Films
Films are thin sheet material extruded
from synthetic polymers and are typically used along with woven cloth
in a laminate (see laminates below).
PET film is the most common film used
in laminated sailcloth. It is an extruded and biaxially oriented
version of PET fiber. In the US and Britain, the most well-known
trade names are Mylar and Melinex.
PEN film is extruded and biaxially
oriented version of PEN fiber. Just as PEN fiber is stronger than PET
fiber, PEN film is stronger than PET film. However, PEN film is
rarely used in standard sailcloth styles because it shrinks more
rapidly than PET, is less resistant to abuse, and reduces the working
life of the sail.
Scrim and strands
Strands are combined from fibers; these
are frequently narrow flat bands or ribbons of high strength
material. Scrim is a loose weave or lattice of strands, typically
bonded where they cross to maintain the grid pattern. Strands and
scrims are used to strengthen or reinforce sailcloth (see laminates
below).
Laminated sailcloth
In the 1970s sailmakers began to
laminate multiple materials with different characteristics to
synergize the qualities of each. Using sheets of PET or PEN reduces
stretch in all directions, where weaves are most efficient in the
direction of the threadlines. Lamination also allow fibers to be
placed in a straight, uninterrupted paths. There are four main
construction styles:
Woven-film-woven
Film is sandwiched in between two
layers of woven taffeta, the film provides most of the stretch
resistance and the taffeta enhances tear and abrasion resistance. The
high-end versions of this method use a woven Spectra or Kevlar
taffeta. In some newer styles, off threadline aramid yarns, are also
laid into the laminate. In some cases the second layer of taffeta is
eliminated for cost and weight savings
Film-scrim-film or film-insert-film
(film-on-film)
In this construction, a scrim or
strands (inserts) are sandwiched between layers of film. Thus
load-bearing members are laid straight, which maximizes the high
modulus of the fibers, where a woven material will have some inherent
stretch to the weave. Laminating film to film around the strands
creates a very strong and dependable bond reducing the amount of
adhesive needed. In high quality cloth, the strands or scrim are
tensioned during the lamination process.
The drawbacks are: film is not as
abrasion or flex resistant as a weave, it does not protect the
structural fibers from UV rays. In some cases UV protection is added.
Woven-film-scrim-film-woven
Woven fabric with high UV and abrasion
protection is added to the film-on-film. This combines the best of
the above, but is costly, heavy, and stiff. This is an attractive
method to combine high modulus fibers with poor UV resistance.
Woven/scrim/woven
Wovens on both sides of a scrim without
the film layer. The problem is getting enough high modulus yarn into
the sandwich, and still being able to get a good bond, because,
dissimilar fabrics don’t often bond well. This technique is more
experimental than practical, but may yield results in time.
