Hydroentanglement technology: a review and projection of markets.

HYDROENTANGLEMENT TECHNOLOGY Hydroentanglement, water jet entanglement and spunlacing are all synonymous terms used to describe a process for imparting strenght or structural integrity to an array of fibers or an nonwoven web. It is not a nonwovens process by itself, but merely a step in the overall process of creating a sheet structure from loose fibers.

The entanglement process consists of subjecting fibers in a web to fine high pressure jets of water. Usually these jets are arranged in multiple rows and directed at the fibrous web supported and carried by a moving screen. As these fibers pass under the high pressure jets of water, they entangle with each other to form a sheet structure with properties related to a vast array of interacting variables.

The concepts repalting to hydroentanglement as a means of imparting strength to a nonwoven web had their roots in mechanical needle punching. In the early 1960s, DuPont had developed "Corfam," a man-made leather replacement based on a specialized needlepunched nonwoven. One of the problems with this nonwoven was broken needles that remained in the web and caused serious problems in a subsequent splitting process if they were not found and removed.

This problem gave impetus to the desire to find a method for imparting strength to a nonwoven that would avoid the broken needles. This led directly to the use of high pressure jets of water to "hydraulically needle" nonwovens. Although the resulting fabrics had different physical characteristics than those produced by conventional needlepunching, the hydraulically needled fabrics were promising enough to continue their development for other applications.

DuPont continued the development through the 1960s and introduced commercial hydroentangled or spunlaced fabrics under the trade name "Sontara" in the early 1970s.

Preceding DuPont's development of spunlaced fabrics was a development in the 1950s by the Chicopee Div. of Johnson & Johnson using pressurized water as a means of rearranging fibers. These rearrangement techniques were subsequently commercialized as "Keybak" apertured nonwoven fabrics. Although the aperturing process fell short of actual fiber entanglement, it did lead to the formation of tenuous yarn-like structures of fiber roping that gave improved fabric tensile properties at low binder levels.

This aperturing process continues as one of the important nonwoven processes in commercial use today and is now even offered as an addition to entanglement systems by one equipment vendor.

The Patent Situation

During the early development of hydroentanglement, DuPont established a body of patents, with applications dating from 1963, that formed the basis for its commercial entry into the technology in the early 1970s. The company is still adding to its patent estate, although at a decreased rate compared to its earlier activity.

During this early period DuPont also entered into a licensing agreement with Johnson & Johnson to avoid conflict with Chicopee's earlier aperturing patents. By the mid-1970s, DuPont established a strong patent position covering the field of hydroentanglement that, it seemed to many, made competitive entry into the field very difficult. Then in the spring of 1976 DuPont unexpectedly dedicated to the public domain five key hydroentanglement patents. These five patents constituted the heart of the hydroentanglement process. No DuPont explanation of any substance was provided for this action.

The strength of the DuPont patent position is evidenced by a count of hydroentanglement or related patents issued between 1965 and 1987, where 20 of the 42 patents issued were assigned to DuPont.

From 1980 onwards a series of patents was granted to Japanese companies active in this field. The initial group covered developments by Asahi Chemical, which disclosed the use of fluid jets to entangle very fine fibers produced from splittable composite fibers to produce substrates for coating for synthetic suede leather products.

At the same time (1979-80), Mitsubishi Rayon was assigned patents that disclosed concepts of the entanglement using high shrink fibers and low pressures on the entanglement jets. A similar patent in 1980 developed the idea of relatively low pressure water jets followed by fiber shrinkage and heat setting.

Some of these ideas were further developed with Uni-Charm. The initial work concentrated on the use of reflected energy from the water jet stream to produce additional entanglement in the web. This effect was achieved by using impervious backing systems based on rolls, curved plates, etc. Although this technology was granted patents issued in the U.K. and France, there do not appear to be corresponding U.S. patents. In more recent work, Uni-Charm has apparently moved away from this idea and the use of water previous backing materials in combination with deflectors has been developed.

This has given rise to speculations as to whether the low energy levels claimed to be possible using the Suzuki/Uni-Charm technology can in fact be achieved.

Commercial Production

During the past two years there has been a considerably more active period in the international development of the hydroentanglement concept. Activities in Japan, the U.S. and throughout Europe have made it very desirable to find some parameters by which the information and data generated from all of this activity can be characterized for comparison purposes.

In a recent comprehensive private study by John R. Starr, Inc., Osterville, MA, the level of amount of applied energy was used as the correlating parameter. A logical choice if one considers hydroentanglement as an energy transfer process. We used the energy application parameter of horsepower-hours per pound of fiber (hp-hr/lb), a term used in most of the patent literature. Alternatively, kilowatt-hours per pound (KW-hr/lb) or kilowatt-hours per kilogram (KW-hr/kg) could be used to define energy applied. With this classification, we chose three levels of energy application--low, medium and high.

Since the amount of energy carried in a jet is a function of its velocity and velocity is in turn a function of pressure, we also considered pressure in judgement of classification. The applied energy increases exponentially by a 1.5 exponent of pressure, thus giving pressure greater importance in the classification criteria.

Calculations for applied energy also include the jet size, the number of jets per unit length and the quantity of fiber or fabric processed. In reality, entanglement is a highly complex process of interacting and interrelated variables that can reduce down in a general sense to how material behaves under different levels of applied energy. This is one of the reasons why hydroentanglement holds so much promise--there are so many variables to manipulate, so many degrees of freedom for innovation to create new products.

The three classification levels (Table 1) are purely arbitrary and will undoubtedly be changed or modified by new inputs from various sources.

Obviously, there can be gaps or overlaps within the classifications depending on the technology practiced. The parameters are infinitely variable, a continuous spectrum of pressure values exist from the low to the high. There are no present dividing lines.

A number of estimates have been made of the costs associated with a hydroentanglement system. One such comparison based on the Starr data is given in Table 2.

With respect to hydroentanglement process economics, there are a number of important factors now known.

* There is no low cost of entry. Following the early work by the process pioneers we entered a phase where low energy systems with less demanding requirements were seen as a low cost entry into this exciting field. This has not proved to be the case and, indeed, some expected low cost solutions may have turned out to be considerably more expensive than predicted.

* The importance of production of the precursor web--line speed per se has not been a problem with entanglement. The limiting factor has been the rate at which a good quality precursor web could be produced. It is interesting to note how much effort the early entrants devoted to this aspect of the process.

* Total system considerations, particularly the filtration requirements, add considerably to the total cost.

* Dedicated systems can be less expensive, but product flexibility is a factor with differing market needs and uneven product growth rates.

* By the application of computer-based techniques to process cost evaluations, some of the more obvious problem areas can be identified and hopefully avoided.

Products and Markets

The opportunity for product innovation with hydroentanglement is essentially unlimited. This is based on the number of variables and degrees of freedom available for manipulation. Starting materials, energy levels and screen patterns all can be varied to achieve a host of end products tailored to specific customer needs.

As better fundamental understanding evolves, entangled products will be created to replace many traditional textiles, first in low end and disposable areas with gradual movement into the higher end durables market.

A major opportunity exists in combination or composite products. The tissue/fiber barrier fabric currently produced by DuPont and Chicopee is an example of such a product, with current output estimated 40 million pounds a year.

The combined North American and Western European volume of water jet entangled nonwovens is forecast to increase from about 45,000 tons in 1988 to about 110,000 by 1992. North America will continue to account for the majority of the volume, but the European market will grow at a faster rate. The largest North American market will continue to be surgical packs and gowns. However, this is a market sector where growth will be slow because of the time factor to achieve acceptance in such a critical area.

Wipes and towels for a variety of industrial, food service, consumer, medical and a number of smaller, specialized applications have started to make in-roads into these markets. A number of new variants of water jet entangled products made from a variety of precursor webs are expected to be directed towards the increasingly specialized wipe and towel applications sector.

Medical sponges and dressings and closely related medical products will develop as the benefits associated with such products are both recognized and quantified in terms of real cost.

In a number of other disposable product categories it is also projected that considerable growth can be achieved, including in disposable sheets and pillow cases, table cloths and napkins and baby nursery products.

In the U.S. it is also predicted that spunlaced coverstock will achieve some significance. As the threshold for successful entanglement is generally considered to be at the 20-25 grmas sq. meter level, this may be more difficult to achieve than many consider.

In Western Europe, major market growth of "conventional" spunlaced materials is expected in medical sponges and dressings, related medical products, wipes and towels, surgical packs and gowns and disposable limited use textile replacement items.

Future Developments

Hydroentanglement technology is one of two major technology growth potential areas identified by most analysts working in the nonwovens sector, the other being melt blown.

After 25 years the technology is catching the imagination and kindling the enthusiasm of many potential participants. The technology is beginning to open up and with more openness will eventually come more progress.

In terms of process economics, the cost of the fiber components in a precursor web are of major significance. The ability to utilize cellulose fibers, even if more sophisticated forms of cellulose pulp are chosen, is therefore of considerable economic benefit.

If this simple cost equation can be combined with other technological and performance benefits and the negative factors further minimized, there is no doubt that wet formed precursor webs with off-line entanglement, drawing on a wide range of precursor web technologies, could prove to be a most attractive manufacturing system. One of the key factors will be the ability to form, reel and transport appropriate wet formed precursors.

Recent developments allowing the hydroentangling of structures based on "Kevlar" or "Nomex" indicate an important development. The use of high performance fibers in the precursor webs, possibly combined with other, less costly support fibers, will extend the use of this technology into the production of composite structures where the absence of a chemical binder isa positive advantage and the relatively high processing costs can be readily assimilated.

Developments by DuPont in this field with the production of spunlaced Kevlar and Nomex aramid fibers are targeted at high performance specialty applications in the automotive, aircraft and filtration markets.

In durable applications, the production of composite structures based on different types of precursor webs, including glass, carbon and high performance organics, will be increasingly targeted at industrial filtration, composite materials and high performance engineering requirements.