1
32
Three Bond Technical News
Issued December 20, 1990
Curing Agents for Epoxy Resin
Introduction
_______________________________________________
•
Epoxy resin was discovered in 1938 by
Pierre Castan, a chemist in Switzerland. As of
1989, 137,000 tons of epoxy resin had been
produced in Japan, and epoxy resin has been
used in a wide range of fields, such as paints,
electricity, civil engineering, and bonds. This is
because epoxy resin has excellent bonding
property, and also after curing, it has excellent
properties on mechanical strength, chemical
resistance, electrical insulation. In addition,
epoxy resin is able to have various different
properties as it is combined and cured together
with various curing agents.
This issue describes the types of curing
agents for epoxy resin and their characteristics
comparing to Three Bond products.
The epoxy resin compositions of Three Bond
currently on the market are the Three Bond
2000 Series (base agent for epoxy resin), the
Three Bond 2100 Series (curing agent for
epoxy resin), and the Three Bond 2200 Series
(one-part thermal cure epoxy compound
resins).
Contents
Introduction.......................................................................................................... 1
1. Amines............................................................................................................. 2
1-1. Aliphatic amine......................................................................................... 2
1-2. Aromatic amine ........................................................................................ 4
1-3. Modified amines ....................................................................................... 4
2. Polyamide resin ............................................................................................... 5
3. Tertiary and secondary amines ....................................................................... 5
4. Imidazoles ....................................................................................................... 6
5. Polymercaptan curing agent............................................................................ 6
5-1. Liquid polymercaptan ............................................................................... 6
5-2. Polysulfide resin ....................................................................................... 6
6. Anhydrides....................................................................................................... 8
7. Latent curing agents........................................................................................ 8
7-1. Boron trifluoride-amine complexes........................................................... 8
7-2. Dicyandiamide.......................................................................................... 8
7-3. Organic acid hydrazide ............................................................................ 9
8. Photo- and ultraviolet-curing agents................................................................ 9
Conclusion......................................................................................................... 10
2
1. Amines
_______________________________________________
•
Amine compounds are classified into primary,
secondary, and tertiary amines, in which one, two,
and three hydrogen molecule(s) of ammonia (NH
3
)
have been substituted for hydrocarbon, respectively.
Amines are called monoamine, diamine, tri-amine,
or polyamine according to the number of amines in
one molecule. Amines are classified into aliphatic,
alicyclic (Three Bond 2106), and aromatic amines
according to the types of hydrocarbons involved,
and the all are important curing agents for epoxy
resin.
Aliphatic amine (Three Bond 2103) is curing
agent for epoxy resin ant able to cure at room
temperature. The cured resin has excellent
properties, and its heat resistance is 100°C.
Aromatic amine has been developed to achieve
greater heat resistance and chemical resistance than
those of aliphatic amine.
The curing of epoxy resin by amine curing agents
is expressed by the formula shown below; the active
hydrogen in primary amine reacts with an epoxy
group to form secondary amine, and the secondary
amine reacts with an epoxy group to cure. Then, the
resultant tertiary amine polymerizes epoxy groups.
In general, curing agent must have more than
three active hydrogen atoms and two amino groups
in a molecule so that the cured resin becomes
crosslinked polymer, according to the reaction of
the above equation. The loading of the curing agent
in epoxy resin becomes optimal when the number
of moles in epoxy groups is equal to that of active
hydrogen.
The curing speed of individual amines depends
on the type and loading of amine, and the type of
epoxy resin. The most commonly used
glycidyl-ether type resins easily cure at room
temperature, but inner epoxy type such as
cyclohexene oxide and epoxidized polybutadiene is
hardly cured. Glycidyl-ester type cures quite faster
than glycidyl-ether type. Diglycidyl ether of
bisphenol A (DGEBA), which is a condensation
product of bisphenol A and epichlorohydrin, is
primarily cured by aliphatic amines at room
temperature, but is slowly cured by aromatic amines
and requires thermal curing.
Table 1 shows the properties and performances of
representative polyamines used as curing agents for
epoxy resin.
1-1. Aliphatic amine (Three Bond 2103)
Aliphatic amine, which rapidly reacts with epoxy
resin, is a representative room-temperature curing agent.
However, it generates a large quantity of heat and has a
short pot life (usable time). Loading of amines
containing no tertiary amine is made at the exact or very
closed amount that is said in stoichiometry, and use
amount of amines containing tertiary amine is made less
than that. If latter curing is performed at high
temperature, properties of curing agents that cure at
room temperature are improved. The heat-deformation
temperature (HDT) of cured object of DGEBA is 120°C
at the highest.
Resins that have been cured using aliphatic amines
are strong, and are excellent in bonding properties. They
have resistance to alkalis and some inorganic acids, and
have good resistance to water and solvents, but they are
not so good to many organic solvents. Aliphatic amine
irritates the skin and possesses toxicity. Although those
that have high molecular weight and low vapor pressure
are less toxic, good cares for handling are required.
3
Table 1. Properties and performance of amine based curing agents
Curing conditions Applicability
Class Subclass
Name of curing
agent
Appearance
Viscosity
cps
(25°C)
Active -
hydrogen
equivale
nt (amine
value)
Loading
amount to
liquid
epoxy
resin (phr)
Specific
gravity
(g/ml)
(20°C)
Pot life
(100 g)
(batch)
Temperature
(°C)
Time
(minutes)
Heat
deformation
temperature
(°C)
Bonding
Lamination
Casting Paint
Remark
Diethylenetriamine (DTA)
Transparent
liquid
5.6 20.7
5 - 10
Standard
value: 8
0.954
20
minutes
Normal to
100
30 minutes
to 4 days
115
Triethylenetetramine
(TTA)
Transparent
liquid
19.4 24.4
6 - 12
Standard
value: 9
0.98
20 to 30
minutes
Normal to
100
30 minutes
to 4 days
115
Tetraethylenepentamine
(TEPA)
Transparent
liquid
51.9 27.1
7 - 14
Standard
value: 12
1.00
30 to 40
minutes
Normal to
100
30 minutes
to 7 days
115
Diproprenediamine
(DPDA)
Transparent
liquid
29.0
12 - 15
20 to 30
minutes
Normal to
200
30 minutes
to 7 days
110
Diethylaminopropylamine
(DEAPA)
Transparent
liquid
65.0
4 - 8
Bonding
= 8,
Casting
= 4,
Lamination
= 6
1 to 4
hours
65 - 115 1 - 4 hours
85
Chain
aliphatic
polyamine
AMINE 248
Transparent
liquid
1000 -
3000
42.9
35 0.83
30
minutes
Normal to
100
30 minutes
to 4 days
92
Rare Hexamethylenediamine
N-aminoethylpiperazine
(N-AEP)
Transparent
liquid
43 20 - 22 0.984
20 to 30
minutes
Normal to
200
30 minutes
to 3 days
103
Lamiron C-260
Transparent
liquid
60
31 - 33 31 - 33 0.945 80+150
2 hours + 2
hours
150
Araldit HY-964
Transparent
liquid
70
15 - 20 0.94
120
minutes
Normal 7 days
Menthane diamine (MDA)
Transparent
liquid
19.0
42.5 22 6 hours
80 - 130
130 - 200
30 minutes
to 2 hours
2+3 hours
158
Isophoronediamine
(IPDA)
Transparent
liquid
18.2
41 24 0.924 1 hour 80+150 4+1 hours
149
S Cure 211
Transparent
liquid
17 - 21 0.96
30
minutes
Normal to
70
2 hours to 7
days
47
S cure 212
Transparent
liquid
12 - 16 0.98
40
minutes
Normal to
70
2 hours to 7
days
48
Wandamin HM
m•p
40°C
53 30 0.95 60+150 3+2 hours
150
Alicyclic
polyamine
1.3 BAC
35.5 0.94
m-xylenediamine
(m-XDA)
Crystalline
liquid
34.1 16 - 18 1.05
20
minutes
Normal to
60
1 hour to 7
days
115
Sho-amine X Liquid
68°
33 - 34 16 - 18 1.05
20
minutes
Normal to
60
1 hour to 7
days
113
Xylylenediamine
Amine black
Viscous
liquid
(50°C)
2000
-
6000
30 - 60 1.20
40
minutes
Normal to
60
1 hour to 7
days
Xylylenediamine trimer
Sho-amine black
Viscous
liquid
6000
-
10000
25 - 35 1.18
40
minutes
Normal to
60
1 hour to 7
days
116
Xylylenediamine trimer
Sho-amine N Liquid
5°
(690) 25 1.18
80
minutes
Normal to
60
1 hour to 7
days
81
Xylylenediamine derivative
Sho-amine 1001 Liquid
100.0
27 1.07
Normal to
60
1 hour to 7
days
73
Xylylenediamine derivative
Aliphatic
polyamine
Aliphatic
aromatic
amine
Sho-amine 1010 Liquid
40.0
27
Normal to
60
1 hour to 7
days
70
Xylylenediamine derivative
Metaphenylene diamine
(MPDA)
Solid
mp62
°C
34 14 - 16 0.95 6 hours
80+150
2+4 hours
150
Diaminodiphenylmethane
(DDM)
Solid
mp8
°C
49.6 25 - 30 1.05 8 hours
80+150
2+4 hours
150
Aromatic
amine
Diaminodiphenylsulfone
(DDS)
Solid
mp17
5°C
62.1 30 - 35 1.33
Approximately
1 year
110+200 °C
2+4 hours
180 - 190
4
1-2. Aromatic amine (Three Bond 2163)
Aromatic amine has weaker basicity than
aliphatic amine and slowly cures at room
temperature due to steric hindrance by the aromatic
ring. The curing virtually stops in the B-stage of a
linear polymer solid due to the large difference in
the reaction of primary and secondary amines.
Normally, the curing of aromatic amine requires
heating in two steps. The first heating is carried out
at a rather low temperature of approximately 80°C
so as to lessen heat generation, and the second
heating is carried out at a high temperature of
150°C to 170°C.
Aromatic amine provides excellent heat
resistance, HDT of 150°C to 160°C, and is good in
mechanical properties and strong. In addition, the
amine has good electrical properties and excellent
chemical resistance, particularly against alkalis, and
thus it is a curing agent that is highly resistant to
solvents.
1-3. Modified amines
The modification of amine curing agents
improves the workability as follows:
1. Extends the pot life
2. Increases or decreases the curing speed
3. Improves compatibility with resins
4. Liquefies curing agents
5. Reduces reactivity to carbon dioxide in the air
6. Reduces toxicity and irritation to the skin
7. Decreases weighing error because loading
amount is increased
(1) Amine adduct (
polyamine epoxy-resin adduct
)
(Three Bond 2102, 2131B)
When epoxy resin is allowed to react with an
excessive amount of polyamine such as DETA and
consumes all of the epoxy groups, an amine adduct
having active hydrogen of the residual amino
groups is formed. As the adduct has a high
molecular weight, it is less volatile, releases less
amine odor, is less toxic, and is less exothermic.
The loading of the adduct in resins is so much, then
the weighing error becomes small.
(2) (Ketimine (Ketoimine)
Ketimine, which is attracting attention as a curing
agent for high solid paints, is formed by the reaction
between aliphatic polyamine such as DTA, TTA,
DPDA, and m-XDA, and ketone such as
methylethyl ketone (MEK) and isobutylketone
(MIBK).
Ketimine cures very slowly when mixed with
epoxy resin, but it works as a kind of latent curing
agent, when it is made to coat or the like, by
absorbing moisture in the air and regenerating
amines to cure at room temperature.
Practically, ketimine cures at normal temperature
in approximately 8 hours, and is used in high solid
paints. The cured resin has properties almost same
as those of resin cured by the original polyamine,
but its application is limited to thin films due to the
fact that it regenerates ketones, and its curing speed
is slow.
Two-part epoxy-compound resin Adhesion between glass and metal Encapsulation of a coil
5
2. Polyamide resin (Three Bond 2105, 2105C, 2105F and 2107)
____
•
Polyamide resin, which has been widely used as a
curing agent for epoxy resin, is formed by the
condensation reaction between dimer acid and
polyamine, and contains reactive primary and
secondary amines in its molecules.
Polyamide amine reacts with bisphenol-A-type
epoxy resin to cure at or below normal temperature
with moderate heat generation. It cures so slowly
that it has a long pot life.
As polyamide has high hydrocarbon moiety in its
molecules, it cures epoxy resin into a highly
plasticized rigid thermosetting polymer. The cured
resin features high tensile, compression, and
bending strengths, while it is stiff, strong, and
excellent in shock resistance.
3. Tertiary and secondary amines
____________________________
•
Tertiary amine, the active hydrogen in which has
been completely replaced with carbon hydroxide,
does not cause an additional reaction with epoxy
resin, but works as a polymerization catalyst. Thus,
the loading is not constant and depends on the type
of curing agent. The curing temperature
significantly influences the curing speed, heat
generation, and the properties of the cured resin.
Thus, the amine is rarely used alone, since,
particularly in large castings, properties at the center
and the outer region are different due to the large
quantity of heat generation. It is used in the fields of
paints and adhesives.
Although tertiary amine is less useful as a curing
agent, it is a very important compound as an
accelerator for acid anhydrides, and is useful as an
accelerator or co-curing agent for polyamine and
polyamide curing agents.
Piperidine N,N-dimethylpiperidine Triethylenediamine 2,4,6-tris
(dimethylaminomethyl)
phenol
(DMP-30)
Benzyldimethylamine 2-(dimethylaminomethyl)phenol
(BDMA) (DMP-10)
One-part epoxy-compound resin Bonding between ferrite and the yoke Impregnated locking of the motor coil
6
4. Imidazoles (Three Bond 2162F, 2163C)
_____________________
•
Like tertiary amines such as BDMA and DMP-30,
imidazoles are a type of anionic polymerizing
curing agent for epoxy resin. Imidazoles are
characterized by a relatively long pot life, the ability
to form cured resin with a high heat deformation
temperature by thermally treating at a medium
temperature (80°C to 120°C) for a short time, and
the availability of various derivatives having
moderate reactivity that improves workability. For
example, imidazole carboxylate, epoxy-imidazole
adduct, metal salt-imidazole complex compounds,
and imidazole that has been reacted with acidic
substances are used as curing agents. All are
intended to improve workability by achieving a
high pot life and rapid curing at a desired
temperature (100°C to 180°C), and have been used
in compound resin compositions such as one-part
thermosetting coating adhesives, casting materials,
and filling materials.
In addition, as in the case of other types of
tertiary amine, imidazoles can be used as a curing
accelerator or co-curing agent for organic-acid
anhydrides, dicyandiamide, polyhydric phenol, and
aromatic amine. In such cases, imidazoles exhibit
better properties than other types of tertiary amines,
including a longer pot life, faster curing speed, and
higher heat resistance of the cured substance.
2-methylimidazole 2-ethyl-4-methylimidazole 1-cyanoethyl-2-undecylimidazolium trimellitate
Epoxy-imidazole adduct
5. Polymercaptan curing agent
______________________________
•
5-1. Liquid polymercaptan (Three Bond 2086B Curing Agent)
Polymercaptan, which cures at 0°C to -20°C, is attracting attention as a low-temperature curing agent. It
requires to add tertiary amine as an accelerator. At normal temperature, polymercaptan has a pot life of 2 to 10
minutes, and rapidly cures and reaches practical strength in 10 to 30 minutes. The following structure shows a
type of polymercaptan curing agent.
5-2. Polysulfide resin (Three Bond 2104)
Like liquid polymercaptan, polysulfide resin has mercaptan groups at its terminals, but the resin does not have
low-temperature and fast-curing properties and is used as a curing agent doubling as a flexibilizer. Normally, the
resin works as a room-temperature curing agent when used in combination with a tertiary amine or polyamine
curing agent. The loading is 50 to 100 wt% and as the loading of polysulfide increases, the cured resin increases in
flexibility, shock resistance, and permittivity, while it decreases in curing shrinkage. Due to its good water
resistance, polysulfide resin has been used in adhesives, sealing agents, and casting materials.
7
Table 2. List of acid anhydrides
Type of curing agent
Product
name
Appearance
Molecular
weight
Acid
anhydride
equivalent
(neutralization
equivalent)
Viscosity
cps. 25°C
Melting
point
°C
Specific
gravity
25°C
Boiling point
°C /mmHg
Phthalic anhydride Solid 148.1 148 - 130.8 1.527 295/760
Trimellitic anhydride Solid 192 - - 168 - 240-245/14
Pyromellitic anhydride Solid 218 109 - 286 1.68 305-310/30
Benzophenone
tracarboxylic anhydride
Solid 322 - 221-255 -
Ethylene glycol
bistrimellitate
Rikaresin
TMEG
Solid ca. 410 204 - 64-72 1.46 -
Glycerol tristrimellitate
Rikaresin
TMTA
Solid ca. 600 210 - ca. 70 1.47 -
Maleic anhydride Solid 98 98 - 52.8 1.48 202/760
Tetrahydrophthalic
anhydride
Rikacid TH Solid 152.1 152 4.65
(105°C)
100< 1.20
(105°C)
120/3
HN-2200 Liquid - (81-85) 50-80 -15> 1.21±0.05 -
Methyltetrahydrophthalic
anhydride
Epiclon
B-570
Liquid 166 166 ca. 40 -15> 1.201 -
Endomethylene
tetrahydrophthalic
anhydride
Kayahard
CD
Solid 164 164 - 164-165 - -
Kayahard
MCD
Liquid 178 - 200-300 10> 1.23 (20°C) 250>
MHAC-P Liquid - (88-93) 150-300 - 1.23±0.01 -
Methylendomethylene
tetrahydrophthalic
anhydride
MHAC-L Liquid - (87-92) 150-300 - 1.24±0.01 -
Methylbutenyl
tetrahydrophthalic
anhydride
YH-306 Liquid 234 117 ca. 130 -15> 1.09±0.01 150/1
Dodecenyl succinic
anhydride
DSA Liquid 266 - 300-800
(20 °C)
- 1.002
(20°C)
180-182/5
Hexahydrophthalic
anhydride
Rikacid HH Solid 154 154 23.0 (40°C) 34.0< 1.18 (40°C) 110/5
Rikacid
MH-700
Liquid 168 161-166 50-70 -15> 1.17 127/5
Epiclon
B-650
Liquid 168 170 ca. 65 -15> 1.17 173/30
Hexahydro-4-Methylphthalic
anhydride
HN-5500 Liquid 168 - 50-80 -15> 1.16±0.01 -
Succinic anhydride Rikacid SA Solid 100 100 - 118.0< 1.503 128.2/10
Methylcyclohexene
dicarboxylic anhydride
Epiclon
EXB-4400
Solid 264 132 - 167 - -
Alkylstyrene-maleic
anhydride copolymer
Smicure
MS-1
Solid - - - ca. 135 - -
Chlorendic anhydride
Kayahard
CLA
Solid 371 371 - 235-239 - -
PAPA Solid - - 200 (99°C) 52-65 - -
Polyazelaic polyanhydride
Rikacid
PAZ-90
Solid - 172 1000 (80°C) 55-65 1.19 -
8
6. Anhydrides (Three Bond 2162G, 2280C)
______________________
•
Anhydrides used as epoxy-resin curing agents
have been used as curing agents for electrical
insulating materials. Anhydrides require severer
curing conditions than amine-based curing agents,
but are suitable for making large moldings, as they
have a long pot life and form cured resins having
relatively well-balanced electrical, chemical, and
mechanical properties while generating a small
quantity of heat.
(1) Aromatic anhydrides
Aromatic anhydrides are generally solid. They
have been used in powder paints for powder
molding, and their varnishes and solutions in liquid
anhydrides have been used in insulating coating for
condensers and casting.
(2) Alicyclic anhydrides
Alicyclic anhydrides are the most common curing
agents for epoxy resin. Most of the generally used
anhydrides fall into this category. Of these, the
principal curing agents are methyltetrahydro
phthalic anhydride, tetrahydro phthalic anhydride,
methyl nadic anhydride, hexahydro phthalic
anhydride, and methylhexahydro phthalic
anhydride.
(3) Aliphatic anhydrides
Polycarboxylic anhydrides, which are formed by
the dehydration condensation reaction between
aliphatic dibasic-acid molecules, exhibit excellent
flexibility and thermal shock resistance, and have
been used alone or in combination with other
anhydrides in powder paints and casting resin
curing agents.
When anhydrides are used as curing agents,
curing accelerators are normally used. Many types
of accelerators, such as tertiary amine, boric-acid
ester, Lewis acid, organic metal compounds,
organic metal salts, and imidazole, have been
studied.
7. Latent curing agents
_____________________________________
•
Latent curing agents are mixtures of curing agents
with epoxy resin that can be stably stored at room
temperature, and rapidly cure by heat, light,
pressure, and others.
7-1. Boron trifluoride-amine complex
(Three Bond 2285B, 2287, 2287B)
Lewis acids such as BF
3
, ZnCl
2
, SnCl
4
, FeCl
3
,
and AlCl
3
have been known as cationic
polymerization catalysts. Unlike anion
polymerization by Lewis bases (e.g., tertiary amine),
Lewis acids work as polymerization catalysts not
only for DGEBA-type resins but also for linear and
alicyclic epoxy resins. The Lewis acids vigorously
react with resins at room temperature, and their pot
life is 30 seconds or less. Therefore, they are
normally used in the form of complexes with
amines. The representative Lewis acid is boron
trifluoride-amine complex, which has the structure
shown below. The complexes have different
properties (e.g., melting point, reactivity) according
to the type of amine.
The BF
3
-amine complex is a catalyzed curing
agent, and thus it is added to resins in small
amounts (1% to 5%). The cured resins have a high
HDT (150°C to 170°C); in particular, the cured
substances of some novolac-type epoxy resins have
a HDT of 230°C, and feature excellent electrical
properties, but their chemical resistance is relatively
weak. Due to the latency and heat resistance of the
cured resins, the complexes have been used in
electrical insulating laminates and carbon fiber
reinforced plastics (CFRP).
7-2. Dicyandiamide
(Three Bond 2220 to 2227)
Dicyandiamide (DICY) is a representative latent
curing agent that forms crystals having a high
melting point of 207°C to 210°C. DICY has a pot
9
life of 24 hours when it is dissolved in epoxy resin
using a solvent or the like, but it is normally used in
the form of fine powder dispersed in the resin,
which has a very long pot life of 6 to 12 months.
DICY cures at high temperatures of 160°C to 180°C
in 20 to 60 minutes, and generates a large quantity
of heat during curing. Thus, it has used only in thin
films such as paints, adhesives, and laminates. The
cured resins have good adhesiveness and are less
prone to staining. DICY has frequently been used in
one-part adhesives, powder paints, and pre-pregs.
Although DICY has good latency, its curing
temperature is so high and its curing time so long
that it requires an accelerator. Commonly used basic
compounds include tertiary amine, imidazole, and
aromatic amine.
7-3. Organic-acid hydrazide
Organic-acid hydrazide, a powder that has a high
melting point and is synthesized from carboxylate
ester and hydrazine, is dispersed in epoxy resin to
work as a latent curing agent.
Normally, organic-acid hydrazide has a pot life of
4 to 6 months, and cures at ca. 150°C in 1 to 2
hours. Organic-acid hydrazide cures at lower
temperatures and has better water resistance and
adhesiveness than DICY, and has been used in
powder paints and one-part adhesives.
8. Light-curing and ultraviolet-curing agents (Three Bond 3101)
____
•
Light-curing and ultraviolet (UV)-curing agents
are stable in epoxy resin, and are decomposed by
exposure to light or UV to cure the resin. The
agents are regarded as a type of latent curing agent,
and are attracting attention as a potential ingredient
of non-polluting paints and printing inks, in which
the agents will be dissolved in liquid resins using no
solvent.
The representative ultraviolet (UV) curing agents
are the following two in the form of onium salt:
Diphenyliodonium hexafluorophosphate
Triphenylsulfonium hexafluorophosphate
In 1975, Crivello used a diaryl iodonium salt for
ring-opening polymerization of epoxy resin.
Above, the cationic polymerization of epoxy resin
using HPF
6
is shown.
Crivello also found that triaryl sulfonium salt
works as a light-curing agent for epoxy resin. It
cures rapidly, particularly in the case of alicyclic
epoxy resin.
The light-curing and UV-curing of epoxy resins
do not involve enzyme inhibitions that may affect
the radical polymerization of photosensitive resins,
and the cured epoxy resin has better properties and
adhesiveness than other resins.
(Solvent)
10
1456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, Japan
Tel: 81-426-61-1333
Conclusion
________________________________________________
•
In this issue, we have reviewed various curing
agents for epoxy resin. The most suitable curing
agent must be selected according to the use
conditions, application, workability, and other
factors. Only the curing agents for epoxy resin are
discussed in this issue; in practical use, however,
they are mixed with diluents, coupling agents,
fillers, and other agents to improve the curing
properties and workability. As closing, I would hope
that epoxy resins are widely used in many fields.
Osamu Hara
Custom Group,
Technical Department
Research Laboratory
Three Bond Co., Ltd.
