There are 3 different kinds of seals these are: Gummed; Press Seal and Peel & Seal.
Gummed:
Gummed envelopes are one of the first types of adhesive seal to
have been created and are still widely used today. The first method used
for sealing envelopes was a wax seal. It was 50 years after the first
envelope making machine was created (back in 1845) before a commercially
successful machine for producing pre-gummed envelopes was created. The
gum you find on envelopes today is a water soluble gum and the most
common sealing method. To activate the adhesion process you must moisten
the layer of adhesive along the envelope flap, this then allows the gum
to glue the flap closed. When stored correctly, gummed envelopes will
last for a number of years. The gum is made using a blend of synthetic
resin and dextrin and so is completely biodegradable.
Press Seal or Latex Seal:
Press and Seal envelopes are another of the most popular sealing
methods. They eradicate the need for moistening the flap and practically
do all the work themselves. All you have to do is apply the two ‘glued’
flaps together. These envelopes have a strip of latex on each flap so
that when they are pressed together, they form an instant bond. Bear in
mind when purchasing these envelopes that they have a shelf life of
approximately 1 year, so only purchase as many as you think you will use
in that time, veering on the side of caution. Having said this, if they
are stored right they may last you a little longer. You will find
security slits on the flap of peel and seal envelopes which causes the
flap to rip in the event of the envelope being tampered with once
sealed.
Peel and Seal:
The peel ans seal envelope (also known as Quick Stik,
strip seal and peel & stick) is up there in the top most secure
ways to seal an envelope. You simply peel away the strip which protects
the latex adhesive and press down to form an instant bond. These
envelopes have a longer shelf life and almost act as a tamper proof
security seal as they are almost impossible to open unless the flap is
torn. Using a peel and seal flap envelopes makes sealing quick and easy.
No more licking the gummed edge, just simply peal back the strip and
seal.
