Combining Nonwovens By Lamination And Other Methods
Combining technologies to make hybrid nonwoven products increases versatility and extends nonwovens' marketplace reach.
Richard G. Mansfield, Technical Editor
Using some of these manufacturing methods, hybrid combinations can be produced, including:
• nonwovens with other nonwovens - spunbond/meltblown/spunbond (SMS) products for surgical wrap and protective clothing;
• nonwovens with film - dry-laid nonwoven/cellophane for battery separators;
• nonwovens with fibers - meltblown/carded web such as 3M's Thinsulate® for boots and outdoor garments;
• nonwovens with foam - needlepunched nonwoven/polyurethane foam/vinyl coating for automotive landau tops;
• nonwovens with an extrusion coating - needlepunched nonwoven/vinyl coating for upholstery fabric; and
• needlepunched nonwovens with meltblown nonwovens for filtration applications.
Use Of Adhesive
Webs For Laminating Fabrics
Hot-melt adhesive webs based on polyamide, polyester, elastomeric urethane and polyolefin polymers provide a one-step process for combining nonwovens with other types of materials, which can include fabrics, papers, films, foams, metals, glass and plastics.
A major producer of adhesive webs for bonding and laminating materials is Spunfab Ltd., Cuyahoga Falls, Ohio. Spunfab was founded in 1987 by Herbert Keuchel and his son, Kenneth Keuchel. Herbert Keuchel is a chemical engineer. Kenneth Keuchel has a bachelors degree in chemical engineering and a masters degree in polymer engineering. Collectively, the Keuchels have been awarded more than 15 patents. In order to better serve its European customers, Spunfab has just started production at its new plant in Iserlohn, Germany.
Spunfab uses proprietary extrusion techniques to produce adhesive webs that are 100-percent solids and do not contain solvents or particulate residues. The extrusion equipment is designed to process a wide range of thermoplastic resins. Spunfab can supply adhesive webs that have melting points between 75°C and 200°C. In addition to providing the proper melting point, the adhesive webs are designed to meet some of the following requirements:
• peel, shear and tensile strength;
• viscosity, elasticity and hardness;
• porosity, breathability and low weight; and
• special properties (washability, dry-cleanability, color, antimicrobial properties, flame resistance).
Applications Using Adhesive Webs
Automotive use of adhesive webs continues to grow, as they help to simplify processing, reduce weight and do not interfere with recyclability. They are used by Tier 1 and Tier 2 automotive suppliers in the United States, Europe and Asia. Adhesive webs are used for bonding, pre-coating, support backing, positioning and molding; and as slip surfaces to facilitate cutting operations. They are used to make headliners, parcel trays, door appliqués and panels, seat parts, and flooring components.
Adhesive webs are used by office seating manufacturers to bond molded foam cushions to upholstery fabrics. In luggage manufacturing, the webs are used to bond leather or vinyl fabrics to foam. In manufacturing composite structures, adhesive webs are used to position glass fibers and carbon strands in the laying-up process. They also are used to bond the film component in making performance sailcloth. In wet filtration materials, the webs are used to bond needlefelts and meltblown nonwovens.
Flame lamination is a process in which a soft foam is passed over an open flame to create a thin layer of molten polymer, which then is used as an adhesive to bond foam, film or fabric to the substrate. Fabric or film can be adhered to one or both sides of the foam in a single pass. The strength of the bond depends upon the film, fabric and foam selected; and the processing conditions. Some of the variables in the process include gas type, flame height and spread, foam burn-off, and nip pressure. The most commonly used foams are open-cell polyester and polyether urethanes, and cross-linked polyethylene.
A major supplier of urethane foam for flame lamination is High Point, N.C.-based Vita Inc., a division of British Vita plc, England. Vita combines Vitafoam Inc. with the Olympic Products Division - producer of fiber webs and polyurethane foam - acquired from Cone Mills in 1996. Vita's foam and highloft nonwoven products are used in automotive products such as headliners, door panels, seats, sunvisors, headrests, carpets and trunkliners.
Figures 1 and 2 illustrate the versatility of the flame lamination process.
Films Used In Flame
And Other Types Of Lamination
Dow Chemical Co., Midland, Mich., supplies several film products that are used in producing laminated composite products by flame laminating and other laminating techniques. Dow's Covelle™ polyolefin-based films are easily printable and are available smooth or embossed. They can be sterilized by ethylene oxide or by gamma rays.
Another line of Dow products suitable for lamination are Saranex™ films. These films are based on saran and modified saran resins. The original saran resin is a copolymer of vinylidene chloride and vinyl chloride. The Saranex films have excellent barrier properties and are used for packaging, medical products and protective clothing. Because of the barrier properties and excellent chemical resistance, protective clothing made from DuPont's Tyvek® spunbonded polyethylene laminated with Saranex is used extensively in hazardous material (hazmat) activities.
HF, RF Laminating And Bonding
High-frequency (HF) and radio-frequency (RF) welding use electromagnetic energy to generate heat, and under pressure will bond films to substrates. Dow's Covelle films are finding applications in which foams and nonwovens are laminated for use in automotive interiors, furniture, shoes and garments.
Shawmut Mills: America's First Laminator
Shawmut Mills, West Bridgewater, Mass., a division of R.H. Wyner Associates, is a fourth-generation family-owned business founded in 1916 by Rudolph H. Wyner as Shawmut Woolen Mills in Stoughton, Mass. Until the late 1950s, the company was a vertical knitting mill making and selling yarns, knitted fabrics and finished apparel. At that time, Shawmut developed lamination technology for a wide range of fabrics and concentrated its manufacturing activities on lamination. The company is now ISO 9002-registered and holds ANSI-RAB and DAR certificates.
The company now practices five types of lamination: flame lamination; urethane cross-linking; thermoplastic adhesion; hot-melt lamination; and solvent-based lamination.
Shawmut Mills has emerged as a market leader for laminating molded automotive seating, headliners and trim, disposable medical products, protective work suits, fashion apparel, footwear, and breathable waterproof films.
In 1996, Shawmut opened a plant in Port Huron, Mich., as an automotive trim mall, integrating foam peeling, lamination and die cutting under one roof in order to provide just-in-time delivery to automotive suppliers. These products include headliners, door panels, sunvisors, bodycloth and barrier film composites for foam-in-place parts.
Schaetti supplies complete coating and laminating systems based on powerdot, pastedot, doubledot and scatter coating.
Schaetti: Coating And
Laminating Systems Supplier
Schaetti AG, Switzerland, represented by Schmid Corp., Spartanburg, supplies complete coating and laminating systems based on thermofusible powder adhesives using the following methods: powderdot; pastedot; doubledot; and scatter coating.
The principle of the powderdot system is that thermofusible powders are applied directly onto the substrate by means of an engraved roller. This system provides very uniform coatings at higher coating weights. A major use of this system is for shirt collar interlinings.
The pastedot system is most effective when working with lightweight substrates, which have a low tolerance to high temperatures such as nonwoven interlinings.
The double dot system is used for reactive adhesives applications.
The scatter coating process is used for carpet backing and upholstery fabrics. In some industries, this type of application has replaced flame lamination. Schaetti supplies a complete product line of Schaetti FIX® thermofusible adhesives. These adhesives are based on polyamides, polyesters and modified ethylene compounds.
Recently, Schaetti acquired the Kannegiesser line of laminating systems and is integrating them into its product line.