Embodiments of the invention relate to non-woven material that can be used to make various products, such as paper towels, tissue paper, wipers, napkins, and the like as well as methods of making such products.
Generally, paper towels or wipers can be made using either a wet-laid or wet-forming process, variations of wet forming known as single recreping and double recreping, or a dry-laid, air-laid, or dry-forming process.
Wet laying or forming includes creating a slurry of water and pulp. The slurry is formed into a web on a paper-making machine. Single recreping (“SRC”) includes impregnating a wet-formed sheet of paper with binder and creping one of its surfaces. Double recreping (“DRC”) includes impregnating a wet-formed sheet of paper with binder and creping both of its surfaces. Dry laying or forming includes applying fibers to a mesh table or conveyor with a vacuum and then bonding the material to hold the fibers together.
The above processes have some shortcomings. Generally, wet-laid materials are held together by hydrogen bonds. However, since hydrogen bonds are dissolvable in water, the wet strength of wet-formed material is inherently limited. In addition, the length or size of the fibers used in wet-formed materials is limited due to the inability of most paper machines to handle relatively long fibers.
SRC and DRC provide generally acceptable end products, but are relatively expensive. This is, in part, because the first step in SRC and DRC relies on paper produced on a traditional, wet-laid paper machine. Such machines are expensive to operate and maintain.
In dry-laid processes, the tensile strength of a non-woven material can be increased by applying a bonding agent, such as latex, to create a film over one or more surfaces of the material. However, applying latex in this manner often decreases softness and wipe-ability.
Accordingly, it would be desirable to have improved methods and devices for creating materials suitable for use as paper towels, wipers, and the like.
In one embodiment, the invention provides a machine for forming a non-woven web. The machine includes one or more forming heads or boxes. Each box has an associated fiber inlet. The forming boxes are positioned above a conveyor table. Fibrous material travels from the inlet through each forming box. A vacuum source is located underneath the conveyor table and generates an air current that pulls the fibrous material onto the conveyor table to form a web or sheet of fibrous material. In one embodiment, the fibrous sheet is formed in three layers.
Vapor or steam boxes are placed adjacent to each forming box. In one embodiment, a steam box is located within the entrance of an oven. The sheet is subjected to a vapor, mist, fog, spray, or steam (generically referred to as a “suspension”) as it passes under each steam box. In one embodiment, the suspension is generated with water. Applying a water suspension to the fibrous materials provides hydrogen atoms to help create hydrogen bonding between at least some of the fibers.
Optional calender rolls can be located within the steam boxes. These optional calender rolls can be used to control the thickness of the sheet. The calender rolls can also be patterned to impart a desired pattern on the sheet or each layer thereof. The calender rolls can also be heated to help maintain the sheet at a desired temperature.
Other aspects and embodiments will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
As is discussed in greater detail below, one feature of certain embodiments of the invention is that loosely-held fibers in an air- or dry-laid web may be passed through a “steam” box or spray station and treated with water or water vapor. These treatment process helps with fiber lay-down (weighing down fibers such that they do not stick out or project from a web) and creates hydrogen bonds to help create sufficient strength for the web to undergo downstream processes such as “printing” (which in one form relates to the application of adhesive, as opposed to ink) and creping processes (discussed below). In alternative embodiments, hydrogen bonding of the web may be supplemented or replaced, in various combinations and permutations, with chemical bonding (e.g., bonding created with adhesives) and thermal bonding (e.g., bonding created by melting the sheath in a bicomponent fiber).
Using dry-forming techniques, as opposed, for example, to wet-laid processes, makes it easier to produce a low-density base web or sheet 16. In addition, dry forming makes it easier to use longer fibers, such as fibers of about 2.5 cm in length. In some instances, this represents an increase of about ten times the length used in webs formed in wet-laid processes. Longer fibers help to increase the bulk and strength of a web.
The fibrous material 13 supplied through inlets 12 can include natural fibers, such as pulp or cellulose fibers, animal hair, fibers from flax, hemp, jute, ramie, sisal, cotton, kapok, glass, old newsprint, elephant grass, sphagnum, seaweed, palm fibers, or the like. Natural fibers that have been processed or modified can also be used. It is also possible to use synthetic fibers or combinations of natural, modified, and synthetic fibers. Synthetic fibers that can be used include polyamide, polyester, polyacrylic, polypropylene, bicomponent, vermiculite fibers, and others. Depending on the particular application or desired use for the end product, the fibers or combination of fibers can be selected to have insulating, absorption, softness, specified chemical reactivity, strength, and other desirable characteristics. One advantage of dry-forming is that relatively long fibers can be used to form a web. Long fibers tend to help increase the strength of a web. The fiber or fibrous material 13 can be shredded and sized prior to being provided to the inlets 12.
In one embodiment, (which for convenience is referred to as the “pulp/binder fiber embodiment”) paper or pulp fibers are used as a primary ingredient in the sheet 16. In one version of this embodiment, the pulp fibers are treated or processed prior to being dry laid. In particular, the fibers are processed using a debonder to reduce hydrogen bonding. As is known, hydrogen bonds are one type of bonding that hold paper fibers together. Reducing the amount of bonding can impact the resulting strength, elasticity, bulk thickness, and softness of paper. Other additives can be used to treat the pulp prior to the dry-laying process.
In one embodiment, dried, direct-entry recycled pulp can be used. In order to debond this pulp, debonder can be applied at a number of places in the process. For example, a liquid debonder can be applied to the pulp in a spray booth or station, an example of which is described below. After being treated with the liquid debonder, the pulp can be dried in a dryer prior to being introduced to a forming head. It is possible when using a multi-head former to introduce recycled fiber, which tends to be rough, in a centrally located head or box while introducing virgin fiber in outer heads or boxes. Mixing fibers in this way tends to increase softness.
Another ingredient in the pulp/binder fiber embodiment is synthetic fiber or binder fiber. The pulp fibers can be mixed with binder fibers prior to being dry laid. As the name suggests, binder fiber helps bind or hold together the other fibers in the sheet. Binder fibers can also impart certain characteristics such as elasticity and strength. An exemplary binder fiber 20 is shown in
It is possible that a bicomponent fiber with a core of Lyocell material may also be used. Lyocell is less expensive than many types of material used in the core of bicomponent fibers. As is known Lyocell is classified as a type of Rayon material and can be manufactured using an organic solvent spinning process.
It is possible that the fibrous material 13 can be supplied into the housing 11 in lumps. Spike rollers 17 and a belt screen 18 combined in an arrangement 19 can be included in the housing 11 to disintegrate or shred the lumps of fibrous material 13 in order to help provide a substantially even distribution of fibrous material 13 on the conveyor table 14. In the particular version illustrated, the former 10 includes two rows of spike rollers. Fibrous material 13 passes a first row of spike rollers 17, the belt screen 18, and a second row of spike rollers 17 as the fibrous material is sucked downward to the conveyor table 14 due to the vacuum 15.
In addition or in the alternative to being processed in the spray station 27, the sheet 16 can be passed through an oven 29 or similar device to heat the sheet 16. The oven 29 can be configured to force or blow hot air through the web or sheet 16. In the pulp/binder fiber embodiment, the binder fiber in the sheet melts, creating thermal bonds that connect or adhere the melted fibers with other fibers to strengthen the sheet 16. Although the spray station 27 and an oven 29 are discussed in this detailed description as one way of bonding a dry-formed sheet of material, it is possible that other techniques of strengthening a loosely-bonded, air-laid sheet can be used. For example, it is possible to spray or otherwise apply an adhesive on or to the sheet, or otherwise bond the fibers in the sheet which after being initially air laid are generally held together by the vacuum force on the former 10.
In some embodiments, the sheet 16 is bonded in the oven 29 such that it is strong enough to be printed and pressed to a dryer, but weak enough to develop bulk during creping. This can be accomplished by adding sufficient binder fiber and thermally bonding the sheet 16 to increase its tensile strength to at least about 280 grams per inch.
Once formed and bonded, the sheet 16 passes through a first bonding-material application station or rotogravure printer 28, where additional bonding material, such as liquid bonding material 30 is applied to a first side 32 of the sheet 16 in a fine pattern corresponding to a pattern in or on a roll 34. The liquid bonding material 30 can be liquid latex. A second side 35 of the sheet 16 can also be modified, as is described below. In some embodiments, the bonding material 30 is applied on the first side 32 of the sheet 16 to produce a 1-to-1 ounces per inch tensile strength ratio to base weight. In some embodiments, the base weight of the sheet 16 is from about 20 to about 200 pounds per ream (for a 3000 square foot ream). In certain embodiments, use of a printer provides an ability to adjust the depth that the bonder material penetrates the sheet 16, primarily by adjusting the depth of the groove in the printer. The ability to adjust the depth of penetration provides flexibility in manufacturing a sheet possessing desired properties. For example, less penetration usually results in greater bulk, but less strength. On the other hand, greater penetration usually increases strength, but decreases bulk. In addition to adjusting the depth of penetration, the surface area to which bonding material is applied can also be adjusted, for example, by adjusting the pattern of printing. In some embodiments, only 40 to 50 percent of the surface area of the sheet is covered with bonding material to provide desired absorbency and desirable dry wipe characteristics.
As bonding material 30 is applied to the sheet 16, the moisture content of the sheet increases. The sheet 16 is delivered or passed to a dryer or heated drum (also known as a creping or Yankee dryer) 38. The sheet 16 is pressed into adhering contact with the drum 38 by press roll 39. The bonding material 30 causes only those portions of the sheet 16 where the bonding material 30 is disposed to adhere tightly to the drum 38.
The sheet 16 is carried on the surface of the drum 38 for a distance sufficient to heat the bonding material 30 enough to tightly adhere the sheet 16 to the drum 38 and dry the sheet 16 (or decrease its moisture content). The sheet 16 is removed from the drum 38 by a creping blade 40. As is known, the blade 40 forces the sheet 16 to change direction very quickly. During this rapid change in direction, the sheet 16 collides into the crepe blade, stops momentarily, and is folded or bent in an accordion-like manner to form a first, controlled-pattern crepe in the sheet 16.
The sheet 16 is pulled from the creping blade 40 through a pair of driven pullrolls 41 and then is advanced about turning rolls 44 and 46 to a second printer or material-application station 48. In some embodiments, the pullrolls 41 are optional, thus the sheet 16 is pulled by action of station 48, a dryer drum (discussed below), or both. The station 48 includes a first roll 50 that is positioned to draw a second bonding material 53 from a trough 56 and a pattern roll 58. In some embodiments, the station 48 is identical or substantially similar to the station 28. Likewise, the bonding material 53 can be the same as the bonding material 30. The station 48 applies bonding material on the second surface 35 of the sheet 16 in a pattern arrangement that can be the same as that of the first bonding material, although alternative patterns can be used.
After applying the second bonding material to the sheet 16, the sheet 16 is delivered to a second dryer or heated drum 60 and pressed into adhering contact with the drum 60 by press roll 65. The sheet 16 is carried on the surface of the second drum 60 for a distance and then removed by action of a second creping blade 67. The second drum 60 and the second creping blade 67 perform a second, controlled-pattern creping operation on or to the sheet 16.
The sheet 16 is then pulled from the creping blade 67 with a second set of driven pullrolls 70 and then advanced to a curing station 72. In some embodiments, the pullrolls 70 are optional and the sheet 16 is advanced directly from the creping blade 67 to the curing station 72 by the action of components in the curing station 72 or subsequent components. The sheet 16 is heated in the curing station 72 to a temperature that is sufficient to cure the bonding material 30 and 56. In one embodiment, the sheet is heated to a temperature of about 380° F. The sheet 16 is then moved to a large cooling roll 75 to lower the temperature of the sheet 16. The sheet 16 is pressed against the large cooling roll 75 by rolls 77 and 79. The sheet 16 is then wound into a roll (often referred to as a parent roll) 82.
In some embodiments, the sheet 16 is processed prior to delivering it to the creping line 26. In particular, running the dry-forming machine or former 10 at a higher speed than the speed of the creping line 26 can create a facsimile of creping in the sheet 16. This pre-processing can, among other things, increase the absorbency of the end product.
Water in the slurry is allowed to evaporate (i.e., the slurry is dried) and dry pulp is created (step 110). Other fibers can be added to the pulp created in step 110, as is shown in step 115. These fibers can include fibers such as cellulose (step 116), synthetic fibers (step 117), binder fibers (step 118) or combinations thereof. As noted above, in one embodiment, binder fiber plays an important role.
The combination of fibers is blended or processed in a manner that is referred to as opening the fiber, as shown in step 120. The blended or opened fibers are provided to a dry-forming machine, which can include a dry-carding machine (step 122) or dry- laid or forming machine (step 124). The dry-forming machine forms the fibers into a web. The web can be calendered (to adjust thickness, for example) or embossed (to, for example, impart a pattern on the web), if desired, as shown in step 125. A binder or binding agent such as a chemical (step 127), water (step 128), debonder (step 129), or steam (step 130) can be added to the web formed in the dry-forming machine (at prior steps 120 or 122), but such a binder is not required and need not be used, as shown in step 131. The sheet is then bonded or cured in an oven or other device (step 133). For example, in one instance if a chemical binder is added, the bonding in step 133 corresponds to the type of chemical binder added. However, if binder fiber is added in step 118, but no binder is added in step 131, then an oven is used to melt the binder fiber in step 133. Optionally, step 133 can be modified by introducing steam into the curing process. For example, steam can be introduced into an oven. Embossing and calendering can also be performed (step 134) after the curing step 133.
As should be apparent to one of ordinary skill in the art upon review of
Once the sheet is bonded in step 133 it is delivered to a creping process (step 135). The creping process 135 includes the steps discussed above with respect to
In some embodiments, the disadvantages of wet-laid forming are reduced because dry-forming processes are used instead of wet-laid processes. In addition, increased costs in raw materials due to the use of binder fiber and the like are believed to be offset by the elimination of the wet-laid processes. Strength is increased due to the use of longer fibers. Absorbency is enhanced in contrast to traditional air-laid materials because, in contrast to using a film of adhesive that covers the entire base web, adhesive is printed upon the web so that it covers, in some embodiments, only about 30 to about 50 percent of the surface of the web. Bulk is increased by the creping process carried out in some embodiments, and desirable hand feel or softness is achieved due to limiting the surface area upon which adhesive is printed or applied. Certain embodiments have advantages over wet-laid processes due to lower equipment costs, operation costs, labor costs, utility costs, and water requirements as compared to wet-laid techniques. In addition, wet strength and bulk are generally enhanced as compared to webs produced using wet-laid processes. Generally, the creping processes described herein exhibit decreased cost, increased bulk, and increased strength as compared to wet-laid creping processes due, at least in part, to the use of longer fibers and less binder. Finally, in some embodiments the air-laying processes have advantages over wet-laid processes because longer fiber may be used.
Vapor or steam boxes 282, 284, and 288 are placed directly adjacent to each forming box 252, 255, and 258, respectively. In the embodiment shown, the steam box 288 is located within the entrance of an oven 295. The sheet 280 is subjected to a vapor, mist, fog, spray, or steam (which for ease of description are collectively and generically referred to as a “suspension”) as it passes under each steam box 282, 284, and 288. In one embodiment, the suspension is generated with water. Applying a water suspension to the fibrous materials provides hydrogen atoms to help create hydrogen bonding between at least some of the fibers.
The embodiment shown in
Another manner in which a pattern may be imparted to the sheet 280 is by constructing the conveyor table 270 with a patterned conveyor belt. (Imparting a pattern on the sheet can be used to increase the bulk or bulk density of an end product, whether accomplished using a pattern-forming belt or embossing rolls). In certain embodiments, the sheet 280 is partially or lightly wetted by the application of a suspension in the steam boxes 282, 284, and 288 or a spray station. In such a state, sufficient vacuum can be applied so that the surface of the sheet conforms to the pattern of the conveyor table. By wetting the sheet, vacuuming it into the conveyor table, and drying it, the sheet retains the pattern of the conveyor belt (or forming fabric). By varying the pattern of the belt, a desirable bulk to basis weight ratio can be achieved. This is helpful when laminating two or more sheets together to create a multi-sheet product with high bulk and absorbency characteristics. In some embodiments, sheets are laid on top of each other or laminated such that an end product with voids between the layers of sheets is formed. These voids can increase the insulating characteristics of the end product. The voids can also hold fluid and, thus, enhance the absorbency of the end product. By varying the patterns formed in the sheets, the number of layers, the offset of the layers, or a combination of some or all of these actions, the bulk density and absorbency of the end product can be varied.
For example,
In another example,
As illustrated in
Once the sheet passes the third steam box 288 it enters the oven 295. The sheet is heated in the oven which helps evaporate the water applied in the steam boxes 282, 284, and 288. The dried sheet is held together in large part due to hydrogen bonding. If desired, the resulting sheet may be processed further through the bonding or creping processes.
As noted, in the embodiment shown, the steam boxes are directly downstream of the forming boxes to create a sealed or unitary environment. This prevents turbulence from disturbing the sheet as it is laid. In addition, a single conveyor is used to reduce transitions from one conveyor to another, which are often implemented in other systems, such as a transfer from a forming table to an oven. In addition the unitary forming and drying environment enables the system to be run at a relatively high speed because the sheet is not exposed to ambient air or turbulence, the sheet is given mass through the addition of water (as a suspension), and there are no transitions through multiple conveyors.
This application claims priority to U.S. Provisional Patent Application No. 60/716,582; filed on Sep. 12, 2005.
Number | Date | Country | |
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60716582 | Sep 2005 | US |