ThreeBond Technical News
Issued July 1, 2012

80

Bolts Pre-Coated with a New Aqueous MEC Process(Acrylic and Epoxy Types)
Introduction
The MEC (Micro Encapsulated Coating) process for bolt pre-coating is a technology where reactive
resins and other materials contained in microcapsules are used to coat threaded surfaces such as
bolts, screws, plugs and piping to provide sealing, locking, lubrication, etc. MEC processing is
widely used with anaerobic adhesive for threaded parts, and as is applied in advance it provides
a huge advantage in quality and process control. Such features give it excellent workability for a
proven track record of long-term use in construction and other industrial applications.
In a typical MEC process, an organic solvent or water is used as a solvent during the process of
coating threaded surfaces with microcapsules. At ThreeBond, we have worked on and released
aqueous types which are environmental friendly while additionally organic solvents are often
restricted by REACH and VOC regulations. Aqueous technology was established for the functionalsurface of threaded parts. However, compared to organic solvent systems, it did not completely
satisfy performance needs such as when these surfaces are subjected to load or compositional
restrictions.
In this publication we will show how we solved issues found in previous aqueous MEC andintroduce a new aqueous MEC which shows performance equal or higher to these of solvent type.
Hereafter, ThreeBond is abbreviated as TB.

Table of Contents

Introduction.................................................1
1. Background.............................................2
1-1 REACH Regulations.........................2
1-2 VOC Regulations..............................2
2. MEC Processing.....................................2
3. Acrylic MEC Processing.........................2
3-1 Solvent Acrylic MEC(TB2411, TBT403, etc.).....................2
3-2 Conventional Aqueous Acrylic MEC(TB2457, TB2475).............................2

3-3 New Aqueous Acrylic MEC(TB2458, TB2468, TB2478)..............2
4. Epoxy MEC Processing..........................4
4-1 Solvent Epoxy MEC(TB2430, TB2440B)..........................4
4-2 Conventional Aqueous Epoxy MEC(TB2446, TB2446B)..........................4
4-3 New Aqueous Epoxy MEC(TB2448, TB2448B)..........................5
Closing........................................................81

1.

Background

1-1 REACH Regulations
The European Union (EU) began implementation ofchemical substance registration and regulation (REACH:
Registration, Evaluation, Authorization and Restrictionof Chemicals) on June 1, 2007 to protect health and theenvironment from potential hazards caused by chemical
substances. Substances considered to have potentiallyserious effects on the environment and health, such as
those that are highly carcinogenic, mutagenic or toxic toreproductive systems, are classified as SVHC (substances ofvery high concern), and 73 substances had been classified assuch as of December 19th, 2011.
Among organic solvents, tertiary candidates for inclusion as
SVHC have been published, as well as substances that should
be listed as such subject to approval, further strengthening
regulation of organic solvents.

1-2 VOC Regulations
VOC (volatile organic compounds) is a general name fororganic compounds that become gaseous when exposed tothe air. They are widely used in paints, adhesives, solventsand inks, and contain a wide variety of substances, suchas toluene, xylene and ethyl acetate. VOC are said to be acausative agent of suspended particulate matter (SPM),
which exerts a negative impact on photochemical oxidants
and the respiratory system.

Next, a polymerization reaction occurs which creates a firmbond to keep the threaded part from loosening or falling out.
At ThreeBond, we offer two main types of MEC processing
products: acrylic and epoxy.

3.

Acrylic MEC Processing

3-1 Solvent Acrylic MEC (TB2411, TB2403, etc.)
Solvent acrylic MEC is mainly composed of
microencapsulated acrylic monomers, binders and fillers.
For the solvent acrylic MEC microcapsules, we use gelatin
for the wall membrane, and coacervation (phase separation
in aqueous solutions) is employed for our microencapsulation
technique.
Using gelatin has several merits. It ensures a microcapsulewith a strong wall film and dry film threaded surface thatis stable after MEC processing. Additionally, a wide rangeof particle sizes can be manufactured for use with a varietyof threaded parts. Further adjusting the amount of acrylic
monomer and wall film reduces residue produced when
excess adhesive overflows while tightening a threaded
part. However, gelatin is difficult to use in aqueous solvent
because it swells in water and is susceptible to moisturedamage.

To suppress VOC emissions, the Air Pollution Control Act
was amended in May of 2004, the Air Pollution Control
Act enforcement ordinance (cabinet order) and enforcement
regulation (ministry order) were amended in May and Juneof 2005, respectively, and VOC emissions began in April of2006.

3-2 Conventional Aqueous Acrylic MEC(TB2457, TB2475)
ThreeBond has been offering aqueous acrylic MEC that uses
water as a diluent since around 1998. The aqueous acrylic
MEC we now offer uses a technique to take the speciallyshaped acrylic monomer that is the main component
and disperse it in water and applies a new microcapsuletechnology. These products are environmentally responsible,
stable and easy to handle.

At the ThreeBond Group Pre-Coated Bolt Factory, we act inaccordance with Article 17-15 of the Air Pollution Control
Act, which states we “...shall endeavor to further controls on
the emission and dispersal of Volatile Organic Compounds
by selecting products that use a smaller quantity of Volatile
Organic Compounds”.

Unfortunately, conventional products have a comparatively
soft dry film and are easy to cosmetically damage due tothe special compounding techniques used. When this kindof cosmetic damage occurs, it can also lead to the coatedfilm peeling off which means that they must be handled with
care.

2.

MEC Processing

Simply stated, the MEC processing technique involves
coating bolts and other threaded surfaces with adhesivecomponents in a dry film state. In order to achieve ourobjective, we apply a microencapsulating technique tomany of the ordinary reactive adhesive components. In thisway, the microencapsulated adhesive components are stable
before the MEC processed item is tightened or screwedin. However, once screwed in or tightened, the shear force
applied causes the microcapsules to burst, releasing theadhesive components, which then mix with the curing agent.

2

To counteract this, we have focused our microencapsulation
technology development on improving aqueous processing
so that can be utilized in the same way as solvent-based
products.

3-3 New Aqueous Acrylic MEC(TB2458, TB2468, TB2478)
Our new aqueous acrylic MEC products utilize a newly
developed special synthetic resin microcapsule for structuralcomponents that are equal to solvent acrylic MEC. This
microcapsule boasts excellent moisture resistance thatstands up even when the diluent is water.

In conventional synthetic resin microcapsules, the wall filmis physically brittle and there is concern regarding both
capsule stability and the limitations of use for certain sizes of
threaded parts (especially encapsulation of large particles).
To solve these issues we employed a special method toimprove microcapsule flexibility and developed a brandnew microencapsulation technique. Exploring techniques tocombine curing agent, binder and filler (Fig. 1) outside of
microcapsules as well as coating amounts on threaded parts,
we were able to solve issues apparent in solvent acrylic
and conventional aqueous MEC and create a product that
performs as well as or even better than they do.

1. Nut/Bolt Side View
Nut

Bolt (Screw)

2. MEC Processed
Bolt Cross-Section

MEC Processing
Component

Enlarged View

3. Tightened MEC
Processed Bolt

Our product lineup (Table 1) contains different levels of
post-curing adhesion strength, weak: TB2458, medium:
TB2468 and strong: TB2478.
There are also grades that leave almost zero residue after
being screwed in due to effective application of synthetic
resin in the microcapsule wall film.

Cross-Section

Nut

Aqueous Emulsion Binder,
Filler, Colorant, etc.
Capsule Wall Film
(Synthetic Resin)

We have created a product with functionality that matchesor surpasses conventional solvent acrylic MEC for use witha wide range of threaded parts.

Acrylic Monomer
Capsule Wall Film
Peroxide
Catalyst

Fig. 1 New Aqueous Acrylic MEC Structure

zStoragez
Stability
Improved acrylic resin microcapsules are used toindividually encapsulate acrylic monomers for storage
stability superior to that of conventional products. As shownin Figure 2 below, stable adhesion is maintained over a long
period of time in high temperatures and humilities more
severe than typical environments.
Table 1 New Aqueous Acrylic MEC Product Lineup
Features

TB2458

TB2468

TB2478Main Component

Methacrylic ester

Methacrylic ester

Methacrylic ester

Appearance

Green

Red

Blue

Adhesive Strength*1

39N·m

45N·m

52N·m

*2

Heat Resistance
Limit

Lock

100°C

100°C

130°C

Seal*3

170°C

170°C

170°C

Curing Speed(20 to 25°C)

Practical Strength*4

30min. to 1hr.

30min. to 1hr.

30min. to 1hr.

Final Strength

6hrs.

6hrs.

6hrs.

Minimum Applicable Screw Diameter

M3

M3

M3

*1. JIS class 2, M10×P1.5, zinc plating chromate treatment, hex bolt/nut
Tightening torque: 30N·m, curing conditions: 25°C×24hrs.
*2. Temperature at which adhesive strength equal or greater than tightening
torque can be achieved
JIS class 2, M10×P1.5, zinc plating chromate treatment, hex bolt/nut
Tightening torque: 30N·m, curing conditions: 25°C×24hrs*3. Pressure: Temperature without leakage at 10MPa
JIS class 2, M10×P1.5, zinc plating chromate treatment, hex bolt/nut
Attaching female screws on iron workpieces, tightening torque: 30N·m,
curing conditions: 25°C×24hrs.
Sealant medium: Turbine oil*4. Time at which adhesive strength equal or greater than 1/2 final strength
can be achieved

3

zHeatz
Resistance and Durability
Stable adhesive strength is maintained at 120°C (Fig. 4).

60

60
40
50
30
20
TB246810TB2403
0
0

5

10

15

20

Storage Time (Days)

25

30

Adhesive Strength (N·m)

Adhesive Strength (N·m)

50

zAxialz
Force
MEC processed bolts have the added characteristic ofpreventing leakage or slacking. As shown in Fig. 3 below,
MEC processed bolts provide higher axial force andstronger fastening power than uncoated bolts. Axial force
demonstrates tendencies similar to that of conventional
products, so no significant changes are required in terms ofhandling tightening torque to make switching over to thisproduct simple.
30
Uncoated
TB2411

Axial Force (kN)

TB2468100Pre-coated bolts were stored in a 40°C,
95%RH environment for a set amount oftime, then left to cool at room temperature
before adhesive strength was measured.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m, curing conditions: 25°C×24hrs.

5

10

15

20

Inserted Time (Days)

25

30

Fig. 4 Acrylic MEC Thermal Deterioration
Testing method:

Pre-coated bolts tightened, cured andplaced in a 120°C environment for a set
amount of time, then left to cool at room
temperature before adhesive strength wasmeasured.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs.

4.

Epoxy MEC Processing

4-1 Solvent Epoxy MEC (TB2430, TB2440B)
Solvent epoxy MEC is mainly composed of
microencapsulated epoxy resin agents, amine curing agents,
binders and fillers. Epoxy MEC demonstrates heat andchemical resistance that is superior to acrylic MEC, but hasa slow curing speed.
Synthetic resin is the main wall film component of the
microcapsules used for solvent epoxy. This process makes it
possible to produce grain sizes smaller than in the capsules
used for acrylic MEC to support compatibility with small
screws, etc.

TB2457
TB245810

Because organic solvents were used in this solvent epoxy
MEC, environmental concerns had to be taken into account.

0
10

20

30

40

50

Tightening Torque (N·m)

60

70Fig. 3 Acrylic MEC Axial Force
Testing Method:
Test piece:

4

20

0

Testing method:

Tester:30

TB2403Fig. 2 Acrylic MEC Storage Stability

20

40

Measured axial force at various tightening
torques using a screwdriving tester withprecoated bolts.
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Screwdriving tester NST-500NM by
Japan Instrumentation System Co., Ltd.

4-2 Conventional Aqueous Epoxy MEC(TB2446, TB2446B)
In order to solve the issue presented by the use of organic
solvent as a diluent in solvent epoxy MEC, we havedeveloped an aqueous epoxy MEC utilizing special
compounding techniques. The basic structure is the same assolvent epoxy MEC, composed of microencapsulated epoxy
resin agents, amine curing agents, binders and fillers, withthe same physical properties, such as chemical and physicalresistance.

Table 2 Epoxy MEC Product Lineup
Features

TB2430

TB2448

TB2440B

TB2448B

Main Component

Epoxy resin

Epoxy resin

Epoxy resin

Epoxy resin

Diluent

Organic solvent

Water

Organic solvent

Water

Appearance

Blue

Blue

OrangeOrangeAdhesive Strength*1

70N·m

70N·m

64N·m

70N·m

Heat Resistance
Limit

Lock*2

120°C

150°C

160°C

160°C

Seal*3

170°C

170°C

170°C

170°C

Curing Speed(20 to 25°C)

Practical Strength*4

30min. to 1hr.

30min. to 1hr.

15hr. to 30hrs.

30min. to 1hr.

Final Strength

24hrs.

24hrs.

72hrs.

24hrs.

Minimum Applicable Screw Diameter

M2

M2

M2

M2

However, issues with curing speed still remained due tocompositional limitations present in conventional aqueous
epoxy MEC.

4-3 New Aqueous Epoxy MEC(TB2448, TB2448B)
The synthetic resin wall film of the microcapsule wasmade even more compact for the new aqueous epoxy MEC
through unique technical improvements. This, in addition toindividually encapsulating the main epoxy resin agents andcuring agents sped up adhesiveness and enabled the creationof a product with excellent maintainability (Table 2).
zBasicz
Structure of TB2448 and TB2448B
The composition of the new aqueous epoxy MEC is shownin Fig. 5, below.

*3. Pressure: Temperature without leakage at 10MPa
JIS class 2, M10×P1.5, zinc plating chromate treatment, hex bolt/nut
Attaching female screws on iron workpieces, tightening torque: 30N·m
Sealant medium: Turbine oil
Curing conditions: 25°C×24hrs. (TB2448, TB2448B)
25°C×48hrs. (TB2430)
25°C×72hrs. (TB2440B)*4. Time at which adhesive strength equal or greater than 1/2 final strength
can be achieved

zCuringz
Speed
For our newly developed aqueous epoxy MEC, elements areencapsulated in a different way than for conventional curing
agents to successfully achieve a curing speed that surpasses
conventional products and new aqueous acrylic MEC.
100

Adhesive Strength (N·m)*1. JIS class 2, M10×P1.5, zinc plating chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448, TB2448B)
25°C×48hrs. (TB2430)
25°C×72hrs. (TB2440B)*2. Temperature at which adhesive strength equal or greater than tightening
torque can be achieved
JIS class 2, M10×P1.5, zinc plating chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448, TB2448B)
25°C×48hrs. (TB2430)
25°C×72hrs. (TB2440B)

80

60

40
TB247820

TB2440B
TB2448B

Capsule Wall Film00Capsule Core Agent(Main Agent: Epoxy Resin)

40

Curing Time (h)6080Fig. 6 Epoxy MEC Curing Speed
Testing method:

Capsule Wall Film
Capsule Core Agent(Curing Agent: Epoxy Resin)

20

Aqueous Emulsion Binder,
Reaction Accelerator, Filler,
Colorant, etc.

Fig. 5 New Aqueous Epoxy MEC Structure

Pre-coated bolts were tightened in a 25°C
environment, then measured for adhesivestrength after a set amount of time had
passed.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m

5

zStoragez
Stability
The newly developed, incredibly dense synthetic resin used
for the wall film of the new aqueous epoxy MEC allows it
to be stored at high temperature and humidity more severe
than typical environments while suppressing reduction inadhesive strength (Fig. 7).
100

100

80

TB2430
TB2448

80

60

40

20

TB2448
TB2430

0
0

5

10

15

20

Storage Time (Days)

25

TB2448B

Adhesive Strength (N·m)

Adhesive Strength (N·m)

zHeatzResistance
One of the defining features of epoxy MEC is its incredible
adhesive strength when hot as described in Fig. 9. Adhesion
strength is high, even at high temperatures. (Temperature
at which adhesive strength equal or greater than tightening
torque that can be achieved is the lock heat resistancethreshold.) Lock heat resistance threshold is 150°C for
TB2448 and 160°C for TB2488B.

60

40

20

30
0

Fig. 7 Epoxy MEC Storage Stability

0

Testing method:

Pre-coated bolts were stored in a 40°C,
95%RH environment for a set amount oftime, then left to cool at room temperature
before adhesive strength was measured.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448)
25°C×48hrs. (TB2430)

zAxialz
Force
Demonstrates axial force characteristics the same as inacrylic MEC described above (Fig. 8).
20
TB2448
TB2430200

Fig. 9 Epoxy MEC Strength When Hot
Pre-coated bolts tightened, cured andkept at various heats for two hours, thenmeasured for adhesive strength at eachtemperature.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448, TB2448B)
25°C×48hrs. (TB2430)

zHeat
zResistance and Durability
Stable adhesive strength is maintained at 150°C, as shownin the Figures 10 and 11 below.
100

5

0
10

20

30

40

50

Tightening torque: 30N·m

60

Testing Method:
Test piece:

80

60

40

20

TB243070

Fig. 8 Epoxy MEC Axial Force

6150

Uncoated

10

Tester:100

Temperature (°C)

Testing method:

Adhesive Strength (N·m)

Axial Force (kN)

15

50

Measured axial force at various tightening
torques using a screwdriving tester withprecoated bolts.
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Screwdriving tester by Japan
Instrumentation System Co., Ltd.
NST-500NM

TB2448
0
0

5

10

15

20

25

30

Time (Days)

Fig. 10 Epoxy MEC Thermal Degradation(TB2430, TB2448)
Testing method:

Pre-coated bolts tightened, cured andplaced in a 150°C environment for a set
amount of time, then left to cool at room
temperature before adhesive strength wasmeasured.

Test piece:

JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448)
25°C×48hrs. (TB2430)

Testing method:

Pre-coated bolts tightened, cured andplaced in various chemicals. Once theset conditions have passed, the bolt isremoved and measured for adhesivestrength.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448)
25°C×48hrs. (TB2430)

100

100

60

TB2448B
TB2440B

0

Testing method:

Pre-coated bolts tightened, cured andplaced in a 150°C environment for a set
amount of time, then left to cool at room
temperature before adhesive strength wasmeasured.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Curing conditions: 25°C×24hrs. (TB2448B)
25°C×72hrs. (TB2440B)

zChemicalz
Resistance
Epoxy MEC demonstrates stability when exposed to various
chemicals as indicated in the Figures 12 and 13 below. Useis stable in a wide range of applications.
100Fig. 13 Epoxy MEC Chemical Resistance(TB2440B, TB2448B)
Testing method:

Pre-coated bolts tightened, cured andplaced in various chemicals. Once theset conditions have passed, the bolt isremoved and measured for adhesivestrength.
Test piece:
JIS class 2, M10×P1.5, zinc plating
chromate treatment, hex bolt/nut
Tightening torque: 30N·m
Curing conditions: 25°C×24hrs. (TB2448)
25°C×72hrs. (TB2440B)

80

60

40

Gear Oil (75W-90)

AT Fluid

Turbine Oil

Engine Oil (5W-20)

Ethylene Glycol 50% aq.

Ethylene Glycol

Water

Methanoln-hexane

Gasoline (Regular)Light Oil0

NaOH 10%aq.

20

Control

Adhesive Strength (N·m)

TB2448
TB2430

Gear Oil (75W-90)

Fig. 11 Epoxy MEC Thermal Degradation(TB2440B, TB2448B)

20

AT FluidTime (Days)

Turbine Oil

30

Engine Oil (5W-20)

25

Ethylene Glycol 50% aq.

20Ethylene Glycol

15

Water

10

Methanol5

n-hexane

040

Gasoline (Regular)

TB2448B
0

60

Light Oil

TB2440B

NaOH 10%aq.

2080Control40

Adhesive Strength (N·m)

Adhesive Strength (N·m)

80Fig. 12 Epoxy MEC Chemical Resistance(TB2430, TB2448)

7

Closing

Our series of new aqueous MEC processed products have been praised for performance equal to or surpassing that of organic
solvent products currently on the market. Through them, we now offer aqueous products that can be used under the same
conditions as those using organic solvents.
Moving forward, we at ThreeBond will continue to develop products in line with laws, regulations and especially environmental
concerns, both domestically and overseas.
<References>
Technical News No. 3, 8, 64, 78
ThreeBond Co., Ltd. R&D Headquarters
Development Division, Functional Materials Department
Yasuo Maeda
Kunihiko Kamata
Tomohiro Onoda

ThreeBond Co., Ltd.
8

4-3-3 Minamiosawa, Hachioji,
Tokyo 192-0398
Tel: +81-42-670-5333