WO1989008281A1

WO1989008281A1 - Image processing apparatus

Info

Publication number: WO1989008281A1
Application number: PCT/GB1988/000982
Authority: WO
Inventors: Colin George Thompson
Original assignee: Transmatic Systems Limited
Priority date: 1988-03-02
Filing date: 1988-11-14
Publication date: 1989-09-08
Also published as: GB8804951D0; GB2215485A

Abstract

An apparatus is described for processing an ink image on a base sheet. The apparatus comprising rollers (122, 131) for engaging and driving the base sheet through a processing station and a wiping roller (129) in the processing station (12) rotatable while in contact with the surface of the base sheet to wipe a processing solution gently over the surface to be treated. In the preferred embodiment, the apparatus has several processing stations (10, 12, 14) and the entire development is automated.

Description

IMAGE PROCESSING APPARATUS

The present invention relates to a processor for processing an ink image on a base sheet.

In making of transfer sheets, it is known to coat a sheet of clear plastics- material carrying a release layer with ink of the desired colour. A layer of adhesive is applied next and finally a photocoat layer is applied over the adhesive. Each layer is allowed to dry before the application of the next. The photocoat layer is imagewise exposed to ultraviolet radiation through a mask carrying a negative of the desired image and the effect of the radiation is to harden the exposed regions.

The processing of such an exposed base sheet to develop the ink image requires first the washing of the sheet in a solvent, usually water, in which the unexposed photocoat will dissolve. This step removes the photocoat from the areas of the sheet from which the ink and the adhesive are to be removed but leaves the hardened photocoat, that is the parts hardened by photo- polymerisation, overlying and protecting the desired image areas of the ink and adhesive.

In the next stage of processing, the ink and adhesive are removed from non-image areas by use of a suitable solvent, commonly an organic solvent such as propanol, which dissolves the ink and adhesive layer but does not affect the hardened photocoat. Finally, the hardened photocoat is removed by the use of a water based solvent to leave only in the desired image area ink covered by an adhesive.

The transfer sheet is now complete and the image can be transferred or rubbed down onto an article such as a card because the image with its adhesive layer sticks more strongly to the article than it does to the release coating, on the base sheet.

As described above, the adhesive is removed from non- image areas because it is developed at the same time as the ink image. This is not necessarily the case and the adhesive layer may alternatively be applied over the entire base sheet after the ink layer has been applied and non-image areas removed by the application, exposure and development of a photocoat.

The above two are only examples of techniques used in the production of images which involve the processing of an ink image on a base sheet. A further example is direct imaging in which the base sheet is a card to which a seal coat has been applied. Here the card itself is the desired end product and the image does need to be transferred later from the base sheet.

In all the above imaging techniques, processing of the ink image requires removal of the unexposed photocoat and subsequent removal of the ink. These steps are usually carried out manually and require the most operator time and skill. The appropriate solvent is poured onto a sponge supported on a relatively rigid backing bar which is drawn evenly over the entire surface of the support sheet. This action may need to be repeated for full removal of any layer. Excessive force can easily damage the delicate layers which is why a skilled operative is needed.

The present invention seeks to provide a processor which can perform the development of an ink image on a support sheet effectively and reliably. By automating the development of the latent image, the invention reduces the amount of time and the level of skill demanded of the operator in producing the finished proof and can additionally provide significant saving by more efficient usage of the chemical solution employed in the development.

According to the present invention, there is provided an apparatus for processing an ink image on an individual flexible base sheet, comprising means for engaging and driving the base sheet through a processing station and a roller in the processing station rotatable while in contact with the surface of the base sheet for applying a processing solution to the surface of the base sheet, characterised in that the roller is a wiping roller made of an absorbent material and is radially compressible so as to exert negligible pressure on the surface of the base sheet and in that the wiping roller rotates in the direction of movement of the base sheet through the processing station.

There are described in the prior art, for example in GB- 1 212 317 and US-4,213,420, apparatus designed for automatic development of printing plates. Such apparatus, while bearing some resemblance to that of the invention, differ from it significantly in the operation of the wiping roller. Whereas in the present invention, the ink layer is very delicate and requires so much care in handling as to deter automatic processing, printing plates are very robust and the development involves scrubbing of the surface with a brush. The brush is always driven in the opposite direction to the movement of the plate to increase the scrubbing action and the brush is usually made of fairly stiff bristles. By contrast, the present invention requires an absorbent roller which applies negligible pressure to the surface of the base sheet. Furthermore, because the base sheet is flexible and is not a continuous web, rotation of the wiping roller in the opposite direction, as in the prior art, would cause it to crumple and prevent its progress through the processing station. In processing of ink images on a flexible base: sheet, once softened by the appropriate solvent, the layer being developed does not need to be scrubbed away but will virtually drip off the base sheet if the latter is suspended. The action of the wiping roller in the invention is not therefore to scrub the surface of the image but to gently pass over it an absorbent surface to remove the surplus solvent and permit fresh solvent to reach the surface. The preferred material for the wiping roller is lamb's wool or a fleece-like material as the soft hairs cannot damage the ink layers but are effective in enabling a clean supply of solvent to reach the surface.

Preferably, the apparatus comprises a plurality of stations for wiping different processing solutions over the surface to be treated. Thus, after the removal of the unexposed photocoat in a first processing station using water, the ink (or ink and overlying adhesive) may be removed in a second station using an organic solvent. Subsequently, the exposed photocoat may be removed in a third processing using a water based solvent.

During the transfer between processing stations, the base sheet risks causing contamination of the solutions. To avoid this problem, it advantageous to pass the sheet between squeegee rollers and to dry the sheet, at least in part, by an air stream.

To effect the transportation of the base sheet through the processing stations, rubber rollers are preferably provided to grip the sheet. The sheet may be gripped by more than one pair of rollers at any one time and slipping of the rollers on the delicate surface would cause damage to the image. The rollers are therefore all driven at the same speed using a common chain or belt drive. The drive rollers may additionally serve as squeegee rollers to remove the surplus liquid from the surface of the base sheet between processing stations.

The lower of the drive rollers may be immersed in the processing solution of the relevant station but the upper roller, contacting the image bearing surface of the base sheet cannot be maintained moist in the same manner and should either roller be dry, there is a risk of damage to the image. To avoid this problem, in addition to the lower drive roller being immersed in the processing solution, the upper roller is sprayed with the processing solution.

In certain applications, only one processing station is required while in others two or three may be necessary. In order to permit the same apparatus to be used in a variety of applications, a removable by-pass guide may conveniently be provided between processing stations. The by-pass guide is arranged in the path of the base sheet to deflect the base sheet from entering the next station in line in a multi-station apparatus.

It is advantageous to be able to remove the drive rollers for cleaning and servicing but these must also be driven in unison. To achieve both these objectives, each drive roller is preferably connected to a sprocket driven by a chain of belt, the coupling between the roller and the sprocket being demountable and capable of tolerating misalignment between the sprocket and the drive rollers. The sprocket and the drive rollers may, for example, each have a linear slideway engaged in mutually perpendicular guides formed on the opposite surfaces of a slider interposed between the sprocket and the drive rollers. Such a coupling is tolerant of misalignment and permits the drive rollers to be retracted without any effort other than catching the slider as the rollers are withdrawn. When water is the solvent, it possible to connect the apparatus permanently to a water supply but this may in some cases be disadvantageous. It is preferred that each processing solution should be stored in a reservoir or tank and that it be pumped from the reservoir to the processing station and that it should be returned to the reservoir after filtration. In this way, the use ^"of solvents is kept to a minimum as well as avoiding the need for permanent plumbing to a water supply and a drain.

The motor driving the chain or belt may be switched on manually as required but alternatively, a photocell may be used to sense the insertion of a base sheet in the apparatus and to maintain the motor running for a fixed length of time following the introduction of each base sheet.

It is an important advantage of the invention that the risk of damage due to operator error is minimised and while the development of the latent image is carried out fully automatically the operator may continue to coat and expose further sheets for processing. The efficiency of operators is thus considerably improved in addition to the improved yield and reduced wastage of materials.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure l is a section through an apparatus of the invention, and

Figure 2 is an exploded section showing the coupling between the drive rollers and their drive sprockets. The illustrated apparatus is intended for automatic processing of an ink image disposed on base sheet. The sheet to be processed consists in the case of a transfer of a plastics material formed with a release coating to which three layers have been applied consecutively. The three layers are first an ink layer, next an adhesive layer and then a photocoat (or photoresist) layer. Each layer is allowed to dry before the next is applied and after the photocoat layer has been applied it is exposed to ultra-violet light through a mask, which is a negative of the image to remain on the base sheet.

All the above steps are conventional in colour imaging and need not therefore be described in detail. In the prior art, this sheet needed to be processed manually first to remove the unexposed parts of the photocoat layer, then to remove the adhesive and ink exposed by the removal of the unexposed photocoat and finally to remove the exposed photocoat overlying the desired image area. This now formed a transfer image which could be rubbed down onto an article.

Not only are the above processing steps time consuming for the operator but they are the steps which require the most operator skill because the ink image can easily be damaged during development. When carried out manually the processing solutions and the applicators can only be used once and this results in significant wastage of materials, which adds to the cost of producing the transfers.

The image processing apparatus shown in the drawing is intended to perform the processing of the sheet automatically. The exposed sheet is introduced into the apparatus and passes through three processing stations 10, 12 and 14 which use different processing solutions. On emerging from the third station 14 the sheet is developed and ready for use. The first station 10.has;a tank 102 containing water and is intended to remove the water soluble unexposed photocoat. The sheet is gripped by two :friction rollers 104 of which the lower one is partly immersed in the water in the tank 102 to wet the under-side of the sheet. The sheet then passes over two support plates. 108, which, like other support plates to be described below, are formed of perforated stainless steel sheet. While resting on the support plates 108 the base sheet is sprayed from above with water by means of spray heads 106 which are connected to a circulation pump 107.

The circulation pump 107 draws water from a pipe 114 in the tank 102 and pumps it to the spray heads 106. A filter is incorporated in the pump 107 to remove particles from the circulating water. Though it is possible to connect the spray heads to a mains water supply, it is preferred to use a pump and filter as this obviates the need for plumbing when installing the apparatus. A further pipe 116 is fitted to the tank at its lowest point to permit drainage.

Before the trailing edge of the sheet is released by the rollers 104, its leading edge is gripped by two further rollers 110 which act as drive rollers and squeegee rollers to remove most of the excess fluid from the surface of the sheet. All the drive rollers are driven at the same speed in order to avoid damage the ink image being stripped off the sheet. The drive train will be described in more detail below.

After removal of the excess water by means of the squeegee rollers, the sheet is dried by means of air directed onto the sheet from above by means of a conduit 120 connected to an air supply. It has been found that even a supply of cold air is adequate for this purpose and the air need not necessarily be heated. The sheet is then driven by a further pair of drive and squeegee rollers 122 into the second processing station 12. Water removed by the rollers 122 drips into a tray which is connected by a pipe 117 to a drain. It is important to remove as much water as possible from the sheet at this stage in order to minimise contamination of the solvent in- the second processing station 12.

The unexposed photocoat will now have been removed from the sheet and the latter enters the second processing station 12 for removal of the ink and adhesive layers exposed by the removal of the unexposed photocoat layer. The ink and adhesive do not dissolve in the water of the first processing station 10 but do dissolve in certain organic solvents, for example propanol. However spraying alone does not suffice to wash away the ink and adhesive layer and when carried out manually, this step requires very gentle wiping of the surface with a pad soaked in solvent.

In the second station 12, the sheet passes over support plates 124 and is sprayed from above with a suitable organic by means of spray heads 126. The first of the spray heads 126 is supplied with solvent from a first pump 121 connected to a reservoir 125. Solvent returns to the reservoir by way of a pipe 123 which extends into the tank 126 of the second station 12 and maintains a constant head of solvent in the tank 126. The second of the spray heads 126 receives solvent from a circulation pump 127 which incorporates a filter and is connected to a second pipe 128 leading into the tank 126. The pipe 128 also acts as a drainage outlet.

If a larger supply of any solvent is needed than can be accommodated in the various tanks, for example the tank 102, then a supply reservoir, such as reservoir 125, can be provided beneath the processing apparatus and conveniently each supply reservoir can be integrated with its pump into a common housing. f

While resting on the second support plate 124, the top surface of the sheet is wiped by means of a wiping roller 129 which is made of lamb's wool and rotates with a higher surface speed than the sheet but in the same direction as the other rollers. Because the wiping roller turns in the same direction as the other rollers, it does not tend to impede the progress of the sheet through the processor. The ink and adhesive layer is thus wiped from the surface of the sheet exposing the release coating of the base sheet and leaving only the parts of the ink and adhesive layers protected by the hardened photocoat layer, which does not dissolve in the organic solvent of the second processing station 12.

The sheet is driven out of the second processing station 12 by a a further pair of drive and squeegee rollers 131 and passes beneath a second stream of air emitted from a conduit 132 before being passed on for further processing.

If a multi-colour transfer is to be produced, the sheet should now be coated with a further ink layer and the above processes repeated before removal of the hardened photocoat layer. The hardened photocoat is required to protect the first image during formation of the second. On the other hand, if a single colour transfer is to be produced, then it only remains to remove the hardened photocoat for the processing to be complete. A by-pass plate 135 is provided between the second and third processing stations to enable the apparatus to be used for either multi-colour or single colour operation. With the by-pass plate in position, as illustrated, the sheet is ejected before entering the third processing station 14 to permit further ink and adhesive layers to be applied. The by-pass plate 135 can however be withdrawn through a cover 136 to permit the sheet to enter directly into the third processing station 14. It will be noted that a second cover 115 overlies the first processing station and this may afford access for a second by-pass plate to permit the sheet to be removed prior to entering the second processing station 12. Such a modification would permit the apparatus to act as a washing station only. One reason for removal of the sheet after washing only is that on some occasions small holes can be found in large areas intended to be covered with ink. This can be caused by dirt during the exposure of the sheet to ultra-violet light. If the sheet is dried and examined after washing only, it is possible at this stage to detect such defects and effect a -repair of the image by applying small spots of the relevant ink by hand and reprocessing the sheet.

If the by-pass plate 135 is withdrawn, the sheet enters the third processing station 14, which in most respects is the same as the first station 10 except that the solution applied to the sheet is water containing a proprietary special water soluble developer capable of dissolving the exposed photocoat without affecting the underlying ink and adhesive layers. The third station thus comprises two set of drive rollers 144, 150, support plates 148, and spray heads 146 powered by a further circulation pump 147. On leaving the third processing station, the sheet is again dried by air from a conduit 160 and is now ready for use as a transfer sheet.

Though the operation of the apparatus has been described by reference to the production of a transfer sheet, it should be clear that it may be used in other imaging processes such as direct imaging or in the making of metal rather than ink transfers.

As mentioned earlier, it is important that the various drive rollers 104, 110 etc. should be driven at the same speed as one another to prevent damage to the ink image. To achieve: this aim, a metal plate 200 (see Figure ^;2) extends parallel to one side of the plastics tanks containing the different-processing solutions. The metal plate carries a sprocket 210 adjacent each pair of 5 rollers, the rollers 104, being shown in Figure 2. All the sprockets are driven by a common chain (not shown) which passes over the sprockets 210 and also over a chain tensioner.

10 The drive rollers 104 are designed such that they may be removed for cleaning without interfering with the drive train and without having to dismantle the apparatus in any way. Each pair of drive rollers can simply be lifted out of the tanks for cleaning, servicing or replacement.

15

For this purpose, each pair of drive rollers, for example 104, is mounted on a plate 212 which can slide into the side of the respective tank, for example 102. One roller is coupled to a disc 220 having a projecting

20 slideway 222. A similar disc 230 with a slideway 232 is fast in rotation with the sprocket 210. A coupling slider disk 240 has mutually perpendicular guide grooves 242 and 244 on its opposite surfaces which receive the respective slideways 222, 232 and transmits the drive

25 from the sprocket 210 to the rollers 104. Because of the nature of the coupling, small misalignment between the rollers and the sprockets can be tolerated. Furthermore, after correctly positioning the rollers so that one of the slideways 222, 232 is vertical, they may

30 be lifted out without disturbing the drive train.

The motor driving the chain may be switched on manually as required but alternatively, a photocell may be used to sense the insertion of a base sheet in the apparatus 35 and to maintain the motor running for a fixed length of time following the introduction of each base sheet.

Claims

1. An apparatus for processing an ink image on an individual flexible base sheet, comprising means (122,131) for engaging and driving the base sheet through a processing station (12) and a roller (129) in the processing station (12) rotatable while in contact with the surface of the base sheet for applying a processing solution to the surface of the base sheet, characterised in that the roller (129) is a wiping roller made of an absorbent material and is radially compressible so as to exert negligible pressure on the surface of the base sheet and in that the wiping roller (129) rotates in the direction of movement of the base sheet through the processing station (12) .

2. An apparatus as claimed in claim 1, wherein the wiping roller (129) is formed of a fleece-like material.

3. An apparatus as claimed in claim 1 or 2, comprising a plurality of stations (10, 12, 14) for applying different processing solutions to the surface to be treated.

4. An apparatus as claimed in claim 3, having three processing station (10, 12, 14) for applying water, an organic solvent and a water based developer, respectively, to the base sheet, at least the station (12) for applying the organic developer being provided with a wiping roller (129) .

5. An apparatus as claimed in claim 3 or 4, wherein means (120, 132) are provided between processing stations (10, 12, 14) to remove surplus liquid and to dry the surface of the base sheet by means of an air stream.

6. Apparatus as .claimed in any of claims 3 to S, wherein a removable by-pass guide (135) is provided between processing stations (12, 14).

7. -Apparatus as claimed in any preceding claim, wherein the means for engaging and driving the base sheet comprise pairs (104, 131,- 144, 150) of drive rollers the lower of the drive rollers being immersed in the processing solution of the respective station.

8. Apparatus as claimed in claim 7, wherein the upper roller, or the base sheet in the vicinity of the upper roller, is sprayed with the respective processing solution.

9. Apparatus as claimed in claim 7 or 8, wherein the drive rollers of the different stations have a common drive train, and wherein each pair of rollers is connected to the drive train by a coupling (220, 230, 240) permitting the rollers to be withdrawn from the apparatus without disturbing the drive train.