The influence and application of fumed silica on the properties of polyester epoxy powder coating and coating film

Fumed silica, also called fumed white carbon black, has a molecular formula of SiO2, which is a white fluffy powder with porosity, high temperature resistance, non-toxic and odorless.

Due to its small particle size (7-40nm), fumed silica has a large specific surface area (100-400m2/g), large surface energy and strong surface adsorption;

At the same time, it has the characteristics of high purity (silica content not less than 99.

We use classic white polyester epoxy powder coating formulation materials, fumed silica from Wuxi, Huzhou Longxiang Company, and Germany Degussa Company AeroSil 200 (hydrophilic, AS200 for short) and AeroSil R972 (hydrophobic) , Referred to as R972), Shanghai Dixiang Company HB215 (hydrophobic) and other five varieties.

2.

3.

1

2

3

4

5

Polyester resin-1

100

 100

100

 100

100

Epoxy resin E-12

100

100

 100

100

100

General leveling agent

4.
0

4.
0

4.
0

4.
0

 4.
0

Dispersant

2.
0

2.
0

2.
0

2.
0

 2.
0

Degassing agent

1.
0

   1.
0

   1.
0

   1.
0

 1.
0

Rutile Titanium Dioxide

75

75

75

75

 75

Precipitated barium sulfate

50

50

50

50

 50

ultramarine

   0.
40

   0.
40

 0.
40

0.
40

0.
40

Fumed silica

3.
5

Produced in Wuxi

3.
5

Huzhou Longxiang Production

3.
5 (AS200, hydrophilic)

3.
5 (HB215, hydrophobic)

3.
5 (R972, hydrophobic)

Powder gel time

/s

  585

  548

  563

   400

  384

Horizontal fluidity of powder melting/mm

  25.
6

  26.
0

 25.
9

26.
0

25.
2

Curing conditions/

℃/min

190/15

190/15

190/15

190/15

190/15

Appearance of coating film

Light orange pattern

Light orange pattern

Light orange pattern

Light orange pattern

Light orange pattern

Film gloss/%

  97.
4

  98.
6

98.
9

98.
7

99.
0

Coating film impact strength/cm

 +50

  -50

 +50

 -50×

+50-50×

  +50

  -50

  +50

  -50×

Note: +50 pass through the forward impact -50 pass through the recoil +50×fail through the forward impact -50×fail through the recoil

The test results in Table 1 above show that fumed silica with different specifications from different vendors has little effect on the melting horizontal fluidity of powder coatings, and there is no significant difference, but the impact on the gel time of powder coatings is very different.
The difference between the two is up to 200 seconds.

This is because the manufacturing process, surface treatment methods, specific surface area and other technical indicators of different manufacturers of fumed silica with different specifications are quite different.
The activity of fumed silica is very different, which affects the activity of powder coatings.
of.

When comparing hydrophilic fumed silica with hydrophobic fumed silica, hydrophilic fumed silica has a greater impact on the gel time of powder coatings than hydrophobic fumed silica, and it is easier to make powder The gel time of the paint becomes longer.

For example, the gel time of the hydrophilic fumed silica AS200 from Degussa is 563 seconds, while the gel time of the hydrophobic fumed silica R972 is 384 seconds.
The difference between the two is 179 seconds.

In addition, the type of fumed silica has a relatively small effect on the appearance and gloss of the powder coating film, but it has a relatively large impact on the impact strength of the film.

Because different types of fumed silica have different effects on the properties of polyester epoxy powder coatings and coatings, it is necessary to select the appropriate fumed silica for different formulation systems, and consider choosing the appropriate dosage.
In order to meet the requirements of coating film performance indicators.

In particular, the addition of fumed silica improves the looseness and storage stability of the powder coating.

However, the activity of the powder coating decreases, and the impact strength and other properties may be reduced.
According to the specific conditions of the formulation and the performance of the coating film, it is sometimes necessary to appropriately add accelerators and other measures to ensure the balance of the activity of the powder coating and the impact strength of the coating film.

3.
2 The influence of the amount of fumed silica

3.
2.
1 The influence of additional dosage

We choose powder coating products without adding fumed silica, and disperse fumed silica in two ways:

One method is to add the fumed silica of one thousandth, two thousandths, four thousandths, and five thousandths of the total powder coatings directly to the polyester epoxy powder coating products, and then mix and disperse them evenly.
(It is best to use a 140 sieve for sieving);

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100ml，40℃，2。

2  （）

2，。

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，，。

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，，，。

，。

，，。

，，，0.
2～0.
4%。

3.
2.
2 

，12，（），，3。

3  （）

：+50  -50   +50×  -50×

，（），，4。

4  （）

：+50  -50   +50×  -50×

，（），，5。

5  （）

：+50  -50   +50×  -50×

3、45，，，；，。

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，3，2-，452-，3。

3、45，，，。

，，，，。

，，。

，，1%，0.
2%。

3、4、5，，，。

Using this feature can improve the corner coverage of the powder coating and prevent the sagging phenomenon when the coating film is thick.
The amount of addition should be selected according to the requirements of the coating film thickness, and it will not affect the leveling and impact strength of the coating film.
Performance is a condition.
Fumed silica is a good modifier for coating film corner coverage of polyester epoxy powder coatings.

Theoretically, when the method of adding fumed silica improves the looseness and storage stability of polyester epoxy powder coating, the amount of fumed silica is relatively small, and continuous production can also be used;

However, in the production of some coatings (such as powder coatings with silicone oil), when added according to this method, the appearance of the coating film is not good, and the method of internal addition must be used to achieve the purpose of improving the storage stability of the powder coating.

At this time, a good addition amount is selected through experiments, which not only meets the requirements of improving the looseness and storage stability of the powder coating, but also meets the requirements of the appearance and impact performance of the coating film.

4.
Conclusion

From the above test results, the following conclusions can be drawn:

1) Different merchants and different specifications of fumed silica have obvious different effects on the gelation time of powder coatings, but have little effect on the melt horizontal fluidity of powder coatings;

In addition, it has a greater impact on the impact strength of the powder coating film, but the impact on the appearance and gloss of the film is not so large.
It is necessary to select the appropriate variety and specifications according to the requirements of the formulation design.

2) After the dry method of fumed silica is added to the polyester epoxy powder coating, the storage stability of the powder coating and the transportability of the powder coating can be improved, but the addition also affects the appearance of the coating film of the electrostatic powder coating.
Choose the right amount

3) When fumed silica is added to the powder coating by melt extrusion mixing method in the polyester epoxy powder coating, the gelation time of the powder coating becomes longer and the melt horizontal fluidity decreases with the increase of the addition amount;

Moreover, the appearance and impact strength of the coating film are obviously deteriorated, and the gloss change is relatively small.
It can be used as a looseness and storage stability modifier of powder coatings, and can also be used as a corner coverage modifier.

However, according to the requirements of powder coating and coating film performance, select the appropriate specifications and varieties of fumed silica, and select the appropriate amount of addition.