ELIX Paintability Guidelines (ES)

2

Paintability of ELIX ABS grades

1. Paintability of ELIX ABS grades

3

2. Recommendations

5

3. Troubleshooting

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3.1 Weld lines

6

3.2 Remains of plastic

7

3.3 Streak Marks or Quarters

8

3.4 Craters

9

3.5 Pinholes

10

3.6 Blistering

11

3.7 Adhesion problems

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3

Paintability of ELIX ABS grades

Many applications involving ELIX products require post-processing, especially in the automotive sector, where about 50-60% of the plastic parts are painted. In this sense, ELIX grades show excellent performance as substrate for post-processes such as painting, flocking or metallizing.

Every ELIX grade has high wettability and surface energy, assuring low scrap rates and high adhesion without the need for pre-treatments. Surface tension for the ELIX automotive grades are measured according to ISO 8296:2003, with surface tension values between 42-46 dyne/cm.

The high surface quality achievable with ELIX grades will guarantee the best appearance of the parts. For demonstration purposes, paintability tests were done at Thierry GmbH, a leading company which supplies the highest quality colour standards and precision painting services to OEMs and paint companies.

Eleven different paint systems for the automotive industry were selected, each of them with paint coats from well-known suppliers (see Table 1).

Painting System LAYER

PAINT SUPPLIER FILM THICKNESS

1

2

23

23

3

4

5

6

23

23

7

8

9

10

11

2K Primer SB*

PETER-LACKE

23

2K Primer WB*

MANKIEWICZ

14

2K Topcoat SB

PETER-LACKE

12

2K Topcoat WB

WÖRWAG

40

Base Coat SB

TECHNICOAT

18

Base Coat WB

AKZONOBEL

9

9

9

9

2K Clear Coat SB

AKZONOBEL

40

40

40

40

TECHNICOAT

28

*SB= Solvent Based

Number of layers

*WB= Water Based

Total thickness

μm

14

14

14 12

12

12

40 18

40

18

28

18

28

28

3

3

3

3

2

2

2

1

1

2

2

69

72

60

63

35

63

26

12

40

46

49

Table 1. Summary of the eleven painting systems analysed by Thierry GmbH and the film thickness used.

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Paintability of ELIX ABS grades

For testing the adhesion of the different paint systems used, cross-cut tests were done according to DIN EN ISO 2409. All ELIX Automotive grades tested had a score of 0, the best possible in the standard, which means that the edges of the cut are completely smooth with optimal adhesion. A minimal score of 1 is required to pass the test (see Table 2).

Table 1 - Classifications of test results

Classification

Description

Apperance of surface of cross-cut area in which flaking has curred (Example for six parallel cuts)

0

The edges of the cuts are completly smooth; none of the squares of the lattice is detached.

1

Detachment of small flakes of the coating at the intersections of the cuts.

A cross-cut area not greater than 5% is affected.

2

The coating has flaked along the edges and/or at the intersections of the cuts. A cross-cut area greater than 5%, but not greater than 15%, is affected.

3

The coating has flaked along the edges of the cuts partly or wholly in large ribbons, and /or it has flaked partly or wholly on different parts of the squares. A cross-cut area greater than 15%, but not greater than 35%, is affected.

4

The coating has flaked along the edges of the cuts in large ribbons and/or some squares have become partly or wholly detached. A cross-cut area greater than 35% but not greater than 65%, is affected.

5

Any degree of flaking that cannot even be classified according to classification 4.

SCORE 0 Table 2. Classification of test results according to DIN EN ISO 2409.

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Paintability of ELIX ABS grades

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ELIX ABS grades also pass the demanding specifications on painted parts from the different OEMs. Table 3 shows some of the most important tests where ELIX grades have been tested with positive results:

TEST

STANDARD

Pressure washer

TL 211 (PV 1503)

Impact

TL 211 (DIN ISO 4532)

Store Impact

TL 211 (DIN EN ISO 20567-1)

Condensed water test

TL 211 (DIN EN ISO 6270-2)

Environmental cycle test

PV1200; NES M0141; TPJLR.52.353

Thermal shock

Land Rover STJLR 51-5241

Table 3. Standards where ELIX ABS parts have been tested

To avoid future problems when painting plastic parts, it is always important to take into account the main factors that can help to make the painting process more controlled and stable. It is well known that there are many different processes for painting plastic parts with very different equipment and application characteristics. Although it is very complicated to reduce them in only four main factors to be taken into account in order to guarantee an efficient painting process, based on our extensive experience in painting processes, ELIX believes that the following factors are common to the vast majority of paint processes and they will help to avoid many issues: 1. Do a check–list of the main parameters of the whole painting process, from power–wash to the unloading area to ensure that during every shift the installation is working at the same conditions.

2. Check the temperature and viscosity of the paint products in the mixing room before being used to be sure that they are always under supplier specifications and under the same conditions.

3. Check the application and painting equipment parameters to guarantee not having surface appearance or colour matching problems, among others.

4. Plan the correct and frequent maintenance of the system and equipment, to make them more efficient and accurate.

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Paintability of ELIX ABS grades

ELIX counts with experimented professionals and resources to support our customers during the injection and painting process. ELIX technical service includes the assistance during the trials in the customer´s facilities, helping them to identify the root cause when dealing with certain issues or to optimize the process. In addition, ELIX laboratory has special tests that make it possible to detect potential issues generated during the injection process that may affect to the results after painting, i.e., residual stress of the part. The aim of this whole service is to work together with our customers in order to find the best solution.

Below is a summary of the main defects that usually occur in the processes of injection and painting of plastic parts. In many cases, injection defects are attributed to the painting process or vice versa. it is essential to perform a thorough analysis of the cause of the defects detected. During the last 20 years equipment such as microtomes and microscopes has been used as efficient analysis methods. This makes it easy to see the origin of the defect and therefore, limit the possible causes.

3.1 Weld lines Cause

Signs

This type of defect is due to air trapped in the plastic during the injection process. Once the part is exposed to temperatures above 80°C during the painting process, the air trapped in the plastic expands, breaking the different layers of paint applied on it.

A clear line is observed on the painted surface after the painting process. If the weld line is not visible, this defect could be confused with craters, cracks, etc.

10mm

Image 1 & 2. Defects produced by weld lines in the moulded part.

Corrective procedure Is the defect caused by the injection process?

YES

1. Increase the mould / melt temperature.

2. Increase injection rate.

3. Increase the holding pressure.

4. Check the tool ventilation.

YES

1. Check the loading line process.

2. Check for the existence of scratches before the painting process.

3. Check the solvent products used.

NO

Is the defect caused by the painting process?

NO

1. Check for possible damage in the mould cavity.

2. Check the type of packaging used.

3. Check the transport process to the painting line.

Paintability of ELIX ABS grades

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3.2 Remains of plastic Cause

Signs

Remains of plastic are usually generated by insufficient compaction, an excessively high temperature in the mold cavity or a short cooling time during the injection process.

A small quantity of plastic remains adhered to the mold cavity when the part is being removed from the cavity.

Sometimes this type of defect is mistaken for being caused by dirt in the painting process (see images 3, 4 & 5).

Image 3, 4 & 5. Traces of material that remain after being painted.

Corrective procedure Is the defect caused by the injection process?

YES

1. Increase the mould / melt temperature.

2. Increase the cooling time.

3. Increase holding pressure.

YES

1. Check for the existence of scratches in the loading line process.

2. Check for remains of plastic in the power-wash system.

3. Check for traces of plastic on the line process skids.

NO

Is the defect caused by the painting process?

NO

1. Check for possible damage in the mould cavity.

2. Check the storage area.

3. Check the transport process to the painting line.

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Paintability of ELIX ABS grades

3.3 Streak Marks or Quarters Cause

Signs

Usually this type of defect is due to the high surface tension of the ABS or residual stress caused during the injection process. Scratches on the parts during the transfer or the painting line loading process could also be the cause.

Most thinners used in the paint products are able to attack the plastic surface, causing streaks on the surface and cracks in the paint layers (see images 6 & 7).

a

b

c

Image 6 & 7. Streak and quartered defect.

Corrective procedure Is the defect caused by the injection process?

YES

1. Increase the mould/melt temperature.

2. Reduce the injection rate.

3. Reduce the screw rpm.

4. Reduce the holding pressure.

YES

1. Check the loading line process.

2. Check for possible scratches during the painting process.

3. Check the surface tension on the injected part.

4. Check the products used to clean the parts before painting.

NO

Is the defect caused by the painting process?

NO

1. The use of a Flash-primer, primer or a colour coat with low content of esters, ketones and aromatics is highly recommended.

2. Check for possible damage to the mould cavity.

3. Check the transport process to the painting line.

Paintability of ELIX ABS grades

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3.4 Craters Cause

Signs

This is possibly one of most difficult painting process defects to locate and solve. Normally they are caused by rest of water, excess paint in one of the applied layers, insufficient evaporation time, low humidity and heating curves which are too pronounced, entrapped air or moulded parts with residual stress.

This defect is characterized because the orifice can easily be detected on the outside by touching (see images 8 & 9).

Image 8 & 9. Crater defect.

Corrective procedure Is the defect caused by the injection process?

YES

1. Increase the mould/melt temperature.

2. Reduce the injection rate.

3. Reduce the screw rpm.

4. Reduce the holding pressure.

YES

1. Check for remains of water on the parts after power – wash.

2. Check the temperature and humidity after painting each layer.

3. Check the type of solvent and the % of dilution used.

4. Check the temperature and humidity of the pressurized air used for painting.

NO

Is the defect caused by the painting process?

NO

1. Check the design of the skids of the painting process.

2. Check the orientation of the blowers in the drying area.

3. The use of a water-repellent agent in the power-wash could be helpful.

4. Use a shaking system after the power-wash.

10 Paintability of ELIX ABS grades

3.5 Pinholes Cause

Signs

The main causes for this defect are remains of demolding agent on the surface of the pieces, the mould cavity or from the work environment.

In the case of water-based paint, the main reason is the excess thickness applied to some of the painted layers, and high temperature with low humidity in the evaporation areas.

This defect is characterized because the orifice is inward and it is very difficult to detect by touching (see images 10, 11& 12).

Image 10, Remains of silicone. Image 11 & 12. Excessive paint thickness.

Corrective procedure Is the defect caused by the injection process?

YES

1. Use a Silicone-free demolding agent.

2. Check that the whole machine is completely clean.

3. Be sure that the air of the injection area is free of grease.

YES

1. Check the loading line process.

2. Replace filters and power-wash water frequently.

3. Avoid using vaseline in the application booths or robots.

4. Check the parameters of the application equipment.

NO

Is the defect caused by the painting process?

NO

1. Store the injected part at least 72 hours before being painted.

2. The parts must be handled with cotton gloves.

3. Check the transport process to the painting process.

4. Clean the moulded parts with solvent, i.e., isopropyl alcohol, to remove grease.

Paintability of ELIX ABS grades 11

3.6 Blistering Cause

Signs

The main causes that generate this defect, especially in water-based application processes, are an inadequate evaporation time, too thick layer, a heating curve that is too pronounced or a very short curing time. Sometimes it could be caused by a small quantity of air trapped during the injection process.

This defect is characterized by bubbles of solvent or evaporated water trapped between the layers of paint (see images 13 & 14).

Image 13 & 14. Blistering defect.

Corrective procedure Is the defect caused by the injection process?

YES

1. Reduce the injection rate.

2. Check the venting system 3. Be sure that the material is properly dried.

YES

1. Check the viscosity or rheology of the paint products.

2. Check the temperature and humidity after painting each layer.

3. Check the application parameters and the layer thicknesses.

NO

Is the defect caused by the painting process?

NO

1. Check for more suitable paint products.

2. Check for changes in the painting process.

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Paintability of ELIX ABS grades

3.7 Adhesion problems Cause

Signs

This is possibly the most serious defect in a painting process line. It is mandatory to guarantee to have a good adhesion. This defect is usually due to rest of demoulding agent on the surface of the part, especially in water-based painting processes an inefficient power-wash process, inadequate painting process due to multiple reasons, insufficient curing time between layers, etc.

Adhesion defects have many different causes and appearances. Some of them are described below (see images 15, 16 & 17).

Image 15, 16 & 17. Different adhesion problems.

Corrective procedure Is the defect caused by the injection process?

YES

1. Use a Silicone-free demolding agent.

2. Check that the injected parts are not stressed.

3. Check the surface tension the injected parts.

YES

1. Check the loading line process.

2. Replace filters and power-wash water frequently.

3. Check the application parameters & layer thickness.

4. Check that the curing process is compliant with the supplier's specifications.

NO

Is the defect caused by the painting process?

NO

1. Store the injected part at least 72 hours before being painted.

2. Avoid using demolding agents, especially in water-based processes.

3. All parts must be handled with white cotton gloves.

4. Choose the most suitable material & paint products for your process.