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From: jwi@lzfme.att.com (Jim Winer @ AT&T, Middletown, NJ)
Newsgroups: comp.misc,comp.lang.postscript
Subject: Re: Laser Printable Checks?
Summary: Electrostatic, not magnetic
Message-ID: <1325@lzfme.att.com>
Date: 8 May 89 17:56:45 GMT
References: <12810@jade.BBN.COM> <555@lzaz.ATT.COM> <1103@cantuar.UUCP> <3148@kitty.UUCP>
Organization: AT&T, Lincroft NJ
Lines: 54

In article <3148@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes:
> In article <1103@cantuar.UUCP>, greg@cantuar.UUCP (G. Ewing) writes:
> > Well, not sure, but I think the toner used in LaserWriter cartridges
> > is *already* magnetic! I dismantled a toner cartridge once, and found
> > it contained a magnetic roller which the toner particles clung to. As
> > the roller was rotated, the toner sort of crept around it in response
> > to the changing flux direction.
> 
> 	I don't known anything about LaserWriters or laser printers
> which use cartridges, but in more rugged laser printers (such as the
> Xerox 4045) there is a magnetic material used that is called "developer".
> The developer is "recirculated" within the laser printer and does not
> mix with the toner after it has been despoited on the drum.  In a
> normally functioning laser printer no portion of the developer is
> actually fused upon the resultant copy paper.

Neither the developer nor the toner is magnetic.  They are
electrostatic.  The xerography process works approximately as
follows (I may have polarity backwards):

1. Developer is charged positive and attracts toner which becomes
charged positive.

2. Drum is charged positive by corotron wire placed just
ahead of laser write area.

3. Laser writes on drum.  Where laser writes, charge leaks off
leaving drum negative.

4. Positive charged toner is attracted to negative (written) durm
are and repelled from positive (cleared) drum area.

5. Paper is charged negative by corotron wire just before impress
area.

6. Positive toner (written areas) jumps from drum to paper.

7. Paper goes through fuser where heat melts toner to paper.

8. As drum continues to rotate, another corotron wire charges drum
positively which causes any remaining toner on drum to jump off.  It
is collected in sump.

This is only approximate, but the important point is that the
process is entirely electrostatic, not magnetic.

Jim Winer ..!lzfme!jwi 

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