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Stiction on plastic cards

Stiction on plastic cards

(OP)
Greeting-
I work for a company that makes ids that are printed on plastic cards the size of credit cards/ drivers licenses. The card stock is coated with silica and some are not. I was tasked recently to resolve the jamming issues we have been experiencing with non-silica card. I've come to the conclusion non-silica cards have a higher level of stiction when compared to silica cards. My question is, what are some of the methods to remove stiction? So far from what I've read:
* use canned air and blow it in between the cards
* increase the surface roughness spec
* store cards in a mylar bag sealed with nitrogen

One interesting thing is non silica cards with magnetic strip do not jam, I contribute this to the mag strip am I correct on this?

regards
frank

RE: Stiction on plastic cards

You correctly attributed this to surface roughness. Perfectly smooth, flat surfaces tend to stick. Anti-block agents are used to give surface roughness. They are simply particles, usually of a mineral filler such as silica, kaolin, diatomacous earth or similar. The particles create many small protrusions and thereby remove the sticking. There are whole book chapters on anti-blocks and information available online if you search for that term.

However, I need to ask why you've been asked to remove silica when it's working. I can think of three reasons.

1. Save cost by removing the additive
2. Perceived safety issue due to respirable silica particles
3. Silica is abrasive and can cause machine wear, especially on the knife when you're stamping out the cards

If we know the reason it's easier to suggest a solution.

Chris DeArmitt - PhD FRSC

Plastics & Materials Consulting
www.phantomplastics.com

Plastic Training Seminars
www.plastictraining.com

RE: Stiction on plastic cards

(OP)
Hi Chris-
Thanks for the reply and the web link, which I read through, excellent information. Below is the answers to your questions:

1. Save cost by removing the additive
Not sure, I believe its the way the cards are being processed, but I'll have to ask.
2. Perceived safety issue due to respirable silica particles

3. Silica is abrasive and can cause machine wear, especially on the knife when you're stamping out the cards
The cards are jamming in a zebra printer; where trying to determine the root cause which I discovered non-silica cards jam more frequently than silica cards.

Now my questions:
Is it possible that silica can come off a card during the printing process?
If silica is coming off the cards during printing, can it contribute to jams?
Is there away to measure the amount of silica on a card before and after printing? Crude method?
Can card coated with silica absorb moisture? If so, what's the best method of storing them?
I ran 500 cards with non silica but a magnetic strip and experienced no jams. I'm assuming its the mag. strip helping out

thanks
Frank

RE: Stiction on plastic cards

Here are some thoughts.

A fine texture on the roller while making cards would achieve the non-stick effect (by introducing roughness) without the need for silica. Could save money.

As above you'd not have any worry about silica in the air or being rubbed off.

Silica is unlikely to come off as the particles are embedded in the polymer.

Silica coming off could contribute to jams because it will coat any rubber rollers making them non-tacky. Same as when the photocopier rollers get dirty and the copier stops working. However, this doesn't seem to fit what you observe i.e. that non-silica cards give less jams.

Silica amount can be measured but I don't know of a crude way. The best ways are XPS/ESCA, TOF-SIMS or EDAX (maybe FTIR)

Silica takes up moisture but not when in the polymer.

I suspect that the magnetic strip prevents jams because it is microscopically thicker or thinner than the rest of the card so it creates a channel letting air between the cards and preventing them from sticking.

Chris DeArmitt - PhD FRSC

Plastics & Materials Consulting
www.phantomplastics.com

Plastic Training Seminars
www.plastictraining.com

RE: Stiction on plastic cards

One possible factor for consideration is wear. Anything surface feature that is solely due to the plastic itself will wear down through handling, over time.

re. silica. That would seem to be a low risk. The surface area of the card is finite, and the amount of silica is finite, and embedded in the plastic. In contrast, silica is used as a flow agent in the making of potato chips, and there is no concern for inhalation, even though one could certainly eat a lot of chips, and some people eat chips through inhalation, or so it seems.

TTFN
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RE: Stiction on plastic cards

Static electricity can be a factor. I was involved with some specialized machinery for a printing company 20-some years ago, and static was a problem in paper and plastic laminates.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Stiction on plastic cards

Silica comes in different forms and sizes. Quartz causes cancer if inhaled for prolonged periods. In order to be inhaled it needs to be a certain size. Quartz is crystalline whereas amorphous silica is not considered dangerous.

Chris DeArmitt - PhD FRSC

Plastics & Materials Consulting
www.phantomplastics.com

Plastic Training Seminars
www.plastictraining.com

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