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| Reply To: | TechNet E-Mail Forum. |
| Date: | Thu, 13 Jul 2000 10:15:25 +0800 |
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Epoxies are thermosetting. Surely this process is not indefinitely two-way? Or
should I say: beyond what temperature is the process no longer two-way (and what
is the technical term for this temp.)?
Michael Fennema
-----原始郵件-----
寄件者: Mike Fenner <[log in to unmask]>
收件者: [log in to unmask] <[log in to unmask]>
日期: Thursday, July 13, 2000 05:58
主旨: Re: [TN] Glass Transition Temperature (Tg) Questions
|Just for completeness, thet Tg is two way:
|When ever the polymer is at a higher temperature than the Tg, the
|chemical bonds are relaxed and the material is relatively floppy. When
|the polymer goes back below the Tg the chemical bonds tighten back up
|and the material reverts to its hard state. The transition from hard
|to soft (or soft to hard) is a repeatable process in either direction.
|
|Mike
|
|----- Original Message -----
|From: "Alain Savard" <[log in to unmask]>
|To: <[log in to unmask]>
|Sent: Wednesday, July 12, 2000 5:35 PM
|Subject: Re: [TN] Glass Transition Temperature (Tg) Questions
|
|
|> My answers marked with 2 asterisks (**) below.
|>
|> Alain Savard, B.Sc.
|> Chemical Process Analyst
|> CAE Electronics Ltd.
|> e-mail: [log in to unmask]
|>
|> -----Original Message-----
|> From: Hiteshew, Michael [mailto:[log in to unmask]]
|> Sent: July 12, 2000 12:06 PM
|> To: [log in to unmask]
|> Subject: [TN] Glass Transition Temperature (Tg) Questions
|>
|> Hi,
|> I've been reading up on laminate materials and have some
|questions
|> that I hope some-one can help me with:
|>
|> 1. What is the "glass transition" ? What is the glass transitioning
|from and
|> to? I'm guessing it's the plastic stage that occurs in a material
|just
|> before it melts.
|>
|> ** Temperature at which the laminate turns from a relatively hard
|and
|> potentially brittle state, to a vicious, semi-liquid stage. Epoxy
|used in
|> the boards is more likely to decompose or burn than it is of ever
|melting.
|>
|> 2. What is gained by a higher Tg in tetrafunctional and
|multifunctional
|> epoxy-glass?
|>
|> ** Higher Tg means that you have a better resistance to heat from
|any
|> source. Your board is more likely to keep it's shape during heat
|related
|> fabrication process or during use if it has a higher Tg.
|>
|> 3. What is meant by the prefixes "tetra" and "multi" as they're
|applied
|> here? Is it a reference to the number on bonds in the chemical
|structure of
|> the epoxy or glass?
|>
|> ** It refers to the number of linkage sites of the epoxy prepolymer.
|>
|> Thanks in advance,
|>
|> Michael Hiteshew
|> Lockheed Martin NE&SS-Baltimore
|> [log in to unmask]
|> (410) 682-1259
|>
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