Stamp adhesives

We subject envelope and stamp adhesives to stringent safety requirements. Since we re likely to swallow traces of the stuff, we have to regulate it as a food. Gum arable from the acacia tree, dextrin from corn starch, and the water soluble resin polyvinyl alcohol are the adhesives we use most often. We also... 

An adhesive is a linear or branched amorphous polymer above its Tg. It must be able to flow on a molecular scale to grip surfaces. (This definition is not to be confused with polymerizable adhesive materials, present in monomeric form. These are tacky or sticky only in the partly polymerized state. Frequently they are cross-linked thermoset, finally. Contact with the surface to be adhered must be made before gelation, in order to work.) An example is the postage stamp adhesive, composed of linear poly(vinyl alcohol), which is plasticized by water (or saliva) from below its Tg to above its Tg. On migration of the water away from the adhesive surface, it sticks. ... 

Stamp adhesives are usually remoistenable and based on dextrin, resin, or dextrin/resin blends. 

Adhesive Transfer Processes. Many polymers, whether dehberately or accidentally, are adhesives, so that much of the adhesive industry can be regarded as a part of the mbber and plastics industry. However, there are several important material-transfer appHcations involving polymer products that are so critically dependent on controlled adhesion that they merit specific mention in that category. They include hot stamping foils, release coatings for pressure-sensitive adhesive products, photocopier materials, transfer coatings, and transfer printing of textiles. 

Starch pyrodextrins and British gums have the abiUty, in aqueous dispersion, to form films capable of bonding like or unlike materials. Thus, they have uses as adhesives for envelopes, postage stamps, and other products. These dextrins are used in glass-fiber siting to protect the extmded fiber from abrasion, and as binders for metal core castings, water color paints, briquettes, and many other composite materials (qv). 

In the manufacture of shaft seals, the molding is the process where the compound and treated metal stamping (phosphated and adhesive applied) are brought together to form the conventional lip type shaft seal. Therefore, it is critical that the compounds used are formulated to suit the molding process. There are three fundamental molding processes in use today compression, injection, and injection/transfer. 

TPEs can be bonded to other materials by adhesive, heat bonding, electromagnetic filling, radio frequency, heat-sealing lamination, friction and spin welding, and ultrasonic welding. For TPUs, the most widely used techniques are radio frequencies, and ultrasonic and hot stamping. A few typical applications include football bladders, valves, and conveyer belts. 

The manufacture of a sandwich fusehead proceeds in the following manner. Brass or other metal foils are fixed on each side of a sheet of pressboard with a suitable adhesive. The pressboard is then stamped into combs of the shape shown in Fig. 10.3 and steps are cut in the tips of the heads. Fine resistance wire is stretched across the heads and soldered to the foil on each side of the pressboard. These operations were originally all carried out by hand now many are carried out mechanically. 

For many applications, it is desirable that the adhesive layer accept printable elements readily in its fully cured state. This characteristic usually requires the layer to be soft in its cured form. Adhesive thin films composed of low-modulus PDMS elastomer meet this requirement well18 and can guide transfer of elements to a target quickly (without exposure to heat or light). Surprisingly, the direction of transfer can be well defined even when the composition of the adhesive is identical to that of the stamp. Successful transfer is thus determined by several factors surface chemistry, conformability (modulus), geometrical/mechanical factors (e.g., adhesive film thickness), and others. 

Meitl, M. A. et al. 2006. Transfer printing by kinetic control of adhesion to an elastomeric stamp. Nature Mater. 5 33-38. 

Hsia, K. J. et al. 2005. Collapse of stamps for soft lithography due to interfacial adhesion. Appl. Phys. Lett. 86 154106. 

Kim, Y.-K. Kim, G T. Ha, J. S. 2007. Simple patterning via adhesion between a buffered-oxide etchant-treated PDMS stamp and a Si02 substrate Adv. Fund. Mater. 17 2125-2132. 

To determine the wet bond strength coated panels were immersed in distilled water for 1500 h, removed and discs 25.4 mm in diameter stamped from them. The surfaces were wiped with a dry tissue and bonded between two cylindrical test pieces using a polyamide cured epoxide adhesive and immediately placed in a sealed container at 100% RH for the adhesive to cure. After 16 h the specimens were broken on an Instron Universal Test Machine with minimum delay. Recovered values were measured after the panels had dried out at room temperature and humidity for 7 days. Clearly, it is unlikely that the values reported represent the minimum bond strengths, as some drying out is almost inevitable, but the values are directly comparable. 

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