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Cold Crack Facts
From Binding Industries of America - Info Share
Much has been said over the past years about Cold Crack (i.e. Class 90 +10°F; Class 110 -10°F; Class 100 0°F; Class 120 -20°F).
So much emphasis has been placed on this feature in vinyl, but little has been considered as to the quality of the material the user is actually receiving. Within the past few years, the Vinyl Industry has had availability of an additive called, "Adipates." When used as an ingredient in vinyl films and sheetings, the manufacture can produce a sheet using 50% reprocessed and 50% virgin vinyl and still come up to meet the specifications of Class 100 or 0 degree cold crack. If cold crack is used as a determining factor of what quality material is being purchased, the user will be making a mistake regarding the actual quality that he is receiving.
How can we solve product specs and at the same time still insure a consistent product? The answer is to put much more emphasis on SPECIFIC GRAVITY (weight of the material.) Why specific gravity? By definition, specific gravity, is employed to control hand and is also a check on the accuracy of formulation. It is also important because it is used to calculate yield.
A compound that is pre-blended accurately will always have the same specific gravity if the raw materials are not changed. Every pre-blend should be checked before it is released to production. How is the test performed? A sample of pre-blend is hot processed and a small chip of sheeting is then placed in one column of liquid referred to as "heavy water", and the sample will settle to its own level. Granulated beads of known specific gravity are suspended in the liquid. The level of the known are plotted on a graph paper and the specific gravity is interpolated from the level of the sample.
If specific gravity is watched, the changes are much better that the vinyl sheeting will remain constant from order to order for one supplier versus others. With 100% virgin vinyl, the specific gravity on all colors, except while and some metallics, should fall between 1.27 and 1.30 on the specific gravity scale. Because of titanium in the white pigment, specific gravity will be a little higher, but should be controlled at 1.32. If the specific gravity increases above these numbers, it indicates more fillers are being added.
If reprocessed vinyl is added to a formulation, more filler is added and the specific gravity increases. The use of reprocessed vinyl is fine for some applications, but when manufacturing clear overlays with a repro opaque, a compatibility problem has a much better chance of happening.
In our title we mentioned cold crack, this does not mean that no matter what the cold crack of the product is, a vinyl item, i.e., ring binder that is manufactured to 0 degree cold crack being let out in 10 degree - 20 degree plus will not crack. It can still crack if dropped, impact crack. The better the specific gravity (lower), the better the chances are of having less impact problems. By watching the specific gravity, the user can be better assured that no changes have occurred in the formulation they are buying from the current suppliers.