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Abstract

A paperboard material having increased strength comprising a strengthening agent at least partially impregnated into at least one of the first and second sides of the paperboard material while the paperboard material is substantially dry, and a method for making same. The strengthening agent comprises a small particle size styrene butadiene resin having a particle size of less than or equal to about 1000 angstroms, and more preferably about 700 angstroms or less. The strengthening agent may also include a stiffening additive having a higher glass transition temperature than the styrene butadiene resin, such as a small particle size polymer resin, preferably a polystyrene pigment have a particle size of 700 angstroms or less. The strengthening agent is preferably applied to the paperboard material during the dry end of the process. To this end, the strengthening agent is preferably impregnated into the paperboard material by a size press, or other standard paper sizing equipment.

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