DE4232187A1 - Separation of photosensitive layer from carrier on printing plate and process appts. - uses PTFE coated band knife running it guides and supplied with lubricant. - Google Patents

Abstract

Sepn. of recyclable material in photosensitive printing plates uses a band knife splitter to part individual layers. Also claimed is a cutting machine comprising a continuous moving band knife (14) aligned in guide strips; a material feeding system (15, 16) and a knife lubricator (25). Both the blade (14) surfaces and the guides are coated in PTFE. USE/ADVANTAGE - For separating recyclable photosensitive or sensitised material from a carrier layer in printing plates. Reduces the environmental problem of scrap material.

Description

The invention relates to a separation process for waste treatment of flexographic photopolymer printing plates.

Flexographic raw photopolymer plates consist of a photosensitive recording layer, a support and if necessary from a protective film.

The material of the recording layer is photopolymerizable and consists essentially of elastomeric binders, unsaturated monomer compounds and an initiator. A Description of the chemical composition can for example the documents DE 22 15 090 or EP 0 469 307.

The layer support or the protective film consists of a transparent film, for example made of a polyester film with a film thickness of 0.1 mm to 0.2 mm. By definition the protective film forms the front of the Raw photopolymer plate.

Obtained from a raw photopolymer plate, or raw plate for short a ready-to-use printing plate by looking at the raw plate exposed through a negative and then washed out. A actinic exposure dissolves in the material of the Recording layer a photopolymerization. Exposed Areas are insoluble in a washout solvent. The unexposed areas, however, are soluble and are in the Washout removed. A relief picture is created, the Raw plate became a photopolymer printing plate, or short Printing plate. The depth of the relief is determined by the Preset intensity of an exposure that covers the entire area  the back and before the imagewise exposure becomes.

This is characteristic of flexographic printing plates elastic and yielding behavior of the relief.

After the period of use or when the image information the printing plate is no longer used arises Printing plate waste. Disposal of printing plate waste increasingly poses problems. There is also waste from the Production, i.e. raw plate waste, the unexposed Contains photopolymer. This waste is classified as hazardous waste to dispose.

It is characteristic of both types of waste that the waste is a is so-called composite plastic. The photopolymer, exposed or unexposed, is liable in both cases on the Layer support. The adhesive forces are so strong that it the polyester film from the is almost impossible Subtract photopolymer layer. If you try to separate to bring about by applying great force, that is the Crack formation not controllable. You can in the non-networked Area or in the networked area. A single variety Separation of the plastics is not possible in this way.

If you start from the idea, recovered Printing plate material back into a production process different results can be achieved become.

First, the recovered printing plate material can again serve for the production of printing plates, the material is so recycled. The material flow corresponds to one Cycle, the so-called "recycling".

Second, the recovered printing plate material can be under Abandonment of material properties the starting material for other products. So the material is recycled. The material flow is not a cycle and corresponds to the so-called "dowcycling".  

For both recycling and reuse the photopolymer waste in a first step separate by type.

Currently, the photopolymer waste is either burned or stored in landfills. This disposal is for the future unsatisfactory, which becomes particularly clear if you consider that, in the case of production waste, a unused resource, the unexposed photopolymer an expensive and environmentally harmful process is disposed of. The return of this photopolymer to the Production for the production of raw panels appears at least possible. The printing plate material of the The recording layer of raw plates is sensitive to light. When Secondary raw material used, the material properties are the same that of the primary material. The secondary raw material can at least partially replace the primary material used.

Different come for the separation of composites thermal or mechanical separation processes in question. From DE 26 36 809 is a cryogenic process for the recovery of rubber known. The process is expensive and complex. A Delamination device is known from EP 0 236 730. Due to the high adhesive forces between photopolymer and This method is layer support for the present Waste problem not suitable.

Even with a conventional screen belt press that works on the It is not a product that has a high shear stress possible, the layer support from the composite satisfactory to solve.

The object of the invention is a method and Specify device with the help of which the photopolymer of Printing plate or raw plate waste from the substrate can be separated according to type, so that the waste problem diminishes and the environment through the manufacture and use is less burdened by photopolymer printing plates.  

This task is solved by using a Band knife splitting machine of raw plates or printing plates separates the photopolymer by type and this material one Recycle or reuse.

It is known that with band knife splitting machines from Plastic sheet layers, even those with a minimal Layer thickness of about 0.5 mm, can be split off. Plate-shaped photopolymer can, however, with such Device can not be separated. In case of Raw panel waste where the front is sticky Photopolymer and the back through the smooth polyester film is formed, the feed rollers can not separate the material lead sufficiently. The tape knife guide glued. The Photopolymer dodges the band knife. If anything if a layer can be split off, the layer thickness is shown strong fluctuations. Even with a freshly sharpened one The knife level is uneven. As a result a more or less thick layer adheres to the substrate Photopolymer.

Surprisingly, it has been shown that one with one known tape knife splitting machine of photopolymer plates Can split off layers, if one during the Cutting forces occurring minimized splitting forces. With a It is designed according to the invention of a band knife splitting machine possible, the layer support of both printing plates as well split off from raw plates.

The band knife splitting machine is so designed that the Frictional forces that occur during the separation process between Photopolymer and band knife are created by moistening and a coating of the band knife as little as possible being held. Are suitable as humectants Soapy water, alcohols or surfactants. It has pointed out that purified water is used with advantage can be. The recovered printing plate material needs  then no longer be cleaned by the humectant, the water dries without residue.

In a preferred embodiment, this is all-round Band knife coated with polytetrafluoroethylene. Hereby are also the frictional forces between the gap surfaces of the band knife and the sticky photopolymer. Consequently, the force of the band knife on the Photopolymer plate lower. The parting material can be separated from the Feed rollers are better guided.

The band knife is advantageous during operation continuously ground. A gap angle between 15 and 25 Degree is preferred. In a very particularly preferred The gap angle is 20 degrees.

The cutting edge of the band knife is preferably close to the Straight lines connecting the center points of the feed rollers. By doing one directly before the photopolymer plates by feed rollers the cutting edge, the material to be separated will evade during of the cut prevented. It is an accurate height Cut possible. The grinding process would the distance from the cutting edge and feed rollers is constant enlarge. This is prevented by an automatic Adjustment device at which the tip of the knife edge is measured and updated.

To ensure safe transport of the material to be separated is preferred, the outer surface of the feed rollers to roughen. The lateral surface is preferably knurled. An increase in roughness can also be caused by others Surface treatment processes such as engraving or sandblasting can be achieved.

The feed rollers are preferably adjustable arranged. As a result, the thickness of the press nip can be increased of the goods to be separated. So it can be different thick plates can be processed. Secondly, it is possible by independently adjusting both rollers, the layer thickness to be split off. Especially at Printing plate waste is preferred that the feed roller is due to the relief, a diameter of less than 50 mm having. The contact pressure to be applied in the gap is thereby  comparatively less and a height-accurate cut is possible.

It is also preferred to coat the knife guide bar with polytetrafluoroethylene. This facilitates the removal of the freshly separated material. In a very particularly advantageous embodiment, the upper gap surface of the knife guide strip is grooved. The weight of the plate increases the frictional forces on the upper gap surface. It has been found that a transverse groove in connection with a longitudinal groove in the rear part of the knife guide strip, in particular when the groove has a spherical ground joint, gives the best results. On raw plate waste, it is even possible with such a band knife splitting machine to carry out the cutting precisely in the boundary layer between unexposed and exposed photopolymer. This result was not to be expected. The person skilled in the art, starting from the known problems of a high-precision cut with sticky materials, would have assumed that a separation that takes place precisely in the boundary layer is not possible at all. A plastic with different Shor hardness is present in the boundary layer: it meets photopolymerized with unpolymerized photopolymer. Measured in degrees of hardness, the first material is about twice as hard as the second. In addition to the known problems of separating a sticky material, there is also the fact that the material is inhomogeneous. Different frictional forces act on the upper and lower gap surface of the band knife. Particularly in the case of the very different surface shape of the production waste, which partly consist of narrow edge strips or of initial or final losses with different edge formation, the person skilled in the art would have expected that the feed rollers would not be able to guide this material and that a flat cut would not be possible. However, the latter is crucial for recycling the raw material:
A parting plane that is too close to the carrier film would split off not only unexposed but also polymerized photopolymer. However, due to the back exposure, this material can no longer accommodate image information. If you use this material to restore raw plates, errors in the relief of the print may occur.

On the other hand, the parting line must not be too deep in the unexposed area of the recording layer, because the effort for the disposal of the residual waste is covered by the Layer thickness of the remaining on the carrier element unexposed photopolymer. As mentioned at the beginning, unexposed photopolymer must be disposed of as special waste.

Just a cut that runs in the boundary layer enables cost-effective reuse of the unexposed photopolymers. It can do that primarily used material directly replaced by the secondary raw material become. A complex intermediate treatment is not required. Essentially, the separated one is sufficient Granulate material. By adding a release agent the regranulate remains free-flowing and does not clump together. When Release agent is suitable for aluminum silicate, calcium carbonate, Diatomaceous earth, magnesium carbonate, pyrogenic silica or Titanium dioxide and stearates. Is preferably used recovered, polymerized printing plate material, which crushes to a particle size in the micro range has been. The regranulate prepared in this way becomes the photopolymerizable composition of melt extrusion added. In a known way you can use this Composition Make photopolymer raw plates. The Print quality of "recycled printing plates" is conventional produced hardly distinguishable printing plates.

There is also a cut in the case of printing plate waste close to the carrier film is desirable. By the precision of the The degree of separation of the materials is determined on average. Out the recovered exposed photopolymer can with known size reduction processes, such as hammer, Cutting, or impact mills the photopolymer into particles  different sizes can be crushed. This material can be used as a filler, for example the production of molded parts, their mechanical Properties not too great demands become.

The residual waste essentially consists of in both cases the polyester carrier film. Depending on the accuracy of the In raw panels, a thin, stick the unexposed layer of photopolymer on the carrier film stay. A brief exposure polymerizes it Plastic completely, so that the residual waste as household waste can be disposed of. With the help of the invention It is possible to remove the landfill from Reduce raw photopolymer plates up to ten percent, d. H. of a 6 mm thick raw plate remains about 0.2 mm thick polyester film and less than 0.4 mm thick Layer of polymerized photopolymer.

The invention is illustrated below in the drawing illustrated, preferred embodiments explained. It shows:

Fig. 1 is a schematic representation of the separation process with a band knife splitting machine in a spatial representation,

Fig. 2 is a cross-sectional view of a schematic representation of a band knife splitting machine,

Fig. 3 is a cross-sectional view of the band knife and the knife guide strip schematically in an enlarged scale;

Fig. 4 is a schematic representation of a cross section of a Rohdruckplatte,

Fig. 5 is a schematic representation of a cross section of a washed-out printing plate.

Fig. 1 shows a pressure plate during the separation process in the band knife splitting machine in a spatial representation. The band knife 14 runs in an endless loop 45 . It is moistened on the top and bottom by a moistening device 25 during the separation process and the knife edge is sharpened by a grinding device (not shown in more detail). The photopolymer plate from which the layer support 1 is split off is guided between the feed rollers 15 , 16 .

Fig. 2 shows a cross-sectional view of a band knife splitting machine in a schematic representation. The band knife 14 is guided in a knife guide bar 23 . The cutting plane 36 lies within the press nip 34 , which is formed by an upper feed roller 15 and by a lower feed roller 16 . The feed rollers are adjustably mounted in the feed device 24, which is not identified in any more detail. Upon rotation of the rollers in the direction of arrows 39 and 40, the photopolymer plate is gripped by the feed rollers 43, drawn in the direction of the arrow 31 in the press nip 34 and pressed against the cutting edge of the band knife. Fig. 2 shows a photopolymer plate 43 which has already been partially split by the band knife. The splitting process is preferably carried out such that the split layer 41 with the layer support lies below and the split photopolymer layer 42 lies above the knife guide bar 23 . The feed of the photopolymer plate can take place, for example, on the input table 44 and the discharge on the output table 45 . The working surface of these tables can be grooved and / or coated to reduce the frictional forces. The photopolymer plate 43 can be a raw plate 7 or a printing plate 8 . Compared to the separating surface 36 , both the distance 37 of the upper feed roller 15 and the distance 38 of the lower feed roller 16 are adjustable. The adjustment of the upper feed roller is independent of the adjustment of the lower feed roller. The distance 25 between the tip of the band knife and the center line 30 is also adjustable. A relatively small distance is preferred here. On the one hand, the separation process should, if possible, take place at the point at which the photopolymer plate is guided. This results in an exact cut. On the other hand, the separation process should produce the lowest possible splitting forces, which leads to a further distance. The most favorable distance is dependent on the plate surface for each plate thickness and - in the case of relief printing plates - and is determined empirically. A distance of 5 mm has proven to be favorable. In Fig. 2 it is shown that the separating surface 36 is orthogonal to the plane which is formed by the family of the center line 30 . This arrangement provides the best separation results for photopolymer plates. A separation process is also possible with other angular positions.

Fig. 3 shows an enlarged section of the band knife splitting machine, the band knife 14 and the knife guide bar 23 in a cross-sectional view. The grinding process reduces the width of the band knife and the cutting edge 29 would move away from the center straight line 30 more and more. Due to the band knife tracking device 44 , not shown, the distance between the cutting edge 29 of the band knife and the center line 30 remains constant during the period of use of the band knife. The gap surfaces 21 , 22 of the band knife and the gap surfaces 26 , 27 of the knife guide strip are coated with polytetrafluoroethylene. In a very particularly preferred embodiment, the gap surface 26 has a transverse groove 32 and a longitudinal groove 33 . This reduces the contact area between the sticky release material and the machine guide, which leads to improved material transport. The polytetrafluoroethylene coating can also enclose the band knife 14 or the knife guide strip 23 on all sides. The cutting edge of the band knife can be a wedge surface tapering to an acute angle, but can also have a serrated edge which is not further identified. The splitting angle 28 of the band knife is preferably 20 degrees.

Fig. 4 schematically shows a Photopolymerrohplatte 7 in cross section. After the protective film 6 has been removed from the raw plates, the layer support 1 together with the polymerized layer part 10 of the recording layer 3 is removed from the other layers. The release layer 5 can optionally be removed by a suitable solvent. The recycled unexposed printing plate material 2 then consists of the printing layer 4 and the photopolymerizable recording layer 3 . The latter can consist of several layers, two layers 17, 18 are shown by way of example in FIG. 4. A separation that runs in the boundary layer 13 is advantageous for recycling the unexposed printing plate material. The substrate 1 with the polymerized part 10 of the recording layer is thus split off from the other layers.

Fig. 5 shows schematically a photopolymer printing plate 8 in cross section. The printing relief 12 is formed by the printing layer 4 and by the photopolymerized recording layer 11 . For further use, the exposed printing plate material 9 is separated in the immediate vicinity of the substrate 1 . The photopolymerized recording layer 11 can consist of several layers. In Fig. 5, two layers, the layer 19 and the layer 20 are located. The relief depth is determined by the imagewise exposure and by the back exposure and can extend over all layers of the recording layer.

Claims (17)

1. A method for separating photopolymerized or photopolymerizable layers from the support, characterized in that the separation is carried out by a band knife splitting machine. 2. The method according to claim 1, characterized in that the photopolymerized or photopolymerizable layers form the recording layer of a printing plate and the separation takes place within a boundary layer ( 13 ) lying on the layer support ( 1 ). 3. The method according to claim 1, characterized in that the band knife ( 14 ) of the band knife splitting machine is moistened during the separation process. 4. The method according to claim 1 and 2, characterized in that the separated from the support, photopolymerizable recording layer ( 3 ) or the photopolymerized recording layer ( 11 ) is crushed. 5. The method according to claim 4, characterized in that the shredded, photopolymerizable recording layer in front of the Feed into an extruder is mixed with a release agent. 6. The method according to claim 5, characterized in that the Release agent powdered, recovered, polymerized Printing plate material is. 7. band knife splitting machine for performing the method according to claim 1, comprising a revolving band knife ( 14 ) which is guided in a knife guide bar ( 23 ), a feed device ( 24 ) and a knife moistening device ( 25 ), characterized in that the gap surfaces ( 21 , 22nd ) of the band knife ( 14 ) and the gap surfaces ( 26 , 27 ) of the knife guide bar ( 23 ) are coated with polytetrafluoroethylene. 8. Band knife splitting machine according to claim 7, characterized in that the band knife ( 14 ) is ground during the cutting process and the splitting angle ( 28 ) of the band knife is between 15 degrees and 25 degrees. 9. Band knife splitting machine according to claim 7, characterized in that the cutting edge ( 29 ) of the band knife ( 14 ) is in the immediate vicinity of the center line ( 30 ) of the feed rollers ( 15 , 16 ). 10. Band knife splitting machine according to claim 7, characterized in that the gap surface ( 26 ) of the knife guide strip ( 23 ) has a groove ( 32 , 33 ). 11. Band knife splitting machine according to claim 10, characterized in that the groove ( 33 ) runs parallel and the groove ( 32 ) transverse to the working direction ( 31 ). 12. Band knife splitting machine according to claim 7, characterized in that the feed device ( 24 ) has a press nip ( 34 ) to which the cut material can be fed. 13. Band knife splitting machine according to claim 12, characterized in that the press nip ( 34 ) is formed by an upper feed roller ( 15 ) and by a lower feed roller ( 16 ). 14. Band knife splitting machine according to claim 13, characterized in that the center distance ( 35 ) between the feed rollers ( 15 , 16 ) is adjustable. 15. Band knife splitting machine according to claim 13, characterized in that the distance ( 37 ) between the upper feed roller ( 15 ) and the separating surface ( 36 ), and the distance ( 38 ) between the lower feed roller ( 16 ) and the separating surface ( 36 ), is adjustable. 16. Band knife splitting machine according to claim 13, characterized in that at least one diameter of the feed rollers ( 15 , 16 ) is less than 50 mm. 17. The apparatus according to claim 13 to 16, characterized in that at least one outer surface of the feed rollers ( 15 , 16 ) is knurled.