U.S. patent application number 10/562161 was filed with the patent office on 2008-11-06 for process for manufacturing a ptfe filament, and a ptfe filament, and a ptfe filament obtained by this process.
This patent application is currently assigned to MANEGRO ADMINISTRACAO E PARTICIPACOES LTDA.. Invention is credited to Jose Antonio Almeida Neto.
Application Number | 20080272327 10/562161 |
Document ID | / |
Family ID | 33520282 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080272327 |
Kind Code |
A1 |
Almeida Neto; Jose Antonio |
November 6, 2008 |
Process For Manufacturing a Ptfe Filament, and a Ptfe Filament, and
a Ptfe Filament Obtained By This Process
Abstract
The present invention consists of an inventive process for
manufacturing a PTFE filament (7) of the type comprising steps of
extrusion, and, subsequently, stretching, heating and cutting, and
an inventive PTFE filament obtained by this process, are provided.
The process of the present invention comprises the following steps
prior to extrusion providing a recipient, which preferably consists
of a cylinder (1) of pre-form machine, having rigid side walls;
arranging a first mixture (A) containing PTFE filler, and a second
mixture (B) containing PTFE, inside the recipient, side by side and
aligned with the side walls; and pressing the first and second
mixtures in a direction parallel to the side walls to form a billet
(5) in which the first and second mixtures (A, B) have different
coefficients of friction. After these steps, the billet (5) is
extruded to form a strand (6), which is subsequently stretched,
heated, rolled and cut by known processes in the art to form the
inventive PTFE filament, which comprises one side with a filler and
the other side without filler, so that these sides have different
coefficients of friction. Also, in a preferred embodiment, the
filament presents each side with a different color.
Inventors: |
Almeida Neto; Jose Antonio;
(Rio de Janeiro, BR) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
MANEGRO ADMINISTRACAO E
PARTICIPACOES LTDA.
Rio de Janeiro
BR
|
Family ID: |
33520282 |
Appl. No.: |
10/562161 |
Filed: |
June 24, 2003 |
PCT Filed: |
June 24, 2003 |
PCT NO: |
PCT/BR2003/000087 |
371 Date: |
June 19, 2008 |
Current U.S.
Class: |
252/8.84 ;
264/172.14 |
Current CPC
Class: |
B29K 2027/18 20130101;
B29C 48/17 20190201; B29C 48/05 20190201; B29C 48/22 20190201; B29C
48/022 20190201; B29C 48/18 20190201; A61C 15/041 20130101 |
Class at
Publication: |
252/8.84 ;
264/172.14 |
International
Class: |
D06M 13/08 20060101
D06M013/08 |
Claims
1. A process for manufacturing a PTFE filament of the type
comprising steps of extrusion, and, subsequently, stretching,
heating and cutting PTFE, characterized by the following steps
prior to extrusion: providing a recipient having rigid side walls;
arranging a first mixture containing PTFE and a filler, and a
second mixture containing PTFE, inside the recipient, side by side
and aligned with the side walls; and pressing the first and second
mixtures in a direction parallel to the side walls to form a billet
in which the first and second mixtures have different coefficients
of friction.
2. The process according to claim 1 is characterized by the fact
that, in the arranging step, the first and the second mixtures are
inserted respectively into two portions of the recipient separated
by a barrier, and, subsequently, the barrier is removed, enabling a
part of the first mixture to contact a part of the second, and be
arranged side by side and aligned with the side walls of the
recipient.
3. The process according to claim 1 or 2 is characterized by the
fact that, in the step of arranging, the first mixture includes a
pigment and the second mixture includes another pigment.
4. A PTFE filament obtained by the process defined in claim 1 is
characterized by comprising one side with a filler, so that this
side has a different coefficient of friction in relation to the
other side.
5. The PTFE filament in claim 4 is characterized by the fact that
the first and the second mixtures have the same shrink
properties.
6. The PTFE filament in claim 4 or 5 is characterized by further
comprising a lubricant.
7. The PTFE filament in any one of claims 4 to 6 is characterized
by the fact that each side has a different color.
8. The PTFE filament in any one of claims 4 to 7 is characterized
by the fact that the filler comprises at least one of silica,
alumina, mica and calcium carbonate.
9. The PTFE filament according to any one of claims 4 to 8 is
characterized by the fact that the quantity of filler in the
respective side ranges from 1 to 25%.
10. The PTFE filament according to any one of claims 4 to 9 is
characterized by the fact that the quantity of pigment in at least
one side ranges from 0.05% to 10%.
11. The PTFE filament according to any one of claims 4 to 10 is
characterized by the fact that said coefficient of friction in the
side with filler ranges from 0.08 to 0.20 and the other side is
less than 0.08.
12. The PTFE filament according to any one of claims 4 to 11,
characterized by comprising a width ranging from 0.5 to 3.0 mm, a
thickness ranging from 20 to 400 .mu.m, a density ranging from 0.7
to 2.2 g/cm3, a tensile strength ranging from 100 to 1100 MPa and a
tenacity ranging from 2.0 to 6.0 cN/dtex.
Description
[0001] This invention refers to a process of manufacturing a
polytetrafluoroethylene (hereinafter called "PTFE") filament, and
the filament obtained by this process.
[0002] Since the development of the material in the U.S. Pat. No.
3,953,566 by Gore, flexible fibers made from expanded PTFE have
been used for several purposes, such as fabric, sewing thread and
dental floss. Such fibers are widely used due to the very good
physical properties of the PTFE resin, and, furthermore, as they
are chemically inert, have excellent high and low temperature
performance, high resistance to ultraviolet radiation and are
highly lubricious. U.S. Pat. Nos. 3,953,566 and 3,962,153 disclose
processes for producing highly porous materials from PTFE that
result in very high strength products. These patents disclose how
strands made of this polymer are produced by paste forming
techniques, where the polymer is converted into a paste and shaped
into a strand, which is then expanded by stretching in one or more
directions under certain conditions so that it becomes much more
porous and stronger. This phenomenon of expansion accompanied by an
increase in strength occurs with certain preferred PTFE resins and
within preferred ranges of stretching rate and preferred
temperature ranges. Accordingly, most of the products are obtained
to when expansion is carried out at high temperatures, preferably
within the range of 35.degree. C. to 327.degree. C.
[0003] In addition, it was found that some resins are much more
suitable for the expansion process than others, since they can be
processed over a wider range of stretching rate and temperature.
The primary requisite of a suitable resin is a very high degree of
crystallinity, preferably in, the range of 98% or above.
[0004] The porous microstructure of the expanded material is
affected by the temperature and the rate at which it is expanded.
The structure consists of nodes interconnected by very small
fibrils. In the case of uni-axial expansion the nodes are
elongated, the longer axis of a node being oriented perpendicular
to the direction of expansion. The fibrils that interconnect the
nodes are oriented parallel to the direction of expansion. The
nodes may vary in size, depending on the conditions used in the
expansion. Products which have been expanded at high temperatures
and high rates have a more homogeneous structure, i.e., they have
smaller and more closely spaced nodes, and these nodes are
interconnected with a greater number of fibrils. These products are
also found to have much greater strength. The expansion process
results in a tremendous increase in the tensile strength of the
PTFE fibers and an increase in the porosity.
[0005] When the expanded products are heated to a temperature above
the lowest crystalline melting point of the PTFE, disorder begins
to occur in the geometric order of the crystallites and the
crystallinity decreases, therefore increasing the amorphous content
of the polymer, typically to 10% or more. These amorphous regions
within the crystalline structure appear to greatly inhibit slippage
along the crystalline axis of the crystallite and appear to lock
fibrils and crystallites so that they resist slippage under stress.
Therefore, the heat treatment may be considered an amorphous
locking process. The important aspect of amorphous locking is that
an increase in amorphous content occurs, regardless of the
crystallinity of the resin at start. When the material is heated
above 327.degree. C. a surprising increase in strengths occurs.
[0006] The increase in strength of the polymer matrix is dependent
upon the strength of the extruded material before expansion, the
degree of crystallinity of the polymer, the rate and temperature at
which the expansion is performed, and amorphous locking. When all
these factors are employed to maximize the strength of the
material, tensile strengths of 10,000 psi and above, with porosity
of 90% or more are obtained. In contrast, the maximum tensile
strength of conventional extruded or molded PTFE after sintering is
generally considered to be about 3,000 psi, and for conventional
extruded and calendered PTFE tape, which has been centered, the
maximum is about 5,100 psi.
[0007] The prior art in dental floss, as exemplified by the U.S.
Pat. Nos. 3,830,246, 3,897,795, 4,215,478 and 4,033,365, is made of
synthetic or natural material, PTFE is not mentioned.
[0008] These patents show that flossing is an extremely important
adjunct to proper dental hygiene. The insufficient consumer
acceptance, despite often repeat directions by dentists to use
floss, may arise from the fact that prior art flosses frequently
caused gingival bleeding and are generally uncomfortable or
difficult to use. Those conditions may arise primarily from the
relatively high coefficient of friction (COF) of such flosses.
[0009] Thus, because prior art flosses have such high coefficients
of friction, consumers must use substantial force to pull them
between the teeth or so-called "contact points". Unfortunately, the
user does not know when the floss will, in fact, pass between the
contact points. When this suddenly occurs, the user does not have
time to release the great force being applied. This appears to
cause the flosses to be pulled into the gum, causing cuts that
bleed, sometimes profusely. Hence, many of the dental flosses
presently on the market have received limited consumer acceptance.
The lack of consumer acceptance of any single dental floss on the
market is due, in part, to the propensity of dental floss to cause
gingival bleeding. In addition, dental floss is generally
considered difficult and uncomfortable to use. The consumer
dissatisfaction with some dental flosses is caused by the
relatively high coefficient of friction.
[0010] In order to solve this problem a new type of dental floss
made from PTFE has become available from a variety of sources. This
type of dental floss has certain beneficial characteristics,
including high lubricity and a lower fraying rate than conventional
flosses. Some patents have been aimed at such products including
U.S. Pat. Nos. 5,033,488 and 5,209,251 to Curtis et al., and U.S.
Pat. No. 5,220,932 to Blass.
[0011] The Curtis patents (U.S. Pat. Nos. 5,033,488 and 5,209,251)
disclose the use of high strength expanded PTFE, which is coated
with a material to increase the PTFE coefficient of friction for
use as a dental floss.
[0012] The Blass patent (U.S. Pat. No. 5,220,932) discloses the use
of a uni-axially stretched, non-porous PTFE having a relatively low
tensile strength, and is coated with wax to increase the PTFE
coefficient of friction for use as a dental floss.
[0013] Expanded PTFE has a rather low coefficient of friction
(below 0.08) compared to a coefficient of friction of about 0.2 for
prior art commercial flosses. The inventors in U.S. Pat. No.
5,033,488 show that microcrystalline wax (MCW) adheres to expanded
PTFE and, unexpectedly, provides a coefficient of friction
sufficiently high to permit the user to securely grasp the floss
and tapes, but generally not so high as that of the prior art. This
coefficient of friction is intermediate between the very low
coefficient of friction of expanded PTFE (below 0.08) and
coefficient of friction of commercial flosses, say about 0.08 and
0.15.
[0014] Other patents, such as U.S. Pat. Nos. 5,657,779 and
5,806,539 teach a method for producing PTFE dental floss,
comprising the passage of an unsintered PTFE tape across a heated
surface in sliding contact therewith, while applying tension to the
tape, wherein the temperature of the heated surface, the passage
speed of the tape and the tension applied are such that the PTFE
tape, when its temperature is raised by contact with the heated
surface, is longitudinally stretched. The dental floss produced
comprises a PTFE tape having opposite faces at which the respective
physical states of the PTFE material differ, the coefficient of
friction being one of these differences. The opposite faces of this
dental floss have different degrees of sintering.
[0015] The U.S. Pat. No. 5,698,300 to Lenzing discloses a film
consisting of two-or more PTFE layers which differ in their shrink
properties providing a bi-component fiber, which can be transformed
into a staple crimp by heating to a temperature above 200+ C. This
U.S. patent further relates to a process for producing a
bi-component film from two types of PTFE. The resultant film
shrinks to different extents under the effect of heat and differs
in Its hot-air shrinkage by at least 1%. Each type of PTFE is
molded in a cylinder and one half is joined to the other half with
the other type of PTFE and then extruded, calendered, dried,
sintered and cut into a staple fiber.
[0016] The U.S. Pat. No. 5,804,290 by Lenzing describes a dental
floss that contains PTFE and whiting filler, and preserves the gum
more than the prior art. By adjusting the amount of whiting
material, the kinetic friction of the dental floss can be modified.
Experiments have disclosed that dental floss containing whiting
from 0.1 to 15% by weight is particularly well suited.
[0017] The U.S. Pat. No. 6,220,256 also discloses a dental floss
made of PTFE and filler, this filler being fumed silica. The dental
floss can have a plurality of layers of PTFE, with at least one of
the layers having fumed silica placed within it. Preferably, the
filament has an inner layer and two outer layers, with the fumed
silica situated in at least one of the two outer layers. The layers
are made separately and then laminated by any conventional
lamination technique, such as calendering together with use of
rotating rollers. The floss obtained through this document provides
increased surface friction.
[0018] In view of the above, it is an objective of the present
invention to provide a bi-color bi-component expanded PTFE dental
floss where each side presents different coefficients of
friction.
[0019] Another objective of the present invention relies on
providing a dental-floss that permits the consumers to choose the
side that they intend to use.
[0020] Another objective of the present invention relies on
providing a dental floss with sides of different colors to aid
identification of the side that is more or less slippery.
[0021] Another objective of the present invention relies on
providing a filament with sides having different coefficients of
friction for other applications besides dental floss.
[0022] Accordingly, an inventive process for manufacturing a PTFE
filament of the type comprising steps of extrusion, and,
subsequently, stretching, heating and cutting, and an inventive
PTFE filament obtained by this process, are provided.
[0023] The process of the present invention comprises the following
steps prior to extrusion:
[0024] providing a recipient, which preferably consists of a
cylinder of a re-form machine, having rigid side walls;
[0025] arranging a first mixture containing PTFE and a filler, and
a second mixture containing PTFE, inside the recipient, side by
side and aligned with the side walls; and
[0026] pressing the first and second mixtures in a direction
parallel to the side walls to form a billet in which the first and
second mixtures have different coefficients of friction.
[0027] After these steps, the billet having the first and second
mixtures is extruded to form a strand, which is subsequently
stretched, heated, rolled and cut by known processes in the art to
form the inventive PTFE filament.
[0028] The filler has the purpose of providing a different
coefficient of friction on each side of the PTFE filament.
Accordingly, the coefficient of friction on the side with filler
preferably ranging from 0.08 to 0.20, and the side without filler
being less than 0.08. The filler can be made of silica, alumina,
mica and/or calcium carbonate, among other components.
[0029] Although, in a preferred embodiment, the second mixture does
not contain such a filler, other embodiments of the present
invention can present a first mixture with a first filler and a
second mixture with a second filler, provided that the billet
formed includes first and second mixtures having different
coefficients of friction.
[0030] In addition, unlike prior arts, the first and second
mixtures may also have the same shrink properties, as the above
difference in the coefficient of friction between the mixtures is
provided by the filler.
[0031] In an embodiment of the present process, different pigments
made of organic and inorganic materials may be mixed with the
mixtures so that each mixture can have a different color.
[0032] In the above or any other embodiment of the present
invention, the step of arranging can also comprise a step of
inserting a barrier, preferably a plate, in the recipient to
separate it into two-portions. Although, in a preferred embodiment,
this barrier is a plate, other embodiments for the barrier can be
used without affecting the scope of the present invention. Then,
the first and the second mixtures are respectively inserted into
these two portions of the recipient. Subsequently, this barrier is
removed, enabling a part of the first mixture to contact a part of
the second mixture and be arranged by side by side and aligned with
the side walls of the recipient.
[0033] The PTFE filament obtained comprises one side with a filler
and another side without filler, so that these sides have different
coefficients of friction, wherein preferably the side with filler
presents a higher coefficient of friction than the other side.
Also, in a preferred embodiment, the filament presents each side
with a different color.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a perspective view of a plate being inserted into
a cylinder of a pre-form machine according to the preferred
embodiment of the present invention.
[0035] FIG. 2 is a perspective view of the cylinder including the
plate according to the embodiment depicted in FIG. 1.
[0036] FIG. 3 is a perspective view of the cylinder including the
plate and mixtures A and B according to the embodiment depicted in
FIG. 1.
[0037] FIG. 4 is a perspective view of the plate being removed from
the cylinder according to the embodiment depicted in FIG. 1.
[0038] FIG. 5 is a perspective view of a billet formed after the
mixtures A and B are pressed in the cylinder according to the
embodiment depicted in FIG. 1.
[0039] FIG. 6 is a perspective view of a strand formed after the
billet is extruded according to the embodiment depicted in. FIG.
1.
[0040] FIG. 7 is a perspective view of a PTFE filament according to
the embodiment depicted in FIG. 1.
DETAILED DESCRIPTION
[0041] The invention will now be described in further detail on the
basis of tests and examples.
[0042] Steps in the process:
[0043] (a) Mixture/Paste-Extrusion/Tape
[0044] Two mixtures, A and B, are produced in the following
manner:
[0045] A--A fine-powder PTFE resin is pre-mixed with silica or
alumina filler and then a liquid lubricant is added until a
compound is formed.
[0046] B--A fine powder PTFE resin is mixed with a liquid
lubricant, until a compound is formed.
[0047] The first and the second mixtures preferentially have the
same shrink properties, and, furthermore, in one or both mixtures a
pigment is added for identification of the compositions.
[0048] The volume of lubricant used in these mixtures should be
sufficient to lubricate the primary particles of the PTFE resin so
as to minimize the possibility of shearing of the particles prior
to extruding. The proportion ranges from 17% to 29%. In mixtures,
the amount of filler can vary from 0% to 25% and the amount of
pigment ranges from 0% to 10%. These mixtures are processed,
preferably for 20 to 30 minutes.
[0049] Other kinds of filler besides silica and alumina can be used
in the compound and the pigments can be organic or inorganic.
[0050] As indicated in FIGS. 1 to 5, a cylinder of a pre-forrm
machine 1 is previously axially split along its length into two
halves by a plate 2 or strip and then the mixture A is fed into one
half and the mixture B into the other half. After feeding the
cylinder 1 with the different compounds, the plate 2 that separates
the same into equal parts is taken out and the material is
preformed. Consequently, a bi-color bi-component billet 5 is
formed, wherein one half comprises mixture A and the other
comprises mixture B, and, furthermore, presenting excellent
adhesion at the interface of the mixtures.
[0051] After these steps, the billet 5 having the mixtures A and B
is extruded to form a strand 6, as depicted in FIG. 6, which is
subsequently rolled, stretched, heated and cut by known processes
in the art to form the inventive PTFE filament (FIG. 7), as
follows.
[0052] In the extrusion process, a reduction ratio of about 10:1 to
1000:1 may be used (i.e. reduction ratio=cross-sectional area of
extrusion cylinder divided by cross-sectional area of the extrusion
die). For most applications, a reduction ratio of 25:1 to 200:1 is
preferred.
[0053] The strand is, in the next stage, pressed through calender
rolls in order to form a tape with a thickness ranging from 50
.mu.m to 1000 .mu.m. In this method, care should be taken that the
strand runs in between the rollers such that the imaginary
separating line of the two material halves lies parallel to the
roller nip. Then a bi-color bi-component tape is produced, where
one side consists of PTFE-filler and the other side is composed of
pure PTFE. These sides can be of a variety of colors. The tape
resulting from the calendering, with one side one color and the
other side another color, passes through a drying oven to remove
the liquid lubricant. The drying temperature ranges from
100.degree. C. to 300.degree. C.
[0054] (b) Stretching and Heat Treatment
[0055] In this invention, it has been found that such composite
tape can be expanded by stretching in at least one direction about
1.1 to 100 times its original length (with about 2 to 50 times
being preferred). The stretching is carried out by passing the dry
composite tape through tensioning rollers between the two units of
pulling rollers that operate with a stretching ratio that is, the
ratio between the entry speed and the exit speed--from 1.1 to 100,
and a stretching temperature ranging from 150 to 300.degree. C. The
expanded PTFE composite tape can be optionally longitudinally
expanded further if desired. The heat element in the expansion
process may be an oven, a hot-air, steam or high-boiling-point
liquid heater, a heated plate or a heated cylinder.
[0056] After the stretching, the composite tape is wound in a
winder.
[0057] The tape may be formed into filaments by slitting the
expanded composite tape into pre-determined widths (between 0.5 to
10 mm), feeding it into the cutting unit, whereby the individual
PTFE filaments are cut and separated.
[0058] Following cutting, the composite expanded PTFE filaments,
where one side is composed of PTFE-filler (one color) and the other
side of pure PTFE (another color), may then be further stretched.
The composite filament is again stretched with a stretching ratio
ranging from 1.1 to 20 (with 1.2 to 8.0 being preferred) under high
temperature (between 300 to 450.degree. C.) in order to subject the
fiber to an amorphous locking step. The stretched filaments are
wound individually in the winding unit.
[0059] The expanded PTFE filament obtained from the technique
described above is depicted in FIG. 7, reference number 7, and
presents two sides with different characteristics, principally
their coefficients of friction, determined according to the method
described below. On side A, the filament contains PTFE-filler (one
color) and, on side, B, contains pure PTFE (another color).
[0060] The final characteristics of the dental floss comprise: a
width of about 0.5 to 3.0 mm; a thickness of about 20 to 400 .mu.m;
a weight/length of about 400 to 2000 dtex; a density of about 0.7
to 2.2 g/cm.sup.3; a tensile strength ranging from 100 to 1100 MPa
and a tenacity ranging from 2.0 to 6.0 cN/dtex. The coefficient of
friction on both sides are different, the side with filler ranging
from 0.08 to 0.20 and the side without filler being less than
0.08.
[0061] Each of these properties is measured in the following manner
length, width and thickness are determined through the use of
calipers; density by dividing the measured weight of the sample by
the computed volume of the sample; the volume is computed by
multiplying the measured length, width and thickness of the
sample.
[0062] The bulk tensile strength of the fibers is measured by a
tensile tester, such as an INSTRON Machine by using the following
conditions. The gauge length is 250 mm and the cross-head speed of
the tensile tester is 250 mm/min.
[0063] Tenacity is calculated by dividing the maximum force
obtained in the tensile tester by its normalized weight per unit
length (tex (grams/1,000 meters) or dtex (grams/10,000 meters) or
denier (grams/9,000 meters)).
[0064] The coefficient of friction is a dimensionless quality which
represents the force required to move an object across a surface.
This test method covers the measurement of kinetic friction between
fiber and solid surfaces of a constant radius in the contact area.
In general, the greater the value of the coefficient of friction,
the more difficult it is to move the object with respect to the
surface, and thus, a greater frictional force is involved. Various
properties of dental floss can be inferred from coefficient of
friction experiments, such as ease of inter-proximal access and
gentleness of the floss on gingival tissue.
[0065] Apparatus required for determination of the coefficient of
friction:
[0066] Instron Machine, friction testing apparatus--with rotating
mandrels and 100 g weight.
[0067] Procedure:
[0068] Preset the Instron with the following parameters:
[0069] Cross-head weight--5 Kg
[0070] Cross-head speed--190 mm/min
[0071] Gauge length--110 mm
[0072] Reference weight--100 g
[0073] Angle of wrap--240=4.189 rad
[0074] Recorder speed--5 cm/min
[0075] (1) Measure 5 pieces of floss, each 110 mm in length
[0076] (2) Attach one strand of floss to upper cross-head. Let it
hang between the mandrels, not touching them.
[0077] (3) Place a 100 g weight at the other end of the sample.
[0078] (4) Measure the force recorded by the recorder resulting
from the weight and the floss sample. When the floss and weight are
raised by the Instron unit, this value remains constant. This value
is the resting weight
[0079] (5) To measure the coefficient of friction, wrap the floss
sample around two mandrels
[0080] (6) Make sure that the floss is not twisted and is very
steady
[0081] (7) Zero the chart recorder and start
[0082] (8) Start the mandrels rotating
[0083] (9) Press the start button to start raising the floss over
the rotating mandrels
[0084] (10) Let the instron raise the floss to approximately 3
inches from the 100 g weight
[0085] (11) Select 10 peaks from chart recorder and average this
data
[0086] (12) Perform calculation below on average this data:
coefficient of friction=( 1/0)*In(T2/T1)
[0087] Where:
[0088] coefficient of friction=coefficient of friction
[0089] 0=angle of wrap in radius
[0090] T2=tension while system is being pulled over mandrels
[0091] T1=tension in floss sample+weight at rest
[0092] (13) Repeat steps 5-12, four more times, using a new floss
sample every time.
[0093] A few examples will be described hereinafter on the basis of
tests performed under different conditions:
EXAMPLE 1
[0094] A bi-color bi-component dental floss of the present
invention is produced as described below:
[0095] Two mixtures, A and B, are produced in the following
manner
[0096] A--A fine-powder PTFE resin is pre-mixed with quartz silica
filler and then a liquid lubricant is added until a compound is
formed.
[0097] B--A fine-powder PTFE resin is pre-mixed with an organic
pigment and then a liquid lubricant is also added until a compound
is formed.
[0098] These mixtures are processed preferably for 20 to 30 minutes
and should have the same pressure extrusion. The proportion of
lubricant in these mixtures ranges from 17% to 29%. In mixture A,
the amount of quartz silica is 4.7% and in the mixture B the amount
of pigment is 0.5%.
[0099] The cylinder of a pre form machine 1 is fed with the mixture
A in one half and the mixture B in another half (FIG. 3). After
feeding the cylinder 1 with the different compounds, the plate 2
that separates the same into equal parts is removed and the
material is pre-formed (FIG. 4). Consequently, a bi-color
bi-component billet 5 is formed, wherein one half comprises mixture
A and the other comprises mixture B (FIG. 5).
[0100] After these steps, this billet is extruded to form a strand
6 (FIG. 6), which is subsequently rolled, stretched, heated and cut
by known processes in the art to form the inventive PTFE filament,
as follows.
[0101] A reduction ratio of 148:1 is used. The bi-color
bi-component tape resulting from calender rolling, one side of
which is white (PTFE-quartz silica) and the other colored side
(PTFE-pigment), with a thickness of 400 .mu.m. This tape is passed
through an oven at a temperature of 220.degree. C. for lubricant
removal. The dry tape is stretched uni-axially in the longitudinal
direction 8.0 times its original length by passing the dry tape
through tensioning rollers between the two units of pulling rollers
that operate with a stretching ratio of 8.0 and a stretching
temperature of 265.degree. C.
[0102] The expanded tape is slit to 3.0 mm widths by passing it
between a set of gapped blades. The slit strands are further
stretched uniaxially in the longitudinal direction over hot plates
at a temperature of 400.degree. C. and at a ratio of 4.0 to form a
bi-color bi-component dental floss.
[0103] The following measures are taken on the bi-color
bi-component expanded PTFE dental floss:
TABLE-US-00001 Filament Number: 850 dtex Tensile Strength: 420 MPa
Tenacity: 3.3 g/dtex Coefficient of friction: White side 0.08
Colored side 0.06
EXAMPLE 2
[0104] A bi-component dental floss is produced, as described in
Example 1. The difference is in the composition of the mixtures.
The proportion of quartz silica in the white side is 12.3%.
[0105] The following measures are taken on the bi-color
bi-component expanded PTFE dental floss:
TABLE-US-00002 Filament Number: 870 dtex Tensile Strength: 340 MPa
Tenacity: 2.8 g/dtex Coefficient of friction: White side 0.10
Colored side 0.06
EXAMPLE 3
[0106] A bi-component dental floss is also produced, as described
in Example 1. In this case, the type of filler used is precipitated
silica (white side) in the proportion of 8.2%.
[0107] The following measures are taken on the bi-color
bi-component expanded PTFE dental floss:
TABLE-US-00003 Filament Number: 860 dtex Tensile Strength: 400 MPa
Tenacity: 3.1 g/dtex Coefficient of friction: White side 0.10
Colored side 0.06
EXAMPLE 4
[0108] A bi-component dental floss is also produced, as described
in Example 1. Alumina is the filler, used in the proportion
12%.
[0109] The following measures are taken on the bi-color
bi-component expanded PTFE dental floss:
TABLE-US-00004 Filament Number: 870 dtex Tensile Strength: 350 MPa
Tenacity: 2.8 g/dtex Coefficient of friction: White side 0.09
Colored side 0.06
[0110] Although described in connection with specific examples, the
present invention is not intended to be limited thereto, but rather
includes such modifications and variations as are within the scope
of the appended claims.
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