1. Field of the Invention
This invention relates to a seam construction useful in protective garments.
2. Description of the Related Art
In the field of protective garments, a variety of types of garment articles have evolved for protection of the body against environmental contaminants, including toxins and other materials which are deleterious or undesirable in contact or exposure to the body.
Such garments range in character from conventional laboratory coats, which protect the trunk and arm areas against immediate contact with liquids or solids, but which are readily permeable to fluids and afford minimal protection to the extremities and head of the wearer, to so-called emergency response suits, which are gas-tight in character and designed to afford maximum whole body protection in applications such as clean-up of toxic wastes and chemical spills.
Between these extremes, there has evolved a need for protective garments which cover the body of the wearer, and afford protection against liquid penetration, as a "splash barrier" in instances where liquids of a toxic or hazardous character are being handled, or where liquid clean-up is required. Such hazardous material suits are not gas-tight as are high-cost emergency response suits, yet they possess a high resistance characteristic to liquid penetration.
Inasmuch as it is generally impractical to integrally form an entire garment as a hazardous material suit, due to material and manufacturing limitations, cost constraints, and the like, there inevitably exist various garment sections or panels which are joined together at seams.
Such seams are critical regions of the garment as regards its utility. The panels of the garment may be formed of polymeric or laminated materials which are intrinsically liquid penetration resistant, or the panels may be sized or otherwise chemically treated with compositions imparting liquid permeation resistance thereto. Nonetheless, the seams afford a path of least resistance to liquid penetration, vis-a-vis the main panel portions of the garment.
Hazardous material suits are a developing field of protective garment technology, for which efficacy standards are currently being evolved by the National Fire Protection Association (NFPA), based on documentation developed by the American Society for Testing Materials (ASTM) F23 Committee. Current efforts in the hazardous material suit field are focused on the development of seams which for the gas-tight suits meet the permeation criterion of ASTM D739-85, and which for the liquid barrier suits meet the penetration criterion of ASTM F903-84. For example, the seams may be evaluated by exposure to a liquid penetration test medium, such as a mixture comprising 4 weight percent polychlorinated biphenyl, 6 weight percent trichlorobenzene, and 90 weight percent mineral spirits, or other multicomponent or single component test medium, which is applied to the seam area of a garment sample, and the breakthrough time to penetration is measured. A minimum suitable breakthrough time is one hour.
Significant difficulty has been experienced in designing seams to meet even such minimum breakthrough standard. There is accordingly a significant and continuing need for protective garments utilizing liquid penetration-resistant seams meeting such standard.
U.S. Pat. No. 3,294,617 to J. W. Way describes a reinforced seam for joining closed cell expanded elastomer panels, e.g., neoprene, in which the panels are butt-joined with a cement medium. In the reinforced seam of this patent, a semi-liquid, high viscosity elastomer is applied to the butt joint, preferably on the lining side of the seam, which then curingly forms an elastomeric ribbon chemically and mechanically bonding with the lining of the garment.
As disclosed at column 3, lines 16-26 of the Way patent, the ribbon-forming elastomers of the disclosed seam are self-curing at ambient temperature and atmosphere, by loss of water or solvent from the applied film. Water loss takes from approximately one to four hours, the loss of solvent(s) requires thirty minutes to one hour, and "curing requires several days to reach an optimum cure". It is therefore apparent that the curing conditions required restrict handling, shipment, and use of the seamed garment for the length of time required for the curing process to come to completion. In addition, when solvent-based elastomeric compositions are applied, it is apparent that there is a significant potential contamination problem due to the evaporation of solvents from the wet elastomeric film.
U.S. Pat. No. 4,272,851 to L. Goldstein discloses a protective garment for use in hazardous environments, the body of the garment being formed of a non-woven spunbonded olefin having a polyethylene film laminated to one side thereof. This garment utilizes bonded seams which are ultrasonically welded. A sewn binding is sewn externally of the bonded seam so that the welded seam is located between the stitching and the interior of the garment.
The Goldstein patent's protective garment utilizes ultrasonic bonding for seam formation, a process which requires close tolerances to be maintained in the thickness of the materials being welded, since even minute variations can result in either the "burn through" of the material if of less than the desired thickness, or of insufficient welding if the material is greater than the desired thickness. Very close control of the ultrasonic bonding apparatus is required in the welding operation for the same reasons, since an increase in ultrasonic generator frequency will produce undesirably higher intensity welding, and a decrease in frequency will result in lessening of the energy flux at the welding site, below the desired level. Further, the seam construction described in this patent entails the practical disadvantage that ultrasonically bonded seams are relatively rigid in character, so that when subjected to tensile load, such seams have a high probability of seam separation. The Goldstein patent does disclose the use of a bound seam in conjunction with the ultrasonically bonded seam, which is desirable to provide a high degree of mechanical integrity and reinforcement of the ultrasonically bonded seam, but does not overcome the intrinsic deficiencies of the ultrasonically welded seam. Among these deficiencies is the fact that the ultrasonically welded area is dimensionally small, and the failure of such welded area will result in extensive penetration of contaminants through the bound seam.
U.S. Pat. No. 4,641,475 to J. Berridge discloses a moisture resistant seam assembly for building structures in which an elongate seam is formed by adjoining mating flanges of adjacent channel-shaped building surface covering members. The assembly comprises a seam cover member, a seal means within the seam cover member, and an anchor clip. The seam cover member is positioned over the elongate seam, and the seal means therein sealingly engages the adjoining mating flanges for preventing fluid migration between the seal cover member and the elongate seam.
Another type of seam which has been employed in the joining of panels is a lap seam assembly in which the respective panels are lapped substantially in the plane of the panels when reposed on a flat surface, and overlaid with an adhesive tape. Such seam construction depends for its mechanical integrity on the shear and peel strength characteristics of the adhesive tape, and the bond produced between the tape and the panel substrate. These constructions are generally of low strength and structural integrity characteristics, and typically are not suitable for protective garments of the type contemplated by the present invention.
Bonded seams formed by hot melt adhesive joining methods are known in various garment applications, but have the disadvantage that they typically weaken the seam's supporting fabric by thermal degradation thereof during the seam-forming operation so that the mechanical properties of the supporting fabric, e.g., its tensile strength, are detrimentally reduced.
Accordingly, it would be highly desirable to provide an improved seam assembly for joining adjacent panels of a protective garment, utilizing a bound seam as desirable to provide a high level of structural integrity and mechanical strength of the garment in use, but which is highly penetration resistant to liquids, beyond the level of resistance provided by a bound seam per se.
It is therefore an object of the invention to provide an improved seam assembly of such type, utilizing a bound seam to impart mechanical strength and structural integrity, and which is moreover highly liquid penetration resistant.
It is another object of the invention to provide an improved seam assembly of such type, which can be formed in a quick, efficient, and economical manner at ambient (room) temperature.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.