U.S. patent application number 10/877843 was filed with the patent office on 2005-12-29 for acrylic and para-aramid pulp and processes of making same.
Invention is credited to Conley, Jill A., Merriman, Edmund A..
Application Number | 20050287344 10/877843 |
Document ID | / |
Family ID | 35057165 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050287344 |
Kind Code |
A1 |
Conley, Jill A. ; et
al. |
December 29, 2005 |
Acrylic and para-aramid pulp and processes of making same
Abstract
The present invention relates to acrylic and para-aramid pulp
for use as reinforcement material in products such as seals and
friction materials. The pulp comprises (a) irregularly shaped,
acrylic fibrous structures, (b) irregularly shaped, para-aramid
fibrous structures, and (c) water, whereby acrylic fibrils and/or
stalks are substantially entangled with para-aramid fibrils and/or
stalks. The invention further relates to processes for making such
acrylic and aramid pulp.
Inventors: |
Conley, Jill A.;
(Chesterfield, VA) ; Merriman, Edmund A.;
(Midlothian, VA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
35057165 |
Appl. No.: |
10/877843 |
Filed: |
June 25, 2004 |
Current U.S.
Class: |
428/292.1 |
Current CPC
Class: |
D21H 13/26 20130101;
Y10T 428/249924 20150401; D21H 13/18 20130101 |
Class at
Publication: |
428/292.1 |
International
Class: |
D04H 005/00 |
Claims
What is claimed is:
1. A process for making an acrylic and para-aramid pulp for use as
reinforcement material, comprising: (a) combining pulp ingredients
including: (1) acrylic fiber comprising acrylonitrile units which
are at least 85 wt % of the total acrylic fiber, the fiber being 10
to 90 wt % of the total solids in the ingredients, and having an
average length of no more than 10 cm; (2) para-aramid fiber being
10 to 90 wt % of the total solids in the ingredients, and having an
average length of no more than 10 cm; and (3) water being 95 to 99
wt % of the total ingredients; (b) mixing the ingredients to a
substantially uniform slurry; (c) co-refining the slurry by
simultaneously: (1) fibrillating, cutting and masticating the
acrylic fiber and the para-aramid fiber to irregularly shaped
fibrillated fibrous structures with stalks and fibrils; and (2)
dispersing all solids such that the refined slurry is substantially
uniform; and (d) removing water from the refined slurry to no more
than 60 total wt % water, thereby producing an acrylic and
para-aramid pulp with the acrylic and the para-aramid fibrous
structures having an average maximum dimension of no more than 5
mm, a length-weighted average of no more than 1.3 mm, and the
acrylic fibrils and/or stalks are substantially entangled with the
para-aramid fibrils and/or stalks.
2. The process of claim 1, wherein the acrylic fiber having a
linear density of no more than 10 dtex; and the para-aramid fiber
having a linear density of no more than 2.5 dtex.
3. The process of claim 1, wherein the pulp being without
substantial aggregates of the same material.
4. The process of claim 1, wherein the ingredients further comprise
substantially or completely fibril-free, granular, para-aramid
particles being no more than 50 wt % of the total solids in the
ingredients, and having an average maximum dimension of 50 to 2000
microns, and in the refining step, masticating at least some of the
para-aramid particles into smaller, rounder, substantially
fibril-free, particles, whereby in the produced acrylic and
para-aramid pulp, the acrylic and para-aramid fibrous structures
contact and are wrapped partially around at least some of the
rounder, substantially fibril-free, para-aramid particles.
5. The process of claim 1, wherein in the combining step, the
acrylic fiber comprises 25 to 60 wt % of the total solids.
6. The process of claim 1, wherein in the combing step, the
para-aramid fiber comprises 40 to 75 wt % of the total solids.
7. The process of claim 1, wherein after the removing step, the
water being 4 to 60 wt % of the entire pulp, and the pulp having a
Canadian Standard Freeness (CSF) of 100 to 700 ml.
8. The process of claim 1, wherein the refining step comprises
passing the mixed slurry through a series of disc refiners.
9. A process for making an acrylic and para-aramid pulp for use as
reinforcement material, comprising: (a) combining ingredients
including water and a first fiber from the group consisting of: (1)
acrylic fiber comprising acrylonitrile units which are at least 85
wt % of the total acrylic fiber, the fiber being 10 to 90 wt % of
the total solids in the pulp; and (2) para-aramid fiber being 10 to
90 wt % of the total solids in the pulp; (b) mixing the combined
ingredients to a substantially uniform suspension; (c) refining the
suspension in a disc refiner thereby cutting the fiber to have an
average length of no more than 10 cm, and fibrillating and
masticating at least some of the fiber to irregularly shaped
fibrillated fibrous structures; (d) combining ingredients including
the refined suspension, the second fiber of the group of (a)(1 and
2) having an average length of no more than 10 cm, and water, if
necessary, to increase the water concentration to 95-99 wt % of the
total ingredients; (e) mixing the ingredients, if necessary, to
form a substantially uniform suspension; (d) co-refining the mixed
suspension by simultaneously: (1) fibrillating, cutting and
masticating solids in the suspension such that all or substantially
all of the acrylic and para-aramid fiber is converted to
irregularly shaped fibrillated acrylic and para-aramid fibrous
structures with stalks and fibrils; and (2) dispersing all solids
such that the refined slurry is substantially uniform; and (h)
removing water from the refined slurry to no more than 60 total wt
% water, thereby producing an acrylic and para-aramid pulp with the
acrylic and the para-aramid fibrous structures having an average
maximum dimension of no more than 5 mm, a length-weighted average
of no more than 1.3 mm, and the acrylic fibrils and/or stalks are
substantially entangled with the para-aramid fibrils and/or
stalks.
10. The process of claim 9, wherein the ingredients further
comprise: substantially or completely fibril-free, granular,
para-aramid particles being no more than 50 wt % of the total
solids in the ingredients, and having an average maximum length of
50 to 2000 microns; and in either the first or second refining
step, masticating at least some of the para-aramid particles into
smaller, rounder, substantially fibril-free, particles, whereby in
the produced acrylic and para-aramid pulp, the acrylic and
para-aramid fibrous structures contact and are wrapped partially
around at least some of the rounder, substantially fibril-free,
para-aramid particles.
11. The process of claim 9, wherein after the removing step, the
irregularly shaped acrylic fibrous structures being 25 to 60 wt %
of the total solids.
12. The process of claim 9, wherein after the removing step, the
irregularly shaped, para-aramid, fibrous structures being 40 to 75
wt % of the total solids.
13. The process of claim 9, wherein after the removing step, the
water being 4 to 60 wt % of the entire pulp, and the pulp having a
Canadian Standard Freeness (CSF) of 100 to 700 ml.
14. An acrylic and para-aramid pulp for use as reinforcement
material, comprising: (a) irregularly shaped, acrylic fibrous
structures comprising acrylonitrile units which are at least 85 wt
% of the total acrylic fibrous structures, the structures being 10
to 90 wt % of the total solids; (b) irregularly shaped, para-aramid
fibrous structures being 10 to 90 wt % of the total solids; and (c)
water being 4 to 60 wt % of the entire pulp, whereby the acrylic
and the para-aramid fibrous structures having an average maximum
dimension of no more than 5 mm, a length-weighted average of no
more than 1.3 mm, and stalks and fibrils where the acrylic fibrils
and/or stalks are substantially entangled with the para-aramid
fibrils and/or stalks.
15. The aramid pulp of claim 14, further comprising substantially
or completely fibril-free, granular, para-aramid particles being no
more than 50 wt % of the total solids.
16. The pulp of claim 14, wherein the irregularly shaped, acrylic
fibrous structures being 25 to 60 wt % of the total solids.
17. The pulp of claim 14, wherein the irregularly shaped,
para-aramid, fibrous structures being 40 to 75 wt % of the total
solids.
18. The pulp of claim 14, wherein the water being 4 to 60 wt % of
the entire pulp, and the pulp having a Canadian Standard Freeness
(CSF) of 100 to 700 ml.
19. A friction material, comprising: a friction modifier; a binder;
and a fibrous reinforcement material comprising the pulp of claim
14.
20. The friction material of claim 19, wherein the friction
modifier is selected from the group consisting of metal powders,
abrasives, lubricants, organic friction modifiers, and mixtures
thereof; and the binder is selected from the group consisting of
thermosetting resins, melamine resins, epoxy resins and polyimide
resins, and mixtures thereof.
21. A sealing material, comprising: a binder; and a fibrous
reinforcement material comprising the pulp of claim 14.
22. The sealing material of claim 21, wherein the binder is
selected from the group consisting of nitrile rubber, butadiene
rubber, neoprene, styrene butadiene rubber, nitrile-butadiene
rubber, and mixtures thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to acrylic and para-aramid pulp for
use as reinforcement material in products, such as seals and
friction materials. The invention further relates to processes for
making such pulp.
[0003] 2. Description of Related Art
[0004] Fibrous and non fibrous reinforcement materials have been
used for many years in friction products, sealing products and
other plastic or rubber products. Such reinforcement materials
typically must exhibit high wear and heat resistance.
[0005] Asbestos fibers have historically been used as reinforcement
materials, but due to their health risks, replacements have been
made or proposed. However, many of these replacements do not
perform as well as asbestos in one way or another.
[0006] Research Disclosure 74-75, published February 1980,
discloses the manufacture of pulp made from fibrillated KEVLAR.RTM.
brand para-aramid fibers of variable lengths and use of such pulp
as a reinforcement material in various applications. This
publication discloses that pulp made from KEVLAR.RTM. brand
para-aramid fibers can be used in sheet products alone, or in
combination with fibers of other materials, such as NOMEX.RTM.
brand meta-aramid, wood pulp, cotton and other natural cellulosics,
rayon, polyester, polyolefin, nylon, polytetrafluoroethylene- ,
asbestos and other minerals, fiberglass and other, ceramics, steel
and other metals, and carbon. The publication also discloses the
use of pulp from KEVLAR.RTM. brand para-aramid fiber alone, or with
KEVLAR.RTM. brand para-aramid short staple, in friction materials
to replace a fraction of the asbestos volume, with the remainder of
the asbestos volume being replaced by fillers or other fibers.
[0007] U.S. Pat. No. 5,811,042 (to Hoiness) discloses a composite
friction or gasketing material made of a thermoset or thermoplastic
matrix resin, fiber reinforcing material, and substantially fibril
free aramid particles. Poly (p-phenylene terephthalamide) and
poly(m-phenylene isophthalamide) are preferred fiber reinforcing
materials, and the fibers can be in the form of floc or pulp.
[0008] U.S. Patent Application 2003/0022961 (to Kusaka et al.)
discloses friction materials made from a friction modifier, a
binder and a fibrous reinforcement made of a mixture of (a) a dry
aramid pulp and (b) wet aramid pulp, wood pulp or acrylic pulp. Dry
aramid pulp is defined as an aramid pulp obtained by "the dry
fibrillation method". The dry fibrillation method is dry milling
the aramid fibers between a rotary cutter and a screen to prepare
the pulp. Wet aramid pulp is defined as an aramid pulp obtained by
"the wet fibrillation method". The wet fibrillation method is
milling short aramid fibers in water between two rotary discs to
form fibrillated fibers and then dehydrating the fibrillated
fibers, i.e., the pulp. Kusaka et al further disclose a method of
mix-fibrillating fibers by first mixing plural types of organic
fibers that fibrillate at a definite ratio, and then fibrillating
the mixture to produce a pulp.
[0009] There is an ongoing need to provide alternative reinforcing
materials that both perform well in products, such as seals and
friction applications, and that are low in cost. Despite the
numerous disclosures proposing lower cost alternative reinforcement
materials, many of these proposed products do not adequately
perform in use, cost significantly more than currently commercial
products, or have other negative attributes. As such, there remains
a need for reinforcement materials that exhibit high wear and heat
resistance, and that are comparable or less expensive than other
commercially available reinforcement materials.
BRIEF SUMMARY OF THE INVENTION
[0010] The invention relates to a first embodiment of a process for
making an acrylic and para-aramid pulp for use as reinforcement
material, comprising:
[0011] (a) combining pulp ingredients including:
[0012] (1) acrylic fiber comprising acrylonitrile units which are
at least 85 wt % of the total acrylic fiber, the fiber being 10 to
90 wt % of the total solids in the ingredients, and having an
average length of no more than 10 cm;
[0013] (2) para-aramid fiber being 10 to 90 wt % of the total
solids in the ingredients, and having an average length of no more
than 10 cm; and
[0014] (3) water being 95 to 99 wt % of the total ingredients;
[0015] (b) mixing the ingredients to a substantially uniform
slurry;
[0016] (c) co-refining the slurry by simultaneously:
[0017] (1) fibrillating, cutting and masticating the acrylic fiber
and the para-aramid fiber to irregularly shaped fibrillated fibrous
structures with stalks and fibrils; and
[0018] (2) substantially uniformly dispersing all solids in the
refined slurry; and
[0019] (d) removing water from the refined slurry to no more than
60 total wt % water,
[0020] thereby producing an acrylic and para-aramid pulp with the
acrylic and the para-aramid fibrous structures having an average
maximum dimension of no more than 5 mm, a length-weighted average
of no more than 1.3 mm, and the acrylic fibrils and/or stalks are
substantially entangled with the para-aramid fibrils and/or
stalks.
[0021] The invention is further related to a second embodiment of a
process for making an acrylic and para-aramid pulp for use as
reinforcement material, comprising:
[0022] (a) combining ingredients including water and a first fiber
from the group consisting of:
[0023] (1) acrylic fiber comprising acrylonitrile units which are
at least 85 wt % of the total acrylic fiber, the fiber being 10 to
90 wt % of the total solids in the ingredients; and
[0024] (2) para-aramid fiber being 10 to 90 wt % of the total
solids in the ingredients;
[0025] (b) mixing the ingredients to a substantially uniform
suspension;
[0026] (c) refining the suspension in a disc refiner thereby
cutting the fiber to have an average length of no more than 10 cm,
and fibrillating and masticating at least some of the fiber to
irregularly shaped fibrillated fibrous structures;
[0027] (d) combining ingredients including the refined suspension,
the second fiber of the group of (a)(1 and 2), and water, if
necessary, to increase the water concentration to 95-99 wt % of the
total ingredients;
[0028] (e) mixing the ingredients, if necessary, to form a
substantially uniform suspension;
[0029] (d) co-refining the mixed suspension by:
[0030] (1) fibrillating, cutting and masticating solids in the
suspension such that all or substantially all of the acrylic and
para-aramid fiber is converted to irregularly shaped fibrillated
acrylic and para-aramid fibrous structures with stalks and fibrils;
and
[0031] (2) substantially uniformly dispersing all solids in the
refined slurry; and
[0032] (h) removing water from the refined slurry to no more than
60 total wt % water,
[0033] thereby producing an acrylic and para-aramid pulp with the
acrylic and the para-aramid fibrous structures having an average
maximum dimension of no more than 5 mm, a length-weighted average
of no more than 1.3 mm, and the acrylic fibrils and/or stalks are
substantially entangled with the para-aramid fibrils and/or
stalks.
[0034] The invention is further directed to an acrylic and
para-aramid pulp for use as reinforcement material, comprising:
[0035] (a) irregularly shaped, acrylic fibrous structures
comprising acrylonitrile units which are at least 85 wt % of the
total acrylic fibrous structures and being 10 to 90 wt % of the
total solids;
[0036] (b) irregularly shaped, para-aramid fibrous structures being
10 to 90 wt % of the total solids; and
[0037] (c) water being 4 to 60 wt % of the entire pulp,
[0038] whereby the acrylic and the para-aramid fibrous structures
having an average maximum dimension of no more than 5 mm, a
length-weighted average of no more than 1.3 mm, and stalks and
fibrils where the acrylic fibrils and/or stalks are substantially
entangled with the para-aramid fibrils and/or stalks.
[0039] The invention is further directed to a friction material,
comprising a friction modifier; optionally at least one filler; a
binder; and a fibrous reinforcement material comprising the pulp of
the present invention.
[0040] Moreover, the invention is directed to a sealing material,
comprising a binder; optionally at least one filler; and a fibrous
reinforcement material comprising the pulp of the present
invention.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0041] The invention can be more fully understood from the
following detailed description thereof in connection with
accompanying drawings described as follows.
[0042] FIG. 1 is a block diagram of apparatus for performing a wet
process for making "wet" pulp in accordance with the present
invention.
[0043] FIG. 2 is a block diagram of apparatus for performing a dry
process for making "dry" pulp in accordance with the present
invention.
[0044] FIG. 3 is an image of a photomicrograph of para-aramid
particles used as an optional ingredient to the process of the
present invention.
[0045] FIG. 4 is an image of a photomicrograph of pulp made
according to the process of the present invention.
GLOSSARY
[0046] Before the invention is described, it is useful to define
certain terms in the following glossary that will have the same
meaning throughout this disclosure unless otherwise indicated.
[0047] "Fiber" means a relatively flexible, unit of matter having a
high ratio of length to width across its cross-sectional area
perpendicular to its length. Herein, the term "fiber" is used
interchangeably with the term "filament" or "end". The cross
section of the filaments described herein can be any shape, but are
typically circular or bean shaped. Fiber spun onto a bobbin in a
package is referred to as continuous fiber. Fiber can be cut into
short lengths called staple fiber. Fiber can be cut into even
smaller lengths called floc. Yarns, multifilament yarns or tows
comprise a plurality of fibers. Yarn can be intertwined and/or
twisted.
[0048] "Fibril" means a small fiber having a diameter as small as a
fraction of a micrometer to a few micrometers and having a length
of from about 10 to 100 micrometers. Fibrils generally extend from
the main trunk of a larger fiber having a diameter of from 4 to 50
micrometers. Fibrils act as hooks or fasteners to ensnare and
capture adjacent material. Some fibers fibrillate, but others do
not or do not effectively fibrillate and for purposes of this
definition such fibers do not fibrillate. Poly(para-phenylene
terephthalamide) fiber fibrillates readily upon abrasion, creating
fibrils. Acrylic fibers of this invention also fibrillate.
[0049] "Fibrillated fibrous structures" means particles of material
having a stalk and fibrils extending therefrom wherein the stalk is
generally columnar and about 10 to 50 microns in diameter and the
fibrils are hair-like members only a fraction of a micron or a few
microns in diameter attached to the stalk and about 10 to 100
microns long.
[0050] "Floc" means short lengths of fiber, shorter than staple
fiber. The length of floc is about 0.5 to about 15 mm and a
diameter of 4 to 50 micrometers, preferably having a length of 1 to
12 mm and a diameter of 8 to 40 micrometers. Floc that is less than
about 1 mm does not add significantly to the strength of the
material in which it is used. Floc or fiber that is more than about
15 mm often does not function well because the individual fibers
may become entangled and cannot be adequately and uniformly
distributed throughout the material or slurry. Aramid floc is made
by cutting aramid fibers into short lengths without significant or
any fibrillation, such as those prepared by processes described in
U.S. Pat. Nos. 3,063,966, 3,133,138, 3,767,756, and 3,869,430.
[0051] "Length-weighted average" means the calculated length from
the following formula: 1 Length-weightedaverage = [ (
Eachindividualpulplength ) 2 ] [ Eachindividualpulplength ]
[0052] "Maximum dimension" of an object means the straight distance
between the two most distal points from one another in the
object
[0053] "Staple fiber" can be made by cutting filaments into lengths
of no more than 15 cm, preferably 3 to 15 cm; and most preferably 3
to 8 cm. The staple fiber can be straight (i.e., non crimped) or
crimped to have a saw tooth shaped crimp along its length, with any
crimp (or repeating bend) frequency. The fibers can be present in
uncoated, or coated, or otherwise pretreated (for example,
pre-stretched or heat-treated) form.
DETAILED DESCRIPTION OF THE INVENTION
[0054] The invention is directed to processes for making an acrylic
and para-aramid pulp for use as reinforcement material. The
invention is also directed to acrylic and para-aramid pulp, that
can be made by the processes of the invention, for use as
reinforcement material. The invention is further directed to
products, such as sealing materials and friction materials,
incorporating the pulp of this invention, and processes for making
them.
I. First Embodiment of the Inventive Process
[0055] In a first embodiment, the process for making an acrylic and
para-aramid pulp comprises the following steps. First, pulp
ingredients are combined, added or contacted together. Second, the
combined pulp ingredients are mixed to a substantially uniform
slurry. Third, the slurry is simultaneously refined or co-refined.
Fourth, water is removed from the refined slurry.
Combining Step
[0056] In the combining step, the pulp ingredients are preferably
added together in a container. The pulp ingredients include (1)
acrylic fiber, (2) para-aramid fiber, (3) optionally substantially
or completely fibril-free, granular, para-aramid particles, (4)
optionally other minor additives, and (5) water.
[0057] Acrylic Fiber
[0058] The acrylic fiber is added to a concentration of 10 to 90 wt
% of the total solids in the ingredients, preferably 25 to 60 wt %
of the total solids in the ingredients, and most preferably 25 to
55 wt % of the total solids in the ingredients.
[0059] The acrylic fiber preferably has an average length of no
more than 10 cm, more preferably 0.5 to 5 cm, and most preferably
0.6 to 2 cm. Prior to combining the pulp ingredients together, any
acrylic fibers in the form of continuous filaments can be cut into
shorter fibers, such as staple fibers or floc.
[0060] Acrylic Polymer
[0061] The acrylic fiber useful in this invention includes
acrylonitrile units which are at least 85 wt % of the total acrylic
fiber. An acrylonitrile unit is --(CH2-CHCN)--. The acrylic fiber
can be made from acrylic polymers made up of 85% by weight or more
of acrylonitrile with 15% by weight or less of an ethylenic monomer
copolymerizable with acrylonitrile and mixtures of two or more of
these acrylic polymers. Examples of the ethylenic monomer
copolymerizable with acylonitrile include acylic acid, methacrylic
acid and esters thereof (methyl acrylate, ethyl acrylate, methyl
methacylate, ethyl methacrylate, etc.), vinyl acetate, vinyl
chloride, vinylidene chloride, acrylamide, methacylamide,
methacrylonitrile, allylsulfonic acid, methanesulfonic acid and
styrenesulfonic acid.
[0062] Para-Aramid Fiber
[0063] The para-aramid fiber is added to a concentration of 10 to
90 wt % of the total solids in the ingredients, preferably 40 to 75
wt % of the total solids in the ingredients, and most preferably 40
to 55 wt % of the total solids in the ingredients. The para-aramid
fiber preferably has a linear density of no more than 10 dtex, more
preferably 0.5 to 10 dtex, and most preferably, 0.8 to 2.5 dtex.
The para-aramid fiber also preferably has an average length along
its longitudinal axis of no more than 10 cm, more preferably an
average length of 0.65 to 2.5 cm, and most preferably an average
length of 0.65 to 1.25 cm.
[0064] Para-Aramid Particles
[0065] Optionally, in one embodiment, the pulp ingredients further
include substantially or completely fibril-free, granular,
para-aramid particles. If these particles are added, they are added
to a concentration of no more than 50 wt % of the total solids in
the ingredients, preferably 20 to 50 wt % of the total solids in
the ingredients, and most preferably 25 to 35 wt % of the total
solids in the ingredients. Being made of para-aramid, they
contribute superior wear resistance and dispersability to the pulp
being produced. Because the particles are substantially
fibril-free, they also serve as a compounding agent to assist in
dispersing the other ingredients in the mixture and slurry.
Particles that perform this function are often known as processing
agents or aids. The substantially or completely fibril-free,
granular, para-aramid particles have an average maximum dimension
of 50 to 2000 microns (0.05 to 2 mm), preferably 50 to 1500
microns, and most preferably 75 to 1000 microns. Particles below
about 50 microns, however, lose effectiveness in friction and
sealing applications. Particles above about 2000 microns do not
adequately stay dispersed in the water with the other ingredients
when mixed. FIG. 5 is an image of a photomicrograph of para-aramid
particles capable of being used as an ingredient to the process of
the present invention.
[0066] Aramid Polymer
[0067] Polymers suitable for use in making the aramid fiber and
aramid particles of this invention are synthetic aromatic
polyamides. The polymers must be of fiber-forming molecular weight
in order to be shaped into fibers. The polymers can include
polyamide homopolymers, copolymers, and mixtures thereof which are
predominantly aromatic, wherein at least 85% of the amide
(--CONH--) linkages are attached directly to two aromatic rings.
The rings can be unsubstituted or substituted. The polymers are
para-aramid when the two rings are para oriented with respect to
each other along the molecular chain. Preferably copolymers have no
more than 10 percent of other diamines substituted for a primary
diamine used in forming the polymer or no more than 10 percent of
other diacid chlorides substituted for a primary diacid chloride
used in forming the polymer. Additives can be used with the aramid;
and it has been found that up to as much as 13 percent by weight of
other polymeric material can be blended or bonded with the aramid.
The preferred para-aramids are poly(para-phenylene
terephthalamide)(PPD-T) and its copolymers.
[0068] Optional Other Additives
[0069] Other additives can optionally be added as long as they stay
suspended in solution in the mixing step and do not significantly
change the effect of the refining step on the mandatory solid
ingredients listed above. Suitable additives include pigments,
dyes, anti-oxidants, flame-retardant compounds, and other
processing and dispersing aids. Preferably, the pulp ingredients do
not include asbestos. In other words, the resulting pulp is
asbestos free or without asbestos.
[0070] Water
[0071] Water is added to a concentration of 95 to 99 wt % of the
total ingredients, and preferably 97 to 99 wt % of the total
ingredients. Further, the water can be added first. Then other
ingredients can be added at a rate to optimize dispersion in the
water while simultaneously mixing the combined ingredients.
Mixing Step
[0072] In the mixing step, the ingredients are mixed to a
substantially uniform slurry. By "substantially uniform" is meant
that random samples of the slurry contain the same wt % of the
concentration of each of the starting ingredients as in the total
ingredients in the combination step plus or minus 10 wt %,
preferably 5 wt % and most preferably 2 wt %. For instance, if the
concentration of the solids in the total mixture is 50 wt % acrylic
fiber plus 50 wt % para-aramid fiber, then a substantially uniform
mixture in the mixing step means each random sample of the slurry
has (1) a concentration of the acrylic fiber of 50 wt % plus or
minus 10 wt %, preferably 5 wt % and most preferably 2 wt % and (2)
a concentration of para-aramid fiber of 50 wt % plus or minus 10 wt
%, preferably 5 wt % and most preferably 2 wt %. The mixing can be
accomplished in any vessel containing rotating blades or some other
agitator. The mixing can occur after the ingredients are added or
while the ingredients are being added or combined.
Refining Step
[0073] In the refining step the pulp ingredients are simultaneously
co-refined, converted or modified as follows. The acrylic fiber and
the para-aramid fiber are fibrillated, cut and masticated to
irregularly shaped fibrous structures having stalks and fibrils. If
para-aramid particles are added with the other ingredients, at
least some of the para-aramid particles are masticated into
smaller, rounder, substantially fibril-free, particles. All solids
are dispersed such that the refined slurry is substantially
uniform. "Substantially uniform" is as defined above. The refining
step preferably comprises passing the mixed slurry through one or
more disc refiner, or recycling the slurry back through a single
refiner. By the term "disc refiner" is meant a refiner containing
one or more pair of discs that rotate with respect to each other
thereby refining ingredients by the shear action between the discs.
In one suitable type of disc refiner, the slurry being refined is
pumped between closely spaced circular rotor and stator discs
rotatable with respect to one another. Each disc has a surface,
facing the other disc, with at least partially radially extending
surface grooves. A preferred disc refiner that can be used is
disclosed in U.S. Pat. No. 4,472,241. If necessary for uniform
dispersion and adequate refining, the mixed slurry can be passed
through the disc refiner more than once or through a series of at
least two disc refiners. When the mixed slurry is refined in only
one refiner, there is a tendency for the resulting slurry to be
inadequately refined and non uniformly dispersed. Conglomerates or
aggregates entirely or substantially of one solid ingredient, or
the other, or both, or all three if three are present, can form
rather than being dispersed forming a substantially uniform
dispersion. Such conglomerates or aggregates have a greater
tendency to be broken apart and dispersed in the slurry when the
mixed slurry is passed through the refiner more than once or passed
through more than one refiner.
[0074] Because a substantially uniform slurry containing multiple
ingredients is co-refined in this step of the process, any one type
of non-pulp ingredient (for example, para-aramid fiber) is refined
into a pulp in the presence of all the other types of non-pulp
ingredients (for example, aramid material pieces and optionally
para-aramid particles) while those other ingredients are also being
refined. This co-refining of non-pulp ingredients forms a pulp that
is superior to a pulp blend generated by merely mixing two pulps
together. Adding two pulps and then merely mixing them together
does not form the substantially uniform, intimately connected,
fibrous components of the pulp generated by co-refining of non-pulp
ingredients into pulp in accordance with the present invention.
Removing Step
[0075] Then water is removed from the refined slurry to no more
than 60 total wt % water, preferably 4 to 60 total wt % water, most
preferably, 5 to 58 total wt % water. The water can be removed by
collecting the pulp on a dewatering device such as a horizontal
filter, and if desired, additional water can be removed by applying
pressure or squeezing the pulp filter cake. The dewatered pulp can
optionally then be dried to a desired moisture content, and/or can
be packaged or wound up on rolls.
FIGS. 1 and 2
[0076] This process will now be described in reference to FIGS. 1
and 2. Throughout this detailed description, similar reference
characters refer to similar elements in all figures of the
drawings.
[0077] Referring to FIG. 1, there is a block diagram of an
embodiment of a wet process for making "wet" pulp in accordance
with the present invention. Pulp ingredients 1 are added to
container 2. Container 2 is provided with an internal mixer,
similar to a mixer in a washing machine. The mixer disperses the
ingredients into the water creating the substantially uniform
slurry. The mixed slurry is transferred to a first refiner 3 which
refines the slurry. Then, optionally, the refined slurry can be
transferred to a second refiner 4, and optionally then to a third
refiner 5. Three refiners are illustrated but any number of
refiners can be used depending on the degree of uniformity and
refining desired. After the last refiner in the series of refiners,
the refined slurry is optionally transferred to a filter or sorter
6 that allows slurry with dispersed solids below a chosen mesh or
screen size to pass and recirculates dispersed solids larger than a
chosen mesh or screen size back to one or more of the refiners such
as through line 7 or to a refiner 8 dedicated to refine this
recirculated slurry from which refined slurry is again passed to
the filter or sorter 6. Suitably refined slurry passes from the
filter or sorter 6 to a horizontal water vacuum filter 9 which
removes water such that the pulp has a concentration of water of no
more than 75 wt % of the total ingredients. Slurry can be
transferred from point to point by any conventional method and
apparatus such as with the assistance of one or more pump 10. Then
the pulp is conveyed to a dryer 11 that removes more water until
the pulp has a concentration of water of no more than 60 wt % of
the total ingredients. Then the refined pulp is packaged in a baler
12.
[0078] Referring to FIG. 2, there is a block diagram of an
embodiment of a dry process for making "dry" pulp in accordance
with the present invention. This dry process is the same as the wet
process except after the horizontal water vacuum filter 9. After
that filter, the pulp goes through a press 13 which removes more
water until the pulp has a concentration of water of no more than
20 wt % of the total ingredients. Then the pulp goes through a
fluffer 14 to fluff the pulp and then a rotor 15 to remove more
water. Then, like the wet process, the pulp is passed through a
dryer 11 and packaged in a baler 12.
II. Second Embodiment of the Inventive Process
[0079] In a second embodiment, the process for making the acrylic
fiber and para-aramid pulp is the same as the first embodiment of
the process described above with the following differences.
[0080] Prior to combining all ingredients together, either the
acrylic fiber or the para-aramid fiber, or both the acrylic fiber
and the para-aramid fiber, may need to be shortened. This is done
by combining water with the fiber ingredient. Then the water and
fiber are mixed to form a first suspension and processed through a
first disc refiner to shorten the fiber. The disc refiner cuts the
fiber to an average length of no more than 10 cm. The disc refiner
will also partially fibrillate and partially masticate the fiber.
The other fiber, that was not previously added, can be shortened
this way too forming a second processed suspension. Then the other
fiber (or the second suspension, if processed in water) is combined
with the first suspension.
[0081] More water is added before or after, or when, other
ingredients are added, if necessary, to increase the water
concentration to 95-99 wt % of the total ingredients. After all
ingredients are combined, they can be mixed, if necessary, to
achieve a substantially uniform slurry.
[0082] The ingredients in the slurry are then co-refined together,
i.e., simultaneously. This refining step includes fibrillating,
cutting and masticating solids in the suspension such that all or
substantially all of the acrylic and para-aramid fiber is converted
to irregularly shaped fibrillated fibrous structures. This refining
step also disperses all solids such that the refined slurry is
substantially uniform. Then water is removed as in the first
embodiment of the process. Both processes produce the same or
substantially the same acrylic and para-aramid pulp.
The Inventive Pulp
[0083] The resulting product produced by the process of this
invention is an acrylic and para-aramid pulp for use as
reinforcement material in products. The pulp comprises (a)
irregularly shaped, acrylic fibrous structures, (b) irregularly
shaped, para-aramid fibrous structures, (c) optionally
substantially fibril-free, granular, para-aramid particles, (d)
optionally other minor additives, and (e) water.
[0084] The concentration of the separate ingredient components in
the pulp correspond, of course, to the concentrations described
beforehand of the corresponding ingredients used in making the
pulp.
[0085] The irregularly shaped, acrylic and para-aramid fibrillated
fibrous structures have stalks and fibrils. The acrylic fibrils
and/or stalks are substantially entangled with the para-aramid
fibrils and/or stalks. The fibrils are important and act as hooks
or fasteners or tentacles which adhere to and hold adjacent
particles in the pulp and final product thereby providing integrity
to the final product.
[0086] The acrylic and para-aramid fibrillated fibrous structures
preferably have an average maximum dimension of no more than 5 mm,
more preferably 0.1 to 4 mm, and most preferably 0.1 to 3 mm. The
acrylic and para-aramid fibrillated fibrous structures preferably
have a length-weighted average of no more than 1.3 mm, more
preferably 0.7 to 1.2 mm, and most preferably 0.75 to 1.1 mm.
[0087] If para-aramid particles are included in the pulp, the
acrylic and para-aramid fibrous structures also additionally
contact and are wrapped partially around at least some of these
rounder, substantially fibril-free, para-aramid particles. These
para-aramid particle also preferably have a dimension of at least
50 microns, more preferably, 50 to 100 microns, and most preferably
50 to 75 microns. Fibrils on and along the acrylic and para-aramid
fibrous structures can contact and form a partial cocoon around the
rounder, substantially fibril-free, para-aramid particles
[0088] The acrylic and para-aramid pulp is without substantial
aggregates or conglomerates of the same material. Further, the pulp
has a Canadian Standard Freeness (CSF) as measured per TAPPI test T
227 om-92, which is a measure of its drainage characteristics, of
100 to 700 ml, and preferably 250 to 450 ml.
[0089] Surface area of pulp is a measure of the degree of
fibrillation and influences the porosity of the product made from
the pulp. Preferably, the surface area of pulp of this invention is
7 to 11 square meters per gram.
[0090] FIG. 4 is an image of a photomicrograph of acrylic and
para-aramid pulp made according to the process of the present
invention.
[0091] It is believed that aramid particles and fibrous structures,
dispersed substantially homogeneously throughout the reinforcement
material, and the friction and sealing materials, provide, by
virtue of the high temperature characteristics of the para-aramid
polymers and the fibrillation propensity of the para-aramid fibers,
many sites of reinforcement and increased wear resistance. When
co-refined, the blending of the acrylic and para-aramid materials
is so intimate that in a friction or sealing material there is
always some para-aramid fibrous structures close to the acrylic
structures, so the stresses and abrasion of service are always
shared.
Sealing Material
[0092] The invention is further directed to sealing material and
processes for making the sealing materials. Sealing materials are
used in or as a barrier to prevent the discharge of fluids and/or
gases and used to prevent the entrance of contaminants where two
items are joined together. An illustrative use for sealing material
is in gaskets. The sealing material comprises a binder; optionally
at least one filler; and a fibrous reinforcement material
comprising the acrylic and para-aramid pulp of this invention.
Suitable binders include nitrile rubber, butadiene rubber,
neoprene, styrene-butadiene rubber, nitrile-butadiene rubber, and
mixtures thereof. The binder can be added with all other starting
materials. The binder is typically added in the first step of the
gasket production process, in which the dry ingredients are mixed
together. Other ingredients optionally include uncured rubber
particles and a rubber solvent, or a solution of rubber in solvent,
to cause the binder to coat surfaces of the fillers and pulp.
Suitable fillers include barium sulfate, clays, talc, and mixtures
thereof.
[0093] Suitable processes for making sealing materials are, for
example, a beater-add process or wet process where the gasket is
made from a slurry of materials, or by what is called a calendering
or dry process where the ingredients are combined in an elastomeric
or rubber solution.
Friction Material
[0094] The pulp of the present invention can be used as a
reinforcement material in friction materials. By "friction
materials" is meant materials used for their frictional
characteristics such as coefficient of friction to stop or transfer
energy of motion, stability at high temperatures, wear resistance,
noise and vibration damping properties, etc. Illustrative uses for
friction materials include brake pads, brake blocks, dry clutch
facings, clutch face segments, brake pad backing/insulating layers,
automatic transmission papers, and friction papers.
[0095] In view of this new use, the invention is further directed
to friction material and processes for making the friction
material. Specifically, the friction material comprises a friction
modifier; optionally at least one filler; a binder; and a fibrous
reinforcement material comprising the acrylic and para-aramid pulp
of this invention. Suitable friction modifiers are metal powders
such as iron, copper and zinc; abrasives such as oxides of
magnesium and aluminum; lubricants, such as synthetic and natural
graphites, and sulfides of molybdenum and zirconium; and organic
friction modifiers such as synthetic rubbers and cashew nut shell
resin particles. Suitable binders are thermosetting resins such as
phenolic resins (i.e., straight (100%) phenolic resin and various
phenolic resins modified with rubber or epoxy), melamine resins,
epoxy resins and polyimide resins, and mixtures thereof. Suitable
fillers include barite, calcium carbonate, wollastonite, talc,
various clays, and mixtures thereof.
[0096] The actual steps for making the friction material can vary,
depending on the type of friction material desired. For example,
methods for making molded friction parts generally involve
combining the desired ingredients in a mold, curing the part, and
shaping, heat treating and grinding the part if desired. Automotive
transmission and friction papers generally can be made by combining
the desired ingredients in a slurry and making a paper on a paper
machine using conventional paper making processes.
Test Methods
[0097] The following test methods were used in the following
Examples.
[0098] Canadian Standard Freeness (CSF) is a well-known measure of
the facility for water to drain from a slurry or dispersion of
particles. Freeness is determined by TAPPI test T227. Data obtained
from conduct of that test are expressed as Canadian Freeness
Numbers, which represent the milliliters of water which drain from
an aqueous slurry under specified conditions. A large number
indicates a high freeness and a high tendency for water to drain. A
low number indicates a tendency for the dispersion to drain slowly.
The freeness is inversely related to the degree of fibrillation of
the pulp, since greater numbers of fibrils reduce the rate at which
water drains through a forming paper mat.
[0099] Length-weighted average is measured using a "FiberExpert"
tabletop analyzer (also now known as "PulpExpertFS", available from
Metso Automation of Helsinki, Finland). This analyzer takes
photographic images of the pulp with a digital CCD camera as the
pulp slurry flows through the analyzer and then an integrated
computer analyzes the fibers in these images and calculates their
length-weighted average.
[0100] Temperature: All temperatures are measured in degrees
Celsius (.degree. C.).
[0101] Denier is measured according to ASTM D 1577 and is the
linear density of a fiber as expressed as weight in grams of 9000
meters of fiber.
[0102] The denier is measured on a Vibroscope from Textechno of
Munich, Germany. Denier times (10/9) is equal to decitex
(dtex).
EXAMPLES
[0103] This invention will now be illustrated by the following
specific examples. All parts and percentages are by weight unless
otherwise indicated. Examples prepared according to the process or
processes of the current invention are indicated by numerical
values.
Example 1
[0104] In this example of the invention, the pulp of this invention
was produced from a feedstock of para-aramid fiber and acrylic
staple. Acrylic staple having a cut length of 2 inches and having a
filament linear density of 3 dpf (3.3 dtex per filament) was
obtained from Solutia, Inc., with offices in St. Louis, Mo.
Para-aramid fiber in the form of commercially available KEVLAR.RTM.
brand floc, Style 1F178, having a 1/4" cut length, was obtained
from E. I. de Pont de Nemours and Company with offices in
Wilmington, Del.
[0105] Acrylic staple and water together were fed directly into a
Sprout-Waldron 12" Single Disc Refiner using a 10 mil plate gap
setting and pre-pulped to reach an acceptable processing length in
the range of 13 mm.
[0106] The pre-pulped acrylic fiber and the cut para-aramid fiber
plus water were then combined into a highly agitated mixing tank at
a solids concentration of 50 wt % para-aramid fiber and 50 wt %
acrylic staple and mixed to form a uniform, pumpable slurry of
about 2-3 wt % of the total ingredients concentration. The slurry
was then recirculated and co-refined through a Sprout-Waldron 12"
Single Disc Refiner.
[0107] The refiner simultaneously:
[0108] (1) fibrillated, cut, and masticated both the para-aramid
fiber and the acrylic staple to irregularly shaped fibrous
structures having stalks and fibrils.
[0109] (2) dispersed all solids such that the refined slurry was
substantially uniform, substantially uniform being as previously
defined.
[0110] This refined slurry was then filtered using a filter bag and
was dewatered through pressing and placed in large ZIPLOC.RTM. type
storage bags. The fibrous structures had an average maximum
dimension of no more than 5 mm and a length-weighted average of no
more than 1.3 mm, as measured by FiberExpert.RTM..
Example 2
[0111] This example illustrates another method by which a
co-refined pulp can be made from a feedstock of para-aramid fiber
and acrylic fiber. Acrylic staple, having a cut length of 2 inches
and having a filament linear density of 3 dpf (3.3 dtex per
filament) available from Solutia, Inc., is cut with a guillotine
cutter two to three times at right angles in order to produce a
random-length fiber with most fibers shorter than 3/4 inch (1.91
cm) and averaging about 1/2 inch (1.27 cm) long.
[0112] Para-aramid fiber in the form of commercially available
KEVLAR.RTM. brand multifilament yarn, available from E. I. de Pont
de Nemours and Company on bobbins, is prepared by cutting the
para-aramid yarn to a nominal 1/2 inch (1.27 cm) cut length on a
Lummus Cutter (available from Lummus Industries with offices in
Columbus, Ga.). Other KEVLAR.RTM. brand para-aramid fiber, which
initially is not on bobbins and is of multiple long lengths, is cut
by a guillotine cutter two to three times at right angles in order
to produce a random-length fiber with most fibers shorter than 3/4
inch (1.91 cm) and averaging about 1/2 inch (1.27 cm) long.
[0113] The two ingredients prepared as described above plus water
are then combined into a highly agitated mixing tank called a
hydrapulper at a solids concentration of 50 wt % para-aramid fiber
and 50 wt % acrylic fiber and mixed to form a substantially
uniform, pumpable slurry having a total solids concentration of
about 2-3 wt % of the total ingredients. The slurry is pumped
through a series of three refiners, as described in U.S. Pat. No.
4,472,241. The refiners simultaneously:
[0114] (1) fibrillate, cut, and masticate the acrylic fiber and the
para-aramid fiber into irregularly shaped fibrous structures having
stalks and fibrils; and
[0115] (2) disperse all solids such that the refined slurry was
substantially uniform with substantially uniform as previously
defined.
[0116] This refined slurry is then dewatered using a horizontal
filter and dried in an oven to a desired moisture content of 50
total wt % for wet pulp. The wet pulp is then packaged into bales
by a baler. When measured by FiberExpert.RTM., all of the
ingredients in the pulp have a length-weighted average of no more
than 1.3 mm.
Example 3
[0117] This example illustrates further process steps and another
embodiment of the pulp of this invention. The procedure of Example
2 is followed. However, after the pulp is dewatered on the
horizontal filter, the pulp is pressed in a mechanical press to
further remove water; and the pulp is then fluffed using a Fluffer
(available from Bepex Corporation with offices at Santa Rosa,
Calif.) to better separate the pressed wet pulp. The fluffed wet
pulp is then dried in an oven to approximately 8 total wt %
moisture and is then further processed in an ultrarotor (model IIIA
available from Altenburger Machinen Jackering GmbH with offices in
Voisterhauser, Germany) such as is disclosed in U.S. Pat. No.
5,084,136 to further fluff and disperse the dried pulp. The dried
pulp is then packaged into bales. When measured by
FiberExpert.RTM., all of the ingredients in the pulp have a
length-weighted average of no more than 1.3 mm.
Example 4
[0118] This example illustrates another embodiment of the pulp of
this invention. The process of Example 2 is followed with the
exception that one third by weight of the para-aramid fiber is
replaced by para-aramid particles. The para-aramid resin particles
are prepared by reacting para-phenylenediamine and teraphthaloyl
chloride continuously in a screw extruder as is generally disclosed
in U.S. Pat. No. 3,884,881, but using N, methyl pyrollidone/calcium
chloride as the solvent, producing a crumb-like polymer that
precipitates from the solvent. The solvent is extracted, and the
polymer crumb washed and dried to a particulate powder of mixed
particle size. The para-aramid resin particles are then treated
substantially the same as the para-aramid fiber is treated in
Example 2. However, the refiner not only refines the fibers but
also cuts and/or masticates the para-aramid particles into rounder,
substantially fibril-free particles. After dewatering, some of the
resulting pulp having a moisture content of 50 total wt percent is
then packaged into bales. The remainder of the resulting pulp is
further pressed to a moisture content of approximately 8 total wt
percent and then fluffed, dispersed, and packaged as in Example 3.
When measured by FiberExpert.RTM., all of the ingredients in the
pulp have a length-weighted average of no more than 1.3 mm.
Example 5
[0119] Disc brake pads incorporating the pulp of this invention
were made in the following manner. Approximately 20 kilograms of a
non-asbestos-containing base compound powder comprising a mixture
of 7 wt % cashew nut shell resin, 17 wt % inorganic fillers, 21 wt
% graphite, coke and lubricants, 18 wt % inorganic abrasives, and
16 wt % soft metals was mixed together for 10 to 20 minutes in a
50-liter Littleford mixer. The mixer had two high-speed choppers
with blades of the "stars and bars" configuration and a slower
rotating plough.
[0120] 5 kilograms of the well-blended base compound powder was
then combined with the pulp of this invention (a co-refined pulp
being 50 wt % para-aramid and 50 wt % acrylic fiber) in an amount
of 3.8 wt %, based on the combined weight of the compound powder
and the pulp. The pulp was then dispersed in the base compound
powder by mixing for an additional 5 to 10 minutes. Once mixed, the
resulting brake pad composition had a normal visual appearance with
the fiber well dispersed in and completely coated with the base
compound powders, with essentially no detectable balling up of the
pulp or segregation of any constituents.
[0121] The brake pad composition was then poured into a
single-cavity steel mold for a front disc brake pad and cold
pressed to a standard thickness of about 5/8 inch (16 mm) then
removed from the mold to form a pre-formed brake pad having an
approximate weight of 200 grams. The pre-form had no excessive
spring-back or swelling, and was robust enough to endure normal
handling without damage. Twelve replicate pre-forms were made. The
pre-forms were then placed in two multi-cavity molds, placed in a
commercial press, and press-cured (the binder phenolic
cross-linking and reacting) at 300.degree. F. (149.degree. C.) for
about 15 minutes, with periodic pressure release to allow phenolic
reaction gases to escape, followed by lightly constrained oven
curing at 340.degree. F. (171.degree. C.) for 4 hours to complete
the phenolic binder crosslinking. The cured, molded pad was then
ground to the desired thickness of about half an inch (13 mm). When
compared visually with a commercial brake pad containing an
equivalent amount of all para-aramid pulp or acrylic pulp, the test
pad was indistinguishable and had good compound flow into the
backing plate holes and no edge chipping.
[0122] A sample of the brake pad incorporating the pulp of this
invention was then tested to determine its frictional performance.
Coupons, typically one inch by one inch and about {fraction (3/16)}
inch (5 mm) thick, from test pads were assessed on the Chase
Machine available from Link Engineering, Detroit, Mich., using test
protocol Society of Automotive Engineers (SAE) J661 to determine
the hot and cold friction coefficient during constant pressure and
controlled temperature drag tests against a heated steel drum. The
sample was periodically measured for wear (thickness loss). This
was repeated with two more test samples cut from other replicate
pads. The samples of the brake pad incorporating the pulp of this
invention exhibited hot and cold friction performance substantially
equivalent to commercially available pads containing a
substantially equivalent amount of all para-aramid pulp. The test
further indicated the pad-to-pad uniformity and an average friction
rating was also substantially equivalent.
[0123] The pad was then tested for friction and wear under various
braking conditions using a dynamometer (single piston dynamometer
with a rolling radius of 289.0 mm at Link Testing Laboratories,
Inc., in Detroit, Mich.) using test protocol J2681 (ISO-SWG4). This
test was comprised of seventeen scenarios of from 5 to 200 brake
applications each, and measured coefficient of friction as a
function of applied brake pressure, temperature, braking speed and
deceleration rate. This test also had two high-temperature fade
sections, during which the brake pad was subjected to increasingly
high initial temperatures during constant deceleration, and reached
temperatures exceeding 600.degree. C. Wear was measured as the
reduction in thickness and weight of the pad at the end of the test
(608 brake applications.) Results for the pads made with the
compound of this example showed very little fade and what fade
there was recovered well (where fade is defined as the loss of
friction at the highest temperature brake applications), acceptable
coefficient of friction of 0.25 to 0.4 in non-fade sections,
absence of pad surface cracking, and acceptable wear rates for both
the pad and the rotor.
Example 6
[0124] This example illustrates how the pulp of this invention can
be incorporated into a beater-add gasket for sealing applications.
Water, rubber, latex, fillers, chemicals, and the pulp of this
invention are combined in desired amounts to form a slurry. On a
circulating wire sieve (such as a paper machine screen or wire),
the slurry is largely drained of its water content, is dried in a
heating tunnel, and is vulcanized on heated calender rolls to form
a material having a maximum thickness of around 2.0 mm. This
material is compressed in a hydraulic press or two-roll calender,
which increases the density and improves sealability.
[0125] Such beater-add gasket materials generally do not have as
good sealability as equivalent compressed-fiber materials and are
best suited for moderate-pressure high-temperature applications.
Beater-add gaskets find applicability in the making of auxiliary
engine gaskets or, after further processing, cylinder head gaskets.
For this purpose, the semi-finished product is laminated onto both
sides of a spiked metal sheet and is physically fixed in place by
the spikes.
Example 7
[0126] This example illustrates how the pulp of this invention can
be incorporated into a gasket made by a calendering process. The
same ingredients as in Example 6, minus the water, are thoroughly
dry mixed together and are then blended with a rubber solution
prepared using an appropriate solvent.
[0127] After mixing, the compound is then generally conveyed
batchwise to a roll calender. The calender consists of a small roll
that is cooled and a large roll that is heated. The compound is fed
and drawn into the calender nip by the rotary movement of the two
rolls. The compound will adhere and wrap itself around the hot
lower roll in layers generally about 0.02 mm thick, depending on
the pressure, to form a gasketing material made from the built-up
compound layers. In so doing, the solvent evaporates and
vulcanization of the elastomer commences.
[0128] Once the desired gasketing material thickness is reached,
the rolls are stopped and the gasketing material is cut from the
hot roll and cut and/or punched to the desired size. No additional
pressing or heating is required, and the material is ready to
perform as a gasket. In this manner gaskets up to about 7 mm thick
can be manufactured. However, most gaskets made in this manner are
much thinner, normally being about 3 mm or less in thickness.
* * * * *