A new interpretation of the coating standard for elastic coatings

According to the definition in the JG/T172-2014 "Elastic Architectural Coatings" standard, elastic coatings are functional coatings that use synthetic resin emulsions as the base material, formulated with pigments, fillers and auxiliaries, and after applying a certain thickness (dry film ≥ 150μm), there is a functional coating

In the elastic coating standard topcoat requires a ≥ ratio of 0.

Keywords: elasticity, function, thickness, contrast ratio, solids content, low carbon

The author | Zuo Qi zero, Lian Kun, Lan Maoren

Jiangsu Badefu Science and Technology Development Co.

preface

An elastinous coating is a functional coating that, unlike other non-inelastic coatings, can cover up tiny cracks

In the practical application scenarios of elastic coatings, it is usually divided into flat coating process and brushed orange peel process

Elastic flat coating process in practical applications is usually the same as the use and dosage of non-elastic exterior wall flat coating latex paint, that is, one bottom and two sides, such as a large manufacturer of the opposite paint is recommended to use 0.

In the elastic coating standard topcoat requires a contrast ratio of ≥ 0.

At this stage, in order to help elastic coatings achieve cost reduction goals and meet the strength performance specified in the standard, often everyone uses the same PVC, reducing the amount of emulsion and powder used year-on-year to reduce the formulation cost of elastic coatings, so it is necessary to cause the solid content of the paint and the volume of solid content to be greatly reduced, if you want to achieve the standard said ≥ 150um dry film thickness to cover the function of the wall micro cracks, you need to paint more overpain, and greatly increase the labor cost
。 If you still follow the traditional construction method, the thickness of the dry film on one bottom and two sides can generally only reach 60-80um, which is too far from the standard film thickness requirements, and the so-called micro cracks in the cover are a bit self-deceptive
.

The standard requires the mechanical properties to be tested and the final film thickness is (1±0.
2) mm for practical application has no guiding significance, if in accordance with JC/T864-2008 "polymer emulsion building waterproof coating" standard stipulated that its solid content ≥65% has a certain echo, so as to achieve the practical application of the external wall elastic coating easy to achieve dry film thickness ≥ 150um functional cover wall micro crack use effect
。 Suppose, if we set the contrast ratio in a certain range, such as the contrast ratio is set at greater than 0.
50, less than 0.
60, according to the amount of conventional brushing can not cover the base color, which forced the formula designer, from the perspective of cost performance, must increase the solid content and volume content, but also to ensure that the dry film thickness ≥ 150um the contrast rate is more than
0.
97 。 In order to reduce the construction process, but also to make the exterior wall elastic coating to meet the functional requirements of the cover of tiny cracks, in the formula design in addition to the emulsion (to meet the mechanical properties and excellent stain resistance and aging resistance) in the choice of the requirements are relatively high, but also to achieve high solidity and low viscosity
.

Below we will focus on four aspects of the experiment to discuss the logical relationship between each other:

● The thickness of dry film reaches 150um, and the contrast ratio design is relatively reasonable?

● The logical relationship between film thickness and covering tiny cracks?

● The relationship between the solid content or volume solid content of the coating and the film thickness and the number of construction channels?

● How much does reducing the solids content affect the scrubbing resistance of elastic coatings?

experiment

▶ The main experimental and testing instruments are shown in Table 1:

▶ The test formula is shown in Table 2:

▶ Test items and test methods:

- Viscosity, thixotropy

Measure the viscosity of the paint sample using the Stormer viscometer, measure the viscosity of the paint sample using the Böhler Fly viscometer, measure the viscosity of the paint sample using the digital rotary viscometer and calculate the thixotropic value of the paint sample;

- Gloss

Tested according to the gloss test method in the standard HG/T 5065-2016 "Gloss Varnish for Architectural Coatings";

- Brush resistance

Test the brush resistance test method in the standard GB/T 9755-2014 "Synthetic Resin Emulsion Exterior Wall Coating" and GB/T 9756-2018 "Synthetic Resin Emulsion Interior Wall Coating" (test the brush resistance of paint samples on asbestos-free cement board and black polyester film respectively);

- Solids content

Using an analytical balance to weigh 1.
0000-2.
0000g of elastic coatings, after placing the paint in a 150 °C oven for 2h, the sample is placed in a dryer for 15 minutes, using the analytical balance to weigh the weight, the formula is calculated with reference to the solid content of the emulsion in gb/T 20623-2006 "Emulsion for Architectural Coatings";

- Specific gravity

Measuring the specific gravity of elastic coatings using specific gravity cups;

- Volumetric solids content

Divide the weight of the solid in the formula for calculating the solid content by the density and convert it into a volume, and the volume solid content can be calculated according to the formula;

- Dry film thickness, contrast ratio

Use 100μm, 200μm, 300μm, 400μm, 500μm wet film preparers to scrape the film on black and white cardboard, and curing in the curing room for 1d, and measure the dry film thickness using a coating thickness gauge; Use a reflectance tester to test the reflectivity of the paint on different parts of the black and white cardboard and calculate the logarithmic value;

- Rain marks

Add 2% Clariant charcoal black paste to the paint sample for color grading, use a wire rod to make a board (120μm + 80μm), the model drips water after 1d maintenance in the maintenance room, drips water after 16h, the sample is taken out to the conservation room for natural drying, and observe whether there are bright spots, rain marks and other phenomena in the dripping area of the model;

- Stain resistance

Tested according to the test methods in the standard JG/T 172-2014 "Elastic Architectural Coatings Standard";

- Dynamic crack resistance

Refer to Appendix B dynamic crack resistance test method in JG/T 157-2009 standard;

On the dynamic crack resistance machine, first crack the asbestos-free board, record the crack width, according to different brush coating amounts (0.
25kg/m2, 0.
35kg/m2, 0.
6kg/m2), apply the paint brush on the 200mm*150mm asbestos-free fiber cement plate, after seven days of maintenance in the standard environment, then top the crack film, and record the crack width again; The difference between the width of the two cracks is the dynamic crack resistance value
.
Prepare 1 sample per sample, test 6 sets of data per sample, and then average;

- Dynamic crack resistance after hot and cold cycles

Refer to Appendix B dynamic crack resistance test method in JG/T 157-2009 standard;

On the dynamic crack resistance machine, first crack the asbestos-free board, record the crack width, according to different brush coating amounts (0.
25kg/m2, 0.
35kg/m2, 0.
6kg/m2), apply the paint brush to 200mm*150mm asbestos-free fiber cement flat, and after seven days of maintenance in the standard environment, the sample is subjected to 3 hot and cold cycles (soaking water 18h, -18°C3h, 50°C3h), and then top the crack film to record the crack width again; The difference between the width of the two cracks is the dynamic crack resistance value
.
Prepare 1 sample per sample, test 6 sets of data per sample, and then average
.

▶ Test results

- Viscosity test results:

- Test results of solid content and specific gravity:

✅ Summary: Formula 1, 5, 7 and 8 meet the requirements
of JC/T864-2008 "Polymer Emulsion Building Waterproof Coating" standard for its solid content ≥ 65%.
The higher the solids content in the formulation, the less the amount of thickener used, the higher the ICI viscosity, the better the fluidity, and the more plump
the paint film appears.

- Test results for gloss at different angles:

✅ Summary: As a decorative coating for the exterior wall, reduce the impact of light pollution on the coating flowering, in the early stage of the formulation design that meets the technical requirements of the standard, the PVC is used to make the PVC high, so that the gloss of all angles is low, according to the actual test results, basically reach the original intention
.

- The correspondence between wet film and the thickness of the formed dry film and the corresponding logarithmic test results:

✅ Brief summary:

*The higher the solids content of the pvc consistent volume, the higher the contrast ratio; The higher the ICI viscosity, the better the leveling and the higher its logarithmic ratio;

*There are certain differences
between the theory and the measured film thickness, and the film thickness results of the frame type and the wire rod.
The thickness of the dry film of the wire rod 100um is obviously thicker than that of the frame 100um, which has both the error of human factors and the unevenness of
the frame coating substrate.
According to theoretical calculations, each coating is 100um, and the high solids content coating formula needs to be brushed three times to meet the standard requirements of dry film thickness of 150um, and the low solids content must be painted at least four times to basically meet the standard requirements
of dry film thickness of 150um.
In the actual testing and use of high solids content formulations, the standard requirements of dry film thickness of 150um are required to be at least one more time, and the low solids content is at least two to three times more, which greatly increases labor costs
.

* From the practical application point of view, to meet the standard requirements of dry film thickness of 150um, with the function of elastic coating that covers tiny cracks, the ratio should be adjusted appropriately; Balance price and performance to avoid unneeded waste
.

- Comparison of the scrubbing resistance of different elastic emulsions with different solids content of PVC on different substrates:

Figure 1 Sample after scrubbing resistance test on cement slabs

Fig.
2 Sample after brush resistance test on polyester film

✅ Brief summary:

* From the test results of the three emulsions selected, the impact of different emulsions on scrub resistance is relatively large, and the adhesion of the emulsion to the substrate and the wrapping of the pigment filler have a certain relationship, and the hydrophilic emulsion scrub resistance is significantly worse than the hydrophobic scrub resistance; In addition, according to the principle of similar solubility, the hydrophilic emulsion adheres poorly to the organic substrate, and its scrub resistance is relatively weak
.
The same formulation is significantly better
than on black polyester on asbestos-free cement slabs.

*With the PVC high solids content elastic coating formulation system, its scrub resistance is obviously better than the low solids content of the scrubbing resistance, this phenomenon is like the paint diluted after testing the scrub resistance is basically consistent
.

* Scrub resistance has a certain relationship with the variety of fillers in the formula, such as flake structure of cloud powder to a certain extent to help
scrub resistance.

- Contribution of different emulsions to stain resistance:

Fig.
3 Sample after stain resistance test (the upper part of the sample is the irradiated ultraviolet part, and the lower part is the uninadiated ultraviolet part)

✅ Brief summary:

* The contribution of different emulsions to stain resistance is not the same, RS-9910's stain resistance is significantly better, RS-9699H compared to RS-9699, its stain resistance is slightly improved;

* The use of elastic emulsion RS-9699 and RS-9699H prepared high solids content elastic coating stain resistance is slightly worse than low solid content stain resistance, regardless of whether it is irradiated ultraviolet light, the result orientation is consistent, but RS-9910 prepared elastic coating film its stain resistance performance with RS-9699H and RS-9699H logic relationship is not completely consistent, the specific reasons need to be further verified, in general, the coating film irradiated ultraviolet light its stain resistance has been significantly improved, paint film drying is relatively more adequate, The surface energy will also be lower;

*Why is high solids content less resistant to staining than low solids content? Personally, I think that part of the reason is that the film formed by the high solids content is thicker, the paint film is not completely dried and sufficiently in the same time, and the coating film agglomeration is not ideal
.

- Mechanical properties test:

✅ Brief summary:

* The elongation at break under the standard state of PVC elastic coatings and high solids content coatings is relatively high, and the elongation at break of -10 °C is exactly the opposite, which needs to be further explored;

* The tensile strength of the coating film becomes slightly higher after irradiation by ultraviolet light, and the elongation at break becomes slightly lower, mainly because it has a certain relationship with the degree of crosslinking on the surface of the coating film;

*All three emulsions show good mechanical properties, especially the elongation
at break of -10 °C.

- Rain mark performance test:

Fig.
5 Sample after rain mark testing

- Film thickness and dynamic crack resistance test:

✅ Brief summary:

* To achieve a dry film thickness of 150um paint film, the amount of elastic paint with low solids content is much more; Coatings prepared with high solids content elastic coatings, whether without treatment or cold and hot cycle treatment, are significantly better in dynamic crack resistance than coatings prepared with low solids content elastic coatings; As for why the dynamic anti-cracking resistance of the coating film after the cold and hot cycle of the elastic coating film becomes better, further research will be done;

*The elastic coatings prepared by the three elastic emulsions are all based on the increase of dosage, and the thicker the paint film formed, the better
its dynamic crack resistance.

summary

● Elastic coatings not only have the decorative properties of general building exterior wall latex paint paints, but also have protection properties
that are different from general exterior wall architectural coatings.

When the wall cracks, the coating suffers from stretch deformation and is not easy to crack and destroy, and the still intact elastic coating effectively blocks a variety of components (water and other liquids, etc.
) to avoid a variety of corrosive components from invading the interior of the wall, and then reasonably maintain the wall from injury, so as to achieve the role of
truly protecting the wall.
Elastic coatings have the function of covering the tiny cracks generated by the wall, which has a lot to do with its mechanical properties, and is proportional to the bond strength, tensile strength and elongation; At the same time, the thicker the thickness of the elastic coating dry film, the better the crack resistance, and the cracks caused by the deformation of the cover wall are slightly wider
.

●From the perspective of pure coating formulation, the standard of elastic coatings that meet the current JG/T172-2014 can meet the requirements
of high solids content or low solids content.

If the elastic coating with low solids content adopts the process of one bottom surface and two, the dry film thickness is difficult to meet the functional requirements of the elastic coating (that is, the dry film thickness is not less than 150um mim cover micro cracks), and the significance of
the elastic coating is lost.
It would be more reasonable
to add the solids content requirements and contrast ratios specified in the JC/T864-2008 standard to the elastic coating standard and design it within a certain range.

● Excellent stain resistance is an eternal topic
for all exterior decorative coatings.

We all know that the current elastic paint is slightly weaker than other non-elastic latex paints
.
As an important new force product for the decorative surface of the exterior wall, how to improve its stain resistance and maintain a long-lasting and beautiful decorative effect is a common problem
faced by all paint people.
The elastic emulsion for Bardfu exterior wall adopts the patented "F-sorb" technology and molecular structure design so that the molecular chain has a special functional group, which crosslinks ultraviolet light through ultraviolet light irradiation, giving the paint film outstanding stain resistance and excellent mechanical properties, and providing a full guarantee
for customers to prepare highly stain-resistant all-weather elastic coatings for the exterior wall.