Substrates

The properties achieved in the finished, molded product is dependent on mold-substrate interaction.   Generally, we have experience with three different types of textile materials:

  1. Tightly woven knits and knitted products
  2. Nonwoven materials
  3. Monofilament fabrics

Product attributes created by deep molding are very broad and are impacted by a number of different parameters. The first and most important is the selection of the substrate. Novolon works with nonwoven, knit and woven products. The mold pattern and the height are then determined to reach the performance specifications desired.

The substrate, the pattern and process parameters are the variables in the equation that add value to the end product. By adjusting one or more of the variables, we can increase air flow, improve water absorption, and/or provide greater compression resistance.
Several considerations drive the moldability of a substrate.

  • The type of textile being used
  • The fiber/polymer type:  at least one thermoplastic element +/-60%
  • The structural characteristics of the fiber:  ODF, Mobility, Amorphous vs. crystalline systems

Compressive resistance is dependent primarily on the firmness of the incoming fabric.  The more rigid the base material is, the more the molded product will be resistant to compression.   If resilience or rebound is a targeted characteristic, then a monofilament base material or composites containing monofilaments are the best candidates.  Resilient fabrics can generally be be charted from low to high:  tightly woven/knitted materials, Nonwovens and Monofilaments (Fig. C).  Dome size and weight also impact the rigidity of the ultimate product (Fig. A). Compression stress increases significantly when the mold pattern is increased from 1/4” to 3/8” (M/F mold) (Fig. B). Weight also plays a role, but not as greatly.




Figure A



Figure B



Figure C

THICKNESS

Final product thickness is dependent on the mold, substrate and process used, therefore, the maximum thickness is difficult to quantify.  For a majority of the patterns in use to date, the maximum thickness is limited to approximately 9mm.  Also, our continuous production equipment generally produces a product with a slightly lower thickness when compared to press production for similar mold and material types.   Nevertheless, substrate selection is still the primary determining factor in product thickness.  Fig. F can be used as a guideline to identify possible maximum thickness when the same mold is used.  Note that there is a broad overlap between these general classes of fabrics. 

Patents have existed for years covering the deep molding of knits and woven substrates. The substrates of choice were generally high denier monofilaments. The key advancement in this technology pertains to nonwovens and finer denier fibers of less than 100 microns.

In general, greater depth and formability have been achieved with nonwoven materials and knits as compared to woven fabrics.  When evaluating a nonwoven substrate as a candidate for deep molding, a few general characteristics should be considered:

  • A more random fiber orientation will react more favorably to the deep molding process and will improve molding depths.
  • Structures that have inherent fiber mobility, such as needlepunched materials, also display improved moldability. 
  • Structures that incorporate partially drawn or amorphous polymer systems will tend to improved molding depths and will maintain their shape more consistently over the life of the product. 
  • Crimped fibers also aid in producing well formed dome structures.

With these considerations in mind, the breadth of candidate nonwoven materials is expansive.  However, not all nonwovens can be molded. Draw ratios of up to 250% can be achieved in some fabrics. The draw ratio is the area of the molded substrate over the area of the unmolded substrate. The draw ratio is dependent upon fiber size, fabric weight, mold pattern and fabric formation.  Three types of nonwovens yield the best molding results:  spunbond polypropylene, hydro entangled microfiber and spunbond polyester. 

Testing shows that deep molding has minimal effect on the mechanical properties of the substrate:  stiff product in produces a stiff product out. 

Multiple substrates can be used to build a composite providing the essential performance requirements. When two of the same substrates are married, the compression performance increases significantly. Nesting the substrates versus stacking the substrates also provides changes in the compression performance.