Consumer products such as toilet tissue, toweling and facial tissue made from cellulosic webs are a pervasive part of modem society. In general, these products need to possess certain key physical properties to be considered acceptable to consumers. While the exact mix of key properties and the absolute value of the individual properties will vary depending on the nature of the product, nonetheless, softness, wet and dry strength, absorbency, and pleasing aesthetic nature are universally desirable properties. Softness is that aspect of the fibrous web that elicits a pleasing tactile response and insures that the product is not harsh or abrasive when it contacts human skin or other fragile surfaces. Strength is the ability of the structure to retain its physical integrity during use. Absorbency is the property of the fibrous structure which allows it to acquire and retain contacted fluids in an acceptable time. Aesthetic nature refers to the psycho-visual response that occurs when the consumer views the product either alone or in the context of the product's surroundings.
The most common method for the manufacture of tissue products is the wet laid papermaking process. In such a process, individual fibers are first suspended in a dilute slurry with water. This slurry is then laid on a foraminous screen to remove a large portion of the water and to form a thin, relatively uniform-weight embryonic web. This embryonic web is then molded and/or dried in a variety of ways to form the final tissue web. As part of this process the molded and/or dried web is usually glued to a drying drum and subsequently creped from the surface of the dryer to impart desirable properties.
Products made by many existing wet laid processes fall under the above description. Examples of such webs that are soft, strong, and absorbent and contain at least two micro regions of elevation can be found in, U.S. Pat No.: 3,301,746 which issued Jan. 31, 1967, to Lawrence H. Sanford and James B. Sisson; U.S. Pat. No. 3,974,025 which issued Aug. 10, 1976, to Peter G. Ayers; U.S. Pat. No. 3,994,771 which issued Nov. 30, 1976, to George Morgan, Jr. and Thomas F. Rich; U.S. Pat. No. 4,191,609 which issued Mar. 4, 1980, to Paul D. Trokhan; and U.S. Pat. No. 4,637,859 which issued Jan. 20, 1987, to Paul D. Trokhan. Each of these papers is characterized by a repeating pattern of high elevation areas and low elevation areas. The elevation areas can be either discrete or continuous. The low elevation areas result from localized compaction of the web during papermaking by raised areas of an imprinting carrier fabric or belt.
Other high-bulk, soft tissue papers are disclosed in U.S. Pat. No. 4,300,981 which issued Nov. 17, 1981, to Jerry E. Carstens; and U.S. Pat. No. 4,440,597 which issued Apr. 3, 1984, to Edward R. Wells and Thomas A. Hensler.
Chemically enhanced paper structures comprising a cellulose substrate and having chemical enhanced features applied thereto are known in the art. For example, achieving high-bulk, soft and absorbent tissue paper through the avoidance of overall compaction in combination with the use of debonders and elastomeric bonders in the papermaking furnish is disclosed in U.S. Pat. No. 3,812,000 which issued May 21, 1974, to J. L. Salvucci, Jr.
Chemical debonders such as those contemplated by Salvucci, referred to above, and their operative theory are disclosed in such representative U.S. Pat. No. 3,755,220 which issued Aug. 28, 1973, to Friemark et al.; U.S. Pat. No. 3,844,880 which issued Oct. 29, 1974, to Meisel et al.; and U.S. Pat. No. 4,158,594 which issued Jan. 19, 1979, to Becker et al.
Tissue paper has also been treated with cationic surfactants, as well as noncationic surfactants to enhance softness. See, for example, U.S. Pat. No. 4,959,125 which issued Sep. 25, 1990, to Spendel; and U.S. Pat. No. 4,940,513 which issued Jul. 10, 1990, to Spendel, that disclose processes for enhancing the softness of tissue paper by treating it with noncationic, preferably nonionic, surfactants.
It has been found that the softness of tissue paper, in particular, high-bulk pattern densified tissue papers, can be improved by treatment with various agents such as vegetable, animal or synthetic oils, and especially polysiloxane materials typically referred to as silicone oils. See, for example, U.S. Pat. No. 5,059,282 which issued Oct. 22, 1991, to Ampulski et al. The Ampulski patent discloses a process for adding a polysiloxane compound to a wet tissue web (preferably at a fiber consistency of between about 20% and about 35%). These polysiloxane compounds impart a silky, soft feeling to the tissue paper.
While the processes described above generally make acceptable product properties, the product properties can be further enhanced. However, processes to make current products and potentially enhanced products suffer from several drawbacks. For example, the chemicals used to strengthen tissue webs are often added to the dilute slurry of water and fibers prior to the initial lay down on the forming screen. This is a relatively convenient and cost effective way to introduce additives. However, other chemicals to aid absorbency or to improve softness are also commonly added to the so called wet end of the tissue making process. Because of the complex nature of the individual chemicals used to generate the key properties, they often interact with each other in an adverse manner. They can compete with each other for the desired retention on the cellulose fibers as well as destroy properties that are inherent in the fibers. For example softening chemicals often reduce the natural tendency of fibers to bond to other fibers and hence reduce the functional strength of the resulting web. Both the process and the product benefit if the chemical papermaking additives introduced in the wet end are kept to a minimum.
Additives introduced in the wet end of the process must be retained by the cellulose fibers if the chemicals are to be functional. This is generally done by using chemicals that possess an ionic charge; most preferably a positive ionic charge which is attracted to the inherent negative ionic charge of cellulose. Many additives which could improve the properties of the web are not charged. Introduction of such chemicals into the dilute fiber slurry at the wet end of the process results in poor retention and exacerbates the interference problems described above.
Examples of patents that disclose processes for adding strength and softness agents to the wet end of the papermaking process include U.S. Pat. No. 5,223,096 which issued Jun. 29, 1993 to Phan and Trokhan, and U.S. Pat. No. 5,217,576 which issued Jun. 8, 1993 to Phan. These wet end processes typically result in a uniform addition of the strength and softening agents to the tissue paper, and thus, will not prevent any potential undesirable interaction of the chemicals.
Another drawback to adding any chemical to the wet end of the process is that the chemical, if retained, is distributed throughout the web. In many instances it is desirable to apply active ingredient(s) only to the surface of the web. This may, for instance, be desirable with lubricious softening materials. Application only to the surface insures efficient use of the material since consumers only tactilely interact with the surface. Application to the surface also avoids interference with other materials, such as strength additives, that might best be included in the center of the sheet.
The chemical papermaking additives can also be added to the cellulose substrate subsequent to formation of the wet web. For example, the chemical additives may be applied to the cellulose substrate from an aqueous chemical solution, then dried to form a chemically enhanced paper structure. Unfortunately, previous methods of adding chemicals to a cellulose substrate result in a uniform or homogeneous distribution of the chemicals on the substrate. This uniform or homogeneous distribution of chemicals can negate many of the performance advantages offered by cellulose substrates containing at least two micro-regions of elevation.
The present invention overcomes all of the above mentioned drawbacks and generates desirable additional benefits. In particular, it has been found that the addition of functional chemicals in register with the micro-regions of the cellulose substrate can maximize the performance advantages of multi-region paper. For example, as will be discussed in detail hereinafter, chemical softeners are optimally added to the high elevation micro-regions of the web to further enhance that function.
Typically, the chemical composition is applied to the cellulose substrate by spraying or printing. Unfortunately, it is difficult to spray the chemical composition onto the substrate in a precise pattern. Printing the chemical composition onto the substrate may result in a pattern having greater definition and precision than obtainable by spraying, but requires a printing roll having raised protuberances or gravure cells. Printing rolls having raised protuberances and gravure plates limit the pattern of the applied chemical composition to that pattern corresponding to the protuberances of the printing roll or the gravure plates, regardless of which pattern may be desirable for a particular capillary substrate. Also, it can be very difficult to register the printed pattern with the micro-regions of the substrate.
This problem may be overcome by providing a plethora of printing rolls and gravure plates, one for each desired pattern. However, such provision increases the expense of the apparatus to a point where it may not be economically feasible to provide a printing roll or a gravure plate for each desired pattern if only a short production run is desired.
Accordingly, it would be desirable to be able to chemically enhance predetermined micro-regions of tissue paper, in particular high bulk, pattern densified tissue papers, by a process that: (1) can be carried out in a commercial papermaking system without significantly impacting on machine operability; (2) uses chemical compositions that are nontoxic and environmently friendly; and (3) can be carried out in a manner so as to maintain desirable tensile strength, absorbency and low lint properties of the tissue paper.
Importantly, by adding functional chemicals in register with desired micro-regions in accordance with teachings of the present invention, the desired functional property can be enhanced without adveresly affecting other properties. For example, tensile strength can be increased without negatively impacting softness; or, alternatively, softness can be improved without negatively impacting tensile strength.
It is an object of this invention to provide soft, absorbent toilet tissue paper products.
It is an object of this invention to provide soft, absorbent facial tissue paper products.
It is an object of this invention to provide soft, absorbent paper towel products.
It is an object of the present invention to provide a paper structure, such as a tissue web, comprising a cellulose substrate containing at least two micro-regions of elevation, wherein chemical papermaking additives are incoporated in register with the micro-regions of the paper structure.
It is a further object of this invention to provide an improved process to incorporate chemical papermaking additives into the tissue web that enhance softness, strength, absorbency, and aesthetics or combinations of these properties.
It is a further object of this invention to provide an improved process to incorporate chemical papermaking additives in register with the micro-regions of the tissue web to maximize the performance advantages of multi-region paper.
These and other objects are obtained using the present invention, as will be seen from the following more detailed disclosure.