Three Bond Technical News
Issued Jun. 1, 2005




Precoat Bolt
— Water-based MEC process and water-based threelock process —Introduction
Precoat bolt is a functional part that can provide screws themselves with the features such as sealing, locking,adjusting, and lubricating by coating microencapsulated reactive resin or special blended synthetic resin on thethread part of screws, bolts, plugs, and pipes in advance. Although there were disadvantages such as working
time, environmental pollution, spotty coating, inadequate coating, eruption, and delayed hardening expression for
liquid-type sealing agents and locking agents previously used at work places to mount screws, in order to resolvethese problems precoat bolt was developed with the precoating technology that coats thread part directly inadvance.
Precoat bolts have product groups such as sealock process, MEC process, and threelock process from theircharacteristics, and they have been field-proven in the automotive industry and electronic/electric industry formany years (see figure 3 on page 3).
These precoat bolts are typically coated in the process shown at figure 1. In this process, organic solvent istypically used as a diluent solvent for precoat resin, and it is the current situation that this solvent is vaporized in
the air during the dry process. It is expected that regulations will be severe by part revision of Air Pollution
Control Law promulgated recently including experimental regulations (for example, VOC regulation), and theuse of de-organic solvents is anticipated through the all manufacturing processes. (Note: ThreeBond is referred toas TB.)

Thread parts

Precoat resin
Organic solvent

Organic solvent

Coating process

Drying process

Precoat bolt

Figure 1, Process to Manufacture Precoat Bolts

Contents
Introduction .............................................................. 1
1, About VOC Regulation........................................ 2
1-1, Action Plans for VOC................................... 2
1-2, Problem to Develop Water-based Solvents..................................................................... 2
2, MEC Process ...................................................... 3
2-1, Solvent-based Acrylic MEC ......................... 3
2-2, Water-based Acrylic MEC ........................... 3
2-3, Acrylic MEC - Comparison between waterbased and solvent-based products.............. 4
2-4, Solvent-based Epoxy MEC.......................... 4
2-5, Water-based Epoxy MEC ............................ 4

2-6, Epoxy MEC - Comparison between waterbased and solvent-based products ............. 4
2-7, Curing speed............................................... 4
2-8, Thermal Resistance .................................... 5
2-9, Chemical Resistance .................................. 5
2-10, Sealing Property.......................................... 6
3, ThreeLock Process............................................. 7
3-1, Water-based ThreeLock Process................ 7
3-2, Water-based ThreeLock Process for SmallScrew Only................................................... 7
4, Conclusion .......................................................... 8

1

1, About VOC Regulation
A partial amendment of the Air Pollution Control
Law was promulgated on May 26th, 2004. This
overview is that volatile organic compound (VOC)
is concerned as causative agent to generatesuspended particulate matter (SPM) andphotochemical oxidant (OX) that may affecthuman bodies, and discharge of them should be
suppressed. The mechanism to generate these
toxic substances is shown as figure 2.
The government ordinance will determine thedetails about VOC regulation guideline in this law
in future. Therefore, use of all organic solvents
will not be inhibited immediately, but it is easily
expected that more severe conditions will be
imposed in near future for their usage.
This law also includes provisions that customers
to use them should select low VOC products, andit seems that some restrictions are applied to bothmanufacturer and user.
1-1, Action Plans for VOC
To limit VOC discharged from the locations foruse when using paints, adhesives, and processing
precoat resins, there may be some methods: tocollect organic solvents by using condensers (1),to change to alternative solvents such as water (2),and to make a non-solvent system such as powder
coating (3). Among these selections, it is aneffective action as a short-term solution to installsolvent recovery equipments to collect organic
solvents, but it is not a permanent countermeasure
because the West and the neighboring countries
like Korea and Taiwan are taking their own more
severe regulations. Solvent-free solution has ahigh technical hurdle due to the characteristics ofthe precoat process and it is not realistic in thistime. In such a situation, we at ThreeBond havediscussed mainly to change the solvent into water
as an action plan for VOC for precoat resins.

1-2, Problem to Develop Water-based
Solvents
It has many advantages such as compliance toenvironment, safety, handling ability to change
precoat resins solvent from organic solvent to water,
but on the other hand, many restrictions or problems
are left in the blending and processing operations:drying property, temperature dependency ofcompounded resins, dissolubility of high polymer
resins. For example, as problems in blending, someissues are left: same adhesive component as before
cannot be used because there are some differences
about dissolubility between water and organic
solvents or solvents are sagged after coated because
drying is slow. To solve these problems, we havediscussed on developing the dispersion technology
to newly microencapsulated components in resins
and water-based adhesive components. It was alsodecided to manage a viscosity for resins in thecoating process operation, ambient temperature andhumidity in drying operation carefully. These
endeavors enabled us to manufacture the same levelproducts as conventional organic solvents and to
introduce them to the market.

SPM(Suspended Particulate Matter)
Non-volatile
Organic Compounds

Primary
Organic Particulate Matter

Organic
Compounds
Volatile
Organic Compounds

OH NO2

RO2

O3

Secondary
Organic Particulate Matter

RO
NO, NO3Photochemical Oxidant

SPM(Suspended Particulate Matter)
NO3N2P5

NO2

O2

O3

AldehydeNOOH, O2, NO3

Peroxyacetylnitrate (PAN)

NH3
NH4NO3

Ozone O3
O2
㧔NH4)2O2

Precursor Gas

NH3
OH, O3, etc.
H2SO4Oxidant

AggregatedParticle

SO2

Figure 2, Mechanism such as atmosphericVOC22, MEC Process
Our precoat bolts are classified according to theircharacteristics as shown in figure 3. MEC process
is one of them, that adhesive component is coatedin the dry film on the surface of the thread parts
such as bolts. Its appearance is shown in photo 1.
Since it is required to make coated component into
the dry film, or to coat reactive resin and curing
agent separately on the same thread surface, thetechnology that partial or multiple components aremicroencapsulated is applied on these precoatedthread parts. Thus it is stable unless screws aretightened, however, tightening the screws, i.e. theshearing force enables to break the microcapsules,
core substances are bled, and curing agents are
mixed. Then the polymerization reaction occurs
and prevents the thread joints from loosening andleaking.
Also
using
microencapsulation
technology can handle the liquid materials as
powder, and it gives us a great advantage toeliminate the problems such as stickiness anddermatitis.

film can be acquired that is adjusted to a given
film thickness. When bolts are tightened,
microcapsules are broken and curing agents are
mixed so that reaction has initiated and thenadhesive power and sealing performance areexerted. MEC process is classified into lowstrength (detachable) to high-strength (permanentadhesive) depending on adhesive strength.
TB2411 is classified into low-strength, TB2403 isclassified into medium-strength, and TB2471 isclassified into high-strength respectively.
2-2, Water-based Acrylic MEC
If diluent solvent is changed into water fromorganic solvent, problems are left: binder dissolution
property to water and stability of microcapsules. For
this reason, water-based acrylic MEC is developed
by applying a technology that acrylic monomer as its
main component is dispersed into water in a special
form and by applying a new microcapsule.

2-1, Solvent-based Acrylic MEC
Solvent-based acrylic MEC consists of
microcapsules that contain acrylic monomer as amain component, binders, and filler. Microcapsule
is not stayed in the thread joints because it is a
powder. Thus binders are used as a component toadhere it on the thread part. Bolts are coated onafter dilution in the organic solvent, and precoat

Solvent vaporized

Photo 1, Water-based MEC-processed bolts

Low-strength (detachable)

Bonding
ThreeBond 1400 Series

LiquidProducts

Low-strength (detachable)

Anaerobic (Reaction-Type)
Bonding
ThreeBond 1300 Series

Sealock Process

High-strength (permanent bonding)
Sealing only

Non-Bonding
ThreeBond 2300 Series

Products

Three-Locking Process

Precoat Bolt

Non-Bonding
ThreeBond 2360 Series

MEC Process
Bonding
ThreeBond 2400 Series

Anti-loosening
Usable repeatedly
Sealing+
Locking

Solvent-based
Water-based

Solvent-based

Low-strength

High-strength

Water-based

Low-strength

High-strength

Figure 3, Three Bond Product Series about Screw Tightening3

2-3, Acrylic MEC - Comparison between
water-based and solvent-based products
Drying process after coating takes a long time
because water is used as solvent. Water-based
solvent uses a special blend technology compared
to conventional solvents, but reaction mechanism
and resin compound after reactive curing remain
nearly unchanged.

2-7, Curing speed
As a characteristic of acrylic MEC, it has anadvantage of fast curing (adsorbing) speed
because curing reaction is radical polymerization.
For acrylic MEC, it will normally be cured in 24
hours at 25 °C. For epoxy MEC, standard curing
time should be in 48 to 72 hours at 25 °C,
depending on curing agents used. Figure 4 andfigure 5 show curing speeds of acrylic MEC andepoxy MEC. Water-based agents indicates same or
highet performance in curing speed compared withsolvent-based agents.

٨TB2 4 7 540
Tightening torques

30

Solvent-based Epoxy MEC contains epoxy resin
in microcapsules, and it consists of the
microcapsules, amine curing agents, binders, filler
agents and so on. Both TB2430 and TB2440B as a
Solvent-based Epoxy MEC are classified into thehigh-strength type.

20
02-6, Epoxy MEC - Comparison between
water-based and solvent-based products

20

40

60

80

100

Time (h)Figure 4, Acrylic MEC - curing speed

ٌTB2 4 4 0 B

2-5, Water-based Epoxy MEC

٨TB2 4 4 6Torque (N m)

60
50
40
Tightening torques

30
20
0

20

40

60

80

100

Time (h)Figure 5, Epoxy MEC - curing speed

TB2446 has the following advantages comparedwith TB2430 and TB2440B:- Curing conditions: Loosening torque was measured
after bolts were tightened at 30N•m and they were
cured for the specified time under 25 °C ambient
atmosphere❏ High strength on applying small screws- Testing Material: Bolts and nuts that are processed with
JIS 2nd grade M10 zinc chaomate-plated are used

❏ Low dregs on tightening screws❏ Low stickiness of processing bolts in hightemperature / high humidity condition❏ No whitening.
Therefore, it is increasing to be used as fixing
screws of chassis and PCB (Print Circuit Board)
for PCs and cellular phones.

450

2-4, Solvent-based Epoxy MEC

Water-based epoxy MEC TB2446 uses the same
microcapsule that solvent-based product uses.
Water-based Epoxy MEC consists of the
microcapsules, amine curing agents, binders, filler
and so on. The problems on solubility same asacrylic MEC are left as mentioned above, but this
could be developed with a new method. TB2446 isclassified into the high-strength type.

ٌTB2 4 7 1

60

Torque (N m)

We have experimented to dilute the solvant withwater and coat the belts. As results, it is possible toobtain equivalent precoat films with organic
solvent. Although it is an water-based product, it ishard to be dissolved into water after drying, andsuperior films with humidity resistance areprovided. There are currently 2 grades according
to the strength, TB2457 is classified into the lowstrength, and TB2475 is classified into the highstrength.

2-8, Thermal Resistance

2-9, Chemical Resistance

Figure of adhesive strength vs temperature isshown below. As shown in the figure, if
temperature is getting higher, adhesive strength isgetting lower than the tightening torques. This
point is referred to as a limit temperature of lockheat resistance. Limit temperature of lock heat
resistance for water-based types is 120 °C for
TB2457, 150 °C for TB2446 and TB2475.

Epoxy has an advantage on heat resistance, heatcycle resistance, and chemical resistance (figure
9).

ٌTB2 4 1 1

70Torque (N m)

60

Torque (N m)

٨TB2 4 5 7

ٌTB2 4 4 0 B
60
50
40
30

Tightening torques

20
10

50
40

Tightening torques

0
㧙50

0

50

100

150

200

Temperature ( C)30
20

Figure 8, Epoxy MEC strength vs temperature

10
0
㧙50

٨TB2 4 4 6

70

0

50

100

150

200

Temperature ( C)

- Curing condition: Bolts are tightened at 30N•m, and are
cured at 25 °C in 24 hours (48 hours, or 72 hours)- Testing Material: Bolts and nuts that are processed with
JIS 2nd grade M10 zinc chromate-plated are used

Figure 6, Adhesive strength of low-strength
acrylic MEC vs temperature

TB2 4 4 0 B

TB2 4 4 6
Tightening torques

٨TB2 4 7 5Blank

ٌTB2 4 7 1

70Light oil

Torque (N m)

60
50

NaOH (10%aq.)

40
30

70
60
50
40
30
20
10
0

Water
LLC

Tightening torques

n-hexane20

Gear oil

100㧙50Gasoline
0

50

100

150

200

Temperature ( C)

Figure 7, Adhesive strength of high-strength
acrylic MEC vs temperature

Engine oil
Turbine oil

Figure 9, Epoxy MEC - Chemical resistance- Curing condition: Bolts are tightened at 30N•m, and are
cured at 25 °C in 48 hours (or 72 hours)- Testing Material: Bolts and nuts that are processed with
JIS 2nd grade M10 zinc chromate-plated are used5

2-10, Sealing Property

are mounted into a hydraulic sealing tester. After
cured, they are pressurized and existing of leakage
is checked visually (figure 10). Temperature
resisting to 8MPa of hydraulic pressure is thesealing limit temperature of heat resistance. The
results are shown in the table 1.

MEC process has an excellent pressure resistancenot only under room temperature but only in more
severe temperature conditions. Method of sealing
test is as follows. MEC processed bolts aremounted into sealing test blocks and these blocks

Sealing fixture
made by aluminum

Thermocouple

Bolts for testing
10 pieces

Oil

Pressure Gauge

Bolts for testing
M10 X P1.5

2 washers

Tank

HydraulicFigure 10, Sealing Tester

Table 1, Sealing property

TB2446
TB2457
TB2475

Testing
Temperature
°C

2

4

6

8

10

25

0/10

0/10

0/10

0/10

0/10

150

0/10

0/10

0/10

0/10

0/10

25

0/10

0/10

0/10

0/10

0/10

150

0/10

0/10

0/10

0/10

0/10

25

0/10

0/10

0/10

0/10

0/10

150

0/10

0/10

0/10

0/10

0/10

Pressure (MPa)- Curing conditions: Bolts are tightened at 30N•m, and are cured at 25 °C in 24 hours (or 48 hours)- Testing Material: Bolts and aluminum blocks (A5052P) that are processed with JIS 2nd grade M10 zinc chromate-plated
are used- Pressurized Conditions: Pressurize up to 10MPa per 1MPa/min

6

3, ThreeLock Process

Photo 2, ThreeLock Process
3-1, Water-based ThreeLock Process
When changing solvent-based ThreeLock
TB2361 to water-soluble, most significant was the
problem that water-based solvent was easy
dropped off in the coating process. Because
thickness of coated film affects the performance, it
is very important to control thickness of the film.
Change on film thickness due to the dropping-off
is concerned since vaporization speed of waterbased agents is slow compared with solvent-based
agents. Therefore, in the water-based TB2365 tosolve this problem, some agents are blended toprevent the dropping off that are not available inthe solvent-based agents. Also, recycling
characteristics are improved by lowering the resin
hardness than solvent-based agents (figure 11).

TB2 3 6 1
10Torque (N m)ThreeLock process is a self-locking coatingprocess that nylon is a main component (Photo 2).
Resistive elasticity of nylon has self-locking effecton the screws to prevent from falling off, and it
provides a function to adjust screws. It also has an
excellent recycling characteristics, and it conforms
to the test according to the JASO standard(Japanese Automobile Standards Organization
standard, JASO F 106-96: Prevailing Torque Type
Self-Locking Hexagon Nut). Conventional
product TB2361 is processed by using solvents as
dilution agents.

TB2 3 6 5Upper limit of allowance8
6
4
2
Lower limit of allowance0

Lower limit of allowance

1st Screw-In
2nd Screw-Back 4th Screw-Back
1st Screw-Back
3rd Screw-Back 5th Screw-Back

Figure 11, M10 Bolt recycling characteristics- Testing Material: Bolts and nuts that are processed with
JIS 2nd grade M10 zinc chromate-plated are used
- Testing Method
1) Set a spacer to coating processed bolts as shown in
the figure.
2) Screw a nut in about 0.8mm to the spacer surface,and measure the maximum value (screw-in torque)during screwing-in.
3) Screw the nut in deeply, and tighten by the specified
tightening torque.
4) Then screw the nut back to measure the torque(loosening torque).
5) Screw the nut back until it falls off, and measure themaximum torque (1st screw-back torque) during
screwing-back.
6) Screw the nut in about 0.8mm to the spacer surface.
7) Screw back the nut until it falls off and measure themaximum torque (2nd screw-back torque) during
screwing-back.
8) Repeat the steps 6) to 7) five times (3rd to 5th screwback torque).

3-2, Water-based ThreeLock Process for
Small Screw Only
ThreeLock was initially developed for standard
bolt (M10) as a standard part. However, recently
coating on small fixing screws (M1 to M3) for
chassis and PCB of PC has been increasing. Using
conventional ThreeLock to these small screws
caused the problem that dispersion of recycling
property is larger. Therefore, we have developed
the water-based product TB2364 that can beapplied in narrow clearance of small screws.
Figure 12 and figure 13 show the comparison ofchanges on torque between TB2364 used speciallyfor small screws and TB2365 used for normal
screws when applying on M3 screws. By
implementing blending to suppress the dispersionof film thickness, dispersion of resistive torqueduring screwing is decreased, and stable repetitive
characteristics could be acquired.

7

Torque (N m)

Torque (N m)

1st Screw-In
2nd Screw-Back 4th Screw-Back
3rd Screw-Back 5th Screw-Back
1st Screw-Back

Figure 12, TB2365 M3 Screw Recycling
Characteristics

1st Screw-In
2nd Screw-Back 4th Screw-Back
3rd Screw-Back 5th Screw-Back
1st Screw-Back

Figure 13, TB2364 M3 Screw Recycling
Characteristics- Testing Material:
Small round-head screw with cross recess M3
Nickel plated brass insert nut M3- Testing Number of testing screws: n=10

4, Conclusion
Making precoat bolts water-soluble has started to spread steadily, although it is not fast. We atThreeBond believe that migration to solubility will contribute to environmental preservation.
It is expected in the industrial world surrounding us, that chemical material is required to be moreenvironment-friendly on the earth for future. ThreeBond keeps challenge to respond to these needs
continuously, not only for the development of precoat bolts with water-soluble resins but also for otherproducts.

<Reference Documents>
1) "Chemical Basic Information Research about Carbon Hydride", Mitsubishi Chemical Safety InstituteLtd.

Yasuo Maeda
Hideki Kanazawa
Material Development Section
Development Department
Research Laboratory
ThreeBond Co., Ltd.

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

8