5. An apparatus according to Claim 3, in which the tape transport mechanism comprises a supply roll (4) and a wind-up roll (5) and at least two rollers (6a, 6b), arranged axially parallel to the substrate width (B), for bringing the transfer film (8) into contact with the substrate surface, the tape transport mechanism (4, 5, 6) and the printing head (2) are mounted on a common traversing unit (3), both the tape transport mechanism (4, 5, 6) and the laser imaging unit (2) having their own carriage with drive and being moveable independently of each other, and, in order to address different writing tracks (14), a means is provided for changing the distance between the tape transport mechanism and the laser imaging unit (2).

is 6. An apparatus according to Claim 3, in which the tape transport mechanism comprises a supply roll (10) and a wind-up roll (11), each arranged in a fixed position, at least two rollers (6a, 6b), arranged parallel to the substrate cylinder (1), for bringing the transfer film (8) into contact with the substrate surface, and at least two further deflection rollers (12a, 12b), it being possible for the contact rollers (6a, 6b) and the deflection rollers (12a, 12b) to be moved over the substrate width (B) by means of a traversing unit, independently of the supply roll (10) and wind-up roll (11) but together with the laser imaging unit (2), and at least the two contact rollers (6a, Gb) arranged in parallel can be axially shifted in a defined way in relation to the laser imaging unit (2) and hence to the laser beams (L).

7. A transfer film which can be used for the method according to Claim 1 and having a width (b) designed to accommodate a number of tracks (14) alongside one another for various imaging operations, it being possible to select an as yet unused track for each imaging operation.

8. At transfer film according to Claim 7, in which the tape length permits a number of successive imaging operations.

9. A transfer film according to Claim 7 or 8, in which the tracks arranged alongside one another on the band width (b) consist of differently coloured parts- 10. A transfer film according to Claim 8, in which in order to image different colour separations, the respective colours are produced successively by various sections along the tape length.

11. A thermal transfer apparatus substantially as described herein with reference to the accompanying drawings.