COLD CREASING OR SCORING OF PLASTICS WITH MICROPERF Scoring or creasing of plastics has historically been accomplished with the use of RF (Radio Frequencyand or the application of significant heat. Both methods may be basically effective but also have their limitations or disadvantages. Overall, RF is often seen as a slow, and expensive off-line process and the applying of heat usually requires a costly heated chase. Additionally, most heated chases require the use of a special rule height (such as 11 mm) at premium prices. For many years, converters have sought to cold score plastics in numerous ways-most found to be ineffective for a variety of reasons. If cold scoring could be effectively done, (especially in-line) the results would be extremely positive and economical. HISTORY Over ten years ago, we found that our saw-tooth shaped microperfs could be effectively used to achieve a cold score or crease on many kinds of plastics. Originally, we tested many different Teeth Per Inch (TPI) patterns, eventually settling on a 50 TPI with an .008” (.20 mm) depth. The premise we employed was a simple, yet effective one. We set out to create an excellent balance of uncut material versus cut material. We made the material weak enough to facilitate effective folding, yet strong enough to stand up to most common production and use stresses. This was primarily achieved by controlling the depth of penetration of the microperf’s teeth into the plastic and taking advantage of the fact that the saw-tooth shaped microperf ( ) created an effective folding “hinge.” Embarrassingly, it must be admitted that over ten years ago, we did not realize the huge potential impact made possible by being able to cold score plastic with our microperfs. We had a couple of customers who made use of the process, but that was really as far as it went for quite some time. EVOLUTION When a large diemaking company asked us about cold scoring plastic over a year ago, we of course told them of our past success with microperf and sent them some samples of the 50TPI rule in a .934” (23.7 mm) height. The results were very good once again, however, their customer felt that the resultant crease edge was, “too rough” and obvious for their liking and they believed that the resultant score was not always strong enough. We went back to the drawing board to develop a “finer” version of microperf and eventually came up with a 120 TPI microperf with a .0035” (.09 mm) depth. We again sent samples and this time the results were deemed, “ excellent”- a good fold, significantly increased strength and a much “smoother” (to the eye and the touch) crease edge. The diemaker and their customer were both highly satisfied and we began to sell much more of this product to several diemakers and plastic converters around the world. This went on successfully for quite some time, but we continued to do research to see if we could develop a rule that would allow a little more “margin for error” than the 120 TPI, especially in regard to use on thicker materials. By this I mean that we had recognized that the shallow depth of the 120 TPI, made it very critical that the penetration levels and the material thickness variation tolerances be almost “ideal” or the converted products would potentially be problematic-either being too weak or too strong. The result of that research was our 100TPI rule with a .006”(.15 mm) depth. This rule has proven to be excellent for the cold scoring or creasing of many different types and thicknesses of plastics, creating an excellent balance of folding and strength and additionally providing an extremely “fine” edge feel and appearance. Let’s look at how the 100T potentially works on a .015” thickness of plastic ( ). Employing a rule height of .934” (23.7 mm) with a tooth pattern of 100TPI x .006” (.15 mm) deep gullets or valleys, we would potentially penetrate the sheet .012” (.30 mm)- leaving the last .003” (.08 mm) of the material untouched. The areas contacted by the gullets or valleys of the rule would add the gullet depth of .006” (.15 mm) to the .003” untouched areas, creating triangular areas .009” (.23 mm) thick or high. This would create 50 areas per inch that would have .009” (.23 mm) high triangles of unaffected areas, in addition to 50 areas that would have rectangles of .003’ (.8 mm). By .004” (.10 mm) This combination of alternating sizes of unaffected areas, produces a very strong burst strength, yet still allows easy and effective folding and an excellent creased edge in regard to appearance and touch. If a thicker plastic was used, say a .020” (.51 MM) thick, we would potentially decrease the perf rule height by a little less than the .005” (.13 mm) difference that existed between the two sheets, possibly creating a . 930” (23.6 mm) rule height to be used in a die with .937 (23.8 mm) cutting height. In this example, the perf teeth would penetrate .007” (.18 mm) less than the cutting height or .013” (.33 mm) deep, thus leaving . 007” uncut or unaffected material in the areas penetrated by the teeth. In the gullet areas, the .006” (.15 mm) depth would be added to the unaffected areas, now creating uncut triangles that would be .013” (.33 mm) high or thick. We have tested several types of .020”(.51 mm) thick plastic that have responded very well to this or very similar rule heights. It is our theory that we may eventually have a few microperforating rule heights (in relation to the cutting rule height, which is normally .937” (23.8 mm)) to handle a few ranges of material. As possible examples, a .934” (23.7 mm) height might effectively handle thicknesses from .008” (.20 mm) to .012” (.30 mm). A . 930” (23.6mm) rule height might handle a range of thickness say from .013” (.33 mm) to .018” (.46 mm) and possibly a .928” (.23.6 mm) height might handle materials from .019” (.48 mm) to .024” (.61 mm) thick, etc. We have seen several customers grind down our standards of .934” and .937” height to achieve something like we have described above. This material is in successful (albeit limited) use around the world, including R&D runs at Bobst Center in Roseland, New Jersey, though we certainly recognize that there may be some fine-tuning that still lies ahead. |
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