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About celluloid sheet FAQ

Author:Jiujiang CelluloidSource:ReproducedDate:2016-01-12

Q: Is celluloid difficult to work?
A: Quite the opposite - it is in many respects a dream material.  It can be cut, drilled, machined, and polished with ease, using standard tooling and equipment.  For optimal results, drill bits and cutting tools should be ground in the same manner as for other cellulosics, such as cellulose acetate, but this is not nearly as critical as it is when working less forgiving materials such as acrylic.  Celluloid cuts cleanly, and without the unpleasant (and sometimes toxic) dusts and vapors given off by more purely synthetic plastics.  

Q: Have you ever seen a ping pong ball explode?  
A:Neither have we.  Ping pong balls are one of the few common everyday articles still made of genuine celluloid.  Celluloid is classified by the US DOT as a "Flammable Solid", not as an explosive.  Guitar picks, eyeglass frames, hair clips, and purse handles are also items that are sometimes still made of celluloid.
The myth of explosive celluloid is not new.  In large part, it seems to be rooted in a fundamental misunderstanding of the nature of one of celluloid's key ingredients, cellulose nitrate.  In its most highly nitrated form, cellulose nitrate can indeed be used as a propellant (smokeless powder) or low explosive (guncotton).  The cellulose nitrate used to make celluloid, however, is much less highly nitrated.  It is then plasticized with camphor, with the addition of colorants and stabilizers.  It burns comparatively slowly - and all the more so when in a solid block (for pyrotechnic applications, cellulose nitrate is not only highly nitrated, but also rolled paper-thin, shredded, granulated, or otherwise finely divided).
You may run across colorful tales of early celluloid billiard balls exploding when they collided.  These stories are often repeated with various embellishments in popular histories of science, but specialist scholars now uniformly regard them as apocryphal - 19th-century urban legends (see here, here, and here).
There were a number of explosions at celluloid factories in the late 19th and early 20th centuries, which surely contributed to the impression that celluloid was dangerously unstable.  Yet the real danger was in the production process, not the finished product.  Celluloid manufacture involved the use of copious quantities of volatile solvents, which had to be extracted or cooked off before the celluloid was ready to be sold.  Most celluloid factories also did their own nitration, with many producing not just ordinary cellulose nitrate for solid celluloid, but also more highly nitrated cellulose for use as film stock as well as very highly nitrated cellulose for use as explosives, significantly increasing the riskiness of the operations.

Q:  Is shrinkage a problem with celluloid?
A: It certainly can be if the material isn't properly made.  Rush the drying process, and the celluloid will behave like green wood, shrinking as excess residual solvents gradually evaporate.  This happened not long ago to a prominent Italian pen company, whose customers began returning their expensive limited-edition pens for loose cap bands and tight caps.  The use of celluloid was blamed, even though tens of thousands of celluloid pens from the 1920s, '30s, and '40s survive to this day with cap bands tight and perfect cap to barrel fit.  Since proper seasoning takes a long time - months in a special oven for large slabs and rod stock - the temptation to cut corners is as obvious as it is short-sighted.  We take great care to insure that our celluloid is fully dried before shipment.
Note that celluloid may exhibit a different kind of shrinkage immediately after being cut.  Because of the long seasoning process, thicker pieces will have a small amount of internal stress.  Once a square rod is turned round and hollowed out, the resulting tube will shrink slightly in the absence of the core material around which it originally solidified.  In recent testing, tubing turned from a sample of our celluloid shrank approximately .0025" to .003" over the first 48 hours, remaining stable thereafter.  There would appear to be no need for further stress relieving measures, as celluloid is far more elastic than hard plastics such as acrylic, and does not suffer from their vulnerability to developing internal stress cracks.
There may be some cases where further curing is desirable.  Perhaps the celluloid article is going to an unusually hot and dry destination, or to high altitude; perhaps design tolerances are especially tight.  In such cases, it is worth noting what Parker Pen did in the old days.  Parker had a special curing room, kept at 100-110F (38-43C), where they held celluloid pen parts for 14 to 30 days, depending on the size of the part.  The parts appear to have been finish-machined before going into the curing room, but threaded only after coming out.  Cap bands would also have been applied afterwards, guaranteeing lasting tightness.

Q: Can you supply celluloid as round rods or tubes?
A: Our celluloid is made the traditional way, in large slabs.  These slabs are then either sliced into sheets, or cut into rectangular slabs and rod stock.  Celluloid is not a material well adapted for extrusion, so round rods must be obtained by turning down square stock - a service we do not offer at the present time.  Celluloid tubing can be made by wrapping sheet stock around a mandrel.  We are considering offering this material in the future, but do not have any currently available.