KNITTED SPACER FABRIC
Abstract
Developments in the field of textile reinforced composites have been increasing in the last
several years. In the first developed composite materials, fibers were used as reinforcement
element. Textile materials such as staple fibers, bands, filament yarns, cables and two
dimensional textiles are widely used as reinforcement elements in composite materials. Spacer
fabrics consist of two outer surfaces and a connection layer between those outer surfaces. Spacer
fabrics can be classified in the three dimensional textiles. Three dimensional textiles are defined
as structures which have three different yarn systems inside. Spacer fabrics can be used in
different application areas. Spacer fabrics have three dimensional structures comprising of two
outer surfaces and a connection layer which combines two outer surfaces. Due to their special
construction spacer fabrics show different properties which cannot be met by conventional
textiles.
1. Introduction
Spacer knits are double-layered circular knits with a cushion of air and spring-like
yarns between the two sides. This unique fabric class is knit in one continuous operation.
Although it looks like several fabrics bonded together, it is actually one fabric which
cannot be separated by layer. Special yarns are selected for aesthetic qualities (i.e.: soft
hand, bright/dull, etc.) and for performance properties (i.e.: moisture transport, thermal
insulation or conductance, anti-microbial, compressibility etc.). [1]
Spacer fabrics are widely used in different products such as mobile textiles (car seat
covers, dashboard cover), industrial textiles (composites), medical textiles (anti-decubitus
blankets), sports textiles and foundation garments (bra cups, pads). Spacer fabric as a
component material is highly breathable, thus creating a moisture free environment,
which in turn reduces the chances of skin maceration. These lead to an increased level of
comfort when compared to materials such as foam, neoprene and laminate fabrics. Spacer
fabrics are regarded as environmentally friendly textile materials (unlike polyurethane
foam), since they can be recycled. These properties make spacer fabrics unique and thus
these fabrics are under investigations and developments so that the qualities can be used
to the fullest. [2]
2. Spacer Fabrics and their Importance
A spacer fabric is a double-faced fabric knitted on a double needle bar machine. The distance
between the two surfaces is retained after compression by the resilience of the pile yarn (usually
mono-lament) that passes between them. One reason for the development of spacer fabrics was
an attempt to replace toxic, laminated-layer foam with a single, synthetic bre type fabric, thus
facilitating future re-cycling. Spacer fabrics are manufactured according to their function and
have three variable components: fabric construction, yarn material and nishing. These 3-D
fabrics also known as sandwich fabrics or hollow fabrics are produced by binding 2-D face
fabrics together using pile yarns. [4]
The specific climate physiological features of spacer fabrics result from their structure as
ventilated elements. The high air volume which spacers keep between its surfaces offers an
excellent precondition for a passive acclimatization.
There is a constant air interchange within the filament space, through which humid air is
promptly carried away. The specific 3D structure offers a permanent insulating air layer between
the surfaces.
The 3D fabric sinks spring-like when being compressed. The material is characterized through its
persistence and its ductility.[4]
Summarized, spacers provide a great many of positive characteristics:
high air permeability
strong reset force and pressure elasticity; the fabric assumes its original shape after having been
loaded
comprehensive options for assessing the climate properties
compensating fluctuations of temperature
noise absorption
lightweight, tear proof and easy-care
can be designed in a great variety
Because of their characteristics, spacer fabrics are employed in many different industry sectors.
They are not only used as substitute for foam material, but also used in:
Mattresses
medical technology
functional textiles
filter technology
shoe soles
automotive sector
protectors
padding
diving suits
insulation [5]
3. Construction
The most common process to produce spacer fabrics is through weft knitting and warp
knitting processes. However warp knitting technology is the most commonly known and
applied technology for the production of spacer fabrics. The first type is knitted on a rib
Rachel machine having two needle bars while the second is knitted on a double jersey
circular machine having a rotatable needle cylinder and needle dial. [2]
3.1.
Warp knitted spacer fabric
Warp knitted spacer fabric, produced on a double-bar Raschel warp knitting machine,
is one kind of three-dimensional textile structure, which consists of two surface layers
and a spacer layer. The pile yarns connecting two independent surface layers cross
over the space to form a special 3D structure which enables the fabric to obtain
versatile properties, such as air permeability, good compressive characteristics, and
thermoregulation. [3]
3.1.1 Structure of warp knitted spacer fabric
One of the special features of warp knitted spacer fabric in its structure is that the two
surface layers connected by pile yarns form a sandwich structure. The surface layers
are knitted on the front and back needle-beds of double-bar warp knitting machines,
respectively, and can be knitted into any kind of mesh or plain structure to get the
dimensional, mechanical and comport properties required; whereas in order to
connect the surface layers together, the pile yarns must lap on both the front and back
needles. During knitting, the pile yarns form stitches successively on the front and
back needles; thus owing to the effect of the draw-off mechanism, the stitches formed
on the front needles will be a half-stitch higher than that formed on the back needles
in the same wale. Furthermore, because the pile yarns are in a tensioned state during
knitting, they tend to relax and bend opposite to the knitting direction.
In order to satisfy the different end-use requirements, pile yarns can be knitted with
different structures and the cross section of spacer fabrics be made to present different
effects. The common effects are the parallel type, crossed type and combined type.
Cross-section shapes are formed by the pile yarns lapping on the front and back
needles, thus varying the lapping methods will lead to different cross-section shapes.
The cross-section shape will affect spacer fabric properties, such as the compressive
property and stability property. [3]
3.1.2. The Compressive Behavior of Warp Knitted Spacer
Fabric
The special compressibility of warp knitted spacer fabric is based
on its construction corresponding to other influential factors. The
performance of spacer fabric as a cushioning material for
distributing surface pressure and relieving pressure depends on the
bending behavior of the pile monofilaments within and beyond the
direct compressing area. Fabrics with higher thicknesses are used
to absorb more energy thus produce less peak stress, while those
with moderate thicknesses are of higher peak efficiency. Although
fabrics with larger rigidity and thickness have lower peak stress,
which are good for body protection, comfort ability should be taken
into consideration as well. [6]
Warp-knitted spacer fabric structures are designed to be quite
flexible in a variety of thicknesses. These spacer fabrics are very
resilient and display good breathing properties and demonstrate
better recovery to compression, thermal properties and
breathability. Furthermore, warp-knitted spacer fabrics retain their
original thickness for longer time and can be easily recycled. [6]
3.2. Weft Knitted Spacer Fabric
Weft knitted spacer fabrics can be produced on circular double jersey machines as well as
electronically controlled flat machines. To produce spacer fabrics using circular knitting
machine requires the use of at least three different yarns for each course. These are:
a) yarn for the cylinder needles;
b) yarn for the dial needles and
c) a spacer yarn,
generally monofilament yarn connecting the two layers by tucks. The distance between the
two fabric layers can be set by the dial height adjustment. Cause of the limitations of
production, the thickness of the fabric is limited with 5 mm practically. The characteristics
of weft knitted spacer fabrics generally change with the space consist of monofilaments and
the trapped air between the two surfaces. The monofilaments act as linear springs when the
fabric is compressed. The major advantages of these structures are:
Plain as well as color and design and surface texture effects can be produced on the
face of the fabric knitted by the cylinder needles; and
Shaped and true three-dimensional structures can be produced on electronically
controlled flat machines.
The
major
limitations
of
weft
knitted
spacer
fabrics
are:
a) The thickness of the spacer is normally limited to between 2 and 10 mm.
b) The basic structure of the spacer fabric is limited to either knitting the spacer threads on
the dial and tucking on the cylinder, or tucking the spacer threads on the dial and cylinder
needles.
It is obviously more practical to use tuck stitches with spacer monofilament yarns in order
to ensure that the spacer yarns lie correctly inside the knitted fabric and prevent the face
and back of the fabric from having a rough or harsh feel. [5]
3.2.1. The Compressive Behavior of Warp Knitted Spacer Fabric
The compression resistance of the spacer fabrics with monofilament spacer yarn is higher
than the fabrics with multifilament spacer yarn. The monofilaments act as linear springs
when the fabric is compressed. The inherent resilience characteristic of multifilament yarns
is poorer than the monofilament yarns; throughout will be less than the monofilament. As a
result, the spacer yarn type influences the compression resistance of the spacer fabrics
significantly. In order to evaluate the effect of surface material type, three different
materials (cotton, polyester and polypropylene) were used for the back and face surface of
the spacer fabrics. There is a significant difference between the spacer fabrics with
polyester and polypropylene surfaces. Spacer fabrics with polyester surfaces have the
highest compression resistance and fabrics with polypropylene surfaces the lowest one.
Polyester yarns and fabrics resist compression and will return to their original state after
distortion. Conversely, polypropylene yarns and fabrics tend to remember a shape when
they have been compressed. Consequently it is obtained from all results and statistical
analysis that, spacer fabrics with polyester surfaces and monofilament spacer yarn have
higher compression resistance. This type of weft knitted spacer fabric can be used for the
application areas such as mattress or the area where compression characteristic plays
important roles. [7]
4.
Conclusion
The future scope of fabric science is very broad. Only innovative products will be
able to open up new markets and new horizons for the textile industry. To achieve
this, it is essential to invest in future research and researches. In the coming years,
knitted fabrics will increasingly take on industrial functions. Fabric will combine the
functions of medium, carrier and interface for an extremely wide range of industrial
applications. This new generation of industrial fabric makes considerable new
demands on the innovative ability within the clothing industry. What is needed is not
simply the conveyance of knowledge but the development of truly creative
researchers. The textile industry needs to shift its emphasis from quantity, quality; to
functionality in the new millennium of Global Competition Era.
References
1. Study of three-dimensional spacer fabrics: Physical and mechanical properties
Joanne Yip, Sun-Pui Ng
ACE Style Institute of Intimate Apparel, Institute of Textiles & Clothing, The
Hong Kong Polytechnic University, Hong Kong
2. Three Dimensional Computer Simulation Of Warp Knitted Spacer Fabric
Li-Zhe Zhang, Gao-Ming Jiang, Xu-Hong Miao
School of textile and clothing, Nantong University, China
3. Application of spacer fabric in composite production
Derin Mecit, Textile engineering department, Izmir, Turkey
4. http://trj.sagepub.com/content/early/2012/04/23/0040517512444331.abstract
5. http://www.highlandindustries.com/products/hiflow-spacer-fabrics/
6. The compression characteristics of warp knitted spacer fabric
Ege University, Textile Engineering Department, Izmir, Turkey
7. The compression characteristics of warp knitted spacer fabric
Southern Yangtze University, China
