Printable composite paperboard for packaging

A printable composite paperboard product exhibiting thicknesses of from 0.026 to 0.044 inches, with corresponding stiffness and compression strength, is disclosed for printable packaging materials of substantial density and compressive strength for products in need of a barrier layer. The invention product is made by a process whereby a thinner bleached (white) paper sheet product is laid atop a thicker unbleached paper product. The topmost sheet layer may be one of a variety of materials including, but not limited to, fine papers and bleached paperboard; whereas, the bottom layer may be one of a variety of materials including, but not limited to, an unbleached folding carton board. Also disclosed is a box formed of the disclosed paperboard product.

DESCRIPTION The invention product is made by bonding a thinner bleached (white), unprinted paper product bonded atop a thicker unbleached paper product. The topmost sheet may be one of a variety of materials including, but not limited to, fine papers and bleached paperboard; whereas, the bottom sheet may be one of a variety of materials including, but not limited to, an unbleached folding carton board. The top layer is made in a fashion whereby it contains a coating on both sides. A non-exhaustive list of coatings that can be used are latex-clay mixtures, polyvinyl alcohol &lsqb;PVOH&rsqb;, polyvinylidene chloride &lsqb;PVDC&rsqb; and acrylic polymers. The top layer caliper may range from above 0.002 to 0.012 inches. The bottom layer is made in a fashion whereby its density may range from 8.0 to 9.0 lb/3000 ft 3 /caliper pt., and its caliper may range from above 0.025 to 0.032 inches. The composition production process is accomplished by applying a continuous film of adhesive to one of the sheets and joining (bonding) it with the other sheet via the adhesive film. The adhesive film may be applied to the topmost sheet, and the two sheets then combined by the action of a nip between two cylindrical rollers. One or more of such rollers may be covered with a resilient cover (preferred) or they may be hard metal (e.g., steel) surfaces. The combined board product may be cut into sheets of desired dimensions or wound onto paperboard cores for later converting steps. A non-exhaustive list of examples of laminating adhesives that may be used include, polyvinyl acetate (PVA), PVOH, PVDC, SBR latex, acrylic emulsions, sodium silicate, cooked starch, and extruded polymer films including, low density polyethylene (LDPE), high density polyethylene (HDPE), polyvinylidene chloride (PVDC), nylon, and polypropylene. The invention paperboard composite offers significant benefits over the currently available boards for similar applications. These benefits are listed below. greater press and diecutting speeds ease of operating under one roof less rejects runs like solid fiber board set up times are not long thus well suited for both small or large volume runs no flute lines performs well for embossing, foil stamping, UV coating which are very difficult with conventional corrugated board. Available in sheets and roll form No warp issues Superior performance in refrigeration/freezer applications. ability to make invention board with specialty internal barrier properties ability to make invention board with extrusion coatings such as polypropylene, polyester, nylon, PMP, and other specialty resins. The invention board can be used for packaging in various market segments such as, but not limited to, consumer electronics, liquor and other beverages, food, hardware, sporting goods, personal care, medical devices, pharmaceuticals, etc. The following examples show the benefits of the invention herein described. 
 EXAMPLE 1 This example compares certain properties of various packaging materials. 2 TABLE II Comparison of Various Materials R-value Thermal Conductivity Caliper (caliper/k) (B/hr*ft* (in.) (hr*ft 2 ° F./Btu) ° F.) (W/m ° C.) Printed Package Invention board 0.0376 0.0730 0.0429 0.0742 MiniFlute 0.0376 0.0719 0.0436 0.0754 The data from Table II show relative R-values (thermal transfer) for the invention board and currently available flute-based packaging substrate. It is noted that the invention board as the same caliper showed higher (i.e., better) R-values compared to the same caliper prior art board. The following table shows a comparison with invention paperboard (samples B, C, and D) compressive strength properties versus those of a commercial prior art packaging material (sample A). 3 TABLE III Box Compression Results-Invention Board versus Small Flute Corrugated Basis Wt. Average & Tappi Caliper Box Compression lbf. Sample lb./3000ft 2 Std. Dev. (10 −3 ) Moisture % T.B. E.E. A-small flute corrugated 300.89 X 38.77 6.35 140.85 242.10 S.D. 0.125 3.69 26.34 B-38 pt invention board 393.17 X 37.34 6.46 147.08 276.28 S.D. 0.317 5.24 14.94 C-37 pt invention board 387.29 X 35.93 6.30 160.75 239.38 S.D. 0.411 4.80 9.50 D-39 pt invention board 399.49 X 37.50 5.95 150.58 269.83 S.D. 0.56 6.73 13.76 The data from Table III show generally comparable or improved compression strengths achieved with the invention paperboard laminates at lower calipers as compared to the prior art. Further examples of the invention board are shown in Table IV. Specifically, Table IV shows further comparison with prior art packaging paperboard. 4 TABLE IV Block and Panel Compression - Kraftpak ® Laminates versus Smallflute Basis Tappi Taber Stiffness Block Compression Panel Compression 4 pt. Bend- Weight Caliper (gm-cm) +Z Tensile psi psi ing psi Sample (lb/1000ft 2 ) (10 −3 ) MD CD psi MD CD MD CD MD CD Invention Board 120 35.13 1700 790 43.20 488 299 102.3 82.7 3.53 1.38 0.11 0.02 Smallflute &lsqb;F-flute&rsqb; 100 39.21 1959 1007 33.86 305 297 95.2 78.7 4.30 1.92 0.11 0.04 The data of Table IV show that the invention paperboard laminate achieves acceptable 4 point bending stiffness and improved z-direction tensile strength and compression (block and panel) at significantly reduced caliper. While the invention has been described above with reference to specific embodiments thereof, it will be apparent to skilled persons that minor changes, modifications, and variations may be made to the details of the invention described herein without departing from the underlying principles of the inventive concept disclosed, including various obvious substitutions, such as substitute pH-modifying acids and/or bases. Nevertheless, the subject matter of the invention is within the bounds of the following claims.