U.S. patent number 3,914,504 [Application Number 05/402,493] was granted by the patent office on 1975-10-21 for sized carbon fibers.
This patent grant is currently assigned to Hercules Incorporated. Invention is credited to Winfred E. Weldy.
United States Patent |
3,914,504 |
Weldy |
October 21, 1975 |
Sized carbon fibers
Abstract
Carbon fibers are coated with a sizing composition comprising a
polyglycidyl ether, cycloaliphatic polyepoxide or their mixtures.
Preferred sizes are mixtures of a liquid diglycidyl ether of
bisphenol A and a solid diglycidyl ether of bisphenol A.
Inventors: |
Weldy; Winfred E. (Wilmington,
DE) |
Assignee: |
Hercules Incorporated
(Wilmington, DE)
|
Family
ID: |
23592134 |
Appl.
No.: |
05/402,493 |
Filed: |
October 1, 1973 |
Current U.S.
Class: |
428/367; 525/524;
528/98; 528/103; 528/418; 523/205; 528/87; 528/99; 528/104 |
Current CPC
Class: |
D01F
11/14 (20130101); C08L 63/00 (20130101); C08L
63/00 (20130101); C08L 2666/54 (20130101); Y10T
428/2918 (20150115) |
Current International
Class: |
D01F
11/14 (20060101); D01F 11/00 (20060101); C08L
63/00 (20060101); B44D 001/092 () |
Field of
Search: |
;117/161ZB,139.5A,139.5CQ,228,121,DIG.11 ;260/37EP,47EP,83TW
;423/447,460 ;8/115.6,140 ;161/176 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sofocleous; Michael
Attorney, Agent or Firm: Rice; Edith A. Keehan; Michael
B.
Claims
What I claim and desire to protect by Letters Patent is:
1. A carbon fiber having coated on the surface thereof from about
0.4 to about 5.0% by weight, based on the weight of the fiber of a
sizing composition selected from the group consisting of
polyglycidyl ethers, cycloaliphatic polyepoxides and mixtures
thereof.
2. A carbon fiber as set forth in claim 1 wherein the sizing
composition is selected from the group consisting of:
a. a liquid diglycidyl ether of bisphenol A;
b. 2,6-diglycidyl phenyl glycidyl ether;
c. a mixture of a solid diglycidyl ether of bisphenol A and a
liquid diglycidyl ether of bisphenol A; and
d. a mixture of bis-2,3-epoxycyclopentyl ether and the diglycidyl
ether of bisphenol A.
3. A carbon fiber as set forth in claim 1 wherein the sizing
composition comprises a mixture of about 50 to about 80% by weight
of a solid diglycidyl ether of bisphenol A having a molecular
weight of about 380 to about 1400 and about 20 to about 50% by
weight of a liquid diglycidyl ether of bisphenol A having a
molecular weight of about 340 to about 380.
4. A carbon fiber as set forth in claim 1 wherein the sizing
composition comprises a mixture of about 20 to about 50% by weight
of a solid diglycidyl ether of bisphenol A having a molecular
weight of about 380 to about 1400 and about 50 to about 80% by
weight of a liquid diglycidyl ether of bisphenol A having a
molecular weight of about 340 to about 380.
Description
This invention relates to protective sizing compositions for carbon
fibers and in particular to protective sizing compositions for
carbon fibers based on certain epoxy compounds.
The term carbon fibers is used in this application in its generic
sense and includes both graphite fibers and amorphous carbon
fibers. Graphite fibers are defined herein as fibers which consist
essentially of carbon and have a predominate X-ray diffraction
pattern characteristic of graphite. Amorphous carbon fibers, on the
other hand, are defined as fibers in which the bulk of the fiber
weight can be attributed to carbon and which exhibit an essentially
amorphous X-ray diffraction pattern. Carbon fibers can be prepared
by known process from polymeric fibrous materials such as
polyacrylonitrile, polyvinyl alcohol, pitch, natural and
regenerated cellulose, which processes include the steps of
carbonizing or graphitizing the fibers.
Carbon fibers are generally fragile and subject to abrasion during
handling. It has now been discovered that sizing compositions based
on certain epoxy compounds protect carbon fibers against such
damage. When carbon fibers are to be used in preparing composite
structures with resin matrix systems, they are frequently subjected
to a surface pretreatment to improve the adhesion between the
carbon fibers and the resin matrix. The fiber surface is usually
oxidized in such a pretreatment, for example by reaction with an
oxidizing agent. Alternatively, the carbon fiber can be oxidized by
electrolytic treatment using an electrolyte which will generate
nascent oxygen at the surface of the carbon fiber during the
electrolysis process. The sizing compositions of this invention do
not detract from the adhesion improvement of such surface treated
fibers.
In accordance with this invention there is provided carbon fibers
coated with a sizing composition comprising an epoxy compound,
selected from the group consisting of polyglycidyl ethers,
cycloaliphatic polyepoxides and mixtures thereof. The sized carbon
fibers are compatible with epoxy resin matrix systems used to
prepare composite structures. The size can be applied to untreated
or surface pretreated carbon fibers to protect them against
abrasion damage.
Polyglycidyl ethers which can be used, in accordance with this
invention, as a protective size for carbon fibers include
diglycidyl ethers, triglycidyl ethers, tetraglycidyl ethers and
higher polyglycidyl ethers. Mixtures of any of the polyglycidyl
ethers can also be used.
Illustrative diglycidyl ethers that can be employed include
diglycidyl ether; diglycidyl ether of 1,3-butanediol;
2,6-diglycidyl phenyl glycidyl ether;
1,8-bis(2,3-epoxypropoxy)octane; 1,3-bis(2,3-epoxypropoxy)benzene;
1,4-bis(2,3-epoxypropoxy)benzene;
1,3-bis(4,5-epoxypentoxy)-5-chlorobenzene;
4,4'-bis(2,3-epoxypropoxy)diphenyl ether;
2,2-bis(2,3-epoxypropoxyphenyl)methane; and
2,2-bis[p-(2,3-epoxypropoxy)phenyl] propane, i.e., the diglycidyl
ether of bisphenol A.
Illustrative triglycidyl ethers that can be employed include
triglycidyl ethers such as the triglycidyl ethers of trihydric
alcohols such as glycerol, 1,1,1-tri(hydroxymethyl)propane,
1,2,6-hexanetriol and the higher alcohols; and the triglycidyl
ethers of trihydric phenols, such as phloroglucinol, the
trihydroxydiphenyl methanes and propanes, the
trihydroxyaminophenols, the trisphenols;
2,2[2,4,4'-tris(epoxypropoxy)diphenyl]propane;
1,1-bis(glycidyloxymethyl)-3,4-epoxycyclohexane; and
N,N,O-tris(epoxypropyl) p-aminophenol.
Illustrative tetra- and higher polyglycidyl ethers that can be
employed include tetraglycidyl ether of p,p'diaminodiphenylmethane
and epoxidized novolac compounds.
Cycloaliphatic polyepoxides which can be used to provide a
protective size on carbon fibers in accordance with this invention
include bis-2,3-epoxycyclopentyl ether;
1,4-bis(2,3-epoxypropoxy)cyclohexane;
1,4-bis(3,4-epoxybutoxy)-2-chlorocyclohexane; the
di(epoxycyclohexanecarboxylates) of aliphatic diols; the
oxyalkylene glycol epoxycyclohexanecarboxylates; the
epoxycyclohexylalkyl epoxycyclohexanecarboxylates;
epoxycyclohexylalkyl dicarboxylates; epoxycyclohexylalkyl
phenylenedicarboxylates; bis(3,4-epoxy-6-methylcyclohexylmethyl)
diethylene glycol ether; dicyclopentadiene dioxide;
bis(2,3-epoxycyclopentyl) ether; glycidyl 2,3-epoxycyclopentyl
ether; 2,3-epoxycyclopentyl 2-methylglycidyl ether; cycloaliphatic
triepoxides; also tetra- and higher homologues which contain more
than three epoxy groups per molecule. Mixtures of the
cycloaliphatic polyepoxides can also be employed.
Illustrative of the di(epoxycyclohexanecarboxylates) of aliphatic
diols which can be employed include the
bis(3,4-epoxycyclohexanecarboxylate) of 1,5-pentanediol,
3,-methyl-1,5-pentanediol,
2-methoxymethyl-2,4-dimethyl-1,5-pentanediol, ethylene glycol,
2,2-diethyl-1,3-propanediol, 1,6-hexanediol and
2-butene-1,4-diol.
Illustrative of the oxyalkylene glycol epoxycyclohexanecarboxylates
which can be employed include bis(2-ethylhexyl-4,5-
epoxycyclohexane-1,2-dicarboxylate) of dipropylene glycol,
bis(3,4-epoxy-6-methylcyclohexanecarboxylate) of diethylene glycol
and bis(3,4-epoxycyclohexanecarboxylate) of triethylene glycol.
Illustrative of the epoxycyclohexylalkyl
epoxycyclohexanecarboxylates which can be employed include
3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate,
3,4-epoxy-1-methylcyclohexylmethyl
3,4-epoxy-1-methylcyclohexanecarboxylate,
3,4-epoxy-2-methylcyclohexylmethyl
3,4-epoxy-2-methylcyclohexanecarboxylate,
3,4-epoxy-6-methylcyclohexylmethyl
3,4-epoxy-6-methylcyclohexanecarboxylate,
(1-chloro-3,4-epoxycyclohexan-1-yl) methyl
1-chloro-3,4-epoxycyclohexanecarboxylate,
(1-bromo-3,4-epoxycyclohexan-1-yl) methyl
1-bromo-3,4-epoxycyclohexanecarboxylate) and
(1-chloro-2-methyl-4,5-epoxycyclohexan-1-yl) methyl
1-chloro-2-methyl-4,5-epoxycyclohexanecarboxylate.
Illustrative of the epoxycyclohexylalkyl dicarboxylates which can
be employed include bis(3,4-epoxycyclohexylmethyl) pimelate and
oxalate and bis(3,4-epoxy-6-methylcyclohexylmethyl) maleate,
succinate, sebacate and adipate.
Illustrative of the epoxycyclohexylalkyl phenylenedicarboxylates
which can be employed include bis(3,4-epoxycyclohexylmethyl)
terephthalate and bis(3,4-epoxy-6-methylcyclohexylmethyl)
terephthalate.
Illustrative cycloaliphatic triepoxides which can be employed
include tris(3,4-epoxycyclohexanecarboxylate) of 1,1,1-trimethylol
propane; and tris(3,4-epoxycyclohexanecarboxylate) of
1,2,3-propanetriol.
The sizing composition can be applied to the fiber in a suitable
solvent to control the amount of size coated onto the fiber.
However, the sizing composition can be applied directly, if
desired. The concentration of the size in the solvent is usually in
the range of from about 0.1 to about 10.0% by weight based on the
total weight of the solution and is preferably from about 0.5 to
about 2.0%. Examples of suitable solvents are polar solvents such
as the halogenated hydrocarbons, for example, methylene chloride
and ethylene dichloride; diacetone alcohol, ketones and esters. If
desired, the sizing composition may also contain a lubricant. The
lubricant serves to permit more even distribution of the size on
the fiber and aids in more effective wetting of the fiber.
Preferred lubricants are fatty acids, amides and esters. Other
additives, such as coupling agents can also be added to the size
solution.
The sizing compositions can be applied to the fibers by known
methods, for example, by drawing the fibers through a bath
containing the size or by spraying the size onto the fibers. The
drawing illustrates a preferred arrangement for sizing carbon
fibers. In the drawing, a carbon fiber strand 2 is drawn from
supply reel 4 and passed into a tube 6. The arrows indicate the
direction the carbon fiber strand 2 travels. The tube 6 is heated
by hot air forced through the inlet tube 8 from a suitable source,
such as an electric heat gun. The temperature of the hot air is
sufficient to heat the tube to above the evaporation temperature of
the solvent. The fiber is passed along the tube and down through an
opening 9 in the bottom of the tube 6 and into the sizing bath 10.
The fiber is directed down into the bath 10, through the bath and
back through opening 9 into heated tube 6 by guide rollers 12, 14
and 16. The fiber is passed through the heated tube to evaporate
the solvent and wound on a conventional take-up roll 18.
The amount of size coated onto the fiber is from about 0.4 to about
5.0%, by weight based on the weight of the fiber, preferably from
about 0.9 to about 1.6%. The amount of size on the fiber is
determined by weighing a given length of sized fiber, then
dissolving the size from the fiber using a solvent for the size,
drying the fiber and then reweighing the unsized fiber. From the
difference in the weights the percentage of size on the fiber,
based on the weight of the fiber, is calculated.
Carbon fibers sized with the epoxy compound sizing compositions of
this invention can be used to prepare fiber reinforced composite
structures. Any of the known methods for preparing such composites
can be employed. For example, carbon fibers can be used to prepare
filament wound composites. The epoxy sizing compositions of this
invention protect the fibers from abrasion during the filament
winding process. The sizing of the fiber also permits a smoother
delivery of the carbon fiber during the filament winding. In
another common method, the reinforced composite structure can be
prepared by incorporating chopped sized carbon fibers into the
matrix resin and then forming the composite structure, for example,
by press molding. Since the sizing compositions of this invention
are based on epoxide compounds, carbon fibers sized therewith are
compatible with and do not interfere with adhesion between the
carbon fibers and the epoxy resin-hardener systems used as the
matrix resin of the composite. This is especially true when both
the size composition and the matrix resin are both based on
diglycidyl ethers of bisphenol A.
The following examples will illustrate the sizing of carbon fibers
using the sizing compositions of this invention and the preparation
of composites using said sized fibers. In the examples, parts and
percentages are by weight unless otherwise specified.
EXAMPLES 1-9
Commercially available surface treated graphite fiber was sized
with epoxy compounds in accordance with this invention in a
suitable application process. The particular size and application
solvent used in each example are shown in Table 1. In each case the
fiber was sized by drawing the fiber through a heated tube and
sizing bath as shown in the drawing. The fiber was pulled through
the size solution at a rate of 2-4 feet per minute. The take-up was
a typical Leesona take-up driver with a motor. The size produced on
the fiber ranged from "soft to hard", as determined by the hand or
feel of the resulting sized fiber. The term "soft" is used to
describe a sized fiber which retains its limp hand and the term
"hard" applies to a sized fiber having a stiff hand.
Table 1
__________________________________________________________________________
(Carbon Fiber Sizes) Concentration % size Based (% Size in on the
Weight Example Size Solvent Solution) of the Fiber Remarks
__________________________________________________________________________
1 76% Compound A Diacetone 1.5 1.6 Hard size 24% Compound B alcohol
2 76% Compound A " 1.1 1.0 " 24% Compound B 3 74.7% Compound A "
1.1 1.0 " 23.6% Compound B 1.7% Compound C 4 74.7% Compound A " 1.5
1.6 " 23.6% Compound B 1.7% Compound C 5 37.5% Compound A " 1.0 1.0
Medium soft 62.5% Compound B size 6 36.9% Compound A " 1.0 0.9 "
61.4% Compound B 1.7% Compound C 7 Compound D CH.sub.2 Cl 1.05 1.0
Soft size 8 Mixture E Ethylene 1.0 1.4 " dichloride 9 Compound B "
1.5 1.4 " Compound A = diglycidyl ether of bisphenol A having a
molecular weight of 380-1400. Compound B = diglycidyl ether of
bisphenol A having a molecular weight of 340-380. Compound C = The
amide of pelargonic acid. Compound D = 2,6-diglycidyl phenyl
glycidyl ether. Mixture E = a mixture of 35% by wt. of
bis-2,3-epoxycyclopentyl ether and 65% by wt. of the diglycidyl
ether of bisphenol A; commercially available as ERLA 2256 from
Union Carbide Corp.
__________________________________________________________________________
EXAMPLE 10
The carbon fibers sized as described in Examples 1-9 were used to
prepare composites employing each of the following epoxy matrix
resin-hardener systems:
1. A matrix resin-hardener system comprising 100 parts by weight of
2,6-diglycidyl phenyl glycidyl ether (see footnote D of Table 1)
and 20 parts by weight of a hardener comprising a eutectic mixture
of metaphenylene diamine and methylene dianiline..sup.F
2. A matrix resin-hardener system comprising 100 parts by weight of
a mixture of 35% by weight of bis-2,3-epoxycyclopentyl ether and
65% by weight of the diglycidyl ether of bisphenol A (see footnote
E of Table 1) and 29 parts by weight of a hardener comprising a
eutectic mixture of metaphenylene diamine and methylene
dianiline..sup.F
3. A matrix resin-hardener system comprising 100 parts by weight of
N,N,N'-tris(epoxypropyl)-p,p'-diaminophenyl methane and 49 parts by
weight of the hardener 4,4'-diaminodiphenyl sulfone.
The composite specimens were made in the form of an NOL ring
containing about 60% by volume of sized carbon fiber. In
preparation of the composite the carbon fiber is passed through the
epoxy resin system, through a tensioning device and onto a rotating
mold. The whole system is enclosed in a vacuum chamber to provide a
low void composite specimen. The mold is removed from the NOL
winding device and placed in a curing oven to cure the resin. The
time and temperature of curing each of the resin matrix-hardener
systems is shown in Table 2. A discussion of NOL ring specimens and
their manufacture may be found in Plastics Technology, November
1958, pp. 1017-1024, and Proceedings of 21st Annual Technical
Conference SPI Reinforced Plastics Division, Section 8-D, February
1966.
Composite samples prepared as described were tested for
interlaminar shear strength in accordance with ASTM-D 2344 (a)
without further treatment and (b) after the samples were boiled in
water for 72 hours. The results, shown in Table 2, show that the
size composition does not detract from the adhesion between the
carbon fibers and the resin matrix.
Table 2
__________________________________________________________________________
NOL Ring Composites: Interlaminar Shear Strength Using Sized Carbon
Fibers Resin Matrix- % Size on Fiber, Interlaminar Shear Strength
Hardener Curing Sized Based on Wt. of (p.s.i.) System Conditions
Fiber the Fiber Dry Wet*
__________________________________________________________________________
1 16 hours at 110.degree.C Unsized -- 12,500 followed by Ex. 1 1.6
14,000 11,600 4 hours at 145.degree.C. Ex. 2 1.0 13,600 Ex. 3 1.0
13,400 Ex. 4 1.6 14,000 Ex. 5 1.0 13,400 10,800 Ex. 6 0.9 13,400
Ex. 7 1.0 12,000 2 1 hour at 125.degree.C. Unsized -- 14,000
followed by Ex. 1 1.6 14,100 12,100 4 hours at 175.degree.C. Ex. 2
1.0 13,000 Ex. 3 1.0 13,900 Ex. 4 1.6 12,800 Ex. 5 1.0 12,100
11,100 Ex. 6 0.9 11,900 Ex. 8 1.4 13,100 3 2 hours at 125.degree.C.
Unsized -- 12,700 followed by Ex. 9 1.4 12,600 4 hours at
160.degree.C.
__________________________________________________________________________
*After 72 hour boil in distilled water.
EXAMPLE 11
Carbon fibers sized with soft, medium soft, and hard sizes as
described in Example 1-9 were tested for abrasion resistance. A
typical filament winding delivery system was set up to assess the
effect on size on the abrasion resistance of carbon fiber during
filament winding. The system consisted of a CTC Tensioner,
commercially available from Compensating Tension Controls, Inc.,
set at 3 pounds tension. The fiber was taken over an aluminum
wheel, a carbon wheel, and onto a 2.6 inch diameter mandrel on a
filament winding machine. The degree of abrasion was measured by
percent retention of original carbon fiber tensile strength. The
results, shown in Table 3, show the improvement in abrasion
resistance of carbon fibers when sized with the epoxy size
compositions.
Table 3 ______________________________________ Abrasion Resistance
of Sized and Unsized Carbon Fibers Tensile Strength Retention after
delivery system, Type of Size handling, %
______________________________________ Unsized 75 Soft Size
(Example 8, Table 1) 85 Medium Soft Size (Example 5, 100 Table 1)
Hard Size (Example 2, Table 1) 98
______________________________________
The preferred sizing compositions of this invention are selected
from the group consisting of (a) a liquid diglycidyl ether of
bisphenol A having a molecular weight of about 340 to about 380;
(b) a mixture of a solid diglycidyl ether of bisphenol A having a
molecular weight of about 380 to 1400 and a liquid diglycidyl ether
of bisphenol A having a molecular weight of about 340 to about 380;
(c) a mixture of bis-2,3-epoxycyclopentyl ether and the diglycidyl
ether of bisphenol A; and (d) 2,6-diglycidyl phenyl glycidyl
ether.
The application of the different sizing compositions produce a
different feel or hand on the fiber ranging from soft to hard. For
example, a soft size is obtained when the fiber is treated with
2,6-diglycidyl phenyl glycidyl ether, the diglycidyl ether of
bisphenol A having a molecular weight in the range of 340 to about
380 or a eutectic mixture of 35% by weight of
bis-2,3-epoxycyclopentyl ether and 65% by weight of the diglycidyl
ether of bisphenol A. A hard size is obtained when the fiber is
treated with a mixture of about 50 to about 80% by weight,
preferably 76% by weight of the solid diglycidyl ether of bisphenol
A having a molecular weight of about 380 to about 1400 and from
about 20 to about 50% by weight, preferably 24% by weight of the
liquid diglycidyl ether bisphenol A having a molecular weight in
the range of about 340 to about 380. A medium soft size is obtained
when the carbon fiber is treated with a mixture of about 20 to
about 50% by weight, preferably 37.5% by weight of the solid
diglycidyl ether of bisphenol A having a molecular weight of about
380 to 1400 and about 50 to about 80% by weight, preferably 62.5%
by weight of the liquid diglycidyl ether of bisphenol A having a
molecular weight in the range of about 340 to 380.
* * * * *