Bonding agent is one of the most important auxiliary materials and is widely used in packaging operations. Adhesives are sticky substances that connect two separate materials together by virtue of their adhesive properties. There are many types of adhesives.
The starch binder is a mixture of water, raw starch, cooked paste, caustic soda, borax and formaldehyde, the approximate ratio is: water 80%; starch 20% (of which raw starch accounts for 85%, cooked starch accounts for 15%); caustic Sodium (total starch) 2.4-2.8%; Borax (total starch) 2.7-3.2%, about 10 moles; trace formaldehyde.
Most of the starch used by some carton factories in the United States is corn starch. Some are untreated pure corn flour, and some have been chemically treated, especially the treated special starch has good stable viscosity and excellent moisture content. Some starches are powdery and some are granular. The granules are just loose pieces surrounded by powder, which are used to make a whole batch of paste in the lower batter.
Some factories use specially processed corn starch to produce a single-viscosity adhesive, with a gelatinization point starting at 61°C and finishing at 63°C. Although the gel point is low, the adhesive gels quickly like a general double-sided machine paste during bonding. The viscosity is usually between 27 and 32 seconds. 680 gallons of paste use 500 kilograms of starch.
After the starch is stirred in water at room temperature, its particles are dispersed into a milky state, but it will not dissolve or absorb water. If the stirring is stopped, the starch will settle at the bottom and gradually form hard lumps. Once the hard lumps are formed, it will not be so easy to disperse again. Starch dispersed in water starts to absorb water and expand when heated. Raw starch is used in the adhesive formulation, which starts to swell at about 70°C. The temperature rises to 90°C and the expansion effect is completed. Gelatinized starch is very viscous, and its degree depends on the amount of starch in the water.
