Requirement Profile Primer

Wg. Specification (technical standard)

Automotive Paints and Coatings

Primer surfacers have to satisfy an extremely wide range of requirements. 

The selection of suitable product formulas is based on the technical requirements, environmental compatibility, the framework conditions imposed by legislation,

manufacturing processes, and finally, the application methods and their associated costs.

 Often, in the case of new projects, it is the cooperation between automobile manufacturers, plant suppliers, and coating manufacturers that results in the

creation of a new product.

Legislative Requirement

Technological Requirements

Film Properties

The test categories include 

mechanical properties, 

climatic-technological properties, 

the characteristics of the liquid coatings, 

and information on the delivery packaging to ensure safe handling and use. 

If the test criteria are successfully satisfied, a basic approval is generally issued.

Mechanical Properties

The surface hardness

Buchholz penetration hardness conforming to DIN EN ISO 2815 and pendulum damping conforming to DIN EN ISO 1522.

Elasticity, by contrast, provides an indication of the potential stone chip protection capacity of the primer surfacer coat alone. It is generally measured using cupping

test according to DIN EN ISO 1520 or mandrel bending test (cylindrical) according to DIN EN ISO 1519.

Adhesion to the electrocoat (CED) primer and to the base coat in the overall coating system is essential and is determined by the crosscut test according to DIN

EN ISO 2409, ASTM 3359.

Climate-Related Technological Properties

water immersion test at increased temperature conforming to DIN EN ISO 2812-2, ASTM 870;

• autoclave test for stresses above 100◦ C with simultaneous humidity testing;

• cold check test (temperature change test);

• resistance to extreme climates.

accelerated weathering tests, for example SAE J1960, ASTM D4587.

Smoothness

Product Specifications

The most important variable from the technical and commercial point of view is the nonvolatile content or nonvolatile matter as defined in DIN-EN-971-1. The methods for determining this variable – that is the specified drying or cross-linking temperature and time can vary from customer to customer according to DIN EN ISO 3251.

In addition, for liquid primers, the viscosity at the time of supply and application are specified. For solventborne coatings, flow cups conforming to DIN EN ISO 2431

are suitable. For waterborne systems, which generally have marked non-Newtonian characteristics, measurement of the viscosity in Pascal second with a defined shear gradient and a rheometer conforming to DIN EN ISO 3219 is indispensable. 

In powder primer surfacers, the particle size and the particle size distribution play an important role in defining the application properties. They are measured

by a variety of methods (see Section 5.5).

The fineness of grind and grain size distribution of the pigments in the primer are generally determined by a brush-on method conforming to DIN EN ISO 1524.

The density of the products to be applied is specified in accordance with DIN EN ISO 2811 in the case of liquid coatings and DIN 55990-3 for powder coatings.

For the packaging, storage, logistics, and transport, the stability features of the primer surfacer are decisive. Solventborne primer surfacers can be stored in steel or

babbitt metal drums. For waterborne systems, plastic hobbocks are generally more suitable. Otherwise, stainless steel packaging, for example, in the form of containers, is necessary. Powder primers can also be stored and transported in low-cost ‘big bags’. The specified temperature limits for storage are generally 5–30◦

C. Within these limits, the physical and chemical stability must be guaranteed for at least 6 months. In individual cases, for waterborne formulas in particular, stability of 3 months is specified.

Application

The requirements for application are highly complex. The testing and definition of

application characteristics are therefore often not standardized. Application begins

with

• delivery, and involves several different steps and characteristics, including

• adjustment and handling in the paint mixing room,

• circulation stability,

• application,

• behavior – that is flow on the vertical and horizontal panel,

• cleaning of the assemblies,

• drying in the oven,

corrections on the inspection line,

Often, bright top coats have a hiding power, which is more than the film of

specified thickness, that is they are transparent. The color of the primer is one way

of attempting to compensate for this problem. Consequently, a range of several

colors in a primer surfacer line is common. Because the primer surfacer is also

seen as a correction layer, high-gloss is often a customer requirement to ensure

optimal defect identification.

• further processing with the top coat.

Raw Materials

For making liquid primer surfacers, the following four elements of the coating formula, namely,

• binders and resins,

• pigments and extenders,

• solvents (VOCs or water), and

• additives

Technical data for the three primer surfacer technologies

Solid content % 

VOC g l−1 

Density g cm−3 

Bake conditions min ◦ C−1 

Film build µm 

Viscosity (20 ◦C) mPa at 1000 s−1 

Storage temperature ◦C 

Shelf life Mo 

Resin Components

The basic properties of the paint like viscosity and reactivity and of the applied film like hardness and elasticity of a primer surfacer are set by the choice of the binder or resin

Pigments and Extenders

Additives

Solvents

Although the majority of surfacer compositions are based on blends of organic solvents and diluents, water is now playing a more significant role because of more

and more stringent environmental controls.