Three Bond Technical News
Issued January 1, 1996

46

Instant Adhesives(Cyanoacrylate Adhesives)<Part 3>Introduction _______________________________________________ •It has passed 38 years since instant adhesives were first introduced to the global market in 1957.
Today, instant adhesives are used in a variety of applications for industrial, medical, and generaldomestic purpose. The main reason that usage fields of instant adhesives have expanded can be foundon its ease of use, which is one-part adhesive and bonds any materials strongly and instantaneously atroom temperature. As it can be used easily, demands of instant adhesives are high, however, especiallyin industrial fields it is not adopted in many cases due to the bonding performance and durability.
Therefore, it is demanded to develop instant adhesives with higher performances.
Three Bond has developed and marketed ThreeBond 1731 / 1733, and ThreeBond 1737 / 1738 as theproducts improving peeling strength and shock resistance that are disadvantages of instant adhesives.
This issue will introduce the background and history of the development of these products and will
describe their characteristics.
ContentsIntroduction
1. Polymer properties and strengthening ............................................................ 2
2. Instant adhesive properties and strengthening ............................................... 3
3. Polymerization-inducing phase-separated structureof cyanoacrylate/rubber alloy .......................................................................... 5
4. Second-generation instant adhesives-ThreeBond 1731 and 1733................. 6
5. Third-generation instant adhesives-ThreeBond 1737 and 1738 ..................... 7
6. The ThreeBond 1700 Series ........................................................................... 81

1.

Polymer properties and strengthening _______________________ •Wu has reported that the properties ofthermoplastic polymers can be classified into thefollowing types based on two molecular parameters:
entanglement density υe (mmole/cc) of the polymer
chain and the characteristic ratio C∞1).
(1) Brittle polymers (hard and brittle polymers)υe ≤ ~ 0.15, C∞ ≥ ~ 7.5(2) Pseudo-ductile polymers (soft polymers)υe ≥ ~0.15, C∞ ≤ ~7.5
(3) Intermediate polymers
υe = ~0.15, C∞ = ~7.5
Figure 1 shows how various polymers are grouped
according to this classification scheme.
Also, regarding polymers alloyed by adding

rubber components, Wu shows optimal dispersion
morphology of the rubber components forstrengthening polymers, as follow.
(1) Optimal diameter of rubber particle exists foralloys consisting of brittle polymers/rubbercomponent (Figure 2).
(2) Optimal surface-to-surface distance between
rubber particles exists for alloys consisting ofpseudo-ductile polymer/rubber component(Figure 3).
(3) Special rubber phase morphology is required foralloys consisting of intermediate polymer/rubbercomponent.

Entanglement density

Pseudo-ductile
polymers

Intermediatepolymers

Brittle polymers

Characteristic ratio

Figure 1: Classification of various thermoplastic polymers

2Optimal particle diameter do (µm)

RubberPolymercomponents

Entanglement density υe (mmole/cc)

Critical distance between particle surfaces τc (µm)

Figure 2: Brittle polymers and optimal particle size

PolymerRubbercomponents

Characteristic ratio C∞

Figure 3: Pseudo-ductile polymers and critical distance between particle surfaces.

2.

Instant adhesive properties and strengthening ________________ •Cyanoacrylate (cyanoacrylic acid ester), the main
constituent of instant adhesives, reacts with trace
amounts of moisture on the surface of the materials
to be bonded and cures by polymerization to formcyanoacrylate polymers (Figure 4).
Because these polymers are hard and brittle, they
feature high shearing strength in the shearing
direction, but are weak in strength for peeling andshock. Figure 5 shows the results of calculationaccording to Wu's method2) of two molecularparameters representing polymer properties for ethyl
cyanoacrylate, the most popular adhesive on themarket today.

CuringCyanoacrylate

Cyanoacrylate polymer

Figure 4: Curing of cyanoacrylate

Ethyl cyanoacrylate polymer

Figure 5: Ethyl cyanoacrylate polymer and values of molecular parameters3

Entanglement density υe (mmole/cc)

When strengthening poly (ethylcyanoacrylates)(PECA), which is a brittle polymer according to
Wu's classification, by adding rubber components, it
is concluded that there an optimal rubber particle
diameter exists. Figure 6 shows the brittleness ofPECA compared to other polymers, and Figure 7

shows the results of calculation for the optimal
diameter of rubber particle.
According to Wu's theory, for alloy consisting ofPECA/rubber, the optimal particle diameter forstrengthening PECA is around 1 µm.

BrittlenessCharacteristic ratio C∞

Figure 6: Brittleness of PECA

Polymer

Optimal particle diameter do (µm)

Rubbercomponent

Entanglement density υe (mmole/cc)

Figure 7: Entanglement density and the optimal particle diameter for PECA4

3.

Polymerization-inducing phase-separated structure ofcyanoacrylate/rubber alloy3,4) ______________________________ •Figure 8: Dispersion of rubber particles within
cured adhesive

Initial stage of curing

Cyanoacrylate monomer

Figure 8 is a transparence type electron
microscope image of the state of rubber component
dispersion within the cured cyanoacrylate adhesive
to which a rubber component has been added.
The rubber is concentrated in the central portionof the cured adhesive, and it was found that therubber particles were dispersed in spheres ofdiameters ranging from the submicron level toaround 1
micrometer.
Thisconcentratedmorphology is understandable in that the curing of
cyanoacrylate is initiated by contact with moistureon the surface of the materials to be bonded. As
stated above, curing progresses from the bonding
surface toward the interior parts of the adhesive.
Therefore, the rubber particles are concentrated at
the central portions of the adhesive, ultimately
leading to phase separation (Figure 9).

Progress of curing andconcentration of rubbercomponents

Curing complete

Cyanoacrylate polymer

Rubbercomponents

Figure 9: Polymerization of cyanoacrylate and phase separation
We developed instant adhesives with higher
peeling strength and excellent shock resistance,
applying the examination for strengthening
polymers through alloying with rubber, and theresults of analysis of the phase separation structure
based on the unique polymerization mechanism of
cyanoacrylate,54.

Second-generation instant adhesives−ThreeBond 1731 and 17335, 6, 7) __________________________ •ThreeBond 1731 and 1733 are second-generation
high-performance
instant
adhesives
withnon-conjugated rubber components dissolved in themain constituent, cyanoacrylate; these components
undergo phase separation as curing progresses(Figure 10). Table 1 shows the properties andgeneral characteristics of these products.
In addition to the properties shown in Table 1,

alloying with rubber improves cold resistance, heat
cycle resistance based on reduction of thermal stress,and heat resistance. Furthermore, with theimprovements of bonding ability for the bonding
resistant materials such as ethylene-propylene-diene
terpolymers (EPDM), it became possible to apply
these adhesives on semi-structure applications that
could not use conventional instant adhesives.

First-generation instant adhesives: ThreeBond 1781, 1782, and 1783
CuringCompatible system

Compatible system

Second-generation instant adhesives: ThreeBond 1731 and 1733
CuringIncompatible system

Compatible system

Figure 10: Phase structures of first-generation and second-generation instant adhesives

Table 1: Properties and general characteristics of ThreeBond 1731 and 1733
Items

Units

TB1731

TB1733

Color and appearance-Lemon yellow

Lemon yellow

ViscositymPa•s {cP}

20 {20}150 {150}

Seconds

1020

19 {190}

16 {160}

10 {100}

11 {110}3.0 {8.0}

3.0 {8.0}

2.0 {5.0}

2.0 {5.0}

34 {35}34 {35}

Set time

Fe/Fe
Fe/Fe

Shearing adhesive strength2

Mps {kgf/cm }
Al/Al
Fe/Fe

Peeling adhesive strengthkN/m {kgf/25mm}
Al/Al

Impact adhesive strength

Fe/Fe

2

2kJ/m {kgf•cm/cm }(TB: abbreviation for ThreeBond)

6

5.

Third-generation instant adhesives−ThreeBond 1737 and 17388) _____________________________ •is not consistent on such surfaces. In other words,
the changes on curing speed result changes ofdispersion state, and appeared as changes ofperformance.
Furthermore, ThreeBond 1737 and 1738 aresemi-gel-typeandgel-type
formulations,
respectively, with high thixotropic properties. Thus,
these products offer improved workability and are
better suited for automated adhesive application.
That thixotropic properties are high mean that there
exists large difference between adhesive viscosities
in stressed conditions (such as when squeezing theadhesive out of the container) and unstressed
conditions (such as after coating onto the material
to be bonded). Thus, these adhesives are good in
fluidity, but also proof against dripping.

ThreeBond 1737 and 1738 are third-generation
high-performance instant adhesives in which the
conjugated rubber components are dispersed within
the main constituent, cyanoacrylate, with apre-designed phase separation structure regardlesscuring of the adhesive (Figure 11). The properties
and general characteristics of these adhesives areshown in Table 2.
A special feature of these third-generation instantadhesives is the pre-designed dispersion state of therubber components. Thus, consistent performance isachieved at all times. One example of where this isadvantageous is on materials to be bonded withacidic surfaces, such as wood, on which adhesives
cure more slowly; as a result, the dispersion of therubber components in second-generation adhesives

Third-generation instant adhesives: ThreeBond 1737 and 1738

CuringIncompatible system

Incompatible system

Figure 11: Phase structure of third-generation instant adhesives
Table 2: Properties and general characteristics of ThreeBond 1737 and 1738
Items

Units

TB1737

TB1738

Color and appearance
Form
Specific gravity
Viscosity
Thixotropic index
NBR/NBR
Setting time
Fe/FeFe/Fe
Shearing adhesive strength
Al/AlPeeling adhesive strength
Al/Al
Impact adhesive strength
Fe/Fe
Dielectric breakdown voltagePa•s {cP}-Light blue
Semi-gel form
1.042 {2000}
5.2
2030
16 {160}
15 {150}
1.3 {3.3}
13 {13}26 {26}
11
3.53 × 10
13{3.53 × 10 }14
2.51 × 10
3.287
0.033

Light blue
Gel form
1.04
5 {5000}
5.630
40
16 {160}
15 {150}
2.0 {5.0}
13 {13}48 {48}11
1.59 × 10
13{1.59 × 10 }14
4.40 × 10
3.375
0.036

Volume resistivity
Surface resistivity
Dielectric constantDielectric loss tangent

Seconds2MPa {kgf/cm }kN/m {kgf/25mm}
22kJ/m {kgf•cm/cm }MV/m {kV/mm}Ω •m{ Ω •cm}Ω-(TB: abbreviation for ThreeBond)7

6.

The ThreeBond 1700 Series ______________________________ •Three Bond instant adhesives and related
products are introduced. These include a variety ofproducts with a wide range of properties andfunctions suited to the workability and usage.
Related products include peelers for removing
cured adhesives, curing accelerators, and primers toenable adhesion of bonding resitant materials suchas polyethylene, polypropylene, and polyacetal.
We also provide automatic coaters, the S-II
Coater, which ejects adhesives via pressurized air,and the SMF-02B Coater, which ejects adhesives
using a tubing pump mechanism.

Table 3: Three Bond instant adhesives and related products
ThreeBond 1700 Series

Color

Viscosity mPa•s [cP]Colorless

3 {3}

1743

Colorless100 {100}

20 g

1745

Lemon yellow

500 {500}

20, 500 g

1741
Multi - purpose
grade

Ethyl type

1747

Lemon yellow

2000 {2000}

1701

Colorless

3 {3}20, 50 g

1702

Colorless35 {35}2, 20, 50 g

1702 BBlue

35 {35}50 g1741 DBlue

3 {3}1743 DBlue

100 {100}

Slow curing type

1713

Colorless100 {100}

20 g

Low-odor low-blooming type

1721

Colorless10 {10}20, 50 g

1731

Lemon yellow

20 {20}20, 50 g

1733

Lemon yellow

150 {150}

20, 50, 500 g

1737

Light blue2000 {2000}

50 g

1738

Light blue

5000 {5000}

20 g

1739

ColorlessGel form

1781

Colorless

3 {3}20, 50, 500 g
20, 50, 500 g

Methyl type

Colored type

Functionality
gradeContent
2, 2, 50 g

High peeling strength andimpact resistant type

Gel type
Impact-resistant andheat-resistant type

20 g

20 g
20, 500 g

20, 500 g

1782

Colorless80 {80}1783

Lemon yellow

1000 {1000}

1785 B

Colorless

3 {3}

1786

Colorless150 {150}

20, 50 g

1787

Lemon yellow

1100 {1100}

20, 50 g

1795

Colorless1.0 {1.0}

50 g

1796

Lemon yellow

0.9 {0.9}

45 g

Curing accelerators

1796 B

Lemon yellow

0.9 {0.9}

45 g

1796 E

Lemon yellow

0.9 {0.9}500 mlAdhesive primers for hard-to-bond surfaces

1797

Lemon yellow

0.85 {0.85}

100 mlFast curing woodwork type
Peeler

50, 500 g
20 g

Hiroyuki Mikuni
Development Division
Structural Materials and Public Works Development Department

1456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, Japan
Tel: 81-426-61-1333

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