Sizing agents for carbon fibers

A sizing agent for carbon fibers has the following three important constituents: an epoxy compound, a copolymer having within its molecule one oxyalkylene derivative of a polycyclic phenol segment and one or two monoester or polyester segments connected through an ester linkage, and oxyalkylene derivative of substituted phenol.

BACKGROUND OF THE INVENTION 
This invention relates to sizing agents for carbon fibers. 
Carbon fiber reinforced plastics (hereinafter referred to as FRP) are made 
from carbon fiber with resin matrix and are one of the most excellent 
kinds of materials in terms of specific modulus and specific strength. 
Because of their superior characteristics and light weight, their 
applications in aerospace industries, as an example, are quickly 
expanding. Carbon fibers used for the production of FRP are drawn and 
arranged in the form of a filament or a tow and after they are formed into 
strands, sheets, textile, or knit materials, they are combined with a 
resin material and used as a prepreg. Alternatively, filaments or tows may 
be cut to uniform lengths to produce chopped fibers and after they are 
combined with a resin material, they may be used as a material for premix, 
a bulk molding compound or a sheet molding compound. Since carbon fibers 
are basically brittle, there tend to arise problems of fluffs due to 
mechanical friction in the molding process before they are made into a 
prepreg if they are not pretreated with a sizing agent. Moreover, they 
cannot be handled easily and the physical characteristics of the FRP are 
also adversely affected. As for chopped fibers, their lengths are usually 
1-100 mm but since thousands or tens of thousands of single fibers 
constitute the carbon fiber filaments or tows which are processed, the 
fibers become disheveled and bulky and tend to scatter around easily if 
they are directly chopped without preprocessing. In order to improve the 
cohesiveness and abrasion resistance of carbon fibers and to make it 
easier to handle them while they are manufactured or transported, 
therefore, it has been a common practice to add a sizing agent to carbon 
fibers but since sizing agents eventually become a part of the produced 
FRP, it is required that they do not adversely affect the characteristics 
of the final products. 
In view of such requirements as described above, the present invention 
relates to multi-purpose sizing agents to be combined with a matrix resin 
and in particular with epoxy resins and unsaturated resins having an ester 
bond. 
As sizing agents for carbon fibers to be used for carbon fiber reinforced 
epoxy resin, a mixture of liquid and solid bisphenol A diglycidylethers 
(Japanese Patent Publication Tokko 57-15229, U.S. Pat. No. 3,914,504) and 
glycidylamines (Japanese Patent Publication Tokko 59-11710, U.S. Pat. No. 
4,107,128) have previously been proposed. As sizing agents for carbon 
fibers to be used for carbon fiber reinforced unsaturated polyester resin, 
on the other hand, epoxidized polybutadiene (Japanese Patent Publication 
Tokkai 56-43335) and a mixture of a diglycidylether derived from bisphenol 
and epichlorohydrin and a prepolymer derived from diallylphthalate 
(Japanese Patent Publication Tokkai 59-228083) have been proposed. As 
still another example, sizing agents of the aqueous emulsion type having 
as indispensable components an epoxy resin, a condensation product of an 
unsaturated dibasic acid and a bisphenol-type alkylene oxide adduct, and 
an alkylene oxide adduct of phenol or polycyclic phenol have also been 
proposed (Japanese Patent Publication Tokko 57-49675, U.S. Pat. No. 
4,167,538). 
Although these prior art sizing agents each have certain advantages, they 
have problems regarding the production of FRP and their physical 
characteristics. For example, since carbon fibers have poor cohesiveness 
and abrasion resistance, problems of fluff and yarn breakage occur 
frequently at the time of their weaving and chopped fibers become 
disheveled. Some are toxic and flammable when exposed to high temperature 
because of the use of an organic solvent. Some may improve the adhesion 
between carbon fibers and epoxy resin matrix but not between carbon fibers 
and unsaturated polyester resin matrix such that interlaminar shear 
strength (ILSS) of the produced FRP is adversely affected. Sometimes, the 
attempt at improving the multi-purpose characteristics has resulted in 
insufficient adhesion characteristics regarding both types of resins. 
SUMMARY OF THE INVENTION 
The present invention provides new sizing agents for carbon fibers which 
eliminate the aforementioned conventional problems. 
This invention has been completed by the present inventor who discovered, 
as a result of diligent investigations in view of the aforementioned 
problems, that the use of specified copolymer and specified oxyalkylene 
derivative of substituted phenol together with epoxy resin provides 
emulsifiable sizing agents for carbon fibers which can improve the 
processability of the fibers during the fabrication and have substantially 
equal adhesion characteristics with epoxy resin matrix and unsaturated 
polyester resin matrix.

DETAILED DESCRIPTION OF THE INVENTION 
This invention relates to sizing agents for carbon fibers containing 
Compound A, Compound B and Compound C to be defined below as important 
constituents: 
Compound A: Epoxy compound. 
Compound B: Copolymer having within its molecule one oxyalkylene derivative 
of a polycyclic phenol segment and one or two monoester or polyester 
segments, both segments being connected through an ester linkage and the 
monoester or polyester segment being obtained by alternately ring-opening 
addition reaction of organic dicarboxylic anhydride and 1,2-epoxide to 
oxyalkylene derivative of a polycyclic phenol in the presence of a 
catalyst. 
Compound C: Oxyalkylene derivative of substituted phenol shown by the 
general formula 
##STR1## 
where Y is alkyl group, phenyl-methyl group or phenyl-ethyl group with 
1-12 carbon atoms, X is benzene residue, diphenyl residue on cumylbenzene 
residue, R is hydrogen atom or methyl group, n is an integer in the range 
of 1-5, and m is an integer in the range of 4-100. 
Examples of Component A according to the present invention include 
straight-chain aliphatic epoxy compounds, glycidylether, glycidylamine, 
glycidylester, glycidylhydantoin, etc. Preferable among these examples are 
glycidylether and glycidylamine. Particularly preferable examples include 
bisphenol-A diglycidylether, bisphenol-A diglycidylether polymer, epoxy 
cresol novolac resins, epoxy phenol novolac resins, 
N,N,N',N'-tetraglycidyl-m-xylylenediamine, N,N,N',N'-tetraglycidyl 
diaminodiphenylmethane, N,N,N',N'-tetraglycidylbisaminomethylcylclohexane 
and m-N,N,-diglycidylaminophenylglycidylether. 
Compound B according to the present invention includes within its molecule 
one oxyalkylene derivative of a polycyclic phenol segment (B.sup.1) and 
one or two monoester or polyester segments (B.sup.2), both segments being 
connected through an ester bond. Thus, Component B of the present 
invention may be expressed as either B.sup.1 -B.sup.2 or B.sup.2 -B.sup.1 
-B.sup.2. 
The aforementioned oxyalkylene derivative of a polycyclic phenol can be 
obtained, for example, by adding alkyleneoxide to polycyclic phenol by a 
known method and its molecule has a hydroxyl terminal group which provides 
active hydrogen. Examples of polycyclic phenolalkyleneoxide derivatives 
that may be advantageous for use in the present invention include 
polyoxyalkylene poly(phenyl-methylated) phenylether, polyoxyalkylene 
poly(phenyl-ethylated) phenylether and polyoxyalkylene 
bisphenolpolyethylene glycol copolymers. They include the following 
compounds: polyoxyethylene (5 mole) diphenyl-methylated) cumylphenyl 
ether, polyoxyethylene (5 mole) tri(phenyl-methylated) diphenyl ether, 
polyoxy (ethylene (2 mole) propylene (2 mole)) tri(phenyl-ethylated) 
phenylether, polyoxyethylene (10 mole) tri(phenyl-ethylated) phenylether, 
polyoxypropylene (4 mole) added bisphenol A, polyoxyethylene (2 mole) 
added bisphenol A, polyoxyethylene (4 mole) added bisphenol S and 
polyoxyethylene (6 mole) added bisphenol A. 
The monoester and polyester segments of Component B according to the 
present invention can be obtained stably in an industrially advantageous 
manner by alternately ring-opening addition reaction of organic 
dicarboxylic anhydride and 1,2-epoxide to aforementioned oxyalkylene 
derivative of a polycyclic phenol in the presence of a catalyst. In this 
case, examples of organic dicarboxylic anhydride include aliphatic or 
ethylenically unsaturated dicarboxylic anhydrides such as succinic 
anhydride, maleic anhydride and alkenyl succinic anhydride, aromatic 
dicarboxylic anhydrides such as phthalic anhydride and naphthalene 
dicarboxylic anhydride, and alicyclic dicarboxylic anhydrides such as 
cyclohexene dicarboxylic anhydride but ethylenically unsaturated 
dicarboxylic anhydride is particularly preferable. Examples of 1,2-epoxide 
include aliphatic epoxides such as ethylene oxide, propylene oxide, 
1,2-butylene oxide and alkyl or alkenylglycidylether with 1-12 carbon 
atoms, aromatic or alicyclic epoxides such as phenylene oxide and 
cylclohexene oxide, and epoxides having aromatic group such as styrene 
oxide and phenylglycidyl ether but ethylene oxide, propylene oxide and 
butylene oxide are particularly preferable. Examples of catalysts include 
lithium halides such as lithium chloride and lithium bromide and 
tetra-alkyl quaternary ammonium salts such as tetramethyl ammonium 
bromide, tetrabutyl ammonium bromide and tetrapropyl ammonium chloride. 
The end groups of the monoester and polyester segments thus formed are 
usually hydroxyl groups, carboxylic groups or a mixture thereof and the 
ratio thereof as end groups is controlled by the molar ratio between the 
organic dicarboxylic anhydride and 1,2-epoxide which participated in the 
reaction. In other words, the ratio of hydroxyl and carboxylic groups as 
end groups can be varied by selecting the aforementioned molar ratio. 
Compounds of Component B according to the present invention having desired 
characteristics can be obtained by properly selecting the molecular 
weights of the oxyalkylene derivative of a polycyclic phenol segment and 
the monoester or polyester segment, their ratio, their structures and 
their compositions. For example, if the molecular ratio of the monoester 
or polyester segment is increased, affinity to unsaturated resins having 
an ester bond as a matrix resin can be improved and if, instead, the 
molecular ratio of the oxyalkylene derivative of a polycyclic phenol 
segment is increased, affinity to epoxy resins as a matrix resin can be 
improved. In order to give reactivity of Component B to other components 
such as Component A, matrix resins and carbon fibers, various reactive 
groups may be introduced into the polyester terminal group of Component B. 
Reactive groups such as ethylenically unsaturated hydrocarbon groups, 
epoxy groups and isocyanate groups are effective. These reactive groups 
can be introduced by reacting a reactive substance with the end hydroxyl 
or carboxylic groups of the polyester segments connected through ether or 
ester bonds. The end hydroxyl groups of the monoester and polyester 
segments can also be modified into carboxylic groups by reacting with a 
polybasic acid (bivalent or greater) or its anhydride. It is effective to 
have more than 95% of the end groups of the monoester or polyester segment 
as carboxylic group, including such modifications. 
Component C according to the present invention is characterized by the 
general formula given above and serves as an emulsifier component for 
emulsifying Components A and B in water. In this formula, the 
polyoxyalkylene segment is a random or block addition of propylene oxide 
and/or ethylene oxide. Examples of Component C include addition reaction 
products of alkyl phenol, phenyl-methylated phenol, phenylethylated 
phenol, phenyl-ethylated phenylphenol, phenyl-methylated cumylphenol or 
-phenyl-ethylated cumylphenol and propylene oxides and/or ethylene oxide. 
The sizing agents of the present invention contain Components A, B and C as 
important constituents. Depending on the purpose for which they are used, 
the weight ratios of these components are preferably such that Component 
A/Component B=10-90/90-10 and Component C/Components A+B=10-40/90-60. If 
necessary, a lubricant and a surfactant may be contained to the extent of 
not seriously affecting the effects of the present invention. 
The matrix resins to which the sizing agents described above as embodying 
the present invention are intended to be applied are epoxy resins and 
unsaturated polyester resins. Epoxy resins include bisphenol A 
glycidylether, epoxy novolac resins, tetraglycidylamine, and unsaturated 
polyester resins include unsaturated polyester resins and vinyl ester 
resins. Unsaturated polyester resins for this purpose are obtained by 
dissolving in styrene monomer or another polymerizable monomer. More 
particularly, they are generally polyesters obtainable by using as 
original material anhydrous maleic acid, orthophthalic acid, isophthalic 
acid, fumaric acid, ethylene glycol and propylene glycol. Vinyl ester 
resins have a molecular structure obtainable by a reaction between epoxy 
resins of bisphenol diglycidylether type or novolac type and acrylic acid 
or metha-acrylic acid and are mixed with a styrene monomer or the like. 
The amount of the sizing agents of the present invention to be applied to 
carbon fibers is generally 0.1-10 wt % (with respect to carbon fibers) and 
preferably 0.5-0.7 wt %. Processing is carried out in the form of a water 
dispersant and the concentration of the sizing agent in the dispersion 
should preferably be 0.3-5.0 wt %. 
The sizing agents of the present invention are extremely effective on 
carbon fibers from pitch materials or carbon fibers from polyacrylonitril 
filaments. They can overcome the conventional problems described above and 
make carbon fibers significantly easier to handle in later processes. 
Because of their superior cohesiveness and lubricity, problems of fluff 
and fiber breakage are prevented when carbon fiber filaments and tows are 
bent many times by guide members and rollers as they are wound or woven, 
and chopped fibers are prevented from becoming disheveled and scattering 
around. In summary, the present invention allows carbon fiber yarns to be 
wound up and woven at a higher speed, makes it easier to cut them cleanly 
and thereby improves their productivity. Moreover, these sizing agents can 
be easily applied to carbon fibers as an aqueous emulsion which is uniform 
and stable, and they are not only safe and hygienically advantageous, but 
also energy-saving. Carbon fibers processed by the sizing agents of the 
present invention improve the cohesion not only between the carbon fibers 
and the epoxy resin matrix but also between the carbon fibers and the 
unsaturated polyester resin matrix with which prior art sizing agents do 
not have satisfactory cohesiveness. Thus, sizing agents of the present 
invention can be used together on these two types of matrix resins to 
obtain FRP of superior quality from each. 
Test experiments using the sizing agents of the present invention are 
described below in order to better explain the present invention but the 
present invention is not intended to be limited by these examples. 
Examples of Component B are shown in Tables 1 and 2 and sizing agents both 
embodying the present invention and for comparison were prepared as shown 
in Tables 3 and 4. Results of tests thereon are shown in Tables 5 and 6. 
EXAMPLE 1: PRODUCTION OF COMPONENT B (B-1) 
808g (2.0 moles) of ethylene oxide (hereinafter abbreviated as EO) 4 moles 
adduct of bisphenol, 784 g (8.0 moles) of maleic anhydride and 1.0 g of 
tetramethylammonium bromide as catalyst were placed inside an autoclave 
and stirred for 30 minutes at 120.degree.-125.degree. C. Next, 464 g (8.0 
moles) of propylene oxide (hereinafter abbreviated as PO) was injected 
thereinto over a period of 4 hours at 125.degree. C. for a reaction and a 
light brown viscous liquid (Product B-1 was obtained. For this Product 
B-1, the acid value was 37, the hydroxyl value was 36 and the molecular 
weight (hereinafter calculated value) was 1540. 
EXAMPLE 2: PRODUCTION OF COMPONENT B (B-7) After 1540 g (1.0 mole) of 
Product B-1 and 100 g (1.0 mole) of succinic anhydride were placed inside 
an autoclave, they were reacted for two hours at 120.degree.-125.degree. 
C. in the presence of nitrogen gas to obtain a light brown viscous liquid 
(Product B-7). The ester segment of this Product B-7 has carboxyl 
terminated polyester segment. Its acid value, hydroxyl value and molecular 
weight were respectively 67, 2.0 and 1640. 
EXAMPLE 3: PRODUCTION OF COMPONENT B (B-10) 
After 2349 g (1.0 mole) of Product B-3 obtained in a way similar to Example 
1 was dissolved in methylethylketone as a solvent inside a flask, 1.0 g of 
tetramethylammonium bromide as catalyst and 722 g (1.9 moles) of bisphenol 
A diglycidylether were successively added thereto and stirred for 3 hours 
at 60.degree.-70.degree. C. Methylethylketone was distilled away under 
reduced pressure to obtain a light brown viscous liquid (Product B-10). 
The ester segment of this Product B-10 has epoxy terminated groups and its 
acid value, hydroxyl value and molecular weight were respectively 1.2, 3.5 
and 3116. 
EXAMPLES OF COMPONENT B WITHOUT END MODIFICATION 
Product B-2 through B-6 were obtained similarly as explained in Example 1 
above. 
TABLE 1 
__________________________________________________________________________ 
Ester Segment Component B 
Derivative 
Organic Wt % Molar Ratio 
Segment 
Dicarboxylic Molec- 
of of End 
of Poly- 
Anhydride 
1,2- ular Ester Groups 
Product 
cyclic (molar ratio) 
Epoxide 
Weight 
Segment 
COOH/OH 
__________________________________________________________________________ 
B-1 *1 MA PO 1540 59.6 50.7/ 
(1 mole) 
(4 moles) 
(4 49.3 
moles) 
B-2 *1 MA PO 1852 78.2 48.5/ 
(1 mole) 
(4.5 moles) 
(8.2 51.5 
FA moles) 
(4.5 moles) 
B-3 *2 MA PO 2393 78.2 42.4/ 
(1 mole) 
(12 moles) 
(11.5 57.6 
moles) 
B-4 *3 MA EO 1378 69.2 45.3/ 
(1 mole) 
(4.5 moles) 
(5.5 54.7 
FA moles) 
(4.5 moles) 
B-5 *4 MA EO 1478 57.7 50.2/ 
(1 mole) 
(6 moles) 
(5.5 49.8 
moles) 
B-5 *5 MA EO 1477 67.3 49.5/ 
(1 mole) 
(7 moles) 
(6.5 50.5 
moles) 
__________________________________________________________________________ 
Notes: 
*1: EO (4 mole) adduct of bisphenol A 
*2: EO (4.0 moles) PO (2 moles) random adduct of bisphenol A 
*3: EO (4 moles) adduct of bisphenol S 
*4: EO (3 moles) PO (1 mole) random adduct of tristyrenated cumylphenol 
*5: EO (3 moles) adduct of tribenzylated phenol 
Specifically: 
*1 bisphenol-A polyethylene glycol (4 moles) copolymer 
##STR2## 
*2 bisphenol-A polyethylene glycol (4 moles) polypropylene 
glycol (2 moles) random copolymer 
##STR3## 
*3 bisphenol-S polyethylene glycol (4 moles) copolymer 
##STR4## 
*4 polyoxyethylene (3 moles) oxypropylene tri(phenyl- 
ethylated) cumylphenylether 
##STR5## 
*5 polyoxyethylene (3 moles) tri(phenyl-methylated 
phenylether 
##STR6## 
MA maleic anhydride 
FA phthalic anhydride 
Products B-7 through B-11 were obtained similarly as explained in Example 2 
or Example 3 above. 
TABLE 2 
__________________________________________________________________________ 
Termi- 
Compound nating 
End Group 
B Agent Molar Ratio 
Product 
(moles) 
(moles) 
COOH/OH 
Structure 
__________________________________________________________________________ 
B-7 B-1 SA 97.0/3.0 
COOH/OH 
(1 mole) 
(0.5 mole) 
B-8 B-1 MA 98.0/2.0 
COOH/OH 
(1 mole) 
(0.5 mole) 
B-9 B-1 FA 97.0/3.0 
COOH/OH 
(1 mole) 
(0.5 mole) 
B-10 B-3 (1 mole) 
*6 (2 moles) 
##STR7## 
B-11 B-3 (1 mole) 
*7 (2 moles) 
##STR8## 
__________________________________________________________________________ 
Notes: 
*6: bisphenol A dyiglycidyl ether 
*7: glycidyl methaacrylate 
SA: succinic anhydride 
PREATION OF SIZING AGENTS 
Sizing agents (Test Examples 1-11) shown in Table 3 and those (Comparison 
Examples 1-9) as shown in Table 4 were prepared. 
TABLE 3 
______________________________________ 
1 2 3 4 5 6 7 8 9 10 11 
______________________________________ 
A-1 4.3 4.0 10.5 5.7 4.5 4.0 5.0 4.0 3.0 
A-2 4.0 2.0 4.0 3.0 4.0 5.0 4.0 
A-3 2.5 5.0 7.0 3.0 
B-1 9.0 
B-2 11.0 
B-3 6.5 
B-4 10.0 
B-5 8.0 
B-6 10.0 
B-7 9.0 
B-8 9.0 
B-9 9.0 
B-10 9.0 
B-11 10.0 
C-1 0.2 0.5 0.3 0.3 0.3 
C-2 2.5 
C-3 2.5 2.5 2.3 2.5 3.0 2.7 2.7 2.7 3.0 3.0 
______________________________________ 
TABLE 4 
______________________________________ 
1 2 3 4 5 6 7 8 9 
______________________________________ 
A-1 4.9 15.6 10.0 20.0 10.9 
A-2 4.6 10.0 
A-3 
B-1 10.5 20.0 
B-2 
B-3 
B-4 
B-5 
B-6 15.4 
B-7 
B-8 
B-9 
B-10 
B-11 
C-1 0.7 
C-2 3.7 1.9 
C-3 4.6 20.0 
*8 7.2 
*9 20.0 
*10 80.0 
*11 80.0 
______________________________________ 
Notes: 
Both in Tables 3 and 4, the numbers indicate weight parts. Except in 
Comparison Examples 7 and 8, water comprises 80 weight parts. 
A-1: bisphenol A diglycidylether (Epikote 828 produced by Yuka Shell 
Chemical Company or Epon 828 produced by Shell Chemical Company, epoxy 
equivalent 190) 
A-2: bisphenol A diglycidylether (Epikote 1002 produced by Yuka Shell 
Chemical Company or Epon 1002 produced by Shell Chemical Company, epoxy 
equivalent 630) 
A-3: tetraglycidyl diaminodiphenyl methane (Sumiepoxy ELM 434 produced by 
Sumitomo Chemical Industries Company, epoxy equivalent 120) 
C-1: polyoxyethylene (6 moles) nonylphenylether 
C-2: polyoxyethylene (70 moles) penta(phenylethylated) cumylphenylether 
C-3: polyoxythylene (30 moles) tri(phenylmethylated) phenylether 
*8: condensation product (acid value 50) of 2.0 moles of EO (2 moles) 
adduct of bisphenol A, 1.5 moles of maleic acid, and 0.50 moles of sebaci 
acid 
*9: epoxidized polybutadiene (BF1000 produced by Adeka Argus Chemical 
Company) 
*10: acetone 
*11: methylethyl ketone 
Evaluation 
By the methods to be described below, each sizing agent described above was 
examined in terms of stability of emulsion, fluffs and fiber breakage in 
carbon fibers sized therewith and inter-laminar shearing strength 
(hereinafter abbreviated as ILSS) of such carbon fibers. Results of these 
tests are shown in Table 5. Sheet molding compounds (SMC) were also 
prepared with such carbon fibers treated with the sizing agents and the 
bending strengths of these composites were measured. Results of these 
measurements are shown in Table 6. 
TABLE 5 
______________________________________ 
ILSS (kg/mm.sup.2) 
Emulsion Fluffs, Breakage 
Epoxy Vinyl Ester 
Stability TM Rubbing Resins Resins 
______________________________________ 
1 A A A 8.2 8.3 
2 A A B 8.2 8.3 
3 A A A 8.2 8.3 
4 A A A 8.2 8.3 
5 A A B 8.2 8.3 
6 A A A 8.2 8.3 
7 A A A 8.4 8.5 
8 A A A 8.4 8.5 
9 A A A 8.4 8.5 
10 A A A 8.5 8.5 
11 A A A 8.4 8.6 
1 ** -- -- -- -- 
2 A D C 7.7 7.0 
3 B C B 7.9 8.2 
4 ** -- -- -- -- 
5 ** -- -- -- -- 
6 A D D 6.4 6.5 
7 -- D D 7.5 7.0 
8 -- B C 7.8 7.1 
9 A C B 7.8 7.9 
______________________________________ 
Note: 
**indicates no emulsification 
TABLE 6 
______________________________________ 
Bending 
Strength (kg/cm.sup.2) 
Modulus (kg/cm.sup.2) 
______________________________________ 
Test Examples 
1 14.5 .times. 10.sub.2 
8.6 .times. 10.sup.4 
3 14.4 .times. 10.sup.2 
8.5 .times. 10.sup.4 
8 14.8 .times. 10.sup.2 
8.8 .times. 10.sup.4 
10 14.8 .times. 10.sup.2 
8.9 .times. 10.sup.4 
11 15.2 .times. 10.sup.2 
9.0 .times. 10.sup.4 
Comparison 
Examples 
1 13.5 .times. 10.sup.2 
6.8 .times. 10.sup.4 
3 13.8 .times. 10.sup.2 
7.5 .times. 10.sup.4 
______________________________________ 
Superior effects obtainable by the present invention are clearly 
demonstrated in Tables 5 and 6. 
Methods of Evaluation and Measurements 
(1) Emulsion Stability 
Each solution of sizing agent with concentration of 20% was left for 7 days 
at 20.degree. C., its separation was evaluated as follows: 
A: No separation 
B: Creamy floating substances 
Sizing Treatment of Carbon Fibers 
(2-1) No-size yarns of carbon fibers (7.mu./6000 filaments) were dipped 
into a solution of each sizing agent for impregnation such that the 
effective amount that was attached became 1.2 wt %. After they were wrung 
by rollers and dried, they were subjected to a heat treatment at 
150.degree. C. for 10 minutes inside an oven and collected by winding. 
(2-2) No-size yarns of carbon fibers (7.mu./3000 filaments) were dipped 
into a solution of each sizing agent for impregnation such that the 
effective amount that was attached became 3.5 wt %. After they were wrung 
by rollers and dried, they were subjected to a heat treatment at 
150.degree. C. for 20 minutes inside an oven and chopped to lengths of 1 
inch to produce chopped fibers. 
(3) Fluffs and Breakage 
A TM type yarn friction and rubbing tester (produced by Daiei Kagaku Seiki 
Company) was used to test the fiber-metal friction of the carbon fibers 
treated according to (2-1) with a load of 100g/6000 filaments, 
.THETA.=150.degree., length of frictional motion=30 mm and a metallic comb 
moved 500 times reciprocatingly at the rate of 150 times/min. Separately, 
a rubbing tester (produced by Toyo Seiki Company) was used to test the 
fiber-fiber friction with internal angle of about 35.degree., one twist, 
length of frictional motion =20 mm and 500 times of reciprocating motion 
at the speed of 100 times/min. The results of these tests were evaluated 
as follows: 
A: Hardly any fluffs or yarn breakage 
B: Fluffs appearing only singly 
C: Fluffs and breakage occurring in groups 
D: Frequent occurrence of fluffs and yarn breakage and cutting in one part. 
(4) Measurement of ILSS 
(4-1) When an Epoxy Resin was Used as Matrix Resin 
After carbon fibers sized according to (2-1) were impregnated with a 
resinous composition which comprises 80 weight parts of bisphenol A 
diglycidyl ether monomer (Epikote 828 produced by Yuka Shell Chemical 
Company or Epon 828 produced by Shell Chemical Company), 20 weight parts 
of bisphenol A diglycidylether polymer (Epkote 1002 produced by Yuka Shell 
Chemical Company or Epon 1002 produced by Shell Chemical Company), 5 
weight parts of boron trifluoride monomethylamine and 25 weight parts of 
methylethyl ketone and methylethyl ketone was removed therefrom, they were 
partially hardened and a unidirectionally reinforced prepreg was produced. 
The prepreg thus obtained was cut and placed inside a mold and a composite 
with V.sub.f (volume percentage of carbon fibers therein)=60% was formed 
by applying a pressure of 7 kg/cm.sup.2 for 90 minutes at 140.degree. C. 
The dimensions of the product were 2.5 mm in thickness, 6 mm in width and 
17 mm in length. ILSS of this product was measured by the short beam 
method (ratio of span length/thickness=5). 
(4-2) When Unsaturated Resin With Ester Bond Was Used as a Matrix Resin 
After carbon fibers size according to (2-1) were impregnated uniformly with 
a resin mixture composed of 100 weight parts of vinyl ester resin (Ripoxy 
R-802 produced by Showa Kobunshi Company), 1 weight part of tertiary 
butylperbenzoate and 1 weight part of butylbenzoylperoxide, a pressure of 
7 kg/cm.sup.2 was applied for 60 minutes at 130.degree. C. in a molding 
production process and a unidirectionally reinforced prepreg with V.sub.f 
=60% was produced. The dimensions of this product were 2.5 mm in 
thickness, 6 mm in width and 17 mm in length. ILSS of this product was 
measured by the short beam method (ratio of span length/thickness=5). 
(6) Measurement of Bending Strength 
After 40 weight parts of styrene solution with 35% of rubber-type low 
shrinkage agent, 60 weight parts of styrene solution with 60% of 
unsaturated polyester resin (Polyset 9109 produced by Hitachi Kasei 
Company, phthalic ester-type) 1.5 weight parts of tertiary 
butylperbenzoate, 3.0 weight parts of zinc stearate, 200 weight parts of 
calcium carbonate powder and 0.3 weight parts of parabenzoquinone were 
uniformly mixed, 2.0 weight parts of magnesium oxide were added and a 
composition for SMC (sheet molding compound) containing 20% of a 
one-to-one mixture of glass fibers of one inch in length and carbon fibers 
of one inch in length treated according to (2-1) was prepared. This 
composition was molded at 140 C. and bending strength was tested on this 
molded product.