FIELD OF THE INVENTION

The present invention relates to compositions, and wet laid articles made from the compositions comprising cellulose fibers, and cellulose ester fibers, as well as wet laid processes to produce the compositions.

BACKGROUND

Wet laid products are generally made by a process in which a stock, or furnish, is prepared by suspending pulped cellulose fibers in water and refining this mixture to prepare a refined pulp slurry or pulp stock containing fibrillated cellulose fibers, and optionally adding one or more of a variety of additives such as retention aids, internal sizing agents, strength polymers and fillers as needed to satisfy end use requirements. The stock is then deposited onto the forming section of a wet laid machine, such as a paper machine, to make a wet laid web. One example of a forming section is a Fourdrinier wire onto which the stock is deposited through the slice of a headbox, to form a continuous wet laid web. Water from the stock drains through the wire to increase the consistency of the web sufficiently to permit it to be processed across rolls unsupported. Water is typically removed through a combination of gravity and vacuum. The web layer is generally pressed through the nip of press rolls to further reduced it water content by mechanical means, after which it enters a drying zone for further removal of moisture from the web by the application of thermal energy. The dried web can then optionally proceed through a sizing press for application of a variety of surface sizing agents. At this stage, because the web is rewet by the application of the sizing agents, the web proceeds through a second drying zone to dry the web to the desired moisture content, and optionally is calendared and taken up on a roll as finished product or product that can be optionally coated and/or super-calendared.

Wet laid machines can operate at high speed and have the ability to produce on the order of more than 400 or even considerably more than 800 tons per day of product, such as paper. One of the rate limiting steps in a wet laid facility is the drainage rate of water from the web on the forming section. Small improvements in drainage rates can have a large effect on production. It is necessary to refine pulp to provide necessary strength and/or toughness to the web, but as more refining energy is applied, the freeness of the pulp (typically measured as the Canadian Standard Freeness CSF) is reduced resulting in a slower drainage rate of water from the web. At a given degree of refining, it would be desirable to increase the drainage rate of water.

It would also be desirable to allow the operator of a wet laid facility the flexibility to increase production by increasing the machine line speed, particularly without additional dryer energy input. This is especially attractive to a mill that is dryer limited; that is, production is limited because the dryers are operating at or near capacity.

Attempts at using certain synthetic fibers, such as polyesters and nylons, in combination with cellulose fibers, to improve the drainage rate of water from the web or to enhance properties of the finished product can be problematic in that they can be damaged or melted or rolled into agglomerates or bundles in the refiner and these defects can lead to web breaks, out of specification sheets, and in some cases the inability to form a web. Additionally, the damaged synthetic fibers may plug or interfere with the operation of the refiner resulting in interruptions to manufacturing to clean synthetic fibers out of the refiner. To avoid this problem, synthetic fibers can be added after the cellulose fibers are refined, but this adds a great deal of process complexity. Many wet laid producers do not have the capability to perform that operation and would have to undertake a significant capital expense to add such equipment. Possibly more importantly, the wet tensile strength of the wet laid web at the forming section may drop so far that the web may become difficult to process because it cannot support its own weight. It would be desirable to improve the drainage rate of a web while minimizing its drop in wet tensile strength in the forming section.

In any wet laid process, there are a variety of energy inputs, one of the largest of which is the energy required to dry the web. It would be desirable to develop a composition containing cellulose that would give the operator a wider operating window and provide the option to maintain the same machine speed energy input to the drying section(s), or increase the machine speed without exceeding the final product % moisture specification. A reduction in energy in the drying zone is advantageous since this section of a wet laid process can have the higher operational expense per unit of water removed. A reduction in the energy input to a dryer section can only be achieved if the web achieves the target level of dryness coming out of the dryer zone. It would be desirable to develop a process and a composition that would allow the operator the flexibility to lower energy consumption in the dryer section or increase the production rate by increasing the machine speed without increasing the energy input to the dryers.

The more efficient removal of water from the web occurs before the dryer section through mechanical means, such as at the nip of a press roll. As the nip gap gets smaller, more water can be forced out of the web, with the result that a dryer web enters the drying zone, requiring less thermal energy input to the expensive drying section. However, there is a practical limit the pressure applied to the web at the press nip in that if the pressure on the web forces the water out of the web faster than the pore and channels between the fibers can allow, the web will fracture, tear, or blow apart, or otherwise interrupt production. It would be desirable to develop a process in which the water removal at the press section can be increased, thereby creating a dryer web prior to the drying section.

The wet laid webs can have many applications. Some of these applications require good air permeability. Others require good water permeability. The air and/or water permeability can be influenced by merely reducing the basis weight of the web/sheet for the desired end application, but by so doing, other properties suffer such as tensile strength, stiffness, tear, and/or burst. It would be desirable to create a web/sheet that has improved air permeability at equivalent basis weight. It would be desirable to create a web/sheet that has improved water permeability at equivalent basis weight.

In some cases, however, the air or water permeability does not necessarily need to improve, and one would rather reduce the cost of the article by reducing the basis weight while retaining at one or more wet laid product properties.

For some applications, a driver is maintaining the thickness of the article while decreasing its basis weight. Therefore, it would be desirable to develop a composition to make the wet laid web that provides a density decrease, enabling the operator to decrease the basis weight while maintaining the same thickness of the web/sheet.

In other applications, a driver is to increase the bulk of the wet laid article, and this usually comes at an expense of employing additives or increasing the basis weight of the composition used to make the web. It would be desirable to develop a composition that increases the bulk of the wet laid web/sheet without having to increase its basis weight or employ additives just to increase bulk.

One of the properties that is important to consider for some applications is the stiffness of the sheet, particularly with paperboard and cardboard. It would be desirable to decrease density at an equivalent basis weight without a significant drop in stiffness.

A decrease in density by reduction of basis weight may also accompanied by a significant decrease in dry tensile strength. It would be desirable to minimize the drop in tensile strength while being able attain one or more of the above stated improvements, such as decreased density, improved air and/or water permeability, or increased bulk.

Maintaining a particular degree of fiber fibrillation may be necessary to impart the needed dry tensile strength for a particular application. Higher amounts of refining energy can increase fibrillation but may also lower the freeness of the pulp and the air and/or water permeability of the resulting web/sheet. It would be desirable to develop a composition and/or process in which increase fibrillation of the pulp fibers can be accomplished without decreasing the drainage rate of the composition or the permeability of the resulting web/sheet.

Many of the wet laid webs/sheets find application in paperboard, cardboard, food packaging, bags, disposable clothing, beverage filtration articles and single use container. While recycling efforts have met with considerable success, not all products find their way into the waste/recycle stream for re-use. Manufacturers and consumers continue to develop their awareness and understanding of the environmental impact of products and their use on the environment. There continues to exist a need and potential to develop wet laid products formed from sustainable materials while also exhibiting environmental non-persistence in product form, while satisfying or improving upon one or more properties for the application.

With the considerable success of waste/recycling efforts, the recycle mill market has grown considerably on a large industrial scale and utilizes many of the same unit processes as would a wet laid facility. Common elements include hydropulping, screening, cleaning, depositing pulp onto a moving wire, draining, and drying. Recycle mills have an additional process step of flotation and de-inking. The waste/recycle mills furnish bales of dried pulp to a wet laid facility, and the waste/recycle pulp is either added to a hydropulper and eventually fed to a refiner, or it is fed to a blend tank downstream of the refiner. The waste/recycle cellulose fibers have already been fibrillated in the course of their manufacture from virgin cellulose fiber. Accordingly, their freeness is already reduced before refining relative to an unrefined virgin pulp, and upon refining, the freeness of the resulting pulp is lower than refining virgin pulp at the same refining energy, resulting in slower water drainage. It would be desirable to develop a composition that can increase the drainage rate of water from a stock containing waste/recycle pulp that has been fed through a refiner.

In addition, it would be desirable to have a composition that has improved texturing. This texturing can be improved by having a texturing that is deeper with the composition comprising cellulose ester staple fibers versus 100% cellulose comparative.

In sum, it would be desirable to develop a composition, process, wet laid product, or articles exhibiting any one of the desired benefits described above. It would also be desirable to develop a composition, process, wet laid product, or articles exhibiting a combination of any two or more of the desired benefits described above.

In addition, it would be desirable to have a paper mill process that is not substantially modified to allow for adding of cellulose ester staple fiber.

SUMMARY OF THE INVENTION

There is now provided a process to produce a composition comprising cellulose fiber and a staple fiber wherein the line speed of a paper mill is increased as compared to a composition comprising 100% cellulose fiber; wherein said staple fiber comprises cellulose ester

There is now provided a process to produce a composition comprising cellulose fiber and a staple fiber, wherein the dryline in said paper mill is moved back toward the headbox by at least 14 inches relative to a composition comprising 100% cellulose fiber.

