Do you know the effect of insulating glass microbead surface treatment on the performance of water-based thermal insulation coatings?

Influence of surface treatment of hollow glass beads on the properties of water-based thermal insulation coatings

Summary

A water-based heat-insulating coating was prepared with water-based silicone acrylic resin as matrix resin and modified hollow glass microspheres as heat-insulating filler

Key words: thermal insulation coating; hollow glass microspheres; thermal conductivity; coupling agent

Background introduction

Water-based thermal insulation coating is an energy-saving and environmentally friendly coating that uses water-based resin as the base material and hollow materials such as hollow ceramic microbeads, hollow glass microbeads, etc.

Liu Yahui et al.

In this study, water-based thermal insulation coatings were prepared with water-based silicone acrylic resin as the base material, modified hollow glass microspheres as fillers, and the corresponding additives

1.

1.

Ethanol: analytically pure, Yangzhou Gold Petrochemical Yangzi Chemical; hollow glass beads (ρ=0.

1.

Taking ethanol solution as the reaction medium, the reaction temperature is 60 ℃, adding the hollow glass microbeads and mixing evenly, then adding the coupling agent (0.
5% of the mass of the hollow glass microbeads, the addition amount is calculated according to the specific surface area of ​​the hollow glass microbeads) , reacted for 1 h, cooled to room temperature, and subjected the reacted packing to suction filtration
.
It was placed in an oven at 120 °C for 2 h and taken out for use
.

The mechanism is that in the ethanol solution, the hydroxyl groups on the surface of the hollow glass beads react with the Si-OH/O-Ti-O groups of the coupling agent, so that the coupling agent is grafted on the surface of the glass beads, thereby improving the hollow glass beads.
Interfacial compatibility of beads with organic resins
.

1.
3 Preparation of water-based thermal insulation coatings

First, 35 parts (mass parts, the same below) of water and 1.
5 parts of film-forming aids were respectively weighed and then added to the container, and premixed at low speed (500 r/min) for about 15 min using a grinding and dispersing integrated machine
.
Subsequently, 20 parts of titanium dioxide and 45 parts of silicone acrylic resin were added, and dispersed at high speed (2 000 r/min) for about 20 min
.
Finally, 8 parts of heat insulating fillers are added at a stirring speed of 100 r/min until the paint is dispersed evenly, that is, the water-based heat insulating paint is prepared
.
When using hollow glass microbeads as insulating fillers, it should be stirred at a low speed and mixed evenly to avoid breaking the structure of the hollow glass microbeads by high-speed stirring
.

1.
4 Testing and Characterization

The coating film is prepared on the cold-rolled steel sheet according to GB/T 9271-2008, and the dry film thickness is about 50 μm
.

1.
4.
1 FTIR analysis and characterization

The treated hollow glass microbeads were first extracted with ethanol for 3 h, dried and then analyzed and characterized by Fourier transform infrared spectrometer (Avatar 370) from Thermoelectric Nicoli Instruments Inc.
KBr tablet was used, the resolution was 4 cm -1 , the wave number was 4 000-500 cm -1 , and the number of scans was 32 times
.

1.
4.
2 Micromorphology analysis and characterization

Scanning electron microscope (JSM-6360LA) of JEOL Ltd.
was used to observe the microscopic surface morphology of hollow glass microspheres before and after modification with different coupling agents
.

1.
4.
3 Mechanical properties

The prepared water-based thermal insulation coating was cast into a film, and the coating film was cut into a specific dumbbell-shaped spline.
The tensile strength and elongation at break of the test samples were recorded at a fixed tensile rate of 50 mm/min
.

1.
4.
4 Thermal conductivity

Prepare a water-based thermal insulation coating film with a thickness of >1 mm and cut it into a circular standard sheet, set the constant temperature time to 300 s, and use the thermal conductivity tester (DRL- II), using the temperature gradient to calculate the thermal conductivity to determine the thermal conductivity of the coating dry film
.

1.
4.
5 Viscosity

The apparent viscosity of the paint was measured by a DV-2+Pro digital viscometer from Brookfield, USA
.

2.
Results and Discussion

2.
1 Performance analysis of modified hollow glass beads

2.
1.
1 FT-IR analysis

It can be seen from Fig.
1 that the bending vibration peak of Si—O—Si at 460 cm-1, the Si—O asymmetric and symmetrical stretching vibration front of SiO2 at 800 cm-1 and 1 100 cm-1, respectively, at 3 450 cm The vibration peak at -1 is the characteristic peak of the hydroxyl group on the surface of SiO2
.
2 928 cm -1 is the stretching vibration absorption peak of -CH 3 and -CH 2
.
Compared with curve a, curves b, c and d show that the intensity of the -OH vibration absorption peak at 3 450 cm -1 is significantly weakened, indicating that the silanol groups on the surface of the hollow glass microbeads are hydrolyzed with the coupling agent to form hydroxyl groups and undergo dehydration condensation
.
Since the matrix of the hollow glass microbeads is silica, the infrared spectrum after the silane coupling agent treatment is not much different, so it is difficult to see the absorption vibration peak of the coupling agent on the infrared spectrum
.
At 1 629 cm-1 of curve e, it can be seen that the infrared peak has a certain degree of shift, and there is a characteristic peak of ester group at 1 730 cm-1, so it can be judged that the titanate coupling agent and the hollow glass microparticles Chemical bonds are also created between the beads
.

2.
1.
2 SEM analysis

Figure 2 is a 300-times SEM image of hollow glass microbeads treated with different coupling agents
.

As can be seen from Figure 2, the surface of the hollow glass microbeads treated with the coupling agent has no obvious change, and the hollow glass microbeads are partially broken.
Branches to the surface of inorganic particles, such monolayers are not observed in SEM
.

2.
2 Influence of hollow glass microspheres treated with different coupling agents on the performance of water-based thermal insulation coatings

2.
2.
1 Influence on the thermal conductivity of the coating film

Figure 3 is the thermal conductivity of the water-based thermal insulation coating film prepared by the hollow glass microspheres treated with different coupling agents
.

It can be seen from Figure 3 that the thermal conductivity of the water-based thermal insulation coatings prepared by using the treated hollow glass microspheres as fillers is reduced to a certain extent.
The compatibility of water-based silicone acrylic resin is good, so that the hollow glass microspheres are dispersed more uniformly in the coating, so that the agglomeration of the hollow glass microspheres in the coating is reduced, the specific surface area is increased, and the thermal conductivity is decreased
.
Among them, the thermal conductivity of the water-based thermal insulation coating prepared by the hollow glass microspheres treated with titanate coupling agent is the lowest
.

2.
2.
2 Influence on paint viscosity

Figure 4 shows the viscosity of water-based thermal insulation coatings prepared from hollow glass beads treated with different coupling agents
.

It can be seen from Figure 4 that the viscosity of the water-based thermal insulation coatings prepared by using the treated hollow glass microspheres as fillers all increased to a certain extent
.
This may be because the compatibility between the hollow glass beads and the acrylic resin is improved after the surface treatment of the hollow glass beads by the coupling agent, and the wettability between the resin and the hollow glass beads is also improved to a certain extent.
A firm chemical bond is produced between the organic functional groups generated by the treatment of the outer layer of the glass microspheres and the organic matrix resin
.
At the same time, it is possible that the untreated and completely free coupling agent modified by the hollow glass microbeads reacts with the silicone-acrylic resin, which eventually leads to an increase in the viscosity of the water-based thermal insulation coating
.

2.
2.
3 Influence on the mechanical properties of the coating film

Figure 5 shows the effects of different coupling agents on the mechanical properties of water-based thermal insulation coatings
.

As can be seen from Figure 5, compared with untreated hollow glass beads as fillers, the water-based thermal insulation prepared by using hollow glass beads treated with KH-550, KH-570 and titanate coupling agent as fillers.
The elongation at break of the coatings both increased and the tensile strength decreased
.
This is because, after the surface of the hollow glass microspheres is treated with a coupling agent, the bonding ability of the interface between the surface of the hollow glass microspheres and the matrix resin is enhanced to a certain extent
.
However, due to the differences of the coupling agents themselves, different coupling agents have different relative molecular masses, and at the same time, different coupling agents have different hydrolysis abilities, resulting in different binding abilities of the coupling agents to the surface of the hollow glass beads after hydrolysis, so the The mechanical properties of water-based thermal insulation coatings prepared from hollow glass microbeads treated with different coupling agents as fillers have different degrees of change
.
05MPa 。 The mechanical properties of the water-based thermal insulation coating prepared by the hollow glass microspheres treated with titanate coupling agent are the best, the elongation at break is increased to 27%, and the tensile strength is only decreased by 0.
05MPa
.

2.
3 Evaluation of thermal insulation performance of water-based thermal insulation coatings

The standard sample tank is used as the heat storage container, and the water-based thermal insulation coating made from untreated/treated hollow glass beads with different coupling agents is used.
3±0.
1) mm, add 100 ℃ hot water to the standard sample tank after spraying treatment, and leave it for 5 minutes.
After the heat transfer is uniform, use a thermocouple to measure the temperature inside and outside the standard sample tank.
The thermal insulation properties of the coatings were evaluated
.
The schematic diagram of the evaluation is shown in Figure 6, and the results are shown in Table 1
.

It can be seen from Figure 6 and Table 1 that the internal temperature of the standard sample tank is 97 °C, and the external temperature is 55~68 °C.
thermal effect
.
At the same time, due to the different thermal conductivity of water-based thermal insulation coatings prepared from hollow glass microspheres treated with different coupling agents, their thermal insulation effects are also different.
Thermal paint provides the best insulation
.

3.
Conclusion

The FT-IR and SEM characterization and analysis showed that both silane coupling agent and titanate coupling agent could effectively treat the surface of hollow glass microbeads and improve the relationship between the surface of hollow glass microbeads and water-based silicone acrylic resin.
Compatibility improves the thermal insulation performance and mechanical properties of the coating.
Among them, the water-based thermal insulation coating prepared by the hollow glass microspheres treated with the titanate coupling agent has the best thermal insulation performance and mechanical properties
.