Bottom paste adhesive

Three adhesives are used in paper bag manufacture side seam adhesives, bottom paste adhesives, and cross pastes. The side seam adhesive is used to form a cylinder from a flat sheet of paper. This adhesive must develop a strong bond quickly, so the tube can be cut for further operation. The viscosity should be about 3,000 cP. and solids about 25%. One formulation is water 68%, dextrin 28% heat to 160°F (71°C), add 3% borax, heat to 190°F (88° C), add 3% preservative. A water-resistant formulation is water 1700 pounds, white dextrin 700, soap 2, urea-formaldehyde 70, heat to 200°F (93°C), dilute with cold water to 260 gal volume, and add 14 pounds ammonium chloride. This formulation should be used immediately. Its pH is about 6. ... 

Bottom paste adhesives are applied to one end of the tube formed above to close that end to form a bag bottom. These pastes are usually made from unconverted starches. Soap and/or salt may be added to produce a thixotropic paste (flows under shear but sets up if left undisturbed). A water-resistant formulation is com starch 13%, poly(vinylalcohol) 4.5%, poly(vinylacetate) 1 %, soap 0.1%, water 81%, heat to 90°C (194°F), cool to room temperature. ... 

Also known as DCM or dichloromethane. Often used as an adhesive solvent for acrylics. Pure DCM can be found in craft stores. DCM must be distilled first from all non-flammable paint strippers beforehand (they contain a paste that holds several unwanted substances.) The paint stripper may also contain methanol (most marine grade paint strippers are 80-90% DCM. Methanol is also an organic solvent. DCM distills at 47° C or 116° F. Pure DCM is best. May cause cancer and blindness. Take necessary precautions. Methylene chloride sinks to the bottom of the jar. 

When exposed to the wave, the adhesive-attached surface-mount devices pick up solder on their metal contacts and the solder bridges from the contact to its corresponding bonding pad on the bottom side of the PWB. In the case of solder-tail components, the molten solder is drawn by capillary action between the lead and the FTH barrel. If the barrel and lead are hot enough and well fluxed, the solder fills up the barrel and wick to form aiets from pin to barrel. As the board continues past the wave, it cools, solder sohdifies, and joint formation is complete. 

The materials used in the surface-mount, area-array assembly process include solder paste, stencils, components, flux, and the PCB. In wave soldering applications, solder paste and paste deposition processes are eUminated, and a cured adhesive is used to retain bottom-side components on a PCB during exposure to a solder wave. 

---