Note: Descriptions are shown in the official language in which they were submitted.
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PARTICLE ENTRAPMENT SYSTEM
BACKGROUND
Dust cloths for removing dust from a surface to be cleaned, such as a table,
are
generally known. Such known dust cloths are typically made of woven or non-
woven
fabrics and are often sprayed or coated with a wet, oily substance for
retaining the dust.
However, such known dust cloths tend to leave an oily film on the surface
after use.
Other known dust cloths include non-woven entangled fibers having spaces
between the entangled fibers for retaining the dust. The entangled fibers are
typically
supported by a network grid or scrim structure, which can provide additional
strength to
such cloths. However, such cloths can become saturated with the dust during
use (i.e.,
dust buildup) and/or may not be completely effective at picking up dense
particles, large
particles or other debris.
Accordingly, it would be advantageous to provide a cleaning sheet that can
pick
up and retain dust and debris. It would also be advantageous to provide a
cleaning sheet
that has an enhanced dust collection capacity. It would also be advantageous
to provide
a cleaning sheet that attracts debris without the use of an oily spray. It
would also be
advantageous to provide a cleaning sheet that retains relatively large and/or
denser
particles of debris. It would further be advantageous to provide a cleaning
sheet
including any one or more of these or other advantageous features.
SUMMARY
The present invention relates generally to the field of cleaning sheets, such
as for
use in cleaning surfaces (e.g., in the home or work environment). More
particularly,
the invention relates to a cleaning sheet for collecting and retaining dust,
larger particles
and/or other debris.
A particle entrapment system or cleaning sheet is provided. The cleaning sheet
is useful for cleaning and removing particles and other debris from a surface
such as a
table, floor, article of furniture or the like. The cleaning sheet may include
a number of
layers or sheets to increase debris retention and/or strength. The sheet
typically
includes a particle retention layer (e.g., base layer) including electret
material for
collecting and retaining the particles. The electret material may be electret
wax that is
deposited on and/or impregnated in at least a portion of the particle
retention layer.
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The sheet may also include an outer layer (e.g., cover layer) covering at
least a
portion of the particle retention layer. The cover layer may include a
plurality of
apertures, which allow the debris to be forced andlor attracted therethrough.
The
apertures may make up a substantial portion of the cover layer, and may
typically have a
cross-sectional dimension of at least about 1.0 mm2. Examples of suitable
cover layers
include materials having a plurality of apertures with an average cross-
sectional
dimension of about 1.0 to about 10.0 mm2. The cover layer is commonly formed
from a
low dust retention material (e.g., perforated sheets formed from
polytetrafluoroethylene
("PTFE'~). The cover layer comprises a low dust retention material and
includes a
surface having a plurality of apertures formed therethrough.
Cleaning utensils incorporating the cleaning sheet are also provided. The
utensil
may include a cleaning head adapted for coupling to the cleaning sheet. The
cleaning
sheets) may also be packaged as part of a cleaning utensil kit for cleaning
surfaces.
The kit may include a cleaning head adapted for coupling to the sheet and a
handle
IS adapted for coupling to the cleaning head.
A method of cleaning a surface is also provided. The method includes
contacting
a surface to be cleaned with the cleaning sheet. The debris from the surface
to be
cleaned may be drawn and/or forced into the particle retention layer and
retained by the
cleaning sheet.
In various embodiments of the cleaning sheet, the particle retention layer may
be
a cover layer, a backing sheet or layer or a core layer. The particle
retention layer may
be a uniform, planar sheet, or a contoured surface including protrusions and
depressions. An electret material, such a wax that has been rendered electret,
is
typically deposited on and/or impregnated into at least portions of the
particle retention
layer to enhance its particle collection and/or retention capabilities.
A method of making a cleaning utensil for collecting and retaining debris is
also
provided. The method includes forming a cleaning sheet that includes particle
retention
material such as woven fiber, non-woven fiber and/or foam. The method includes
applying non-electret wax to at least a portion of the particle retention
material. An
electric field is applied to sheet to induce a permanent electric charge in at
least the wax.
This can commonly be accomplished by heating the sheet to a temperature
sufficient to
melt the wax without substantially softening the particle retention material.
While the
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wax is still in a molten state, an electric field is applied to sheet. The
electric field is of
sufficient magnitude and duration to cause the wax to become electrically
charged. For
example, this can be accomplished by passing the sheet with the molten wax
through a
corona discharge. The charged wax is then cooled to solidify the wax thereby
rendering
it relatively permanently charged.
The present sheets can also be formed via a method in which molten wax is
subjected to an electric field as the wax is being applied to the particle
retention
material. For example, molten wax can be sprayed onto portions of a layer of
particle
retention material in a continuous or discontinuous pattern in such a manner
that the wax
passes through an electric field while still in a molten state. It is
generally advantageous
to hold the particle retention material at a low enough temperature such that
the wax
solidifies on contact (or shortly thereafter) with the material.
The cleaning sheet typically has a relatively low overall breaking strength in
order to preserve a relative amount of flexibility. The term "breaking
strength" as used
in this disclosure means the value of a load (i. e. , the first peak value
during the
measurement of the tensile strength) at which the cleaning sheet begins to
break when a
tensile load is applied to the cleaning sheet. The breaking strength of the
sheet should,
however, be high enough to prevent "shedding" or tearing of the cleaning sheet
during
use. The breaking strength of the cleaning sheet is typically at least about
500 g/30 cm
and cleaning sheets with breaking strengths of 1,500 g/30 cm to 4,000 g/30 cm
are quite
suitable for use with the cleaning implements described herein.
When intended to be used with a cleaning utensil, mounting structure or the
like,
the cleaning sheet typically has a relatively low overall elongation to assist
in resisting
"bunching" or 'puckering" of the cleaning sheet. The term "elongation" as used
in this
disclosure means the elongation percentage ( % ) of the cleaning sheet when a
tensile load
of 500 g/30 mm is applied. For example, when designed to be used in
conjunction with
a mop or similar cleaning implement where the cleaning sheet is fixedly
mounted, the
present cleaning sheets typically have an elongation of no more than about 25
% and,
preferably, no more than about IS % .
The terms "surface" and "surface to be cleaned" as used in this disclosure are
broad terms and are not intended as terms of limitation. The term surface as
used in
this disclosure includes substantially hard or rigid surfaces (e.g., articles
of furniture,
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tables, shelving, floors, ceilings, hard furnishings, household appliances,
and the Iike),
as well as relatively softer or semi-rigid surfaces (e.g., rugs, carpets, soft
furnishings,
linens, clothing, and the like).
The term "debris" as used in this disclosure is a broad term and is not
intended as
a term of limitation. In addition to dust and other fine particulate matter,
the term
debris includes relatively large-sized particulate material, e.g., having an
average
diameter greater than about 1 mm, such as large-sized dirt, food particles,
crumbs, soil,
sand, lint, and waste pieces of fibers and hair, which may not be collected
with
conventional dust rags, as well as dust and other fine particulate matter.
Throughout this disclosure, the text refers to various embodiments of the
cleaning sheet and/or methods of using or forming the sheet. The various
embodiments
discussed are merely illustrative and are not meant to limit the scope of the
present
invention. The various embodiments described are intended to provide a variety
of
illustrative examples and should not necessarily be construed as descriptions
of
alternative species since the descriptions of the various embodiments may be
of
overlapping scope.
BRIEF DESCRIPTION OF THE FIGURES
FIGURE 1 is a perspective view of a cleaning utensil according to an exemplary
embodiment.
FIGURE 2 is a cross-sectional view of a cleaning sheet taken along line 2-2 of
FIGURE 1 according to an exemplary embodiment.
FIGURE 3 is a fragmentary partially exploded sectional view of a cleaning
sheet
according to another exemplary embodiment.
FIGURE 4 is a fragmentary partially exploded sectional view of a cleaning
sheet
according to another exemplary embodiment.
FIGURE 5 is a fragmentary partially exploded sectional view of a cleaning
sheet
according to another exemplary embodiment.
FIGURE 6 is a top plan view of a scrim according to a suitable embodiment.
FIGURE 7 is a fragmentary top plan view of the cleaning sheet according to a
suitable embodiment.
FIGURE 8 is a fragmentary top plan view of a hole of a cleaning sheet
according
to a suitable embodiment of the present invention.
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FIGURE 9 shows a stress-strain curve where the vertical axis represents the
stress, the horizontal axis represents the strain, and O represents the
origin.
FIGURE 10 is a sectional view of an apparatus for rendering a wax electret.
FIGURE 11 is a sectional view of an electret wax formed by the apparatus
shown in FIGURE 10.
FIGURE 12 is a sectional view of a cleaning sheet including an electret layer
and
a micro-fiber layer.
FIGURE 13 is a top plan view of a cleaning sheet including an electret wax
distributed in a discontinuous pattern.
FIGURE 14 is a sectional view of a cleaning sheet including an electret wax
distributed in a row pattern.
FIGURE 15 is a sectional view of the cleaning sheet of FIGURE 3 showing an
electret wax deposited in a depression of a particle retention layer.
DETAILED DESCRIPTION
One example of a cleaning sheet (shown as a dusting pad 10) for collecting,
attracting and retaining particulate matter and other debris (e.g., dust,
soil, other
airborne matter, lint, hair, etc.) is shown in FIGURE 1. Pad 10 includes an
"electret"
base or core particle retention layer 30 permanently charged with an
electrostatic force
for attracting (e.g., collecting) and retaining particulate matter (shown as
debris 68 in
FIGURE 2). Debris 68 is drawn and/or forced into the particle retention layer
30 when
pad 10 is moved along a surface to be cleaned (shown as a work surface 66 in
FIGURE 1). Pores (shown as cavities 34) of core 30 retain and/or entrain
debris 68
within cavities 32 of pad 10 (see, e.g., FIGURE 2).
The particulate matter may be further retained by a cover sheet, which can
cover
or surround all or a portion of the electret material, to "trap" and retain
the particulate
matter in the electret material. An outer or cover layer 20 may be made of a
material
that has a relatively low debris retention capacity (i.e., that does not
significantly attract
or collect the debris), and generally has a lower debris retention than the
core, so the
exterior surface of cover layer 20 remains substantially free of debris 68.
Examples of
exemplary materials that do not significantly collect dust include perforated
sheets
formed from polytetrafluoroethylene. Typically, the cover layer is configured
to retain
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no more than about 10 g/m2 of particulate matter, more suitably no more than
about 1 to
glm2.
1. PARTICLE RETENTION LAYER
The present cleaning sheet includes a particle retention layer, at least a
portion of
5 which includes electret material (i.e., has been rendered permanently
electrically
charged). The sheet can include core 30 which includes a particle retention
surface 32
located within pad 10 adjacent cover layer 20. In other embodiments, the
cleaning sheet
may simply consist of the particle retention layer (e.g., a scrim-supported
layer of non-
woven microfibers and at least portion of which have been coated with an
electret wax).
Cavities 34 of particle retention surface 32 trap, collect and retain a
significant amount
of debris 68. For example, debris may be embedded against a wall of the
cavity.
According to suitable embodiments, the particle retention layer may be a
shaped fabric,
a continuous sheet of flexible material, or multiple sheets of material.
Referring to
FIGURE 2, cavities 34 can be formed from pores randomly distributed in core
30.
Cavities 34 having a circular shape, but may be any shape or combination of
shapes
such as rounded, jagged, irregular, etc. as shown in FIGURE 2. For example,
the
cavities may be rectangular, star, oval, or irregular shaped. The cavities may
be
disposed in a regular pattern, as depicted in FIGURE 3 and may be randomly
arranged.
The size and depth of the cavities should preferably be large enough to create
a
sufficient sized 'docket" or cavity to keep entrained debris from scratching
or damaging
the surface being cleaned. The cavities are preferably not so deep, however,
that it is
difficult for debris to be brought into contact with the cavity. The cavities
typically
have an average width in the range of about 1 to 10 mm, more suitably 2 to 5
mm,
depending in part on the size of the particles intended to be retained. The
cavities
typically have an average depth in the range of about 0.1 to 5 mm, more
suitably 1 to
3 mm.
FIGURE 3 shows a sectional view of a pad 110, an exemplary embodiment of
the cleaning sheet. Pad 110 differs substantially from pad 10 in one respect:
the
structure of core 30 is changed. Other than this modification, the
construction,
performance and function of pad 110 shown in FIGURE 3 is substantially the
same as
pad 10, and like reference numerals are used to identify like elements. A core
130 of
pad 110 is textured to form the pores (shown as depressions 134). Protrusions
(shown
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as outwardly extending, flexible, semi-rigid fingers 136) extend from core 130
toward
cover layer 20. Fingers 136 are generally rectangular shaped, but may be of
other
shapes (e.g., zigzag, rounded, wave-like, etc.) according to other
embodiments.
Fingers 136 are shown arranged in a row-like pattern, but may be arranged in
other
patterns or configurations (e.g., circular, random, etc.) according to other
suitable
embodiments. Fingers 136 define depressions 134 for retaining debris 68 (e.g.,
between
two protrusions). When retained inside depressions 134, debris 68 is
substantially
prevented from escaping the interior of pad 110 by cover layer 20.
FIGURE 4 shows a pad 210, another exemplary embodiment of the cleaning
sheet. Pad 210 differs substantially from pad 10 in two respects: the
structure of core
30 is changed, and the material of core 30 is changed. Other than these
modifications,
the construction, performance and function of pad 210 is substantially the
same as pad
10, and like reference numerals are used to identify like elements. A core 230
of pad
210 is shaped (e.g., as a sinusoidal wave) to form the pores (shown as
depressions 234)
for retaining debris 68. A top cover layer 20 "sandwiches" or presses core 230
against a
bottom cover layer 20. Protrusions (shown as projections 236) extend from core
230 to
form depressions 234. Projections 236 are generally blunt shaped and include
an
inclined or sloping wall 240. The sloping shape of projections 236 provides
additional
surface area in depressions 234 for collecting and retaining debris 68. As
shown in
FIGURE 4, projections 236 are arranged in a row-like or corrugated pattern.
Projections 236 of a top particle retention surface 232 are shown arranged in
an
alternating pattern, such that projections 236 of surface 232 correspond to
depressions
234 of a bottom particle retention surface 238. According to other suitable
embodiments, the protrusions (i.e., projections) and the pores (i.e.,
depressions) may be
arranged in a variety of other patterns (e.g., protrusions of the top particle
retention
surface corresponding to the protrusions of the bottom particle retention
surface and
arranged in a row-like or wave-like manner). According to other suitable
embodiments
(as shown in FIGURES 4 and 5) the particle retention layer (i.e., core)
includes at least
two sides, and the pores (i.e., cavities) are arranged on each side of the
particle
retention layer.
FIGURE 5 shows a pad 310, another exemplary embodiment of the cleaning
sheet. Pad 310 differs substantially from pad 10 in two respects: the
structure of core
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30 is changed, and the materials of core 30 are changed. Other than these
modifications, the construction, performance and function of pad 310 is
substantially the
same as pad 10, and like reference numeral are used to identify like elements.
Core 330
of pad 310 is shown made of an entangled network of non-woven fibers. The
pores for
trapping the debris are formed by the spaces between the entangled fibers (i.
e. , the
debris is retained between the fibers that form the core). According to other
suitable
embodiments, the core may be made from a variety of combinations of materials
formed
in a variety of structures.
The term "non-woven" as used in this disclosure includes a web having a
structure of individual fibers or threads which are interlaid, but not
necessarily in a
regular or identifiable manner as in a knitted fabric. The term also includes
individual
filaments and strands, yarns or "tows" as well as foams and films that have
been
fibrillated, apertured, or otherwise treated to impart fabric-like properties.
Non-woven
fabrics or webs have been formed from many processes such as for example,
meltblowing processes, spunbonding processes, and bonded carded web processes.
The
basis weight of non-woven fabrics is usually expressed in ounces of material
per square
yard ("osy'~ or grams per square meter ("gsm'~ and the fiber diameters useful
are
usually expressed in microns. Basis weights can be converted from osy to gsm
simply
by multiplying the value in osy by 33.91. According to another suitable
embodiment,
the fibers may be woven.
According to an exemplary embodiment, a web or lattice (shown as a scrim 50 in
FIGURE 6) may support the fibers of a non-woven sheet. This allows the
production of
sheets that have a relatively low entanglement coefficient (e.g., no more than
about
800 m) while retaining sufficient strength to be used for cleaning. As shown
in
FIGURE 5, scrim may be integrally embedded within the fibers to form a unitary
support structure. In FIGURE 6 scrim 50 includes a net having horizontal
members 52
attached to vertical members 54 arranged in a "network" configuration. Spaces
(shown
as holes 56) are formed between vertical members 54 and horizontal members 52
to give
scrim 50 a mesh or lattice-like structure. According to various embodiments,
the
horizontal and vertical members of the scrim may be connected together in a
variety of
ways such as woven, spot welded, cinched, tied, etc. The average diameter of
holes 56
generally falls within the range of 20 to 500 mm, and more suitably between
100 to 200
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mm. The distance between the fibers typically falls within about 2 to 30 mm,
and more
suitably within about 4 to 20 mm. Alternatively, the nonwoven sheet may be
reinforced
by filaments embedded in the sheet which are held in place simply by the
mechanical
forces resulting from hydroentangling microfibers around the filaments.
S The fibers may be overlaid on each side of scrim 50 to attach the fibers to
scrim
50, thereby forming pad 310 as a unitary piece or structure. A low-pressure
water jet
may be subsequently applied to entangle the fibers to each other and to scrim
50 (i.e.,
hydroentanglement) to form a relatively lose entanglement of non-woven fibers.
Hydroentanglement of the fibers may be further increased during removal (e.g.,
drying)
of the water from the water jet. (The scrim may also "shrink" somewhat during
drying
to create a fabric having a "puckered" or contoured surface.) The fibers may
also be
attached to the web (i.e., scrim) by a variety of other conventional methods
(e.g., air
laid, adhesive, woven, etc.). The fibers are typically entangled onto the web
to form a
unitary body, which assists in preventing "shedding" of the fibers from the
web during
cleaning. The web may be formed from a variety of suitable materials, such as
polypropylene, nylon, polyester, etc. An exemplary web (i.e., scrim) is
described in
U.S. Patent No. 5,525,397, the disclosure of which is hereby incorporated by
reference.
The degree of entanglement of the fibers in the core can be measured by an
"entanglement coefficient". The entanglement coefficient is also referred to
as the "CD
initial modulus ". The term "entanglement coefficient" as used in this
disclosure refers to
the initial gradient of the stress-strain curve measured with respect to the
direction
perpendicular to the fiber orientation in the fiber aggregate (cross machine
direction).
The term "stress" as used in this disclosure means a value which is obtained
by dividing
the tensile load value by the chucking width (i. e. , the width of the test
strip during the
measurement of the tensile strength) and the basis weight of the non-woven
fiber
aggregate. The term "strain" as used in this disclosure is a measure of the
elongation of
the cleaning sheet material.
Suitable non-woven fiber aggregates fox use in forming the cleaning sheet have
an entanglement coefficient in the range of about 20 to 500 m (as measured
after any
reinforcing filaments or network has been removed from the non-woven fibrous
web)
and, more typically, no more than about 250 m. A small value of the
entanglement
coefficient generally represents a smaller degree of entanglement of the
fibers. The
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entanglement coefficient may be controlled in part by selection of the type
and quantity
of fibers, the weight of the fibers, the amount and pressure of the water,
etc. (See U.S.
Patent No. 5,525,397 at col. 4, line 52 - col. 5, line 26 discussing
entanglement of
fibers.)
The core (e.g., core 330 as shown in FIGURE 5) may include a non-woven
aggregate layer having fibers with a large degree freedom and sufficient
strength, which
may be advantageous for effectively collecting and retaining dust and larger
particulates
within the cleaning sheet. In general, a non-woven fabric formed by the
entanglement
of fibers involves a higher degree of freedom of the constituent fibers than
in a non-
woven fabric formed only by fusion or adhesion of fibers. The non-woven fabric
formed by the entanglement of fibers can exhibit better dust collecting
performance
through the entanglement between dust and the fibers of the non-woven fabric.
The
degree of the entanglement of fibers can have a large effect on the retention
of dust.
That is, if the entanglement becomes too strong, the freedom of fibers to move
will be
lower and the retention of dust is generally decreased. In contrast, if the
entanglement
of the fibers is very weak, the strength of the non-woven fabric can be
markedly lower,
and the processability of the non-woven fabric may be problematic due to its
lack of
strength. Also, shedding of fibers from the non-woven fabric is more likely to
occur
from a non-woven aggregate with a very low degree of entanglement.
A suitable non-woven aggregate for use in producing the present cleaning sheet
can be formed by hydroentangling a fiber web (with or without embedded
supporting
filaments or a network sheet) under a relatively low pressure. For example,
the fibers
in a carded polyester non-woven web can be sufficiently entangled with a
network sheet
by processing the non-woven fiber webs with water jetted at high speed under
about 25-
50 kg/cm3 of pressure. The water can be jetted from orifices positioned above
the web
as it passes over substantially smooth non-porous supporting drum or belt. The
orifices
typically have a diameter ranging between 0.05 and 0.2 mm and can be suitably
arranged in rows beneath a water supply pipe at intervals of 2 meters or less.
In cases where the entanglement coefficient of the fiber aggregate is to be
set at a
maximum value of about 800 m, it may be difficult for a sheet, 'which is
constituted only
of a fiber aggregate, to achieve the values of sufficient breaking strength
and the
elongation. By entangling the fibers to scrim 50 into a unitary body, and the
elongation
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of this layer is kept low and its processability can be enhanced. Shedding of
the fibers
from the cleaning sheet can often be markedly prevented as compared with a
conventional entangled sheet, which is constituted only of a fiber aggregate
in
approximately the same entanglement state as that in the fiber aggregate of
the cleaning
sheet.
If the entanglement coefficient is too small (e.g., no more than about 10 to
20 m), the fibers will not be sufficiently entangled together. In addition,
the
entanglement between the fibers and the scrim will likely be poor as well. As
a result,
shedding of the fibers may occur frequently. If the entanglement coefficient
is too large
(e.g., greater than about 700 to 800 m), a sufficient degree of freedom of the
fibers
cannot be obtained due to too strong entanglement. This can prevent the fibers
from
easily entangling with dust, hair and/or other debris, and the cleaning
performance of
the sheet may not be satisfactory.
The cleaning sheet typically includes a non-woven fiber aggregate as a core
layer
having a relatively Iow basis weight. The basis weight of the non-woven fiber
aggregate
generally falls within the range of 30 to 100 g/m2 and, typically is no more
than about
75 g/m2. If the basis weight of the non-woven fiber aggregate is less than
about 30
g/m2, dust may pass too easily through the non-woven fiber aggregate during
the
cleaning operation and its dust collecting capacity may be limited. If the
basis weight of
the non-woven fiber aggregate is too large (e.g., substantially greater than
about 150
g/mZ), the fibers in the non-woven fiber aggregate (if any) generally may not
be
sufficiently entangled with each other to achieve a desirable degree of
entanglement. In
addition, the processability of the non-woven fiber aggregate can worsen, and
shedding
of the fibers from the cleaning sheet may occur more frequently. The denier of
the
fibers in the non-woven fiber aggregate, the length, the cross-sectional shape
and the
strength of the fibers used in the non-woven fiber aggregate are generally
determined
with an eye toward processability and cost, in addition to factors relating to
performance.
The cleaning sheet typically includes an outer non-woven fiber layer or
net/web
that has a relatively low basis weight as an outer fabric layer (i. e. , the
material on the
cleaning surface of the sheet). According to a particularly suitable
embodiment, the
non-woven Iayer or net has a basis weight in the range of about 20 to 150
g/rnz,
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preferably 30 to 75 g/m2. A low basis weight can assist in providing a "stream-
line" or
compact look and feel to the cleaning sheet. The basis weight of the cleaning
sheet may
be about 50 to 250 g/m2 (or greater or lesser depending on the intended use
for the
cleaning sheet) .
The cleaning sheet may include a non-woven fabric formed from fibers or micro-
fibers. The term "denier" as used in this disclosure is defined as the weight
in grams of
a 9000 meter length of fiber. The denier of the fibers of the particle
retention layer is
suitably about 0.1-6, more suitably about 0.5-3.
a. Electrostatic Properties of the Particle Retention Laver_
The particle retention lay may include a dielectric material that may be
rendered
"electret" in whole or in part. Electrets retain an electrostatic charge over
a prolonged
period (e.g., years). Electrets are believed to be a relatively permanent
source of an
electric or electrostatic field. Thus, the rendering electret of a dielectric
material in a
cleaning sheet (e.g., particle retention layer, cover layer, backing layer,
etc.) may
thereby cause an electrostatic charge to build-up on the cleaning sheet. Such
build-up of
an electrostatic charge may enhance the ability of the cleaning sheet to
attract, collect,
trap and retain debris during the cleaning process. (Compare conventional non-
electret
materials, which typically only physically contact debris, with the debris
adhering to, or
being enveloped by, the conventional non-electret material.)
The application of an external electric field may render a dielectric material
"electret". The molecules and charges in the dielectric are 'polarized" or
oriented in a
certain direction or moment. The resulting electret is believed to possess an
electric
internal volume polarization that produces a permanent electrostatic field.
The opposing
outer faces of the electret exhibit opposite electrostatic charges. Since the
internal
molecules and charges are polarized, not merely exterior surface molecules and
charges,
the electrostatic orientation extends throughout the entire mass of the
electret. Thus, the
breaking or division of an electret yields multiple electrets (e.g., similar
to the breaking
of a permanent magnet).
Rendering a dielectric material electret can involve heterocharges,
homocharges,
or both, depending on the dielectric starting materials and the method of
preparation. A
"homocharge" as used in this disclosure is an electric charge on the
dielectric of the
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same sign as the polarity of an adjacent forming electrode. The forming
electrode
applies an electric field to the dielectric to render the dielectric
"electret". Homocharges
are believed to often develop in compounds containing esters and/or alcohols.
A
"heterocharge" as used in this disclosure is an electric charge on the
dielectric of an
opposite sign as the polarity of the forming electrode. Heterocharges are not
typically
stable. After the application of the electric field by the forming electrode,
the charge of
the heterocharge decreases until a polarity reversal occurs and an apparent
equilibrium is
reached. The resulting electret carries a surface charge (i.e., homocharge)
that has the
same polarity as the corresponding forming electrode.
i. Wax Electrets '
Waxes may be rendered electret. The. wax, in either an electret or non-
electret
state, may be applied to the .cleaning sheet. One method for rendering a wax
electret
follows. According to the one method, suitable wax (shown as a paraffin 400 in
FIGURE 10) in a molten state is poured into a condenser or mold (shown as a
flat brass
dish 402 covered with a wrap shown as a tin foil 404). A heater (shown as a
gas burner
406) may facilitate melting of paraffin 400. Particularly suitable results may
be
obtained if paraffin 400 is melted to a thoroughly fluid state when the
electric field is
applied. According to an alternative embodiment, the electret may be formed
without
melting the wax. In such an embodiment, the wax is generally heated to attain
a
softened state before being exposed to the electric field.
As paraffin 400 is cooled (e.g., to about room temperature) and solidified, an
electric voltage is applied by an electric field source 410. Electric field
source 410 is
shown having a positive forming electrode 412, a negative forming electrode
414 and a
ground 416 electrically connected to condenser 402. Paraffin 400 solidifies
under an
electric stress at a sufficiently high potential to render paraffin 400
electrically
"saturated". Some waxes may be rendered electret by electric fields as low as
about 10
V/cm and in excess of fields as high as about 15 kV/cm. A high potential
direct voltage
of about 500-10000 V may be sufficient to permanently set the charge in the
wax,
another suitable voltage is about 1800 V, which corresponds to an electric
field of about
11 kV/cm. (According to suitable embodiments, an AC or a DC current may
produce
the electric field.) The electric field may depend, in part, on the time
required for the
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wax to solidify. Suitable results may be obtained when the electric field is
removed
after paraffin 400 has thoroughly solidified, but still remains at an elevated
temperature.
According to another suitable embodiment, the charge is applied to paraffin
400 for
about one hour.
Electrodes 412 and 414 may be any conventional electrode such as a tin, brass
or
copper disk having a diameter in the range of about 2-5 cm. Electrodes 412 and
414
may also be wrapped in foil 404 to inhibit soiling by paraffin 400, and foil
404
facilitates removal of paraffin 400 after solidification. After removing the
electric field,
a lower layer of foil 404 may be left on the resulting electret paraffin 400.
An upper
layer of foil 404 may be removed and replaced by a loose foil (not shown),
arranged to
"short" the electret. A cross-sectional view of the resulting electret
paraffin 400 is
shown in FIGURE 11. The wax may be rendered electret by other methods known to
one of skill who reviews this disclosure.
Without intending to be limited to any particular theory, it is believed that
when
the electric field is applied to the paraffin, the molecules or clusters of
the molecules
orient themselves with their axes in the direction of the electric field so
that, when the
paraffin solidifies, the molecules retain their orientation. Such orientation
of the
molecules causes the paraffin to retain a permanent electric polarization (i.
e. , upon
cooling molecular dipoles within the paraffin are "frozen" into an orientation
determined
by the field applied).
The resulting electret wax may have polarized charges present in an amount of
at
least about 5 X 10-11 C/cm2, suitably in the range of about 1 X 10-1°
C/cmz to 2 X 10-9
C/cm2 and possibly as high as about 30 kV/cm to 1.7 nC/cm2. The charge in the
resulting electret wax is not believed to dissipate for a prolonged period.
For example,
U.S. Patent No. 2,284,039 predicts that an electret wax may remain electret
for at least
"a number of years". For additional information on the formation of electret
waxes, see
U.S. Patent No. 2,986,524 discussing the preparation of an electret wax, the
disclosure
of which is hereby incorporated by reference.
ii. Suitable Waxes
A "wax" as used in this disclosure is a substance that is a plastic solid at
ambient
temperature and becomes a low viscosity liquid when subjected to moderately
elevated
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temperatures. Suitable waxes are in the solid state at about room temperature
and
commonly have a melting point in the range of about 40 to 85°C to avoid
melting,
burning or softening of the cleaning sheet during manufacture. Examples of
such
suitable waxes include polyolefin, polyester and fluoropolymer waxes with
melting
points within this range. Other suitable waxes may have a melting point above
about
85° C (e.g., carnauba wax), especially if applied to the cleaning sheet
after the wax has
been rendered "electret". An electret wax may lose its charge (e.g., the
polarization of
the charge may randomize) if the wax melts after being rendered electret.
According to
suitable embodiments, it rnay be advantageous to use wax that has a relatively
low
shrinkage coefficient on cooling. In order to avoid too great a degree of
stiffness in the
cleaning sheet, it is often advantageous to use a wax with a somewhat
relatively lower
melting point, e.g., within the range of about 45 to 70°C. This may
also be
accomplished by choosing a wax that has a relatively low penetration hardness
value (as
measured by ASTM D 1321).
Since waxes are relatively plastic, they tend to deform or flex under pressure
with the application of relatively insubstantial heat. Suitable waxes such as
paraffin are
relatively malleable and may be applied to follow the contours of the cleaning
sheet.
Waxes having a greater hardness, such as carnauba wax, may also be acceptable.
A
wax that is too hard may "shear off" or be removed from the cleaning sheet
during
cleaning. Such removal of the wax from the sheet may disadvantageously
transfer the
wax from the sheet to the surface to be cleaned. The use of higher hardness
wax can
also tend to impart stiffness to the cleaning sheet. The stiffness of the
sheet will of
course be a function of a variety of parameters including the material used to
form the
particle retention layer, the configuration of this layer, the type of wax
employed, the
amount and positioning of the wax on the layer, etc. A suitable wax commonly
has a
penetration hardness of at least about 0.2 mm at 25°C, more typically
about 0.5 to 3
mm at 25° C, as measured by ASTM D 1321, the disclosure of which is
hereby
incorporated by reference.
The color of the wax in the solid state is preferably white or clear, and does
not
easily degrade or discolor. Suitable colorless waxes include paraffin,
hydrogenated
waxes such as tristearin wax and other hydrogenated vegetable oils. Other
suitable
waxes include colored waxes such as beeswax and carnauba wax, which may have a
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yellow-orange color. Natural waxes may be treated with a preservative
according to
suitable embodiments to inhibit degradation or contamination by bacteria
and/or pests.
Suitable waxes should remain "electret" for a relatively prolonged period.
Electret neutralizing variables such as moisture, humidity and ionization of
ambient air
may have a slight effect on such electret waxes. Normal atmospheric changes in
temperature, humidity and altitude probably do not affect the electret wax
significantly.
Such neutralizing variables may be minimized by allowing them to "leak off" or
dissipate within a relatively brief period (e.g. hours) to restore the
effective charge on
the electret. Such neutralizing variables may also be minimized by packaging
with a
desiccating material such as CaCl2, by assumption of thin water layer or foil
layer (e.g.,
short circuit) that shields the surface of the electret until removed, or by
other methods
known to one of skill who reviews this disclosure.
Suitable waxes are capable of carrying a permanent electric moment after
charging by a forming electrode. Suitable categories of waxes include insect
and animal
waxes, such as beeswax secreted by bees. Beeswax has a melting point of
64° C, a
hardness (penetration) of 2.0 mm at 25 ° C and 7.6 mm at 43 .3 °
C. Suitable waxes also
include vegetable waxes, resins and rosins. Vegetable waxes include, without
limitation, candelilla, ouricury, Japan wax, ouricury wax, Douglas-fir bark
wax, rice-
bran wax, johoba, castor wax, bayberry wax and carnauba wax. Carnauba wax is
in a
solid state from room temperature to about 75°C, and in a liquid state
above 83°C.
Suitable waxes also include mineral waxes. Mineral waxes include, without
limitation, montan wax, peat waxes, ozokerite, ceresin waxes and petroleum
waxes.
Petroleum waxes include semicrystaline, microcrystalline and paraffin waxes.
Microcrystalline waxes generally have a melting point within the range of 60-
93 ° C, a
viscosity ranging from 10-25 mm2/s at 98.9°C, and 30-75 carbon atoms
per molecule.
Paraffin waxes consist principally of alkanes, and typically have a melting
range of
about 45-70°C, a viscosity range of 4.2-7.4 mm2/s at 98.9°C, and
20-36 carbon atoms
per molecule.
Suitable waxes also include synthetic waxes and asphaltums. Synthetic waxes
include, without limitation, polyethylene waxes, Fischer-Tropsch waxes,
chemically
modified hydrocarbon waxes, substituted amide waxes, synthetic waxes such as
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synthetic beeswax and synthetic sperm, oxidized polyethylene wax, hydrogenated
johoba
oil, and silicone waxes such as alkyl methyl siloxanes (silicone compounds).
Other suitable waxes include polyethylene waxes. Polyethylene waxes include
low molecular weight (less than approximately 10,000) polyethylenes having wax-
like
properties, and are typically used in conjunction with petroleum waxes.
Polyethylene
waxes include, without limitation, olefin polymers, homopolymers of ethylene,
copolymers of theyleen, propylene, butadiene and acrylic acid with wax-like
properties.
One polythylene wax includes Polywax 500° polyethylene synthetic
hydrocarbon wax
(commercially available from Petrolite Corporation of St. Louis, Missouri)
having a
melting point of 86 ° C, a hardness of 0.7 mm at 25 ° C and 6.1
mm at 60 ° C (according to
ASTM D 1321). According to an alternative embodiment, the "wax" may be a
polymer,
such as a polyurethane, a polyethylene, and/or a fluorocarbons. Such polymers
may be
rendered electret without substantially raising the temperature beyond their
melting
points.
The wax may be relatively 'lure" or used in combination with other waxes and
materials. For example, suitable electrets may be prepared using waxes having
equal
weights of resin and carnauba, 40 % rosin and 60 % carnauba, or 45 %
colophony, 45
carnauba, and 10% beeswax (to recite a few). Other suitable electrets may be
prepared
using one part carnauba wax, one part rosin and one part beeswax. These
proportions
may be varied widely.
According to alternative embodiments, the wax may include minor proportions
of other constituents such as ethyl cellulose (a white granular solid in which
hydroxyl
radicals of cellulose have been replaced by ethoxy group (OEt)), methacrylate
resins
(i. e. , a solid ester of methacrylic acid polymerized by the action of heat,
light or benzyl
peroxide) and/or titanium compounds (e.g., titanium dioxide and barium
titanate). The
inclusion of a titanium compound may reduce the particle size of the
constituents, such
as carnauba wax, during the cooling period, and may decidedly increase the
charges on
the surfaces of the electret.
iii. Fibrous and Other Electrets_
Fibers (e.g., woven and non-woven) and foams may be rendered "electret"
directly (e. g. , without the application of an electret wax) . Fiber
electrets may be
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produced in a sheet or film form (or as a fiber) with one surface positively
charged and
the other surface negatively charged. For additional information on rendering
fibers
electret, see Bernard Gross, "Electret Devices for Pollution Control", State
of the Art
Review, Vol. 6, Optosonic Press 1972 (discussing the properties of electret
materials),
U.S. Patent No. 5,057,710 issued to Nishiura et al. (discussing a method for
preparing
electret materials), U.S. Patent No. 5,429,848 issued to Ando et al.
(disclosing electret
tubular non-woven fabric formed by catching the fibers carried by a fluid in a
DC field),
U.S. Patent No. 5,726,107 (discussing a non-woven electret fiber mixture
including at
least two types of electret fibers made from different materials) and U.S.
Patent No.
4,486,365 (discussing a process and apparatus for the preparation of electret
filaments,
textile fibers and similar articles), the disclosures of each which are hereby
incorporated
by reference. ,
According to suitable embodiments, dielectric materials may also be rendered
electret by ferroelectric effects, wherein a ferroelectric material exhibits
oppositely
polarized charge on its two surfaces because of applied pressure. According to
other
suitable embodiments, dielectric materials may be rendered electret by
applying light
(instead of a charge) at room temperature (e.g., illumination with 6000 lux of
light).
According to still other suitable embodiments, certain photoelectric
insulating or semi-
conducting materials may be rendered electret under the combined influence of
illumination and a strong electric field. According to still other suitable
embodiments,
dielectric materials may be rendered electret by triboelectric effects.
b. Materials of the Particle Retention Laver_.
The fibers used in the core are typically formed from thermoplastic materials.
Thermoplastics materials are believed to retain an electrostatic charge for
long periods,
have relatively good insulating properties, and may be formed in a roll film,
which
permits continuous charging techniques. The fibers may also include semi-
synthetic
fibers (such as acetate fibers), regenerated fibers (such as cupra and rayon),
natural
fibers (such as cotton and blends of cotton), and other fibers or combinations
of natural
or synthetic fibers. The exterior of the fiber may be coated with an electret
wax.
The base layer (i.e., core) may also be made of a porous sponge or foam as
shown in FIGURE 2. Suitable foams include polyurethane foams and latex foams.
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Such foams are typically prepared by using a blowing agent that reacts with a
chemical
to generate a gas (e. g. , carbon dioxide), which is trapped as bubbles during
a
polymerization process, thereby forming the foam. Other suitable foams include
phenolic resin foams. Phenolic resin foams are typically prepared by reacting
phenol
and formaldehyde in the presence of a basic catalyst, such as sodium hydroxide
or
potassium hydroxide, followed by neutralizing the solution and distilling off
water.
Such reaction is believed to produce resol (i.e., an A-stage resin) including
reactive
methol groups. The A-stage resin can by "cured" by reacting it further in the
presence
of an acid catalyst and in the presence of a blowing agent to form a phenolic
resin.
(During curing, some formaldehyde and water are typically liberated.) The
reactive
methol groups of the A-stage resin can react further to enlarge the polymeric
chain
length and/or cross-Iink to form a three-dimensional network.
The base layer (i.e., core) may be made of a fabric material (e.g., a
continuous
sheet) according to an exemplary embodiment as shown in FIGURE 4. The fabric
may
be woven, such as those traditional textile fabrics made by weaving (i.e., the
interlacing
of two or more yarn sets at right angles on a loom), or by knitting (i.e., the
interlooping
of one or more yarns upon itself or themselves). According to a suitable
embodiment as
shown in FIGURE 4, the fabric may be non-woven. Non-woven fabrics may be made
by mechanically (such as by hydroentanglement), chemically or thermally
interlocking
layers or networks of fibers (or filaments or yarns). Interlocking fibers or
filaments
may also make non-woven fabrics concurrent with their extrusion and/or by
perforating
relatively thin films.
The materials of the core may be rendered electret by any variety of known
methods. For example, the core materials can be rendered electret by coating
them with
an electret material such as a wax. The core materials may also be rendered
electret by
spinning fibers in a strong electrostatic field. The core materials may also
be rendered
electret by using triboelectret effects (i.e., inducing a charge by rubbing
the fibers with
other media). According to a suitable embodiment, at least 20% of the core
materials
are electret (by weight % ), and in some instances as much as 50-100 % of the
core
materials may be electret. The core materials have a charge suitably in the
range of
about 1.0 x 10'11 to 1.0 x 10'3 coulombs/cm2, more suitably 1.0 x 10-5 to 1.0
x 10'3
coulombs/cm2. The core material may have the capacity to retain debris having
a size of
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at least about 20 g/m2. The electric charge of the core or other material of
the cleaning
sheet may affect the density of the particle intended to be collected, in
part. The core
may include non-electret natural or synthetic fibers to increase the breaking
strength and
elongation of the core. Such non-electret fibers may include, without
limitation, wool,
cotton, cellulose, polypropylene, polyethylene, polyester, polytetraflourine
(PTE),
nylon, rayon, acrylic, etc. and combinations thereof.
APPLICATION OF ELECTRET WAX TO THE CLEANING SHEET
An electret wax may be applied to the cleaning sheet, or any element of the
cleaning sheet such as the core, cover, backing layer, etc. The wax is
particularly
suited for application on a fabric structure such as non-woven particle
retention layer
330 as shown in FIGURE 5. The wax may be applied to the cleaning sheet, such
as a
non-woven cellulose paper towel, hydroentangled polyester, or PLEDGES GRAB-
ITTM
sweeper cleaning cloth (commercially available from S.C. Johnson & Son,
Incorporated
of Racine, Wisconsin) before and/or after the wax has been rendered
"electret". The
wax may also be applied to a foam particle retention layer of the type shown
in
FIGURES 2-4, or a cover sheet (e.g., cover sheet 20 shown in FIGURE 2).
According
to another embodiment, the electret wax may be applied to a backing layer of a
cleaning
sheet (e.g., backing layer 20 as shown in FIGURE 4). According to other
alternative
embodiments, the wax may be applied to a central particle retention layer
(e.g., of the
type shown in FIGURES 2-5) to attract and collect debris through apertures of
a cover
layer.
Referring to FIGURE 12, a cleaning sheet 420 is shown having a woven (or
alternatively non-woven) micro-fiber layer 422 attached to an electret layer
424.
Electret layer 424 may be a woven or non-woven fabric material coated with an
electret
wax (or alternatively with fibers rendered electret by another method). Both
electret
layer 424 and micro-fiber layer 422 are particularly suited to cleaning dry
surfaces.
Microfiber layer 422 suitably is about 1-2 mm thick and is composed of fibers
having
denier in the range of about 0.1 to about 5. It may be advantageous to employ
a
microfiber layer formed from a mixture of relatively thicker microfibers
having a denier
of 1 to 3 and finer fibers having a denier of no more than about 0.9 and
generally at
least about 0.2 (preferably about 0.5 to 0.9).
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The wax may be applied to the cleaning sheet according to a variety of methods
and in a variety of configurations and patterns. Melted wax 434 may be
"dripped" or
applied as discontinuous spots or "islands" to a particle retention layer 432
of a cleaning
sheet 430 as shown in FIGURE 13. Melted wax 434 may also be applied in a fluid
spray (such as by an air spray gun) to particle retention layer 432 as a
discontinuous
pattern of droplets (as shown in FIGURE 13) or as a uniform spray, sheet or
layer.
According to a suitable embodiment, the wax may be combined with a solvent to
decrease the viscosity of the wax, and sprayed on the particle retention
layer. The
solvent layer may then be "flashed off" or evaporated, leaving the melted or
solidified
wax on the particle retention layer. Suitable solvents for paraffin wax
include toluene,
benzene, other hydrocarbon solvents, chloroform, ether and mixtures thereof.
According to an alternative embodiment, melted wax 434 may be applied in a
"bead" or row of corrugations 436 as shown in FIGURE 14. The wax may cover the
exterior of the fiber on material on which it is applied, and may further
impregnate or
saturate or "soak" into the material 432 in whole or in part. The wax may
collect
between the intersections of the fibers, and/or may bond the fibers together.
According
to another alternative embodiment, melted wax 434 may be deposited in
depressions 134
of particle retention layer 130 as shown in FIGURE 15. According to other
alternative
embodiments, the melted wax may be deposited in a single, continuous layer on
any side
or surface of the particle retention layer. According to a suitable
embodiment, about
0.1 - 10 wt. % of the wax (relative to the dry weight of the particle
retention material to
which the wax is applied) may be applied to the particle retention layer, more
suitably
0.5 - 5 wt % , most suitably about 0.7 - 2 wt. % . The weight of the wax is
related in
part to the area over which the wax may cover. According to a suitable
embodiment,
the wax covers at least about 10 % (relative to the surface area of the
particle retention
layer), more suitably at least about 30 to 50 % . It may be advantageous to
leave a
substantial percentage (e.g. 50% or more) of the particle retention layer
untreated with
the wax. The amount of wax applied preferably should render the material to
which the
wax is applied (e.g., particle retention layer) to have a particle retention
capacity of at
least about 20 g/m2.
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OUTER OR COVER LAYER
The present cleaning sheets may include a cover, which surrounds to covers a
portion or the entire particle retention layer. Referring to FIGURE 2, core 30
is shown
covered or surrounded by cover layer 20, such that core 30 is not
substantially in
contact with a work surface or surface to be cleaned 66. Cover layer 20 is
substantially
continuous and generally planar. According to an exemplary embodiment as shown
in
FIGURE 4, core 30 may be located between a top cover layer 322 and a bottom or
backing layer 320 in a "sandwich" or packed fashion. Cover layer 322 is a
generally
smooth and compliant (e.g., flexible) generally planar sheet for cleaning
delicate
surfaces (e.g., wood, glass, plastic, etc.) or hard surfaces. According to
other suitable
embodiments, a space or other intermediate layers may be positioned between
the core
and the cover layer or layers.
The backing layer may be more rigid and/or have a greater basis weight than
the
core or the cover layer to provide support and structure to the cleaning
sheet.
According to other suitable embodiments, a space or other intermediate layers)
may be
positioned between the backing layer and the outer fabric layer. A variety of
materials
are suitable for use as a backing layer, as this layer has the desired degree
of flexibility
and is capable of providing sufficient support to the sheet as a whole.
Examples of
suitable materials for use as a backing layer include a wide variety of
lightweight (e.g.,
having a basis weight of about 10 to 75 g/m2), flexible materials capable of
providing
the sheet with sufficient strength to resist tearing or stretching during use.
The backing
layer is typically relatively thin (e.g., has a thickness of about 0.05 mm to
about
0.5 mm) and can be relatively non-porous. Examples of suitable materials
include
spunbond and thermal bond non-wovens sheets formed from synthetic and/or
natural
polymers. Other backing materials that can be utilized to produce the cleaning
sheet
include relatively non-porous, flexible layers formed from polyester,
polyamide,
polyolefin or mixtures thereof. The backing layer could also be made of
hydroentangled
non-woven fibers, if it meets the performance criteria necessary for the
particular
application. One specific example of a suitable backing layer is a spunbond
polypropylene sheet with a basis weight of about 20 to 50 g/m2.
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As shown in FIGURE 5, apertures (shown as holes 22) may be integrally formed
in cover layer 322, which may be a continuous sheet of material. The holes may
be
circular shaped (as shown in FIGURE 7), but may be other shapes (e.g.,
rectangular,
star, oval, irregular, etc.) or combinations of shapes according to
alternative
embodiments. Hole 122, another embodiment of hole 22, is shown having an
irregular
shape in FIGURE 8. According to a suitable embodiment, creating perforations
in the
cover layer may form the holes. Holes 22 are generally of a sufficient size to
allow
significantly sized debris (e.g., up to 0.5-100.0 mm) to pass through to the
particle
retention layer. After passing through the holes, the debris flows in the
pores (i.e.,
cavities) of the particle retention layer. Each of holes 22 has a major
diameter D1
greater than any other diameter of the hole, and a secondary diameter D2,
which is the
greatest cross-sectional axis perpendicular to major diameter D1 (see, e.g.,
FIGURE 8).
According to a suitable embodiment, the average major diameter of all of the
holes may
be in the range of about 1 to 10 mm, more suitably in the range of about 2 to
5 mm.
Each of holes 22 may have a cross-sectional dimension. The average cross-
sectional dimension is equal to one-half of the sum of D1 of the hole plus DZ
(i.e.,
average cross-sectional dimension = (D1 + DZ)/2). The average cross-sectional
dimension of each of the holes is typically at least about 1 mm2, more
typically in the
range of about 1 to 100 mm2, most suitably in the range of about 5 to about 25
mmz.
According to a suitable embodiment, the cross-sectional dimension of all the
holes
relative to the total surface area of the exterior surface of the cover layer
is typically
about 30 % to 95 % and more suitably 70 % to 90 % . The number of holes and
the
average cross-sectional dimension of the holes is selected to allow maximum
amount of
debris through the holes, while separating the core from the surface to be
cleaned and
maintaining the debris in the core.
The cover layer may be made of a material that has a low debris retention
(i.e.,
that does not significantly attract or collect the debris) and generally has a
lower debris
retention than the core. According to a suitable embodiment, the cover layer
may be
made of a thermoplastic material. Thermoplastic materials or fibers may
include,
without limitation polyesters, polyamides and polyolefins, polypropylene,
polyethylene,
polystyrene, polycarbonate, nylon, rayon, acrylic, etc. and combinations
thereof. The
thermoplastic materials may be produced by a melt blown process. Other
materials that
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do not significantly attract debris include fibrous woven and non-woven
fabrics having
tightly packed fibers with a relatively high degree of entanglement
coefficient. Still
other such materials include non-fibrous materials such as a perforated
polymer fibers or
sheets. According to a suitable embodiment, the cover layer can be a spunbond
or
thermal bond polypropylene. According to other suitable embodiments, the cover
layer
may be made of natural materials (such as rubber, latex, and the like), as
well as
synthetic materials such as polyolefins (such as, polypropylene and
polybutene),
polyesters (such as polyethylene, polyurethane terephthalate and polybutylene
terephthalate), polyamides (such as nylon 6 and nylon 66), acrylonitriles,
vinyl polymers
and vinylidene polymers (such as polyvinyl chloride and polyvinylidene
chloride), and
modified polymers, alloys or mixtures thereof, and other materials that have a
relatively
high dust retention capacity.
COUPLING OF THE COVER LAYER AND THE PARTICLE RETENTION LAYER
The cover layer may be attached to the core by a fastener such as melt bonding
(shown
IS as a stitch I26 in FIGURE 3). The fastener is intended to function as a way
to bond
(physically and/or chemically) or otherwise secure the cover layer to the
core.
According to a suitable embodiment, an adhesive may attach the cover layer to
the core,
The adhesive should be of a type that is relatively soft and non-abrasive
relative to the
surface to be cleaned. The adhesive should also permit the debris to pass
through the
apertures of the cover layer and should not substantiality retain the debris.
The adhesive
may be applied as a solid Layer, a continuous pattern (e.g., a circle or
serpentine
pattern), a discontinuous pattern (e.g., a series of lines of a matrix of
dots), or any other
desired pattern such as checkerboard, cross, crisscross, etc. The adhesive
material may
be applied to the cover Layer, the core, or to any other suitable intermediary
surface (if
any) or backing layer. According to other suitable embodiments, the cover
layer, in
whole or in part, and the core may be welded together (e.g., ultrasonic,
infrared, melt
bonding of thermoplastic in localized locations, spot welding, etc.).
According to still
other suitable embodiments, the cover layer may be attached to the core by
entanglement
(e.g., hydroentanglement) or by other fasteners (e.g., construction adhesives,
clips,
embossing, etc.).
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DIMENSIONS OF THE CLEANING SHEET
The physical dimensions of the cover layer and the core are generally not
thought to be critical. The outer perimeter of cover layer 20 is typically
larger than the
outer perimeter of core 30, as shown in the FIGURES, so that debris 68 may
pass
through holes 22 of cover layer 20 before being retained in core 30. Cover
layer 20, . as
shown in FIGURE 2, has a thickness Ti that is typically less than a thickness
T2 of core
30. By way of a non-limiting example, the cover layer can have an average
thickness of
up to about 1 mm, preferably 0.05 to 0.5 mm. The core can have an average
thickness
up to about 5 mm, preferably 1 to 2 mm. According to a suitable embodiment as
shown
in FIGURE 1, cover layer 20 has a shape and configuration similar to that of
core 30.
The cleaning sheet may have a length of about 8 inches and a width of about 12
inches.
CLEANING IMPLEMENTS AND METHODS OF USE
Pad 10 may be used alone (e.g., as a rag) or in combination with other
implements and utensils to clean surface 66. Pad 10 is generally flexible for
following
any contour (e.g., smooth, jagged, irregular, creviced, etc.) of a surface 66
to be
cleaned. Accordingly, pad 10 is particularly suitable for cleaning hard, rigid
surfaces.
According to another embodiment, pad 10 may be semi-rigid and particularly
suitable
for cleaning planar surfaces. Pad 10 may also be used to clean relatively soft
surfaces
such as carpets, rugs, upholstery and other soft articles.
Referring to FIGURE 1 pad 10 is shown attached to a cleaning head 62 of a
cleaning utensil (shown as a dust mop 60) according to an exemplary
embodiment.
Head 62 includes a carriage 80 providing a fastener (shown as a spring clip
82) for
mounting pad 10. A mounting structure 84 attaches an elongate rigid member
(shown
as a segmented handle 64) is attached to carriage 80. Mounting structure 84
includes a
yoke (shown as an arm 86) having a y-shaped end 88 pivotally mounted to a
socket
(shown as a ball joint 90). An adapter (shown as a connector 92) threadably
attaches
arm 86 to handle 64. According to suitable embodiments, the cleaning utensil
may be a
broom, brush, polisher, handle or the like adapted to secure the cleaning
sheet. The
cleaning sheet may be attached to the cleaning utensil by any of a variety of
fasteners
(e.g., friction clips, screws, adhesives, retaining fingers, etc.). According
to other
suitable embodiments, the cleaning sheet may be attached as a single unit, or
as a
plurality of sheets (e.g., strips or "hairs" of a mop).
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The components of the cleaning utensil, namely the mounting structure,
adapter,
handle, and wax that has been rendered electret may be provided individually
or in
combinations (e.g., as a kit or package). The components of the cleaning
utensil may be
readily, easily and quickly assembled and disassembled in the field (e.g.,
work site,
S home, office, etc.) or at the point of sale for compactablity and quick
replacement. The
cleaning utensil may also be provided in a pre-assembled and/or unitary
condition.
According to a suitable embodiment, the cleaning sheet is configured for use
with the
PLEDGES GRAB-ITT"~ sweeper (commercially available from S.C. Johnson & Son,
Incorporated of Ravine, Wisconsin).
To clean surface 66, pad 10 may be secured to head 62 of mop 60 by clip 82.
Pad 10 is brought into contact with surface 66 and moved along surface 66
{e.g., in a
horizontal direction, vertical direction, rotating motion, linear motion,
etc.). Debris 68
from surface 66 is provided or attracted through holes 22 in cover layer 20.
An
electrostatic charge of an electret material in core 30 may pull or draw
debris 68 through
holes 22 of cover layer 20 and into core 30 (see FIGURE 2). Pores (shown as
cavities
34) of core 30 retain and/or entrain debris 68 within cavities 32 of pad 10.
The exterior
surface of cover layer 20 does not substantially attract or retain debris 68,
so the
exterior surface of cover layer 20 of pad 10 remains substantially free of
debris 68.
After use, pad 10 may be removed from mop 60 for disposal or cleaning (e.g.,
washing,
shaking, removing debris, etc.). According to other suitable embodiments, the
cleaning
sheet may be used alone (e.g., hand held) to clean the surface. According to
an
alternative embodiment as shown in FIGURE 1, an electret wax may be applied to
pad
10 at room temperature.
INDUSTRIAL APPLICABILITY
The cleaning sheet of the present invention can be manufactured using
commercially available techniques, equipment and material. In addition, the
cloth may
be used on a variety of surfaces such as plastic, wood, carpet, fabric, glass
and the like.
Cleaning implements and methods of cleaning surfaces using the cleaning sheet
are also
provided herein. The cleaning implement may be produced as an intact implement
or in
the form of a cleaning utensil kit. Intact implements include gloves, dusters
and rollers.
Kits according to the present invention, which are designed to be used for
cleaning
surfaces, commonly include a cleaning head and a cleaning sheet capable of
being
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coupled to the cleaning head. In addition, the kit can include a yoke capable
of
installation on the cleaning head and an elongate handle for attachment to the
yoke.
Whether provided as a completely assembled cleaning implement or as a kit, the
cleaning implement may include a cleaning head that allows the cleaning sheet
to be
removably attached to the cleaning head.
TEST METHODS
c. Breaking strength (cross machine direction)
From each of the cleaning sheets, samples having a width of 30 mm may be cut
out in the direction perpendicular to the fiber orientation in the sheet
(i.e., in the cross
machine direction). The sample may be chucked with a chuck-to-chuck distance
of 100
mm in a tensile testing machine and elongated at a rate of 300 mm/min in the
direction
perpendicular to the fiber orientation. The value of load at which the sheet
began to
break (the first peak value of the continuous curve obtained by the
stress/strain
measurement) may be taken as the breaking strength.
d. Elongation at a load of 500 g/30 mm
The elongation of a sample, at a load of 500 g in the measurement of the
breaking strength in the cross machine direction described above, may be
measured.
For the purposes of this test, "elongation" is defined as the relative
increase in length (in
of a 30 mm strip of cleaning sheet material when a tensile load of 500 g is
applied to
the strip.
c. Entanglement Coefficient
The scrim may be removed from the non-woven fiber aggregate. Where the
scrim has a lattice-like net structure, this is typically accomplished by
cutting the fibers
which make up the network sheet at their junctures and carefully removing the
fragments of the network sheet from the non-woven fiber aggregate with a
tweezers. A
sample having a width of 15 mm may be cut out in the direction perpendicular
to the
fiber orientation in the sheet (i.e., in the cross machine direction). The
sample may be
chucked with a chuck-to-chuck distance of 50 mm in a tensile testing machine,
and
elongated at a rate of 30 mm/min in the direction perpendicular to the fiber
orientation
(in the cross machine direction). The tensile load value F (in grams) with
respect to the
elongation of the sample may be measured. The value, which is obtained by
dividing
the tensile load value F by the sample width (in meters) and the basis weight
of the non-
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woven fiber aggregate W (in g/m2), is taken as the stress, S (in meters). A
stress-strain
curve is obtained by plotting stress ("S'~ against the elongation ("strain" in
%) (i.e.,
stress S [m]=(F/0.015)/W).
For a non-woven fiber aggregate, which is held together only through the
entanglement of the fibers, a straight-line relationship is generally obtained
at the initial
stage of the stress-strain (elongation) curve. The gradient of the straight
line is
calculated as the entanglement coefficient E (in meters). For example, in the
illustrative
stress-strain curve shown in FIGURE 9 (where the vertical axis represents the
stress, the
horizontal axis represents the strain, and O represents the origin), the limit
of straight-
line relationship is represented by P, the stress at P is represented by Sp,
and the strain
at P is represented by yP. In such cases, the entanglement coefficient is
calculated as
E=SP/yp. For example, when Sp=60 m and yp=86%, E is calculated as E=60/0.86=70
m. It should be noted that the line OP is not always strictly straight. In
such cases, a
straight line approximates the line OP.
Although only a few exemplary embodiments have been described, the present
invention is not limited to one particular embodiment. Indeed, to practice the
invention
in a given context, those skilled in the art may conceive of variants to the
embodiments
described herein (e.g., variations in sizes, structures, shapes and
proportions of the
various elements, values of parameters, mounting arrangements, or use of
materials)
without materially departing from the true spirit and scope of the invention.
Various
modifications may be made to the details of the disclosure without departing
from the
spirit of the invention.
