[0001] The present invention relates to composite sheeting, and more especially to fabrics
suitable for use in the manufacture of printers' blankets and to blankets incorporating
such fabrics.
[0002] Conventional offset printing blankets are composite materials composed of layers
of woven fabric and rubber, presenting a smooth rubberised surface to receive the
ink to be transferred. The woven fabric is usually composed of combed cotton in warp
and weft, but may have high modulus spun rayon in either warp or weft. The main requirements
for such a fabric are that it should have a high modulus in the warp direction (to
prevent stretching of the blanket on the printing machine), be smooth and without
slubs or knots, be stable under vulcanizing conditions (when this is utilized) and
afford adequate adhesion to the rubber layers. The blanket should also be sufficiently
flexible to pass round rollers in the printing machine, and afford adequate cushioning
for printing.
[0003] The present invention seeks to provide a novel smooth-surfaced fabric of improved
properties and an improved printers' blanket incorporating the fabric.
[0004] The fabric according to the invention comprises a rigid warp knitted base fabric
composed of relatively fine yarns of continuous man-made filaments, closely spaced
and relatively coarse inlaid warp yarns and relatively coarse weft insertion yarns,
the inlaid and insertion yarns being also composed of man-made fibres and extending
through the knitted structure without interlacing with one another, one face of the
fabric being substantially constituted by the inlaid warp yarns.
[0005] By 'rigid' is herein meant that the fabric resists two-dimensional distortion in
its own plane.
[0006] The fabric according to the invention has several advantages over the conventional
fabric, because, apart from the basic knitted structure of fine yarn, the relatively
coarse load-carrying warp and weft yarns do not interlace and lie completely flat,
and there is no crimp in the warp and weft such as is imposed by a woven structure
of similar strength. In consequence, the fabric has a higher modulus than a woven
structure.
[0007] Preferred fabrics employ continuous filament yarns for both the inlaid warp and inserted
weft. Moreover, for use in printers' blankets, it is preferred that the inserted weft
yarns should be bulked or textured, and preferably also closely spaced.
[0008] The absence of yarn interlacings, and especially the use of smooth continuous filament
yarns in the closely spaced inlaid warp, give the fabric and outstandingly smooth
surface on the warp face.
[0009] The preferred yarns for the warp knitted base fabric are 33 dtex 6F polyester filament
yarns. These fine yarns, preferably having a count in the range 33-110 dtex, contribute
little to the load-carrying properties of the fabric or to the surface, but confer
two-dimensional rigidity on the inlaid and inserted, but not interlaced, structure
of the warp and weft.
[0010] The preferred inlaid warp yarns are 550 dtex 96F polyester. These yarns are relatively
coarse, for example in the range 110 - 1100 dtex but are smooth and untextured. In
the preferred fabrics, the inlaid warp yarns are disposed in pairs, with only one
wale of the knitted base between each pair. Being closely spaced in the fabric, and
held rigidly in position by the knitted base, the inlaid warps provide a substantially
continuous, smooth surface on one face of the fabric
[0011] Particularly in the case of fabrics intended
* for use in printers' blankets, the weft insertion yarns are preferably textured or
bulked yarns, more especially having a count in the range 120 - 1220 dtex.
[0012] Examples of suitable yarns are air-textured nylon or polyester yarns, which may be
analogous to 'Tsslanized' yarns although much heavier than the yarns usually textured
by that process. Alternative yarns suitable for this purpose are torque-textured polyester
yarns.
[0013] The bulked or textured weft yarns afford the desired cushioning and also offer a
greater adhesion key to the layer of rubber or other elastomer in the manufacture
of printers' blankets.
[0014] In the manufacture of printers' blankets from the fabric of this invention, the fabric
is prepared as necessary to receive one or more elastomeric coatings and is then coated
and, if appropriate, vulcanized, for which purposes conventional techniques may be
employed. The blanket may include more than one layer of fabric, of which not all
need be fabrics according to this invention. However, in any layer of fabric according
to this invention the warp face should be directed towards the face of the blanket.
[0015] After being knitted, the fabric may be stretched in the warp direction and heat set
in this condition to adjust the modulus as desired, followed by calendering to assist
in closing gaps in the fabric structure and to increase the smoothness of the fabric
surface.
[0016] If a key coat, for example an isocyanate coat, is to be applied to enhance adhesion
between the fabric and the elastomeric layer, this is conveniently coated after the
calendering operation.
[0017] Alternatively, a rubber-receptive yarn may be used, for example in the warp, with
a resorcinol/formal- dehyde latex adhesive dip treatment or other adhesive system
known in the art.
[0018] The elastomers that may be used in conjunction with the fabric of this invention
in the fabrication of printers' blankets include:
(1) vulcanizable elastomers, such as natural and synthetic rubbers;
(2) cross-linkable elastomers, such as non-thermoplastic polyurethurethanes, which
may be of either the polyester or the polyether type;
(3) thermoplastic rubbers, such as block polystyrene/ butadiene polymers or styrene/butadiene
block copolymers; and
(4) thermoplastic polyurethane.
[0019] Printers' blankets according to the invention are thinner and lighter than conventional
blankets of comparable strength without any sacrifice of performance. They are also
cheaper. Because of their reduced thickness, they are able to pass round smaller rollers
without buckling at the inside surface and are therefore more adaptable in their application.
[0020] In the drawings:
Fig. 1 shows the structure of a preferred fabric for use in this invention; and
Fig. 2 is a knitting diagram for the fabric of Fig. 1.
[0022] In the knitting pattern shown in the diagram of Fig. 2, the warp yarns follow the
arrangement:

[0023] Although when knitted with yarns of the character set forth above, the fabric structure
described is outstandingly well adapted for use in composite sheeting such as printers'
blankets, the structure is believed to be novel in its own right and,with the substitution
of yarns of different characteristics (for example extensible yarns), can be used
to provide smooth-faced fabrics for a variety of different end uses.
1. A smooth-faced fabric comprising a rigid warp knitted fabric composed of relatively
fine yarn of continuous man-made filaments, closely spaced and relatively coarse inlaid
warp yarns and relatively coarse weft insertion yarns, the inlaid and insertion yarns
being also composed of man-made fibres and extending through the knitted structure
without interlacing with one another, and one face of the fabric being substantially
constituted by the inlaid warp yarns.
2. A fabric according to claim 1 wherein the inserted weft yarn is a bulked or textured
nylon or polyester filament yarn.
3. A fabric according to claim 1 or 2 wherein the inlaid warp yarns are disposed in
pairs, with one wale of the knitted fabric between each pair.
4. A printers' blanket comprising at least one layer of a fabric according to claim
1, 2 or 3 embedded in at least one elastomeric layer, the smooth surface of the or
each such fabric being directed towards the face of the blanket.
5. A printers' blanket according to claim 4 wherein the or each elastomeric layer
is composed of vulcanized rubber.