Patent Application
20110045261
Embodiments of the invention relate to non-woven materials and, more particularly, to laminates of non-woven materials.
Non-woven materials are used to make a variety of products such as dry and wet wipes (or wipers), towels, and industrial absorbents. Non-woven materials are also used to make filters, disposable medical products (such as gowns and masks), and diapers.
Non-woven materials are created from a non-woven web of fibers. Nonwoven technologies are categorized by both the manner in which non-woven webs are formed and also the manner in which the webs are held or bonded together.
Non-woven webs may be made from a single type of fiber (or material). It is also possible to use multiple types of fibers or to add other materials to the fibers, such as particulates, to make a non-woven product. Creating a laminate is one approach to making a non-woven, composite product, as the layers of the laminate can be made, for example, from different fibers. Another way of making a non-woven, composite product is to mix different types of fibers within each layer with one or more other types of fibrous materials, particulates, or a combination of fibrous materials and particulates.
One way of making a non-woven web is to use what is referred to as a melt-blown process. In a melt-blown process, fibers are formed from a thermo-plastic material that is heated to a liquid or molten state and then forced through small openings, die bodies, or nozzles of an extruder. Jets of air are directed at the molten material exiting the nozzles such that fibers of the material are formed. The fibers may then be collected or deposited on a moving screen (a continuous belt) (sometimes referred to as a “forming table”) to create a non-woven web of the thermo-plastic material.
One way of creating a composite non-woven web made (at least in part) from melt-blown material is to use a process with two or mores streams of material. For example, U.S. Pat. No. 5,350,624, (the “'624 patent”) discloses a process for making a non-woven composite structure in which a stream of cellulose materials is sandwiched between two streams of melt-blown materials. The cellulose stream contacts the two streams of melt-blown material before the melt-blown fibers are completely hardened (or cooled). At least some of the cellulose fibers and melt-blown fibers are mechanically entangled. In addition, at least some of the cellulose adheres to the semi-molten or tacky thermo-plastic fibers. A composite, non-woven material having a graduated distribution of fibers is created (where thermo-plastic fibers and cellulose are present at the exterior surfaces of the end-product at a percentage of about 60 percent or more thermo-plastic. In the middle, thermo-plastic and cellulose are present at a percentage of about 60 percent or more cellulose and about 40 percent or less of thermo-plastic.
Although the non-woven materials and methods of manufacturing described above are known, there continues to be a need for high-strength, high-performance wipes that are made cost effectively. As noted, wipes are sometimes made from thermo-plastic materials. Thermo-plastic materials are made from petroleum. As a consequence, wipes and other non-woven products that use thermo-plastic fibers are very cost sensitive. At the same time, the market continues to demand higher and higher performance, which in accordance to conventional wisdom generally requires the use of petroleum-derived, synthetic fibers to achieve.
Fiber made from thermoplastic materials can be manufactured as a continuous filament and can be quite strong. Melt-blown continuous filament fibers can be quite soft. Cellulose fibers (made from trees) are quite short and can produce linting, but they are highly absorbent. Cellulose fiber can sometimes be coarse to the touch compared to some thermoplastic fibers. Thermoplastic fibers are, in general, much more expensive than cellulose fibers.
While wipes may appear very simple, a number of attributes are considered in their design and manufacture. Chief among these are strength, softness, absorbency, bulk (i.e. thickness), linting, and cost. Embodiments of the invention provide a wipe that is strong, soft, absorbent, and bulky, with low linting at an economic cost. The inventors have designed a new laminate structure for a composite, non-woven wipe and methods of making such a wipe where the use of high-cost materials can be reduced and the use of lower cost cellulose and other natural fibers can be increased. In addition, embodiments of the invention still provide high-performance in terms of, for example, limited linting (a problem associated with non-woven materials made with short cellulose fibers). Further still, certain embodiments improve the strength of the wipe.
The inventors have also designed a new laminate structure for a composite, non-woven wipe and methods of making such a wipe, where complex mixing of fibers in a melt-blown process is reduced. For example, in the melt-blown process described in the '624 patent, the velocity of the air stream carrying cellulose fibers and streams carrying the melt-blown fibers must be regulated and controlled so that a desired, graduated distribution of fibers is created in the non-woven web. While such control and regulation appears to be possible to achieve, it does, in the opinion of the inventors, tend to increase the complexity of the manufacturing process.
Accordingly, embodiments of the invention provide a composite, non-woven product that includes multiple layers of material. In one form, the non-woven product includes a first, outer layer made from melt-blown fibers and no other type of fibers; a second outer layer also made from melt-blown fibers and no other type of fibers; and a third, middle layer positioned between the first and second outer layers. In one embodiment, the melt-blown fibers in the first and second outer layers are high-strength fibers. In a particular embodiment, the high-strength fibers exhibit a strength or fiber tenacity (measured in grams per denier (“gpd”)) of at least about 5.0. Such fibers can be produced in a process in which a flow of quench air is directed at molten fibers exiting the nozzles of an extruder parallel to the direction in which the fibers exit the nozzles.
The third, middle layer is made from cellulose fibers or a combination of different types of fibers. For example, in one embodiment, a homogenization of melt-blown fibers and cellulose is used. The melt-blown fibers in the third, middle layer can be low-strength fibers (e.g., fibers having a fiber tenacity of about 4 gpd or less) or high-strength fibers (such as those mentioned above). The lower strength meltbown fibers tend to be of high denier (i.e. thicker). When combined with the cellulose fibers, these thicker denier fibers produce a bulky middle layer that is also more absorbent. Other combinations or substitutions of fibers are also possible. For example, the third, middle layer can be made exclusively of cotton fibers, cellulose and cotton fibers, or a combination of cellulose, cotton fibers, and melt-blown fibers.
One method is to use diebodies with multiple rows of holes. This enables the fiber to be run at a much lower throughput per hole and at a cooler temperature. As a consequence, the fiber is attenuated or drawn to a greater degree (than is otherwise possible). Attenuating the fiber orients the molecular chains of the fiber in a manner that increases the strength of the fiber. However, since the fiber is cooler than ordinary melt-blown fibers, it may not adhere to other fibers in the same way that melt-blown produced in an ordinary manner would. To address this concern, bicomponent fiber may be extruded through the diebodies to create a bicomponent melt-blown fiber. The bicomponent melt-blown fiber can be later heated to help create bonds between fibers.
Melt-blown fibers in the first, second, and third layers may be comprised of bicomponent fibers (i.e., fibers with a co-axial or side-by-side arrangement of synthetic fibers with different melting points, where a higher-melting point fiber is surrounded by or adjacent to a lower-melting point fiber).
Once the multiple-layer or laminate sheet is formed the three layers (the first and second outer layers and the third, middle layer) are bonded or more securely attached to one another. In one embodiment, the laminate sheet is heated so that the lower-melting point fiber in the bicomponent fibers melts. The molten fiber adheres to other fibers in the laminate and when the laminate is cooled, bonds are created between the fibers in the different layers. In another embodiment, usually when bicomponent fiber is not used, the laminate is secured through hydroentangling the fibers in the layers.
Unlike the product disclosed in the '624 patent, embodiments of the invention do not have a graduated distribution (where there is a gradual transition from one fiber type to a second fiber type within a single, unitary matrix or web of fibers). Instead, embodiments of the invention provide a non-woven product with a laminate structure and more distinct layers of different types of fibers.
Other aspects and embodiments of the invention 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, the third, middle layer 16 is made from cellulose, a mixture of cellulose and synthetic fibers (such as melt-blown fibers), or other fibers whether alone or in a mixture. By reducing the thickness of the layers 12 and 14 and keeping the use of petroleum-based, synthetic fibers in the middle layer 16 relatively low, cost sensitivity due to changes in the price of oil is reduced.
A first extruder 18 having a die body 19 produces a stream 20 of melt-blown fibers that form the first layer 12. The die body 19 (like other die bodies discussed) may include a plurality of rows of holes from which the melt-blown fibers are extruded. A die body suitable for use in at least some embodiments is a Biax type die body available from Biax-Fiberfilm Corporation. A second extruder 22 having a die body 23 produces a stream 24 of melt-blown fibers that form the second layer 14. In one embodiment, the middle layer 16 is made from a single type of fiber such as cellulose fibers.
If melt-blown fibers are used in the third, middle layer, they can be low-strength fibers (e.g., fibers having a fiber tenacity of about 4 gpd or less) or high-strength fibers (e.g., fibers having a fiber tenacity of about 5 gpd or more). Other combinations or substitutions of fibers are also possible. For example, the third, middle layer can be made exclusively of cotton fibers, cellulose and cotton fibers, or a combination of cellulose, cotton fibers, and melt-blown fibers. As noted, lower strength meltbown fibers tend to be of high denier (i.e. thicker). When combined with the cellulose fibers, these thicker denier fibers produce a bulky middle layer that is also more absorbent.
Fibers in the first, second, and third layers may also be mixed with bicomponent fibers (e.g., fibers with a co-axial or side-by-side arrangement of synthetic fibers with different melting points, where a higher-melting point fiber is surrounded by or adjacent to a lower-melting point fiber).
In the embodiment shown, the first and second outer layers 12 and 14 are substantially identical and are made from melt-blown fibers having a relatively low denier. Using a low-denier or fine fiber produces a smooth surface. Removing cellulose from the first and second outer layers reduces linting (because cellulose fibers tend to lint). As noted above, the sheet 10 can be produced using five fiber streams. Three center streams 30, 32, and 34 are used to make the middle layer 16. Each stream 30 and 34 is generated by an extruder having a die or nozzle sized to produce fibers with a higher denier than the melt-blown fibers produced by the extruders 18 and 22 (which are used in the first and second outer layers 12 and 14). Using higher denier or coarser fibers in the middle layer 16 helps to provide bulk to the sheet 10.
In alternative embodiments, the composition of the middle layer 16 is varied. In one example, the stream 32 consists of cotton or other natural fibers instead of cellulose. In another example, the stream 32 is a mixture of cellulose and cotton fibers. In another embodiment, bicomponent staple fiber (i.e., a fiber cut to length) is added to the middle layer 16 instead of or in combination with the melt-blown fibers from streams 30 and 34.
The streams 20 and 24 are directed onto a continuous belt 50 of a forming table 52. The forming table includes a vacuum box or plenum 53. The vacuum plenum 53 is connected to a vacuum source which pulls or vacuums the fibers onto the continuous web 50 to form a non-woven web of material. The die bodies 19 and 23 are oriented so that the streams 20 and 24 do not mix with the stream 36. As a consequence, the sheet 10 has three, distinct layers: two outer layers that are composed of melt-blown fibers and a middle-layer that is a mixture of fibers formed by the streams 30, 32, and 34.
In an alternative embodiment of the invention, the melt-blown fibers are bicomponent fibers (e.g., fibers with a co-axial or side-by-side arrangement of synthetic fibers with different melting points, where a higher-melting point fiber is surrounded by or adjacent to a lower-melting point fiber). Melt-blown bicomponent fibers are continuous fibers. After the product 10 is formed using bicomponent fibers, it is heated in an oven (or similar device) such that the lower-melting point layer of the bicomponent fibers melts or becomes tacky. Fibers in the product (both melt-blown, cellulose, and other fibers) adhere to the molten layer of the bicomponent fibers. When the product 10 cools, thermal bonds are created between the fibers. Bonding or fusing through the use of bicomponent fibers aids in the adhesion of all of the fibers (which increases the overall strength of the product 10) and also increases the strength and decreases the linting of the shorter fibers in the product 10.
In a second alternative embodiment, once the multiple-layer or laminate sheet is formed the three layers (the first and second outer layers and the third, middle layer) are bonded or more securely attached to one another through hydroentangling the fibers in the layers. Hyrdoentangling the layers 12, 14, and 16 helps bond the layers together and prevents the layers from separating from one another. Hyrdoentangling may be use as a substitute to using bicomponent fibers or in combination with the use of bicomponent and thermal bonding.
In embodiments that use bicomponent fiber (instead of hydroentangling), the sheet is passed through an oven 86 and cooling station 88 before being sent to the winder 90.
Thus, embodiments of the invention provide, among other things, laminate non-woven wipes in which the amount of melt-blown material may be controlled. Various features and advantages of the invention are set forth in the following claims.
This application claims priority to U.S. Provisional Patent Application No. 61/029,531 filed on Feb. 18, 2008, and to U.S. Provisional Patent Application No. 61/029,533 filed on Feb. 18, 2008. The contents of these two applications are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/34427 | 2/18/2009 | WO | 00 | 9/27/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61029533 | Feb 2008 | US | |
| 61029531 | Feb 2008 | US |
