U.S. patent application number 15/968480 was filed with the patent office on 2018-10-11 for fiber reinforced thermoset composites and methods of making.
The applicant listed for this patent is JOHNS MANVILLE. Invention is credited to Jawed Asrar, Klaus Friedrich Gleich, Asheber Yohannes, Mingfu Zhang.
Application Number | 20180291161 15/968480 |
Document ID | / |
Family ID | 52469614 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180291161 |
Kind Code |
A1 |
Zhang; Mingfu ; et
al. |
October 11, 2018 |
FIBER REINFORCED THERMOSET COMPOSITES AND METHODS OF MAKING
Abstract
Methods of making a fiber-reinforced composite are described.
The methods may include applying a sizing composition to a
plurality of fibers to make sized fibers, where the sizing
composition may include at least one of a curing agent or an
accelerator for a resin composition. The sized fibers may be
contacted with the resin composition to form a resin-fiber amalgam,
where the resin composition includes 50 wt. % or less of a total
amount of the curing agent and the accelerator that is also present
on the sized fibers. The resin-fiber amalgam may then be cured to
form the fiber-reinforced composite.
Inventors: |
Zhang; Mingfu; (Highlands
Ranch, CO) ; Asrar; Jawed; (Englewood, CO) ;
Yohannes; Asheber; (Littleton, CO) ; Gleich; Klaus
Friedrich; (Nuremberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JOHNS MANVILLE |
Denver |
CO |
US |
|
|
Family ID: |
52469614 |
Appl. No.: |
15/968480 |
Filed: |
May 1, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15639906 |
Jun 30, 2017 |
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15968480 |
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14172947 |
Feb 5, 2014 |
9725563 |
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15639906 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 5/08 20130101; C08J
5/06 20130101; C08J 3/242 20130101; C08J 2363/00 20130101 |
International
Class: |
C08J 5/08 20060101
C08J005/08; C08J 3/24 20060101 C08J003/24; C08J 5/06 20060101
C08J005/06 |
Claims
1. A treated fiber comprising: an organic or inorganic fiber; a
curing agent contacting a surface of the organic or inorganic
fiber; and an accelerator contacting the surface of the organic or
inorganic fiber.
2. The treated fiber of claim 1, wherein the organic or inorganic
fiber is a glass fiber.
3. The treated fiber of claim 2, wherein the glass fiber is made of
glass selected from the group consisting of E-glass, A-glass,
C-glass, S-glass, ECR-glass, and T-glass.
4. The treated fiber of claim 1, wherein the curing agent comprises
one or more epoxy resin curing agents selected from the group
consisting of an aliphatic amine, a cycloaliphatic amine, an
aromatic amine, a polyamide, an amidoamine, a polyol, an acid
anhydride, dicyandiamide, guanidine, and a formaldehyde resin.
5. The treated fiber of claim 1, wherein the accelerator comprises
one or more epoxy resin curing accelerators selected from the group
consisting of an alcohol, a carboxylic acid, an amine, a urea
compound, and a Lewis acid.
6. The treated fiber of claim 1, wherein the treated fiber further
comprises a film former.
7. The treated fiber of claim 1, wherein the treated fiber is
operable for incorporation in a fiber-reinforced composite.
8. The treated fiber of claim 7, wherein the fiber-reinforced
composite is an epoxy-containing composite.
9. The treated fiber of claim 8, wherein the epoxy-containing
composite is formed from an epoxy resin selected from the group
consisting of a diglycidyl ether of bisphenol A, a diglycidyl ether
of bisphenol F, an aliphatic epoxy resin, a cycloaliphatic epoxy
resin, a glycidyl epoxy resin, a glycidylamine epoxy resin, an
epoxy phenol novolac, and an epoxy cresol novolac.
10. The treated fiber of claim 9, wherein the epoxy resin comprises
a diglycidyl ether of bisphenol A.
11. A plurality of treated fibers comprising: at least two
different types of fibers selected from the group consisting of
glass fibers, mineral fibers, carbon fibers, and organic polymer
fibers; a curing agent contacting surfaces of at least one of the
at least two different types of fibers; and an accelerator
contacting the surfaces of at least one of the at least two
different types of fibers.
12. The plurality of treated fibers of claim 11, wherein the at
least two different types of fibers comprise glass fibers and
organic polymer fibers.
13. The plurality of treated fibers of claim 11, wherein the curing
agent comprises one or more epoxy resin curing agents selected from
the group consisting of an aliphatic amine, a cycloaliphatic amine,
an aromatic amine, a polyamide, an amidoamine, a polyol, an acid
anhydride, dicyandiamide, guanidine, and a formaldehyde resin.
14. The plurality of treated fibers of claim 11, wherein the
accelerator comprises one or more epoxy resin curing accelerators
selected from the group consisting of an alcohol, a carboxylic
acid, an amine, a urea compound, and a Lewis acid.
15. The plurality of treated fibers of claim 11, wherein at least
one of the at least two different types of fibers further comprise
a film former.
16. The plurality of treated fibers of claim 11, wherein the at
least two different types of fibers are operable for incorporation
in a fiber-reinforced composite.
17. The plurality of treated fibers of claim 16, wherein the
fiber-reinforced composite is an epoxy-containing composite.
18. The plurality of treated fibers of claim 17, wherein the
epoxy-containing composite is formed from an epoxy resin selected
from the group consisting of a diglycidyl ether of bisphenol A, a
diglycidyl ether of bisphenol F, an aliphatic epoxy resin, a
cycloaliphatic epoxy resin, a glycidyl epoxy resin, a glycidylamine
epoxy resin, an epoxy phenol novolac, and an epoxy cresol
novolac.
19. The plurality of treated fibers of claim 18, wherein the epoxy
resin comprises a diglycidyl ether of bisphenol A.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of pending U.S.
application Ser. No. 15/639,906 filed Jun. 30, 2017, which is a
division of U.S. application Ser. No. 14/172,947, filed Feb. 5,
2014. now U.S. Pat. No. 9,725,563 issued Aug. 8, 2017.
BACKGROUND OF THE INVENTION
[0002] Thermoset resins have been used in many varieties of
fiber-reinforced composites to make parts and articles used in
automobiles, aircraft, watercraft, wind turbines, construction
materials, and many other types of equipment. Prior to curing, many
of these resin compositions have relatively low viscosity, making
them easy to mix with glass fibers and pellets to form a curable
amalgam that is hardened into the final fiber-reinforced
composite.
[0003] Typically, the resin compositions include polymerizable
organic compounds and one or more agents that facilitate the
polymerization of the organic compounds under curing conditions. In
many instances, the agents are mixed with the polymerizable organic
compounds just before the resin composition is introduced to the
fibers. When the agents are mixed too early with the polymerizable
organic compounds, they tend to cure prematurely and have to be
discarded. In other words, the curable resin composition that
includes both the polymerizable organic compounds and the requisite
polymerization agents tend to have a relatively short shelf life or
pot life.
[0004] In many instances, even if the pot life of the mixture of
agents and polymerizable organic compounds is long enough to permit
pre-mixing before the resin composition is introduced to the
fibers, low threshold temperatures are required to prevent
premature resin curing. At lower temperature, the resin composition
typically has a higher viscosity that requires higher processing
pressures when forming the resin-fiber amalgam.
[0005] The short pot life and low threshold temperature of the
resin compositions can create many difficulties in the
manufacturing process. For example, production slowdowns caused by
equipment breakdowns and clogs, quality control checks, and
adjustments during manufacturing can waste large quantities of a
prematurely hardening resin composition. These breakdowns are
generally more frequent when the system is stressed by
low-temperature, high-viscosity resin compositions. Because most
thermoset resins are not recyclable like metal and glass, the
hardened resins cannot be recovered. The short pot life often
requires rapid mixing of the polymerizable organic compounds with
the polymerization agents. This can require additional processing
equipment to monitor and maintain a homogeneous resin composition
just when it's needed during manufacturing. Thus, there is a need
for new manufacturing methods to produce fiber-reinforced resin
composites that reduce or eliminate the problems created by the
short pot life and/or low threshold temperatures for many thermoset
resin compositions. This and other problems are addressed in the
present application.
BRIEF SUMMARY OF THE INVENTION
[0006] Methods of making fiber-reinforced composites are described
where one or more curatives are provided on sized fibers used in
the composite. The curatives on the fibers faciliate the
polymerization of the thermoset resin that forms the polymer matrix
of the composite. Exemplary curatives may include curing agents
that become part of the cured thermoset resin, and accelerators
that increase the rate of curing in the thermoset resin. The
present methods allow the partial (and in some instances complete)
removal of a curative from the resin compostion introduced to the
sized fibers during the making of the fiber-reinforced composite.
The reduction or removal of the one or more curatives from the
resin composition provides it a longer pot life and/or higher
curing temperature.
[0007] Also described are fiber-reinforced composites that are made
with sized fibers that contain one or more curatives. Exemplary
sized fibers may include glass fibers that are first mixed with a
sizing composition that include the curatives, or precursors to the
compounds. The sizing composition can leave the surfaces of the
sized fibers with some or all of a curative needed to faciliate the
polymerization of the resin composition that makes contact with the
fibers. In some examples, more than one type of curative may be
provided on the sized fibers and at the same time reduced or
removed from the resin composition.
[0008] The reduction and removal of the curatives from the
pre-polymerized resin can significanity increase the pot life of
the resin. While these curatives are desirably designed to
faciliate polymerization of the resin under raised-temperature
curing conditions, they can often start polymerization even under
more mild conditions when the resin is mixed with the fibers. If
polymerization occurs to a great extent, the resin becomes too
viscous to mix properly with the fibers and often has to be
discarded. For the purposes of the present Application, the pot
life is measured from the time all the components have been added
to the pre-polymerized resin composition to the time the
composition becomes too viscous to properly mix with the
fibers.
[0009] Embodiments of the present methods of making a
fiber-reinforced composite may include applying a sizing
composition to a plurality of fibers to make sized fibers, where
the sizing composition may include at least one of a curing agent
or an accelerator for a resin composition. The sized fibers may be
contacted with the resin composition to form a resin-fiber amalgam,
where the resin composition includes 50 wt. % or less of a total
amount of the curing agent and the accelerator that is also present
on the sized fibers. The resin-fiber amalgam may then be cured to
form the fiber-reinforced composite.
[0010] Embodiments of the invention also include methods of
extending a shelf-life of a resin composition used to make a
fiber-reinforced composite. The methods may include applying a
sizing composition to a plurality of fibers to make sized fibers,
where the sizing composition comprises at least one of a curing
agent or an accelerator for a resin composition. The methods may
further include contacting the sized fibers with the resin
composition to form a resin-fiber amalgam, and curing the
resin-fiber amalgam to form the fiber-reinforced composite. The
resin composition has at least twice the shelf-life of a resin
mixture comprising the resin composition mixed with the entire
curing agent or accelerator.
[0011] Embodiments of the invention further include
fiber-reinforced composites made from sized fibers. The sized
fibers are made by contacting a plurality of fibers with a sizing
composition that includes at least one of a curing agent and an
accelerator. The fiber-reinforced composites also include a resin
composition that lacks at least one of the curing agent and the
accelerator.
[0012] Additional embodiments and features are set forth in part in
the description that follows, and in part will become apparent to
those skilled in the art upon examination of the specification or
may be learned by the practice of the invention. The features and
advantages of the invention may be realized and attained by means
of the instrumentalities, combinations, and methods described in
the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings wherein like
reference numerals are used throughout the several drawings to
refer to similar components. In some instances, a sublabel is
associated with a reference numeral and follows a hyphen to denote
one of multiple similar components. When reference is made to a
reference numeral without specification to an existing sublabel, it
is intended to refer to all such multiple similar components.
[0014] FIG. 1 shows selected steps in a method of making a
fiber-reinforced composite according to embodiments of the
invention;
[0015] FIG. 2 shows exemplary fiber-reinforced composites made with
the present thermoset resin and sized fiber combinations; and
[0016] FIG. 3 is a graph showing the change in viscosity over time
for an expoxy resin at three different curing agent
concentrations.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present methods include combining a thermoset resin with
fibers sized with a sizing composition that includes a curing
agent, accelerator, or both for the thermoset resin. The placement
of some or all of the curing agent and/or accelearator on the sized
fibers permits lower concentrations of these components in the
thermoset resin. The lower concentration, or in some instances the
absence, of the curatives in the resin increases its pot-life. The
low curative concentrations may also permit lowering the resin's
viscosity by heating it to higher temperatures without premature
curing.
[0018] FIG. 1 shows selected steps in methods 100 of making a
fiber-reinforced composite according to present methods. The
methods 100 may include providing the a sizing composition 102 that
has at least one of a curing agent or an accelerator for the
thermoset resin used in the fiber-reinforced composite. The curing
agent and/or accelerator present in the sizing composition varies
depending on the thermoset resin. For example, if the thermoset
resin is an epoxy resin, the curing agent and accelerator are
selected to help harden the epoxy polymer under curing conditions.
The curing agent reacts with the reactive epoxy oligomers to become
part of the final hardened thermoset polymer structure of the
fiber-reinforced composite. The curing agent is often
polyfunctional and capable of bonding with more than one reactive
site of the epoxy oligomers. The multiple bonding reactions between
the curing agent and the epoxy oligomers forms a crosslinked
network of the hardened thermoset polymer in the fiber-reinforced
composite. The accelerator may increase the curing rate of the
thermoset resin, reduce its curing temperature, or both. It may or
may not be incorporated into the hardened polymer structure of the
composite. In some instances, an accelerator that is not
irreversibly chemically altered during the curing of the thermoset
resin may be referred to as a catalyst. In additional instances, an
accelerator that is irreversibly altered during the curing.
[0019] Exemplary curing agents for an epoxy resin may include
amines, organic acids, organic anhydrides, alcohols, amides, and
thiols, among other epoxy resin curing agents. In some specific
applications, epoxy resin curing agents may also include
phenol-formaldehyde compounds and amino-formaldehyde compounds, and
polyamide compounds. Exemplary amine curing agents may include
aliphatic amines, cycloaliphatic amines, polyether polyamines,
dicyandiamide amines, and aromatic amines, among other amines. The
amines may include primary amines, secondary amines, and tertiary
amines. The amines may include monoamines, and polyamines having
two or more amine groups. They may also include unmodified amines,
and modified amines that contain other functional groups capable of
reacting with the epoxy resin, such as hydroxyl groups (--OH),
carboxyl groups (--COOH), amide groups (--C(.dbd.O)N--), and
anhydride groups, among other groups. For example, the amine curing
agent may be a polyfunctional primary amine that undergoes an
addition reaction with the epoxy resin to form a hydroxyl group and
a secondary amine. The secondary amine may react with another epoxy
group on the epoxy resin to form a tertiary amine and a second
hydroxyl group. Specific examples of amine curing agents may
include ethylene amines (e.g., ethylene diamine (EDA), diethylene
triamine (DETA), triethylene tetramine (TETA), and tetraethylene
pentamine (TEPA)); 3,3'-dimethylmethylene-di(cyclohexylamine);
methylene-di(cyclohexylamine); 4,4'-diaminodiphenyl methane (DDM);
m-phenylene diamine (MPD); 3,3'-diaminodiphenyl sulphone
(3,3'-DDS); 4,4'-diaminodiphenyl sulphone (4,4'-DDS); and
dicyandiamide among other amine curing agents. Exemplary curing
agents may also include dicyandiamide and guanidine.
[0020] Exemplary organic acids and organic acid anhydrides may
include organic diacids such as phthalic acid, tetrahydrophthalic
acid, hexahydrophthalic acid, trimellitic acid, pyromellitic acid,
methylnadic acid, chlorendic acid, tetrabromophthalic acid, and
dichloromaleic acid, among other organic acid. They may also
include the corresponding organic anhydrides such as phthalic
anhydride, tetrahydrophthalic anhydride, hexahydrophthalic
anhydride, trimellitic anhydride, pyromellitic anhydride,
methylnadic anhydride, chlorendic anhydride, tetrabromophthalic
anhydride, and dichloromaleic anhydride, among other organic
anhydrides.
[0021] Exemplary alcohols may include polyols and polyfunctional
alcohols that have one or more functional groups capable of
reacting with the epoxy resin beyond a hydroxyl group. Exemplary
alcohols may include phenols, and polyphenols such as bisphenol A.
Exemplary thiols (also known as mercaptans) may include
polymercaptan compounds, and polysulfide resins.
[0022] As noted above, the thermoset resin may be combined with an
accelerator, and in some instances where an accelerator used, at
least a portion of the accelerator may be found in the sizing
composition used to make sized fibers. Exemplary accelerators that
may be used in conjunction with an epoxy resin may include
alcohols, carboxylic acids, amines, and urea compounds, and lewis
acids, among other accelerators. For example, alcohol accelerators
may include benzyl alcohol, and carboxylic accelerators may include
salicylic acid. Amine accelerators may include tertiary amines such
as benzyl dimethyl amine (BDMA), and
2,4,6-tris-dimethylaminomethyl-phenol. They may also include amine
complexes such as monoethylamine boron trifluoride amine complexes,
and boron trichloride amine complexes. Exemplary accelerators may
also include urea compounds such as aryl dimethylurea compounds
like 3-(4-chlorophenyl)-1,1-dimethyl urea (Monuron), and toluene
bisdimethylurea.
[0023] It should be appreciated that some compounds may act as both
a curing agent and an accelerator as those terms are used in the
present application. For example imidazoles may function as both
curing agents and accelerators for epoxy resins. Exemplary
imidazole curing agents/accelerators may include unmodified
imidazoles and modified imidazoles that include additional
functional groups capable of reacting with the epoxy resin, such as
hydroxyl groups, cyano groups, and carboxylic acid groups, among
others. Specific examples of imidazoles may include
2-methylimidazole, 2-ethyl-4-methylimidazole,
1-cyanoethyl-2-undecylimidazolium trimellitate, among other
imidazoles.
[0024] The sizing composition may also include additional compounds
beyond the curing agent and/or accelerator for the thermoset resin.
For example, the sizing composition may include a solvent (e.g.,
water, ethyl alcohol), coupling agents, film-forming agents,
lubricants, and wetting agent, among other compounds. The coupling
agents may act as chemical linking agents by bonding to both the
glass fiber and the plastic matrix. Exemplary coupling agents may
include silanes containing organosilane groups may be coupling
agents for glass fibers and organic polymers, and serve to bond the
two materials in the composite article. Film forming agents may
provide a desired degree of bonding between the fibers in the fiber
strands to avoid fuzzing during processing in fiber manufacturing
operations and/or fiber composite fabrication operations.
Lubricants help protect the surface of the fibers from scratches
and abrasions commonly caused by fiber-to-fiber contact and
friction during processing. Wetting agents facilitate the wetting
of the sizing composition on the surface of the fibers, and may
also facilitate the wetting of the thermoset resin on the surface
of the sized fibers.
[0025] Returning to FIG. 1, the above-described sizing composition
may be applied to the fibers 104. The application of the sizing
composition to the fibers may be achieved by kiss-roll coating,
spraying, dipping, contacting, and/or mixing the liquid sizing
composition and the fibers. The wet sized fibers may be exposed to
elevated temperature and/or turbulent flow conditions to accelerate
their drying.
[0026] Exemplary fibers used in the present sizing applications may
include one or more types of fibers chosen from glass fibers,
ceramic fibers, carbon fibers, metal fibers, and organic polymer
fibers, among other kinds of fibers. Exemplary glass fibers may
include "E-glass`, "A-glass", "C-glass", "S-glass", "ECR-glass"
(corrosion resistant glass), "T-glass", and fluorine and/or
boron-free derivatives thereof. Exemplary ceramic fibers may
include aluminum oxide, silicon carbide, silicon nitride, silicon
carbide, and basalt fibers, among others. Exemplary carbon fibers
may include graphite, semi-crystalline carbon, and carbon nano
tubes, among other types of carbon fibers. Exemplary metal fibers
may include aluminum, steel, and tungsten, among other types of
metal fibers. Exemplary organic polymer fibers may include poly
aramid fibers, polyester fibers, and polyamide fibers, among other
types of organic polymer fibers.
[0027] The fiber length may range from short-to-intermediate
chopped fibers (e.g., about 0.5 inches or less in length), long
fibers (e.g., more than about 0.5 inches in length), to continuous
fibers. In addition to imparting reactive curing properties to the
fibers, the sizing composition fibers may enhance the fibers'
physical characteristics in a number of ways including increased
hardness, increased mechanical strength, greater wettability, and
increased adhesion between the fibers and resin.
[0028] Once the fibers are sized, they may then be contacted with
the thermoset resin composition to make a fiber-resin amalgam 106.
As noted above, one exemplary thermoset resin is an epoxy resin.
Exemplary epoxy resins may include reactive epoxy oligomers,
prepolymers, and polymers that contain reactive epoxy groups that
can react with the curing agent to form a hard thermoset polymer
with high temperature and chemical resistance. In the present
embodiments, the thermoset epoxy polymer forms the polymer matrix
of a fiber-reinforced composite.
[0029] Exemplary epoxy resins may include the class of resins
formed by the reaction of epichlorohydrins with bisphenol A to form
diglycidyl ethers of bisphenol A. These epoxy resins are sometimes
referred to as DGEBA (diglycidyl ethers of bisphenol A) or BADGE
epoxy resins. Another class of epoxy resins substitute bisphenol F
for the bisphenol A used in the DGEBA resins. Exemplary epoxy
resins may also include aliphatic epoxy resins, cycloaliphatic
epoxy resins, glycidyl epoxy resins, glycidylamine epoxy resins,
epoxy phenol novolacs (EPNs), and epoxy cresol novalacs (ECN),
among other epoxy resins.
[0030] The thermoset resin may include curing agent and/or
accelerator that is added to the resin prior to contact with the
sized fibers. When the sized fibers include a curing agent and/or
accelerator for the thermoset resin, a lower concentration of
curing agent and/or accelerator is required in the resin to
complete the curing. For example, sized fibers that include a
curing agent may contact a resin composition having 50 wt. % or
less of the curing agent in the resin composition. For example the
resin composition may have 50 wt. % or less, 40 wt. % or less, 30
wt. % or less, 25 wt. % or less, 20 wt. % or less, 15 wt. % or
less, 10 wt. % or less, 5 wt. % or less, etc., of the total amount
of curing agent while the remainer is supplied by the sized fibers.
In some embodiments, all the curing agent may be provided by the
sized fibers and there is no curing agent present in the resin
composition. Similarly, sized fibers that include an accelerator
may contact a resin composition having 50 wt. % or less of the
accelerator in the resin composition. For example the resin
composition may have 50 wt. % or less, 40 wt. % or less, 30 wt. %
or less, 25 wt. % or less, 20 wt. % or less, 15 wt. % or less, 10
wt. % or less, 5 wt. % or less, etc., of the total amount of
accelerator while the remainder is supplied by the sized fibers. In
some embodiments, all the accelerator may be provided by the sized
fibers and there is no accelerator present in the resin
composition.
[0031] Exemplary weight percentage distribution ratios for the
curing agent and/or accelerator in the resin composition and the
sized fibers may be 50:50 [resin:fibers], 40:60, 30:70, 20:80,
15:85, 10:90, 5:95, and 0:100. These exemplary weight percentage
distribution ratios also include ranges, including 50:50 to 40:60,
40:60 to 30:70, 30:70 to 20:80, 20:80 to 15:85, 15:85 to 10:90,
10:90 to 5:95, and 5:95 to 0:100. They may also be extended across
two or more of the above-described ranges, for example 50:50 to
30:70, 50:50 to 0:100, 40:60 to 10:90, and so forth.
[0032] In embodiments where both a curing agent and an accelerator
are used, either or both of the curing agent and the accelerator in
the resin composition may be reduced by the above-describe amounts
and distribution ratios for the individual curing agent and
accelerator components. In further embodiments where both a curing
agent and an accelerator are used, the combined amount of the
curing agent and accelerator in the resin composition may be 50 wt.
% or less, 40 wt. % or less, 30 wt. % or less, 25 wt. % or less, 20
wt. % or less, 15 wt. % or less, 10 wt. % or less, 5 wt. % or less,
etc., of the total amount of curing agent and accelerator, while
the remainder is supplied by the sized fibers. For example, when
the combined amount of the curing agent and accelerator in the
resin composition is 50 wt. %. As noted above, the combined amounts
of curing agent and accelerator may have the above-described weight
percentage distribution ratios.
[0033] The combination of the sized fibers and thermoset resin to
make the fiber-resin amalgam may be achieved by thermoset composite
manufacturing techniques, including resin-injection molding (RIM),
structural resin-injection molding (SRIM), resing transfer molding
(RTM), vacuum infusion, wet lay-up processes, spray-up processes,
filament winding processes, and pultrusion processes, among other
processes. In some embodiments, the fiber-resin amalgam may be
formed into sheet molding compounds (SMCs) and/or bulk molding
compounds (BMCs) that can be used as raw materials in compression
molding techniques to produce the fiber-reinforced composite.
[0034] Accompanying or following the formation of the fiber-resin
amalgam, the thermoset resin may be cured to form the
fiber-reinforced composite 108. The curing conditions may include
elevating the temperature of the fiber-resin amalgam above a
curing-threshold temperature. They may alternately (or
additionally) include exposing the resin-fiber amalgam to light at
an energetic enough wavelength (e.g., ultraviolet light) to
initiate a chemical reaction between thermoset resin components.
The exemplary epoxy resin systems may have a curing-threshold
temperature ranging from room temperature (e.g., about 20.degree.
C.) to about 180.degree. C. (e.g., 100.degree. C. to 150.degree.
C.).
[0035] FIG. 2 shows an exemplary fiber-reinforced composite wind
turbine blade 202 formed by the present fiber-resin amalgams. The
blade 202 is one of many types of articles that can be formed by
the amalgams. Other articles may include vehicle parts (e.g.,
aircraft parts, automotive parts, etc.), appliance parts,
containers, etc.
EXAMPLES
[0036] Experiments were conducted to measure the effects of curing
agent concentration in an epoxy resin composition, and also to
measure the effectiveness of transferring a curing agent from an
epoxy resin composition to reactive fibers that have been sized
with the curing agent. The experiments demonstrate that lowering
the concentration of the curing agent in the epoxy resin
composition substantially increases the composition's shelf-life
(a.k.a, pot-life), as measured by the elapsed time for the
composition to reach a particular viscosity. By transferring a
portion of the curing agent from the epoxy composition to the sized
fibers, the reduced-curing agent resin composition can have at
least twice the shelf-life of a conventional resin composition
having all the curing agent present in the composition.
[0037] The experiments also demonstrate that the curing agent on
the sized fibers is capable of curing the epoxy resin composition
as effectively as curing agent premixed and present in the resin
composition. Thus, the longer shelf-life demonstrated for the epoxy
resin compositions with reduced curing agent concentration does not
come at the expense of less efficient curing for the fiber-resin
amalgams.
Example 1--Measuring Effect of Curing Agent Concentration on Pot
Life
[0038] The change in viscosity over time was measured for a series
of resin mixtures made from an epoxy resin (EPON 828 from Momentive
Specialty Chemicals, Inc.) and different concentrations of a curing
agent (EPIKURE 3253 from Momentive Specialty Chemicals, Inc.) to
show the effect of curing agent concentration on the pot life of a
resin composition. EPON 828 is an undiluted clear difunctional
bisphenol A/epichlorohydrin derived liquid epoxy resin. EPIKURE
3253 is tris (dimethyl amion-methyl) phenol. Three samples,
including neat EPON 828 epoxy resin and two EPON 828/EPIKURE 3253
mixtures with different mixing ratios were tested.
[0039] The viscosity tests were conducted on an AR2000 Rheometer
from TA Instruments. A 40 mm 1.degree. steel cone was used for the
testing. The viscosity-time profiles of three epoxy resin samples
were determined at 30.degree. C. with the oscillation frequency of
100 Hz and the strain of 2%.
[0040] FIG. 3 shows the change in viscosity over time for an EPON
828 epoxy resin at three concentrations of EPIKURE 3253. As
expected, the neat EPON 828 epoxy resin with no curing agent had a
stable and unchanging viscosity throughout the time period
measured. Because the neat sample contains no curing agent, the pot
life of this sample extended beyond the measurement period.
However, after a small amount of EPIKURE 3253 was added to the
epoxy resin, the viscosity of EPON 828 started to increase. For
example, when 3% EPIKURE 3253 (i.e., w/w of EPON 828/EPIKURE
3253=100/3) was added, the viscosity of the mixture doubled in
<17 minutes and quadrupled in 43 minutes. When a lower
concentration of 1.4% EPIKURE 3253 was used, the viscosity
increased at a slower but still significant rate, doubling in
approximately 49 minutes.
[0041] The rate of change in the viscosity of the three measured
samples demonstrates that an increasing concentration of a curing
agent in a resin composition can significantly reduce its pot life.
Conversely, reducing the concentration of the curing agent can
significantly extend the resin composition's pot life, and removing
the curing agent altogether may extend the pot life indefinitely.
By transferring some or all of the required curing agent from the
resin composition to the sized reinforcing fibers, the pot life of
the resin compositing can be increased substantially. The longer
pot life of the resin composition facilitates the manufacturing
process of composite materials, enabling especially the production
of large composite parts.
Example 2--Measuring Resin Curing Time for Fibers Sized with Curing
Agent
[0042] The curing time for an epoxy resin (EPON 828) combined with
glass fibers was measured to test the reactivity of the fibers with
the epoxy resin. Except for the comparative measurement with
unsized glass fibers, an aqueous sizing composition with the
ingredients listed in Table 1 was applied to the fibers:
TABLE-US-00001 TABLE 1 Makeup of the Sizing Composition Ingredient
Amount (g) Water 850 Epoxy curing agent.sup.1 100 Film former.sup.2
50 .sup.1EPIKURE 3253 curing agent from Momentive (Columbus, OH,
USA) .sup.2Filco 75007 film former from COIM SPA (Italy)
[0043] The sizing composition was made by adding 850 grams of DI
water and 100 grams of EPIKURE 3253 to a 1-liter beaker. The
mixture was stirred until a homogeneous solution was obtained.
Under agitation, 50 grams of Filco 75007 emulsion was added. The
mixture was stirred for at least 5 minutes until a homogeneous
sizing mixture was obtained.
[0044] The sizing composition of Table 1 was applied to glass
fibers using kiss-roll applicator, after the glass fiber filaments
were drawn from a 200-tip bushing. The sized glass fibers were
dried in an oven. The LOI (loss on ignition) of the sized fibers
was determined to be 4.4%.
[0045] The reactivity of the sized fibers was tested in test tubes
with EPON 828 resin. As shown in Table 2, without curing agent (Run
1), neat EPON 828 resin is stable at the temperature of 120.degree.
C. When 3% EPIKURE 3253 was added (Run 2), EPON 828 resin cured
rapidly and the resin mixture solidified after 40 minutes. When the
entire curing agent was added onto reinforcing glass fibers,
through the application of sizing composition of Table 1, EPON 828
epoxy resin can be cured solely with the curing agent on the sized
fibers. As shown in Run 3, when mixed with the sized glass fibers
that contain the same amount of curing agent as in Run 2, EPON 828
resin cured and solidified after 40 minutes, indicating a similar
rate of curing between Run 2 and Run 3.
TABLE-US-00002 TABLE 2 Rate of Resin Curing Resin EPON EPIKURE
Sized Glass Run # 828 (g) 3253 (g) Fiber (g) Resin Cure.sup.1 1 10
0 0 No reacation after 1-hour 2 10 0.3 0 Solidified after 40 min. 3
10 0 8.3 Solidified after 40 min. .sup.1Cure temperature:
120.degree. C.
[0046] Having described several embodiments, it will be recognized
by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the invention. Additionally, a number
of well-known processes and elements have not been described in
order to avoid unnecessarily obscuring the present invention.
Accordingly, the above description should not be taken as limiting
the scope of the invention.
[0047] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limits of that range is also specifically disclosed. Each
smaller range between any stated value or intervening value in a
stated range and any other stated or intervening value in that
stated range is encompassed. The upper and lower limits of these
smaller ranges may independently be included or excluded in the
range, and each range where either, neither or both limits are
included in the smaller ranges is also encompassed within the
invention, subject to any specifically excluded limit in the stated
range. Where the stated range includes one or both of the limits,
ranges excluding either or both of those included limits are also
included.
[0048] As used herein and in the appended claims, the singular
forms "a", "an", and "the" include plural referents unless the
context clearly dictates otherwise. Thus, for example, reference to
"a process" includes a plurality of such processes and reference to
"the fiber" includes reference to one or more fibers and
equivalents thereof known to those skilled in the art, and so
forth.
[0049] Also, the words "comprise," "comprising," "include,"
"including," and "includes" when used in this specification and in
the following claims are intended to specify the presence of stated
features, integers, components, or steps, but they do not preclude
the presence or addition of one or more other features, integers,
components, steps, acts, or groups.
* * * * *