Summary and analysis of coating testing methods

Paint performance testing

The performance test of raw paint refers to the quality condition
of the paint after packaging, after transportation, storage, and until use.
The main performance is as follows

Status in container:

Visually observe whether the coating has delamination, muddy, thickening, gelatinization, crusting, precipitation and other phenomena
.

(1) Delamination, precipitation: the coating may appear delamination after storage, generally can be checked with a scraper, if the settlement layer is soft, easy to insert with a scraper, the precipitation layer is easy to be stirred up and redispersed, the coating can continue to use the coating online coatingol.
com
.

(2) Crust: Alkyd, phenolic, natural oils and other coatings often produce crusts, the crust layer can not be used, after removing the lower layer can continue to be used, the use should be stirred evenly
.

(3) Thickening and gelatinization: can be stirred or added with an appropriate amount of diluent to stir and use; If it cannot be stirred and dispersed into a normal state, the paint cannot be used
.

Density:

The weight
of the volume of the object at a specified temperature.
Its determination is carried out according to GB/T 6750-1986

Fineness:

That is
, the fineness of the solid substance of the coating.
The fineness has a great influence
on the quality of film formation, film gloss, durability, and storage stability of the coating.
However, it is not the finer the better, too fine will affect the adhesion
of the paint film.
Measured
according to GB/T 1724—1979(89).

Viscosity:

An item that represents the flow and deformation characteristics of a fluid under external force is a measure of the internal resistance of a fluid against flow, also known as the internal friction coefficient
.
The detection methods are:

(1) Outflow method: suitable for the detection
of transparent varnish and low viscosity paint.
That is, the viscosity
of this paint is expressed by the time it flows out of a container of a certain volume.

(2) Falling ball method: the use of solid substances in the liquid flow speed to determine the viscosity
of liquid.

(3) Bubble method: the use of air flow speed in the liquid to determine the viscosity of the coating, only suitable for transparent varnishes
.

Non-volatile content:

The non-volatile content, also known as the solid content, is the part of the coating component that remains after construction to become a dry coating film, and its content has a great relationship
with the quality of film formation and the use value of the coating.
In order to reduce the pollution of organic volatiles to the environment, the production of high solids coating is one of the directions of
coating manufacturers.
The common method of determination is to heat and bake the paint at a certain temperature, and the remaining substance after drying is compared with the mass of the sample, expressed as a percentage
.
Its standard is GB/T 9272-1988
.

Freeze-thaw stability:

It is mainly used for water-based paint
based on synthetic resin emulsion.
If it can still maintain the original properties after being frozen and thawed several times, it has freeze-thaw stability
.
It can be determined
according to GB/T 9268—1988.

Coating application performance testing

Coatings can only work
through application.
The application properties of coatings, including the coating on the substrate and the beginning of the formation of the paint film, the main properties are as follows:

Workability:

According to different construction methods, the workability is divided into brushing, spraying, scraping, that is, when the paint is constructed by brush, spray and scraping method, it is easy to apply, and the coating film can be leveled quickly, without sagging, wrinkling, shrinking edge, bleeding bottom or yellowing
.
The determination method is according to GB/T 6753.
6-1986 standard
.

Drying time:

The drying process of the coating is divided into different stages
according to the change process of the physical properties of the coating film (mainly viscosity).
It is customarily divided into three stages
: surface drying, actual drying and complete drying.

(1) Surface drying time: latex paint at room temperature of 25 °C, surface drying time of 2 hours, commonly used GB/T 1728-1979 (89) in the blowing cotton ball method, finger touch method and other detection
.

(2) Actual drying time: the actual (complete) drying time of latex paint at room temperature of 25 °C is 7 days, and the filter press method, cotton ball method, blade method and thick layer drying method in GB/T 1728-1979 (89) are commonly used
.

Coating rate:

The coating rate refers to the coating area
of the quality [or volume] of the paint when it reaches the specified coating film thickness or scrub resistance under normal application conditions.
It is ㎡/kg or ㎡/L
.

Leveling:

Refers to the ability
of the coating film to flow into a flat and smooth surface after application.
The leveling of the coating film is a combination of
gravity, surface tension and shear forces.
Measured
by GB/T 1750—1979(89).

Sagging:

Liquid paint is coated on the surface of vertical objects, affected by gravity, the surface of part of the wet film is easy to have downward flow, forming the upper part thinning, the lower part thickening or serious formation of hemispherical [teardrop-shaped] and corrugated phenomena
.
The main reasons for this are that the flow characteristics of the coating are unsuitable and the wet film is too thick
.
GB/T 9264-1988 medium sagging instrument was used for measurement
.

Film thickness:

The coating film thickness is divided into wet film thickness and dry film thickness, and the wet film thickness is determined by GB/T 1345.
2-1992 wheel gauge and comb gauge; The thickness of the dry film is carried out by magnetic method and mechanical method, and the thickness of the coating film is usually measured by mm as the thickness
of the nuclear latex paint.

Hiding power:

The ability of the color paint to be evenly painted on the surface of the object, through the absorption, reflection and scattering of light by the coating film, so that the color of the substrate no longer appears is called hiding power
.
GB/T 1726-1979(89) and GB/T 9270-1988 standards can be determined
.
That is, the minimum amount of paint required for the hiding area (g/㎡) is expressed as the hiding power
.

Hours of use:

It is mainly for the application time of two-component or multi-component coatings (that is, the components can still be used normally after being mixed in the container for a specified period of time).

Film performance testing

Film appearance:

After the sample prepared in the indoor standard state is dried, it is observed with the naked eye under natural light to check whether the paint film has defects such as brush marks, particles, blistering, wrinkling, shrinkage holes, etc.
, and compare
it with the standard template.

Luster:

Light shines on a smooth surface, partly reflected and partly refracted through the interior
.
The ratio of the intensity of reflected light to the intensity of incident light is called reflectivity
.
The gloss of the paint film is the ability of the surface of the paint film to reflect the light shining on it in a certain direction, also known as mirror gloss
.
The greater the reflectivity, the higher the
gloss.
China according to GB/T 1743-1979 (89) to determine gloss.

Vividness:

It is mainly to evaluate the decorative properties of the coating film of aircraft and high-end cars
.

Color:

Color is a kind of vision, which is the reflection
caused in the brain after different wavelengths of light stimulate the human eye.
Therefore, the color of the coating film is determined by the irradiated light source, the coating film itself and the
human eye.
Due to the limitations of factors such as color memory ability and natural conditions, it is inevitable that there will be human error
.
It can be carried out
in accordance with the provisions of GB/T 9761-1988 standards.

Hardness:

Hardness is the resistance
of the paint film to another hardened object acting on it.
The methods for determining the hardness of the coating film include pendulum damping hardness method, scratch hardness method and indentation hardness method
.
The scratch hardness method
is mainly introduced here.
The scratch hardness method is to determine the hardness
of the coating film with a hard object scratching the surface of the paint film.
Commonly used is pencil hardness
.
GB/T 6739-1986 stipulates that the pencil used in the use of 13 levels from 6B to 6H can be operated manually or tested by instruments
.

Impact strength:

Also known as impact resistance, it is used to detect the resistance of the coating film to instantaneous deformation under the action of high-speed gravity without cracking and falling off
.
It combines film flexibility and adhesion to the substrate
.
It can be measured by impact tester
according to GB/T 1732-1979 (88).

Flexibility:

When the paint film is bent by external force, the comprehensive properties of elasticity, plasticity and adhesion are called flexibility
.
It was measured
by a flexibility tester in GB/T 1731-1993.

Adhesion:

A general term for
the adhesion force generated by the physical and chemical effects of the coating film on the surface of the substrate.
The methods of determination include grid method, circle method and pull method
.
The grid method is to use knives to cut lattices with a spacing of 1mm horizontally and horizontally, the number of grids is 5×5, and then graded according to the rating standards specified in GB/T 9286-1988, grade 0 is the best, and grade 5 is the worst
.

Abrasion resistance:

The ability of the coating to resist mechanical wear is a combination of
film hardness, adhesion and cohesion.
It is mainly used for the detection
of road sign paint and floor paint.

Recoatability and topcoat compatibility:

Recoatability refers to the ease and effect
of repainting with the same paint on the surface of the film.
The test is to apply the same coating according to the prescribed method after polishing on the dried paint film according to the specified method, check the difficulty of the coating under the thickness required by the product, visually inspect the condition of the coating film after coating, and check whether the coating film is defective
after drying at the specified time.
Topcoat matching is the measurement item of primer, and its significance and measurement method are similar
to recoatability.

Brush resistance:

Determine the relative abrasiveness
of coatings when they are repeatedly washed during use to remove contaminants.
In particular, interior wall paints are easy to be soiled and need to be scrubbed, and washing resistance is an assessment index
for this performance.
The national standard is GB/T 9266-1988
.

Light fastness:

The ability of the coating film to maintain its original color, gloss, and other optical properties after being irradiated by light is called optical rotation
.
It can be tested
in terms of optical rotation, color retention, yellowing resistance, etc.

(1) Light retention, color retention: the prepared sample is covered with a part, and after irradiating under sunlight or artificial light for a certain period of time, the gloss and color of the irradiated part and the unirradiated part can be compared to obtain its retention ability
.

(2) Yellowing resistance: the sample is coated on frosted glass, dried and put into a dryer containing saturated potassium sulfate solution, and after a certain period of time, the three stimulus values X, Y, and Z of the color are determined, and then the yellowing degree value D
is calculated.

Calculation formula: D=1.
28X-1.
06Z/Y

Note: X, Y, Z are the three parameters in the C, I and E coordinate system issued by the International Illumination Commission, that is, under a fixed light source, the reflectivity measured by the red filter is X value; The green piece measures the Y value; The blue chip measures the Z value
.

Water resistance:

The methods for determining water resistance include room temperature immersion method, boiling water immersion method, 40 °C constant temperature flow water immersion method, etc
.
The common method
of immersion at room temperature is used.
The national standard is GB/T 1733-1993
.

Stain resistance:

It usually refers to the degree to which dirt on the surface of the paint is scrubbed off with a damp towel (or an appropriate amount of laundry detergent in water), also known as contamination resistance
.

In addition, salt water resistance, chemical resistance, solvent resistance, moisture resistance, atmospheric aging resistance, etc
.