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Powder bonded nonwovens.

although one of the less publicized nonwovens technologies, powder bonding has potential in many different nonwoven applications

Although the nonwovens technology called "powder bonding" may be new to some, this idea for creating a nonwoven has found its place in specialized markets that take advantage of its features. Sales of powder bonded nonwovens are international with markets in Europe, North America and the Pacific Rim.

Powder bonding is based on carded staple fibers that are bound together by using a hot melt "powdered" adhesive as the consolidating agent. The adhesive is presented to the unbonded carded web in powder form. The powder becomes entrapped in the fiber matrix. Uniformity of the carded web is a critical element of this process. With the binder and fiber united, the web is heated to soften the adhesive. Some flow occurs, but the high viscosity of the melt limits the range. The web passes through a consolidating nip to force the fibers and melted binder together.

While the idea of powder bonding is simple, the versatility and performance engineering options are complex. Any cardable fiber or blends of fiber can be powder bonded. Fundamentally, the requirement is that the fiber matrix must have a higher melt temperature than the chosen hot melt powdered adhesive. The selection of fiber chemistry and size, the powder melt characteristics and particle distribution, the processing time and temperature all have discreet influences on the resultant physical properties of the nonwoven manufactured. Each of these attributes is controlled to engineer the technical fit for a particular application or customer.

Since its beginnings in 1985, a number of major nonwoven manufacturers have installed pilot facilities. Bonar Fabrics, Greenville, SC, has been committed to this technology from its inception. Another dedicated producer is HDK Industries, located in Rogersville, TN.

Powder bonding has taken its place as an important option for the nonwoven user. The following is a market breakdown with the features that powder bonding brings to each. Every application is engineered for a specific use or customer requirement. The purpose is to highlight the versatility and capabilities of this growing technology.

Specialty Wipes - diskette liners, coated film wipes, cleaning wipes, wet wipes. Features include:

* Excellent dust wiping and holding

* Soft non-scratching surface

* Very low inherent debris

* Excellent chemical resistance

* Can be made anti-static

* High strength

* Very uniform thickness

* Attractive appearance

Medical/Hygiene - Coverstock, dry bridge, comfort liner, dressings, garments, sachets, wipes. Features include:

* Very soft touch

* Non-irritating

* Heat sealable

* Embossable

* Excellent wetting and dryness

* Autoclavable

* High strength and extensibility

* Attractive appearance

Filtration - Automotive, water, air, face mask, specialty products. Features include:

* Excellent uniformity

* High strength in wet and dry environments

* Moldable

* High loft

* Heat sealable for composite laminations

* Excellent debris holding capacity

* Chemical resistance

* Durable

Home Furnishings/Apparel - Interlinings, bra cups shoulder pads, shoe composites, glove liner, insulation, drapery lining, quilt backing, wallcovering. Features include:

* Very soft hand

* Moldable

* Durable to washing and dry cleaning

* Heat sealable

* Uniform and attractive appearance

* Excellent thermal properties

* High strength and extensibility

* Formaldehyde free

Automotive/Industrial - Headliners, door panels, seating slip scrim, cable insulation, carpet backing, geotextiles, envelopes, synthetic leather. Features include:

* Direct lamination

* Moldable

* Durable

* Stitch holding strength

* Attractive appearance

* Excellent uniformity

* High strength and extensibility

* Non-scratching

The above markets represent only part of the opportunity for powder bonding. While other technologies can provide some of these attributes, it is the combination of engineered features that gives the added value performance to our customers. Another exciting aspect of powder bonding is the potential generated by "reactivation" of the powdered adhesive. A powder bonded nonwoven can also be viewed as an adhesive carrying medium.

The reactivation of the powder has had significant impact on some of the above markets. For example, in the manufacture of 5.25 inch floppy diskettes, the nonwoven is heat laminated to the PVC jacket. A traditional thermal bonded polyester liner required the PVC to melt and grab the nonwoven to achieve an acceptable bond strength. With a powder bonded nonwoven, the liner itself sticks to the PVC, increasing the bond strength six fold. This allows the converter to increase its line speed dramatically resulting in significant efficiency improvements. Powder bonded nonwovens not only gave the manufacturer a higher performance product, but also a lower total cost.

Reactivation of the powdered adhesive allows for direct lamination without additional adhesives required. It will laminate to itself, other nonwovens, films, woven fabrics, paper, scrims and foils. Each application, however, requires the nonwoven system to be engineered for a particular performance requirement.

The addition of heat to Bonar's "Ultraloft" style powder bonded nonwoven adds an interesting dimension, literally, to this product. Using a coarse denier polyester fiber and a polyester adhesive system, this product is manufactured in the traditional manner. The result is a relatively thin, dense fabric. However, adding heat without pressure allows this fabric to "rebulk" or loft. Thickness will increase up to four to six times from the original "dense" thickness. The benefit is higher density packaging for transportation, easier roll handling for cutting and processing, and once rebulked, having a soft, highloft nonwoven incorporated into your application.

The future of powder bonding is bright. This technology is driven by partnerships that together create new and exciting applications. Partnerships are made with converters, suppliers and end users. In the business climate of today, relationships and resource sharing are the key factors for commercial success.

New fibers and bonding techniques are extending the technology base. The powder bonding process will create new markets for nonwovens by achieving levels of performance unavailable from other nonwoven processes. This technology has passed through the nurturing phase and has emerged as a unique and vital part of the nonwovens technology base. Powder bonding, while representing a small specialized segment of the nonwovens industry, will continue to grow in its chosen markets.
COPYRIGHT 1993 Rodman Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

Article Details
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Author:Burge, David
Publication:Nonwovens Industry
Article Type:Cover Story
Date:Oct 1, 1993
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