Heat Sealers
Heat Sealers
The construction of gastight containers using barrier films relies primarily on heat-sealing to make oxygen-impermeable unions. One surface of a heat-
sealable barrier film must consist of a polymer, usually either polyethylene or polypropylene, that has a softening point below 177 °C and is fusible in a man- ner that forms a nonleaking, oxygen-tight seal. Creating the perfect seal requires
a balance of hand pressure, sealer temperature, and press time. Doing this cor- rectly is an acquired skill, but with practice and diligence most conservators develop a degree of skill that allows them to turn barrier film into perfect anoxia bags easily and competently.
Heat-sealing has long been used in the manufacture of industrial packaging for such diverse, atmospherically sensitive materials as food and electronic compo- nents. A wide range of heat-sealing equipment is commercially available. Sources include bagging supply companies, general equipment suppliers, and more specialized sellers of materials for conservation. Table 3.5 describes several different sizes and types of heat sealers. The handheld bar sealer is the most commonly used tool for conservation purposes. Tacking irons, such as the Sealector II or the Seal King, are less frequently used but they are cheaper. Some conservators claim that with experience, they can seal faster with tacking irons than with bar sealers, although the tacking irons must be used with a suitable soft and flat undersurface. A tacking iron's broader seal width—4.45 cm (1¾ in.)
compared to 1.43 cm ( 9 / 16 in.) for the handheld bar sealer—can be an advantage for making larger, flexible chambers. The automatic impulse sealer is more expensive, but it is cost-effective if there is a large amount of bag sealing to be done. Spatula and spade-tip tacking irons provide much smaller heating surfaces but can get into locations where the larger tools may not fit. A small tacking iron is especially suitable when a transparent window is called for in a metallized bag.
It can be used to heat-seal the edges of a barrier-film patch to a metallized film into which a smaller window opening has been cut. Robert Hinerman, working with the conservation staff at the Mendicino County Museum in northern Cali- fornia, has fabricated a sealing tool for this purpose. It consists of a metal ring at
Chapter 3
Table 3.5
Heat sealers.
Cost Type
Description
M odel
Supplier
(1996 US$)
Bar sealer
Handheld
Futura
Packaging Aids
1½ lb (0.68 kg)
Portable
6 in. (15.24 cm) long
Barrier Model
9 / 16 in. (1.43 cm) wide 100-260 °F
(38-127 °C)
Tacking iron
One surface
Sealector II
Conservation Materials 63
thermostated 150-350 °F (65-177 °C)
Tacking iron
Heating area:
Seal King
McMaster-Carr
4 in. (10.16 cm) wide 1¾ in. (4.45 cm) long 150-400 °F (65-205 °C)
Automatic impulse sealer
24 in. (60.96 cm), 2 jaws
92-96348
National Bag Company 637
tabletop model automatic time set
Spatula tacking iron
Heating area:
Tacking tool
McMaster-Carr
11 / 16 in. (2.38 cm) wide
74535A2
¾ in. (1.91 cm) long temperature to 450 °F (230 °C)
Spade-tip tacking iron
Similar in size to the above
Adem C6
Conservation Materials 48
the end of an electric heating iron. The ring, which heats to over 177 °C, has an outer diameter of 5.08 cm and a bar width of about 1.27 cm, and conveniently heat-seals a very functional circular window into the metallized film.