Abstract:
A method of constructing a compact protective hood comprising the steps of vulcanizing a heat-resistant, non-elastic crown to an elastomeric neck dam, the neck dam formed by injection molding directly to the crown.

Description:
FIELD OF INVENTION 
     This invention relates to a compact protective escape hood design that provides high fluid impermeability, mechanical strength, and efficient assembly. 
     BACKGROUND OF THE INVENTION 
     Compact protective hoods enclose the head of a wearer in a crown either of transparent material or of opaque material with a transparent visor. Respiration is typically filtered through a mouth piece, oral-nasal cup or a full-face piece. The hood is sealed about the neck by an elastomeric dam. To make the package compact and portable the hood assembly size must be as small as possible which is accomplished by folding the hood assembly for storage until deployment. 
     Limitations in Fluid Impermeability Technology 
     Protective hoods require fluid impermeability to maintain a target protection factor. Fluid impermeability is tested by a number of methods. In one method, the hood is inflated with air and a soapy solution is applied to the exterior of the hood. Alternatively the inflated hood may be partially submerged to detect leaks. Leaks in the hood are detected by bubbles forming proximate to the leak. Leaks are most likely to occur about material interfaces such as those between the crown and the elastomeric neck dam. 
     As noted above, the material requirements between the crown and neck dam differ. The crown must provide a fluid impermeable three dimensional surface to surround the head of a wearer. It must interface with a visor for outward vision or be constructed of transparent material. The crown must also interface with a filtered respiratory pathway between the interior and exterior of the hood. 
     The neck dam must be substantially elastomeric to fit over the wearer&#39;s head and seal against the neck of the wearer. However, the neck dam must also create a fluid impermeable seal with the crown. As the crown and neck dam are typically made from different materials, this seal can be challenging to achieve effectively. Many bonding agents, tape and other methods produce an acceptable fluid impermeable seal but do not provide high mechanical strength. Stitching and other mechanical fasteners provide mechanical strength but sacrifice fluid impermeability. Both mechanical strength and fluid impermeability are inextricably intertwined as the donning of the hood introduces substantial mechanical strain on the neck dam-crown interface as the neck dam must be stretched to accommodate the greater diameter of the head of the wearer before contracting around the lesser diameter of the neck of the wearer. Additional stress is also incurred during the folding and unfolding process. 
     SUMMARY OF INVENTION 
     The present invention includes a method of constructing a compact protective hood comprising the steps of vulcanizing a heat-resistant, non-elastic crown to an elastomeric neck dam that is directly injected molded to the crown. 
     Vulcanization is a chemical process in which polymer molecules are linked to other polymer molecules by atomic bridges of sulfur atoms or carbon to carbon bonds. The molecules become cross-linked which makes the bulk material harder, much more durable and also more resistant to chemical attack. It also makes the surface of the material smoother and prevents it from sticking to metal or plastic chemical catalysts. This heavily cross-linked polymer has strong covalent bonds, with strong forces between the chains, and is therefore an insoluble and infusible, thermosetting polymer. All these characteristics make the material ideal for creating mechanically strong, fluid impermeable hood assemblies. 
     High vulcanization temperatures may increase bonding speed and therefore result in a higher manufacturing output. For this reason, fluoropolymer resins such as those sold under the brand TEFLON PFA 345 by DuPont Fluoroproducts out of Wilmington, Del., USA are ideal materials as they can be made transparent and have high melting points that exceed typical vulcanization temperatures of 338 degrees Fahrenheit. It should be noted that any other heat-resistant materials may be utilized provided they have a sufficiently high enough melting point to withstand a vulcanization process. 
     In an embodiment of the invention, the crown is pre-molded so that visor cutouts, filter pathways and other features are already formed when the crown comes out of the mold. Advantages of pre-forming these features include reduced assembly time and higher precision in their location on the crown. The crown is defined by a lower perimeter opening which receives the head of the wearer and an upper portion in which the wearer&#39;s head is enclosed when the hood is donned. It should be noted that embodiments of the hood include using certain resins to form an entirely transparent crown wherein no distinct visor assembly is needed. In yet another embodiment of the invention surface texture in the crown mold may impart opacity in certain areas of the hood and transparency in other areas such as needed for outward vision. Surface texture may provide an additional advantage of diffusing reflected light so that hood wearers are better camouflaged. 
     Direct molding of the elastomeric neck dam to the crown may be accomplished by a variety of methods including, but not limited to, compaction plus sintering, injection molding, compression molding, transfer molding, and dip molding. In any mold process selected, the lower perimeter of the crown both mechanically engages and fluidly seals to the elastomeric neck dam. 
     Also formed within the mold are three-dimensional variations about the lower perimeter opening of the crown. In one embodiment a plurality of apertures about the lower perimeter of the crown are provided whereby the liquid elastomeric material of the neck dam flows into the interstial space of the apertures before cooling to a solid state. This provides a mechanical engagement between the crown and neck dam. The apertures may be of any predetermined geometric configuration. In an alternative embodiment, protrusions may be formed by the crown mold to engage the elastomeric material. In yet another embodiment, convex or concave concentric rings about the lower perimeter of the crown may be used to enhance the bond between the crown and the elastomeric material. 
     In an alternative embodiment of the invention, the hood is pre-molded in a semi-folded state whereby folding is facilitated as the hood is naturally biased towards a folded state and expanded against the folded bias when deployed. This provides yet another advantage as the hood assembly may be repacked for reuse with minimal packing expertise. 
     The present invention includes a number of advantages over the state of the art. These include: 
     Adhesives not necessary: Adhesives break down over time. Vulcanization does not. Accordingly, hoods manufactured with this method will have longer shelf lives and greater reliability. 
     Mechanical strength: Liquid elastomeric material in the neck dam mold migrates to the interstitial space formed by apertures perforated about the lower perimeter of the crown. Alternatively the liquid elastomeric material engages any other three-dimensional surface variation on the lower perimeter of the crown. As the elastomeric material cures, a strong mechanical interface is formed. Longer life and a greater protection factor are achieved. 
     Transparent hood: Using this method, a substantially transparent hood is possible thereby providing a wider field of view and removing a point of failure at the visor-hood interface which is obviated. 
     Manufacturing Expense: Using this method obviates the need for a multi-part neck seal. Manufacturing costs are reduced and fewer points of failure exist. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
         FIG. 1  is an elevated view of an embodiment of the invention showing a hood crown with a plurality of apertures about its lower perimeter. 
         FIG. 2  is an elevated view of an embodiment of the invention showing a hood crown with three-dimensional surface variations pre-molded about its lower perimeter. 
         FIG. 3A  is a cross-section view of an exemplary injection mold cavity for forming the elastomeric neck dam. 
         FIG. 3B  is a partially sectional, perspective view of an exemplary neck dam shape. 
         FIG. 4  is a partially sectional, front elevation view of an exemplary injection mold cavity for forming the elastomeric neck dam. 
         FIG. 5  is a partially sectional, elevated isometric view of an exemplary injection mold cavity for forming the elastomeric neck dam. 
         FIG. 6  is a front elevated view of the crown engaged in the injection mold cavity for forming the elastomeric neck dam. 
         FIG. 7  is a front elevated view of the crown and elastomeric neck dam removed from the mold cavity and ready for vulcanization. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1 , crown  10  has pre-molded visor aperture  20  and pre-molded respiration aperture  30 . Lower perimeter  40  receives the head of a wearer and in this embodiment, a plurality of apertures  50  about lower perimeter are either preformed in the crown&#39;s mold or die cut after the crown is molded. Apertures  50  are sized to permit liquid elastomeric material to fill the interstitial space of each aperture during the injection molding of the neck dam. The purpose of apertures  50  is to provide mechanical strength to the bond between crown and neck dam. This is particularly important due to the stresses that occur between neck dam and crown. When the hood is donned, the neck dam must be stretched over the head of the wearer before it resiliently engages the neck of the wearer to create a substantially fluid-tight seal. This stretching puts strain on the interface between the neck dam and the crown.  FIG. 2  illustrates an alternative embodiment to apertures  50  wherein three-dimensional surface variations  55  provide a substrate upon which the elastomeric material can engage. Surface variations  55  may be formed on the interior of crown  10 , exterior of crown  10  or on both sides. Surface variations  55  may be formed from crown&#39;s mold whereby no additional labor is required for their formation. Surface variations  55  may include, but are not limited to, projections, concentric convex rings, concentric concave rings, predetermined geometric shapes, dimples and the like. It is also anticipated that a combination of apertures  50  and surface variations  55  may be used. 
       FIG. 3A  is an illustrative embodiment of an injection mold  60  that forms the elastomeric neck dam  80  ( FIG. 3B ). Lower perimeter  40  of crown  10  is received through mold opening  70 . Heated elastomeric material in a liquid state forms in cavity  90 . Cavity  90  forms a substantially conical ring defined by neck opening  100  formed by lower mold terminus  120  and outer ring perimeter  110  formed by upper mold terminus  130 . It should be noted that neck dam  80  in  FIG. 3B  is shown for illustrative purposes detached from crown  10 . Anvil  140  fills the interstitial space of injection mold  60  to give neck dam  80  predetermined thickness by forming cavity  90 . Chamfer  170  in anvil  140  receives lower perimeter  40  of crown  10 . In the embodiment illustrated in  FIG. 3A , lower perimeter  40  has alternating rings of apertures  50 , a smooth surface  180  and surface variations  55 . It should be noted that any combination of alternating surfaces may be used. However, an enhanced protection factor is achieved by alternating a ring of smooth surface  180  (for fluid impermeability) with a ring of surface variations  55  or apertures  50  (for enhanced mechanical bonding). 
       FIG. 4  shows an embodiment of the invention wherein injection mold  60  is formed by two outer molds halves  150 A and  150 B secured by clamps  160  about inner mold surface  140  to form cavity  90 . It should be noted that clamps  160  are provided as a simplified embodiment of the invention. High-volume mold design may employ an alternative embodiment wherein the two halves  150 A and  150 B are aligned and engaged via hydraulic pistons or the like.  FIG. 5  shows an isometric view of outer mold half  150 A and inner mold surface  140  forming cavity  90 . Upper mold terminus  130  engages crown  10  lower perimeter  40  and seals cavity  90  so that liquid elastomeric material injected into mold  60  via injection port  70  does not leak out.  FIG. 6  shows crown  10  engaged with mold  60 . It should be noted that alternatively, mold  60  may entirely encase crown  10  from top to bottom during the injection mold process.  FIG. 7  shows crown  10  removed from mold  60  whereby neck dam  80  is fused by only one  170  to lower perimeter  40 . 
     It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. Now that the invention has been described,