Field of the Invention
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The present invention relates generally to fibrous web material
intended for use in infusion packages for brewed beverages, such as
tea, coffee and the like. It is more particularly concerned with a new
and improved fibrous non-heat seal nonwoven web material having an
improved dry crimped seam strength.
Background of the Invention
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Infusion packages for brewing beverages, such as tea bags and
coffee bags, are generally produced by enclosing beverage precursor
materials within a porous web material. The infusion package is either
placed in a cup or pot containing boiling water, or alternatively, the
infusion package is placed in an empty cup or pot and subsequently
boiling water is added. In either event, the boiling water passes
through the web material into the bag to extract the beverage precursor
materials and the extract passes outwardly of the bag to form the
brew.
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Infusion packages are generally made of fibrous nonwoven web
materials that are free from perforations or punctures yet possess a
high degree of porosity. Particularly favored for infusion packages are
those wet laid fibrous materials made on inclined wire paper making
machines using long natural fibers. These web materials are generally
soft, tissue-thin fibrous materials characterized by their light weight and
superior infusion characteristics.
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While it is desirable for the infusion package to allow extraction
of the beverage precursor materials, physical release of the solid
materials from the sealed infusion package into the cup is undesirable.
To prevent movement of solid beverage precursor materials from the
sealed infusion package into the brewing container the porosity and
"sifting" characteristics of the nonwoven web material are carefully
controlled. More importantly, the seam maintaining the beverage
precursor materials within the infusion package must maintain integrity
to prevent opening of the infusion package and the subsequent
undesirable discharge of beverage precursor materials into the brew.
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Infusion package seams may be of either the "heat seal" or "non-heat
seal" variety. Heat seal infusion packages are typically produced
from a nonwoven web material comprising two layers or phases. One
of the two phases typically includes more than twenty-five percent by
dry weight of fusible polymeric fibers. The web material is folded so
that the surfaces containing the fusible fibers are in contact.
Application of heat and pressure melts, flows and fuses the touching
fusible fibers and creates a heat seal seam joining the layers of web
material. The surface of the second layer is free of fusible fibers and
functions to prevent sticking of the melted polymeric fibers to the
heated dies used to create the heat seal seam.
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Contrastingly, in non-heat seal infusion packages, the edges of
the web material are brought together, folded a number of times, and
this multiple fold is crimped to provide a mechanical crimped seam
which seals the infusion package. Typically, the nonwoven web
material used for non-heat seal infusion packages includes a single layer
comprised of vegetable fibers and does not incorporate fusible
polymeric fibers.
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There is, in some instances, a problem with non-heat seal
infusion packages in that the seams may become opened due to a
weakening of the web material at the crimped fold or to opening of the
fold in the boiling water environment due to pressure may be exerted
on the fold by the expansion of gases trapped within the infusion
package. As previously discussed, even partial opening of the seams
leads to an undesirable physical discharge of the beverage precursor
materials such as tea leaves into the brewing container.
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Naturally, the fibers used for the production of infusion packages
must be approved by the Food and Drug Administration (FDA) for use
as packaging for food products.
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It is known to use synthetic fibers as a binder to impart strength
to non-heat seal web materials. The known synthetic binders require
application of heat and pressure sufficient to melt and flow
substantially all of the binder fibers, so that they can flow and fuse
with the other web materials and, upon cooling, bind the web together.
Such processing of synthetic binder materials tends to lessen the
porosity of the resulting web material. These synthetic binder web
materials are used in applications such as battery cell separators, but
have not traditionally been approved for use in food packaging. To the
inventors' knowledge, a fibrous, non-heat seal nonwoven web material
incorporating synthetic binder fibers has not been used to create an
infusion package.
Summary of the Invention
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It is an object of the present invention to provide a new and
improved non-heat seal, nonwoven fibrous web material with improved
mechanical fold or crimp strength.
-
It is another object of the invention to provide nonwoven fibrous
web material which can be processed on existing infusion package
sealing equipment to provide a higher strength mechanical seam than
conventional web materials.
-
It is a further object of the invention to provide a nonwoven
fibrous web material which retains the desirable porosity and infusion
characteristics of conventional non-heat seal infuser web materials
while providing greater mechanical fold strength.
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Other features and advantages of the present invention will be
in part obvious and in part pointed out in more detail hereinafter.
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In accordance with the present invention, it has been found that
mechanical seam integrity can be enhanced by incorporating controlled
amounts of solid synthetic materials into conventional non-heat seal
type web materials. Solid synthetic materials as used in this application
refers to both synthetic fibers and synthetic pulp. The resulting non-heat
seal nonwoven web materials exhibit improved stiffness and
memory characteristics which lead to significantly increased crimp
strength when compared to conventional non-heat seal web materials.
The increased crimp strength translates to an increased strength for the
finished infusion package crimped seal.
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In one disclosed embodiment, the fibrous non-heat seal web
material comprises a single-phase porous sheet material containing
throughout its extent 0.5 to 25 percent by weight of synthetic
materials and preferably 3 to 10 percent. Typically, 6 percent by
weight of the synthetic material is used. In another embodiment, the
synthetic materials are incorporated into at least one phase of a fibrous
multi-phase non-heat seal web material. The synthetic materials
incorporated will account for 0.5 to 25 percent by weight of the
resulting web material. Preferably, the multi-phase fibrous web material
will incorporate 1 to 10 percent, and typically 6 percent, synthetic
materials. The inventive materials do not require substantial activation
of the synthetic material. Further, even at the higher amounts of
synthetic materials, the inventive non woven web materials are not
capable of forming an effective heat seal seam.
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A better understanding Qf the invention will be obtained from the
following detailed disclosure of the article and the desired features,
properties, characteristics, and the relation of the elements as well as
the process steps, one with respect to each of the others, as set forth
and exemplified in the description and illustrative embodiments.
Description of a Preferred Embodiment
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Broadly, the present invention comprises fibrous, non-woven,
porous web materials, including natural fibers and synthetic materials.
The resulting web materials are especially suited for the production of
infusion packages. The inventive web materials are of the non-heat
seal variety, i.e. they can not form an effective seam upon application
of heat and pressure and, thus, require mechanical fastening, i.e.,
folding and crimping for the formation of the infusion package. The
inventive web materials exhibit surprisingly increased mechanical seam
strength compared to conventional non-heat seal web materials which
do not utilize synthetic fibers or pulps.
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The predominant fibers utilized in the inventive web materials
may be any of the well known natural paper making fibers or mixtures
thereof. They must be approved by the Food and Drug Administration
(FDA) for use in food and beverage applications and preferably include
long natural fibers such as jute, abaca, sisal, hemp, kenaf and mixtures
of the above. These long natural fibers are substantially uniform in
length, varying from 4 to 7 millimeters (mm) and are substantially free
of minute fibers. The long fibers are relatively cylindrical, are slightly
tapered and have little tendency to curl or twist when dispersed in
solution. Shorter wood fibers, such as bleached or unbleached kraft,
may also be used, either alone or in combination with other fiber types.
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A variety of webs may be made from these fibers and utilized in
accordance with the present invention. It will be appreciated that such
materials, while being extremely porous and highly wettable, are
generally free from perforations and will not permit the fine particles of
the beverage precursor material to filter or sift through the infusion
packages made therefrom.
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According to one aspect of the present invention, a slurry of the
previously described natural fibers is prepared. Details of the
previously described natural fibers and their preparation into a slurry are
well known to those of ordinary skill in the art. To this slurry an
amount of synthetic material is dispersed.
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The synthetic materials may be polyesters, thermoplastic
materials such as polyolefins or mixtures thereof. The synthetic
materials may include those with fiber morphologies of synthetic
shortcut fibers, synthetic pulps or mixtures thereof. The synthetic
fibers exhibit conventional smooth cylindrical or rod-like morphology
with low specific surface area. Synthetic fibers have typical lengths of
1 - 25 mm, typical denier of 0.5 - 15 and typically low surface areas.
Synthetic fibers are usually formed by a process such as melt spinning.
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The synthetic pulps are synthetic thermoplastic materials, such
as polyolefins, having a structure more closely resembling wood pulp
than synthetic fibers. That is, they contain a micro-fibrillar structure
comprised of micro-fibrils exhibiting a high surface area as contrasted
with the smooth, rod-like morphology of conventional synthetic fibers.
The synthetic thermoplastic pulp-like material can be dispersed to
achieve excellent random distribution throughout the aqueous
dispersing media in a paper-making operation and, consequently, can
achieve excellent random distribution within the resultant sheet
product. The pulps found particularly advantageous in the manufacture
of infusion sheet materials are those made of the high density
polyolefins of high molecular weight and low melt index.
-
The fibrils can be formed under high shear conditions in an
apparatus such as a disc refiner or can be formed directly from their
monomeric materials. Patents of interest with respect to the formation
of fibrils are the following: U.S. Patent Nos. 3,997,648, 4,007,247
and 4,010,229. As a result of these processes, the resultant
dispersions are comprised of particles having a typical size and shape
comparable to the size and shape of natural cellulosic fibers and are
commonly referred to as "synthetic pulp". The particles exhibit an
irregular surface configuration, have a surface area in excess of one
square meter per gram, and may have surface areas of even 100
square meters per gram. The particles exhibit a morphology or
structure that comprises fibrils which in turn are made up of micro-fibrils,
all mechanically inter-entangled in random bundles generally
having a width in the range of 1 to 20 microns (µ). In general, the
pulp-like fibers of polyolefins such as polyethylene, polypropylene, and
mixtures thereof have a fiber length well suited to the paper-making
technique, e.g., in the range of 0.4 to 2.5 mm with an overall average
length of about 1 to 1.5 mm.
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The resulting "furnish", comprising the slurry of natural fibers to
which the synthetic fibrous material (either fibers, pulp or mixtures
thereof) has been added and dispersed, is wet laid on an inclined wire
paper making machine in a fashion also well known to those of ordinary
skill in the art. The resulting web material will have a synthetic material
content of 0.5 to 25 percent, more preferably 1 to 10 percent, and
typically 6 percent, by weight. While the inventive web materials have
a surprisingly increased crimp strength at low synthetic fiber
concentrations, this increased strength is diluted below 1 percent. It
should be understood that this amount of synthetic fibrous material
used in a non-woven web material is not sufficient to enable the web
material to create an adequate heat seal seam. Thus, the inventive
non-woven material cannot be used as a substitute for heat-seal type
web materials.
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As previously mentioned, the invention is also applicable to multi-phase
non-woven web materials. In this connection, numerous
different techniques have been employed to make multi-phase fibrous
webs. Typical of those techniques found useful in the production of
multi-phase web materials is the dual head box technique described in
U.S. Patent No. 2,414,833. In accordance with that process, a first
furnish flows through a primary head box and continuously deposits as
a bottom layer or base phase on an inclined, web forming wire screen.
A second furnish or slurry for the top layer or second phase is
introduced into the primary head box at a location immediately after or
at the point of deposition of the base phase on the inclined wire screen.
This may be carried out by means of an inclined trough or by a
secondary head box in such a manner that the top phase fibers
commingle slightly with the base fibers flowing through the primary
head box. In this way, the base fibers have a chance to provide a base
mat or phase, prior to the deposition of the second or top phase. As
can be appreciated, the top phase is secured to the base phase by an
interface formed by the intermingling of the particles within the
aqueous suspension. Typically, webs produced in this manner have the
first phase covering the entire area of the web surface in contact with
the inclined wire screen while the opposing side of the web has a
mixture of fibers with the top phase fibers greatly predominating. In
this way there is not a clear line of demarcation between the two
phases of the multi-phase sheet materials; yet there is a predominance
of top phase fibrous material on the top surface or top phase of the
multi-phase sheet. The center or interface boundary, of course, is
composed of a mixture of the two different types of fibers. It should
be appreciated that the invention also covers webs comprising three or
more layers.
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Although the technique or process described in the
aforementioned U.S. Patent No. 2,414,883 is preferably followed, the
materials used in preparing the furnishes for each phase of the web
material will be different. The predominant fibers utilized for the top
and bottom phases comprise the previously mentioned natural fibers.
It should be understood that the top phase will generally account for 25
to 35 percent of the total basis weight of the resulting web material.
To one or both of the top or bottom phase slurries, the previously
discussed synthetic material is added. Preferably, the above synthetic
material is added to the top phase. The resulting fibrous web material
(both phases) will have a synthetic material content of 0.5 to 25
percent, more preferably 1 to 10 percent, and typically 6 percent.
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The inventive wet laid web materials in either single or multi
phase form are subjected to a drying step to reduce water present in
the web. The drying step may comprise vacuum drying, passage
around heated drying cylinders or through heated pass through dryers
or combinations of the above.
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It should be noted that heat sealable type web materials typically
undergo an additional heated fusing step subsequent to the drying step
to fully "activate" the synthetic fibers. As used herein, activation refers
to the imposition of energy to a substance so that the substance will
undergo subsequent chemical or physical change more rapidly or
completely. Before activation, synthetic materials retain their pre-activation
polymer crystallinity and physical morphology. As synthetic
materials are subjected to heat and become activated they undergo
changes in crystallinity accompanied by reticulation (physical
contraction and wrinkling). Continued application of heat will bring the
synthetic materials toward their melting point, accompanied by further
changes in crystallinity and physical changes such as softening. As the
synthetic materials reach their melting point, there is limited fusion of
the synthetic materials at the point of contact with touching fibers,
either cellulosic or synthetic. Continued application of heat to the stage
of overactivation or overfusing will cause the synthetic materials to
break up into discrete portions. Thus, activation spans a continuum
between no activation and overfusing. Substantial activation of heat
seal type non-woven web materials is required for subsequent creation
of an adequate heat seal bond in that material.
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The inventive web materials receive only the drying step and do
not require the subsequent heated activation step. Thus the inventive
web materials are preferably only lightly activated. Less preferably, the
inventive web materials may be more highly activated, or even
overfused. While substantial activation of the inventive materials is not
preferred, they will continue to show increased dry crimped seam
strength when more highly activated or even when overfused. It
should be noted that the inventive non-woven web materials even
when substantially activated or overfused will not form an adequate
heat seal bond and thus are not replacements for heat seal type non-woven
web materials.
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It is believed one predominant mechanism of non-woven web
material strength is hydrogen bonding of the cellulosic fibers.
Replacement of a quantity of cellulosic fibers with an equivalent
quantity of synthetic materials lessens the hydrogen bonding within the
web material, resulting in decreased tensile strength. Activation of
synthetic materials close to, and beyond, their melting point creates a
weak bond between the synthetic material and touching fibers at their
contact points. However, this bond is of lower strength than the
hydrogen bonding of replaced-cellulosic materials and the resulting web
material will again exhibit lesser or equal strengths when compared to
fully cellulosic web materials.
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The inventive web materials are also distinguishable from non-woven
web materials using synthetic materials as binders. During
processing, synthetic binders undergo substantial heating and flow
leading to increased bonding within the web material. The substantial
flow of synthetic materials leads to the typically increased tensile
strengths (greater than 20 %) found with such materials and binder
systems. In the present materials the synthetic materials exhibit little
flow and lesser or equal strength as compared to a fully cellulosic web
material.
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The inventive web materials may incorporate additional
conventional materials and processing. As an example, the materials
and processes of United States Patent No. 5,431,997 to Scott et al,
which is hereby incorporated by reference, may be used with the
inventive web materials.
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In any embodiment, it is preferred that the inventive web material
has a thickness in the range of 30 to 100 µ, more typically in the
region of 40 to 60 µ. The web material of the invention preferably has
a basis weight of 9 to 19 grams per meter squared (g/m 2) and more
preferably 11 to 16 g/m2. Typically the basis weight will be about 12-13
g/m2. The synthetic materials will account for 0.5 to 25 percent
and more preferably 1 to 10 percent of the resulting dry web weight.
Typically the synthetic materials will be present at 6 percent of the
resulting web weight.
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One of the measured characteristics which determines the
acceptability of a mechanical seam is crimped seam strength, which is
a measurement of the amount of force necessary to pull open a
crimped mechanical seam. It is desirable that the dry, crimped seam
strength be as high as possible to ensure mechanical seam integrity.
While not wishing to be held to any theory, it is believed the synthetic
materials impart stiffness and "memory" to the inventive web material
which leads to the increased crimped seam strength.
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In one test method for dry, crimped seam strength, web material
having a preformed and crimped seam is excised to obtain a one inch
wide test sample. The excision is such that the crimped seam will
horizontally traverse the one inch width of the test sample and be
perpendicular to the excised sides. The test sample is mounted in a
tensile test instrument, with a top or bottom edge of the sample
fastened to a fixed anchor and the opposing edge fastened to a
crosshead. The crimped seam is parallel to the fastened top and
bottom edges. The crosshead is linearly displaceable in a direction
perpendicular to the mechanical seam to be tested. The crosshead is
arranged to move away from the anchor at a predetermined speed,
placing the test sample and crimped seam under an increasing tensile
force. The tensile test instrument will read and record the highest
tensile force imposed on the sample, which is indicative of the force at
which the mechanically folded and crimped seam failed. The obtained
crimped seam strength will be dependant not only on the material but
also on the machinery used to form and crimp a seam in the material.
For the test equipment used in the following examples, crimped seam
strengths of less than 40 grams/inch (g/in) are unacceptable for an
infusion package seam and crimp strengths of 40 to 50 g/in are typical.
On different equipment, crimp strengths of 60 to 150 g/in may be seen.
There is no significant difference between the crimp strength obtained
for a conventional single phase web material and a conventional multi-phase
material of the same composition and basis weight.
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The test procedure to quantify the dry, heat seal seam strength
measures the maximum force required to separate the heat sealed seam
in a manner similar to that of the above mechanical seam test. A strip
of test material is folded in half with the fusible fiber containing phases
contacting each other. The heat seal seam is formed by pressing the
folded heat seal web material together with heated platens. The
platens are maintained at 375°F and a pneumatic cylinder pressure of
72 psi imposes a force on the platens which is maintained for a dwell
time of 0.38 seconds. The heat sealed sample is cut to obtain a one
inch wide test sample with the heat sealed seam horizontally traversing
the sample. The unsealed top and bottom edges are clamped in the
jaws of a tensile test instrument. The seam is placed under an
increasing tensile force and the maximum force required to effect seam
failure is recorded. Minimum acceptable heat seal seam strengths will
be at least 150 g/in and more typically the heal seal seam strength is
about 300 g/in.
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It should be realized that a variety of web materials may be made
from the above fibers, however not every non-woven web material is
suited for use in infusion packaging. Suitable infuser web materials
must also have a minimum combination of porosity, sifting and infusion
properties. For ease of understanding and clarity of description, the
invention is below described in its application to non-heat sealable
porous infusion web materials for use in the manufacture of tea bags
and the like.
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The "infusion" characteristics of importance relative to heat seal
web material relate to the rate at which water can pass into the tea bag
and tea liquor can pass out of the tea bag as well as the degree of
extraction which is able to take place within a specified time. This is
usually reported in terms of "first color" and "percent transmittance",
respectively. When testing for first color, a tea bag made from the
material to be tested is carefully placed in quiet distilled water after the
water has been brought to a boil. Using a stopwatch, the time is
recorded at which the first amber stream appears at the bottom of the
sample. A first color time of less than 12 seconds is required with less
than 10 seconds being preferred. A first color of about 5 -7 seconds
is considered indicative of excellent infusion characteristics. Of course,
thicker, heavier basis weight materials typically will have higher first
color values than lighter basis weight materials.
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The percent transmittance test is conducted by measuring the
transmittance of the brew after a 60 second steep time using a
Markson Colorimeter Model T-600 at a wavelength of 530 mµ and
using a 1 cm cell. A target value for good infusion is in the mid-sixty
percentile range with transmittance decreasing as infusion improves.
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Having generally described the invention, the following examples
are included for purposes of illustration so that the invention may be
more readily understood and are in no way intended to limit the scope
of the invention unless otherwise specifically indicated. All parts are
given by dry weight unless otherwise specified.
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The materials resulting from all of the trials, both with and
without synthetic materials, comprised an acrylic agent applied as an
aqueous emulsion during processing. It is believed the acrylic agent
imparts strength to the resulting web materials in a known fashion. It
is also believed that other aqueous agents as disclosed by the
previously incorporated U.S. Patent No. 5,431,997 would also be
compatible with the present invention.
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Since the basis weight of a web material may influence its
physical properties, the physical test results were normalized to a
theoretical basis weight of 12.3 g/m2. Normalizing was accomplished
by dividing a theoretical basis weight (in the present examples 12.3
g/m2) by the actual web basis weight to obtain a ratio. The ratio (or
the inverse of the ration for porosity and sand sift results) was
multiplied by the physical test results to obtain the normalized physical
test results. Normalizing of the physical test results had the effect of
raising the porosity and sand sifting results and lowering the remaining
results. The reported tensile strengths are an average of the tensile
strength of the web material in the direction of machine travel and in
the direction perpendicular to machine travel.
EXAMPLE 1
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One single phase and five two-phase, fibrous, non-heat seal,
non-woven web materials were made-on an inclined wire papermaking
machine. For the two phase materials, the top phase represented
approximately twenty five percent of the resulting web material with
the base phase accounting for the remaining seventy five percent.
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The composition of the furnishes varied as shown in Table I. The
top phase furnishes for trials A3 and A5 each contained twenty percent
polyethylene pulp with differing base phase compositions. The
polyethylene pulp represented approximately five percent of the total
web material composition for trials A3 and A5.
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The web material resulting from furnish A3 exhibited porosity
characteristics similar to conventional materials resulting from similar
conventional furnishes A2 or A4 and sifting characteristics intermediate
those materials. The dry crimped seam strength of the inventive
material was about twelve percent higher than material A2 and twenty
percent higher than material A4.
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Web material resulting from trial A5 exhibited substantially
increased dry crimp strength when compared to the other nonwoven
web materials of Table I. The web material of furnish A5 also exhibited
similar porosity and better sifting characteristics (with the exception of
material A2) when compared to web materials resulting from the other
trial compositions.
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The inventive material of trial A3 exhibited lower average tensile
strength than materials A2 or A4. The material of trial A5 also
exhibited lower average tensile strength than the conventional non-woven
web materials. The average tensile strength results for the
inventive materials demonstrate the minimal activation and bonding of
the synthetic materials within the non-woven web.
| TRIAL | A1 | A2 | A3 | A4 | A5 |
| TOP PHASE (%) | none | - - | - - | - - | - - |
| Wood | | 100 | 80 | 80 | 80 |
| Hemp | | - - | - - | 20 | -- |
| Polyethylene pulp | | - - | 20 | - - | 20 |
| BASE PHASE (%) |
| Wood | 70 | 70 | 70 | 70 | 50 |
| Kenaf | - - | - - | - - | - - | 25 |
| Hemp | 30 | 30 | 30 | 30 | 25 |
| WEB BASIS WT g/m2 | 14.4 | 14.4 | 14.3 | 14.8 | 14.0 |
| INFUSION |
| 1st color seconds | 6.9 | 6.8 | 6.9 | 6.5 | 7.0 |
| % Transmittance | 69.4 | 68.8 | 69.5 | 68.9 | 68.8 |
| NORMALIZED PHYSICALS |
| WEB BASIS WT g/m2 | 12.3 | 12.3 | 12.3 | 12.3 | 12.3 |
| POROSITY L/min | 613 | 674 | 639 | 656 | 636 |
| AVG DRY TENSILE G/25mm | 1355 | 973 | 963 | 1147 | 787 |
| A SAND % LOSS | 0.91 | 0.21 0.26 | 0.78 | 0.34 |
| DRY CRIMP g/in | 64 | 94 109 | 86 | 131 |
| MD TEAR g | 13 | 13 15 | 16.6 | 11 |
| CD TEAR g | 17 | 14.5 15.4 | 17 | 11.3 |
EXAMPLE 2
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Three single phase, fibrous, non-heat seal, non-woven web
materials were made on an inclined wire papermaking machine. The
single phase web materials differed only in the replacement of twenty
percent Kenaf fiber with twenty percent polyethylene pulp (trial B2) or
twenty percent polypropylene pulp (trial B3).
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As can be seen from the results in Table II, the substitution of
modest amounts of either synthetic pulp material for the Kenaf fiber
resulted in surprisingly large increases in dry crimp strength. Trial B3,
while having the greatest improvement in dry crimped seam strength,
exhibited highest porosity and sifting within the B1 - B3 test material
group.
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Both of the inventive web materials, B2 and B3, exhibited lower
tensile strengths than the comparison material: The lowered tensile
strengths again demonstrate the limited activation of the synthetic
materials and fusion of the synthetic materials within the web.
| TRIAL | B1 | B2 | B3 |
| SINGLE PHASE (%) |
| Wood | 22 | 22 | 22 |
| Kenaf | 28 | 8 | 8 |
| Abacca | 50 | 50 | 50 |
| Polyethylene pulp | - - | 20 | - - |
| Polypropylene pulp | - - | - - | 20 |
| WEB BASIS WT g/m2 | 16.4 | 15.2 | 16.2 |
| INFUSION |
| 1st color seconds | 6.8 | 6.6 | 6.7 |
| % Transmittance | 69.4 | 68.7 | 69.6 |
| NORMALIZED PHYSICALS |
| WEB BASIS WT g/m2 | 12.3 | 12.3 | 12.3 |
| POROSITY L/min | 766 | 698 | 911 |
| AVG TENSILE g/25mm | 1758 | 1326 | 1174 |
| "A" SAND SIFT % | 1.12 | 0.76 | 3.1 |
| DRY CRIMP g/in | 45.2 | 73.8 | 135 |
| MD TEAR g | 23 | 22.1 | 25.6 |
| CD TEAR g | 23 | 23.6 | 21.9 |
| MODIFIED DELAM 0.38 sec, g/in | 0 | 38.2 | 33.4 |
| MODIFIED DELAM 0.76 sec, g/in | 0 | 49.4 | 52.6 |
| MODIFIED DELAM 1.52 sec, g/in | 0 | 50.8 | 48.8 |
EXAMPLE 3
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Trial B4 created a two-phase, nonwoven web material with the
top phase containing one hundred percent wood fibers. Trial B5
created a two-phase nonwoven web material similar to trial B4, with
twenty percent polyethylene pulp replacing twenty percent of the wood
fiber in the top phase. The polyethylene pulp represented
approximately five percent of the total web material composition of trial
B5. The top phase represented approximately twenty five percent of
the resulting web material with the base phase accounting for the
remaining seventy-five percent.
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As can be seen in Table III the replacement of twenty percent
wood fiber with twenty percent polyethylene pulp in the top phase
significantly increased the dry crimp strength (approximately 28
percent) as well as improved the sifting characteristics and lowered the
porosity of the resulting web material. The average tensile strength for
the material of trial B5 was similar to that of comparison material B4
when machine repeatability is considered.
| TRIAL | B4 | B5 |
| TOP PHASE (%) |
| Wood | 100 | 80 |
| Polyethylene pulp | - - | 20 |
| BASE PHASE (%) |
| Kenaf | 35 | 35 |
| Abacca | 65 | 65 |
| WEB BASIS WT g/m2 | 13.4 | 14.89 |
| INFUSION |
| 1st COLOR SECONDS | 6.5 | 6.5 |
| % TRANSMITTANCE | 69.3 | 67.8 |
| NORMALIZED PHYSICALS |
| WEB BASIS WT g/m2 | 12.3 | 12.3 |
| POROSITY L/min | 907 | 796 |
| AVG DRY TENSILE g/25mm | 1354 | 1342 |
| "A" SAND SIFT % | 0.54 | 0.27 |
| DRY CRIMP g/in | 52.5 | 73.6 |
| MD TEAR g | 15.9 | 14.25 |
| CD TEAR g | 15.9 | 16.1 |
| MODIFIED DELAM 0.38 sec, g/in | 0 | 19.3 |
| MODIFIED DELAM 0.76 sec, g/in | 0 | 31.8 |
| MODIFIED DELAM 1.52 sec, g/in | 0 | 21.7 |
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Materials from trials B1 - B5 were also tested for heat seal seam
strength. Since samples B1 and B4 contained no fusible fibers, when
these samples. were placed under either standard or the below
described "aggressive" heat seal test conditions, there was, as
expected, no measurable bond formed. Samples B2, B3 and B5,
containing up to twenty percent synthetic fibrous material, also showed
insignificant heat seal seam strengths under normal test conditions
(results not shown in Tables II or III). In fact, the inventive web
materials displayed no evidence of "tackiness" at all under the normal
test conditions.
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In an effort to "force" heat sealing of the inventive web
materials, samples B1 - B5 were subjected to an aggressively modified
heat seal seam strength test. The test temperature was unchanged
from the standard test, however the cylinder pressure was increased
to 80 psi, the maximum possible or the test equipment. Attempts were
made to create a heat seal seam at the normal dwell time of 0.38
seconds, twice the normal dwell time (0.76s) and four times the normal
dwell time (1.52s). Even under these aggressive test conditions, the
samples containing fusible fibers exhibited heat seal seam strengths
(see MODIFIED DELAM rows in TABLES II and III) of only 24 to 70 g/in.
These bond strengths are well below the 300 g/in achieved by a typical
heat sealable web material under normal test conditions and
substantially below the 150 g/in needed to be considered an acceptable
bond. Thus, while some minimal heat sealing may be achieved with
the inventive materials under unusually aggressive conditions, these
materials are not suitable replacements for heat seal type web materials
or for use on heat sealing equipment.
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Even if the synthetic materials have been substantially activated,
the web material would not be expected to exhibit adequate heat seal
seam bonding under normal test conditions. The lack of not only heat
seal seam strength, but also any evidence of tackiness under normal
test conditions, again demonstrates the lack of activation and minimal
fusion of the synthetic materials within the inventive web material.
EXAMPLE 4
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Three two phase, fibrous, non-heat seal, non-woven web
materials were produced. The basis weight for the materials of this
example was higher than the other examples. The top phase of the
materials of Example 4 represented about one third of the resulting web
material while the base phase accounted for the remaining two thirds.
-
The two phase web materials differed from a comparison web
material (trial C1) only in the replacement of Kenaf fiber in the base
phase with three percent polypropylene fiber (trial C2) or four and one
half percent polypropylene fiber (trial C3). The synthetic fiber materials
represent approximately two percent (trial D2) and three percent (trial
C3) of the respective web material compositions. The polypropylene
fibers used had an average fiber length of 5 mm and an average denier
of about 2.2.
-
The dry crimp strengths shown in Table IV are an average of
twenty-one tests. As can be seen, the substitution of minimal amounts
of synthetic fiber material resulted in surprisingly large increases in dry
crimp strength, greater than 30 percent for the material resulting from
trial C2 and 70 percent for material resulting from trial C3. The
surprising improvements in dry crimp strength were achieved with
relatively little impact on the remaining properties of the inventive web
materials as compared to the comparison material.
| TRIAL | C1 | C2 | C3 |
| TOP PHASE (%) |
| wood | 100 | 100 | 100 |
| BASE PHASE (%) |
| Kenaf | 35 | 32 | 30.5 |
| Abaca | 65 | 65 | 65 |
| Polypropylene fiber | - - | 3 | 4.5 |
| WEB BASIS WT g/m2 | 16.9 | 15.9 | 16.0 |
| INFUSION |
| 1st COLOR SECONDS | 7.1 | 7.2 | 6.9 |
| % TRANSMITTANCE | 68.8, | 67.5 | 68.2 |
| NORMALIZED PHYSICALS |
| BASIS WT g/m2 | 12.3 | 12.3 | 12.3 |
| POROSITY L/min | 993 | 875 | 1070 |
| AVG DRY TENSILE g/25mm | 1620 | 1610 | 1605 |
| "A" SAND SIFT % | 3.0 | 2.1 | 2.0 |
| AVG. DRY CRIMP G/IN | 73.5 | 102 | 134 |
| MD TEAR g | 19.1 | 16.2 | 14.8 |
| CD TEAR g | 17.8 | 13.9 | 14.8 |
EXAMPLE 5
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Three two phase, fibrous, non-heat seal non-woven web
materials were produced. The top phase represented approximately
twenty five percent of the resulting web material with the base phase
accounting for the remaining seventy five percent.
-
The two phase web materials differed from a comparison web
material (trial D1) only in the replacement of wood fiber in the top
phase with forty percent polypropylene pulp (trial D2) or forty percent
polyester fibers (trial D3). The synthetic materials represented
approximately ten percent of the total web material compositions of
trials D2 and D3. The polyester fibers used had an average fiber length
of 5 mm and an average denier of about 1.5 to 2.0.
-
As can be seen from the results in Table V, the substitution in
trial D2 of forty percent polypropylene pulp material for wood fiber in
the top phase resulted in a large increase in dry crimp strength. The
substitution in trial D3 of forty percent polyester fiber for wood fiber
increased the dry crimp strength a greater amount than the similar
polypropylene pulp substitution of trial D2.
-
Porosity of the material resulting from trial D3 was greater than
comparison material (trial D1) but was less than that of the material
resulting from trial D2. The sifting of both trial materials D2 and D3
was greater than the comparison material, although the polyester fiber
modified material was somewhat lower than the polypropylene pulp
modified material.
-
Notably, even with large amounts of synthetic materials the
average tensile strengths for trial materials D2 and D3 were lower than
the comparison material.
| TRIAL | D1 | D2 | D3 |
| TOP PHASE (%) |
| wood | 100 | 60 | 60 |
| Polypropylene pulp | - - | 40 | - - |
| Polyester fiber | - - | - - | 40 |
| BASE PHASE (%) |
| Kenaf | 35 | 35 | 35 |
| Abaca | 65 | 65 | 65 |
| WEB BASIS WT g/m2 | 14.9 | 14.7 | 15.3 |
| INFUSION |
| 1st COLOR SECONDS | 6.7 | 6.9 | 6.7 |
| % TRANSMITTANCE | 65.4 | 67.3 | 67.8 |
| NORMALIZED PHYSICALS |
| BASIS WT g/m2 | 12.3 | 12.3 | 12.3 |
| POROSITY L/min | 876 | 1345 | 993 |
| AVG DRY TENSILE g/25mm | 1925 | 1295 | 1607 |
| "A" SAND SIFT % | 0.36 | 2.98 | 1.24 |
| DRY CRIMP g/in | 155.0 | 197.0 | 223.0 |
| MD TEAR g | 17.3 | 20 | 23.3 |
| CD TEAR g | 18.1 | 17.5 | 20.2 |
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The results of the above Examples show that the crimped
mechanical seam strength for a non-woven, natural fiber web material
may be increased by the addition synthetic materials. The synthetic
materials may be synthetic fibers, synthetic pulps or mixtures thereof
and include both thermoplastic and thermoset materials. Further, the
effect is achieved over a wide range synthetic material concentrations,
with minimal amounts of added synthetic material creating a surprising
increase in crimped mechanical seam strength.
-
As will be apparent to persons skilled in the art, various
modifications, adaptations and variations of the foregoing specific
disclosure can be made without departing from the teaching of the
present invention.