New toughening technologies have been developed for FBE powder coatings

The molten adhesive epoxy (
FBE
) powder coating was first developed by
3M
and is used worldwide in areas requiring long-term corrosion protection, such as troughs, tracheas and water pipes. However,
performance
a challenge for the FBE industry. Because the coating film with high hardness and high crosslinking needs to meet the conditions of the pipe manufacturing and installation process, it is necessary to maintain the performance at higher temperatures. This can usually improve the performance of the FBE
pipe
by improving the toughness of the coating.
many methods are used to make epoxy resins tougher, usually using composite systems, where tougheners provide action through a variety of agents. Tougheners used such as liquid rubber, nuclear shell particles, glass beads and thermoplastic modified epoxy, and their mixtures.
but at the same time, tougheners often have side effects, such as significantly improving the viscosity of the composition. Affected by the molecular morphology of curing dynamics, it is also necessary to use a variety of mixing methods to disperse the modifier, or to add other additives (e.g. endobutylbutylene acrylic
CTBN
and other liquid rubber modifiers) to pre-mix with un cured epoxy resins to prevent particle aggregation. Tougheners are phase-separated during the curing of epoxy mixtures and are usually used to form spherical objects
(
as shown in figure
1a )
. The particle size and shape of the spherical object depends on the curing dynamics. In
,
addition of these additives tends to reduce the glass transition temperature (
Tg
)
,
because part of the
CTBN
dissolves in the epoxy substate and remains as a plasticizer.
other toughening methods include the use of completely incompatible or preformed modifiers, such as thermoplastics or nuclear shell rubber. However, they are difficult to spread evenly in the epoxy mixture, or will make the viscosity of the mixture greatly improved. However, they generally do not reduce the Tg
of cured
.
according to
Bates
, etc., using a small amount of applicable segment co-esters as rubber tougheners can solve these problems. With minimal use, reduced viscosity and the impact on performance, such as
Tg
, can be minimized. In addition, in some cases, the molecular morphology of the segmented co-polymer was found to change when mixed with the un cured resin (as shown in figure
1b
). Curiously, the molecular form remains constant during the curing process so that it is not affected by curing conditions. Recently,
Leibler
et al. added
ABC
trilayer copolymers to cured epoxy to study their molecular morphology in an attempt to improve impact resistance using three-inlay copolymers.
this paper discusses the increase in the value of
FBE
performance of powder coatings, including increased flexibility and impact resistance, while maintaining their corrosion resistance. It should be noted that the role of segment copolymers is to produce a second phase state, rather than the compatible of the various
FBE
s various parts.
The toughening of molten bonded epoxy powder coatings
For many years, epoxy powder coatings have been used as standard corrosion protection systems for the oil, trachea and water pipe industry due to their outstanding adhesion, chemical resistance, temperature resistance and corrosion resistance. These coatings are built on pipes in the plant and then transported to the site for welding and assembly.
welded joints are protected with specially constructed powder coatings, or other systems such as liquid coatings or shrink plastic sleeves. These coatings require protection
20

30
years, without major overhaul. In order to achieve this durability, the coating film must be applied in good condition and the metal must not be exposed to the environment.
, however, coating may be damaged during transport or installation, especially if the pipe needs to be installed in a remote area (difficult to transport or through rocky areas). To solve this problem, a multi-layer coating system was developed in the mid-1980s by coating epoxy coatings with high-density polyethylene (
HDPE
) or polypropylene.
although the system can improve the damage resistance of a single layer of epoxy, the construction cost per unit area can be increased by about
30%
. If a thicker and tougher single- or double-layer epoxy powder coating system can be developed, and its performance can reach the level of a three-coated system, it can be a low-cost alternative to a three-coated system.
is used to illustrate the inlay co-
FBE
toughening effects in powder coatings, as shown in table
1
to a standard
pipe coating mixture. The mixture is pre-ground for
45
seconds in a high-intensity mixer, crushed with a twin screw extruder, and cooled and ground into a powder coating with an average particle size of approximately
50
microns. Powder coating coated with fluidized bed, hot-rolled steel rods
2.5
cm ×
0.95
cm×
15.24
cm (pre-sand blasting, anchoring) The cross-section
60
to
100
microns) is coated with a film thickness of
350
to
400
microns). The rods are preheated to
250
degrees C, and after
250
degrees C curing
2
minutes, the rods are quickly quenched in water for
2
minutes, dropping to room temperature. Steel rods are used to test flexibility with a four-point bending device commonly used in this application. The bending test is performed below zero for
10
seconds. After the rod reaches room temperature and stabilizes, the number of cracks produced by the coating film is counted. If no cracks indicate that the coating film is tougher, it will not be destroyed during use.
test results are shown
table
2. Usually
the coating of the pipe powder coating can not be more than
400
microns thick, as this will lead to flexible testing. In the control case, there are some cracks at
375
microns, and the toughening formula can still pass the (
-38
degrees C) flexibility test when the film is thick at
500
microns or more. Similarly, the control case cannot pass a flexible test at a lower temperature. The toughened coating film can be tested to be crack-free
-45
degrees C (as shown in
2
2). The Tg
film
measured
DSC
, almost the same. This indicates that the toughening effect is not simply flexible, it is achieved in different ways.
in order to help to better understand the impact of segment co-adhesive tougheners on
FBE
the effects of coating properties such as fluidity, glass transition temperature and impact resistance, using statistical design experiments (
DOE
) for detailed evaluation. Three independent variables were selected in the study, introducing the
Box-BehnkenDOE
, which required
15
trials or an evaluation of
15
formulations (including three parallel trials).

%
, based on total mixture mass
)
:
2.5
,
5.0
and
7.5
.
volume concentration (17
). FVC%
):
10
,
20
and
30
.
·
DICY
chemical equivalent ratio (
%
):
45
,
60
and
75
.
the co-cohesive toughening effect
coating powder fluidity
an important performance of powder coatings is its fluidity prior to gelization. Most thermoplastic or nuclear shell particles used as tougheners increase the molten viscosity of epoxy resins, reducing the fluidity of coating powders and causing attachment problems due to poor surface cover.
ball flow is a laboratory test method that provides information about the fluidity of coatings prior to gelization. Measure and record the linear distance, in millimeters, of spter flow. The sample test is repeated three times.
as shown
3
, the inlay
-segment co-adhesive toughener does not significantly affect the spular flow of the powder coating during the test range. The curves in the figure show how the predicted values change when a single
X
coordinate values (toughener,
FVC
and
DICY
) variables are changed. The dot curve around the predicted value trajectory shows that the confidence interval of the predicted value
95%
.
glass transition temperature of powder coatings
improves the flexibility and impact resistance of
FBE
powder coatings without affecting the fluidity of the coating and the glassing transition temperature, which visually seems unlikely, as shown in Figure
4
,

Tg
on free membranes measured by
DMTA
) using dynamic thermal analysis (
DMTA
is only slightly affected by the toughener. In addition,
Tg
is more affected by the chemical equivalent ratio
curing agents (
DICY) chemical equivalents.
resistance to powder coatings
tested against
CAN/CSA-Z245.20
standards. The impact test results from
-30
to
-55
degrees C are shown in figures
5
,
6
and
7
.
powder coatings without tougheners
10% FVC
clearly show damage, with most peeling. With the same
FVC
, the toughened powder coating with
5%
toughener showed good impact resistance, small impact diameter, and no film peeling when the substrate temperature dropped to
-40
degrees C.
Figure
8
shows the
DICY
chemical equivalent ratio with high filler concentration and optimum
using inlay co-concentration tougheners, which can significantly improve the impact resistance of
FBE
coatings (Figure
7
). In order to make comparison, the control system with high filler content and no toughener was tested, and the result was that the paint film was very brittle and not suitable for pipe corrosion protection.
according to
CSA-Z245.20
other tests such as gel time, cathode dissociation, and hot and humid adhesion were conducted and no negative effects of tougheners were found on these properties.
Conclusion
These studies clearly show that the new segment co-entity toughener technology can significantly improve the flexibility and impact resistance of
FBE
coatings without affecting other key performance, such as
Tg
, mobility and corrosion resistance. This new technology breaks the traditional
-Tg-
-toughness interconnected pattern, i.e. to obtain toughness will affect viscosity and curing products
Tg
.
:
1 Kehr, J. A. InFusion-Bonded Epoxy (FBE): A Foundation for Pipeline Corruption Protection; NACE, 2003.
2 Pham, H. Q.; Marks, M. J.In Epoxy Resins, Ullmann
'
s Encylo- pedia ofIndustrial Chemistry, Wiley-VCH Verlag GmbH & Co., KGaA, 2006.
3 Yee, A. F.; Pearson, R.A. In Fractography and Failure Mechanisms of Polymers and Composites, Roulin-Moloney, A.C., Ed. Elsevier Science Publishers: London, 1989,291-350.
4 Sultan, J. N.; McGa。