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    Home > Coatings News > Paints and Coatings Market > The influence and application of fumed silica on the properties of polyester epoxy powder coating and coating film

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

    • Last Update: 2021-06-04
    • Source: Internet
    • Author: User
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    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.
    8%), chemical stability, reinforcement, abrasion resistance, looseness, thickening, and special thixotropy.
    It is used in rubber, plastics, coatings, It is widely used in medicine and other fields.


    Due to the above-mentioned characteristics of fumed silica, it is also commonly used in general coatings and powder coatings as additives .
    Online coatingol.
    com
    .


    In powder coatings, the characteristics of large specific surface area and large oil absorption of fumed silica are mainly used.
    The most commonly used in powder coatings is as a loosening agent (bulking agent).
    When making powder coatings, it is dried during the crushing process of the paint flakes.
    Method to disperse into powder coating products;


    Sometimes it is added to the raw materials for the preparation of powder coatings and dispersed into the powder coatings by means of melt extrusion mixing.
    In addition, fumed silica is also used to reduce the melt horizontal fluidity of the powder coating, and it is added to the powder coating as a coating film corner covering power modifier.


    The effect of fumed silica on the properties of different resin-based powder coatings and coating films is obviously different.
    This article mainly discusses the effect of fumed silica on the properties of polyester epoxy powder coatings and coating films and the application test situation.


    2.
    Test part

    2.
    1 Raw materials for testing


    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.
    2 Test method


    We choose the classic white formula of polyester epoxy powder coating, prepared by the laboratory powder coating preparation method, sieved with a 180-mesh standard sieve, and measured the gel time and melt level fluidity of the powder coating, and then the powder coating is cooled at 0.
    5mm After electrostatic spraying on the rolled steel plate, it is baked and cured under specified conditions to prepare a test sample plate, and various properties of the coating film are measured.

     

    3.
    Results and discussion

    3.
    1 The influence of fumed silica varieties


    We use five varieties of fumed silica from different businesses.
    In the classic white polyester epoxy powder coating formulation system, we fix the composition and dosage of all formulas except fumed silica (including the amount of fumed silica).
    Only change the type of fumed silica to formulate powder coatings, and measure the performance of powder coatings and coating films.


    Compare the effects of different fumed silicas on the properties of polyester epoxy powder coatings and coating films.
    The test formulations and test results are shown in Table 1.


    Table 1 White polyester epoxy powder coating test formula (parts by mass) and the influence of fumed silica from different vendors on the performance of powder coatings and coating films


    Recipe number

      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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    3.
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    3  ()


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       100

      100

     100

      100

     100

    E-12

       100

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    4.
    0

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    0

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    0

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    75

     75

     75

    75

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     50

     50

     50

    50

     50

      0.
    40

       0.
    40

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    40

     0.
    40

    ()

      0.
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       3.
    5

     7.
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     10.
    5

    14

    /s

      319

      548

      621

      711

      853

    /mm

    25.
    9

    26.
    0

    23.
    7

    21.
    5

    19.
    1

    /℃/min

    190/15

    190/15

    190/15

    190/15

    190/15

    ,

    /%

      98.
    4

      98.
    6

      97.
    7

      96.
    6

      86.
    9

    /cm

      +50

      -50

     +50

    -50×

    +50×

     -50×

    +50×

     -50×

    +50×

     -50×


    :+50  -50   +50×  -50×

     

    ,(),,4。


    4  ()


    11

    12

    13

    14

    15

    -2

       100

       100

       100

      100

    100

    E-12

       78

       78

       78

       78

       78

    503

       24

       24

       24

       24

       24


    2


    2


    2


    2


    2


    1


    1


    1


    1


    1

       67

       67

       67

       67

       67

       34

       34

       34

       34

       34

      0.
    20

      0.
    20

      0.
    20

     0.
    20

    0.
    20

    2-

      0.
    06

      0.
    06

      0.
    06

    0.
    06

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    06

    ()

       0.
    0

       3.
    0

       6.
    0

       9.
    0

       12

    /s

       160

       200

       240

       310

    320

    /mm

    27.
    3

    28.
    2

    26.
    3

    22.
    2

    18.
    5

    /

    ℃/min

    180/20

    180/20

    180/20

    180/20

    180/20

    /%

    100.
    1

      98.
    9

      99.
    0

      97.
    9

    96.
    9

    /cm

     +50

      -50

      +50

      -50

    +50

    -50×

    +50×

    -50×

    +50×

    -50×

    :+50  -50   +50×  -50×

     

    ,(),,5。


    5  ()


    16

    17

    18

    19

    20

    -2

       100

       100

       100

       100

    100

    E-12


    78


    78


    78


    78


    78

    503

       24

       24

       24

       24

       24


    2.
    0


    2.
    0


    2.
    0


    2.
    0


    2.
    0


    1.
    0


    1.
    0


    1.
    0


    1.
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       67

       67

       67

       67

       67

       34

       34

       34

       34

       34

     0.
    20

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    0.
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       12

    /s

      160

      185

      195

      230

      240

    /mm

     27.
    3

     25.
    2

     19.
    7

     16.
    0

      15.
    0

    ℃/min

     180/20

    180/20

    180/20

    180/20

      180/20

    /%

    100.
    1

      97.
    3

      100

    96.
    4

      97.
    7

    /cm

      +50

      -50

      +50

      -50

     +50 

    -50×

    +50

    -50×

      +50×

      -50×


    :+50  -50   +50×  -50×

     

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    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.



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