Low density paperboard sheet and tube incorporating the same

Abstract

The present invention provides a low-density paperboard sheet of at least one paperboard layer made from a stock solution that includes a proportion of standard wood flour or fine sawdust in addition to traditional cellulose fibers. The proportion of sawdust can range from 1% to 40% by weight. Advantageously the sawdust of the present invention does not require a costly refining or micronization operation in order to produce low-density, high yield paperboard layers. Additionally, the low-density layers of the present invention may be readily combined with other layers of varying densities in order to tailor the physical properties of the resulting multi-layer sheet to a given application.

Description

FIELD OF THE INVENTION [0001] The invention relates to paperboard sheets, a process for making them, and to paperboard tubes made from such sheets. BACKGROUND OF THE INVENTION [0002] Paperboard is used in a wide variety of applications throughout numerous industries. For example, paperboard sheets are used as slip sheets for separating products, as a backing for laminates and as floor mats. Paperboard is also used to make partitions and roofing felt as needed for the construction of residential and commercial buildings. Additionally, paperboard sheet material can be wound into tubes and used as winding cores for winding filamentary materials such as yams and threads, or for winding continuous sheet materials such as paper, plastic film, and metal foils or sheets. Such tubes can also be used to make containers for food products such as frozen juices, bread dough and snack products. Paperboard tubes are used as forms in the construction industry, e.g., for molding concrete columns and...

AI Technical Summary

Benefits of technology

[0006] The present invention addresses the above needs and achieves other advantages by providing a low-density paperboard sheet of at least one paperboard layer made from a stock that includes a proportion of standard wood flour or fine sawdust in addition to traditional cellulose fibers. The proportion of sawdust can be up to 40% or more by weight. Advantageously, the sawdust of the present invention does not require a costly refining or micronization operation in order to produce low-density, high-yield paperboard sheets.

[0007] The fine sawdust described for use according to the present invention is of a type readily produced by thin curf band saw blades. Commercial sawmills commonly use these blades and, in fact, sell the desired sawdust daily by the ton, for use as boiler fuel. As mentioned above, the fine sawdust of the present invention does not require a costly micronization operation. Instead, only a simple sifting or screening step is needed to remove excessively large pieces of wood. The screened sawdust is then placed in the stock with the cellulose fibers. The stock is fed into a distribution chamber, also called a headbox, former, forming chamber, vat, or the like, depending on the paperboard making machine used. The distribution chamber injects the stock onto a forming wire, and provides the necessary turbulence to the stock to keep it well dispersed. The stock is dewatered through the forming wire, then pressed and dried as discussed above. The low-density paperboard of the present invention may be readily produced via standard papermaking machines that are commonly known in the art (e.g., fourdrinier, cylinder, etc.).

[0008] Standard paperboard making machines may be provided with multiple distribution chambers to produce paperboard sheets of multiple layers. A paperboard layer consists of a single web of paperboard material that has been injected onto a forming wire from a given distribution chamber as discussed above. Often, these individual webs or layers are removed from their respective forming wires and placed one atop the other, dewatered in a press and then dried. The layering of paperboard in this way encourages bonding between fibers of adjacent layers, thereby joining the layers firmly together and ultimately resulting in a unitary paperboard sheet. Alternatively, a multi-layer sheet can be produced by injecting multiple stock flows through a multiple-slice distribution chamber onto a forming wire.

[0009] In preferred embodiments of the present invention, low-density paperboard sheets may possess a single layer or multiple layers. In multiple-layer sheets, the various layers may be produced from stocks of differing sawdust filler concentrations. As a result, sheets may be produced that have layers of various densities. Relatively low-density paperboard, as referenced in this application, is that which has been produced from a stock having greater than 1 percent sawdust by weight. As described in greater detail below, layering paperboard of various densities allows paperboard designers to minimize manufacturing costs while simultaneously tailoring the physical properties of their designs to meet the requirements of a given application.

[0010] For example, in one preferred embodiment of the present invention, paperboard sheets as described in this application may be converted into partitions, support posts, slip sheets, floor mats or the like which serve to protect delicate objects from damage. By incorporating the low-density paperboard of the present invention into the multi-layer sheets used to produce such applications, the desired cushioning properties may be attained without need for additional and often costly lining or coating operations.

Problems solved by technology

Low-density sheets however, tend to be weaker, more compressible or sponge-like and thus capable of greater absorption.

Secondary operations, such as the micronization process described above, add additional and often prohibitive costs to papermaking.