Anti-static roll cover

A transfer roll cover has an inner surface made of conductive and elastic material to fit snugly around and make conductive contact with a transfer roll, and an outer surface made of looped yarns which are attached to the inner surface and have outer looped ends which make light rolling contact with a sheet transported over the transfer roll. The looped yarns are a composite of a cleaning yarn for cleaning particulate contaminants and an antistatic yarn for removing static charges from the transported sheet. In a preferred embodiment, the transfer roll cover has an inner surface made of nylon knitted yarn as a base yarn that holds the cover together and a LYCRA.TM. inlayed yarn which has an elasticity that allows the cover to stretch over and fit snugly onto the transfer roll. As an alternative, a heat-shrinkable polyvinyl acetate (PVA) yarn may be used as the elastic material. The preferred outer surface includes rayon knitted yarn with looped outer ends as the cleaning yarn, and BEKINTEX.TM. conductive knitted yarn with looped outer ends as the antistatic yarn.

TECHNICAL FIELD 
This invention generally relates to a roll cover for printing presses and 
web fed converting equipment, and more particularly, to a roll cover 
having a simplified construction with anti-static and particulate removal 
properties. 
BACKGROUND OF INVENTION 
Static buildup on preprinted sheet material is an historic and troublesome 
problem for the printer. Static charges tend to build up when the sheet or 
web material is transported through a printing press. The resulting static 
buildup can cause web/sheet guidance problems. A second problem involves 
particulate contamination on the surface of the preprinted sheet. 
Particulate contamination is strongly attracted to a statically charged 
sheet or web and often degrades print quality. 
Printing press manufacturers have attempted to deal with the static charge 
buildup problem by using various types of static elimination devices which 
are wrapped around printing rolls or festooned around a printing press. 
These devices conduct static charges to a ground by contacting or dragging 
against the surface of the sheet or web material as it passes through the 
press. 
For example, in U.S. Pat. No. 3,235,772 to Gurin, a printing blanket is 
provided for conducting electrostatic charges away from a sheet to an 
underlying metal roll mounting the blanket. The printing blanket may have 
an elastomeric outer layer with conductive pigment embedded therein in 
contact with conductive intermediary and/or backing layers wrapped on the 
printing cylinder. In U.S. Pat. No. 3,867,027 to Weigl, drum rollers made 
of an electrically conductive mat of metallized fibers are provided for 
removing static charges from continuously transported sheet material. In 
U.S. Pat. No. 5,508,879 to Kitamura, a charge removal brush for a 
photocopier is constructed with long conductive filaments planted in a 
conductive cloth wrapped around a metal shaft. 
In U.S. Pat. No. 3,635,158 to Budinger, a printing roller is provided with 
a high density felt of polyester fibers adhered to an underlying core for 
removing debris and particles from transported sheets. The felted layer 
can be formed on a heat-shrinkable tube of PET fibers that is slipped over 
the roller core and shrunk down to securely grip the roller core. The 
felted layer is used to remove particles from the transported sheets, but 
is not used for static charge removal. 
The prior art thus shows the general concept of using a printing roll 
blanket or brush having an outer conductive layer or fibers for removal of 
static charges to a conductive core, or a felted layer as a roll cover for 
particulate removal. The prior art devices are effective under limited 
conditions but do not solve the problem entirely. Trials have shown that 
in some circumstances the use of a cover to remove particulates from the 
sheets can exacerbate static problems and cause particulate contamination 
to be attracted to the sheets later in the process. It is especially 
desirable to provide a transfer roll cover that is convenient to install 
and replace on a transfer roll and that can both dissipate static charges 
effectively and remove particulate contaminants from printed sheet or web 
material. 
SUMMARY OF INVENTION 
In accordance with the present invention, a transfer roll cover comprises 
an inner surface made of conductive and elastic material to fit snugly 
around and make conductive contact with a transfer roll, and an outer 
surface made of looped yarns which are attached to the inner surface and 
have looped outer ends which make light rolling contact with a sheet 
transported over the transfer roll. The looped yarns are a composite of a 
cleaning yarn for cleaning particulate contaminants from the surface of 
the transported sheet and an antistatic yarn for removing static charges 
from the sheet. 
In a preferred embodiment, the transfer roll cover has an inner surface 
which includes an elastic or heat-shrinkable yarn and a nylon base yarn 
that provides strength and holds the cover together. This enables the roll 
cover to be installed snugly onto the transfer roll and to transfer 
electrostatic charges to the roll. The outer surface consists of a looped 
rayon yarn for cleaning the preprinted sheet, and a looped conductive yarn 
to provide the antistatic properties. The conductive looped yarns are 
knitted into the roll cover structure in such a manner that they 
intertwine with the inner surface and make conductive contact with the 
transfer roll thus providing a direct conductive path between the printed 
sheet and the roll to ensure that electrostatic charges are dissipated. 
The transfer roll cover of the present invention solves the static charge 
buildup problem while at the same time cleans the surface of the 
preprinted sheet or transported web material. It is also easy to install, 
inexpensive, and disposable, yet effective to solve the static and debris 
problems. 
Other objects, features, and advantages of the present invention will be 
explained in the following detailed description of the invention having 
reference to the appended drawings.

DETAILED DESCRIPTION OF INVENTION 
Referring to FIG. 1, a transfer roll cover in accordance with the present 
invention has an inner surface 10 made of conductive and elastic material 
that fits onto and makes conductive contact with a transfer roll 12 which 
is made of metal or other conductive material. Preferably, the inner 
surface 10 includes a combination of elastic yarns to provide elasticity 
and nylon yarns to provide strength. The elastic yarns ensure that the 
sleeve fits snugly around the transfer roll 12. A suitable elastic yarn is 
sold under the tradename 420 Denier LYCRA.TM. by Dupont Company in the 
U.S. A suitable nylon yarn is sold under the tradename 70 Denier Two-Ply 
Nylon by Jefferson Mills, Inc., in the U.S. An alternate inner surface 
construction can utilize heat-shrinkable yarn or other material (in place 
of the elastic yarn) which is activated by applying heat to the cover 
after the cover is installed on the roll. 
The outer surface 14 of the roll cover is made of a composite of looped 
yarns which are intimately intertwined with the yarns of the inner surface 
10 during a yarn knitting process, for example. The looped yarns 
preferably comprise a cleaning yarn 14a such as rayon to provide cleaning 
properties and a conductive yarn 14b to provide antistatic properties. A 
suitable rayon yarn is sold under the tradename 200 Denier Rayon by 
Kuraray Company in Japan. A suitable conductive yarn is sold under the 
tradename BK NM 50/1 by Bekintex NV in Belgium. The inner ends of the 
looped yarns are knitted with the yarns of the inner surface to form a 
knitted backing that fits snugly on and makes good conductive contact with 
the transfer roll. The outer ends of the looped yarns make light rolling 
contact with a sheet 20 transported over the transfer roll 12 in order to 
perform its antistatic and particulate removal functions without adversely 
affecting sheet transport over the roll. The static charges are conducted 
by the conductive yarns 14b from the outer surface to the inner surface of 
the cover then to ground via the metal transfer roll. 
As a surprising aspect of the invention, it is found that the rolling 
contact between the looped antistatic yarns of the roll cover and the 
sheet material effectively dissipates static charges. Combining the looped 
rayon cleaning yarns with the antistatic yarns allows the particulate 
removal function to be performed effectively at the same time as static 
dissipation. 
A suitable transfer roll cover may be constructed by utilizing a 
combination of yarns for their respective functions: 
1. 70 denier, 2 ply nylon knit yarn used as a base yarn that holds the 
fabric together. The nylon knit yarn is preferably in the range of 5% to 
20% of the total yarn content of the cover. 
2. 420 denier LYCRA.TM. inlayed yarn is used to provide elasticity that 
allows the cover to stretch over the transport roll. The elasticity in the 
LYCRA.TM. yarn prevents the cover from "walking" on the transfer roll 
during the process of transferring sheet material. The LYCRA.TM. inlayed 
yarn is preferably in the range of 10% to 30% of the total yarn content of 
the cover. 1000 denier polyvinyl acetate (PVA) yarn may be substituted for 
the LYCRA.TM. inlayed yarn. If PVA yarn is used, the application of heat 
is required to shrinkfit the cover to the transfer roll. 
3. 200 denier rayon is used as a Terry yarn which is knitted to form loops 
over sinkers. The looped rayon yarn serves as a cleaning yarn which cleans 
the surface of the sheet or web material transported over it. The looped 
rayon yarn is preferably in the range of 30% to 60% of the total yarn 
content of the cover. 
4. 50/1 BK BEKINTEX.TM. conductive yarn, is used as a Terry yarn which is 
knitted to form loops over sinkers. The looped conductive yarn serves as 
an antistatic yarn which removes static charges from the surface of the 
sheet or web material transported over it. The looped antistatic yarn is 
preferably in the range of 15% to 40% of the total yarn content of the 
cover. 
A preferred example of the transfer roll cover is a Terry knitted fabric 
constructed of four yarns: 
______________________________________ 
Yarn Description 
% of Sleeve Fabric 
Supplier 
______________________________________ 
200 denier rayon 
47% Kuraray (Japan) 
70 denier 2-ply nylon 
10% Jefferson Mills 
420 denier LYCRA 
18% Dupont 
BK NM 50/1 Bekintex 
______________________________________ 
(Belgium) 
The four yarns of the preferred example of the roll cover may be knitted 
together using knitting machines manufactured by Moorgate or Tritex 
Company of Leicester, England. It should be understood that knitting 
machines produced by other manufacturers could also be used to knit the 
roll cover. 
FIG. 2 illustrates the thread-up of a knitting head 20 of a knitting 
machine using the four types of yarns for the transport roll cover fabric. 
The 70 denier, 2 ply nylon yarn is applied through opposing knit tubes 22. 
The 420 denier LYCRA.TM. yarn is applied through opposing inlay tubes 24. 
The 200 denier rayon and 50/1 BEKINTEX.TM. BK yarns are applied through 
opposing terry tubes 26, 28, respectively. The resulting fabric has a 
total weight of 37.5 grams/linear inch of the cover. The cover has a 
thickness of approximately 3/16 inch (lofted). 
In summary, the transfer roll cover of the present invention utilizes the 
composite of outer looped cleaning and antistatic yarns to make rolling 
contact with the transported sheet so as to effectively remove static 
charges and at the same time clean particulate contaminants from the 
surface of the transported sheet. The elastic or heat-shrinkable material 
of the inner surface allows the outer surface to be securely anchored to 
the cover while at the same time enabling the cover to be easily installed 
or removed from the transfer roll. The overall construction of the roll 
cover is also simple and inexpensive to fabricate. 
It is understood that many modifications and variations may be devised 
given the above description of the principles of the invention. Other 
types of conductive and elastic materials may be used for the inner part 
of the transfer roll cover, and other yarns or fibrous materials may be 
substituted for the cleaning and static removal functions of the outer 
part of the roll cover. It is intended that all such modifications and 
variations be considered as within the spirit and scope of this invention, 
as it is defined in the following claims.