Paperboard material having increased strength and method for making same
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.
1 . A paperboard material having increased strength comprising:
at least one layer of paperboard material having a first side and a second side, the paperboard material also having a thickness;
a strengthening agent at least partially impregnated into at least one of the first and second sides of the paperboard material,
wherein the strengthening agent is impregnated into paperboard material which is substantially dry, and
wherein the strengthening agent comprises a styrene butadiene resin having a particle size of less than or equal to about 1000 angstroms.
2 . The paperboard material of claim 1 wherein the styrene butadiene resin strengthening agent has a particle size of less than or equal to about 700 angstroms.
3 . The paperboard material of claim 1 wherein the styrene butadiene resin strengthening agent has a particle size of about 700 angstroms.
4 . The paperboard material of claim 1 wherein the strengthening agent is impregnated into both the first and second sides of the paperboard material.
5 . The paperboard material of claim 1 wherein the strengthening agent does not substantially affect the thickness of the paperboard material as compared to the thickness of the paperboard material without impregnation of the strengthening agent.
6 . The paperboard material of claim 5 wherein the strengthening agent increases the density of the paperboard material as compared to the density of the paperboard material without impregnation of the strengthening agent.
7 . The paperboard material of claim 1 wherein the strengthening agent penetrates at least one of the first and second sides of the paperboard material by about 10% to about 50% of the thickness of the paperboard material.
8 . The paperboard material of claim 7 wherein the strengthening agent penetrates at least one of the first and second sides of the paperboard material by about 20% to about 50% of the thickness of the paperboard material.
9 . The paperboard material of claim 8 wherein the strengthening agent penetrates at least one of the first and second sides of the paperboard material by about 35% of the thickness of the paperboard material.
10 . The paperboard material of claim 1 wherein the at least one layer of paperboard material comprises liner board.
11 . The paperboard material of claim 1 wherein the at least one layer of paperboard material comprises a corrugating medium.
12 . The paperboard material of claim 1 wherein the strengthening agent has a glass transition temperature of about 15° C. to about 20° C.
13 . The paperboard material of claim 1 wherein the strengthening agent increases the stiffness of the paperboard material.
14 . The paperboard material of claim 1 wherein the strengthening agent further comprises a stiffening additive.
15 . The paperboard material of claim 14 wherein the stiffening additive comprises a polystyrene resin.
16 . The paperboard material of claim 15 wherein the polystyrene resin has a particle size of less than or equal to about 700 angstroms.
17 . The paperboard material of claim 15 wherein the polystyrene resin is a polystyrene pigment.
18 . The paperboard material of claim 14 wherein the stiffening additive has a glass transition temperature of about 70° C. to about 100° C.
19 . The paperboard material of claim 18 wherein the stiffening additive has a glass transition temperature of about 80° C. to about 90° C.
20 . The paperboard material of claim 19 wherein the stiffening additive has a glass transition temperature of about 90° C.
21 . The paperboard material of claim 15 wherein the strengthening agent comprises:
about 80% to about 90% by weight of the styrene butadiene resin having a particle size of less than or equal to about 1000 angstroms, and
about 10% to about 20% by weight of the stiffening additive.
22 . The paperboard material of claim 21 wherein the stiffening additive comprises a polystyrene resin.
23 . The paperboard material of claim 1 wherein the strengthening agent further comprises a water resistance additive.
24 . The paperboard material of claim 23 wherein the water resistance additive is present in an amount of about 1 wt. % to about 2 wt. % based upon the dry weight of the styrene butadiene resin.
25 . The paperboard material of claim 23 wherein the water resistance additive is selected from the group consisting of alkyl ketene dimers, rosins and alkyl succinic anhydrides.
26 . The paperboard material of claim 25 wherein the water resistance additive comprises an alkyl ketene dimer.
27 . A method for manufacturing paperboard having increased strength comprising the following steps:
impregnating at least one side of a paperboard material having a first side and a second side with a strengthening agent, the first and second sides each having a surface and the paperboard material also having a thickness,
the strengthening agent penetrating at least one side of the paperboard material to a depth below the surface of at least one of the first and second sides,
the step of impregnating the paperboard material occurring after the paperboard material is substantially dry,
wherein the strengthening agent comprises a styrene butadiene resin having a particle size of less than or equal to about 1000 angstroms.
28 . The method of claim 27 wherein the step of impregnating the paperboard material is carried out with a size press.
29 . The method of claim 27 wherein the step of impregnating the paperboard material comprises impregnating both the first and second sides of the paperboard material with the strengthening agent.
30 . The method of claim 27 wherein the styrene butadiene resin strengthening agent has a particle size of less than or equal to about 700 angstroms.
31 . The method of claim 27 wherein the styrene butadiene resin strengthening agent has a particle size of about 700 angstroms.
32 . The method of claim 27 wherein during the step of impregnating the paperboard material, the strengthening agent penetrates below the surface of at least one of the first and second sides of the paperboard material without substantially affecting the thickness of the paperboard material as compared to the thickness of the paperboard material without impregnation of the strengthening agent.
33 . The method of claim 27 wherein during the step of impregnating the paperboard material, the strengthening agent penetrates at least one of the first and second sides of the paperboard material by about 10% to about 50% of the thickness of the paperboard material.
34 . The method of claim 33 wherein the strengthening agent penetrates at least one of the first and second sides of the paperboard material by about 20% to about 50% of the thickness of the paperboard material.
35 . The method of claim 27 wherein the strengthening agent has a glass transition temperature of about 15° C. to about 20° C.
36 . The method of claim 27 further including the step of diluting the styrene butadiene resin to a solids loading of about 10 wt. % to about 50 wt. % prior to the step of impregnating the paperboard material with the styrene butadiene resin.
37 . The method of claim 36 further including the step of diluting the styrene butadiene resin to a solids loading of about 10 wt. % to about 25 wt. % prior to the step of impregnating the paperboard material with the styrene butadiene resin.
38 . The method of claim 27 wherein the strengthening agent further comprises a stiffening additive.
39 . The method of claim 38 wherein the stiffening additive comprises a polystyrene resin.
40 . The method of claim 39 wherein the polystyrene resin has a particle size of less than or equal to about 700 angstroms.
41 . The method of claim 40 wherein the polystyrene resin is a polystyrene pigment.
42 . The method of claim 38 wherein the stiffening additive has a glass transition temperature of about 70° C. to about 100° C.
43 . The method of claim 42 wherein the stiffening additive has a glass transition temperature of about 80° C. to about 90° C.
44 . The method of claim 43 wherein the stiffening additive has a glass transition temperature of about 90° C.
45 . The paperboard material of claim 38 wherein the strengthening agent comprises:
about 80% to about 90% by weight of the styrene butadiene resin having a particle size of less than or equal to about 1000 angstroms, and
about 10% to about 20% by weight of the stiffening additive.
46 . The method of claim 27 wherein the strengthening agent further comprises a water resistance additive.
47 . The method of claim 46 wherein the water resistance additive is present in an amount of about 1 wt. % to about 2 wt. % based upon the dry weight of the styrene butadiene resin.